M. Czuba

Demethylation and excretion of methyl mercury by the guinea pig

Female guinea pigs were dosed po with 1.0 mg CH3 203Hg/kg as methylmercuric chloride, 10 times over a 3-week period. Tissue distribution, excretion, and accumulation of inorganic and organic mercury were studied. The highest concentration of mercury was found in the kidney. The greatest decreases of mercury levels were observed in the small bowel, red blood cells, liver, and cerebrum. The half-life of whole body clearance, based on a single compartment model, was 31.6 days. Mercury in the kidney, liver, and cerebrum was bound mainly by nuclear and soluble fractions. The highest ratio of inorganic to total mercury was seen in the kidney, 60% of this being as inorganic mercury. Excretion of mercury in the feces was measured throughout the experiment. The relationship of organic to inorganic mercury was relatively constant at about 1:3. Data on the effects of methyl mercury on tissue concentrations of zinc and copper show that the only change in the copper content was a marked increase in the kidney.

Long-term cadmium exposure accelerates oxidant injury: Significance of bound/free water states during long-term metal stress

Lepidium sativum (cress) and Lycopersicon esculentum (tomato) plants were grown in peatlite in controlled environments with or without long-term (4 weeks) cadmium stress (Cd) (100 micrograms/ml every fourth day) and with a single exposure (6 hr at 35 parts per hundred million (pphm)) or no exposure to the oxidant ozone (O3). Cress plants which received Cd wilted faster during O3 exposure and became a gray-green color by the end of a 6-hr O3 exposure. Those receiving O3 alone also wilted but were normal in color during wilting. Leaf water content (percentage) significantly declined in both O3 + Cd- and O3-treated plants. However, leaves after Cd + O3 exposure were severely dessicated and necrotic, whereas O3-treated plants recovered their water content completely but had some injury. Increased stomatal aperture in cress but not tomato before O3 exposure and significantly lower water content at 1 and 24 hr after the end of O3 exposure were associated with the higher Cd content of leaves before and subsequent to O3 exposure. These factors contributed to a greater injury and cell death observed in the leaves of combined cadmium-oxidant stress. Dielectric properties of Thlaspi arvense (field penny cress) leaves grown at continuous exposure to Cd and/or nickel (Ni) indicated that there were measurable differences between metal-containing vs control leaves with regard to bound/unbound water status. This indicated that there was more free water under metal stress, and that the bound water content significantly declined in the leaves of these plants.

Differential mitotic toxicity of methylmercury in various meristematic tissues (apex, bud, root) of Elodea densa☆

Elodea densa plants were grown in flowing water for 25 days at methylmercury (MMC) concentrations of 7.5 × 10−10, 7.5 × 10−9, and 7.5 × 10−8 M. Toxicity development was different within and among the three types of meristematic tissues—apex, root, and bud. Apical cells were most sensitive to MMC and developed aberrant nuclear and mitotic characteristics at lower concentrations than did roots. Root meristems had a total inhibition of mitotic activity at 7.5 × 10−9 M with no aberrant symptoms at lower MMC levels. Conversely, the mitotic activity in bud meristems was zero in the control and increased in the presence of MMC. However, the divisions were abnormal. Higher concentrations of MMC (up to 2.5 × 10−6 M) had the unusual effect of stimulating the development of additional buds. The formation and development of root and bud initials were inhibited at levels of 7.5 × 10−8 and 0.25 × 10−6 M MMC in the water.

Structural damage to leaf chloroplasts of Elodea densa caused by methylmercury accumulated from water

Elodea densa plants exposed to low levels of methylmercury in water (7.5 × 10−10 M) accumulate sufficient methylmercury within 25 days to severely damage the surface membrane and the internal structure of the leaf chloroplast.

Biological and NMR markers for cancer.

The search for a universal tumor marker continues. Present markers range from tumor products (polyamines, glycoproteins, peptides, hormones or carbohydrate-linked markers) to reaction products produced by the host tissues during tumor invasion. Techniques used to identify them include the classical methods of histology and cytochemistry as well as the more recent radioimmunoassay and metabolic probes. The in vivo techniques of increasing use for patient monitoring are MRS (magnetic resonance spectroscopy) and MRI (magnetic resonance imaging). The efficiency of some markers and statistical methods used in analyzing data are discussed, as are the ethical problems surrounding the use of new testing methods. Recent developments in MRI and MRS, marker elucidation, and evidence for a new autocrine differentiation-inhibiting factor (ADIF) are reviewed. Future needs and approaches focus on greater utilization of indicators of the preneoplastic state and of risk to cancer, as well as more careful attention to statistical analysis.

Methyl mercury toxicity in plant cultures: Modification of resistance and demethylation by light and/or 2,4-dichlorophenoxyacetic acid

Cultures of Daucus carota, Ca-68-10, and Lactuca sativa, Le-67, were grown at increasing methyl mercury (MeHg) concentrations ranging from initial doses of 0.05 to 5.0 micrograms/ml per day for 4 days with or without 0.15 microgram/ml 2,4-dichlorophenoxyacetic acid (2,4-D) in the presence or absence of light. The presence of 2,4-D interacted with light synergistically in the expression of MeHg toxicity within the whole range of concentrations. Demethylation patterns increased or decreased depending on the species, the 2,4-D concentration in the medium, and methyl mercury concentration used in the treatment. Lettuce was more sensitive to this interaction than carrot. In lettuce, the presence of 2,4-D in the light lowered the concentration of total Hg (or MeHg) required to reduce growth by 50%, about 13 times relative to that in the dark (i.e., it sensitized the cells). In the absence of 2,4-D the pattern was reversed. In carrot the pattern was similar but less pronounced. This suggests that, in these cell populations, MeHg toxicity is partly a hormone-mediated and light-sensitive event.

Effects of methyl mercury on arrays of microtubules and macromolecular synthesis in Daucus carota cultures

Cell suspension cultures of Daucus carota were exposed to methyl mercury at concentrations between 0 and 6 micrograms/ml for 1, 3, or 24 hr. Microtubule arrays exhibited no detectable disruption (as compared with controls) when treated with 1, 2, and 3 micrograms/ml methyl mercury. Disorganization of microtubules did occur at higher concentrations (4-6 micrograms/ml) in a concentration/time-dependent manner. No recovery of microtubule arrays was evident when cells were placed in methyl mercury-free medium for up to 7 days. Analyses of soluble protein and carbohydrate content, dry weight, and cell viability (reducing capacity) indicate that methyl mercury exposure has inhibitory effects on cell metabolism. The observed disruption of plant cell microtubules, induced by exposure to methyl mercury, may be secondary in response to an initial inhibition of synthetic pathways and membrane perturbations.

The fate of Cd, Cu, Ca, Zn, and Fe in rat during the recovery period following cessation of repeated exposure to Cd

Cadmium was administered subcutaneously to male Wistar rats, 0.1 mL/rat in 0.9% saline 3 times a wk for 4 wk at 3 mg Cd/kg. Saline was administered to control animals in an equivalent manner, without Cd. After the end of the dosing period, the distribution and excretion of Cd, Cu, Ca, Zn, and Fe were observed in some organs and excreta for 35 d (1, 7, 14, 21, 28, and 35 d). Cadmium dosing caused significant disturbances in the metabolism of Zn, Cu, Fe, and Ca, especially during the recovery period. Growth in Cd-dosed animals did not accelerate, even after 5 wk of recovery. There was evidence of mobilization of some elements among organs. Accumulation of Cd occurred in liver, kidney, and spleen during dosing, and during the recovery period it was retained in kidney and testes (for 2 wk) and cleared steadily in liver and RBC (for 5 wk), but increased in spleen (first 3 wk). The pattern of Cd excretion was closely associated with the binding of Cd with metallothioneins in kidney and liver for the first 21 and 7 d, respectively. This was associated with the excretion of Cd-metallothioneins (Cd-MT) in urine from d 1 to 21 during recovery. Cadmium caused higher Ca accumulations in testes and liver, which were probably associated with the lesions observed in these organs. Significant increases of Cu (in kidney d 7) and Fe (in liver) were observed during recovery. Furthermore, significant reductions of Cu and Fe were found in plasma, spleen, and RBC (after 5 wk) and kidney, spleen, and testes (on d 7), and blood (after 5 wk).

Relative resistance of and delayed toxicity in undifferentiated plant cells to methyl mercury

Meristematic cells of carrot (Daucus carota L., Ca68-10) and lettuce (Lactuca sativa L., LE-67) cultured in 71-V medium (with 0.15 microgram/ml 2, 4-D) were given one initial dose (0.0001, 0.001, or 0.01 microgram/ml) of methyl mercury (MeHg) at 0 hr, cultured for 288 hr. and then subcultured for 4 weeks. In another experiment, MeHg was added in four daily doses (0.05, 0.10, 0.50, 1.0, 2.5, or 5.0 micrograms/ml) starting at 72 hr for 120 hr and then subcultured for 168 hr. The resulting 50% growth reduction (Gr50) levels were high--1570 and 540 micrograms Hg/g dry wt for carrot and lettuce, respectively. Methyl mercury was taken up completely by cells but retention decreased at higher MeHg concentrations in the medium. The resistance of undifferentiated cells of both species to MeHg was markedly greater than that observed in multicellular plants. Cells derived from Hg-treated cultures did not recover their growth potential when subcultured in Hg-free medium. The Gr50 levels were lowered during successive subculturing in both carrot (50 micrograms Hg/g) and lettuce (10 micrograms Hg/g), indicating increased sensitivity to residual Hg in cells. This effect depended on the initial Hg concentration and on the number of cell divisions. At low MeHg concentrations, it was observed in cells 12 generations after one initial dose of 0.01 microgram/ml MeHg.

Effects of heavy metals absorbed from water on the laser-induced fluorescence in Elodea densa

Comparative rates of absorption of copper, lead, cadmium, nickel, tin, and inorganic and methylmercury ions from water by Elodea densa were measured. Methylmercury, at relatively low tissue concentrations, was the only ion that quenched the laser-induced fluorescence.