Cognitive impairments by formaldehyde exposure in Alzheimer's disease

Formaldehyde (FA) is a highly reactive molecule that is considered as a community concern due to the huge human exposure in industries, dissection unit in hospitals and academics. Furthermore, it is used in manufacturing paper and plywood, and preservation of biological specimens. FA is present normally in certain concentration in the brain and its metabolism plays a major role in methylation and demethylation of DNA, RNA and histones. However, excess concentration of FA reduces the cognitive function and causes dementia especially in aging brain. Recent studies investigated the link between excess exposure to FA and age-related cognitive impairment through NMDA-receptor dysregulation and other mechanisms including amyloid-β (Aβ) accumulation, alterations in alcohol dehydrogenase-5 (ALDH5) and Tau dysmetabolism and aggregation which serves as major causes of Alzheimer's disease (AD). Recent hypothesis agreed that when FA causes Aβ to accumulate in extracellular space, it prevents the medications that are dissolved in the interstitial fluid from permeating the injured cortical neurons and leads to neurons death. Although treatment of AD with phototherapy has been achieved before which involves the destruction of Aβ deposit; however, reducing the amount of exposure to FA and its derivatives remains a golden step in the prevention.