Histopathologic findings in the sacrocaudalis dorsalis medialis muscle of horses with vitamin E-responsive muscle atrophy and weakness

The role of selenium and vitamin E in a Transylvanian enzootic equine recurrent rhabdomyolysis syndrome

A severe form of recurrent exertional rhabdomyolysis occurs enzootically in a well-defined region of Transylvania, Harghita county. At the highest lying two settlements (more than 800 m above sea level), the prevalence of equine rhabdomyolysis is between 17 and 23%, while in the neighbouring villages in the valley it is less than 2%. The objective of our study was to clarify the role of selenium and vitamin E in the high prevalence of rhabdomyolysis in that region. Soil and hay samples were collected from each area to evaluate mineral content. Ten horses from the non-affected and 20 horses from the affected area were tested for serum selenium, vitamin E, glutathione peroxidase (GSH-Px), muscle enzymes, lactate and electrolytes. Hay samples collected from the affected area had lower selenium content. Horses in the affected regions had significantly lower serum selenium (P = 0.006) and GSH-Px levels than animals living in the non-affected regions. A good correlation between erythrocyte GSH-Px and serum selenium concentration could be demonstrated (r = 0.777, P < 0.001). Serum vitamin E levels were low independently of the origin of the horse. Based on our results, selenium deficiency possibly has a role in the Transylvanian enzootic equine recurrent rhabdomyolysis syndrome.

Influence of specific management practices on blood selenium, vitamin E, and beta-carotene concentrations in horses and risk of nutritional deficiency

Background

Selenium or alpha‐tocopherol deficiency can cause neuromuscular disease. Beta‐carotene has limited documentation in horses.

Objective

To evaluate the effect of owner practices on plasma beta‐carotene concentration and risk of selenium and alpha‐tocopherol deficiencies.

Animals

Three‐hundred and forty‐nine adult (≥1 year), university and privately owned horses and mules.

Methods

Cross‐sectional study. Whole blood selenium, plasma alpha‐tocopherol, and plasma beta‐carotene concentrations were measured once. Estimates of daily selenium and vitamin E intake, pasture access, and exercise load were determined by owner questionnaire. Data were analyzed using t tests, Mann‐Whitney tests, parametric or nonparametric analysis of variance (ANOVA), Kruskal‐Wallis test, Spearman's correlation and contingency tables (P < .05).

Results

Nearly 88% of the horses received supplemental selenium; 71.3% received ≥1 mg/d. Low blood selenium concentration (<80 ng/mL) was identified in 3.3% of horses, and 13.6% had marginal concentrations (80‐159 ng/mL). Non‐supplemented horses were much more likely to have low blood selenium (odds ratio [OR], 20.2; 95% confidence interval [CI], 9.26‐42.7; P < .001). Supplemental vitamin E was provided to 87.3% of horses; 57.7% received ≥500 IU/d. Deficient (<1.5 μg/mL) and marginal (1.5‐2.0 μg/mL) plasma (alpha‐tocopherol) occurred in 15.4% and 19.9% of horses, respectively. Pasture access (>6 h/d) and daily provision of ≥500 IU of vitamin E was associated (P < .001) with higher plasma alpha‐tocopherol concentrations. Plasma beta‐carotene concentration was higher in horses with pasture access (0.26 ± 0.43 versus 0.12 ± 0.13 μg/mL, P = .003).

Conclusions and Clinical Importance

Suboptimal blood selenium and plasma alpha‐tocopherol concentrations occurred in 16.7% and 35.5% of horses, respectively, despite most owners providing supplementation. Inadequate pasture access was associated with alpha‐tocopherol deficiency, and reliance on selenium‐containing salt blocks was associated with selenium deficiency.

Impact of alpha-tocopherol deficiency and supplementation on sacrocaudalis and gluteal muscle fiber histopathology and morphology in horses

BACKGROUND

A subset of horses deficient in alpha-tocopherol (α-TP) develop muscle atrophy and vitamin E-responsive myopathy (VEM) characterized by mitochondrial alterations in the sacrocaudalis dorsalis medialis muscle (SC).

OBJECTIVES

To quantify muscle histopathologic abnormalities in subclinical α-TP deficient horses before and after α-TP supplementation and compare with retrospective (r)VEM cases.

ANIMALS

Prospective study; 16 healthy α-TP-deficient Quarter Horses. Retrospective study; 10 retrospective vitamin E-responsive myopathy (rVEM) cases .

METHODS

Blood, SC, and gluteus medius (GM) biopsy specimens were obtained before (day 0) and 56 days after 5000 IU/450 kg horse/day PO water dispersible liquid α-TP (n = 8) or control (n = 8). Muscle fiber morphology and mitochondrial alterations were compared in samples from days 0 and 56 and in rVEM cases.

RESULTS

Mitochondrial alterations more common than our reference range (<2.5% affected fibers) were present in 3/8 control and 4/8 treatment horses on day 0 in SC but not in GM (mean, 2.2; range, 0%-10% of fibers). Supplementation with α-TP for 56 days did not change the percentage of fibers with mitochondrial alterations or anguloid atrophy, or fiber size in GM or SC. Clinical rVEM horses had significantly more mitochondrial alterations (rVEM SC, 13% ± 7%; GM, 3% ± 2%) and anguloid atrophy compared to subclinical day 0 horses.

CONCLUSIONS AND CLINICAL IMPORTANCE

Clinically normal α-TP-deficient horses can have mitochondrial alterations in the SC that are less severe than in atrophied VEM cases and do not resolve after 56 days of α-TP supplementation. Preventing α-TP deficiency may be of long-term importance for mitochondrial viability.

Improving Reproducibility of Phenotypic Assessments in the DyW Mouse Model of Laminin-α2 Related Congenital Muscular Dystrophy

Laminin-α2 related Congenital Muscular Dystrophy (LAMA2-CMD) is a progressive muscle disease caused by partial or complete deficiency of laminin-211, a skeletal muscle extracellular matrix protein. In the last decade, basic science research has queried underlying disease mechanisms in existing LAMA2-CMD murine models and identified possible clinical targets and pharmacological interventions. Experimental rigor in preclinical studies is critical to efficiently and accurately quantify both negative and positive results, degree of efficiency of potential therapeutics and determine whether to move a compound forward for additional preclinical testing. In this review, we compare published available data measured to assess three common parameters in the widely used mouse model DyW, that mimics LAMA2-CMD, we quantify variability and analyse its possible sources. Finally, on the basis of this analysis, we suggest standard set of assessments and the use of available standardized protocols, to reduce variability of outcomes in the future and to improve the value of preclinical research.

Effects of feeding two RRR-α-tocopherol formulations on serum, cerebrospinal fluid and muscle α-tocopherol concentrations in horses with subclinical vitamin E deficiency

BACKGROUND

Alpha-tocopherol (α-TP) supplementation is recommended for the prevention of various equine neuromuscular disorders. Formulations available include RRR-α-TP acetate powder and a more expensive but rapidly water-dispersible liquid RRR-α-TP (WD RRR-α-TP). No cost-effective means of rapidly increasing serum and cerebrospinal fluid (CSF) α-TP with WD RRR-α-TP and then sustaining concentrations with RRR-α-TP acetate has yet been reported.

OBJECTIVES

To evaluate serum, CSF and muscle α-TP concentrations in an 8-week dosing regimen in which horses were transitioned from WD RRR-α-TP to RRR-α-TP acetate.

STUDY DESIGN

Non-randomised controlled trial.

METHODS

Healthy horses with serum α-TP of <2 μg/mL were divided into three groups and followed for 8 weeks. In the control group (n = 5), no α-TP was administered. In the second group (Group A; n = 7), 5000 IU/day RRR-α-TP acetate was administered. In the third group (Group WD-A; n = 7), doses of 5000 IU/day of WD RRR-α-TP were administered over 3 weeks, followed by a 4-week transition from WD RRR-α-TP to RRR-α-TP acetate, and a final 1 week of treatment with RRR-α-TP acetate. Serum samples were obtained weekly; muscle biopsies were obtained before, at 2.5 weeks and after supplementation. CSF samples were obtained before and after the 8-week period of supplementation.

RESULTS

Serum α-TP increased significantly in Group WD-A at week 1 and remained significantly higher than in Group A and the control group throughout the transition, with inter-individual variation in response. Serum α-TP increased significantly by week 7 in Group A. CSF α-TP increased significantly in Group WD-A only. Muscle α-TP concentrations did not differ significantly across groups. Serum and CSF α-TP were closely correlated (r = 0.675), whereas serum and muscle-α-TP concentrations were not correlated.

MAIN LIMITATIONS

The study duration was short and data on pre-transition CSF was lacking.

CONCLUSIONS

The administration of 5000 IU/day of water-dispersible RRR-α-TP rapidly increases serum α-TP. Serum and CSF α-TP concentrations are sustained with a gradual transition to 5000 IU/day of RRR-α-TP acetate. Periodic evaluation of serum α-TP concentrations is recommended because responses vary among individuals.

Pigment retinopathy in warmblood horses with equine degenerative myeloencephalopathy and equine motor neuron disease

OBJECTIVE

A pigment retinopathy has been reported in adult horses with equine motor neuron disease (EMND) arising from chronic α-tocopherol (α-TP) deficiency. A pigment retinopathy has not been identified in horses with neuroaxonal dystrophy/equine degenerative myeloencephalopathy (NAD/EDM) that affects genetically susceptible young horses with α-TP deficiency. The objective of this report is to describe, for the first time, a pigment retinopathy in a family of α-TP-deficient Warmbloods (WB) with clinically apparent NAD/EDM or EMND.

ANIMALS AND PROCEDURES

Twenty-five WB horses from one farm underwent complete neurologic and ophthalmic examinations and serum α-TP concentrations were assessed. Two of the most severely ataxic horses were euthanized and postmortem examinations performed.

RESULTS

Alpha-TP deficiency was widespread on this farm (22 of 25 horses). Eleven of 25 horses were clinically normal (age range 2-12 years), one had signs of EMND (6 years of age), 10 had signs of ataxia consistent with NAD/EDM (1-10 years), and two of these were postmortem confirmed concurrent NAD/EDM and EMND. A pigment retinopathy characterized by varying amounts of granular dark pigment in the tapetal retina was observed in four clinically apparent NAD/EDM horses (two postmortem confirmed concurrent NAD/EDM and EMND) and one horse with clinical signs of EMND.

CONCLUSIONS

A pigment retinopathy can be present in young α-TP-deficient Warmblood horses with clinical signs of EMND as well as those with signs of NAD/EDM.

Eosinophilic Enteritis in Horses with Motor Neuron Disease

BACKGROUND

Equine motor neuron disease (EMND) is a neuromuscular disorder that affects adult horses. Although EMND has been linked to vitamin E deficiency, its etiopathogenesis is poorly understood.

OBJECTIVES

To describe clinical features, laboratory results, and postmortem findings in a series of young horses with motor neuron disease (MND).

ANIMALS

A herd of 15 young Andalusian horses with weakness, weight loss, muscle atrophy, and muscle fasciculations related to restricted intake of green forage.

METHODS

A case series is presented in which horses were subjected to a clinical examination and plasma vitamin E measurement. Five severely affected horses were euthanized for detailed postmortem examination. Muscle specimens were taken from the M. sacrocaudalis dorsalis medialis and the M. gluteus medius for histopathologic and morphometric evaluation.

RESULTS

MND was diagnosed in 5 horses based on clinical signs, low serum levels of vitamin E (0.11 ± 0.05 mg/dL; normal range,: 0.3-1.5 mg/dL), changes in muscle histopathology (neurogenic atrophy), and spinal cord lesions (neuronal chromatolysis in ventral horns). An unexpected postmortem finding was the presence of intestinal inflammation (catarrhal enteritis, edema, and eosinophilic infiltrate) associated with the presence of giant ciliated protozoa in all of the horses.

CONCLUSIONS

Although a mechanistic link could not be established, it is hypothesized that intestinal inflammation may have been involved in the decreased absorption of vitamin E, thus favoring the development of MND.

Evidence of positive selection for a glycogen synthase (GYS1) mutation in domestic horse populations

A dominantly inherited gain-of-function mutation in the glycogen synthase (GYS1) gene, resulting in excess skeletal muscle glycogen, has been identified in more than 30 horse breeds. This mutation is associated with the disease Equine Polysaccharide Storage Myopathy Type 1, yet persists at high frequency in some breeds. Under historical conditions of daily work and limited feed, excess muscle glycogen may have been advantageous, driving the increase in frequency of this allele. Fine-scale DNA sequencing in 80 horses and genotype assays in 279 horses revealed a paucity of haplotypes carrying the mutant allele when compared with the wild-type allele. Additionally, we found increased linkage disequilibrium, measured by relative extended haplotype homozygosity, in haplotypes carrying the mutation compared with haplotypes carrying the wild-type allele. Coalescent simulations of Belgian horse populations demonstrated that the high frequency and extended haplotype associated with the GYS1 mutation were unlikely to have arisen under neutrality or due to population demography. In contrast, in Quarter Horses, elevated relative extended haplotype homozygosity was associated with multiple haplotypes and may be the result of recent population expansion or a popular sire effect. These data suggest that the GYS1 mutation underwent historical selection in the Belgian, but not in the Quarter Horse.