Effect of l-Carnitine on Acetyl-CoA Content and Activity of Blood Platelets in Healthy and Diabetic Persons

Abstract

Background: Excessive blood platelet activity contributes to vascular complications in diabetic persons. Increased acetyl-CoA in platelets from diabetic persons has been suggested to be a cause of this hyperactivity. We therefore investigated whether L-carnitine, which up-regulates metabolism of acetyl-CoA in muscles and brain, may affect platelet function in healthy and diabetic individuals. Methods: We obtained platelets from healthy and diabetic persons and measured acetyl-CoA concentrations, malonyl dialdehyde (MDA) synthesis, and platelet aggregation in the absence and presence of L-carnitine. Activities of selected enzymes involved in glucose and acetyl-CoA metabolism were also assessed. Results: Fasting glucose, fructosamine, and hemoglobin A 1c were present in significantly higher amounts in the blood of diabetic patients than in healthy individuals. Activities of carnitine acetyltransferase, glucose-6-phosphate dehydrogenase, oxoglutarate dehydrogenase, and fatty acid synthase were 17%-62% higher in platelets from diabetic patients. Mitochondrial acetyl-CoA was increased by 98% in platelets from diabetic patients, MDA synthesis was increased by 73%, and platelet aggregation by 60%. L-Carnitine had no or only a slight effect on these indices in platelets from healthy individuals, but in platelets from diabetic patients, L-carnitine caused a 99% increase in acetyl-CoA in the cytoplasmic compartment along with increases in MDA synthesis and platelet aggregation.

Alterations of Adenine Nucleotide Metabolism and Function of Blood Platelets in Patients With Diabetes

“…Such an experimental design was justified by our previous data (10) showing that diabetes-evoked changes both in the activities of enzymes of acetyl-CoA metabolism and in acetyl-CoA level depend on the degree of chronic hyperglycemia and not on other factors specific for a particular type of diabetes (9,10,23). Also, this study revealed that all laboratory markers of the disease, as well as levels of ATP/ADP in platelets, were increased to a similar extent in both type 1 and 2 diabetic patients (Tables 1 and 2 and data not shown).…”

“…Increased glucose influx into megacariocytes in the course of sustained diabetic hyperglycemia is a likely cause of the increased activity of several enzymes involved in glycolytic, energy-producing, and fatty acid-synthesizing pathways, and it activates acetyl-CoA synthesis (9,10). Elevated levels of acetyl-CoA in the platelets of diabetic subjects correlate with increased synthesis of thromboxane A 2 /malonyl dialdehyde and lipid peroxidation as well as spontaneous and thrombin-, ADP-, or collagen-evoked aggregation (9,10).…”

“…In addition, platelet exocytosis and aggregation require metabolic energy in the form of ATP (13). Therefore, in diabetes the increase of acetyl-CoA-dependent oxidative metabolism in platelets or in their precursors might cause an excessive accumulation of ATP/ADP (7,9,10,14). However, the relationships between ATP/ADP accumulation in platelets and their activity in patients with diabetes have not yet been examined.…”

“…For studies of ATP/ADP metabolism in activated platelets, 0.15 IU of thrombin was added along with 2.5 mmol/l GPRP peptide (17). Such conditions prevented platelet aggregation and decomposition but did not affect platelet activation by the thrombin (10,18). Incubation was started by the addition of platelet suspension (0.7-0.8 mg of protein) and carried for 30 min at 37°C in polystyrene flat-bottom vessels in a water bath with continuous shaking at 100 cycles/min.…”

“…Acetyl-CoA assay. Platelet acetyl-CoA was assayed by phosphotransacetylase-citrate synthase cycling assay as described previously (10,20). Platelet aggregation and thiobarbituric acid-reactive species assays.…”