Bradykinin enhances insulin receptor tyrosine kinase in 32D cells reconstituted with bradykinin and insulin signaling pathways

We have previously shown that bradykinin potentiated insulin-induced glucose uptake through GLUT4 translocation in canine adipocytes and skeletal muscles. The aim of this study was to determine the molecular mechanism of bradykinin enhancement of the insulin signal. For this purpose, 32D cells, which express a limited number of insulin receptors and lack endogenous bradykinin B2 receptor (BK2R) or insulin receptor substrate (IRS)-1 were transfected with BK2R cDNA and/or insulin receptor cDNA and/or IRS-1 cDNA, and analyzed. In 32D cells that expressed BK2R and insulin receptor (32D-BKR/IR), bradykinin alone had no effect on the phosphorylation of the insulin receptor, but it enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor. In 32D cells that expressed BK2R, insulin receptor and IRS-1 (32D-BKR/IR/IRS1), bradykinin also enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1. An increase in insulin-stimulated phosphorylation of IRS-1 by treatment with bradykinin in 32D-BKR/IR/IRS1 cell was associated with increased binding of 85 kD subunit of phosphatidylinositol 3 (PI 3)-kinase and increased IRS-1 associated PI 3-kinase activity. These effects of bradykinin were not observed in 32D cells which lack the expression of BK2R (32D-IR/IRS1) or insulin receptor (32D-BKR/IRS1). Furthermore, tyrosine phosphatase activity against insulin receptor beta-subunit in plasma membrane fraction of 32D-BKR/IR cells was significantly reduced by bradykinin, suggesting that the effect of bradykinin was in part mediated by inhibition of protein tyrosine phosphatase(s). Our results clearly demonstrated that bradykinin enhanced insulin-stimulated tyrosine kinase activity of the insulin receptor and downstream insulin signal cascade through the BK2R mediated signal pathway.

Cost-effectiveness of intensive insulin therapy for type 2 diabetes: a 10-year follow-up of the Kumamoto study

To evaluate the cost and effectiveness of intensive insulin therapy for type 2 diabetes on the prevention of diabetes complications in Japan, we performed economic evaluation based on a randomized controlled trial. A total of 110 patients with type 2 diabetes were randomly assigned into two groups, a multiple insulin injection therapy (MIT) group or a conventional insulin injection therapy (CIT) group, and were followed-up for 10 years. Economic evaluation (cost-consequences analysis) was applied to evaluate both health and economic outcomes. As outcome measures for effectiveness of intensive insulin therapy, the frequency of complications, such as retinopathy, nephropathy, neuropathy, macrovascular event, and diabetes-related death, was used. For estimating costs, a viewpoint of the payer (the National Health Insurance) was adopted. Direct medical costs associated with diabetes care during 10 years were calculated and evaluated. In a base case analysis, all costs were discounted to the present value at an annual rate of 3%. Sensitivity analyses were carried out to assess the robustness of the results to changes in the values of important variables. MIT reduced the relative risk in the progression of retinopathy by 67%, photocoagulation by 77%, progression of nephropathy by 66%, albuminuria by 100% and clinical neuropathy by 64%, relative to CIT. Moreover, MIT prolonged the period in which patients were free of complications, including 2.0 years for progression of retinopathy (P<0.0001), 0.3 years for photocoagulation (P<0.05), 1.5 years for progression of nephropathy (P<0.01) and 2.2 years for clinical neuropathy (P<0.0001). The total cost (discounted at 3%) per patient during the 10-year period for each group was $30310 and 31525, respectively. The reduction of total costs in MIT over CIT was mainly due to reduced costs for management of diabetic complications. Our results show that MIT is more beneficial than CIT in both cost and effectiveness. Therefore, MIT is recommended for the treatment of type 2 diabetic patients who require insulin therapy as early as possible from the perspective of both patients and health policy.

Long-term results of the Kumamoto Study on optimal diabetes control in type 2 diabetic patients

OBJECTIVE

To examine whether intensive glycemic control could decrease the frequency or severity of diabetic microvascular complications, an 8-year prospective study of Japanese patients with type 2 diabetes was performed.

RESEARCH DESIGN AND METHODS

A total of 110 patients with type 2 diabetes (55 with no retinopathy [the primary prevention cohort] and 55 with simple retinopathy [the secondary intervention cohort]) were randomly assigned to multiple insulin injection therapy (MIT) groups and administered three or more daily insulin injections or assigned to conventional insulin injection therapy (CIT) groups and administered one or two daily intermediate-acting insulin injections. Worsening of microvascular complications was regularly assessed during 8 years. Two or more steps up in the 19 stages of the modified Early Treatment of Diabetic Retinopathy Study classification in retinopathy and one or more stages up among three stages in nephropathy (normoalbuminuria, microalbuminuria, and albuminuria) were defined as worsening of complications.

RESULTS

In both primary prevention and secondary intervention cohorts, the cumulative percentages of worsening in retinopathy and nephropathy were significantly lower (P < 0.05) in the MIT group than in the CIT group. In neurological tests after 8 years, the MIT group showed significant improvement (P < 0.05) in the median nerve conduction velocities (motor and sensory nerves), whereas the CIT group showed significant deterioration (P < 0.05) in the nerve conduction velocities and vibration threshold. From this study, the glycemic threshold to prevent the onset and progression of diabetic microvascular complications was as follows: HbA1c < 6.5%, fasting blood glucose concentration < 110 mg/dl, and 2-h postprandial blood glucose concentration < 180 mg/dl.

CONCLUSIONS

Intensive glycemic control can delay the onset and progression of the early stages of diabetic microvascular complications in Japanese patients with type 2 diabetes.

Endothelin-1 inhibits apoptosis of vascular smooth muscle cells induced by nitric oxide and serum deprivation via MAP kinase pathway

Endothelin (ET)-1, an endothelium-derived vasoconstrictor and mitogen, acts as an antiapoptotic factor against serum deprivation-induced apoptosis of endothelial cells and fibroblasts but enhances apoptosis of some cancer cells. In the present study, we examined whether nitric oxide (NO) and ET-1 modulate apoptosis of rat vascular smooth muscle cells (VSMCs) via the mitogen-activated protein (MAP) kinase pathway. Both serum deprivation and NO donors (FK409 and SNAP) caused apoptosis of VSMCs, as demonstrated by TdT-mediated dUTP-biotin nick end-labeling, appearance of fragmented DNA, and induction of caspase-3 activity. ET-1 dose-dependently antagonized apoptosis induced by serum deprivation and NO donors. A selective ET(A) receptor antagonist (BQ123) and a nonselective ET(A/B) receptor antagonist (TAK044), but not a selective ET(B) receptor antagonist (BQ788), inhibited the antiapoptotic effect of ET-1, indicating that the antiapoptotic effect of ET-1 is mediated via the ET(A) receptor. ET-1 activated MAP kinase, whose effect was inhibited by FK409. Transfection with an unphosphorylated wild-type MAP kinase kinase-1 (MAPKK-1) or its constitutively activated mutant protected VSMCs against apoptosis induced by serum deprivation and NO donors. Inhibition of MAP kinase activity with PD98059, a specific inhibitor of MAPKK-1, or by transfection of a dominant-negative MAPKK-1 mutant antagonized the antiapoptotic effect of ET-1, suggesting the involvement of MAP kinase in the antiapoptotic effect. The potent inhibitory effect of ET-1 on apoptosis of VSMCs induced by serum deprivation and NO suggests that the counterbalance between the 2 endothelium-derived factors contributes to the process of vascular remodeling by determining VSMC survival and death, respectively, via a common MAP kinase pathway.

[Decision levels of diabetes mellitus and hyperlipidemia in elderly Japanese subjects]

Decision levels of diabetes mellitus and hyperlipidemia in elderly subjects as well as younger subjects should be determined to prevent complications of these diseases such as microvascular and macrovascular diseases. Therefore, prospective follow-up study is necessary to decide the decision levels. In the case of diabetes mellitus, there are some useful studies such as KUMAMOTO STUDY show that strict glycemic control can prevent microvascular diseases, but there are few studies in elderly subjects. However, hypoglycemia causes macrovascular events, and chronic hypoglycemia leads to dementia and apathy. It is generally accepted that the glycemic control level can be milder than that in younger subjects. We suggest that the following decision levels are reasonable for elderly diabetic subjects, 1. FPG > 140-160 mg/dl, 2. PG(2 h) > 200-250 mg/dl, 3. HbA1c > 7-8%. Decision level of hyperlipidemia in elderly subjects should also be determined to prevent cardiovascular disease. It is demonstrated that anti-hyperlipidemic treatment can prevent CHD even in elderly subjects by many prospective studies. Japan Atherosclerosis Society recommend that the decision levels of hyperlipidemia in elderly subjects can be the same as younger subjects. The decision levels indicating diet therapy and medication for risk factor free subjects(category A) are LDL-C > or = 140 and 160 mg/dl, respectively. Those for subjects without CHD but have some risk factors(category B) are LDL-C > or = 120 and 140 mg/dl, respectively. Those for subjects with CHD(category C) are LDL-C > or = 100 and 120 mg/dl, respectively.

Sites of action of protein kinase C and phosphatidylinositol 3-kinase are distinct in oxidized low density lipoprotein-induced macrophage proliferation

Oxidized low density lipoprotein (Ox-LDL) can induce macrophage proliferation in vitro. To explore the mechanisms involved in this process, we reported that activation of protein kinase C (PKC) is involved in its signaling pathway (Matsumura, T., Sakai, M., Kobori, S., Biwa, T., Takemura, T., Matsuda, H., Hakamata, H., Horiuchi, S., and Shichiri, M. (1997) Arterioscler. Thromb. Vasc. Biol. 17, 3013-3020) and that expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) and its subsequent release in the culture medium are important (Biwa, T., Hakamata, H., Sakai, M., Miyazaki, A., Suzuki, H., Kodama, T., Shichiri, M., and Horiuchi, S. (1998) J. Biol. Chem. 273, 28305-28313). However, a recent study also demonstrated the involvement of phosphatidylinositol 3-kinase (PI3K) in this process. In the present study, we investigated the role of PKC and PI3K in Ox-LDL-induced macrophage proliferation. Ox-LDL-induced macrophage proliferation was inhibited by 90% by a PKC inhibitor, calphostin C, and 50% by a PI3K inhibitor, wortmannin. Ox-LDL-induced expression of GM-CSF and its subsequent release were inhibited by calphostin C but not by wortmannin, whereas recombinant GM-CSF-induced macrophage proliferation was inhibited by wortmannin by 50% but not by calphostin C. Ox-LDL activated PI3K at two time points (10 min and 4 h), and the activation at the second but not first point was significantly inhibited by calphostin C and anti-GM-CSF antibody. Our results suggest that PKC plays a role upstream in the signaling pathway to GM-CSF induction, whereas PI3K is involved, at least in part, downstream in the signaling pathway after GM-CSF induction.

Cis-acting DNA elements of mouse granulocyte/macrophage colony-stimulating factor gene responsive to oxidized low density lipoprotein

We previously demonstrated that the induction of granulocyte/macrophage colony-stimulating factor (GM-CSF) played an important role in oxidized low density lipoprotein (Ox-LDL)-induced macrophage growth as a growth priming factor. The present study was undertaken to elucidate the transcriptional regulation of the GM-CSF gene using Raw 264.7 cells, a mouse macrophage cell line. Transient transfection into Raw 264.7 cells of several 5'-flanking regions of GM-CSF gene-luciferase fusion plasmids revealed the presence of two positive regulatory sites in regions spanning from -97 to -59 and from -59 to -37 and one negative regulatory site from -120 to -97 in unstimulated cells. When cells were stimulated by Ox-LDL, there was one positive responsive site from -225 to -120 and one negative responsive site from -97 to -59, which contained the NF-kappaB binding site. Computer analysis revealed the presence of a putative AP-2 binding site from -169 to -160. Mutagenesis of a putative AP-2 binding site and tandem repeat of this site in plasmid resulted in a complete loss and increased responsiveness to Ox-LDL, respectively. Electrophoretic mobility shift assay showed that Ox-LDL increased the binding of certain nuclear protein(s) to a putative AP-2 binding site but decreased their binding to NF-kappaB binding site. Supershift assay showed that nuclear proteins bound to NF-kappaB binding site contained, at least, p50 and p65 but could not demonstrate nuclear protein(s) bound to a putative AP-2 binding site. Our results suggested that a putative AP-2 binding site from -169 to -160 was a positive responsive element to Ox-LDL and that the NF-kappaB binding site from -91 to -82 was a negative responsive element in Ox-LDL-induced GM-CSF transcription.

Adrenomedullin receptor antagonism by calcitonin gene-related peptide(8-37) inhibits carotid artery neointimal hyperplasia after balloon injury

Intimal injury by angioplasty results in a series of changes, including smooth muscle cell hyperplasia, that lead to vascular restenosis. Adrenomedullin, a potent vasodilator peptide, has natriuretic effects, and its plasma concentration is elevated in cardiovascular diseases. Adrenomedullin is secreted by endothelial and vascular smooth muscle cells, but its role in neointimal hyperplasia after balloon injury has not been previously described. We investigated the role of endogenous adrenomedullin in neointimal hyperplasia using an in vivo rat model of postinjury vascular restenosis. In the injured rats, bromodeoxyuridine-labeled nuclei in the media of untreated common carotid arteries were increased 2 days after injury, which were suppressed by in vivo treatment with the adrenomedullin receptor antagonist calcitonin gene-related peptide (CGRP)(8-37). Inhibition of neointimal hyperplasia by CGRP(8-37) was distinct at 7 and 14 days, whereas CGRP(1-37) had no effect. The expression of adrenomedullin in the media of both untreated and treated common carotid arteries was elevated at 2 days and further enhanced in hyperplastic intima of untreated common carotid arteries at 7 days. Our findings suggest a novel role for endogenous adrenomedullin in balloon injury-induced restenosis and indicate that CGRP(8-37) may be useful for the prevention of vascular restenosis.

Non-invasive blood glucose measurement by Fourier transform infrared spectroscopic analysis through the mucous membrane of the lip: application of a chalcogenide optical fiber system

Non-invasive blood glucose measurement through the mucous membrane of the lip was investigated using Fourier transform infrared (FT-IR) spectroscopy with an attenuated total reflection (ATR) prism. To achieve easy attachment and easy control of attachment pressure of the ATR prism to the mucous membrane of the lip, a chalcogenide optical fiber with an ATR prism built in the tip was used. The same glucose-specific peaks at wave numbers of 1080 and 1033 cm-1 as glucose solutions were found in a spectrum through the mucous membrane of the lip. With a constant pressure of the ATR prism to the mucous membrane of the lip of 6.7 x 10(3) dyn/cm2, coefficients of variation of measurements within the day and of day-to-day measurements were 3.8 and 5.4% respectively. To eliminate baseline drifts and interference of body constituents other than glucose, the difference absorbances at 1080 cm-1 between spectra measured at the postprandial state and background spectrum obtained at the fasting state as an individual characteristic were evaluated. Following i.v. pulsatile injection of glucose, the difference absorbances at 1080 cm-1 nicely followed the changes in blood glucose concentrations with a time delay of 4 min. In daily blood glucose monitoring, a highly significant correlation between the difference absorbances and increases in blood glucose concentrations above the fasting level was obtained (r = 0.920, P < 0.01). From these experiments, it was suggested that FT-IR spectroscopy with a chalcogenide optical fiber could be useful clinically for non-invasive monitoring of glucose through the mucous membrane of the lip.

Induction of max by adrenomedullin and calcitonin gene-related peptide antagonizes endothelial apoptosis

Adrenomedullin is a novel vasodilatory peptide originally isolated from pheochromocytoma. Recently, we found that adrenomedullin acts as an autocrine/paracrine apoptosis survival factor for rat endothelial cells. In the present study, we show that adrenomedullin induces the expression of Max, a heterodimeric partner of c-Myc, which may contribute to its ability to rescue endothelial cells from apoptosis. Max is a basic-helix-loop-helix-leucine zipper protein that forms heterodimers with its alternative partners, Mad and Mxi-1, to behave as an antagonist for Myc-Max heterodimer through competition for common DNA targets. The expression of Max is reported to be constitutive and more stable than c-Myc, and serum induces immediate c-Myc stimulation followed by modest Max up-regulation. In quiescent rat endothelial cells, adrenomedullin stimulated the expression of Max without affecting c-Myc. Quantitation with real-time quantitative PCR detected on the ABI Prism 7700 Sequence Detection System revealed that adrenomedullin and calcitonin gene-related peptide (CGRP), as well as serum, up-regulated Max mRNA levels and that down-regulation of Max mRNA after serum deprivation was prevented by adrenomedullin. Neither adrenomedullin nor CGRP affected c-Myc expression. Transfection of a Max-expressing plasmid into endothelial cells rescued the apoptosis induced by serum deprivation. Neutralization with anti-adrenomedullin antiserum or blockade with a CGRP receptor antagonist, CGRP(8-37), reduced Max mRNA levels in growing endothelial cells and enhanced apoptosis after serum starvation. Introduction of an antisense oligodeoxynucleotide against Max mRNA using transferrin receptor-operated transfer led to inhibition of both adrenomedullin-induced up-regulation of Max transcripts and its cell survival effect, whereas random, sense, or missense oligonucleotides were without effect. The negative regulation of E-box-driven transcription by adrenomedullin was demonstrated by using preproendothelin-1 promoter containing c-Myc-Max binding consensus sequence; the promoter activity of preproendothelin-1 was reduced by cotransfecting Max- and Mad-expressing plasmids as well as addition of adrenomedullin and CGRP. The present results demonstrate that adrenomedullin antagonizes serum deprivation-induced endothelial apoptosis by up-regulation of the max gene in an autocrine/ paracrine manner.

Genomic organization and expression analysis of the mouse qkI locus

qkI, encoding a KH domain-containing RNA binding protein, has been isolated as a candidate gene for the mouse neurological mutation quaking. Here, we describe detailed studies on its genomic structure and expression pattern. We isolated approximately 1 Mb of genomic region containing the quaking locus and determined its genomic organization. The qkI locus contains at least 9 exons spanning approximately 65 kb of DNA. It gives rise to six distinct transcripts encoding, theoretically, five different protein isoforms. Exons 1 through 4 are shared by all the transcripts, whereas coding exons and two distinct 3'-UTRs downstream to the exon 4 are differentially utilized. One isoform has a truncated KH domain and may act as an antagonist to the others. These findings and identification of a single transcription initiation site suggest that differential expression of each transcript is regulated by alternative splicing. Expression of each alternative transcript and protein product was also examined. Two types of transcripts, 5 kb-A and B, are most abundant in the brain of newborn mice and are gradually downregulated thereafter. In contrast, the other three messages, 6 kb, 7 kb-A and B, increase as myelination proceeds and peak at 2 weeks of age, corresponding to the most active stage of myelination. Although the qkI messages and their products are abundant in brain and heart, a lower level of expression was found in various other tissues tested. Alternative transcripts that share the same 3'-UTR showed very similar expression patterns, suggesting a regulatory role of the 3'-UTRs in qkI gene expression.

Glucocorticoid inhibits oxidized LDL-induced macrophage growth by suppressing the expression of granulocyte/macrophage colony-stimulating factor

Glucocorticoid, an anti-inflammatory agent, inhibits the development of atherosclerosis in various experimental animal models. This is partially explained by its ability to inhibit smooth muscle cell migration and proliferation in the intima and to reduce chemotaxis of circulating monocytes and leukocytes into the subendothelial spaces. We have recently demonstrated that oxidized LDL (Ox-LDL) has a mitogenic activity for macrophages in vitro in which Ox-LDL-induced granulocyte/macrophage colony-stimulating factor (GM-CSF) production plays an important role. Proliferation of cellular components is one of the characteristic events in the development and progression of atherosclerotic lesions. In the present study, we investigated the effects of glucocorticoids on Ox-LDL-induced macrophage growth. Dexamethasone, prednisolone, and cortisol inhibited Ox-LDL-induced thymidine incorporation into macrophages by 85%, 70%, and 50%, respectively. Ox-LDL induced a significant production of GM-CSF by macrophages, which was effectively inhibited by dexamethasone, prednisolone, and cortisol by 80%, 65%, and 50%, respectively. Dexamethasone-mediated inhibition of Ox-LDL-induced GM-CSF mRNA expression and macrophage growth was significantly abrogated by RU-486, a glucocorticoid receptor antagonist. Our results suggest that the inhibitory effects of glucocorticoids on macrophage growth may be due to the inhibition of Ox-LDL-induced GM-CSF production through transactivation of the glucocorticoid receptor.

[Serum uric acid level and fractional excretion of urate in fluid and electrolyte disturbances]

Changes in renal urate clearance may reflect altered glomerular dynamics more precisely than other commonly used indices. Extracellular fluid volume expansion is known to be correlated with uricosuria, while volume depletion is associated with decreased urate excretion. The diagnostic usefulness of measuring serum urate levels and fractional excretions of urate in SIADH, incipient diabetic nephropathy, and prerenal azotemia have been reviewed. In SIADH, profound hypouricemia and markedly increased fractional excretion of urate (FEUA) accompany the extracellular fluid volume expansion. In prerenal azotemia, decreased FEUA may represent a reliable indicator of prerenal azotemia in the differential diagnosis of acute renal failure. In incipient diabetic nephropathy, glomerular hyperfiltration may increase renal urate clearance and lower the serum uric acid level. Hypouricemia may also predict the future progression of incipient nephropathy in type II diabetes.

Insulin inhibits glucagon secretion by the activation of PI3-kinase in In-R1-G9 cells

Intracellular mechanisms through which insulin inhibits glucagon secretion remain to be elucidated in glucagon secreting cells. In this study, we confirmed that, in In-R1-G9 cells, a pancreatic alpha cell line, insulin stimulated phosphorylation of insulin receptor substrate-1 (IRS-1) and activated phosphatidylinositol 3-kinase (PI3-kinase). We further studied, using wortmannin, an inhibitor of PI3-kinase, whether the inhibitory effect of insulin on glucagon secretion was mediated through PI3-kinase pathway in these cells. In static incubation studies, insulin significantly inhibited glucagon secretion at 2, 6 and 12 h, which was completely abolished by pretreatment with wortmannin. In perifusion studies, insulin significantly suppressed glucagon secretion after 10 min, which was also blocked by wortmannin. Insulin also reduced glucagon mRNA at 6 and 12 h but not at 2 h. Wortmannin also abolished insulin-induced reduction of glucagon mRNA. Insulin increased the amount of 85 kDa subunit of PI3-kinase in plasma membrane fraction (PM), with a reciprocal decrease of the kinase in cytosol fraction (CY). Insulin also increased PI3-kinase activity in PM, but not in CY. Our results suggest that insulin suppressed glucagon secretion by inhibiting glucagon release and gene expression. Both actions were mediated by activation of PI3-kinase. Recruitment and activation of PI3-kinase in plasma membrane might be relevant at least in part to insulin-induced inhibition of glucagon release.

Differential inhibitory actions by glucocorticoid and aspirin on cytokine-induced nitric oxide production in vascular smooth muscle cells

Glucocorticoids and nonsteroidal antiinflammatory drugs (NSAIDs) are widely used for the treatment of inflammatory and immune diseases. Nitric oxide (NO) has a diversity of physiological functions, but its excess production has been implicated in the inflammatory process. The present study was designed to elucidate the mechanisms by which glucocorticoids and NSAIDs affect inducible nitric oxide synthase (iNOS) expression in cultured rat vascular smooth muscle cells (VSMCs). Both interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha potently stimulated nitrite/nitrate (NOx) production with a concomitant expression of iNOS mRNA and protein as demonstrated by Northern and Western blot analysis, respectively. Both IL-1beta and TNF-alpha activated nuclear factor (NF)-kappaB as demonstrated by electrophoretic mobility shift assay. Dexamethasone, salicylate and aspirin, but not indomethacin, dose dependently inhibited cytokine-stimulated NOx production and iNOS protein expression. Dexamethasone decreased cytokine-induced NF-kappaB activation and iNOS mRNA expression, but neither salicylate nor aspirin affected NF-kappaB activation or iNOS mRNA expression. IL-1beta caused a rapid increase in phosphorylated IkappaB-alpha levels and subsequent transient decrease in IkappaB-alpha levels, an inhibitor of NF-kappaB, as revealed by Western blot analysis using specific antibodies for phosphorylated and nonphosphorylated IkappaB-alpha. These effects were blocked by pretreatment with dexamethasone. Aspirin dose dependently inhibited iNOS enzymatic activity, whereas salicylate and dexamethasone had limited effect. The present study demonstrates that 1) inhibitory effect of dexamethasone on cytokine-induced iNOS expression and NO production in rat VSMCs, although potentially acting at multiple levels, is partly mediated by inhibition of NF-kappaB activation resulting from decreased phosphorylation and degradation of IkappaB-alpha, 2) both salicylate and aspirin inhibit cytokine-stimulated NO production at translational and/or posttranslational levels without affecting NF-kappaB- mediated iNOS gene expression, and 3) aspirin directly inhibits iNOS enzyme activity. These data suggest the differential inhibitory mechanisms of iNOS-mediated NO synthesis by glucocorticoids and NSAIDs in the vasculature.

[Indication of intensive insulin therapy and its practice]

DCCT and Kumamoto Study demonstrated that optimal glycemic control with intensive insulin therapy could delay the onset and progression of the early stages of diabetic microvascular complications in Japanese patients with noninsulin dependent diabetes as well as in patients with insulin dependent diabetes mellitus. To obtain optimal glycemic control, the prandial insulin supplements before each meal are recommended for insulin requiring patients with noninsulin dependent diabetes mellitus whose residual B cell functions are retained to some extent, whereas the combined basal at bedtime plus prandial insulin supplements are essential for the patients with noninsulin dependent diabetes mellitus whose residual B cell functions are severely exhausted as well as in the patients with insulin dependent diabetes mellitus. The glycemic threshold to prevent the onset and progression of diabetic microvascular complications in the Kumamoto Study was indicated as follows; HbA1c < 6.5%, fasting blood glucose concentration < 110 mg/dl, and 2-hour postprandial blood glucose concentration < 180 mg/dl.

[Design and development strategy for wearable and implantable artificial endocrine pancreas]

The ultimate goal of development of an artificial endocrine pancreas is for long-term strict glycemic control, and therefore, the trend in development is now from bedside-type to wearable- or implantable-type. With either a miniaturized extracorporeal glucose monitoring system based on microdialysis sampling method or a ferrocene-mediated needle-type glucose sensor covered with highly biocompatible membrane, and with subcutaneous insulin infusion algorithm using short-acting insulin analogue, long-term physiological glycemic control could be obtained by wearable artificial endocrine pancreas. The next step will be directed to the implantable one. Non-invasive infrared absorbance spectroscopy to fit into an artificial tooth prosthesis, an implantable artificial endocrine pancreas, in which measured glucose concentrations are transmitted telemetrically to implanted computer and pump system, might be developed.

Possible involvement of atypical protein kinase C (PKC) in glucose-sensitive expression of the human insulin gene: DNA-binding activity and transcriptional activity of pancreatic and duodenal homeobox gene-1 (PDX-1) are enhanced via calphostin C-sensitive but phorbol 12-myristate 13-acetate (PMA) and Gö 6976-insensitive pathway

Pancreatic and duodenal homeobox gene-1 (PDX-1) is a transcription factor which regulates the insulin gene expression. In this study, we tried to elucidate the role of PDX-1 in the glucose-induced transcriptional activation of the human insulin gene promoter in MIN6 cells. Electrophoretic mobility shift assay (EMSA) and chloramphenicol acetyltransferase (CAT) assay demonstrated that both DNA-binding activity and transcriptional activity of PDX-1 were increased with 20 mmol/l glucose more than with 2 mmol/l glucose. The DNA-binding activity of PDX-1 induced by high glucose was blocked by phosphatase treatment, suggesting the involvement of PDX-1 phosphorylation in this event. In an in vitro phosphorylation study, PDX-1 was phosphorylated by protein kinase C (PKC), but not by cAMP dependent protein kinase (PKA) or mitogen-activated protein kinase (MAPK). Furthermore, increased PDX-1 function induced by high glucose was blocked by calphostin C, an inhibitor of all PKC isoforms, but unaffected by phorbol 12-myristate 13-acetate (PMA), an activator of classical and novel PKC, or Gö 6976, an inhibitor of classical and novel PKC, which suggested that the PKC family which activated PDX-1 in MIN6 cells was atypical PKC. Western blot and immunocytochemical studies with anti-PKC zeta antibody confirmed the presence of PKC zeta, one of the isoforms of atypical PKC, in MIN6 cells. Furthermore, PKC zeta activity was significantly increased by glucose stimulation. These results suggest that high glucose increased DNA-binding activity of PDX-1 by activating atypical PKC including PKC zeta, resulting in transcriptional activation of the human insulin gene promoter.

Cloning from insulinoma cells of synapsin I associated with insulin secretory granules

Synapsin I is a synaptic vesicle-associated protein involved in neurotransmitter release. The functions of this protein are apparently regulated by Ca2+/calmodulin-dependent protein kinase II (CaM kinase II). We reported evidence for CaM kinase II and a synapsin I-like protein present in mouse insulinoma MIN6 cells (Matsumoto, K., Fukunaga, K., Miyazaki, J., Shichiri, M., and Miyamoto, E. (1995) Endocrinology 136, 3784-3793). Phosphorylation of the synapsin I-like protein in these cells correlated with the activation of CaM kinase II and insulin secretion. In the present study, we screened the MIN6 cDNA library with the full-length cDNA probe of rat brain synapsin Ia and obtained seven positive clones; the largest one was then sequenced. The largest open reading frame deduced from the cDNA sequence of 3695 base pairs encoded a polypeptide of 670 amino acids, which exhibited significant sequence similarity to rat synapsin Ib. The cDNA contained the same sequence as the first exon of the mouse synapsin I gene. These results indicate that synapsin Ib is present in MIN6 cells. Synapsin I was expressed in normal rat islets, as determined by reverse transcriptase-polymerase chain reaction analysis. Immunoblot analysis after subcellular fractionation of MIN6 cells demonstrated that synapsin Ib and delta subunit of CaM kinase II co-localized with insulin secretory granules. By analogy concerning regulation of neurotransmitter release, our results suggest that phosphorylation of synapsin I by CaM kinase II may induce the release of insulin from islet cells.

Natriuretic peptides and nitric oxide induce endothelial apoptosis via a cGMP-dependent mechanism

Apoptosis is a mode of cell death in which the cell participates in its own demise. We studied whether endothelium-derived relaxing factor, nitric oxide (NO), and natriuretic peptides affect apoptosis of rat vascular endothelial cells via a cGMP-dependent pathway and whether such effects are antagonized by an endothelium-derived vasoconstrictor, endothelin-1 (ET-1). Three natriuretic peptides (atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide) induced endothelial apoptosis as demonstrated by nucleosomal laddering on agarose gel electrophoresis and by the terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling method. This dose-dependent relation was assessed by quantifying the fragmented and intact DNA contents by the diphenylamine method. The atrial natriuretic peptide-induced endothelial apoptosis was completely blocked by a guanylate cyclase-coupled receptor antagonist (HS-142-1) and an inhibitor of cGMP-dependent protein kinase (KT5823). An NO donor, NOR3 ((+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide; FK409) also induced endothelial apoptosis; the effect of this compound was abrogated by KT5823 and an inhibitor of soluble guanylate cyclase, ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one). A cGMP derivative, 8-bromo-cGMP, but not the cAMP derivative 8-bromo-cAMP, caused endothelial apoptosis; the effect of ODQ was also abrogated by KT5823. Endothelial apoptosis induced by ANP, NOR3, and 8-bromo-cGMP was similarly antagonized by ET-1. ANP, NOR3, and 8-bromo-cGMP caused marked accumulations of the tumor suppressor gene product p53 but not of bcl-2, as determined by Western blot analysis. These results demonstrate for the first time that endothelium-derived NO and natriuretic peptides are proapoptotic factors for endothelial cells, whereas the endothelium-derived vasoconstrictor ET-1 is an antiapoptotic factor, suggesting that the countervailing balance between these vasodilators and vasoconstrictors, in addition to regulation of vascular tonus, may contribute to endothelial cell integrity.

Cellular characterization of pituitary adenoma cell line (AtT20 cell) transfected with insulin, glucose transporter type 2 (GLUT2) and glucokinase genes: insulin secretion in response to physiological concentrations of glucose

We investigated the mechanisms of insulin secretion by transfecting into a pituitary adenoma cell line (AtT20) a combination of genes encoding human insulin (HI), glucose transporter type 2 (GLUT2) and glucokinase (GK), followed by studying the characteristics of these cells. In static incubation, a cell line transfected with insulin gene alone (AtT20HI) secreted mature human insulin but this was not in a glucose-dependent manner. Other cell lines transfected with insulin and GLUT2 genes (AtT20HI-GLUT2-3) or with insulin and GK genes (AtT20HI-GK-1) secreted insulin in response to glucose concentrations of only less than 1 mmol/l. In contrast, cell lines transfected with insulin, GLUT2 and GK genes (AtT20HI-GLUT2-GK-6, AtT20HI-GLUT2-GK-7 and AtT20HI-GLUT2-GK-10) showed a glucose-dependent insulin secretion up to 25 mmol/l glucose. Glucose utilization and oxidation were increased in AtT20HI-GLUT2-GK cell lines but not in AtT20HI, AtT20HI-GLUT2-3 and AtT20HI-GK-1 cells at physiological glucose concentrations, compared with AtT20 cells. Diazoxide, nifedipine and 2-deoxy glucose suppressed (p < 0.05) glucose stimulated insulin secretion in AtT20HI-GLUT2-GK-6 cells. Glibenclamide, KCl or corticotropin releasing factor (CRF) stimulated (p < 0.05) insulin secretion both in AtT20HI and AtT20HI-GLUT2-GK-6 cells. Insulin secretion stimulated by glibenclamide, KCl or CRF was further enhanced by the addition of 25 mmol/l glucose in AtT20HI-GLUT2-GK-6 cells but not in AtT20HI cells. In perifusion experiments, a stepwise increase in glucose concentration from 5 to 25 mmol/l stimulated insulin secretion in AtT20HI-GLUT2-GK cell lines but the response lacked a clear first phase of insulin secretion. Our results suggest that both GLUT2 and glucokinase are necessary for the glucose stimulated insulin secretion in at least rodent cell lines, and that other element(s) are necessary for a biphasic insulin secretion typically observed in beta cells.

Role of nuclear factor-kappaB activation in cytokine- and sphingomyelinase-stimulated inducible nitric oxide synthase gene expression in vascular smooth muscle cells

Inflammatory cytokines, such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF alpha), are known to activate sphingomyelinase (SMase) and nuclear factor-kappaB (NF-kappaB) in certain cell types, which also stimulate inducible nitric oxide synthase (iNOS) gene in vascular smooth muscle cells (VSMCs). However, it remains unknown whether the SMase pathway is involved in iNOS gene expression in VSMCs. Therefore, the present study was designed to examine whether SMase induces iNOS gene expression via the NF-kappaB activation pathway similar to that of IL-1beta and TNF alpha in cultured rat VSMCs. Neutral SMase, although less potently than IL-1beta and TNF alpha, stimulated nitrite/nitrate (NOx) production, and iNOS messenger RNA and protein expression, as assessed by Northern and Western blot analyses, respectively. Neutral SMase, IL-1beta, and TNF alpha activated NF-kappaB, as revealed by electrophoretic mobility shift assay, and its nuclear translocation, as demonstrated by immunocytochemical study. Neutral SMase potentiated NOx production, iNOS expression, and NF-kappaB activation stimulated by TNF alpha, but not by IL-1beta. Aldehyde peptide proteasome inhibitors completely blocked NOx production, iNOS expression, NF-kappaB activation, and its nuclear translocation induced by cytokines and neutral SMase. IL-1beta and TNF alpha, but not neutral SMase, caused a transient decrease in IkappaB-alpha protein levels, whereas IkappaB-beta protein expression was not affected by either agent. Proteasome inhibitors prevented cytokine-mediated IkappaB-alpha degradation. Several cell-permeable ceramide analogs (C2, C6, and C8), hydrolysis products of sphingomyelin, activated NF-kappaB less potently than neutral SMase, but had no effect on NOx production. These results demonstrate an essential role of NF-kappaB activation in mediation of neutral SMase-induced iNOS expression, but distinct from the proteasome-mediated IkappaB-alpha degradation by cytokines, suggesting the possible involvement of an additional signaling pathway(s).

NO inhibits cytokine-induced iNOS expression and NF-kappaB activation by interfering with phosphorylation and degradation of IkappaB-alpha

Nitric oxide (NO) is known to have antiatherogenic and anti-inflammatory properties, but its effects on the cytokine-induced nuclear factor-kappa B (NF-kappaB) activation pathway in relation to the regulation of inducible nitric oxide synthase (iNOS) gene in vascular smooth muscle cells (VSMCs) remain elusive. To elucidate the roles of NO in the regulation of cytokine-induced NF-kappaB activation and consequent iNOS gene expression, we studied the effects of NO donors [(+/-)-(E)-ethyl-2-[(E)-hydroxyamino]-5-nitro-3-hexeneamide (NOR3) and sodium nitroprusside] on interleukin (IL)-1beta-induced NF-kappaB activation and IkappaB-alpha degradation and subsequent iNOS expression in rat VSMCs. Northern blot and Western blot analyses demonstrated that NO donors decreased IL-1beta-induced iNOS mRNA and protein expression. Electrophoretic mobility shift assay using synthetic oligonucleotide corresponding to the downstream NF-kappaB site of rat iNOS promoter as a probe showed that NOR3 inhibited IL-1beta-induced NF-kappaB activation and its nuclear translocation, as demonstrated with immunocytochemical study. These effects were independent of guanylate cyclase activation; an inhibitor of soluble guanylate cyclase (1H-oxadiazolo-1,2,4-[4,3-alpha]quinoxaline-1-one) had no effect on NOR3-induced inhibition of NF-kappaB activation or iNOS mRNA expression by IL-1beta, and a cGMP derivative (8-bromo-cGMP) failed to mimic the effects of NO donors. Western blot analysis using anti-IkappaB-alpha and anti-phospho-IkappaB-alpha antibodies revealed that IL-1beta induced a transient degradation of IkappaB-alpha preceded by a rapid appearance of phosphorylated IkappaB-alpha, both of which were completely blocked by NOR3. A proteasome inhibitor (MG115) blocked IL-1beta-induced transient degradation of IkappaB-alpha and stabilized the appearance of phosphorylated IkappaB-alpha stimulated by IL-1beta. NOR3 inhibited the appearance of IL-1beta-induced phosphorylated IkappaB-alpha even in the presence of MG115. Our results indicate that an inhibitory action by NO on cytokine-induced NF-kappaB activation and iNOS gene expression is due to its direct blockade on phosphorylation and subsequent degradation of IkappaB-alpha via the cGMP-independent pathway in rat VSMCs.