Abstract
Boswellic acids constitute a group of unique pentacyclic triterpene acids from Boswellia serrata with multiple pharmacological activities that confer them anti-inflammatory and anti-tumoral
properties. A subgroup of boswellic acids, characterized by an 11-keto group, elevates
intracellular Ca2+ concentrations [Ca2+ ]i and causes moderate aggregation of human platelets. How different BAs and their mixtures
in pharmacological preparations affect these parameters in activated platelets has
not been addressed, so far. Here, we show that boswellic acids either antagonize or
induce Ca2+ mobilization and platelet aggregation depending on defined structural determinants
with inductive effects predominating for a B. serrata gum resin extract. 3-O -Acetyl-11-keto-β -boswellic acid potently suppressed Ca2+ mobilization (IC50 = 6 µM) and aggregation (IC50 = 1 µM) when platelets were activated by collagen or the thromboxane A2 receptor agonist U-46619, but not upon thrombin. In contrast, β -boswellic acid and 3-O -acetyl-β -boswellic acid, which lack the 11-keto moiety, were weak inhibitors of agonist-induced
platelet responses, but instead they elicited elevation of [Ca2+ ]i and aggregation of platelets (≥ 3 µM). 11-Keto-β -boswellic acid, the structural intermediate between 3-O -acetyl-11-keto-β -boswellic acid and β -boswellic acid, was essentially inactive independent of the experimental conditions.
Together, our study unravels the complex agonizing and antagonizing properties of
boswellic acids on human platelets in pharmacologically relevant preparations of B. serrata gum extracts and prompts for careful evaluation of the safety of such extracts as
herbal medicine in cardiovascular risk patients.
Key words
Boswellia serrata
- Burseraceae - boswellic acids - platelets - calcium - collagen - aggregation
