Dinitrotoluene-induced alterations in rat aortic smooth muscle cell proliferation

Prolonged exposures to technical grade dinitrotoluene (DNT), a mixture of isomers used in the manufacture of several commercial products, may cause atherosclerotic heart disease in humans. However, the cellular/molecular basis the DNT-induced atherogenesis has not been investigated. As increased smooth muscle cell (SMC) proliferation is observed during the initial stages of atherosclerosis, the present studies were conducted to evaluate the proliferative capability of cultured SMC obtained from rats treated with two predominant isomers of technical grade DNT. Sprague-Dawley rats were treated for 8 weeks with 2,4- or 2,6-DNT (0.5, 5 or 10 mg/kg) or saline. The extent of 3H-thymidine incorporation into DNA was used as an index of cell proliferation. Additional studies were conducted to determine if 2,4- or 2,6-DNT was toxic to SMC in vitro as measured by lactate dehydrogenase (LDH) release and cell glutathione content. The extent of 3H-thymidine incorporation was 270% and 148% higher in SMC obtained from 5 and 10 mg/kg 2,4-DNT, respectively, than cells obtained from control animals. In contrast, SMC obtained from 2,6-DNT did not show an increase in 3H-thymidine incorporation at any of the doses tested. Acute exposure of cells to DNT (1-100 μM) in vitro did not cause measurable cell damage. Direct cytotoxic effects of 2,4-DNT on SMC may not account for the alterations in thymidine incorporation observed in cells obtained from DNT-treated animals. The sterospecific enhancement of vascular SMC proliferation following subchronic exposure to DNT in vivo supports the hypothesis that 2,4-DNT is atherogenic