The gut is able to maintain tolerance to microbial and food antigens. The intestine minimizes the number of harmful bacteria by shaping the microbiota through a symbiotic relationship. In healthy human intestine, a constant homeostasis is maintained by the perfect regulation of microbial load and the immune response generated against it. Failure of this balance may result in various pathological conditions. Innate immune sensors, such as Toll-like receptors (TLRs), may be considered an interface among intestinal epithelial barrier, microbiota, and immune system. TLRs pathway, activated by pathogens, is involved in the pathogenesis of several infectious and inflammatory diseases. The alteration of the homeostasis between physiologic and pathogenic bacteria of intestinal flora causes a condition called dysbiosis. The breakdown of homeostasis by dysbiosis may increase susceptibility to inflammatory bowel diseases. It is evident that environment, genetics, and host immunity form a highly interactive regulatory triad that controls TLR function. Imbalanced relationships within this triad may promote aberrant TLR signaling, critically contributing to acute and chronic intestinal inflammatory processes, such as in IBD, colitis, and colorectal cancer. The study of interactions between different components of the immune systems and intestinal microbiota will open new horizons in the knowledge of gut inflammation.

We previously reported that photodynamic therapy (PDT) using Purpurin-18 (Pu-18) induces apoptosis in HL60 cells. Using flow cytometry, two-dimensional electrophoresis coupled with immunodetection of carbonylated proteins and mass spectrometry, we now show that PDT-induced apoptosis is associated with increased reactive oxygen species generation, glutathione depletion, changes in mitochondrial transmembrane potential, simultaneous downregulation of mitofilin and carbonylation of specific proteins: glucoseregulated protein-78, heat-shock protein 60, heat-shock protein cognate 71, phosphate disulphide isomerase, calreticulin, b-actin, tubulin-a-1-chain and enolase-a. Interestingly, all carbonylated proteins except calreticulin and enolase-a showed a pI shift in the proteome maps. Our results suggest that PDT with Pu-18 perturbs the normal redox balance and shifts HL60 cells into a state of oxidative stress, which systematically induces the carbonylation of specific chaperones. As these proteins normally produce a prosurvival signal during oxidative stress, we hypothesize that their carbonylation represents a signalling mechanism for apoptosis induced by PDT.

Due to the bivalent nature of DAMP, it is often difficult to explain the relative role of DAMP in inflammation versus its role in tissue repair. However, this point is crucial as DAMP-related treatments move into clinical practice.

Thiols (RSH) are potent nucleophilic agents, the rates of which depend on the pKa of the sulfhydryl. Unlike compounds having other nucleophile moieties (-OH or -NH(2)), RSH are involved in reactions, such as conjugations, redox and exchange reactions. Although protein SH groups (PSH) react like non-protein thiols (NPSH), the biochemistry of proteins is much more complex for reasons such as steric hindrance, charge distribution and accessibility of PSH to the solvent (protein conformation). The reaction rates and types of end-products of PSH vary a lot from protein to protein. The biological problem is even more complex because in all compartments and tissues, there may be specific competition between thiols (namely between GSH and PSH), regulated by the properties of antioxidant enzymes. Moreover, PSH are divided biologically into essential and non-essential and their respective influence in the various biological systems is unknown. It follows that during phenomena eliciting a prompt thiol response (oxidative stress), the antioxidant PSH response and reaction mechanisms vary considerably from case to case. For example, in spite of a relatively low pKa that should guarantee good antioxidant capacity, PSH of albumin has much less propensity to form adducts with conjugating agents than NPSH; moreover, the structural characteristics of the protein prevent albumin from forming protein disulfides when exposed to oxidants (whereas protein-thiol mixed disulfides are formed in relative abundance). On the other hand, proteins with a relatively high reactivity, such rat hemoglobin, have much greater antioxidant capacity than GSH, but although human hemoglobin has a pKa similar to GSH, for structural reasons it has less antioxidant capacity than GSH. When essential PSH are involved in S-thiolation and S-nitrosation reactions, a similar change in biological activity is observed. S-thiolated proteins are a recurrent phenomenon in oxidative stress elicited by reactive oxygen species (ROS). This event may be mediated by disulfides, that exchange with PSH, or by the protein intermediate sulfenic acid that reacts with thiols to form protein-mixed disulfides. During nitrosative stress elicited by reactive nitrogen species (RNS), depending on the oxygen concentration of the system, nitrosation reactions of thiols may also be accompanied by protein S-thiolation. In this review we discuss a number of cell processes and biochemical modifications of enzymes that indicate that S-thiolation and S-nitrosation may occur simultaneously in the same protein in the presence of appropriate interactions between ROS and RNS.

No abstract