Cytidine 3'-(dihydrogen phosphate)

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1983

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

bioaccessibility (or bioavailability)

distribution

excretion

toxicokinetics

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

2 animals/dose

GLP compliance:

not specified

Specific details on test material used for the study:

RADIOLABELLING INFORMATION
CDP-choline was prepared by the Radiochemical Center of Amercham by an enzymatic process from phosphoryl (14C-methyl) choline and cytidine 5'-triphosphate.
- Radiochemical purity: It was purified by ionic exchange chormatography and the radiochemical purity was determied to be 99%.
- Specific activity: it was 50 mCi/mol
- Locations of the label: (14C-methyl) choline

Radiolabelling:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: own colony
- Weight at study initiation: 175-225 g
- Housing: metabolic cages
- Diet: fasted up to 24h after administration and then with free access to food
- Water: ad libitum
- Fasting period: 16-h prior to administration.

Route of administration:

intravenous

Vehicle:

other: in a solution not specified

Duration and frequency of treatment / exposure:

Administered only in one occasion into jugular vein.

Dose / conc.:

4 mg/kg bw (total dose)

Remarks:

with an activity of 10 microCi per animal

No. of animals per sex per dose / concentration:

2

Control animals:

not specified

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled:
Blood samples (about 100 ml) were obtained by means of small cuts in the tail at the scheduled times and evaluated by weighing.
Urine and feces produced in the periods of 0-24h and 24-72h were collected.
The organs studied were brain, lung, kidney, liver and heart. The animals used fo the determination of organ levels were collected under anesthesia with ether before the extraction of the respective organ. The organs were immediatelly and carefully removed. Aliquot parts of 100 mg of tissue were digested and decolorised. Then, they were measured in the scintillation counter.
- Other:
Blood was put to digest decolorise in a mixture of hydrogen peroxide and Packard soluene-isopropanol before being counted in a liquid scintillation counter LS-7500 Beckman in the presence of 10 ml of Instagel-0.5 N HCl, according to the programme for 14C-counting.
Urines were diluted in to water up to a volume of 50 ml.
Feces were homogenized and diluted up to a volume of 250 ml.
From the diluted urine and feces, sampels of 1 ml were taken as to evaluate them with scintillation counter in the presence of Instagel, according to the prgramme for 14C.

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, faeces, blood, brain, lung, kidney, liver and heard tissues.
- Method type(s) for identification: The samples were counted with a liquid scintillation counter LS-750, according to the programme for 14C.

Type:

distribution

Results:

CDP-choline and metabolites are widely distributed

Type:

excretion

Results:

inestimable by fecal route and low by urinary route

Details on distribution in tissues:

A fall in values of the radioactivity corresponding to CDP-choline administered by intravenous route is observed between 1/2 and 1 hour after administration. Later, on the blood concentration shows a trend to come back slowly to the initial values. Thus, a redistribution phase is made evident.

CDP-Choline or its labelled metabolites are widely distributed, the cerebral radioactivity evolving in a different way from the blood which would confirm the inclusion of the product in the pool of phospholipids.

Details on excretion:

The elimination is inestimable by fecal route and low by urine route, giving rise to the high hematic levels obtained at long times.

The values obtained ranged between 6-7% of total recovery, corresponding to a large degreee to the urinary elimination. An important percentage is eliminated in the form of CO2. Moreover, it seems taht there is a fixation of CDP- Choline or its metabolites in the structure components of the blood such as a red blood corpuscles and leukocytes, because these products are problably included in the metabolic processes of inclusion in cellular structures.

Key result

Test no.:

#1

Toxicokinetic parameters:

AUC: 77.42

Remarks:

0-24 h

Metabolites identified:

not measured

Bioaccessibility (or Bioavailability) testing results:

The CDP-choline is completely absorbed when administered by intravenous route. The bioavailability is practically complete.

Table 1: Bood kinetics of the total radioactivity after intravenous administration of 4 mg/kg of CDP-Choline to male rats, expressed as percentage of radioactivity per 10 ml of blood, as average and standard deviation:

Time	Average	Standard deviation
10 min	3.05	0.24
20 min	2.59	0.31
30 min	1.47	0.22
1 h	1.40	0.02
2 h	2.84	0.02
3 h	2.50	0.05
4 h	2.77	1.00
5 h	3.37	0.31
6 h	3.68	0.02
7 h	-	-
24 h	3.12	0.19

Table 2: Urinary and fecal recovery of radioactivity after the administration of 4 mg/kg of CDP-choline intravenously, as percentage related to the administered dose, expressed as the average with standard deviation:

Urine/fecal collection period	Average	Standard deviation
0-24	1.78	0.38
24-72	4.84	0.61
0-24	0.12	0.10
24-72	0.56	0.23

Table 3: Organic distribution of CDP-Choline and labelled metabolites, expressed as percentage of total dose, after intravenous administration of 4 mg/kg of labelled CDP-choline:

Time	5 h		24 h
	Average	Standard Deviation	Average	Standard Deviation
Brain	0.26	0.03	0.23	0.18
Lung	2.27	0.29	2.32	1.68
Liver	2.32	6.82	15.52	6.81
Kidney	5.86	1.61	1.45	0.98
Heart	0.85	0.72	1.03	0.87

Conclusions:

The CDP-choline administered by intravenous route on rats is widely distributed in the organs and eliminated very slowly. The value of AUC (0-24h) is 77.42.

Executive summary:

The bioavailability of radiollableled CDP-choline was studied by intravenous route on Sprague-Dawley rats. The amount of 4 mg/kg bw (total dose) was administered in a solution into jugular vein and the absortion, distribution on brain, lung, kidney, liver and heart and excretion of the substance was evaluated. The product was widely distributed in the organs and a very low urinary and fecal elimination was observed, thus producing mantained blood levels. The AUC (0-24h) was determined to be 77.42.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1983

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

bioaccessibility (or bioavailability)

distribution

excretion

toxicokinetics

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

2 animals/dose

GLP compliance:

not specified

Specific details on test material used for the study:

RADIOLABELLING INFORMATION
CDP-choline was prepared by the Radiochemical Center of Amercham by an enzymatic process from phosphoryl (14C-methyl) choline and cytidine 5'-triphosphate.
- Radiochemical purity: It was purified by ionic exchange chormatography and the radiochemical purity was determied to be 99%.
- Specific activity: it was 50 mCi/mol
- Locations of the label: (14C-methyl) choline

Radiolabelling:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: own colony
- Weight at study initiation: 175-225 g
- Housing: metabolic cages
- Diet: fasted up to 24h after administration and then with free access to food
- Water: ad libitum
- Fasting period: 16-h prior to administration.

Route of administration:

oral: gavage

Vehicle:

water

Duration and frequency of treatment / exposure:

Administered only in one occasion.

Dose / conc.:

4 mg/kg bw (total dose)

Remarks:

with an activity of 10 microCi per animal

No. of animals per sex per dose / concentration:

2

Control animals:

not specified

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled:
Blood samples (about 100ml) were obtained by means of small cuts in the tail at the scheduled times and evaluated by weighing.
Urine and feces produced in the periods of 0-24h and 24-72h were collected.
The organs studied were brain, lung, kidney, liver and heart. The animals used fo the determination of organ levels were collected under anesthesia with ether before the extraction of the respective organ. The organs were immediatelly and carefully removed. Aliquot parts of 100 mg of tissue were digested and decolorised. Then, they were measured in the scintillation counter.
- Other:
Blood was put to digest decolorise in a mixture of hydrogen peroxide and Packard soluene-isopropanol before being counted in a liquid scintillation counter LS-7500 Beckman in the presence of 10 ml of Instagel-0.5 N HCl, according to the programme for 14C-counting.
Urines were diluted in to water up to a volume of 50 ml.
Feces were homogenized and diluted up to a volume of 250 ml.
From the diluted urine and feces, sampels of 1 ml were taken as to evaluate them with scintillation counter in the presence of Instagel, according to the prgramme for 14C.

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, faeces, blood, brain, lung, kidney, liver and heard tissues.
- Method type(s) for identification: The samples were counted with a liquid scintillation counter LS-750, according to the programme for 14C.

Type:

absorption

Results:

absorved slowly and completely. Complete bioavailability.

Type:

distribution

Results:

CDP-choline and metabolites are widely distributed

Type:

excretion

Results:

inestimable by fecal route and low by urinary route ( 6-7% of total recovery)

Details on absorption:

The radioactivity corresponding to CDP-choline administered by oral route is absorved slowly and completely, no residual radioactivity being found in the instestinal contents after 24 h. Blood labels are high and sustained. The maximum levels were found after 5 h and 30 min, the blood levels decreasing later on very slowly.

Details on distribution in tissues:

CDP-Choline or its labelled metabolites are widely distributed, the cerebral radioactivity evolving in a different way from the blood which would confirm the inclusion of the product in the pool of phospholipids.

Details on excretion:

The elimination is inestimable by fecal route and low by urine route, giving rise to the high hematic levels obtained at long times.

The values obtained ranged between 6-7% of total recovery, corresponding to a large degreee to the urinary elimination. An important percentage is eliminated in the form of CO2. Moreover, it seems taht there is a fixation of CDP- Choline or its metabolites in the structure components of the blood such as a red blood corpuscles and leukocytes, because these products are problably included in the metabolic processes of inclusion in cellular structures.

Key result

Test no.:

#1

Toxicokinetic parameters:

Tmax: 5 h and 30 min

Key result

Test no.:

#1

Toxicokinetic parameters:

Cmax: 4.19%

Key result

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: 23.1 h

Key result

Test no.:

#1

Toxicokinetic parameters:

AUC: 71.58

Remarks:

0-24 h

Test no.:

#1

Toxicokinetic parameters:

other: Bioavailability (dpm) p.o.

Remarks:

0.92

Metabolites identified:

not measured

Bioaccessibility (or Bioavailability) testing results:

The CDP-choline is completely absorbed when administered in aqueous solution by oral route. The bioavailability of the oral route is practically complete.

Table 1: Bood kinetics of the total radioactivity after oral administration of 4 mg/kg of CDP-Choline to male rats, expressed as percentage of radioactivity per 10 ml of blood, as average and standard deviation:

Time	Average	Standard deviation
10 min	0.26	0.12
20 min	0.40	0.02
30 min	0.74	0.01
1 h	1.32	0.40
2 h	2.33	0.63
3 h	3.31	0.86
4 h	3.57	0.88
5 h	4.17	0.83
6 h	4.18	0.03
7 h	3.81	0.73
24 h	2.48	0.40

Table 2: Urinary and fecal recovery of radioactivity after the administration of 4 mg/kg of CDP-choline, as percentage related to the administered dose, expressed as the average with standard deviation:

Urine/fecal collection period	Average	Standard deviation
0-24	2.60	0.95
24-72	2.56	0.67
0-24	0.09	0.04
24-72	0.17	0.15

Table 3: Organic distribution of CDP-Choline and labelled metabolites, expressed as percentage of total dose, after oral administration of 4 mg/kg of labelled CDP-choline:

Time	5 h		24 h
	Average	Standard Deviation	Average	Standard Deviation
Brain	0.21	0.04	0.40	0.08
Lung	0.45	0.07	1.18	0.24
Liver	37.65	2.62	23.11	1.12
Kidney	2.39	0.86	2.83	-
Intest, contents	9.10	4.38	-	-
Heart	0.25	0.18	0.35	0.13

Conclusions:

The CDP-choline administered by oral route on rats is absorbed slowly and completely, with a complete bioavailability. The product is widely distributed in the organs and eliminated very slowly. The Tmax was 5 h 30 min, Cmax 4.19%, half life 23.1h and AUC (0-24h) 71.58.

Executive summary:

The bioavailability of radiollableled CDP-choline was studied by oral route on Sprague-Dawley rats. The amount of 4 mg/kg bw (total dose) was administered by gastric catheter and the absortion, distribution on brain, lung, kidney, liver and heart and excretion of the substance was evaluated. The CDP-choline was absorved slowly and completely, with a complete bioavailability. The product was widely distributed in the organs and a very low urinary and fecal elimination was observed, thus producing mantained blood levels. The total recovery for this routes ranged the 6 -7%. These study allowed the determination of the following parameters; the Tmax was 5 h 30 min, Cmax 4.19%, half life 23.1h and AUC (0-24h) 71.58.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1983

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

excretion

metabolism

Qualifier:

no guideline followed

GLP compliance:

not specified

Specific details on test material used for the study:

RADIOLABELLING INFORMATION
- Specific activity:
U-14C cytidine 120 microCi/mmol giving a radioactive dose of 35 micrCi.
Methyl 14C choline 54 microCi/mmol and thus 35 microCi.
- Locations of the label: The formulation of radiollabeled (14C) CDP-choline used consisted of a mixture of the compound labelled at two different sites together with the unmodified compound. One CDP-choline moiety was ring labelled in the cytidine residue, the other in the methyl position of the choline moiety.

Radiolabelling:

yes

Species:

other: human

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
A group of six adult healthy male volunteers were fully informed about the nature of the study, and gave their written consent to participate in the study.
- Source: volunteers
- Age at study initiation: mean age 24.5 years (range 20-32)
- Weight at study initiation: 66.3-83.4 kg (mean 75.4 kg)
- Fasting: For at least 12 h before dosing and then 3 h following dosing
- Diet: Standard lunch was provided
- Water:. ad libitum

Route of administration:

oral: feed

Vehicle:

water

Duration and frequency of treatment / exposure:

A single dose

Dose / conc.:

300 other: mg

Remarks:

of 14C CDP choline (50:50 mixture of methyl-14C and U-14C)

No. of animals per sex per dose / concentration:

6

Control animals:

yes

Details on study design:

- Rationale for animal assignment: random

A full clinical examination was conducted on each subject before and after the study, along with an extensive analyses of haematology, blood chemistry and urynalisis.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: Blood, respiratory carbon dioxide samples, tidal volume and respiration rate, urine, faeces
- Time and frequency of sampling:
Blood: before administration, after administration at 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24, 48, 72, 96, andf 120 h post-dose.
Respiratory carbon dioxide samples:
Subject no. 1: 0.67, 1.25, 2.5, 4.08, 6.5, 8.5, 12.5, 16, 24.5, 36, 48.5, 72.5 and 96 h post-dose.
Subject no. 2: 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 10, 12, 24, 48, 72 ad 96 h post-dose.
The 4 remaining subjects: 1, 2, 3, 4, 6, 8, 10, 12, 24, 72, 96 and 120 h post-dose.
Tidal volume and resipration rate at pre-dose, 3, 6, 10, 24, 48, 72, 96 and 120 h post-dose.
All urine was colected during the following intervals: 0-2, 2-4, 4-8, 8-12, 12-24, 24-48, 48-72, 72-96 and 96-120 h post-dose.
All faeces were collected during the following times: 0-24, 24-48, 48-72, 72-96, and 96-120 h post-dose.

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: blood, urine, faeces
- Time and frequency of sampling: mentioned in previous section
- From how many animals: (samples pooled or not) : all
- Method type(s) for identification: Liquid scintillation counting LKB 1213.

Type:

absorption

Results:

Complete

Type:

excretion

Results:

Elimination via respiratory CO2 and urinary excretion. Only 1% in the faeces

Type:

metabolism

Results:

extensive hepatic metabolism

Details on absorption:

On the mean plasma CDP concentration there were two peaks in concentrations of radioactivity. The first maximum appeared at approximatelly 1h after dosing, followed by a trought of concentration with the minimum amount ocurring between 3 and 4h post-dose. A secondary rise in radiactivity followed, resulting in a further peak at 24h which was followed thereafter by a decline.

Details on excretion:

During the evaluation of 14CO2 excretion, it was observed an initial peak followed by a rapid decline in the excretion to between 10 and 18 h post- dose, and this was followed by a much less rapid decline for up to 108 h post-dose.
During the urine excretion evaluation, it was observed that, as in the case of 14CO2, there was an initial rapid decline in excretion rate to 36 h post-dose followed by a much slower decline in excretion rate up to 108 h post-dose.
Regarding faecal excretion, it was observed that trhe maximum period of excretion rate occurred at 36 h post-dose with a steady decline towards a very low excretion rate at 108 h post-dose.
The total amount of CDP-choline excreted during the five days after dosing, calculated as percentage of the dose, averaged 16% of the total dose. It was observed that the majority of the radioactivity was excreted as radioactive respiratory carbon dioxide (14CO2).

Key result

Test no.:

#1

Toxicokinetic parameters:

Cmax: 1.53 µ/ml

Remarks:

First peak

Key result

Test no.:

#1

Toxicokinetic parameters:

Tmax: 1.08 h

Remarks:

First peak

Key result

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: 3.49 h

Remarks:

first peak

Key result

Test no.:

#1

Toxicokinetic parameters:

other: apparent elimination rate constant (h-1)

Remarks:

0.2043 (first peak)

Key result

Test no.:

#1

Toxicokinetic parameters:

Cmax: 3.10 µ/ml

Remarks:

Second peak

Key result

Test no.:

#1

Toxicokinetic parameters:

Tmax: 22 h

Remarks:

Second peak

Key result

Test no.:

#1

Toxicokinetic parameters:

half-life 2nd: 125.68 h

Remarks:

second peak

Key result

Test no.:

#1

Toxicokinetic parameters:

other: apparent elimination rate constant (h-1)

Remarks:

0.0059 (second peak)

Test no.:

#1

Toxicokinetic parameters:

AUC: 4.15

Remarks:

0-4h

Test no.:

#1

Toxicokinetic parameters:

AUC: 263.29

Remarks:

4-120h

Key result

Test no.:

#1

Toxicokinetic parameters:

AUC: 267.44

Remarks:

0-120h

Metabolites identified:

not specified

Bioaccessibility (or Bioavailability) testing results:

The bioavailability of CDP-choline appeared to be high since less than 1% of the compound was excreted in the faeces during the five days post-dose, indicating that the reminder of the dose was absorbed though the gastrointestinal tract.

Table 1: Mean plasma concetrations of radioactivity expressed as CDP-choline equivalents in  µg/ml, and mean total amounts of radioactivity in expressed CO2, urine and faeces expressed as CDP-choline equivalents % total dose, resulting from a single dose of 300 mg/14C CDP-choline to adult healthy subjects.

Time	Plasma (µg/ml)	CO2 (CDP-choline equivalents % total dose)	Urine (CDP-choline equivalents % total dose)	Faeces (CDP-choline equivalents % total dose)
0	0.0	1.04	0.32	0.07
0.25	0.19
0.5	0.73
1	1.47
		1.20
1.5	1.43
2	1.16
		0.99	0.23
3	1.00
		0.89
4	1.03
		1.07	0.33
6	1.50
		0.52
8	2.15
		0.28	0.20
10	-
		0.18
12	2.87
		0.90	0.32
24	3.05
		1.21	0.31	0.33
48	2.60
		1.03	0.27	0.27
72	2.00
		0.59	0.24	0.16
96	1.81
		0.59	0.18	0.07
120	1.63

Table 2: Mean pharmacokinetics of the radioactivity expressed as excretion rates of CDP-choline equivalents in resipred CO2, urine and faeces, in 6 adult subjects (4 only for CO2):

	CO2	Urine	Faeces
Maximum excretion rate (% dose/h)	1.22	0.159	0.021
Time of maximum excretion rate (h)	1.60	1.3	56
First phase of elimination Apparent half-life (h) Apparent elimination rate (h-1)	2.58 0.2791	6.62 0.1076	- -
Second phase of elimination Apparent half-life (h) Apparent elimination rate (h-1)	56.22 0.00307	71.08 0.0135	19.39 0.0297

Table 3: Total excretion of 14C-CDP-choline (equivalents % total dose) from 6 subjects durigng 5 days collections after a single dose od 14C-CDP-choline

	Mean	Standard deviation
14CO2 Urine Faeces	12.93 2.40 0.81	7.69 0.63 0.29
Total	16.14	7.60

Conclusions:

In humans, citicoline is absorbed completely and two peaks appear on plasma, when it is administered orally. Then it is metabolized in the gut wall and in the liver. Elimination occurs via respiratory CO2 and through urinary excretion. Both routes exhibit biphasic patterns.

Executive summary:

The absorption, metabolism and excretion of citicoline were investigated in six adult healthy subjects after a single dose of 300 mg of the 14C labelled compound. Sample collection of blood, urine, faecal samples and CO2 from the respiratory tract was performed before administration and up to 120h post-dose. The labelled 14C was evaluated with a liquid scintillation counting. It was determined that citicoline is absorbed completely and less than 1% of the dose was found in the faeces. Two peaks were found in the plasma; the first at 1h post-dose, and the second larger peak at 24h post-dose. It suggests a metabolism in the gut wall and in the liver. On the other hand, elimination occurs via respiratory CO2 and through urinary excretion; the former predominating and both routes exhibit biphasic patterns characterized by an early phase followed by a slower decline.

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to other study

Objective of study:

distribution

metabolism

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

not specified

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Test material synthetized in the laboratory from [5-3H]CMP and [methyl.14C]Pcholine obtained from Radiochemical Centre, Amersham, Bucks, U.K.

RADIOLABELLING INFORMATION
- Radiochemical purity: The purity of the compound was checked by HPLC analysis and spectroscopic characterization.
- Specific activity: [5-3H]CMP free acid (102 Ci/mol) and [methyl-14C]Pcholine (50 Ci/mol), [methyl-14C,5-3H]CDPcholine(4.44 Ci/mol 14C; 8.88 Ci/mol 3H).
- Locations of the label: methyl- 14C,5-3H]CDPcholine.

Radiolabelling:

yes

Species:

dog

Strain:

Beagle

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 1 year old
- Weight at study initiation: 10 +/- 1 kg body wt.

Route of administration:

oral: gavage

Vehicle:

not specified

Duration and frequency of treatment / exposure:

One single administration

Dose / conc.:

10 mg/kg bw/day (nominal)

Remarks:

of [methyl-14C,5-3H]CDPcholine

No. of animals per sex per dose / concentration:

4

Control animals:

not specified

Details on study design:

Treatment of tissues:
Aliquots corresponding to 1-2 g wet tissue were processed. The samples were homogenized in 20 ml ethanol/water (2: 1, v/v) for 1 min heated in a boiling water bath for 20 min in closed tubes and centrifuged . The precipitate was washed and then extracted. The pooled aqueous ethanol supernatants were concentrated under reduced pressure and then extracted with 100 ml of ether. The ether excess was removed under vacuum and the water-so!u!~le metabolites were characterized by HPLC. For the lipid extraction,
1-2 g of tissue were homogenized, lyophilized and then extracted. Quantitative evaluation of radioactivity associated with the phospholipid fraction was carried out after purification of crude lipid extract.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: liver, brain.
- Time and frequency of sampling: At different time intervals (4h, 24h, 48h) the animals were sacrificed and the organs promptly frozen in liquid nitrogen.

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: liver, brain.
- Time and frequency of sampling: At different time intervals (4h, 24h, 48h) the animals were sacrificed and the organs promptly frozen in liquid nitrogen.
- From how many animals: 4
- Method type(s) for identification:
HPLC analysis: model LC-65T Perkin-EImer Liquid Chromatograph, high performance model LC-15 UV detector
Spectroscopic characterization: Proton and m3C NMR spectra WH-270 Bruker Spectrospin spectrometer.
Absolute radioactivity was measured in a Beckman LS 7800 scintillation counter, equipped with an automatic quench correction system.

Type:

distribution

Results:

The uptake of CDP--choline and their metabolites is high in liver, slower in brain.

Type:

metabolism

Results:

The metabolism pattern is close to that found in rats

Details on distribution in tissues:

The figure attached shows the radioactivity distribution in liver (panel a) and brain (panel b) at different time intervals .Both patterns do not significantly differ from those previously observed in
rats.

Metabolites identified:

yes

Details on metabolites:

Liver appears to be the major CDP-choline metabolizing organ. It is characterized by a fast and extensive uptake of choline metabolites, followed by a slow release.
Conversely the rate of uptake of both 3H. and 14C-labelled fragments by the brain is significantly slower and reaches a steady-state level 20 h after treatment.
The pattern of labelled metabolites present in these organs also closely resembles that observed in rats.

Conclusions:

In dogs, liver appears to be the major CDP-choline metabolizing organ, whereas the levels are lower on brain. The metabolism pattern is similar among mammals.

Executive summary:

A pharmacokinetic analysis of CDP-choline has been carried out treating female Beagle dogs by oral administration of 10 mg/kg bw of double labelled molecule. [methyl-14C,5-3H]CDP-choline is used to study the distribution and metabolism of CDP-choline. Furthermore, the identification of the labelled metabolites of the exogenously administered CDP-choline in the various organs allow determining the pharmacological mechanisms. It is observed that the distribution of the molecule and their metabolites do not differ significantly from those observed in rats. Liver appears to be the major CDP-choline metabolizing organ . It is characterized by a fast and extensive uptake of choline metabolites, followed by a slow release. Conversely the rate of uptake by the brain is significantly slower and reaches a steady-state level 20 h after treatment. The pattern of labelled metabolites present in these organs also closely resembles that observed in rats.

Reference 5

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

excretion

metabolism

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

not specified

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Test material synthetized in the laboratory from [5-3H]CMP and [methyl.14C]Pcholine obtained from Radiochemical Centre, Amersham, Bucks, U.K.

RADIOLABELLING INFORMATION
- Radiochemical purity: The purity of the compound was checked by HPLC analysis and spectroscopic characterization.
- Specific activity: [5-3H]CMP free acid (102 Ci/mol) and [methyl-14C]Pcholine (50 Ci/mol), [methyl-14C,5-3H]CDPcholine(4.44 Ci/mol 14C; 8.88 Ci/mol 3H).
- Locations of the label: methyl- 14C,5-3H]CDPcholine.

Radiolabelling:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

not specified

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 12 weeks old.
- Weight at study initiation: 210 +/- 10 g body wt

Route of administration:

oral: gavage

Vehicle:

not specified

Duration and frequency of treatment / exposure:

One single administration

Dose / conc.:

10 mg/kg bw/day (nominal)

Remarks:

of [methyl-14C,5-3H]CDPcholine

No. of animals per sex per dose / concentration:

10

Control animals:

not specified

Details on study design:

Treatment of tissues:
Aliquots corresponding to 1-2 g wet tissue were processed. The samples were homogenized in 20 ml ethanol/water (2: 1, v/v) for 1 min heated in a boiling water bath for 20 min in closed tubes and centrifuged . The precipitate was washed and then extracted. The pooled aqueous ethanol supernatants were concentrated under reduced pressure and then extracted with 100 ml of ether. The ether excess was removed under vacuum and the water-so!u!~le metabolites were characterized by HPLC. For the lipid extraction,
1-2 g of tissue were homogenized, lyophilized and then extracted. Quantitative evaluation of radioactivity associated with the phospholipid fraction was carried out after purification of crude lipid extract.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: stomach, gastric content, intestine and intestinal content, plasma, liver, brain, urine, fecal excretions.
- Time and frequency of sampling: At different time intervals the animals were sacrificed and the organs promptly frozen in liquid nitrogen.

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: plasma, liver, brain, urine, fecal excretions.
- Time and frequency of sampling: At different time intervals the animals were sacrificed and the organs promptly frozen in liquid nitrogen.
- From how many animals: 10
- Method type(s) for identification:
HPLC analysis: model LC-65T Perkin-EImer Liquid Chromatograph, high performance model LC-15 UV detector
Spectroscopic characterization: Proton and m3C NMR spectra WH-270 Bruker Spectrospin spectrometer.
Absolute radioactivity was measured in a Beckman LS 7800 scintillation counter, equipped with an automatic quench correction system.
- Other: molecules analyzed CDPcholine, cytidine nucleotides, methionine, betaine, Pcholine, choline. Identified by their different retention times. Methionine and cytidine nucleotides could be discriminated by virtue of their different labelling.

Type:

absorption

Results:

very fast, efficient gastro-intestinal absorption

Type:

excretion

Results:

low renal and fecal excretion

Type:

metabolism

Results:

CDP-choline is metabolised to Pcholine and CMP, followed by the transformation to choline and cytidine fragments.

Details on absorption:

Less than 30% of the radioactivity administered can be detected in the gastro-intestinal tract, even 30 min after ingestion. This result suggests a very fast absorption process of CDPcholine and/or of its metabolites. On the other hand the 3H/~4C ratio of the gastro-intestinal content shows a time-dependent decrease, indicative of a preferential absorption of the 3H-cytidine moiety.
The kinetic analysis of plasma 3H and 14C radioactivity indicates the presence of labelled metabolites in the blood stream even 10 min after treatment. The plasma radioactivity shows a linear increase in the first 5 h, followed by a gradual decrease over 48 h. The value of the 3H/14C ratio confirms the preferential absorption of 3H radioactivity at the gastrointestinal level. The subsequent decrease of the isotopic ratio, observed up to 8 h, can be explained with the differential utilization and release of the labelled CDPcholine metabolites by the various organs.

Details on excretion:

The total CDP-choline catabolites excreted in the urine over 48 h represents only 3% and 6% of the total 14C and 3H radioactivity, respectively. On the other hand the fecal excretion in the same time interval never exceeds 3% of the administered dose. Therefore an active utilization of the administered molecule by the peripheral metabolic compartments can be inferred.

Metabolites identified:

yes

Details on metabolites:

The liver appears to be very active in the utilization of the CDP-choline, with a preferential uptake of the [14C]choline fragment. The 3H uptake is strikingly lower and the radioactivity level reached at 2 h gradually decreases suggesting a very slow release of 3H-labelled metabolites by this organ. At short time intervals, betaine and Pcholine are the major radioactive 14Clabelled compounds detected in the organ, while at 48 h an active recovery of choline into phospholipids is observed. Most of the 3H radioactivity, initially associated with cytidine nucleotides, is subsequently incorporated into nucleic acid fraction.

The analysis of the labelled compounds detected in the liver confirms the metabolic pathway of the exogenously administered CDPcholine. The cleavage of the molecule at the membrane level, yielding Pcholine and CMP is followed by the uptake of choline and cytidine fragments. Cytidine, salvaged in the nucleotide pool, can be subsequently incorporated into nucleic acid. The choline moiety is in part rephosphorylated into Pcholine which, through the Kennedy's pathway is converted into choline phospholipids. choline alcoholic group can also be oxidized to an aldehydic one by the mitochondrial choline dehydrogenase; the product of the reaction is then converted, at the mitochondrial level, into betaine. One of the three methyl groups of betaine can be transferred to homocysteine yielding methionine, which is then subsequently incorporated into proteins. The other two methyls can also reenter the one-carbon pool as 5-10-methylene-4H folate, via formaldehyde.

The brain is characterized by a particularly slow release of CDPcholine labelled catabolites in that no decreases in either 3H and 14C radioactivity can be observed up to 48 h. In fact, the major 14C-labelled compounds present in this organ at 30 min are Pcholine and methionine, which are efficiently incorporated, over a longer time, into phospholipids and proteins, respectively. The 3H-labelled moiety of CDPcholine is also actively utilized in the nucleic acid biosynthesis via the cytidine nucleotide pool.
The pattern of metabolites present in the brain tissue is indicative of a rapid salvage of choline into phospholipid fraction and of cytosine into nucleic acid. It is worth noting that methionine is one of the major 14C-labelled metabolites present in the brain 1 h after the oral administration.

Labelled metabolites present in rat liver after oral administration of double labelled CDP-choline:

Labelled molecular species	% liver radioactivity
Time (h):	0.5	1	48
[3H]cytidine and cytidine nucleotides	49.6	31.4	7.8
[3H]nucleic acid	36.4	53.2	76.2
[14C]betaine	34.2	25.2	7.9
[14C] P-choline	34.8	21.3	3.3
[14C]choline	2.1	1.9	0.5
[14C]methionine	1.7	1.9	8.1
[14C]phospholipids	7.3	23.2	54.8
[ 14C]proteins	5.2	10.6	11.1

Labelled metabolites present in rat brain after oral administration of double-labelled CDP-choline

 

Labelled molecular species	% brain radioactivity
Time (h):	0.5	1	48
[3H]cytidine and cytidine nucleotides	64.7	56.2	14.4
[3H]nucleic acid	21.3	29.6	71.3
[14C]betaine	<0.1	2.3	0.9
[14C] P-choline	47.1	27.2	8.9
[14C]choline	<0.1	<0.1	Not detectable
[14C]methionine	21.9	34.4	2.6
[14C]phospholipids	11.8	13.2	47.3
[ 14C]proteins	4.3	9.7	24.8

Conclusions:

In rats, there is a fast and efficient gastro-intestinal absorption of CDP-choline and/or of its metabolites. This molecule is metabolised on the liver to P-choline and CMP, followed by a second transformation step to choline and cytidine fragments. Cytidine is incorporated into nucleic acid and choline is converted into choline phospholipids. In the brain tissue, there is a rapid salvage of choline into phospholipid fraction and of cytosine into nucleic acid. The excretion is very low by renal and faecal route.

Executive summary:

A pharmacokinetic analysis of CDP-choline has been carried out treating Sprague-Dawley rats by oral administration of 10 mg/kg bw of double labelled molecule.[methyl-14C,5-3H]CDPcholine is used to study the absorption, excretion and transmembrane transport and to follow the metabolic fate of cytidine and choline fragments. Furthermore, the identification of the labelled metabolites of the exogenously administered CDP-choline in the various organs allow determining the pharmacological mechanisms. It is observed that the molecule is rapidly cleaved at the level of the pyrophosphate bridge and a fast uptake of the hydrolytic products occurs. The metabolism of the molecule is characterized by a differential utilization of the two moieties by the various organs. Liver is the most active organ in utilizing CDPcholine with a preferential uptake of the choline fragment. The [3H]cytidine moiety, in all the organs examined, appears to be incorporated into the nucleic acid fraction via the cytidine nucleotide pool. The uptake of CDPcholine by the brain is relatively low; however, a good metabolic utilization of the CDPcholine can be observed. Finally, the analysis of urine and faecal excretions show that the excretion of the molecule and their metabolites is very low.

Reference 6

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

metabolism

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test: Study the metabolism of citicoline after intravenous administration in humans.
- Short description of test conditions: Four healthy adult males received a solution containing CDP-choline (3g/ 500 ml of physiological saline) by infusion for 30 min. Blood samples were taken at 0, 10, 20, 30 and 31 min, and 1, 3 and 6 h after beginning of infusion. Samples were then centrifuged and plasmas are stored at -70ºC until assay.
- Parameters analysed / observed: Choline, cytidine, CMP and citicoline levels were analysed from the plasma samples by different assays.

GLP compliance:

no

Radiolabelling:

no

Species:

other: Human

Details on species / strain selection:

Healthy adult males. Mean age: 20-30 years. Mean weight: 70 Kg.

Sex:

male

Route of administration:

infusion

Vehicle:

physiological saline

Details on exposure:

A solution of 3 g of CDP-choline in 500 ml of physiological saline was administered by infusion into a forearm vein.

Duration and frequency of treatment / exposure:

A single dose was administrated by infusion, which took 30 min.

Dose / conc.:

6 other: mg/ml

No. of animals per sex per dose / concentration:

4

Control animals:

no

Details on dosing and sampling:

Blood samples were withdrawn from another vein in the opposite forearm at 0, 10, 20, 30, and 31 min, and 1, 3 and 6 h after the beginning of the infusion. Samples were stored at -70ºC until assay.

Type:

metabolism

Results:

Citicoline is rapidly metabolised and converted to choline and cytidine.

Metabolites identified:

yes

Details on metabolites:

Intravenously-administered CDP-choline was rapidly hydrolysed in humans, plasma CDP-choline levels attained 4.3 µM at the end of the infusion period, but were no longer elevated 30 min later (Fig. 3). Plasma choline peaked at the end of the infusion, rising from 1.2 to 32 µM at the end of the infusion. Plasma levels of both substances remained significantly elevated for at least 6 h after initiation of the infusion (Fig. 3).

Conclusions:

After intravenous administration in human, CDP- choline is rapidly metabolized and is converted to at least two major metabolites, choline and cytidine. The levels of these metabolites remain significantly elevated for at least 6 h.

Executive summary:

A study was conducted to study the metabolism of CDP-choline (citicoline) after intravenous administration in human. A solution of 3 g of CDP-choline in 500 ml of physiological saline was administered by infusion into a forearm vein of 4 healthy adult males (mean age: 20 -30; mean weight: 70 kg). Blood samples were withdrawn from another vein in the opposite forearm at 0, 10, 20, 30, and 31 min, and 1, 3 and 6 h after the beginning of the infusion. Samples were stored at -70ºC until assay. The plasma levels of cytidine, choline, and unchanged CDP-choline were analysed. Intravenously-administered CDP-choline was rapidly hydrolysed in humans. After giving CDP-choline by infusion over 30 min, plasma CDP-choline fell to undetectable levels almost immediately after the end of the infusion period; plasma choline and cytidine peaked at that time, but their concentrations remained significantly elevated for at least 6 h. These observations show that CDP-choline is rapidly metabolized and is converted to at least two major circulating metabolites, choline and cytidine, after intravenous administration in human.

Reference 7

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

metabolism

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test: Study the metabolism of citicoline after oral administration in humans.
- Short description of test conditions: Two groups of healthy adult males were administered a single oral dose (2 g) or three doses of 2 g each, after receiving a diet containing less than 1 g of choline per day, and standard amounts of lipids, carbohydrates and proteins. Blood samples were taken every 2 hours after breakfast, for 10 h for the first group, and for 6 h from the second group. Samples were then centrifuged and plasmas are stored at -70ºC until assay.
- Parameters analysed / observed: Choline, cytidine, CMP and citicoline levels were analyzed from the plasma samples by different assays.

GLP compliance:

no

Radiolabelling:

no

Species:

other: Human

Details on species / strain selection:

Healthy adult males. Mean age: 20-30 years. Mean weight: 70 Kg.

Sex:

male

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: 2 g of CDP-choline with breakfast.

Dose / conc.:

2 other: g/day

Dose / conc.:

6 other: g/day

Remarks:

3 doses of 2 g/day.

No. of animals per sex per dose / concentration:

4

Control animals:

no

Details on study design:

On the day before the experiment, two groups of healthy adult males consumed three meals (at 8 a.m., 12 a.m. and 5 p.m.) containing less than 1 g of choline per day, and standard amounts of lipids, carbohydrates and proteins. On the following day, the first group received a similar diet, and ingested a single dose of CDP-choline (2 g) with breakfast. The second group ingested three doses (2 g each) of CDP-choline; the first at 8 a.m., the second at 10 a.m., and the third at noon; lunch was omitted.

Details on dosing and sampling:

Blood samples were taken every two hours, starting immediately before breakfast, for 10 h from the first group, and for 6 h from the second group. Samples were immediately centrifuged and the plasmas were stored at -70ºC until assay.

Type:

metabolism

Results:

Citicoline is rapidly metabolised and converted to choline and cytidine.

Metabolites identified:

yes

Details on metabolites:

A single dose of 2 g of CDP-choline given to humans increased plasma choline levels from 8.9 to 13.5 µM 2 h after its administration, concurrently doubling plasma cytidine levels (from 11.36 to 26.17 µM). Plasma concentrations of both of the metabolites returned to initial levels 8 h after administration of the drug (Fig. 1). Among subjects receiving three oral doses ( 2 g each) of the CDP-choline at two-hour intervals, plasma choline peaked (30% over baseline) four hours after the initial CDP-choline dose, while plasma cytidine levels increased steadily, rising to five times basal levels 6 h after administration of the first CDP-choline dose (P<0.01; Fig 2).

Conclusions:

CDP-choline (Citicoline) is rapidly metabolized and it is converted to at least two major metabolites, choline and cytidine, after oral administration in human. Two hours after the single oral dose, plasma choline levels were increased by 48% and plasma cytidine by 136%. They returned to initial levels 8 h after administration.

Executive summary:

A study was conducted to know the metabolism of CDP-choline (citicoline) after oral administration in human. On the day before the experiment, two groups of healthy adult males (mean age: 20 -30; mean weight: 70 Kg) were given three meals (at 8 a.m., 12 a.m. and 5 p.m.) containing less than 1 g of choline per day, and standard amounts of lipids, carbohydrates and proteins. On the following day, the first group received a similar diet, and ingested a single dose of CDP-choline (2 g) with breakfast. The second group ingested three doses (2 g each) of CDP-choline at 8 a.m., 10 a.m., and at noon. Blood samples were taken every two hours, starting immediately before breakfast, for 10 h from the first group, and for 6 h from the second group. The plasma levels of cytidine, choline, and unchanged CDP-choline were analyzed. After a single dose of 2 g of CDP-choline plasma choline levels were increased in human 2 h after its administration, concurrently doubling plasma cytidine levels. Two hours after the single oral dose, plasma choline levels were increased by 48% and plasma cytidine by 136%. Plasma concentrations of both of the metabolites returned to initial levels 8 h after administration of the drug. Among subjects receiving three oral doses (2 g each) of the CDP-choline at two-hour intervals, plasma choline peaked (30% over baseline) four hours after the initial CDP-choline dose, while plasma cytidine levels increased steadily, rising to five times basal levels 6 h after administration of the first CDP-choline dose. These observations show that CDP-choline is rapidly metabolized and is converted to at least two major circulating metabolites, choline and cytidine, after oral administration in human.

Reference 8

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

metabolism

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test: Study the metabolism of citicoline after intravenous administration in rats.
- Short description of test conditions: Male rats received 50 mg/Kg of CDP-choline via a single bolus injection (0.2 ml) into the cannula. Blood samples were taken from the same cannula at 0, 10, 30 and 60 min after the injection. Samples were then centrifuged and plasmas are stored at -70ºC until assay.
- Parameters analysed / observed: Choline, cytidine, CMP and citicoline levels were analysed from the plasma samples by different assays.

GLP compliance:

no

Radiolabelling:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Wilmington, Mass.
- Weight at study initiation: 200-300 g.
- Housing: The animals were housed in individual hanging cages.
- Diet (e.g. ad libitum): Standard rat chow (20% protein) at libitum.
- Water (e.g. ad libitum): ad libitum.

ENVIRONMENTAL CONDITIONS
- Photoperiod (hrs dark / hrs light): 12 h dark / 12 h light

Route of administration:

intravenous

Vehicle:

physiological saline

Duration and frequency of treatment / exposure:

It was a single administration.

Dose / conc.:

50 mg/kg bw (total dose)

No. of animals per sex per dose / concentration:

5

Control animals:

yes, concurrent vehicle

Details on study design:

Two days before administration, the right jugular vein of the rats were cannulated with silastic P-10 tubing (Medical Equipment, Co., Mass.)

Details on dosing and sampling:

Blood samples were taken from the same cannula at 0, 10, 30, and 60 min after the injection, were immediately centrifuged, and the plasmas were stored at -70ºC until assay.

Type:

metabolism

Results:

Citicoline is rapidly metabolised to CMP and then mostly converted to cytidine.

Metabolites identified:

yes

Details on metabolites:

Intravenous CDP-choline rapidly disappears from the plasma, plasma levels increasing to 2.9 µM 1 min after a single bolus injection, but falling to undetectable amounts 5 min later. Plasma cytidine levels also increased markedly in this species (from 1.5 to 124 µM), and remained elevated for at least 60 min. Levels of CMP (cytidine monophosphate), a metabolite of CDP-choline that was not detectable in plasmas of untreated rats, were detectable (0.85 µM) one minute after CDP-choline administration, but not thereafter (Fig. 4).

Conclusions:

CDP-choline administered in rats by intravenous route is rapidly hydrolised to CMP and then mostly converted to cytidine. Plasma levels of cytidine increase markedly and remain elevated for at least 60 minutes.

Executive summary:

A study was conducted to know the metabolism of CDP-choline (citicoline) after intravenous administration in rats. The jugular veins of 5 Sprague-Dawley rats were cannulated, two days later they received 50 mg/kg of CDP-choline via a single bolus injection (0.2 ml) into the cannula. Blood samples were taken from the same cannula at 0, 10, 30, and 60 minutes after the injection, centrifuged and stored at -70ºC until assay. The plasma levels of cytidine, CMP, and unchanged CDP-choline were analysed. Intravenously-administered CDP-choline was rapidly hydrolysed in rats. Plasma levels of cytidine increased markedly and remained elevated for at least 60 minutes after injection. Levels of cytidine monophosphate (CMP), not detectable in plasmas of untreated rats, were detectable (0.85 µM) one minute after CDP-choline administration, but not thereafter. These observations show that CDP-choline is rapidly metabolized to CMP and then mostly converted to cytidine, after intravenous administration in rats.

Description of key information

Weight of evidence.

Studies on the analogue substance Citicoline:

Adsorption:

In the study of Agut et al. 1983 citicoline was administered by oral route in Sprague-Dawley rats is observed a complete absorption and bioavailability with a Tmax of 5 h 30 min, a Cmax of 4.19%, and a half-life of 23.1h. Additionally, the study of Galletti et al. 1991 determined a fast and efficient gastro-intestinal absorption of citicoline and their metabolites on Sprague-Dawley rats by oral route.

The oral administration in humans show that citicoline is also absorbed completely and two peaks appear on plasma.

 

Distribution:

The study of Agut et al. 2983 determined a widely distribution of this molecule and their metabolites in the organs, when citicoline is administered by oral and intravenous route on rat.

 

Metabolism:

According to a study of Galletti et al. 1991 or rats by oral route, citicoline is metabolised on the liver to P-choline and CMP, followed by a second transformation step to choline and cytidine fragments. Cytidine is incorporated into nucleic acid and choline is converted into choline phospholipids. In the brain tissue, there is a rapid salvage of choline into phospholipid fraction and of cytosine into nucleic acid. These data was also observed in dogs, where liver appeared to be the major CDP-choline metabolizing organ, and the levels were lower on brain.

Lopez et al. 1987 also studied the metabolism of citicoline by oral route in humans and by intravenous administration in humans and rats. It was determined that citicoline is rapidly converted to CMP (cytidine monophosphate) and phosphocholine and these metabolites to choline and cytidine. The citicoline oral administration on humans also showed that its metabolism is performed not only in the liver, but also in the gut wall (Dinsdale et al. 1983).

 

Excretion:

A study which evaluated the excretion of citicoline and their metabolites on rat after oral administration (Agut et al. 1983) using radiolabelling, determined a very slow elimination via renal and faecal route, with only a 6 -7% of recovery. The study of Galletti et al. 1991 also evaluated the excretion of the metabolites, they found a total excretion of 9% in urine, over a 48h period, and the faecal excretion in the same time never exceeds 3%.

In a study of citicoline to humans via oral route (Dinsdale et al 1983) was observed that elimination occurs via respiratory CO2 and through urinary excretion and both routes exhibit biphasic patterns.

As CDP-choline is rapidly transformed to cytidine monophosphate (also known as CMP, cytidine 3'-(dihydrogen phosphate)) and P-choline, which are then converted to choline and cytidine, the data and studies provided for CDP-choline are also applicable for the test item, cytidine 3'-(dihydrogen phosphate).

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Weight of evidence:

- A study of the bioavailability of CDP-choline by oral and intravenous route on rat performed by Agut et al. 1983 showed that citicoline is absorbed slowly and completely, with a complete bioavailability. The product is widely distributed in the organs and eliminated very slowly via renal and faecal route, with only a 6 -7% of recovery. After the administration via oral route, it was determined a Tmax for citicoline of 5 h 30 min, a Cmax of 4.19% and a half life of 23.1h.

 

- A study of the pharmacokinetics of the orally administered CDP-choline in rats and dogs by oral route was conducted (Galletti et al. 1991). On rats, there was a fast and efficient gastro-intestinal absorption of CDP-choline. It was observed that this molecule is metabolised on the liver to P-choline and CMP, followed by a second transformation step to choline and cytidine fragments. Cytidine is incorporated into nucleic acid and choline is converted into choline phospholipids. In the brain tissue, there is a rapid salvage of choline into phospholipid fraction and of cytosine into nucleic acid. The excretion is very low by renal and faecal route. In fact, they found a total excretion of 9% in urine, over a 48h period, and the faecal excretion in the same time never exceeds 3%. The study in dogs, detected a high metabolisation of the substance in the liver, but also detected levels of citicoline and their metabolites on the brain. Moreover, this study allowed to determine that the metabolism pattern is similar among mammals.

- The study of Dinsdale et al. 1983 also studied the absorption, metabolism and excretion of CDP-choline in humans by oral route. It was observed that citicoline is absorbed completely and two peaks appear on plasma, the first at 1h post-dose, and the second larger peak at 24h post-dose. Then it is metabolized in the gut wall and in the liver. Elimination occurs via respiratory CO2 and through urinary excretion. Both routes exhibit biphasic patterns.

- The metabolism of CDP-choline following oral and intravenous administration to human, and intravenously to rats was studied by Lopez et al. 1987. It was determined that citicoline is rapidly metabolized and is converted to at least two major metabolites, choline and cytidine. Two hours after a single oral dose plasma choline levels were increased by 48% and plasma cytidine by 136%. Intravenously-administered CDP-choline was rapidly hydrolysed, in both the human and the rat. In humans given the CDP-choline by infusion, plasma CDP-choline fell to undetectable levels almost immediately after the end of the infusion period; plasma choline and cytidine peaked at that time, but their concentrations remained significantly elevated for at least 6 h.