To fight fat, scientists had to figure out how to pin down a greasy, slippery target. Researchers at Emory University and Baylor College of Medicine have identified compounds that potently activate LRH-1, a liver protein that regulates the metabolism of fat and sugar. These compounds have potential for treating diabetes, fatty liver disease and inflammatory bowel disease.
Their findings were recently published online in Journal of Medicinal Chemistry.
LRH-1 is thought to sense metabolic state by binding a still-undetermined group of greasy molecules: lipids or phospholipids. It is a nuclear receptor, a type of protein that turns on genes in response to hormones or vitamins. The challenge scientists faced was in designing drugs that fit into the same slot occupied by the lipids.
“Phospholipids are typically big, greasy molecules that are hard to deliver as drugs, since they are quickly taken apart by the digestive system,” says Eric Ortlund, PhD, associate professor of biochemistry at Emory University School of Medicine. “We designed some substitutes that don’t fall apart, and they’re highly effective – 100 times more potent that what’s been found already.”
Previous attempts to design drugs that target LRH-1 ran into trouble because of the grease. Two very similar molecules might bind LRH-1 in opposite orientations. Ortlund’s lab worked with Emory chemist Nathan Jui, PhD and his colleagues to synthesize a large number of compounds, designing a “hook” that kept them in place. Based on previous structural studies, the hook could stop potential drugs from rotating around unpredictably. Read more
Imagine a key that opens a pin tumbler lock. A very similar key can also fit into the lock, but upside down in comparison to the first key.
Biochemist Eric Ortlund and colleagues have obtained analogous results in their study of how potential diabetes drugs interact with their target, the protein LRH-1. Their research, published in Journal of Biological Chemistry, shows that making small changes to LRH-1-targeted compounds makes a huge difference in how they fit into the protein’s binding pocket.
First author Suzanne Mays, a graduate student in Emory’s MSP program
This research was selected as “Paper of the Week” by JBC and is featured on the cover of the December 2 issue.
LRH-1 (liver receptor homolog-1) is a nuclear receptor, a type of protein that turns on genes in response to small molecules like hormones or vitamins. LRH-1 acts in the liver to regulate metabolism of fat and sugar.
Previous research has shown that activating LRH-1 decreases liver fat and improves insulin sensitivity in mice. Because of this, many research teams have been trying to design synthetic compounds that activate this protein, which could have potential to treat diabetes and nonalcoholic fatty liver disease. This has been a difficult task, because not much is known about how synthetic compounds interact with LRH-1 and switch it into the active state. Read more
Drugs that interfere with bile acid recycling can prevent several aspects of NASH (nonalcoholic steatohepatitis) in mice fed a high-fat diet, scientists from Emory University School of Medicine and Children’s Healthcare of Atlanta have shown.
The findings suggest that these drugs, known as ASBT inhibitors, could be a viable clinical strategy to address NASH, an increasingly common liver disease. The results were published in Science Translational Medicine on September 21, 2016.
“By targeting a process that takes place in the intestine, we can improve liver function and reduce insulin resistance in a mouse model of NASH,” says senior author Saul Karpen, MD, PhD. “We can even get fat levels in the liver down to what we see in mice fed a regular diet. These are promising results that need additional confirmation in human clinical trials.”
Karpen is Raymond F. Schinazi distinguished professor of pediatrics at Emory University School of Medicine and chief of the Division of Pediatric Gastroenterology, Hepatology and Nutrition at Children’s Healthcare of Atlanta. He and Paul Dawson, PhD, Emory professor of pediatrics, jointly run a lab that investigates the role of bile acids in liver disease.
Saul Karpen, MD, PhD
Many people in developed countries have non-alcoholic fatty liver disease, an accumulation of fat in the liver that is linked to diet and obesity. Fatty liver disease confers an elevated risk of type II diabetes and heart disease. NASH is a more severe inflammation of the liver that can progress to cirrhosis, and is a rising indication for liver transplant. Besides diet and exercise, there are no medical treatments for NASH, which affects an estimated 2 to 5 percent of Americans. Read more
Frank Anania, MD
Lots of people in the United States consume a diet that is high in sugar and fat, and many develop non-alcoholic fatty liver disease, a relatively innocuous condition. NASH (non-alcoholic steatohepatitis) is the more unruly version, linked to elevated risk of cardiovascular and metabolic diseases, and can progress to cirrhosis. NASH is expected to become the leading indication for liver transplant. But only a fraction of people with non-alcoholic fatty liver disease go on to develop NASH.
Thus, many researchers are trying to solve this equation:
High-sugar, high-fat diet plus X results in NASH.
Emory hepatologist Frank Anania and colleagues make the case in a recent Gastroenterology paper that a “leaky gut”, allowing intestinal microbes to promote liver inflammation, could be a missing X factor.
Anania’s lab started off with mice fed a diet high in saturated fat, fructose and cholesterol (in the figure, HFCD). This combination gives the mice moderate fatty liver disease and metabolic syndrome (see this 2015 paper, and we can expect to hear more about this model soon from Saul Karpen). Leaky gut, brought about by removing a junction protein from intestinal cells, sped up and intensified the development of NASH.
The authors say that this model could be useful for the study of NASH, which has been difficult to reproduce in mice.
The researchers could attenuate liver disease in the mice by treatment with antibiotics or sevelamer, a phosphate binding polymer that soaks up inflammatory toxins from bacteria. Sevelamer is now used to treat excess phosphate in patients with chronic kidney disease, and is being studied clinically in connection with insulin resistance.
Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver conditions in the United States, affecting 30 percent of the population, and increasing — and likely to catch up in prevalence with obesity and diabetes. In NAFLD, fat content of the liver is elevated to 6 percent or more in people who drink in moderation or not at all. Patients will first present with elevated liver enzyme values in blood tests, but then an imaging test or tissue biopsy may be ordered to evaluate the extent of the damage. NAFLD is mostly asymptomatic and is variable in severity; a majority of those afflicted do not need drug treatments. However, NAFLD is thought to be a preliminary condition that can eventually progress to severe manifestations, such as cirrhosis, hepatocellular carcinoma, and end stage liver failure.
Progression of liver disease, from NIDDK.
This is a guest post from Kristina Bargeron Clark, a MMG graduate student at Emory and communications chair for Women in Bio-Atlanta. Her website is www.inkcetera.org.
At Emory, Frank Anania, director of the Department of Medicineâ€™s Division of Digestive Diseases, and his colleagues are developing a tool to treat liver disease. A recent publication in the FASEB Journal describes their investigation into the potential for the hormone adiponectin to modulate liver fibrosis.
Adiponectin is produced by adipose tissue, but is known to decrease in overweight people with metabolic disease. Research by others indicates that it may prevent heart and kidney fibrosis. The Emory teamâ€™s studies were conducted to determine if adiponectin could also reduce liver fibrosis.