ICH is a stroke type with a very high mortality rate. Askenase M.H.et al reviewed the four stages of the ICH response. At the beginning, tissue damage activated local inflammation(0–6 Hours), then the BBB was destroyed(~6 Hours), followed by the recruitment of circulating inflammatory cells and subsequent secondary immunopathological changes(12 Hours–7 Days), and finally the response of tissue repair(~72 Hours–?)[16]. Preclinical data suggested that elimination of initial neuroinflammation should be a key step in the treatment of ICH injury. For a long time, researchers have been looking for drugs to reduce inflammation and edema after intracerebral hemorrhage. A recent study experiments demonstrated that activator protein 1 inhibitor SR11302 could reduce the expression of microglial IL-6 and TNF-α and brain-infiltrating leukocytes and thus attenuating inflammation and edema in ICH mice[17]. Another ICH mouse model also showed that treatment with low dosage of siponimod (BAF-312), a selective modulator of sphingosine 1-phosphate receptors type 1 and type 5, could attenuate perihemorrhagic edema and improves survival after ICH injury[18].Our study demonstrates that treatment with NBP can partially relieve the symptoms of intracerebral hemorrhage, including the improvement of neurological outcomes, reduction of brain edema, attenuation of the BBB permeability, also decrease of ICH-induced injured area. The mechanism is to suppress the inflammatory reaction after ICH. The findings of our investigation provide new evidence that NBP may be effective in the treatment of ICH in addition to confirming the previously hypothesized therapeutic effect of NBP on ischemic stroke. To date, there have been few reports on the evaluation of NBP in an ICH model. Our group is the first to show that NBP can reduce inflammation and brain edema in ICH rats.
Brain edema plays an important role in secondary brain injury after ICH[19]. Accumulating data from preclinical and clinical studies suggest that inflammation could be the key mechanism of edema formation after ICH, causing cell swelling and BBB disruption. Previous studies have demonstrated that the inflammatory response could take place in and around the hematoma, with an infiltration of neutrophils, macrophages, and activated microglia[20]. Microglia mediated neuroinflammation plays an important role in the inflammatory injury of intracerebral hemorrhage[21, 22]. It has been reported that other chemical compounds like minocycline, curcumin, and magnolol, can also reduce microglia mediated neuroinflammation in ICH animal models, showing the potential application value in the treatment of intracranial hemorrhage.[15, 22, 23]. Neutrophils or polymorphonuclear leukocytes (PMNs) are the first leukocytes to infiltrate the nervous system after ICH, and could cause direct neurotoxicity to brain tissue and cell swelling by releasing TNF-α, matrix metalloproteinases (MMPs), and other cytokines[3, 24]. TNF-α, which is a pleiotropic cytokine with a diverse range of biological functions, is known for its ability to cause inflammatory reactions. TNF-α appears to be involved in inflammation, BBB, thrombogenesis, and vascular changes associated with brain injury. TNF-α has been shown to upregulate MMP expression, especially MMP-9, in inflammatory reactions. MMP-9 is one of the most important MMPs associated with BBB damage and could lead to an increase in cerebral vessel permeability [11, 25]. MMPs might also cause further damage by stimulating microglia, which could also be activated by thrombin and heme after ICH [26-28]. The main purpose of microglia cell activation is to clear the hematoma, but excessive activation can also result in neurotoxicity to brain tissue by releasing diverse toxic factors such as cytokines, chemokines, proteases, reactive oxygen species (ROS), and heme oxygenase, among others[27, 29]. In brief, intracerebral hemorrhage can cause inflammatory reactions by activating PMNs, microglia, and other cells, which can upregulate the expression of TNF-α, MMP-9, and other inflammatory cytokines, thereby causing BBB destruction and cell swelling and aggravating cerebral edema (Fig. 6).
Despite numerous promising preclinical studies on ICH, only a few experimental approaches are aimed at reducing edema after ICH, and these treatments are limited in terms of their clinical utility [30-36]. Previous studies have shown that NBP has an obvious therapeutic effect on acute ischemic stroke by alleviating the inflammatory response, reducing brain edema [10, 11, 37]. Therefore, to assess the overlapping inflammatory and brain edema pathological mechanisms in ischemic and hemorrhagic stroke, we used an intracerebral hemorrhage model in our study and explored the therapeutic effect of NBP in rats with intracerebral hemorrhage.
In our study, the data showed that treatment with NBP reduced the brain water content after ICH. Consistent with the reduction in cerebral edema, the BBB permeability was also reduced. These data suggest that NBP could reduce brain edema and alleviate BBB disruption after ICH. The T2-weighted images showed that the expanded hematoma volume, which is one of the most important factor enhancing brain injury after ICH[25, 38], was significantly reduced in the NBP group. These images indicated that treatment with NBP post-ICH did not increase the risk of re-bleeding or hematoma enlargement, and might even reduce such risks after ICH.
Compared with the vehicle group, the initial (4h) hemorrhage volume of the NBP group appeared a little bit larger than that of the vehicle group, but there was no statistically significant difference (p >0.05). Previous study showed that NBP has antiplatelet effects, and antiplatelet medicines may increase the risk of intracerebral hemorrhage[39-41]. This was consistent with our results. Moreover, increasing the number of test animals can eliminate the influence of individual differences. However, 48 hours later, the volume of the hemorrhage in the NBP group became a little bit smaller than that in the vehicle group but without statistically significant difference. It was worthwhile pointing out that the enlarged hemorrhage became smaller in the 4-48h period after NBP treatment. In NBP group, the volume of cerebral hemorrhage at 48h was not significantly different from that at 4h, while in the vehicle group, the volume of hemorrhage at 48h was significantly expanded compare with that at 4h. The aggravation of clinical symptoms of intracerebral hemorrhage is related to the expansion of hemorrhagic foci and cerebral edema, and this re-expansion occurs mostly in the early stage[38, 42]. Therefore, the decrease of hematoma expansion after NBP treatment also shows the safety of NBP in ICH treatment.
We also noted that Antihypertensive Treatment of Acute Cerebral Hemorrhage II(ATACH-II)trial found that antihypertensive treatment could reduce hematoma expansion, but had no significant effect on outcome of ICH[43]. Early hematoma enlargement is still an important cause of aggravation and poor prognosis of cerebral hemorrhage[38]. The ATACH-2 trial did not show that the benefit of hypotensive therapy may be related to over hypotension. In addition to the re-expansion of cerebral hemorrhage volume, there may be other factors such as initial lesion size or ICH localization play key roles in recovery. In clinical trials, treatment such as antiplatelet or anticoagulant therapy will affect the outcome of ICH[44]. In our animal model, neurological function tests indicated that NBP contributes to the partial recovery of brain function after ICH injury.
The data from the western blot analysis showed that NBP could inhibit the expression of both TNF-α and MMP-9 protein content around the hematoma, which play key roles in the mechanism of the inflammatory response and edema formation after ICH. The results of this study showed the underlying molecular mechanism of NBP in ICH rats via an inhibitory action on inflammation (Fig. 6). A recent study also confirmed that NBP had an anti-inflammatory properties and thus promote the survival of oligodendrocytes in a mouse cuprizone demyelination model[45]. Decreasing the expression of TNF-α and other inflammatory cytokines could reduce cell swelling and cytotoxic edema after ICH. In addition, reducing the inflammatory response-associated activation of MMP-9 could alleviate the damage to BBB permeability and vasogenic edema that occur after ICH.
Our research providing the potential application value of NBP. However, there are still some limitations in this study. First, our results demonstrated NBP contributes to short term recovery of brain functions at least. A study involving 536 patients with acute cerebral hemorrhage showed that the early stage of cerebral hemorrhage was aggravated by neurological deficit. About 83% of patients have hematoma enlargement in early stage[46]. Clinically, the majority of hematoma enlargement in the early stage of cerebral hemorrhage occurred within 3-24 hours[42]. We investigated the early therapeutic effects of NBP in ICH injury. However, as mentioned above, ICH response lasts for 72 hours or even longer [16]. The extension of investigating period to 72 hours or longer time periods post ICH will help us better track the efficacy of NBP. Second, a previous study showed that after a single oral administration of 100 mg/kg NBP, the highest inhibition rate of NBP on platelets was 56% in the first 2 hours in normal rats[47]. Considering the inhibition of NBP on platelets, we only used a safe low dose of NBP in this investigation. In the follow-up experiment, we will use multiple doses to see whether NBP is dose-dependent on the treatment of ICH. Third, female animals shall be utilized in future studies to address any sex-related differences that may exist. In addition, the therapeutic effects of NBP, which might involve other mechanisms in addition to anti-inflammation, are not fully understood. Therefore, for the future treatment of ICH, further animal studies that focus on the molecular mechanism by selective blockade of the ICH relative pathway are necessary. Finally, previous studies showed that NBP could significantly inhibit platelet activation and might be an effective antiplatelet drug for ischemic stroke [39-41]. Therefore, future preclinical and translational studies are also needed to address the safety effects of NBP for the treatment ICH.