EFFECTS OF INDICAXANTHIN ON HUMAN MOTOR CORTICAL EXCITABILITY AND PLASTICITY

Abstract

The role of nutraceuticals has risen interest in the last decade for complex biological activities exerted on pathophysiological processes such as oxidative stress, inflammatory conditions and excitotoxicity. In this regard, the effects of nutraceuticals on basic functions of neuronal processes, such as cortical excitability and cortical plasticity are still to be unveiled. Translational studies performed on phytochemicals (PhC) with anti-inflammatory and antioxidant properties could trace the path for the possible modulation of neuronal excitability in humans, phenomena involved in neurodegenerative alterations and cell stress. In this context, Opuntia ficus indica is a mediterranean plant containing a betalaine pigment, indicaxanthin, that has been studied for its numerous activities, in particular the ability to cross the Blood-brain barrier (BBB) and to influence neuronal excitability in rats. On these bases we aimed to assess the effects of acute intake of indicaxanthin (IX) on human cortical excitability and plasticity. Eight healthy, right handed male subjects (mean age: 20-45 years) were recruited . No-one had a history or clinical signs of neurological diseases, brain trauma or use of drugs affecting cortical excitability as assessed by a clinical neurologist. Safety guidelines for Non Invasive Brain Stimulation (NIBS) studies were rigidly applied for both stimulation and inclusion criteria. Intracortical facilitation (ICF), short-lasting intracortical inhibition (SICI) and test stimulus (TEST) were recorded (10 times each in a pseudo-randomized order) by means of a paired pulse Transcranial Magnetic Stimulation (TMS) stimulator (Magstim Co, Dyfed UK) before (PRE-TDCS) and after (POST-TDCS) 20’ of anodal transcranial direct current stimulation (tDCS, Neuroconn, Ilmenau, Germany) delivered over right M1. The same data were recorded in baseline condition (T0) and 2 hours after intake of 400g of cactus pear fruit (T1) in separate sessions. IX significantly increased PRE-TDCS TEST (p<0.01), and PRE-TDCS ICF( p<0.05) whereas PRE-TDCS SICI was unchanged, and significantly reduced POST-TDCS ICF (p<0.0001) and SICI (p<0.001). Our data support the hypothesis that IX is able to modulate human cortical excitability consistently with preclinical evaluations, and specifically to increase excitability of Human Motor Cortex. Moreover, the paradoxical effects after anodal tDCS seems to suggest that the excitatory drive exerted by IX is also able to induce homeostatic responses on motor cortical plasticity.