Letter to the Editor “Paradoxical HDL-C/ApoA1 associations in osteoarthritis progression: a call for functional lipidomics and personalized thresholds”

To the Editor,

We approached with considerable intrigue the prospective cohort study conducted by Wang et al, which scrutinizes serum lipid metabolites as prognostic indicators for joint arthroplasty in individuals afflicted with hip/knee osteoarthritis (OA)[1]. The authors’ pioneering utilization of Fine & Gray competing-risk models unveiled counterintuitive correlations: increased levels of HDL-C and ApoA1 – lipids conventionally viewed as cardioprotective – exhibited a significant association with hastened OA progression (Sub-HR 1.05 and 1.05, respectively; P<0.001). This unexpected revelation highlights a substantial lacuna in the understanding of OA pathophysiology, thus necessitating a transition from traditional lipid measurement to functional lipidomics – evaluating particle composition, oxidation status, and efflux efficiency – to effectively differentiate between protective and pathogenic HDL/ApoA1 isoforms[2]. All assertions related to AI conform to the TITAN guidelines[3], thereby ensuring methodological rigor.

Mechanistically, Waldecker-Gall et al elucidated that persistent inflammatory rheumatic disorders are correlated with heightened levels of oxidized HDL in serum, indicating a dysfunction in HDL – this condition is associated with a reduced cholesterol efflux capacity and a pro-inflammatory transformation, as evidenced by previous research[4]. Likewise, dissociated ApoA1 triggers TLR4-mediated expression of IL-6 and MMP-3, directly promoting cartilage degradation[5]. These findings underscore the need to transition from traditional lipid quantification to functional lipidomics – evaluating particle composition, oxidation state, and efflux efficiency – to differentiate between protective and pathogenic HDL/ApoA1 isoforms in OA joints.

The subgroup analyses further reveal a high-risk phenotype: obese women under 60 years with hip OA and heightened genetic predisposition demonstrated the most pronounced lipid-arthroplasty associations (P<0.001). This “metabolic-inflammatory-genetic triad” synergistically exacerbates OA severity through dysregulation of adipokines (for instance, leptin-mediated TLR4/MMP-13 expression via the JAK2-STAT3-CD14 pathway, with SOCS3 functioning as a negative feedback regulator)[6] and compromised chondrocyte autophagy[7]. Nonetheless, the inadequately powered polygenic risk score analysis (n = 15,894) hindered definitive genetic insights. We propose triad-targeted clinical trials – utilizing agents such as PCSK9 inhibitors or adipokine modulators – in this subgroup to disrupt the lipid–adiposity–inflammation continuum.

The identification of lipid thresholds by Wang et al (e.g., HDL-C >1.347 mmol/L) represents a significant advancement in the realm of personalized management. Nonetheless, these thresholds necessitate validation across a spectrum of cohorts and OA phenotypes. A pronounced correlation between hip OA and lipid levels was observed in comparison with knee OA (P <0.001), likely indicative of underlying biomechanical and vascular disparities. The integration of site-specific thresholds with obesity metrics (e.g., HDL-C ≤1.3 mmol/L for obese women with hip OA) could enhance risk stratification. Furthermore, external validation within multi-ethnic populations is imperative, given that the homogeneity of the UK Biobank (95.8% White) imposes limitations on generalizability.

Lastly, while lipoprotein(a) and triglycerides exhibited no significant associations, triglycerides may exert an indirect influence on OA through crystalline arthropathies. Broadening biomarker panels to encompass oxidized LDL or lipoprotein-associated phospholipase A2 (Lp-PLA2) may elucidate residual pathways.

In conclusion, the pioneering work of Wang et al positions lipid metabolites as prognostic instruments for OA; however, the mechanistic and phenotypic subtleties warrant further exploration. The application of functional lipidomics, triad-targeted interventions, and the establishment of validated site-specific thresholds have the potential to transition lipid biomarkers from mere predictors to modifiable therapeutic targets, ultimately delaying the necessity for arthroplasty among high-risk OA populations.

Ethical approval

This study does not include any individual-level data and thus does not require any ethical approval.

Sources of funding

No funding to declare.

Conflicts of interest disclosure

No potential competing interests to declare.

Research registration unique identifying number (UIN)

1. Name of the registry: not applicable. 2. Unique identifying number or registration ID: not applicable. 3. Hyperlink to your specific registration (must be publicly accessible and will be checked): not applicable.

Guarantor

Zhiming Lu.

Provenance and peer review

Not commissioned.

Data availability statement

This letter did not generate any new data.