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S Sandler

Publications and source records attributed to S Sandler.

At least 109 records · Page 6Linked to original sources
PubMed1992

Role of receptor binding and gene transcription for both the stimulatory and inhibitory effects of interleukin-1 in pancreatic beta-cells.

A brief exposure of pancreatic islets to the cytokine interleukin-1 beta (IL-1 beta) induces an initial stimulatory phase, which is followed by inhibition of islet function and eventually beta-cell damage. In the present study we have investigated the effects of IRAP, a blocker of type I IL-1 receptor and actinomycin D, an inhibitor of DNA transcription, on both the stimulatory and inhibitory effects of IL-1 beta on rat pancreatic islets in vitro. The two test agents counteracted the initial stimulatory actions of IL-1 beta on both islet glucose-induced insulin release and glucose oxidation rates. Furthermore, cycloheximide, an inhibitor of protein synthesis, could also prevent the early IL-1 beta-induced stimulation of insulin release. When islets were exposed for 1 hr to IL-1 beta and studied after 12 hr, there was a 75% inhibition of glucose induced insulin release, a 50% decrease in glucose oxidation rates and a 30% decrease in (pro)insulin biosynthesis. These effects were completely counteracted by coincubation with IRAP or actinomycin D, but were not affected by coincubation with pertussis toxin. Islet exposure to IL-1 alpha also induced a 60-80% inhibition of glucose-induced insulin release after 12 hr. As observed with rIL-1 beta, IRAP was also able to block the suppressive effects of IL-1 alpha on islet function. Mouse islets exposed for 2 hr to IL-1 beta and studied after 12 hr presented a 50% decrease in the glucose-induced insulin release. This effect was completely blocked by coincubation with a rat monoclonal antibody generated against the type I mouse IL-1 receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Exposure of pancreatic islets to different alkylating agents decreases mitochondrial DNA content but only streptozotocin induces long-lasting functional impairment of B-cells.

Pancreatic B-cells exposed in vivo or in vitro to streptozotocin (SZ), the N-nitrosourea derivative of glucosamide, present a long-lasting impairment in the production and release of insulin while other cell functions are better preserved. This functional impairment is associated with a defective mitochondrial function. To further study the mechanisms behind SZ actions, mouse pancreatic islets were exposed in vitro to SZ (1.5 mM) or to different concentrations of methyl methanesulfonate (MMS; 2, 4 and 6 mM). The effect of the aglucone moiety of SZ, nitroso-N-methylurea (NMU; 2, 4 and 6 mM) was also tested. Islets were either studied immediately after exposure to the drugs (day 0) or after six days in culture following toxin treatment (day 6). On day 0 the islets showed a decrease in the NAD + NADH content, decreased glucose oxidation rates and an impaired insulin release in response to glucose. Six days after exposure to SZ there was still impaired glucose oxidation and insulin release, and decreased islet insulin mRNA and insulin content, but the NAD + NADH content was again similar to the control group. On the other hand, islets which survived for 6 days in culture following exposure to either MMS or NMU were able to regain normal B-cell function. The mouse islets exposed to SZ, NMU and MMS showed on day 6 a 30-40% decrease in the content of the mitochondrial DNA encoded cytochrome b mRNA and a 60-70% decrease in total mitochondrial DNA, as evaluated by dot and Southern blot analysis. Only SZ decreased the insulin mRNA content whereas both MMS and NMU decreased the glucagon mRNA content. As a whole, the data obtained indicate that SZ, NMU and MMS induce damage to the mitochondrial genome, and this may contribute to the B-cell dysfunction observed after SZ treatment. It is conceivable that the glucose moiety of SZ may direct the methylation to other intracellular sites besides the mitochondrial DNA, thus explaining the different functional responses of islets following exposure to SZ and NMU.

Adenine↗
PubMed1991

Partial pancreatectomy in rats causes an impairment of the glucose-induced stimulation of pancreatic islet blood flow.

Adult rats were subjected to either a sham operation (S-rats) or a 60% partial pancreatectomy (P-rats). Both P- and S-rats were normoglycemic and normoinsulinemic after surgery. Four weeks later, the animals were injected i.v. with 1 ml of either 0.9% (w/v) saline or 30% (w/v) D-glucose, and after 5 min whole pancreatic blood flow (PBF) and islet blood flow (IBF) were measured, using a microsphere technique. In the saline-injected P-rats both PBF and IBF values were higher than in S-rats (p less than 0.001 for both values). Administration of glucose had no effects on PBF in either S- or P-rats when compared to saline-injected animals. IBF was, however, markedly increased (p less than 0.01) by glucose in S-rats in comparison with saline-injected S-rats, whilst no difference in IBF was observed between glucose- and saline-injected P-rats. The fraction of PBF diverted through the islets (fIBF) was approximately 10% in S-rats and 20% in P-rats. Glucose increased fIBF in S-rats, but had no effect in P-rats. In conclusion, in S-rats a glucose-stimulated insulin release is accompanied by an increase in IBF, but this is not observed in P-rats.

Animals↗
PubMed1991

An interleukin-1 receptor antagonist protein protects insulin-producing beta cells against suppressive effects of interleukin-1 beta.

The cytokine interleukin-1 beta may have an important role in the autoimmune mediated damage of pancreatic Beta cells in insulin-dependent diabetes mellitus. In the present study we have investigated the effects of an interleukin-1 receptor antagonist protein, a blocker of the type I interleukin-1 receptor, on the suppressive actions of recombinant interleukin-1 beta on insulin-producing cells. Brief exposure (1-2 h) of rat and mouse pancreatic islets to 10 ng/ml recombinant interleukin-1 beta induced an 70-80% inhibition of insulin response to glucose after 12 h. These effects were completely counteracted by co-incubation with 100 ng/ml interleukin-1 receptor antagonist protein. When rat islets were cultured for 48 h in the presence of recombinant interleukin-1 beta (5 ng/ml) higher concentrations of interleukin-1 receptor antagonist protein (5000 ng/ml) were required to protect Beta-cell function. Interleukin-1 receptor antagonist protein also counteracted the inhibitory effects of recombinant interleukin-1 beta on the growth of the rat insulinoma cell line RINm5F. These data suggest that interleukin-1 receptor antagonist protein can protect insulin-producing cells from the deleterious effects of recombinant interleukin-1 beta, and that these cells possess type I interleukin-1 receptors.

Animals↗
PubMed1991

Prolonged exposure of pancreatic islets isolated from "pre-diabetic" non-obese diabetic mice to a high glucose concentration does not impair beta-cell function.

In the early stages of Type 1 (insulin-dependent) diabetes mellitus patients present a deficient insulin response to glucose. The reasons for this defective response are unknown, but it has been suggested that it reflects a deleterious effect of excessive glucose stimulation on a reduced Beta-cell mass. Female non-obese diabetic (NOD) mice from our colony, at the age of 12-13 weeks, have a normal basal glycaemia but an impaired intravenous glucose tolerance test, insulitis and a defective insulin response to glucose. In order to characterize the potential effect of glucose on the Beta cells at that "pre-diabetic" stage, pancreatic islets were isolated from 12-13 week old female NOD mice. Immediately after isolation (day 0) the NOD islets displayed a defective insulin response to an acute stimulation with 16.7 mmol/l glucose. After seven days in culture at both 11 and 28 mmol/l glucose these islets showed an increased insulin release in response to an acute glucose stimulation. This increase was more pronounced in the islets cultured at 28 mmol/l glucose. Experiments performed in parallel, using islets obtained from a non-diabetes prone strain of mice (Naval Medical Research Institute, NMRI) showed that these islets had a similar insulin release in response to glucose both on day 0 and after seven days in culture at 11 mmol/l glucose. The insulin mRNA levels of NOD islets did not change over one week in culture at 11 or 28 mmol/l glucose, but culture at the high glucose concentration induced a decrease in the islet insulin content.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Decrease in insulin-containing secretory granules and mitochondrial gene expression in mouse pancreatic islets maintained in culture following streptozotocin exposure.

We have previously described a preferential reduction in the secretory response to nutrient secretagogues in pancreatic mouse islets maintained in culture after in vitro exposure to streptozotocin (SZ). This reduction was associated with an impaired substrate metabolism at the mitochondrial level. To further clarify this issue, mouse pancreatic islets were exposed in vitro to 2.2 mM SZ for 30 min. At 4 h after SZ treatment ultrastructural changes were apparent in the endoplasmic reticulum and Golgi areas of the B-cells. However, 2 and 6 days following SZ exposure the B-cells appeared well preserved, except for a marked decrease in the number of insulin-containing secretory granules. A morphometric analysis of the B-cells 6 days after SZ exposure showed a normal B-cell size and a normal volume fraction of B-cell mitochondria. However, there was a decrease in total islet size and a 13% decrease in the volume fraction of B-cells in the islets. These mouse islets exhibited a decreased content of the mitochondrial DNA-encoded cytochrome b mRNA, as evaluated by dot-blot analysis. As a whole, the data obtained indicate that SZ treatment does not induce a decrease in the number of mitochondria or long-lasting ultrastructural damage to this organelle. However, there is a clear decrease in the cytochrome b mRNA, suggesting that SZ can induce damage to the mitochondrial DNA.

Animals↗
PubMed1991

Short exposure of rat pancreatic islets to interleukin-1 beta induces a sustained but reversible impairment in beta-cell function: influence of protease activation, gene transcription, and protein synthesis.

In an attempt to gain further knowledge about the mechanism of action of recombinant interleukin-1 beta (rIL-1 beta) on rat pancreatic beta-cells, we studied the effects of short term rIL-1 beta exposure (50 U/ml for 1 h) on islet function over the next 72 h. There was an initial increase in glucose-induced insulin release, followed by a decrease in islet function, reaching a nadir (values of insulin release about 20% of those observed in control islets) 10-12 h after treatment with the cytokine. Thereafter, the islets recovered their function, reaching levels of insulin secretion similar to the control values after 72 h. Short term exposure to rIL-1 beta did not induce a decrease in either islet DNA or islet insulin content. Using this experimental approach, we tested whether 1-h incubation of islets in the presence of various agents plus rIL-1 beta could counteract the inhibitory effects of the cytokine 10-12 h later. Both actinomycin-D (5 micrograms/ml), an inhibitor of DNA transcription, and N alpha-p-tosyl-L-lysine chloromethyl ketone (0.1 mM), a protease inhibitor, could protect the islets. There was also a weak protection by dimethyl urea (61 mM), a free radical scavenger, but no protection by cycloheximide (10 micrograms/ml), an inhibitor of protein synthesis, or amiloride (12.5 microM), a blocker of Na+/H+ exchange. In a subsequent series of experiments, the islets were exposed for 6 h to different test agents after the initial 1-h exposure to rIL-1 beta. In this context, there was a clear protection by cycloheximide and actinomycin-D and a lesser protection by N alpha-p-tosyl-L-lysine chloromethyl ketone. These data suggest that early steps of the actions of rIL-1 beta on rat pancreatic islets are mediated by protease activation and gene transcription, followed by protein synthesis. The identity of the protein(s) remains to be clarified.

Animals↗
PubMed1991

The nitric oxide synthase II inhibitor NG-nitro-L-arginine stimulates pancreatic islet insulin release in vitro, but not in the perfused pancreas.

The effects of L-arginine and its derivatives NG-methyl-L-arginine (Meth-arg) and NG-nitro-L-arginine (Nit-arg) on the insulin release and glucose oxidation of isolated rat islets were investigated to evaluate possible influences of nitric oxide. Also, the insulin release and flow distribution within the perfused rat pancreas were studied in response to these agents. Arginine, Meth-arg, and Nit-arg stimulated insulin release in cultured islets, but had no effect on glucose oxidation. Arginine and Meth-arg, an inhibitor of the enzyme nitric oxide synthase I (NS-I) stimulated insulin release from the perfused pancreas. Nit-arg, however, which inhibits nitric oxide synthase II (NS-II) had no such effect. Neither arginine nor Nit-arg or Met-arg changed the distribution of microspheres within the perfused pancreas. We conclude that interference with NS type I or II has no effect on insulin release from cultured islets, but inhibition of NS-II abolishes the insulin response in the perfused pancreas, which may be mediated by factors released from endothelial cells. These effects are not due to any changes in the flow distribution within the pancreas. The lack of inhibitory effect by Nit-arg in cultured islets may reflect the absence of endothelial or nervous cells in the cultured islets.

Amino Acid Oxidoreductases↗
PubMed1991

Interleukin-1 beta-induced nitric oxide production in isolated rat pancreatic islets requires gene transcription and may lead to inhibition of the Krebs cycle enzyme aconitase.

The aim of this study was to characterize the dynamics and functional relevance of interleukin-1 beta (IL-1 beta)-induced nitric oxide production in isolated pancreatic islets. Thus, islets were isolated from adult rats, precultured for 3-5 days in medium RPMI-1640 plus 10% fetal calf serum, and then exposed to IL-1 beta for different time periods, after which islet nitrite production and aconitase activity were determined. IL-1 beta (5 ng/ml) did not increase islet nitrite production during the first hour of incubation. Moreover, the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (Meth-arg; 5 mM) failed to prevent the initial (90 min) IL-1 beta-induced increase in islet insulin release. After 4, 7, and 24 h, however, nitrite production was increased by 50%, 93%, and 139%, respectively. Islet aconitase activity and glucose oxidation rates were decreased by 70% after incubation for 24 h with IL-1 beta. Both Meth-arg and N alpha-p-tosyl-L-lysine chloromethyl ketone (0.1 mM), a protease inhibitor, could completely counteract the IL-1 beta-induced increases in nitrite production and inhibition of aconitase activity and glucose oxidation rates. In a separate series of experiments, islets were incubated for 60 min with or without IL-1 beta and the RNA synthesis inhibitor actinomycin-D (5 micrograms/ml) and subsequently incubated for another 9 h without any additions. The presence of actinomycin-D during the 1-h IL-1 beta incubation period prevented the IL-1 beta-induced rise in nitrite production and the IL-1 beta-induced inhibition of aconitase activity and insulin release. It is concluded that IL-1 beta-induced nitric oxide production is a late event which requires gene transcription and does not mediate the initial stimulatory effects of IL-1 beta on beta-cell function. However, the gradually augmented rate of nitric oxide production may inhibit the enzyme aconitase, leading to a suppressed mitochondrial activity and a defective insulin release in response to nutrient secretagogues.

Aconitate Hydratase↗
PubMed1991

Liposomal delivery of purified heat shock protein hsp70 into rat pancreatic islets as protection against interleukin 1 beta-induced impaired beta-cell function.

Recently it has been demonstrated that heat shock protein 70 (hsp70) is induced in pancreatic islet cells during prolonged exposure to interleukin 1 beta (IL-1 beta). It is unclear whether this represents a cellular defense against the noxious action of IL-1 beta or whether hsp70 is involved in the suppressive action of the cytokine. To assess the role for hsp70 in isolated islets exposed to IL-1 beta, hsp70 was purified and introduced into cells of isolated rat pancreatic islets via the liposome technique. Delivery of hsp70 was efficient according to immunoblot analysis, but delivered hsp70 disappeared within 16 h. Hsp70-containing liposomes did not affect protein synthesis, insulin secretion, or islet insulin mRNA content. However, when hsp70 liposome-incubated islets were further exposed to IL-1 beta (25 U/ml) for 16 h, these islets released more insulin in response to glucose stimulation and contained more insulin mRNA than islets incubated with control liposomes and subsequently exposed to the cytokine. No protective effect of liposomes containing bovine serum albumin or ovalbumin were observed. We conclude that hsp70 may protect against IL-1 beta-induced impairment of pancreatic beta-cell function.

Animals↗
PubMed1991

Influence of protease on inhibitory and stimulatory effects of interleukin 1 beta on beta-cell function.

To elucidate the putative role of proteases in the action of interleukin 1 beta (IL-1 beta) on pancreatic beta-cells, we studied the effects on islet function of different protease inhibitors when added together with recombinant IL-1 beta to isolated rat pancreatic islets. It was found that the trypsin inhibitor N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) counteracted the acute stimulatory effects of IL-1 beta on islet glucose oxidation, insulin release, and biosynthesis. TLCK also partially or completely counteracted the long-term inhibitory effects of IL-1 beta on islet glucose oxidation, insulin biosynthesis, content, and release. This protease inhibitor also counteracted IL-1 beta-induced beta-cell cytotoxicity as assessed by DNA content measurements. Of the other group-specific protease inhibitors investigated, only N-tosyl-L-phenylalanine chloromethyl ketone, N alpha-p-tosyl-L-arginine methyl ester, and chloromercuriphenylsulfonic acid were found to partially protect against IL-1 beta action. We concluded that protease activation, putatively a serine protease, may be an early and perhaps primary event in the action of IL-1 beta on beta-cells.

Animals↗
PubMed1991

Interleukin-1 beta increases the biosynthesis of the heat shock protein hsp70 and selectively decreases the biosynthesis of five proteins in rat pancreatic islets.

Prolonged exposure to high concentrations of human recombinant interleukin-1 beta (rIL-1 beta) has been reported to exert both suppressive and cytotoxic effects on pancreatic beta-cells during culture in vitro. In order to investigate the molecular mechanism(s) underlying the actions of rIL-1 beta on the beta-cell, we have exposed isolated rat pancreatic islets for 3 or for 24 h to 25 U/ml of rIL-1 beta. Subsequently the biosynthesis of heat shock proteins, as assessed by western blot analysis, and total protein biosynthesis patterns were studied, using one and two-dimensional gel electrophoresis of [35S]methionine labelled islet proteins from different subcellular compartments. It was found that rIL-1 beta exerted no specific effects on protein synthesis when added during a 3 h incubation period. However, after a 24 h incubation period, the synthesis of a group of acidic proteins with the approximate molecular weight of 35 kD was specifically inhibited in the rIL-1 beta treated islets. This alteration was predominantly associated with the endoplasmic reticulum fraction. The cytokine also inhibited the synthesis of four cytosolic proteins with the molecular weights 75, 85, 95 and 120 kD. In contrast, rIL-1 beta increased the expression of the heat shock protein hsp70 both in the microsomal and cytosolic fractions, in contrast to the islet nuclei in which no increase was found. These results show that exposure of pancreatic islets to rIL-1 beta is accompanied by specific alterations in the protein synthesis of the islet cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Metabolism and beta-cell function of rat pancreatic islets exposed to human interleukin-1 beta in the presence of a high glucose concentration.

It has been postulated that one of the factors causing immune-mediated pancreatic beta-cell destruction in insulin-dependent diabetes mellitus (IDDM) is interleukin-1 (IL-1). Rat pancreatic islets exposed to human recombinant IL-1 beta (rIL-1 beta) for 48 h in vitro exhibit a markedly reduced glucose-stimulated insulin secretion. Also, a deleterious effect of glucose on beta-cell function, especially under conditions of a reduced beta-cell mass, which may exist in the early phase of IDDM has been suggested. In this study the response of rat pancreatic islets in vitro to a combination of the cytokine and high glucose concentration have therefore been assessed. Thus, islets were cultured for 48 h at either 11.1 or 56 mM glucose with or without 25 U/ml rIL-1 beta. Exposure to the cytokine reduced the islet DNA content at both glucose concentrations by 20-25%. In short-term incubations in the absence of rIL-1 beta after the preceding culture with the cytokine, the glucose-stimulated insulin release was reduced by 70% in islets cultured at 11.1 mM glucose and by only 40% after culture at 56 mM glucose, when compared to the corresponding control islets. The utilization of D-[5-3H]glucose, i.e., the catabolism of glucose in the glycolytic pathway, was the same in all groups of islets. However, the D-[6-14C]glucose oxidation rate, i.e., the metabolism of glucose in the Krebs cycle, was reduced by about 65% in rIL-1 beta exposed islets kept at 11.1 mM glucose and 46% in islets cultured at 56 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

Evaluation of the rapid Patho Dx Latex Strep Grouping Kit.

A variety of clinical specimens from throat, nose, ear, eye, wounds, urine, and vagina were collected, cultured, and screened for beta-hemolytic streptococci. The Patho Dx Latex Strep Grouping Kit (Diagnostic Product Corp., Los Angeles, Calif.) technique was applied to colonies taken right from the primary cultures. Isolated strains were sent to the reference laboratory where they were grouped by standard techniques. The kappa coefficient of agreement between the Patho Dx Kit and the standard method was 0.958. We believe that, although better agreement was achieved by others with isolated colonies, a very good agreement is also achieved with primary cultures. The fact that the laboratory is able to report an accurate answer after only 24 h seems most advantageous.

Diagnostic Errors↗
PubMed1990

Role of polyamines in mitogenic and secretory responses of pancreatic beta-cells to growth factors.

We have investigated the effects of glucose and the polypeptide growth factor growth hormone (GH), platelet-derived growth factor (PDGF), insulin-like growth factor I (IGF-I), epidermal growth factor (EGF), and transforming growth factor alpha (TGF alpha) on the polyamine content, in relation to proliferation and insulin secretion and content, of pancreatic beta-cells. Fetal rat pancreatic islets containing a high proportion of beta-cells were cultured for 3 days with growth factors. beta-cell replication was significantly increased by glucose, GH, and PDGF plus IGF-I in parallel with increased islet polyamine contents. In contrast, neither EGF nor TGF alpha influenced the islet DNA synthesis rate, polyamine content, insulin content, or insulin accumulation in culture medium. When the increased polyamine content evoked by growth-promoting agents was prevented by inhibitors of polyamine synthesis, elevated DNA synthesis rates persisted or were even augmented. However, subcellular fractionation analysis of islet homogenates revealed that the nuclear polyamine content was not affected by the inhibitors. On the other hand, islet insulin content and glucose-regulated insulin release were decreased by polyamine synthesis inhibitors. Glucose oxidation rates remained unchanged, suggesting that inhibitors were not toxic to islet cells. We conclude that prevention of increases in total cellular content of polyamines in response to glucose, GH, or PDGF plus IGF-I does not prevent mitogenicity of these growth factors. However, when their synthesis is inhibited normal levels of polyamines seem to be maintained in the cell nucleus, an event that may be sufficient to permit a mitotic signal to be translated into a proliferative response.

Animals↗