An interleukin-1 receptor antagonist protein protects insulin-producing Beta cells against suppressive effects of interleukin-1β

Summary The cytokine interleukin-1 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 on insulin-producing cells. Brief exposure (1–2 h) of rat and mouse pancreatic islets to 10 ng/ml recombinant interleukin-1 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 (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 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, and that these cells possess type I interleukin-1 receptors.     

Differential interleukin-1 receptor antagonism on pancreatic beta and alpha cells. Studies in rodent and human islets and in normal rats

Summary The monokines interleukin-1 and - have been implicated as effector molecules in the immune-mediated pancreatic beta-cell destruction leading to insulin-dependent diabetes mellitus. Here we investigated the effects of interleukin-1 receptor antagonism on insulin and glucagon release of rat, mouse and human islets exposed to recombinant human interleukin-1, and on interleukin-1 induced changes in blood glucose, serum insulin and serum glucagon levels in Wistar Kyoto rats. The interleukin-1 receptor antagonist reduced the co-mitogenic effect of interleukin-1 on mouse and rat thymocytes with a 50% inhibitory concentration of 10- and 100-fold molar excess, respectively. Complete inhibition was obtained with a 100–1,000-fold molar excess. However, at a 100-fold molar excess the interleukin-1 receptor antagonist did not antagonise the potentiating effect of interleukin-1on rat islet insulin accumulation during 3 and 6 h of exposure or of interleukin-1-induced inhibition of insulin release after 24 h. In contrast, interleukin-1-stimulated islet glucagon release was completely antagonised by a 100-fold molar excess of interleukin-1 receptor antagonist. A 10,000-fold molar excess of interleukin-1 receptor antagonist was needed to antagonise interleukin-1 stimulatory and inhibitory effects on rat beta-cell function in vitro. A 100-fold excess of interleukin-1 receptor antagonist could not counteract interleukin-1 effects on mouse and human beta cells, excluding species difference in the efficacy of the human interleukin-1 receptor antagonist. An anti-mouse interleukin-1 receptor type I antibody completely abolished interleukin-1 effects on isolated mouse islets. A 10–100-fold molar excess of interleukin-1 receptor antagonist antagonised interleukin-1-induced fever, hypercorticosteronaemia and hyperglucagonaemia, but not interleukin-1-induced reduction in insulin/glucose ratio in normal rats. In conclusion, our results suggest that antagonism of interleukin-1 effects on beta cells requires higher concentrations of interleukin-1 receptor antagonist than those necessary to block interleukin-1 action on islet alpha cells and other interleukin-1 targets in vitro and in vivo. This may contribute to the understanding of the specificity of the immunological beta-cell destruction leading to insulin-dependent diabetes.     

Presence of Two Signaling TGF-β Receptors in Human Pancreatic Cancer Correlates with Advanced Tumor Stage

Transforming growth factor- (TGF-)signal transduction is mediated via specific cellsurface signaling TGF- receptors, most notably thetype I ALK5 (TR-I_ALK5)and the type II(TR-II). We evaluated TR-I_ALK5 andTR-II expression in 41 human pancreatic cancertissue samples and correlated these findings withclinical data of the patients. Northern blot analysisindicated that, in comparison with the normal pancreas,pancreatic adenocarcinomas exhibited 8.0-fold and4.5-fold increases (P < 0.01), respectively, in mRNAlevels encoding TR-I_ALK5 andTR-II. In situ hybridization showed that both TR-I_ALK5 mRNAwere highly expressed in the majority of pancreaticcancer cells. Immunohistochemical analysis ofTR-I_ALK5 and TR-II revealedpositive immunostaining in 73% and 56% of the tumors, respectively. Both receptorswere concomitantly present in 54% of the pancreaticcancer samples. The presence ofTR-I_ALK5 or TR-II and theconcomitant presence of TR-I_ALK5 and TR-II in the cancer cells was associatedwith advanced tumor stage (P < 0.01). These findingsshow that in many human pancreatic cancers, increasedlevels of the two signaling TRs are present. The presence of the signaling TRs inadvanced tumor stages indicates a role in diseaseprogression.     

Pharmacological evidence for beta3 adrenoceptors in the control of rat gastric acid secretion

The effect of the ₃-adrenoceptor agonist BRL37344 on gastric acid secretion evoked by different secretory stimuli was investigated in anaesthetized rats with lumen-perfused stomachs in comparison with the ₂-adrenoceptor agonist clenbuterol. Intravenous injections of BRL37344 (1–10 mol/kg) and clenbuterol (0.01–1 mol/kg) dose-dependently reduced 2-deoxy-D-glucose-induced acid secretion, with BRL37344 about forty times less potent than clenbuterol. BRL37344 (0.1–3 mol/kg) inhibited pentagastrin-induced acid output, whereas clenbuterol was effective only at high doses (10–100 mol/kg). The inhibitory effect of BRL37344 on pentagastrin-induced acid secretion was not modified by the nonselective –adrenoceptor antagonist propranolol, but it was prevented by bupranolol, a ₃-adrenoceptor antagonist. Furthermore, neither BRL37344 (10 mol/kg) nor clenbuterol (100 mol/kg) modified the acid secretion induced by histamine. These data suggest that ₃ adrenoceptors have an inhibitory role in the control of rat gastric acid secretion induced by indirect stimuli.     

Heat shock protein induction in rat pancreatic islets by recombinant human interleukin 1β

Summary Interleukin 1, potentiated by tumour necrosis factor , is cytotoxic to pancreatic Beta cells in vitro. We have hypothesized that interleukin 1 induces oxygen free radicals in Beta cells. Since cytotoxicity induced by free radicals and by heat may activate the same cellular repair mechanism (the heat shock response), the aim of this study was to investigate the pattern of protein synthesis in isolated islets after exposure to interleukin 1 (150 pg/ml, 24 h), tumour necrosis factor (50 ng/ml, 24 h), heat shock (43°C, 30 min) and H₂O₂ (0.1 mmol/l, 20 min). By polyacrylamide gel electrophoresis, autoradiography, Western-blot analysis and partial peptide mapping of ³⁵S-methionine labelled islets, interleukin 1 was found to induce a 73 kilodalton protein belonging to the heat shock protein family heat shock protein 70, a heat shock protein 90, and haem oxygenase. A minor induction of heat shock protein 73 and haem oxygenase was seen after H₂O₂. Interleukin 1 did not induce heat shock proteins in rat thyroid cells, rat mesangial cells or in human monocytes. Tumour necrosis factor did not induce selective protein synthesis. Pre-exposure of islets to heat, tumour necrosis factor , or H₂O₂ did not prevent the impairment of glucose-stimulated insulin release seen after 24 h of interleukin 1 exposure. The data are compatible with free radical induction by interleukin 1. However, the heat shock response is not specific for oxidative injury, and previous studies have shown discrepant effects as to a protective effect of free radical scavengers against interleukin 1-mediated beta-cytotoxicity. Thus, a role for free radicals in this context is not definitely proven.     

The insulin receptor: signalling mechanism and contribution to the pathogenesis of insulin resistance

Summary The insulin receptor is a heterotetrameric structure consisting of two -subunits of M_r135 kilodalton on the outside of the plasma membrane connected by disulphide bonds to -subunits of M_r95 kilodalton which are transmembrane proteins. Insulin binding to the -subunit induces conformational changes which are transduced to the -subunit. This leads to the activation of a tyrosine kinase activity which is intrinsic to the cytoplasmatic domains of the -subunit. Activation of the tyrosine kinase activity of the insulin receptor represents an essential step in the transduction of an insulin signal across the plasma membrane of target cells. Signal transduction on the post-kinase level is not yet understood in detail, possible mechanisms involve phosphorylation of substrate proteins at tyrosine residues, activation of serine kinases, the interaction with G-proteins, phospholipases and phosphatidylinositol kinases. Studies in multiple insulin-resistant cell models have demonstrated that an impaired response of the tyrosine kinase to insulin stimulation is one potential mechanism causing insulin resistance. An impairment of the insulin effect on tyrosine kinase activation in all major target tissues of insulin, in particular the skeletal muscle was demonstrated in Type 2 (non-insulin-dependent) diabetic patients. There is no evidence that the impaired tyrosine kinase response in the skeletal muscle is a primary defect, however, it is likely that this abnormality of insulin signal transduction contributes significantly to the pathogenesis of the insulin-resistant state in Type 2 diabetes.Given as the Minkowski Lecture, EASD Meeting, Lisbon, Portugal 1989.     

Distribution of β-Adrenoceptor Subtypes in Gastrointestinal Tract of Nondiabetic and Diabetic BB Rats A Longitudinal Study

The effects of aging and diabetes on thedistribution of -adrenoceptor subtypes in the gutwere investigated in the BB rat.[¹²⁵I]Cyanopindolol binding to 10-msections was evaluated using film autoradiography. Cyanopindolol binding to -,₁-, and₂-adrenoceptors was displaced by 1M propranolol, 50 nM ICI-89-406, and 100 nMICI-118-551, respectively. -Adrenoceptor bindingwas highest in the circular muscle of proximal colon and lowest in thepylorus of 4- to 5-month-old rats. Aging (8- to10-month-old vs. 4- to 5-month-old rats) was associatedwith increased -adrenoceptor binding in thepylorus and reduced binding in the proximal colon.Diabetes had a time-dependent effect on the level of-adrenoceptor binding. It was increased in theantral and pyloric stomach but longer periods ofdiabetes caused a reduction in -adrenoceptorbinding in the pylorus. Those in the intestine werereduced time-dependently and involved₁- or ₂-adrenoceptorsor both.     

Distribution pattern of α and β myosin in normal and diseased human ventricular myocardium

Summary All fibers in three normal, four dilated, and two ischemic human ventricles were classified according to their myosin content using three sets of monoclonal antibodies each specific for one myosin heavy chain isoform (, and ). Numerous fibers contained only myosin heavy chain (denoted as fibers), others contained either and , or and myosin heavy chain (denoted as and fibers, respectively). The percentages of fibers were systematically determined along the walls of seven homologous regions of the ventricular myocardium.In all ventricles, there was an -fiber transmural gradient, with less fiber in the subendocardium than in the subepicardium. More fibers were found in the right than in the left ventricular wall but there was no difference between the mid-portion and the apex of the free wall of each ventricle. The diseased ventricles contained a lower fiber percentage than the normal hearts. fibers were very rare in the normal ventricles (less than 5%) and almost inexistent in pathological hearts. The correlation between the mean fiber percentages of the diseased hearts and their cardiac indices (r=0.88, P<0.05) suggests that the small amount of myosin distributed in a large number of ventricular fibers could play a role in the contractile performance of the heart. In conclusion, this study provides evidence for 1) an fiber transmural gradient, and 2) a lower myosin ratio in discased than in normal human ventricle.This work was supported in part by L'Institut National de la Santé et de la Recherche Médicale 101 rue de Tolbiac, 75013 Paris     

Detection of anti-bovine β2-glycoprotein I antibody in sera from patients with antiphospholipid syndrome

We studied and characterized anti-bovine ₂ I antibodies (aB₂-GPI) in sera from patients with antiphospholipid syndrome (APS) by ELISA. Bovine ₂-glycoprotein I ₂-GPI was purified by heparin affinity and DEAE ion-exchange chromatography, and identified on immunoblots using a monoclonal antibody against human ₂-GPI and by amino acid sequence analysis. aB₂-GPI levels in the sera from 36 APS patients were measured by ELISA using purified bovine ₂-GPI as an antigen. The mean±standard deviation level of aB₂-GPI was 17.4±22.0 units in the 58% of APS patients who were positive. There was a significant correlation (P=0.003) between aB₂-GPI and anticardiolipin antibody (aCL) levels. aB₂-GPI from the sera of patients with APS was inhibited by bovine ₂-GPI itself. Purified IgG from the sera of patients with APS showed that bovine ₂-GPI was capable of acting as a cofactor for aCL. Purified bovine ₂-GPI was useful antigen for conventional ELISA. aB₂-GPI may contribute to the further development of aCL analysis and to the understanding of the pathogenesis of APS.     

Macrophages enhance binding of beta-VLDL and cholesterol ester accumulation in cultured aortic smooth muscle cells

Summary The effect of macrophages on the uptake of -very low-density lipoprotein (-VLDL) by smooth muscle cells (SMC) expressing different morphological phenotypes was examined in culture. The SMC were grown alone and in co-culture with macrophages for four days, then incubated with different concentrations of¹²⁵I--VLDL for 3 h at 4°C or with 75 ug/ml -VLDL for 24h at 37°C. The binding of -VLDL to SMC at 4°C was enhanced in the presence of macrophages irrespective of the phenotype expressed by SMC. This occurred through modification of the lipoprotein, since binding of re-isolated macrophage-conditioned -VLDL to SMC was 12.5 times that of fresh -VLDL. This modified form of -VLDL competed with fresh -VLDL for binding to SMC. Binding was inhibited in the presence of probucol, suggesting that an oxidative mechanism may be involved.The presence of macrophages also enhanced the accumulation of -VLDL-derived cholesterol in SMC. While most of this is a consequence of the enhanced binding, macrophages may also act directly on SMC to increase cholesterol accumulation, since the activity of acid cholesterol ester hydrolase and neutral cholesterol ester hydrolase in SMC was reduced in the presence of macrophages.     

TNFα, IL-1β and IL-6 plasma levels in neutropenic patients after onset of fever and correlation with the C-reactive protein (CRP) kinetic values

Summary Cytokines, especially tumor necrosis factor (TNF), interleukin-1 (IL-1), and interleukin-6 (IL-6) play an important role in the genesis and progression of the septic shock syndrome. We performed a study monitoring levels of these three cytokines in ten neutropenic oncology patients in whom an infectious syndrome was suspected. A comparison was made with a population of nine non-neutropenic patients on the intensive care unit. Unfortunately the results of this study do not allow specific profiles to be established for each cytokine in the populations studied. Levels of IL-6, TNF and IL-1 were not statistically higher in the non-neutropenic patients when compared with the neutropenic group. However, the highest IL-6 levels were observed for four non-neutropenic patients, three of whom died. High levels of C-reactive protein (CRP), haptoglobin and fibrinogen were found, reflecting the inflammatory status of each patient. CRP levels were higher in the non-neutropenic patients and correlated with IL-6 levels, indicating the importance of CRP determination in this group of patients.

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TNF-, IL-1, und IL-6 Plasmaspiegel bei neutropenischen Patienten nach Fieberbeginn und Beziehung zur Kinetik der CRP-Werte

Zusammenfassung Zytokine, vor allem Tumornekrosefaktor alpha (TNF-), Interleukin-1 (IL-1) und Interleukin-6 (IL-6) spielen eine große Rolle in der Entstehung und Progression des Syndroms des septischen Schocks. Wir haben diese drei Zytokine bei zehn neutropenischen onkologischen Patienten mit Verdacht auf Infektion untersucht. Neun nicht-neutropenische Patienten einer Intensivpflegestation wurden als Kontrollen herangezogen. Leider erlauben die Ergebnisse dieser Studie keine spezifischen Profile für das jeweilige Zytokin in der untersuchten Patientengruppe. Im Vergleich zu nicht-neutropenischen Patienten fanden sich bei den neutropenischen Patienten keine signifikant höheren Spiegel von IL-6, TNF- und IL-1. Die höchsten IL-6 Spiegel wurden bei vier nicht neutropenischen Patienten gemessen. Drei von ihnen starben. Entsprechend dem Entzündungszustand bei den Patienten waren die Spiegel von C-reaktivem Protein (CRP), Haptoglobin und Fibrinogen hoch. Bei den nicht-neutropenischen Patienten wurden höhere CRP-Spiegel gemessen, sie korrelierten mit den IL-6 Spiegeln und weisen auf die Bedeutung der CRP-Bestimmung bei diesen Patienten hin.

     

Glucokinase is not the pancreatic B-cell glucoreceptor

Summary A series of recent experimental findings are reviewed to indicate that glucokinase does not represent the pancreatic B-cell glucoreceptor. (1) Whether in liver, pancreatic islet or insulin-producing tumoral cell homogenates, glucokinase fails to yield a higher reaction velocity with -than -D-glucose. (2) At a high glucose concentration (40 mmol/l), when the phosphorylation of glucose by glucokinase is indeed higher with - than -D-glucose, no preference for -D-glucose is observed in intact islets, as judged from the utilization of D-[5-³H]glucose, production of lactic acid, oxidation of D-[U-¹⁴C] glucose, net uptake of ⁴⁵Ca or release of insulin. (3) The glucose 6-phosphate content of intact islets is higher in the presence of - than -D-glucose. (4) At a low glucose concentration (3.3 mmol/l), when the participation of glucokinase to hexose phosphorylation is minimal, -D-glucose is still better metabolized and stimulates both ⁴⁵Ca net uptake and insulin release more efficiently than -D-glucose, despite the fact that hexokinase yields a higher reaction velocity with - than -D-glucose. (5) In intact islets, -D-glucose is used preferentially to -D-glucose in the pentose cycle pathway as judged from the oxidation of - or -D-[1-¹⁴C]glucose relative to that of - or -D-[6-¹⁴C]glucose. (6) In islets removed from fasted rats, the rate of glycolysis is more severely decreased than expected from the repression of glucokinase. (7) The metabolism of glucose in tumoral insulin-producing cells differs, in several respects, from that in normal pancreatic islets, although the pattern of hexokinase and glucokinase activities is similar in these two types of cells. All these observations point to the participation of regulatory sites distal to glucose phosphorylation in the control of glucose metabolism in islet cells.     

Estrogen Receptor Beta mRNA Expression in Normal and Adenomatous Pituitaries

Estrogen (E2), acting via its nuclear receptors, has been implicated in tumor development and growth, particularly in the pathogenesis of breast cancer. E2 also modulates anterior pituitary hormone production and is a potent cell mitogen. Until recently, the actions of E2 were thought to be mediated by a single estrogen receptor (ER) isoform (ER), and currently little is known of the pathophysiological relevance of the ER isoform. The presence of ER mRNA has been demonstrated by RT-PCR in the normal human pituitary, although expression of ER mRNA in human pituitary tumors has not been described. We have used semiquantitative RT-PCR to determine the relative levels of expression of ER mRNA in normal human pituitaries, non-functioning pituitary adenomas and GH-secreting tumors. ER mRNA was detected in normal pituitaries and all pituitary tumors examined. The ratio of ER mRNA to -actin mRNA expression was significantly reduced in non-functioning pituitary tumors (NFTs; 0.92 ± 0.09; mean ± SE; n=23) compared with findings in normal pituitaries (1.56 ± 0.21; mean ± SE; n=5; p<0.05 Student's t-test). Studies of ER protein expression are required to determine the functional significance of reduced ER mRNA expression in NFTs.     

Expression and secretion of alpha1-proteinase inhibitor are regulated by proinflammatory cytokines in human pancreatic islet cells

Aims/hypothesis Alpha1-proteinase inhibitor (1-PI) has been considered a key player in inflammatory processes. In humans, the main production site of 1-PI is the liver, but other tissues, including pancreatic islets, also synthesise this molecule. The aims of this study were to assess the islet cell types that produce 1-PI, to determine whether 1-PI is actually secreted by islet cells, and to assess how its production and/or secretion are regulated.Methods Expression of 1-PI in human islet cells was assessed by immunofluorescence, electron microscopy and western blotting. Release of 1-PI was analysed by reverse haemolytic plaque assay and ELISA. The effects of cytokines on 1-PI synthesis and secretion were tested.Results Immunofluorescence showed that alpha and delta cells do express 1-PI, whereas beta cells do not. By electron microscopy, we demonstrated a colocalisation of 1-PI with glucagon and somatostatin within secretory granules. Immunolabelling also revealed localisation of 1-PI within the Golgi apparatus, related vesicles and lysosomal structures. The expression of 1-PI in islet cells was also demonstrated by western blotting and ELISA of protein extracts. ELISA and reverse haemolytic plaque assay showed that 1-PI is secreted into the culture medium. Treatment of islet cells with IL-1 and oncostatin M for 4 days increased the production and release of 1-PI.Conclusions/interpretation Our results demonstrate that 1-PI is expressed by the alpha and delta cells of human islets, and that proinflammatory cytokines enhance the production and release of this inhibitor.     

Expression of 14-3-3 ζ and interaction with protein kinase C in the rat retina in early diabetes

Aims/hypothesis The present study aimed to investigate the expression levels of and the relationship between 14-3-3 and protein kinase C (PKC) in the retina of early diabetes.Methods Changes in the expression levels of, and interaction between, 14-3-3 and PKC were investigated by Northern and Western blot analyses, immunoprecipitation and double immunostaining in the retina of diabetic rats after 6 weeks of diabetes. PKC activity was examined using a PKC assay.Results In the diabetic retina, the molecular levels of 14-3-3 were reduced, while those of PKC and were increased. Direct interaction between 14-3-3 and PKC was markedly decreased in the retina after 6 weeks of diabetes, while PKC activity was increased.Conclusions/interpretation These findings show that a reduction in 14-3-3 can induce PKC activation, suggesting that this is a main cause of visual dysfunction in the retina during diabetes.     

In vitro and in vivo investigations for the development of cytostatic methylhydrazones

Summary In in vitro short-term (3 h) assays, the -chloroethyl-methyl-hydrazones B 1 and B 2 inhibit the uptake of ³H-thymidine by EAC and L 1210 leukemia cells, B 2 being 5 to 10 times more effective than B 1. The growth inhibitory effect of both compounds was also confirmed in long-term (7 days) clonal assays using agar-containing glass capillaries, B 2 again being more effective than B 1. In contrast to these differences in vitro, in vivo both substances showed remission to the same degree in EAC- and complete resistance in L 1210-bearing mice. The diverging in vitro/in vivo sensitivities were thought to result from differences in the affinity of the methylhydrazones to the tumor cells: using short exposure periods (3 h) B 1 was more inhibitory than B 2 on both EAC and L 1210 colony growth; i.e., the more hydrophilic B 2 could more easily be washed off. To further test the idea of different cell membrane affinities, the methylhydrazones ZB 1 and P 1 with increasing lipophilic properties were synthesized. In vitro, after both pulse and continuous exposure ZB 1 and P 1 showed enforced inhibitory effects on colony growth. In vivo, ZB 1 and P 1 reduced the tumor weight of EAC mice, while only P 1 increased the survival time of L 1210 mice. The results suggest that from the combination of in vitro/in vivo assays mechanistic conclusions can be derived that are valuable for further development of these cystostatics.Abbreviations B 1 N-methyl-N--chloroethyl-benzaldehyde-hydrazone - B 2 N-methyl-N--chloroethyl(p-dimethylamino)benzaldehyde-hydrazone - EAC Ehrlich Ascites Carcinoma - FCS fetal calf serum - ³H-dThd 6-³-H-thymidine - L 1210 Leukemia L 1210 - P 1 N-methyl-N--chloroethyl-pentadiene-benzaldehyde-hydrazone - ZB 1 N-methyl-N--chloroethyl-cinnamoylaldehyde-hydrazone     

Ciglitazone,a new hypoglycaemic agent. 4. Effect on pancreatic islets of C57BL/6J-ob/ob and C57BL/KsJ-db/db mice

Summary Pancreases of treated and control male C57BL/6J-ob/ob and C57BL/KsJ-db/db mice were evaluated by qualitative and morphometric microscopic techniques to determine the effects of chronic ciglitazone treatment on the morphology of cells and surface area and number of pancreatic islets. The cells of treated ob/ob and db/db mice displayed moderate to heavy granulation whereas most cells of untreated obese and diabetic mice were extensively degranulated. Although moderate proliferation of the rough endoplasmic reticulum and Golgi apparatus was evident in some cells of treated db/db mice, both groups of treated ob/ob and db/db mice displayed an improved pattern of insulin synthesis and storage. In contrast, the cells of untreated ob/ob and db/db mice were in a severe state of stress which was indicated by extensive hypertrophy of the rough endoplasmic reticulum, Golgi apparatus and mitochondria. Some cells of untreated db/ db mice also displayed lysosome aggregates indicative of early stages of necrosis. Morphometric analysis revealed that the surface area of islets of treated ob/ob mice was significantly smaller in comparison with that of untreated ob/ob mice. Since the surface area of islets of treated C57BL/6J-+/? mice (lean littermates of ob/ob mice) was less than that of treated ob/ob mice, the progression of islet hypertrophy in the obese mice was probably arrested or attenuated but not to the level of the treated +/? mice. The number of pancreatic islets was significantly greater in treated than in untreated db/ db mice. A majority of the islets of untreated db/db mice were atrophie and consisted of acinar and endocrine cells whereas most of the islets of treated db/db mice appeared to be intact and unremarkable. The results of this study suggest that ciglitazone is an effective hypoglycaemic agent which may directly or indirectly promote -cell regranulation and an improved pattern of insulin synthesis and storage in ob/ob and db/db mice. However, in treated db/db mice, there still was some evidence of stress in the cells. Overall, the prolonged treatment with ciglitazone also seemed to inhibit the hypertrophy of islets in ob/ob mice and protect the structural integrity and viability of islets in db/db mice.     

B cell adrenoceptors and sulphonylurea-induced insulin release in mouse islets

Summary Interactions of tolbutamide and glibenclamide with B cell adrenoceptors have been reported. This study evaluated the possible role of such interactions in the stimulation of insulin release. Mouse islets were incubated in the presence of 10 mmol/l glucose alone or with tolbutamide (10 mol/l) or glibenclamide (0.02 mol/l). At 0.01–10 mol/l, blockers of ₂-adrenoceptors (yohimbine, idazoxan) or ₁-adrenoceptors (prazosin) had practically no effect on glucose-induced insulin release and did not affect its potentiation by sulphonylureas, except for a slight increase by 10 mol/l prazosin and idazoxan. Nonspecific -blockers (phentolamine, dihydroergotamine) increased control release at 10 mol/l, but only the latter amplified the response to tolbutamide. Blockers of -adrenoceptors were tested at 0.1–100 mol/l: propranolol (₁, ₂), metoprolol (₁) and compound ICI 118-551 (₂). They increased glucose-induced insulin release at 100 mol/l but variably altered the effect of sulphonylureas. Blockers of adrenoceptors have, thus, no effect on insulin release in vitro at therapeutic concentrations. At high concentrations, they non-specifically affect the action of sulphonylureas. We conclude that an interaction with B cell adrenoceptors is not involved in the insulinotropic action of sulphonylureas.     

Functional and morphological effects of interleukin-1β on the perfused rat pancreas

Summary We recently reported a potentiating effect of recombinant human interleukin-1 on glucose-stimulated insulin release from the isolated perfused pancreas. With the aim of determining whether the stimulatory effect of recombinant interleukin-1 on the B cell in the intact gland was modulated by varying the concentration, time of exposure to recombinant interleukin-1 or B-cell activity, and to elucidate a possible mechanism of action, we measured in the perfused rat pancreas the release of insulin, glucagon and/or prostaglandin E₂ according to the following three different protocols: (1) perfusion with 20 ng/ml of recombinant interleukin-1 for 92 min at 5 and 20 mmol/1 D-glucose (2) perfusion with varying concentrations of recombinant interleukin-1 ranging from 0.1×10^–3 ng/ml to 100 ng/ml at 5 and 20 mmol/l D-glucose (3) perfusion with 20 ng/ml of recombinant interleukin-1 at 5,11 or 20 mmol/l D-glucose. Furthermore, in a separate set of experiments we examined the influence of the cytokine on the morphology of the endocrine pancreas. Interleukin-1 stimulated insulin secretion at 11 and 20 mmol/l D-glucose and potentiated first as well as second phase insulin release in a dose-dependent fashion, with decreasing effect at higher concentrations. Glucagon secretion was also stimulated by recombinant interleukin-1, irrespective of increasing glucose (5, 11, 20 mmol/l) and insulin concentrations. The potentiating effect of recombinant interleukin-1 on insulin secretion was evident even after discontinued perfusion with the cytokine, suggesting a priming effect on B-cell function. Furthermore, we did not observe any relation between the recombinant interleukin-1 mediated insulin and glucagon release and prostaglandin E₂. Electron microscopy of the pancreata perfused with recombinant interleukin-1 revealed significant B cell and to a lesser extent A-cell lysis as well as induction of cell protrusions (blebs) in B cells only, accompanied by peripheral degranulation and rearrangement of rough endoplasmatic reticulum. We suggest that in addition to a paracrine effect of locally produced interleukin-1 systemic interleukin-1 may have an endocrine effect on A- and B-cell function and viability. Interleukin-1 should be considered to be a physiological modulator of insulin and glucagon secretion e.g. during the acute phase response, but also as a pathogenetic factor in Type 1 (insulin-dependent) diabetes mellitus.     

Human Plasma Fibronectin Mediates Adhesion of U937 Cells by RGD and CS1

Fibronectin specifically binds to U937 cells (monocytic cell line) in a dose-dependent manner. The specific receptors for the RGD sequence have been identified as ₅₁ and _IIb3, and that for CS1 has been defined as ₄₁. RGDS, CS1 peptide, and two peptides together showed similar inhibitory activities on this adhesion, while the 29-kD dispase-digested fragment of the C-terminal heparin-binding domain did not. Thus, the adhesion of fibronectin to U937 cells is mainly mediated by RGDS in the cell-binding domain and CS1 in the alternatively spliced region. Flow cytometry using monoclonal antibodies revealed expressions of ₃₁, ₄₁, and ₅₁, and not expression of ₂₁. Adhesion of U937 cells to fibronectin-coated wells is specific and is inhibited by anti-₄₁ and anti- ₅₁ monoclonal antibodies. The IC-50 for anti-₅₁ antibody was almost a log lower than the value for anti-₄₁ antibody. These results demonstrated that interactions of RGDS and CS1 sequence of fibronectin with ₅₁ and ₄₁ on U937 cells were required for the adhesion of U937 cells to fibronectin. These results may provide further information to understand the mechanism(s) of tumor cell adhesion and atherogenesis.