Initial Harm Reduction by N-Acetylcysteine Alleviates Cartilage Degeneration after Blunt Single-Impact Cartilage Trauma in Vivo

Abstract

Joint injuries are highly associated with the development of post-traumatic osteoarthritis. Previous studies revealed cell- and matrix-protective effects of N-acetylcysteine (NAC) after ex vivo cartilage trauma, while chondroanabolic stimulation with bone morphogenetic protein 7 (BMP7) enhanced type II collagen (COL2) expression. Here, as a next step, we investigated the combined and individual efficacy of intra-articular antioxidative and chondroanabolic treatment in a rabbit in vivo cartilage trauma model. Animals were randomly divided into group A (right joint: trauma (T); left joint: T+BMP7) and group B (right joint: T+NAC; left joint: T+BMP7+NAC). Condyles were impacted with the use of a spring-loaded impact device to ensure defined, single trauma administration. After 12 weeks, histopathological analysis was performed and the presence of matrix metalloproteinase 13 (MMP-13) and COL2 was assessed. Trauma-induced hypocellularity, MMP-13 expression, and cell cluster formation were reduced in NAC-treated animals. In contrast, BMP7 further increased cluster formation. Moreover, synovial concentrations of COL2 carboxy propeptide (CPII) and proteoglycan staining intensities were enhanced in NAC- and NAC+BMP7-treated joints. For the first time, the efficacy of NAC regarding early harm reduction after blunt cartilage trauma was demonstrated in vivo. However, parallel administration of BMP7 was not significantly superior compared to NAC alone.

Pathomechanisms of Posttraumatic Osteoarthritis: Chondrocyte Behavior and Fate in a Precarious Environment

“…In general, chondrocyte death leads to hypocellularity, which not only comes along with reduced capacities for ECM production, but also promotes cell cluster formation, which is commonly regarded as a possible compensatory response of the cells. In our rabbit in vivo cartilage trauma model, severe hypocellularity was observed 12 weeks after traumatic impact of about 1.0 J, though occasional proliferation was found as indicated by cell cluster formation [124,125]. Comparable findings could be demonstrated in our human ex vivo cartilage trauma model after an impact of 0.59 J; trauma-related cell loss at day 7 after impact was sort of compensated by cluster formation as shown at day 14 [66].…”

“…The following in vivo study confirmed, that combination of BMP7 and NAC did not result in more beneficial effects as compared to the monotherapeutic approaches [124]. Although we expected that the efficacy of the growth factors would be enhanced with respect to the NAC-mediated clearance of ROS and NO, we rather observed mutual interference between the therapeutic substances to some extent [66,124]. These experiences led to the conclusion that a sequential application-that first aims at initial harm reduction by addressing the upstream events and respective effector molecules, thus paving the path for a subsequent chondroanabolic stimulation-might provide a more promising outcome [22,66].…”

“…However, multidirectional therapeutic strategies do not generally result in additive or synergic effects as we observed in practice: While BMP7 and IGF-1 exhibited significant chondroanabolic features after cartilage trauma and during chondrogenic differentiation of CSPC [22,66], combination with chondro-and cell protective NAC revealed a thoroughgoing suppression of aggrecan and collagen type II synthesis [66]. The following in vivo study confirmed, that combination of BMP7 and NAC did not result in more beneficial effects as compared to the monotherapeutic approaches [124]. Although we expected that the efficacy of the growth factors would be enhanced with respect to the NAC-mediated clearance of ROS and NO, we rather observed mutual interference between the therapeutic substances to some extent [66,124].…”

“…On one hand, the cell clusters might contribute little to the actual regeneration of the cartilage since the cells produce an inferior repair tissue, containing collagen type X [126], and express rather hypertrophic and osteogenic markers, respectively, such as Runx2 [127], osteocalcin [128] and osteopontin [129]. Moreover, the cells are associated with excessive expression of detrimental cytokines, FGF2 and MMP-13 [124,127,130]. On the other hand, studies have demonstrated the enhanced expression of chondroanabolic and stem cell-associated markers, respectively, implying a regenerative potential of the proliferating cells [131,132].…”

“…Oxidative stress ROS/NO generation NAC [38,66,124]; rotenone [175]; resveratrol [176]; catalpol [177];…”