Human Leukocyte Elastase Inhibition

Dual inhibition of 5-LO and HLE enzymes is unique to the Boswellic acids

Boswellic acids have been found to inhibit 5-lipoxygenase (5-LO), as well as, human leukocyte elastase (HLE), the serine protease produced and released by polymorphonuclear leukocytes (PMNLs), which have been suggested to play a role in several diseases (pulmonary emphysema, cystic fibrosis, chronic bronchitis, acute respiratory distress syndrome, glomerulonephritis, and rheumatic arthritis) due to their aggressive and destructive properties.

This dual inhibitory action of two pathophysiologically important enzyme activities (HLE and 5-LO) is unique to the pentacyclic triterpenes from the boswellic acid series. Several leukotriene biosynthesis inhibitors furnished no HLE inhibitory activity (as shown below). The β-boswellic acid, acetyl-11-keto-β-boswellic acid (AKBBA), ursolic acid, and amyrin significantly inhibited HLE. The HLE inhibition activity of AKBBA and ursolic acid were comparable; however, ursolic acid’s mode of inhibition is competitive (Safayhi et al., 1997).

HLE activity in the presence of leukotriene synthesis inhibitors and cyclic as well as noncyclic hydrophobic compounds