Octreotide prevents the early increase in renal insulin-like growth factor binding protein 1 in streptozotocin diabetic rats

The emerging role of NO and IGF-1 in early renal hypertrophy in STZ-induced diabetic rats

BACKGROUND

Diabetic nephropathy (DN) is a major complication of diabetes mellitus, and the most common cause of end-stage renal disease. DN is characterized by early hyperfiltration and renal hypertrophy, which are associated with increased renal insulin-like growth factor-1 (IGF-1) levels. The relationship between IGF-1 and nitric oxide (NO) in DN is not established. The aim of this study was to investigate the effects of NO system modulation on the IGF-1-mediated hypertrophy and hyperfiltration during the first week after diabetes induction.

METHODS

Diabetes was induced in rats by streptozotocin (STZ) injection. Diabetic rats were treated with NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME). Various serum IGF-binding proteins (IGFBPs) and renal IGFBP1 expression was evaluated. Urine and plasma NO(2) + NO(3) level analysis was also performed.

RESULTS

STZ induced hyperglycaemia decreased plasma insulin levels and brought about a decrease in body weight. L-NAME administration to diabetic rats significantly prevented renal hypertrophy and hyperfiltration. Serum IGFBP3, IGFBP4 and 30-kDa IGFBP fraction were all significantly reduced in diabetic rats, compared with those in non-diabetic control rats. However, the renal IGFBP1 mRNA expression in diabetic rats was significantly higher. These changes were accompanied by an increased in NO production. L-NAME administration prevented the serum IGFBP decline, without significantly affecting the renal IGFBP1 mRNA expression.

CONCLUSIONS

We have shown that increased renal IGF-1 and increased NO production during the very early stages of STZ-induced DN are associated with renal hypertrophy and hyperfiltration in diabetic rats. Modulating the IGF-1 availability to the kidney by nitric oxide synthase inhibition significantly reduced renal hypertrophy and hyperfiltration during the first week of STZ-induced diabetes mellitus.

Function and expression of somatostatin receptors of the endocrine pancreas

Somatostatin (SST) regulates multiple biological processes via five genetically distinct, G-protein coupled receptors. Clinical interest in therapy for neuroendocrine and metabolic disorders has resulted in the development of new tools for exploring the function of somatostatin receptors (SSTRs). The development of highly SSTR-selective agonists and antagonists, animal models with the deletion of individual SSTRs, as well as SSTR-specific antibodies have all been utilized in delineating SSTR functions. In the pancreas, SST is a potent regulator of insulin and glucagon secretion. Indeed, the inappropriate regulation of pancreatic A- and B-cell function in metabolic diseases provides an impetus to evaluate the SSTRs as therapeutic targets. By combining the results obtained from molecular biology, pharmacology and immunochemical studies the current review provides a summary of important recent developments which have extended our knowledge of SST actions in the endocrine pancreas.

New drug development in digestive neuroendocrine tumors

The traditional cytotoxic agents are of limited efficacy in the treatment of neuroendocrine tumors of the gastrointestinal tract (NETs). Recent investigations have brought up a number of biological features in this family of neoplasms that could represent targets for anticancer treatment. NETs seem to have an extraordinary tumor vascularization with high expression of proangiogenic molecules such as the vascular endothelial growth factor along with overexpression of certain tyrosine kinase receptors such as the epidermal growth factor receptor (EGFR), the insulin growth factor receptor (IGFR) and their downstream signaling pathway components (PI3K-AKT-mTOR). The rationale of an antiangiogenic approach in the treatment of NETs and the use of other pharmacological strategies such as EGFR, IGFR and mammalian target of rapamycin inhibitors are discussed. Additionally, the emerging results of recent clinical trials with these targeted drugs are presented.

Intrarenal octreotide treatment prevents sodium retention in liver cirrhotic rats: evidence for direct effects within the thick ascending limb of Henle's loop

We have previously shown that systemic treatment with the somatostatin analog octreotide has marked beneficial effects on renal function in rats with liver cirrhosis induced by common bile duct ligation (CBL; Jonassen TEN, Christensen S, Sørensen AM, Marcussen N, Flyvbjerg A, Andreasen F, and Petersen JS. Hepatology 29: 1387-1395, 1999). In the present study, we tested the hypothesis that octreotide has a direct effect on renal tubular function. Rats (CBL or Sham-CBL) were intrarenally treated with low-dose octreotide in a long-acting release formulation, which had no systemic actions (100 microg/kg body wt as a single dose). Rats receiving low-dose octreotide (sc) were used as controls. The rats were chronically instrumented, and renal function was examined 4 wk after CBL or Sham-CBL. Intrarenal octreotide administration (IROA) prevented sodium retention in CBL rats without changes in renal plasma flow, glomerular filtration rate, or circulating levels of aldosterone and vasopressin. Renal clearance studies revealed that IROA normalized the increased natriuretic efficacy of furosemide found in CBL rats. Furthermore, IROA protected against the development of hypertrophy of the inner stripe of the outer medulla and thereby the increased the volume of thick ascending limb of Henle's loop (TAL) epithelium found in CBL rats. Finally, Western blot analyses of outer medullary homogenates showed increased abundance of the furosemide-sensitive Na-K-2Cl (NKCC2) cotransporter. IROA did not affect the abundance of NCKK2 within the outer medulla. Together with the histological findings, these results indicate that IROA reduces the total number of NKCC2 within the outer medulla. In conclusion, the results indicate a direct intrarenal effect of octreotide on TAL function and morphology in cirrhotic rats.

Polymorphisms in IGF-binding protein 1 are associated with impaired renal function in type 2 diabetes

The dysregulation of the IGF system has been implicated in the pathogenesis of obesity, diabetes, and diabetes complications such as nephropathy, but little is known about the genomics of the IGF system in health and disease. We genotyped 13 single nucleotide polymorphisms (SNPs) in IGFBP1 gene in 732 representative type 2 diabetic patients from the Salford Diabetes Register. Of the 13 SNPs, 8 were polymorphic and 7 of those had minor allele frequencies >0.1, one of which was in the gene promoter and one of which was nonsynonymous in exon 4. The minor alleles of these SNPs and two others were associated with a reduced prevalence of diabetic nephropathy. Haplotype analysis revealed that 97% of the genetic variation for IGFBP1 in the population sample could be accounted for using two of the "reno-protective" SNPs, with other SNPs adding little extra information. One of these two SNPs was the nonsynonymous mutation in exon 4, lying close to the integrin-binding RGD motif, which is thought to affect tissue delivery of IGF-I by IGF-binding protein 1 (IGFBP-1), possibly suggesting a "reno-protective" effect via altered IGFBP-1 binding. In conclusion, we have described the first genomic markers to be associated with diabetic microvascular complications within the human IGFBP1 gene.

Agents in development for the treatment of diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease, and accounts for significant morbidity and mortality in patients with diabetes. Diabetic nephropathy seems to occur as a result of an interaction between metabolic and haemodynamic factors, which activate common pathways that lead to renal damage. In the past, the treatment of diabetic nephropathy has focused on the control of hyperglycaemia. Newer targets, some of which are linked to glucose-dependent pathways, appear to be a major focus of new treatments directed against the development and progression of renal damage as a result of diabetes. It is anticipated that additional therapeutic approaches that inhibit both metabolic and haemodynamic pathways will include strategies that target growth factors, cytokines and intracellular second messengers. Such an approach is expected to lead to improved therapies for the treatment of diabetic nephropathy.

The physiological and pathophysiological roles of the GH/IGF-axis in the kidney: lessons from experimental rodent models

The growth hormone (GH)/insulin-like growth factor (IGF) system plays an important role in renal development, growth, function and pathophysiology. IGF-I has been associated with renal/glomerular hypertrophy and compensatory renal growth. Potential effects on glomerular size are of interest, since an increase in glomerular size may be permissive for the development of glomerulosclerosis. In an effort to abolish the decline of renal function and possibly to restore the renal structure, different approaches have been tested in experimental models of nephropathy, focusing mainly on early renal changes. The involvement of the GH/IGF system in renal pathophysiology has been studied in much detail in the rat. In view of the growing interest in murine physiology, occurring in large part by genetically modified animals, this review examines those aspects of GH, IGFs, their receptors and binding proteins that relate both to mouse kidney physiology and to a number of conditions characterized by pathophysiological renal changes. A deeper understanding of the role of the GH/IGF system in renal dysfunction may stimulate the development of novel therapeutic approaches aiming at preventing or retarding various kidney diseases.

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.

Administration of human insulin-like growth factor-binding protein-1 increases circulating levels of growth hormone in mice

GH is the major regulator of circulating IGF-I, which, in return, controls pituitary GH secretion by negative feedback. IGF-binding protein-1 (IGFBP-1) is believed to modify this feedback through its effects on free IGF-I. In the present study we investigated the potential influence of IGFBP-1 on GH secretion in the absence or presence of a GH receptor antagonist (GHRA) that specifically blocks peripheral GH action. We administered human (h) IGFBP-1 and GHRA to mice alone or in combination for 2 or 7 d. GHRA was administered in a dose previously shown to block GH action without an effect on circulating GH or IGF-I levels. hIGFBP-1 administration increased stimulated circulating GH levels and serum total IGF-I and IGFBP-3 levels. Coadministration of GHRA abolished the hIGFBP-1-induced increase in serum IGF-I and IGFBP-3 levels, whereas stimulated GH levels remained increased. Free IGF-I levels in serum were unchanged in all treatment groups. In conclusion, GH serum levels increased in response to hIGFBP-1 administration, even in the setting of normal IGF-I levels. This finding suggests a direct involvement of IGFBP-1 in GH secretion.

Growth factors and the development of diabetic nephropathy

Growth factors play an important role in the development of functional and structural changes associated with diabetic nephropathy. Although it has been known for years that these factors are important for early renal hypertrophy and subsequent development of glomerulosclerosis and tubulointerstitial fibrosis, the exact molecular mechanism of many of these factors has only recently been more elucidated. Furthermore, growth factors also link the metabolic theory of diabetic complications with renal hemodynamic changes in diabetic nephropathy because some growth factors could directly influence glomerular hemodynamics and tubular transport in diabetic nephropathy. The high glucose environment with stimulated cellular uptake of glucose and accelerated nonenzymatic reactions resulting in Amadori-modified proteins and the later-developing advanced glycation end products are the main stimulators for intrarenal induction of growth factors. Intracellular generation of reactive species is an important signal intermediate in these stimulated expressions of growth factors. Taking into consideration the pivotal role of growth factors in the development of diabetic nephropathy, a therapeutic strategy to antagonize growth factor effects appears to be straightforward. However, the pleiotropic function of many of these factors and their physiologic role in normal renal homeostasis may make this approach difficult.

Possible involvement of IGF-1 receptor and IGF-binding protein in insulin-induced enhancement of noradrenaline response in diabetic rat aorta

1. We investigated the mechanisms underlying the changes in vascular contractile responsiveness induced by chronic treatment with insulin in controls and established streptozotocin (STZ)-induced diabetic rats. 2. The aortic contractile response to noradrenaline (NA) showed no significant difference between controls and diabetics, but it was significantly greater in insulin-treated diabetic rats than in the other groups. To investigate the mechanism, we examined the changes in NA-induced contractility following treatment with insulin and insulin-like growth factor-1 (IGF-1) in organ-cultured control and diabetic aortas. 3. The contractile response to NA in organ-cultured diabetic rat aortas treated with insulin (500 ng ml-1, 16 h) or IGF-1 (20 ng ml-1, 16 h) was significantly greater than the corresponding values for (a) diabetic rat aortas cultured in serum-free medium, and (b) control aortas incubated with insulin or IGF-1. Incubating control aortas with insulin or IGF-1 had no significant effect on the contraction induced by NA. 4. The expressions of the IGF-1 receptor mRNA and protein were increased in STZ-induced diabetic aortas and further increased in insulin-treated diabetics. The mRNA expressions of IGF-binding protein (IGFBP)-2 and IGFBP-3 were normal in diabetic aortas. In contrast, those of IGFBP-4 and IGFBP-5 were significantly decreased in diabetic aortas, and not restored by insulin treatment. 5. These results suggest that the insulin deficiency and chronic hyperinsulinemia in diabetes upregulate the IGF-1 receptor and downregulate IGFBP-4 and IGFBP-5 in the aorta. This may be a major cause of the increased vascular contractility induced by insulin administration and by hyperinsulinemia in established diabetes, resulting in hypertension.

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.

Octreotide (somatostatin analog) treatment reduces endothelial cell dysfunction in patients with diabetes mellitus

Octreotide is a long-acting somatostatin analog that has been shown to have various effects in diabetes. This study was performed to evaluate whether octreotide affects the vascular complications of diabetes mellitus. Albuminuria and serum thrombomodulin were used as markers of vascular and renal dysfunction. We studied the effect of octreotide in 27 patients with insulin-dependent diabetes mellitus (IDDM). They received 200 microg octreotide per day over a period of 6 months. As a marker of endothelial cell damage, we measured the serum thrombomodulin level. We also measured urinary albumin excretion, hemoglobin A1c (HbA1c), insulin-like growth factor-1 (IGF-1), and other parameters. IGF-1 decreased from 123 ng/mL before treatment to 114 ng/mL after 6 months of octreotide treatment (P = .009), while no significant change was observed in the unblinded control group (from 103 ng/mL to 102 ng/mL after 6 months of treatment). Urinary albumin excretion in patients with macroalbuminuria declined from 1,124 mg/L before octreotide treatment to 556 mg/L after 6 months of treatment (P < .05), whereas no change was observed in the control group. There was also a reduction of the plasma thrombomodulin level from 61.8 ng/mL to 46.1 ng/mL (P < .07) after 6 months of treatment. Furthermore, HbA1c decreased from 8.75% +/- 1.27% to 8.12% +/- 1.23% (P < .07) after octreotide treatment.

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.