Effect of insulin on ketogenesis and fatty acid synthesis in rat hepatocytes incubated with dichloroacetate

Successful long-term xenoperfusion of the pig liver: continuous administration of prostaglandin E1 and insulin

For clinical utilization of extracorporeal liver perfusion as an artificial liver assist device, we examined the possibility of long-term xenoperfusion of the pig liver by the continuous administration of prostaglandin E1 (PGE1) and insulin. After a 3-hr perfusion period, pig livers that were xenoperfused with human blood exhibited a drastic decrease in the perfusate volume, a progressive elevation of the hepatic artery pressure, a gradual deterioration of bile production, and a marked increase in the release of creatine kinase-BB component. The continuous administration of PGE1 (25 microg/hr) and insulin (1 U/hr) significantly improved these derangements (P<0.05) and allowed stable perfusion for up to 9 hr. This manipulation also inhibited leukocyte aggregation in the graft, the characteristic perfusate hemolysis, and acceleration of ketogenesis. Histological examination revealed that the interlobular edema and hemorrhage, characteristics of tissue injuries in xenogeneic hyperacute rejection, were markedly alleviated in the PGE1 and insulin-treated group. This study clarifies the finding that the combined administration of PGE1 and insulin is effective for long-term xenogeneic extracorporeal liver perfusion, with the graft viability well maintained.

The pharmacology of dichloroacetate

Dichloroacetate (DCA) exerts multiple effects on pathways of intermediary metabolism. It stimulates peripheral glucose utilization and inhibits gluconeogeneis, thereby reducing hyperglycemia in animals and humans with diabetes mellitus. It inhibits lipogenesis and cholesterolgenesis, thereby decreasing circulating lipid and lipoprotein levels in short-term studies in patients with acquired or hereditary disorders of lipoprotein metabolism. By stimulating the activity of pyruvate dehydrogenase, DCA facilitates oxidation of lactate and decreases morbidity in acquired and congenital forms of lactic acidosis. The drug improves cardiac output and left ventricular mechanical efficiency under conditions of myocardial ischemia or failure, probably by facilitating myocardial metabolism of carbohydrate and lactate as opposed to fat. DCA may also enhance regional lactate removal and restoration of brain function in experimental states of cerebral ischemia. DCA appears to inhibit its own metabolism, which may influence the duration of its pharmacologic actions and lead to toxicity. DCA can cause a reversible peripheral neuropathy that may be related to thiamine deficiency and may be ameliorated or prevented with thiamine supplementation. Other toxic effects of DCA may be species-specific and reflect marked interspecies variation in pharmacokinetics. Despite its potential toxicity and limited clinical experience, DCA and its derivatives may prove to be useful in probing regulatory aspects of intermediary metabolism and in the acute or chronic treatment of several metabolic disorders.

Regulation of renal and hepatic pyruvate dehydrogenase complex on carbohydrate re-feeding after starvation. Possible mechanisms and a regulatory role for thyroid hormone

The work investigated the mechanisms for modulation of renal and hepatic pyruvate dehydrogenase complex (PDH) activities after carbohydrate re-feeding of 48 h-starved rats, and identified a regulatory role for tri-iodothyronine. Glucose re-feeding decreased blood concentrations of lipid fuels in both euthyroid and hyperthyroid rats. This treatment was not associated with re-activation of hepatic PDH in either group of rats, or of renal PDH in hyperthyroid rats (where activity was already high), but it increased renal PDH in euthyroid rats. Dichloroacetate (DCA), an activator of PDH kinase, increased renal PDH activities in euthyroid rats, but not hyperthyroid rats, and effects of glucose re-feeding or hyperthyroidism were no longer apparent. These treatments therefore exert their effects on renal PDH through changes in PDH kinase. DCA re-activation of hepatic PDH was more marked in hyperthyroid than in euthyroid rats, suggesting that, under conditions of inhibited kinase activity, PDH phosphatase is more active in livers of hyperthyroid rats. The limited effect of DCA on hepatic PDH in euthyroid rats was potentiated by glucose re-feeding or insulin, but not by inhibition of lipolysis, demonstrating a direct effect of insulin to increase hepatic PDH phosphatase. Glucose re-feeding, inhibition of lipolysis or insulin administration did not increase hepatic PDH in DCA-treated hyperthyroid rats, indicating that effects of hyperthyroidism and of insulin on PDH phosphatase are not additive.

Hepatic pyruvate metabolism during liver regeneration after partial hepatectomy in the rat

Hepatic pyruvate kinase (PK) and pyruvate dehydrogenase (PDHa) specific activities were decreased after partial hepatectomy or sham operation. The decreases were more marked and sustained after partial hepatectomy. These activity changes ensure that hepatic carbon flux after partial hepatectomy is predominantly in the direction of gluconeogenesis. The decrease in PK specific activity observed after partial hepatectomy was associated with a decreased PK activation ratio (activity measured at 0.15 mM PEP: activity measured at 5.0 mM PEP), and hepatic concentrations of PEP were increased. The low hepatic PDHa activity observed at the first day after partial hepatectomy occurred concomitantly with an increased fatty acid concentration. PDHa activity increased after inhibition of lipolysis. The results indicate that carbohydrate utilization is unimportant for hepatic energy supply during liver regeneration. There was no evidence that the control of PK or PDH in the regenerative liver after partial hepatectomy differed from that observed in the liver of the unoperated rat.

Regulation of flux through pyruvate dehydrogenase and pyruvate carboxylase in rat hepatocytes. Effects of fatty acids and glucagon

The regulation of flux through pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) by fatty acids and glucagon was studied in situ, in intact hepatocyte suspensions. The rate of pyruvate metabolized by carboxylation plus decarboxylation was determined from the incorporation of [1-14C]pyruvate into 14CO2 plus [14C]glucose. The flux through PDH was determined from the rate of formation of 14CO2 from [1-14C]pyruvate corrected for other decarboxylation reactions (citrate cycle, phosphoenolpyruvate carboxykinase and malic enzyme), and the flux through PC was determined by subtracting the flux through PDH from the total pyruvate metabolized. With 0.5 mM pyruvate as substrate the ratio of flux through PDH/PC was 1.9 in hepatocytes from fed rats and 1.4 in hepatocytes from 24 h-starved rats. In hepatocytes from fed rats, octanoate (0.8 mM) and palmitate (0.5 mM) increased the flux through PDH (59-76%) and PC (80-83%) without altering the PDH/PC flux ratios. Glucagon did not affect the flux through PDH but it increased the flux through PC twofold, thereby decreasing the PDH/PC flux ratio to the value of hepatocytes from starved rats. In hepatocytes from starved rats, fatty acids had similar effects on pyruvate metabolism as in hepatocytes from fed rats, however glucagon did not increase the flux through PC. 2[5(4-Chlorophenyl)pentyl]oxirane-2-carboxylate (100 microM) an inhibitor of carnitine palmitoyl transferase I, reversed the palmitate-stimulated but not the octanoate-stimulated flux through PDH, in cells from fed rats, indicating that the effects of fatty acids on PDH are secondary to the beta-oxidation of fatty acids. This inhibitor also reversed the stimulatory effect of palmitate on PC and partially inhibited the flux through PC in the presence of octanoate suggesting an effect of POCA independent of fatty acid oxidation. It is concluded that the effects of fatty acids on pyruvate metabolism are probably secondary to increased pyruvate uptake by mitochondria in exchange for acetoacetate. Glucagon favours the partitioning of pyruvate towards carboxylation, by increasing the flux through pyruvate carboxylase, without directly inhibiting the flux through PDH.

Acute effects of tumor-promoting phorbol esters on hepatic intermediary metabolism

In hepatocytes isolated from meal-fed rats, phorbol 12-myristate 13-acetate as well as phorbol 12,13-didecanoate stimulated de novo fatty acid synthesis in a dose-dependent manner. Moreover, phorbol 12-myristate 13-acetate inhibited ketogenesis from exogenous oleate, but slightly enhanced oleate esterification. The stimulation of esterification was more pronounced with endogenously synthesized fatty acids. In hepatocytes from 24h-starved rats a moderate stimulation of gluconeogenesis and ureogenesis was observed with glutamine as substrate. It is concluded that tumor-promoting phorbol esters mimic the short-term effects of insulin on hepatic fatty acid metabolism.