Loss of neuronal protein expression in mouse hippocampus after irradiation.

The effects of radiation on neurons are incompletely characterized. We evaluated changes in the expression of neuronal nuclear and other proteins in the mouse hippocampus after 17-Gy whole-brain irradiation. Expression of neuronal nuclei (NeuN), neuron-specific enolas, prospero-related homeobox 1 (Prox1), calbindin D28k, and synaptophysin 1 in the CA1, CA3, and dentate gyrus of the hippocampus was determined by immunohistochemistry; neuronal numbers were estimated by design-based stereology. At 7 days after irradiation, there was a marked reduction of NeuN neurons in CA3. Stereologic estimates confirmed a significant reduction in NeuN neurons in CA3 at 7 days, in the dentate gyrus at 7 days, 3 weeks and 2 months, and in CA1 at 2 months compared with controls; neuron-specific enolase and prospero-related homeobox 1-positive neurons in the CA3 subregion were also decreased at 7 days. The numbers of granule and pyramidal cells identified by 4'6-diamidino-2-phenylindole nuclear staining, however, remained unchanged, and there were no changes in calbindin D28k or synaptophysin 1 immunoreactivity after irradiation. We conclude that irradiation may result in a temporary loss of neuronal protein expression in mouse hippocampus. These changes do not necessarily indicate loss of neurons and indicate the need for caution regarding the use of phenotypic markers such as NeuN to estimate changes in neuronal numbers after irradiation.

Increase of Candida cell virulence by anticancer drugs and irradiation.

The influence of anticancer drugs and irradiation on Candida cell proliferation, adherence to HeLa cells and susceptibility to antifungal drugs (amphotericin B and miconazole) and neutrophils were examined using two Candida albicans strains. After treatment with 5-fluorouracil (25 microg/ml to 250 microg/ml), cis-diammine-dichloroplatinum (10 microg/ml to 100 microg/ml), peplomycin (0.5 microg/ml to 5 microg/ml) or 137Cs (20 Gy to 40 Gy) for 3 days or more, surviving Candida cells proliferated more rapidly than did untreated control cells. Anticancer agent-pretreated Candida cells revealed an increased adhesion to HeLa cells corresponding to an increase of binding to the lectins. The concentration of half limited colony formation (IC50) of amphotericin B and miconazole was increased to near two-fold that of the control by pretreatment of Candida cells with the anticancer agents, except peplomycin, which only weakly increased IC50. In addition, the enolase and Candida acid proteinase activities in the culture supernatants were increased by pretreatment with the drugs and irradiation. Correspondingly, surviving Candida cells after these treatments were resistant to neutrophils, with a reduction to half of the killing. These results indicate that anti-cancer drugs and irradiation potentiate the virulence of Candida cells, or they eliminate Candida cells with low virulence, thereby enhancing the risk of oral and systemic candidiasis.

The molecular chaperone alpha-crystallin inhibits UV-induced protein aggregation.

Solutions of gamma-crystallin, and various enzymes, at neutral pH and 24-26 degrees C, became turbid upon exposure to UV radiation at 295 or 308 nm. SDS-PAGE analysis revealed interchain cross-linking and aggregate formation compared to dark control solutions as reported previously. When alpha-crystallin was added to the protein solutions in stoichiometric amounts, UV irradiation resulted in significantly less turbidity than in the absence of alpha-crystallin. For example, addition of 0.5 mg of alpha-crystallin to 0.5 mg of gamma-crystallin in 1.0 ml solution yielded only 25% of the turbidity seen in the absence of alpha-crystallin. Addition of 2.0 mg of alpha-crystallin resulted in 20% of the turbidity. Given the molecular weights of alpha- and gamma-crystallin (about 800 kDa and 20 kDa, respectively), a gamma/alpha 1:1 weight ratio corresponds to a 40:1 molar ratio, and a gamma/alpha 1:4 weight ratio corresponds to a 10:1 molar ratio. Hence, the molar ratio of alpha-crystallin needed to effectively protect gamma-crystallin from photochemical opacification was gamma/alpha = n:1, where n was in the range 10-40. In terms of subunits, this ratio is gamma/alpha = 1:m, where m = 1-4. Thus, each gamma-crystallin molecule needs 1-4 alpha subunits for protection. Similar stoichiometries were observed for protection of the other proteins studied. The protection stems in part from screening of UV radiation by alpha-crystallin but more importantly from a chaperone effect analogous to that seen in thermal aggregation experiments.

Frequency-dependent alterations in enolase activity in Escherichia coli caused by exposure to electric and magnetic fields.

Some neurochemical effects of low-intensity electric and magnetic fields have been shown to be nonlinear functions of exposure parameters. These effects occurred within narrow ranges of frequency and intensity. Previous studies on membrane-associated endpoints in cell culture preparations demonstrated changes in calcium efflux and in acetylcholinesterase activity following exposure to radiofrequency radiation, amplitude modulated (AM) at 16 and at 60 Hz, at a specific absorption rate of 0.05 W/kg. In this study, these modulation frequencies were tested for their influence on the activity of a cytoplasmic enzyme, enolase, which is being tested clinically for detection of neoplasia. Escherichia coli cultures containing a plasmid with a mammalian gene for enolase were exposed for 30 min, and cell extracts were assayed for enolase activity by measuring absorbance at 240 nm. The enolase activity in exposed cultures was compared to the activity in paired control cultures. Exposure to 147 MHz carrier waves at 0.05 W/kg, AM at 16 Hz showed enolase activity enhanced by 62%, and AM at 60 Hz showed enolase activity reduced by 28%. Similarly, exposure to 16 Hz fields alone, at 21.2 V/mrms (electric) and 97 nTrms (magnetic), showed enhancement in enolase activity by 59%, whereas exposure to 60 Hz fields alone, at 14.1 V/mrms (electric) and 65 nTrms (magnetic), showed reduction in activity by 24%. Sham exposures as well as exposure to continuous-wave 147 MHz radiation at 0.05 W/kg showed no change in enolase activity.(ABSTRACT TRUNCATED AT 250 WORDS)