Resolvin D1-loaded Liposomal Nanocarriers for the Treatment of Osteoarthritis
Osteoarthritis (OA) is the most common disorder of the joints and currently affects >300 million patients worldwide. In this disease, the articulating cartilage undergoes progressive damage which leads to severe pain and loss of function. Current treatment for OA does not target the etiology of the disease but instead focuses only on alleviating pain by administration of steroidal analgesics. Steroidal analgesics are not ideal for the long-term treatment of the disease because they generate chronic chondrotoxicity and cartilage thinning. Eventually, as the disease progresses towards severe stages, the patients have to undergo a highly invasive and costly joint replacement surgery. Currently, there is no disease-modifying OA drug (DMOAD) approved for human use. OA-associated damage is driven by chronic low-grade inflammation, and several cells are involved in the cross-talk that contributes to the inflammation. Targeting the OA-related chronic inflammation using antagonists and antibodies against inflammatory cytokines is a viable strategy to treat OA and has shown promise in pre-clinical trials. However, previous attempts to deliver anti-inflammatory molecules to the site of damage did not translate into therapy for humans. The failure of these trials can be attributed to the fast clearance of the small molecules by synovial vasculature and of the macromolecules by the lymphatics, which results in short half-lives in the joint (1- 4h) for commonly used steroids. The limiting in vivo half-lives of small-molecule drugs can be extended by encapsulating the molecules in particle-based systems. Liposomes are ideal for efficient delivery because of their biodegradability, low toxicity, stability, flexible synthesis methods, and ability to incorporate versatile cargo. Specialized proresolution mediators (SPMs) are potent molecules that actively reduce inflammatory factors from the site of damage in a process called resolution of inflammation. Chronic inflammatory diseases, including OA, are known to have impaired inflammation resolution pathways. Exogenously supplied SPMs like Resolvin D1 (RvD1) reduce the severity of OA, but strategies involving the direct IA injection of such molecules require administration of doses before OA-causing injury has taken place. In this study, we generate a liposomal-RvD1(lipo-RvD1) formulation to increase the bioavailability of the molecule in the pathology-affected joint. Liposomes were actively loaded with RvD1 using a pH gradient strategy. This formulation was stable and acted as a source of RvD1 for ~11 days in vitro in near-physiological conditions. We evaluated the prophylactic efficacy of our formulation in the widely used, Destabilization of Medial Meniscus (DMM) mouse model of OA. Our histology results show that only lipo-RvD1 treated joints reduced the severity of OA, whereas free RvD1 did not have any protective effect on the joint. We conducted the same experiment in an obesity-related OA model in mice to reproduce the contribution of obesity to the pathology of the disorder. The pathology of obesity-related OA is much more severe due to the contribution of adipose tissue to OA-associated inflammation. In this model also, only the lipo-RvD1 treated joints had shown efficacy whereas free-RvD1 had no protective effect on the joint. The results from the latter model established the ability of lipo-RvD1 to treat diseases in diverse stages of progression. Most OA patients report to the clinics in the later stages of the disease. Thus, there is a requirement for a good therapeutic agent for the treatment of OA. In the therapeutic study, we administered the formulation to the animals after significant damage is known to have ensued. Lipo-RvD1 treated joints showed much healthier articular cartilage compared to free-RvD1 and surgery-only joints in both mouse models. We observed that administration of lipo-RvD1 was more effective in alleviating the allodynia than DMM mice and free RvD1 injected mice in the therapeutic regimen of administration. Our results show that the sustained presence of RvD1 in the affected knee joint helps alleviate OA-associated pain.