scholarly journals Evidence that metformin exerts its anti-diabetic effects through inhibition of complex 1 of the mitochondrial respiratory chain

2000 ◽  
Vol 348 (3) ◽  
pp. 607-614 ◽  
Author(s):  
Mark R. OWEN ◽  
Elena DORAN ◽  
Andrew P. HALESTRAP
Keyword(s):  
Respiratory Chain ◽  
Rat Hepatocytes ◽  
Mitochondrial Respiratory Chain ◽  
Time Dependent ◽  
Succinate Oxidation ◽  
Isolated Rat Hepatocytes ◽  
Peripheral Tissues ◽  
Dependent Inhibition ◽  
Insulin Dependent ◽  
Mitochondrial Oxidation

Although metformin is widely used for the treatment of non-insulin-dependent diabetes, its mode of action remains unclear. Here we provide evidence that its primary site of action is through a direct inhibition of complex 1 of the respiratory chain. Metformin (50 μM) inhibited mitochondrial oxidation of glutamate+malate in hepatoma cells by 13 and 30% after 24 and 60 h exposure respectively, but succinate oxidation was unaffected. Metformin also caused time-dependent inhibition of complex 1 in isolated mitochondria, whereas in sub-mitochondrial particles inhibition was immediate but required very high metformin concentrations (K0.5, 79 mM). These data are compatible with the slow membrane-potential-driven accumulation of the positively charged drug within the mitochondrial matrix leading to inhibition of complex 1. Metformin inhibition of gluconeogenesis from L-lactate in isolated rat hepatocytes was also time- and concentration-dependent, and accompanied by changes in metabolite levels similar to those induced by other inhibitors of gluconeogenesis acting on complex 1. Freeze-clamped livers from metformin-treated rats exhibited similar changes in metabolite concentrations. We conclude that the drug's pharmacological effects are mediated, at least in part, through a time-dependent, self-limiting inhibition of the respiratory chain that restrains hepatic gluconeogenesis while increasing glucose utilization in peripheral tissues. Lactic acidosis, an occasional side effect, can also be explained in this way.

Inhibition of GSH efflux from rat liver by methionine: effects of GSH synthesis in cells and perfused organ

1990 ◽  
Vol 258 (6) ◽  
pp. G967-G973 ◽  
Author(s):  
J. C. Fernandez-Checa ◽  
T. Maddatu ◽  
M. Ookhtens ◽  
N. Kaplowitz
Keyword(s):  
Rat Liver ◽  
Reduced Glutathione ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Perfused Liver ◽  
Isolated Rat Hepatocytes ◽  
Dependent Inhibition ◽  
Krebs Henseleit Buffer ◽  
Isolated Rat ◽  
In Cells

The inhibition of efflux of intracellular reduced glutathione (GSH) by methionine was determined in isolated rat hepatocytes suspended either in Krebs-Henseleit buffer or in modified Fisher's medium. Methionine (1 mM) added to Krebs-Henseleit suspensions of isolated rat hepatocytes inhibited GSH efflux, with greater retention of GSH in the cells compared with control. Results were similar with methionine and 0.3 mM propargylglycine cystathionase inhibitor), suggesting no net synthesis of GSH from methionine. In Fisher's medium, the inhibitory effect of methionine on GSH efflux was masked due to increasing cellular GSH; however, the inhibitory effect of methionine was unmasked by propargylglycine, which prevented the utilization of methionine for GSH synthesis. The addition of serine (0.1 mM) to methionine in Krebs-Henseleit buffer raised cellular GSH, overcoming the inhibition of GSH efflux. In the perfused liver, infusion of 1 and 5 mM methionine initially inhibited GSH efflux, but the inhibition was reversed with continued methionine infusion. After removal of methionine, GSH efflux increased immediately. The reversal and rebound were blocked by propargylglycine, revealing concentration-dependent inhibition of sinusoidal GSH efflux by methionine. Thus, when methionine is utilized to promote GSH synthesis, its inhibitory effect on GSH efflux tends to be overcome.

scholarly journals Modulation of glucagon-induced glucose production by dexfenfluramine in rat hepatocytes

1995 ◽  
Vol 310 (1) ◽  
pp. 61-66 ◽  
Author(s):  
B Comte ◽  
A Romanelli ◽  
S Tchu ◽  
G van de Werve
Keyword(s):  
Cyclic Amp ◽  
Pyruvate Kinase ◽  
Glucose Production ◽  
Rat Hepatocytes ◽  
Significant Drop ◽  
Isolated Rat Hepatocytes ◽  
Dependent Inhibition ◽  
Dose Dependent Inhibition ◽  
Inhibition Of Glycolysis ◽  
State Concentration

The mechanism of the antihyperglycaemic action of dexfenfluramine (DEXF) was investigated in isolated rat hepatocytes exposed to glucagon. Preincubation of hepatocytes with DEXF caused a dose-dependent inhibition of cyclic AMP formation by 100 nM glucagon (Ki = 0.29 mM) that was almost complete at 1 mM DEXF. Surprisingly, glucagon-induced phosphorylase activation was not affected by DEXF despite the significant drop in cyclic AMP levels. Glucose production stimulated by glucagon was inhibited by up to 48% by 1 mM DEXF, and the rate of glucose production correlated positively with the steady-state concentration of glucose 6-phosphate. DEXF also partially restored lactate + pyruvate production which was abolished by an optimal concentration of glucagon. Although DEXF was not able to prevent the inactivation of pyruvate kinase by glucagon, the lack of further accumulation of phosphoenolpyruvate in DEXF-treated cells supports the conclusion that the flux through pyruvate kinase is stimulated, probably via the increase in fructose 2,6-bisphosphate, thereby increasing glycolysis. Our results thus indicate that DEXF counteracts the inhibition of glycolysis by glucagon and that this property might contribute to the antihyperglycaemic effect of this drug. Furthermore, this study shows that, in the presence of the drug, glucagon caused phosphorylase activation and pyruvate kinase inactivation without a significant increase in cyclic AMP levels.

Time-dependent alterations in the pathway of glucose incorporation into glycogen in primary cultures of rat hepatocytes following glucose starvation

1988 ◽  
Vol 66 (2) ◽  
pp. 143-147 ◽  
Author(s):  
M. A. Parniak ◽  
N. Kalant
Keyword(s):  
Amino Acids ◽  
Glycogen Synthesis ◽  
Primary Cultures ◽  
Rat Hepatocytes ◽  
Time Dependent ◽  
Glucose Starvation ◽  
Isolated Rat Hepatocytes ◽  
Glucose Incorporation ◽  
Gluconeogenic Substrates ◽  
Isolated Rat

Isolated rat hepatocytes maintained in primary culture were able to use glucose for glycogen synthesis by both direct and indirect mechanisms. Cells that had been isolated from fed animals and then cultured in the absence of glucose, but in the presence of gluconeogenic substrates such as pyruvate and amino acids, had decreased glycogen contents compared with similar cells that had been cultured in the presence of glucose. Upon reexposure to glucose, the glucose-starved cells showed time-dependent changes in the preferred pathway for the use of glucose for glycogen synthesis. These changes were noted either in the absence or presence of insulin; however, net accumulation of glycogen was observed only in the presence of the hormone.

scholarly journals Homologous β-adrenergic desensitization in isolated rat hepatocytes

1987 ◽  
Vol 246 (2) ◽  
pp. 331-336 ◽  
Author(s):  
J A García-Sáinz ◽  
B Michel
Keyword(s):  
Rat Hepatocytes ◽  
Time Dependent ◽  
Adrenergic Agonists ◽  
Isolated Rat Hepatocytes ◽  
Beta Adrenergic ◽  
Beta Adrenergic Agonists ◽  
Cyclic Amp Accumulation ◽  
Homologous Desensitization ◽  
Isolated Rat ◽  
Stimulation Of

Hepatocytes from hypothyroid rats have a marked beta-adrenergic responsiveness. Preincubation of these hepatocytes with isoprenaline induced a time-dependent and concentration-dependent desensitization of the beta-adrenergic responsiveness without altering that to glucagon (homologous desensitization). The desensitization was evidenced both in the cyclic AMP accumulation and in the stimulation of ureagenesis induced by the beta-adrenergic agonists. Under the same conditions, preincubation with glucagon induced no desensitization. Propranolol was also unable to induce desensitization, but blocked that induced by isoprenaline. Pertussis-toxin treatment did not alter the homologous beta-adrenergic desensitization induced by isoprenaline.

Sign in / Sign up

Export Citation Format

Share Document