Assessing Als3 Peptide-Binding Cavity and Amyloid-Forming Region Contributions to Candida albicans Invasion of Human Oropharyngeal Epithelial Cells

Although it is widely recognized that disruption of ALS3 reduces the invasion of Candida albicans germ tubes into mammalian oral epithelial cells, the mechanism of this interaction was unexplored. C. albicans strains with structurally informed mutations to remove adhesive activity of the peptide-binding cavity (PBC) or aggregative activity mediated by the amyloid-forming region (AFR) were assessed for their ability to invade cultured human oropharyngeal epithelial cells. Initial assays utilized untreated fungal and epithelial cells. Subsequent work used epithelial cells treated with cytochalasin D and C. albicans cells treated with thimerosal to investigate invasion mediated by active penetration of germ tubes and epithelial cell induced endocytosis, respectively. Results demonstrated the importance of the PBC for the invasion process: loss of PBC function resulted in the same reduced-invasion phenotype as a C. albicans strain that did not produce Als3 on its surface. Invasion via active penetration was particularly compromised without PBC function. Loss of AFR function produced a wild-type phenotype in the untreated and thimerosal-treated invasion assays but increased invasion in cytochalasin D-treated epithelial cells. In previous work, reduced AFR-mediated Als3 aggregation increased C. albicans adhesion to cultured epithelial cell monolayers, presumably via increased PBC accessibility for ligand binding. Collectively, results presented here demonstrate that Als3 PBC-mediated adhesion is integral to its invasive function. These new data add to the mechanistic understanding of the role of Als3 in C. albicans invasion into mammalian oral epithelial cells.

Consequences of thimerosal on human erythrocyte hemoglobin: Assessing functional and structural protein changes induced by an organic mercury compound

BACKGROUND

Thimerosal (TM) is an organic mercury compound used as a preservative in many pharmacological inputs. Mercury toxicity is related to structural and functional changes in macromolecules such as hemoglobin (Hb) in erythrocytes (Ery).

METHOD

Human Hb and Ery were used to evaluate O2 uptake based on the TM concentration, incubation time, and temperature. The influence of TM on the sulfhydryl content, production of reactive oxygen species (ROS), and membrane fragility was also evaluated. Raman spectra and atomic force microscopy (AFM) profiles for Ery in the presence and absence of TM were calculated, and docking studies were performed.

RESULTS

At 37 °C, with 2.50 μM TM (higher concentration) and after 5 min of incubation in Hb and Ery, we observed a reduction in O2 uptake of up to 50 %, while HgCl2, which was used as a positive control, showed a reduction of at least 62 %. Total thiol assays in the presence of NEM (thiol blocker) quantified the preservation of almost 60 % of free SH in Ery. Based on the Raman spectrum profile from Ery-TM, structural differences in the porphyrinic ring and the membrane lipid content were confirmed. Finally, studies using AFM showed changes in the morphology and biomechanical properties of Ery. Theoretical studies confirmed these experimental results and showed that the cysteine (Cys) residues present in Hb are involved in the binding of TM.

CONCLUSION

Our results show that TM binds to human Hb via free Cys residues, causing conformation changes and leading to harmful effects associated with O2 transport.

Mercury as a hapten: A review of the role of toxicant-induced brain autoantibodies in autism and possible treatment considerations

BACKGROUND

Mercury has many direct and well-recognized neurotoxic effects. However, its immune effects causing secondary neurotoxicity are less well-recognized. Mercury exposure can induce immunologic changes in the brain indicative of autoimmune dysfunction, including the production of highly specific brain autoantibodies. Mercury, and in particular, Thimerosal, can combine with a larger carrier, such as an endogenous protein, thereby acting as a hapten, and this new molecule can then elicit the production of antibodies.

METHODS

A comprehensive search using PubMed and Google Scholar for original studies and reviews related to autism, mercury, autoantibodies, autoimmune dysfunction, and haptens was undertaken. All articles providing relevant information from 1985 to date were examined. Twenty-three studies were identified showing autoantibodies in the brains of individuals diagnosed with autism and all were included and discussed in this review.

RESULTS

Research shows mercury exposure can result in an autoimmune reaction that may be causal or contributory to autism, especially in children with a family history of autoimmunity. The autoimmune pathogenesis in autism is demonstrated by the presence of brain autoantibodies (neuroantibodies), which include autoantibodies to: (1) human neuronal progenitor cells; (2) myelin basic protein (MBP); (3) neuron-axon filament protein (NAFP); (4) brain endothelial cells; (5) serotonin receptors; (6) glial fibrillary acidic protein (GFAP); (7) brain derived neurotrophic factor (BDNF); (8) myelin associated glycoprotein (MAG); and (9) various brain proteins in the cerebellum, hypothalamus, prefrontal cortex, cingulate gyrus, caudate putamen, cerebral cortex and caudate nucleus.

CONCLUSION

Recent evidence suggests a relationship between mercury exposure and brain autoantibodies in individuals diagnosed with autism. Moreover, brain autoantibody levels in autism are found to correlate with both autism severity and blood mercury levels. Treatments to reduce mercury levels and/or brain autoantibody formation should be considered in autism.

Methylmercury degradation by Pseudomonas putida V1

Environmental contamination of mercury (Hg) has caused public health concerns with focuses on the neurotoxic substance methylmercury, due to its bioaccumulation and biomagnification in food chains. The goals of the present study were to examine: (i) the transformation of methylmercury, thimerosal, phenylmercuric acetate and mercuric chloride by cultures of Pseudomonas putida V1, (ii) the presence of the genes merA and merB in P. putida V1, and (iii) the degradation pathways of methylmercury by P. putida V1. Strain V1 cultures readily degraded methylmercury, thimerosal, phenylmercury acetate, and reduced mercuric chloride into gaseous Hg(0). However, the Hg transformation in LB broth by P. putida V1 was influenced by the type of Hg compounds. The merA gene was detected in P. putida V1, on the other hand, the merB gene was not detected. The sequencing of this gene, showed high similarity (100%) to the mercuric reductase gene of other Pseudomonas spp. Furthermore, tests using radioactive (14)C-methylmercury indicated an uncommon release of (14)CO2 concomitant with the production of Hg(0). The results of the present work suggest that P. putida V1 has the potential to remove methylmercury from contaminated sites. More studies are warranted to determine the mechanism of removal of methylmercury by P. putida V1.

Thimerosal exposure and the role of sulfation chemistry and thiol availability in autism

Autism spectrum disorder (ASD) is a neurological disorder in which a significant number of the children experience a developmental regression characterized by a loss of previously acquired skills and abilities. Typically reported are losses of verbal, nonverbal, and social abilities. Several recent studies suggest that children diagnosed with an ASD have abnormal sulfation chemistry, limited thiol availability, and decreased glutathione (GSH) reserve capacity, resulting in a compromised oxidation/reduction (redox) and detoxification capacity. Research indicates that the availability of thiols, particularly GSH, can influence the effects of thimerosal (TM) and other mercury (Hg) compounds. TM is an organomercurial compound (49.55% Hg by weight) that has been, and continues to be, used as a preservative in many childhood vaccines, particularly in developing countries. Thiol-modulating mechanisms affecting the cytotoxicity of TM have been identified. Importantly, the emergence of ASD symptoms post-6 months of age temporally follows the administration of many childhood vaccines. The purpose of the present critical review is provide mechanistic insight regarding how limited thiol availability, abnormal sulfation chemistry, and decreased GSH reserve capacity in children with an ASD could make them more susceptible to the toxic effects of TM routinely administered as part of mandated childhood immunization schedules.

Breastfeeding is an essential complement to vaccination

AIM

This article explores the role of breastfeeding in different aspects of vaccination in the first 6 months when infants are still developing: (1) pain management; (2) immunomodulation of infants' vaccine responses; (3) metabolism of thimerosal.

METHODS

Major databases were searched for studies that addressed outcomes of related issues.

RESULTS

Studies reveal that breastfeeding can: (1) help mothers and infants to cope with the stressful situations that accompany parenteral vaccines; (2) improve response to vaccines in the still maturing immunologic and enterohepatic systems of infants; (3) influence physiologic parameters that can change metabolism of ethylmercury derived from some vaccines.

CONCLUSION

Health promotion that supports vaccinations should also emphasize early initiation and maintenance of exclusive breastfeeding up until 6 months for maximum protection of the infants with a possible beneficial effect on the vaccine response. Paediatric professionals should inform mothers of the proven benefits of breastfeeding and its importance in complementing vaccination and lowering stress and the risk of untoward reactions on susceptible infants.

Hair mercury in breast-fed infants exposed to thimerosal-preserved vaccines

Because of uncertainties associated with a possible rise in neuro-developmental deficits among vaccinated children, thimerosal-preserved vaccines have not been used since 2004 in the USA (with the exception of thimerosal-containing influenza vaccines which are routinely recommended for administration to pregnant women and children), and the EU but are widely produced and used in other countries. We investigated the impact of thimerosal on the total Hg in hair of 82 breast-fed infants during the first 6 months of life. The infants received three doses of the hepatitis-B vaccine (at birth, 1 and 6 months) and three DTP (diphtheria, tetanus, and pertussis) doses at 2, 4 and 6 months, according to the immunization schedule recommended by the Ministry of Health of Brazil. The thimerosal in vaccines provided an ethylmercury (EtHg) exposure of 25 microgHg at birth, 30, 60 and 120 days, and 50 microgHg at 180 days. The exposure to vaccine-EtHg represents 80% of that expected from total breast milk-Hg in the first month but only 40% of the expected exposure integrated in the 6 months of breastfeeding. However, the Hg exposure corrected for body weight at the day of immunization was much higher from thimerosal- EtHg (5.7 to 11.3 microgHg/kg b.w.) than from breastfeeding (0.266 microgHg/kg b.w.). While mothers showed a relative decrease (-57%) in total hair-Hg during the 6 months lactation there was substantial increase in the infant's hair-Hg (446%). We speculate that dose and parenteral mode of thimerosal-EtHg exposure modulated the relative increase in hair-Hg of breast-fed infants at 6 months of age.

Biodegradation of thiomersal containing effluents by a mercury resistant Pseudomonas putida strain

Thiomersal, a toxic organomercurial with a strong bactericidal effect, is the most widely used preservative in vaccine production. As a result, vaccine production wastewaters are frequently polluted with thiomersal concentrations above the European limit for mercury effluent discharges for which there is, presently, no remediation technology available. This work proposes a biotechnological process for the remediation of vaccine production wastewaters based on the biological degradation of thiomersal to metallic mercury, under aerobic conditions, by a mercury resistant bacterial strain. The kinetics of thiomersal degradation by a pure culture of Pseudomonas putida spi3 was firstly investigated in batch reactors using a thiomersal amended mineral medium. Subsequently, a continuous stirred tank reactor fed with the same medium was operated at a dilution rate of 0.05 h(-1), and the bioreactor performance and robustness was evaluated when exposed to thiomersal shock loads. In a second stage, the bioreactor was fed directly with a real vaccine wastewater contaminated with thiomersal and the culture ability to grow in the wastewater and remediate it was evaluated for dilution rates ranging from 0.022 to 0.1 h(-1).

Thimerosal stimulates Ca2+ flux through inositol 1,4,5-trisphosphate receptor type 1, but not type 3, via modulation of an isoform-specific Ca2+-dependent intramolecular interaction

Thiol-reactive agents such as thimerosal have been shown to modulate the Ca2+-flux properties of IP3 (inositol 1,4,5-trisphosphate) receptor (IP3R) via an as yet unidentified mechanism [Parys, Missiaen, De Smedt, Droogmans and Casteels (1993) Pflügers Arch. 424, 516-522; Kaplin, Ferris, Voglmaier and Snyder (1994) J. Biol. Chem. 269, 28972-28978; Missiaen, Taylor and Berridge (1992) J. Physiol. (Cambridge, U.K.) 455, 623-640; Missiaen, Parys, Sienaert, Maes, Kunzelmann, Takahashi, Tanzawa and De Smedt (1998) J. Biol. Chem. 273, 8983-8986]. In the present study, we show that thimerosal potentiated IICR (IP3-induced Ca2+ release) and IP3-binding activity of IP3R1, expressed in triple IP3R-knockout R23-11 cells derived from DT40 chicken B lymphoma cells, but not of IP3R3 or [D1-225]-IP3R1, which lacks the N-terminal suppressor domain. Using a 45Ca2+-flux technique in permeabilized A7r5 smooth-muscle cells, we have shown that Ca2+ shifted the stimulatory effect of thimerosal on IICR to lower concentrations of thimerosal and thereby increased the extent of Ca2+ release. This suggests that Ca2+ and thimerosal synergetically regulate IP3R1. Glutathione S-transferase pull-down experiments elucidated an interaction between amino acids 1-225 (suppressor domain) and amino acids 226-604 (IP3-binding core) of IP3R1, and this interaction was strengthened by both Ca2+ and thimerosal. In contrast, calmodulin and sCaBP-1 (short Ca2+-binding protein-1), both having binding sites in the 1-225 region, weakened the interaction. This interaction was not found for IP3R3, in agreement with the lack of functional stimulation of this isoform by thimerosal. The interaction between the IP3-binding and transmembrane domains (amino acids 1-604 and 2170-2749 respectively) was not affected by thimerosal and Ca2+, but it was significantly inhibited by IP3 and adenophostin A. Our results demonstrate that thimerosal and Ca2+ induce isoform-specific conformational changes in the N-terminal part of IP3R1, leading to the formation of a highly IP3-sensitive Ca2+-release channel.

Intracytoplasmic sperm injection of bovine oocytes with stallion spermatozoa

Five experiments were designed to study the fertilizability and development of bovine oocytes fertilized by intracytoplasmic sperm injection (ICSI) with stallion spermatozoa. Experiment 1 determined the time required for pronuclear formation after ICSI. Equine sperm head decondensation began 3 h after ICSI; 42% were decondensed 6 h after ICSI. Male pronuclei (MPN) began to form 12 h after ICSI. Female pronuclei (FPN), however, formed as early as 6 h after ICSI. In Experiment 2, ionomycin, ionomycin plus 6-dimethylaminopurine (DMAP), and thimerosal were used to activate ICSI ova. None of the ICSI ova cleaved after treatment with thimerosal. Ionomycin activation after 24 and 30 h of oocyte maturation resulted in 29 and 48% cleavage rates, respectively. Ionomycin combined with DMAP resulted in 49, 6 and 3% cleavage, morula and blastocyst rates, respectively, when oocytes were activated after 24 h maturation. In Experiment 3, rates of cleavage (45-60%) and development to morulae (4-13%) and blastocysts (1-5%) stages following ICSI were not different (P>0.05) among three stallions. Treatment of stallion spermatozoa with ionomycin did not affect cleavage or development of ova fertilized by ICSI. The chromosomal constitution of blastocysts derived from ICSI was bovine, not bovine and equine hybrids. In Experiment 4, to make male and FPN form synchronously, colchicine and DMAP were used for 4 h to inhibit oocytes at metaphase during activation; 63% of oocytes were still at metaphase 8h after ICSI when treated with colchicine, and 50% of sperm nuclei were decondensed. About 18 h after ICSI, 21 and 50% male and FPN had formed, respectively, but cleavage rates were low, and only 1% developed to morulae. In Experiment 5, to test if capacitated equine sperm could fuse with the bovine oolemma, capacitated spermatozoa were injected subzonally (SUZI). Of the 182 SUZI oocytes, 49 (27%) contained extruded second polar bodies. After activation of oocytes with second polar bodies, 44, 22 and 15% developed to 2-, 4- and 8-cell stages, respectively, but development stopped at the 8-cell stage. None of the unactivated oocytes cleaved. In conclusion, equine spermatozoa can decondense and form MPN in bovine oocytes after ICSI, but subsequent embryonic development is parthenogenetic with only bovine chromosomes being found.

Mercury concentrations and metabolism in infants receiving vaccines containing thiomersal: a descriptive study

BACKGROUND

Thiomersal is a preservative containing small amounts of ethylmercury that is used in routine vaccines for infants and children. The effect of vaccines containing thiomersal on concentrations of mercury in infants' blood has not been extensively assessed, and the metabolism of ethylmercury in infants is unknown. We aimed to measure concentrations of mercury in blood, urine, and stools of infants who received such vaccines.

METHODS

40 full-term infants aged 6 months and younger were given vaccines that contained thiomersal (diptheria-tetanus-acellular pertussis vaccine, hepatitis B vaccine, and in some children Haemophilus influenzae type b vaccine). 21 control infants received thiomersal-free vaccines. We obtained samples of blood, urine, and stools 3-28 days after vaccination. Total mercury (organic and inorganic) in the samples was measured by cold vapour atomic absorption.

FINDINGS

Mean mercury doses in infants exposed to thiomersal were 45.6 microg (range 37.5-62.5) for 2-month-olds and 111.3 microg (range 87.5-175.0) for 6-month-olds. Blood mercury in thiomersal-exposed 2-month-olds ranged from less than 3.75 to 20.55 nmol/L (parts per billion); in 6-month-olds all values were lower than 7.50 nmol/L. Only one of 15 blood samples from controls contained quantifiable mercury. Concentrations of mercury were low in urine after vaccination but were high in stools of thiomersal-exposed 2-month-olds (mean 82 ng/g dry weight) and in 6-month-olds (mean 58 ng/g dry weight). Estimated blood half-life of ethylmercury was 7 days (95% CI 4-10 days).

INTERPRETATION

Administration of vaccines containing thiomersal does not seem to raise blood concentrations of mercury above safe values in infants. Ethylmercury seems to be eliminated from blood rapidly via the stools after parenteral administration of thiomersal in vaccines.

[Thiomersal in gammaglobulin for pregnant travellers may not be safe for the fetus. National Coordination Center for Travel Advisory]

It is not advisible to use thiomersal-containing gammaglobulin preparations for the prevention of hepatitis A in pregnant women. The current preparation of Sanquin-Centraal Laboratorium voor de Bloedtransfusiedienst will yield per 5 ml about 285 micrograms of ethylmercury. This exposure to ethylmercury may not be safe for the foetus and alternatives without ethylmercury are readily available.

Determination of mercury and organomercurial resistance in obligate anaerobic bacteria

A methodology for determining the minimum inhibitory concentration of inorganic and organomercurial compounds for obligate anaerobic bacteria is described. A wide variation in the susceptibility of anaerobic clinical and sewage isolates was observed. Isolates of Bacteroides ruminicola and Clostridium perfringens resistant to mercury were examined for their plasmid content and ability to demonstrate inducible resistance. None of the resistant anaerobes contained any plasmids, while resistant facultative isolates from the same source contained several plasmids. In 24 h, resistant strains of clostridia and Bacteroides volatilized 20 and 43% of the 203Hg2+ added to cultures, while Escherichia coli R100 and a sewage isolate of Enterobacter cloacae volatilized 63 and 27%, respectively, of the added 203Hg2+. Attempts to induce mercury resistance in the aerobic isolates were successful, but no induction was seen in the anaerobes. Thus, mercury resistance in these anaerobic isolates was neither inducible nor plasmid mediated.

Tissue concentrations of mercury after chronic dosing of squirrel monkeys with thiomersal

Squirrel monkeys were dosed intranasally with saline or thiomersal (sodium ethylmercurithiosalicylate, 0.002 percent w/v) daily for six months. The total amounts of thiomersal given during the six months period were 418 mug (low dose group) and 2280 mug (high dose group). This was equivalent to 207 and 1125 mug mercury. The dose differential was achieved by more frequent administration to the high dose group. Mercury concentrations were significantly raised over control values in brain (high dose group only), liver, muscle and kidney, but not in blood. Concentrations were highest in the kidney, moderate in liver and lowest in brain and muscle. Much of the mercury was present in the inorganic form (37-91 percent). No evidence of toxicity due to thiomersal was seen in any animal. Nevertheless accumulation of mercury from chronic use of thiomersal-preserved medicines is viewed as a potential health hazard for man.