Erol Cerasi

Regulation of insulin gene transcription.

Abstract. The mammalian insulin gene is exclusively expressed in the beta cells of the endocrine pancreas. Two decades of intensive physiological and biochemical studies have led to the identification of regulatory sequence motifs along the insulin promoter and to the isolation of transcription factors which interact to activate gene transcription. The majority of the islet-restricted (BETA2, PDX-1, RIP3b1-Act/C1) and ubiquitous (E2A, HEB) insulin-binding proteins have been characterized. Transcriptional regulation results not only from specific combinations of these activators through DNA-protein and protein-protein interactions, but also from their relative nuclear concentrations, generating a cooperativity and transcriptional synergism unique to the insulin gene. Their DNA binding activity and their transactivating potency can be modified in response to nutrients (glucose, NEFA) or hormonal stimuli (insulin, leptin, glucagon like peptide-1, growth hormone, prolactin) through kinase-dependent signalling pathways (PI3-K, p38MAPK, PKA, CaMK) modulating their affinities for DNA and/or for each other. From the overview of the research presented, it is clear that much more study is required to fully comprehend the mechanisms involved in the regulated-expression of the insulin gene in the beta cell to prevent its impairment in diabetes. [Diabetologia (2002) 45: 309–326]

Splanchnic and peripheral glucose and amino acid metabolism in diabetes mellitus

Splanchnic and leg exchange of glucose, lactate, pyruvate, and individual plasma amino acids was studied in diabetics 24 hr after withdrawal of insulin and in healthy controls. Measurements were made in the basal postabsorptive state and during the administration of glucose at a rate of 2 mg/kg per min for 45 min. In the basal state, net splanchnic glucose production did not differ significantly between diabetics and controls. However, splanchnic uptake of alanine and other glycogenic amino acids was 1(1/2)-2 times greater in the diabetics, while lactate and pyruvate uptake was increased by 65-115%. Splanchnic uptake of these glucose precursors could account for 32% of hepatic glucose output in the diabetics, as compared to 20% in the controls. This increase in precursor uptake was a consequence of a two- to threefold increment in fractional extraction of these substrates inasmuch as arterial levels of alanine, glycine, and threonine were reduced in the diabetics, while the levels of the remaining substrates were similar in the two groups. Peripheral output of alanine and other glycogenic amino acids as reflected in arterio-femoral venous differences was similar in both groups. An elevation in arterial valine, leucine, and isoleucine was observed in the diabetics, but could not be accounted for on the basis of alterations in splanchnic or peripheral exchange of these amino acids. Administration of glucose (2 mg/kg per min) for 45 min resulted in an 80% reduction in splanchnic glucose output in controls, but failed to inhibit hepatic glucose release in the diabetics despite a twofold greater increment in arterial glucose levels. In both groups no consistent changes in arterial glucagon were observed during the infusion. It is concluded that in nonketotic diabetics (a) total splanchnic output of glucose is comparable to controls, but the relative contribution of gluconeogenesis may be increased by more than 50%; (b) accelerated splanchnic uptake of glucose precursors is a consequence of increased hepatic extraction of available substrates rather than a result of augmented substrate supply; and (c) the failure of glucose infusion to inhibit hepatic glucose output suggests that the exquisite sensitivity of the liver to the infusion of glucose in normal man is a consequence of glucose-induced insulin secretion.

Induction of Long-Term Glycemic Control in Newly Diagnosed Type 2 Diabetic Patients by Transient Intensive Insulin Treatment

OBJECTIVE Type 2 diabetes is a slowly progressive disease, in which the gradual deterioration of glucose tolerance is associated with the progressive decrease in β-cell function. Hyperglycemia per se has deleterious effects on both beta-cell function and insulin action, which are partially reversible by the short-term control of blood glucose levels. We hypothesized that the induction of euglycemia, using intensive insulin therapy at the time of clinical diagnosis, could lead to a significant improvement in insulin secretion and action and thus alter the clinical course of the disease. RESEARCH DESIGN AND METHODS Thirteen newly diagnosed diet-unresponsive type 2 diabetic patients were treated with continuous subcutaneous insulin infusion (CSII) for 2 weeks and followed longitudinally while being treated with diet alone. RESULTS Four patients were considered therapeutic failures since CSII failed to induce euglycemia (n = 1) or glucose control deteriorated within 6 months after CSII (n = 3). The remaining nine patients were maintained on diet alone with adequate control from 9 to > 50 months (median ± SE, 26 ± 4.8 months). In five patients, glycemic control deteriorated after 9–36 months, but a repeat 2-week CSII treatment reestablished control in four patients. One of these patients underwent a third CSII treatment 13 months later. At the time this article was written, six patients of the initial group were still controlled without medication 16–59 months (median ± SE, 45.5 ± 6.6 months) after the initiation of treatment. Body weight remained unchanged in all patients. CONCLUSIONS These findings suggest that in a significant proportion of type 2 diabetic patients who fail to respond to dietary measures, short-term intensive insulin treatment can effectively establish responsiveness, allowing long-term glycemic control without medication. Further studies are required to establish whether simpler treatment regimens could be equally effective. If the hypothesis offered here finds support, present approaches to the management of newly diagnosed type 2 diabetes may need to be revised.

Translocation Inhibitors Define Specificity of Protein Kinase C Isoenzymes in Pancreatic β-Cells

The protein kinase C (PKC) family consists of 11 isoenzymes. Following activation, each isoenzyme translocates and binds to a specific eceptor for ctivated inase (RACK) (Mochly-Rosen, D. (1995) Science 268, 247-251) that provides an anchoring site in close proximity to the isoenzymes specific substrate. Pancreatic islet cells contain at least six PKC isoenzymes (Knutson, K. L., and Hoenig, M. (1994) Endocrinology 135, 881-886). Although PKC activation enhances insulin release, the specific function of each isoenzyme is unknown. Here we show that following stimulation with glucose, αPKC and εPKC translocate to the cells periphery, while δPKC and ζPKC translocate to perinuclear sites. βC2-4, a peptide derived from the RACK1-binding site in the C2 domain of βPKC, inhibits translocation of αPKC and reduces insulin response to glucose. Likewise, εV1-2, an εPKC-derived peptide containing the site for its specific RACK, inhibits translocation of εPKC and reduces insulin response to glucose. Inhibition of islet-glucose metabolism with mannoheptulose blocks translocation of both αPKC and εPKC and diminishes insulin response to glucose while calcium-free buffer inhibits translocation of αPKC but not εPKC and lowers insulin response by 50%. These findings illustrate the unique ability of specific translocation inhibitors to elucidate the isoenzyme-specific functions of PKC in complex signal transduction pathways.

Pre‐clinical Cushing's syndrome: an unexpected frequent cause of poor glycaemic control in obese diabetic patients

OBJECTIVE Autonomous cortisol secretion without clinical stigmata of Cushings syndrome (CS) has been recently recognized and termed pre‐clinical or sub‐clinical CS. The common assumption is that CS is an extremely rare cause of uncontrolled diabetes; however, the prevalence of this entity has not been studied. We assessed the prevalence of pre‐clinical CS among obese patients with uncontrolled diabetes.

“What Is Inherited – What Is Added” Hypothesis for the Pathogenesis of Diabetes Mellitus

A working hypothesis for the pathogenesis of diabetes mellitus has been drawn up which has found partial support in experimental data in human subjects. An impaired insulin response, common to all types of diabetes including prediabetes, has been brought to attention as a major possible inherited pathogenetic component. Other factors besides the impaired insulin production have been suggested as significant in the subsequent development of manifest diabetes.

Functional conservation of regulatory elements in the pdx-1 gene: PDX-1 and hepatocyte nuclear factor 3beta transcription factors mediate beta-cell-specific expression.

ABSTRACT The PDX-1 transcription factor plays a key role in pancreatic development and in the regulation of the insulin gene in the adult β cell. As its functions appear to be similar in humans and mice, we analyzed the functional conservation of homologous sequences important for the maintenance and the cell-specific regulation of thepdx-1 gene. Apart from the proximal promoter region, three highly homologous (PH1 to PH3) sequences were apparent in the human and mouse 5′ flanking regions of the gene. By transient transfections in β and non-β cells, we show that mainly PH1 and PH2 preferentially confer β-cell-specific activation on a heterologous promoter. DNase I footprinting and binding analyses revealed that both bind to and are transactivated by hepatocyte nuclear factor 3β (HNF-3β). Furthermore, the PH1 enhancer element also binds the PDX-1 transcription factor itself, which acts cooperatively with adjacent HNF-3β to regulate its transcriptional potency. This finding suggests a possible autoregulatory loop as a mechanism for PDX-1 to control its own expression.

Dose-response relation between plasma-insulin and blood-glucose levels during oral glucose loads in prediabetic and diabetic subjects

Abstract An inadequate insulin response to orally administered glucose was demonstrated by prediabetic and diabetic subjects. The insulin deficiency was even more pronounced when oral and intravenous glucose loads were combined. The dose-response curves relating plasma-insulin to the blood-glucose level showed that the secretory capacity of the β-cells is progressively impaired during the development of diabetes from prediabetes. Comparison of the results with previous studies on the glucose/insulin dose-response relation after intravenously administered glucose suggested that intestinal factors enhance the insulinogenic effect of glucose by a factor of 3-4, and that the mechanisms which mediate the potentiating effect of intestinal factors on glucose-induced insulin release are not deranged in prediabetes and diabetes.

Sulphonylurea treatment of NIDDM patients with cardiovascular disease : a mixed blessing ?

SummaryNon-insulin-dependent diabetic (NIDDM) patients show a high incidence of cardiovascular disease, with greater risk of recurrent myocardial infarction and a less favourable clinical outcome than non-diabetic patients. The majority of NIDDM patients are treated with sulphonylurea (SU) derivatives. In the 1970s the University Group Diabetes Program concluded that tolbutamide treatment caused increased cardiovascular mortality; the study, which led to curtailment of oral antidiabetic treatment in the USA, was received with scepticism in Europe. Later criticism of its methodology reduced the impact of the study; however, the question of the safety of SU in NIDDM patients with cardiovascular disease has been re-opened in the face of new experimental data. The heart and vascular tissues do have prerequisites for SU action, i.e. SU receptors and ATP-dependent K+ (K+ATP) channels. These channels play an important role in the protection of the myocardium against ischaemia-reperfusion damage, and their closure by SU could lead to amplified ischaemic damage. Here we review evidence from animal and human studies for deleterious SU effects on ischaemia-induced myocardial damage, either by direct action or through diminished cardioprotective preconditioning. Closure of K+ATP channels by SU can lead to reduction of post-infarct arrhythmias; the drug has also been claimed to improve various atherosclerosis risk factors. The evidence for these beneficial effects of SU is also reviewed. We look at the major difficulties that hamper transfer of information from experimental studies to clinical decision-making: a) The affinity of SU for heart K+ATP channels is orders of magnitude lower than for beta-cell channels; is it reasonable to expect in vivo cardiac effects with therapeutic ‘pancreatic’ SU doses? b) Most studies utilized high doses of acutely administered SU; are effects similar in the chronic steady-state of the SU-treated diabetic patient? c) Convincing SU effects have been demonstrated in acutely induced ischaemia by acutely administering the drug; do such effects persist in the clinical situation of gradually progressive ischaemia? d) Ischaemia and modification of K+ATP channel activity induce complex events, some with opposing effects; what is the net result of SU action, and do different SU derivatives lead to different outcomes? e) In the chronic (and hence clinically relevant) situation, how can direct (deleterious or beneficial) SU effects be separated from beneficial effects mediated by the metabolic action of the drug? Only large prospective clinical studies, making use of advanced technology for assessment of cardiovascular function, can answer these questions. Millions of NIDDM patients are treated with SU derivatives; many are in the age group where cardiovascular risks are extremely high. The question of whether SU derivatives are beneficial or deleterious for these patients must finally be settled unequivocally.

ROLE OF ADRENERGIC RECEPTORS IN GLUCOSE-INDUCED INSULIN SECRETION IN MAN

Abstract Administration to healthy volunteers of a β-receptor blocker (propranolol) in most instances significantly inhibited the insulin response to glucose infusion, while α-receptor blocking (by phentolamine) enhanced the insulin release. The inhibition induced by the β-blocking agent was totally or partially overcome by simultaneous administration of aminophylline. These results indicate that, in man, glucose-induced insulin release is mediated by adenyl cyclase and, consequently, by the intracellular level of cyclic adenosine monophosphate.