肾脏是体内N~G-D-硝基精氨酸单向手性转化的主要器官

目的　研究NG D 硝基精氨酸 (NG nitro D arginine,D NNA)在体内发生手性转化的的部位。方法　考察肾脏结扎对于D NNA诱导大鼠动脉压升高活性的变化 ,并运用毛细管电色谱 (capillaryelectrochromatography ,CEC)分析技术测定D NNA在体内手性转化的情况。结果　肾脏结扎使大鼠完全丧失对D NNA (32mg·kg-1)升高血压反应 ,但不影响由NG L 硝基精氨酸 (NG nitro L arginine ,L NNA)(16mg·kg-1)引起的升压反应。而D NNA/肾匀浆孵育液(32mg·kg-1)则可使肾脏结扎大鼠产生升压反应。CEC血药检测证实D NNA在大鼠体内转化生成L NNA ,而L NNA在体内未被代谢生成D NNA ;肾脏结扎则使D NNA的手性转化大量减少。结论　D NNA在大鼠体内可单向代谢转化L NNA ,肾脏是D NNA发生手性转化的主要器官     

D-dopa is unidirectionally converted to L-dopa by D-amino acid oxidase, followed by dopa transaminase

1. Many studies have shown that administration of d-3, 4-dihydroxyphenylalanine (D-dopa) produces contralateral rotation in hemi-parkinsonian animals comparable to L-dopa, with less potency and slower onset. It was postulated that D-dopa was converted to L-dopa to produce these effects. 2. To investigate the postulated chiral inversion of D-dopa to L-dopa and the related mechanism, an enantiomeric separation method for D- and L-dopa using HPLC was first established. Then, rat kidney homogenates containing D-dopa or L-dopa were incubated and subjected to HPLC to detect traces of respective enantiomer generation. The mechanism of the chiral inversion of d-dopa was explored by direct measurement of the production of L-dopa in kidney homogenates. D-dopa incubations containing different concentrations of an inhibitor of D-amino acid oxidase (DAAO) and an inhibitor of dopa transaminase were measured for L-dopa generation using HPLC. The role of DAAO in the chiral inversion of D-dopa to L-dopa was further investigated by using purified DAAO and mutant ddY/DAAO- mouse kidney lacking DAAO activity. 3. In rat kidney homogenate, D-dopa was, indeed, converted to L-dopa, whereas L-dopa was not converted to D-dopa. Sodium benzoate, a selective inhibitor of DAAO, blocked L-dopa generation in a concentration-dependant manner. In contrast with kidney homogenates of wild-type ddY/DAAO+ mice, those of mutant ddY/DAAO- mice lacking DAAO activity did not convert D-dopa to L-dopa unless exogenous DAAO protein was added. Conversely, when carbidopa, an inhibitor of dopa transaminase, was added to the homogenates, significant inhibition of L-dopa production was noted. 4. These results prove the proposal that d-dopa undergoes unidirectional chiral inversion and further suggest that D-dopa is first oxidatively deaminated by DAAO to its alpha-keto acid and then transaminated by dopa transaminase to L-dopa.     

Biological implications of oxidation and unidirectional chiral inversion of D-amino acids

Recent progress in chiral separation of D- and L-amino acids by chromatography ascertained the presence of several free Damino acids in a variety of mammals including humans. Unidirectional chiral inversion of many D-amino acid analogs such as exogenous NG-nitro-D-arginine (D-NNA), endogenous D-leucine, D-phenylanine and D-methionine have been shown to take place with inversion rates of 4-90%, probably dependent on various species D-amino acid oxidase (DAAO) enzymatic activities. DAAO is known to catalyze the oxidative deamination of neutral and basic D-amino acids to their corresponding α-keto acids, hydrogen peroxide and ammonia, and is responsible for the chiral inversion. This review provides an overview of recent research in this area: 1) oxidation and chiral inversion of several D-amino acid analogs in the body; 2) the indispensable but insufficient role of DAAO particularly in the kidneys and brain for the oxidation and chiral inversion of D-amino acids analogs; and 3) unidentified transaminase(s) responsible for the second step of chiral inversion. The review also discusses the physiological significance of oxidation and chiral inversion of D-amino acids, which is still a subject of dispute.     

Effects of clofibric acid on the biliary excretion of benoxaprofen glucuronide and taurine conjugate in rats

Benoxaprofen (BOP) is a 2-methyl propionic acid derivative with anti-inflammatory activity. BOP has an asymmetric carbon, and receives chiral inversion from R to S in vivo. BOP is metabolized to glucuronide (BOP-G) and taurine conjugate (BOP-T). The configuration of BOP-G is mainly S, and that of BOP-T is R. Chiral inversion of R to S of the propionic acid moiety and amino acid conjugation of carboxyl compounds proceed via an acyl CoA intermediate. It is known that fibrates, used in hyperlipidemia, induce acyl CoA synthetase and increase CoA concentration. We administered racemic BOP (10 mg/kg body weight) to rats (CFA+) pre-administered clofibric acid (CFA, 280 mg/kg/day), and studied BOP, BOP-G, and BOP-T enantiomer concentrations in plasma and bile up to 12 h after administration. The findings were compared with those in rats (CFA-) that had not received CFA. Furthermore, we studied the amounts of BOP-G enantiomer produced by glucuronidation in vitro using microsomes pretreated with CFA. The amounts of (S)-BOP-G in CFA+ rats were 2.7-fold larger than that in CFA- rats. Although (R)-BOP-T was excreted in CFA- rats, BOP-T could not be detected in CFA+ rats. Plasma clearance values of racemic BOP and (S)-BOP in CFA+ rats were 5-fold and 6-fold larger than those in CFA- rats, respectively. (S)-BOP-G formation activities were higher than (R)-BOP-G formation activities in both CFA+and CFA- microsomes. These findings suggest that CFA increases biliary excretion of (S)-BOP-G and facilitates plasma elimination of BOP, and further suggests that CFA predominantly induces chiral inversion to S rather than metabolic reaction to (R)-BOP-T, resulting in an increase of (S)-BOP-G.     

Stereoselectivity in Pharmacokinetics of Rivoglitazone,A Novel Peroxisome Proliferator-Activated Receptor γ Agonist,in Rats and Monkeys: Model-Based Pharmacokinetic Analysis and In Vitro-In Vivo Extrapolation Approach

Stereoselectivity in pharmacokinetics of rivoglitazone, a novel peroxisome proliferator-activated receptor γ agonist, in rats and monkeys was examined. The pharmacokinetic model involving chiral inversion explained well the plasma profiles of R-isomer and S-isomer after intravenous and oral administration of (R)-rivoglitazone or (S)-rivoglitazone to rats and monkeys. The high stereoselectivity was evaluated in chiral inversion clearance (R/S ratio: 7.92), metabolic clearance (5.78), and volume of distribution (4.04) in rats; however, these were low (1.73, 1.31, and 1.06) in monkeys. The stereoselectivity in chiral inversion was also observed in in vitro incubation studies in plasma, and the R/S ratio of chiral inversion showed high correlation with the R/S ratio of plasma unbound fraction. The metabolic clearance of the primary five metabolic pathways of rivoglitazone was evaluated from an in vitro–in vivo extrapolation approach using rat and monkey liver microsomes. The high stereoselectivity in metabolic clearance in rat was evaluated (R/S ratio: 5.78), which was assumed to be because of the stereoselectivity in plasma unbound fraction, on the contrary, that in monkeys exhibited low stereoselectivity (0.774). Thus, the stereoselectivity in plasma unbound fraction was estimated to be a major determinant of stereoselectivity in pharmacokinetics of rivoglitazone in rats and monkeys.     

Pharmacokinetics of selected chiral flavonoids: hesperetin, naringenin and eriodictyol in rats and their content in fruit juices

The majority of pharmacokinetic studies of individual flavonoids or after ingestion of foodstuffs have overlooked the chirality of some of these xenobiotics. In order to characterize for the first time the stereoselective pharmacokinetics of three flavonoids, hesperetin, naringenin and eriodictyol were intravenously administered (20 mg/kg) to male Sprague-Dawley rats, and their stereospecific content was assessed in various fruit juices. Concentrations in serum, urine and fruit juices were characterized via HPLC and verified by LC/MS. Short half-lives (3-7 h) in serum were observed, while a better estimation of half-life (12-48 h) and the other pharmacokinetic parameters was observed using urinary data. The three flavonoids are predominantly excreted via non-renal routes (fe values of 3-7%), and undergo rapid and extensive phase II metabolism. The (2S)-epimers of the flavonoid glycosides and the S(-)-enantiomers of the aglycones were predominant and in some instances the organic fruit juices had higher concentrations than the conventional fruit juices. This study reports for the first time the stereospecific pharmacokinetics of three chiral flavonoids and their stereospecific content in fruit juices. It also reports for the first time the stereospecific pharmacokinetics of flavonoids employing urine as a more reliable biological matrix.     

N(G)-nitro-L-arginine impairs the anticonvulsive action of ethosuximide against pentylenetetrazol

N(G)-nitro-L-arginine (NNA; an inhibitor of nitric oxide synthase) in a dose of 40 mg/kg impaired the protective activity of ethosuximide against the clonic phase of pentylenetetrazol-induced seizures in mice. The ED50 value of ethosuximide was significantly increased from 108 to 158 mg/kg. NNA (40 mg/kg) was ineffective against the protective effects of diazepam, phenobarbital and valproate against pentylenetetrazol-induced seizures. NNA (40 mg/kg) did not influence the plasma levels of the antiepileptic drugs studied, so a pharmacokinetic interaction is not probable. L-Arginine (500 mg/kg) prevented the NNA-induced reduction of the anticonvulsive activity of ethosuximide. It can be concluded that nitric oxide participates in the expression of the anticonvulsive action of ethosuximide, but not that of diazepam, phenobarbital and valproate, against pentylenetetrazol-induced seizures.     

Effect of i1 imidazoline receptor agonist, moxonidine, in nitric oxide-deficient hypertension in pregnant rats

Decreased nitric oxide production has been reported in preeclampsia, which is also frequently associated with glucose intolerance. It was thus considered of interest to investigate the effects of moxonidine, a centrally acting antihypertensive drug that reduces insulin resistance, in a rat model of preeclampsia. Hypertension was induced in Wistar rats by dietary l-NNA (N(omega)-nitro-L-arginine, 0.063%, 31 mg/kg/d, days 13-19 of gestation) and, over the same period, moxonidine or vehicle was administered orally (2 mg/kg/d by gavage). On day 20, blood pressure was measured in the pentobarbital anesthetized animals, glucose tolerance was tested (2 g/kg glucose i.p.), and morphologic studies were conducted on the litter to determine the benefits with respect to fetal outcome. Hypertension was reduced with daily moxonidine treatment (P < 0.05). Basal plasma insulin and insulin/glucose index were decreased with moxonidine treatment evidencing improved insulin sensitivity in the control and l-NNA-treated pregnant rats (P < 0.05). After glucose challenge, plasma insulin increased in all the groups as expected and plasma insulin and insulin/glucose index were significantly higher in the l-NNA group than in the control, moxonidine, or l-NNA + moxonidine groups (P < 0.05 for time 60 minutes). Thus, moxonidine improved glucose tolerance in l-NNA-treated pregnant rats. Moreover, moxonidine treatment very effectively decreased the number of necroses (1 necrosis in 71 fetuses in the l-NNA + moxonidine group versus 15 necroses in 79 fetuses in the l-NNA group, P < 0.01). In conclusion, the 7-day treatment with moxonidine suppressed hypertension and reduced glucose intolerance and fetal necrosis, thus demonstrating the effectiveness of moxonidine in the preeclamptic model.     

Stereoselective pharmacokinetic analysis of valnoctamide, a CNS-active chiral amide analogue of valproic acid, in dogs, rats, and mice

The purpose of this study was to evaluate the stereoselective pharmacokinetics of valnoctamide (VCD) in dogs, rats, and mice; which are the most common animal models for pharmacokinetic, pharmacologic, and toxicologic evaluation; and to compare it with previously published human data. Racemic VCD (mixture of four stereoisomers) was administered intravenously to six mongrel dogs and to rats (five rats per time-point), and intraperitoneally to mice (five mice per time-point). Plasma concentrations of the individual stereoisomers were measured by a stereospecific gas chromatography assay. In dogs, (2S,3R)-VCD had a larger clearance (0.33 L/h x kg) and a larger volume of distribution (0.79 L/kg) than its two diastereomers (0.24-0.25 L/h x kg and 0.65 L/kg, respectively). A tendency toward slightly higher clearance and volume of distribution values for (2S,3R)-VCD was observed in rats and mice as well. Consequently, in all three animal species the half-life (t1/2) of (2S,3R)-VCD was not different from the t1/2 of the other three VCD stereoisomers. The stereoselective pharmacokinetics of VCD as observed in dogs, rats, and mice is in line with the stereoselectivity previously observed in healthy subjects and epileptic patients.     

Nitric oxide and convulsions in 4-aminopyridine-treated mice

We studied whether N(G)-nitro-L-arginine (NNA), an inhibitor of nitric oxide (NO) synthase as well as L-arginine and molsidomine, two agents elevating NO, influenced convulsions caused by 4-aminopyridine, a K+ channel blocker in mice. NNA, in a dose known to decrease level of NO (40 mg x kg(-1)), enhanced the seizure susceptibility to intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) 4-aminopyridine. L-arginine (500 mg x kg(-1)) and molsidomine (20 mg x kg(-1)) alone did not influence 4-aminopyridine-induced seizure activity. Surprisingly, the proconvulsant effect of NNA upon clonic and tonic seizures was potentiated by molsidomine (20 mg x kg(-1)). No influence of L-arginine on the proconvulsant effect of NNA was found.Taking into account the proconvulsant effect of NNA, an involvement of NO-mediated events in the mechanism of convulsive activity of 4-aminopyridine might be postulated. However, the ineffectiveness of L-arginine and molsidomine to suppress the convulsive activity of 4-aminopyridine as well as a paradoxical potentiation of the proconvulsant effect of NNA by molsidomine seem to exclude the impact of NO pathway on 4-aminopyridine-induced convulsions in mice. Our data suggest that the proconvulsant effect of NNA in this seizure model is caused by other, not related to NO, mechanisms.     

N omega-nitro-L-arginine attenuates the accumulation of aortic cyclic GMP and the hypotension produced by zaprinast.

To determine if N omega-nitro-L-arginine (NNA), an inhibitor of the synthesis and/or release of endothelium-derived relaxing factor (EDRF), alters the response to zaprinast, a selective inhibitor of cyclic GMP (cGMP) phosphodiesterase, zaprinast (3-30 mg/kg) or vehicle (1 ml/kg) was given to conscious, spontaneously hypertensive rats (SHR) in a cumulative i.v. dose-response manner 30 min after pretreatment with NNA (1 or 3 mg/kg) or saline (1 ml/kg). Mean arterial pressure (MAP) was measured 5 min after each dose of zaprinast. Five minutes after the last dose of zaprinast (30 mg/kg), the rats were anesthetized with pentobarbital (25 mg i.v.). A segment of the abdominal aorta was freeze-clamped in situ and removed for the determination of cGMP levels. NNA (3 mg/kg) decreased basal aortic cGMP levels by 54% and increased MAP by 37 +/- 2 mm Hg. Zaprinast (30 mg/kg) increased aortic cGMP by 187% and decreased MAP by 49 +/- 4 mm Hg. NNA (3 mg/kg) reduced the accumulation of cGMP in aortic tissue (from 4.1 +/- 0.4 to 1.3 +/- 0.1 fmol/microgram protein) and attenuated the depressor response (from -49 +/- 4 to -31 +/- 4 mm Hg) produced by zaprinast. These data are consistent with the hypothesis that NNA inhibits the tonic release of EDRF and that the depressor effects of zaprinast are due, at least in part, to the potentiation of the vasodilator effects of EDRF in vivo. Moreover, since the changes in MAP produced by NNA and zaprinast were significantly correlated with cGMP levels in aortic tissue, the concentration of cGMP in vascular tissue may be a determinant of blood pressure in SHR.     

Pharmacokinetics of halofantrine in the rat: stereoselectivity and interspecies comparisons

The antimalarial drug, halofantrine, is chiral and is administered clinically as the racemate. In order to define the pharmacokinetic properties of halofantrine enantiomers in the rat, male Sprague-Dawley rats (264-311 g) were given halofantrine HCl orally (n = 5; 14 mg/kg) or intravenously (i.v.) (n = 5; 2 mg/kg). Plasma samples were collected over a 72 h period, and these were assayed for halofantrine enantiomer concentrations using a stereospecific reverse phase HPLC assay. After dosing by both routes of administration the (+) enantiomer was found to have significantly higher AUC, and higher Cmax after oral dosing. Pharmacokinetic analysis indicated that in the rat, the (+) enantiomer is cleared slower, and is less extensively distributed than its antipode. The bioavailability of the enantiomers after oral administration was less than 27%. Urinary excretion was a negligible route of elimination of unchanged drug. Using allometry, the pharmacokinetics of (+/-)-halofantrine in rats scaled nicely with literature data from dogs and humans. The pharmacokinetic properties of halofantrine enantiomers in the rat resembled those seen in humans, indicating that the rat is a good model for the study of halofantrine pharmacokinetics.     

Stereospecific interaction of tocainide with the cardiac sodium channel

The antiarrhythmic action of type I antiarrhythmic drugs may be mediated via binding of the drugs to a receptor associated with the cardiac sodium channel. This suggested that the effects of type I drugs might be stereospecific. We measured the effect of the tocainide stereoisomers (which have stereospecific antiarrhythmic effects) on conduction time and on radioligand binding to the cardiac sodium channel. The concentration-dependent effects of the individual enantiomers of tocainide on interventricular conduction time measured during constant rate ventricular pacing at 350 msec were assessed in 47 isolated perfused rabbit heart preparations. Significant increases (p less than 0.05) in conduction time occurred for both R-(-)-tocainide (75 microM, 10 +/- 5 msec) and S-(+)-tocainide (150 microM, 4 +/- 1 msec). R-(-)-Tocainide was more potent than the S-(+)-tocainide in prolonging conduction time (p less than 0.05). This stereospecific prolongation of conduction time suggested a stereospecific interaction with the sodium channel. The affinities of the enantiomers for the channel were measured with a radioligand binding assay using [3H]batrachotoxinin benzoate and freshly isolated cardiac myocytes. Both enantiomers inhibited [3H]batrachotoxin benzoate binding, but the IC50 (+/- SD) values were different: R-(-)-tocainide 184 +/- 8 microM; S-(+)-tocainide, 546 +/- 37 microM (p less than 0.003). Tocainide isomers are stereospecific in terms of prolonging conduction time and in binding to the sodium channel. The stereospecific electrophysiologic effects of tocainide may result from binding to a receptor associated with the cardiac sodium channel.     

Different effects of nitric oxide synthase inhibitors on convulsions induced by nicotine in mice

Acute intraperitoneal (i.p.) administration of N(G)-nitro-L-arginine (NNA, 10, 20 and 40 mg/kg), a non-selective nitric oxide synthase (NOS) inhibitor, significantly and dose-dependently decreased the incidence of convulsions induced by i.p. nicotine (NIC) in mice, whereas 7-nitroindazole (7NI, 50 and 100 mg/kg i.p.), a selective neuronal NOS inhibitor, had a proconvulsant effect. Aminoguanidine (100 mg/kg ip), a specific inducible NOS inhibitor, remained without an effect on convulsive behavior. L-arginine, a nitric oxide (NO) precursor, which independently has no effect on convulsions, markedly reversed the anticonvulsant effect of NNA; yet only partially reversed the proconvulsant effect of 7NI when injected at 500 mg/kg i.p.. Convulsions evoked by intracerebroventricular injection of NIC were significantly suppressed by ip NNA(40 mg/kg i.p.) and enhanced by i.p. 7NI (100 mg/kg i.p.); however, these effects of NNA and 7NI were less potent than those seen when NIC was administered i.p.. The present study revealed essential differences in the action of NOS inhibitors in NIC-induced convulsions. It appears that only NO produced by constitutive NOS is involved in the mechanism of NIC-induced convulsions. The proconvulsant effect of 7NI may result from the mechanisms unrelated to NOS inhibition.     

17-beta estradiol independently regulates erythropoietin synthesis and NOS activity during hypoxia

We reported previously that 17-beta estradiol (E2-beta) attenuates hypoxic induction of erythropoietin (EPO) synthesis in rats. We hypothesized this attenuation is mediated by increased nitric oxide (NO) bio-availability. To investigate this hypothesis, ovariectomized estrogen-depleted rats were instrumented with arterial and venous catheters and treated with either E2-beta (20 microg/24 hrs) or vehicle (polypropylene glycol) for 7 days. Rats were placed in Plexiglas boxes and administered a bolus of either the NO synthase inhibitor, Nomega-nitro-L-arginine (l-NNA, 15 mg/kg) or saline. Following this bolus, saline or l-NNA was continuously infused (15 mg/kg/h) throughout the 8 hours of hypoxic exposure (12% O2). Hypoxia increased plasma NO metabolites (NOx) in both saline groups but more in E2-beta-treated rats. l-NNA prevented this increase in both groups. Renal endothelial NO synthase (NOS) expression was unaltered by hypoxia, l-NNA, or E2-beta. Despite preventing increases in plasma NOx during hypoxia, l-NNA did not affect E2-beta attenuation of EPO synthesis. We conclude that E2-beta independently attenuates hypoxic induction of EPO and augments hypoxic increases in NO synthesis.     

Disparate effects of neuropeptide Y and clonidine on the excretion of sodium and water in the rat

Previous studies have demonstrated a similarity between the ability of neuropeptide Y (NPY) and clonidine to inhibit renin release and inhibit cAMP production. We therefore compared the effects of clonidine and NPY on the excretion of sodium and water in anesthetized rats which were unilaterally nephrectomized (right kidney) 10 days prior to the experiment. On the experimental day, rats were anesthetized (nembutal) and the left kidney exposed for the intrarenal infusion of the study drugs. The lowest dose of NPY (0.3 microgram/kg per min) investigated failed to alter renal function. Clonidine (0.3 microgram/kg per min) and NPY (1 microgram/kg per min) produced a similar increase in urine volume. Only NPY increased sodium excretion and osmolar clearance. Free water clearance was only increased by clonidine. Blood pressure and creatinine clearance were similar in all groups investigated. These effects were attenuated by pretreatment with pertussis toxin (5 days). The ability of pertussis toxin to block these effects suggests that the renal effects of NPY and clonidine are coupled to a G protein, conceivably the inhibitory Gi protein of the adenylate cyclase system. The disparate effects on sodium excretion and on free water and osmolar clearance indicate that the effects of these compounds may be mediated through the inhibition of different pools of hormonally stimulated cAMP.     

Pharmacology of chiral compounds: 2-arylpropionic acid derivatives

Molecules exist as three dimensional structures. Therefore they can exist in symmetrical and asymmetrical forms. Molecules with an asymmetric centre are chiral. If the molecule and its mirror image are non-superimposable, the relationship between the two molecules is enantiomeric and the two stereoisomers are enantiomers. Since enantiomers have very similar or identical physicochemical properties, it is very difficult to distinguish between them in an achiral environment. However, once in a chiral environment, as in the body, they exhibit clear differences. In fact, most of the physiological processes in nature are stereospecific. Stereospecificity can occur in pharmacokinetic processes, in particular that utilise a carrier protein, receptor or enzyme. In addition, stereoselectivity occurs in pharmacodynamic processes and the differences between enantiomers can be either qualitative and quantitative. 2-arylpropionic acid derivatives (2APAs - profens) are an important subgroup within the class of NSAIDs. These are chiral compounds marketed as racemic mixtures. Some members of the group in an species-dependent manner undergo a special type of metabolic transformation leading to partial inversion to the optical antipode through a specific conjugation with CoA (coenzyme A) and subsequent epimerization. This metabolic inversion has not only pharmacological consequences (related to clinical effect) but also toxicological consequences such as, formation of hybrid triglycerides and even inhibition of fatty acid beta-oxidation. Differences on inversion rate between compounds and species will be discussed as well as its modification by different patho-physiologic processes such as, inflammation.     

Stereoselective Systemic Disposition of Ibuprofen Enantiomers in the Dog

The pharmacokinetics of ibuprofen are complicated by the unidirectional metabolic inversion of the (–)-R- to ( + )-S-enantiomer. Chiral inversion is of therapeutic significance since the drugs pharmacologic activity has been shown to depend upon the ( + )-S-isomer. As a result, the present study was undertaken to determine if chiral inversion occurs systemically and to elucidate further the kinetics of the inversion process. Experiments were performed in the beagle dog after intravenous bolus injections of ibuprofen enantiomers separately [100 mg (–)-R, n = 4; 100 mg ( + )-S, n = 4] and as admixtures of varying proportions [100 mg (–)-R + 100 mg ( + )-S, n = 4; 100 mg (–)-R + 200 mg ( + )-S, n = 2]. Plasma samples of (–)-R-and ( + )-S-enantiomers were measured by a stereospecific HPLC assay after all drug administrations. Based on the area under the plasma concentration–time curves for ( + )-S after administration of each enantiomer alone, chiral inversion was 70 to 75%. A progressive reduction in total plasma clearance of (–)-R-ibuprofen is also observed as increasing amounts of ( + )-S-enantiomer are added to the system. The results demonstrate that chiral inversion occurs to a significant extent in the systemic circulation in dog and that R-to-S inversion of ibuprofen may be inhibited by its ( ( + )-S-enantiomer.     

Stereoselective hepatic disposition of ibuprofen in the perfused liver of rat with adjuvant-induced arthritis

1.?The effects of adjuvant-induced arthritis (AA) on the stereoselective hepatic disposition and chiral inversion of “profens” have scarcely been investigated. Ibuprofen (IB) undergoes unidirectional chiral inversion from R-IB to S-IB and is metabolized to IB-glucuronide (IB-Glu).

2.?We used an in situ perfused rat liver system to clarify the effects of inflammation on the metabolic activities and chiral inversion of IB without protein binding.

3.?After dosing of R-IB, AA had minimal effect on the elimination of R-IB from the perfusate. Larger amounts of S-IB-Glu than R-IB-Glu were observed in the bile at the dose of 2.4 and 4.8?μmol. However, after dosing of S-IB, the elimination of S-IB from the perfusate in AA rats was delayed, indicating a significant decrease in the hepatic clearance in AA rats. The cumulative biliary excretion of S-IB-Glu in AA rats was promoted after dosing with S-IB. There was little difference between the chiral inversion ratios of the control and AA rats.

4.?The present study demonstrated that AA results in the delayed elimination of S-IB, the active form, without changes to the chiral inversion ratio. Thus, further attention to the altered stereoselective pharmacokinetics of IB during inflammation is required.     

Effects of experimental hyperlipidaemia on the pharmacokinetics of docetaxel in rats

Hyperlipidaemia correlates with an increased risk of occurrence of various cancers. In this study, the effects of hyperlipidaemia on the pharmacokinetics of docetaxel, a member of the taxane class of anti-cancer drugs, were investigated in rats with experimental hyperlipidaemia; we focused on the alterations in docetaxel metabolism and plasma distribution. Docetaxel (5?mg/kg intravenously (i.v.) and 40 mg/kg per oral (p.o.)) was administered to control rats and rats with poloxamer-407 (P-407)-induced hyperlipidaemia (1?g/kg, intraperitoneally). In vitro studies were conducted on hepatic metabolism in S9 fractions and plasma protein binding using the ultrafiltration method. Hyperlipidaemia dramatically increased the area under the plasma concentration-time curve from time 0 to infinity (AUC(0-∞)) of docetaxel after i.v. (1.86-fold) or p.o. (10.8-fold) administration and decreased total body clearance (0.574-fold) and apparent volume of distribution at steady state (0.615-fold) of docetaxel after i.v. administration. Compared with the control rats, the metabolism of docetaxel by hepatic S9 fractions and the unbound fraction in the plasma in the hyperlipidaemic rats were decreased, i.e., by 20.1 and 79.8%, respectively. In conclusion, the alterations in docetaxel pharmacokinetics in rats with P-407-induced hyperlipidaemia may be due, at least in part, to a decrease in hepatic metabolism and the unbound fraction of docetaxel in the plasma. These findings have potential therapeutic implications for predicting human pharmacokinetic responses to hyperlipidaemia.