Methods for Identifying a Default Cross-Species Scaling Factor

The need to identify “toxicologically equivalent” doses across different species is a major issue in toxicology and risk assessment. In this article, we describe an approach for establishing default cross-species extrapolation factors used to scale oral doses across species for non-carcinogenic endpoints. This work represents part of an on-going effort to harmonize the way animal data are evaluated for carcinogenic and non-carcinogenic endpoints. In addition to considering default scaling factors, we also discuss how chemical-specific data (e.g., metabolic or mechanistic data) can be incorporated into the dose extrapolation process. After first examining the required properties of a default scaling methodology, we consider scaling approaches based on empirical relationships observed for particular classes of compounds and also more theoretical approaches based on general physiological principles (i.e, allometry). The available data suggest that the empirical and allometric approaches each provide support for the idea that toxicological risks are approximately equal when daily oral doses are proportional to body weight raised to the 3/4-power. We also discuss specific challenges for dose scaling related to different routes of exposure, acute versus chronic toxicity, and extrapolations related to particular life stages (e.g., childhood).     

Dosimetric impact of Acuros XB on cervix radiotherapy using RapidArc technique: a dosimetric study

BackgroundAcuros XB (AXB) may predict better rectal toxicities and treatment outcomes in cervix carcinoma. The aim of the study was to quantify the potential impact of AXB computations on the cervix radiotherapy using the RapidArc (RA ) technique as compared to anisotropic analytical algorithm (AA) computations.Materials and methodsA cohort of 30 patients previously cared for cervix carcinoma (stages II–IIIB) was selected for the present analysis. The RA plans were computed using AA and AXB dose computation engines under identical beam setup and MLC pattern.ResultsThere was no significant (p > 0.05) difference in D_95% and D_98% to the planning target volume (PTV); moreover, a significant (p < 0.05) rise was noticed for mean dose to the PTV (0.26%), D_50% (0.26%), D_2% (0.80%) and V_110% (44.24%) for AXB computation as compared to AA computations. Further, AXB estimated a significantly (p < 0.05) lower value for maximum and minimum dose to the PTV. Additionally, there was a significant (p < 0.05) reduction observed in mean dose to organs at risk (OARs) for AXB computation as compared to AA, though the reduction in mean dose was non-significant (p > 0.05) for the rectum. The maximum difference observed was 4.78% for the rectum V_50Gy, 1.72%, 1.15% in mean dose and 2.22%, 1.48% in D_2% of the left femur and right femur, respectively, between AA and AXB dose estimations.ConclusionFor similar target coverage, there were significant differences observed between the AAA and AXB computations. AA underestimates the V_50Gy of the rectum and overestimates the mean dose and D_2% for femoral heads as compared to AXB. Therefore, the use of AXB in the case of cervix carcinoma may predict better rectal toxicities and treatment outcomes in cervix carcinoma using the RA technique.     

Involvement of p53 in gemcitabine mediated cytotoxicity and radiosensitivity in breast cancer cell lines

Gemcitabine (2',2'-difluoro-2'-deoxycytidine; dFdCyd) is one of the anti-metabolites drugs that target DNA replication. We evaluated dFdCyd cytotoxicity and its radiosensitizing ability in human breast cancer cell lines, MCF-7 (wild-type p53) and MDA-MB-231 (mutant-type p53) along with normal mammary epithelial cell line (MCF-12) for comparison. Radiosensitivity and cytotoxicity were measured by the clonogenic survival assays. DNA DSBs was studied by Pulse Field Gel Electrophoresis (PFGE) and cell cycle distribution was analyzed by flow cytometry. MDA-MB-231 cells were the most sensitive to the cytotoxicity of dFdCyd (IC(50) 5 nM) then MCF-7 (IC(50) 10nM), whereas MCF-12 cells were the most resistant to the cytotoxicity of dFdCyd (IC(50) 70 nM). MCF-12 and MCF-7 cell lines did not show any radiosensitization to dFdCyd, whereas the MDA-MB-231 cells showed significantly increased radioresistant to dFdCyd at equimolar concentration (p=0.002) and at IC(50) concentration (p<0.001). The DNA double strand breaks (DSBs) repair showed that dFdCyd neither increases DNA DSBs nor decreases the rate of their repair in MCF-12 and MCF-7 cell lines, while the same treatment in MDA-MB-231 cell line led to decrease the rate of DSBs or increase the rate of DNA repair (p=0.034). Therefore, dFdCyd is a cytotoxic agent, especially in the cancer cells irrespective of having wild-type or mutated p53 protein, but it is not effective as radiosensitizer in the cell lines used in this study. dFdCyd combined with radiation reduces the efficacy of chemo-radiotherapy in p53 mutated cells. Therefore, p53-mutated cancer could be a counter-indication for radiation-gemcitabine combined treatment.     

The associations of IL-18 serum levels and promoter polymorphism with tacrolimus pharmacokinetics and hepatic allograft dysfunction in Chinese liver transplantation recipients

Interleukin 18 (IL-18) is a potent proinflammatory cytokine, which promotes the secretions of TNF-α, IL-1β, IL-2 and IFN-γ. All those inflammatory cytokines can influence the CYP450 and MDR dependent drug disposition. On the other side, those cytokines can induce hepatic allograft dysfunction. We investigated the effects of serum IL-18 and IL-18 gene promoter polymorphisms on tacrolimus pharmacokinetics and hepatic allograft dysfunction in liver transplant recipients. A total of 155 liver transplant recipients were enrolled into this study (34 females and 121 males). The mean follow-up was 52 months (range 16-96 months).The total liver transplant recipients were divided into hepatic allograft dysfunction (N = 14) and no hepatic allograft dysfunction (N = 141). We studied two single-nucleotide polymorphisms in the promoter region of IL-18 gene at the position G-137C (rs187238) and A-607C (rs1946518) by HRM analysis (high-resolution melting curve analysis). Tacrolimus dosage, tacrolimus blood concentration, serum levels of IL-18 and IFN-γ were also investigated. We found the recipients with higher IL-18 and IFN-γ serum levels had lower tacrolimus concentration/dose (C/D) ratios (P < 0.05). In the mean time, after transplantation hepatic allograft dysfunction was more likely to happen to those recipients. However, there was no significant difference in the frequencies of A-607C and G-137C allelic distribution in recipients' tacrolimus concentration/dose (C/D) ratios. This study identifies IL-18 reduced tacrolimus concentration/dose (C/D) ratio through up regulation of P-glycoprotein (P-gp).     

Systematic assessment of reduced representation bisulfite sequencing to human blood samples: A promising method for large-sample-scale epigenomic studies

Complementary to the time- and cost-intensive direct bisulfite sequencing, we applied reduced representation bisulfite sequencing (RRBS) to the human peripheral blood mononuclear cells (PBMC) from YH, the Asian individual whose genome and epigenome has been deciphered in the YH project and systematically assessed the genomic coverage, coverage depth and reproducibility of this technology as well as the concordance of DNA methylation levels measured by RRBS and direct bisulfite sequencing for the detected CpG sites. Our result suggests that RRBS can cover more than half of CpG islands and promoter regions with a good coverage depth and the proportion of the CpG sites covered by the biological replicates reaches 80-90%, indicating good reproducibility. Given a smaller data quantity, RRBS enjoys much better coverage depth than direct bisulfite sequencing and the concordance of DNA methylation levels between the two methods is high. It can be concluded that RRBS is a time and cost-effective sequencing method for unbiased DNA methylation profiling of CpG islands and promoter regions in a genome-wide scale and it is the method of choice to assay certain genomic regions for multiple samples in a rapid way.     

Terrorist Radiological Dispersive Device (RDD) Scenario and Cancer Risk Assessment

Terrorist attacks using radiological dispersal devices (RDD) are important threats that can lead to major environmental, economic, and public health concerns. In a simulation using a Gaussian model, we sought to determine dose curves as a function of distance from the explosion core site and from these data to determine the relative risk of developing tumors as well as the probability of causation (i.e., the statistical correlation between occurrence of malignancies and previous exposure to radiation). Calculation confirmed the cause dependence on age at exposure and the probability of tumor causation. This study aimed at emphasizing the importance of responding rapidly and efficiently, with a user-friendly user methodology that initially may help to guide the response from basic actions to the complete decision process.     

The working of a pulsatory liposome

Under positive osmotic stress, a greater lipid vesicle swells to a critical diameter, when suddenly a transbilayer pore appears and grows to a maximum radius, then decreases and finally disappears. An amount of liquid was leaked out through the pore and the vesicle returns to the initial state and can start another cycle. This is a pulsatory lipid liposome. In this paper, we have considered the problem of such liposomes. We have obtained the condition that a pulsatory liposome to run an a priori settled number of cycles. The length time of each cycle and its activity life was calculated. Also, we have calculated the quantities of solute leaked out through a pore in each cycle. The pulsatory liposome may be regarded as a biotechnological device to dose drugs at fixed intervals time.     

Entamoeba histolytica: lipid rafts are involved in adhesion of trophozoites to host extracellular matrix components

Adhesion is an important virulence function for Entamoeba histolytica, the causative agent of amoebic dysentery. Lipid rafts, cholesterol-rich domains, function in compartmentalization of cellular processes. In E. histolytica, rafts participate in parasite-host cell interactions; however, their role in parasite-host extracellular matrix (ECM) interactions has not been explored. Disruption of rafts with a cholesterol extracting agent, methyl-β-cyclodextrin (MβCD), resulted in inhibition of adhesion to collagen, and to a lesser extent, to fibronectin. Replenishment of cholesterol in MβCD-treated cells, using a lipoprotein-cholesterol concentrate, restored adhesion to collagen. Confocal microscopy revealed enrichment of rafts at parasite-ECM interfaces. A raft-resident adhesin, the galactose/N-acetylgalactosamine-inhibitable lectin, mediates interaction to host cells by binding to galactose or N-acetylgalactosamine moieties on host glycoproteins. In this study, galactose inhibited adhesion to collagen, but not to fibronectin. Together these data suggest that rafts participate in E. histolytica-ECM interactions and that raft-associated Gal/GalNAc lectin may serve as a collagen receptor.