Ortho-hydroxybenzoates may act at the protein fraction to enhance membrane permeability.

Experimental observation suggests that the ability of ortho-hydroxybenzoates to alter the permeability of rat rectal epithelial membrane may involve an interaction between the ortho-isomer and the membrane protein. Such an interaction may cause a temporary structural modification of the protein rendering the membrane permeable to compounds normally poorly absorbed from the rectal compartment.

Inhibitory effect of salicylate on 2,4-dinitrophenol and diethyl maleate in isolated rat intestinal epithelial cells.

Studies on the mechanism of chemically induced intestinal epithelial injury were carried out using isolated, rat small intestinal epithelial cells. Compounds such as 2,4-dinitrophenol (DNP) and diethyl maleate (DEM), caused NADH loss, an increase in cytosolic Ca2+ concentration and protein thiol loss. Further, these compounds accelerated cell aggregation and decreased cell viability. Calmodulin antagonists inhibited protein thiol loss induced by either of the compound, inhibited cell aggregation and prolonged cell viability, but did not influence NADH loss. It has been reported that the calmodulin-binding protein may regulate cytoskeletal activity. Therefore, the inhibition of protein thiol loss by calmodulin antagonist may be due to a dissociation of calmodulin-binding proteins from cytoskeletal elements. Salicylate also inhibited protein thiol loss induced by DNP and DEM, and inhibited cell aggregation. However, salicylate may have a direct effect in reducing the cytosolic free Ca2+ concentration by complexation and subsequent facilitated release of Ca2+ from cells. Further, in the present study, the induction of cell aggregation may be caused by the appearance of specific sites on the cell membrane surface to which arsenazo III could adsorb, since adsorption of arsenazo III to the isolated epithelial cells seemed to correlate with increased cell aggregation.

Enhanced intestinal absorption of insulin in rats in the presence of sodium 5-methoxysalicylate.

Sodium 5-methoxysalicylate, previously shown to enhance the rectal absorption of several drugs, facilitates the absorption of insulin from the upper gastrointestinal tract, resulting in significantly elevated insulin levels and lowered glucose concentrations in the plasma of rats. Restricting the movement of insulin and adjuvant down the intestine by either ligation or use of a more viscous vehicle further increased the absorption of insulin.

Promoting effect of concanavalin A on transport of sodium cefoxitin and phenol red from rat rectal compartment.

Concanavalin A enhanced the rat rectal absorption of phenol red and cefoxitin at pH 7.4 and the uptake of cefoxitin into brush border membrane vesicles prepared from rat rectal membrane. The enhancing action of concanavalin A demonstrated a sodium ion dependency and was inhibited by the presence of 4,4'-diisothiocyano-2,2'-disulfonate stilbene and phlorizin. This inhibition suggests the involvement of the membrane protein fraction.

Possible mechanism of uptake for several compounds in ionized form through human erythrocyte membrane.

The mechanism underlying uptake of certain compounds in ionized form across human red blood cell membrane was examined. The ionized forms of salicylate, 5-methoxy-salicylate and phenylalanylphenylalanine were significantly taken up into the interior space of human red blood cells instead of remaining in the membrane. Inhibition of the uptake of these compounds by 4,4'-diisothiocyano-2,2'-disulfonate stilbene and phlorizin indicates that their permeation of the erythrocyte membrane may involve the membrane protein fraction. Chelation at the protein site does not appear to occur. Instead, an amino group in the protein structure may mediate the transport of these ionized compounds.

Salicylate-promoted permeation of cefoxitin, insulin and phenylalanine across red cell membrane. Possible mechanism.

Uptake of sodium cefoxitin, D-phenylalanine and insulin into human red blood cells was significantly enhanced by the presence of salicylate and 5-methoxysalicylate in the medium. The mechanism of adjuvant action appeared to depend on an affinity between the adjuvant and the protein fraction in the erythrocyte membrane. The inhibitory effect of DIDS and phlorizin on the salicylate-enhanced uptake of these compounds strongly suggests that the ability of salicylate to permeate the membrane may be essential for it to act as an adjuvant.

Effects of sodium salicylate on epithelial cells of the rectal mucosa of the rat: a light and electron microscopic study.

Using a ligation method, rat rectal epithelium was exposed to 2% sodium salicylate, and light and electron microscopic methods were used to assay for: 1) permeability of the epithelium to a marker dye, trypan blue, and 2) damage expressed in terms of disruption of the epithelial surface. Rectal mucosa was exposed to salicylate at pH 4.8, 7.0, and 9.0, and the effects of pretreatment with phlorizin were also studied. Results indicated that 2% sodium salicylate does very little damage to rectal epithelial cells at pH 7.0 while enhancing their permeability to trypan blue, an effect that is reversed upon washing out the sodium salicylate. The major cellular change induced by salicylate was a reduction in the length or distribution of glycocalyx filaments on microvilli of epithelial cells. It was also noted that pretreatment with phlorizin counteracted some of the effects of salicylate treatment.

Enhanced rectal absorption of theophylline, lidocaine, cefmetazole, and levodopa by several adjuvants.

Ten potential adjuvants for rectal absorption which are structurally similar to salicylate have been examined using an in situ perfusion of the rat rectum technique as well as an in vivo absorption method from microenemas. All of the adjuvants studied readily disappeared from the perfusate at pH 4.5; however, several were not absorbed well at pH 7.4. Only those that were lost rapidly from the perfusate at pH 7.4 were effective in enhancing the disappearance of the drugs (theophylline, lidocaine, cefmetazole, and levodopa) at either a pH of 4.5 or 7.4. The compounds that were effective in promoting the disappearance of drugs from the rectal perfusate all had hydroxy and carboxy groups. Those substances lacking a hydroxy group were not effective. The binding of these potential adjuvants and salicylates to rat rectum tissue was studied by equilibrium dialysis. Those adjuvants with relatively high binding to rat rectal tissue were better absorbed themselves and promoted the disappearance of drugs more than those substances exhibiting little binding. Thus, adjuvant binding to some feature of the rectal membrane appears to be important in the enhanced absorption of drugs from the rectum under the conditions of this study.

Effect of salicylate on the rectal absorption of lidocaine, levodopa, and cefmetazole in rats.

Salicylic acid and sodium salicylate have been found to enhance the absorption of lidocaine, levodopa, and cefmetazole after rectal administration to rats. These drugs represent a base (lidocaine), an acid (cefmetazole), and a substance (levodopa) which exists as a zwitterion in solution. The rectal absorption of each type of drug, as well as theophylline, a neutral compound, was enhanced by salicylate, particularly at pH values where the substances exist primarily in their ionic form. A requirement for the observed enhancement is that salicylate be present in the rectal membrane. The loss of drug from the perfusing solution was greater from solutions having an ionic strength of 0.75 than from those with mu = 0.15.

Effects of salicylate on rectal absorption of theophylline.

The rectal absorption of theophylline in rats was facilitated by concurrent administration of salicylic acid or sodium salicylate. The absorption of theophylline depended on the simultaneous absorption of salicylate and increased with an increasing concentration of salicylate. Calcium and magnesium ions inhibited the effects of salicylate at pH 7.4 but not at pH 4.5. Sodium lauryl sulfate caused lasting changes in rectal absorption, whereas the effects of salicylate on absorption were observed only when salicylate was present Strong chelating agents, such as ethylenediaminetetraacetic acid and sodium citrate did not effect the absorption of theophylline, except at very high concentrations (30%), where membrane damage was observed. Rectal drug absorption was not enhanced by vasodilation or inflammation alone since sodium nicotinate and histamine did not facilitate the disappearance of theophylline from the perfusate.

Possible mechanism behind the adjuvant action of phosphate derivatives on rectal absorption of cefoxitin in rats and dogs.

The mechanism underlying the ability of phosphate derivatives to act as adjuvants and coadjuvants was examined in in vivo and in situ preparations in rats and dogs. The adjuvant effect of DL-alpha-glycerophosphate on the rectal absorption of sodium cefoxitin was greatly augmented by the presence of either sodium phytate or sodium tripolyphosphate. These coadjuvants only slightly enhanced cefoxitin rectal absorption when administered alone. Therefore, enhancement of the permeation of tripolyphosphate and phytate by alpha-glycerophosphate may be necessary before the coadjuvants can significantly affect cefoxitin absorption. The inhibitory effect of disodium 4,4'-diisothiocyano-2,2'-disulfonate stilbene, which is known to interact with the amino group in the protein fraction, on enhanced cefoxitin absorption suggests the involvement of the protein fraction in transport of cefoxitin across the rectal membrane.

Combined effect of alcohol and urea on the in vitro transport of indomethacin across rat dorsal skin.

An aqueous gel, prepared with hydrogenated soya phospholipid, increased the in vitro transport of indomethacin across rat dorsal skin. The addition of various alkanols further accelerated the transport, with an increasing effect as the chain length of the alkanol increased. The addition of urea alone did not significantly affect the transport of indomethacin. However, the addition of urea markedly accelerated the transport of indomethacin when included in an aqueous gel containing an alkanol such as 1-octanol, 1-decanol, or 1-dodecanol. Thus, it appears that a combination of urea and these alkanols strongly enhances the transdermal absorption of indomethacin. Urea appears to accelerate enhanced drug transport into the stratum corneum by a mechanism involving the transport of urea enhanced by these alkanols.

Adjuvant effects of glyceryl esters of acetoacetic acid on rectal absorption of insulin and inulin in rabbits.

The promoting effect of glyceryl esters of acetoacetic acid on the rectal absorption of insulin and inulin was studied. A decrease in the serum glucose level was observed in rabbits following the administration of an insulin suppository containing glyceryl-1,3-diacetoacetate (adjuvant II) or 1,2-isopropylideneglycerine-3-acetoacetate (adjuvant IV). The promoting effects of adjuvants II and IV on the rectal absorption of insulin and inulin were suppressed by the addition of calcium and magnesium to the suppository. This indicates that adjuvant interaction with the calcium and magnesium ion located in the rectal membrane is involved in the enhanced absorption of insulin and inulin. Adjuvant release from the suppository formulation in addition to adjuvant lipid solubility were found to be other important factors for enhanced absorption of insulin and inulin.

The effects of salicylate on the rectal absorption of phenylalanine and some peptides, and the effects of these peptides on the rectal absorption of cefoxitin and cefmetazole.

The disappearance of phenylalanine and phenylalanylglycine from a perfusate circulated across rat rectal tissue was enhanced significantly in the presence of salicylate or 5-methoxysalicylate at pH 4.5, 7.4, and 8.5. The disappearance of di-, tri-, and tetraphenylalanine from a perfusate at pH 7.4, although facilitated by the presence of salicylate and 5-methoxysalicylate, was also fairly substantial when no adjuvant was present. These peptide analogues of phenylalanine also enhanced the rectal absorption of cefoxitin and cefmetazole, two highly water soluble antibiotics. Phenylalanine and phenylalanylglycine, both poorly absorbed across the rectal membrane when administered alone, did not enhance the rectal absorption of either antibiotic.

Enhanced rectal absorption of cefmetazole and cefoxitin in the presence of epinephrine metabolites in rats and a high-performance liquid chromatographic assay for cephamycin antibiotics.

4-Hydroxy-3-methoxymandelic acid and 3,4-dihydroxymandelic acid were found to be potent adjuvants for the rectal absorption of water-soluble compounds in rats. Both adjuvants enhanced the absorption of two cephamycin antibiotics, cefmetazole and cefoxitin. Maximum plasma levels of the antibiotics were obtained within 30 min after rectal administration. The bioavailability of both antibiotics appeared to depend on the concentration of the adjuvant in the microenema, the dosage form used in these experiments. Instead of a microbial assay, a new chemical method involving high-performance liquid chromatography with an ion-pairing technique was developed for analyzing the cephamycin antibiotic plasma levels.

Intestinal absorption of sodium cefoxitin in rats: effect of formulation.

The absorption of cefoxitin from rat intestine, rectum and small intestine was greater when the powdered form was administered than when an aqueous solution was given. Cefoxitin absorption from the small intestine was significantly increased after its administration in suppository form prepared with a triglyceride base, although rectal absorption from the suppository did not differ from that of the drug in powdered form. The increase in absorption by the small intestine from the suppository form may be due to fatty acids produced from triglyceride by lipase.

Small intestinal absorption of bropirimine in rats and effect of bile salt on the absorption.

The intestinal absorption characteristics of a poorly water-soluble drug, bropirimine, were investigated by the in-situ small intestinal loop method using male Sprague-Dawley rats. Bropirimine in solution was well absorbed in the overall small intestine, following first-order kinetics. The rate determining step for the disappearance of bropirimine from the small intestinal loop after dosing in the suspension was the dissolution process from suspension. Bropirimine was solubilized by sodium glycocholate. The disappearance of bropirimine from the small intestinal loop was suppressed by sodium glycocholate contained in the solution, because of the loss of thermodynamic activity of bropirimine after its involvement in the micellar complex, not by the direct effect of bile salt on the permeability of intestinal mucosa. The disappearance of bropirimine was also suppressed by sodium glycocholate contained in the suspension. The suppression by sodium glycocholate seemed to be caused by the greater influence of sodium glycocholate on the thermodynamic activity of bropirimine than on the dissolution from suspension.

Use of enzymatic activity for design of orally administered enteric dosing forms.

Liquid and semi-solid enteric dosage forms were prepared by entrapping drug with an appropriate partition coefficient in a lipid base vehicle which would then be released by the action of intestinal enzymes. Lipid ester derivatives such as glyceryl monocaprylate and polysorbate 80 were used as vehicles. These vehicles readily dissolved the poorly water-soluble compounds used in the study, itazigrel, indomethacin and the dye, sudan II, and were digested by lipase and esterase, releasing the test drugs with time profiles similar to those observed in dissolution studies. The vehicles released little or only a small amount of the drugs into aqueous medium in the absence of an appropriate enzyme. The enzyme-sensitive enteric vehicles when containing sudan II did not release the dye in the stomach of rats after oral administration, but released significant amounts of the dye in the small intestine.

Enhanced rectal absorption of itazigrel formulated with polysorbate 80 micelle vehicle in rat: role of co-administered esterase.

We investigated the effect of esterase on rectal absorption in the rat of itazigrel using polysorbate 80 (PS-80) micelle as a vehicle to overcome the poor aqueous solubility of itazigrel. The itazigrel formulation prepared with PS-80 increased the absorption compared with a 0.25% carmellose sodium suspension, probably by supplying the itazigrel solute to keep a high concentration at the epithelial surface. When esterase was co-administered with the formulations containing PS-80, the absorption of itazigrel from rat rectum was accelerated further, by rapid release of itazigrel from the micelle vehicle after enzymatic degradation of the PS-80 micelle.

Glycogenolysis in the rat isolated perfused liver as a measure of chemically induced liver toxicity.

The relationship between chemically induced glycogenolysis and decreased thiol content in the rat isolated, perfused liver has been examined. Chemicals such as 2,4-dinitrophenol (DNP), diethyl maleate, alcohols and anti-inflammatory agents (except for sodium salicylate) accelerated glycogenolysis. Protein thiol loss correlated well with a marked increased rate of glucose release. Non-protein thiol loss, without significant loss of protein thiol, caused by a slight increase in the rate of glycogenolysis compared with controls. Since it has been reported that protein thiol loss rather than non-protein thiol loss is correlated to liver cell injury, a marked glucose release from the perfused liver may be a convenient measure of hepatic toxicity for a variety of chemicals.