Elsevier

Toxicology

Volume 201, Issues 1–3, 1 September 2004, Pages 197-207
Toxicology

How does peripheral lipopolysaccharide induce gene expression in the brain of rats?

https://doi.org/10.1016/j.tox.2004.04.015Get rights and content

Abstract

Lipopolysaccharide (LPS), the principal cell-wall component of gram-negative bacteria, is responsible for alterations in the central and peripheral tissues associated with gram-negative infections. However, the mechanism by which peripheral LPS cause central effects is not fully known. This study showed that peripheral LPS sequentially increased IL-1β and iNOS mRNA levels, NO2 level, and CRF mRNA level in the hypothalamic PVN, and corticosterone concentration in blood. Brain-endothelium, but not hypothalamic PVN samples, from LPS injected rats contained ions for LPS lipids, bound BODIPY-LPS (bLPS), and expressed TLR-4, TLP-2 and CD14 mRNAs. This suggests that (1) LPS does not cross the blood–brain barrier, and (2) brain-endothelial cells contain LPS binding sites, TLR-4, TLR-2 and CD14. Systemic LPS injection increased [14C]sucrose uptake, but did not affect [14C]dextran uptake into the brain. Thus, when injected systemically, LPS binds to its receptor and enter the endothelial cells where it increase BBB permeation in a mass-selective manner and triggers a series of signaling events leading to the development of inflammatory response in the brain.

Section snippets

Animal protocol

Groups of male Wistar rats (weighing around 225–270 g) were housed with light–dark cycle such that their adrenocortical activity was highest between 9 and 11 a.m. Prior to the start of the experiment, each rat was familiarized for 1 week with the experimental procedures to reduce stress-induced changes in the HPA axis. Then, the animals were injected with LPS (100 μg/kg) or the vehicle alone (for control) by i.p. injection (Bahrami et al., 1994). At specific time intervals after the injection,

CRF, iNOS, IL-1β and GR mRNA expression, and NO levels in the hypothalamus

Fig. 1 shows the RT-PCR analysis of iNOS, CRF, GR, IL-1β and β-actin mRNA. The IL-1β mRNA was detectable at 0.5 h after and peaked at 4 h after LPS injection. The iNOS mRNA appeared at 0.5 h after and peaked at 2 h after LPS injection. CRF mRNA appeared at 2 h after and peaked at 4 h after LPS injection. GR mRNA appeared at 3 h after and peaked at 6 h after LPS injection. iNOS mRNA values returned to the basal level within 3 to 4 h after LPS exposure. CRF mRNAs returned to the basal level within 6 h

Discussion

Peripheral LPS has been shown to activate a cascade of pro-inflammatory genes including IL-1β and iNOS genes that induce inflammatory reaction in the brain (Chao et al., 1992, Van Dam et al., 1998, Raber et al., 1995, Karanth et al., 1993, Lee et al., 1999, Uribe et al., 1999), although possible mechanism(s) for the central effects of peripheral LPS is not fully understood. In this study, we have hypothesized that either LPS crossed the BBB and directly induced pro-inflammatory cytokine and

Acknowledgements

This project was partially funded by grants from the Graduate School, College of Veterinary Medicine, and Center for Food Safety of the University of Minnesota.

References (53)

  • D.J Jaworowicz et al.

    Nitric oxide and prostaglandin E2 formation parallels blood–brain barrier disruption in an experimental rat model of bacterial meningitis

    Br. Res. Bull.

    (1998)
  • W.G Mayhan

    Effect of lipopolysaccharide on the permeability and reactivity of the cerebral microcirculation: role of inducible nitric oxide synthase

    Br. Res.

    (1998)
  • T Minami et al.

    Penetration of cisplatin into mouse brain by lipopolysaccharide

    Toxicology

    (1998)
  • N.C Olson et al.

    Mediators and vascular effects in response to endotoxin

    Br. Vet. J.

    (1995)
  • C.R Plata-Salaman

    Immunoregulators in the nervous system

    Neurosci. Biobehav. Rev.

    (1991)
  • N Quan et al.

    Time course and localization patterns of interleukin-1beta messenger RNA expression in brain and pituitary after peripheral administration of lipopolysaccharide

    Neuroscience

    (1998)
  • R.N Ramachandra et al.

    Neuro-hormonal host defense in endotoxin shock

    Brain Behav. Immun.

    (1992)
  • A Silipo et al.

    Ammonium hydroxide hydrolysis: a valuable support in the MALDI-TOF mass spectrometry analysis of lipid A fatty acid distribution

    J. Lipid Res.

    (2002)
  • C Szabo

    Physiological and pathophysiological roles of nitric oxide in the central nervous system

    Brain Res. Bull.

    (1996)
  • E Takahashi et al.

    Expression of c-fos, rather than c-jun or glucocorticoid-receptor mRNA, correlates with decreased glucocorticoid response of peripheral blood mononuclear cells in asthma

    Int. Immunopharmacol.

    (2002)
  • S Veszelka et al.

    Human serum amyloid P component attenuates the bacterial lipopolysaccharide-induced increase in blood–brain barrier permeability in mice

    Neurosci. Lett.

    (2003)
  • H Xaio et al.

    Effects of LPS on the permeability of the blood–brain barrier to insulin

    Brain Res.

    (2001)
  • C Zimmermann et al.

    Lipopolysaccharide-induced ischemic tolerance is associated with increased levels of ceramide in brain and in plasma

    Br. Res.

    (2001)
  • B.K Armatrong et al.

    Six-dependent blood–brain barrier opening demonstrated with [14C]sucrose and 200,000-Da [14C]dextran

    Exp. Neurol.

    (1987)
  • S Bahrami et al.

    Similar cytokine but different coagulation response to lipopolysaccharide injection in d-galactosamine-sensitized versus nonsensitized rats

    Infect. Immun.

    (1994)
  • W.A Banks et al.

    Passage of cytokines across the blood–brain barrier

    Neuroimmunomodulation

    (1995)
  • Cited by (192)

    View all citing articles on Scopus
    View full text