Background: Diabetic foot ulcers are a common diabetic complication leading to alarming figures of amputation, disability, and early mortality. The diabetic glucooxidative environment impairs the healing response, promoting the onset of a 'wound chronicity phenotype'. In 50% of ulcers, these non-healing wounds act as an open door for developing infections, a process facilitated by diabetic patients' dysimmunity. Infection can elicit biofilm formation that worsens wound prognosis. How this microorganism community is able to take advantage of underlying diabetic conditions and thrive both within the wound and the diabetic host is an expanding research field.
Objectives: 1) Offer an overview of the major cellular and molecular derangements of the diabetic healing process versus physiological cascades in a non-diabetic host. 2) Describe the main immunopathological aspects of diabetics' immune response and explore how these contribute to wound infection susceptibility. 3) Conceptualize infection and biofilim in diabetic foot ulcers and analyze their dynamic interactions with wound bed cells and matrices, and their systemic effects at the organism level. 4) Offer an integrative conceptual framework of wound-dysimmunity-infection-organism damage.
Evidence aquisition: We retrieved 683 articles indexed in Medline/PubMed, SciELO, Bioline International and Google Scholar. 280 articles were selected for discussion under four major subheadings: 1) normal healing processes, 2) impaired healing processes in the diabetic population, 3) diabetic dysimmunity and 4) diabetic foot infection and its interaction with the host.
Development: The diabetic healing response is heterogeneous, torpid and asynchronous, leading to wound chronicity. The accumulation of senescent cells and a protracted inflammatory profile with a pro-catabolic balance hinder the proliferative response and delay re-epithelialization. Diabetes reduces the immune system's abilities to orchestrate an appropriate antimicrobial response and offers ideal conditions for microbiota establishment and biofilm formation. Biofilm-microbial entrenchment hinders antimicrobial therapy effectiveness, amplifies the host's pre-existing immunodepression, arrests the wound's proliferative phase, increases localized catabolism, prolongs pathogenic inflammation and perpetuates wound chronicity. In such circumstances the infected wound may act as a proinflammatory and pro-oxidant organ superimposed onto the host, which eventually intensifies peripheral insulin resistance and disrupts homeostasis.
Conclusions: The number of lower-limb amputations remains high worldwide despite continued research efforts on diabetic foot ulcers. Identifying and manipulating the molecular drivers underlying diabetic wound healing failure, and dysimmunity-driven susceptibility to infection will offer more effective therapeutic tools for the diabetic population.
Keywords: Diabetic foot; amputation; biofilms; infections; microbiota.