Anti-proliferative activity of oral anti-hyperglycemic agents on human vascular smooth muscle cells: thiazolidinediones (glitazones) have enhanced activity under high glucose conditions

Peter J Little,Mandy Ballinger,Narin Osman,Julie Nigro,Nelly Cemerlang,Stephanie T De Dios

doi:10.1186/1475-2840-6-33

Abstract

BackgroundInhibition of vascular smooth muscle cell (vSMC) proliferation by oral anti-hyperglycemic agents may have a role to play in the amelioration of vascular disease in diabetes. Thiazolidinediones (TZDs) inhibit vSMC proliferation but it has been reported that they anomalously stimulate [3H]-thymidine incorporation. We investigated three TZDs, two biguanides and two sulfonylureas for their ability of inhibit vSMC proliferation. People with diabetes obviously have fluctuating blood glucose levels thus we determined the effect of media glucose concentration on the inhibitory activity of TZDs in a vSMC preparation that grew considerably more rapidly under high glucose conditions. We further explored the mechanisms by which TZDs increase [3H]-thymidine incorporation.MethodsVSMC proliferation was investigated by [3H]-thymidine incorporation into DNA and cell counting. Activation and inhibition of thymidine kinase utilized short term [3H]-thymidine uptake. Cell cycle events were analyzed by FACS.ResultsVSMC cells grown for 3 days in DMEM with 5% fetal calf serum under low (5 mM glucose) and high (25 mM glucose) increased in number by 2.5 and 4.7 fold, respectively. Rosiglitazone and pioglitazone showed modest but statistically significantly greater inhibitory activity under high versus low glucose conditions (P < 0.05 and P < 0.001, respectively). We confirmed an earlier report that troglitazone (at low concentrations) causes enhanced incorporation of [3H]-thymidine into DNA but did not increase cell numbers. Troglitazone inhibited serum mediated thymidine kinase induction in a concentration dependent manner. FACS analysis showed that troglitazone and rosiglitazone but not pioglitazone placed a slightly higher percentage of cells in the S phase of a growing culture. Of the biguanides, metformin had no effect on proliferation assessed as [3H]-thymidine incorporation or cell numbers whereas phenformin was inhibitory in both assays albeit at high concentrations. The sulfonylureas chlorpropamide and gliclazide had no inhibitory effect on vSMC proliferation assessed by either [3H]-thymidine incorporation or cell numbers.ConclusionTZDs but not sulfonylureas nor biguanides (except phenformin at high concentrations) show favorable vascular actions assessed as inhibition of vSMC proliferation. The activity of rosiglitazone and pioglitazone is enhanced under high glucose conditions. These data provide further in vitro evidence for the potential efficacy of TZDs in preventing multiple cardiovascular diseases. However, the plethora of potentially beneficial actions of TZDs in cell and animal models have not been reflected in the results of major clinical trials and a greater understanding of these complex drugs is required to delineate their ultimate clinical utility in preventing macrovascular disease in diabetes.

Highlights

Inhibition of vascular smooth muscle cell proliferation by oral anti-hyperglycemic agents may have a role to play in the amelioration of vascular disease in diabetes
Under "low" glucose conditions which equate to normoglycemia (i.e. DMEM with 5 mM glucose) and in the presence of 5 per cent Foetal bovine serum (FBS), cell numbers over 3 days increased from 36,800 ± 3,800 to 91,900 ± 8500 cells/well
Under high glucose conditions (DMEM containing 25 mM glucose) and in the presence of 5 per cent FBS, vascular smooth muscle cell (vSMC) numbers increased from 54,400 ± 5500 to 250,500 ± 28,000 cells/well

Summary

Introduction

Inhibition of vascular smooth muscle cell (vSMC) proliferation by oral anti-hyperglycemic agents may have a role to play in the amelioration of vascular disease in diabetes. Coronary artery by-pass grafting (CABG) was initially the preferred intervention over angioplasty in people with diabetes and coronary artery disease [3] the introduction of coronary artery stents and drug coated stents and possibly supplemented with systemic therapy has raised the possibility that this less invasive treatment may be suitable for this population [4,5] Factors such as proteoglycan mediated lipid deposition [6,7] and inflammation [8,9] are clearly important in the process of atherosclerosis and restenosis, in the setting of diabetes vSMC proliferation is clearly critical and a target for therapy [2]. It is further possible that an oral anti-proliferative agent may be useful as adjunct therapy following vascular intervention even in the absence of diabetes [11]

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