Islet changes induced by hyperglycemia in rats. Effect of insulin or chlorpropamide therapy

Significance of Interleukin-6/STAT Pathway for the Gene Expression of REG Iα, a New Autoantigen in Sjögren's Syndrome Patients, in Salivary Duct Epithelial Cells

The regenerating gene, Reg, was originally isolated from a rat regenerating islet complementary DNA (cDNA) library, and its human homologue was named REG Iα. Recently, we reported that REG Iα messenger RNA (mRNA), as well as its product, was overexpressed in ductal epithelial cells in the salivary glands of Sjögren's syndrome patients. Furthermore, autoantibodies against REG Iα were found in the sera of Sjögren's syndrome patients, and the patients who were positive for the anti-REG Iα antibody showed significantly lower saliva secretion than antibody-negative patients. We found the mechanism of REG Iα induction in salivary ductal epithelial cells. Reporter plasmid containing REG Iα promoter (-1190/+26) upstream of a luciferase gene was introduced into human NS-SV-DC and rat A5 salivary ductal cells. The cells were treated with several cytokines (interleukin (IL)-6, IL-8, etc.), upregulated in Sjögren's syndrome salivary ducts, and the transcriptional activity was measured. IL-6 stimulation significantly enhanced the REG Iα promoter activity in both cells. Deletion analysis revealed that the -141∼-117 region of the REG Iα gene was responsible for the promoter activation by IL-6, which contains a consensus sequence for signal transducer and activator of transcription (STAT) binding. The introduction of small interfering RNA for human STAT3 abolished IL-6-induced REG Iα transcription. These results indicated that IL-6 stimulation induced REG Iα transcription through STAT3 activation and binding to the REG Iα promoter in salivary ductal cells. This dependence of REG Iα induction upon IL-6/STAT in salivary duct epithelial cells may play an important role in the pathogenesis/progression of Sjögren's syndrome.

Regulatory Forum Opinion Piece: Review-Toxicological Pathology Profile and Regulatory Expectations for Nonclinical Development of Insulins and Insulin Analogues

The toxicological profile of insulins is exclusively due to exaggerated pharmacology resulting in hypoglycemic findings. Insulin analogues displaying modifications and aimed at improving pharmacokinetics do not induce different toxicity. The main target is the brain displaying neuronal necrosis. Wallerian degeneration of nerves occurs rarely after severe hypoglycemia. These findings are of potential human relevance; nevertheless, these changes are induced in normoglycemic animals whereas diabetic patients suffer from hyperglycemia. Therefore, it is usually not difficult to achieve a therapeutic window for subsequent use in patients. Based upon this and in the absence of classical toxicity, there has been no scientific need for diabetic animal models. A greater challenge is the mitogenicity already inherent with regular insulin. Thus, the focus for preclinical safety evaluation of analogues is to demonstrate that modifications in regular insulin do not result in enhanced mitogenicity. The approaches used to assess the mitogenic potential of insulin analogues have changed over time driven by scientific progression and changes within the regulatory environment. Therefore, in vitro and in vivo evaluation of cell proliferation has become common practice, and to date there has been no evidence that the mitogenic potential of insulin analogues may be increased compared to regular insulin.

Regenerating gene (REG) product and its potential clinical usage

INTRODUCTION

The regenerating gene (Reg) was identified in regenerating islets and its related genes were revealed to constitute the Reg gene family. Reg family proteins act as growth factors for several cells. Recently, autoimmunity against the Reg family proteins has been reported in several diseases. In addition, the Reg family genes were found to be expressed in a large number of cancers and to influence prognosis.

AREAS COVERED

The historical background and current view of the structure, function, and expression of Reg family genes/proteins and their physiological/pathological significance in several diseases are described. Based on the findings, the diagnostic/therapeutic potential of Reg family genes/proteins is also discussed.

EXPERT OPINION

Autoimmunity against Reg family proteins may be a new diagnostic marker and/or therapeutic target for immune-mediated diseases. Treatment aimed at the expansion of the β-cell mass by the Reg genes/proteins, combined with the abrogation of autoimmunity, constitutes a potential approach for the treatment of diabetes. Conversely, some cancer cells have gained the ability to overexpress the Reg genes/proteins, thereby enhancing their proliferative capacities, resulting in these cells having a considerable growth advantage. Thus, the Reg genes/proteins are expected to be a new prognostic marker in cancer and/or a future therapeutic target.

A review of islet of Langerhans degeneration in rodent models of type 2 diabetes

Type 2 diabetes mellitus (TTDM) is characterized by progressive loss of glucose control through multifactorial mechanisms. The search for an understanding of TTDM has relied on animal models since the realization of the importance of the pancreas in controlling plasma glucose concentration. Rodent models of TTDM are developed to express hyperglycemia and not islet degeneration per se. Degeneration of the islets of Langerhans with beta-cell loss is secondary to insulin resistance and is regarded as the more important lesion. Despite this, differences between models are seen in the development and progression of islet degeneration. Assessing the differences between the models is important to appreciate the various aspects of TTDM and understand their advantages as well as their deficiencies. Relevant animal models of TTDM provide opportunities to investigate important physiological and cell biological processes that may ultimately lead to development of targeted therapies. This article reviews the importance, advantages, and limitations of rodent models of TTDM in relation to the histopathological changes that characterize islet degeneration. Pathophysiological mechanisms that contribute to islet degeneration are also discussed and are placed into the context of changes in islet histological appearances.

New agents for Type 2 diabetes

Current agents for the treatment of Type 2 diabetes mellitus improve the metabolic profile but do not reinstate normality. They also reduce chronic diabetic complications, but they do not eliminate them. Thus, new agents with novel actions are required to complement and extend the capabilities of existing treatments. Insulin resistance and beta-cell failure, which are crucial components in the pathogenesis of Type 2 diabetes, remain the underlying targets for new drugs. Recently introduced agents include a short-acting non-sulphonylurea insulin-releaser, repaglinide, which synchronizes insulin secretion with meal digestion in order to reduce post-prandial hyperglycaemia. The thiazolidinedione drugs, troglitazone, rosiglitazone and pioglitazone represent a new class of agonists for the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma). PPARgamma increases the transcription of certain insulin-sensitive genes, thereby improving insulin sensitivity. The intestinal lipase inhibitor orlistat and the satiety-inducer sibutramine are new weight-reducing agents that may benefit glycaemic control in obese Type 2 diabetes patients. Several further new insulin-releasing agents, and agents to retard carbohydrate digestion and modify lipid metabolism stand poised to enter the market. The extent to which they will benefit glycaemic control remains to be seen. However, the prospect of permanently arresting or reversing the progressive deterioration of Type 2 diabetes continues to evade therapeutic capture.

No glucotoxicity after 53 hours of 6.0 mmol/l hyperglycaemia in normal man

In vitro and in vivo studies have suggested that metabolic deterioration can be induced by hyperglycaemia per se. The effect of 53 h of 2.2 mg glucose.kg ideal body weight-1.min-1 was examined in four normal male subjects. This produced overnight hyperglycaemia of 6.0 mmol/l on the two nights of the study compared with 4.7 mmol/l on the control night (p less than 0.05). In response there was a sustained, two-fold increase in basal plasma insulin (p less than 0.005) and C-peptide (p less than 0.05) levels. After two days of hyperglycaemia an increased Beta-cell response was demonstrated in response to an additional glucose infusion stimulus (estimated Beta-cell function median of 84% on the control day to 100% after two days glucose infusion). Plasma insulin and C-peptide responses to a 10.0 mmol/l hyperglycaemic clamp increased over the two days of the study (insulin from median 48 mU/l to 73 mU/l and C-peptide from median 2.0 pmol/ml to 2.6 pmol/l). Glucose tolerance to the additional glucose infusion stimulus improved, suggesting that the increased insulin response during hyperglycaemia was enhancing peripheral glucose uptake. The calculated peripheral insulin sensitivity was unchanged during the hyperglycaemic clamp. Thus, in response to the two days of basal hyperglycaemia, both the basal and stimulated Beta-cell responses were enhanced and there was no evidence for 'glucose toxicity' to the Beta-cells.

Long-term gliclazide treatment improves the in vitro glucose-induced insulin release in rats with type 2 (non-insulin-dependent) diabetes induced by neonatal streptozotocin

Neonatal rats treated with streptozotocin on the day of birth (n0-STZ) or on day 5 (n5-STZ) exhibited when fully grown a very mild or frank basal hyperglycaemia respectively and a specific failure of insulin release in response to glucose. To determine whether short (1 day) or long-term (30 days) gliclazide treatment modifies the pancreatic insulin content and the B-cell response to secretagogues, diabetic rats were given oral gliclazide (10 mg/kg per day) and compared to control diabetic and non-diabetic rats. Insulin secretion in the isolated perfused pancreas was studied the day after the last gliclazide administration. In severely hyperglycaemic n5-STZ rats (plasma glucose levels greater than 16 mmol/l) long-term gliclazide treatment did not lower the plasma glucose values, did not affect the pancreatic insulin stores, nor did it significantly modify the insulin release in vitro in response to glucose or arginine. In moderately hyperglycaemic n5-STZ rats (plasma glucose levels less than 16 mmol/l) the plasma glucose levels declined progressively reaching 8 mmol/l as a mean at the end of the gliclazide therapy. In the n5-STZ rats responsive to gliclazide the pancreatic insulin stores were increased twofold as compared to values in untreated n5-STZ rats, however, this difference did not reached significance and the pancreatic insulin stores in the responsive gliclazide treated rats remained depleted by 76% compared to normal insulin stores. In the n0-STZ rats (very mild hyperglycaemia) the long-term gliclazide treatment did not significantly modify the plasma glucose levels or the pancreatic insulin stores.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural history of intrahepatic canine islet cell autografts

We have serially followed the function of intrahepatic canine islet autografts in 15 beagle dogs for up to 24 mo. Of these, only 20% sustained normal levels of fasting blood glucose for greater than 15 mo posttransplant. Failure of autograft function was accompanied by a preferential loss of well-granulated beta cells in the engrafted islets. The chronic stimulation of an initially marginal intrahepatic beta-cell mass ultimately resulted in metabolic deterioration and loss of beta cells below the minimal threshold required to maintain normal fasting blood glucose levels. It is possible that transplantation of a larger mass of islets would result in indefinite graft function in dogs. However, it remains to be demonstrated in larger mammals, including humans, whether an islet cell mass that is initially adequate in a heterotropic site such as the liver can remain functionally competent over a prolonged period.

Chronic hyperglycemia is associated with impaired glucose influence on insulin secretion. A study in normal rats using chronic in vivo glucose infusions

We have proposed that chronic hyperglycemia alters the ability of glucose to modulate insulin secretion, and have now examined the effects of different levels of hyperglycemia on B cell function in normal rats using chronic glucose infusions. Rats weighing 220-300 g were infused with 0.45% NaCl or 20, 30, 35, or 50% glucose at 2 ml/h for 48 h, which raised the plasma glucose by 18 mg/dl in the 30% rats, 37 mg/dl in the 35% rats, and 224 mg/dl in the 50% group. Insulin secretion was then examined using the in vitro isolated perfused pancreas. Glucose-induced insulin secretion remained intact in the normoglycemic 20% glucose rats and it was potentiated in the mildly hyperglycemic 30% glucose rats. However, with even greater hyperglycemia in the 35% glucose group the insulin response to a high glucose perfusate was severely blunted, and it was totally lost in the most hyperglycemic 50% glucose rats. In a second protocol that examined glucose potentiation of arginine-stimulated insulin release, a similar impairment in the ability of glucose to modulate the insulin response to arginine was found with increasing levels of chronic hyperglycemia. On the other hand, the ability of a high glucose concentration to inhibit arginine-stimulated glucagon release was preserved in all glucose-infused rats, but the glucagon levels attained in response to the arginine at 2.8 mM glucose were much less in the 50% glucose rats than in all the other groups. These data clearly show that after 48 h of marked hyperglycemia, glucose influence upon insulin secretion in the rat is severely impaired. This model provides a relatively easy and reproducible method to study the effects of long-term hyperglycemia on B cell function.

Hyperglycaemia as an inducer as well as a consequence of impaired islet cell function and insulin resistance: implications for the management of diabetes

It is postulated that hyperglycaemia influences the natural history of Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes mellitus. Hyperglycaemia, even when mild, can attenuate the secretory response of pancreatic beta and alpha cells to increments in glucose and can impair insulin-mediated glucose transport, thus impeding its own correction and initiating a cycle of progressive self-exacerbation and metabolic deterioration. Both reduced islet function and insulin action may be the consequence of a generalized down-regulation and/or occupation of glucose transporters by hyperglycaemia so that the islets respond less to further increments in glycaemia. The postulated hyperglycaemic cycle can be initiated by any environmental perturbation that increases insulin demand in previously normoglycaemic patients in whom insulin secretion has already reached a maximum level of compensation for peripheral insulin resistance (as in obese pre-Type 2 diabetes) or for a reduced beta-cell mass (as in pre-Type 1 diabetes). Elimination of hyperglycaemia by any means can halt this cycle of progressive metabolic deterioration and may restore transiently metabolic recompensation both in Type 1 and Type 2 diabetes. There is experimental evidence that long-standing severe hyperglycaemia may irreversibly damage beta cells.

One hundred pancreas transplants at a single institution

Clinical pancreas transplantation at the University of Minnesota began in 1966. An initial series of 14 whole pancreas grafts was reported in part to the American Surgical Association in 1970. Only one patient survived for more than 1 year with a functioning graft. Twenty attempts at islet allotransplantation in the mid-1970s were unsuccessful. In 1978 we resumed performing pancreas transplants by the segmental technique, allowing the use of related donors. The current series (July 25, 1978 to December 20, 1983) includes 86 pancreas transplants (51 cadaver, 35 related) in 75 patients (41 with and 34 without previous kidney grafts). Variations in management of the pancreatic duct include three ligated, 15 duct-open, 39 duct-injected, and 29 pancreaticojejunostomies. The latter technique is currently preferred. Currently (April 1984) 61 patients are alive (81%), 24 have functioning grafts (32%), and 21 are insulin-independent (28%), three with open-duct grafts for 4.4 to 5.7 years, seven with silicone-injected grafts from 10 to 39 months, and 14 with pancreaticojejunostomies for 3 to 31 months; 15 of the grafts have functioned for greater than 1 year. Twenty-two of the grafts (25%) failed for technical reasons (thrombosis, infection, or ascites); 35 grafts functioned for 1 to 13 months before totally failing from either rejection, fibrosis, or recurrent disease; five patients died with functioning grafts. The graft survival rate has been higher for pancreases from related (15/35, 43% functioning) than from cadaver (9/51, 18% functioning) donors. The success rate has increased, e.g., 11/22 recipients of pancreas transplants in 1983 currently have functioning grafts (50%). Metabolic studies show most patients with functioning grafts to be euglycemic; however, three of 24 have chronic hyperglycemia unless supplemented with insulin, but they are no longer ketosis-prone. Glucose tolerance test results are normal or nearly normal in 12 and abnormal in 12 of the recipients with currently functioning grafts. Regression of diabetic nephropathy has been documented in two long-term recipients. Pancreas transplantation is currently applicable as treatment for selected diabetics who have demonstrated their propensity to develop serious secondary complications.

Adaptation of B and A cell function during prolonged glucose infusion in human subjects

States of insulin resistance are characterized by hyperinsulinemia that often appears to be out of proportion to the minimal degree of hyperglycemia. One possible explanation for these findings is that mild hyperglycemia per se can cause an adaptive increase in islet sensitivity to glucose, leading to increased insulin output at a given glucose level. To test this hypothesis, we compared acute insulin responses (AIR) and acute glucagon responses (AGR) to 5-g arginine injections before and after 20-h glucose infusions (200 mg X m-2 X min-1) in 11 healthy men of varying age and degree of adiposity. The 20-h glucose infusion caused an increase in fasting plasma glucose (PG) in all subjects (95 +/- 2 vs. 130 +/- 3 mg/dl). PG was clamped at three levels (approximately 95, 165, and 235 mg/dl) before and after the 20-h glucose infusion. Despite matching of PG levels, consistent increases of AIR were observed after the 20-h glucose infusion: 86 +/- 10 vs. 57 +/- 8 at PG = 95 (P = 0.002); 241 +/- 20 vs. 192 +/- 22 at PG = 165 (P = 0.02); and 508 +/- 59 vs. 380 +/- 50 microU/ml at PG = 235 mg/dl (P = 0.009). In addition, the slope of the relationship between AIR and PG level (potentiation slope), a measure of B cell sensitivity to glucose, increased consistently from 2.28 +/- 0.35 (control) to 3.07 +/- 0.45 (P = 0.004) after the 20-h infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial pancreatectomy in the rat and subsequent defect in glucose-induced insulin release

To define the consequences of a known reduction of B cell mass in rats, 90% partial pancreatectomies were performed. For the 6 wk following surgery moderate hyperglycemia was maintained in the fed state but there were no differences in body weight nor plasma insulin concentrations compared with sham-pancreatectomized controls. 8-10 wk following surgery regeneration of the remnant was evident with remnant weight being 26%, B cell mass being 42%, and non-B cell mass being 47% of values found for control whole pancreas. There were comparable increases in the remnant content of insulin, glucagon, and somatostatin. Following meal challenges, intraperitoneal and intravenous glucose tolerance tests and intravenous arginine challenge given 6-7 wk after surgery, the insulin responses to glucose were blunted or absent but the responses following the meals or arginine were intact. Similarly, when the pancreatic remnant was perfused in vitro, insulin release after challenge with 300 mg/dl glucose was markedly reduced whereas intact responsiveness to 10 mM arginine was retained. These data suggest that the chronic stimulation of a reduced B cell mass can lead to a selective loss of glucose-induced insulin secretion.