The research team, led by investigators affiliated with Zhongshan Hospital of Fudan University, began with a spontaneous intestinal tumor model, the Apc-Min mouse, in which animals were placed on a 5:2 intermittent fasting schedule consisting of two nonconsecutive 24-hour fasts per week. Compared with mice fed ad libitum, the fasting animals gained less body weight and, more importantly, carried a markedly reduced intestinal tumor burden, with fewer and smaller tumors and diminished Ki-67 staining indicating slower tumor-cell proliferation. Immunostaining revealed denser infiltration of CD3-positive CD8-positive T cells within the fasting-treated tumors, and flow cytometry showed that these T cells were functionally energized, expressing higher levels of the effector molecules interferon-gamma and granzyme B while displaying reduced PD-1, a marker associated with exhaustion.

To confirm that CD8-positive T cells were not merely bystanders, the researchers depleted them with a specific antibody in a syngeneic MC38 colorectal cancer model. The depletion largely abolished the tumor-suppressive effect of fasting, establishing that the dietary intervention works through, rather than alongside, this cytotoxic lymphocyte population. In the same model, fasting increased levels of the immunogenic stress signals HMGB1 and interferon-beta in tumor interstitial fluid, the extracellular fluid bathing the tumor, along with elevated SEC61-beta expression in tumor tissue, an early hint that a distinctive form of endoplasmic reticulum stress was underway inside the malignant cells.

The search for the responsible metabolite turned to untargeted serum metabolomics in the fasting and freely fed mice. Among the most prominently reduced metabolites was taurine, a finding validated by direct quantification in serum, tumor interstitial fluid, and tumor tissue. Because the liver is a major site of taurine biosynthesis, the team measured hepatic cysteine dioxygenase 1, a rate-limiting enzyme upstream of taurine production, and found that fasting suppressed its expression, pointing to reduced systemic taurine synthesis. The functional test was decisive: oral taurine supplementation largely reversed the tumor suppression achieved by fasting, whereas guanidinoethyl sulfonate, an inhibitor of the taurine transporter SLC6A6, suppressed tumor growth even under unrestricted feeding. In human tissue cohorts, high SLC6A6 expression in colorectal tumors correlated negatively with CD8-positive T-cell abundance and predicted poorer overall survival, while taurine concentrations in tumor interstitial fluid rose progressively from normal mucosa through adenoma to carcinoma.

The mechanistic centerpiece of the study is the identification of GRP78, the endoplasmic reticulum’s master chaperone, as a direct taurine-associated protein. Using a drug affinity responsive target stability screen coupled to mass spectrometry, the researchers found that taurine protected GRP78 from proteolytic digestion in a dose-dependent manner, and a biotinylated taurine pulldown assay confirmed physical enrichment of GRP78 that could be competed away by excess free taurine. The downstream consequence was selective: in tumors from fasting mice, the PERK arm of the unfolded protein response lost protein abundance while IRE1-alpha and ATF6 remained unchanged, and messenger RNA levels of all the relevant genes were untouched, indicating that fasting regulates PERK post-translationally.

Under short-term starvation in cultured cells, PERK protein decayed after protein synthesis was blocked with cycloheximide, but taurine supplementation preserved PERK in a concentration-dependent fashion. Proteasome inhibition with MG132 partially rescued PERK, implicating ubiquitin-dependent degradation, and indeed starvation increased PERK ubiquitination while taurine attenuated it. Starvation also weakened the physical association between GRP78 and PERK, an interaction taurine restored. When the researchers knocked down GRP78, taurine lost much of its ability to stabilize PERK, cementing the chaperone as the mediator through which the metabolite exerts its protective effect on the stress kinase.

What happens when PERK disappears under nutrient stress proved to be the most striking discovery of the study. PERK-deficient colorectal cancer cells exposed to starvation developed extensive cytoplasmic vacuolization and endoplasmic reticulum swelling, hallmarks of paraptosis, a non-apoptotic, caspase-independent form of regulated cell death. A pharmacological screen showed that inhibitors of apoptosis, necroptosis, ferroptosis, pyroptosis, and autophagy failed to rescue the cells, whereas blocking protein synthesis did. Critically, taurine supplementation could not reverse the vacuolization or the death once PERK was gone, demonstrating that the metabolite acts upstream of the kinase rather than on the death program itself. The dying cells also became immunologically loud: they exposed calreticulin on their surface, released HMGB1, produced interferon-beta, and were killed more efficiently by peripheral blood mononuclear cells, which in turn activated type I interferon signaling programs.

In living animals, PERK knockdown in MC38 tumors reproduced the fasting phenotype, suppressing growth, increasing CD8-positive T-cell infiltration and activation, expanding antigen-presenting conventional dendritic cells, shrinking myeloid-derived suppressor cell populations, and shifting macrophages toward an inflammatory M1-like state. A bilateral tumor model revealed that a PERK-deficient tumor could even slow the growth of a genetically intact tumor implanted on the opposite flank, evidence of a systemic immune response. Transcriptomic analysis identified ERO1A, a CHOP-associated endoplasmic reticulum stress gene, as the dominant fasting-suppressed output of the PERK axis; ERO1A overexpression accelerated tumor growth and blunted T-cell activity, while ERO1A restoration in PERK-deficient tumors partially rescued tumor volume and reversed the immune activation, confirming it as a functional downstream effector.

The translational payoff came in combination experiments with immune checkpoint blockade. In both MC38 and CT26 syngeneic models, intermittent fasting plus anti-PD-1 antibody suppressed tumor growth more effectively than either treatment alone, and the transporter inhibitor guanidinoethyl sulfonate similarly strengthened PD-1 blockade in CT26 tumors. The authors propose a coherent model in which fasting restricts systemic and intratumoral taurine, disrupting taurine-dependent GRP78 maintenance of PERK, dismantling the ATF4-CHOP-ERO1A stress-adaptation axis, and converting nutrient stress from a survival buffer into paraptosis-like immunogenic cell death that fuels CD8-positive T-cell immunity. The team acknowledges open questions, including the unresolved structural basis of the taurine-GRP78-PERK interface and the need for paired metabolomic and immune-profiling data from the same human specimens. Still, the work suggests that taurine restriction, whether through dietary scheduling or transporter inhibition, could offer a metabolically grounded strategy to convert immunologically cold colorectal tumors into ones that respond to immunotherapy.

Subject of Research: Taurine restriction and PERK attenuation in intermittent fasting-mediated antitumor immunity in colorectal cancer

Article Title: Intermittent Fasting Reduces Taurine Availability and Promotes Antitumor Immunity Through PERK Attenuation‐Associated Paraptosis‐Like Cell Death in Colorectal Cancer

Article References: Song, B., Kam, S., Liu, J., Lv, R., Huo, X., Chen, Z., Dong, Y., Cai, S., Li, B., Ren, R., Zhong, Y., & Cai, M. (2026). Intermittent Fasting Reduces Taurine Availability and Promotes Antitumor Immunity Through PERK Attenuation‐Associated Paraptosis‐Like Cell Death in Colorectal Cancer. Advanced Science, Article e78107. https://doi.org/10.1002/advs.78107

Image Credits: AI Generated

DOI: 10.1002/advs.78107

Keywords: intermittent fasting, taurine, colorectal cancer, PERK, GRP78, paraptosis, CD8 T cells, SLC6A6, ERO1A, anti-PD-1, tumor immunology, metabolomics

The article begins with the fundamentals of bile acid physiology. Roughly 95 percent of the bile acids secreted into the intestine are actively reabsorbed in the ileum and recycled back to the liver through the portal vein, a circuit known as the enterohepatic circulation. Primary bile acids, chiefly cholic acid and chenodeoxycholic acid, are synthesized from cholesterol in the liver through pathways driven by the enzymes CYP7A1 and CYP27A1. Once they reach the intestine, gut bacteria convert them by dehydroxylation into secondary bile acids such as deoxycholic acid and lithocholic acid. These microbial derivatives do not simply linger in the gut; they enter the systemic circulation and exert far-reaching effects on host metabolism, intestinal health and inflammatory tone.

The mechanistic heart of the commentary lies in the receptors through which bile acids act. The farnesoid X receptor, or FXR, is a nuclear receptor abundant in liver, intestine and kidney that functions as the body’s bile acid thermostat. When bile acid concentrations rise, FXR binds them and triggers a negative feedback loop that suppresses CYP7A1, curbing further synthesis and preventing toxic accumulation. But FXR’s portfolio extends well beyond metabolic housekeeping. The authors highlight evidence that FXR activation restrains tumor invasion by downregulating matrix metalloproteinases, enzymes that degrade the extracellular matrix, and by dampening pro-inflammatory signaling and cell-cycle progression. The FXR agonist obeticholic acid, already validated in a phase 3 trial for non-alcoholic steatohepatitis, is flagged as a candidate for cancer therapy, potentially in combination with conventional chemotherapy.

A second receptor, TGR5, operates through entirely different circuitry. As a G protein-coupled receptor expressed on immune cells, intestinal epithelial cells and adipose tissue, TGR5 mediates non-genomic, rapid signaling. Its activation raises intracellular cyclic AMP, promotes thermogenesis in brown fat, improves insulin sensitivity and, critically, can halt the runaway proliferation of cancer cells by interfering with cell-cycle progression. TGR5 also modulates macrophages and T cells within the tumor microenvironment, reducing the chronic inflammation that fuels tumor growth. Together, the authors contend, FXR and TGR5 represent a paired molecular handle for therapeutic intervention in bile acid signaling.

The commentary is equally candid about bile acids’ dark side. Secondary bile acids such as deoxycholic acid can be frankly carcinogenic at high concentrations, particularly when they persist in the intestine for extended periods. They induce the production of reactive oxygen species, generating oxidative stress that damages DNA, proteins and lipids and seeds the mutations from which cancers arise—a mechanism considered especially relevant to colorectal cancer. Deoxycholic acid can also activate the Wnt/beta-catenin pathway, driving proliferation while suppressing apoptosis, and both deoxycholic and lithocholic acid trigger the release of pro-inflammatory cytokines such as TNF-alpha and IL-6 through JAK/STAT and NF-kappaB signaling. Chronic inflammation of this kind is regarded as a major pathogenic mechanism in digestive tract cancers, including colorectal and esophageal malignancies.

Woven through the analysis is the bidirectional relationship between bile acids and the gut microbiome. Bile acids shape which microbes thrive: their amphipathic structure allows them to disrupt bacterial membranes, induce DNA damage and provoke oxidative stress in susceptible organisms, while bacteria that express bile acid-metabolizing enzymes gain a survival advantage. In turn, microbes chemically transform bile acids. Bacteria secreting bile salt hydrolases cleave the glycine or taurine groups from conjugated bile acids, converting them into free bile acids with altered solubility and biological activity. Recent work has even uncovered entirely novel microbial bile acid species, such as the succinylated bile acid 3-sucCA, which promotes the growth of the beneficial bacterium Akkermansia muciniphila by regulating its glucose-utilizing NagB enzyme. The authors note that much remains to be learned about how manipulating the bile acid pool reshapes host-microbe communication.

One of the most provocative threads in the commentary concerns taurine, the amino sulfonic acid conjugated to many bile acids. Long celebrated as an antioxidant that neutralizes reactive oxygen species, protects DNA integrity and restrains inflammation by inhibiting NF-kappaB and steering macrophages away from a pro-inflammatory M1 phenotype, taurine has generally been viewed as protective against cancer. Studies cited in the article show it can downregulate cyclins D1 and E and inhibit CDK4 and CDK6, blocking the G1-to-S transition and slowing tumor cell proliferation. Approximately 20 percent of the body’s taurine pool derives from the breakdown of taurine-conjugated bile acids, tying this amino acid intimately into bile acid metabolism.

Yet the picture is not so simple. The authors spotlight a 2024 Cell study identifying the taurine transporter SLC6A6 as a determinant of gastric cancer progression and recurrence. Tumor cells overexpress SLC6A6 and outcompete CD8-positive T cells for taurine, starving the immune cells and driving their exhaustion. Mechanistically, taurine depletion in T cells heightens endoplasmic reticulum stress, activating PERK-JAK1-STAT3 signaling and the transcription factor ATF4, which switches on multiple immune checkpoint genes. In gastric cancer, chemotherapy can upregulate the transcription factor SP1, further boosting SLC6A6 expression and intensifying this nutritional competition—a mechanism that may underlie both immune dysfunction and chemotherapy resistance. Taurine supplementation, the authors suggest, could serve as an adjunct therapy by protecting T cells and enhancing chemotherapy efficacy, but only in the right context.

That context-dependence is the commentary’s central message. Taurine’s function, like that of bile acids generally, is jointly determined by microenvironmental conditions, cell-type-specific metabolic capacity and host immune status—not by any single molecular property. This framing aligns with the integrative medicine philosophy articulated by Academician Daiming Fan, whose concepts of anti-cancer treatment, tumor control and life support emphasize restoring the body’s intrinsic regulatory forces rather than simply eliminating lesions. From this perspective, bile acid dysregulation is both a marker and a driver of the systemic imbalance that underlies cancer, and the liver-gut-immune axis becomes a concrete intervention point: modifying bile acid composition through diet, nutritional support or metabolic regulation may help rebuild an antitumor immune environment and ease treatment-related side effects.

The authors conclude that a multidimensional strategy centered on bile acid signaling offers a route from treating cancer as a local lesion toward managing it as a disorder of systemic homeostasis. By integrating molecular mechanisms with lifestyle and supportive therapies, and by individualizing approaches to taurine and bile acid pathways rather than applying blanket supplementation or inhibition, the framework points toward a more holistic, patient-centered integrative oncology—one in which the humble detergent molecules of digestion are recognized as key arbiters of life and disease.

Subject of Research: The roles of bile acids, their receptors and taurine metabolism in cancer biology and integrative oncology

Article Title: An integrative view of bile acids

Article References: Bai, X., Liu, B., Liu, L., Lu, Y., & Zhao, X. (2026). An integrative view of bile acids. Holistic Integrative Oncology, 5(1), Article 67. https://doi.org/10.1007/s44178-026-00290-9

Image Credits: AI Generated

DOI: 10.1007/s44178-026-00290-9

Keywords: bile acids, FXR, TGR5, gut microbiota, taurine, SLC6A6, tumor microenvironment, colorectal cancer, obeticholic acid, integrative oncology, bile salt hydrolase, immune evasion