Abnormal inflammatory response to trauma: the paradoxical meaning of the ischaemia-reperfusion phenomenon

Oxidative stress, lipid rafts, and macrophage reprogramming

Oxidant stress, induced under a variety of conditions, is known to lead to the molecular reprogramming of the tissue-fixed macrophage. This reprogramming is associated with an altered response to subsequent inflammatory stimuli, such as lipopolysaccharide (LPS), leading to enhanced liberation of proinflammatory chemokines and cytokines. Due to this altered response, dysregulated immunity ensues, leading to the development of clinical syndromes such as multiple organ dysfunction syndrome (MODS). Although the mechanisms responsible for this altered macrophage activity by oxidant stress remains complex and poorly elucidated, it appears, based on recent research, that early and direct alterations within lipid rafts are responsible. This early and direct interaction with lipid rafts by oxidants leads to the mobilization of annexin VI from lipid raft constructs, leading to the release of calcium. This increased cytosolic concentration of this secondary messenger, in turn, results in the activation of calcium-dependent kinases, leading to further alterations in lipid raft lipids and eventually lipid raft proteins. Due to these lipid raft compositional changes, preassembly of receptor complexes occur, leading to enhanced proinflammatory activation. Within this review, the complexity of oxidant-induced reprogramming within the tissue fixed macrophage as currently understood is explained.

The inflammatory response recapitulates phylogeny through trophic mechanisms to the injured tissue

The post-traumatic local acute inflammatory response is described as a succession of three functional phases of possible trophic significance: 1. Nervous or immediate (ischemia-reperfusion); 2. Immune or intermediate (infiltration by inflammatory and bacterial cells) and 3. Endocrine or late (angiogenesis with regeneration and/or cicatrization). Each of these phases emphasizes the trophic role of the mechanisms in the damaged tissue. Hence, the nervous phase is predominated by nutrition by diffusion; in the immune phase trophism is mediated by inflammatory cells and bacteria and, finally, in the endocrine phase, the blood circulation and oxidative metabolism play the most significant nutritive role. Since these trophic mechanisms are of increasing complexity, progressing from anoxia to total specialization in the use of oxygen to obtain usable energy, it could be speculated that they represent the successive reappearance of the stages that take place during the evolution of life on Earth, from ancient times without oxygen. In this sense, the inflammatory response could recapitulate phylogeny through the successive expression of pathophysiologic mechanisms that have a trophic meaning to the injured tissue.