Elisa Mariani

Respiratory Complex I Dysfunction Due to Mitochondrial DNA Mutations Shifts the Voltage Threshold for Opening of the Permeability Transition Pore toward Resting Levels

We have studied mitochondrial bioenergetics in HL180 cells (a cybrid line harboring the T14484C/ND6 and G14279A/ND6 mtDNA mutations of Leber hereditary optic neuropathy, leading to an ∼50% decrease of ATP synthesis) and XTC.UC1 cells (derived from a thyroid oncocytoma bearing a disruptive frameshift mutation in MT-ND1, which impairs complex I assembly). The addition of rotenone to HL180 cells and of antimycin A to XTC.UC1 cells caused fast mitochondrial membrane depolarization that was prevented by treatment with cyclosporin A, intracellular Ca2+ chelators, and antioxidant. Both cell lines also displayed an anomalous response to oligomycin, with rapid onset of depolarization that was prevented by cyclosporin A and by overexpression of Bcl-2. These findings indicate that depolarization by respiratory chain inhibitors and oligomycin was due to opening of the mitochondrial permeability transition pore (PTP). A shift of the threshold voltage for PTP opening close to the resting potential may therefore be the underlying cause facilitating cell death in diseases affecting complex I activity. This study provides a unifying reading frame for previous observations on mitochondrial dysfunction, bioenergetic defects, and Ca2+ deregulation in mitochondrial diseases. Therapeutic strategies aimed at normalizing the PTP voltage threshold may be instrumental in ameliorating the course of complex I-dependent mitochondrial diseases.

An inherited mitochondrial DNA disruptive mutation shifts to homoplasmy in oncocytic tumor cells

A disruptive frameshift mtDNA mutation affecting the ND5 subunit of complex I is present in homoplasmy in a nasopharyngeal oncocytic tumor and inherited as a heteroplasmic germline mutation recurring in two of the patients siblings. Homoplasmic ND5 mutation in the tumor correlates with lack of the ND6 subunit, suggesting complex I disassembly. A few oncocytic areas, expressing ND6 and heteroplasmic for the ND5 mutation, harbor a de novo homoplasmic ND1 mutation. Since shift to homoplasmy of ND1 and ND5 mutations occurs exclusively in tumor cells, we conclude that complex I mutations may have a selective advantage and accompany oncocytic transformation. Hum Mutat 0, 1–6, 2008.

Combined oesophageal impedance‐pH monitoring in preterm newborn: comparison of two options for layout analysis

Abstract  Gastro‐oesophageal reflux (GOR) is common in preterm infants. Combined multichannel intraluminal impedance and pH monitoring (pH‐MII) is emerging as an useful tool to study both acid and non‐acid GOR in this population. We aimed to highlight main advantages and limits of pH‐MII in preterm infants and to test whether the inclusion of GOR episodes detected only by pH monitoring details better the features of GOR. Fifty‐two symptomatic preterm infants underwent a 24‐hour, continuous and simultaneous measurement of pH‐MII. Each layout was analyzed using two different options: option 1 included GOR episodes detected by MII and then classified as acid or non‐acid according to the associated pH change; option 2 included GOR episodes detected by MII and also GOR episodes detected only by pH sensor. By adopting option 1, a total number of 2834 GOR episodes was detected by MII: 2162 of them were characterized as non‐acid and 672 were characterized as acid. The median (range) number of acid MII‐GOR episodes was 10 (1–52); the median (range) number of non‐acid MII‐GOR episodes was 36.5 (2–119). Median (range) acid MII‐GOR‐bolus exposure index was 0.28% (0.02–2.73%); median (range) non‐acid MII‐GOR‐bolus exposure index was 1.03% (0.06–38.15%). By adopting option 2, an average of 53.2 acid GOR episodes and an average of 11% oesophageal exposure to acid GOR more than by option 1 was detected. An accurate and detailed description of GOR in preterm infants can be obtained only by including in the analysis all acid GOR episodes detected by pH sensor.

The frequency of apneas in very preterm infants is increased after non‐acid gastro‐esophageal reflux

Background  To evaluate whether physical and/or chemical features of gastro‐esophageal reflux (GER) influence its relationship with apnea of prematurity (AOP).

The efficacy of sodium alginate (Gaviscon) for the treatment of gastro-oesophageal reflux in preterm infants.

Background  Gastro‐oesophageal reflux is common in preterm newborns; at present, no studies have evaluated the efficacy of sodium alginate in this population.

Gamma rays induce a p53-independent mitochondrial biogenesis that is counter-regulated by HIF1α

Mitochondrial biogenesis is an orchestrated process that presides to the regulation of the organelles homeostasis within a cell. We show that γ-rays, at doses commonly used in the radiation therapy for cancer treatment, induce an increase in mitochondrial mass and function, in response to a genotoxic stress that pushes cells into senescence, in the presence of a functional p53. Although the main effector of the response to γ-rays is the p53-p21 axis, we demonstrated that mitochondrial biogenesis is only indirectly regulated by p53, whose activation triggers a murine double minute 2 (MDM2)-mediated hypoxia-inducible factor 1α (HIF1α) degradation, leading to the release of peroxisome-proliferator activated receptor gamma co-activator 1β inhibition by HIF1α, thus promoting mitochondrial biogenesis. Mimicking hypoxia by HIF1α stabilization, in fact, blunts the mitochondrial response to γ-rays as well as the induction of p21-mediated cell senescence, indicating prevalence of the hypoxic over the genotoxic response. Finally, we also show in vivo that post-radiotherapy mitochondrial DNA copy number increase well correlates with lack of HIF1α increase in the tissue, concluding this may be a useful molecular tool to infer the trigger of a hypoxic response during radiotherapy, which may lead to failure of activation of cell senescence.

Extensively hydrolyzed protein formula reduces acid gastro-esophageal reflux in symptomatic preterm infants☆

BACKGROUND Gastro-esophageal reflux (GER) is diagnosed frequently in preterm infants. Pharmacological treatment of GER has some potential side effects. Conservative treatment of GER should be the first-line approach and should include body positioning and diet modifications. Formula-fed preterm infants experience frequently symptoms of feeding intolerance. Hydrolyzed protein formula (HPF) is often used in these infants due to their effects on gastrointestinal motility. AIMS To investigate the role of an extensively HPF (eHPF) on GER indexes in formula-fed preterm infants with symptoms of both GER and feeding intolerance. STUDY DESIGN Randomized crossover trial. SUBJECTS Preterm infants (gestational age ≤33 weeks) with symptoms of feeding intolerance (large gastric residuals, abdominal distension and constipation) and GER (frequent regurgitations and/or postprandial desaturations). OUTCOME MEASURES GER indexes detected by 24-h combined multichannel intraluminal impedance and pH monitoring. GER indexes detected after 4 feeds of an eHPF were compared to those detected after 4 feeds of a standard preterm formula (SPF) by Wilcoxon signed ranks test. A p<0.05 was considered statistically significant. RESULTS eHPF significantly reduced the number of GERs detected by pH monitoring (p=0.036) and also the reflux index (p=0.044) compared to SPF. No differences in impedance bolus exposure indexes nor in GER height were detected. CONCLUSIONS The use of an eHPF should be evaluated for reducing esophageal acid exposure in preterm infants with feeding intolerance and symptoms of GER. Future research should focus on the evaluation of an eHPF adequate for preterm infants in improving clinical symptoms of GER.

A thickened formula does not reduce apneas related to gastroesophageal reflux in preterm infants.

Background: Apnea of prematurity (AOP) occurs frequently in preterm infants and a variable proportion of AOP can be induced by gastroesophageal reflux (GER). Conservative treatment, including dietary modifications, should be the first-line approach for both GER and GER-related apneas in this population. Objectives: To evaluate the efficacy of a starch-thickened preterm formula (PF) in reducing the frequency of apneas related to GER. Methods: Preterm infants with AOP were studied by combined impedance and pH monitoring and polysomnography. The 6-hour study period included two feeds, one of a commercially available PF and one of the same formula thickened with amylopectin (TPF). GER indexes, apneas and GER-related apneas detected after TPF and PF feeds were compared by Wilcoxon signed-rank test. Results: 24 infants were studied. During 140 h of registration, 289 apneas (147 after TPF and 142 after PF; p = 0.876), and 861 GER episodes (400 after TPF and 461 after PF; p = 0.465) were recorded. No difference in the number of AOP was found between TPF and PF. A significant reduction in acid exposure was found after TPF; there was no influence on non-acid GER indexes. The frequency of GER-related apneas did not differ between TPF and PF. Conclusions: A formula thickened with amylopectin did not reduce the number of AOP or GER-related apneas. It reduced acid GER features but had no effect on non-acid GER indexes. Future research should focus on exploring different conservative strategies to treat GER-related apneas in preterm infants.

The RET51/FKBP52 complex and its involvement in Parkinson disease

The tyrosine kinase receptor RET51 is expressed in distinct families of neurons where it promotes different functions. FKBP52 is an immunophilin with neuroprotective effects on different kinds of neurons. In this paper, we demonstrate that RET51 activation by both glial cell line-derived neurotrophic factor (GDNF) and NGF triggers the formation of RET51/FKBP52 complex. The substitution of the tyrosine 905 of RET51, a key residue phosphorylated by both GDNF and NGF, disrupts the RET51/FKBP52 complex. NGF and GDNF have a functional role in dopaminergic (DA) neurons where RET51 and FKBP52 are expressed with a yet undefined function. To clarify if RET51/FKBP52 complex should exert its function in DA neurons, we used an indirect approach by screening the genes encoding for RET51 and FKBP52 in a group of 30 Parkinsons disease patients. The degeneration of DA neurons is the main feature of PD, which is associated to a complex multifactorial aetiology combining environmental, age-related and genetic factors. We found a compound heterozygous carrying two mutations in RET and FKBP52 that are sufficient to disrupt the RET51/FKBP52 complex, indicating its potential role in PD.

Protein content and fortification of human milk influence gastroesophageal reflux in preterm infants.

Objectives: Preterm human milk (HM) may provide insufficient energy and nutrients and thus may need to be fortified. Our aim was to determine whether fat content, protein content, and osmolality of HM before and after fortification may affect gastroesophageal reflux (GER) in symptomatic preterm infants. Methods: Gastroesophageal reflux was evaluated in 17 symptomatic preterm newborns fed naïve and fortified HM by combined pH/intraluminal-impedance monitoring (pH-MII). Human milk fat and protein content was analysed by a near-infrared reflectance analysis. Human milk osmolality was tested before and after fortification. Gastroesophageal reflux indexes measured before and after fortification were compared and were also related to HM fat and protein content and osmolality before and after fortification. Results: An inverse correlation was found between naïve HM protein content and acid reflux index (RIpH: P = 0.041, ρ =−0.501). After fortification, osmolality often exceeded the values recommended for infant feeds; furthermore, a statistically significant (P < 0.05) increase in nonacid reflux indexes was observed. Conclusions: Protein content of naïve HM may influence acid GER in preterm infants. A standard fortification of HM may worsen nonacid GER indexes and, due to the extreme variability in HM composition, may overcome both recommended protein intake and HM osmolality. Thus, an individualised fortification, based on the analysis of the composition of naïve HM, could optimise both nutrient intake and feeding tolerance.