The thesis is devoted to solving of such an urgent issue of modern ophthalmology as the study of morphofunctional changes in the organ of sight (retina and optic nerve) of rats at increased intake of hexavalent chromium from the environment. A research presented in the thesis is aimed to clarify the features of hexavalent chromium neurotoxic effects and to broaden the idea of pathogenetically directed corrective actions and prevention of detected changes.
Heavy metal pollution is growing every year and it raises serious concerns about the possible negative consequences. According to the European Chemicals Agency, every third case of the disease on the planet is due to a chemical factor. Assessment of the heavy metals impact on the organ of sight (retina and optic nerve) as an environmental factor is timely and relevant, because today insufficient attention is paid to this problem.
A limited number of scientific papers devoted to the study of pathogenetic mechanisms of heavy metals (as environmental factors) on the retina and optic nerve determines the practical necessity and significance of this thesis, because understanding the pathogenesis of harmful effects together with the correct diagnostics makes it possible to make an adequate diagnosis of a pathology and enable to provide timely etiological treatment.
An experimental study of morphofunctional changes in R and ON under conditions of exposure to Cr (VI) was performed on 72 adult male rats. All experimental manipulations with animals were carried out in compliance with the rules adopted by the "European Convention for the Protection of Vertebrate Animals Used for Experimental and Scientific Purposes" (Strasbourg, 1986), General Ethical Principles of Animal Experiments, approved by the 3rd National Congress of Bioethics , 2007) and in accordance with the provisions of ARVO (The Association for research in vision and ophthalmology) on the use of animals in ophthalmic research. The protocol of research work (№3 dated 26.10.2020), drawn up by the Commission on Bioethics of KhMAPE, certifies the absence of ethical, moral and legal violations during the experiment.
According to the research program, rats were divided into three groups of 24 rats in each: (I) control group, (II) - rats receiving drinking water enriched with Cr (VI) (K2Cr2O7) - 0.02 mol / l, typical for soil of the northern part of Sumy region and (III) – rats drinking water saturated with K2Cr2O7 and methyl-silicic acid hydrogel as a correcting agent. Animals were taken out of the experiment on the 20th, 40th and 60th days.
The solution of this problem and analysis of the obtained results were achieved using modern methods of retinal and optic nerve research: histological and histomorphometric - to study pathological changes in neurocytes and their processes and cells of macroglial origin, histochemical - to assess the deformation degree of myelin sheath of intracranial part in the cranial nerve, immunohistochemical - to determine the activity of endogenous reparative proteins under stress. Statistical and mathematical calculations were used for processing the study results. Trace element composition was studied using crystal diffraction and energy dispersion spectrophotometers in a scanning electron microscope.
When hexavalent chromium gets into the rat organism, degenerative changes of neurons and neuroglia develop in its R and ON. Nature and severity of the latter depended on the duration of exposure to Cr (VI) with achievement of the highest level of pathological changes after 60 days of the experiment. Edematous changes were found in all layers of the retina: such as increase in total thickness - 216.79 ± 8.47 μm (+ 16.2%) (p <0.02) and deformation of layers structure. Bodies of I, II and III neurons had signs of karyolysis, chaotic arrangement and fragmentation of processes. Intracranial part of optic nerve had a defect of cytoarchitectonics due to frequent deformations of axons of retinal ganglion cells (RGC), derangement of their parallel location and edema increase from 9.86 ± 1.37 μm to 15.7 ± 1.3 μm (+59.22 %) (p <0.01). Reactive changes of astrocytes with increase of shadow cells number to 3060 ± 180 in 1 mm2 (+ 70%) (p <0,01) were revealed, which is a sign of diffuse reactive gliosis development.
It was concluded that hexavalent chromium penetrates through the blood-brain barrier (BBB) and blood-ocular barrier (BOC), with accumulation in R on the 20th day of the experiment - 0.03 ± 0.01% in R and ON -0.1 ± 0, 01%; 0.13 ± 0.01% on the 40th day and 2.69 ± 0.62% (p <0.02) and 1.23 ± 0.1% (p <0.02), respectively, at the end of the experiment with simultaneously dysregulated levels of essential trace elements - calcium (↓ 23.83%), magnesium (↑ 55.6%), chlorine (↑ 46.7 %) in R and sodium (↑ 108.3%) and calcium (↓ 17.8%) (p <0.05) in ON.
