Blood-labyrinth barrier (BLB) (BLB)

The blood-labyrinth barrier (BLB) is a highly specialized physiological interface that separates the systemic circulation from the fluid-filled compartments of the inner ear, including the cochlea and vestibular system (Shi, 2016). Structurally, it is composed of non-fenestrated endothelial cells connected by tight junctions, pericytes, and a basement membrane, primarily located within the stria vascularis (Nyberg et al., 2019). Its primary biological function is to maintain the unique ionic environment of the endolymph and perilymph, which is essential for the proper transduction of sound and balance signals (Zhu et al., 2020). The BLB also serves a protective role by restricting the entry of toxins, pathogens, and many systemic drugs into the sensitive neural tissues of the ear. Dysfunction of the BLB is implicated in several inner ear disorders, including Meniere's disease, sudden sensorineural hearing loss, and autoimmune inner ear disease (Zhang et al., 2021). From a pharmacological perspective, the BLB presents a significant challenge for drug delivery, as it limits the bioavailability of systemic medications like corticosteroids and antioxidants. Conversely, certain ototoxic drugs, such as cisplatin and aminoglycoside antibiotics, are known to cross or damage the BLB, leading to permanent hearing loss (Belyantseva, 2016).

Other names

Strial blood-labyrinth barrierCochlear blood-barrierInner ear blood-fluid barrierBlood-perilymph barrier

Drugs cross the blood-labyrinth barrier via passive diffusion, carrier-mediated transport, or paracellular transport; localized delivery (e.g., intratympanic) is frequently used to bypass the barrier and increase drug concentration in the inner ear extracellular space (Shi, 2016; Nyberg et al., 2019).