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The present study aimed to investigate the effect of APAP treatment on the expression of pro-inflammatory cytokines in the astrocytes. The mouse astrocyte cells (C8-D1A) were treated with APAP at the concentration of 100 μM for 24 h, 16 and 28 days. The expressions of pro-inflammatory cytokines and NF-kB were determined using western blot analysis. Furthermore, the expression and localization of phosphorylation of NF-kB were detected by immunohistochemical and immunofluorescent analysis. The ultrastructure of C8-D1A cells was as well monitored. The results revealed that acute APAP treatment (24 h) had no effect on the expression of pro-inflammatory cytokines and pNF-kB. This treatment did not alter the ultrastructure of C8-D1A cells when compared with those in the control cells. However, the results obtained from the study on chronic APAP-treated cells (16 and 28 days) showed the different effect of APAP treatment. The results obtained from western blot analysis showed the increment of pro-inflammatory cytokine (IL-1β and TNF-α) expressions and the activation of NF-kB signaling pathway. Nuclear translocation of pNF-kB and alteration of several cell structures were well observed in the C8-D1A cells with chronic APAP treatment. The results obtained from this study suggest that chronic APAP treatment can induce an upregulation of pro-inflammatory cytokines (IL-1β and TNFα) in astrocytes. This alteration implies the involvement of the activation of NF-kB signaling pathway.

Previously, our group has demonstrated that chronic paracetamol (APAP) treatment induces alterations to the trigeminovascular nociceptive system in the cortical spreading depression (CSD) migraine animal model. The calcitonin gene related peptide (CGRP) is a key neuropeptide involved in the activation of the trigeminovascular nociceptive system. Therefore, this study examined the expression levels of CGRP in the trigeminal ganglion (TG) after chronic APAP exposure (0, 15, and 30 days) using a CSD model. Rats were divided into control, CSD only, APAP only and APAP treatment with CSD groups. A single injection (i.p.) of APAP (200 mg/kg body weight) was given to the 0-day APAP-treated groups, while the other APAP-treated groups received daily injections for 15 and 30 days. CSD was induced by the topical application of KCl to the parietal cortex. The protein expression of CGRP in the TG was evaluated by immunohistochemistry, and the CGRP mRNA level was investigated by real-time quantitative reverse transcription polymerase chain reaction. The results revealed that the induction of CSD significantly increased the level of CGRP protein but had no effect on CGRP mRNA level. Pretreatment with APAP 1 hour before CSD activation significantly reduced CGRP expression induced by CSD. In contrast, chronic treatment with APAP (15 and 30 days) significantly enhanced CGRP expression in both protein and mRNA levels when compared with the control groups. In combination with CSD, the expression of CGRP further increased in the animal with 30 day treatment. These findings indicate that chronic treatment with APAP induces an increase of CGRP expression in the TG. This alteration may be associated with the increased trigeminovascular nociception observed in our previous studies., (Copyright © 2015 Elsevier Ltd. All rights reserved.)