Elucidation of the Mechanisms By Which Anesthetics Induce Blood-Brain Barrier Breakdown and Delirium in the Elderly

Delirium is a highly prevalent neuropsychiatric or neurocognitive disorder that presents a major problem to modern healthcare. Patients suffering from delirium normally have a worse prognosis, prolonged hospital stay, increased hospital cost, long-term cognitive impairment, and higher mortality rates. Many factors can predispose one to develop delirium, which makes treating this disorder a daunting task. Unfortunately, delirium is the most common psychiatric syndrome found in the hospital setting. In fact, a form of delirium known as postoperative delirium (POD) is one of the most common postoperative complications faced by elderly patients undergoing surgery. POD is a major problem in modern healthcare, and it will only become worse because the world’s older population (65+) is projected to triple between 2009 and 2050. This realization caused POD to emerge as an area of research interest. Many precipitating factors can cause one to develop POD, including exposure to anesthetics. Studies have indicated that many patients who were given general anesthesia have developed delirium; however, no studies have explained the mechanism by which anesthesia induces POD in patients. Unraveling this mechanism is the main goal of the research being presented here. Our lab has hypothesized that POD is caused by a temporary, anesthesia- or drug-induced breakdown of the blood-brain barrier (BBB). The BBB, which is formed by the vascular endothelium in the brain, is a highly selective barrier that separates the circulating blood from the brain and prevents a large number of substances from entering the brain. We believe that BBB breakdown after exposure to anesthetics allows an influx of plasma components into the brain tissue that disrupts brain homeostasis and causes neuronal misfiring. In the short-term, this culminates into the array of symptoms that hallmark POD. In the long-term, if not reversed or only partially reversed, this could trigger subsequent Postoperative Cognitive Decline (POCD) and Dementia. A preliminary anesthesia study conducted in our lab revealed that exposure to the inhalation anesthetics (IAs) Sevoflurane and Isoflurane causes immediate structural changes in brain vascular endothelial cells (BVECs), including an overall flattening of surface membranes and loss of the tight junction ridge. These structural changes can lead to the formation of holes in the vascular endothelial lining. This study also revealed that exposure to Sevoflurane leads to an increase in BBB permeability. A subsequent study revealed that Sevoflurane increases BBB permeability in preadolescent and elderly rats, age-dependent changes occur in the luminal surface topography of brain vascular endothelial cells associated with development and maintenance of the BBB, and Sevoflurane and Isoflurane induce changes in BVEC luminal surface topography that may be linked to increased BBB permeability. In vitro experiments using a human brain endothelial cell line (hCMEC/D3) that can form a BBB-like barrier yielded the following results: (1) hCMEC/D3 cells express tight junction proteins, (2) transendothelial electrical resistance (TEER) decreases and barrier permeability increases after hCMEC/D3 cells are exposed to anesthesia, (3) the distribution and expression of the tight junction protein ZO-1 in hCMEC/D3 cells is not affected by exposure to anesthesia, (4) addition of DMSO or floating cells to the cell culture medium does not aid the transfer of anesthetics from the air to the cell monolayer, and (5) Histamine and Acetaminophen induce contraction in hCMEC/D3 cells, which can compromise barrier functional integrity. Finally, studies on the effects of the specialized pro-resolving lipid mediator (SPM) Lipoxin in resolving BBB insults revealed the following: (1) bacterial lipopolysaccharide (LPS) injections led to an increase in BBB permeability, as evidenced by detecting IgG, a serum component normally restricted to blood vessels, in rat brain tissue. (2) Lipoxin reduces LPS-induced BBB permeability, as evidenced by decreased levels of IgG in rat brain tissue. (3) LPS induces a number of luminal surface changes in rat BVECs, as shown by scanning electron microscopy. (4) Lipoxin helps restore key luminal surface features of rat BVECs to near normal, and most importantly, blocks the death of BVECs and the associated loss of barrier integrity