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Biomedical subjects

W C Liao

Publications and source records attributed to W C Liao.

At least 19 recordsLinked to original sources
PubMed2004

Analysis of heart donation for cardiac transplantation at the National Taiwan University Hospital: fifteen-year cases review.

The demand for organ transplantation is disparate to the supply of organ donors. The organ shortage is a limitation for transplantation. This study analyzed the status of heart donors at the National Taiwan University Hospital (NTUH) from July 1987 through November 2001 using registry records. One hundred ninety-four total heart donors yielded about 25 donors per year in the late era (years of 1995-2001). The majority of heart donors were men (78.4%) of O blood type (46.9%) with a mean age of 29.8 (SD = 11.9) years. Though head injury was the main source of heart donors (78.4%), cerebrovascular accident patients have increased (15%) since 1995. However, the number of donors from head injury decreased in the year of 1997, when Taiwan passed a law to force motorcycle drivers to wear safety helmets. The average interval from brain death to donation was 75.4 (SD = 71.2) hours. One hundred fifty-six (80.4%) of the 194 donor hearts came from outside hospitals. However, the majority of heart transplantations (166 cases, 85.6%) were done at the NTUH. Implementing a program for a smooth donation and organ procurement processes should provide better donor management in cardiac transplantation.

ABO Blood-Group System↗
PubMed2001

Omapatrilat versus lisinopril: efficacy and neurohormonal profile in salt-sensitive hypertensive patients.

Omapatrilat, a vasopeptidase inhibitor, simultaneously inhibits neutral endopeptidase and ACE. The efficacy and hormonal profile of omapatrilat and lisinopril were compared in salt-sensitive hypertensive patients. On enrollment, antihypertensive medications were withdrawn, and patients received a single-blind placebo. On day 15, salt-sensitivity determinations were made. Salt-sensitive hypertensive patients returned within 5 to 10 days for baseline evaluations of ambulatory diastolic blood pressure, ambulatory systolic blood pressure, and atrial natriuretic peptide. Salt-sensitive hypertensive patients were randomized to receive double-blind omapatrilat (n=28) or lisinopril (n=33) at initial doses of 10 mg for 1 week, increasing to 40 and 20 mg, respectively, for an additional 3 weeks. Ambulatory blood pressure and urinary atrial natriuretic peptide were assessed at study termination. Both omapatrilat and lisinopril significantly reduced mean 24-hour ambulatory diastolic and systolic blood pressures; however, omapatrilat produced significantly greater reductions in mean 24-hour ambulatory diastolic blood pressure (P=0.008), ambulatory systolic blood pressure (P=0.004), and ambulatory mean arterial pressure (P=0.005) compared with values from lisinopril. Both drugs potently inhibited ACE over 24 hours. Omapatrilat significantly (P<0.001) increased urinary excretion of atrial natriuretic peptide over 0- to 24-hour (3.8-fold) and 12- to 24-hour (2-fold) intervals; lisinopril produced no change. Omapatrilat significantly (P<0.001) increased urinary excretion of cGMP over the 0- to 24- and 4- to 8-hour intervals compared with that from lisinopril. Neither drug had a diuretic, natriuretic, or kaliuretic effect. In conclusion, in salt-sensitive hypertensive patients, omapatrilat demonstrated the hormonal profile of a vasopeptidase inhibitor and lowered ambulatory diastolic and systolic blood pressures more than lisinopril.

Adult↗
PubMed2001

Cell autonomous apoptosis defects in acid sphingomyelinase knockout fibroblasts.

A body of evidence suggests that stress-induced sphingomyelin hydrolysis to the second messenger ceramide initiates apoptosis in some cells. Although studies using lymphoblasts from Niemann-Pick disease patients or acid sphingomyelinase (ASMase)-deficient mice have provided genetic support for this hypothesis, these models have not been universally accepted as definitive. Here, we show that mouse embryonic fibroblasts (MEFs) prepared from asmase mice manifest cell autonomous defects in apoptosis in response to several stresses. In particular, asmase(-/-) MEFs failed to generate ceramide and were totally resistant to radiation-induced apoptosis but remained sensitive to staurosporine, which did not induce ceramide. asmase(-/-) MEFs were also partially resistant to tumor necrosis factor alpha/ actinomycin D and serum withdrawal. Thus, resistance to apoptosis in asmase(-/-) MEFs was not global but rather stress type specific. Most importantly, the sensitivity to stress could be restored in the asmase(-/-) MEFs by administration of natural ceramide. Overcoming apoptosis resistance by natural ceramide is evidence that it is the lack of ceramide, not ASMase, that determines apoptosis sensitivity. The ability to rescue the apoptotic phenotype without reversing the genotype by the product of the enzymatic deficiency provides proof that ceramide is obligate for apoptosis induction in response to some stresses.

Animals↗
PubMed2001

The cardiovascular actions of omapatrilat in spontaneously hypertensive rats.

Omapatrilat is a newly developed vasopeptidase inhibitor that inhibits both angiotensin-converting enzyme (ACE) and neutral endopeptidase and has potent antihypertensive efficacy. However, the specific effect of omapatrilat on cardiac function and left ventricular hypertrophy with hypertension remains controversial. Therefore, we investigated the effect of omapatrilat on blood pressure, cardiac hypertrophy, and cardiac function in spontaneously hypertensive rats (SHR). Studies were performed in SHR that received vehicle (n = 9), omapatrilat (n = 10), or fosinopril (ACE inhibitor, n = 7) by daily gavage for 56 days. Systolic blood pressure (SBP) and mean blood pressure (MBP) were measured by tail plethysmography. Left ventricular fractional shortening and left ventricular mass were measured by echocardiography at day 56. Omapatrilat and fosinopril significantly decreased SBP and MBP from day 1 through day 56, and omapatrilat markedly reduced SBP and MBP compared with fosinopril from day 21 to day 56. Although both omapatrilat and fosinopril decreased left ventricular mass and left ventricular mass-to-body weight ratio with increased LV fractional shortening, omapatrilat had a more potent effect on the reduction of left ventricular mass and improvement of cardiac function. This study shows that in SHR, omapatrilat mediated a potent and stable antihypertensive effect and a reduction in left ventricular mass with improvement of cardiac function, compared with ACE inhibition alone.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Oral bioavailability and disposition of [14C]omapatrilat in healthy subjects.

The objective of this study was to determine the absolute oral bioavailability and disposition of omapatrilat. This single-dose, randomized, crossover study of 20 mg intravenous and 50 mg oral [14C]omapatrilat was conducted in 12 healthy male subjects to determine the disposition and oral bioavailability of omapatrilat, an orally active vasopeptidase inhibitor. Blood samples were collected up to 120 hours, and the excreta were collected over 168 hours postdose. Plasma concentrations of omapatrilat were determined by a validated LC/MS/MS procedure. Radioactivity in blood, plasma, urine, and feces was determined by liquid scintillation counting. Urinary excretion of radioactivity averaged 80% and 64% of intravenous and oral doses, respectively; < 1% of oral dose was excreted unchanged in urine. The absolute oral bioavailability of omapatrilat averaged 31%. Total body clearance of omapatrilat (80 L/h) exceeded liver plasma flow. Apparent steady-state volume of distribution of omapatrilat (21 L/kg) was extremely high compared with total body water. Omapatrilat undergoes substantial presystemic first-pass metabolism after oral administration. Omapatrilat is eliminated primarily by metabolism, and its metabolites are eliminated primarily in urine. Extrahepatic organs may be involved in the elimination of omapatrilat. Plasma concentrations of omapatrilat exhibit a prolonged terminal elimination phase, which represents elimination from a deep compartment.

Absorption↗
PubMed2001

Pharmacodynamics and pharmacokinetics of omapatrilat in heart failure.

The purpose of this study was to determine the pharmacodynamics and pharmacokinetics of omapatrilat, administered orally (25 mg) or intravenously (10 mg) in 19 New York Heart Association class II and class III congestive heart failure (CHF) patients versus 17 healthy controls matched for age, race, gender, and weight. The plasma concentrations of atrial natriuretic peptide (ANP) increased by approximately 20% and 30% in CHF and control subjects, respectively, at 4 hours after intravenous or oral omapatrilat administration. Similar elevation in the cyclic guanosine monophosphate concentration (25% to 35%) and ANP urinary excretion (21 ng/24 h to 22 ng/24 h) was seen in all treatment groups after omapatrilat administration. Angiotensin-converting enzyme activity was > 90% inhibited at 4 hours after dosing and remained approximately 60% to 70% inhibited at 24 hours after dosing. The levels of endothelin-1 and endothelin-2 remained unchanged after oral or intravenous administration of omapatrilat. The maximal reduction in seated blood pressure compared with baseline was similarfor CHF and control subjects. Clinical pharmacokinetic parameters were similar in both groups after intravenous dosing, but maximum concentration and area under the concentration-time curve were elevated in CHF patients compared with controls after oral dosing. Omapatrilat was well tolerated; differences in systemic exposure and metabolism between CHF patients and controls did not appear to be clinically significant.

Administration, Oral↗
PubMed2001

Omapatrilat: neurohormonal and pharmacodynamic profile when administered with furosemide.

Pharmacodynamic effects of combination therapy with omapatrilat and furosemide were evaluated. Two groups of 13 healthy subjects each received furosemide 20 mg dailyfor 15 days coadministered with either placebo on days 6 to 15 or omapatrilat 10 mg on days 6 to 10 and 25 mg on days 11 to 15. In the omapatrilat group, urinary excretion of atrial natriuretic peptide increased, and greater blood pressure reductions were seen compared with placebo. Concomitant omapatrilat treatment did not affect the acute diuresis, natriuresis, and kaliuresis observed with chronic administration of furosemide. Neither effective renal plasma flow nor glomerularfiltration rate changed in either treatment group. No clinically significant safety issues were observed. Daily coadministration of omapatrilat 10 or 25 mg with furosemide 20 mg does not affect the pharmacodynamics offurosemide at steady state.

Adult↗
PubMed2000

Quantitative structure-activity relationships for the pre-steady-state inhibition of cholesterol esterase by 4-nitrophenyl-N-substituted carbamates.

4-Nitrophenyl-N-substituted carbamates (1-6) are the pseudo-substrate inhibitors of porcine pancreatic cholesterol esterase. Thus, the first step of the inhibition (Ki step) is the formation of the enzyme inhibitor tetrahedral adduct and the second step of the inhibition (kc) is the formation of the carbamyl enzyme. The formation of the enzyme inhibitor tetrahedral adduct is further divided into two steps, the formation of the enzyme-inhibitor complex with the dissociation constant, KS, at the first step and the formation of the enzyme-inhibitor tetrahedral adduct from the complex at the second step. The two-step mechanism for the formation of the enzyme-inhibitor tetrahedral adduct is confirmed by the pre-steady-state kinetics. The results of quantitative structure-activity relationships for the pre-steady-state inhibitions of cholesterol esterase by carbamates 1-6 indicate that values of -logKs and logk2/k-2 are correlated with the Taft substituent constant, sigma*, and the rho* values from these correlations are -0.33 and 0.1, respectively. The negative rho* value for the -logKS-sigma*-correlation indicates that the first step of the two-step formation of the enzyme-inhibitor tetrahedral adduct (KS step) is the formation of the positive enzyme inhibitor complex. The positive rho* value for the logk2/k-2 -sigma*-correlation indicates that the enzyme inhibitor tetrahedral adduct is more negative than the enzyme inhibitor complex. Finally, the two-step mechanism for the formation of the enzyme inhibitor tetrahedral adduct is proposed according to these results. Thus, the partially positive charge is developed at nitrogen of carbamates 1-6 in the enzyme-inhibitor complex probably due to the hydrogen bonding between the lone pair of nitrogen of carbamates 1-6 and the amide hydrogen of the oxyanion hole of the enzyme. The second step of the two-step formation of the enzyme-inhibitor tetrahedral adduct is the nucleophilic attack of the serine of the enzyme to the carbonyl group of carbamates 1-6 in the enzyme-inhibitor complex and develops the negative-charged oxygen in the adduct.

Animals↗
PubMed2000

Comparison of the pharmacokinetics of fosinoprilat with enalaprilat and lisinopril in patients with congestive heart failure and chronic renal insufficiency.

AIMS: To compare the serum pharmacokinetics of fosinoprilat with enalaprilat and lisinopril after 1 and 10 days of dosing with fosinopril, enalapril and lisinopril. METHODS: Patients with congestive heart failure (CHF, NYHA Class II-IV) and chronic renal insufficiency (creatinine clearance </=30 ml min-1 ) were randomized to receive fosinopril, enalapril or lisinopril in two parallel-group studies. In the first study 24 patients were treated with 10 mg fosinopril (n=12 patients) or 2.5 mg enalapril (n=12) every morning for 10 consecutive days. In the second study 31 patients were treated with 10 mg fosinopril (n=16 patients) or 5 mg lisinopril (n=15) every morning for 10 consecutive days. Samples of blood were collected for determination of pharmacokinetic parameters. The area under the curve (AUC) between the first and last days of treatment and the accumulation index (AI) were the primary outcome measures. RESULTS: All three angiotensin converting enzyme (ACE) inhibitors exhibited a significant increase in AUC between the first and last days of treatment in both studies. The difference between the AI for fosinoprilat (1.41) and enalaprilat (1.96) was statistically significant (95% CI: 1.05, 1.84). Similarly, the difference between the AI for fosinoprilat (1.21) and lisinopril (2.76) was statistically significant (95% CI: 1.85, 2.69). All three ACE inhibitors completely inhibited serum ACE for 24 h. All treatments were well tolerated. CONCLUSIONS: Fosinoprilat exhibits significantly less accumulation than enalaprilat or lisinopril in patients with CHF and renal insufficiency, most probably because fosinoprilat is eliminated by both the kidney and liver, and increased hepatic elimination can compensate for reduced renal clearance in patients with kidney dysfunction.

Adolescent↗
PubMed2000

Binary/ternary combined effects of vitamin K3 with other antitumor agents in nasopharyngeal carcinoma CG1 cells.

Nasopharyngeal carcinoma (NPC) is a prevalent cancer in Taiwan. To improve the treatment of NPC, we have extensively searched for effective combination chemotherapies. Our previous studies indicated that vitamin K3 (VK3) inhibits the growth of NPC CG1 cells in vitro. In this study, we further studied the binary/ternary combined effects of VK3 with other anticancer drugs against NPC cells. The antitumor effects of different VK3 combinations against CG1 cells were determined by using MTT assay, and the combined effects were evaluated by a taibologram, a modified isobolographic method being developed in our laboratory for the analyses of binary/ternary combinations of anticancer agents. Binary combinations of VK3 with doxorubicin (DOX), vinblastine (VBL), or 5-fluorouracil (5-FU) result in synergistic effects. For three-drug combinations, a remarkable synergy was found in the combination of VK3, VBL, and 5-FU. These in vitro results will provide useful information not only for further mechanistic studies and but also for future clinical trials of VK3-based cancer chemotherapy of NPC.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2000

Weight-correction formula for maternal serum screening for Down syndrome in Taiwan.

BACKGROUND AND PURPOSE: This study examined the relationship between maternal weight and serum marker concentrations (alpha-fetoprotein [AFP] and human chorionic gonadotropin [hCG]) to develop a weight-correction formula for second-trimester Down syndrome screening in Taiwan. METHODS: We conducted a prospective observational study based on data from 18, 016 pregnant Taiwanese women who participated in a second-trimester Down syndrome screening program at Taiwan Adventist Hospital. The relationship between maternal weight and the multiple of median (MoM) concentrations of serum markers was analyzed using two methods; one involved all the observational data (all point method), while the other involved only the median concentrations at various gestational ages (median regression method). In each method, several statistical approaches were used, including simple-linear, reciprocal, quadratic, and log-transformation linear regression. RESULTS: The correlation between maternal body weight and serum marker concentrations using the all point regression method was very poor, while the median regression method achieved a good fit. The reciprocal regression analysis had the best fit between AFP MoM concentration and maternal weight, while the best fit between hCG MoM concentration and maternal weight was achieved with quadratic regression analysis. CONCLUSION: The present study has developed a race-specific weight-correction formula for Taiwanese women. This formula is expected to be helpful in second-trimester Down syndrome screening programs in Taiwan.

Adolescent↗
PubMed1999

Reversal of radiation resistance in LNCaP cells by targeting apoptosis through ceramide synthase.

Cell lines derived from human prostate cancer are regarded as relatively resistant to both radiation-induced clonogenic death and apoptosis. Here we attempted to modulate the response of LNCaP prostate cancer cells to radiation therapy (XRT) by pretreatment with 12-O-tetradecanoylphorbol acetate (TPA), a known apoptogenic agent in LNCaP cells. Using plateau-phase cultures, we investigated the response of these cells to XRT, TPA, and a combination of XRT and TPA. LNCaP irradiation did not result in ceramide generation or apoptosis. However, pretreatment with TPA enabled XRT to generate ceramide via activation of the enzyme ceramide synthase and signal apoptosis. Apoptosis was abrogated by the competitive inhibitor of ceramide synthase, fumonisin B1. Furthermore, when transplanted orthotopically into the prostate of nude mice, LNCaP cells produced tumors that recapitulated the responses of LNCaP cells in vitro. XRT or TPA failed to signal apoptosis in LNCaP tumors, whereas a combination of the two resulted in substantial (20-25%) apoptosis within 24 h. There was an additional benefit associated with this regimen because TPA pretreatment protected the adjacent rectum from radiation-induced apoptosis. This represents the first description of signaling-based therapy designed to overcome one form of radiation resistance expressed preferentially in LNCaP human prostate cancer cells.

Animals↗
PubMed1999

Ataxia telangiectasia-mutated gene product inhibits DNA damage-induced apoptosis via ceramide synthase.

DNA double-stranded breaks (dsb) activate surveillance systems that identify DNA damage and either initiate repair or signal cell death. Failure of cells to undergo appropriate death in response to DNA damage leads to misrepair, mutations, and neoplastic transformation. Pathways linking DNA dsb to reproductive or apoptotic death are virtually unknown. Here we report that metabolic incorporation of 125I-labeled 5-iodo-2'deoxyuridine, which produces DNA dsb, signaled de novo ceramide synthesis by post-translational activation of ceramide synthase (CS) and apoptosis. CS activation was obligatory, since fumonisin B1, a fungal pathogen that acts as a specific CS inhibitor, abrogated DNA damage-induced death. X-irradiation yielded similar results. Furthermore, inhibition of apoptosis using the peptide caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone did not affect CS activation, indicating this event is not a consequence of induction of apoptosis. ATM, the gene mutated in ataxia telangiectasia, is a member of the phosphatidylinositol 3-kinase family that constitutes the DNA damage surveillance/repair system. Epstein-Barr virus-immortalized B cell lines from six ataxia telangiectasia patients with different mutations exhibited radiation-induced CS activation, ceramide generation, and apoptosis, whereas three lines from normal patients failed to manifest these responses. Stable transfection of wild type ATM cDNA reversed these events, whereas antisense inactivation of ataxia telangiectasia-mutated gene product in normal B cells conferred the ataxia telangiectasia phenotype. We propose that one of the functions of ataxia telangiectasia-mutated gene product is to constrain activation of CS, thereby regulating DNA damage-induced apoptosis.

Animals↗
PubMed1999

Molecular recognition by acetylcholinesterase at the peripheral anionic site: structure-activity relationships for inhibitions by aryl carbamates.

Substituted phenyl-N-butyl carbamates (1-9) are potent irreversible inhibitors of Electrophorus electricus acetylcholinesterase. Carbamates 1-9 act as the peripheral anionic site-directed irreversible inhibitors of acetylcholinesterase by the stop-time assay in the presence of a competitive inhibitor, edrophonium. Linear relationships between the logarithms of the dissociation constant of the enzyme inhibitor adduct (Ki), the inactivation constant of the enzyme-inhibitor adduct (k2), and the bimolecular inhibition constant (k(i)) for the inhibition of Electrophorus electricus acetylcholinesterase by carbamates 1-9 and the Hammett substituent constant (sigma), are observed, and the reaction constants (ps) are -1.36, 0.35 and -1.01, respectively. Therefore, the above reaction may form a positive charged enzyme-inhibitor intermediate at the peripheral anionic site of the enzyme and may follow the irreversible inactivation by a conformational change of the enzyme.

Acetylcholinesterase↗
PubMed1999

Fosinopril: pharmacokinetics and pharmacodynamics in Chinese subjects.

This study examined thepharmacokinetics and pharmacodynamics of fosinopril (IVand oral) in Chinese subjects to determine whether they were different from a group of somewhat heavier and older Western control subjects previously published using the same methods. It was an open-label, randomized, balanced, two-way crossover study comparing oral and IV pharmacokinetics in 12 healthy Chinese subjects in a clinic in Taiwan. Each subject received 10 mg of oral fosinopril or 7.5 mg of IV fosinoprilatin a randomized sequence with sampling for fosinoprilat concentrations over 48 hours. Standard pharmacokinetics, including AUC, Cmax Tmax, T 1/2, Vss, bioavailability, total clearance, and renal and nonrenal clearance, were determined as well as pharmacodynamic effects on angiotensin-converting enzyme (ACE) activity. Following oral administration of 10 mg fosinopril, AUC0-T and AUCinf were 1,556 +/- 586 ng x hr/mL and 1,636 +/- 620 ng x hr/mL, respectively; T 1/2 was 17.4 +/- 11.4 hr; Cmax was 183.4 +/- 59.4 ng/mL; and median Tmax was 4.0 hr, with > 99% protein binding. Following IV administration of 7.5 mg fosinoprilat, AUC0-T and AUCinf were 7,727 +/- 2,638 ng x hr/mL and 7,816 +/- 2,693 ng x hr/mL, respectively; T 1/2 was 13.0 +/- 5.2 hr; and median Tmax was 4.0 hr, with 99.5% +/- 0.22% protein binding and a Vss of 5,850 +/- 2,780 mL. Bioavailability was 22.3% +/- 7.9%. Percent urinary excretion was 7.6% +/- 2.6% after oral dosing and 42.6% +/- 6.1% after IV dosing. After IV, dosing total clearance was 1,088 +/- 439 mL/hr, renal clearance was 472 +/- 213 mL/hr, and nonrenal clearance was 617 +/- 246 mL/hr. ACE inhibition was essentially complete through 12 hours and markedly reduced through 24 hours. Compared to a somewhat heavier and older previously reported control group, pharmacokinetic values were similar except for a slightly lower AUC and total clearance in Chinese and a statistically significantly lower nonrenal clearance. Pharmacodynamic effects on ACE activity were essentially identical. There is no reason to expect significant differences in fosinopril dosing or effect in a Chinese population compared to a Western population.

Administration, Oral↗
PubMed1998

Enantiomeric inhibitors of cholesterol esterase and acetylcholinesterase.

Enantiomers of N-methyl-N,alpha-methylbenzylbutyramide (1), 1-butyl-3-methyl-3'-alpha-methylbenzylurea (2), 1,2,3, 4-tetrahydro-1-naphthyl-N-butylcarbamate (3), 1,1'-bi-2-naphthyl-2, 2'-di-N-butylcarbamate (4), 1, 1'-bi-2-naphthyl-2-ol-2'-N-butylcarbamate (5), and 1, 1'-bi-2-naphthyl-2-butyrate-2'-N-butylcarbamate (6) are inhibitors of porcine pancreatic cholesterol esterase-catalyzed hydrolysis of 4-nitrophenyl butyrate and of electric eel acetylcholinesterase-catalyzed hydrolysis of acetylthiocholine in the presence of 5,5'-dithiobis-2-nitrobenzoate. For competitive inhibitors, values of the inhibition constant (Ki) and the enantiomeric ratio (Ecomp.) are investigated. For active site-directed irreversible inhibitors, values of the inhibition constant (Ki), the carbamylation constant (k2), the bimolecular rate constant (ki), and the enantiomeric ratio (E) are investigated. Toward both enzymes, compounds 1 are poor competitive inhibitors (Ki=102-104 microM) but have good enantioselectivities (Ecomp.=10-50, the preference for R). R-2 and S-2 are competitive inhibitors of acetylcholinesterase with Ki=26 and 80 microM, respectively (the preference for R) but are active site-directed irreversible inhibitors of cholesterol esterase with ki=4 and 16 M-1 sec-1, respectively (the preference for S). For those competitive inhibitions, both leaving group hydrophilic and hydrophobic binding sites of cholesterol esterase or both anionic substrate binding site and peripheral anionic binding site of acetylcholinesterase bind to N,N-methyl-alpha-methylbenzyl disubstituted amide parts of these inhibitors and the enzyme does not catalyze the hydrolysis of these inhibitors. The opposite stereopreference (S) for the inhibition of cholesterol esterase by compounds 2 may be due to the fact that N, N-methyl-alpha-methylbenzyl disubstituted amide parts of these inhibitors bind to the alkyl chain binding site of the enzyme. Compounds 3-6 are active site-directed irreversible inhibitors of cholesterol esterase (ki=1-13000 M-1 s-1) and peripheral anionic binding site-directed irreversible inhibitors of acetylcholinesterase (ki=1.7-1300 M-1 s-1). Compounds 3 have low enantioselectivities (E=1.3-1.4) for both enzymes. The stereopreference for atropisomers 4 and 6 is S-form toward both enzymes (E=2-30) and is identical to that of cholesterol esterase-catalyzed hydrolysis of 1,1'-bi-2-naphthyl-2,2'-diacylate. This stereopreference (S) may be due to the fact that the butyryl group or one of two butylcarbamate groups of S-atropisomers binds more effectively to the leaving group hydrophobic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase than that of R-atropisomers. The opposite stereopreference (R) for atropisomers 5 toward both enzymes may be due to a favorable interaction between the hydroxyl group of the inhibitors and the leaving group hydrophilic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase.

Acetylcholinesterase↗
PubMed1998

12-O-tetradecanoylphorbol-13-acetate-induced apoptosis in LNCaP cells is mediated through ceramide synthase.

Protein kinase C (PKC) activation is often antiapoptotic, although in a few cell types PKC initiates apoptosis by an unknown mechanism. Recent investigations showed that activation of PKC alpha by 12-O-tetradecanoylphorbol 13-acetate (TPA) induced apoptosis in LNCaP prostate cancer cells. The present studies examine the mechanism of this effect and show that de novo ceramide generation through the enzyme ceramide synthase is required. TPA induced rapid ceramide generation, which was detectable by 1 h and increased linearly for 12 h. TPA-induced apoptosis was measurable by 12 h and was progressive for 48 h. Investigations into the mechanism of TPA-induced ceramide generation revealed that acid and neutral sphingomyelinase activities were not enhanced. However, TPA induced an increase in ceramide synthase activity that persisted for at least 16 h. Treatment with fumonisin B1, a specific natural inhibitor of ceramide synthase, abrogated both ceramide production and TPA-induced apoptosis. Ceramide analogues bypassed fumonisin B1 inhibition to initiate apoptosis directly. Thus, ceramide appears to be a necessary signal for TPA-induced apoptosis in LNCaP cells. This represents the first description of a pathway by which PKC may signal apoptosis.

Amidohydrolases↗