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Cardiovascular disease has remained the number one cause of death worldwide.  Multiple clinical trials have revealed that a common and modifiable risk factor for cardiovascular disease is high cholesterol, and if a person lowers their cholesterol, they can lower their risk for heart-related diseases.

Most of us have heard of cholesterol, but what is it? Why is having too much cholesterol a bad thing? How do we get cholesterol in our bodies? What can you do to lower your cholesterol to healthy levels? 

Cholesterols are a broad and useful type of fat found in the body. The body needs them to create hormones, essential vitamins (like vitamin D), and other molecules. They float on the surface of our cells, helping to maintain the structure and function of cell barriers. Cholesterols regulate cell activity and act outside of cells. They insulate the neurons in our brain, allowing us to think.  In fact, cholesterol is so important to daily function, that every cell in the body can make cholesterol from basic materials, except your eyelashes!

There are times when cholesterol is downright bad. LDL cholesterol and Lipoprotein a [Lp(a)] have some particularly sticky portions that can get stuck to the inside of our bloodstream. We call one of these portions ApoB. Sticky cholesterol obstructs blood flow in the form of plaques. Without help, this leads to atherosclerosis, scarring, and hardening of the arteries. Atherosclerosis further cascades into cardiovascular disease, clots, heart attacks, and stroke. This is very bad. Unfortunately, it is also very common; atherosclerosis in the neck is found in ¼ of people worldwide. Lowering excess cholesterol is a global health concern.

Our liver creates enough cholesterol to supply our bodies. We are also able to absorb cholesterol from our diets and make some in other cells. The most effective methods of reducing cholesterol are lifestyle and diet changes. However, for some people, diet and exercise don’t seem to budge their cholesterol numbers at all. For others, the ability to exercise and dietary restrictions may be limited. This is where medications can step in.

To understand how a medication may reduce LDL and/or Lp(a), we need to learn a bit about how the body makes things from DNA. Genes are bits of DNA that contain the blueprint for a protein. Genes provide the blueprint to messenger RNA (mRNA). The mRNA translates genetic code into proteins. The cells then fold proteins into complicated, machine-like shapes. Proteins interact with molecules and other proteins to create all sorts of things for the body – including cholesterol. Clinical research has been expanding which of these steps we can target for medications.

Statins are the first line treatment for reducing cholesterol. They target hydroxymethylglutaryl coenzyme A (HMG-CoA). HMG-CoA is a protein used to construct cholesterol molecules. Reducing HMG-CoA slows the body’s ability to create cholesterol, lowering cholesterol levels. Statins block the production of the “bad” LDL-C cholesterol and lower levels by as much as 60%. The benefits for statins to reduce cardiovascular events have been proven in multiple clinical trials over a diverse patient population.

Other oral medications, including ezetimibe and bempedoic acid, can be taken with statins. Ezetimibe can lower LDL-C levels by approximately 20% by inhibiting cholesterol absorption in the intestines, making it a useful add-on medication when statins alone are insufficient. Bempedoic acid can lower LDL-C by 15-25% by decreasing cholesterol synthesis in the liver.  Because bempedoic acid is converted to an enzyme found only in the liver and not the muscles (like statins), it is often an alternative for patients who have statin-associated muscle myalgias.    

Monoclonal antibodies (MoAbs) are a newer class of medication. MoAbs like alirocumab and evolocumab act like signaling molecules. These two stay outside of cells and tell the liver to produce less of the protein PCSK9. Controlling PCSK9 is a newer method of changing a person’s cholesterol profile. PCSK9 controls how much extra LDL cholesterol is absorbed and recycled by cells. MoAb medications affect this by targeting signaling receptors on the outside of the liver.

Even newer medications target the process by which genes get turned on inside the cells.  They are called gene silencing therapies because they aim to “silence” the gene’s effects.  Antisense oligonucleotides (ASOs) and small interfering RNA (siRNA) stop the liver from producing functional LDL or Lp(a) mRNA molecules. These act at different, very early stages of the cholesterol process. In addition, specialized packaging on the medications deliver them to the liver and not other cells. This can make for very targeted medications that (hopefully) have fewer side effects.

Inclisiran is the first FDA-approved siRNA therapy to lower LDL cholesterol.  It is a subcutaneous injection taken twice a year.  Imagine going to your physician’s office just twice a year to get your “cholesterol vaccine”!

Even more amazing, gene editing tools such as CRISPR could reduce overexpression of PCSK9 or other genes on a long-term basis. These are still in early phase trials, but the future is looking bright.

Lipoprotein a,or “L-P-little-a”,  or Lp(a), is a new target for decreasing the risk of cardiovascular disease. Lp(a) is genetically inherited and increases the risk for both heart disease and stroke because it can promote plaque buildup, blood clots, and inflammation.  New gene silencing therapies are in clinical trials right now using both ASO and siRNA technology.

Diet, lifestyle changes, and statins remain the front-line defense against high cholesterol. New medicines may work with or replace these classical defenses. As technologies move through the clinical research apparatus, we may be able to tailor custom combinations of medications for individual patients. ENCORE Research Group has been involved in every step along this path, helping to study medications in every category. Join our team and help pave the way for new medications to help combat high cholesterol! 

Sources:

Craig, M., Yarrarapu, S. N. S., & Dimri, M. (2018). Biochemistry, cholesterol. https://www.ncbi.nlm.nih.gov/books/NBK513326/

Fernandez-Prado, R., Perez-Gomez, M. V., & Ortiz, A. (2020). Pelacarsen for lowering lipoprotein (a): implications for patients with chronic kidney disease. Clinical Kidney Journal, 13(5), 753-757. https://doi.org/10.1093%2Fckj%2Fsfaa001

Prati, P., Vanuzzo, D., Casaroli, M., Di Chiara, A., De Biasi, F., Feruglio, G. A., & Touboul, P. J. (1992). Prevalence and determinants of carotid atherosclerosis in a general population. Stroke, 23(12), 1705-1711. https://doi.org/10.1161/01.str.23.12.1705

Tokgözoğlu, L., & Libby, P. (2022). The dawn of a new era of targeted lipid-lowering therapies. European Heart Journal. https://doi.org/10.1093/eurheartj/ehab841

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The Role of Apolipoprotein C-III (apoC-III) in Atherosclerosis and Cardiovascular Disease

After we eat a meal, all that energy has to go somewhere. Body cells can use freely floating glucose sugar in the bloodstream, but fats are a bit trickier. Just like oil and water don’t mix, fats have trouble moving through the blood in our veins and arteries. They must be packaged inside special containers called lipoproteins in order to travel where they need to go. For fats that we eat, the fats (called triglycerides) are packaged into ultra-low-density chylomicrons by the digestive system. Our liver also processes and repackages fats. The liver makes very low-density lipoproteins (VLDL) out of triglycerides and ejects them into the bloodstream. VLDLs can then use the bloodstream to travel to fat cells or be converted into other forms of energy storage. The number of triglycerides in the bloodstream at once needs to be well regulated.

For adults, fasting triglyceride levels should be under 150 mg/dL. This number decreases to below 90 mg/dL for people under 19 years of age. Unfortunately, one in ten adults have high levels, called hypertriglyceridemia. When there are too many triglycerides, they can stick to the inside of the bloodstream. They can create and contribute to hard plaques, a condition called atherosclerosis. These put stress on the cardiovascular system and can lead to atherosclerotic cardiovascular disease (ASCVD). Very high triglycerides above 500 mg/dL is called severe hypertriglyceridemia. This can lead to even more problems, including chylomicronemia, pancreatitis, and death.

What contributes to high triglyceride levels? A lot, actually! A diet that is high in sugars and fats, excessive alcohol consumption, being overweight, and a sedentary lifestyle can contribute. Some conditions, such as diabetes, kidney and liver disease, and thyroid problems increase your chances. Anything that affects liver function is likely to change how the body processes fats and may increase triglycerides. This means some life-saving medications, including several cancer, hypertension, and HIV treatments may increase triglycerides. Some people have high or very high triglycerides – usually in the form of chylomicrons – even without these risk factors. This may be because of our genes.

One of the major genetic culprits for increased triglycerides is a gene called APOC-3. This gene codes for a protein of the same name: Apolipoprotein C-III (apoC-III). You can tell these apart because the gene is uppercase, italicized, and uses a (3), while the protein is mostly lowercase and uses roman numerals (III). The protein apoC-III can lead to some detrimental effects. Normal triglycerides bind to a different protein, apoC-II. This helps them get broken down in the bloodstream. ApoC-III binds to triglycerides in the same place as apoC-II but makes them less able to be processed. These triglycerides build up in the bloodstream and can cause atherosclerosis and ASCVD. Scientists also have evidence that apoC-III makes triglyceride-rich molecules stickier to the arteries. ApoC-III binds to chylomicrons very well, making these fats especially resistant to breaking down.

So why do we have apoC-III anyway? It turns out, not all of us do! Different people have different variations of the APOC-3 gene. Some people have a gene that produces excessive apoC-III protein, and a few have genes that produce none! People with defective APOC-3 genes seem to be just as healthy as everyone else. Maybe healthier, as their levels of triglycerides are very low, even after a fatty meal! Researchers consider a defective APOC-3 gene to be cardioprotective, meaning that it lowers the chances of heart disease.

Are there methods for us to lower the production of apoC-III and our triglyceride-rich chylomicrons? It looks possible. The liver produces more apoC-III in response to high levels of blood sugar and most fats, so lowering these may help. It decreases production of apoC-III when it encounters high levels of insulin or polyunsaturated fats (such as Omega-3 fatty acids). This may be helpful, but is bad news for those with type 2 diabetes. In these patients the bloodstream has extra glucose and lacks insulin.

Treating high triglycerides can be complicated. A diet low in alcohol, carbs, and fats but high in omega-3 fatty acids can help. Exercise and weight loss are often helpful. Doctors may also prescribe fibrates, nicotinic acid (niacin), or statins. Unfortunately, these medications may not work if you have excessive levels of apoC-III and high chylomicrons. A diet that is very low in fats – under 20 grams a day – has been the only option for some patients. New classes of medication may be helpful as well. Antisense oligonucleotides, gene therapy, and custom antibodies can be used to target the production of specific proteins. Antisense oligonucleotides, for instance, bind to APOC-3 mRNA in the cell, preventing it from creating apoC-III proteins. They do this with extreme specificity, targeting only the gene in question. They can also do this only in liver cells by being packaged in a special way. Drugs that target apoC-III production may be able to bring down otherwise stubbornly high triglycerides without too many side effects. A side effect of being on this ENCORE Research Group mailing list is learning about these new medicines and when they may be available for you in a trial!

Sources:

Alves-Bezerra, M., & Cohen, D. E. (2017). Triglyceride metabolism in the liver. Comprehensive Physiology, 8(1), 1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6376873/

Goldberg, R. B., & Chait, A. (2020). A comprehensive update on the chylomicronemia syndrome. Frontiers in endocrinology, 11, 593931. https://doi.org/10.3389/fendo.2020.593931

National Institute of Health, National Heart, Lung, and Blood Institute. (April 7, 2022). High blood triglycerides. U.S. Department of Health and Human Services. https://www.nhlbi.nih.gov/health/high-blood-triglycerides

Rahmany, S., & Jialal, I. (July 18, 2022). Biochemistry, Chylomicron. https://www.ncbi.nlm.nih.gov/books/NBK545157/

Taskinen, M. R., Packard, C. J., & Borén, J. (2019). Emerging evidence that ApoC-III inhibitors provide novel options to reduce the residual CVD. Current atherosclerosis reports, 21(8), 1-10. https://doi.org/10.1007/s11883-019-0791-9