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

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 ɛ4 (apoE ɛ4) 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 ɛ4 carriers exhibited less temporal variation in salivary protein carbonyls relative to noncarriers. Thus, protein carbonyl content exhibits diurnal variation in adult human saliva. ApoE ɛ4 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 ɛ4 allele carrier status may attenuate this temporal variability in salivary redox homeostasis and thereby impact the natural history of oropharyngeal diseases.

Salivary Markers of Oxidative Stress and Antioxidant Status: Influence of External Factors

“…Previously, significantly highest TBARS levels were observed in the morning hours [18]. On the other hand Su et al observed diurnal variations in salivary protein carbonyl concentrations with highest concentrations at 2:00 p.m. [50]. Significant daily variations were observed in salivary FRAP levels (F = 3.019, p < 0.01, ANOVA) representing antioxidant status.…”

“…Assessment of circadian rhythm could be also valuable for optimization of therapeutic interventions according to expected redox homeostasis [50].…”

Age-related variations of protein carbonyls in human saliva and plasma: is saliva protein carbonyls an alternative biomarker of aging?

“…Pandey observed an age-dependent increase in plasma protein carbonyl level (r=0.768) and protein carbonyls/ FRAP ratio (r=0.917), and plasma protein carbonyl levels were between 20 and 70 nmol/L (Pandey et al 2010). Su reported that the salivary protein carbonyl level among healthy adults was 1.80±0.15 nmol/mg (Su et al 2008), but he denied the relationship between levels of log protein carbonyls and age (Su et al 2012). Baltacioglu discovered that the average levels of serum and gingival crevicular fluid protein carbonyls were 1.22 and 1.10 nmol/mg (Baltacioglu et al 2008).…”

“…After collection, tubes with samples were kept at 4°C while further process must be done in 1 h. The tubes were centrifuged at 4000 rpm for 20 min at 4°C (Eppendorf Co., Hamburg, Germany), and the supernatants were gathered and stored in 1-mL aliquots for less than half a month ahead of detection. Samples mixed with blood or other visible impurities were discarded immediately, and each sample should not be frozen and thawed twice or more (Pandey et al 2010;Su et al 2008Su et al , 2009Su et al , 2012Zeng et al 2012). …”

“…For its relative early formation, chemical stability, and uncomplicated detection method, protein carbonyl content has become by far one of the most widely used markers of protein oxidation Chevion et al 2000), and elevated amount of protein carbonyls has been detected in several human aging-related diseases including Alzheimer's disease, cancer, cardiovascular diseases, diabetes, and in plasma of elderly ones (Miriana and Denisa 2013;Mannello et al 2013;Ian et al 2013;Mediha et al 2010;Pandey et al 2010). Until recently, few research about saliva protein carbonyls have emerged while most focused on plasma or tissue protein carbonyls over the past decades (Pandey et al 2010;Hensley et al 1995;Su et al 2008Su et al , 2009). Unlike plasma, saliva test which is currently promising has the advantage of no-pain, noninvasiveness, infection-free, and convenience, and the relevance of protein carbonyl content between saliva and plasma has never been explored.…”