Targeting Celastrol Delivery to Inflamed Joints in Rheumatoid Arthritis

Celastrol has anti-inflammatory, antioxidant, and immunomodulatory activity that could be useful in rheumatoid arthritis (RA), but its poor water solubility, low bioavailability, and dose-dependent toxicity have limited its therapeutic potential. Because of this, Shen and colleagues explored whether a targeted drug-delivery system could address these limitations by packaging celastrol in folate-modified liposomes (FA-Cel-LPs). The rationale centers on folate receptor–mediated targeting: activated macrophages involved in RA synovial inflammation express high levels of folate receptor beta, potentially allowing folate-coated liposomes to preferentially deliver their payload to inflamed joints.

Building and Testing a Targeted Nanocarrier

The investigators prepared FA-Cel-LPs using thin-film hydration and extrusion and evaluated their physicochemical properties, cellular effects, joint localization, therapeutic activity, and preliminary safety. The formulation had a mean particle size of 110.65 nm and an encapsulation efficiency of 84.67%. It also remained stable during two weeks of storage and demonstrated sustained celastrol release, with somewhat greater release under acidic conditions that may resemble the inflammatory joint microenvironment.

Cellular experiments used lipopolysaccharide (LPS)-activated RAW264.7 macrophages. The investigators then extended their evaluation to a collagen-induced arthritis (CIA) rat model. Thirty male Sprague-Dawley rats were randomly assigned to five groups of six: healthy control, untreated CIA, free celastrol, non-targeted celastrol liposomes, or FA-Cel-LPs. Celastrol-containing groups received equivalent 1-mg/kg doses every three days for five doses. Investigators assessing arthritis scores, imaging, and histology were blinded to treatment allocation.

Folate Modification Enhanced Anti-inflammatory Effects

In activated macrophages, folate-modified liposomes showed greater cellular uptake than non-targeted liposomes, while competition with free folate reduced uptake—supporting involvement of a folate receptor–related process. FA-Cel-LPs also produced the greatest reductions in TNF-α, IL-1β, IL-6, and iNOS expression among the celastrol formulations. Western blot analysis showed significant attenuation of LPS-induced NF-κB activation and COX-2 and iNOS expression with FA-Cel-LPs (all p<0.001 vs LPS), with greater suppression than non-targeted Cel-LPs (p<0.05).

Reactive oxygen species (ROS), which can amplify inflammatory signaling, followed a similar pattern. LPS increased ROS to 10.7-fold above control levels; treatment reduced this to 6.5-fold with free celastrol, 3.2-fold with Cel-LPs, and 1.1-fold with FA-Cel-LPs.

Joint Protection Extended Beyond Inflammatory Markers

In CIA rats, FA-Cel-LPs showed greater apparent accumulation in inflamed joints and produced the largest reductions in paw swelling and arthritis scores. Micro-CT provided additional evidence of structural protection: compared with untreated CIA, FA-Cel-LPs increased bone volume fraction by approximately 80%, decreased bone surface-to-tissue volume ratio by approximately 45%, and restored bone mineral density by approximately 60%. MRI and histology similarly showed improvements in joint damage, synovial inflammation, and bone erosion.

Preliminary safety findings were also encouraging. ALT and AST remained within physiological ranges with FA-Cel-LPs and were significantly lower than with free celastrol (both p<0.001), while major-organ histology showed no obvious treatment-related abnormalities.

Promising Preclinical Findings, With Important Questions Remaining

These findings suggest that folate modification may enhance celastrol delivery and its anti-inflammatory and bone-protective activity while reducing systemic toxicity. However, this remains preclinical evidence. The study lacked quantitative biodistribution and pharmacokinetic analyses, long-term safety testing, primary synovial macrophages, and a standard-of-care comparator. Importantly, the observed ROS/NF-κB/COX-2 changes were associative rather than proof that this pathway caused the therapeutic effects, and folate receptor beta–specific uptake was not definitively established. Further mechanistic, pharmacokinetic, and translational studies will therefore be needed to determine whether the advantages observed in this experimental RA model can extend toward clinical use.

Reference:

Shen J, Zhou C, Wang X, et al. Folate-modified liposomal celastrol for rheumatoid arthritis: therapeutic efficacy and modulation of ROS/NF-κB/COX-2-related inflammatory signaling. Front Immunol. 2026;17:1841496. Published 2026 Sep 1. doi:10.3389/fimmu.2026.1841496