Microminipig, a Non-rodent Experimental Animal Optimized for Life Science Research: In Vivo Proarrhythmia Models of Drug-Induced Long QT Syndrome: Development of Chronic Atrioventricular Block Model of Microminipig

Differentiation Capacity of Porcine Skeletal Muscle-Derived Stem Cells as Intermediate Species between Mice and Humans

Large animal experiments are important for preclinical studies of regenerative stem cell transplantation therapy. Therefore, we investigated the differentiation capacity of pig skeletal muscle-derived stem cells (Sk-MSCs) as an intermediate model between mice and humans for nerve muscle regenerative therapy. Enzymatically extracted cells were obtained from green-fluorescence transgenic micro-mini pigs (GFP-Tg MMP) and sorted as CD34+/45- (Sk-34) and CD34-/45-/29+ (Sk-DN) fractions. The ability to differentiate into skeletal muscle, peripheral nerve, and vascular cell lineages was examined via in vitro cell culture and in vivo cell transplantation into the damaged tibialis anterior muscle and sciatic nerves of nude mice and rats. Protein and mRNA levels were analyzed using RT-PCR, immunohistochemistry, and immunoelectron microscopy. The myogenic potential, which was tested by Pax7 and MyoD expression and the formation of muscle fibers, was higher in Sk-DN cells than in Sk-34 cells but remained weak in the latter. In contrast, the capacity to differentiate into peripheral nerve and vascular cell lineages was significantly stronger in Sk-34 cells. In particular, Sk-DN cells did not engraft to the damaged nerve, whereas Sk-34 cells showed active engraftment and differentiation into perineurial/endoneurial cells, endothelial cells, and vascular smooth muscle cells, similar to the human case, as previously reported. Therefore, we concluded that Sk-34 and Sk-DN cells in pigs are closer to those in humans than to those in mice.

NR6A1 Allelic Frequencies as an Index for both Miniaturizing and Increasing Pig Body Size

BACKGROUND/AIM

The number of vertebrae in swine varies from 19 to 23 and is associated with body size. Nuclear receptor subfamily 6 group A member 1 (NR6A1) is considered a strong candidate for affecting the number of vertebrae in swine. Wild boars, which uniformly have 19 vertebrae, have the wild type allele while multi-vertebrae European commercial pigs have the mutated allele. Our aim was to confirm the factor of the miniaturization.

MATERIALS AND METHODS

We examined vertebrae number and NR6A1 polymorphism in the Microminipig and three domestic breeds that vary in body size.

RESULTS

The Microminipig had 19 or less vertebrae and a wild type NR6A1 genotype. Three domestic breeds had more than 21 vertebrae while the largest vertebrae number was observed in multi-vertebrae-fixed Large White. Heterozygous genotypes were observed in the middle-sized indigenous pig while homozygous NR6A1 mutations were observed in European commercial breeds.

CONCLUSION

NR6A1 could be a useful index for both miniaturizing and increasing pig body size.

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.

Translational Models of Arrhythmia Mechanisms and Susceptibility: Success and Challenges of Modeling Human Disease

We discuss large animal translational models of arrhythmia susceptibility and sudden cardiac death, focusing on important considerations when interpreting the data derived before applying them to human trials. The utility of large animal models of arrhythmia and the pros and cons of specific translational large animals used will be discussed, including the necessary tradeoffs between models designed to derive mechanisms vs. those to test therapies. Recent technical advancements which can be applied to large animal models of arrhythmias to better elucidate mechanistic insights will be introduced. Finally, some specific examples of past successes and challenges in translating the results of large animal models of arrhythmias to clinical trials and practice will be examined, and common themes regarding the success and failure of translating studies to therapy in man will be discussed.

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.

[Current progress of research and use of microminipigs in drug development]

The use of minipigs has been increasing in the areas of pharmacology researches and drug development. The microminipig developed by Fuji Micra Inc. (Shizuoka, Japan) inherits characteristics of other pig strains showing several similarities to humans in anatomy, physiology, omnivorousness and diurnal, but at the same time has several advantages over other pig strains because of its small size which allows easy keeping, handling and dosing, and saving of test substances. The microminipig weighs about 10 kg at the age of 6 months. Canine cages can be used to keep the animal. Swine leukocyte antigens (SLA) are defined in each individual animal which is useful for testing immunological reactions. As there are many similarities in metabolic enzymes and transporters to those in humans, the microminipig is a powerful animal model for toxicokinetic studies. Unfortunately as in other minipigs the microminipig is not appropriate for embryo-fetal development studies of antibody drugs due to its poor placental transfer, but can be used for other reproductive and developmental studies. Repeat dose toxicity, safety pharmacology, immunotoxicity and local tolerance studies should be also other arenas of this animal model.

A Toxoplasma gondii strain isolated in Okinawa, Japan shows high virulence in Microminipigs

Toxoplasma gondii strains have been isolated all over the world and their virulence has been examined mainly using laboratory mice. However, T. gondii differs in virulence depending on the host animal species. Therefore, to evaluate the virulence of each strain in domestic animals, it is necessary to examine using not only mice but also the concerned animals. We have shown that TgCatJpOk4, a T. gondii strain recently isolated in Okinawa, Japan, has a high virulence against laboratory mice, comparable to highest virulent RH strain in mice; however, the virulence to domestic animals remains unknown. In this study, we examined the virulence using the Microminipig. After infection, four out of five infected pigs showed severe clinical symptoms: inappetence, hypoactivity and tachypnea. Eventually, three out of the five infected pigs succumbed before the end of the observation. Among the three dead pigs, histological analysis revealed that interstitial pneumonia and spotty necrosis in the liver indicating that the TgCatJpOk4 strain has a high virulence not only in laboratory mice, but in pigs as well.

Use of microminipigs for unveiling unknown mechanisms of azithromycin-induced cardiovascular death

Although azithromycin can suppress cardiac I_Na, I_Kr, I_Ks, I_Ca,L and I_K1, its onset mechanisms for cardiovascular death have not been fully investigated. We examined electropharmacological effects of azithromycin in intravenous doses of 0.3, 3 and 30 mg/kg using microminipigs under the halothane anesthesia (n = 4), which provided plasma concentrations of 3.1, 11.2 and 120.4 μg/mL, respectively. The low dose did not alter any of the cardiohemodynamic or electrocardiographic variables. The middle dose significantly shortened QT interval for 10-20 min and QTc for 10-30 min. The high dose significantly decreased mean blood pressure for 5-60 min, prolonged QRS width at 20 min, but shortened QT interval for 15-20 min and QTc for 15-30 min (n = 3). Cardiohemodynamic collapse occurred in 1 animal after the start of the high dose infusion, which might be associated with the cardiovascular death in patients with vasomotor dysfunction. Prolongation of QRS width indicates that azithromycin may suppress ventricular I_Na in vivo, which may unmask latent type of Brugada electrocardiographic genotype. Meanwhile, abbreviation of the QTc might cause potentially lethal, short QT-related, cardiac arrhythmia syndrome. These findings with microminipigs suggest the possible entry point for analyzing the mechanisms of cardiovascular death clinically seen with this antibiotic.

Changes of electrocardiogram and hemodynamics in response to dipyridamole: In vivo comparative analyses using anesthetized beagle dogs and microminipigs

Microminipigs are expected as a novel animal model for cardiovascular pharmacological experiments. Since inherent vulnerability of coronary circulation of microminipigs has not been characterized, we performed dipyridamole-stress test to both microminipigs and beagle dogs, and compared the results. Dipyridamole in doses of 0.056 and 0.56 mg/kg were intravenously infused over 10 min (n = 4 for each animal). Dipyridamole decreased the systolic/diastolic blood pressures and double product in dogs as well as in microminipigs; but it did not significantly alter the heart rate or the global balance between the myocardial oxygen demand and supply in either animal. While organic coronary arterial stenosis was not detected in either animal, dogs have well-developed epicardial intracoronary networks unlike microminipigs. Like in humans, dipyridamole did not affect the ST segment of microminipigs, whereas it substantially depressed that in dogs. The results indicate the onset of subendocardial ischemia by dipyridamole in dogs may be partly associated with their well-developed native coronary collateral channels. Microminipigs would be more useful to evaluate the drugs which may affect the coronary circulation in the pre-clinical study than dogs.

Corpus luteum Regression Induced by Prostaglandin F2α in Microminipigs During the Normal Estrous Cycle

Induction of corpus luteum regression and subsequent estrus using prostaglandin F2α (PGF2α) in microminipigs was investigated. Microminipigs with normal estrous cycle were treated with PGF2α as 0.75 mg (0.75 PG group, n=3) or 1.5 mg (1.5 PG group, n=4) dinoprost injected into the vulva at 24-h intervals at 10 days after the onset of estrus (D0), D1 and D2. Three microminipigs were not treated (control group). The estrous interval in the 1.5 PG group was significantly shortened compared to the control and 0.75 PG groups. Plasma progesterone levels started to decline and reached the base line in the 1.5 PG group significantly faster than in the control group. In conclusion, we demonstrate that multiple PGF2α treatments can induce corpus luteum regression and estrous synchronization in female microminipigs.

Pharmacological characterization of microminipig as a model to assess the drug-induced cardiovascular responses for non-clinical toxicity and/or safety pharmacology studies

We tried to establish the halothane-anesthetized microminipigs as an alternative animal model for non-clinical toxicity and/or safety pharmacology studies. In order to characterize the halothane-anesthetized microminipigs, we firstly clarified the effects of halothane anesthesia on their cardiovascular system (n = 5). Then, we examined the cardiovascular effects of dl-sotalol in doses of 0.1, 0.3 and 1 mg/kg, i.v. on the halothane-anesthetized microminipigs (n = 6). Induction of the halothane anesthesia by itself prolonged the QT interval as well as QTcF, suggesting that the halothane anesthesia can reduce the cardiac repolarization reserve in microminipigs like in dogs. dl-Sotalol showed more potent negative chronotropic, dromotropic and hypotensive effects together with repolarization delay in microminipigs than in dogs, although each cardiovascular response to dl-sotalol was directionally similar between them, suggesting greater basal sympathetic tone and/or smaller volume of distribution of the drug in microminipigs than in dogs. Analyses of proarrhythmic surrogate markers indicate that T_peak-T_end and short-term variability of QT interval may be more sensitive to detect the dl-sotalol-induced direct electrophysiological changes in microminipigs than in dogs, but its reverse will be true for J-T_peakc. Thus, these results may help better understand the drug-induced cardiovascular responses in microminipigs.

Characterization of microminipigs as an in vivo experimental model for cardiac safety pharmacology

We pharmacologically characterized microminipigs as an in vivo experimental model by assessing cardiovascular effects of pilsicainide, verapamil and E-4031, which can preferentially inhibit cardiac Na⁺, Ca²⁺ and K⁺ channels, respectively. Intravenous infusion of 1 mg/kg of pilsicainide (n = 4), 0.1 mg/kg of verapamil (n = 4) and 0.01 followed by 0.1 mg/kg of E-4031 (n = 5) over 10 min decreased the heart rate, mean blood pressure and ventricular contractility. Moreover, pilsicainide prolonged the PR interval, QRS width and QTc; verapamil prolonged the PR interval, but shortened the QRS width and QTc; and E-4031 prolonged the QTc, whereas no substantial change was detected in the PR interval or QRS width. Peak plasma concentrations of pilsicainide, verapamil and E-4031 in microminipigs were 1.7-4.8 times higher than those expected in humans and dogs, possibly due to smaller effective volume of drug distribution. The extent of the drug-induced cardiovascular responses was generally greater in microminipigs than in humans and dogs, which could be explained by the following possibilities; namely unique pharmacokinetic profile, less great reflex-mediated increase of sympathetic tone and/or smaller repolarization reserve in microminipigs. These information may make it feasible to apply this new-type animal to a tool for assessing cardiac safety profiles of new chemical entities.

Analysis of gene expression for microminipig liver transcriptomes using parallel long-read technology and short-read sequencing

The microminipig is one of the smallest minipigs that has emerged as a possible experimental animal model, because it shares many anatomical and/or physiological similarities with humans, including the coronary artery distribution in the heart, the digestive physiology, the kidney size and its structure, and so on. However, information on gene expression profiles, including those on drug-metabolizing phase I and II enzymes, in the microminipig is limited. Therefore, the aim of the present study was to identify transcripts in microminipig livers and to determine gene expression profiles. De novo assembly and expression analyses of microminipig transcripts were conducted with liver samples from three male and three female microminipigs using parallel long-read and short-read sequencing technologies. After unique sequences had been automatically aligned by assembling software, the mean contig length of 50843 transcripts was 707 bp. The expression profiles of cytochrome P450 (P450) 1A2, 2C, 2E1 and 3A genes in livers in microminipigs were similar to those in humans. Liver carboxylesterase (CES) precursor, liver CES-like, UDP-glucuronosyltransferase (UGT) 2C1-like, amine sulfotransferase (SULT)-like, N-acetyltransferases (NAT8) and glutathione S-transferase (GST) A2 genes, which are relatively unknown genes in pigs and/or humans, were expressed strongly. Furthermore, no significant gender differences were observed in the gene expression profiles of phase I enzymes, whereas UGT2B17, SULT1E1, SULT2A1, amine SULT-like, NAT8 and GSTT4 genes were different between males and females among phase II enzyme genes under the present sample conditions. These results provide a foundation for mechanistic studies and the use of microminipigs as model animals for drug development in the future. Copyright © 2016 John Wiley & Sons, Ltd.

The Microminipig as an Animal Model for Influenza A Virus Infection

Pigs are considered a mixing vessel for the generation of novel pandemic influenza A viruses through reassortment because of their susceptibility to both avian and human influenza viruses. However, experiments to understand reassortment in pigs in detail have been limited because experiments with regular-sized pigs are difficult to perform. Miniature pigs have been used as an experimental animal model, but they are still large and require relatively large cages for housing. The microminipig is one of the smallest miniature pigs used for experiments. Introduced in 2010, microminipigs weigh around 10 kg at an early stage of maturity (6 to 7 months old) and are easy to handle. To evaluate the microminipig as an animal model for influenza A virus infection, we compared the receptor distribution of 10-week-old male pigs (Yorkshire Large White) and microminipigs. We found that both animals have SAα2,3Gal and SAα2,6Gal in their respiratory tracts, with similar distributions of both receptor types. We further found that the sensitivity of microminipigs to influenza A viruses was the same as that of larger miniature pigs. Our findings indicate that the microminipig could serve as a novel model animal for influenza A virus infection.

IMPORTANCE

The microminipig is one of the smallest miniature pigs in the world and is used as an experimental animal model for life science research. In this study, we evaluated the microminipig as a novel animal model for influenza A virus infection. The distribution of influenza virus receptors in the respiratory tract of the microminipig was similar to that of the pig, and the sensitivity of microminipigs to influenza A viruses was the same as that of miniature pigs. Our findings suggest that microminipigs represent a novel animal model for influenza A virus infection.

Estrus synchronization in microminipig using estradiol dipropionate and prostaglandin F2α

The induction of pseudopregnancy by the exogenous administration of estradiol dipropionate (EDP) was investigated in cyclic Microminipigs (MMpigs) and the effects of exogenous administration of prostaglandin (PG) F2α on estrus exhibition were assessed in pseudopregnant MMpigs. In experiment 1, ovariectomized MMpigs were given a single intramuscular injection of 0.5, 1.5, or 2.5 mg of EDP. The estradiol-17β level at each of these doses was significantly higher 1 to 3 days after EDP administration than on the day of the injection. In experiment 2, animals were given 1.5 mg of EDP once at 9 to 12 days after the end of estrus (D0) and then no (1.5 mg × 1 group), one (D0 and D4; 1.5 mg × 2 group), or two (D0, D4 and D7; 1.5 mg × 3 group) additional treatments. The pseudopregnancy rate was significantly higher in the 1.5 mg × 3 than in the 1.5 mg × 1 group. In experiment 3, PGF2α was administered twice between 26 and 28 days after EDP treatment to five pseudopregnant gilts with a 24-h interval between the two injections. Estrus after PGF2α treatment and LH surge were observed in 100% and 80% pseudopregnant MMpigs, respectively. The interval from the day of the first PGF2α treatment to the onset of estrus was 6.5 ± 0.2 days. These results indicate that multiple EDP treatments are required for induction of pseudopregnancy in MMpigs and estrus exhibition can be controlled in MMpigs by treatment with EDP and PGF2α.

Coronary artery vasospasms in a microminipig occurred after placing an ameroid constrictor

A 12-month-old microminipig, weighing 12.6 kg, showed 3 repeated episodes of transient ST-segment elevation in 24 hr Holter electrocardiogram after placing an ameroid constrictor around the left anterior descending coronary artery. Ventricular fibrillation was noticed just after the cessation of the 24 hr Holter-electrocardiogram recording. Direct current defibrillations and cardiopulmonary resuscitation were performed; however, they were unsuccessful, leading to the animal's death. Its heart was excised for macroscopic analysis, which indicated that lumen of the ameroid constrictor was not narrowed and that there was no dissection, embolus or thrombus in the coronary arteries, indirectly suggesting that coronary artery vasospasm may have caused the ischemic attacks. Thus, microminipig may possess some potential to have coronary vasospasm.

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.

Feasible induction of coronary artery vasospasm occurred during cardiac catheterization in a microminipig

A 14 month-old intact microminipig, weighing 8 kg, showed ST-segment elevation in A-B lead electrocardiogram during cardiac catheterization followed by ventricular tachycardia, which degenerated into ventricular fibrillation. Although a direct current defibrillation of 360 J was applied, ventricular tachycardia re-occurred for another 2 times and the direct defibrillation was repeated. After returning to normal sinus rhythm, a marked ST-segment elevation was still observed on leads II, III and aVF together with a remarkable decrease in contractility of inferior wall. The heart was excised for precise macroscopic and histological examinations, but there was no dissection, embolus or thrombus in the coronary arteries. These findings suggest that right coronary artery vasospasm could have caused the ischemic attack, leading to lethal arrhythmias.

Characterization of platelet aggregation responses in microminipigs: Comparison with miniature pigs and the influence of dual antiplatelet administration of aspirin plus prasugrel

We aimed to characterize platelet aggregation responses and the impact of dual antiplatelet therapy in microminipigs. In this in vitro study, both adenosine-5'-diphosphate (ADP, 5-50μM) and collagen (2-20μg/ml) induced concentration-related platelet aggregation in the microminipigs; 20μM ADP and 5 and 12.5μg/ml collagen were selected for further ex vivo studies. Aspirin plus prasugrel were administered orally for 7days (n=4/each group). Ex vivo platelet aggregation was analyzed on Day 1 (1 and 4h after administration), Day 4 (4h), and Day 7 (4h) under three different prasugrel dosing regimens: LD0/MD1 (1mg/kg/day), LD0/MD3 (3mg/kg/day), and LD10/MD1 (10mg/kg loading dose and 1mg/kg/day maintenance dose). Aspirin (10mg/kg/day) was administered to all groups. In the presence of aspirin, prasugrel at 3 and 10mg/kg significantly inhibited ADP-induced platelet aggregation on Day 1. On Days 4 and 7, significant inhibition of platelet aggregation (IPA) was also observed in each group. With 5μg/ml collagen-induced platelet aggregation, all three groups showed significant IPA at 4h on Day 1 or later. In 12.5μg/ml collagen-induced platelet aggregation, all groups showed significant effects on Days 4 and 7; however, the 30%-35% IPA was considerably lower than that (50%-60%) found with 5μg/ml collagen. In Clawn miniature pigs, similar inhibitory patterns were observed for both ADP- and collagen-induced ex vivo platelet aggregation. In conclusion, these results indicated that microminipigs as well as miniature pigs may represent useful experimental animals for thrombosis research.

Involvement of the autonomic nervous system in diurnal variation of corrected QT intervals in common marmosets

Our previous study has shown that the corrected QT (QTc) interval of the electrocardiogram is longer during the dark period than during the light period in telemetered common marmosets. In the present study, we investigated the involvement of sympathetic and parasympathetic nervous activities in the changes of QTc interval associated with the light-dark cycle.Telemetry transmitters were implanted in six common marmosets to continuously record the electrocardiogram. The QT intervals obtained were corrected for the RR interval by applying individual probabilistic QT-rate correction formulae. Power spectral analysis of heart rate variability was performed to quantify each autonomic nervous function. Changes in QTc intervals and autonomic nervous tones were associated with the light-dark cycle. Parasympathetic nervous activity and QTc intervals significantly increased by approximately 10 ms during the dark period.Atropine, a muscarinic receptor antagonist, suppressed the increased parasympathetic tone and QTc prolongation during the dark period. In contrast, propranolol, a β-adrenoceptor antagonist, decreased the sympathetic activity and increased QTc intervals during the light period. These results suggest that the parasympathetic nerve functions prolong QTc intervals during the dark period, while the sympathetic nerve functions shorten them during the light period in common marmosets.

A dermal phototoxicity study following intravenous infusion administration of ciprofloxacin hydrochloride in the novel microminipigs

The authors evaluated dermal phototoxicity using the world smallest minipig (MMPig: Microminipig). MMPigs were administered 100 mg/kg ciprofloxacin hydrochloride with an infusion pump. The dorsal area of each animal was irradiated with ultraviolet-A irradiation. The left dorsal skin was irradiated at intensities of 5, 10, 15, and 20 J/cm(2), and the right dorsal back skin was set as a nonirradiated site. Gross and histopathological examinations were conducted before irradiation and from 1 to 72 hr after irradiation. Initial changes in the skin were necrosis of the basal and/or prickle cell layer and cellular infiltration from 24 hr after irradiation. Vesicle formation observed from 48 hr after irradiation was considered similar to bullous eruptions, a known side effect of fluoroquinolones in humans. Therefore, the authors suggest that the MMPig may be a useful experimental animal model for dermal phototoxicity studies.

Reference values of hematological and biochemical parameters for the world smallest microminipigs

In this study, we demonstrated growth curves and reference values for hematological and serum biochemical parameters of Microminipigs, the world smallest experimental minipigs. In both male and female animals, the body weights (BWs) at 3 and 6 months of age were <5 kg and <10 kg, respectively, and growth curve revealed almost plateau (approximately 20 kg BW) after 18 months of age. Major hematological and serum biochemical parameters showed no gender differences and the values were very similar to those in Göttingen and Yukatan minipigs. The values obtained in this study can serve as fundamental reference, and thereby facilitate the use of Microminipig in life science research.

Microminipig, a non-rodent experimental animal optimized for life science research: preface

Fuji Micra Inc. has recently achieved success in a challenging and prospective project that produces the smallest pig in the world, the "Microminipig", at a breeding farm at the foothills of Mt. Fuji in Japan. Microminipigs weigh approximately 7.0 kg at 6 months of age when they are mature. Microminipigs have been provided to several research organizations in Japan as a non-rodent experimental animal optimized for life science research.