Role of gastrointestinal multidrug resistance (MDR1) gene and P-glycoprotein (P-gp) in the oral absorption of methadone in horses

Methadone is a mu-opioid receptor agonist which is a very effective analgesic used to treat moderate to severe acute and chronic pain in humans. Due to methadone’s minimal undesirable side-effects in people, we believed it could be of use in horses as an analgesic agent. As found with the majority of lipophilic drugs, absorption of methadone occurs primarily in the small intestine via transcellular transport and its absorption is regulated by P-glycoprotein. P-glycoprotein is a transmembrane transporter protein encoded by the multidrug resistance gene, which is constitutively expressed in the apical membrane of enterocytes of various species. This protein may impair the therapeutic efficacy of oral opioids including methadone, by decreasing absorption through the small intestinal mucosa and altering drug’s pharmacokinetics. The overall hypothesize was that the expression of P-glycoprotein in the equine small intestine affects absorption and bioavailability of methadone after oral administration to horses. In Vivo and in vitro studies presented here investigated the oral pharmacokinetics of methadone, expression of the multidrug resistance (MDR1) gene, and the role of intestinal P-glycoprotein on methadone flux or transport in equine jejunal mucosa. The contribution of this protein to in vivo absorption of this opioid drug after oral administration in horses is evaluated. Oral administration of methadone hydrochloride to healthy horses showed rapid absorption, reaching high serum concentrations without typical undesirable opioid-induced side effects. Drug absorption appears to be limited in the small intestine, supported by the observed low drug serum concentrations, low area under the drug serum concentration vs. time curve, and low drug bioavailability after intragastric administration. In addition, methadone was absorbed by oral mucosa and may be an important way that methadone gains entrance into equine plasma. Multidrug resistance (MDR1) gene expression was determined in several different tissues including those of the small intestine of horses. High MDR1 mRNA levels mainly in the duodenum and jejunum of horses may explain, at least in part, the limited intestinal absorption of methadone in vivo. P-glycoprotein, located in the apical membrane of epithelial intestinal cells of jejunum in horses impairs the flux of methadone across the intestinal mucosa and its drug efflux activity is minimized by verapamil HCl, a P-glycoprotein inhibitor. Therefore, these studies confirmed that the expression of P-glycoprotein in the equine small intestine affects absorption and bioavailability of methadone after oral administration to horses

First report on orally administered methadone to multi-drug resistance (MDR1) gene normal horses

Opioids are potent analgesics and are believed to be the best choice for moderate and severe nociceptive pain. Investigating all the possible administration route options for pain management in the different animal species is warranted in horses as systemic administration of these drugs in horses is difficult. In this study the authors describe for the first time in the literature the administration of methadone orally to MDR1 genotipically normal horses. Twelve adult healthy horses (6 females and 6 males) were studied. Horses randomly received one of the doses of methadone (0.1, 0.2, and 0.4mg/kg) per os, which was administered using a 60cc syringe containing 30ml of corn syrup The results showed all doses produced plasma levels compatible to analgesic plasma levels in human beings. The authors conclude that methadone is absorbed when orally administered in horses at doses of 0.1, 0.2, and 0.4 mg.kg -1. It does not produce excitement, sedation, nor undesirable side effects in healthy horses. Further studies are necessary in order to establish clinical guidelines for oral methadone as an alternative for pain management in the horse

Primeiro relato da administração oral de metadona em cavalos normais para o gene de resistência múltipla às drogas (MDR1)

Opioids are potent analgesics and are believed to be the best choice for moderate and severe nociceptive pain. Investigating all the possible administration route options for pain management in the different animal species is warranted in horses as systemic administration of these drugs in horses is difficult. In this study the authors describe for the first time in the literature the administration of methadone orally to MDR1 genotipically normal horses. Twelve adult healthy horses (6 females and 6 males) were studied. Horses randomly received one of the doses of methadone (0.1, 0.2, and 0.4mg/kg) per os, which was administered using a 60cc syringe containing 30ml of corn syrup The results showed all doses produced plasma levels compatible to analgesic plasma levels in human beings. The authors conclude that methadone is absorbed when orally administered in horses at doses of 0.1, 0.2, and 0.4 mg.kg-1. It does not produce excitement, sedation, nor undesirable side effects in healthy horses. Further studies are necessary in order to establish clinical guidelines for oral methadone as an alternative for pain management in the horse.Os derivados opióides são analgésicos potentes e acredita-se os fármacos de escolha para tratamento da dor nociceptiva moderada ou severa. A investigação de todas as opções de vias de administração deve ser garantida no eqüino em razão das dificuldades do uso sistêmico destes fármacos nesta espécie. Neste estudo, os autores descrevem pela primeira vez na literatura a administração de metadona oral em cavalos genotipicamente normais para o gene MDR1. Foram estudados 12 eqüinos adultos (6 machos e 6 fêmeas). Os cavalos receberam aleatoriamente uma das doses de metadona (0.1, 0.2, and 0.4 mg.kg-1) per os, que foram administradas utilizando-se uma seringa de 60cc contendo 30ml de xarope de milho. Os resultados demonstraram que doses variáveis de 0.1, 0.2, e 0.4 mg.kg-1 produzem concentrações plasmáticas similares as concentrações analgésicas obtidas em seres humanos. Estas doses não produzem excitação, sedação ou efeitos colaterais indesejáveis em eqüinos hígidos. Estudos futuros são necessários para se estabelecer as diretrizes para o uso clínico de metadona oral como alternativa para o controle da dor no cavalo

Influence of the aerobic training on cortisol and glucose levels in horses

Estudou-se a resposta do cortisol e da glicemia em 12 equinos da raça Puro Sangue Árabe destreinados (T0) por oito meses e submetidos a um período de 90 dias de treinamento aeróbio (T90). Para avaliação dos efeitos do treinamento, empregou-se teste ergométrico constituído de exercício progressivo em esteira rolante, acompanhado por colheitas de sangue 15 segundos antes do término de cada etapa de esforço. A velocidade (intensidade) do treino foi definida como sendo 80% da V4 (velocidade na qual a lactacidemia atinge 4mmol/L). Adicionalmente, no último mês de treinamento, foi instituído, uma vez por semana, exercício com velocidades variáveis, chamado "fartlek". Após 90 dias de treinamento, a concentração plasmática de cortisol elevou-se e após o teste de esforço (20min), houve aumento da glicemia. Este resultado reflete a possibilidade de adaptação ao treinamento. Conclui-se que o cortisol plasmático pode ser utilizado como ferramenta na avaliação de um programa de treinamento em equinos. _________________________________________________________________________________________________________ ABSTRACTCortisol and glucose responses were evaluated in 12 Arabian (PSA) horses submitted to a detraining period of eight months (T0) and to 90 days of aerobic training (T90). For the evaluation of the effect of training, a standardized incremental exercise test in a treadmill was used. Fifteen seconds before the ending of each effort step, blood samples were collected. The speed (intensity) of the training was defined as being 80% of the V4 (speed at which the blood lactate concentration reaches 4mmol/L). Additionally, in the last month of training, velocity play, a type of exercise with varying velocities called "fartlek" was instituted, once a week. Results showed that after 90 days of training, the plasmatic concentrations of cortisol and glucose increased when compared to the untrained horses. This result reflects the possibility of adaptation to the training. The blood cortisol levels may be used as a tool for the evaluation of a training program in horses

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ABSTRACT (MDR1) gene expressed in tumor cells and also in several normal tissues, such as intestine, liver, kidney, bloodbrain barrier, spinal cord, and placenta. P-gp has been identified in INTRODUCTION There is a wide difference of therapy response between species involving several drugs in Veterinary Medicine. Many factors can affect drug disposition such as physicochemical properties of the drug and biological factors including gastric and intestinal time, luminal pH, and mucosal blood flow, when orally administered. Once the drug is in the bloodstream its distribution to diverse cells and tissues, such as the brain, testes, and fetus is also limited by physiologic barrier

Multi-drug resistance (MDR1) gene and P-glycoprotein influence on pharmacokinetic and pharmacodymanic of therapeutic drugs

(MDR1) gene expressed in tumor cells and also in several normal tissues, such as intestine, liver, kidney, blood-brain barrier, spinal cord, and placenta. P-gp has been identified in mice, rat, bovine, monkey, rodents, and human beings and has been receiving a particular clinical relevance because this protein expression limits brain access and intestinal absorption of many drugs. This protein plays a role as a protective barrier against a wide variety of substrates, avoiding drug entry into the central nervous system. P-glycoprotein also interferes with drug bioavailability and disposition, including absorption, distribution, metabolization, and excretion, influencing pharmacokinetic and pharmacodynamic of drugs. Modulation of P-gp may help the efficacy of treatment of several diseases and can explain some adverse central nervous system effects induced by drugs after intravenous administration and the poor response of oral administration in patients. Alteration in P-gp expression or function has been associated with several diseases susceptibility in humans and animals. Furthermore, additional studies relating MDR1 and P-gp expression has an important clinical implication also in terms of treatment efficacy

Making of an in vitro experimental model of equine subarachnoid space to test hyperbaric opioids

Com o objetivo de avaliar as características de distribuição de agentes hiperbáricos no líquido cérebroespinhal (LCE) eqüino, é apresentado um modelo in vitro do espaço subaracnóide confeccionado em policloreto de vinila (PVC) transparente, no qual se adaptou um cateter para a infusão contínua de glicose a 10%, morfina hiperbárica, buprenorfina hiperbárica e metadona hiperbárica marcadas com azul de metileno para permitir a visualização da distribuição destas substâncias no LCE. Avaliaram-se a distância alcançada pelos diferentes agentes minuto a minuto e a forma de distribuição dos mesmos. Todas as substâncias testadas mostraram comportamento de distribuição vertical a partir da extremidade do cateter, quando se deu o início da migração cranial no LCE, sendo que o avanço máximo registrado foi aos 15 minutos após o término da infusão, com migração de 15cm para glicose a 10%, 13cm para a morfina hiperbárica, 18cm para a buprenorfina hiperbárica e 17cm para a metadona hiperbárica. O modelo proposto mostrou-se eficiente para a avaliação do comportamento físico dos agentes hiperbáricos no interior do espaço subaracnóide, oferecendo a possibilidade de teste de substâncias a serem utilizadas pela via subaracnóide de cavalos.The aim of this study was to evaluate the distribution characteristics of hyperbaric solutions in equine cerebrospinal fluid (CSF), in an in vitro model of the subarachnoid space. The model was made with transparent PVC in which a catheter was adapted to infuse 10% glucose, 10% hyperbaric morphine, hyperbaric buprenorphine, and hyperbaric methadone, dyed with methilene blue in order to visualize the solutions distribution in the CSF. The distance in cm reached by the different agents every minute as well as the pattern of distribution were evaluated. All tested solutions distributed itself in a forward and vertically pattern from the tip of the catheter. Maximum distance reached after 15 minutes were 15cm for 10% glucose, 13cm for hyperbaric morphine, 18cm for hyperbaric buprenorphine, and 17cm for hyperbaric methadone. The proposed model was efficient to evaluate the distribution pattern of hyperbaric solutions in equine CSF, offering a new possibility to physically test the administration of solutions in the equine subarachnoid space

Confecção de um modelo experimental in vitro do espaço subaracnóide eqüino para teste de opióides hiperbáricos Making of an in vitro experimental model of equine subarachnoid space to test hyperbaric opioids

Com o objetivo de avaliar as características de distribuição de agentes hiperbáricos no líquido cérebro-espinhal (LCE) eqüino, é apresentado um modelo in vitro do espaço subaracnóide confeccionado em policloreto de vinila (PVC) transparente, no qual se adaptou um cateter para a infusão contínua de glicose a 10%, morfina hiperbárica, buprenorfina hiperbárica e metadona hiperbárica marcadas com azul de metileno para permitir a visualização da distribuição destas substâncias no LCE. Avaliaram-se a distância alcançada pelos diferentes agentes minuto a minuto e a forma de distribuição dos mesmos. Todas as substâncias testadas mostraram comportamento de distribuição vertical a partir da extremidade do cateter, quando se deu o início da migração cranial no LCE, sendo que o avanço máximo registrado foi aos 15 minutos após o término da infusão, com migração de 15cm para glicose a 10%, 13cm para a morfina hiperbárica, 18cm para a buprenorfina hiperbárica e 17cm para a metadona hiperbárica. O modelo proposto mostrou-se eficiente para a avaliação do comportamento físico dos agentes hiperbáricos no interior do espaço subaracnóide, oferecendo a possibilidade de teste de substâncias a serem utilizadas pela via subaracnóide de cavalos.The aim of this study was to evaluate the distribution characteristics of hyperbaric solutions in equine cerebrospinal fluid (CSF), in an in vitro model of the subarachnoid space. The model was made with transparent PVC in which a catheter was adapted to infuse 10% glucose, 10% hyperbaric morphine, hyperbaric buprenorphine, and hyperbaric methadone, dyed with methilene blue in order to visualize the solutions distribution in the CSF. The distance in cm reached by the different agents every minute as well as the pattern of distribution were evaluated. All tested solutions distributed itself in a forward and vertically pattern from the tip of the catheter. Maximum distance reached after 15 minutes were 15cm for 10% glucose, 13cm for hyperbaric morphine, 18cm for hyperbaric buprenorphine, and 17cm for hyperbaric methadone. The proposed model was efficient to evaluate the distribution pattern of hyperbaric solutions in equine CSF, offering a new possibility to physically test the administration of solutions in the equine subarachnoid space