Effects of Cigarette Smoking on Glomerular Structure and Function in Type 2 Diabetic Patients

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Abstract
Prospective studies have established smoking as an independent risk factor for diabetic nephropathy, suggesting an adverse effect of smoking on glomerular structure and function. To test this hypothesis, this study evaluated GFR, metabolic profile, and smoking habits in 96 patients with type 2 diabetes and abnormal albumin excretion rate (AER). All patients underwent percutaneous kidney biopsy: mesangial fractional volume [Vv (mes/glom)] and glomerular basement membrane (GBM) width were estimated by electron microscopic morphometric analysis; interstitial fibrosis was estimated semiquantitatively by light microscopy. Forty-eight patients were smokers. Compared with nonsmokers, smokers had higher values of HbA1c (P = 0.002), AER (P = 0.026), GFR (P = 0.004), and GBM width (P = 0.002); moreover, GFR was higher in current smokers than in former smokers (P = 0.001), and GBM width was related to heavy smoking (F = 5.4; P = 0.006). Multiple linear regression analyses revealed that HbA1c was associated with fasting blood glucose (β coef = 0.52; P < 0.001), smoking habit (β coef = 0.31; P < 0.001), insulin therapy (β coef = 0.22; P = 0.012), and male gender (β coef = −0.20; P = 0.020); AER was related to Vv (mes/glom) (β coef = 0.32; P = 0.003), GBM width (β coef = 0.28; P = 0.016), and interaction between smoking habit and HbA1c (β coef = 0.24; P = 0.040). GFR was negatively correlated with Vv (mes/glom) (β coef = −0.57; P < 0.001) and age (β coef = −0.29; P = 0.001) and positively correlated with GBM width (β coef = 0.27; P = 0.012), heavy current smoking (β coef = 0.24; P = 0.028), and HbA1c (β coef = 0.28; P = 0.040); GBM width was explained by Vv (mes/glom) (β coef = 0.53; P < 0.001), interaction between heavy smoking and HbA1c levels (β coef = 0.25; P = 0.003), and diabetes duration (β coef = 0.23; P = 0.010). Smoking habit did not affect the index of interstitial fibrosis. In conclusion, cigarette smoking affects glomerular structure and function in type 2 diabetes and may be an important factor for the onset and progression of diabetic nephropathy.

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