Introduction
The blood-brain barrier (BBB) describes the anatomical structure which surrounds the endothelial cells of cerebral capillaries (1). Its function is to serve as a selectively permeable barrier for brain parenchyme (2) and this is achieved ordinarily through highly regulated expression of endothelial tight junctions within the paracellular spaces.
A disruption in BBB integrity permits the cerebral extravasation of plasma-borne molecules, which may activate astrocytes and microglia and promote neuroinflammation (3). Chronically exaggerated astrocytosis and microgliosis lead to heightened oxidative stress, which consequently promotes degeneration of neurons (4). Indeed, BBB dysfunction is commonly observed in various neurodegenerative disorders such as Alzheimer's disease and multiple sclerosis, suggesting a causal association (5–8).
Energy drinks are highly caffeinated, carbonated beverages first marketed in Europe and Asia in the 1960's (9). The primary ingredients with popular energy drinks such as Red BullTM, MotherTM, and MonsterTM include caffeine/guarana [~160 mg per serving (375 ml)], remarkable abundance of taurine (~2,000 mg per serving), B6/B12 vitamins (1.0 mg/0.5 μg per serving, respectively), and in sugar-formulated energy drinks (~51 g sucrose per serving).
Recent population studies report significantly accelerating ingestion trends of energy drinks, particularly in young adults (10). Due to their complex formulations, both negative and positive effects on BBB integrity may be realized with regular, significant consumption of energy drinks. Evidence consistent with the latter are findings that energy drinks can have acute hypertensive effects on blood pressure, but paradoxically, hypotensive effects with chronic ingestion (11–17).
Chronic consumption of sugar-formulated energy drinks may also have secondary indirect neurovascular effects, exacerbating hyperglycaemia, insulin resistance (18–22) and neurovascular integrity and neuroinflammation (23–25).
To gain better insight into the potential effects of energy drinks on BBB integrity, in this pilot study, genetically unmanipulated wild-type mice were chronically provided with diluted energy drinks as their sole drinking solution. The putative effects of MotherTM, Sugar-free MotherTM, and Coca-ColaTM (which lacks taurine, B-group vitamins and has substantially less caffeine) were studied in the context of neurovascular integrity and neuroinflammation.
