Niacin catabolism in rodents

Area of Science:

• Pharmacology
• Metabolism Studies
• Comparative Toxicology

Background:

• Nicotinamide (vitamin B3) is essential for cellular metabolism.
• Understanding its metabolic pathways and excretion is crucial for drug development and toxicology.
• Rodent models are frequently used to study xenobiotic metabolism, but species-specific differences exist.

Purpose of the Study:

• To investigate and compare the urinary excretion of nicotinamide and its metabolites in mouse, guinea pig, and hamster.
• To elucidate species-specific differences in nicotinamide catabolism following administration of nicotinamide or N1-methylnicotinamide (MNA).

Main Methods:

• Administration of pharmacological doses of nicotinamide or MNA to mouse, guinea pig, and hamster.
• Analysis of urinary excretion of nicotinamide and its metabolites (nicotinamide N-oxide, N1-methyl-2-pyridone-5-carboxamide (2-Pyr), N1-methyl-4-pyridone-3-carboxamide (4-Pyr), nicotinic acid, nicotinuric acid, and MNA).
• Quantitative assessment of metabolite proportions in urine.

Main Results:

• Mouse primarily excretes nicotinamide N-oxide (35%) and 2-Pyr (20%).
• Guinea pig predominantly excretes 2-Pyr (80%).
• Hamster primarily excretes nicotinamide (44%) and 2-Pyr (21%).
• Nicotinic acid and nicotinuric acid were not detected in mice but were significant in guinea pigs (50.4%, 26.3%) and hamsters (7.7%, 79.5%) after nicotinamide injection.
• Nicotinamide N-oxide dominated mouse excretion post-injection (79.7%), while deamidated metabolites predominated in guinea pigs and hamsters.

Conclusions:

• Rodent species exhibit distinct urinary excretion profiles for nicotinamide and its metabolites.
• Metabolic pathways, particularly deamidation, vary significantly among mouse, guinea pig, and hamster.
• These findings underscore the importance of considering species-specific differences in nicotinamide metabolism research.