Protection against oxidative stress-induced insulin resistance in rat L6 muscle cells by mircomolar concentrations of alpha-lipoic acid.
In diabetic patients, alpha-lipoic acid (LA) improves skeletal muscle glucose transport, resulting in increased glucose disposal; however, the molecular mechanism of action of LA is presently unknown. We studied the effects of LA on basal and insulin-stimulated glucose transport in cultured rat L6 muscle cells that overexpress GLUT4. When 2-deoxy-D-glucose uptake was measured in these cells, they were more sensitive and responsive to insulin than wild-type L6 cells. LA, at concentrations < or = 1 mmol/l, had only small effects on glucose transport in cells not exposed to oxidative stress. When cells were exposed to glucose oxidase and glucose to generate H2O2 and cause oxidative stress, there was a marked decrease in insulin-stimulated glucose transport. Pretreatment with LA over the concentration range of 10-1,000 pmol/l protected the insulin effect from inhibition by H2O2. Both the R and S isomers of LA were equally effective. In addition, oxidative stress caused a significant decrease (approximately 50%) in reduced glutathione concentration, along with the rapid activation of the stress-sensitive p38 mitogen-activated protein kinase. Pretreatment with LA prevented both of these events, coincident with protecting insulin action. These studies indicate that in muscle, the major site of insulin-stimulated glucose disposal, one important effect of LA on the insulin-signaling cascade is to protect cells from oxidative stress-induced insulin resistance.
Diabetes Research Laboratory, Mount Zion Hospital, San Francisco, California 94143-1616, USA. bmaddux@itsa.ucsf.edu
B A
BA
Maddux
W
W
See
J C
JC
Lawrence
A L
AL
Goldfine
I D
ID
Goldfine
J L
JL
Evans
D000818:Animals; D016923:Cell Death / Q000502:physiology; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D005949:Glucose Oxidase / Q000494:pharmacology; D051275:Glucose Transporter Type 4; D005978:Glutathione / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D007333:Insulin Resistance / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000187:drug effects / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D009994:Osmolar Concentration; D016877:Oxidants / Q000378:metabolism; D018384:Oxidative Stress / Q000502:physiology*; D051381:Rats; D012016:Reference Values; D008063:Thioctic Acid / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases
D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D016877:Oxidants; C495694:Slc2a4 protein, rat; D008063:Thioctic Acid; D006861:Hydrogen Peroxide; D007770:L-Lactate Dehydrogenase; D005949:Glucose Oxidase; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D005978:Glutathione; D005947:Glucose