Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm

We present a new measurement of the positive muon magnetic anomaly, a_{μ}≡(g_{μ}-2)/2, from the Fermilab Muon g-2 Experiment using data collected in 2019 and 2020. We have analyzed more than 4 times the number of positrons from muon decay than in our previous result from 2018 data. The systematic error is reduced by more than a factor of 2 due to better running conditions, a more stable beam, and improved knowledge of the magnetic field weighted by the muon distribution, ω[over ˜]_{p}^{'}, and of the anomalous precession frequency corrected for beam dynamics effects, ω_{a}. From the ratio ω_{a}/ω[over ˜]_{p}^{'}, together with precisely determined external parameters, we determine a_{μ}=116 592 057(25)×10^{-11} (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain a_{μ}(FNAL)=116 592 055(24)×10^{-11} (0.20 ppm). The new experimental world average is a_{μ}(exp)=116 592 059(22)×10^{-11} (0.19 ppm), which represents a factor of 2 improvement in precision.

Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm

We present the first results of the Fermilab National Accelerator Laboratory (FNAL) Muon g-2 Experiment for the positive muon magnetic anomaly a_{μ}≡(g_{μ}-2)/2. The anomaly is determined from the precision measurements of two angular frequencies. Intensity variation of high-energy positrons from muon decays directly encodes the difference frequency ω_{a} between the spin-precession and cyclotron frequencies for polarized muons in a magnetic storage ring. The storage ring magnetic field is measured using nuclear magnetic resonance probes calibrated in terms of the equivalent proton spin precession frequency ω[over ˜]_{p}^{'} in a spherical water sample at 34.7 °C. The ratio ω_{a}/ω[over ˜]_{p}^{'}, together with known fundamental constants, determines a_{μ}(FNAL)=116 592 040(54)×10^{-11} (0.46 ppm). The result is 3.3 standard deviations greater than the standard model prediction and is in excellent agreement with the previous Brookhaven National Laboratory (BNL) E821 measurement. After combination with previous measurements of both μ^{+} and μ^{-}, the new experimental average of a_{μ}(Exp)=116 592 061(41)×10^{-11} (0.35 ppm) increases the tension between experiment and theory to 4.2 standard deviations.

Identification of OAT1/OAT3 as Contributors to Cisplatin Toxicity

Cisplatin is among the most widely used anticancer drugs and known to cause a dose‐limiting nephrotoxicity, which is partially dependent on the renal uptake carrier OCT2. We here report a previously unrecognized, OCT2‐independent pathway of cisplatin‐induced renal injury that is mediated by the organic anion transporters OAT1 and OAT3. Using transporter‐deficient mouse models, we found that this mechanism regulates renal uptake of a mercapturic acid metabolite of cisplatin that acts as a precursor of a potent nephrotoxin. The function of these two transport systems can be simultaneously inhibited by the tyrosine kinase inhibitor nilotinib through noncompetitive mechanisms, without compromising the anticancer properties of cisplatin. Collectively, our findings reveal a novel pathway that explains the fundamental basis of cisplatin‐induced nephrotoxicity, with potential implications for its therapeutic management.

Suppression of PU.1-linked TLR4 expression by cilostazol with decrease of cytokine production in macrophages from patients with rheumatoid arthritis

BACKGROUND AND PURPOSE

The present study assessed the effects of cilostazol on LPS-stimulated TLR4 signal pathways in synovial macrophages from patients with rheumatoid arthritis (RA). These effects were confirmed in collagen-induced arthritis (CIA) in mice.

EXPERIMENTAL APPROACH

Expression of TLR4, PU.1, NF-κB p65 and IκBα on synovial fluid macrophages from RA patients was determined by Western blotting, and cytokines were measured by ELISA. Anti-arthritic effects were evaluated in CIA mice.

KEY RESULTS

Intracellular cAMP was concentration-dependently raised by cilostazol (1-100 μM). Cilostazol significantly suppressed LPS-stimulated increase of TLR4 expression by blocking PU.1 transcriptional activity in RA macrophages. In addition, cilostazol decreased LPS-induced myeloid differentiation factor 88 (MyD88) expression, but not that of TNF receptor-associated factor 6 (TRAF6). Cilostazol also suppressed IkBα degradation and NF-κB p65 nuclear translocation. Moreover, LPS-induced increase of cytokine production (TNF-α, IL-1β) was inhibited by cilostazol, an effect which was accompanied by suppression of IκBα degradation, and NF-κB p65 nuclear translocation. However, expression of anti-inflammatory IL-10 was elevated by cilostazol and forskolin/IBMX. In mice with CIA, post-treatment with cilostazol (30 mg kg⁻¹ day⁻¹) decreased expression of TLR4 in knee joints in association with decreased recruitment of macrophages. Consequently, synovial inflammation, proteoglycan depletion and bone erosion were significantly inhibited by cilostazol treatment.

CONCLUSIONS AND IMPLICATIONS

Cilostazol down-regulated LPS-stimulated PU.1-linked TLR4 expression and TLR4/MyD88/NF-κB signal pathways, and then suppressed inflammatory cytokine production in synovial macrophages from RA patients. Also cilostazol markedly inhibited the severity of CIA in mice.

High mortality associated with Acinetobacter species infection in liver transplant patients

BACKGROUND

Acinetobacter species have become increasingly important nosocomial pathogens worldwide and can result in a wide range of infections, including bacteremia, pneumonia, urinary tract infection, peritonitis, among others. The aim of this study was to investigate clinical characteristics, mortality, and outcomes among liver transplant recipients with Acinetobacter species infections.

METHODS

We retrospectively analyzed 451 subjects who had undergone living donor liver transplantations between January 2001 and May 2010. Pandrug-resistant (PDR) Acinetobacter species were defined as resistant to all commercially available antibiotics except colistin.

RESULTS

Infectious complications due to Acinetobacter species appeared in 26 patients (5.8%) with a total of 37 episodes. Of the species identified, 34 were Acinetobacter baumannii and 3 Acinetobacter Iwoffiii. The presumed sources of infection were the biliary tract (n = 21, 56.8%), lung (n = 7, 18.9%), intra-abdomen (n = 6, 16.2%), catheter (n = 2, 5.4%), and urinary tract (n = 1, 3.6%). Among the 37 Acinetobacter species, 75.7% (28/37) were PDR species. Age, duration of intensive care unit stay, Child-Pugh score, and Model for End-stage Liver Disease score were not significant risk factors for Acinetobacter species infection. However, the overall mortality among patients with Acinetobacter species infections was 50% (13/26), which was significantly higher than that among those free of infection (50% vs 11.5%, P < .05). Multivariate analysis using a Cox regression model showed that inappropriate antimicrobial treatment was a significant independent risk factor for mortality among patients with Acinetobacter species infections (hazard Ratio = 4.19, 95% confidence interval 1.1-18.7; P = .06).

CONCLUSION

Patients with Acinetobacter species infections after liver transplantation show a significantly worse prognosis. PDR Acinetobacter species have been a major problem in our center.

Effects of Polyamines on TNFalpha- or Tamoxifen-induced Apoptosis in Human Breast Cancer Cells

PURPOSE

To investigate the effects of polyamines on tumor necrosis factor alpha (TNFalpha)-or tamoxifen (TAM)-induced apoptosis in estrogen receptor (ER)-positive MCF- 7 and ER-negative MDA-MB-231 human breast cancer cells.

MATERIALS AND METHODS

Cell viability was assessed by using MTT assay. Reactive oxygen species (ROS) generation was measured using 2', 7'-dichlorofluorescin diacetste (DCFDA) by fluorescence plate reader. DNA fragmentation was assessed by 1.5% agarose gel electrophoresis.

RESULTS

TNFalpah and TAM showed significant dose- and time- dependent inhibitory effects on the growth of MCF-7 human cells. However, the growth of MDA-MB-231 cells were not inhibited by TNFalpha or TAM treatment. The generation of ROS was increased in dose-and time-dependent manner by TNFalpha treatment in MCF-7 cells. Polyamines, especially spermine suppressed TNFalpha-induced ROS generation in MCF-7 cells. Antioxidant effects of polyamines were also demonstrated by DNA fragmentation, cell morphology as well as ROS generation assay. Polyamines also blocked TAM-induced cell death in MCF-7 cell. However, MDA-MB-231 cells showed resistance to the cytotoxic effects of TNFalpha or TAM.

CONCLUSION

These results suggest that polyamines may prevent TNFalpha or TAM-induced apoptosis in MCF-7 human breast cancer cells.

Involvement of NADH/NADPH oxidase-derived superoxide in experimental vasospasm induced by periarterial blood in rat femoral artery

To elucidate the mechanism(s) involved in periarterial blood-mediated vasospasm in the rat femoral artery, vascular production of superoxide and related expression of intercellular adhesion molecule-1 (ICAM-1) were assessed with subsequent perivascular mobilization of granulocytes and macrophages. Arterial vasospasm characterized by increased wall thickness and decreased lumen size was observed on the side exposed to blood at 7 to 12 days, and these vascular changes were significantly ameliorated by pretreatment with NADH/NADPH oxidase inhibitor, diphenyleneiodonium (200 microM, locally). Increased mobilization of granulocytes was paralleled with the expression of ICAM-1 in the vessels at 24 hours after periarterial application of blood to the femoral artery, and then both declined. Subsequently, infiltration of macrophage progressively increased at all layers throughout 7 to 12 days. In in vitro study, a large amount of superoxide that was inhibitable by diphenyleneiodonium (20 and 100 microM) was produced at 3 hours upon application of 10% autologous blood to the aortic segments. Furthermore, ICAM-1 expression by autologous blood was well correlated with generation of superoxide anion in the aortic segment (r=0.975, P<0.05). Taken together, it is suggested that NADH/NADPH oxidase-derived superoxide is implicated in periarterial blood-induced vasospasm via increased expression of ICAM-1 with subsequent mobilization of granulocyte/macrophage.

Restoration of vasodilation and CBF autoregulation by genistein in rat pial artery after brain injury

This study determined whether, after fluid percussion injury (FPI), tyrosine kinase activation is coupled to inhibition of K(+) channels and alteration in cerebral blood flow (CBF) autoregulation in the rat pial artery. Injury of moderate severity (2--2.5 atm) was produced by FPI in anesthetized rats equipped with a closed cranial window. The suppressed vasodilation of the pial arterioles to calcitonin gene-related peptide (CGRP) and levcromakalim (LMK) and altered lower limit of CBF autoregulation after FPI were restored by genistein but not by daidzein, an inactive analog. Vasodilation to S-nitroso-N-acetyl penicillamine (0.1--10 micromol/l) was, however, little influenced after FPI. The restored vasodilation was decreased by sodium orthovanadate, suggesting the reciprocal action of tyrosine phosphorylation and dephosphorylation. After FPI, CGRP-induced vasodilation restored by genistein (10 micromol/l) was strongly antagonized by iberiotoxin but not by glibenclamide, whereas LMK-induced vasodilation was, in contrast, inhibited by glibenclamide but not by iberiotoxin. Taken together, we suggest that, after FPI, activation of tyrosine kinase links the inhibition of K(+) channels to impaired autoregulatory vasodilation in response to acute hypotension and alteration in CBF autoregulation in the rat pial artery.

Translocational inefficiency of intracellular proteins in senescence of human diploid fibroblasts

In order to investigate signal transduction pathways and related changes of actin cytoskeleton organization in cellular senescence, H-ras double mutants--V12S35, V12G37, and V12C40--were constitutively expressed in human foreskin fibroblast (HDF). Senescent HDF cells as well as the H-ras mutant expressers accumulated p-Erk1/2 in the cytoplasm with increased MEK activity and failed to translocate it to nuclei on EGF stimulation. Senescent HDF cells, V12S35 and V12G37 expressers, revealed a failure to export actin fiber from nucleus to cytoplasm and also to form stress fibers. Perinuclear expression of Rac1 was prominent in the HDF cells and V12C40 expresser; however, in the V12S35 expresser, translocation of Rac1 from perinucleus to nucleus and strong expression of RhoA were obvious. In summary, the H-ras double mutant expressers induced premature senescence through the MEK pathway, accompanied by nuclear accumulation of actin and Rac1 proteins, cytoplasmic retention of p-Erk1/2, and marked induction of RhoA expression, suggesting the translocational inefficiency of the intracellular proteins in the senescent HDF cells.

Antiangiogenic effect of KR31372 in rat sponge implant model

A rat sponge implant model was used to examine the antiangiogenic effect of KR31372. Topical administration of angiotensin II (AII, 100 ng, daily) into the sponges enhanced the basal sponge-induced neovascularization, leading to higher clearance of (99m)Tc, increased retention of dye in the vessels, and increased numbers of blood vessels. These AII-induced changes were significantly suppressed by oral administration of KR31372 (1 mg/kg for 7 days). Angiogenic effect of recombinant human VEGF(165) (200 ng) was modestly higher than that of AII, which was also significantly inhibited by KR31372. KR31372-mediated suppression of (99m)Tc clearance was reversed by glibenclamide. Levcromakalim showed a modestly suppressive effect on the AII-induced angiogenesis. In conclusion, KR31372 exerted a strong inhibitory effect on the sponge-induced neovascularization, in part, through mediation of glibenclamide-sensitive K(+) channel activation. It is suggested that it may have therapeutic potential in the treatment of angiogenic disorders.

KR 31372, a benzopyran derivative, inhibits oxidized LDL-stimulated proliferation and migration of vascular smooth muscle cells

KR 31372 is a benzopyran derivative. Both [3H]thymidine incorporation and migrations (chemotactic and wound-edge) of cultured smooth muscle cells (SMCs) were greatly stimulated by oxidized low-density lipoprotein (LDL). These effects were significantly suppressed by KR 31372 (10(7) - 10(6) M) and PDGF-BB antibody (10(8) - 10(6) M). Preincubation with KR 31372 led to a decrease in the synthesis of PDGF-BB-like immunoreactivity (PDGF-BB-LI) that had been stimulated by oxidized LDL. Otherwise, KR 31372 and probucol strongly inhibited the production of thiobarbituric acid reactive substances (TBARS) caused by the incubation of LDL with Cu2+ ion, and significantly reduced the intracellular oxidative stress when stimulated with H,O2. Taken together, it is suggested that KR 31372 may inhibit the oxidized LDL-stimulated syntheses of DNA and PDGF-BB, and migration of the SMCs, in part, via the antioxidant activity.

Rebamipide inhibits neutrophil adhesion to hypoxia/reoxygenation-stimulated endothelial cells via nuclear factor-kappaB-dependent pathway

This study was designed to determine whether rebamipide can inhibit neutrophil adhesion to human umbilical vein endothelial cells (HUVECs) stimulated with 1 h of hypoxia followed by 4 h of reoxygenation (H/R). Furthermore, to define the action mechanisms, we determined the effect of rebamipide on the surface expression of endothelial cell adhesion molecules E-selectin, P-selectin, and intercellular adhesion molecule-1 (ICAM-1) on H/R-stimulated HUVECs. Under resting conditions, both E-selectin and P-selectin were not expressed on the surface of HUVECs in contrast to ICAM-1, which was constitutively expressed. After stimulation with H/R, HUVECs showed an enhanced neutrophil adhesivity in association with an increased surface expression of E-selectin and P-selectin with a marginal increase in ICAM-1 expression. In parallel, the increased nuclear translocation of nuclear factor-kappaB in H/R-stimulated HUVECs was monitored by electrophoretic mobility shift assay (adjusted volume units, 11.9 +/- 2.5 x 10(4) counts x mm(2) in unstimulated cells versus 24.2 +/- 3.0 x 10(4) counts x mm(2) in H/R-stimulated cells). Rebamipide suppressed the surface expression of E-selectin and P-selectin with a subsequent inhibition of neutrophil adhesion to H/R-stimulated HUVECs. In line with these results, rebamipide (100, 300, and 1000 microM) inhibited H/R-induced nuclear translocation of nuclear factor-kappaB in a concentration-dependent manner. Taken together, this study demonstrates that rebamipide inhibits neutrophil adhesion to HUVECs by a mechanism involving inhibition of transcription-dependent surface expression of E-selectin and P-selectin in H/R-stimulated endothelial cells.

Implication of adenosine A2A receptors in hypotension-induced vasodilation and cerebral blood flow autoregulation in rat pial arteries

This study aimed to evaluate the role for adenosine A2A receptors in the autoregulatory vasodilation to hypotension in relation with cerebral blood flow (CBF) autoregulation in rat pial arteries. Changes in pial artery diameters were observed directly through a closed cranial window. Vasodilation induced by adenosine was markedly suppressed by ZM 241385 (1 micromol/l, A2A antagonist) and alloxazine (1 micromol/l, A2B antagonist), but not by 8-cyclopentyltheophylline (CPT, 1 micromol/l, A1 antagonist). CGS-21680-induced vasodilation was more strongly inhibited by ZM 241385 (25.3-fold; P<0.05) than by alloxazine. In contrast, 5'-N-ethylcarboxamido-adenosine (NECA)-induced vasodilation was more prominently suppressed by alloxazine (12.0-fold; P<0.001) than by ZM 241385. The autoregulatory vasodilation in response to acute hypotension of the pial arteries was significantly suppressed by ZM 241385, but not by CPT and alloxazine. Consistent with this finding, the lower limit of CBF autoregulation significantly shifted to a higher blood pressure by 1 micromol/l of ZM 241385 (53.0+/-3.9 mm Hg to 69.2+/-2.9 mm Hg, P<0.01) and 10 micromol/l of glibenclamide (54.7+/-6.5 mm Hg to 77.9+/-4.2 mm Hg, P<0.001), but not by CPT and alloxazine. Thus, it is suggested that adenosine-induced vasodilation of the rat pial artery is mediated via activation of adenosine A2A and A2B receptors, but not by A1 subtype, and activation of adenosine A2A receptor preferentially contributes to the autoregulatory vasodilation via activation of ATP-sensitive K+ channels in response to hypotension and maintenance of CBF autoregulation.

Expression of intracellular adhesion molecule–1 linking superoxide to mobilization of granulocytes and macrophages after periarterial blood in rat femoral artery: effect of rebamipide

Object

To clarify the mechanism(s) involved in the perivascular mobilization of granulocytes and macrophages by periarterial autologous blood (PAAB) in the vicinity of the femoral artery (FA) in rats, superoxide production as well as expression of intercellular adhesion molecule–1 (ICAM-1) were determined by conducting both in vitro and in vivo experiments.

Methods

In an in vitro study, a significant amount of superoxide inhibited by diphenyleneiodonium (20 μM and 100 μM) was identified at 3 hours after application of 10% whole blood to the aortic segments, and these results were correlated with in vitro ICAM-1 expression. High expression of ICAM-1 was subsequently demonstrated in these segments at 24 hours in in vitro and in vivo studies. In the in vivo study, an increased mobilization of granulocytes paralleled with a high expression of ICAM-1 in the vessels at 24 hours after administration of PAAB to the FA and then declined. Subsequently, macrophage infiltration progressively increased at all layers throughout a period of 7 to 12 days. Pretreatment with rebamipide (100 and 300 mg kg−1 day−1, orally) significantly inhibited the expression of ICAM-1 with inhibition of mobilization of granulocyte/macrophage.

Conclusions

These findings suggest that application of PAAB to the rat FA causes superoxide-linked expression of ICAM-1 and mobilization of granulocyte and macrophages. Thus, the potential value in suppressing these variables stimulated by PAAB is indicated in therapeutic strategies for prevention and possible regression of vasospasm after subarachnoid hemorrhage.

Role of adenosine A(2B) receptors in vasodilation of rat pial artery and cerebral blood flow autoregulation

This study was aimed to investigate the underlying mechanism of vasodilation induced by the activation of A(2B) adenosine receptors in relation to cerebral blood flow (CBF) autoregulation. Changes in pial arterial diameters were observed directly through a closed cranial window. N(omega)-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor) significantly suppressed the concentration-dependent vasodilations induced by adenosine and 5'-N-ethylcarboxamido-adenosine (NECA) but not the vasodilation by CGS-21680 (A(2A)-receptor agonist). Moreover, NECA-induced vasodilation was suppressed by alloxazine (1 micromol/l) but not by ZM-241385 (1 micromol/l, A(2A) antagonist), which suggests mediation by A(2B)- receptor activation. Otherwise, the level of nitrite/nitrate was concentration dependently increased in the artificial cerebrospinal fluid (CSF) when adenosine and NECA were suffused over the cortical surface. L-NAME and alloxazine, but not ZM-241385, largely inhibited their releases. The lower limit of CBF autoregulation was little affected following pretreatment with L-NAME or alloxazine. Thus it is suggested that adenosine-induced vasodilation via activation of A(2B)-adenosine receptors of the rat pial artery is coupled to the production of nitric oxide, which contributes little to CBF autoregulation.

Cysteinyl-tRNA formation: the last puzzle of aminoacyl-tRNA synthesis

With the exception of the methanogenic archaea Methanococcus jannaschii and Methanobacterium thermoautotrophicum deltaH, all organisms surveyed contain orthologs of Escherichia coli cysteinyl-tRNA synthetase (CysRS). The characterization of CysRS-encoding (cysS) genes and the demonstration of their ability to complement an E. coli cysSts mutant reveal that Methanococcus maripaludis and Methanosarcina barkeri, two other methanogenic archaea, possess canonical CysRS proteins. A molecular phylogeny inferred from 40 CysRS sequences indicates that the CysRS of M. maripaludis and Methanosarcina spp. are specific relatives of the CysRS of Pyrococcus spp. and Chlamydia, respectively. This result suggests that the CysRS gene was acquired by lateral gene transfer in at least one euryarchaeotic lineage.

SKP-450 inhibits migration and DNA synthesis stimulated by oxidized low density lipoprotein in smooth muscle cells

This study was carried out to examine the inhibitory effects of SKP-450 (2-[2"(1", 3"-dioxolone)-2-methyl]-4-(2'-oxo-1'-pyrrolidinyl)-6-nitro-2H-1-be nzo pyran), a potassium channel opener, on the proliferation and migration stimulated by oxidized low density lipoprotein (LDL) of cultured smooth muscle cells of Wistar Kyoto rat aorta. SKP-450 (10(-7) and 10(-6) M) as well as probucol (10(-7)-10(-5) M) reduced the production of thiobarbituric acid reactive substances from LDL submitted to CuSO(4) (10 microM). The increased [3H]thymidine incorporation and migration (chemotactic and wound-edge) of the cultured smooth muscle cells in association with increased production of platelet-derived growth factor (PDGF)-BB-like immunoreactivity stimulated by oxidized LDL were significantly reduced by SKP-450 (10(-7)-10(-6) M). Inhibition by SKP-450 of the oxidized LDL-stimulated [3H]thymidine incorporation was antagonized by iberiotoxin (10(-7) M), but not by glibenclamide (10(-6) M), suggestive of mediation of Ca(2+)-activated K(+) channel opening in the action of SKP-450. Taken together, SKP-450 inhibited the proliferation and migration of the smooth muscle cells as well as PDGF production stimulated by oxidized LDL, accompanying with its antiperoxidative action.

Metabolism of cAMP to adenosine: role in vasodilation of rat pial artery in response to hypotension

The purpose of this experiment was to examine whether the cAMP-adenosine pathway is implicated in the autoregulatory vasodilation in response to hypotension. Suffusion with cAMP (1-100 micromol/l) or adenosine (0.01-10 micromol/l) caused a sustained vasodilation of the resting pial arteries in a concentration-dependent manner. In contrast, N6,2'-O-dibutyryl-cAMP and 8-bromo-cAMP exerted a weak dilation at high concentration (100 micromol/l). The vasodilation to cAMP (1-100 micromol/l), adenosine (0.01-10 micromol/l), and hypotension was significantly reduced by pretreatment with 3,7-dimethyl-1-propargylxanthine (1 micromol/l), an A2 receptor antagonist, as well as 3-isobutyl-1-methylxanthine (3 micromol/l), an inhibitor of endo- and ectophosphodiesterase, 1, 3-dipropyl-8-p-sulfophenylxanthine (100 micromol/l), an inhibitor of ecto-5'-phosphodiesterase, or alpha,beta-methylene-adenosine 5'-diphosphate (100 micromol/l), an inhibitor of ecto-5'-nucleotidase. However, 8-cyclopentyltheophylline (1 micromol/l), an A1 antagonist, did not elicit a similar response. The increased release of adenosine when the cortical surface was suffused with cAMP (100 micromol/l) was significantly reduced by 3-isobutyl-1-methylxanthine, 1,3-dipropyl-8-p-sulfophenylxanthine, and alpha,beta-methylene-adenosine 5'-diphosphate (each 100 micromol/l). These results indicate that the cAMP-adenosine pathway as a viable metabolic mechanism is implicated in the production of adenosine in the rat pial artery and contributes to the regulation of vasodilation in response to hypotension.

Effect of omega-conotoxin GVIA and omega-agatoxin IVA on the capsaicin-sensitive calcitonin gene-related peptide release and autoregulatory vasodilation in rat pial arteries

This study assesses the effect of neuronal voltage-sensitive Ca2+ channel blockers, omega-conotoxin GVIA (CTX), and omega-agatoxin IVA (AgTX) on the vasodilation and release of calcitonin gene-related peptide (CGRP), both of which were induced by either application of capsaicin or acute stepwise hypotension. Changes in pial arterial diameter were determined directly through a closed cranial window. The vasodilation of pial artery induced by either CGRP (0.1 micromol/L) or capsaicin (0.3 micromol/L) was significantly inhibited by CGRP(8-37) (0.1 micromol/L) (P < 0.05 and P < 0.05, respectively). The autoregulatory vasodilation to acute stepwise hypotension was severely attenuated by pretreatment with either CTX or AgTX. When the hypotension was kept for 2, 4, and 10 minutes, the releasable CGRP-like immunoreactivity (CGRP-LI) level (vehicle, 13.4+/-1.5 fmol/mm2/30 min) by 10 micromol/L capsaicin from the isolated pial arteries was significantly reduced in the 4- and 10-minute hypotension groups (11.3+/-1.2 fmol/mm2/30 min, P < 0.05, and 11.1+/-1.5 fmol/mm2/30 min, P < 0.05, respectively), but not in 2-min group. Moreover, the CGRP-LI level released by 10 micromol/L capsaicin (13.7+/-0.9 fmol/mm2/30 min) also was significantly depressed by pretreatment with 1 micromol/L CTX to 10.4+/-1.0 fmol/mm2/30 min (P < 0.01) and with 0.1 micromol/L AgTX to 8.7(1.7 fmol/mm2/30 min (P < 0.001), as well as by pretreatment with 10 micro-mol/L capsaicin (6.0+/-1.6 fmol/ mm2/30 min, P < 0.001). These results suggest that the neuronal N- and P-type voltage-sensitive Ca2+ channels are implicated in the release of CGRP from capsaicin-sensitive perivascular sensory nerves in response to acute hypotension, and that the released CGRP may contribute to the autoregulatory vasodilation in the cerebral microcirculation.

Inhibitory effect of rebamipide on the neutrophil adherence stimulated by conditioned media from Helicobacter pylori-infected gastric epithelial cells

We investigated the mechanism or mechanisms by which rebamipide protects against the gastric mucosal inflammation associated with Helicobacter pylori. The production of interleukin (IL)-8 in association with expression of IL-8 mRNA was greatly increased in the H. pylori-infected Kato III cells in a concentration- and time-dependent manner, whereas the secretion of IL-6 and tumor necrosis factor-alpha was not detectable. The increased production of IL-8 and expression of IL-8 mRNA were significantly inhibited by rebamipide (100-1000 microM) in a concentration-dependent manner. Formyl-methionyl-leucyl-phenylalanine (1 nM), as well as conditioned medium (CM) that was produced from H. pylori-infected Kato III cells, caused an increase in surface expression of CD11b on human neutrophils and an increase in neutrophil adhesion to the human umbilical vein endothelial cells. Rebamipide also suppressed the adherence of neutrophils to endothelial cells as well as the expression of CD11b on neutrophils induced by formyl-methionyl-leucyl-phenylalanine and CM. Furthermore, CM-induced neutrophil adhesion to the endothelial cells was significantly inhibited by IL-8-neutralizing antibody, suggesting that IL-8 is implicated in the CM-induced neutrophil adhesion to the cultured human umbilical vein endothelial cells. It is concluded that rebamipide exerts its preventive effect against H. pylori-evoked gastric mucosal cell inflammation by inhibition of the neutrophil adherence to the endothelial cells as well as by suppressing the surface expression of CD11b on neutrophils and the production of proinflammatory cytokine such as IL-8 from gastric epithelial cells.

Pharmacological profiles of SKP-450 and its family, a K+ channel opener, in comparison with levcromakalim

This study was carried out to characterise the vasodepressor and vasorelaxant actions of a benzopyran derivative, SKP-450 and its family, (+/-)-racemate SKP-411, (+)-enantiomer SKP-451, and the metabolites of SKP-450 (SKP-818 and SKP-310) in comparison with levcromakalim (LCRK) in the canine coronary, rabbit basilar and vertebral arterial segments. SKP-450, its family (SKP-411 and SKP-451) and the metabolite of SKP-450 (SKP-818) caused concentration-dependent relaxations as well as LCRK in the canine coronary artery and rabbit basilar and vertebral arteries. The relaxant potency of SKP-450 was significantly higher than that of LCRK in the three arteries in terms of EC50 values. SKP-450- and LCRK-induced vasorelaxations were competitively antagonised by glibenclamide with pA2 values of 7.60 (slope 1.22) and 7.99 (slope, 1.00), respectively. SKP-450 (0.1 and 1.0 microM) caused a significant stimulation of the 86Rb efflux from canine coronary arteries in a concentration-dependent manner as well as LCRK (1 and 10 microM), and their effects were antagonised by glibenclamide (10 microM). SKP-450 as well as LCRK produced long-lasting decreases in mean arterial pressure in the spontaneously hypertensive rats (SHR). These results suggest that SKP-450 has a significantly higher potency than LCRK in in vitro vasorelaxation, and it exerts potent and long-lasting vasodepressor effects with its active metabolite (SKP-818).

Effect of rebamipide on liver damage and increased tumor necrosis factor in a rat model of endotoxin shock

We investigated the effect of rebamipide, a novel antiinflammatory agent, on liver damage in a rat model of circulatory shock induced by bacterial endotoxin (E. coli lipopolysaccharide, LPS). Endotoxemia for 6 hr resulted in a 5.9-fold rise in the serum levels of nitrite (P < 0.05) with a significant rise in the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactic dehydrogenase (LDH), suggestive of liver dysfunction. The increased activities of serum ALT, AST, and LDH, but not serum nitrite were significantly inhibited by rebamipide (100 mg/kg, orally for five days). Myeloperoxidase activity in the liver was significantly elevated in the rats with endotoxemia by 2.4-fold (P < 0.05), which was also significantly inhibited by rebamipide. Upon LPS injection, serum TNF-alpha levels peaked at 1 hr after LPS (from 167.4 +/- 20.0 to 1570.0 +/- 100.0 pg/ml) and thereafter rapidly declined. The increased TNF-alpha level measured at 1 hr was significantly inhibited by pretreatment with rebamipide (100 mg/kg for five days). It is suggested that rebamipide exerts a strong protective effect on the LPS-induced liver damage through inhibition of activation of neutrophils and TNF-alpha production.

Retracing the evolution of amino acid specificity in glutaminyl-tRNA synthetase

Molecular phylogenetic studies of glutaminyl-tRNA synthetase suggest that it has relatively recently evolved from the closely related enzyme glutamyl-tRNA synthetase. We have now attempted to retrace one of the key steps in this process by selecting glutaminyl-tRNA synthetase mutants displaying enhanced glutamic acid recognition. Mutagenesis of two residues proximal to the active site, Phe-90 and Tyr-240, was found to improve glutamic acid recognition 3-5-fold in vitro and resulted in the misacylation of tRNA(Gln) with glutamic acid. In vivo expression of the genes encoding these misacylating variants of glutaminyl-tRNA synthetase reduced cellular growth rates by 40%, probably as a result of an increase in translational error rates. These results provide the first biochemical evidence that glutaminyl-tRNA synthetase originated through duplication and consequent diversification of an ancestral glutamyl-tRNA synthetase-encoding gene.

The terminal adenosine of tRNA(Gln) mediates tRNA-dependent amino acid recognition by glutaminyl-tRNA synthetase

Sequence-specific interactions between Escherichia coli glutaminyl-tRNA synthetase and tRNA(Gln) have been shown to determine the apparent affinity of the enzyme for its cognate amino acid glutamine during aminoacylation. Specifically, structural and biochemical studies suggested that residues Asp66, Tyr211, and Phe233 in glutaminyl-tRNA synthetase could potentially facilitate cognate amino recognition through their specific interactions with both A76 of tRNA(Gln)++ and glutamine. These residues were randomly mutated and the resulting glutaminyl-tRNA synthetase variants were screened in vivo for changes in their ability to recognize noncognate tRNAs and retention of tRNA-glutaminylation activity. When the variants selected in this way were characterized in vitro, they all showed dramatic decreases in apparent affinity (KM) for glutamine but little or no change in cognate tRNA affinity. Conservative replacements such as Y211F, F233L, and D66E resulted in 60-, 19-, and 18-fold increases compared to wild-type in the KM for glutamine, respectively, but had little effect on the turnover number (kcat). Nonconservative replacements affected both KM for glutamine and kcat; Y211S, F233D, and D66F displayed 1700, 3700, and 1200-fold decreases in kcat/KM for glutamine compared to wild-type. Double mutant cycle analysis indicated that Tyr211, and Phe233 interact strongly to enhance glutamine binding. These data now show that Asp66, Tyr211 and Phe233 mediate tRNA-dependent cognate amino acid recognition via the invariant 3'-terminal adenosine of tRNA(Gln).

tRNA-dependent amino acid transformations

Aminoacyl-tRNAs are either synthesized directly by aminoacyl-tRNA synthetases or indirectly by tRNA-dependent transformation of mischarged tRNAs. The enzymes which participate in the indirect routes may be interesting targets in the development of novel therapeutic compounds. We have purified one such enzyme, Glu-tRNA(Gln) amidotransferase from Bacillus subtilis, to homogeneity and present the initial biochemical characterization data.

The in vitro pharmacological profile of KR31080, a nonpeptide AT1 receptor antagonist

KR31080 (2-butyl-5-methyl-6-(1-oxopyridin-2-yl)-3-[[2'-(1H-tetrazol- 5-yl) biphenyl-4-yl]methyl]-3H-imidazo[4,5-b] pyridine) is a potent inhibitor of angiotensin type 1 (AT1) receptors in rabbit aorta and human recombinant AT1 receptors. In the isolated rabbit thoracic aorta, KR31080 caused a nonparallel shift to the right of the concentration-response curves to angiotensin II (AII) with decreased maximal response (pD'2 = 10.1 +/- 0.1), but had no effect on the contractile response induced by norepinephrine. KR31080 inhibited specific [125I]AII binding to rabbit aortic membranes (AT1 receptors) and [125I][Sar1, Ile8]AII binding to human recombinant AT1 receptors in a concentration-dependent manner with IC50 values of 0.84 +/- 0.08 nM and 1.92 +/- 0.15 nM, respectively, but did not inhibit specific [125I]AII binding to bovine cerebellum membranes (AT2 receptors). In the Scatchard analysis, KR31080 interacted with rabbit aortic AT1 receptors in a competitive manner, similar to losartan. These results demonstrate that KR31080 is a potent and AT1 selective angiotensin receptor antagonist which exerts a competitive antagonism in the [125I]AII binding assay and insurmountable AT1 receptor antagonism in the functional study.

A nuclear genetic lesion affecting Saccharomyces cerevisiae mitochondrial translation is complemented by a homologous Bacillus gene

A novel Bacillus gene was isolated and characterized. It encodes a homolog of Saccharomyces cerevisiae Pet112p, a protein that has no characterized relative and is dispensable for cell viability but required for mitochondrial translation. Expression of the Bacillus protein in yeast, modified to ensure mitochondrial targeting, partially complemented the phenotype of the pet112-1 mutation, demonstrating a high degree of evolutionary conservation for this as yet unidentified component of translation.

Age-dependent changes in particulate and soluble guanylyl cyclase activities in urinary tract smooth muscle

Regional and age specific differences are observed in the sodium nitroprusside induced relaxation responses in the urinary tract. To clarify these differences, guanylyl cyclase activity is assayed in particulate and soluble fractions from the ureter, bladder dome, and urethra of young (11-18 days), adult (90-100 days), and old adult (2-3 years) guinea pigs. The rank order of soluble guanylyl cyclase activities is urethra = ureter > bladder dome with the largest decreases with aging occurring in the bladder. Atrial natriuretic factor (10(7) M) increases particulate guanylyl cyclase activity in the three tissues at all ages tested, with the activity being highest in the ureter. ATP (0.5 mM) activates particulate guanylyl cyclase in the ureter, bladder and urethra of old adult guinea pigs, and enhances atrial natriuretic factor induced activation of particulate guanylyl cyclase in all tissues and at all ages tested. The higher levels of soluble guanylyl cyclase activity in the urethra and ureter compared to the bladder parallel sodium nitroprusside induced relaxation in these tissues.

Preventive effect of rebamipide on gastric mucosal cell damage evoked by activation of formyl-methionyl-leucyl-phenylalanine receptors of rabbit neutrophils

We investigated the underlying mechanism by which rebamipide exerts a preventive effect on neutrophil-mediated gastric mucosal cell damage. The release of 2',7'-bis-(2-carboxyethyl)-5-(and -6)-carboxyfluorescein (an index of cytotoxicity) was significantly increased by 16.7% (P < .05) when 2',7'-bis-(2-carboxyethyl)-5-(and -6)-carboxyfluorescein-acetomethyl ester (5 microM) loaded gastric mucosal cells were incubated with neutrophils (5 x 10(6) cells/well) that were activated by cytochalasin B (5 microM) and formyl-methionyl-leucyl-phenylalanine (fMLP) (1 nM). In the in vitro study, upon application of cytochalasin B and fMLP, formation of superoxide anion and release of myeloperoxidase increased with increased neutrophil aggregation. These parameters were attenuated by pretreatment with rebamipide (100-1000 microM) in a concentration-dependent manner. In the Scatchard analysis, the maximum binding of [3H]fMLP to neutrophils decreased from 0.57 to 0.44 pmol/2 x 10(6) cells (P < .05) by application of rebamipide (300 microM) with little change in K(D). Neutrophils isolated from rabbits orally treated with rebamipide (100 mg/kg for 3 days) also showed a decrease in the production of superoxide anion upon stimulation with fMLP and a decrease in the binding of [3H]fMLP to its receptors on the neutrophil plasma membrane (0.59-0.45 pmol/2 x 10(6) cells, P < .05). Taken together, it is suggested that the inhibitory effect of rebamipide on the neutrophil-mediated gastric mucosal cell injury is due, in part, to alterations in the neutrophil membrane that ultimately result in a decrease in the number of binding sites for fMLP to its receptors.

Decreased CGRP level with increased sensitivity to CGRP in the pial arteries of spontaneously hypertensive rats

It was aimed to investigate the importance of calcitonin gene-related peptide (CGRP) in maintenance of normal cerebral microcirculation. We examined both the functional (in vivo) and biochemical effects (in vitro) of CGRP on the pial arteries of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). When mock cerebrospinal fluid containing capsaicin (3 x 10(-7) M) was suffused over the cortical surface, the diameter of pial arteries of SHR was transiently increased and rapidly returned to the baseline level, while the capsaicin-induced increase in pial arterial diameters of WKY was large and sustained for a longer duration (> 10 min). Capsaicin-induced vasodilation was significantly attenuated by pretreatment with CGRP8-37, a CGRP1, receptor antagonist, in both WKY and SHR. On the other hand, cortical suffusion with CGRP (10(-9) approximately 10(-6) M) exerted a larger enhancement in the vasodilation of pial artery of SHR than WKY. The CGRP-induced vasodilation was significantly antagonized by CGRP8-37 in both WKY and SHR. The released level of CGRP-like immunoreactivity (CGRP-LI) from the pial artery was significantly lower in SHR (12.3 +/- 1.2 fmol/mm2/hr) than that in WKY (24.5 +/- 3.9 fmol/mm2/hr). CGRP (10(-6) M)-induced stimulation of cyclic AMP formation was rather larger in the pial arteries from SHR (50.2 +/- 5.8 fmol/mm2/30 min, p < 0.05) than those from WKY (34.5 +/- 3.8 fmol/mm2/30 min). These data suggest that, in the pial arteries of SHR, the transient vasodilation to capsaicin and enhanced vasodilation to CGRP are related to the decreased CGRP level in the cerebral microvascular beds, consequently leading to increased sensitivity of the CGRP receptors to CGRP.

Genetic analysis of functional connectivity between substrate recognition domains of Escherichia coli glutaminyl-tRNA synthetase

It has previously been shown that the single mutation E222K in glutaminyl-tRNA synthetase (GlnRS) confers a temperature-sensitive phenotype on Escherichia coli. Here we report the isolation of a pseudorevertant of this mutation, E222K/C171G, which was subsequently employed to investigate the role of these residues in substrate discrimination. The three-dimensional structure of the tRNA(Gln): GlnRS: ATP ternary complex revealed that both E222 and C171 are close to regions of the protein involved in interactions with both the acceptor stem and the 3' end of tRNA(Gln). The potential involvement of E222 and C171 in these interactions was confirmed by the observation that GlnRS-E222K was able to mischarge supF tRNA(Tyr) considerably more efficiently than the wild-type enzyme, whereas GlnRS-E222K/C171G could not. These differences in substrate specificity also extended to anticodon recognition, with the double mutant able to distinguish supE tRNA(CUA)(Gln) from tRNA2(Gln) considerably more efficiently than GlnRS E222K. Furthermore, GlnRS-E222K was found to have a 15-fold higher K(m) for glutamine than the wild-type enzyme, whereas the double mutant only showed a 7-fold increase. These results indicate that the C171G mutation improves both substrate discrimination and recognition at three domains in GlnRS-E222K, confirming recent proposals that there are extensive interactions between the active site and regions of the enzyme involved in tRNA binding.

Interactions between tRNA identity nucleotides and their recognition sites in glutaminyl-tRNA synthetase determine the cognate amino acid affinity of the enzyme

Sequence-specific interactions between aminoacyl-tRNA synthetases and their cognate tRNAs both ensure accurate RNA recognition and prevent the binding of noncognate substrates. Here we show for Escherichia coli glutaminyl-tRNA synthetase (GlnRS; EC 6.1.1.18) that the accuracy of tRNA recognition also determines the efficiency of cognate amino acid recognition. Steady-state kinetics revealed that interactions between tRNA identity nucleotides and their recognition sites in the enzyme modulate the amino acid affinity of GlnRS. Perturbation of any of the protein-RNA interactions through mutation of either component led to considerable changes in glutamine affinity with the most marked effects seen at the discriminator base, the 10:25 base pair, and the anticodon. Reexamination of the identity set of tRNA(Gln) in the light of these results indicates that its constituents can be differentiated based upon biochemical function and their contribution to the apparent Gibbs' free energy of tRNA binding. Interactions with the acceptor stem act as strong determinants of tRNA specificity, with the discriminator base positioning the 3' end. The 10:25 base pair and U35 are apparently the major binding sites to GlnRS, with G36 contributing both to binding and recognition. Furthermore, we show that E. coli tryptophanyl-tRNA synthetase also displays tRNA-dependent changes in tryptophan affinity when charging a noncognate tRNA. The ability of tRNA to optimize amino acid recognition reveals a novel mechanism for maintaining translational fidelity and also provides a strong basis for the coevolution of tRNAs and their cognate synthetases.

Glutaminyl-tRNA synthetase: from genetics to molecular recognition

Accurately aminoacylated tRNAs are an a priori requirement for translation of the genetic code. They are synthesized by the aminoacyl-tRNA synthetases which select both the correct amino acid and tRNA from a total of more than 400 possible combinations. Genetic, biochemical and structural studies have begun to reveal the mechanisms by which this specificity is achieved by Escherichia coli glutaminyl-tRNA synthetase (GlnRS). Sequence-specific interactions between GlnRS and tRNA(Gln) determine both the accuracy of tRNA selection and the efficiency of aminoacylation. Thus, amino acid recognition is tRNA-dependent. Consequently, while a noncognate tRNA may be recognized by GlnRS, the resulting tRNA-enzyme complex displays a considerably reduced affinity for glutamine compared to wild-type. This mechanism now provides a ready explanation as to why the majority of tRNA mischarging events, including those originally described over 25 years ago for GlnRS, impair cellular viability only to a limited degree.

Transfer RNA-dependent cognate amino acid recognition by an aminoacyl-tRNA synthetase

An investigation of the role of tRNA in the catalysis of aminoacylation of Escherichia coli glutaminyl-tRNA synthetase (GlnRS) has revealed that the accuracy of specific interactions between GlnRS and tRNAGln determines amino acid affinity. Mutations in GlnRS at D235, which makes contacts with nucleotides in the acceptor stem of tRNAGln, and at R260 in the enzyme's active site were found to be independent during tRNA binding but interactive for aminoacylation. Characterization of mutants of GlnRS at position 235, showed amino acid recognition to be tRNA mediated. Aminoacylation of tRNA(CUA)Tyr [tyrT (UAG)] by GlnRS-D235H resulted in a 4-fold increase in the Km for the Gln, which was reduced to a 2-fold increase when A73 was replaced with G73. These and previous results suggest that specific interactions between GlnRS and tRNAGln ensure the accurate positioning of the 3' terminus. Disruption of these interactions can change the Km for Gln over a 30-fold range, indicating that the accuracy of aminoacylation is regulated by tRNA at the level of both substrate recognition and catalysis. The observed role of RNA as a cofactor in optimizing amino acid activation suggests that the tRNAGln-GlnRS complex may be partly analogous to ribonucleoprotein enzymes where protein-RNA interactions facilitate catalysis.

Homologous expression and purification of mutants of an essential protein by reverse epitope-tagging

Purification of mutant enzymes is a prime requirement of biophysical and biochemical studies. Our investigations on the essential Escherichia coli enzyme glutaminyl-tRNA synthetase demand mutant enzymes free of any wild-type protein contamination. However, as it is not possible to express noncomplementing mutant enzymes in an E. coli glnS-deletion strain, we developed a novel strategy to address these problems. Instead of following the common tactic of epitope-tagging the mutant protein of interest on an extrachromosomal genetic element, we fused a reporter epitope to the 5' end of the chromosomal glnS-gene copy: this is referred to as 'reverse epitope-tagging.' The corresponding strain, E. coli HAPPY101, displays a normal phenotype, and glutaminyl-tRNA synthetase is exclusively present as an epitope-tagged form in cell-free extracts. Here we report the use of E. coli HAPPY101 to express and purify a number of mutant glutaminyl-tRNA synthetases independently of their enzymatic activity. In this process, epitope-tagged wild-type protein is readily separated from mutant enzymes by conventional chromatographic methods. In addition, the absence of wild-type can be monitored by immunodetection using a monoclonal antibody specific for the epitope. The strategy described here for expression and purification of an essential enzyme is not restricted to glutaminyl-tRNA synthetase and should be applicable to any essential enzyme that retains sufficient activity to sustain growth following reverse epitope-tagging.

Pharmacological coupling and functional role for CGRP receptors in the vasodilation of rat pial arterioles

In this study, we investigated the signal transduction underlying the vasodilator action of calcitonin gene-related peptide (CGRP) in the rat pial arterioles. In an in vivo experiment, changes in pial arterial diameters (20.2 +/- 1.9 microns) were observed under suffusion with mock cerebrospinal fluid containing CGRP (10(-9)-10(-7) M) directly through a closed cranial window. Changes in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in response to CGRP and levcromakalim were measured in the pial arterioles in an in vitro experiment. CGRP-induced vasodilation and cAMP production were significantly inhibited by specific CGRP antibody serum and CGRP-(8-37) fragment, suggesting involvement of the CGRP1 receptor subtype. Vasodilation and increase in cAMP production evoked by CGRP were inhibited not only by glibenclamide (ATP-sensitive K+ channel blocker) but also by charybdotoxin (large-conductance Ca(2+)-activated K+ channel blocker), but this was not the case for the isoproterenol-induced vasodilation and cAMP production. These findings implicate the ATP-sensitive K+ channels and the large-conductance Ca(2+)-activated K+ channels in the CGRP receptor-coupled cAMP production for vasodilation. Further study is required to identify whether the cAMP-dependent K+ channel activation is related to CGRP-induced vasorelaxation of the rat pial arterioles.

Preventive effect of rebamipide on gastric lesions induced by ischemia-reperfusion in the rat

Rebamipide (2-(4-chlorobenzoylamino)-3-[2-(1H)-quinolinon-4-yl] propionic acid), a novel antiulcer agent, has been reported to prevent various acute experimental gastric mucosal lesions and to accelerate the healing of chronic gastric ulcers. We investigated the effect of rebamipide on rat gastric mucosa damaged by exposure to 30 min of ischemia and 60 min of reperfusion (I/R) with continuous intragastric instillation of 0.1 N HCl (1 ml/100 g body weight) into the stomach. Rebamipide, at 30 and 100 mg/kg, i.p., reduced the mucosal damage score from 2.28 (I/R vehicle group) to 1.54 and 1.07, respectively. Pretreatment with rebamipide significantly reduced the activity of myeloperoxidase (an index of neutrophil infiltration) and preserved the activities of superoxide dismutase and nitric oxide synthase in the gastric mucosa with inhibition of malondialdehyde production. Thus, a negative correlation between the activities of nitric oxide synthase and myeloperoxidase (y = 4.35-9.45x, r = .67, P < .01) was observed. In an in vitro study, rebamipide inhibited N-formyl-met-leu-phe-induced chemotaxis of neutrophils and production of superoxide anion from opsonized zymosan-stimulated neutrophils. However, it did not affect the production of superoxide anion either by the xanthine-xanthine oxidase reaction or phorbol 12-myristate 13-acetate-stimulated neutrophils. Based on these results, it is suggested that rebamipide exerts a protective effect on the I/R-induced gastric mucosal damage through inhibition of mobilization and activation of neutrophils in association with an attenuation of the decreases in both superoxide dismutase and nitric oxide synthase activities, thereby preventing the gastric microcirculation from deterioration.

Characterization of PD 121981- and CGP 42112-induced unmasking of low concentration effects of angiotensin II in rabbit abdominal aorta

The unmasking of the low concentration effect of angiotensin II (AII) was identified within the concentration ranges of 10(-13) to 10(-11) M of AII by PD 121981 (5-diphenylacetyl-1-(4-methoxy-3-methylbenzyl)- 4,5,6,7-tetrahydro-1H-imidazo[4,5-c]-pyridine-6-carboxylic acid) and 10(-12) to 3 x 10(-10) M of AII by CGP 42112 (nicotinic acid-Tyr-(N alpha-benzyl-oxycarbonyl-Arg)Lys-His-Pro-IIe-OH), AT2 antagonists, in association with the ordinary contraction curve, i.e., high concentration effect (at 3 x 10(-10)-10(-6) M of AII), in the rabbit abdominal aorta. Thus, they showed clear biphasic features of AII-induced contraction curves. However, this was not the case for angiotensin I and angiotensin III. This PD 121981-evoked low concentration effect of AII was selectively inhibited by DuP 753 (0.01-1 nM), dithiothreitol (10 and 100 microM), pertussis toxin (50 and 300 ng/ml, for 2 hr), nifedipine (1 and 10 microM) and 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (1 and 3 microM), which suggests the receptors were the AT1 subtype. However, the high concentration effect of AII was not affected by these drugs within the concentration ranges used in the present studies. These myographic results were almost consistent with the features of the intracellular Ca++ changes. Thus, it was concluded that the receptors that mediate the low concentration effect of AII belong to the AT1 subtype. However, the current study did not determine the mechanism by which PD 121981 and CGP 42112 evoked the up-regulation of the AT1 receptors.

Relaxant effects of cromakalim and ATP depletion in dog and rat mesenteric arteries--species differences

In the present study, the effects of cromakalim on tension and 86Rb+ efflux rate were evaluated in strips of dog and rat mesenteric arteries and compared with the variables obtained from ATP-depleted strips of both species. The cromakalim-induced relaxation was competitively antagonized by glibenclamide, with similar pA2 values, in both dog and rat mesenteric arteries. Glibenclamide caused an enhancement of the precontraction or a reversal of the cromakalim-induced inhibition in the mesenteric arteries of both species when cromakalim was applied prior to or during phenylephrine-contraction. The 86Rb+ efflux rate from the mesenteric arteries was significantly increased in both species after application of cromakalin (10 microM). However, in the ATP-depleted mesenteric artery (verified by high performance liquid chromatography), an increase in 86Rb+ efflux and a glibenclamide-induced enhancement of contraction were observed in the rat, but not in the dog. Taken together, between dog and rat mesenteric arterial strips, a differential effect of ATP depletion with 2-deoxyglucose plus oligomycin was identified in the activation of ATP-sensitive K+ channels, but not of cromakalim.

Relaxation by cromakalim and pinacidil of isolated smooth muscle cells from canine coronary artery-multiple sites of action

Dispersed cells were isolated from the canine coronary artery by enzymatic digestion. Their contraction and relaxation were determined by measuring their length using a video microscaler system. The cells remained structurally intact when examined by Trypan blue exclusion and electron microscopy. The cells showed a concentration-dependent contraction (EC50: 2.3 +/- 0.36 x 10(-12) M) to phenylephrine. The phenylephrine-induced contraction of the intact cells was inhibited by cromakalim (IC50: 1.24 +/- 0.27 x 10(-10) M) and pinacidil (IC50: 6.8 +/- 1.89 x 10(-10) M). The sensitivity of the dispersed cells to cromakalim was approximately 3 orders of magnitude larger than that of the muscle strips (EC50: 1.94 +/- 0.22 x 10(-7) M). Glibenclamide (a selective inhibitor of the ATP-sensitive K+ channel in pancreatic beta-cells) competitively antagonized the cromakalim-induced inhibition of the phenylephrine-contraction in intact cells (pA2:9.12; slope: 1.13) as well as in muscle strips (pA2: 7.84; slope: 0.95). Permeabilized cells were made by a brief exposure of the cells to saponin and were suspended in a buffer medium containing 100 mM KCl and 0.18 microM Ca++. The cells showed a concentration-dependent contraction to phenylephrine (EC50:2.2 +/- 0.40 x 10(-12) M) and inositol 1,4,5-triphosphate (EC50: 5.3 +/- 1.05 x 10(-11) M). These contractions were concentration-dependently inhibited by cromakalim and pinacidil. The inhibition by cromakalim of the inositol-induced contraction was markedly antagonized by apamin and, to a lesser extent, by glibenclamide. Thus, it is suggested that cromakalim and pinacidil exert a potent relaxation by acting on multiple sites: the glibenclamide-sensitive K+ channels of the plasma membrane and the intracellular site sensitive to inositol and apamin.

Pharmacological evidence that calcitonin gene-related peptide is implicated in cerebral autoregulation

In anesthetized rats, we examined the possibility that calcitonin gene-related peptide (CGRP, a neuropeptide) released in response to transient hypotension may contribute to the reflex autoregulation of cerebral blood flow. Changes in pial arterial diameter (mean 33.0 +/- 1.1 microns) with changes in systemic arterial blood pressure (mean 101.9 +/- 2.7 mmHg) were observed directly through a closed cranial window. In capsaicin-treated rats (depletor of CGRP and substance P, 50 nmol capsaicin injected intracisternally 24 h before experiment), vasodilatation, which was evoked on transient hypotension, and vasoconstriction on reverse of hypotension were markedly attenuated or almost abolished. When changes in pial arterial diameter were plotted as a function of changes in blood pressure, the slopes of regression lines for vasodilatation and vasoconstriction were markedly reduced after capsaicin treatment. Similar reductions were evidenced under suffusion of CGRP antibody serum (1:1,000) and after CGRP receptor desensitization but not after substance P receptor desensitization. Pretreatment with glibenclamide, a K(+)-channel antagonist, also caused severe alterations in the autoregulatory vasomotor responses to hypotension and its reverse. Suffusion with mock cerebrospinal fluid, containing either CGRP or cromakalim, a K(+)-channel opener, dilated the pial artery in a concentration-dependent manner, and their effects were antagonized by glibenclamide. Substance P produced a vasodilatation, which was unaffected by glibenclamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ouabain on relaxation induced by cromakalim in human and canine mesenteric arteries

We investigated the effect of cromakalim, a K+ channel opener, that activates indirectly the Na(+)-K+ pump, in association with increased K+ conductance in the mesenteric arteries. In 65% of human mesenteric arteries tested, the concentration-dependent relaxation curves for cromakalim were biphasic: the low concentration (< 10(-7) M) effect was preferentially inhibited by ouabain, whereas the higher concentration effect was significantly inhibited by glibenclamide. In branches of canine mesenteric artery, the cromakalim-induced relaxation was inhibited by pretreatment with ouabain (1 microM) as well as by glibenclamide (1 microM). The reduction in contraction of human and canine mesenteric arterial strips caused by cromakalim was totally reversed by pretreatment with ouabain (1 microM) or glibenclamide (1 microM). On the other hand, in canine mesenteric artery, cromakalim caused a significant stimulation of 22Na+ influx and ouabain-sensitive 86Rb+ uptake in association with increased 86Rb+ efflux, all of which were inhibited by glibenclamide (1 microM). Thus, it is suggested that cromakalim possesses the additional property to stimulate the Na(+)-K+ pump through an elevation in intracellular Na+, resulting in strong relaxation of blood vessels.

Disturbances in autoregulatory responses of rat pial arteries by sulfonylureas

It was aimed to test the role of ATP-sensitive K+ channels in the autoregulatory response of cerebral arterioles in vivo. Changes in pial arterial caliber (mean, 43.2 +/- 2.3 microns in diameter) in response to changes in systemic arterial blood pressure (mean, 104.3 +/- 1.4 mmHg) were observed directly through closed cranial windows in anesthetized normotensive rats. During superfusion with vehicle, pial arterial caliber automatically increased in response to hypotension induced by arterial bleeding into a reservoir and decreased on reverse of arterial blood pressure by infusion of blood. After pretreatment with sulfonylureas, glibenclamide (1 and 3 microM) and glipizide (30 and 100 microM), arteriolar dilatation and constriction observed during hypotension and its reverse were disturbed. A similarity was evidenced when hypotension was induced by sodium nitroprusside (750 nmol kg-1min-1, i.v.). Cromakalim, a K+ channel opener, exerted a concentration-dependent vasodilatation of the pial artery and its effect was antagonized by glibenclamide. These data suggest that the endogenous glibenclamide-sensitive K+ channel opener is involved in the modulation of cerebral microvascular autoregulation.

Similarities between effects of superoxide-mediated endothelium-derived relaxing factor and cromakalim

A stable endothelium-derived relaxing factor has been reported to be generated on exposure of endothelial cells to the superoxide anion. In this study, we first evaluated the effects of the relaxing factor and cromakalim on mechanical tone and, second, assessed their consequences on the 86Rb efflux rate. On application of hypoxanthine-xanthine oxidase to a bath for generating superoxide anion, the precontracted rabbit mesenteric artery exhibited another transient increase in contraction, followed by sustained relaxation. This relaxation was lost in the K(+)-physiological salt solution (PSS) (greater than 35 mM) and was inhibited by glibenclamide (10 microM) but not by N-methyl-L-arginine or methylene blue. Hypoxanthine-xanthine oxidase application did not increase either basal or stimulated synthesis of guanosine 3',5'-cyclic monophosphate. In the presence of 2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and 10 mM MgCl2, the relaxing factor caused a significant increase in 86Rb efflux from the aortic and mesenteric arterial segments, as did the cromakalim. The increased 86Rb efflux, either by the relaxing factor or by cromakalim, was wholly inhibited by glibenclamide. These results suggest that superoxide-mediated endogenous relaxing factor may have a similar mechanism of action to cromakalim in vasodilatation.

Release of superoxide-dependent relaxing factor(s) from endothelial cells

In the present work, an experimental system was designed to study superoxide anion radical, implicated as the cause of vascular dilatation. To circumvent its direct effect, we employed a two-bath system. When the endothelial cells (EC) were exposed to electrical field stimulation (EFS) or to a hypoxanthine-xanthine oxidase system in bath A plus its physiological buffer solution suffused on a helical strip of cat basilar artery in bath B, the contraction to 5-hydroxytryptamine (5-HT) was depressed to approximately 40-50% of the control value. The reduction was not elicited on EFS in a state of calcium deficiency or in the absence of EC. The depression could be prevented by pretreatment with superoxide dismutase (SOD), but not with an effective dose of catalase, dimethyl sulfoxide (DMSO), mannitol, or indomethacin. The percent depression of contraction was paralleled by an increase in SOD-inhibitable cytochrome c reduction, which was not associated with cyclic guanosine 3',5'-monophosphate formation. These results suggest that superoxide-dependent relaxing factor is released from EC differently than the endothelium-derived relaxing factor mediated by acetylcholine.

Assessment of superoxide-mediated release of vascular-inhibitory factor(s) from endothelial cells by using a two-bath system

Release of a vascular-inhibitory factor from endothelial cells (EC), different from endothelium-derived relaxant factor (EDRF), was identified through use of a two-bath system. This two-bath system precluded the effects of oxygen-free radicals that appear when electrical field stimulation (EFS) is directly imposed on detector muscle.

Increased alpha 1- and decreased alpha 2-adrenoceptor sensitivities upon chronic treatment with imipramine in mediating cardiovascular responses in pithed rats

After chronic treatment with imipramine (20 mg/kg, i.p., twice daily for 14 days) the pressor dose-response curves to phenylephrine, methoxamine and cirazoline (alpha 1-adrenoceptor agonists) significantly shifted to the left with decreased PD50 values in pithed rats; however, the dose-response curve to Sgd 101/75, a selective alpha 1-adrenoceptor agonist was not affected. On the other hand, the alpha 2-adrenoceptor agonists such as B-HT 920, xylazine and clonidine produced a rightward shift for both the pressor (increased PD50) and cardioinhibition (increased ID50) dose-response curves in these rats. These results required treatment with imipramine over 2 weeks. Chronic treatment with imipramine has reduced the antagonism by prazosin of the pressor effect of phenylephrine when compared with the dose-ratios between the 2 groups. On the contrary, the antagonism by piperoxan of the cardioinhibitory effect of B-HT 920 was rather enhanced by the treatment, but that of the pressor effect of B-HT 920 was little changed. In cerebrocortical membrane fractions obtained from rats pretreated with imipramine, Ki of phenylephrine to displace [3H]prazosin was decreased, whereas that of clonidine and yohimbine to displace [3H]yohimbine was increased. In conclusion, it is demonstrated that after chronic imipramine treatment the peripheral alpha 2-adrenoceptors (both presynaptic and postsynaptic sites) as well as central alpha 2-adrenoceptors respond with a decreased sensitivity to the alpha 2-adrenoceptor agonists, and moreover, this treatment produces an increased sensitivity of the central and peripheral alpha 1-adrenoceptors to the alpha 1-adrenoceptor full agonists.