Major species differences between humans and rodents in the susceptibility to pancreatic beta-cell injury

The ability of beta cells to endure assaults may be relevant in the development of insulin-dependent diabetes mellitus. This study examines the susceptibility of human pancreatic islets to agents that are cytotoxic for rodent beta cells--i.e., sodium nitroprusside (NP, a nitric oxide donor), streptozotocin (SZ), or alloxan. After 5-8 days in tissue culture, human or rodent islets were exposed for 14 h to NP (50-200 microM) or for 30 min to SZ or alloxan (1-3 mM). Glucose oxidation by human islets was not reduced by NP, but there was a dose-dependent inhibition in rat (40-90% inhibition; P < 0.001) and mouse (10-60% inhibition; P < 0.05) islet glucose oxidation. Glucose (16.7 mM)-induced insulin release by human islets was not impaired after a 30-min exposure to SZ or alloxan, at concentrations that inhibited insulin release from rat (30-80% inhibition; P < 0.001) or mouse (10-70% inhibition; P < 0.05) islets. The viability of human beta cells purified by flow cytometry was not affected by SZ or alloxan (5 mM), as judged 1 or 4 days after a 10-min exposure and subsequent culture; these conditions were cytotoxic for rat beta cells, with 65-95% (P < 0.01) dead beta cells after 4 days. Human islets transplanted under the kidney capsule of nude mice were not affected by in vivo alloxan exposure, as suggested by preserved graft morphology and insulin content, whereas the endogenous beta cells of the transplanted mice were severely damage (80% decrease in pancreatic insulin content and morphological signs of beta-cell destruction). Thus human beta cells are resistant to NP, SZ, or alloxan at concentrations that decrease survival and function of rat or mouse beta cells. These marked interspecies differences emphasize the relevance of repair and/or defense mechanisms in beta-cell destruction and raise the possibility that such differences may also be present among individuals of the same species.

Physiologic relevance of heterogeneity in the pancreatic beta-cell population

In vitro studies on purified rat beta cells have indicated a functional diversity among insulin-containing cells. Intercellular differences were found in the rates of glucose-induced insulin synthesis and release. They are attributed to differences in cellular thresholds for glucose utilization and oxidation, as can be caused by varying activities in rate limiting steps such as glucokinase-dependent phosphorylation. The percent of functionally active beta cells increases dose-dependently with the glucose concentration, making cellular heterogeneity and its regulation by glucose major determinants for the dose-response curves of the total beta-cell population. Beta cells which are already responsive to low glucose concentrations are characterized by a higher content in pale immature granules; their activated biosynthetic and secretory activity accounts for preferential release of newly-formed hormone by the total beta-cell population. At any glucose level, the amplitude of insulin release depends on the percent glucose-activated cells and their cyclic AMP content, an integrator of (neuro)hormonal influences. The in vitro described heterogeneity in beta-cell functions may bear physiological relevance as several of its characteristics are also detectable in intact pancreatic tissue; furthermore, in vitro signs of heterogeneity can be altered by prior in vivo treatment indicating that they express properties of the cells in their in situ configuration. Elevated basal levels of (pro)insulin may reflect the existence of an increased number of beta cells that are activated at low physiologic glucose concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose induces oscillatory Ca2+ signalling and insulin release in human pancreatic beta cells

Mechanisms of pulsatile insulin release in man were explored by studying the induction of oscillatory Ca2+ signals in individual beta cells and islets isolated from the human pancreas. Evidence was provided for a glucose-induced closure of ATP-regulated K+ channels, resulting in voltage-dependent entry of Ca2+. The observation of step-wise increases of capacitance in response to depolarizing pulses suggests that an enhanced influx of Ca2+ is an effective means of stimulating the secretory activity of the isolated human beta cell. Activation of muscarinic receptors (1-10 mumol/l carbachol) and of purinergic P2 receptors (0.01-1 mumol/l ATP) resulted in repetitive transients followed by sustained elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i). Periodic mobilisation of intracellular calcium was seen also when injecting 100 mumol/l GTP-gamma-S into beta cells hyperpolarized to -70 mV. Individual beta cells responded to glucose and tolbutamide with increases of [Ca2+]i, manifested either as large amplitude oscillations (frequency 0.1-0.5/min) or as a sustained elevation. Glucose regulation was based on sudden transitions between the basal and the two alternative states of raised [Ca2+]i at threshold concentrations of the sugar characteristic for the individual beta cells. The oscillatory characteristics of coupled cells were determined collectively rather than by particular pacemaker cells. In intact pancreatic islets the glucose induction of well-synchronized [Ca2+]i oscillations had its counterpart in 2-5 min pulses of insulin. Each of these pulses could be resolved into regularly occurring short insulin transients. It is concluded that glucose stimulation of insulin release in man is determined by the number of beta cells entering into a state with Ca(2+)-induced secretory pulses.

Preservation of glucose-responsive islet beta-cells during serum-free culture

This study describes a serum-free medium in which adult rat islet beta-cells can be cultured in suspension for at least 9 days without a detectable loss in cell number or function. The medium is composed of Ham's F-10 with 10 mM glucose, 1% BSA, and 50 microM isobutylmethylxanthine. After 9 days of culture, beta-cell aggregates had preserved their initial DNA content, with more than 80% ultrastructurally intact cells. Their rates of glucose-inducible insulin synthesis (64 +/- 13 fmol/10(3) cells.2 h) and release (173 +/- 44 fmol/10(3) cells.2 h) were comparable to those previously determined in overnight cultured beta-cells. Their secretory response to 20 mM glucose plus 10(-8) M glucagon was biphasic and 10-fold elevated above the basal level. Their secretory and biosynthetic activities at basal (1.25 mM) glucose levels were significantly higher than after culture with serum. These elevated basal activities are attributed to a rise in the proportion of beta-cells with high content in pale secretory granules. Supplementing the serum-free medium with GH (1 micrograms/ml) plus glucagon (10(-8) M) further increased basal activities, leading to cellular degranulation and reduced hormone release after stimulation. Control cultures in Ham's F-10 with 10 mM glucose and 10% fetal calf serum reduced the initial DNA content by 40% and, consequently, the total amount of hormone synthesis and release. Surviving cells exhibited a lower secretory responsiveness than those recovered from serum-free medium; their lower basal activities coincided with an absence of cells with high content in pale granules. It is concluded that preservation of glucose-responsive beta-cells during suspension culture requires conditions that keep the cells recruited into glucose-dependent functions. Such a condition is achieved by the presently defined serum-free medium. It is characterized by the presence of a subpopulation of beta-cells with a high proportion of pale secretory granules.

Effect of nutrients, hormones and serum on survival of rat islet beta cells in culture

This study quantifies the survival of purified single rat beta cells under different culture conditions. Less than 10% of the cells survive 9 days of culture in Ham's F10 medium without supplements. Addition of fetal calf serum (5%) increases cell survival to 54% in the absence and to 78% in the presence of isobutylmethylxanthine (50 mumol/I). The effect of serum is explained, at least partly, by the presence of albumin and of low molecular weight constituents. In serum-free Ham's F10 with 50 mumol/l isobutylmethylxanthine, 75% of cells survive after the addition of bovine serum albumin (1%) and of ultroser (0.2%), a commercial serum substitute. Survival of at least 75% of cells is also maintained in Ham's F10 with isobutylmethylxanthine plus albumin, and supplemented by metabolizable nutrients or by the peptides glucagon (10(-8) mol/l) or growth hormone (1 micrograms/ml) plus insulin like growth factor-I (50 ng/ml). D-Glucose increases beta-cell survival in a dose-dependent manner up to 10 mmol/l; a beneficial effect is also observed with other metabolizable compounds (leucine and glutamine) but not with non-metabolizable monosaccharides. Glucose-induced survival of islet beta cells can be attributed to its dose-dependent recruitment of cells into metabolic activities; however, a 9-day exposure to excessively high nutrient concentrations (> 20 mmol/l glucose) is deleterious to the cells. These results define culture media, with or without serum, wherein at least 75% of single rat islet beta cells can survive for a minimum of 9 days. This will allow for studies on beta-cell toxic conditions and potentially protective agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced glutamate decarboxylase activity in rat islet beta cells which survived streptozotocin-induced cytotoxicity

Rat pancreatic beta cells exhibit a 16-fold higher glutamate decarboxylase (GAD) activity than islet non-beta cells, but a similar glutamate dehydrogenase (GDH) activity. beta Cells which survive exposure to 2 mM streptozotocin only contain 10 percent of the GAD activity of control cells, but their GDH activity remains unaltered. Culture of streptozotocin-treated beta cell preparations with 2 mM nicotinamide reduces the number of dead cells and prevents in part the decline in GAD activity of surviving beta cells. These data indicate that loss in activity of the beta cell specific enzyme GAD can serve as marker for beta cells which survived a destructive process. It is furthermore demonstrated that nicotinamide increases the percent surviving cells and decreases their loss in GAD activity.

Effect of streptozotocin and nicotinamide upon FAD-glycerophosphate dehydrogenase activity and insulin release in purified pancreatic B-cells

Purified rat pancreatic insulin-producing B-cells, which display a 12-fold higher activity of FAD-linked glycerophosphate dehydrogenase than other islet endocrine cells, were exposed for 30 min to 2 mM streptozotocin and subsequently cultured for 2 days in the absence or presence of 2 mM nicotinamide. Streptozotocin decreased by 54% the number of B-cells and, in surviving cells, lowered by 75% the activity of FAD-linked glycerophosphate dehydrogenase, whilst failing to affect that of glutamate dehydrogenase. This coincided with a 42-51% reduction of insulin secretion, when expressed relative to either the DNA or hormonal content of surviving cells. After exposure to streptozotocin, the presence of nicotinamide in the culture medium reduced cell death by 44% and also reduced the deleterious effects of streptozotocin upon both the enzymic and secretory activities of surviving cells. These findings indicate that the decreased activity of FAD-linked glycerophosphate dehydrogenase previously documented in pancreatic islets from streptozotocin-injected rats, as well as the protective effect of nicotinamide thereupon, are not attributable solely to changes in the number of B-cells but also to an altered enzymic activity in surviving B-cells. The latter anomaly may account, in part at least, for an impaired B-cell secretory response to D-glucose.

Interaction of interleukin-1 with islet beta-cells. Distinction between indirect, aspecific cytotoxicity and direct, specific functional suppression

A 5-day culture of adult rat islets with human recombinant IL-1 beta (3 U/ml) resulted in the death of most alpha-cells and 50% of beta-cells. The IL-1--exposed islet tissue contained--in addition to poorly granulated beta-cells--patches of outgrowing monolayers and dispersed activated macrophages. In purified alpha- and beta-cell preparations, no cytodestructive effects of IL-1 (as high as 30 U/ml) were noticed, indicating that the cytokine is in itself not a beta-cell--selective killer. Pure beta-cells were, on the other hand, more sensitive (from 0.3 U/ml on) than intact islets to an IL-1--induced suppression of hormone synthesis. This inhibitory action was reversible and affected predominantly the production of insulin, leading to degranulated cells with modified shape and attachment. Further studies with IL-1 should take into account that isolated islet preparations do not allow distinction between its irreversible, indirect, and aspecific beta-cell toxicity and its reversible, direct, and specific suppression of beta-cell functions. It is not yet known whether IL-1--suppressed beta-cells exhibit an altered sensitivity to beta-cell--toxic conditions.

Aldehyde tanning: the villain in bioprosthetic calcification

Preservation of bioprosthetic valves may play a role in valvular calcification. Subcutaneous implants in rats were used to test the effect of different preservation solutions. Fifty male Sprague-Dawley rats were divided into five groups. Fresh bovine pericardium was treated in one of five ways: group A: 99.5% glycerol for 1 week; group B: as group A, then normal saline wash and 0.25% formaldehyde storage for 24 h; group C: as group A, then normal saline wash and 4% formaldehyde storage for 24 h; group D: as group A, then normal saline wash and 0.625% glutaraldehyde storage for 24 h; group E: 0.625% glutaraldehyde and 4% buffered formaldehyde storage. Treated bovine pericardium was cut into 1-cm2 pieces and washed for 30 min with normal saline before implantation. In each animal, three pieces were implanted in the subcutaneous tissue of the back. After 70 days, retrieved specimens were examined grossly, and X-ray densitometry, calcium analysis, and histological examinations were carried out. The results showed that glycerol-treated tissue (group A) had less calcification (calcium 6.92 +/- 4.46 micrograms/mg dry weight) than other groups: group B (calcium 323.12 + 63.56 micrograms/mg dry weight); group C (calcium 240.65 + 13.47 micrograms/mg dry weight); group D (calcium 232.29 + 13.01 micrograms/mg dry weight). These differences were markedly significant (p less than 0.0001). It appears that aldehydes play an important role in the calcification of bioprosthetic valves. Experience with glutaraldehyde- and glycerol-treated pericardium in valvular applications in sheep support these observations.

Corneal oxygen scavenging systems: lysis of corneal epithelial cells by superoxide anions

The cornea has inherent protection from superoxide radicals from the presence of superoxide dismutase. However, the dismutation of these radicals results in the generation of hydrogen peroxide. The corneal scavenging systems for hydrogen peroxide is minimal as there are only low levels of catalase and glutathione peroxidase present. We have demonstrated the cytolytic capabilities of oxygen radicals in the cornea and reversed this lysis with catalase. These data indicate that hydrogen peroxide is the primary damaging agent in this system.