Effects of pretreatment with 8018 on the toxicokinetics of soman in rabbits and distribution in mice

The effects of 8018 [3-(2'-phenyl-2'-cyclopentyl-2'-hydroxyl-ethoxy)quinuclidine] on the elimination of soman in rabbits blood and distribution in mice brain and diaphragm were investigated using the chirasil capillary gas chromatographic analysis method. In all experiments, the concentration of P(+)soman was below the detection limit (<0.1 ng x mL(-1)). 8018 (1 mg x kg(-1), im, 10 min pre-treated) could significantly reduce the concentration of P(-)soman in rabbit blood from 53.6 +/- 13.3 to 26.2 +/- 9.70 ng x mL(-1) blood as compared to soman-treated control animal at 15 s following soman injection (43.2 microg x kg(-1), iv). Toxicokinetic parameters showed 8018 could increase clearance (CL((S))) from 20.8 +/- 1.54 to 38.2 +/- 15.3 mLx kg(-1) x s(-1) and reduce AUC of P(-)soman from 2.08 +/- 0.151 to 1.30 +/- 0.564 mg x s x L(-1). 8018 could reduce the concentration P(-)soman in diaphragm from 74.7, 70.5, 88.7 ng x g(-1) to 54.5 45.6, 50.0 ng x g(-1) at the time of 30, 90, 120 s after intoxication of soman subcutaneously vs. soman control respectively, but it had no influence on the concentration of free P(-)soman in brain. Isotope trace experiments showed that it could significantly increase the distribution amount of bound [3H]soman in mice plasma and small intestine during 0-120 min after mice received [3H]soman (0.544 GBq.119 microg x kg(-1), sc) compared to soman control group.     

Stereoselective disposition and tissue distribution of carvedilol enantiomers in rats.

After intravenous bolus injection of rac-carvedilol at 2 mg/kg to the rat, the (+)-(R)- and (-)-(S)-enantiomer levels in the blood and tissues (liver, kidney, heart, muscle, spleen, and aorta) were measured by stereospecific HPLC assay. As compared with the (+)-(R), the (-)-(S) had a larger Vdss (3.32 vs. 2.21 liter/kg), MRT (33.4 vs. 25.6 min), and CLtot (96.1 vs. 83.8 ml/min/kg). AUC comparison after iv and po administration showed systemic bioavailability of the (-)-(S) to be about half that of its antipode, explained by the fact that the free fraction of the (-)-(S) in blood was 1.65-fold greater than that of the (+)-(R). Tissue-to-blood partition coefficient values for the (-)-(S) were 1.6- to 2.1-fold greater than those for the (+)-(R) in all tissues, showing that the (-)-(S) accumulates more extensively in the tissues. These results were consistent with the greater Vdss for the (-)-(S) estimated from systemic blood data. The stereoselective tissue distribution of carvedilol enantiomers results from an enantiomeric difference in plasma protein binding rather than in tissue binding.     

Stereoselective plasma protein binding and target tissue distribution of clausenamide enantiomers in rats

Stereoselective differences in pharmacokinetics between clausenamide (CLA) enantiomers have been found after intravenous and oral administration of each enantiomer to rats. The differences could be associated with protein binding of CLA enantiomers. By equilibrium dialysis methods, the binding of CLA enantiomers to rat plasma protein was investigated. The results showed that mean percentages of (-) and (+)CLA in the bound form were 28.5% and 38.0%, respectively, indicating that the unbound fraction of (-)CLA was higher than that of (+)CLA, which provided an explanation for stereoselective pharmacokinetics of CLA enantiomers in rats. The results also showed that there were species differences in plasma protein binding of (-)-isomer between rats (28.5%) and rabbits (47.2%). Furthermore, effects of plasma protein binding on the distribution of CLA enantiomers to their possible target tissues were observed. The amount of (-)CLA in brain was greater than that of (+)CLA 15 min after administration of each enantiomer to rats. But the results were reverse at 4 h postdose. Further studies in distributional kinetics showed that (-)CLA had a more rapid absorption and distribution to hippocampus, cortex, and cerebellum than (+) CLA. (+)CLA had greater values for T(max), t(1/2) (beta), and AUC(0) (-->infinity), and smaller ones for CL/F and V(d)/F than its antipode. The data indicated that the distribution of (-) and (+)CLA in their target tissues was stereoselective. The stereoselective distribution might be involved in the metabolism and transport of two enantiomers in the central nerve system.     

Stereoselective pharmacokinetics of diniconazole enantiomers in rabbits

Diniconazole [(E)-(RS)-1-(2,4,-dichlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazole-1-yl)pent-1-en-3-ol)] is a potent triazole fungicide. The enantioselective pharmacokinetics of diniconazole enantiomers in rabbits was studied via intravenous (i.v.) injection. The pharmacokinetics and the enantiomer fraction (EF) were determined using normal high-performance liquid chromatography with diode array detection and a cellulose-tris-(3,5-dimethylphenylcarbamate)-based chiral stationary phase (CDMPC-CSP). The time-concentration curves in plasma were fitted by a two-compartment open mode. The results showed that the concentration of S-diniconazole in plasma decreased faster than that of R-diniconazole, and EFs increased with time after administration of racemic diniconazole (rac-diniconazole). The R-/S-enantiomer ratio of the area under the time-plasma concentration curve (AUC(0-infinity)) after administration was 1.52. The total plasma clearance value of S-enantiomer was 1.57-fold higher than that of the R-diniconazole. These results indicate substantial stereoselectivity in the kinetics of diniconazole enantiomers in rabbit.     

The tissue distribution in mice and pharmacokinetics in rabbits of oxaliplatin liposome

A rapid, sensitive, and simple high-performance liquid chromatographic (HPLC) method with an ultraviolet detector (UV) has been developed for the determination of oxaliplatin in the plasma of rabbits and tissues of mice. The sample preparation was carried out by complexation with 0.5?mL of DETC (diethyl-dithiocarbamate) solution and extracted by ether and chloroform. Then, 20?μL of supernatant was injected into the HPLC system with 0.25?mol/L of sodium chloride solution and methanol (30:70 v/v) as the mobile phase at a flow rate of 1.0?mL/min. Separation was performed with a C₁₈ column at 25°C. The peak was detected at 254?nm. The calibration curve was linear (R²?≥?0.9995) in the concentration range of 0.1~200?μg/mL in plasma and tissues. The intra- and interday variation coefficients were not more than 2.61 and 3.83%, respectively. The limit of detection was 20?ng/mL. The mean recoveries of oxaliplatin were ranged from 97.83 to 104.17% in plasma and tissues. The present method has been successfully applied to the pharmacokinetic study of oxaliplatin liposome in mice and rabbits.     

Stereoselective degradation kinetics of tebuconazole in rabbits

Tebuconazole[(RS)-1-p-chlorophenyl-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)pentan-3-ol] is a potent triazole fungicide and consists of a pair of enantiomers. The enantioselective degradation kinetics of tebuconazole was investigated in rabbits by intravenous (iv) injection. The concentrations of (-)-(R)-tebuconazole and (+)-(S)-tebuconazole in plasma and tissues were determined by HPLC with a cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phase. Enantioselective analysis methods for this fungicide in plasma and tissues were developed and validated. Good linearities were obtained over the concentration range of 0.25-25 mg/l for both enantiomers. The degradation followed pseudo-first-order kinetics and the degradation of the (+)-(S)-tebuconazole was much faster than that of the (-)-(R)-tebuconazole in plasma after administration of racemic tebuconazole. This study also indicated that environmental assessment of enantiomeric degradation may be needed to fully evaluate risks of tebuconazole use.     

Stereoselective metabolism of the herbicide fluroxypyr methylheptyl ester in rabbits

We investigated the stereoselective degradation kinetics of fluroxypyr methylheptyl ester (FPMH) in rabbits using a chiral high-performance liquid chromatographic method. In 20% rabbit plasma, the half lives of (+)-FPMH and (-)-FPMH were 2.5 and 10.9 min, respectively. Thus, the enantioselective degradation was faster for (+)-FPMH than for (-)-FPMH in rabbit plasma in vitro, and there was no chiral conversion or transformation during incubation of the plasma. The degradation of (+)-FPMH was also much faster than that of the (-)-FPMH in the kidney, lung, and muscle after the intravenous administration of 50 mg/kg racemic FPMH (rac-FPMH), whereas the concentrations of FPMH were below the limit of quantification in other tissues. Furthermore, 98% rac-FPMH was quickly (within 10 min) hydrolyzed to fluroxypyr (FP) in rabbit liver microsomes. Therefore, we examined FP in rabbit plasma and tissues in vivo. We detected FP in all tissues; its concentration was higher in the urine than in the other tissues. FP was rapidly excreted unchanged, principally in the urine. The data presented here are important for a more thorough understanding of this pesticide and should be useful for its full environmental assessment.     

Stereoselective metabolism of fenoxaprop‐ethyl and its chiral metabolite fenoxaprop in rabbits

The stereoselective metabolism of the enantiomers of fenoxaprop‐ethyl (FE) and its primary chiral metabolite fenoxaprop (FA) in rabbits in vivo and in vitro was studied based on a validated chiral high‐performance liquid chromatography method. The information of in vivo metabolism was obtained by intravenous administration of racemic FE, racemic FA, and optically pure (−)‐(S)‐FE and (+)‐(R)‐FE separately. The results showed that FE degraded very fast to the metabolite FA, which was then metabolized in a stereoselective way in vivo: (−)‐(S)‐FA degraded faster in plasma, heart, lung, liver, kidney, and bile than its antipode. Moreover, a conversion of (−)‐(S)‐FA to (+)‐(R)‐FA in plasma was found after injection of optically pure (−)‐(S)‐ and (+)‐(R)‐FE separately. Either enantiomers were not detected in brain, spleen, muscle, and fat. Plasma concentration–time curves were best described by an open three‐compartment model, and the toxicokinetic parameters of the two enantiomers were significantly different. Different metabolism behaviors were observed in the degradations of FE and FA in the plasma and liver microsomes in vitro, which were helpful for understanding the stereoselective mechanism. This work suggested the stereoselective behaviors of chiral pollutants, and their chiral metabolites in environment should be taken into account for an accurate risk assessment. Chirality, 2011. © 2011 Wiley‐Liss, Inc.     

Fibronectin involvement in granulation tissue and wound healing in rabbits

This study describes the distribution of fibronectin and its association with reticulin fibers (type III collagen) and hyaluronic acid in shallow rabbit wounds. Linear incisions were made dorsally with a surgical blade. Animals were sacrificed and 1,2,3,4,5, and 8 day wounds were examined using peroxidase-antiperoxidase to localize affinity-purified antibodies to fibronectin. Tissue samples were also stained with hematoxylin and eosin in addition to silver stains for reticulin, and Alcian blue for hyaluronic acid. After wounding, the incision filled with a fibrin clot that stained positively for fibronectin. The underlying dermis and adjacent, unwounded dermis also contained fibronectin. Epidermal cells that migrate from the wound margin between the clot and the dermis were in direct association with fibronectin in these wound components. By 72 hr, epidermal continuity was reestablished. Early granulation tissue formation was apparent just below the epidermis 5 day wounds. Fibronectin was observed in the matrix surrounding individual fibroblasts and codistributed with reticulin fibers and hyaluronic acid in both 5 and 8 day wounds. Granulation tissue of 8 day wounds stained intensely for fibronectin and extended to a greater depth in the reticular dermis. Dense fibrillar networks of fibronectin and fibroblasts were aligned parallel to the epidermis, giving the granulation tissue a highly structured and organized appearance. Fibroblasts contained fibronectin and were surrounded by less fibronectin at the wound periphery than within the granulation tissue. These findings suggest that fibronectin may be important in the reconstruction of tissues during repair by functioning as an extracellular scaffold for migrating cells.     

Studies on hepatotoxicity and toxicokinetics of colchicine

Colchicine (COL) is an alkaloid existing in plants of Liliaceous colchicum. It has widely been used in the treatments of many diseases, such as gout, Familial Mediterranean Fever, and tumor. However, the adverse effects of COL are an obstacle to its safe use. The present studies explored the role of metabolic demethylation in the development of COL‐induced hepatotoxicity. We found that inhibition of CYP3A increased the susceptibility of mice to COL hepatotoxicity, and induction of CYP3A decreased the susceptibility of animals to the hepatotoxicity. The toxicokinetic study demonstrated that pretreatment with ketoconazole caused elevated area under the concentration‐time curve of COL. Three demethylation metabolites of COL were found to be less hepatotoxic than the parent compound. It appears that the formation of electrophilic demethylation metabolites was not involved in the development of COL‐induced liver injury.     

Inhibition of epicuticular wax deposition on cabbage by ethofumesate

The weight of epicuticular wax on the surface of cabbage (Brassica oleracea var. Capitata `Market Prize') leaves was reduced by soil treatments of ethofumesate (2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate) and EPTC (S-ethyl dipropylthiocarbamate). Separation of epicuticular wax into major components by gas-liquid chromatography indicated that ethofumesate decreased the deposition of n-nonocosane and n-nonocosan-15-one on cabbage leaves but increased the deposition of a minor component, the long chain waxy esters. EPTC was less inhibitory to n-nonocosan-15-one deposition than was ethofumesate. EPTC did not increase long chain waxy ester deposition. Scanning electron micrographs revealed that ethofumesate almost totally eliminated the epicuticular wax on cabbage leaves while EPTC only diminished it. Cuticular transpiration was increased by ethofumesate but not by EPTC. Ethofumesate appears to be a more potent inhibitor of epicuticular wax deposition than EPTC.     

Serology and tissue lesions in rabbits immunized with Streptococcus mutans

Rabbits were immunized i.v. or i.d. with sterile suspensions of disrupted Streptococcus mutans strain MT703 or K1R. Indirect immunofluorescence assays indicated that sera from four of 10 rabbits immunized i.d. contained antibodies reactive with monkey and human heart and kidney components; 19 of 24 rabbits immunized i.v. had antibodies reactive with these tissues. Heart-reactive antibodies were also detected by immunoelectrophoresis and indirect radioimmunoassay. These antibodies were absorbed well by cytoplasmic membranes, a whole cell extract, and an alkali extract of S. mutans but only weakly by intact bacteria. Between 6 and 8 weeks after the first i.v. administration of S. mutans vaccines, rabbits developed proteinuria and hematuria with subsequent weight loss and lethargy. Approximately 25% of the animals died from illness between the fifth and sixth month of immunization. In 13 of 15 rabbits, immune deposits of C3 and IgG, IgM, or IgA and fibrinogen were seen in kidneys within the glomeruli, basement membranes of the peritubular capillaries, and in the interstitium. In the heart, deposits were seen along the capillaries of the myocardium. In 8 of 14 rabbits, focal deposits of S. mutans antigen were detected in glomeruli and in the kidney interstitium. The kidneys showed gross pathologic and histopathologic changes. Most kidneys were pale and enlarged. Microscopic examination revealed hypercellularity of the glomeruli, presence of neutrophils, thickening of glomerular and tubular basement membranes, tubular atrophy, edema, and fibrosis of the interstitium. The kidney disease presented features of poststreptococcal glomerulonephritis. Microscopic examination of heart sections revealed mild perivascular infiltration by polymorphonuclear leukocytes and plasma cells in some of the rabbits.     

Ectopic spleen tissue in the pancreas of Himalayan rabbits

Ectopic foci of splenic tissue were observed in the pancreas of nine of 48 Himalayan rabbits. One of 24 males and eight of 24 females were affected.     

Artesunate: developmental toxicity and toxicokinetics in monkeys

BACKGROUND: The developmental toxicity, toxicokinetics, and hematological effects of the antimalarial drug, artesunate, were previously studied in rats and rabbits and have now been studied in cynomolgus monkeys. METHODS: Groups of up to 15 pregnant females were dosed on Gestation Days (GD) 20–50 or for 3–7‐day intervals. RESULTS: At 30 mg/kg/day, 6 embryos died between GD30 and GD40. Histologic examination of 3 live embryos (GD26–GD36) revealed a marked reduction in embryonic erythroblasts and cardiomyopathy. At 12 mg/kg/day, 6 embryos died between GD30 and GD45. Four surviving fetuses examined on GD100 had no malformations, but long bone lengths were slightly decreased. At the developmental no‐adverse‐effect‐level (4 mg/kg/day), maternal plasma AUC was 3.68 ng.h/mL for artesunate and 6.93 ng.h/ml for its active metabolite, dihydroartemisinin (DHA). No developmental toxicity occurred with administration of 12 mg/kg/day for 3 or 7 days, GD29–31 or GD27–33 (maternal plasma AUC of 9.84 ng.h/mL artesunate and 16.4 ng.h/mL DHA). Exposures at embryotoxic doses were substantially lower than human therapeutic exposures. However, differences in monkey and human Vss for artesunate (0.5 L/kg vs. 0.18 L/kg) confound relying solely on AUC for assessing human risk. Decreases in reticulocyte count occur at therapeutic doses in humans. Changes to reticulocyte counts at embryotoxic doses in monkeys (≥12 mg/kg/day) were variable and generally minor. CONCLUSIONS: Artesunate was embryolethal at ≥12 mg/kg/day when dosed for at least 12 days at the beginning of organogenesis, but not when dosed for 3 or 7 days, indicating that developmental toxicity of artesunate is dependent upon duration of dosing in cynomologus monkeys. Birth Defects Res (Part B) 83:418–434, 2008. © 2008 Wiley‐Liss, Inc.