Naturally-occurring porphyrins in a spontaneous-tumour bearing mouse model

Abstract

An increase in naturally-occurring porphyrins has been described in the blood of subjects bearing different kinds of tumours, that has been proposed as an additional parameter for the diagnosis of occult cancer, although at present the reason for the phenomenon is not exactly defined. In this work the increase of porphyrins in plasma of tumour-bearing subjects has been investigated in parallel with their occurrence in other tissues, considering the systemic iron homeostasis subversion taking place in the presence of cancer. The transgenic female MMTV-neu mouse-developing spontaneous mammary adenocarcinoma has been used as an experimental model, in comparison to non-transgenic C1 mouse as a control. The spleen, accomplishing both hemocatheretic and hemopoietic functions in rodents, and the liver have been considered because of their deep engagement in heme metabolism, entailing both the fate of protoporphyrin IX (PpIX) as its ultimate precursor, and iron homeostasis. Investigations have been performed by means of microspectrofluorometric and image analysis of tissue autofluorescence (AF), and histochemical detection of non-heme iron. In tumour-bearing mouse, along with a marked PpIX presence in tumour, a PpIX enhancement in spleen and liver is observed, that is accompanied by a significant increase in plasma. The phenomenon can be related to a systemic alteration of heme metabolism induced by tumour cells to face their survival and proliferation requirements.