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Studies on age related changes in cytochrome P-450, cytochrome b-5 and mixed function oxidase activity in mouse liver
Abstract:
Liver microsomes were isolated from male mice of various defined ages, and their ability to metabolise ethylmorphine, p-nitroanisole, p-aminobenzoic acid and aniline was assessed as was their content of cytochrome P-450, cytochrome b-5 and protein, and their lipid composition. The rising capacity of the microsomes to metabolise these substrates in the first half of the lifespan was associated with a rise in the cytochrome P-450 and cytochrome b-5 content as well as an increase in the ratio of phosphatidylcholine to both phosphatidylethanolamine and sphingomyelin and, in early adult life, decreasing saturation of phospholipid fatty acids. The lipid changes would be expected to increase microsomal membrane fluidity. Declining mixed function oxidase activity in later life paralleled a decline in the ratio of phosphatidylcholine to phosphatidylethanolamine and sphingomyelin, and progressively reduced saturation of phospholipid fatty acids. Cytochrome content showed only a slight irregular decline with advancing age until the oldest animals were investigated, in which cytochrome b-5 was considerably reduced. Unfortunately, cytochrome P-450 was not measured in the oldest available group. Inducing the mixed function oxidase system with daily phenobarbitone injections for 4 days substantially increased enzyme activity in animals up to the middle of the age range tested. Older animals showed progressively reduced induction and none at all was seen in the oldest group. In contrast with the situation in non-induced mice, these changes were more closely associated with changes in cytochrome P-450 content than with alterations of lipid composition.
Insights
Liver microsome metabolism and enzyme activity change with age, influenced by cytochrome P-450 and lipid composition. Phenobarbital induction shows reduced effectiveness in older mice, highlighting age-related metabolic decline.
Area of Science:
- Biochemistry
- Pharmacology
- Gerontology
Background:
- Liver microsomes are crucial for drug metabolism.
- Age-related changes in liver function can impact drug efficacy and toxicity.
- Understanding these changes is vital for personalized medicine and geriatrics.
Purpose of the Study:
- To investigate age-dependent alterations in mouse liver microsomal metabolism.
- To correlate metabolic activity with changes in cytochrome P-450, cytochrome b-5, and lipid composition.
- To assess the impact of phenobarbital induction on mixed-function oxidase activity across different ages.
Main Methods:
- Isolation of liver microsomes from male mice of various ages.
- Assay of metabolic activity using substrates like ethylmorphine and aniline.
- Quantification of cytochrome P-450, cytochrome b-5, protein, and lipid profiles.
- Administration of phenobarbital to assess enzyme induction response.
Main Results:
- Metabolic capacity increased in early life, linked to higher cytochrome P-450/b-5 and altered phospholipid ratios, enhancing membrane fluidity.
- Later in life, mixed-function oxidase activity declined, correlating with reduced phospholipid ratios and fatty acid saturation.
- Phenobarbital induction was less effective in older mice, with minimal response in the oldest group, more closely tied to cytochrome P-450 levels.
Conclusions:
- Age significantly impacts mouse liver microsomal function, affecting drug metabolism.
- Changes in cytochrome content and membrane lipid composition play key roles in age-related metabolic shifts.
- Reduced inducibility of the mixed-function oxidase system in aging suggests impaired drug response in elderly populations.