Background: Lubricin, or proteoglycan 4 (PRG4), is a glycoprotein responsible for joint boundary lubrication. PRG4 has been shown previously to be down-regulated after traumatic joint injury such as a meniscal tear. Preliminary evidence suggests that intra-articular injection of PRG4 after injury will reduce cartilage damage in rat models of surgically induced posttraumatic osteoarthritis.
Objective: To determine the efficacy of intra-articular injection of full-length recombinant human lubricin (rhPRG4) for reducing cartilage damage after medial meniscal destabilization (DMM) in a preclinical large animal model.
Study design: Controlled laboratory study.
Methods: Unilateral DMM was performed in 29 Yucatan minipigs. One week after DMM, animals received 3 weekly intra-articular injections (3 mL per injection): (1) rhPRG4 (1.3 mg/mL; n = 10); (2) rhPRG4+hyaluronan (1.3 mg/mL rhPRG4 and 3 mg/mL hyaluronan [~950 kDA]; n = 10); and (3) phosphate-buffered saline (PBS; n = 9). Hindlimbs were harvested 26 weeks after surgery. Cartilage integrity was evaluated by use of macroscopic (India ink) and microscopic (safranin O-fast green and hematoxylin and eosin) scoring systems. Secondary outcomes evaluated via enzyme-linked immunosorbent assay (ELISA) included PRG4 levels in synovial fluid, carboxy-terminal telepeptide of type II collagen (CTX-II) concentrations in urine and serum, and interleukin 1β (IL-1β) levels in synovial fluid and serum.
Results: The rhPRG4 group had significantly less macroscopic cartilage damage in the medial tibial plateau compared with the PBS group ( P = .002). No difference was found between the rhPRG4+hyaluronan and PBS groups ( P = .23). However, no differences in microscopic damage scores were observed between the 3 groups ( P = .70). PRG4 production was elevated in the rhPRG4 group synovial fluid compared with the PBS group ( P = .033). The rhPRG4 group presented significantly lower urinary CTX-II levels, but not serum levels, when compared with the PBS ( P = .013) and rhPRG4+hyaluronan ( P = .011) groups. In serum and synovial fluid, both rhPRG4 ( P = .006; P = .017) and rhPRG4+hyaluronan groups ( P = .009; P = .03) presented decreased IL-1β levels.
Conclusion: All groups exhibited significant cartilage degeneration after DMM surgery. However, animals treated with rhPRG4 had the least amount of cartilage damage and less inflammation, providing evidence that intra-articular injections of rhPRG4 may slow the progression of posttraumatic osteoarthritis.
Clinical relevance: Patients with meniscal trauma are at high risk for posttraumatic osteoarthritis. This study demonstrates that an intra-articular injection regimen of rhPRG4 may attenuate cartilage damage after meniscal injury.
Keywords: PRG4; hyaluronan; inflammation; lubricin; meniscus; osteoarthritis.