Nicotine induces endothelial TNF-alpha expression, which mediates growth retardation in vitro

Purpose. Atherosclerosis is understood as the common pathologic manifestati on of arterial injury caused by a variety of etiologies. One well-establish ed etiologic agent is nicotine. We hypothesized that cytokines of endotheli al origin are involved with the pathologic changes found in atherosclerosis associated with smoking. We chose to assay for TNF-alpha due to its many b iologic actions that are similar to those found in peripheral vascular dise ase. Methods. Human umbilical vein endothelial cells (HUVEC) were plated in endo thelial growth medium (EGM-2) on plastic coverslips until 75% confluent. Fr ee base nicotine (FBN) was diluted in EGM-2 to a concentration of 10 (-8) M and added to experimental cells. At 1, 3, and 24 h, coverslips were remove d and fixed. Immunohistochemical staining was performed using anti-TNF-alph a. Digital image analysis (DIA,) was performed to quantify expression of TN F-alpha. An intensity stain index measuring area and intensity of stain/tot al cellular area was determined for each time point (n = 5). Additional HUV EC were plated in 12-well plates in EGM-2 at 2 x 10(3) cells/cm(2) on T-2 d ay. FBN was diluted in medium to 10(-9) M and added to wells with and witho ut 0.9 mug/ml anti-TNF-alpha on T-0, day. Cell counts were performed in tri plicate on days T2-5 utilizing hemocytometry. Data was analyzed using Stude nt's t test and ANOVA, with a 95% confidence interval. Results. Dose response determinations showed that the minimal concentration required to show statistically significant cell retardation is 10 (-9) M. Accordingly, this concentration was used for subsequent proliferation studi es. DIA showed a threefold increase in TNF-alpha activity at I h and a twof old increase at 3 h. Activity returned to baseline by 24 h. Cell growth was significantly decreased in cells exposed to nicotine when compared to cont rols on days T-2-T-5 (P < 0.05). In cells exposed to anti-TNF-alpha and nic otine there was inhibition of the growth retardation seen in the cells cont aining nicotine alone. Differences between the control group and the anti-T NF-alpha group were not statistically significant. Conclusion. These data demonstrate the ability of endothelial cells to secr ete TNF-alpha in response to nicotine at levels found in serum after smokin g and also shows that endothelial cell growth retardation as a consequence of nicotine exposure may be TNF-alpha mediated. (C) 2001 Academic Press.