[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; · 5.27 Impact Factor
[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: 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. · 3.97 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. · 2.66 Impact Factor
[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
[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: 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.
Human & Experimental Toxicology 05/2007; 26(4):355-60. · 1.45 Impact Factor
[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: 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.
Environmental Toxicology and Pharmacology 05/2005; 19(3):395-400. · 2.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An in vitro model, the aggregating brain cell culture of fetal rat telencephalon, has been used to investigate the influence of glial cells on the neurotoxicity of two organophosphorus pesticides (OPs), chlorpyrifos and parathion. Mixed-cell aggregate cultures were treated continuously for 10 days between DIV 5 and 15. Parathion induced astrogliosis at concentration at which MAP-2 immunostaining, found here to be more sensitive than neuron-specific enzyme activities, was not affected. In contrast, chlorpyrifos induced a comparatively weak gliotic reaction, and only at concentrations at which neurons were already affected. After similar treatments, increased neurotoxicity of parathion and chlorpyrifos was found in aggregate cultures deprived of glial cells. These results suggest that glial cells provide neuroprotection against OPs toxicity. To address the question of the difference in toxicity between parathion and chlorpyrifos, the toxic effects of their leaving groups, p-nitrophenol and trichloropyridinol, were studied in mixed-cell aggregates. General cytotoxicity was more pronounced for trichloropyridinol and both compounds had similar toxic effects on neuron-specific enzyme activities. In contrast, trichloropyridinol induced a much stronger decrease in glutamine synthetase activity, the enzymatic marker of astrocytes. Trichloropyridinol may exert a toxic effect on astrocytes, compromising their neuroprotective function, thus exacerbating the neurotoxicity of chlorpyrifos. This is in line with the suggestion that glial cells may contribute to OPs neurotoxicity, and with the view that OPs may exert their neurotoxic effects through different mechanisms.
Toxicology and Applied Pharmacology 01/2005; 201(2):97-104. · 3.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polybrominated diphenyl ethers (PBDEs) are an important class of flame retardants. Because of their presence in maternal milk and their structural similarity to polychlorinated biphenyls (PCBs), concern has been raised on their possible developmental neurotoxicity. Aim of the present study was to investigate the in vitro effects of PBDE-99 (2,2′, 4,4′, 5-pentabromodiphenyl ether) on astroglial cells (human 132-1N1 astrocytoma cells) and comparing it with those of the PCB mixture Aroclor 1254. Both PBDE-99 and Aroclor 1254 caused a concentration-dependent inhibition of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) reduction, however, only the latter increased lactate dehydrogenase (LDH) release or cell death, assessed by the trypan blue assay. PBDE-99 caused translocation of the three protein kinase C (PKC) isozymes (α, ɛ, ζ) present in 132-1N1 astrocytoma cells, while Aroclor 1254 affected only PKCα and ɛ translocation. However, pre-incubation with the PKC inhibitor GF109203X or PKC down-regulation by the phorbol ester PMA, had minimal or no effect on PBDE-99 or Aroclor 1254-induced cytotoxicity. Similarly, the calcium chelator BAPTA-AM, the tyrosine kinase inhibitor genistein, and the MEK (mitogen activated protein kinase kinase) inhibitor PD98059 had no effect on PBDE-99 and Aroclor 1254 cytoxicity. On the other hand, the phosphatidylinositol 3 kinase (PI-3K) inhibitor LY290042 enhanced PBDE-99 toxicity, but did not affect Aroclor 1254. Because of the involvement of PI-3K in apoptotic cell death, the ability of PBDE-99 and Aroclor 1254 to induce apoptosis in astrocytoma cells was investigated. PBDE-99, but not Aroclor 1254, caused apoptotic cell death in astrocytoma cells, assessed by the TUNEL method and by Hoechst 33258 staining, via a p53 dependent mechanism. These results suggest that PBDE-99 and Aroclor 1254 exert differential cytotoxic effects on human astroglial cells.
[Show abstract][Hide abstract] ABSTRACT: Central nervous system dysfunctions (most notably microencephaly and mental retardation) are among the most significant effects of in utero exposure to ethanol. Ethanol causes alterations of both neuronal and glial cells. In particular, ethanol has been shown to inhibit proliferation of astroglial cells stimulated by certain, but not all mitogens. Here, we review evidence that acetylcholine, by activating the M(3) subtype of muscarinic receptors, increases DNA synthesis in rat and human astroglial cells and that this effect is inhibited by low ethanol concentrations (10-100mM). Of the several signal transduction pathways activated by these receptors in astrocytes or astrocytoma cells, ethanol appears to target activation of phospholipase D, leading to a decrease in phosphatidic acid, a decreased activation of the atypical protein kinase C zeta and decreased down-stream activation of p70S6 kinase and of nuclear factor-kappaB. Inhibition of this pathway by ethanol occurs at the same concentrations which effectively inhibit proliferation. Inhibition of astroglial cell proliferation by ethanol may contribute to the microencephaly present in most children diagnosed with the fetal alcohol syndrome.
[Show abstract][Hide abstract] ABSTRACT: In mammals, serum paraoxonase (PON1) is tightly associated with high-density lipoprotein (HDL) particles. In human populations, PON1 exhibits a substrate dependent activity polymorphism determined by an Arg/Gln (R/Q) substitution at amino acid residue 192. The physiological role of this protein appears to be involvement in the metabolism of oxidized lipids. Several studies have suggested that the PON1R192 allele may be a risk factor in coronary artery disease. PON1 also plays an important role in the metabolism of organophosphates including insecticides and nerve agents. The PON1R192 isoform hydrolyzes paraoxon rapidly, but diazoxon, soman and sarin slowly compared with the PON1Q192 isoform. Both PON1 isoforms hydrolyze phenylacetate at approximately the same rate, while PON1R192 hydrolyzes chlorpyrifos oxon slightly faster than PONQ192. Animal model studies involving injection of purified rabbit PON1 into mice clearly demonstrated the ability of PON1 to protect cholinesterases from inhibition by OP compounds. The consequence of having low PON1 levels has been addressed with toxicology studies in PON1 knockout mice. These mice showed dramatically increased sensitivity to chlorpyrifos oxon, diazoxon and some increased sensitivity to the respective parent compounds. These observations are consistent with earlier studies that showed a good correlation between high rates of OP hydrolysis by serum PON1 and resistance to specific OP compounds. They are also consistent with the observations that newborns have an increased sensitivity to OP toxicity, due in part to their not expressing adult PON1 levels for weeks to months after birth, depending on the species. Together, these studies point out the importance of considering the genetic variability of PON1192 isoforms and levels as well as the developmental time course of PON1 appearance in serum in developing risk assessment models
Human and Ecological Risk Assessment 01/2004; 8(1):31-43. · 1.29 Impact Factor