A randomized clinical trial of ascorbic acid in open abdominal aortic aneurysm repair

BACKGROUND: Open AAA repair is associated with ischaemia-reperfusion injury where systemic inflammation and endothelial dysfunction can lead to multiple organ injury including acute lung injury. Oxidative stress plays a role that may be inhibited by ascorbic acid.

METHODS: A double blind, allocation concealed, randomized placebo-controlled trial was performed to test the hypothesis that a single bolus dose (2g) of intra-operative parenteral ascorbic acid would attenuate biomarkers of ischaemia-reperfusion injury in patients undergoing elective open AAA repair.

RESULTS: Thirty one patients completed the study; 18 received placebo and 13 ascorbic acid. Groups were comparable demographically. Open AAA repair caused an increase in urinary Albumin:Creatinine Ratio (ACR) as well as plasma IL-6 and IL-8. There was a decrease in exhaled breath pH and oxygenation. Lipid hydroperoxides were significantly higher in the ascorbic acid group following open AAA repair. There were no other differences between the ascorbic acid or placebo groups up to 4 hours after removal of the aortic clamping.

CONCLUSIONS: Open AAA repair caused an increase in markers of systemic endothelial damage and systemic inflammation. Administration of 2g parenteral ascorbic acid did not attenuate this response and with higher levels of lipid hydroperoxides post-operatively a pro-oxidant effect could not be excluded.

TRIAL REGISTRATION: ISRCTN27369400.

Measuring a cell's response to stress:the p53 pathway.

Marine Biosilica as a Tool to Understand the Therapeutic Benefit of Silica in Bone Repair

It is widely accepted that silicon-substituted materials enhance bone formation, yet the mechanism by which this occurs is poorly understood. This work investigates the potential of using diatom frustules to answer on fundamental questions surrounding the role of silica in bone healing. Biosilica with frustules 20m were isolated from Cyclotella meneghiniana a unicellular microalgae that was sourced from the Mississippi River, USA. Silanisation chemistry was used to modify the surface of C. meneghiniana with amine (–NH2) and thiol (–SH) terminated silanes. Untreated frustules and both functionalised groups were soaked in culture medium for 24hrs. Following the culture period, frustules were separated from the conditioned medium by centrifugation and both were tested separately in vitro for cytotoxicity using murine-monocyte macrophage (J774) cell line. Cytotoxicity was measured using LDH release to measure damage to cell membrane, MTS to measure cell viability and live-dead staining. The expression and release of pro-inflammatory cytokines (IL-6 and TNF) were measured using ELISA. Our results found that diatom frustules and those functionalised with amino groups showed no cytotoxicity or elevated cytokine release. Diatom frustules functionalised with thiol groups showed higher levels of cytotoxicity. Diatom frustules and those functionalised with amino groups were taken forward to an in vivo mouse toxicity model, whereby the immunological response, organ toxicity and route of metabolism/excretion of silica were investigated. Histological results showed no organ toxicity in any of the groups relative to control. Analysis of blood Si levels suggests that modified frustules are metabolised quicker than functionalised frustules, suggesting that physiochemical attributes influence their biodistribution. Our results show that diatom frustules are non cytotoxic and are promising materials to better understand the role of silica in bone healing.

Alpha particles induce pan-nuclear phosphorylation of H2AX in primary human lymphocytes mediated through ATM

The use of high linear energy transfer radiations in the form of carbon ions in heavy ion beam lines or alpha particles in new radionuclide treatments has increased substantially over the past decade and will continue to do so due to the favourable dose distributions they can offer versus conventional therapies. Previously it has been shown that exposure to heavy ions induces pan-nuclear phosphorylation of several DNA repair proteins such as H2AX and ATM in vitro. Here we describe similar effects of alpha particles on ex vivo irradiated primary human peripheral blood lymphocytes. Following alpha particle irradiation pan-nuclear phosphorylation of H2AX and ATM, but not DNA-PK and 53BP1, was observed throughout the nucleus. Inhibition of ATM, but not DNA-PK, resulted in the loss of pan-nuclear phosphorylation of H2AX in alpha particle irradiated lymphocytes. Pan-nuclear gamma-H2AX signal was rapidly lost over 24h at a much greater rate than foci loss. Surprisingly, pan-nuclear gamma-H2AX intensity was not dependent on the number of alpha particle induced double strand breaks, rather the number of alpha particles which had traversed the cell nucleus. This distinct fluence dependent damage signature of particle radiation is important in both the fields of radioprotection and clinical oncology in determining radionuclide biological dosimetry and may be indicative of patient response to new radionuclide cancer therapies.

DNA mismatch repair and the DNA damage response to ionizing radiation:making sense of apparently conflicting data

The DNA mismatch repair (MMR) pathway detects and repairs DNA replication errors. While DNA MMR-proficiency is known to play a key role in the sensitivity to a number of DNA damaging agents, its role in the cytotoxicity of ionizing radiation (IR) is less well characterized. Available literature to date is conflicting regarding the influence of MMR status on radiosensitivity, and this has arisen as a subject of controversy in the field. The aim of this paper is to provide the first comprehensive overview of the experimental data linking MMR proteins and the DNA damage response to IR. A PubMed search was conducted using the key words "DNA mismatch repair" and "ionizing radiation". Relevant articles and their references were reviewed for their association between DNA MMR and IR. Recent data suggest that radiation dose and the type of DNA damage induced may dictate the involvement of the MMR system in the cellular response to IR. In particular, the literature supports a role for the MMR system in DNA damage recognition, cell cycle arrest, DNA repair and apoptosis. In this review we discuss our current understanding of the impact of MMR status on the cellular response to radiation in mammalian cells gained from past and present studies and attempt to provide an explanation for how MMR may determine the response to radiation.

DNA mismatch repair and the transition to hormone independence in breast and prostate cancer

The molecular basis for the progression of breast and prostate cancer from hormone dependent to hormone independent disease remains a critical issue in the management of these two cancers. The DNA mismatch repair system is integral to the maintenance of genomic stability and suppression of tumorigenesis. No firm consensus exists regarding the implications of mismatch repair (MMR) deficiencies in the development of breast or prostate cancer. However, recent studies have reported an association between mismatch repair deficiency and loss of specific hormone receptors, inferring a potential role for mismatch repair deficiency in this transition. An updated review of the experimental data supporting or contradicting the involvement of MMR defects in the development and progression of breast and prostate cancer will be provided with particular emphasis on their implications in the transition to hormone independence.

Recognition of O6MeG lesions by MGMT and mismatch repair proficiency may be a prerequisite for low-dose radiation hypersensitivity

Low-dose hyper-radiosensitivity (HRS) is the phenomenon whereby cells exposed to radiation doses of less than approximately 0.5 Gy exhibit increased cell killing relative to that predicted from back-extrapolating high-dose survival data using a linear-quadratic model. While the exact mechanism remains to be elucidated, the involvement of several molecular repair pathways has been documented. These processes in turn are also associated with the response of cells to O6-methylguanine (O6MeG) lesions. We propose a model in which the level of low-dose cell killing is determined by the efficiency of both pre-replicative repair by the DNA repair enzyme O6-methylguanine methyltransferase (MGMT) and post-replicative repair by the DNA mismatch repair (MMR) system. We therefore hypothesized that the response of cells to low doses of radiation is dependent on the expression status of MGMT and MMR proteins. MMR (MSH2, MSH6, MLH1, PMS1, PMS2) and MGMT protein expression signatures were determined in a panel of normal (PWR1E, RWPE1) and malignant (22RV1, DU145, PC3) prostate cell lines and correlated with clonogenic survival and cell cycle analysis. PC3 and RWPE1 cells (HRS positive) were associated with MGMT and MMR proficiency, whereas HRS negative cell lines lacked expression of at least one (MGMT or MMR) protein. MGMT inactivation had no significant effect on cell survival. These results indicate a possible role for MMR-dependent processing of damage produced by low doses of radiation.

Variation in DNA repair genes XRCC3, XRCC4, XRCC5 and susceptibility to myeloma

Cytogenetic analysis in myeloma reveals marked chromosomal instability. Both widespread genomic alterations and evidence of aberrant class switch recombination, the physiological process that regulates maturation of the antibody response, implicate the DNA repair pathway in disease pathogenesis. We therefore assessed 27 SNPs in three genes (XRCC3, XRCC4 and XRCC5) central to DNA repair in patients with myeloma and controls from the EpiLymph study and from an Irish hospital registry (n = 306 cases, 263 controls). For the haplotype-tagging SNP (htSNP) rs963248 in XRCC4, Allele A was significantly more frequent in cases than in controls (86.4 versus 80.8%; odds ratio 1.51; 95% confidence interval 1.10-2.08; P = 0.0133), as was the AA genotype (74 versus 65%) (P = 0.026). Haplotype analysis was performed using Unphased for rs963248 in combination with additional SNPs in XRCC4. The strongest evidence of association came from the A-T haplotype from rs963248-rs2891980 (P = 0.008). For XRCC5, the genotype GG from rs1051685 was detected in 10 cases from different national populations but in only one control (P = 0.015). This SNP is located in the 3'-UTR of XRCC5. Overall, these data provide support for the hypothesis that common variation in the genes encoding DNA repair proteins contributes to susceptibility to myeloma.

A review of excision repair cross-complementation group 1 in colorectal cancer

Oxaliplatin-based chemotherapy is the standard of care in patients with high-risk stage II and stage III colorectal cancer as well as in patients with advanced disease. Unfortunately, a large proportion of patients offered oxaliplatin fail to benefit from it. In the era of personalized treatment, there are strong efforts to identify biomarkers that will predict efficacy to oxaliplatin-based treatments. Excision repair cross-complementation group 1 (ERCC1) is a key element in the nucleotide excision repair (NER) pathway, which is responsible for repairing DNA adducts induced by platinum compounds. ERCC1 has recently been shown to be closely associated with outcome in patients with non-small-cell lung cancer (NSCLC): both high ERCC1 protein and gene expression are associated with resistance to cisplatin-based chemotherapy and better outcome without treatment. Therefore, ERCC1 has the potential to be used as a strong candidate biomarker, both predictive and prognostic, for colorectal cancer. This review will focus on the preclinical and clinical evidences supporting ERCC1 as a major molecule in oxaliplatin resistance. In addition, the important technologies used to assess ERCC1 gene and protein expression will be highlighted.

Assessment of DNA double-strand breaks induced by intravascular iodinated contrast media following in vitro irradiation and in vivo, during paediatric cardiac catheterization

Paediatric cardiac catheterizations may result in the administration of substantial amounts of iodinated contrast media and ionizing radiation. The aim of this work was to investigate the effect of iodinated contrast media in combination with in vitro and in vivo X-ray radiation on lymphocyte DNA. Six concentrations of iodine (15, 17.5, 30, 35, 45, and 52.5 mg of iodine per mL blood) represented volumes of iodinated contrast media used in the clinical setting. Blood obtained from healthy volunteers was mixed with iodinated contrast media and exposed to radiation doses commonly used in paediatric cardiac catheterizations (0 mGy, 70 mGy, 140 mGy, 250 mGy and 450 mGy). Control samples contained no iodine. For in vivo experimentation, pre and post blood samples were collected from children undergoing cardiac catheterization, receiving iodine concentrations of up to 51 mg of iodine per mL blood and radiation doses of up to 400 mGy. Fluorescence microscopy was performed to assess γH2AX-foci induction, which corresponded to the number of DNA double-strand breaks. The presence of iodine in vitro resulted in significant increases of DNA double-strand breaks beyond that induced by radiation for ≥17.5 mg/mL iodine to blood. The in vivo effects of contrast media on children undergoing cardiac catheterization resulted in a 19% increase in DNA double-strand breaks in children receiving an average concentration of 19 mg/mL iodine to blood. A larger investigation is required to provide further information of the potential benefit of lowering the amount of iodinated contrast media received during X-ray radiation investigations.