Scientists at the University of California San Diego School of Medicine discovered that they can block inflammation in mice with a naturally occurring antibody that binds oxidized phospholipids (OxPL), molecules on cell surfaces that get modified by inflammation. Even while on a high-fat diet, the antibody protected the mice from arterial plaque formation, hardening of the arteries, and liver disease, and prolonged their lives.
The study (“Oxidized Phospholipids Are Proinflammatory and Proatherogenic in Hypercholesterolaemic Mice”), published in Nature, marks the first demonstration in a living system that OxPL triggers inflammation and leads to plaque formation, according to the researchers, who add that the results also suggest a new approach for preventing or reversing a number of inflammatory diseases.
“Oxidized phospholipids (OxPL) are ubiquitous, are formed in many inflammatory tissues, including atherosclerotic lesions, and frequently mediate proinflammatory changes. Because OxPL are mostly the products of non-enzymatic lipid peroxidation, mechanisms to specifically neutralize them are unavailable and their roles in vivo are largely unknown. We previously cloned the IgM [immunoglobulin M] natural antibody E06, which binds to the phosphocholine headgroup of OxPL, and blocks the uptake of oxidized low-density lipoprotein (OxLDL) by macrophages and inhibits the proinflammatory properties of OxPL. Here, to determine the role of OxPL in vivo in the context of atherogenesis, we generated transgenic mice in the Ldlr−/− background that expressed a single-chain variable fragment of E06 (E06-scFv) using the Apoe promoter. E06-scFv was secreted into the plasma from the liver and macrophages, and achieved sufficient plasma levels to inhibit in vivo macrophage uptake of OxLDL and to prevent OxPL-induced inflammatory signaling,” write the investigators.
“Compared to Ldlr−/− mice, Ldlr−/−E06-scFv mice had 57–28% less atherosclerosis after 4, 7 and even 12 months of 1% high-cholesterol diet. Echocardiographic and histologic evaluation of the aortic valves demonstrated that E06-scFv ameliorated the development of aortic valve gradients and decreased aortic valve calcification. Both cholesterol accumulation and in vivo uptake of OxLDL were decreased in peritoneal macrophages, and both peritoneal and aortic macrophages had a decreased inflammatory phenotype. Serum amyloid A was decreased by 32%, indicating decreased systemic inflammation, and hepatic steatosis and inflammation were also decreased. Finally, the E06-scFv prolonged life as measured over 15 months. Because the E06-scFv lacks the functional effects of an intact antibody other than the ability to bind OxPL and inhibit OxLDL uptake in macrophages, these data support a major proatherogenic role of OxLDL and demonstrate that OxPL are proinflammatory and proatherogenic, which E06 counteracts in vivo. These studies suggest that therapies inactivating OxPL may be beneficial for reducing generalized inflammation, including the progression of atherosclerosis, aortic stenosis and hepatic steatosis.”
“Wherever you get inflammation, you get OxPL,” said senior author Joseph Witztum, M.D., professor of medicine at UC San Diego School of Medicine. “It doesn't mean OxPL is the cause, but it definitely plays a major role.” Dr. Witztum led the study with first author Xuchu Que, Ph.D., a senior project scientist at UC San Diego School of Medicine.
Some phospholipids are prone to modification by reactive oxygen species, forming OxPL. This event is particularly common in inflammatory conditions such as atherosclerosis, in which artery-blocking plaques form. Prior to this study, researchers were unable to control phospholipid oxidation in a way that would allow them to study its role in inflammation and atherosclerosis.
Drs. Witztum and Que and colleagues engineered mice with two special attributes. They have a gene mutation that makes them a good model for atherosclerosis and they generate a piece of an antibody called E06 that's just enough to bind OxPL and prevent their ability to cause inflammation in immune cells, but not enough to cause inflammation on its own. They fed the mice a high-fat diet.
Compared to control mice, the mice with E06 antibodies had 28% to 57% less atherosclerosis, even after one year and despite having high levels of cholesterol. The antibody also decreased aortic valve calcification (hardening and narrowing of the aortic valves), hepatic steatosis (fatty liver disease), and liver inflammation. E06 antibody-producing mice had 32% less serum amyloid A, a marker of systemic inflammation.
The E06 antibody also prolonged the life of the mice. After 15 months, all of the E06 antibody-producing mice were alive, compared to 54% of the control mice.
“We showed for the first time that OxPL are truly proinflammatory and proatherogenic and, moreover, that they can be counteracted by E06 antibody,” Dr. Witztum said. “This suggests that therapies that inactivate OxPL may be beneficial for reducing inflammation in general, and in particular in the case of diseases such as atherosclerosis, aortic stenosis, and hepatic steatosis.”
The team is now testing the E06 antibody in mouse models of human diseases linked to inflammation, such as osteoporosis (bone loss) and nonalcoholic steatohepatitis (NASH, a type of liver disease).