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PMN elastase, a proteolytic enzyme, is a biochemical marker for pathologic granulocyte stimulation. In the presence of sepsis, excessive neutrophil stimulation occurs and significant amounts of PMN elastase are released into the plasma and serve as an indicator for the severity of the disease and the prognosis. PMN elastase is also a useful parameter for preoperative diagnostic management and postoperative follow-up of bone and joint infections.
In patients with osteomyelitis and joint empyema (n = 48) PMN elastase had a sensitivity of 77%, which was only exceeded by that of the unspecific erythrocyte sedimentation rate (sensitivity 89%). Sensitivities of other inflammation parameters were lower: C-reactive protein (CRP) 67%, fibrinogen 50%, neopterin 32% and leukocyte count 21%. Determination of PMN elastase levels was also helpful in postoperative follow-up of patients with bone and joint infections. In the early postoperative period PMN elastase levels normalized more quickly than the other parameters unless patients actually developed complications. At the first postoperative determination (day 2-4 after surgery) 38% of the patients (n = 24) already had PMN elastase levels within the normal range (less than or equal to 40 micrograms/l) (CRP 13%). After 10 days PMN elastase was normal in 57% and CRP in 30% of the patients. Later on both parameters reacted similarly: by the time of discharge from hospital levels of PMN elastase were normal in 70% and CRP levels in 74%.
PMN-Elastase from human polymorphnuclear granulocytes is a glycoprotein of 30 kDa and belongs to the group of serine proteases. Active PMN-Elastase is released from azurophil granula of neutrophil granulocytes after irritation or disintegration. The determination of the PMN-Elastase in stool is used to record inflammatory reactions where neutrophils are involved. Especially in Crohn´s disease the inflammatory process go hand in hand with an increased phagocytic activity and the biological decay of these cells and thus leads to an increased release of PMN-Elastase and other lysosomal enzymes.
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Elastase is an enzyme from the class of proteases, or peptidases, that break down proteins. Elastase breaks down elastin, an elastic fiber that, together with collagen, determines the mechanical properties of connective tissue. The neutrophil form breaks down the Outer membrane protein A (OmpA) of E. coli and other Gram-negative bacteria, and also breaks down Shigella virulence factors. This is accomplished through the cleavage of peptide bonds in the target proteins. The specific peptide bonds cleaved are those on the carboxy side of small, hydrophobic amino acids such as glycine, alanine, and valine. For more on how this is accomplished, see serine protease.
Elastase is inhibited by the acute phase protein alpha1-antitrypsin (A1AT), which binds almost irreversibly to the active site of elastase and trypsin. A1AT is normally secreted by the liver cells into the serum. alpha-antitryspin deficiency (A1AD) leads to uninhibited destruction of elastic fiber by elastase; the main result is pulmonary emphysema.
Elastase has been shown to disrupt tight junctions, cause proteolytic damage to tissue, break down cytokines and alpha proteinase inhibitor, cleave immunoglobuline A and G (IgA, IgG), and cleave both C3bi, a component of the complement system, and CR1, a receptor on neutrophils for another complement molecule involved in phagocytosis. The cleavage of IgA, IgG, C3bi, and CR1 contributes to a decrease of the ability of neutrophils to kill bacteria by phagocytosis. Together all these factors contribute to human pathology.
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