Glomerular and tubular dysfunctions and their relationship to adiponectin and oxidative stress in obese subjects

Abstract

Obesity is an independent risk factor for renal disease. Microalbuminuria (MA) is the first sign of renal injury. Tubular dysfunction may present early in obesity but this has not been well studied. This study aimed at assessing glomerular and tubular dysfunctions and their relationship to adiponectin and oxidative stress in obese participants. This study was conducted on 60 participants. Group 1 included 20 healthy individuals as controls, Group 2 included 20 obese individuals with normal albumin excretion rate (AER), and Group 3 included 20 obese individuals with increased AER. Clinical assessment, anthropometric measurements, and laboratory investigations included: estimation of serum high-density lipoprotein (HDL)-cholesterol, urinary albumin to creatinine ratio, and calculation of estimated glomerular filtration rate. Serum adiponectin, thiobarbituric acid-reactive substances (TBARs) as a marker of oxidative stress, and urinary gamma glutamyl transferase (UGGT) as a marker of tubular function were also estimated. The estimated glomerular filtration rate was higher in obese individuals with normal AER and significantly lower in those with abnormal AER compared to controls. Adiponectin was lower and TBARs and UGGT significantly higher in obese individuals with normal and abnormal AER than controls. Adiponectin was negatively correlated with TBARs, AER, and UGGT. There were positive correlations between TBARs and both AER and UGGT. HDL-cholesterol was positively correlated with adiponectin and negatively correlated with TBARs and UGGT. Glomerular and tubular dysfunctions in obese individuals are related to low adiponectin and HDL-cholesterol levels and to oxidative stress. Tubular dysfunction precedes MA, so UGGT may be used as an early marker for obesity related nephropathy. 背景: 肥胖症是腎病的獨立危險因子，微白蛋白尿症(MA)則是腎損傷的最早期徵兆。腎小管功能障礙可能早於肥胖症初期出現，但這尚未獲得充分的研究探討。本研究旨在評估肥胖症患者間的腎小球與腎小管功能，並調查後兩者與adiponectin及氧化壓力的關係。 方法: 研究對象為60人，包括健康對照組的20人(組I)、20位白蛋白排泄率(AER)正常的肥胖症患者(組II)、及20位AER過高的肥胖症患者(組III)。所有人均接受了全面的體格與臨床評估、及醫學檢驗，後者包括：血清HDL-cholesterol、尿液albumin與creatinine比例、及腎絲球過濾率估算值(e-GFR)。此外，氧化壓力指標包括血清adiponectin、thiobarbituric acid-reactive substances (TBARs)；腎小管功能指標則為尿液的gamma glutamyl transferase (UGGT)濃度。 結果: 相比於對照組，較高的e-GFR出現在AER正常的肥胖症患者間；明顯較低的e-GFR則出現在AER異常的肥胖症患者之中。同時，不論AER是否正常，肥胖症患者的adiponectin濃度較低，TBARs與UGGT則明顯較高。Adiponectin與TBARs、AER、及UGGT三者之間存在負相關的關係；TBARs則與AER及UGGT兩者呈正相關。此外，HDL-cholesterol與adiponectin呈正相關，與TBARs及UGGT兩者則呈負相關的關係。 結論: 肥胖症患者的腎小球與腎小管功能障礙與較低的adiponectin及HDL-cholesterol有關，亦與氧化壓力有關。腎小管功能障礙在MA之前出現，因此UGGT可以作為肥胖症相關腎病變的早期指標。