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Modulation of rat liver cytochrome P450 by protein restriction assessed by biochemical and bacterial mutagenicity
L Cancino-Badías1, R E Reyes, R Nosti
1CIBIOMED, ICBP Victoria de Girón, Ciudad Habana, Cuba.
Abstract:
Protein restriction (PR) significantly inhibits spontaneous and chemical carcinogenesis. Several factors seem to be involved in this effect, including a decrease in body weight, cellular proliferation and DNA damage and an increase in antioxidant defenses. The current study was designed to determine modifications in some hepatic cytochromes P450 (CYPs) due to a hypoproteic diet and to investigate its implications on chemical mutagenesis. Western blot analysis showed decreases of 73, 40 and 74% in CYP1A, CYP2B and CYP2E1 protein concentrations in hepatic microsomes from animals fed a protein-restricted (6% protein) diet for 6 weeks in comparison with microsomes from rats fed a 24% protein diet during the same period. In the same way, low protein fed animals showed a 3.5-fold decrease in hepatic CYP1A1-associated ethoxyresorufin O-deethylase activity, a 6-fold decrease in CYP1A2-associated methoxyresorufin O-demethylase activity, a 1.7-fold decrease in CYP2B1-associated penthoxyresorufin O-dealkylase activity, a 9-fold decrease in CYP2B2-associated benzyloxyresorufin O-dealkylase and, finally, a 3.4-fold decrease in CYP2E1-associated 4-nitrophenol hydroxylase activity. As a result of decreased CYP hepatic protein concentrations and enzymatic activities, liver S9 from rats fed a hypoproteic diet was less efficient in activating promutagens than S9 prepared from rats fed a 24% protein diet in the Ames test. Mutagenic potency obtained with protein-restricted S9 was reduced 25-fold for 2-aminoanthracene, 1.5-fold for N-nitrosodipropylamine, 12.5-fold for N-nitrosodibutylamine, 2-fold for cyclophosphamide and N-nitrosopyrrolidine and 71-fold for N-nitrosodimethylamine. However, the mutagenic potency of benzo[a]pyrene was the same (4 revertants/ microg) with S9 derived from rats fed either a 6 or 24% protein diet.
Insights
Protein restriction significantly reduces carcinogenic potential by decreasing key liver enzymes (cytochromes P450). This dietary change impairs the liver
Area of Science:
- Biochemistry
- Toxicology
- Nutritional Science
Background:
- Protein restriction (PR) is known to inhibit carcinogenesis.
- Hepatic cytochromes P450 (CYPs) are crucial in metabolizing xenobiotics and procarcinogens.
- Understanding CYP modifications under PR is vital for explaining its chemoprotective effects.
Purpose of the Study:
- To investigate the impact of a hypoproteic diet on hepatic CYP protein concentrations and enzymatic activities.
- To assess the consequences of these CYP alterations on chemical mutagenesis in rats.
Main Methods:
- Western blot analysis to quantify CYP1A, CYP2B, and CYP2E1 protein levels.
- Enzymatic activity assays (ethoxyresorufin O-deethylase, methoxyresorufin O-demethylase, etc.) to measure CYP function.
- Ames test using rat liver S9 fractions to evaluate mutagenic potency of various promutagens.
Main Results:
- A 6-week hypoproteic diet (6% protein) significantly decreased CYP1A, CYP2B, and CYP2E1 protein concentrations (73%, 40%, 74% respectively).
- Correspondingly, activities of CYP1A1, CYP1A2, CYP2B1, CYP2B2, and CYP2E1 were substantially reduced (3.5 to 9-fold).
- Liver S9 from protein-restricted rats showed reduced mutagenic activation of most tested promutagens (e.g., 71-fold for N-nitrosodimethylamine), except for benzo[a]pyrene.
Conclusions:
- Dietary protein restriction markedly reduces hepatic CYP levels and activities.
- This suppression of CYPs diminishes the liver's capacity to activate procarcinogens, contributing to the observed inhibition of chemical carcinogenesis.
- The study highlights the role of CYP modulation in the chemoprotective effects of protein restriction.