Hypoxia significantly reduces aminolaevulinic acid-induced protoporphyrin IX synthesis in EMT6 cells

We have studied the effects of hypoxia on aminolaevulinic acid (ALA)-induce d protoporphyrin IX (PplX) synthesis in EMT6 monolayer cultures characteriz ed by different cell densities and proliferation rates. Specifically, after ALA incubation under hypoxic or normoxic conditions, we detected spectrofl uorometrically the PplX content of the following populations: (a) low-densi ty exponentially growing cells; (b) high-density fed-plateau cells; and (c) high-density unfed-plateau cells. These populations were selected either f or the purpose of comparison with other in vitro studies (low-density expon entially growing cells) or as representatives of tumour regions adjacent to (high-density fed-plateau cells) and further away from (high-density unfed -plateau cells) capillaries. The amount of PplX per cell produced by each o ne of these populations was higher after normoxic ALA incubation. The magni tude of the effect of hypoxia on PplX synthesis was dependent on cell densi ty and proliferation rate. A 42-fold decrease in PplX fluorescence was obse rved for the high-density unfed-plateau cells. PplX production by the low-d ensity exponential cells was affected the least by ALA incubation under hyp oxic conditions (1.4-fold decrease), whereas the effect on the high-density fed-plateau population was intermediate (20-fold decrease).