Palmitate-induced beta-cell insensitivity to glucose is coupled to decreased pyruvate dehydrogenase activity and enhanced kinase activity in rat pancreatic islets.
We previously found that long-term exposure to fatty acids impairs glucose-induced insulin release. In the present study, we investigated whether impairment is related to decreased pyruvate dehydrogenase (PDH) and increased PDH kinase activity. Rat pancreatic islets were cultured for 48 h in RPMI-1640 medium with or without 0.125 mmol/l palmitate. Potentiation of insulin responses to succinic acid monomethylester (SAM) by 10 mmol/l acetate and pyruvate were subsequently compared in order to assess whether generation of acetyl-coenzyme A (CoA) from pyruvate was deficient in the intact beta-cell. Potentiation by acetate was similar in control and palmitate-preexposed islets. In contrast, pyruvate potentiated SAM-induced response by 122% in control but by only 39% in palmitate-exposed islets (P < 0.001). In extracts of palmitate-exposed islets, the active (unphosphorylated) form of PDH was decreased by 50% and total PDH activity (assessed after phosphatase treatment) by 25%. The proportion of active form to total PDH activity was also reduced (42.7 +/- 2.6% after palmitate vs. 66.6 +/- 4.3% in control islets, P < 0.01). In the same preparations, PDH kinase activity was enhanced 1.7-fold by palmitate in terms of the rate constant of ATP-dependent inactivation of PDH (P < 0.05). To test for a role of free (not PDH-bound) kinase, a PDH-free mitochondrial fraction was prepared, and its kinase activity was tested against a pig heart PDH preparation. Free kinase activity was increased 1.9-fold in palmitate-treated islets (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Zhou
Y P
YP
Department of Molecular Medicine, Karolinska Hospital, Karolinska Institute, Stockholm, Sweden.
Grill
V E
VE
D000085:Acetates / Q000494:pharmacology; D000818:Animals; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000201:enzymology*; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D010168:Palmitates / Q000494:pharmacology*; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D011770:Pyruvate Kinase / Q000378:metabolism*; D011773:Pyruvates / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012636:Secretory Rate / Q000187:drug effects; D013386:Succinates / Q000494:pharmacology
D000085:Acetates; D007328:Insulin; D010168:Palmitates; D011768:Pyruvate Dehydrogenase Complex; D011773:Pyruvates; D013386:Succinates; D011770:Pyruvate Kinase; D005947:Glucose