Treatment of Cardiovascular Dysfunction with PDE3-Inhibitors in Moderate and Severe Hypothermia-Effects on Cellular Elimination of Cyclic Adenosine Monophosphate and Cyclic Guanosine Monophosphate.

Introduction: Rewarming from accidental hypothermia is often complicated by hypothermia-induced cardiovascular dysfunction, which could lead to shock. Current guidelines do not recommend any pharmacological treatment at core temperatures below 30°C, due to lack of knowledge. However, previous in vivo studies have shown promising results when using phosphodiesterase 3 (PDE3) inhibitors, which possess the combined effects of supporting cardiac function and alleviating the peripheral vascular resistance through changes in cyclic nucleotide levels. This study therefore aims to investigate whether PDE3 inhibitors milrinone, amrinone, and levosimendan are able to modulate cyclic nucleotide regulation in hypothermic settings. Materials and methods: The effect of PDE3 inhibitors were studied by using recombinant phosphodiesterase enzymes and inverted erythrocyte membranes at six different temperatures-37°C, 34°C, 32°C, 28°C, 24°C, and 20°C- in order to evaluate the degree of enzymatic degradation, as well as measuring cellular efflux of both cAMP and cGMP. The resulting dose-response curves at every temperature were used to calculate IC50 and Ki values. Results: Milrinone IC50 and Ki values for cGMP efflux were significantly lower at 24°C (IC50: 8.62 ± 2.69 µM) and 20°C (IC50: 7.35 ± 3.51 µM), compared to 37°C (IC50: 22.84 ± 1.52 µM). There were no significant changes in IC50 and Ki values for enzymatic breakdown of cAMP and cGMP. Conclusion: Milrinone, amrinone and levosimendan, were all able to suppress enzymatic degradation and inhibit extrusion of cGMP and cAMP below 30°C. Our results show that these drugs have preserved effect on their target molecules during hypothermia, indicating that they could provide an important treatment option for hypothermia-induced cardiac dysfunction.

Treatment of Cardiovascular Dysfunction With PDE5-Inhibitors - Temperature Dependent Effects on Transport and Metabolism of cAMP and cGMP.

INTRODUCTION: Cardiovascular dysfunction is a potentially lethal complication of hypothermia. Due to a knowledge gap, pharmacological interventions are not recommended at core temperatures below 30°C. Yet, further cooling is induced in surgical procedures and survival of accidental hypothermia is reported after rewarming from below 15°C, advocating a need for evidence-based treatment guidelines. In vivo studies have proposed vasodilation and afterload reduction through arteriole smooth muscle cGMP-elevation as a favorable strategy to prevent cardiovascular dysfunction in hypothermia. Further development of treatment guidelines demand information about temperature-dependent changes in pharmacological effects of clinically relevant vasodilators. MATERIALS AND METHODS: Human phosphodiesterase-enzymes and inverted erythrocytes were utilized to evaluate how vasodilators sildenafil and vardenafil affected cellular efflux and enzymatic breakdown of cAMP and cGMP, at 37°C, 34°C, 32°C, 28°C, 24°C, and 20°C. The ability of both drugs to reach their cytosolic site of action was assessed at the same temperatures. IC50- and K i -values were calculated from dose-response curves at all temperatures, to evaluate temperature-dependent effects of both drugs. RESULTS: Both drugs were able to reach the intracellular space at all hypothermic temperatures, with no reduction compared to normothermia. Sildenafil IC50 and K i -values increased during hypothermia for enzymatic breakdown of both cAMP (IC50: 122 ± 18.9 µM at 37°C vs. 269 ± 14.7 µM at 20°C, p < 0.05) and cGMP (IC50: 0.009 ± 0.000 µM at 37°C vs. 0.024 ± 0.004 µM at 32°C, p < 0.05), while no significant changes were detected for vardenafil. Neither of the drugs showed significant hypothermia-induced changes in IC50 and K i- values for inhibition of cellular cAMP and cGMP efflux. CONCLUSION: Sildenafil and particularly vardenafil were ableto inhibit elimination of cGMP down to 20°C. As the cellular effects of these drugs can cause afterload reduction, they show potential in treating cardiovascular dysfunction during hypothermia. As in normothermia, both drugs showed higher selectivity for inhibition of cGMP-elimination than cAMP-elimination at low core temperatures, indicating that risk for cardiotoxic side effects is not increased by hypothermia.

Identification and experimental confirmation of novel cGMP efflux inhibitors by virtual ligand screening of vardenafil-analogues.

BACKGROUND: Clinical studies have reported overexpression of PDE5 and elevation of intracellular cyclic GMP in various types of cancer cells. ABCC5 transports cGMP out of the cells with high affinity. PDE5 inhibitors prevent both cellular metabolism and cGMP efflux by inhibiting ABCC5 as well as PDE5. Increasing intracellular cGMP is hypothesized to promote apoptosis and growth restriction in tumor cells and also has potential for clinical use in treatment of cardiovascular disease and erectile dysfunction. Vardenafil is a potent inhibitor of both PDE5 and ABCC5-mediated cGMP cellular efflux. Nineteen novel vardenafil analogs that have been predicted as potent inhibitors by VLS were chosen for tests of their ability to inhibit ATP- dependent transport of cGMP by measuring the accumulation of cyclic GMP in inside-out vesicles. AIM: In this study, we investigated the ability of nineteen new compounds to inhibit ABCC5- mediated cGMP transport. We also determined the Ki values of the six most potent compounds. METHODS: Preparation of human erythrocyte inside out vesicles and transport assay. RESULTS: Ki values for six of nineteen compounds that showed more than 50 % inhibition of cGMP transport in the screening test were determined and ranged from 1.1 to 23.1 µM. One compound was significantly more potent than the positive control, sildenafil. CONCLUSION: Our findings show that computational screening correctly identified vardenafil-analogues that potently inhibit cGMP efflux-pumps from cytosol and could have substantial clinical potential in treatment of patients with diverse disorders.

A sensitive method for the analysis of glutathione in porcine hepatocytes.

BACKGROUND: Reduced glutathione (γ-glutamylcysteinylglycine), GSH, is essential when protecting cells from oxidative stress and also an indicator of disease risk. Reported concentrations of GSH and its oxidized form, glutathione disulfide (GSSG), varies considerably, primarily due to the instability of GSH and various analytical methods. METHODS: We designed a sensitive method to analyze GSH and GSSG in porcine hepatocytes using liquid chromatography-tandem mass spectrometry (LC-MS/MS) after stabilization with N-ethylmaleimide (NEM). This method includes stable isotope labeled internal standards and simple synthesis of labeled GSSG which commercial sources rarely offer. GSH and GSSG were analyzed in porcine liver biopsies giving a reference interval based on a large number of samples (26 pigs; 3 parallels). RESULTS: The LC-MS/MS results revealed excellent linearity for both GSH and GSSG, with interday coefficient of variation (%CV) for GSH-NEM and GSSG <10 %. Accuracy for recovery tests was between 95.6% and 106.7% (n = 3) for GSH and between 92.3% and 107.7% (n = 3) for GSSG. The limits of quantification were 0.1 µM for GSH-NEM and 0.08 µM for GSSG. The mean concentration of GSH was 3.5 (95% CI = 1.5-8.1) mmol/liter and of GSSG 0.0023 (95% CI = 0.0003-0.019) mmol/liter. CONCLUSION: For the first time GSH and GSSG are analyzed in porcine hepatocytes by LC-MS/MS yielding a reference level of GSH and GSSG. The method is reproducible in any laboratory with LC-MS/MS service and will probably be applicable in all soft tissues and cell suspensions, essentially with no modification.

[ABC transporters' impact on effect and metabolism of drugs]. / ABC-transportørenes betydning for effekt og omsetning av legemidler.

BACKGROUND: Drugs must be transported to reach the site of action and to be removed from the body. Several proteins within the large family of ABC transporters (ATP-binding domain), are important for pharmacokinetics. In this review article we present, from a clinical point of view, ABC transporters that are known to be important for basic and clinical pharmacology. MATERIAL AND METHOD: This overview is based on literature identified through a non-systematic search in PubMed and on results from our own work. RESULTS: Members of the subfamilies ABCB and ABCC, are most known for contributing to multidrug resistance towards cytostatic and antibiotic drugs. ABCB1 (P-glycoprotein) is shown to form a functional intestinal barrier and the blood-brain barrier by pumping out potentially toxic substances. More recent research indicates that ABC transporters play an important role in absorption, distribution and elimination of many drugs and that their function is dependent on the individual genotype. INTERPRETATION: Individualized therapy may become feasible when more knowledge about ABC transporters is available.