Spontaneous DNA repair in human mononuclear cells is calcium-dependent

Spontaneous DNA repair in peripheral blood mononuclear cells (PBMC) has been recently described. The aim of this study was to evaluate whether spontaneous DNA repair is Ca(2+)-dependent, as in vitro-stimulated DNA repair. Spontaneous DNA repair in PBMC was measured in a 1mM Ca2+ medium. The effect of extracellular Ca2+ chelation by EGTA, intracellular Ca2+ chelation by bapta-AM, and Ca2+ loading by the ionophore A23187 was examined. The signal transduction pathway was evaluated by inhibiting protein tyrosine kinase with genistein, calmodulin with W7, and calcineurin with cyclosporin A and tacrolimus. Extracellular Ca2+ chelation had no effect on spontaneous DNA repair, while both intracellular chelation and calcium overloading inhibited the DNA repair. Inhibition of protein tyrosine kinase, calmodulin or calcineurin reduced DNA repair. In conclusion, spontaneous DNA repair is mainly Ca(2+)-dependent at a narrow range of intracellular Ca2+ concentrations. The signal transduction cascade includes protein tyrosine kinase, calmodulin, and calcineurin.     

Inhibition of interleukin-10 by the immunomodulator AS101 reduces mesangial cell proliferation in experimental mesangioproliferative glomerulonephritis: association with dephosphorylation of STAT3

Mesangial cell (MC) proliferation is essential for the pathogenesis and progression of glomerular disease. Using an acute model of mesangial proliferative glomerulonephritis (Thy1 GN), we show that neutralization of interleukin (IL)-10 greatly ameliorated the disease as expressed by both decreased MC expansion and proteinuria. Treatment with the tellurium compound AS101 (ammonium trichloro(dioxoethylene-o,o')tellurate) resulted in favorable effects provided that the compound was administered 24 h before insult, whereas partial effects were obtained when administered after insult. We identified STAT3 as playing a pivotal role in IL-10-induced MC proliferation in vitro and in vivo. IL-10 activates MC STAT3 in vitro as expressed by its phosphorylation and nuclear translocation. The role of STAT3 in MC proliferation induced by IL-10 was deduced from results showing that IL-10-induced proliferation was abrogated if MC transfected with STAT3 antisense oligonucleotides were used or if cells were incubated with inhibitors of STAT3. AS101 deactivates STAT3 in control but not in MC transfected with IL-10 antisense oligonucleotides. Inactivation of STAT3 prevents reduction of MC proliferation by AS101. We further demonstrate the role of STAT3 in the regulation of cell cycle and survival regulatory proteins by AS101 in MC via inhibition of IL-10. IL-10 increased MC expression of Bcl-2 and Bcl-X1 and simultaneously decreased the levels of p27kip1. These survival factors were decreased by AS101 in a STAT3- and IL-10-dependent manner, whereas p27kip1 was similarly increased. In Thy1 GN, phosphorylated STAT3 in glomerular MC peaked at day 6 and correlated with MC expansion. Neutralization of IL-10 or its inhibition by AS101 abolished phosphorylation of STAT3. This effect positively correlated with amelioration of the disease. These in vitro and in vivo studies indicate that the autocrine MC growth factor IL-10 induces MC proliferation via STAT3. We suggest that IL-10 or its downstream target STAT3 might be therapeutic targets for kidney diseases induced by mesangial proliferation.     

Effect of Acetazolamide on Obesity-Induced Glomerular Hyperfiltration: A Randomized Controlled Trial

Aims

Obesity is an important risk factor for the development of chronic kidney disease. One of the major factors involved in the pathogenesis of obesity-associated kidney disease is glomerular hyperfiltration. Increasing salt-delivery to the macula densa is expected to decrease glomerular filtration rate (GFR) by activating tubuloglomerular feedback. Acetazolamide, a carbonic anhydrase inhibitor which inhibits salt reabsorption in the proximal tubule, increases distal salt delivery. Its effects on obesity-related glomerular hyperfiltration have not previously been studied. The aim of this investigation was to evaluate whether administration of acetazolamide to obese non diabetic subjects reduces glomerular hyperfiltration.

Materials and Methods

The study was performed using a randomized double-blind crossover design. Obese non-diabetic men with glomerular hyperfiltration were randomized to receive intravenously either acetazolamide or furosemide at equipotent doses. Twelve subjects received the allocated medications. Two weeks later, the same subjects received the drug which they had not received during the first study. Inulin clearance, p-aminohippuric acid clearance and fractional lithium excretion were measured before and after medications administration. The primary end point was a decrease in GFR, measured as inulin clearance.

Results

GFR decreased by 21% following acetazolamide and did not decrease following furosemide. Renal vascular resistance increased by 12% following acetazolamide, while it remained unchanged following furosemide administration. Natriuresis increased similarly following acetazolamide and furosemide administration. Sodium balance was similar in both groups.

Conclusions

Intravenous acetazolamide decreased GFR in obese non-diabetic men with glomerular hyperfiltration. Furosemide, administered at equipotent dose, did not affect GFR, suggesting that acetazolamide reduced glomerular hyperfiltration by activating tubuloglomerular feedback.

Trial Registration

ClinicalTrials.gov NCT01146288     

Spontaneous DNA repair in human peripheral blood mononuclear cells

DNA molecules are constantly damaged during mitosis and by oxygen-free radicals produced by either cellular metabolism or by external factors. Populations at risk include patients with cancer-prone disease, patients under enhanced oxidative stress, and those treated with immunosuppressive/cytotoxic therapy. The DNA repair process is crucial in maintaining the genomal DNA integrity. The aim of this study was to evaluate spontaneous DNA repair capacity of peripheral blood mononuclear cells (PBMC) from normal blood donors. PBMC DNA repair ability represents DNA repair by other tissues as well. It is shown in the present study that in vitro incorporation of [3H]thymidine in non-stimulated PBMC expresses the ability of the cells to repair DNA damage. This method was validated by double-stranded DNA measurements. Both catalase and Fe2+ increased DNA repair, the former by preventing re-breakage of newly repaired DNA and the latter by introducing additional DNA damage, which enhanced DNA repair. Better understanding of DNA repair processes will enable to minimize DNA damage induced by oxidative stress.