Brain glucose-6-phosphate dehydrogenase protects against endogenous oxidative DNA damage and neurodegeneration in aged mice.

Glucose-6-phosphate dehydrogenase (G6PD) protects the embryo from endogenous and xenobiotic-enhanced oxidative DNA damage and embryopathies. Here we show in aged mice that G6PD similarly protects against endogenous reactive oxygen species (ROS)-mediated neurodegeneration. In G6PD-normal (G6PD(+/+)) and heterozygous (G6PD(+/def)) and homozygous (G6PD(def/def)) G6PD-deficient male and female mice at about 2 years of age, oxidative DNA damage in various brain regions was assessed by 8-oxo-2'-deoxyguanosine formation using high-performance liquid chromatography and immunohistochemistry. Morphological changes in brain sections were assessed by H&E staining. DNA oxidation was increased in G6PD(def/def) mice in the cortex (p < 0.02), hippocampus (p < 0.01) and cerebellum (p < 0.006) compared to G6PD(+/+) mice, and was localized to distinct cell types. Histologically, in G6PD(+/def) mice, enhanced regionally and cellularly specific neurodegenerative changes were observed in those brain regions exhibiting elevated DNA oxidation, with a 53% reduction in the Purkinje cell count. These results show G6PD is important in protecting against the neurodegenerative effects of endogenous ROS in aging, and suggest that common hereditary G6PD deficiencies may constitute a risk factor for some neurodegenerative diseases.

Reduced DNA oxidation in aged prostaglandin H synthase-1 knockout mice.

Prostaglandin H synthase (PHS)-2 (COX-2) is implicated in the neurodegeneration of Alzheimer and Parkinson diseases. Multiple mechanisms may be involved, including PHS-catalyzed bioactivation of neurotransmitters, precursors, and metabolites to neurotoxic free radical intermediates. Herein, in vitro studies with the purified PHS-1 (COX-1) isoform and in vivo studies of aging PHS-1 knockout mice were used to evaluate the potential neurodegenerative role of PHS-1-catalyzed bioactivation of endogenous neurotransmitters to free radical intermediates that enhance reactive oxygen species formation and oxidative DNA damage. The brains of 2-year-old wild-type (+/+) PHS-1 normal and heterozygous (+/-) and homozygous (-/-) PHS-1 knockout mice were analyzed for 8-oxo-2'-deoxyguanosine formation, characterized by high-performance liquid chromatography with electrochemical detection and by immunohistochemistry. Compared to aging PHS-1(+/+) normal mice, aging PHS-1(-/-) knockout mice had less oxidative DNA damage in the cortex, hippocampus, cerebellum, and brain stem. This PHS-1-dependent oxidative damage was not observed in young mice. In vitro incubation of purified PHS-1 and 2'-deoxyguanosine with dopamine, L-DOPA, and epinephrine, but not glutamate or norepinephrine, enhanced oxidative DNA damage. These results suggest that PHS-1-dependent accumulation of oxidatively damaged macromolecules including DNA may contribute to the mechanisms and risk factors of aging-related neurodegeneration.

Reduced 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy)-initiated oxidative DNA damage and neurodegeneration in prostaglandin H synthase-1 knockout mice.

The neurodegenerative potential of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) and underlying mechanisms are under debate. Here, we show that MDMA is a substrate for CNS prostaglandin H synthase (PHS)-catalyzed bioactivation to a free radical intermediate that causes reactive oxygen species (ROS) formation and neurodegenerative oxidative DNA damage. In vitro PHS-1-catalyzed bioactivation of MDMA stereoselectively produced free radical intermediate formation and oxidative DNA damage that was blocked by the PHS inhibitor eicosatetraynoic acid. In vivo, MDMA stereoselectively caused gender-independent DNA oxidation and dopaminergic nerve terminal degeneration in several brain regions, dependent on regional PHS-1 levels. Conversely, MDMA-initiated striatal DNA oxidation, nerve terminal degeneration, and motor coordination deficits were reduced in PHS-1 +/- and -/- knockout mice in a gene dose-dependent fashion. These results confirm the neurodegenerative potential of MDMA and provide the first direct evidence for a novel molecular mechanism involving PHS-catalyzed formation of a neurotoxic MDMA free radical intermediate.

Oxoguanine glycosylase 1 protects against methamphetamine-enhanced fetal brain oxidative DNA damage and neurodevelopmental deficits.

In utero methamphetamine (METH) exposure enhances the oxidative DNA lesion 7,8-dihydro-8-oxoguanine (8-oxoG) in CD-1 fetal mouse brain, and causes long-term postnatal motor coordination deficits. Herein we used oxoguanine glycosylase 1 (ogg1) knock-out mice to determine the pathogenic roles of 8-oxoG and OGG1, which repairs 8-oxoG, in METH-initiated neurodevelopmental anomalies. Administration of METH (20 or 40 mg/kg) on gestational day 17 to pregnant +/- OGG1-deficient females caused a drug dose- and gene dose-dependent increase in 8-oxoG levels in OGG1-deficient fetal brains (p < 0.05). Female ogg1 knock-out offspring exposed in utero to high-dose METH exhibited gene dose-dependent enhanced motor coordination deficits for at least 12 weeks postnatally (p < 0.05). Contrary to METH-treated adult mice, METH-exposed CD-1 fetal brains did not exhibit altered apoptosis or DNA synthesis, and OGG1-deficient offspring exposed in utero to METH did not exhibit postnatal dopaminergic nerve terminal degeneration, suggesting different mechanisms. Enhanced 8-oxoG repair activity in fetal relative to adult organs suggests an important developmental protective role of OGG1 against in utero genotoxic stress. These observations provide the most direct evidence to date that 8-oxoG constitutes an embryopathic molecular lesion, and that functional fetal DNA repair protects against METH teratogenicity.

Variable in vivo embryoprotective role for ataxia-telangiectasia-mutated against constitutive and phenytoin-enhanced oxidative stress in atm knockout mice.

Knockout mice lacking the ataxia-telangiectasia-mutated (Atm) protein exhibit impaired detection and repair of DNA damage and increased embryopathies from ionizing radiation in vivo, and vehicle or phenytoin in embryo culture. Here we determined if Atm-deficient mice are more susceptible in vivo to phenytoin embryopathies. Wild-type (+/+) or heterozygous (+/-) Atm knockout dams were mated with +/- males, pregnant dams were treated with phenytoin (65 mg/kg ip) or its vehicle, and resorptions and fetuses were genotyped and characterized. This strain proved resistant to phenytoin-initiated cleft palates but not to other spontaneous and phenytoin-enhanced embryopathies. With vehicle-treated +/- dams, fetal body weight was lower in homozygous Atm-null (-/-) fetuses compared to +/- and +/+ littermates (p < 0.05). Phenytoin enhanced this Atm-dependent embryopathic pattern (p < 0.05). It also enhanced DNA oxidation in -/- Atm-deficient embryos compared to its +/- Atm-deficient (p < 0.001) and +/+ Atm-normal (p < 0.001), phenytoin-exposed littermates and to its -/- vehicle controls (p < 0.01). Postpartum lethality was greater in both +/- and -/- Atm-deficient fetuses compared to +/+ littermates, independent of treatment (0.05 < p < 0.1). By maternal genotype, +/- Atm-deficient dams had fewer implantations than +/+ dams, independent of treatment, and phenytoin decreased litter size (p < 0.05). Conversely, phenytoin-exposed +/+ fetuses were more likely than -/- littermates to die in utero (p < 0.05), and in +/+ dams fetal resorptions and postpartum lethality were variably higher and enhanced by phenytoin (p < 0.05). Despite variable actions in vivo, the embryoprotective effects of Atm suggest a role for reactive oxygen species and oxidative DNA damage in some spontaneous and phenytoin-enhanced embryopathies.

Prostaglandin H synthase-catalyzed bioactivation of amphetamines to free radical intermediates that cause CNS regional DNA oxidation and nerve terminal degeneration.

Reactive oxygen species (ROS) are implicated in amphetamine-initiated neurodegeneration, but the mechanism is unclear. Here, we show that amphetamines are bioactivated by CNS prostaglandin H synthase (PHS) to free radical intermediates that cause ROS formation and neurodegenerative oxidative DNA damage. In vitro incubations of purified PHS-1 with 3,4-methylenedioxyamphetamine (MDA) and methamphetamine (METH) demonstrated PHS-catalyzed time- and concentration-dependent formation of an amphetamine carbon- and/or nitrogen-centered free radical intermediate, and stereoselective oxidative DNA damage, evidenced by 8-oxo-2'-deoxyguanosine (8-oxo-dG) formation. Similarly in vivo, MDA and METH caused dose- and time-dependent DNA oxidation in multiple brain regions, remarkably dependent on the regional PHS levels, including the striatum and substantia nigra, wherein neurodegeneration of dopaminergic nerve terminals was evidenced by decreased immunohistochemical staining of tyrosine hydroxylase. Motor impairment using the rotarod test was evident within 3 wk after the last drug dose, and persisted for at least 6 months. Pretreatment with the PHS inhibitor acetylsalicylic acid blocked MDA-initiated DNA oxidation and protected against functional motor impairment for at least 1.5 months after drug treatment. This is the first direct evidence for PHS-catalyzed bioactivation of amphetamines causing temporal and regional differences in CNS oxidative DNA damage directly related to structural and functional neurodegenerative consequences.

Molecular and biochemical mechanisms in teratogenesis involving reactive oxygen species.

Developmental pathologies may result from endogenous or xenobiotic-enhanced formation of reactive oxygen species (ROS), which oxidatively damage cellular macromolecules and/or alter signal transduction. This minireview focuses upon several model drugs (phenytoin, thalidomide, methamphetamine), environmental chemicals (benzo[a]pyrene) and gamma irradiation to examine this hypothesis in vivo and in embryo culture using mouse, rat and rabbit models. Embryonic prostaglandin H synthases (PHSs) and lipoxygenases bioactivate xenobiotics to free radical intermediates that initiate ROS formation, resulting in oxidation of proteins, lipids and DNA. Oxidative DNA damage and embryopathies are reduced in PHS knockout mice, and in mice treated with PHS inhibitors, antioxidative enzymes, antioxidants and free radical trapping agents. Thalidomide causes embryonic DNA oxidation in susceptible (rabbit) but not resistant (mouse) species. Embryopathies are increased in mutant mice deficient in the antioxidative enzyme glucose-6-phosphate dehydrogenase (G6PD), or by glutathione (GSH) depletion, or inhibition of GSH peroxidase or GSH reductase. Inducible nitric oxide synthase knockout mice are partially protected. Inhibition of Ras or NF-kB pathways reduces embryopathies, implicating ROS-mediated signal transduction. Atm and p53 knockout mice deficient in DNA damage response/repair are more susceptible to xenobiotic or radiation embryopathies, suggesting a teratological role for DNA damage, consistent with enhanced susceptibility to methamphetamine in ogg1 knockout mice with deficient repair of oxidative DNA damage. Even endogenous embryonic oxidative stress carries a risk, since untreated G6PD- or ATM-deficient mice have increased embryopathies. Thus, embryonic processes regulating the balance of ROS formation, oxidative DNA damage and repair, and ROS-mediated signal transduction may be important determinants of teratological risk.

Methamphetamine-enhanced embryonic oxidative DNA damage and neurodevelopmental deficits.

Methamphetamine (METH) causes dopaminergic nerve terminal degeneration and functional deficits in adult mice, but its neurodevelopmental effects are unclear. We investigated METH-initiated oxidative DNA damage in brain during the embryonic and fetal periods, and the postnatal histological and functional consequences. Pregnant CD-1 mice were treated with a single dose of METH (20 or 40 mg/kg ip) or its saline vehicle on Gestational Day 14 or 17. METH enhanced conceptal DNA oxidation, determined by 8-oxoguanine formation, in brain and liver by at least 2-fold at 1 h (P < 0.05), and more so in some fetal brains at 4 h. After birth, motor coordination on the rotarod apparatus in the METH-exposed offspring was impaired for at least 12 weeks (P < 0.05). Unlike in adults, this postnatal functional deficit in offspring exposed in utero to METH was not associated with degeneration of striatal dopaminergic nerve terminals at 12 weeks of age determined by tyrosine hydroxylase staining, suggesting a novel pathological mechanism in utero. This is the first evidence of oxidative DNA damage in embryonic and fetal brain caused by amphetamines, leading to long-term postnatal neurodevelopmental deficits via a mechanism different from that underlying the neurodegeneration observed in METH-exposed adults.

Relation between apolipoprotein E genotype, hepatitis B virus status, and thyroid status in a sample of older persons with Down syndrome.

Dementia of the Alzheimer type (DAT) is common in older persons with Down syndrome (DS). There are three common alleles of the apolipoprotein E (ApoE) gene (Sigma 2, Sigma 3, and Sigma 4) resulting in three different isoforms (E2, E3, and E4) and six different genotypes (2,2; 2,3; 2,4; 3,3; 3,4; and 4,4). Sigma 4 is a risk factor for DAT whereas Sigma 2 appears prophylactic. As hepatitis B virus (HBV) infection and hypothyroidism also are common in DS, we evaluated associations between ApoE type, HBV status, and thyroid status in a sample of older persons with DS (n = 55; mean age, 44.3 +/- 10.8 years) using chi-squared analysis. Participants were classified as E2 (2,2 or 2,3), E3 (3,3), or E4 (3,4 or 4,4); positive for markers of HBV infection in the present or past (i.e., total HBcAb+ and/or HBsAg+ with or without infectivity, defined as HBV+) or negative for markers of HBV infection (defined as HBV-) and, currently receiving thyroid hormone supplement (defined as "hypothyroidism") or having normal thyroid function. The majority of the HBV+ were currently HBcAb+ and HBsAb+, but not HBsAg+. In females, there was an ApoE allele effect on thyroid status (P < or = 0.01), E2 being negatively (P < or = 0.01) and E4 being positively (P < or = 0.05) associated with "hypothyroidism". There was no evidence for an ApoE allele effect on thyroid status in males. There was no evidence for an ApoE allele effect on HBV status, or for an HBV status effect on thyroid status. As thyroid status can affect cognitive function, ApoE allele effects in DAT may, in part, be thyroid effects.