RESUMO
AIM: Cotinine, the main stable metabolite of nicotine, has been shown to have a biological half-life approximately 10 times longer than nicotine. It has also been demonstrated to have a powerful effect on vascular smooth muscle cell (VSMC) proliferation. Telomerase activation is known to play an important role in cell viability and proliferation. The purpose of our experiment was to evaluate the effect of cotinine on proliferative potential of vascular smooth muscle cells via its effects on telomerase activity. METHODS: Primary cultures of human VSMC obtained from greater saphenous veins were used in this experiment from 3(rd) to 5(th) passage. Cotinine was added in doses equivalent to plasma levels of cotinine in an active smoker by dissolving, 0.0, 2.88x10(-6), 5.76x10(-6), and 1.44x10(-5) mol/L of cotinine in the media. The number of viable cells was assessed by trypan blue exclusion. The Telomeric Repeat Amplification Protocol (TRAP) was used to detect telomerase activity. TRAP products were detected by ELISA. RESULTS: The mitogenic effect of cotinine in VSMC was observed at 48 hours after treatment. The viable cell numbers were significantly increased (4.0x10(7)) at lower doses of cotinine exposure as compared to untreated cultures (2.5x10(5)). At the concentration of 1.44x10(-5) mol/L, cotinine was cytotoxic to VSMCs. Telomerase activity was detected in all sets of VSMC cultures treated with cotinine (P<0.01). CONCLUSIONS: Cotinine causes abnormal cell proliferation as demonstrated by increased cell numbers and reactivation of telomerase in a dose dependent manner. This study demonstrated cotinine's stimulatory effect on human SMC proliferation in vitro at low doses while high doses of cotinine had a toxic effect. These data correlate with the results of other studies concerning the mitogenic effect of cotinine and telomerase activation during cellular proliferative response.