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. 2008 Mar;30(1):1-9.
doi: 10.1007/s11357-007-9042-z. Epub 2008 Jan 4.

Diurnal variations in salivary protein carbonyl levels in normal and cognitively impaired human subjects

Haixiang Su  1 , Mervyn Gornitsky, Guoyan Geng, Ana M Velly, Howard Chertkow, Hyman M Schipper
Affiliations

Diurnal variations in salivary protein carbonyl levels in normal and cognitively impaired human subjects

Haixiang Su et al. Age (Dordr). 2008 Mar.

Abstract

Oxidative stress has been documented in tissues and biofluids of subjects with sporadic Alzheimer disease (AD) and mild cognitive impairment (MCI). The aim of this study was to determine whether (a) salivary protein carbonyls are elevated in AD and MCI subjects, (b) salivary protein carbonyl contents in these groups exhibit diurnal variation, and (c) apolipoprotein E epsilon 4 (apoE epsilon 4) carrier status impacts salivary carbonyl concentrations or rhythmicity in the AD and MCI cohorts. Unstimulated saliva was collected at fixed intervals between 8 AM: and 10 PM: from 15 AD subject , 21 MCI subjects, and 30 cognitively-intact controls. Salivary protein carbonyl concentrations were measured by ELISA. ApoE genotyping was performed on the AD and MCI individuals. For all groups, mean protein carbonyl contents were significantly elevated at 2 PM: relative to other time points surveyed. Mean salivary protein carbonyl concentrations did not differ among the diagnostic groups. ApoE epsilon 4 carriers exhibited less temporal variation in salivary protein carbonyls relative to noncarriers. Thus, protein carbonyl content exhibits diurnal variation in adult human saliva. ApoE epsilon 4 carrier status may impact oropharyngeal disease expression by attenuating the inherent diurnal variability in salivary redox homeostasis. Salivary protein carbonyls do not differentiate AD and MCI from normal individuals. In conclusion, oxidative stress has been documented in tissues and biofluids of subjects with sporadic AD and MCI. This article demonstrates that levels of protein carbonyls, a marker of oxidative stress, exhibit robust diurnal variation in the saliva of normal elderly, MCI, and AD subjects. Apolipoprotein E epsilon 4 allele carrier status may attenuate this temporal variability in salivary redox homeostasis and thereby impact the natural history of oropharyngeal diseases.

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Figures

Fig. 1
Fig. 1
Salivary protein carbonyl levels as a function of diagnosis and sampling time. Depicted are protein carbonyl concentration (nmol/mg protein) in control, MCI, and AD subjects over a 14-hour sampling period. Results shown in Figs. 1 and 2 are averaged from ELISA run in triplicate. n = 30 per control group, n = 21 per MCI, and n = 15 per AD group. For Figs. 1 and 2, statistical significance values are provided in the text
Fig. 2
Fig. 2
Salivary protein carbonyl levels as a function of apoE status. Protein carbonyl concentration (nmol/mg protein) in ApoE ɛ4 allele carriers (n = 8) and non-carriers (n = 22) over a 14-hour sampling period
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