Hisayuki Miura

Increase in insulin release from rat pancreatic islets by quinolone antibiotics

1 The present study was undertaken to elucidate the mechanism(s) of hypoglycaemia caused by quinolone antibiotics. We investigated the effects of various quinolone antibiotics on insulin release in rat pancreatic islets. 2 At a non‐stimulatory concentration of 3 mM glucose, lomefloxacin (LFLX) or sparfloxacin at 1 mM and pipemidic acid (0.1‐1 mM) induced slight insulin release but tosufloxacin or enoxacin up to 100 μm did not. 3 At the stimulatory concentration of 10 mM glucose, all quinolones augmented insulin release in a dose‐dependent manner. LFLX (100 μm) shifted the dose‐response curve of glucose‐induced insulin release to the left without altering the maximal response. 4 At 10 mM glucose, LFLX (100 μm) increased insulin release augmented by forskolin (5 μm) or 12‐0‐tetradecanoyl phorbol‐13‐acetate (100 nM) but not by raising the K+ concentration from 6 to 25 mM. 5 Verapamil (50 μm) or diazoxide (50–400 μm) antagonized the insulinotropic effect of LFLX. 6 These data suggest that quinolone antibiotics may cause hypoglycaemia by increasing insulin release via blockade of ATP‐sensitive K+ channels.

Inhibition of angiogenesis on glycated collagen lattices

Summary Advanced glycation endproduct (AGE) accumulation in extracellular matrix proteins has been demonstrated in diabetic patients with a significant correlation with the severity of diabetic complications. AGE accumulation induces matrix protein cross-link formation, resulting in an increased stiffness of matrix fibres and the reduction of the susceptibility of matrix proteins to proteolytic degradation. We examined whether glycation-induced collagen cross-linking may affect vascular endothelial cell behaviours such as invasion, proliferation and differentiation, using the in vitro angiogenesis model of capillary-like structure formation in three-dimensional matrices of collagen type I. Endothelial cells cultured on collagen gel with angiogenic factors (the combination of fibroblast growth factor-2 and vascular endothelial growth factor) invaded the underlying collagen matrix, and organized capillary-like cord structures in the gel. We found that endothelial cell invasion into glycated collagen gel was significantly attenuated without any effect on proteinase activity including cell-associated plasminogen activator and matrix metalloproteinase in the conditioned medium. In addition, subsequent capillary-like cord formation was also inhibited in glycated collagen gel. In contrast, endothelial cell proliferation was enhanced on glycated collagen gel with or without angiogenic factors compared with control collagen gel. These results suggest that the structural alterations of extracellular matrix proteins through the glycation-induced cross-link formation affect the interaction between endothelial cell and extracellular matrix, resulting in the impairment of an adequate neovascularization in diabetic patients. [Diabetologia (1998) 41: 491–499]

Up-regulation of vascular endothelial growth factor in response to glucose deprivation

Vascular endothelial growth factor (VEGF), also known as a vascular permeability factor (VPF), is an endothelial specific mitogen and is a potent inducer of angiogenesis. Recently it has been reported that hypoxia induces VEGF mRNA expression in various cells. Since both oxygen and glucose are required for efficient production of energy, we examined the effect of glucose deprivation on VEGF mRNA expression and VEGF protein production in U‐937 (a human monocytic cell line) cells. Both the mRNA expression and secretion of VEGF increased after exposure to low glucose. Addition of L‐glucose, the L‐stereoisomer of D‐glucose, did not prevent the up‐regulation of VEGF expression. The conditioned medium from glucose‐deprived cells, followed by supplementation with glucose, did not up‐regulate VEGF mRNA expression in U‐937 cells. The low glucose‐induced VEGF mRNA expression returned to the control level after supplementation with D‐glucose. Furthermore, oligomycin, a mitochondrial ATP synthase inhibitor, increased VEGF protein production. The results suggest that the up‐regulation of VEGF mRNA in U‐937 cells in response to glucose deprivation is not mediated by autocrine factors from the cells nor is the osmotic change of the medium mediated by the deficiency of glucose metabolism in the cells. Our results also suggest that the intracellular ATP depletion due to glucose deprivation may be one of the causes for increased VEGF mRNA expression. We speculate that local hypoglycemia may act as an essential trigger for angiogenesis through the VEGF gene expression.

Validity of the Kihon Checklist for assessing frailty status

The Kihon Checklist is extensively used in Japan to identify elderly persons who are at risk of requiring support/care. We aimed to determine whether or not the Kihon Checklist can estimate frailty status defined by the Cardiovascular Health Study criteria.

Cognitive function in Japanese elderly with type 2 diabetes mellitus

The current study was conducted to investigate the cognitive function in Japanese elderly with type 2 diabetes mellitus (DM). Participants included 69 diabetic and 27 nondiabetic subjects (60 to 85 years old). The cognitive functional tests conducted were the Mini-Mental State Examination (MMSE), Word Lists Recall (immediate, delayed), Digit Symbol Test (Wechsler Adult Intelligence Scale-Revised [WAIS-R]), and the Stroop Color Word Test. Hemoglobin A1c (HbA1c) was measured as the index of glycemic control, and information about recent hypoglycemic episodes was gathered by using questionnaires. Students t test showed that DM subjects had significantly lower scores in the MMSE (P<.01) and Digit Symbol Test (P<.05) than non-DM subjects. The scores of the Digit Symbol Test in diabetes subjects had a significant negative relationship with HbA1c (r=-.433; P<.001), and insulin-use had a significant relationship with the scores of the MMSE and Digit Symbol Test. Subjects in the DM group were further divided by insulin use. Comparison of insulin-treated DM subjects, non-insulin-treated DM subjects, and nondiabetic subjects by analysis of variance followed by Bonferronis post hoc test showed that insulin-treated DM subjects had significantly lower scores in the MMSE and Digit Symbol Tests than both non-insulin-treated DM subjects (P<.05) and nondiabetic subjects (P<.01). Our study suggests that Japanese elderly DM subjects, especially those with insulin treatment, have poor cognitive function.

Long-term multiple risk factor interventions in Japanese elderly diabetic patients: the Japanese Elderly Diabetes Intervention Trial--study design, baseline characteristics and effects of intervention.

Aim:  To evaluate long‐term, multiple risk factor intervention on physical, psychological and mental prognosis, and development of complications and cardiovascular disease in elderly type 2 diabetes patients.

Dietary fat-induced increase in blood pressure and insulin resistance in rats.

Objectives To determine whether the dietary-fat-induced increase in blood pressure is caused by excess energy intake or the fat composition of the diet, what type of fat increases the blood pressure, and whether insulin resistance is involved in the dietary-fat-induced increase in blood pressure. Methods In a series of experiments, rats received: chow alone or chow supplemented with lard or sucrose to provide 33% of a total energy content increased by 50%; chow alone or chow in which 50% of the energy content was from substituted lard, safflower oil or medium-chain triglyceride oil; or chow alone or chow in which 50% of the energy content was from substituted lard, with or without troglitazone. Systolic blood pressure (SBP) was measured every week during each 8-week feeding period. A steady state serum glucose method was used to determine the insulin sensitivity after the lard substitution with or without troglitazone. Results Both the lard and sucrose enrichment increased SBP and body weight compared with controls. Lard substitution significantly increased SBP and immunoreactive insulin, although body weight did not differ from control. Neither a diet substituted with safflower oil nor one substituted with medium-chain triglyceride oil influenced SBP. Troglitazone completely inhibited the increase in SBP and immunoreactive insulin induced by the lard. The steady-state serum glucose concentration was significantly greater after the lard substitution than after isoenergetic chow; this effect also was reversed by troglitazone. Conclusion Chronic feeding with lard increased SBP in rats, independently of excess energy intake. Of the fats tested, lard exerted an intrinsic pressor effect. Troglitazone reversed the lard-induced increase in SBP.

Neostigmine-induced hyperglycemia is mediated by central muscarinic receptor in fed rats

We previously reported that neostigmine injected into the third cerebral ventricle stimulated adrenal secretion of epinephrine, secretion of glucagon from the pancreas, and direct neural innervation of the liver, resulting in hepatic venous plasma hyperglycemia in anesthetized fed rats. However, receptor type of these 3 mechanisms is not known. Therefore, we examined the effects of intraventricularly injected cholinergic or adrenergic antagonists on neostigmine-induced catecholamines in intact rats, glucagon secretion which is mediated by direct neural innervation of pancreas in bilateral adrenalectomized (ADX) rats, and hepatic venous hyperglycemia which is mediated by direct neural innervation of liver in ADX rats receiving constant infusion of somatostatin from femoral vein. Atropine injected into the third cerebral ventricle suppressed epinephrine secretion and dose-dependently inhibited hepatic venous hyperglycemia induced by neostigmine in intact rats. The neostigmine-induced glucagon secretion which occurs in ADX rats was suppressed by atropine. Atropine also prevented the neostigmine-induced hyperglycemia in ADX rats receiving constant somatostatin infusion through femoral vein (ADX-Somato rats). On the other hand, phentolamine, propranolol and hexamethonium showed no significant inhibitory effect on neostigmine-induced hyperglycemia, epinephrine and glucagon secretion in intact rats, glucagon secretion in ADX rats, or hyperglycemia in ADX-Somato rats. These results suggest that neostigmine-induced epinephrine and glucagon secretion and increased hepatic glucose output stimulated by direct neural innervation to liver is mediated by central muscarinic receptor in fed rats.

Non-high-density lipoprotein cholesterol: an important predictor of stroke and diabetes-related mortality in Japanese elderly diabetic patients.

Aims:  To evaluate the association of low‐density lipoprotein, high‐density lipoprotein and non‐high‐density lipoprotein cholesterol with the risk of stroke, diabetes‐related vascular events and mortality in elderly diabetes patients.

The elevation of plasma adrenocorticotrophic hormone and expression of c-Fos in hypothalamic paraventricular nucleus by microinjection of neostigmine into the hippocampus in rats: comparison with acute stress responses.

We have reported that the microinjection of neostigmine into the hippocampus of rats induced responses similar to stress responses in terms of catecholamines and glucose in plasma. In order to test the hypothesis that hippocampal neostigmine injection is a possible animal model of acute stress responses, we investigated c-Fos expression in the hypothalamic paraventricular nucleus (PVN) and plasma levels of adrenocorticotrophic hormone (ACTH) after hippocampal neostigmine injection and compared these levels with those resulting from stressful conditions such as immobilization and insulin-induced hypoglycemia. The patterns of expression of Fos-ir in the PVN after microinjection of neostigmine into the hippocampus were not different from those seen in the two stressful situations. After microinjection of neostigmine, plasma ACTH levels significantly increased. Taken together, the results of this study indicate that microinjection of neostigmine into the hippocampus is a potential experimental model for acute stress responses.