Effects of a new lipid-based drug delivery system on the absorption of low molecular weight heparin (Fragmin) through monolayers of human intestinal epithelial Caco-2 cells and after rectal administration to rabbits

A novel physiologically based pharmacokinetic model of rectal absorption, evaluated and verified using clinical data on 10 rectally administered drugs

We present a physiologically based pharmacokinetic (PBPK) model simulating systemic drug concentrations following administration to the human rectum. Rectum physiology is parameterized based on literature data. The model utilizes in vitro release (IVRT) profiles from which drug mass transfer through the rectal fluid and tissue and into the systemic circulation are predicted. Due to a lack of data, rectal fluid and tissue absorption parameters are predicted either from colon absorption, with modifications relevant to rectal physiology, or optimized. The PBPK model is evaluated by simulating 29 clinical studies for 10 drugs. For 8 drugs (diazepam, diclofenac, indomethacin, naproxen, paracetamol, pentobarbital, phenobarbital and theophylline) the bias (average fold error, AFE) and precision (absolute average fold error, AAFE) of Cmax, AUC0-t and AUC0-inf simulations range from 0.87 to 2.22, indicating good agreement with observed values. For prochlorperazine and promethazine, the AFEs and AAFEs of Cmax predictions are 1.30 and 2.52, respectively. TheAUC0-t and AUC0-inf are overpredicted for both compounds(AFEs and AAFEs from 2.66 to 4.90). This results from a lack of reliable elimination data for prochlorperazine and the relevance of the IVRT profiles used in the promethazine model. The model paves the way for more mechanistic rectal drug absorption studies and virtual bioequivalence methods for rectal drug products.

A Tribute to Professor Per Artursson - Scientist, Explorer, Mentor, Innovator, and Giant in Pharmaceutical Research

This issue of the Journal of Pharmaceutical Sciences is dedicated to Professor Per Artursson and the groundbreaking contributions he has made and continues to make in the Pharmaceutical Sciences. Per is one of the most cited researchers in his field, with more than 30,000 citations and an h-index of 95 as of September 2020. Importantly, these citations are distributed over the numerous fields he has explored, clearly showing the high impact the research has had on the discipline. We provide a short portrait of Per, with emphasis on his personality, driving forces and the inspirational sources that shaped his career as a world-leading scientist in the field. He is a curious scientist who deftly moves between disciplines and has continued to innovate, expand boundaries, and profoundly impact the pharmaceutical sciences throughout his career. He has developed new tools and provided insights that have significantly contributed to today's molecular and mechanistic approaches to research in the fields of intestinal absorption, cellular disposition, and exposure-efficacy relationships of pharmaceutical drugs. We want to celebrate these important contributions in this special issue of the Journal of Pharmaceutical Sciences in Per's honor.

Development, in vitro and in vivo evaluation of a self-emulsifying drug delivery system (SEDDS) for oral enoxaparin administration

AIM

The aim of this study was to develop SEDDS for oral enoxaparin administration and evaluate it in vitro and in vivo.

METHODS

The emulsifying properties of SEDDS composed of long chain lipids (LC-SEDDS), medium chain lipids (MC-SEDDS), short chain lipids (SC-SEDDS) and no lipids (NL-SEDDS) were evaluated. Thereafter, enoxaparin was incorporated via hydrophobic ion pairing in the chosen SEDDS, which were evaluated regarding their mucus permeating properties, stability towards pancreatic lipase, drug release profile and cytotoxicity. Finally, in vivo performance of SEDDS was evaluated.

RESULTS

The average droplet size of chosen LC-SEDDS, MC-SEDDS and NL-SEDDS ranged between 30 and 40nm. MC-SEEDS containing 30% Captex 8000, 30% Capmul MCM, 30% Cremophor EL and 10% propylene glycol and NL-SEDDS containing 31.5% Labrafil 1944, 22.5% Capmul PG-8, 9% propylene glycol, 27% Cremophor EL and 10% DMSO exhibited 2-fold higher mucus diffusion than LC-SEDDS and were therefore chosen for further studies. The enoxaparin-dodecylamine complex (ENOX/DOA) was incorporated in a payload of 2% (w/w) into MC-SEDDS and NL-SEDDS. After 90min 97% of MC-SEDDS and 5% of NL-SEDDS were degraded by pancreatic lipase. Both MC-SEDDS and NL-SEDDS showed sustained in vitro enoxaparin release. Furthermore, orally administrated MC-SEDDS and NL-SEDDS yielded an absolute enoxaparin bioavailability of 2.02% and 2.25%, respectively.

CONCLUSION

According to the abovementioned findings, SEDDS could be considered as a potential oral LMWH delivery system.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Cell-based in vitro models for predicting drug permeability

INTRODUCTION

In vitro cell models have been used to predict drug permeation in early stages of drug development, since they represent an easy and reproducible method, allowing the tracking of drug absorption rate and mechanism, with an advantageous cost-benefit ratio. Such cell-based models are mainly composed of immortalized cells with an intrinsic ability to grow in a monolayer when seeded in permeable supports, maintaining their physiologic characteristics regarding epithelium cell physiology and functionality.

AREAS COVERED

This review summarizes the most important intestinal, pulmonary, nasal, vaginal, rectal, ocular and skin cell-based in vitro models for predicting the permeability of drugs. Moreover, the similitude between in vitro cell models and in vivo conditions are discussed, providing evidence that each model may provisionally resemble different drug absorption route.

EXPERT OPINION

Despite the widespread use of in vitro cell models for drug permeability and absorption evaluation purposes, a detailed study on the properties of these models and their in vitro-in vivo correlation compared with human data are required to further use in order to consider a future drug discovery optimization and clinical development.

Evaluation of intestinal absorption of ginsenoside Rg1 incorporated in microemulison using parallel artificial membrane permeability assay

In the present study, ginsenoside Rg(1) (Rg(1)), a naturally occurring drug which is hardly absorbed in gastrointestinal (GI) tract due to its high hydrophilicity and low membrane permeability, was incorporated in different compositions of water-in-oil microemulsions (MEs). And parallel artificial membrane permeability assay (PAMPA) that have been mainly utilized for the evaluation of in vitro permeability of early drug candidates was introduced in present study, as well as rat in vivo pharmacokinetics and in vitro permeability measurements, to investigate the effect of w/o ME on Rg(1) absorption. Correlation between various models as mentioned above was further performed to estimate the feasibility of PAMPA in the application of pharmaceutical preparation studies. After being administrated intraduodenally to rats, most of MEs can enhance the intestinal absorption of Rg(1) to various extents with relative bioavailability (F(re)) ranging from 268 to 1270% using drug solution as control. This enhanced absorption of Rg(1) may be related to its increased membrane permeability induced by ME as exhibited in the PAMPA and rat in vitro permeability measurements. Meanwhile, rat in vivo pharmacokinetics-PAMPA correlation (r(2)=0.6082) is significant (p<0.05) for ME, representing a potential prospect for the application of PAMPA in the study of pharmaceutical preparation in some conditions.

The use of lipid-based formulations to increase the oral bioavailability of Panax notoginseng saponins following a single oral gavage to rats

PURPOSE

This article was intended to improve the absorption of ginsenoside Rg1 and Rb1 of Panax notoginseng saponins (PNS).

METHODS

PNS-Phospholipid complex and a lipid-based formulation by dissolving the complex in the medium chain fattyglycerides were prepared, and their oral relative bioavailability was determined in rats and compared with an aqueous solution of PNS for each component.

RESULTS

The study gave evidence that the phospholipids could combine with the two active constitutes of PNS and form a PNS-phospholipid complex. The complex efficiently increased the solubility of hydrophilic ginsenoside Rg1 and Rb1 in some selected hydrophobic esters, such as fatty glycerides, and constructed the lipid-based formulations of PNS. The experimental result in rats in vivo showed that the oral relative bioavailability was enhanced remarkably by these lipid-based formulations composed of the PNS-Phospholipid complex and various esters. The absorption enhancement of the medium-chain glyceride (Labrafac cc and Capmul MCM (3:1)) was somewhat greater than that of other fatty glyceride. The area under the plasma concentration-time curve (AUC) of ginsenoside Rg1 and Rb1 of the PNS-complex in the medium-chain glyceride were 27.38 microg.mL-1.h and 600.08 microg.mL-1.h, compared with 2.52 microg.mL-1.h and 92.29 microg.mL-1.h of the PNS aqueous solution, respectively.

CONCLUSIONS

The oral relative bioavailability of ginsenoside Rg1 and Rb1 of PNS was enhanced remarkably by the lipid-based formulations. These findings reveal a new strategy to increase oral bioavailability by lipophilicity enhancement for some highly water-soluble but poorly absorbed drugs.

Improvement of the intestinal membrane permeability of low molecular weight heparin by complexation with stem bromelain

The aim of this study was to investigate the influence of the proteolytic enzyme bromelain on the permeation of heparin across the gastrointestinal epithelial barrier. Stability of the complex and effect of heparin on the enzymatic activity of bromelain was analysed photometrically by measuring bromelain enzymatic activity in complex with the heparin. In vitro permeation studies were performed with Caco-2 cell monolayer and rat small intestinal mucosa in Ussing-type chambers, respectively. Results revealed that enzymatic activity of bromelain remained uninfluenced by the immobilization of heparin on it. Transport studies across Caco-2 cell monolayer and rat small intestine showed that the permeation of heparin could be significantly increased in presence of bromelain. In the study with Caco-2 cells, the most effective molar ratio of bromelain to heparin was 2:1, leading to 6.7-fold improvement in uptake, whereas the molar ratio 1:1 showed the highest permeation enhancing effect in the study on intestinal mucosa. This study provides evidence that heparin and bromelain form stable complexes leading to a significantly improved uptake of heparin.

The effect of delta G on the transport and oral absorption of macromolecules

Delta G (DeltaG) is the biologically active fragment of Zonula Occludens Toxin (Zot), an absorption enhancer, that reversibly opens the tight junctions of epithelial and endothelial cells in the small intestine and brain. This study evaluates the possible use of DeltaG in enhancing the oral bioavailability of macromolecules using large paracellular markers as model agents. The transport of [(14)C]Inulin and [(14)C]PEG4000 was evaluated across Caco-2 cells with DeltaG (0, 100, 180 microg/ml). The apparent permeability coefficients (P(app)) were calculated. The in vitro toxicity of DeltaG (180 microg/ml) was assessed. Sprague Dawley rats were dosed intraduodenally (ID) with the following treatments: [(14)C]Inulin or [(14)C]PEG4000 (30 microci/kg) w/o DeltaG (720 microg/kg)/protease inhibitors (PI). Blood was collected and plasma was analyzed for radioactivity. DeltaG (180 microg/ml) increased [(14)C]Inulin and [(14)C]PEG4000 P(app) by 82.6 and 24.4%, respectively, without any toxicity. After ID administration with DeltaG/PI, C(max) and AUC were significantly (p < 0.05) increased for both Inulin and PEG4000. However, Inulin displayed greater enhancement ratios in vitro and in vivo. This study suggests that DeltaG may be used to enhance the oral bioavailability of macromolecules (e.g., proteins) after coadministration through modulation of paracellular transport.

Do surface-active lipids in food increase the intestinal permeability to toxic substances and allergenic agents?

The incidence of many common diseases has increased during the last decades. High fat intake is a risk factor for many diseases. We propose that some of the negative effects of fat are caused by lipid-induced damage of the gastrointestinal epithelium, thus compromising the epithelial function as a barrier for passage of toxic substances and allergenic agents to the circulatory system. Monoglycerides (MGs), phospholipids and fatty acids (FAs) are surface-active molecules that in pharmaceutical studies act as permeability enhancers for hydrophilic drugs with low absorption. Three possible mechanisms were proposed: (a) lipid-induced alterations in intracellular events may cause destabilization of tight junctions between the GI epithelial cells, (b) lipids may destabilize cell membranes, (c) lipids cause intestinal cell damage, which increase the permeability of the GI epithelium. These "side effects" of lipids may partly explain the association between fat intake and disease observed in epidemiological studies.

Hexarelin--evaluation of factors influencing oral bioavailability and ways to improve absorption

Hexarelin, a hexapeptide with growth hormone-releasing activity, has been found in man to have a biological bioavailability (estimated from growth hormone levels) of 0.3+/-0.1% after oral administration. The cause of the low oral efficacy of hexarelin and means of improving its absorption have been evaluated. It was found that hexarelin was degraded in the presence of the contents of the intestine. The metabolite was identified as hexarelin deamidated at the lysine residue. The degradation of hexarelin in the contents of rat ileum was inhibited by the addition of chymostatin, Pefabloc SC, EDTA, and EGTA. Furthermore, the presence of pancreatic proteases from pancrease substitute drugs caused a degradation of hexarelin that could be inhibited by the addition of Pefabloc SC. The same hexarelin metabolite that was found with the contents of rat ileum was found in the presence of human, porcine and bovine trypsin. Hexarelin permeability across rat ileum and in Caco-2 cell monolayers was low. An increase in hexarelin permeability was observed in the presence of different permeability enhancing agents.

Intestinal permeation enhancers

This review addresses the field of improving oral bioavailability through the use of excipients that increase intestinal membrane permeability. The critical issues to consider in evaluating these approaches are 1) the extent of bioavailability enhancement achieved, 2) the influence of formulation and physiological variables, 3) toxicity associated with permeation enhancement, and 4) the mechanism of permeation enhancement. The categories of permeation enhancers discussed are surfactants, fatty acids, medium chain glycerides, steroidal detergents, acyl carnitine and alkanoylcholines, N-acetylated alpha-amino acids and N-acetylated non-alpha-amino acids, and chitosans and other mucoadhesive polymers. Some of these approaches have been developed to the stage of initial clinical trials. Several seem to have potential to improve oral bioavailabilities of poorly absorbed compounds without causing significant intestinal damage. In addition, the possible use of excipients that inhibit secretory transport is reviewed.

Absorption enhancement in intestinal epithelial Caco-2 monolayers by sodium caprate: assessment of molecular weight dependence and demonstration of transport routes

Sodium caprate (C10), a medium chain fatty acid, is used clinically to enhance rectal absorption of the low molecular weight (MW) drug ampicillin. The main aim of this study was to investigate whether C10 also enhances the permeability of high MW model drugs in a model of the intestinal epithelium. The second aim was to present visual evidence of the route of enhanced transport across the epithelial cell layer. The studies were performed in Caco-2 monolayers cultured on permeable supports. The effects of non-toxic concentrations (< or = 13 mM) of C10 on drug transport across the monolayers was studied using monodisperse 14C-polyethylene glycols (MW 238-502; 14C-PEGs), 125I-Arg5-vasopressin (MW 1,208), 125I-insulin (MW 6,000) and FITC-labelled dextrans (MW 4,400 and 19,600; FD4 and FD20 respectively) as model drugs. Electron and confocal laser scanning microscopy were used to demonstrate transport routes across the epithelium. 10 mM C10 increased the permeability of all 14C-PEGs to approximately the same extent. 13 mM C10 increased the permeability of 125I-Arg8-vasopressin 10-fold. Only small increases in FD4 and FD20 permeabilities were observed. After C10 exposure, both tight junctions with normal morphology and those with dilatations showed an increased permeability to ruthenium red, indicating that C10 enhanced the paracellular transport of molecules with a MW < 1,000. Confocal microscopy showed that C10 increased the transport of FD4 and FD20 by the paracellular route. In conclusion, non-toxic concentrations of C10 can be used to enhance the permeability of drugs of MW up to approximately 1,200. Enhancement of the absorption of molecules larger than 4,000 is quantitatively insignificant. The enhanced permeability occurred via the paracellular pathway.

The effect of a drug-delivery system consisting of soybean phosphatidyl choline and medium-chain monoacylglycerol on the intestinal permeability of hexarelin in the rat

The aim of this study was to investigate if the effective in-situ permeability (Peff) of a new growth hormone-releasing peptide, hexarelin, along rat intestine was enhanced by a lipid matrix drug-delivery system comprising a mixture of soybean phosphatidyl choline and medium-chain monoacylglycerol (PC-MG). The study was performed with and without a protease inhibitor, Pefabloc SC. To enable better understanding of the mechanism of action of this delivery system we also studied the uptake of a small hydrophilic molecule, atenolol. PC-MG at a concentration of 15 mmol L(-1) increased the jejunal Peff of hexarelin approximately 20-fold, both in the presence and absence of Pefabloc SC, whereas Peff was not increased in the ileum and colon. PC-MG had no effect on the jejunal, ileal and colonic Peff of atenolol. Complete recovery of the non-absorbable molecule PEG 4000 showed that functional intestinal viability was maintained in all experiments. Although the results obtained in this study are promising, pharmacokinetic and toxicological studies are required to investigate if this delivery system is a suitable and safe candidate for improving the oral bioavailability of hexarelin.