Brendan T. Griffin

Interactions between antidepressants and P‐glycoprotein at the blood–brain barrier: clinical significance of in vitro and in vivo findings

The drug efflux pump P‐glycoprotein (P‐gp) plays an important role in the function of the blood–brain barrier by selectively extruding certain endogenous and exogenous molecules, thus limiting the ability of its substrates to reach the brain. Emerging evidence suggests that P‐gp may restrict the uptake of several antidepressants into the brain, thus contributing to the poor success rate of current antidepressant therapies. Despite some inconsistency in the literature, clinical investigations of potential associations between functional single nucleotide polymorphisms in ABCB1, the gene which encodes P‐gp, and antidepressant response have highlighted a potential link between P‐gp function and treatment‐resistant depression (TRD). Therefore, co‐administration of P‐gp inhibitors with antidepressants to patients who are refractory to antidepressant therapy may represent a novel therapeutic approach in the management of TRD. Furthermore, certain antidepressants inhibit P‐gp in vitro, and it has been hypothesized that inhibition of P‐gp by such antidepressant drugs may play a role in their therapeutic action. The present review summarizes the available in vitro, in vivo and clinical data pertaining to interactions between antidepressant drugs and P‐gp, and discusses the potential relevance of these interactions in the treatment of depression.

Lipid-based nanocarriers for oral peptide delivery.

This article is aimed to overview the lipid-based nanostructures designed so far for the oral administration of peptides and proteins, and to analyze the influence of their composition and physicochemical (particle size, zeta potential) and pharmaceutical (drug loading and release) properties, on their interaction with the gastro-intestinal environment, and the subsequent PK/PD profile of the associated drugs. The ultimate goal has been to highlight and comparatively analyze the key factors that may be determinant of the success of these nanocarriers for oral peptide delivery. The article ends with some prospects on the challenges to be addressed for the intended commercial success of these delivery vehicles.

Comparison of in vitro tests at various levels of complexity for the prediction of in vivo performance of lipid-based formulations: Case studies with fenofibrate

The objectives of this study were to characterise three prototype fenofibrate lipid-based formulations using a range of in vitro tests with differing levels of complexity and to assess the extent to which these methods provide additional insight into in vivo findings. Three self-emulsifying drug delivery systems (SEDDS) were prepared: a long chain (LC) Type IIIA SEDDS, a medium chain (MC) Type IIIA SEDDS, and a Type IIIB/IV SEDDS containing surfactants only (SO). Dilution, dispersion and digestion tests were performed to assess solubilisation and precipitation behaviour in vitro. Focussed beam reflectance measurements and solid state characterisation of the precipitate was conducted. Oral bioavailability was evaluated in landrace pigs. Dilution and dispersion testing revealed that all three formulations were similar in terms of maintaining fenofibrate in a solubilised state on dispersion in biorelevant media. During in vitro digestion, the Type IIIA formulations displayed limited drug precipitation (<5%), whereas the Type IIIB/IV formulation displayed extensive drug precipitation (~70% dose). Solid state analysis confirmed that precipitated fenofibrate was crystalline. The oral bioavailability was similar for the three lipid formulations (65-72%). In summary, the use of LC versus MC triglycerides in Type IIIA SEDDS had no impact on the bioavailability of fenofibrate. The extensive precipitation observed with the Type IIIB/IV formulation during in vitro digestion did not adversely impact fenofibrate bioavailability in vivo, relative to the Type IIIA formulations. These results were predicted suitably using in vitro dilution and dispersion testing, whereas the in vitro digestion method failed to predict the outcome of the in vivo study.

A comparison of intestinal lymphatic transport and systemic bioavailability of saquinavir from three lipid-based formulations in the anaesthetised rat model

Saquinavir is a lipophilic, poorly water‐soluble HIV protease inhibitor that undergoes extensive first‐pass metabolism and exhibits poor oral bioavailability. Redirection of the absorption pathway of anti‐HIV compounds from the portal blood to the HIV‐rich intestinal lymphatics may enhance therapeutic efficacy and reduce the extent of the first‐pass effect. This study investigates the potential of targeted intestinal lymphatic transport of saquinavir via a lipid formulation approach. Three formulations containing oleic acid were examined: cremophor‐oleic acid mixed micelles, d‐alpha tocopheryl polyethylene glycol 1000 succinate (TPGS)‐oleic acid mixed micelles and an oleic acid microemulsion. The mesenteric lymph duct cannulated anaesthetised rat model was employed. Plasma and lymph samples were analysed by HPLC. Lymph triglyceride was measured using an enzymatic colorimetric technique. The extent of lymphatic transport from the lipid vehicles was 0.025‐0.05% of the dose administered. The microemulsion produced higher and more prolonged mesenteric lymph concentrations than the micellar formulations. A strong correlation existed between the concentration of saquinavir in intestinal lymph and lymph triglyceride levels. The systemic bioavailability was estimated to be 8.5% and 4.8% for the cremophor mixed micelle and the microemulsion, respectively. The cremophor mixed micelles produced higher bioavailability than TPGS mixed micelles, implying that the nature of the surfactant can influence the distribution of drug between lymph and plasma.

Lactococcus lactis-expressing listeriolysin O (LLO) provides protection and specific CD8(+) T cells against Listeria monocytogenes in the murine infection model.

Abstract Lactococcus lactis has previously been proposed as a vaccine platform for the safe delivery of heterologous antigens. Here we utilized L. lactis as a live vector for expression of listeriolysin O (LLO), a major Listeria monocytogenes antigen and virulence factor. A variety of plasmid constructs were designed to permit either constitutive or nisin-inducible expression of secreted or non-secreted LLO in L. lactis. Recombinant strains were subsequently tested in a murine model for vaccination efficacy against L. monocytogenes infection. CD8+ T lymphocytes specific for the LLO91–99 epitope were detected when strains were administered via the intraperitoneal (IP) but not the oral route. Challenge with live L. monocytogenes revealed different levels of protection among the three vaccine strains tested with the nisin-inducible LLO-secreting L. lactis strain providing the greatest protection against secondary infection. This work highlights the usefulness of the GRAS (Generally Regarded As Safe) organism L. lactis as the basis of a live vaccine vector against L. monocytogenes. The work suggests that LLO-expressing L. lactis strains may also have the potential to act as a platform for directing other co-expressed antigens towards the cytosolic MHC class I pathway for enhanced stimulation of the CD8+ T-cell response.

Lactococcus lactis as a Cell Factory for Delivery of Therapeutic Proteins

The food-grade bacterium Lactococcus lactis has been extensively investigated during the last two decades as a delivery vector for therapeutic proteins, DNA and vaccine antigens. The bacterium represents a safe, genetically tractable vector capable of producing heterologous therapeutic proteins at mucosal sites. Here we review recent work in which recombinant L. lactis strains have been exploited as agents to treat inflammatory bowel disease, allergy and cancer. We also describe the ability of L. lactis to deliver proteins with adjuvant potential, vaccines and DNA and discuss the therapeutic possibilities of this approach.

A novel lipid-based solid dispersion for enhancing oral bioavailability of Lycopene--in vivo evaluation using a pig model.

Lycopene is a potent anti-oxidant, which has been widely reported for its potential benefits at reducing the risks of certain types of cancer e.g. prostate cancer. The oral bioavailability of this highly lipophilic carotenoid is low and highly influenced by the extent of intestinal lymphatic uptake. The aim of this study was to develop an optimised formulation, which allows for efficient absorption following oral administration. A self-emulsifying drug delivery system (SEDDS) and solid dispersion of Lycopene were developed initially. Subsequently, a novel lipid based solid dispersion (LBSD) was designed. Processing via a solid dispersion approach was found to alter the solid state characteristics of Lycopene, as determined by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The bioavailability of Lycopene was significantly increased after oral administration of LBSD to fasted pigs, relative to the commercial product (Lycovit(®)). A clear distinction in terms of Cmax and AUC was observed between Lycovit(®) and LBSD. In conclusion, a novel LBSD formulation was developed to enhance the oral bioavailability of the model lipophilic compound, Lycopene, by enhancing dissolution in the gastrointestinal tract and promoting intestinal lymphatic uptake utilising digestible lipid excipients.

Inhibition of P-glycoprotein enhances transport of imipramine across the blood–brain barrier: microdialysis studies in conscious freely moving rats

Recent studies indicate that efflux of antidepressants by the multidrug resistance transporter P‐glycoprotein (P‐gp) at the blood–brain barrier (BBB) may contribute to treatment‐resistant depression (TRD) by limiting intracerebral antidepressant concentrations. In addition, clinical experience shows that adjunctive treatment with the P‐gp inhibitor verapamil may improve the clinical outcome in TRD. Therefore, the present study aimed to investigate the effect of P‐gp inhibition on the transport of the tricyclic antidepressant imipramine and its active metabolite desipramine across the BBB.

Bioavailability of lycopene in the rat: the role of intestinal lymphatic transport

Objectives As a natural antioxidant derived from dietary sources, lycopene has attracted considerable attention as a potent chemopreventative agent. Lycopene is an extremely lipophilic compound and absorption from dietary sources is estimated to be low and highly variable. As a result, plasma lycopene concentrations are poorly correlated with dietary intake of lycopene rich food stuffs. The development of an oral formulation remains a challenge that requires a better understanding of the mechanisms involved in the intestinal absorption of this compound.

PEGylated cyclodextrins as novel siRNA nanosystems: Correlations between polyethylene glycol length and nanoparticle stability

Silencing disease-related genes in the central nervous system (CNS) using short interfering RNA (siRNA) holds great promise for treating neurological disorders. Yet, delivery of RNAi therapeutics to the brain poses major challenges to non-viral systems, especially when considering systemic administration. Cationic nanoparticles have been widely investigated for siRNA delivery, but the tendency of these to aggregate in physiological environments limits their intravenous application. Thus, strategies to increase the stability of nanoparticles have been developed. Here, we investigated the ability of modified cationic amphiphilic or PEGylated amphiphilic cyclodextrins (CD) to formulate stable CD.siRNA nanoparticles. To this end, we describe a simple method for post-modification of pre-formed cationic CD.siRNA nanoparticles at their surface using PEGylated CDs of different PEG lengths. PEGylated CD.siRNA nanoparticles presented reduced surface charges and increased stability in physiological salt conditions. Stability of PEGylated CD.siRNA nanoparticles in vitro increased with both PEG length and PEG density at the surface. Furthermore, in a comparative pharmacokinetic study, increased systemic exposure and reduced clearance were achieved with CD-formulations when compared to naked siRNAs. However, no significant differences were observed among non-PEGylated and PEGylated CD.siRNAs suggesting that longer PEG lengths might be required for improving stability in vivo.