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D Pipeleers

Publications and source records attributed to D Pipeleers.

At least 73 records · Page 4Linked to original sources
PubMed1989

Co-secretion of carboxypeptidase H and insulin from isolated rat islets of Langerhans.

The release of carboxypeptidase H activity from isolated rat islets was determined and compared to the secretion of immunoreactive insulin. Analysis of pancreatic islet cells sorted into beta and non-beta types indicated that approx. 80% of islet carboxypeptidase H activity is present in the beta cell. The release of both insulin and carboxypeptidase H was stimulated markedly by increasing the glucose concentration in the medium from 2.8 to 28 mM. The fractional release was in accordance with the observed cellular distribution of both proteins. The secretory response was biphasic with time, with an initial rapid transient phase of release within 5 min, followed by a more sustained response. The concentration-dependencies of glucose stimulation of release of insulin and carboxypeptidase H were similar, with a threshold for stimulation around 5.6 mM-glucose and maximal stimulatory response at 16.7-28 mM-glucose. The release of both proteins was inhibited by 20 mM-mannoheptulose, removal of Ca2+ from the medium and addition of 1 microM-noradrenaline. The combination of 10 mM-4-methyl-2-oxopentanoate and 10 mM-glutamine stimulated the release of carboxypeptidase H and insulin, as did 3-isobutyl-1-methylxanthine and 350 microM-tolbutamide in the presence of glucose. It is evident that carboxypeptidase H is released from the pancreatic beta-cell by an exocytotic process from the same intracellular compartment as insulin. The release of carboxypeptidase H by a constitutive process was at best equivalent to 0.4%/h, or less than 2% of the maximal rate of release via the regulated pathway. It is concluded that carboxypeptidase H can be used as a sensitive index of beta-cell secretion and an alternative marker to the insulin-related peptides.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Cell surface antibodies in type 1 (insulin-dependent) diabetic patients. I. Presence of immunoglobulins M which bind to rat pituitary cells.

A standardized method has been developed for the assay of cell surface antibodies in IgM- and IgG-fractions from human serum. Suspensions of adult rat islet B cells, islet non-B cells, and anterior pituitary cells were used as antigen source and a cell sorter as analyser of the immunoglobulin binding to individual cells. Assay conditions were selected wherein no surface antibodies were detected in 33 control subjects younger than 20 years. In 30% of Type 1 (insulin-dependent) diabetic patients, surface antibodies were measured with rat anterior pituitary cells as well as with rat islet B cells. Binding to pituitary cells occurred with IgM- and IgG-fractions and correlated positively with IgG binding to islet B cells. At onset of the disease, the prevalence of IgM-rat anterior pituitary cell surface antibodies was higher than that of IgG-rat anterior pituitary cell surface antibodies. Cell surface antibodies were also detected in first-degree relatives of Type 1 diabetic patients, but corresponded primarily to IgM-rat anterior pituitary cell surface antibodies. It is concluded that the development of Type 1 diabetes in subjects younger than 20 years is associated with the generation of both IgM and IgG cell surface antibodies. The IgM surface antibodies may result from stimulated production of polyreactive natural autoantibodies and could precede the switch to the formation of monoreactive IgG autoantibodies. The assay of IgM cell surface antibodies can be useful in studies on the sequence of immune events in diabetes and other autoimmune disease.

Adolescent↗
PubMed1989

Cell surface antibodies in type 1 (insulin-dependent) diabetic patients. II. Presence of immunoglobulins M which bind to lymphocytes.

A standardized cell surface antibody assay was used to measure binding of circulating human immunoglobulins to rat or piglet splenocytes. In 100-fold diluted serum fractions, lymphocyte surface antibodies were detected in 30% of Type 1 (insulin-dependent) diabetic patients under 20 years of age but in none of 33 control subjects. Binding occurred with T and B lymphocytes, appeared unrelated to Fc receptors or protein glycosylation and was not attributable to insulin or albumin antibodies. At clinical onset of the disease, the lymphocyte surface antibodies belonged primarily to the IgM-class. Their presence was positively correlated to that of IgM-pituitary cell surface antibodies and their absorption by anterior pituitary cells occurred as well as by splenocytes. Lymphocyte surface antibodies remained present during the first years of insulin treatment. They were also detected in first degree relatives of lymphocyte surface antibody-positive patients. It is unlikely that IgM-lymphocyte surface antibodies mark the destructive process in the pancreatic B cell population. They may, instead, express a state of immune reactivity which precedes the formation of IgG-autoantibodies and therefore be associated with an event in the development of diseases such as Type 1 (insulin-dependent) diabetes.

Adolescent↗
PubMed1987

Glucose stimulates the entry of Ca2+ into the insulin-producing beta cells but not into the glucagon-producing alpha 2 cells.

Rat pancreatic beta and alpha 2 cells were purified by autofluorescence-activated cell sorting and used for electrophysiological patch clamp studies and measurements of the initial uptake of 45Ca. Both beta and alpha 2 cells were electrically active, the action potentials of the latter cells also were detected in the absence of glucose. Furthermore, alpha 2 cells differed from beta cells in lacking a glucose-sensitive K+ channel with a single conductance of 50-60 pS (in symmetric 140 mM K+ solutions). The rate of Ca2+ entry into the alpha 2 cells was slower than that into the beta cells, being equivalent to 0.2 mmol, kg-1 dry wt min-1. Whereas raising the glucose concentration to 20 mM significantly increased the amount of Ca2+ entering the beta cells, the sugar was without effect on Ca2+ entry into the alpha 2 cells.

Animals↗
PubMed1987

Spontaneously diabetic BB rats have age-dependent islet beta-cell-specific surface antibodies at clinical onset.

Diabetes-prone BB rats were examined before, during, and after clinical onset of diabetes for the occurrence of circulating islet cell surface antibodies (ICSAs) with a specific binding to islet beta-cells. The presence of ICSA was assessed by incubating serum immunoglobulin fractions with normal Wistar rat islet cells and identifying cell-bound immunoglobulins by indirect immunofluorescence and by a complement-induced cell toxicity reaction. Under the selected experimental conditions, none of the diabetes-resistant rats were ICSA positive over the entire study period (45-120 days of age). In two diabetes-prone BB rat strains, 19 animals developed diabetes with onset between 50 and 120 days. At day 45, none of these animals was positive for ICSA. In rats developing diabetes between 50 and 85 days of age, 7 of 9 animals presented ICSA at clinical onset, determined by either the immunofluorescence or cytotoxicity test. The antibodies bound to insulin-containing beta-cells but not to other islet cell types, and binding was not eliminated by absorption with liver powder. In animals developing diabetes between 85 and 120 days, only 1 of 10 was positive for beta-cell-specific surface antibodies at onset of the disease. After 30 days of insulin treatment, beta-cell-specific antibodies were detectable in 3 of 4 animals of age 50-85 days, whereas only 3 of 12 older rats presented ICSAs that were, in addition, of low titer or affinity. Our data confirm that ICSAs develop in diabetic BB rats and indicate that these antibodies can bind specifically to islet beta-cells compared with other islet cell types.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1986

Pancreatic B cells possess defense mechanisms against cell-specific toxicity.

Insulin-dependent diabetes develops when more than 90% of the insulin containing B cells are destroyed. The present study investigates whether the target B cells can counteract the damaging effects of cytotoxic substances. Purified islet cells were first exposed for 3-10 min to t-butylhydroperoxide, alloxan, streptozotocin, or B-cell surface antibodies plus complement, then cultured for 20 hr before the percent of dead cells was counted. t-Butylhydroperoxide destroyed all islet cell types whereas the three other agents exerted a dose-dependent toxicity upon islet B cells only. The survival of drug- and complement-treated cells varied with the culture conditions present between the initial cellular attack and the moment of cell death. For the four B-cell toxic agents tested, an increase in medium glucose following any of these treatments reduced the percent of dead cells. This protective effect was not observed with galactose or fructose, nor could it be induced in islet non-B cells; it was additive to the protective action glucose induced during preincubation of the cells prior to their exposure to certain cytotoxic agents such as alloxan. Nicotinamide also enhanced the survival of drug-treated B cells, irrespective of the damaging compound. The vitamin was most effective when applied immediately after the initial drug or complement treatment; it also protected islet non-B cells--in contrast to glucose. The present in vitro study has led to the recognition of defense mechanisms in pancreatic B cells. Physiologic compounds such as glucose and nicotinamide were found to stimulate islet B cells to counteract the damaging effects of B-cell toxic conditions. It is conceivable that the events involved in this protection are implicated in the pathogenesis and/or prevention of insulin-dependent diabetes.

Alloxan↗
PubMed1985

Gap junctions between pancreatic B-cells are modulated by cyclic AMP.

Gap junction morphology was studied on freeze fracture replicas of pancreatic islet tissue, using morphometric techniques. In rat islets in situ, 60 percent of the connexions were polygonally packed in gap junctions, whereas the remaining part occurred in linear strands. After collagenase isolation, the islets presented similar numbers of gap junctions but contained virtually no linear strands. The distribution of connexions over polygonal or linear arrays also varied with the culture conditions: at 11.2 mM glucose, a higher percentage of particles occurred in gap junctions than at 5.6 mM glucose; this was also the case in other conditions with elevated cellular cyclic AMP levels. The total number of connexions increased when islets were cultured with dibutyryl cyclic AMP or with a phosphodiesterase inhibitor; conditions with an augmented number of gap junctions also displayed an elevated islet cyclic AMP content. A similar association was noted in newly formed aggregates of pancreatic B-cells purified by autofluorescence-activated. cell sorting. These results indicate that the number of classically defined gap junctions is not only dependent on the total number of connexions but also on their organization within the membrane. It is suggested that the distribution of connexions over polygonal and linear arrays follows a dynamic equilibrium varying with the extracellular conditions. Cyclic AMP appears to modulate the number of gap junctions between pancreatic B-cells both through an induction of new connexions and through an assembly of linearly organized particles into polygonal arrays.

Animals↗
PubMed1984

Effects of glucose and 3',5'-cyclic adenosine monophosphate upon reaggregation of single pancreatic B-cells.

Single B-cells have been previously shown to respond poorly to glucose, in contrast to B-cells lodged in intact islets or in small groups of structurally coupled B-cells, isolated as such from islets. To analyze the role of cell coupling in glucose-induced insulin release, single B-cells were reaggregated in vitro and then tested for their secretory capability. Glucose as well as (Bu)2cAMP stimulated the degree of reaggregation during short shaking incubations (up to 180 min); onset of this process was most rapidly observed with (Bu)2cAMP (within 20 min), but after 180 min a comparable extent was measured with either 20 mM glucose or 0.5 mM (Bu)2cAMP. Calcium was an absolute prerequisite for reaggregation of B-cells. Glucose-induced insulin release from reaggregated B-cells was 4-fold higher than from single B-cells; this difference was not caused by some metabolic priming effect of glucose or (Bu)2cAMP, but appeared primarily mediated by the aggregated state of the cells. It is concluded that the secretory response of pancreatic B-cells is highly dependent on their aggregation with other B-cells. Both glucose and cAMP promote the adhesion of B-cells, and this may contribute to their well known insulinotropic effects.

Animals↗
PubMed1983

Autofluorescence-activated cell sorting of pancreatic islet cells: purification of insulin-containing B-cells according to glucose-induced changes in cellular redox state.

Autofluorescence-activated cell sorting can be employed for the subfractionation of insulin-containing islet B-cells according to their responsiveness to their physiologic stimulus, glucose. The method utilizes a flow cytometric detection of the rapid variations in endogenous NAD (P) H - and FAD - fluorescence after exposure to 20 mM glucose. Under these conditions, a two-fold increase in NAD (P) H and a 40% decrease in FAD was observed in more than 75% of B-cells isolated from fed normal rats. The technique makes it possible to study the metabolic behaviour of the B-cell population in (physio)pathological conditions of impaired glucose-induced insulin release; the availability of functionally homogenous B-cell preparations facilitates studies on stimulus-secretion coupling. In view of the universal role of the cellular metabolic redox state in cell regulation, it is suggested that similar techniques can be developed for the metabolic analysis of other cell types and for their purification according to their responsiveness to specific stimuli.

Animals↗
PubMed1983

Five cases of somatostatinoma: clinical heterogeneity and diagnostic usefulness of basal and tolbutamide-induced hypersomatostatinemia.

Five cases of somatostatinoma are reported, four being primarily located in the pancreas and one in the duodenum. The diagnosis was based upon the histological and immunochemical characteristics of tumoral and metastatic tissue. A marked clinical heterogeneity was noted: one patient presented with gallstones, steatorrhea, and diabetes, two patients suffered from severe hypoglycemic attacks, and two cases were admitted for obstructive jaundice. This varying symptomatology was related to differences in the circulating levels of biologically active somatostatin and to a variable cellular composition of the tumor. In all cases, a basal and/or tolbutamide-induced hypersomatostatinemia was measured. It is concluded that the clinical and hormonal features of the earlier defined somatostatinoma syndrome are no requisite for the diagnosis of somatostatinoma; the analysis of plasma somatostatin immunoreactivity might lead to a higher detection rate of this endocrine tumor.

Adenoma, Islet Cell↗
PubMed1983

A case of duodenal somatostatinoma: diagnostic usefulness of calcium--pentagastrin test.

A duodenal somatostatinoma is described in a patient suffering from a tumoral obstruction of the bile duct. The diagnosis was based upon histologic and immunocytochemical characterization of tumoral fragments and later confirmed by immunochemical analysis of liver metastases. Basal peripheral somatostatin immunoreactivity levels were normal until liver failure developed. A hypersomatostatinemia was induced by combined injection of calcium and pentagastrin, which was not the case in normal volunteers or in patients with disseminated pancreatic adenocarcinoma. This test was also positive in a case of generalized pancreatic somatostatinoma 4 yr after streptozotocin treatment. It was concluded that the calcium-pentagastrin test might be useful in the diagnosis of somatostatinomas.

Adenoma, Islet Cell↗