Abstract WP268: Roles And Regulation Of Ketogenesis In Cultured Astroglia And Neurons Under Hypoxia

Abstract

Purpose: Although exogenous ketone bodies (KBs), acetoacetate (AA) and β-hydroxybutyrate (BHB) can serve as alternative energy substrates in neural cells under starvation, the exact roles and the regulation of ketogenesis in the brain remain uncertain. The present study examined the ketogenic capacity of cultured rat astroglia under hypoxia and possible roles and the regulation of KBs in neuronal energy metabolism. Methods: Primary neurons and secondary astroglia were prepared from SD rats. Palmitic acid (PA) and L-carnitine (LC) were added to the nutrient medium. AA and BHB produced and released in the medium during 24h were measured using the cyclic thio-NADH method. 14 C-labeled acid-soluble products (i.e., KBs) and 14 CO 2 produced from [1- 14 C]PA were measured to assess the role of PA and KBs as energy substrates in the TCA cycle. [U- 14 C]lactate or [1- 14 C]BHB was used to compare the oxidative metabolism of the end-products of glycolysis with those of the β-oxidation of fatty acid. Some cells were placed in a hypoxic chamber (1%O 2 ) for 12h-24h to evaluate the effects of hypoxia and re-oxygenation on KB metabolism. Results: PA (100 μM) and LC (1 mM) induced higher KB production (mean ± SD in pmol/μg /24h, n=6) in astroglia (AA: 40.8 ± 1.3, BHB: 9.6 ± 1.4) than in neurons (AA: 0.3 ± 1.5, BHB: 2.2 ± 2.7), while CO 2 production from PA was less than 5% of the KB production in astroglia. KB production was augmented by AICAR (500 μM), a cell-permeable AMPK activator (AA: 66.8 ± 8.7, BHB: 12.7 ± 0.9) as well as hypoxia (AA: 59.4 ± 5.1, BHB: 30.0 ± 14.4) in astroglia. [1- 14 C]BHB oxidation (mean ± SD in pmol/μg/h, n=4) in neurons (2.9 ± 0.6) was about 1.5 times as high as that in astroglia (1.8 ± 0.1). [U- 14 C]lactate oxidation in astroglia (14.0 ± 4.6) was not affected by addition of BHB (13.3 ± 4.7) in astroglia, while that in neurons (21.5 ± 2.8) was reduced by 15% (18.1 ± 1.2, P <0.05). Conclusions: Astroglia responded to hypoxia by enhancing KB production in the presence of PA and LC, and KBs produced by astroglia might serve as a neuronal energy substrate for the TCA cycle in place of lactate, since pyruvate dehydrogenase is susceptible to ischemia. The activation of astroglial ketogenesis may reduce ischemic cell damage after stroke.