Mechanistic basis for unexpected bioavailability enhancement of polyelectrolyte complexes incorporating BCS class III drugs and carrageenans

Beyond carrots: Evaluation of gelling agents as wet feeds for Tenebrio molitor L. (Coleoptera: Tenebrionidae) larvae

Previous studies have shown that larvae of the yellow mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae), need a source of moisture to grow and perform well. Currently, much research has been oriented towards the effect of dry feed on larval growth and performance. The effect of different wet feeds as moisture source on the performance traits of T. molitor larvae has not been thoroughly investigated yet. This study aims to investigate in laboratory trials the effect of various gelling agents (agar, carrageenans, guar gum, xanthan gum, sodium alginate, modified starch, and pectin) on the growth and performance of T. molitor larvae. A number of 50 newly emerged larvae obtained from the rearings of the LEAZ were inserted in plastic vials together with 4 g of wheat bran as dry feed. Additionally, 1 g of gelling agents was provided 3 times per week as moisture sources. Carrot slices served as control. Larval survival and weight were recorded weekly until the appearance of the first pupa. Dry feed was replenished when depleted. Our data showed that gelling agents efficiently supported the growth of T. molitor larvae, in terms of larval survival and weight, as well as feed utilization expressed as FCR. Interestingly, carrageenans seem to be the most appropriate gelling agent for T. molitor larvae rearing as it can enhance their weight and is also able to reduce their development time and their specific growth rate.

Promising strategies for improving oral bioavailability of poor water-soluble drugs

INTRODUCTION

Oral administration of poorly water-soluble drugs (PWSDs) is generally related to low bioavailability, leading to high drug doses, multiple side effects, and low patient compliance. Thus, different strategies have been developed to increase drug solubility and dissolution in the gastrointestinal tract, opening new venues for these drugs.

AREAS COVERED

This review outlines the current challenges in PWSD formulation development and the strategies to overcome the oral barriers and increase their solubility and bioavailability. Conventional strategies include altering crystalline and molecular structures and modifying oral solid dosage forms. In contrast, novel strategies comprise micro- and nanostructured systems. Recent representative studies involving how these strategies have improved the oral bioavailability of PWSDs were also reviewed and reported.

EXPERT OPINION

New approaches to enhance PWSD bioavailability have sought to improve water solubility and dissolution rates, drug protection by overcoming biological barriers, and increased absorption. Still, only a handful of studies have focused on quantifying the increase in bioavailability. Improving the oral bioavailability of PWSDs remains an exciting unexplored field of research and has become an important issue for successfully developing pharmaceutical products.

Citric Acid Enhances the Activities of Astilbin on Psoriasis via Down-Regulation of P-Glycoprotein

Astilbin (AS) has been confirmed to be an attractive candidate drug for psoriasis; however, the low oral absorption limits its further development and utilization. Herein, a simple method was discovered to solve this problem, which was combined with citric acid (CA). The efficiency was estimated by imiquimod (IMQ)-induced psoriasis-like mice, and the absorption was predicted by the Ussing chamber model, HEK293-P-gp cells were used to validate the target. Compared with the AS group, the combination with CA significantly reduced the PASI score and down-regulated the protein expression of IL-6 and IL-22, which showed that the combination of CA enhanced the anti-psoriasis effect of AS. Moreover, AS concentration in psoriasis-like mice plasma was significantly increased (3.90-fold) in the CA combined group, and the mRNA and protein levels of P-gp in the small intestine of the combined group were decreased by 77.95 and 30.00%, respectively. In addition, when combined with CA, AS absorption significantly increased while the efflux ratio decreased in vitro. Furthermore, CA significantly elevated the uptake of AS by 153.37% and decreased the protein expression of P-gp by 31.70% in HEK293-P-gp cells. These results indicated that CA enhanced the therapeutic efficacy of AS by improving its absorption via down-regulation of P-gp.

Enhanced dissolution/caco-2 permeability, pharmacokinetic and pharmacodynamic performance of re-dispersible eprosartan mesylate nanopowder

Eprosartan mesylate is an angiotensin receptor blocker which suffers from extremely poor bioavailability owing to its poor solubility and poor permeability. The rationale of the present work was to design the drug delivery system capable of overcoming these constraints. Nanoformulation of eprosartan mesylate was developed using ultrasonic wave-assisted liquid-antisolvent technique. Nanoformulation was further freeze dried with the addition of 1% of mannitol resulting in formation of re-dispersible EPM nanopowder. To prove our proof of principle, the re-dispersed nanopowder with z-average particle size 165.2 ± 1.8 nm was evaluated enormously for in-vitro dissolution behaviour and permeability assay through Caco-2 cell model. In-vitro dissolution study was performed at pH 1.2, pH 4.5 and pH 6.8. Result demonstrates enhanced dissolution from EPM nanopowder with negligible pH dependence. Transport studies accomplished using validated Caco-2 based cell model showed 11-fold enhanced apparent permeability of redispersed nanopowder when compared to pure EPM and corresponding physical mixture (p < 0.0001). In-vivo study reveals, exceptionally strong variations in plasma concentration of EPM through nanopowder (62 mg/kg) formulation when compared with physical mixture and pure EPM (62 mg/kg) group. Moreover, study manifests that 5-fold lower dose (12.4 mg/kg) of developed formulation yields higher exposure (4600 ± 36 ng·mL^-1·h) than pure EPM (2349 ± 34 ng·mL^-1·h) and corresponding physical mixture (2456 ± 49 ng·mL^-1·h) at therapeutic dose (62 mg/kg). Further, L-NAME induced hypertensive model was undertaken to investigate effect of reduced dose of EPM nanopowder on systolic blood pressure, biochemical analysis and histopathology of heart. Results revealed pronounced antihypertensive potential of re-dispersed EPM nanopowder at 5-fold lower dose (12.4 mg/kg). In conclusion, our study indicates that nanopowder delivery might be the promising approach for providing enhanced oral bioavailability at lower dose.

Lipopolysaccharide Polyelectrolyte Complex for Oral Delivery of an Anti-tubercular Drug

Anti-tuberculosis drug delivery has remained a challenge due to inconsistent bioavailability and inadequate sustained-release properties leading to treatment failure. To resolve these drawbacks, a lipopolysaccharide polyelectrolyte complex (PEC) encapsulated with rifampicin (RIF) (as the model drug) was fabricated, using the solvent injection technique (SIT), with soy lecithin (SLCT), and low-molecular-weight chitosan (LWCT). The average particle size and surface charge of RIF-loaded PEC particulates was 151.6 nm and + 33.0 nm, respectively, with noted decreased particle size and surface charge following increase in SLCT-LWCT mass ratio. Encapsulation efficiency (%EE) and drug-loading capacity (%LC) was 64.25% and 5.84%, respectively. Increase in SLCT-LWCT mass ratio significantly increased %EE with a marginal reduction in %LC. In vitro release studies showed a sustained-release profile for the PEC particulate tablet over 24 h (11.4% cumulative release) where the dominant release mechanism involved non-Fickian anomalous transport shifting towards super case II release as SLCT ratios increased (6.4% cumulative release). PEC-tablets prepared without SIT presented with rapid Fickian-diffusion-based drug release with up to 90% RIF release within 4 h. Ex vivo permeability studies revealed that lipopolysaccharide PEComplexation significantly increased the permeability of RIF by ~ 2-fold within the 8-h study period. These results suggest successful encapsulation of RIF within a PEC structure while imparting increased amorphic regions, as indicated by x-ray diffraction, for potential benefits in improved drug dissolution, bioavailability, and dosing.

The effect of chitosan on the bioaccessibility and intestinal permeability of acyclovir

Chitosan is object of pharmaceutical research as a candidate permeability enhancer. However, chitosan was recently shown to reduce the oral bioavailability of acyclovir in humans. The effect of chitosan on two processes determining the oral bioavailability of acyclovir, bioaccessibility and intestinal absorption, was now investigated. Acyclovir's bioaccessibility was studied using the dynamic TNO gastro-Intestinal Model (TIM-1). Four epithelial models were used for permeability experiments: a Caco-2 cell model in absence and presence of mucus and both rat and porcine excised intestinal segments. Study concentrations of acyclovir (0.8 g/l) and chitosan (1.6 g/l and 4 g/l) were in line with those used in the aforementioned human study. No effect of chitosan was measured on the bioaccessibility of acyclovir in the TIM-1 system. The results obtained with the Caco-2 models were not in line with the in vivo data. The tissue segment models (rat and porcine intestine) showed a negative trend of acyclovir's permeation in presence of chitosan. The Ussing type chamber showed to be the most biopredictive, as it did point to an overall statistically significantly reduced absorption of acyclovir. This model thus seems most appropriate for pharmaceutical development purposes, in particular when interactions between excipients and drugs are to become addressed.

Impact of mucoadhesive polymeric nanoparticulate systems on oral bioavailability of a macromolecular model drug

Nanoparticles (NP) only different in mucoadhesivity are compared for impact on drug oral bioavailability. Two polymeric NP types based on quaternary ammonium-chitosan (NP QA-Ch) and S-protected thiolated derivative thereof (NP QA-Ch-S-pro), respectively, containing the macromolecular drug model, FD4, were prepared by crosslinking each polymer with reduced MW hyaluronic acid. The structure of basic polymers was determined by H¹NMR analysis. NP were similar in size (371 ± 38 vs. 376 ± 82 nm); polydispersity index (0.39 ± 0.08 vs. 0.41 ± 0.10); zeta potential (13.4 ± 0.9 vs. 11.9 ± 1.2 mV); reversible interactions with drug (bound drug, 67 vs. 66%); encapsulation efficiency (23 ± 5 vs. 23 ± 8%); release properties (15% released in 15 h in both cases); and apparent permeation across excised rat intestine (P_app, 8.8 ± 0.8 vs. 10 ± 1 cm/s). Then the differences in NP transport ratio through mucus (TR, 0.75 vs. 0.37) and adhesion to excised rat intestinal mucosa (adsorbed fraction, 23 ± 3 vs. 45 ± 2%) were ascribed to higher mucoadhesivity of NP QA-Ch-S-pro compared to NP QA-Ch. This directly influenced drug oral bioavailability in rats (T_max, 1 vs. 2 h; AUC, 1.7 ± 0.3 vs. 2.9 ± 0.4 μg/mL min, for NP QA-Ch and NP QA-Ch-S-pro, respectively). Mucoadhesivity increases drug bioavailability by retaining NP at its absorption site and opposing its transit down the GI tract. Data on drug accumulation in rat liver allows the assertion that NP is absorbed by transcytosis across intestinal epithelium and transported from blood into liver by Kuppfer cells.

Interactions Between Emodin and Efflux Transporters on Rat Enterocyte by a Validated Ussing Chamber Technique

Emodin, a major active anthraquinone, frequently interacts with other drugs. As changes of efflux transporters on intestine are one of the essential reasons why the drugs interact with each other, a validated Ussing chamber technique was established to detect the interactions between emodin and efflux transporters, including P-glycoprotein (P-gp), multidrug-resistant associated protein 2 (MRP2), and multidrug-resistant associated protein 3 (MRP3). Digoxin, pravastatin, and teniposide were selected as the test substrates of P-gp, MRP2, and MRP3. Verapamil, MK571, and benzbromarone were their special inhibitors. The results showed that verapamil, MK571, and benzbromarone could increase digoxin, pravastatin, and teniposide absorption, and decrease their E_r values, respectively. Verapamil (220 μM) could significantly increase emodin absorption at 9.25 μM. In the presence of MK571 (186 μM), the P_app values of emodin from M-S were significantly increased and the efflux ratio decreased. With the treatment of emodin (185, 370, and 740 μM), digoxin absorption was significantly decreased while teniposide increased. These results indicated that emodin might be the substrate of P-gp and MRP2. Besides, it might be a P-gp inducer and MRP3 inhibitor on enterocyte, which are reported for the first time. These results will be helpful to explain the drug–drug interaction mechanisms between emodin and other drugs and provide basic data for clinical combination therapy.

Release mechanism of doxazosin from carrageenan matrix tablets: Effect of ionic strength and addition of sodium dodecyl sulphate

The polyelectrolyte matrix tablets loaded with an oppositely charged drug exhibit complex drug-release mechanisms. In this study, the release mechanism of a cationic drug doxazosin mesylate (DM) from matrix tablets based on an anionic polyelectrolyte λ-carrageenan (λ-CARR) is investigated. The drug release rates from λ-CARR matrices are correlated with binding results based on potentiometric measurements using the DM ion-sensitive membrane electrode and with molecular characteristics of the DM-λ-CARR-complex particles through hydrodynamic size measurements. Experiments are performed in solutions with different ionic strength and with the addition of an anionic surfactant sodium dodecyl sulphate (SDS). It is demonstrated that in addition to swelling and erosion of tablets, the release rates depend strongly on cooperative interactions between DM and λ-CARR. Addition of SDS at concentrations below its critical micelle concentration (CMC) slows down the DM release through hydrophobic binding of SDS to the DM-λ-CARR complex. On the contrary, at concentrations above the CMC SDS pulls DM from the complex by forming mixed micelles with it and thus accelerates the release. Results involving SDS show that the concentration of surfactants that are naturally present in gastrointestinal environment may have a great impact on the drug release process.

Dissolution and dissolution/permeation experiments for predicting systemic exposure following oral administration of the BCS class II drug clarithromycin

In order to save time and resources in early drug development, in vitro methods that correctly predict the formulation effect on oral drug absorption are necessary. The aim of this study was to 1) evaluate various BCS class II drug formulations with in vitro methods and in vivo in order to 2) determine which in vitro method best correlates with the in vivo results. Clarithromycin served as model compound in formulations with different particle sizes and content of excipients. The performed in vitro experiments were dissolution and dissolution/permeation experiments across two types of membrane, Caco-2 cells and excised rat intestinal sheets. The in vivo study was performed in rats. The oral absorption was enhanced by downsizing drug particles and by increasing the excipient concentration. This correlated strongly with the flux across Caco-2 cells but not with the other in vitro experiments. The insufficient correlation with the dissolution experiments can be partly explained by excipient caused problems during the filtration step. The very poor correlation of the in vivo data with the flux across excised rat intestinal sheets might be due to an artificially enlarged mucus layer ex vivo. In conclusion, downsizing BCS class II drug particles and the addition of surfactants enhanced the in vivo absorption, which was best depicted by dissolution/permeation experiments across Caco-2 cells. This setup is proposed as best model to predict the in vivo formulation effect. Also, this is the first study to evaluate the impact of the nature of the permeation membrane in dissolution/permeation experiments.

Optimization of the Ussing chamber setup with excised rat intestinal segments for dissolution/permeation experiments of poorly soluble drugs

CONTEXT

Prediction of the in vivo absorption of poorly soluble drugs may require simultaneous dissolution/permeation experiments. In vivo predictive media have been modified for permeation experiments with Caco-2 cells, but not for excised rat intestinal segments.

OBJECTIVE

The present study aimed at improving the setup of dissolution/permeation experiments with excised rat intestinal segments by assessing suitable donor and receiver media.

METHODS

The regional compatibility of rat intestine in Ussing chambers with modified Fasted and Fed State Simulated Intestinal Fluids (Fa/FeSSIF_mod) as donor media was evaluated via several parameters that reflect the viability of the excised intestinal segments. Receiver media that establish sink conditions were investigated for their foaming potential and toxicity. Dissolution/permeation experiments with the optimized conditions were then tested for two particle sizes of the BCS class II drug aprepitant.

RESULTS

Fa/FeSSIF_mod were toxic for excised rat ileal sheets but not duodenal sheets, the compatibility with jejunal segments depended on the bile salt concentration. A non-foaming receiver medium containing bovine serum albumin (BSA) and Antifoam B was nontoxic. With these conditions, the permeation of nanosized aprepitant was higher than of the unmilled drug formulations.

DISCUSSION

The compatibility of Fa/FeSSIF_mod depends on the excised intestinal region. The chosen conditions enable dissolution/permeation experiments with excised rat duodenal segments. The experiments correctly predicted the superior permeation of nanosized over unmilled aprepitant that is observed in vivo.

CONCLUSION

The optimized setup uses FaSSIF_mod as donor medium, excised rat duodenal sheets as permeation membrane and a receiver medium containing BSA and Antifoam B.

Novel insights into excipient effects on the biopharmaceutics of APIs from different BCS classes: Lactose in solid oral dosage forms

Excipients encompass a wide range of properties that are of importance for the resulting drug product. Regulatory guidelines on biowaivers for immediate release formulations require an in depth understanding of the biopharmaceutic effects of excipients in order to establish bioequivalence between two different products carrying the same API based on dissolution tests alone. This paper describes a new approach in evaluating biopharmaceutic excipient effects. Actually used quantities of a model excipient, lactose, formulated in combination with APIs from different BCS classes were evaluated. The results suggest that companies use different (relative) amounts depending on the characteristics of the API. The probability of bioinequivalence due to a difference in lactose content between test and reference products was classified as low for BCS class I APIs and medium for BCS class II and III APIs, whereas a high probability was assigned to the combination of lactose and BCS class IV APIs. If repeated for other excipients, this retrospective, top-down approach may lead to a new database and more widespread applications of the biowaiver approach.