Potential Absorption Enhancer Research Articles

Improvement of Intranasal Drug Delivery with Intravail® Alkylsaccharide Excipient as a Mucosal Absorption Enhancer Aiding in the Treatment of Conditions of the Central Nervous System.

Intranasal drug administration is a commonly used route for therapeutic formulations, but there may be challenges associated with a lack of absorption and bioavailability, as well as damage to mucosal tissue. To address these issues, potential absorption enhancers that are generally nonirritating to nasal mucosal tissue have been investigated as excipients in intranasal formulations. Among those studied are alkylsaccharides, which are composed of sugars covalently coupled to at least one alkyl chain. Alkylsaccharides have been shown to be nontoxic and have been used in food products as emulsifiers. In clinical trials, alkylsaccharide excipients have demonstrated substantially increased absorption of therapeutic agents across mucosal membranes and have been shown to be applicable to a wide range of types of molecules and molecular weights. Because they are water and oil soluble, alkylsaccharide excipients can be used in formulations with both hydrophilic and hydrophobic drugs. They are also effective in safely stabilizing protein therapeutics. An example of an alkylsaccharide excipient is dodecyl maltoside (Intravail®; 511 Da, stable long term when stored cold), which provides absorption enhancement by paracellular and transcellular routes. Dodecyl maltoside has been shown to be generally nonirritating to the nose and to promote systemic bioavailability. Dodecyl maltoside is used in US Food and Drug Administration-approved intranasal formulations of sumatriptan for migraine headaches and diazepam nasal spray for patients with epilepsy with acute seizure clusters.

Propylene Glycol Caprylate as a Novel Potential Absorption Enhancer for Improving the Intestinal Absorption of Insulin: Efficacy, Safety, and Absorption-Enhancing Mechanisms

Sodium caprate (C10) acts as an absorption enhancer. However, the absorption-enhancing effects of compounds with structures similar to C10 have not been characterized. In the present study, insulin was used as a model drug. We examined the effects of C10 and its related compounds on intestinal absorption of insulin using an in situ closed loop in rats. Insulin absorption was significantly enhanced by propylene glycol caprylate (Sefsol-218), a C10-related compound, after large intestinal administration. In addition, activity of lactate dehydrogenase did not increase in the intestinal epithelium in the presence of Sefsol-218 at concentrations equivalent to or lower than 1% (v/v). However, a significant increase in lactate dehydrogenase activity was observed in response to C10. These findings suggested that Sefsol-218 was safer than C10. Furthermore, mechanistic studies showed that increased membrane fluidity and loosening of tight junctions (TJs) might be underlying mechanisms by which this compound improved intestinal absorption of insulin. Furthermore, Sefsol-218 opened TJs by reducing the expression of claudin-4, which is a major TJ protein. These findings suggested that Sefsol-218 effectively enhanced intestinal insulin absorption without causing serious damage to the intestinal epithelium.

Hydrophobic Amino Acid Tryptophan Shows Promise as a Potential Absorption Enhancer for Oral Delivery of Biopharmaceuticals.

Cell-penetrating peptides (CPPs) have great potential to efficiently deliver drug cargos across cell membranes without cytotoxicity. Cationic arginine and hydrophobic tryptophan have been reported to be key component amino acids for cellular internalization of CPPs. We recently found that l-arginine could increase the oral delivery of insulin in its single amino acid form. Therefore, in the present study, we evaluated the ability of another key amino acid, tryptophan, to enhance the intestinal absorption of biopharmaceuticals. We demonstrated that co-administration with l-tryptophan significantly facilitated the oral and intestinal absorption of the peptide drug insulin administered to rats. Furthermore, l-tryptophan exhibited the ability to greatly enhance the intestinal absorption of other peptide drugs such as glucagon-like peptide-1 (GLP-1), its analog Exendin-4 and macromolecular hydrophilic dextrans with molecular weights ranging from 4000 to 70,000 g/mol. However, no intermolecular interaction between insulin and l-tryptophan was observed and no toxic alterations to epithelial cellular integrity—such as changes to cell membranes, cell viability, or paracellular tight junctions—were found. This suggests that yet to be discovered inherent biological mechanisms are involved in the stimulation of insulin absorption by co-administration with l-tryptophan. These results are the first to demonstrate the significant potential of using the single amino acid l-tryptophan as an effective and versatile bioavailability enhancer for the oral delivery of biopharmaceuticals.

The effect of phytic acid on tight junctions in the human intestinal Caco-2 cell line and its mechanism

This study investigated the effect of phytic acid (IP6), a potential absorption enhancer of flavonoid components, on tight junction (TJ) integrity in Caco-2 cell monolayers and its possible mechanisms. Transepithelial electrical resistance (TEER) across the monolayers decreased rapidly, and the flux of fluorescein sodium (a paracellular marker) increased after treating with IP6 in a concentration-dependent manner. Confocal microscopy results showed that IP6 produced a concentration-dependent attenuation in the distribution of occludin, ZO-1, and claudin-1. Immunoblot analysis revealed that IP6 could down-regulate the expression level of these TJ proteins, which resulted in the opening of TJ. Additionally, the divalent cations Ca2+ and Mg2+ influenced the IP6-induced distribution of occludin, ZO-1, and claudin-1 in different directions, which enhanced barrier function. In conclusion, IP6 can decrease the integrity of Caco-2 cell monolayers by modulating the TJ proteins' localization and down-regulating the expression levels of TJ proteins including claudin-1, occludin, and ZO-1; the reduction effects of divalent cations such as Ca2+ and Mg2+ on the regulation of TJ induced by IP6 should be addressed. The present work will offer some useful guidance for the application of IP6 in drug delivery area.

Region-Dependent Role of Cell-Penetrating Peptides in Insulin Absorption Across the Rat Small Intestinal Membrane.

We have reported that the cell-penetrating peptide (CPP) penetratin acts as a potential absorption enhancer in oral insulin delivery systems and that this action occurs through noncovalent intermolecular interactions. However, the region-dependent role of CPPs in intestinal insulin absorption has not been clarified. To identify the intestinal region where CPPs have the most effect in increasing insulin absorption, the region-dependent action of penetratin was investigated using in situ closed intestinal loops in rats. The order of the insulin area under the insulin concentration-time curve (AUC) increase effect by L-penetratin was ileum > jejunum > duodenum > colon. By contrast, the AUC order after coadministration of insulin with D-penetratin was colon > duodenum ≥ jejunum and ileum. We also compared the effects of the L- and D-forms of penetratin, R8, and PenetraMax on ileal insulin absorption. Along with the CPPs used in this study, L- and D-PenetraMax produced the largest insulin AUCs. An absorption study using ilea pretreated with CPPs showed that PenetraMax had no irreversible effect on the intestinal epithelial membrane. The degradation of insulin in the presence of CPPs was assessed in rat intestinal enzymatic fluid. The half-life (t 1/2) of insulin increased from 14.5 to 23.7 and 184.7 min in the presence of L- and D-PenetraMax, respectively. These enzymatic degradation-resistant effects might contribute partly to the increased ileal absorption of insulin induced by D-PenetraMax. In conclusion, this study demonstrated that the ability of the L- and D-forms of penetratin to increase intestinal insulin absorption was maximal in the ileum and the colon, respectively, and that D-PenetraMax is a powerful but transient enhancer of oral insulin absorption.

Phytic acid enhances the oral absorption of isorhamnetin, quercetin, and kaempferol in total flavones of Hippophae rhamnoides L.

AimTotal flavones of Hippophae rhamnoides L. (TFH) have a clinical use in the treatment of cardiac disease. The pharmacological effects of TFH are attributed to its major flavonoid components, isorhamnetin, kaempferol, and quercetin. However, poor oral bioavailability of these flavonoids limits the clinical applications of TFH. This study explores phytic acid (IP6) enhancement of the oral absorption in rats of isorhamnetin, kaempferol, and quercetin in TFH. MethodsIn vitro Caco-2 cell experiments and in vivo pharmacokinetic studies were performed to investigate the effects of IP6. The aqueous solubility and lipophilicity of isorhamnetin, quercetin, and kaempferol were determined with and without IP6, and mucosal epithelial damage resulting from IP6 addition was evaluated by MTT assays and morphology observations. ResultsThe Papp of isorhamnetin, kaempferol, and quercetin was improved 2.03-, 1.69-, and 2.11-fold in the presence of 333μg/mL of IP6, respectively. Water solubility was increased 22.75-, 15.15-, and 12.86-fold for isorhamnetin, kaempferol, and quercetin, respectively, in the presence of 20mg/mL IP6. The lipophilicity of the three flavonoids was slightly decreased, but their hydrophilicity was increased after the addition of IP6 in the water phase as the logP values of isorhamnetin, kaempferol, and quercetin decreased from 2.38±0.12 to 1.64±0.02, from 2.57±0.20 to 2.01±0.04, and from 2.39±0.12 to 1.15±0.01, respectively. The absorption enhancement ratios were 3.21 for isorhamnetin, 2.98 for kaempferol, and 1.64 for quercetin with co-administration of IP6 (200mg/kg) in rats. In addition, IP6 (200mg/kg, oral) caused neither significant irritation to the rat intestines nor cytotoxicity (400μg/mL) in Caco-2 cells. ConclusionsThe oral bioavailability of isorhamnetin, kaempferol, and quercetin in TFH was enhanced by the co-administration of IP6. The main mechanisms are related to their enhanced aqueous solubility and permeability in the presence of IP6. In summary, IP6 is a potential absorption enhancer for pharmaceutical formulations that is both effective and safe.

Polyamidoamine dendrimers as novel potential absorption enhancers for improving the small intestinal absorption of poorly absorbable drugs in rats

Effects of polyamidoamine (PAMAM) dendrimers on the intestinal absorption of poorly absorbable drugs were examined by an in situ closed loop method in rats. 5(6)-Carboxyfluorescein (CF), fluorescein isothiocyanate-dextrans (FDs) with various molecular weights, calcitonin and insulin were used as model drugs of poorly absorbable drugs. The absorption of CF, FD4 and calcitonin from the rat small intestine was significantly enhanced in the presence of PAMAM dendrimers. The absorption-enhancing effects of PAMAM dendrimers for improving the small intestinal absorption of CF were concentration and generation dependent and a maximal absorption-enhancing effect was observed in the presence of 0.5% (w/v) G2 PAMAM dendrimer. However, G2 PAMAM dendrimer had almost no absorption-enhancing effect on the small intestinal absorption of macromolecular drugs including FD10 and insulin. Overall, the absorption-enhancing effects of G2 PAMAM dendrimer in the small intestine decreased as the molecular weights of drug increased. However, G2 PAMAM dendrimer did not enhance the intestinal absorption of these drugs with different molecular weights in the large intestine. Furthermore, we evaluated the intestinal membrane damage with or without G2 PAMAM dendrimer. G2 PAMAM dendrimer (0.5% (w/v)) significantly increased the activities of lactate dehydrogenase (LDH) and the amounts of protein released from the intestinal membranes, but the activities and amounts of these toxic markers were less than those in the presence of 3% Triton X-100 used as a positive control. Moreover, G2 PAMAM dendrimer at concentrations of 0.05% (w/v) and 0.1% (w/v) did not increase the activities and amounts of these toxic markers. These findings suggested that PAMAM dendrimers at lower concentrations might be potential and safe absorption enhancers for improving absorption of poorly absorbable drugs from the small intestine.

Novel dry powder inhaler formulation of glucagon with addition of citric acid for enhanced pulmonary delivery

Glucagon, a gut hormone, is one of the key regulatory elements in glucose homeostasis, and is clinically used for treatment of hypoglycemia and premedication in peroral endoscopy. Dry powder inhaler (DPI) form of glucagon is believed to be a promising new dosage form, and the present study aimed to develop a novel glucagon-DPI using absorption enhancer for improved pharmacological effects. The cytotoxicity of citric and capric acids, the potential absorption enhancers, at 1 and 10 mM was assessed by monitoring extracellular LDH levels in rat alveolar L2 cells, and a concentration- and time-dependent release of LDH was observed in capric acid, but not in citric acid-treated cells. DPI form of glucagon containing citric acid was prepared with a jet mill, and laser diffraction and cascade impactor analyses of the newly developed glucagon-DPI suggested high dispersion and deposition in the respiratory organs with an emitted dose and fine particle fraction of 99.5 and 25%, respectively. Addition of citric acid in glucagon-DPI improved the dissolution behavior, and did not impair the solid-state stability of glucagon-DPI. Intratracheal administration of glucagon-DPI (50 μg-glucagon/kg body weight of rat) containing citric acid led to 2.9-fold more potent hyperglycemic effect in rats, as compared to inhaled glucagon-DPI without citric acid. Based on these physicochemical and pharmacological characterization, the dry powder inhaler of glucagon with addition of citric acid would be of use as an alternative to injection form.

Trypsin as a novel potential absorption enhancer for improving the transdermal delivery of macromolecules

The aim was to assess the effect of trypsin on the transdermal delivery of macromolecules by applying its specific biochemical properties to the stratum corneum of the skin. Fluorescein isothiocyanate (FITC)-labelled dextrans (FDs), with molecular weights of 4 to 250 kDa, and FITC-insulin were used as model macromolecules and a model polypeptide, and the in-vitro transdermal permeation experiments, with or without trypsin (0.1-2.5%), were carried out using rat skin and cultured human epidermis. The mechanism for the enhancement of trypsin was also studied using fluorescence and conventional light microscopy. Trypsin significantly increased the transdermal permeability of all FDs through the rat skin (2.0- to 10.0-fold). It also markedly enhanced the permeation of FD4 through three-dimensional cultured human epidermis (3.1-fold), which was used to evaluate the transport pathways other than the transfollicular route. Furthermore, the permeation flux of FITC-insulin was increased by 10.0-fold with trypsin pretreatment (from 0.02 +/- 0.00 to 0.20 +/- 0.07 microg/cm(2) per h). Mechanistic studies indicated that trypsin affects both the intercellular pathway and the hair follicular route, and may alter stratum corneum protein structures, thereby affecting skin barrier properties. This study suggests that trypsin could be effective as a biochemical enhancer for the transdermal delivery of macromolecules including peptide and protein drugs.

Trypsin as a novel potential absorption enhancer for improving the transdermal delivery of macromolecules

Abstract Objectives The aim was to assess the effect of trypsin on the transdermal delivery of macromolecules by applying its specific biochemical properties to the stratum corneum of the skin. Methods Fluorescein isothiocyanate (FITC)-labelled dextrans (FDs), with molecular weights of 4 to 250 kDa, and FITC-insulin were used as model macromolecules and a model polypeptide, and the in-vitro transdermal permeation experiments, with or without trypsin (0.1–2.5%), were carried out using rat skin and cultured human epidermis. The mechanism for the enhancement of trypsin was also studied using fluorescence and conventional light microscopy. Key findings Trypsin significantly increased the transdermal permeability of all FDs through the rat skin (2.0- to 10.0-fold). It also markedly enhanced the permeation of FD4 through three-dimensional cultured human epidermis (3.1-fold), which was used to evaluate the transport pathways other than the transfollicular route. Furthermore, the permeation flux of FITC-insulin was increased by 10.0-fold with trypsin pretreatment (from 0.02 ± 0.00 to 0.20 ± 0.07 μg/cm2 per h). Mechanistic studies indicated that trypsin affects both the intercellular pathway and the hair follicular route, and may alter stratum corneum protein structures, thereby affecting skin barrier properties. Conclusions This study suggests that trypsin could be effective as a biochemical enhancer for the transdermal delivery of macromolecules including peptide and protein drugs.

Glycerol monooleate/solvents systems for progesterone transdermal delivery: In vitro permeation and microscopic studies

Transdermal delivery of most drugs is precluded by the barrier characteristics of the stratum corneum (SC). Chemical penetration enhancers are capable of interacting with SC constituents, inducing a temporary reversible increase in the skin permeability. The aim of this work was to assess the influence of glycerol monooleate (GMO)/solvents systems on percutaneous absorption across hairless mouse SC of a lipophilic drug, progesterone (PG), as well as its effect on the SC structural characteristics, by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The morphological changes observed in the hairless mouse SC suggest a GMO effect on the skin barrier. In addition, the increase in the In vitro PG flux and in vivo penetration of a fluorescent label point towards GMO as a potential absorption enhancer. The results obtained showed that GMO/solvents systems provoked changes in the SC that could be causing increased permeation of PG across hairless mouse skin, optimising in this way the transdermal delivery of this drug.

In vivo effects of highly purified docosahexaenoic acid on rectal insulin absorption

The purpose of this study was to evaluate the effectiveness and the toxicity of polyunsaturated fatty acid, such as oleic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), as a potential absorption enhancer for rectal delivery of insulin, using a water-in-oil-in-water (W/O/W) multiple emulsion. In a single administration study, rectal insulin absorption was enhanced markedly, and marked hypoglycemia was induced by the emulsion incorporating various fatty acids in an insulin dose-related fashion. The pharmacological availability of the emulsion incorporating 2% oleic acid, EPA and DHA was ≈7.7, 11.0 and 25.4%, respectively. The insulin absorption enhancement effect was not increased in proportion to the amount of DHA in the emulsion at >1%. In addition, by incorporating Pluronic F 127 (PF 127) into the emulsion, the mean T max value of the serum glucose–time curve could be extended to twice that of the emulsion without PF 127. In a multiple administration study, the mean AUC glucose values of the emulsion incorporating DHA showed almost the same value on the first and the tenth day. From the morphological appearance of the mucosal surface, the emulsion incorporating DHA induced no or little mucosal damage. Our findings demonstrated that DHA has a strong insulin permeability enhancement effect and little toxicity. Thus, DHA is an attractive candidate as an absorption enhancer for intestinal delivery of insulin.

N-trimethyl chitosan chloride as a potential absorption enhancer across mucosal surfaces: in vitro evaluation in intestinal epithelial cells (Caco-2).

Previous studies have established that chitosan hydrochloride and glutamate are potent absorption enhancers for large hydrophilic compounds across mucosal surfaces. However, these compounds lack solubility at neutral pH values. A partially quaternized and well-soluble derivative of chitosan, N-trimethyl chitosan chloride, was synthesized and the effects of this polymer on the transepithelial electrical resistance and permeability of intestinal epithelial cells were investigated in vitro. N-trimethyl chitosan chloride was synthesized by reductive methylation and characterized with NMR. The effect of this polymer (1.0-2.5% w/v) on the transepithelial electrical resistance of intestinal epithelial cells, using Caco-2 cell monolayers, was investigated. Permeation of the hydrophilic model compounds [14C]-mannitol (MW 182.2), FITC-Dextran (MW 4400) and the peptide drug buserelin (MW 1299.5), in the presence of N-trimethyl chitosan chloride (1.5-2.5% w/v), was followed for 3 hours. The transport process of the fluorescent marker, FITC-Dextran 4400, across the cell monolayers was visualised with confocal laser scanning microscopy. Viability of the cells was checked with the trypan blue exclusion technique. N-trimethyl chitosan chloride was found to be a perfectly water-soluble, partially quaternized (about 12%) derivative of chitosan. This polymer (1.5-2.5% w/v) caused a pronounced and immediate reduction (25-85%) in the transepithelial electrical resistance of Caco-2 cells. Large increases in the transport rate of [14C]-mannitol (32-60 fold), FITC-Dextran 4400 (167-373 fold) and buserelin (28-73 fold) were demonstrated. Confocal laser scanning microscopy confirmed that N-trimethyl chitosan chloride opens the tight junctions of intestinal epithelial cells to allow increased transport of hydrophilic compounds through the paracellular transport pathway. No deleterious effects to the cells could be demonstrated with trypan blue. The potential use of N-trimethyl chitosan chloride as an absorption enhancer across mucosal surfaces could be an important contribution towards the development of effective delivery systems for hydrophilic drugs.

A novel in vitro screen to discover agents which increase the absorption of molecules across the intestinal epithelium

A major obstacle in the development of many new pharmaceuticals, particularly proteins and peptides, is their absorption across the small intestine mucosal barrier. We have developed a cell culture screen to discover novel compounds that increase the intestinal absorption of poorly transported molecules. The absorption screen uses Caco-2 cells, a human-derived intestinal epithelial cell line, grown as monolayer cultures on a permeable membrane which separates apical (luminal) and basal (serosal) chambers. The baseline absorption of the Caco-2 cell system was measured by adding marker molecules to the apical chamber and measuring their appearance in the basal chamber. The amount of these marker molecules in the basal chamber after a 1 h(37°C) incubation was used as a measure of baseline absorption (< 1% of the amount administered). Known absorption enhancers such as polyoxyethylene-9-lauryl ether (POE 9) increased the transport of both the radiolabeled and fluorescent markers. POE 9 enhanced the transport of mannitol to a greater extent than the fluorescent markers SR 101 (MW 625) and the dextran FD10 (MW 10,000). Transport of the higher molecular weight marker (FD10) was enhanced the least. In the same assay, cytotoxicity of the absorption enhancer was quantitated by measuring the release of cellular lactate dehydrogenase (LDH) into the apical solution. Neither the fluorochromes used for monitoring absorption nor the enhancers themselves interfered with the LDH detection, therefore the effect of agents on absorption and cytotoxicity could be measured simultaneously. The change in the flux of the fluorochromes across the Caco-2 cell monolayer, as well as the cytotoxic effects, were measured for five compounds that have been reported to increase epithelial absorption. This assay has been used as a screen to identify a number of potential absorption enhancers. A modification of the assay was used to assess the reversibility of the increased absorption following removal of the putative absorption enhancer. The cell culture screen should allow the identification of novel nontoxic agents which can be used to facilitate the oral absorption of pharmaceuticals.