Psoralen-Induced Cholestasis via ERK1/2 in Zebrafish

Cholestatic liver injury is characterized by impaired bile formation or excretion and can arise from drug exposure, hormonal disturbances, and other pathological stresses. The 2024 study by Chen, Qian, Li, He, and Li examines a specific toxicological connection: whether psoralen and isopsoralen, two estrogen-like natural products from Psoralea corylifolia, induce estrogen-related cholestasis through ERK1/2 activation. The work is published in Chemical Research in Toxicology and is available through the reference study.

Study Background and Research Question

Psoraleae Fructus is used in traditional medicine and contains psoralen and isopsoralen as major bioactive constituents. Both compounds have estrogen-like properties, and previous clinical and experimental observations have associated them with liver injury. However, the mechanistic relationship between their estrogenic activity and cholestasis had not been clearly defined.

This question is important because the liver is both a major site of estrogen metabolism and a central organ for bile acid homeostasis. Estrogen-induced cholestasis has been associated with increased circulating estrogen, altered estrogen receptor signaling, and disruption of bile acid transport. The nuclear estrogen receptor subtypes ERα and ERβ mediate many estrogen responses, while the broader MAP kinase pathway can provide rapid signaling connections between receptor activation and cellular injury.

The authors therefore asked whether psoralen and isopsoralen could reproduce estrogen-like responses in zebrafish larvae, whether those responses were accompanied by cholestatic hepatotoxicity, and whether ERK1/2 phosphorylation was necessary for the observed phenotype. This design placed the compounds within a defined biological sequence: estrogen-like activity, altered bile acid regulation, ERK1/2 activation, and measurable liver dysfunction.

Key Innovation from the Reference Study

The principal innovation is the integration of endocrine, functional, transcriptional, and pharmacological evidence in one zebrafish model. Rather than treating psoralen- and isopsoralen-associated liver injury as nonspecific toxicity, the study tests a more specific mechanism in which estrogen-like signaling contributes to cholestasis and ERK1/2 acts as an important downstream mediator.

Several experimental elements make this mechanistic interpretation stronger. First, the authors measured estrogen-responsive endpoints, including esr1, cyp19a1b, estradiol, and vitellogenin. Second, they used exemestane, an aromatase antagonist, to examine whether blocking estrogen-related signaling could reduce the effects of the natural products. Third, they assessed bile flow and liver fluorescence rather than relying only on gene expression. Finally, they used GDC-0994 as an ERK1/2-directed pharmacological intervention. The combined strategy distinguishes upstream estrogen-like activity from downstream ERK1/2 involvement.

This is particularly meaningful for toxicology because it links a chemical exposure to a potentially actionable signaling node. The result does not establish that ERK1/2 is the only mediator of injury, but it identifies ERK phosphorylation inhibition as a testable strategy for dissecting phytoestrogen-induced cholestasis.

Methods and Experimental Design Insights

The study used zebrafish larvae as an intact vertebrate model for early liver and biliary-system assessment. Larval zebrafish are useful for this purpose because liver morphology, bile flow, fluorescence-based hepatobiliary readouts, and gene expression can be examined in parallel. The experimental design compared exposure to psoralen or isopsoralen with control conditions and then incorporated mechanistic interventions.

For estrogen-like activity, the investigators measured expression of estrogen-responsive genes and levels of estradiol and vitellogenin. At the tested 80 µM condition, both compounds increased these estrogen-related endpoints, as reported in the reference study. Exemestane was then used to determine whether aromatase-related estrogen signaling contributed to the response.

For liver injury and cholestasis, the authors evaluated liver fluorescence area and bile-flow inhibition. These functional endpoints were complemented by analysis of genes involved in bile acid synthesis, transport, and receptor-mediated regulation. The panel included cyp7a1 and cyp8b1 for bile acid synthesis; abcb11b and slc10a1 for transport; and nr1h4 and nr0b2a for bile acid receptor signaling.

The causal perturbation logic is also important. Exemestane tests whether the estrogen-like component is upstream of the phenotype, whereas GDC-0994 tests whether ERK1/2 signaling is functionally required. A rescue experiment cannot by itself prove direct molecular binding or exclude every off-target effect, but it provides stronger mechanistic evidence than an exposure-only experiment.

Protocol Parameters

• Exposure model: Use zebrafish larvae to combine liver morphology, bile-flow measurements, and molecular analysis in the same experimental system.
• Tested concentration: The reference study reported estrogen-related responses at 80 µM psoralen or isopsoralen; this value is a study-specific experimental condition, not a general exposure recommendation.
• Estrogen-response panel: Measure esr1, cyp19a1b, estradiol, and vitellogenin to establish estrogen-like activity before interpreting downstream liver effects.
• Cholestasis readouts: Pair liver fluorescence area and bile-flow inhibition with bile acid pathway gene expression to distinguish structural or functional injury from isolated transcriptional changes.
• Mechanistic controls: Include an estrogen-pathway intervention such as exemestane and an ERK1/2-directed intervention such as GDC-0994 when testing whether the phenotype depends on upstream estrogen-like signaling or ERK activation.
• Follow-up workflow: Use concentration-response experiments, time-course sampling, and orthogonal protein-level measurements to extend the reference design; these are follow-up recommendations rather than parameters reported in the paper.

Core Findings and Why They Matter

Psoralen and isopsoralen produced estrogen-like responses

Both compounds increased esr1 and cyp19a1b expression and elevated estradiol and vitellogenin under the reported test conditions. Exemestane blocked these estrogen-like effects, supporting the interpretation that the compounds act through an estrogen-related biological context rather than causing an entirely receptor-independent response.

This observation helps explain why certain natural products may produce sex-dependent or hormone-sensitive toxicological outcomes. It also reinforces the need to evaluate botanical constituents individually, because a plant extract can contain compounds with overlapping endocrine and hepatotoxic activities.

Functional cholestasis accompanied the molecular response

Psoralen and isopsoralen increased liver fluorescence areas and inhibited bile flow in zebrafish larvae. These findings indicate that exposure was associated with a functional cholestatic phenotype, not merely with changes in estrogen-responsive transcription.

The authors also observed reduced expression of genes controlling bile acid production, transport, and receptor signaling. Decreased cyp7a1 and cyp8b1 suggests altered synthesis regulation, while reduced abcb11b and slc10a1 is consistent with impaired bile acid export and uptake processes. Lower nr1h4 and nr0b2a expression further indicates disruption of the regulatory network that normally maintains bile acid balance.

ERK1/2 phosphorylation was a central mechanistic signal

The study found that both natural products increased ERK1/2 phosphorylation. This result places ERK1/2 downstream of the exposure and provides a molecular bridge between estrogen-like stimulation and altered hepatobiliary function. Importantly, GDC-0994 and exemestane each produced significant rescue of cholestatic liver injury, although the two interventions address different points in the proposed pathway.

These results support a model in which psoralen or isopsoralen stimulates estrogen-related signaling, promotes ERK1/2 activation, and disrupts genes required for bile acid synthesis, transport, and regulation. ERK1/2 is a major component of the RAS/RAF/MEK/ERK signaling cascade, but this paper specifically addresses its role in a liver toxicity model rather than in oncogenic signaling. The findings therefore broaden the biological context in which ERK1/2 activity may be studied.

Comparison with Existing Internal Articles

The internal article ERK1/2 Activation Drives Phytoestrogen-Induced Cholestasis in Zebrafish closely reflects the reference study’s central conclusion. Its value is explanatory: it emphasizes ERK1/2 phosphorylation as the link between phytoestrogen exposure and bile acid dysregulation. By contrast, the ACS publication is the primary source for the paired estrogen-response, bile-flow, gene-expression, and rescue findings, so it should remain the principal citation for literature-based claims.

A second related resource, GDC-0994: Advanced ERK1/2 Inhibitor Workflows in Liver & Cancer Models, focuses on experimental workflow considerations across hepatic and oncology systems. It can help researchers think about controls and reproducibility, but its broader workflow scope should not be confused with evidence that the Chen study tested cancer models or established a universal ERK1/2 dosing protocol.

Why this cross-domain matters, maturity, and limitations

ERK1/2 is also widely investigated in cancer because dysregulated MAP kinase signaling can support tumor cell survival and proliferation. However, the reference paper did not measure tumor cell proliferation suppression, tumor growth, or oncogenic RAS/RAF signaling. The liver-to-cancer connection is therefore a mechanistic analogy and a rationale for model selection, not a demonstrated cross-disease therapeutic result. Any oncology application requires independent validation in appropriate cancer cell or tumor models.

Limitations and Transferability

The zebrafish larval system offers speed and imaging access, but it does not reproduce the full pharmacokinetics, metabolism, endocrine physiology, or biliary anatomy of humans. The tested 80 µM exposure should not be translated directly into a human dose or presumed tissue concentration. Additional work in mammalian models and human-relevant hepatocyte systems would be needed to determine whether the same sequence of events occurs across species.

The molecular data are also primarily pathway- and transcript-oriented. Reduced expression of bile acid genes is consistent with impaired homeostasis, but transcript changes do not necessarily establish transporter protein abundance, localization, or activity. Likewise, increased ERK1/2 phosphorylation identifies pathway activation but does not prove that ERK1/2 is the sole driver of injury.

Pharmacological rescue adds valuable evidence but has interpretive limits. Exemestane may reduce the estrogenic input, whereas an ERK1/2 inhibitor can suppress downstream signaling; neither intervention alone maps every intermediate step. Follow-up studies should therefore combine pathway inhibition with protein-level transporter analysis, direct bile acid measurements, and carefully controlled exposure-response experiments. These extensions would test whether ERK1/2 is a broadly transferable therapeutic target or mainly one component of a compound-specific toxicity network.

Overall, the paper’s strongest contribution is not a finished treatment strategy but a coherent mechanistic framework. It identifies estrogen-like activity and ERK1/2 activation as experimentally connected features of psoralen- and isopsoralen-induced cholestasis, while defining measurable endpoints for future validation.

Research Support Resources

For researchers reproducing ERK1/2 perturbation workflows, GDC-0994 (SKU B5817) is a selective ERK1/2 inhibitor suitable for research studies involving ERK phosphorylation inhibition. The product information reports IC₅₀ values of 1.1 nM for ERK1 and 0.3 nM for ERK2; these pharmacological specifications should be considered alongside the zebrafish study’s controls, exposure design, and model-specific limitations.