Introduction
The condition hydrocephalus can be distinguished as the dilation of the cerebral ventricles due to an excessive accumulation of cerebrospinal fluid (CSF) (1)–(4). This fluid buildup can be caused by an imbalance between the production and absorption of the CSF within the brain with the root variable etiology, including precursors such as hemorrhage, congenital malformations, and tumors(1),(2),(5). Treatment typically involves the insertion of a shunt system, including a shunt catheter into the brain’s ventricular space to drain excess CSF (6). Shunt failure is one of the highest among all neurological devices with 40-50% requiring revision within the first two years and 80% within 10 years (7),(8). Obstruction of the ventricular catheter accounts for 70% of shunt failures, which makes it the most prevalent failure modality compared to infection, over-drainage, and loculated ventricles (6). The dominant cell types involved in the blocking of these holes are astrocytes and cells of the monocyte-macrophage lineage, suspected to be due to inflammatory stimuli(6),(9),(10).
Posthemorrhagic hydrocephalus (PHH), one of the most common forms of hydrocephalus, is a result of an intraventricular hemorrhage (IVH). In premature infants, IVH is generally a consequence of a germinal matrix hemorrhage (GMH); in adults, IVH can result from an intracerebral hemorrhage (ICH) (11)–(13). The development of PHH in adults begins with an ICH that advances into an IVH in 42-52% of adult patients (11). For neonates born prematurely, 20% develop an IVH or GMH, while 50% of those individuals develop PHH(14). These hemorrhages introduce blood into the CSF, resulting in the disruption of cells of the ventricular zone (VZ) that leads to increased dilation and permeability of the ventricle(2),(14).
In addition to etiology, blood brain barrier (BBB) breakdown from shunt insertion can play a major role in the CSF blood content(10),(15),(16). The BBB, like the ventricular zone, is composed of a layer of ependymal cells held together by tight junctions regulating the movement of molecules, ions, and cells between the blood and the interstitial fluid of the brain (16). Initial insertion of the ventricular catheter is concurrent with the trauma resulting in the disruption of cells, tissue, and blood vessels. This disruption during shunting can cause hemorrhages and edema in the ventricular space (17). Edema reaches a maximum at day one post-surgery while healing of the BBB insult can take two to three weeks resulting in further exposure of the VZ to blood products(15),(17),(18). Disruption of the VZ, following blood exposure, is a result of an overall loss of ependymal cells allowing for increased CSF accumulation and prolonged inflammation(11). Ependymal cell loss can be attributed to cell junction dislocation and neural stem cell (NSC) differentiation impairment creating denuded areas for astrocyte exposure to the blood products (13),(14).
An inflammatory response occurs within the ventricles following the infiltration of blood, which stimulates the activation of astrocytes and microglia (10),(19). This astrocyte and microglia activation is maintained for up to 28 days post shunt insertion(20). Glial activation is a result of various cytokines and growth factors produced by the activated microglia and leads to the rapid proliferation of astrocytes(20)–(22). In response to this activation, an astrocyte layer is created to cover the denuded areas, from loss of ependymal cells, which was shown to increase cellular migration and attachment to the shunt surface (19),(23). Blood within the CSF has been shown, in vivo , to cause an increase in shunt obstruction causing failure making up 34.8% of shunt revisions(24). It has been theorized that the loss of VZ integrity allows for a higher infiltration of astrocytes into the ventricular zone by astrogliosis (14).
The current study aims to investigate the impact of whole blood exposure on mouse astrocyte cells and its direct influence on ventricular shunt catheter obstruction. In this way, we examine the role blood plays on the foreign body response to chronic indwelling shunt catheters. Other studies have shown that the disruption of ependymal layer in the VZ allows for the activation of astrocytes resulting in the infiltration into the ventricular space (25). In this study anin vitro model has been developed to mimic the introduction of blood to the CSF by breaking of the BBB following catheter insertion and the response of astrocytes to this stimulus is evaluated. This 3D model can be applied in various tests to allow for a catheter to be exposed to various stimuli in static culture. We hypothesize that the activation of astrocytes will occur when exposed to blood over a two-week period, representing the healing time of the permeable BBB, and result in an increase of cellular attachment to the surface of the catheter.