Impact of Obesity on IgA Nephropathy: Comparative Ultrastructural Study between Obese and Non-Obese Patients

Background: The pathological role of obesity in the progression of glomerular lesions has rarely been studied in primary glomerular diseases. The purpose of this study is to investigate the influence of non-diabetic obesity on clinicopathological findings in IgA nephropathy. Methods: 74 patients with biopsy-proven IgA nephropathy were retrospectively divided into two groups according to the criteria for obesity in Japan: non-obese group (group N: n = 50) with BMI < 25 kg/m(2), and obese group (group O: n = 24) with BMI >= 25 kg/m(2). Clinical and pathological data at the time of renal biopsy were analyzed. Moreover, the outcome of proteinuria in patients treated with angiotensin-converting enzyme inhibitors (ACE-I) or angiotensin II receptor blockers (ARB) was evaluated in different groups after a 1-year follow-up. Results: Urinary protein excretion was significantly greater in the obese group compared to normal-weight patients (p < 0.05). There was no significant difference in the prevalence of hypertension and hyperlipidemia. By light microscopy, the obese group showed significantly larger glomerular size (p < 0.0001). On the other hand, the severity of mesangial matrix expansion and crescent formation revealed no difference between the two groups. By electron microscopy, glomerular basement membrane (GBM) thickness was significantly increased in obese patients (p < 0.001). Among 61 patients who were followed up for 1 year in our institute, 15 patients were treated with ACE-I or ARB without steroids. ACE-I or ARB treatment without steroids tended to reduce proteinuria in the obese patients, but this change did not achieve statistical significance. Conclusions: In IgA nephropathy, obesity induces not only glomerular enlargement but also ultrastructural modification of GBM, which would contribute to increase proteinuria. Copyright (C) 2009 S. Karger AG, Basel