Effect of insulin-like growth factor I infusion on renal hypertrophy in experimental diabetes mellitus in rats

Risk of breast cancer by individual insulin use: an international multicenter study

OBJECTIVE Several studies have been published in 2009 suggesting a possible association between insulin glargine and increased risk of malignancies, including breast cancer. The objective of this study was to assess the relation between the individual insulins (glargine, aspart, lispro, and human insulin) and development of breast cancer. RESEARCH DESIGN AND METHODS Seven hundred seventy-five incident cases of primary invasive or in situ carcinoma breast cancer occurring in women with diabetes from 92 centers in the U.K., Canada, and France were matched to a mean of 3.9 diabetic community control subjects (n = 3,050; recruited from 580 general practices) by country, age, recruitment date, and diabetes type and management. The main risk model was a multivariate conditional logistic regression model with case/control status as the dependent variable and individual insulin use, 8 years preceding the index date, as the independent variable, controlling for past use of any insulin, oral antidiabetes drugs, reproductive factors, lifestyle, education, hormone replacement therapy and history of contraceptive use, BMI, comorbidities, diabetes duration, and annual number of physician visits. Glargine was also compared with every other insulin by computing all ratios using the variance-covariance matrix of logistic model parameters. RESULTS Adjusted odds ratios of breast cancer for each type of insulin versus no use of that insulin were 1.04 (95% CI 0.76-1.44) for glargine, 1.23 (0.79-1.92) for lispro, 0.95 (0.64-1.40) for aspart, and 0.81 (0.55-1.20) for human insulin. Two-by-two comparisons found no difference between glargine and the different types of insulins. Insulin dosage or duration of use and tumor stage did not change the results. CONCLUSIONS This international study found no difference in the risk of developing breast cancer in patients with diabetes among the different types of insulin with short- to mid-term duration of use. Longer-term studies would be of interest.

Effects of long-term experimental diabetes on adrenal gland growth and phosphoribosyl pyrophosphate formation in growth hormone-deficient dwarf rats

The availability of growth hormone (GH)-deficient dwarf rats with otherwise normal pituitary function provides a powerful tool to examine the relative role of hyperglycaemia and the reordering of hormonal factors in the hypertrophy-hyperfunction of the adrenal gland that is seen in experimental diabetes. Here, we examine the effects of long-term (6 months) experimental diabetes on the growth of the adrenal glands; their content of phosphoribosyl pyrophosphate (PRPP); and the activity of the PRPP synthetase, G6P dehydrogenase and 6PG dehydrogenase enzymes in GH-deficient dwarf rats compared to heterozygous controls. These parameters were selected in view of the known role of PRPP in both de novo and salvage pathways of purine and pyrimidine synthesis and in the formation of NAD, and in view of the role of the oxidative enzymes of the pentose phosphate pathway in both R5P formation and the generation of the NADPH that is required in reductive synthetic reactions. This study shows that GH deficiency prevents the increase in adrenal gland weight, PRPP synthetase, PRPP content and G6P dehydrogenase and 6PG dehydrogenase. This contrasts sharply with the heterozygous group that showed the expected increase in these parameters. The blood glucose levels of the groups of long-term diabetic rats, both GH-deficient and heterozygous, remained at an elevated level throughout the experiment. These results are fully in accord with earlier evidence from studies with somatostatin analogues which showed that the GH-insulin-like growth factor I (IGF-I)-axis plays a key role in the adrenal diabetic hypertrophy-hyperfunction syndrome.

Effects of long-acting somatostatin analogues on adrenal growth and phosphoribosyl pyrophosphate formation in experimental diabetes

Adrenal growth and increased adrenal function occur in experimental diabetes. Previously, we have shown that phosphoribosyl pyrophosphate (PRPP) and PRPP synthetase increased rapidly between 3 and 7 days after induction of diabetes with streptozotocin (STZ), with less marked changes in enzymes of the pentose phosphate pathway. The present study examines the earlier phase of 1-3 days following induction of diabetes, seeking to elucidate whether control of PRPP production is a result of diabetic hyperglycaemia, or to a more general re-ordering of hormonal factors. To investigate this question, the role of insulin and two different long-acting somatostatin analogues, Angiopeptin and Sandostatin, were used in a well-established animal model. PRPP was chosen specifically as a target for these studies in view of its central role in nucleotide formation and nicotinamide mononucleotide synthesis via Nampt which is the rate-limiting step in the synthesis of NAD and which has been shown to have multiple roles in cell signalling in addition to its known function in glycolysis and energy production. Treatment with the somatostatin analogues ab initio effectively abolished the adrenal growth, the increase in PRPP formation and the rise of PRPP synthetase activity in the first 7 days of diabetes, without having any significant effect on blood glucose values. This suggests that elevated glucose per se is not responsible for the diabetic adrenal hypertrophy and implies that growth factors/hormones, regulated by somatostatin analogues, play a significant role in adrenal growth processes.

Identification of compounds that inhibit IGF-I signaling in hyperglycemia

Increased responsiveness of vascular cells to the growth factor IGF-I has been implicated in complications associated with diabetes. Here we describe the development of an assay and screening of a library of compounds for their ability to accelerate cleavage of the transmembrane protein integrin-associated protein (IAP) thereby disrupting the association between IAP and SHPS-1 which we have shown as critical for the enhanced response of vascular cells to IGF-I. The cell-based ELISA utilizes an antibody that specifically detects cleaved, but not intact, IAP. Of the 1040 compounds tested, 14 were considered active by virtue of their ability to stimulate an increase in antibody-binding indicative of IAP cleavage. In experiments with smooth muscle and retinal endothelial cell cultures in hyperglycemic conditions, each active compound was shown to accelerate the cleavage of IAP, and this was associated with a decrease in IAP association with SHPS-1 as determined by coimmunoprecipitation of the proteins from cell lysates. As a consequence of the acceleration in IAP cleavage, the compounds were shown to inhibit IGF-I-stimulated phosphorylation of key signaling molecules including Shc and ERK1/2, and this in turn was associated with a decrease in IGF-I-stimulated cell proliferation. Identification of these compounds that utilize this mechanism has the potential to yield novel therapeutic approaches for the prevention and treatment of vascular complications associated with diabetes.

Therapeutic Potential of Insulin-Like Growth Factor-1 in Patients with Diabetes Mellitus

Insulin-like growth factor-1 (IGF-1) and its receptors share considerable homology with insulin and insulin receptors, and their respective signaling pathways interact at the post receptor level. While the growth hormone (GH)-IGF-1 axis principally regulates tissue growth and differentiation, insulin exerts it primary effects on fuel metabolism. However, these two endocrine systems interact at multiple levels and in diabetes mellitus the GH-IGF-1 axis is grossly disturbed, with increased secretion of GH, reduced plasma levels of IGF-1, and complex tissue-specific changes in IGF binding proteins (IGFBPs). These observations have given rise to the view that GH-IGF-1 axis dysfunction, particularly low plasma levels of circulating IGF-1, probably play a significant role in several aspects of the pathophysiology of diabetes mellitus, including insulin resistance and poor glycemic control, and may also influence the development of microvascular complications. The availability of recombinant human IGF-1 (rhIGF-1; mecasermin), used either alone or in combination with insulin, has led to experimental studies and clinical trials in humans testing these hypotheses. These studies have examined the impact of subcutaneous rhIGF-1 injections on sensitivity and metabolic parameters. In patients with type 1 and 2 diabetes mellitus, insulin sensitivity is significantly improved, insulin requirements are reduced, and glycemic control of dyslipidemia is generally improved in short-term studies. rhIGF-1 is a particularly attractive possibility in patients with type 2 diabetes mellitus, where insulin resistance is the fundamental problem. Some patients with genetic syndromes of severe insulin resistance also benefit from treatment with rhIGF-1, which can bypass blocks in the insulin signaling pathway. The common adverse effects reported for rhIGF-1 are dose-related and include edema, jaw pain, arthralgia, myalgia, hypotension, injection site pain, and less commonly, Bell's palsy and raised intracranial pressure. Although disturbance of the GH-IGF-1 axis participates in the development of diabetic complications, the functional consequences of the complex changes in IGFBP expression at the tissue level are uncertain, and it is not known whether systemic IGF-1 therapy or other manipulations of the GH-IGF-1 axis would be helpful or harmful. Experimentally, IGF-1 has a protective effect on neuropathy, and could find an application in the healing of neuropathic ulcers. The potential benefits of IGF-1 therapy in diabetes mellitus have yet to be realised.

Circulating IGF-I and its protective role in the pathogenesis of diabetic angiopathy

Poor glycaemic control in type 1 diabetes is associated with elevated serum IGFBP-1 levels and reduced rather than elevated serum IGF-I levels. Increasing age is accompanied by a further decrease in serum IGF-I levels as well as an increase in IGFBP-l levels in adult diabetic type 1 and type 2 subjects. This is especially observed in diabetic type 1 subjects with manifest microvascular complications. IGFBP-I has been proposed as one of the IGF-I inhibitors in the serum of diabetics. Lowered IGF-I and increased IGFBP-1 levels in the blood may thus result in decreased IGF-I bioavailability at the tissue level. We hypothesize that the premature and progressive decline in serum IGF-I bioactivity during ageing in diabetics ultimately results in insufficient protective effects by IGF-I in the kidneys, eyes and neurones, and thus the progression of diabetic microvascular complications. If this hypothesis is proven to be right, treatment of diabetic patients with IGF-I (eventually complexed to IGFBPs) as an adjunct to insulin might prevent and not worsen the development of diabetic microvascular complications.

Renal enlargement and insulin-like growth factor-1 accumulation in the Wistar rat model of experimental diabetes is not prevented by angiotensin converting enzyme inhibition

Experimental diabetes is associated with renal enlargement and glomerular hyperfiltration. Possible mechanisms for these changes could be the direct effects of growth factors such as insulin-like growth factor-1 and angiotensin II. We investigated whether treatment with trandolapril, an angiotensin converting enzyme inhibitor, prevented renal enlargement in streptozotocin-diabetic rats. Seven groups of male Wistar rats were studied: C (control + placebo); CL (control + low-dose trandolapril, 0.01 mg.kg-1.day-1); CH (control + high-dose trandolapril, 0.5 mg.kg-1.day-1; DP (diabetic + placebo); DI (diabetic, insulin-treated); DL (diabetic + low-dose trandolapril); DH (diabetic + high-dose trandolapril) and DI (diabetic + insulin). From day 2 glucose concentrations and body weight were similar in the non-diabetic and diabetic animals treated with insulin. Diabetic animals treated with placebo and low-dose trandolapril weighed significantly less compared to the control group. The diabetic groups, not treated with insulin, showed marked hyperglycaemia throughout the study. Kidney weight was greater in the diabetic, non insulin-treated groups compared with the control and insulin-treated groups. After 24 h of diabetes, kidney insulin-like growth factor-1 content was significantly increased from baseline levels in groups DP, DL and DH but by 48 h these levels had returned to normal. Renal tissue angiotensin converting enzyme activity was similar in groups C and DI but significantly reduced in all trandolapril-treated animals. Despite inhibiting renal angiotensin converting enzyme activity renal enlargement with increased tissue insulin-like growth factor-1 still occurred. This suggests that neither angiotensin II nor glomerular hyperfiltration, with raised intraglomerular pressure, play a role in the initial renal enlargement seen in experimental diabetes. Renal accumulation of insulin-like growth factor-1 appears to be an important factor in early renal hypertrophy and its effects are not modulated by angiotensin converting enzyme or angiotensin II.

The insulin-like growth factor system in vascular smooth muscle: interaction with insulin and growth factors

Vascular smooth muscle cells (SMCs) occur throughout the vascular tree and have important physiological functions. They are also involved in pathological processes such as development and progression of atherosclerotic lesions, restenosis following angioplasty, and in hypertension. This review is focused on the role of the insulin-like growth factor (IGF) system in proliferation, migration, and hypertrophy of vascular SMCs and its interaction with insulin and other growth factors. The IGF-I receptor is highly expressed in SMCs in intact arteries and in cultured SMCs and is activated by binding of IGF-I to the two alpha-subunits. Insulin and IGF-II from the circulation can interact with the IGF-I receptor at higher concentrations. Insulin receptors are few or absent in SMCs and circulating insulin concentrations in vivo are probably too low for a direct action of insulin on the IGF-I receptor in SMCs. Receptor activation initiates a number of signal transduction pathways. Increased phosphatidylinositol turnover and calcium mobilization correlates with actin filament reorganization and stimulation of directed migration of the SMC in a gradient of IGF-I. The effects of IGF-I receptor activation on signal transduction pathways (eg, the MAP kinase cascade) implicated in DNA synthesis and proliferation are weak and this correlates with the meager mitogenic activity of IGF-I in SMC. Several components of the IGF-system in SMC are regulated by growth factors such as platelet-derived growth factor (PDGF)-BB and basic fibroblast growth factor (bFGF).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of growth hormone, insulin-like growth factors (IGFs), and IGF-binding proteins in experimental diabetic kidney disease

Early renal changes in type I diabetes are characterized by an increase in renal size, glomerular volume, and kidney function, and later by development of mesangial proliferation, accumulation of glomerular extracellular matrix, and increased urinary albumin excretion (UAE). Growth hormone (GH) and insulin-like growth factors (IGFs) have a long and distinguished history in diabetes mellitus, with possible participation in the development of long-term complications. In experimental diabetes in dwarf rats with isolated GH and IGF-I deficiency, a slower and lesser renal and glomerular hypertrophy is observed as compared with diabetic control animals with intact pituitary. Furthermore, diabetic dwarf rats with a diabetes duration of 6 months display a smaller increase in UAE, indicating that GH and IGF-I may be involved in the development of diabetic kidney changes. In line with this, administration of octreotide to streptozotocin (STZ)-diabetic animals with normal pituitary inhibits initial renal growth without affecting blood glucose levels, and 6 months' administration of octreotide to diabetic rats reduces long-term renal/glomerular hypertrophy and UAE. In addition, the initial increase in renal size and function in experimental diabetes is preceded by an increase in renal IGF-I, IGF-binding proteins (IGFBPs), and IGF-II/mannose-6-phosphate receptor (IGF-II/Man-6-P receptor) concentration. Finally, specific changes occur in renal GH-binding protein (GHBP) mRNA, IGF-I receptor mRNA, and IGFBP mRNA expression in long-term diabetes. In conclusion, the knowledge we have today indicates that GH and IGFs, through a complex system consisting of GHBP, IGFs, IGF receptors, and IGFBPs, may be responsible for both early and late renal changes in experimental diabetes.

Inhibition of renal ornithine decarboxylase activity fails to reduce kidney size and urinary albumin excretion in diabetic rats with manifest kidney hypertrophy

Formation of polyamines has previously been shown to play an important role for initial kidney growth in experimental diabetes, as treatment of diabetic rats with a selective ornithine decarboxylase (ODC) inhibitor, initiated immediately after diabetes induction, abolishes the initial kidney growth. In order to investigate the role of polyamine formation for the maintenance of diabetic kidney hypertrophy, ODC inhibition was initiated after manifest kidney hypertrophy had occurred. The kidney weight in diabetic rats was significantly larger than in control rats after a diabetes duration of 7, 14, 50 and 71 days and the total glomerular volume was increased in kidneys from diabetic rats after a diabetes duration of 71 days. Renal activity of ODC was increased in diabetic rats throughout the study period of 71 days. Treatment of diabetic rats with the selective ODC inhibitor di-fluoro-methyl-ornithine (DFMO) was maintained for two periods (days 7-14 and days 50-71). DFMO treatment had no effect on 24-h food consumption, blood glucose concentration or body weight. However, despite almost total inhibition of the kidney ODC activity, there was no effect on kidney growth or total glomerular volume in the DFMO treated diabetic rats compared to placebo treated diabetic rats. Finally, the urinary albumin excretion was markedly increased in diabetic rats with no effects of ODC-inhibition. In conclusion, inhibition of ODC initiated in diabetic rats with manifest kidney enlargement had no effect on renal size, glomerular volume or urinary albumin excretion. These findings together with our previous findings indicate that the role of polyamines in diabetic kidney enlargement is restricted to the first week after diabetes induction.

The role of insulin-like growth factors in diabetic kidney disease

Early renal manifestations of type I diabetes include kidney enlargement, increased glomerular filtration rate, and renal plasma flow. These hemodynamic changes may be caused by a number of factors, including growth hormone and/or insulin-like growth factor-I (IGF-I). Streptozotocin-induced insulinopenic diabetes in rats represents a model of human type I diabetes and is associated with the early hemodynamic changes in the kidney seen in poorly controlled type I diabetic patients. These changes are preceded by an accumulation of IGF-I peptide in the kidney. Insulin-like growth factor-I is not locally produced, but rather accumulates from circulating IGF-I, trapped by increased levels of IGF-binding proteins, particularly IGF-binding protein-1. The hemodynamic effects, reproduced by infusions of recombinant human IGF-I in normal rats, may be blocked by co-infusion of a kinin-receptor antagonist, suggesting that at least one of the mechanisms involved is the kallikrein-kinin system. These studies strongly support the notion that the IGF system may play a role in early hemodynamic manifestations of the diabetic kidney. Whether these effects lead to long-term diabetic renal disease remains to be studied.

Inhibition of renal ornithine decarboxylase activity prevents kidney hypertrophy in experimental diabetes

The selective ornithine decarboxylase (ODC) inhibitor difluoromethyl ornithine (DFMO) was used to investigate the role of polyamines in initial diabetic renal enlargement. ODC activity in kidneys from diabetic animals was increased (fivefold) 24 h after diabetes induction (P < 0.05), and throughout the study (7 days) the activity remained 2- to 3-fold elevated (P < 0.05). Insulin treatment normalized renal ODC activity, whereas DFMO treatment totally inhibited the kidney ODC activity. The kidney weight in diabetic rats was 21% higher than that of control rats (1,074 +/- 35 mg and 889 +/- 16 mg, P < 0.001). Insulin treatment normalized kidney weight (847 +/- 13 mg). Despite unaltered diabetic metabolic aberrations the kidney weight in DFMO-treated diabetic rats was normalized (911 +/- 7 mg). In conclusion, the ODC activity in diabetic kidneys undergoing hypertrophy was increased. Insulin treatment normalized both kidney weight and kidney ODC activity. Finally, selective inhibition of ODC activity by DFMO resulted in kidneys of normal size, despite unaltered diabetic metabolic aberrations. These findings support the hypothesis that polyamines play an important role in initial diabetic renal enlargement.

Kidney IGF-I and renal hypertrophy in GH-deficient diabetic dwarf rats

Insulin-like growth factor I (IGF-I) has been proposed as a renotropic factor in initial diabetic kidney growth. To examine the effects of an isolated growth hormone (GH) and IGF-I deficiency on diabetic renal hypertrophy, dwarf rats were made diabetic and studied over a period of 7 days. Diabetic dwarf rats treated with human GH (hGH) or insulin and diabetic rats with intact pituitary were used as controls. In diabetic control animals kidney weight had increased by day 2 (P less than 0.01), and the increase amounted to 27% after 7 days, whereas untreated diabetic dwarf rats had a slower and lesser degree of kidney weight increase, reaching significance on day 7 only, amounting to 8%. hGH administration in diabetic dwarf rats increased the kidney weight on day 7 when compared with untreated diabetic dwarf rats (P less than 0.05) and was 19% over that of insulin-treated diabetic dwarf rats. The glomerular volume had increased by 43% in untreated diabetic control rats at day 7, compared with a 29% increase in untreated diabetic dwarf rats (P less than 0.05). hGH administration in diabetic dwarf rats increased the glomerular volume by 46%, comparable to the increase seen in diabetic control animals. Kidney IGF-I was increased on day 2 by 51 and 46% in saline- and hGH-injected diabetic dwarf rats, respectively, but a significantly higher increase in kidney IGF-I amounting to 96% was seen in diabetic control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Uridine and cytidine nucleotide synthesis in renal hypertrophy: biochemical differences in response to the growth stimulus of diabetes and unilateral nephrectomy

The effects of unilateral nephrectomy (UN) and streptozotocin (STZ) diabetes on the activities of enzymes involved in uridine and cytidine synthesis in early renal growth (3-14 days after stimulus to growth) have been compared. Measurements were also made of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) and of glucose 6-phosphate (G6P), UDP-glucose, and glycogen, in relation to phosphoribosyl pyrophosphate, ribonucleotide, and complex carbohydrate formation. There were striking differences in the activities of CTP synthetase, G6PDH, and 6PGDH in the two conditions, with a three-fold increase in all three enzymes at 3 and 5 days and a two-fold increase above basal values at 14 days of STZ diabetes. The UN group showed no significant change in CTP synthetase at any stage and the activity of G6PDH and 6PGDH only kept pace with renal growth. Changes in routes of uridine synthesis were less marked, with a more rapid rise in carbamoyl-phosphate synthetase (glutamine) and a lesser response of dihydroorotate dehydrogenase in the UN relative to the STZ-diabetic groups. The enzymes of complex II and of uracil phosphoribosyltransferase showed essentially similar patterns during renal hypertrophy in UN and STZ diabetes. The parallel increase in CTP synthetase, G6PDH, and 6PGDH in the kidney in diabetes, also known to increase in growth situations in hepatomas and in renal tumors, is discussed in relation to hormone signals involved in renal growth. The importance of the concentration of CTP, and thus of CTP synthetase, in the CTP-cytidyltransferase reaction, an enzyme with a high Km for CTP, makes the present observation of the striking increase in CTP synthetase in STZ diabetes of particular interest in relation to phosphatidylcholine formation and hormone signal transduction.