[Show abstract][Hide abstract] ABSTRACT: Paraoxonase 2 (PON2), a member of a gene family that also includes PON1 and PON3, is expressed in most tissues, including the brain. In mouse brain, PON2 levels are highest in dopaminergic areas (e.g. striatum), and are higher in astrocytes than in neurons. PON2 is primarily located in mitochondria and exerts a potent antioxidant effect, protecting mouse CNS cells against oxidative stress. The aim of this study was to characterize PON2 expression and functions in the brains of male and female mice. Levels of PON2 (protein, mRNA, and lactonase activity) were higher in brain regions and cells of female mice. Astrocytes and neurons from male mice were significantly more sensitive (by 3-4-fold) to oxidative stress-induced toxicity than the same cells from female mice. Glutathione levels did not differ between genders. Importantly, no significant gender differences in susceptibility to the same oxidants were seen in cells from PON2(-/-) mice. Treatment with estradiol induced a time- and concentration-dependent increase in the levels of PON2 protein and mRNA in male (4.5-fold) and female (1.8-fold) astrocytes, which was dependent on activation of estrogen receptor alpha. In ovariectomized mice, PON2 protein and mRNA were decreased to male levels in brain regions and in liver. Estradiol protected astrocytes from wild-type mice against oxidative stress-induced neurotoxicity, but did not protect cells from PON2(-/-) mice. These results suggest that PON2 is a novel major intracellular factor that protects CNS cells against oxidative stress, and confers gender-dependent susceptibility to such stress. The lower expression of PON2 in males may have broad ramifications for susceptibility to diseases involving oxidative stress, including neurodegenerative diseases.
Free Radical Biology and Medicine 01/2013; 58. DOI:10.1016/j.freeradbiomed.2013.01.019 · 5.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cholesterol is a major component of all membranes. Lipid rafts, organized membrane domains rich in cholesterol, play important roles in the transduction of many signal transduction pathways including signaling pathways involved in morphogenesis. Cholesterol is also the precursor of steroid hormones. Cholesterol plays an important role during fetal development. Cholesterol plays a pivotal role in brain development. Inhibition of cholesterol synthesis, as a consequence of genetic syndromes or exposure to cholesterol inhibitors during gestation, is known to cause neurodevelopmental and teratogenic effects. Recent research demonstrated that cholesterol homeostasis in the brain can be affected by the modulation of ABC cholesterol transporter levels and activity. Altered cholesterol homeostasis through the upregulation of cholesterol transporters appears to be involved in the developmental effects of ethanol and retinoic acid. Any chemical that affects cholesterol homeostasis may therefore be regarded as a potential developmental neurotoxicant.
[Show abstract][Hide abstract] ABSTRACT: Human paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated serum enzyme that exhibits a broad substrate specificity. In addition to protecting against exposure to some organophosphorus (OP) pesticides by hydrolyzing their toxic oxon metabolites, PON1 is important in protecting against vascular disease by metabolizing oxidized lipids. Recently, PON1 has also been shown to play a role in inactivating the quorum sensing factor N-(3-oxododecanoyl)-l-homoserine lactone (3OC12-HSL) of Pseudomonas aeruginosa. Native, untagged engineered recombinant human PON1 (rHuPON1) expressed in Escherichia coli and purified by conventional column chromatographic purification is stable, active, and capable of protecting PON1 knockout mice (PON1(-/-)) from exposure to high levels of the OP compound diazoxon. The bacterially derived rHuPON1 can be produced in large quantities and lacks the glycosylation of eukaryotic systems that can produce immunogenic complications when inappropriately glycosylated recombinant proteins are used as therapeutics. Previous studies have shown that the determination of PON1 status, which reveals both PON1(192) functional genotype and serum enzyme activity level, is required for a meaningful evaluation of PON1's role in risk of disease or exposure. We have developed a new two-substrate assay/analysis protocol that provides PON1 status without use of toxic OP substrates, allowing for use of this protocol in non-specialized laboratories. Factors were also determined for inter-converting rates of hydrolysis of different substrates. PON1 status also plays an important role in revealing changes in HDL-associated PON1 activities in male patients with Parkinson disease (PD). Immunolocalization studies of PONs 1, 2 and 3 in nearly all mouse tissues suggest that the functions of PONs 1 and 3 extend beyond the plasma and the HDL particle.
[Show abstract][Hide abstract] ABSTRACT: Polybrominated diphenyl ethers (PBDEs) are an important group of flame retardants.Though several PBDEs have been banned or restricted in recent years, their past wide useand leach from the polymers, have made them worldwide environmental contaminants.Of special concern is the high body burden in infants and toddlers, as a result of exposurethrough maternal milk and house dust, particularly in North America. A number ofstudies have indicated the potential developmental neurotoxicity of PBDEs, however, thepossible underlying mechanisms are still unknown. Evidence accumulating in the pastfew years is suggesting that PBDEs may cause oxidative stress. Increases in reactiveoxygen species and/or lipid peroxidation have been observed in vitro in primary rodentneurons (cerebellum, hippocampus), in neuroblastoma and hepatoma cells, in neutrophilgranulocytes, and in fetal hematopoietic cells. Evidence of PBDE-induced oxidativestress has also been found upon in vivo administration in American kestrels anddeveloping mice. A series of studies in our own laboratory have shown that theantioxidant glutathione (GSH) is an important determinant of PBDE neurotoxicity.Genetically-determined reduced GSH levels increase PBDE-induced oxidative stress andensuing neurotoxicity which is primarily apoptotic in nature, both in vitro and in vivo.The developing brain is particularly sensitive to oxidative stress, due to its richness infree iron and a limited antioxidant capacity, and oxidative stress may contribute topathological apoptosis during brain development. Available evidence for oxidative stressin PBDE neurotoxicity, its possible relevance, and potential underlying mechanisms arediscussed in this commentary.
[Show abstract][Hide abstract] ABSTRACT: In mouse cerebellar granule neurons (CGNs) low concentrations of domoic acid (DomA) induce apoptotic cell death, which is mediated by oxidative stress; apoptosis is more pronounced in CGNs from Gclm (-/-) mice, which lack the modifier subunit of glutamate cysteine ligase (GCL) and have very low GSH levels. By activating M(3) muscarinic receptors, the cholinergic agonist carbachol inhibits DomA-induced apoptosis, and the anti-apoptotic action of carbachol is more pronounced in CGNs from Gclm (+/+) mice. Carbachol does not prevent DomA-induced increase in reactive oxygen species, suggesting that its anti-apoptotic effect is downstream of reactive oxygen species production. Carbachol inhibits DomA-induced activation of Jun N-terminal (JNK) and p38 kinases, increased translocation to mitochondria of the pro-apoptotic protein Bax, and activation of caspase-3. Carbachol activates extracellular signal-regulated kinases 1/2 (ERK1/2) MAPK and phospahtidylinositol-3 kinase (PI3K) in CGNs from both genotypes. However, while the protective effect of carbachol is mediated by ERK1/2 MAPK in CGNs from both mouse genotypes, inhibitors of PI3K are only effective at antagonizing the action of carbachol in CGNs from Gclm (+/+) mice. In CGNs from both Gclm (+/+) and (-/-) mice, carbachol induces a MAPK-dependent increase in the level of the anti-apoptotic protein Bcl-2. In contrast, carbachol causes a PI3K-dependent increase in GCL activity and of GSH levels only in CGNs from Gclm (+/+) mice. Such increase in GCL is not because of a transcriptionally-mediated increase in glutamate cysteine ligase catalytic subunit or glutamate cysteine ligase modifier subunit, but rather to an increase in the formation of the GCL holoenzyme. The results indicate that multiple pathways may contribute to the protective action of carbachol toward DomA-induced apoptosis. Compromised GCLM expression, which is also found in a common genetic polymorphism in humans, leads to lower GSH levels, which can exacerbate the neurotoxicity of DomA, and decreases the anti-apoptotic effectiveness of muscarinic agonists.
Journal of Neurochemistry 03/2009; 109(2):525-38. DOI:10.1111/j.1471-4159.2009.05969.x · 4.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In mouse cerebellar granule neurons (CGNs) the marine neurotoxin domoic acid (DomA) induces neuronal cell death, either by apoptosis or by necrosis, depending on its concentration, with apoptotic damage predominating in response to low concentrations (100 nM). DomA-induced apoptosis is due to selective activation of AMPA/kainate receptors, and is mediated by DomA-induced oxidative stress, leading to mitochondrial dysfunction and activation of caspase-3. The p38 MAP kinase and the c-Jun NH2-terminal protein kinase (JNK) have been shown to be preferentially activated by oxidative stress. Here we report that DomA increases p38 MAP kinase and JNK phosphorylation, and that this effect is more pronounced in CGNs from Gclm (-/-) mice, which lack the modifier subunit of glutamate-cysteine ligase, have very low glutathione (GSH) levels, and are more sensitive to DomA-induced apoptosis than CGNs from wild-type mice. The increased phosphorylation of JNK and p38 kinase was paralleled by a decreased phosphorylation of Erk 1/2. The AMPA/kainate receptor antagonist NBQX, but not the NMDA receptor antagonist MK-801, prevents DomA-induced activation of p38 and JNK kinases. Several antioxidants (GSH ethyl ester, catalase and phenylbutylnitrone) also prevent DomA-induced phosphorylation of JNK and p38 MAP kinases. Inhibitors of p38 (SB203580) and of JNK (SP600125) antagonize DomA-induced apoptosis. These results indicate the importance of oxidative stress-activated JNK and p38 MAP kinase pathways in DomA-induced apoptosis in CGNs.
Neurochemistry International 06/2008; 52(6):1100-5. DOI:10.1016/j.neuint.2007.11.004 · 3.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Paraoxonase (PON1) is a high density lipoprotein-associated enzyme capable of hydrolyzing multiple substrates, including several
organophosphorus (OP) insecticides and nerve agents, oxidized lipids and a number of drugs or pro-drugs. Several polymorphisms
in the PON1 gene have been described, which have been shown to affect either the catalytic efficiency of hydrolysis or the
expression level of the enzyme. Animal studies have shown that PON1 is an important determinant of the toxicity of certain
OPs. Evidence for this was provided by cross-species comparisons, by administration of exogenous PON1 and by experiments in
PON1 knockout and transgenic mice. Low PON1 plays also a role in the higher susceptibility of the young to OP toxicity. Recent
findings also suggest that PON1 may modulate the toxicity resulting from exposure to mixtures of OP compounds
[Show abstract][Hide abstract] ABSTRACT: Early research on population distributions of plasma PON1 paraoxonase activity indicated a polymorphic distribution with high,
intermediate and low metabolizers. Cloning and characterization of the cDNA encoding human PON1 and follow-on experiments
demonstrated that the molecular basis of the activity polymorphism (PM) was a Q192R PM with PON1R192 specifying high paraoxonase activity. Further research demonstrated that the PON1192 polymorphism had little effect on the catalytic efficiencies of hydrolysis of phenylacetate and diazoxon (DZO), but did affect
the efficiencies of hydrolysis of chlorpyrifos oxon (CPO), soman and sarin, with PON1R192 having a higher efficiency of CPO hydrolysis and PON1Q192 having higher rates of hydrolysis of soman and sarin. Plots of rates of DZO hydrolysis (at a salt concentration that differentially
inhibited PON1R192) vs. paraoxon hydrolysis clearly separated the three PON1192 phenotypes (QQ, QR, RR) and also showed a wide range of activity among individuals with the same PON1192 genotype. The term PON1 status was introduced to include both PON1192 functional genotype and plasma PON1 level,both important in determining risk for either exposure to specific organophosphorus
compounds (OPs) or disease. Characterization of 5 promoter-region polymorphisms by several groups indicated that an Sp1 binding
site was responsible for significant(~30%) variation in plasma PON1 levels. Re-sequencing of the PON1 genes of 47 individuals
(24 African-American/23 European) revealed an additional 180 polymorphisms in 27 kb of the PON1 genomic DNA including 8 more
5' regulatory region PMs, 1 coding region polymorphism (W194X), 162 additional intronic PMs and 9 additional 3' UTR PMs. The generation of PON1 null mice and “PON1 humanized mice” expressing either tgHuPON1R192 or tgHuPON1Q192 at the same levels on the PON1−/− background allowed for a functional analysis of the Q192R PM under physiological conditions.
Toxicology experiments with the PON1 humanized mice and the PON1 null mice injected with purified human PON1192 alloforms clearly demonstrated that the catalytic efficiency of substrate hydrolysis is important in determining whether
PON1 is able to protect against a given OP exposure. HuPON1R192 protects well against CPO and DZO exposure, but HuPON1Q192 does not protect well against CPO exposure and neither protects
against PO exposure. Studies on PON1 status and carotid artery disease show that low PON1 levels are a risk factor. The effects
of PON1192 alloforms on rates of hydrolysis of quorum sensing factors are not yet known. Taken together, these data along with those
of the leading researchers in the PON1 field indicate that it is important to measure PON1 levels/activities in any epidemiological
study. SNP analysis alone is inadequate for epidemiological studies, due to the wide variability of PON1 levels within the
three PON1192 genotypes Q/Q, Q/R R/R). Even the most comprehensive PON1 SNP analyses are unable to accurately predict PON1 levels. PON1
activity or level accurately predicts CHD risk, while genotype does not
The Paraoxonases: Their Role in Disease Development and Xenobiotic Metabolism, 12/2007: pages 267-281;
[Show abstract][Hide abstract] ABSTRACT: Cholesterol is an essential component of cell membranes and plays an important role in signal transduction. This brief overview presents evidence from the literature that ethanol may affect cholesterol homeostasis and that, in the developing brain, this may be involved in its developmental neurotoxicity. The effects caused by inborn errors of cholesterol synthesis and by in utero ethanol exposure present several similarities in humans (eg, Smith-Lemli-Opitz syndrome and fetal alcohol syndrome), as well as in animal models. Ethanol has a cholesterol-reducing effect on the cardiovascular system, and a protective effect against Alzheimer's disease, whose pathogenesis has been linked to altered cholesterol homeostasis in the brain. In vitro, ethanol affects several functions that are mediated by cholesterol and important for brain development, such as glial cell proliferation, synaptogenesis, neuronal survival and neurite outgrowth. The brain contains high levels of cholesterol, mostly synthesized in situ. Astrocytes produce large amounts of cholesterol that can be released by these cells and utilized by neurons to form synapses. Ethanol up-regulates the cholesterol transporter ATP binding cassette A1 and cholesterol efflux from primary astrocyte cultures without affecting cholesterol synthesis.
[Show abstract][Hide abstract] ABSTRACT: This study investigated the role of cellular antioxidant defense mechanisms in modulating the neurotoxicity of domoic acid (DomA), by using cerebellar granule neurons (CGNs) from mice lacking the modifier subunit of glutamate-cysteine ligase (Gclm). Glutamate-cysteine ligase (Glc) catalyzes the first and rate-limiting step in glutathione (GSH) biosynthesis. CGNs from Gclm (-/-) mice have very low levels of GSH and are 10-fold more sensitive to DomA-induced toxicity than CGNs from Gclm (+/+) mice. GSH ethyl ester decreased, whereas the Gcl inhibitor buthionine sulfoximine increased DomA toxicity. Antagonists of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate receptors and of N-methyl-D-aspartate (NMDA) receptors blocked DomA toxicity, and NMDA receptors were activated by DomA-induced l-glutamate release. The differential susceptibility of CGNs to DomA toxicity was not due to a differential expression of ionotropic glutamate receptors, as evidenced by similar calcium responses and L-glutamate release in the two genotypes. A calcium chelator and several antioxidants antagonized DomA-induced toxicity. DomA caused a rapid decrease in cellular GSH, which preceded toxicity, and the decrease was primarily due to DomA-induced GSH efflux. DomA also caused an increase in oxidative stress as indicated by increases in reactive oxygen species and lipid peroxidation, which was subsequent to GSH efflux. Astrocytes from both genotypes were resistant to DomA toxicity and presented a diminished calcium response to DomA and a lack of DomA-induced L-glutamate release. Because polymorphisms in the GCLM gene in humans are associated with low GSH levels, such individuals, as well as others with genetic conditions or environmental exposures that lead to GSH deficiency, may be more susceptible to DomA-induced neurotoxicity.
[Show abstract][Hide abstract] ABSTRACT: Polymorphisms in the paraoxonase (PON1) gene influence both the quality and the quantity of PON1. Evidence provided by animal studies indicates that PON1 plays a relevant role in the metabolism of certain organophosphates (OPs), and modulates their toxicity and developmental neurotoxicity. Careful in vitro studies carried out under physiological conditions, together with in vivo studies in various lines of PON1 transgenic mice, have been shown to be extremely useful in dissecting the functional significance of PON1. The influence of PON1 status on inferring susceptibility or protection toward OPs needs to be evaluated for each individual compound. It is somewhat ironic that the toxicity of paraoxon, the OP after which PON1 was named, is not significantly influenced by PON1 status. Although there is strong evidence to indicate that PON1 levels and, in some cases, the Q192R polymorphism determine the efficiency with which an individual will detoxify a specific OP; however, further proof in human populations is still needed. In particular, studies are needed in which PON1 status is correlated with the degree of exposure, and with signs and symptoms of toxicity. Animal studies have also pointed out the potential therapeutic use of PON1 in treating individuals with exposure to OP insecticides and/or nerve agents. The recent expression of active human PON1 in Escherichia coli and the elucidation of PON1 structure provide the necessary breakthroughs for producing, recombinant variants that have catalytic efficiency sufficient for therapeutic applications.
[Show abstract][Hide abstract] ABSTRACT: In certain cases, the consumption of food or beverages can lead to intoxication and disease. Such food-induced intoxications may be due to microbial toxins, to toxic substances naturally occurring in some foods, or to contaminants or residues of various kinds. Some of these agents have neurotoxic properties and may contribute to the etiology of certain psychiatric disorders or neurodegenerative diseases. This paper reviews a selected number of dietary neurotoxicants that naturally, or as a result of human interventions, find their way into food or beverages, and have been associated with neurotoxic outcomes in humans. Chosen examples include domoic acid, a phycotoxin associated with amnesic shellfish poisoning; β-N-oxalylamine-l-alanine (l-BOAA), present in chickling peas and believed to be responsible for neurolathyrism; and two alcohols, methanol and ethanol, which can cause severe neurotoxic effects in adults and the developing fetus.