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G Leibowitz

Publications and source records attributed to G Leibowitz.

At least 19 recordsLinked to original sources
PubMed2000

[Type 2 diabetes and beta cell apoptosis].

Type 2 diabetes mellitus features an asymptomatic insulin resistance phase preceding the onset of diabetes. Hyperglycemia occurs when a relative insulin deficiency appears, meaning that beta cell secretory dysfunction is a key element in type 2 diabetes pathophysiology. So far, insulin secretion deficiency is explained by pancreatic beta cell "exhaustion" phenomena. Recent data suggest that apoptotic mechanisms could explain insulin deficiency through a reduction in the absolute pancreatic beta cell number. Psammomys obesus (sand rat) is an animal model for type 2 diabetes mellitus, initially characterized by hyperinsulinism followed by insulin deficiency linked with a reduction in the number of pancreatic beta cells. Transition to diabetes can be observed following changes in usual lifestyle of the sand rat. In the desert, caloric intake is low and physical expenditure is heavy. In the laboratory, animals turn diabetic as early as 4 days following a high calorie diet. At a later stage, diabetes is irreversible and animals die from diabetic ketoacidosis. beta cell apoptosis rate is low in non diabetic animals and increases 14-fold by 20 days after diabetes onset. At this stage, cells undergoing apoptosis can be observed, coexisting with necrotic cells without any insulitis. Similar results were obtained in vitro in isolated pancreatic islets that were exposed to increasing glucose concentrations, suggesting that chronic hyperglycemia plays a role in the onset or the deterioration of the process. However, precise mechanisms of apoptosis in this case remain poorly understood. Aminoguanidin does not prevent beta cell apoptosis in vitro, suggesting that advanced glycation products or NO production are not involved in this beta cell destruction process. Similar mechanisms secondary to hyperglycemia could play a role in the diabetes process in man and explain the marked insulin secretory deficiency that is sometimes observed in these patients. In addition to its preventing role on diabetes complication, the obtention of normoglycemia could help maintaining beta cell function.

Animals↗
PubMed1999

Presenilin 1 facilitates the constitutive turnover of beta-catenin: differential activity of Alzheimer's disease-linked PS1 mutants in the beta-catenin-signaling pathway.

Although an association between the product of the familial Alzheimer's disease (FAD) gene, presenilin 1 (PS1), and beta-catenin has been reported recently, the cellular consequences of this interaction are unknown. Here, we show that both the full length and the C-terminal fragment of wild-type or FAD mutant PS1 interact with beta-catenin from transfected cells and brains of transgenic mice, whereas E-cadherin and adenomatous polyposis coli (APC) are not detected in this complex. Inducible overexpression of PS1 led to increased association of beta-catenin with glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of beta-catenin, and accelerated the turnover of endogenous beta-catenin. In support of this finding, the beta-catenin half-life was dramatically longer in fibroblasts deficient in PS1, and this phenotype was completely rescued by replacement of PS1, demonstrating that PS1 normally stimulates the degradation of beta-catenin. In contrast, overexpression of FAD-linked PS1 mutants (M146L and DeltaX9) failed to enhance the association between GSK-3beta and beta-catenin and interfered with the constitutive turnover of beta-catenin. In vivo confirmation was demonstrated in the brains of transgenic mice in which the expression of the M146L mutant PS1 was correlated with increased steady-state levels of endogenous beta-catenin. Thus, our results indicate that PS1 normally promotes the turnover of beta-catenin, whereas PS1 mutants partially interfere with this process, possibly by failing to recruit GSK-3beta into the PS1-beta-catenin complex. These findings raise the intriguing possibility that PS1-beta-catenin interactions and subsequent activities may be consequential for the pathogenesis of AD.

Adenomatous Polyposis Coli↗
PubMed1999

Towards gene therapy of diabetes mellitus.

A definitive treatment for diabetes mellitus will be one that maintains a normal blood glucose concentration in the face of fluctuating dietary intake. To accomplish this, there must be mechanisms to sense the amount of blood glucose coupled to rapid release of the right amount of insulin. While mechanical devices to accomplish this are being developed, ultimately the best approach is likely to be based on genetic modification of cells. These could be pancreatic beta-cells, which are the only cells that produce insulin, or other cells that are involved in the pathogenesis of diabetes. Although definitive treatment of diabetes using genetically modified cells is a long-term goal, much progress is being made. This review discusses various approaches to modifying cells genetically, both in vitro and in vivo, for the treatment of diabetes.

Animals↗
PubMed1999

Telomerase activity is sufficient to allow transformed cells to escape from crisis.

The introduction of simian virus 40 large T antigen (SVLT) into human primary cells enables them to proliferate beyond their normal replicative life span. In most cases, this temporary escape from senescence eventually ends in a second proliferative block known as "crisis," during which the cells cease growing or die. Rare immortalization events in which cells escape crisis are frequently correlated with the presence of telomerase activity. We tested the hypothesis that telomerase activation is the critical step in the immortalization process by studying the effects of telomerase activity in two mortal SVLT-Rasval12-transformed human pancreatic cell lines, TRM-6 and betalox5. The telomerase catalytic subunit, hTRT, was introduced into late-passage cells via retroviral gene transfer. Telomerase activity was successfully induced in infected cells, as demonstrated by a telomerase repeat amplification protocol assay. In each of nine independent infections, telomerase-positive cells formed rapidly dividing cell lines while control cells entered crisis. Telomere lengths initially increased, but telomeres were then maintained at their new lengths for at least 20 population doublings. These results demonstrate that telomerase activity is sufficient to enable transformed cells to escape crisis and that telomere elongation in these cells occurs in a tightly regulated manner.

Antigens, Polyomavirus Transforming↗
PubMed1999

Gene transfer to human pancreatic endocrine cells using viral vectors.

We have studied the factors that influence the efficiency of infection of human fetal and adult pancreatic endocrine cells with adenovirus, murine retrovirus, and lentivirus vectors all expressing the green fluorescent protein (Ad-GFP, MLV-GFP, and Lenti-GFP, respectively). Adenoviral but not retroviral vectors efficiently infected intact pancreatic islets and fetal islet-like cell clusters (ICCs) in suspension. When islets and ICCs were plated in monolayer culture, infection efficiency with all three viral vectors increased. Ad-GFP infected 90-95% of the cells, whereas infection with MLV-GFP and Lenti-GFP increased only slightly. Both exposure to hepatocyte growth factor/scatter factor (HGF/SF) and dispersion of the cells by removal from the culture dish and replating had substantial positive effects on the efficiency of infection with retroviral vectors. Studies of virus entry and cell replication revealed that cell dispersion and stimulation by HGF/SF may be acting through both mechanisms to increase the efficiency of retrovirus-mediated gene transfer. Although HGF/SF and cell dispersion increased the efficiency of infection with MLV-GFP, only rare cells with weak staining for insulin were infected, whereas approximately 25% of beta-cells were infected with Lenti-GFP. We conclude that adenovirus is the most potent vector for ex vivo overexpression of foreign genes in adult endocrine pancreatic cells and is the best vector for applications where high-level but transient expression is desired. Under the optimal conditions of cell dispersion plus HGF/SF, infection with MLV and lentiviral vectors is reasonably efficient and stable, but only lentiviral vectors efficiently infect pancreatic beta-cells.

Adenoviridae Infections↗
PubMed1999

Sustained proliferation of PDX-1+ cells derived from human islets.

Ex vivo expansion of human beta-cells is an important step toward the development of cell-based insulin delivery systems in type 1 diabetes. Here, we report that human pancreatic endocrine cells can be expanded through 15 cell doublings in vitro for an estimated total 30,000-fold increase in cell number. We believe that the cells resulting from these cultures are of beta-cell origin, since they uniformly express the transcription factor PDX-1 (STF-1, IDX-1, IPF-1), which is initially seen only in cells positive for insulin and negative for the ductal cell marker cytokeratin (CK)-19. To rule out the possibility that PDX-1 expression might be induced by the culture conditions used here, cells from isolated human pancreatic ducts were cultured under the same conditions as the islet cells. Cells in these cultures expressed CK-19 but not PDX-1. Although the expanded beta-cells continued to express PDX-1, insulin expression was lost over time. Whether reexpression of islet-specific genes in vitro is essential for successful cell transplantation remains to be determined.

Cell Count↗
PubMed1999

Impaired beta-cell functions induced by chronic exposure of cultured human pancreatic islets to high glucose.

In type 2 diabetes, chronic hyperglycemia has been suggested to be detrimental to beta-cell function, causing reduced glucose-stimulated insulin secretion and disproportionately elevated proinsulin. In the present study, we investigated the effect on several beta-cell functions of prolonged in vitro exposure of human pancreatic islet cultures to high glucose concentrations. Islets exposed to high glucose levels (33 mmol/l) for 4 and 9 days showed dramatic decreases in glucose-induced insulin release and in islet insulin content, with increased proportion of proinsulin-like peptides relative to insulin. The depletion in insulin stores correlated with the reduction in insulin mRNA levels and human insulin promoter transcriptional activity. We also demonstrated that high glucose dramatically lowered the binding activity of pancreatic duodenal homeobox 1 (the glucose-sensitive transcription factor), whereas the transcription factor rat insulin promoter element 3b1 activator was less influenced and insulin enhancer factor 1 remained unaffected. Most of these beta-cell impairments were partially reversible when islets first incubated for 6 days in high glucose were transferred to normal glucose (5.5 mmol/l) concentrations for 3 days. We conclude that cultured human islets are sensitive to the deleterious effect of high glucose concentrations at multiple functional levels, and that such mechanisms may play an important role in the decreased insulin production and secretion of type 2 diabetic patients.

Adult↗
PubMed1997

Sporadic phaeochromocytomas are rarely associated with germline mutations in the von Hippel-Lindau and RET genes.

OBJECTIVE: von Hippel-Lindau (VHL) disease and multiple endocrine neoplasia type 2 (MEN2) are autosomal dominant cancer syndromes. In both conditions, phaeochromocytoma is a prominent feature. It has recently been suggested that phaeochromocytoma can be the presenting and sole clinical manifestation of these multi-organ syndromes. The aim of this study was to ascertain the incidence of VHL and MEN2 among patients with sporadic phaeochromocytoma by mutational analysis. PATIENTS: Twenty-seven unrelated patients with biochemically and/or anatomically proven sporadic phaeochromocytoma were evaluated. DESIGN AND MEASUREMENTS: Constitutional DNA obtained from the patients was analysed by single stranded conformational analysis (SSCP) for mutations within the VHL gene coding sequence and by denaturing gradient gel electrophoresis (DGGE) for predominant mutations in exons 10, 11 and 16 of the RET proto-oncogene. The incidence of patients positive for either VHL or RET germline mutations was assessed. RESULTS: Twenty-six of 27 patients had normal SSCP patterns in all three VHL gene exon segments and only one patient, with an atypical clinical presentation, had an aberrant pattern in exon 3 which upon DNA sequencing was shown to harbor a G to A transversion mutation at nucleotide 695. All patients had normal RET exon 10, 11 and 16 DGGE migration patterns. CONCLUSION: Most, if not all, patients with typical unilateral sporadic phaeochromocytoma do not have von Hippel-Lindau disease or MEN2. Thus, clinical and/or molecular investigation for von Hippel-Lindau disease and MEN2 in this patient population does not appear to be indicated.

Adolescent↗
PubMed1996

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

Non-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 1970's 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 settle unequivocally.

ATP-Binding Cassette Transporters↗
PubMed1996

Normal proinsulin processing despite beta-cell dysfunction in persistent hyperinsulinaemic hypoglycaemia of infancy (nesidioblastosis).

Persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI) is a genetic disorder which causes severe hypoglycaemia in the neonate. The beta cells fail to respond to changes in blood glucose levels in all the stages of the disease, which often ends with NIDDM. Fasting insulin, intact proinsulin and des 31,32 split proinsulin levels were measured in PHHI patients with active disease, patients after partial pancreatectomy, and those in clinical remission. All but one of the pancreatectomized patients developed diabetes and were hyperglycaemic on evaluation. Fasting insulin was comparable in pancreatectomized and medically treated patients. Des 31,32 split proinsulin levels were much higher in pancreatectomized compared to non-pancreatectomized patients (10.7 +/- 2.5 vs 3.4 +/- 0.8 pmol/l, p = 0.001) and age-matched control subjects (3.8 +/- 1.4 pmol/l, p = 0.018). Also the ratio of des 31,32 split proinsulin to total insulin plus proinsulin-like peptides was higher in pancreatectomized patients (18.7 +/- 2.8 vs 7.2 +/- 0.8% in non-pancreatectomized patients, p = 0.001, and 6.8 +/- 2.1% in normal control subjects, p = 0.004). Furthermore, des 31,32 split proinsulin was the dominating species of proinsulin-like molecules in the pancreatectomized patients (62.7 +/- 1.6% vs 45.5 +/- 3.8%, and 49.0 +/- 3.2% in non-pancreatectomized patients and control subjects, respectively, p = 0.001 and p = 0.0002). Intact proinsulin levels, and the proinsulin percentage, tended to be higher in pancreatectomized patients; however, the differences did not reach statistical significance. All parameters were similar in non-pancreatectomized patients and age-matched control subjects. Subgroup analysis showed comparable proinsulin-like peptide levels in patients with active disease and those in apparent clinical remission. Fasting levels of insulin and proinsulin-like peptides were also measured in a larger group of healthy children and young adults. Insulin and des 31,32 split proinsulin increased with age, the differences being most prominent when the young age group (0-8 years) was compared to the older groups (8-16 and > 16 years). The fasting levels of plasma insulin were correlated with those of intact proinsulin and des 31,32 split proinsulin (r = 0.82 and 0.81, respectively). Fasting insulin, intact proinsulin and des 31,32 split proinsulin were correlated with BMI (r = 0.55, 0.56 and 0.53, respectively). In summary, relative hyperproinsulinaemia was noted only in PHHI patients with increased secretory demand following pancreatectomy, but not in patients with active disease or those in spontaneous clinical remission. These findings suggest that abnormal proinsulin processing is not an intrinsic feature of PHHI despite the severe beta-cell dysfunction.

Adolescent↗
PubMed1996

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 Cushing's 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. PATIENTS AND DESIGN: (1) In a retrospective analysis, the medical records of 63 patients with endogenous CS were reviewed. (2) In a cross-sectional study, 90 obese patients (BMI > 25 kg/m2) followed in a University Hospital and the local Health Fund endocrine and diabetes clinics, with poorly controlled diabetes (glycosylated haemoglobin > 9%), underwent an overnight 1 mg dexamethasone suppression. In patients with non-suppressible cortisol levels (> 140 nmol/l), Liddle's 2 and 8 mg dexamethasone suppression tests and imaging studies were performed. MEASUREMENTS: The prevalence of poorly controlled diabetes, the major presenting symptom of CS, was assessed in the retrospective analysis. The prevalence of "true' CS and the false positive rate in the overnight dexamethasone suppression test were calculated. The endocrine evaluation of the patients with pre-clinical CS and the effects of surgical cure on glycaemic control are described. RESULTS: In the retrospective analysis, 11 (17.5%) had diabetes and 2 (3.2%) lacked the classic physical characteristics of the syndrome. In the cross-sectional study, 4 patients failed to suppress plasma cortisol (< 140 nmol/l). In one patient the diagnosis of CS was not confirmed by a standard Liddle's test and was therefore considered false positive. In the other 3, the diagnosis of CS was confirmed (prevalence of 3.3%, 95% confidence interval 1-9%). In all other patients the overnight cortisol suppression test was normal (cortisol level 47.3 +/- 2.5 nmol/l (mean +/- SEM)). After surgical treatment of CS, glycaemic control was markedly improved in all 5 patients (2 from retrospective and 3 from cross-sectional studies). CONCLUSIONS: The prevalence of pre-clinical Cushing's syndrome in obese patients with poorly controlled diabetes appears to be considerably higher than previously believed. The overnight dexamethasone suppression test proved to be a simple, sensitive and highly specific screening test for Cushing's syndrome despite the presence of obesity and hyperglycaemia.

Adult↗
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

Transesophageal versus transthoracic echocardiography in the evaluation of right atrial tumors.

The purpose of this study was to define the contribution of transesophageal echocardiography to the diagnosis of right atrial tumors in a large series of patients with this rare finding. Transesophageal echocardiography (TEE) has been found to be valuable in evaluating patients with intracardiac masses and has been shown to be superior to transthoracic echocardiography (TTE) in evaluating left heart masses. Between 1989 and 1993, 23 patients with either known tumors elsewhere or right atrial masses that were detected on TTE were evaluated with TEE. TEE studies were performed in the noninvasive cardiology laboratory. All patients were studied with 5 MHz biplane or omniplane transducers. The right atrium was evaluated for the presence, characteristics, extent, and attachment of any masses and for extension of these masses into the great vessels or other cardiac chambers. No complications occurred. Six patients had primary right atrial tumors. In 10 patients the tumors reached the right atrium via the inferior vena cava. Seven patients had malignant secondary tumors. TEE demonstrated three tumors not detected by TTE. Furthermore TEE provided 16 additional findings not seen on TTE. In conclusion, TEE is superior to TTE in the evaluation of right atrial tumors. TEE should be considered in patients with right atrial tumors even when these tumors have been demonstrated with TTE.

Adolescent↗
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

[Glucose phosphate isomerase deficiency with congenital nonspherocytic hemolytic anemia].

Glucose phosphate isomerase (GPI) deficiency is an unusual cause of hereditary nonspherocytic hemolytic anemia described in Israel in 2 families of Arab ancestry. The disease, inherited as an autosomal recessive disorder, manifests itself by symptoms and signs of chronic hemolysis which are often ameliorated by splenectomy. A variety of defective GPI variants, characterized by modified physicochemical and/or kinetic properties of the enzyme have been reported, suggesting extensive polymorphism for this enzyme deficiency. We recently diagnosed GPI deficiency in a 23-year-old Jewish Ashkenazi man. Since the age of 1 year, when a diagnosis of hemolytic anemia of undetermined etiology was made, he has required frequent blood transfusion. Since splenectomy, performed when he was 6 years old, the requirement for blood transfusions diminished drastically, restricted to hemolytic crises following intercurrent febrile illnesses. To the best of our knowledge, this is the first report of GPI deficiency in an Israeli family of Ashkenazi-Russian origin.

Adult↗