Impact of emergent new psychoactive substances (NPS) on neuronal and microglial function

Abstract

The abuse of new psychoactive substances (NPS) represents a threat to public health. Emergent NPS N-ethylhexedrone (NEH), N-ethylpentylone (NEP) and 4-chloroethcathinone (4-CEC) are among the most harmful and seized synthetic cathinones, a prominent NPS class. We previously showed that NEH decreases neuronal and microglial viabilities. However, studies on neuroinflammatory processes and intra-/inter-cellular signalling dysregulation by synthetic cathinones are scarce. In this thesis, we aimed to evaluate how: (i) these substances trigger inflammation and disrupt cellular homeostasis in vitro; and (ii) cathinone-exposed microglia impact neuronal function. For that, we used differentiated SH-SY5Y (neuronal) and CHME3 (microglial) human cell lines exposed to (i) either 100 or 400 μM of each NPS or (ii) secretome from exposed microglia for 24 h, using non-exposed cells as control. We demonstrated that cathinone exposure causes neuronal and microglial dysfunction, namely: (i) increased cell demise, via apoptosis and necrosis; (ii) mitochondrial impairment; and (iii) lysosomal distress. Neuroimmune responses, marked by the upregulation of several pro-/anti-inflammatory markers (S100B, iNOS, nNOS, TNF-α, IL-1β, IL-10) were observed on cells exposed to NPS. Additionally, cathinones dysregulated the genes encoding for synaptic proteins synaptophysin and Dlg4 in neurons; in microglia, these substances caused the overexpression of phagocytosis-related markers TREM2 and MFG-E8 and increased phagocytic activity (non-specific phagocytosis). We also demonstrated that the secretome from NPS-exposed microglia disturbed the neuronal immunoregulatory response and dysregulated synaptic protein plasticity, suggesting that cathinone-activated microglia may negatively impact neuronal function via paracrine signalling. Taken together, our findings highlight the ability of prevalent synthetic cathinones to trigger neuronal and microglial disabilities and homeostatic imbalance, while altering synaptic plasticity and causing inflammation that may precede (and contribute to) the onset of neurotoxic events, ultimately compromising brain function. Our data shines new light on the general and specific mechanisms underlying the detrimental impact of synthetic cathinones in human brain health.