Alimentary tract mucositis: NF-kB and pro-inflammatory cytokines in the tissues and serum following chemotherapy.

Abstract

Mucositis refers to the widespread damage of mucosal surfaces throughout the length of the alimentary tract (AT) that can occur during cancer treatment. Its development is an important clinical problem that complicates and limits treatment options as well as adversely affecting the quality of life and treatment outcomes for patients. Recent studies directed at determining the pathobiology of mucositis have indicated increasing evidence for the role of transcription factors, such as nuclear factor-κB (NF-κB), and certain pro-inflammatory cytokines, for example tumour necrosis factor (TNF), interleukin-1β (IL-1β) and interleukin- 6 (IL-6), in its development. This thesis developed from an initial clinical investigation in which the expression of NF-κB and COX-2 in oral mucosa was investigated in patients undergoing chemotherapy. Increased levels of NF-κB were demonstrated in the buccal mucosa following chemotherapy. It is well established that mucositis occurs in different sites of the AT. The aims of this research, therefore, were to compare and contrast the changes that do occur at different sites of the AT following chemotherapy in an established animal model (Dark Agouti (DA) rat). Furthermore, the studies were conducted to determine whether changes in tissue and serum levels of NF-κB and pro-inflammatory cytokines occurred following chemotherapy and, with respect to tissue levels, identify whether there were differences in expression at different sites throughout the AT. The final aim was to examine whether the histological changes and changes in pro-inflammatory cytokines were affected by the type of chemotherapy drug used. The effects of three chemotherapy drugs with different mechanisms of action (irinotecan, methotrexate and 5-fluorouracil) were investigated, all of which can cause mucositis in the clinical setting. The thesis is divided into a Literature Review (Chapter 1) followed by 4 research papers: Chapter 2 – “Nuclear factor- κB (NF- κB) and cyclooxygenase-2 (COX-2) expression in the oral mucosa following cancer chemotherapy” Chapter 3 -“Characterisation of mucosal changes in the alimentary tract following administration of irinotecan: Implications for the pathobiology of mucositis” Chapter 4 – “Is the pathobiology of chemotherapy-induced alimentary tract mucositis influenced by the type of mucotoxic drug administered?”, Chapter 5 – “Serum levels of NF-κB and pro-inflammatory cytokines following administration of mucotoxic drugs”. Chapter 6 provides an overall summary and discussion of the results. Previous research has indicated that following administration of chemotherapeutic agents there may be subclinical changes occurring in the mucosa prior to obvious clinical manifestations. The results presented in this thesis also demonstrate this in both humans and animals following administration of chemotherapy. Immunohistochemical analysis of tissue taken from the oral cavity, jejunum and colon from the DA rats following chemotherapy demonstrated that changes in NF-κB and the pro-inflammatory cytokines, TNF, IL-1β and IL- 6, occurred at all sites over a 72 hour time period. This was evident before severe histological evidence of mucositis were observed such as epithelial atrophy in the oral mucosa, atrophy, blunting and fusion of the villi in the jejunum and crypt ablation in the jejunum and colon. Furthermore, each of the three drugs caused different patterns of NF-κB and pro-inflammatory cytokine expression in the tissues; in spite of this, however, histological features of damage were similar. With respect to serum levels of NF-κB and pro-inflammatory cytokines, differences were observed between the serum and tissue levels. Generally, serum changes followed initial histological changes in the tissues, or occurred simultaneously with histological changes. The mechanisms behind this are unclear; however it may be that elevated cytokines in the tissues “overflow” into the serum as tissue damage increases. Furthermore, the use of serum cytokine level measurement to predict mucosal damage is limited because of the differences in timing and short time intervals between changes in the serum and tissues. This thesis has provided additional important information on mucositis pathobiology and highlights its complexity. In particular, it has provided new evidence supporting the notion that mucositis is not restricted to the oral cavity and that other sites of the AT are also affected. Furthermore, these results confirm previous data indicating that subclinical changes occur in the mucosa prior to the development of obvious histological damage or clinical manifestations of mucositis. Contrary to previous reports, these studies have indicated that, although the clinical and histological changes may be similar, the alterations in NF-κB and pro-inflammatory cytokines in the tissues are affected by the type of drug used. This has important implications in the management and prevention of mucositis in the clinical setting particularly when multi-drug or chemotherapy-radiotherapy regimens are used. A common pathway that leads to mucosal damage is yet to be determined. The fact that serum levels appear to reflect the “global” nature of the effects of chemotherapy, highlights the fact that ongoing research needs to be directed, not necessarily at specific side effects, but rather how side effects of chemotherapy are interrelated so that better patient management can be achieved and ultimately provide optimum treatment and better survival for patients with cancer.