The Role of Proinflammatory Cytokine Gene Polymorphisms for Development of Insulin Resistance After Renal Transplantation

Abstract

Background Insulin resistance, a frequent prediabetic metabolic complication after renal transplantation, is generally linked to immunosuppressive drugs including corticosteroids, cyclosporine (CsA) or tacrolimus, as well as to age, cadaveric donors and ethnic factors. Cytokines are known to be inflammation modulatory substances that contribute to metabolic derangements after transplantation. The present study investigated the effects of cytokine gene polymorphisms on insulin resistance in renal transplant recipients. Patients and methods Sixty-one renal transplant recipients (37 men, 24 women; mean age: 39.3 ± 10.8 years) who attended regular clinical visits without a known history of diabetes were enrolled in the study. All patients were on a regimen of steroid, CsA, and mycophenolate mofetil. Venous blood samples were collected for biochemical analyses after an overnight fast at 08:00 pm. CsA trough levels, C-reactive protein, and fibrinogen were also estimated. Additional 10 mL of blood was withdrawn into an ethylenediamine tetraacetic acid–containing tube to determine cytokine genotypes (tumor necrosis factor-alpha [TNF-α] -238 G/A, transforming growth factor-beta [TGF-β] codon 10 -869 T/C). Insulin resistance was calculated by the homeostasis model assessment (HOMA) method using the values of fasting blood glucose (FBG) and insulin levels. Anthropometric indices as well as body height, weight, waist and hip circumferences were measured simultaneously to calculate body mass index (kg/m 2) and waist-to-hip ratio. Impaired fasting glucose (IFG) was described as an FBG ≥ 110 but < 126 mg/dL. Results IFG was detected in 27.9% of this study group. The HOMA index was significantly higher among patients with IFG compared with normal FBG (NoGT) (6.3 ± 4.5 vs 3.7 ± 1.5; P = .01). Neither FBG and insulin nor HOMA values correlated with antrophometric, metabolic, or inflammatory parameters. Cytokine genotype allele frequencies, age, sex, immunosuppressive and antihypertensive drug type and doses, CsA trough levels, and donor source (cadaveric/living) were similiar for patients with IFG and NoGT. Mutant allele carrier genotypes (AA + GA) for TNF-α -238 G/A showed higher fasting insulin (14.0 ± 7.9 vs 34.1 ± 17.7 μIU/mL; P = .04) and HOMA (4.01 ± 2.01 vs 7.95 ± 5.44; P = .002) levels than GG homozygote subjects. FBG, HOMA, and other metabolic and anthropometric indices were similiar between TGF-β codon 10 -869 T/C genotypes. The daily dose of steroid (mg/d) and A allele frequency for TNF-α -238 G/A genotype were significant predictors of HOMA index in linear regression analysis. Conclusion The present study revealed that beside the daily dose of steroids, TNF-α -238 G/A genotype may contribute to insulin resistance in renal transplant recipients. Further investigations may highlight the effects of cytokine gene heterogenity on insulin resistance in those patients.