Pancreatic beta cell toxicity by streptozotocin anomers.

D-glucose in the pyranose (ring) form exists as two anomers. The alpha-anomer is more effective than the beta-anomer in promoting insulin secretion, suppressing that of glucagon, and protecting beta-cells against alloxan toxicity. Streptozotocin (SZ), a beta cell toxin, is composed of a cytotoxic moiety, 1-methyl 1-nitrosourea, attached to carbon-2 of glucose and exists as either of two anomers in the pyranose form. In 24-hour-fasted male rats, predominantly alpha- or predominantly beta-SZ was injected intravenously and plasma glucose levels were obtained 48 hours later. The alpha-anomer produced significantly greater beta-cell necrosis at doses of 30, 35, and 40 mg./kg. body weight. At higher doses, no differences between the alpha and beta anomers were observed. 3-O-Methyl glucose (3-OMG) protected against both SZ anomers; however, the alpha-SZ remained more toxic. Larger doses of glucose protected against the lower doses of SZ and, under such conditions, the individual glucose anomers appeared equally potent. Finally, mannitol at comparable molar concentrations was ineffective in protecting against the SZ toxicity. This study suggests that streptozotocin's beta cell toxicity is mediated through recognition by the beta cell. In addition, 3-OMG and, to a lesser but significant extent, glucose were shown to protect against the streptozotocin toxicity, whereas mannitol did not.

Renal amyloidosis in KK mice that may be misinterpreted as diabetic glomerulosclerosis.

A normoglycemic, normoinsulinemic, "lean" phenotype KK mouse having a morphologically normal pancreatic islet had renal lesions reminiscent of diabetic glomerulosclerosis described in the literature for KK mice. Most of these animals also had splenomegaly. Using histochemical and ultrastructural methods, the renal and splenic lesions were demonstrated to be amyloidotic. Extensive deposits of amyloid were found in the liver and adrenals. Amyloidosis was found in all lean KK mice 4 months of age or older and in five of 11 C57BL/6J mice over 1 year of age. The validity of data attributing glomerulosclerosis to diabetes in mice that are neither glucosuric nor hyperglycemic or that show normal tolerance to glucose load should be questioned until amyloidosis is ruled out.

Effect of diabetogenic nitrosourea on the activity of the pentose phosphate hunt in isolated islets.

The effect of streptozotocin (STZ) on the activity of the pentose phosphate shunt in islets was studied. Isolated rat islets were pre-incubated with glucose (1.7 mM) alone or with streptozotocin (STZ) or N-methyl-N-nitrosourea (MNU). The effects of these pretreatments on glucose metabolism and insulin secretion were assessed during subsequent incubation with either (1.14C), (6.14C). or (U.14C). glucose (16.7 mM) alone or plus phenazine methosulfate (PMS). Islets pretreated with STZ (1.5 mM) metabolized less (1.14C) and (U.14C). glucose. The order of inhibition by STZ of (14C)-glucose metabolism by islets was: (1.14C). greater than (U.14C). greater than (6.14C)-glucose. Whereas PMS (0.5 mM) increased the metabolism of both (U.14C). and (1.14C)-glucose, the metabolism of (6.14C)-glucose by STZ-pretreated islets was not increased by PMS. In a separate series of experiments, the total NADP+ + NADPH, but not the NAD content of the islets decreased after 2 min exposure of islets of STZ. At 30-min exposure, the levels of both pyridine coenzymes and that of 6-phosphogluconate were significantly decreased. The level of NADP+ + NADPH in islets was decreased more than the level of NAD. Insulin secretion was suppressed by the nitrosoureas. PMS (0.5 mM) increased the level of NADP+ + NADPH content of islets and augmented insulin secretion. It is concluded that the pentose phosphate pathway is inhibited on brief exposure of islets to STZ or MNU. Such inhibition may contribute to the suppression of insulin secretion caused by these nitrosoureas.

A comparison of the effects of streptozotocin, N-methylnitrosourea and alloxan on isolated islets of Langerhans.

Isolated normal rat islets were pre-incubated with Streptozotocin (STZ), N-methylnitrosourea (MNU) or alloxan for 5, 10, 30 or 60 minutes at 0 degree C or 37 degrees C, and then were washed and incubated at 37 degrees C for 60 minutes with glucose (16.7 mM). Suppression of the insulinotropic response to glucose during incubation required 10 minutes of pre-incubation with the nitrosoureas whose effects were directly related to concentration and were temperature dependent. The suppressive effects of both nitrosoureas could be reduced or abolished by simultaneous addition to the pre-incubation media of nicotinamide, 2-deoxyglucose or 3-0-methyl-glucose, but were unaffected by reduced glutathione, glucosamine, N-acetylglucosamine or mannoheptulose. Unlike the nitrosoureas, alloxan was B-cytotoxic at 0 degree C. The effect of alloxan at 0 degree C was blocked by glutathione but not by glucose. The evidence in this study is inconsistent with the concept that the glucose moiety of STZ promotes entry and action of this nitrosourea in pancreatic islet cells. Secondly, it shows that the immediate B-cytotoxic action of alloxan differ from that of STZ or MNU and is not abolished by decrease in temperature.

The characterization of phenazine methosulfate stimulated insulin secretion.

This investigation was initiated to characterize the stimulation of insulin secretion by phenazine methosulfate (PMS). Islets of Langerhans, isolated by the collagenase method from normal rats and rats pre-injected with either streptozotocin or 6-aminonicotinamide, were exposed to PMS under various experimental conditions and insulin secretion in response to PMS, glucose and pyridine nucleotides was determined. Insulin releasing action of PMS was dose-, time- and temperature-related, occurred in the absence of glucose, and was inhibited by epinephrine, but not by mannoheptulose. In the perifusion system, the pattern of response induced by PMS was spike-like release reaching a maximum in 5 min and declining rapidly to half-maximal value in 10 min. After exposure of islets to beta-cytotoxin either in vivo or in vitro, complete reversal of the cytotoxic effect was obtained with PMS which induced release of insulin in both normal and beta-cytotoxin islets pre-treated. It is concluded that islets depleted of coenzymes could still secrete insulin in response to a reactive proton donor, which might act by substituting for coenzymes and that the immediate action of beta-cytotoxins does not completely arrest the secretory mechanisms in islets of Langerhans.

Abnormalities in pelvic visceral nerves. A basis for neurogenic bladder in the diabetic Chinese hamster.

In order to determine whether bladder dysfunction and hydronephrosis in diabetic Chinese hamsters are associated with nerve pathology, the pelvic visceral nerves of diabetic and normal hamsters were examined with histochemical and electron microscopic techniques. Acetylcholinesterase activity was reduced in the nerves and on smooth muscle fibers in the urinary bladder of diabetic hamsters when compared to controls. Depression of enzyme staining was most marked in those hamsters with the most severe hydronephrosis. Frequent examples of aberrant myelination were found in the pelvic plexus and urinary bladder of diabetics. Many of these myelinated fibers exhibited wide periaxonal spaces lined by unusual processes of Schwann cells. An increase in the number of microtubules in axons and circular profiles of Schwann cells, which failed to enclose axons, gave evidence of axonal degeneration or Schwann cell injury in diabetic nerves. These findings suggest that pathologic changes in pelvic visceral nerves may underlie urinary bladder dysfunction in the diabetic Chinese hamster.