Citation: Riolo, G.; Ricci, C.; De Angelis, N.; Marzocchi, C.; Guerrera, G.; Borsellino, G.; Giannini, F.; Battistini, S. BDNF and Pro-BDNF in Amyotrophic Lateral Sclerosis: A New Perspective for Biomarkers of Neurodegeneration. Brain Sci. 2022, 12, 617. https://doi.org/10.3390/ brainsci12050617 Academic Editor: Chiara Villa Received: 30 March 2022 Accepted: 6 May 2022 Published: 9 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). brain sciences Article BDNF and Pro-BDNF in Amyotrophic Lateral Sclerosis: A New Perspective for Biomarkers of Neurodegeneration Giulia Riolo 1 , Claudia Ricci 1, * , Nicoletta De Angelis 1 , Carlotta Marzocchi 1 , Gisella Guerrera 2 , Giovanna Borsellino 2 , Fabio Giannini 1 and Stefania Battistini 1 1 Department of Medical, Surgical and Neurological Sciences, University of Siena, 53100 Siena, Italy; giulia.riolo@gmail.com (G.R.); nicoletta.deangelis91@gmail.com (N.D.A.); carlottamarzocchi@libero.it (C.M.); fabio.giannini@unisi.it (F.G.); stefania.battistini@unisi.it (S.B.) 2 Neuroimmunology Unit, Santa Lucia Foundation IRCCS, 00143 Rome, Italy; g.guerrera@hsantalucia.it (G.G.); g.borsellino@hsantalucia.it (G.B.) * Correspondence: claudia.ricci@unisi.it Abstract: Amyotrophic Lateral Sclerosis (ALS) is characterized by the progressive degeneration of upper or lower motor neurons, leading to muscle wasting and paralysis, resulting in respiratory failure and death. The precise ALS aetiology is poorly understood, mainly due to clinical and genetic heterogeneity. Thus, the identification of reliable biomarkers of disease could be helpful in clinical practice. In this study, we investigated whether the levels of brain-derived neurotrophic factor (BDNF) and its precursor Pro-BDNF in serum and cerebrospinal fluid (CSF) may reflect the pathological changes related to ALS. We found higher BDNF and lower Pro-BDNF levels in ALS sera compared to healthy controls. BDNF/Pro-BDNF ratio turned out to be accurate in distinguishing ALS patients from controls. Then, the correlations of these markers with several ALS clinical variables were evaluated. This analysis revealed three statistically significant associations: (1) Patients carrying the C9orf72 expansion significantly differed from non-carrier patients and showed serum BDNF levels comparable to control subjects; (2) BDNF levels in CSF were significantly higher in ALS patients with faster disease progression; (3) lower serum levels of Pro-BDNF were associated with a shorter survival. Therefore, we suggest that BDNF and Pro-BDNF, alone or in combination, might be used as ALS prognostic biomarkers. Keywords: Amyotrophic Lateral Sclerosis; BDNF; Pro-BDNF; biomarkers; disease progression; CSF; serum 1. Introduction Amyotrophic Lateral Sclerosis (ALS) is a heterogeneous condition resulting from the progressive degeneration of motor neurons in the brain and spinal cord. The classical disease has a focal onset, characterized by the loss of function of upper or lower motor neurons, resulting in no muscle nourishment and leading to inevitable paralysis [1,2]. Importantly, atrophy quickly progresses from the region of onset to close spinal regions and very often the failure of respiratory muscles is fatal for ALS patients [3]. Riluzole and edaravone, the only FDA approved drugs so far, marginally enhance survival and slow the clinical progression of the disease, increasing the urgency for new effective therapeutic treatments [4]. The worldwide incidence of ALS accounts for 1.6/100,000 people each year [5]. Al- most 90% of cases are classified as sporadic (sALS) and only the remaining 10% have a family history of disease (fALS), characterized by a Mendelian dominant inheritance with incomplete penetrance [6]. Despite decades of research, the precise aetiology of ALS is definitely poorly under- stood. Diagnosis, commonly made with a considerable delay from symptom onset, is mostly based on electrophysiological examinations and clinical judgment, because there is Brain Sci. 2022, 12, 617. https://doi.org/10.3390/brainsci12050617 https://www.mdpi.com/journal/brainsci