Associative and predictive biomarkers of dementia in HIV-1-infected patients

Abstract

Background: Infection with HIV can result in a debilitating CNS disorder known as HIV dementia (HIV-D). Since the advent of highly active antiretroviral therapy (HAART), the incidence of HIV-D has declined, but the prevalence continues to increase. In this new era of HIV-D, traditional biomarkers such as CSF viral load and monocyte chemotactic protein 1 levels are less likely to be associated with dementia in patients on HAART and biomarkers that can predict HIV-D have not yet been identified.

Objective: To identify biomarkers that are associated with and can predict HIV-D.

Methods: We grouped patients with HIV based on changes in cognitive status over a 1-year period and analyzed sphingolipid, sterol, triglyceride, antioxidant, and lipid peroxidation levels in CSF.

Results: We found that increased levels of the vitamin E and triglyceride C52 predicted the onset or worsening of dementia. Elevated levels of sphingomyelin were associated with inactive dementia. Elevated levels of ceramide and the accumulation of 4-hydroxynonenals were associated with active dementia.

Conclusions: We interpret these findings to indicate that early in the pathogenesis of HIV dementia, there is an up-regulation of endogenous antioxidant defenses in brain. The failure of this attempted neuroprotective mechanism leads to the accumulation of sphingomyelin and moderate cognitive dysfunction. The breakdown of this enlarged pool of sphingomyelin to ceramide and the accumulation of highly reactive aldehydes are associated with declining cognitive function. Thus, elevations in endogenous protective mechanisms may identify patients who are at increased risk of the development of HIV dementia.

Figure 1. Schematic representation of study design

Patients were classified using the Memorial Sloan-Kettering Scale (MSK). Associative biomarkers were identified by grouping patients based on changes in MSK score from visit 1 to visit 2 into no dementia (HIV-ND); active dementia (HIV-AD; n = 10), defined as a transition from a nondemented status to dementia within the last 6 months; and inactive dementia (HIV-ID; n = 17), defined as a dementia status unchanged over the preceding 6-month period. Predictive biomarkers were identified by grouping patients based on changes in MSK scores from visit 2 to visit 3 as stable (HIV-stb), defined as a dementia status unchanged over the 6-month period; worsening cognitive function (MSK-wor), defined by an MSK score that increased from visit 2 to visit 3; and improved cognitive function (MSK-imp), defined by an MSK score that decreased from visit 2 to visit 3. CSF drawn at visit 2 was used for analysis.

Figure 2. Viral load and monocyte chemotactic protein 1 (MCP-1) levels are not associated with an active dementia and cannot predict changes in cognitive status

(A to C) Plasma (A) or CSF (B) viral load or CSF MCP-1 levels (C) were not associated with changes in cognitive status when we compared HIV-infected patients with no dementia (HIV-ND), inactive dementia (HIV-ID), or active dementia (HIV-AD). (D through F) Plasma (D) or CSF (E) viral load, or MCP-1 levels (F) were not predictive of changes in cognitive status when we compared HIV-infected patients with HIV-ID, worsening cognitive function (MSK-wor), or improved cognitive function (MSK-imp) MSK = Memorial Sloan-Kettering Scale.

Figure 3. Increased CSF levels of ceramide and 4-hydroxynoneal (4-HNE) are associated with active dementia

CSF levels of sphingolipids, sterols, triglyceride C52, reactive aldehyde, and tocopherol were determined by electrospray ionization tandem mass spectrometry (ESI/MS/MS). (A) Levels of sphingomyelin C16:0, C18:0, C20:0, C22:0, and C24:0 were increased in patients with inactive dementia (HIV-ID) compared with patients with no dementia (HIV-ND) or patients with active dementia (HIV-AD). (B) The ceramides C22:0, C24:0, and C24:1 and sulfatide were increased in HIV-AD patients compared with HIV-ND and HIV-ID patients. (C) Sphingomyelinase activity was increased in HIV-AD compared with HIV-ND or HIV-ID patients. (D) Levels of free cholesterol and the cholesterol esters C16:0 and C18:1 were similar in all HIV patient groups. (E) Levels of 25-hydroxycholesterol in CSF were decreased in HIV-AD patients compared with HIV-ND and HIV-ID groups. 25-OH = 25-hydroxy. (F) Triglyceride C52 levels were similar in all patient groups. (G) CSF levels of the reactive aldehydes 2-pentilpyrrole histidine-hydroxynoneal and 2-pentilpyrrole lysine-hydroxynoneal were increased in HIV-AD patients compared with HIV-ND and HIV-ID patients. (H) Vitamin E levels were decreased in patients with HIV-AD compared with HIV-ND and HIV-ID patient groups. **p < 0.01; ***p < 0.001. Analysis of variance with Tukey post hoc comparisons.

Figure 4. Increased CSF levels of triglyceride C52 and vitamin E predict the onset or worsening of dementia in HIV-infected patients

(A and B) There were no differences in the levels of any sphingomyelins or ceramides tested when we compared MSK-stb, MSK-imp and MSK-wor patient groups. (C) Although levels of free cholesterol were similar in all groups, the cholesterol esters C16:0 and C18:1 were decreased in MSK-wor patients compared with MSK-stb and MSK-imp patient groups. (D) Levels of 25-hydroxycholesterol were similar in all patient groups. (E) The long-chain triglyceride C52 was increased in MSK-wor patients compared with MSK-stb or MSK-imp. (F) 4-Hydroxynonenal (4-HNE) levels were similar in all patient groups. (G) The antioxidant vitamin E was increased in the CSF of patients with MSK-wor compared with the MSK-stb and MSK-imp patient groups. 25-OH = 25-hydroxy; ND = no dementia; MSK = Memorial Sloan-Kettering Scale; stb = stable; imp = improved; wor = worse.

Figure 5. Biomarkers that are predictive of or are associated with dementia

Early in the course of HIV dementia (HIV-D), when no dementia is apparent, increased levels of endogenous antioxidants (vitamin E), may predict the worsening of cognitive function. Mild cognitive impairment is associated with the accumulation of sphingomyelin and decreased levels of vitamin E (inactive dementia). Worsening cognitive function is associated with increased levels of sphingomyelin, ceramide, and the reactive aldehyde 4-hydroxynonenal (4-HNE).