Thymoquinone has a synergistic effect with PHD inhibitors to ameliorate ischemic brain damage in mice

A blockage in a blood vessel can cause reduced blood flow to the brain, which eventually leads to the death of surrounding tissue. Several studies have attempted to develop an effective intervention to reverse this process and improve the health status of affected individuals. Due to its indirect effect on cellular functions and metabolism, the hypoxia-inducible factor (HIF-1α) protein has been proposed as a promising transcription factor in the treatment of stroke.

The current study aims to explore the relation between HIF-1 α and thymoquinone (TQ) in the attenuation of ischemic brain damage and the possible mechanism of this relation to reduce cell death.

For this purpose, dimethyloxallyl glycine (DMOG), 8 mg/kg, Acriflavine (ACF), 1.5 mg/kg, and both combined with TQ (5 mg/kg) were assessed. Male C57 mice were used to establish an ischemic stroke model by using endothelin-1 (ET-1) (400 pmole/μl) intra- cranial injection. The ultrastructure alterations of neuronal soma, axons, and mitochondria after stroke and treatment were well addressed. Besides, the expression levels of VEGF, HIF-1α, Nrf2, and HO-1 were evaluated. Meanwhile, apoptosis and autophagy-related proteins were also investigated.

Treatment of ischemic stroke by TQ can activate the HIF-1α pathway and its downstream genes such as VEGF, TrkB, and PI3K, which in turn enhance angiogenesis and neurogenesis. Our study revealed that TQ has the same effect as DMOG to activate HIF-1 α and can improve motor dysfunction after ischemic stroke. Further, we demonstrated that both TQ and DMOG effectively attenuate the organelle's damage following ischemic stroke, which was confirmed by the cryogenic transmission electron microscope. The synergistic effect of TQ and DMOG may lead to a chemo-modulation action in the autophagy process after stroke onset and this result is validated by the western blot and rt-qPCR techniques.

Our finding revealed the potential role of TQ as a HIF-1 α activator to reduce cell death, modulate autophagy and decrease the infarct volume after ischemic stroke onset. The neuroprotective effect of TQ is achieved by decreasing the inflammation and increasing angiogenesis as well as neurogenesis via induction of the HIF-1α-VEGF/Nrf2-HO-1-TrkB-PI3K pathway.