Masahiko Igarashi

Hypersecretion of Truncated Glucagon‐like Peptide‐1 and Gastric Inhibitory Polypeptide in Obese Patients

Postprandial insulin secretion is modulated by both neural and humoral gastrointestinal insulinotropic factors in addition to the absorbed nutrient. To investigate the involvement of the potent insulinotropic hormones gastric inhibitory polypeptide (GIP) and truncated glucagon‐like peptide‐1 (tGLP‐1) in the postprandial hyperinsulinaemia of obesity, we examined the changes in plasma levels of GIP and tGLP‐1 by an oral glucose tolerance test (OGTT) in nine normal subjects (controls), nine obese subjects without glucose intolerance (Group A), and six obese mild diabetic patients (Group B). Following the OGTT, plasma GIP levels in Group B were increased more markedly than those in the other two groups. Plasma levels of tGLP‐1 were estimated by the difference between the values measured with the N‐terminal directed antiserum (GLP‐1NT) and those with the C‐terminal directed antiserum (GLP‐1 CT). Plasma levels of GLP‐1 NT were increased in Group B, but decreased in the other two groups. Plasma GLP‐1 CT levels were increased in all groups with the highest response in Group B. These results suggest that the combined augmentation of plasma GIP and tGLP‐1 responses were involved in the delayed and considerable increases in plasma insulin after glucose ingestion in obese diabetic patients. Since tGLP‐1 is suppressed in the hyperglycaemic hyperinsulinaemic state in normal subjects, the augmented tGLP‐1 response appears to be characteristic of obese Type 2 diabetes.

Prevalence of Diabetes and Impaired Glucose Tolerance in Funagata Area, Japan

OBJECTIVE To determine the prevalence of diabetes mellitus and IGT in the Funagata area of Japan. RESEARCH DESIGN AND METHODS The total eligible subjects was 1163, all were > or ≥45 yr of age, and 52 were known diabetic patients. Data collected included body height, weight, and answers to medical questionnaires. A 75-g OGTT was done in the morning. WHO criteria were used to classify the current diabetes status of study participants. RESULTS Of the 1111 scheduled for the OGTT, 868 took the test; the participation rate was 77.8%. The prevalence of diabetes was 10.5 and 12.9%, and the prevalence of IGT was 14.7 and 18.0% for men and women, respectively. The prevalence of undiagnosed diabetes (4.9%) was almost equal to that of previously diagnosed diabetes (4.5%). CONCLUSIONS The prevalence of diabetes in the Funagata area was two to four times higher than that of previous reports in Japan, in which many investigators used a urinary glucose test as a preliminary test. This difference is attributed to the method of determining the prevalence of diabetes.

Calpain 10 gene polymorphisms are related, not to type 2 diabetes, but to increased serum cholesterol in Japanese

A G-to-A (UCSNP-43) polymorphism of the calpain-10 gene was significantly associated with type 2 diabetes (DM) in Mexican-American, and was postulated, together with a T-to-C (UCSNP-44) polymorphism, as a risk factor for DM. We examined the association of these genotypes with DM in Japanese. Eighty-one subjects with DM and 81 non-diabetic subjects (NGT) were recruited. The number of subjects with genotypes UCSNP-43 G/G, G/A and A/A were 76, 5 and 0, respectively, for the DM and NGT groups. The number of subjects with genotypes UCSNP-44 T/T, T/C and C/C were 66, 14 and 1 for the DM group and 64, 17 and 0 for the NGT group. There was no difference between the groups in terms of frequency of any genotype combinations. No association between the genotypes and DM was observed. We next examined the differences between the genotypes or genotype combinations in terms of the traits related to DM, obesity, hypertension and dyslipidemia. No differences were observed between the genotypes UCSNP43 G/G and G/A, between UCSNP-44 T/T and the others, or between the genotype combination UCSNP-43 G/G and UCSNP-44 T/T and the others, except that the individuals with the genotype combination had significantly increased serum cholesterol levels (212.6 +/- 34.3 vs. 198.5 +/- 29.9, P=0.020). The genotype combination might be a risk factor, not for DM, obesity and hypertension, but for increased serum cholesterol.

Suppression of neointimal thickening by a newly developed HMG-CoA reductase inhibitor, BAYw6228, and its inhibitory effect on vascular smooth muscle cell growth

The aim of this study was to determine whether BAYw6228 (BAYw), a newly developed 3‐hydroxy‐3‐methylglutaryl‐CoA (HMG‐CoA) reductase inhibitor, could suppress an atherogenic process such as intimal thickening by a mechanism other than lowering the level of serum cholesterol. First, we evaluated the in vitro effect of BAYw on the proliferation of vascular smooth muscle cells (SMC) from various species: Sprague‐Dawley (SD) rats, New Zealand (NZ) white rabbits, intimal cells from Watanabe hereditary hyperlipidemic (WHHL) rabbit and SMC from the new‐born human aorta. The increasing rate of total protein content of these cells was inhibited by the addition of BAYw in a dose‐dependent fashion. In the presence of 2% foetal calf serum (FCS), the value of IC50 was 1.0 μm in SD rats. 2.1 μm in NZ white rabbits, and 0.3 μm in WHHL rabbits. With human SMC, the value was 0.02 μm in the presence of 10% FCS and 0.2 μm with a mixture of growth factors. Based on these above in vitro findings, we next examined the in vivo effect of the agent to determine whether it could suppress rabbit intimal thickening induced by balloon catheterization. A balloon catheter was inserted from a peripheral branch of the left external carotid artery to the aorta to denude the endothelium of the left common carotid artery in Japanese white rabbits. After 12 days they were divided into control and BAYw groups. The former were subcutaneously injected with saline and the latter with BAYw 1 mg kg−1 day−1. Two days after the beginning of treatment, a second balloon injury was performed to the previously injured left common carotid artery in both groups. After another two weeks, the left common carotid artery was removed and variously stained. Although the total serum cholesterol in the BAYw group was significantly lower than in the control (P<0.05), the difference was not enough to affect intimal thickening. In addition, the BAYw group had a smaller intima/media ratio than the control group, decreasing to 45% of control (P<0.05). By anti‐α smooth muscle actin antibody staining, these intimal thickening areas were entirely occupied by SMCs, and their amount was attenuated by BAYw. By anti‐rabbit macrophage antibody (RAM 11) staining, the number of positive cells in the intimal thickening was markedly decreased in the BAYw group compared to control (P<0.01). These results indicate that BAYw has an inhibitory effect on intimal thickening by attenuating intimal SMC proliferation and infiltration of macrophages, suggesting that BAYw could be effective in the prevention of the progression of atherosclerotic plaque‐like restenosis after angioplasty.

Altered PDGF-BB–Induced p38 MAP Kinase Activation in Diabetic Vascular Smooth Muscle Cells: Roles of Protein Kinase C-δ

Objective—We investigated the regulation of p38 mitogen-activated protein kinase (MAPK) by platelet-derived growth factor (PDGF)-BB and its biological effects in cultured normal and diabetic rat vascular smooth muscle cells (VSMCs). Methods and Results—VSMC growth from diabetic rats was faster than that from normal rats. The expression of the PDGF &bgr;-receptor in diabetic VSMCs was significantly elevated compared with that in normal cells, and PDGF-BB–induced p38 phosphorylation in diabetic cells was more enhanced via MAPK kinase (MKK) 3/6. The level of PKC activity in diabetic cells increased more than that in normal cells with or without PDGF-BB. Although protein kinase C (PKC)-&bgr;II and PKC-&dgr; were activated by diabetes, PDGF-BB could further enhance the level of PKC-&dgr; alone. PDGF-BB–induced cell migration was more elevated in diabetic VSMCs, and the increase was significantly inhibited by SB-203580, rottlerin, and antisense oligodeoxynucleotides for PKC-&dgr;. PDGF-BB–induced p38 phosphorylation also regulated cell growth, cyclooxygenase-2 levels, and arachidonic acid release, but not apoptosis. These levels were more elevated in diabetic cells, which were inhibited by SB-203580. Conclusions—Our study established that PDGF-BB phosphorylated p38 via PKC-&dgr; and the subsequent MKK 3/6, leading to cell growth regulation and the progression of a chronic inflammatory process in diabetic VSMCs.

Nifedipine suppresses neointimal thickening by its inhibitory effect on vascular smooth muscle cell growth via a MEK-ERK pathway coupling with Pyk2

The aim of this study was to determine whether nifedipine could suppress an atherogenic process such as balloon‐injured intimal thickening in vivo and the proliferation of vascular smooth muscle cells (VSMC) in vitro. First, we examined the in vivo effect of nifedipine to determine whether it could suppress intimal thickening induced by balloon catheterization. Sprague‐Dawley (SD) rats were divided into three groups (L, nifedipine 0.3 mg kg−1 day−1; H, nifedipine 3 mg kg−1 day−1; C, no nifedipine), and Alzet® osmotic pumps were implanted in their backs for continuous administration. The neointimal layers were completely occupied by proliferated VSMC, and the area ratios of neointima/media treated with nifedipine significantly decreased dose‐dependently compared to those of the control. Neither blood pressure nor lipid levels changed among the three groups. We next evaluated the in vitro effect of nifedipine on the proliferation of cultured rat VSMC. Nifedipine decreased the values of [3H]‐thymidine incorporation and total cellular protein content as well as the levels of phosphorylated extracellular signal‐regulated protein kinase (ERK) 1/2, mitogen‐activated protein kinase kinase (MEK) 1/2, and even the phosphorylation of Pyk2, in dose‐dependent fashions. In addition, nifedipine suppressed the levels of proliferative cell nuclear antigen (PCNA) dose‐dependently in both VSMC and balloon‐injured thoracic aortae. These results indicate that nifedipine has an inhibitory effect on intimal thickening by attenuating intimal VSMC proliferation, suggesting that nifedipine could be effective for preventing the progression of atherosclerotic plaque as in restenosis after angioplasty.

Differences in glucagon-like peptide- 1 and GIP responses following sucrose ingestion

To investigate the mechanism of oral carbohydrate-stimulated secretion of the two most potent incretin candidates, gastric inhibitory polypeptide (GIP) and truncated glucagon-like peptide-1 (tGLP-1), we studied the changes in the plasma levels of these peptides in five healthy men after sucrose ingestion with or without pretreatment with an alpha-D-glucosidase inhibitor (AO-128). After sucrose ingestion, plasma levels of GIP peaked at 15 min and remained high up to 120 min. Plasma levels of GLP-1 NT measured with antiserum R1043 (N-terminal specific) tended to decrease gradually and those of GLP-1 CT measured with antiserum R2337 (C-terminal specific) increased. Therefore, estimated plasma levels of tGLP-1 increased markedly within 30 min, then declined slightly over the next 60 min. After treatment with AO-128 (0.6 mg/day) for 1 week, increases in plasma glucose and insulin levels were attenuated and the increase in plasma GIP levels was diminished, while the increase in tGLP-1 levels was sustained much longer. It is concluded that GIP secretion is stimulated by glucose absorption and tGLP-1 secretion by the presence of sucrose in the gut.

Diagnostic criteria for Werner syndrome based on Japanese nationwide epidemiological survey

Aim:  Werner syndrome (WS) is an autosomal recessive disorder of progeroid symptoms and signs. It is caused by mutations in the WRN gene, which encodes a RecQ DNA helicase. The aim of this study was to revise the diagnostic criteria for Japanese Werner syndrome.

Response of truncated glucagon-like peptide-1 and gastric inhibitory polypeptide to glucose ingestion in non-insulin dependent diabetes mellitus : effect of sulfonylurea therapy

Gastric inhibitory polypeptide (GIP) and truncated glucagon like peptide-1 (tGLP-1) are potent gastrointestinal insulinotropic factors (incretin), mostly released after a meal or ingestion of glucose in man and animals. To investigate whether sulfonylurea (SU) affects the secretion of incretin, the modulation of plasma GIP and tGLP-1 levels following glucose ingestion in non-insulin-dependent diabetic type 2 patients with or without SU therapy was studied. A 75-g oral glucose tolerance test (OGTT) was carried out on 9 healthy subjects (controls) and 18 patients with non-obese type 2, 9 of whom were treated by diet alone (NIDDM-diet) and the other 9 with SU (glibenclamide 2.5 mg or gliclazide 40 mg) once a day (NIDDM-SU). Plasma GIP was measured by radioimmunoassay (RIA) with R65 antibody, and GLP-1 was measured by RIA with N-terminal-directed antiserum R1043 (GLP-1NT) and C-terminal-directed antiserum R2337 (GLP-1CT). Following OGTT, plasma glucose, GIP, GLP-1NT, and GLP-1CT in type 2 patients increased more markedly than in controls, despite the lower response of insulin. However, there were no significant differences in plasma levels of these peptides between the NIDDM-diet and NIDDM-SU groups. Therefore, it is unlikely that SU is involved in the high response of GIP and GLP-1s to OGTT in type 2 patients.

Effects of seishin-renshi-in and Gymnema sylvestre on insulin resistance in streptozotocin-induced diabetic rats

Although there is no concept of insulin resistance in traditional Kampo (Chinese) medicine and Indian medicine, we had the hypothesis that some drug in a mixture of crude drugs which was believed to ameliorate diabetes mellitus may have had the effect of improving insulin resistance. To test this hypothesis, the effects of Seishin-renshi-in (Chinese medicine) and Gymnema sylvestre (Indian medicine) on the insulin resistance of streptozotocin-induced diabetic rats was studied by the glucose clamp technique. Oral administration of Seishin-renshi-in (800 mg/kg/day) with injections of a minimum dose of Ultralente insulin decreased urine volume and urinary glucose excretion during a 7-day treatment period and improved the insulin stimulated glucose uptake in peripheral tissues, as well as improving the insulin suppressed hepatic glucose output during glucose clamp. However, G. sylvestre (120 mg/kg/day) treatment did not improve insulin resistance. We conclude that Seishin-renshi-in, with a small dose of insulin, improved insulin resistance in streptozotocin-induced diabetic rats, but Gymnema sylvestre did not.