Hypoglycemic effect of intestinally administered monosaccharide-modified insulin derivatives in rats

Symmetrical Phosphinic Acids: Synthesis and Esterification Optimization toward Potential HIV Prodrugs

A highly efficient method to synthesize diverse symmetrical phosphinic acids with the potential to act as pivotal candidates in the design of HIV-1 protease inhibitors has been developed. Such compounds have been designed based on the enzyme-substrate specificity, and their elongated analogues are expected to demonstrate significant inhibition against the HIV-1 protease with IC50 values in the low nanomolar range. Moreover, a highly efficient esterification protocol with carbohydrates and flavonoids has been devised to address the inherent absorption challenges associated with phosphinic-based drugs. These esters not only exhibit low toxicity but also have the potential to generate flavonoid moieties in situ, which are associated with hepatoprotective effects, or naturally occurring carbohydrate metabolites. The methodology utilizes effective peptide coupling reagents, such as aminium-based TBTU and carbodiimide-based DIC, and affords the target products in excellent to quantitative yields. This research represents a promising avenue for the development of novel HIV-1 protease inhibitors with significant therapeutic benefits.

Novel glycosyl prodrug of RXP03 as MMP-11 prodrug: design, synthesis and virtual screening

Like most phosphinic acids, the potent and selective RXP03 inhibitor of different MMPs exhibited moderate absorption and low bioavailability, which impaired its use. In an unprecedented attempt, we present an interesting synthetic approach to a new class of phosphinate prodrug, glycosyl ester of RXP03, to provide a potentially improved blood-brain barrier (BBB) behavior compared to the former lead compound RXP03. To validate this speculation, a predictive study for permeability enhancer of glycosyl ester of RXP03 showed encouraging insights to improve drug delivery across biological barriers.

Synthesis and characterization of stimuli-sensitive hydrogels having a different length of ethylene glycol chains carrying phosphate groups: loading and release of lysozyme

In order to prepare a polymer matrix capable of loading protein at high density, anionic hydrogels were synthesized by copolymerizing a monomer carrying a pendant phosphate group, methacryloyl-polyoxyethyl phosphate, with N-isopropylacrylamide and N,N'-methylene-bis-acrylamide, and the stumuli-sensitivity of hydrogels was characterized. The number of repeating ethylene glycol units in the phosphate carrying monomer was 1, 2, 5 or 8. Lysozyme bearing a positive net charge was immobilized in the hydrogel through formation of polyelectrolyte complex. It was shown that the amount of complexed lysozyme reached to 1.7 g/g dry gel, when high content of a phosphate-carrying monomer with 5 ethylene glycol units was incorporated into a hydrogel. It was further found that lysozyme complexed with phosphate-carrying network could be released by immersion of the lysozyme/hydrogel composite in a phosphate buffer solution of pH 7.4 owing to the pH-sensitivity of the hydorgel but no lysozyme was released at pH 1.4. The initial rate of lysozyme release was varied depending on the length of the ethylene glycol chains possessed by a network polymer and the content of the phosphate-carrying monomer unit. Lysozyme released from the phosphate-carrying hydrogel was proved to retain enzymatic activity at a level similar to the activity of lysozyme, which had been kept in buffer solution.

Improved Intestinal Membrane Permeability of Hexose-Quinoline Derivatives via the Hexose Transporter, SGLT1

Intestinal membrane permeability is an important factor affecting the bioavailability of drugs. As a strategy to improve membrane permeability, membrane transporters are useful targets since essential nutrients are absorbed efficiently via specific transporters. For example, there are reports that intestinal hexose transporters could be used as a tool to improve permeability; however, there has been no direct evidence that the transporter protein, sodium/glucose cotransporter 1 (SGLT1), is involved in the transport of hexose analogs. Accordingly, we examined directly whether the intestinal membrane permeability of hexose analogs can be improved by utilizing SGLT1. Three hexose-quinoline derivatives were synthesized and their interactions with SGLT1 were evaluated. Among the three derivatives, the glucose-quinoline molecule exhibited an inhibitory effect on D-glucose uptake by both rat intestinal brush-border membrane vesicles (BBMVs) and Xenopus oocytes expressing SGLT1. In addition, significant uptake of the glucose-quinoline derivative by Xenopus oocytes expressing SGLT1 was observed by both an electrophysiological assay and direct measurement of the uptake of the compound, while the galactose-quinoline derivative did not show significant uptake via SGLT1. Thus, it was directly demonstrated that SGLT1 could be used as a tool for the improvement of intestinal membrane permeability of drugs by modification to the glucose analogs.

Membrane transporter/receptor-targeted prodrug design: strategies for human and veterinary drug development

The bioavailability of drugs is often severely limited due to the presence of biological barriers in the form of epithelial tight junctions, efflux proteins and enzymatic degradation. Physicochemical properties, such as lipophilicity, molecular weight, charge, etc., also play key roles in determining the permeation properties of drug candidates. As a result, many potential drug candidates may be dropped from the initial screening portfolio. Prodrug derivatization targeting transporters and receptors expressed on mammalian cells holds tremendous potential. Enhanced cellular delivery can significantly improve drug absorption. Such approaches of drug targeting and delivery have been the subject of intense research. Various prodrugs have been designed that demonstrate enhanced bioavailability and tissue specificity. This approach is equally applicable to human and veterinary pharmaceuticals since most of the transporters and receptors expressed by human tissues are also expressed in animals. This review highlights studies conducted on the use of transporters and receptors in an effort to improve drug bioavailability and to develop targeted drug delivery systems.

Electrical charge on protein regulates its absorption from the rat small intestine

The effect of the electrical charge on the intestinal absorption of a protein was studied in normal adult rats. Chicken egg lysozyme (Lyz), a basic protein with a molecular weight of 14,300, was selected and several techniques for chemical modification were applied. Then the intestinal absorption of Lyz derivatives was evaluated by measuring the radioactivity in plasma and tissues, after the administration of an (111)In-labeled derivative to an in situ closed loop of the jejunum. After the administration of (111)In-Lyz, the level of radioactivity in plasma was comparable with the lytic activity of Lyz, supporting the fact that the radioactivity represents intact Lyz. (111)In-cationized Lyz showed a 2-3 times higher level of radioactivity in plasma, whereas the radioactivity of (111)In-anionized Lyz was much lower. The absorption rate of (111)In-Lyz derivatives calculated by a deconvolution method was correlated for the strength of their positive net charge. A similar relationship was observed using superoxide dismutase. These findings indicate that the intestinal absorption of a protein is, at least partially, determined by its electrical charge.

Prodrug based optimal drug delivery via membrane transporter/receptor

The carrier-mediated absorption of drugs and prodrugs across epithelial and endothelial barriers is emerging as a novel trend in biotherapeutics. This review examines the important advances in this field in the past decade. The feasibility of drug absorption of the parent drug or the appropriately modified prodrug via these transporters is discussed in detail. Several successful examples of synthesis of prodrugs recognised by the targeted transporters are described. The applicability of this approach in translocating drugs across the almost impenetrable blood-brain barrier (BBB) has also been examined.

Synthesis and characterization of an acylated di-peptide (Myr-Trp-Leu) with modified transmucosal transport properties

In order to improve the buccal absorption of a dipeptide model compound, Tryptophan-Leucine (Trp-Leu), we have synthesised a lipophilic derivative by myristoylation of the N- terminal amino group of Trp-Leu. The acylated peptide (Myr-Trp-Leu) was characterized by HPTLC, purified and isolated by chromatography on a silica gel column. Its structure was confirmed by (13)C and (1)H NMR and mass spectroscopy. The increased lipophilicity of the Myr-Trp-Leu was compared to that of the native peptide by chromatography and by its partition coefficient between n-octanol and saline phosphate buffer. In addition, the sensitivity towards hydrolytic enzymes was studied. The interaction of Trp-Leu with liposomes as model membranes was also studied. The phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) was lowered in the presence of Myr-Trp-Leu, while it was increased in the presence of native parent peptide. Permeation experiments performed in vitro with pig buccal mucosa showed that the Myr-Trp-Leu accumulated in the tissue at the various concentrations tested. In contrast, the native peptide was able to pass through the membrane at all concentrations used. Lipophilic modification of the peptide by acylation drastically changes its behaviour towards tissue systems.

Self-assembled hydrogel nanoparticle of cholesterol-bearing pullulan as a carrier of protein drugs: complexation and stabilization of insulin

Insulin (Ins) spontaneously and easily complexed with the hydrogel nanoparticle of hydrophobized cholesterol-bearing pullulan (CHP) in water. The complexed nanoparticles (diameter 20-30 nm) thus obtained formed a very stable colloid. The thermal denaturation and subsequent aggregation of Ins were effectively suppressed upon complexation. The complexed Ins was significantly protected from enzymatic degradation. Spontaneous dissociation of Ins from the complex was barely observed, except in the presence of bovine serum albumin. The original physiological activity of complexed Ins was preserved in vivo after i.v. injection.

Improvement of intestinal absorption of peptide drugs by glycosylation: transport of tetrapeptide by the sodium ion-dependent D-glucose transporter

A tetrapeptide (Gly-Gly-Tyr-Arg, GGYR), which is not transported by di- or tripeptide transporters, was glycosylated with p-(succinylamido)phenyl alpha- or beta-D-glucopyranoside (alpha,beta-SAPG) to investigate whether these glycosylated molecules are transported by the Na+-dependent D-glucose transporter. Their uptake into brush border membrane vesicles (BBMVs) and transport through the intestinal membrane were examined using the rapid filtration technique and the everted sac method. It was observed that glycosylation at the alpha-amino position of GGYR increased resistance to aminopeptidase activity and inhibited its degradation. When alpha- and beta-SAPG-GGYR were incubated with BBMVs, overshoot uptake was observed about 2 min after the start of incubation in the presence of an inward Na+ gradient. This uptake remained unaffected by the addition of GGYR while it was significantly inhibited when Na+ was replaced with K+ or alpha- and beta-SAPG-GGYR were incubated with BBMVs at 4 degrees C. Uptake was also markedly inhibited either with 1 mM phloridzin or 10 mM D-glucose. These findings suggested that the Na+-dependent glucose transporter (SGLT-1) played an important role in the uptake of both alpha- and beta-SAPG-GGYR into BBMVs. A comparison of alpha- with beta-SAPG-GGYR revealed that the amount of beta-SAPG-GGYR taken up was greater than that of alpha-SAPG-GGYR. From the everted sac method data, it was shown that the elimination clearance from the mucosal side, CLel, and permeation clearance to the serosal side, CLp, were 15.82+/-6.83 and 0.83+/-0.06 microL/min/cm for alpha-SAPG-GGYR and 44.52+/-3.61 and 3.50+/-0.81 microL/min/cm for beta-SAPG-GGYR, respectively, and that alpha-SAPG-GGYR was more resistant to enzymatic degradation than beta-SAPG-GGYR. Permeation of both alpha- and beta-SAPG-GGYR was inhibited in the presence of D-glucose and in the absence of a Na+ gradient, suggesting that both alpha- and beta-SAPG-GGYR were transported by the Na+-dependent D-glucose transporter. The permeation clearance transported by the Na+-dependent D-glucose transporter, (CLp)Na+, of beta-SAPG-GGYR was about 5 times greater than that for alpha-SAPG-GGYR. This result may be ascribable to the fact that the beta-form of glucose has higher affinity to SGLT-1 than the alpha-form. The results of the present study encourage further investigations on improvements in intestinal absorption of peptide drugs by glycosylation.

Carrier-mediated intestinal transport of drugs

Recent advances in the field of carrier-mediated intestinal absorption of of amino acids, oligopeptides, monosaccharides, monocarboxylic acids, phosphate, bile acids and several water-soluble vitamins across brush-border and basolateral membranes are summarized. An understanding of the molecular and functional characteristics of the intestinal membrane transporters will be helpful in the utilization of these transporters for the enhanced oral delivery of poorly absorbed drugs. Some successful examples of the synthesis of prodrugs recognized by the targeted transporters are described. Functional expression of the multidrug resistance gene product, P-glycoprotein, as a primary active transporter in the intestinal brush-border membrane leads to net secretion of some drugs such as anticancer agents in the blood-to-luminal direction, serving as a secretory detoxifying mechanism and as a part of the absorption barrier in the intestine.