Protective Effects of Heat-Killed Lactobacilli against Plasma-Induced Neurotoxicity in Multiple Sclerosis

Heat-killed lactobacilli seem to have protective effects against oxidative stress and neurotoxicity. This study aimed to evaluate the antioxidant properties of specific heat-killed lactobacilli extracts and determine their neuroprotective effects against the neurotoxicity induced by blood plasma from people with multiple sclerosis (MS). The antioxidant activity of the three heat-killed lactobacilli was measured using the DPPH assay. For neuroprotective evaluations of lactobacilli, human neuroblastoma cells (SK-N-SH) were exposed to plasma from individuals with relapsing-remitting MS (RRMS) and healthy controls, with or without pre-treatment of heat-killed lactobacilli including Lactiplantibacillus plantarum (L. plantarum), Levilactobacillus brevis (L. brevis), and Lacticaseibacillus rhamnosus (L. rhamnosus). The morphological changes of SK-N-SH cells associated with plasma-induced apoptosis were observed using an inverted microscope. The neurotoxic effects of plasma samples were assessed using flow cytometry as the percentage of apoptosis in neuronal cells treated with plasma from RRMS patients and healthy controls. The neuroprotective effects of the lactobacilli were also evaluated using flow cytometry, which showed an increased viability percentage in cells pretreated with heat-killed lactobacilli extracts compared to those without pre-treatment. Compared to plasma from healthy controls, plasma from RRMS patients caused morphological changes characteristic of apoptosis such as rounding, detachment, and shrinkage in SK-N-SH cells on microscopy observations. Significant apoptosis in MS plasma-treated neuronal cells was identified by flow cytometry analysis compared to cells treated with plasma from healthy controls (p < 0.01). Heat-killed lactobacilli extracts showed antioxidant activity above 50% in the DPPH radical scavenging assay. Pre-treatment of cells with heat-killed lactobacilli significantly reduced the morphological changes and apoptosis percentage in neuronal cells induced by MS plasma samples. L. plantarum and L. rhamnosus had considerable neuroprotective effects (p < 0.001), followed by L. brevis (p < 0.05). These findings demonstrate that heat-killed lactobacilli extracts as bacterial fractions free of live microorganisms, are suitable safe candidates for adjunctive therapy with potential antioxidant and neuroprotective properties in MS.