Glucose metabolism and oscillatory behavior of pancreatic islets

A variety of oscillations are observed in pancreatic islets.We establish a model, incorporating two oscillatory systems of different time scales: One is the well-known bursting model in pancreatic beta-cells and the other is the glucose-insulin feedback model which considers direct and indirect feedback of secreted insulin. These two are coupled to interact with each other in the combined model, and two basic assumptions are made on the basis of biological observations: The conductance g_{K(ATP)} for the ATP-dependent potassium current is a decreasing function of the glucose concentration whereas the insulin secretion rate is given by a function of the intracellular calcium concentration. Obtained via extensive numerical simulations are complex oscillations including clusters of bursts, slow and fast calcium oscillations, and so on. We also consider how the intracellular glucose concentration depends upon the extracellular glucose concentration, and examine the inhibitory effects of insulin.Comment: 11 pages, 16 figure

Microbial engineering for production of N-functionalized amino acids and amines

Mindt M, Walter T, Kugler P, Wendisch VF. Microbial engineering for production of N-functionalized amino acids and amines. Biotechnology Journal . 2020;15(7): 1900451.N‐ functionalized amines play important roles in nature and occur, for example, in the antibiotic vancomycin, the immunosuppressant cyclosporine, the cytostatic actinomycin, the siderophore aerobactin, the cyanogenic glucoside linamarin, and the polyamine spermidine. In the pharmaceutical and fine‐chemical industries N‐ functionalized amines are used as building blocks for the preparation of bioactive molecules. Processes based on fermentation and on enzyme catalysis have been developed to provide sustainable manufacturing routes to N‐ alkylated, N‐ hydroxylated, N‐ acylated, or other N‐ functionalized amines including polyamines. Metabolic engineering for provision of precursor metabolites is combined with heterologous N‐ functionalizing enzymes such as imine or ketimine reductases, opine or amino acid dehydrogenases, N‐ hydroxylases, N‐ acyltransferase, or polyamine synthetases. Recent progress and applications of fermentative processes using metabolically engineered bacteria and yeasts along with the employed enzymes are reviewed and the perspectives on developing new fermentative processes based on insight from enzyme catalysis are discussed

Placental lactogens induce serotonin biosynthesis in a subset of mouse beta cells during pregnancy

AIMS/HYPOTHESIS: Upregulation of the functional beta cell mass is required to match the physiological demands of mother and fetus during pregnancy. This increase is dependent on placental lactogens (PLs) and prolactin receptors, but the mechanisms underlying these events are only partially understood. We studied the mRNA expression profile of mouse islets during pregnancy to gain a better insight into these changes. METHODS: RNA expression was measured ex vivo via microarrays and quantitative RT-PCR. In vivo observations were extended by in vitro models in which ovine PL was added to cultured mouse islets and MIN6 cells. RESULTS: mRNA encoding both isoforms of the rate-limiting enzyme of serotonin biosynthesis, tryptophan hydroxylase (TPH), i.e. Tph1 and Tph2, were strongly induced (fold change 25- to 200-fold) during pregnancy. This induction was mimicked by exposing islets or MIN6 cells to ovine PLs for 24 h and was dependent on janus kinase 2 and signal transducer and activator of transcription 5. Parallel to Tph1 mRNA and protein induction, islet serotonin content increased to a peak level that was 200-fold higher than basal. Interestingly, only a subpopulation of the beta cells was serotonin-positive in vitro and in vivo. The stored serotonin pool in pregnant islets and PL-treated MIN6 cells was rapidly released (turnover once every 2 h). CONCLUSIONS/INTERPRETATION: A very strong lactogen-dependent upregulation of serotonin biosynthesis occurs in a subpopulation of mouse islet beta cells during pregnancy. Since the newly formed serotonin is rapidly released, this lactogen-induced beta cell function may serve local or endocrine tasks, the nature of which remains to be identified

A Practical Guide to Rodent Islet Isolation and Assessment

Pancreatic islets of Langerhans secrete hormones that are vital to the regulation of blood glucose and are, therefore, a key focus of diabetes research. Purifying viable and functional islets from the pancreas for study is an intricate process. This review highlights the key elements involved with mouse and rat islet isolation, including choices of collagenase, the collagenase digestion process, purification of islets using a density gradient, and islet culture conditions. In addition, this paper reviews commonly used techniques for assessing islet viability and function, including visual assessment, fluorescent markers of cell death, glucose-stimulated insulin secretion, and intracellular calcium measurements. A detailed protocol is also included that describes a common method for rodent islet isolation that our laboratory uses to obtain viable and functional mouse islets for in vitro study of islet function, beta-cell physiology, and in vivo rodent islet transplantation. The purpose of this review is to serve as a resource and foundation for successfully procuring and purifying high-quality islets for research purposes

Inositol 1,4,5- Trisphosphate Receptor Function in Drosophila Insulin Producing Cells

The Inositol 1,4,5- trisphosphate receptor (InsP3R) is an intracellular ligand gated channel that releases calcium from intracellular stores in response to extracellular signals. To identify and understand physiological processes and behavior that depends on the InsP3 signaling pathway at a systemic level, we are studying Drosophila mutants for the InsP3R (itpr) gene. Here, we show that growth defects precede larval lethality and both are a consequence of the inability to feed normally. Moreover, restoring InsP3R function in insulin producing cells (IPCs) in the larval brain rescues the feeding deficit, growth and lethality in the itpr mutants to a significant extent. We have previously demonstrated a critical requirement for InsP3R activity in neuronal cells, specifically in aminergic interneurons, for larval viability. Processes from the IPCs and aminergic domain are closely apposed in the third instar larval brain with no visible cellular overlap. Ubiquitous depletion of itpr by dsRNA results in feeding deficits leading to larval lethality similar to the itpr mutant phenotype. However, when itpr is depleted specifically in IPCs or aminergic neurons, the larvae are viable. These data support a model where InsP3R activity in non-overlapping neuronal domains independently rescues larval itpr phenotypes by non-cell autonomous mechanisms

Rapid Insulinotropic Action of Low Doses of Bisphenol-A on Mouse and Human Islets of Langerhans: Role of Estrogen Receptor β

Bisphenol-A (BPA) is a widespread endocrine-disrupting chemical (EDC) used as the base compound in the manufacture of polycarbonate plastics. It alters pancreatic β-cell function and can be considered a risk factor for type 2 diabetes in rodents. Here we used ERβ−/− mice to study whether ERβ is involved in the rapid regulation of KATP channel activity, calcium signals and insulin release elicited by environmentally relevant doses of BPA (1 nM). We also investigated these effects of BPA in β-cells and whole islets of Langerhans from humans. 1 nM BPA rapidly decreased KATP channel activity, increased glucose-induced [Ca2+]i signals and insulin release in β-cells from WT mice but not in cells from ERβ−/− mice. The rapid reduction in the KATP channel activity and the insulinotropic effect was seen in human cells and islets. BPA actions were stronger in human islets compared to mouse islets when the same BPA concentration was used. Our findings suggest that BPA behaves as a strong estrogen via nuclear ERβ and indicate that results obtained with BPA in mouse β-cells may be extrapolated to humans. This supports that BPA should be considered as a risk factor for metabolic disorders in humans

Usporedba djelovanja blokatora kalcijevih kanala, blokatora autonomnoga živčanog sustava te inhibitora slobodnih radikala na hiposekreciju inzulin iz izolirnih langerhansovih otočića štakora uzrokovanu diazinonom

Hyperglycaemia has been observed with exposure to organophosphate insecticides. This study was designed to compare the effects of calcium channel blockers, alpha-adrenergic, beta-adrenergic, and muscarinic receptor blockers, and of free radical scavengers on insulin secretion from diazinon-treated islets of Langerhans isolated from the pancreas of rats using standard collagenase digestion, separation by centrifugation, and hand-picking technique. The islets were then cultured in an incubator at 37 °C and 5 % CO2. In each experimental set 1 mL of 8 mmol L-1 glucose plus 125 µg mL-1 or 625 µg mL-1 of diazinon were added, except for the control group, which received 8 mmol L-1 glucose alone. The cultures were then treated with one of the following: 30 µmol L-1 atropine, 100 µmol L-1 ACh + 10 µmol L-1 neostigmine, 0.1 µmol L-1 propranolol, 2 µmol L-1 nifedipine, 50 µmol L-1 phenoxybenzamine, or 10 µmol L-1 alphatocopherol. In all experiments, diazinon significantly reduced glucose-stimulated insulin secretion at both doses, showing no dose dependency, as the average inhibition for the lower dose was 62.20 % and for the higher dose 64.38 %. Acetylcholine and alpha-tocopherol restored, whereas atropine potentiated diazinoninduced hyposecretion of insulin. Alpha-, beta- and calcium channel blockers did not change diazinoninduced effects. These findings suggest that diazinon affects insulin secretion mainly by disturbing the balance between free radicals and antioxidants in the islets of Langerhans and by inducing toxic stress.U osoba izloženih organofosfatnim insekticidima zamijećen je nastanak hiperglikemije. Svrha je ovo istraživanja bila usporediti djelovanje blokatora kalcijevih kanala, alfa i beta-adrenergičkih i muskarinskih receptora te inhibicije slobodnih radikala na lučenje inzulina iz Langerhansovih otočića izoliranih iz štakora tretiranih diazinonom. Otočići su izolirani iz gušterače štakora s pomoću standardnog postupka digestije kolagenazom, odvajanja centrifugiranjem i metodom ručnog probira (engl. hand-picking) te su kultivirani u inkubatoru pri 37 °C i 5 % CO2. Pokusne su kulture inkubirane s 1 mL glukoze u koncentraciji od 8 mmol L-1 te diazinonom u dozi od 125 μg mL-1, odnosno 625 μg mL-1. U kontrolu je dodana samo glukoza u koncentraciji od 8 mmol L-1. Nakon toga je u kulture dodan jedan od sljedećih agenasa: 30 µmol L-1 atropin, 100 µmol L-1 ACh + 10 µmol L-1 neostigmin, 0,1 µmol L-1 propranolol, 2 µmol L-1 nifedipin, 50 µmol L-1 fenoksibenzamin, odnosno 10 µmol L-1 alfa-tokoferol. U svim je pokusima diazinon značajno smanjio lučenje inzulina, s time da je doza od 125 μg mL-1 dovela do 62,2 %-tne inhibicije, a doza od 625 μg mL-1 do 64,38 %-tne inhibicije lučenja inzulina, što upućuje na djelovanje neovisno o dozi. Acetilkolin i alfa-tokoferol su ponovno potaknuli lučenje inzulina, za razliku od atropina koji ga je dodatno smanjio. Primjena blokatora alfa i beta-adrenergičkih receptora te blokatora kalcijevih kanala nije utjecala na djelovanje diazinona. Autori zaključuju da diazinon utječe na lučenje inzulina ponajviše narušavanjem ravnoteže između slobodnih radikala i antioksidansa u Langerhansovim otočićima te dovodi do toksičnoga stresa