Interpretation of Nature Literature: Metabolomics helps to reveal the mechanism by which low temperature exposure inhibits the growth of solid tumors

Recently, the research group of Academician Yihai Cao of Karolinska Institutet in Sweden, in cooperation with researchers from Fudan University, Shandong University, Wenzhou Medical University and other universities, published a paper entitled "Brown-fat-mediated tumor suppression by cold-altered global metabolism" in Nature.
The research results revealed the mechanism of low temperature exposure inhibiting tumor growth by activating brown adipose tissue and changing the overall metabolism, and proposed new ideas for the treatment of malignant tumors
.
Baiqu provided the central carbon metabolism-related metabolomics detection and analysis service for this study
.


Prof.
Yihai Cao, a foreign academician of the Chinese Academy of Engineering and Karolinska Institutet in Sweden, is the corresponding author of this work
.
Dr.
Takahiro Seki from Karolinska Institutet in Sweden and researcher Yang Yunlong from the Department of Cellular and Genetic Medicine, School of Basic Medicine, Fudan University are the co-first authors of this article
.


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Metabolic remodeling, one of the hallmark features of cancer, is manifested by high glucose uptake
.
Under aerobic conditions, cancer cells use the glycolysis pathway to rapidly decompose glucose, produce a small amount of ATP and a large amount of lactic acid, and provide the material and energy basis for their growth, invasion and metastasis, that is, aerobic glycolysis, also known as "Warburg effect" "
.


Brown adipose tissue (BAT) is a specific thermogenic tissue that plays an important role in maintaining body temperature in mammals
.
Low temperature exposure, diet, and drug intervention activate BAT, which converts mitochondrial transmembrane proton gradient potential into heat by uncoupling the electron transport process during oxidative phosphorylation from ATP production, a process known as non-shudder.
Thermogenesis (Non-shivering thermogenesis, NST)
.
BAT-mediated NST is a potent energy expenditure mechanism that reduces body weight and improves metabolic dysfunction in obese and diabetic animals
.
Because of the abundant brown adipose tissue in adults, BAT activation of thermogenesis offers a very attractive approach for the treatment of obesity and type 2 diabetes
.
This article elucidates the physiological mechanism by which low temperature exposure induces brown adipose tissue activation, alters overall metabolism and thus inhibits solid tumor growth
.


Results
01
Low temperature exposure-induced tumor suppression and survival
Malignant tumors are considered a metabolic disorder, and most solid tumors obtain the energy needed for growth and development by accelerating glycolytic metabolism (ie, the Warburg effect)
.
Activation of lipid metabolism can cause rearrangement of tumor metabolic pathways, which in turn alter tumor growth rate, proliferation potential, and drug response
.
To investigate the effects of adipose tissue thermogenesis-related metabolism on tumor growth and tumor host survival, the researchers first tested the effects of hypothermia exposure on tumor growth and progression
.

Subcutaneous implantation of colorectal cancer (CRC) into C57BL/6 mice showed a significant inhibitory effect on tumor growth at 4°C compared to mice at 30°C
.
As shown, the tumor suppression induced by hypothermia exposure was very pronounced, and the inhibition of tumor growth by hypothermia exposure was reversible after hypothermia was stopped
.
The researchers further validated hypothermia-induced tumor suppression in other cancer types, and in animal models including fibrosarcoma, breast cancer, melanoma, and pancreatic ductal adenocarcinoma, hypothermia exposure also significantly suppressed the growth rates of these tumors
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Consistently, the survival time of colorectal cancer tumor-bearing mice almost doubled at 4°C
.
Immunohistochemical analysis showed that hypoxic conditions in colorectal cancer tumor tissues were improved by cold exposure
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Similar results were observed in various subcutaneous tumor models, including fibrosarcoma, breast cancer, melanoma, and pancreatic cancer
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We also further validated hypothermia exposure-induced tumor suppression in two genetically spontaneous tumor models (MMTV-PyMT breast cancer, ApcMin/+ intestinal adenoma)
.


In subcutaneous tumor models, hypothermia exposure may inhibit tumor growth by reducing local temperature at the subcutaneous site
.
The researchers also reproduced hypothermia-induced tumor suppression in the liver tissue of immunodeficient mice
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These findings rule out the possibility that hypothermia induces tumor suppression directly through skin contact
.


02Low
temperature induces activation of brown adipose tissue and browning of white adipose tissue
Since hypothermia does not directly induce tumor suppression, by what mechanism does it occur? Histological and immunofluorescent staining results showed that, similar to tumor-free mice, brown adipose tissue in xenografted and genetically spontaneous tumor-bearing mice displayed a highly dense structure, manifesting as smaller multilocular structures, which are indicative of BAT activation typical morphological phenotype
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Consistent with phenotypic changes, mitochondrial COX4 ⁺ content and CD31 ⁺Microvessel density was significantly increased in brown adipose tissue under cold acclimation
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Uncoupling protein (UCP1), a key thermogenic protein, has a correspondingly increased expression level in the BAT of tumor-bearing mice, consistent with tumor-free mice
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This suggests that implanting tumors into mice did not significantly affect hypothermia-triggered BAT activation
.


It is known that low temperature exposure also activates white adipose tissue, especially subcutaneous white adipose tissue (sWAT), and exhibits a browning phenotype
.
The results suggest that tumors do not interfere with sWAT browning
.


By PET-CT imaging analysis, it was found that under thermoneutral conditions, in xenograft and spontaneous tumor models, ¹⁸ F-FDG distribution mainly accumulated in tumor tissue, with lower signal in BAT
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While low temperature exposure significantly stimulated the enrichment of ¹⁸ F-FDG in BAT, the signal was barely detectable in tumors
.
Quantitative analysis further validated the conclusion that hypothermia induces redistribution of ¹⁸
F-FDG between iBAT and tumors .
These results suggest that hypothermia exposure may increase glucose uptake by stimulating BAT, thereby reducing glucose uptake in tumor tissue
.


03Tumor
suppression depends on brown adipose tissue
It is well known that cold acclimation can accelerate thermogenic metabolism in mice, so what is the effect of low temperature exposure on thermogenic metabolomics in tumor-bearing mice? Oxygen consumption testing showed that hypothermia exposure increased metabolism in colorectal cancer tumor-bearing mice relative to the thermoneutral group
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In both xenograft and spontaneous tumor models, fasting blood glucose levels were significantly reduced in hypothermic-exposed tumor-bearing mice
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Insulin tolerance and glucose tolerance tests showed significantly improved insulin sensitivity and rapid glucose clearance under cold exposure
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These experiments showed that cold exposure significantly reduced blood glucose levels and increased insulin sensitivity in tumor-bearing mice
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To confirm the role of BAT activation in tumor suppression, the researchers surgically removed brown adipose tissue from tumor-bearing mice
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Excision of BAT was found to significantly increase blood glucose levels at 4°C, suggesting that BAT activation is a major factor in blood glucose consumption
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What's more, removing BAT almost eliminated the tumor suppressive effect of cold acclimation
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In contrast, under thermoneutral conditions, removal of BAT had no effect on tumor growth
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These results suggest that activation of BAT is the primary cause of hypothermia-induced tumor suppression
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Removal of BAT also significantly promoted tumor hypoxia, angiogenesis, and tumor cell proliferation
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In addition to the xenografted colorectal cancer model, the above results were also validated in a breast cancer genetic spontaneous tumor model, where hypothermia-induced reductions in blood glucose levels were also pulled back to thermoneutral levels
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These data suggest a brown adipose tissue-dependent tumor suppressor mechanism
.


04
Metabolic reorganization
in tumors Removal of BAT abolished hypothermia-induced tumor suppression revealed that BAT activation under hypothermia may alter tumor metabolism
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Gene set enrichment analysis (GSEA) by RNA sequencing (RNA-seq) showed that both glycolysis and lipid metabolism were attenuated in cryogenically exposed CRC tumors
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Targeted metabolomic analysis revealed significantly increased glycolysis in brown adipose tissue of hypothermic-exposed colorectal cancer tumor-bearing mice
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Several key intermediates in the glycolytic pathway, including glucose-1-phosphate, glucose-6-phosphate, fructose-1,6-diphosphate, glyceraldehyde-3-phosphate, 3-phosphoglycerate, 2-phosphoglycerol Acid, phosphoenolpyruvate, pyruvic acid, and lactic acid were all significantly increased
.

Further experiments showed that the transcriptional expression levels of glucose transporters, including Glut1, Glut4, and Glut7, were significantly reduced in cryogenically exposed tumor tissues
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In contrast, Glut4 and glycolysis-related genes were significantly elevated in brown adipose tissue
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Consistent with the inhibition of tumor glycolysis, cold exposure also significantly inhibited the activation of phosphatidylinositol-3-kinase (PI3K), heat shock protein (AKT), and mammalian target of rapamycin (mTOR) in CRC tumors
.
Similar inhibition of PI3K activation was also found in cryogenically exposed melanoma
.
These data suggest that low temperature exposure alters metabolic reorganization in tumors by inhibiting the glycolytic pathway, thereby affecting tumor energy supply and growth
.


05High
-glucose feeding can restore tumor growth
So is the blood glucose competition between activated brown adipose tissue and tumor tissue the key to the mechanism of hypothermia-induced tumor suppression? When colorectal cancer tumor-bearing mice were fed with 15% glucose, the tumor-suppressive effect of hypothermia was completely lost
.
Tumor cell proliferation, tumor hypoxia, microvessel density and inflammation levels in the 4°C group were not different from those in the 30°C group
.
In melanoma and pancreatic ductal adenocarcinoma models, the effect of high-glucose feeding to restore tumor growth was further demonstrated
.
Targeted metabolomics data consistently showed that high-glucose feeding largely restored aerobic glycolysis that was inhibited by cold exposure
.
These data demonstrate that glycemic compensation by high-glucose feeding abolishes hypothermia-induced tumor suppression, suggesting that increased glucose uptake in activated brown adipose tissue is an important mechanism of tumor suppression
.
To further elucidate the possible mechanism by which high-glucose feeding restores tumor growth, the researchers analyzed the expression of GLUT1 in colorectal cancers exposed to low temperature
.
It was found that in addition to restoring glucose uptake at 4°C to a level comparable to 30°C, high-glucose feeding also increased the level of Glut1 transcription and protein expression in the low temperature-exposed group, and significantly enhanced the activation of PI3K and AKT through phosphorylation
.
These data suggest that high-glucose feeding restores the suppressed glucose uptake in the hypothermia group through a GLUT1-mediated pathway
.


06
Ucp1 deletion eliminates tumor suppression
Since brown adipose tissue competitively inhibits blood glucose uptake in tumor tissue, and activated brown adipose tissue uptakes blood glucose in large quantities for non-shivering thermogenesis, Ucp1 is responsible for non-shivering thermogenesis in adipose tissue (NST).
) is a key mitochondrial protein, and the mechanism of hypothermia-induced tumor suppression can be further elucidated by experiments in Ucp1-null mice
.
In wild-type (WT) mice, hypothermia exposure significantly reduced mouse body weight and Ucp1 deletion abolished this effect
.
At the same time, Ucp1 deletion also abolished the tumor suppressive effect of low temperature exposure
.
Consistent with this, UCP1 protein deletion significantly reduced thermogenesis under cold acclimation
.
PET-CT scan analysis showed that in Ucp1-null mice, glucose uptake in the BAT of the hypothermia-exposed group was not significant, whereas glucose uptake in the tumor tissue was not affected
.


Tumor, BAT and sWAT sizes in the 4°C group of Ucp1-null mice were similar to those in the 30°C group
.
Similarly, Ucp1 deletion elevates tumor cell proliferation and hypoxia to thermoneutral levels
.
Targeted metabolomic analysis showed that aerobic tumor glycolysis was largely restored in Ucp1-null mice
.
These findings support the inference that UCP1-mediated mechanisms are critical for tumor suppression
.


07
Activation of brown adipose tissue in cancer patients
To validate the animal model results, the researchers conducted human experiments
.
Healthy volunteers (3 males and 3 females aged 22-25) wore single clothes and stayed in a slightly cold environment of 16°C for 2-6 hours every day
.
After 14 consecutive days, PET-CT scans revealed marked BAT activation in volunteers' bilateral supraclavicular, neck, and parasternal regions
.
demonstrated the presence of abundant brown adipose tissue in adult males and females and was activated by tolerable low temperature exposure
.


The researchers further conducted a preliminary study of an 18-year-old patient with Hodgkin lymphoma
.
After allowing the patient to wear light clothing and live in a mild hypothermia environment of 22°C for 7 days, PET-CT scans showed a large number of activated BAT in the supraclavicular, neck, and parasternal bilateral areas, and a large uptake of ¹⁸ F- FDG
.
^{In this patient, 18} F-FDG uptake and BAT activation were significantly reduced after returning to a warm environment at 28°C for 4 days
.
Imaging analysis confirmed the presence of lymphoma in the mediastinal region and significantly increased ¹⁸ F-FDG uptake in warm environments
.
These preliminary human experiments show that:
(1) large amounts of brown adipose tissue are present in adults;
(2) brown adipose tissue can be activated after mild tolerable exposure to low temperature;
(3) brown adipose tissue is also activated by hypothermia in cancer patients Activated by exposure;
(4) Exposure of cancer patients to mild cold conditions significantly reduced glucose uptake in tumor tissue
.


Conclusion In conclusion
, exposure to a physiologically tolerable low temperature environment activates brown adipose tissue to initiate thermogenic metabolism, competitively inhibits aerobic glycolysis in tumor tissue, thereby inhibiting tumor growth
.
This result provides a completely new concept for cancer treatment, which is clearly simple, cost-effective, feasible in almost all hospitals and even at home, and is likely to be applicable to all cancer types
.
While the concept still requires a large number of rigorously designed clinical studies to validate, it also offers a glimmer of hope and a ray of light for cancer patients suffering from the disease
.
Let us look forward to the day when cancer is "starved to death"!

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