Nitric oxide inhibits aggrecan degradation in explant cultures of equine articular cartilage.

The research explores the role of nitric oxide (NO) in suppressing the degradation of a main component of cartilage, aggrecan, thereby suggesting its potential protective effect against arthritis, a joint disease that causes cartilage loss.

Understanding the Problem

• Arthrosis is a group of diseases that impair joints by causing the disintegration of articular cartilage, a rubber-like substance that cushions the joints.
• While the inflammatory compound nitric oxide (NO) is known to intensify the effects of interleukin-1 (IL-1), an inflammation-promoting compound associated with arthritis, its role in controlling proteoglycan (a family of proteins including aggrecan) degradation in joint cartilage was previously unexplored.

Research Methodology

• The researchers tested the effect of NO on proteoglycan synthesis (creation) and degradation (breakdown) in equine cartilage. They studied the impact of NO whether degradation was triggered by IL-1 or all-trans retinoic acid (RA).
• To observe the action of NO precisely, the investigators used an NO donor, DETA-NONOate, and an iNOS inhibitor, L-NIO. This allowed them to manipulate levels of NO in their samples.

Findings

• NO fully mediated the influence of IL-1 in reducing proteoglycan synthesis. However, NO also combated proteoglycan degradation regardless of the initiating compound, displaying an anticatabolic role.
• In the presence of exogenous (externally sourced) NO, there was less ‘aggrecanase’ cleavage epitope, an indication of aggrecan breakdown, suggesting that NO lowers aggrecan degradation.
• Changes in the appearance of G1 fragment expressing the ‘aggrecanase’ cleavage epitope in media paralleled the decrease in glycosaminoglycan, a component of aggrecan, in the tissue.

Implications

• These findings support the idea that NO could have an protective role in the degradation of cartilage proteoglycans, specifically aggrecan.
• In arthritis treatment, NO could serve as a target for drug design. However, its dual roles – both destructive (catabolic) and protective (anticatabolic) – in joint tissue turnover should be considered during pharmacological interventions.