Effect of DA-8031, a novel oral compound for premature ejaculation, on male rat sexual behavior.

OBJECTIVES: DA-8031 is a potent and selective serotonin transporter inhibitor developed for the treatment of premature ejaculation. The aim of the present study was to investigate the effects of DA-8031 on male sexual behavior in a rat model. METHODS: Sexual behavior was examined after an acute oral administration of 10, 30 or 100 mg/kg of DA-8031 in copulation studies with female rats. Pharmacokinetic parameters were calculated after oral administration of DA-8031 at a dose level of 30 mg/kg. RESULTS: DA-8031 treatment produced a dose-dependent increase in ejaculation latency time and showed statistical significance at 30 and 100 mg/kg dosage levels compared with the vehicle (P < 0.05). In addition, DA-8031 treatment reduced the mean number of ejaculations in a dose-dependent manner. No changes in post-ejaculatory interval, numbers of mounts, intromissions or ejaculations were observed at any dose. In pharmacokinetic study, the blood concentration of DA-8031 peaked at 0.38 ± 0.14 h after oral administration, and then rapidly declined with a half-life of 1.79 ± 0.32 h. CONCLUSIONS: Treatment with DA-8031 delays the ejaculation latency time without affecting the initiation of mounting behavior or post-ejaculatory interval in rats. Furthermore, DA-8031 is rapidly absorbed and eliminated after oral administration in rats. These preclinical findings provide a clue for the clinical testing of DA-8031 as an "on-demand" agent for premature ejaculation.

Ejaculatory responses are inhibited by a new chemical entity, DA-8031, in preclinical rodent models of ejaculation.

OBJECTIVE: To investigate the efficacy of DA-8031, a novel compound for the treatment of premature ejaculation (PE), we performed in vivo pharmacological studies using 2 preclinical animal models, electrical stimulation of sensory branch of pudendal nerve (SBPdn) and para-chloroamphetamine (PCA)-induced ejaculation model. METHODS: First of all, in electrical stimulation of an SBPdn model, an SBPdn in the pelvic canal of the spinal cord transected from rats was identified. Then an electromyogram (EMG) of the bulbospongiosus (BS) muscle was recorded during electrical stimulation of SBPdn after single intravenous (IV) dosing of DA-8031 and its reference drug, dapoxetine. In the second model, both seminal vesicle pressure (SVP) and the EMG profile of the BS muscle were recorded in PCA-induced ejaculation animals after treated with the same dosing regimen. RESULTS: Area under the curve (AUC) of the BS muscle by EMG wave exhibited a significant reduction in the DA-8031 and dapoxetine 3 mg/kg treated groups, and maximum amplitudes were also significantly decreased in DA-8031 1, 3 mg/kg and dapoxetine 3 mg/kg dose level in the SBPdN stimulation model. Consistent with these findings, in a PCA-induced ejaculation model, SVP increase was significantly inhibited from DA-8031 0.3 mg/kg dose level, and AUC of BS muscle EMG significantly decreased in the DA-8031 1, 3 mg/kg groups. CONCLUSION: The present study implied that DA-8031 contributed to an effective co-coordinated inhibition of the expulsion phase of ejaculation by modulating BS muscle activity and the emission phase through blocking SVP rise. From these findings, DA-8031 is further expected to have clinical efficacy in human studies.

Dipeptidyl peptidase-4 inhibitor with ß-amino amide scaffold: synthesis, SAR and biological evaluation.

Inhibitors of dipeptidyl peptidase-4 (DPP4) have been shown to be effective treatments for type 2 diabetes. Several series of ß-amino amide containing piperazine derivatives have been prepared and evaluated as a inhibitor of DPP4. Finally compound 5m was selected for further evaluation.

Protective effects of acetyl-L-carnitine on neurodegenarative changes in chronic cerebral ischemia models and learning-memory impairment in aged rats.

This study investigated the effects of acetyl-L-carnitine (ALC) in secondarily-induced cerebral chronic ischemia models using rats with permanent ligation of bilateral common carotid arteries (BCCL) and spontaneously hypertensive rats (SHR). Additionally, we used normal aged rats as a primary dementia model. Chronic ALC administration at 100 mg/kg (p.o.) for 4 weeks significantly attenuated neurodegenerative changes. In groups receiving 50 mg/kg or 100 mg/kg, ALC inhibited the active astrocyte increase in cerebral tissues of both BCCL and SHR models. In BCCL rats, ALC administration (50 mg/kg or 100 mg/kg, p.o.) resulted in significant promotion of glutathione levels in brain tissues. We also confirmed behavioral improvement after ALC treatment (100 mg/kg for 8 weeks, p.o.) on learning-memory function using aged rats (18 months old) in a passive avoidance task and preservation of CA1 pyramidal neurons was coincided on histopathological observation. In conclusion, chronic ALC administration may ameliorate cerebral ischemia progress after a cerebrovascular disorder as well as spontaneous ageing-related cerebral dysfunction via hippocampal protection.

DA-1229, a novel and potent DPP4 inhibitor, improves insulin resistance and delays the onset of diabetes.

AIM: To characterize the pharmacodynamic profile of DA-1229, a novel dipeptidyl peptidase (DPP) 4 inhibitor. MAIN METHODS: Enzyme inhibition assays against DPP4, DPP8 and DPP9. Antidiabetic effects of DA-1229 in HF-DIO mice and young db/db mice. KEY FINDINGS: DA-1229 was shown to potently inhibit the DPP4 enzyme in human and murine soluble forms and the human membrane-bound form with IC(50) values of 0.98, 3.59 and 1.26 nM, respectively. As a reversible and competitive inhibitor, DA-1229 was more selective to human DPP4 (6000-fold) than to human DPP8 and DPP9. DA-1229 (0.1-3mg/kg) dose-dependently inhibited plasma DPP4 activity, leading to increased levels of plasma GLP-1 and insulin, and thereby lowering blood glucose levels in mice. In high fat diet-fed (HF) mice, a single oral dose of 100mg/kg of DA-1229 reduced plasma DPP4 activity by over 80% during a 24h period. Long-term treatment with DA-1229 for 8 weeks revealed significant improvements in glucose intolerance and insulin resistance, accompanied by significant body weight reduction. However, it remains unclear whether there is a direct causal relationship between DPP4 inhibition and body weight reduction. In young db/db mice, the DA-1229 treatment significantly reduced blood glucose excursions for the first 2 weeks, resulting in significantly lower levels of HbA1c at the end of the study. Furthermore, the pancreatic insulin content of the treatment group was significantly higher than that of the db/db control. SIGNIFICANCE: DA-1229 as a novel and selective DPP4 inhibitor improves the insulin sensitivity in HF mice and delays the onset of diabetes in young db/db mice.

DA6034 promotes gastric epithelial cell migration and wound-healing through the mTOR pathway.

BACKGROUND AND AIM: 7-Carboxymethyloxy-3',4',5-trimethoxy flavone (DA6034), a synthetic derivative of eupatilin, has a protective effect on gastric mucosa against various ulcerogens, and is currently in the phase III clinical trial in the treatment of peptic ulcer disease. Cell migration and/or growth plays a role in the repair process of gastric ulcer, so this study investigated the effect of DA6034 on the movement and proliferation of gastric epithelial cells and its associated signaling pathway. METHODS: The migration of AGS or SNU484 human gastric epithelial cells was shown by scratch-induced wound healing and transwell assays, and the proliferation of the cells was assessed by FACS and proliferation assays. RESULTS: Treatment of DA6034 promoted the migration of gastric epithelial cells in a concentration-dependent manner. DA6034 treatment facilitated the phosphorylation of mTOR that led to an increase in the activity of S6K1, indicating its ability to activate mTOR and S6K1. Rapamycin aborted the wound-healing effect of DA6034, which supported the role of mTOR activation in the wound-healing process. In addition, DA6034 treatment increased PI3K-dependent Akt phosphorylation, which was necessary for the enhancement of cell migration. DA6034, however, did not stimulate the proliferation of gastric epithelial cells, being consistent with no activation of ERK1/2 by the agent. CONCLUSIONS: DA6034 has the ability to heal scratch wounds, which may result from an increase in gastric epithelial cell migration as mediated by PI3K-Akt-dependent activation of mTOR and S6K1. Our finding may be of help in understanding the molecular basis of the anti-ulcer effect of DA6034.

Discovery of DA-1229: a potent, long acting dipeptidyl peptidase-4 inhibitor for the treatment of type 2 diabetes.

A series of ß-amino amide containing substituted piperazine-2-one derivatives was synthesized and evaluated as inhibitors of dipeptidyl pepdidase-4 (DPP-4) for the treatment of type 2 diabetes. As results of intensive SAR study of the series, (R)-4-[(R)-3-amino-4-(2,4,5-trifluorophenyl)-butanoyl]-3-(t-butoxymethyl)-piperazin-2-one (DA-1229) displayed potent DPP-4 inhibition pattern in several animal models, was selected for clinical development.

Chronic administration of udenafil, a selective phosphodiesterase type 5 inhibitor, promotes erectile function recovery in an animal model of bilateral cavernous nerve crush injury.

INTRODUCTION: Preservation of the cavernous nerves (CNs) during radical prostatectomy is crucial for the patient's erectile function. Despite advances in operative technique, the majority of men report compromised erectile function postprostatectomy or complete loss of potency due to CN trauma even with nerve-sparing modifications. AIM: This study was designed to investigate whether repeated dosing of udenafil, a phosphodiesterase type 5 inhibitor, helps to improve erectile function after CN injury. METHODS: Using the CN crush injury model, 8-week-old male Sprague Dawley rats were divided into the following groups; sham-operated group, bilateral CN crush injury exposed to either no udenafil (vehicle) or udenafil (5, 20 mg/kg) daily for two different durations (4 and 8 weeks, p.o.). MAIN OUTCOME MEASURES: At both time points, CN electrical stimulation was used to assess erectile function by measuring the intracavernous pressure. The expressions of hypoxia-inducible factor 1-alpha (HIF-1α), transforming growth factor-beta (TGF-ß1), nerve growth factor (NGF), endothelin B receptor (ET(B) ), endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and sonic hedgehog homolog (SHH) in penile tissue were examined. Immunohistochemical antibody staining was performed for NGF, eNOS, nNOS, CD31, and alpha-smooth muscle actin (α-SMA). Additionally, terminal deoxynucleotidyl transferase-mediated nick-end labeling assay was performed to quantify apoptosis and the tissue slides were stained for Masson's trichrome to assess the smooth muscle/collagen ratio. RESULTS: Udenafil improved erectile function in a dose- and time-dependent manner with the maximum erectile function recovery achieved by 20 mg/kg udenafil at an 8-week time point. CN injury increased the expression of HIF-1α, TGF-ß1, NGF, and ET(B) , however, decreased the expression of eNOS, nNOS, and SHH. Udenafil significantly suppressed these alterations. The results from the histological analyses show that udenafil markedly reduces apoptosis induced by CN injury and augments the smooth muscle/collagen ratio. CONCLUSIONS: CN injury induces significantly impaired erectile function and altered gene/protein expression. Chronic administration of udenafil preserves erectile function and has a beneficial role against the pathophysiological consequences of CN injury.

Candidate molecule for premature ejaculation, DA-8031: in vivo and in vitro characterization of DA-8031.

OBJECTIVES: To evaluate the efficacy of DA-8031 against premature ejaculation, we performed in vitro and in vivo pharmacologic studies. METHODS: We used a monoamine transporter binding affinity assay, receptor binding affinity assay, monoamine reuptake inhibition assay, and serotonin uptake inhibition assay in platelets and chemically induced ejaculation models in rats. RESULTS: The present study reports on the pharmacologic profile of the putative antipremature ejaculation drug, DA-8031. DA-8031 exhibits high affinity and selectivity to the serotonin transporter (Ki value 1.94 nM for 5-hydroxytryptamine transporter, 22 020 nM for norepinephrine transporter, and 77 679 nM for dopamine transporter) and potency to inhibit serotonin reuptake into the rat brain synaptosome in vitro (half maximal inhibitory concentration 6.52 nM for 5-hydroxytryptamine, 30.2 µM for norepinephrine, and 136.9 µM for dopamine). In the platelet serotonin uptake study, DA-8031 exhibited significant inhibition at oral doses of 10 and 30 mg/kg in a dose-dependent manner. In the sexual response studies, after oral and intravenous administration of DA-8031, ejaculation was significantly inhibited in both para-chloroamphetamine- and meta-chlorophenylpiperazine-mediated ejaculation models in rats. CONCLUSIONS: The pharmacologic profiles observed in the present study suggest the potential for DA-8031 as a therapeutic agent useful in the treatment of premature ejaculation.

A novel dipeptidyl peptidase IV inhibitor DA-1229 ameliorates streptozotocin-induced diabetes by increasing ß-cell replication and neogenesis.

We studied the effect of a novel dipeptidyl peptidase IV (DPP IV) inhibitor, DA-1229, on blood glucose profile and pancreatic ß-cell mass in established diabetes after streptozotocin (STZ) treatment. Mice that developed diabetes after administration of STZ 100mg/kg were treated with DA-1229 for 13 weeks. DA-1229 significantly reduced plasma DPP IV activity, and enhanced glucagon-like peptide 1 (GLP-1) levels. In STZ-treated mice fed DA-1229 (STZ-DA), blood glucose levels were significantly lower than those in diabetic mice fed normal chow (STZ-NC). Basal and glucose-stimulated insulin secretion and glucose tolerance assessed by intraperitoneal glucose tolerance test were significantly improved by DA-1229 administration. Volume density of ß-cell was significantly increased in STZ-DA mice compared to STZ-NC mice, suggesting that DA-1229-mediated amelioration of established diabetes was due to beneficial effect of DA-1229 on ß-cell mass. The number of replicating ß-cells and that of scattered small ß-cell unit representing ß-cell neogenesis were significantly increased in STZ-DA mice compared to STZ-NC mice, explaining increased ß-cell mass by DA-1229. The expression of PDX-1, a downstream mediator of GLP-1 action, was increased in islets of STZ-DA mice compared to STZ-NC mice. These results suggest a therapeutic potential of DA-1229 in diabetes, particularly that associated with decreased ß-cell mass.

PAR-1622 is a selective peroxisome proliferator-activated receptor gamma partial activator with preserved antidiabetic efficacy and broader safety profile for fluid retention.

Peroxisome proliferator-activated receptor (PPAR) gamma is known to be a key regulator of insulin resistance. PAR-1622 is a novel small molecule compound synthesized in Dong-A research center. In this study, we characterized the pharmacological profiles of PAR-1622, a selective partial activator of PPARgamma. In transient transactivation assays, PAR-1622 [(S)-2-ethoxy-3(4-(5-(4-(5-(methoxymethyl)isoxazol-3-yl)phenyl)-3-methylthiophen-2-yl)methoxy)phenyl)propanoic acid] showed a partial activator against human PPARgamma with an EC(50) of 41 nM and a maximal response of 37% relative to the full agonist rosiglitazone without activating human PPARdelta. PAR-1622 was 56 folds more selective for human PPARgamma than for human PPARalpha (EC(50), 2304 nM), which means that it is a selective partial activator of PPARgamma. PAR-1622 also showed a partial activator against mouse PPARgamma with an EC(50) of 427 nM and a maximal response was 57% of that of rosiglitazone. INT-131, a selective PPARgamma partial agonist in clinical stage, also was a partial activator against human PPARgamma with an EC(50) of 83 nM and a maximal response achieved by INT-131 was 49% of that observed with full agonist rosiglitazone. In functional assays using human mesenchymal stem cells, PAR-1622 induced adipocyte differentiation, which was 3-fold more potent with a comparable maximum response compared to INT-131. Furthermore, PAR-1622 significantly improved hyperglycemia in db/db when orally administered at a dose of 1 mg/kg/day for 5 days. In hemodilution assays with Evans Blue, rosiglitazone significantly increased the plasma volume in ICR mice that were orally administered 30 mg/kg/day for 9 days; however, PAR-1622 showed no significant effects on plasma volume, similar to INT-131. These results suggest that PAR-1622 is a selective partial activator of PPARgamma and has excellent antihyperglycemic activities and a broad safety profile for fluid retention.

Design, synthesis, and evaluation of novel aryl-tetrahydropyridine PPARalpha/gamma dual agonists.

Aryl-tetrahydropyridine derivatives were prepared and their PPARalpha/gamma dual agonistic activities were evaluated. Among them, compound (S)-5b was identified as a potent PPARalpha/gamma dual agonist with an EC(50) of 1.73 and 0.64 microM in hPPARalpha and gamma, respectively. In diabetic (db/db) mice, compound (S)-5b showed good glucose lowering efficacy and favorable pharmacokinetic properties.

PAR-5359, a well-balanced PPARalpha/gamma dual agonist, exhibits equivalent antidiabetic and hypolipidemic activities in vitro and in vivo.

Peroxisome proliferator-activated receptor (PPAR) alpha and gamma are key regulators of lipid homeostasis and insulin resistance. In this study, we characterize the pharmacological profiles of PAR-5359, a dual agonist of PPARalpha and gamma with well-balanced activities. In transient transactivation assay, PAR-5359 (3-(4-(2[4-(4chloro-phenyl)-3,6-dihydro-2H-pyridin-1-yl]-ethoxy)-phenyl)-(2S)-ethoxy-propionic acid) significantly activated human and mouse PPARalpha and gamma without activating PPARdelta. In functional assays using human mesenchymal stem cells and human hepatoma HepG2 cells, PAR-5359 significantly induced adipocyte differentiation and human ApoA1 secretion, which coincided with its transactivation potencies against the corresponding human receptor subtypes. Interestingly, PAR-5359 showed equivalent potencies against the mouse receptor subtypes (alpha and gamma; 2.84 microM and 3.02 microM, respectively), which suggests the possibility that PAR-5359 could simultaneously activates each subtype of receptors subtype in under physiological conditions. In an insulin-resistant ob/ob mouse model, PAR-5359 significantly reduced plasma insulin levels, improved insulin sensitivity (HOMA-IR), and completely normalized plasma glucose levels. In a severe diabetic db/db mouse model, PAR-5359 dose-dependently reduced the plasma levels of glucose (ED(30) = 0.07 mg/kg). Furthermore, it lowered plasma levels of non HDL- (ED(30) = 0.13 mg/kg) and total cholesterol (ED(30) = 0.03 mg/kg) in high cholesterol diet-fed rats for 4 days treatment. These results suggest that PAR-5359 has the balanced activities for PPARalpha and PPARgamma in vivo as well as in vitro. And its balanced activities may render PAR-5359 as a pharmacological tool in elucidating the complex roles of PPARalpha/gamma dual agonists.

Inhibitory effect of DA-125, a new anthracyclin analog antitumor agent, on the invasion of human fibrosarcoma cells by down-regulating the matrix metalloproteinases.

Matrix metalloproteinases (MMPs), zinc-dependent proteolytic enzymes, play a pivotal role in tumor metastasis by cleavage of extracellular matrix as well as non-matrix substrates. In this study, we examined the influence of DA-125, a new anthracyclin analog, on the gene expression of MMPs (MMP-2, MMP-9 and MT1-MMP), tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) and in vitro invasiveness of human fibrosarcoma cells. Dose-dependent decreases of MMPs and TIMPs mRNA levels were observed in DA-125-treated HT1080 human fibrosarcoma cells detected by reverse transcriptase-polymerase chain reaction. Gelatin zymography analysis also showed a significant down-regulation of MMP-2 and MMP-9 expression in HT1080 cells treated with DA-125 compared to controls. In addition, DA-125 inhibited the invasion, motility and cell migration, and colony formation of tumor cells. These data, therefore, provide direct evidence for the role of DA-125 as a potential cancer chemotherapeutic agent, which can markedly inhibit the invasive capacity of malignant cells. Further, to clarify the transcriptional regulatory pathway, we primarily investigated the role of nuclear factor-kappaB (NF-kappaB) in the expression of MMPs by DA-125 in HT1080 cells. Electrophoretic mobility shift assay demonstrated that DA-125 modulates the binding activity of NF-kappaB. Using the luciferase reporter gene assay, a dose-dependent down-regulation of NF-kappaB-mediated luciferase expression was also observed. These results suggest that DA-125 down-regulates MMPs expression in HT1080 cells through the NF-kappaB-mediated pathway.

Metabolism of eupatilin in rats using liquid chromatography/electrospray mass spectrometry.

Eupatilin (5,7-dihydroxy-3',4',6-trimethoxy flavone) is an active ingredient of an ethanol extract of Artemisia asiatica (DA-9601) that is used in the treatment of gastritis. In vitro and in vivo metabolism of eupatilin in the rats has been studied by LC-electrospray mass spectrometry. Rat liver microsomal incubation of eupatilin in the presence of NADPH and UDPGA resulted in the formation of four metabolites (M1-M4). M1, M2, M3 and M4 were tentatively identified as 3'- or 4'-O-demethyl-eupatilin glucuronide, eupatilin glucuronide, 6-O-demethyleupatilin and 3'- or 4'-O-demethyl-eupatilin, respectively. Those metabolites from in vitro study were also characterized in bile, plasma or urine samples after an intravenous administration of eupatilin to rats. In rat bile, plasma and urine samples, eupatilin glucuronide (M2) was a major metabolite, whereas M3, M4 and M4 glucuronide (M1) were the minor metabolites.

Anti-diabetic effects of DA-11004, a synthetic IDPc inhibitor in high fat high sucrose diet-fed C57BL/6J mice.

DA-11004 is a synthetic, potent NADP-dependent isocitrate dehydrogenase (IDPc) inhibitor where IC50 for IDPc is 1.49 microM. The purpose of this study was to evaluate the effects of DA-11004 on the high fat high sucrose (HF)-induced obesity in male C57BL/6J mice. After completing a 8-week period of experimentation, the mice were sacrificed 1 hr after the last DA-11004 treatment and their blood, liver, and adipose tissues (epididymal and retroperitoneal fat) were collected. There was a significant difference in the pattern of increasing body weight between the HF control and the DA-11004 group. In the DA-11004 (100 mg/kg) treated group the increase in body weight significantly declined and a content of epididymal fat and retroperitoneal fat was also significantly decreased as opposed to the HF control. DA-11004 (100 mg/ kg) inhibited the IDPc activity, and thus, NADPH levels in plasma and the levels of free fatty acid (FFA) or glucose in plasma were less than the levels of the HF control group. In conclusion, DA-11004 inhibited the fatty acid synthesis in adipose tissues via IDPc inhibition, and it decreased the plasma glucose levels and FFA in HF diet-induced obesity of C57BL/6J mice.

DA-7911, 188Rhenium-tin colloid, as a new therapeutic agent of rheumatoid arthritis.

Radiation synovectomy is one of the most useful methods for treating patients with refractory synovitis because of its convenience, long-term effects, repeatability and the avoidance of surgery. In this study, we investigated the toxicity, stability and biodistribution of a rhenium-188 (188Re)-tin colloid to evaluate its suitability as a synovectomy agent. Twenty four hours after injecting the 188Re-tin colloids (74 KBq/0.1 mL) into the tail vein of ICR mice, most of the 188Retin colloidal particles was found in the lungs. In addition, there were no particle size changes at either room temperature or at 37 degrees C after injecting the 188Re-tin colloids in human plasma and synovial fluid. In vitro stability tests showed that the 188Re-tin colloid remained in a colloidal form without a critical size variation over a 2-day period. We investigated the leakage of 188Retin colloids from the intraarticular injection site with gamma counting in New Zealand white rabbits. The 188Re-tin colloids (55.5 MBq/0.15 mL) were injected at the cavum articular and the mean retention percentage of the 188Re-tin colloid was 98.7% for 1 day at the injection site, which suggests that there was neither change in the particle size nor leakage at the injection sites. In the biodistribution study with the SD rats, the liver showed the highest radioactivity (0.0427% ID/organ) except for the injected knees (99.49%). In the SD rats, mild toxicities including the skin or a synovium inflammation were observed as a result of a radioactivity of 15 mCi/kg at the intraarticular injection site. However, there was no systemic toxicity. In the Ovalbumin (OVA)-induced arthritic rabbits, the 188Re-tin colloid improved the macroscopic, the histological score and reduced the knee joint diameter when compared to the arthritic control. In conclusion, a 188Re-tin-colloid is considered as a strong candidate for radiation synovectomy with a superior efficacy and safety.

Determination of a new phosphodiesterase V inhibitor, DA-8159, in plasma and urine by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) method using liquid-liquid extraction for sample preparation was developed for the determination of a new phosphodiesterase V inhibitor, DA-8159, in rat plasma and urine using sildenafil citrate as an internal standard. A 100 microl aliquot of 0.1 M Na(2)CO(3) (containing sildenafil citrate, 3 microg/ml as free sildenafil) and a 1 ml aliquot of ether were added to a 100 microl aliquot of biological samples (urine samples were diluted 20 times with distilled water). After vortex centrifugation at 9000 x g for 3 min, the ether layer was collected and dried under nitrogen gas. The residue was reconstituted with a 150 microl aliquot of the mobile phase, centrifuged, and a 100 microl aliquot of the supernatant was injected onto a reversed-phase column. The mobile phases, 20 mM KH(2)PO(4) (pH 4.7):acetonitrile (70:30, v/v for plasma and tissue samples, and 75:25, v/v for urine samples), were run at a flow rate of 1.0 ml/min. The column effluent was monitored by an ultraviolet detector set at 292 nm. The retention times for DA-8159 and the internal standard were approximately 10.7 and 9.1 min, respectively, in plasma and tissue samples and the corresponding values in urine samples were 47 and 33 min. The detection limits for DA-8159 in rat plasma and urine were 20 and 100 ng/ml, respectively. The coefficients of variation of the assay were generally low: below 10% for plasma and 9.9% for urine. No interferences from endogenous substances were found.

Mechanism of erectogenic effect of the selective phosphodiesterase type 5 inhibitor, DA-8159.

DA-8159, a new Phosphodiesterase (PDE) 5 inhibitor, has exhibited potent erectogenic potential in a penile erection test in rats and anesthetized dogs. In this study, we investigated the mechanism of its erectogenic activity by measuring the activity of DA-8159 against a various PDE isozymes and assessing cGMP and cAMP formation in a rabbit corpus cavernosum in vitro. DA-8159 inhibited the PDE 5 activity in rabbit and human platelets, which the IC50 was 5.84 +/- 1.70 nM and 8.25 +/- 2.90 nM, respectively. The IC50 of DA-8159 on PDE 1, PDE 2, PDE 3 and PDE 6 were 870+/- 57.4 nM, 101 +/- 15 microM, 52.0 +/- 3.53 microM and 53.3 +/- 2.47 nM, respectively. This suggests that DA-8159 is a potent, highly selective, competitive inhibitor of PDE 5-catalyzed cGMP hydrolysis. The rates of cGMP hydrolysis catalyzed by human platelets-derived PDE 5 as a function of the cGMP concentration (5-100 nM) and two-fixed DA-8159 concentration (11.3 and 18.8 nM) were investigated in order to characterize the mode of PDE 5 inhibition by DA-8159. DA-8159 increased the apparent Km value for cGMP hydrolysis but had no effect on the apparent Vmax, indicating a competitive mode of inhibition. DA-8159 increased the cGMP concentrations in the rabbit corpus cavernosum dose dependently. In the presence of sodium nitroprusside (SNP), DA-8159 significantly stimulated the accumulation of cGMP when compared to the control level. This indicated that the enhancement of a penile erection by DA-8159 involved the relaxation of the cavernosal smooth muscle by NO-stimulated cGMP accumulation. In conclusion, DA-8159 is a selective inhibitor of PDE 5-catalyzed cGMP hydrolysis and the enhancement of a penile erection by DA-8159 is mediated by the relaxation of the cavernosal smooth muscle by the NO-stimulated cGMP accumulation.