Inhibition of homogenous formation of calcium carbonate by poly (acrylic acid). The effect of molar mass and end-group functionality

The ability of poly(acrylic acid) (PAA) with different end groups and molar masses prepared by Atom Transfer Radical Polymerization (ATRP) to inhibit the formation of calcium carbonate scale at low and elevated temperatures was investigated. Inhibition of CaCO3 deposition was affected by the hydrophobicity of the end groups of PAA, with the greatest inhibition seen for PAA with hydrophobic end groups of moderate size (6–10 carbons). The morphologies of CaCO3 crystals were significantly distorted in the presence of these PAAs. The smallest morphological change was in the presence of PAA with long hydrophobic end groups (16 carbons) and the relative inhibition observed for all species were in the same order at 30 °C and 100 °C. As well as distorting morphologies, the scale inhibitors appeared to stabilize the less thermodynamically favorable polymorph, vaterite, to a degree proportional to their ability to inhibit precipitation.

Inhibition of integrative cartilage repair by proteoglycan 4 in synovial fluid

To determine the effects of the articular cartilage surface, as well as synovial fluid (SF) and its components, specifically proteoglycan 4 (PRG4) and hyaluronic acid (HA), on integrative cartilage repair in vitro. Methods. Blocks of calf articular cartilage were harvested, some with the articular surface intact and others without. Some of the latter types of blocks were pretreated with trypsin, and then with bovine serum albumin, SF, PRG4, or HA. Immunolocalization of PRG4 on cartilage surfaces was performed after treatment. Pairs of similarly treated cartilage blocks were incubated in partial apposition for 2 weeks in medium supplemented with serum and 3 H-proline. Following culture, mechanical integration between apposed cartilage blocks was assessed by measuring adhesive strength, and protein biosynthesis and deposition were determined by incorporated 3 H-proline. Results. Samples with articular surfaces in apposition exhibited little integrative repair compared with samples with cut surfaces in apposition. PRG4 was immunolocalized at the articular cartilage surface, but not in deeper, cut surfaces (without treatment). Cartilage samples treated with trypsin and then with SF or PRG4 exhibited an inhibition of integrative repair and positive immunostaining for PRG4 at treated surfaces compared with normal cut cartilage samples, while samples treated with HA exhibited neither inhibited integrative repair nor PRG4 at the tissue surfaces. Deposition of newly synthesized protein was relatively similar under conditions in which integration differed significantly. Conclusion. These results support the concept that PRG4 in SF, which normally contributes to cartilage lubrication, can inhibit integrative cartilage repair. This has the desirable effect of preventing fusion of apposing surfaces of articulating cartilage, but has the undesirable effect of inhibiting integrative repair.

Paradoxical enhancement of fear extinction memory and synaptic plasticity by inhibition of the histone acetyltransferase p300

It is well established that the coordinated regulation of activity-dependent gene expression by the histone acetyltransferase (HAT) family of transcriptional coactivators is crucial for the formation of contextual fear and spatial memory, and for hippocampal synaptic plasticity. However, no studies have examined the role of this epigenetic mechanism within the infralimbic prefrontal cortex (ILPFC), an area of the brain that is essential for the formation and consolidation of fear extinction memory. Here we report that a postextinction training infusion of a combined p300/CBP inhibitor (Lys-CoA-Tat), directly into the ILPFC, enhances fear extinction memory in mice. Our results also demonstrate that the HAT p300 is highly expressed within pyramidal neurons of the ILPFC and that the small-molecule p300-specific inhibitor (C646) infused into the ILPFC immediately after weak extinction training enhances the consolidation of fear extinction memory. C646 infused 6 h after extinction had no effect on fear extinction memory, nor did an immediate postextinction training infusion into the prelimbic prefrontal cortex. Consistent with the behavioral findings, inhibition of p300 activity within the ILPFC facilitated long-term potentiation (LTP) under stimulation conditions that do not evoke long-lasting LTP. These data suggest that one function of p300 activity within the ILPFC is to constrain synaptic plasticity, and that a reduction in the function of this HAT is required for the formation of fear extinction memory.

Inhibition of myeloperoxidase- and neutrophil-mediated oxidant production by tetraethyl and tetramethyl nitroxides

The powerful oxidant HOCl (hypochlorous acid and its corresponding anion, −OCl) generated by the myeloperoxidase (MPO)–H2O2–Cl− system of activated leukocytes is strongly associated with multiple human inflammatory diseases; consequently there is considerable interest in inhibition of this enzyme. Nitroxides are established antioxidants of low toxicity that can attenuate oxidation in animal models, with this ascribed to superoxide dismutase or radical-scavenging activities. We have shown (M.D. Rees et al., Biochem. J. 421, 79–86, 2009) that nitroxides, including 4-amino-TEMPO (4-amino-2,2,6,6-tetramethylpiperidin-1-yloxyl radical), are potent inhibitors of HOCl formation by isolated MPO and activated neutrophils, with IC50 values of ~1 and ~6 µM respectively. The utility of tetramethyl-substituted nitroxides is, however, limited by their rapid reduction by biological reductants. The corresponding tetraethyl-substituted nitroxides have, however, been reported to be less susceptible to reduction. In this study we show that the tetraethyl species were reduced less rapidly than the tetramethyl species by both human plasma (89–99% decreased rate of reduction) and activated human neutrophils (62–75% decreased rate). The tetraethyl-substituted nitroxides retained their ability to inhibit HOCl production by MPO and activated neutrophils with IC50 values in the low-micromolar range; in some cases inhibition was enhanced compared to tetramethyl substitution. Nitroxides with rigid structures (fused oxaspiro rings) were, however, inactive. Overall, these data indicate that tetraethyl-substituted nitroxides are potent inhibitors of oxidant formation by MPO, with longer plasma and cellular half-lives compared to the tetramethyl species, potentially allowing lower doses to be employed.

Inhibition of myeloperoxidase-mediated hypochlorous acid production by nitroxides

Tissue damage resulting from the extracellular production of HOCl (hypochlorous acid) by the MPO (myeloperoxidase)-hydrogen peroxide-chloride system of activated phagocytes is implicated as a key event in the progression of a number of human inflammatory diseases. Consequently, there is considerable interest in the development of therapeutically useful MPO inhibitors. Nitroxides are well established antioxidant compounds of low toxicity that can attenuate oxidative damage in animal models of inflammatory disease. They are believed to exert protective effects principally by acting as superoxide dismutase mimetics or radical scavengers. However, we show here that nitroxides can also potently inhibit MPO-mediated HOCl production, with the nitroxide 4-aminoTEMPO inhibiting HOCl production by MPO and by neutrophils with IC50 values of approx. 1 and 6 μM respectively. Structure–activity relationships were determined for a range of aliphatic and aromatic nitroxides, and inhibition of oxidative damage to two biologically-important protein targets (albumin and perlecan) are demonstrated. Inhibition was shown to involve one-electron oxidation of the nitroxides by the compound I form of MPO and accumulation of compound II. Haem destruction was also observed with some nitroxides. Inhibition of neutrophil HOCl production by nitroxides was antagonized by neutrophil-derived superoxide, with this attributed to superoxide-mediated reduction of compound II. This effect was marginal with 4-aminoTEMPO, probably due to the efficient superoxide dismutase-mimetic activity of this nitroxide. Overall, these data indicate that nitroxides have considerable promise as therapeutic agents for the inhibition of MPO-mediated damage in inflammatory diseases.

Effect of poly(acrylic acid) end-group functionality on inhibition of calcium oxalate crystal growth

A number of series of poly(acrylic acids) (PAA) of differing end-groups and molecular weights prepared using atom transfer radical polymerization were used as inhibitors for the crystallization of calcium oxalate at 23 and 80°C. As measured by turbidimetry and conductivity and as expected from previous reports, all PAA series were most effective for inhibition of crystallization at molecular weights of 1500–4000. However, the extent of inhibition was in general strongly dependent on the hydrophobicity and molecular weight of the end-group. These results may be explicable in terms of adsorption/desorption of PAA to growth sites on crystallites. The overall effectiveness of the series didn't follow a simple trend with end-group hydrophobicity, suggesting self-assembly behavior or a balance between adsorption and desorption rates to crystallite surfaces may be critical in the mechanism of inhibition of calcium oxalate crystallization.

Effect of group formation on performance, task management and social loafing

Engineering graduates of today are required to adapt to a rapidly changing work environment. In particular, they are expected to demonstrate enhanced capabilities in both mono-disciplinary and multi-disciplinary teamwork environments. Engineering education needs, as a result, to further focus on developing group work capabilities amongst engineering graduates. Over the last two years, the authors trialed various group work strategies across two engineering disciplines. In particular, the effect of group formation on students' performance, task management, and social loafing was analyzed. A recently developed online teamwork management tool, Teamworker, was used to collect students' experience of the group work. Analysis showed that students who were allowed to freely allocate to any group were less likely to report loafing from other team members, than students who were pre-allocated to a group. It also showed that performance was more affected by the presence or absence of a leader in pre-allocated rather than free-allocated groups.