Schiff-base cross-linked pullulan-chondroitin sulfate hydrogel incorporating raloxifene-poly(2-methyl-2-oxazoline) micelles for localized therapy of postmenopausal osteoarthritis

Postmenopausal osteoarthritis (OA) is a degenerative joint disorder characterized by cartilage erosion and subchondral bone loss, intensified by estrogen deficiency in menopausal women. Raloxifene (RLX), a selective estrogen receptor modulator, shows anti-inflammatory and chondroprotective potential but is associated with limited oral bioavailability (~2%) and systemic side effects. Therefore, in the present investigation, raloxifene-conjugated poly(2-methyl-2-oxazoline) micelles hybridized self-cross-linking hydrogel (R-PMeOZ@SCH) was engineered for intra-articular therapy. Next, the R-PMeOZ micelles exhibited a narrow particle size distribution with an average hydrodynamic diameter of 147.63 ± 0.66 nm, a polydispersity index (PDI) of 0.14 ± 0.01, and a ζ-potential of -7.33 ± 1.75 mV. The hydrogel was synthesized via Schiff-base reaction between oxidized pullulan (OxyPul) and chondroitin sulfate-adipic hydrazide (CSADH), enabling controlled release and site-specific delivery. R-PMeOZ@SCH demonstrated suitable rheology, swelling, and controlled release profile for intra-articular administration. In a postmenopausal OA rats treated with R-PMeOZ@SCH demonstrated a progressive improvement in motor coordination, cartilage integrity, subchondral bone architecture and reduced inflammatory cytokine levels compared to disease control. X-ray and μ-CT analyses unveiled improvement in articular space width and reduction in Kellgren-Lawrence score for R-PMeOZ@SCH treated group compared to the disease control. It also reduced mRNA expression of MMP-9, ADAMTS-4, and ADAMTS-5 by 5.89, 2.54, and 7.12-fold, respectively, compared to disease control. Histological evaluation demonstrated a significant reduction in OARSI and modified Mankin's scores and an improvement in relative GAG level in comparison to disease control, highlighting the disease-modifying potential of R-PMeOZ@SCH for clinical translation.