Melatonin's role in ameliorating perturbed circadian immune molecular links with aging and sleep deprivation in central and peripheral clocks in male Wistar rats.

Sleep deprivation (SD) and aging are linked to chronic inflammation, a contributor to age-associated diseases. Circadian rhythms, governed by suprachiasmatic nucleus (SCN), regulate immune and inflammatory responses. While aging and SD elevate pro-inflammatory cytokines such as IL-1β, TNF-α, and IL-6, their impact on temporal dynamics of inflammation across tissues and age groups remains unclear. This study examines age-dependent effects of chronic total SD on daily expression rhythms of inflammatory markers in central (SCN) and peripheral (cerebral cortex, liver, intestine) clocks of male Wistar rats aged 3 (adult), 12 (middle-aged), and 24 (old) months (m). Nitric oxide (NO), linked to inflammation and metabolism, was also evaluated in liver and intestine. Animals were sampled at four Zeitgeber (ZT) times. Further, the study examined the effects of melatonin, a circadian-regulated antioxidant, anti-inflammatory agent, and sleep synchronizer, on daily rhythms of inflammatory markers with aging and upon SD were studied. The mRNA expression levels of rTnf-α, rIl-6 and rIl-1β were assessed using qRT-PCR. NO levels were measured using Griess assay. Rats were grouped as control, SD, SD + melatonin and vehicle control groups. Significant SD-induced misalignment, especially in rIl-6 and rTnf-α in cerebral cortex and liver was observed in 12 m. SD altered circadian phases and expression levels were significantly greater in older rats (24 m > 12 m > 3 m) and in peripheral clock as compared to central clock liver > cerebral cortex > intestine > SCN. Melatonin differentially restored these rhythms, most effectively for rIl-1β and in the cerebral cortex and liver. SCN showed highest resilience, reinforcing its role as the central circadian pacemaker, while the liver and cerebral cortex emerged as the most vulnerable to SD and aging.