Neurotoxicity Research

The outbreak of SARs-CoV-2 with emerging new variants is leading to global health crisis and has brought a major concern for patients with comorbidities. Parkinson’s disease (PD) is a motor neurodegenerative disease involving various metabolic and psychological ailments along with the common occurrence of hyposmia as observed in COVID-19 patients. In addition, the observed surplus inflammatory responses in both diseases are also alarming. Alongside, angiotensin-converting enzyme 2 (ACE2) receptor, essentially required by SARS-CoV-2 to enter the cell and dopamine decarboxylase (DDC), required for dopamine synthesis is known to co-regulate in the non-neuronal cells. Taken together, these conditions suggested the probable reciprocal pathological relation between COVID-19 and PD and also suggested that during comorbidities, the disease diagnosis and therapeutics are critical and may engender severe health complications. In this review, we discuss various events and mechanisms which may have implications for the exacerbation of PD conditions and must be taken into account during the treatment of patients.

Epidemiological studies have shown a reduced incidence of cancer in Parkinson’s disease. Since nearly all parkinsonian patients with clinical impairment are treated with L-β-3,4-dihydroxyphenylalanine (L-DOPA) and dopamine (DA)ergic agonists, a possibility exists that these therapeutic agents can influence the risk of cancer. We studied the antiproliferative effect of these therapeutic agents (and substances structurally correlated) on Chinese hamster ovary (CHO)-K1 cell growth. Among the compounds tested, apomorphine proved to be the most potent inhibitor of CHO-K1 cell growth, with an EC50 of 3.35 ± 0.12 μM. The apomorphine analogues, apocodeine and hydroxyethylnorapomorphine, were less active as inhibitors of CHO-K1 cell growth. The activity of DA, 6-hydroxydopamine (6-OHDA), phe-nylethylamine (PEA), L-DOPA and bromocriptine as antiproliferative was one order of magnitude lower than that of apomorphine while pergolide was ineffective. To test whether or not the oxidative potential of these compounds was important for their antiproliferative effect, several antioxidants were assayed. Among them, glutathione (GSH) and dithio-threitol (DTT) were effective in reversing the antiproliferative effect of apomorphine, DA, 6-OHDA and PEA, conversely they did not work with bromocriptine. GSH and DTT are sulphydryl-reducing agents; while their effect could explain the efficacy against apomorphine, DA and 6-OHDA, it is difficult to understand why they should have any effect on PEA as this substance does not react with sulphydryl groups. The oxidative potential as a mechanism of action was also questioned by the results obtained with dihydrorhodamine 123, a probe that changes its fluorescent emission wave when oxidized. None of the compounds, with the exception of 6-OHDA, had any effect on the fluorescent emission wave of the probe at the maximal concentrations used to inhibit CHO-K1 cell growth. At concentrations five times higher, apomorphine and DA generated reactive oxygen species but PEA and bromocriptine did not. These data demonstrate that the antiproliferative effect of these compounds is not due to their oxidative potential, but another mechanism must be postulated.

Preconditioning brain cultures with moderate concentrations of ethanol (EtOH) or trans-resveratrol (RES), key red wine constituents, can prevent amyloid-β (Aβ) neurotoxicity. Past studies have indicated that moderate EtOH activates synaptic N-methyl-D-aspartate receptors (NMDAR) that, in part, signal via protein kinase C (PKC) to increase protective antioxidant proteins such as peroxiredoxin-2 (Prx2). RES preconditioning also is reported to involve NMDAR and PKC. However, although moderate, the EtOH and RES concentrations used have been noticeably above circulating levels from two glasses of wine, a daily intake linked to reduced risk of cognitive decline among older social drinkers. Given their mechanistic parallels, we speculated that subprotective EtOH and RES concentrations in a combinatorial preconditioning paradigm might elicit synergistic neuroprotection. To examine this notion, rat cerebellar cultures were pretreated with 10 mM EtOH (circulating concentration after ~ 2 drinks), 5 μM RES, EtOH + RES combinatorially, or media alone (controls). After 3 days, media were removed, and fresh media aliquots containing Aβ25–35 (25 μM) were added. Assessing apoptosis 24 h later with Hoescht 33342, neurodegeneration did not differ from controls in cultures separately preconditioned with 10 mM EtOH or 5 μM RES. However, apoptosis was prevented in combinatorially preconditioned cultures. Also, immunoblotting revealed elevated Prx2 levels due to combinatorial pretreatment that correlated with subsequent neuroprotection, whereas Prx2 was unchanged in separately pretreated cultures. Although the protective mechanisms require clarification, synergistically upregulated NMDAR-PKC-Prx2 (and other antioxidant proteins) is a reasonable component. These findings imply that EtOH + RES antioxidant synergy could be involved in neurobenefits attributed to low-moderate wine consumption.

N-Ethylhexedrone (NEH) and buphedrone (Buph) are emerging synthetic cathinones (SC) with limited information about their detrimental effects within central nervous system. Objectives: To distinguish mice behavioural changes by NEH and Buph and validate their differential harmful impact on human neurons and microglia. In vivo safety data showed the typical induced behaviour of excitation and stereotypies with 4–64 mg/kg, described for other SC. Buph additionally produced jumping and aggressiveness signs, while NEH caused retropulsion and circling. Transient reduction in body-weight gain was obtained with NEH at 16 mg/kg and induced anxiolytic-like behaviour mainly with Buph. Both drugs generated place preference shift in mice at 4 and 16 mg/kg, suggestive of abuse potential. In addition, mice withdrawn NEH displayed behaviour suggestive of depression, not seen with Buph. When tested at 50–400 μM in human nerve cell lines, NEH and Buph caused neuronal viability loss at 100 μM, but only NEH produced similar results in microglia, indicating different cell susceptibilities. NEH mainly induced microglial late apoptosis/necrosis, while Buph caused early apoptosis. NEH was unique in triggering microglia shorter/thicker branches indicative of cell activation, and more effective in increasing microglial lysosomal biogenesis (100 μM vs. 400 μM Buph), though both produced the same effect on neurons at 400 μM. These findings indicate that NEH and Buph exert neuro-microglia toxicities by distinct mechanisms and highlight NEH as a specific inducer of microglia activation. Buph and NEH showed in vivo/in vitro neurotoxicities but enhanced specific NEH-induced behavioural and neuro-microglia dysfunctionalities pose safety concerns over that of Buph.

Recently, the number of new psychoactive substances has significantly increased. Despite the systematic introduction of prohibition in trade of medicinal products which mimic the effects of illegal drugs, the problem concerning this group of drugs is still important although knowledge about the mechanism of action of those types of substances is scarce. This study aimed to follow the neurotoxic effect of N-benzylpiperazine (BZP), the central nervous system psychostimulant, using the human cancer LN-18 cell model. The statistically significant elevation of LDH levels, increased mitochondrial membrane potential, decreased ATP and increased ROS production, increased levels of DNA damage marker (8-OHdG) and activation of caspases: -3 and -9 confirmed by Real-Time PCR imply the activation of mitochondrial proapoptotic pathways induced by BZP after 24 h incubation. This study is a novel, preliminary attempt to explain the toxicity of one of the most popular designer drug of abuse at the cellular level.

We recently demonstrated that Δ9-tetrahydrocannabinol (THC) chronic administration in female adolescent rats induces alterations in the emotional circuit ending in depressive-like behavior in adulthood. Since cognitive dysfunction is a major component of depression, we assessed in these animals at adulthood different forms of memory. Adolescent female rats were treated with THC or its vehicle from 35 to 45 post-natal days (PND) and left undisturbed until their adulthood (75 PND) when aversive and spatial memory was assessed using the passive avoidance and radial maze tasks. No alteration was found in aversive memory, but in the radial maze THC pre-treated animals exhibited a worse performance than vehicles, suggesting a deficit in spatial working memory. To correlate memory impairment to altered neuroplasticity, level of marker proteins was investigated in the hippocampus and prefrontal cortex, the most relevant areas for learning and memory. A significant decrease in synaptophysin and PSD95 proteins was found in the prefrontal cortex of THC pre-treated rats, with no alterations in the hippocampus. Finally, proteomic analysis of the synapses in the prefrontal cortex revealed the presence of less active synapses characterized by reduced ability in maintaining normal synaptic efficiency. This picture demonstrates the presence of cognitive impairment in THC-induced depressive phenotype.