ALS Patients Exhibit Altered Levels of Total and Active MMP-9 and Several Other Biomarkers in Serum and CSF Compared to Healthy Controls and Other Neurologic Diseases

Matrix metalloproteinases 2 and 9 (MMP-2, MMP-9) have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, their protein levels and correlation with other biomarkers are not well understood. We measured total and active MMP-2/-9 and additional biomarkers (creatinine, neurofilament light, cystatin C, and alkaline phosphatase) in the serum of people with ALS (ALS, n = 30) and compared their levels with age-matched healthy controls (HC, n = 20) and other neurological diseases (diabetic nephropathy, Alzheimer's disease, Parkinson's disease; n = 8 each). We also measured MMP-2/-9 in a set of CSF samples from ALS (n = 30) and age-matched other neurological diseases (OND, n = 14). Lastly, we measured the competitive binding behavior of a dual MMP-2/MMP-9 inhibitor, AQU-118, against active MMP-9 in situ within the serum of ALS. We found significantly elevated levels of both total MMP-9 protein (two studies, 7.5 and 9.5-fold; both <i>p</i> < 0.0001) and active MMP-9 (2.5-fold; <i>p</i> < 0.0001) in ALS serum compared to HC. Serum NfL was significantly elevated (6-fold, <i>p</i> < 0.0001) and serum creatinine was significantly decreased (40%, <i>p</i> < 0.0001) in ALS compared to HC. There were significantly decreased levels of MMP-2 (two studies, 26 and 33%; <i>p</i> < 0.001 and <i>p</i> = 0.0001, respectively) in the serum of ALS as compared to HC. ALS also had significantly higher active MMP-9 in serum than patients with Alzheimer's disease and higher than Parkinson's disease or diabetic nephropathy. We confirmed that active MMP-9 in ALS is fully available for proteolytic activity in both serum and CSF and can be inhibited using an MMP-2/-9 inhibitor. Active MMP-9 is systemically elevated in ALS and therefore a therapeutic target for ALS drug development.