In a new study, researchers found that organoids (tiny tissue cultures made from human cells that simulate whole organs) known as “mini-brains” can be infected by the COVID-19 virus.
The results suggest that the virus can infect human brain cells.
The research was conducted by a team from two Johns Hopkins University institutions.
Early reports from Wuhan, China, the origin of the COVID-19 pandemic, have suggested that 36% of patients with the disease show neurological symptoms, but it has been unclear whether or not the virus infects human brain cells.
In their study, the researchers demonstrated that certain human neurons express a receptor, ACE2, which is the same one that the SARS-CoV-2 virus uses to enter the lungs.
Therefore, they surmised, ACE2 also might provide access to the brain.
When the researchers introduced SARS-CoV-2 virus particles into a human mini-brain model, the team found—for what is believed to be the first time—evidence of infection by and replication of the pathogen.
The human brain is well-shielded against many viruses, bacteria, and chemical agents by the blood-brain barrier, which in turn, often prevents infections of the brain.
Whether or not the SARS-CoV-2 virus passes this barrier has yet to be shown.
However, it is known that severe inflammations, such as those observed in COVID-19 patients, make the barrier disintegrate.
The impermeability of the blood-brain barrier also can present a problem for drug developers targeting the brain.
The impact of SARS-CoV-2 on the developing brain is another concern raised by the study.
Previous research has shown that the virus crosses the placenta, and embryos lack the blood-brain barrier during early development.
However, the mini-brains—which model the growing human brain—contain the ACE2 receptor from their earliest stages of development.
Therefore, the findings suggest that extra caution should be taken during pregnancy.
The human stem cell-derived mini-brain models—known as BrainSpheres—were developed at the Bloomberg School of Public Health four years ago.
They were the first mass-produced, highly standardized organoids of their kind, and have been used to model a number of diseases, including infections by viruses such as Zika, dengue, and HIV.
One author of the study is Thomas Hartung, M.D., Ph.D., chair for evidence-based toxicology at the Bloomberg School of Public Health.
The study is published in the journal ALTEX: Alternatives to Animal Experimentation.
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