Immune status modifies the association between plasma zonulin-1 and skeletal-related events in treated HIV: a case-cohort study

Chronic inflammation driven by microbial translocation is implicated in the increased risk of skeletal-related events (SREs) among people with HIV (PWH) on antiretroviral therapy (ART). We aimed to assess the association between plasma biomarkers of gut barrier dysfunction and incident SREs in PWH on suppressive ART, and whether the host's baseline immune status modifies this association. We employed a nested case-cohort design within the Spanish CoRIS cohort. We quantified baseline plasma markers (zonulin-1, LPS, LBP, flagellin) in 65 incident SRE cases and a randomly selected subcohort of 263 PWH. Borgan II-weighted Cox regression models were used to test for associations and interactions between log2-transformed biomarkers and baseline CD4+ T-cell counts (<500 vs. ≥500 cells/mm³). In the overall population, zonulin-1 was not significantly associated with SRE risk (aHR 1.54; 95% CI 0.90-2.62). However, we detected a significant interaction between zonulin-1 and immune status (interaction p < 0.001). In participants with suboptimal immune recovery (CD4 + <500 cells/mm³), higher zonulin-1 levels were associated with incident SREs (aHR 5.14; 95% CI 2.25-11.77; interaction q < 0.001). Conversely, this association was absent in participants with preserved immune status (CD4 + ≥500 cells/mm³; aHR 0.98; 95% CI 0.58-1.67). LPS, LBP, and flagellin showed no association with SREs regardless of immune status. Gut barrier dysfunction, measured by plasma zonulin-1, is associated with a higher risk of SREs; however, this association is restricted to PWH with incomplete immune reconstitution. These findings support a "two-hit" model in which immune competence and aging modulate the skeletal consequences of gut leakage.