α-Tocopherol attenuates lipopolysaccharide-induced sickness behavior in mice☆
Introduction
Lipopolysaccharide is a highly conserved cell wall component of Gram-negative bacteria that is recognized by the immune system of higher vertebrates as a pathogen-associated molecular pattern (PAMP). LPS binding to immune cells initiates signaling cascades that activate the transcription factor nuclear factor κB (NFκB) to up-regulate expression of, among other genes, the inflammatory cytokines IL-1β, IL-6, and TNF-α. In addition to the local physiological changes ascribed to inflammatory cytokines, it is now appreciated that they also signal the brain to coordinate “sickness behaviors” through vagus nerve stimulation and by their targeted release at circumventricular organs (Konsman et al., 2002).
In the very early stages of localized cellular responses to LPS, endothelial and smooth muscle cells release hydrogen peroxide (H2O2), which functions to enhance microvascular blood flow to the site of infection (Khodr and Khalil, 2001). The later phase inflammatory response to LPS creates an abundance of peroxides and reactive oxygen species (ROS), primarily from macrophages and infiltrating neutrophils (Khodr and Khalil, 2001). During infection, intracellular ROS are generated by highly respiring mitochondria and phagolysosomes, which produce ROS to destroy invading bacteria. ROS and peroxides are also well documented to serve as intracellular second messengers to induce signal transduction and activate transcription factors such as NFκB (Cadenas and Cadenas, 2002; Haddad, 2002; Macdonald et al., 2003; Zhang et al., 2001). Therefore, production of ROS and peroxides is important for host defense and may influence sickness behavior via NFκB-dependent cytokine production.
There appears to be a delicate balance between the levels of ROS and peroxides optimum for clearing localized infections and levels that overcome endogenous antioxidant defenses and result in a state of oxidative stress-mediated pathology. If not neutralized, ROS and peroxides attack lipid membranes, oxidize intracellular proteins and DNA, and can up-regulate NFκB-induced transcription of inflammatory cytokines to detrimental levels. In fact, ROS and peroxides are thought to play a critical role in the pathogenesis of septic shock, a condition of systemic inflammation that results in over 80% mortality (Macdonald et al., 2003). Patients undergoing septic shock consistently experience increased markers of oxidative stress in conjunction with deficits in plasma antioxidants and glutathione, suggesting endogenous sources are being depleted (Galley et al., 1996; Ogilvie et al., 1991). However, the role of ROS and peroxides, if any, in mediating the severity of sickness behaviors displayed at sub-lethal exposures to LPS has been less thoroughly investigated.
One approach to investigate the role of ROS and peroxides in LPS-induced sickness is the use of antioxidant treatments through intraperitoneal, intravenous, or dietary administration. Importantly, several antioxidants have been shown to completely or partially block LPS-induced ROS and/or NFκB activation in cell culture systems and animal models: N-acetyl-l-cysteine (NAC; Li et al., 2002), β-carotene (Palozza et al., 2003), α-T (Pathania et al., 1999), and α-lipoate (Packer, 1998). Furthermore, Kheir-Eldin et al. (2001) showed that combined α-T and selenium treatment provided the greatest protection against brain oxidative stress induced by LPS administration when compared to NAC and β-carotene. The synergism between α-T and selenium appears to result from their ability to modulate two distinct pathways of oxidative stress. It is well established that α-T is a major lipid soluble antioxidant that prevents lipid peroxidation of membranes while selenium is required by a large family of selenoproteins, namely glutathione peroxidases and thioredoxin reductases, that function to reduce hydroperoxides. Intraperitoneal injections of α-T are reported to increase tissue and plasma levels of α-T to a greater extent than intramuscular, or dietary routes in various animals (Hidiroglou and Charmley, 1990) as well as provide functional protection against oxidative stress (Naziroglu and Cay, 2001; Naziroglu et al., 1999) and LPS-induced cytokine production (Webel et al., 1998). Importantly, dietary supplementation of α-T in rats has resulted in increased brain concentrations (Zhang et al., 1996) and the α-T transport protein was recently localized in the cerebral cortex to the Bergman glial cells within the Purkenje cell layer (Hosomi et al., 1998). However, there remains little research discerning the mechanisms and interactions of antioxidant treatment on cytokine regulated behaviors of sick animals. Therefore, we have chosen to investigate the effects of i.p. α-T injections and dietary α-T and selenium supplementation on LPS-induced depression of social behavior.
Section snippets
Animals
Three- to six-month-old male BALBc mice from our in-house specific pathogen-free colony were used in all studies. They were kept in groups of eight in polypropylene cages until three months of age, and housed individually thereafter. Mice were maintained under a reverse 12:12 h light/dark cycle (lights off 09.00 h) at 25 °C and allowed ad libitum access to water and Harlan Teklad rodent chow or semi-purified experimental diets (Dyets Bethlehem, PA, Table 1). Male juvenile conspecifics (4- to
Effects of bolus injection of α-T on LPS-induced sickness behavior
To establish a protocol that could be used to investigate the effects of α-T on LPS-induced depression of social behavior, mice were injected daily with vehicle, 2, or 20 mg α-T for 3 days, and 1 day later α-T levels in plasma and liver, and TBARS in liver were determined (Table 2). One-way ANOVA of liver α-T levels indicated a significant main effect of α-T injection (p<.02). As expected, α-T injected i.p. increased liver α-T in a dose-dependent manner. Relative to vehicle injected controls
Discussion
Antioxidants are being investigated for the ability to prevent cardiovascular, hepatic, and pulmonary damage caused by LPS-induced production of ROS, peroxides, and cytokines (Cadenas and Cadenas, 2002). Because cytokines are behaviorally active, we hypothesized that antioxidants would inhibit LPS-induced sickness behavior. The important finding of this study is that α-T ameliorated a sickness behavior caused by LPS. Specifically, α-T injections protected mice against depressed social
Acknowledgements
We thank the laboratory of Dr. John Erdman, especially Susan Zaripheh, for the excellent training and use of their HPLC system. We acknowledge the generous assistance of Trisha Toepfer-Berg and Kimberely Bielarczyk for their help performing laboratory assays and collecting behavioral data from video records, respectively. This research was supported by NIH Grant AG 16710.
References (39)
- et al.
Modulation of lipopolysaccharide-mediated activation in rat Kupffer cells by antioxidants
J. Lab. Clin. Med.
(1998) - et al.
Fighting the stranger-antioxidant protection against endotoxin toxicity
Toxicology
(2002) - et al.
Noninvasive diagnostic tool for inflammation-induced oxidative stress using electron spin resonance spectroscopy and an extracellular cyclic hydroxylamine
Arch. Biochem. Biophys.
(2002) - et al.
Ascorbyl radical formation in patients with sepsis: effect of ascorbate loading
Free Radic. Biol. Med.
(1996) Antioxidant and prooxidant mechanisms in the regulation of redox(y)-sensitive transcription factors
Cell. Signal.
(2002)- et al.
Inhibition of glutathione-related enzymes augments LPS-mediated cytokine biosynthesis: involvement of an IkappaB/NF-kappaB-sensitive pathway in the alveolar epithelium
Int. Immunopharmacol.
(2002) - et al.
Vitamin E concentrations in blood plasma of sheep and in sheep tissues after a single intraruminal or intraperitoneal administration of DL-alpha-tocopheryl acetate
Res. Vet. Sci.
(1990) - et al.
Localization of alpha-tocopherol transfer protein in rat brain
Neurosci. Lett.
(1998) - et al.
Protective effect of vitamin E, beta-carotene and N-acetylcysteine from the brain oxidative stress induced in rats by lipopolysaccharide
Int. J. Biochem. Cell Biol.
(2001) - et al.
Modulation of inflammation by reactive oxygen species: implications for aging and tissue repair
Free Radic. Biol. Med.
(2001)
Interpretation of the thiobarbituric acid reactivity of rat liver and brain homogenates in the presence of ferric ion and ethylenediaminetetraacetic acid
Anal. Biochem.
Cytokine-induced sickness behaviour: mechanisms and implications
Trends Neurosci.
Supplementation of N-acetylcysteine normalizes lipopolysaccharide-induced nuclear factor kappaB activation and proinflammatory cytokine production during early rehabilitation of protein malnourished mice
J. Nutr.
Oxidative stress and gene expression in sepsis
Br. J. Anaesth.
Vitamin E supplementation suppresses prostaglandin E1(2) synthesis and enhances the immune response of aged mice
Mech. Ageing Dev.
Assay for lipid peroxides in animal tissues by thiobarbituric acid reaction
Anal. Biochem.
β-Carotene regulates NF-kappaB DNA-binding activity by a redox mechanism in human leukemia and colon adenocarcinoma cells
J. Nutr.
Low levels of circulating inflammatory cytokines—do they affect human brain functions
Brain Behav. Immun.
Molecular insights on the cerebral innate immune system
Brain Behav. Immun.
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This research was supported by NIH grant AG 16710.