PCSK9 inhibition therapies dramatically reduce cholesterol levels in the bloodstream, and seem set to take over from statins as the next generation approach to cholesterol management in the context of cardiovascular disease risk. Atherosclerosis results from the ability of a combination of damaged lipids - such as oxidized cholesterol - and overall level of lipids to overwhelm macrophage cells called in to clean up points of irritation in blood vessel walls. A feedback loop of inflammation and cell death sets in, as macrophages, filled with lipids and in the process of dying, call for further help, secreting cytokines that produce inflammation. The fatty deposits that weaken and narrow blood vessels in the later stages of atherosclerosis are composed of dead macrophages and the lipids they failed to clean up.
One way to try to slow down this runaway process of damage is to reduce the input of cholesterol. This is the basis of the success of statins in lowering cardiovascular risk, and the evidence suggests that further lowering of cholesterol levels will reduce that risk to a greater degree. This is still, however, only a stepping stone on the way to an effective and complete solution. PCSK9 inhibition doesn't halt or significantly reverse atherosclerosis, it still only slows it down somewhat. The research community must focus on different mechanisms and strategies, such as perhaps ways to make macrophages more resilient and more effective, allowing them to continue to operate in old people just as well as they do in young people. The SENS approach of removing oxidized lipids via delivery of bacterial enzymes is one example.
Unknown 15 years ago, PCSK9 (proprotein convertase subtilisin/kexin type 9) is now common parlance among scientists and clinicians interested in prevention and treatment of atherosclerotic cardiovascular disease. What makes this story so special is not its recent discovery nor the fact that it uncovered previously unknown biology but rather that these important scientific insights have been translated into an effective medical therapy in record time. Indeed, the translation of this discovery to novel therapeutic serves as one of the best examples of how genetic insights can be leveraged into intelligent target drug discovery.
Initial clues were provided by a French family with familial hypercholesterolemia (FH) in 2003. Gain-of-function mutations in PCSK9 were linked with hypercholesterolemia and ultimately uncovered a key new player in lipid metabolism. This seminal discovery led to a series of investigations that demonstrated that loss-of-function (LOF) mutations in PCSK9 associate with lifelong low cholesterol levels and marked reductions in the risk of atherosclerotic cardiovascular disease (ASCVD). The rare individuals with homozygous LOF mutations in PCSK9 (and no circulating protein) demonstrated extremely LDL cholesterol (LDL-C; ≈15 mg/dL), normal health and reproductive capacity, and no evidence of neurological or cognitive dysfunction.
This complementary set of observations has been leveraged into the most important therapy for the treatment of hypercholesterolemia and ASCVD since the introduction of statins. Indeed, the so-called PCSK9 inhibitors, fully human monoclonal antibodies that bind PCSK9, reduce LDL-C by ≈60% and risk of myocardial infarction and stroke by ≈20% after more than 2 years of treatment. Remarkably, these agents antagonizing PCSK9 action were approved by regulatory agencies spanning the globe only a decade after its discovery - although the scientific and medical communities have swiftly uncovered many facets of PCSK9 biology, there is still much to learn.