ANTIOXIDANT GENE-EXPRESSION IN RAT LUNG AFTER EXPOSURE TO CIGARETTE-SMOKE

To investigate the effects of cigarette smoke on the expression of gen es encoding intracellular antioxidant species, we exposed rates to who le cigarette smoke or air (control) daily for 1, 2, 7, or 14 days, Aft er sacrifice, RNA was extracted from one lung and expression of mRNA f or catalase (CAT), manganese superoxide dismutase (MnSOD), copper-zinc superoxide dismutase (CuZnSOD), glutathione peroxidase (GPX), and met allothionein (MT) was determined by Northern blots and dot blots. The anatomical distribution of expression of these genes was determined by ill situ hybridization studies on sections of the contralateral lung, We found that expression of both MnSOD and MT was significantly incre ased (to levels 70 to 400% greater than in controls) at days 1 and 2 a nd returned to control levels by day 7. GPX expression was slightly bu t significantly increased at days 7 and 14 in smoke-exposed animals, C uZnSOD and CAT expression did not change from control levels, In contr ol lungs, MnSOD was expressed in all cell types, with the highest expr ession seen in bronchial epithelial cells; a notable finding was a mos aic pattern of expression in the bronchial epithelium, with contiguous areas of bronchial epithelium composed of cells expressing MnSOD at h igh levels (hot spots), compared with the adjacent epithelium. In smok e-exposed lungs, the hot spots became less prominent after 1 and 2 day s of exposure to smoke, but after 7 and 14 days the distribution of Mn SOD expression was similar in control and smoke-exposed animals, CAT, CuZnSOD, GPX, and MT also showed widespread expression in the lung by in situ hybridization; GPX, CuZnSOD and MT were all most highly expres sed in bronchial epithelium, whereas CAT expression levels were simila r in all cell types, In contrast to MnSOD, expression of CAT, CuZnSOD, GPX, and MT was uniform within the bronchial epithelium, and the dist ribution of expression was the same in control and smoke-exposed anima ls at all time points, We conclude that most of these antioxidant enzy mes and scavengers show prominent bronchial expression but that MnSOD shows a unique pattern, with intense hot spots in the epithelium of th e small airways, This pattern is similar to the phenomenon of clonal h eterogeneity described in other tissues but not Previously reported in the lung. We conclude that cigarette smoke, like other forms of oxida nt attack, transiently increases expression of MnSOD, and upregulation of MnSOD expression appears to occur particularly in bronchial epithe lial cells, which normally express MnSOD at relatively low levels, MT expression is also transiently increased by smoke whereas GPX expressi on increases after prolonged (7 to 14 days) exposure to cigarette smok e.