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Complex Regional Pain Syndrome (CRPS) occurs in about 2% of patients after fracture of the limbs. In an earlier clinical study with 102 probands we have shown that the serum protease network in CRPS might be less effective. Based on these results we hypothesized that angiotensin-converting enzyme (ACE) and carboxypeptidase N (CPN) activity contribute to the differences of labeled bradykinin (DBK) degradation by patients' sera. Details of the enzymatic processes remained however unclear. The contributions of ACE and CPN in the serum degradation of DBK were studied using specific inhibitors. CPN1-ELISA was performed in serum. It was confirmed that the majority of DBK was degraded by ACE and CPN. The data delivered proof that the ACE serum activity was lowered in CRPS. High-resolution mass spectrometry was additionally used for protein expression analysis of sera of above study cohort (CRPS vs. healthy probands). According to principal component analysis of these data, significant differences between CRPS and control samples only occurred in sera of females younger than 46 years. In these CRPS patients, a number of defence / immunity-related proteins and members of the renin-angiotensin system (RAS) protein network were regulated. The impact of CPN in CRPS pathophysiology is subject to further investigation. The data support the hypothesis that both the RAS and the innate immune system might be affected in CRPS. A database of regulated serum proteins was established for future research., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Abstract: It has been proposed that complex regional pain syndrome (CRPS) is a posttraumatic autoimmune disease. Previously, we observed that B cells contribute to CRPS-like changes in a mouse tibia fracture model, and that early (<12 months duration) CRPS patient IgM antibodies have pronociceptive effects in the skin and spinal cord of muMT fracture mice lacking B cells. The current study evaluated the pronociceptive effects of intraplantar or intrathecal injections of early CRPS IgM (5 µg) in muMT fracture mice. Skin and lumbar spinal cord were collected for immunohistochemistry and polymerase chain reaction analyses. Wild-type mice exhibited postfracture increases in complement component C5a and its receptor expression in skin and spinal cord, predominantly on dermal macrophages and spinal microglia. Intraplantar IgM injection caused nociceptive sensitization in muMT fracture mice with increased complement component C1q and inflammatory cytokine expression, and these IgM effects were blocked by a C5a receptor antagonist (PMX53) or a global cytokine inhibitor (pentoxifylline). Intrathecal IgM injection also had pronociceptive effects with increased spinal cytokine expression, effects that were blocked by PMX53 or pentoxifylline treatment. Intrathecal injection of chronic (>12 months duration) CRPS patient IgM (but not IgG) caused nociceptive sensitization in muMT fracture mice, but intraplantar injection of chronic CRPS IgM or IgG had no effect. We postulate that CRPS IgM antibodies bind to neoantigens in the fracture limb skin and corresponding spinal cord to activate C5a complement signaling in macrophages and microglia, evoking proinflammatory cytokine expression contributing to nociceptive sensitization in the injured limb., (Copyright © 2021 Written work prepared by employees of the Federal Government as part of their official duties is, under the U.S. Copyright Act, a “work of the United States Government” for which copyright protection under Title 17 of the United States Code is not available. As such, copyright does not extend to the contributions of employees of the Federal Government.)

It has been proposed that complex regional pain syndrome (CRPS) is a post-traumatic autoimmune disease. Previously, we observed that B cells are required for the full expression of CRPS-like changes in a mouse tibia fracture model and that serum immunoglobulin M (IgM) antibodies from fracture mice have pronociceptive effects in muMT fracture mice lacking B cells. The current study evaluated the pronociceptive effects of injecting CRPS patient serum or antibodies into muMT fracture mice by measuring hind paw allodynia and unweighting changes. Complex regional pain syndrome serum binding was measured against autoantigens previously identified in the fracture mouse model. Both CRPS patient serum or IgM antibodies had pronociceptive effects in the fracture limb when injected systemically in muMT fracture mice, but normal subject serum and CRPS patient IgG antibodies had no effect. Furthermore, CRPS serum IgM antibodies had pronociceptive effects when injected into the fracture limb hind paw skin or intrathecally in the muMT fracture mice. Early (1-12 months after injury) CRPS patient (n = 20) sera were always pronociceptive after systemic injection, and chronic (>12 months after injury) CRPS sera were rarely pronociceptive (2/20 patients), while sera from normal subjects (n = 20) and from patients with uncomplicated recoveries from orthopedic surgery and/or fracture (n = 15) were never pronociceptive. Increased CRPS serum IgM binding was observed for keratin 16, histone 3.2, gamma actin, and alpha enolase autoantigens. We postulate that CRPS patient IgM antibodies bind to neoantigens in the fracture mouse skin and spinal cord to initiate a regionally restricted pronociceptive complement response potentially contributing to the CRPS disease process.

Complex regional pain syndrome (CRPS) develops after fracture. The acute CRPS phenotype resembles exaggerated inflammation, which is explained by local and systemic activation of a proinflammatory network including peptides and cytokines. Epidemiologic data suggest that inactivation of the peptidase angiotensin-converting enzyme in patients treated for hypertension increases the odds to develop CRPS. This hint leads us to investigate the serum protease network activity in patients with CRPS vs respective controls. For this purpose, we developed a dabsyl-bradykinin (DBK)-based assay and used it to investigate patients with CRPS, as well as healthy and pain (painful diabetic neuropathy [dPNP]) controls. The major result is that the degradation of DBK to fragments 1-8 and 1-5 in healthy control and dPNP is shifted to higher values for DBK1-8 and lower values for DBK1-5 at 1 hour of incubation in patients with CRPS. Using this novel reporter peptide assay, we have been able to show that the resolving protease network for mediators such as BK might be different in patients with CRPS; having a look at the clinical signs, which resemble inflammation, this resolving protease network is probably less effective in CRPS.

Wound infection in burns is a relevant cause of morbidity and mortality in children. We aimed to determine the relationship between antibacterial chemotherapy and Gram-negative burn wound colonization and infection. All children admitted to the pediatric intensive care unit for burn trauma from June 1, 2005 to January 31, 2013 were included. We obtained 141 wound samples, of which 88 (65.7%) showed growth of Gram-positive bacteria. Treatment with antimicrobial chemotherapy was necessary in 23 (31.1%) patients. The proportion of Gram-negative isolates seems to increase linear from 12.5% (95% confidence interval (CI): 4.4%-28.7%) without antibacterial chemotherapy to 36.8% (95% CI: 25.5%-49.6%) with one to 48.9% (95% CI: 35.3%-62.8%) with 2 antimicrobial agents. The Odds ratio for a Gram-negative isolate, in comparison to patients without antibacterial chemotherapy, increased from 4.083 (95% CI: 1.140-15.961) for one administered substance to 6.708 (95% CI: 1.832-26.786) if 2 or more were used., Conclusion: We found that antibacterial chemotherapy seems to facilitate burn wound colonization and results in an increased number of gram-negative isolates from children with burn wounds., Competing Interests: Interessenkonflikt: Die Autoren erklären hiermit, dass kein Interessenkonflikt besteht., (© Georg Thieme Verlag KG Stuttgart · New York.)