Novel approaches for oral delivery of macromolecules

The Effects of Probiotic/Synbiotic on Serum Level of Zonulin as a Biomarker of Intestinal Permeability: A Systematic Review and Meta-Analysis

Background:

This systematic review and meta-analysis was conducted to obtain a conclusive result on the influence of probiotics/synbiotic on serum levels of zonulin. Data related to serum levels of zonulin were extracted to determine the effects of probiotic/synbiotic on intestinal permeability.

Methods:

The literature search was conducted across the Cochrane Central Register of Controlled Trials, Pub-Med, Scopus and ISI Web of Science, Search up to Nov 2018. Clinical trials evaluating the effect of probiotic/synbiotic on serum zonulin levels of all human subjects were included.

Results:

Nine studies (including 496 intervention and 443 control subjects) met the inclusion criteria for the meta-analysis. According to the meta-analysis, probiotic/synbiotic has a significant effect on serum zonulin reduction (WMD=−10.55 [95% CI: −17.76, −3.34]; P=0.004). However, the high level of heterogeneity was observed among the studies (I²=97.8, P<0.001). The subgroup analysis suggested study quality, blinding, study duration, Participants age, subject’s health status and supplement type as sources of heterogeneity.

Conclusion:

Probiotic/synbiotic have favorable effects on serum levels of zonulin as a measure of intestinal permeability. However, the results should be interpreted with caution due to the high heterogeneity and further evidence is required before definitive recommendations can be made.

Relationship between amorphous solid dispersion in vivo absorption and in vitro dissolution: phase behavior during dissolution, speciation, and membrane mass transport

Enzalutamide is a fast crystallizing, hydrophobic compound that has solubility limited absorption in vivo. Given the low aqueous solubility of this compound, it was of interest to evaluate amorphous formulations in vitro and in vivo. Amorphous solid dispersions (ASD) of enzalutamide were prepared with the hydrophilic polymers, hydroxypropyl methylcellulose acetate succinate (HPMCAS) and copovidone (PVPVA). A side-by-side diffusion cell was developed as an in vitro characterization tool to discriminate enzalutamide ASDs based upon the solute thermodynamic activity achieved during dissolution and its impact on the subsequent membrane transport rates, phase behavior, and drug speciation. The same formulations were then tested in vivo in rats using oral dosing of ASD suspensions. Different levels of plasma exposure were observed between the ASDs, which could be correlated to the phase behaviors of the ASDs following dissolution. Unsurprisingly, ASDs that underwent crystallization show lower plasma exposures. However, differences were also observed between ASDs that dissolved to form nanosized amorphous drug aggregates versus those that dissolved to yield only supersaturated solutions, with the former outperforming the latter in terms of the plasma exposure. These observations highlight the importance of thoroughly understanding the phase behavior of an amorphous formulation following dissolution and the need to discriminate between different types of precipitation, specifically crystallization versus glass liquid phase separation to form nanosized amorphous aggregates.

Encapsulation of OZ439 into Nanoparticles for Supersaturated Drug Release in Oral Malaria Therapy

Malaria poses a major burden on human health and is becoming increasingly difficult to treat due to the development of antimalarial drug resistance. The resistance issue is further exacerbated by a lack of patient adherence to multi-day dosing regimens. This situation motivates the development of new antimalarial treatments that are less susceptible to the development of resistance. We have applied Flash NanoPrecipitation (FNP), a polymer-directed self-assembly process, to form stable, water-dispersible nanoparticles (NPs) of 50–400 nm in size containing OZ439, a poorly orally bioavailable but promising candidate for single-dose malaria treatment developed by Medicines for Malaria Venture (MMV). During the FNP process, a hydrophobic OZ439 oleate ion paired complex was formed and was encapsulated into NPs. Lyophilization conditions for the NP suspension were optimized to produce a dry powder. The in vitro release rates of OZ439 encapsulated in this powder were determined in biorelevant media and compared with the release rates of the unencapsulated drug. The OZ439 NPs exhibit a sustained release profile and several-fold higher release concentrations compared to that of the unencapsulated drug. In addition, XRD suggests the drug was stabilized into an amorphous form within the NPs, which may explain the improvement in dissolution kinetics. Formulating OZ439 into NPs in this way may be an important step toward developing a single-dose oral malaria therapeutic, and offers the possibility of reducing the amount of drug required per patient, lowering delivery costs, and improving dosing compliance.

Enhanced Performance of Blended Polymer Excipients in Delivering a Hydrophobic Drug through the Synergistic Action of Micelles and HPMCAS

Blends of hydroxypropyl methylcellulose acetate succinate (HPMCAS) and dodecyl (C₁₂)-tailed poly(N-isopropylacrylamide) (PNIPAm) were systematically explored as a model system to dispense the active ingredient phenytoin by rapid dissolution, followed by the suppression of drug crystallization for an extended period. Dynamic and static light scattering revealed that C₁₂-PNIPAm polymers, synthesized by reversible addition-fragmentation chain-transfer polymerization, self-assembled into micelles with dodecyl cores in phosphate-buffered saline (PBS, pH 6.5). A synergistic effect on drug supersaturation was documented during in vitro dissolution tests by varying the blending ratio, with HPMACS primarily aiding in rapid dissolution and PNIPAm maintaining supersaturation. Polarized light and cryogenic transmission electron microscopy experiments revealed that C₁₂-PNIPAm micelles maintain drug supersaturation by inhibiting both crystal nucleation and growth. Cross-peaks between the phenyl group of phenytoin and the isopropyl group of C₁₂-PNIPAm in 2D ¹H nuclear Overhauser effect (NOESY) spectra confirmed the existence of drug-polymer intermolecular interactions in solution. Phenytoin and polymer diffusion coefficients, measured by diffusion-ordered NMR spectroscopy (DOSY), demonstrated that the drug-polymer association constant increased with increasing local density of the corona chains, coincident with a reduction in C₁₂-PNIPAm molecular weight. These findings demonstrate a new strategy for exploiting the versatility of polymer blends through the use of self-assembled micelles in the design of advanced excipients.

Paracellular permeation-enhancing effect of AT1002 C-terminal amidation in nasal delivery

BACKGROUND

The identification of permeation enhancers has gained interest in the development of drug delivery systems. A six-mer peptide, H-FCIGRL-OH (AT1002), is a tight junction modulator with promising permeation-enhancing activity. AT1002 enhances the transport of molecular weight markers or agents with low bioavailability with no cytotoxicity. However, AT1002 is not stable in neutral pH or after incubation under physiological conditions, which is necessary to fully uncover its permeation-enhancing effect. Thus, we increased the stability or mitigated the instability of AT1002 by modifying its terminal amino acids and evaluated its subsequent biological activity.

METHODS

C-terminal-amidated (FCIGRL-NH2, Pep1) and N-terminal-acetylated (Ac-FCIGRL, Pep2) peptides were analyzed by liquid chromatography-mass spectrometry. We further assessed cytotoxicity on cell monolayers, as well as the permeation-enhancing activity following nasal administration of the paracellular marker mannitol.

RESULTS

Pep1 was nontoxic to cell monolayers and showed a relatively low decrease in peak area compared to AT1002. In addition, administration of mannitol with Pep1 resulted in significant increases in the area under the plasma concentration-time curve and peak plasma concentration at 3.63-fold and 2.68-fold, respectively, compared to mannitol alone. In contrast, no increase in mannitol concentration was shown with mannitol/AT1002 or mannitol/Pep2 compared to the control. Thus, Pep1 increased the stability or possibly reduced the instability of AT1002, which resulted in an increased permeation-enhancing effect of AT1002.

CONCLUSION

These results suggest the potential usefulness of C-terminal-amidated AT1002 in enhancing nasal drug delivery, which may lead to the development of a practical drug delivery technology for drugs with low bioavailability.

Microscopic examination of the intestinal wall and selected organs of minipigs orally supplemented with humic acids

Humic acids are used to prophylactically treat intestinal diseases in a wide number of species, yet the mechanism of action remains unknown. The general assumption has been that humic acids act locally; however studies using young piglets show orally supplemented humic acids can penetrate the intestinal wall, and thus potentially act systemically. The objective of this study was to determine if humic acids could also cross the intestinal barrier in adult pigs and be detected in other organs. Adult minipigs (>18 months old) orally received either 1g humic acids/kg body weight (verum, n=3) or placebo (control, n=3), for 2 weeks. At the end of the feeding period tissue samples were harvested from the intestine, various glands and organs. Unstained tissue samples were examined by light microscopy for the presence of humic acid particles. No humic acid particles were detected in any of the unstained tissues from verum or control pigs.

Mucoadhesive intestinal devices for oral delivery of salmon calcitonin

One of the major challenges faced by therapeutic polypeptides remains their invasive route of delivery. Oral administration offers a potential alternative to injections; however, this route cannot be currently used for peptides due to their limited stability in the stomach and poor permeation across the intestine. Here, we report mucoadhesive devices for oral delivery that are inspired by the design of transdermal patches and demonstrate their capabilities in vivo for salmon calcitonin (sCT). The mucoadhesive devices were prepared by compressing a polymeric matrix containing carbopol, pectin and sodium carboxymethylcellulose (1:1:2), and were coated on all sides but one with an impermeable and flexible ethyl cellulose (EC) backing layer. Devices were tested for in vitro dissolution, mucoadhesion to intestinal mucosa, enhancement of drug absorption in vitro (Caco-2 monolayer transport) and in vivo in rats. Devices showed steady drug release with ≈75% cumulative drug released in 5h. Devices also demonstrated strong mucoadhesion to porcine small intestine to withstand forces up to 100 times their own weight. sCT-loaded mucoadhesive devices exhibited delivery of sCT across Caco-2 monolayers and across the intestinal epithelium in vivo in rats. A ≈52-fold (pharmacokinetic) and ≈44-fold (pharmacological) enhancement of oral bioavailability was observed with mucoadhesive devices when compared to direct intestinal injections. Oral delivery of devices in enteric coated capsules resulted in significant bioavailability enhancement.

Noninvasive insulin delivery: the great potential of cell-penetrating peptides

Insulin, a potent therapeutic peptide used in the treatment of diabetes, is administered to patients via subcutaneous injections because of the poor pharmacokinetics associated with alternative routes of administration such as oral, nasal and pulmonary delivery. Noninvasive nasal and oral formulations are appealing to patients who need consecutive daily treatments of insulin. However, to achieve mucosal absorption of insulin via oral or nasal administration, two barriers must be overcome: the impermeability of insulin through the epithelial membranes and local digestion and enzymatic degradation. Cell-penetrating peptides (CPPs), which efficiently bring exogenous proteins and nucleic acids into cells, have great potential to facilitate insulin permeation from the intestinal lumen or nasal cavity into systemic circulation via efficient uptake by epithelial cells. In fact, the coadministration of insulin with the peptide penetratin, a typical CPP, increased intestinal and nasal insulin bioavailability to 35 and 50%, respectively. In this review, the authors describe recent findings using this novel CPP-based formulation for noninvasive delivery of insulin.

Near-infrared fluorescent ribonuclease-A-encapsulated gold nanoclusters: preparation, characterization, cancer targeting and imaging

Ultra-small gold nanoclusters (AuNCs) have unique size-dependent optical, electrical and chemical properties. They have emerged as a new nanomaterial with broad applications in optoelectronics, catalysis, biosensing, and bioimaging. Several strategies have been exploited to prepare AuNCs of different "magic number" sizes, using different templates e.g. dendrimers, polyethyleneimines, peptides, and more recently, proteins. Notwithstanding, almost all bio-template-protected AuNCs reported so far exhibit fairly low fluorescence quantum yields (QYs), typically <5%, which is especially true for AuNCs prepared using the protein templates. In this paper, we report a facile, one-pot aqueous synthesis of highly fluorescent AuNCs using bovine pancreatic ribonuclease A (RNase-A) as the bio-template. The as-prepared AuNCs not only fluoresce strongly at the near-infrared (NIR) region (λ(em) = 682 nm), but also exhibit an elevated QY of ∼12%. Additionally, the RNase-A-encapsulated AuNC (RNase-A-AuNC) displays an exceptionally large Stokes shift of ∼210 nm as well as a single dominant fluorescence lifetime of ∼1.5 μs, about three orders of magnitude longer than biological autofluorescence. Furthermore, by coupling vitamin B(12) (VB(12)) to the RNase-A-AuNC, we develop a multifunctional nanoplatform that is suitable for simultaneous targeting and imaging of cancer at the cellular level using Caco-2 cell lines as an in vitro model. Since VB(12) has effective uptake pathways in the digestive system, this nanoplatform may have potential for targeted oral drug delivery in vivo.

Evidence of oral translocation of anionic G6.5 dendrimers in mice

Development of carrier systems to improve oral bioavailability and target drugs to specific sites continues to be an unmet need. The goal of this study was to evaluate the potential of anionic generation (G) 6.5 poly(amido amine) (PAMAM) dendrimers in oral drug delivery by assessing their in vivo oral translocation. G6.5-COOH dendrimers were characterized for their physiochemical characteristics and acute oral toxicity was assessed in CD-1 mice. The dendrimers were labeled with (125)I and their stability evaluated. Oral bioavailability was assessed in the same mouse model. Investigation of the radioactivity profile in plasma revealed presence of both large and small molecular weight compounds. Detailed area under the curve analysis suggests an effective 9.4% bioavailability of radiolabeled marker associated with G6.5-COOH. Results reported here suggest the potential of dendrimers in permeating gastrointestinal barriers in vivo.

Metabolic stability of long-acting luteinizing hormone-releasing hormone antagonists

Long-acting luteinizing hormone-releasing hormone (LHRH) antagonists designed to be protease resistant consisted of a series of novel decapeptides structurally similar to LHRH. The aim of this study was to evaluate the in vitro metabolic stability of the LHRH decapeptides using pancreatin and homogenates models and identify the metabolites in rat liver homogenate for the purpose of illustrating the metabolic features of the decapeptides. The major metabolites in rat liver homogenate were identified by LC-ESI-MS(n). The half-lives of the 11 LHRH decapeptides were from 44 to 330 min in the pancreatin model. The half-lives of the five decapeptides in rat liver, kidney and lung homogenates were between 8 and 462 min. The most stable decapeptides were the LY616 and LY608 peptides with half-lives of 36 min in liver homogenate. Two major cleavage sites were found by analysing the metabolites of the LY618 peptide in rat liver homogenate, between the Pal(3)-Ser(4) and the Leu(7)-Ilys(8) peptide bonds. The major metabolites were produced via cleavages of peptide bonds at these sites, and further metabolic reactions such as hydroxylation, oxidative dechlorination, alcohol dehydration and isopropyl dealkylation were also observed.

Peptide and protein drugs: the study of their metabolism and catabolism by mass spectrometry

Peptide and protein drugs have evolved in recent years into mainstream therapeutics, representing a significant portion of the pharmaceutical market. Peptides and proteins exhibit highly diverse structures, broad biological activities as hormones, neurotransmitters, structural proteins, metabolic modulators and therefore have a significant role as both therapeutics and biomarkers. Understanding the metabolism of synthetic or biotechnologically derived peptide and protein drugs is critical for pharmaceutical development as metabolism has a significant impact on drug efficacy and safety. Although the same principles of pharmacokinetics and metabolism of small molecule drugs apply to peptide and protein drugs, there are few notable differences. Moreover, the study of peptide and protein drug metabolism is a rather complicated process which requires sophisticated analytical techniques, and mass spectrometry based approaches have provided the capabilities for efficient and reliable quantification, characterization, and metabolite identification. This review article will focus on the current use of mass spectrometry for the study of the metabolism of peptide and protein drugs.

Noninvasive routes of proteins and peptides drug delivery

Recent advances in the field of pharmaceutical biotechnology have led to the formulation of many protein and peptide-based drugs for therapeutic and clinical application. The route of administration has a significant impact on the therapeutic outcome of a drug. The needle and syringe is a well established choice of protein and peptide delivery which has some drawback related to patient and to formulation such as pain, cost, sterility etc. Thus, the noninvasive routes which were of minor importance as parts of drug delivery in the past have assumed added importance in protein and peptide drug delivery and these include nasal, ophthalmic, buccal, vaginal, transdermal and pulmonary routes. The pharmaceutical scientists have some approaches to develop the formulations for protein and peptide delivery by noninvasive routes. But, due to the physiochemical instability and enzymatic barrier of proteins and peptides there are several hurdle to develop suitable formulation. So there is need of penetration enhancers, enzyme inhibitors and suitable vehicles for noninvasive delivery to increase the bioavailability. In this review, the aim is to focus on the approaches to formulation of protein and peptide based drug administration by noninvasive route.

Cellular evaluation of synthesized insulin/transferrin bioconjugates for oral insulin delivery using intelligent complexation hydrogels

Insulin transport across the epithelial cell layer in the small intestine was studied using insulin/transferrin conjugates with and without the presence of P(MAA-g-EG) microparticles in contact with a co-culture of Caco-2/HT29-MTX cells. The insulin/transferrin conjugate was shown to increase transport relative to pure insulin by a factor of 7, achieving an apparent permeability of 37 x 10(9) cm . s(-1). The presence of P(MAA-g-EG) microparticles increased conjugate transport by a factor of 14 times relative to insulin, achieving an apparent permeability of 72.8 x 10(9) cm . s(-1). The presence of the microparticles in solution was found to improve conjugate transport by nearly 100% with little to no change in cell monolayer integrity.

Pharmacokinetic comparison of orally-disintegrating metoclopramide with conventional metoclopramide tablet formulation in healthy volunteers

BACKGROUND

Oral tablet formulations of metoclopramide are effective therapies for gastroparesis and gastro-oesophageal reflux disease; however, difficulty swallowing tablets or nausea/vomiting may reduce patient adherence to therapy. Because of this, a metoclopramide orally-disintegrating tablet (ODT) has been developed.

AIM

To evaluate the bioequivalence of a single administration of a 10-mg metoclopramide ODT and a conventional 10-mg oral metoclopramide tablet in healthy volunteers.

METHODS

In a randomized, single-dose, crossover study, healthy volunteers received single administration of 10-mg metoclopramide ODT and 10-mg conventional metoclopramide tablet, with a 7-day interval between treatments. Serial blood samples were collected before dosing and during 24 h post-treatment.

RESULTS

Forty-one volunteers completed both treatment arms. Metoclopramide ODT was bioequivalent to conventional tablets; 90% CIs for geometric mean treatment ratios of C(max) [91.6% (90% CI, 87.7-95.8%)], AUC(last) [97.3% (90% CI, 94.5-100.2%)] and AUC(inf) [97.6% (90% CI, 94.5-100.8%)] were within the predefined range. Of the 44 volunteers included in the safety analysis, 9 (20%) reported AEs after ODT, compared with 13 (30%) after conventional tablets.

CONCLUSION

In healthy volunteers, single administration of 10-mg metoclopramide ODT was well tolerated and bioequivalent to single administration of a conventional 10-mg metoclopramide tablet.

Engineering strategies to enhance nanoparticle-mediated oral delivery

Oral delivery is the most preferred route of drug administration due to convenience, patient compliance and cost-effectiveness. Despite these advantages it remains difficult to achieve satisfactory bioavailability levels via oral administration due to the harsh environment of the gastrointestinal (GI) tract, particularly for biomacromolecules. One promising method to increase the bioavailability of macromolecular drugs such as proteins and nucleic acids is to encapsulate them in nanoparticles before oral administration. This review describes innovative strategies for increasing the efficacy of nanoparticle-mediated delivery to the GI tract. Approaches to optimize nanoparticle formulation by exploiting mucoadhesion, environmental responsiveness and external delivery control mechanisms are discussed. The application of recent advances in nanoparticle synthesis using supercritical fluids, microfluidics and imprint lithography to oral delivery are also presented, as well as possible strategies for incorporating nanoparticles into micro- and macroscale oral delivery devices.

Structure-activity relationship studies of permeability modulating peptide AT-1002

AT-1002 a 6-mer synthetic peptide belongs to an emerging novel class of compounds that reversibly increase paracellular transport of molecules across the epithelial barrier. The aim of this project was to elaborate on the structure-activity relationship of this peptide with the specific goal to replace the P2 cysteine amino acid. Herein, we report the discovery of peptides that exhibit reversible permeability enhancement properties with an increased stability profile.

Design of Estradiol Loaded PLGA Nanoparticulate Formulations: A Potential Oral Delivery System for Hormone Therapy

Estradiol (E2), a highly lipophilic molecule with good oral absorption but poor oral bioavailability, was incorporated into poly(lactide-co-glycolide) (PLGA) nanoparticles to improve its oral bioavailability. Nanoparticles were prepared by using polyvinyl alcohol (PVA) or didodecyldimethylammonium bromide (DMAB) as stabilizer, leading to negatively (size 410.9+/-39.4 nm) and positively (size 148.3+/-10.7 nm) charged particles, respectively. Both preparations showed near zero order release in vitro with about 95% drug being released within 45 and 31 days for PVA and DMAB, respectively. In situ intestinal uptake studies in male Sprague-Dawley (SD) rats showed higher uptake of DMAB stabilized nanoparticles. Following oral administration to male SD rats, E2 could be detected in blood for 7 and 2 days from DMAB and PVA stabilized nanoparticles, respectively. Histopathological examination and blood counts indicated the absence of inflammatory response. These data suggest that DMAB stabilized PLGA nanoparticles have great potential as carriers for oral delivery of estradiol.

Is the oral route possible for peptide and protein drug delivery?

Oral delivery of peptides and proteins remains an attractive alternative to parenteral delivery and has challenged various attempts at delivery development. Incorporation of new tools into the delivery systems that can raise membrane permeability of macromolecules is essential to attain high oral bioavailability that is acceptable in clinical applications. In developing oral protein delivery systems with high bioavailability, three practical approaches might be most helpful: (1) modification of the physicochemical properties of macromolecules; (2) addition of novel function to macromolecules; or (3) use of improved delivery carriers. Clearly, it is essential that these approaches maintain the biological activity of the proteins.

Nanoscale analysis of protein and peptide absorption: insulin absorption using complexation and pH-sensitive hydrogels as delivery vehicles

Recent advances in the discovery and delivery of drugs to cure chronic diseases are achieved by combination of intelligent material design with advances in nanotechnology. Since many drugs act as protagonists or antagonists to different chemicals in the body, a delivery system that can respond to the concentrations of certain molecules in the body is invaluable. For this purpose, intelligent therapeutics or "smart drug delivery" calls for the design of the newest generation of sensitive materials based on molecular recognition. Biomimetic polymeric networks can be prepared by designing interactions between the building blocks of biocompatible networks and the desired specific ligands and by stabilizing these interactions by a three-dimensional structure. These structures are at the same time flexible enough to allow for diffusion of solvent and ligand into and out of the networks. Synthetic networks that can be designed to recognize and bind biologically significant molecules are of great importance and influence a number of emerging technologies. These synthetic materials can be used as unique systems or incorporated into existing drug delivery technologies that can aid in the removal or delivery of biomolecules and restore the natural profiles of compounds in the body.

Particle uptake by Peyer's patches: a pathway for drug and vaccine delivery

Particle uptake by Peyer's patches offers the possibility of tailoring vaccines that can be delivered orally. However, particle uptake by the follicle-associated epithelium in the gastrointestinal tract depends on several different factors that are the physicochemical properties of the particles, the physiopathological state of the animal, the analytical method used to evaluate the uptake and finally the experimental model. These parameters do not allow a clear idea about the optimal conditions to target the Peyer's patches. The goal of this review is to clarify the role of each factor in this uptake.

Current strategies used to enhance the paracellular transport of therapeutic polypeptides across the intestinal epithelium

The intent of this paper is to update the reader on various strategies which have been utilized to increase the paracellular permeability of protein and polypeptide drugs across the intestinal epithelium. Structural features of protein and polypeptide drugs, together with the natural anatomical and physiological features of the gastrointestinal (GI) tract, have made oral delivery of this class of compounds extremely challenging. Interest in the paracellular route for the transport of therapeutic proteins and polypeptides following oral administration has recently intensified and continues to be explored. The assumption that molecules with a large molecular weight are not able to diffuse through the tight junctions of the intestinal membrane has been challenged by current research, along with an increased understanding of tight junction physiology.

Segment-selective absorption of lysozyme in the intestine

Absorption of fluorescein isothiocyanate-labeled lysozyme (FITC-lysozyme) was examined in rat small intestine. Messenger RNA of megalin, an endocytic receptor for lysozyme in the kidney, was expressed in the lower but not in the upper intestine. In in situ closed loop and recirculation methods, absorption of FITC-lysozyme from the upper intestine was much higher than from the lower intestine. The absorption rate of FITC-lysozyme in the upper intestine was significantly higher than FITC-dextran and was inhibited by unlabeled lysozyme in a concentration-dependent manner. The absorption of FITC-lysozyme was also inhibited by spermine and phenylarsine oxide. These results indicate that the intestinal absorption of lysozyme is segment-selective and occurs preferentially from the upper intestine. Megalin expressed in the lower intestine appears not to have a significant role in the absorption of lysozyme. In the upper intestine, lysozyme appears to be absorbed by an endocytic pathway, and cationic charge may be important for lysozyme absorption.

Pharmacokinetic aspects of biotechnology products

In recent years, biotechnologically derived peptide and protein-based drugs have developed into mainstream therapeutic agents. Peptide and protein drugs now constitute a substantial portion of the compounds under preclinical and clinical development in the global pharmaceutical industry. Pharmacokinetic and exposure/response evaluations for peptide and protein therapeutics are frequently complicated by their similarity to endogenous peptides and proteins as well as protein nutrients. The first challenge frequently comes from a lack of sophistication in various analytical techniques for the quantification of peptide and protein drugs in biological matrices. However, advancements in bioassays and immunoassays--along with a newer generation of mass spectrometry-based techniques--can often provide capabilities for both efficient and reliable detection. Selection of the most appropriate route of administration for biotech drugs requires comprehensive knowledge of their absorption characteristics beyond physicochemical properties, including chemical and metabolic stability at the absorption site, immunoreactivity, passage through biomembranes, and active uptake and exsorption processes. Various distribution properties dictate whether peptide and protein therapeutics can reach optimum target site exposure to exert the intended pharmacological response. This poses a potential problem, especially for large protein drugs, with their typically limited distribution space. Binding phenomena and receptor-mediated cellular uptake may further complicate this issue. Elimination processes--a critical determinant for the drug's systemic exposure--may follow a combination of numerous pathways, including renal and hepatic metabolism routes as well as generalized proteolysis and receptor-mediated endocytosis. Pharmacokinetic/pharmacodynamic (PK/PD) correlations for peptide and protein-based drugs are frequently convoluted by their close interaction with endogenous substances and physiologic regulatory feedback mechanisms. Extensive use of pharmacokinetic and exposure/response concepts in all phases of drug development has in the past been identified as a crucial factor for the success of a scientifically driven, evidence-based, and thus accelerated drug development process. Thus, PK/PD concepts are likely to continue and expand their role as a fundamental factor in the successful development of biotechnologically derived drug products in the future.

Channel-forming peptide modulates transepithelial electrical conductance and solute permeability

NC-1059, a synthetic channel-forming peptide, transiently increases transepithelial electrical conductance (g(TE)) and ion transport (as indicated by short-circuit current) across Madin-Darby canine kidney (MDCK) cell monolayers in a time- and concentration-dependent manner when apically exposed. g(TE) increases from <2 to >40 mS/cm(2) over the low to middle micromolar range. Dextran polymer (9.5 but not 77 kDa) permeates the monolayer following apical NC-1059 exposure, suggesting that modulation of the paracellular pathway accounts for changes in g(TE). However, concomitant alterations in junctional protein localization (zonula occludens-1, occludin) and cellular morphology are not observed. Effects of NC-1059 on MDCK g(TE) occur in nominally Cl(-)- and Na(+)-free apical media, indicating that permeation by these ions is not required for effects on g(TE), although two-electrode voltage-clamp assays with Xenopus oocytes suggest that both Cl(-) and Na(+) permeate NC-1059 channels with a modest Cl(-) permselectivity (P(Cl):P(Na) = 1.3). MDCK monolayers can be exposed to multiple NC-1059 treatments over days to weeks without diminution of response, alteration in the time course, or loss of responsiveness to physiological and pharmacological secretagogues. Together, these results suggest that NC-1059 represents a valuable tool to investigate tight junction regulation and may be a lead compound for therapeutic interventions.

Enhanced permeability of molecular weight markers and poorly bioavailable compounds across Caco-2 cell monolayers using the absorption enhancer, zonula occludens toxin

PURPOSE

Zonula occludens toxin (Zot), a protein elaborated from Vibrio cholerae, has been shown to be capable of reversibly opening tight junctions. The objective of this work was to determine the stability of Zot and to examine the permeability of a series of molecular weight hydrophilic markers and therapeutic agents in the presence of Zot.

METHOD

The transport of molecular weight markers (i.e., PEG 4000, FITC-dextran 10.000 and inulin) and therapeutic agents (i.e., acyclcovir, cyclopsorin, paclitaxel. doxorubicin) was evaluated with Zot (0, 2, and 4 microg/mL) using Caco-2 cell monolayers.

RESULTS

Zot was found to be stable over a 10-day period. Significantly higher (p < 0.05) permeability of the molecular weight markers, in lin, and PEG4000 were observed with Zot (4 microg/mL). The transport of each therapeutic marker was significantly increased with paclitaxel displaying a >3-fold enhancement in Papp values with Zot (4 microg/mL). A 30% decrease in transepithelial electrical resistance values wa observed, which returned to baseline 30 min after Zot was removed.

CONCLUSIONS

Considering the problems of poor oral bioavailability, it is concluded that Zot is a promising drug delivery technology to be used to enhance drug transport across the intestinal mucosa. Future applications are targeted at assessing its usefulness in oral drug delivery using in vivo systems.

Protein drug oral delivery: the recent progress

Rapid development in molecular biology and recent advancement in recombinant technology increase identification and commercialization of potential protein drugs. Traditional forms of administrations for the peptide and protein drugs often rely on their parenteral injection, since the bioavailability of these therapeutic agents is poor when administered nonparenterally. Tremendous efforts by numerous investigators in the world have been put to improve protein formulations and as a result, a few successful formulations have been developed including sustained-release human growth hormone. For a promising protein delivery technology, efficacy and safety are the first requirement to meet. However, these systems still require periodic injection and increase the incidence of patient compliance. The development of an oral dosage form that improves the absorption of peptide and especially protein drugs is the most desirable formulation but one of the greatest challenges in the pharmaceutical field. The major barriers to developing oral formulations for peptides and proteins are metabolic enzymes and impermeable mucosal tissues in the intestine. Furthermore, chemical and conformational instability of protein drugs is not a small issue in protein pharmaceuticals. Conventional pharmaceutical approaches to address these barriers, which have been successful with traditional organic drug molecules, have not been effective for peptide and protein formulations. It is likely that effective oral formulations for peptides and proteins will remain highly compound specific. A number of innovative oral drug delivery approaches have been recently developed, including the drug entrapment within small vesicles or their passage through the intestinal paracellular pathway. This review provides a summary of the novel approaches currently in progress in the protein oral delivery followed by factors affecting protein oral absorption.

Alginate/poly-L-lysine microparticles for the intestinal delivery of antisense oligonucleotides

PURPOSE

A microparticle carrier based on alginate and poly-L-lysine was developed and evaluated for the delivery of antisense oligonucleotides at the intestinal site. Formulations of oligonucleotide-loaded microparticles having differences in the carrier molecular weight and composition were characterized in vitro and in vivo.

METHODS

Polymeric microparticles were prepared by ionotropic gelation and crosslinking of alginate with calcium ions and poly-L-lysine. The loading of the antisense oligonucleotide into the microparticles was achieved by absorption in aqueous medium. The association capacity, loading and particle size of the microparticles were characterized. The in vivo performances of various formulations after intrajejunal administration were studied in rat and in dog models.

RESULTS

Microparticles had a sponge-like structure and an oligonucleotide loading of 27-35%. The composition of the medium affected the particle size and the in vitro release profiles. The oligonucleotide bioavailability after intrajejunal administration to rats in the presence of permeation enhancers was good for most of the tested systems. The application of microparticles in powder form compared to an equivalent suspension improved the intrajejunal bioavailability of the oligonucleotide (25% and 10% respectively) in rats. On the contrary, the intrajejunal administration to dogs resulted in poor oligonucleotide bioavailability (0.42%).

CONCLUSIONS

The formulation of antisense oligonucleotides within alginate and poly-L-lysine microparticles is a promising strategy for the oral application.

Enhancement of paracellular transport of heparin disaccharide across Caco-2 cell monolayers

The enhancement of paracellular transport of heparin disaccharide using several absorption enhancers across Caco-2 cell monolayers was tested. The cytotoxicity of these enhancers was also examined. The enhancing effects by Quillaja saponin, dipotassium glycyrrhizinate, 18beta-glycyrrhetinic acid, sodium caprate and taurine were determined by changes in transepithelial electrical resistance (TEER) and the amount of heparin disaccharide transported across Caco-2 cell monolayers. Among the absorption enhancers, 18beta-glycyrrhetinic acid and taurine decreased TEER and increased the permeability of heparin disaccharide in a dose-dependent and time-dependent manner with little or negligible cytotoxicity. Our results indicate that these absorption enhancers can widen the tight junction, which is a dominant paracellular absorption route of hydrophilic compounds. It is highly possible that these absorption enhancers can be applied as pharmaceutical excipients to improve the transport of macromolecules and hydrophilic drugs having difficulty in permeability across the intestinal epithelium.

Targeted PEG-based bioconjugates enhance the cellular uptake and transport of a HIV-1 TAT nonapeptide

We previously described the enhanced cell uptake and transport of R.I-K(biotin)-Tat9, a large ( approximately 1500 Da) peptidic inhibitor of HIV-1 Tat protein, via SMVT, the intestinal biotin transporter. The aim of the present study was to investigate the feasibility of targeting biotinylated PEG-based conjugates to SMVT in order to enhance cell uptake and transport of Tat9. The 29 kDa peptide-loaded bioconjugate (PEG:(R.I-Cys-K(biotin)-Tat9)8) used in these studies contained eight copies of R.I-K(biotin)-Tat9 appended to PEG by means of a cysteine linkage. The absorptive transport of biotin-PEG-3400 (0.6-100 microM) and the bioconjugate (0.1-30 microM) was studied using Caco-2 cell monolayers. Inhibition of biotin-PEG-3400 by positive controls (biotin, biocytin, and desthiobiotin) was also determined. Uptake of these two compounds was also determined in CHO cells transfected with human SMVT (CHO/hSMVT) and control cells (CHO/pSPORT) over the concentration ranges of 0.05-12.5 microM and 0.003-30 microM, respectively. Nonbiotinylated forms of these two compounds, PEG-3350 and PEG:(R.I-Cys-K-Tat9)8, were used in the control studies. Biotin-PEG-3400 transport was found to be concentration-dependent and saturable in Caco-2 cells (K(m)=6.61 microM) and CHO/hSMVT cells (K(m)=1.26 microM). Transport/uptake was significantly inhibited by positive control substrates of SMVT. PEG:(R.I-Cys-K(biotin)Tat9)8 also showed saturable transport kinetics in Caco-2 cells (K(m)=6.13 microM) and CHO/hSMVT cells (K(m)=8.19 microM). Maximal uptake in molar equivalents of R.I-Cys-K(biotin)Tat9 was 5.7 times greater using the conjugate versus the biotinylated peptide alone. Transport of the nonbiotinylated forms was significantly lower (P<0.001) in all cases. The present results demonstrate that biotin-PEG-3400 and PEG:(R.I-Cys-K(biotin)Tat9)8 interact with human SMVT to enhance the cellular uptake and transport of these larger molecules and that targeted bioconjugates may have potential for enhancing the cellular uptake and transport of small peptide therapeutic agents.

Permeability measurement of macromolecules and assessment of mucosal antigen sampling using in vitro converted M cells

INTRODUCTION

M cells are located in the epithelial layer covering the gut-associated lymphoid tissue and are responsible for delivery of macromolecules and microorganisms to the underlying lymphoid cells. It has been shown that the human colonic cell line Caco-2 can be converted to M cells in vitro following coculture with isolated lymphocytes from murine Peyer's patches. Studies were undertaken to evaluate and characterize the transepithelial transport of select macromolecules across these in vitro derived M cells.

METHODS

Caco-2 cells were converted to M cells as reported previously. The morphology of Caco-2 cells and M cells was compared by transmission electron microscopy (TEM). The transport properties of macromolecules such as horseradish peroxidase, FITC-conjugated polystyrene beads, and radiolabeled dextrans were examined. The activation of murine antigen-specific T cells following transport of the antigen ovalbumin across the M-cell barrier was assessed by measuring cytokine production.

RESULTS

M cells were shown to be irregular in shape and have fewer and shorter microvilli compared to the Caco-2 cell progenitors. These cells were still able to form tight junctions and monolayers on polycarbonate membranes. Time-course studies demonstrated that the transport of polystyrene beads and large-molecular-weight dextrans at physiological temperature across M-cell-containing monolayers was size dependent and more rapid than across Caco-2 cell monolayers. The transport of dextrans was also shown to be temperature and concentration dependent. Befitting the role of the M cell in mucosal defense, protein antigen could be delivered by these cells in order to be processed and presented to antigen-specific CD4+ T lymphocytes.

DISCUSSION

The M-cell permeability model is a functional and practical system for evaluating the transport properties of macromolecules and assessing the potential for intestinal mucosal antigen sampling to elicit immunological responses.

Functional modeling of tight junctions in intestinal cell monolayers using polyethylene glycol oligomers

Despite significant advances in the characterization of tight junction (TJ) proteins, little is known about how molecular changes relate to function due primarily to the limitations of conventional paracellular probes. To address this, the paracellular pathway in Caco-2 and T84 cell lines was profiled by measuring the permeabilities of 24 polyethylene glycols (PEG) of increasing molecular radius (3.5--7.4 A) analyzed by mass spectrometry. When combined with a paracellular sieving model, these data provided quantitative descriptors of the pathway under control conditions and after exposure to TJ modulators. PEG profiles in both cell lines conformed to a biphasic process involving a restrictive pore (radius 4.3--4.5 A) and a nonrestrictive component responsible for permeability of larger molecules. PEG profiling revealed significant differences between the effects of EGTA and sodium caprate (C10). The restrictive component of EGTA-treated cells lost all size discrimination due to an increase in pore radius. Sodium caprate had no effect on pore radius but increased permeability via a different mechanism possibly involving increased numbers of functional pores. PEG profiling provides a useful tool for probing the functional regulation of the paracellular route.

Characterization of complexes of an antisense oligonucleotide with protamine and poly-L-lysine salts

The objectives of this work were to study the interaction of an antisense oligonucleotide (ISIS 2302) with poly-L-lysine (PLL) and protamine salts, to determine the physico-chemical characteristics of the resulting complex systems and to analyze the influence of permeation enhancers (Na-chenodeoxycholate and Na-caprate) on the dissociation of the complexes. Specific conductivity, zeta potential, particle size distribution and dialysis studies of the resulting complex systems were performed. Conductometric titration defined the molar ratios between the ionic species in the complex. Zeta potential data confirmed the conductometric equivalence points and explained the good physical stability of charged complexes when compared to neutral complexes (+/-40 mV for PLL-based complexes and +/-25 mV for protamine sulfate complexes). The particle size was less than 175 nm for most systems. The incorporation of Na-chenodeoxycholate promoted complex dissociation, while Na-caprate gave opposite results. An increase in the ionic strength of the environment had a destabilizing effect and promoted dissociation of the complexes.

Intestinal absorption of peptides through the enterocytes

Transport of intact peptides and proteins from the intestinal lumen into the blood is a unique phenomenon, which differs from the regular process of food digestion and absorption. Intestinal absorption of minute amounts of proteins is, however, being considered as a normal physiological process. It is thus important to define and understand the routes for protein transfer from the intestinal lumen to the blood and the mechanisms by which the macromolecules overcome the sieving barrier of the intestinal wall. The study on insulin has demonstrated that, upon proper introduction into the intestinal lumen, insulin is absorbed by the epithelial cells and transferred to the circulation. The peptides absorbed and transferred to the blood retained their biological activity and induced significant lowering of blood glucose levels. The efficiency of the absorption does not differ among the ileum, duodenum, and colon. Morphological examination demonstrated no alteration of the structural integrity of the epithelia, the enterocytes stay intact with well-developed microvilli, and the cells remain joined by tightly closed junctions. Application of immunocytochemistry on thin tissue sections revealed insulin antigenic sites at different locations depending on the time point. Insulin detected in the lumen of the intestinal tract is absorbed through the endosomal compartment of the epithelial cells rather than passing between cells. Internalization occurs through invaginations of the luminal plasma membrane and vesicular structures of the endosomal compartment. In 5-10 minutes, insulin is transferred to the basolateral membrane and released into the interstitial space to reach the circulation. Definition of the transcytotic pathway will contribute to a better understanding of drug delivery for potential therapeutic applications.

Recent technological advances in oral drug delivery - a review

Despite disadvantages, oral drug delivery remains the preferred route of drug delivery. Novel technologies with improved performance, patient compliance, and enhanced quality have emerged in the recent past. Oral fast-dispersing dosage forms, three-dimensional Printing (3DP) and electrostatic coating are a few examples of a few existing technologies with the potential to accommodate various physico-chemical, pharmacokinetic and pharmacodynamic characteristics of drugs. This article provides a comprehensive review of these three technologies.