Oxysterol analysis in neurodegenerative diseases and traumatic brain injury
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Iyer, Vignesh
Background: There is increasing evidence that an adverse cholesterol profile is associated with neurodegenerative diseases and CNS injury. Oxysterols are oxygenated metabolites of Cholesterol that may provide the link between peripheral cholesterol levels and neuropathology. Specific changes in oxysterol influenced cholesterol homeostasis and correlate with MRI outcomes in MS disease progression. The goal of this study is to examine oxysterol levels in the blood and brain and examine their associations with neurodegenerative diseases. Methods: A Liquid Chromatography/Mass Spectrometry (LC/MS) method was developed and validated for simultaneous determination of vitamin D3, oxysterols and cholesterol in plasma, cerebrospinal fluid (CSF) and brain tissue samples. This method was further optimized for optimal quantification of 7-ketocholesterol (7-KC). Oxysterol levels in matched serum and CSF samples from patients with Clinically Isolated Syndrome (CIS) were measured to estimate their associations using Spearman's rank correlation coefficient (rSp). Serum samples from clinically defined Multiple Sclerosis (MS) patients with different MS subtypes were tested using Kruskal-Wallis (KW) ANOVA to identify significant differences between different subtypes. Groups with significant differences were then followed up with Mann-Whitney (Wilcoxon Rank Sum) to test the differences in the medians between individual study categories. Brain tissue and serum samples from a noise blast induced traumatic brain injury (TBI) rat model were analyzed for oxysterols to investigate their association in TBI. Brain section from rats sacrificed 6 weeks after the noise blast were stained using specific antibodies for CYP46A1 protein expression induced by TBI. Results: Erucamide, a common plasticizer caused interferences in 7-KC levels at the lower level of quantification. Oxysterol levels in TBI rat serum were not significant as analysis was limited by sample availability. Immunohistochemical staining results indicated region-specific expression of CYP46A1 with increased expression in hippocampus, MGB, thalamus and cortex. In MS clinical patient samples, significant reduction in 27-OHC levels was seen in all neurological disorder groups. Plasma levels for 7α-OHC, a major bile acid synthesis precursor, were reduced significantly and specifically in MS subtypes. Lower plasma levels of 7α-OHC further demonstrated a correlation with greater T2 lesion volume (a detrimental marker of MS disease) as determined by magnetic resonance (MRI) imaging. Conclusions: Our results indicate the presence of 7α-OHC in the CNS and suggest a possible bile acid signaling mechanism in the brain. Peripheral levels of 7α-OHC influencing the bile acid synthesis machinery could be associated with the progression of neurodegeneration in MS. This study provides interesting pilot data for the possible association of 7α-OHC and other oxysterols with MS disease. Further research is required to shed light on this aspect.