Hexaraphane Dual-Targets Keap1 and Gsk-3β to Activate Nrf2

Hexaraphane (6-MSITC), a compound found in Japanese wasabi, has attracted attention primarily as a natural compound that activates Nrf2 signaling. A study published in 2025, however, showed that its activity cannot be fully explained by removing just one “brake” on Nrf2. ¹

The study, by García-Yagüe and colleagues and published in Free Radical Biology and Medicine, suggests that hexaraphane not only releases the established Keap1 brake but may also directly suppress a separate degradation pathway involving Gsk-3β (glycogen synthase kinase 3 beta). In other words, there may be two mechanisms that protect Nrf2 rather than one. The findings deepen our understanding of cellular defense systems that tend to decline with aging and chronic disease. ¹

What You Will Learn

Hexaraphane produced effects that cannot be explained solely by Keap1-dependent Nrf2 activation.
The additional mechanism may involve inhibition of Nrf2 degradation through Gsk-3β inhibition.
This property was less evident with broccoli-derived sulforaphane, and the difference may be related to molecular structure, particularly carbon-chain length.
The findings may be relevant to conditions in which reduced Nrf2 activity and increased Gsk-3β activity occur together, including aging and chronic disease.

Background: Nrf2 Is Degraded Through Two Pathways

Nrf2 is normally degraded inside the cell so that it becomes active only when needed. One of the principal mechanisms responsible for this degradation is the Keap1 pathway. The basic functions of Nrf2 are explained in this article.

Keap1 binds Nrf2 and marks it with ubiquitin, a cellular “disposal tag.” Ubiquitinated Nrf2 is then transported to the proteasome for degradation. Keap1 can therefore be understood as a brake that prevents excessive Nrf2 accumulation. ³

However, this is not the only route by which Nrf2 is degraded. A second route is known as the Gsk-3β/β-TrCP pathway.

In this pathway, Gsk-3β first phosphorylates Nrf2. β-TrCP then recognizes this modification and directs Nrf2 to the degradation machinery. This pathway marks Nrf2 for disposal through a mechanism distinct from the Keap1 pathway. ²

Ubiquitin: A “disposal tag” attached to proteins that are no longer needed.
Proteasome: An intracellular processing system that degrades tagged proteins.
Phosphorylation: A reaction that adds a phosphate group to a protein, altering its activity or susceptibility to degradation.
β-TrCP: A protein that recognizes phosphorylated Nrf2 and directs it toward degradation.

This second pathway is important because Gsk-3β activity has been reported to increase with aging and in conditions such as Alzheimer’s disease and type 2 diabetes. Under these conditions, both Keap1- and Gsk-3β-mediated degradation may proceed, potentially making Nrf2 more likely to decline. ³ ⁴

An analogy

Nrf2 is like the leader of a cellular defense team that responds when needed. Under normal conditions, two guards monitor this leader.

Keap1 attaches an on-site “disposal tag.”
Gsk-3β adds a different mark that allows a carrier protein to escort the leader to degradation.

The new findings suggest that hexaraphane may act on both guards rather than only one.

The Research Question: Does Hexaraphane Act Beyond Keap1?

Like sulforaphane, hexaraphane is known to activate Nrf2 signaling through Keap1. ¹

The authors, however, focused on a further question: Can hexaraphane’s activity truly be explained by Keap1 alone? Earlier work had suggested that 6-MSITC could inhibit Gsk-3β in vitro, but whether this effect stabilizes Nrf2 inside cells had not been adequately demonstrated. ⁵

The study addressed this unresolved question by sequentially testing:

whether hexaraphane remains active in cells without Keap1;
whether it acts on Gsk-3β itself rather than through an indirect pathway; and
how its effects differ from those of sulforaphane. ¹

What the Study Found

1. Nrf2 Increased Even Without Keap1

The first key finding was that hexaraphane increased Nrf2 even in Keap1-deficient cells. In normal cells with Keap1, both hexaraphane and sulforaphane increased Nrf2 and downstream defense proteins. In cells lacking Keap1, however, the effect of sulforaphane largely disappeared, whereas hexaraphane continued to increase Nrf2. ¹

Keap1-deficient cells: Cells engineered to lack Keap1. They are used to determine whether an effect depends on Keap1.

This finding indicates that hexaraphane retains a Keap1-independent component of activity. The conventional view of hexaraphane simply as a compound that removes Keap1-mediated inhibition is therefore incomplete, and another molecular target may be involved.

2. Major Indirect Pathways Were Not Activated

Some compounds increase Nrf2 by indirectly suppressing Gsk-3β through intracellular pathways such as Erk, p38 MAPK, Jnk, and Pten/Pi3k/Akt. In this study, however, hexaraphane increased Nrf2 without substantially altering these major pathways. ¹

This result supports the possibility that hexaraphane did not inhibit Gsk-3β through an indirect signaling detour, but instead acted more directly on Gsk-3β itself.

3. Gsk-3β Inhibition Prevented Nrf2 Degradation

This is the central finding of the study. The authors used multiple experiments to test the hypothesis that hexaraphane prevents Nrf2 degradation by inhibiting Gsk-3β itself. ¹

The main results were as follows:

When Gsk-3β was activated to reduce Nrf2, adding hexaraphane attenuated the reduction in Nrf2.
Nrf2 ubiquitination decreased in a hexaraphane concentration-dependent manner.
This behavior closely resembled that of SB216763, a known Gsk-3β inhibitor.
Hexaraphane reduced Nrf2 phosphorylation and weakened its association with Gsk-3β.

Ubiquitination: The attachment of ubiquitin to a protein, making it more likely to be recognized as a target for degradation.

These observations suggest that hexaraphane acted before a degradation mark could be attached to Nrf2. ¹

The Keap1 pathway is one route that prevents the attachment of a degradation tag, whereas the Gsk-3β pathway prevents a separate phosphorylation-dependent route to degradation. The study provides relatively detailed evidence that hexaraphane may also act on the latter pathway.

4. Hexaraphane Directly Reduced Nrf2 Phosphorylation

In an in vitro kinase assay, hexaraphane inhibited the phosphorylation of Nrf2 by Gsk-3β itself. ¹

Kinase assay: An in vitro test that directly measures the activity of a kinase, an enzyme that catalyzes phosphorylation.

This finding more directly supports the interpretation that hexaraphane inhibits Gsk-3β activity itself, rather than merely affecting a surrounding pathway associated with Gsk-3β.

5. Molecular Simulations Supported Binding to Gsk-3β

Computer simulations using molecular docking and molecular dynamics predicted that hexaraphane could fit relatively stably within the catalytic pocket of Gsk-3β and adopt a binding mode similar to that of established inhibitors. ¹

Based on this result, the authors proposed that hexaraphane may suppress Gsk-3β activity by occupying a region near the ATP-binding pocket.

ATP-binding pocket: The site where ATP, the energy-carrying molecule required for enzyme activity, binds. Enzyme activity can decrease when another molecule occupies this site.

6. Carbon-Chain Length May Explain the Difference from Sulforaphane

Hexaraphane and sulforaphane have similar structures, but hexaraphane has two additional carbon atoms in its chain. The authors suggest that this difference may affect binding stability within the Gsk-3β pocket. ¹

Thus, even closely related compounds do not necessarily act at identical molecular targets. Hexaraphane may be distinctive not only because it is derived from wasabi, but also because a structural difference could translate into a functional difference.

Why the Dual Pathway Matters

The major significance of this study is that it reframes hexaraphane not simply as a Keap1-inhibiting Nrf2 activator, but as a compound that may stabilize Nrf2 through two pathways. ¹

During aging and in chronic disease, Nrf2 activity may decline while Gsk-3β activity increases. If both changes occur simultaneously, a compound that can engage both Keap1 and Gsk-3β may, in theory, have greater relevance than one targeting Keap1 alone. ³ ⁴

In Alzheimer’s disease, for example, oxidative stress and inflammation occur in cells. Dysregulated Gsk-3β is also known to be involved with tau, the abnormal protein that accumulates in neurons. The relationship between hexaraphane and tau pathology is discussed in detail in this article. A similar intersection may occur in type 2 diabetes. Insulin signaling, which regulates blood glucose, becomes impaired, while oxidative stress is also present. Gsk-3β and Nrf2 lie at the intersection of these processes. In both diseases, reduced Nrf2 activity and increased Gsk-3β activity can occur together. The possibility that hexaraphane acts on both pathways helps explain why the compound is attracting attention across multiple disease contexts. This study provides a molecular-level rationale for that interest. ⁴

Limitations and Future Directions

The study also has clear limitations.

First, the evidence is based primarily on cultured cells and computational analyses. The paper therefore does not establish that hexaraphane acts in the same way in humans. In the body, additional factors—including absorption, metabolism, and tissue distribution—must be considered. Further in vivo studies are needed. ¹

Second, molecules that target the ATP-binding pocket could theoretically affect other enzymes. Further research is needed to determine how selective the observed activity is for Gsk-3β. Such unintended activity at other molecular targets is known as an off-target effect.

Off-target effect: An effect of a drug or compound on a molecule other than its intended target.

Finally, although Nrf2 is generally considered protective, it is not necessarily true that more is always better. Future research will need to determine in which disease contexts, to what degree, and for how long Nrf2 stabilization may be desirable. ³

Summary

Hexaraphane (6-MSITC) may stabilize Nrf2 through direct inhibition of Gsk-3β, in addition to the previously recognized inhibition of Keap1.
The persistence of Nrf2 elevation in Keap1-deficient cells, the limited changes in major indirect signaling pathways, and the convergence of multiple Gsk-3β-related experiments provide a relatively detailed picture of a second, Keap1-independent pathway.
The difference from sulforaphane may reflect greater binding stability associated with carbon-chain length.
In the context of aging and chronic diseases characterized by reduced Nrf2 activity together with increased Gsk-3β activity, the study adds a new dimension to the scientific understanding of hexaraphane.
The current evidence is centered on cell-based and computational studies; in vivo and human studies remain necessary.

References

García-Yagüe AJ, Cueto-Díaz EJ, Escoll M, Okunishi I, Hayes JD, Rodríguez-Franco MI, Rojo AI, Cuadrado A. Dual targeting of Keap1 and Gsk-3 by hexaraphane in the regulation of transcription factor Nrf2. Free Radical Biology and Medicine. 2025;239:579-593. ↩
Rada P, Rojo AI, Chowdhry S, McMahon M, Hayes JD, Cuadrado A. SCF/β-TrCP promotes glycogen synthase kinase 3-dependent degradation of the Nrf2 transcription factor in a Keap1-independent manner. Molecular and Cellular Biology. 2011;31(6):1121-1133. ↩
Cuadrado A, Rojo AI, Wells G, et al. Therapeutic targeting of the NRF2 and KEAP1 partnership in chronic diseases. Nature Reviews Drug Discovery. 2019;18(4):295-317. ↩
Bartkowiak-Wieczorek J, Jodynis-Liebert J, Kujawska M. Methylsulfinyl Hexyl Isothiocyanate (6-MSITC) from Wasabi Is a Promising Candidate for the Treatment of Cancer, Alzheimer's Disease, and Obesity. Nutrients. 2024;16(15):2509. ↩
Yoshida J, Nomura S, Nishiumi S, et al. Glycogen synthase kinase-3beta inhibition by 6-(methylsulfinyl)hexyl isothiocyanate derived from wasabi (Wasabia japonica Matsum). Bioscience, Biotechnology, and Biochemistry. 2011;75(1):136-139. ↩

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Hexaraphane Simultaneously Inhibits Keap1 and Gsk-3β: New Evidence for Dual-Pathway Nrf2 Activation