Identification and clearance involved in the formation of glucuronides of RT-3003, a new peripheral blood flow enhancer, and its metabolite in rats

Glucuronides of RT-3003 and its metabolite (9-OH-RT-3003), which was hydroxylated at the 9 position on the benzene ring, were separated by HPLC and identified by liquid chromatography (LC)/MS/MS and NMR. The conjugation sites of these glucuronides were determined by nuclear Overhauser effects (NOE) irradiation; RT-3003 was conjugated at an alcoholic hydroxyl group of the hydroxymethyl moiety, and 9-OH-RT-3003 at a phenolic hydroxyl group on a benzene ring and at an alcoholic hydroxyl group of a hydroxymethyl moiety. On a reversed-phase HPLC of 9-OH-RT-3003, alcoholic glucuronide was eluted later than phenolic glucuronide, indicating the high hydrophobicity of alcoholic glucuronide. Clearance for the glucuronidation (ClG) of RT-3003 was lower than the summation of ClG for two types of glucuronidation of 9-OH-RT-3003. ClG of 9-OH-RT-3003 was high in phenolic glucuronide. The activity of UDP-glucuronyltransferase (UDPGT) for RT-3003 was 9.63 times that for 9-OH-RT-3003, and the activity ratio of the two types of glucuronidation of 9-OH-RT-3003 was similar to the ratio of the corresponding ClG. The difference between ClG and UDPGT activity is discussed in association with clearance for the hydroxylation and interaction of substrates with UDPGT.

Key fragments for identification of positional isomer pair in glucuronides from the hydroxylated metabolites of RT-3003 (Vintoperol) by liquid chromatography/electrospray ionization mass spectrometry

The mass spectral properties of glucuronides of the 9- and 10-hydroxylated metabolites of RT-3003 (Vintoperol; (-)-1beta-ethyl-1alpha-hydroxymethyl-1,2,3,4,6,7, 12balpha-octahydroindolo[2,3-a]quinolizine), which were fractionated by high-performance liquid chromatography with fluorescence detection, were investigated using the positive ion electrospray ionization mode. These glucuronides showed predominantly the protonated molecular ion ([M + H](+) ion), and the [M + H](+) ion provided a characteristic product ion spectrum in which abundant ions were obtained at m/z 301, 160 and 142. The first ion, corresponding to the [aglycone + H](+) ion, was produced by neutral loss of the glucuronic acid moiety from the [M + H](+) ion. The product ion spectrum of the [M + H](+) ion of hydroxy-RT-3003 revealed a number of ions common to the glucuronide spectra, suggesting that other two ions observed most likely represent fragmentation of hydroxy-RT-3003. In turn, these glucuronides were positional isomers with respect to the binding site of glucuronic acid. The structures of the isomer pairs were discriminated by the presence of the ion of m/z 318 or 336 in the product ion spectrum. These ions were produced by fission of the C-ring, the same as for the formation of the ions of m/z 160 and 142, as were observed in the product ion spectrum from the [M + H](+) ion of hydroxy-RT-3003. For the formation of these ions, an unusual fragmentation process was proposed, and these ion structures were supported by evidence from the accurate mass measurement data. Additionally, in the sulfates of hydroxylated metabolites, a similar product ion corresponding to the ion of m/z 336 found in the phenolic glucuronides was observed, and was applied for identification of the sulfate metabolites.

Physiologically based pharmacokinetic prediction of p-phenylbenzoic acid disposition in the pregnant rat

Disposition of p-phenylbenzoic acid (PPBA) in the pregnant Wistar rat (for both mother and fetuses) was predicted by using a physiologically based pharmacokinetic model. This model was constructed from ten organs for the mother and eight organs for fetuses, with fetal blood flow based on anatomical circulation in uteri and skin-amniotic fluid drug exchange. Plasma total clearance, and renal and nonrenal clearances were measured, and transplacental clearance, skin-amniotic fluid clearances and fetal metabolic clearance were taken from previously reported compartment analysis. Tissue-to-plasma partition coefficients (Kp) for the mother were almost the same as that of the interstitial fluid space (0.055-0.28), except for the kidney and liver. In contrast, Kp values for fetuses were small when membrane restricted and diffusion-limited uptakes were assumed in brain, gut, spleen, muscle, fat, and skin for the mother. The physiological model successfully predicted the PPBA concentration-time profiles for both mother and fetuses after intravenous injection into the mother. Further, the model could be applied to predict the results obtained via two other routes of administration. Fetal plasma PPBA concentrations were well predicted after PPBA injection into umbilical vein and fetal muscle.

Developmental changes in hepatic microsomal interactions between UDP-glucuronyltransferase and phospholipid in the rat fetus

The interaction of hepatic microsomal UDP-glucuronyltransferase (UDPGT) and phospholipid was studied using rat fetuses from the 16th to 21st day of gestation. UDPGT activity for phenol and p-phenylbenzoic acid, and phospholipid content and fluidity increased with day of gestation. Digestion of microsomes with phospholipase A2 removed a similar ratio of phospholipids throughout the gestation days, whereas UDPGT activity decreased with day of gestation, indicating that UDPGT and phospholipids interacted strongly with day of gestation. Use of various modifiers showed a prominent decrease of UDPGT activity in the later part of gestation with changes in tryptophane residues and amino groups, and no change in activity with modification of thiol groups. These results suggest that tryptophane residues and amino groups interact with phospholipids. The results of this work will be useful in analyzing fetotoxicity associating with glucuronidation.

Disposition kinetics of chemicals with carboxylic, hydroxyl, and amino groups in the near-term fetus of the rat: effect of van der Waals volume on disposition kinetic characteristics

Disposition kinetics from the near-term fetus of the rat were studied by subcutaneous injection of chemicals into the fetus. These studies were conducted with a series of chemicals having carboxylic, hydroxyl, and amino groups. In homologous groups, the mean residence time (MRT) increased with molecular weight, and clearance (Cl) decreased. These pharmacokinetic parameters in each series were correlated significantly with van der Waals volume (Vw). MRT of the hydroxyl group series was higher and Cl lower when compared with chemicals of other series with similar Vw. The steady-state volume of distribution (Vss) of each series showed no remarkable change with molecular weight. Vss of the hydroxyl group series was the highest, followed in order by those of carboxylic and amino groups. The tissue/plasma concentration ratio of the amino group series was higher than those of other series.

The electronic effects of benzoic acid substituents on glycine conjugation

The electronic properties of 3- and 4-substituted benzoic acids were determined by the Pariser-Parr-Pople (PPP) molecular orbital (MO) method and were then related to glycine conjugation using the mitochondria fraction of rat liver. With the exception of nitro- and cyano-substituted compounds, the conjugation activity increased linearly with the decrease in the energy (Elumo) of the lowest unoccupied molecular orbital (LUMO) and the energy (Ehomo) of the highest occupied molecular orbital (HOMO). The differences shown by the nitro- and cyano-substituted compounds have related to the low values of the atomic orbital coefficient (Cl,e) of the carboxyl carbon of LUMO and the negativity of the net charge on the substituent atom. These parameters are discussed in terms of the reactivity of the carboxyl carbon and the interaction between the compounds and enzymes. Regression analysis of the combination of these electronic parameters showed that there was a significant correlation. As far as the effect of the alkyl substituent was concerned, steric hindrance effect was noted in the case of methoxy and dimethylamino groups.

The relationship between the effect of biphenylcarboxylic acid analogs on glyceride synthesis and conformation

The inhibition of biphenylcarboxylic acid analogs on glyceride synthesis was studied in association with conformation of the chemicals. Chemicals used were benzoic acid substituted with phenyl, benzoyl and phenoxy groups, phenylphenyloxyacetic acid and p-phenylacetic acid. Twist angles were calculated by a molecular orbital method. Following oral administration of p-phenylbenzoic acid to the rats for 7 days, the decrease of the triglyceride synthesized from [14C]oleic acid was observed in the adipose tissue. The in vitro inhibitions on the formation of fatty acyl-CoA thioester were examined from the influence on the hippuric acid formation from [14C]benzoic acid using the rat liver slices. In the homologous series, high inhibition was observed in para and meta substituents. None, or low inhibitions of ortho-substituted chemicals were related to the steric hindrance of the phenyl ring against carboxyl groups. This hinderance was associated with conformation and with the geometrical relationship between substituted phenyl rings and carbon atoms of carboxylic acid. In the in vitro inhibition on overall formation of diglyceride and triglyceride from [14C]glycerol, o-phenylbenzoic acid showing no inhibition on hippuric acid formation did not show inhibition. However, other ortho-substituted chemicals showed higher inhibition in comparison with the inhibition on hippuric acid formation. The inhibition of para- and meta-substituted chemicals were higher than the corresponding values of ortho substituted compounds.

A new method of long-term bile collection from unrestrained dogs

A method of long-term bile collection from unrestrained dogs was developed. A steel needle was passed subcutaneously from the animal's right side into the abdomen. A catheter, threaded through this needle, was inserted from the side and brought out below the abdomen. The catheter was introduced into the common bile duct and a vest was then fitted on the dog. The external catheter tip was placed in a collection bottle in the pocket of the vest. This method allows the animal to move freely in its cage. The bile of an unrestrained dog weighing 10 kg was collected for 3 weeks at an output rate of 4.2-4.6ml per hour.

Influence of dietary lipids on glucuronidation and sulfation of phenol and its para substituent in the rat

Rats were fed corn oil-free or corn oil-containing diets for 4 weeks to determine their effect on the competition between glucuronidation and sulfation in phenol and its para substituents. The activities of uridine diphosphate-glucuronyltransferase (UDPGT) on chemicals were enhanced with a 12% corn oil diet, whereas sulfotransferase activity showed no significant change. Following the intravenous injection of p-ethylphenol and p-tert-butylphenol, an increase of glucuronide and a decrease of sulfate were observed in the rats fed the corn oil diet. In contrast, no significant changes were observed in phenol and p-phenylphenol. These results are discussed in association with van der Waals volume (Vw) of substituent and phospholipid dependence of UDPGT.

A new method for the long-term collection of the bile from the unrestrained rabbit

A method for the long term bile collection of the unrestrained rabbit was developed. A steel needle was tunneled subcutaneously from the dorsum of the neck to the abdomen of the animal. A catheter was threaded through this needle from the dorsum and brought out below the abdomen. The catheter was introduced into the common bile duct and the tip on the dorsum was passed through a steel protective coil which was attached to the dorsal skin. This method allows the animal to move freely in the metabolic cage. The bile of the unrestrained rabbit weighing 3.7 kg was collected for 120 hr at 8.9-10.2 ml per hour of the output rate.

Influence of para substituent of phenol on phospholipid dependence of uridine diphosphate-glucuronyltransferase

The influence of para substituent of phenol on the property of phospholipid dependence of uridine diphosphate-glucuronyltransferase (UDPGT) was studied using hepatic microsomes of the rats. para Substituents used were p-ethyl, p-tert-butyl and p-phenyl. Glucuronidations of phenol and its derivatives were inhibited with each other. When phospholipids of the microsomes were removed with phospholipase A2, Vmax and Km decreased in the order phenol, p-ethylphenol, p-tert-butylphenol, p-phenylphenol, indicating that this change by delipidation increased with van der Waals volume (Vw) of para substituent. Arrhenius plots of glucuronidation for phenol and p-ethylphenol exhibited a change in slope, responding to thermotropic property of the membrane labelled with 1,6-diphenyl-1,3,5-hexatriene (DPH). In contrast, p-tert-butyl and p-phenyl substituents showed linear Arrhenius plots. The activation energy (Ea) for glucuronidation of p-phenylphenol was increased by delipidation, whereas Ea of other substrates did not show any remarkable change.

Distribution and disposition associated with compartmentation of body fluid in the developing fetus of the rat

The relationship between the developmental change of the disposition kinetic character for p-phenylbenzoic acid (PPBA) and compartmentalized fluid of the body was investigated in the rat fetus. [14C]Inulin injected into the umbilical vein attained the steady state distribution at 8 min on Day 17 of gestation and at 10 min on Day 21 of gestation. Inulin space (Vi) on Day 17 of gestation was 0.686 ml/g body wt and decreased to 0.542 ml/g on Day 21 of gestation. [14C]Inulin injected into the fetuses on Days 18 and 21 of gestation remained in the fetal body. Hence a determination method of the apparent volume of distribution (Vd) for PPBA was developed using Vi. Vd on Day 17 of gestation was 0.640 ml/g body wt and decreased to 0.454 ml/g on Day 21 of gestation. Body water based on wet body weight showed no significant change. The analysis of PPBA distribution by the compartmentalization of body fluid suggests that the developmental change of Vd is reflected by that of Vi. The elimination rate (K(el)) from the fetus decreased rapidly in the earlier stages of gestation and slowly in the later stages of gestation. The change of the transplacental clearance (Cl) was mainly reflected by that of K(el) throughout the gestation period. However, the change of Vd partly influenced the change of Cl in the later stage of gestation.

The relationship between Van der Waals volume of 4-substituent of phenol and sulfation in the rat

The influence of 4-substituent of phenol on the sulfate conjugation was studied in the rat. 4-Substituents used were 4-ethyl, 4-tert-butyl and 4-phenyl. The in vivo and in vitro sulfations decreased in the order of phenol, 4-ethylphenol, 4-tert-butylphenol and 4-phenylphenol. The activity of sulfotransferase was correlated with the van der Waals volume of 4-substituent. The modification of thiol and arginyl residues of cytosol protein showed a similar degree of inactivation of sulfotransferase to all substituents used. Inactivation by the modification of histidyl residue of the protein increased with the increase of the van der Waals volume of 4-substituent. This result suggests that histidyl residue recognized van der Waals volume of 4-substituent.

Phospholipid dependency of hepatic uridine diphosphate-glucuronyltransferase in the developing fetus of the rat

The developmental change of uridine diphosphate-glucuronyltransferase (UDPGT) was studied using hepatic microsomes of rat fetuses on days 18 and 21 of gestation. Total phospholipid content was higher on day 21 than on day 18, although no significant difference in the composition between the two stages was observed. Lipid removal with phospholipase A2 greatly reduced UDPGT activity for phenol in the later stage of gestation, even though the delipidation ratios in both stages were similar. The fluidity in the hydrocarbon region of the microsomal membrane was higher on day 21 than on day 18. No significant difference in the polarization of N-dansylaziridinyl protein was observed between the stages.

Disposition kinetics in the rat fetus

Disposition kinetics of drug from the fetus were studied by subcutaneous injection of indomethacin, salicylic acid, and diazepam into the fetuses of the rats. The mean residence time (MRT) for drugs increased with the day of gestation and the clearance decreased. The values of MRT were in the order indomethacin greater than salicylic acid greater than diazepam, and degrees of the developmental change of MRT were in the order indomethacin greater than salicylic acid greater than diazepam. The steady-state volume of distribution (Vss) for drugs showed little change, corresponding to no significant change in the tissue/plasma drug concentration ratio. The developmental profile of the rate of transplacental transference calculated from a one-compartment open model decreased with the day of gestation.

A method to inject the umbilical vein of the rat

A technique for injection into the umbilical vein was developed for pharmacokinetic analysis of the fetus, using rats on days 18 and 20 of gestation. The fetus was drawn out of the amniotic sac and incubated in lactated Ringer's solution; this technique showed no influence on the activity of serum enzymes or drug metabolizing enzymes or on the elimination rate for p-phenylbenzoic acid (PPBA). Elimination rate constants (Kel) obtained by using the present method were 6.49 h-1 (18th day) and 5.17 h-1 (20th day) for PPBA, and 1.24 h-1 (18th day) and 0.765 h-1 (20th day) for indomethacin. The experimental results show that the present method gives the actual elimination rate constant of the fetus and distinguishes metabolites in the fetus from those formed in the mother. Indomethacin was found not to be metabolized by the fetus.

Pharmacokinetics of clearance in the maternal-fetal amniotic fluid system of the rat

A pharmacokinetic model of the maternal-fetal amniotic fluid system was designed to permit calculation of clearances from the steady-state concentrations of p-phenylbenzoic acid (PPBA) during infusion of PPBA into the maternal vein and the amniotic fluid of pregnant rats on the 16th to the 21st day of gestation. Transplacental clearance from the fetus to the mother maintained fairly constant values until the 19th day of gestation but decreased on Days 20 and 21 of gestation. Both clearances from the fetus into the amniotic fluid and from the amniotic fluid into the fetus showed higher values during the earlier stages of gestation, indicating that amniotic fluid may play an important role in the pharmacokinetics of PPBA in the fetus during the earlier stage of gestation. Fetal tissue clearance appeared to contribute to the elimination of PPBA in the fetus on Days 20 and 21 of gestation. Transplacental clearance from the mother to the fetus and clearance by nonplacental elimination in the mother increased with the day of gestation. The relationship between developmental changes in clearances and physiological changes in placenta and fetal tissues is discussed. The present model provides a basis for calculation of clearances in the maternal-fetal amniotic fluid system.

Developmental change in clearance of glucuronide of p-phenylbenzoic acid from in vitro kinetic parameters and its correlation with clearance from in vivo in fetus of rat

The developmental change of the intrinsic clearance (Clint) and the hepatic clearance (ClH) for the glucuronidated p-phenylbenzoic acid (PPBA) by uridine 5'-phosphoglucronic acid-glucuronyltransferase (UDPGT) in liver of rat fetus was investigated. The UDPGT activity was stimulated by 225% by Brij 58 which is a detergent. The Clint increased with the day of gestation, remarkably between the 19th and 21st day of gestation, showing nearly the same developmental profile as the Vmax. The Clint in a whole liver on the 21st day of gestation was 246-fold and 7.0-fold higher than those on the 15th and 19th day of gestation, respectively. The ClH showed the similar developmental profile to the Clint. The ClH on the 21st day of gestation was 48.7 times and 6.7 times those on the 17th and 19 the day of gestation, respectively. The ClH on the 20th and 21st day of gestation was about 30% of the corresponding values of the fetal tissue clearance (Clf) from the in vivo data using isolated fetuses. The similarity between the ClH/Clf ratio and the PPBA glucuronide/biliary excretion ratio indicated that the ClH from the in vitro data corresponded with that in the in vivo condition.

Studies on the absorption mechanism for the glucuronide of p-phenyl benzoic acid in fetal compartment

The mechanism responsible for the deconjugation of the glucuronide of p-phenyl benzoic acid (PPBA) in fetal intestine and amniotic fluid was studied in rats. Non-enzymatic hydrolysis of PPBA glucuronide in intestine was little before birth. The activity of beta-glucuronidase (beta-G) in fetus was the highest in intestine, followed by lung and skin. The activity of beta-G in fetal intestine increased with the day of gestation, and increased remarkably between the 18th and 21st day of gestation. PPBA glucuronide injected intraamniotically distributed as PPBA in fetal skin. The fluid of trachea and esophagus showed high distribution of radioactivity and the ratio of PPBA glucuronide in radioactive substances in fetal lung tended to be higher than that in fetal plasma after intraamniotic injection of 14C-PPBA glucuronide. In summary, PPBA glucuronide in amniotic fluid is absorbed into fetal body through skin, lung and intestine after deconjugation.

Change in kinetic properties and metabolic clearance of UDP-glucuronyltransferase for p-phenyl benzoic acid in developing fetus of rat

The hepatic microsomal UDP-glucuronyltransferase (UDPGT) for p-phenyl benzoic acid (PPBA) in the developing fetus of rat was investigated. The kinetic properties of UDPGT in microsome of fetus changed during developmental period. The value of the Vmax for PPBA and uridine 5'-phosphoglucuronic acid (UDPGA) per mg protein increased with the day of gestation, remarkably between the 19th and 21st day of gestation. The developmental profile of the Vmax per g liver was similar to the Vmax per mg protein. Whereas the Vmax in whole liver showed rapid increase during development comparing with the Vmax per g liver. The Km for PPBA and UDPGA showed slower increase with the day of gestation than the corresponding Vmax.

Pharmacokinetics in maternal-fetal unit after intravenous administration of p-phenyl benzoic acid to rat

The pharmacokinetics in maternal-fetal unit of 14C-p-phenyl benzoic acid was studied in intact and bile-duct-cannulated pregnant rats following the intravenous administration. The half life of the maternal blood level was shortened by bile duct-cannulation. However, the effect of bile duct-cannulation on the decay curve of fetal blood level was not recognized. There was no difference in the distribution pattern from whole body autoradiogram and tissue binding between mother and fetus. PPBA level in fetal plasma was different from that in maternal central and peripheral compartment based on pharmacokinetic analysis. The glucuronide levels in fetal intestine and amniotic fluid increased with time. The levels of PPBA and its glucuronide in fetal tissues on the 18th day of gestation were lower than the corresponding levels on the 20th day of gestation. The elimination rate of the glucuronide in amniotic fluid was higher on the 18th day of gestation.

Change in pharmacokinetic character of a p-phenyl benzoic acid in developing fetus of rat

The change in the pharmacokinetic character of p-phenyl benzoic acid (PPBA) in developing fetus of rat was investigated by a constant infusion of 14C-PPBA. PPBA level in tissues increased with the day of gestation. The hepatic clearance for PPBA showed the increase with the stage of development. The excretion of the glucuronide from liver into bile increased with the stage, remarkably between the 19th and 21st day of gestation. The developmental profile of UDP-glucuronyltransferase activity in hepatic microsomes of fetus resembled that of the hepatic excretory function for the glucuronide. The glucuronide level in the amniotic fluid increased with the day of gestation, remarkably between the 19th and 21st day of gestation. The elimination rate of the glucuronide from amniotic fluid determined by intraamniotic injection of the glucuronide decreased linearly with the day of gestation.