Structure, biochemistry and biology of hepoxilins: an update.

Hepoxilins are biologically relevant epoxy-hydroxy eicosanoids synthesized through the 12S-lipoxygenase (12S-LOX) pathway of the arachidonic acid (AA) metabolism. The pathway is bifurcated at the level of 12S-hydroperoxy-eicosatetraenoic acid (12S-HpETE), which can either be reduced to 12S-hydro-eicosatetraenoic acid (12S-HETE) or converted to hepoxilins. The present review gives an update on the biochemistry, biology and clinical aspects of hepoxilin-based drug development. The isolation, cloning and characterization of a rat leukocyte-type 12S-LOX from rat insulinoma RINm5F cells revealed a 12S-LOX possessing an intrinsic 8S/R-hydroxy-11,12-epoxyeicosa-5Z,9E,14Z-trienoic acid (HXA(3)) synthase activity. Site-directed mutagenesis studies on rat 12S-LOX showed that the HXA(3) synthase activity was impaired when the positional specificity of AA was altered. Interestingly, amino acid Leu353, and not conventional sequence determinants Met419 and Ile418, was found to be a crucial sequence determinant for AA oxygenation. The regulation of HXA(3) formation is dependent on the cellular overall peroxide tone. Cellular glutathione peroxidases (cGPxs) compete with HXA(3) synthase for 12S-HpETE as substrate either to reduce to 12S-HETE or to convert to HXA(3), respectively. Therefore, RINm5F cells, which are devoid of GPxs, are capable of converting AA or 12S-HpETE to HXA(3) under basal conditions, whereas cells overexpressing cGPx are unable to do so. HXA(3) exhibits a myriad of biological effects, most of which are associated with the stimulation of intracellular calcium or the transport of calcium across the membrane. The activation of HXA(3)-G-protein-coupled receptors explains many of the extracellular effects of HXA(3), including AA- and diacylglycerol (DAG) release in human neutrophils, insulin secretion in rat pancreatic beta-cells or islets, and synaptic actions in the brain. The availability of stable analogs of HXA(3), termed 10-hydroxy-11,12-cyclopropyl-eicosa-5Z,8Z,14Z-trienoic acid derivatives (PBTs), recently made several animal studies possible and explored the role of HXA(3) as a therapeutic in treatment of diseases. Thus, PBT-3 induced apoptosis in K562 tumour cells and inhibited growth of K562 CML solid tumours in nude mice. HXA(3) inhibited bleomycin-evoked lung fibrosis and inflammation in mice and the raised insulin level in the circulation of rats. At low glucose concentrations (0-3 mm), HXA(3) also stimulated insulin secretion in RINm5F cells through the activation of IRE1alpha, an endoplasmic reticulum-resident kinase. The latter regulates the protein folding for insulin biosynthesis. In conclusion, HXA(3)-mediated signaling may be involved in normal physiological functions, and hepoxilin-based drugs may serve as therapeutics in diseases such as type II diabetes and idiopathic lung fibrosis.

A new approach to chemical modification protocols of Aspergillus niger and sorption of lead ion by fungal species

Biomasses of five fungi species (Aspergillus niger, Penicillium austurianum, Saccharomyces cerevisiae, Mucor arcindloides and Trichoderma reesi were evaluated for their uptake of lead ion from aqueous solution using batch systems. Both dead and live fungal biomasses were comparatively studied for their adsorption efficiencies. The effect of pH as one of the primary factors that influences sorption efficiency of metal ions in solution was also studied. Modification of the fungal biomass with the least sorption capacity was carried out using a four-step procedure. Three different modifying agents under the optimised experimental conditions were used. The percentage uptake of lead ion by fungi species ranged from: Aspergillus niger: 6.71-64.95 percent and 66.91-95.27 percent; Penicillium austurianum: 44.47-98.85 percent and 75.57-94.21 percent; Saccharomyces cerevisiae: 52.61-88.68 percent and 61.20-89.95 percent; Mucor arcindloides: 83.78-93.13 percent and 62.91-97.65 percent and Trichoderma reesi: 52.52-80.70 percent and 35.31-88.13 percent for dead and live biomass respectively. The influence of pH on metal uptake was evaluated at pH of 2, 4, 6 and 7. A regular pattern of sorption efficiency among the dead fungi species with respect to pH was observed and the percent adsorption decreased in the order pH 7 > 2 > 6 > 4 with the exception of Mucor (pH 7 > 2 > 4 > 6). Modified biomass of Aspergillus niger with oxalic acid, malic acid and ethylenediamine tetraacetic acid (EDTA) recorded 92.84 percent, 48.11 percent and 39.83 percent uptake of Pb respectively which correspond to 69.65 percent, 41.23 percent and 29.25 percent increase when compared to 28.18 percent of the unmodified biomass. These quantitative adsorptions demonstrate the potential application of modified biomass for the removal of Pb ion from aqueous solution.