mitochondria AND (mercury OR methylmercury OR ethylmercury OR thimerosal) - quercetin

[Guest guest]

This post may be forwarded hither and yon. In appreciation, cites 1 & 3

include Sidhur Gupta, MD, PhD, and long-time friend of ARI/DAN!, friend

and colleague of Bernie Rimland.

The pubmed search

mitochondri*[ti] AND (mercury OR methylmercury OR ethylmercury OR

thimerosal)

is instructive, eg,

Cites 1-3, 5-6 document thimerosal effects upon mitochondria.

Cite 4 documents a GSH-related positive effected of quercetin

Cite 6 documents inorganic mercury effects upon mitochondria.

Cite 7 documents that some injected thimerosal becomes inorganic mercury

in brain of primates.

The search provides many more citations. This post is not intended to

imply that thimerosal injections are the only etiologically significant

factor in the epidemics of autism and other ASDs. Nonetheless, these

citations support the model wherein thimerosal may exacerbate

mitochondria disorder or mitochondria dysfunction.

1: Int J Mol Med. 2005 Dec;16(6):971-7.

*Thimerosal induces neuronal cell apoptosis by causing cytochrome c and

apoptosis-inducing factor release from mitochondria.*

Yel L, Brown LE, Su K, Gollapudi S, Gupta S.

Department of Medicine, University of California, Irvine, CA 92697, USA.

lyel@...

There is a worldwide increasing concern over the neurological risks of

thimerosal (ethylmercury thiosalicylate) which is an organic mercury

compound that is commonly used as an antimicrobial preservative. In this

study, we show that thimerosal, at nanomolar concentrations, induces

neuronal cell death through the mitochondrial pathway. Thimerosal, in a

concentration- and time-dependent manner, decreased cell viability as

assessed by calcein-ethidium staining and caused apoptosis detected by

Hoechst 33258 dye. Thimerosal-induced apoptosis was associated with

depolarization of mitochondrial membrane, generation of reactive oxygen

species, and release of cytochrome c and apoptosis-inducing factor (AIF)

from mitochondria to cytosol. Although thimerosal did not affect

cellular expression of Bax at the protein level, we observed

translocation of Bax from cytosol to mitochondria. Finally, caspase-9

and caspase-3 were activated in the absence of caspase-8 activation. Our

data suggest that thimerosal causes apoptosis in neuroblastoma cells by

changing the mitochondrial microenvironment.

PMID: 16273274

2: Neurotoxicology. 2005 Jun;26(3):407-16.

*

Mitochondrial mediated thimerosal-induced apoptosis in a human

neuroblastoma cell line (SK-N-SH).*

Humphrey ML, Cole MP, Pendergrass JC, Kiningham KK.

Department of Pharmacology, Joan C. School of Medicine, Marshall

University, Huntington, WV 25704-9388, USA.

Environmental exposure to mercurials continues to be a public health

issue due to their deleterious effects on immune, renal and neurological

function. Recently the safety of thimerosal, an ethyl mercury-containing

preservative used in vaccines, has been questioned due to exposure of

infants during immunization. Mercurials have been reported to cause

apoptosis in cultured neurons; however, the signaling pathways resulting

in cell death have not been well characterized. Therefore, the objective

of this study was to identify the mode of cell death in an in vitro

model of thimerosal-induced neurotoxicity, and more specifically, to

elucidate signaling pathways which might serve as pharmacological

targets. Within 2 h of thimerosal exposure (5 microM) to the human

neuroblastoma cell line, SK-N-SH, morphological changes, including

membrane alterations and cell shrinkage, were observed. Cell viability,

assessed by measurement of lactate dehydrogenase (LDH) activity in the

medium, as well as the

3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT)

assay, showed a time- and concentration-dependent decrease in cell

survival upon thimerosal exposure. In cells treated for 24 h with

thimerosal, fluorescence microscopy indicated cells undergoing both

apoptosis and oncosis/necrosis. To identify the apoptotic pathway

associated with thimerosal-mediated cell death, we first evaluated the

mitochondrial cascade, as both inorganic and organic mercurials have

been reported to accumulate in the organelle. Cytochrome c was shown to

leak from the mitochondria, followed by caspase 9 cleavage within 8 h of

treatment. In addition, poly(ADP-ribose) polymerase (PARP) was cleaved

to form a 85 kDa fragment following maximal caspase 3 activation at 24

h. Taken together these findings suggest deleterious effects on the

cytoarchitecture by thimerosal and initiation of mitochondrial-mediated

apoptosis.

PMID: 15869795

3: Free Online:

http://www.nature.com/gene/journal/v3/n5/pdf/6363854a.pdf

Genes Immun. 2002 Aug;3(5):270-8.

*Biochemical and molecular basis of thimerosal-induced apoptosis in T

cells: a major role of mitochondrial pathway.*

Makani S, Gollapudi S, Yel L, Chiplunkar S, Gupta S.

Cellular and Molecular Immunology Laboratories, Division of Basic and

Clinical Immunology, University of California, Irvine 92697, USA.

The major source of thimerosal (ethyl mercury thiosalicylate) exposure

is childhood vaccines. It is believed that the children are exposed to

significant accumulative dosage of thimerosal during the first 2 years

of life via immunization. Because of health-related concerns for

exposure to mercury, we examined the effects of thimerosal on the

biochemical and molecular steps of mitochondrial pathway of apoptosis in

Jurkat T cells. Thimerosal and not thiosalcylic acid (non-mercury

component of thimerosal), in a concentration-dependent manner, induced

apoptosis in T cells as determined by TUNEL and propidium iodide assays,

suggesting a role of mercury in T cell apoptosis. Apoptosis was

associated with depolarization of mitochondrial membrane, release of

cytochrome c and apoptosis inducing factor (AIF) from the mitochondria,

and activation of caspase-9 and caspase-3, but not of caspase-8. In

addition, thimerosal in a concentration-dependent manner inhibited the

expression of XIAP, cIAP-1 but did not influence cIAP-2 expression.

Furthermore, thimerosal enhanced intracellular reactive oxygen species

and reduced intracellular glutathione (GSH). Finally, exogenous

glutathione protected T cells from thimerosal-induced apoptosis by

upregulation of XIAP and cIAP1 and by inhibiting activation of both

caspase-9 and caspase-3. These data suggest that thimerosal induces

apoptosis in T cells via mitochondrial pathway by inducing oxidative

stress and depletion of GSH.

PMID: 12140745

4: Chem Res Toxicol. 2007 Dec;20(12):1919-26. Epub 2007 Oct 19.

*Mercurial-induced hydrogen peroxide generation in mouse brain

mitochondria: protective effects of quercetin.*

Franco JL, Braga HC, Stringari J, Missau FC, Posser T, Mendes BG, Leal

RB, Santos AR, Dafre AL, Pizzolatti MG, Farina M.

Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade

Federal de Santa Catarina, 88040-900, Florianópolis, SC, Brazil.

Plants of the genus Polygala have been shown to possess protective

effects against neuronal death and cognitive impairments in

neurodegenerative disorders related to excitotoxicity. Moreover,

previous reports from our group have shown the neuroprotective effects

of the plant Polygala paniculata against methylmercury (MeHg)-induced

neurotoxicity. In this work, we have examined the potential protective

effects of three compounds (7-prenyloxy-6-methoxycoumarin, quercetin,

and 1,5-dihidroxi-2,3-dimethoxy xanthone) from Polygala species against

MeHg- and mercuric chloride (HgCl2)-induced disruption of mitochondrial

function under in vitro conditions using mitochondrial-enriched

fractions from mouse brain. MeHg and HgCl2 (10-100 microM) significantly

decreased mitochondrial viability; this phenomenon was positively

correlated to mercurial-induced glutathione oxidation. Among the

isolated compounds, only quercetin (100-300 microM) prevented

mercurial-induced disruption of mitochondrial viability. Moreover,

quercetin, which did not display any chelating effect on MeHg or HgCl2,

prevented mercurial-induced glutathione oxidation. The present results

suggest that the protective effects of quercetin against

mercurial-induced mitochondrial dysfunction is related to the removal of

oxidant species generated in the presence of either MeHg or HgCl2.

Reinforcing this hypothesis, MeHg and HgCl2 increased the production of

hydrogen peroxide in the brain mitochondria, as well as the levels of

malondialdehyde. These oxidative phenomena were prevented by

co-incubation with quercetin or catalase. These results are the first to

show the involvement of hydrogen peroxide as a crucial molecule related

to the toxic effects of both organic and inorganic mercurials in brain

mitochondria. In addition, the study is the first to show the protective

effect of quercetin against mercurial-induced toxicity, pointing to its

capability to counteract mercurial-dependent hydrogen peroxide

generation as a potential molecular mechanism of protection. Taken

together, these data render quercetin a promising molecule for

pharmacological studies with respects to mercurials' poisoning.

PMID: 17944542

5: FEBS Lett. 1980 Aug 11;117(1):149-51.

*Inhibition of malate transport and activation of phosphate transport in

mitochondria by ethylmercurithiosalicylate*.

Freitag H, Kadenbach B.

PMID: 7409159 [PubMed - indexed for MEDLINE]

6: FEBS Lett. 1980 Jun 2;114(2):295-8.

*Ethylmercurithiosalicylate--a new reagent for the study of phosphate

transport in mitochondria.*

Freitag H, Kadenbach B.

PMID: 7389907

7: *Inorganic mercury & mitochondria*

J Pharmacol Exp Ther. 1992 Apr;261(1):166-72.

*Comparative action of methylmercury and divalent inorganic mercury on

nerve terminal and intraterminal mitochondrial membrane potentials.*

Hare MF, Atchison WD.

Department of Pharmacology and Toxicology, Michigan State University,

East Lansing.

Both methylmercury (MeHg) and inorganic divalent mercury (Hg++) alter

the flux of ions and small molecules across nerve terminal membranes by

mechanisms that may involve membrane depolarization. We compared the

effects of MeHg and Hg++ on plasma (psi p) and mitochondrial membrane

potentials (psi m) in synaptosomes using the potentiometric carbocyanine

dye 3,3'-diethylthiadicarbocyanine iodide [diS-C2(5)]. Both mercurials

(1-20 microM) produced concentration-dependent increases in dye

fluorescence after 5 min of exposure which were not altered by removal

of Ca++ from the medium. To determine directly effects of mercurials on

psi p, predepolarization of psi m using NaN3 and oligomycin was

necessary. Under this condition, MeHg- and Hg(++)-induced increases in

fluorescence were associated with depolarization of psi p. A second

approach was used to assess changes in psi p. In synaptosomes, the

magnitude of the increase in fluorescence resulting from depolarization

of psi p with a stimulus of constant intensity is a function of the

resting psi p. The fluorescence response to depolarization of

synaptosomes previously exposed to either MeHg or Hg++ (1-20 microM

each) was reduced in a concentration-dependent manner relative to

mercury-free controls. The concentration-dependent depolarization of psi

p calculated in this manner correlated (r = 0.958) with calculations of

psi p using direct measurements of increases in fluorescence intensity.

MeHg- and Hg(++)-induced depolarizations were not altered by lowering

Na+e or by the addition of the Na+ and Ca++ channel blockers

tetrodotoxin and Co++, respectively. Thus, the effects of these two

neurotoxic mercurials on synaptosomal membrane potentials were similar

with respect to their loci but differed in magnitude.(ABSTRACT TRUNCATED

AT 250 WORDS)

PMID: 1560362

8: *Inorganic mercury from thimerosal* - free online

http://www.ehponline.org/members/2005/7712/7712.pdf

Environ Health Perspect. 2005 Aug;113(8):1015-21.

*Comparison of blood and brain mercury levels in infant monkeys exposed

to methylmercury or vaccines containing thimerosal.*

Burbacher TM, Shen DD, Liberato N, Grant KS, Cernichiari E, son T.

Thimerosal is a preservative that has been used in manufacturing

vaccines since the 1930s. Reports have indicated that infants can

receive ethylmercury (in the form of thimerosal) at or above the U.S.

Environmental Protection Agency guidelines for methylmercury exposure,

depending on the exact vaccinations, schedule, and size of the infant.

In this study we compared the systemic disposition and brain

distribution of total and inorganic mercury in infant monkeys after

thimerosal exposure with those exposed to MeHg. Monkeys were exposed to

MeHg (via oral gavage) or vaccines containing thimerosal (via

intramuscular injection) at birth and 1, 2, and 3 weeks of age. Total

blood Hg levels were determined 2, 4, and 7 days after each exposure.

Total and inorganic brain Hg levels were assessed 2, 4, 7, or 28 days

after the last exposure. The initial and terminal half-life of Hg in

blood after thimerosal exposure was 2.1 and 8.6 days, respectively,

which are significantly shorter than the elimination half-life of Hg

after MeHg exposure at 21.5 days. Brain concentrations of total Hg were

significantly lower by approximately 3-fold for the thimerosal-exposed

monkeys when compared with the MeHg infants, whereas the average

brain-to-blood concentration ratio was slightly higher for the

thimerosal-exposed monkeys (3.5 +/- 0.5 vs. 2.5 +/- 0.3). A higher

percentage of the total Hg in the brain was in the form of inorganic Hg

for the thimerosal-exposed monkeys (34% vs. 7%). The results indicate

that MeHg is not a suitable reference for risk assessment from exposure

to thimerosal-derived Hg. Knowledge of the toxicokinetics and

developmental toxicity of thimerosal is needed to afford a meaningful

assessment of the developmental effects of thimerosal-containing vaccines.

PMID: 16079072

*eof*