Cold-inflammaging: When a state of homeostatic-imbalance associated with aging precedes the low-grade pro-inflammatory-state (inflammaging): Meaning, evolution, inflammaging phenotypes.

ABSTRACT

The age-related pro-inflammatory state, discovered and called 'inflammaging' by Franceschi et al. (2000) plays an important role in the pathogenesis of age-related chronic diseases. A substantial body of data established that inflammaging is accompanied by a '2-fold to 4-fold' increase in plasma levels of pro-inflammatory mediators in healthy elderly people, when compared to the healthy adult population. This review focuses on the pre-inflammaging phase, here we reported as 'cold-inflammaging', a state where plasma levels of cytokines are slightly increased, but below the lower limit of 2-fold increase established for inflammaging. Slightly altered cytokine levels by innate immunity are known to be associated with homeostasis imbalances, this functional pleiotropy of cytokines as signal transducers, have a physiological counterpart, representing an adaptive process aimed at restoring (or achieving a new) homeostatic stability. If a dyshomeostatic state persists, the cytokine response by innate immunity increases and becomes a driver of inflammaging. A scenario where cytokines are characterised as major players in homeostasis imbalances at the beginning (cold-inflammaging) and then in chronic low-grade pro-inflammatory-state (inflammaging). Other important drivers of inflammaging are cellular senescence with its senescence-associated secretory phenotype, the altered gut microbiota, and the age-related dysregulation in the production of endogenous molecular waste (Garb-aging). The main purpose of this review being to thoroughly investigate each step of the pathway from cold-inflammaging to overt-inflammaging, because aging, cold-inflammaging, overt-inflammaging and the pathogenesis of age-related diseases have been shown to share some established basic pillars of geroscience that largely converge on inflammaging.