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

Focal segmental glomerulosclerosis in which urinary protein improved after surgical treatment for acromegaly: a case report

Background

Focal segmental glomerulosclerosis is characterized by partial (segmental) sclerotic lesions in some glomeruli (focal). Primary focal segmental glomerulosclerosis is generally considered resistant to steroid therapy. However, acromegaly is a disease that causes peculiar facial features, body types, and metabolic abnormalities due to the excessive secretion of growth hormone by a pituitary adenoma. Growth hormone has been reported to be involved in glomerular cell growth, mesangial proliferation, and glomerulosclerosis in the kidney.

Case presentation

We report a case of a Japanese patient with focal segmental glomerulosclerosis in whom decreased urinary protein was observed after surgical treatment for acromegaly.

Conclusion

The patient’s urinary protein improved as the concentration of growth hormone/insulin-like growth factor 1 decreased.

Growth hormone and ocular dysfunction: Endocrine, paracrine or autocrine etiologies?

The eye is a target site for GH action and growth hormone has been implicated in diabetic retinopathy and other ocular dysfunctions. However, while this could reflect the hypersecretion of pituitary GH, the expression of the GH gene is now known to occur in ocular tissues and it could thus also reflect excess GH production within the eye itself. The possibility that ocular dysfunctions might arise from endocrine, autocrine or paracrine etiologies of GH overexpression is therefore the focus of this brief 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.

Therapeutic uses of somatostatin and its analogues: Current view and potential applications

Somatostatin is an endogeneous cyclic tetradecapeptide hormone that exerts multiple biological activities via five ubiquitously distributed receptor subtypes. Classified as a broad inhibitory neuropeptide, somatostatin has anti-secretory, anti-proliferative and anti-angiogenic effects. The clinical use of native somatostatin is limited by a very short half-life (1 to 3min) and the broad spectrum of biological responses. Thus stable, receptor-selective agonists have been developed. The majority of these somatostatin therapeutic agonists bind strongly to two of the five receptor subtypes, although recently an agonist of wider affinity has been introduced. Somatostatin agonists are established in the treatment of acromegaly with recently approved indications in the therapy of neuroendocrine tumours. Potential therapeutic uses for somatostatin analogues include diabetic complications like retinopathy, nephropathy and obesity, due to inhibition of IGF-1, VEGF together with insulin secretion and effects upon the renin-angiotensin-aldosterone system. Wider uses in anti-neoplastic therapy may also be considered and recent studies have further revealed anti-inflammatory and anti-nociceptive effects. This review provides a comprehensive, current view of the biological functions of somatostatin and potential therapeutic uses, informed by the wide range of pharmacological advances reported since the last published review in 2004 by P. Dasgupta. The pharmacology of somatostatin receptors is explained, the current uses of somatostatin agonists are discussed, and the potential future of therapeutic applications is explored.

Neuropeptides and diabetic retinopathy

Diabetic retinopathy, a common complication of diabetes, develops in 75% of patients with type 1 and 50% of patients with type 2 diabetes, progressing to legal blindness in about 5%. In the recent years, considerable efforts have been put into finding treatments for this condition. It has been discovered that peptidergic mechanisms (neuropeptides and their analogues, activating a diverse array of signal transduction pathways through their multiple receptors) are potentially important for consideration in drug development strategies. A considerable amount of knowledge has been accumulated over the last three decades on human retinal neuropeptides and those elements in the pathomechanisms of diabetic retinopathy which might be related to peptidergic signal transduction. Here, human retinal neuropeptides and their receptors are reviewed, along with the theories relevant to the pathogenesis of diabetic retinopathy both in humans and in experimental models. By collating this information, the curative potential of certain neupeptides and their analogues/antagonists can also be discussed, along with the existing clinical treatments of diabetic retinopathy. The most promising peptidergic pathways for which treatment strategies may be developed at present are stimulation of the somatostatin-related pathway and the pituitary adenylyl cyclase-activating polypeptide-related pathway or inhibition of angiotensinergic mechanisms. These approaches may result in the inhibition of vascular endothelial growth factor production and neuronal apoptosis; therefore, both the optical quality of the image and the processing capability of the neural circuit in the retina may be saved.

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.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

Medical treatment of diabetic retinopathy with somatostatin analogues

Traditional management strategies for retinal neovascularisation accompanying proliferative diabetic retinopathy include photocoagulation laser therapy. The development of preventative pharmacological treatments aimed at replacing or delaying this acute intervention has been an active research area and somatostatin analogues have shown promise in reducing the progression of retinal vascular pathologies. This review summarises the present knowledge on the molecular and cellular mechanisms of neovascularisation, and the rationale for the therapeutic use of somatostatin analogues as well as the results of two key recent clinical trials using octreotide. The potential use of octreotide and other somatostatin analogues in reducing the risk of severe visual impairment in proliferative diabetic retinopathy is discussed and pharmacological treatment regimens are proposed as an additional strategy or a less invasive alternative to laser therapy.

The potential role of octreotide in the treatment of diabetic retinopathy

Proliferative diabetic retinopathy is the main cause of vision loss in young and middle-aged adults. There is no accepted pharmaceutical therapy for this disease, although analogs of the naturally occurring growth hormone inhibitor, somatostatin, have been considered leading candidates for developing such therapies. This review examines the history of somatostatin analogs, especially octreotide, in the treatment of ocular complications of diabetes mellitus. The historical observations that indicated a role for somatostatin in retinopathy are discussed from an endocrinology perspective. The molecular mechanisms by which somatostatin may exert its anti-angiogenic effects, both indirect (through antagonism of the growth hormone axis) and direct (through direct antiproliferative and apoptotic effects on endothelial cells mediated by specific receptor subtypes) are described. Animal models that were used to demonstrate an anti-angiogenic effect of octreotide are detailed, as are the results of numerous clinical trials that used octreotide and other somatostatin analogs to treat diabetic retinopathy. The mixed results of these clinical results are examined along with possible explanations as to why these analogs both have and have not shown efficacy in limited clinical settings. Even with these mixed results, somatostatin analogs remain the only therapeutic alternative to patients with proliferative diabetic retinopathy who have failed to respond to panretinal photocoagulation.

The role of growth factors in the pathogenesis of diabetic retinopathy

Diabetic retinopathy (DR) is the most severe of several ocular complications of diabetes. The earliest clinical signs of DR are microaneurysms and haemorrhages. Later signs include dilated, tortuous irregular veins and retinal non-profusion, leading to retinal ischaemia that ultimately results in neovascularisation. Diabetic macular oedema, which involves the breakdown of the blood-retinal barrier, also occurs and is responsible for a major part of vision loss, particularly in Type 2 diabetes. The pathogenesis of DR is very complex. Many biochemical mechanisms have been proposed as explanations for the development and progression of DR. Chronic hyperglycaemia leads to oxidative injury, microthrombi formation, cell adhesion molecule activation, leukostasis and cytokine activation. Next, ischaemia-mediated overexpression of growth factors and cytokines occurs. These factors include vascular endothelial growth factor, insulin-like growth factor-1, angiopoetin-1 and -2, stromal-derived factor-1, fibroblast growth factor-2 and tumour necrosis factor. Because of the complex interplay between these factors, targeting a single growth factor will be unlikely to result in therapeutic inhibition of angiogenesis. These growth factors no doubt act in synergy to mediate the steps of angiogenesis, including protease production, endothelial cell proliferation, migration and tube formation. This review attempts to provide an overview of perspectives regarding the pathogenesis of this disease. The focus, however, is on describing the unique features of selected relevant factors and how each growth factor may act in a synergistic manner with other factors.

Inhibition of endothelial proliferation by the somatostatin analogue SOM230

OBJECTIVE

Somatostatin (SST) modulates exocrine and endocrine secretion, proliferation and apoptosis via five G protein-linked receptors (SSTRs 1-5). Long-acting SST analogues such as Octreotide, and the new analogue SOM230, have been developed for the treatment of neuroendocrine tumours. Octreotide has previously been reported to inhibit endothelial proliferation. We wished to determine if SOM230 is a more potent inhibitor of endothelial cell proliferation than Octreotide.

DESIGN

We have determined the expression of SSTRs in proliferating human umbilical vein endothelial cells (HUVECs) in vitro, and determined their response to the somatostatin analogues SOM230 and Octreotide, following vascular endothelial growth factor (VEGF) stimulation.

MEASUREMENTS

Quantitative RT-PCR and western blotting were used to determine the expression of SSTRs 1-5 in proliferating HUVECs. These cells were grown in media containing 200 pg/ml VEGF and treated with 10(-11) to 10(-6) M Octreotide or SOM230. The WST-1 assay was then used to determine the effects of these analogues on HUVEC proliferation.

RESULTS

Using quantitative RT-PCR and western blotting, HUVECs were found to express SSTRs 1, 2 and 5. SSTRs 3 and 4 were not detected. Using the WST-1 assay, SOM230 was found to significantly inhibit proliferation by up to 46.0% +/- 9.4% (10(-6)-10(-7) M; P < 0.05), whereas in parallel studies Octreotide failed to inhibit HUVEC proliferation.

CONCLUSIONS

The pan SST analogue SOM230 inhibits proliferation of HUVECs, which are unaffected by Octreotide. SOM230 may thus represent a suitable candidate drug for antiangiogenic therapy.

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.

Somatostatin regulates intracellular signaling in human carotid endothelial cells

Somatostatin (somatotropin release inhibitory factor; SRIF) is an endogenous peptide produced at sites of inflammation, making the SRIF a candidate in regulating vascular inflammation. We have used primary human coronary artery endothelial cells (hCAEC) as a model to study SRIF's vascular actions. RT-PCR analysis of hCAEC total mRNA demonstrated the presence of the sst(4) receptor subtype, providing a target for SRIF intracellular signaling. Western blotting with phospho-specific ERK1/2 antibodies showed that SRIF-14 acutely inhibited basal phosphorylation of the extracellular regulated kinases (ERK1/2) by 80%. In addition, SRIF-14 treated hCAEC cell lysates showed a 2.6-fold increase in phosphatase activity, which was inhibited by sodium vanadate. Furthermore, SRIF-14 appeared to be anti-inflammatory in hCAEC as IL-1beta-induced adhesion molecule expression was reduced by 50%. Together, these results show that the coronary artery endothelium is a direct target of SRIF action.

Diabetes mellitus and retinopathy

The role of somatostatin and growth hormone in eye diseases recently became a matter of interest because of its link with proliferative diabetic retinopathy. In diabetic patients the pathologic proliferation of blood vessels as a result of retinal ischemia is a major cause of blindness. The hypoxic portions of the retina release angiogenic factors, stimulating neovascularization. Somatostatin is a natural peptide hormone that affects the release of a number of other hormones, such as growth hormone, glucagon, insulin and gastrin. The somatostatin analog promises to be safe and effective treatment for severe diabetic retinopathy. This compound has been shown to block the local and systemic production of insulin-like growth factor 1 and growth hormone, which promote the angiogenesis and endothelial cell proliferation associated with proliferative retinopathy. Several studies have confirmed that using somatostatin analogs to block insulin-like growth factor 1 production is effective in reducing neovascularization and preventing disease progression to proliferative stage of diabetic retinopathy. Long-acting somatostatin analogs are currently being tested for the treatment of diabetic retinopathy. The development of somatostatin analogs with increased selectivity for receptor subtypes will provide improved outcomes in the management of patients with diabetic retinopathy.

The therapeutic potential of somatostatin receptor ligands in the treatment of obesity and diabetes

Since the development of synthetic somatostatin analogues, several therapeutic applications for somatostatin receptor agonist molecules have been defined. Established applications for somatostatin analogue treatment include pituitary tumours (growth hormone and thyrotropin-secreting adenomas), neuroendocrine tumours of the pancreas and gastrointestinal tract (so-called carcinoid tumours, vasoactive intestinal tumours) and gastroenterological conditions (pancreatitis, gastrointestinal bleedings, refractory diarrhoeas, pancreatic and intestinal fistulas, diarrhoea in AIDS). Further areas for development of somatostatin analogue therapy include obesity, polycystic ovary syndrome and diabetes mellitus, dysmetabolic conditions that are often interrelated. The challenge for the future will be to transform results from clinical trials conducted in heterogeneous clinical situations into novel options of somatostatin analogue use. Since obesity and diabetes mellitus both are disorders of marked heterogeneity, the subgroup of patients that will benefit most from somatostatin analogue treatment has yet to be defined. In addition, the development of more universal ligands covering all of the known somatostatin receptor molecules as well as receptor subtype specific agents is currently underway. The establishment of slow-release depot formulations of octreotide and lanreotide has already provided a more acceptable and consistent delivery mechanism. Use of biodegradable polymer microsphere formulations provides the basis for the development of novel applications, which include hyperinsulinaemia, obesity and polycystic ovary syndrome as components of the dysmetabolic syndrome. The most developed thus far is the use of octreotide in hyperinsulinaemic forms of obesity and in distinct stages of diabetic retinopathy.

Is medical treatment for diabetic retinopathy still an unreal dream?

Diabetic retinopathy is a highly specific vascular complication of both type 1 and type 2 diabetes, estimated to be the most frequent cause of new cases of blindness in the working population of the Western world. The prevalence of retinopathy is strongly related to the duration of diabetes and glycemic control, even though a multifactorial pathogenesis should be probably considered in genetically susceptible subjects. Intensive diabetes management, with the goal of achieving near-normal glycemia, has been shown to prevent and/or delay the onset of diabetic retinopathy and laser photocoagulation has an established clinical efficacy in preventing visual loss. However, as laser scars always destroy the retinal anatomy permanently, a medical approach to nonproliferative retinopathy should be preferred if its clinical efficacy could be demonstrated. In this paper, recently published reports supporting this hypothesis are reviewed and their conclusions critically discussed.

Octreotide reduces ischaemia-reperfusion injury in the retina

PURPOSE

To investigate the role of octreotide on retinal lipid peroxidation and histopathological changes during ischaemia/reperfusion (I/R).

METHODS

Three groups of seven pigmented guinea pigs each were formed. These represented a control group, an ischaemia group and an ischaemia/octreotide group. One eye of each animal was selected for histopathological evaluation and the other for biochemical assay. Bilateral pressure-induced retinal ischaemia was instigated for 90 min and was followed by 24 hours of reperfusion. Animals in the ischaemia/octreotide and ischaemia groups received either 10 micro g/kg of octreotide or saline, repeated five times at 6-hourly intervals, with the first dose administered 15 min prior to the ischaemic insult. Retinal malondialdehyde (MDA) levels and the thickness of the retinal layers were measured. These were compared with equivalent measurements of the control group.

RESULTS

The mean MDA level increased in the ischaemia group (p < 0.01) but not in the octreotide group (p > 0.05). Significant increases in the thickness of the overall retina (p < 0.01), inner retina (p < 0.05) ganglion cell layer (p < 0.01) inner plexiform layer (p < 0.01) and inner nuclear layer (p < 0.01) were observed in the ischaemia group. No significant difference in thickness was found in any of the layers in the ischaemia/octreotide group.

CONCLUSION

Octreotide reduces the increases in retinal MDA levels and retinal thickness observed during I/R.