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Unsaturated aldehydes cause reduction of salivary LDH enzyme activity

Katherine Avezov and Avraham Reznick

Volatile aldehydes and reactive nitrogen species (RNS) are important oxidative agents in cigarette smoke (CS). The smoke constitutes one of the largest environmental sources of saturated (e.g. acetaldehyde) and unsaturated aldehydes (e.g. acrolein) and RNS (nitric oxide and peroxynitrite). Salivary lactate  dehydrogenase (LDH) originates from oral epithelial cells and was identified as a marker of oral epithelium state. Its activity in saliva decreases after exposure to CS. Identifying specific damaging agents in CS responsible for LDH activity reduction may assist in understanding the molecular mechanisms of oxidative damage to the oral cavity tissues and salivary enzymes.

This study investigated the effect of direct exposure of purified and salivary LDH enzyme to CS, comparing it to isolated effect of RNS and aldehydes. Unsaturated aldehydes were identified as the main cause to salivary LDH activity reduction. The effect of saturated aldehydes, peroxynitrite and RNS donors was negligible. Unsaturated aldehydes content in CS is capable of introducing carbonyl groups into proteins, causing their dysfunction. These results provide a molecular explanation for enzymatic activity decrease in saliva.