Cerebrospinal fluid ceramides from patients with multiple sclerosis impair neuronal bioenergetics

Axonal damage is a prominent cause of disability and yet its pathogenesis is incompletely understood. Using a xenogeneic system, here we define the bioenergetic changes induced in rat neurons by exposure to cerebrospinal fluid samples from patients with multiple sclerosis compared to control subjects. A first discovery cohort of cerebrospinal fluid from 13 patients with multiple sclerosis and 10 control subjects showed that acute exposure to cerebrospinal fluid from patients with multiple sclerosis induced oxidative stress and decreased expression of neuroprotective genes, while increasing expression of genes involved in lipid signalling and in the response to oxidative stress. Protracted exposure of neurons to stress led to neurotoxicity and bioenergetics failure after cerebrospinal fluid exposure and positively correlated with the levels of neurofilament light chain. These findings were validated using a second independent cohort of cerebrospinal fluid samples (eight patients with multiple sclerosis and eight control subjects), collected at a different centre. The toxic effect of cerebrospinal fluid on neurons was not attributable to differences in IgG content, glucose, lactate or glutamate levels or differences in cytokine levels. A lipidomic profiling approach led to the identification of increased levels of ceramide C16:0 and C24:0 in the cerebrospinal fluid from patients with multiple sclerosis. Exposure of cultured neurons to micelles composed of these ceramide species was sufficient to recapitulate the bioenergetic dysfunction and oxidative damage induced by exposure to cerebrospinal fluid from patients with multiple sclerosis. Therefore, our data suggest that C16:0 and C24:0 ceramides are enriched in the cerebrospinal fluid of patients with multiple sclerosis and are sufficient to induce neuronal mitochondrial dysfunction and axonal damage.

Cerebrospinal fluid sphingolipids, β-amyloid, and tau in adults at risk for Alzheimer's disease

Cellular studies suggest sphingolipids may cause or accelerate amyloid-beta (Aβ) and tau pathology but in vivo human studies are lacking. We determined cerebrospinal fluid levels of sphingolipids (ceramides and sphingomyelins), amyloid-beta (Aβ1-42, AβX-38, AβX-40, and AβX-42) and tau (T-tau and p-tau181) in 91 cognitively normal individuals, aged 36-69 years, with a parental history of Alzheimer's disease. The 18-carbon acyl chain length ceramide species was associated with AβX-38 (r = 0.312, p = 0.003), AβX-40 (r = 0.327, p = 0.002), and T-tau (r = 0.313, p = 0.003) but not with AβX-42 (r = 0.171, p = 0.106) or p-tau (r = 0.086, p = 0.418). All sphingomyelin species correlated (most p < 0.001) with all Aβ species and T-tau; many also correlated with p-tau. Results remained in regression models after controlling for age and APOE genotype. These results suggest in vivo relationships between cerebrospinal fluid ceramides and sphingomyelins and Aβ and tau levels in cognitively normal individuals at increased risk for Alzheimer's disease, indicating these sphingolipids may be associated with early pathogenesis.

Disturbance in cerebral spinal fluid sphingolipid content is associated with memory impairment in subjects infected with the human immunodeficiency virus

Despite widespread use of antiretroviral therapies to control replication of the human immunodeficiency virus (HIV), dysfunctions of cognition that are collectively termed HIV-associated neurocognitive disorders (HAND) still occur in approximately 50% of those infected by the virus. Currently there is not a biomarker that can identify HIV-infected people who are at risk for the development of HAND. Previous studies have identified particular sphingolipid species that are dysregulated in HAND, but the neurocognitive correlates of these biochemical findings are not currently understood. To address this question, we compared cerebrospinal fluid (CSF) levels of sphingomyelin, ceramide, and sterol species with performance on standard neurological tests designed to assess the function of multiple cognitive and motor domains in HIV-infected subjects. We found that sphingomyelin:ceramide ratios for acyl chain lengths of C16:0, C18:0, C22:0, and C24:0 were associated with worse performance on several indices of memory. The most striking finding was for the acyl chain of C18:0 that consistently associated with performance on multiple tests of memory. These findings suggest that the sphingomyelin:ceramide ratio for C18:0 may be a reasonable surrogate marker for memory dysfunction in HIV-infected subjects.

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

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.

Astroglial expression of ceramide in Alzheimer's disease brains: a role during neuronal apoptosis

Accumulating evidences indicate that ceramide is closely involved in apoptotic cell death in neurodegenerative disorders and aging. We examined ceramide levels in the cerebrospinal fluid (CSF) or brain tissues from patients with neurodegenerative disorders and the mechanism of how intra- and extracellular ceramide was regulated during neuronal apoptosis. We screened the ceramide levels in the CSF of patients with neurodegenerative disorders, and found that ceramide was significantly increased in patients with Alzheimer's disease (AD) than in patients with age-matched amyotrophic lateral sclerosis (ALS) and other neurological controls. With immunohistochemistry in AD brains, ceramide was aberrantly expressed in astroglia in the frontal cortices, but not detected in ALS and control brains. To explore for the regulation of ceramide in astroglia in Alzheimer's disease brains, we examined the metabolism of ceramide during neuronal apoptosis. In retinoic acid (RA)-induced neuronal apoptosis, RA slightly increased de novo synthesis of ceramide, but interestingly, RA dramatically inhibited conversion of [14C] ceramide to glucosylceramide (GlcCer), suggesting that the increase of ceramide mass is mainly due to inhibition of the ceramide-metabolizing enzyme GlcCer synthase. In addition, a significant increase of the [14C] ceramide level in the culture medium was detected by chasing and turnover experiments without alteration of extracellular [14C] sphingomyelin levels. A 2.5-fold increase of ceramide mass in the supernatant was also detected after 48 h of treatment with RA. These results suggest a regulatory mechanism of intracellular ceramide through inhibition of GlcCer synthase and a possible role of ceramide as an extracellular/intercellular mediator for neuronal apoptosis. The increased ceramide level in the CSF from AD patients, which may be derived from astroglia, raises a possibility of neuronal apoptosis by the response to intercellular ceramide in AD.