Kenzo Uchida

Receptor gene expression of glucagon-like peptide-1, but not glucose-dependent insulinotropic polypeptide, in rat nodose ganglion cells.

We previously reported that afferent signals of the rat hepatic vagus increased upon intraportal appearance of insulinotropic hormone glucagon-like peptide-1(7-36) amide (GLP-1), but not glucose-dependent insulinotropic polypeptide (GIP). To obtain molecular evidence for the vagal chemoreception of GLP-1, the concept derived from those electrophysiological observations, receptor gene expressions of GLP-1 and GIP in the rat nodose ganglion were examined by means of reverse transcriptase-mediated polymerase chain reaction (RT-PCR) and Northern blot analysis. Gene expression of the GLP-1 receptor was clearly detected by both RT-PCR and Northern blot analysis. In situ hybridization study confirmed that the expression occurs in neuronal cells of the ganglion. As to the GIP receptor, RT-PCR amplified the gene transcript faintly though Northern blot analysis failed to detect any messages. However, semi-quantitative RT-PCR revealed that the ratio of the gene expression level of the GIP receptor to that of the GLP-1 receptor was less than 1:250, indicating that receptor gene expression of GIP is practically negligible in the ganglion. Additionally, an equal level of GLP-1 receptor gene expressions between left- and right-side ganglia was evidenced by semi-quantitative RT-PCR, implying possible extrahepatic occurrence of vagal GLP-1 reception in addition to the reception through the hepatic vagus (originating from the left-side ganglion). The present results offer, for the first time, the molecular basis for the vagal chemoreception of GLP-1 via its specific receptor.

Increased basal levels of plasma nitric oxide in Type 2 diabetic subjects Relationship to microvascular complications

To assess the underlying mechanisms of decreased endothelial function and advanced vascular complications in patients with Type 2 diabetes, we determined basal levels of plasma nitric oxide (NO(x): NO(2)(-) and NO(3)(-)) using a newly developed high-performance liquid chromatography (HPLC)-Griess method in hospitalized 129 diabetic and 76 nondiabetic subjects, and examined their clinical characteristics. Serum lipid peroxide and advanced glycation end products (AGEs) as markers of oxidative stress were also measured, and intima-media thickness (IMT) of the carotid artery was evaluated as a marker of atherosclerosis. In diabetic subjects, microvascular complications were newly evaluated during their admission. There were no differences in age or sex between the diabetic and nondiabetic subjects. Although there was no difference in basal plasma NO(2)(-) levels between the two groups, the basal levels of plasma NO(3)(-) in diabetic subjects were significantly higher than those in nondiabetic subjects. Plasma NO(x) levels in neither diabetic nor nondiabetic subjects correlated with serum lipids, HbA1c, or IMT. In diabetic subjects, plasma NO(3)(-) levels were related not only to the presence of hypertension but also to advanced microvascular complications. Moreover, plasma NO(3)(-) levels were positively correlated with both serum lipid peroxide and AGEs. Multiple regression analysis revealed that serum AGEs level was strongly associated with plasma NO(3)(-) level. Thus, the findings are consistent with the hypothesis that decreased endothelium-dependent vasodilation in diabetic subjects is associated with the impaired action of NO secondary to its inactivation resulting from increased oxidative stress, rather than decreased NO production from vascular endothelium, and that abnormal NO metabolism is related to advanced diabetic microvascular complications.

The hepatic vagal reception of intraportal GLP-1 is via receptor different from the pancreatic GLP-1 receptor.

Glucagon-like peptide-1 (7-36)amide (tGLP-1), a representative humoral incretin, released into the portal circulation in response to a meal ingestion, exerts insulinotropic action through binding to the tGLP-1 receptor known to be a single molecular form thus far. We previously reported that the hepatic vagal nerve is receptive to intraportal tGLP-1, but not to non-insulinotropic full-length GLP-1-(1-37), through a mechanism mediated by specific receptor to the hormone. In the present study, we aimed to examine how modification of the receptor function alters this neural reception of tGLP-1, by using the specific agonist, exendin-4, and the specific antagonist, exendin (9-39)amide, of the receptor at doses known to exert their effects on the insulinotropic action of tGLP-1. Intraportal injection of 0.2 or 4.0 pmol tGLP-1, a periphysiological and pharmacological dose, respectively, facilitated significantly the afferent impulse discharge rate of the hepatic vagus in anesthetized rats, as reported previously. However, unexpectedly, intraportal injection of exendin-4 at a dose of 0.2 or 4.0 pmol, or of even 40.0 pmol, did not facilitate the afferents at all. Moreover, intraportal injection of exendin (9-39)amide at 100 times or more molar dose to that of tGLP-1, either 5 min before or 10 min after injection of 0.2 or 4.0 pmol tGLP-1, failed to modify the tGLP-1-induced facilitation of the afferents. The present results suggest that the neural reception of tGLP-1 involves a receptor mechanism distinct from that in the well-known humoral insulinotropic action.

The hepatic vagal nerve is receptive to incretin hormone glucagon-like peptide-l, but not to glucose-dependent insulinotropic polypeptide, in the portal vein

To examine whether incretin hormones, truncated glucagon-like peptide-1 (tGLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are recognized by the hepatic vagal nerve, changes of the impulse discharge rate in the afferent vagus upon their intraportal administrations were measured in situ in rats anesthetized with urethan and chloralose. One-min injection of tGLP-1 at a periphysiological dose of 0.2 pmol or a pharmacological dose of 4.0 pmol, but not of the vehicle, significantly facilitated the hepatic vagal afferents. However, the injection of GIP at either a physiological dose of 0.2 pmol, a periphysiological dose of 4.0 pmol, or an even much larger dose of 40.0 pmol did not change the afferents at all. The present results indicate that the hepatic vagus specifically recognizes an intraportal appearance of tGLP-1 in the hepatoportal area, suggesting that the vagal monitoring system for intraportal levels of the incretin hormone operates on ingestion of a mixed meal.

Testosterone inhibits tumor necrosis factor-α-induced vascular cell adhesion molecule-1 expression in human aortic endothelial cells

We investigated the effect of testosterone (T) on tumor necrosis factor‐α (TNF‐α)‐induced expression of vascular cell adhesion molecule‐1 (VCAM‐1) in human aortic endothelial cells. Incubation of these cells with T resulted in a dose‐dependent reduction in the expression, with this reduction completely abolished by a selective androgen receptor blocker. Electrophoretic mobility shift assay demonstrated that T inhibited TNF‐α‐induced activation of the transcriptional nuclear factor‐κB, which is critical for the inducible expression of VCAM‐1, probably through the suppression of the nuclear translocation. Our results may suggest an inhibitory effect of T on atherogenesis, providing a novel insight into the consideration of the pathogenesis of atherosclerosis.

Circadian Rhythm of Blood Pressure in Normotensive NIDDM Subjects: Its Relationship to Microvascular Complications

Objective To investigate the relationship between circadian rhythm of mean blood pressure (MBP) and microvascular complications in non-insulin-dependent diabetes mellitus (NIDDM) subjects. Research Design and Methods Seventy-six normotensive NIDDM subjects without azotemia were studied under ordinary hospital conditions with a noninvasive ambulatory blood pressure monitoring device. Time series data were analyzed by the cosinor method. Results Fifty-four subjects had a circadian MBP rhythm similar to that of 34 age-matched nondiabetic control subjects, with a peak value in the afternoon (group 1). In contrast, 22 had a reversed circadian MBP rhythm, with a peak value during the night (group 2). Obvious complications were found in 65% of group 1 and in all of group 2. The prevalence of retinopathy and somatic neuropathy and the degree of retinopathy were similar in the two groups. The prevalence and degree of autonomic neuropathy (postural hypotension and reduced beat-to-beat heart-rate variation) and nephropathy were greater in group 2 than group 1. Linear discriminant analysis revealed a correlation between the reversed circadian MBP rhythm and postural hypotension (F = 32.2, P < 0.001) and overt nephropathy (F = 5.1, P < 0.05) but not with beat-to-beat heart-rate variation (F = 0.17, NS). Conclusions These results suggest that in the hospitalized normotensive NIDDM subjects, there are normal and reversed circadian MBP rhythms and that the reversal of normal circadian MBP rhythm may be related to the degree of postural hypotension and/or nephropathy.

Effect of 24 weeks of treatment with epalrestat, an aldose reductase inhibitor, on peripheral neuropathy in patients with non-insulin-dependent diabetes mellitus

The effects of treatment with epalrestat, an aldose reductase inhibitor, on peripheral neuropathy were studied in 45 patients with non-insulin-dependent diabetes mellitus (NIDDM). Epalrestat 150 mg three times daily was given for 24 weeks. Subjective symptoms, such as spontaneous pain in the lower extremities and numbness and hypoesthesia of the extremities or trunk, were significantly (P < 0.001) relieved after 12 and 24 weeks of epalrestat treatment. Vibratory perception thresholds, as measured by using a tuning fork (C-128) and a vibrometer, were improved after 24 weeks of treatment. Furthermore, there were no adverse effects on glucose or lipid metabolism during treatment. These results suggest that long-term (24-week) epalrestat therapy can be used effectively to treat peripheral neuropathy in NIDDM patients without affecting glucose or lipid metabolism.

Reversed circadian blood pressure rhythm independently predicts endstage renal failure in non-insulin-dependent diabetes mellitus subjects.

To investigate the significance of reversed circadian blood pressure (BP) rhythm as a predictor for diabetic endstage renal failure, introduction of hemodialysis (HD) was determined as an end point in 325 noninsulin-dependent diabetes mellitus (NIDDM) subjects, in whom 24-h BPs had been monitored during their first admissions between 1988 and 1996. Circadian BP rhythm was analyzed by the COSINOR method, as previously reported. After exclusion of 68 dropout subjects, 257 were recruited for further analyses, in which 194 had normal circadian BP rhythms (N), and the remaining 63 had reversed rhythms (R). During this follow-up period, the numbers of HD-introduced subjects in N and R were 6 and 16, respectively, showing a higher prevalence in the latter (p < 0.001, chi2 test). Follow-up periods were significantly shorter in HD-introduced diabetic subjects of N and R than those in HD-free subjects of each group. In baseline characteristics, there were no differences in age, gender, or serum creatinine between HD-free and HD-introduced subjects of N or R. With regard to microvascular complications, the degree of retinopathy and nephropathy in N and R tended to be more pronounced in HD-introduced subjects than in HD-free subjects. Further, mean levels of circadian mean BP rhythms in HD-introduced subjects of N or R were similarly high, compared with those in HD-free subjects of each group, irrespective of circadian BP pattern. Unadjusted HD-free times were estimated by the Kaplan-Meier method, with a significant difference noted between N and R (p < 0.001; log-rank test). The Cox proportional-hazards model adjusted for circadian BP pattern, age, gender, blood pressure level, glycemic control, duration of diabetes, serum total protein, and serum creatinine demonstrated that circadian BP pattern, age, gender (female), blood pressure level (hypertension), and serum creatinine exhibited significant high relative risks. Thus, our data suggest that reversed circadian BP rhythm is an independent predictor of endstage renal failure in NIDDM subjects.

Mitochondrial DNA Mutations Are Associated with Both Decreased Insulin Secretion and Advanced Microvascular Complications in Japanese Diabetic Subjects

To assess the roles of various mitochondrial (Mt) DNA mutations in diabetic and nondiabetic subjects, we screened Mt DNAs at the 3243 base pair (bp) and its adjacent portion in unrelated Japanese diabetic and nondiabetic subjects. Furthermore, to clarify the clinical features of diabetic subjects harboring a Mt DNA mutation, we evaluated the ability of insulin secretion and microvascular complications in diabetic subjects. Five hundred thirty-seven diabetic patients and 612 unrelated nondiabetic subjects were recruited into this study. In Mt DNA analyses, Mt DNA was isolated from peripheral leukocytes of the subjects, and then an Mt DNA fragment surrounding the tRNA(Leu(UUR)) site was amplified by the polymerase chain reaction (PCR) using two sets of primers. These fragments were further digested with three kinds of restriction endonucleases and were subjected to agarose gel electrophoresis. When a mutation was present, Mt DNA fragments were directly sequenced with an autosequencer. Baseline characteristics in all subjects were examined, and microvascular complications and insulin secretory capacity in diabetic subjects were newly evaluated. Eight kinds of Mt DNA mutations, which were point mutations, were found in 74 subjects. Each affected subject had only one mutation in the Mt DNA examined. Among them, the mutations at np 3316, 3394, 3593, and 3391 were accompanied by amino acid replacement. Thirty-eight diabetic patients were affected (7.1%), including two subjects with a point mutation at np 3243, and 26 nondiabetic subjects were affected (4.2%). Thus, there was a higher prevalence in diabetic subjects than in nondiabetic subjects. There was no significant difference in the prevalence of maternally inherited diabetes between these two groups. The mean level of urinary C-peptide excretion was lower in diabetic subjects with an Mt DNA mutation (DM+) than in those without it (DM-). Although the prevalence of hypertension in DM+ was higher than that in DM-, diabetic retinopathy and nephropathy in DM+ were problematic, in comparison with those in DM-, when statistical corrections were performed for the effect of hypertension. Furthermore, a strategy based on logistic regression analysis revealed that advanced retinopathy and decreased urinary C-peptide excretion in all diabetic subjects studied were strongly related to the presence of Mt DNA mutation. Our results suggest that Mt DNA mutations in Japanese diabetic subjects are related to the development of diabetes, and also that these mutations are associated with not only a decrease in insulin secretion but also advanced diabetic microvascular complications.

Insulin Resistant State in Type 2 Diabetes Is Related to Advanced Autonomic Neuropathy

To elucidate the relationships between obesity, glycemic control, dyslipidemia, hypertension, microvascular complications, and insulin resistance assessed using an euglycemic hyperinsulinemic clamp technique, we studied 54 hospitalized type 2 diabetic subjects (DM) and 10 age‐ and sex‐matched normotensive, nonobese control subjects (C). Glucose infusion rate (GIR) derived from the clamp study was used as an index of insulin resistance. Body mass index (BMI), the prevalence of hypertension, HbA1c and serum nonesterified fatty acids (NEFA) were significantly higher, and serum high‐density‐lipoprotein (HDL)‐cholesterol was significantly lower in DM than in C (p < 0.05 or less). The median GIR level was significantly lower in DM than in C (p = 0.038). The difference in GIR between the two groups was still statistically significant even after adjustment for BMI, mean BP, HbA1c, NEFA, and HDL‐cholesterol. However, after simultaneous adjustment for these factors, there was no difference in GIR between the two groups. Body mass index, mean BP, HbA1c, and NEFA showed negative correlations, and serum HDL‐cholesterol showed a positive correlation with GIR, but neither age nor duration of diabetes correlated with GIR. When GIR values in DM were divided according to the degree of neuropathy, retinopathy, and nephropathy, and compared to those in C, GIR levels tended to be decreased with increasing severity of each microvascular complication, but there was no difference in median GIR levels among the diabetic subgroups. Relationships between the GIR levels and confounding factors such as age, sex, BMI, mean BP, HbA1c, serum NEFA, and serum HDL‐cholesterol, were examined simultaneously with a multiple regression analysis. This analysis revealed that HbA1c and serum NEFA may affect the GIR level. Furthermore, together with these two factors, the relationships between the GIR levels and the severity of each microvascular complication were explored with the same analysis. This model clearly demonstrated that both the decreased CVR‐R and pronounced orthostatic fall in systolic BP were independent factors for the decreased GIR. These findings suggest that marked autonomic dysfunction, rather than other confounding factors, is related to increased insulin resistance in DM.