A large dose of PLA2 is delivered in venom from snakes, spiders, and bees (experienced as pain and stinging) and is responsible for much of the toxicity of these venoms. Microorganisms such as Candida albicans and certain Clostridia species produce PLA2, which increases the ability of the microorganism to infect the host. This same enzyme is produced in the body as a response to invading microorganisms and foreign proteins such as allergens, particularly house dust and cats. Physical trauma may also cause significant increases in PLA2, contributing to tissue damage and brain injury.
Phospholipase A2 is in fact a family of enzymes that are categorised by location and function. They have strong antibacterial and antiviral properties as part of the innate immune system, but also participate in many other biochemical processes that include cell signaling, cell proliferation and differentiation, cell migration and apoptosis, and modulation of inflammatory response. PLA2 is not only released in tissues and cells of the immune system, it is also produced by the pancreas and released into the small intestine following a fatty meal, to assist in the digestion and absorption of phospholipids. Additionally, PLA2 is expressed in neuronal tissue and is involved in the degranulation process that releases neurotransmitters from neurons. Research efforts have focused on the role that derangement of normal PLA2 activity plays in the etiology of many chronic illnesses. The specific roles, interactions, and interdependencies of PLA2 have been a major area of interest as it relates to chronic inflammatory conditions, cardiovascular disease, and cancer.
PLA2 and Inflammatory Disease
Research has implicated PLA2 in the pathophysiology of neurodegenerative diseases such as multiple sclerosis (MS) and Alzheimer’s disease (AD). Multiple sclerosis involves both antigen-specific mechanisms and components of the innate immune system that result in inflammatory response. Elevated PLA2 activity was found to be ongoing among MS patients, with the highest levels measured in patients with progressive disease. In the development of Alzheimer’s disease, the abnormal PLA2 levels appear to be related to oxidative signaling pathways involving NADPH oxidase and production of ROS species that lead to impairment and destruction of neurons and inflammation of glial cells.
Inflammation is the hallmark of rheumatoid arthritis (RA), a joint-destructive autoimmune disease. PLA2 is found in synovial fluid of RA-affected individuals and in the cartilage of RA patients as compared to cartilage from osteoarthritic and normal individuals.
Measurement of PLA2 is emerging as an important tool for evaluating the chance of cardiovascular disease (CVD), including future stroke, myocardial infarction, heart failure, and other vascular events. PLA2 appears to be more specific than hsCRP for CVD risk and may also have a pivotal role as a mediator of cardiovascular pathology. In atherosclerosis, PLA2 not only activates macrophages and formation of foam cells, but it also hydrolyzes LDL and HDL, spawning increased numbers of pro-atherogenic small LDL particles, and impairing anti-atherogenic HDL. PLA2 activity may even precipitate bleeding from atherosclerotic plaques.
PLA2 is expressed normally in pancreatic, gall bladder, and GI epithelial cells, but is significantly increased in inflammatory gastrointestinal disorders. In ulcerative colitis and Crohn’s disease, all intestinal cell types increase expression of PLA2, which increases gut permeability and may actually contribute to infectivity.
PLA2 and Cancer
Elevations of PLA2 have been found in gastrointestinal cancers including colonic adenomas and carcinomas and pancreatic ductogenic carcinomas, among others. Patients with lung tumors positive for PLA2 had a greatly increased tumor growth rate and a markedly reduced survival rate. Patients with lung cancer also had higher plasma levels of PLA2 than patients with benign nodules. A similar pattern has been observed in prostate cancer, although metastatic tumors expressed lower PLA2 than primary tumors. As PLA2 releases arachidonic acid and other fatty acids from cell membranes, they initiate downstream production of tumor-promoting eicosanoids. In cancer, the spread of tumor cells from a primary tumor to the secondary sites within the body is a complicated process involving cell proliferation and migration, degradation of basement membranes, invasion, adhesion, and angiogenesis. Continued research on PLA2 expression in cancer will certainly reveal valuable new insights.