Is diabetic nephropathy inherited? Studies of glomerular structure in type 1 diabetic sibling pairs

Methylglyoxal in diabetes: link to treatment, glycaemic control and biomarkers of complications

Diabetic complications are major health problems worldwide, with the cost of caring for diabetes rising to US$245 billion in 2012 in the U.S.A. alone. It is widely recognized that non-enzymatic glycation in diabetes is a major cause of damage and dysfunction of key vascular cells. MG (methylglyoxal) is directly toxic to tissues, and is a major precursor of AGEs (advanced glycation end-products). Various propensities to diabetic complications are seen among individuals with diabetes, with accelerated rates occurring in some individuals with modest hyperglycaemia, while others never progress in spite of poor glycaemic control over many years. Since production and detoxification of MG is ultimately controlled by enzymatic mechanisms, both genetic and environmental factors could regulate tissue glycation and potentially account for these variable complication rates. Activation of pathways that determine MG levels occurs in susceptible patients, indicting an important role in pathogenesis. MG leads to formation of specific AGEs, which are likely to predict propensity to diabetic complications. We have shown recently that three specific plasma AGE biomarkers [MG-H1 (MG-derived hydroimidazolones), CEL (Nε-carboxyethyl-lysine) and CML (Nε-carboxymethyl-lysine)] predict biopsy-documented fast DN (diabetic nephropathy) progression. Since two of the predictive biomarkers are MG end-products, these outcomes support a role for MG in the development of DN. Our studies on MG and its end-products have also shown anti-complication effects of the drug metformin, which binds and inactivates MG, thus reducing MG-related AGEs. We have also shown that reducing post-meal glucose decreases MG levels, as well as levels of MG-related AGEs. Our clinical outcome studies have been based on the novel concept that the unique glycation products that we can measure reflect the activity of specific chemical pathways that are selectively activated by hyperglycaemia in patients that are inherently more susceptible to diabetic complications, and can be used to solve other diabetes-related medical questions.

Early progression of diabetic nephropathy correlates with methylglyoxal-derived advanced glycation end products

OBJECTIVE

Increased advanced glycation end products (AGEs) and oxidation products (OPs) are proposed to lead to progression of diabetic nephropathy (DN). We investigated the relationship between AGEs, OPs, and progression of DN in 103 subjects with type 1 diabetes participating in the Natural History of Diabetic Nephropathy Study.

RESEARCH DESIGN AND METHODS

Mean age of subjects was 17.6±7.4 years, and mean duration of diabetes was 8.3±4.9 years. All patients were normoalbuminuric. Change in glomerular basement membrane (GBM) width from baseline to 5 years, measured using electron micrographs of renal biopsies, was our primary end point, and mesangial fractional volume was a secondary end point. Fast progressors (FPs) were defined as those in the upper quartile of GBM change, and the remaining patients were classified as slow progressors (SPs). AGEs (3-deoxyglucosone and methylglyoxal hydroimidazolones [MGHI]), carboxymethyl lysine (CML), carboxyethyl lysine (CEL), and OPs (methionine sulfoxide and 2-aminoadipic acid) were measured at year 5 by liquid chromatography/triple-quadruple mass spectroscopy on 10-K plasma filtrates.

RESULTS

We found that MGHI, CEL, and CML levels were significantly higher in FPs relative to SPs. No product predicted mesangial expansion. A model containing only HbA1c accounted for 4.7% of GBM width variation, with the total variability explained by the model increasing to 11.6% when MGHI, CEL, and CML were added to the regression model (7.9% increase). MGHI was a significant independent predictor of FP. Using a logistic regression model to relate each biomarker to the probability of a subject's classification as an FP, CML, CEL, and MGHI, but not HbA1c, showed a significant relationship to the probability of FP.

CONCLUSIONS

The results suggest that these three major AGEs may be early indicators of progression of important DN lesions.

Glycation and biomarkers of vascular complications of diabetes

Propensity to diabetic nephropathy (DN), retinopathy (DR), and cardiovascular disease (CVD) varies between individuals. Current biomarkers such as indicators of glycemia (HbA1c), retinal examinations, and albuminuria, cannot detect early tissue damage. HbAIc also doesn't reflect most glycative and oxidative chemical pathways that cause complications, and studies of new biomarkers to measure their end-products are needed. This review proposes the study of advanced glycation end products (AGEs) and oxidation end-products (OPs) in long-term diabetes outcome studies. AGEs integrate the activity of glycation pathways that form dicarbonyls, while OPs reflect superoxides, hydroxyl radicals, and peroxides. We discuss using these biomarkers to predict risk of development and progression of DN, DR, and CVD, and to determine if they confer risk independently of the level of HbA1c. We also discuss methods and guidelines to document sample quality in such studies. These studies have the potential to validate unique biomarkers during the early stages of diabetes in those who are at high risk of diabetic complications. Information on basic mechanisms responsible for complications could also stimulate development of therapeutic approaches to delay or arrest them. The ultimate goal is to predict those requiring aggressive therapies during the earliest stages, when prevention or reversal of complications is still possible.

Genetic variant in the promoter of connective tissue growth factor gene confers susceptibility to nephropathy in type 1 diabetes

BACKGROUND The evidence for genetic susceptibility in the pathogenesis of diabetic nephropathy is well recognised, but the genes involved remain to be identified. It is hypothesised that mutations within the gene encoding connective tissue growth factor (CTGF/CCN2) will increase the propensity of diabetic subjects to develop nephropathy. METHODS AND RESULTS Genomic screening was performed for single nucleotide polymorphisms (SNPs) within the CTGF gene in 862 subjects from the DCCT/EDIC cohort of type 1 diabetes. A novel SNP was identified in the promoter region that changes a C-G at the position -20. The frequency of GG genotype in microalbuminuric patients (albumin excretion rate (AER) >40 mg/24 h) is significantly greater than diabetics with AER <40 mg/24 h, p<0.0001. The relative risk (RR) to develop microalbuminuria in diabetic subjects with the polymorphism is 3X higher than diabetic subjects without the polymorphism (RR 3.142, 95% CI 1.9238 to 5.1249; p<0.05). Kaplan-Meier survival curves demonstrated that the GG genotype group developed microalbuminuria and macroalbuminuria at a more rapid rate than the GC or CC genotypes. Functional studies demonstrated that the basal activity of the substituted allele/promoter (-20 GG allele) was significantly greater than that of the wild type promoter (-20 CC genotype). This higher level of basal activity of substituted allele CTGF/CCN2 promoter was abrogated upon suppression of Smad1 levels, indicating that SNP region in the CTGF/CCN2 promoter plays a vital role in the gene expression. CONCLUSIONS These findings provide the first evidence that variants within the promoter region of the CTGF/CCN2 gene predisposes diabetic subjects to develop albuminuria and demonstrate that Smad1 [corrected] controls the expression of CTGF/CCN2 promoter through this region.

Cellular basis of diabetic nephropathy: V. Endoglin expression levels and diabetic nephropathy risk in patients with Type 1 diabetes

Endoglin is an accessory receptor molecule that, in association with transforming growth factor beta (TGF-beta) family receptors Types I and II, binds TGF-beta1, TGF-beta3, activin A, bone morphogenetic protein (BMP)-2 and BMP-7, regulating TGF-beta dependent cellular responses. Relevant to diabetic nephropathy, endoglin, expressed in vascular endothelial and smooth muscle cells, fibroblasts, and mesangial cells, negatively regulates extracellular matrix (ECM). The aim of this study was to evaluate endoglin expression in cultured skin fibroblasts from patients with Type 1 diabetes with and without diabetic nephropathy. Kidney and skin biopsies were performed in 125 Type 1 diabetic patients. The 20 with the fastest rate of mesangial expansion (estimated by electron microscopy) and proteinuria ("fast-track") and the 20 with the slowest rate and normoalbuminuria ("slow-track"), along with 20 controls were studied. Endoglin mRNA expression was assessed by microarray and quantitative real-time polymerase chain reaction (QRT-PCR) and protein expression by Western blot. Age and sex distribution were similar among groups. Diabetes duration was similar (20+/-8 vs. 24+/-7 years), hemoglobin A1c lower (8.4+/-1.2% vs. 9.4+/-1.5%), and glomerular filtration rate higher (115+/-13 vs. 72+/-20 ml/min per 1.73 m2) in slow-track vs. fast-track patients. Microarray endoglin mRNA expression levels were higher in slow-track (1516.0+/-349.9) than fast-track (1211.0+/-274.9; P=.008) patients or controls (1223.1+/-422.9; P=.018). This was confirmed by QRT-PCR. Endoglin protein expression levels correlated with microarray (r=0.59; P=.044) and QRTPCR (r=0.61; P=.034) endoglin mRNA expression. These studies are compatible with the hypothesis that slow-track Type 1 diabetic patients, strongly protected from diabetic nephropathy, have distinct cellular behaviors that may be associated with reduced ECM production.

Albuminuria in children

PURPOSE OF REVIEW

Albuminuria is a marker of present and future cardiovascular and renal morbidity, and mortality, in adults. Because the roots of these diseases extend back into childhood, assessment of albuminuria has become relevant to child and adolescent clinical care.

RECENT FINDINGS

Normal levels of albumin excretion in children are well below the cut-off for microalbuminuria. In healthy children, albuminuria relates to fasting insulin, but not blood pressure, BMI, lipid levels, fasting glucose, or insulin resistance. In obese children, albuminuria relates to multiple measures of insulin resistance. In children with type 1 diabetes, hemoglobin A1c seems to be the most consistent clinical predictor of microalbuminuria although multiple mechanisms seem to be involved, including genetic polymorphisms. Children with type 2 diabetes and hypertension already exhibit microalbuminuria.

SUMMARY

When considering the population as a whole, children make ideal subjects in which to study the natural history of albuminuria given their relative lack of multiple morbidities commonly seen in adults. The unfortunate rise in 'adult' diseases in the pediatric age group makes this especially relevant. There is a need for longitudinal studies examining predictors of elevated urinary albumin levels as well as potential treatment strategies.

Progression of diabetic nephropathy in type 1 diabetic patients

Understanding pathogenetic mechanisms of diabetic nephropathy progression risk factors is important. Structural-functional relationship studies have increased our understanding of the glomerular, vascular and tubulointerstitial lesions evolution at various stages of diabetic nephropathy. Classical and more recently described lesions of diabetic nephropathy are discussed. Structural changes associated with progression toward proteinuria and GFR loss are summarized. The relationships of renal structure and function in diabetic nephropathy are best described by non-linear models which mimic the natural history of the disease, i.e., renal pathology develops in clinical silence but, once established, leads to proteinuria and GFR decline.

The kidney in diabetes: dynamic pathways of injury and repair. The Camillo Golgi Lecture 2007

Diabetic nephropathy is the most common cause of end-stage renal disease (ESRD). The natural history of diabetic nephropathy has changed over the last decades, as a consequence of better metabolic and blood pressure management. Thus, it may now be possible to delay or halt the progression towards ESRD in patients with overt diabetic nephropathy, and the decline of renal function is not always inexorable and unavoidable. Also, the rate of progression from microalbuminuria to overt nephropathy is much lower than originally estimated in the early 80s. Furthermore, there is now evidence that it is possible, in humans, to obtain reversal of the established lesions of diabetic nephropathy. This review focuses on the contribution of kidney biopsy studies to the understanding of the pathogenesis and natural history of diabetic nephropathy and the identification of patients at high risk of progression to ESRD. The classic lesions of diabetic nephropathy and the well-established structural-functional relationships in type 1 diabetes will be briefly summarised and the renal lesions leading to renal dysfunction in type 2 diabetes will be described. The relevance of these biopsy studies to diabetic nephropathy pathogenesis will be outlined. Finally, the evidence and the possible significance of reversibility of diabetic renal lesions will be discussed, as well as future directions for research in this field.

Having one kidney does not accelerate the rate of development of diabetic nephropathy lesions in type 1 diabetic patients

OBJECTIVE

Reduced nephron number is hypothesized to be a risk factor for chronic kidney disease and hypertension. Whether reduced nephron number accelerates the early stages of diabetic nephropathy is unknown. This study investigated whether the rate of development of diabetic nephropathy lesions was different in type 1 diabetic patients with a single (transplanted) kidney compared with patients with two (native) kidneys.

RESEARCH DESIGN AND METHODS

Three groups of volunteers were studied: 28 type 1 diabetic kidney transplant recipients with 8-20 years of good graft function, 39 two-kidney patients with duration of type 1 diabetes matched to the time since transplant in the one-kidney group, and 30 age-matched normal control subjects. Electron microscopic morphometry was used to estimate glomerular structural parameters on 3.0 +/- 1.4 glomeruli per biopsy.

RESULTS

In the one- versus two-kidney diabetic subject groups, respectively, serum creatinine (means +/- SD 1.3 +/- 0.4 vs. 0.9 +/- 0.2 mg/dl; P < 0.001), systolic blood pressure (133 +/- 13 vs. 122 +/- 11 mmHg; P < 0.001), and albumin excretion rate (median [range] 32.1 microg/min [2-622] vs. 6.8 microg/min [2-1,495]; P = 0.006) were higher. There were no differences in the one- versus two-kidney diabetic subject groups, respectively, in glomerular basement membrane width (median [range] 511 nm [308-745] vs. 473 nm [331-814]), mesangial fractional volume (mean +/- SD 0.30 +/- 0.06 vs. 0.27 +/- 0.07), mesangial matrix fractional volume (0.16 +/- 0.05 vs. 0.16 +/- 0.06), and mesangial matrix fractional volume per total mesangium (0.61 +/- 0.07 vs. 0.64 +/- 0.09). However, these glomerular structural parameters were statistically significantly higher in both diabetic subject groups compared with normal control subjects. Results were similar when patients receiving ACE inhibitors were excluded from the analyses.

CONCLUSIONS

Reduced nephron number is not associated with accelerated development of diabetic glomerulopathy lesions in type 1 diabetic patients.

Diabetic nephropathy in children and adolescents

Type 1 diabetes mellitus (T1DM) commonly occurs in childhood or adolescence, although the rising prevalence of type 2 diabetes mellitus (T2DM) in these age groups is now being seen worldwide. Diabetic nephropathy (DN) develops in 15-20% of subjects with T1DM and in similar or higher percentage of T2DM patients, causing increased morbidity and premature mortality. Although overt DN or kidney failure caused by either type of diabetes are very uncommon during childhood or adolescence, diabetic kidney disease in susceptible patients almost certainly begins soon after disease onset and may accelerate during adolescence, leading to microalbuminuria or incipient DN. Therefore, all diabetics warrant ongoing assessment of kidney function and screening for the earliest manifestations of renal injury. Pediatric health care professionals ought to understand about risk factors, strategy for prevention, method for screening, and treatment of early DN. This review considers each form of diabetes separately, including natural history, risk factors for development, screening for early manifestations, and strategy recommended for prevention and treatment of DN in children and adolescents.

A predisposição genética para o desenvolvimento da microangiopatia no DM1

Acredita-se que o controle glicêmico e a duração do diabetes sejam os fatores de risco mais importantes para o desenvolvimento das microangiopatias diabéticas, contudo, as velocidades de progressão da nefropatia, da retinoaptia e da polineuropatia variam consideravelmente entre os pacientes. Além da presença de fatores de risco, como a hipertensão arterial, a dislipidemia e o fumo, existem evidências sugerindo que uma predisposição genética desempenha um papel na susceptibilidade para as complicações microvasculares. Com base na patogênese dessas complicações crônicas do diabetes, polimorfismos de vários genes candidatos que atuam em diferentes vias desse processo têm sido investigados, como os genes relacionados aos mecanismos dos danos induzidos pela hiperglicemia (os produtos finais de glicação avançada, o aumento na formação de espécies reativas de oxigênio e a atividade aumentada da via da aldose-redutase), os genes relacionados ao sistema renina-angiotensina; os genes que codificam a síntese das citoquinas, dos fatores de crescimento e dos seus receptores e dos transportadores de glicose entre muitos outros. Este artigo discute alguns estudos que corroboram com a importância da predisposição genética no desenvolvimento da microangiopatia diabética.

The role of inflammatory cytokines in diabetic nephropathy

Cytokines act as pleiotropic polypeptides regulating inflammatory and immune responses through actions on cells. They provide important signals in the pathophysiology of a range of diseases, including diabetes mellitus. Chronic low-grade inflammation and activation of the innate immune system are closely involved in the pathogenesis of diabetes and its microvascular complications. Inflammatory cytokines, mainly IL-1, IL-6, and IL-18, as well as TNF-alpha, are involved in the development and progression of diabetic nephropathy. In this context, cytokine genetics is of special interest to combinatorial polymorphisms among cytokine genes, their functional variations, and general susceptibility to diabetic nephropathy. Finally, the recognition of these molecules as significant pathogenic mediators in diabetic nephropathy leaves open the possibility of new potential therapeutic targets.

Multiple superoxide dismutase 1/splicing factor serine alanine 15 variants are associated with the development and progression of diabetic nephropathy: the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Genetics study

BACKGROUND

Despite familial clustering of nephropathy and retinopathy severity in type 1 diabetes, few gene variants have been consistently associated with these outcomes.

RESEARCH DESIGN AND METHODS

We performed an individual-based genetic association study with time to renal and retinal outcomes in 1,362 white probands with type 1 diabetes from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study. Specifically, we genotyped 1,411 SNPs that capture common variations in 212 candidate genes for long-term complications and analyzed them for association with the time from DCCT baseline to event for renal and retinal outcomes using multivariate Cox proportion hazards models. To address multiple testing and assist interpretation of the results, false discovery rate q values were calculated separately for each outcome.

RESULTS

We observed association between rs17880135 in the 3' region of superoxide dismutase 1 (SOD1) and the incidence of both severe nephropathy (hazard ratio [HR] 2.62 [95% CI 1.64-4.18], P = 5.6 x 10(-5), q = 0.06) and persistent microalbuminuria (1.82 [1.29-2.57], P = 6.4 x 10(-4), q = 0.46). Sequencing and fine-mapping identified additional SOD1 variants, including rs202446, rs9974610, and rs204732, which were also associated (P < 10(-3)) with persistent microalbuminuria, whereas rs17880135 and rs17881180 were similarly associated with the development of severe nephropathy. Attempts to replicate the findings in three cross-sectional case-control studies produced equivocal results. We observed no striking differences between risk genotypes in serum SOD activity, serum SOD1 mass, or SOD1 mRNA expression in lymphoblastoid cell lines.

CONCLUSIONS

Multiple variations in SOD1 are significantly associated with persistent microalbuminuria and severe nephropathy in the DCCT/EDIC study.

Familial Clustering of Chronic Kidney Disease

The incidence and prevalence rates of most forms of chronic kidney disease (CKD) had steadily been increasing for the past 30 years, although these rates now appear to have reached a plateau. It is clear that an individual's likelihood of developing progressive CKD results from complex interactions between multiple genetic and environmental factors. Familial clustering of CKD and end-stage renal disease (ESRD) is observed among all the common etiologies of nephropathy. This article reviews the epidemiology of the familial clustering of kidney disease, as well as potential environmental and genetic contributors. The related impact of familial clustering of cardiovascular disease (CVD) and the impact of CVD on the current epidemic of ESRD is also discussed. It is imperative that nephrologists and primary care physicians recognize that individuals who have relatives with advanced nephropathy are themselves at high risk for subsequent kidney disease, proteinuria, and atherosclerotic cardiovascular complications. Until kidney failure genes are identified, it is reasonable to use "family history" (FH) as a surrogate marker for risk of future nephropathy. The detection of kidney disease genes holds great promise for detecting novel pathways that initiate renal fibrosis and lead to progressive loss of renal function. These pathways are likely to offer new therapies that may slow or halt development of chronic kidney failure.

Mining the genome for susceptibility to diabetic nephropathy: the role of large-scale studies and consortia

Approximately 30% of individuals with type 1 and type 2 diabetes develop persistent albuminuria, lose renal function, and are at increased risk for cardiovascular and other microvascular complications. Diabetes and kidney diseases rank within the top 10 causes of death in Westernized countries and cause significant morbidity. Given these observations, genetic, genomic, and proteomic investigations have been initiated to better define basic mechanisms for disease initiation and progression, to identify individuals at risk for diabetic complications, and to develop more efficacious therapies. In this review we have focused on linkage analyses of candidate genes or chromosomal regions, or coarse genome-wide scans, which have mapped either categorical (chronic kidney disease or end-stage renal disease) or quantitative kidney traits (albuminuria/proteinuria or glomerular filtration rate). Most loci identified to date have not been replicated, however, several linked chromosomal regions are concordant between independent samples, suggesting the presence of a diabetic nephropathy gene. Two genes, carnosinase (CNDP1) on 18q, and engulfment and cell motility 1 (ELMO1) on 7p14, have been identified as diabetic nephropathy susceptibility genes, but these results require authentication. The availability of patient data sets with large sample sizes, improvements in informatics, genotyping technology, and statistical methodologies should accelerate the discovery of valid diabetic nephropathy susceptibility genes.

Histopathology of diabetic nephropathy

The clinical manifestations of diabetic nephropathy, proteinuria, increased blood pressure, and decreased glomerular filtration rate, are similar in type 1 and type 2 diabetes; however, the renal lesions underlying renal dysfunction in the 2 conditions may differ. Indeed, although tubular, interstitial, and arteriolar lesions are ultimately present in type 1 diabetes, as the disease progresses, the most important structural changes involve the glomerulus. In contrast, a substantial subset of type 2 diabetic patients, despite the presence of microalbuminuria or proteinuria, have normal glomerular structure with or without tubulointerstitial and/or arteriolar abnormalities. The clinical manifestations of diabetic nephropathy are strongly related with the structural changes, especially with the degree of mesangial expansion in both type 1 and type 2 diabetes. However, several other important structural changes are involved. Previous studies, using light and electron microscopic morphometric analysis, have described the renal structural changes and the structural-functional relationships of diabetic nephropathy. This review focuses on these topics, emphasizing the contribution of research kidney biopsy studies to the understanding of the pathogenesis of diabetic nephropathy and the identification of patients with a higher risk of progression to end-stage renal disease. Finally, evidence is presented that the reversal of established lesions of diabetic nephropathy is possible.

Expression of Smad1 is directly associated with mesangial matrix expansion in rat diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease, and glomerular mesangial matrix expansion is the hallmark in diabetic nephropathy. However, the precise mechanism for the development of mesangial matrix expansion has remained unknown. The key component involved in mesangial matrix expansion is type IV collagen (Col4). Recently, we have reported that Smad1 transcriptionally regulates expression of Col4 under diabetic conditions in vitro. Here we show that this direct regulator of Col4 also plays a crucial role for mesangial matrix expansion in vivo. Streptozotocin-induced diabetic rats are the model of incipient diabetic nephropathy, and showed various levels of mesangial matrix expansion at 24 weeks. The glomerular expression of Smad1 was significantly increased in diabetic rats with more mesangial matrix expansion by Western blot and immunohistochemical analysis. Furthermore, the glomerular expression of Smad1 was closely correlated with the glomerular expression of Col4 and smooth muscle alpha actin (alpha-SMA), while albuminuria or glomerular filtration rate was not correlated with mesangial matrix expansion. We also found that urinary excretion of Smad1 was closely associated with the severity of mesangial matrix expansion. In cultured mesangial cells expression of Smad1 upregulated the transcriptional activity of key molecules in mesangial matrix expansion, such as Col4 and alpha-SMA. These data indicate the critical involvement of Smad1 in mesangial matrix expansion in the early phase of diabetic nephropathy. Our data imply that urinary Smad1 might be a representative diagnostic marker for mesangial matrix expansion in diabetic nephropathy.

Susceptibility to diabetic nephropathy is related to dicarbonyl and oxidative stress

Dicarbonyl and oxidative stress may play important roles in the development of diabetes complications, and their response to hyperglycemia could determine individual susceptibility to diabetic nephropathy. This study examines the relationship of methylglyoxal, 3-deoxyglucosone (3DG), and oxidative stress levels to diabetic nephropathy risk in three populations with diabetes. All subjects in the Overt Nephropathy Progressor/Nonprogressor (ONPN) cohort (n = 14), the Natural History of Diabetic Nephropathy study (NHS) cohort (n = 110), and the Pima Indian cohort (n = 45) were evaluated for clinical nephropathy, while renal structural measures of fractional mesangial volume [Vv(Mes/glom)] and glomerular basement membrane (GBM) width were determined by electron microscopy morphometry in the NHS and Pima Indian cohorts. Methylglyoxal and 3DG levels reflected dicarbonyl stress, while reduced glutathione (GSH) and urine 8-isoprostane (8-IP) measured oxidative stress. Cross-sectional measures of methylglyoxal production by red blood cells incubated in 30 mmol/l glucose were increased in nephropathy progressors relative to nonprogressors in the ONPN (P = 0.027) and also reflected 5-year GBM thickening in the NHS cohort (P = 0.04). As nephropathy progressed in the NHS cohort, in vivo levels of methylglyoxal (P = 0.036), 3DG (P = 0.004), and oxidative stress (8-IP, P = 0.007 and GSH, P = 0.005) were seen, while increased methylglyoxal levels occurred as nephropathy progressed (P = 0.0016) in the type 2 Pima Indian cohort. Decreased glyceraldehyde-3-phosphate dehydrogenase activity also correlated with increased methylglyoxal levels (P = 0.003) in the NHS cohort. In conclusion, progression of diabetic nephropathy is significantly related to elevated dicarbonyl stress and possibly related to oxidative stress in three separate populations, suggesting that these factors play a role in determining individual susceptibility.

Early Diabetes-Related Complications in Adolescents

Micro- and macrovascular complications account for the major part of the morbidity and mortality associated with diabetes developing in childhood. Although advanced complications are exceptionally rare in the adolescent age group, it is during this phase that the progression of risk may accelerate. A number of potentially important factors have been identified which might contribute to risk of complication development: some provide insights into the genetics of these complications, while others are potentially modifiable, such as metabolic control, hypertension, smoking, obesity and hyperlipidemia. Recently, both consensus and evidence-based guidelines have been developed to guide those involved in the care of adolescents with diabetes in the prevention, screening and management of early diabetes-related complications in this vulnerable population. This article reviews the literature that underpins the available guidelines and stresses the pivotal role of excellent metabolic control in complication prevention.

Predicting the development of diabetic nephropathy and its progression

Diabetes remains the number one cause of end-stage renal disease worldwide. Only about one third of diabetic patients develop nephropathy, and the risk appears to be, in part, genetically determined. In this article, we review clinical and genetic markers for the development and progression of diabetic nephropathy. Microalbuminuria remains the best available predictor of the subsequent development of nephropathy, even though in recent years it has become clear that less than 50% of individuals with type 1 diabetes progress to overt proteinuria over a period of less than 10 years. It is of great interest for early recognition of risk of nephropathy that small elevations in nighttime blood pressure predict microalbuminuria in type 1 diabetes. Genetic markers for diabetic nephropathy have not been conclusively identified. The occurrence of renal events in diabetic patients, however, appears to be influenced by the angiotensin-converting enzyme (ACE) genotype, with a dominant deleterious effect of the D allele (D/D or I/D) versus I/I genotype. Some patients with the DD genotype also appear less susceptible to the renoprotective effects of conventional doses of ACE inhibitors, suggesting that ACE genotyping might be useful in selecting those patients that could benefit from higher doses of ACE inhibitors and more aggressive treatment to prevent or delay disease progression.

A novel polymorphism in the 5' flanking region of the glucose transporter (GLUT1) gene is strongly associated with diabetic nephropathy in patients with Type 1 diabetes mellitus

Glucose transporter 1 (GLUT1) activity has been implicated in renal hypertrophy and extracellular matrix formation in mesangial cells. Recent studies have suggested that polymorphisms in the GLUT1 gene are associated with susceptibility to diabetic nephropathy (DN) in patients with diabetes mellitus. In this study, a novel polymorphism (A-2841T) in the 5' flanking region of GLUT1 was examined in 288 patients with Type 1 diabetes mellitus (T1DM) and 101 normal controls. The polymorphisms were amplified and the fragment digested with the enzyme HpyCH4V. There was a highly significant increase in the frequency of the TT-2841 genotype in patients with nephropathy (n=131) compared with those with either no microvascular complications after a 20-year duration of diabetes (uncomplicated; n=72; 54.5% vs. 2.7%, chi=79.4, P<.000001). There was no difference between the uncomplicated group and those who only had retinopathy (n=50; 2.7% vs. 4.0%, respectively). The frequency in recently diagnosed patients was 17.1% and only 2.0% in normal controls. In contrast, the AA genotype was found in 13.6% of the nephropaths, 76.3% of uncomplicated, 48.0% of retinopaths, and 65% of normal controls. These results confirm previous reports of an association between the GLUT1 gene and susceptibility to DN but not retinopathy. The localisation of this polymorphism suggests that it may be involved in the expression of the gene.

Cellular basis of diabetic nephropathy: III. In vitro GLUT1 mRNA expression and risk of diabetic nephropathy in type 1 diabetic patients

AIMS/HYPOTHESIS

Altered glucose transporter expression has been implicated in the pathogenesis of diabetic nephropathy. There is increasing evidence that genetic factors convey risk of, or protection from, diabetic nephropathy and that the behaviour of cultured skin fibroblasts from type 1 diabetic patients may reflect these genetic influences. This study aimed to compare GLUT1 mRNA expression levels in skin fibroblasts from type 1 diabetic patients with either rapid ("fast-track", n=25) or slow ("slow-track", n=25) development of diabetic nephropathy and from non-diabetic normal control subjects (controls, n=25).

METHODS

Skin fibroblasts were cultured in Dulbecco's Modified Eagle's Medium with 25 mmol/l glucose for 36 h. Total RNA was isolated, and GLUT1 mRNA levels were estimated by microarray analysis and RT-PCR.

RESULTS

Levels of GLUT1 mRNA expression in skin fibroblasts from "slow-track" patients were greater than those from "fast-track" patients (p=0.02), as initially detected by microarray. GLUT1 mRNA expression levels were confirmed by RT-PCR to be higher in skin fibroblasts from "slow-track" patients (4.59+/-2.04) than in those from "fast-track" patients (3.34+/-1.2, p=0.02), and were also higher than in skin fibroblasts from control subjects (3.52+/-1.66, p=0.03). There was no statistically significant difference between levels of expression in the "fast-track" patients and the control subjects.

CONCLUSIONS/INTERPRETATION

This finding is consistent with the presence of cellular protection factors against diabetic nephropathy in the "slow-track" patients. These factors could be associated with the regulation of the GLUT1 pathway and may be genetically determined.

Population-based assessment of familial clustering of diabetic nephropathy in type 1 diabetes

We determined the magnitude of familial aggregation in the development of diabetic nephropathy (DN) among a population-based cohort of Finnish type 1 diabetic patients. Probands with type 1 diabetes were identified from the nationwide register of all Finnish cases diagnosed during 1965-1979. By 1998, there were 537 families with at least two siblings with type 1 diabetes. These 537 probands and their 616 diabetic siblings were followed for a diagnosis of DN until the end of 2001. We identified 323 cases of DN in these families. If the proband had DN, 38% of the siblings also had DN, whereas out of the diabetic siblings of the probands without DN, only 17% had DN (P = 0.001). Diabetic siblings of the nephropathic probands had a 2.3 times (95% CI 1.4-2.7) higher risk of DN compared with siblings of probands free of DN. The presence of a severe form of DN in the proband increases the risk threefold for diabetic siblings. Sex, the DN of the proband, the age at the onset of diabetes, and parental type 2 diabetes were significant predictors of DN among diabetic siblings. Although the majority of sibpairs with type 1 diabetes are discordant for DN, its presence in one sibling doubles the risk for the other diabetic siblings.

BIOACTIVE COMPOUNDS IN NUTRITION AND HEALTH-RESEARCH METHODOLOGIES FOR ESTABLISHING BIOLOGICAL FUNCTION: The Antioxidant and Anti-inflammatory Effects of Flavonoids on Atherosclerosis

Identifying bioactive compounds and establishing their health effects are active areas of scientific inquiry. There are exciting prospects that select bioactive compounds will reduce the risk of many diseases, including chronic diseases such as cardiovascular disease. Recent findings have established that cardiovascular disease is a disease of inflammation, and consequently is amenable to intervention via molecules that have anti-inflammatory effects. In addition, research demonstrating adverse effects of oxidants on atherogenesis raises the possibility that antioxidants can confer cardioprotective effects. This review provides an overview of research approaches that can be used to unravel the biology and health effects of bioactive compounds. Because of the number of bioactive compounds and the diversity of likely biological effects, numerous and diverse experimental approaches must be taken to increase our understanding of the biology of bioactive compounds. Recognizing the complexity of this biology, sophisticated experimental designs and analytical methodologies must be employed to advance the field. The discovery of novel health effects of bioactive compounds will provide the scientific basis for future efforts to use biotechnology to modify/fortify foods and food components as a means to improve public health.

Epigenetic and genetic analysis of p16 in dermal fibroblasts from type 1 diabetic patients with nephropathy

BACKGROUND

Several studies have shown that cultured skin fibroblasts from patients with diabetic nephropathy (DN) exhibit a hyperplastic growth phenotype. Increased DNA synthesis in cells from patients with DN may ultimately involve alterations in cell cycle regulatory proteins. p16 protein is a member of INK4 family of cyclin-dependent kinase inhibitors, which plays an important role in cell cycle regulation. In this study, we examined the correlation between p16 protein expression in cultured dermal fibroblasts from type 1 diabetic patients and the presence of DN.

METHOD

Western blot analysis was performed to compare p16 protein expression in skin fibroblasts from patients with DN as compared to control subjects, diabetic patients without DN, and nondiabetic patients with nephropathy. Transcriptional regulation of the p16 gene was assessed using competitive reverse transcription-polymerase chain reaction (RT-PCR). Methylation status of the promoter region of p16 was examined using methylation-specific PCR, and we used single-stranded conformational polymorphism (SSCP)-PCR to assess p16 single-nucleotide polymorphism.

RESULTS

Cells from diabetic patients with DN had nondetectable to significantly lower protein expression of p16. Similarly, mRNA expression of p16 was significantly lower in diabetic patients with DN. No hypermethylation of p16 gene was detected, and no abnormal migrating bands were noticed on SSCP-PCR analysis in cells from patients with DN.

CONCLUSION

Our data indicate that cells from patients with DN exhibit significantly lower protein and mRNA expression of p16. This study could have not only important implications for the understanding of the pathogenesis of DN, but also the absence of p16 may ultimately serve as an early marker for DN.

Genetics of kidney disease

Multiple lines of evidence suggest that susceptibility to develop end-stage renal disease (ESRD) has a significant genetic component. These studies include familial aggregation studies, comparisons of incidence rates between different racial or ethnic populations, and segregation analysis. Multiple approaches have been employed in an effort to identify genes that contribute to this genetic susceptibility. Many studies have now been carried out assessing the contribution of specific "candidate genes," that is, genes with functions consistent with involvement in renal pathogenesis. Independent evaluations of specific candidate genes have frequently provided contradictory results. This may be due, in part, to the modest contribution to genetic susceptibility that these genes impart. In contrast to the focused analysis of candidate genes, the genome scan approach employs a comprehensive evaluation of inheritance throughout the genome. The great potential advantage of the genome scan is the ability to identify chromosomal regions harboring novel, previously unrecognized, genes that contribute to renal disease. Results from whole genome scans of family collections are now beginning to appear and give the promise that multiple comprehensive genetic evaluations of end-stage renal disease will soon be available for evaluation.

The early natural history of nephropathy in type 1 diabetes: I. Study design and baseline characteristics of the study participants

This report describes the design and baseline demographic and clinical data in the study of the early natural history of diabetic nephropathy (DN) in type 1 diabetes carried out by the International Diabetic Nephropathy Study Group. The study enrolled 243 patients ages 10-40 years (16.8 +/- 6.0, mean +/- SD) with type 1 diabetes for 2-20 years (8.0 +/- 4.2) at centers in the United States (Minneapolis), Canada (Montreal), and France (Paris). At baseline, all patients were normotensive, none had reduced glomerular filtration rate (GFR), and all but eight were normoalbuminuric (NA). All patients had baseline renal biopsies. During the study, patients will have multiple measurements of blood pressure (BP), renal function, albumin excretion rate (AER), glycemia, and other variables, with repeat renal biopsies planned at 5 years after baseline. The 31.3% of the approached patients who agreed to participate were similar in age, diabetes duration, HbA(1c), AER, and sex to those refusing participation. Age, diabetes duration, HbA(1c), and AER were similar among the three centers, but systolic BP, GFR, renal plasma flow (RPF), and filtration fraction were lower in the Paris center. The 153 patients with hyperfiltration (GFR >130 ml x min(-1) x 1.73 m(-2)) had greater RPF than those with normal GFR. The eight microalbuminuric patients tended to have longer duration of diabetes but were otherwise similar to the NA patients. The role of these and other variables in determining the development rate of the early lesions of DN over the 5 years between biopsies is the central issue under study.

The early natural history of nephropathy in type 1 diabetes: II. Early renal structural changes in type 1 diabetes

Renal structural abnormalities are known to precede the development of proteinuria, hypertension, and reduced renal function in patients with type 1 diabetes. The determinants of these early structural abnormalities are, however, largely unknown. The International Diabetic Nephropathy Study (IDNS) has recruited 243 children and adults (aged 10-40 years) in Montreal, Minneapolis, and Paris to identify and quantify these determinants. All study subjects were normotensive and had normal-to-high glomerular filtration rates (GFRs) and urinary albumin excretion rates (AERs) <100 microg/min at study entry. Only 8 of 243 had an AER > or =20 microg/min (microalbuminuria). Two renal biopsies are obtained at a 5-year intervals, with baseline and follow-up measures of renal function, blood pressure (BP), HbA(1c), plasma lipids, and AER. Herein, we examine the baseline renal biopsy morphometric findings in these subjects and in 87 kidney donor control subjects and explore the associations between findings and clinical and demographic variables. The principal morphometric abnormalities were increased glomerular basement membrane (GBM) width and fractional volume of mesangium [Vv(Mes/glom)] and mesangial matrix [Vv(MM/glom)]. The frequency of these abnormalities increased with increasing duration of diabetes but was observed as early as 2-8 years after onset. Diastolic BP (DBP), but not HbA(1c), was directly associated with these abnormalities. Elevated GFR was associated with only a small increase in peripheral glomerular capillary basement membrane filtration surface density. Center differences were detected in renal structural, renal functional, and BP parameters, especially between the Paris and North American centers. GBM width, Vv(Mes/glom), and Vv(MM/glom) are significantly increased even within a few years of onset of type 1 diabetes. These changes are detectable in normoalbuminuric patients and are related to duration, BP, and study site. Changes in these and other morphometric measures over 5-year follow-up should help clarify the roles of glycemia and other determinants of the rates of development of diabetic nephropathy lesions, as well as their relationships to early changes in BP, albumin excretion, and renal function.

Genetics of diabetes complications

Long-term exposure to the hyperglycemia characteristic of diabetes patients leads to serious and frequently disabling or fatal complications. Emerging evidence suggests that genes are a significant contributor to an individual's risk of developing complications. This evidence is from evaluations of familial aggregation, differences in incidence in racial and ethnic groups, and statistical analysis of family data. Evidence to date suggests that complication genes are, distinct from the genes contributing to diabetes. Molecular geneticists have taken several approaches to identify genes contributing to complications, ranging from relatively simple analysis of specific candidate genes in small case-control comparisons to systematic evaluations of the human genome using genome scans and linkage analysis in large collections of families. Results suggest that genetic contributions to diabetes complications are diverse and complex in nature, presenting a significant challenge to researchers. Diabetes-affected families are frequently enriched for complications such as cardiovascular disease or nephropathy. In addition to their value in the study of diabetes complications, such families may be valuable resources for understanding cardiovascular disease and nephropathy in the nondiabetic population also.

Reversibility of glucose-induced changes in mesangial cell extracellular matrix depends on the genetic background

Adequate glycemic control protects most patients with diabetes from nephropathy, but a substantial fraction of patients develop progressive disease despite lowering glycemia. We isolated mesangial cells (MC) from the glomeruli of mouse strains that model these two outcomes in patients with diabetes, namely those that have the propensity (ROP) or resistance (B6) to develop progressive diabetic nephropathy. We determined the nature and reversibility of changes in selected extracellular matrix-related molecules after chronic exposure to elevated glucose concentration. MC were exposed to 25 mmol/l glucose for 5 weeks followed by 6 mmol/l glucose and 19 mmol/l mannitol for an additional 5 weeks. Matrix metalloproteinase-2 (MMP-2) and transforming growth factor-beta(1) (TGF-beta(1)) levels increased in B6 MC exposed to 25 mmol/l glucose but returned to baseline levels when the glucose concentration was reduced to 6 mmol/l. MMP-2 and TGF-beta(1) were higher in ROP MC at baseline and increased in response to 25 mmol/l glucose, but remained elevated when glucose concentration was reduced. Type I collagen expression and accumulation increased in a reversible manner in B6 MC exposed to 25 mmol/l glucose. However, type I collagen expression was higher in ROP MC at baseline and remained unaffected by changes in glucose concentration. Thus, 25 mmol/l glucose induced reversible changes in MMP-2, TGF-beta(1), and type I collagen in MC of sclerosis-resistant mice but not in MC from sclerosis-prone mice. Therefore, progressive diabetic nephropathy may be secondary to stable alterations in the phenotype of MC as a result of the interplay between the genetic background and elevated glucose concentrations.

Cellular basis of diabetic nephropathy: 1. Study design and renal structural-functional relationships in patients with long-standing type 1 diabetes

This study was designed to elucidate the cellular basis of risk of or protection from nephropathy in patients with type 1 diabetes. Entry criteria included diabetes duration of > or =8 years (mean duration, 22.5 years) and glomerular filtration rate (GFR) >30 ml x min(-1) x 1.73 m(-2). Patients were classified, on the basis of the estimated rate of mesangial expansion, as "fast-track" (upper quintile) or "slow-track" (lower quintile). A total of 88 patients were normoalbuminuric, 17 were microalbuminuric, and 19 were proteinuric. All three groups had increased glomerular basement membrane (GBM) width and mesangial fractional volume [Vv(Mes/glom)], with increasing severity from normoalbuminuria to microalbuminuria to proteinuria but with considerable overlap among groups. Vv(Mes/glom) (r = 0.75, P < 0.001) and GBM width (r = 0.63, P < 0.001) correlated with albumin excretion rate (AER), whereas surface density of peripheral GBM per glomerulus [Sv(PGBM/glom)] (r = 0.50, P < 0.001) and Vv(Mes/glom) (r = -0.48, P < 0.001) correlated with GFR. Vv(Mes/glom) and GBM width together explained 59% of AER variability. GFR was predicted by Sv(PGBM/glom), AER, and sex. Fast-track patients had worse glycemic control, higher AER, lower GFR, more hypertension and retinopathy, and, as expected, worse glomerular lesions than slow-track patients. Thus, there are strong relationships between glomerular structure and renal function across the spectrum of AER, but there is considerable structural overlap among AER categories. Given that normoalbuminuric patients may have advanced glomerulopathy, the selection of slow-track patients based on glomerular structure may better identify protected patients than AER alone.

Approaches to understanding susceptibility to nephropathy: from genetics to genomics

The incidence of end-stage renal disease (ESRD) is increasing worldwide despite efforts to slow the progression of chronic renal failure (CRF) by controlling blood pressure and hyperglycemia. Two available therapies for ESRD, dialysis and transplantation, are expensive and are at best palliative. Recently, data from several laboratories have demonstrated that ESRD is under substantial genetic control, and efforts to identify these genetic determinants are underway. Identifying genes for ESRD pathogenesis has several goals. First, understanding the genetic basis of ESRD offers a means to clarify the mechanisms that result in kidney pathobiology. Second, better and new treatments for prevention of progression of CRF to ESRD may be developed. Third, individuals at risk could be identified early in their course and targeted for intensive therapy. Finally, the products of genes causing disease become target molecules for gene therapy. In this article, we discuss data from our laboratories, which employ two different molecular genetic strategies for identifying ESRD pathogenesis genes. In contrast to traditional experimental design, both approaches are hypothesis generating, identifying candidate molecules for further study, rather than hypothesis driven and may provide novel insights into mechanisms of renal disease progression.

The angiotensin-converting enzyme DD genotype is associated with glomerulopathy lesions in type 2 diabetes

Genetic factors are important in conferring diabetic nephropathy (DN) risk. The insertion/deletion (I/D) polymorphism of the ACE gene has been described to be associated with DN risk and progression. The renal lesions underlying DN in type 2 diabetes are heterogeneous; only a subset of patients, characterized by a faster decline of renal function, have diabetic glomerulopathy. This study explored the relations between diabetic glomerulopathy and the ACE genotype distribution in 77 type 2 diabetic patients with an albumin excretion rate > or = 20 microg/min. Using morphometric analysis of kidney biopsies, mesangial and mesangial matrix fractional volumes [Vv(mes/glom) and Vv(MM/glom)] and glomerular basement membrane (GBM) width were estimated. We found that 13 patients were II, 30 were ID, and 34 were DD. Clinical features and renal function were similar in the three groups; in contrast, the DD patients had the highest Vv(MM/glom) and GBM width. Subdividing patients in tertiles of GBM width and Vv(MM/glom), from the lowest (I) to the highest (III) values, the DD carriers had an odds ratio of 6.11 (95% CI 1.84-20.3) and 10.67 (2.51-45.36), respectively, for the likelihood of being in tertile III than I for GBM width and Vv(MM/glom). Multiple regression analysis revealed the I/D polymorphism as an independent determinant of GBM thickening in addition to diabetes duration and HbA(1c). In conclusion, the ACE DD genotype is associated with diabetic glomerulopathy lesions, making the study of this polymorphism helpful in identifying those type 2 diabetic patients at higher risk of fast DN progression.

Risk predictors in patients with diabetic nephropathy

Diabetic nephropathy is currently the most common cause of end-stage renal disease in the Western countries. Only approximately one third of patients with type 1 diabetes develop nephropathy; thus, because it is not feasible to aggressively treat all patients, it becomes very important to find early markers in order to identify patients at high nephropathy risk. To date the best available predictor of overt nephropathy is microalbuminuria. In this article we review the validity of microalbuminuria as a predictor of overt nephropathy and consider other markers of nephropathy risk.

Electrophoretic analysis of urinary proteins in diabetic adolescents

Pathological changes in the urine sodium dodecyl sulphate gel electrophoresis (SDS PAGE) patterns often precede the occurrence of any sign of renal involvement in diabetes. However, data concerning the most frequent SDS PAGE pattern of the urine in early stages of type I diabetes mellitus are controversial. In the present study an SDS PAGE technique has been used that provides an adequate sensitivity for the detection of the abnormal pattern. Urinary proteins have been analyzed by SDS PAGE in twenty two diabetic adolescents and twenty four age matched controls. Albumin concentration, and N acetyl-beta-D-glucosaminidase (NAG) activity were also measured in the same samples. There was no significant difference in urine albumin concentration and NAG activity between diabetic children and controls. However twelve patients showed an electrophoretic pattern characteristic for glomerulopathy, two had a pattern indicating tubular dysfunction and another two patients had a mixed pattern. Among the twenty four controls only three showed abnormal electrophoretic patterns. The results support the view that early stages of diabetic nephropathy may involve both glomerular and tubular dysfunction. However the exact clinical and prognostic significance of the information provided by SDS PAGE analysis remains to be elucidated.

Polymorphism screening of four genes encoding advanced glycation end-product putative receptors. Association study with nephropathy in type 1 diabetic patients

Advanced glycation end-products (AGEs) may play an important role in the pathogenesis and progression of cardiovascular and renal complications of diabetes. Four putative AGE receptors (RAGEs), AGE-R1, AGE-R2, and AGE-R3 have been described. In this study, we scanned the sequence of the genes encoding these AGE receptors in 48 patients with type 1 diabetes and investigated the identified polymorphisms (n = 19) in 199 type 1 diabetic patients with nephropathy and 193 type 1 diabetic patients without nephropathy. Overall, none of the polymorphisms was strongly associated with nephropathy. The minor allele of a polymorphism located in the promoter region of the RAGE gene (C-1152A) conferred a weak protective effect (P < 0.05) and was associated with a longer duration of nephropathy-free diabetes (P = 0.08).

No evidence of an exaggerated albuminuric response to physical exercise in non-diabetic siblings of type 1 diabetic patients with diabetic nephropathy

Substantial evidence suggests a role for genetic factors in the development of diabetic nephropathy in both type 1 and type 2 diabetes. In support of this view, non-diabetic relatives of type 2 diabetic patients with nephropathy have been found to display abnormalities of urinary albumin excretion rate (AER) both when measured at rest and during physical exercise. The aim of the present study was to assess the albuminuric response to physical exercise in non-diabetic relatives of type 1 diabetic patients with nephropathy. AER was measured from urine collections performed (i) overnight, (ii) during an oral glucose tolerance test (OGTT), and (iii) during a submaximal bicycle ergometer test in 21 and 24 non-diabetic siblings of type 1 diabetic patients with (DN+; AER > 200 microg/min) and without diabetic nephropathy (DN-; AER < 20 microg/min). No difference was found in AER (median [range]) measured overnight (DN+ vs DN-: 3.8 [1.3-24.1] vs 3.5 [2.0-21.0] microg/min; P=NS), during the OGTT (DN+ vs DN-: 6.3 [3.2-26.0] vs 4.8 [1.9-15.7] microg/min; P = NS) or during the exercise test (DN+ vs DN-: 44.8 [7.0-535] vs 30.0 [3.4-1614] microg/min; P = NS). In conclusion, we found no evidence of an exaggerated albuminuric response to physical exercise in non-diabetic relatives of type 1 diabetic patients with nephropathy. This differs from previous findings in type 2 diabetes and may suggest differences in the mode of inheritance of albuminuria between type 1 and type 2 diabetes.

Albuminuria in nondiabetic relatives of IDDM patients with and without diabetic nephropathy

BACKGROUND

In non-insulin-dependent diabetes mellitus (NIDDM), there is a clustering of an elevated urinary albumin excretion rate (U-AER) in nondiabetic relatives of albuminuric patients. Whether this is also the case in insulin-dependent diabetes mellitus (IDDM) is unknown.

METHODS

Overnight U-AER was measured in 186 nondiabetic first-degree relatives of 80 IDDM patients with diabetic nephropathy (U-AER > 200 microg/min or 300 mg/24 hours; DN+) and in 52 relatives of 25 IDDM patients without nephropathy (U-AER < 20 microg/min; DN-). The two groups of relatives were comparable regarding gender distribution, age, obesity, blood pressure, prevalence of antihypertensive therapy, and smoking habits.

RESULTS

No difference was found in overnight U-AER between relatives of patients with DN+ and DN- [median (range), 3.4 (0.1 to 372) vs. 4.0 (0.2 to 62) microg/min, respectively, P = NS]. The proportion of relatives with a U-AER = 10 microg/min was 12% in DN+ compared with 8% in DN- (P = NS). Among relatives of DN+, those with antihypertensive treatment (AHT+) had higher U-AER compared with those without [AHT+ vs. AHT-, 5.0 (0.5 to 372) vs. 3.4 (0.1 to 26.5) microg/min, P < 0.01], a phenomenon that was not seen among relatives of DN-[AHT + vs. AHT-, 3.6 (2.1 to 24.3) vs. 4.0 (0. 2 to 61.5) microg/min, P = NS]. However, this analysis was impaired by the small number of relatives of DN- with hypertension (N = 7).

CONCLUSIONS

In IDDM, we found no clustering of elevated U-AER in nondiabetic relatives of patients with nephropathy. This is different from what has been reported in NIDDM, and suggests heterogeneity in the genesis of albuminuria in diabetes.

Genes and renal disease

The identification of genetic linkage between polymorphic markers and common kidney diseases, including focal and segmental glomerulosclerosis and diabetic nephropathy, clearly demonstrates that inherited factors contribute to renal failure susceptibility. These breakthroughs reveal the powerful contribution that molecular genetic techniques can make in the search for inherited factors that initiate renal failure and lead to its progression. Additionally, the environmental factors predisposing to nephropathy will be more readily detectable when evaluated in genetically similar populations. This manuscript reviews the developments in genetic epidemiology and molecular genetics of chronic renal failure.

Polymorphism of the 5' untranslated region of NHE1 gene associated with type-I diabetes

The ubiquitous form of the sodium-hydrogen exchanger, NHE1, is devoted to the regulation of intracellular pH and cell volume. In addition, NHE1 activity is stimulated by growth factors and increased NHE rates are found in both circulating and immortalized cells during diabetes or diabetic nephropathy. In this context, we searched for polymorphisms of the 5'-flanking regulatory region of NHE1 gene in subjects with type-I diabetes. We identified a C/T transition 696 bases upstream the translation initiation start site which disrupts a repeated palindromic GC sequence. The TT genotype was significantly more frequent in type-1 diabetics and may have functional importance. Genetic linkage between NHE1 and diabetes has been previously described in NOD mice strains with consequences on NHE rates. Hence, the polymorphism described hereby may act as a predisposition factor to type-I diabetes or to diabetic complications, and may be useful to investigate the genetic involvement of NHE1 in human pathophysiology.

Insulin-dependent diabetic sibling pairs are concordant for sodium-hydrogen antiport activity

Insulin-dependent diabetic sibling pairs are concordant for sodium-hydrogen antiport activity.

BACKGROUND

Recent findings of enhanced Na+/H+ antiport activity in cultured fibroblasts and immortalized lymphoblasts from type 1 diabetic patients with nephropathy support the view that a phenotypic or genotypic factor(s) underlies nephropathy risk. This study evaluated the kinetic properties of Na+/H+ antiporter in cultured fibroblasts from families with two siblings affected by type 1 (insulin-dependent) diabetes.

METHODS

Seventeen diabetic sibling pairs were studied. The age was 38 +/- 10 years (mean +/- SD) in probands, the first to develop diabetes, and 39 +/- 7 in siblings; the duration of diabetes was, by definition, longer in probands (24 +/- 12 vs. 17 +/- 8 years in siblings). Na+/H+ antiport activity was determined using a microfluorometric technique with the pH sensitive dye 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein in skin fibroblasts cultured for at least six passages.

RESULTS

There were no significant differences between probands and siblings for the following parameters: glycated hemoglobin, 8.3 +/- 0.8% in probands and 8.6 +/- 1.4% in siblings; creatinine clearance, 103 +/- 24 ml/min/1.73 m2 in probands and 103 +/- 25 in siblings; albumin excretion rate, 6.8 (1 to 860) microgram/min (median and range) in probands and 4.9 (2 to 1334) in siblings. Intracellular pH and buffering capacity were superimposable in the sibling pairs. The Vmax for the antiport was 39.2 +/- 14.7 mmol/liter cell/min in probands and 40.3 +/- 17.6 in siblings. The internal pH for half-maximal activation (Km) and Hill coefficient was also similar in probands and siblings. There were correlations between probands and siblings in values for intracellular pH (r = 0.51, P < 0.04), Vmax (r = 0.84, P < 0.0001), and buffering capacity (r = 0.53, P < 0. 03). Glycated hemoglobin values over five years were not significantly correlated in the sibling pairs (r = 0.3, P > 0.1). Vmax was related with the albumin excretion rate (r = +0.49, P = 0. 005) and glycated hemoglobin (r = +0.41, P = 0.017) in the total cohort of sibling pairs. However, multiple regression analysis, using Vmax as the dependent variable, found no correlations between any of the subjects' clinical and demographic variables.

CONCLUSIONS

Familial concordance for Na+/H+ antiport activity in long-term cultured skin fibroblasts from type 1 diabetic siblings suggests that at least some of the in vitro phenotypical characteristics of these cells are likely to be genetically determined and to be, at least in part, independent of in vivo metabolic control.