A multicenter comparison of quantification methods for antisense oligonucleotide-induced DMD exon 51 skipping in Duchenne muscular dystrophy cell cultures

Background

Duchenne muscular dystrophy is a lethal disease caused by lack of dystrophin. Skipping of exons adjacent to out-of-frame deletions has proven to restore dystrophin expression in Duchenne patients. Exon 51 has been the most studied target in both preclinical and clinical settings and the availability of standardized procedures to quantify exon skipping would be advantageous for the evaluation of preclinical and clinical data.

Objective

To compare methods currently used to quantify antisense oligonucleotide–induced exon 51 skipping in the DMD transcript and to provide guidance about the method to use.

Methods

Six laboratories shared blinded RNA samples from Duchenne patient-derived muscle cells treated with different amounts of exon 51 targeting antisense oligonucleotide. Exon 51 skipping levels were quantified using five different techniques: digital droplet PCR, single PCR assessed with Agilent bioanalyzer, nested PCR with agarose gel image analysis by either ImageJ or GeneTools software and quantitative real-time PCR.

Results

Differences in mean exon skipping levels and dispersion around the mean were observed across the different techniques. Results obtained by digital droplet PCR were reproducible and showed the smallest dispersion. Exon skipping quantification with the other methods showed overestimation of exon skipping or high data variation.

Conclusions

Our results suggest that digital droplet PCR was the most precise and quantitative method. The quantification of exon 51 skipping by Agilent bioanalyzer after a single round of PCR was the second-best choice with a 2.3-fold overestimation of exon 51 skipping levels compared to digital droplet PCR.

Surfactant and perfluorocarbon aerosolization during different mechanical ventilation strategies by means of inhalation catheters: an in vitro study

BACKGROUND

Aerosol delivery of surfactant and perfluorocarbon (PFC) is a desirable therapeutic approach for the treatment of various lung diseases in patients undergoing mechanical ventilation. However, the behavior of these substances during aerosolization differs significantly from that of aqueous solutions. In particular, the high vapor pressure of many PFCs tends to result in greater evaporation during mechanical ventilation.

METHODS

Three PFCs and surfactant were aerosolized during mechanical ventilation by means of three intratracheal inhalation catheters (IC) with different air flow rates (IC-1.23, IC-1.1, and IC-1.4), with their aerosol generating tip placed at the distal end of the endotracheal tube (i.d. 4 mm). The influence of four different ventilation strategies on aerosol production rate and PFC and surfactant recovery was studied. The changes in intrapulmonary pressure produced by the air jets of each IC were measured.

RESULTS

With IC-1.23 and IC-1.1, the highest rates of aerosol production were achieved using FC75 (2.27±0.18 and 0.76±0.01, respectively) followed by PFOB (1.74±0.06 and 0.56±0.04), PFD (0.82±0.01 and 0.21±0.01), and surfactant (0.42±0.05 and 0.092±0.01). With IC-1.4 modest aerosol production was obtained irrespective of the aerosolized compound. Mechanical ventilation influenced aerosol recovery, with the trend being toward recovering higher percentages of the compounds with lower peak inspiratory pressure (PIP) and lower respiratory rate (RR) settings. The highest percentages of the initial volume were recovered with IC-1.23 (between 65.43%±4.2 FC75 and 90.21%±4.71 surfactant) followed by IC-1.1 (between 46.48%±4.46 FC75 and 73.19%±2.82 PFOB) and IC-1.4 (between 4.65%±4.36 FC75 and 63.24%±9.71 surfactant). Each of three of the ICs were found to increase the intrapulmonary pressure by about 2-3 cmH₂O during mechanical ventilation.

CONCLUSIONS

Despite of mechanical ventilation, IC-1.23 and IC-1.1 were able to deliver significant amounts of surfactant and perfluorocarbon to the lung model. Changes in PIP and RR directly influence the percentage of surfactant and perfluorocarbon recovered.

Bronchoalveolar lavage versus bolus administration of lucinactant, a synthetic surfactant in meconium aspiration in newborn lambs

This study was designed to study effects of lung lavage versus the classical bolus instillation with a peptide-based synthetic surfactant (lucinactant) in a model of Meconium Aspiration Syndrome (MAS). Eighteen newborn lambs received meconium and were randomized to: the experimental meconium installation (eMAS) group-lambs with eMAS kept on conventional mechanical ventilation (control); the SF-Bolus group-eMAS receiving a lucinactant bolus (30 mg/ml); or the D-SF-Lavage group-eMAS treated with dilute lucinactant bronchoalveolar lavage (10 mg/ml). Systemic and pulmonary arterial pressures, blood gases, and pulmonary mechanics were recorded for 180 min. In addition, the intrapulmonary distribution of the lucinactant was determined using dye-labeled microspheres. Following meconium instillation, severe hypoxia, hypercapnia, acidosis, and pulmonary hypertension developed, and dynamic compliance decreased (50% from baseline). After lung lavage with dilute lucinactant, gas exchange significantly improved versus bolus instillation (P < 0.05). Further, only in the lavage group did pulmonary arterial pressure return to basal values and dynamic compliance significantly increased. Both lung lavage and bolus techniques for the administration of lucinactant resulted in a non-uniform lung distribution. In conclusion, in newborn lambs with respiratory failure and pulmonary hypertension induced by meconium, lung lavage with dilute lucinactant seems to be an effective and safe alternative for treatment for MAS.

Early Cerebral Hemodynamic, Metabolic, and Histological Changes in Hypoxic-Ischemic Fetal Lambs during Postnatal Life

The hemodynamic, metabolic, and biochemical changes produced during the transition from fetal to neonatal life may be aggravated if an episode of asphyxia occurs during fetal life. The aim of the study was to examine regional cerebral blood flow (RCBF), histological changes, and cerebral brain metabolism in preterm lambs, and to analyze the role of oxidative stress in the first hours of postnatal life following severe fetal asphyxia. Eighteen chronically instrumented newborn lambs were randomly assigned to either a control group or the hypoxic-ischemic (HI) group, in which case fetal asphyxia was induced just before delivery. All the animals were maintained on intermittent positive pressure ventilation for 3 h after delivery. During the HI insult, the injured group developed acidosis, hypoxia, hypercapnia, lactic acidosis, and tachycardia (relative to the control group), without hypotension. The intermittent positive pressure ventilation transiently improved gas exchange and cardiovascular parameters. After HI injury and during ventilatory support, there continued to be an increased RCBF in inner regions among the HI group, but no significant differences were detected in cortical flow compared to the control group. Also, the magnitude of the increase in TUNEL positive cells (apoptosis) and antioxidant enzymes, and decrease of ATP reserves was significantly greater in the brain regions where the RCBF was not higher. In conclusion, our findings identify early metabolic, histological, and hemodynamic changes involved in brain damage in premature asphyxiated lambs. Such changes have been described in human neonates, so our model could be useful to test the safety and the effectiveness of different neuroprotective or ventilation strategies applied in the first hours after fetal HI injury.