Captopril-induced reduction of serum levels of transforming growth factor-beta1 correlates with long-term renoprotection in insulin-dependent diabetic patients

Renal fibrosis as a hallmark of diabetic kidney disease: Potential role of targeting transforming growth factor-beta (TGF-β) and related molecules

INTRODUCTION

Diabetic kidney disease (DKD) is the most common cause of end-stage renal disease (ESRD) worldwide. Currently, there is no effective treatment to completely prevent DKD progression to ESRD. Renal fibrosis and inflammation are the major pathological features of DKD, being pursued as potential therapeutic targets for DKD.

AREAS COVERED

Inflammation and renal fibrosis are involved in the pathogenesis of DKD. Anti-inflammatory drugs have been developed to combat DKD but without efficacy demonstrated. Thus, we have focused on the mechanisms of TGF-β-induced renal fibrosis in DKD, as well as discussing the important molecules influencing the TGF-β signaling pathway and their potential development into new pharmacotherapies, rather than targeting the ligand TGF-β and/or its receptors, such options include Smads, microRNAs, histone deacetylases, connective tissue growth factor, bone morphogenetic protein 7, hepatocyte growth factor, and cell division autoantigen 1.

EXPERT OPINION

TGF-β is a critical driver of renal fibrosis in DKD. Molecules that modulate TGF-β signaling rather than TGF-β itself are potentially superior targets to safely combat DKD. A comprehensive elucidation of the pathogenesis of DKD is important, which requires a better model system and access to clinical samples via collaboration between basic and clinical researchers.

MicroRNAs and their delivery in diabetic fibrosis

The global prevalence of diabetes mellitus was estimated to be 463 million people in 2019 and is predicted to rise to 700 million by 2045. The associated financial and societal costs of this burgeoning epidemic demand an understanding of the pathology of this disease, and its complications, that will inform treatment to enable improved patient outcomes. Nearly two decades after the sequencing of the human genome, the significance of noncoding RNA expression is still being assessed. The family of functional noncoding RNAs known as microRNAs regulates the expression of most genes encoded by the human genome. Altered microRNA expression profiles have been observed both in diabetes and in diabetic complications. These transcripts therefore have significant potential and novelty as targets for therapy, therapeutic agents and biomarkers.

Mitochondrial Pathophysiology on Chronic Kidney Disease

In healthy kidneys, interstitial fibroblasts are responsible for the maintenance of renal architecture. Progressive interstitial fibrosis is thought to be a common pathway for chronic kidney diseases (CKD). Diabetes is one of the boosters of CKD. There is no effective treatment to improve kidney function in CKD patients. The kidney is a highly demanding organ, rich in redox reactions occurring in mitochondria, making it particularly vulnerable to oxidative stress (OS). A dysregulation in OS leads to an impairment of the Electron transport chain (ETC). Gene deficiencies in the ETC are closely related to the development of kidney disease, providing evidence that mitochondria integrity is a key player in the early detection of CKD. The development of novel CKD therapies is needed since current methods of treatment are ineffective. Antioxidant targeted therapies and metabolic approaches revealed promising results to delay the progression of some markers associated with kidney disease. Herein, we discuss the role and possible origin of fibroblasts and the possible potentiators of CKD. We will focus on the important features of mitochondria in renal cell function and discuss their role in kidney disease progression. We also discuss the potential of antioxidants and pharmacologic agents to delay kidney disease progression.

The relationship between monocyte to high-density lipoprotein cholesterol ratio and diabetic nephropathy

Objective:

This study aims to investigate the relationship of monocyte to high-density lipoprotein cholesterol ratio (MHR) with diabetes mellitus (DM) and diabetic nephropathy.

Methods:

This study included 262 Type-2 diabetes mellitus patients, of which 60 had diabetic nephropathy and 202 did not have diabetic nephropathy who presented to the internal diseases polyclinic at Firat University Medical Faculty Hospital between May 2018 and October 2018 and 50 healthy control subjects. A retrospective scan of patient files was conducted and information relevant to nephropathy such as hemoglobin, glycated hemoglobin levels (HbA1c), hematocrit count (HCT), monocyte count, LDL, HDL, triglyceride levels, and microvascular complications were acquired.

Results:

We determined MHR values as 11.9±5.5 and 8.4±2.9 respectively for the diabetic and healthy groups. There was a statistically significant difference between the two groups in terms of MHR, with a positive correlation between diabetes and MHR (< 0.001; r: 0.241). Moreover, glucose, HDL, and triglyceride levels were different between the two groups with statistical significance (respectively, p< 0.001; p< 0.001; p< 0.001). Our study found higher MHR levels for patients with diabetic nephropathy compared to those without diabetic nephropathy (respectively, 17.1±7.9 and 10.3±3.3) and determined statistical significance and a negative correlation (p< 0.001; r: -0.512).

Conclusion:

Our results suggest that an elevated MHR can be a biomarker for diabetic nephropathy, allowing the detection of diabetic nephropathy with simple and inexpensive laboratory tests.

Investigation of the Role of a Supplementation with Taurine on the Effects of Hypoglycemic-Hypotensive Therapy Against Diabetes-Induced Nephrotoxicity in Rats

This study has examined the role of supplementing a treatment of diabetic rats with captopril (CAP), metformin (MET) or CAP-MET with the antioxidant amino acid taurine (TAU) on biochemical indices of diabetes-induced metabolic changes, oxidative stress and nephropathy. To this end, groups of 6 male Sprague-Dawley rats (250-375 g) were made diabetic with a single, 60 mg/kg, intraperitoneal dose of streptozotocin (STZ) in 10 mM citrate buffer pH 4.5 and, after 14 days, treated daily for up to 42 days with either a single oral dose of CAP (0.15 mM/kg), MET (2.4 mM/kg) or TAU (2.4 mM/kg), or with a binary or tertiary combination of these agents. Rats receiving only 10 mM citrate buffer pH 4.5 or only STZ served as negative and positive controls, respectively. All rats were sacrificed by decapitation on day 57 and their blood and kidneys collected. In addition, a 24 h urine sample was collected starting on day 56. Compared to normal rats, untreated diabetic ones exhibited frank hyperglycemia (+313%), hypoinsulinemia (-76%) and elevation of the glycated hemoglobin value (HbA1c, +207%). Also they showed increased plasma levels of Na+ (+35%), K+ (+56%), creatinine (+232%), urea nitrogen (+158%), total protein (-53%) and transforming growth factor-β1 (TGF-β1, 12.4-fold) values. These changes were accompanied by increases in the renal levels of malondialdehyde (MDA, +42%), by decreases in the renal glutathione redox state (-71%), and activities of catalase (-70%), glutathione peroxidase (-71%) and superoxide dismutase (-85%), and by moderate decreases of the urine Na+ (-33%) and K+ (-39%) values. Following monotherapy, MET generally showed a greater attenuating effect than CAP or TAU on the changes in circulating glucose, insulin and HbA1c levels, urine total protein, and renal SOD activity; and CAP appeared more potent than TAU and MET, in that order, in antagonizing the changes in plasma creatinine and urea nitrogen levels. On the other hand, TAU generally provided a greater protection against changes in glutathione redox state and in CAT and GPx activities, with other actions falling in potency between those of CAP and MET. Adding TAU to a treatment with CAP, but not to one with MET, led to an increase in protective action relative to a treatment with drug alone. On the other hand, the actions of CAP-MET, which were about equipotent with those of MET, became enhanced in the presence of TAU, particularly against the changes of the glutathione redox state and activities of antioxidant enzymes. In short, the present results suggest that the addition of TAU to a treatment of diabetes with CAP or CAP-MET, and sometimes to one with MET, will lead to a gain in protective potency against changes in indices of glucose metabolism and of renal functional impairment and oxidative stress.

The Role for Protein Restriction in Addition to Renin-Angiotensin-Aldosterone System Inhibitors in the Management of CKD

In experimental studies a low-protein diet (LPD) and renin-angiotensin-aldosterone system (RAAS) inhibitors are both reported to slow the progression of chronic kidney disease (CKD) and reduce proteinuria. RAAS activity contributes to increased blood pressure, fluid retention, and positive sodium balance, but also to kidney damage by enhancing glomerular capillary filtration pressure and synthesis of profibrotic molecules such as transforming growth factor β. It has been well established that an LPD decreases glomerular hyperfiltration and the generation of uremic toxins, as well as the burden of acid load, phosphorus, and sodium. In different animal CKD models, a significant reduction in proteinuria and glomerulosclerosis has been achieved when an RAAS inhibitor and LPD were combined. To date, high-quality intervention trials investigating this combined strategy are lacking. We summarize the experimental and clinical studies that have examined a potential additive action of these therapies on CKD progression. We outline potential mechanisms of action and additive efficacy of an LPD and RAAS inhibitors in CKD, with a particular emphasis on phosphate levels, uremic toxin production, acid load, and salt intake. Finally, although the evidence is inadequate to recommend combining RAAS inhibitors and an LPD to slow the progression of CKD, we provide a perspective to support a large-scale randomized clinical trial to study this combination.

Transforming Growth Factor-β Protects against Inflammation-Related Atherosclerosis in South African CKD Patients

Background

Transforming growth factor-β (TGF-β) may inhibit the development of atherosclerosis. We evaluated serum levels of TGF-β isoforms concurrently with serum levels of endotoxin and various inflammatory markers. In addition, we determined if any association exists between polymorphisms in the TGF-β1 gene and atherosclerosis in South African CKD patients.

Methods

We studied 120 CKD patients and 40 healthy controls. Serum TGF-β1, TGF-β2, TGF-β3, endotoxin, and inflammatory markers were measured. Functional polymorphisms in the TGF-β1 genes were genotyped using a polymerase chain reaction-sequence specific primer method and carotid intima media thickness (CIMT) was assessed by B-mode ultrasonography.

Results

TGF-β isoforms levels were significantly lower in the patients with atherosclerosis compared to patients without atherosclerosis (p<0.001). Overall, TGF-β isoforms had inverse relationships with CIMT. TGF-β1 and TGF-β2 levels were significantly lower in patients with carotid plaque compared to those without carotid plaque [TGF-β1: 31.9 (17.2 – 42.2) versus 45.9 (35.4 – 58.1) ng/ml, p=0.016; and TGF-β2: 1.46 (1.30 – 1.57) versus 1.70 (1.50 – 1.87) ng/ml, p=0.013]. In multiple logistic regression, age, TGF-β2, and TGF-β3 were the only independent predictors of subclinical atherosclerosis in CKD patients [age: odds ratio (OR), 1.054; 95% confidence interval (CI): 1.003 – 1.109, p=0.039; TGF-β2: OR, 0.996; 95% CI: 0.994–0.999, p=0.018; TGF-β3: OR, 0.992; 95% CI: 0.985–0.999, p=0.029). TGF-β1 genotypes did not influence serum levels of TGF-β1 and no association was found between the TGF-β1 gene polymorphisms and atherosclerosis risk.

Conclusion

TGF-β isoforms seem to offer protection against the development of atherosclerosis among South African CKD patients.

A Randomized Controlled Trial of Lisinopril to Decrease Lymphoid Fibrosis in Antiretroviral-Treated, HIV-infected Individuals

BACKGROUND

In HIV infection, lymphoid tissue is disrupted by fibrosis. Angiotensin converting enzyme inhibitors have anti-fibrotic properties. We completed a pilot study to assess whether the addition of lisinopril to antiretroviral therapy (ART) reverses fibrosis of gut tissue, and whether this leads to reduction of HIV RNA and DNA levels.

METHODS

Thirty HIV-infected individuals on ART were randomized to lisinopril at 20mg daily or matching placebo for 24 weeks. All participants underwent rectal biopsies prior to starting the study drug and at 22 weeks, and there were regular blood draws. The primary end point was the change in HIV RNA and DNA levels in rectal tissue. Secondary outcomes included the change in 1) HIV levels in blood; 2) Gag-specific T-cell responses; 3) levels of T-cell activation; and 4) collagen deposition.

RESULTS

The addition of lisinopril did not have a significant effect on the levels of HIV RNA or DNA in gut tissue or blood, Gag-specific responses, or levels of T-cell activation. Lisinopril also did not have a significant impact on lymphoid fibrosis in the rectum, as assessed by quantitative histology or heavy water labeling.

CONCLUSIONS

Treatment with lisinopril for 24 weeks in HIV-infected adults did not have an effect on lymphoid fibrosis, immune activation, or gut tissue viral reservoirs. Further study is needed to see if other anti-fibrotic agents may be useful in reversing lymphoid fibrosis and reducing HIV levels.

Higher plasma transforming growth factor (TGF)-β is associated with kidney disease in older community dwelling adults

Background

TGF-β is induced in the vasculature with aging suggesting that high plasma TGF-β levels may be a risk factor for chronic kidney disease (CKD) in older adults.

Methods

We conducted a cross-sectional analysis of the association between plasma TGF-β levels and CKD including data for 1722 older adults who had participated in the 1996/97 visit of the Cardiovascular Health Study (CHS). Prevalent CKD was defined as eGFR < 60 mL/min/1.73 m² or urinary albumin/creatinine ratio (ACR) ≥30 mg/g. We also evaluated whether baseline TGF-β levels predicted change in eGFR, cardiovascular (CV) events, or mortality in longitudinal analysis.

Results

Plasma TGF-β levels were significantly and independently associated with lower eGFR in cross-sectional analysis. Doubling of TGF-β was significantly associated with lower eGFR (β estimate after adjusting for CV risk factors = −1.18, 95% CI −2.03, −0.32). We observed no association with albuminuria. There was no association between baseline TGF-β and change in eGFR, but each doubling of TGF-β at baseline was associated with increased risk of a composite outcome of CV events and mortality, adjusted HR 1.10 (95% C.I. 1.02– 1.20, p = 0.006).

Conclusion

In this large cohort of community-dwelling older individuals, high plasma TGF-β levels are modestly, but independently associated with lower eGFR but not with albuminuria in cross-sectional analysis. In addition, TGF-β levels are associated with increased risk of CV events and mortality. Further research is needed to determine the direction of association between plasma TGF-β and the risk of CKD and CKD-associated morbidities in older adults.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-017-0509-6) contains supplementary material, which is available to authorized users.

Anti-TGF-β1 Antibody Therapy in Patients with Diabetic Nephropathy

TGF-β has been implicated as a major pathogenic factor in diabetic nephropathy. This randomized, double-blind, phase 2 study assessed whether modulating TGF-β1 activity with a TGF-β1-specific, humanized, neutralizing monoclonal antibody (TGF-β1 mAb) is safe and more effective than placebo in slowing renal function loss in patients with diabetic nephropathy on chronic stable renin-angiotensin system inhibitor treatment. We randomized 416 patients aged ≥25 years with type 1 or type 2 diabetes, a serum creatinine (SCr) level of 1.3-3.3 mg/dl for women and 1.5-3.5 mg/dl for men (or eGFR of 20-60 ml/min per 1.73 m2), and a 24-hour urine protein-to-creatinine ratio ≥800 mg/g to TGF-β1 mAb (2-, 10-, or 50-mg monthly subcutaneous dosing for 12 months) or placebo. We assessed a change in SCr from baseline to 12 months as the primary efficacy variable. Although the Data Monitoring Committee did not identify safety issues, we terminated the trial 4 months early for futility on the basis of their recommendation. The placebo group had a mean±SD change in SCr from baseline to end of treatment of 0.33±0.67 mg/dl. Least squares mean percentage change in SCr from baseline to end of treatment did not differ between placebo (14%; 95% confidence interval [95% CI], 9.7% to 18.2%) and TGF-β1 mAb treatments (20% [95% CI, 15.3% to 24.3%], 19% [95% CI, 14.2% to 23.0%], and 19% [95% CI, 14.0% to 23.3%] for 2-, 10-, and 50-mg doses, respectively). Thus, TGF-β1 mAb added to renin-angiotensin system inhibitors did not slow progression of diabetic nephropathy.

The Effect of Ramipril Therapy on Cytokines and Parameters of Incipient Diabetic Nephropathy in Patients with Type 1 Diabetes Mellitus

We compared the levels of transforming growth factor β1 (TGF-β1), vascular endothelial growth factor (VEGF) and other biochemical parameters in patients with type 1 diabetes mellitus with and without incipient diabetic nephropathy (iDN) and compared them with healthy control subjects. We also measured the effect of 3 and 6 months of ramipril treatment in diabetes patients with iDN. Compared with healthy controls, TGF-β1 levels were increased in both groups of diabetes patients, whereas VEGF was only elevated in patients with iDN. Ramipril did not have a significant effect on TGF-β1 or VEGF levels. We observed a significant decrease in microalbuminuria and cystatin C following ramipril treatment. Increased VEGF levels in patients with iDN suggest a role for this cytokine in the pathogenesis of diabetic nephropathy. Cystatin C would make a suitable marker for the screening and assessment of iDN, and for the evaluation of the therapeutic efficacy of drugs.

Potential renoprotective effects of piceatannol in ameliorating the early-stage nephropathy associated with obesity in obese Zucker rats

Obesity-associated nephropathy is considered to be a leading cause of end-stage renal disease. Resveratrol supplementation represents a promising therapy to attenuate kidney injury, but the poor solubility and limited bioavailability of this polyphenol limits its use in dietary intervention. Piceatannol, a resveratrol analogue, has been suggested as a better option. In this study, we aimed to provide evidence of a preventive action of piceatannol in very early stages of obesity-associated nephropathy. Thirty obese Zucker rats were divided into three experimental groups: one control and two groups orally treated for 6 weeks with 15 and 45 mg piceatannol/kg body weight/day. Enzyme-linked immunosorbent assays (ELISA) were used to determine renal and urinary kidney injury molecule-1 (Kim-1), renal fibrosis markers (transforming growth factor β1 and fibronectin) and renal sirtuin-1 protein. Oxidative stress was assessed in the kidney by measuring lipid peroxidation and nitrosative stress (thiobarbituric acid reactive substrates and 3-nitrotyrosine levels, respectively) together with the activity of the antioxidant enzyme superoxide dismutase. Renal fatty acids profile analysis was performed by thin-layer and gas chromatography. Piceatannol-treated rats displayed lower levels of urinary and renal Kim-1. Renal fibrosis biomarkers and lipid peroxidation exhibited a tendency to decrease in the piceatannol-treated groups. Piceatannol treatment did not modify superoxide dismutase activity or sirtuin-1 protein levels, while it seemed to increase the levels of polyunsaturated and omega-6 polyunsaturated fatty acids in the kidneys. Our findings suggest a mild renoprotective effect of piceatannol in obese Zucker rats and the need of intervention at early stages of renal damage.

Role of upstream stimulatory factor 2 in diabetic nephropathy

Diabetic nephropathy (DN) is the most common cause of end-stage renal disease (ESRD). About 20%-30% of people with type 1 and type 2 diabetes develop DN. DN is characterized by both glomerulosclerosis with thickening of the glomerular basement membrane and mesangial matrix expansion, and tubulointerstitial fibrosis. Hyperglycemia and the activation of the intra-renal renin-angiotensin system (RAS) in diabetes have been suggested to play a critical role in the pathogenesis of DN. However, the mechanisms are not well known. Studies from our laboratory demonstrated that the transcription factor-upstream stimulatory factor 2 (USF2) is an important regulator of DN. Moreover, the renin gene is a downstream target of USF2. Importantly, USF2 transgenic (Tg) mice demonstrate a specific increase in renal renin expression and angiotensin II (AngII) levels in kidney and exhibit increased urinary albumin excretion and extracellular matrix deposition in glomeruli, supporting a role for USF2 in the development of diabetic nephropathy. In this review, we summarize our findings of the mechanisms by which diabetes regulates USF2 in kidney cells and its role in regulation of renal renin-angiotensin system and the development of diabetic nephropathy.

Functional and structural impact of pirfenidone on the alterations of cardiac disease and diabetes mellitus

A synthetic compound, termed pirfenidone (PFD), is considered promising for the treatment of cardiac disease. It leads to beneficial effects in animal models of diabetes mellitus (DM); as well as in heart attack, atrial fibrillation, muscular dystrophy, and diabetic cardiomyopathy (DC). The latter is a result of alterations linked to metabolic syndrome as they promote cardiac hypertrophy, fibrosis and contractile dysfunction. Although reduced level of fibrosis and stiffness represent an essential step in the mechanism of PFD action, a wide range of functional effects might also contribute to the therapeutic benefits. For example, PFD stimulates L-type voltage-gated Ca(2+) channels (LTCCs), which are pivotal for a process known as excitation-contraction coupling (ECC). Recent evidence suggests that these two types of actions - namely structural and functional - aid in treating both cardiac disease and DM. This view is supported by the fact that in DC, for example, systolic dysfunction arises from both cardiac stiffness linked to fibrosis and down-regulation of ECC. Thus, not surprisingly, clinical trials have been conducted with PFD in the settings of DM, for treating not only cardiac but also renal disease. This review presents all these concepts, along with the possible mechanisms and pathophysiological consequences.

HIV-1 latency: an update of molecular mechanisms and therapeutic strategies

The major obstacle towards HIV-1 eradication is the life-long persistence of the virus in reservoirs of latently infected cells. In these cells the proviral DNA is integrated in the host’s genome but it does not actively replicate, becoming invisible to the host immune system and unaffected by existing antiviral drugs. Rebound of viremia and recovery of systemic infection that follows interruption of therapy, necessitates life-long treatments with problems of compliance, toxicity, and untenable costs, especially in developing countries where the infection hits worst. Extensive research efforts have led to the proposal and preliminary testing of several anti-latency compounds, however, overall, eradication strategies have had, so far, limited clinical success while posing several risks for patients. This review will briefly summarize the more recent advances in the elucidation of mechanisms that regulates the establishment/maintenance of latency and therapeutic strategies currently under evaluation in order to eradicate HIV persistence.

Immune activation and HIV persistence: considerations for novel therapeutic interventions

PURPOSE OF REVIEW

One of the potential barriers to current HIV cure strategies is the persistence of elevated levels of immune activation despite otherwise effective antiretroviral therapy (ART). The purpose of this review is to examine the relationship between immune activation and HIV persistence, and to review the novel therapeutic interventions that are currently being pursued to target immune activation in treated HIV disease.

RECENT FINDINGS

Multiple groups have consistently observed that elevated levels of inflammation, immune activation, and immune dysfunction persist in ART-treated individuals, despite the successful suppression of plasma viremia. Increased immune activation may lead to viral persistence through multiple mechanisms. Several novel interventions aimed at decreasing persistent immune activation are being pursued and include studies aimed at decreasing low-level viral replication, approaches aimed at decreasing microbial translocation, interventions to treat co-infections, and therapies that directly target immune activation.

SUMMARY

There appears to be a clear and consistent relationship between immune activation and viral persistence in treated HIV disease. Whether this relationship is causal or mediated through other mechanisms is still unknown. Small-scale, pathogenesis-oriented interventional studies are necessary to further evaluate this relationship and the effect of potential interventions.

Nephropathy in diabetes

The most common cause of end stage renal disease (ESRD) requiring dialysis is diabetes. Both environmental and genetic factors have been postulated as the risk factors of Diabetic Nephropathy (DN). Hyperglycemia-induced metabolic and hemodynamic pathways are recognized to be mediators of kidney injury. Multiple biochemical pathways have been postulated that explain how hyperglycemia causes tissue damage: Non-enzymatic glycation that generates advanced glycation end products, activation of protein kinase C, acceleration of the polyol pathway and oxidative stress. Three major histologic pathological changes occur in DN: Mesangial expansion, GBM thickening, and glomerular sclerosis. It now seems clear in targeting a therapeutic regimen to achieve blood glucose, blood pressure and proteunuric goals, dietary protein and salt restriction, weight reduction, aggressive lipid lowering, smoking cessation and exercise. Multiple intensive interventions reduce cardiovascular events as well as nephropathy by about half when compared with conventional multifactorial treatment.

Circulating bone morphogenetic protein-7 and transforming growth factor-β1 are better predictors of renal end points in patients with type 2 diabetes mellitus

Albuminuria and a reduced glomerular filtration rate are conventional predictors of a future decline in kidney function in patients with type 2 diabetes mellitus. Using a nested case-control study we assessed whether circulating transforming growth factor-β1 (TGF-β1) and bone morphogenetic protein-7 (BMP-7) levels more accurately predict renal end points than the conventional markers. Cases were defined as those who developed a renal end point (doubling of serum creatinine to at least 200 μmol/l, the need for renal replacement therapy, or death due to renal disease) during the study. Using propensity scoring, two controls were selected for each of 281 cases. Participants who developed renal end points had significantly higher total TGF-β1, lower BMP-7 levels, and a higher total TGF-β1 to BMP-7 ratio at baseline. A graded increase in risk was found in individuals with lower BMP-7 levels (odds ratio 24.07, for the lowest to the highest tertile), or significantly higher TGF-β1 levels (odds ratio for the highest to the lowest tertile, 8.43). The area under the receiver operating characteristic curve (c-statistic) for the conventional predictors was 0.73. Using BMP-7 and total and active TGF-β1, the c-statistic was 0.94 (significantly higher to conventional predictors). Thus, our results suggest these novel kidney markers are better predictors of renal progression than the conventional predictors in patients with type 2 diabetes mellitus.

Urinary MCP-1 and RBP: independent predictors of renal outcome in macroalbuminuric diabetic nephropathy

BACKGROUND

Albuminuria has been considered a sine qua non condition for the diagnosis of diabetic nephropathy (DN) and has been widely used as a surrogate outcome of chronic kidney disease (CKD). However, recent data suggest that albuminuria may fail as a biomarker in a subset of patients, and the search for novel markers is intense.

METHODS

We analyzed the role of urinary RBP and of serum and urinary cytokines (TGF-beta, MCP-1 and VEGF) as predictors of the risk of dialysis, doubling of serum creatinine or death (primary outcome, PO) in 56 type 2 diabetic patients with macroalbuminuric DN.

RESULTS

Mean follow-up time was 30.7±10 months. Urinary RBP and MCP-1 were significantly higher in patients presenting the PO, whereas no difference was shown for TGF-β or VEGF. In the Cox regression, urinary RBP, MCP-1 and VEGF were positively associated and serum VEGF was inversely related to the risk of the PO. However, after adjustments for creatinine clearance, proteinuria, and blood pressure only urinary RBP (OR 11.6; 95% CI 2.7-49.2, p=0.001 for log RBP) and urinary MCP-1 (OR 11.0; 95% CI 1.6-76.4, p=0.02 for log MCP-1) remained as significant independent predictors of the PO.

CONCLUSION

Urinary RBP and MCP-1 are independently related to the risk of CKD progression in patients with macroalbuminuric DN. Whether these biomarkers have a role in the setting of normoalbuminuria and microalbuminuria in DN should be further investigated.

Pirfenidone for diabetic nephropathy

Pirfenidone is an oral antifibrotic agent that benefits diabetic nephropathy in animal models, but whether it is effective for human diabetic nephropathy is unknown. We conducted a randomized, double-blind, placebo-controlled study in 77 subjects with diabetic nephropathy who had elevated albuminuria and reduced estimated GFR (eGFR) (20 to 75 ml/min per 1.73 m²). The prespecified primary outcome was a change in eGFR after 1 year of therapy. We randomly assigned 26 subjects to placebo, 26 to pirfenidone at 1200 mg/d, and 25 to pirfenidone at 2400 mg/d. Among the 52 subjects who completed the study, the mean eGFR increased in the pirfenidone 1200-mg/d group (+3.3 ± 8.5 ml/min per 1.73 m²) whereas the mean eGFR decreased in the placebo group (-2.2 ± 4.8 ml/min per 1.73 m²; P = 0.026 versus pirfenidone at 1200 mg/d). The dropout rate was high (11 of 25) in the pirfenidone 2400-mg/d group, and the change in eGFR was not significantly different from placebo (-1.9 ± 6.7 ml/min per 1.73 m²). Of the 77 subjects, 4 initiated hemodialysis in the placebo group, 1 in the pirfenidone 2400-mg/d group, and none in the pirfenidone 1200-mg/d group during the study (P = 0.25). Baseline levels of plasma biomarkers of inflammation and fibrosis significantly correlated with baseline eGFR but did not predict response to therapy. In conclusion, these results suggest that pirfenidone is a promising agent for individuals with overt diabetic nephropathy.

Drug-Induced Changes in Risk/Biomarkers and Their Relationship with Renal and Cardiovascular Long-Term Outcome in Patients with Diabetes

BACKGROUND

Optimal renal and cardiovascular risk management in diabetic patients includes optimal maintenance of blood pressure and control of glucose and lipids. Although the optimal control of these risk factors or “risk/biomarkers” has proven to be effective, it often is difficult to achieve. Consequently, the risk for renal and cardiovascular complications remains devastatingly high. Many risk/biomarkers have been discovered that accurately predict long-term renal and cardiovascular outcome. However, the aim of measuring risk/biomarkers may not be only to determine an individual's risk, but also to use the risk/biomarker level to guide therapy and thereby improve long-term clinical outcome.

CONTENT

This review describes the effects of various drugs on novel risk/biomarkers and the relationship between (drug induced) short-term changes in risk/biomarkers and long-term renal and cardiovascular outcome in patients with diabetes.

SUMMARY

In post hoc analyses of large trials, the short-term reductions in albuminuria, transforming growth factor-β, and N-terminal pro-B–type natriuretic peptide (NT-proBNP) induced by inhibitors of the renin-angiotensin-aldosterone system were associated with a decreased likelihood of long-term adverse renal and cardiovascular outcomes. However, the few studies that systematically investigated the utility of prospectively targeting novel risk/biomarkers such as hemoglobin or NT-proBNP failed to demonstrate long-term cardiovascular protection. The latter examples suggest that although a risk/biomarker may have superior prognostic ability, therapeutically changing such a risk/biomarker does not necessarily improve long-term outcome. Thus, to establish the clinical utility of other novel risk/biomarkers, clinical trials must be performed to prospectively examine the effects of therapeutically-induced changes in single or multiple risk/biomarkers on long-term risk management of patients with diabetes.

New pharmacological treatments for improving renal outcomes in diabetes

Diabetic nephropathy is the most common and most rapidly growing cause of end-stage renal failure in developed countries. Diabetic nephropathy results from complex interactions between genetic, metabolic and hemodynamic factors. Improvements in our understanding of the pathogenesis of fibrosis associated with diabetic kidney disease have led to the identification of several novel targets for the treatment of diabetic nephropathy. Albuminuria is a useful clinical marker of diabetic nephropathy, as it can be used to predict a decline in renal function. A reduction in albuminuria might not, however, be reflective of a protective effect of therapies focused on ameliorating renal fibrosis. Although new strategies for slowing down the progression of several types of renal disease have emerged, the challenge of arresting the relentless progression of diabetic nephropathy remains. In this Review, we discuss novel pharmacological approaches that aim to improve the renal outcomes of diabetic nephropathy, including the use of direct renin inhibitors and statins. We also discuss the promise of using antifibrotic agents to treat diabetic nephropathy. The need for novel biomarkers of diabetic nephropathy is also highlighted.

Infusion of angiotensin-(1-7) reduces glomerulosclerosis through counteracting angiotensin II in experimental glomerulonephritis

Recent identification of a counterregulatory axis of the renin-angiotensin system, called angiotensin-converting enzyme 2-angiotensin-(1-7) [ANG-(1-7)]-Mas receptor, may offer new targets for the treatment of renal fibrosis. We hypothesized that therapy with ANG-(1-7) would improve glomerulosclerosis through counteracting ANG II in experimental glomerulonephritis. Disease was induced in rats with the monoclonal anti-Thy-1 antibody, OX-7. Based on a three-dose pilot study, 576 microg x kg(-1) x day(-1) ANG-(1-7) was continuously infused from day 1 using osmotic pumps. Measures of glomerulosclerosis include semiquantitative scoring of matrix proteins stained for periodic acid Schiff, collagen I, and fibronectin EDA+ (FN). ANG-(1-7) treatment reduced disease-induced increases in proteinuria by 75%, glomerular periodic acid Schiff staining by 48%, collagen I by 24%, and FN by 25%. The dramatic increases in transforming growth factor-beta1, plasminogen activator inhibitor-1, FN, and collagen I mRNAs seen in disease control animals compared with normal rats were all significantly reduced by ANG-(1-7) administration (P < 0.05). These observations support our hypothesis that ANG-(1-7) has therapeutic potential for reversing glomerulosclerosis. Several results suggest ANG-(1-7) acts by counteracting ANG II effects: 1) renin expression in ANG-(1-7)-treated rats was dramatically increased as it is with ANG II blockade therapy; and 2) in vitro data indicate that ANG II-induced increases in mesangial cell proliferation and plasminogen activator inhibitor-1 overexpression are inhibited by ANG-(1-7) via its binding to a specific receptor known as Mas.

Effect of RAS inhibition on TGF-β, renal function and structure in experimentally induced diabetic hypertensive nephropathy rats

OBJECTIVE

Transforming growth factor-β (TGF-β) implicated in the pathogenesis of diabetic nephropathy. Hence, developing agents that antagonize fibrogenic signals is a critical issue facing researchers.

MATERIAL AND METHODS

Fifty rats were allocated to five groups: 1=control rats, 2=diabetic hypertensive rats 3=diabetic hypertensive rats treated with spironolactone, 4=diabetic hypertensive rats treated with moexpril, 5=diabetic hypertensive rats treated with both spironolactone and moexpril. Measurement of TGF-β, aldosterone, creatinine and ACE. Degree of fibrosis was calculated.

RESULTS

Serum creatinine, mean arterial blood pressure (MAP), aldosterone, ACE, TGF-β and renal fibrosis increased significantly in untreated diabetic hypertensive rats compared with control rats. Administration of spironolactone, moexpril, or both decreased these changes.

CONCLUSIONS

Addition of the spironolactone to moexpril was more effective in reducing fibrosis and improvement of renal function than monotherapy with either drug, possibly due to a dual inhibitory effect on the RAS, and thus suppression of TGF-β.

Diabetic nephropathy

Diabetic nephropathy is the leading cause of chronic renal disease and a major cause of cardiovascular mortality. Diabetic nephropathy has been categorized into stages: microalbuminuria and macroalbuminuria. The cut-off values of micro- and macroalbuminuria are arbitrary and their values have been questioned. Subjects in the upper-normal range of albuminuria seem to be at high risk of progression to micro- or macroalbuminuria and they also had a higher blood pressure than normoalbuminuric subjects in the lower normoalbuminuria range. Diabetic nephropathy screening is made by measuring albumin in spot urine. If abnormal, it should be confirmed in two out three samples collected in a three to six-months interval. Additionally, it is recommended that glomerular filtration rate be routinely estimated for appropriate screening of nephropathy, because some patients present a decreased glomerular filtration rate when urine albumin values are in the normal range. The two main risk factors for diabetic nephropathy are hyperglycemia and arterial hypertension, but the genetic susceptibility in both type 1 and type 2 diabetes is of great importance. Other risk factors are smoking, dyslipidemia, proteinuria, glomerular hyperfiltration and dietary factors. Nephropathy is pathologically characterized in individuals with type 1 diabetes by thickening of glomerular and tubular basal membranes, with progressive mesangial expansion (diffuse or nodular) leading to progressive reduction of glomerular filtration surface. Concurrent interstitial morphological alterations and hyalinization of afferent and efferent glomerular arterioles also occur. Podocytes abnormalities also appear to be involved in the glomerulosclerosis process. In patients with type 2 diabetes, renal lesions are heterogeneous and more complex than in individuals with type 1 diabetes. Treatment of diabetic nephropathy is based on a multiple risk factor approach, and the goal is retarding the development or progression of the disease and to decrease the subject's increased risk of cardiovascular disease. Achieving the best metabolic control, treating hypertension (<130/80 mmHg) and dyslipidemia (LDL cholesterol <100 mg/dl), using drugs that block the renin-angiotensin-aldosterone system, are effective strategies for preventing the development of microalbuminuria, delaying the progression to more advanced stages of nephropathy and reducing cardiovascular mortality in patients with diabetes.

Rab34 and its effector munc13-2 constitute a new pathway modulating protein secretion in the cellular response to hyperglycemia

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease requiring dialysis in the Western world. Clinical studies reveal that stringent control of blood glucose levels reduces the risk of most diabetic complications, underscoring the importance of understanding the cellular response to hyperglycemia. Our work identifies a new pathway of potential significance in this response, linking hyperglycemia to the stimulation of constitutive protein secretion via a pathway involving munc13 and rab34. These two proteins have previously been shown to interact at the Golgi via the munc13 homology domain 2 (MHD2). In the present study, using cultured rat mesangial cells (RMC), we show that high glucose-induced upregulation of endogenous munc13-2 increases secretion of the model protein, vesicular stomatitis virus glycoprotein-green fluorescent protein (VSVG-GFP), while small interfering (si)RNA-mediated knockdown of either munc13-2 or rab34 abolishes this effect. Similarly, increased secretion of VSVG-GFP is observed following transfection of HeLa cells with wild-type munc13-2, but not when HeLa cells are transfected with a mutant protein in which the MHD2 domain is deleted. Finally, we show that high glucose-stimulated secretion of fibronectin in RMC is abolished by siRNA knockdown of munc13-2. Collectively, our results demonstrate that the mechanistic basis for our observed high glucose-induced protein secretion is through interaction of munc13 and rab34, indicating a potentially critical role for this newly described pathway in the pathogenesis of DN.

TGF-beta and fibrosis in different organs - molecular pathway imprints

The action of transforming-growth-factor (TGF)-beta following inflammatory responses is characterized by increased production of extracellular matrix (ECM) components, as well as mesenchymal cell proliferation, migration, and accumulation. Thus, TGF-beta is important for the induction of fibrosis often associated with chronic phases of inflammatory diseases. This common feature of TGF-related pathologies is observed in many different organs. Therefore, in addition to the description of the common TGF-beta-pathway, this review focuses on TGF-beta-related pathogenetic effects in different pathologies/organs, i. e., arthritis, diabetic nephropathy, colitis/Crohn's disease, radiation-induced fibrosis, and myocarditis (including their similarities and dissimilarities). However, TGF-beta exhibits both exacerbating and ameliorating features, depending on the phase of disease and the site of action. Due to its central role in severe fibrotic diseases, TGF-beta nevertheless remains an attractive therapeutic target, if targeted locally and during the fibrotic phase of disease.

Diabetic complications: a role for the prorenin-(pro)renin receptor-TGF-beta1 axis?

Morbidity and mortality of diabetes mellitus are strongly associated with cardiovascular disease including nephropathy. A discordant tissue renin-angiotensin system (RAS) might be a mediator of the endothelial dysfunction leading to both micro- and macrovascular complications of diabetes. The elevated plasma levels of prorenin in diabetic subjects with microvascular complications might be part of this discordant RAS, especially since the plasma renin levels in diabetes are low. Prorenin, previously thought of as an inactive precursor of renin, is now known to bind to a (pro)renin receptor, thus activating locally angiotensin-dependent and -independent pathways. In particular, the stimulation of the transforming growth factor-beta (TGF-beta) system by prorenin could be an important contributor to diabetic disease complications. This review discusses the concept of the prorenin-(pro)renin receptor-TGF-beta(1) axis, concluding that interference with this pathway might be a next logical step in the search for new therapeutic regimens to reduce diabetes-related morbidity and mortality.

Circulating transforming growth factor-beta1 levels and the risk for kidney disease in African Americans

Transforming growth factor-β1 (TGF-β1) is well known to induce progression of experimental renal disease. Here we determined whether there is an association between serum levels of TGF-β1 and the risk factors for progression of clinically relevant renal disorders in 186 black and 147 white adults none of whom had kidney disease or diabetes. Serum TGF-β1 protein levels were positively and significantly associated with plasma renin activity along with the systolic and diastolic blood pressure in blacks but not whites after controlling for age, gender and body mass index. These TGF-β1 protein levels were also significantly associated with body mass index and metabolic syndrome and more predictive of microalbuminuria in blacks than in whites. The differential association between TGF-β1 and renal disease risk factors in blacks and whites suggests an explanation for the excess burden of end-stage renal disease in the black population but this requires validation in an independent cohort. Whether these findings show that it is the circulating levels of TGF-β1 that contributes to renal disease progression or reflects other unmeasured factors will need to be tested in longitudinal studies.

Association of oxidized low-density lipoprotein and transforming growth factor-beta in type 2 diabetic patients: a cross-sectional study

Recent in vitro evidence suggests that oxidized low-density lipoprotein (ox-LDL) stimulates the expression of transforming growth factor-beta (TGF-beta) by human glomerular epithelial cells. An elevated level of TGF-beta, which is a multifunctional growth cytokine, is also reported in diabetic patients. This study aimed to determine the association between ox-LDL and TGF-beta in healthy and type 2 diabetic participants. A total of 80 type 2 diabetic patients, who were referred to the outpatient diabetes clinic of a university general hospital, and 80 healthy controls matched for sex, age, and body mass index (BMI) were recruited. Fasting blood samples were obtained, and fasting plasma glucose, cholesterol, high-density lipoprotein-cholesterol (HDL-c), LDL-cholesterol, triglycerides, creatinine, HbA1C, ox-LDL, and TGF-beta were measured. Ox-LDL and TGF-beta were significantly greater in diabetic patients than healthy controls (72.66 +/- 3.11, 46.02 +/- 1.64, P < 0.001 and 4.75 +/- 0.43, 2.06 +/- 0.31, P < 0.001, respectively). Ox-LDL was significantly correlated to TGF-beta in diabetic patients (r = 0.318, P = 0.004). This significant association was not observed in healthy controls (r = 0.148, P = 0.191). In multivariate linear regression analysis after adjustment for age, sex, BMI, and creatinine, ox-LDL was a significant independent predictor of TGF-beta (beta = 0.308, P = 0.007). In conclusion, this study demonstrated that ox-LDL is significantly correlated to TGF-beta in type 2 diabetic patients.

Different roles for TGF-beta and VEGF in the pathogenesis of the cardinal features of diabetic nephropathy

Hemodynamic stress in concert with metabolic pathways that are activated by hyperglycemia, glycated proteins, and oxidative stress induce a host of growth factors in the kidney. The fibrogenic cytokine transforming growth factor-beta (TGF-beta), through its Smad3 signaling pathway, is the etiologic agent of renal hypertrophy and the accumulation of mesangial extracellular matrix components in diabetes. Neutralizing anti-TGF-beta antibodies, antisense TGF-beta1 oligodeoxynucleotides or knocking off the Smad3 gene prevent and/or reverse the hypertrophic and profibrotic effects of the diabetic state in mice. However, there is limited evidence to support a role for TGF-beta in the development of albuminuria. Podocyte-derived vascular endothelial growth factor (VEGF), a permeability and angiogenic factor whose expression is also increased in animal models of diabetic kidney disease, appears to act in a novel autocrine signaling mode to induce the podocytopathy of diabetes, especially the genesis of albuminuria. Future strategies for therapy of diabetic nephropathy may therefore need to involve interception of both the TGF-beta and the VEGF signaling pathways to counter the matrix accumulation and to improve the albuminuria. Interception of the renin-angiotensin system may achieve this goal but other novel strategies will need to be developed that would be more efficacious. However, a note of caution should be raised not to lower the heightened activities of these two signaling pathways much below normal levels because a basal activity for each is essential for the optimal homeostasis of glomerular cells.

Agents in development for the treatment of diabetic nephropathy

BACKGROUND

Nephropathy is a major cause of morbidity and mortality in diabetic patients. Current treatments include optimization of glycemic and blood pressure control, but more innovative strategies are needed for the prevention and treatment of diabetic nephropathy.

OBJECTIVES

To review emerging therapies for diabetic nephropathy.

METHODS

This paper discusses the molecular mechanisms of diabetic nephropathy and the potential therapeutic interventions.

RESULTS/CONCLUSION

New therapies, including those targeting the accumulation of advanced glycation end products (AGEs) and reactive oxygen species (ROS) generation, are likely to feature in future treatment regimens. Other approaches that at this stage do not appear to be progressing include the glycosaminoglycan sulodexide and the protein kinase C-beta (PKC-beta) inhibitor, ruboxistaurin.

Fibrosis in diabetes complications: pathogenic mechanisms and circulating and urinary markers

Diabetes mellitus is characterized by a lack of insulin causing elevated blood glucose, often with associated insulin resistance. Over time, especially in genetically susceptible individuals, such chronic hyperglycemia can cause tissue injury. One pathological response to tissue injury is the development of fibrosis, which involves predominant extracellular matrix (ECM) accumulation. The main factors that regulate ECM in diabetes are thought to be pro-sclerotic cytokines and protease/anti-protease systems. This review will examine the key markers and regulators of tissue fibrosis in diabetes and whether their levels in biological fluids may have clinical utility.

The pathogenesis of diabetic nephropathy

Between 20% and 40% of patients with diabetes ultimately develop diabetic nephropathy, which in the US is the most common cause of end-stage renal disease requiring dialysis. Diabetic nephropathy has several distinct phases of development and multiple mechanisms contribute to the development of the disease and its outcomes. This Review provides a summary of the latest published data dealing with these mechanisms; it focuses not only on candidate genes associated with susceptibility to diabetic nephropathy but also on alterations in various cytokines and their interaction with products of advanced glycation and oxidant stress. Additionally, the interactions between fibrotic and hemodynamic cytokines, such as transforming growth factor beta1 and angiotensin II, respectively, are discussed in the context of new information concerning nephropathy development. We touch on the expanding clinical data regarding markers of nephropathy, such as microalbuminuria, and put them into context; microalbuminuria reflects cardiovascular and not renal risk. If albuminuria levels continue to increase over time then nephropathy is present. Lastly, we look at advances being made to enable identification of genetically predisposed individuals.

ACE inhibitor reduces growth factor receptor expression and signaling but also albuminuria through B2-kinin glomerular receptor activation in diabetic rats

Diabetic nephropathy (DN) is associated with increased oxidative stress, overexpression and activation of growth factor receptors, including those for transforming growth factor-β1 (TGF-β-RII), platelet-derived growth factor (PDGF-R), and insulin-like growth factor (IGF1-R). These pathways are believed to represent pathophysiological determinants of DN. Beyond perfect glycemic control, angiotensin-converting enzyme inhibitors (ACEI) are the most efficient treatment to delay glomerulosclerosis. Since their mechanisms of action remain uncertain, we investigated the effect of ACEI on the glomerular expression of these growth factor pathways in a model of streptozotocin-induced diabetes in rats. The early phase of diabetes was found to be associated with an increase in glomerular expression of IGF1-R, PDGF-R, and TGF-β-RII and activation of IRS1, Erk 1/2, and Smad 2/3. These changes were significantly reduced by ACEI treatment. Furthermore, ACEI stimulated glutathione peroxidase activity, suggesting a protective role against oxidative stress. ACEI decreased ANG II production but also increased bradykinin bioavailability by reducing its degradation. Thus the involvement of the bradykinin pathway was investigated using coadministration of HOE-140, a highly specific nonpeptidic B2-kinin receptor antagonist. Almost all the previously described effects of ACEI were abolished by HOE-140, as was the increase in glutathione peroxidase activity. Moreover, the well-established ability of ACEI to reduce albuminuria was also prevented by HOE-140. Taken together, these data demonstrate that, in the early phase of diabetes, ACEI reverse glomerular overexpression and activation of some critical growth factor pathways and increase protection against oxidative stress and that these effects involve B2-kinin receptor activation.

Renal disease in recipients of nonrenal solid organ transplantation

Worldwide, more than 250,000 individuals who have received a liver, heart, lung, or intestinal transplant are living longer. Twenty percent to 25% of these recipients experience perioperative acute renal failure, with 10% to 15% requiring renal replacement therapy. Chronic kidney disease (CKD) is also highly prevalent, affecting 30% to 50% of the nonrenal organ transplant population with an annual end-stage renal disease risk of 1.5% to 2.0%. Both acute renal failure and CKD contribute to increased morbidity and premature mortality. The dominant causative factor for renal disorders seen in nonrenal transplant recipients are the calcineurin inhibitors (CNI) and rapamycin analogues, which singly or in combination lead to a variety of nephrotoxic injury. However, 25% to 30% of nonrenal transplant recipients with CKD have other conditions such as hypertension, focal segmental glomerulosclerosis, diabetes mellitus, and hepatitis C infection as the principal underlying cause. Management strategies for renal disease in the nonrenal transplant recipients include the following: (1) delayed introduction of CNI after graft implantation, (2) withdrawal or minimization of long-term CNI therapy, (3) timely use of an appropriate dialysis modality, and (4) expeditious introduction of supportive measures such as anemia management, phosphate binding therapy, and dietary modification. Compared with maintenance dialysis, kidney transplantation reduces long-term mortality by 60% to 70% in nonrenal transplant recipients with end-stage renal disease.

Pharmacological management of renal fibrotic disease

Chronic kidney diseases frequently advance to end-stage renal failure, and the number of patients affected is steadily increasing worldwide. At the molecular level, progression of renal insufficiency correlates closely with ongoing pathological matrix protein expansion (i.e., renal fibrosis), in a manner independent of the underlying disorder. Overactivity of the renin-angiotensin system and of the TGF-beta system have been identified as key mediators of kidney matrix accumulation, and are principal targets in the management of chronic renal disease. This review provides a recent overview of the therapeutic options that are clinically established, and of novel molecular strategies that will approach clinical practice in the near future.

Effect of combination therapy with enalapril and the TGF-β antagonist 1D11 in unilateral ureteral obstruction

In unilateral ureteral obstruction (UUO), the kidney is characterized by increased fibrosis and apoptosis. Both transforming growth factor-β (TGF-β) and ANG II have been implicated, and ANG II may mediate its effects through TGF-β. Previous studies demonstrated amelioration of renal damage when either TGF-β or ANG II has been individually targeted. In this study, we sought to determine whether combining 1D11 (monoclonal antibody to TGF-β) and an ACE inhibitor, enalapril, would be more effective in UUO than either individual treatment, as has been shown in diabetic and glomerulonephritic models. Rats underwent UUO and were given either control monoclonal antibody, 1D11 or enalapril, or 1D11/enalapril combination, for 14 days. Kidneys were harvested and examined for fibrosis [trichrome; collagen (real-time PCR, Sircol assay) and fibroblast-specific protein expression (immunohistochemistry), apoptosis (TUNEL), macrophage infiltration (immunohistochemistry), and TGF-β expression (real-time PCR and tubular localization with immunohistochemistry)]. UUO was found to induce fibrosis, apoptosis, macrophage infiltration, and TGF-β expression in the obstructed kidney. Administration of either 1D11 or enalapril individually significantly decreased all these changes; when 1D11 and enalapril were combined, there was little additive effect, and the combination did not provide full protection against damage. The results demonstrate that, for the most part, combination therapy is not additive in UUO. This could be due to the continued presence of a physical obstruction or to biochemical differences between UUO and other renal disease models. Furthermore, it suggests that other targets may be amenable to pharmacological manipulation in UUO.

Transforming growth factor-beta in human diabetic nephropathy: effects of ACE inhibition

OBJECTIVE

Studies in rodent models have suggested that reduction in renal transforming growth factor (TGF)-beta1 may underlie the renoprotective effects of the renin-angiotensin system (RAS) blockade. However, the role of the RAS blockade in abrogating TGF-beta in human disease is unknown. Accordingly, we sought to examine TGF-beta gene expression and biological activity in human renal biopsies, before and after ACE inhibition.

RESEARCH DESIGN AND METHODS

RNA was extracted from renal biopsies taken from participants in the Diabiopsies study, a randomized controlled 2-year trial of 4 mg/day perindopril versus placebo that reported a reduction in proteinuria and cortical matrix expansion in type 2 diabetic nephropathy. Biopsies taken at study entry and at 2 years were obtained in 12 patients (6 placebo and 6 taking perindopril). TGF-beta1 and its receptor mRNA were quantified by real-time PCR, and its biological activity was assessed by examining the activation of its intracellular signaling pathway (phosphorylated Smad2) and the expression TGF-beta-inducible gene H3 (betaig-H3).

RESULTS

At baseline, TGF-beta1 expression was similar in both placebo- and perindopril-treated groups and was unchanged over a 2-year period in biopsies of placebo-treated subjects. In contrast, perindopril treatment led to a substantial diminution in TGF-beta1 mRNA (mean 83% reduction, P < 0.05). Phosphorylated Smad2 immunolabeling and betaig-H3 mRNA were similarly reduced with ACE inhibition (P < 0.05) but unchanged in the placebo group. No differences were noted in the gene expression of TGF-beta receptor II in biopsies of either placebo- or perindopril-treated subjects.

CONCLUSIONS

This study demonstrates that over a 2-year period, treatment with perindopril in patients with type 2 diabetes and nephropathy leads to a reduction in both renal TGF-beta1 gene expression and its downstream activation.

Transforming growth factor-beta 1 stimulates angiotensinogen gene expression in kidney proximal tubular cells

The present study investigated whether transforming growth factor-beta 1 (TGF-beta1) exerts an autocrine positive effect on angiotensinogen (ANG) gene expression in rat kidney proximal tubular cells, and delineates its underlying mechanism(s) of action. Rat immortalized renal proximal tubular cells (IRPTCs) and freshly isolated mouse renal proximal tubules were incubated in the absence or presence of active human TGF-beta1. IRPTCs were also stably transfected with rat TGF-beta1 or p53 tumor suppressor protein (p53) cDNA in sense (S) and antisense (AS) orientations. ANG mRNA and p53 protein expression were assessed by reverse transcription-polymerase chain reaction and Western blotting, respectively. Reactive oxygen species (ROS) generation was quantified by lucigenin assay. Active TGF-beta1 evoked ROS generation and stimulated ANG mRNA and p53 protein expression, whereas a superoxide scavenger and inhibitors of nicotinamide adenine dinucleotide oxidase and p38 mitogen-activated protein kinase (p38 MAPK) abolished the TGF-beta1 effect. Stable transfer of p53 cDNA (S) enhanced and p53 cDNA (AS) abolished the stimulatory effect of TGF-beta1 on ANG mRNA expression in IRPTCs. Our results demonstrate that TGF-beta1 stimulates ANG gene expression and its action is mediated, at least in part, via ROS generation, p38 MAPK activation, and p53 expression, suggesting that angiotensin II and TGF-beta1 may form a positive feedback loop to enhance their respective gene expression, leading to renal injury.

Dual blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers in chronic kidney disease

Despite the renoprotective effects of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs), many patients with chronic kidney disease develop end-stage kidney disease. Combination treatment with an ACEI and an ARB is a recently introduced approach to obtain more complete blockade of the renin-angiotensin system, based on the different mechanisms of action of the two classes of drug. To assess the shortcomings of single treatment with ACEIs and ARBs, and the potential benefits of combination treatment, we reviewed the experimental and clinical evidence suggesting that combination treatment offers more complete blockade of the renin-angiotensin system and identified areas in which further research is necessary to confirm the benefits of combination treatment. The available data suggest that combination treatment with an ACEI and an ARB has a greater renoprotective effect than either drug alone. In addition, more recent data have shown that combination treatment is more potent in suppressing renal fibrosis, and is well tolerated in patients with advanced chronic kidney disease. Clinical trials with rigorous endpoints are needed to further establish the benefits of combination treatment in renal protection.