Age-related effects on markers of inflammation and cartilage metabolism in response to an intra-articular lipopolysaccharide challenge
Eighteen Quarter Horses were utilized in a randomized complete design to evaluate age-related effects on inflammation and cartilage turnover after induction of a single inflammatory insult using lipopolysaccharide (LPS). Treatments consisted of age with yearlings (n = 3 males, n = 3 females), 2/3 yr olds (n = 2 males, n = 4 females), or mature 5 to 8 yr olds (n = 2 males, n = 4 females) for a 14 d experiment. For 14 d prior to the start of the experiment all horses were housed in individual stalls and fed diets that met or exceeded NRC (2007) requirements. On d 0, horses were challenged with an intra-articular injection of LPS. Radial carpal joints were randomly assigned to receive LPS using 0.5 ng LPS solution obtained from Escherichia coli O55:B5, or sterile lactated Ringer’s solution as a contralateral control. Synovial fluid was collected prior to LPS injection (0 h) and 6, 12, 24, 168, and 336 h post-injection. Samples were later analyzed using commercial ELISA kits for prostaglandin E2 (PGE2), collagenase cleavage neoepitope (C2C), and carboxypeptide of type II collagen (CPII). Rectal temperature (RT), heart rate (HR), and respiratory rate (RR) were monitored prior to sample collection over the first 24 h, and carpal circumference and joint surface temperature were recorded. Data were analyzed using PROC MIXED procedure of SAS. All values for RT, HR, and RR were within normal range and unaffected by treatment (P ≤ 0.21). Joint circumference was not influenced by treatment (P = 0.84), but circumference and surface temperature increased (P ≤ 0.01) across all treatments in response to intra-articular LPS. Synovial PGE2 levels were influenced by age with yearlings tending to have lesser (P = 0.09) values than 2/3 yr olds and mature horses. This was particularly evident at 12 h when PGE2 values peaked for all horses and yearlings had lesser values (P ≤ 0.01) than mature horses. Synovial C2C was influenced by treatment with yearlings and 2/3 yr olds having lesser (P ≤ 0.01) concentrations than mature horses. Synovial CPII was influenced by treatment at 24, 168 and 336 h with yearlings having lesser concentrations (P ≤ 0.01, P ≤ 0.06, and P ≤ 0.03, respectively) compared to 2/3 yr olds and mature horses. These results indicate that inflammation and corresponding cartilage turnover in response to LPS administration vary with age.
Keywords: LPS, horse, synovial fluid, PGE2, CPII, C2C