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Biotransformation and kinetics

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Administrative data

Endpoint:
biotransformation and kinetics
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Not GLP study, no guideline followed. Read across from a similar substance which has the same main component and with a different counter ion that doesn't influence the characteristics related to the specific end-point
Cross-reference
Reason / purpose:
reference to same study

Data source

Reference
Reference Type:
publication
Title:
Uptake, tissue distribution, and metabolism of malachite green in the channel catfish (Ictalurus punctatus)
Author:
Plakas S.M ; El Said K.R. ; Stehly G.R. ; Gingerich W.H ; Allen J.L.
Year:
1995
Bibliographic source:
Canadian journal of fisheries and aquatic sciences. 53 (1996)
Report Date:
1995

Materials and methods

Principles of method if other than guideline:
Procedures for cannulation of the dorsal aorta and urinary bladder of catfish and the collection of blood and urine specimens were previously described by Stehly and Plakas 1993 and Plakas et al. 1994. The disposition of malachite green was determined in channel catfish after intravascular dosing as mean plasma concentrations of the parent compound.
GLP compliance:
not specified
Type of medium:
aquatic

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material: Malachite Green Chloride
- Source: synthesized by Chemsyn Science Laboratories (Lexena, Kans)
- Source reagents: Sigma Chemical Co. (St. Louis Mo.)
- Radiochemical and chemical purities: ≥ 98%
- Determination of purity: HPLC, using visible light (618 nm) and radioactivity detector

Results and discussion

Transformation products:
yes
Identity of transformation products
No.:
#1
Reference
Reference substance name:
Unnamed
IUPAC name:
Leucomalachite green
Identifier:
common name
Identity:
Leucomalachite green

Any other information on results incl. tables

Kinetic parameters: MG-C elimination: Half-life of 6.2 h

Metabolite: Leucomalachite Green was a major metabolite in the plasma

PLASMA

Intravascular dosing- plasma concentration:

Exposure period After dosing peak conc. at 0.75 h [µg/ml] Conc. at 10 h [µg/mL] Mean conc. at the end (12h) [µg/mL]
Malachite Green Chloride (MG-C) 0.599 0.049  2.77
Leucomalachite Green (MG-L) 0.875 0.197 1.56

The sum of MG-C and MG-L accounted for approximately 70% of the total drug equivalents at each sampling time.

Waterborne exposure- plasma concentration:

Conc. at 10 h

[µg/mL]

Mean conc. at the end (12h) [µg/mL]

MG-C

0.025

2.77

MG-L

30 times higher than MG-C

1.56

MG-L levels continued to increase after dosing, achieving a maximum concentration of 2.36 mg×mL1 at 1 h after transfer of the fish to clean water. As with the intravascularly dosed fish, mean plasma concentrations of MG-C exhibited a triphasic decline after waterborne exposure. The terminal elimination half-life was 4.7 h.

MG-C and its metabolites were widely distributed and concentrated in the tissues. Residue concentrations were highest in the excretory tissues and fat and lowest in the muscle and plasma. At 2 h, the tissue to plasma concentration ratios of total drug equivalents ranged from 6.2 in fat to 0.72 in muscle; at 336 h (14 days), the ratios ranged from 157 in fat to 4.2 in muscle. Total residue concentrations in fat increased with time. In plasma, residues declined more rapidly than in other tissues.

PLASMA COLLECTED IN THE TISSUE

  Immediately after dosing [µg/mL] At 1 day [µg/mL]
MG-C 3.29 limit of determination 
MG-L 1.94 persist up to 14 days 0.106

MUSCLE           

  End of waterborne exposure [µg/g] Mean at 14 days [µg/g] Beyond 14 days[µg/g]
MG-C 1.18 0.012 Detectable, but not quantifiable
MG-L 1.45 0.518 0.019 up to 42 days

The elimination of MG-C in muscle appeared biphasic, with a terminal half-life of approximately 67 h.

The percentage of total residues composed of MG-L increased from 49% at 0 h to 80% at 336 h. Although MG-L was the major metabolite in muscle, additional unidentified metabolites eluted before MGL during HPLC. These individual metabolites constituted between 2 and 21% of the total radioactive residues, depending on sampling time.

RADIOACTIVITY

Total radioactivity in the exposure water for each group of fish decreased by approximately 15% during the 1-h exposure period. MG-C constituted > 98% of the total drug in the water throughout the dosing period, as determined by HPLC.

In intravascularly dosed fish, < 5% of the radioactive dose was found in the gallbladder at 48 h. The mean concentration of total drug equivalents in the bile was 22.8 mg/mL. In the urine, <0.5% of the dose was cumulatively excreted over a 48-h period. Concentrations in the urine did not exceed 0.05 mg/mL at each collection time.

INFLUENCE OF pH

Tissue levels of MG-C and MG-L increased with the pH of the dosing solution. The sums of the MG-C and MG-L concentrations in plasma and in muscle after exposure at pH 8 were eight and five times higher, respectively, than after exposure at pH 6. At pH 7, the levels were comparable with those observed in the tissue distribution study in which the mean pH of the exposure water was 7.1

DISCUSSION

Parent MG-C concentrations in the plasma of channel catfish increased rapidly during waterborne exposure, suggesting efficient

uptake of the dye cation and (or) carbinol compound across the gills.

The head kidney, composed primarily of inter-renal and hematopoietic tissue, also was a site of residue accumulation in catfish with concentrations similar to those in the trunk kidney. In the highly perfused spleen, concentrations were consistently lower than those in the head and trunk kidneys. Multiple factors may be involved in the distribution of residues, including blood perfusion rates and lipid contents of the tissues. In abdominal fat, residue concentrations increased with time, probably as a result of metabolism and redistribution of residues among the tissues. Residue concentrations in the fat were much higher than in any other tissue at sampling times beyond 4 h. Fat may serve as a deep storage compartment that prolongs residue elimination.

Concentrations of MG-L declined more slowly than those of MG-C in catfish muscle and plasma. Both MG-C and MG-L were more persistent in muscle than in plasma. Metabolism has a major role in the clearance of MG-C.

In summary, the disposition of malachite green in channel catfish is characterized by rapid and pH-dependent uptake during waterborne exposure, wide distribution and concentration in the tissues, and extensive metabolism primarily to MG-L.

Persistent in tissue

Applicant's summary and conclusion

Conclusions:
The disposition of Malachite Green in channel catfish is characterized by rapid and pH-dependent uptake during waterborne exposure, wide distribution and concentration in the tissues, and extensive metabolism primarily to MG-L. Persistent in tissue
Executive summary:

The disposition of malachite green was determined in channel catfish (Ictalurus punctatus) after intravascular dosing (0.8 mg/kg) or waterborne exposure (0.8 mg/L for 1 h). After intravascular dosing, mean plasma concentrations of the parent compound exhibited a triphasic decline with a terminal elimination half-life of 6.2 h. Malachite green was rapidly absorbed and concentrated in the tissues during waterborne exposure. The rate of accumulation was directly related to pH of the exposure water. After waterborne exposure, elimination of the parent compound from plasma also was triphasic with a terminal half-life of 4.7 h. In muscle, the half-life of the parent compound was approximately 67 h. Malachite green and its metabolites were widely distributed in all tissues. In fish exposed to 14^C-labeled malachite green, total drug equivalent concentrations were highest in abdominal fat and lowest in plasma. Malachite green was rapidly and extensively metabolized to its reduced form, leucomalachite green, which was slowly eliminated from the tissues. Leucomalachite green is an appropriate target analyte for monitoring exposure of channel catfish to this drug.

Conclusion

Malachite Green (MG) and its metabolites were widely distributed in all tissues. MG is rapidly and extensively metabolized to its reduced form, Leucomalachite Green (LG), which is slowly eliminated from the tissues. MG is rapidly absorbed and concentrated in the tissues during waterborne exposure. The rate of accumulation was directly related to pH of the exposure water. In muscle, the half-life of the parent compound was approximately 67 h.