Dietary magnesium, not calcium, prevents vascular calcification in a mouse model for pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a heritable disorder characterized by ectopic calcification of connective tissue in skin, Bruch’s membrane of the eye, and walls of blood vessels. PXE is caused by mutations in the ABCC6 gene, but the exact etiology is still unknown. While observations on patients suggest that high calcium intake worsens the clinical symptoms, the patient organization PXE International has published the dietary advice to increase calcium intake in combination with increased magnesium intake. To obtain more data on this controversial issue, we examined the effect of dietary calcium and magnesium in the Abcc6−/− mouse, a PXE mouse model which mimics the clinical features of PXE. Abcc6−/− mice were placed on specific diets for 3, 7, and 12 months. Disease severity was measured by quantifying calcification of blood vessels in the kidney. Raising the calcium content in the diet from 0.5% to 2% did not change disease severity. In contrast, simultaneous increase of both calcium (from 0.5% to 2.0%) and magnesium (from 0.05% to 0.2%) slowed down the calcification significantly. Our present findings that increase in dietary magnesium reduces vascular calcification in a mouse model for PXE should stimulate further studies to establish a dietary intervention for PXE

Enhanced levels of deoxycytidine kinase and thymidine kinase 1 and 2 after pulsed low dose rate irradiation as an adaptive response to radiation

After pulsed low dose rate irradiation the activities of deoxycytidine kinase and thymidine kinase 1 and 2 were increased 1.5-2-fold 6 h after treatment. Twenty-four hours after treatment the activities of these enzymes had returned to control levels. We presume that the increase of enzyme activities is part of an adaptive response to irradiation and that this increase could be an explanation for the increased survival in the initial part of the SW-1573 cell survival curve. The observation that not only S-phase specific thymidine kinase I but also mitochondrial thymidine kinase 2 increases, implies that both these enzymes play a role in an adaptive response of cells to irradiatio

Sensitivity to ionizing radiation and chemotherapeutic agents in gemcitabine-resistant human tumor cell lines

Purpose: To determine cross-resistance to anti-tumor treatments in 2',2'difluorodeoxycytidine (dFdC, gemcitabine)-resistant human tumor cells. Methods and Materials: Human lung carcinoma cells SW-1573 (SWp) were made resistant to dFdC (SWg). Sensitivity to cisplatin (cDDP), paclitaxel, 5-fluorouracil (5-FU), methotrexate (MTX), cytarabine (ara-C), and dFdC was measured by a proliferation assay. Radiosensitivity and radioenhancement by dFdC of this cell panel and the human ovarian carcinoma cell line A2780 and its dFdC-resistant variant AG6000 were determined by clonogenic assay. Bivariate flowcytometry was performed to study cell cycle changes. Results: In the SWg, a complete deoxycytidine kinase (dCK) deficiency was found on mRNA and protein level. This was accompanied by a 10-fold decrease in dCK activity which resulted in the >1000-fold resistance to dFdC. Sensitivity to other anti-tumor drugs was not altered, except for ara-C (>100-fold resistance). Radiosensitivity was not altered in the dFdC-resistant cell lines SWg and AG6000. High concentrations (50-100 muM dFdC) induced radioenhancement in the dFdC-resistant cell lines similar to the radioenhancement obtained at lower concentrations (10 nM dFdC) in the parental lines. An early S-phase arrest was found in all cell lines after dFdC treatment where radioenhancement was achieved. Conclusions: In the dFdC-resistant lung tumor cell line SWg, the deficiency in dCK is related to the resistance to dTdC and ara-C. No cross-resistance was observed to other anti-tumor drugs used for the treatment in lung cancer. Sensitivity to ionizing radiation was not altered in two different dFdC-resistant cell lines. Resistance to dFdC does not eliminate the ability of dFdC to sensitize cells to radiation. (C) 2002 Elsevier Science In

Staurosporine increases toxicity of gemcitabine in non-small cell lung cancer cells: role of protein kinase C, deoxycytidine kinase and ribonucleotide reductase

Gemcitabine, a deoxycytidine analog, active against non-small cell lung cancer, is phosphorylated by deoxycytidine kinase (dCK) to active nucleotides. Earlier, we found increased sensitivity to gemcitabine in P-glycoprotein (SW-2R160) and multidrug resistance-associated protein (SW-2R120), overexpressing variants of the human SW1573 non-small cell lung cancer cells. This was related to increased dCK activity. As protein kinase C (PKC) is higher in 2R120 and 2R160 cells and may control the dCK activity, we investigated whether gemcitabine sensitivity was affected by the protein kinase C inhibitor, staurosporine, which also modulates the cell cycle. Ten nmol/l staurosporine enhanced the sensitivity of SW1573, 2R120 and 2R160 cells 10-fold, 50-fold and 270-fold, respectively. Staurosporine increased dCK activity about two-fold and the activity of thymidine kinase 2, which may also activate gemcitabine. Staurosporine also directly increased dCK in cell free extracts. Staurosporine decreased expression of the free transcription factor E2F and of ribonucleotide reductase (RNR), a target for gemcitabine inhibition. In conclusion, staurosporine may potentiate gemcitabine by increasing dCK and decreasing E2F and RNR, which will lead to a more pronounced RNR inhibition. Anti-Cancer Drugs 21:591-599 (C) 2010 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkin

New mutations in the NHS gene in Nance-Horan Syndrome families from the Netherlands

Mutations in the NHS gene cause Nance-Horan Syndrome (NHS), a rare X-chromosomal recessive disorder with variable features, including congenital cataract, microphthalmia, a peculiar form of the ear and dental anomalies. We investigated the NHS gene in four additional families with NHS from the Netherlands, by dHPLC and direct sequencing. We identified an unique mutation in each family. Three out of these four mutations were not reported before. We report here the first splice site sequence alteration mutation and three protein truncating mutations. Our results suggest that X-linked cataract and NHS are allelic disorder