Interaction of metals with peroxidase--mediated luminol-enhanced, chemiluminescence (PLmCL)

The peroxidase-mediated luminol-enhanced chemiluminescence (PLmCL) method has been used to study the in vitro effect of contaminants such as heavy metals on the reactive oxygen species production by immunocytes. We were interested to know whether metals could directly affect peroxidase-mediated luminescence, taking horseradish peroxidase (HRP) as a model enzyme, since this could contribute to the inhibition of immunocyte LmCL. Copper inhibited PLmCL in a dose-dependent manner, while cadmium, iron, silver and lead only partly decreased the signal in the concentration range tested. In contrast, zinc enhanced the signal at high concentrations. Eventually, chromium, mercury and aluminium did not affect PLmCL. It is suggested that these effects reflect the ability of the metals to interact with the active site of the peroxidase. These results demonstrate that such interactions have to be considered when interpreting the effects of metals on immunocytes using the LmCL method.