Dual influence of aging and vitamin B6 deficiency on delta-6-desaturation of essential fatty acids in rat liver microsomes

Delta-6-desaturase (D6D) activity is influenced by many nutritional and non-nutritional factors, among which one of the most important is aging. D6D activity could be susceptible to the dual influence of aging itself and of nutritional deficiencies, due to the reduced intake and/or absorption of essential nutrients. Particularly, vitamin B-6 deficiency might be a crucial factor for D6D activity in aged people. Using 20 month old Sprague-Dawly rats fed a diet with a subnormal lever of vitamin B-6, we evaluated D6D activity for linoleic acid (LA) and alpha-linolenic acid (ALA) in liver microsomes, and the fatty acid composition of microsomal total lipids. We observed a diminished D6D activity for LA and also for ALA in vitamin B-6-deficient animals, being approximately 63% and 81% respectively of the corresponding activity in control rats. As a consequence, significant modifications in the relative molar content of microsomal fatty acids were observed. The content of arachidonic and docosahexaenoic acid, the main products of the conversion of LA and ALA respectively, decreased, LA content increased and a decrease in the unsaturation index was observed in liver microsomes of B-6-deficient rats. The foregoing results suggest that the impairment of D6D activity by vitamin B-6 deficiency might be an important factor in decreasing the synthesis of n-6 and n-3 PUFAs. This may be particularly important in aging, where D6D activity is already impaired.