Abstract: Recent studies associate obesity and insulin resistance in horses with development of abnormal reproductive function and debilitating laminitis. The factors contributing to insulin resistance in obese horses are unknown. However, human studies provide evidence that elevated inflammatory cytokines such as tumor necrosis factor alpha (TNFalpha), IL1, and IL6 play direct roles in development of obesity-associated insulin resistance. Thus, inflammation may be a key link between obesity and insulin resistance in horses. The aim of the current investigation was to examine possible relationships between obesity, inflammatory cytokines, and insulin sensitivity (IS) in the horse. Age was recorded and BCS and percent body fat (% FAT) were determined as measures of obesity in 60 mares. In addition, blood mRNA expression of IL1, IL6, and TNFalpha and circulating concentrations of TNFalpha protein (TNFp) were determined in each mare. Finally, fasted concentrations of insulin were determined, and IS was determined using the hyperinsulinemic, euglycemic clamp. Significant correlations between several variables provided evidence for the design of 4 population regression models to estimate relationships between measures of obesity, inflammatory factors, and IS in the sample population. The results of these analyses revealed that IS decreased as BCS and % FAT increased (P < 0.001) in the sample population. Additionally, increased IL1 (P < 0.05) and TNFp (P < 0.01) were associated with decreased IS. However, increased TNFalpha (P < 0.001) was associated with decreased IS only in mares 20 yr of age and older. Increased BCS and % FAT were associated with increased expression of TNFalpha (P = 0.053) and IL1 (P < 0.05), and increased TNFp (P < 0.05). Surprisingly, increased BCS and % FAT were associated with decreased IL6 expression (P = 0.05) in mares <20 yr of age. Finally, evaluation of the influence of obesity and inflammatory cytokines on IS within the same model suggested that BCS and % FAT (P < 0.001) with TNFalpha [mRNA (P = 0.07) and protein (P < 0.05)] are inversely associated with IS independently of one another. Combined, these results provide the first evidence associating obesity with increased inflammatory factors in the horse. Furthermore, the results suggest that an interrelationship exists among obesity, inflammatory cytokines, and IS in the horse and emphasize the need for further studies to elucidate the nature of these relationships.
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This research paper investigates the connection between obesity, inflammation, and insulin sensitivity in horses, concluding that obesity is linked with increased inflammatory factors in horse populations, affecting insulin sensitivity differently depending on the horses’ age.
Study Methodology
The study involved 60 mares whose age, Body Condition Score (BCS), and body fat percentage (% FAT) were recorded.
The team determined the mRNA expression levels of inflammatory cytokines IL1, IL6, and tumor necrosis factor alpha (TNFalpha) in each horse’s blood.
The TNFalpha protein (TNFp) circulating concentrations and fasting insulin concentrations were also determined.
The insulin sensitivity (IS) of the horses was ascertained through the hyperinsulinemic, euglycemic clamp method.
Four population regression models were designed to determine the relationships between variables of obesity, inflammatory factors, and insulin sensitivity.
Study Findings
The insulin sensitivity was found to decrease as body condition score and fat percentages increased.
Increased IL1 and TNFp levels were associated with a reduction in insulin sensitivity.
Higher TNFalpha levels were correlated with decreased insulin sensitivity in horses aged 20 years and above.
Increased BCS and % FAT were related to an increase in expression of TNFalpha and IL1, and increased TNFp.
However, BCS and % FAT were linked with decreased IL6 expression in horses aged under 20 years.
BCS and % FAT, with TNFalpha were identified as inversely affecting insulin sensitivity.
Implication and Conclusion
The significant correlation found in this research forms the first evidence of obesity in horses being linked with increased inflammatory factors.
Therefore, it is believed that an interlinking relationship exists among obesity, inflammatory cytokines, and insulin sensitivity in horses.
The study concludes by emphasizing the need for further research to understand the intricate nature of these relationships.
Cite This Article
APA
Vick MM, Adams AA, Murphy BA, Sessions DR, Horohov DW, Cook RF, Shelton BJ, Fitzgerald BP.
(2007).
Relationships among inflammatory cytokines, obesity, and insulin sensitivity in the horse.
J Anim Sci, 85(5), 1144-1155.
https://doi.org/10.2527/jas.2006-673
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