Biosilicification (chalcedony) in human cerebral cortex, hippocampus and cerebellum from aged patients

Modern Views on Desilicification: Biosilica and Abiotic Silica Dissolution in Natural and Artificial Environments

“…Besides quartz and silica forms discussed above, also chalcedony has recently been identified in animal and human tissues. Chalcedony of a biogenic origin has been reported previously in electric organs from living Psammobatis extenta during oxidative stress. , …”

“…Chalcedony of a biogenic origin has been reported previously in electric organs from living Psammobatis extenta during oxidative stress. 58,66 Chalcedony is a microcrystalline fibrous form of silica that can occur in optically length-fast or length-slow forms but actually consists of nanoscale intergrowths of quartz and the optically length-slow fibrous silica polymorph moganite. 201 A slight oversaturation of silicon is necessary for allowing chalcedony precipitation from solution.…”

“…It was also identified in the human cerebral cortex and brain hippocampus. 66 The large amount and size of chalcedony identified in the human hippocampus is very surprising. The hippocampus receives a large cholinergic innervation.…”

“…It was suggested that silica degradation in electric organs of fishes may be mediated by the CAs (silicase). 66 However, no convincing evidence has been found that ferredoxin-NADP reductase from diatom Thalassiosira pseudonana is involved in silica restructuring or maintenance. 208 Thus far in this review desilicification phenomena have been described in living systems (in ViVo).…”

Organosilicon Biotechnology

“…This may be due in part to a dominant theme in bioorganosilicon chemistry which has focussed on the use of enzymes in the synthesis of chemical bonds at or near silicon, rather than their cleavage. However, given the implication of carbonic anhydrases in the biosilification processes (chalcedony) that have been observed to occur in degenerated brain tissue and the brain tissue of elderly individuals, it is anticipated that chemical explorations utilizing this class of enzymes will be very quickly moving into the forefront [104,105].…”