Blood neurofilament light (NfL) levels have been linked to multiple sclerosis (MS) activity and progression but are affected by factors such as age and body mass index (BMI). Less is known about what factors affect blood levels of Glial Fibrillary Acid Protein (GFAP), Ubiquitin Carboxy-Terminal Hydrolase L1 (UCH-L1), and Tau. Single Molecule Array (SIMOA) platforms allow multiplex measurement of these biomarkers with high sensitivity.
To evaluate factors associated with higher levels of four plasma biomarkers—NfL, GFAP, UCH-L1, and Tau—in individuals with MS on immunotherapy.
Subjects with MS between 18-65 years taking dimethyl fumarate (n=40), fingolimod (n=37), natalizumab (n=47), or rituximab (n=90) for at least 1 year were identified from Rocky Mountain MS Center Biorepository. Neuro 4-plex A plasma assays were conducted on the Quanterix SR-X SIMOA platform. Biomarker concentrations were log transformed. For each biomarker, summary statistics were generated, and logistic regressions on the probability of having a level in the top quartile, adjusting for age, were performed with different explanatory variables including gender, BMI, disease duration, length on disease modifying therapy (DMT), DMT type, and MS subtype (relapsing MS [RMS] or progressive MS [PMS]). All statistics were generated in SAS.
Included were 214 subjects (194 RMS, 20 PMS; 70.3% female; 86.9% Caucasian) with mean age of 44.1(SD 9.8). Mean disease and treatment durations were 150.7(SD 95.7) and 49.7(SD 33.5) months, respectively. Means (IQR) for NfL, GFAP, UCH-L1 and Tau were 6.6(3.9-7.1), 66.9(45.5-81.4), 11.5(7.1-13.8), and 1.2(0.8-1.5) pg/ml, respectively. NfL, GFAP, and UCH-L1 increased with age. (Remainder of results are given age-adjusted.) PMS was more likely than RMS to be in the top quartile for NfL (OR 3.5,p=0.01), GFAP (OR 2.6,p=0.06), and UCH-L1 (OR 2.8,p=0.04). Longer disease duration (5 years) increased the likelihood of elevated NfL (OR 1.3,p=0.02) and elevated GFAP (OR 1.3,p=0.03). Higher BMI (5 units) decreased the likelihood of elevated NfL (OR 0.6,p=0.0007) and GFAP (OR 0.8,p=0.03) but increased the likelihood of having an elevated Tau (OR 1.4,p=0.002). Ethnicity and treatment duration had no effect, but men were more likely to have elevated UCH-L1 (OR 2.1,p=0.03) and lower Tau (OR 0.2,p=0.0004). Comparing DMTs, no biomarker differences were observed except subjects on rituximab and dimethyl fumarate were less likely to have elevated Tau.
Plasma NfL, GFAP, and UCH-L1 are promising biomarkers to differentiate relapsing from progressive MS. Age and BMI should be incorporated into biomarker models to determine normal thresholds. No differences were observed between treatments for NFL, GFAP, or UCH-L1, but subjects on dimethyl fumarate and rituximab were less likely to have elevated Tau. Lack of randomization or repeated measures limited comparative effectiveness analyses.