Cognition, Cytokines, Blood–Brain Barrier, and Beyond in COVID-19: A Narrative Review

Numerous studies report cognitive impairment in COVID-19 patients from the acute to post-acute phases, linked to blood inflammation affecting blood-brain barrier (BBB) permeability and causing leakage of glial and neuronal proteins. However, a clear classification of these cognitive deficits and molecular blood events over time is still lacking. This narrative review summarizes the neuropsychological consequences of COVID-19 and evidence of altered cytokines and BBB disruption as potential mediators of cognitive impairment across post-infection phases. Post-COVID-19 cognitive dysfunction appears to follow a temporal course, evolving from acute focal deficits in attention, working memory, and executive function to more persistent multidomain impairments. We reviewed key cytokines released into the blood during COVID-19 infection, including antiviral (IFNγ, CXCL1, CXCL10), inflammatory (IL-1β, IL-2, IL-4, IL-6, IL-7, IL-8, IL-10, GM-CSF, TNFα), and monocyte chemoattractants (MCP1/CCL2, MCP3/CCL7, MIP-1α/CCL3, GM-CSF, G-CSF). This analysis shows that several inflammatory and viral cytokines remain elevated beyond the acute phase and are associated with cognitive deficits, including IL-6, IL-13, IL-8, IL-1β, TNFα, and MCP1 in long-term post-COVID-19 patients. In addition, we examined studies analyzing changes over time in neurovascular unit proteins as biomarkers of BBB disruption, including extracellular matrix proteins (PPIA, MMP-9), astrocytes (S100β, GFAP), and neurons (NFL). These proteins are elevated in acute COVID-19 but generally return to control levels within six months, suggesting BBB restoration. However, in patients followed for over a year, BBB disruption persists only in those with cognitive impairment and is associated with systemic inflammation, with TGFβ as a related biomarker. Although cognitive sequelae can persist for over 12 months after SARS-CoV-2 infection, further studies are needed to investigate long-term neurocognitive outcomes and their link to sustained proinflammatory cytokine elevation and brain impact.