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Biomedical subjects

E Cerasi

Publications and source records attributed to E Cerasi.

At least 55 records · Page 3Linked to original sources
PubMed1996

Increased susceptibility of islets from diabetes-prone Psammomys obesus to the deleterious effects of chronic glucose exposure.

Patients with noninsulin-dependent diabetes (NIDDM) show an increase in the relative plasma levels of proinsulin and proinsulin conversion intermediates, which is corrected by strict glycemic control. This observation suggests that hyperglycemia per se may be responsible for generating the aberrant plasma hormone profile. The question remains, however, whether a genetic predisposition to NIDDM underlies the failure of the insulin production machinery to meet a prolonged increase in secretory demand. In this study, islet monolayer cultures from the diabetes-prone Psammomys obesus and normal diabetes-resistant rats were exposed to RPMI 1640 medium containing either 11.1 or 33.3 mM glucose; insulin-related peptides were resolved by HPLC. Prolonged exposure (10 days) of rat islets to high glucose resulted in a reduced a secretory response to an acute glucose stimulus associated with a 37% reduction in the insulin content but no change in the proinsulin/insulin ratio. When subjected to a similar protocol, islets from prediabetic Psammomys lost the insulin response to glucose; beta-cell insulin content was reduced by about 70%, and the proportion of proinsulin-related peptides increased from 18% to 38%. In the in vivo situation, pancreatic extracts from nonfasted diabetic Psammomys contained 36% proinsulin-related peptides in contrast to 15% in pancreatic extracts from nondiabetic animals. Thus, prolonged in vitro exposure of prediabetic Psammomys islets to high levels of glucose could reproduce the modified beta-cell secretory profiles observed in vivo in the diabetic animal. These results support the hypothesis that hyperproinsulinemia in NIDDM is secondary to the inability of beta-cells to meet a sustained increase in insulin demand, whereas individuals with normal beta-cells may meet such demand with an adequate output of mature insulin.

Animals↗
PubMed1995

Insulin secretion in obese and non-obese NIDDM.

Both the insulin response to glucose and the sensitivity to insulin show large variation in the normal population. Many subjects have either a markedly low insulin response or low sensitivity to insulin, with nevertheless normal glucose tolerance. For such subjects to become diabetic, insulin secretion or insulin action must further deteriorate with time, or other factors are added which tip the balance towards diabetes. Most evidence to date indicates that reduced beta-cell responsiveness and reduced insulin sensitivity co-exist in subjects prior to developing NIDDM. Both insulin secretion and insulin action are genetically controlled and influenced by intrauterine and neonatal factors. Insulin secretion and insulin action vary inversely in a closely linked manner; inability to fully compensate for changes in one variable may generate a functional deficit in glucose homeostasis. Subjects combining low functions would run a proportionately larger risk of decompensating the glucose tolerance and be more vulnerable, in terms of diabetes susceptibility, to factors that further reduce insulin output or insulin action. Careful analysis of existing data prompts us to ascribe a dominating role to the impairment of insulin secretion in the pathogenesis of IGT and NIDDM. Patients with NIDDM also exhibit increased proportions of proinsulin and proinsulin conversion intermediates. We used hyperinsulinaemic diabetic and non-diabetic Psammomys obesus to study the possible relationship between steady-state pancreatic insulin stores and the proportion of proinsulin-related peptides in the plasma and the pancreas. A marked increase in these peptides was associated with 90% reduction in insulin stores of the pancreas. After food deprivation, the depletion of pancreatic insulin in the diabetic animals was partially corrected, and the proinsulin/insulin ratio normalized. In contrast, non-diabetic psammomys showed only 50% reduction in pancreatic insulin stores under non-fasting conditions, with no change in proinsulin/insulin ratio. These findings suggest that in the diabetic Psammomys obesus, pancreatic capacity for storage/production of insulin is limited; the metabolic consequences of this limitation are amplified by increased secretory demand secondary to insulin resistance, thus facilitating the establishment of hyperglycaemia, which may in itself further exacerbate the pancreatic dysfunction.

Animals↗
PubMed1995

Hyperproinsulinemia in the diabetic Psammomys obesus is a result of increased secretory demand on the beta-cell.

We have recently shown that the diabetic syndrome in Psammomys obesus is characterized by severe depletion of islet immunoreactive insulin (IRI) stores together with a marked increase in the islet proinsulin to insulin ratio. In the present in vitro studies, we show marked enhancement of proinsulin biosynthesis in islets from diabetic P. obesus (approximately 8-fold compared to nondiabetic islets). Proinsulin to insulin conversion and insulin degradation do not differ significantly between diabetic and nondiabetic islets. The rate of IRI secretion at a stimulatory concentration of glucose (16.7 mM) is comparable in diabetic and nondiabetic animals, but at a nonstimulatory glucose concentration (0 mM), islets obtained from diabetic animals show significant IRI release. beta-Cells from diabetic P. obesus also exhibited increased secretion of newly synthesized proinsulin and conversion intermediates under stimulatory conditions. Moreover, a novel secretory compartment, highly enriched in newly synthesized C peptide, characterized the beta-cells of diabetic animals. Our data suggest that the marked insulin depletion observed in diabetic islets is probably due to a hyperglycemia-driven increase in secretory demand that is not met by the enhanced biosynthetic capacity of these islets. This leads to relative enrichment of the depleted diabetic islets with immature secretory granules of a higher proinsulin content.

Animals↗
PubMed1995

Hyperinsulinemic hypoglycemia of infancy (nesidioblastosis) in clinical remission: high incidence of diabetes mellitus and persistent beta-cell dysfunction at long-term follow-up.

In persistent hyperinsulinemic hypoglycemia of infancy (PHHI), the long term outcome of the disease is not well documented. Previous reports suggested that partial pancreatectomy in infants does not endanger future islet function. We evaluated endocrine pancreatic function in 14 PHHI patients 6.5-21 yr after diagnosis. Eight underwent early subtotal pancreatectomy, and 6 were medically treated; all were in clinical remission. Intravenous glucose tolerance and C-peptide suppression tests were performed, with multiple determinations of hormone levels. The insulin response to glucose was blunted in all pancreatectomized and in 2 conservatively treated patients. Glucose disposal was reduced in 6 pancreatectomized patients and in 2 medically treated subjects. Six of the pancreatectomized patients, including two with normal glucose disposal at first evaluation, developed overt diabetes during puberty. None in the medically treated group became diabetic; however, only 2 patients have reached puberty. C-Peptide suppression in response to hypoglycemia was inadequate in 4 of 5 pancreatectomized and 3 of 5 nonpancreatectomized patients studied. These results show that children with PHHI have impaired insulin responses to glucose and lack of suppressibility of endogenous insulin secretion several years after clinical remission. Thus, the beta-cell defect responsible for the disease in infancy is not corrected with time despite the disappearance of spontaneous hypoglycemia. Insulin secretion seems more disturbed in pancreatectomized patients; the majority develop insulin-requiring diabetes during puberty. An effort should be made to treat PHHI patients medically to avoid pancreatectomy; this may reduce the incidence of diabetes at puberty.

Adolescent↗
PubMed1994

Transcription of the insulin gene: towards defining the glucose-sensitive cis-element and trans-acting factors.

Previous work has shown that the sequence -196 to -247 of the rat insulin I gene mediates the stimulatory effect of glucose in fetal islets. We have used adult rat and human islets to delineate the glucose-sensitive cis-element to the sequence -193 to -227. In electrophoretic mobility shift assays, a 22 bp nucleotide corresponding to the sequence -206 to -227 bound all the nuclear proteins that could be bound by the entire minienhancer sequence -196 to -247. The rat insulin I sequence -206 to -227 formed three major complexes; in contrast, the corresponding human insulin sequence formed one single band with human and rat islet nuclear extracts, corresponding to the complex C1 of the rat insulin gene. Incubation of islets with varying glucose levels resulted in a dose-dependent increase in the intensity of the C1 band, while the other nuclear complexes formed with the insulin sequence, or the AP1 and SP1 binding activities used as control, were glucose insensitive. This is thus the first demonstration of a physiologic glucose-sensitive trans-acting factor for the insulin gene, whose further study may markedly enhance our understanding of the regulation of insulin biosynthesis in normal and diabetic beta cells. Furthermore, once cloned, the introduction of this glucose sensitive factor may enable the construction of truly physiologic artificial beta cells.

Animals↗
PubMed1994

Hyperproinsulinemia and insulin deficiency in the diabetic Psammomys obesus.

Patients with noninsulin-dependent diabetes mellitus exhibit increased proportions of plasma proinsulin and proinsulin conversion intermediates. We used hyperinsulinemic diabetic and nondiabetic Psammomys obesus to study the possible relationship between steady state pancreatic insulin stores and the proportion of proinsulin-related peptides in the plasma and pancreas. Insulin-like peptides were separated by reverse phase HPLC and identified by pulse-chase experiments. A marked increase in the proportions of proinsulin and proinsulin conversion intermediates in the plasma and pancreas of diabetic nonfasted Psammomys was associated with 90% reduction in insulin stores of the pancreas. After a 16- to 20-h fast, the depletion of pancreatic insulin in the diabetic animals was partially corrected, and the proinsulin/insulin ratio was normalized. In contrast, nondiabetic Psammomys showed only 50% reduction in pancreatic insulin stores under nonfasting conditions, with no change in the proinsulin/insulin ratio. These findings suggest that in the diabetic Psammomys obesus, the pancreatic capacity for storage of insulin may be limited; the metabolic consequences of this limitation are amplified by increased secretory demand secondary to insulin resistance, thus facilitating the establishment of hyperglycemia, which may in itself further exacerbate pancreatic dysfunction.

Animals↗
PubMed1993

Glucose modulates the binding of an islet-specific factor to a conserved sequence within the rat I and the human insulin promoters.

In cultured rat and human pancreatic islets, glucose stimulated transcription of the rat insulin I gene through the mini-enhancer (FF) located between residues -196 and -247. The glucose-sensitive element was delineated to the region -193 to -227. The mini-enhancer bound islet nuclear proteins to form three major complexes (C1-C3). A 22-bp subfragment, spanning the sequence -206 to -227, was sufficient to retain all binding activities of the entire FF. The homologous sequence of the human insulin promoter interacted with rat islet nuclear extracts to form a single complex, corresponding to the C1 complex of the rat insulin I sequence. C1 was present only in insulin-producing cells; it was the major complex detected in isolated human islets with both rat and human insulin sequences. Furthermore, the DNA binding activity of the C1 factor(s) was selectively modulated by extracellular glucose in a dose-dependent manner; a 4.5-fold increase in binding intensity was detected when rat islets were incubated for 1-3 h in the presence of 20 vs. 1-2 mM glucose. We therefore suggest that the factor(s) involved in the C1 complex corresponds to the glucose-sensitive factor and, consequently, may play a determining role in glucose-regulated expression of the insulin gene.

Animals↗
PubMed1992

Glucose regulates its transport in L8 myocytes by modulating cellular trafficking of the transporter GLUT-1.

The effect of culture conditions simulating hypo- and hyper-glycaemia on glucose transport and on the subcellular localization of the glucose transporter GLUT-1 was studied in L8 myocytes. Incubation of the cells with 20 mM-glucose for 25 h decreased the rate of 2-deoxy-D-[3H]glucose (dGlc) uptake to 0.106 +/- 0.016 nmol/min per 10(6) cells compared with 0.212 +/- 0.025 in cells maintained at 2 mM-glucose (final glucose concentrations at the end of the incubation period were 16-17 mM and 0.7-1.0 mM respectively). An additional 5 h incubation of these cells with medium containing the opposite glucose concentration (i.e. change from 17 mM to 1 mM and from 1 mM to 17 mM) increased the transport rate to 0.172 +/- 0.033 nmol/min per 10(6) cells in cultures initially conditioned at high glucose, and decreased the transport to 0.125 +/- 0.029 in those conditioned at low glucose. Plasma-membrane- and microsomal-membrane-enriched fractions were prepared from these cells for [3H]cytochalasin B (CB) binding and Western-blot analysis with antibodies against GLUT-1 and GLUT-4. A decrease in glucose concentration increased the number of D-glucose-displaceable CB-binding sites and GLUT-1 protein in the plasma-membrane fraction to the same extent as the increase in dGlc transport. Under downregulatory conditions, the lower dGlc-transport capacity could be accounted for by a decreased number of transporters in the plasma membrane of the cells. No apparent modification of the intrinsic activity of the glucose transporters was observed in up- or down-regulated cells. Under downregulatory conditions, the CB-binding data indicated a large increase in the number of transporters in the intracellular membranes of the myocytes. Western blots of the same membranes also indicated an increase in GLUT-1 content. However, the interaction of the intracellular GLUT-1 protein with the polyclonal antibodies was much weaker than that of the plasma-membrane-associated GLUT-1. The GLUT-4 concentration was too low to permit quantification in membrane fractions. Our findings suggest that autoregulation of glucose transport in L8 myocytes is accompanied by parallel changes in the number of GLUT-1 transporters in the plasma membrane, and that the rate of transporter degradation may be augmented in the upregulated myocytes. These glucose-induced changes are fully reversible.

Animals↗
PubMed1992

Long-term stability of low insulin responses to glucose in non-diabetic subjects.

We investigated the stability of the insulin response to glucose in healthy subjects by making retrospective comparisons of insulin responses after two 60 min glucose infusion tests performed many years apart. The subjects (N = 49) were divided into two lower and two higher quartiles as assessed by the incremental 0-10 min insulin area during the initial glucose infusion test. Ages were initially 32.3 +/- 2.8 years in lower quartiles and 26.6 +/- 1.1 in higher quartiles and body mass indexes 21.6 +/- 0.6 kg/m2 and 21.8 +/- 0.5, respectively. The interval between the first and second glucose infusion tests was 8.1 +/- 2.8 years for lower quartiles and 10.4 +/- 1.3 for higher quartiles. In lower quartiles, the 0-10 min insulin area at first testing was 157.1 +/- 15.9 mU/l x 10 min and at follow-up 202.2 +/- 26.6 (+29%, NS). In higher quartiles, the insulin area decreased from 654.8 +/- 70.6 mU/l x 10 min at first testing to 489.8 +/- 53.6 at follow-up (-25%, p less than 0.05). The 0-60 min glucose area did not change significantly between glucose infusion tests in lower quartiles (+5%), but did increase by 12% (p less than 0.005) in higher quartiles. Only one subject of the lowest quartile at first testing changed to higher quartiles at follow-up. Predictable "regression toward the mean" at follow-up was moderate, hence the individual insulin response to glucose was relatively stable with time. This finding is compatible with the hypothesis that genetic factors are of major importance for the insulin response to glucose.

Adult↗
PubMed1992

Glycosylated serum protein levels assayed with highly sensitive immunoradiometric assay accurately reflect glycemic control of diabetic patients.

OBJECTIVE: To develop a sensitive and reliable immunoreadiometric assay to measure glycosylated lysine residues on serum proteins (GSP) and to evaluate its efficacy in monitoring glycemic control. RESEARCH DESIGN: The effect of acute and chronic in vitro and in vivo changes in glucose levels on GSP concentration was evaluated. GSP determinations from insulin-dependent diabetic (IDDM) patients, non-insulin-dependent diabetic (NIDDM) patients, and control subjects were correlated with other indices of glycemic control. RESULTS: The GSP levels were unaffected by acute glucose changes after food or intravenous glucose administration but increased during storage at -20 degrees C due to in vitro glycosylation by endogenous glucose. Immediate acidification of the serum prevented this, permitting long-term storage despite high ambient glucose levels. In randomly selected diabetic patients, 96% of GSP values were greater than the mean +3SD of nondiabetic control subjects. In diabetic patients, GSP levels correlated with mean plasma glucose concentrations (Kendall correlation statistics 0.47, P less than 0.001), fasting plasma glucose levels (Kendall statistics 0.42, P less than 0.001), and glycosylated hemoglobin (GHb, Kendall statistics 0.30, P less than 0.005). Induction of near-normal glycemia in poorly controlled NIDDM patients reduced GSP levels with a slope consistent with a half time of disappearance of 4.7 +/- 0.4 days. GSP levels remained elevated in 6 of 10 well-controlled NIDDM patients, despite normal GHb concentrations. Chronic hypoglycemic states, like pregnancy and hyperinsulinemic hypoglycemia, were associated with significantly low GSP levels. CONCLUSION: We describe a reproducible and sensitive immunoradiometric assay for GSP that closely reflects the degree of glycemic control in diabetic patients. Further studies are needed to determine whether this assay may be useful in screening for glucose intolerance or gestational diabetes.

Blood Glucose↗
PubMed1992

Acute and chronic effects of dexfenfluramine on glucose and insulin response to intravenous glucose in diabetic and non-diabetic obese subjects.

Fenfluramine improves glucose tolerance in obese subjects independently of its anorectic effect. Increased insulin action has been reported, but such an effect may be secondary to reduced hyperglycemia following augmented insulin secretion. For this reason, we investigated whether the dextro-enantiomer of fenfluramine (dexfenfluramine, dF) has a direct effect on insulin secretion using the glucose infusion test, a technique that can also be used to indirectly evaluate insulin action. Ten lean controls (BMI 21 +/- 0.4 kg/m2), 9 non-diabetic obese subjects (BMI 32.3 +/- 1.1) and 10 obese mild non-insulin dependent diabetics (BMI 36 +/- 2.6, fasting plasma glucose (FPG) 7.9 +/- 0.9 mmol/l) were studied with a random, double blind cross-over protocol. Each subject received 15 mg dF (or placebo) twice daily for 3 days prior to glucose infusion; 30 mg dF (or placebo) were given 90 min before the test. Obese control and diabetic subjects continued treatment with either dF or placebo for one month after which they were retested. There was no significant change in weight or fasting plasma glucose or insulin in any group. Biphasic insulin secretion was demonstrated in both non-diabetic groups, whereas a complete lack of first-phase and a delayed and reduced second phase insulin response was demonstrated in the diabetic subjects. There was no acute or chronic (obese subjects) effect of dF on insulin secretion in any group. In lean control subjects, plasma glucose curves during glucose infusion were unchanged by dF, whereas in non-diabetic obese subjects the glucose slope was improved after both acute and chronic dF, implying augmented glucose disposal. In diabetic patients, no significant acute or chronic effect of dF on glucose response was registered. When all obese subjects were re-grouped according to fasting plasma insulin levels (FPI) and not glucose tolerance, those with relative fasting hyperinsulinemia (> 100 pmol/l, mean +/- SE = 144 +/- 12 pmol/l) showed significant improvement of insulin action after dF, whereas those with low FPI (< 100 pmol/l, mean +/- SE = 65 +/- 7 pmol/l) did not. These findings, together with previously published results of improved insulin action in diabetics during hyperinsulinemic clamps, suggest that dF-mediated improvement in glucose clearance may require substantial plasma insulin concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1991

Effect of 6-month gliclazide treatment on insulin release and sensitivity to endogenous insulin in NIDDM: role of initial continuous subcutaneous insulin infusion-induced normoglycemia.

In 10 obese, new-onset non-insulin-dependent diabetes mellitus (NIDDM) patients (group A), continuous subcutaneous insulin infusion (CSII) was used to induce normoglycemia during 14 days. Fasting blood glucose was 4.6 +/- 0.2 mmol/L and mean daily blood glucose 5.8 +/- 0.2 mmol/L at the end of the CSII period. This excellent glycemic control was obtained with 35 +/- 4.8 U of insulin per day, corresponding to 0.47 +/- 0.06 U/kg/24 hours. Endogenous insulin production was markedly suppressed, since urinary C-peptide was reduced from 18.5 +/- 0.12 to 7.9 +/- 0.25 nmol/24 hours. Gliclazide was given to group A following CSII, and to five obese NIDDM patients (group B) in their habitual hyperglycemic state. Gliclazide maintained in group A, and induced in group B, excellent metabolic control. This was accompanied by the appearance of a small first-phase insulin response to intravenous glucose, and significant increases in the mean-daily-insulin to mean-daily-blood-glucose ratio, as well as in the 24-hour urinary C-peptide-to-glucose ratio. The gliclazide effects tended to be more pronounced in group A. No significant effect was seen on efficacy of endogenous insulin (slope of disappearance of blood glucose divided by insulin levels). During 6 months of gliclazide treatment, excellent glycemic control was maintained in all patients. This was paralleled by unchanged stimulation by gliclazide of first-phase insulin response to glucose, and augmented mean 48-hour insulin-to-glucose and urinary C-peptide-to-glucose ratios. No change in the ratio of glucose disposal to endogenous insulin was noted. We conclude that physiologic insulin replacement may induce normoglycemia in NIDDM, indicating that insulin resistance is not of clinical significance; gliclazide has a beta-cell-stimulating action that is maintained quantitatively unchanged for at least 6 months; the therapeutic effect of gliclazide in NIDDM seems to be mainly, if not exclusively, the result of its beta-cytotrophic action. Initial normoglycemia, induced here by CSII, may have a lasting enhancing effect on the gliclazide action.

Blood Glucose↗