The second year of the pandemic, I think, finally showed everyone how terrible and dangerous the disease COVID-19 is. This is not an ordinary flu, or even a new strain of it, and certainly not an ordinary cold. So, today there is growing evidence that the new coronavirus is damaging the brain. Recent studies have shown that the coronavirus's attack on the brain can be multifaceted: it can directly attack certain brain cells, reduce blood flow to brain tissue, or trigger the production of immune molecules that can harm brain cells. Moreover, infection with the SARS-CoV-2 coronavirus can cause memory loss, strokes and other unpleasant consequences. The question, according to the researchers, is: "Can we intervene at an early stage of infection to correct these abnormalities in order to avoid long-term problems?" I note that many people were affected - neurological symptoms appeared in 80% of those who were hospitalized with COVID-19. the researchers hope the growing evidence base will point the way to better treatments.
Coronavirus and the brain: what you need to know?
SARS-CoV-2 could have serious consequences: In a recent study, scientists compared images of the brains of people before and after they were diagnosed with COVID-19. The results showed that in some areas of the cerebral cortex there is a loss of gray matter, we talked in more detail here.
In fact, early in the pandemic, researchers suggested that the virus could wreak havoc on the brain by somehow infiltrating it and infecting neurons - the cells responsible for transmitting and processing information. But since then, numerous studies have shown that it is difficult for the virus to penetrate the brain's defense system - the blood-brain barrier - and that it does not necessarily attack neurons in any significant way.
Coronavirus damages the brain, now we know for sure.
And yet, it is becoming clearer how exactly COVID-19 damages the brain. A new study published in the journal Nature has shown that the coronavirus attack on the brain can be multifaceted: it can directly attack certain brain cells, reduce blood flow to brain tissue, or trigger the production of immune molecules that can harm brain cells. Moreover, infection with the SARS-CoV-2 coronavirus can cause memory loss and other serious consequences.
Penetration into the brain
According to experts, one of the ways in which SARS-CoV-2 can gain access to the brain is by passing through the nasal mucosa, which borders the brain. Despite the fact that “there is not a ton of virus in the brain,” this does not mean that it does not infect any cells. Thus, the results of the scientific studies available to date show that the SARS-CoV-2 coronavirus can infect astrocytes, a type of cell that is found in abundance in the brain and has many functions.
“Astrocytes do quite a lot to keep the brain functioning normally, including providing neurons with the nutrients to keep them working,” says Arnold Kriegstein, a neurologist at the University of California, San Francisco.
Before you are bright green cells with many branches and blue nuclei. Astrocytes are stellate cells in the central nervous system that perform many functions, including providing neurons with nutrients.
Interestingly, in another paper published in January, Kriegstein and colleagues reported that SARS-CoV-2 preferentially infects astrocytes (compared to other brain cells). In the course of the work, scientists exposed the brain organelles to the virus - miniature brain-like structures grown from stem cells in a laboratory.
The results showed that SARS-CoV-2 infected astrocytes almost exclusively compared to all other cells present.
Corroborating the lab results, the team said they analyzed brain samples from 26 people who died from COVID-19. Of the five brain cells that showed signs of SARS-CoV-2 infection, 66% of the affected cells were astrocytes.
The authors of the research note that infected astrocytes may explain some of the neurological symptoms associated with COVID-19, especially fatigue, depression and “head fog” - the so-called long-term covid - which includes confusion and forgetfulness.
Given the results so far, scientists want to understand how many brain cells must be infected or damaged in order to cause neurological symptoms. Unfortunately, there is probably no simple answer to this question.
Impaired cerebral circulation
In addition to everything described above, there is evidence that the new coronavirus reduces blood flow to the brain, negatively affecting the functioning of neurons, ultimately killing them. In April, David Attwell, a neuroscientist at University College London, and colleagues published a paper showing evidence that SARS-CoV-2 can influence pericyte behavior.
The coronavirus causes serious damage to the brain.
Pericytes are cells located on small blood vessels called capillaries throughout the body, including the brain. The authors of the scientific work noticed that in hamster brain slices, SARS-CoV-2 blocks the functioning of receptors on the pericytes, causing narrowing of the capillaries in the tissue. Researchers speculate that drugs used to treat hypertension may be helpful in some cases of COVID-19.
There is also growing evidence that some neurological symptoms and damage are the result of an overreaction of the body's immune system following exposure to the coronavirus. Over the past 15 years, it has become clear that in response to infection, some people's immune systems inadvertently produce "autoantibodies" that attack their own tissues.
"It can cause long-term conditions such as optic neuromyelitis, in which people experience symptoms such as loss of vision and weakness in the limbs," the researchers write.
In a review published in May 2010, scientists summarized the evidence that these autoantibodies can cross the blood-brain barrier and contribute to neurological disorders ranging from memory impairment to psychosis.