Correlation between the Indexes of Insulin Resistance and Renal Function in the Presence of Hypertension

Background/Aims: It is important to establish the association between insulin resistance and renal function; however, the reported associations differ across studies. Different underlying pathophysiologies of the studied populations may affect the associations. There have been no reports on the relationship between insulin resistance and renal function in the presence of hypertension (HT). We investigated the correlation between a homeostasis model assessment of insulin resistance (HOMA-IR) and the estimated glomerular filtration rate (eGFR) in subjects with and without HT. Methods: The study included 214 individuals (mean age: 65.6 years) who were nonmedicated and cardiovascular disease-free. Clinical variables, including blood pressure (BP), creatinine, glucose and lipid panels, were measured. Results: The HT group showed significantly higher levels of systolic/diastolic BP than the non-HT group. A multiple linear regression analysis revealed that the eGFR in the non-HT group was independently, significantly and inversely correlated with HOMAIR, while the eGFR in the HT group was independently, significantly and inversely correlated with systolic BP, but not with HOMA-IR. Conclusions: A clearer correlation between HOMA-IR and eGFR was observed in the non-HT group than Received: November 30, 2009 Accepted: April 12, 2010 Published online: June 24, 2010 Kazuhiko Kotani, MD, PhD Department of Clinical Laboratory Medicine Jichi Medical University 3311-1 Yakushiji, Shimotsuke-City, Tochigi, 329-0498 (Japan) Tel. +81 285 58 7386, Fax +81 285 44 9947, E-Mail kazukotani @ jichi.ac.jp © 2010 S. Karger AG, Basel 1420–4096/10/0333–0209$26.00/0 Accessible online at: www.karger.com/kbr K.K. and N.T. assisted in study design and data interpretation. K.K. and H.M. assisted in data collection and manuscript preparation. All authors reviewed the manuscript and approved the final version submitted for publication. D ow nl oa de d by : 54 .7 0. 40 .1 1 11 /2 3/ 20 17 2 :4 3: 10 A M Matsunaga/Kotani/Taniguchi Kidney Blood Press Res 2010;33:209–212 210 in type-1 diabetic patients with mild nephropathy [4] and in non-diabetic men [5] , as well as between HOMA-IR and inulin clearance (the gold standard of GFR) in obese type-2 diabetic patients with renal insufficiency [6] . On the other hand, others have reported no significant relationships between HOMA-IR and eGFR in non-diabetic patients with CKD [7] or obese non-diabetic patients [8] , or between HOMA-IR and urinary albumin excretion rate in type-1 diabetic patients with mild nephropathy [9] . One study has also demonstrated that visceral adiposity (an IR-related manifestation), not HOMA-IR, is inversely associated with the eGFR in obese subjects [10] . An additional report has documented that waist circumference and metabolic syndrome (IR-related manifestations) are associated with micro-albuminuria, not eGFR, in type-2 diabetic patients [11] . These discrepancies seem largely due to the differences in such characteristics of the study population as the absence/presence of obesity and diabetes or the stage of CKD. Because renal function appears to be modulated by the states of obesity and diabetes, it is crucial to determine the situation in which the relationship between IR and renal function is most critical. While hypertensive states may also be associated with both IR and renal function, there are no reports that have examined the association of both indexes in the presence of HT. The present study therefore investigated the correlation between HOMA-IR and eGFR in the subjects with or without HT. Subjects and Methods A total of 214 nonmedicated participants (males/females = 80/134, mean age = 65.6 years, range = 30–80) were recruited from health check-ups. The eligible subjects had no severe CKD (defined as an eGFR level ! 50 ml/min/1.73 m 2 in this study [12] ) or diabetes mellitus (defined as ̂ 7.0 mmol/l of fasting plasma glucose [13] ; HOMA-IR is not applicable for diabetics), as well as no apparent histories of cardiovascular, thyroid, hematological or liver diseases. The study population was composed of the HT group (n = 101) and the non-HT group (n = 113; table 1 ). The study was approved by the Jichi Medical University Ethics Committee, and all subjects gave their informed consent. Current smoking habits were self-reported. In addition to body mass index (BMI), fasting serum total cholesterol, triglyceride, high-density lipoprotein cholesterol, creatinine and plasma glucose levels were measured by standard enzymatic methods. The plasma insulin was measured using an ELISA method (Tosoh Co. Ltd., Tokyo, Japan). Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured in the seated subject’s right-arm with a mercury sphygmomanometer after 5 min of rest. HT was diagnosed in subjects with 6 140 mm Hg of SBP and/or 6 90 mm Hg of DBP [14] . HOMA-IR was calculated using the following formula: (fasting plasma insulin ! plasma glucose)/22.5 [15] . The eGFR was calculated using the following formula (the Modification of Diet in Renal Disease Study Group equation): 0.741 ! 175 ! serum creatinine –1.154 ! age –0.203 ( ! 0.742 if female) [12] . The data were expressed as the mean 8 standard deviation (SD) or the median plus interquartile range. The data between the groups were compared using a t test or  2 test. A simple and multivariate-adjusted linear regression model was utilized to observe the correlation between eGFR and HOMA-IR. In a multivariateadjusted analysis, all the measured variables were used. Because of a close correlation between glucose and HOMA-IR, these variables were not simultaneously entered in the multivariate-adjusted analysis model in this study. The triglyceride, HOMA-IR and eGFR data were log-transformed for all the analyses because of their skewed distributions. A p value of ̂ 0.05 was considered to be statistically significant.