During inflammation, myeloperoxidase
released from activated phagocytes
generates the highly reactive oxidant hypochlorous acid (HOCl). This
oxidant plays an important role in the immune response but can also
promote tissue damage and has been strongly linked with the development
of numerous inflammatory diseases. HOCl reacts with cellular DNA forming
chlorinated nucleobases, which induce strand breaks, mutations, and
cross-links. Although it has been shown that chlorinated nucleosides
are present within inflammatory pathologies and diseased tissue, whether
or not these species are biomarkers formed as a byproduct of chronic
inflammation or play a role in the disease progression has not been
ascertained. In this study, we show that exposure of J774A.1 macrophage-like
cells to chlorinated ribose and deoxyribose nucleosides results in
the incorporation of 5-chloro-cytidine (5ClC), 8-chloro-adenosine
(8ClA), and 8-chloro-guanosine (8ClG) into the cellular RNA and 5-chloro-deoxycytidine
(5CldC) but not 8-chloro-deoxyguanosine (8CldG) or 8-chloro-deoxyadenosine
(8CldA) into cellular DNA. Evidence was obtained for the clearance
of 5ClC from the RNA, with a loss of 8ClA and 8ClG observed to a lesser
extent, whereas an increase in the level of 5CldC in DNA was seen
on further incubation of treated cells in the absence of chlorinated
nucleosides. Importantly, exposure of the macrophages to chlorinated
nucleosides, particularly 8ClG and 5ClC, resulted in the increased
expression of interleukin-1β, and other pro-inflammatory cytokines
and chemokines. With 5ClC, this inflammatory response was associated
with the increased nuclear translocation of the NF-κB subunit,
p65, rather than inflammasome activation. This alteration in gene
expression appeared to be unrelated to the extent of incorporation
of the chlorinated nucleosides into RNA or DNA and was not associated
with any significant changes in cell viability or proliferation. Taken
together, these results highlight a potential biological role for
chlorinated nucleosides to promote inflammatory disease, in addition
to their utility as biomarkers.