Ascorbic acid inhibits chemically induced uroporphyria in ascorbate-requiring rats

Area of Science:

• Biochemistry
• Toxicology
• Nutritional Science

Background:

• Uroporphyrin (URO) accumulation can be induced by certain chemicals.
• Ascorbate (vitamin C) has shown potential in suppressing URO accumulation in vitro.
• The Osteogenic Disorder Shionogi (ODS) mutant rat lacks endogenous ascorbic acid synthesis, making it a model for in vivo studies.

Purpose of the Study:

• To investigate the in vivo effect of ascorbic acid on hepatic uroporphyrin accumulation in ODS mutant rats.
• To determine the dose-dependency of dietary ascorbic acid in preventing chemically-induced uroporphyria.

Main Methods:

• ODS mutant rats were fed varying dietary levels of ascorbic acid (15, 200, 800 ppm).
• Rats were treated with 3-methylcholanthrene (MC) and 5-aminolevulinate (ALA) to induce uroporphyrin accumulation.
• Hepatic and plasma ascorbic acid levels were measured.
• Cytochrome P450 levels and enzyme activities were assessed.

Main Results:

• Hepatic URO accumulated in ODS rats at low dietary ascorbic acid levels (15, 200 ppm) but not at 800 ppm.
• High dietary ascorbic acid (800 ppm) normalized hepatic ascorbic acid levels and prevented URO accumulation.
• MC/ALA treatment did not induce URO accumulation in normal Fischer 344 rats, which had higher hepatic ascorbate concentrations.
• Ascorbic acid's protective effect was also observed with hexachlorobenzene induction.

Conclusions:

• Dietary ascorbic acid is crucial for preventing hepatic uroporphyrin accumulation in vivo, particularly in individuals with impaired vitamin C synthesis.
• Adequate ascorbic acid levels are necessary to counteract the toxic effects of certain xenobiotics on porphyrin metabolism.