Activity Behaviour of Minipigs Transgenic for the Huntington Gene

BACKGROUND

To increase the reliability of translating preclinical findings to humans, large animal models, such as the transgenic (tg) Libechov minipig, were established. As minipigs possess high genetic homology with humans and have similarities in anatomy, physiology and metabolism to humans, they are considered for studying neurodegenerative diseases longitudinally. Recently, sleep abnormalities and changes in circadian rhythm in Huntington's disease (HD) patients were acknowledged to present one of the early symptoms in HD.

OBJECTIVE

The aim of the present study was to explore the activity behaviour of Libechov minipigs and to investigate whether tgHD and wildtype (wt) minipigs exhibit differences in activity behaviour. Furthermore, it was investigated whether activity assessments may serve as reliable endpoints for phenotyping minipigs transgenic for the Huntington gene.

METHODS

Activity behaviour of minipigs was studied by video recording the stables twice a week over a total study period of five weeks for a cohort of five tgHD minipigs and five wt minipigs. Statistical analysis was performed using the linear mixed model. Once a week, the distances covered by two minipigs in focus (tgHD, wt) were measured using the VideoMotionTracker® software.

RESULTS

Libechov minipigs showed a biphasic pattern of activity, spending most of the time inactive or grubbing in litter. Differences in activity behaviour (rooting, resting and standing) were detected between wt and tgHD minipigs. The influence of the genotype on behavioural patterns was observed during circadian monitoring. TgHD minipigs covered longer distances on average and during every 24 h observation period than wt minipigs.

CONCLUSION

Activity behaviour may be a viable marker for phenotyping minipigs transgenic for the Huntington gene. Video recordings of behavioural patterns provide a non-invasive opportunity to capture potential disease signs. Phenotypic progression including the age of disease manifestation may be explored by documentation of circadian characteristics.

Vocalisation as a Viable Assessment for Phenotyping Minipigs Transgenic for the Huntington Gene?

BACKGROUND

Large animal models, such as the transgenic (tg) Huntington disease (HD) minipig, have been proposed to improve translational reliability and assessment of safety, efficacy and tolerability in preclinical studies. Minipigs are characterised by high genetic homology and comparable brain structures to humans. In addition, behavioural assessments successfully applied in humans could be explored in minipigs to establish similar endpoints in preclinical and clinical studies. Recently, analysis of voice and speech production was established to characterise HD patients.

OBJECTIVE

The aim of this study was to investigate whether vocalisation could also serve as a viable marker for phenotyping minipigs transgenic for Huntington's disease (tgHD) and whether tgHD minipigs reveal changes in this domain compared to wildtype (wt) minipigs.

METHODS

While conducting behavioural testing, incidence of vocalisation was assessed for a cohort of 14 tgHD and 18 wt minipigs. Statistical analyses were performed using Fisher's Exact Test for group comparisons and McNemar's Test for intra-visit differences between tgHD and wt minipigs.

RESULTS

Vocalisation can easily be documented during phenotyping assessments of minipigs. Differences in vocalisation incidences across behavioural conditions were detected between tgHD and wt minipigs. Influence of the genotype on vocalisation was detectable during a period of 1.5 years.

CONCLUSION

Vocalisation may be a viable marker for phenotyping minipigs transgenic for the Huntington gene. Documentation of vocalisation provides a non-invasive opportunity to capture potential disease signs and explore phenotypic development including the age of disease manifestation.

Minipigs as a Large-Brained Animal Model for Huntington's Disease: From Behavior and Imaging to Gene Therapy

Large animal models offer novel opportunities in exploring safety, biology, and efficacy of novel therapeutic approaches for Huntington's disease (HD). Challenges in the development of, for example, gene therapy, such as delivery, distribution, and persistence of virus vectors or oligo sense nucleotides, can be explored in large brains and organisms approaching human size. We here introduce the transgenic Libechov minipig as a large animal model of HD. Methods developed to assess motor, cognitive, and behavioral features expected to manifest in an HD model are described. We also outline established protocols for magnetic resonance imaging (MRI) including magnetic resonance spectroscopy (MRS) for minipigs. The successful conduct of long-term follow-up studies over several years with repeated behavioral testing and imaging is reported. We discuss the advantages and limitations of using this model with regard to translational reliability, homology to humans and with respect to feasibility, breeding, housing, handling, and finally ethical considerations. It is concluded that minipigs can fulfill an important role in preclinical development to bridge the gap between rodents and nonhuman primate research in the translation to humans.

Behavioral testing of minipigs transgenic for the Huntington gene-A three-year observational study

BACKGROUND

Large animal models of Huntington's disease (HD) may increase the reliability of translating preclinical findings to humans. Long live expectancy offers opportunities particularly for disease modifying approaches, but also challenges. The transgenic (tg) HD minipig model assessed in this study exhibits a high genetic homology with humans, similar body weight, and comparable brain structures. To test long-term safety, tolerability, and efficacy of novel therapeutic approaches in this model reliable assessments applicable longitudinally for several years are warranted for all phenotypical domains relevant in HD.

OBJECTIVE

To investigate whether the tests proposed assessing motor, cognitive and behavioral domains can be applied repetitively over a 3-year period in minipigs with acceptable variability or learning effects and whether tgHD minipigs reveal changes in these domains compared to wildtype (wt) minipigs suggesting the development of an HD phenotype.

METHODS

A cohort of 14 tgHD and 18 wt minipigs was followed for three years. Tests applied every six months included a tongue coordination and hurdle test for the motor domain, a color discrimination test for cognition, and a dominance test for assessing behavior. Statistical analyses were performed using repeated ANOVA for longitudinal group comparisons and Wilcoxon-tests for intra-visit differences between tgHD and wt minipigs.

RESULTS

All tests applied demonstrated feasibility, acceptable variance and good consistency during the three-year period. No significant differences between tgHD and wt minipigs were detected suggesting lack of a phenotype before the age of four years.

CONCLUSIONS

The assessment battery presented offers measures in all domains relevant for HD and can be applied in long-term phenotyping studies with tgHD minipigs. The observation of this cohort should be continued to explore the timeline of phenotype development and provide information for future interventional studies.

Behavioral phenotyping of minipigs transgenic for the Huntington gene

BACKGROUND

While several novel therapeutic approaches for HD are in development, resources to conduct clinical trials are limited. Large animal models have been proposed to improve assessment of safety, tolerability and especially to increase translational reliability of efficacy signals obtained in preclinical studies. They may thus help to select candidates for translation to human studies. We here introduce a battery of novel tests designed to assess the motor, cognitive and behavioral phenotype of a transgenic (tg) HD minipig model.

NEW METHODS

A group of tgHD and wildtype (wt) Libechov minipigs (n=36) was available for assessment with (1) a gait test using the GAITRite(®) automated acquisition system, (2) a hurdle-test, (3) a tongue coordination test, (4) a color discrimination test, (5) a startbox back and forth test and (6) a dominance test. Performance of all tests and definition of measures obtained is presented.

RESULTS

Minipigs were able to learn performance of all tests. All tests were safe, well tolerated and feasible. Exploratory between group comparisons showed no differences between groups of tgHD and wt minipigs assessed, but low variability within and between groups.

COMPARISON WITH EXISTING METHOD(S)

So far there are no established or validated assessments to test minipigs in the domains described.

CONCLUSIONS

The data shows that the tests presented are safe, well tolerated and all measures defined can be assessed. Prospective longitudinal application of these tests is warranted to determine their test-retest reliability, sensitivity and validity in assessing motor, cognitive and behavioral features of tg and wt minipigs.

Neuroimaging of a minipig model of Huntington's disease: Feasibility of volumetric, diffusion-weighted and spectroscopic assessments

BACKGROUND

As novel treatment approaches for Huntington's disease (HD) evolve, the use of transgenic (tg) large animal models has been considered for preclinical safety and efficacy assessments. It is hoped that large animal models may provide higher reliability in translating preclinical findings to humans, e.g., by using similar endpoints and biomarkers.

NEW METHOD

We here investigated the feasibility to conduct MRI assessments in a recently developed tgHD model in the Libechov minipig. The model is characterized by high genetic homology to humans and a similar body mass and compartments. The minipig brain provides anatomical features that are attractive for imaging studies and could be used as endpoints for disease modifying preclinical studies similar to human HD.

RESULTS

We demonstrate that complex MRI protocols can be successfully acquired with tgHD and wild type (wt) Libechov minipigs. We show that acquisition of anatomical images applicable for volumetric assessments is feasible and outline the development of a segmented MRI brain atlas. Similarly diffusion-weighted imaging (DWI) including fiber tractography is presented. We also demonstrate the feasibility to conduct in vivo metabolic assessments using MR spectroscopy.

COMPARISON WITH EXISTING METHODS

In human HD, these MRI methods are already validated and used as reliable biomarker of disease progression even before the onset of a clinical motor phenotype.

CONCLUSIONS

The results show that the minipig brain is well suited for MRI assessments in preclinical studies. We conclude that further characterization of phenotypical differences between tg and wt animals in sufficiently powered cross-sectional and longitudinal studies is warranted.