Glomerular structure and function in proteinuric type 2 (non-insulin-dependent) diabetic patients

Glucagon receptor activation contributes to the development of kidney injury

The underlying causes of diabetic kidney disease are still largely unknown. New insights into the contributing causes of diabetic nephropathy are important to prevent this complication. Hyperglycemia and hypertension are some of the risk factors for diabetic nephropathy. However, the incidence of diabetic nephropathy is increasing despite efforts to normalize blood glucose levels and blood pressure. Therefore, other factors should be investigated as causes of diabetic nephropathy. We investigated whether long-term increased plasma levels of glucagon contribute to the development of pathophysiological changes in kidney function as seen in patients with diabetic nephropathy. Using mouse models of chronic activation and inactivation of glucagon receptor signaling, we investigated whether glucagon is involved in changes in renal function, renal structure, and transcriptional changes. We found several histopathological changes in the kidney, such as thickening of the parietal layer of Bowman's capsule, glomerular mesangial cell expansion, and significant albuminuria in the mice with activated glucagon receptor signaling. Opposite effects on mesangial area expansion and the development of albuminuria were demonstrated in mice with glucagon receptor inactivation. RNA sequencing data revealed that transcription of genes related to fatty acid metabolism, podocytes, Na+-K+-ATPase, and sodium/glucose transport was significantly changed in mice with activated glucagon receptor signaling. These data implicate that glucagon receptor signaling is involved in the development of kidney injury, as seen in type 2 diabetes, and that glucagon receptor is a potential therapeutic target in the treatment of diabetes. NEW & NOTEWORTHY This study suggests that the glucagon receptor is a potential therapeutic target in the treatment of diabetic kidney disease. We show, in mice, that long-term treatment with a glucagon analog showed not only pathophysiological changes and changes in renal function but also transcriptional changes in the kidneys, whereas opposite effects were demonstrated in mice with glucagon receptor inactivation. Therefore, the use of glucagon in a treatment regimen requires investigation of possible metabolic and renal abnormalities.

Youth versus adult-onset type 2 diabetic kidney disease: Insights into currently known structural differences and the potential underlying mechanisms

Type 2 diabetes (T2D) is a global health pandemic with significant humanitarian, economic, and societal implications, particularly for youth and young adults who are experiencing an exponential rise in incident disease. Youth-onset T2D has a more aggressive phenotype than adult-onset T2D, and this translates to important differences in rates of progression of diabetic kidney disease (DKD). We hypothesize that youth-onset DKD due to T2D may exhibit morphometric, metabolic, and molecular characteristics that are distinct from adult-onset T2D and develop secondary to inherent differences in renal energy expenditure and substrate metabolism, resulting in a central metabolic imbalance. Kidney structural changes that are evident at the onset of puberty also serve to exacerbate the organ’s baseline high rates of energy expenditure. Additionally, the physiologic state of insulin resistance seen during puberty increases the risk for kidney disease and is exacerbated by both concurrent diabetes and obesity. A metabolic mismatch in renal energetics may represent a novel target for pharmacologic intervention, both for prevention and treatment of DKD. Further investigation into the underlying molecular mechanisms resulting in DKD in youth-onset T2D using metabolomics and RNA sequencing of kidney tissue obtained at biopsy is necessary to expand our understanding of early DKD and potential targets for therapeutic intervention. Furthermore, large-scale clinical trials evaluating the duration of kidney protective effects of pharmacologic interventions that target a metabolic mismatch in kidney energy expenditure are needed to help mitigate the risk of DKD in youth-onset T2D.

Structural Lesions on Kidney Biopsy in Youth-Onset and Adult-Onset Type 2 Diabetes

OBJECTIVE

Type 2 diabetes (T2D) is a leading cause of end-stage kidney disease worldwide. Recent studies suggest a more aggressive clinical course of diabetic kidney disease in youth-onset compared with adult-onset T2D. We compared kidney structural lesions in youth- and adult-onset T2D to determine if youth onset was associated with greater early tissue injury.

RESEARCH DESIGN AND METHODS

Quantitative microscopy was performed on kidney tissue obtained from research kidney biopsies in 161 Pima Indians (117 women, 44 men) with T2D. Onset of T2D was established by serial oral glucose tolerance testing, and participants were stratified as youth onset (age <25 years) or adult onset (age ≥25 years). Associations between clinical and morphometric parameters and age at onset were tested using linear models.

RESULTS

At biopsy, the 52 participants with youth-onset T2D were younger than the 109 with adult-onset T2D (39.1 ± 9.9 vs. 51.4 ± 10.2 years; P < 0.0001), but their diabetes duration was similar (19.3 ± 8.1 vs. 17.0 ± 7.8 years; P = 0.09). Median urine albumin-to-creatinine ratio was higher in the youth-onset group (58 [25th-75th percentile 17-470] vs. 27 [13-73] mg/g; P = 0.02). Youth-onset participants had greater glomerular basement membrane (GBM) width (552 ± 128 vs. 490 ± 114 nm; P = 0.002) and mesangial fractional volume (0.31 ± 0.10 vs. 0.27 ± 0.08; P = 0.001) than adult-onset participants. Glomerular sclerosis percentage, glomerular volume, mesangial fractional volume, and GBM width were also inversely associated with age at diabetes onset as a continuous variable.

CONCLUSIONS

Younger age at T2D onset strongly associates with more severe kidney structural lesions. Studies are underway to elucidate the pathways underlying these associations.

Pima Indian Contributions to Our Understanding of Diabetic Kidney Disease

Prospective studies in informative populations are crucial to increasing our knowledge of disease. In this perspective, we describe a half century of studies in an American Indian population that transformed our understanding of kidney disease in type 2 diabetes, now recognized as the leading cause of kidney failure worldwide. Serial examinations conducted for many years that included the collection of data and samples across multiple domains captured an unprecedented volume of clinical, physiologic, morphometric, genomic, and transcriptomic data. This work permitted us to extensively characterize the course and determinants of diabetic kidney disease, its pathophysiologic underpinnings, and important secular trends of urgent concern to populations worldwide, including the emergence of youth-onset type 2 diabetes and its effect on development of diabetic kidney disease in midlife. By combining these data using the tools of integrative biology, we are developing new mechanistic insights into the development and progression of diabetic kidney disease in type 2 diabetes. These insights have already contributed to the identification and successful therapeutic targeting of a novel pathway in DKD. We anticipate that this work will continue to expand our understanding of this complex disease and influence its management in the coming years.

Roles of Hydrogen Sulfide Donors in Common Kidney Diseases

Hydrogen sulfide (H2S) plays a key role in the regulation of physiological processes in mammals. The decline in H2S level has been reported in numerous renal disorders. In animal models of renal disorders, treatment with H2S donors could restore H2S levels and improve renal functions. H2S donors suppress renal dysfunction by regulating autophagy, apoptosis, oxidative stress, and inflammation through multiple signaling pathways, such as TRL4/NLRP3, AMP-activated protein kinase/mammalian target of rapamycin, transforming growth factor-β1/Smad3, extracellular signal-regulated protein kinases 1/2, mitogen-activated protein kinase, and nuclear factor kappa B. In this review, we summarize recent developments in the effects of H2S donors on the treatment of common renal diseases, including acute/chronic kidney disease, renal fibrosis, unilateral ureteral obstruction, glomerulosclerosis, diabetic nephropathy, hyperhomocysteinemia, drug-induced nephrotoxicity, metal-induced nephrotoxicity, and urolithiasis. Novel H2S donors can be designed and applied in the treatment of common renal diseases.

Cutaneous microangiopathy in patients with type 2 diabetes: Impaired vascular endothelial growth factor expression and its correlation with neuropathy, retinopathy and nephropathy

AIMS/INTRODUCTION

To examine the three-dimensional morphology and vascular endothelial growth factor (VEGF) expression of skin microvasculature in patients with type 2 diabetes in relation to neuropathy, retinopathy and nephropathy.

MATERIALS AND METHODS

The present study enrolled 17 individuals with type 2 diabetes and 16 without. Skin sections were double-immunostained for type IV collagen and VEGF-A or protein gene product 9.5. Projected images from confocal microscopy served to quantify the occupancy rate of subepidermal type IV collagen-immunoreactive microvascular basement membrane area (OR-T4MBM), subepidermal VEGF-A-immunoreactive area and the VEGF/T4MBM ratio, as well as the protein gene product 9.5-immunoreactive intraepidermal nerve fiber density. Reduced intraepidermal nerve fiber density was applied for the diagnosis of neuropathy, fundic ophthalmoscopy and fluorescein angiography for retinopathy, and microalbuminuria or persistent proteinuria for nephropathy.

RESULTS

A total of 12 patients with diabetes had neuropathy, 10 had retinopathy and eight had nephropathy. Regardless of the presence or absence of neuropathy, retinopathy or nephropathy, OR-T4MBM was significantly increased in patients with diabetes compared with individuals without diabetes. In contrast, VEGF/T4MBM ratio was significantly decreased in those with neuropathy and retinopathy, as well as in those with and without nephropathy, whereas a trend toward a decreased VEGF/T4MBM ratio was seen in patients without retinopathy, as compared with individuals without diabetes.

CONCLUSIONS

The present study is the first report to show that cutaneous microangiopathy, as indicated by subepidermal microvascular proliferation and impaired VEGF expression, appears to occur before the development of overt clinical neuropathy, retinopathy or nephropathy in patients with type 2 diabetes.

Participation of the AngII/TRPC6/NFAT axis in the pathogenesis of podocyte injury in rats with type 2 diabetes

The canonical transient receptor potential channel 6 ion channel is expressed in podocytes and is an important component of the glomerular slit diaphragm. Focal segmental glomerulosclerosis is closely associated with TRPC6 gene mutations, and TRPC6 mediates podocyte injury induced by high glucose. Angiotensin II (AngII) has been revealed to enhance TRPC6 currents in certain types of cells, including podocytes and ventricular myocytes. It has been reported that glucose regulated TRPC6 expression in an AngII‑dependent manner in podocytes and that this pathway is critical in diabetic nephropathy. In the present study, the role of TRPC6 detected by western blotting and reverse transcription‑quantitative polymerase chain reaction in AngII‑mediated podocyte injury was evaluated in rats with type 2 diabetes induced by high‑calorie diets and streptozotocin. The results demonstrated that urinary albumin excretion was elevated, and morphological changes, including glomerular basement membrane thickening and podocyte process effacement, were observed. There was increased expression of AngII and TRPC6 in diabetic rats. The angiotensin receptor blocker valsartan significantly reduced TRPC6 and nuclear factor of activated T‑cells (NFAT) overexpression in diabetic rats. These results in vivo were confirmed by studies in vitro, which demonstrated that inhibition of TRPC6 ameliorated high glucose‑induced podocyte injury by decreasing NFAT mRNA levels. Taken together, the present results suggested that the AngII/TRPC6/NFAT axis may be a crucial signaling pathway in podocytes that is necessary for maintaining the integrity of the glomerular filtration barrier. In addition, TRPC6 may represent a potential therapeutic target for diabetic nephropathy.

Complement 7 Is Up-Regulated in Human Early Diabetic Kidney Disease

There is a temporal window from the time diabetes is diagnosed to the appearance of overt kidney disease during which time the disease progresses quietly without detection. Currently, there is no way to detect early diabetic nephropathy (EDN). Herein, we performed an unbiased assessment of gene-expression analysis of postmortem human kidneys to identify candidate genes that may contribute to EDN. We then studied one of the most promising differentially expressed genes in both kidney tissue and blood samples. Differential transcriptome analysis of EDN kidneys and matched nondiabetic controls showed alterations in five canonical pathways, and among them the complement pathway was the most significantly altered. One specific complement pathway gene, complement 7 (C7), was significantly elevated in EDN kidney. Real-time PCR confirmed more than a twofold increase of C7 expression in EDN kidneys compared with controls. Changes in C7 gene product level were confirmed by immunohistochemistry. C7 protein levels were elevated in proximal tubules of EDN kidneys. Serum C7 protein levels were also measured in EDN and control donors. C7 levels were significantly higher in EDN serum than control serum. This latter finding was independently confirmed in a second set of blood samples from a previously collected data set. Together, our data suggest that C7 is associated with EDN, and can be used as a molecular target for detection and/or treatment of EDN.

The relationship between the thickness of glomerular basement membrane and renal outcomes in patients with diabetic nephropathy

AIMS

Glomerular basement membrane (GBM) thickening is considered as one of the earliest detectable pathological features of diabetic nephropathy (DN). However, whether the thickness of GBM will impact the prognosis of DN remains largely unknown. Our aim was to explore the relationship between thickness of GBM and DN progression in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 118 patients with T2DM and biopsy-proven DN who received follow-up for at least 1 year were recruited. The patients were divided into two groups according to the median (787 nm) of the GBM thickness: Group 1: GBM thickness < 787 nm (n = 59), and Group 2: GBM thickness ≥ 787 nm (n = 59). The GBM width was estimated by the direct GBM measurements as recently modified by Haas. Renal outcomes were defined by progression to ESRD and/or doubling of serum creatinine (D-Cr). The influence of GBM thickness on renal outcomes was assessed using Cox regression.

RESULTS

Compared with the Group 1, patients in Group 2 had more serious renal insufficiency and glomerular lesions. During the follow-up, ESRD occurred in 39.8% of patients, and 8.5% of patients progressed to D-Cr. The univariate analysis indicated the greater width of GBM the higher risk of renal outcomes in T2DM patients with DN (HR [95% CI] = 2.180 [1.246-3.814], p = 0.006). However, the multivariate COX analysis demonstrated that the GBM thickness was not an independent risk factor for progression to ESRD or D-Cr (HR [95% CI] = 0.825 [0.404-1.685], p = 0.597) when adjusting for important clinical variables and pathological findings.

CONCLUSIONS

In conclusion, the DN patients with greater width of GBM had relatively poorer renal prognosis, although it did not emerge as an independent indicator of disease progression.

Management of patients with diabetes and CKD: conclusions from a "Kidney Disease: Improving Global Outcomes" (KDIGO) Controversies Conference

The prevalence of diabetes around the world has reached epidemic proportions and is projected to increase to 642 million people by 2040. Diabetes is already the leading cause of end-stage kidney disease (ESKD) in most developed countries, and the growth in the number of people with ESKD around the world parallels the increase in diabetes. The presence of kidney disease is associated with a markedly elevated risk of cardiovascular disease and death in people with diabetes. Several new therapies and novel investigational agents targeting chronic kidney disease patients with diabetes are now under development. This conference was convened to assess our current state of knowledge regarding optimal glycemic control, current antidiabetic agents and their safety, and new therapies being developed to improve kidney function and cardiovascular outcomes for this vulnerable population.

N-glycosylation proteome enrichment analysis in kidney reveals differences between diabetic mouse models

Background

Diabetic nephropathy (DN) is a late complication in both type 1 diabetes mellitus (T1DM) and T2DM. Already at an early stage of DN morphological changes occur at the cell surface and in the extracellular matrix where the majority of the proteins carry N-linked glycosylations. These glycosylated proteins are highly important in cell adhesion and cell–matrix processes but not much is known about how they change in DN or whether the distinct etiology of T1DM and T2DM could have an effect on their abundances.

Method

We enriched for the N-glycosylated kidney proteome in db/db mice dosed with insulin or vehicle, in streptozotocin-induced (STZ) diabetic mice and healthy control mice dosed with vehicle. Glycopeptides were analyzed with label-free shotgun mass spectrometry and differential protein abundances identified in both mouse models were compared using multivariate analyses.

Results

The majority of the N-glycosylated proteins were similarly regulated in both mouse models. However, distinct differences between the two mouse models were for example seen for integrin-β1, a protein expressed mainly in the glomeruli which abundance was increased in the STZ diabetic mice while decreased in the db/db mice and for the sodium/glucose cotransporter-1, mainly expressed in the proximal tubules which abundance was increased in the db/db mice but decreased in the STZ diabetic mice. Insulin had an effect on the level of both glomerular and tubular proteins in the db/db mice. It decreased the abundance of G-protein coupled receptor-116 and of tyrosine-protein phosphatase non-receptor type substrate-1 away from the level in the healthy control mice.

Conclusions

Our finding of differences in the N-glycosylation protein profiles in the db/db and STZ mouse models suggest that the etiology of DN could give rise to variations in the cell adhesion and cell–matrix composition in T1DM and T2DM. Thus, N-glycosylated protein differences could be a clue to dissimilarities in T1DM and T2DM at later stages of DN. Furthermore, we observed insulin specific regulation of N-glycosylated proteins both in the direction of and away from the abundances in healthy control mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-016-9123-z) contains supplementary material, which is available to authorized users.

Diabetic Kidney Disease in Adolescents With Type 2 Diabetes: New Insights and Potential Therapies

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) and dialysis in the Western world. Early DKD, including microalbuminuria and renal hyperfiltration, is common in adolescents with type 2 diabetes (T2D). Furthermore, youth-onset T2D carries a higher risk of progressive DKD than adult-onset T2D of similar diabetes duration. DKD is characterized by a long clinically silent period without signs of disease. Therefore, a major challenge in preventing DKD is the difficulty in identifying high-risk T2D patients at an early stage. The Type 2 Diabetes in Adolescents and Youth (TODAY) study demonstrated a high initial prevalence that increased over time, irrespective of treatment arm. This key observation underscores the importance of discovering new therapeutic targets to supplement conventional management, in order to reduce DKD risk. In this review, we focus on early DKD in T2D and summarize potential novel biomarkers and therapeutic targets.

Structural Predictors of Loss of Renal Function in American Indians with Type 2 Diabetes

BACKGROUND AND OBJECTIVES

Diabetes is the leading cause of kidney failure in the United States, but early structural determinants of renal function loss in type 2 diabetes are poorly defined. We examined the association between morphometrically determined renal structural variables and loss of renal function in 111 American Indians with type 2 diabetes who volunteered for a research kidney biopsy at the end of a 6-year clinical trial designed to test the renoprotective efficacy of losartan versus placebo. Participants were subsequently followed in an observational study, in which annual measurements of GFR (iothalamate) initiated during the clinical trial were continued.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Renal function loss was defined as ≥40% loss of GFR from the research examination performed at the time of kidney biopsy. Associations with renal function loss were evaluated by Cox proportional hazards regression. Hazard ratios (HRs) were reported per 1-SD increment for each morphometric variable.

RESULTS

Of 111 participants (82% women; baseline mean [±SD] age, 46 years old [±10]; diabetes duration, 16 years [±6]; hemoglobin A1c =9.4% [±2.2]; GFR=147 ml/min [±56]; median albumin-to-creatinine ratio, 41 mg/g [interquartile range, 13-158]), 51 (46%) developed renal function loss during a median follow-up of 6.6 years (interquartile range, 3.1-9.0). Fourteen had baseline GFR <90 ml/min, and three had baseline GFR <60 ml/min. Higher mesangial fractional volume (HR, 2.27; 95% confidence interval [95% CI], 1.58 to 3.26), percentage of global glomerular sclerosis (HR, 1.63; 95% CI, 1.21 to 2.21), nonpodocyte cell number per glomerulus (HR, 1.50; 95% CI, 1.10 to 2.05), glomerular basement membrane width (HR, 1.48; 95% CI, 1.05 to 2.08), mean glomerular volume (HR, 1.42; 95% CI, 1.02 to 1.96), and podocyte foot process width (HR, 1.28; 95% CI, 1.03 to 1.60); lower glomerular filtration surface density (HR, 0.62; 95% CI, 0.41 to 0.94); and fewer endothelial fenestrations (HR, 0.68; 95% CI, 0.48 to 0.95) were each associated with GFR decline after adjustment for baseline age, sex, duration of diabetes, hemoglobin A1c, GFR, and treatment assignment during the clinical trial.

CONCLUSIONS

Quantitative measures of glomerular structure predict loss of renal function in type 2 diabetes.

Management of diabetic nephropathy: Recent progress and future perspective

Diabetic nephropathy (DN), a leading cause of end-stage renal disease (ESRD) affecting ∼20-30% diabetics, is associated with increased cardiovascular mortality. The progression of kidney disease in patients with diabetes can take many years. It occurs as a result of interaction between both genetic and environmental factors in individuals with both type 1 and type 2 diabetes. Hyperglycaemia, hypertension, and genetic pre-disposition are the main risk factors besides elevated serum lipids, smoking habits, and the amount of dietary proteins. Interventions such as glycaemic control, blood pressure control and inhibition of the renin-angiotensin-aldosterone system have been shown to slow this progression. Despite the implementation of these strategies, the number of patients with diabetes that ultimately develop end-stage renal disease remains high. The treatment of DN, therefore, has posed a formidable challenge besides optimization of renin-angiotensin-aldosterone system blockade in patients with DN; additional investigation has focused on the potential of novel therapies that target various pathways upregulated by hyperglycaemia or other targets believed to promote the progression of DN such as oxidative stress, inflammation, endothelin system and vitamin D receptors. This review article addresses the pathogenesis and some of the well established principles regarding the progression and accepted management of DN, and also includes the perspectives of novel anti-DN agents and the future directions for the prevention of DN.

A glimpse of matrix metalloproteinases in diabetic nephropathy

Matrix metalloproteinases (MMPs) are proteolytic enzymes belonging to the family of zinc-dependent endopeptidases that are capable of degrading almost all the proteinaceous components of the extracellular matrix (ECM). It is known that MMPs play a role in a number of renal diseases, such as, various forms of glomerulonephritis and tubular diseases, including some of the inherited kidney diseases. In this regard, ECM accumulation is considered to be a hallmark morphologic finding of diabetic nephropathy, which not only is related to the excessive synthesis of matrix proteins, but also to their decreased degradation by the MMPs. In recent years, increasing evidence suggest that there is a good correlation between the activity or expression of MMPs and progression of renal disease in patients with diabetic nephropathy and in various experimental animal models. In such a diabetic milieu, the expression of MMPs is modulated by high glucose, advanced glycation end products (AGEs), TGF-β, reactive oxygen species (ROS), transcription factors and some of the microRNAs. In this review, we focused on the structure and functions of MMPs, and their role in the pathogenesis of diabetic nephropathy.

Diabetic kidney disease in children and adolescents

Diabetes, more frequently type 1, but increasingly also type 2, commonly occurs in childhood. While more advanced diabetic kidney disease (DKD), e.g., loss of glomerular filtration rate (GFR), does not occur until adulthood, kidney biopsies show DKD structural changes as early as 1.5-5 years after the onset of type 1 diabetes. Earliest clinical sign of DKD, increased urine albumin excretion, commonly appears during childhood and adolescence and presents an important opportunity to detect and intervene in early DKD, perhaps more successfully than later in the disease course. Longitudinal studies of type 1 diabetes have enriched our understanding of the DKD natural history and modifiable risk factors for DKD progression. These studies have also shown that the presence of DKD marks a subset of people with diabetes who are at the highest risk of early mortality, supporting an enhanced focus on DKD detection, prevention, and treatment. Early studies suggest that youth-onset type 2 diabetes is associated with a higher prevalence of comorbidities and risk factors and follows a more aggressive natural history. A deeper understanding of the natural history, risk factors, underlying mechanisms and therapeutic options for DKD in young-onset type 2 diabetes awaits further studies.

Renal histological heterogeneity and functional progress in normoalbuminuric and microalbuminuric Japanese patients with type 2 diabetes

BACKGROUND AND OBJECTIVES

Renal histological injury patterns in type 2 diabetes are heterogeneous. We compared renal histological injury patterns using renal biopsy findings with renal function and followed up renal functional changes in normoalbuminuric and microalbuminuric patients with type 2 diabetes to determine whether renal function progresses according to injury patterns.

DESIGN SETTING PARTICIPANTS AND MEASUREMENTS

We examined 111 patients with type 2 diabetes with percutaneous renal biopsy (78 men, 52±11 years old, 59 normoalbuminuria, 52 microalbuminuria) and followed up 37 cases for 11 years. Light microscopy of tissues revealed renal injury patterns as: category I (CI), normal or near-normal structure; category II (CII), typical diabetic glomerulopathy; category III (CIII), atypical (disproportionately severe tubulointerstitial/vascular damage with no/mild glomerulopathy).

RESULTS

There were 29 CI, 62 CII, and 20 CIII patients. CII patients had a higher frequency of chronic kidney disease (CKD) G3-4, while the injury pattern distribution was not different among the albuminuria stages. The mean glomerular volume and volume fraction of cortical interstitium were larger than those of controls. The arteriolar hyalinosis index was larger in CII and CIII, while the percent global glomerular sclerosis was larger in CKD G3-4 compared with CKD G1-2. Renal function at follow-up was decreased in CII and CIII compared with the baseline estimated glomerular filtration rate (eGFR), while the GFR decline rate was faster in CII.

CONCLUSIONS

In normoalbuminuric and microalbuminuric patients with type 2 diabetes, loss of GFR could indicate typical diabetic glomerulosclerosis and a high frequency of global glomerular sclerosis. Urinary biomarkers identifying histological patterns of renal injury are necessary because GFR decline rates differed according to histological injury patterns.

Early diabetic nephropathy in type 1 diabetes: new insights

PURPOSE OF REVIEW

Despite improvements in glycemic and blood pressure control in patients with type 1 diabetes, diabetic nephropathy remains the most common cause of chronic kidney disease worldwide. A major challenge in preventing diabetic nephropathy is the inability to identify high-risk patients at an early stage, emphasizing the importance of discovering new therapeutic targets and implementation of clinical trials to reduce diabetic nephropathy risk.

RECENT FINDINGS

Limitations of managing patients with diabetic nephropathy with renin-angiotensin-aldosterone system blockade have been identified in recent clinical trials, including the failure of primary prevention studies in T1D and the demonstration of harm with dual renin-angiotensin-aldosterone system blockade. Fortunately, several new targets, including serum uric acid, insulin sensitivity, vasopressin, and sodium-glucose cotransporter-2 inhibition, are promising in the prevention and treatment of diabetic nephropathy.

SUMMARY

Diabetic nephropathy is characterized by a long clinically silent period without signs or symptoms of disease. There is an urgent need for improved methods of detecting early mediators of renal injury, to ultimately prevent the initiation and progression of diabetic nephropathy. In this review, we will focus on early diabetic nephropathy and summarize potential new therapeutic targets.

Hyperglycemia decreases the expression of ATP synthase β subunit and enolase 2 in glomerular epithelial cells

Glomerular epithelial cells (GECs) are known to play a key role in maintaining the structure and function of the glomerulus. GEC injury induced by hyperglycemia is present in early-stage diabetic nephropathy (DN), which is the most common cause of renal failure. In an attempt to identify target proteins involved in the pathogenesis of GEC injury at early DN, we performed the proteomic analysis using primary cultures of GECs, prepared from the dissected rat glomeruli. The protein expression profiles in the two-dimensional electrophoresis gels were compared between GECs treated for three days with normal glucose (5 mM) and those with high glucose (30 mM) concentrations. These concentrations correspond to blood glucose concentrations under normoglycemia and hyperglycemia, respectively. Proteins with differential expression levels were identified using ESI-Q-TOF tandem mass spectrometry. The primary GECs cultured in hyperglycemic conditions showed cellular hypertrophy and increased production of reactive oxygen species, both of which reflect the GEC injury. Our proteomic analysis identified eight proteins with differential expression profiles, depending on glucose concentrations. Among them, we selected ATP synthase β subunit and enolase 2 that are related to energy metabolism and are down-regulated under hyperglycemia, and confirmed that hyperglycemia decreased the expression levels of ATP synthase β subunit and enolase 2 proteins by western blotting analysis. Hyperglycemia may impair mitochondrial function and alter glycolysis in GECs by down-regulating the expression of ATP synthase β subunit and enolase 2. The present study may provide a better understanding of the pathogenic mechanisms of GEC injury in early DN.

Molecular and cellular events mediating glomerular podocyte dysfunction and depletion in diabetes mellitus

The essential function of the kidney is to ensure formation of a relatively protein-free ultra-filtrate, urine. The rate of filtration and composition of the primary renal filtrate is determined by the transport of fluid and solutes across the glomerular filtration barrier consisting of endothelial cells, the glomerular basement membrane, and podocyte foot processes. In diabetes mellitus (DM), components of the kidney that enable renal filtration get structurally altered and functionally compromised resulting in proteinuria that often progresses to end-stage renal disease. Histological alterations in DM include early hypertrophy of glomerular and tubular components, subsequent thickening of basement membrane in glomeruli and tubules, progressive accumulation of extracellular matrix proteins in the glomerular mesangium and loss of podocytes, together constituting a clinical condition referred to as diabetic nephropathy (DN). The glomerulus has become the focus of research investigating the mechanism of proteinuria. In particular, the progressive dysfunction and/or loss of podocytes that is contemporaneous with proteinuria in DN have attracted intense scientific attention. The absolute number of podocytes predicts glomerular function and podocyte injury is a hallmark of various glomerular diseases. This review discusses the importance of podocytes in normal renal filtration and details the molecular and cellular events that lead to podocyte dysfunction and decreased podocyte count in DN.

Mesenchymal stem cell-based treatment for microvascular and secondary complications of diabetes mellitus

The worldwide increase in the prevalence of Diabetes mellitus (DM) has highlighted the need for increased research efforts into treatment options for both the disease itself and its associated complications. In recent years, mesenchymal stromal cells (MSCs) have been highlighted as a new emerging regenerative therapy due to their multipotency but also due to their paracrine secretion of angiogenic factors, cytokines, and immunomodulatory substances. This review focuses on the potential use of MSCs as a regenerative medicine in microvascular and secondary complications of DM and will discuss the challenges and future prospects of MSCs as a regenerative therapy in this field. MSCs are believed to have an important role in tissue repair. Evidence in recent years has demonstrated that MSCs have potent immunomodulatory functions resulting in active suppression of various components of the host immune response. MSCs may also have glucose lowering properties providing another attractive and unique feature of this therapeutic approach. Through a combination of the above characteristics, MSCs have been shown to exert beneficial effects in pre-clinical models of diabetic complications prompting initial clinical studies in diabetic wound healing and nephropathy. Challenges that remain in the clinical translation of MSC therapy include issues of MSC heterogeneity, optimal mode of cell delivery, homing of these cells to tissues of interest with high efficiency, clinically meaningful engraftment, and challenges with cell manufacture. An issue of added importance is whether an autologous or allogeneic approach will be used. In summary, MSC administration has significant potential in the treatment of diabetic microvascular and secondary complications but challenges remain in terms of engraftment, persistence, tissue targeting, and cell manufacture.

Nodular lesions and mesangiolysis in diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal failure all over the world. Advanced human diabetic nephropathy is characterized by the presence of specific lesions including nodular lesions, doughnut lesions, and exudative lesions. Thus far, animal models precisely mimicking advanced human diabetic nephropathy, especially nodular lesions, remain to be fully established. Animal models with spontaneous diabetic kidney diseases or with inducible kidney lesions may be useful for investigating the pathogenesis of diabetic nephropathy. Based on pathological features, we previously reported that diabetic glomerular nodular-like lesions were formed during the reconstruction process of mesangiolysis. Recently, we established nodular-like lesions resembling those seen in advanced human diabetic nephropathy through vascular endothelial injury and mesangiolysis by administration of monocrotaline. Here, in this review, we discuss diabetic nodular lesions and its animal models resembling human diabetic kidney lesions, with our hypothesis that endothelial cell injury and mesangiolysis might be required for nodular lesions.

Renal protection of in vivo administration of tempol in streptozotocin-induced diabetic rats

The present study was carried out to investigate the protective effects of tempol on renal function and the underlying mechanism in streptozotocin-induced diabetic rats. The diabetic rats were randomly divided into the model group (without tempol) and tempol group (1 mM tempol in drinking water for 6 weeks). Nondiabetic rats were served as the Control group. The mRNA expression of canonical transient receptor potential 6 (TRPC6), transforming growth factor (TGF)-β1, and type IV collagen (Col IV) were examined. The malondialdehyde (MDA) level, activities of superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) in renal tissues were measured to assess redox status in kidneys. We found that tempol significantly reduced 24-h urine output and urine albuminuria excretion in the diabetic rats. Compared with the model group, the concentration of MDA was significantly lower in the tempol group. In addition, diabetes decreased activities of SOD and GSH-Px and these responses were prevented by tempol treatment. Moreover, in diabetic rats, the mRNA expression levels of TGF-β1 and Col IV were upregulated. TRPC6 mRNA expression level was down-regulated in diabetic kidneys. However, all of these diabetic effects were significantly suppressed by tempol treatment. These results suggest that chronic treatment of diabetic rats with tempol can protect kidneys, possibly by reducing expression of TGF-β1, Col IV, and upregulating TRPC6 expression level.

Histological predictors for renal prognosis in diabetic nephropathy in diabetes mellitus type 2 patients with overt proteinuria

AIM

Although several clinical risk factors for end-stage renal disease in diabetic nephropathy are known, the pathological findings that may help predict renal prognosis have not yet been defined.

METHODS

We enrolled 69 diabetes mellitus type 2 patients with overt proteinuria and biopsy-confirmed diabetic nephropathy with mesangial expansion, and retrospectively examined the association of histological and clinical findings with renal outcome. The median follow-up duration was 52 months. Histological scoring was made according to that of Tervaert et al. Patients were divided into four groups according to glomerular classification (class 2a, mild mesangial expansion, n=11; class 2b, severe mesangial expansion without nodular sclerosis, n=15; class 3, nodular sclerosis, n=36; class 4, global glomerulosclerosis observed in more than 50% of glomeruli, n=7). Interstitial and vascular lesions were scored for each patient. A renal event was defined as a condition requiring the initiation of chronic dialysis or doubling of the serum creatinine level.

RESULTS

Cox proportional hazard analysis showed that the glomerular classes were not significant variables, while interstitial fibrosis, tubular atrophy and interstitial inflammation were independent variables associated with renal end-point (HR: 3.36 (95% confidence interval: 1.21-9.32), 4.74 (1.26-17.91)). There were no significant differences in the renal survival rates between the glomerular classes 2a and 2b combined group and the glomerular class 3 group (P=0.17, log-rank test).

CONCLUSION

Interstitial lesions but not glomerular lesions were a significant predictor for renal prognosis in diabetic nephropathy in type 2 diabetes patients with overt proteinuria.

Arjunolic acid: beneficial role in type 1 diabetes and its associated organ pathophysiology

In this review article, we describe the most recent development of the beneficial effect of arjunolic acid (AA) in reducing type 1 diabetic pathophysiology. Diabetic mellitus is a serious and growing health problem worldwide. Increasing evidence suggest that oxidative stress plays a pivotal role in the pathogenesis of diabetes and its associated complications. Use of antioxidant supplements as a complimentary therapeutic approach in diabetes has, therefore, been seriously considered worldwide. AA, a natural pentacyclic triterpenoid saponin, is well known for various biological functions including antioxidant activity. It could prevent the increased production of ROS, RNS, AGEs, and the 8OHdG/2dG ratio and increase the intracellular antioxidant defence system. Signal transduction studies showed that AA could prevent hyperglycaemia induced activation of MAPKs, PKC, NF-κB signalling cascades and apoptotic cell death. Combining, AA supplements could be regarded as beneficial therapeutics in the treatment of diabetes and its associated complications.

Urine IgM-excretion as a prognostic marker for progression of type 2 diabetic nephropathy

Although the clinical manifestations of type 2 diabetic nephropathy and decline in kidney function are similar to those in type 1, the clinical course and the renal structural changes are more heterogeneous in type 2 diabetic patients. Previous studies have shown that an increased urine IgM excretion in patients with type 1 diabetic nephropathy was associated with poor outcome. In the present follow-up study we examine the prognostic value of baseline urine IgM excretion in patients with type 2 diabetes mellitus.

METHODS

A cohort of 106 (74 male and 32 female) patients with type 2 diabetes regularly attending our diabetes out-patient clinic at Skane University Hospital in Lund. They were recruited prospectively under the period between 1992 and 2004. Patients were followed-up until January 2009. The end point was cardiovascular (CV) death or end-stage renal disease (ESRD). The median follow-up time was 5 years (0.5-13 years). Participants were divided according to degree of albuminuria and IgM-uria.

RESULTS

During follow-up time, 28 (19 male and 9 female) patients died of CV events and 41 (26 male and 15 female) developed ESRD. The risk of CV mortality was 2.4 fold, and the risk of renal failure 4.9 fold higher in patients with increased urine IgM excretion compared to patients with low urine IgM excretion. Stratified analysis showed that an increased urine IgM excretion was an independent predictor of renal and cardiovascular death irrespective of the degree of albuminuria (HR=3.6, 95% CI: 2.1-6.0, P<0.001). In conclusion, type 2 diabetic nephropathy patients with high urine IgM excretion rates carry an increased risk of renal and cardiovascular death.

Pyridorin in type 2 diabetic nephropathy

Pyridoxamine dihydrochloride (Pyridorin, NephroGenex) inhibits formation of advanced glycation end products and scavenges reactive oxygen species and toxic carbonyls, but whether these actions translate into renoprotective effects is unknown. In this double-blind, randomized, placebo-controlled trial, we randomly assigned 317 patients with proteinuric type 2 diabetic nephropathy to twice-daily placebo; Pyridorin, 150 mg twice daily; or Pyridorin, 300 mg twice daily, for 52 weeks. At baseline, the mean age ± SD was 63.9±9.5 years, and the mean duration of diabetes was 17.6±8.5 years; the mean serum creatinine level was 2.2±0.6 mg/dl, and the mean protein-to-creatinine ratio was 2973±1932 mg/g. Regarding the primary end point, a statistically significant change in serum creatinine from baseline to 52 weeks was not evident in either Pyridorin group compared with placebo. However, analysis of covariance suggested that the magnitude of the treatment effect differed by baseline renal function. Among patients in the lowest tertile of baseline serum creatinine concentration, treatment with Pyridorin associated with a lower average change in serum creatinine concentration at 52 weeks (0.28, 0.07, and 0.14 mg/dl for placebo, Pyridorin 150 mg, and Pyridorin 300 mg, respectively; P=0.05 for either Pyridorin dose versus placebo); there was no evidence of a significant treatment effect in the middle or upper tertiles. In conclusion, this trial failed to detect an effect of Pyridorin on the progression of serum creatinine at 1 year, although it suggests that patients with less renal impairment might benefit.

Diabetic nephropathy in humans: pathologic diversity

PURPOSE OF REVIEW

Both type 1 and type 2 diabetes are associated with severe complications including diabetic nephropathy. With the rapidly rising number of patients with diabetes worldwide, diabetic nephropathy is becoming one of the most common causes of renal disease. Much research effort is being put into how to identify diabetic nephropathy in patients with diabetes. A considerable number of biomarker studies were recently published on markers in plasma or urine, either with the aim to distinguish patients with or without diabetic nephropathy, or with the aim to predict renal outcome in those patients with diabetic nephropathy. We review the most recent findings on this subject and discuss the lack of histologically proven diabetic nephropathy in the majority of these studies.

RECENT FINDINGS

Most conspicuous in the field of diabetic nephropathy was the recent identification of a number of biomarkers used either in the diagnosis of diabetic nephropathy or in the evaluation of therapies meant to prevent, slow down, or reverse the processes causing diabetic nephropathy. For the histopathology of diabetic nephropathy, a new classification system was launched in 2010, which will be discussed together with future perspectives.

SUMMARY

Combining histopathological grading of and biomarkers for diabetic nephropathy will further our understanding of this complex disease manifestation.

Modulation of Nrf2 expression alters high glucose-induced oxidative stress and antioxidant gene expression in mouse mesangial cells

Reactive oxygen species (ROS) play an important role in the pathogenesis of diabetic nephropathy. Nuclear factor erythroid 2-related factor 2 (Nrf2) can up-regulate the expression of antioxidant genes and protect cells from oxidative damage. The current study is aimed at examining the effect of modulation of Nrf2 expression on high glucose-induced oxidative stress and Nrf2-targeting antioxidant expression in mouse mesangial cells. In this study, mouse mesangial cells were transiently transfected with Nrf2-plasmid or the Nrf2-specific siRNA. The high glucose-induced intracellular ROS, malondialdehyde, cell proliferation, and TGF-β1 secretion were measured. The levels of Nrf2, heme oxygenase-1 (HO-1), γ-glutamylcysteine synthethase (γ-GCS) expression, and nuclear expression of Nrf2 in mouse mesangial cells were determined. We found that high glucose induced ROS and malondialdehyde generation in mouse mesangial cells. Induction of Nrf2 over-expression reduced the high glucose-induced ROS and malondialdehyde production, inhibited cell proliferation and TGF-β1 secretion, accompanied by up-regulating the expressions of HO-1 and γ-GCS in mouse mesangial cells. However, knockdown of Nrf2 expression displayed reverse effects in mouse mesangial cells. All these results indicated that Nrf2 and its downstream antioxidants, HO-1 and γ-GCS, are negative regulators of high glucose-induced ROS-related mouse mesangial cell dysfunction.

The response to antihypertensive therapy is dependent on renal structural changes. A 5-year prospective study of renal biopsy in type 2 diabetic patients with micro-macroalbuminuria

A substantial fraction of patients with diabetes mellitus develop end-stage renal disease. We wanted to study the influence of renal structural changes on the response to treatment of the systemic blood pressure (BP) in type 2 diabetic patients with micro- or macroalbuminuria.

METHODS

A 5-year observational prospective study of 40 type 2 diabetic patients. Renal biopsy was performed on the indication micro-macroalbuminuria. Twenty-four-hour ambulatory BP and urine sampling were performed yearly. The goal for treatment was a nightly systolic BP below 140 mmHg. Glomerular filtration rate was examined early with plasma clearance of iohexol.

RESULTS

The nightly systolic BP goal <140 mmHg was achieved in 23 of 40 patients. The nightly systolic BP at start of study was correlated to the mean level of nightly systolic BP during the observation period. The glomerular basement membrane (GBM) thickness (BMT) was of prognostic significance for achieving the goal for antihypertensive treatment. Of the 12 patients with BMT below the median of 478 nm, 9 (75%) achieved the goal, while only 5 of 12 (42%) with BMT above 478 nm achieved a nightly systolic BP <140 mmHg. Also, the degree of interstitial fibrosis correlated to the nightly systolic BP.

CONCLUSION

A thick basement membrane and the degree of interstitial fibrosis were associated with a lower number of patients achieving the goal of a nightly systolic BP <140 mmHg.

Pathologic classification of diabetic nephropathy

Although pathologic classifications exist for several renal diseases, including IgA nephropathy, focal segmental glomerulosclerosis, and lupus nephritis, a uniform classification for diabetic nephropathy is lacking. Our aim, commissioned by the Research Committee of the Renal Pathology Society, was to develop a consensus classification combining type1 and type 2 diabetic nephropathies. Such a classification should discriminate lesions by various degrees of severity that would be easy to use internationally in clinical practice. We divide diabetic nephropathy into four hierarchical glomerular lesions with a separate evaluation for degrees of interstitial and vascular involvement. Biopsies diagnosed as diabetic nephropathy are classified as follows: Class I, glomerular basement membrane thickening: isolated glomerular basement membrane thickening and only mild, nonspecific changes by light microscopy that do not meet the criteria of classes II through IV. Class II, mesangial expansion, mild (IIa) or severe (IIb): glomeruli classified as mild or severe mesangial expansion but without nodular sclerosis (Kimmelstiel-Wilson lesions) or global glomerulosclerosis in more than 50% of glomeruli. Class III, nodular sclerosis (Kimmelstiel-Wilson lesions): at least one glomerulus with nodular increase in mesangial matrix (Kimmelstiel-Wilson) without changes described in class IV. Class IV, advanced diabetic glomerulosclerosis: more than 50% global glomerulosclerosis with other clinical or pathologic evidence that sclerosis is attributable to diabetic nephropathy. A good interobserver reproducibility for the four classes of DN was shown (intraclass correlation coefficient = 0.84) in a test of this classification.

Prophylactic role of arjunolic acid in response to streptozotocin mediated diabetic renal injury: activation of polyol pathway and oxidative stress responsive signaling cascades

Diabetic nephropathy is a common cause for end-stage renal disease. Present study investigated the beneficial role of arjunolic acid (AA) against streptozotocin (STZ) induced diabetic nephropathy in rats. Diabetic renal injury was associated with increased kidney weight to body weight ratio, glomerular area and volume, blood glucose (hyperglycemia), urea nitrogen and serum creatinine. This nephro pathophysiology increased the productions of reactive oxygen species (ROS) and reactive nitrogen species (RNS), enhanced lipid peroxidation, protein carbonylation and decreased intracellular antioxidant defense in the kidney tissue. In addition, hyperglycemia activates polyol pathway by increasing aldose reductase (AR) with a concomitant reduction in Na+-K+-ATPase activity. Investigating the oxidative stress responsive signaling cascades, we found the activation of PKCdelta, PKCvarepsilon, MAPKs and NF-kappaB (p65) in the renal tissue of the diabetic animals. Furthermore, hyperglycemia disturbed the equilibrium between the pro and anti-apoptotic members of Bcl-2 family of proteins as well as reduced mitochondrial membrane potential, elevated the concentration of cytosolic cytochrome C and caspase-3 activity. Treatment of AA effectively ameliorated diabetic renal dysfunctions by reducing oxidative as well as nitrosative stress and deactivating the polyol pathways. Histological studies also support the experimental findings. Results suggest that AA might act as a beneficial agent against the renal dysfunctions developed in STZ-induced diabetes.

Epithelial-mesenchymal transition as a potential explanation for podocyte depletion in diabetic nephropathy

BACKGROUND

Depletion of glomerular podocytes is an important feature of progressive diabetic nephropathy. Although the most plausible explanation for this podocyte depletion is detachment from the glomerular basement membrane after cellular apoptosis, the mechanism is unclear. Fibroblast-specific protein 1 (FSP1; encoded by the S100A4 gene) is a member of the S100 family of calcium-binding proteins and is constitutively expressed in the cytoplasm of tissue fibroblasts or epithelial cells converted into fibroblasts by means of epithelial-mesenchymal transition.

STUDY DESIGN

Retrospective cross-sectional analysis.

SETTINGS & PARTICIPANTS

109 patients with type 2 diabetes mellitus, of whom 43 (39%) underwent kidney biopsy.

PREDICTOR

Clinical stage (4 categories) and histological grade (5 categories) of diabetic nephropathy.

OUTCOME

FSP1 expression in podocytes in urine and glomeruli in kidney biopsy specimens.

MEASUREMENTS

Immunohistochemistry, real-time polymerase chain reaction, and in situ hybridization.

RESULTS

38 of 109 patients (35%) were normoalbuminuric, 16 (15%) had microalbuminuria, 8 (7%) had macroalbuminuria, and 47 (43%) had decreased kidney function. Approximately 95% of podocytes in urine sediment were not apoptotic, and 86% expressed FSP1. The number of FSP1-positive podocytes in urine sediment was significantly larger in patients with macroalbuminuria than in those with normoalbuminuria (P = 0.03). Intraglomerular expression of FSP1 occurred almost exclusively in podocytes from patients with diabetes, and the number of FSP1-positive podocytes was larger in glomeruli showing diffuse mesangiopathy than in those showing focal mesangiopathy (P = 0.01). The number also was larger in glomeruli with nodular lesions than in those without nodular lesions (P < 0.001). FSP1-positive podocytes selectively expressed Snail1 and integrin-linked kinase, a known trigger for epithelial-mesenchymal transition.

LIMITATIONS

Nonrepresentative study population.

CONCLUSIONS

These results suggest that the appearance of FSP1 in podocytes of patients with diabetes is associated with more severe clinical and pathological findings of diabetic nephropathy, perhaps because of induction of podocyte detachment through epithelial-mesenchymal transition-like phenomena.

Renal structure as an indicator for development of albuminuria in normo- and microalbuminuric type 2 diabetic patients

Baseline glomerular structure in microalbuminuric (MA) and proteinuric Caucasian type 2 diabetic patients predicted progressive glomerular filtration rate decline while baseline urinary albumin excretion (UAE) did not. Little is known about whether or not renal structure at the early stages of diabetic nephropathy (DN) in type 2 diabetic patients can predict further functional development of DN. Baseline renal structure and function and follow-up data of renal function were examined in 17 type 2 diabetic patients (11 men, 45+/-7 (mean+/-S.D.) years old) with known diabetes duration 11+/-8 years without definable renal disease other than DN. Six patients showed normoalbuminuria (NA), 11 microalbuminuria (MA), and were followed up for 6.4+/-1.8 years after the baseline renal biopsy. Light and electron microscopic morphometric analyses provided quantitative glomerular and tubulointerstitial structural changes. No statistically significant difference was observed in hemoglobin A1c (HbA1c) values or mean blood pressure (MBP) between baseline and follow-up, even though the number of patients placed on antihypertensive drugs increased from 3 to 7. Follow-up UAE was not significantly different from the baseline UAE although 13 of 17 cases showed an increase. Baseline UAE did not correlate with the follow-up UAE or morphometric measures. Glomerular basement membrane width and volume fraction of the mesangium and mesangial matrix positively correlated with follow-up UAE. In NA and MA Japanese type 2 diabetic patients, baseline renal structural measures are more reliable indicators for the development of UAE than baseline UAE.

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.

Prevalence of atubular glomeruli in type 2 diabetic patients with nephropathy

BACKGROUND

Atubular glomeruli have been identified in a number of chronic renal diseases and have been linked to declining renal function. In type 1 diabetes they are present predominantly in proteinuric patients. We investigated the prevalence of atubular glomeruli in type 2 diabetes and their relationship to renal function.

METHODS

Renal biopsies from 12 type 2 diabetic patients with nephropathy were processed for light and electron microscopy and analysed using standard stereological techniques. Abnormalities at the glomerular tubular junction were quantified using an index of junctional atrophy (IJA).

RESULTS

There was no relationship between the degree of proteinuria and the presence of atubular glomeruli or atrophic tubules. Creatinine clearance correlated with the IJA (r = -0.70, P = 0.011), percent sclerosed glomeruli (r = -0.59, P = 0.027) and interstitial volume fraction (r = -0.54, P = 0.037). The IJA also correlated with foot process width and volume fraction interstitium (r = 0.58, P = 0.049 for both). Percent sclerosed glomeruli correlated with mesangial (r = 0.65, P = 0.012) and interstitial (r = 0.69, P = 0.007) volume fractions.

CONCLUSIONS

In contrast to type 1 diabetes, atubular glomeruli and atrophic tubules occur in type 2 diabetic patients with low levels of proteinuria; their development may influence the progressive change in GFR. Both glomerular and interstitial damage may lead to the development of atubular glomeruli in type 2 diabetic nephropathy.

Detailed glomerular ultrastructure in Japanese type 2 diabetic patients by the quick-freezing and deep-etching method

Mesangial expansion and glomerular basement membrane (GBM) thickening did not correlate with urinary albumin excretion (UAE) in type 2 diabetic patients in our previous studies; therefore, it was necessary to elucidate more detailed ultrastructural changes in the early stages of diabetic nephropathy (DN) in type 2 diabetic patients. The quick-freezing and deep-etching (QF-DE) method allows us to examine three-dimensional ultrastructures of human renal glomeruli in vivo at high resolution. The QF-DE method was applied to six type 2 diabetic patients without definable renal diseases other than DN. Four patients were normoalbuminuric (NA) and the other two were microalbuminuria (MA). Three control specimens were the normal parts from nephrectomies due to renal cell carcinomas. Electron microscopic morphometric analyses provided quantitative glomerular structural changes. Replica membranes were prepared by the QF-DE method, and diameters of mesh structures at the GBM and mesangial matrix (MM) were measured on electron micrographs as previously described. By the QF-DE method, both the GBM middle layer and MM were composed of polygonal meshwork structures. The mesh pores of the GBM and MM were more enlarged and irregular in shape in NA diabetic patients than those of the controls, and these ultrastructural changes became more obvious in MA patients. The mesh diameters of the GBM and MM in the diabetic patients were also larger than those of the controls. Such a mesh diameter of the GBM was well correlated with the amount of UAE, while the mesh diameter of MM showed a slight correlation with UAE. Although there were small number of subjects in the present study, the detailed ultrastructural changes in NA and MA type 2 diabetic patients, which had not been disclosed by conventional electron microscopy, were revealed by the QF-DE method. Increased mesh diameters of GBM might be related with the increase of UAE.

Are glomerular volume differences between type 1 and type 2 diabetic patients pathologically significant?

The observation that patients with type 2 diabetes tend to have larger glomeruli than patients with type 1 diabetes was first made more than 10 years ago. It has also been noted that type 2 diabetic patients with nephropathy often have more heterogeneous renal function and structure than type 1 patients. However, whether these observations are linked or have any bearing on the progression of nephropathy in the two types of diabetes remains uncertain. Here we put forward several hypotheses as to why glomerular volume in type 1 differs from that in type 2 diabetes. We suggest that although type 1 and type 2 diabetic patients appear to progress through similar stages of diabetic nephropathy, the route they take may differ. Differences in the way in which the glomeruli respond to the diabetic milieu may enable some type 2 diabetic patients to preserve their filtration surface in the face of an expanding mesangium.

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.

Nodular glomerulosclerosis in patients without any manifestation of diabetes mellitus

AIM/METHODS

Diabetic nodular glomerulosclerosis is considered to be the specific renal lesion of diabetes mellitus (DM). However, some cases, in which nodular glomerulosclerosis was found without any manifestation of DM, have also occasionally been reported. We clinicopathologically examined seven cases without a prior history of DM. They consisted of six men and one woman with a mean age of 57 years, and included three cases with family history of DM and six cases with hypertension.

RESULTS

Mean body mass index was 26.2 +/- 5.9 (means +/- SD) kg/m(2) and haemoglobin A1c 5.3 +/- 1.1% or haemoglobin A1 7.0 +/- 0.6%. Mean plasma glucose levels were 5.3 +/- 0.7 mmol/L at fasting and 10.1 +/- 1.9 mmol/L at 2 h of 75 g OGTT (normal: 1 patient; impaired glucose tolerance: 4 patients; DM: 2 patients). None of them showed diabetic retinopathy in fundoscopic ophthalmoscopy. Mean serum creatinine was 268 +/- 215 micromol/L, urinary protein 5.2 +/- 4.0 g/day, and three patients had mild haematuria. Renal biopsy revealed typical nodular glomerulosclerosis, a negative deposition based on an immunofluorescence study, and neither any significant electron dense deposits nor fibrils on electron microscopy.

CONCLUSION

These patients at presentation had no overt clinical manifestations of glucose intolerance. Diabetic nodular glomerulosclerosis can occur in patients without overt DM, suggesting the role of factors additional to prolonged hyperglycaemia in the pathogenesis of this disorder.