Age-Related Effects on Markers of Inflammation and Cartilage Metabolism in Response to an Intra-Articular Lipopolysaccharide Challenge

Abstract

Eighteen Quarter Horses were utilized in a randomized complete design for a 28 d experiment to evaluate age-related effects on inflammation and cartilage turnover after induction of a single inflammatory insult using lipopolysaccharide (LPS). Horses were grouped by age, with yearlings (yearling; n = 3 males, n = 3 females), 2 to 3 yr olds (2/3; n = 2 males, n = 4 females), and mature 5 to 8 yr olds (mature; n = 2 males, n = 4 females). On d 0, all horses were housed individually and fed diets that met or exceeded NRC (2007) requirements. On d 14, horses were challenged with an intra-articular injection of LPS. Carpal joints were randomly assigned to receive 0.5 ng LPS solution obtained from E. coli O55:B5, or 0.8mL sterile lactated Ringer?s solution as a contralateral control. Synovial fluid was collected prior to LPS injection at pre-injection h 0 (PIH 0) 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 carboxypropeptide of type II collagen (CPII). Heart rate (HR), respiratory rate (RR), and rectal temperature (RT) were monitored over the first 24 h and carpal circumference and surface temperature were recorded with additional measurements at 168 and 336 h. Data were analyzed using PROC MIXED procedure of SAS.

Values for RT, HR, and RR were within normal range. HR and RT were influenced by age (P < 0.01), while RR was unaffected by age (P ? 0.21). Joint circumference was not influenced by age (P = 0.84), but circumference and surface temperature increased (P < 0.01) over time across all age groups. Synovial PGE2 concentrations tended (P = 0.09) to be influenced by age with yearlings having lower (P = 0.03) concentrations than mature horses. Synovial C2C concentrations were affected by age with yearlings and 2/3 yr olds having lower (P < 0.01) concentrations than mature horses. Concentrations of synovial CPII were influenced by age with yearlings and 2/3 yr old having lower (P ? 0.02) concentrations than mature horses. Ratios of CPII:C2C were influenced by age with mature and 2/3 yr old horses having increased (P < 0.01) values compared to yearlings. These results indicate that inflammation and corresponding cartilage turnover in response to LPS administration vary with age.