Physiology and pharmacology of the brushtail possum gastrointestinal tract: relationship to the human gastrointestinal tract

Pharmacokinetics in Penguins Compared to Other Avian Species: A Review of Enrofloxacin and Voriconazole

Australasia is home to unique and endangered avian species. Drug administration to this group of animal patients for prophylaxis and treatment is challenging from a number of different perspectives. A key limitation for optimal drug dosing in birds is the lack of published pharmacokinetic studies to guide dose requirements. The aim of this review was to systematically investigate published literature on pharmacokinetics in penguin species and compare that with the pharmacokinetics of other avian species with a focus on two drugs: enrofloxacin and voriconazole. The review was conducted following PRISMA guidelines. A systematic literature search was performed in Pubmed, Embase, Scopus, and Web of Science databases. A key finding is that penguin pharmacokinetics differs from other avian species, with weight-adjusted AUC and Cmax values higher than most other avian species (e.g., for enrofloxacin, the AUC in the African penguin is 85.7 μg h/mL, which is more than double the other bird species). Doses for some avian species may be successfully extrapolated from other avian species; however, it appears important to consider factors other than just body weight (e.g., clearance mechanism and drug physicochemical characteristics). Consequently, there is an important need for robust pharmacokinetic data in wildlife species to ensure optimal therapy for this special group of patients. As part of this review, we identify key aspects that should be considered when estimating dose in species for which there is limited pharmacokinetic information available.

Warmer Ambient Temperatures Depress Detoxification and Food Intake by Marsupial Folivores

Ambient temperature is an underappreciated determinant of foraging behaviour in wild endotherms, and the requirement to thermoregulate likely influences food intake through multiple interacting mechanisms. We investigated relationships between ambient temperature and hepatic detoxification capacity in two herbivorous marsupials, the common ringtail possum (Pseudocheirus peregrinus) and common brushtail possum (Trichosurus vulpecula) that regularly feed on diets rich in plant toxins. As an indicator of hepatic detoxification capacity, we determined the functional clearance rate of an anaesthetic agent, Alfaxalone, after possums were acclimated to 10°C [below the thermoneutral zone (TNZ)], 18°C [approximately lower critical temperature (LCT)], and 26°C [approximately upper critical temperature (UCT)] for either 7 days or less than 24 h. We then measured intake of foods with high or low plant secondary metabolite (PSM) concentrations under the same temperature regimes. After 7 days of acclimation, we found a positive correlation between the functional clearance rate of Alfaxalone and ambient temperature, and a negative relationship between ambient temperature and intake of foods with high or low PSM concentrations for both species. The effect of ambient temperature on intake of diets rich in PSMs was absent or reduced when possums were kept at temperatures for less than 24 h. Our results underscore the effects of ambient temperature in hepatic metabolism particularly with respect intake of diets containing PSMs. Given that the planet is warming, it is vital that effects of ambient temperature on metabolism, nutrition and foraging by mammalian herbivores is taken into account to predict range changes of species and their impact on ecosystems.

Intestinal Excretion, Intestinal Recirculation, and Renal Tubule Reabsorption Are Underappreciated Mechanisms That Drive the Distribution and Pharmacokinetic Behavior of Small Molecule Drugs

Drug reabsorption following biliary excretion is well-known as enterohepatic recirculation (EHR). Renal tubular reabsorption (RTR) following renal excretion is also common but not easily assessed. Intestinal excretion (IE) and enteroenteric recirculation (EER) have not been recognized as common disposition mechanisms for metabolically stable and permeable drugs. IE and intestinal reabsorption (IR:EHR/EER), as well as RTR, are governed by dug concentration gradients, passive diffusion, active transport, and metabolism, and together they markedly impact disposition and pharmacokinetics (PK) of small molecule drugs. Disruption of IE, IR, or RTR through applications of active charcoal (AC), transporter knockout (KO), and transporter inhibitors can lead to changes in PK parameters. The impacts of intestinal and renal reabsorption on PK are under-appreciated. Although IE and EER/RTR can be an intrinsic drug property, there is no apparent strategy to optimize compounds based on this property. This review seeks to improve understanding and applications of IE, IR, and RTR mechanisms.

Designing pH-Responsive Biodegradable Polymer Coatings for Controlled Drug Release via Vapor-Based Route

We present the design of a novel pH-responsive drug release system that is achieved by solventless encapsulation of drugs within a microporous membrane using a thin capping layer of biodegradable poly(methacrylic anhydride) (PMAH) coating. The coating was synthesized via a mild vapor polymerization process, namely, initiated chemical vapor deposition, which allowed perfect retention of the anhydride groups during deposition. The synthesized polyanhydride underwent degradation upon exposure to aqueous buffers, resulting in soluble poly(methacrylic acid). The degradation behavior of PMAH is highly pH-dependent, and the degradation rate under pH 10 is 15 times faster than that under pH 1. The release profile of a model drug rifampicin clearly exhibited two stages: the initial stage when the coatings were being degraded but the drugs were well stored and the second stage when drugs were gradually exposed to the medium and released. The drug release also showed strong pH responsiveness where the duration of the initial stage under pH 1 was more than 7 and 3 times longer than that under pH 10 and 7.4, respectively, and the release rates at pH 7.4 and 10 were significantly faster than that at pH 1. The pH-dependent degradation of the encapsulant thus enabled good preservation of drugs under low-pH environment but high drug release efficiency under neutral and alkaline environment, suggesting potential applications in site-specific drug delivery systems.

Digestibilidade do amido in vitro e valor calórico dos grupos de farinhas de mandioca brasileiras

Resumo A preferência cultural do brasileiro originou grupos e subclassificações da farinha de mandioca em função dos processos adotados. Diferenças de processamento das farinhas de mandioca podem afetar a digestibilidade do amido, assim seu teor calórico foi investigado. Foram selecionadas cinco amostras dos três grupos de farinha de mandioca: Seca, Bijusada e D’água. O teste de digestibilidade do amido foi realizado in vitro, incubando a suspensão de farinha com amilase (alfa-1,4-glucano-4-glucanohidrolase) em condições de temperatura e pH que simulam a digestão humana. Alíquotas foram coletadas a cada 15 minutos, durante 1 hora e o teor de glicose liberado foi expresso em calorias rapidamente disponíveis. Os resultados mostraram que o valor calórico de todas as amostras de farinha de mandioca permaneceu ao redor de 300 kcal. 100 g–1. Considerando a cinética de liberação em função do tempo e do grupo, as amostras de farinha de mandioca diferiram. As farinhas de mandioca com menor granulometria, Biju Fina e Furnas (Grupo Bijusada e Seca), apresentaram rápida liberação de açúcares aos 15 minutos, variando de 110 a 215 kcal. 100 g–1, respectivamente. A farinha de mandioca Fina (Grupo Seca) teve liberação uniforme de glicose durante a avaliação. O açúcar liberado pelas farinhas de mandioca com maior granulometria, Biju Grossa e D’água (Grupo Bijusada e D’água), apresentaram dois picos de liberação: o primeiro aos 15 minutos de incubação (liberando 84,2 e 120,48 kcal. 100 g–1, respectivamente); enquanto o segundo pico para a amostra Biju Grossa ocorreu aos 45 minutos (112 kcal. 100 g–1), para a farinha D’água foi após 60 minutos (67,88 kcal. 100 g–1). Pela avaliação microscópica foi observada a presença de grânulos de amido residuais não hidrolisados, variando de 2,42 a 17,85%. Os resultados mostraram que o valor calórico das farinhas de mandioca variou em função do processamento, que afetou a granulometria da farinha, que por sua vez influenciou a gelatinização do amido, fatores esses que determinaram a intensidade da ação das enzimas na liberação de glicose.

Preclinical pharmacokinetic evaluation and metabolites identification of methyl salicylate-2-O-β-d-lactoside in rats using LC-MS/MS and Q-TOF-MS methods

Methyl salicylate-2-O-β-d-lactoside (MSL) is a natural salicylate derivative from the traditional Chinese medicine of Gaultheria yunnanensis (Franch.) Rehder (G. yunnanensis). As a non-steroidal anti-inflammatory drug (NSAID), MSL exerts a significant anti-arthritis effect but hardly has any gastrointestinal toxicity. In this paper, the pharmacokinetics, distribution, excretion and identification of MSL and its metabolites are described following rat oral and intravenous administration. The biological samples were quantified by UPLC-MS/MS and the metabolites in urine and feces were identified by using Q-TOF-MS. These results will support future investigations leading to clinical development of this drug.

Polymeric micelles, a promising drug delivery system to enhance bioavailability of poorly water-soluble drugs

Oral administration is the most commonly used and readily accepted form of drug delivery; however, it is find that many drugs are difficult to attain enough bioavailability when administered via this route. Polymeric micelles (PMs) can overcome some limitations of the oral delivery acting as carriers able to enhance drug absorption, by providing (1) protection of the loaded drug from the harsh environment of the GI tract, (2) release of the drug in a controlled manner at target sites, (3) prolongation of the residence time in the gut by mucoadhesion, and (4) inhibition of efflux pumps to improve the drug accumulation. To explain the mechanisms for enhancement of oral bioavailability, we discussed the special stability of PMs, the controlled release properties of pH-sensitive PMs, the prolongation of residence time with mucoadhesive PMs, and the P-gp inhibitors commonly used in PMs, respectively. The primary purpose of this paper is to illustrate the potential of PMs for delivery of poorly water-soluble drugs with bioavailability being well maintained.

Synthesis and physicochemical characterization of amphiphilic triblock copolymer brush containing pH-sensitive linkage for oral drug delivery

A novel and well-defined pH-sensitive amphiphilic triblock copolymer brush poly(lactide)-b-poly(methacrylic acid)-b-poly(poly(ethylene glycol) methyl ether monomethacrylate) (PLA-b-PMAA-b-PPEGMA) and its self-assembled micelles were developed for oral administration of hydrophobic drugs. The copolymer and its precursors were synthesized by the combination of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and ring-opening polymerization (ROP) techniques. The molecular structures and characteristics were confirmed by GPC, (1)H NMR, and FT-IR. The critical micelle concentration (CMC) values of PLA-b-PMAA-b-PPEGMA in aqueous medium varied from 1.4 to 2.6 mg/L, and the partition equilibrium constant (K(v)) of pyrene in micellar solutions ranged from 2.873 × 10(5) to 3.312 × 10(5). The average sizes of the self-assembled blank and drug-loaded micelles were 140-250 nm determined by DLS in aqueous solution. The morphology of the micelles was found to be spherical by SEM. Nifedipine (NFD), a poorly water-soluble drug, was selected as the model drug and wrapped into the core of micelles via dialysis method. The in vitro release behavior of NFD from the micelles was pH-dependent. In simulated gastric fluid (SGF, pH 1.2), the cumulative release percent of NFD was relative low, while in simulated intestinal fluid (SIF, pH 7.4), more than 96% was released within 24 h. All the results showed that the pH-sensitive PLA-b-PMAA-b-PPEGMA micelle may be a prospective candidate as oral drug delivery carrier for hydrophobic drugs with controlled release behavior.

Hydrotropic polymer micelles containing acrylic acid moieties for oral delivery of paclitaxel

Hydrotropic polymers (HPs) and their micelles have been recently developed as vehicles for delivery of poorly water-soluble drugs, such as paclitaxel (PTX), by oral administration. The release of PTX from HP micelles, however, was slow and it took more than a day for complete release of the loaded PTX. Since the gastrointestinal (GI) transit time is known to be only several hours, pH-sensitive HP micelles were prepared for fast release of the loaded PTX responding to pH changes along the GI tract. Acrylic acid (AA) was introduced, as a release modulator, into HPs by copolymerization with 4-(2-vinylbenzyloxy)-N,N-(diethylnicotinamide) (VBODENA). The AA content was varied from 0% to 50% (in the molar ratio to VBODENA). HPs spontaneously produced micelles in water, and their critical micelle concentrations (CMCs) ranged from 31 microg/mL to 86 microg/mL. Fluorescence probe study using pyrene showed that blank HP micelles possessed a good pH sensitivity, which was clearly observed at relatively high AA contents and pH>6. The pH sensitivity also affected the PTX loading property. Above pH 5, the PTX loading content and loading efficiency in HP micelles were significantly reduced. Although this may be primarily due to the AA moieties, other factors may include PTX degradation and polymer aggregation. The PTX release from HP micelles with more than 20% (mol) AA contents was completed within 12 h in a simulated intestinal fluid (SIF, pH=6.5). The HP micelles without any AA moiety showed very slow release profiles. In the simulated gastric fluid (SGF, pH=1.6), severe degradation of the released PTX was observed. The pH-dependent release of PTX from HP micelles can be used to increase the bioavailability of PTX upon oral delivery.