ROLE OF THE KYNURENINE PATHWAY IN CARDIOVASCULAR DISEASE RISK IN A COHORT OF PEOPLE LIVING WITH HIV

BACKGROUND: Despite the virological and immunological success achieved with always more effective ART drugs, PLWH are burdened by abnormal immune activation and inflammation, characterized by elevated biomarkers such as IL-6, D-dimer, C-reactive protein (CRP), and sCD14. Chronic inflammation, even low-grade one, and immune activation are known risk factors for the development of cardiovascular (CV) diseases (D), which are an increasing burden for PLWH during ART and became the first non-AIDS cause of death in this population. The complexity of this inter-relations between abnormal immune activation, inflammation and comorbidities, and the implications for the quality of life and disease-free time of PLWH, make this a matter of utmost importance. It is fundamental to completely understand the mechanisms by which HIV interacts with the human organism to stop the abnormal immune activation and inflammation and improve the outcomes of non-AIDS-related disorders in PLWH. AIMS: The aims of this study were to understand which tryptophan metabolites of the kynurenine pathway correlate with membership of an inflammatory cluster associated with increased cardiovascular disease risk in people living with HIV. Moreover, we also wanted to study the correlations between kynurenine pathway catabolites and immunological profiles of people living with HIV. METHODS: Metabolite analysis was carried out at an outsource facility, Metabolon Inc. Samples were prepared using the automated MicroLab STAR® system from Hamilton Company. The resulting extract was divided into multiple fractions: two for analysis by two separate reverse phase (RP)/UPLC-MS/MS methods with positive ion mode electrospray ionization (ESI), one for analysis by RP/UPLC-MS/MS with negative ion mode ESI, one for analysis by HILIC/UPLC-MS/MS with negative ion mode ESI. Descriptive statistical analysis was performed with Jamovi version (v.) 2.3.19.0 for MacOS (OpenSource, R language based), while inferential statistics was performed with RStudio v. 2023.12.1+402 (OpenSource, R language based). RESULTS: Ninety-three people living with HIV were included in this study, 32 belonged to cluster 1, 29 to cluster B and 32 to cluster 3. Fifty PLWH (53.8%) were Caucasian. Median age was 45 years (IQR 40-70), and they had a median CD4+ T-cell count of 616 cells/µL (IQR 456-797) at the time of the sampling. A significant difference was found between the clusters regarding the CD4+ T-cell count and CD4/CD8 ratio (p = 0.023 and p = 0.007, respectively). KP metabolites show the strongest correlation with markers of inflammation in the cluster with the lowest levels of inflammation, suggesting KP acts as an adjunctive inflammation control pathway at low levels of inflammation. KP metabolites with anti-inflammatory properties are expressed at higher levels in PLWH with a history of CVD in the low inflammation cluster, while KP metabolites with pro-inflammatory properties are expressed at higher levels in PLWH with a history of CVD in the high inflammation cluster. KP metabolites with anti-inflammatory properties are expressed at lower levels in PLWH with a history of CVD in the moderate inflammation cluster. CONCLUSIONS: KP metabolites correlate with IL-6 and VCAM in cluster 1 but not in cluster 2 and 3. The correlations existing with IL-6 and VCAM in cluster 1 support the hypothesis that KP works as an adjunctive inflammation control pathway, especially during low level inflammation. This hypothesis is also supported by the scarce correlation with markers of inflammation and immune correlation when expressed at higher levels in clusters 2 and 3. Moreover, KP metabolites correlates with CVD risk. In PLWH who have a history of CVD, KP metabolites with anti-inflammatory properties are expressed at higher levels in cluster 1, while they are expressed at lower levels in cluster 2. Moreover, in cluster 3, KP metabolites with proinflammatory properties are expressed at higher levels in PLWH who have a history of CVD. More studies and larger cohorts are needed to better understand the mechanisms linking immune activation, inflammation, and comorbidities in people living with HIV in order to improve their outcomes.