P-glycoprotein (ABCB1) but not multidrug resistance-associated protein 1 (ABCC1) is induced by doxorubicin in primary cultures of rat astrocytes

At least two drug efflux pumps involved in multidrug resistance, P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 (Mrp1), are expressed in rat astrocyte primary cultures. The aim of this study was to compare the expression of P-gp and Mrp1 in primary cultures exposed to 50 or 500 ng/mL doxorubicin (DOX). Among the two P-gp genes expressed in rodents, mdr1a and mdr1b, a time- and dose-dependent increase in mdr1b mRNA levels was revealed by northern blot analysis. This up-regulation was inhibited by actinomycin D and occurred as early as 2 h after exposure to 50 or 500 ng/mL DOX, whereas mdr1a and mrp1 transcripts were not modified by the DOX exposure. In addition, DOX also strongly enhanced, in a time- and dose-dependent manner, P-gp but not Mrp1 expression. Moreover, DOX raised the cellular efflux of vincristine, a substrate for both P-gp and Mrp1. This efflux was inhibited by the P-gp modulators PSC833 and GW918, but not by the Mrp1 modulator MK571. On the other hand, a 24-h exposure to 500 ng/mL DOX, but not 50 ng/mL DOX, induced apoptosis in primary cultures of rat astrocytes. Fumonisin B1, a ceramide synthase inhibitor, reduced DOX-induced apoptosis, suggesting that de novo synthesis of the ceramide regulatory pathway might be involved in DOX-induced apoptosis. Moreover, western blot analysis showed that fumonisin B1 was not able to decrease the overexpression of P-gp induced by DOX. Our results provide evidence that DOX up-regulates a functional P-gp in primary cultures of rat astrocytes and might cause astrocyte apoptosis via the ceramide pathway.

Evidence for an active transport of morphine-6-beta-d-glucuronide but not P-glycoprotein-mediated at the blood-brain barrier

Morphine-6-beta-d-glucuronide (M6G) is an active metabolite of morphine with high analgesic potency despite a low blood-brain barrier (BBB) permeability. The aim of the study was to elucidate its transport mechanism across the BBB. We first checked if M6G was effluxed by the P-glycoprotein (P-gp), as previously reported by others. Second, we investigated the role of anionic transporters like the multidrug resistance-associated protein mrp1 and the glucose transporter GLUT-1. The brain uptake of [14C]M6G was measured by the in situ brain perfusion technique in wild-type and deficient mice [mdr1a(-/-) and mrp1(-/-)], with and without probenecid, digoxin, PSC833 or d-glucose. No difference was found between P-gp and mrp1 competent and deficient mice. The brain uptake of [14C]M6G co-perfused with probenecid in wild-type mice was not significantly different from that found in group perfused with [14C]M6G alone. The co-perfusion of [14C]M6G with digoxin or PSC833 was responsible of a threefold decrease of its uptake in mdr1a competent and deficient mice, suggesting that another transporter than P-gp and sensitive to digoxin and PSC833, may be involved. The co-perfusion of [14C]M6G with d-glucose revealed a threefold decrease in M6G uptake. In conclusion, P-gp and mrp1 are not involved in the transport of M6G at the BBB level in contrast to GLUT-1 and a digoxin-sensitive transporter (probably oatp2), which can actively transport M6G but with a weak capacity.

Improved brain uptake and pharmacological activity of dalargin using a peptide-vector-mediated strategy

The blood-brain barrier restricts the passage of substances into the brain. Neuropeptides, such as enkephalins, cannot be delivered into the brain when given systemically because of this barrier. Therefore, there is a need to develop efficient transport systems to deliver these drugs to the brain. Recently, we have demonstrated that conjugation of doxorubicin or penicillin to peptide vectors significantly enhances their brain uptake. In this study, we have conjugated the enkephalin analog dalargin with two different peptide vectors, SynB1 and SynB3, to improve its brain delivery and its pharmacological effect. We show by in situ brain perfusion that vectorization markedly enhances the brain uptake of dalargin. We also show using the hot-plate model that this enhancement in brain uptake results in a significant improvement in the observed antinociceptive effect of dalargin. These results support the usefulness of peptide-mediated strategies for improving the availability and efficacy of central nervous system drugs.

Apparent lack of Mrp1-mediated efflux at the luminal side of mouse blood-brain barrier endothelial cells

PURPOSE

The purpose of this work was to determine mrpl-mediated efflux across the luminal membrane of endothelial cells at the blood-brain barrier (BBB) in mice.

METHODS

The transport of radiolabeled etoposide, 17beta-estradiol-D-17beta-glucuronide (E217betaG), vincristine, and doxorubicin across the BBB of mrp1(-/-) and wild-type mice was evaluated by in situ brain perfusion. Etoposide transport was also determined in P-glycoprotein-deficient mdr1a(-/-) mice perfused with both etoposide and mrpl inhibitors like probenecid or MK571. Cerebral vascular volume was determined by co-perfusion with labeled sucrose.

RESULTS

Sucrose perfusion indicated that the vascular space was close to normal in all the studies, indicating that the BBB remained intact. The transport of etoposide, E217betaG, vincristine, and doxorubicin into the brain was not affected by the lack of mrp1. Trans-efflux studies in mrp1-deficient mice with etoposide and E217betaG confirmed that mrpl was not involved in the efflux of these substrates across the BBB. There was also a significant P-gp-mediated efflux of etoposide in studies with P-glycoprotein-deficient mdr1a(-/-) mice. Perfusion of mdr1a(-/-) mice etoposide plus probenecid or MK571 did not affect the brain transport of etoposide.

CONCLUSION

Efflux mediated by mrp1 does not seem to occur across the luminal membrane of the endothelial cells forming the mouse BBB.

Nonlinear accumulation in the brain of the new taxoid TXD258 following saturation of P-glycoprotein at the blood-brain barrier in mice and rats

1. TXD258, a new taxoid antitumor agent, is a poor substrate for the P-glycoprotein (P-gp) in Caco-2 cells. In this study, we investigated the amount of drug accumulating in the brains of rats and mice under a variety of conditions (dose and infusion time, species and plasma concentration) using conventional in vivo pharmacokinetic techniques and in situ brain perfusion. 2. Mice were infused with radiolabeled TXD258 at 15, 30, 45 and 90 mg m(-2) for 45 s or 1 h and rats were infused with 15 and 60 mg m(-2) over 2.3 min. The radioactivity in the plasma and brains was measured. The brain concentrations of TXD258 in mice and rats were maximal from 2 min to 1 h postinfusion and radioactivity was still detectable at 168 h. While the plasma concentration of TXD258 increased linearly in mice with the infused dose, the brain content increased more than proportionally with the dose between 15 and 90 mg m(-2). This nonlinear uptake of TXD258 also occurred in the plasma and brain of the rat. 3. These findings suggest that the protein-mediated efflux across the blood-brain barrier (BBB) becomes saturated. In situ brain perfusion studies confirmed that TXD258 is a P-gp substrate at the BBB of mice and rats. The P-gp of both species was saturated at the half-inhibitory concentration ( approximately 13 micro M) produced by i.v. infusion. 4 Thus, the observed nonlinear accumulation of TXD258 in the brain seems to occur by saturation of the P-gp at the rodent BBB. This saturation could have several advantages, such as overcoming a P-gp-mediated efflux, but the nonlinear pharmacokinetics could increase the risk of toxicity.

Study of uranium transfer across the blood-brain barrier

Uranium is a heavy metal which, following accidental exposure, may potentially be deposited in human tissues and target organs, the kidneys and bones. A few published studies have described the distribution of this element after chronic exposure and one of them has demonstrated an accumulation in the brain. In the present study, using inductively coupled plasma mass spectrometry (ICP-MS) for the quantification of uranium, uranium transfer across the blood-brain barrier (BBB) has been assessed using the in situ brain perfusion technique in the rat. For this purpose, a physiological buffered bicarbonate saline at pH 7.4 containing natural uranium at a given concentration was perfused. After checking the integrity of the BBB during the perfusion, the background measurement of uranium in control rats without uranium in the perfusate was determined. The quantity of uranium in the exposed rat hemisphere, which appeared to be significantly higher than that in the control rats, was measured. Finally, the possible transfer of the perfused uranium not only in the vascular space but also in the brain parenchyma is discussed.

[Exchanges through the blood-brain barrier]

The blood-brain barrier (BBB) is the main interface controlling the exchange of nutrients and drugs between the blood and brain. Its specificity is given by some specific properties of the endothelium of the brain capillaries. They include the presence of tight junctions sealing adjacent endothelial cells and the absence of fenestrations preventing paracellular transport pathway across the BBB. The BBB is also a metabolic and pharmacological barrier because of the activity of many cytosolic enzymes and transporters expressed both or either at the luminal or abluminal faces of the brain microvessel endothelial cells. Macromolecules like insulin, leptin and transferrin may cross the BBB via receptor mediated transcytosis. More recently the discovery of P-glycoprotein, an ABC protein, at the luminal membrane of the brain endothelial cells has shown that several lipophilic antimitotic and psychotropic drugs are pumped out of the brain by this transporter. All these properties illustrate how complex the exchanges of nutrients and drugs across the BBB are.

Peptide delivery to the brain via adsorptive-mediated endocytosis: advances with SynB vectors

Biological membranes normally restrict the passage of hydrophilic molecules. This impairs the use of a wide variety of drugs for biomedical applications. To overcome this problem, researchers have developed strategies that involve conjugating the molecule of interest to one of a number of peptide entities that are efficiently transported across the cell membranes. In the past decade, a number of different peptide families with the ability to cross the cell membranes have been identified. Certain of these families enter the cells by a receptor-independent mechanism, are short (10-27 amino acid residues), and can deliver successfully various cargoes across the cell membrane into the cytoplasm or nucleus. Surprisingly, some of these vectors, the SynB vectors, have also shown the ability to deliver hydrophilic molecules across the blood-brain barrier, one of the major obstacles to the development of drugs to combat diseases affecting the CNS.

Drug delivery to brain via the blood-brain barrier

1. Many neurodegenerative diseases, cancer and infections of the brain become more prevalent as populations become older. Despite major advances in neuroscience, the blood-brain barrier (BBB) ensures that many potential therapeutic cannot reach the central nervous system (CNS). The BBB is formed by the complex tight junctions between the endothelial cells of the brain capillaries and their low endocytic activity. This results in the capillary wall that behaves as a continuous lipid bilayer and prevents the passage of polar and lipid-insoluble substances. It is, therefore, the major obstacle to drugs that may combat diseases affecting the CNS. 2. Several strategies for delivering drugs to the CNS have been developed. These enhance the capacity of therapeutic molecules to cross the BBB by modifying the drug itself, or by coupling it to a vector for receptor-mediated or adsorption-mediated transcytosis. 3. The current challenge is to develop drug-delivery systems that ensure that drugs cross the BBB in a safe and effective manner. This review focuses on the strategies developed to enhance drug delivery across the BBB.

Improved brain delivery of benzylpenicillin with a peptide-vector-mediated strategy

Previous studies from our laboratory have demonstrated that the coupling of doxorubicin with SynB1 vector dramatically increases its brain uptake. In the present study, we have evaluated the broad application of this approach using another molecule: benzylpenicillin (B-Pc). We, therefore, have coupled the beta-lactam antibiotic B-Pc with SynB1 and assessed its ability to cross the blood-brain barrier (BBB) using the in situ rat brain perfusion method. We first confirmed the very low brain uptake of free radiolabeled B-Pc. When B-Pc was coupled to SynB1, its uptake in brain was increased by a factor of 7, without compromising the BBB integrity. The vectorised B-Pc was distributed in all the gray areas assessed (frontal, parietal, and occipital cortex, thalamus, hippocampus, and striatum). Moreover, using a wash-out procedure and a capillary depletion method, we have shown that the radiolabeled B-Pc was associated mainly with brain parenchyma. In summary, this study demonstrates the successful application of the use of SynB1 vector for the transport of B-Pc across the BBB.

Molecular and functional MDR1-Pgp and MRPs expression in human glioblastoma multiforme cell lines

The aim of our study was to investigate the functional expression of P-glycoprotein (Pgp) and multidrug resistance-associated proteins (MRPs) in 2 distinct glioma cells (GL15 and 8MG) from patients with glioblastoma multiforme. MDR1 gene and Pgp expression was not detected in either cell line by RT-PCR and Western blotting, respectively. In contrast, MRP1 was detected at both mRNA and protein level in both cell lines, with a higher expression in the 8MG cells that occur predominantly at the cell membrane. Three other MRPs (MRP3, MRP4 and MRP5) were detected by RT-PCR in both cell lines, whereas MRP2 was not expressed. In addition, MRP3 protein was also detected by immunocytochemistry in both GL15 and 8MG cell lines. Indomethacin and probenecid, 2 modulators of MRPs activity, increased the accumulation of vincristine and etoposide, 2 substrates of MRPs, by both cell lines. These modulators also decreased the efflux of vincristine from both cell lines with a more pronounced effect in 8MG cells. In conclusion, our results show functional expression of MRPs leading to a decrease in the intracellular vincristine and etoposide concentrations in human glioblastoma cell lines. Furthermore, our results that exhibit protein expression of MRP1 and MRP3 and gene expression of MRP4 and MRP5 in these 2 glioblastoma cell lines suggest new mechanisms that could lead to a MDR phenotype of tumour cells in patients with glioblastoma multiforme.

[Cationization, a process for the delivery of antibodies to the central nervous system. Problems encountered in its application for immunotherapy strategies such as those for clostridial poisoning]

The central nervous system is separated from the rest of the body by the blood-brain barrier. This barrier prevents many substances, such as the antibodies, to penetrate into the brain making it difficult to use them for the treatment of brain diseases, such as tetanus and botulism. These two diseases are caused by the development of bacilli of the genus Clostridium which release neurotropic toxins. Specific antibodies can neutralize toxin activity when the toxin is in the blood but are ineffective when it is transported into nerve cells. Various invasive strategies have been used to deliver antibodies to the brain. However, they can induce seizures and transient neurologic deficits and may be applicable only for diseases restricted to the brain surface. Physiologically based strategies utilizing transport systems naturally present at the blood-brain barrier appear to be a more promising approach to brain delivery of antibodies. Cationization is a chemical treatment that causes the conversion of superficial carboxyl groups on a protein into extended primary amino groups. This is used to increase interactions of this protein with the negative charges at the luminal plasma membrane of the brain endothelial cells. The cationized protein can then undergo adsorptive mediated transcytosis through the blood-brain barrier. There are many problems yet to be solved in successfully carrying out in vivo applications of cationized antibodies. One of these problems is that cationization can cause damage to an antibody molecule and, thus, can compromise its binding affinity. Depending on the radiolabelling of the cationized antibodies, a serum inhibition phenomenon can possibly alter the pharmacokinetics and the organ distribution of these molecules. The antibodies can be cationized using various, synthetic (hexamethylenediamine) or naturally occuring (e.g., putrescine) polyamines. Hexamethylenediamine-induced and putrescine-induced brain uptakes of various antibodies and proteins have been shown, but the results obtained suggest that cationization with putrescine may be a more efficient approach to blood-brain barrier delivery. The development of animal or cellular models to check for therapeutic efficacy of cationized antibodies is necessary. In spite of the difficulties, the studies described in this paper indicate that cationization can be a realistic delivery strategy for carrying antibodies across the blood-brain barrier. The advances made in antibody technologies help generate more appropriate immunological structures for brain transfer with better effector functions and decreased immunogenicity or toxicity. Taken together, these two aspects can lead to further developments in treatment of intoxications caused by the clostridial neurotoxins.

Vector-mediated drug delivery to the brain

As a consequence of the growing ageing population, many neurodegenerative diseases, cancer and infections of the brain will become more prevalent. Despite major advances in neuroscience, many potential therapeutic agents are denied access to the central nervous system (CNS) because of the existence of the blood-brain barrier (BBB). This barrier is formed by the endothelial cells of the brain capillaries and its primary characteristic is the impermeability of the capillary wall due to the presence of complex tight junctions and a low endocytic activity. The BBB behaves as a continuous lipid bilayer and prevents the passage of polar and lipid-insoluble substances. The BBB is, therefore, the major obstacle to drugs that are potentially useful for combating diseases affecting the CNS. Extensive efforts have been made to develop CNS drug delivery strategies in order to enhance delivery of therapeutic molecules across the BBB. The current challenge is to develop drug-delivery strategies that will allow the passage of therapeutic drugs through the BBB in a safe and effective manner. This review focuses specifically on the strategies developed to enhance drug delivery across the BBB with an emphasis on the vector-mediated strategy.

[Biodynamics of the antigen-antibody reaction in vivo]

The success of the toxin neutralization by a specific antibody in a living system depends on multiple factors. First, the type of the actual available antibody structures (immunoglobulin G, Fab2 or Fab fragments) must be selected according to the toxin molecular weight: Fab is adapted to the neutralization of haptens, IgG and Fab2 to macromolecular toxins. Other factors involved in the success of immunotherapy are issued from the pharmacokinetic properties of the toxin: non reversible binding to the receptor, intracellular distribution of a macromolecular toxin are disadvantageous. Finally, the selection of the antibody dose according to its association constant value for the toxin allows to administer the optimal capacity of immunoneutralization. The control of all these factors inserted in the biodynamics of the living system contributes to the success of immunotherapy.

Doxorubicin-peptide conjugates overcome multidrug resistance

A well-known mechanism leading to the emergence of multidrug-resistant tumor cells is the overexpression of P-glycoprotein (P-gp), which is capable of lowering intracellular drug concentrations. To overcome this problem, we tested the capability of two peptide vectors that are able to cross cellular membranes to deliver doxorubicin in P-gp-expressing cells. The antitumor effect of peptide-conjugated doxorubicin was tested in human erythroleukemic (K562/ ADR) resistant cells. The conjugate showed potent dose-dependent inhibition of cell growth against K562/ADR cells as compared with doxorubicin alone. Doxorubicin exhibited IC50 concentrations of 65 microM in the resistant cells, whereas vectorized doxorubicin was more effective with IC50 concentrations of 3 microM. After treatment of the resistant cells with verapamil, the intracellular levels of doxorubicin were markedly increased and consequent cytotoxicity was improved. In contrast, treatment of resistant cells with verapamil did not cause any further enhancement in the cell uptake nor in the cytotoxic effect of the conjugated doxorubicin, indicating that the conjugate bypasses the P-gp. Finally, we show by the in situ brain perfusion method in P-gp-deficient and competent mice that vectorized doxorubicin bypasses the P-gp present at the luminal site of the blood-brain barrier. These results indicate that vectorization of doxorubicin with peptide vectors is effective in overcoming multidrug resistance.

Screening of multidrug-resistance sensitive drugs by in situ brain perfusion in P-glycoprotein-deficient mice

PURPOSE

This study was conducted to assess the influence of P-glycoprotein (P-gp) on brain uptake of multidrug resistance sensitive drugs using an in situ brain perfusion technique in P-gp-deficient (mdr1a[-/-]) and wild-type mice.

METHODS

The blood-brain transport of radiolabeled vinblastine, vincristine, doxorubicin, colchicine, and morphine was evaluated in mdr1a(-/-) and wild-type CF-1 mice with the in situ brain perfusion technique. Brain uptake of drugs after intravenous pretreatment with P-gp reversal agents, (PSC 833, GF 120918, or (+/-)-verapamil), or vehicle also was studied in wild-type mice. In all experiments, cerebral vascular volume was determined by co-perfusion of sucrose.

RESULTS

Cerebral vascular volume was preserved during perfusion, indicating maintenance of blood-brain barrier integrity in both types of mice within the concentration range of substrates in the perfusate. The apparent brain transport of colchicine. vinblastine, doxorubicin, and morphine was increased 3.0, 2.7, 1.5, and 1.4-fold, respectively, in mdr1a(-/-) mice compared with the wild-type: the brain uptake of vincristine was not affected by P-gp. Preadministration of PSC 833 or GF 120918 in wild-type mice led to a -3-fold increase in the brain transport of colchicine and vinblastine, but no effect was observed for the other compounds. Intravenous verapamil enhanced colchicine brain transport (1.8-fold), but failed to increase the brain uptake of vinblastine and morphine.

CONCLUSION

The in situ brain perfusion technique appears to be a sensitive and powerful tool for medium throughput screening of the brain uptake of multidrug resistance sensitive drugs. The effect of P-gp is characterized more efficiently with mdr1a(-/-) mice than by using modulators of P-gp in wild-type mice.

Enhanced delivery of doxorubicin into the brain via a peptide-vector-mediated strategy: saturation kinetics and specificity

Doxorubicin delivery to the brain is often restricted because of the poor transport of this therapeutic molecule through the blood-brain barrier (BBB). To overcome this problem, we have recently developed a technology, Pep:trans, based on short natural-derived peptides that are able to cross efficiently the BBB without compromising its integrity. In this study, we have used the in situ mouse brain perfusion method to evaluate the brain uptake of free and vectorized doxorubicin. Doxorubicin was coupled covalently to small peptide vectors: L-SynB1 (18 amino acids), L-SynB3 (10 amino acids), and its enantio form D-SynB3. We first confirmed the very low brain uptake of free radiolabeled doxorubicin, which is most likely due to the efflux activity of the P-glycoprotein at the level of the BBB. Vectorization with either L-SynB1, L-SynB3, or D-SynB3 significantly increased the brain uptake of doxorubicin (about 30-fold). We also investigated the mechanism of transport of vectorized doxorubicin. We show that vectorized doxorubicin uses a saturable transport mechanism to cross the BBB. The effect of poly(L-lysine) and protamine, endocytosis inhibitors, on the transport across the brain was also investigated. Both inhibitors reduced the brain uptake of vectorized doxorubicin in a dose-dependent manner. These studies indicate that the transport of vectorized doxorubicin appears to occur via an adsorptive-mediated endocytosis.

Enhanced cellular uptake and transport of polyclonal immunoglobulin G and fab after their cationization

Antibodies are poorly transported across cell membranes and biological barriers in vivo. Cationization of antibody molecules by the derivatization of surface carboxyl groups generating primary amino groups could represent a strategy for intracellular antibody delivery. Before cationization of polyclonal colchicine-specific IgG and Fab, using hexamethylenediamine the isoelectric point (pl) of native IgG and Fab (nIgG and nFab) was in the range of 5.9 9.0 and 8.7-9.3, respectively. The pI of cationized IgG and Fab (cIgG and cFab) were both higher at 8.7, 10.3 and 9.5 -11, respectively. The affinity and specificity of both IgG and Fab were not modified by cationization. When HL 60 cells were incubated with the native or cationized 125I-BSA. -IgG and -Fab, the maximal cellular uptake of clgG and cFab was 3.2 and 2.4 times higher than that of nIgG and nFab at an extracellular concentration of 500 ng/ml. Results also indicated that the uptake was dose- and temperature-dependent suggesting absorptive-mediated endocytosis of cationized antibodies by HL 60 cells. Confocal microscopy analysis indicated that the cationized antibodies were present in the plasma membranes and cytoplasm of HL 60 cells. Finally, a study with bovine arterial endothelial monolayer cells showed that the transport of cIgG and cFab through the monolayer cells was 3.3- and 4.3-fold higher for 125I-cIgG and 125I-cFab than those of the corresponding native forms.

Functional expression of P-glycoprotein and multidrug resistance-associated protein (Mrp1) in primary cultures of rat astrocytes

Although it has been well established that the drug efflux pump P-glycoprotein (P-gp) protects the brain against the entry of cytotoxic drugs, its real in situ localization, i.e., at brain capillary endothelial cells or on astrocyte foot processes, is still controversial. The aim of this study was to compare the expression of P-gp and of multidrug resistance-associated protein (Mrp1), another drug efflux pump, in cultured neonatal rat brain astrocytes and in cultured brain capillary endothelial cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed that the mdr1b gene was preferentially expressed in astrocytes, whereas both mdr1a and mdr1b mRNA were detected in endothelial cells. Moreover, the mrp1 gene encoding Mrp1 was expressed in both cell types. Western blotting analysis revealed higher expression of P-gp in endothelial cells as compared with astrocytes, but higher expression of Mrp1 in astrocytes. Moreover, P-gp and Mrp1 expression was not modified in more differentiated astrocytes obtained when cultured with db-cAMP for 48 hr. Our functional analysis of P-gp showed a modest effect of P-gp modulators (CsA, verapamil, PSC 833) on the uptake of colchicine (a substrate of P-gp) by astrocytes, whereas they increased by about 50% the uptake of vincristine (a common substrate of P-gp and MRP) by astrocytes. MRP modulators (genistein, probenecid, and sulfinpyrazone) did not modify the uptake of colchicine but increased that of vincristine with a major effect found for sulfinpyrazone. Moreover, indomethacin, probenecid, and sulfinpyrazone increased the uptake of fluorescein (a substrate of MRP but not of P-gp). Taken together, our results provide the first biochemical and functional evidence supporting the expression of P-gp and Mrp1 in rat cultured astrocytes.

Functional expression of P-glycoprotein and multidrug resistance-associated protein (Mrp1) in primary cultures of rat astrocytes

Although it has been well established that the drug efflux pump P-glycoprotein (P-gp) protects the brain against the entry of cytotoxic drugs, its real in situ localization, i.e., at brain capillary endothelial cells or on astrocyte foot processes, is still controversial. The aim of this study was to compare the expression of P-gp and of multidrug resistance-associated protein (Mrp1), another drug efflux pump, in cultured neonatal rat brain astrocytes and in cultured brain capillary endothelial cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed that the mdr1b gene was preferentially expressed in astrocytes, whereas both mdr1a and mdr1b mRNA were detected in endothelial cells. Moreover, the mrp1 gene encoding Mrp1 was expressed in both cell types. Western blotting analysis revealed higher expression of P-gp in endothelial cells as compared with astrocytes, but higher expression of Mrp1 in astrocytes. Moreover, P-gp and Mrp1 expression was not modified in more differentiated astrocytes obtained when cultured with db-cAMP for 48 hr. Our functional analysis of P-gp showed a modest effect of P-gp modulators (CsA, verapamil, PSC 833) on the uptake of colchicine (a substrate of P-gp) by astrocytes, whereas they increased by about 50% the uptake of vincristine (a common substrate of P-gp and MRP) by astrocytes. MRP modulators (genistein, probenecid, and sulfinpyrazone) did not modify the uptake of colchicine but increased that of vincristine with a major effect found for sulfinpyrazone. Moreover, indomethacin, probenecid, and sulfinpyrazone increased the uptake of fluorescein (a substrate of MRP but not of P-gp). Taken together, our results provide the first biochemical and functional evidence supporting the expression of P-gp and Mrp1 in rat cultured astrocytes.

Brain drug delivery technologies: novel approaches for transporting therapeutics

The blood-brain barrier (BBB) denies many therapeutic agents access to brain tumours and other diseases of the central nervous system (CNS). Despite remarkable advances in our understanding of the mechanisms involved in the development of the brain diseases and the actions of neuroactive agents, drug delivery to the brain remains a challenge. For more than 20 years, extensive efforts have been made to enhance delivery of therapeutic molecules across vascular barriers of the CNS. The current challenge is to develop drug-delivery strategies that will allow the passage of drug molecules through the BBB in a safe and effective manner, and this review will provide an insight into some of the strategies developed to enhance drug delivery across the BBB.

New advances in the transport of doxorubicin through the blood-brain barrier by a peptide vector-mediated strategy

Many therapeutic drugs are excluded from entering the brain, due to their lack of transport through the blood-brain barrier (BBB). To overcome this problem, we have developed a novel method in which short, naturally derived peptides (16-18 amino acids) cross the cellular membranes of the BBB with high efficiency and without compromising its integrity. The antineoplastic agent doxorubicin (dox) was coupled covalently to two peptides, D-penetratin and SynB1. The ability of dox to cross the BBB was studied using an in situ rat brain perfusion technique and also by i.v. injection in mice. In the brain perfusion studies, we first confirmed the very low brain uptake of free radiolabeled dox because of the efflux activity of P-glycoprotein at the BBB. By contrast, we have demonstrated that when dox is coupled to either the D-penetratin or SynB1 vectors, its uptake was increased by a factor of 6, suggesting that the vectorized dox bypasses P-glycoprotein. Moreover, using a capillary depletion method, we have shown that vectorization of dox led to a 20-fold increase in the amount of dox transported into brain parenchyma. Intravenous administration of vectorized dox at a dose of 2.5 mg/kg in mice led to a significant increase in brain dox concentrations during the first 30 min of postadministration, compared with free dox. Additionally, vectorization led to a significant decrease of dox concentrations in the heart. In summary, our results establish that the two peptide vectors used in this study enhance the delivery of dox across the BBB.

Development of an in situ mouse brain perfusion model and its application to mdr1a P-glycoprotein-deficient mice

An in situ mouse brain perfusion model predictive of passive and carrier-mediated transport across the blood-brain barrier (BBB) was developed and applied to mdr1a P-glycoprotein (Pgp)-deficient mice [mdr1a(-/-)]. Cerebral flow was estimated from diazepam uptake. Physical integrity of the BBB was assessed with sucrose/inulin spaces; functional integrity was assessed with glucose uptake, which was saturable with a Km of approximately 17 mmol/L and Vmax of 310 mmol x 100 g(-1) x min(-1). Brain uptake of a Pgp substrate (colchicine) was significantly enhanced (two- to fourfold) in mdr1a(-/-) mice. These data suggest that the model is applicable to elucidating the effects of efflux transporters, including Pgp, on brain uptake.

Transport of cationized anti-tetanus Fab'2 fragments across an in vitro blood-brain barrier model: involvement of the transcytosis pathway

Tetanus neurotoxin reaches the CNS by axonal retrograde transport and thus becomes inaccessible to current treatments. A possible strategy to improve current therapy for tetanus disease would be the vectorization of Fab'2 fragments, allowing their delivery into the CNS. The purpose of this study was to investigate whether after cationization anti-tetanus Fab'2 fragments are able to cross the blood-brain barrier, the first obstacle to CNS delivery. We used primary cocultures of bovine brain capillary endothelial cells and newborn rat astrocytes as an in vitro model to study the binding and transport of cationized Fab'2 (cFab'2) fragments across the brain endothelium. We first show that cationization does not alter Fab'2 affinity for tetanus toxin. Then we demonstrate that after cationization Fab'2 fragments are able to bind to the negative charges on the surface of endothelial cells and subsequently to be transported across the endothelial cell monolayer without any modification of affinity. Finally, using fluorescence microscopy, we show that cFab'2 fragments are transported through endocytotic vesicles. The present study demonstrates that cationization allows Fab'2 directed against tetanus toxin to be transported through brain endothelium by adsorptive-mediated transcytosis. We suggest that this vectorization way could be a promising delivery strategy for carrying anti-tetanic immunoglobulin fragments across the blood-brain barrier to improve tetanus treatment.

Single- and repeated-dose pharmacokinetics of intramuscular thiocolchicoside in healthy volunteers

OBJECTIVE

The aim of this study was to investigate the pharmacokinetics and the accumulation and stationarity of thiocolchicoside after repeated intramuscular administration.

METHOD

The pharmacokinetics of thiocolchicoside were studied in 6 healthy male volunteers after one single dose and repeated intramuscular doses of 4 mg twice a day for seven days. Plasma and urine samples were assayed for thiocolchicoside levels by a radioimmunoassay (RIA) using a cross-reacting colchicine-specific polyclonal antibody. The pharmacokinetic parameters between the first and the last days were compared using Student's t-test.

RESULTS

Thiocolchicoside pharmacokinetic parameters, calculated after the single dose using non-compartmental analysis, were in good agreement with those obtained in previous studies. Following the repeated-dose regimen, the terminal half-life was not significantly different (2.7 (0.3) h) from that predicted from a single-dose (2.8 (0.2) h). The accumulation ratio, based on the repeated-dose/single-dose ratio of AUCtau was approximately 1.25. A decrease of CLT/f was found between day 1 (24.1 (5.2) l/h) and day 7 (19.9 (3.4) l/h), suggesting that moderate time-related alterations occur in the pharmacokinetics of thiocolchicoside, which may be due to a change in its CL(NR) (CL(R) was constant) or to the extent of bioavailability, explained by enterohepatic recirculation.

CONCLUSION

Serum thiocolchicoside concentrations accumulated to steady-state when the drug was given twice a day for seven days and the pharmacokinetics were modified. But no adjustments of dose or dosing interval were necessary because the accumulation did not lead to marked change in the plasma levels.

Elevated concentrations of morphine 6-beta-D-glucuronide in brain extracellular fluid despite low blood-brain barrier permeability

1 This study was done to find out how morphine 6-beta-D-glucuronide (M6G) induces more potent central analgesia than morphine, despite its poor blood-brain barrier (BBB) permeability. The brain uptake and disposition of these compounds were investigated in plasma and in various brain compartments: extracellular fluid (ECF), intracellular space (ICS) and cerebrospinal fluid (CSF). 2 Morphine or M6G was given to rats at 10 mg kg(-1) s.c. Transcortical microdialysis was used to assess their distributions in the brain ECF. Conventional tissue homogenization was used to determine the distribution in the cortex and whole brain. These two procedures were combined to estimate drug distribution in the brain ICS. The blood and CSF pharmacokinetics were also determined. 3 Plasma concentration data for M6G were much higher than those of morphine, with Cmax and AUC 4-5 times more higher, Tmax shorter, and VZf-1 (volume of distribution) and CL f(-1) (clearance) 4-6 times lower. The concentrations of the compounds in various brain compartments also differed: AUC values for M6G were lower than those of morphine in tissue and CSF and higher in brain ECF. AUC values in brain show that morphine levels were four times higher in ICS than in ECF, whereas M6G levels were 125 higher in ECF than in ICS. 4 Morphine entered brain cells, whereas M6G was almost exclusively extracellular. This high extracellular concentration, coupled with extremely slow diffusion into the CSF, indicates that M6G was predominantly trapped in the extracellular fluid and therefore durably available to bind at opioid receptors.

Time- and dose-dependent digoxin redistribution by digoxin-specific antigen binding fragments in a rat model

To study the influence of the interval between digoxin intake and digoxin-specific antigen binding fragment (DSFab) administration, we developed a rat kinetic model. 3H-digoxin (0.77 nmol/kg) was injected by intravenous route and DSFab was injected at different times (12, 30 or 60 min) corresponding to different levels of 3H-digoxin distribution (50, 83 and 100%). The effect of increasing the molar DSFab/3H-digoxin ratio from 1 to 5 was also investigated. To evaluate DSFab effect on the 3H-digoxin pharmacokinetics, we also investigated the pharmacokinetics of the 125I-DSFab and DSFab-3H-digoxin complex. 3H-digoxin and DSFab-3H-digoxin complex pharmacokinetics showed that DSFab altered immunoreactive 3H-digoxin pharmacokinetics. In redistribution studies performed 12, 30 or 60 min after 3H-digoxin injection, DSFab bound immunoreactive 3H-digoxin including native 3H-digoxin and active metabolites of 3H-digoxin. This binding induced a redistribution process of immunoreactive 3H-digoxin in the DSFab distribution compartment and was evaluated by the redistribution fraction (F(R)). F(R) was 23% lower at 60 min than at 12 and 30 min, and by increasing the DSFab/3H-digoxin ratio from 1 to 5, F(R) increased by 60%. In conclusion, the longer the time interval between digoxin intake and DSFab administration, the lower the efficacy of the redistribution process. This effect could be reduced by increasing the DSFab dose.

Rapid determination of valaciclovir and acyclovir in human biological fluids by high-performance liquid chromatography using isocratic elution

A rapid high-performance liquid chromatographic assay with isocratic elution is developed for the simultaneous quantification of valaciclovir (VACV) prodrug and its active converted compound, acyclovir (ACV), in biological fluids of treated patients. For serum, the samples are deproteinized with perchloric acid in presence of 1-methylguanosine as the internal standard (IS). For urine and dialysis liquid, the samples are diluted with a mobile phase containing the IS, then filtered. VACV, ACV and the IS are separated on a SymmetryShield RP-8 column with acetonitrile-ammonium phosphate buffer as the mobile phase and detected at 254 nm. The chromatographic time is about 12 min. The relative standard deviations (RSD) of VACV and ACV standards are between 0.5 and 3.5%. Most endogenous nucleosides and their metabolites, psychotropic drugs and drugs of abuse are shown not to interfere with this technique. The method has been applied to study the pharmacokinetics of VACV and ACV in serum, dialysis liquid and urine of renal failure patients on continuous ambulatory peritoneal dialysis (CAPD) under oral treatment of VACV.

The human and rat recombinant receptors for advanced glycation end products have a high degree of homology but different pharmacokinetic properties in rats

The accelerated formation of advanced glycation end products (AGEs) is implicated in diabetic microvascular and macrovascular complications. The binding of AGEs to their cellular surface receptor (RAGE) induces vascular dysfunction and in particular an increase in vascular permeability. We previously demonstrated that rat recombinant RAGE (rR-RAGE) produced in insect cells corrected the hyperpermeability due to RAGE-AGE interaction and that pharmacokinetic properties of rR-RAGE after i.v. administration in rats were compatible with a potential therapeutic use. In the present study, we showed that recombinant human RAGE (rH-RAGE) had a similar efficacy in inhibiting AGE-induced endothelial alteration and in reducing the hyperpermeability observed in streptozotocin-induced diabetic rats. (125)I-rH-RAGE elimination half-life after i.v. administration was similar in diabetic and normal rats (53.7 +/- 7.6 and 45.3 +/- 4.0 h, respectively). The presence of AGEs is responsible for a higher distribution volume in diabetic rats compared with normal rats (15.3 +/- 2.7 and 7.7 +/- 0. 7 l/kg, respectively). Immunoreactive (125)I-rH-RAGE decreased more rapidly than did immunoreactive (125)I-rR-RAGE. The differences between (125)I-rH-RAGE and (125)I-rR-RAGE pharmacokinetics in rat may be related to differences in potential O-glycosylation and protease cleavage sites between the two RAGE molecules.

Effect of social isolation on the metabolism of morphine and its passage through the blood-brain barrier and on consumption of sucrose solutions

RATIONALE

We have previously shown that place preference conditioning to morphine was observed in social mice at the dose of 8 mg/kg, whereas 4 weeks of isolation impairs the place preference conditioning to morphine (8-100 mg/kg).

OBJECTIVE

The present study, aimed at explaining this phenomenon, tested three hypotheses: firstly, a reduced sensitivity to reinforcers induced by isolation; secondly, a difference in morphine disposition in isolated and social mice; thirdly, an altered blood-brain barrier transport of morphine in isolated mice.

METHODS

In the sucrose experiments, mice had the choice (for 24 h) between a bottle containing tap water and a bottle containing a sucrose solution. Three sucrose concentrations were used: 0.5, 1 and 2% (weight/weight). In the morphine disposition experiments, the plasma levels of morphine and of morphine-3-glucuronide (M3G) were measured for 240 min. The brain concentrations of morphine was measured at 15 and 30 min. The passage of morphine through the blood-brain barrier was measured using a method modified from that of Takasato (1984).

RESULTS

The preference for the sucrose solutions was significantly greater in isolated than in social mice for the concentration of 2%. Isolation reduced the plasma levels of morphine and of M3G, but did not alter the brain concentration of morphine. The passage of morphine through the blood-brain barrier was altered by isolation in neither of the eight structures examined.

CONCLUSIONS

We conclude that the behavioural effect of isolation observed in the conditioned place preference to morphine may depend on changes both in morphine disposition and in the sensitivity to reinforcers in isolated mice.

Production and characterization of 22 monoclonal antibodies directed against S 20499, a new potent 5-HT1A chiral agonist: influence of the hapten structure on specificity and stereorecognition

PURPOSE

An immunoconjugate model was proposed to produce stereoselective monoclonal antibodies (MAbs) for the quantitation of a 5-HT1A agonist, S 20499. MAbs produced were characterized in terms of stereoselectivity and specificity towards the opposite enantiomer and structural analogs.

METHODS

The immunogen was formed following the effective addition of a butanoic acid spacer arm between the parent S 20499 structure and bovine serum albumin (BSA). After fusion (modified Köhler and Milstein's procedure), specificity of MAbs was obtained using the Abraham's criteria. Experimental and calculated partition coefficients were determined.

RESULTS

Twenty-two hybridoma cell lines were established secreting MAbs (apparent association constants ranging from 1.1 x 10(8) to 2.8 X 10(9) M(-1)). Several MAbs showed cross-reactivity levels of less than 5% with S 20500 (optical antipode), which could allow a stereospecific assay to be set up. Both chroman and azaspiro moieties were part of the epitopic site. Dealkylation and hydroxylation(s) led to various crossreactivity levels. Four antibody families were described in terms of specificity.

CONCLUSIONS

This study highlighted the influence of the immunoconjugate construction (coupling site and type of spacer arm) in the immuno-stereospecificity of Abs. The results obtained for two monohydroxylated metabolites suggest that the lipophilicity behavior could be a valuable tool for predicting Ab-crossreactivity.

Pharmacokinetics and organ distribution of cationized colchicine-specific IgG and Fab fragments in rat

Pharmacokinetics of cationized goat colchicine-specific polyclonal immunoglobulin G (IgG) and antigen binding fragment (Fab) (cIgG and cFab, respectively) were studied in male adult Sprague-Dawley rats and compared with those of the native proteins (nIgG and nFab). All proteins were radioiodinated by the Iodogen method, and kinetics were investigated following trichloroacetic acid (TCA) precipitation or immunoprecipitation. Deiodination and catabolism were more pronounced with the cationized than the native proteins, especially for cFab. Both cIgG and cFab in plasma decreased more rapidly than nIgG and nFab. The elimination half-lives were 52.9 and 81.8 h for cIgG and nIgG, respectively. In addition, there was a 74-fold increase in the volume of distribution and a 114-fold increase in the systemic clearance of cIgG compared with nIgG. For cFab, the volume of distribution and systemic clearance were increased 6.4- and 3.5-fold, respectively. Organ uptake of cIgG and cFab was markedly increased compared with that of nIgG and nFab, especially in kidney, liver, spleen, and lung. Renal clearance of cIgG and cFab was also increased 30- and 10-fold compared with that of nIgG and nFab, respectively. The present data suggest that cationization of colchicine-specific IgG and Fab fragments increased the organ distribution and greatly altered their pharmacokinetics. Nevertheless, the smaller molecular size of Fab versus IgG did not enhance the distribution and clearance of cFab. These data pave the way for evaluating the biological efficacy of these more tissue-organ-interactive antibodies.

A cross-over pharmacokinetic study of a double viral inactivated factor IX concentrate (15 nm filtration and SD) compared to a SD factor IX concentrate

A double blind randomized cross-over multi-center study has been conducted to compare the pharmacokinetic and coagulation activation markers of high-purity factor IX concentrate subjected to both solvent/ detergent (SD) treatment and 15 nm-filtration (FIX-SD-15) with the licensed product subjected only to solvent-detergent (FIX-SD). This filtration process allows the elimination of small particles, such as non-enveloped viruses (i.e., hepatitis A and parvovirus B19). Eleven severe hemophilia B patients (FIX coagulant activity <2 IU/dl) received one infusion of 60 IU/kg of FIX-SD and one infusion of 60 IU/kg of FIX-SD-15 at least at 10 days interval. Blood samples were obtained before and at various time up to 72 h after infusion. The decay curves of factor IX (FIX:C and FIX:Ag) were evaluated by a model independent method. Bioequivalence was found between the two concentrates using the Schuirmann test. The mean FIX:C and FIX:Ag recovery of FIX-SD-15 was 1.08 and 0.89 IU/dl/IU/kg respectively with a mean half-life of 33.3 h for FIX:C and 25.6 h for FIX:Ag. Six months after initial enrollment, pharmacokinetic parameters were similar in the 7 patients tested. There was no significant variation of prothrombin fragment 1+2 and thrombin-antithrombin complexes measured up to 6 h after infusion, indicating that there was no activation process after administration of FIX. In conclusion, these data demonstrate that the introduction of a 15 nm filtration does not alter the pharmacokinetic profile of a well characterized SD FIX concentrate while providing additional viral safety.

Influence of various combinations of specific antibody dose and affinity on tissue imipramine redistribution

1. This study was designed to evaluate the distribution kinetics of imipramine (Imip) in the brain and the main peripheral organs (heart, kidney, liver and lung) of rats, and to establish the relationship between the redistribution of Imip from these tissues and the immunoreactive capacity (dose and affinity) of anti-TCA IgG. 2. [3H]-Imip (1 nmol kg(-1) body weight) was injected intravenously 6 min before the i.v. injection of antibodies. At this time, the concentrations of Imip and its main metabolites in plasma were determined. The radioactivity measured corresponded to 91.7% Imip, indicating that the pharmacokinetics reflected essentially Imip. Plasma and tissue Imip contents were measured over the interval 1 to 90 min in control and in treated rats. The antibodies used were a murine monoclonal IgG1 (Ka=3.8 10(7) M(-1)) at an IgG1/Imip molar ratio of 1000 (IgG1 1000), and a sheep polyclonal IgG (TAb, Ka=1.3 10(10) M(-1)) at IgG/ Imip molar ratios of 1, 10 and 100 (TAb1, TAb10 and TAb100). 3. The anti-TCA IgG increased the plasma [3H]-Imip concentrations: the AUC1-->60 min for [3H]-Imip were 4 (IgG1 1000), 9 (TAb1), 33.9 (TAb10) and 41.4 (TAb100) times higher in the treated groups than in the controls. The opposite effect occurred in the brain, heart and lungs, with large, rapid decreases in Imip. The increase in plasma Imip and the decrease in tissue Imip depended on the immunoreactive capacity (NKa) of the antibody, where N=molar concentration of IgG binding sites and Ka=IgG affinity constant. Maximal plasma and tissue redistribution occurred when NKa=33.8 x 10(4). 4. Imip redistribution can be controlled using various doses or affinities of specific antibodies, and the resulting rapid, extensive Imip redistribution from the main target organs could be very promising for TCA detoxification.

Hepatic disposition and toxicity of cationized goat immunoglobulin G and fab fragments in isolated perfused rat liver

Colchicine-specific goat IgG and Fab fragments were cationized by covalent coupling of hexamethylenediamine. The immunoreactivity of antibodies was not changed following cationization. The interaction of 125I-radiolabeled native (nIgG and nFab) and cationized immunoglobulin G (cIgG) and Fab fragments (cFab) with liver was investigated using isolated perfused rat liver (IPRL) and isolated rat hepatic parenchymal cells (PCs) and nonparenchymal cells (NPCs) in suspension. 125I-cIgG or 125I-cFab were more rapidly cleared from the perfusate than the corresponding native proteins. Both cIgG and cFab declined biexponentially over time in the perfusate. In contrast, the native IgG and Fab decreased monoexponentially. The half-lives of the initial and terminal phases were 5.2 +/- 1.6 min and 355.1 +/- 17.2 min for cIgG and 14.7 +/- 3.4 min and 552.4 +/- 23.7 min for cFab. The terminal half-lives of nIgG (467.4 +/- 11.6 min) and nFab (880.1 +/- 39.6 min) were longer than those of cationized molecules. The biliary protein extraction ratio of cationized IgG and Fab was greater than that of native IgG and Fab: 0.13% (cIgG), 0.02% (nIgG), 0.23% (cFab), and 0.17% (nFab). The uptake of cIgG and cFab by both PCs and NPCs was dose-dependent and was about 6-fold and 8-fold higher than that of their native counterparts, respectively. Throughout the experiment, liver viability was determined, and no toxicity was observed according to physiological analysis (bile flow rate, portal vein pressure, and pH) and biochemical analysis (glucose and hepatic enzymes: alanine transaminase, aspartate transaminase, lactate dehydrogenase) in perfusate.

Interspecies scaling of clearance and volume of distribution for horse antivenom F(ab')2

F(ab')2 fragments are sometimes preferred to whole IgG for therapeutic or diagnostic uses. Preclinical pharmaceutical development studies are necessary before their use in humans. Here we propose an allometric approach among three mammalian species to predict F(ab')2 pharmacokinetic parameters in humans. Plasma disposition of horse antivenom F(ab')2 fragments labeled with iodine 125 was studied at a dose of 10 mg/kg i.v. in mice, rats, and rabbits. Using the allometric method, we demonstrate that the pharmacokinetic parameters that correlated with body weight were distribution volume (Vdc (ml) = 0.125 W0.87; Vdss (ml) = 0.251 W0.87; Vd beta (ml) = 0.290 W0.87, r2 = 1), total clearance (Cltot (ml/h) = 0.049 W0.53, r2 = 0.99), and terminal half-life (t1/2 beta (h) = 4.35 W0.33). The F(ab')2 plasma concentration-time data plotted as a complex Dedrick relationship were superimposable. Using these allometric techniques, Vdss, Vd beta, Cltot, and t1/2 beta were calculated as 4.12 liter, 4.78 liter, 19.07 ml/h, and 7.2 days, respectively, for a human subject of 70 kg body wt. Predicted human pharmacokinetic parameters were comparable for volume of distribution with the value reported by Hnatowich et al. (Cancer Res. 47, 6111-6117, 1987): 3.5 liter. However, the clearance was six-fold lower than values given by Hnatowich et al. (130 ml/h) and Ho et al.

Intestinal absorption and stability of morphine 6-glucuronide in different physiological compartments of the rat

Morphine 6-glucuronide (M6G) is an active metabolite of morphine that could be used as a drug, but its hydrolysis into morphine remains controversial. We investigated the acidic hydrolysis of M6G and found that the recovery of morphine did not exceed 5%. The stability of M6G was studied in different physiological compartments of male Sprague-Dawley rats. The formation of morphine after M6G incubation in feces was under 2% in the small intestine, whereas the formation of morphine in colon feces represented 85.6 +/- 12.9% of the initial concentration of M6G. The stability of M6G was also determined ex vivo using the isolated perfused rat liver. The hepatic extraction ratio of M6G was very low (0.04 +/- 0.02), but 88. 7 +/- 11.2% of the dose was excreted in bile. The elimination half-life of M6G in the perfusate (66.4 +/- 20.6 min) was higher than the elimination half-life in bile (18.6 +/- 2.5 min). The hydrolysis of M6G was low, with only 7.7% and 0.03% of morphine in the perfusate and bile, respectively. The perfusate level of morphine 3-glucuronide (M3G) resulting from morphine conjugation was 4.9 +/- 3.6%. An in vivo experiment demonstrated that after oral administration, M6G was absorbed per se in the proximal intestine, and the process was prolonged over the 24-hr experiment due to its reabsorption following enterohepatic recirculation. Finally, 10.5 +/- 4.3% of morphine and 12.9 +/- 5.1% of M3G compared with M6G AUCs were found in plasma. These results show that M6G is weakly converted into morphine when orally absorbed, with a kinetic profile similar to a slow release formulation.

Redistribution of imipramine from regions of the brain under the influence of circulating specific antibodies

The kinetics of brain-to-blood redistribution of imipramine (IMI) was assessed in nine brain regions of control rats and rats given anti-tricyclic antidepressant (anti-TCA) antibody. Two antibodies were given intravenously 6 min after intravenous [3H]IMI (1 nmol/kg). One was a murine monoclonal IgG1 (Ka = 3.8 x 10(7) M(-1)) at an IgG/IMI molar ratio of 1,000 (IgG1,000), and the other was a sheep polyclonal IgG (TAb; Ka = 1.3 x 10(10) M(-1)) at IgG/IMI molar ratios of 1, 10, and 100 (TAb1, TAb10, and TAb100). In the control rats, IMI was rapidly taken up by the brain (Cmax at 5 min) with no significant differences among the brain regions (4.1 +/- 0.4 to 5.4 +/- 0.6 pmol/ g), and brain IMI then declined monoexponentially with a half-life of 44.2 min (cerebellum) to 77.3 min (hippocampus). The greatest IMI content was in the frontal cortex and the lowest in the cerebellum. The antibodies (except TAb1) stimulated the extent and rate of IMI redistribution from all the brain regions depending on the immunoreactive capacity (NKa) of the antibody. The antibody with the highest NKa (TAb100) had the greatest effect. The fraction of IMI removed from the brain was 58-74%, and the redistribution half-life was 7.9-15.6 min; the mean residence time was reduced by 66-75% (11.8-23.9 min). These results demonstrate that circulating anti-TCA IgG rapidly and reliably removes IMI from the brain, indicating that immunotoxicotherapy could be an efficient procedure for accelerating the removal of TCA from the brain.

P-glycoprotein is more efficient at limiting uptake than inducing efflux of colchicine and vinblastine in HL-60 cells

PURPOSE

To investigate the role of the P-glycoprotein (P-gp) drug efflux pump in the intracellular disposition of colchicine and vinblastine.

METHODS

Uptake and efflux kinetics were studied in vitro in human lymphocytes and in HL-60 cells with or without the P-gp modulator, verapamil.

RESULTS

In human lymphocytes, colchicine was slowly taken up (uptake half-life was 18.9+/-1.1 hr.) and verapamil increased colchicine uptake by 37%, whereas it did not modify colchicine efflux from cells. In HL-60 cells, colchicine uptake was non-linear and slower than that of vinblastine, the colchicine uptake half-life (11.1+/-0.5 hr.) being 25-fold longer than that of vinblastine at 25 nM. Verapamil did not significantly modify colchicine uptake half-life, but increased its intracellular accumulation by 23% and that of vinblastine by 81%. Immuno-flow cytometry showed that P-gp expression in HL-60 cells increased significantly from 24 hr. following colchicine or vinblastine exposure. The significant increase in colchicine uptake induced by verapamil at 24 hr. was correlated with this enhanced P-gp expression. The drug efflux half-life was 11.5-fold higher for colchicine (23+/-0.9 hr) than vinblastine, indicating a much slower elimination of colchicine from cells that could be related to its longer dissociation half-life from the tubulin receptor. Verapamil treatment did not modulate either colchicine or vinblastine efflux kinetics, suggesting that the intracellular drugs are not available to the transmembrane P-gp binding sites.

CONCLUSIONS

P-gp may not be the main reason for the slowness of colchicine uptake. It may be more efficient at controlling entry of colchicine and vinblastine through the plasma membrane than at mediating their efflux from HL-60 cells.

Renal tolerance of digoxin-specific Fab fragments in the rat

Renal markers were investigated over 96 h in male Sprague-Dawley rats after i.v. administration of 10.7 mg kg(-1) of digoxin-specific Fab fragments (DSFab). The dose was calculated by an allometric equation as equivalent to a high clinical dose. DSFab both alone and pre-incubated with digoxin were tested. None of the markers (creatinine clearance, fractional excretion of sodium, urinary activities of gamma-glutamyl transferase and alkaline phosphatase) were significantly altered in treated rats compared to control rats. Thus no renal toxicity due to DSFab alone or bound to digoxin was observed when administered at 10.7 mg kg(-1) in rats.

Simultaneous microdialysis in brain and blood of the mouse: extracellular and intracellular brain colchicine disposition

A simultaneous brain and blood microdialysis system was developed to study the passage of colchicine through the blood-brain barrier in the mouse. Colchicine was administered as a bolus in the jugular vein (1.5 mg kg-1) and its hippocampal extracellular fluid (ECF) and blood kinetics were determined over a 4 h period using two microdialysis probes, one in the dorsal hippocampus, the other in the inferior vena cava. Colchicine rapidly diffused into the hippocampus (maximum concentration in the first dialysate sample) and brain and blood concentrations declined in parallel, suggesting rapid equilibration between these two compartments. However, only 6. 7% of total blood colchicine, 14% of unbound colchicine was present in the hippocampus suggesting that the P-glycoprotein efflux pump limits colchicine uptake by the brain. We also found, using conventional tissue homogenate analysis in parallel, that the concentration of colchicine in the hippocampal ECF was 10 times less than that in the intracellular space and that the hippocampus colchicine concentration was 2.8 times higher than that of the rest of the brain. This study shows that the simultaneous brain and blood microdialysis can be used to measure the passage of colchicine through the blood-brain barrier and to estimate the brain extra- and intracellular distribution of colchicine.

Preclinical assessment of immunoreactivity of a new purified equine F(ab')2 against European viper venom

The immunological and pharmacokinetic properties of a new, further purified, pasteurized preparation of equine F(ab')2 (VIPERFAV) against Vipera aspis, Vipera berus, and Vipera ammodytes venom were compared with the current equine F(ab')2 preparation (IPSER Europe). Affinity constants of the V. aspis-specific F(ab')2 were determined using biosensor technology and found to be in the range of 10(8) M-1 for the four antigenic fractions of V. aspis toxins and for both F(ab')2 preparations. The improvement of 51% in the specific activity (LD50 mg-1) of the new F(ab')2 was in close agreement with the 1.8-fold increase in the immunoreactive fraction of the new preparation. In vivo investigations of venom immunocomplexation by F(ab')2 in rabbits confirmed the ability of F(ab')2 to neutralize and redistribute toxin venom. Infusion of a stoichiometric molar ratio (i.e., 1 mg kg-1) of the new antivenom induced a 2.3-fold elevation of the plasma venom concentration with a Tmax observed 8 h after F(ab')2 administration and a decline in the terminal half-life from 31.92 +/- 4.49 h to 16.73 +/- 4.34 h, in contrast, for the venom alone. The area under the curve was 1.4-fold greater in the VIPERFAV group than in the IPSER Europe group during the post-F(ab')2 infusion period. Increasing the F(ab')2 dose to 3 mg kg-1 increased by 27% the percent of venom bound to F(ab')2. Finally, the greater the venom distribution, the smaller and less pronounced the plasma redistribution. These results demonstrate that the purification and pasteurization steps involved in the preparation of the new F(ab')2 have no deleterious influence on F(ab')2 affinity but, on the contrary, improve the protective efficacy. Alteration of viper venom kinetics by specific F(ab')2 antivenom was also shown to be dependent on the interval between of F(ab')2 administration and venom bite and on the specific F(ab')2 dose administered.

Stereoselectivity of antibodies for the bioanalysis of chiral drugs

The use of immunoassay techniques represents an alternative approach to the more common chromatographic methods for the determination of the concentrations of chiral drugs. In the development of the former technique, the inherent stereoselectivity of the antibodies used appears to be an important parameter to be studied. The structural features of the drug, including the environment around the asymmetric center, the flexibility of the molecule and the ability of the molecule to undergo racemization, contribute to the molecule's ability to be recognized by stereoselective antibodies. These parameters are intrinsic and can not be influenced by the investigator. On the other hand, other parameters can be modified to favor the raising of highly stereoselective antibodies. These include the synthesis of an appropriate hapten; the selection of an optimal spacer arm between the hapten and the carrier protein used for the immunization procedure; and the choice of appropriate immunization and antibody-screening procedures. The purification of antibodies using affinity chromatography may also facilitate the selection of stereoselective antibodies.

Pharmacokinetics of digoxin-specific Fab: effects of decreased renal function and age

AIMS

To study the influence of age and renal function on digoxin-specific Fab (DS-Fab) pharmacokinetics.

METHODS

Sixteen patients (35-91 years) with creatinine clearance ranging from 10.6 to 122.1 ml min(-1) who had been admitted to hospital with severe digoxin or digitoxin self-poisoning were treated with DS-Fab (80 to 800 mg). Plasma DS-Fab concentrations were determined by radioimmunoassay.

RESULTS

The mean (s.d.) distribution and elimination half-lives, apparent volume of distribution and total body clearance were 1.1 +/- 0.4 h, 20.2 +/- 7.3 h, 13.1 +/- 5.8 l, and 17.6 +/- 10.8 ml min(-1), respectively. Interindividual variability of DS-Fab total body clearance was linked linearly with the decrease in creatinine clearance or with the increase in age and DS-Fab distribution volume was not dependent on creatinine clearance or age.

CONCLUSIONS

The data suggest that DS-Fab should be given to elderly and renal-impaired patients at doses similar to those given to younger or normal renal function patients.

Recombinant advanced glycation end product receptor pharmacokinetics in normal and diabetic rats

Vascular dysfunction in patients with diabetes mellitus is related to advanced glycation end product (AGE) formation. We previously showed that AGEs produce an increase in vascular permeability and generated an oxidant stress after binding to the receptor (RAGE) present on endothelium. RAGE, a 35-kDa protein that belongs to the immunoglobulin superfamily, has been cloned from a rat lung cDNA library, and recombinant rat soluble RAGE (rR-RAGE) has been produced in insect cells. The sequence of RAGE is highly conserved between human and rat. We studied the biological effect of rR-RAGE and pharmacokinetics of 125I-rR-RAGE after intravenous or intraperitoneal administration in normal and streptozotocin-induced diabetic rats. rR-RAGE prevented albumin or inulin transfer through a bovine aortic endothelial cell monolayer, restored the hyperpermeability observed in diabetic rats or induced in normal rats by diabetic rat red blood cells, and corrected the reactive oxygen intermediate production after intravenous or intraperitoneal administration. After intravenous injection of 125I-rR-RAGE, the distribution half-life was longer (p < or = 0.01) in diabetic (0.15 and 4.01 hr) than in normal (0.02 and 0.21 hr) rats, as was the case for the elimination half-lives (diabetic, 57.17 hr; normal, 26.02 hr; p < or = 0.01). Distribution volume was higher in diabetic than in normal rats (6.94 and 3.24 liter/kg, respectively; p = 0.049). Our study showed that rR-RAGE was biologically active in vivo and slowly cleared, which suggests it could be considered as a potential therapy.

Role of P-170 glycoprotein in colchicine brain uptake

To study the role of P-glycoprotein (P-gp) in the delivery of colchicine from blood to brain, the pharmacokinetics of colchicine in plasma and brain was studied in the rat by an in vivo method and by the in situ brain perfusion technique. Colchicine was administered intravenously at three doses (1, 2.5, and 5 mg/kg) with or without an inhibitor of P-gp, verapamil (0.5 mg/kg i.v.); blood and brain samples were taken at t = 1, 2, and 3 hr. Areas under the colchicine curve at doses from 2.5 to 5 mg/kg were proportional to dose for plasma but not for brain. At a colchicine dose of 5 mg/kg, verapamil co-treated rats showed a 1.65-fold enhancement of the colchicine concentration in plasma but a 4.5-fold enhancement in brain. During short experimental times (in situ brain perfusion technique), a comparable enhancement was found (4.26-fold): mean distribution volumes of colchicine were enhanced from 0.23 +/- 0.17 to 0.98 +/- 0.19 microl/g for the eight gray areas, and no effect was observed in the choroid plexus, which do not express P-gp. These results clearly show that P-gp, present at the luminal surface of the capillary endothelial cells, is responsible for the weak penetration of colchicine into the brain.

Production and characterization of polyclonal anti-S 20499 antibodies: influence of the hapten structure on stereospecificity

Immunoassays were studied as an alternative to HPLC methods for the stereoselective determination of a chiral drug, S 20499, a new anxiolytic compound that is chemically related to buspirone. The production of highly stereospecific polyclonal antibodies was sought following the construction of appropriately optimized hapten-protein conjugates. This process involved the selection of the structure and the length of the spacer arm used to couple S 20499 to the carrier protein as well as deciding on the location of the coupling site with respect to the chiral center. Two haptens were prepared: one a derivative resembling the original structure of S 20499, with the effective addition of a carboxylic acid group, and a second with the effective addition of a butanoic acid moiety that is supposed to favor stereorecognition. Six stereospecific polyclonal antisera were obtained in rabbits with two groups of antibody families defined in terms of specificity. Both approaches gave high levels of stereospecificity (cross-reactivity towards the optical antipode of S 20499 ranged from 4.1% to < 0.1%). Although it did not decrease the mean apparent affinity constant, the longer spacer improved antibody specificity by decreasing cross-reactions towards dealkylated S 20499 derivatives. Hence, the addition of a four carbon atom bridge should be a valuable tool for increasing antibody stereospecificity with no drawbacks in terms of specificity and affinity. It was also shown that long immunization periods appear to have no effect on the stereospecificity of the antibodies obtained.