Taurine blunts doxorubicin cardiotoxicity: chronic and acute effects

Funding Acknowledgements Type of funding sources: None. Aim. To study the functional statement of the isolated heart inherent to doxorubicin cardiotoxicity under the chronic and acute action of taurine. Material and methods. Doxorubicin (Dx) cardiotoxicity manifested by heart failure development was reproduced classically by anthracycline i/p administration in rats in cumulative dose of 16 mg/kg (4 mg/kg four times during 2 weeks) – Dx series. Series with chronic action of taurine (Tr) included rats receiving this aminoacid daily per os during Dx administration (100 mg/kg) – Dx + Tr series. Rats of both series were sacrificed by euthanasia and the isolated heart was perfused by Krebs solution according to Langendorff (isovolumic heart) and Neely-Rovetto (working heart) methods in conditions of diverse hemodynamic and neuroendocrine efforts applying. Acute action of taurine was studied during its infusion in the perfusate of isolated hearts in final concentration of 40 µM. The hearts of intact rats constituted the control series. Results. Chronic action of taurine has identified certain important functional benefits, the most important being underlined beneath. The first, taurine reversed the negative inotropic effect of isolated heart on endothelin-1 (ET-1) action (10-7 M), detected in Dx series and manifested by both systolic pressure of left ventricle (LV) and cardiac output fall by about 9,1%. Taurine assured increase of these indices during ET-1 stimulation. The second, Tr notably improved both isovolumic relaxation and contraction of myocardium exhibited by significant enhancement of Veragut index (118,6 ± 9,6 vs 94,8 ± 6,5 1/sec), +dP/dPmax (8389 ± 445 vs 7216 ± 363 mm Hg/sec) and -dP/dTmax (7526 ± 378 vs 5684 ± 322 mm Hg/sec) during efforts with volume and resistance. The third, Tr significantly decreased LV end diastolic pressure (LVSDP) when coronary pressure of isovolumic heart elevated by 50% (from 80 up to 120 cm H20 column): 16,2 ± 1,2 vs 18,8 ± 1,4 mm Hg. Acute Tr action manifested by: (i) significant LVSDP diminution during 30 min of ischemia (52,4 ± 3,1 vs 63,7 ± 4,4 mm Hg) and on 45th min of reperfusion (18,3 ± 1,3 vs 22,8 ± 1,4 mm Hg), (ii) increased time of LV extrasystole appearance when the glucose content of Krebs solution was reduced by 50% (28,6 ± 2,8 vs 22,5 ± 2,4 min), and (iii) increased time of LV tachyarrhythmia appearance when the potassium content of Krebs solution raised up to 6,5 meq/L (9,2 ± 0,5 vs 6,9 ± 0,3 min). Conclusion. Taurine, a natural calcium modulator of the heart, notably improves functional reserves of the myocardium exposed to cardiotoxic action of Dx, and could be seen as a relevant remedy of primary and secondary prophylaxis of Dx induced heart failure in oncologic patients.

A234 EVALUATING THE EFFECT OF STOOL SUPERNATANTS FROM IBS PATIENTS AND HEALTHY CONTROLS ON THE EXCITABILITY OF DRG NEURONS

Background Abdominal pain is commonly described in chronic disorders such as irritable bowel syndrome (IBS), but the underlying mechanisms are currently unclear. The stool metabolomic and microbiota profiles of IBS and healthy patients have shown distinct differences. Additionally, IBS stool supernatants have previously been demonstrated to induce hypersensitivity of nociceptive nerves in the ex vivo mouse colon, suggesting that mediators in the stool can sensitize nociceptors. However, the effects of healthy control (HC) or IBS patient stool supernatants on the excitability of DRG neurons have not been clarified. Aims To evaluate the effect of HC and IBS supernatant on DRG neurons. Methods HC (n=8 patients) or IBS (n=10 patients) stool was collected, dissolved and homogenized with bicarbonate-buffered Krebs solution at 37°C in a 1/10 dilution. DRG neurons from C57BL/6 mice were dissociated and incubated overnight with HC or IBS supernatant in a Krebs dissolution. Changes in DRG neuronal excitability were recorded using perforated patch-clamp techniques to measure the rheobase (amount of current needed to elicit an action potential). The effect of the IBS and HC stool supernatants on the resting membrane potential (RMP) was also recorded. Results Overnight incubations with supernatant of HC stool diluted in Krebs solution (n=28 neurons) did not significantly decrease the rheobase compared to control neurons (n=22) (62.7 ± 3.9 pA vs 64.2 ± 2.7 pA). In a parallel experiment, we evaluated the effect of IBS stool supernatants diluted in Krebs (n=52 neurons) and found that they significantly decreased the rheobase compared to the supernatant of HC diluted in Krebs and control neurons (52.3 ± 2.3; p<0.05). The data were analyzed with a one-way ANOVA and Tukey’s test. Incubations with IBS supernatant decreased the RMP compared to HC supernatant (-42.6 ± 0.6 mV vs. -46.0 ± 0.9 mV; p<0.01), which was calculated with an unpaired t-test. Conclusions These findings suggest that mediators in IBS stool increase the excitability of DRG neurons compared to HC stool supernatant, and thus may contribute to pain signaling in IBS patients. Funding Agencies CIHR

Endothelium-Independent Vasodilatory Effects of Isodillapiolglycol Isolated from Ostericum citriodorum

Ostericum citriodorum is a plant with a native range in China used in herbal medicine for treating angina pectoris. In this study, we investigated the vasodilatory effects of isodillapiolglycol (IDG), which is one of the main ingredients isolated from O. citriodorum ethyl acetate extract, in Sprague–Dawley rat aortic rings, and measured intracellular Ca2+ ([Ca2+]in) using a molecular fluo-3/AM probe. The results show that IDG dose-dependently relaxed endothelium-intact or -denuded aortic rings pre-contracted with noradrenaline (NE) or potassium chloride (KCl), and inhibited CaCl2-induced contraction in high K+ depolarized aortic rings. Tetraethyl ammonium chloride (a Ca2+-activated K+ channel blocker) or verapamil (an L-type Ca2+ channel blocker) significantly reduced the relaxation of IDG in aortic rings pre-contracted with NE. In vascular smooth muscle cells, IDG inhibited the increase in [Ca2+]in stimulated by KCl in Krebs solution; likewise, IDG also attenuated the increase in [Ca2+]in induced by NE or subsequent supplementation of CaCl2. These findings demonstrate that IDG relaxes aortic rings in an endothelium-independent manner by reducing [Ca2+]in, likely through inhibition of the receptor-gated Ca2+ channel and the voltage-dependent Ca2+ channel, and through opening of the Ca2+-activated K+ channel.

ROLE OF NA+, K+, 2CL- - COTRANSPORT IN REGULATION OF THE PULMONARY ARTERY TONE

Purpose. We studied the role of Na+, K+, 2Cl- cotransport (NKCC) in contractile activity of pulmonary artery seg- ments with intact endothelium induced by incubation in nonisosmotic solutions. Materials and methods. The influence of nonisosmotic solutions and blocker of NKCC on vascular segments mechanical tension was studied in isometric regime with organ bath technique performed with the 4-channel Myobath II and software complex LAB-TRAX-4/16 (Germany). Hyperosmotic shrinkage was induced by adding 50-300 mM su- crose to the Krebs solution, the hypoosmotic environment was created by reducing the concentration of NaCl from 70 mM to 40 mM. Bumetanide was used as an NKCC blocker. The amplitude of the contractile responses was evaluated as a percentage of the control contraction in highpotassium solution. Results. The addition of 50-300 mM sucrose to the Krebs incubation solution caused a development of dose- dependent of sustained contractile responses. The amplitude of hyperosmotic striction increased with inhibition of NKCC. Incubation of segments in hypoosmotic solution caused the development of transient contractile responses, the amplitude of which decreased in the presence of NKCC inhibitor. Conclusion. Iincubation of pulmonary artery vascular segments in hyper- and hyposmotic solutions induces con- tractile responses, the amplitude of which depends on the NKCC activity.

Effects of the New Aldose Reductase Inhibitor Benzofuroxane Derivative BF-5m on High Glucose Induced Prolongation of Cardiac QT Interval and Increase of Coronary Perfusion Pressure

This study investigated the effects of the new aldose reductase inhibitor benzofuroxane derivative 5(6)-(benzo[d]thiazol-2-ylmethoxy)benzofuroxane (BF-5m) on the prolongation of cardiac QT interval and increase of coronary perfusion pressure (CPP) in isolated, high glucose (33.3 mM D-glucose) perfused rat hearts. BF-5m was dissolved in the Krebs solution at a final concentration of 0.01 μM, 0.05 μM, and 0.1 μM. 33.3 mM D-glucose caused a prolongation of the QT interval and increase of CPP up to values of 190 ± 12 ms and 110 ± 8 mmHg with respect to the values of hearts perfused with standard Krebs solution (11.1 mM D-glucose). The QT prolongation was reduced by 10%, 32%, and 41%, respectively, for the concentration of BF-5m 0.01 μM, 0.05 μM, and 0.1 μM. Similarly, the CPP was reduced by 20% for BF-5m 0.05 μM and by 32% for BF-5m 0.1 μM. BF-5m also increased the expression levels of sirtuin 1, MnSOD, eNOS, and FOXO-1, into the heart. The beneficial actions of BF-5m were partly abolished by the pretreatment of the rats with the inhibitor of the sirtuin 1 activity EX527 (10 mg/kg/day/7 days i.p.) prior to perfusion of the hearts with high glucose + BF-5m (0.1 μM). Therefore, BF-5m supplies cardioprotection from the high glucose induced QT prolongation and increase of CPP.

Abstract 241: Endothelial Function is Preserved with Endoscopic Vein Harvest for Lower Extremity Bypass

Objective: Endoscopic vein harvest for lower extremity arterial bypass technique has been questioned due to concern for endothelial damage during procurement. We sought to compare NO mediated endothelial dependent relaxation (EDR) in vein segments harvested with open surgical (OH) versus endoscopic (EH) techniques. Methods: Saphenous vein segments were harvested for lower extremity bypass. 3-4mm vein rings were mounted on force transducers. Segments were mounted in 37° oxygenated Krebs solution and maximally contracted using KCl. NE was used to achieve submaximal contraction. EDR was determined using increasing concentrations of bradykinin (BDK). Endothelial independent relaxation was confirmed using sodium nitroprusside. Two-way ANOVA was used to analyze differences between harvest techniques across BDK concentration. Student t-test was used to examine nitrite levels in each cohort. Results: Vein segments harvested from patients (n=13) led to 28 rings (11 rings; 5 patients EH v. 17;8 OH). Both cohorts achieved moderate relaxation to maximal BDK concentration, [10 -6 M]; (49.5% EH vs. 40.55%, OH, P = .270). Analysis by two way ANOVA for mean % relaxation for BDK concentration [10 -11 - 10 -6 M] showed improved EDR in EH samples compared to OH (P =.029). Mean nitrite tissue bath concentration measurements post-BDK were 279 nM (EH) v. 194 nM (OH) (P = .264). Histology and IHC confirmed intact endothelium by morphometric analysis and CD31 staining. Conclusion: Endothelial function is preserved when utilizing endoscopic harvesting techniques. The advantages of minimally invasive vein procurement for lower extremity bypass can be obtained without concern for damaging venous endothelium.

Effects of Ursolic Acid on Contractile Activity of Gastric Smooth Muscles

Ursolic acid (UA) in concentrations of 1×10−7 mol/L - 5×10−5 mol/L induced relaxation in gastric smooth muscle (SM) tissues, in a concentration-dependent manner. The relaxation did not change membrane potential and slow wave contraction patterns. A significant decrease in amplitude and frequency of spike-potentials was observed. UA-induced reactivity was removed when SM preparations were treated with nifedipine (1×10−6 mol/L). Ca2+- induced contractions of the depolarized SM preparations (42 mmol/L K+; Ca2+- free Krebs solution) were substantially reduced in the presence of UA. It was determined that, in certain concentrations, UA influenced L – type Ca2+ channels, and reduced the Ca2+ influx.

Butylidenephthalide Blocks Potassium Channels and Enhances Basal Tension in Isolated Guinea-Pig Trachea

Butylidenephthalide (Bdph, 30~300 μM), a constituent ofLigusticum chuanxiongHort., significantly enhanced tension in isolated guinea-pig trachea. In this study, we investigate the mechanism(s) of Bdph-induced contraction in the tissue. Isolated trachea was bathed in 5 mL of Krebs solution containing indomethacin (3 μM), and its tension changes were isometrically recorded. Cromakalim (3 μM), an ATP-dependent K+channel opener, significantly antagonized the Bdph-induced enhancement of baseline tension. Bdph (300 μM) also significantly antagonized cromakalim-induced relaxation. Bdph (300 μM) did not significantly influence the antagonistic effects of glibenclamide (GBC, 1 μM) and tetraethylammonium (TEA, 8 mM) against the cromakalim-induced relaxation. However, Bdph (300 μM) and 4-aminopiridine (4-AP, 5 mM), a blocker of Kv1 family of K+channels, in combination significantly rightward shifted the log concentration-relaxation curve of cromakalim. The antagonistic effect of the combination almost equals the sum of the individual effects of Bdph and 4-AP, suggesting that the antagonistic mechanism of Bdph may be similar to that of 4-AP. All calcium channel blockers influenced neither the baseline tension nor antagonistic effect of Bdph against cromakalim. In conclusion, Bdph may be similar to 4-AP, a blocker of Kv1 family of K+channels, to enhance the baseline tension of guinea-pig trachea.

Simo Decoction Stimulates Contractions of Antral Longitudinal Smooth Muscle via Multitudinous Mechanisms

The aim of the study was to investigate Simo decoction–induced contractions of antral smooth muscles of rats and its mechanisms. The contractile responses of longitudinal strips to consecutive concentrations of Simo decoction were characterized by atropine, gallamine, 4-diphenylacetoxy-N-methylpiperidine methiodide, and adrenaline, hexamethonium, L-arginine, and nifedipine and compared with Krebs solution (control) and acetylcholine-induced contractions. Simo decoction dose-dependently increased contractions of antral strips ( P = .000 vs control); its maximal effect was higher than acetylcholine (10−3 mol L−1; P < .05); Simo decoction–induced contractions were completely inhibited by atropine, 4-diphenylacetoxy-N-methylpiperidine methiodide, or 4-diphenylacetoxy-N-methylpiperidine methiodide + gallamine ( P = .000 for all) but were partly suppressed by gallamine, adrenaline, hexamethonium, L-arginine, and nifedipine ( P = .000 for all). Simo decoction promotes the contractions of antral strips mainly through activation of muscarinic M3 receptor, while partly through activation of M2 receptor, Ca2+ channel, nicotinic receptor, and inhibition of adrenergic receptor as well as release of nitric oxide.