First Department of Internal Medicine Nara Medical University Nara Japan Email: kanauchi{at}nmu-gw.naramed-u.ac.jp
Sir,
Although obesity is considered to be a cause of albuminuria and several studies have indicated a significant correlation between urinary albumin excretion and increasing body mass index (BMI) in both non-diabetic [1,2] and diabetic subjects [3], the majority of these studies were reported in Caucasians. Only limited data exist for Japanese subjects, probably because Japanese people are relatively lean. Furthermore, there is very little information about the association between obesity-related albuminuria and renal histology. The aim of this study was to determine a possible association between obesity and albuminuria analysed by renal biopsy in Japanese subjects with incipient diabetic nephropathy.
We studied 49 type 2 diabetic patients who had undergone renal biopsy at Nara Medical University Hospital. Inclusion criteria were age 75 years or less, serum creatinine concentration <2.0 mg/dl and persistent microalbuminuria (defined as an albumin excretion rate of between 30 and 300 mg/day). Obesity was defined as a BMI >25 kg/m2, because Japanese subjects are relatively lean. Creatinine clearance (Ccr) was defined using 24 h urine. Tissue specimens obtained by renal biopsy were processed for evaluation using light microscopy. The severity of both diffuse and nodular changes was graded from 0+ to 4+ using Gellman's criteria [4]. The severity of arteriolar changes was graded from 0+ to 3+ using Takazakura's criteria [5]. The severity of tubulointerstitial lesions was determined by a semi-quantitative estimate of the space occupied by fibrous tissue and/or interstitial infiltrates as follows: 0+ (normal); 1+ (damaged area <10%); 2+ (10% <damaged area <30%); and 3+ (30% <damaged area). The total injury score was the sum of the above 4 scores. No patient showed evidence of other types of primary renal disease superimposed on diabetic nephropathy.
No difference between obese (n=17) and non-obese (n=32) patient groups was found for mean age, systolic and diastolic blood pressure, HbA1c or urinary albumin excretion rate (Table 1). The known duration of diabetes was significantly shorter in the obese group than in the non-obese group. Adjusted Ccr per 1.73 m2 BSA was significantly higher in obese group than in non-obese group. There were no significant differences in the diffuse, nodular or tubulointerstitial scores between the two groups, but the arteriolar score was significantly higher in non-obese group than in obese group. The total injury score showed a trend toward higher values in the non-obese group, but the difference did not reach the level of statistical significance (P=0.08).
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In summary, in Japanese microalbuminuric type 2 diabetic patients with mild renal failure, renal lesions are similar in patients with and without obesity. The longitudinal studies are important for further investigation.
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