Profibrotic COVID-19 subphenotype exhibits enhanced localized ER-dependent HSP47+ expression in cardiac myofibroblasts in situ

We recently described a subgroup of autopsied COVID-19 subjects (∼40%), termed 'profibrotic phenotype,' who exhibited clusters of myofibroblasts (Mfbs), which were positive for the collagen-specific chaperone heat shock protein 47 (HSP47+) in situ. This report identifies increased, localized (hot spot restricted) expression of αSMA, COLα1, POSTN and FAP supporting the identity of HSP47+ cells as myofibroblasts and characterizing a profibrotic extracellular matrix (ECM) phenotype. Coupled with increased GRP78 in COVID-19 subjects, these data could reflect induction of the unfolded protein response for mitigation of proteostasis (i.e., protein homeostasis) dysfunction in discrete clusters of cells. ECM shifts in selected COVID-19 subjects occur without significant increases in either global trichrome positive staining or myocardial injury based quantitively on standard H&E scoring. Our findings also suggest distinct mechanism(s) for ECM remodeling in the setting of SARS-CoV-2 infection. The ratio of CD163+/CD68+ cells is increased in hot spots of profibrotic hearts compared with either controls or outside of hot spots in COVID-19 subjects. In sum, matrix remodeling of human COVID-19 hearts in situ is characterized by site-restricted profibrotic mediated (e.g., HSP47+ Mfbs, CD163+ Mφs) modifications in ECM (i.e., COLα1, POSTN, FAP), with a strong correlation between COLα1 and HSP47+cells within hot spots. Given the established associations of viral infection (e.g., human immunodeficiency virus; HIV), myocardial fibrosis and sudden cardiac death, early screening tools (e.g., plasma biomarkers, noninvasive cardiac magnetic resonance imaging) for diagnosis, monitoring and treatment of fibrotic ECM remodeling are warranted for COVID-19 high-risk populations.

Effects of Aging on Cardiac Oxidative Stress and Transcriptional Changes in Pathways of Reactive Oxygen Species Generation and Clearance

Background Age-related heart diseases are significant contributors to increased morbidity and mortality. Emerging evidence indicates that mitochondria within cardiomyocytes contribute to age-related increased reactive oxygen species (ROS) generation that plays an essential role in aging-associated cardiac diseases. Methods and Results The present study investigated differences between ROS production in cardiomyocytes isolated from adult (6 months) and aged (24 months) Fischer 344 rats, and in cardiac tissue of adult (18-65 years) and elderly (>65 years) patients with preserved cardiac function. Superoxide dismutase inhibitable ferricytochrome c reduction assay (1.32±0.63 versus 0.76±0.31 nMol/mg per minute; P=0.001) superoxide and H2O2 production, measured as dichlorofluorescein diacetate fluorescence (1646±428 versus 699±329, P=0.04), were significantly higher in the aged versus adult cardiomyocytes. Similarity in age-related alteration between rats and humans was identified in mitochondrial-electron transport chain-complex-I-associated increased oxidative-stress by MitoSOX fluorescence (53.66±18.58 versus 22.81±12.60; P=0.03) and in 4-HNE adduct levels (187.54±54.8 versus 47.83±16.7 ng/mg protein, P=0.0063), indicative of increased peroxidation in the elderly. These differences correlated with changes in functional enrichment of genes regulating ROS homeostasis pathways in aged human and rat hearts. Functional merged collective network and pathway enrichment analysis revealed common genes prioritized in human and rat aging-associated networks that underlay enriched functional terms of mitochondrial complex I and common pathways in the aging human and rat heart. Conclusions Aging sensitizes mitochondrial and extramitochondrial mechanisms of ROS buildup within the heart. Network analysis of the transcriptome highlights the critical elements involved with aging-related ROS homeostasis pathways common in rat and human hearts as targets.

Biphasic effect of metformin on human cardiac energetics

Metformin is the first-line medication for treatment of type 2 diabetes and has been shown to reduce heart damage and death. However, mechanisms by which metformin protects human heart remain debated. The aim of the study was to evaluate the cardioprotective effect of metformin on cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) and mitochondria isolated from human cardiac tissue. At concentrations ≤2.5 mM, metformin significantly increased oxygen consumption rate (OCR) in the hiPSC-CMs by activating adenosine monophosphate activated protein kinase (AMPK)-dependent signaling and enhancing mitochondrial biogenesis. This effect was abrogated by compound C, an inhibitor of AMPK. At concentrations >5 mM, metformin inhibited the cellular OCR and triggered metabolic reprogramming by enhancing glycolysis and glutaminolysis in the cardiomyocytes. In isolated cardiac mitochondria, metformin did not increase the OCR at any concentrations but inhibited the OCR starting at 1 mM through direct inhibition of electron-transport chain complex I. This was associated with reduction of superoxide production and attenuation of Ca2+-induced mitochondrial permeability transition pore (mPTP) opening in the mitochondria. Thus, in human heart, metformin might improve cardioprotection due to its biphasic effect on mitochondria: at low concentrations, it activates mitochondrial biogenesis via AMPK signaling and increases the OCR; at high concentrations, it inhibits the respiration by directly affecting the activity of complex I, reduces oxidative stress and delays mPTP formation. Moreover, metformin at high concentrations causes metabolic reprogramming by enhancing glycolysis and glutaminolysis. These effects can be a beneficial adjunct to patients with impaired endogenous cardioprotective responses.

Abstract 344: Circulating MicroRNA Signature as a Predictive Biomarker for Postoperative Heart Failure

Background: Advancements in cardiac surgical techniques have led to decreasing operative risk. However, postoperative heart failure (PoHF) continues to be a major risk factor for adverse cardiac events in 20-35% of patients after cardiac surgery, with a 10-fold increase in 30-day mortality. Prediction of PoHF is challenging, particularly in patients with preserved ventricular function. Circulating microRNAs (miRNAs) recently were identified to predict HF or AF after surgery, but their role in predicting PoHF is not known. This study aimed to find novel noninvasive circulating biomarkers along with clinical factors that can identify patients at risk of developing PoHF immediately after surgery.

Methods: Patients undergoing CABG surgery with no previous history of HF, ventricular or supraventricular tachycardia were recruited, and preoperative blood assessed for circulating levels of protein biomarkers using ELISA. Differences in relative plasma levels of 13 miRNAs between the PoHF and no-PoHF groups were assessed by qPCR. Preoperative echocardiography was obtained. SAS was used for statistical analysis and ROC curve.

Results: Out of 68 patients, 13 developed PoHF (19.1%, mean age 64.1±11.6y, 53.8% males), whereas 55 (mean age 68.3±12.4y) remained free of HF. Patients who developed PoHF had lower LVEF (51.4±13.7 vs 58.2±9.9, P<0.05) with no differences in prevalence of hypertension, diabetes, hyperlipidemia, obesity, previous myocardial infarction, stroke, COPD, sleep apnea, or use of cardiac medications. The correlation matrix of all 13 miRNAs was transformed in a principal component (PC), resulting in 3 main clusters with eigenvalue >1. PC cluster2 consisted of miR-23a, -23b, -25 and -26a2, principally involved in oxidatives stress, fibrosis and contractility, and had the strongest association (AUC=0.797; P<0.01) with PoHF. A model combining PC cluster2 with age and LVEF improved sensitivity and specificity of the model to identify patients at risk of PoHF (AUC=0.880; 95% CL, 0.761-0.991; P<0.001)

Conclusion: Our study demonstrates that miR-23a, -23b, -25 and -26a2 may be useful predictors of PoHF. Circulating miRNA as biomarkers may have diagnostic potential to preoperatively, noninvasively identify patients at risk of developing PoHF.

Noninvasive biomarker-based risk stratification for development of new onset atrial fibrillation after coronary artery bypass surgery

BACKGROUND

Postoperative atrial fibrillation (PoAF) is a common complication after cardiac surgery. A pre-existing atrial substrate appears to be important in postoperative development of dysrhythmia, but its preoperative estimation is challenging. We tested the hypothesis that a combination of clinical predictors, noninvasive surrogate markers for atrial fibrosis defining abnormal left atrial (LA) mechanics, and biomarkers of collagen turnover is superior to clinical predictors alone in identifying patients at-risk for PoAF.

METHODS

In patients without prior AF undergoing coronary artery bypass grafting, concentrations of biomarkers reflecting collagen synthesis and degradation, extracellular matrix, and regulatory microRNA-29s were determined in serum from preoperative blood samples and correlated to atrial fibrosis extent, alteration in atrial deformation properties determined by 3D speckle-tracking echocardiography, and AF development.

RESULTS

Of 90 patients without prior AF, 34 who developed PoAF were older than non-PoAF patients (72.04 ± 10.7 y; P = 0.043) with no significant difference in baseline comorbidities, LA size, or ventricular function. Global (P = 0.007) and regional longitudinal LA strain and ejection fraction (P = 0.01) were reduced in PoAF vs. non-PoAF patients. Preoperative amino-terminal-procollagen-III-peptide (PIIINP) (103.1 ± 39.7 vs. 35.1 ± 19.3; P = 0.041) and carboxy-terminal-procollagen-I-peptide levels were elevated in PoAF vs. non-PoAF patients with a reduction in miR-29 levels and correlated with atrial fibrosis extent. Combining age as the only significant clinical predictor with PIIINP and miR-29a provided a model that identified PoAF patients with higher predictive accuracy.

CONCLUSIONS

In patients without a previous history of AF, using age and biomarkers of collagen synthesis and regulation, a noninvasive tool was developed to identify those at risk for new-onset PoAF.

Impact of statins on cellular respiration and de-differentiation of myofibroblasts in human failing hearts

AIMS

Fibroblast to myofibroblast trans-differentiation with altered bioenergetics precedes cardiac fibrosis (CF). Either prevention of differentiation or promotion of de-differentiation could mitigate CF-related pathologies. We determined whether 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors-statins, commonly prescribed to patients at risk of heart failure (HF)-can de-differentiate myofibroblasts, alter cellular bioenergetics, and impact the human ventricular fibroblasts (hVFs) in HF patients.

METHODS AND RESULTS

Either in vitro statin treatment of differentiated myofibroblasts (n = 3-6) or hVFs, isolated from human HF patients under statin therapy (HF + statin) vs. without statins (HF) were randomly used (n = 4-12). In vitro, hVFs were differentiated by transforming growth factor-β1 (TGF-β1) for 72 h (TGF-72 h). Differentiation status and cellular oxygen consumption rate (OCR) were determined by α-smooth muscle actin (α-SMA) expression and Seahorse assay, respectively. Data are mean ± SEM except Seahorse (mean ± SD); P < 0.05, considered significant. In vitro, statins concentration-dependently de-differentiated the myofibroblasts. The respective half-maximal effective concentrations were 729 ± 13 nmol/L (atorvastatin), 3.6 ± 1 μmol/L (rosuvastatin), and 185 ± 13 nmol/L (simvastatin). Mevalonic acid (300 μmol/L), the reduced product of HMG-CoA, prevented the statin-induced de-differentiation (α-SMA expression: 31.4 ± 10% vs. 58.6 ± 12%). Geranylgeranyl pyrophosphate (GGPP, 20 μmol/L), a cholesterol synthesis-independent HMG-CoA reductase pathway intermediate, completely prevented the statin-induced de-differentiation (α-SMA/GAPDH ratios: 0.89 ± 0.05 [TGF-72 h + 72 h], 0.63 ± 0.02 [TGF-72 h + simvastatin], and 1.2 ± 0.08 [TGF-72 h + simvastatin + GGPP]). Cellular metabolism involvement was observed when co-incubation of simvastatin (200 nmol/L) with glibenclamide (10 μmol/L), a K_ATP channel inhibitor, attenuated the simvastatin-induced de-differentiation (0.84 ± 0.05). Direct inhibition of mitochondrial respiration by oligomycin (1 ng/mL) also produced a de-differentiation effect (0.33 ± 0.02). OCR (pmol O₂ /min/μg protein) was significantly decreased in the simvastatin-treated hVFs, including basal (P = 0.002), ATP-linked (P = 0.01), proton leak-linked (P = 0.01), and maximal (P < 0.001). The OCR inhibition was prevented by GGPP (basal OCR [P = 0.02], spare capacity OCR [P = 0.008], and maximal OCR [P = 0.003]). Congruently, hVFs from HF showed an increased population of myofibroblasts while HF + statin group showed significantly reduced cellular respiration (basal OCR [P = 0.021], ATP-linked OCR [P = 0.047], maximal OCR [P = 0.02], and spare capacity OCR [P = 0.025]) and myofibroblast differentiation (α-SMA/GAPDH: 1 ± 0.19 vs. 0.23 ± 0.06, P = 0.01).

CONCLUSIONS

This study demonstrates the de-differentiating effect of statins, the underlying GGPP sensitivity, reduced OCR with potential activation of K_ATP channels, and their impact on the differentiation magnitude of hVFs in HF patients. This novel pleiotropic effect of statins may be exploited to reduce excessive CF in patients at risk of HF.

Abstract 759: Circulating Preoperative microRNA-29, Biomarkers of Collagen Synthesis, and Age Predictive of Postoperative Atrial Fibrillation After Coronary Artery Bypass Grafting

Background: Postoperative atrial fibrillation (PoAF) is a common complication occurring in 35-50% patients within 2-3 days after cardiac surgery. Identification of patients, especially those with no prior history of atrial fibrillation before surgery, is a challenge. A pre-existing atrial substrate appears to be an important factor in the development of PoAF. The aim of this study was to assess the role of biomarkers in identifying patients at risk of PoAF in a pathophysiology-based risk predictive model by combining clinical and biochemical risk factors.

Methods: Preoperative blood from patients undergoing cardiac surgery with no previous history of AF was assessed for circulating levels of biomarkers reflecting collagen synthesis/degradation and extracellular matrix remodeling using ELISA. Reverse transcriptase polymerase chain reaction assessed microRNA29 in the serum and correlated to extent of atrial fibrosis. Echocardiographic evaluation of LA mechanics was performed preoperatively using M-mode, 2D Doppler, and 3D Speckle tracking.

Results: Out of 55 patients, 31 patients (56.4%) who developed PoAF after surgery during their hospital stay were older in age (70.0 ± 4.0 years vs.63.4±9.9; p<0.01) with abnormal global longitudinal stain (6.9±0.69 vs.10.9±0.93, p=0.007), higher amino-terminal peptide procollagen III (PIIINP) levels (101.1±42.7 vs.36.6±20.0; p=0.043) with increased collagen to myocardial ratio (0.20±0.09 vs. 0.09±0.01, p= 0.026), and reduced preoperative circulating microRNA-29a, -29b and -29c levels. By combining the clinical risk factors, circulating biochemical and molecular biomarkers, we developed a model that identified PoAF patients (AUC=0.7987; 95% CI, 0.6174—0.98) with reduced preoperative atrial ejection fraction (32±2% vs. 42±2 %; p=0.01) as an independent risk factor for PoAF.

Conclusion: Our study developed a noninvasive tool to identify those who are at risk for new-onset PoAF in patients with no previous history of AF when combining age, biomarkers of collagen synthesis and microRNA-29a.

Aging-related increase in store-operated Ca2+ influx in human ventricular fibroblasts

Senescence-related fibrosis contributes to cardiac dysfunction. Profibrotic processes are Ca²⁺ dependent. The effect of aging on the Ca²⁺ mobilization processes of human ventricular fibroblasts (hVFs) is unclear. Therefore, we tested whether aging altered intracellular Ca²⁺ release and store-operated Ca²⁺ entry (SOCE). Disease-free hVFs from 2- to 63-yr-old trauma victims were assessed for cytosolic Ca²⁺ dynamics with fluo 3/confocal imaging. Angiotensin II or thapsigargin was used to release endoplasmic reticulum Ca²⁺ in Ca²⁺-free solution; CaCl₂ (2 mM) was then added to assess SOCE, which was normalized to ionomycin-induced maximal Ca²⁺. The angiotensin II experiments were repeated after phosphoenolpyruvate pretreatment to determine the role of energy status. The expression of genes encoding SOCE-related ion channel subunits was assessed by quantitative PCR, and protein expression was assessed by immunoblot analysis. Age groups of <50 and ≥50 yr were compared using unpaired t-test or regression analysis. Ca²⁺ release by angiotensin II or thapsigargin was not different between the groups, but SOCE was significantly elevated in the ≥50-yr group. Regression analysis showed an age-dependent phosphoenolpyruvate-sensitive increase in SOCE of hVFs. Aging did not alter the mRNA expression of SOCE-related genes. The profibrotic phenotype of hVFs was evident by sprouty1 downregulation with age. Thus, an age-associated increase in angiotensin II- and thapsigargin-induced SOCE occurs in hVFs, independent of receptor mechanisms or alterations of mRNA expression level of SOCE-related ion channel subunits but related to the cellular bioenergetics status. Elucidation of mechanisms underlying enhanced hVF SOCE with aging may refine SOCE targets to limit aging-related progression of Ca²⁺-dependent cardiac fibrosis. NEW & NOTEWORTHY Human ventricular fibroblasts exhibit an age-related increase in store-operated Ca²⁺ influx induced by angiotensin II, an endogenous vasoactive hormone, or thapsigargin, an inhibitor of endoplasmic reticulum Ca²⁺-ATPase, independent of receptor mechanisms or genes encoding store-operated Ca²⁺ entry-related ion channel subunits. Selective inhibition of this augmented store-operated Ca²⁺ entry could therapeutically limit aging-related cardiac fibrosis.

Prolonged post-differentiation culture influences the expression and biophysics of Na+ and Ca2+ channels in induced pluripotent stem cell-derived ventricular-like cardiomyocytes

Several studies have been reported in various domains from induction methods to utilities of somatic cell pluripotent reprogramming. However, one of the major struggles facing the research field of induced pluripotent stem cell (iPSC)-derived target cells is the lack of consistency in observations. This could be due to variety of reasons including varied culture periods post-differentiation. The cardiomyocytes (CMs) derived from iPSCs are commonly studied and proposed to be utilized in the comprehensive in vitro proarrhythmia initiative for drug safety screening. As the influence of varied culture periods on the electrophysiological properties of iPSC-CMs is not clearly known, using whole-cell patch clamp technique, we compared two groups of differentiated ventricular-like iPSC-CMs that are cultured for 10 to 15 days (D10-15) and more than 30 days (≥ D30) both under current and voltage clamps. The prolonged culture imparts increased excitability with high-frequency spontaneous action potentials, robust increase in the magnitude of peak Na⁺ current density, relatively shallow inactivation kinetics of Na⁺ channels, faster recovery from inactivation, and augmented Ca²⁺ current density. Quantitative real-time PCR studies of α-subunit transcripts showed enhanced mRNA expression of SCN1A, SCN5A Na⁺ channel subtypes, and CACNA1C, CACNA1G, and CACNA1I Ca²⁺ channel subtypes, in ≥ D30 group. Conclusively, the prolonged culture of differentiated iPSC-CMs affects the excitability, single-cell electrophysiological properties, and ion channel expressions. Therefore, following standard periods of culture across research studies while utilizing ventricular-like iPSC-CMs for in vitro health/disease modeling to study cellular functional mechanisms or test high-throughput drugs' efficacy and toxicity becomes crucial.

Abstract 535: Differences in Energetic Remodeling Between Right and Left Atria in Patients With Atrial Fibrillation

Introduction: Right and left atria have different susceptibilities toward developing atrial fibrillation (AF). The molecular bases of these differences are not well characterized. Given the complexity of AF development and progression, understanding AF-associated changes in myocardial energetics between the atria will help improve mechanistic insights and therapeutics for better clinical management of AF. The aim was to compare changes in mitochondrial oxidative phosphorylation system (OXPHOS), glycolysis and Krebs cycle metabolites in right atrial (RAA) and left atrial (LAA) appendage tissue from patients with (AF) and without (non-AF) AF.

Methods: RAA and LAA from well-matched AF (n=54) and non-AF (n=58) patients undergoing elective open heart surgery was collected. Functional activity of OXPHOS complexes I-V was measured spectrophotometrically. Protein expression level of OXPHOS complexes was determined by Western blot. OXPHOS gene expression level was performed using RT-PCR. Metabolites were profiled using high performance liquid chromatography coupled to tandem mass spectrometry. Comparison between groups was done applying the 2 sample t - and Wilcoxon rank sum tests with 5% level of significance.

Results: The most significant AF-associated alterations in myocardial energetics were observed in RAA. In AF patients, out of 84 OXPHOS genes, expression of 14 genes was significantly reduced in RAA (p<0.05) and 2 genes was reduced in LAA (p<0.05). There was AF-associated reduction in complex I (p=0.01) and IV (p=0.04) protein expression in RAA without changes in LAA. Unlike LAA, mitochondria from RAA revealed decline in complex I (p=0.01) and II (p=0.03) activity in AF compared to non-AF patients. In AF patients, glycolysis metabolites level of glucose-6-phosphate and phosphoenolpyruvate was reduced in RAA (p=0.03), whereas 2-phosphoglycerate was reduced in LAA (p=0.02). AF was related with decrease in NAD + (p=0.03), GDP (p=0.05), citrate (p=0.03), total pool of adenine nucleotides (p=0.02) and glutathione (p=0.03) level in RAA without changes in LAA.

Conclusion: AF is associated with different energetic remodeling in right and left atria, suggesting that dissimilar mechanisms may contribute to development and progression of AF.

Lactobacillus spp. impair the ability of Listeria monocytogenes FBUNT to adhere to and invade Caco-2 cells

OBJECTIVES

The objective of this study was to evaluate the ability of Lactobacillus curvatus CRL705, CRL1532, and CRL1533 and Lactobacillus sakei CRL1613 to survive under simulated gastrointestinal conditions. Moreover, a microencapsulation approach was proposed to improve gastrointestinal survival. Finally, experiments were performed to demonstrate that Lactobacillus spp. can modulate the ability of Listeria monocytogenes FBUNT to adhere to and invade Caco-2 cells.

RESULTS

Lactobacillus strains were encapsulated in alginate beads to enhance the survival of bacteria under in vitro gastrointestinal conditions. All strains hydrolyzed bile salts using chenodeoxycholic acid as a substrate and adhered to Caco-2 cells. Cell-free supernatants (CFSs) showed antimicrobial activity against L. monocytogenes as demonstrated by agar diffusion assays. The average percentages of L. monocytogenes adhesion decreased from 67.74 to 41.75 and 38.7% in the presence of 50 and 90% (v/v), respectively, for all CFSs tested. The highest concentrations of CFSs completely inhibited the L. monocytogenes invasion of Caco-2 cells.

CONCLUSIONS

The studied Lactobacillus strains have protective effects against the adhesion and invasion of L. monocytogenes FBUNT. Alginate encapsulation of these bacteria improved gastrointestinal tolerance such that they could be further studied as potential probiotics against intestinal pathogenic bacteria.

Abstract 110: Statin Therapy Alters the Transcriptome of Ventricular Fibroblasts From Human Failing Heart

Introduction: The mechanical and electrical dysfunction in heart failure (HF) is associated with excessive cardiac fibrosis (CF). Activation of human ventricular fibroblasts (hVF) and transdifferentiation to myofibroblasts underlies the increased CF. We recently reported that statin therapy reduced differentiation of hVF in HF patients. However, the underlying mechanism is not known. Therefore, we studied the effect of statin therapy on the transcriptome of hVF from HF patients.

Hypothesis: We tested the hypothesis that statin therapy alters the expression of differentiation-associated transcription factors (TF) in hVFs from HF patients.

Methods: Primary cultures of hVF obtained from HF patients undergoing left ventricular assist device implantation either under statin therapy for at least 1 year (n=3) or not (n=3). The extent of transcriptomic changes induced by statin therapy in hVFs was studied from total RNA using RT 2 Profiler TM PCR array - human transcription factors (Qiagen, Catalog No: PAHS-075Z ) run on Roche LightCycler 96-well block. Fold change was calculated by 2 -ΔΔCt method. Data were analyzed by Student’s t test, and P value <0.05 was considered significant.

Results: Out of the 84 related genes profiled, statin therapy upregulated significantly (P<0.05) at least two-fold the following genes: CREB1 (Cyclic AMP-responsive element-binding protein 1), SMAD1, TCF7L2 (transcription factor 7-like 2 ), MEF2A(myocyte enhancer factor-2), ATF1(activating transcription factor 1), and SP3. CREB1, SMAD1, TCFL2, and MEF2A are mainly involved in signaling pathways of G-protein coupled receptors, bone morphogenetic proteins, Wnt, and mitogen-activated protein kinases/extracellular signal-regulated kinases, respectively, while ATF1 and SP3 are involved in various signaling pathways. TFAP2A (transcription factor AP-2 alpha) tends to be downregulated by two-fold, however, did not reach statistical significance.

Conclusion: Statin therapy mitigates differentiation of hVFs from human failing heart patients by associated changes in the transcriptome. Selective targeting of hVF transcription factor may be a potential therapeutic strategy to de-differentiate myofibroblasts and mitigate the progression of CF and HF.

Abstract 123: Increased Susceptibility of Mitochondria to Permeability Transition Pore Opening in Alcoholic Cardiomyopathy

Introduction: Although generations of reactive oxygen species and mitochondrial dysfunction have been implicated in pathogenesis of alcoholic cardiomyopathy (ACM), molecular target(s) responsible for myocardial dysfunction in ACM are not well known.

Objective: To determine the impact of chronic alcohol exposure on mitochondrial oxidative phosphorylation system (OXPHOS), permeability transition pore (mPTP) opening, and oxidative stress using a rat model of ACM.

Methods: Sprague Dawley male rats (1 mo old) were exposed to alcohol (7.5% ethanol) for 3 months to develop ACM. Activity of OXPHOS was assessed enzymatically and by measuring mitochondrial oxygen consumption rate (OCR). The mPTP opening was determined by monitoring abrupt release of Ca 2+ after exposure of mitochondria to Ca 2+ . Western blot and RT-PCR were used to assess the expression of OXPHOS and mPTP protein components and corresponding genes. Malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were determined in heart tissue homogenates.

Results: There was no significant change in OCR or activity of OXPHOS complexes I-V, despite a decrease in complex V protein and Atp6v1e2 gene expression (-1.7-fold, p<0.01) in Alc rats. Mitochondria from Alc rats were more sensitive to Ca 2+ -induced mPTP opening. This was associated with increase in protein expression level of adenine nucleotide translocase 1/2 and voltage dependent anion channel 1. There was no difference in MDA or 4-HNE levels.

Conclusion: Increased sensitivity of mitochondria to mPTP opening during long-term alcohol consumption may compromise cardiac energetic reserves and contractility, leading to ACM development and progression.

Enhanced store-operated Ca2+ influx and ORAI1 expression in ventricular fibroblasts from human failing heart

Excessive cardiac fibrosis, characterized by increased collagen-rich extracellular matrix (ECM) deposition, is a major predisposing factor for mechanical and electrical dysfunction in heart failure (HF). The human ventricular fibroblast (hVF) remodeling mechanisms that cause excessive collagen deposition in HF are unclear, although reports suggest a role for intracellular free Ca²⁺ in fibrosis. Therefore, we determined the association of differences in cellular Ca²⁺ dynamics and collagen secretion/deposition between hVFs from failing and normal (control) hearts. Histology of left ventricle sections (Masson trichrome) confirmed excessive fibrosis in HF versus normal. In vitro, hVFs from HF showed increased secretion/deposition of soluble collagen in 48 h of culture compared with control [85.9±7.4 µg/10⁶ cells vs 58.5±8.8 µg/10⁶ cells, P<0.05; (Sircol™ assay)]. However, collagen gene expressions (COL1A1 and COL1A2; RT-PCR) were not different. Ca²⁺ imaging (fluo-3) of isolated hVFs showed no difference in the thapsigargin-induced intracellular Ca²⁺ release capacity (control 16±1.4% vs HF 17±1.1%); however, Ca²⁺ influx via store-operated Ca²⁺ entry/Ca²⁺ release-activated channels (SOCE/CRAC) was significantly (P≤0.05) greater in HF-hVFs (47±3%) compared with non-failing (35±5%). Immunoblotting for I_CRAC channel components showed increased ORAI1 expression in HF-hVFs compared with normal without any difference in STIM1 expression. The Pearson's correlation coefficient for co-localization of STIM1/ORAI1 was significantly (P<0.01) greater in HF (0.5±0.01) than control (0.4±0.01) hVFs. The increase in collagen secretion of HF versus control hVFs was eliminated by incubation of hVFs with YM58483 (10 µM), a selective I_CRAC inhibitor, for 48 h (66.78±5.87 µg/10⁶ cells vs 55.81±7.09 µg/10⁶ cells, P=0.27). In conclusion, hVFs from HF have increased collagen secretion capacity versus non-failing hearts and this is related to increase in Ca²⁺ entry via SOCE and enhanced expression of ORAI, the pore-forming subunit. Therapeutic inhibition of SOCE may reduce the progression of cardiac fibrosis/HF.

Summary: The excessive collagen secretory phenotype found in failing human hearts is associated with ventricular fibroblast remodeling, caused by an elevated influx of intracellular calcium via SOC channels.

Abstract 97: Ca 2+ Influx Via I CRAC Channels is Involved in Increased Secretion/Deposition of Collagen by Human Failing Heart Ventricular Fibroblasts

Introduction: Excessive cardiac fibrosis (CF) underlies mechanical and electrical dysfunction in heart failure (HF). However, the underlying mechanisms of increased CF are unclear. Recently, we reported increased Orai1 expression and I CRAC (calcium release-activated channels) -Ca 2+ influx in failing heart ventricular fibroblasts (hVF). Therefore, we studied the magnitude of collagen secretion/deposition by hVF from failing hearts and the involvement of Ca 2+ influx through I CRAC channels in this process.

Hypothesis: We tested the hypothesis that collagen secretion/deposition by hVFs from failing hearts will be high and sensitive to inhibition of I CRAC channels, compared to normal hearts.

Methods: Primary cultures of hVF obtained from HF patients undergoing LV assist device implantation (n=9) were compared to non-diseased hVF from trauma victims (n=4). The degree of fibrosis was analyzed by histology of LV tissue sections (5μm) with Masson’s trichrome staining. Collagen secretion/deposition after 48 h culture of hVFs from failing or normal hearts in the presence or absence of I CRAC inhibitor, YM-58483(10 μM), was assayed calorimetrically using Sircol™ kit. Data were analyzed by unpaired Student’s t-test.

Results: Histology of the failing heart LV sections with Masson’s trichome staining showed severe fibrosis compared to control sections. The percentage of positive staining area to total area, measured using custom-developed ImageJ macro, was significantly (p<0.05) higher in the failing heart (4.5±0.2%) compared to that of normal (0.1± 0.01%). The secretion/deposition of soluble collagen was significantly (p<0.05) higher in failing heart hVF (86± 7.6 μg/10 6 cells) than normal heart hVF (58.4±8.8 μg/10 6 cells). Incubation of fibroblasts with the I CRAC inhibitor YM58486 (10 μM) for 48 h eliminated the increase in collagen secretion of HF fibroblasts (55.8± 7 μg/10 6 cells vs 66.8± 6 μg/10 6 cells, p=0.27).

Conclusion: LV fibrosis is severe in HF patients. The magnitude of pro-fibrotic collagen secretion/deposition by hVF from HF patients is significantly high but sensitive to I CRAC inhibition. Selective targeting of fibroblast I CRAC may be a potential therapeutic tool to mitigate progression of CF and HF.

Sepiapterin ameliorates chemically induced murine colitis and azoxymethane-induced colon cancer

The effects of modulating tetrahydrobiopterin (BH4) levels with a metabolic precursor, sepiapterin (SP), on dextran sodium sulfate (DSS)-induced colitis and azoxymethane (AOM)-induced colorectal cancer were studied. SP in the drinking water blocks DSS-induced colitis measured as decreased disease activity index (DAI), morphologic criteria, and recovery of Ca(2+)-induced contractility responses lost as a consequence of DSS treatment. SP reduces inflammatory responses measured as the decreased number of infiltrating inflammatory macrophages and neutrophils and decreased expression of proinflammatory cytokines interleukin 1β (IL-1β), IL-6, and IL-17A. High-performance liquid chromatography analyses of colonic BH4 and its oxidized derivative 7,8-dihydrobiopterin (BH2) are inconclusive although there was a trend for lower BH4:BH2 with DSS treatment that was reversed with SP. Reduction of colonic cGMP levels by DSS was reversed with SP by a mechanism sensitive to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a specific inhibitor of the NO-sensitive soluble guanylate cyclase (sGC). ODQ abrogates the protective effects of SP on colitis. This plus the finding that SP reduces DSS-enhanced protein Tyr nitration are consistent with DSS-induced uncoupling of NOS. The results agree with previous studies that demonstrated inactivation of sGC in DSS-treated animals as being important in recruitment of inflammatory cells and in altered cholinergic signaling and colon motility. SP also reduces the number of colon tumors in AOM/DSS-treated mice from 7 to 1 per unit colon length. Thus, pharmacologic modulation of BH4 with currently available drugs may provide a mechanism for alleviating some forms of colitis and potentially minimizing the potential for colorectal cancer in patients with colitis.

Evidence for the putative cannabinoid receptor (GPR55)-mediated inhibitory effects on intestinal contractility in mice

BACKGROUND

Cannabinoids inhibit intestinal motility via presynaptic cannabinoid receptor type I (CB1) in enteric neurons while cannabinoid receptor type II (CB2) receptors are located mainly in immune cells. The recently de-orphanized G-protein-coupled receptor, GPR55, has been proposed to be the 'third' cannabinoid receptor. Although gene expression of GPR55 is evident in the gut, functional evidence for GPR55 in the gut is unknown. In this study, we tested the hypothesis that GPR55 activation inhibits neurogenic contractions in the gut.

METHODS

We assessed the inhibitory effect of the atypical cannabinoid O-1602, a GPR55 agonist, in mouse colon. Isometric tension recordings in colonic tissue strips were used from either wild-type, GPR55(-/-) or CB1(-/-)/CB2(-/-) knockout mice.

RESULTS

O-1602 inhibited the electrical field- induced contractions in the colon strips from wild-type and CB1(-/-)/CB2(-/-) in a concentration-dependent manner, suggesting a non-CB1/CB2 receptor-mediated prejunctional effect. The concentration-dependent response of O-1602 was significantly inhibited in GPR55(-/-) mice. O-1602 did not relax colonic strips precontracted with high K(+) (80 mmol/l), indicating no involvement of Ca(2+) channel blockade in O-1602-induced relaxation. However, 10 µmol/l O-1602 partially inhibited the exogenous acetylcholine (10 µmol/l)-induced contractions. Moreover, we also assessed the inhibitory effects of JWH015, a CB2/GPR55 agonist on neurogenic contractions of mouse ileum. Surprisingly, the effects of JWH015 were independent of the known cannabinoid receptors.

CONCLUSION

Taken together, these findings suggest that activation of GPR55 leads to inhibition of neurogenic contractions in the gut and are predominantly prejunctional.

Opioid-induced hypernociception is associated with hyperexcitability and altered tetrodotoxin-resistant Na+ channel function of dorsal root ganglia

Opiates are potent analgesics for moderate to severe pain. Paradoxically, patients under chronic opiates have reported hypernociception, the mechanisms of which are unknown. Using standard patch-clamp technique, we examined the excitability, biophysical properties of tetrodotoxin-resistant (TTX-R) Na(+) and transient receptor potential vanilloid 1 (TRPV1) channels of dorsal root ganglia neurons (DRG) (L(5)-S(1)) from mice pelleted with morphine (75 mg) or placebo (7 days). Hypernociception was confirmed by acetic acid-writhing test following 7-day morphine. Chronic morphine enhanced the neuronal excitability, since the rheobase for action potential (AP) firing was significantly (P < 0.01) lower (38 ± 7 vs. 100 ± 15 pA) while the number of APs at 2× rheobase was higher (4.4 ± 0.8 vs. 2 ± 0.5) than placebo (n = 13-20). The potential of half-maximum activation (V(1/2)) of TTX-R Na(+) currents was shifted to more hyperpolarized potential in the chronic morphine group (-37 ± 1 mV) vs. placebo (-28 ± 1 mV) without altering the V(1/2) of inactivation (-41 ± 1 vs. -33 ± 1 mV) (n = 8-11). Recovery rate from inactivation of TTX-R Na(+) channels or the mRNA level of any Na(+) channel subtypes did not change after chronic morphine. Also, chronic morphine significantly (P < 0.05) enhanced the magnitude of TRPV1 currents (-64 ± 11 pA/pF) vs. placebo (-18 ± 6 pA/pF). The increased excitability of sensory neurons by chronic morphine may be due to the shift in the voltage threshold of activation of TTX-R Na(+) currents. Enhanced TRPV1 currents may have a complementary effect, with TTX-R Na(+) currents on opiate-induced hyperexcitability of sensory neurons causing hypernociception. In conclusion, chronic morphine-induced hypernociception is associated with hyperexcitability and functional remodeling of TTX-R Na(+) and TRPV1 channels of sensory neurons.

The role of β-arrestin2 in the mechanism of morphine tolerance in the mouse and guinea pig gastrointestinal tract

β-Arrestin2 has been reported to play an essential role in analgesic tolerance. Analgesic tolerance without concomitant tolerance to constipation is a limiting side effect of chronic morphine treatment. Because tolerance to morphine develops in the mouse ileum but not the colon, we therefore examined whether the role of β-arrestin2 in the mechanism of morphine tolerance differs in the ileum and colon. In both guinea pig and mouse, chronic in vitro exposure (2 h, 10 μM) to morphine resulted in tolerance development in the isolated ileum but not the colon. The IC(50) values for morphine-induced inhibition of electrical field stimulation contraction of guinea pig longitudinal muscle myenteric plexus shifted rightward in the ileum from 5.7 ± 0.08 (n = 9) to 5.45 ± 0.09 (n = 6) (p < 0.001) after morphine exposure. A significant shift was not observed in the colon. Similar differential tolerance was seen between the mouse ileum and the colon. However, tolerance developed in the colon from β-arrestin2 knockout mice. β-Arrestin2 and extracellular signal-regulated kinase 1/2 expression levels were determined further by Western blot analyses in guinea pig longitudinal muscle myenteric plexus. A time-dependent decrease in the expression of β-arrestin2 and extracellular signal-regulated kinase 1/2 occurred in the ileum but not the colon after 2 h of morphine (10 μM) exposure. Naloxone prevented the decrease in β-arrestin2. In the isolated ileum from guinea pigs chronically treated in vivo with morphine for 7 days, neither additional tolerance to in vitro exposure of morphine nor a decrease in β-arrestin2 occurred. We conclude that a decrease in β-arrestin2 is associated with tolerance development to morphine in the gastrointestinal tract.

Blockade of endocannabinoid hydrolytic enzymes attenuates precipitated opioid withdrawal symptoms in mice

Δ(9)-Tetrahydrocannbinol (THC), the primary active constituent of Cannabis sativa, has long been known to reduce opioid withdrawal symptoms. Although THC produces most of its pharmacological actions through the activation of CB(1) and CB(2) cannabinoid receptors, the role these receptors play in reducing the variety of opioid withdrawal symptoms remains unknown. The endogenous cannabinoids, N-arachidonoylethanolamine (anandamide; AEA) and 2-arachidonylglycerol (2-AG), activate both cannabinoid receptors but are rapidly metabolized by fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively. The objective of this study was to test whether increasing AEA or 2-AG, via inhibition of their respective hydrolytic enzymes, reduces naloxone-precipitated morphine withdrawal symptoms in in vivo and in vitro models of opioid dependence. Morphine-dependent mice challenged with naloxone reliably displayed a profound withdrawal syndrome, consisting of jumping, paw tremors, diarrhea, and weight loss. THC and the MAGL inhibitor 4-nitrophenyl 4-(dibenzo[d][1,3]dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate (JZL184) dose dependently reduced the intensity of most measures through the activation of CB(1) receptors. JZL184 also attenuated spontaneous withdrawal signs in morphine-dependent mice. The FAAH inhibitor N-(pyridin-3-yl)-4-(3-(5-(trifluoromethyl)pyridin-2-yloxy)benzyl)-piperdine-1-carboxamide (PF-3845) reduced the intensity of naloxone-precipitated jumps and paw flutters through the activation of CB(1) receptors but did not ameliorate incidence of diarrhea or weight loss. In the final series of experiments, we investigated whether JZL184 or PF-3845 would attenuate naloxone-precipitated contractions in morphine-dependent ilea. Both enzyme inhibitors attenuated the intensity of naloxone-induced contractions, although this model does not account mechanistically for the autonomic withdrawal responses (i.e., diarrhea) observed in vivo. These results indicate that endocannabinoid catabolic enzymes are promising targets to treat opioid dependence.

Ion channel remodeling in gastrointestinal inflammation

BACKGROUND

 Gastrointestinal inflammation significantly affects the electrical excitability of smooth muscle cells. Considerable progress over the last few years have been made to establish the mechanisms by which ion channel function is altered in the setting of gastrointestinal inflammation. Details have begun to emerge on the molecular basis by which ion channel function may be regulated in smooth muscle following inflammation. These include changes in protein and gene expression of the smooth muscle isoform of L-type Ca(2+) channels and ATP-sensitive K(+) channels. Recent attention has also focused on post-translational modifications as a primary means of altering ion channel function in the absence of changes in protein/gene expression. Protein phosphorylation of serine/theronine or tyrosine residues, cysteine thiol modifications, and tyrosine nitration are potential mechanisms affected by oxidative/nitrosative stress that alter the gating kinetics of ion channels. Collectively, these findings suggest that inflammation results in electrical remodeling of smooth muscle cells in addition to structural remodeling.

PURPOSE

The purpose of this review is to synthesize our current understanding regarding molecular mechanisms that result in altered ion channel function during gastrointestinal inflammation and to address potential areas that can lead to targeted new therapies.

Adrenomedullin relaxes rat uterine artery: mechanisms and influence of pregnancy and estradiol

Uterine arteries play a major role in regulating uteroplacental blood flow. Failure to maintain blood flow to the uteroplacental compartment during pregnancy often results in intrauterine growth retardation. Immunohistochemical staining of adrenomedullin (AM), an endogenous vasoactive peptide, in uterine artery was intense in pregnant compared to nonpregnant rats, but it is not known whether AM directly relaxes uterine artery or not. In this study, we elucidated the mechanisms of uterine artery relaxation by AM and its regulation by pregnancy and female sex steroids. AM was able to relax uterine artery, and this relaxation was influenced positively by pregnancy and estradiol as evidenced by the increased pD(2) and E(max) values of AM. Both pregnancy and estradiol treatment to ovariectomized rats amplified RAMP(3) expression in uterine arteries while progesterone had no effect. AM-induced uterine artery relaxation is predominantly endothelium-dependent. The AM receptor antagonist CGRP(8-37) is more potent than AM(22-52) in inhibiting the AM relaxation, indicating the involvement of AM(2) receptor subtype. Moreover, AM uses the classical nitric oxide-cyclic guanosine monophosphate pathway along with K(Ca) channels to mediate the vasodilatory effect in uterine artery. In conclusion, sensitivity of uterine artery to AM-induced relaxation is increased with pregnancy or estradiol treatment by increasing RAMP(3) expression, suggesting an important role for AM in regulating the uterine hemodynamics, probably maintaining uterine blood flow during pregnancy and in pre- and postmenopausal cardiovascular adaptation differences.

Colonic inflammation alters Src kinase-dependent gating properties of single Ca2+ channels via tyrosine nitration

Nitration of L-type calcium channels during colonic inflammation impairs phosphorylation by the tyrosine kinase, Src kinase. This results in decreased calcium currents. The purpose of this study was to determine the mechanism of the downregulation of Ca2+ currents in colonic inflammation. In whole cell voltage clamp of mouse single smooth muscle cells, long-duration depolarization produced noninactivating calcium currents that were significantly reduced by the Src kinase inhibitor, protein phosphatase 2 (PP2). Unitary Ba2+ currents were recorded upon repolarization from positive potentials in cell-attached patches of smooth muscle and hCa(v)1.2b-transfected cells to assess the properties of the single channels attributed to the noninactivating open state. Repolarization to -40 mV from 0 mV resulted in single-channel events with conductance of approximately 23 pS. The ensemble average of the tail currents from 1,000 sweeps was 337 +/- 27 fA in control and 218 +/- 49 fA (P < 0.05) in inflamed cells. Neither open-probability nor open-time constants were significantly different between control and inflamed cells. However, the transition to the open state measured as channel availability was significantly reduced from 19 +/- 3% to 6.4 +/- 1%. Similarly, peak ensemble average current and channel availability were significantly reduced by PP2 and treatment with peroxynitrite in control cells. Mutation of COOH-terminal tyrosine residues in hCa(v)1.2b Chinese hamster ovarian cells also decreased peak ensemble average tail currents and availability. The present findings suggest that the transition of Ca2+ channels to the noninactivating open state is Src kinase dependent. Tyrosine nitration prevents Src-mediated transitions, leading to decreased calcium currents.

The effect of tyrosine nitration of L-type Ca2+ channels on excitation-transcription coupling in colonic inflammation

BACKGROUND AND PURPOSE

Excitation-transcriptional coupling involves communication between plasma membrane ion channels and gene expression in the nucleus. Calcium influx through L-type Ca(2+) channels induces phosphorylation of the transcription factor, cyclic-AMP response element binding protein (CREB) and downstream activation of the cyclic-AMP response element (CRE) promoter regions. Tyrosine nitration of Ca(2+) channels attenuates interactions with c-Src kinase, decreasing Ca(2+) channel currents and smooth muscle contraction during colonic inflammation. In this study we examined the effect of tyrosine nitration and colonic inflammation on Ca(2+) channel mediated phosphorylation of CREB and CRE activation.

EXPERIMENTAL APPROACH

CREB and phospho-CREB were detected by Western blots and CRE activation measured by dual luciferase assay. Chinese hamster ovary (CHO) cells were transfected with hCa(v)1.2b and hCa(v)1.2b c-terminal mutants. Colonic inflammation was induced by intracolonic instillation of 2,4,6 trinitrobenzene sulphonic acid in mouse colon.

KEY RESULTS

In hCa(v)1.2b transfected CHO cells and in native colonic smooth muscle, depolarization with 80 mM KCl induced CREB phosphorylation (pCREB). Treatment with peroxynitrite inhibited KCl-induced pCREB. Following experimental colitis, KCl-induced CREB phosphorylation was abolished in smooth muscle, concomitant with tyrosine nitration of Ca(2+) channels. Depolarization increased CRE activation in hCa(v)1.2b CHO cells by 2.35 fold which was blocked by nifedipine and by protein nitration of Ca(2+) channels with peroxynitrite. The Src-kinase inhibitor, PP2, blocked depolarization-induced CRE activation. Mutation of the C-terminus tyrosine residue, Y2134F, but not Y1861F, blocked CRE activation.

CONCLUSIONS AND IMPLICATIONS

Post-translational modification of Ca(2+) channels due to tyrosine nitration modified excitation-transcriptional coupling in colonic inflammation.

Morphine tolerance in the mouse ileum and colon

Repeated administration of morphine is associated with tolerance to its antinociceptive properties. However, constipation remains the major side effect of chronic exposure to morphine. In contrast, previous studies suggest that tolerance to opioids develops in the ileum of several species. In this study, we provide evidence that constipation may arise due to a lack of tolerance development to morphine in the colon. Mice received implants with either placebo or 75 mg of morphine pellets, and they were examined for morphine tolerance to antinociception, defecation, and intestinal and colonic transit after 72 h. Tissues were obtained from the ileum and distal colon, and contractile responses were measured from longitudinal and circular muscle preparations. In morphine-pelleted mice, a 5.5-fold tolerance developed to antinociception after 72 h, and a 53.2-fold tolerance developed in mice that received an additional daily morphine injection. In both models, intestinal transit but not defecation or colonic transit developed tolerance. In isolated longitudinal muscles, electrical field stimulation-induced cholinergic contractions were dose-dependently inhibited by morphine in both the ileum and colon of placebo pelleted with a pD(2) of 7.1 +/- 0.4 and 7.8 +/- 0.4, respectively. However, the dose response to morphine inhibition was shifted to the right for the ileum from morphine-pelleted mice (pD(2) = 5.1 +/- 0.4) but not the colon (pD(2) = 6.9 +/- 0.4). In circular muscle preparations, morphine induced atropine-insensitive contractions in both tissue segments. Tolerance to morphine developed in the ileum but not the colon upon repeated administration of morphine. These findings indicate that a lack of tolerance development in the colon is the basis for opioid bowel dysfunction.

COOH-terminal association of human smooth muscle calcium channel Ca(v)1.2b with Src kinase protein binding domains: effect of nitrotyrosylation

The carboxyl terminus of the calcium channel plays an important role in the regulation of calcium entry, signal transduction, and gene expression. Potential protein-protein interaction sites within the COOH terminus of the L-type calcium channel include those for the SH3 and SH2 binding domains of c-Src kinase that regulates calcium currents in smooth muscle. In this study, we examined the binding sites involved in Src kinase-mediated phosphorylation of the human voltage-gated calcium channel (Ca(v)) 1.2b (hCav1.2b) and the effect of nitrotyrosylation. Cotransfection of human embryonic kidney (HEK)-293 cells with hCa(v)1.2b and c-Src resulted in tyrosine phosphorylation of the calcium channel, which was prevented by nitration of tyrosine residues by peroxynitrite. Whole cell calcium currents were reduced by 58 + 5% by the Src kinase inhibitor PP2 and 64 + 6% by peroxynitrite. Nitrotyrosylation prevented Src-mediated regulation of the currents. Glutathione S-transferase fusion protein of the distal COOH terminus of hCa(v)1.2b (1809-2138) bound to SH2 domain of Src following tyrosine phosphorylation, while binding to SH3 required the presence of the proline-rich motif. Site-directed mutation of Y(2134) prevented SH2 binding and resulted in reduced phosphorylation of hCa(v)1.2b. Within the distal COOH terminus, single, double, or triple mutations of Y(1837), Y(1861), and Y(2134) were constructed and expressed in HEK-293 cells. The inhibitory effects of PP2 and peroxynitrite on calcium currents were significantly reduced in the double mutant Y(1837-2134F). These data demonstrate that the COOH terminus of hCa(v)1.2b contains sites for the SH2 and SH3 binding of Src kinase. Nitrotyrosylation of these sites prevents Src kinase regulation and may be importantly involved in calcium influx regulation during inflammation.

Cyclic AMP-independent CGRP8-37-sensitive receptors mediate adrenomedullin-induced decrease of CaCl2-contraction in pregnant rat mesenteric artery

OBJECTIVES

We tested the hypothesis that adrenomedullin reduces calcium influx independent of potassium channels in depolarized endothelium-denuded mesenteric artery from pregnant rats.

RESULTS

Adrenomedullin reduced the CaCl(2)-induced contraction, while the receptor antagonist calcitonin gene-related peptide (CGRP)(8-37), but not adrenomedullin(22-52), reversed these effects. Adenylate cyclase inhibition by SQ22536 did not prevent adrenomedullin effects on CaCl(2)-induced contraction. Adrenomedullin did not inhibit depolarization-induced calcium entry to isolated vascular smooth muscle. Inhibition of myosin light-chain (MLC) phosphatase by calyculin A reversed the effects of adrenomedullin on contraction caused by submillimolar concentrations of CaCl(2), while adrenomedullin still inhibited contraction caused by higher concentrations of CaCl(2). However, the ratio of phosphorylated to total myosin phosphatase target 1, the regulatory subunit of MLC phosphatase, did not change with adrenomedullin, indicating a lack of MLC phosphatase activation. Interestingly, sodium fluoride, a nonspecific protein phosphatase inhibitor, completely blocked the effect of adrenomedullin on CaCl(2)-induced contraction. Adrenomedullin inhibited calcium mobilization from intracellular stores induced by thapsigargin.

CONCLUSION

Adrenomedullin inhibits CaCl(2)-induced contraction, without affecting calcium influx, through a CGRP(8-37)-sensitive receptor, but not using the cyclic adenosine monophosphate pathway, probably through activation of protein phosphatases. Inhibition of intracellular calcium release is an additional role played by adrenomedullin in calcium homeostasis in vascular smooth muscle.

Nitrotyrosylation of Ca2+ Channels Prevents c-Src Kinase Regulation of Colonic Smooth Muscle Contractility in Experimental Colitis

Basal levels of c-Src kinase are known to regulate smooth muscle Ca(2+) channels. Colonic inflammation results in attenuated Ca(2+) currents and muscle contraction. Here, we examined the regulation of calcium influx-dependent contractility by c-Src kinase in experimental colitis. Ca(2+)-influx induced contractions were measured by isometric tension recordings of mouse colonic longitudinal muscle strips depolarized by high K(+). The E(max) to CaCl(2) was significantly less in inflamed tissues (38.4 +/- 7.6%) than controls, indicative of reduced Ca(2+) influx. PP2 [4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine], a selective Src kinase inhibitor, significantly reduced the contractile amplitude and shifted the pD(2) from 3.88 to 2.44 in controls, whereas it was ineffective in inflamed tissues (3.66 versus 3.43). After pretreatment with a SIN-1 (3-morpholinosydnonimine)/peroxynitrite combination, the maximal contraction to CaCl(2) was reduced by 46 +/- 7% in controls but unaffected in inflamed tissues (13 +/- 11%). Peroxynitrite also prevented the inhibitory effect of PP2 in control tissues. In colonic single smooth muscle cells, PP2 inhibited Ca(2+) currents by 84.1 +/- 3.9% in normal but only 36.2 +/- 13% in inflamed tissues. Neither the Ca(2+) channel Ca(v)1.2b, gene expression, nor the c-Src kinase activity was altered by inflammation. Western blot analysis showed no change in the Ca(2+) channel protein expression but increased nitrotyrosylated-Ca(2+) channel proteins during inflammation. These data suggest that post-translational modification of Ca(2+) channels during inflammation, possibly nitrotyrosylation, prevents c-Src kinase regulation resulting in decreased Ca(2+) influx.

Adrenomedullin-2, a novel calcitonin/calcitonin-gene-related peptide family peptide, relaxes rat mesenteric artery: influence of pregnancy

Adrenomedullin-2 (ADM2), a novel calcitonin/calcitonin-gene-related peptide family peptide, is reported to reduce blood pressure in both normal and hypertensive rats. This study demonstrates gestational regulation of circulatory ADM2 in rat plasma. ADM2 dose-dependently reduces the mean arterial pressure in rats, whereas the hypotensive effect of ADM2 is significantly higher during pregnancy. In addition, immunoreactive ADM2 protein is distributed in perivascular fibers of rat mesenteric artery, and levels of pre-pro-ADM2 are significantly (P<0.05) elevated in pregnant compared with nonpregnant rat mesenteric artery. Furthermore, incubation of endothelium intact arterial tissue from pregnant rats with ADM217-47, an ADM2 antagonist, shifted the dose-dependent relaxation curve to the right in wire myography. Inhibition of soluble guanylate cyclase with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM) or endothelial nitric oxide synthase with N-nitro-L-arginine methyl ester (100 microM) reduced the relaxation of mesenteric artery induced by ADM2. Inhibition of adenylate cyclase with SQ22536 (10 microM) or protein kinase A with the Rp diastereomer of cyclic adenosine 3',5'-phosphorothioate (10 microM) also reduced the maximal relaxation responses induced by ADM2. Blockade of calcium-activated potassium channels with tetraethylammonium chloride (1 mM) inhibited the ADM2-induced relaxation, whereas blockade of ATP-sensitive potassium channels with glybenclamide (10 microM) did not affect the relaxation response. Hence the mechanism of ADM2-induced vasorelaxation is nitric oxide and receptor mediated and cGMP and cAMP dependent and occurs through activation of calcium-activated potassium channels. In conclusion, rat pregnancy is associated with increased levels of circulatory and vascular tissue ADM2 with concomitant increase in the in vivo hypotensive effect of ADM2 and vascular reactivity of mesenteric artery to ADM2, thus suggesting involvement of ADM2 in vascular adaptations during pregnancy.

Vascular hyperresponsiveness to adrenomedullin during pregnancy is associated with increased generation of cyclic nucleotides in rat mesenteric artery

Cardiovascular adaptation is a hallmark of pregnancy. Here we report on vascular hyperresponsiveness to an endogenous vasodilator, adrenomedullin (ADM), during pregnancy. Intravenous administration of ADM dose dependently decreased the mean arterial pressure, and the decrease was significantly greater in pregnant compared with nonpregnant rats without affecting the heart rate. In endothelium-intact mesenteric artery precontracted by ED70 concentration of norepinephrine, the potency and efficacy of ADM in causing the vasodilation of mesenteric arterial rings from pregnant rats are significantly higher compared with nonpregnant females at diestrus. The magnitude of inhibition of concentration-dependent response to ADM by the inhibition of either soluble guanylate cyclase or adenylate cyclase was greater in pregnant rats. Moreover, ADM-induced cyclic nucleotide generation, both cGMP and cAMP, in the mesenteric artery was elevated during pregnancy and was sensitive to the receptor antagonist, ADM22-52. These findings suggest that during pregnancy the vasodilatory effects of ADM are greater and are associated with increased generation of cyclic nucleotides in resistance vessels, and these changes may be part of the cardiovascular adaptations that occur during pregnancy.

Relative contribution of intracellular and extracellular Ca2+ to alpha2-adrenoceptor-mediated contractions of ovine pulmonary artery

We have examined the mechanism of contractions elicited by guanfacine, a selective agonist for alpha(2A/D)-adrenoceptors and its modulations by cyclic nucleotides in isolated ovine resistance intra-pulmonary artery. Guanfacine (10 nM-30 microM) produced concentration-dependent contraction of the pulmonary artery rings mounted for isometric recording. Yohimbine (0.1 microM), a nonspecific alpha(2)-adrenoceptor antagonist caused a parallel shift to the right (1.2 log unit) in the concentration-response curve of guanfacine without depressing the maxima. Preincubation of the tissues with Ca(2+)-free solution (EGTA 1mM) for 30 min caused a rightward shift (0.8 log unit) of the concentration-response curve of guanfacine with the inhibition of the maxima by 30+/-4.6%. L-type calcium channel blocker, nifedipine (1 microM) slightly inhibited (20%) the maximal contraction elicited with guanfacine (10 microM). On the other hand, brief exposure to cyclopiazonic acid (10 microM), an inhibitor of IP3-sensitive sarcoplasmic reticulum Ca(2+)-ATPase, resulted in marked inhibition of concentration-dependent contractions elicited with guanfacine (10 nM-30 microM), with the maxima being inhibited by 51+/-3.11%. In addition, agents that increase intracellular cAMP and cGMP suppressed guanfacine-induced contractions. The results of the present study suggest that alpha(2)-adrenoceptor-mediated contractions in ovine resistance pulmonary artery is primarily dependent on intracellular Ca(2+) with a small contribution from Ca(2+)-influx through voltage-dependent L-type calcium channels.

Endothelium-independent relaxation by adrenomedullin in pregnant rat mesenteric artery: role of cAMP-dependent protein kinase A and calcium-activated potassium channels

The mechanisms of relaxation of adrenomedullin were investigated in isolated mesenteric artery from pregnant rats. Adrenomedullin (1 nM-0.3 microM) produced concentration-dependent relaxation of endothelium-denuded mesenteric artery rings precontracted with norepinephrine at a concentration required to produce 70% of maximal response (ED70). The concentration-response curve of adrenomedullin was shifted to the right by adrenomedullin receptor antagonist adrenomedullin(22-52) (10 microM) or calcitonin gene-related peptide(8-37) (1 microM). Inhibition of adenylate cyclase by 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536) (10 microM) or protein kinase A [Rp-cyclic adenosine monophosphorothioate (Rp-cAMP); 10 microM] reduced the adrenomedullin-induced relaxation to the same magnitude. Adrenomedullin increased the intracellular cAMP level from 0.38 +/- 0.07 to 2.00 +/- 0.47 pmol/mg tissues, which was completely inhibited by adrenomedullin(22-52) (100 microM). Extracellular high potassium (80 mM), which inactivates the potassium channels, reduced the adrenomedullin-induced relaxation. Blockade of ATP-sensitive, voltage-gated, or inward rectifier potassium channels did not affect the adrenomedullin-induced relaxation. Blockade of calcium-activated K+ channels (KCa) by tetraethylammonium (1 mM) or iberiotoxin (100 nM) inhibited the adrenomedullin-induced relaxation, whereas there was no additional inhibition by SQ22536 or Rp-cAMP when KCa channels were already inhibited. In conclusion, this study provides evidence that cAMP-dependent protein kinase A and KCa channels seem to mediate as the cellular pathways in the adrenomedullin-induced endothelium-independent relaxation of mesenteric artery from pregnant rats.

Female sex steroids increase adrenomedullin-induced vasodilation by increasing the expression of adrenomedullin2 receptor components in rat mesenteric artery

Based on the favorable effects of female sex steroids in vascular functions and the potent hypotensive effects of adrenomedullin (AM), we hypothesized that AM-induced vasodilation is gender dependent, and female sex steroids enhance this effect. In endothelium-intact rat mesenteric artery, AM (1 nm-0.3 microM)-induced concentration-dependent relaxation was significantly (P < 0.05) higher in females [pD2(-log EC50 of the molar concentration), 7.05 +/- 0.10; maximal relaxation response (Emax), 69.2 +/- 3.46%] than males (pD2, 6.53 +/- 0.08; Emax, 53.28 +/- 4.86%). The increased relaxation was lost when the females were ovariectomized (OVX) (pD2, 6.14 +/- 0.24; Emax, 39.68 +/- 5.68%). The reduced relaxation response in OVX rats was reversed by administration of either progesterone (P4; pD2, 7.18 +/- 0.07; Emax, 72.4 +/- 2.76%) or 17beta-estradiol (E2; pD2, 7.00 +/- 0.14; Emax, 70.4 +/- 4.79%). AM mediates its effects through either AM(22-52)-sensitive AM1 receptors [composed of calcitonin receptor-like receptors (CLs) and receptor activity-modifying protein (RAMP)2] or AM2 receptors (CL/RAMP3), which can be antagonized more potently by calcitonin gene-related peptide(8-37) than AM(22-52). Pharmacological characterization suggested the involvement of AM2 receptors in the increased vasodilatory effect of AM in both P4- and E2-treated animals as calcitonin gene-related peptide(8-37) (10 microM) was more potent in antagonizing the AM effects (Emax, P(4): 25.92 +/- 5.32%; E2: 29.11 +/- 7.41%) than AM(22-52) (100 microM). RT-PCR studies also supported the involvement of AM2 receptors because expression of mRNA levels encoding CL (previously reported) and RAMP3 were increased in P4- or E2-treated OVX rats. In conclusion, AM-induced vasodilation is gender-dependent and increased by female sex steroids by increased expression of AM2 receptor components.

Ascorbic acid metabolism and polyol pathway in diabetes

It has been reported previously that the plasma concentration of ascorbic acid (AA) is reduced in streptozocin-induced diabetic rats and can be normalized by treatment with the aldose reductase inhibitor tolrestat. This study was designed to investigate further the relationship between the polyol pathway and AA metabolism in diabetic rats. Disturbance of AA metabolism was demonstrable after 1 wk of diabetes. Dietary myo-inositol supplementation was effective in normalizing plasma AA levels, as was treatment with tolrestat. In untreated diabetes, despite low plasma AA concentration, there was increased urinary excretion of AA that was reversed by treatment with either tolrestat or myo-inositol. In contrast, AA supplementation normalized plasma AA concentrations while further increasing urinary AA excretion. The abnormality of AA metabolism was less severe in galactose-fed rats, which had normal plasma AA levels and only minor increases in urinary AA excretion. These studies demonstrated a disturbance in the regulation of plasma and urinary AA concentration in experimental diabetes and confirmed the relationship of AA with the polyol pathway. Because AA has many important biological functions, abnormalities of AA metabolism could be important in the pathogenesis of some diabetic complications. The interaction of the polyol and AA pathways suggests that this could be another site of action for aldose reductase inhibitors.

Deficiency of ascorbic acid in experimental diabetes. Relationship with collagen and polyol pathway abnormalities

The plasma and tissue concentration of ascorbic acid (AA) is reduced in diabetes. This study was designed to investigate the mechanism and significance of this phenomenon. The low plasma AA concentration of diabetic rats can be normalized by dietary AA supplement (20-40 mg/day), a dosage approximately equal to the maximal synthetic rate of this substance in the rats. Treatment of diabetic rats with this regime prevented the decrease in activity of granulation tissue prolyl hydroxylase (PRLase), an AA-dependent enzyme required for maintaining the normal properties of collagen. The decreased plasma AA concentration and granulation tissue PRLase activity in diabetes can also be normalized by the aldose reductase inhibitor tolrestat. We conclude that in diabetic animals there is a true deficiency of AA that may be responsible for some of the changes of collagen observed in diabetes. Treatment with AA or an aldose reductase inhibitor may prevent some of the diabetic complications with underlying collagen abnormalities.

Hepatoma, arterioportal shunting, and hyperkinetic portal hypertension: therapeutic embolization

Four patients with hepatocellular carcinoma, shunting of blood from the hepatic artery to the portal vein, and hyperkinetic portal hypertension were treated by transcatheter embolization of the hepatic artery. In three acutely bleeding patients variceal hemorrhage was controlled by the embolization. Following embolization hepatofugal portal venous flow became hepatopetal in all four patients. No serious complications were encountered. When hepatoma is complicated by arterioportal shunting and hyperkinetic portal hypertension, occlusion of the fistula by transcatheter embolotherapy can reduce the portal pressure.

Hemobilia following transhepatic biliary drainage: occlusion of an hepatoportal fistula by balloon tamponade

Acute clinically significant hemobilia occurred after percutaneous transhepatic biliary drainage. Investigations revealed a fistula between a peripheral bile duct and a branch of the portal vein. Hemostasis was obtained by balloon tamponade at the site of the fistula.