Evaluation of conjugated linoleic acid supplementation on markers of joint inflammation and cartilage metabolism in young horses challenged with lipopolysaccharide

Abstract

Seventeen yearling Quarter Horses were used in a randomized complete block design for a 56-d trial to determine ability of dietary CLA to mitigate joint inflammation and alter cartilage turnover following an inflammatory insult. Horses were blocked by age, sex, and BW, and randomly assigned to dietary treatments consisting of commercial concentrate offered at 1% BW (as-fed) supplemented with either 1% soybean oil (CON; n = 6), 0.5% soybean oil and 0.5% CLA (LOW; n = 5; 55% purity; Lutalin, BASF Corp., Florham Park, NJ), or 1% CLA (HIGH; n = 6) top-dressed daily. Horses were fed individually every 12 h and offered 1% BW (as-fed) coastal bermudagrass (Cynodon dactylon) hay daily. This study was performed in 2 phases: phase I (d 0 to d 41) determined incorporation of CLA into plasma and synovial fluid; phase II (d 42 to d 56) evaluated potential of CLA to mitigate intra-articular inflammation and alter cartilage metabolism. Blood and synovial fluid were collected at 7- and 14-d intervals, respectively, to determine fatty acid concentrations. On d 42, carpal joints within each horse were randomly assigned to receive intra-articular injections of 0.5 ng lipopolysaccharide (LPS) derived from Escherichia coli 055:B5 or sterile lactated Ringer's solution. Synovial fluid samples were obtained at preinjection h 0 and 6, 12, 24, 168, and 336 h postinjection, and analyzed for prostaglandin E2 (PGE2), carboxypeptide of type II collagen (CPII), and collagenase cleavage neopeptide (C2C). Data were analyzed using PROC MIXED procedure of SAS. Horses receiving the CON diet had undetectable levels of CLA for the duration of the study. A quadratic dose response was observed in concentrations of CLA in plasma and synovial fluid (P < 0.01). A negative quadratic dose response was observed for plasma arachidonic acid (20:4) with a reduction in concentration to d 14 in HIGH horses (P = 0.04). Synovial fluid 20:4 tended to decrease in horses receiving the HIGH diet (P = 0.06). Post LPS injection, synovial PGE2 was not affected by dietary treatment (P = 0.15). Synovial C2C was lower in HIGH horses (P = 0.05), and synovial CPII tended to be greater in LOW horses than HIGH and CON horses (P = 0.10). In conclusion, dietary CLA incorporated into plasma and synovial fluid prior to LPS challenge. Dietary CLA did not influence inflammation; however, there was a reduction in cartilage degradation and an increase in cartilage regeneration.

Figure 1.

Clinical assessment of HR (panel A), RR (panel B), and RT (panel C) after intra-articular LPS (derived from Escherichia coli O55:B5) injection. Treatments were 1% diet soybean oil (CON; n = 6), 0.5% diet soybean oil with 0.5% diet CLA (LOW; n = 5), and 1% diet CLA (HIGH; n = 6).

Figure 2.

Carpal joint circumference (cm; least squares mean ± SEM) after intra-articular LPS (derived from Escherichia coli O55:B5) injection at preinjection h 0 and 6, 12, 24, 168, and 336 h postinjection. Treatments were 1% diet soybean oil (CON; n = 6), 0.5% diet soybean oil with 0.5% diet CLA (LOW; n = 5), and 1% diet CLA (HIGH; n = 6). Main effects include dietary treatment (P = 0.74) and time (P < 0.01).

Figure 3.

Carpal joint surface temperature (°C; least squares mean ± SEM) at preinjection h 0 and 6, 12, 24, 168, and 336 h post LPS injection. Treatments were 1% diet soybean oil (CON; n = 6), 0.5% diet soybean oil with 0.5% diet CLA (LOW; n = 5), and 1% diet CLA (HIGH; n = 6). Main effects include dietary treatment (P = 0.12) and time (P < 0.01).

Figure 4.

Mean synovial fluid concentrations (pg/mL) of PGE₂ over time (h) after intra-articular injection of 0.5 ng LPS or 0.8 mL sterile lactated Ringer’s solution (LRS). Main effect includes LPS (P = 0.01). ^a,bSuperscript denotes difference between knee (P < 0.05).

Figure 5.

Mean synovial fluid concentrations (ng/mL) of C2C over time (h) after intra-articular injection of 0.5 ng LPS (panel A; LPS; derived from Escherichia coli 055:B5) or 0.8 mL sterile lactated Ringer’s solution (panel B; LRS). Treatments were 1% diet soybean oil (CON; n = 6), 0.5% diet soybean oil with 0.5% diet CLA (LOW; n = 5), and 1% diet CLA (HIGH; n = 6). Main effects include dietary treatment (P = 0.05), time (P < 0.01), and LPS (P = 0.08). ^a,bSupersripts denote differences between dietary treatments (P < 0.05).

Figure 6.

Mean synovial fluid concentrations (ng/mL) of CPII after intra-articular injection of 0.5 ng LPS (panel A; LPS; derived from Escherichia coli O55:B5) or 0.8 mL sterile lactated Ringer’s solution (panel B; LRS). Treatments were 1% diet soybean oil (CON; n = 6), 0.5% diet soybean oil with 0.5% diet CLA (LOW; n = 5), and 1% diet CLA (HIGH; n = 6). Main effects include dietary treatment (P = 0.10), time (P < 0.01), and LPS (P = 0.06). ^a,bSupersripts denote differences between dietary treatments (P < 0.05).