Epidermal growth factor receptor (EGFR) is a target of the tumor-suppressor E3 ligase FBXW7

FBXW7 is an E3 ubiquitin ligase that targets proteins for proteasome-mediated degradation and is mutated in various cancer types. Here, we use CRISPR base editors to introduce different FBXW7 hotspot mutations in human colon organoids. Functionally, FBXW7 mutation reduces EGF dependency of organoid growth by ~10,000-fold. Combined transcriptomic and proteomic analyses revealed increased EGFR protein stability in FBXW7 mutants. Two distinct phosphodegron motifs reside in the cytoplasmic tail of EGFR. Mutations in these phosphodegron motifs occur in human cancer. CRISPR-mediated disruption of the phosphodegron motif at T693 reduced EGFR degradation and EGF growth factor dependency. FBXW7 mutant organoids showed reduced sensitivity to EGFR-MAPK inhibitors. These observations were further strengthened in CRC-derived organoid lines and validated in a cohort of patients treated with panitumumab. Our data imply that FBXW7 mutations reduce EGF dependency by disabling EGFR turnover.

Dietary lipids fuel GPX4-restricted enteritis resembling Crohn's disease

The increased incidence of inflammatory bowel disease (IBD) has become a global phenomenon that could be related to adoption of a Western life-style. Westernization of dietary habits is partly characterized by enrichment with the ω-6 polyunsaturated fatty acid (PUFA) arachidonic acid (AA), which entails risk for developing IBD. Glutathione peroxidase 4 (GPX4) protects against lipid peroxidation (LPO) and cell death termed ferroptosis. We report that small intestinal epithelial cells (IECs) in Crohn’s disease (CD) exhibit impaired GPX4 activity and signs of LPO. PUFAs and specifically AA trigger a cytokine response of IECs which is restricted by GPX4. While GPX4 does not control AA metabolism, cytokine production is governed by similar mechanisms as ferroptosis. A PUFA-enriched Western diet triggers focal granuloma-like neutrophilic enteritis in mice that lack one allele of Gpx4 in IECs. Our study identifies dietary PUFAs as a trigger of GPX4-restricted mucosal inflammation phenocopying aspects of human CD.

Dietary lipids are linked to the development of inflammatory bowel diseases through unclear mechanisms. Here, the authors report that dietary polyunsaturated fatty acids trigger intestinal inflammation resembling aspects of Crohn’s disease, which is restricted by glutathione peroxidase 4 in the intestinal epithelium.

PGAM5 is a key driver of mitochondrial dysfunction in experimental lung fibrosis

RATIONALE

Mitochondrial homeostasis has recently emerged as a focal point in the pathophysiology of idiopathic pulmonary fibrosis (IPF), but conflicting data have been reported regarding its regulation. We speculated that phosphoglycerate mutase family member 5 (PGAM5), a mitochondrial protein at the intersection of multiple cell death and mitochondrial turnover pathways, might be involved in the pathogenesis of IPF.

METHODS

PGAM5-deficient mice and human pulmonary epithelial cells were analyzed comparatively with PGAM5-proficient controls in a bleomycin-based model of pulmonary fibrogenesis. Mitochondria were visualized by confocal and transmission electron microscopy. Mitochondrial homeostasis was assessed using JC1 (ΔΨ) and flow cytometry.

RESULTS

PGAM5 plays an important role in pulmonary fibrogenesis. Pgam5-/- mice displayed significantly attenuated lung fibrosis compared to controls. Complementary, in vitro studies demonstrated that PGAM5 impaired mitochondrial integrity on a functional and structural level independently of mtROS-production. On a molecular level, reduced mitophagy caused by PGAM5 deficiency improved mitochondrial homeostasis.

CONCLUSIONS

Our study identifies PGAM5 as an important regulator of mitochondrial homeostasis in pulmonary fibrosis. Our data further indicate PGAM5-mediated mitophagy itself as a pivotal gateway event in the mediation of self-sustaining mitochondrial damage and membrane depolarization. Our work hereby highlights the importance of mitochondrial dynamics and identifies a potential therapeutic target that warrants further studies. Toxic agents lead to mitochondrial damage resulting in depolarization of the mitochondrial membrane potential (ΔΨ) which is a gateway event for the initiation of PGAM5-mediated mitophagy. PGAM5-mediated mitophagy in turn leads to a self-perpetuating escalation of ΔΨ depolarization. Loss of the mitophagy-based damage-enhancing loop under PGAM5-deficient conditions breaks this vicious cycle, leading to improved mitochondrial homeostasis.

Interferon Lambda Promotes Paneth Cell Death Via STAT1 Signaling in Mice and Is Increased in Inflamed Ileal Tissues of Patients With Crohn's Disease

BACKGROUND & AIMS

Interferon lambda (IFNL) is expressed at high levels by intestinal epithelial cells (IECs) and mucosal immune cells in response to infection and inflammation. We investigated whether IFNL might contribute to pathogenesis of Crohn's disease (CD).

METHODS

We obtained serum samples and terminal ileum biopsies from 47 patients with CD and 16 healthy individuals (controls). We measured levels of IFNL by enzyme-linked immunosorbent assay and immunohistochemistry and location of expression by confocal microscopy. Activation of IFNL signaling via STAT1 was measured in areas of no, mild, moderate, and severe inflammation and correlated with Paneth cell homeostasis and inflammation. IFNL expression and function were studied in wild-type mice and mice with intestinal epithelial cell-specific (ΔIEC) disruption or full-body disruption of specific genes (Mlkl^-/-, Stat1^ΔIEC, Casp8^ΔIEC, Casp8^ΔIECRipk3^-/-, Casp8^ΔIECTnfr^-/-, Casp8^ΔIECMlkl^-/-, and Nod2^-/- mice). Some mice were given tail vein injections of a vector encoding a secreted form of IFNL. Intestinal tissues were collected from mice and analyzed by immunohistochemistry and immunoblots. We generated 3-dimensional small intestinal organoids from mice and studied the effects of IFNL and inhibitors of STAT-signaling pathway.

RESULTS

Patients with CD had significant increases in serum and ileal levels of IFNL compared with controls. Levels of IFNL were highest in ileum tissues with severe inflammation. High levels of IFNL associated with a reduced number of Paneth cells and increased cell death at the crypt bottom in inflamed ileum samples. Intestinal tissues from the ileum of wild-type mice injected with a vector expressing IFNL had reduced numbers of Paneth cells. IFNL-induced death of Paneth cells in mice did not occur via apoptosis, but required Mixed Lineage Kinase Domain Like (MLKL) and activation of Signal transducer and activator of transcription 1 (STAT1). In organoids, inhibitors of Janus kinase (JAK) signaling via STAT1 (glucocorticoids, tofacitinib, or filgotinib) reduced expression of proteins that mediate cell death and prevented Paneth cell death.

CONCLUSIONS

Levels of IFNL are increased in serum and inflamed ileal tissues from patients with CD and associated with a loss of Paneth cells. Expression of a secreted form of IFNL in mice results in loss of Paneth cells from intestinal tissues, via STAT1 and MLKL, controlled by caspase 8. Strategies to reduce IFNL or block its effects might be developed for treatment of patients with CD affecting the terminal ileum.

P1530Vasorelaxation as a mechanism of procyanidin B2 cardioprotective effect

Introduction

Findings from epidemiological studies indicate that polyphenols, widespread in human diet and with numerous biological activities, act cardioprotectively. Procyanidins are subclass of polyphenols with high content in commonly consumed foods and beverages, such as grapes, tea, chocolate, nuts and apples. Cardioprotective abilities of procyanidins, might, at least in part, attribute to their vasodilator properties.

Purpose

Because the exact mechanisms by which procyanidin B2 causes vasorelaxation are unclear, we aimed to investigate relaxant effect of procyanidin B2 on the isolated human internal mammary artery (HIMA) and its underlying mechanisms.

Methods

The HIMA segments were collected from patients suffering from coronary artery disease who were undergoing coronary artery bypass surgery and studied in organ bath.

Results

Procyanidin B2 induced strong concentration-dependent relaxation of HIMA rings pre-contracted by phenylephrine. Pretreatment with L-NAME, a NO synthase inhibitor, hydroxocobalamin, a NO scavenger, and ODQ, an inhibitor of soluble guanylate cyclase, significantly inhibited procyanidin B2-induced relaxation of HIMA, while indomethacin, a cyclooxygenase inhibitor, considerably reduced effects of low concentrations. Among K+ channel blockers, iberiotoxin, a selective blocker of large conductance Ca2+-activated K+ channels (BKCa), abolished procyanidin B2-induced relaxation, glibenclamide, a selective ATP-sensitive K+ (KATP) channel blocker, induced partial inhibition, while 4-aminopyridine, a blocker of voltage-gated K+ (KV) channels, and TRAM-34, an inhibitor of intermediate-conductance Ca2+-activated K+ (IKCa) channels, slightly reduced maximal relaxation of HIMA.

Conclusion

Our results demonstrate that, in HIMA, procyanidin B2 produces strong endothelium-dependent vasorelaxant effect. It seems that this relaxation is primarily the result of an increased NO synthesis and secretion by endothelial cells and partially of prostacyclin, although it involves activation of BKCa and KATP, as well as KV and IKCa channels in high concentrations of procyanidin B2.

Acknowledgement/Funding

The study was supported by a Scientific Research Grant (P175088) from Ministry of Science and Technology Serbia.

Oral Mucosal Organoids as a Potential Platform for Personalized Cancer Therapy

Previous studies have described that tumor organoids can capture the diversity of defined human carcinoma types. Here, we describe conditions for long-term culture of human mucosal organoids. Using this protocol, a panel of 31 head and neck squamous cell carcinoma (HNSCC)-derived organoid lines was established. This panel recapitulates genetic and molecular characteristics previously described for HNSCC. Organoids retain their tumorigenic potential upon xenotransplantation. We observe differential responses to a panel of drugs including cisplatin, carboplatin, cetuximab, and radiotherapy in vitro. Additionally, drug screens reveal selective sensitivity to targeted drugs that are not normally used in the treatment of patients with HNSCC. These observations may inspire a personalized approach to the management of HNSCC and expand the repertoire of HNSCC drugs. SIGNIFICANCE: This work describes the culture of organoids derived from HNSCC and corresponding normal epithelium. These tumoroids recapitulate the disease genetically, histologically, and functionally. In vitro drug screening of tumoroids reveals responses to therapies both currently used in the treatment of HNSCC and those not (yet) used in clinical practice.See related commentary by Hill and D'Andrea, p. 828.This article is highlighted in the In This Issue feature, p. 813.

Intestinal epithelial Caspase-8 signaling is essential to prevent necroptosis during Salmonella Typhimurium induced enteritis

Although induction of host cell death is a pivotal step during bacteria-induced gastroenteritis, the molecular regulation remains to be fully characterized. To expand our knowledge, we investigated the role of the central cell death regulator Caspase-8 in response to Salmonella Typhimurium. Here, we uncovered that intestinal salmonellosis was associated with strong upregulation of members of the host cell death machinery in intestinal epithelial cells (IECs) as an early event, suggesting that elimination of infected IECs represents a host defense strategy. Indeed, Casp8^∆IEC mice displayed severe tissue damage and high lethality after infection. Additional deletion of Ripk3 or Mlkl rescued epithelial cell death and lethality of Casp8^∆IEC mice, demonstrating the crucial role of Caspase-8 as a negative regulator of necroptosis. While Casp8^∆IECTnfr1^-/- mice showed improved survival after infection, tissue destruction was similar to Casp8^∆IEC mice, indicating that necroptosis partially depends on TNF-α signaling. Although there was no impairment in antimicrobial peptide secretion during the early phase of infection, functional Caspase-8 seems to be required to control pathogen colonization. Collectively, these results demonstrate that Caspase-8 is essential to prevent Salmonella Typhimurium induced enteritis and to ensure host survival by two different mechanisms: maintenance of intestinal barrier function and restriction of pathogen colonization.

Regression of apoptosis-resistant colorectal tumors by induction of necroptosis in mice

He et al. demonstrate that SMAC mimetic is efficient to target caspase-8–deficient colorectal cancer by induction of necroptosis. This study represents an attractive strategy for overcoming apoptosis resistance in colorectal cancer for the development of more effective personalized therapy.

Cancer cells often acquire capabilities to evade cell death induced by current chemotherapeutic treatment approaches. Caspase-8, a central initiator of death receptor–mediated apoptosis, for example, is frequently inactivated in human cancers via multiple mechanisms such as mutation. Here, we show an approach to overcome cell death resistance in caspase-8–deficient colorectal cancer (CRC) by induction of necroptosis. In both a hereditary and a xenograft mouse model of caspase-8–deficient CRC, second mitochondria-derived activator of caspase (SMAC) mimetic treatment induced massive cell death and led to regression of tumors. We further demonstrate that receptor-interacting protein kinase 3 (RIP3), which is highly expressed in mouse models of CRC and in a subset of human CRC cell lines, is the deciding factor of cancer cell susceptibility to SMAC mimetic–induced necroptosis. Thus, our data implicate that it may be worthwhile to selectively evaluate the efficacy of SMAC mimetic treatment in CRC patients with caspase-8 deficiency in clinical trials for the development of more effective personalized therapy.

PGAM5-mediated programmed necrosis of hepatocytes drives acute liver injury

OBJECTIVES

Autoimmune hepatitis (AIH) is a severe necroinflammatory liver disease associated with significant mortality. Although loss of hepatocytes is generally recognised as a key trigger of liver inflammation and liver failure, the regulation of hepatic cell death causing AIH remains poorly understood. The aim of this study was to identify molecular mechanisms that drive hepatocyte cell death in the pathogenesis of acute liver injury.

DESIGN

Acute liver injury was modelled in mice by intravenous administration of concanavalin A (ConA). Liver injury was demonstrated by serum transaminases and histological assessment of liver sections. PGAM5-deficient mice (PGAM5-/-) were used to determine its role in experimental hepatitis. Mdivi-1 was used as an inhibitor of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission. Mitochondrial fission and the expression of PGAM5 were compared between liver biopsies derived from patients with AIH and control patients.

RESULTS

PGAM5 was highly expressed in hepatocytes of patients with AIH and in mice with ConA-induced experimental hepatitis. Deficiency of PGAM5 protected mice from ConA-induced hepatocellular death and liver injury. PGAM5 regulated ConA-induced mitochondrial fission in hepatocytes. Administration of the Drp1-inhibitor Mdivi-1 blocked mitochondrial fission, diminished hepatocyte cell death and attenuated liver tissue damage induced by ConA.

CONCLUSIONS

Our data demonstrate for the first time that PGAM5 plays an indispensable role in the pathogenesis of ConA-induced liver injury. Downstream of PGAM5, Drp1-mediated mitochondrial fission is an obligatory step that drives the execution of hepatic necrosis and tissue damage. Our data highlight the PGAM5-Drp1 axis as a potential therapeutic target for acute immune-mediated liver injury.

The pseudokinase MLKL mediates programmed hepatocellular necrosis independently of RIPK3 during hepatitis

Although necrosis and necroinflammation are central features of many liver diseases, the role of programmed necrosis in the context of inflammation-dependent hepatocellular death remains to be fully determined. Here, we have demonstrated that the pseudokinase mixed lineage kinase domain-like protein (MLKL), which plays a key role in the execution of receptor-interacting protein (RIP) kinase-dependent necroptosis, is upregulated and activated in human autoimmune hepatitis and in a murine model of inflammation-dependent hepatitis. Using genetic and pharmacologic approaches, we determined that hepatocellular necrosis in experimental hepatitis is driven by an MLKL-dependent pathway that occurs independently of RIPK3. Moreover, we have provided evidence that the cytotoxic activity of the proinflammatory cytokine IFN-γ in hepatic inflammation is strongly connected to induction of MLKL expression via activation of the transcription factor STAT1. In summary, our results reveal a pathway for MLKL-dependent programmed necrosis that is executed in the absence of RIPK3 and potentially drives the pathogenesis of severe liver diseases.

[Determination of trace gallium by graphite furnace atomic absorption spectrometry in urine]

OBJECTIVE

To establish a method for determination trace gallium in urine by graphite furnace atomic absorption spectrometry (GFAAS).

METHODS

The ammonium dihydrogen phosphate was matrix modifier. The temperature effect about pyrolysis (Tpyr) and atomization temperature were optimized for determination of trace gallium. The method of technical standard about within-run, between-run and recoveries of standard were optimized.

RESULTS

The method showed a linear relationship within the range of 0.20~80.00 μg/L (r=0.998). The within-run and between-run relative standard deviations (RSD) of repetitive measurement at 5.0, 10.0, 20.0 μg/L concentration levels were 2.1%~5.5% and 2.3%~3.0%. The detection limit was 0.06 μg/L. The recoveries of gallium were 98.2%~101.1%.

CONCLUSION

This method is simple, low detection limit, accurate, reliable and reproducible. It has been applied for determination of trace gallium in urine samples those who need occupation health examination or poisoning diagnosis.

Programming of Intestinal Epithelial Differentiation by IL-33 Derived from Pericryptal Fibroblasts in Response to Systemic Infection

The intestinal epithelium constitutes an efficient barrier against the microbial flora. Here, we demonstrate an unexpected function of IL-33 as a regulator of epithelial barrier functions. Mice lacking IL-33 showed decreased Paneth cell numbers and lethal systemic infection in response to Salmonella typhimurium. IL-33 was produced upon microbial challenge by a distinct population of pericryptal fibroblasts neighboring the intestinal stem cell niche. IL-33 programmed the differentiation of epithelial progenitors toward secretory IEC including Paneth and goblet cells. Finally, IL-33 suppressed Notch signaling in epithelial cells and induced expression of transcription factors governing differentiation into secretory IEC. In summary, we demonstrate that gut pericryptal fibroblasts release IL-33 to translate bacterial infection into an epithelial response to promote antimicrobial defense.

Caspase-8 controls the gut response to microbial challenges by Tnf-α-dependent and independent pathways

OBJECTIVES

Intestinal epithelial cells (IEC) express toll-like receptors (TLR) that facilitate microbial recognition. Stimulation of TLR ligands induces a transient increase in epithelial cell shedding, a mechanism that serves the antibacterial and antiviral host defence of the epithelium and promotes elimination of intracellular pathogens. Although activation of the extrinsic apoptosis pathway has been described during inflammatory shedding, its functional involvement is currently unclear.

DESIGN

We investigated the functional involvement of caspase-8 signalling in microbial-induced intestinal cell shedding by injecting Lipopolysaccharide (LPS) to mimic bacterial pathogens and poly(I:C) as a probe for RNA viruses in vivo.

RESULTS

TLR stimulation of IEC was associated with a rapid activation of caspase-8 and increased epithelial cell shedding. In mice with an epithelial cell-specific deletion of caspase-8 TLR stimulation caused Rip3-dependent epithelial necroptosis instead of apoptosis. Mortality and tissue damage were more severe in mice in which IECs died by necroptosis than apoptosis. Inhibition of receptor-interacting protein (Rip) kinases rescued the epithelium from TLR-induced gut damage. TLR3-induced necroptosis was directly mediated via TRIF-dependent pathways, independent of Tnf-α and type III interferons, whereas TLR4-induced tissue damage was critically dependent on Tnf-α.

CONCLUSIONS

Together, our data demonstrate an essential role for caspase-8 in maintaining the gut barrier in response to mucosal pathogens by permitting inflammatory shedding and preventing necroptosis of infected cells. These data suggest that therapeutic strategies targeting the cell death machinery represent a promising new option for the treatment of inflammatory and infective enteropathies.

Heparin- and basic fibroblast growth factor-incorporated degradable stent: comparison with traditional transmyocardial revascularization

AIM

We have recently developed a novel method transmyocardial drilling revascularization (TMDR) combined with heparinized bFGF-incorporating degradable tubular stent implantation to revascularize ischemic myocardium. The aim of the present study was to compare the effect of this new method on left ventricular (LV) remodeling and global function to traditional transmyocardial revascularization (TMR) in acute myocardial ischemia.

METHODS

Eighteen miniswine underwent ligation of the left anterior descending (LAD) at the mid-third and were divided into three groups (N.=6 in each group): no treatment (control), TMDR (T), and TMDR+stent implantation (TS) groups. Two channels with 3.5 mm in diameter were established (T and TS groups), followed by implantation of two stents (TS group). LV function, myocardial perfusion, expression of von Willebrand factor (vWF), transforming growth factor-β3 (TGF-β3), vascular endothelial growth factor (VEGF), interleukin-1beta (IL-1β), vascular density, and histologic and morphologic analyses were evaluated at different time-points.

RESULTS

Six weeks post-treatment, there were no differences between T and control groups. TS group showed significant improvement compared to T group as to: expressions of TGF-β3, VEGF, vWF and IL-1β (P<0.001), neovascular density (2.561±391 vs. 6.201±443 pixels/hpf, P<0.001), myocardial viability (18.913±2775 vs. 94.800±14.076 pixels/hpf, P<0.001), and dp/dtmax (1.735±161 vs. 2.242±223 mmHg/s, P<0.001), Further, there were significant decreases in changes of Mass Defect Percent (2.05±0.22% vs. -1.79±0.45%, P<0.001) and LV end diastolic volume (164.83±10.74 vs. 147.00±7.32 mL, P=0.048) in the TS group.

CONCLUSION

TMDR and stent implantation is more effective in enhancement of myocardial viability, improvement of global LV function, and attenuation of LV remodeling than TMDR.

Global phosphoproteomic effects of natural tyrosine kinase inhibitor, genistein, on signaling pathways

Genistein is a natural protein tyrosine kinase inhibitor that exerts anti-cancer effect by inducing G2/M arrest and apoptosis. However, the phosphotyrosine signaling pathways mediated by genistein are largely unknown. In this study, we combined tyrosine phosphoprotein enrichment with MS-based quantitative proteomics technology to globally identify genistein-regulated tyrosine phosphoproteins aiming to depict genistein-inhibited phosphotyrosine cascades. Our experiments resulted in the identification of 213 phosphotyrosine sites on 181 genistein-regulated proteins. Many identified phosphoproteins, including nine protein kinases, eight receptors, five protein phosphatases, seven transcriptical regulators and four signal adaptors, were novel inhibitory effectors with no previously known function in the anti-cancer mechanism of genistein. Functional analysis suggested that genistein-regulated protein tyrosine phosphorylation mainly by inhibiting the activity of tyrosine kinase EGFR, PDGFR, insulin receptor, Abl, Fgr, Itk, Fyn and Src. Core signaling molecules inhibited by genistein can be functionally categorized into the canonial Receptor-MAPK or Receptor-PI3K/AKT cascades. The method used here may be suitable for the identification of inhibitory effectors and tyrosine kinases regulated by anti-cancer drugs.

The relaxant effect of urocortin in rat pulmonary arteries

Urocortin is a potent vasodilator, which plays physiological or pathophysiological roles in systemic circulation. However, little is known about its action on pulmonary circulation. The present study was aimed to characterize some cellular mechanisms underlying the relaxant effect of urocortin in isolated rat pulmonary arteries. Changes in isometric tension were measured on small vessel myographs. Urocortin inhibited U46619-induced contraction with reduction of the maximal response. Urocortin-induced relaxation was independent of the presence of endothelium. Inhibitors of nitric oxide (NO)-dependent dilator, NG-nitro-L-arginine methyl ester or 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one, did not affect the relaxation. Astressin (100-500 nM), a corticotropin-releasing factor (CRF) receptor antagonist and KT5720, a protein kinase A (PKA) inhibitor reduced urocortin-induced relaxation. Urocortin produced less relaxant effect in 30 mM K+- than U46619-contracted arterial rings. Urocortin did not reduce CaCl2-induced contraction in 60 mM K+-containing solution. Ba2+ (100-500 microM) but not other K+ channel blockers reduced the relaxant responses to urocortin. Urocortin also relaxed the rings preconstricted by phorbol 12,13-diacetae in normal Krebs solution while this relaxation was less in a Ca2+-free solution. Our results show that urocortin relaxed rat pulmonary arteries via CRF receptor-mediated and PKA-dependent but endothelium/NO or voltage-gated Ca2+ channel-independent mechanisms. Stimulation of Ba2+-sensitive K+ channel may contribute to urocortin-induced relaxation. Finally, urocortin relaxed pulmonary arteries partly via inhibition of a PKC-dependent contractile mechanism.

Epoxyeicosatrienoic acids (EET(11,12)) may partially restore endothelium-derived hyperpolarizing factor-mediated function in coronary microarteries

BACKGROUND

Endothelial cells derive nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor (EDHF). The cytochrome P-450-monooxygenase metabolites of arachidonic acid (epoxyeicosatrienoic acids [EETs]) have been suggested to be EDHF. This study was designed to examine the effect of EET(11,12) with regard to the possibility of restoring EDHF function when added into hyperkalemic cardioplegic solution.

METHODS

Porcine coronary microartery rings were studied in a myograph. In groups 1 and 2, paired arteries were incubated in either hyperkalemic solution (K+ 20 mmol/L) or Krebs' solution (control). In group 3, the paired arteries were incubated in hyperkalemia plus EET(11,12) (1 x 10(-6.5) mol/L) or hyperkalemia alone (control) at 37 degrees C for 1 hour, followed by Krebs' washout and then precontracted with 1 x 10(-8.5) mol/L U46619. The EDHF-mediated relaxation to EET(11,12) (group 1) or bradykinin (groups 2 and 3) was studied in the presence of N(G)-nitro-L-arginine, indomethacin, and oxyhemoglobin.

RESULTS

After exposure to hyperkalemia, the EDHF-mediated maximal relaxation by bradykinin (72.5% +/- 7.8% versus 41.6% +/- 10.6%; p < 0.05), but not by EET(11,12) (18.4% +/- 3.3% versus 25.1% +/- 4.9%; p > 0.05) was significantly reduced. Incubation with EET(11,12) partially restored EDHF function (33.3% +/- 9.5% versus 62.0% +/- 8.5%; p < 0.05).

CONCLUSIONS

In coronary microarteries, hyperkalemia impairs EDHF-mediated relaxation, and EET(11,12) may partially mimic the EDHF function. Addition of EET(11,12) into cardioplegic solution may partially restore EDHF-mediated function reduced by exposure to hyperkalemia.

Comparison of nitric oxide release and endothelium-derived hyperpolarizing factor-mediated hyperpolarization between human radial and internal mammary arteries

BACKGROUND

Arterial grafts for CABG have been used increasingly, and the radial artery (RA) has become a preferable graft, secondary to the internal mammary artery (IMA). In the present study, we investigated and compared NO release and endothelium-derived hyperpolarizing factor (EDHF)-mediated hyperpolarization for IMA and RA.

METHODS AND RESULTS

IMA and RA segments taken from CABG patients were placed in an organ chamber. An NO-sensitive electrode (to directly measure NO release) or intracellular glass microelectrode (to measure membrane potential) was used to study NO or EDHF in response to acetylcholine (ACh) and bradykinin (BK) before and after incubation with indomethacin (a cyclooxygenase inhibitor), N(G)-nitro-L-arginine (an NO synthase inhibitor), and oxyhemoglobin (an NO scavenger). The resting membrane potential of the smooth muscle cells of IMA and RA was -58+/-0.84 (n=61) and -61+/-1.3 (n=46) mV, respectively (P=0.03). BK-induced EDHF-mediated hyperpolarization in the IMA was significantly greater than that in RA (BK 10(-)(7) mol/L: -10.9+/-1.5 [n=7] versus -5.8+/-0.9 [n=6] mV, P=0.04). The basal (16.8+/-1.9 versus 11.1+/-1.0 nmol/L, n=12, P=0.02) and stimulated releases of NO in IMA were significantly greater for BK (44.3+/-4.0 versus 25.8+/-3.6 nmol/L, n=8, P=0.004) and lasting longer for ACh (9.5+/-2.0 versus 6.6+/-3.6 minutes, n=12, P=0.03) than those in RA.

CONCLUSIONS

The basal and stimulated releases of NO and EDHF-mediated hyperpolarization in the IMA are significantly greater than that in the RA. The lower capacity of NO release may contribute to the susceptibility of RA to the perioperative vasospasm and may have an impact on the long-term graft patency.

Inhibition of vasoconstriction by AJ-2615, a novel calcium antagonist with alpha(1)-adrenergic receptor blocking activity in human conduit arteries used as bypass grafts

AIMS

Graft spasm may develop during coronary artery bypass grafting and reversal of spasm is still challenging. The purpose of this study was to investigate the in vitro vascular relaxant properties of AJ-2615 in human internal mammary artery (IMA).

METHODS

We studied 264 IMA rings taken from 65 patients undergoing coronary artery bypass grafting surgery with organ bath technique. The interaction between AJ-2615 and various vasoconstrictors was investigated in two ways.

RESULTS

AJ-2615 caused complete relaxation in methoxamine-contracted IMA rings (100.0+/-0.0%; n = 8) and nearly full relaxation in potassium chloride-contracted IMA rings (91.4+/-5.7%; n = 8) or noradrenaline-contracted IMA rings (89.3+/-2.8%; n = 8). AJ-2615 also induced remarkable relaxation in IMA rings contracted by other vasoconstrictors. In comparison with the alpha1-adrenoceptor antagonist prazosin, AJ 2615 showed similar maximal relaxation in IMA rings contracted by methoxamine or norepinephrine. On the other hand, incubation with AJ-2615 (0.1-1 microM) significantly inhibited all the vasoconstrictor-mediated vasoconstriction except endothelin-1 in a concentration-dependent manner.

CONCLUSIONS

The results suggested that in human IMA, AJ-2615 has an inhibitory effect on vasoconstriction mediated by a variety of vasoconstrictors and the mechanism of relaxation may be related to its calcium antagonism and alpha1-adrenergic receptor blocking activity. AJ-2615 may have important clinical implications for patients undergoing coronary artery bypass surgery for reversing and preventing graft spasm.

Antinociceptive effect of astragalosides and its mechanism of action

AIM

To study the effect and mechanism of astragalosides (AST) related to the antinociceptive activity.

METHODS

The standardized formalin test was performed to induce the direct stimulation of nociceptors followed by inflammatory process in the Kunming strain mice. The involvement of opioid and nitric oxide was studied by subcutaneous injection of morphine with/without naloxone 30 min before formalin test, or peritoneal injection of L-arginine with/without L-NAME 20 min before formalin.

RESULTS

AST 20, 40, and 80 mg/kg significantly lowered pain score of the second phase of formalin response as compared with control group (P<0.01). The maximum analgesic effect of AST 40 mg/kg was found at 4 h after the administration of AST (34.4 % inhibition at the second phase). Injection of morphine 5 mg/kg significantly inhibited pain response of both phases (P<0.01) and this was reversed by naloxone 2 mg/kg (P<0.01). However, naloxone did not alter the effect of AST on the second phase. Antinociceptive effect of AST 40 mg/kg was partially blocked by L-arginine 400 or 800 mg/kg (P<0.01).

CONCLUSION

AST has an antinociceptive effect on formalin test in mice that is not mediated by the endogenous opioid system but related to its inhibitory effect on the production of NO.

ATP-sensitive potassium channel openers may mimic the effects of hypoxic preconditioning on the coronary artery

BACKGROUND

This study was designed to investigate the effects of the potassium channel opener KRN4884 in mimicking hypoxic preconditioning on coronary arteries and to explore the possible mechanisms.

METHODS

In the organ chamber, porcine coronary artery rings (n = 96) were studied in 6 groups (n = 16 in each group): I.

CONTROL

normoxia (pO2 > 200 mmHg); II. Hypoxia-reoxygenation: 60-minute hypoxia (pO2 < 15 mmHg) followed by 30-minute reoxygenation; III. Preconditioning: 5-minute hypoxia followed by 10-minute reoxygenation prior to hypoxia-reoxygenation; IV. KRN4884-pretreatment: KRN4884 (30 microM) was added into the chamber 20 minutes before hypoxia-reoxygenation; V. 5-HD-pretreatment: sodium 5-hydroxydecanoate (5-HD, 10 microM) was given 20 minutes prior to KRN4884-pretreatment; and VI. GBC-pretreatment: glibenclamide (GBC, 3 microM) was added 20 minutes prior to KRN4884-pretreatment. Concentration-contraction curves for U46619 (n = 8 in each group) were constructed. Concentration-relaxation curves for bradykinin (n = 8 in each group) related to endothelium-derived hyperpolarizing factor (EDHF) were established in the rings precontracted with U46619 (30 microM) in the presence of Nomega-nitro-L-arginine (L-NNA, 300 microM) and indomethacin (7 microM).

RESULTS

The maximal relaxation induced by bradykinin was reduced in hypoxia-reoxygenation (54.6 +/- 4.3% versus 85.2 +/- 5.7% in control, p = 0.001). This reduced relaxation was recovered in KRN4884-pretreatment (78.9 +/- 3.7%, p = 0.014) or preconditioning (79.9 +/- 3.7%, p = 0.009). 5-HD- but not GBC-pretreatment abolished the effect of KRN4884-pretreatment (78.9 +/- 3.7% versus 53.5 +/- 4.7%, p = 0.009).

CONCLUSIONS

Hypoxia-reoxygenation reduces the relaxation mediated by EDHF in the coronary artery. This function can be restored by either hypoxic preconditioning or the potassium channel opener KRN4884. The mechanism of such effect is mainly related to the mitochondrial ATP-sensitive K+ channels.

Vascular endothelial growth factor-mediated endothelium-dependent relaxation is blunted in spontaneously hypertensive rats

The vasodilatory effect of VEGF has not been characterized in the setting of hypertension. This study investigated the in vitro vasorelaxant effects of VEGF in organ chambers in the aorta of the adult (12-week-old) spontaneously hypertensive rats (SHR), young (4-week-old) SHR without hypertension, and age-matched Wistar-Kyoto (WKY) rats compared with acetylcholine (ACh). Cumulative concentration-relaxation curves were established for VEGF (approximately 10(-12)-10(-8.5) M) and ACh (approximately 10(-10)-10(-5) M) in U46619 (10(-8) M)-induced contraction. VEGF induced endothelium-dependent relaxation that was significantly reduced in the adult SHR compared with the age-matched WKY control (87.8 +/- 2.8 versus 61.4 +/- 8.6%, P = 0.01). These responses were significantly attenuated by pretreatment with N(omega)-nitro-L-arginine (L-NNA, 300 microM) alone (SHR: 25.1 +/- 1.9%; WKY: 21.0 +/- 2.6%; P = 0.01) or indomethacin (7 microM) + L-NNA (SHR: 30.2 +/- 2.1%; WKY: 35.0 +/- 2.9%; P = 0.01). Further addition of oxyhemoglobin (20 microM) abolished the residual relaxation and reduced the relaxation induced by nitroglycerin. ACh induced similar responses to VEGF. In contrast, pretreatment with indomethacin alone enhanced VEGF- or ACh-induced relaxations and the effect was greater in the adult SHR than in WKY rats. In contrast to the adult SHR versus WKY rats, there were no significant differences of VEGF- or ACh-induced relaxations between young SHR and WKY rats. The results demonstrate that VEGF induces endothelium- or nitric oxide-dependent relaxation, which is blunted in the adult SHR. The mechanism of this impairment may be related to decreased release of NO although increased release of contracting factors from the dysfunctional endothelium may also be involved.

Effects of potassium channel opener aprikalim on the receptor-mediated vasoconstriction in the human internal mammary artery

BACKGROUND

Arterial grafts for coronary artery bypass grafting such as the internal mammary artery (IMA) may develop spasm perioperatively. The purpose of this study was to investigate the effects of the potassium channel opener, aprikalim, on the receptor-mediated vasoconstriction in the human IMA in vitro.

METHODS

We studied 160 IMA rings taken from coronary artery surgery in organ baths. The interaction between aprikalim and four vasoconstrictors 5-hydroxytryptamine (5-HT), norepinephrine (NE), endothelin-1 (ET-1), and angiotensin II (AII) was investigated in two ways.

RESULTS

Aprikalim relaxed IMA rings precontracted by the vasoconstrictors to 66.40 +/- 5.9% for 5-HT (EC50: -6.78 +/- 0.26 LogM), 57.40 +/- 5.5% for NE (-6.54 +/- 0.39 LogM), 81.00 +/- 6.7% for ET-1 (-6.58 +/- 0.26 LogM), and 93.90 +/- 2.5% for AII (-7.80 +/- 0.23 LogM). The relaxation in endothelium-denuded rings contracted by AII was similar to that in the endothelium-intact rings. The relaxation was attenuated by glibenclamide (3 microM) in 5-HT or NE-precontracted IMA. Pretreatment with aprikalim at 1 microM depressed AII-induced contraction (33.20 +/- 7.5% versus 59.70 +/- 7.3%, p < 0.01) but only shifted the curves rightward for 5-HT or NE (EC50 3.1 or 4.3-folds higher, p < 0.05), whereas at 30 microM it also significantly depressed the maximal contraction for 5-HT (35.70 +/- 4.9% versus 103.30 +/- 9.8%, p < 0.001) and NE (90.60 +/- 15.6% versus 125.60 +/- 7.9%, p < 0.05). In contrast, aprikalim did not significantly depress the contraction induced by ET-1 (p > 0.05).

CONCLUSIONS

We conclude that aprikalim has vasorelaxant effects on IMA and the effect is vasoconstrictor-selective and endothelium-independent. Aprikalim may provide clinically useful vasorelaxant effects in coronary bypass surgery.

Direct measurement of nitric oxide release from saphenous vein: abolishment by surgical preparation

BACKGROUND

Surgical preparation (distension) of the saphenous vein (SV) is applied routinely during harvesting in coronary artery bypass grafting (CABG). However, mechanical distension may impair the endothelium, which plays an important role in long-term patency. The present study investigated the effect of surgical preparation of the SV on nitric oxide (NO) release from the endothelium by direct measurement of NO.

METHODS

Saphenous vein segments taken from CABG patients were cut open longitudinally and placed in an organ chamber. An NO-sensitive electrode and NO meter were used to directly measure NO release induced by acetylcholine (ACh) and bradykinin (BK) from the surgically prepared veins (PV) compared with the control (nondistended) veins.

RESULTS

The basal release of NO in the PV group was significantly lower than that in the control group (3.4 +/- 1.4 nM, n = 9 versus 9.9 +/- 2.8 nM, n = 13, p = 0.002). The maximum concentrations of NO release induced by ACh and BK in the PV group were also significantly lower than those in the control veins (for ACh 10(-6) mol/L: 9.6 +/- 3.1 nM, n = 8 versus 41.9 +/- 11.2 nM, n = 12, p = 0.005; for BK 10(-8) mol/L: 8.3 +/- 3.7 nM, n = 7 versus 37.9 +/- 6.1 nM, n = 9, p = 0.003). Further, the duration of NO release in the PV group was significantly shorter than that in control veins (1.5 +/- 1.3 minutes, n = 8 versus 8.1 +/- 1.9 minutes, n = 8, p < 0.001).

CONCLUSIONS

Surgical preparation almost abolishes NO release by the SV and this may significantly contribute to the low long-term patency rate of the vein graft.

Inhibition of vasoconstriction by angiotensin receptor antagonist GR117289C in arterial grafts

BACKGROUND

Angiotensin II (AII) has been suggested to be one of the important factors for genesis of graft spasm in coronary artery bypass surgery. The aim of this work was to investigate the effects of the nonpeptide angiotensin receptor AT1 antagonist GR117289C on the contraction induced by AII and other vasoconstrictors in isolated human internal mammary artery (IMA) preparations.

METHODS

Two hundred eight IMA rings taken from 64 patients undergoing coronary artery bypass grafting were studied in organ baths. The interaction between GR117289C and AII or the other vasoconstrictors (U46619, norepinephrine, endothelin-1, and potassium chloride) was investigated in two ways.

RESULTS

GR117289C induced near-maximal relaxation (94.5% +/- 2.9%) in IMA rings precontracted by AII. In IMA rings incubated with 1 or 10 nmol/L GR117289C, contractile responses to AII were attenuated in a concentration-related manner, whereas the dose-response curve did not shift to the right when higher doses of AII were administered, suggesting that the AT1 receptor blockade was noncompetitive in nature. Moreover, GR117289C also induced significant relaxation (82.9% +/- 8.1%) in IMA rings precontracted by U46619, but no inhibitory responses to U46619 could be observed when IMA rings were incubated with GR117289C. GR117289C did not alter responses to potassium chloride, norepinephrine, and endothelin-1.

CONCLUSIONS

These results indicate that GR117289C is a potent, selective, noncompetitive AT1 receptor antagonist that may have a possible antagonistic effect on the thromboxane A2 receptor. Because AII and thromboxane A2 are important vasoconstrictors in the genesis of graft spasm, GR117289C may become an alternative treatment to relieve graft spasm.

Difference in endothelium-derived hyperpolarizing factor-mediated hyperpolarization and nitric oxide release between human internal mammary artery and saphenous vein

BACKGROUND

The greater nitric oxide (NO) release that occurs in the internal mammary artery (IMA) when compared with the saphenous vein (SV) has been suggested by more endothelium-dependent relaxation in the IMA or measured by bioassay; however, no direct measurement of NO- or endothelium-derived hyperpolarizing factor (EDHF)-mediated hyperpolarization has been reported. The present study measured such hyperpolarization, as well as NO release, in these vessels.

METHODS AND RESULTS

IMA (n=46) and SV (n=61) segments taken from patients undergoing coronary surgery were studied in the organ chamber. Hyperpolarization (by intracellular glass microelectrode) and NO release (by NO-sensitive electrode) in response to acetylcholine and bradykinin, with and without incubation with N(G)-nitro-L-arginine, indomethacin, and oxyhemoglobin, were measured. The resting membrane potential of the smooth muscle cells from the IMA (58+/-0.8 mV; n=15) was higher than that in those from the SV (-62+/-0.9 mV; n=23; P:=0.0001). The EDHF-mediated hyperpolarization induced by acetylcholine (10(-5) mol/L: -9.4+/-1.5 mV in IMA, n=10, versus -4. 5+/-1.0 mV in SV, n=17; P:<0.01) and bradykinin (10(-7) mol/L: -10. 9+/-1.5 mV in IMA, n=8, versus -5.1+/-0.5 mV in SV, n=8; P:<0.01) and the basal release of NO (16.8+/-1.6 nmol/L in IMA, n=13, versus 9.9+/-2.8 nmol/L in SV, n=13; P:<0.001) were significantly greater in the IMA than in the SV. The duration of acetylcholine- and bradykinin-induced NO release was longer in the IMA than in the SV.

CONCLUSIONS

The basal release of NO and EDHF-mediated hyperpolarization were significantly greater in the IMA than in the SV. In addition, the duration of the stimulated release of NO was longer in the IMA than in the SV. These differences may contribute to the superior long-term patency of IMA grafts.

Effects of biatrial pacing in prevention of postoperative atrial fibrillation after coronary artery bypass surgery

BACKGROUND

Atrial fibrillation (AF) is common after coronary artery bypass surgery (CABG) and results in prolonged hospitalization. The purpose of this study was to evaluate the efficacy of biatrial pacing in preventing post-CABG AF compared with single-site atrial pacing.

METHODS AND RESULTS

A total of 132 patients who had no history of AF and who underwent CABG were randomized to 1 of the following 4 groups: biatrial pacing (BiA), left atrial pacing (LA), right atrial pacing (RA), or no pacing (control) in postoperative period. Overdrive atrial pacing was performed for 5 days. The incidence of AF was significantly reduced in the BiA group (12.5%) compared with the other 3 groups (LA, 36.4%; RA, 33.3%; control, 41. 9%; P<0.05). The mean length of hospital stay was significantly reduced in the BiA group. At baseline, the mean P-wave duration (P(dur)) and dispersion (P(dis)) were not prolonged. BiA pacing resulted in the most significant percentage of reduction in P(dis) when compared with the LA or RA groups (BiA, 42+/-8%; LA, 13+/-6%; RA, 10+/-9%; P<0.05 for BiA versus LA or RA). No significant differences existed in mean P(dur) and P(dis) between patients who developed AF and those who remained in sinus rhythm at baseline. However, only those patients who remained in sinus rhythm had a significant reduction in mean P(dur) and P(dis) after pacing therapy.

CONCLUSIONS

Biatrial overdrive pacing is more effective in preventing post-CABG AF than single-site atrial pacing; this therapy also results in a shortened hospital stay. The overall reduction in atrial activation time with BiA pacing was reflected in the reduction in P(dis).

Effects of potassium channel opener KRN4884 on human conduit arteries used as coronary bypass grafts

AIMS

The effects of a new potassium channel opener KRN4884 on human arteries have not been studied. This study was designed to investigate the effects of KRN4884 on the human internal mammary artery (IMA) in order to provide information on possible clinical applications of KRN4884 for preventing and relieving vasospasm of arterial grafts in coronary artery bypass grafting.

METHODS

IMA segments (n = 140) taken from patients undergoing coronary surgery were studied in the organ chamber. Concentration-relaxation curves for KRN4884 were established in the IMA precontracted with noradrenaline (NA), 5-hydroxytryptamine (5-HT), angiotensin II (ANG II), and endothelin-1 (ET-1). The effect of glibenclamide (GBC) on the KRN4884-induced relaxation was also examined in NA or 5-HT-precontracted IMA. Concentration-contraction curves for the four vasoconstrictors were constructed without/with pretreatment of KNR4884 (1 or 30 microM) for 15 min.

RESULTS

KRN4884 induced less relaxation (P < 0.05) in the precontraction induced by ET-1 (72.9 +/- 5.5%) than by ANG II (94.2 +/- 3.2%) or NA (93.7 +/- 4.1%) with lower EC50 (P < 0.05) for ANG II (-8.54 +/- 0.54 log M) than that for NA (-6.14 +/- 0.15 log M) or ET-1 (-6.69 +/- 0.34 log M). The relaxation in the IMA pretreated with GBC was less than that in control (P < 0.05). KRN4884-pretreatment significantly reduced the contraction (P < 0.05) induced by NA (151.3 +/- 18.4% vs 82.7 +/- 8. 7%), 5-HT (82.7 +/- 12.2% vs 30.1 +/- 7.3%), and ANG II (24.3 +/- 6. 3% vs 5.4 +/- 1.6%), but did not significantly reduce the contraction induced by ET-1 (P > 0.05).

CONCLUSION

KRN4884 has marked vasorelaxant effects on the human IMA contracted by a variety of vasoconstrictors and the effect is vasoconstrictor-selective.

Comparison of University of Wisconsin and St Thomas' Hospital solutions on endothelium-derived hyperpolarizing factor-mediated function in coronary micro-arteries

BACKGROUND

It is controversial whether coronary endothelial function is impaired after cold exposure to University of Wisconsin (UW) or St. Thomas' Hospital (ST) solution during heart transplantation. We therefore examined the effects of cold storage of coronary micro-arteries with UW or ST solution on endothelium-derived hyperpolarizing factor (EDHF)-mediated function.

METHODS

Porcine and human coronary arteries were immersed in either UW or ST solution at 4 degrees C for 4 hr and then normalized in a wire myograph.

RESULTS

In the rings (normalized diameter: 200-500 microM) precontracted by U46619, EDHF-mediated relaxation and hyperpolarization were initiated by bradykinin (BK) or A23187 in the presence of indomethacin and NG-nitro-L-arginine. In the human coronary arteries, the EDHF-mediated relaxation to BK was reduced by UW solution from 53.2+/-5.6% to 24.0+/-2.7% (P=0.006). The reduced EDHF-mediated relaxation occurred concurrently with the decreased hyperpolarization to BK (17.0+/-1.5 vs. 10.5+/-1.1 mV, n=10, P=0.004) or A23187 in porcine coronary arteries. In the control arteries, K+ channel blockers, either glybenclamide or tetraethylammonium reduced the EDHF-mediated relaxation. After exposure to UW solution, the EDHF-mediated relaxation was further significantly inhibited. In contrast, ST solution did not affect these responses.

CONCLUSIONS

These results show that in coronary micro-arteries, UW, but not ST, solution impairs the EDHF-mediated function and inhibits the Ca2+-activated and ATP-sensitive K+ channels. Our comparative study suggests that ST solution may be superior to UW solution in preserving the EDHF-related endothelial function of coronary micro-arteries.

Endothelium-dependent hyperpolarization and relaxation resistance to N(G)-nitro-L-arginine and indomethacin in coronary circulation

OBJECTIVE

It is controversial whether endothelium-dependent relaxation resistance to inhibitors of nitric oxide (NO) and prostacyclin synthases is completely attributed to endothelium-derived hyperpolarizing factor (EDHF). This study examined NO release and K+ channels involved in endothelium-dependent relaxation and hyperpolarization resistance to N(G)-nitro-L-arginine (L-NNA) and indomethacin in coronary arteries with emphasis on the microarteries.

METHODS

NO release, isometric force, and membrane potential of porcine coronary arteries were measured using a NO-specific electrode, wire myograph, and microelectrode, respectively.

RESULTS

In large arteries pretreated with indomethacin, bradykinin (BK) evoked a rise in [NO] from 5.5+/-2.4 nM to 105.0+/-19.6 nM and hyperpolarization. L-NNA treatment significantly reduced the BK-stimulated rise in [NO] to 32.1+/-11.3 nM but did not affect the hyperpolarization. In the presence of indomethacin and L-NNA, U46619 contracted and depolarized (from -51+/-3 mV to -30+/-4 mV) vascular smooth muscle in microarteries. The addition of BK produced dose-dependent relaxation (maximal: 70.2+/-5.7%) and repolarization (membrane potential: -50+/-4 mV). Oxyhemoglobin eliminated indomethacin and L-NNA-resistance rise in [NO] but not relaxation (42.3+/-4.4%) and repolarization (-40+/-2 mV) by BK. Tetraethylammonium, charybdotoxin, and iberiotoxin partially decreased the BK-induced responses. Apamin alone did not affect the relaxation by BK; however, in combination with charybdotoxin it almost completely abolished the BK-induced relaxation and hyperpolarization.

CONCLUSIONS

In porcine coronary arteries, both EDHF and NO contribute to BK-induced relaxation resistance to indomethacin and L-NNA. Large conductance Ca2+-activated K+ channels (BK(Ca)) may play an important role in mediating the BK-induced responses and small conductance Ca2+-activated K+ channels might function as 'backup' mechanisms when BK(Ca) is curtailed.

Vasorelaxant effect of phosphodiesterase-inhibitor milrinone in the human radial artery used as coronary bypass graft

OBJECTIVE

The radial artery is a spastic coronary bypass graft. We investigated the effect of the phosphodiesterase III inhibitor milrinone on the human radial artery.

METHODS

Radial artery segments (n = 76) taken from 15 patients were studied in an organ chamber. Concentration-relaxation curves for milrinone were established in the radial artery precontracted with 3 vasoconstrictors (phenylephrine, K(+), and U46619). In radial artery rings incubated with therapeutic plasma concentrations of milrinone (7 and 70 micromol/L) for 10 minutes, concentration-contraction curves for the 3 vasoconstrictors were constructed.

RESULTS

Milrinone caused a submaximal relaxation in phenylephrine- (98.6% +/- 1.4%), K(+)- (89.1 +/- 4.5%), or U46619- (74.2 +/- 8.0%) precontracted radial arteries at -4.5 log(10) M. The EC(50) was higher against K(+) (-5.85 +/- 0.24 log(10) M, P =.02) or U46619 (-5. 21 +/- 0.61 log(10) M, P =.03) than phenylephrine (-6.68 +/- 0.11 log(10) M). Pretreatment with milrinone depressed the contraction by phenylephrine from 70.0% +/- 7.9% to 23.5% +/- 9.3% (P =.003) and by K(+) from 138.6% +/- 5.8% to 73.0% +/- 13.9% (P =.006) and shifted the EC(50) 3.8-fold higher (P =.03) for phenylephrine and 2.2-fold higher for K(+) (P =.01). Milrinone reduced the U46619 contraction at low concentration (-8.5 log(10) M) but had little effect on the maximal contraction.

CONCLUSION

Milrinone is a potent vasodilator for the radial artery, with possibly higher potency in alpha-adrenoceptor- and depolarizing agent K(+)-mediated, but less potency in thromboxane A(2)-mediated, contraction. Because it also has a positive inotropic effect, this vasodilator may be particularly indicated for use in patients receiving radial artery grafts in coronary artery bypass grafting.

Injection of vasodilators into arterial grafts through cardiac catheter to relieve spasm

Both native coronary artery and coronary bypass grafts may develop vasospasm after coronary artery bypass grafting. We recommend that whenever there is a high suspicion of vasospasm in arterial grafts and the native coronary artery unresponsive to or not suitable for usual vasodilator therapy, prompt selective graft arteriogram should be performed. Intraluminal injection of vasodilators such as calcium antagonists in combination with nitroglycerin may provide an effective antispastic therapy and this procedure could be lifesaving as demonstrated in the present report.

Comparative study on calcium channel antagonists in the human radial artery: clinical implications

OBJECTIVES

The radial artery is spastic, and calcium channel antagonists have been used clinically in the radial artery for their antispastic effects. To choose a proper calcium channel antagonist for such a purpose, we compared the in vitro antispastic effects of 4 clinically used calcium channel antagonists (nicardipine, nifedipine, verapamil, and diltiazem) in the human radial artery.

METHODS

Radial artery segments taken from patients undergoing coronary bypass operations were studied in the organ bath. The relaxation by the calcium channel antagonists was compared in the potassium-precontracted (25 mmol/L) radial artery. The inhibitory effect of the calcium channel antagonists at the clinically relevant plasma concentration and a higher concentration was also studied for the calcium channel antagonists.

RESULTS

All calcium channel antagonists induced a full relaxation (97.8%-100%, n = 5-7 for each), with higher sensitivity (P =.005, analysis of variance [ANOVA] among the calcium channel antagonists for the effective concentration of the constrictor [or dilator] agent that caused 50% of maximal contraction [or relaxation]) to nifedipine (-7.37 +/- 0. 20 log(10) M) than nicardipine (-6.43 +/- 0.39 log(10) M, P =.1), verapamil (-6.08 +/- 0.13 log(10) M, P =.03), and diltiazem (-5.87 +/- 0.07 log(10) M, P =.01). Pretreatment with the plasma concentration of the calcium channel antagonists (60 nmol/L for diltiazem and 20 nmol/L for the others) inhibited the potassium-induced contraction (n = 6 for each) by nicardipine (from 138.6% +/- 5.8% to 101.4% +/- 7.6%, P =.001) and nifedipine (to 87. 7% +/- 6.8%, P =.0003) but not by verapamil (to 140.3% +/- 15.2%, P =.9) or diltiazem (to 132.8% +/- 7.3%, P =.8), although at higher contractions (-4.5 log(10) M) all 4 calcium channel antagonists abolished the contraction.

CONCLUSIONS

Although all calcium channel antagonists have antispastic effects in the radial artery, the vessel has different sensitivities to them. Dihydropyridine derivatives may be the most potent calcium channel antiagonists and therefore are recommended for the clinical use for this purpose.

Myocardial protection during cardiac surgery from the viewpoint of coronary endothelial function

1. During cardiac surgery, the heart is arrested and subject to ischaemia-reperfusion injury. 2. To protect the heart, cardioplegia is usually used to initially stop and then maintain the still condition of the heart, which not only facilitates the precise operation but, more importantly, minimizes the energy consumption of the heart during this period. 3. The ischaemia-reperfusion injury may involve both myocytes and coronary endothelium-smooth muscle and, therefore, the protection of the heart should also involve these two aspects. 4. Injury to the heart involves: (i) ischaemia-reperfusion injury to the myocytes and coronary circulation; and (ii) possible injury to the coronary circulation by cardioplegia due to its hyperkalaemic components. 5. Injury to the coronary circulation may involve both endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) mechanisms. The EDNO mechanism is susceptible to ischaemia-reperfusion, whereas the EDHF mechanism may be altered by hyperkalaemic cardioplegia. 6. To further protect the heart, supplemental therapy for EDNO and optimizing the components of cardioplegia to restore the EDHF mechanism may be important.

Inhibition of vasoconstriction by the thromboxane A2 antagonist GR32191B in the human radial artery

AIMS

The newly revived coronary bypass graft, the radial artery (RA), is more spastic than the internal mammary artery. Thromboxane A2 is a potent vasoconstrictor for arterial grafts. This study was therefore designed to determine whether the specific thromboxane A2 (TP) receptor antagonist, GR32191B, is effective in inhibition of prostanoid or nonprostanoid receptors in the RA.

METHODS

The effect of GR32191B was studied in human RA segments, taken from coronary bypass patients, in organ chambers. Two effects of GR32191B were tested: (1) the relaxation induced by GR32191B in the RA precontracted with the TP receptor agonists U46619 and PGF2alpha or nonprostanoid vasoconstrictors (noradrenaline [NA], angiotensin II [AII], and K+ ) and (2) the inhibitory effect of GR32191B on TP receptor agonists and nonprostanoid vasoconstrictors.

RESULTS

In U46619 (10 nm, n=7) and PGF2alpha (1 microm, n=7) precontracted RA, GR32191B induced 100% relaxation (10-100 microm ) but not after precontraction with nonprostanoid stimuli (5.8% for K+, 25 mm, n=6, 24.4% for NA, 3 microm, n=8, and 53.2% for AII, 3 nm, n=5) (P<0.001). Treatment with GR32191B (30 nm ) significantly depressed the contraction with U46619 (from 160.1+/-11.0% to 116.8+/-13.1%, P<0. 05) or PGF2alpha (from 91.3+/-12.3% to 42.2+/-9.2%, P<0.01). The contraction was further abolished by 3 microm GR32191B. However, GR32191B at 3 microm did not significantly inhibit the contraction induced by either NA, AII, or K+.

CONCLUSIONS

GR32191B is a highly potent and specific TP receptor antagonist for the human RA. It may be particularly useful in inhibiting TXA2-mediated vasoconstriction and therefore in reducing the complications related to vasospasm in this graft.

Comparison of the vasorelaxant effect of nitroprusside and nitroglycerin in the human radial artery in vitro

AIMS

In recent years the radial artery (RA) has been re-introduced for coronary artery bypass grafting (CABG). However, the potential for vasospasm remains a clinical problem when this vessel is employed and effective vasodilator agents are required to combat vasospastic events. This in vitro study was designed to compare the vasodilator effects of sodium nitroprusside (SNP) and nitroglycerin (NTG) in the human RA.

METHODS

Human RA segments (n=70) were taken from vessels employed for grafting in patients undergoing CABG. Concentration-relaxation curves for SNP and NTG were established in RA which had been precontracted with various vasoconstrictors (potassium chloride [K+], the thromboxane A2 mimetic agent U46619 or endothelin-1 [ET-1]).

RESULTS

Both SNP and NTG caused complete relaxation and EC50s were similar except that NTG was 6.2-fold more potent than SNP in U46619-induced contraction (-7.50+/-0.16 vs -6. 71+/-0.38 log m, P=0.04). After treatment with verapamil and NTG solution during harvesting, the RA segments responded with reduced maximal relaxation to NTG (84.9+/-3.9%, compared with 98.8+/-0.8% in the control, P=0.004). The vessel became less sensitive to NTG (EC50: -6.29+/-0.4 vs -7.50+/-0.16 log m, P=0.01). In investigations carried out with SNP, tolerance was only seen in the magnitude of the relaxation (87.4+/-4.7% vs 99.2+/-0.6% in the control, P=0.03).

CONCLUSIONS

Both NTG and SNP are potent vasodilators in the RA. NTG may have more potent effects in certain situations (constriction related to thromboxane A2). However, tolerance to NTG may develop. A cross tolerance to SNP may exist but the effect is weak so that SNP may be preferable to NTG as a vasodilator in the RA postoperatively. Other vasodilators may be the drugs of choice under such circumstances.

Altered endothelium-derived hyperpolarizing factor-mediated endothelial function in coronary microarteries by St Thomas' Hospital solution

OBJECTIVES

We examined the effect of St Thomas' Hospital solution on endothelium-derived hyperpolarizing factor-mediated function in the porcine coronary microarteries with emphasis on the effect of temperature and washout time.

METHODS

Microartery rings (diameter, 200-450 micrometers) were studied in myograph. The arteries were incubated in St Thomas' Hospital or Krebs solution (control) at 4 degrees C for 4 hours followed by 45 minutes (group Ia) or 90 minutes washout (group Ib) or at 22 degrees C for 1 hour followed by 45 minutes (group IIa) or 90 minutes washout (group IIb) and precontracted with -8.5 log M U 46619. The endothelium-derived hyperpolarizing factor-mediated relaxation to bradykinin was studied when endothelium-derived nitric oxide and prostaglandin I2 were inhibited with the presence of 7 micromol/L indomethacin and 300 micromol/L NG-nitro-L -arginine.

RESULTS

After exposure to St Thomas' Hospital solution, the maximal endothelium-derived hyperpolarizing factor-mediated relaxation (percentage of the precontraction) was significantly reduced at either temperature after washout for 45 minutes (group Ia, 42.7% +/- 3.5% vs 69.0% +/- 5.3%; n = 9; P =.000; and group IIa, 12.3% +/- 1.6% vs 56.1% +/- 4. 4%; n = 8; P =.000) but fully recovered after washout for 90 minutes. The U46619-induced contraction force was also significantly reduced after washout for 45 minutes (P <.001) but fully recovered at 90 minutes.

CONCLUSIONS

Under profound and moderate hypothermia, St Thomas' Hospital solution impairs endothelium-derived hyperpolarizing factor-mediated relaxation and smooth muscle contraction in the coronary microarteries. These effects exist during the reperfusion period for at least 45 minutes after exposure to St Thomas' Hospital solution and may account for the possible myocardial dysfunction during reperfusion.

Surgical management of blunt traumatic rupture of the descending thoracic aorta

Acute rupture of the descending thoracic aorta following blunt trauma is a life-threatening injury that requires emergent operative intervention. From February 1989 to January 1997, 4 patients with multiple injuries including traumatic rupture in the region of the aortic isthmus were surgically treated at our institution. Diagnosis was confirmed in all patients by aortogram prior to aortic repair. One patient had preoperative paraplegia secondary to an unstable spinal fracture. All patients underwent repair under cardiopulmonary bypass (3 partial, 1 total with hypothermic arrest). The site of rupture was resected and replaced with an interposition artificial graft. There was no perioperative mortality and no additional occurrence of paraplegia. Our experience and a review of the literature indicate that for survivors of traumatic aortic rupture, excellent outcomes can be achieved only if the diagnosis is made early and the surgical treatment is prompt.

Pharmacology of coronary artery bypass grafts

Spasm of arterial and venous graft conduits can occur both during harvesting and after the graft is connected. Attempts to overcome spasm during harvesting by probing or hydraulic distension can cause structural damage to the graft, which may impair short- and long-term patency. After a coronary artery bypass graft is connected, spasm can cause major problems with myocardial perfusion. To select the best pharmacologic agent to prevent or reverse vasoconstriction in a graft requires an understanding of the reactivity of that particular type of graft to vasoconstrictor and vasodilator agents. The pharmacologic reactivity of venous and arterial graft conduits has been documented through extensive studies of isolated vessels in the organ bath and of in situ grafts in the body. In this review we summarize the current state of knowledge of the reactivity of arterial and venous grafts to vasoconstrictor and vasodilator agents and describe the practical application of this knowledge in the operating room and in the postoperative period.

Arterial grafts for coronary artery bypass grafting: biological characteristics, functional classification, and clinical choice

Various arterial grafts have been used for coronary artery bypass grafting, but a unanimous opinion on how to best use these grafts has not been formed. Arterial grafts are not uniform in their biological characteristics. Differences between the perioperative behavior of the grafts and their long-term patency may be related to different characteristics. These characteristics should be taken into account in the use of arterial grafts, some of which are subject to more active pharmacologic intervention during and after operation to obtain satisfactory results. Clinical choice of grafts must be based on the general condition of the patient, the biological characteristics of the graft, the anatomy of the coronary artery, the match between the coronary artery and the graft, and technical considerations, including antispastic management.

A non-fatal impalement injury of the thorax

Impalement is an uncommon injury with only occasional reports in the literature. There are even fewer reports of impalement injuries limited to the thorax. We report herein the case of a 24-year-old man who survived impalement injury of the left side of the thorax with a steel rod while working at a construction site. The great vessels of the thorax were spared but the second thoracic vertebra was fractured resulting in complete paralysis of the left lower limb. The precise nature and extent of the injury were determined pre-operatively by computed tomography and aortography. The important principles of surgical management contributing to the successful outcome are described, these being minimal manipulation of the impalement object before and during transport, careful pre-operative planning and a multidisciplinary approach.

Repair of ruptured sinus of valsalva aneurysm: determinants of long-term survival

BACKGROUND

Ruptured sinus of Valsalva aneurysm is a rare cardiac anomaly and long-term survival after surgical treatment is not well established. This study was designed to investigate the determinants of long-term survival after repair of ruptured sinus of Valsalva aneurysm.

METHODS

From April 1978 to April 1996, 53 patients underwent operation for ruptured sinus of Valsalva aneurysm. The incidence among our cardiac surgical population was 0.56%. Long-term survival was investigated in 46 patients (13 to 65 years) who survived the operation, with 96.2% follow-up completeness (mean+/-standard deviation, 6.5+/-4.9 years; maximum, 17.2 years), by univariate and multivariate analyses.

RESULTS

There was no early operative death and no recurrence after the initial repair. Actuarial survival was 83.8%+/-8.4% at 15 years. Reoperation, aneurysm draining into the left ventricle, aortic prosthetic dehiscence, bacterial endocarditis, and aortic cross-clamp time (<70 minutes) were significant factors in long-term survival (p < 0.05). Multivariate analysis revealed that only aortic prosthesis dehiscence was the significant factor influencing late survival (p = 0.0001).

CONCLUSIONS

Surgical treatment for ruptured sinus of Valsalva aneurysm is safe and has satisfactory results. Aortic prosthesis dehiscence is the independent determinant for long-term survival. Other factors including bacterial endocarditis, concomitant ventricular septal defect repair, and aortic valve replacement did not independently influence long-term survival.

Potassium-channel opener in cardioplegia may restore coronary endothelial function

BACKGROUND

Depolarizing (hyperkalemic) solutions impair the coronary endothelial function through an endothelium-derived hyperpolarizing factor mechanism. I examined the hypothesis that potassium-channel openers may restore the impaired endothelium-derived hyperpolarizing factor-mediated coronary vasorelaxation when added to hyperkalemic cardioplegia.

METHODS

The porcine coronary arteries were exposed to hyperkalemia (potassium, 20 or 50 mmol/L) or hyperkalemia plus the potassium-channel opener aprikalim at 0.1 mmol/L for 1 hour. Endothelium-derived hyperpolarizing factor-mediated relaxation (percentage of 30 nmol/L U46619 precontraction) was induced by calcium ionophore A23187 and bradykinin in the presence of indomethacin (7 micromol/L) and Nomega-nitro-L-arginine (300 micromol/L).

RESULTS

The endothelium-derived hyperpolarizing factor-mediated relaxation was significantly impaired by exposure to hyperkalemia (20 mmol/L: 24.9%+/-14.1% versus 88.0%+/-3.3% in control, p = 0.002 for A23187; 50 mmol/L: 40.5%+/-12.3% versus 76.5%+/-3.8%, p = 0.003 for bradykinin). This reduced relaxation was significantly recovered by addition of aprikalim into the hyperkalemic (20 mmol/L) solution in A23187 experiments (81.2%+/-4.8%, p = 0.002) but only slightly recovered when added into the higher concentration of potassium (50 mmol/L) in bradykinin experiments (56.1%+/-4.7%, p = 0.2).

CONCLUSIONS

Potassium-channel openers may preserve endothelium-derived hyperpolarizing factor-mediated coronary relaxation when added to traditional hyperkalemic cardioplegia. This effect is significant when the potassium concentration is 20 mmol/L but partially lost when it reaches 50 mmol/L. This study may provide new insights into cardioprotection during open heart operations.

Effect and mechanism of cardioplegic arrest on the coronary endothelium-smooth muscle interaction

1. During cardiac surgery, the heart is arrested and protected by hyperkalaemic cardioplegia. The coronary endothelium may be damaged by ischaemia-reperfusion and cardioplegia. Subsequently, this may affect cardiac function immediately after cardiac surgery and cause mortality and morbidity. 2. We investigated coronary endothelium-smooth muscle interaction after exposure to depolarizing (hyperkalaemic; K+ 20 or 50 mmol/L) and hyperpolarizing (the K+ channel opener aprikalim) cardioplegia and organ preservation solution (University of Wisconsin (UW) solution). Endothelium-dependent relaxation and hyperpolarization of the coronary smooth muscle were studied in the porcine and human large conductance and micro-coronary arteries. Intracellular free calcium concentration in endothelial cells was also measured. 3. The endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation to A23187, bradykinin, and substance P in arteries contracted by either U46619 (10 nmol/L) or K+ (25 mmol/L) was reduced after exposure to either high K+ or UW solution, but was maximally preserved after exposure to aprikalim. The hyperpolarization of the membrane potential in response to the above endothelium-derived relaxing factor stimuli was also reduced by exposure to depolarizing cardioplegia. Studies in microcoronary arteries are in accordance with findings in large arteries. The intracellular free calcium concentration remained unchanged after exposure to hyperkalaemia. 4. We concluded that: (i) during cardiac surgery, the function of coronary circulation may be changed due to exposure to depolarizing cardioplegia or preservation solutions; (ii) the functional change in the coronary circulation is related to the altered interaction between the endothelium and smooth muscle; (iii) depolarizing (hyperkalaemia) cardioplegia or hyperkalaemic organ preservation solutions affect endothelium-smooth muscle interaction through the EDHF pathway; (iv) EDHF relaxes the porcine large and microcoronary arteries through multiple K+ channels; and (v) that hyperpolarizing vasodilators (K+ channel openers) may protect EDHF-mediated endothelial function when used as cardioplegia.

Risk factors for development of acute renal failure (ARF) requiring dialysis in patients undergoing cardiac surgery

Acute renal failure (ARF) is one of the major complications after cardiopulmonary bypass for open heart operations. The present study was undertaken to identify the risk factors for the development of ARF following cardiopulmonary bypass (CPB). Four hundred and forty-seven consecutive patients who underwent open heart procedures from July 1994 to June 1995 were analyzed retrospectively. Their mean age was 55.6 +/- 14.2 (SD) years (range, 18 to 80). Dialysis was instituted whenever a patient exhibited inadequate urine output (<0.5 mL/kg/hr) for 2 to 3 hours despite correction of hemodynamic status and diuretic therapy, especially if fluid overload, hyperkalemia, or metabolic acidosis were also present. Twenty variables were analyzed by univariate analysis; these included nine preoperative variables--age, sex, hypertension, atherosclerosis, diabetes mellitus, left ventricular end-diastolic dimension (LVEDD) >5 cm, preoperative congestive heart failure, renal insufficiency (serum creatinine > or =130 micromol/L on two occasions), and sepsis--10 intraoperative variables--duration of CPB, redo procedures, emergency surgery, use of intraaortic balloon pump (IABP) in operating room, use of gentamicin, use of ceftriaxone, use of sulbactam/ampicillin, requirement of deep hypothermic circulatory arrest, duration of low mean perfusion pressure (mean pressure <50 mmHg for more than 30 minutes), operation on multiple valves--and one postoperative variable--significant hypotension (systolic blood pressure less than 90 mmHg for more than 1 hour). Significant variables or the variables having a trend (p<0.1) to be associated with ARF were included in stepwise multiple logistic regression analyses. Three regression analyses were performed separately. The incidence of ARF requiring dialysis in the study period was 15.0%. Significant risk factors for whole group of patients (regression I) were preoperative renal insufficiency (p<0.0001), postoperative hypotension (p<0.0001), cardiopulmonary bypass time more than 140 min (p<0.005), preoperative congestive heart failure (p<0.01), and history of diabetes mellitus (p<0.01). The risk factors in the valve group of patients (regression II) were preoperative renal insufficiency (p<0.0001) and postoperative hypotension (p<0.05). Risk factors in the CABG patients (regression III) were postoperative hypotension (p=0.0001), CPB time more than 140 min (p<0.05), preoperative renal insufficiency (p<0.05), and age (p<0.05). The authors conclude that preoperative renal insufficiency and postoperative hypotension are the most important independent risk factors for ARF in postcardiac surgical patients. In addition, CPB time greater than 140 minutes and old age are also independent risk factors for ARF in CABG patients. CPB time more than 140 minutes, history of diabetes mellitus, and preoperative congestive heart failure are independent risk factors for development of ARF in our total group of patients. These findings may have important clinical implications in the prevention of ARF in postcardiac surgical patients.