In vitro, isatis leaf inhibits COX-2 with preferential effects on COX-2–catalysed prostaglandin synthesis ⁽¹⁰⁾. The alkaloid tryptanthrin has been identified as the inhibitor of COX-2 ⁽¹⁰⁾ and 5-lipoxygenase (5-LOX) ^(13) (18). Indirubin, another active component, inhibits cyclin-dependent kinases and prevents proliferation by arresting cells in the G2/M phase ⁽⁴⁾. Other alkaloids isolated from isatis inhibit leukocyte function and attenuate production of mediators related to inflammatory responses ⁽¹¹⁾. A compound derived from isatisine A showed moderate anti-HIV-1 activity ⁽⁷⁾, but better virucidal activity has been reported with the leaf, not root, extracts using a swine pseudorabies model ⁽⁸⁾.

Other animal models suggest that isatis leaf can reduce allergic airway inflammation and hyper-responsiveness by inhibiting production of Th2 cytokines IL-4 and IL-5, and RANTES ⁽⁹⁾. And when used as post-exposure prophylaxis, isatis leaf attenuated lung tissue damage and reduced lung virus titers ⁽⁶⁾. Findings also showed induction of hepatocellular cancer cell death by isatis via a caspase-independent apoptotic pathway ⁽¹²⁾.

In other mechanistic studies, Qing Dai prevented bisphosphonate-induced gastrointestinal injury by suppressing mitochondrial ROS production, the main cause of cellular lipid peroxidation ⁽²⁷⁾. Qing Dai may cause PAH via NO synthase inhibition and endothelial dysfunction in the pulmonary artery ⁽³²⁾.