title: LDH enzyme activity in human saliva: the effect of exposure to cigarette smoke and its different components.
abstract: OBJECTIVE
  Aldehydes and reactive nitrogen species (RNS) are important chemically active agents in cigarette smoke (CS). Salivary lactate dehydrogenase (LDH) originates predominantly from oral epithelium and was identified as an oral state marker. Its activity in saliva decreases after CS exposure. The aims of the current study were to identify the specific damaging agents in CS responsible for this activity reduction and to understand the mechanisms participating in CS oxidative damage to the salivary enzymes.
  
  
  METHODS
  Purified and salivary LDH samples were exposed to different levels of CS, pure acrolein, acetaldehyde, peroxynitrite and RNS donors. Each response of the isolated agent to the exposure was examined by a spectrophotometric enzyme activity assay and a Western blot.
  
  
  RESULTS
  CS exposure caused a 34% reduction in LDH activity. Isolated treatment with unsaturated-aldehydes (acrolein, 10μmol) caused a 61% reduction, while saturated-aldehydes (acetaldehyde, 200μmol), peroxynitrite (200μM) and RNS donor (SIN-1, 2mM) caused no substantial effect. All five LDH isoenzymes reacted similarly. The carbonyl immunoblotting assay revealed a fourfold increase in carbonyl content when treated with CS and a sevenfold increase when treated with acrolein.
  
  
  CONCLUSIONS
  α,β-Unsaturated-aldehydes were identified as the main CS ingredient responsible for salivary LDH activity diminution. The effect of saturated-aldehydes and RNS donors was negligible. Unsaturated-aldehydes are capable of introducing carbonyl group into proteins, causing their dysfunction. This provides a molecular explanation for a decrease in LDH enzymatic activity in saliva.
authors.affiliation: Department of Anatomy and Cell Biology, Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel; Orthodontic and Craniofacial Department, School of Graduate Dentistry Rambam Health Care Campus, Haifa, Israel.
authors.forename: Katia
authors.initials: K
authors.lastname: Avezov
authors.affiliation: Department of Anatomy and Cell Biology, Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel.
authors.forename: Abraham Z
authors.initials: AZ
authors.lastname: Reznick
authors.affiliation: Department of Anatomy and Cell Biology, Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel; Orthodontic and Craniofacial Department, School of Graduate Dentistry Rambam Health Care Campus, Haifa, Israel. Electronic address: aizenbud@ortho.co.il.
authors.forename: Dror
authors.initials: D
authors.lastname: Aizenbud
mesh_terms: D000079:Acetaldehyde / Q000737:chemistry; D000171:Acrolein / Q000737:chemistry; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008297:Male; D030421:Peroxynitrous Acid / Q000737:chemistry; D026361:Reactive Nitrogen Species / Q000737:chemistry; D012463:Saliva / Q000187:drug effects* / Q000201:enzymology*; D012471:Salivary Proteins and Peptides / Q000378:metabolism; D012906:Smoke; D014026:Nicotiana
chemical_list: D026361:Reactive Nitrogen Species; D012471:Salivary Proteins and Peptides; D012906:Smoke; D030421:Peroxynitrous Acid; D000171:Acrolein; D007770:L-Lactate Dehydrogenase; D000079:Acetaldehyde
keywords: Cigarette smoke; Lactate dehydrogenase; Protein carbonylation; Reactive nitrogen species; α,β-Unsaturated aldehydes