Petrov type I electric silent universes must possess symmetries: G1, G2 or G3

We prove that all Petrov type I, silent universe solutions of Einstein's field equations with a zero cosmological constant must possess symmetries: G1, G2 or G3.

The importance of human FcyRI in mediating protection to malaria

The success of passive immunization suggests that antibody-based therapies will be effective at controlling malaria. We describe the development of fully human antibodies specific for Plasmodium falciparum by antibody repertoire cloning from phage display libraries generated from immune Gambian adults. Although these novel reagents bind with strong affinity to malaria parasites, it remains unclear if in vitro assays are predictive of functional immunity in humans, due to the lack of suitable animal models permissive for P. falciparum. A potentially useful solution described herein allows the antimalarial efficacy of human antibodies to be determined using rodent malaria parasites transgenic for P. falciparum antigens in mice also transgenic for human Fc-receptors. These human IgG1s cured animals of an otherwise lethal malaria infection, and protection was crucially dependent on human FcγRI. This important finding documents the capacity of FcγRI to mediate potent antimalaria immunity and supports the development of FcγRI-directed therapy for human malaria.

Cell cycle sensing of oxidative stress in saccharomyces cerevisiae by oxidation of a specific cysteine residue in the transcription factor Swi6p

Yeast cells begin to bud and enter S phase when growth conditions are favourable during G1 phase. When subjected to some oxidative stresses, cells delay entry at G1 allowing repair of cellular damage. Hence, oxidative stress sensing is coordinated with the regulation of cell cycle. We identified a novel function of the cell-cycle regulator of Saccharomyces cerevisiae, Swi6p, as a redox sensor through its cysteine residue at position 404. When alanine was substituted at this position, the resultant mutant, C404A, was sensitive to several reactive oxygen species and oxidants including linoleic acid hydroperoxide, the superoxide anion and diamide. This mutant lost the ability to arrest in G1 phase upon treatment with lipid hydroperoxide. The Cys404 residue of Swi6p in wild-type cells was oxidised to a sulfenic acid when cells were subjected to linoleic acid hydroperoxide. Mutation of Cys404 to Ala abolished the down-regulation of expression of the G1 cyclin genes CLN1, CLN2, PCL1 and PCL2 that occurred when cells of the wild type were exposed to the lipid hydroperoxide. In conclusion, oxidative stress signaling for cell-cycle regulation occurs through oxidation of the G1/S-speicific transcription factor Swi6p and consequently leads to suppression of the expression of G1-cyclins and delay in cells entering the cell cycle.

PPARγ ligands, 15-deoxy-Δ12,14-prostaglandin J2 and rosiglitazone regulate human cultured airway smooth muscle proliferation through different mechanisms

1. The influence of two peroxisome proliferator-activated receptor γ (PPARγ) ligands, a thiazolidinedione, rosiglitazone (RG) and the prostaglandin D2 metabolite 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) on the proliferation of human cultured airway smooth muscle (HASM) was examined.

2. The increases in HASM cell number in response to basic fibroblast growth factor (bFGF, 300 pm) or thrombin (0.3 U ml−1) were significantly inhibited by either RG (1–10 μm) or 15d-PGJ2 (1–10 μm). The effects of RG, but not 15d-PGJ2, were reversed by the selective PPARγ antagonist GW9662 (1 μm).

3. Neither RG nor 15d-PGJ2 (10 μm) decreased cell viability, or induced apoptosis, suggesting that the regulation of cell number was due to inhibition of proliferation, rather than increased cell death.

4. Flow-cytometric analysis of HASM cell cycle distribution 24 h after bFGF addition showed that RG prevented the progression of cells from G1 to S phase. In contrast, 15d-PGJ2 caused an increase in the proportion of cells in S phase, and a decrease in G2/M, compared to bFGF alone.

5. Neither RG nor 15d-PGJ2 inhibited ERK phosphorylation measured 6 h post mitogen addition. The bFGF-mediated increase in cyclin D1 protein levels after 8 h was reduced in the presence of 15d-PGJ2, but not RG.

6. Although both RG and 15d-PGJ2 can inhibit proliferation of HASM irrespective of the mitogen used, only the antiproliferative effects of RG appear to be PPARγ-dependent. The different antimitogenic mechanisms of 15d-PGJ2 and synthetic ligands for PPARγ may be exploited to optimise the potential for these compounds to inhibit airway remodelling in asthma.

Epigallocatechin-3-gallate induces the apoptosis of hepatocellular carcinoma LM6 cells but not non-cancerous liver cells

Epigallocatechin-3-gallate (EGCG) is a constituent of green tea and has been associated with anticancer activity. In the present study, the inhibitory effect of EGCG on human hepatocellular cancer cells was examined by cell viability assay, in vitro apoptosis assay and cell cycle analysis. In addition, gene expression was measured to elucidate the molecular mechanisms of action of EGCG by mitochondrial membrane potential (MMP) determination and western blot analysis. We demonstrated that EGCG induced apoptosis, decreased mitochondrial membrane potential and promoted G0/G1 phase cell cycle arrest of HCCLM6 cells but not that of non-cancerous liver cells (HL-7702). The EGCG-induced apoptosis of HCCLM6 cells was associated with a significant decrease in Bcl-2 and NF-κB expression. In addition, the expression of Bax, p53, caspase-9 and caspase-3 increased, and cytochrome c was released. These results suggest that EGCG inhibits the progression of cancer through cytocidal activity and that it is a potential therapeutic compound for hepatocellular carcinoma (HCC).

Suberoylanilide hydroxamic acid radiosensitizes tumor hypoxic cells in vitro through the oxidation of nitroxyl to nitric oxide

The pharmacological effects of hydroxamic acids are partially attributed to their ability to serve as HNO and/or NO donors under oxidative stress. Previously, it was concluded that oxidation of the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) by the metmyoglobin/H2O2 reaction system releases NO, which was based on spin trapping of NO and accumulation of nitrite. Reinvestigation of this system demonstrates the accumulation of N2O, which is a marker of HNO formation, at similar rates under normoxia and anoxia. In addition, the yields of nitrite that accumulated in the absence and the presence of O2 did not differ, implying that the source of nitrite is other than autoxidation of NO. In this system metmyoglobin is instantaneously and continuously converted into compound II, leading to one-electron oxidation of SAHA to its respective transient nitroxide radical. Studies using pulse radiolysis show that one-electron oxidation of SAHA (pKa=9.56 ± 0.04) yields the respective nitroxide radical (pKa=9.1 ± 0.2), which under all experimental conditions decomposes bimolecularly to yield HNO. The proposed mechanism suggests that compound I oxidizes SAHA to the respective nitroxide radical, which decomposes bimolecularly in competition with its oxidation by compound II to form HNO. Compound II also oxidizes HNO to NO and NO to nitrite. Given that NO, but not HNO, is an efficient hypoxic cell radiosensitizer, we hypothesized that under an oxidizing environment SAHA might act as a NO donor and radiosensitize hypoxic cells. Preincubation of A549 and HT29 cells with 2.5 μM SAHA for 24h resulted in a sensitizer enhancement ratio at 0.01 survival levels (SER0.01) of 1.33 and 1.59, respectively. Preincubation of A549 cells with oxidized SAHA had hardly any effect and, with 2mM valproic acid, which lacks the hydroxamate group, resulted in SER0.01=1.17. Preincubation of HT29 cells with SAHA and Tempol, which readily oxidizes HNO to NO, enhanced the radiosensitizing effect of SAHA. Pretreatment with SAHA blocked A549 cells at the G1 stage of the cell cycle and upregulated γ-H2AX after irradiation. Overall, we conclude that SAHA enhances tumor radioresponse by multiple mechanisms that might also involve its ability to serve as a NO donor under oxidizing environments.

Competitive inhibition of survivin using a cell-permeable recombinant protein induces cancer-specific apoptosis in colon cancer model

Endogenous survivin expression has been related with cancer survival, drug resistance, and metastasis. Therapies targeting survivin have been shown to significantly inhibit tumor growth and recurrence. We found out that a cell-permeable dominant negative survivin (SurR9-C84A, referred to as SR9) competitively inhibited endogenous survivin and blocked the cell cycle at the G1/S phase. Nanoencapsulation in mucoadhesive chitosan nanoparticles (CHNP) substantially increased the bioavailability and serum stability of SR9. The mechanism of nanoparticle uptake was studied extensively in vitro and in ex vivo models. Our results confirmed that CHNP-SR9 protected primary cells from autophagy and successfully induced tumor-specific apoptosis via both extrinsic and intrinsic apoptotic pathways. CHNP-SR9 significantly reduced the tumor spheroid size (three-dimensional model) by nearly 7-fold. Effects of SR9 and CHNP-SR9 were studied on 35 key molecules involved in the apoptotic pathway. Highly significant (4.26-fold, P≤0.005) reduction in tumor volume was observed using an in vivo mouse xenograft colon cancer model. It was also observed that net apoptotic (6.25-fold, P≤0.005) and necrotic indexes (3.5-fold, P≤0.05) were comparatively higher in CHNP-SR9 when compared to void CHNP and CHNP-SR9 internalized more in cancer stem cells (4.5-fold, P≤0.005). We concluded that nanoformulation of SR9 did not reduce its therapeutic potential; however, nanoformulation provided SR9 with enhanced stability and better bioavailability. Our study presents a highly tumor-specific protein-based cancer therapy that has several advantages over the normally used chemotherapeutics.