Stimulation by acetate of gluconeogenesis in hepatocyte suspensions

Acetyl-CoA carboxylase 1 and 2 inhibition ameliorates steatosis and hepatic fibrosis in a MC4R knockout murine model of nonalcoholic steatohepatitis

Acetyl-CoA carboxylase (ACC) catalyzes the rate-limiting step in de novo lipogenesis, which is increased in the livers of patients with nonalcoholic steatohepatitis. GS-0976 (firsocostat), an inhibitor of isoforms ACC1 and ACC2, reduced hepatic steatosis and serum fibrosis biomarkers such as tissue inhibitor of metalloproteinase 1 in patients with nonalcoholic steatohepatitis in a randomized controlled trial, although the impact of this improvement on fibrosis has not fully been evaluated in preclinical models. Here, we used Western diet-fed melanocortin 4 receptor-deficient mice that have similar phenotypes to nonalcoholic steatohepatitis patients including progressively developed hepatic steatosis as well as fibrosis. We evaluated the effects of ACC1/2 inhibition on hepatic fibrosis. After the confirmation of significant hepatic fibrosis with a 13-week pre-feeding, GS-0976 (4 and 16 mg/kg/day) treatment for 9 weeks lowered malonyl-CoA and triglyceride content in the liver and improved steatosis, histologically. Furthermore, GS-0976 reduced the histological area of hepatic fibrosis, hydroxyproline content, mRNA expression level of type I collagen in the liver, and plasma tissue metalloproteinase inhibitor 1, suggesting an improvement of hepatic fibrosis. The treatment with GS-0976 was also accompanied by reductions of plasma ALT and AST levels. These data demonstrate that improvement of hepatic lipid metabolism by ACC1/2 inhibition could be a new option to suppress fibrosis progression as well as to improve hepatic steatosis in nonalcoholic steatohepatitis.

Mitochondrial pyruvate carrier--a possible link between gluconeogenesis and ketogenesis in the liver

Effects of various ketogenic substrates on gluconeogenesis from lactate or alanine were compared. The results suggest that, in intact liver cells, cytoplasmic pyruvate is transported into mitochondria in exchange for intramitochondrially generated acetoacetate. An interrelationship between gluconeogenesis and ketogenesis may thus exist in the liver at the level of mitochondrial pyruvate carrier.

Possible interrelationship between gluconeogenesis and ketogenesis in the liver

Effects of various ketogenic substrates on gluconeogenesis from lactate were examined. D,L-3-Hydroxybutyrate (5 mM) stimulated gluconeogenesis by 41%, the effect being the same as that of 5 mM acetate (49%). No stimulating effect of acetoacetate was observed; conversely, acetoacetate (up to 40 mM) partially or completely abolished the observed stimulating effects of acetate, oleate, and 3-hydroxybutyrate. The results suggest that, in intact liver cells, pyruvate is transported into mitochondria in exchange for acetoacetate and that an interrelationship between gluconeogenesis and ketogenesis at the level of mitochondrial pyruvate carrier may exist in the liver.

Metabolic capability of rat hepatocytes isolated by perfusion and tissue slice techniques

The metabolic capability of hepatocytes prepared by the perfusion method (P cells) and the tissue slice method (S cells) has been compared using standardised procedures. Yields of P cells were four times greater than for S cells. Trypan blue exclusion viability and oxygen utilization were similar although the viability of S cells deteriorated faster with time. P cells had a lower endogenous rate of glycogenolysis and showed better glucagon stimulation than S cells. Similarly, P cells performed gluconeogenesis at a higher rate. However, there was no significant differences in the metabolism of the xenobiotic ethoxycoumarin. It is concluded that while S cells are probably satisfactory for studies of drug metabolism their use for work involving surface receptor binding and energy demanding processes should be questioned.

A multichannel perifusion system for the continuous monitoring of glycogenolysis and gluconeogenesis in isolated rat hepatocytes

A multichannel perifusion system for isolated rat hepatocytes entrapped in a Sephadex matrix is described and criteria for the choice of matrices are discussed. This system overcomes the usual problem of clogged filters and impaired flow rates encountered in suspension perifusion systems, and is assembled from standard widely available components. Gluconeogenic capability and mitochondrial respiratory control ratios were unaltered. Decreases in trypan blue viability index and respiration rate were small when compared with flask-incubated hepatocytes. The endogenous rate of glycogenolysis was slightly higher in perifused hepatocytes but hormone response, as judged by glucagon stimulation of glycogenolysis, was unimpaired. The potential of this system is indicated by experiments monitoring glycogenolysis and gluconeogenesis in recycling and non-recycling modes.