Blood-brain barrier dysfunction in status epileptics: Mechanisms and role in epileptogenesis

Central nervous system diseases associated with blood brain barrier breakdown - A Comprehensive update of existing literatures

Blood vessels that supply and feed the central nervous system (CNS) possess unique and exclusive properties, named as blood–brain barrier (BBB). It is responsible for tight regulation of the movement of ions, molecules, and cells between the blood and the brain thereby maintaining controlled chemical composition of the neuronal milieu required for appropriate functioning. It also protects the neural tissue from toxic plasma components, blood cells and pathogens from entering the brain. In this review the importance of BBB and its disruption causing brain pathology and progression to different neurological diseases like Alzheimer’s disease (AD), Parkinson’s disease (PD), Amyotrophic lateral sclerosis (ALS), Huntington’s disease (HD) etc. will be discussed.

Midazolam and isoflurane combination reduces late brain damage in the paraoxon-induced status epilepticus rat model

Organophosphates (OPs) are widely used as pesticides and have been employed as warfare agents. OPs inhibit acetylcholinesterase, leading to over-stimulation of cholinergic synapses and can cause status epilepticus (SE). OPs poisoning can result in irreversible brain damage and death. Despite termination of SE, recurrent seizures and abnormal brain activity remain common sequelae often associated with long-term neural damage and cognitive dysfunction. Therefore, early treatment for prevention of seizures is of high interest. Using a rat model of paraoxon poisoning, we tested the efficacy of different neuroprotective and anti-epileptic drugs (AEDs) in suppressing early seizures and preventing brain damage. Electrocorticographic recordings were performed prior, during and after injection of 4.5 LD₅₀ paraoxon, followed by injections of atropine and toxogonin (obidoxime) to prevent death. Thirty minutes later, rats were injected with midazolam alone or in combination with different AEDs (lorazepam, valproic acid, phenytoin) or neuroprotective drugs (losartan, isoflurane). Outcome measures included SE duration, early seizures frequency and epileptiform activity duration in the first 24 -hs after poisoning. To assess delayed brain damage, we performed T2-weighted magnetic resonance imaging one month after poisoning. SE duration and the number of recurrent seizures were not affected by the addition of any of the drugs tested. Delayed brain injury was most prominent in the septum, striatum, amygdala and piriform network. Only isoflurane anesthesia significantly reduced brain damage. We show that acute treatment with isoflurane, but not AEDs, reduces brain damage following SE. This may offer a new therapeutic approach for exposed individuals.

In Vitro Models of the Blood-Brain Barrier

Knowledge about the transport of active compounds across the blood-brain barrier is of essential importance for drug development. Systemically applied drugs for the central nervous system (CNS) must be able to cross the blood-brain barrier in order to reach their target sites, whereas drugs that are supposed to act in the periphery should not permeate the blood-brain barrier so that they do not trigger any adverse central adverse effects. A number of approaches have been pursued, and manifold in silico, in vitro, and in vivo animal models were developed in order to be able to make a better prediction for humans about the possible penetration of active substances into the CNS. In this particular case, however, in vitro models play a special role, since the data basis for in silico models is usually in need of improvement, and the predictive power of in vivo animal models has to be checked for possible species differences. The blood-brain barrier is a dynamic, highly selective barrier formed by brain capillary endothelial cells. One of its main tasks is the maintenance of homeostasis in the CNS. The function of the barrier is regulated by cells of the microenvironment and the shear stress mediated by the blood flow, which makes the model development most complex. In general, one could follow the credo "as easy as possible, as complex as necessary" for the usage of in vitro BBB models for drug development. In addition to the description of the classical cell culture models (transwell, hollow fiber) and guidance how to apply them, the latest developments (spheroids, microfluidic models) will be introduced in this chapter, as it is attempted to get more in vivo-like and to be applicable for high-throughput usage with these models. Moreover, details about the development of models based on stem cells derived from different sources with a special focus on human induced pluripotent stem cells are presented.