Transport of drugs through human erythrocyte membranes. Change of transport by introduction of amino group or amino acids in benzoic acid

The transporting properties of benzoic acid (BA) and its derivatives such as hippuric acid (HPA), p-aminohippuric acid (AHPA), N-benzoyl-beta-alanine (NBA), p-amino-N-benzoyl-beta-alanine (ANBA), N-benzoyl-6-aminocaproic acid (NBC), p-amino-N-benzoyl-6-amino-caproic acid (ANBC), o-, m- or p-hydroxybenzoic acid (o-, m- or p-HBA) and alpha- or gamma-resorcylic acid (alpha- or gamma-RA) through erythrocyte membranes were examined in two aspects of the inward direction from a drug-containing medium into the erythrocyte and the outward direction from the drug-containing erythrocyte to the drug-free medium. The significant difference in the rate of transport was observed between both directions. The introduction of a few methylene groups into the amino acid moieties of BA derivatives was slower in the rate of transport than that of more methylene groups. The rate of transport was slowed down by the introduction of amino group at p-position: NBC greater than NBA greater than HPA much greater than ANBC greater than ANBA greater than AHPA. The rate of transport in these drugs was correlated with the changes in partition coefficients. The same correlation was also observed in the drugs to which hydroxyl groups were introduced except alpha- or gamma-RA. This transport of alpha- or gamma-RA suggested the participation of the band 3 anion transporter protein.     

Transport of drugs through human erythrocyte membranes: pH dependence of drug transport through labeled human erythrocytes in the presence of band 3 protein inhibitor.

To reveal the role of the band 3 anion transport protein of the erythrocyte membrane in drug transport through the membrane, the possible effects of inhibitors of anion transport on the permeability of some anionic drugs were examined. The amounts of these drugs that permeated varied markedly with the pH of the outer medium around human erythrocytes that contained the band 3 protein inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS). In the pH range 7.0-8.0, the membrane permeability of drugs through DIDS-treated erythrocytes was affected by a slight pH change (0.2), whereas that through the intact erythrocytes was not pH dependent. These results suggest that the band 3 protein acts not only as a channel for the transport of anions or some anionic drugs but also as protection for the transport system from changes in the pH of the outer medium.     

Interaction of benzoic acid derivatives with the transport system of glucose in human erythrocytes

The effect of benzoic acid derivatives on glucose uptake in human erythrocytes was studied. It was observed that all compounds competitively inhibit glucose transport and that the inhibition was a reversible process. The kinetic analysis revealed that benzoic acid derivatives form complexes with the transport system with either one or two molecules bound to the transport site. Elongation of the methyl group of the ester to the butyl group led to a higher affinity of the benzoic acid derivatives to the transport system. Their inhibitory potency (except some compounds with free COOH groups) correlated with their octanol-water partition coefficients, i.e. with their hydrophobicity. Comparing the inhibitory potencies of the local anesthetics with those of the benzoic acid derivatives it was found that the substituted NH₂ groups did not intensify the effect of the local anesthetics.     

Colloidal, partition and binding properties of phenothiazine derivatives. 4. Relationships between partition coefficients and association properties]

Colloidal, Partition and Binding Properties of Phenothiazine Derivates, IV: Relationships Between Partition Coefficients and Molecular Association Partition coefficients of 17 phenothiazine derivatives were determined in octanol/acetate buffer (pH 4.3) and arachis oil/acetate buffer (pH 4.3 and 5.3). They were found to be higher in octanol/acetate buffer of pH 4.3 than in arachis oil/acetate buffer of pH 4.3, and they are remarkably influenced by the substituents in 2-position. There is a linear relationship between surface tension and partition coefficients of the amino derivatives and a functional one for the piperazine derivatives of phenothiazine. Similar relationships exist between partition coefficients and aggregation numbers.     

Application of diffusion theory to the relationship between partition coefficient and biological response

A diffusion model for transport through multilaminates is studied as a possible way to predict the optimal biological response of a set of congeners with respect to the oil-water partition coefficient, P. The model predicts the bilinear form typical of biological response data and, unlike the earlier kinetic model, also relates the results to physical processes, predicts the structure with the optimal response in terms of diffusion constants, and shows such an optimum prior to steady state for an infinite dose. Diffusion through an oil-water multilaminate causes extraordinary separation of permeating species based on partition coefficient and diffusion constant for times shorter than the lag time.     

Effect of hydrocarbon chain length on renal transport of monosubstituted sulfamyl benzoic acid derivatives and probenecid.

The characteristics of renal transport of a homologous series of hydrocarbon derivatives of sulfamyl benzoic acid were examined in cortical slices of rabbit kidney. The length of the hydrocarbon substituent varied from C₁ to C₅ and the compounds differed from the previously examined probenecid series [5] in having only one hydrocarbon substituent, instead of two, at the sulfamyl group. Transport rate, maximal accumulation and affinity of the monosubstituted compounds for transport were enhanced by an increase in the length of the hydrocarbon substituent. In comparison with the probenecid series less binding by tissue constituents under anaerobic conditions was observed. Competition experiments indicated that the monosubstituted compounds were transported by the same transport system as that of PAH. Octanoate and fumarate exerted a biphasic effect on accumulation (i.e. stimulation at low and inhibition at high metabolite concentrations), as in the case of other organic anions. In comparison with probenecid the monosubstituted compounds were more susceptible to inhibition by PAH, fumarate and octanoate. Nevertheless, pentylsulfamyl benzoic acid exerted a somewhat more powerful inhibitory effect on the accumulation of phenol red and PAH than did probenecid. The monosubstituted compounds were less hydrophobic than probenecid as evidenced by less extractability from an aqueous phase into an organic liquid (1,2-dichloroethane). It is concluded that for the sulfamyl benzoic acid derivatives moderate hydrophobicity results not only in a higher affinity, but also in an enhanced turnover rate of the carrier system for organic anions.     

2-phenylethanol and some of its amphiphilic derivatives as inhibitors of platelet aggregation. Structure-activity relationship.

The relationship between chemical structure and inhibitory activity of some simple water soluble phenylalkyl derivatives has been investigated. The inhibitory effect of the following analogous and homologous derivatives increases in the sequence: phenylacetic acid less than 2-phenylethanol less than 2-phenylethylamine = 4-phenylbutyric acid less than 3-phenylpropanol less than 4-phenylbutylamine, i.e., the inhibitory effect is potentiated. 1. by elongation of the alkyl chain, which is accompanied by an increase of the lipophilic character, and 2. when the polar portion is represented by the positively charged amino-group. The effect of these amphiphilic compounds on platelet aggregation appears to be mediated through polar and apolar interactions with the outer layers of the plasma membrane. The fact that the amino derivatives are the most active inhibitors suggests that negatively charged groups may be involved in the polar binding of these inhibitors. Experiments with neuraminidase-treated platelets revealed that the enzymatically removable sialic acid residues are not those negatively charged binding sites. Phentolamine and propranolol which block adrenergic alpha- and beta-receptors, respectively, do not influence the inhibitory effect of these agents.     

Transport in quantitative structure-activity relationships. VI: Relationship between transport rate constants and partition coefficients

The transport rate constant of a drug partitioned in a two-phase system from an aqueous to an organic phase (k1obs) and vice versa (k2obs) is a function of the partition coefficient P and of a solvent system-dependent parameter beta. Drug transport is shown to be independent of molecular structure for a number of arbitrary compounds.     

Binding of the membrane active drugs to bovine serum albumin and human erythrocyte membranes.

The binding of 14 non-steroidal anti-inflammatory drugs, 3 beta-adrenolytics and 8 miscellaneous drugs to bovine serum albumin (BSA) and human erythrocyte membranes (HEM) was investigated by using 8-anilino-1-naphthalene sulphonate (ANS) as a fluorescent probe. Anionic drugs which are known to protect proteins against denaturation strongly quench the fluorescence of the ANS-BSA complex, and to a lesser extent the fluorescence of the ANS-HEM complex. None of cationic or nonionic drugs tested so far are able to displace ANS from the ANS-BSA complex but some of them, known as “membrane active” agents, intensify the fluorescence of the ANS—HEM complex. Within the group of nonsteroidal anti-inflammatory drugs only those drugs which are inhibitors of prostaglandin biosynthesis have been found to quench the fluorescence of the complexes of ANS with BSA or HEM. Both anionic and cationic “membrane active” drugs protect erythrocytes against hypotonic hemolysis but the mechanisms of this effect are different.     

Transport of anionic drugs across the basolateral membrane of proximal S2 segments of the rabbit kidney. Inverse relationship between the affinity to the p-aminohippurate transport system and the transport rate

The renal p-aminohippurate (PAH) transport system, which resides in the S2 segments of proximal tubules, is a main tubular secretory system for drugs. Previous studies have shown that the hydrophobicity of drugs is positively correlated with their affinity for the basolateral PAH transporter. Affinity was deduced from inhibition of tubular 3H-PAH uptake. However, up to now, no studies are available which tested the relationship between hydrophobicity and transport rate of drugs. Therefore, in the present study, the basolateral transport rates of several drugs (probenecid, CAS 57-66-9, furosemide, CAS 54-31-9, bumetanide, CAS 28395-03-1, mefruside, CAS 7195-27-9) which are substrates of the PAH transporter and which differ markedly regarding their hydrophobic properties (log P values ranging from 1-3) were determined on non-perfused proximal S2 segments microdissected from rabbit kidneys without the use of enzymatic solutions. To measure the transport rate advantage of the finding was taken that the PAH transporter in the basolateral membrane of proximal S2 segments acts as a countertransporter which exchanges PAH with dicarboxylates (glutarate or alpha-keto-glutarate). Hence, the stimulatory effect of a drug on the 14C-glutarate efflux rate of 14C-glutarate preloaded S2 segments is a measure of its translocation across the basolateral cell membrane. The results revealed that with increasing hydrophobicity (mefruside < furosemide < bumetanide < probenecid) the stimulating effect of the drugs on 14C-glutarate efflux decreased indicating that the compounds are more slowly translocated although their potency to inhibit 3H-PAH uptake increased. Thus, an inverse relationship between hydrophobicity and hence affinity of the drugs for the PAH transporter and transport rate could be established.     

Kinetics and thermodynamics of chloroquine and hydroxychloroquine transport across the human erythrocyte membrane

Chloroquine (CQ) and hydroxychloroquine (HCQ) have almost identical molecular volumes but showed very different permeability characteristics. The permeability coefficient for the unionised species of CQ (2.0 cm/sec at 25 degrees) was about fifty times that of HCQ (0.039 cm/sec at 25 degrees), but the apparent activation energy for transport (85 kJ/mol for CQ, 81 kJ/mol for HCQ) was almost identical for the two drugs. The partition coefficient of CQ into various organic solvents was much higher than for HCQ, but the different permeability behaviour cannot be quantitatively explained by partitioning behaviour into hexane or octanol, two solvents commonly used to mimic the membrane interior. A comparison of permeability and partitioning characteristics suggests that the barrier phase for these drugs within the membrane can be modelled by a mixed solvent of 5% octanol in hexane. The results suggest that interactions with hydrogen bonding groups within the membrane are important in the membrane transport of these drugs, and that the membrane does not behave functionally as a simple hydrocarbon barrier.     

Modeling of purine derivatives transport across cell membranes based on their partition coefficient determination and quantum chemical calculations

Mercaptopurine (6-MP), thioguanine (6-TG), and azathioprine (AZA) are purine antimetabolites introduced as anticancer or immunosuppressive drugs decades ago. Methylated AZA, called MAZA, is among the investigational drugs. The present study compares MAZA to the widely recognized drugs AZA, 6-MP, and 6-TG with respect to the ability of being transported across cell membranes. The obtained octanol/water phases partition coefficients and results of quantum chemical calculations predict the following sequence of hydrophobicity: MAZA > AZA > 6-TG > 6-MP.     

In vitro permeation of several drugs through the human nail plate: relationship between physicochemical properties and nail permeability of drugs.

The objectives of the present study are to clarify the relationship between the physicochemical properties and the nail permeability of drugs through human nail plates. Homologous p-hydroxybenzoic acid esters were used to investigate the relationship between the octanol/water partition coefficient and the permeability coefficient of several drugs. The nail permeability was found to be independent of the lipophilicity of a penetrating drug. However, the nail permeability of several model drugs was found to markedly decrease as their molecular weights increased. The nail permeability of an ionic drug was found to be significantly lower than that of a non-ionic drug, and the nail permeability of these drugs markedly decreased as their molecular weights increased. The permeation of a model drug, 5-fluorouracil (5-FU), through healthy nail plates was also determined and compared with that through nail plates with fungal infections. The drug permeation through a nail plate decreased with an increase in nail plate thickness. Nail plates with fungal infections exhibited approximately the same 5-FU permeation as healthy nail plates. We suggest that the permeability of a drug is mainly influenced by its molecular weight and permeability through nails with fungal infection can be estimated from data on healthy nail permeability.     

Effect of a second solubilizate on the partition coefficient of drugs in micellar solution and their permeation rate across an artificial membrane.

The distribution of a solubilizate between micelles and the aqueous phase does not obey a simple partition law when a second solubilizate species is present. Alterations of the apparent partition coefficient cannot be explained in terms of a simple displacement mechanism, following the interaction of both solubilizates with the same site of the micelle. A non linear increase in solubilizate association to micelles following an increase in surfactant concentration is observed in the presence of a second solubilizate. A depression in the cloud point temperature follows the addition of a second species and is such that cannot be interpreted as a simple additive effect. Alteration of the apparent partition coefficient in a miscellar solution has an effect on the permeation rate of the solubilizate across an artificial membrane. Biopharmaceutical implications are discussed.