Lab Barrier Models Show Serum Protein Binding Shapes Antiviral Entry into the Brain

Researchers have reported that serum protein concentration strongly influences how antiviral drugs move across the two major barriers guarding the central nervous system, according to a study published in Cellular and Molecular Neurobiology. The work, led by Johid R. Malik and Sean N. Avedissian with a multi-institution team, used complementary in vitro models of the blood–brain barrier (BBB) and the blood–cerebrospinal fluid barrier (BCSFB) to test the permeability of nine antiviral agents under both low and high serum conditions.

The BBB and BCSFB are dynamic neurovascular interfaces that maintain central nervous system homeostasis by tightly regulating paracellular and transcellular molecular transport. Intercellular communication between adjacent cells is critical for maintaining barrier function, and serum protein binding is a key factor influencing how much of a drug ultimately penetrates the CNS. Because these interactions are difficult to disentangle in whole organisms, the team argued that accurate human cell-based models offer valuable alternatives to animal-based systems for screening CNS-targeted drugs.

The study built on the group’s previously published human primary cell-based BBB model. Barrier integrity in the current experiments was confirmed using transepithelial electrical resistance (TEER) measurements and FITC-dextran permeability assays, ensuring that observed drug movement reflected a functioning barrier rather than a leaky monolayer.

The central finding concerned the effect of serum conditions. Under high serum conditions, antivirals with extensive protein binding, such as dolutegravir and efavirenz, demonstrated significantly reduced permeability across both barrier models.

Importantly, the permeability profiles generated in the models were fairly consistent with reported higher clinical cerebrospinal fluid concentrations for drugs that exhibit low protein binding. In other words, the in vitro systems did not merely rank compounds in the abstract; they reproduced patterns of CNS antiviral penetration that have been observed clinically, which the authors describe as clinically relevant.

The study also examined transporter biology in astrocytes exposed to antiviral drugs. Astrocytes exposed to dolutegravir and emtricitabine showed upregulation of the ATP-binding cassette transporters multidrug resistance protein (MRP1) and P-glycoprotein, while lacking breast cancer resistant protein (BCRP) and MRP4 transporters.

According to the authors, their validated in vitro BBB and BCSFB models reproduce clinically relevant patterns of CNS antiviral penetration. With further optimization, they write, these systems can provide reliable, human-relevant platforms for preclinical CNS drug screening and align with current efforts to reduce animal use in biomedical research.

The findings carry the usual scope of an in vitro study. The models capture barrier transport and selected transporter responses in isolated human cell systems, and the authors themselves position the platforms as tools that require further optimization before broader preclinical use. The work is published as an open-access article, released early as a peer-reviewed, accepted version that is citable and carries a permanent DOI, subject to further edits before the final Version of Record.

For researchers studying why some antiviral therapies reach the brain and cerebrospinal fluid poorly, the study offers a controlled experimental framework in which serum protein concentration, barrier type and drug binding can be varied systematically. The reported results suggest that protein binding is a decisive variable in whether highly bound antivirals such as dolutegravir and efavirenz cross the BBB and BCSFB, and that human primary cell-based barrier models can reflect that reality well enough to support early-stage drug screening.

Subject of Research: In vitro blood–brain and blood–CSF barrier models for evaluating antiviral drug CNS penetration under different serum protein conditions.

Article Title: Evaluation of Antiviral Drugs’ Central Nervous System Distribution Using In Vitro Blood–Brain and Blood-CSF Barrier Models: The Impact of Serum Protein Concentration

Article References: Malik, J. R., Modebelu, U. O., Fletcher, C. V., Byrareddy, S. N., Anand, R. K., Zhang, T., Le, J., Märtson, A.-G., Brown, A. N., Neely, M. N., Rhodes, N. J., & Avedissian, S. N. (2026). Evaluation of Antiviral Drugs’ Central Nervous System Distribution Using In Vitro Blood–Brain and Blood-CSF Barrier Models: The Impact of Serum Protein Concentration. Cellular and Molecular Neurobiology. https://doi.org/10.1007/s10571-026-01829-0

Image Credits: AI Generated

DOI: 10.1007/s10571-026-01829-0

Keywords: blood–brain barrier, blood–CSF barrier, antiviral drugs, serum protein binding, CNS penetration, dolutegravir, efavirenz, in vitro models, drug transporters, TEER, neuropharmacology, drug screening