Abstract
Background: Smoking-derived nicotine (N) and oral contraceptives (OC) synergistically exacerbate both global and focal ischemic brain damage in females. While the underlying mechanisms remain elusive, our published study showed that OC exacerbate N toxicity via altered mitochondrial electron transport chain function. Because mitochondria play a central role in cellular metabolism, we examined the metabolic fingerprint of adolescent and adult female rat brains exposed to N +/- OC. Methods: Adolescent (6 weeks old) and adult (12 weeks old) Sprague-Dawley female rats were randomly (n = 8/group) exposed to either saline, N (4.5 mg/kg) +/- OC for 16-21 days. Following treatment, brain tissue was harvested for unbias metabolomic analysis (performed by Metabolon Inc.). The metabolomic profile was complemented with western blot analysis and enzyme activity measurements. Results: Pathway enrichment analysis showed significant alterations in lipid metabolism. Adolescent but not adult females treated with N, OC and N+OC compared to saline showed significant increases in carnitine conjugated fatty acid metabolites such as arachidonoylcarnitine (C20:4), docosahexaenoylcarnitine (C22:6) and stearoylcarnitine (C18). These changes in fatty acyl carnitines were accompanied by an increase in a subset of free fatty acids, suggesting elevated fatty acid β-oxidation in the mitochondria to meet energy demand. In support, 3-hydroxybutyrate (BHBA) was significantly lower in OC and N+OC treatment group in adolescent animals, implying a complete shunting of acetyl CoA for energy production via TCA cycle. BHBA is a ketone body that increases in concentration as lipid oxidation rates increase with acetyl CoA accumulation. Reduced BHBA levels may also suggest mitochondrial dysfunction in response to OC and N+OC treatment. Conclusion: The observed changes in the metabolic fingerprint and fatty acid metabolism reflect a general alteration in energy metabolism with nicotine treatment exclusively in young animals and these changes are enhanced by N+OC treatment. Discerning the exact effects of N +/- OC on overall brain metabolism and the molecular mechanisms affecting mitochondrial function at different ages will open a new window for future therapeutic intervention.