Hg2+ and small-sized polyethylene glycols have inverse effects on membrane permeability, while both impair neutrophil cell motility

Toxic effects after exposure to mercury are well documented in human. Little is, however, known about how Hg(2+) affect host defense in general and neutrophil functions in particular. We show here that exposure of human neutrophils to HgCl(2) dose-dependently impairs chemoattractant-stimulated motility. Long-term exposure (5-10 min) to Hg(2+) yields a rapid influx of extracellular Ca(2+) followed by leakage of cytosolic fluorophores, as assessed using fura-2 and ratio imaging microscopy. The inhibition on motility was partly reversible, since pre-treated neutrophils placed in an Hg(2+)-free environment displayed higher migration rates. The Hg(2+)-induced fluxes were prevented by addition of small-sized polyethylene glycols (PEG 200-400), which also dose-dependently inhibited neutrophil transmigration. Localized, minute micropipette additions of Hg(2+) or PEG caused retraction of the leading edge and redirection of cell migration. Since Hg(2+) increases and PEGs decrease membrane permeability in a partially competitive manner, we suggest that the known aquaporin-inhibitor Hg(2+) alters membrane permeability by affecting the bidirectional flux through the leukocyte aquaporin-9 (AQP9) while small-sized PEGs yield decreased membrane permeability by becoming trapped in the promiscuous channel. The local additions of Hg(2+) or PEG probably force other cell regions to take over from those with blocked AQPs. Hence, the cells turn direction of motility away from the micromanipulator needle.     

Oral bacteria resistant to mercury and to antibiotics are present in children with no previous exposure to amalgam restorative materials

Dental plaque from 76 children without amalgam restorations was screened for bacteria resistant to mercuric chloride. Seventy-one per cent of the children harboured mercury-resistant oral bacteria and the median percentage of the total oral microflora resistant to mercuric chloride was 0.007% (range 0-5.3%). Eighty-seven mercury-resistant bacteria were isolated and 86% of these were streptococci with Streptococcus mitis predominating. Sixty per cent of the mercury-resistant isolates were also resistant to at least one of the four antibiotics tested (penicillin, ampicillin, erythromycin and tetracycline) with resistance to tetracycline (40% of isolates) most frequently encountered.     

Effect of ligands and other metals on the uptake of mercury and methylmercury across the gills and the intestine of the blue crab (Callinectes sapidus)

Using the perfusion method, we compared the accumulation and flux of inorganic mercury (Hg) and methylmercury (CH(3)Hg) across the gills and intestine of the blue crab, Callinectes sapidus. The accumulation and transfer processes were studied for each form by exposing the organs in the presence of specific ligands and other metals. While binding of Hg and CH(3)Hg to organic ligands reduced the rate of uptake in most instances, the differences in accumulation could not be explained only in terms of passive diffusive uptake. Thus, it appears that Hg and CH(3)Hg accumulation is dominated by ligand exchange or facilitated transport processes. Exposure of the gills and intestine in the presence of a suite of metals and metalloids showed that inorganic Hg and CH(3)Hg uptake was largely by different mechanisms to that of the other elements, as there was little interaction in terms of uptake rate. Overall, the results of this study suggest that inorganic Hg and CH(3)Hg uptake into the gills and intestine of this invertebrate is by a variety of pathways, both active and passive.     

Mercury-binding capacity of organic and inorganic selenium in rat blood and liver

The mercury-binding capacity of seleno-DL-methionine and selenium dioxide was assessed in male Wistar rats. Mercury was supplied as fish loaves made of northern pike or rainbow trout. We used a selenium concentration of 3.4 mg/kg fish, about sixfold compared to the equivalent quantity of mercury. Seleno-DL-methionine had a tendency to increase both methyl mercury and total mercury in blood, although it also seemed to reduce the proportion of methyl mercury of total mercury. Selenium dioxide lowered mercury levels by 24–29% both in the blood and in the liver of rats that were fed with northern pike.     

Cyanoglycosylation products of 17-O-acetyl-testosterone

17-O-Acetyl testosterone, which has no susceptible hydroxyl or carboxyl group for glycosylation, was glycosylated with 2,3,4,6-tetra-O-acetyl-α- -glucopyranosyl bromide in the presence of a mixed catalyst, Hg(CN)₂ and HgBr₂, in benzene–nitromethane. Reaction occurred on the α,β-unsaturated ketone on the six–membered A-ring to give six 3-O-glycosides, each bearing a cyano group at the 3- or 5-position of the aglycon, and a 3-O-glycoside bearing a CONH₂ group at the 3-position. Structural analyses of these products were carried out by various NMR (¹H, ¹³C NMR, ¹H–¹H and ¹H–¹³C COSY, HMBC, and DEPT), FABMS and X-ray analyses. The mechanisms of the formations of the products are discussed. It was determined that mercuric cyanide was essential as a catalyst for the progress of the cyanoglycosylation.     

Temporal changes of blood mercury concentrations in Chinese newborns and the general public from 1980s to 2020s

Mercury (Hg) is a global pollutant that threatens the environment and human health. As a major producer, emitter and consumer of Hg, China is currently taking different measures to curb mercury pollution in accordance with the requirements of the Minamata Convention on Mercury. Blood Hg can reflect the human body's recent exposure to Hg. This review summarized the temporal changes in blood Hg concentrations in newborns and the general public in China from 1980 s to 2020 s. It was shown that the blood Hg concentrations of newborns showed the downward trend, although it was not significant. The general public Hg concentrations showed a trend of first increase and then decrease trend. Most of the cord blood Hg and venous blood Hg concentrations in China were lower than the USEPA reference concentration of 5.8 µg/L. Since low-dose prenatal Hg exposure can affect fetal and neonatal development, continuous attention needs to be paid to reduce maternal and neonatal Hg exposure. The information provided in this review may lay a basis for the effectiveness evaluation on the implementation of Minamata Convention on Mercury.     

Studies on the mercury volatilizing enzymes in nitrogen-fixing Beijerinckia mobilis

Beijerinckia mobilis KDr₂, a broad-spectrum, mercury-resistant nitrogen-fixing organism, possesses multiple metal-resistance properties. Mercuric reductase and organomercurial lyase activities of this bacterial strain were determined using different mercury compounds and heavy metal salts of copper, nickel, cobalt, cadmium, silver, zinc, lead and arsenate as inducers and substrates. Mercuric reductase was partially purified and the effect of some enzyme inhibitors and heavy metal ions on the enzyme activity was studied. The enzyme activity was completely inhibited by CdCl₂, Bi(NO₃)₃ and KCN at 10^-5 M and by AgNO₃, CoCl₂ and CuSO₄ at 10^-4 M.     

Mercury and selenium distribution in human kidney cortex

Concentration of mercury and selenium were analyzed in tissue fractions of human kidney cortex samples from seven autopsy cases. Total mercury content ranged between 0.3–9.0 nmol Hg/g wet wt. Between 27–61% of the total mercury was found in the 105,000g supernatant of the tissue homogenate from six cases. In kidney cortex from the seventh case, a deceased dentist with the highest concentration of mercury, only 3% of the total mercury was found in the 105,000g supernatant and about 88% in a SDS-insoluble fraction. In this fraction the molar ratio between mercury and selenium was close to 1∶1. This study supports results from previous animal studies and indicates that mercury in human kidney cortex could be deposited in forms with different solubility. It could be of importance to speciate different forms of mercury in tissues according to solubility and association to selenium when interpretations of mercury concentrations are made.     

The effect of mercury on the growth rate of Fragilaria crotonensis kitton and Asterionella formosa Hass.

The effects of two mercury salts Hg(NO₃)₂ and HgCl₂ on the growth rate ofFragilaria crotonensis Kitton andAsterionella formosa Hass. were investigated.Fragilaria crotonensis showed total inhibition at 0.1 ppm and a 4 day increase in lag phase along with a 2–4 fold reduction in growth rate at 0.05 ppm.Asterionella formosa showed a gradual increase in lag phase and reduction in growth rate with increasing concentrations of mercury up to 0.25 ppm with total inhibition at 0.5 ppm. Mercury salts in cultures of both species with soil extract additives were significantly less toxic than in totally defined systems. Cultures ofA. formosa deviated from the typical 8–16 celled stellate colony at sublethal concentrations to form large cylindrical stacks composed of 25 to 30 colonies.This study was supported in part by funds provided by the Navajo and Kaiparowits project participants.This study was supported in part by funds provided by the Navajo and Kaiparowits project participants.     

Changes in concentrations of glycolysis and Krebs cycle metabolites in mosquitofish,Gambusia holbrooki,induced by mercuric chloride and starvation

Synopsis Concentrations of glycolysis and Krebs cycle metabolites in the tail tissues of mosquitofish,Gambusia holbrooki, were measured in response to starvation and to exposure to 0.62 mg Hg l^–1 (as HgCl₂) for 48 h. In control fish, starvation caused decreased concentrations of glucose-6-phosphate (GO, –58%) and fructose-6-phosphate (F6P, –79%). Mercury exposure resulted in decreased concentrations of G6P (– 56%) and F6P (– 79%), and to increased concentrations of pyruvate (+ 75%), -ketoglutarate (+ 41%), succinate (+ 39%), and malate (+ 47%). Krebs cycle activity increased in response to mercury exposure, perhaps in response to greater energy needs associated with maintaining homeostasis under stressful conditions. We conclude that glycolytic activity is reduced in fish exposed to mercury and that this response is similar to that caused by a cessation of feeding.