TNF-ALPHA AND IL-6 SYNERGISTICALLY INHIBIT KETOGENESIS FROM FATTY-ACIDS AND ALPHA-KETOISOCAPROATE IN ISOLATED RAT HEPATOCYTES

Background: During sepsis, lipid metabolism is shunted toward triacylg lycerol synthesis and hepatic lipogenesis. A decrease in ketogenesis f rom free fatty acids also is observed, probably mediated by cytokines involved in host response to infection. Whether such an inhibition of ketogenesis occurs with other ketone body precursors such as ketoacids is not known. The aim of this study was to determine the effects of t umor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) on hep atic ketone body production from octanoic acid, a medium-chain fatty a cid, and from alpha-ketoisocaproate (KIC), the ketoanalogue of leucine ; Methods: The experiments were conducted in cultured hepatocytes isol ated from 24-hour-fasted Sprague-Dawley rats. Hepatocyte monolayers we re incubated for 6 hours, with either KIC or octanoic acid (1 mmol/L), in the presence of glucagon and TNF-alpha (25 mu g/L) IL-6 (15 mu g/L ) and/or IL-6. Acetoacetate, beta-hydroxybutyrate, and free fatty acid s were determined in culture medium by enzymatic methods and KIC was m easured by high-performance liquid chromatography. Results: KIC and oc tanoic acid uptake by hepatocytes was 79% and 92%, respectively, over 6 hours, and cytokines had no influence. However, TNF-alpha and IL-6 c aused inhibition of ketogenesis fi om alpha-ketoisocaproate (5.6% +/- 2.3% and 4.4% +/- 3.0%, respectively), and from octanaic acid (7.9% +/ - 2.9%, 5.7% +/- 3.2%, respectively). In addition, when the two cytoki nes were present together in the culture medium, the inhibition was en hanced (inhibition of ketogenesis from KIC: 14.0% +/- 4.8%; from octan oic acid: 11.6% +/- 3.4%). Conclusions: In our experimental conditions , cytokines mediate an inhibition of ketogenesis; this process could b e explained by a direct effect of cytokines on metabolic pathways of o ctanoic acid and KIC oran indirect effect by modification of the mitoc hondrial redox state.