Influence of endotoxin on the stereoselective pharmacokinetics of oxprenolol, propranolol, and verapamil in the rat

Vitexin along with verapamil downregulates efflux pump P-glycoprotein in macrophages and potentiate M1 to M2 switching via TLR4-NF-κB-TNFR2 pathway in lipopolysaccharide treated mice

The lipopolysaccharide, a microbial toxin, is one of the major causative agents of sepsis. P-gp expression and its functions are altered during inflammation. LPS has been known to impair the functions of P-gp, an efflux transporter. But the effect of LPS on P-gp expression in murine peritoneal macrophages is poorly understood. Molecular docking studies reveal that vitexin is a potent substrate and verapamil a potent inhibitor of P-gp. In the present experimental study, the curative potential of vitexin as a fruit component and verapamil treated as a control inhibitor of P-gp was examined in a murine LPS sepsis model. The effects of vitexin and verapamil on P-gp expression in macrophages correlating with changes in macrophage polarization and associated functional responses during LPS induced sepsis were studied. Peritoneal macrophages of LPS (10 mg/kg body weight) challenged mice exhibited elevated levels of H2O2, superoxide, and NO in parallel with lower antioxidant activity. LPS treatment increased P-gp expression through increased TLR4/expression. However, LPS challenged mice treated with vitexin (5 mg/kg body weight) + verapamil (5 mg/kg body weight) showed higher anti-oxidant enzyme activity (SOD, CAT and GRx) resulting in reduced oxidative stress. This combination treatment also elevated TNFR2, concomitant with down-regulation of TLR4, NF-κB and P-gp expression in murine peritoneal macrophages, resulting in a switch from M1 to M2 polarisation of macrophages and reduced inflammatory responses. In conclusion, combined vitexin and verapamil treatment could be used as a promising therapy to regulate P-gp expression and protection against LPS mediated sepsis and inflammatory damages.

The atypical β-blocker S-oxprenolol reduces cachexia and improves survival in a rat cancer cachexia model

BACKGROUND

Beta-blockers and selected stereoisomers of beta-blockers, like bisoprolol and S-pindolol (ACM-001), have been shown to be effective in preclinical cancer cachexia models. Here, we tested the efficacy of stereoisomers of oxprenolol in two preclinical models of cancer cachexia-the Yoshida AH-130 rat model and the Lewis lung carcinoma (LLC) mouse model.

METHODS AND RESULTS

In the Yoshida AH130 hepatoma rat cancer cachexia model and compared with placebo, 50 mg/kg/d S-oxprenolol (HR: 0.49, 95% CI: 0.28-0.85, P = 0.012) was superior to 50 mg/kg/d R-oxprenolol (HR: 0.83, 95% CI 0.38-1.45, P = 0.51) in reducing mortality (= reaching ethical endpoints). Combination of the three doses (12.5, 25 and 50 mg/kg/d) that had a significant effect on body weight loss in the S-oxprenolol groups vs the same combination of the R-oxprenolol groups lead to a significantly improved survival of S-oxprenolol vs R-oxprenolol (HR: 1.61, 95% CI: 1.08-2.39, P = 0.0185). Interestingly, there is a clear dose dependency in S-oxprenolol-treated (5, 12.5, 25 and 50 mg/kg/d) groups, which was not observed in groups treated with R-oxprenolol. A dose-dependent attenuation of weight and lean mass loss by S-oxprenolol was seen in the Yoshida rat model, whereas R-oxprenolol had only had a significant effect on fat mass. S-oxprenolol also non-significantly reduced weight loss in the LLC model and also improved muscle function (grip strength 428 ± 25 and 539 ± 37 g/100 g body weight for placebo and S-oxprenolol, respectively). However, there was only a minor effect on quality of life indicators food intake and spontaneous activity in the Yoshida model (25 mg/kg/S-oxprenolol: 11.9 ± 2.5 g vs placebo: 4.9 ± 0.8 g, P = 0.013 and also vs 25 mg/kg/d R-oxprenolol: 7.5 ± 2.6 g, P = 0.025). Both enantiomers had no effects on cardiac dimensions and function at the doses used in this study. Western blotting of proteins involved in the anabolic/catabolic homoeostasis suggest that anabolic signalling is persevered (IGF-1 receptor, Akt) and catabolic signalling is inhibited (FXBO-10, TRAF-6) by S-pindolol, but not he R-enantiomer. Expression of glucose transporters Glut1 and Glut 4 was similar in all groups, as was AMPK.

CONCLUSIONS

S-oxprenolol is superior to R-oxprenolol in cancer cachexia animal models and shows promise for a human application in cancer cachexia.

Drug-disease interaction: Clinical consequences of inflammation on drugs action and disposition

Inflammation is a culprit in many conditions affecting millions of people worldwide. A plethora of studies has revealed that inflammation and inflammatory mediators such as cytokines and chemokines are associated with altered expression and activity of various proteins such as those involved in drug metabolism, specifically cytochrome P450 enzymes (CYPs). Emphasis of most available reports is on the inflammation-induced downregulation of CYPs, subsequently an increase in their substrate concentrations, and the link between the condition and the inflammatory mediators such as interleukin-6 and tumor necrosis factor alpha. However, reports also suggest that inflammation influences expression and/or activity of other proteins such as those involved in the drug-receptor interaction. These multifaced involvements render the clinical consequence of the inflammation unexpected. Such changes are shown in many inflammatory conditions including rheumatoid arthritis, Crohn's disease, acute respiratory illnesses as well as natural processes such as aging, among others. For example, some commonly used cardiovascular drugs lose their efficacy when patients get afflicted with inflammatory conditions such as rheumatoid arthritis and Crohn's disease. Interestingly, this is despite increased concentration subsequent to reduced clearance. The observation is attributed to a simultaneous reduction in the expression of target receptor proteins such as the calcium and potassium channel and β-adrenergic receptor as well as the metabolic enzymes. This narrative review summarizes the current understanding and clinical implications of the inflammatory effects on both CYPs and drug-receptor target proteins.

Increased brain penetration of diphenhydramine and memantine in rats with adjuvant-induced arthritis

Brain penetration of cationic drugs is an important determinant of their efficacy and side effects. However, the effects of alterations in the activity of uptake transporters in the brain under inflammatory conditions on the brain penetration of cationic drugs are not fully understood. The aim of this study was to examine changes in brain penetration of cationic drugs, including diphenhydramine (DPHM), memantine (MMT), and cimetidine (CMD), and changes in the expression of uptake transporters such as organic cation transporter (Oct) in brain microvascular endothelial cells (BMECs) under inflammatory conditions. To clarify the effects of inflammation on the brain penetration of DPHM, MMT, and CMD, we performed brain microdialysis studies in a rat model of adjuvant-induced arthritis (AA). Further, differences in transporter mRNA expression levels between BMECs from control and AA rats were evaluated. Brain microdialysis showed that the unbound brain-to-plasma partition coefficient (K_p,uu,brain) for DPHM and MMT was significantly lower in AA rats compared with control rats. OCT mRNA levels were increased and proton-coupled organic cation (H⁺/OC) antiporter mRNA levels were decreased in AA rats compared with control rats. Taken together, our findings suggest that inflammation decreases the brain penetration of H⁺/OC antiporter substrates such as DPHM and MMT.

Changes in Radixin Expression and Interaction with Efflux Transporters in the Liver of Adjuvant-Induced Arthritic Rats

Scaffold proteins such as radixin help to modulate the plasma membrane localization and transport activity of the multidrug resistance-associated protein 2 (MRP2/ABCC2) and P-glycoprotein (P-gp/ABCB1) efflux transporters in the liver. We examined changes in radixin expression and interaction with efflux transporters in adjuvant-induced arthritic (AA) rats, an animal model of rheumatoid arthritis, as well as in human liver cancer (HepG2) cells because inflammation affects drug pharmacokinetics via the efflux transporters. The expression levels of radixin and phosphorylated radixin (p-radixin) were measured 24 h after treatment with inflammatory cytokines comprising tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 or sodium nitroprusside (SNP; a nitric oxide donor). The protein levels of radixin, MRP2, and P-gp in the rat liver were next examined. We also investigated whether inflammation affected the formation of complexes between radixin and MRP2 or P-gp. The mRNA and protein levels of radixin in HepG2 cells were significantly decreased by TNF-α treatment, while minimal changes were observed after treatment with IL-1β, IL-6 or SNP. TNF-α also significantly decreased the protein levels of p-radixin, suggesting that TNF-α inhibited the activation of radixin and thereby reduced the activity of the efflux transporters. Complex formation of radixin with MRP2 and P-gp was significantly decreased in AA rats but this was reversed by prednisolone and dexamethasone treatment, indicating that decreased interactions of radixin with MRP2 and P-gp likely occur during liver inflammation. These data suggest that liver inflammation reduces radixin function by decreasing its interactions with MRP2 and P-gp.

Polyinosinic/Polycytidylic Acid-mediated changes in maternal and fetal disposition of lopinavir in rats

Maintenance of optimal lopinavir (LPV) concentration is essential for effective antiretroviral therapy and prevention of mother-to-child transmission of human immunodeficiency virus. However, little is known about the effects of inflammation on the pharmacokinetics of this protease inhibitor and drug transporter substrate, particularly during gestation. Our objective was to study the effect of polyinosinic/polycytidylic acid [poly(I:C)], a viral mimetic, on key maternal drug transporters, and to examine the effect on maternal and fetal disposition of LPV in rats. Poly(I:C) (5.0 mg/kg i.p.) or saline vehicle was administered to pregnant Sprague-Dawley rats on gestational days 17-18. At 24 hours postinjection, all rats were administered LPV (10 mg/kg i.v.), and plasma and tissues were collected at 5-120 minutes postadministration. Plasma interferon-γ (IFN-γ) levels were measured by enzyme-linked immunosorbent assay, and transporter expression was measured via real-time polymerase chain reaction. Maternal plasma, hepatic, placental, and fetal LPV concentrations were determined by liquid chromatography-tandem mass spectrometry. Administration of poly(I:C) induced IFN-γ plasma levels and downregulated the expression of several important ATP-binding cassette (ABC) drug efflux transporters in the placenta and liver of pregnant rats, compared with controls (P < 0.05). Maternal LPV plasma concentration and area under the concentration-versus-time curve were significantly increased in the poly(I:C) group. Plasma protein binding was also significantly higher in poly(I:C)-treated rats. Pronounced increases in hepatic, placental, and fetal LPV tissue:unbound plasma concentrations were seen in the poly(I:C) group; however, absolute tissue concentrations were not changed. Since the majority of commonly used and clinically important antiretroviral drugs are known to be ABC transporter substrates, inflammation-mediated changes in transporter expression could affect their maternal disposition and fetal exposure.

Prediction of metabolic clearance of diclofenac in adjuvant-induced arthritis rats using a substrate depletion assay

1. The purpose of this study was to evaluate drug clearance measured by the metabolic intrinsic clearance (CL(int)) in a substrate depletion assay in comparison with the in vivo clearance (CL(tot)) observed in adjuvant-induced arthritis (AA) rats. 2. After intravenous administration of diclofenac as a model drug, CL(tot) was 2.8-fold higher in AA rats than in control rats. In two different substrate depletion assays with liver microsomes for glucuronidation and hydroxylation, the CL(int) values for glucuronidation was significantly decreased in AA rats to 60% of the value in control rats, whereas the CL(int) values for hydroxylation were similar. The unbound fraction of diclofenac in plasma (f(u, plasma)) was significantly higher (2.8-fold) in AA rats than in control rats. 3. Hepatic clearance predicted from the CL(int) values for both biotransformation pathways and f(u, plasma) was higher in AA rats than in control rats, with good consistency between predicted and observed values. The same results were obtained for experiments using hepatocytes. 4. The plasma protein-binding activities, rather than metabolic clearance, in both types of rats would be a determining factor in the pharmacokinetic behaviour differences between control and AA rats. 5. In summary, substrate depletion assays with liver microsomes and hepatocytes in combination with protein binding assessment can help to predict changes in pharmacokinetics under AA conditions.

Effects of angiotensin II blockade on inflammation-induced alterations of pharmacokinetics and pharmacodynamics of calcium channel blockers

BACKGROUND AND PURPOSE

Inflammation elevates plasma verapamil concentrations but diminishes pharmacological response. Angiotensin II is a pro-inflammatory mediator. We examined the effect of angiotensin II receptor blockade on the pharmacokinetics and pharmacodynamics of verapamil, as well as the binding properties and amounts of its target protein in calcium channels, in a rat model of inflammation.

EXPERIMENTAL APPROACH

We used 4 groups of male Sprague-Dawley rats (220-280 g): inflamed-placebo, inflamed-treated, control-placebo and control-treated. Inflammation as pre-adjuvant arthritis was induced by injecting Mycobacterium butyricum on day 0. From day 6 to 12, 30 mg kg(-1) oral valsartan or placebo was administered twice daily. On day 12, a single oral dose of 25 mg kg(-1) verapamil was administered and prolongation of the PR interval measured and plasma samples collected for verapamil and nor-verapamil analysis. The amounts of the target protein Ca(v)1.2 subunit of L-type calcium channels in heart was measured by Western blotting and ligand binding with (3)H-nitrendipine.

KEY RESULTS

Inflammation reduced effects of verapamil, although plasma drug concentrations were increased. This was associated with a reduction in ligand binding capacity and amount of the calcium channel target protein in heart extracts. Valsartan significantly reversed the down-regulating effect of inflammation on verapamil's effects on the PR interval, and the lower level of protein binding and the decreased target protein.

CONCLUSIONS AND IMPLICATIONS

Reduced responses to calcium channel blockers in inflammatory conditions appeared to be due to a reduced amount of target protein that was reversed by the angiotensin II antagonist, valsartan.

Decreased intestinal CYP3A and P-glycoprotein activities in rats with adjuvant arthritis

Adjuvant-induced arthritis (AA) rats have been used as an animal model for rheumatoid arthritis. Several studies have shown that the pharmacokinetics of a number of drugs are altered in AA rats. We investigated the effects of AA on the barrier functions of the intestine using a rat model. Intestinal CYP3A activities (midazolam 1'-hydroxylation and 7-benzyloxy-4-(trifluoromethyl)-coumarin 7-hydroxylation) in AA rats were significantly decreased compared with those in normal rats, with marked decrease observed in the upper segment of intestine. Intestinal P-glycoprotein (P-gp) activity at upper segment was also significantly decreased in AA rats to 60% of that in normal rats, and the other segments (middle and lower) of intestine also exhibited tendencies toward decrease in P-gp activity. This decrease was supported by the finding that levels of mdr1a mRNA and P-gp protein were decreased in AA rats. No significant differences were observed in intestinal paracellular and transcellular permeability between AA and normal rats. These results suggest that intestinal CYP3A and P-gp activities are decreased in AA rats, and that the pharmacokinetics and bioavailabilities of drugs whose membrane permeation is limited by intestinal CYP3A and/or P-gp may be altered in rheumatic diseases.

EFFECT OF EARLY PHASE ADJUVANT ARTHRITIS ON HEPATIC P450 ENZYMES AND PHARMACOKINETICS OF VERAPAMIL: AN ALTERNATIVE APPROACH TO THE USE OF AN ANIMAL MODEL OF INFLAMMATION FOR PHARMACOKINETIC STUDIES

The objective of this study was to evaluate the suitability of the early phase of adjuvant arthritis (pre-AA) as a model of inflammation for pharmacokinetic studies. Pre-AA is associated with little or no pain and discomfort as compared with fully developed adjuvant arthritis. Pre-AA was induced in male Sprague-Dawley rats with a tail base injection of Mycobacterium butyricum. Animals were monitored for symptoms of arthritis and levels of the proinflammatory mediators, serum nitrite, C-reactive protein (CRP), and tumor necrosis factor alpha (TNFalpha). On day 6, rats were administered single i.v. (2 mg/kg) or oral (20 mg/kg) doses of racemic verapamil, and S- and R-verapamil concentrations were determined by high-performance liquid chromatography. Hepatic cytochrome P450 (P450) content and verapamil protein binding were also measured. All experiments were carried out in both pre-AA and control rats. Serum nitrite, CRP, and TNFalpha levels were significantly elevated in pre-AA rats while signs of pain and arthritis were absent. Pre-AA also significantly elevated plasma concentrations of S- and R-verapamil after both i.v. and oral doses, due, likely, to decreased drug clearance. This was accompanied by a significant reduction in hepatic cytochrome P450, CYP3A, and CYP1A content as well as significantly reduced verapamil free fraction in pre-AA. The early phase of AA is marked by increased proinflammatory mediators and reduced verapamil clearance, as well as decreased hepatic P450 enzymes. Hence, pre-AA is a suitable model of inflammation for pharmacokinetic studies that avoids unnecessary exposure of animals to the pain and distress of fully developed adjuvant arthritis.

Despite increased plasma concentration, inflammation reduces potency of calcium channel antagonists due to lower binding to the rat heart

1. Rheumatoid arthritis reduces verapamil oral clearance thereby increases plasma concentration of the drug. This coincides with reduced drug effects through an unknown mechanism. 2. The effect of interferon-induced acute inflammation on the pharmacokinetics and electrocardiogram of verapamil (20 mg kg(-1), p.o.) and nifedipine (0.1 mg kg(-1), i.v.) was studied in Sprague-Dawley rats. 3. The effect of both acute and chronic inflammation on radioligand binding to cardiac L-type calcium channels was also investigated. 4. Acute inflammation resulted in increased plasma concentration of verapamil but had no effect on that of nifedipine. Verapamil binding to plasma proteins was unaffected. 5. As has been reported for humans, the increased verapamil concentration coincided with a reduction in the degree to which PR interval is prolonged by the drug. The effect of nifedipine on PR interval was also reduced by inflammation. 6. Maximum binding of (3)H-nitrendipine to cardiac cell membrane was significantly reduced from 63.2+/-2.5 fmol mg(-1) protein in controls to 46.4+/-2.0 in acute inflammation and from 66.8+/-2.2 fmol mg(-1) protein in controls to 42.2+/-2.0 in chronic inflammation. 7. Incubation of the normal cardiac cell membranes with 100 and 1000 pg ml(-1) of rat tissue necrosis factor-alpha did not influence the binding indices to the calcium channels. 8. Our data suggest that the reduced calcium channel responsiveness is because of altered binding to channels.

Automated online dual-column extraction coupled with teicoplanin stationary phase for simultaneous determination of (R)- and (S)-propranolol in rat plasma using liquid chromatography-tandem mass spectrometry

An automated online sample extraction method for rat plasma was developed and validated for the quantification of (R)- and (S)-propranolol following the intravenous administration of either the racemate or the individual enantiomers at 5 mg/kg. A dual-column extraction system coupled to a chiral stationary phase (CSP) was used in conjunction with liquid chromatography-tandem mass spectrometry. In this method, two Oasis HLB extraction columns (50x1.0 mm) in parallel were used for online plasma sample purification and teicoplanin CSP (Chirobiotic T) was used for the enantiomeric separation. This method allowed the use of one of the extraction columns for purification while the other was being equilibrated. Hence, the time required for re-conditioning the extraction columns did not contribute to the total analysis time per sample, which resulted in a relatively shorter run time and higher throughput. The lower limit of detection was 0.5 ng/ml and the lower limit of quantification was 2 ng/ml for each enantiomer using 25 microl of rat plasma. The method was validated with a linear calibration curve between 2 and 2000 ng/ml for (R)- and (S)-propranolol, respectively. The intra- and inter-day precision (C.V.) was no more than 7.6% and the accuracy of the assay was between 92 and 103%. The teicoplanin CSP proved to be rugged with excellent reproducibility of chromatographic parameters.

Disease-drug interaction: Reduced response to propranolol despite increased concentration in the rat with inflammation

Inflammatory conditions reduce clearance, hence increase plasma concentration of drugs such as propranolol that are efficiently cleared by the liver. The therapeutic consequences of this increased plasma drug concentration is mainly unknown. However, for sotalol, another beta-adrenergic antagonist, inflammation causes reduced potency. Sotalol, however, is renally cleared; hence, its clearance is unaffected by inflammation. We examined if the inflammation-induced increased plasma propranolol concentration compensates for the reduced responsiveness. A modified lead I ECG was used to record PR interval and heart rate (HR). ECG was monitored following oral administration of 3, 5, 10, 15, 20, 25, and 30 mg/kg propranolol to both control and adjuvant arthritis (AA) rats. To confirm altered pharmacokinetics, single 25 mg/kg doses of propranolol were administered to both AA and control rats, with an inserted cannula in their right jugular vein for serial blood sampling. As expected, AA caused a significant reduction in the propranolol oral clearance and subsequently substantial increases in plasma total and unbound drug concentration. Interestingly, however, despite the elevated propranolol concentrations, the effect on HR remained unchanged and the prolongation of PR interval was significantly reduced in AA compared with control rats. The reduced sensitivity to propranolol in AA rats is suggestive of altered beta-adrenergic receptors function.

Decreased dromotropic response to verapamil despite pronounced increased drug concentration in rheumatoid arthritis

AIMS

Inflammation reduces hepatic clearance of many drugs with unknown therapeutic consequences. This study was carried out to examine the effect of rheumatoid arthritis (RA) on the pharmacokinetics and pharmacodynamics of verapamil.

METHODS

Eight RA patients were age- and sex-matched with eight healthy volunteers. The disease severity was assessed, and ECG, blood pressure and verapamil enantiomers concentrations were measured for 12 h post 80 mg oral verapamil. Serum interleukin-6 (IL-6) and nitrite (NO2-) were measured in predose samples.

RESULTS

IL-6 and NO2- concentrations were significantly increased in parallel with disease severity. Oral clearance of both S- and R-verapamil was significantly decreased by RA. While the unbound fraction of S- and R-verapamil decreased by 5 and 7-fold, respectively, the unbound AUC remained unchanged for the more potent enantiomer, S-verapamil. AUC of norverapamil enantiomers was increased 2-3-fold. Despite elevated serum drug concentrations in RA, the potential to prolong the PR-interval was significantly reduced by one fold and the effect on the heart rate and blood pressure did not increase.

CONCLUSIONS

RA results in increased verapamil concentrations due likely to changes in protein binding, decreased clearance and/or altered hepatic blood flow. A significant decrease in dromotropic effect, despite increased serum drug concentrations, may be attributed to receptor down regulation caused by pro-inflammatory cytokines and/or NO.

Stereoselective binding of zopiclone to human plasma proteins

The binding of racemic zopiclone (ZOP) and of its two enantiomers to plasma proteins, albumin and alpha 1-acid glycoprotein were compared. Our work shows that the binding of ZOP to human plasma proteins is stereoselective. The total plasma protein binding percentages were 79.3 +/- 5.5%, 83.8 +/- 5.2%, and 75.1 +/- 2.1%, for racemic zopiclone, (-)zopiclone and (+)zopiclone, respectively. These results were confirmed by the analysis of samples obtained from healthy volunteers after the oral administration of ZOP. The anticoagulant used for sampling was also shown to have an influence on the percentage binding and on its stereoselectivity. Considering albumin and alpha 1-acid glycoprotein separately, stereoselectivity was also observed.

Detection of endotoxin using an evanescent wave fiber-optic biosensor

The lipopolysaccharide endotoxin is the most powerful immune stimulant known and a causative agent in the clinical syndrome known as sepsis. Sepsis is responsible for more than 100,000 deaths annually, in large part due to the lack of a rapid, reliable, and sensitive diagnostic technique. This study describes the detection of LPS from E. coli at concentrations as low as 10 ng/mL, in 30 s using an evanescent wave fiber-optic biosensor. Polymyxin B, covalently immobilized onto the surface of the fiber-optic probe, selectively bound fluorescently labeled LPS. Unlabeled LPS was detected in a competitive assay format using labeled LPS for signal generation. The competitive assay format worked in both buffer and plasma with similar sensitivities. This method can be used with other LPS capture molecules such as antibodies, lectins, or antibiotics, to simultaneously detect LPS and to determine the LPS serotype. The LPS assay using the fiber-optic biosensor is applicable to both clinical and environmental testing.

Drug-protein binding sites. New trends in analytical and experimental methodology

In the last few years, continuous progress in instrumental analytical methodology has been achieved with a substantial increase in the number of new, more specific and more flexible methods for ligand-protein assays. In general, the methods used for drug-protein binding studies can be divided into two main groups: separation methods (enabling the calculation of binding parameters, i.e. the number of binding sites and their respective affinity constants) and non-separation methods (describing predominantly qualitative parameters of the ligand-protein complex). This review will be focussed particularly on recent trends in the development of drug-protein binding methods including stereoselective and non-stereoselective aspects using chromatography, capillary electrophoresis and microdialysis as compared to the "conventional approach" using equilibrium dialysis, ultrafiltration or size exclusion chromatography. The advantages and limitations of various methods will be discussed including a focus on "optimal" experimental strategies taking into account in vitro, ex vivo and/or in vivo studies. Furthermore, the importance of some particular aspects concerning the drug binding to proteins (covalent binding of drugs and metabolites, stereoselective interactions and evaluation of binding data) will be outlined in more detail.

Protein binding of propranolol and verapamil enantiomers in maternal and foetal serum

The protein binding of the enantiomers of propranolol and verapamil was measured in 19 pairs of maternal and foetal serum obtained at delivery. The binding of the enantiomers of both drugs was lower in foetal than in maternal serum. In maternal serum the mean (+/- s.d.) unbound percentages were 22.4 +/- 6.2 and 20.7 +/- 6.6 for R- and S-propranolol, and 16.8 +/- 5.5 and 22.5 +/- 6.2 for R- and S-verapamil; in foetal serum the values were 38.8 +/- 8.6 and 40.4 +/- 10.6 for R- and S-propranolol, and 34.7 +/- 10.5 and 44.8 +/- 10.7 for R- and S-verapamil. For propranolol, in maternal, but not in foetal serum, the difference between the binding of the R- and S-enantiomers was significant; the R/S ratio was significantly (P < 0.01) larger in the mother (1.099 +/- 0.072) than in the foetus (0.973 +/- 0.068). For verapamil, the difference in binding between the R- and S-enantiomers was significant in both maternal and foetal serum, but the R/S ratio was similar in mother (0.735 +/- 0.098) and foetus (0.763 +/- 0.070). Serum alpha 1-acid glycoprotein (AAG) concentrations were markedly higher and albumin concentrations slightly lower in maternal than in foetal samples. The binding of the four enantiomers in maternal and foetal serum was correlated (P < 0.001) with the AAG concentration (r propranolol: R 0.749, S 0.746; r verapamil: R 0.753, S 0.782). Our findings show that measurement of concentrations of total, unresolved drug allow a reasonably accurate assessment of transplacental gradients of individual isomers.

Stereoselective pharmacokinetics of oxprenolol, propranolol, and verapamil: species differences and influence of endotoxin

The influence of endotoxin-induced inflammation was studied on the pharmacokinetics of the enantiomers of the racemic drugs oxprenolol, propranolol, and verapamil in rabbits and dogs. Enantioselective pharmacokinetics were seen for oxprenolol and propranolol in the rabbit and for propranolol and verapamil in the dog. In the dog, the enantioselective differences in plasma concentrations are due to differences in both protein binding and metabolism, whereas in the rabbit the differences are due solely to differences in metabolism. In both species endotoxin treatment increases the plasma concentrations of the enantiomers of the three drugs; both protein binding and metabolism are influenced. In rabbits and in dogs, the influence of endotoxin on the disposition of the three drugs is less enantioselective than was previously observed in the rat.