Driuk M. Neuroactive environmental pollutants: membrane-associated mechanisms of action and ways to overcome neurotoxicity

Driuk M.M. Neuroactive environmental pollutants: membrane-associated mechanisms of action and ways to overcome neurotoxicity. Qualifying scientific work submitted as a manuscript. Dissertation submitted for the degree of Doctor of Philosophy in Specialty 091 “Biology.” – Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv, 2026. The PhD thesis is devoted to elucidating the molecular mechanisms of the acute neurotoxic effects of mercury ions (Hg2+) in presynaptic nerve terminals of the rat brain, investigating the features of the combined action of Hg2+ and carbonaceous smoke particles, as well as evaluating the potential of various nanomaterials as prospective adsorbents/detoxifying agents for this metal ion in biological systems. The relevance of the study is determined by the widespread prevalence of neurodegenerative and neurological diseases, the development of which is associated, in particular, with environmental contamination by heavy metals and airborne particulate matter. Mercury is of particular concern because of its ability to accumulate in the body and disrupt the functioning of the central nervous system. Despite the considerable body of research, the molecular mechanisms underlying the neurotoxic effects of Hg2+, particularly under conditions of combined exposure to carbonaceous smoke particles, remain insufficiently understood. Another promising research direction is the search for biocompatible nanomaterials capable of binding mercury ions and reducing their toxic effects on the organism. During the course of the study, it was established that Hg2+ disrupts glutamatergic neurotransmission in the nerve terminals of the rat brain. It was shown that, starting from a concentration of 10 μM, Hg2+ decreases the initial rate of L-[14C]glutamate transport and accumulation by synaptosomes, which is accompanied by an excitotoxic increase in its extracellular level. It was established that this increase results from the inhibition of the functional activity of glutamate transporters rather than from impaired plasma membrane integrity or enhanced tonic neurotransmitter release. For the first time, a comparative study of the biocompatibility and Hg2+-adsorbing properties of different types of nanomaterials in the biological system of nerve terminals was performed. It was established that only carbon dots synthesized from citric acid and urea, as well as from coffee beans, are biocompatible and capable of attenuating the Hg2+-induced excitotoxic increase in the extrasynaptosomal level of L-[14C]glutamate. In contrast, carbon dots synthesized from β-alanine, as well as nanodiamonds, did not demonstrate the ability to adsorb Hg2+ in the biological system under study. The developed methodological approach can be applied to monitor the ability of various particles/compounds to exhibit Hg2+-adsorbing properties in biological systems. It was established that mesoporous silica nanoparticles functionalized with SH-, SO3H-, and NH2-groups do not exhibit signs of acute neurotoxicity and are characterized by high biocompatibility; however, they do not reduce the neurotoxic effects of Hg2+, indicating the absence of their adsorptive activity toward this metal. The obtained results demonstrate the potential of using such nanoparticles as carriers of biologically active substances and pharmaceutical agents capable of eliminating the toxic effects of mercury. For the first time, it was shown that solid carbonaceous particles derived from wood smoke increase the unstimulated release of L-[14C]glutamate from synaptosomes, and that their combined action with Hg2+ exerts a neurotoxic effect on the accumulation and release of L-[14C]glutamate and [3H]GABA. It was established that both Hg2+ and carbonaceous particles derived from wood smoke separately induce depolarization of the plasma membrane of nerve terminals, whereas their combined exposure does not exceed the effect of either factor alone. A similar pattern of interaction was also observed in the study of synaptic vesicle acidification. Keywords: Neurotoxicity, mercury (Hg2+), heavy metals, carbonaceous particulate matter, carbon dots, mesoporous silicon dioxide nanoparticles, nanomaterials, glutamate, synaptosomes, presynaptic nerve terminals, nervous system, aggregometry, animal models, biocompatibility.