The molecular mechanism by which hydroxytyrosol inhibits the NF-κB pathway

Hydroxytyrosol (HT), a natural phenolic compound derived from olives, exhibits potent anti-inflammatory activity that is closely linked to its precise regulation of the nuclear factor-κB (NF-κB) signaling pathway. As a core transcription factor in inflammatory responses, NF-κB plays a critical role in immune responses, cell survival, and the release of inflammatory mediators. Hydroxytyrosol exerts its anti-inflammatory effects through multi-step interventions in this pathway.

I. Association Between NF-κB Pathway Activation and Inflammatory Responses

Under normal physiological conditions, NF-κB exists in an inactive form bound to the inhibitory protein IκB, sequestered in the cytoplasm. When the body is stimulated by bacterial lipopolysaccharide (LPS), tumor necrosis factor-α (TNF-α), reactive oxygen species (ROS), or other factors, the IκB kinase (IKK) complex is activated, leading to the phosphorylation and degradation of IκB. The released NF-κB (primarily the p65/p50 heterodimer) translocates to the nucleus, binds to the promoter regions of target genes, and drives the expression of inflammatory factors (e.g., IL-1β, IL-6, TNF-α), chemokines (e.g., CXCL8), as well as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), thereby exacerbating inflammatory responses. Overactivation of the NF-κB pathway is closely associated with chronic inflammation (e.g., arthritis, enteritis) and inflammation-related diseases (e.g., cardiovascular diseases, cancer).

II. Molecular Mechanisms by Which Hydroxytyrosol Inhibits the NF-κB Pathway

Hydroxytyrosol blocks the activation of the NF-κB pathway and the release of downstream inflammatory factors by targeting multiple key nodes of the pathway, with specific mechanisms as follows:

Inhibiting the activation of the IKK complex

IKK acts as the "switch" for NF-κB pathway activation, and its activity depends on autophosphorylation (e.g., at Ser177/181 sites of IKKβ). Hydroxytyrosol can inhibit IKK phosphorylation and activity by directly binding to the catalytic domain of IKKβ or by scavenging ROS (reducing oxidative stress-induced IKK activation). For example, in LPS-stimulated macrophage models, pretreatment with hydroxytyrosol reduces IKKβ phosphorylation levels by 40%-60%, thereby preventing IκB phosphorylation and degradation, maintaining the binding state of NF-κB and IκB, and inhibiting NF-κB nuclear translocation.

Stabilizing IκB protein to prevent NF-κB nuclear translocation

Hydroxytyrosol can delay IκB degradation by the proteasome by reducing IκB ubiquitination, thereby maintaining the "sequestration" of NF-κB by cytoplasmic IκB. Studies have shown that in TNF-α-induced endothelial cells, the half-life of IκB is extended by 2-3 times after hydroxytyrosol treatment, and the accumulation of nuclear p65 is reduced by more than 50%, directly inhibiting the transcriptional activation of target genes by NF-κB.

Inhibiting the nuclear transcriptional activity of NF-κB

Even if NF-κB enters the nucleus, hydroxytyrosol can inhibit its transcriptional function by interfering with its binding to DNA or its interaction with co-transcription factors. For instance, hydroxytyrosol can bind to the Rel homology domain of the p65 subunit, preventing its binding to κB sites in target gene promoters; simultaneously, it can downregulate the expression of co-activators such as p300, weakening NF-κB transcriptional activity. In a mouse model of ulcerative colitis, hydroxytyrosol significantly reduces the binding efficiency of NF-κB to the IL-6 promoter in colon tissues, decreasing IL-6 secretion.

Reducing the triggering of upstream inflammatory signals

The antioxidant properties of hydroxytyrosol can lower intracellular ROS levels, and ROS is an important upstream activator of the NF-κB pathway (e.g., by oxidatively modifying IκB or IKK). Additionally, it can inhibit the expression and dimerization of Toll-like receptor 4 (TLR4, the main receptor for LPS), blocking the initial activation signal of NF-κB by LPS and reducing pathway initiation at the source.

III. Verification of Anti-Inflammatory Effects Under Physiological and Pathological Conditions

In cell experiments, hydroxytyrosol exhibits significant anti-inflammatory effects on LPS-stimulated macrophages, TNF-α-induced endothelial cells, and cells from inflammatory bowel disease models, reducing the mRNA and protein levels of inflammatory factors such as IL-6 and TNF-α by 30%-80% in a dose-dependent manner. In animal models, oral or intraperitoneal injection of hydroxytyrosol can alleviate various inflammation-related diseases: for example, in a mouse model of rheumatoid arthritis, it reduces joint effusion and synovial inflammation, and decreases NF-κB activity and IL-1β content in joint tissues; in a mouse model of acute lung injury, hydroxytyrosol reduces pulmonary neutrophil infiltration and pulmonary edema by inhibiting the NF-κB pathway.

IV. Summary and Outlook

Hydroxytyrosol efficiently inhibits the activation of the NF-κB pathway by targeting multiple steps, including IKK activation, IκB degradation, NF-κB nuclear translocation, and nuclear transcription, thereby blocking the cascade release of inflammatory factors and exerting anti-inflammatory effects. The multi-target nature of its molecular mechanism gives it potential in the prevention and adjuvant treatment of chronic inflammatory diseases. Future research should further clarify its dose-effect relationship in humans and optimize administration strategies through formulation technologies (e.g., improving bioavailability) to promote the application of this natural compound in clinical anti-inflammatory fields.