Increase in ODC Activity in Organs of Animals Exposed to 60-Hz Linear, Sinusoidal Continuous-Wave Magnetic Fields of Different Intensities

Abstract

Discovered in 1968, ornithine decarboxylase (ODC) is one of the most studied of mammalian enzymes. ODC catalyzes the conversion of ornithine to putrescine, the first member of naturally occurring polyamines. Polyamines are essential for cell growth and differentiation, and their depletion results in growth inhibition2. In the case of tumor growth, the activity of polyamines is increased and their catabolism is slowed down. This leads to an accumulation of these substances in the affected organs3. ODC turns over rapidly (t 1/2 15–30 min) and is induced by a variety of growth-promoting stimuli4. ODC is low in quiescent cells and variations in its activity essentially reflect variations in its synthesis and thus, changes in polyamine intracellular levels. Several lines of evidence suggest that ODC plays an important role in carcinogenesis. Accordingly, ODC activity is higher in adenocarcinomas of the stomach and large intestine than in normal surrounding tissues 5,6. In tumors of skin and nervous system a correlation exists between ODC activity and differentiation7,8. ODC activity is elevated in some human premalignant lesions of the brain. Actually, high ODC activity represents a reliable biochemical marker of malignancy in brain tumors, but low values do not prove benignity9. In EMF studies, in vitro exposure of cultured hepatoma to athermal (450 Mhz, 1.0 mW/cm2) microwave field sinusoidally amplitude-modulated at 16 Hz during 1-hr significantly increased ODC activity (up to 50%) in comparison to the unexposed cultures10. Similar increase in basal ODC activity of CHO and melanoma cells was also observed. Simultaneous exposure to MFs and TPA further increased ODC activity11 Moreover, Cain et al 12 demonstrated that 60-Hz electric fields prolongs ODC response to TPA in C3H10T1/2 fibroblasts, and a one hour exposure of Jurkat cells (human lymphoblastoid cells) to vertical AC fields, increased both ODC and putrescine levels. In the later study, the authors suggested that E-fields induced by MFs are of decisive nature13. In L929 cells, Litovitz et al 14 reported a large increase in ODC activity after a 4-hr exposure to 10μT, 60 Hz magnetic fields. The exposures used by Litovitz et al ranged up to 100 μT. ODC activity was reported not to be critically dependent on the magnitude of the field, but the investigators found maximal enhancement of ODC levels with a 60 Hz MFs of 10 μT.