To study glucose and fructose metabolism in tumors the they traced the breakdown of the molecules.

1. The scientists labeled glucose and fructose with a radioactive atom that can be traced even as the molecule is broken down.
2. They incubated tumor tissues with labeled-glucose, labeled-fructose or a mix of labeled-glucose + fructose, or a mix of labeled-fructose + glucose. These tumor tissues absorb the sugars and metabolize them. Note: Adding a mixture of sugars to the tumor allows the scientists to determine how the metabolic pathways are related.
3. The different components after metabolism are then determined in lab to trace the metabolic pathway of how tumors break down sugars.

This paragraph details the pathway of fructose and glucose metabolism within cells. In normal cells this is how glucose and fructose are broken down and converted into energy. It is unknown how tumors metabolize these molecules and so the scientists move on to explore this in their next series of experiments.

This is a mechanism to control production in biological settings. This means when something is being made (ex. protein) and reaches a certain concentration then the production is stopped. This can also be called a negative-feedback loop.

Summarizing findings from the experiments up till this point: 1) fructose often reaches the colon at high concentrations when passive transporters in the upper intestines are saturated. 2) tumors in the lower intestines and colon absorb fructose efficiently, as demonstrated by decreased fructose in the liver in tumor-bearing mice 3) colorectal tumors are able to absorb more fructose than healthy intestinal cells because they have more fructose transporters

Colorectal tumor fructose metabolism has been looked at in the past. In these studies the enzymes required to break down fructose were studied, rather than looking at fructose transporters as this paper did. The past research found similar results where tumors had higher levels of enzymes that break down fructose than normal human tissues did.

In order to investigate tumor metabolism in human tissues scientists used a tissue microarray where tiny samples of human tumors or tissues were cultured and studied. They compared metabolism between 25 different tumors, of varying severity, to normal human intestinal cells.

Investigating tumor uptake of fructose further, the scientists looked at sugar uptake proteins in colorectal tumors of both mice and human tissues. They found that colorectal tumor cells expressed more of the passive fructose transporter than normal intestinal cells do.

The scientists also looked at how much fructose and was reaching the liver and blood to test metabolism of the sugar. They found that in tumor-bearing mice there was less fructose metabolized in the liver and less reached the blood. This suggests that the tumors consumed more of the fructose.

After administering high fructose corn syrup with the labeled carbons on glucose and fructose to a mouse with colorectal tumors the scientists found that the tumor took up and metabolized both glucose and fructose.

The authors wanted to test whether tumors near the end (distal) of the intestines or in the colon consume fructose since it can be found in much higher concentrations in the colon than glucose can. Approach: They marked glucose and fructose molecules with C14 (radioactive carbon) which can be traced as the sugars get broken down and metabolized. This way if they find C14 from fructose and glucose in a tumor they can conclude that it metabolizes both sugars.

The scientists repeated experiments from previous work to validate their methods. They fed mice (oral bolus) high fructose corn syrup and then 30 minutes later (to allow for digestion) measured fructose levels in the colon. Similar to previous studies, they found elevated fructose in the colon suggesting the passive transporters in the intestine were saturated and allowed fructose to pass through undigested.

The same results seen in human studies looking at gastrointestinal discomfort after fructose consumption were recapitulated in mouse studies. In animal models scientists are able to more closely control variables and more inversely monitor outcomes. In this case they were able to directly measure fructose concentrations in the colon rather than relying on gastrointestinal symptoms. They found high concentrations of fructose in the colon after oral delivery, suggesting that the passive transporters in the intestine were unable to uptake fructose at levels higher than 1g per kg of weight.

A past study administered various amounts of fructose to people after fasting. They then assessed gastrointestinal symptoms that stem from fructose passing through into the intestines and colon undigested (malabsorption). They found that even 5g of fructose can lead to the saturation of passive transporters in the intestine. Ingestion of any amount of fructose over 5g will result in high levels of fructose in the colon.

Fructose is only absorbed through diffusion into a cell, this means it relies on there being a lower concentration of fructose in a cell compared to the intestine. Passive absorption often leads to a saturation of the channels and so not as much fructose can be absorbed.

Sodium-coupled glucose transporters are found in the intestine. They use energy gathered from sodium ion transport into the bloodstream to generate energy to import glucose into a cell. Using energy to import a molecule up a concentration gradient (there is more glucose inside the cell than outside so it costs energy to import more) is termed active transport.

Summarizing their results: In APC deficient mice (where colorectal tumors readily develop) consumption of even small amounts of high fructose corn syrup increases tumor growth.

Previous study of another genetically modified mouse model (where tumors were induced to grow mostly in the colon) demonstrated similar results. This suggests that this mouse model or genetic manipulation (APC deletion) itself is not somehow more sensitive to high fructose corn syrup than other mutations that lead to colorectal cancer. Comparing previous results increases confidence that any colorectal cancer tumors will respond to high fructose corn syrup in a similar fashion.

Results from experiment Part 2: Comparing mice fed with different amounts of high fructose corn syrup did not change the number of tumors formed. However, the size of the tumors, and the aggressiveness of the cancer differed between the mice fed a small amount of high fructose corn syrup and the control group with no high fructose corn syrup. This demonstrates that even a small amount of high fructose corn syrup is increasing tumor growth.

Result from experiment Part 1: Mice given a small amount of high fructose corn syrup did not become obese (as intended) and they did not develop metabolic syndrome. This suggests that high fructose corn syrup itself is not causing metabolic syndrome, but rather obesity is causing these health complications.

Here they did a two-part experiment: 1) They tested whether high fructose corn syrup itself induced metabolic dysfunction by giving mice a limited about of high fructose corn syrup so that they did not become obese.

2) To test the effects of high fructose corn syrup on colorectal tumor formation and growth the authors compared tumor characteristics between mice fed with different amounts of high fructose corn syrup. First, they treated all mice with tamoxifen to activate tumor formation. Then they broke them down into three groups: HFCS- mice that were treated with a limited amount of high fructose corn syrup to prevent obesity, WB- mice that had high fructose corn syrup mixed in with water so they consume a lot of it, and Con- a control group with no high fructose corn syrup administered. They then compared the formation of tumors and their characteristics to look at the effects of high fructose corn syrup.

In response to consumption of high fructose corn syrup mice in both groups gained a lot of weight and began displaying symptoms of metabolic dysfunction (high blood pressure, abnormal cholesterol etc.). It was unclear as to whether high fructose corn syrup consumption or obesity led to the development of metabolic dysfunction so the authors went on to test this next.

The scientists were first interested in looking at how high fructose corn syrup affects an entire mouse, and compare the effects on normal mice and their genetically modified mouse (APC -/-). They did this by mixing high fructose corn syrup into their water and allowing them to drink as much as they wanted (ad libitum). They monitored the mice's weight over time.

Scientists have found that in a high majority of colorectal cancers the APC gene is defective. This high correlation suggests that the APC gene is a major cause for the development of colorectal cancer and tumors.

Wnt signaling is group of a pathways that regulate gene transcription and growth. Normally APC controls and limits growth that Wnt stimulates but when APC is deleted or mutated Wnt signaling is uncontrolled and leads to cancer formation.

Adenomatous Polyposis Coli is a tumor suppresor gene meaning that when it is functional, APC controls cell growth and prevents tumor formation. When it becomes mutated or deleted (as in the mouse models), uncontrolled cell growth leads to tumor formation.

The scientists need a mouse model that will develop intestinal tumors so that they can study the effects of sugar-sweetened beverages on the tumor. They manipulated the mouse genes so that after injecting a drug (Tamoxifen) a gene in the intestine is deleted and tumors begin to form. With this genetically engineered mouse the scientists can induce tumor formation of the mouse, then track tumor size and metabolism to look at the effects of high fructose corn syrup in a diet.

A system of glands in the body that produce hormones that regulate metabolism, mood, sleep, development etc.

A cluster of factors such as high blood pressure, high blood sugar, excess body fat and abnormal cholesterol which contribute to diseases such as diabetes, heart-disease and strokes.

Multiple factors at play which can affect an outcome or result. In this case it is impossible to separate the variables of obesity, which causes a host of complications such as high blood pressure, and abnormal cholesterol, from the direct effects of sugar-sweetened beverages.

Taking big data sets such as questionnaires or patient data, computational biologists can run statistical tests to look at correlations between variables. In this case data has shown that people who drink a lot of sugar-sweetened beverages (such as soda) tend to be more overweight and in men there was a significant correlation to developing colorectal cancer.

The fluid component of blood left after cells and clotting factors are removed.

Lumen; The inside space of a tubular structure. The intestine is a long digestive organ that contains a tube of cells which absorb nutrients of food that is passing through the inside of the tube, which is called the intestinal lumen.

A scale on which tumors are judged by abnormality and the cells' likelihood to spread.

A sweetener made from corn starch. It contains a mixture of glucose and fructose molecules which taste the same and have the same calories, though they are processed differently in the body.

formation of cancerous clusters of cells (tumors), where cell growth is uncontrolled

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ADDING EMPHASIS

Tandem means having two in a row. and mass spectrometry is a method used to analyze samples to look at chemical makeup by looking at charge-to-mass signatures of individual atoms in a sample. Putting two mass spectrometers in a row increases the sensitivity of this method so that ions that are close in mass can be told apart. A great analogy and explanation can be found in this Youtube video.

adjective; far from the center. The end-most part of the intestines.

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adverb; as much as desired. The authors put high-fructose corn syrup in water for the mice to drink as much as they wanted.

Noun; large and diverse amount of

Define APC