Biomedical subjects

S Varadarajan

Publications and source records attributed to S Varadarajan.

15 recordsLinked to original sources

PubMed2001

Different mechanisms of oxidative stress and neurotoxicity for Alzheimer's A beta(1--42) and A beta(25--35).

Oxidative stress induced by amyloid beta-peptide (A beta) has been implicated in the neurodegeneration observed in Alzheimer's disease (AD) brain. However, the mechanism by which the predominant form of A beta found in AD brains, A beta(1--42), causes oxidative stress and neurotoxicity remains unknown. Numerous laboratories have used the smaller 11-amino acid fragment of the full-length peptide, A beta(25--35), as a convenient alternative in AD investigations since the smaller peptide mimics several of the toxicological and oxidative stress properties of the native full-length peptide. Our observation that the truncated peptide is more rapidly toxic and causes more oxidative damage than the parent A beta(1--42) led us to investigate the cause for this enhanced toxicity of A beta(25--35) in order to gain insight into the mechanism of action of these peptides. These studies reveal that two different mechanisms may be operative in the two peptides; however, the single methionine residue in the peptides appears to play a crucial role in both mechanisms. That methionine is C-terminal in A beta(25--35) seems to be the cause for its exaggerated effects. When the next amino acid in the sequence of A beta(1--42) (valine) is appended to A beta(25--35), the resultant peptide, A beta(25--36), in which methionine is no longer C-terminal, is neither toxic to cultured neurons nor does it cause oxidative damage. Additionally, oxidizing the sulfur of methionine to a sulfoxide abrogates the damaging effects of both A beta(25--35) and A beta(1--42). The putative mechanistic role of methionine in the observed properties of A beta peptides is discussed in the context of the obtained results as is the role of A beta(1--42)-induced oxidative stress in the neurodegeneration found in AD brain.

Alzheimer Disease↗

PubMed2001

Role of spermine in amyloid beta-peptide-associated free radical-induced neurotoxicity.

The polyamines, relatively low-molecular-weight aliphatic compounds, are the main inducers of eukaryotic cell growth and proliferation. Although polyamine requirements for cell growth are well defined, their role is still enigmatic. We have previously reported that amyloid beta-peptide (A beta), the main constituent of senile plaques in Alzheimer's disease (AD) brain, is toxic to neurons through a free radical-dependent oxidative stress mechanism and that A beta(1--42), the principal form of A beta in AD brain, causes an increase in polyamine metabolism manifested by up-regulated polyamine uptake and increased ornithine decarboxylase (ODC) activity. Both effects were prevented by the free radical scavenger vitamin E. Spermine has been reported to function directly as a free radical scavenger. In the current study, we aimed to address whether up-regulation of polyamine metabolism is a defense against, or a result of, A beta-induced oxidative stress by investigating the capability of spermine to quench A beta-associated free radicals in solution and to assert a protective function of spermine in neuronal culture against A beta. Pretreatment of cultured neurons with spermine prior to A beta exposure failed to prevent A beta-induced cell death. Indeed, A beta plus spermine added to cultured neurons was even more neurotoxic than either agent alone. Additionally, inhibition of the polyamine synthesis by difluoromethylornithine (DFMO) did not protect cells from A beta-induced free radical toxicity, and stimulation of the synthesis of putrescine and spermine by the aminopropyltransferase inhibitor S-adenosyl-1,8-diamino-thiooctane (AdoDATO), rather, further enhanced A beta-induced toxicity. Although spermine is capable of scavenging free radicals generated by A beta in solution as measured by electron paramagnetic resonance (EPR) spectroscopy, the up-regulated transport of exogenously added spermine together with A beta may lead to overaccumulation of a cellular spermine pool, with resulting enhanced neurotoxicity.

Adenosine↗

PubMed2001

Vulnerability of synaptosomes from apoE knock-out mice to structural and oxidative modifications induced by A beta(1-40): implications for Alzheimer's disease.

Apolipoprotein E (apoE) plays an important role in the response to central nervous system injury. The e4 allele of apoE and amyloid beta-peptide (Abeta) are associated with Alzheimer's disease (AD) and may be central to the pathogenesis of this disorder. Recent studies demonstrate evidence for neurodegeneration and increased lipid peroxidation in transgenic mice lacking apoE (KO). In the current study, synaptosomes were prepared from apoE KO mice to determine the role of apoE in synaptic membrane structure and to determine susceptibility to oxidative damage by Abeta(1-40). ApoE KO mice exhibited structural modifications to lipid and protein components of synaptosomal membranes as determined by electron paramagnetic resonance in conjunction with lipid- and protein- specific spin labels. Incubation with 5 microM Abeta(1-40) resulted in more severe oxidative modifications to proteins and lipids in apoE KO synaptosomes as measured by protein carbonyls, an index of protein oxidation, and TBARs and protein-bound 4-hydroxynonenal (HNE), markers of lipid oxidation. Together, these data support a role for apoE in the modulation of oxidative injury and in the maintenance of synaptic integrity and are discussed with reference to alterations in AD brain.

Alzheimer Disease↗

PubMed2000

Formation of a protein-bound pyrazinium free radical cation during glycation of histone H1.

Glycation, the nonenzymatic reaction between protein amino groups and reducing sugars, induces protein damage that has been linked to several pathological conditions, especially diabetes, and general aging. Here we describe the direct identification of a protein-bound free radical formed during early glycation of histone H1 in vitro. Earlier EPR analysis of thermal browning reactions between free amino acids and reducing sugars has implicated the sugar fragmentation product glycolaldehyde in the generation of a 1,4-disubstituted pyrazinium free radical cation. In order to evaluate the potential formation of this radical in vivo, the early glycation of BSA, lysozyme, and histone H1 by several sugars (D-glucose, D-ribose, ADP-ribose, glycolaldehyde) under conditions of physiological pH and temperature was examined by EPR. The pyrazinium free radical cation was identified on histone H1 glycated by glycolaldehyde (g = 2.00539, aN = 8.01 [2N], aH = 5.26 [4H], aH = 2.72 [4H]), or ADP-ribose. Reaction of glycoaldehyde with poly-L-lysine produced an identical signal, whereas reaction with BSA or lysozyme produced only a minor unresolved singlet signal. In the absence of oxygen the signal was stable over several days. Our results raise the possibility that pyrazinium radicals may form during glycation of histone H1 in vivo.

Acetaldehyde↗

PubMed2000

The pyrrolopyrimidine U101033E is a potent free radical scavenger and prevents Fe(II)-induced lipid peroxidation in synaptosomal membranes.

The pyrrolopyrimidine U101033E is a therapeutic compound potentially useful in stroke, head injury and other oxidative stress conditions. Electron paramagnetic resonance (EPR) techniques of spin labeling and spin trapping in conjunction with measures of lipid and protein oxidation have been used to investigate the proposed antioxidant capacity of U101033E. We report potent antioxidant activity of this agent in aqueous cell-free solution as measured by spin trapping. U101033E significantly (P<0.005) reduces the formation of the EPR active spin trap N-t-butyl-alpha-phenylnitrone (PBN)-radical adduct by 17.1% at a concentration of 1 microM, four orders of magnitude less than the concentration of PBN. As measured by the decrease in signal intensity of lipid-resident nitroxide stearate spin probes, an EPR assay for lipid peroxidation, this pyrrolopyrimidine compound efficiently protected against hydroxyl radical-induced lipid peroxidation in cortical synaptosomal membranes deep within the membrane bilayer, but not closer to the membrane surface. In addition, U101033E partially prevents synaptosomal protein oxidation in the presence of Fe(II); however, U101033E demonstrates some protein oxidative effects itself. These results are supportive of the proposed role of U101033E as a lipid-specific antioxidant, especially for protection against lipid peroxidation that occurs deep within the membrane bilayer, but raise some potential concerns about the oxidative nature of this agent toward proteins.

Animals↗

PubMed2000

Review: Alzheimer's amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity.

Alzheimer's disease, the major dementing disorder of the elderly that affects over 4 million Americans, is related to amyloid beta-peptide, the principal component of senile plaques in Alzheimer's disease brain. Oxidative stress, manifested by protein oxidation and lipid peroxidation, among other alterations, is a characteristic of Alzheimer's disease brain. Our laboratory united these two observations in a model to account for neurodegeneration in Alzheimer's disease brain, the amyloid beta-peptide-associated oxidative stress model for neurotoxicity in Alzheimer's disease. Under this model, the aggregated peptide, perhaps in concert with bound redox metal ions, initiates free radical processes resulting in protein oxidation, lipid peroxidation, reactive oxygen species formation, cellular dysfunction leading to calcium ion accumulation, and subsequent neuronal death. Free radical antioxidants abrogate these findings. This review outlines the substantial evidence from multiidisciplinary approaches for amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity and protection against these oxidative processes and cell death by free radical scavengers. In addition, we review the strong evidence supporting the notion that the single methionine residue of amyloid beta-peptide is vital to the oxidative stress and neurotoxicological properties of this peptide. Further, we discuss studies that support the hypothesis that aggregated soluble amyloid beta-peptide and not fibrils per se are necessary for oxidative stress and neurotoxicity associated with amyloid beta-peptide.

Alzheimer Disease↗

PubMed1999

Catalytic Upgrading of Fermentation-Derived Organic Acids.

The production of organic acids in low-cost, high-efficiency fermentation processes makes available a new route to chemical production from biomass. Because of their multiple functional groups and high reactivity, organic acids can undergo a variety of reactions that are effectively catalyzed by inorganic heterogeneous or homogeneous catalysts. Lactic acid and succinic acid, in particular, are approaching large-scale production via fermentation and show excellent promise as feedstocks for catalytic conversion routes such as hydrogenation, dehydration, or condensation. A number of catalytic conversion pathways of organic acids are potentially competitive with petroleum-based routes in the current economic environment, particularly when integrated into existing biomass/crop processing schemes. This article reviews some of the key reaction pathways available using fermentation-derived organic acids as feedstocks and presents recent results from the authors' lab on succinate hydrogenation to 1,4-butanediol and tetrahydrofuran. By a judicious choice of support properties and reaction conditions, it is possible to achieve yields of either of these two products in excess of 80%.

Journal Article↗

PubMed1999

Methionine residue 35 is important in amyloid beta-peptide-associated free radical oxidative stress.

Amyloid beta-peptide (Abeta), the central constituent of senile plaques in Alzheimer's disease (AD) brain, has been shown to be a source of free radical oxidative stress that may lead to neurodegeneration. In the current study Abeta(1-40), found in AD brain, and the amyloid fragment Abeta(25-35) were used in conjunction with electron paramagnetic resonance spin trapping techniques to demonstrate that these peptides mediate free radical production. The methionine residue in these peptides is believed to play an important role in their neurotoxicity. Substitution of methionine by structurally similar norleucine in both Abeta(1-40) and Abeta(25-35), and the substitution of methionine by valine, or the removal of the methionine in Abeta(25-35), abrogates free radical production and protein oxidation of and toxicity to hippocampal neurons. These results are discussed with relevance to the hypothesis that neurodegeneration in Alzheimer's disease may be due in part to Abeta-associated free radical oxidative stress that involves methionine, and to the use of spin trapping methods to infer mechanistic information about Abeta.

Alzheimer Disease↗

PubMed1999

scalloped functions in a regulatory loop with vestigial and wingless to pattern the Drosophila wing.

The development of the Drosophila wing involves progressive patterning events. In the second larval instar, cells of the wing disc are allotted wing or notum fates by a wingless-mediated process and dorsal or ventral fates by the action of apterous and wingless. Notch-mediated signalling is required for the expression of the genes vestigial and scalloped in the presumptive wing blade. Later, wingless, Notch and cut are involved in cell fate specification along the wing margin. The function of scalloped in this process is not well understood and is the focus of this study. We show that patterning downstream of Notch and wingless pathways is altered in scalloped mutants. Reduction in scalloped expression results in a loss of expression of wing blade- and margin-specific markers. Misexpression of scalloped in the presumptive wing causes misexpression of scalloped, vestigial and wingless reporter genes. However, high levels of scalloped expression have a negative influence on wingless, vestigial and its own expression. Our results demonstrate that scalloped functions in a level-dependent manner in the presumptive wing blade in a loop that involves vestigial and itself. We suggest that wing development requires the regulated expression of scalloped together with vestigial-the "wing formation" effects of Vestigial in other imaginal discs are probably due to its interaction with the scalloped gene product normally expressed in these discs.

Animals↗

PubMed1999

Elevated oxidative stress in models of normal brain aging and Alzheimer's disease.

Age-associated neurodegenerative disorders are becoming more prevalent as the mean age of the population increases in the United States over the next few decades. Both normal brain aging and Alzheimer's disease (AD) are associated with oxidative stress. Our laboratory has used a wide variety of physical and biochemical methods to investigate free radical oxidative stress in several models of aging and AD. Beta-amyloid (A beta), the peptide that constitutes the central core of senile plaques in AD brain, is associated with free radical oxidative stress and is toxic to neurons. This review summarizes some of our studies in aging and A beta-associated free radical oxidative stress and on the modulating effects of free radical scavengers on neocortical synaptosomal membrane damage found in aging and A beta-treated systems.

Aging↗

PubMed1999

Amyloid beta-peptide-associated free radical oxidative stress, neurotoxicity, and Alzheimer's disease.

Given the increasing evidence of oxidative stress in AD brain and studies from different perspectives that appear to show a converging, central role for A beta in the pathogenesis and etiology of AD, insight into A beta-associated free radical oxidative stress will likely lead to a greater understanding of AD and, potentially, to better therapeutic strategies in this disorder. This article outlined methods to investigate markers of oxidative stress induced by A beta in brain membrane systems. Especially important are markers for protein oxidation, lipid peroxidation, and ROS generation by A beta. Oxidative stress and its sequelae are likely related to both necrotic and apoptotic mechanisms of neurotoxicity, and A beta-associated free radical oxidative stress may be of fundamental importance in Alzheimer's disease etiology and pathogenesis. The methods described here provide some means for investigating this possibility.

Alzheimer Disease↗

PubMed1999

Peroxynitrite-induced alterations in synaptosomal membrane proteins: insight into oxidative stress in Alzheimer's disease.

Peroxynitrite (ONOO ) is a highly reactive, oxidizing anion with a half-life of <1 s that is formed by reaction of superoxide radical anion with nitric oxide. Several reports of ONOO--induced oxidation of lipids, proteins, DNA, sulfhydryls, and inactivation of key enzymes have appeared. ONOO- has also been implicated as playing a role in the pathology of several neurodegenerative disorders, such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis, among others. Continuing our laboratory's interest in free radical oxidative stress in brain cells in AD, the present study was designed to investigate the damage to brain neocortical synaptosomal membrane proteins and the oxidation-sensitive enzyme glutamine synthetase (GS) caused by exposure to ONOO-. These synaptosomal proteins and GS have previously been shown by us and others to have been oxidatively damaged in AD brain and also following treatment of synaptosomes with amyloid beta-peptide. The results of the current study showed that exposure to physiological levels of ONOO- induced significant protein conformational changes, demonstrated using electron paramagnetic resonance in conjunction with a protein-specific spin label, and caused oxidation of proteins, measured by the increase in protein carbonyls. ONOO- also caused inactivation of GS and led to neuronal cell death examined in a hippocampal cell culture system. All these detrimental effects of ONOO- were successfully attenuated by the thiol-containing antioxidant tripeptide glutathione. This research shows that ONOO- can oxidatively modify both membranous and cytosolic proteins, affecting both their physical and chemical nature. These findings are discussed with reference to the potential involvement of ONOO- in AD neurodegeneration.

Alzheimer Disease↗

PubMed1997

Multiple mechanisms for the inhibition of entry and uncoating of superinfecting Semliki Forest virus.

Recombinant Semliki Forest viruses (SFV) that express one or none of the viral structural proteins were used to infect cells and to analyze the fate of incoming superinfecting wild-type viruses. It was found that in addition to the previously described block in replication that superinfecting viruses encounter within 15 min of infection, other mechanisms of superinfection inhibition occurred at later times. Over a 6-hr infection period, inhibition was seen in binding of virus to the cell surface, in acid-activated penetration into the cytoplasm, and in uncoating of nucleocapsids. For each of these processes, the inhibitory mechanism was investigated. In summary, we found that infection evoked several independent mechanisms for blocking the entry and uncoating of superinfecting viruses. The results also offered new insights into the normal processes of penetration and uncoating of SFV.

Animals↗

PubMed1995

Primary cutaneous osteosarcoma.

A 78-year-old man had a 1-cm cutaneous nodule on his shoulder; subsequent excisional biopsy showed osteosarcoma. There was no connection to deeper structures, and no primary bone lesion was found. The tumor recurred at the same site 9 months after diagnosis and was reexcised. We believe this to be the first well-illustrated case of primary cutaneous osteosarcoma, which should now be included on the list of sarcomas that may occur in the skin.

Aged↗

PubMedDate not supplied

In vitro and in vivo oxidative stress associated with Alzheimer's amyloid beta-peptide (1-42)

The amyloid beta-peptide (A beta)-associated free radical oxidative stress model for neuronal death in Alzheimer's disease (AD) brain predicts that neuronal protein oxidation is a consequence of A beta-associated free radicals [8]. In this study we have used both in vitro and in vivo models of beta-amyloid (A beta) toxicity to detect free radical induced oxidative stress by the measure of protein carbonyl levels. These model systems employed cultured hippocampal neurons exposed to exogenous synthetic A beta(1-42) and transgenic Caenorhabditis elegans (C. elegans) animals expressing A beta(1-42). We also investigated the importance of the A beta(1-42) Met35 residue for free radical formation in peptide solution and for peptide-induced protein oxidation and neuronal toxicity in these model systems. A beta(1-42) in solution yielded an EPR spectrum, suggesting that free radicals are associated with this peptide; however, neither the reverse [A beta(42-1)] nor methionine-substituted peptide [A beta(1-42)Met35Nlc] gave significant EPR spectra, suggesting the importance of the methionine residue in free radical formation. A beta(1-42) addition to cultured hippocampal neurons led to both neurotoxicity (30.1% cell death, p < 0.001) and increased protein oxidation (158% of controls, p < 0.001). and both of those effects were not observed with reverse or Met35Nle substituted peptides. C. elegans transgenic animals expressing human A beta(1-42) also had significantly increased in vivo protein carbonyls (176% of control animals, p < 0.001), consistent with our model. In contrast, transgenic animals with a Met35cys substitution in A beta(1-42) showed no increased protein carbonyls in vivo, in support of the hypothesis that methionine is important in A beta-associated free radical oxidative stress. These results are discussed with reference to the A beta-associated free radical oxidative stress model of neurotoxicity in AD brain.

Alzheimer Disease↗