D (heat inactivated) PEG-SOD groups (green) obtained at two weeks after administration of citrate buffer (controls) or streptozotocin (hyperglycemia) (n = 6 animals/group). PEG-SOD and denatured PEG-SOD were administered intraperitoneally at Day 7 after the initial injection for a total duration of seven days. Administration of PEG-SOD largely restored diaphragm force generation in hyperglycemic animals to that of controls, whereas denatured PEG-SOD had no effect; recovery of diaphragm specific force with PEG-SOD was not due to normalization of glucose levels. (P 0.001, *control and hyperglycemic + PEG-SOD groups significantly different compared to ICG-001 site hyperglycemia and hyperglycemia + denatured PEG-SOD groups).analysis). We found that the protective effect of PEG-SOD on force generation in single fibers was observed in all diaphragm fiber types (Figure 5). However, there were no fiber type specific differences in pCa50 values (calcium sensitivity) or N values (Hill coefficient) between control, HG, HG + PEG-SOD and HG + dnPEG-SOD groups. Hyperglycemia significantly decreased Type IIA fiber cross sectional area, which was not restored by administration of PEG-SOD.Contractile protein levels and indices of protein oxidationThere are several mechanisms by which pathological stresses can alter contractile protein function. One possible mechanism is via activation of proteolytic pathways with resultant cleavage and loss of specific contractile elements. A second process is via chemical modification ofcontractile elements through kinase-mediated phosphorylation reactions or sidegroup modifications by reactive species (for example, nitrosylation of tyrosine residues by peroxynitrite or carbonyl PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28388412 formation in response to reaction with ROS species). Moreover, a number of previous studies have shown that oxidative stress in the diaphragm is associated with alterations in diaphragm contractile performance [26,38,39]. To determine if hyperglycemia altered the level of contractile proteins, we measured levels of four proteins known to play key functions in contractile force generation, including actin, actinin, tropomyosin and troponin T (Figure 6). We found that hyperglycemia did not result in depletion of either actin, actinin or tropomyosin but significantly reduced levels of troponin T, one of the key proteins involved in the regulation of crossbridge cycling. We also found that PEG-SOD attenuated this selectiveCallahan and Supinski Critical Care 2014, 18:R88 http://ccforum.com/content/18/3/RPage 9 ofControl Hyperglycemia Hyperglycemia + PEG-SOD Hyperglycemia + denatured PEG-SODSingle Fiber Contractile Force ( Fmax)100 80 60 40 20 0 6.5 6.0 5.5 5.0 2+ pCa (-log[Ca ])Figure 4 PEG-SOD restores hyperglycemia-induced reductions in diaphragm permeabilized single fiber contractile force generation. Force pCa relationships in single permeabilized diaphragm fibers from control (black), hyperglycemia (red), hyperglycemia + PEG-SOD (blue), and hyperglycemia + denatured (heat inactivated) PEG-SOD groups (green) were evaluated at two weeks after administration of citrate buffer (controls) or streptozotocin (hyperglycemia) (n = 6 animals/group). A total of 15 fibers from each animal were assessed (90 fibers/experimental group, total 360 fibers). As shown, PEG-SOD substantially improved the force-pCa relationship in single permeabilized diaphragm fibers from hyperglycemic animals, whereas denatured PEG-SOD had no effect to restore single fiber force generating ca.
