Noninvasive metabolic syndrome model using an extremely small minipig, the microminipig

Microminipig: A suitable animal model to estimate oral absorption of sustained-release formulation in humans

We investigated the gastrointestinal absorption characteristics of oral sustained-release formulations in microminipigs, dogs, and monkeys in order to clarify the similarities in absorption properties between these animals and humans. Time profiles of oral absorption of nifedipine and valproic acid were calculated from the plasma concentration-time profiles of the drugs by a deconvolution method. The curves for both drugs in microminipigs were close to or slightly higher than those in humans, whereas those in monkeys were lower. Furthermore, the plasma concentration-time profiles of the drugs were subjected to non-compartmental analysis. The fractions of a dose absorbed into the portal vein (FaFg) in microminipigs ranged from 50 to 100% of the human values, whereas those in monkeys were less than half the human values. In addition, the other absorption-related parameters for the sustained-release formulation in microminipigs, as well as monkeys, were comparable to those in humans. In conclusion, the oral absorption properties of microminipigs and humans were similar regarding the sustained-release formulations. Therefore, microminipig is a suitable animal model to estimate the oral absorption of sustained-release formulations in humans.

Activation of adenosine A2A but not A2B receptors is involved in uridine adenosine tetraphosphate-induced porcine coronary smooth muscle relaxation

Activation of both adenosine A_2A and A_2B receptors (A_2BR) contributes to coronary vasodilation. We previously demonstrated that uridine adenosine tetraphosphate (Up₄A) is a novel vasodilator in the porcine coronary microcirculation, acting mainly on A_2AR in smooth muscle cells (SMC). We further investigated whether activation of A_2BR is involved in Up₄A-mediated coronary SMC relaxation. Both A_2AR and A_2BR may stimulate H₂O₂ production leading to activation of K_ATP channels in SMCs, we also studied the involvement of H₂O₂ and K_ATP channels in Up₄A-mediated effect. Coronary small arteries dissected from the apex of porcine hearts were mounted on wire myograph for Up₄A concentration responses. Up₄A-induced coronary SMC relaxation was attenuated by A_2AR but not A_2BR antagonism or non-selective P2R antagonism, despite greater endogenous A_2BR expression vs. A_2AR in both coronary small arteries and primary cultured coronary SMCs. Moreover, Up₄A-induced coronary SMC relaxation was blunted by H₂O₂ catabolism. This effect was not altered by K_ATP channel blockade. Combination of H₂O₂ catabolism and A_2AR antagonism attenuated Up₄A-induced coronary SMC relaxation to the similar extent as A_2AR antagonism alone. Collectively, Up₄A-induced porcine coronary SMC relaxation is mediated by activation of A_2AR-H₂O₂ pathway. This process does not involve A_2BR, P2R or K_ATP channels.

Spontaneous Age-Related Histopathological Changes in Microminipigs

Microminipigs have become an attractive animal model for toxicology and pharmacology studies and for human disease models, owing to their manageable size. Although there are numerous reports of spontaneous age-related lesions in mice, rats, dogs, and monkeys, those in minipigs are scarce. In the present study, spontaneous age-related histopathological changes were investigated using 37 microminipigs (20 males and 17 females) that were 6 months to 10 years of age. Abnormal deposits of materials were evident in several animals from 6 years of age, and these deposits included amyloid in the renal medulla, thyroid gland, and adrenal gland, hyaline droplets in glomeruli, and fibrillar inclusions in neurons. Arterial sclerosing changes (intimal thickening, intimal proliferation, and medial mineralization) and proliferative lesions (hyperplasia of hepatocytes, follicular cells, Leydig cells, and uterine endometrial glands) were present at 4 years of age and beyond. Renal adenoma, uterine leiomyoma, and Leydig cell tumor were observed in several microminipigs. Moreover, glomerulosclerosis, renal interstitial fibrosis, thymic involution, and adrenocortical cell vacuolation were common in aging microminipigs. Since knowledge of age-related changes is helpful for pathologists, the basic information obtained in this study will be a useful reference for all future toxicity evaluations in microminipigs.

Spermatogenesis in the Microminipig

The microminipig has considerable potential as an animal model to evaluate general toxicity; however, there are few studies on the male reproductive system, particularly regarding spermatogenesis. The objectives of the present study were to clarify the stages of the seminiferous epithelium cycle on the basis of spermiogenesis and to determine the duration of spermatogenesis in the microminipig. Eleven microminipigs from 6 to 9 months of age were used for histological analyses. Spermiogenesis and stages of the seminiferous epithelium cycle were classified according to the degree of acrosomal development as shown by the periodic acid-Schiff reaction. Three of the animals were intravenously injected with 5-bromo-2-deoxyuridine to determine the duration of spermatogenesis by immunohistochemistry. Spermiogenesis was classified into 15 steps according to the morphological development of the acrosome, nucleus, and flagellum. The seminiferous epithelium cycle was classified into 11 stages based on the steps of spermatid development and germ cell associations. The length of the seminiferous epithelium cycle and the overall spermatogenesis process in the microminipig were estimated to be approximately 9.1 and 40.9 days, respectively. The results indicate the potential application of the microminipig in the evaluation of testicular toxicity, such as spermatogenesis disruption, in general toxicity studies.

Percutaneous carbon dioxide mist treatment has protective effects in experimental myocardial infarction

Percutaneous treatment with carbon dioxide (CO2) mist, CO2 gas dissolved in water, contributes to improved cardiac function after myocardial infarction (MI). In this study, we investigated the effects of repeated pretreatment with CO2 mist on cardiac dysfunction after MI. The CO2 mist was generated by a dry mist production unit. The whole body of rats below the axilla was wrapped in a polyethylene bag, which was sealed and filled with the CO2 mist in the draft cabinet for 30 min daily for 7 days. MI was induced by ligation of the coronary artery in untreated (UT), CO2 gas-pretreated (CG), and CO2 mist-pretreated (CM) rats. The infarct size and the increase in oxidative stress due to MI were significantly smaller in the CM rats than in the UT rats. Furthermore, the expression of inflammation-related genes, such as monocyte chemoattractant protein-1, and fibrosis-related genes, such as transforming growth factor-β1, was significantly suppressed in the CM rats. The CM rats had a better left ventricular ejection fraction than the UT rats 7 days after MI. These parameters in the CG rats were the same as in the UT group. Thus, CO2 mist preparative treatment may be potentially useful for the reduction of MI.