Protease activities of Acanthamoeba polyphaga and Acanthamoeba castellanii

Acanthamoeba spp. are free-living amoebae that cause amoebic granulomatous encephalitis, skin lesions, and ocular amoebic keratitis in humans. Several authors have suggested that proteases could play a role in the pathogenesis of these diseases. In the present work, we performed a partial biochemical characterization of proteases in crude extracts of Acanthamoeba spp. and in conditioned medium using 7.5% SDS-PAGE copolymerized with 0.1% m/v gelatin as substrate. We distinguished a total of 17 bands with proteolytic activity distributed in two species of Acanthamoeba. The bands ranged from 30 to 188 kDa in A. castellanii and from 34 to 144 kDa in A. polyphaga. Additionally, we showed that the pattern of protease activity differed in the two species of Acanthamoeba when pH was altered. By using protease inhibitors, we found that the proteolytic activities belonged mostly to the serine protease family and secondly to cysteine proteases and that the proteolytic activities from A. castellanii were higher than those in A. polyphaga. Furthermore, aprotinin was found to inhibit crude extract protease activity on Madin-Darby canine kidney (MDCK) monolayers. These data suggest that protease patterns could be more complex than previously reported.     

Annexin A4 is a possible biomarker for cisplatin susceptibility of malignant mesothelioma cells

Mesothelioma is a highly malignant tumor with a poor prognosis and limited treatment options. Although cisplatin (CDDP) is an effective anticancer drug, its response rate is only 20%. Therefore, discovery of biomarkers is desirable to distinguish the CDDP-susceptible versus resistant cases. To this end, differential proteome analysis was performed to distinguish between mesothelioma cells of different CDDP susceptibilities, and this revealed that expression of annexin A4 (ANXA4) protein was higher in CDDP-resistant cells than in CDDP-susceptible cells. Furthermore, ANXA4 expression levels were higher in human clinical malignant mesothelioma tissues than in benign mesothelioma and normal mesothelial tissues. Finally, increased susceptibility was observed following gene knockdown of ANXA4 in mesothelioma cells, whereas the opposite effect was observed following transfection of an ANXA4 plasmid. These results suggest that ANXA4 has a regulatory function related to the cisplatin susceptibility of mesothelioma cells and that it could be a biomarker for CDDP susceptibility in pathological diagnoses.     

Binding of islet amyloid polypeptide to supported lipid bilayers and amyloid aggregation at the membranes

Amyloid deposition of human islet amyloid polypeptide (hIAPP) in the islets of Langerhans is closely associated with the pathogenesis of type II diabetes mellitus. Despite substantial evidence linking amyloidogenic hIAPP to loss of β-cell mass and decreased pancreatic function, the molecular mechanism of hIAPP cytotoxicity is poorly understood. We here investigated the binding of hIAPP and nonamyloidogenic rat IAPP to substrate-supported planar bilayers and examined the membrane-mediated amyloid aggregation. The membrane binding of IAPP in soluble and fibrillar states was characterized using quartz crystal microbalance with dissipation monitoring, revealing significant differences in the binding abilities among different species and conformational states of IAPP. Patterned model membranes composed of polymerized and fluid lipid bilayer domains were used to microscopically observe the amyloid aggregation of hIAPP in its membrane-bound state. The results have important implications for lipid-mediated aggregation following the penetration of hIAPP into fluid membranes. Using the fluorescence recovery after photobleaching method, we show that the processes of membrane binding and subsequent amyloid aggregation are accompanied by substantial changes in membrane fluidity and morphology. Additionally, we show that the fibrillar hIAPP has a potential ability to perturb the membrane structure in experiments of the fibril-mediated aggregation of lipid vesicles. The results obtained in this study using model membranes reveal that membrane-bound hIAPP species display a pronounced membrane perturbation ability and suggest the potential involvement of the oligomeic forms of hAPP in membrane dysfunction.     

Lysophospholipids and lysophospholipase D in rabbit aqueous humor following corneal injury

We previously found that lysophosphatidic acid (LPA)-like activity eliciting Cl(-) currents in Xenopus oocytes is increased in rabbit aqueous humor (AH) following corneal freeze wounds. The purpose of this study was to examine whether actual levels of LPA in AH from wounded eyes are higher than those from control eyes, and to determine the sources and enzymatic pathways of AH LPA in control and wounded conditions. Lysophospholipase D (lysoPLD) activity was measured by the enzymatic determination of choline following incubation of AH samples with exogenous lysophosphatidylcholines (LPCs). The molecular species compositions of LPA and LPC in fresh and incubated AH were determined by liquid chromatography-tandem mass spectrometry. A high, but similar activity of lysoPLD in the samples from both control and freeze-wounded eyes was detected. Its enzymatic properties resemble those of plasma lysoPLD, identified as autotaxin. Levels of LPCs, predominant substrates of lysoPLD in AH, were several times higher in the AH samples from injured eyes than those from the control eyes. Our results suggest that lysoPLD is constitutively released from corneal tissues and/or ciliary body into the AH, with no injury-induced increase in release following freeze-wounding. They also suggest that wound-induced increases in LPA-like biological activity are due to linoleoyl species-rich molecular composition in AH from wounded eyes. A possible mechanism of the altered molecular composition is an increase in the AH concentrations of LPCs, linoleoyl species of which are preferentially converted to corresponding unsaturated LPA by the constitutively active lysoPLD.     

Design and synthesis of novel DFG-out RAF/vascular endothelial growth factor receptor 2 (VEGFR2) inhibitors: 2. Synthesis and characterization of a novel imide-type prodrug for improving oral absorption

As an alternative to the previously reported solid dispersion formulation for enhancing the oral absorption of thiazolo[5,4-b]pyridine 1, we investigated novel N-acyl imide prodrugs of 1 as RAF/vascular endothelial growth factor receptor 2 (VEGFR2) inhibitors. Introducing N-acyl promoieties at the benzanilide position gave chemically stable imides. N-tert-Butoxycarbonyl (Boc) introduced imide 6 was a promising prodrug, which was converted to the active compound 1 after its oral administration in mice. Cocrystals of 6 with AcOH (6b) possessed good physicochemical properties with moderate thermodynamic solubility (19μg/mL). This crystalline prodrug 6b was rapidly and enzymatically converted into 1 after its oral absorption in mice, rats, dogs, and monkeys. Prodrug 6b showed in vivo antitumor regressive efficacy (T/C=-6.4%) in an A375 melanoma xenograft model in rats. Hence, we selected 6b as a promising candidate and are performing further studies. Herein, we report the design, synthesis, and characterization of novel imide-type prodrugs.     

Analyses of group III secreted phospholipase A2 transgenic mice reveal potential participation of this enzyme in plasma lipoprotein modification, macrophage foam cell formation, and atherosclerosis

Among the many mammalian secreted phospholipase A2 (sPLA2) enzymes, PLA2G3 (group III secreted phospholipase A2) is unique in that it possesses unusual N- and C-terminal domains and in that its central sPLA2 domain is homologous to bee venom PLA2 rather than to other mammalian sPLA2s. To elucidate the in vivo actions of this atypical sPLA2, we generated transgenic (Tg) mice overexpressing human PLA2G3. Despite marked increases in PLA2 activity and mature 18-kDa PLA2G3 protein in the circulation and tissues, PLA2G3 Tg mice displayed no apparent abnormality up to 9 months of age. However, alterations in plasma lipoproteins were observed in PLA2G3 Tg mice compared with control mice. In vitro incubation of low density (LDL) and high density (HDL) lipoproteins with several sPLA2s showed that phosphatidylcholine was efficiently converted to lysophosphatidylcholine by PLA2G3 as well as by PLA2G5 and PLA2G10, to a lesser extent by PLA2G2F, and only minimally by PLA2G2A and PLA2G2E. PLA2G3-modified LDL, like PLA2G5- or PLA2G10-treated LDL, facilitated the formation of foam cells from macrophages ex vivo. Accumulation of PLA2G3 was detected in the atherosclerotic lesions of humans and apoE-deficient mice. Furthermore, following an atherogenic diet, aortic atherosclerotic lesions were more severe in PLA2G3 Tg mice than in control mice on the apoE-null background, in combination with elevated plasma lysophosphatidylcholine and thromboxane A2 levels. These results collectively suggest a potential functional link between PLA2G3 and atherosclerosis, as has recently been proposed for PLA2G5 and PLA2G10.