Ventilator-associated respiratory infections in children on home invasive mechanical ventilation.

Ventilator-associated respiratory tract infections (VARTI) are among the most common indications for hospitalization among children with chronic respiratory failure requiring at-home ventilation. This review aims to provide an overview of the key clinical features, diagnostic approaches, and management strategies for home VARTIs while highlighting the challenges in diagnosis and management.

Intrinsic mitochondrial DNA repair defects in Ataxia Telangiectasia.

Ataxia Telangiectasia (A-T) is a progressive childhood disorder characterized most notably by cerebellar degeneration and predisposition to cancer. A-T is caused by mutations in the kinase ATM, a master regulator of the DNA double-strand break response. In addition to DNA-damage signaling defects, A-T cells display mitochondrial dysfunction that is thought to contribute to A-T pathogenesis. However, the molecular mechanism leading to mitochondrial dysfunction in A-T remains unclear. Here, we show that lack of ATM leads to reduced mitochondrial DNA (mtDNA) integrity and mitochondrial dysfunction, which are associated to defective mtDNA repair. While protein levels of mtDNA repair proteins are essentially normal, in the absence of ATM levels specifically of DNA ligase III (Lig3), the only DNA ligase working in mitochondria is reduced. The reduction of Lig3 is observed in different A-T patient cells, in brain and pre-B cells derived from ATM knockout mice as well as upon transient or stable knockdown of ATM. Furthermore, pharmacological inhibition of Lig3 in wild type cells phenocopies the mtDNA repair defects observed in A-T patient cells. As targeted deletion of LIG3 in the central nervous system causes debilitating ataxia in mice, reduced Lig3 protein levels and the consequent mtDNA repair defect may contribute to A-T neurodegeneration. A-T is thus the first disease characterized by diminished Lig3.

Mononuclear and dinuclear mechanisms for catalysis of phosphodiester cleavage by alkaline earth metal ions in aqueous solution.

In biological systems, enzymes often use metal ions, especially Mg(2+), to catalyze phosphodiesterolysis, and model aqueous studies represent an important avenue of examining the contributions of these ions to catalysis. We have examined Mg(2+) and Ca(2+) catalyzed hydrolysis of the model phosphodiester thymidine-5'-p-nitrophenyl phosphate (T5PNP). At 25 degrees C, we find that, despite their different Lewis acidities, these ions have similar catalytic ability with second-order rate constants for attack of T5PNP by hydroxide (k(OH)) of 4.1x10(-4)M(-1)s(-1) and 3.7x10(-4)M(-1)s(-1) in the presence of 0.30M Mg(2+) and Ca(2+), respectively, compared to 8.3x10(-7)M(-1)s(-1) in the absence of divalent metal ion. Examining the dependence of k(OH) on [M(2+)] at 50 degrees C indicates different kinetic mechanisms with Mg(2+) utilizing a single ion mechanism and Ca(2+) operating by parallel single and double ion mechanisms. Association of the metal ion(s) occurs prior to nucleophilic attack by hydroxide. Comparing the k(OH) values reveals a single Mg(2+) catalyzes the reaction by 1800-fold whereas a single Ca(2+) ion catalyzes the reaction by only 90-fold. The second Ca(2+) provides an additional 10-fold catalysis, significantly reducing the catalytic disparity between Mg(2+) and Ca(2+).