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.