They used 22 protein levels to assess an aging index called SASP:

Here are the 22 proteins:

> As in our previous studies28,30, the 22 proteins included in the SASP index used in the present study are IGFBP-6, IGFBP-2, MIP-1β, IL-1β, GMC-SF, PLGF, Angiogenin, MIF-1, MIP-1α, Gro-α, IL-6, MCP-4, Gp130, ICAM-1, MCP-1, IL-8, MIP-3 α, Osteoprotegerin, TIMP-1, uPAR, TNFRI and TNFRII. The raw values were log transformed and standardized to z scores, and the SASP index for each participant was calculated

> Cellular senescence11 has emerged as a pivotal hallmark of the biology of ageing. It is a complex stress response in which cells irreversibly lose their proliferative capacity, become resistant to apoptosis12 and develop a multicomponent secretory phenotype13, referred to as the senescence-associated secretory phenotype (SASP)12. The SASP includes proteins involved in cycle control, intercellular communication, the immune-inflammatory response and tissue remodelling14. Under non-pathological conditions, SASP proteins are essential for embryonic development and tissue patterning throughout life15. However, the accumulation of senescent cells and the increased secretion of SASP proteins with age is linked to tissue deterioration and the emergence of physical disorders prevalent in older adults16. Human and animal studies found that the increased expression of SASP proteins drives multiple age-related phenotypes, such as atherosclerosis17, osteoarthritis18, cancer19, kidney dysfunction20 and a shortened health span21. In humans, an increase in SASP proteins is related to obesity, cardiometabolic dysregulation22 and frailty14. Several studies characterized the role of cellular senescence and SASP proteins in the brain. Aged microglia, astrocytes and neurons exhibit various features of senescence, including the expression of SASP proteins23,24,25.

> While the cellular source of SASP proteins is unknown, some evidence suggests that the SASP index is relevant to brain health and that brain cells express SASP proteins23,24,25. In ageing and psychiatric disorders, the blood–brain barrier permeability is increased71, leading to an enhanced passage of proteins. Some studies suggest that plasma from old mice accelerates brain ageing in young mice72, and senolytic interventions targeting the periphery alleviate the effect of SASP proteins on the brain71.

Unknown !

Blood brain barrier permeability increased.