4. Discussion
Although Vit D deficiency has been shown to correlate with poor
prognosis in cancer therapy-induced mucositis, no animal model study
experimentally tested whether Vit D supplementation could have
therapeutic effects on mucositis course. IL-22 is a critical cytokine
for gastrointestinal homeostasis and restoration of damaged
intestinal/mucosal tissues. Absence of IL-22 exacerbates mucositis
outcome in the murine models and Vit D-mediated signaling was shown to
regulates IL-22 production in both mice and humans. However, whether
recombinant IL-22 or its genetic overexpression would have therapeutic
benefit has not yet been put to test neither in animal models, nor in
humans. In this study, our data revealed that in a preclinical model of
methotrexate-induced mucositis, Vit D supplementation could improve
mucositis, and the protection may be IL-22 mediated.
Our data revealed that Vit D injections ameliorated mucositis pathology.
Injections were initiated 4 days prior to methotrexate injection in
order to give Vit D time to have its effects on mucosal cells, thus, it
was considered for prophylaxis. These results are consistent with
previous findings that Vit D deficiency is associated with more severe
mucositis both in adults and pediatrics.9,21Nejatinamini et al. reported that lower intake of vitamins and
plasma 25-hydroxy Vit D (25-OHD) was associated with mucositis in head
and neck cancers treatments.21 The patients included
both radiation and chemotherapy or combined therapy groups (22%
radiotherapy, 71% chemotherapy, 7% both). Similar observations were
made in acute lymphoblastic leukemia in children.9Safety of Vit D supplementation in pediatric cases prior to
hematopoietic cell transplantation have also been
reported.22 Data from a study by Anand et
al.23 with adult oral cancer patients revealed that
Vit D supplementation significantly improved treatment associated
mucositis. Another study with smaller patient cohort size (n=14) found
no significant benefit.24 Therefore collectively,
these data argue for a beneficial role for Vit D in improving
treatment-associated mucositis in cancers and perhaps hematopoietic stem
cell transplantation.25
IL-22 is an important cytokine in gut homeostasis. Intestinal epithelial
cells express IL-22 receptors and IL-22R signaling in these cells
promotes regeneration of epithelial tissue. Indeed, its absence renders
mice susceptible to dextran sulfate sodium (DSS)-induced models of
colitis.26 This also is valid for CD4+ naïve T cell
induced models of colitis. 19, 26, 27 In addition to
intestinal tissue remodeling IL-22 signaling stimulates production of
mucus, anti-microbial peptides which are crucial for epithelial barrier
immunity and homeostasis.28 In the intestinal lamina
propria or other mucosal tissues, IL-22 is produced by Th17 cells,
ILC3s, mucosal-associated invariant T (MAIT) and gamma delta T cells.
Vit D and VDR signaling was shown to be critical for development and
function of ILC3s and forkhead box P3 (FOXP3)+ Treg
cells in gastrointestinal system. 11, 12 Thus,
diminished number of ILC3s and subsequently reduced levels of IL-22 and
IL-10 was reported in the deficiency of Vit D.11, 12Our cytokine data of IL-22 levels are in line with these reports. Vit D
treatment augmented intestinal IL-22 production. IL-22 hydrodynamic
delivery also increased IL-22 levels. The effect of Vit D IL-22 was more
profound than hydrodynamic delivery group. This was also reflected in
the histopathology scores. In our model, Vit D did not appear have an
impact on total ILC levels. This might be due to relatively short
treatment time.
In summary, our results show that Vit D treatment may provide partial
protection from chemically-induced mucositis in mice.