In the past decades, hospital admissions for acute brain injury have continued to rise. For instance, intracerebral hemorrhage (ICH) and traumatic brain injury (TBI) are just two subtypes of acute brain injury that have increased in annual incidence without a decrease in mortality.
ICH is a type of stroke in which blood accumulates in the brain after a vessel ruptures. When the fluids press against the surrounding tissue, the resulting high pressure leads to mechanical damage within the first minutes to hours. Subsequently, the surrounding brain regions experience secondary damage caused by processes such as loss of blood flow, oxidative stress, and inflammation. Additionally, microglia, brain cells that function in immune defense and as scavengers of dead cells and debris, may further complicate the problem by releasing substances that are toxic to cells. Released chemicals such as nitric oxide, hydrogen peroxide, proteases, cytokines, and acids work together to further damage brain tissue surrounding the lesion but also help eliminate the dead cells at the lesion site.
In TBI, the initial blunt trauma to the parenchyma, which is composed of neurons and glial cells, is almost impossible to prevent, and the secondary injury pathways are similar to those of ICH. Consequently, finding viable drugs to ameliorate the effects of secondary injury may be crucial to helping patients recover.
Pinocembrin is one such compound that has shown promise for treating secondary brain injury. It is a natural product found in plants such as ginger root, marjoram, and propolis. Pinocembrin has been found to decrease oxidative stress, inhibit microglial activation, and suppress neuroinflammation. However, pinocembrin’s efficacy and its mechanism of action in ICH and TBI models were unknown. Hence, we investigated its effectiveness for treating ICH and TBI in rat models. The ICH model is created by injecting the enzyme collagenase into the rat’s brain. The enzyme causes blood vessel walls to break down and thus produces bleeding. TBI is induced in rats with a device that drops a piston directly onto the surface of the brain with a pre-set force.
Our novel findings from both studies indicate that pinocembrin has neuroprotective effects against secondary brain injury. It reduced lesion volume and brain fluid accumulation while promoting functional recovery in the ICH model. Similarly, in the TBI model, neuronal survival around the lesion site was greater in animals treated with pinocembrin than in a group that received an inactive compound. Moreover, pinocembrin inhibited activation of microglia and astrocytes. This inhibition, in turn, reduced toxic cytokine production protected the brain.
In the ICH model, CD68, a lysosome marker essential to cell metabolism, and active microglia were observed near the injury site 24 hours after the hemorrhage and were increased significantly at 72 hours. In contrast, the pinocembrin group showed a significantly reduced number of CD68-positive microglia at both time points in comparison to that of the control group. Pinocembrin also suppressed inflammatory signaling proteins, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6, which are toxic to the brain. Finally, the ICH study suggested that inhibition of the toll-like receptor (TLR) 4 signaling pathway, the major toxic and proinflammatory signaling pathway, might be the major mechanism by which pinocembrin promotes neuroprotection. Six hours after ICH, analysis showed elevated levels of TLR4 and its downstream molecules, MyD88 and TRIF: the two adapters that propagate TLR4 signaling cascades.
This finding indicates the presence of a local immune response that may cause secondary brain damage. Additional experiments showed that at 24 hours, application of pinocembrin reduced TLR4 and the expression of associated TLR4 downstream proteins, affirming its neuroprotective property. The neuroprotective effect was not present in microglia-depleted mice or in mice that lacked TLR4. Together, the two studies indicate that pinocembrin improves early outcomes after ICH and TBI through a variety of pathways.
In summary, pinocembrin is a promising drug candidate for treating ICH and TBI. These findings are described in two articles recently published in the journal Brain, Behavior, and Immunity in 2017.1,2 The potential application of pinocembrin to other diseases was described in a review article published in the journal Molecular Neurobiology in 2016. This work was conducted by Drs. Xi Lan, Wenzhu Wang, Jinyuan Zhou, Jian Wang, and others and was supported by grants from the National Institutes of Health, Johns Hopkins University, and the American Heart Association.
- Lan X, Han X, Li Qian, Li Qiang, Gao Y, Cheng T, Wan J, Zhu W, Wang J. Pinocembrin protects intracerebral hemorrhagic brain primarily by inhibiting toll-like receptor 4 and reducing M1 phenotype microglia. Brain Behav Immun 2017; 61: 326–339. PMCID: PMC5453178
- Wang W, Zhang H, Lee DH, Yu J, Cheng T, Hong M, Jiang S, Fan H, Huang X, Zhou J, Wang J. Using functional and molecular MRI techniques to detect neuroinflammation and neuroprotection after traumatic brain injury. Brain Behav Immun 2017; 64: 344–353. PMCID: PMC5572149
- Lan X, Wang W, Li Q, Wang J. The natural flavonoid pinocembrin: molecular targets and potential therapeutic applications. Mol Neurobiol 2016; 53: 1794–1801. PMCID: PMC4561606