Secretory phospholipase A₂, or sPLA₂, is a family of enzymes directly involved in the acute and chronic steps of an inflammatory response. sPLA₂ activity is highly elevated during the early stages of inflammation, and its acute effects serve to substantially amplify the inflammatory process. The sPLA₂ enzyme catalyzes the first step in the arachidonic acid pathway of inflammation, one of the main metabolic processes for the production of inflammatory mediators, which, when amplified, are responsible for causing damage to cells and tissue. Specifically, sPLA₂ breaks down phospholipids that result in the formation of fatty acids such as arachidonic acid. Arachidonic acid is subsequently metabolized to form several pro-inflammatory and thrombogenic molecules associated with more frequent and subsequent cardiovascular events. Historical and recent clinical results have demonstrated circulating levels of sPLA₂ are significantly correlated with CRP, a well-established inflammatory marker. These studies have also demonstrated that sPLA₂ independently predicts coronary events in patients that have recently experienced an acute coronary syndrome and patients with stable coronary artery disease independent of other standard risk factors.

There are 10 known enzymes in the sPLA₂ family of which group IIA is considered the prototypic inflammatory isoform. It has been implicated in a number of inflammatory diseases and tissue injury. By generating important intermediates such as arachidonic acid or lysoplatelet activating factor (Lyso-PAF), sPLA₂ may play an important role as a mediator in the process of inflammation.

sPLA₂ and Cardiovascular Disease

In cardiovascular diseases such as acute coronary syndrome, excess sPLA₂ activity has acute and chronic implications on disease progression and patient outcomes. In published studies and our own clinical studies, significant elevations in sPLA₂ activity and mass have been seen from 24 hours to two weeks following an acute coronary syndrome and can persist for up to an additional 12 weeks thereafter. Shortly after a heart attack, sPLA₂ is dramatically elevated, amplifying inflammation that is associated with more frequent and subsequent cardiovascular events. This resulting elevated level of inflammation is problematic for acute coronary syndrome patients who are already at elevated risk of complications during the weeks following their initial event. For example, increased inflammation can destabilize vulnerable vascular lesions or atherosclerotic plaque, destroy damaged but viable cardiac cells, and adversely modify lipids, any of which may lead to the recurrence of a major adverse cardiovascular event, or MACE. In a stable cardiovascular patient, sPLA₂ also sustains chronic vascular inflammation as discussed earlier, but it also adversely remodels lipoproteins such as LDL. sPLA₂ interacts with LDL in a series of reactions that result in smaller, more pro-atherogenic and pro-inflammatory LDL particles. Moreover, these modified lipoproteins have a reduced affinity for LDL receptors, which are responsible for removal of cholesterol from the body. As a result, LDL remains in circulation longer and has a greater tendency to deposit in the artery wall. This increased LDL deposition and sustained chronic vascular inflammation lead to atherosclerosis. The family of sPLA₂ enzymes includes at least three forms that play a role in inflammation and the development of cardiovascular disease or lung injury. While sPLA₂ enzymes are a member of the phospholipase family that includes a lipoprotein associated phospholipase A2, or Lp-PLA2, there are important distinctions. Based on our clinical and nonclinical studies, we believe that our sPLA₂ inhibitor, A-002, has the potential to treat both acute and chronic cardiovascular diseases and have differentiating properties compared to other PLA2 enzyme inhibitors:

• Synergistic with HMG-CoA reductase inhibitors, or statins, in reducing LDL, total cholesterol, and Non-HDL cholesterol in patients with coronary artery disease
• Lowers circulating small, dense and pro-atherogenic, or plaque building LDL particles
• Lowers CRP, a well-established marker of inflammation
• Reduces plaque volume and aneurysms in standard rodent models of atherosclerosis and has demonstrated synergistic reductions of plaque volume in standard rodent models of atherosclerosis when used in combination with statins

sPLA₂ and Acute Chest Syndrome in Sickle Cell Disease

In diseases such as acute chest syndrome, a very serious form of lung injury associated with sickle cell disease, sPLA₂ acts acutely on a number of substrates that amplify the inflammatory disease process. Sickle cell disease is a genetic disorder which leads to the structural alteration, or “sickling,” of otherwise healthy red blood cells. Patients with sickle cell disease experience periods of intense pain known as vaso-occlusive crisis, or VOC, as structurally altered red blood cells bind together and occlude small blood vessels that supply blood and nutrients to vital tissue and bone. sPLA₂ levels are dramatically elevated in sickle cell patients during an episode of VOC as well as within 24 to 48 hours of the onset of acute chest syndrome. During VOC, microscopic fat emboli, or droplets of fat from the bone marrow, are prevalent and can break free and become lodged in the lung. These embolisms are substrates for sPLA₂ enzymes and provide fuel, such as arachidonic acid and lysophospholipids, for an already established inflammatory response increasing lung injury. In addition, sPLA₂ has been demonstrated to degrade human lung surfactant, a component necessary in maintaining appropriate lung function, which further complicates lung injury.