Frontiers in neuroscienceJul 9, 2026

How Different Chemicals Affect Brain Health Through the Aryl Hydrocarbon Receptor: From Environmental Harm to Gut-Related Protection

Gut-Brain Axis Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Jul 10, 2026

Abstract

The aromatic hydrocarbon receptor (AhR) is linked to both neurotoxic and neuroprotective effects on brain function.

AhR signaling can be influenced by environmental chemicals and gut microbiota metabolites.
Environmental polycyclic aromatic hydrocarbons (PAHs) activate AhR in a sustained manner, potentially leading to neuroinflammation and cognitive decline.
Gut microbiota-derived metabolites like indole-3-propionic acid (IPA) and kynurenic acid (KYNA) activate AhR transiently, promoting protective effects such as anti-inflammatory responses and neuronal health.
The impact of AhR activation is dependent on factors such as ligand pharmacokinetics, cell-type identity, and tissue-specific conditions.
The balance of harmful and beneficial ligands associated with AhR may influence the progression of Alzheimer's and Parkinson's diseases.
Therapeutic strategies targeting the AhR-gut-brain axis could potentially enhance cognitive function and mitigate neurodegeneration.

Simplified

The aromatic hydrocarbon receptor (AhR) is a key molecular interface integrating environmental chemical signals with host-microbiome metabolism, with profound effects on brain function. This review systematically addresses the ligand-specific duality of AhR signaling in cognitive health, comparing the predominantly neurotoxic signaling driven by environmental polycyclic aromatic hydrocarbons (PAHs) with the predominantly neuroprotective signaling mediated by gut microbiota-derived tryptophan metabolites. However, this dichotomy is context-dependent rather than absolute. PAHs activate AhR in a sustained, high-affinity manner, engaging downstream NF-κB neuroinflammation, NLRP3 inflammasome activation, oxidative stress, synaptic dysfunction, and transgenerational epigenetic alterations. In contrast, microbiota-derived metabolites such as indole-3-propionic acid (IPA) and kynurenic acid (KYNA) elicit transient, low-affinity AhR activation that engages cell-type-specific programs promoting anti-inflammatory responses, neurogenesis, blood-brain barrier integrity, and neuronal homeostasis. Critically, the outcome of AhR activation is modulated by ligand pharmacokinetics, cell-type identity, temporal dynamics of receptor engagement, and tissue-specific co-factor availability. These contextual variables determine whether AhR functions as a driver of neurodegeneration or a guardian of cognitive resilience. We further examine the divergent roles of AhR in Alzheimer's and Parkinson's diseases, where the balance between detrimental and protective ligands determines disease progression. Finally, we discuss therapeutic strategies targeting the AhR-gut-brain axis, including dietary modulation, probiotic interventions, and selective AhR modulators. Understanding the context-dependent outcomes of AhR activation provides a framework for developing precision approaches to preserve cognitive function and prevent neurodegeneration.

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Competing interests

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

PubMed

How Different Chemicals Affect Brain Health Through the Aryl Hydrocarbon Receptor: From Environmental Harm to Gut-Related Protection

Abstract

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Abstract

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