Effect of octreotide, captopril or insulin on renal changes and UAE in long-term experimental diabetes

Does Enalapril Prevent Peritoneal Fibrosis Induced by Hypertonic (3.86%) Peritoneal Dialysis Solution?

Objective

Peritoneal fibrosis (PF) is one of the most serious causes of failure in continuous ambulatory peritoneal dialysis (PD). Although the underlying mechanism responsible for the genesis of PF is still unknown, transforming growth factor p (TGFβ1) has been shown to be associated with PF. Angiotensin converting enzyme inhibitors have been shown to prevent the stimulating effect of growth factors. The aim of the present study was to investigate the effect of enalapril on peritoneal function and morphology in a rat model of experimental PF.

Methods

Twenty-one albino Wistar rats were divided into three groups: ( 1 ) the control group (C) received 10 mL isotonic saline intraperitoneally (IP), ( 2 ) the dextrose (Dx) group 10 mL 3.86% dextrose PD solution IP, and ( 3 ) the enalapril-treated group (ENA) 10 cc 3.86% dextrose PD solution IP plus 100 mg/L enalapril in drinking water. After 4 weeks, a 1-hour peritoneal equilibration test was performed with 20 mL 2.27% dextrose PD solution. Dialysate-to-plasma urea ratio (D/P urea), glucose reabsorption (D1/D0 glucose), ultrafiltration (UF) volume, and levels of dialysate protein, TGFβ1, and cancer antigen 125 (CA125) were determined. The parietal peritoneum was evaluated histologically by light microscopy.

Results

Administration of enalapril resulted in preserved UF (-0.2 ± 0.7 mL vs 1.7 ± 0.3 mL, p < 0.05), protein loss (2.3 ± 0.5 g/L vs 1.6 ± 0.2 g/L, p > 0.05), and peritoneal thickness (77 ± 7 μ vs 38 ± 5 μ, p < 0.001). D/P urea increased significantly in the Dx group ( p < 0.05). Both higher levels of TGFβ1 (undetectable vs 298 ± 43 pg/mL, p < 0.001) and lower levels of CA125 in dialysate effluent (0.94 ± 0.5 U/L vs 0.11 ± 0.1 U/L, p > 0.05) were determined in the Dx group.

Conclusion

These findings show that peritoneal morphology and function tests were dramatically deranged in the Dx group. The same properties were partially preserved in the ENA group. The production of TGFβ1 was significantly reduced but peritoneal thickness was not completely inhibited. In conclusion, by inhibiting the production of TGFβ1, enalapril can preserve peritoneal histology, peritoneal function, and remodeling of mesothelial cells.

The roles of sodium-glucose cotransporter 2 inhibitors in preventing kidney injury in diabetes

Diabetic nephropathy (DN) is the leading cause of end stage renal disease (ESRD) worldwide. The early effective treatment of high plasma glucose could delay or prevent the onset of DN. Sodium-glucose cotransporter 2 (SGLT2) inhibitors are new target treatments for ameliorating high plasma glucose and help to maintain glucose homeostasis in diabetic patients. Reduced renal glucose reabsorption by SGLT2 inhibition seems to have high potential to improve glycemic control in diabetes mellitus (DM) not only through glucose lowering but also through glucose-independent effects such as blood pressure-lowering and direct renal effects in diabetes. Of note, the important events in the pathogenesis of glucose-induced renal injury and DN including oxidative stress, inflammation, fibrosis and apoptosis conditions have shown to be ameliorate after the treatment with SGLT2 inhibitors. Interestingly, SGLT2 inhibitors have been reported to reduce albuminuria in DM via an activation of renal tubuloglomerular feedback by increased macula densa sodium and chloride delivery, leading to afferent vasoconstriction and attenuated diabetes-induced renal hyperfiltration. These effects also help to conserve glomerular integrity. Thus, the treatment of diabetes mellitus using SGLT2 inhibitors could be one of the effective approach for the management of diabetic-associated kidney disease like DN. This review summarizes the up to date information and discusses the bidirectional relationship between the SGLT2 inhibitor treatments and the renal functions that are available from both basic research and clinical reports. The details of renal outcomes of SGLT2 inhibitors in DN are also provide in this review.

Diabetic nephropathy: What does the future hold?

The consensus management of diabetic nephropathy (DN) in 2015 involves good control of glycaemia, dyslipidaemia and blood pressure (BP). Blockade of the renin-angiotensin-aldosterone system using angiotensin-converting enzyme inhibitors, angiotensin-2 receptor blockers or mineralocorticoid inhibitors are key therapeutic approaches, shown to be beneficial once overt nephropathy is manifest, as either, or both, of albuminuria and loss of glomerular filtration rate. Some significant additional clinical benefits in slowing the progression of DN was reported from the Remission clinic experience, where simultaneous intensive control of BP, tight glycaemic control, weight loss, exercise and smoking cessation were prioritised in the management of DN. This has not proved possible to translate to more conventional clinical settings. This review briefly looks over the history and limitations of current therapy from landmark papers and expert reviews, and following an extensive PubMed search identifies the most promising clinical biomarkers (both established and proposed). Many challenges need to be addressed urgently as in order to obtain novel therapies in the clinic; we also need to examine what we mean by remission, stability and progression of DN in the modern era.

Mechanisms of diabetic complications

It is increasingly apparent that not only is a cure for the current worldwide diabetes epidemic required, but also for its major complications, affecting both small and large blood vessels. These complications occur in the majority of individuals with both type 1 and type 2 diabetes. Among the most prevalent microvascular complications are kidney disease, blindness, and amputations, with current therapies only slowing disease progression. Impaired kidney function, exhibited as a reduced glomerular filtration rate, is also a major risk factor for macrovascular complications, such as heart attacks and strokes. There have been a large number of new therapies tested in clinical trials for diabetic complications, with, in general, rather disappointing results. Indeed, it remains to be fully defined as to which pathways in diabetic complications are essentially protective rather than pathological, in terms of their effects on the underlying disease process. Furthermore, seemingly independent pathways are also showing significant interactions with each other to exacerbate pathology. Interestingly, some of these pathways may not only play key roles in complications but also in the development of diabetes per se. This review aims to comprehensively discuss the well validated, as well as putative mechanisms involved in the development of diabetic complications. In addition, new fields of research, which warrant further investigation as potential therapeutic targets of the future, will be highlighted.

Resveratrol ameliorates early diabetic nephropathy associated with suppression of augmented TGF-β/smad and ERK1/2 signaling in streptozotocin-induced diabetic rats

Diabetic nephropathy (DN) is the major cause of end-stage renal disease. The early changes in DN are characterized by an increased in kidney size, glomerular volume, and kidney function, followed by the accumulation of glomerular extracellular matrix, increased urinary albumin excretion (UAE), glomerular sclerosis, and tubular fibrosis. Resveratrol (RSV) has been shown to ameliorate hyperglycemia and hyperlipidemia in streptozotocin-induced diabetic rats. In the present study, we examined the beneficial effects of RSV on DN and explored the possible mechanism of RSV action. Male Sprague-Dawley rats were injected with streptozotocin at 65mg/kg body weight. The induction of diabetes mellitus (DM) was confirmed by a fasting plasma glucose level ≥300mg/dL and symptoms of polyphagia and polydipsia. The DM rats were treated with or without RSV at 0.75mg/kg body weight 3 times a day for 8 weeks. Animals were sacrificed and kidney histology was examined by microscopy. Urinary albumin excretion, glomerular hypertrophy and expressions of fibronectin, collagen IV, and TGF-β in the glomeruli were alleviated in RSV-treated DM rats, but not in untreated DM rats. In addition, RSV treatment reduced the thickness of the glomerular basement membrane (GBM) to the original thickness and increased nephrin expressions to normal levels in DM rats. Moreover, RSV inhibited phosphorylation of smad2, smad3 and ERK1/2 in diabetic rat kidneys. This is the first report showing that RSV alleviates early glomerulosclerosis in DN through TGF-β/smad and ERK1/2 inhibition. In addition, podocyte injuries of diabetic kidneys are lessened by RSV.

What is the mechanism of microalbuminuria in diabetes: a role for the glomerular endothelium?

Microalbuminuria is an important risk factor for cardiovascular disease and progressive renal impairment. This holds true in the general population and particularly in those with diabetes, in whom it is common and marks out those likely to develop macrovascular disease and progressive renal impairment. Understanding the pathophysiological mechanisms through which microalbuminuria occurs holds the key to designing therapies to arrest its development and prevent these later manifestations. Microalbuminuria arises from the increased passage of albumin through the glomerular filtration barrier. This requires ultrastructural changes rather than alterations in glomerular pressure or filtration rate alone. Compromise of selective glomerular permeability can be confirmed in early diabetic nephropathy but does not correlate well with reported glomerular structural changes. The loss of systemic endothelial glycocalyx--a protein-rich surface layer on the endothelium--in diabetes suggests that damage to this layer represents this missing link. The epidemiology of microalbuminuria reveals a close association with systemic endothelial dysfunction and with vascular disease, also implicating glomerular endothelial dysfunction in microalbuminuria. Our understanding of the metabolic and hormonal sequelae of hyperglycaemia is increasing, and we consider these in the context of damage to the glomerular filtration barrier. Reactive oxygen species, inflammatory cytokines and growth factors are key players in this respect. Taken together with the above observations and the presence of generalised endothelial dysfunction, these considerations lead to the conclusion that glomerular endothelial dysfunction, and in particular damage to its glycocalyx, represents the most likely initiating step in diabetic microalbuminuria.

Inhibitory effect of somatostatin on inflammation and nociception

The present review focuses on promising new opportunities for anti-inflammatory and analgesic therapy. The theoretical background is an original observation based on our own experimental results. These data demonstrate that somatostatin is released from capsaicin-sensitive, peptidergic sensory nerve endings in response to noxious heat and chemical stimuli such as vanilloids, protons or lipoxygenase products. It reaches distant parts of the body via the circulation and exerts systemic anti-inflammatory and analgesic effects. Somatostatin binds to G-protein-coupled membrane receptors (sst(1)-sst(5)) and diminishes neurogenic inflammation by prejunctional action on sensory-efferent nerve terminals, as well as by postjunctional mechanisms on target cells. It decreases the release of pro-inflammatory neuropeptides from sensory nerve endings and also acts on receptors of vascular endothelial, inflammatory and immune cells. Analgesic effect is mediated by an inhibitory action on peripheral terminals of nociceptive neurons, since circulating somatostatin cannot exert central action. Somatostatin itself is not suitable for drug development because of its broad spectrum and short elimination half life, stable, receptor-selective agonists have been synthesized and investigated. The present overview is aimed at summarizing the physiological importance of somatostatin and sst receptors, pharmacological significance of synthetic agonists and their potential in the development of novel anti-inflammatory and analgesic drugs. These compounds might provide novel perspectives in the pharmacotherapy of acute and chronic painful inflammatory diseases, as well as neuropathic conditions.

An IGF-I antagonist does not inhibit renal fibrosis in the rat following subtotal nephrectomy

Insulin-like growth factor I (IGF-I) has been proposed as a mediator of kidney scarring, although no interventional studies on the role of IGF-I in models of chronic kidney disease have been reported. The effect of a peptide IGF-I receptor antagonist (JB3) has been examined on kidney fibrosis and function in the rat following 5/6 subtotal nephrectomy (SNx). Male Wistar rats were anesthetized with halothane and subjected to SNx. JB3 was delivered by subcutaneous infusion using Alzet osmotic minipumps. In vitro studies showed JB3 to displace125I-IGF-I binding to isolated rat glomeruli and to inhibit IGF-I-induced receptor phosphorylation in renal tubular cells in culture. In the 7-day SNx rats, IGF-I immunostain was present in collecting tubules and JB3 inhibited compensatory renal growth, the maximum effect occuring at 10 μg·kg−1·day−1. After 90 days, the SNx rats developed proteinuria, hypertension, and a fall in glomerular filtration rate. IGF-I immunostain was present in the tubulointerstitial space of the remnant kidney together with marked tubulointerstitial fibrosis. Treatment with JB3 at a dose of 10 μg·kg−1·day−1had no effect on the renal fibrosis measured by Masson's trichrome staining or immunostain for collagen III and collagen IV. The proteinuria, hypertension, and lower creatinine clearance all remained unchanged. The remnant kidney was associated with a 50% decrease in renal IGF-I mRNA, which was partially restored by treatment with JB3. Thus an interventional study with an IGF-I receptor antagonist does not support a role for IGF-I in the development of renal fibrosis in the SNx rat, although IGF-I does make an important contribution to compensatory kidney growth.

Role of endoethelin-1 in development of neprhopathy induced with streptozocin

The main aim of our study was to detect changes in plasma level of endoethelin-1 after experimentally induced diabetes and diabetic nephropathy with streptozocin in rats. The effects of ACE inhibitors are well known and thus, we wanted to analyze the influence of enalapril (ACE inhibitor) on plasma concentrations of endoethelin-1 as well as its effects in the treatment of diabetic nephropathy. Single i.p. administration of streptozocin (STZ) caused a significant increase of endoethelin-1 plasma concentrations associated with distinct signs and symptoms of diabetic nephropathy (microalbuminuria, increased urine N-acetyl-D-glucosamidase, increased serum concentrations of urea and creatinine, polyuria). Four-week treatment with endoethelin-1 resulted in significant reduction of endoethelin-1 plasma concentrations and improved sings and symptoms of diabetic nephropathy. The results obtained have confirmed that endoethelin-1 may play an important role in development and progression of diabetic nephropathy and ACE inhibitors, that is enalapril, may alleviate and delay the progression of diabetic nephropathy

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Real-time observation of glomerular hemodynamic changes in diabetic rats: Effects of insulin ARB

BACKGROUND

The progression of diabetic nephropathy is closely related to disturbances in glomerular hemodynamics, such as glomerular hypertension and/or hyperperfusion. The aim of this study was to observe and to analyze glomerular hemodynamics in rats with diabetes mellitus (DM) in vivo using confocal laser scan microscopy (CLSM). We also examined the effects of candesartan cilexetil (TCV-116), a selective angiotensin II type 1 receptor blocker (ARB), on glomerular hemodynamics in DM.

METHODS

Munich-Wistar rats were divided into six groups: (1) four-day control; (2) four-day DM; (3) 28-day control; (4) 28-day DM; (5) DM treated with insulin; (6) DM treated with TCV-116. The kidney-to-body weight ratio, glomerular volume, and proteinuria were estimated. Glomerular hemodynamic changes were observed using CLSM and renal expression of endothelial nitric oxide synthase (eNOS), and neuronal nitric oxide synthase (nNOS) was evaluated by immunofluorescence.

RESULTS

The kidney-to-body weight ratio, glomerular volume, the diameters of afferent arterioles (AA) and efferent arterioles (EA), erythrocyte velocities within glomeruli, and volume flow in glomerular capillary loops in four-day DM were significantly higher than in control rats, and increases were even more pronounced in the 28-day DM. TCV-116 treatment ameliorated all these findings and significantly decreased proteinuria, but there was no effect on the blood glucose level. On the other hand, insulin treatment was followed by normalization of all these changes induced in DM. Enhanced renal expression of eNOS in DM was suppressed when treated with either TCV-116 or insulin, while expression of nNOS was unaltered among the four groups.

CONCLUSION

This imaging procedure allowed us to evaluate glomerular microcirculation in vivo, including the diameters of AA and EA, erythrocyte velocity, and volume flow. DM significantly induced glomerular hemodynamic alteration and renal hypertrophy. DM treated with either insulin or ARB ameliorated these changes. This study shows that progress in imaging technology promises to make major contributions to revealing the involvement of hemodynamic changes in glomerular diseases, aiding prognosis and the monitoring of therapeutic effects, as well.

Somatostatin analogues: multiple roles in cellular proliferation, neoplasia, and angiogenesis

Angiogenesis, the development of new blood vessels is a crucial process both for tumor growth and metastatic dissemination. Additionally, dysregulation in angiogenesis has been implicated in the pathogenesis of cardiovascular disease, proliferative retinopathy, diabetic nephropathy, and rheumatoid arthritis (RA). The neuropeptide somatostatin has been shown to be a powerful inhibitor of neovascularization in several experimental models. Furthermore, somatostatin receptors (sst) are expressed on endothelial cells; particularly, sst2 has been found to be uniquely up-regulated during the angiogenic switch, from quiescent to proliferative endothelium. The present manuscript reviews the anti-angiogenic activity of somatostatin and its analogues in neoplastic and nonneoplastic disease. The role of sst subtypes particularly sst2 in mediating its angioinhibitory activity is described. Somatostatin agonists may also exert their anti-angiogenic activity indirectly by inhibition of growth factors like vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis or through its immunomodulatory effects. However, the therapeutic utility of somatostatin agonists as anti-angiogenic drugs in these diseases remains confusing because of conflicting results from different studies. More basic research, as well as patient-oriented studies, is required to firmly establish the clinical potential of somatostatin agonists in therapeutic angiogenesis. The currently available somatostatin agonists have high affinity of sst2 with lower affinities for sst3 and sst5. The emergence of novel somatostatin agonists especially bispecific analogues (agonists targeting multiple cellular receptors) and conjugates (synthesized by chemically linking somatostatin analogues with other antineoplastic agents) with improved receptor specificity signify a new generation of anti-angiogenics, which may represent novel strategies in the treatment of neovascularization-related diseases.

The serum levels somatostatin in type 2 diabetes mellitus

The dynamic study of somatostatin secretion was performed in 105 patients, with noninsulin dependent diabetes mellitus and 40 healthy volounteers. The patients were divided into groups in relation to the presence of autonomic neuropathy and metabolic control of diabetes mellitus. Serum somatostatin secretion was determined employeing a specific RIA method. An oral administration of a protein rich meal was performed in all subjects. The serum levels of somatostatin were not significantly different between type 2 diabetics and controls. There were no significant difference between the group with and the group without autonomic neuropathy. Diabetics in poor metabolic control had significantly increased in somatostatin (54.0 ? 22.2 pmol/L) levels compared with group well compensated (48.8 ? 16.5 pmol/L) (p < 0.01). Data of increased somatostatin levels in poor controlled diabetics suggest it-s pathophysiological role in type 2 diabetes mellitus.

Role of insulin and the IGF system in renal hypertrophy in diabetic Psammomys obesus (sand rat)

BACKGROUND

Diabetic nephropathy is caused by multiple factors related to the altered metabolic environment in diabetes mellitus (DM). Experimental diabetic kidney disease is characterized by renal hypertrophy associated with increased tissue concentrations of insulin-like growth factor I (IGF-I). To assess the specific roles of serum insulin and glucose in mediating the development of diabetic nephropathy, the effects of both hyperinsulinaemic and hypoinsulinaemic DM were studied in Psammomys obesus (sand rat), a model of type 2 DM.

METHODS

The IGF-I system was studied in normal Psammomys obesus gerbils and at 5, 15 and 70 days after the induction of either hyper- or hypoinsulinaemic DM. To induce hyperinsulinaemic DM, Psammomys were raised on a high-energy diet. Hypoinsulinaemic DM was induced by either administration of streptozotocin or a specially designed diet.

RESULTS

Hyperinsulinaemic hyperglycaemic Psammomys did not exhibit renal hypertrophy (unchanged kidney/body-weight ratio) and renal IGF-I levels were in the normal range on days 5, 15 and 70. In contrast, Psammomys with hypoinsulinaemic hyperglycaemia induced either by streptozotocin injection or by pancreas exhaustion brought on by a long-term caloric excess diet, had significant increases in kidney/body-weight ratio which were associated with elevated renal IGF-I and mRNA and protein levels of kidney IGF binding protein I.

CONCLUSIONS

This study shows that serum insulin levels in the presence of hyperglycaemia have an important role in the development of experimental diabetic nephropathy in the Psammomys model. The implication of this finding is that the pathophysiological mechanisms for diabetic kidney disease in experimental models may be different for type 1 and type 2 DM.

Induction of B1 receptors in streptozotocin diabetic rats: possible involvement in the control of hyperglycemia-induced glomerular Erk 1 and 2 phosphorylation

We investigated the effects of a 3-week treatment with various combinations of angiotensin-converting enzyme inhibitor (ACEI) and B1 and B2 bradykinin receptor (B1R and B2R) antagonists (B1A and B2A) and AT1 receptor antagonist on ERK 1 and 2 phosphorylation in isolated glomeruli from streptozotocin-treated diabetic rats (STZ rats). Body weight, glycemia, and blood pressure were monitored. The rats were divided into nine groups: (1) control; and groups 2-9 were STZ treated with (3) insulin, (4) ACEI, (5) ACEI + B1A, (6) ACEI + B2A, (7) B2A, (8) B1A, (9) AT1 antagonist. ERK 1 and 2 phosphorylation and expression of B1R and B2R were assessed by Western blot analysis. ERK 1 and 2 phosphorylation was higher in STZ rats; this activation was normalized by insulin and reduced by ACEI but not by AT1 antagonist. The reduction of ERK 1 and 2 phosphorylation by the ACEI was reversed by B1A and B2A. The induction of B1R was confirmed by increased expression of mRNA and B1 receptor protein. Since ERK 1 and 2 phosphorylation is an early event in the induction of matrix secretion and hyperproliferation associated with diabetic nephropathy, activation of B1R and B2R appears to be a useful pharmacological target in the management of this pathology.

Effects of amino acids and glucagon on renal hemodynamics in type 1 diabetes

Increased dietary protein and circulating amino acids raise glomerular filtration rate (GFR) and pressure. In diabetes, this glomerular hyperfiltration response is augmented. The purpose of this study was to determine whether glucagon mediates the augmented GFR response to amino acids in diabetes and whether the responses to amino acids and glucagon depend on prostaglandins. Patients with type 1 diabetes mellitus (n = 12) and normal control subjects (n = 12) were studied in a series of six experiments, each on different occasions. Baseline GFR was not significantly increased, but filtration fraction was higher in diabetes. In response to amino acid infusion, GFR increased more and filtration fraction was greater among those with diabetes. Their augmented GFR response to amino acids was not inhibited by octreotide or indomethacin. Participants with diabetes also had enhanced GFR and renal plasma flow responses to glucagon infusion, both of which were inhibited by indomethacin. Glomerular hyperfiltration responses induced by amino acids or glucagon occur by divergent pathways in diabetes; only the response to glucagon is prostaglandin dependent.

A novel somatostatin analogue prevents early renal complications in the nonobese diabetic mouse

BACKGROUND

PTR-3173 (S) is a novel somatostatin analogue that has been found to exert a prolonged inhibitory action on the growth hormone (GH)-insulin-like growth factor (IGF)-I axis, but not on insulin secretion. We investigated the potential effect of this agent on the development of markers of diabetic nephropathy in the nonobese diabetic (NOD) mouse model of insulin-dependent diabetes.

METHODS

Female diabetic NOD mice treated with PTR-3173 (DS group) or saline (D) and their control groups of nonhyperglycemic age-matched littermates (C) and C mice treated with PTR-3173 (CS) were sacrificed three weeks after onset of diabetes.

RESULTS

Serum GH was elevated in the D group, decreased in the DS group, and unchanged in the CS group. Serum IGF-I was significantly decreased in both the D and DS groups. Kidney weight, glomerular volume, albuminuria, and creatinine clearance were increased in the D animals and showed a trend toward normalization in the DS animals. Renal extractable IGF-I protein and IGFBP1 mRNA were increased in the D group and normalized in the DS group.

CONCLUSIONS

GH antagonism by PTR-3173 has a blunting effect on renal/glomerular hypertrophy, albuminuria, and glomerular filtration rate (GFR) in diabetic NOD mice. This phenomenon is apparently associated with the prevention of renal IGF-I accumulation. Thus, modulation of GH effects may have beneficial therapeutic implications in diabetic nephropathy.

Segmental expression of somatostatin receptor subtypes sst(1) and sst(2) in tubules and glomeruli of human kidney

Somatostatin is known to modulate mesangial and tubular cell function and growth, but the somatostatin receptor (sst) subtypes responsible for these effects have not been defined. There are at least five different sst receptor subtypes (sst(1)-sst(5)). We used RT-PCR to demonstrate that normal human kidney consistently expresses mRNA for sst(1) and sst(2) (9 of 9 donors). Some donors expressed sst(4) or sst(5) mRNA, but none expressed sst(3) mRNA. Expression of sst(1) and sst(2) was further assessed by staining serial sections of normal human kidney with sst(1) and sst(2) antisera, Arachis hypogaea (AH) lectin (to define distal tubule/collecting duct cells), Phaseolus vulgaris lectin (proximal tubules), and Tamm-Horsfall protein (THP) antiserum (thick ascending limb of the loop of Henle). Specificity of antisera was demonstrated by transfection and absorption studies. Sst(2), but not sst(1), was expressed in glomeruli. Intense sst(1) and sst(2) staining localized exclusively to AH+ and THP+ tubules. Thus sst(1) and sst(2) subtype-selective analogs may be useful to beneficially modulate renal cell function in pathological conditions.

Aminoguanidine ameliorates changes in the IGF system in experimental diabetic nephropathy

BACKGROUND

Formation of advanced glycation end-products (AGEs) has been implicated in the development of diabetic complications. As well as causing changes in structural proteins, AGEs may also alter gene expression of growth factors in vitro. The insulin-like growth factor (IGF) system, including IGF-I and modulatory IGF binding proteins (IGFBPs), is dysregulated during the development of diabetic nephropathy.

METHODS

Quantitative in situ hybridization histochemistry and immunohistochemistry were used to determine the effects of aminoguanidine, an inhibitor of AGE formation, on gene expression of IGF-I and IGFBPs in kidneys of long-term (8 months duration) streptozotocin-diabetic rats.

RESULTS

Diabetes was associated with increased renal expression of IGFBP-1 mRNA (diabetes 824+/-236 vs control 264+/-76 arbitrary units, P<0.01) and decreased expression of mRNAs for IGF-I (diabetes 39+/-7 vs control 185+/-23 arbitrary units, P<0.001) and IGFBP-4 (diabetes 139+/-25 vs control 383+/-54 arbitrary units, P<0.001). Aminoguanidine treatment inhibited the effects of diabetes on renal expression of mRNA for IGF-I, IGFBP-1 and IGFBP-4. The changes in IGF-I and IGFBP-1 mRNA levels were reflected in altered peptide levels. In diabetic kidneys, IGFBP-5 mRNA levels were slightly decreased to 75% of control levels (P<0.01); aminoguanidine had no effect on IGFBP-5 mRNA levels.

CONCLUSIONS

These results suggest that amelioration of changes in the renal IGF system by aminoguanidine may contribute to the renoprotective effects of the latter, which have been previously shown to inhibit structural and functional aspects of diabetic nephropathy in the rat.

Growth hormone receptor antagonism prevents early renal changes in nonobese diabetic mice

The growth hormone (GH)/insulin-like growth factor (IGF) axis is involved in diabetic renal disease. The role of a specific GH receptor (GHR) antagonist in the development of early renal changes in nonobese diabetic (NOD) mice was investigated. Female diabetic (nonketotic) NOD mice treated with a polyethylene glycol-treated GHR antagonist (2 mg/kg, every other day) (DA group) or saline (D group) and their nonhyperglycemic age-matched littermates (control animals) were euthanized 3 wk after the onset of diabetes. Body weights at euthanasia were similar among the groups. Serum GH levels were markedly elevated, and serum IGF-I levels were significantly decreased in D and DA animals, compared with controls. The increases in kidney weights and glomerular volumes observed for the D group were absent in the DA group. Albuminuria was increased in the D group but was normalized in the DA group. Extractable renal IGF-I protein levels were increased in the D group but were partially normalized in the DA group. Renal IGF-binding protein 1 mRNA levels were increased in the D group but returned to almost normal levels in the DA animals. Kidney IGF-I and GHR mRNA levels were decreased in both the D and DA groups. Renal GH-binding protein mRNA levels remained unchanged in both diabetic groups. GHR antagonism had a blunting effect on renal/glomerular hypertrophy and albuminuria in diabetic NOD mice. These salutary effects were associated with concomitant inhibition of increased renal IGF-I protein levels and were obtained without affecting either somatic growth or circulating GH and IGF-I levels. Therefore, modulation of GH effects may have beneficial therapeutic implications in diabetic nephropathy.

Pathogenesis of diabetic nephropathy: the role of oxidative stress and protein kinase C

Hyperglycemia, a well recognized pathogenetic factor of long-term complications in diabetes mellitus, not only generates more reactive oxygen species but also attenuates antioxidative mechanisms through glycation of the scavenging enzymes. Therefore, oxidative stress has been considered to be a common pathogenetic factor of the diabetic complications including nephropathy. A causal relationship between oxidative stress and diabetic nephropathy has been established by observations that (1) lipid peroxides and 8-hydroxydeoxyguanosine, indices of oxidative tissue injury, were increased in the kidneys of diabetic rats with albuminuria; (2) high glucose directly increases oxidative stress in glomerular mesangial cells, a target cell of diabetic nephropathy; (3) oxidative stress induces mRNA expression of TGF-beta1 and fibronectin which are the genes implicated in diabetic glomerular injury, and (4) inhibition of oxidative stress ameliorates all the manifestations associated with diabetic nephropathy. Proposed mechanisms involved in oxidative stress associated with hyperglycemia are glucose autooxidation, the formation of advanced glycosylation end products, and metabolic stress resulting from hyperglycemia. Since the inhibition of protein kinase C (PKC) effectively blocks not only phorbol ester-induced but also high glucose- and H2O2-induced fibronectin production, the activation of PKC under diabetic conditions may also have a modulatory role in oxidative stress-induced renal injury in diabetes mellitus.

Pathophysiological Role of Growth Factors in Diabetic Kidney Disease: Focus on Innovative Therapy

Various growth factors have been proposed to be players in the development of diabetic microvascular complications. In particular, the growth hormone/insulin-like growth factor system and the transforming growth factor beta system have measurable effects on the development of diabetic kidney disease through a complex intrarenal system. Recent findings indicating that these growth factors might be responsible for early renal changes in diabetes have provided insight into processes that might be relevant to the future development of new drugs useful in the treatment of diabetic kidney disease.