Denysenko A. Pathomorphological characteristics of meningioma biomineralization

Biomineralization is a phenomenon characteristic of living organisms, consisting of forming biominerals. The central nervous system of the human body is no exception; biomineralization can occur in both normal conditions (age changes) and in various pathologies. For example, it is typical for meningiomas (tumours of the brain membranes), which are the most common non-malignant tumours of the central nervous system. This dissertation work is devoted to a relevant problem, namely, improving the possibilities of the diagnostic and treatment process for patients with meningiomas. To solve this problem, we used the following research methods: histological (hematoxylin-eosin staining), histochemical (alizarin red S staining, von Koss staining, Van Gieson method and PAS reaction), immunohistochemical (panel of osteoblastic antibodies OPN, SPARC, RANKL and OPG, apoptosis marker Casp-3), electron microscopic (scanning electron microscopy, transmission electron microscopy) and statistical (parametric and non-parametric criteria). The design of the dissertation provides for the formation of 4 research groups: meningiomas with signs of biomineralization (30 samples), meningiomas without signs of biomineralization (30 samples), dura mater with signs of biomineralization (30 samples), dura mater without signs of biomineralization (30 samples). Tumours of the meninges (meningiomas) during macroscopic examination were often described as spherical or hemispherical, rarely plaque-like formations, the size of which varied from 0.5 cm to 3.0 cm. They were characterized by a grey colour, a smooth or slightly bumpy surface, moderate or increased density, and specific crunch when cut. During the histological examination, meningiomas were often classified as meningothelial, psammomatous or fibrous histological subtypes. They were characterized by the presence of cells of the endothelial phenotype (by the type of meninges). The next step for the detection of calcium compounds was a histochemical study. Alizarin red S staining identified calcium (all forms) and iron compounds (may indicate effects of cerebral haemorrhage; Perl's reaction is recommended for confirmation). Von Koss's staining narrowed the circle to calcium phosphate compounds. Van Gieson's method, PAS-reaction and immunohistochemical study indicate that psammoma bodies contain glycoproteins and proteins in addition to the biomineral component, which is an organic-mineral composite. A significantly higher level of Casp-3 and specific features of the expression of osteoblastic markers (a lower level of OPG expression and a higher level of RANKL in the group with biomineralization, no fluctuations in SPARC expression) may indicate the predominance of a passive mechanism (by dystrophic type) in the pathogenesis of psammoma bodies. Based on the results of scanning electron microscopy with energy dispersive X-ray spectroscopy and transmission electron microscopy with electron diffraction, it was established that calcium hydroxyapatite Ca10(PO4)6(OH)2 is the main biomineral in psammoma bodies of meningiomas. The dura mater is one of the meninges, represented by fibrous tissue and contains fibroblasts and extracellular collagen. Histochemical methods identified small calcifications, and the PAS reaction, unlike meningiomas, is negative in biomineral formations). Based on the results of the immunohistochemical examination of the dura mater tissue using a panel of osteoblastic antibodies (OPN, SPARC, RANKL ̶ p˂0.001) and the apoptosis marker Casp-3 (p˃0.05), it is possible to conclude that the active mechanism of formation of calcium-phosphorus biominerals predominates in this tissue. According to the results of scanning electron microscopy with energy dispersive X-ray spectroscopy and transmission electron microscopy with electron diffraction, it was established that calcium hydroxyapatite Ca10(PO4)6(OH)2.is the main biomineral in the tissue of the dura mater. The obtained results make it possible to distinguish calcifications in meningiomas and the dura mater: they have a similar chemical composition (according to the Ca/P ratio, they correspond to mature hydroxyapatite), but differ in structure and morphology. Based on our dissertation research results, we propose optimising the diagnostic process by implementing the developed diagnostic algorithm for the differential diagnosis of neoplasms of the dura mater based on the existing signs of tissue calcification. In addition, the detailed pathomorphological and material science (physico-chemical) study of biomineral deposits can help create biomaterials based on the type of dura mater. It can improve the treatment process of patients with defects of the meninges after traumatic injuries and neurosurgical operations.