We rely on insulin supplied by our pancreas at the right dose and at the right time to control our blood glucose levels and energy storage. Insulin works by regulating the energy usage of various cell types in the body. When this process goes awry, it can cause diabetes.
There are two types of diabetes, defined by how insulin is
dysregulated. In Type 1 Diabetes (T1D), the pancreas produces too little
insulin. Patients need to give themselves insulin in order to respond to
glucose in the diet. In Type 2 Diabetes (T2D), patients do not respond well to
the insulin produced in their body. Therefore, they need to give themselves
more to avoid hyperglycemia (high blood glucose).
Glucose is an energy metabolite necessary for cellular survival and growth whether or not the cell is part of a tumor. Not only do cancer cells switch from oxidative phosphorylation to aerobic glycolysis (the Warburg effect) to gain more glucose, a hallmark of cancer, but they also increase the amount of glucose taken up from the surrounding extracellular space. However, the lack of glucose can have a negative effect on cells, causing them to become apoptotic in the absence of this metabolite. Cancer cells have methods to get around the requirement for glucose, including upregulating glucose transporters to improve access to the energy metabolite. In this Redox Biology article, researchers describe how activating androgen receptor in response to a lack of glucose affects the amount of GLUT1 expressed on prostate cancer cells, making the cells resistant to glucose deprivation.
To set the stage, two prostate cancer cell lines, LNCaP, an androgen-sensitive cell line, and LNCaP-R, an androgen-insensitive cell line, were deprived of glucose. Both cell lines showed signs of cell death, but LNCaP-R cells died in greater numbers. To probe how LNCaP cells died, several inhibitors (a pan-caspase inhibitor, two necroptosis inhibitors and a ferroptosis inhibitor) were added but did not change the way the cells died. However, an autophagy inhibitor enhanced cell death, suggesting the cells were necrotic not apoptotic. Teasing apart if the necrosis of LNCaP cells was due to glucose availability or merely disrupted glycolysis, the glucose analog 2DG was added to the medium with glucose. The cells survived when treated with 2DG, suggesting it was the absence of glucose that induced necrosis. When LNCaP cells were cultivated in medium that replaced glucose with mannose or fructose, the cells survived, another point in favor of sugar depletion causing cell death. Continue reading “How Prostate Cancer Cells Survive Glucose Deprivation”
Cancer has been studied for decades by scientists trying to find a vulnerability to exploit and testing compounds to develop as potential drugs. As the “Emperor of All Maladies”, cancer has proven itself to be a wily beast with many varieties of genetic mutations for eluding cellular control, tireless in its ability to divide and spread. In the end, a cancer cell is still a cell and subject to its environment even though cancer does not play by the same rules as the normal cells that exist around it. To be able to grow, a cell needs access to metabolites, molecules needed for building the materials and machinery needed by the cell to function and divide. These requirements also offer potential pathways to target for halting cancer growth and spread.
All cells use glucose to generate ATP, but normal and cancer cells differ in how glucose is converted to ATP. Most cells use glucose in oxidative phosphorylation, but cancer cells use aerobic glycolysis, converting glucose to lactate without oxygen. This Warburg effect (glucose converted to lactate) is a hallmark of cancer cells as they take up glucose at a much higher rate than normal cells. Blocking glucose uptake is one way to target cancer cells. While 2-deoxyglucose (2DG) has been shown to slow glucose uptake in vitro, the compound proved toxic in clinical trials and lower dosages do not seem to be an effective treatment against cancer. While not an ideal drug target, glucose uptake has been helpful in monitoring cancer response to therapies via fluorodeoxyglucose positron emission tomography (FDG-PET). Continue reading “Finding Chinks in the Armor: Cancer’s Need for Metabolites”
Many think of glucose as something diabetics have to test each day using a blood monitor, or a quick energy boost for someone exercising intensely. However, the simple sugar glucose, a monosaccharide, fuels most of the cells in our bodies. Disaccharides that contain glucose (e.g., sucrose is comprised of glucose and fructose) and glucose polymers (e.g., starch and glycogen) are carbohydrates that are consumed by organisms from bacteria to humans to produce energy. These carbohydrates are broken down into component monosaccharides like glucose and lactose. The process of glycolysis generates the energy currency of cells, ATP, as well as precursor molecules for nucleotides, lipids and amino acids. Because glucose is the cell fuel source, the uptake of glucose and its subsequent metabolism is increased by cells that divide rapidly like cancer cells. The more energy and precursor molecules the cancer cell can create for itself, the more rapidly the tumor can grow.
Because glucose metabolism is central to cellular functioning, changes that decrease glucose uptake or increase glycolysis have a widespread effect on on both the cells and organism. How does a simple sugar molecule create such broad effects on health? For example, diabetes results from the inability to store glucose because of a lack of insulin, a hormone that draws glucose from the blood and stores it as glycogen in the liver, muscles and adipose tissue. High levels of sugar in the blood negatively affect the body over the long term, damaging blood vessels and eyesight, making the kidneys work harder to excrete the excess sugar and increasing the risk of stroke and coronary artery disease. Because cancer cells have such a high metabolic demand for glucose, many of the mutations in cancers affect pathways that regulate glucose uptake and glucose breakdown, allowing the cancer cells to survive and grow, crowding out nearby normal cells.
Glucose metabolism is altered by processes other than mutations or an reduced production of a hormone. Throughout its life cycle, a cell will vary its requirements for glucose. For example, the cells that comprise our innate immune response are typically in a quiescent or steady state. However, when these immune cells encounter an foreign invader, they become activated and increase their demand for glucose. To respond to a potential pathogen, the activated cells need glucose to fuel cell proliferation and the production of cytokines, chemicals that activate other immune cells and initiate an inflammatory response. The typical signs of inflammation are red inflamed area that may be painful to the touch, such as a cut that becomes infected. Most inflammation resolves when the infection is eliminated, leaving behind whole skin in the instance of a cut, and the activated immune cells become quiescent again.
An Interesting Observation about Glucose Metabolism in M2 Macrophages
Glucose uptake, immunity and metabolism are cellular pathways that are intertwined such that understanding how glucose is utilized in macrophages illuminates gene induction and regulation in activated macrophages. In a recently published eLife article, Covarrubias et al. studied how activation of murine bone marrow-derived macrophages (BMDMs) by interleukin-4 (IL-4), a signaling cytokine, altered glucose metabolism in the cells and regulated a subset of genes involved in macrophage activation. Continue reading “Finding a Connection Between Glucose Metabolism and Macrophage Activation”