Peroxisome proliferator-activated receptor gamma polymorphism Pro12Ala is associated with nephropathy in type 2 diabetes

The impact of PPARγ and ApoE gene polymorphisms on susceptibility to diabetic kidney disease in type 2 diabetes mellitus: a meta-analysis

BACKGROUND

Globally, diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease, imposing substantial social and economic costs. This meta-analysis was designed to provide valuable insights into gene-disease interactions by investigating the potential association between lipid metabolism gene polymorphisms and the risk of DKD.

METHODS

An electronic literature search was conducted on MEDLINE Complete, Web of Science, Embase, and PubMed. A total of 18 studies on the peroxisome proliferator-activated receptor γ (PPARγ) Pro12Ala variant and 20 publications concerning apolipoprotein E (ApoE) gene polymorphism were included in the meta-analysis.

RESULTS

Overall, the PPARγ Pro12Ala polymorphism was found to be significantly associated with a decreased DKD risk (OR = 0.74, 95% CI: 0.62-0.88). In subgroup analysis, Ala carriers were less susceptible to DKD than Pro homozygotes among Asian (OR = 0.73, 95% CI: 0.56-0.95) and Caucasian populations (OR = 0.74, 95% CI: 0.59-0.93). Subgroup analysis stratified by albuminuria categories showed that the PPARγ Pro12Ala polymorphism reduced the risk of both microalbuminuria and macroalbuminuria with corresponding ORs of 0.58 (95% CI: 0.43-0.78) and 0.68 (95% CI: 0.53-0.86). Sensitivity analysis confirmed the robustness of the meta-analysis results. However, publication bias was identified in the subgroup analysis of the Caucasian population. The primary analysis of the ApoE gene polymorphism yielded significant findings, indicating that ApoE ε2/ε2, ApoE ε2/ε3, and ApoE ε2/ε4 genotypes increase the risk of DKD (ε2/ε2 vs. ε3/ε3: OR = 1.93, 95% CI: 1.03-3.61; ε2/ε3 vs. ε3/ε3: OR = 1.63, 95% CI: 1.19-2.25; ε2/ε4 vs. ε3/ε3: OR = 1.87, 95% CI: 1.37-2.55). However, sensitivity analysis suggested that influential and Hardy-Weinberg equilibrium (HWE)-violating studies may impact the overall effect estimates.

CONCLUSIONS

A meta-analysis showed that PPARγ gene polymorphism may be a protective factor for DKD, whereas the ApoE ε2/ε2, ApoE ε2/ε3, and ApoE ε2/ε4 genotypes are associated with an increased risk of DKD. However, the role of ApoE gene polymorphism in susceptibility to DKD is less certain and requires further evaluation.

The genetic side of diabetic kidney disease: a review

BACKGROUND

Diabetic kidney disease (DKD) is one of the most common complications of diabetes, with approximately 30-40% of patients with type 1 diabetes mellitus and 20% of patients with type 2 diabetes mellitus eventually developing DKD. If DKD is not controlled in the early clinical stage and proteinuria develops, the disease will progress to end-stage renal disease. The pathogenesis of DKD remains largely unknown and is multifactorial, likely due to interactions between genetic and environmental factors. Familial clustering also supports a critical role of hereditary factors in DKD. The development of gene detection technology has promoted the exploration of DKD susceptibility genes in different cohorts of patients with diabetes. Identifying susceptibility genes can provide insights into the pathogenesis of DKD, as well as a basis for its clinical diagnosis and therapy.

RESULTS

Numerous candidate gene loci have been found to be associated with DKD, many of which play critical regulatory roles in the pathogenesis of this disease, including genes involved in glycol-metabolism, lipid metabolism, the renin-angiotensin-aldosterone system, inflammation and oxidative stress. In this review, we summarize the functions of several susceptibility genes involved in the development of DKD.

CONCLUSION

Based on our findings, we recommend that studying susceptibility gene polymorphisms can lead to a better understanding of the pathogenesis of DKD and could help prevent this disease or improve its outcomes.

PPARG Pro12Ala Polymorphism with CKD in Asians: A Meta-Analysis Combined with a Case-Control Study-A Key for Reaching Null Association

BACKGROUND

So far, numerous meta-analyses have been published regarding the correlation between peroxisome proliferator-activated receptor gamma (PPARG) proline 12 alanine (Pro12Ala) gene polymorphism and chronic kidney disease (CKD); however, the results appear to be contradictory. Hence, this study is formulated with the objective of using existing meta-analysis data together with our research population to study the correlation between PPARG Pro12Ala gene polymorphism and CKD and evaluate whether an accurate result can be obtained.

METHODS

First, literature related to CKD and PPARG Pro12Ala available on the PubMed and EMBASE databases up to December 2016 was gathered from 20 publications. Then, the gathered results were combined with our case-control study of 1693 enrolled subjects and a trial sequential analysis (TSA) was performed to verify existing evidence and determine whether a firm conclusion can be drawn.

RESULTS

The TSA results showed that the cumulative sample size for the Asian sample was 6078 and was sufficient to support a definite result. The results of this study confirmed that there is no obvious correlation between PPARG Pro12Ala and CKD for Asians (OR = 0.82 (95% CI = 0.66-1.02), I² = 63.1%), but this was not confirmed for Caucasians. Furthermore, the case-control sample in our study was shown to be the key for reaching this conclusion.

CONCLUSIONS

The meta-analysis results of this study suggest no significant correlation between PPARG Pro12Ala gene polymorphism and CKD for Asians after adding our samples, but not for Caucasian.

Peroxisome proliferator activating receptor-γ and the podocyte

Over the past two decades it has become clear that the glomerular podocyte is a key cell in preventing albuminuria, kidney failure and cardiovascular morbidity. Understanding the key pathways that protect the podocyte in times of glomerular stress, which can also be therapeutically manipulated, are highly attractive. In the following review we assess the evidence that the peroxisome proliferator activating receptor (PPAR) agonists are beneficial for podocyte and kidney function with a focus on PPAR-γ. We explain our current understanding of the mechanisms of action of these agonists and the evidence they are beneficial in diabetic and non-diabetic kidney disease. We also outline why these drugs have not been widely used for kidney disease in the past but they may be in the future.

Association analysis of PPARγ (p.Pro12Ala) polymorphism with type 2 diabetic retinopathy in patients from north India

BACKGROUND

The present study aimed to examine the association of PPARγ (p.Pro12Ala) polymorphism with type 2 diabetic retinopathy (DR) in patients from north India.

MATERIAL AND METHODS

In this case-control association study a total of 1325 subjects (717 DR patients and 608 individuals with confirmed type 2 diabetes mellitus (T2DM) without retinopathy taken as controls (CDR)), were recruited. Genotyping for PPARγ (p.Pro12Ala) polymorphism was performed by Taqman SNP Genotyping Assays using Real time PCR.

RESULTS

Statistically significant differences were observed between the two analyzed groups in the duration of diabetes and random blood glucose levels (p = 0.000 and p = 0.011, respectively). However, genotype and allele frequency distribution of PPARγ (p.Pro12Ala) polymorphism did not differ significantly between DR and CDR groups (p = 0.507 and 0.625, respectively).

CONCLUSIONS

These findings suggest no significant association of p.Pro12Ala polymorphism with retinopathy in tested type 2 diabetic retinopathy patients as compared to T2DM individuals take as controls. To our knowledge, this is the first report of association analysis of p.Pro12Ala polymorphism in PPARγ in DR patients from India.

The PPARγ2 Pro12Ala variant is protective against progression of nephropathy in people with type 2 diabetes

Objective

Cross-sectional studies suggest the association between diabetic nephropathy and the PPARγ2 Pro12Ala polymorphism of the peroxisome proliferator-activated receptor γ2 (PPARγ2). Prospective data are limited to microalbuminuria and no information on renal function is available to date. The present study evaluates the association between the Pro12Ala polymorphism of PPARγ2 and the progression of albuminuria and decay in glomerular filtration rate (GFR) in type 2 diabetes.

Patients and measurements

We studied 256 patients with an average 5-year follow-up. Among others, urinary albumin excretion rate (UAER) was measured on spot sample, GFR was estimated with the CKD-EPI Equation.

Results

Baseline UAER and GFR were similar for carriers or non-carriers of the polymorphism. At follow-up no significant changes from baseline were observed for UAER or eGFR in carriers of the Pro12Ala polymorphism whereas a significant increase in UAER [17 (11.3-37.9) versus 24.5 (13.8-49.9) μg/mg, p < 0.006)] and a significant reduction in the eGFR (82.8 ± 14.5 versus 80.3 ± 17.3 ml/min/1.73, m² p = 0.02), were observed in non carriers of the Pro12Ala polymorphism. Progression of nephropathy - defined according to a combined end point of UAER and eGFR- i.e. doubling of baseline UAER to at least 100 μg/mg, or new onset microalbuminuria, or progression from micro to macroalbuminuria, or 25% reduction of eGFR, or annualized eGFR decline >3 ml/min/year - was significantly less frequent in Ala carriers than non carriers (11.4% vs 35.8%; p < 0.01); HR adjusted for baseline age, AER, eGFR, HbA1c, diabetes duration and blood pressure was 0.32 (0.12-0.80).

Conclusions

This study found that among patients with type 2 diabetes, the PPARγ2 Pro12Ala polymorphism is protective against progression of nephropathy and decay of renal function independent of major confounders.

Peroxisome proliferator‑activated receptor γ polymorphisms as risk factors for dyslipidemia

Peroxisome proliferator‑activated receptor γ (PPARγ) may play an important role in lipid metabolism directly or by inducing the transcription of target genes. The aim of the present study was to investigate the association between common variants at the PPARγ locus (C1431T and Pro12Ala polymorphisms) and lipid serum levels. The studied population consisted of 820 subjects randomly selected from the Prevention of Multiple Metabolic Disorders and Metabolic Syndrome in Jiangsu Province cohort population. All subjects were interviewed and blood samples were obtained for laboratory analysis and DNA extraction. The TaqMan single nucleotide polymorphism genotyping assay was used for polymorphism genotyping. Individual polymorphisms and haplotype data were available for analysis. The 12Ala allele was found to be associated with significantly increased levels of triglyceride (TG) (P<0.01), whilst the 1431T allele was found to be associated with significantly increased levels of TG, total cholesterol (TC) and non‑high‑density lipoprotein (non‑HDL) (P<0.01). When P‑C, the most common haplotype, was used as the reference group, the P‑T, A‑C and A‑T haplotypes were found to be associated with significantly increased levels of TG (P<0.01). In addition, the A‑T haplotype was shown to be associated with significantly increased levels of TC and non‑HDL (P<0.01). In conclusion these results suggest that PPARγ gene variability may increase the risk of dyslipidemia.

Association of peroxisome proliferator-activated receptor γ Pro12Ala gene polymorphism with type 2 diabetic nephropathy risk in Caucasian population

Association of peroxisome proliferator-activated receptor gamma (PPARγ) Pro12Ala gene polymorphism with type 2 diabetic nephropathy (T2DN) risk in Caucasians is still not clear. This investigation was conducted to assess if there was an association between the PPARγ Pro12Ala gene polymorphism and T2DN risk in Caucasians using meta-analysis. The relevant literatures were identified from PubMed, and Cochrane Library on 10 October 2013, and eligible studies were included and synthesized. Six reports including eight studies were recruited into this meta-analysis for the association of the PPARγ Pro12Ala gene polymorphism with T2DN risk in Caucasians. The Pro/Pro genotype was shown to be associated with T2DN risk in Caucasians. However, the Ala/Ala genotype and Ala allele were not associated with T2DN risk in Caucasians. In the sensitivity analysis, according to the control source from hospital, the control source from population, the genotyping methods using PCR-RFLP, Taqman, sample size of case <100, the association of the PPARγ Pro12Ala gene polymorphism with T2DN risk was similar to those in non-sensitivity analysis. In conclusion, the PPARγ Pro/Pro genotype was associated with T2DN risk in Caucasians, but the Ala/Ala genotype and Ala allele not. However, additional studies are required to firmly establish a correlation between the PPARγ Pro12Ala gene polymorphism and T2DN risk in Caucasians.

PPAR α and PPAR γ polymorphisms as risk factors for dyslipidemia in a Chinese Han population

BACKGROUND

The PPAR α and PPAR γ are the key messengers responsible for the translation of nutritional stimuli into changes for the expression of genes, particularly genes involved in lipid metabolism. However, the associations between PPAR α/γ polymorphisms and lipid serum levels in the general population were rarely studied, and the conclusions were conflicting. The objective was to investigate the associations of the PPAR α and PPAR γ polymorphisms with dyslipidemia.

METHODS

820 subjects were randomly selected from the Prevention of Multiple Metabolic Disorders and MS in Jiangsu Province cohort populations. The logistic regression model was used to examine the association between these polymorphisms and dyslipidemia. SNPstats was used to explore the haplotype association analyses.

RESULTS

In the codominant and log-additive models, rs1800206, rs1805192 and rs3856806 were all associated with dyslipidemia (P < 0.005). When the most common haplotype L-G (established by rs1800206, rs4253778) was treated as the reference group, the V-G haplotype was associated with dyslipidemia (P < 0.001), higher TC and TG levels (P < 0.01). Moreover, when compared to Pro-C haplotype (established by rs1805192, rs3856806), the Pro-T, Ala-C, Ala-T haplotypes were associated with dyslipidemia (p < 0.001). A-T haplotype was associated with higher TC levels, (p < 0.01), and the P-T, A-C, A-T haplotypes were associated with higher TG levels (p < 0.01).

CONCLUSIONS

PPAR α and PPAR γ polymorphisms and haplotypes may be the genetic risk factors for dyslipidemia.

The association between the PPARγ2 Pro12Ala polymorphism and nephropathy susceptibility in type 2 diabetes: a meta-analysis based on 9,176 subjects

Background

The polymorphism Pro12Ala in peroxisome proliferator-activated receptor­γ2 gene (PPARγ2) has been reported to be associated with diabetic nephropathy (DN) in some studies, though the results remain inconclusive. To explore this relationship between PPARγ2 Pro12Ala polymorphism and the susceptibility for DN, a cumulative meta-analysis was performed in this study.

Method

PubMed, Medline, Embase and Web of Science databases have been systematically searched to identify relevant studies. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated.

Results

18 studies were included in this meta-analysis, involving 3,361 cases and 5,815 controls. The PPARγ2 Ala12 allele was significantly associated with decreased risk of DN based on dominant model (OR=0.778; 95%CI=0.618–0.981; P_{heterogeneity}=0.008; P=0.034). In the stratified analysis by ethnicity, significantly decreased risks were found among Caucasians for dominant model (OR=0.674; 95%CI=0.500–0.909; P_{heterogeneity}=0.079; P=0.010), while there was no significant association was found in Asians.

Conclusions

The results from the present meta-analysis indicated that the Pro12Ala polymorphism in PPARγ2 gene is not a risk factor for DN in type 2 diabetes (T2D). Further large and well-designed studies are needed to confirm this conclusion.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/7491348341027320.

Role of the ACE ID and PPARG P12A Polymorphisms in Genetic Susceptibility of Diabetic Nephropathy in a South Indian Population

BACKGROUND

Diabetic nephropathy (DN) is one of the life-threatening disorders characterized by persistent albuminuria, raised arterial blood pressure, a lowered glomerular filtration rate, and high risk of cardiovascular morbidity and mortality. The vascular genes ACE (Angiotensin-converting enzyme), and PPARG (peroxisome proliferator activated receptor gamma) are involved in alterations in vascular endothelium, and are suggested to play a role in the susceptibility of diabetic nephropathy.

OBJECTIVES

The aim of our study was to find out the role of ACE ID and PPARG P12A polymorphisms in genetic susceptibility of diabetic nephropathy in south Indian population.

PATIENTS AND METHODS

A total of 54 cases with diabetic nephropathy and 67 control subjects with diabetes were enrolled for our study. DNA was isolated from peripheral blood leucocytes, and genotyped using PCR-electrophoresis (ACE ID) or PCR-RFLP (PPARG P12A) methods.

RESULTS

ACE ID genotypes followed Hardy-Weinberg equilibrium in both cases and controls. But P12A genotypes deviated from Hardy-Weinberg equilibrium in diabetic controls. Chi(2) test was applied for the analysis of genotypic distributions in genotypic and dominant models. Odds ratios were also calculated. No significant differences in genotype frequencies of ACE ID and PPARG P12A polymorphisms were found on comparing patients with diabetic nephropathy with diabetic controls. The synergistic role of ACE ID* PPARG P12A interaction, did not show any association in patients with diabetic nephropathy when compared to diabetic controls.

CONCLUSIONS

In conclusion, the ACE and PPARG genes do not have a key role in conferring risk for diabetic nephropathy.

Peroxisome proliferator-activated receptor γ polymorphism Pro12Ala Is associated with nephropathy in type 2 diabetes: evidence from meta-analysis of 18 studies

OBJECTIVE

Insulin resistance plays a part in diabetic nephropathy (DN). The association between the peroxisome proliferator-activated receptor γ Pro to Ala alteration at codon 12 (Pro12Ala) polymorphism and the risk of insulin resistance has been confirmed. The association between the polymorphism and DN risk has also been widely studied recently, but no consensus was available up to now.

RESEARCH DESIGN AND METHODS

A systematic search of electronic databases (MEDLINE, Embase, and China National Knowledge Infrastructure) and reference lists of relevant articles was carried out, and then 18 case-control studies involving 3,361 DN cases and 5,825 control subjects were identified.

RESULTS

In the overall analysis, the Ala12 variant was observed to be significantly associated with decreased DN risk (odds ratio 0.76 [95% CI 0.61-0.93]). Some evidence of heterogeneity among the included studies was detected, which could be explained by the difference of ethnicity and stage of DN. Subgroup analyses stratified by ethnicity and stage of DN were performed, and results indicated the Pro12Ala polymorphism was associated with the risk of DN in Caucasians but no similar association was observed in Asians. Additionally, we observed that Ala12 was associated with decreased risk of albuminuria. With only a few of subjects were available, we failed to detect statistically significant association between the polymorphism and end-stage renal disease (ESRD).

CONCLUSIONS

Our results indicated that the Ala12 variant is a significantly protective factor for DN. Future research should focus on the effect of Pro12Ala polymorphism on ESRD and gathering data of Africans.

PPARγ as a therapeutic target in diabetic nephropathy and other renal diseases

PURPOSE OF REVIEW

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear transcription factor that regulates many important physiological processes including glucose and lipid metabolism, energy homeostasis, cell proliferation, inflammation, immunity and reproduction. The current review aims to summarize and discuss recent findings evaluating the protective effects of PPARγ against kidney diseases with a focus on diabetic nephropathy. We will also delineate the potential underlying mechanisms.

RECENT FINDINGS

PPARγ plays important roles in renal physiology and pathophysiology. Agonists of PPARγ exert protective effects against various kidney diseases including diabetic nephropathy, ischemic renal injury, IgA nephropathy, chemotherapy-associated kidney damage, polycystic kidney diseases and age-related kidney diseases via both systemic and renal actions.

SUMMARY

PPARγ agonists are effective in delaying and even preventing the progression of many renal diseases, especially diabetic nephropathy. PPARγ may represent a promising target for the treatment of renal diseases.

Null association between ACE gene I/D polymorphism and diabetic nephropathy among multiethnic Malaysian subjects

BACKGROUND:

Wide inter-ethnic allelic variations of the Angiotensin Converting Enzyme (ACE) i nsertion-deletion (I/D) gene polymorphism were thought to be responsible for the conflicting gene–diabetic nephropathy disease association worldwide. We have investigated the genetic susceptibility of the ACE gene to diabetic nephropathy in the multiethnic Malaysian population.

MATERIALS AND METHODS:

A total of 137 healthy (control) and 256 diabetic subjects were recruited. The diabetic subjects were further subdivided according to their nephropathy status based on urinary albumin-creatinine ratio (ACR) and glomerular filtration rate (GFR). Triple primer polymerase chain reaction (PCR) was used for ACE I/D genotyping. Subsequently, populationwide genetic analysis and gene-disease association studies were performed.

RESULTS:

The genotype frequencies in all subgroups were in Hardy-Weinberg equilibrium. Similar allelic and genotypic frequency of ACE I/D gene polymorphism was observed between healthy controls versus pooled type 2 diabetes mellitus (T2DM) subjects, and normoalbuminuria versus microalbuminuria, macroalbuminuria and End Stage Renal Failure (ESRF) (P > 0.05). Neither ethnicity nor gender exerted any influence on the ACE I/D gene polymorphism (P > 0.05), with the exception of the Chinese ethnic group which exhibited a higher frequency of ID genotype (P = 0.042). A multinomial logistic regression model showed that predictive factors including age, systolic blood pressure (SBP), high density lipoprotein (HDL) and glycosylated hemoglobin (HbA1C) were independently associated with diabetic nephropathy, in that order.

CONCLUSION:

The I/D polymorphism of the ACE gene is not significantly associated with both T2DM and/or diabetic nephropathy in this Malaysian population regardless of ethnicity and gender.

PPARγ2 P12A polymorphism and albuminuria in patients with type 2 diabetes: a meta-analysis of case-control studies

BACKGROUND

Insulin resistance has a role in diabetic nephropathy. The A12 variant of the PPARγ2 P121A polymorphism has been firmly associated with reduced risk of insulin resistance, while its role on the risk of albuminuria in patients with type 2 diabetes is uncertain. This study investigated whether the PPARγ2 P12A polymorphism modulates the risk of albuminuria in these patients.

METHODS

We tested the association between the A12 variant and albuminuria in three new case-control studies in diabetic patients from Italy (n = 841, n = 623 and n = 714 patients, respectively) and then performed a meta-analysis of all studies available to date. The nine studies we meta-analysed (six previously published and three presented here) comprised a total of 2376 cases and 4188 controls.

RESULTS

In none of the three new studies was a significant association observed with odds ratio (OR) [95% confidence intervals (95% CI)] being 1.115, 0.799 and 0.849 (P = 0.603, 0.358 and 0.518, respectively). At meta-analysis, the overall OR (95% CI) for association between A12 and albuminuria was 0.694 (0.528-0.912). A significant heterogeneity of the genetic effect was observed (P = 0.026), which was totally explained by the different method of urine collection and albuminuria definition utilized across the studies. In fact, most of the effect was observed in the four studies determining albumin excretion rate rather than in those using albumin concentration in a single spot (OR, 95% CI: 0.529, 0.397-0.706, P = 0.0000164 and 0.919, 0.733-1.153, P = 0.47, respectively).

CONCLUSION

The present study shows that the PPARγ2 Ala12 variant is significantly associated with a reduced risk of albuminuria among patients with type 2 diabetes.

Tagging single nucleotide polymorphisms in the PPAR-γ and RXR-α gene and type 2 diabetes risk: a case-control study of a Chinese Han population

Peroxisome proliferator-activated receptor (PPAR-γ),which is mainly involved in adipocyte differentiation, has been suggested to play an important role in the pathogenesis of insulin resistance and atherosclerosis. We investigated the frequencies of two common tagging polymorphisms of the PPAR-γ gene and two of PPAR-α with minor allele frequency (MAF) ≥0.05 in the Chinese Han population and analyzed the correlation between the different genotypes and the risk of type 2 diabetes mellitus (T2DM). TaqMan® assay was performed to test the genotypes in T2DM patients (n = 1,105) and normal controls (n = 1,107). Serum adiponectin concentration was measured by ELISA kit. The variant genotypes rs17817276GG, rs3856806CT and rs3856806CT/TT of PPAR-γ were associated with T2DM, P = 0.023,0.037 and 0.018, respectively. Furthermore, the prevalence of haplotype GT in PPAR-γ was less frequent in the case subjects (0.3%) than in the controls (1.9%) [P < 0.001,OR(95%CI)=0.13 (0.06-0.31)]. Patients with genotype TT of rs3856806 had a higher serum level of adiponectin than those with the genotype CC and CT (P = 0.031 and 0.038, respectively). There was no statistically significant difference between patients and controls in genotype distribution of rs6537944 and rs1045570 of the RXR-α gene. The present study suggests that the variant genotypes in the PPAR-γ gene could decrease the risk for the development of T2DM in the Chinese Han population.

Pro12Ala polymorphism in the PPARG gene contributes to the development of diabetic nephropathy in Chinese type 2 diabetic patients

OBJECTIVE

Oxidative stress is a major contributing factor in the development of diabetic nephropathy. Peroxisome proliferator-activated receptor gamma heterozygous mice and Pro12Ala polymorphism in PPARG exhibited increased resistance to oxidative stress. Smoking increases the production of reactive oxygen species, which accelerates oxidative stress under hyperglycemia. To determine whether the Pro12Ala polymorphism, alone or in combination with smoking, contributes to the development of diabetic nephropathy, a case-control study was performed in 760 Chinese patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Among patients, 532 had diabetic nephropathy with microalbuminuria (n = 245) or overt albuminuria (n = 287), and 228 did not show either of these symptoms but had had diabetes for > or =10 years and were not undergoing anti-hypertension treatment.

RESULTS

After adjustment for confounders, the Pro/Pro genotype was significantly associated with diabetic nephropathy (odds ratio 2.30 [95% CI 1.18-4.45], P = 0.014); smoking was also an independent risk factor for diabetic nephropathy (1.99 [1.08-3.68], P = 0.029). In addition, we identified possible synergistic effects; i.e., the high-risk group (smokers with the Pro/Pro genotype) showed 4.52 times higher risk (1.78-11.48, P = 0.002) of diabetic nephropathy than the low-risk group (nonsmokers with the Pro/Ala genotype) in a multiple logistic regression analysis controlled for the confounders.

CONCLUSIONS

Our results indicated that the Pro/Pro genotype and smoking were significant independent risk factors for diabetic nephropathy. The possible synergistic effects of genotype and smoking may aggravate oxidative stress and contribute to the development of diabetic nephropathy.

APOC1 T45S polymorphism is associated with reduced obesity indices and lower plasma concentrations of leptin and apolipoprotein C-I in aboriginal Canadians

Apolipoprotein (apo) C-I is a constituent of chylomicrons, very low density lipoprotein, and high density lipoprotein. The role of apo C-I in human metabolism is incompletely defined. We took advantage of a naturally occurring amino acid polymorphism that is present in aboriginal North Americans, namely apo C-I T45S. We assessed the hypothesis that metabolic traits, including obesity-related and lipoprotein-related traits, would differ between carriers and noncarriers of apo C-I T45S. A genotyping assay was developed for APOC1 T45S and genotypes were determined in a sample of 410 Canadian Oji-Cree subjects. The allele frequency of the apo C-I S45 allele was approximately 8% in this sample. We observed the apo C-I S45 allele was significantly associated with 1) lower percent body fat (P < 0.05), 2) lower waist circumference (P = 0.058), 3) lower serum leptin levels (P < 0.05), and 4) lower plasma apo C-I levels (P < 0.0001), using a newly developed ELISA-based method. Taken together, these results suggest that at the whole human phenotype level, apo C-I is associated with the complex metabolic trait of obesity as well as with serum leptin levels.

Retinoid X receptor heterodimer variants and cardiovascular risk factors

Nuclear receptors are transcription factors that can be activated by specific ligands. Recent progress has shown that retinoid X receptor (RXR) and its heterodimerization partners, including peroxisome proliferator-activated receptors, regulate many important genes involved in energy homeostasis and atherosclerosis, and should be promising therapeutic targets of metabolic syndrome. RXR heterodimers regulate a number of complex cellular processes, and genetic studies of RXR heterodimers have provided important clinical information in addition to knowledge gained from basic research. Genetic variants of RXR heterodimers were screened and investigated, and some variants were shown to have a considerable impact on metabolic disorders, including phenotypic components of familial combined hyperlipidemia. The combined efforts of basic and clinical science regarding nuclear receptors have achieved significant progress in unraveling the inextricably linked control system of energy expenditure, lipid and glucose homeostasis, inflammation, and atherosclerosis.This review summarizes the current understanding regarding RXR heterodimers based on their human genetic variants, which will provide new clues to uncover the background of multifactorial disease, such as metabolic syndrome or familial combined hyperlipidemia.

Papel dos lipídeos da dieta na nefropatia diabética

O objetivo do presente manuscrito foi revisar o possível papel dos lipídeos dietéticos na nefropatia diabética (ND), considerando as alterações do perfil lipídico associadas e a interação entre aspectos dietéticos e genéticos. Os lipídeos dietéticos podem ter um papel importante no desenvolvimento e na progressão da ND. A composição das gorduras da dieta tem sido associada com a ND, particularmente à microalbuminúria e às anormalidades lipídicas e de função endotelial. Entretanto, ainda não está comprovado o benefício da modificação da ingestão de gorduras em pacientes com ND, em especial sobre desfechos definitivos, como incidência e progressão da ND, insuficiência renal e morte. Além disso, a resposta do perfil lipídico à ingestão de gorduras pode ser influenciada por fatores genéticos. A identificação de polimorfismos genéticos específicos associados a essa interação poderá permitir a individualização de estratégias nutricionais na ND.

PPARγ2 polymorphism and human health

The nuclear hormone receptor peroxisome proliferator activated receptor gamma (PPARγ) is an important transcription factor regulating adipocyte differentiation, lipid and glucose homeostasis, and insulin sensitivity. Numerous genetic mutations of PPARγ have been identified and these mutations positively or negatively regulate insulin sensitivity. Among these, a relatively common polymorphism of PPARγ, Pro12Ala of PPARγ2, the isoform expressed only in adipose tissue has been shown to be associated with lower body mass index, enhanced insulin sensitivity, and resistance to the risk of type 2 diabetes in human subjects carrying this mutation. Subsequent studies in different ethnic populations, however, have revealed conflicting results, suggesting a complex interaction between the PPARγ2 Pro12Ala polymorphism and environmental factors such as the ratio of dietary unsaturated fatty acids to saturated fatty acids and/or between the PPARγ2 Pro12Ala polymorphism and genetic factors such as polymorphic mutations in other genes. In addition, this polymorphic mutation in PPARγ2 is associated with other aspects of human diseases, including cancers, polycystic ovary syndrome, Alzheimer disease and aging. This review will highlight findings from recent studies.

PPARgamma in Kidney Physiology and Pathophysiology

Involvement of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) in kidney physiology has been explored recently. Synthetic PPARγ ligands can ameliorate the diabetic kidney disease through different mechanisms, involving inhibition of mesangial cell growth, reduction of mesangial matrix, and cytokine production of glomerular cells as well as promoting endothelial cell survival within the kidney glomeruli. Activation of PPARγ has additional profibrotic consequences, which can contribute to wound healing in diabetic glomerulonephritis. Beside many beneficial effects, PPARγ activation, however, can lead to severe water retention, a common side effect of thiazolidinedione therapy. This unwanted effect is due to the activation of PPARγ in the mesonephric distal collecting system, where PPARγ positively regulates sodium and water resorbtion leading to the expansion of interstitial fluid volume. Recent studies indicate that PPARγ is also involved in the normal kidney development, renal lipid metabolism, and activation of the renin-angiotensin system. In this paper, we give a synopsis of the current knowledge on PPARγ functions in kidney phyisology and pathophysiology.

Role of PPARgamma in renoprotection in Type 2 diabetes: molecular mechanisms and therapeutic potential

DN (diabetic nephropathy) is a chronic disease characterized by proteinuria, glomerular hypertrophy, decreased glomerular filtration and renal fibrosis with loss of renal function. DN is the leading cause of ESRD (end-stage renal disease), accounting for millions of deaths worldwide. TZDs (thiazolidinediones) are synthetic ligands of PPARgamma (peroxisome-proliferator-activated receptor gamma), which is involved in many important physiological processes, including adipose differentiation, lipid and glucose metabolism, energy homoeostasis, cell proliferation, inflammation, reproduction and renoprotection. A large body of research over the past decade has revealed that, in addition to their insulin-sensitizing effects, TZDs play an important role in delaying and preventing the progression of chronic kidney disease in Type 2 diabetes. Although PPARgamma activation by TZDs is in general considered beneficial for the amelioration of diabetic renal complications in Type 2 diabetes, the underlying mechanism(s) remains only partially characterized. In this review, we summarize and discuss recent findings regarding the renoprotective effects of PPARgamma in Type 2 diabetes and the potential underlying mechanisms.