Serum phospholipase A in hematological diseases

Phospholipase A2: its usefulness in laboratory diagnostics

Phospholipase A2 (PLA2) is an enzyme that catalyzes the hydrolysis of membrane phospholipids. This article reviews the source and structure of PLA2, the involvement of the enzyme in various biological and pathological phenomena, and the usefulness of PLA2 assays in laboratory diagnostics. Of particular importance is the role of PLA2 in the cellular production of mediators of inflammatory response to various stimuli. Assays for PLA2 activity and mass concentration are discussed, and the results of enzyme determinations in plasma from patients with different pathological conditions are presented. The determination of activity and mass concentration in plasma is particularly useful in the diagnosis and prognosis of pancreatitis, multiple organ failure, septic shock, and rheumatoid arthritis. A very important result is the demonstration that PLA2 is an acute phase protein, like CRP. Indeed, there is a close correlation between PLA2 mass concentration and CRP levels in several pathological conditions. Although the determination of C-reactive protein is much easier to perform and is routinely carried out in most clinical laboratories, the assessment of PLA2 activity or mass concentration has to be considered as a reliable approach to obtain a deeper understanding of some pathological conditions and may offer additional information concerning the prognosis of several disorders.

Elevation of serum phospholipase A2 in patients at an intensive care unit

To evaluate the organ specificity of pancreatic phospholipase A2 (PLA2) and the diagnostic value of the elevation of serum PLA2 levels in patients with serious diseases not involving the pancreas, we studied the organ distribution of PLA2 in autopsy specimens and serum level of PLA2 in patients who required admission to an intensive care unit (ICU). PLA2 was measured by a specific radioimmunoassay (RIA), using monoclonal antibody against human pancreatic PLA2. Organ distribution of PLA2 revealed that the pancreas showed a much higher content of pancreatic PLA2 immunoreactivity than any other organ. An abnormally high value of serum PLA2 was observed in 18 of 30 patients (60%) at ICU. Both serum PLA2 and pancreatic isoamylase were elevated in 11 patients (37%). Of 11 patients with hyperphospholipasemia and hyperamylasemia, serum creatinine was elevated in five patients and blood urea nitrogen in nine patients. Serum PLA2 levels did not always rise comparably to serum creatinine and blood urea nitrogen levels. Serum PLA2 values showed the best correlation with serum lactate dehydrogenase levels among routine blood-chemistry tests. The elevation of serum PLA2 was ascribable to renal dysfunction or ischemic pancreatic damage secondary to circulatory collapse with multiple organ failure.

Serum phospholipase--regulatory and pathophysiological aspects

The development of a photometric procedure to measure phospholipase A activity has extended previous observations that this enzyme activity increases in several pathological states including pancreatic and inflammatory diseases. Serum phospholipase A in pancreatitis was characterized as a mixture of the pancreatic enzyme and a different phospholipase with a pH optimum at 8.0. The latter enzyme was also observed in nonpancreatic diseases like septicemia and acute lung failure which are characterized by an increase in tissue phagocyte activity. The possible pathogenic role of phospholipase(s) A, their intracellular regulation and the proposed mechanisms of release into the blood stream are discussed with respect to the present pathobiochemical knowledge. This includes the mechanism of activation of phagocytosis and the possible role of lipocortins known to be stimulated by glucocorticoid treatment.