Insulin Derived Fibrils Induce Cytotoxicity in vitro and Trigger Inflammation in Murine Models

Background: Effective exogenous insulin delivery is the cornerstone of insulin dependent diabetes mellitus management. Recent literature indicates that commercial insulin-induced tissue reaction and cellular cytotoxicity may contribute to variability in blood glucose as well as permanent loss of injection or infusion site architecture and function. It is well accepted that insulin formulations are susceptible to mechanical and chemical stresses that lead to insulin fibril formation. This study aims to characterize in vitro and in vivo toxicity, as well as pro-inflammatory activity of insulin fibrils. Method: In vitro cell culture evaluated cytotoxicity and fibril uptake by macrophages and our modified murine air-pouch model quantified inflammatory activity. The latter employed FLOW cytometry and histopathology to characterize fibril-induced inflammation in vivo, which included fibril uptake by inflammatory phagocytes. Results: These studies demonstrated that insulin derived fibrils are cytotoxic to cells in vitro. Furthermore, inflammation is induced in the murine air-pouch model in vivo and in response, macrophages uptake fibrils both in vitro and in vivo. Conclusions: Administration of insulin fibrils can lead to cytotoxicity in macrophages. In vivo data demonstrate insulin fibrils to be pro-inflammatory which over time can lead to cumulative cell/tissue toxicity, inflammation, and destructive wound healing. Long term, these tissue reactions could contribute to loss of insulin injection site architecture and function.

The Janus-like role of neuraminidase isoenzymes in inflammation

The processes of activation, extravasation, and migration of immune cells to a site are early and essential steps in the induction of an acute inflammatory response. These events are part of the inflammatory cascade which involves multiple regulatory steps. Using a murine air-pouch model of inflammation with LPS as an inflammation inducer we demonstrate that isoenzymes of the neuraminidase family (NEU1, 3, and 4) play essential roles in this process acting as positive or negative regulators of leukocyte infiltration. Genetically knocked-out (KO) mice for different NEU genes (Neu1 KO, Neu3 KO, Neu4 KO, and Neu3/4 double KO mice) were induced with LPS, leukocytes at the site of inflammation were counted, and the inflamed tissue was analyzed using immunohistochemistry. Our data show that leukocyte recruitment was decreased in NEU1 and NEU3-deficient mice, while it was increased in NEU4-deficient animals. Consistent with these results, systemic levels of pro-inflammatory cytokines and those in pouch exudate were reduced in Neu1 and increased in Neu4 KO mice. We found that pharmacological inhibitors specific for NEU1, NEU3, and NEU4 isoforms also affected leukocyte recruitment. We conclude that NEU isoenzymes have distinct – and even opposing – effects on leukocyte recruitment, and therefore warrant further investigation to determine their mechanisms and importance as regulators of the inflammatory cascade.

Anti-inflammatory effects of DhHP-6 in LPS-induced RAW264.7 macrophages and carrageenan-induced air pouch model in rat

DhHP-6 (Deuterohemin-Ala-His-Thr-Val-Glu-Lys) is a novel peptide mimic of peroxidases that was previously designed in our laboratory. Here, we explored the anti-inflammatory potential of DhHP-6 against lipopolysaccharide(LPS)stimulated inflammatory response in RAW264.7 cells and carrageenan-induced air pouch model rats. DhHP-6 treatment dramatically attenuated the production of nitric oxide (NO), IL-6, andTNF-α in LPS induced RAW264.7 cells. Also, it blocked phosphorylation and degradation of IκBα and suppressed the nuclear translocation of p65. DhHP-6 (0.2, 0.6, and 2.0 mg/kg) significantly reduced the levels of total proteins and WBC counts in the exudates of the air pouch model rats. Moreover, MDA contents in the plasma of rats were reduced and SOD activities were enhanced in the DhHP-6-treatment group. Our results strongly show the effectiveness of DhHP-6 as an anti-inflammatory agent. The mechanism could be related to the reduction of Reactive oxygen species(ROS), inhibition of NF-κB nuclear translocation, and reduction of pro-inflammatory cytokines.

Influence of streptococcal arginine deiminase on the leukocyte infiltration in murine air pouch model

Numerous pathogens express arginine deiminase, an enzyme that catalyzes the hydrolysis of L-arginine in a chain of biochemical reactions aimed at the synthesis of ATP in bacterial cells. L-arginine is a semi-essential, proteinogenic amino acid that plays an important role in regulating the functions of the immune system cells in mammals. Depletion of L-arginine may cause a weakening of the immune reaction. In order to improve the conditions of dissemination, many pathogens use a strategy of L-arginine depletion in the microenvironment of host cells. Bacterial arginine deiminase can be a pathogenicity factor aimed for dysregulating the processes of inflammation and immune response. In general, the effect of arginine deiminase on immune cells may result into disturbed production of regulatory proinflammatory molecules, such as NO, and related substances, inhibition of activation, migration and differentiation of individual leukocyte subsets. The aim of this study was to investigate the effect of arginine deiminase on the formation of inflammatory infiltrate in murine air pouch model of streptococcal infection. Materials and methods: The study was performed using S. pyogenes M49-16 expressing arginine deiminase and its isogenic mutant S. pyogenes M49-16delArcA with inactivated arginine deiminase gene. The flow cytometry analysis of the inflammatory infiltrate leukocytes subpopulation in mice infected with the original strain of S. pyogenes M49-16 and its isogenic mutant S. pyogenes M49-16delArcA at different periods of infection was performed. It was shown that the inflammation reached its peak 6 hours after streptococcal inoculation, being more pronounced in mice infected with the mutant strain. Тhis finding was affirmed by a simultaneous and more pronounced increase in the absolute numbers of all leukocyte subsets in the focus of inflammation in this group of mice when compared to mice infected with original bacterial strain. Despite the decrease in the absolute number of all leukocyte types in the inflammatory infiltrate in both groups of mice for 24 hours, this trend was more pronounced in the group of mice infected with mutant microbial strain. Comparison of the inflammatory infiltrates developing in mice infected with original versus mutant strains showed that arginine deiminase may be a pathogenicity factor leading to dysregulation of protective immune response, due to impaired migration of white blood cells to the site of infection.