Circulating TNF receptors 1 and 2 predict ESRD in type 2 diabetes

Hypertension and hyperglycemia synergize to cause incipient renal tubular alterations resulting in increased NGAL urinary excretion in rats

Background

Hypertension and diabetes are the two leading causes of chronic kidney disease (CKD) eventually leading to end stage renal disease (ESRD) and the need of renal replacement therapy. Mortality among CKD and ESRD patients is high, mostly due to cardiovascular events. New early markers of risk are necessary to better anticipate the course of the disease, to detect the renal affection of additive risk factors, and to appropriately handle patients in a pre-emptive and personalized manner.

Methods

Renal function and NGAL urinary excretion was monitored in rats with spontaneous (SHR) or L-NAME induced hypertension rendered hyperglycemic (or not as controls).

Results

Combination of hypertension and hyperglycemia (but not each of these factors independently) causes an increased urinary excretion of neutrophil gelatinase-associated lipocalin (NGAL) in the rat, in the absence of signs of renal damage. Increased NGAL excretion is observed in diabetic animals with two independent models of hypertension. Elevated urinary NGAL results from a specific alteration in its tubular handling, rather than from an increase in its renal expression. In fact, when kidneys of hyperglycaemic-hypertensive rats are perfused in situ with Krebs-dextran solution containing exogenous NGAL, they excrete more NGAL in the urine than hypertensive rats. We also show that albuminuria is not capable of detecting the additive effect posed by the coexistence of these two risk factors.

Conclusions

Our results suggest that accumulation of hypertension and hyperglycemia induces an incipient and quite specific alteration in the tubular handling of NGAL resulting in its increased urinary excretion.

TNF receptors: signaling pathways and contribution to renal dysfunction

Tumor necrosis factor (TNF), initially reported to induce tumor cell apoptosis and cachexia, is now considered a central mediator of a broad range of biological activities from cell proliferation, cell death and differentiation to induction of inflammation and immune modulation. TNF exerts its biological responses via interaction with two cell surface receptors: TNFR1 and TNFR2. (TNFRs). These receptors trigger shared and distinct signaling pathways upon TNF binding, which in turn result in cellular outputs that may promote tissue injury on one hand but may also induce protective, beneficial responses. Yet the role of TNF and its receptors specifically in renal disease is still not well understood. This review describes the expression of the TNFRs, the signaling pathways induced by them and the biological responses of TNF and its receptors in various animal models of renal diseases, and discusses the current outcomes from use of TNF biologics and TNF biomarkers in renal disorders.

Circulating TNF receptors are significant prognostic biomarkers for idiopathic membranous nephropathy

Idiopathic membranous nephropathy (iMN) is a common cause of nephrotic syndrome in adults. A biomarker to accurately indicate the severity of iMN and predict long-term prognosis is insufficient. Here, we evaluated the clinical significance of circulating tumor necrosis factor receptors (cTNFRs) as prognostic biomarkers of iMN with nephrotic syndrome. A total of 113 patients with biopsy-proven iMN and 43 healthy volunteers were enrolled in this study. Ninety patients with iMN had nephrotic range proteinuria. Levels of cTNFRs were measured by using serum samples collected at the time of initial diagnosis. Levels of cTNFRs were higher in the patients with nephrotic syndrome than in those with subnephrotic range proteinuria or in the healthy volunteers (P for trend <0.001). Estimated glomerular filtration rate and proteinuria tended to worsen as the cTNFRs levels increased. Having a cTNFR1 level within the highest tertile was a significant risk factor for renal progression after adjustment, in comparison with the other tertiles (hazard ratio [HR], 3.39; 95% confidence interval [95% CI], 1.48-7.78; P = 0.004). The cTNFR2 level within the highest tertile also significantly increased the risk of renal progression (HR, 3.29; 95% CI, 1.43-7.54; P = 0.005). Renal tubular TNFRs expression was associated with cTNFRs level. However, the cTNFRs levels were not associated with autoantibody against phospholipase A2 receptor reactivity/levels or treatment response. This study demonstrated that cTNFRs levels at the time of initial diagnosis could predict renal progression in patients with iMN.

Added value of soluble tumor necrosis factor-α receptor 1 as a biomarker of ESRD risk in patients with type 1 diabetes

OBJECTIVE

Recent studies have suggested that circulating levels of the tumor necrosis factor-α receptor 1 (sTNFαR1) may be a useful predictor for the risk of end-stage renal disease (ESRD) in patients with diabetes. However, its potential utility as a biomarker has not been formally quantified.

RESEARCH DESIGN AND METHODS

Circulating levels of sTNFαR1 were assessed in 429 patients with type 1 diabetes and overt nephropathy from the Finnish Diabetic Nephropathy (FinnDiane) cohort study. Predictors of incident ESRD over a median of 9.4 years of follow-up were determined by Cox regression and Fine-Gray competing risk analyses. The added value of sTNFαR1 was estimated via time-dependent receiver operating characteristic curves, net reclassification index (NRI), and integrated discrimination improvement (IDI) for survival data.

RESULTS

A total of 130 individuals developed ESRD (28%; ESRD incidence rate of 3.4% per year). In cause-specific modeling, after adjusting for baseline renal status, predictors of increased incidence of ESRD in patients with overt nephropathy were an elevated HbA1c, shorter duration of diabetes, and circulating levels of sTNFαR1. Notably, sTNFαR1 outperformed estimated glomerular filtration rate in terms of R(2). Circulating levels of the sTNFαR1 also remained associated with ESRD after adjusting for the competing risk of death. A prediction model including sTNFαR1 (as a -0.5 fractional polynomial) was superior to a model without it, as demonstrated by better global fit, an increment of R(2), the C index, and area under the curve. Estimates of IDI and NRI(>0) were 0.22 (95% CI 0.16-0.28; P < 0.0001) and 0.98 (0.78-1.23; P < 0.0001), respectively. The median increment in the risk score after including sTNFαR1 in the prediction model was 0.18 (0.12-0.30; P < 0.0001).

CONCLUSIONS

Circulating levels of sTNFαR1 are independently associated with the cumulative incidence of ESRD. This association is both significant and biologically plausible and appears to provide added value as a biomarker, based on the absolute values of NRI and IDI.

Progressive renal decline as the major feature of diabetic nephropathy in type 1 diabetes

Despite almost universal implementation of renoprotective therapies over the past 25 years, the risk of end-stage renal disease (ESRD) in type 1 diabetes (T1D) is not decreasing, and ESRD remains the major cause of excess morbidity and premature mortality [1]. Such a state of affairs prompts a call to action. In this review we re-evaluated the proteinuria-centric model of diabetic nephropathy and showed its deficiencies. On the basis of extensive studies that we have been conducting on the patients attending the Joslin Clinic, we propose that progressive renal decline, not abnormalities in urinary albumin excretion, should be considered as the major feature of disease processes leading to ESRD in T1D. The etiology of diabetic nephropathy should be reconsidered in light of our new findings so our perspective can be broadened regarding new therapeutic targets available for interrupting the progressive renal decline in T1D. Reduction in the loss of glomerular filtration rate, not reduction of albumin excretion rate, should become the measure for evaluating the effectiveness of new therapeutic interventions. We need new accurate methods for early diagnosis of patients at risk of progressive renal decline or, better still, for detecting in advance which patients will have rapid, moderate or minimal rate of progression to ESRD.

Renal histologic changes and the outcome in patients with diabetic nephropathy

BACKGROUND

The progression of diabetic nephropathy (DN) is frequently determined by clinical parameters; however, the predictive value of histologic lesions remains largely unknown. Our aim was to evaluate the relationship between histologic changes and renal outcome in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 396 patients with T2DM and biopsy-proven DN who received follow-up for at least 1 year were recruited. The severity of different histologic lesions was assessed using the pathologic classification established by the Renal Pathology Society. Renal outcomes were defined by progression to end-stage renal disease and doubling of serum creatinine. The influence of histologic findings on renal outcomes was assessed using univariate and multivariate Cox regression.

RESULTS

A univariate Cox regression showed that the severity of glomerular and interstitial lesions had a significant impact on renal outcomes (P < 0.001). Scores of vascular lesions demonstrated no association with renal outcomes (P > 0.05). A multivariate COX analysis demonstrated that the glomerular classes and scores of interstitial fibrosis and tubular atrophy were significantly associated with renal outcomes when adjusting for baseline proteinuria, mean arterial pressure and estimated glomerular filtration rate (P < 0.05). The glomerular and interstitial lesions correlated significantly among each other. However, in several patients, the severity of interstitial lesions did not correlate with glomerular lesions.

CONCLUSION

These findings indicated that the severity of glomerular and interstitial lesions were significantly associated with renal outcomes in patients with DN, whereas the vascular indexes did not have any impact on renal outcomes.

Clinical therapeutic strategies for early stage of diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of chronic kidney disease, leading to end-stage renal disease and cardiovascular disease. The overall number of patients with DKD will continue to increase in parallel with the increasing global pandemic of type 2 diabetes. Based on landmark clinical trials, DKD has become preventable by controlling conventional factors, including hyperglycemia and hypertension, with multifactorial therapy; however, the remaining risk of DKD progression is still high. In this review, we show the importance of targeting remission/regression of microalbuminuria in type 2 diabetic patients, which may protect against the progression of DKD and cardiovascular events. To achieve remission/regression of microalbuminuria, several steps are important, including the early detection of microalbuminuria with continuous screening, targeting HbA1c < 7.0% for glucose control, the use of renin angiotensin system inhibitors to control blood pressure, the use of statins or fibrates to control dyslipidemia, and multifactorial treatment. Reducing microalbuminuria is therefore an important therapeutic goal, and the absence of microalbuminuria could be a pivotal biomarker of therapeutic success in diabetic patients. Other therapies, including vitamin D receptor activation, uric acid-lowering drugs, and incretin-related drugs, may also be promising for the prevention of DKD progression.

Sphingomyelinase-like phosphodiesterase 3b expression levels determine podocyte injury phenotypes in glomerular disease

Diabetic kidney disease (DKD) is the most common cause of ESRD in the United States. Podocyte injury is an important feature of DKD that is likely to be caused by circulating factors other than glucose. Soluble urokinase plasminogen activator receptor (suPAR) is a circulating factor found to be elevated in the serum of patients with FSGS and causes podocyte αVβ3 integrin-dependent migration in vitro. Furthermore, αVβ3 integrin activation occurs in association with decreased podocyte-specific expression of acid sphingomyelinase-like phosphodiesterase 3b (SMPDL3b) in kidney biopsy specimens from patients with FSGS. However, whether suPAR-dependent αVβ3 integrin activation occurs in diseases other than FSGS and whether there is a direct link between circulating suPAR levels and SMPDL3b expression in podocytes remain to be established. Our data indicate that serum suPAR levels are also elevated in patients with DKD. However, unlike in FSGS, SMPDL3b expression was increased in glomeruli from patients with DKD and DKD sera-treated human podocytes, where it prevented αVβ3 integrin activation by its interaction with suPAR and led to increased RhoA activity, rendering podocytes more susceptible to apoptosis. In vivo, inhibition of acid sphingomyelinase reduced proteinuria in experimental DKD but not FSGS, indicating that SMPDL3b expression levels determined the podocyte injury phenotype. These observations suggest that SMPDL3b may be an important modulator of podocyte function by shifting suPAR-mediated podocyte injury from a migratory phenotype to an apoptotic phenotype and that it represents a novel therapeutic glomerular disease target.

Molecular mechanisms of diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of kidney failure worldwide and the single strongest predictor of mortality in patients with diabetes. DKD is a prototypical disease of gene and environmental interactions. Tight glucose control significantly decreases DKD incidence, indicating that hyperglycemia-induced metabolic alterations, including changes in energy utilization and mitochondrial dysfunction, play critical roles in disease initiation. Blood pressure control, especially with medications that inhibit the angiotensin system, is the only effective way to slow disease progression. While DKD is considered a microvascular complication of diabetes, growing evidence indicates that podocyte loss and epithelial dysfunction play important roles. Inflammation, cell hypertrophy, and dedifferentiation by the activation of classic pathways of regeneration further contribute to disease progression. Concerted clinical and basic research efforts will be needed to understand DKD pathogenesis and to identify novel drug targets.

Lipid biology of the podocyte--new perspectives offer new opportunities

In the past 15 years, major advances have been made in understanding the role of lipids in podocyte biology. First, susceptibility to focal segmental glomerulosclerosis (FSGS) and glomerular disease is associated with an APOL1 sequence variant, is expressed in podocytes and encodes apolipoprotein L1, an important component of HDL. Second, acid sphingomyelinase-like phosphodiesterase 3b encoded by SMPDL3b has a role in the conversion of sphingomyelin to ceramide and its levels are reduced in renal biopsy samples from patients with recurrent FSGS. Furthermore, decreased SMPDL3b expression is associated with increased susceptibility of podocytes to injury after exposure to sera from these patients. Third, in many individuals with membranous nephropathy, autoantibodies against the phospholipase A2 (PLA2) receptor, which is expressed in podocytes, have been identified. Whether these autoantibodies affect the activity of PLA2, which liberates arachidonic acid from glycerophospholipids and modulates podocyte function, is unknown. Fourth, clinical and experimental evidence support a role for ATP-binding cassette sub-family A member 1-dependent cholesterol efflux, free fatty acids and glycerophospolipids in the pathogenesis of diabetic kidney disease. An improved understanding of lipid biology in podocytes might provide insights to develop therapeutic targets for primary and secondary glomerulopathies.

Advice to follow a low-carbohydrate diet has a favourable impact on low-grade inflammation in type 2 diabetes compared with advice to follow a low-fat diet

BACKGROUND

Inflammation may play an important role in type 2 diabetes. It has been proposed that dietary strategies can modulate inflammatory activity.

METHODS

We investigated the effects of diet on inflammation in type 2 diabetes by comparing a traditional low-fat diet (LFD) with a low-carbohydrate diet (LCD). Patients with type 2 diabetes were randomized to follow either LFD aiming for 55-60 energy per cent (E%) from carbohydrates (n = 30) or LCD aiming for 20 E% from carbohydrates (n = 29). Plasma was collected at baseline and after 6 months. C-reactive protein (CRP), interleukin-1 receptor antagonist (IL-1Ra), IL-6, tumour necrosis factor receptor (TNFR) 1 and TNFR2 were determined.

RESULTS

Both LFD and LCD led to similar reductions in body weight, while beneficial effects on glycaemic control were observed in the LCD group only. After 6 months, the levels of IL-1Ra and IL-6 were significantly lower in the LCD group than in the LFD group, 978 (664-1385) versus 1216 (974-1822) pg/mL and 2.15 (1.65-4.27) versus 3.39 (2.25-4.79) pg/mL, both P < 0.05.

CONCLUSIONS

To conclude, advice to follow LCD or LFD had similar effects on weight reduction while effects on inflammation differed. Only LCD was found significantly to improve the subclinical inflammatory state in type 2 diabetes.

Association of serum concentration of TNFR1 with all-cause mortality in patients with type 2 diabetes and chronic kidney disease: follow-up of the SURDIAGENE Cohort

OBJECTIVE

Renal dysfunction is a key risk factor for all-cause mortality in patients with type 2 diabetes (T2D). Circulating tumor necrosis factor receptor 1 (TNFR1) was recently suggested as a strong biomarker for end-stage renal failure in T2D. However, its relevance regarding all-cause death has yet to be conclusively established. We aimed to assess the prognostic value of serum TNFR1 concentration for all-cause death in T2D and diabetic kidney disease (DKD) from the SURDIAGENE (Survie, Diabete de type 2 et Genetique) study.

RESEARCH DESIGN AND METHODS

A total of 522 T2D patients with DKD (estimated glomerular filtration rate [eGFR] <60 and/or urinary albumin-to-creatinine ratio [uACR] >30 mg/mmol) were followed for a median duration of 48 months, and 196 deaths occurred.

RESULTS

Incidence rate (95% CI) for death increased as quartiles of TNFR1 concentration increased (first quartile: 4.7% patient-years [3.0-6.3%]; second quartile: 7.7% [5.4-10.0%]; third quartile: 9.3% [6.7-11.9%]; fourth quartile: 15.9% [12.2-19.5%]). In multivariate analysis taking age, diabetes duration, HbA1c, uACR, and eGFR into account, compared with the first quartile, patients from the fourth quartile had an adjusted hazard ratio for death of 2.98 (95% CI 1.70-5.23). The integrated discrimination improvement index was statistically significant when adding TNFR1 concentration to the UK Prospective Diabetes Study outcome equation (P = 0.031).

CONCLUSIONS

TNFR1 is a strong prognostic factor for all-cause mortality in T2D with renal dysfunction, and its clinical utility is suggested in addition to established risk factors for all-cause mortality.

Enhanced glomerular Toll-like receptor 4 expression and signaling in patients with type 2 diabetic nephropathy and microalbuminuria

Toll-like receptor 4 (TLR4), a component of the innate immune system, is recognized to promote tubulointerstitial inflammation in overt diabetic nephropathy (DN). However, there is no information on immune activation in resident renal cells at an early stage of human DN. In order to investigate this, we studied TLR4 gene and protein expression and TLR4 downward signaling in kidney biopsies of 12 patients with type 2 diabetes and microalbuminuria, and compared them with 11 patients with overt DN, 10 with minimal change disease (MCD), and control kidneys from 13 patients undergoing surgery for a small renal mass. Both in microalbuminuria and in overt DN, TLR4 mRNA and protein were overexpressed 4- to 10-fold in glomeruli and tubules compared with the control kidney and in MCD. In addition, NF-κB signaling was about fourfold higher in the glomeruli. TNF-α, IL6, CCR2, CCL5, and CCR5 mRNAs were markedly (about three- to fivefold) upregulated in microdissected glomeruli. While IL6, CCL2 and CCR5-mRNA, and CD68 were overexpressed in the tubulointerstitial compartment in clinical DN, they were not expressed in microalbuminuria. In a 6-year follow-up of microalbuminuric patients, glomerular TLR4 gene expression was associated with the subsequent loss of kidney function. Thus, innate immunity is activated in the glomeruli of patients with diabetic microalbuminuria. Enhanced TLR4 signaling may contribute to the progression occurring after the incipient, microalbuminuric form of nephropathy evolves to overt disease.

Circulating TNF receptor 2 is closely associated with the kidney function in non-diabetic Japanese subjects

AIM

Chronic kidney disease (CKD) is associated with cardiovascular events. Tumor necrosis factor (TNF) and/or its receptors have been postulated to be involved in renal pathophysiology. It is unclear whether an increased TNF system activity is present before the development of apparent CKD.

METHODS

Four hundred and twenty non-diabetic Japanese subjects with an estimated GFR (eGFR) greater than 60 ml/min/1.73 m(2) were recruited for measurement of the HbA1c, insulin, TNF system activity (TNF-α, soluble TNF receptor 1 (sTNF-R1) and sTNF-R2) levels and various parameters, including the lipid, high-sensitivity C-reactive protein (hsCRP), high-molecular-weight (HMW) adiponectin and leptin levels. The subjects were stratified according to the eGFR: the G1 level (eGFR ≧90 ml/min/1.73 m(2)) and the G2 level (90 ＞eGFR ≧60 ml/min/1.73 m(2)).

RESULTS

Whereas no significant differences were observed in gender, body mass index (BMI), blood pressure, insulin, TNF-α, hsCRP, HMW adiponectin or leptin between the two groups, the values for age, HbA1c, triglycerides, sTNF-R1 and sTNF-R2 were significantly higher in the subjects with a G2 level of eGFR than in those with a G1 level. In contrast, the HDL cholesterol levels were significantly lower in the subjects with a G2 level than in those with a G1 level. Linear negative correlations were also observed between eGFR and age, BMI, HbA1c, triglycerides, sTNF-R1 and sTNFR2, respectively. A multiple logistic regression analysis revealed that only sTNF-R2 was associated with the presence of a G2 level of eGFR (Odds ratio 1.092, 95% CI 1.013-1.177, P=0.021).

CONCLUSIONS

The circulating sTNF-R2 level is closely associated with the kidney function in non-diabetic Japanese subjects.

Role of podocyte B7-1 in diabetic nephropathy

Podocyte injury and resulting albuminuria are hallmarks of diabetic nephropathy, but targeted therapies to halt or prevent these complications are currently not available. Here, we show that the immune-related molecule B7-1/CD80 is a critical mediator of podocyte injury in type 2 diabetic nephropathy. We report the induction of podocyte B7-1 in kidney biopsy specimens from patients with type 2 diabetes. Genetic and epidemiologic studies revealed the association of two single nucleotide polymorphisms at the B7-1 gene with diabetic nephropathy. Furthermore, increased levels of the soluble isoform of the B7-1 ligand CD28 correlated with the progression to ESRD in individuals with type 2 diabetes. In vitro, high glucose conditions prompted the phosphatidylinositol 3 kinase-dependent upregulation of B7-1 in podocytes, and the ectopic expression of B7-1 in podocytes increased apoptosis and induced disruption of the cytoskeleton that were reversed by the B7-1 inhibitor CTLA4-Ig. Podocyte expression of B7-1 was also induced in vivo in two murine models of diabetic nephropathy, and treatment with CTLA4-Ig prevented increased urinary albumin excretion and improved kidney pathology in these animals. Taken together, these results identify B7-1 inhibition as a potential therapeutic strategy for the prevention or treatment of diabetic nephropathy.

Role of the TNF pathway in the progression of diabetic nephropathy in KK-A(y) mice

Chronic inflammation promotes the progression of diabetic nephropathy (DN). However, the role of TNF-α remains unclear. The objectives of the present study were to examine whether TNF-α inhibition with a soluble TNF receptor (TNFR)2 fusion protein, i.e., etanercept (ETN), improves the early stage of DN in the type 2 diabetic model of the KK-A(y) mouse and to also investigate which TNF pathway, TNFR1 or TNFR2, is predominantly involved in the progression of this disease. ETN was injected intraperitoneally into mice for 8 wk. Renal damage was evaluated by immunohistochemistry, Western blot analysis, and/or real-time PCR. In vitro, mouse tubular proximal cells were stimulated by TNF-α and/or high glucose (HG) and treated with ETN. ETN dramatically improved not only albuminuria but also glycemic control. Renal mRNA and/or protein levels of TNFR2, but not TNF-α and TNFR1, in ETN-treated KK-A(y) mice were significantly decreased compared with untreated KK-A(y) mice. mRNA levels of ICAM-1, VCAM-1, and monocyte chemoattractant protein-1 and the number of F4/80-positive cells were all decreased after treatment. Numbers of cleaved caspase-3- and TUNEL-positive cells in untreated mice were very few and were not different from ETN-treated mice. In vitro, stimulation with TNF-α or HG markedly increased both mRNA levels of TNFRs, unlike in the in vivo case. Furthermore, ETN partly recovered TNF-α-induced but not HG-induced TNFR mRNA levels. In conclusion, it appears that ETN may improve the progression of the early stage of DN predominantly through inhibition of the anti-inflammatory action of the TNF-α-TNFR2 pathway.

Markers of and risk factors for the development and progression of diabetic kidney disease

Diabetic kidney disease (DKD) occurs in 25%-40% of patients with diabetes. Given the dual problems of a significant risk of progression from DKD to end-stage renal disease (ESRD) and increased cardiovascular morbidity and mortality, it is important to identify patients at risk of DKD and ESRD and initiate protective renal and cardiovascular therapies. The importance of preventive therapy is emphasized further by worldwide increases in the incidence of diabetes. This review summarizes the evidence regarding the prognostic value and benefits of targeting established and novel risk markers for DKD development and progression. Family history of DKD, smoking history, and glycemic, blood pressure, and plasma lipid level control are established factors for identifying people at greatest risk of DKD development and progression. Absolute albumin excretion rate (AER) and glomerular filtration rate (GFR) measurements also are important, although AER categorization generally lacks the necessary specificity and sensitivity, and estimates of declining GFR are compromised by methodological limitations for GFRs in the normal-to-high range. Emerging risk markers for progressive loss of kidney function include markers of oxidation and inflammation, profibrotic cytokines, uric acid, advanced glycation end products, functional and structural markers of vascular dysfunction, kidney structural changes, and tubular biomarkers. Among these, the most promising are serum uric acid and soluble tumor necrosis factor receptor (type 1 and type 2) levels, especially in relation to GFR changes. At present, these can only be considered as risk markers because they only identify an individual at increased risk of progressive DKD and not necessarily related to the causal pathway promoting kidney damage. Further work is needed to establish whether modulating these factors improves the prognosis in DKD. Although change in urinary peptidome levels also is a promising marker, there currently is neither a clinical assay nor adequate studies defining its prognostic value. Until these or other novel markers become available for clinical use, predictive accuracy often may be increased with greater attention to established markers.

Novel therapies for diabetic kidney disease

The number of people diagnosed with diabetes is rising throughout the world, which in turn drives upward the global frequency of diabetic kidney disease (DKD). Individuals with DKD are at an increased risk for premature death, cardiovascular disease, and other severe illnesses that result in frequent hospitalizations and increased health-care utilization. Current treatments concentrate on controlling hyperglycemia and hypertension with the specific use of renin-angiotensin system inhibitors. Although such measures reduce the risk of progressive kidney disease, DKD remains the leading cause of ESRD and the major risk amplifier for death in this population. Therefore, novel therapeutic approaches are urgently needed. Ideas for novel targets for therapy are founded on recent advances in understanding DKD mechanisms that are based on experimental models and human observations. The purpose of this review is to describe the epidemiology and present knowledge of DKD pathophysiology as the basis for novel therapies including inhibitors of Janus kinases (JAK), protein kinase C, fibrosis, advanced glycation end products treatments, and endothelin.

Soluble TNF receptors and kidney dysfunction in the elderly

The importance of TNF-α and its soluble receptors (sTNFR1 and sTNFR2) in the development of kidney disease is being unraveled. Yet, community-based data regarding the role of sTNFRs are lacking. We assessed serum sTNFRs and aspects of kidney damage cross-sectionally in two independent community-based cohorts of elderly participants: Prospective Investigation of the Vasculature in Uppsala Seniors (n=815; mean age, 75 years; 51% women) and Uppsala Longitudinal Study of Adult Men (n=778; mean age, 78 years). Serum sTNFR1 correlated substantially with different aspects of kidney pathology in the Uppsala Longitudinal Study of Adult Men cohort (R=-0.52 for estimated GFR, R=0.22 for urinary albumin-to-creatinine ratio, and R=0.17 for urinary kidney injury molecule-1; P<0.001 for all), with similar correlations in the Prospective Investigation of the Vasculature in Uppsala Seniors cohort. These associations remained significant after adjustment for age, sex, inflammatory markers, and cardiovascular risk factors and were also evident in participants without diabetes. Serum sTNFR2 was associated with all three markers in the Prospective Investigation of the Vasculature in Uppsala Seniors cohort (P<0.001 for all). Our findings from two independent community-based cohorts confirm and extend results of previous studies supporting circulating sTNFRs as relevant biomarkers for kidney damage and dysfunction in elderly individuals, even in the absence of diabetes.

Uremic solutes and risk of end-stage renal disease in type 2 diabetes: metabolomic study

Here we studied plasma metabolomic profiles as determinants of progression to ESRD in patients with Type 2 diabetes (T2D). This nested case-control study evaluated 40 cases who progressed to ESRD during 8-12 years of follow-up and 40 controls who remained alive without ESRD from the Joslin Kidney Study cohort. Controls were matched with cases for baseline clinical characteristics; although controls had slightly higher eGFR and lower levels of urinary albumin excretion than T2D cases. Plasma metabolites at baseline were measured by mass spectrometry-based global metabolomic profiling. Of the named metabolites in the library, 262 were detected in at least 80% of the study patients. The metabolomic platform recognized 78 metabolites previously reported to be elevated in ESRD (uremic solutes). Sixteen were already elevated in the baseline plasma of our cases years before ESRD developed. Other uremic solutes were either not different or not commonly detectable. Essential amino acids and their derivatives were significantly depleted in the cases, whereas certain amino acid-derived acylcarnitines were increased. All findings remained statistically significant after adjustment for differences between study groups in albumin excretion rate, eGFR or HbA1c. Uremic solute differences were confirmed by quantitative measurements. Thus, abnormal plasma concentrations of putative uremic solutes and essential amino acids either contribute to progression to ESRD or are a manifestation of an early stage(s) of the disease process that leads to ESRD in T2D.

How to find a prognostic biomarker for progressive diabetic nephropathy

As a prognostic biomarker for progression of diabetic nephropathy, albuminuria fails in terms of sensitivity and specificity. Better urinary or plasma biomarkers are needed that can predict which diabetic patients are at highest risk for progression. Bhensdadia et al. report proteomic investigations that identified urinary haptoglobin as a potential prognostic biomarker for progressive diabetic nephropathy. Although as a single marker urinary haptoglobin adds little to albuminuria, together the two appear to provide better diagnostic accuracy than albuminuria alone.

Metabolism, energetics, and lipid biology in the podocyte - cellular cholesterol-mediated glomerular injury

Chronic kidney disease (CKD) is associated with a high risk of death. Dyslipidemia is commonly observed in patients with CKD and is accompanied by a decrease in plasma high-density lipoprotein, and an increase in plasma triglyceride-rich lipoproteins and oxidized lipids. The observation that statins may decrease albuminuria but do not stop the progression of CKD indicates that pathways other than the cholesterol synthesis contribute to cholesterol accumulation in the kidneys of patients with CKD. Recently, it has become clear that increased lipid influx and impaired reverse cholesterol transport can promote glomerulosclerosis, and tubulointerstitial damage. Lipid-rafts are cholesterol-rich membrane domains with important functions in regulating membrane fluidity, membrane protein trafficking, and in the assembly of signaling molecules. In podocytes, which are specialized cells of the glomerulus, they contribute to the spatial organization of the slit diaphragm (SD) under physiological and pathological conditions. The discovery that podocyte-specific proteins such as podocin can bind and recruit cholesterol contributing to the formation of the SD underlines the importance of cholesterol homeostasis in podocytes and suggests cholesterol as an important regulator in the development of proteinuric kidney disease. Cellular cholesterol accumulation due to increased synthesis, influx, or decreased efflux is an emerging concept in podocyte biology. This review will focus on the role of cellular cholesterol accumulation in the pathogenesis of kidney diseases with a focus on glomerular diseases.

Early progressive renal decline precedes the onset of microalbuminuria and its progression to macroalbuminuria

OBJECTIVE Progressive decrease in the glomerular filtration rate (GFR), or renal decline, in type 1 diabetes (T1D) is observed in patients with macroalbuminuria. However, it is unknown whether this decline begins during microalbuminuria (MA) or normoalbuminuria (NA). RESEARCH DESIGN AND METHODS The study group (second Joslin Kidney Study) comprises patients with T1D and NA (n = 286) or MA (n = 248) who were followed for 4-10 years (median 8 years). Serial measurements (median 6, range 3-16) of serum creatinine and cystatin C were used jointly to estimate GFR (eGFRcr-cys) and assess its trajectories during follow-up. RESULTS Renal decline (progressive eGFRcr-cys loss of at least 3.3% per year) occurred in 10% of the NA and 35% of the MA (P < 0.001). In both groups, the strongest determinants of renal decline were baseline serum concentrations of uric acid (P < 0.001) and tumor necrosis factor receptor 1 or 2 (TNFR-1 or -2, P < 0.001). Other significant risk factors included baseline HbA1c, age/diabetes duration, and systolic blood pressure. Relative impacts of these determinants were similar in NA and MA. Renal decline was not associated with sex or baseline serum concentration of TNF-α, IL-6, IL-8, IP-10, MCP-1, VCAM, ICAM, Fas, or FasL. CONCLUSIONS Renal decline in T1D begins during NA and it is determined by multiple factors, similar to MA. Thus, this early decline is the primary disease process leading to impaired renal function in T1D. Changes in albumin excretion rate, such as the onset of MA or its progression to macroalbuminuria, are either caused by or develop in parallel to the early renal decline.

Advanced glycation endproducts in diabetes and diabetic complications

This review presents insights from studies of advanced glycation end products (AGEs) in humans and mice. Although the emphasis is on the effects of exogenous AGEs and the suppression of specific host defense mechanisms, AGEs are also formed intracellularly, where they may contribute to several normal intracellular functions. It is only when the overall levels of AGEs in the extracellular and the intracellular spaces exceeds the ability of the native antioxidant (and AGE) defenses that they pose a problem.

Regulation of TIMP3 in diabetic nephropathy: a role for microRNAs

Diabetic nephropathy (DN) is the major cause of chronic kidney disease in developed countries and contributes significantly to increased morbidity and mortality among diabetic patients. Morphologically, DN is characterized by tubulo-interstitial fibrosis, thickening of the glomerular basement membrane and mesangial expansion mainly due to accumulation of extracellular matrix (ECM). ECM turnover is regulated by metalloproteinases and tissue inhibitors of metalloproteinases (TIMPs) activities. In diabetic conditions, TIMP3 expression in kidney is strongly reduced, but the causes of this reduction are still unknown. The aim of this study was to elucidate at least one of these mechanisms which relies on differential expression of TIMP3-targeting microRNAs (miRs) in a hyperglycemic environment either in vitro (MES13 cell line) or in vivo (mouse kidney and human biopsies). Among the TIMP3-targeting miRs, miR-21 and miR-221 were significantly upregulated in kidneys from diabetic mice compared to control littermates, and in a mesangial cell line grown in high glucose conditions. In human samples, only miR-21 expression was increased in kidney biopsies from diabetic patients compared to healthy controls. The expression of miR-217, which targets TIMP3 indirectly through downregulation of SirT1, was also increased in diabetic kidney and MES13 cell line. In agreement with these result, SirT1 expression was reduced in mouse and human diabetic kidneys as well as in MES13 mesangial cell line. TIMP3 deficiency has recently emerged as a hallmark of DN in mouse and human. In this study, we demonstrated that this reduction is due, at least in part, to increased expression of certain TIMP3-targeting miRs in diabetic kidneys compared to healthy controls. Unveiling the post-transcriptional mechanisms responsible for TIMP3 downregulation in hyperglycemic conditions may orient toward the use of this protein as a possible therapeutic target in DN.

Diabetic nephropathy: diagnosis and treatment

Nephropathy remains a major cause of morbidity and a key determinant of mortality in patients with type 1 or type 2 diabetes mellitus. Research is ongoing to identify biomarkers that in addition to albuminuria and glomerular filtration rate assist in the prediction and monitoring of renal disease in diabetes mellitus. Current strategies to treat this condition focus on intensification of glycaemic control and excellent control of blood pressure using regimens based on blockade of the renin-angiotensin system. Other approaches to control blood pressure and afford renoprotection are under active clinical investigation, including renal denervation and endothelin receptor antagonism. With increasing understanding of the underlying pathophysiological processes implicated in diabetic nephropathy, new specific renoprotective treatment strategies are anticipated to become available over the next few years.

Plasma apolipoprotein L1 levels do not correlate with CKD

Polymorphisms in APOL1 are associated with CKD, including HIV-related CKD, in individuals of African ancestry. The apolipoprotein L1 (APOL1) protein circulates and is localized in kidney cells, but the contribution of APOL1 location to CKD pathogenesis is unclear. We examined associations of plasma APOL1 levels with plasma cytokine levels, dyslipidemia, and APOL1 genotype in a nested case-control study (n=270) of HIV-infected African Americans enrolled in a multicenter prospective observational study. Patients were designated as having CKD when estimated GFR (eGFR) decreased to <60 ml/min per 1.73 m(2) (eGFR<60 cohort) or protein-to-creatinine ratios became >3.5 g/g (nephrotic proteinuria cohort). Circulating APOL1 levels did not associate with APOL1 genotype, CKD status, or levels of proinflammatory cytokines, but did correlate with fasting cholesterol, LDL cholesterol, and triglyceride levels. At ascertainment, CKD-associated polymorphisms (risk variants) in APOL1 associated with the eGFR<60 cohort, but not the nephrotic-range proteinuria cohort. Of note, in both the eGFR<60 and nephrotic proteinuria cohorts, CKD cases with two APOL1 risk variants had significant declines in eGFR over a median of 4 years compared with individuals with one or no risk variants. APOL1 risk genotype was not associated with changes in proteinuria. Higher circulating proinflammatory cytokine levels were independently associated with CKD but not APOL1 genotype. In conclusion, the function of variant APOL1 proteins derived from circulation or synthesized in the kidney, but not the level of circulating APOL1, probably mediates APOL1-associated kidney disease in HIV-infected African Americans.

A story of microalbuminuria and diabetic nephropathy

CONTEXT

It is estimated that more than 346 million people worldwide have diabetes mellitus . By the year 2030, it is predicted that diabetes will become the seventh leading cause of death in the world. Development of chronic kidney disease (CKD) in patients with diabetes adds significantly to the morbidity and mortality and significantly increases health care costs, even before the development of end stage renal disease (ESRD). Evidence  acquisitions: Directory of Open Access Journals (DOAJ), Google Scholar, Pubmed (NLM), LISTA (EBSCO) and Web of Science have been searched.

RESULTS

Diabetic nephropathy (DN) is increasing rapidly worldwide. It is the leading cause of new cases of ESRD in the USA.  Interestingly, although DN is the most common cause of ESRD in diabetic patients, diabetes mellitus is also an independent and strong risk factor for ESRD ascribed to causes other than DN (e.g. hypertensive nephropathy).

CONCLUSIONS

It is important to be aware of the pitfalls of using the urine albumin level in predicting development and progression of diabetic nephropathy in order to treat and advise the patients accurately.  Research into finding new markers is rapidly evolving but current progress makes it likely we will be using the urine albumin level for some years into the future.

Novel biomarkers for the progression of diabetic nephropathy: soluble TNF receptors

Despite 2 decades of advances in therapy of diabetic patients, the prevalence of diabetic nephropathy among patients with diabetes has not decreased. However, large-scale multicenter studies have achieved great success in terms of the reduction of albuminuria, suggesting that albuminuria might not be an accurate surrogate marker for slowing the rate of renal function decline. It is important to be able to identify individuals at high risk for renal function decline, or ultimately, end-stage kidney disease (ESKD) and its associated cardiovascular disease (CVD). More sensitive early biomarkers, other than albuminuria and the estimated glomerular filtration rate (eGFR), should be required. Recently, serum concentrations of soluble tumor necrosis factor (TNF), receptor 1 (TNFR1), and TNFR2 have predicted future GFR loss and ESKD in patients of a wide variety of stages and both types of diabetes. Longitudinal interventional studies are needed to validate these biomarkers in a broad range of populations prior to implementation in routine diabetes management.

Baseline markers of inflammation are associated with progression to macroalbuminuria in type 1 diabetic subjects

OBJECTIVE

The current study aimed to determine in the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications cohort whether or not abnormal levels of markers of inflammation and endothelial dysfunction measured in samples collected at DCCT baseline were able to predict the development of macroalbuminuria.

RESEARCH DESIGN AND METHODS

Levels of inflammation and endothelial cell dysfunction biomarkers were measured in 1,237 of 1,441 patients enrolled in the DCCT study who were both free of albuminuria and cardiovascular disease at baseline. To test the association of log-transformed biomarkers with albuminuria, generalized logistic regression models were used to quantify the association of increased levels of biomarkers and development of abnormal albuminuria. Normal, micro-, and macroalbuminuria were the outcomes of interest.

RESULTS

In the logistic regression models adjusted by DCCT treatment assignment, baseline albumin excretion rate, and use of ACE/angiotensin receptor blocker drugs, one unit increase in the standardized levels of soluble E-selectin (sE-selectin) was associated with an 87% increase in the odds to develop macroalbuminuria and one unit increase in the levels of interleukin-6 (IL-6), plasminogen activator inhibitor 1 (PAI-1; total and active), and soluble tumor necrosis factor receptors (TNFR)-1 and -2 lead to a 30-50% increase in the odds to develop macroalbuminuria. Following adjustment for DCCT baseline retinopathy status, age, sex, HbA1c, and duration of diabetes, significant associations remained for sE-selectin and TNFR-1 and -2 but not for IL-6 or PAI-1.

CONCLUSIONS

Our study indicates that high levels of inflammatory markers, mainly E-selectin and sTNRF-1 and -2, are important predictors of macroalbuminuria in patients with type 1 diabetes.

Diabetic nephropathy in a sibling and albuminuria predict early GFR decline: a prospective cohort study

BACKGROUND

Diabetic nephropathy is a growing clinical problem, and the cause for >40% of incident ESRD cases. Unfortunately, few modifiable risk factors are known. The objective is to examine if albuminuria and history of diabetic nephropathy (DN) in a sibling are associated with early DN progression or mortality.

METHODS

In this longitudinal study of adults >18 yrs with diabetes monitored for up to 9 yrs (mean 4.6 ± 1.7 yrs), 435 subjects at high risk (DN family history) and 400 at low risk (diabetes >10 yrs, normoalbuminuria, no DN family history) for DN progression were evaluated for rate of eGFR change using the linear mixed effects model and progression to ESRD. All-cause mortality was evaluated by Kaplan-Meier analyses while controlling for baseline covariates in a Cox proportional hazards model. Covariates included baseline eGFR, age, gender, race, diabetes duration, blood pressure, hemoglobin A1c and urine albumin:creatinine ratio. Propensity score matching was used to identify high and low risk group pairs with balanced covariates. Sensitivity analyses were employed to test for residual confounding.

RESULTS

Mean baseline eGFR was 74 ml/min/1.73 m2 (86% of cohort >60 ml/min/1.73 m2). Thirty high risk and no low risk subjects developed ESRD. eGFR decline was significantly greater in high compared to low risk subjects. After controlling for confounders, change in eGFR remained significantly different between groups, suggesting that DN family history independently regulates GFR progression. Mortality was also significantly greater in high versus low risk subjects, but after controlling for baseline covariates, no significant difference was observed between groups, indicating that factors other than DN family history more strongly affect mortality. Analyses of the matched pairs confirmed change in eGFR and mortality findings. Sensitivity analyses demonstrated that the eGFR results were not due to residual confounding by unmeasured covariates of a moderate effect size in the propensity matching.

CONCLUSIONS

Diabetic subjects with albuminuria and family history of DN are vulnerable for early GFR decline, whereas subjects with diabetes for longer than 10 years, normoalbuminuria and negative family history, experience slower eGFR decline, and are extremely unlikely to require dialysis. Although we would not recommend that patients with low risk characteristics be neglected, scarce resources would be more sensibly devoted to vulnerable patients, such as the high risk cases in our study, and preferably prior to the onset of albuminuria or GFR decline.

Review and discussion of tubular biomarkers in the diagnosis and management of diabetic nephropathy

The prevalence of diabetic nephropathy has tremendously increased with the relentless rise in the incidence of diabetes over the last couple decades. Diabetic nephropathy is a leading cause of morbidity and mortality, and it invariably leads to an end-stage renal disease (ESRD). In an effort to delay the onset of ESRD systematic screening and appropriate management are needed to evaluate the progression of renal damage in diabetic nephropathy. The reliability of current tests in predicting the onset, progression and response to various regimens for diabetic nephropathy is still under debate; and it has engendered a search for more sensitive and specific urinary biomarkers, especially those reflective of tubular dysfunctions. It is well-known that there is a good correlation between the degree of damage to the tubulo-interstitial compartment and the deterioration of renal functions. In view of this, the utility of urinary biomarkers, reflective of tubular injury, reported in the literature is discussed in this brief review.

Can improved glycemic control slow renal function decline at all stages of diabetic nephropathy?

Observational studies have shown the strong association between level of glycemic control and the key outcome measure, risk of glomerular filtration rate (GFR) loss rather than subsequent course of albumin excretion, in type 1 diabetes patients at all stages of nephropathy. However, it has not been clear if clinical interventions designed to normalize glycemic control are equally effective at all stages, such as primary prevention in normoalbuminuric patients, secondary prevention in microalbuminuria and macroalbuminuria, or tertiary prevention aimed at slowing or reversing further loss of GFR once impaired. Substantial randomized controlled trial data from the Diabetes Control and Complications Trial and Epidemiology of Diabetes Interventions and Complications exists to support postponement, but not outright prevention, of GFR loss in normoalbuminuric patients. Although secondary and tertiary prevention systematic studies are limited to methodologically insufficient insulin pump and transplantation trials, the reversal of advanced glomerular lesions observed in whole-pancreas transplant recipients who experienced long-term glycemic normalization offers convincing support for further research into glycemic interventions specifically for GFR preservation. In light of existing literature, we encourage the design of secondary and tertiary prevention trials that incorporate biomarker methods for identifying patients at highest risk of GFR loss because interventions to normalize hyperglycemia are resource-intensive and may be applied unnecessarily to clinical populations at low long-term GFR loss risk.

High risk of ESRD in type 1 diabetes: new strategies are needed to retard progressive renal function decline

Care of patients with type 1 diabetes (T1D) has changed during the past 30 years. Tools to control hyperglycemia have improved and it was shown that improvement in glycemic control diminished the risk of late diabetic complications, including nephropathy. Moreover, in patients with impaired renal function, aggressive treatment of hypertension and renoprotective blockade of the renin-angiotensin system were shown to postpone end-stage renal disease (ESRD), albeit for a short while. Despite these achievements, the incidence of ESRD caused by T1D in the US population has not decreased but rather has increased over the past 20 years, although it now occurs at slightly older ages. This state of affairs is a call to action. This should begin with adopting a new model of diabetic nephropathy in human beings. In that model, instead of microalbuminuria or proteinuria, the focus should be on diagnosis and treatment of progressive renal function decline that leads to ESRD. Such a model has received significant support in clinical and epidemiologic studies. Investigation of mechanisms of such progressive renal function decline should help in the identification of new therapeutic targets and the development of new interventions. To evaluate these interventions, accurate diagnostic algorithms are needed so T1D patients will be stratified according to time to onset to ESRD. Consistent with concepts of personalized medicine, the new interventions should be tailored to and evaluated in patients predicted to have rapid, moderate, or even slow progression to ESRD.

Tumor necrosis factor-α: regulation of renal function and blood pressure

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine that becomes elevated in chronic inflammatory states such as hypertension and diabetes and has been found to mediate both increases and decreases in blood pressure. High levels of TNF-α decrease blood pressure, whereas moderate increases in TNF-α have been associated with increased NaCl retention and hypertension. The explanation for these disparate effects is not clear but could simply be due to different concentrations of TNF-α within the kidney, the physiological status of the subject, or the type of stimulus initiating the inflammatory response. TNF-α alters renal hemodynamics and nephron transport, affecting both activity and expression of transporters. It also mediates organ damage by stimulating immune cell infiltration and cell death. Here we will summarize the available findings and attempt to provide plausible explanations for such discrepancies.

Risk of ESRD and all cause mortality in type 2 diabetes according to circulating levels of FGF-23 and TNFR1

INTRODUCTION

Recent studies demonstrated that circulating fibroblast growth factor (FGF)-23 was associated with risk of end stage renal disease (ESRD) and mortality. This study aims to examine whether the predictive effect of FGF-23 is independent from circulating levels of tumor necrosis factor receptor 1 (TNFR1), a strong predictor of ESRD in Type 2 diabetes (T2D).

METHODS

We studied 380 patients with T2D who were followed for 8-12 years and were used previously to examine the effect of TNFR1. Baseline plasma FGF-23 was measured by immunoassay.

RESULTS

During follow-up, 48 patients (13%) developed ESRD and 83 patients (22%) died without ESRD. In a univariate analysis, baseline circulating levels of FGF-23 and TNFR1 were significantly higher in subjects who subsequently developed ESRD or died without ESRD than in those who remained alive. In a Cox proportional hazard model, baseline concentration of FGF-23 was associated with increased risk of ESRD, however its effect was no longer significant after controlling for TNFR1 and other clinical characteristics (HR 1.3, p = 0.15). The strong effect of circulating level of TNFR1 on risk of ESRD was not changed by including circulating levels of FGF-23 (HR 8.7, p<0.001). In the Cox multivariate model, circulating levels of FGF-23 remained a significant independent predictor of all-cause mortality unrelated to ESRD (HR 1.5, p<0.001).

CONCLUSIONS

We demonstrated that the effect of circulating levels of FGF-23 on the risk of ESRD is accounted for by circulating levels of TNFR1. We confirmed that circulating levels of FGF-23 have an independent effect on all-cause mortality in T2D.

Transcriptome analysis of proximal tubular cells (HK-2) exposed to urines of type 1 diabetes patients at risk of early progressive renal function decline

Background

In patients with Type 1 Diabetes (T1D) who develop microalbuminuria, progressive decline in glomerular filtration rate (GFR) may be initiated by leakage into the urine of toxic proteins (txUPs). This study tested this hypothesis.

Methods

After archiving baseline urine, we followed T1D patients with microalbuminuria for 8–12 years to distinguish those in whom GFR declined (Decliners) and those in whom it remained stable (Non-decliners). Human proximal tubular cells (HK-2 cells) were grown in serum-free medium enriched with pooled urines from Decliners or Non-decliners. We determined genome-wide expression profiles in extracted mRNA.

Results

The two pooled urines induced differential expression of 312 genes. In terms of gene ontology, molecular functions of the 119 up-regulated genes were enriched for protein binding and peptidase inhibitor activities. Their biologic processes were enriched for defense response, responses to other organisms, regulation of cellular processes, or response to stress or stimulus, and programmed cell death. The 195 down-regulated genes were disproportionately represented in molecular functions of cation binding, hydrolase activity, and DNA binding. They were disproportionately represented in biological processes for regulation of metabolic processes, nucleic acid metabolic processes, cellular response to stress and macromolecule biosynthesis. The set of up-regulated genes in HK-2 cells overlaps significantly with sets of over-expressed genes in tubular and interstitial compartments of kidney biopsies from patients with advanced DN (33 genes in one study and 25 in the other compared with 10.3 expected by chance, p<10⁻⁹ and p<10⁻⁴, respectively). The overlap included genes encoding chemokines and cytokines. Overlap of down-regulated genes was no more than expected by chance.

Conclusions

Molecular processes in tubules and interstitium seen in advanced diabetic nephropathy can be induced in vitro by exposure to urine from patients with minimal microalbuminuria who subsequently developed progressive renal function decline, presumably due to putative txUPs.

Loss of TIMP3 underlies diabetic nephropathy via FoxO1/STAT1 interplay

ADAM17 and its inhibitor TIMP3 are involved in nephropathy, but their role in diabetic kidney disease (DKD) is unclear. Diabetic Timp3^−/− mice showed increased albuminuria, increased membrane thickness and mesangial expansion. Microarray profiling uncovered a significant reduction of Foxo1 expression in diabetic Timp3^−/− mice compared to WT, along with FoxO1 target genes involved in autophagy, while STAT1, a repressor of FoxO1 transcription, was increased. Re-expression of Timp3 in Timp3^−/− mesangial cells rescued the expression of Foxo1 and its targets, and decreased STAT1 expression to control levels; abolishing STAT1 expression led to a rescue of FoxO1, evoking a role of STAT1 in linking Timp3 deficiency to FoxO1. Studies on kidney biopsies from patients with diabetic nephropathy confirmed a significant reduction in TIMP3, FoxO1 and FoxO1 target genes involved in autophagy compared to controls, while STAT1 expression was strongly increased.

Our study suggests that loss of TIMP3 is a hallmark of DKD in human and mouse models and designates TIMP3 as a new possible therapeutic target for diabetic nephropathy.

Circulating TNF receptor 2 is associated with the development of chronic kidney disease in non-obese Japanese patients with type 2 diabetes

AIMS

Chronic low-grade inflammation and/or obesity are suggested to induce chronic kidney disease (CKD) in patients with type 2 diabetes. This cross-sectional study was performed to investigate the relationship between inflammatory biomarkers and CKD in non-obese patients with type 2 diabetes.

METHODS

106 non-obese Japanese patients with type 2 diabetes were recruited for the measurement of GFR, TNF, HMW adiponectin, leptin, hsCRP and some variables including urinary albumin. BMI, serum creatinine, and urinary albumin levels were 22.2 ± 0.2 kg/m(2) (17.1-24.9 kg/m(2)), 0.76 ± 0.02 mg/dl (0.39-1.38 mg/dl), 40.4 ± 4.3mg/gCr (1.6-195.0mg/gCr), respectively. They were stratified into two groups based on the value of eGFR: low eGFR (eGFR<60 ml/min/1.73 m(2)) and normal eGFR (eGFR>60 ml/min/1.73 m(2)). Logistic regression analysis was used for statistical analysis.

RESULTS

Whereas univariate logistic regression analysis showed that gender, diabetes duration, triglyceride, HDL cholesterol, uric acid, urinary albumin, and soluble TNF receptors (sTNF-R1, sTNF-R2) are associated with the development of stage 3 CKD, multivariate logistic regression analysis revealed that sTNF-R2 (Odds ratio 1.003, 95% confidence interval 1.000 to 1.005, P=0.030) showed significant associations with the development of stage 3 CKD.

CONCLUSIONS

Circulating TNF receptor 2 is an independent risk factor for CKD in non-obese Japanese patients with type 2 diabetes.

Coming full circle in diabetes mellitus: from complications to initiation

Glycaemic control, reduction of blood pressure using agents that block the renin-angiotensin system and control of dyslipidaemia are the major strategies used in the clinical management of patients with diabetes mellitus. Each of these approaches interrupts a number of pathological pathways, which directly contributes to the vascular complications of diabetes mellitus, including renal disease, blindness, neuropathy and cardiovascular disease. However, research published over the past few years has indicated that many of the pathological pathways important in the development of the vascular complications of diabetes mellitus are equally relevant to the initiation of diabetes mellitus itself. These pathways include insulin signalling, generation of cellular energy, post-translational modifications and redox imbalances. This Review will examine how the development of diabetes mellitus has come full circle from initiation to complications and suggests that the development of diabetes mellitus and the progression to chronic complications both require the same mechanistic triggers.

Comparison of serum cystatin C, serum creatinine, measured GFR, and estimated GFR to assess the risk of kidney failure in American Indians with diabetic nephropathy

BACKGROUND

We compared values of baseline serum cystatin C (SCysC), serum creatinine (SCr), and measured glomerular filtration rate (mGFR) for predicting end-stage renal disease (ESRD) in patients with type 2 diabetes and elevated albuminuria.

STUDY DESIGN

Observational longitudinal study.

SETTING & PARTICIPANTS

Pima Indians with type 2 diabetes and elevated albumin-creatinine ratio (ACR ≥30 mg/g).

PREDICTORS

Baseline SCysC, SCr, and mGFR.

OUTCOMES & MEASUREMENTS

Individuals were followed up from their first examination with diabetes and ACR ≥30 mg/g until December 2010, onset of ESRD, or death, whichever came first. Incidence rates adjusted for age and sex were computed by Mantel-Haenszel stratification. The abilities of SCysC, SCr, and mGFR values to predict ESRD were compared with receiver operating characteristic curves.

RESULTS

Of 234 Pima Indians with a mean age of 42.8 years who were followed up for a median of 10.7 (range, 0.6-21.3) years, 68 (29%) developed ESRD. The incidence of ESRD was significantly higher in patients in the lowest versus highest tertile of 1/SCysC (incidence rate ratio, 2.43; 95% CI, 1.31-4.50). By contrast, mGFR and 1/SCr had J-shaped associations with ESRD. In unadjusted analyses, 1/SCysC had the highest area under the receiver operating characteristic curve (AUROC; 0.719 ± 0.035) and mGFR had the lowest (0.585 ± 0.042; P < 0.001); the AUROC for 1/SCr was intermediate (0.672 ± 0.040; P = 0.1 and P = 0.03 vs 1/SCysC and mGFR, respectively). In analyses adjusted for age, sex, diabetes duration, height, weight, hemoglobin A1c level, and ACR, 1/SCysC had the highest AUROC (0.845 ± 0.026). Models with mGFR or 1/SCr alone had similar AUROCs (P = 0.9) and both were lower than the model with 1/SCysC alone (P = 0.02 and P = 0.03, respectively).

LIMITATIONS

The predictive values of the filtration markers are limited to the extent that their precision is based on a single measurement.

CONCLUSIONS

SCysC level was a better predictor of ESRD than mGFR or SCr level in Pima Indians with type 2 diabetes and elevated albuminuria.

Expression of HIV transgene aggravates kidney injury in diabetic mice

With the widespread use of combination antiretroviral agents, the incidence of HIV-associated nephropathy has decreased. Currently, HIV-infected patients live much longer and often suffer from comorbidities such as diabetes mellitus. Recent epidemiological studies suggest that concurrent HIV infection and diabetes mellitus may have a synergistic effect on the incidence of chronic kidney disease. To address this, we determined whether HIV-1 transgene expression accelerates diabetic kidney injury using a diabetic HIV-1 transgenic (Tg26) murine model. Diabetes was initially induced with low-dose streptozotocin in both Tg26 and wild-type mice on a C57BL/6 background, which is resistant to classic HIV-associated nephropathy. Although diabetic nephropathy is minimally observed on the C57BL/6 background, diabetic Tg26 mice exhibited a significant increase in glomerular injury compared with nondiabetic Tg26 mice and diabetic wild-type mice. Validation of microarray gene expression analysis from isolated glomeruli showed a significant upregulation of proinflammatory pathways in diabetic Tg26 mice. Thus, our study found that expression of HIV-1 genes aggravates diabetic kidney disease.

Arsenic and the epigenome: interindividual differences in arsenic metabolism related to distinct patterns of DNA methylation

Biotransformation of inorganic arsenic (iAs) is one of the factors that determines the character and magnitude of the diverse detrimental health effects associated with chronic iAs exposure, but it is unknown how iAs biotransformation may impact the epigenome. Here, we integrated analyses of genome-wide, gene-specific promoter DNA methylation levels of peripheral blood leukocytes with urinary arsenical concentrations of subjects from a region of Mexico with high levels of iAs in drinking water. These analyses revealed dramatic differences in DNA methylation profiles associated with concentrations of specific urinary metabolites of arsenic (As). The majority of individuals in this study had positive indicators of As-related disease, namely pre-diabetes mellitus or diabetes mellitus (DM). Methylation patterns of genes with known associations with DM were associated with urinary concentrations of specific iAs metabolites. Future studies will determine whether these DNA methylation profiles provide mechanistic insight into the development of iAs-associated disease, predict disease risk, and/or serve as biomarkers of iAs exposure in humans.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

TNF-α mediates increased susceptibility to ischemic AKI in diabetes

Diabetes is a risk factor for the development of acute kidney injury (AKI) in humans and rodents. However, the mechanistic basis for this observation is unknown. The present studies evaluated the role of inflammation and TNF-α in ischemic AKI in a model of type 2 diabetes mellitus (DM). Diabetic (db/db) and nondiabetic (db/+) littermates were subjected to 20 min of bilateral renal ischemia. The nondiabetic mice developed only mild and transient renal dysfunction. In contrast, the equivalent ischemic insult provoked severe and sustained renal dysfunction in the db/db mice. The expression of TNF-α and Toll-like receptor 4 (TLR4) mRNA was measured in the kidneys of diabetic mice before and after renal ischemia; db/db mice exhibited greater increases in TNF-α and TLR4 mRNA expression following ischemia than did db/+. In addition, urinary excretion of TNF-α after ischemia was higher in db/db mice than in db/+ mice. To determine the possible role of TNF-α in mediating the enhanced susceptibility of diabetic mice to ischemic injury, db/db mice were injected with either a neutralizing anti-mouse TNF-α antibody or nonimmune globulin and then subjected to 20 min of bilateral renal ischemia. Treatment of the db/db mice with the TNF-α antibody provided significant protection against the ischemic injury. These data support the view that diabetes increases the susceptibility to ischemia-induced renal dysfunction. This increased susceptibility derives from a heightened inflammatory response involving TNF-α and perhaps TLR4 signaling.

Incident atrial fibrillation and risk of end-stage renal disease in adults with chronic kidney disease

BACKGROUND

Atrial fibrillation (AF) frequently occurs in patients with chronic kidney disease (CKD). However, the long-term impact of development of AF on the risk of adverse renal outcomes in patients with CKD is unknown. In this study, we determined the association between incident AF and risk of end-stage renal disease (ESRD) among adults with CKD.

METHODS AND RESULTS

We studied adults with CKD (defined as estimated glomerular filtration rate eGFR <60 mL/min per 1.73 m(2) by the Chronic Kidney Disease Epidemiology Collaboration equation) enrolled in Kaiser Permanente Northern California who were identified between 2002 and 2010 and who did not have previous ESRD or previously documented AF. Incident AF was identified by using primary hospital discharge diagnoses or 2 or more outpatient visits for AF. Incident ESRD was ascertained from a comprehensive health plan registry for dialysis and renal transplant. Among 206 229 adults with CKD, 16 463 developed incident AF. During a mean follow-up of 5.1±2.5 years, there were 345 cases of ESRD that occurred after development of incident AF (74 per 1000 person-years) in comparison with 6505 cases of ESRD during periods without AF (64 per 1000 person-years, P<0.001). After adjustment for potential confounders, incident AF was associated with a 67% increase in the rate of ESRD (hazard ratio, 1.67; 95% confidence interval, 1.46-1.91).

CONCLUSIONS

Incident AF is independently associated with increased risk of developing ESRD in adults with CKD. Further study is needed to identify potentially modifiable pathways through which AF leads to a higher risk of progression to ESRD.