1. Introduction
Mucositis is the painful inflammation and ulceration of oral or gastrointestinal tract and is usually caused by cancer therapies.1 Thinning of the oral mucosa, a late side effect of cancer treatment can cause chronic or non-healing ulcers. Gastrointestinal obstruction, necrosis and perforation can also lead to gastrointestinal damage.1,2 Side effects of cancer treatment occur more in cells with rapid proliferation and normal tissues containing rapidly growing cell populations of the host can also be damaged.3 Chemotherapy and radiotherapy cause DNA damage; they stimulate the formation of free oxygen radicals and can directly affect non-DNA targets. As a result, macrophages are activated and molecules that activate transcription factors, including nuclear factor kappa B (NF-κB), are triggered. The production of proinflammatory cytokines such as Tumor necrosis factor alpha (TNF-α), Interleukin (IL)-6 and IL-1 increase. The mucosa becomes susceptible to bacterial contamination because of tissue damage and ulceration. The mucosal integrity in the epithelial cells is rearranged with the proliferation, differentiation and migration and the recovery phase begins.2,4 Mucositis may cause significant problems such as abdominal pain, ulceration, dysphagia and diarrhea, decreased fluid and nutrient intake, dehydration and weight loss. These problems require parenteral nutrition of the patient and prolonged hospitalization. Furthermore, they cause speech difficulties, communication disorder, consequently, lowers the quality of life. The prevalence of mucositis is three-fold higher in children than in adults and can lead to serious respiratory disorders.5 The development and recovery phase of mucositis vary according to the dose and frequency of the drugs used and the tolerance of the patient.2
Vitamin D (Vit D) is a crucial fat-soluble micronutrient that plays key roles in bone and teeth development, protection from cardiovascular diseases, cancer and regulation of immune system.6 Vit D induces intestinal stem cell maturation and may suppress colitis by protecting the mucosal epithelial barrier.7,8 Data suggest that Vit D levels may impact mucositis severity. In pediatric acute lymphoblastic leukemia patients above the age of 4, Vit D deficiency has been reported. During methotrexate (MTX) therapy, 25(OH)D3 level was low and more severe oral mucositis was observed in these patients.9 Importantly, a 59-year old patient with breast carcinoma treated by docetaxel, trastuzumab and carboplatin who had low Vit D levels initially, has been given Vit D and his chemotherapy-dependent oral mucositis has improved.10Studies show that in Vit D receptor (VDR)-/- mice, levels of IL-1β and TNF-α following induction of colitis were elevated.11,12 Thus, these studies suggest that Vit D may be beneficial may limit the severity of chemotherapy-induced mucositis. However, to our knowledge, this has not yet been tested in an animal model of mucositis.
IL-22, is a critical cytokine in modulating tissue responses during inflammation. IL-22 is expressed by many lymphocytes, including T helper (Th) 17, Th22, Natural killer T (NKT) cells, Group 3 Innate Lymphoid Cells (ILC3s) and neutrophils.13 IL-22 binds to a heterodimeric receptor composed of IL-22RA1 and IL-10RB subunits which mainly expressed by non-hematopoietic cells, such as epithelial cells of the gastrointestinal tract and skin.14 IL-22 is constitutively expressed in the normal colon mucosa, and is critical in barrier immunity, containment of microbiota on the luminal side of the intestine, and intestinal tissue homeostasis.15 More importantly, ILC3s cells have been shown to be play a protective role in the murine methotrexate-induced mucositis model via IL-22 mediated mechanisms.16 However, to our knowledge, whether recombinant IL-22 or its over expression could be therapeutically exploited to suppress or improve the severity of mucositis has not yet been tested.
In this project, we aimed to test the therapeutic impact of Vit D treatment or IL-22 overexpression on the methotrexate-induced mucositis pathogenesis in Balb/c mice.