Registration Dossier

Toxicological information

Basic toxicokinetics

Currently viewing:

Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Publication the metabolism of a representative member of the chemical aliphatic nitrate esters, which meets generally accepted standards.

Data source

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
The cardiovascular drug glyceryl trinitrate (CAS 55-63-0, considered a representative member of the chemical aliphatic nitrate esters), while stable at 37°C in neutral aqueous solution, decomposes in the presence of blood and other tissue preparations to yield inorganic nitrite. The mechanism and kinetics of this reductive breakdown was investigated by measuring nitrite formation from glyceryl trinitrate and glutathione (GSH, CAS 70-18-8) incubated with a protein fraction from hog liver.
GLP compliance:
no

Test material

Radiolabelling:
no

Results and discussion

Main ADME results
Type:
metabolism
Results:
Nitroglycerin incubated with reduced glutathione (GSH) was found to undergo a reaction forming nitrite and oxidized glutathione after incubation with hog liver enzymes in vitro. Kinetics: See attached image (figure 2 of the publication).

Toxicokinetic / pharmacokinetic studies

Toxicokinetic parameters
Toxicokinetic parameters:
half-life 1st: Half-life of nitroglycerin is <2 h, carefully estimated from figure 2 of the publication (attached).

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
Nitroglycerin (CAS 55-63-0) and reduced glutathione (GSH, CAS 70-18-8) were found to undergo a reaction forming Nitrite (CAS 14797-65-0) and oxidized glutathione (CAS 27025-41-8). This reaction took place when crude tissue extracts were present and was catalysed by a specific enzyme, which has been purified from hog liver. It had a pH optimum between 7 and 8 (about physiologic pH). The rate and extent of the reaction could be correlated with the GSH content.

Any other information on results incl. tables

1. Nitroglycerin (CAS 55-63-0) and reduced Glutathione (GSH, CAS 70-18-8) were found to undergo a reaction forming Nitrite (CAS 14797-65-0) and Oxidized glutathione (CAS 27025-41-8). Reduction of Nitroglycerin preceded via hydrolysis because inorganic nitrate did not react with GSH. The rate of nitrite formation was appreciable in neutral aqueous solution but increased rapidly as the pH became more alkaline. GSH could be replaced by cysteine (CAS 52 -90 -4) or cysteinylglycine (CAS 19246-18-5).

2. An enzyme has been purified from hog liver acetone powder which catalyses the reaction between nitroglycerin and GSH. It had a pH optimum between 7 and 8 (about physiologic pH) and was sensitive to traces of cupric salts. The enzyme did not stimulate the reaction between cysteine and nitroglycerin.

3. When crude tissue extracts were incubated with nitroglycerin, nitrite was formed. The rate and extent of the reaction could be correlated with the GSH content of these extracts.

4. When inorganic nitrate was incubated with GSH, no measurable amount of nitrite was formed. Thus the reaction seems specific to organonitrates.

5. The attached figure (figure 2 of the publication) shows the kinetics of the in vitro transformation. It can be concluded that the half-life of nitroglycerin is less than two hours based on the formation of nitrite in the figure.

Applicant's summary and conclusion

Conclusions:
It can be concluded that the half-life of nitroglycerin is less than two hours based on the formation of nitrite in curve 1 in the figure. Based on the results in this publication, the nitrite metabolite from nitroglycerin is expected to be similar or identical to the metabolite formed during 2-EHN metabolism to 2-EH and nitrate/nitrite.