Misaligned Feeding May Aggravate Pain by Disruption of Sleep-Awake Rhythm

Increasing evidence suggests that patients with eating disorders are more likely to develop chronic pain. A misaligned diet has been reported to disrupt the sleep-awake rhythms. Combined with our previous investigation on circadian pain, we aimed to investigate the role of misaligned diet in the pain sensitivity and the underlying mechanisms.

Two-month-old C57BL/6J male mice were administered chronic constriction injury (CCI) surgery to establish neuropathic pain models. CCI mice were randomized to scheduled food access throughout the whole day (CCI-free), during the daytime (CCI-misaligned), and at night (CCI-aligned), respectively. The paw withdrawal mechanical threshold, indicating pain behavior, was measured by Von Frey. The gross motor activity pattern indicating the sleep-awake rhythm was monitored by Mini-Mitter. Melatonin (Mel) was administered to ameliorate the sleep-awake rhythm (CCI-free + Mel and CCI-misaligned + Mel). The expressions of circadian pain-related proteins were detected by quantitative polymerase chain reaction and western blot. The primary outcome is the pain threshold and the secondary outcome is the sleep-awake rhythm.

Misaligned diet during the peri-CCI surgery period significantly decreased the paw withdrawal mechanical threshold compared with the CCI-free mice (day 14: 0.40 ± 0.09 vs 0.64 ± 0.15; P = .03;) and altered the sleep-awake rhythm. Mel pretreatment alleviated the increased pain (day 14, CCI-misaligned + Mel versus CCI-misaligned: day 14: 0.60 ± 0.13 vs 0.35 ± 0.12; P = .022) and the disrupted sleep-awake rhythm caused by misaligned feeding. The mRNA levels of N-methyl-D-aspartate receptor subtype 2B (NR2B), Ca/calmodulin-dependent protein kinase II (CaMKII), and cyclic adenosine monophosphate-response element binding protein (CREB) in the spinal dorsal horn increased in CCI-misaligned mice compared with the CCI-free mice. The phosphor-NR2B, phosphor-CaMKII, and phosphor-CREB also increased in CCI-misaligned mice compared with the CCI-free mice. However, the expressions of NR2B, CaMKII, and CREB were decreased in CCI-misaligned + Mel mice compared to CCI-misaligned mice at both transcriptional and translational levels.

Misaligned diet might aggravate pain sensitivity through the disruption of the sleep-awake cycle, which could be recovered by Mel. NR2B-CaMKII-CREB may participate in the disruption of sleep-awake rhythm-mediated pain aggravation.