Diabetic nephropathy: of mice and men

Arachidonic acid metabolism as a therapeutic target in AKI-to-CKD transition

Arachidonic acid (AA) is a main component of cell membrane lipids. AA is mainly metabolized by three enzymes: cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (CYP450). Esterified AA is hydrolysed by phospholipase A2 into a free form that is further metabolized by COX, LOX and CYP450 to a wide range of bioactive mediators, including prostaglandins, lipoxins, thromboxanes, leukotrienes, hydroxyeicosatetraenoic acids and epoxyeicosatrienoic acids. Increased mitochondrial oxidative stress is considered to be a central mechanism in the pathophysiology of the kidney. Along with increased oxidative stress, apoptosis, inflammation and tissue fibrosis drive the progressive loss of kidney function, affecting the glomerular filtration barrier and the tubulointerstitium. Recent studies have shown that AA and its active derivative eicosanoids play important roles in the regulation of physiological kidney function and the pathogenesis of kidney disease. These factors are potentially novel biomarkers, especially in the context of their involvement in inflammatory processes and oxidative stress. In this review, we introduce the three main metabolic pathways of AA and discuss the molecular mechanisms by which these pathways affect the progression of acute kidney injury (AKI), diabetic nephropathy (DN) and renal cell carcinoma (RCC). This review may provide new therapeutic targets for the identification of AKI to CKD continuum.

Increased Renal Medullary NOX-4 in Female but Not Male Mice during the Early Phase of Type 1 Diabetes: Potential Role of ROS in Upregulation of TGF-β1 and Fibronectin in Collecting Duct Cells

Chronic diabetes mellitus (DM) can lead to kidney damage associated with increased reactive oxygen species (ROS), proteinuria, and tubular damage. Altered protein expression levels of transforming growth factor-beta 1 (TGF-β1), fibronectin, and renal NADPH oxidase (NOX-4) are associated with the profibrotic phenotype in renal tubular cells. NOX-4 is one of the primary sources of ROS in the diabetic kidney and responsible for the induction of profibrotic factors in collecting duct (CD) cells. The renal medulla is predominantly composed of CDs; in DM, these CD cells are exposed to high glucose (HG) load. Currently there is no published literature describing the expression of these markers in the renal medulla in male and female mice during the early phase of DM, or the role of NOX-4-induced ROS. Our aim was to evaluate changes in transcripts and protein abundances of TGF-β1, fibronectin, and NOX-4 along with ROS levels in renal medullary tissues from male and female mice during a short period of streptozotocin (STZ)-induced type 1 DM and the effect of HG in cultured CD cells. CF-1 mice were injected with or without a single dose of STZ (200 mg/kg) and euthanized at day 6. STZ females showed higher expression of fibronectin and TGF-β1 when compared to control mice of either gender. Interestingly, STZ female mice showed a >30-fold increase on mRNA levels and a 3-fold increase in protein levels of kidney medullary NOX-4. Both male and female STZ mice showed increased intrarenal ROS. In primary cultures of inner medullary CD cells exposed to HG over 48 h, the expression of TGF-β1, fibronectin, and NOX-4 were augmented. M-1 CD cells exposed to HG showed increased ROS, fibronectin, and TGF-β1; this effect was prevented by NOX-4 inhibition. Our data suggest that at as early as 6 days of STZ-induced DM, the expression of profibrotic markers TGF-β1 and fibronectin increases in renal medullary CD cells. Antioxidants mechanisms in male and female in renal medullary tissues seems to be differentially regulated by the actions of NOX-4.

Spin-lock relaxation rate dispersion reveals spatiotemporal changes associated with tubulointerstitial fibrosis in murine kidney

PURPOSE

To develop and evaluate a reliable non-invasive means for assessing the severity and progression of fibrosis in kidneys. We used spin-lock MR imaging with different locking fields to detect and characterize progressive renal fibrosis in an hHB-EGF^Tg/Tg mouse model.

METHODS

Male hHB-EGF^Tg/Tg mice, a well-established model of progressive fibrosis, and age-matched normal wild type (WT) mice, were imaged at 7T at ages 5-7, 11-13, and 30-40 weeks. Spin-lock relaxation rates R_{1 ρ} were measured at different locking fields (frequencies) and the resultant dispersion curves were fit to a model of exchanging water pools. The obtained MRI parameters were evaluated as potential indicators of tubulointerstitial fibrosis in kidney. Histological examinations of renal fibrosis were also carried out post-mortem after MRI.

RESULTS

Histology detected extensive fibrosis in the hHB-EGF^Tg/Tg mice, in which collagen deposition and reductions in capillary density were observed in the fibrotic regions of kidneys. R₂ and R_{1 ρ} values at different spin-lock powers clearly dropped in the fibrotic region as fibrosis progressed. There was less variation in the asymptotic locking field relaxation rate R 1 ρ ∞ between the groups. The exchange parameter S_ρ and the inflection frequency ω_infl changed by larger factors.

CONCLUSION

Both S_ρ and ω_infl depend primarily on the average exchange rate between water and other chemically shifted resonances such as hydroxyls and amides. Spin-lock relaxation rate dispersion, rather than single measurements of relaxation rates, provides more comprehensive and specific information on spatiotemporal changes associated with tubulointerstitial fibrosis in murine kidney.

Noninvasive quantitative magnetization transfer MRI reveals tubulointerstitial fibrosis in murine kidney

Excessive tissue scarring, or fibrosis, is a critical contributor to end stage renal disease, but current clinical tests are not sufficient for assessing renal fibrosis. Quantitative magnetization transfer (qMT) MRI provides indirect information about the macromolecular composition of tissues. We evaluated measurements of the pool size ratio (PSR, the ratio of immobilized macromolecular to free water protons) obtained by qMT as a biomarker of tubulointerstitial fibrosis in a well-established murine model with progressive renal disease. MR images were acquired from 16-week-old fibrotic hHB-EGF^Tg/Tg mice and normal wild-type (WT) mice (N = 12) at 7 T. QMT parameters were derived using a two-pool five-parameter fitting model. A normal range of PSR values in the cortex and outer stripe of outer medulla (CR + OSOM) was determined by averaging across voxels within WT kidneys (mean ± 2SD). Regions in diseased mice whose PSR values exceeded the normal range above a threshold value (tPSR) were identified and measured. The spatial distribution of fibrosis was confirmed using picrosirius red stains. Compared with normal WT mice, scattered clusters of high PSR regions were observed in the OSOM of hHB-EGF^Tg/Tg mouse kidneys. Moderate increases in mean PSR (mPSR) of CR + OSOM regions were observed across fibrotic kidneys. The abnormally high PSR regions (% area) detected by the tPSR were significantly increased in hHB-EGF^Tg/Tg mice, and were highly correlated with regions of fibrosis detected by histological fibrosis indices measured from picrosirius red staining. Renal tubulointerstitial fibrosis in OSOM can thus be assessed by qMT MRI using an appropriate analysis of PSR. This technique may be used as an imaging biomarker for chronic kidney diseases.

Serum pigment epithelium-derived factor: Relationships with cardiovascular events, renal dysfunction, and mortality in the Veterans Affairs Diabetes Trial (VADT) cohort

BACKGROUND

To determine if serum pigment epithelium-derived factor (PEDF) levels predict cardiovascular events, renal dysfunction and mortality in the Veterans Affairs Diabetes Study (VADT).

METHODS

PEDF was evaluated in relation to subsequent cardiovascular outcomes, mortality, and renal dysfunction (defined as urinary albumin creatinine ratio (ACR) ≥300 mg/g), or chronic kidney disease (CKD) stages 3 (eGFR<60 ml/min) or 4 (eGFR<60 and <30 ml/min respectively). PEDF was measured by ELISA on sera from 881 participants collected a median (range) of 1.7 (0-5.0) years post-baseline, and later, from 832 participants 4.0 (1.5-6.9) years post-baseline.

RESULTS

In 743 participants, PEDF was measured at both time-points. PEDF increased over time from (mean ± SD) 10.5 ± 4.03 to 11.0 ± 4.86 ng/ml (paired t-test p = 0.0092). Lower eGFR (p < 0.01), higher serum creatinine (p < 0.01) and urinary ACR (p < 0.01) were associated with increasing PEDF. Multivariate event time models included either one or two follow-up windows (i.e., between first and second PEDF measures; and, when available, from second PEDF measure until study-end). PEDF tertiles were not associated with cardiovascular events, but were significantly associated with all-cause mortality [HR = 2.00 (1.03, 3.89) comparing first to third tertile] in models adjusted for age, minority status, VADT treatment arm and prior cardiovascular event status. Higher PEDF levels also associated with development of kidney dysfunction with adjusted HRs (95% CI comparing third to first PEDF tertiles: 2.74 (1.71, 4.39) for stage 3 CKD; and 3.84 (95% CI: 1.17, 12.5) for stage 4 CKD.

CONCLUSIONS

Over 2-years, higher serum PEDF levels predicted advanced nephropathy in patients with type 2 diabetes.

Assessment of renal fibrosis in murine diabetic nephropathy using quantitative magnetization transfer MRI

PURPOSE

Renal fibrosis is a hallmark of progressive renal disease; however, current clinical tests are insufficient for assessing renal fibrosis. Here we evaluated the utility of quantitative magnetization transfer MRI in detecting renal fibrosis in a murine model of progressive diabetic nephropathy (DN).

METHODS

The db/db eNOS-/- mice, a well-recognized model of progressive DN, and normal wild-type mice were imaged at 7T. The quantitative magnetization transfer data were collected in coronal plane using a 2D magnetization transfer prepared spoiled gradient echo sequence with a Gaussian-shaped presaturation pulse. Parameters were derived using a two-pool fitting model. A normal range of cortical pool size ratio (PSR) was defined as Mean±2SD of wild-type kidneys (N = 20). The cortical regions whose PSR values exceeded this threshold (threshold PSR) were assessed. The correlations between the PSR-based and histological (collagen IV or picrosirius red stain) fibrosis measurements were evaluated.

RESULTS

Compared with wild-type mice, moderate increases in mean PSR values and scattered clusters of high PSR region were observed in cortex of DN mouse kidneys. Abnormally high PSR regions (% area) that were detected by the threshold PSR were significantly increased in renal cortexes of DN mice. These regions progressively increased on aging and highly correlated with histological fibrosis measures, while the mean PSR values correlated much less.

CONCLUSION

Renal fibrosis in DN can be assessed by the quantitative magnetization transfer MRI and threshold analysis. This technique may be used as a novel imaging biomarker for DN and other renal diseases.

Sphingosine kinase 1 mediates AGEs-induced fibronectin upregulation in diabetic nephropathy

Activation of sphingosine kinase 1 (SphK1) signaling pathway mediates fibronectin (FN) upregulation in glomerular mesangial cells (GMCs) under high glucose (HG) condition. However, the roles of SphK1 in advanced glycation end products (AGEs)-induced DN have not been elucidated. Here we show that AGEs upregulated FN and SphK1 and SphK1 activity. Inhibition of SphK1 signaling attenuated AGEs-induced FN synthesis in GMCs. Inhibition of AGE receptor (RAGE) signaling reduced the upregulation of FN and SphK1 and SphK1 activity in GMCs induced by AGEs. Treatment of aminoguanidine ameliorates the renal injury and fibrosis in STZ-induced diabetic mice and attenuated SphK1 expression and activity in diabetic mouse kidneys. The renal injury and fibrosis in diabetic SphK1^-/- mice was significantly attenuated than WT mice. Furthermore, AGEs upregulated SphK1 by reducing its degradation and prolonging its half-life. Conclusion: SphK1 mediates AGEs-induced FN synthesis in GMCs and diabetic mice under hyperglycemic condition.

Mechanisms of metabolic memory and renal hypoxia as a therapeutic target in diabetic kidney disease

Diabetic kidney disease (DKD) is a worldwide public health problem. The definition of DKD is under discussion. Although the term DKD was originally defined as ‘kidney disease specific to diabetes,’ DKD frequently means chronic kidney disease with diabetes mellitus and includes not only classical diabetic nephropathy, but also kidney dysfunction as a result of nephrosclerosis and other causes. Metabolic memory plays a crucial role in the progression of various complications of diabetes, including DKD. The mechanisms of metabolic memory in DKD are supposed to include advanced glycation end‐products, deoxyribonucleic acid methylation, histone modifications and non‐coding ribonucleic acid including micro ribonucleic acid. Regardless of the presence of diabetes mellitus, the final common pathway in chronic kidney disease is chronic kidney hypoxia, which influences epigenetic processes, including deoxyribonucleic acid methylation, histone modification, and conformational changes in micro ribonucleic acid and chromatin. Therefore, hypoxia and oxidative stress are appropriate targets of therapies against DKD. Prolyl hydroxylase domain inhibitor enhances the defensive mechanisms against hypoxia. Bardoxolone methyl protects against oxidative stress, and can even reverse impaired renal function; a phase 2 trial with considerable attention to heart complications is currently ongoing in Japan.

Aldose reductase (-106) C/T gene polymorphism and possibility of macrovascular complications in Egyptian type 2 diabetic patients

INTRODUCTION

Over the past three decades, the number of people with diabetes mellitus (DM) has more than doubled globally, making it one of the most important public health challenges to all nations. Aldose reductase (AR) is a rate-limiting enzyme in the polyol pathway, which has been implicated in the pathogenesis of diabetic microvascular complications; however, the association of the AR gene with diabetic macrovascular complications has rarely been investigated.

AIM

The study aimed to identify the possible association between C(-106) T polymorphism of the AR gene and diabetic macroangiopathy in a cohort of Egyptian patients with type 2 DM.

SETTINGS AND DESIGN

This study was conducted on 100 Egyptian subjects, the control group (n = 20) and the patient group (n = 80) with type 2 diabetes which were further subdivided into two subgroups with (n = 48) and without macroangiopathic complications (n = 32) as evidenced by carotid intima-media thickness, electrocardiography (ECG) ischemic changes, cerebrovascular insufficiency, and peripheral vascular insufficiency.

SUBJECTS AND METHODS

All studied subjects were subjected to detailed history taking, clinical examination, ECG, carotid ultrasonography, routine laboratory investigations, and molecular studies including the detection of AR C(-106) T gene polymorphisms using the polymerase chain reaction (PCR)/restriction fragment length polymorphism technique.

RESULTS

The genotype distribution and allele frequency of AR C(-106) T showed no statistical significance also the genotypes were not associated with any of the different studied parameters.

CONCLUSIONS

The results suggest that the C(-106) T polymorphism in the AR gene is not involved in the pathogenesis of macroangiopathy in type 2 diabetes.

Renal iron overload in rats with diabetic nephropathy

Diabetic nephropathy (DN) remains incurable and is the main cause of end-stage renal disease. We approached the pathophysiology of DN with systems biology, and a comprehensive profile of renal transcripts was obtained with RNA-Seq in ZS (F1 hybrids of Zucker and spontaneously hypertensive heart failure) rats, a model of diabetic nephropathy. We included sham-operated lean control rats (LS), sham-operated diabetic (DS), and diabetic rats with induced renal ischemia (DI). Diabetic nephropathy in DI was accelerated by the single episode of renal ischemia. This progressive renal decline was associated with renal iron accumulation, although serum and urinary iron levels were far lower in DI than in LS. Furthermore, obese/diabetic ZS rats have severe dyslipidemia, a condition that has been linked to hepatic iron overload. Hence, we tested and found that the fatty acids oleic acid and palmitate stimulated iron accumulation in renal tubular cells in vitro. Renal mRNAs encoding several key proteins that promote iron accumulation were increased in DI. Moreover, renal mRNAs encoding the antioxidant proteins superoxide dismutase, catalase, and most of the glutathione synthetic system were suppressed, which would magnify the prooxidant effects of renal iron loads. Substantial renal iron loads occur in obese/diabetic rats. We propose that in diabetes, specific renal gene activation is partly responsible for iron accumulation. This state might be further aggravated by lipid-stimulated iron uptake. We suggest that progressive renal iron overload may further advance renal injury in obese/diabetic ZS rats.

Species differences in regulation of renal proximal tubule transport by certain molecules

Renal proximal tubules (PTs) play important roles in the regulation of acid/base, plasma volume and blood pressure. Recent studies suggest that there are substantial species differences in the regulation of PT transport. For example, thiazolidinediones (TZDs) are widely used for the treatment of type 2 diabetes mellitus, but the use of TZDs is associated with fluid overload. In addition to the transcriptional enhancement of sodium transport in distal nephrons, TZDs rapidly stimulate PT sodium transport via a non-genomic mechanism depending on peroxisome proliferator activated receptor γ/Src/epidermal growth factor receptor (EGFR)/MEK/ERK. In mouse PTs, however, TZDs fail to stimulate PT transport probably due to constitutive activation of Src/EGFR/ERK pathway. This unique activation of Src/ERK may also affect the effect of high concentrations of insulin on mouse PT transport. On the other hand, the effect of angiotensin II (Ang II) on PT transport is known to be biphasic in rabbits, rats, and mice. However, Ang II induces a concentration-dependent, monophasic transport stimulation in human PTs. The contrasting responses to nitric oxide/guanosine 3’,5’-cyclic monophosphate pathway may largely explain these different effects of Ang II on PT transport. In this review, we focus on the recent findings on the species differences in the regulation of PT transport, which may help understand the species-specific mechanisms underlying edema formation and/or hypertension occurrence.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Targeting NADPH oxidase with a novel dual Nox1/Nox4 inhibitor attenuates renal pathology in type 1 diabetes

Reactive oxygen species (ROS) generated by Nox NADPH oxidases may play a critical role in the pathogenesis of diabetic nephropathy (DN). The efficacy of the Nox1/Nox4 inhibitor GKT137831 on the manifestations of DN was studied in OVE26 mice, a model of type 1 diabetes. Starting at 4-5 mo of age, OVE26 mice were treated with GKT137831 at 10 or 40 mg/kg, once-a-day for 4 wk. At both doses, GKT137831 inhibited NADPH oxidase activity, superoxide generation, and hydrogen peroxide production in the renal cortex from diabetic mice without affecting Nox1 or Nox4 protein expression. The increased expression of fibronectin and type IV collagen was reduced in the renal cortex, including glomeruli, of diabetic mice treated with GKT137831. GKT137831 significantly reduced glomerular hypertrophy, mesangial matrix expansion, urinary albumin excretion, and podocyte loss in OVE26 mice. GKT137831 also attenuated macrophage infiltration in glomeruli and tubulointerstitium. Collectively, our data indicate that pharmacological inhibition of Nox1/4 affords broad renoprotection in mice with preexisting diabetes and established kidney disease. This study validates the relevance of targeting Nox4 and identifies GKT137831 as a promising compound for the treatment of DN in type 1 diabetes.

Renal C3 complement component: feed forward to diabetic kidney disease

BACKGROUND

Diabetic nephropathy is the main cause of end-stage renal disease and has reached epidemic proportions.

METHODS

Comprehensive genomic profiling (RNAseq) was employed in the ZS (F1 hybrids of Zucker and spontaneously hypertensive heart failure) model of diabetic nephropathy. Controls were lean littermates.

RESULTS

Diabetic nephropathy in obese, diabetic ZS was accelerated by a single episode of renal ischemia (DI). This rapid renal decline was accompanied by the activation of the renal complement system in DI, and to a lesser extent in sham-operated diabetic rats (DS). In DI there were significant increases in renal mRNA encoding C3, C4, C5, C6, C8, and C9 over sham-operated lean normal controls (LS). Moreover, mRNAs encoding the receptors for the anaphylatoxins C3a and C5a were also significantly increased in DI compared to LS. The classic complement pathway was activated in diabetic kidneys with significant increases of C1qa, C1qb, and C1qc mRNAs in DI over LS. In addition, critical regulators of complement activation were significantly attenuated in DI and DS. These included mRNAs encoding CD55, decay accelerating factor, and CD59, which inhibit the membrane attack complex. C3, C4, and C9 proteins were demonstrated in renal tubules and glomeruli. The complement RNAseq data were incorporated into a gene network showing interactions among C3-generating renal tubular cells and other immune competent migratory cells.

CONCLUSIONS

We conclude that local activation of the complement system mediates renal injury in diabetic nephropathy.

Renal injury induced in alloxan diabetic rats. Role of Mycophenolate Mofetil as therapeutic agent

BACKGROUND

Renal injury may develop in uncontrolled chronic hyperglycemia due to increased oxidative stress and release of pro-inflammatory mediators, leading to diabetic complications.

METHODS

Mycophenolate Mofetil (MMF) is an immunosuppressant drug, an inhibitor of inosine monophosphate dehydrogenase (IMPDH), relevant to inflammation processes. MMF effect was tested in alloxan-diabetic rats on selected parameters like oxidative stress, gene expression of tumor necrosis factor-α (TNF-α) and transforming growth factor-β1 (TGF-β1), in relation to microalbuminuria and renal function.

RESULTS

We found that the onset of microalbuminuria preceded the increase in serum glucose after alloxan treatment. Gene expression of TNF-α and TGF-β1 showed gradual increase after one and two weeks of alloxan administration as compared to the normal group. MMF administration decreased the gene expression of TNF-α and TGF-β1 in kidney tissues, serum glucose, fructosamine, urea, creatinine, C-reactive protein, malondialdehyde, urinary microalbumin and total protein. Histological examination of kidney tissues showed significant improvement in MMF treated rats as compared to diabetic control.

CONCLUSIONS

MMF modulated renal injury of alloxan diabetic rats. Collective data may support its therapeutic effect but further clinical trials may be requested.

Pyridoxamine, an inhibitor of protein glycation, in relation to microalbuminuria and proinflammatory cytokines in experimental diabetic nephropathy

Diabetic nephropathy (DN) is one of the major complications that develop as consequence of chronic and uncontrolled hyperglycaemia. Hyperglycaemia initiates various processes, one of which is protein glycation, leading to the formation of advanced glycation end products. Alteration of intracellular signalling, gene expression, release of proinflammatory molecules and free radicals are examples of such changes and they contribute to the initiation of diabetic complications. In the current manuscript, we studied the effect of pyridoxamine (PM) on protein glycation, oxidative stress, interleukin-1α (IL-1α), IL-6, C-reactive protein (CRP), gene expression of tumour necrosis factor-α (TNF-α) and transforming growth factor-β1 (TGF-β1) in relation to microalbuminuria and kidney functions in a model of alloxan-induced diabetic rats. We have observed that onset of microalbuminuria has preceded the gradual increase of blood sugar level in diabetic rats. In diabetic rats, gene expression of TNF-α and TGF-β1 recorded a gradual increase and marked increase was observed after one and two weeks of alloxan administration, in comparison with normal rats. PM induced significant decrease in kidney malondialdehyde content and the gene expression of TNF-α and TGF-β1, in addition to levels of serum glucose, fructosamine, urea, creatinine, IL-1α, IL-6, CRP and urine microalbumin. Histopathological examination of kidney tissues showed certain improvements as compared with diabetic control. In conclusion, our results may provide a supporting evidence for the therapeutic benefit of PM in DN.

Gender, clamped hyperglycemia and arterial stiffness in patients with uncomplicated type 1 diabetes mellitus

BACKGROUND

Diabetes mellitus (DM) reduces female gender-mediated protection against the development of renal disease possibly through effects on hyperglycemia. Women with DM also exhibit increased arterial stiffness, which may promote renal disease progression. The mechanisms responsible for increased arterial stiffness in women and the possible role of acute changes in ambient glycemia remain unknown.

METHODS

Blood pressure, augmentation index (AIx), pulse wave velocity (PWV) and circulating mediators of the renin angiotensin system and nitric oxide (cGMP) were measured in men (n = 22) and women (n = 19) with uncomplicated type 1 DM under clamped euglycemic and hyperglycemic conditions.

RESULTS

At baseline, men exhibited higher levels of angiotensin II (p = 0.030) and lower cGMP levels (p = 0.004), higher systolic blood pressure (124 ± 2 versus 109 ± 2 mmHg, p < 0.0001) and pulse pressure (42 ± 2 versus 58 ± 2 beats per minute, p < 0.0001). For arterial stiffness, radial (-8.0 ± 2.6% versus +5.4 ± 3.7%, p < 0.0001) and carotid AIx (-4.7 ± 2.9 versus +12.5 ± 3.0, p < 0.0001) were lower in men versus women. In contrast, carotid-femoral PWV was similar in men and women (5.20 ± 0.30 versus 5.13 ± 0.17, respectively, p = 0.853). In response to clamped hyperglycemia, systolic blood pressure increased in women (109 ± 2 to 112 ± 2 mmHg, p = 0.005) but not men. Serum aldosterone increased and cGMP declined in women but not in men. Clamped hyperglycemia did not influence arterial stiffness in either group and radial and carotid AIx remained higher in women.

CONCLUSIONS

Arterial stiffness is higher in women with type 1 DM. This effect is not dependent on the effects of clamped hyperglycemia or neurohormonal activation.

Comprehensive genomic profiling in diabetic nephropathy reveals the predominance of proinflammatory pathways

Despite advances in the treatment of diabetic nephropathy (DN), currently available therapies have not prevented the epidemic of progressive chronic kidney disease (CKD). The morbidity of CKD, and the inexorable increase in the prevalence of end-stage renal disease, demands more effective approaches to prevent and treat progressive CKD. We undertook next-generation sequencing in a rat model of diabetic nephropathy to study in depth the pathogenic alterations involved in DN with progressive CKD. We employed the obese, diabetic ZS rat, a model that develops diabetic nephropathy, characterized by progressive CKD, inflammation, and fibrosis, the hallmarks of human disease. We then used RNA-seq to examine the combined effects of renal cells and infiltrating inflammatory cells acting as a pathophysiological unit. The comprehensive systems biology analysis of progressive CKD revealed multiple interactions of altered genes that were integrated into morbid networks. These pathological gene assemblies lead to renal inflammation and promote apoptosis and cell cycle arrest in progressive CKD. Moreover, in what is clearly a major therapeutic challenge, multiple and redundant pathways were found to be linked to renal fibrosis, a major cause of kidney loss. We conclude that systems biology applied to progressive CKD in DN can be used to develop novel therapeutic strategies directed to restore critical anomalies in affected gene networks.

The use of animal models in diabetes research

Diabetes is a disease characterized by a relative or absolute lack of insulin, leading to hyperglycaemia. There are two main types of diabetes: type 1 diabetes and type 2 diabetes. Type 1 diabetes is due to an autoimmune destruction of the insulin-producing pancreatic beta cells, and type 2 diabetes is caused by insulin resistance coupled by a failure of the beta cell to compensate. Animal models for type 1 diabetes range from animals with spontaneously developing autoimmune diabetes to chemical ablation of the pancreatic beta cells. Type 2 diabetes is modelled in both obese and non-obese animal models with varying degrees of insulin resistance and beta cell failure. This review outlines some of the models currently used in diabetes research. In addition, the use of transgenic and knock-out mouse models is discussed. Ideally, more than one animal model should be used to represent the diversity seen in human diabetic patients.

The glomerular basement membrane as a model system to study the bioactivity of heparan sulfate glycosaminoglycans

The glomerular basement membrane and its associated cells are critical elements in the renal ultrafiltration process. Traditionally the anionic charge associated with several carbohydrate moieties in the glomerular basement membrane are thought to form a charge selective barrier that restricts the transmembrane flux of anionic proteins across the glomerular basement membrane into the urinary space. The charge selective function, along with the size selective component of the basement membrane, serves to limit the efflux of plasma proteins from the capillary lumen. Heparan sulfate glycosaminoglycans are anionically charged carbohydrate structures attached to proteoglycan core proteins and have a role in establishing the charge selective function of the glomerular basement membrane. Although there are a large number of studies in the literature that support this concept, the results of several recent studies using molecular genetic approaches to minimize the anionic charge of the glomerular basement membrane would suggest that the role of heparan sulfate glycosaminoglycans in the glomerular capillary wall are still not yet entirely resolved, suggesting that this research area still requires new and novel exploration.

Glomerulopathy in spontaneously obese rhesus monkeys with type 2 diabetes: a stereological study

BACKGROUND

Animal models could provide insights into the diabetic nephropathy pathogenesis; however, available rodent models do not mirror the heterogeneity of lesions in type 2 diabetic patients, and do not progress to end-stage renal disease. Previous studies showed that spontaneously obese type 2 diabetic rhesus monkeys develop many of the features of human diabetic glomerulopathy, and may progress to end-stage renal disease. Here, in order to further characterize diabetic glomerulopathy in this model, we used electron microscopic stereology.

METHODS

Renal biopsies from 17 diabetic, 17 pre-diabetic/metabolic syndrome and 11 non-diabetic monkeys were studied. Fractional volumes of mesangium [Vv(Mes/glom)], mesangial matrix [Vv(MM/glom)] and mesangial cells [Vv(MC/glom)], glomerular basement membrane width and peripheral glomerular basement membrane surface density per glomerulus [Sv(PGBM/glom)] were estimated. Glomerular filtration and albumin excretion rates were measured in a limited number of animals. Glomerular structural and biochemical/metabolic data were compared among the groups.

RESULTS

Compared to non-diabetic monkeys, diabetic rhesus monkeys showed classic diabetic nephropathy changes, including glomerular basement membrane thickening (p = 0.001), increased fractional volumes of mesangium (p = 0.02), and reduced peripheral glomerular basement membrane surface density per glomerulus (p = 0.03) compared to non-diabetic monkeys. Increased fractional volumes of mesangium was primarily due to increased mesangial matrix (p = 0.03). Glomerular structural parameter inter-relationships in diabetic monkeys mirrored those of human diabetic glomerulopathy. Albumin excretion rate was greater (p = 0.03) in diabetic vs. non-diabetic monkeys. There was trend for a positive correlation between albumin excretion rate and fractional volumes of mesangium.

CONCLUSIONS

This rhesus primate model shares many features of human diabetic glomerulopathy. Mesangial expansion in this model, similar to human diabetic nephropathy and different from available rodent models of the disease, is primarily due to increased mesangial matrix.

BTBR Ob/Ob mutant mice model progressive diabetic nephropathy

There remains a need for robust mouse models of diabetic nephropathy (DN) that mimic key features of advanced human DN. The recently developed mouse strain BTBR with the ob/ob leptin-deficiency mutation develops severe type 2 diabetes, hypercholesterolemia, elevated triglycerides, and insulin resistance, but the renal phenotype has not been characterized. Here, we show that these obese, diabetic mice rapidly develop morphologic renal lesions characteristic of both early and advanced human DN. BTBR ob/ob mice developed progressive proteinuria beginning at 4 weeks. Glomerular hypertrophy and accumulation of mesangial matrix, characteristic of early DN, were present by 8 weeks, and glomerular lesions similar to those of advanced human DN were present by 20 weeks. By 22 weeks, we observed an approximately 20% increase in basement membrane thickness and a >50% increase in mesangial matrix. Diffuse mesangial sclerosis (focally approaching nodular glomerulosclerosis), focal arteriolar hyalinosis, mesangiolysis, and focal mild interstitial fibrosis were present. Loss of podocytes was present early and persisted. In summary, BTBR ob/ob mice develop a constellation of abnormalities that closely resemble advanced human DN more rapidly than most other murine models, making this strain particularly attractive for testing therapeutic interventions.

Aldose reductase and cardiovascular diseases, creating human-like diabetic complications in an experimental model

Hyperglycemia and reduced insulin actions affect many biological processes. One theory is that aberrant metabolism of glucose via several pathways including the polyol pathway causes cellular toxicity. Aldose reductase (AR) is a multifunctional enzyme that reduces aldehydes. Under diabetic conditions AR converts glucose into sorbitol, which is then converted to fructose. This article reviews the biology and pathobiology of AR actions. AR expression varies considerably among species. In humans and rats, the higher level of AR expression is associated with toxicity. Flux via AR is increased by ischemia and its inhibition during ischemia reperfusion reduces injury. However, similar pharmacological effects are not observed in mice unless they express a human AR transgene. This is because mice have much lower levels of AR expression, probably insufficient to generate toxic byproducts. Human AR expression in LDL receptor knockout mice exacerbates vascular disease, but only under diabetic conditions. In contrast, a recent report suggests that genetic ablation of AR increased atherosclerosis and increased hydroxynonenal in arteries. It was hypothesized that AR knockout prevented reduction of toxic aldehydes. Like many in vivo effects found in genetically manipulated animals, interpretation requires the reproduction of human-like physiology. For AR, this will require tissue specific expression of AR in sites and at levels that approximate those in humans.

Metabolic syndrome components in murine models

Animal models have enriched understanding of the physiological basis of metabolic disorders and advanced identification of genetic risk factors underlying the metabolic syndrome (MetS). Murine models are especially appropriate for this type of research, and are an excellent resource not only for identifying candidate genomic regions, but also for illuminating the possible molecular mechanisms or pathways affected in individual components of MetS. In this review, we briefly discuss findings from mouse models of metabolic disorders, particularly in light of issues raised by the recent flood of human genome-wide association studies (GWAS) results. We describe how mouse models are revealing that genotype interacts with environment in important ways, indicating that the underlying genetics of MetS is highly context dependant. Further we show that epistasis, imprinting and maternal effects each contribute to the genetic architecture underlying variation in metabolic traits, and mouse models provide an opportunity to dissect these aspects of the genetic architecture that are difficult if not impossible to ascertain in humans. Finally we discuss how knowledge gained from mouse models can be used in conjunction with comparative genomic methods and bioinformatic resources to inform human MetS research.

Critical role for osteopontin in diabetic nephropathy

The profibrotic adhesion molecule, osteopontin (OPN), is upregulated in kidneys of humans and mice with diabetes. The thiazolidinedione (TZD) insulin sensitizers decrease albuminuria in diabetic nephropathy (DN) and reduce OPN expression in vascular and cardiac tissue. To examine whether OPN is a critical mediator of DN we treated db/db mice with insulin, rosiglitazone, or pioglitazone to achieve similar fasting plasma glucose levels. The urine albumin-to-creatinine ratio and glomerular OPN expression were increased in diabetic mice, but both were reduced by the TZDs more than by insulin. We administered streptozotocin to OPN-null and OPN-wild-type mice, and OPN-null mice were bred into both type 1 (Ins2(akita/+)) and 2 (db/db) diabetic mice. In each case, OPN deletion decreased albuminuria, mesangial area, and glomerular collagen IV, fibronectin and transforming growth factor (TGF)-beta in the diabetic mice compared with their respective controls. In cultured mouse mesangial cells, TZDs but not insulin decreased angiotensin II-induced OPN expression, while recombinant OPN upregulated TGF-beta, ERK/MAPK, and JNK/MAPK signaling. These studies show that OPN expression in DN mouse models enhances glomerular damage, likely through the expression of TGF-beta, while its deletion protects against disease progression, suggesting that OPN might serve as a therapeutic target.

RAGE, glomerulosclerosis and proteinuria: roles in podocytes and endothelial cells

The multi-ligand Receptor for Advanced Glycation Endproducts (RAGE) is expressed in podocytes and endothelial cells in the human and murine glomerulus. Although present at low levels in homeostasis, RAGE expression is increased during disease. Pharmacological antagonism of RAGE or its genetic deletion imparts marked protection from podocyte effacement, albuminuria and glomerular sclerosis in disease models. In human subjects, associations between specific genetic polymorphisms of RAGE and levels of soluble forms of RAGE are linked to disease states in the kidney. In this review, we summarize the evidence from mouse to man, linking RAGE to the pathogenesis of nephropathy.

Postischemic inflammatory syndrome: a critical mechanism of progression in diabetic nephropathy

Diabetes is a major epidemic, and diabetic nephropathy is the most common cause of end-stage renal disease. Two critical components of diabetic nephropathy are persistent inflammation and chronic renal ischemia from widespread vasculopathy. Moreover, acute ischemic renal injury is common in diabetes, potentially causing chronic kidney disease or end-stage renal disease. Accordingly, we tested the hypothesis that acute renal ischemia accelerates nephropathy in diabetes by activating proinflammatory pathways. Lean and obese-diabetic ZS rats (F(1) hybrids of spontaneously hypertensive heart failure and Zucker fatty diabetic rats) were subjected to bilateral renal ischemia or sham surgery before the onset of proteinuria. The postischemic state in rats with obesity-diabetes was characterized by progressive chronic renal failure, increased proteinuria, and renal expression of proinflammatory mediators. Leukocyte number in obese-diabetic rat kidney was markedly increased for months after ischemia. Intrarenal blood flow velocity was decreased after ischemia in lean control and obese-diabetic rats, although it recovered in lean rats. At 2 mo after ischemia, blood flow velocity decreased further in sham-surgery and postischemia obese-diabetic rats, so that RBC flow velocity was only 39% of control in the obese-diabetic rats after ischemia. In addition, microvascular density remained depressed at 2 mo in kidneys of obese-diabetic rats after ischemia. Abnormal microvascular permeability and increases in interstitial fibrosis and apoptotic renal cell death were also more pronounced after ischemia in obese-diabetic rats. These data support the hypothesis that acute renal ischemia in obesity-diabetes severely aggravates chronic inflammation and vasculopathy, creating a self-perpetuating postischemia inflammatory syndrome, which accelerates renal failure.

Human cerebral neuropathology of Type 2 diabetes mellitus

The cerebral neuropathology of Type 2 diabetes (CNDM2) has not been positively defined. This review includes a description of CNDM2 research from before the 'Pubmed Era'. Recent neuroimaging studies have focused on cerebrovascular and white matter pathology. These and prior studies about cerebrovascular histopathology in diabetes are reviewed. Evidence is also described for and against the link between CNDM2 and Alzheimer's disease pathogenesis. To study this matter directly, we evaluated data from University of Kentucky Alzheimer's Disease Center (UK ADC) patients recruited while non-demented and followed longitudinally. Of patients who had come to autopsy (N = 234), 139 met inclusion criteria. These patients provided the basis for comparing the prevalence of pathological and clinical indices between well-characterized cases with (N = 50) or without (N = 89) the premortem diagnosis of diabetes. In diabetics, cerebrovascular pathology was more frequent and Alzheimer-type pathology was less frequent than in non-diabetics. Finally, a series of photomicrographs demonstrates histopathological features (including clinical-radiographical correlation) observed in brains of persons that died after a history of diabetes. These preliminary, correlative, and descriptive studies may help develop new hypotheses about CNDM2. We conclude that more work should be performed on human material in the context of CNDM2.

Selecting the "right" mouse model for metabolic syndrome and type 2 diabetes research

This is not a "Methods" chapter in the traditional sense. Rather, it is an essay designed to help address one of the most frequently asked questions by investigators about to embark on a study requiring an animal model of diabetes - what is the "right" model for the reader's specific research application. Because genetic heterogeneity and the requirement for complex gene-environment interaction characterize the various mouse models of Type 2 diabetes as well as the human disease manifestations, the readers may come to share the author's conclusion that more than one model is required if the investigator is interested in knowing how broadly effective a given compound with putative therapeutic efficacy might be.

Improved elucidation of biological processes linked to diabetic nephropathy by single probe-based microarray data analysis

BACKGROUND

Diabetic nephropathy (DN) is a complex and chronic metabolic disease that evolves into a progressive fibrosing renal disorder. Effective transcriptomic profiling of slowly evolving disease processes such as DN can be problematic. The changes that occur are often subtle and can escape detection by conventional oligonucleotide DNA array analyses.

METHODOLOGY/PRINCIPAL FINDINGS

We examined microdissected human renal tissue with or without DN using Affymetrix oligonucleotide microarrays (HG-U133A) by standard Robust Multi-array Analysis (RMA). Subsequent gene ontology analysis by Database for Annotation, Visualization and Integrated Discovery (DAVID) showed limited detection of biological processes previously identified as central mechanisms in the development of DN (e.g. inflammation and angiogenesis). This apparent lack of sensitivity may be associated with the gene-oriented averaging of oligonucleotide probe signals, as this includes signals from cross-hybridizing probes and gene annotation that is based on out of date genomic data. We then examined the same CEL file data using a different methodology to determine how well it could correlate transcriptomic data with observed biology. ChipInspector (CI) is based on single probe analysis and de novo gene annotation that bypasses probe set definitions. Both methods, RMA and CI, used at default settings yielded comparable numbers of differentially regulated genes. However, when verified by RT-PCR, the single probe based analysis demonstrated reduced background noise with enhanced sensitivity and fewer false positives.

CONCLUSIONS/SIGNIFICANCE

Using a single probe based analysis approach with de novo gene annotation allowed an improved representation of the biological processes linked to the development and progression of DN. The improved analysis was exemplified by the detection of Wnt signaling pathway activation in DN, a process not previously reported to be involved in this disease.

Physiological regulation of prostaglandins in the kidney

Cyclooxygenase-derived prostanoids exert complex and diverse functions within the kidney. The biological effect of each prostanoid is controlled at multiple levels, including (a) enzymatic reactions catalyzed sequentially by cyclooxygenase and prostanoid synthase for the synthesis of bioactive prostanoid and (b) the interaction with its receptors that mediate its functions. Cyclooxygenase-derived prostanoids act in an autocrine or a paracrine fashion and can serve as physiological buffers, protecting the kidney from excessive functional changes during physiological stress. Through these actions, prostanoids play important roles in maintaining renal function, body fluid homeostasis, and blood pressure. Renal cortical COX2-derived prostanoids, particularly PGI2 and PGE2, play critical roles in maintaining blood pressure and renal function in volume-contracted states. Renal medullary COX2-derived prostanoids appear to have an antihypertensive effect in individuals challenged with a high-salt diet. Loss of EP2 or IP receptor is associated with salt-sensitive hypertension. COX2 also plays a role in maintaining renal medullary interstitial cell viability in the hypertonic environment of the medulla. Cyclooxygenase-derived prostanoids also are involved in certain pathological processes. The cortical COX2-derived PGI2 participates in the pathogenesis of renal vascular hypertension through stimulating renal renin synthesis and release. COX-derived prostanoids also appear to be involved in the pathogenesis of diabetic nephropathy. COXs, prostanoid synthases, and prostanoid receptors should provide fruitful targets for intervention in the pharmacological treatment of renal disease.

Animal models to test drugs with potential antidiabetic activity

Although medicinal plants have been historically used for diabetes treatment throughout the world, few of them have been validated by scientific criteria. Recently, a large diversity of animal models has been developed to better understand the pathogenesis of diabetes mellitus and new drugs have been introduced in the market to treat this disease. The aim of this work was to review the available animal models of diabetes and some in vitro models which have been used as tools to investigate the mechanism of action of drugs with potential antidiabetic properties. In addition, a MEDLINE/PUBMED search for articles on natural products, pancreatectomy and diabetes mellitus treatment published between 1996 and 2006 was done. In the majority of the studies, natural products mainly derived from plants have been tested in diabetes models induced by chemical agents. This review contributes to the researcher in the ethnopharmacology field to designs new strategies for the development of novel drugs to treat this serious condition that constitutes a global public health.

Can rodent models of diabetic kidney disease clarify the significance of early hyperfiltration?: recognizing clinical and experimental uncertainties

In the past, hyperfiltration and increased glomerular capillary pressure have been identified as important determinants of the development of DN (diabetic nephropathy). Recently, some basic research and clinical reviews on DN have omitted identifying hyperfiltration as an important risk factor. At the same time, different rodent models of DN have been described without and with documented hyperfiltration. In the present review, the importance of hyperfiltration is reassessed, reviewing key clinical and research studies, including the first single nephron studies in a mouse model of DN. From clinical studies of Type 1 and Type 2 diabetes mellitus, it is clear that many patients do not have early hyperfiltration and, even when present, its contribution to subsequent DN remains uncertain. Key mechanisms underlying hyperfiltration in rodent models are reviewed. Findings on intrarenal NO metabolism and the control of single-nephron GFR (glomerular filtration rate) in rodent models of DN are also presented. Characterization of valid experimental models of DN should include a careful delineation of the absence or presence of early hyperfiltration, with special efforts made to establish the specific role hyperfiltration may play in the emergence of DN.

The vascular ectonucleotidase ENTPD1 is a novel renoprotective factor in diabetic nephropathy

Ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1) (also known as CD39) is the dominant vascular ectonucleotidase. By hydrolyzing ATP and ADP to AMP, ENTPD1 regulates ligand availability to a large family of P2 (purinergic) receptors. Modulation of extracellular nucleotide metabolism is an important factor in several acute and subacute models of vascular injury. We hypothesized that aberrant nucleotide signaling would promote chronic glomerular injury in diabetic nephropathy. Inducing diabetes in ENTPD1-null mice with streptozotocin resulted in increased proteinuria and more severe glomerular sclerosis compared with matched diabetic wild-type mice. Diabetic ENTPD1-null mice also had more glomerular fibrin deposition and glomerular plasminogen activator inhibitor-1 (PAI-1) staining than wild-type controls. In addition, ENTPD1-null mice showed increased glomerular inflammation, in association with higher levels of monocyte chemoattractant protein-1 (MCP-1) expression. Mesangial cell PAI-1 and MCP-1 mRNA expression were upregulated by ATP and UTP but not ADP or adenosine in vitro. The stable nucleotide analog ATPgammaS stimulated sustained expression of PAI-1 and MCP-1 in vitro, whereas the stable adenosine analog NECA [5'-(N-ethylcarboxamido)adenosine] downregulated expression of both genes. Extracellular nucleotide-stimulated upregulation of MCP-1 is, at least in part, protein kinase C dependent. We conclude that ENTPD1 is a vascular protective factor in diabetic nephropathy that modulates glomerular inflammation and thromboregulation.

Leptin is a coactivator of TGF-beta in unilateral ureteral obstructive kidney disease

Progressive tubulointerstitial fibrosis is the common end point leading to end-stage renal disease in experimental and clinical settings. Since the peptide hormone leptin is involved not only in the regulation of obesity but also in the regulation of inflammation and fibrosis, we tested the hypothesis whether leptin deficiency has an impact on tubulointerstitial fibrosis in mice. Leptin-deficient (ob/ob) and leptin receptor-deficient mice (db/db) were exposed to 14 days of unilateral ureteral obstruction (UUO). The degree of fibrosis and inflammation was compared with that in sham-operated mice by performing immunohistochemistry, quantitative PCR, and Western blotting. We found that tubulointerstitial fibrosis was significantly reduced in the obstructed kidneys of ob/ob compared with db/db mice or control mice. Detailed analysis of infiltrating inflammatory cells by immunohistochemistry revealed a significant reduction of CD4(+) cells at 14 days after UUO in both ob/ob and db/db mice. In contrast, we could not detect significant differences in CD8(+) cells and macrophage content. Transforming growth factor (TGF)-beta mRNA levels, TGF-beta-induced Smad-2/3 activation, and the upregulation of downstream target genes were significantly reduced in ob/ob mice. In addition, we demonstrated that leptin could enhance TGF-beta signaling in normal rat kidney fibroblasts in vitro. We conclude that leptin can serve as a cofactor of TGF-beta activation and thus plays an important role in renal tubulointerstitial fibrosis. Therefore, selective blockade of the leptin axis might provide a therapeutic possibility to prevent or delay fibrotic kidney disease.

Physiologic and pathophysiologic roles of lipid mediators in the kidney

Small lipids such as eicosanoids exert diverse and complex functions. In addition to their role in regulating normal kidney function, these lipids also play important roles in the pathogenesis of kidney diseases. Cyclooxygenase (COX)-derived prostanoids play important role in maintaining renal function, body fluid homeostasis, and blood pressure. Renal cortical COX2-derived prostanoids, particularly (PGI2) and PGE2 play critical roles in maintaining blood pressure and renal function in volume contracted states. Renal medullary COX2-derived prostanoids appear to have antihypertensive effect in individuals challenged with a high salt diet. 5-Lipoxygenase (LO)-derived leukotrienes are involved in inflammatory glomerular injury. LO product 12-hydroxyeicosatetraenoic acid (12-HETE) is associated with pathogenesis of hypertension, and may mediate angiotensin II and TGFbeta induced mesengial cell abnormality in diabetic nephropathy. P450 hydroxylase-derived 20-HETE is a potent vasoconstrictor and is involved in the pathogenesis of hypertension. P450 epoxygenase derived epoxyeicosatrienoic acids (EETs) have vasodilator and natriuretic effect. Blockade of EET formation is associated with salt-sensitive hypertension. Ceramide has also been demonstrated to be an important signaling molecule, which is involved in pathogenesis of acute kidney injury caused by ischemia/reperfusion, and toxic insults. Those pathways should provide fruitful targets for intervention in the pharmacologic treatment of renal disease.

Roles of Lipid Mediators in Kidney Injury

Small lipids such as eicosanoids exert diverse and complex functions. In addition to their role in regulating normal kidney function, these lipids also play important roles in the pathogenesis of kidney diseases. Increased glomerular cyclooxygenase (COX)1 or COX2 expression has been reported in patients with nephritis and in animal models of nephritis. COX inhibitors have shown beneficial effects on lupus nephritis and passive Heymann nephritis, but not anti-Thy1.1-induced nephritis. 5-Lipoxygenase-derived leukotrienes are involved in inflammatory glomerular injury. Lipoxygenase product 12-hydroxyeicosatetraenoic acid may mediate angiotensin II and transforming growth factor beta-induced mesangial cell abnormality in diabetic nephropathy. P450 arachidonic acid mono-oxygenase-derived 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids are involved in several forms of kidney injury, including renal injury in metabolic syndrome. Ceramide also has been shown to be an important signaling molecule that is involved in the pathogenesis of acute kidney injury caused by ischemia/reperfusion and toxic insults. Those pathways should provide fruitful targets for intervention in the pharmacologic treatment of renal disease.

Renal effects of S18886 (Terutroban), a TP receptor antagonist, in an experimental model of type 2 diabetes

Thromboxane A(2) (TxA(2)) is assumed to contribute to the development of diabetes complications, including nephropathy. We investigated whether the selective thromboxane-prostanoid endoperoxide receptor antagonist, S18886, ameliorates renal damage in uninephrectomized (UNX) obese Zucker rats (OZR). S18886, at doses of 10 (S18886-10) and 30 (S18886-30) mg x kg(-1) x day(-1), was administered to UNX-OZR by gavage over 8 weeks (n = 8 each group). UNX lean rats (n = 12) and OZR rats that received placebo (OZR-PLAC, n = 8) served as controls. As compared with the OZR-PLAC, S18886 had no significant effect on the elevated blood pressure and the enhanced creatinine clearance, while augmented proteinuria was partially prevented (-12 and -37%, low and high dose, respectively; NS). The increased excretion of transforming growth factor beta(1) (TGF-beta(1)) and of the thromboxane metabolite 2,3-dinor thromboxane B(2) (TxB(2)) was lowered (P < 0.05). S18886 prevented both the enhanced mesangiolysis (P < 0.01) in the OZR-PLAC as well as enlargement and degeneration of podocytes. In the blood, S18886-30 augmented the antioxidant enzymes (P < 0.01) and lessened the increase of plasma advanced oxidation protein products (-25%, NS). Body weight, hyperglycemia, and dyslipidemia remained uninfluenced under both doses of treatment. S18886 has renoprotective properties in the model of UNX-OZR. It prevents mesangiolysis, reduces urinary TGF-beta(1) and 2,3-dinor-TxB(2) excretion, and enhances the antioxidative defense.

Endothelial nitric oxide synthase deficiency produces accelerated nephropathy in diabetic mice

Functionally significant polymorphisms in endothelial nitric oxide synthase (eNOS) and reduced vascular eNOS activity have been associated with increased human diabetic nephropathy (DN), but the pathogenic role of eNOS deficiency in the development of DN has not yet been confirmed. This study characterizes the severity of DN in eNOS(-/-) mice that were backcrossed to C57BLKS/J db/db mice. Although the severity of hyperglycemia was similar to C57BLKS/J db/db mice, by 26 wk, eNOS(-/-) C57BLKS/J db/db mice exhibited dramatic albuminuria, arteriolar hyalinosis, increased glomerular basement membrane thickness, mesangial expansion, mesangiolysis, and focal segmental and early nodular glomerulosclerosis. Even more remarkable, eNOS(-/-) C57BLKS db/db exhibited decreases in GFR to levels <50% of that in eNOS(+/+) C57BLKS db/db, as confirmed by increased serum creatinine. In summary, eNOS(-/-) db/db mice provide the most robust model of type II DN that has been described to date and support a role for deficient eNOS-derived NO production in the pathogenesis of DN.

Altered vitamin D metabolism in type II diabetic mouse glomeruli may provide protection from diabetic nephropathy

The db/db mouse develops features of type II diabetes mellitus as the result of impaired signaling through its abnormal leptin receptor. In spite of accurate metabolic features of diabetes, renal disease manifestations in these mice are not as severe as in humans suggesting the presence of protective genes. There is a growing body of evidence in humans for the relevance of vitamin D in diabetes. Here we followed a large cohort of db/db mice and their non-diabetic db/+ littermates. Transcriptional profiling revealed significant upregulation of 23 genes involved in Ca2+ homeostasis and vitamin D metabolism in db/db glomeruli relative to db/+ glomeruli. Increased glomerular expression of vitamin D3 1alpha-hydroxylase, vitamin D binding protein, calbindins D9K and D28K, and calcyclin mRNA was confirmed by quantitative reverse transcription-polymerase chain reaction in 20-, 36-, and 52-week-old db/db glomeruli. Although vitamin D3 1alpha-hydroxylase protein was primarily expressed and upregulated in db/db renal tubules, it was also expressed in glomerular podocytes in vivo. Serum 1,25-dihydroxyvitamin D3 and urinary Ca2+ excretion were increased >3-fold in db/db mice compared to db/+ mice. Cultured glomerular podocytes had mRNA for vitamin D3 1alpha-hydroxylase, vitamin D receptor, and calbindin D28K, each of which was increased in high glucose conditions. High glucose also led to enhanced production of fibronectin and collagen IV protein, which was blocked by 1,25-dihydroxyvitamin D3. These results show that vitamin D metabolism is altered in db/db mice leading to metabolic and transcriptional effects. The podocyte is affected by paracrine and potentially autocrine effects of vitamin D, which may explain why db/db mice are resistant to progressive diabetic nephropathy.

ACE and ACE2 activity in diabetic mice

ACE-related carboxypeptidase (ACE2) may counterbalance the angiotensin (ANG) II-promoting effects of ACE in tissues where both enzymes are found. Alterations in renal ACE and ACE2 expression have been described in experimental models of diabetes, but ACE2 activity was not assessed in previous studies. We developed a microplate-based fluorometric method for the concurrent determination of ACE and ACE2 activity in tissue samples. Enzymatic activity (relative fluorescence unit [RFU] . microg protein(-1) . h(-1)) was examined in ACE and ACE2 knockout mice and in two rodent models of diabetes, the db/db and streptozotocin (STZ)-induced diabetic mice. In kidney cortex, preparations consisting mainly of proximal tubules and cortical collecting tubules, ACE2 activity had a strong positive correlation with ACE2 protein expression (90-kDa band) in both knockout models and their respective wild-type littermates (r = 0.94, P < 0.01). ACE activity, likewise, had a strong positive correlation with renal cortex ACE protein expression (170-kDa band) (r = 0.838, P < 0.005). In renal cortex, ACE2 activity was increased in both models of diabetes (46.7 +/- 4.4 vs. 22.0 +/- 4.7 in db/db and db/m, respectively, P < 0.01, and 22.1 +/- 2.8 vs. 13.1 +/- 1.5 in STZ-induced diabetic versus untreated mice, respectively, P < 0.05). ACE2 mRNA levels in renal cortex from db/db and STZ-induced diabetic mice, by contrast, were not significantly different from their respective controls. In cardiac tissue, ACE2 activity was lower than in renal cortex, and there were no significant differences between diabetic and control mice (db/db 2.03 +/- 0.23 vs. db/m 1.85 +/- 0.10; STZ-induced diabetic 0.42 +/- 0.04 vs. untreated 0.52 +/- 0.07 mice). ACE2 activity in renal cortex correlated positively with ACE2 protein in db/db and db/m mice (r = 0.666, P < 0.005) as well as in STZ-induced diabetic and control mice (r = 0.621, P < 0.05) but not with ACE2 mRNA (r = -0.468 and r = -0.522, respectively). We conclude that in renal cortex from diabetic mice, ACE2 expression is increased at the posttranscriptional level. The availability of an assay for concurrent measurement of ACE and ACE2 activity should be helpful in the evaluation of kidney-specific alterations in the balance of these two carboxypeptidases, which are involved in the control of local ANG II formation and degradation.

Characterization of diabetic nephropathy in a transgenic model of hypoinsulinemic diabetes

Genetic mouse models provide a unique opportunity to investigate gene function in the natural course of the disease. Although diabetic nephropathy (DN) in models of type II diabetes has been well characterized, diabetic renal disease in hypoinsulinemic diabetic mice is still incompletely understood. Here, we characterized renal changes in the pdx1(PB)-HNF6 transgenic mouse that exhibits beta-cell dysfunction and nonobese hypoinsulinemic diabetes. Male transgenic mice developed hyperglycemia by the age of 7 wk and survived for over 1 yr without insulin treatment. Diabetes ensued earlier and progressed more severely in the HNF6 males than the females. The HNF6 males exhibited albuminuria as early as 10 wk of age, and the urinary albumin excretion increased with age, exceeding 150 microg/24 h at 11 mo of age. Diabetic males developed renal hypertrophy after 7 wk of age, whereas glomerular hyperfiltration was not observed in the mice. Hypertension and hyperlipidemia were not observed in the diabetic mice. Histological analysis of the HNF6 kidneys displayed diabetic glomerular changes, including glomerular enlargement, diffuse mesangial proliferation and matrix expansion, thickened glomerular basement membrane, and arteriolar hyalinosis. Mesangial matrix accumulation increased with age, resulting in nodular lesions by 44 wk of age. Immunohistochemistry showed accumulation of type IV collagen and TGF-beta1 in the mesangial area. No significant immune complex deposition was observed in the HNF6 glomeruli. Thus the HNF6 mouse exhibits diabetic renal changes that parallel the early phase of human DN. The model should facilitate studies of genetic and environmental factors that may affect DN in hypoinsulinemic diabetes.

Modulation of single-nephron GFR in the db/db mouse model of type 2 diabetes mellitus

Hyperfiltration has been implicated in the progression toward diabetic nephropathy in type 2 diabetes mellitus (DM2). This study focuses for the first time on the in vivo modulation of single-nephron GFR (SNGFR) in the classic B6.Cg-m(+/+)Lepr(db)/J (db/db) mouse model of DM2. To obtain stable preparations, it was necessary to use a sustaining infusion of 3.3 ml.100 g body wt(-1) x h(-1), or higher. SNGFR (measured both proximally and distally) was greater in db/db vs. heterozygote (db/m) mice (P < 0.05) but not vs. the wild-type (WT) mice. The tubuloglomerular feedback (TGF) responses, determined as free-flow proximal vs. distal SNGFR differences, were significant in db/db mice (11.6 +/- 0.8 vs. 9.3 +/- 1.0 nl/min, P < 0.01), in db/m mice (8.0 +/- 0.8 vs. 7.2 +/- 0.6 nl/min, P < 0.02), and WT mice (9.9 +/- 0.6 vs. 8.9 +/- 0.7 nl/min, P < 0.05). After increasing the sustaining infusion in the db/db mice, to offset glycosuric urine losses, the SNGFR increased significantly, and the TGF response was abolished. In these volume-replete db/db mice, absolute fluid reabsorption measured both at the late proximal and distal tubular sites were significantly increased vs. db/m mice infused at 3.3 ml.100 g body wt(-1) x h(-1). After infusion of the neuronal nitric oxide synthase (nNOS) inhibitor S-methylthiocitrulline, SNGFR fell in both db/db and db/m mice. These studies show that SNGFR is elevated in this mouse model of DM2, is suppressed by nNOS inhibition, and is modulated by TGF influences that are altered by the diabetic state and responsive to changes in extracellular fluid volume.