Pomegranate ellagitannin-gut microbial-derived metabolites, urolithins, inhibit neuroinflammation in vitro

Abstract

Objectives: Urolithins, ellagitannin-gut microbial-derived metabolites, have been reported to mediate pomegranate’s neuroprotective effects against Alzheimer’s disease (AD), but there are limited data on their effects against neuroinflammation. Herein, we: (1) evaluated whether urolithins (urolithins A and B and their methylated derivatives) attenuate neuroinflammation in murine BV-2 microglia and human SH-SY5Y neurons, and (2) evaluated hippocampus of transgenic AD (R1.40) mice administered a pomegranate extract (PE; 100 or 200 mg/kg/day for 3 weeks) for inflammatory biomarkers.

Methods: Effects of urolithins (10 μM) on inflammatory biomarkers were evaluated in lipopolysaccharide (LPS)-stimulated BV-2 microglia. In a non-contact co-culture cell model, SH-SY5Y cell viability was assessed after exposure to media collected from LPS-BV-2 cells treated with or without urolithins. Effects of urolithins on apoptosis and caspase 3/7 and 9 release from H₂O₂-induced oxidative stress of BV-2 and SH-SY5Y cells were assessed. Hippocampal tissues of vehicle and PE-treated transgenic R1.40 mice were evaluated for gene expression of inflammatory biomarkers by qRT-PCR.

Results: Urolithins decreased media levels of nitric oxide, interleukin 6 (IL-6), prostaglandin E₂, and tumor necrosis factor alpha from LPS-BV-2 microglia. In the co-culture cell model, media from LPS-BV-2 cells treated with urolithins preserved SH-SY5Y cell viability greater than media from cells treated without urolithins. Urolithins mitigated apoptosis and caspase 3/7 and 9 release from H₂O₂-induced oxidative stress of BV-2 and SH-SY5Y cells. While not statistically significant, inflammatory biomarkers (TNF-α, COX-2, IL-1, and IL-6) appeared to follow a decreasing trend in the hippocampus of high-dose PE-treated animals compared to controls.

Discussion: The attenuation of neuroinflammation by urolithins may contribute, in part, toward pomegranate’s neuroprotective effects against AD.

GRAPHICAL ABSTRACT

Keywords:

• Pomegranate
• Urolithins
• Gut microflora
• Neuroinflammation
• Neuroprotective

Disclaimer statements

Contributors None.

Funding None.

Conflicts of interest The authors declare no conflicts of interest.

Ethics approval Animals were used in compliance with all applicable laws and regulations and with the principles expressed by the NIH Guide for the Care and Use of Laboratory Animals.

ORCID

Nicholas A. DaSilva http://orcid.org/0000-0003-1925-0790

Hang Ma http://orcid.org/0000-0001-7565-6889

Susan Meschwitz http://orcid.org/0000-0001-9477-5410

Navindra P. Seeram http://orcid.org/0000-0001-7064-2904