A novel insulin mimetic without a proliferative effect on vascular smooth muscle cells

Background: Insulin induces vascular smooth muscle cell. (VSMC) proliferation, which is an important step in the atherosclerotic process. Recently, a nonpeptidyl fungal metabolite originally referred to as L-783,281, but also known as demethylasterriquinone B-1 (DMAQB-1), was found to have hypoglycemic activity in diabetic mice through interaction with the intracellular beta subunit of the insulin receptor. This study was designed to determine whether DMAQB-1 has an insulin-like proliferative effect on human infragenicular VSMCs. Methods: Human infragenicular VSMCs were isolated from diabetic patients undergoing amputations. DMAQB-1 cell culture dose response was measured in both serum-free media and media with 1% fetal bovine serum (PBS). A working, concentration of DMAQB-1 that ranged from 0.5 to 500 nmol/L was studied in the presence of varying concentrations of glucose and insulin. The ability of DMAQB-1 to stimulate glucose transport at less than or equal to 100 nmol/L was determined by [C-14]-2-deoxyglucose uptake. DNA synthesis was used as the marker for proliferative stimulus and detected by [H-3]-thymidine uptake measured at 24 hours. Analysis of variance was used to compare the results among the groups; a P value less than .05 was considered significant. Polynomial regression was used to calculate the median lethal dose. Results: In normal glucose media (100 mg/dL), various concentrations of DMAQB-1 demonstrated a small but statistically significant decrease in DNA synthesis at 0.5 nmol/L in serum-free media and at 0.5 nmol/L in media supplemented with 1% FBS. The corresponding median lethal dose mas 107 nmol/L in serum-free media and 650 nmol/L in media supplemented with 1% FBS. A DMAQB-1 concentration of 5 nmol/L induced glucose transport that was equivalent to an insulin concentration of 100 muU/mL. In serum-free, high glucose media (200 mg/dL), DMAQB-1 concentrations up to 500 nmol/L did not cause a statistically significant change in DNA synthesis. When serum-free, high glucose media was combined with mild (100 muU/mL) or moderate (250 muU/mL) concentrations of insulin, DMAQB-1 caused no statistically significant increase in DNA synthesis. Conclusion: Nontoxic doses of DMAQB-1 can induce glucose transport equivalent to insulin in the physiologic range. However, DMAQB-1 does not have an insulin-like proliferative effect on human VSMCs in normal-glucose, high-glucose, or high-insulin environments.