The Role of the Osteoimmune Axis in the Inflammation of the Inner Auditory Ear and with Regard to the Putative Anticarcinogenetic Principle: Part 2

Having defined a putative anticarcinogenic principle under physiological conditions of the auditory inner ear in the previous part of this study, part 2 is the continuation to evaluate this hypothesis under pathological conditions, i.e. with regard to the inflamed auditory inner ear. Inflammation of the auditory inner ear shows three characteristic phases. It starts with an acute phase, progresses to a fibrotic one and ends with ossification as the last phase. At the end of the fibrotic phase the inflammatory cells disappear, probably due to apoptosis, the ganglion neurons die and the fibrous matrix ossifies. No proliferating cells can be found in this area any more. Thus this kind of inflammation does not result in a restoration of the former state, but always in the destruction of the hearing organ and corresponding neurons. The osteoimmune axis is involved in this characteristic type of inflammation. Important factors hereby are M-CSF, RANKL/RANK and osteoprotegerin. In the inner auditory ear they inhibit the resorption of the fibrotic matrix, induce apoptosis of inflammatory cells and calcification. This inflammatory osteoimmune axis plays an important role at the cancer site as well. The relation of each factor to the other ones is however fundamentally different from that in the inner ear. Consequently inflammatory processes induced by a tumour foster its progression and may induce bone metastasis. Instead of a dominating and enclosing osteoblastic activity like in the inner ear, matrix resolving and often osteoclastic properties are developed allowing the spread of cancer cells. These processes allows us to set out the anticarcinogenic hypothesis more precisely and define its putative mechanistic rationale for the inflamed auditory inner ear.