HYDROXYCOBALAMIN[C-LACTAM] INCREASES TOTAL COENZYME-A CONTENT IN PRIMARY CULTURE HEPATOCYTES BY ACCELERATING COENZYME-A BIOSYNTHESIS SECONDARY TO ACYL-COA ACCUMULATION

Hydroxycobalamin[c-lactam] (HCCL) treatment in rats results in decreas ed hepatic L-methylmalonyl-CoA mutase activity and increased hepatic t otal CoA content. To test the hypothesis that HCCL increases hepatic C oA biosynthesis secondary to propionyl- and methylmalonyl-CoA accumula tion, CoA homeostasis was studied in primary culture rat hepatocytes. Conversion of [C-14]pantothenic acid to [C-14]CoA in the primary cultu re system was accelerated to rates 3-5 times control by acute incubati on with the acyl-CoA-generating carboxylic acids pivalate (10 mmol/L) or propionate (10 mmol/L). HCCL (1 mg/L included from 24 to 72 h of cu lture) had no affect on the distribution of the hepatocyte CoA pool or total CoA content. However, culture in the presence of HCCL and propi onate (2 mmol/L) resulted in accumulation of methylmalonyl-CoA and a 5 9% increase in total CoA content. The combination of HCCL (1 mg/L) and propionate (0.5 mmol/L), but not HCCL alone, increased the rate of [C -14]pantothenic acid conversion to [C-14]CoA by 150%. Degradation of [ C-14]CoA in the primary culture hepatocyte system was unaffected by ch ronic exposure to 2 mmol/L propionate, but was increased 90% by the co mbination of HCCL and 2 mmol/L propionate. Thus, in the presence of a source of propionyl-CoA, HCCL treatment results in methylmalonyl-CoA a ccumulation and accelerated CoA biosynthesis. The increased CoA biosyn thesis leads to increased hepatocyte total CoA content, which may cont ribute to cellular metabolic homeostasis under conditions of acyl-CoA accretion.