APOE polymorphisms and the development of diabetic nephropathy in type 1 diabetes: results of case-control and family-based studies

The Association between Apolipoprotein E Genotypes and Serum Malondialdehyde Level with End-Stage Renal Disease

Background

The Apolipoprotein E (ApoE) polymorphism plays an important role in the pathophysiology of end-stage renal disease (ESRD). Additionally, ApoE may contribute to the progression of oxidative stress. Thus, this study aimed to determine the ApoE gene polymorphism and evaluate the malondialdehyde (MDA) level in ESRD patients and healthy individuals.

Methods

The present cross-sectional study was conducted at 2010 at Kermanshah University of Medical Sciences (Kermanshah, Iran). The study population comprised ESRD patients (n=136) and healthy individuals (n=137). The MDA level was assessed using high-performance liquid chromatography (HPLC), and the frequencies of ApoE gene alleles were analyzed using restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR). The data were analyzed using Statistical Package for Social Sciences (SPSS), version 13. The significant differences of ApoE genotypes in case and control groups were assessed using Pearson's Chi square tests, and two-tailed Student's tests. A logistic regression model was used to calculate the odd ratio. P<0.05 was considered statistically significant.

Results

According to the results, ESRD patients had a higher frequency of the E2/E3 genotype than the healthy group (P<0.001). The results indicated that E3/E4 genotype frequency in the patients' group was higher than that of the control group (P=0.026). Furthermore, the E3/E2 (OR=5.7, 95% CI=2.68-12.14) (P<0.001) and E3/E4 (OR=1.57, 95% CI=1.05-2.34) (P=0.029) genotypes were found to increase the risk of ESRD. Moreover, the MDA level in ESRD patients was higher than the healthy individuals (P<0.001). The patients with E3/E2 (P<0.001) and E3/E4 (P<0.001) genotypes had a higher level of MDA than the control group.

Conclusion

According to the findings, patients with ESRD had higher genotypes of E3/E2 and E3/E4, which suggests a higher risk of developing ESRD.

The Journey of Thiazolidinediones as Modulators of PPARs for the Management of Diabetes: A Current Perspective

Peroxisome Proliferator-Activated Receptors (PPARs) also known as glitazone receptors are a family of receptors that regulate the expression of genes and have an essential role in carbohydrate, lipid and protein metabolism apart from other functions. PPARs come in 3 sub-types: PPAR-α, PPAR-β/δ and PPAR-γ - with PPAR-γ having 2 isoforms - γ1 and γ2. Upon activation, the PPARs regulate the transcription of various genes involved in lipid and glucose metabolism, adipocyte differentiation, increasing insulin sensitivity, prevention of oxidative stress and to a certain extent, modulation of immune responses via macrophages that have been implicated in the pathogenesis of insulin resistance. Hence, PPARs are an attractive molecular target for designing new anti-diabetic drugs. This has led to a boost in the research efforts directed towards designing of PPAR ligands - particularly ones that can selectively and specifically activate one or more of the PPAR subtypes. Though, PPAR- γ full agonists such as Thiazolidinediones (TZDs) are well established agents for dyslipidemia and type 2 diabetes mellitus (T2D), the side effect profile associated with TZDs has potentiated an imminent need to come up with newer agents that act through this pathway. Several newer derivatives having TZD scaffold have been designed using structure based drug designing technique and computational tools and tested for their PPAR binding affinity and efficacy in combating T2D and some have shown promising activities. This review would focus on the role of PPARs in the management of T2D; recently reported TZD derivatives which acted as agonists of PPAR- γ and its subtypes and are potentially useful in the new drug discovery for the disease.

Association of Apolipoprotein E Polymorphisms with White Matter Lesions and Brain Atrophy

OBJECTIVE

Apolipoprotein E (ApoE) is mainly synthesized in the liver. So far, it is unknown the relationship among APOE gene polymorphisms and WML, brain atrophy. Therefore, the aim of the study was to assess the associations of APOE gene polymorphisms in patients with WML and brain atrophy.

METHODS

A total of 58 patients with WML, 128 patients with brain atrophy, 112 patients with co-occurrence of WML and brain atrophy and 95 healthy elderly volunteers were recruited from Renmin Hospital of WuHan University.

RESULTS

Allele E3 was the most common allele. The alleles E2 had significantly higher levels of ApoB and lower age in WML group. The alleles E2 was associated with the lower level of ApoB, LDL-Ch, TCh, and sdLDL in co-occurrence group. The E3/E3 genotype has higher level of sdLDL, but lower age and female frequency in WML. The E3/E4 genotype had higher level of TG, but lower age in WML. Gender, Age, E2, Hyperhomocysteinemia and UA were also significantly associated with disease progression.

CONCLUSION

This study found that clinical data, lipids and metabolic complications were closely related to ApoE genotypes and alleles, and also disease progression and type.

Apolipoprotein E-related glomerular disorders

Of the glomerular disorders that occur due to apolipoprotein E (apoE) mutations, apoE2 homozygote glomerulopathy and lipoprotein glomerulopathy (LPG) have been characterized. ApoE2 homozygote glomerulopathy has been found in individuals expressing homozygous apoE2/2. This was characterized histologically by glomerulosclerosis with marked infiltration of foam cells derived from macrophages, and occasionally with non-lamellated lipoprotein thrombi. Recently, several cases of apoE Toyonaka (Ser197Cys) combined with homozygous apoE2/2 have been reported, in which non-immune membranous nephropathy-like features were observed in glomeruli. Interestingly, in these cases, apoE accumulation was identified by tandem mass spectrometry. Therefore, it is speculated that these findings may arise from apoE molecules without lipids, which result from hinge damage by apoE Toyonaka and may cross the glomerular basement membrane as small molecules. LPG is primarily associated with heterozygous apoE mutations surrounding the low-density lipoprotein-receptor binding site, and it is histologically characterized by lamellated lipoprotein thrombi that lack foam cells. Recent studies have suggested that LPG can be induced by thermodynamic destabilization, hydrophobic surface exposure, and the aggregation of apoE resulting from the incompatibility of apoE mutated residues within helical regions. Additionally, apoE5 may play a supporting role in the development of LPG and in lipid-induced kidney diseases via hyperlipoproteinemia. Thus, it is interesting that many apoE mutations contribute to characteristic glomerular disorders through various mechanisms. In particular, macrophages may uptake lipoproteins into the cytoplasm and contribute to the development of apoE2 homozygote glomerulopathy as foam cells, and their dysfunction may contribute to the accumulation of lipoproteins in the glomerulus, causing lipoprotein thrombi in LPG.

Apolipoprotein E Gene Polymorphisms in Saudi Patients with Systemic Lupus Erythematosus

Apolipoprotein E (APOE) is a glycosylated protein with multiple biological properties. APOE gene polymorphism plays a central role in lipid metabolism and has recently been suggested to regulate inflammation. Our objective is to evaluate whether APOE polymorphism affects susceptibility to SLE. APOE genotyping was performed using ApoE StripAssay™ kit. Results indicated significantly higher frequencies of allele ε4 and genotype ε3/ε4 and lower frequencies of allele ε3 and genotype ε3/ε3 in SLE patients than controls. APOE ε2 allele was found in three patients, whereas it was absent in controls. The frequencies of allele ε4 and genotype ε3/ε4 were significantly higher in SLE patients with renal involvement and those of alleles ε2, ε4 and genotypes ε2/ε3, ε3/ε4 were higher in patients with neuropsychiatric symptoms. It is concluded that APOE allele ε4 is associated with susceptibility risk/clinical manifestations of SLE and ε2 may increase its severity while ε3 is protective for SLE in Saudis.

Association between Apolipoprotein E Polymorphism and Chronic Kidney Disease in the Korean General Population: Dong-gu Study

Background

Few studies have investigated the association between Apolipoprotein E (APOE) polymorphisms and chronic kidney disease (CKD) in the general population, and their results are inconsistent.

Methods

The current study population was composed of 9,033 subjects aged ≥ 50 years who participated in the baseline survey of the Dong-gu Study, which was conducted in Korea between 2007 and 2010. APOE polymorphisms were identified by polymerase chain reaction, and the estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease equation.

Results

Individuals with the APOE E2 allele had significantly lower total and low density lipoprotein cholesterol levels, those with the APOE E4 allele had lower high density lipoprotein (HDL) cholesterol levels, and those with the APOE E3 allele had lower log-triglyceride levels. Adjusting for covariates (sex, age, body mass index, smoking, systolic blood pressure, hypertension, diabetes, total cholesterol, HDL cholesterol, log-transformed triglycerides, and log-transformed albumin to creatinine ratio), mean eGFR was not significantly different among APOE alleles (E2, 69.4 mL/min/1.73 m²; E3, 69.5 mL/min/1.73 m²; E4, 69.4 ml/min/1.73 m²; P = 0.873). Additionally, the odds ratios (ORs) indicated that APOE polymorphisms were not independent risk factors for CKD (OR, 1.07; 95% confidence interval [CI], 0.91 to 1.26 for the E2 vs. E3 allele; OR, 1.01; 95% CI, 0.88 to 1.16 for the E4 vs. E3 allele).

Conclusion

APOE polymorphisms were not associated with either eGFR or CKD in the general Korean population.

Novel biomarkers in glomerular disease

Glomerular diseases are major contributors to the global burden of end-stage kidney disease. The clinical course and outcome of these disorders are extremely variable and difficult to predict. The clinical trajectories range from a benign and spontaneously remitting condition to a symptomatic and rapidly progressive disease. The diagnosis is based entirely on the evaluation of kidney biopsy, but this invasive procedure carries multiple risks and often fails to predict the clinical course or responsiveness to treatment. However, more recent advances in genetics and molecular biology have facilitated elucidation of novel pathogenic mechanisms of these disorders. These discoveries fuel the development of novel biomarkers and offer prospects of noninvasive diagnosis and improved prognostication. Our review focuses on the most promising novel biomarkers that have recently emerged for the major types of glomerular diseases, including immunoglobulin A nephropathy, membranous nephropathy, focal segmental glomerulosclerosis, and membranoproliferative glomerulonephritis.

Apolipoprotein E gene variants on the risk of end stage renal disease

Objective

End-stage renal disease (ESRD) is a severe health concern over the world. Associations between apolipoprotein E (apoE) gene polymorphisms and the risk of ESRD remained inconclusive. This study aimed to investigate the association between apoE gene polymorphisms and ESRD susceptibility.

Methods

Databases including PubMed, Embase, Web of Science and the Cochrane Library were searched to find relevant studies. Meta-analysis method was used synthesize the eligible studies.

Results

Sixteen pertinent case-control studies which included 3510 cases and 13924 controls were analyzed. A significant association was found between ε2 allele and the ESRD risk (odds ratio (OR) = 1.30, 95% confidence interval (CI) 1.15–1.46, P < 0.0001; I² = 18%, P for heterogeneity = 0.24). The ε2ε3, ε2ε4, ε3ε3, ε3ε4, ε4ε4, ε3 and ε4 were not associated with the susceptibility of ESRD. In the subgroup analysis by ethnicity, there was a statistically significant association between ε2ε3 or ε2 allele and ESRD risk in East Asians (OR = 1.66, 95% CI 1.31–2.10, P < 0.0001; OR = 1.62, 95% CI 1.31–2.01, P < 0.0001, respectively), but not in Caucasians. E2 carriers had higher plasma apoE (mean difference = 16.24 mg/L, 95% CI 7.76-24.73, P = 0.0002) than the (ε3 + ε4) carriers in patients with ESRD. The publication bias was not significant.

Conclusion

The ε2 allele of apoE gene might increase the risk of ESRD. E2 carriers expressed higher level of plasma apoE in patients with ESRD. More well-designed studies are needed to confirm these associations in the future.

Dyslipoproteinemia and impairment of renal function in diabetic kidney disease: an analysis of animal studies, observational studies, and clinical trials

Dyslipoproteinemia is highly prevalent in diabetes, chronic kidney disease, and diabetic kidney disease (DKD). Both diabetes and chronic kidney disease (CKD) are associated with hypertriglyceridemia, lower high-density lipoprotein, and higher small, dense low-density lipoprotein. A number of observational studies have reported that dyslipidemia may be associated with albuminuria, renal function impairment, and end-stage renal disease (ESRD) in the general population, and especially in CKD and DKD patients. Diabetic glomerulopathy and the related albuminuria are the main manifestations of DKD. Numerous animal studies support the finding that glomerular atherosclerosis is the main mechanism of glomerulosclerosis in CKD and DKD. Some randomized, controlled trials suggest the use of statins for the prevention of albuminuria and renal function impairment in CKD and DKD patients. However, a large clinical study, the Study of Heart and Renal Protection (SHARP), does not support that statins could reduce ESRD in CKD. In this article, we analyze the complex association of dyslipoproteinemia with DKD and deduce its relevance from animal studies, observational studies, and clinical trials. We show that special subgroups could benefit from the statin treatment.

Serum amyloid A and C-reactive protein levels may predict microalbuminuria and macroalbuminuria in newly diagnosed type 1 diabetic patients

BACKGROUND

In this study we evaluated the association of baseline levels of six different candidate proteins for the development of microalbuminuria and macroalbuminuria in type 1 diabetic patients, who were followed for approximately 30 years. Two of the proteins are markers of inflammation: serum amyloid A (SAA) and C-reactive protein (CRP), three are involved in lipid metabolism: apolipoprotein A1, apolipoprotein E and adiponectin and the last protein, fibronectin, is related to structural changes.

METHODS

A nested case control study population of 60 patients from an inception cohort of type 1 diabetic patients where 20 developed microalbuminuria followed by macroalbuminuria and 40 stayed normoalbuminuric during approximately 30 years of follow-up time was used to evaluate baseline levels of the six candidate biomarkers. The proteins were quantified by multiplexed immunoassays.

RESULTS

Log SAA levels were borderline predictor of microalbuminuria, HR 2.31 (1-5.4) p=0.053 in a univariate Cox regression model and predicted the development of macroalbuminuria HR 2.432 (1-6) p=0.049, also univariate. When adjusting for covariates, log SAA predicted the development of microalbuminuria with an HR 4.131 (1.1-15) p=0.03. Log CRP predicted the development of microalbuminuria, HR 2.928 (1.4-6.1) p=0.004, and macroalbuminuria, HR 2.785 (1.3-5.8) p=0.007 in univariate models. When adjusting for covariates, log CRP predicted the development of microalbuminuria with an HR 5.882 (1.7-20.9) p=0.006 and macroalbuminuria with an HR 3.233 (1.1-9.8) p=0.038. Apolipoprotein A1, apolipoprotein E, fibronectin and adiponectin were not associated with development of elevated albumin excretion rate.

CONCLUSIONS

SAA and CRP baseline levels predicted development of micro- and macroalbuminuria during 30 years of follow up, supporting the theory that inflammation is involved in the progression of diabetic nephropathy. Further studies are needed to fully establish the two proteins' potential as additional biomarkers for the development of diabetic nephropathy.

Searching for new biomarkers of renal diseases through proteomics

BACKGROUND

Technological advances have resulted in a renaissance of proteomic studies directed at finding markers of disease progression, diagnosis, or responsiveness to therapy. Renal diseases are ideally suited for such research, given that urine is an easily accessible biofluid and its protein content is derived mainly from the kidney. Current renal prognostic markers have limited value, and renal biopsy remains the sole method for establishing a diagnosis. Mass spectrometry instruments, which can detect thousands of proteins at nanomolar (or even femtomolar) concentrations, may be expected to allow the discovery of improved markers of progression, diagnosis, or treatment responsiveness.

CONTENT

In this review we describe the strengths and limitations of proteomic methods and the drawbacks of existing biomarkers, and provide an overview of opportunities in the field. We also highlight several proteomic studies of biomarkers of renal diseases selected from the plethora of studies performed.

SUMMARY

It is clear that the field of proteomics has not yet fulfilled its promise. However, ongoing efforts to standardize sample collection and preparation, improve study designs, perform multicenter validations, and create joint industry-regulatory bodies offer promise for the recognition of novel molecules that could change clinical nephrology forever.

Expression of the human apoE2 isoform in adipocytes: altered cellular processing and impaired adipocyte lipogenesis

Expression of apoE in adipocytes has been shown to have an important role in modulating adipocyte triglyceride (TG) metabolism and gene expression that is independent of circulating and extracellular apoE. The impact of adipocyte expression of common human apoE isoforms was evaluated using adipocytes harvested from human apoE2, -3, and -4 knock-in mice. Expression of the apoE2 isoform was associated with an increase in adipocyte apoE gene expression and apoE synthesis. Newly synthesized apoE2 was unstable in adipocytes and demonstrated increased degradation and decreased secretion. ApoE2-expressing mice were hyperlipidemic, and had increased size of gonadal fat pads and of adipocytes, compared with apoE3 mice. In isolated cells, however, expression of the apoE2 isoform produced defective lipogenesis and increased TG hydrolysis. Incubation of adipose tissue with apoE3-containing TG-rich lipoproteins resulted in a significant increase in TG in adipose tissue from apoE3 and -E4 mice, but not apoE2 mice. Reduced capacity to internalize FFA as lipogenic substrate contributed to defective lipogenesis. Newly synthesized apoE2 is unstable in adipocytes and results in decreased adipocyte TG synthesis and defective FA uptake. These changes recapitulate those observed in apoE knockout adipocytes and have implications for understanding metabolic disturbances in humans expressing the E2 isoform.

Role of apolipoprotein E in renal damage protection

It is well-known that nephrotic syndrome and chronic renal failure are associated with lipid and lipoprotein abnormalities. For a long time, it has been thought that hyperlipidemia is a secondary and insignificant condition of these renal injuries. Recently, it has been shown that dyslipidaemia may contribute to the development and progression of chronic kidney disease. Apolipoprotein E (apoE) null mice are a very popular model for studying spontaneous hypercholesterolemia, but only limited data are available for the role of apolipoprotein E in kidney disease. The purpose of this study is to evaluate kidney disease in apolipoprotein E deficient mice. For this study, apoE null mice and control mice at different ages (6 weeks and 15 months) were used. Kidney morphological damage and proteins involved in oxidative stress and aging (TNF-α and NF-kB) were analyzed. ApoE deficient mice have morphological alterations that are the hallmark of kidney pathogenesis, which increase with the age of the animals. In apoE null mice kidneys, there is also increased oxidative stress as compared to control mice at the same age and fewer antioxidant enzymes. Our findings add to the growing list of protective effects that apoE possesses.

Genetics of diabetic nephropathy

The increasing prevalence of diabetes mellitus has led to a growing number of chronic complications including diabetic nephropathy (DN). In addition to its high prevalence, DN is associated with high morbidity and mortality especially due to cardiovascular diseases. It is well established that genetic factors play a role in the pathogenesis of DN and genetically susceptible individuals can develop it after being exposed to environmental factors. DN is probably a complex, polygenic disease. Two main strategies have been used to identify genes associated to DN: analysis of candidate genes, and more recently genome-wide scan. Great efforts have been made to identify these main genes, but results are still inconsistent with different genes associated to a small effect in specific populations. The identification of the main genes would allow the detection of those individuals at high risk for DN and better understanding of its pathophysiology as well.

Quantitative iTRAQ-Based Proteomic Identification of Candidate Biomarkers for Diabetic Nephropathy in Plasma of Type 1 Diabetic Patients

Introduction

As part of a clinical proteomics programme focused on diabetes and its complications, it was our goal to investigate the proteome of plasma in order to find improved candidate biomarkers to predict diabetic nephropathy.

Methods

Proteins derived from plasma from a cross-sectional cohort of 123 type 1 diabetic patients previously diagnosed as normoalbuminuric, microalbuminuric or macroalbuminuric were enriched with hexapeptide library beads and subsequently pooled within three groups. Proteins from the three groups were compared by online liquid chromatography and tandem mass spectrometry in three identical repetitions using isobaric mass tags (iTRAQ). The results were further analysed with ingenuity pathway analysis. Levels of apolipoprotein A1, A2, B, C3, E and J were analysed and validated by a multiplex immunoassay in 20 type 1 diabetic patients with macroalbuminuria and 10 with normoalbuminuria.

Results

A total of 112 proteins were identified in at least two out of three replicates. The global protein ratios were further evaluated by ingenuity pathway analysis, resulting in the recognition of apolipoprotein A2, B, C3, D and E as key nodes in the top-rated network. The multiplex immunoassay confirmed the overall protein expression patterns observed by the iTRAQ analysis.

Conclusion

The candidate biomarkers discovered in this cross-sectional cohort may turn out to be progression biomarkers and might have several clinical applications in the treatment and monitoring of diabetic nephropathy; however, they need to be confirmed in a longitudinal cohort.

Electronic supplementary material

The online version of this article (doi:10.1007/s12014-010-9053-0) contains supplementary material, which is available to authorized users.

Genetic diversity of the apolipoprotein E gene and diabetic nephropathy: a meta-analysis

In the past decade, a number of case-control studies have been carried out to investigate the relationship between the ApoE polymorphism and diabetic nephropathy. However, the results have been inconclusive. To investigate this inconsistency, we performed a meta-analysis of all available studies dealing with the relationship between the ApoE polymorphism and DN. The 23 studies in the meta- analysis included 6,012 diabetic patients with (n = 2,979) and without (n = 3,033) DN. The ApoE ε2 allele was significantly associated with DN (OR = 1.64, 95% CI: 1.26-2.13; P(Z) = 0.00027), whereas the ε4 allele was non-significantly associated with DN (OR = 0.93, 95% CI: 0.78-1.11; P(Z) = 0.418). However, significant heterogeneity was detected. In further subgroup analyses, genotyping methods, outcome of cases and duration of diabetes in controls were found to explain some of the heterogeneity. Genotypic analysis also found a strong association between the ε2 carriers and DN (OR = 1.61, 95% CI: 1.22-2.13; P(Z) = 0.001) and indicated that ε4 tended to have a marginally significant protective effect for DN (OR = 0.82, 95% CI: 0.65-1.03; P(Z) = 0.085). The results of our meta-analysis support a genetic association between the ApoE polymorphism and DN. ε2 increases the risk of DN in diabetes patients, while ε4 trends to be protective. These findings may have implications for therapeutic intervention in diabetic nephropathy.

Association of APOE polymorphism with chronic kidney disease in a nationally representative sample: a Third National Health and Nutrition Examination Survey (NHANES III) Genetic Study

Background

Apolipoprotein E polymorphisms (APOE) have been associated with lowered glomerular filtration rate (GFR) and chronic kidney disease (CKD) with e2 allele conferring risk and e4 providing protection. However, few data are available in non-European ethnic groups or in a population-based cohort.

Methods

The authors analyzed 5,583 individuals from the Third National Health and Nutrition Examination Survey (NHANES III) to determine association with estimated GFR by the Modification of Diet in Renal Disease (MDRD) equation and low-GFR cases. Low-GFR cases were defined as GFR <75 ml/min/1.73 m²; additionally, GFR was analyzed continuously.

Results

In univariate analysis, the e4 allele was negatively associated with low-GFR cases in non-Hispanic whites, odds ratio (OR): 0.76, 95% confidence interval (CI): 0.60, 0.97. In whites, there was a significant association between increasing APOE score (indicating greater number of e2 alleles) and higher prevalence of low-GFR cases (OR: 1.21, 95%CI: 1.01, 1.45). Analysis of continuous GFR in whites found the e4 allele was associated with higher levels of continuous GFR (β-coefficient: 2.57 ml/min/1.73 m², 95%CI: 0.005, 5.14); in non-Hispanic blacks the e2 allele was associated with lower levels of continuous GFR (β-coefficient: -3.73 ml/min/1.73 m², 95%CI: -6.61, -0.84). APOE e2 and e4 alleles were rare and not associated with low-GFR cases or continuous GFR in Mexican Americans.

Conclusion

In conclusion, the authors observed a weak association between the APOE e4 allele and low-GFR cases and continuous GFR in non-Hispanic whites, and the APOE e2 allele and continuous GFR in non-Hispanic blacks, but found no association with either measure of kidney function in Mexican Americans. Larger studies including multiethnic groups are needed to determine the significance of this association.

Involvement of the PRKCB1 gene in autistic disorder: significant genetic association and reduced neocortical gene expression

Protein kinase C enzymes play an important role in signal transduction, regulation of gene expression and control of cell division and differentiation. The fsI and betaII isoenzymes result from the alternative splicing of the PKCbeta gene (PRKCB1), previously found to be associated with autism. We performed a family-based association study in 229 simplex and 5 multiplex families, and a postmortem study of PRKCB1 gene expression in temporocortical gray matter (BA41/42) of 11 autistic patients and controls. PRKCB1 gene haplotypes are significantly associated with autism (P<0.05) and have the autistic endophenotype of enhanced oligopeptiduria (P<0.05). Temporocortical PRKCB1 gene expression was reduced on average by 35 and 31% for the PRKCB1-1 and PRKCB1-2 isoforms (P<0.01 and <0.05, respectively) according to qPCR. Protein amounts measured for the PKCbetaII isoform were similarly decreased by 35% (P=0.05). Decreased gene expression characterized patients carrying the 'normal' PRKCB1 alleles, whereas patients homozygous for the autism-associated alleles displayed mRNA levels comparable to those of controls. Whole genome expression analysis unveiled a partial disruption in the coordinated expression of PKCbeta-driven genes, including several cytokines. These results confirm the association between autism and PRKCB1 gene variants, point toward PKCbeta roles in altered epithelial permeability, demonstrate a significant downregulation of brain PRKCB1 gene expression in autism and suggest that it could represent a compensatory adjustment aimed at limiting an ongoing dysreactive immune process. Altogether, these data underscore potential PKCbeta roles in autism pathogenesis and spur interest in the identification and functional characterization of PRKCB1 gene variants conferring autism vulnerability.

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.

The relationship of the apolipoprotein E gene polymorphism Turkish Type 2 diabetic patients with and without nephropathy

OBJECTIVE

Apolipoprotein E (ApoE) genetic variation which is a major constituent of plasma lipoproteins causes diabetic nephropathy progress. Chronic kidney disease is associated with increased E2 allele and the decreased E4 allele risk. The aim of this study was to investigate the association between ApoE gene polymorphism in the development of diabetic nephropathy in Type 2 diabetes Turkish patients.

RESEARCH DESIGN AND METHODS

The objective of the study is to investigate the influence of ApoE gene polymorphism in the development of diabetic nephropathy in Turkish Type 2 diabetes. The ApoE genotypes were determined retrospectively in 46 patients with nephropathy and 56 without nephropathy and a control group of 35 healthy individuals. Genomic DNA was extracted from peripheral leukocytes of the subjects using the High Pure PCR Template Preparation Kit. For the detection of the presence of the three ApoE E alleles epsilon2, epsilon3, and epsilon4 (codon 112 and 158) were analyzed by the commercial LightCycler ApoE Mutation Detection Kit.

RESULTS

No differences in ApoE genotype or the allelic frequencies of epsilon2, epsilon3 or epsilon4 were found between the Type 2 diabetic patient group (with and without nephropathy) and a control group.

CONCLUSIONS

We conclude that the ApoE gene polymorphism is not associated with the development of diabetic nephropathy in Turkish Type 2 diabetic patients. Lack of association between ApoE gene polymorphism and Type 2 diabetic nephropathy might be due to ethnic differences.

Genetics of diabetic nephropathy

Genetic susceptibility has been proposed as an important factor for the development and progression of diabetic nephropathy, and research efforts have been invested worldwide to identify the susceptibility gene for diabetic nephropathy. Although, several candidate genes were shown to be associated with the disease, the results were not always consistent; most of the genes conferring susceptibility to diabetic nephropathy remain to be identified. Recent development of the single nucleotide polymorphism (SNP) typing technology and collation of information on linkage disequilibrium in the human genome have facilitated genome-wide association studies (GWASs) for investigating novel disease-susceptibility genes across the entire human genome. GWASs are considered a powerful and promising approach and are expected to be useful for identifying convincing susceptibility genes for several common diseases; however, to date, these studies have not been able to completely cover the entire human genome.

Quantitative trait loci for urinary albumin in crosses between C57BL/6J and A/J inbred mice in the presence and absence of Apoe

We investigated the effect of apolipoprotein E (Apoe) on albuminuria in the males of two independent F2 intercrosses between C57BL/6J and A/J mice, using wild-type inbred strains in the first cross and B6-Apoe(-/-) animals in the second cross. In the first cross, we identified three quantitative trait loci (QTL): chromosome (Chr) 2 [LOD 3.5, peak at 70 cM, confidence interval (C.I.) 28-88 cM]; Chr 9 (LOD 2.0, peak 5 cM, C.I. 5-25 cM); and Chr 19 (LOD 1.9, peak 49 cM, C.I. 23-54 cM). The Chr 2 and Chr 19 QTL were concordant with previously found QTL for renal damage in rat and human. The Chr 9 QTL was concordant with a locus found in rat. The second cross, testing only Apoe(-/-) progeny, did not identify any of these loci, but detected two other loci on Chr 4 (LOD 3.2, peak 54 cM, C.I. 29-73 cM) and Chr 6 (LOD 2.6, peak 33 cM, C.I. 11-61 cM), one of which was concordant with a QTL found in rat. The dependence of QTL detection on the presence of Apoe and the concordance of these QTL with rat and human kidney disease QTL suggest that Apoe plays a role in renal damage.

Genetic predictors of renal failure

BACKGROUND

Both environmental and genetic factors contribute to the development and progression of chronic kidney disease. The completion of the human genome sequence and advances in genomic technology make possible identification of gene variants associated with renal failure.

OBJECTIVE

This review discusses the relevant genetic studies in chronic kidney disease, with particular emphasis on the most common causes of end stage renal failure, diabetic nephropathy and glomerulonephritis.

METHODS

Most of the studies presented were performed in recent years and employed association studies, both population-based and with candidate genes, as well as the genome-wide association and genome-wide scan approaches.

RESULTS/CONCLUSION

Increasing evidence supports an important role of genetic susceptibility in the development and progression of renal failure. Identification of disease genes will allow the identification of patients at high risk and the development of new strategies to prevent or delay the renal disease process.

Relationship between Apolipoprotein E polymorphism and nephropathy in type-2 diabetic patients

Twenty to forty percent of type-2 diabetic patients (DM2) present nephropathy. Genetic polymorphism of Apolipoprotein E (Apo E) has been proposed as a risk factor in the development and progression of diabetic nephropathy. The purpose of the study was to evaluate the relationship between Apo E polymorphism and presence of nephropathy in DM2 patients. We studied 85 DM2 patients with a similar nutritional state, environmental and socioeconomic condition and more than 10 years of evolution. They were grouped in DM2 patients with kidney complications (n=56) and without kidney complications (n=29; control group). Apo E genotype was determined by restriction fragment-length polymorphism analysis. A plasmatic biochemical characterization was performed on all the subjects studied. The 85 DM2 patients had arterial hypertension in treatment. The nephropathy diabetic group showed differences (p<0.001) in BMI, systolic blood pressure, glycemia, cholesterol (total, HDL and LDL), HbA1c and creatinine. The e4 allelic frequency was 8% in the nephropathy group versus 25.9% in the control group. Apo e3 allele and E3/3 genotype frequency were higher and E3/4 genotype was lower in the nephropathy group than in controls. These groups also showed differences in total, HDL and LDL cholesterol. DM2 patients without nephropathy presented a higher frequency of e4 allele. These results could suggest a protective role of e4 allele in the development and progression of diabetic nephropathy.

Association of lipoprotein lipase S447X, apolipoprotein E exon 4, and apoC3 -455T>C polymorphisms on the susceptibility to diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. In DN patients, triglyceride (TG) level is elevated and lipoprotein lipase (LPL) activity, which hydrolyzes TG, is decreased. The LPL S447X and apolipoprotein E (APOE) exon 4 polymorphisms affect TG levels, and the APOC3 -455T>C polymorphism affects LPL activity. Our aim was to examine the association of these polymorphisms with nephropathy in type 2 diabetes. We examined these polymorphisms in a case-control study of type 2 diabetic patients including 374 with DN and 392 without DN. LPL 447X-containing genotypes (447X+) were significantly decreased in DN patients [18.6 vs 25.6%, odds ratio (OR) = 0.66, p = 0.02], as were APOE epsilon3/epsilon3 genotypes (64.8 vs 73.1%, OR = 0.68, p = 0.01). In addition, combinations of genotypes [APOE epsilon3/epsilon3 and LPL 447X+ (OR = 0.56), APOC3 CC and LPL 447X+ (OR = 0.31), APOE epsilon3/epsilon3 and APOC3 CC (OR = 0.61] were protective for DN compared with the most common combination of the respective polymorphisms. Our findings suggest the importance of interactions among lipid genes in modulating the risk of DN.

Investigational PPAR-gamma agonists for the treatment of Type 2 diabetes

The tremendous increase in the global prevalence of Type 2 diabetes (T2D) and its conglomeration of metabolic disorders has dramatically intensified the search for innovative therapies to fight this emerging epidemic. Over the last decade, the family of nuclear receptors, especially the peroxisome proliferator-activated receptors (PPARs), has emerged as one of the most important drug targets aimed at combating the metabolic syndrome. Consequently, compounds that activate the PPARs have served as potential therapeutics for the treatment of T2D and the metabolic anomalies associated with this disorder. This review focuses on the currently marketed compounds and also describes the discovery and development of the next generation of PPAR ligands that are under investigation for the potential treatment of T2D and the metabolic syndrome.

A retrospective study on the influence of apolipoprotein e and serum lipids in progressive renal failure

BACKGROUND

Progression of renal failure is associated with altered lipoprotein metabolism. Apolipoprotein E polymorphism is an important genetic marker for dyslipidemia. The main purpose of this retrospective study was to examine the influence of apolipoprotein E polymorphism and serum lipids level on the progression rate in a group of patients with kidney diseases of diverse etiology.

METHODS

Progression rate, with regard to apolipoprotein E polymorphism and initial serum creatinine value, median (162 micromol/l), was determined by reviewing the charts of 385 patients on renal replacement therapy with a median follow-up time of 4.85 years.

RESULTS

Progression rate was negatively correlated to serum cholesterol in the group with type 2 diabetes (p= 0.001). In addition, the urine albumin excretion rate (UAER) was higher in type 2 diabetics carrying the epsilon2 allele (2.1 g/l) as compared to non-epsilon2 allele carriers (1.2 g/l) (p=0.009). Although serum cholesterol in patients with autosomal dominant polycystic kidney disease (ADPKD) carrying the apolipoprotein epsilon4 allele was 5.87 +/- 1.0 mmol/l, which was significantly higher compared to non-epsilon4 carriers, 4.97 +/- 1.1 mmol/l (p=0.026), progression rate was similar in the two groups, 4.4 +/- 0.8 micromol/l/year. An increase in the relative frequency of the apolipoprotein epsilon4 allele was found in patients with ADPKD (0.29), as compared to (0.16) in the rest of the diagnostic groups (p=0.0023). In addition, in the whole study population a positive correlation was found between progression rate and underlying disease (p < 0.005), UAER (p < 0.005) and blood pressure (p < 0.005).

CONCLUSIONS

The results of the present study indicate that the decline of renal function in patients with diabetes type 2 may not be associated with levels of plasma cholesterol, but with triglyceride lipoproteins, considered remnant lipoproteins. Any association between cholesterol and apolipoprotein epsilon4 allele with progression in ADPKD may not necessarily be straightforward since this disease is influenced by other genetic and unidentified factors.

Polymorphisms of the protein kinase C-beta gene (PRKCB1) accelerate kidney disease in type 2 diabetes without overt proteinuria

OBJECTIVE

We investigated the contribution of PKC-beta gene (PRKCB1) polymorphisms to diabetic kidney disease in a prospective observational follow-up study.

RESEARCH DESIGN AND METHODS

A total of 364 Japanese subjects with type 2 diabetes without overt proteinuria were enrolled during 1996-1998 and followed until 2004. Five single nucleotide polymorphisms (-1504C/T, -546C/G, -348A/G, -278C/T, and -238C/G) in the promoter region of PRKCB1 were genotyped. The end points were transition from stage to stage of diabetic nephropathy as a time-to-event outcome and the annual decline rate of estimated glomerular filtration rate (eGFR) as a slope-based outcome.

RESULTS

During the study (median 6 years), 34 of 364 subjects (9.3%) progressed. Kaplan-Meier estimation revealed that subjects with both T allele at -1054 C/T and G allele at -546 C/G polymorphisms frequently showed transition to advanced stages of diabetic nephropathy (P = 0.015). The annual change rate in eGFR in the subjects with both alleles was also significantly higher than in others (-2.96 +/- 0.62 vs. -1.63 +/- 0.15 ml/min per 1.73 m(2)/year, P = 0.02). The estimated frequency of this risk T-G haplotype was significantly higher in the progressors who showed transition to advanced nephropathy stages (12%) than in the nonprogressors (5%) (odds ratio 2.3 [95% CI 1.0-5.2]), and it was also higher in those with accelerated decline of the Delta eGFR (> or =3 ml/min per 1.73 m(2)/year) than in those without (2.1 [1.1-3.9]).

CONCLUSIONS

Our study indicates that PRKCB1 is a predictor for worsening of kidney disease in Japanese subjects with type 2 diabetes.

Impact of Lipoprotein Glomerulopathy on the Relationship Between Lipids and Renal Diseases

Lipoprotein glomerulopathy (LPG) is a unique entity of renal lipidosis characterized by peculiar histopathologic characteristics of lipoprotein thrombi and an abnormal plasma lipoprotein profile resembling type III hyperlipoproteinemia, with a marked increase in serum apolipoprotein E (apoE) concentrations. At present, 65 cases have been reported worldwide, although most patients are found in Japan and east Asian countries. Recently, we identified 4 types of novel apoE mutations associated with LPG. In particular, a mutation designated apoE Sendai, in which arginine 145 is substituted with proline, occurs in the majority of Japanese patients. The virus-mediated transduction of apoE Sendai resulting in the development of LPG in apoE-deficient mice confirms the etiologic role of apoE mutation in LPG. Conversely, experimental graft-versus-host disease induced in Fc receptor gamma-chain-deficient mice showed LPG-like lesions in glomeruli without apoE mutations. Considered together, we believe that intrinsic factors in the kidney also contribute to the induction of LPG. Today, apoE and related lipid abnormalities are reported to have an important role in the development of various renal diseases, eg, diabetic nephropathy and immunoglobulin A nephropathy. In this article, we review clinical and histopathologic features of LPG, describe the etiologic role of apoE variants and intrinsic renal factors, and discuss the impact of LPG on mechanisms of other renal diseases.

Genetic basis of diabetic nephropathy

Diabetes mellitus is the leading cause of end-stage renal disease. Development and progression of diabetic nephropathy result from a combination of genetic susceptibility and metabolic and hemodynamic abnormalities. In America, some racial and ethnic minorities have a significant burden of diabetic nephropathy, and, although genetic studies suggest that inherited factors play a major role in the pathogenesis of diabetic nephropathy, little information has been gained on the genes and molecular mechanisms involved. The genetic background of diabetic nephropathy is believed to be polygenic, and the genes predisposing to the development and progression of diabetic nephropathy are actively being investigated. New knowledge in identifying and understanding the role of susceptibility gene(s) will provide valuable information that could help develop new preventive and therapeutic strategies.

Assessing genetic susceptibility to diabetic nephropathy

Diabetic nephropathy is a serious complication of diabetes and the leading cause of end-stage renal disease. Studies indicate both environmental and genetic factors contribute to the development and progression of diabetic nephropathy. In particular, epidemiological evidence shows a familial clustering of nephropathy in siblings with diabetes, supporting an important role of genetic susceptibility in the pathogenesis of diabetic nephropathy. A common approach in genetic research is assessment of candidate gene polymorphisms using case-control analysis; a number of studies have evaluated predictable candidate genes for diabetic nephropathy. In contrast, only a few studies have used a whole genome approach, such as scanning of micro-satellite markers, in the assessment of genetic susceptibility to diabetic nephropathy. A whole genome linkage analysis using families of Pima Indians showed susceptibility loci for diabetic nephropathy on chromosome 3, 7, and 20. Another linkage analysis using discordant sib-pairs of Caucasian families with type 1 diabetes identified a critical area on chromosome 3q. However, these results have been inconclusive and further investigation is required. Recently, a genome-wide, case-control analysis identifying susceptibility genes for diabetic nephropathy was performed. As a result, a single nucleotide polymorphism in exon 23 of the solute carrier family 12 (sodium-chloride cotransporter) member 3 gene was found to be strongly associated with diabetic nephropathy. Although further assessment of this polymorphism is needed, this strategy offers great promise in the identification of genetic factors predisposing patients to diabetic nephropathy. Identification of genetic susceptibility markers may offer new hope in the diagnosis and treatment of diabetic nephropathy.

Assessment of 115 candidate genes for diabetic nephropathy by transmission/disequilibrium test

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.

Evidence for different susceptibility genes for proteinuria and ESRD in type 2 diabetes

Proteinuria and impaired kidney function are 2 major traits of diabetic nephropathy that aggregate (are heritable) in families of diabetic individuals. Although both traits are heritable, they are not genetically correlated. These findings not only support the hypothesis that the development of diabetic nephropathy consists of 2 distinct disease processes (ie, increasing proteinuria and declining kidney function) but also strongly justify searches for the putative genes that separately determine variation in these processes. These searches have used both genome-wide scans and candidate-gene approaches. By use of genome-scan approaches, several research groups have identified genetic regions on chromosomes 7q, 18q, and 22q that harbor genes that determine either variation in urinary albumin excretion or susceptibility to proteinuria in families who have type 2 diabetes. The evidence for linkage in these 3 genetic regions was suggestive or strong, but, except for 7q, the regions did not overlap across studies. Two genome scans performed in families who have type 2 diabetes identified genetic regions on chromosome 3q, 6q, 7p, and 18q that harbor susceptibility genes that determine variation in glomerular filtration rate or susceptibility to the development of end-stage renal disease (ESRD). The region on 7p overlapped in both studies. Optimism is growing that a positional cloning approach applied to these putative genetic regions will lead to the isolation of the susceptibility genes for proteinuria and ESRD. Meanwhile, significant efforts that make use of the candidate-gene approach have been directed to the search for susceptibility genes for diabetic nephropathy. Unfortunately, positive findings have not been consistent.

The Family Investigation of Nephropathy and Diabetes (FIND): design and methods

BACKGROUND

The Family Investigation of Nephropathy and Diabetes (FIND) is a multicenter study designed to identify genetic determinants of diabetic nephropathy. It is conducted in eight U.S. clinical centers and a coordinating center, and with four ethnic groups (European Americans, African Americans, Mexican Americans, and American Indians). Two strategies are used to localize susceptibility genes: a family-based linkage study and a case-control study using mapping by admixture linkage disequilibrium (MALD).

METHODS

In the family-based study, probands with diabetic nephropathy are recruited with their parents and selected siblings. Linkage analyses will be conducted to identify chromosomal regions containing genes that influence the development of diabetic nephropathy or related quantitative traits such as serum creatinine concentration, urinary albumin excretion, and plasma glucose concentrations. Regions showing evidence of linkage will be examined further with both genetic linkage and association studies to identify genes that influence diabetic nephropathy or related traits. Two types of MALD studies are being done. One is a case-control study of unrelated individuals of Mexican American heritage in which both cases and controls have diabetes, but only the case has nephropathy. The other is a case-control study of African American patients with nephropathy (cases) and their spouses (controls) unaffected by diabetes and nephropathy; offspring are genotyped when available to provide haplotype data.

CONCLUSIONS

Identification of genes that influence susceptibility to diabetic nephropathy will lead to a better understanding of how nephropathy develops. This should eventually lead to improved treatment and prevention.

Pancreas transplantation: indications and consequences

Pancreas transplantation continues to evolve as a strategy in the management of diabetes mellitus. The first combined pancreas-kidney transplant was reported in 1967, but pancreas transplant now represents a number of procedures, each with different indications, risks, benefits, and outcomes. This review will summarize these procedures, including their risks and outcomes in comparison to kidney transplantation alone, and how or if they affect the consequences of diabetes: hyperglycemia, hypoglycemia, and microvascular and macrovascular complications. In addition, the new risks introduced by immunosuppression will be reviewed, including infections, cancer, osteoporosis, reproductive function, and the impact of immunosuppression medications on blood pressure, lipids, and glucose tolerance. It is imperative that an endocrinologist remain involved in the care of the pancreas transplant recipient, even when glucose is normal, because of the myriad of issues encountered post transplant, including ongoing management of diabetic complications, prevention of bone loss, and screening for failure of the pancreas graft with reinstitution of treatment when indicated. Although long-term patient and graft survival have improved greatly after pancreas transplant, a multidisciplinary team is needed to maximize long-term quality, as well as quantity, of life for the pancreas transplant recipient.

Mouse models of diabetic nephropathy

Mice provide an experimental model of unparalleled flexibility for studying mammalian diseases. Inbred strains of mice exhibit substantial differences in their susceptibility to the renal complications of diabetes. Much remains to be established regarding the course of diabetic nephropathy (DN) in mice as well as defining those strains and/or mutants that are most susceptible to renal injury from diabetes. Through the use of the unique genetic reagents available in mice (including knockouts and transgenics), the validation of a mouse model reproducing human DN should significantly facilitate the understanding of the underlying genetic mechanisms that contribute to the development of DN. Establishment of an authentic mouse model of DN will undoubtedly facilitate testing of translational diagnostic and therapeutic interventions in mice before testing in humans.

Influence of apolipoprotein E polymorphisms on serum creatinine levels and predicted glomerular filtration rate in healthy subjects

BACKGROUND

There are conflicting results regarding the effect of apolipoprotein (ApoE) polymorphisms on the progression of a variety of renal diseases. However, there are no data on the possible effect of the ApoE alleles on serum creatinine levels and predicted glomerular filtration rate (GFR) in healthy subjects.

METHODS

290 apparently healthy individuals were studied. ApoE genotyping was performed by the polymerase chain reaction; the Modification of Diet in Renal Disease equation (MDRD) predicted the GFR.

RESULTS

ApoE2 was associated with lower levels of total cholesterol, low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol, as well as with higher levels of triglycerides in our population. Furthermore, the ApoE2 allele was associated with increased serum creatinine levels compared with both the E3 and E4 alleles (1.04+/-0.13 vs 0.92+/-0.13 vs 0.88+/- 0.11 mg/dl, respectively, P = 0.0077), while the MDRD-predicted GFR was decreased in ApoE2 carriers compared with both E3 and E4 carriers (80.3+/-10.2 vs 88.1+/-9.6 vs 89.3+/-9.7 ml/min/1.73 m(2), respectively, P = 0.031). These observations remained significant statistically even if the effect of ApoE polymorphisms on age- and body-mass index-adjusted serum creatinine and MDRD-predicted GFR was separately analysed in both men and women. Although, ApoE4 carriers tended to exhibit lower levels of serum creatinine and higher values of predicted GFR compared with the E3 carries, these differences did not reach statistical significance.

CONCLUSIONS

ApoE2 allele seems to be associated with increased serum creatinine levels and decreased MDRD-predicted GFR in healthy subjects.

Apolipoprotein E and renal disease

Apolipoprotein E (ApoE) is a major constituent of plasma lipoproteins with many biological actions of great significance. Beyond the known influence of ApoE polymorphisms on serum lipid profile, the pathogenesis of atherosclerosis, and the development of neurodegenerative disorders, ApoE also has a major role in the pathogenesis and progression of a variety of renal diseases, as well as in the atherosclerotic complications associated with them. Briefly, the polymorphisms of ApoE are major determinants of plasma lipid levels in uremic patients. They may affect the risk for cardiovascular disease in this population, predispose to the development of diabetic nephropathy, influence the severity of certain glomerulopathies, and regulate mesangial and glomerular functions locally in the kidney microenvironment. Finally, certain mutations of the ApoE gene are associated with a recently described nephropathy, termed lipoprotein glomerulopathy.

C-106T polymorphism of AKR1B1 is associated with diabetic nephropathy and erythrocyte aldose reductase content in Japanese subjects with type 2 diabetes mellitus

BACKGROUND

The C-106T polymorphism of AKR1B1, which encodes aldose reductase (AR), was reported to be associated with diabetic nephropathy (DN). However, this association in Japanese patients with type 2 diabetes mellitus and its potential role as a clinical marker remain unclear.

METHODS

The C-106T polymorphism was genotyped in 228 cases (microalbuminuria or overt proteinuria) and 220 controls (normoalbuminuria with diabetes duration > or =10 years) for a case-control comparison, and the association with erythrocyte AR content was investigated. In addition, a new C-11G polymorphism in the promoter region of AKR1B1 was genotyped.

RESULTS

The distribution of genotypes of the C-106T polymorphism in cases was significantly different from that in controls (P = 0.031). Carriers of the TT genotype at the C-106T polymorphism were more frequent in cases than controls, with an odds ratio of 4.7 (95% confidence interval, 1.3 to 17). Erythrocyte AR content was significantly elevated in TT carriers in comparison to non-TT carriers (13.1 +/- 1.2 versus 10.2 +/- 1.2 ng/mg hemoglobin [Hb]; P < 0.001) and in cases in comparison to controls (10.6 +/- 1.3 versus 10.1 +/- 1.2 ng/mg Hb; P = 0.041). However, distribution of genotypes of the C-11G polymorphism and estimated frequencies of haplotypes defined by these 2 polymorphisms did not differ between cases and controls.

CONCLUSION

The TT genotype of the C-106T polymorphism of AKR1B1 increases the risk for DN in Japanese subjects with type 2 diabetes mellitus, which could be linked in part to greater expression of AR.

APOE polymorphism and the progression of diabetic nephropathy in Japanese subjects with type 2 diabetes: results of a prospective observational follow-up study

OBJECTIVE

The aim of this study is to clarify the conflicting results of the epsilon2/epsilon3/epsilon4 APOE polymorphism as a risk factor on diabetic nephropathy by a cohort study.

RESEARCH DESIGN AND METHODS

A total of 429 Japanese subjects with type 2 diabetes and with normoalbuminuria (n = 299) or with microalbuminuria (n = 130) were enrolled in a prospective observational follow-up study during 1995-1998 and followed until 2001 (for at least 3 years). The endpoint was the occurrence of a renal event defined as the progression to a higher stage of diabetic nephropathy.

RESULTS

During the study (the mean follow-up period: 4.4 +/- 1.0 years), 31 of 429 subjects progressed: 21 from normoalbuminuria to microalbuminuria and 10 from microalbuminuria to overt proteinuria. The allele frequency of the APOE polymorphism was significantly different between the progressors and the nonprogressors. Eight of 42 epsilon2 carriers (19%) progressed, whereas 23 of 387 noncarriers (6%) progressed with a relative risk of 3.2 (95% CI 1.5-6.7). When subjects were stratified by renal status at baseline, each relative risk for the progression in the epsilon2 carriers was 2.7 (0.99-7.4) in those with normoalbuminuria and 4.2 (1.3-13.3) in those with microalbuminuria. Furthermore, when analyzed only in subjects with normoalbuminuria and short duration of diabetes (<15 years) at baseline, the risk in the epsilon2 carriers became higher to 3.2 (1.2-8.8).

CONCLUSIONS

Our follow-up study indicates that the epsilon2 allele of the APOE polymorphism is a prognostic risk factor for both the onset and the progression of diabetic nephropathy in Japanese type 2 diabetes.

Genomic strategies for diabetic nephropathy

Insight into the molecular mechanisms that underlie the origin and progression of diabetic nephropathy remains limited in part because conventional research tools have restricted investigators to focus on single genes or isolated pathways. Microarray technologies provide opportunities for evaluating genetic factors and environmental effects at a genomic scale during the pathogenesis of diabetic nephropathy. Despite the enormous power of the microarray technology, there are several pitfalls that need to be considered. This article discusses conceptual, practical, statistical, and logistical considerations for the use of microarrays in studies of experimental and human diabetic renal disease. New knowledge in this field will facilitate new approaches for molecular diagnosis and drug discovery.

Identification of a common risk haplotype for diabetic nephropathy at the protein kinase C-beta1 (PRKCB1) gene locus

Abnormal activation of protein kinase C-beta isoforms in the diabetic state has been implicated in the development of diabetic nephropathy. It is thus plausible that DNA sequence differences in the protein kinase C-beta1 gene (PRKCB1), which encodes both betaI and betaII isoforms, may influence susceptibility to nephropathy. Nine single-nucleotide polymorphisms (SNP) in PRKCB1 were tested for association with diabetic nephropathy in type I diabetes mellitus, by using both case-control and family-study designs. Allele and genotype distributions of two SNP in the promoter (--1504C/T and --546C/G) differed significantly between case patients and control patients (P < 0.05). These associations were particularly strong with diabetes mellitus duration of <24 yr (P = 0.002). The risk of diabetic nephropathy was higher among carriers of the T allele of the --1504C/T SNP, compared with noncarriers (odds ratio, 2.54; 95% confidence interval, 1.39 to 4.62), and among carriers of the G allele of the --546C/G SNP (odds ratio, 2.45; 95% confidence interval, 1.37 to 4.38). Among individuals with diabetes mellitus duration of >/==" BORDER="0">24 yr, these two SNP were not associated with diabetic nephropathy. These positive findings were confirmed by using the family-based transmission disequilibrium test. The T-G haplotype, with both risk alleles, was transmitted more frequently than expected from heterozygous parents to offspring who developed diabetic nephropathy during the first 24 yr of diabetes mellitus. It is concluded that DNA sequence differences in the promoter of PRKCB1 contribute to diabetic nephropathy susceptibility in type I diabetes mellitus.

Diabetes and nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy is the single most common disorder leading to renal failure. Its annual incidence has more than doubled in the past decade to reach 44% of all end-stage renal disease, despite recent therapeutic advances. Thus, research into diabetic nephropathy pathophysiology that could lead to new treatment approaches is urgently needed and this review aims to summarize the work performed in this area in the past year.

RECENT FINDINGS

There have been advances in the understanding of diabetic nephropathy pathology. Clearly, structural changes may be advanced before any clinical findings are apparent. Not all functional consequences of the condition are explained by current structural analyses. Genetic studies have connected the disorder risk to multiple candidate genes and a few genetic loci, but the exact genetic predisposition or protectors are not fully described. Perturbations in multiple metabolic pathways are associated with diabetic nephropathy in animals and humans, but their relative importance requires further work. Glycemia and blood pressure control are crucial for diabetic nephropathy prevention and treatment, but new modalities are needed.

SUMMARY

Recent advances in molecular biology and genetics will bring new insights to the mechanisms involved in diabetic nephropathy development. This will allow early identification of patients at risk of, or safe from, diabetic nephropathy and will hopefully lead to preventive strategies, based on the understanding of the pathophysiology of the disorder. Meanwhile, aggressive implementation of proven therapies to prevent (glycemic control) and slow (antihypertensive therapy, especially with renin-angiotensin system blockers) the progression of diabetic nephropathy are strongly recommended.