Epidermal growth factor induces adult human islet cell dedifferentiation

Given the inherent therapeutic potential of the morphogenetic plasticity of adult human islets, the identification of factors controlling their cellular differentiation is of interest. The epidermal growth factor (EGF) family has been identified previously in the context of pancreatic organogenesis. We examined the role of EGF in an in vitro model whereby adult human islets are embedded in a collagen gel and dedifferentiated into duct-like epithelial structures (DLS). We demonstrated that DLS formation was EGF dependent, while residual DLS formation in the absence of added EGF was abrogated by EGF receptor inhibitor treatment. With respect to signaling, EGF administration led to an increase in c-Jun NH2-terminal kinase (JNK) phosphorylation early in DLS formation and in AKT and extracellular signal-regulated kinase (ERK) phosphorylation late in the process of DLS formation, concomitant with the increased proliferation of dedifferentiated cells. In the absence of EGF, these phosphorylation changes are not seen and the typical increase in DLS epithelial cell proliferation seen after 10 days in culture is attenuated. Thus, in our model, EGF is necessary for islet cell dedifferentiation, playing an important role in both the onset of DLS formation (through JNK) and in the proliferation of these dedifferentiated cells (through AKT and ERK).     

Evidence for increased levels of a circulating ouabainlike factor in essential hypertension

The effect of plasma from normotensive and hypertensive subjects on the binding of [3H]ouabain on human erythrocytes was investigated. The binding of [3H]ouabain on human erythrocytes was saturable and highly specific; linear Scatchard plots indicated the presence of a single type of binding site. Human plasma decreased the binding of [3H]ouabain on its receptor to a greater extent than could be accounted for by the plasma potassium concentration. The level of this circulating ouabainlike factor (or factors) was quantitated using a radioreceptor assay. Plasma from 22 hypertensive subjects (systolic blood pressure greater than 160 mm Hg or diastolic blood pressure greater than 90 mm Hg) displayed higher levels than that from 24 normotensive subjects; furthermore there was a positive and significant correlation (r = 0.42, n = 46, p less than 0.004) between the ouabainlike content and the individual subject's systolic blood pressure. The receptor assay described is relatively simple and should be useful for further work on the nature and clinical importance of the endogenous ouabainlike factor.     

Advanced-glycation end products in insulin-resistant states

Insulin resistance is a central component of a number of clinical conditions, including the metabolic syndrome, diabetes, and hypertension. There is emerging evidence that the consequent hyperinsulinemia and visceral adiposity may be directly responsible for the excess cardiovascular morbidity and mortality seen in these conditions. Advanced-glycation end products, a chemically diverse group of compounds found in higher levels in insulin-resistant states, have also been shown to adversely affect endothelial function as well as activate numerous intracellular signaling pathways implicated in the atherosclerotic pathway. In this review, we summarize the factors thought to be important in both the initiation and exacerbation of the insulin-resistant state, and directly examine the potential role of advanced-glycation end products in this process.     

Evidence of a circulating growth hormone stimulating factor other than growth hormone releasing hormone in a patient with pituitary tumour and acromegaly

This study is a report on the growth hormone (GH) stimulatory effect of serum and plasma from a patient with notably active acromegaly due to a GH producing pituitary adenoma. Pituitary adenomatous tissue from 7 patients with GH producing adenomas, one with a prolactin (Prl) producing adenoma, one with a TSH producing adenoma, and one with a non-secreting adenoma, were cultured in vitro for 8-10 days. Media were changed every 48-72 h and contained Neumann Tytell buffer with the addition of 1) foetal calf serum, 2) patients' own serum or plasma, 3) serum or plasma from the patient with notably active acromegaly. GH release expressed as microgram GH/1/48-72 h between day 6 and 8 in culture did not differ when adenomatous tissue was cultured in buffer, foetal calf serum or the patients' own serum or plasma. In contrast, GH release was increased in 9/10 patients, when media contained serum or plasma from the patient with notably active acromegaly. This GH stimulatory effect was demonstrated in vitro in human pituitary adenomatous tissue from patients with pathological as well as normal GH secretion in vivo. Furthermore, this GH releasing plasma in a concentration of 10% increased GH release in cultures of dispersed rat anterior pituitary cells. In the same system, synthetic growth hormone-releasing hormone (GRF)-44 stimulated the release of GH in a dose-dependent manner. However, at all dose levels including maximally stimulating doses of GRF, an additive effect on GH release was seen with 10% of the GH releasing plasma.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of islet amyloid polypeptide secretion in insulin-resistant humans

Summary Although it is generally accepted that islet amyloid polypeptide is cosecreted with insulin, relatively few data on its kinetics are available. We therefore studied the dynamics of islet amyloid polypeptide release following oral and frequently sampled intravenous glucose tolerance tests in comparison to insulin and C-peptide using mathematical model techniques in 14 control subjects, 10 obese and 11 hypertensive patients. The fractional clearance rate of islet amyloid polypeptide (0.034±0.004 min^–1 in control subjects, 0.058±0.008 in the obese and 0.050±0.008 in the hypertensive patients) was significantly different (p<0.01) in each group compared with that of insulin (0.14±0.03 min^–1) and similar to that of C-peptide (0.061±0.007 min^–1), at least in the insulin-resistant subjects. Based on the insulin sensitivity index derived from the minimal model analysis of intravenous glucose tolerance test data, both the hypertensive (2.4±0.4 min^–1/(μU/ml); p<0.0005) and the obese (2.7±0.5; p<0.001) patients demonstrated severe insulin resistance compared to control subjects (8.1±1.3). Marked insulin hypersecretion was found in the hypertensive (57.6±5.2 nmol·l^–1 in 180 min; p<0.001) and obese (60.8±10.1; p<0.003) patients in comparison with control subjects (32.4±3.2). The release of islet amyloid polypeptide was significantly higher in the hypertensive (83.1±16.6 pmol/l in 180 min; p<0.02) and obese (78.6±13.1; p<0.005) patients than in control subjects (40.5±6.4). No correlation was found between islet amyloid polypeptide release and the insulin sensitivity index in any group. We conclude that, due to a significantly slower clearance of islet amyloid polypeptide in comparison to insulin, reliance on molar ratios between these two peptides might be misleading in the interpretation of islet amyloid polypeptide secretion especially under non-steady-state conditions. [Diabetologia (1994) 37: 188–194] Received: 10 June 1993 and in revised form: 20 August 1993     

Role of insulin receptors in insulin-resistant states

The interaction of insulin with its receptor represents one of the key intermediate steps between secretion of insulin and its final biologic effects. Alterations in this interaction have been found in a number of disease states, including obesity, non-insulin-dependent diabetes mellitus (NIDDM), glucocorticoid excess, and acromegaly, as well as several rare forms of severe insulin resistance. The major factor regulating the receptor in obesity and NIDDM appears to be insulin. In obesity this alteration in normal regulation occurs secondary to overeating, whereas in the diabetic state the nature of the primary defect is uncertain. The role of the receptor in insulin resistance and methods for its evaluation are discussed.     

Insulin-like growth factor II allows prolonged blood glucose normalization with a reduced islet cell mass transplantation

IGF-II has been reported to decrease neonatal islet cell apoptosis and in vitro adult islet cell necrosis and apoptosis, but the usefulness of IGF-II in a transplantation setting is unknown. We evaluated the effect of in vitro IGF-II incubations on microencapsulated rat islet survival both in vitro and in minimal mass transplantations into diabetic mice. After 6 d in culture, fresh examinations, histology, fluorescence microscopy, sodium 3'-[1-(phenyl-amino-carbonyl)-3,4-tetrazolium]-bis (4-methoxy-6-nitro)-benzene sulfonic acid hydrate assay, and apoptosis studies all indicated that IGF-II significantly improves islet cell viability in a dose-dependent fashion. IGF-II 100 ng/ml and 500 ng/ml induced a 51% and 83% increase of viable islets (P = 0.052, P < 0.01). A 20%, 29%, and 33% reduction of the apoptotic index was observed with 50, 100, and 500 ng/ml incubations respectively (P < 0.05; P < 0.005; P < 0.001). Ten weeks after transplantation of 150 encapsulated rat islet equivalents incubated with IGF-II 500 ng/ml, 80% of diabetic mice were normoglycemic. Without IGF-II preincubation, only 8% of the recipients remained normoglycemic with the transplantation of 150 islets and 42% with 300 islets (P < 0.05). In conclusion, IGF-II promotes islet cell survival, and allows successful transplantation using a smaller number of islets.     

Evidence that potassium deficiency induces growth retardation through reduced circulating levels of growth hormone and insulin-like growth factor I.

Growth retardation and impaired protein synthesis are major characteristics of potassium (K)-deficiency in animals and man. We have evaluated the effect of K-deficiency on growth, serum growth hormone (s-GH), insulin-like growth factor I (s-IGF-I), and insulin (s-insulin) in young rats. After 10 days on K-deficient fodder, 4 1/2-week-old rats showed a 54% reduction in serum potassium (s-K) and a weight gain that was reduced by 97%, compared with pair-fed controls. In addition, tail length, tibia length, and muscle weight of soleus in K-depleted animals were all significantly reduced compared with pair-fed controls. The growth retardation was accompanied by a 46% reduction in s-IGF-I, while s-insulin showed no decrease. K-repletion in animals depleted for 7 days showed complete normalization of s-K within 24 hours, in addition to a significant increase in both s-IGF-I and weight. In 4-week-old rats maintained on K-deficient fodder with variable K-content (1 to 260 mmol/kg) for 1 week, a strong correlation between the K-content of fodder and s-IGF-I could be established (r = .88, P less than .001), as well as between s-IGF-I and weight gain (r = .90, P less than .001). Furthermore, a stepwise reduction in basal s-GH was seen with the graded reduction of dietary K-content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypoglycemia associated with the production of insulin-like growth factor II in a pancreatic islet cell tumor: a case report

An insulinoma is characterized by endogenous hyperinsulinemia and hypoglycemia. However, it has been reported that insulinomas with normal levels of plasma insulin and a normal insulin to glucose ratio occur in patients with hypoglycemia. Although overproduction of Insulin-like growth factor II (IGF-II) by non-islet cell tumors such as large mesenchymal tumors, can cause hypoglycemia, no cases of circulating plasma IGF-II from an islet cell tumor contributing to hypoglycemia have been reported. We report here a rare case of a pancreatic islet tumor in a patient with hypoglycemia that was associated with increased plasma IGF-II, which returned to normal after tumor resection.     

Evidence for a role of basic fibroblast growth factor in rat embryonic growth and differentiation

The possibility that basic fibroblast growth factor (FGF) plays a role in the regulation of mammalian embryogenesis was investigated. When transplanted under the renal capsule of syngeneic juvenile hosts, 10-day-old rat embryos grow rapidly, and tissue differentiation occurs in an essentially normal manner. Infusion of antiserum to bovine FGF into the renal artery of kidneys bearing such transplants significantly retarded their growth, and differentiation of all tissues of endodermal and some of those of mesodermal origin was completely suppressed; differentiation of other tissues of mesodermal origin was partially inhibited. Infusion of nonimmune serum had no such effects. Infusion of recombinant bovine FGF into the renal artery stimulated growth of embryo transplants on the infused kidney, but not of those under the renal capsule of the contralateral kidney, and it did not affect growth of the infused kidney itself. These results suggest that FGF may be important for growth and differentiation of endodermal and some mesodermal tissues of mammalian embryos.     

Biologically active circulating proinsulin-like materials from an islet cell carcinoma patient

Summary Circulating immunoreactive insulin (IRI) material was obtained from a hypoglycemic patient with a pancreatic islet cell carcinoma. On gel filtration, 85% of this material eluted as a homogeneous proinsulin peak (PLM) and 15% as insulin. On polyacrylamide gel electrophoresis, in addition to a small amount of insulin, two peaks were obtained. One had the migration of intact human proinsulin. The second electrophoresed as an intermediate species compatible with desdipeptide proinsulin. Trypsin treatment of PLM resulted in IRI material eluting as insulin on gel filtration. When comparable amounts of IRI material were tested, PLM showed about one half of the biological activity of porcine insulin in the rat hemidiaphragm system. No evidence of conversion to insulin was found after PLM had exerted its biological activity. In addition to large amounts of proinsulin, islet cell tumors may secrete significant amounts of intermediate species into the circulation.Supported by VA Research Funds and NIH Grant AM 11578     

On the paradox of insulin-induced hyperandrogenism in insulin-resistant states

I have reviewed recent studies that shed light on the paradox of insulin-induced ovarian hyperandrogenism in insulin-resistant states. Depending on the circumstances of the particular syndrome, insulin could act on the ovaries of insulin-resistant patients by activating IGF-I receptors, insulin receptors, hybrid insulin/IGF-I receptors, or any combination of these receptors. Further studies will uncover precise mechanisms of insulin-induced ovarian hyperstimulation in specific syndromes of insulin resistance.     

Insulin-like growth factor 2 expressed in a novel fetal liver cell population is a growth factor for hematopoietic stem cells

Hematopoietic stem cells (HSCs) undergo dramatic expansion during fetal liver development, but attempts to expand their numbers ex vivo have failed. We hypothesized that unidentified fetal liver cells produce growth factors that support HSC proliferation. Here we describe a novel population of CD3+ and Ter119- day-15 fetal liver cells that support HSC expansion in culture, as determined by limiting dilution mouse reconstitution analyses. DNA array experiments showed that, among other proteins, insulin-like growth factor 2 (IGF-2) is specifically expressed in fetal liver CD3+ cells but not in several cells that do not support HSCs. Treatment of fetal liver CD3+Ter119- cells with anti-IGF-2 abrogated their HSC supportive activity, suggesting that IGF-2 is the key molecule produced by these cells that stimulates HSC expansion. All mouse fetal liver and adult bone marrow HSCs express receptors for IGF-2. Indeed, when combined with other growth factors, IGF-2 supports a 2-fold expansion of day-15 fetal liver Lin-Sca-1+c-Kit+ long-term (LT)-HSC numbers. Thus, fetal liver CD3+Ter119- cells are a novel stromal population that is capable of supporting HSC expansion, and IGF-2, produced by these cells, is an important growth factor for fetal liver and, as we show, adult bone marrow HSCs.     

Evidence for a growth hormone releasing factor mediating alpha-adrenergic influence on growth hormone secretion in the rat

The effects of adrenergic receptor agonists on GH secretion were studied in adult, male rats pretreated with reserpine and somatostatin antiserum. Frequent blood samples were obtained from intra-aortic cannulae. Plasma GH was determined by radioimmunoassay. Reserpine (10 mg/kg i.p.) caused a complete suppression of the normal, pulsatile secretion of GH in all animals. Administration of somatostatin antiserum resulted in rapid elevations of plasma GH in reserpine-pretreated rats with peak levels at 30 min. GH levels then fell but remained slightly elevated for the duration of the sampling period (8 h). Apomorphine (0.5 mg/kg i.p.) had no effect on plasma GH levels, whereas clonidine (0.5 mg/kg i.p.) induced release of GH in both antiserum treated and control rats. The results indicate that the alpha-adrenergic influence on the secretion of GH is mediated not by inhibition of somatostatin release but rather by effects on the release of a GHRF.     

Insulin and glucagon secretion in diabetic and non-diabetic patients with circulating islet cell antibodies

Summary Thirty-nine patients (14 non-diabetics, 8 chemical diabetics, and 17 overt diabetics) with circulating islet cell antibodies (ICA) were studied. Insulin and glucagon secretion after oral (100 g) and intravenous glucose loading (200 mg/kg bolus injection followed by an infusion of 20 mg/min over 60 min) and arginine infusion (25 g over 30 minutes) were evaluated in these patients and in non diabetic and diabetic ICA-negative controls. In the non-diabetic groups with or without ICA, insulin and glucagon responses to glucose were similar. Moreover, in ICA positive patients the response of these hormones to arginine infusion was reduced. Similar alterations in insulin and glucagon secretion were observed in the ICA positive and negative patients with chemical or overt diabetes. In particular, fasting hyperglucagonaemia and glucagon hyperresponse to arginine are associated with a lack of insulin secretion in the patients with overt diabetes. Hormonal differences between diabetics with and without ICA could not be detected.This work was previously presented at the 12th Meeting of the European Association for the Study of Diabetes, Helsinki, September 1976 and published in abstract form in Diabetologia12, 422 (1976)     

The mechanism of HDL lowering in hypertriglyceridemic, insulin-resistant states

Hypertriglyceridemia and reduced plasma levels of high-density lipoprotein cholesterol (HDL-c) are the most frequent forms of dyslipidemia observed in insulin-resistant states, such as obesity, impaired fasting glucose, and Type 2 diabetes, and are highly atherogenic in these settings. The hypertriglyceridemia of insulin resistance is primarily due to an overproduction of very low-density lipoproteins (VLDL), and in some instances, is also due to reduced VLDL clearance and postprandial accumulation of VLDL, chylomicrons, and their remnants [i.e., triglyceride (TG)-rich lipoproteins]. TG-rich lipoproteins actively exchange their core lipids with HDL in vivo, a process that is facilitated by cholesteryl ester (CE) transfer protein (CETP), and in hypertriglyceridemic states, this process is enhanced. This results in TG enrichment of HDL in hypertriglyceridemic states. There is accumulating evidence that TG enrichment of HDL plays an important role in determining the rate at which HDL particles are cleared from the circulation. Here, we review the evidence that TG-enriched HDL, when modulated by lipolytic enzymes in the circulation, are catabolized more rapidly than native HDL, and may ultimately explain the lowering of HDL-c in insulin-resistant, hypertriglyceridemic states. Since we have recently reviewed in detail the evidence by Lamarche et al. [Clin. Chim. Acta 286 (1999) 145; J. Clin. Invest. 103 (8) (1999) 1191.] to support this hypothesis, in the present brief review, we will focus predominantly on our own recent research in this area.