Now showing 1 - 10 of 56
  • Publication
    The Centenary of the Discovery of Insulin: An Update on the Quest for Oral Delivery
    (Frontiers Media, 2021-09-15)
    Not many topics in drug delivery science have exercised so many pharmaceutical, formulation, and bioengineering minds than the oral delivery of macromolecules, especially when insulin is the focus. The year 2021 marks a hundred years since the discovery of insulin by Banting and Best to treat Type 1 diabetes. Repeated efforts to deliver it orally since then have met with failure, with particular disappointment resulting from encouraging preclinical studies in the 1980s. Here, the barriers to synthesizing successful oral inulin formulations are discussed. It is apparent that this peptide has chemistry and pharmacology features that make its oral delivery one of the toughest challenges in delivery science. At this seminal point in its history, the question is whether oral delivery of insulin will ever be possible, or even if this quest is still desirable?
  • Publication
    Safety concerns over the use of intestinal permeation enhancers: A mini-review
    Intestinal permeation enhancers (PEs) are key components in ∼12 oral peptide formulations in clinical trials for a range of molecules, primarily insulin and glucagon-like-peptide 1 (GLP-1) analogs. The main PEs comprise medium chain fatty acid-based systems (sodium caprate, sodium caprylate, and N-[8-(2-hydroxybenzoyl) amino] caprylate (SNAC)), bile salts, acyl carnitines, and EDTA. Their mechanism of action is complex with subtle differences between the different molecules. With the exception of SNAC and EDTA, most PEs fluidize the plasma membrane causing plasma membrane perturbation, as well as enzymatic and intracellular mediator changes that lead to alteration of intestinal epithelial tight junction protein expression. The question arises as to whether PEs can cause irreversible epithelial damage and tight junction openings sufficient to permit co-absorption of payloads with bystander pathogens, lipopolysaccharides and its fragment, or exo- and endotoxins that may be associated with sepsis, inflammation and autoimmune conditions. Most PEs seem to cause membrane perturbation to varying extents that is rapidly reversible, and overall evidence of pathogen co-absorption is generally lacking. It is unknown however, whether the intestinal epithelial damage-repair cycle is sustained during repeat-dosing regimens for chronic therapy.
    Scopus© Citations 100  353
  • Publication
    Stability, toxicity and intestinal permeation enhancement of two food-derived antihypertensive tripeptides, Ile-Pro-Pro and Leu-Lys-Pro
    Two food-derived ACE inhibitory peptides, Ile-Pro-Pro (IPP) and Leu-Lys-Pro (LKP), may have potential as alternative treatments for treatment of mild- or pre-hypertension. Lack of stability to secretory and intracellular peptidases and poor permeability across intestinal epithelia are typical limiting factors of oral delivery of peptides. The stability of IPP and LKP was confirmed in vitro in rat intestinal washes, and intestinal and liver homogenates over 60min. A positive protein control for peptidases, insulin, was significantly digested in each format over the same period. Neither tripeptide showed cytotoxic activity on Caco-2 and Hep G2 cells using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, even after chronic exposure. The basal Papp of fluorescein isothiocyanate (FITC)-labeled IPP and FITC-LKP across isolated rat jejunal and colonic mucosae were low, but were significantly increased in each tissue type by the medium chain fatty acids (MCFA) permeation enhancers, sodium caprate (C10) and the sodium salt of 10-undecylenic acid (uC11). IPP and LKP were therefore stable against intestinal and liver peptidases and were non-cytotoxic; their Papp values across rat intestinal mucosae were low, but could be increased by MCFA. There is potential to make on oral dosage form once in vivo pharmacology is confirmed. 
      655Scopus© Citations 37
  • Publication
    A comparison of three Peyer's patch "M-like" cell culture models: particle uptake, bacterial interaction, and epithelial histology
    Intestinal Peyer's patch (PP) microfold (M) cells transport microbes and particulates across the follicle-associated epithelium (FAE) as part of the mucosal immune surveillance system. In vitro human M-like cell co-culture models are used as screens to investigate uptake of antigens-in-nanoparticles, but the models are labour-intensive and there is inter-laboratory variability. We compared the three most established filter-grown Caco-2/Raji B cell co-culture systems. These were Model A (Kerneis et al, 1997), Model B (Gullberg et al., 2000), and Model C (Des Rieux et al. 2007). The criteria used were transepithelial resistance (TEER), the apparent permeability coefficient (Papp) of [(14)C]-mannitol, M cell-like histology, as well as latex particle and Salmonella typhimurium translocation. Each co-culture model displayed substantial increases in particle translocation. Truncated microvilli compared to mono-cultures was their most consistent feature. The inverted model developed by des Rieux et al. (2007) displayed reductions in TEER and an increased (Papp), accompanied by the largest increase in particle translocation compared to the other two models. The normally-oriented model developed by Gullberg et al. (2000) was the only one to consistently display an increased translocation of salmonella typhimurium. By applying a double Matrigel¿¿¿ coating on filters, altering the medium feeding regime for Raji B cells, and restricting the passage number of B cells, improvements to the Gullberg model B were achieved, as reflected by increased particle translocation and improved histology. In conclusion, this is the first time all three designs have been compared in one study and each displays phenotypic features of M-like cells. While Model C was the most robust co-culture, the Model B protocol could be improved by optimizing several variables and is less complicated to establish than the two inverted models..
      320Scopus© Citations 23
  • Publication
    Safety and efficacy of sodium caprate in promoting oral drug absorption : from in vitro to the clinic
    A major challenge in oral drug delivery is the development of novel dosage forms to promote absorption of poorly permeable Class III drugs across the intestinal epithelium. To date, no absorption promoter has been approved in a formulation specifically designed for oral delivery of Class III molecules. Promoters that are designated safe for human consumption have been licensed for use in a recently approved buccal insulin spray delivery system and also for many years as part of an ampicillin rectal suppository. Unlike buccal and rectal delivery, oral formulations containing absorption promoters have the additional technical hurdle whereby the promoter and payload must be co-released in high concentrations at the small intestinal epithelium in order to generate significant but rapidly reversible increases in permeability. The most advanced promoter in the clinic is the medium chain fatty acid (MCFA), sodium caprate (C10) , a compound already approved as a direct food additive. We discuss how it has evolved to a matrix tablet format suitable for administration to humans under the headings of mechanism of action at the cellular and tissue level and in vitro and in vivo efficacy and safety studies. In specific clinical examples, we review how C10-based formulations are being tested for oral delivery of bisphosphonates using Gastro Intestinal Permeation Enhancement Technology, GIPET (Merrion Pharmaceuticals, Ireland) and in a related solid dose format for anti-sense oligonucleotides (ISIS Pharmaceuticals, USA).
      4576Scopus© Citations 187
  • Publication
    Antibacterial effects of poly(2-(dimethylamino ethyl)methacrylate) against selected Gram-positive and Gram-negative bacteria
    Antimicrobial coatings can reduce the occurrence of medical device-related bacterial infections. Poly(2-(dimethylamino ethyl)methacrylate)) (pDMAEMA) is one such polymer that is being researched in this regard. The aims of this study were to (1) elucidate pDMAEMA’s antimicrobial activity against a range of Gram-positive and Gram-negative bacteria and (2) to investigate its antimicrobial mode of action. The methods used include determination of minimum inhibitory concentration (MIC) values against various bacteria and the effect of pH and temperature on antimicrobial activity. The ability of pDMAEMA to permeabilise bacterial membranes was determined using the dyes 1-N-phenyl-naphthylamine (NPN) and Calcein-AM. Flow cytometry was used to investigate pDMAEMA’s capacity to be internalised by bacteria and to determine effects on bacterial cell cycling. pDMAEMA was bacteriostatic against Gram-negative bacteria with MIC values between 0.1–10 mg/ml. MIC values against Gram-positive bacteria were variable. pDMAEMA was active against Gram-positive bacteria around its pKa and at lower pH values, while it was active against Gram-negative bacteria around its pKa and at higher pH values. pDMAEMA inhibited bacterial growth by binding to the outside of the bacteria, permeabilising the outer membrane and disrupting the cytoplasmic membrane. By incorporating pDMAEMA with erythromycin, it was found that the efficacy of the latter was increased against Gram-negative bacteria. Together, the results illustrate that pDMAEMA acts in a similar fashion to other cationic biocides.
      1341Scopus© Citations 209
  • Publication
    Restoration of rat colonic epithelium after in situ intestinal instillation of the absorption promoter, sodium caprate
    Sodium caprate (C10) is an oral absorption promoter that is currently in clinical trials as a component of solid dosage forms for poorly permeable small molecules and peptides. Clinical data with zoledronic acid tablets suggest that significant delivery along with acceptable safety can be achieved from a once-a-week dosing regime. C10 has surfactant-like properties at the high doses used in vivo and therefore we examined its effects on rat intestinal epithelium following intestinal instillation. Results: Addition of 100 mM concentrations of C10 with the paracellular flux marker, fluorescein isothiocyanate-dextran 4 kDa, permitted a bioavailability of 33% to be achieved. When C10 was added 10, 30 and 60 min in advance of fluorescein isothiocyanate-dextran 4 kDa, enhancement still occurred, but was progressively reduced. Histology revealed that the permeability increase was likely related in part to superficial epithelial damage caused in the first few minutes of exposure, which was rapidly repaired within 30–60 min. Conclusions: Design of optimized dosage forms containing C10 should co-release the payload and promoter close to the epithelium in high concentrations. While C10 induces some epithelial damage, its remarkable capacity for epithelial repair may render this effect insignificant in vivo.
      914Scopus© Citations 43
  • Publication
    Labrasol® and Salts of Medium-chain Fatty Acids Can Be Combined in Low Concentrations to Increase the Permeability of a Macromolecule Marker Across Isolated Rat Intestinal Mucosae
    In addition to their solubilizing properties, excipients used in lipid-based formulations can improve intestinal permeability of macromolecules. We determined whether admixing of medium-chain fatty acid (MCFA) permeation enhancers with a lipoidal excipient (Labrasol®) could potentiate transepithelial flux of a poorly permeable macromolecule (fluorescein isothiocyanate dextran 4 kDa [FD4]) across rat intestinal mucosae mounted in Ussing chambers. Low concentrations of sodium caprate (C10), sodium undecylenate (C11:1), or sodium laurate (C12) combined with Labrasol® increased the apparent permeability coefficient (Papp) of FD4 to values typically seen with higher concentrations of MCFAs or Labrasol® alone. For example, combination of C11:1 (0.5 mg/mL) with Labrasol® (1 mg/mL) increased the Papp of FD4 by 10- and 11-fold over the respective individual agents at the same concentrations where no enhancement was evident. The increased enhancement ratios seen with the combinations were associated with some perturbation in intestinal histology and with attenuation of an epithelial functional measure, carbachol-stimulated inward short-circuit current. In conclusion, combining three MCFAs separately with Labrasol® increased the Papp of FD4 to values greater than those seen for MCFAs or Labrasol® alone. Ultimately, this may permit lower concentrations of MCFA to be used in combination with other excipients in oral formulations of poorly permeable molecules.
      605Scopus© Citations 19
  • Publication
    Effects of surfactant-based permeation enhancers on mannitol permeability, histology, and electrogenic ion transport responses in excised rat colonic mucosae
    Surfactant-based intestinal permeation enhancers (PEs) are constituents of several oral macromolecule formulations in clinical trials. This study examined the interaction of a test panel of surfactant-based-PEs with isolated rat colonic mucosae mounted in Ussing chambers in an attempt to determine if increases in transepithelial permeability can be separated from induction of mucosal perturbation. The aim was to establish assess if increases in permeability (i) intestinal permeability (the apparent permeability coefficient (Papp) of [14C]-mannitol), (ii) epithelial histology, and (iii) short-circuit current (ΔIsc) responses to a cholinomimetic (carbachol, CCh). Enhancement ratio increases for Papp values followed the order: C10 > C9 = C11:1 > a bile salt blend > sodium choleate > sucrose laurate > Labrasol® >C12E8 > C12 > Cremophor® A25 > C7 > sucrose stearate > Kolliphor® HS15 > Kolliphor® TPGS. Exposures that increased the Papp by ≥2-fold over 120 min were accompanied by histological damage in 94% of tissues, and by a decreased ΔIsc response to CCh of 83%. A degree of separation between the increased Papp of [14C]-mannitol, histological damage, and diminution of the ΔIsc response to CCh was observed at selected PE concentrations (e.g. Labrasol® at 2 mg/mL). Overall, this surfactant-based PE selection caused transcellular perturbation at similar concentrations to those that enhanced permeability.
      823Scopus© Citations 34
  • Publication
    Formulation strategies to improve oral peptide delivery
    Delivery of peptides by the oral route greatly appeals due to commercial, patient convenience and scientific arguments. While there are over 60 injectable peptides marketed worldwide, and many more in development, most delivery strategies do not yet adequately overcome the barriers to oral delivery. Peptides are sensitive to chemical and enzymatic degradation in the intestine, and are poorly permeable across the intestinal epithelium due to sub-optimal physicochemical properties. A successful oral peptide delivery technology should protect potent peptides from presystemic degradation and improve epithelial permeation to achieve a target oral bioavailability with acceptable intra-subject variability. This review provides a comprehensive up-to-date overview of the current status of oral peptide delivery with an emphasis on patented formulations that are yielding promising clinical data.
      3262Scopus© Citations 56