Non-classical monocyte levels correlate negatively with HIV-associated cerebral small vessel disease and cognitive performance

Abstract

Background: Despite antiretroviral treatment (cART), aging people living with HIV (PWH) are more susceptible to neurocognitive impairment (NCI) probably due to synergistic/additive contribution of traditional cerebrovascular risk factors. Specifically, transmigration of inflammatory CD16+ monocytes through the altered blood brain barrier (BBB) may exacerbate cerebral small vessel disease (CSVD), a known cause of vascular cognitive impairment.

Methods: PWH on cART (n=108) and age, sex, and Reynold's cardiovascular risk score-matched uninfected individuals (PWoH, n=111) were enrolled. This is a longitudinal observational study but only cross-sectional data from entry visit are reported. Neuropsychological testing and brain magnetic resonance imaging (MRI) were performed. CSVD was diagnosed by Fazekas score ≥1. Flow cytometric analyses of fresh whole blood were conducted to evaluate circulating levels of monocyte subsets (classical, intermediate, and non-classical) and markers of monocyte activation (CCR2, CD40, PSGL-1, TNFR2 and tissue factor). ELISAs were used to measure sCD14, ICAM, and Osteoprotegerin. Two-way analysis of variance (ANOVA), and linear regression models were performed to study the effects of HIV status, CSVD status, and their interaction to outcome variables such as cognitive score. Two-sample t-tests and correlation analyses were performed between and within PWoH with CSVD and PWH with CSVD participants.

Results: PWH with CSVD (n=81) had significantly lower total cognitive scores, higher levels of NCMs and soluble CD14 and intracellular adhesion molecule 1 (ICAM-1) as compared to PWoH with CSVD group (n=68). sCD14 and ICAM1 were positively correlated with each other indicating that monocyte and endothelial activation are associated with each other. Cognition was negatively correlated with NCMs, especially in the PWH with CSVD group. Among other blood biomarkers measured, osteoprotegerin levels showed mild negative correlation with cognitive performance in individuals with CSVD irrespective of HIV status.

Conclusions: Elevated levels of NCMs may contribute to neuroinflammation, CSVD and subsequent cognitive impairment. This finding is of particular relevance in aging PWH as both HIV and aging are associated with increased levels of NCMs. NCMs may serve as a potential biomarker to address these comorbidities. Further longitudinal studies are needed to evaluate whether changes in NCM levels are associated with changes in CSVD burden and cognitive impairment.

Keywords: HIV/AIDS; MRI; cerebral small vessel disease; cognitive impairment; non-classical monocytes.

Figure 1

Neuropsychological battery domain scores in study participants. (A) Total cognitive score. Individual domain scores for (B) Verbal and Visual Learning, (C) Verbal and Visual Memory, (D) Processing speed, (E) Executive function, (F) Fine Motor Skill, (G) Verbal/language and, (H) Attention and working memory. Blue data points represent PWoH with CSVD group (n=66), and red represents PWH with CSVD group (n=77). Two group comparisons were made using Welch’s t-test. * p<0.05, ** p<0.01, *** p<0.001, **** p<0.0001.

Figure 2

Peripheral monocyte levels and markers of monocyte and endothelial cell activation. (A) Circulating levels of NCM and, (B) Percentages of NCMs expressing TF were significantly higher in PWH with CSVD group as compared to PWoH with CSVD group. Plasma levels of (C) sCD14, and (D) ICAM were higher in the PWH WITH CSVD group as compared to the PWoH with CSVD group. (E) sCD14 and ICAM levels showed a robust positive correlation, indicating that monocyte and endothelial activation co-occur (p<0.0001, r_s=0.4708). Blue data points represent the PWoH with CSVD group (n=66), and red represents the PWH with CSVD group (n=77). Two group comparisons were made using Mann Whitney U test. Correlation between sCD14 and ICAM was done via the Spearman test. * p<0.05, ** p<0.01, **** p<0.0001.

Figure 3

Correlation analysis between total cognitive Z score and blood markers of monocyte and endothelial cells. Percentages of NCMs and total cognitive score showed statistically significant negative correlation (A) when data from the CSVD+ groups was pooled together (p=0.0043, r_s = -0.2631). (B) This correlation became stronger among PWH with CSVD (p=0.0032, r_s = -0.3579). (C) There was no correlation when data from only PWoH with CSVD individuals was used (r_s = 0.09705). (D) Osteoprotegerin showed a mild negative correlation with total cognitive scores only when data from both CSVD+ groups was pooled together (p=0.0409, r_s=-0.1743). Blue data points represent the PWoH with CSVD group (n=66), and red represents the PWH with CSVD group (n=77). Correlations were done via the Spearman test.