Effects of glucose on beta cells in pancreatic monolayer cultures

A High-content In Vitro Pancreatic Islet β-cell Replication Discovery Platform

Loss of insulin-producing β-cells is a central feature of diabetes. While a variety of potential replacement therapies are being explored, expansion of endogenous insulin-producing pancreatic islet β-cells remains an attractive strategy. β-cells have limited spontaneous regenerative activity; consequently, a crucial research effort is to develop a precise understanding of the molecular pathways that restrain β-cell growth and to identify drugs capable of overcoming these restraints. Herein an automated high-content image-based primary-cell screening method to identify β-cell replication-promoting small molecules is presented. Several, limitations of prior methodologies are surmounted. First, use of primary islet cells rather than an immortalized cell-line maximizes retention of in vivo growth restraints. Second, use of mixed-composition islet-cell cultures rather than a β-cell-line allows identification of both lineage-restricted and general growth stimulators. Third, the technique makes practical the use of primary islets, a limiting resource, through use of a 384-well format. Fourth, detrimental experimental variability associated with erratic islet culture quality is overcome through optimization of isolation, dispersion, plating and culture parameters. Fifth, the difficulties of accurately and consistently measuring the low basal replication rate of islet endocrine-cells are surmounted with optimized immunostaining parameters, automated data acquisition and data analysis; automation simultaneously enhances throughput and limits experimenter bias. Notable limitations of this assay are the use of dispersed islet cultures which disrupts islet architecture, the use of rodent rather than human islets and the inherent limitations of throughput and cost associated with the use of primary cells. Importantly, the strategy is easily adapted for human islet replication studies. This assay is well suited for investigating the mitogenic effect of substances on β-cells and the molecular mechanisms that regulate β-cell growth.

Repurposing cAMP-modulating medications to promote β-cell replication

Loss of β-cell mass is a cardinal feature of diabetes. Consequently, developing medications to promote β-cell regeneration is a priority. cAMP is an intracellular second messenger that modulates β-cell replication. We investigated whether medications that increase cAMP stability or synthesis selectively stimulate β-cell growth. To identify cAMP-stabilizing medications that promote β-cell replication, we performed high-content screening of a phosphodiesterase (PDE) inhibitor library. PDE3, -4, and -10 inhibitors, including dipyridamole, were found to promote β-cell replication in an adenosine receptor-dependent manner. Dipyridamole's action is specific for β-cells and not α-cells. Next we demonstrated that norepinephrine (NE), a physiologic suppressor of cAMP synthesis in β-cells, impairs β-cell replication via activation of α(2)-adrenergic receptors. Accordingly, mirtazapine, an α(2)-adrenergic receptor antagonist and antidepressant, prevents NE-dependent suppression of β-cell replication. Interestingly, NE's growth-suppressive effect is modulated by endogenously expressed catecholamine-inactivating enzymes (catechol-O-methyltransferase and l-monoamine oxidase) and is dominant over the growth-promoting effects of PDE inhibitors. Treatment with dipyridamole and/or mirtazapine promote β-cell replication in mice, and treatment with dipyridamole is associated with reduced glucose levels in humans. This work provides new mechanistic insights into cAMP-dependent growth regulation of β-cells and highlights the potential of commonly prescribed medications to influence β-cell growth.

Adult tissue sources for new β cells

The diabetes pandemic incurs extraordinary public health and financial costs that are projected to expand for the foreseeable future. Consequently, the development of definitive therapies for diabetes is a priority. Currently, a wide spectrum of therapeutic strategies-from implantable insulin delivery devices to transplantation-based cell replacement therapy, to β-cell regeneration-focus on replacing the lost insulin-producing capacity of individuals with diabetes. Among these, β-cell regeneration remains promising but heretofore unproved. Indeed, recent experimental work has uncovered surprising biology that underscores the potential therapeutic benefit of β-cell regeneration. These studies have elucidated a variety of sources for the endogenous production of new β cells from existing cells. First, β cells, long thought to be postmitotic, have demonstrated the potential for regenerative capacity. Second, the presence of pancreatic facultative endocrine progenitor cells has been established. Third, the malleability of cellular identity has availed the possibility of generating β cells from other differentiated cell types. Here, we review the exciting developments surrounding endogenous sources of β-cell production and consider the potential of realizing a regenerative therapy for diabetes from adult tissues.

Identification of a pathway by which glucose regulates β-catenin signalling via the cAMP/protein kinase A pathway in β-cell models

Pancreatic β-cells are highly responsive to changes in glucose, but the mechanisms involved are only partially understood. There is increasing evidence that the β-catenin signalling pathway plays an important role in regulating β-cell function, but the mechanisms regulating β-catenin signalling in these cells is not well understood. In the present study we show that β-catenin levels and downstream signalling are regulated by changes in glucose levels in INS-1E and β-TC6-F7 β-cell models. We found a glucose-dependent increase in levels of β-catenin in the cytoplasm and nucleus of INS-1E cells. Expression of cyclin D1 also increased with glucose and required the presence of β-catenin. This was associated with an increase in phosphorylation of β-catenin on Ser552, which is known to stabilize the molecule and increase its transcriptional activity. In a search for possible signalling intermediates we found forskolin and cell-permeable cAMP analogues recapitulated the glucose effects, suggesting a role for cAMP and PKA (cAMP-dependent protein kinase/protein kinase A) downstream of glucose. Furthermore, glucose caused sustained increases in cAMP. Two different inhibitors of adenylate cyclase and PKA signalling blocked the effects of glucose, whereas siRNA (small interfering RNA) knockdown of PKA blocked the effects of glucose on β-catenin signalling. Finally, reducing β-catenin levels with either siRNA or pyrvinium impaired glucose- and KCl-stimulated insulin secretion. Taken together the results of the present study define a pathway by which changes in glucose levels can regulate β-catenin using a mechanism which involves cAMP production and the activation of PKA. This identifies a pathway that may be important in glucose-dependent regulation of gene expression and insulin secretion in β-cells.

Signaling pathways implicated in the stimulation of beta-cell proliferation by extracellular matrix

Laminin-5-rich extracellular matrix derived from 804G cells (804G-ECM) induces spreading, improves glucose-stimulated insulin secretion, and increases survival and proliferation of rat pancreatic beta-cells. The aim of the study was to determine growth signaling pathways activated by ECM with a particular focus on Ca(2+)-dependent transcription factors. 804G-ECM increased rat beta-cell proliferation, and this stimulation was glucose and Ca(2+) dependent. NF-kappaB nuclear translocation as well as IkappaBalpha gene expression were also Ca(2+) dependent. Inhibition of NF-kappaB almost completely blocked 804G-ECM-stimulated beta-cell proliferation as did the soluble IL-1 receptor antagonist IL-1Ra. 804G-ECM-induced proliferation was also blocked by cyclosporin A and the VIVIT peptide, suggesting involvement of nuclear factor of activated T cells (NFAT)/calcineurin. Use of selective inhibitors further implicated other pathways in this process. Inhibition of phosphatidylinositol 3-kinase and protein kinase A both prevented beta-cell replication stimulated by 804G-ECM. Conversely, inhibition of MAPK, c-Jun N-terminal kinase, p38, and glycogen synthase kinase-3beta increased beta-cell proliferation on 804G-ECM. Our results suggest that Ca(2+) entry, which is necessary for increased beta-cell proliferation on 804G-ECM, is also involved in 804G-ECM-induced NF-kappaB activity. It is proposed that increased cytosolic Ca(2+) leads to activation of the transcription factors NFAT and NF-kappaB that in turn increase beta-cell proliferation. Activation of phosphatidylinositol 3-kinase by 804G-ECM also increases proliferation possibly by synergistic coactivation of NFAT via inhibition of glycogen synthase kinase-3beta, whereas IL-1beta may amplify the process by feed-forward activation of NF-kappaB. Conversely, inhibition of the MAPK pathway increased beta-cell proliferation, indicating a counterregulatory restraining role for this signaling pathway.

Defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly in the Goto-Kakizaki rat model of type 2 diabetes

AIMS/HYPOTHESIS

The Goto-Kakizaki (GK) rat is a spontaneous model of type 2 diabetes. Defective beta cell mass detectable in late fetal age precedes the onset of hyperglycaemia. Our hypothesis was that an embryonic IGF production deficiency might be involved in beta cell mass anomaly in the diabetic GK rat. To test this, we evaluated during pancreatic organogenesis: (1) the beta cell development in GK rats on embryonic day (E) 13.5 and E18.5; (2) IGF2 and IGF1 receptor (IGF1R) pancreatic protein production on E13.5 and E18.5; (3) the in vitro development of GK pancreatic rudiment on E13.5; and (4) the in vitro effect of IGF2 addition on beta cell mass.

MATERIALS AND METHODS

Beta cell quantitative analyses were determined by immunohistochemistry and morphometry. IGF2 and IGF1R pancreatic protein production was evaluated using western blot analyses. Dorsal pancreatic rudiments were dissected on E13.5, separated from surrounding mesenchyme and cultured for 7 days without or with recombinant IGF2.

RESULTS

While beta cell mass was already decreased on E18.5, the differentiation of the first beta cells was in fact normal in E13.5 GK pancreas. Moreover, defective IGF2 and IGF1R protein production was detected in GK pancreatic rudiment as early as E13.5. The isolated GK pancreatic rudiment as maintained in vitro mimics the GK beta cell deficiency observed in vivo. This last approach enabled us to show that GK beta cells were fully responsive to IGF2 as far as their net growth is concerned.

CONCLUSIONS/INTERPRETATION

In diabetic GK rat, defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly. IGF2 supplementation expands the pool of beta cells.

Enhanced β-adrenergic receptors in the brain and pancreas during pancreatic regeneration in weanling rats

Adrenergic stimulation has an important role in the pancreatic beta-cell proliferation and insulin secretion. In the present study, we have investigated how sympathetic system regulates the pancreatic regeneration by analyzing Epinephrine (EPI), Norepinephrine (NE) and beta-adrenergic receptor changes in the brain as well as in the pancreas. EPI and NE showed a significant decrease in the brain regions, pancreas and plasma at 72 hrs after partial pancreatectomy. We observed an increase in the circulating insulin levels at 72 hrs. Scatchard analysis using [(3)H] propranolol showed a significant increase in the number of both the low affinity and high affinity beta-adrenergic receptors in cerebral cortex and hypothalamus of partially pancreatectomised rats during peak DNA synthesis. The affinity of the receptors decreased significantly in the low and high affinity receptors of cerebral cortex and the high affinity hypothalamic receptors. In the brain stem, low affinity receptors were increased significantly during regeneration whereas there was no change in the high affinity receptors. The pancreatic beta-adrenergic receptors were also up regulated at 72 hrs after partial pancreatectomy. In vitro studies showed that beta-adrenergic receptors are positive regulators of islet cell proliferation and insulin secretion. Thus our results suggest that the beta-adrenergic receptors are functionally enhanced during pancreatic regeneration, which in turn increases pancreatic beta-cell proliferation and insulin secretion in weanling rats.

Muscarinic M1 and M3 receptor binding alterations in pancreas during pancreatic regeneration of young rats

The importance of muscarinic receptors in proliferation of different cell types and in insulin secretion from pancreatic beta cells has been extensively studied. However, the role of pancreatic muscarinic receptors during pancreatic regeneration has not yet been studied. For the first time, the functional status of the muscarinic M1 and M3 receptors in regeneration of the pancreas is investigated here. It is observed that the number and affinity of high-affinity muscarinic M3 receptors increased at the time of regeneration. The low-affinity M3 receptors also showed a similar trend. In the case of muscarinic M1 receptors, the receptor number increased with a decrease in affinity. We also observed an increase in the circulating insulin levels at the time of active regeneration. The in vitro studies confirmed that muscarinic receptors are stimulatory to insulin secretion. Our results suggest that the increased muscarinic M1 and M3 receptor subtypes stimulate insulin secretion and islet cell proliferation during the regeneration of pancreas.

Development and retroviral transduction of porcine neonatal pancreatic islet cells in monolayer culture

To learn more about the potential of neonatal porcine pancreatic duct and islet cells for xenotransplantation, the development of these cells when cultured as monolayers was evaluated. Immunostaining for islet hormones and cytokeratin-7 revealed that day eight monolayers consisted of approximately 70% duct cells and less than 10% beta cells. Using Ki-67 immunostaining as a proliferation marker, the fraction of beta cells in the cell cycle was shown to decrease from 20% at day three to 10% at day eight, and for duct cells from 36 to 19%. Insulin secretion increased 2.4-fold upon glucose stimulation, and 38-fold when 10 mm theophylline was added, showing the responsiveness of the neonatal beta cells. Reaggregated monolayers consisted mostly of duct cells, but 4 weeks after transplantation, grafts contained predominantly endocrine cells, with duct cells being almost absent, suggesting in vivo differentiation of duct cells to endocrine cells. Monolayer susceptibility to retroviral transduction was also investigated using a Moloney Murine Leukemia Virus-based vector. Approximately 60% of duct cells but less than 5% of beta cells expressed the transgene, indicating that precursor duct cells are better targets for transgene expression. These results show that porcine neonatal pancreatic cells can be cultured as monolayers in preparation for transplantation. Furthermore, in such a culture setting, precursor duct cells have a high rate of proliferation and are more efficiently transduced with a retrovirus-based reporter gene than are beta cells.

Uncoupling protein 2 knockout mice have enhanced insulin secretory capacity after a high-fat diet

Uncoupling protein 2 (UCP2) may act as an important regulator of insulin secretion. In this study, beta-cell function in UCP2-deficient mice was examined after a 45% high-fat diet (HFD) to assess its role during the development of diet-induced type 2 diabetes. HFD-fed UCP2 (-/-) mice have lower fasting blood glucose and elevated insulin levels when compared with wild-type (WT) mice. UCP2 (-/-) mice also have enhanced beta-cell glucose sensitivity compared with WT mice after HFD, a result that is due in part to the deterioration of glucose responsiveness in WT mice. HFD-fed UCP2 (-/-) mice have increased insulin secretory capacity as a result of increased pancreatic beta-cell mass and insulin content per islet. Islets from WT mice exposed to 0.5 mmol/l palmitate for 48 h have significantly reduced mitochondrial membrane potential, ATP concentrations, and glucose responsiveness compared with UCP2 (-/-) islets, suggesting that elevated UCP2 in WT mice increases proton leak and decreases mitochondrial ATP production. Highly increased carnitine palmitoyl transferase-1 gene expression in UCP2 (-/-) mice is suggestive of enhanced fatty acid oxidizing capacity, particularly after HFD stress. These results further establish UCP2 as a component in glucose sensing and suggest a possible new aspect of UCP2 function during the progression of type 2 diabetes.

Pancreatic cell proliferation in normal rats studied by in vivo autoradiography with 3H-thymidine

In vivo 3H-Thymidine autoradiographic investigations of DNA synthesis in acinar, islet and duct cells in the pancreas of normal rats showed that activity was dependent on age. The proliferation of acinar and islet cells, which was high in young animals, decreased exponentially with age; proliferation of the ductal cells on the other hand, increased until the animals became mature. These findings suggest that the physiological regeneration of acinar and islet cells, as well as their replacement after injury in adult animals commences from pancreatic ducts.

Islet B-cell dysfunction and the time course of recovery following chronic overinsulinisation of normal rats

Appropriate insulin therapy may preserve or improve islet B-cell function whereas the effects of overinsulinisation are unclear. Pancreatic islet B-cell function was therefore studied after overinsulinisation of normal rats for 4 weeks (fed blood glucose 2.2-4.5 mmol/l, controls 4.1-7.0 mmol/l). Insulin secretion was assessed by a 3-h hyperglycaemic clamp (10.0 mmol/l) performed 1, 48, and 120 h after insulin withdrawal (n = 6 in each group). When the clamp was performed 1 h after insulin withdrawal, clamp insulin concentration was 1.6 +/- 0.1 micrograms/l, compared to 9.3 +/- 1.0 micrograms/l in control rats. The integrated area under the plasma insulin concentration curve was also significantly decreased (4.8 +/- 0.4 vs 20.3 +/- 2.2 micrograms.l-1.h-1, p less than 0.001), but recovered to 9.4 +/- 1.0 micrograms.l-1.h-1 after 48 h, and to 17.5 +/- 1.4 micrograms.l-1.h-1 after 120 h. Pancreatic insulin contents were decreased at 1 h (6 +/- 1 micrograms/g wet wt) and 48 h (54 +/- 12 micrograms/g wet wt) but not at 120 h (221 +/- 30 micrograms/g wet wt) after withdrawal (controls, 303 +/- 29 micrograms/g wet wt) and there was a strong relationship with pancreatic preproinsulin mRNA and the clamp insulin response. Thus, overinsulinisation with prolonged periods of low blood glucose concentrations impairs islet B-cell function, but is reversible over 5 days.

Insulin, glucagon and somatostatin secretion by cultured islets from normal and diabetic hamsters

The interhormonal relationship within the pancreatic islets have been studied by previous investigators, but the cellular interplay and the sequence of events in the islet cell's response to stimulators has remained unclear. In the present study, pancreatic islets were isolated by collagenase digestion from normal and streptozotocin-diabetic hamsters the latter being maintained with insulin treatment. The diabetic animals were used to provide A- and B-cell enriched islets. The islets from normal and diabetic hamsters were cultured in medium 199 plus 10% fetal calf serum with 0.8 or 5 mg/ml glucose. The cultures were maintained for up to seven days with medium changes every third day. At specified intervals, media were collected and assayed for insulin, glucagon and somatostatin. Our results showed the expected increased insulin secretion by the B-cells in response to high glucose. However, after two days of culture accumulative insulin secretory response was reduced and at the end of seven days was less than the insulin produced in low glucose medium. Glucagon secretion by the A-cells was similar for low and high glucose media for the entire culture period. Somatostatin secretion by D-cells was stimulated by high glucose but was attenuated after 2 days. No correlation could be found between the concentration of hormone in the media and a possible effect on a specific islet secretion. However, the fact that insulin secretion by islets cultured in high glucose was decreased after two days may indicate a refractoriness produced by persistent hyperglycemia. Islets isolated from diabetic animals secreted more glucagon and less insulin than control islets. Somatostatin secretion was the same in both groups. It was concluded that paracrine relationships were relatively insignificant in the regulation of islet secretion in a prolonged culture environment and persistent high glucose reduced the B-cell response to glucose stimulation.

Islet cell growth and function. A reappraisal of the role of progesterone and prednisolone

The mechanism of the inhibitory effect of steroid hormones, progesterone and prednisolone on the incorporation of [3H]-thymidine into pancreatic islet cell DNA was investigated. Treatment with either hormone had no effect on the incorporation of 32P-orthophosphate into islet cell DNA. Both prednisolone (10 microM) and progesterone (3 microM) markedly stimulated the activity of the enzyme thymidylate synthetase of islet cells possibly leading to increased synthesis of endogenous thymidine which resulted in dilution of the [3H]-thymidine added to the islets in tissue culture. Prednisolone (10 microM) significantly increased both insulin biosynthesis and release, while at 5 microM it was effective in increasing only insulin release. In contrast, progesterone at the two concentrations employed did not affect insulin biosynthesis or release. The smaller doses of both hormones markedly stimulated the total protein biosynthesis.

Glucocorticoids stimulate the division of rat pancreatic islet tumour cells in tissue culture

The effects of hormones on the growth of beta cells, obtained from an X-ray induced transplantable rat islet cell tumour, were studied in tissue culture. Cells were cultured in Dulbecco's modified medium containing 1% bovine serum albumin, which did not permit fibroblast outgrowth. Among a variety of different hormones tested, the most potent growth promoters were found to be the corticosteroids whose potency was related to their glucocorticoid activity. After 5 weeks in culture with prednisolone (270 nmol/l), all cells stained immunohistochemically for insulin, although the insulin content was decreased to 10% that of fresh cells. Growth hormone (10 micrograms/ml) stimulated DNA replication to a small extent in the presence or absence of glucocorticoids. Insulin secretion from freshly prepared tumour cells was not stimulated by glucose but was increased two- to threefold by leucine (20 mmol/l) plus theophylline (5 mmol/l). This pattern of stimulation was observed still in cells cultured for 4 weeks in prednisolone-supplemented medium.

Submandibular glands as organs of synthesis and accumulation of insulin-like protein

Experiments are presented to determine the endocrine function of submandibular salivary glands in the light of a hypothesis about synthesis of insulin-like protein (ILP) and participation of these organs in regulation of the glucose level in the organism. ILP was discovered in submandibular glands of male mice, rats, hamsters, cats, rabbits, pigs, bulls, and men. Electrophoretical and immunological studies of insulin-like protein, extracted from these glands, showed its similarity with pancreatic insulin. Immunofluorescent studies showed that ILP was localized in the granular duct cells of mice and rats. Studies by immunoperoxidase method illustrated that insulin-like protein was distributed along the periphery of the electron-dense secretory granules. In submandibular glands of animals which do not contain granular ducts, ILP was revealed in the striated tubules (by immunofluorescent method). Study of submandibular glands in vitro showed that ILP was synthesized in glands and not simply accumulated there. Under the condition of insulin deficiency (in vivo) and increased glucose concentration in culture media (in vitro), duct cells of submandibular glands released ILP in increasing amounts. Injection of ILP into mice caused a decrease of glucose concentration in the blood and a convulsive reaction. This fact indicates the similarity of ILP with insulin in its physiological action. Our studies permit to draw the conclusion on the participation of submandibular glands in the regulation of glucose homeostasis.

Effects of the rodenticide Vacor on cultured rat pancreatic beta cells

Human ingestion of the rodenticide Vacor has been implicated in the onset of diabetes mellitus. We report here studies of the effects of Vacor on cultured rat pancreatic beta cells and fibroblasts to determine if this agent preferentially intoxicates insulin-producing beta cells. Cytotoxicity in beta cells was monitored both by phase contrast microscopy and the release of insulin into the culture medium. Changes in cellular protein were correlated with morphologic observations to determine fibroblast viability. Beta cells were 10-fold more sensitive to the toxic effects of Vacor than were fibroblasts. Vacor toxicity was reduced by treatment with nicotinamide but was unchanged by 3-O-methyl glucose. Both of these agents reduced the toxic effects of the known beta cell poison streptozotocin. The present studies indicate that Vacor possesses a toxic affinity for pancreatic beta cells and that its mechanism of toxicity may be similar but not identical to that of streptozotocin.

Use of pancreatic beta cells in culture to identify diabetogenic N-nitroso compounds

Epidemiological observations suggest that environmental factors play a role in the pathogenesis of insulin dependent diabetes mellitus (1). Several chemicals have been identified as specific beta cell toxins (2-4). We report here studies to determine the feasibility of using monolayer cultures of pancreatic beta cells from neonatal rat to screen potential diabetogenic chemicals. Cytotoxicity was monitored both by phase microscopy and the release of insulin into the culture medium. In comparative studies, cellular protein and release of 51chromium (51Cr) were measured after addition of test compounds to cultures of fibroblasts derived from pancreatic tissue. The nitrosoamides 1 methyl-l-nitrosourea (MNU), 1,3 bis (2-choroethyl) nitrosourea (BCNU), chlorozotocin (CLZ), and the beta cell toxin, streptozotocin (SZ), were examined. CLZ and SZ were more toxic to pancreatic beta cells than to fibroblasts. In contrast, MNU and BCNU damaged both beta cells and fibroblasts at identical concentrations. These results suggest that in vitro techniques can be used to identify chemicals that selectively injure beta cells. Although SZ-induced toxicity was ameliorated with addition of nicotinamide to cultures of beta cells, nicotinamide did not prevent damage caused by CLZ. This observation indicates different mechanisms of drug-induced cytotoxicity.

Microcarriers: a new approach to pancreatic islet cell culture

Free islet cell suspensions were prepared from isolated fetal rat islets using a modified enzyme dispersion technique. The islet cells were dispensed into a culture flask containing microcarriers (Cytodex) suspended in culture medium RPMI 1640 by a slowly rotating bar magnet. Microscopical examination of the beads showed that the islet cells attached and then progressively proliferated on the surface of the beads as a monolayer. A highly sustained release of insulin from the beads to the medium was observed during the 7 d culture period. The functional viability of the cultured islet cells was further demonstrated by the ability of batches of the cell-coated beads to synthesize insulin and to increase the insulin release in response to an acute challenge (16.7 mmol/l glucose plus 5 mmol/l theophylline). The results suggest that bead microcarriers may provide a new approach to monolayer islet cell culture providing functional monolayers, which can easily be transferred to different test systems and further manipulated.

Maintenance of adult hamster pancreas cells on fibroblastic cells

The maintenance of primary cultures of adult hamster pancreatic cells on layers of irradiated C3H/10T1/2 cells was studied. Various types of pancreatic cells, acinar, islet and ductular cells could be identified in the cultures by light and electron microscopy. Morphologically the various pancreatic cells retained many differentiated characteristics of their respective in vivo cells types. Insulin production was maintained at near Day 1 levels for the 16 d in culture for which it was measured. Colonies of epithelial cells continued to grow during a 20 d culture period. It is believed that this procedure for maintaining functional and growing pancreas cells in culture may be a useful in vitro model for studying the initiation of pancreatic carcinogenesis.

Cyclic adenosine-3',5'-monophosphate stimulates islet B cell replication in neonatal rat pancreatic monolayer cultures

A possible role for cyclic adenosine 3',5'-monophosphate (cAMP) in islet B cell replication was examined in neonatal rat pancreatic monolayer cultures. Islet cells deteriorated and insulin release decreased during 12 d of culture in medium with 5.6 mM glucose, whereas the cells survived and insulin release increased during culture in medium with 5.6 mM glucose plus the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX, 0.1 mM), or in medium with 16.7 mM glucose with or without IBMX. IBMX also increased the mitotic index and stimulated dose-dependent increases in [(3)H]thymidine incorporation in nuclei of islet B cells in aldehydethionine stained radioautographs; maximal stimulation of B cell replication occurred with addition of 0.1 mM IBMX to 5.6 mM glucose (+170%, P < 0.001), and this increase was similar to that observed with 16.7 mM glucose (+185%, P < 0.001). Also, 8-bromo-adenosine-3',5-monophosphate, but not 8-bromo-guanosine-3',5'-monophosphate produced dose-dependent increases in islet B cell replication in medium with 5.6 mM glucose. Measurement of cAMP levels in the cultures revealed dissociations between effects on B cell replication and insulin release. Thus, addition of 0.1 mM IBMX, or 0.1 nM cholera toxin, to 5.6 mM glucose produced slightly greater increases in cAMP levels and B cell replication than did 16.7 mM glucose, whereas insulin release was increased significantly more with 16.7 mM glucose. Also, addition of 0.1 mM IBMX, or 0.1 nM cholera toxin, to 16.7 mM glucose stimulated further increases in cAMP levels and insulin release in the cultures, but no further increases in B cell replication. We conclude that (a) cAMP stimulates islet B cell replication, (b) cAMP may mediate the effects of glucose on B cell replication, and (c) mechanisms regulating B cell replication may be more sensitive to cAMP and/or different from those regulating insulin secretion.

Multichannel analysis of intracellular control and intercellular transfer of molecules

The metabolic regulation and exchanges within intracellular organelles or a cell cluster are studied by multichannel microfluorometry and microinjection of metabolites or tracers. The determination of structure-function relationships relies on the retrieval of cells after microfluorometry, for subsequent morphological evaluation. Rate constants of coenzyme reduction-reoxidation were deduced from a mathematical model of NAD(P) in equilibrium with NAD(P)H transients due to microinjection of metabolites into cultured cells belonging to a variety of normal or malignant lines. Nuclear and cytoplasmic sites operate synchronously or not, depending upon metabolic demand or pathological alterations. Intercellular transit times are determined for tracers and metabolites. Within cell clusters 'communicating territories' are described, which can show metabolically a multicellular integrated state. Microfluorometry in conjunction with ultrastructural and other studies can be used to develop a cybernetic model of the living cell, also yielding dynamic models of cooperative and regulatory interactions between different kinds of specialised cells within a cell cluster.

Fetal and neonatal rat pancreas in organ culture: age-related effects of corticosterone on the development of the islet cells

Fetal (18 days postcoitum) and neonatal (3-day) pancreatic explants were grown in organ culture with or without supplementation with corticosterone (0.1 micrograms/ml). After 0, 4, and 8 days of culture, the specific hormone-positive, islet cell volumes were determined by the use of immunocytochemical and morphometric methods. The insulin, glucagon, and somatostatin contents of the explants were estimated by radioimmunoassays. In the fetal explants, all of the islet cell populations increased in volume and the content of each of the hormones increased over an 8-day period of culture. Supplementation with corticosterone resulted in a restriction of the increases of the alpha and delta cell volumes and in the somatostatin content of the explants. In the neonatal explants, the volumes of the alpha and delta cells and the glucagon and somatostatin contents decreased over a 4-day culture period. The presence of corticosterone in the culture medium preserved these cells and their hormone content. Co-culture of 18-day fetal and 3-day neonatal pancreata in control medium for 8 days resulted in a significant decrease in the content of all three of the islet hormones in the fetal explants. These results suggest that a substance harmful to the islet cells is released from the degenerating acinar cells. Thus, the effects of the steroid on the islets may be mediated through its effects on the acinar tissue.

Intercellular communication in pancreatic islet monolayer cultures: a microfluorometric study

Single islet cells in monolayer cultures of neonatal rat pancreas were microinjected with fluorescein and scanned topographically by microfluorometry. Fluorescein spread from an injected islet cell directly into neighboring islet cells, and, in the presence of 16.7 millimolar glucose, significantly more islet cells communicated with the injected cell than in glucose-free medium. Islet cells were also microinjected with glycolytic substrates and activators that produced transient changes in cellular levels of reduced pyridine nucleotides-nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate [NAD(P)H]. Changes in NAD(P)H fluorescence were observed in islet cells incubated first for 18 hours in very low glucose concentrations and then in a glucose-free medium and injected with glycolytic substrates and activators; however, little change of fluorescence occurred in adjacent islet cells. In contrast, after adding 16.7 millimolar glucose to the medium, injection of glycolytic substrates and activators produced transient changes in NAD(P)H fluorescence in the injected cell and in neighboring cells.

Development in vitro of epithelial-cell monolayers derived from fetal rat pancreas

Purified epithelial-cell monolayers were generated in vitro from explants of fetal rat pancreas. The extent of the development of the epithelial monolayer, as determined by planimetric analysis, was enhanced by the application of two methodological procedures: (a) preincubation of fetal pancreas in situ at 27 degrees C for 5 hr prior to dissection and explantation; and (b) incubation of the explants in medium containing a high concentration (50% to 70%) of fetal bovine serum. By utilizing such culture conditions, sheets of contiguous epithelial cells, with little or no peripheral fibroblastic contamination, were maintained for 9 days. Whereas the majority of cells within the monolayer had morphological characteristics of pancreatic ductal cells, endocrine cells were identified by the specific immunocytochemical localization of insulin and glucagon. In addition, insulin could be detected in the incubation medium throughout the course of experiment. The simplicity of this preparation offers some advantages over other techniques including reduced chance of contamination and reduced cellular damage or death. It provides a model for future studies directed toward developing individual cell strains derived from pancreatic epithelial cells.

Isolated mouse pancreatic islets in culture: effects of serum and different culture media on the insulin production of the islets

Various conditions for tissue culture of collangenase-isolated mouse pancreatic islets were studied in an attempt to optimize the maintenance of glucose stimulated insulin biosynthesis and release in the cultured specimens. Islets which had been cultured at a physiological glucose concentration (5.5 mmol/1) in the absence of serum had an impaired glucose-stimulated insulin biosynthesis and release as well as a reduced insulin content. Thus, insulin biosynthesis was three times higher after culture in a serum supplemented medium. Further, the insulin secretion of islets cultured in the presence of serum was markedly enhanced in acute incubations with high concentrations of glucose. This response was most pronounced in islets which had been cultured free-floating. A comparison between different culture media showed that islets cultured in RPMI 1640 had the highest insulin production. The present data suggest that the most favourable conditions for long-term storage of isolated islets in culture may be obtained when the islets are maintained as free-floating explants in a culture medium consisting of RPMI 1640 supplemented with serum.

"Somatostatinoma": a somatostatin-containing tumor of the endocrine pancreas

We studied the pancreatic and enteric hormone profile of a 46-year-old woman who had hyperglycemia and a pancreatic tumor. Before operation, there was no evidence of overproduction of glucagon or insulin. The tumor's ultrastructure had a distinctive endocrine morphology, resembling D cells. Prompted by the recent demonstration of somatostatin in D cells of pancreatic islets, we analyzed the tumor and found a large quantity of immunoreactive somatostatin (301 ng per milligram of tissue). Insulin, glucagon, gastrin, vasoactive intestinal polypeptide and human pancreatic polypeptide were present in only trace quantities. The tumor cells were cultured in monolayers, which remained viable up to 51 days and released somatostatin into the culture medium. In seven insulinomas and two glucagonomas, we found the somatostatin content either much lower (less than 0.6 ng per milligram of tissue) or undetectable. After complete resection of the tumor, our patient became euglycemic and has remained so for the past 20 months.

The ultrastructure of polyploid B-cells in the islets of normal mice

Light and electron microscopic studies of diploid, tetraploid and octaploid B-cells in the islets of normal C57BL/KsJ mice revealed that polyploid cells were characterized by a wider range of granulated states than diploid B-cells. The maximum granule densities were similar for polyploid and diploid cells; however, some polyploid cells were almost devoid of granules, while the least granulated diploid cells contained intermediate granule densities. The tetraploid cell also appeared to be characterized by an increased mitochondrial stage which suggests compensation for the greater degree of degranulation. These observations were confirmed by morphometric analysis. Two interpretations of the apparent polyploidy are discussed; that polyploid B-cells may be more responsive to insulin releasing stimuli than diploid B-cells and that tetraploid cells may only be diploid cells in the G2 phase of the mitotic cycle.

Pancreatic-islet fibrosis in young infants of diabetic mothers

Pancreatic-islet fibrosis was found at necropsy in six out of ten infants (aged 11-142 days) born to diabetic mothers. Fibrosis covered an islet area of 5-10% in three cases, 10-20% in two cases, and more than 20% in one case. The three infants with the most pronounced islet fibrosis were heavier than normal at birth, and at least two of them were of "diabetic appearance" at birth. Five of the six cases with islet fibrosis had major malformations.

Beta cell culture on synthetic capillaries: an artificial endocrine pancreas

Beta cells from neonatal rats were cultured on bundles of artificial capillaries perfused with tissue culture medium. Cells continued to release insulin and remained responsive to changes in glucose concentration. The quantity of insulin released was similar to that of conventional flask cultures.

Proliferative and functional impairment of pancreatic epithelial cells maintained in vitro

Studies on the proliferative and functional properties of epithelial cells from human and guinea pig pancreatic tissue were presented and discussed. A novel technique for the isolation of epithelial cell groupings as colonial aggregates in two dimensional culture was utilized. More conventio;al clonal analyses were also performed. Irrespective of the methodology employed, epithelial cells from both species exhibited reduced proliferative activity with time in vitro. Total degeneration occurred in less than five months in every case studied. Aggregates and colonial aggregates, formed using fractionated suspensions containing up to 95% guinea pig acinar cells, were found to release amylase only during the first few days in vitro. Positive response to secretogogue stimulation was interpreted as evidence favoring the thesis that permanent cellular damage had not been sustained during tissue dissociation. These findings were discussed with reference to the phenomenon of human fibroblast degeneration with time in culture. Differences between fibroblast and epithelial cell behavior in vitro and in vivo were emphasized.

Purification of monolayer cell cultures of the endocrine pancreas

Experimental use of primary cultures of endocrine pancreas is constrained by early, vigorous proliferation of fibroblastoid cells. The addition of heavy metals, sodium ethylmercurithiosalicylate, phenyl mercuric acetate, phenyl mercuric nitrate and sodium aurothiomalate to the culture media selectively destroys these fibroblastoid cells yielding highly enriched, morphologically intact, functionally competent endocrine cells that are capable of cell replication. This action of heavy metals appears to be due to reversible inhibition of sulfhydryl enzymes since glutathione and thioglycolate were demonstrated to completely inhibit the cytotoxic effects of the mercury and gold containing agents, respectively. Certain variables in the application of the mercurial agents to pancreatic endocrine cell cultures were defined, most notably the enhanced sensitivity of fetal vs. neonatal tissue, and in inverse relationship of cell density to effective toxicity. After removal of the heavy metal agent from the culture media, many pancreatic islets send out cytoplasmic projections, containing large numbers of oriented microtubules which serve as bridging units to adjacent endocrine cells. The sustained availability of virtually pure pancreatic endocrine cell cultures, which results from the application of mercury to the culture media will undoubtedly permit many aspects of the cell biology of the endocrine pancreas to be directly and sequentially assailed.

Monolayer cultures derived from neonatal hamster pancreas. Light and electron microscopy

Cells derived by trypsinization of neonatal golden hamster pancreas were cultured in modified Eagle's medium for 120 h in the presence of glucose (0.8 mg/ml) and for an additional 48 h in medium containing glucose (0.8 or 3.1 mg/ml) or tolbutamide (1,000 microg/ml) plus glucose (0.8 mg/ml). At day 7, cultures were stained differentially for light microscopy or examined by electron microscopy. Immunoreactive insulin (IRI) and immunoreactive glucagon (IRG) in the culture medium were measured by standard immunoassay procedures. Staining properties and ultrastructural appearance of cultured cells were comparable to those of the intact neonatal hamster pancreas. Cultures consisted predominantly of cells possessing aldehyde fuchsin positive (AF(+)) cytoplasmic granules resembling ultrastructurally those of the intact neonatal pancreatic beta cells and additionally, those of fibroblastoid, acinar, acino-insular, and aldehyde fuchsin negative (AF(-)) argyrophilic cells. IRI release rate by the cultured cells was increased in the presence of elevated glucose or tolbutamide which paralleled the loss of AF(+) granulation, but IRG release rate was suppressed by elevated glucose concentration. These findings indicate that these monolayer cultures consist of most of the cell types occurring in the neonatal pancreas, including endocrinologically competent islet cells.