Reducing the late sodium current improves cardiac function during sodium pump inhibition by ouabain.

Inhibition by cardiac glycosides of Na(+), K(+)-ATPase reduces sodium efflux from myocytes and may lead to Na(+) and Ca(2+) overload and detrimental effects on mechanical function, energy metabolism, and electrical activity. We hypothesized that inhibition of sodium persistent inward current (late I(Na)) would reduce ouabain's effect to cause cellular Na(+) loading and its detrimental metabolic (decrease of ATP) and functional (arrhythmias, contracture) effects. Therefore, we determined effects of ouabain on concentrations of intracellular sodium (Na(+)(i)) and high-energy phosphates using (23)Na and (31)P NMR, the amplitude of late I(Na) using the whole-cell patch-clamp technique, and contractility and electrical activity of guinea pig isolated hearts, papillary muscles, and ventricular myocytes in the absence and presence of inhibitors of late I(Na). Ouabain (1-1.3 µM) increased Na(+)(i) and late I(Na) of guinea pig isolated hearts and myocytes by 3.7- and 4.2-fold, respectively. The late I(Na) inhibitors ranolazine and tetrodotoxin significantly reduced ouabain-stimulated increases in Na(+)(i) and late I(Na). Reductions of ATP and phosphocreatine contents and increased diastolic tension in ouabain-treated hearts were also markedly attenuated by ranolazine. Furthermore, the ouabain-induced increase of late I(Na) was also attenuated by the Ca(2+)-calmodulin-dependent kinase I inhibitors KN-93 [N-[2-[[[3-(4-chlorophenyl)-2-propenyl]methylamino]methyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulphonamide] and autocamide-2 related inhibitory peptide, but not by KN-92 [2-[N-(4'-methoxybenzenesulfonyl)]amino-N-(4'-chlorophenyl)-2-propenyl-N-methylbenzylamine phosphate]. We conclude that ouabain-induced Na(+) and Ca(2+) overload is ameliorated by the inhibition of late I(Na).

Preclinical pharmacokinetics and metabolism of MNP001, a piperidine analog of 3-carbamyl compounds.

MNP001 is a newly synthesized 3-carbamyl-4-methylpyrrole analog with dual pharmacophores simultaneously to inhibit phosphodiesterase type 4 (PDE4) and to antagonize L-type calcium channels. The physicochemical properties of MNP001, including solubility, pKa, Log P, plasma protein binding and plasma/blood partitioning, were determined to support the pharmacokinetic characterization. The preclinical pharmacokinetic parameters were determined in an in vivo rat model and the metabolic pathways of MNP001 were characterized by incubating the compound in vitro in rat or human microsomes/supersomes cocktails. MNP001 was found to have a low solubility in simulated intestinal fluid but a high solubility in simulated gastric fluid. MNP001 is a highly lipophilic compound with a Log P value greater than 4. MNP001 was highly bound to the plasma protein and had an uneven partition between red blood cells and plasma. MNP001 exhibited a rapid absorption, broad distribution, slow systemic clearance and a low but pharmacologically relevant oral bioavailability in rats. The low oral bioavailability was possibly caused by the low aqueous solubility of MNP001 in the gastrointestinal tract. However, 8 h after oral dosing, the mean plasma level of MNP001 was able to remain about 2-fold greater than the minimum effective concentration. The major metabolite of MNP001 was defined as a tetrahydropyridine product (MNP001-M4) of CYP3A4-mediated phase I oxidation. The possibility that the major metabolite MNP001-M4 may have a comparable antihypertensive efficacy to MNP001 needs to be studied.

TJ-41 Induces Apoptosis and Potentiates the Apoptotic Effects of 5-FU in Breast Cancer Cell Lines.

Recent studies suggest that TJ-41, a herbal drug, possesses chemotherapeutic effects. Accordingly, this study was undertaken to investigate the anticarcinogenic effects of TJ-41 on human breast cancer cells lines. TJ-41 inhibited the proliferation of human breast cancer cell lines dose dependently. Flow cytometric analysis showed that this decrease in DNA synthesis is to be associated with induction of apoptosis. In both cell lines, apoptosis was abolished by caspase-9 inhibitor Z-LEHD-fmk but was weakly inhibited by caspase-8 inhibitor Z-IETD-fmk, indicating that caspase-9 activation was involved in TJ-41 induced apoptosis. Additionally, TJ-41 stimulated phosphorylation of c-Jun NH2-terminal kinase (JNK) and pretreatment of breast cancer cells with JNK inhibitor SP600125 completely abolished TJ-41 induced apoptosis. Our data also demonstrate that combined treatment of TJ-41 and 5-FU significantly potentiates the apoptotic effects of 5-FU in both breast cancer cell lines. Taken together, these data suggest that TJ-41 might provide a novel chemotherapeutic treatment for breast cancer.

HPLC/MS/MS analysis of 3-carbamyl-4-methylpyrrole analog MNP001, a highly potent antihypertensive agent, in rat plasma.

Chemically synthesized 3-carbamyl-4-methylpyrroles were characterized as a group of antihypertensive agents with dual-targeting mechanism to simultaneously inhibit type 4 phosphodiesterase (PDE4) and L-type calcium channels. A 5-butyl analog of the pyrrole family, MNP001, was found to have high potency in reducing animal blood pressure and heart rate. A method for measuring MNP001 using high performance liquid chromatography combined with tandem mass spectrometry (HPLC/MS/MS) was developed. The calibration curve for MNP001 showed good linearity with the value of correlation coefficient greater than 0.987 over the range of 0.25-500 ng/mL. The results for inter-day and intra-day precision as well as accuracy were acceptable according to the criteria established by FDA. The lower limit of quantification was 0.25 ng/mL. This method was quick, sensitive and sufficient for in vivo pharmacokinetic and pharmacodynamic studies on this novel antihypertensive pyrrole compound.

[The comparison study on effects of water-soluble components of fine particulate matter on vasomotor functions in aortas from rats after exposure in different time].

OBJECTIVE: To compare the difference of vasomotor functions in aortas segments from Wistar rats between 1-hour and 6-hours after exposure of water-soluble components of fine particulate matter (PM2.5). METHODS: All 30 Wistar rats were assigned to five groups (n=6 for each group) at random: the blank control group, control group for 1-hour and 6-hours, exposure group for 1-hour and 6-hours. The rats were sacrificed 1-hour or 6-hours later and aorta ring segments were mounted on wire myographs. RESULTS: (1) There was no significant difference in vasomotor functions among three control groups (P>0.05). (2) 1-hour or 6-hours after exposure there was a decrease of contraction elicited by 60 mmol/L KCl in contrast to the control group (P<0.05), whereas no significant change between the exposure group for 1-hour and 6-hours (P>0.05). (3) On the level of 10(-5) or 10(-7) mol/L, 1-hour after exposure there was a decrease in endothelium-dependent acetylcholine (ACh) elicited relaxation precontracted by 10(-6) mol/L NE compared with the control group (P<0.01 or P<0.05), on the level from 10(-5) to 10(-7) mol/L there was a decrease compared with the exposure group for 6-hours (P<0.05), whereas no difference between the exposure group for 6-hours and the control group (P>0.05). On the level from 10(-5) to 10(-9) mol/L, 1-hour after exposure there was a decrease in endothelium-independent sodium nitroprusside (SNP) elicited relaxation precontracted by 10(-6) mol/L NE as compared with the control group (P<0.01 or P<0.05) and a decrease on the level of 10(-6) or 10(-9) mol/L compared with the exposure group for 6-hours (P<0.05), 6-hours after exposure a decrease was caused as compared with the control group on the level from 10(-5) to 10(-7) mol/L (P<0.01 or P<0.05). CONCLUSIONS: Inhibition of contraction and impairment of relaxation in aortas should be caused 1-hour after exposure to water-soluble components of PM2.5 in the air, which is weaken 6-hours after exposure.

High performance liquid chromatographic analysis of MS23 piperidine analog MSP001 in rat plasma.

MSP001 is a newly synthesized piperidine analog of the lead antihypertensive compound MS23 that dually targets cAMP-specific type 4 phosphodiesterase and L-type calcium channels. We validated an analytical protocol for MSP001 in rat plasma using high performance liquid chromatographic method. A C18 column and a phosphate/acetonitrile buffer were used to perform the chromatographic separation. UV detection was carried out at 307 nm, a wavelength at which an absorption peak was detected for this group of compounds. The calibration curve for MSP001 was linear in the range from 25 to 10,000 ng/ml. The limit of quantification (LOQ) was 25 ng/ml. The results demonstrate that this method has high linearity (R=0.99995), compound specificity, and acceptable precision/accuracy. The protocol is suitable for in vivo pharmacokinetic studies on the compound.

Validation of HPLC analysis method of a novel antihypertensive agent MS23 in rat plasma.

MS23 is a vasodilator with unique dual action pharmacological profile to inhibit type 4 PDE and antagonize L-type calcium channels. We validated an analytical protocol for MS23 in rat plasma using high performance liquid chromatography (HPLC). A C18 column and a phosphate/acetonitrite buffer were used for chromatographic separation. UV detection was performed at 307 nm. The calibration curve for MS23 was linear in the range from 50 to 10,000 ng/ml. The limit of quantification (LOQ) was 50 ng/ml. The results demonstrate that the method has linearity (R = 0.9989), specificity, and acceptable precision/accuracy. This method is simple, economic, and sufficient for in vivo pharmacokinetic studies on the compound.

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) enhances triggered afterdepolarizations in rat ventricular myocytes.

The effects of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on action potential and afterdepolarizations were studied in rat ventricular myocytes using nystatin-perforated whole-cell patch-clamp technique. TCDD treatment, in the concentration range of 1 to 100 nM, significantly prolonged action potential duration measured at 90% of repolarization (APD90). The triggered delayedafterdepolarizations (DADs) were observed in 6 out of 8 cells after exposure of TCDD (10 nM). In the presence of isoproterenol (ISO, 10 nM) or Bay K 8644 (1 microM), TCDD (10 nM) markedly augmented the amplitude and frequency of the arrhythmogenic DADs and triggered sustained spontaneous firings in ventricular myocytes. Voltage-clamp data indicated that TCDD (10 nM) exposure significantly enhanced the transient inward current (Iti). The triggered earlyafterdepolarizations (EADs) were evoked only in cells simultaneously exposed to TCDD (10 nM) and ISO (or Bay K 8644). Further study indicated that TCDD treatment increased L-type Ca2+ current. These results indicate that activation of TCDD signaling pathway can prolong action potential duration and cause abnormal triggered afterdepolarizations. These effects may lead to clinically relevant ventricular arrhythmia especially when susceptible individuals are under elevated sympathetic stress or suffering from other myocardiopathies coincided with Ca2+-overload.

Evaluation of PDE4 inhibition for COPD.

Targeting type 4 phosphodiesterase (PDE4) for treatment of COPD has multilevel benefits to patients by reducing inflammation, relieving bronchoconstriction, and improving pulmonary circulation. The isoenzyme-specific narrow spectrum PDE4 inhibitors such as cilomilast and roflumilast may have limited clinical efficacy in managing severe and very severe COPD. Development of dual therapy by combining PDE4 inhibition with Ca2+ channel antagonism may introduce an effective novel armory for physicians to manage patients with severe COPD.

Novel approaches to using PDE4 inhibitors for antihypertensive therapy.

Phosphodiesterase (PDE)4 inhibitors are effective vasodilators. In addition to the treatment of asthma and other inflammatory diseases, such as chronic obstructive pulmonary disease, wide-spectrum PDE4 inhibitors may also be developed for use in antihypertensive therapy, especially in patients with impaired renal function and elevated pulmonary arterial pressure. Rational approaches to overcoming the intrinsic emetogenic response associated with PDE4 inhibition are discussed, and a dual-action drug development that incorporates L-type Ca2+ channel antagonism and selective PDE4 inhibition is proposed. The potential for research and development of such a dual-action agent should eventually provide healthcare professionals with a new category of therapeutic options with which to attempt to combat hypertension.