Differential inhibitory effects of antidiabetic drugs on arterial smooth muscle cell proliferation

We compared three drugs representing different classes of antidiabetic pharmacology (glyburide, a sulfonylurea; pioglitazone, a thiazolidinedione; and metformin, a biguanide) in terms of their direct effects on proliferation of cultured arterial smooth muscle cells (SMC). Rat aortic SMC were seeded at 4 X 10(4)/35 mm well. After 24 h, they were treated every 2 to 4 days for 2 weeks with 5% fetal bovine serum (FBS) in normal culture medium containing either drug vehicles or a low and a high but nontoxic level of glyburide (0.5 and 2.5 mu mol/L), pioglitazone (1 and 5 mu mol/L), and metformin (20 and 100 mu mol/L). Vehicle-treated cells increased from 2 +/- 0 to 6 +/- 1 to 42 +/- 3 to 210 +/- 14 (cells per well x 10(4); 5 wells each) from day zero to 4 to 9 to 14. From day 9 to 14 these cell numbers were decreased an average of 20% by the 2.5 mu mol/L glyburide (P <.05) and 43% by the 5 mu mol/L pioglitazone (P <.05). The low levels of glyburide and pioglitazone and both the low and high levels of metformin failed to influence cell numbers. In a second experiment, even half the abovementioned high level of pioglitazone (2.5 mu mol/L) still exerted a markedly greater antiproliferative effect on aortic SMC than a high level of 2.0 mu mol/L glyburide (P <.05). In addition, neither drug's antiproliferative effect was influenced by a high level of insulin added to the medium (10 mU/mL). Similarly, a small but significant stimulatory effect of this high insulin on cell proliferation (P <.05) was not significantly affected by these two drugs (although pioglitazone tended to inhibit it). These results suggest that thiazolidinediones may be more useful antidiabetic agents than sulfonylureas and biguanides in inhibiting abnormal arterial SMC proliferation associated with atherosclerosis and postangioplastic restenosis which are common in diabetic patients.