Assessment of the FAM174A 11G allele as a risk allele for equine metabolic syndrome.

An 11G nucleotide repeat in the 3' UTR of FAM174A was recently postulated as a risk allele with a dominant mode of inheritance for equine metabolic syndrome (EMS) and laminitis status in Arabian horses. The objective of this project was to evaluate this hypothesis in a large and diverse across-breed population. A total of 301 ponies, 292 Morgans, 64 Arabians, 49 Tennessee Walking Horses and 59 Quarter Horses were genotyped for six observed G repeat alleles in the FAM174A 3' UTR. Phenotype data included laminitis status, baseline insulin, glucose, non-esterified fatty acids, triglycerides, adiponectin, leptin, ACTH, insulin and glucose post oral sugar test, and two proxies for insulin resistance. The 11G allele frequencies were 18.8, 6.9, 1.8, 0.2 and 0.0% in the Arabians, Tennessee Walkers, ponies, Morgans and Quarter Horses respectively. Association analyses between FAM174A genotype and EMS phenotypes, and between allele count and EMS phenotypes, identified no statistically significant associations. When a dominant effect for the 11G allele was evaluated, a statistically significant association with adiponectin levels was identified in the ponies, and pairwise comparisons revealed that the estimated marginal means were higher in ponies with the 11G allele vs. alternative alleles (i.e. the allele had a protective effect). In conclusion, our data do not support the FAM174A 11G allele as a risk allele for EMS in our studied breeds.

Inclusion of herdmate data improves genomic prediction for milk-production and feed-efficiency traits within North American dairy herds.

Genomic data are widely available in the dairy industry and provide a cost-effective means of predicting genetic merit to inform selection decisions and increase genetic gains. As more dairy farms adopt genomic selection practices, dairy producers will soon have genomic data available on all of the animals within their herds. This is a very rich, but currently underused, source of information. Herdmates provide an excellent indication of how a selection candidate's genetics will perform within a given herd, noting that herdmates often include close relatives that share a similar environment. The study objective was to evaluate the utility of incorporating herdmate data into genomic predictions in a data set composed of 3,303 Holsteins from one herd in Canada and 6 herds throughout the United States. Within-herd prediction accuracy was assessed for milk-production and feed-efficiency traits determined from genomic best linear unbiased prediction under 4 different scenarios. Scenario 1 did not include herdmates in the training population. Scenarios 2 through 4 included herdmates in the training population, and scenarios 3 and 4 also included modeling of herd-specific marker effects. Leave-one-out cross validation was used to maximize the number of herdmates in the training population in scenarios 2 through 4, while maintaining constant training population size with scenario 1. Results from the present study reveal the importance of incorporating herdmate data into genomic evaluations. Inclusion of herdmates in the training population improved mean within-herd prediction accuracy for milk-production traits (± standard error) by 0.08 ± 0.03 (milk yield), 0.07 ± 0.03 (fat percentage), and 0.05 ± 0.01 (protein percentage) and feed-efficiency traits by 0.07 ± 0.02 (milk energy), 0.03 ± 0.02 (DMI), and 0.08 ± 0.01 (metabolic body weight). Modeling herd-specific marker effects further improved mean within-herd prediction accuracy for milk yield and energy by 0.03 ± 0.01 and 0.02 ± 0.01, respectively. Herds with higher within-herd heritability and low genomic correlation with the remaining herds benefitted most from the inclusion of herdmate data.

Heritability of metabolic traits associated with equine metabolic syndrome in Welsh ponies and Morgan horses.

BACKGROUND: Equine metabolic syndrome (EMS) is a complex clinical disorder with both environmental and genetic factors contributing to EMS phenotypes. Estimates of heritability determine the proportion of variation in a trait that is attributable to genetics. OBJECTIVES: To provide heritability estimates for nine metabolic traits associated with EMS in two high-risk breeds. STUDY DESIGN: Retrospective cohort study. METHODS: High-density single-nucleotide polymorphism (SNP) genotype data was used to estimate the heritability (h2 SNP ) of nine metabolic traits relevant to EMS in a cohort of 264 Welsh ponies and 286 Morgan horses. Traits included measurements of insulin, glucose, non-esterified fatty acids (NEFA), triglycerides, leptin, adiponectin, ACTH, and glucose (GLU-OST) and insulin (INS-OST) following an oral sugar challenge. RESULTS: In Welsh ponies, seven of the nine traits had statistically significant h2 SNP estimates that were considered moderately to highly heritable (h2 SNP >0.20) including: triglycerides (0.313; s.e. = 0.146), glucose (0.408; s.e. = 0.135), NEFA (0.434; s.e. = 0.136), INS-OST (0.440; s.e. = 0.148), adiponectin (0.488; s.e. = 0.143), leptin (0.554; s.e. = 0.132) and insulin (0.808; s.e. = 0.108). In Morgans, six of the nine traits had statistically significant h2 SNP estimates that were also determined to be moderately to highly heritable including: INS-OST (0.359; s.e. = 0.185), leptin (0.486; s.e. = 0.177), GLU-OST (0.566 s.e. = 0.175), insulin (0.592; s.e. = 0.195), NEFA (0.684; s.e. = 0.164), and adiponectin (0.913; s.e. = 0.181). MAIN LIMITATIONS: Insufficient population size may have limited power to obtain statistically significant h2 SNP estimates for ACTH (both breeds), glucose and triglycerides in Morgans and GLU-OST in Welsh ponies. CONCLUSIONS: This study provides the first concrete evidence of a genetic contribution to key phenotypes associated with EMS. Eight of these nine traits had moderate to high h2 SNP estimates in this cohort. These data demonstrate that continued research for identification of the genetic risk factors for EMS phenotypes within and across breeds is warranted.

Associations between endocrine disrupting chemicals and equine metabolic syndrome phenotypes.

Equine Metabolic Syndrome (EMS) is characterized by abnormalities in insulin regulation, increased adiposity and laminitis, and has several similarities to human metabolic syndrome. A large amount of environmental variability in the EMS phenotype is not explained by commonly measured factors (diet, exercise, and season), suggesting that other environmental factors play a role in EMS development. Endocrine disrupting chemicals (EDCs) are associated with metabolic syndrome and other endocrine abnormalities in humans. This led us to hypothesize that EDCs are detectable in horse plasma and play a role in the pathophysiology of EMS. EDCs acting through the aryl hydrocarbon and estrogen receptors, were measured in plasma of 301 horses from 32 farms. The median (range) TEQ (2,3,7,8-TCDD equivalent) and EEQ (17ß-estradiol equivalent) were 19.29 pg/g (0.59-536.36) and 10.50 pg/ml (4.35-15000.00), respectively. TEQ was negatively associated with plasma fat extracted and batch analyzed. EEQ was positively associated with pregnancy and batch analyzed, and negatively associated with being male and superfund score ≤100 miles of the farm. Of particular interest, serum glucose and insulin, glucose and insulin post oral sugar challenge, and leptin concentrations were associated with EEQ, and serum triglyceride concentration was associated with TEQ. Overall, we demonstrated that EDCs are present in the plasma of horses and may explain some of the environmental variability in measured EMS phenotypes. This is the first example of EDCs being associated with clinical disease phenotype components in domestic animals.

Equine multiple acyl-CoA dehydrogenase deficiency (MADD) associated with seasonal pasture myopathy in the midwestern United States.

BACKGROUND: Seasonal pasture myopathy (SPM) is a highly fatal form of nonexertional rhabdomyolysis that occurs in pastured horses in the United States during autumn or spring. In Europe, a similar condition, atypical myopathy (AM), is common. Recently, a defect of lipid metabolism, multiple acyl-CoA dehydrogenase deficiency (MADD), has been identified in horses with AM. OBJECTIVE: To determine if SPM in the United States is caused by MADD. ANIMALS: Six horses diagnosed with SPM based on history, clinical signs, and serum creatine kinase activity, or postmortem findings. METHODS: Retrospective descriptive study. Submissions to the Neuromuscular Diagnostic Laboratory at the University of Minnesota were reviewed between April 2009 and January 2010 to identify cases of SPM. Inclusion criteria were pastured, presenting with acute nonexertional rhabdomyolysis, and serum, urine, or muscle samples available for analysis. Horses were evaluated for MADD by urine organic acids, serum acylcarnitines, muscle carnitine, or histopathology. RESULTS: Six horses had clinical signs and, where performed (4/6 horses), postmortem findings consistent with SPM. Affected muscle (4/4) showed degeneration with intramyofiber lipid accumulation, decreased free carnitine concentration, and increased carnitine esters. Serum acylcarnitine profiles (3/3) showed increases in short- and medium-chain acylcarnitines and urinary organic acid profiles (3/3) revealed increased ethylmalonic and methylsuccinic acid levels, and glycine conjugates, consistent with equine MADD. CONCLUSIONS AND CLINICAL IMPORTANCE: Similar to AM, the biochemical defect causing SPM is MADD, which causes defective muscular lipid metabolism and excessive myofiber lipid content. Diagnosis can be made by assessing serum acylcarnitine and urine organic acid profiles.

Potentiation of atracurium toxicity in isolated rat hepatocytes by inhibition of its hydrolytic degradation pathway.

This study tested the hypothesis that the esters of acrylic acid might be responsible for the previously observed cytotoxic effect of atracurium. Rats were pretreated with triorthotolyl phosphate (TOTP), an inhibitor of the hydrolytic degradation of atracurium. Because hydrolysis of acrylates is also inhibited by TOTP and because the hydrolysis represents a detoxification pathway for these esters, we postulated that the leak of lactic dehydrogenase (LDH) induced by atracurium would be enhanced in hepatocytes harvested from rats pretreated with TOTP. Hepatocytes isolated from rats previously treated with TOTP (25 or 50 mg/kg intraperitoneally, 20 hr before induced death) were incubated for 4 hr in the absence of muscle relaxants or in the presence of either atracurium (0.008-0.8 mM) or metocurine (0.015-0.85 mM). Atracurium produced a concentration-dependent leakage of LDH. The leakage out of cells obtained from TOTP-pretreated rats was greater than was the leakage out of hepatocytes harvested from animals pretreated only with corn oil (a vehicle for TOTP). Metocurine did not produce a leak of LDH. It is concluded that the LDH leakage was produced by ester-type products of atracurium degradation. Acrylates appear to be the toxic agent.

Mechanisms of chloroform and carbon tetrachloride toxicity in primary cultured mouse hepatocytes.

Mechanisms of chloroform (CHCl3) and carbon tetrachloride (CCl4) toxicity to primary cultured male B6C3F1 mouse hepatocytes were investigated. The cytotoxicity of both CHCl3 and CCl4 was dose- and duration-dependent. Maximal hepatocyte toxicity, as determined by lactate dehydrogenase leakage into the culture medium, occurred with the highest concentrations of CHCl3 (5 mM) and CCl4 (2.5 mM) used and with the longest duration of treatment (20 hr). CCl4 was approximately 16 times more toxic than CHCl3 to the hepatocytes. The toxicity of these compounds was decreased by adding the mixed function oxidase system (MFOS) inhibitor, SKF-525A (25 microM) to the cultures. The addition of diethyl maleate (0.25 mM), which depletes intracellular glutathione (GSH)-potentiated CHCl3 and CCl4 toxicity. The toxicity of CHCl3 and CCl4 could also be decreased by adding the antioxidants N,N'-diphenyl-p-phenylenediamine (DPPD) (25 microM), alpha-tocopherol acetate (Vitamin E) (0.1 mM), or superoxide dismutase (SOD) (100 U/mL) to the cultures. These results suggest that: in mouse hepatocytes, both CHCl3 and CCl4 are metabolized to toxic components by the MFOS; GSH plays a role in detoxifying those metabolites; free radicals are produced during the metabolism of CHCl3 and CCl4; and free radicals may be important mediators of the toxicity of these two halomethanes.

Comparative toxicity of atracurium and metocurine in isolated rat hepatocytes.

Primary cultures of liver cells isolated from seven rats were used to study the possible toxicity of atracurium and metocurine. The muscle relaxants were separately added to the culture medium and the cells then incubated for 4 hr. The amount of lactic dehydrogenase (LDH) that leaked into the culture medium was determined at the end of incubation. The customary assumption was made that the exudation of LDH reflects the toxic effects of the relaxants. In untreated dishes, approximately 11% of the total intracellular LDH leaked out during the incubation. The net leakage of LDH produced by the relaxants was obtained by subtracting this amount from the LDH activity determined in the media of dishes with the relaxants added. On this basis, metocurine, in concentrations of 12-850 X 10(-6)M, did not cause a net leak of LDH. On the other hand, atracurium, in similar molar concentrations, caused a statistically significant and concentration-dependent leak of LDH that, at its maximum, amounted to more than one half of the intracellular LDH. The results are interpreted in terms of damage to cellular membranes produced by atracurium or its metabolites. Although the exact biochemical process was not identified, we hypothesize that acrylates--produced by Hofmann elimination from atracurium--might be the likely toxic species.