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Updated: Jul 11, 2026
Brain Ventricular Microinjections of Lipopolysaccharide into Larval Zebrafish to Assess Neuroinflammation and Neurotoxicity
Published on: August 23, 2022
Lipopolysaccharide is a frequent and significant contaminant in microglia-activating factors
Jonathan R Weinstein1, Sarah Swarts, Caroline Bishop
1Department of Neurology, School of Medicine, University of Washington, Seattle, Washington 98195, USA. jweinste@u.washington.edu
Abstract:
Lipopolysaccharide (LPS/endotoxin) is a potent immunologic stimulant. Many commercial-grade reagents used in research are not screened for LPS contamination. LPS induces a wide spectrum of proinflammatory responses in microglia, the immune cells of the brain. Recent studies have demonstrated that a broad range of endogenous factors including plasma-derived proteins and bioactive phospholipids can also activate microglia. However, few of these studies have reported either the LPS levels found in the preparations used or the effect of LPS inhibitors such as polymyxin B (PMX) on factor-induced responses. Here, we used the Limulus amoebocyte lysate assay to screen a broad range of commercial- and pharmaceutical-grade proteins, peptides, lipids, and inhibitors commonly used in microglia research for contamination with LPS. We then characterized the ability of PMX to alter a representative set of factor-induced microglial activation parameters including surface antigen expression, metabolic activity/proliferation, and NO/cytokine/chemokine release in both the N9 microglial cell line and primary microglia. Significant levels of LPS contamination were detected in a number of commercial-grade plasma/serum- and nonplasma/serum-derived proteins, phospholipids, and synthetic peptide preparations, but not in pharmaceutical-grade recombinant proteins or pharmacological inhibitors. PMX had a significant inhibitory effect on the microglia-activating potential of a number of commercial-, but not pharmaceutical-grade, protein preparations. Novel PMX-resistant responses to alpha(2)-macroglobulin and albumin were incidentally observed. Our results indicate that LPS is a frequent and significant contaminant in commercial-grade preparations of previously reported microglia-activating factors. Careful attention to LPS levels and appropriate controls are necessary for future studies in the neuroinflammation field.
Insights
Commercial reagents often contain lipopolysaccharide (LPS) contamination, which activates microglia. This study found significant LPS in many commercial preparations, impacting neuroinflammation research. Careful screening and controls are essential.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Lipopolysaccharide (LPS) is a potent immune stimulant that triggers proinflammatory responses in microglia, the brain's immune cells.
- Many research reagents are not screened for LPS contamination, potentially confounding studies on microglial activation by endogenous factors.
- LPS inhibitors like polymyxin B (PMX) are used, but their efficacy against factor-induced responses in the presence of LPS is not always clear.
Purpose of the Study:
- To screen commercial and pharmaceutical-grade reagents for LPS contamination using the Limulus amoebocyte lysate assay.
- To evaluate the impact of LPS contamination on microglial activation by various factors.
- To characterize the ability of polymyxin B (PMX) to inhibit factor-induced microglial responses.
Main Methods:
- Limulus amoebocyte lysate assay for LPS detection in proteins, peptides, lipids, and inhibitors.
- Microglial cell line (N9) and primary microglia assays to assess activation parameters (surface antigen expression, proliferation, NO/cytokine/chemokine release).
- Treatment with various reagents and polymyxin B (PMX) to evaluate inhibitory effects.
Main Results:
- Significant LPS contamination was found in numerous commercial-grade proteins, phospholipids, and synthetic peptides, but not in pharmaceutical-grade recombinant proteins or inhibitors.
- PMX significantly inhibited microglial activation by some commercial-grade protein preparations, but not pharmaceutical-grade ones.
- Novel PMX-resistant microglial responses were observed for alpha(2)-macroglobulin and albumin.
Conclusions:
- LPS is a frequent and significant contaminant in commercial-grade reagents used for studying microglia-activating factors.
- Researchers must carefully assess LPS levels and implement appropriate controls in neuroinflammation studies.
- The presence of LPS can significantly influence experimental outcomes and the interpretation of microglial activation pathways.
