Stereoselectivity and species difference in plasma protein binding of KE-298 and its metabolites.

In vitro protein binding of KE-298 and its plasma metabolites, deacetyl-KE-298 (M-1) and S-methyl-KE-298 (M-2), was high in rat (>97%), dog (>89%) and human plasma (>99%), respectively. Human serum albumin (>93%) was the main protein involved in the binding to plasma proteins, while the binding to human serum globulins was low (16-33%). The binding of KE-298 and its metabolites in all species of plasma was stereoselective. The (+)-(S)-enantiomers of these compounds bound rat, dog and human plasma proteins to a greater extent than did the (-)-(R)-enantiomers, except that the case of KE-298 was opposite in rat plasma. The stereoselective plasma levels of these compounds in rats, dogs, or humans would likely be due to stereoselective differences in binding to plasma albumin. The protein binding of M-1 in adjuvant-induced arthritis rat plasma was >97%, and the stereoselectivity was similar to the case of normal rat plasma. KE-298 and its metabolites remarkably displaced [14C]warfarin, which bound on albumin in a solution of diluted rat serum albumin. Similarly, there was a displacement of [14C]warfarin in solutions of dog and human serum albumin, and concomitantly the displacement of [14C]diazepam. [3H]Digitoxin was not displaced by any of the enantiomers in each albumin solution. No stereoselectivity was found in displacement by enantiomers of the three compounds. These results suggest that stereoselective protein binding can be attributed to quantitative differences in binding to albumin rather than to the different binding sites.     

Effects of KE-758; an active metabolite of the new anti-rheumatic drug KE-298, D-penicillamine, bucillamine and auranofin on the proliferation of murine lymphocytes, and the production of nitric oxide by murine macrophages

2-Mercaptomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (KE-758), which is the active metabolite of 2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (KE-298), is a novel sulphydryl anti-rheumatic drug. In this study we analyzed the effect of KE-758 on the proliferation of murine lymphocytes, and on the production of nitric oxide (NO) by RAW264.7 murine macrophage cells. We compared its effect with other sulphydryl drugs such as D-penicillamine, bucillamine and auranofin. The proliferation of lymphocytes was measured by 3H-thymidine incorporation assay. Nitrite was measured using Griess Reagent. In the absence of copper ions, KE-758, D-penicillamine and bucillamine rarely affected the proliferation of concanavarin A (ConA) activated murine splenocytes. However, in the presence of copper, pharmacological concentrations of KE-758 but not D-penicillamine and bucillamine suppressed the proliferation of murine splenocytes through a hydrogen peroxide-dependent mechanism. Auranofin markedly suppressed the proliferation regardless of the presence of copper ions by reducing the cellular viability. Furthermore, only KE-758 markedly suppressed the proliferation of phorbol myristate acetate (PMA) plus ionomycin activated murine whole blood lymphocytes (WBL) even in the absence of exogenous copper ions by a hydrogen peroxide-independent mechanism. Meanwhile, lipopolysaccharide (LPS) or LPS plus interferon-gamma (IFN-gamma) induced NO production by RAW264.7 cells were suppressed by KE-758 and auranofin but not by D-penicillamine and bucillamine. In conclusion, KE-758 is a novel immunosuppressive drug, which inhibits both lymphocyte and macrophage functions and its unique anti-rheumatic profile is distinct from that of D-penicillamine, bucillamine and auranofin.     

Delayed elimination of triamterene and its active metabolite in chronic renal failure

Summary The kinetics of triamterene and its active phase II metabolite were studied in 32 patients with various degrees of impaired renal function; the creatinine clearances ranged from 135 to 10 ml/min. The area under the plasma concentration-time curves (AUC) for triamterene were not influenced by kidney function, but the AUCs for the effective metabolite OH-TA-ester were significantly elevated in renal failure, indicating accumulation of the metabolite. Urinary recovery of triamterene and its metabolite over a 48 h collection period was significantly reduced in renal failure. This is considered to be due to delayed urinary excretion, corresponding to reduced renal clearance. The renal clearance of the native drug exceeded that of the metabolite, because of their different protein binding, 55% for triamterene and 91% for the metabolite. The latter is eliminated almost exclusively via tubular secretion and extrarenal elimination is less important. Administration of this antikaliuretic is therefore considered hazardous in patients with impaired kidney function.     

甲氧滴滴涕及其代谢产物2,2-二(4-羟基苯基)-1,1,1-三氯乙烷在大鼠体内的毒代动力学

目的探讨甲氧滴滴涕(MXC)及其代谢产物2,2-二(4-羟基苯基)-1,1,1-三氯乙烷(HPTE)在大鼠体内的毒代动力学。方法雄性SD大鼠单次ig给予MXC 500 mg.kg-1染毒后,于不同时间点收集血液样本。应用高效液相色谱-紫外法测定大鼠血浆中MXC和HPTE的含量,用DAS 2.0软件的房室模型进行拟合,计算代谢动力学参数。结果 MXC的毒代动力学参数血浆最大浓度(cmax)为(5.52±1.21)mg.L-1;分布半衰期(t1/2α)为(4.12±1.21)h;消除半衰期(t1/2β)为(22.54±6.31)h;曲线下面积〔AUC(0-t)〕为(65.97±17.94)mg.h.L-1;AUC(0-∞)为(69.06±18.61)mg.h.L-1;清除率(Cl)为(7.94±2.31)L.h-1.kg-1;和表观分布容积(V)为(66.16±20.21)L.kg-1。代谢产物HPTE的毒代动力学参数cmax为(1.32±0.37)mg.L-1,t1/2α为(3.13±0.91)h;t1/2β为(31.12±10.91)h,AUC(0-t)为(14.69±2.99)mg.h.L-1,AUC(0-∞)为(17.23±3.66)mg.h.L-1,Cl为(30.14±6.09)L.h-1.kg-1,V为(232.55±36.44)L.kg-1。结论 MXC及其代谢产物HPTE的毒代动力学均符合二室模型。MXC和HPTE的清除半衰期均较长,易发生体内蓄积。     

Changes in CNS levels of serotonin and its metabolite in SART-stressed (repeatedly cold-stressed) rats.

Central nervous system levels of serotonin (5-HT) and 5-hydroxy-indoleacetic acid (5-HIAA) in SART (specific alternation of rhythm in temperature)-stressed (repeatedly cold-stressed) rats were examined by HPLC-ECD. In SART-stressed rats, the levels of both 5-HT and 5-HIAA decreased in many brain areas. In the spinal cord, only the 5-HT level decreased. Therefore, the ratio of 5-HIAA to 5-HT increased only in the spinal cord. These results suggest that SART-stressed rats have some form of abnormality in the synthetic system of 5-HT.     

Hepatobiliary excretion of acetaminophen glutathione conjugate and its derivatives in transport-deficient (TR-) hyperbilirubinemic rats.

The involvement of the canalicular multidrug resistance protein 2 (Mrp2) in the hepatobiliary excretion of acetaminophen (APAP)-glutathione (GSH) conjugate and its derivatives was investigated using transport-deficient (TR- rats. Although no differences in the biliary concentration of APAP itself were detected between normal Wistar and TR- rats, significant differences in the biliary disposition of several conjugated metabolites of APAP were detected. APAP-GSH was virtually absent in bile from TR- rats. Also, biliary concentrations of APAP-mercapturate (NAC; N-acetylated l-cysteine) and APAP-GLU were significantly reduced in TR- rats. No differences in the biliary concentration of APAP-cysteinylglycine/cysteine (CG/CYS) were detected between normal and mutant rats. The cumulative amounts of APAP-CG/CYS and APAP-NAC excreted in urine of mutant rats were decreased, whereas APAP-GLU was markedly increased. Analysis of liver samples revealed that APAP-GSH and APAP-NAC accumulate in mutant rat livers. Our results support the direct involvement of Mrp2 in the hepatobiliary excretion of several conjugated metabolites of APAP, including APAP-GSH and APAP-NAC, and provide relevant information on processes that may be involved with both their hepatic basolateral transport and renal elimination.     

Pharmacokinetics of afobazole metabolite (M-11) in rats

Pharmacokinetics of compound M-11 (main metabolite of afobazole) after administration via different routes was studied in rats. After oral and intravenous administration, M-11 exhibited weakly pronounced bioconversion with the formation of a few metabolites that could be detected in plasma samples for about 3 hours. The absolute bioavailability of M-11 after oral administration was 68.3%. It was found that M-11 was completely absorbed from gastrointestinal tract of rats and characterized by "the first pass effect", after which approximately 70% of administered dose entered the circulation. The parent substance was determined neither in urine nor in feces.     

Dose-independent pharmacokinetics of trimethadione and its metabolite in rats

The aim of the present study was to examine the dose-independent kinetics of trimethadione (1) and its only metabolite dimethadione, 5,5-dimethyl-2,4-oxazolidinedione (2), after oral administration of 1-, 2-, and 4-mg/kg doses of 1 to rats. Pharmacokinetic parameters determined after oral administration of these doses showed that the half-life (t 1/2), metabolic clearance (CL), and apparent volume of distribution (Vd) were not significantly changed by increasing or decreasing the dose of 1, whereas there was a linear relationship between the dose of 1 and the area under the curve (AUC) (1, r = 0.912; 2, r = 0.976) or the maximum serum concentration (Cmax) (1, r = 0.990; 2, r = 0.980). The ratios of 2 to 1 at 1 and 2 h after oral administration of 1 were not significantly different. These experiments indicate that serum pharmacokinetic behavior of 1 and 2 1 or 2 h after oral administration of 1 to the rat is independent of the dose of 1 in the 1-4 mg/kg range.     

Hepatobiliary elimination of bendamustin (Cytostasan) in rats.

Biliary excretion of bendamustin (Cytostasan, 5-[bis(2-chloroethyl)amino]-i-methylbenzimidazole-2-butyric acid; 1) and its metabolites was studied in rats after i.v. administration of 14C-1. The most significant finding was the rapid excretion of 1 related radioactivity in the bile occurring shortly after injection. While radioactivity eliminated by bile within 2 h was 41.8%, in the course of subsequent 22 h it amounted only to 3.2%. Bile samples analyzed by TLC indicated that the total amount of radioactivity was excreted in the form of conjugates and two hydroxy metabolites. A significant amount of radioactivity was excreted in urine. The diversion of bile by cannulation of the bile duct led to a significant decrease of elimination by feces.     

Novel type of ornithine-glutathione double conjugate excreted as a major metabolite into the bile of rats administered clebopride

Rats orally given radioactive Clebopride [[14C]CP; N-(1'-benzyl-4'-piperidyl)-2-[14C]methoxy-4-amino-5-chlorobenzamide++ +], an antiulcer agent, excreted a novel type of ornithine (Orn)-GSH double conjugate in the bile as a major metabolite [( 14C]BMCP), corresponding to 18% of the dose. The present study provides the first evidence for Orn conjugation of a xenobiotic in mammals and demonstrates that the structure of the radioactive conjugate differs fundamentally from those known in birds and reptiles. The structure of the biliary metabolite, [14C]BMCP, purified to homogeneity by silica gel thin layer and reverse phase high pressure liquid chromatography, was elucidated as S-[2-ornithylamino-4-[14C]methoxy-5-(1'-methyl-4'-piperidylamin o) carboxyphenyl]glutathione, based mainly on the following facts: 1) BMCP showed a protonated molecular ion (M + H)+ peak at m/z 683 in the secondary ion mass spectrum and 2) [14C]BMCP afforded Orn, glutamic acid, glycine, S-(2-amino-4-[14C]methoxy-5-carboxyphenyl)cysteine [( 14C]AMCC), and 1-methyl-4-aminopiperidine (MAP) quantitatively, in an equal molar ratio, by complete hydrolysis with peptidase. Thus, BMCP was a metabolite with three enzymatically hydrolyzable amide bonds in addition to the one existing originally in the parent structure of the drug, which produces MAP by peptic digestion. Of the three additional amide bonds of BMCP, one was a novel type of bond formed by condensation of the alpha-carboxylic acid group of Orn with the primary aromatic amino group of the drug and the other two were in the S-glutathionyl residue, substituted for the chlorine atom vicinal to the Orn-conjugating primary amino group in the aromatic ring and affording glutamic acid, glycine, and the S-cysteine conjugate AMCC by hydrolysis of BMCP with the peptidase. Substitution of a methyl group for the benzyl group at the piperidine ring nitrogen atom, leading to the formation of MAP by peptic digestion, also occurred during metabolism of CP to BMCP.     

Metabolism of protein conjugate of desacetyl-alacepril and its effect on angiotensin converting enzyme in renal hypertensive rats

The fate of protein conjugate of desacetyl-alacepril (DU-1227) and its effect on angiotensin I converting enzyme (ACE) activity in renal hypertensive rats were studied. [14C]DU-1227-protein conjugate was prepared by ultrafiltration method and administered intravenously in rats. Elimination of radioactivity of [14C]DU-1227-protein from plasma after injection seemed much slower than that reported of [14C]alacepril (1-[(S)-3-acetylthio-2-methylpropanoyl]-L-prolyl-L-phenylalanine, DU-1219) given orally. In the plasma unbound fraction, captopril and captopril-cysteine were detected. Most tissue levels were higher than plasma levels. Significant reduction of tissue ACE activity was seen after administration of the conjugate. Radioactivity was mostly excreted in feces. Captopril, captopril disulfide and captopril-cysteine were found as urinary metabolites. These findings indicate that protein-bound DU-1227 readily dissociated and released DU-1227 was converted to captopril in vivo and can therefore participate in prolonged hypotensive effect exerted by alacepril.     

Pharmacokinetics of absorption,distribution and elimination of fenfluramine and its main metabolite in man

Previously reported data (Beckett & Brookes, 1967) for the excretion of (±)-fenfluramine and its main metabolite, norfenfluramine, have been examined pharmacokinetically using an analogue computer. A three compartment open model was proposed to simulate the biological processes with one peripheral compartment rapidly equilibrating with the central compartment and the second (tissue) compartment only slowly attaining equilibrium. Good agreement between experimental and computed data was obtained, although marked inter-subject variation was recorded. This was attributed to inter-subject differences in the three body compartments. Differences between the pharmacokinetic parameters obtained after oral and intravenous administration of fenfluramine indicated that the drug was significantly N-dealkylated in the intestine or on a first-pass through the liver.     

Synthesis of N-hydroxyacetaminophen, a postulated toxic metabolite of acetaminophen, and its phenolic sulfate conjugate.

The synthesis of N-hydroxyacetaminophen (N-acetyl-N-hydroxy-p-aminophenol, 4), a postulated toxic metabolite of acetaminophen (N-acetyl-p-aminophenol, 3), and its phenolic sulfate conjugate (potassium N-acetyl-N-hydroxy-p-aminophenyl sulfate) (13) is described. Potassium p-nitrophenyl sulfate was reduced to the hydroxylamine, acetylated, and treated with sulfatase to yield N-hydroxyacetaminophen. The structures assigned are supported by the spectral data (IR, UV, MS, 1H NMR, and 13C NMR). N-Hydroxyacetaminophen was found to be moderately unstable at physiological pH and temperature, whereas it phenolic sulfate conjugate was stable.     

高效液相法测定大鼠血浆中阿苯达唑及其代谢产物

目的：采用HPLC法建立快速测定大鼠血浆中阿苯达唑（ABZ）和阿苯达唑亚砜（ABZSX）的含量,为新制剂的处方筛选和药动学研究奠定基础。方法：在碱性条件下,用乙酸乙酯对血浆进行提取;采用高效液相色谱法,色谱柱为C18柱,流动相为甲醇-乙腈（1∶1）,调节水相比例进行梯度洗脱,在0～28 min,水相比例由70%～30%,在28～30 min其比例由30%～70%;检测波长为292 nm;柱温为35 ℃;流速为1 mL•min-1。结果：ABZ和ABZSX分别在0.025～1.992 mg•L-1和0.025～16.208 mg•L-1呈良好的线性;平均提取回收率分别为96.94%和99.71%;准确度分别为100.42%和102.66%;ABZ和ABZSX日内和日间精密度RSD均＜8%。结论：此法可用于新制剂的药动学研究中。     

Carcinogenicity study of tetramethylthiuram disulfide (thiram) in F344 rats

The carcinogenic potential of tetramethylthiuram disulfide (thiram) was examined in F344 rats. Groups of 50 male and 50 female rats were given thiram in their diet at concentrations of 0.1% and 0.05% for 104 weeks. Similar numbers of male and female rats received the basal diet throughout the experiment. All surviving rats were sacrificed at week 112. The rats given the chemical at 0.1% showed reduced body weight gain, especially in females, and liver dysfunction in biochemical examination of blood in males. Histopathologically, however, no significant lesions or tumor induction attributable to the treatment were observed in any tissue except for dose-dependent reduction of spontaneous leukemia in both sexes and slightly reduced incidences of pituitary and thyroid adenomas in females. Under the present experimental conditions, thiram was not carcinogenic in F344 rats.