In the late 1970s and early 1980s, University of Milan researchers found that a male inhabitant (Valerio Dagnoli) of the lakeside town Limone sul Garda in Northern Italy had a very low level of HDL cholesterol (the good cholesterol that tends to protect arteries from cholesterol-plaque buildup) and high levels of triglycerides (a bad form of fat in blood that can lead to cholesterol-plaque deposit in the arteries). Despite this highly abnormal lipid profile, the middle-aged man had no evidence of cardiovascular disease, and his parents had enjoyed longevity.
When blood tests were done on the entire 1,000 inhabitants of Limone, about 40 individuals had a similar lipid abnormality. Using birth records maintained in the local church going back several hundred years, it was found that these 40 individuals were all traceable to common ancestors from 1780 (Giovanni Pomaroli and Rosa Giovaneli). This then led to the discovery that these 40 individuals had a genetic mutation in the gene that makes a protein called apo A-1, which becomes a part of the HDL cholesterol particle.
In the normal apo A-1 there is arginine at position 173, whereas in the mutant form of apo A-1 (now called apo A-1 Milano) from these 40 individuals, instead of arginine there is cysteine. It was speculated that this mutant form of apo A-1 may be protecting its carriers from cardiovascular disease. However, there was no evidence to support this until 1994, when Dr. P.K. Shah and his colleagues at Cedars-Sinai Medical Center showed for the first time that intravenous injection of a genetically engineered form of apo A-1 Milano complexed to phospholipid (creating a synthetic form of HDL or HDL mimetic agent) and markedly reduced arterial plaque buildup in rabbits fed a high cholesterol diet (published in Circulation in October 1994 and also discussed in a 60 Minutes television segment in October 1994).
Dr. Shah's laboratory provided further evidence, based on experimental studies done in genetically altered mice with high cholesterol levels, that repeated intravenous injections of apo A-1 Milano would halt the progression of plaque buildup and induce reversal (regression) of preexisting plaque within five weeks (published in Circulation in 1998). Furthermore, Dr. Shah's laboratory also reported that a single large intravenous dose of apo A-1 Milano could remove cholesterol and inflammation out of arterial plaque within 48 hours, creating a more stable form of plaque (published in Circulation in 2001). Dr. Sanjay Kaul from Dr. Shah's laboratory also showed that local injection of a tiny amount of recombinant apo A-1 Milano directly at the site of coronary stent implantation in pig coronary arteries dramatically reduced the buildup of scar tissue inside the stent, raising the interesting possibility that local delivery of apo A-1 Milano could be useful in preventing re-clogging of coronary stents (published in Circulation in 2003).
Based on the body of evidence provided by these various studies from Cedars-Sinai and additional confirmatory studies from Dr. Cesare Sirtori's laboratory in Milan, Esperion Therapeutics initiated human trials of recombinant apo A-1 Milano. In the small Phase 2 study (reported in the November 5, 2003 issue of JAMA), investigators showed that as in animal studies reported from Dr. Shah's lab, once-a-week intravenous administration of recombinant apo A-1 Milano (ETC-216) for five weeks led to a significant and measurable shrinkage of human coronary artery plaques as measured by intravascular ultrasound technique. These findings are unprecedented in that reversal of plaque size has been shown in five short weeks. Among the currently available agents (e.g., statins), reversal of plaque is rare, and even when it occurs it takes many months to years to see regression. Although this human trial of recombinant apo A-1 Milano (ETC-216) is a small study and did not have clinical endpoints, results are extremely provocative and provide proof of concept that HDL mimetic based therapy has the potential to rapidly and favorably change human atherosclerotic plaques. Larger and more definitive trials will be needed to confirm the exciting results reported. Pfizer Pharmaceuticals has recently acquired Esperion Therapeutics and will be designing and launching more definitive human trials over the next two to three years before seeking FDA approval.
Potential limitations include the fact that producing the drug is quite expensive and laborious, the drug has to be given intravenously and repeated intravenous use may be needed to sustain the benefits. Alternatively, initial benefits from short-term intravenous use may be sustained by oral agents currently available (such as statins and niacin) and newer orally effective HDL boosting agents currently in development (such as CETP inhibitors, apo A mimetic peptides, etc.). No serious side effects were noted in this study.
Another approach in the future could be the gene transfer or gene therapy approach in which the actual DNA (gene) that codes for apo A-1 Milano protein is transferred into the body, where it stimulates the production of apo A-1 Milano by the host without need for exogenous repeated supply. Dr. Shah's laboratory is currently using this approach in animals models with the support of a grant from the NIH and in collaboration with researchers from the City of Hope Medical Center. In this project, Dr. Shah and his colleagues have successfully used a virus called the adeno-associated virus (AAV) to ferry the apo A-1 Milano gene into the body of genetically altered mice and shown that such gene transfer is feasible and reduces atherosclerotic plaque buildup after a single injection of the gene carried by the viral vector. Dr. Shah and his colleagues hope to be able to test this approach in humans sometime in the future.