Ultrasonic and jet aerosolization of phospholipids and the effects on surface activity

New modes of surfactant delivery

The provision of exogenous surfactant to premature infants with respiratory distress syndrome has revolutionized the way we care for these patients, significantly improving survival and decreasing morbidity. Currently, the Intubate-SURfactant-Extubate (INSURE) to non-invasive ventilation method remains the standard method for surfactant delivery in the United States. However, the INSURE method requires intubation via direct visualization with a laryngoscope and possible need for sedation. Both carry significant risk to the patients, prompting the development of less invasive ways of safely and efficaciously providing surfactant to newborn infants. The present article reviews and describes the benefits and limitations of several of these alternative methods, including Less Invasive Surfactant Administration (LISA), Minimally Invasive Surfactant Therapy (MIST), via aerosolization, laryngeal mask airway (LMA), and direct nasopharyngeal deposition, focusing on assessment of clinical benefits and the level/risk of invasiveness.

Pulmonary surfactant as a versatile biomaterial to fight COVID-19

The COVID-19 pandemic has wielded an enormous pressure on global health care systems, economics and politics. Ongoing vaccination campaigns effectively attenuate viral spreading, leading to a reduction of infected individuals, hospitalizations and mortality. Nevertheless, the development of safe and effective vaccines as well as their global deployment is time-consuming and challenging. In addition, such preventive measures have no effect on already infected individuals and can show reduced efficacy against SARS-CoV-2 variants that escape vaccine-induced host immune responses. Therefore, it is crucial to continue the development of specific COVID-19 targeting therapeutics, including small molecular drugs, antibodies and nucleic acids. However, despite clear advantages of local drug delivery to the lung, inhalation therapy of such antivirals remains difficult. This review aims to highlight the potential of pulmonary surfactant (PS) in the treatment of COVID-19. Since SARS-CoV-2 infection can progress to COVID-19-related acute respiratory distress syndrome (CARDS), which is associated with PS deficiency and inflammation, replacement therapy with exogenous surfactant can be considered to counter lung dysfunction. In addition, due to its surface-active properties and membrane-interaction potential, PS can be repurposed to enhance drug spreading along the respiratory epithelium and to promote intracellular drug delivery. By merging these beneficial features, PS can be regarded as a versatile biomaterial to combat respiratory infections, in particular COVID-19.

Deposition of Aerosolized Lucinactant in Nonhuman Primates

Background: Lucinactant for inhalation is an investigational noninvasive, aerosolized surfactant replacement therapy for treatment of preterm neonates with respiratory distress syndrome. Lucinactant for inhalation consists of lyophilized lucinactant and the Aerosurf^® Delivery System (ADS). The objective of this study was to characterize the total and regional pulmonary deposition of lucinactant delivered by the ADS in nonhuman primates (NHPs).

Methods: Lucinactant was radiolabeled by the addition of technetium-99m (^99mTc)-sulfur colloid. The radiolabeled aerosol was characterized and validated using a Mercer cascade impactor. An in vivo deposition study was performed in three cynomolgus macaques. Radiolabeled lucinactant was aerosolized using the ADS and delivered via nasal cannula under 5 cm H₂O nasal continuous positive airway pressure (nCPAP) for 5–9 minutes. A two-dimensional planar image was acquired immediately after aerosol administration, followed by a three-dimensional single-photon emission computed tomography (SPECT) image and a second planar image. The images were analyzed to determine the pulmonary (lungs) and extrapulmonary (nose + mouth, trachea, stomach) distribution. The SPECT data were used to determine regional deposition.

Results: The radiolabed lucinactant aerosol had a mass median aerodynamic diameter = 2.91 μm, geometric standard deviation (GSD) = 1.81, and an activity median aerodynamic diameter = 2.92 μm, GSD = 2.06. Aerosolized lucinactant was observed to deposit in the lungs (11.4%), nose + mouth (79.9%), trachea (7.3%), and stomach (1.4%). Analysis of the SPECT image demonstrated that the regional deposition within the lung was generally homogeneous. Aerosolized lucinactant was deposited in both the central (52.8% ± 1.2%) and peripheral (47.2% ± 1.2%) regions of the lungs.

Conclusion: Aerosolized lucinactant, delivered using the ADS via constant flow nCPAP, is deposited in all regions of the lungs demonstrating that surfactant can be aerosolized and delivered noninvasively to NHPs.

Aerosolized surfactant in neonatal respiratory distress syndrome: Phase I study

BACKGROUND

Treating respiratory distress syndrome (RDS) with intratracheal surfactant requires endotracheal intubation and mechanical ventilation, (MV) with their attendant risks. Use of non-invasive respiratory support in the delivery room averts the need for MV but delays surfactant administration.

OBJECTIVE

We hypothesized that aerosolized surfactant is feasible and safe in infants 24^0/7-36^6/7 weeks gestational age (GA) with RDS, receiving non-invasive respiratory support.

DESIGN/METHODS

In an unblinded Phase I study, sequentially enrolled infants with RDS stratified by GA received increasing doses (100 or 200 mg/kg of phospholipid) and dilutions (12.5 or 8.3 mg/ml) of surfactant using a jet nebulizer. Infants were monitored clinically and with cerebral oximetry.

RESULTS

Seventeen infants were enrolled. Age at start of first dose and dose duration were 4.9 (3.4-10.1) and 2.1 (1.0-2.8) hours respectively. Two infants in the lowest GA stratum (24^0/7-28^6/7) required intubation within 2 h after the first dose. Fifteen infants completed the study; 13 received two doses. Infants tolerated the aerosol treatment well. No other significant adverse events were identified. Parental permission for cerebral oximetry was obtained in 16 infants. In the two infants who later exited the study, values prior to start of aerosolized surfactant were lower compared to 14 infants who completed the study (p = 0.0835), increased after start of study intervention (p = 0.0105) and decreased after intubation (p = 0.0003).

CONCLUSIONS

We have demonstrated the feasibility and safety of aerosolized surfactant in preterm infants receiving non-invasive respiratory support. The treatment was well tolerated by infants and clinical caregivers.

Polymer Lung Surfactants

Animal-derived lung surfactants annually save 40 000 infants with neonatal respiratory distress syndrome (NRDS) in the United States. Lung surfactants have further potential for treating about 190 000 adult patients with acute respiratory distress syndrome (ARDS) each year. To this end, the properties of current therapeutics need to be modified. Although the limitations of current therapeutics have been recognized since the 1990s, there has been little improvement. To address this gap, our laboratory has been exploring a radically different approach in which, instead of lipids, proteins, or peptides, synthetic polymers are used as the active ingredient. This endeavor has led to an identification of a promising polymer-based lung surfactant candidate, poly(styrene-b-ethylene glycol) (PS-PEG) polymer nanomicelles. PS-PEG micelles produce extremely low surface tension under high compression because PS-PEG micelles have a strong affinity to the air-water interface. NMR measurements support that PS-PEG micelles are less hydrated than ordinary polymer micelles. Studies using mouse models of acid aspiration confirm that PS-PEG lung surfactant is safe and efficacious.

Lung deposition of nebulized surfactant in newborn piglets

BACKGROUND

It would be advantageous for the treatment of neonatal respiratory distress syndrome if effective amounts of surfactant could be delivered by nebulization.

OBJECTIVE

To investigate lung deposition and distribution of nebulized porcine surfactant using an investigational eFlow neonatal nebulizer.

METHODS

While lying on one side, 1-day-old piglets inhaled 200 mg·kg(-1) of nebulized surfactant via mask, nasal prongs, or tracheal tube. The surfactant was diluted with normal saline to 40 mg·ml(-1) and labeled with (99m)technetium-labelled nanocolloid. Undiluted surfactant (80 mg·ml(-1)) was instilled tracheally in a fourth group. Each group had 8 animals. Lung deposition was measured by gamma scintigraphy, and deposition values were presented as a percentage of the nebulized or instilled dose.

RESULTS

The median lung deposition of inhaled surfactant was 5% (range 3-16) via mask, 14% (2-40) via prongs, and 45% (25-56) via tracheal tube (p < 0.05). It was 88% (71-96) with instillation. In all groups, the surfactant preferentially went to the dependent lung. Deposition ratios (upper lung/both lungs) were 0.32 (0.13-0.58), 0.15 (0.05-0.58), 0.16 (0.11-0.23), and 0.08 (0.03-0.46).

CONCLUSIONS

Using this nebulizer, the lung depositions of porcine surfactant were 45% via endotracheal tube and 14% via nasal-continuous positive airway pressure (prongs). These figures might be physiologically relevant, but still have to be confirmed in efficacy studies.

Therapeutic effects of inhaling aerosolized surfactant alone or with dexamethasone generated by a novel noninvasive apparatus on acute lung injury in rats

BACKGROUND

Pulmonary surfactant (PS) administration has been attempted for the treatment of adults with acute lung injury (ALI)/adult respiratory distress syndrome. Aerosolized surfactants inhaled by spontaneous breathing may be an effective method of surfactant-based therapies. Using a noninvasive apparatus, we evaluated the therapeutic effects of aerosolized PS alone or together with dexamethasone (Dex) on a rat model of ALI.

METHODS

Severe ALI was induced by intravenous injection of 20% oleic acid (0.2 mL/kg) into adult Sprague-Dawley rats. Animals were divided into eight groups: sham (n = 10); model (injury only, n = 10); normal saline (NS) aerosol driven by compressed air (air-NS, n = 13); PS aerosol driven by compressed air (air-PS, n = 13); NS aerosol driven by O2 (O2-NS, n = 13); PS aerosol driven by O2 (O2-PS, n = 13); Dex aerosol driven by O2 (O2-Dex, n = 13); and PS and Dex aerosol driven by O2 (O2-PS-Dex, n = 13). Blood gases, breathing rate, lung index, total protein, and proinflammatory cytokines (tumor necrosis factor-α, interleukin 1β, interleukin 6) in the bronchoalveolar lavage fluid (BALF), and lung histology were examined.

RESULTS

Animals treated with air-PS for 20 minutes had significantly improved lung function, reduced pulmonary edema, decreased concentration of total protein and proinflammatory cytokines in BALF, ameliorated lung injury, and improved animal survival. In the O2-PS group, the breathing rates and lung injury scores were significantly lower than that of the air-PS group. In the O2-PS-Dex group, lung edema, total protein, and inflammatory cytokines in BALF were significantly reduced in comparison with the O2-PS group.

CONCLUSION

Inhalation of aerosolized PS generated by the noninvasive apparatus could significantly reduce lung injury, while using oxygen line available in the clinical wards to generate PS aerosol is more convenient and adds further benefits. This method can also be used to deliver Dex and other therapeutic agents to ameliorate lung injury.

Surfactant therapy for acute lung injury and acute respiratory distress syndrome

This article examines exogenous lung surfactant replacement therapy and its usefulness in mitigating clinical acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). Surfactant therapy is beneficial in term infants with pneumonia and meconium aspiration lung injury, and in children up to age 21 years with direct pulmonary forms of ALI/ARDS. However, extension of exogenous surfactant therapy to adults with respiratory failure and clinical ALI/ARDS remains a challenge. This article reviews clinical studies of surfactant therapy in pediatric and adult patients with ALI/ARDS, focusing on its potential advantages in patients with direct pulmonary forms of these syndromes.

Aerosolised surfactant generated by a novel noninvasive apparatus reduced acute lung injury in rats

Introduction

Exogenous surfactant has been explored as a potential therapy for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). In the present study, a nebuliser driven by oxygen lines found in the hospital was developed to deliver aerosolised porcine pulmonary surfactant (PPS). We hypothesised that aerosolised surfactant inhaled through spontaneous breathing may effectively reduce severe lung injury.

Methods

Rats were intravenously injected with oleic acid (OA) to induce ALI and 30 minutes later they were divided into five groups: model (injury only), PPS aerosol (PPS-aer), saline aerosol (saline-aer), PPS instillation (PPS-inst), and saline instillation (Saline-Inst). Blood gases, lung histology, and protein and TNF-α concentrations in the bronchoalveolar lavage fluid (BALF) were examined.

Results

The PPS aerosol particles were less than 2.0 μm in size as determined by a laser aerosol particle counter. Treatment of animals with a PPS aerosol significantly increased the phospholipid content in the BALF, improved lung function, reduced pulmonary oedema, decreased total protein and TNF-α concentrations in BALF, ameliorated lung injury and improved animal survival. These therapeutic effects are similar to those seen in the PPS-inst group.

Conclusions

This new method of PPS aerosolisation combines the therapeutic effects of a surfactant with partial oxygen inhalation under spontaneous breathing. It is an effective, simple and safe method of administering an exogenous surfactant.

Surfactant for pediatric acute lung injury

This article reviews exogenous surfactant therapy and its use in mitigating acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) in infants, children, and adults. Biophysical and animal research documenting surfactant dysfunction in ALI/ARDS is described, and the scientific rationale for treatment with exogenous surfactant is discussed. Major emphasis is placed on reviewing clinical studies of surfactant therapy in pediatric and adult patients who have ALI/ARDS. Particular advantages from surfactant therapy in direct pulmonary forms of these syndromes are described. Also discussed are additional factors affecting the efficacy of exogenous surfactants in ALI/ARDS.

Aerosolized surfactants

PURPOSE OF REVIEW

To present existing data on the potential use of aerosolized surfactants for treatment of neonatal respiratory distress syndrome in the era of noninvasive ventilatory support.

RECENT FINDINGS

Current surfactant therapy requires endotracheal intubation and application of positive pressure ventilation. Instillation of the drug itself can be complicated by 'peridosing adverse events' including, but not limited to, desaturations, bradycardias, changes in blood pressure, drug reflux and even the need for reintubations. Increasing use of noninvasive ventilatory support for neonatal respiratory distress syndrome has motivated clinicians and researchers to look for alternate ways of introducing surfactants to patients. Aerosolized surfactants have been tested in animal models of respiratory distress syndrome. In addition, four small clinical studies have been performed to date. The effectiveness of this form of treatment requires further study, however, which will need to include optimizing the dose of aerosolized surfactant, choosing particle size, developing the best delivery system, and using a surfactant formulation that maintains its activity once aerosolized.

SUMMARY

Aerosolized surfactants for neonatal respiratory distress syndrome may prevent the need for endotracheal intubation. Appropriately designed randomized controlled studies are required to determine if this form of surfactant administration is as effective and safe as tracheal instillation.

Ultrasonic surfactant nebulization with different exciting frequencies

Intratracheal bolus instillation of natural lung surfactant is the treatment of choice in neonatal respiratory distress syndrome and an increasing part in adults' therapy. For reasons of hemodynamics, surfactant distribution and efficiency the application mode should be improved. Nebulization seems to have some advantages but its technical realization is difficult. The aim of the present study was to investigate if ultrasonic nebulization with exciting frequencies higher than 2.8 MHz can improve the efficiency of surfactant nebulization without changing the surface-active properties of the material. Exciting frequencies of 1.7, 3.3 and 4.0 MHz were used to produce a surfactant aerosol. The phospholipid content in the liquefied aerosol and particle size distinctly dropped with higher frequencies. The surface activity was not altered in the produced aerosol and neither in the surfactant remaining in the nebulizer. Although possible, ultrasonic nebulization of surfactant suspensions is ineffective because of a striking decrease in phospholipid content.

Nebulisation of surfactants in an animal model of neonatal respiratory distress

AIMS

To evaluate pulmonary deposition and gas exchange following nebulisation of two surfactants by either a jet or an ultrasonic nebuliser.

METHOD

After bronchoalveolar lavage (BAL), 19 rabbits were ventilated in four groups. Group A1 (n = 5) and A2 (n = 6) received Technetium-99m labelled Exosurf, and groups B1 (n = 4) and B2 (n = 4) received radiolabelled Survanta. Groups A1 and B1 received jet nebuliser therapy, whereas groups A2 and B2 received ultrasonic nebuliser. Pulmonary deposition, distribution, and blood gases were determined.

RESULTS

Pulmonary deposition as per cent of initial dose and mg lipid) was 0.28(0.10)% or 0.59(0.21) mg in group A1, 1.05(0.23)% or 2.21(0.48) mg in group A2, 0.08(0.02)% or 0.30(0.08) mg in group B1, and 0.09(0.02)% or 0.34(0.08) mg in group B2. Deposition in group A2 was greater than in other groups (p = 0.001). Group A2 showed a small improvement in blood gases.

CONCLUSIONS

Even the highest deposition--ultrasonic nebuliser with Exosurf--achieved limited clinical effect. The aerosol route is currently not effective for surfactant treatment.

The effect of exogenous surfactant therapy on lung function following cardiopulmonary bypass

OBJECTIVE

Pilot study to investigate the effect of exogenous surfactant therapy on lung function following cardiopulmonary bypass (CPB).

DESIGN

Prospective randomized controlled study.

SETTING

Adult intensive care unit of a postgraduate cardiothoracic hospital.

PATIENTS

Sixteen adult patients undergoing elective coronary artery revascularization surgery without a history of preoperative respiratory disease.

INTERVENTIONS

Artificial lung-expanding compound (ALEC, Britannia Pharmaceuticals, Crawley, UK) 3.2 g, was given via a bronchoscope 60 min after bypass in eight patients. Eight control subjects received air.

MAIN OUTCOME MEASUREMENTS

Lung function tests during IPPV (arterial blood gas tensions, Crs, FRC, TLco, KCO) were measured prior to CPB, before therapy, and at regular intervals up to 180 min afterwards.

RESULTS

The CPB caused a significant impairment of lung function in both groups with an increase in A-a gradient (+47 +/- 11 mm Hg in the ALEC group and +44 +/- 17 mm Hg in controls) and reductions in FRC (-290 +/- 121 ml in the ALEC group and -470 +/- 132 ml in controls), TLco (-1.6 +/- 0.3 ml/min/mm Hg in the ALEC group and -2.2 +/- 0.3 ml/min/mm Hg in controls), and Crs (-10 +/- 1 ml/cm H2O in the ALEC group and -21 +/- 4 ml/cm H2O in controls). The ALEC therapy did not affect A-a gradient, FRC, and Crs compared with controls. However, TLco was significantly lower in the ALEC group following therapy (120 min after treatment -0.1 +/- 0.3 ml/min/mm Hg in ALEC group and +1.0 +/- 0.3 ml/min/mm Hg in controls).

CONCLUSIONS

A single 3.2-g dose of ALEC administered as a bolus bronchoscopically does not improve lung function following CPB and may impair gas transfer.

Acute effects of a single dose of porcine surfactant on patients with the adult respiratory distress syndrome

In an attempt to restore functional surfactant to the lungs of patients with the adult respiratory distress syndrome (ARDS), we have treated six patients within the first 2 days of the onset of ARDS with a single dose of hydrophobic components of porcine surfactant. Surfactant (4 g in 50 ml) delivered via a bronchoscope in aliquots to each of the lobar bronchi was well tolerated and caused a modest transient improvement in gas exchange. No significant changes in chest radiograph or lung compliance were detected. Analysis of bronchoalveolar lavage (BAL) fluid showed no change in albumin, alpha-1-proteinase inhibitor specific activity, or cell count. Bronchoalveolar lavage phospholipid concentrations were elevated 3 h after surfactant administration relative to preadministration levels and fell by 24 h. In addition, in two patients we found reduced inhibition of surfactant function in BAL after surfactant replacement. These observations suggest a role for surfactant replacement in the treatment of patients with ARDS and support the need for continuing investigation.

Multicentre randomised trial comparing high and low dose surfactant regimens for the treatment of respiratory distress syndrome (the Curosurf 4 trial)

A randomised trial was conducted in 82 centres using the porcine surfactant extract, Curosurf, to compare two regimens of multiple doses to treat infants with respiratory distress syndrome and arterial to alveolar oxygen tension ratio < 0.22. Infants were randomly allocated to a low dosage group (100 mg/kg initially, with two further doses at 12 and 24 hours to a maximum cumulative total of 300 mg/kg; n = 1069) or a high dosage group (200 mg/kg initially with up to four further doses of 100 mg/kg to a maximum cumulative total of 600 mg/kg; n = 1099). There was no difference between those allocated low and high dosage in the rates of death or oxygen dependency at 28 days (51.1% v 50.8%; difference -0.3%, 95% confidence interval (CI) -4.6% to 3.9%), death before discharge (25.0% v 23.5%; difference -1.5%, 95% CI -5.1% to 2.2%), and death or oxygen dependency at the expected date of delivery (32.2% v 31.0%; difference -1.2%, 95% CI -5.2% to 2.7%). For 14 predefined secondary measures of clinical outcome there were no significant differences between the groups but the comparison of duration of supplemental oxygen > 40% did attain significance; 48.4% of babies in the low dose group needed > 40% oxygen after three days compared with 42.6% of those in the high dose group. The total amount of surfactant administered in the low dose regimen (mean 242 mg phospholipid/kg) was probably enough to replace the entire pulmonary surfactant pool. Adopting the low dose regimen would lead to considerable cost savings, with no clinically significant loss in efficacy.

Delivery of therapeutic aerosols to intubated babies

Delivery of drug aerosols to the lungs of ventilated neonates by metered dose inhaler and spacer (Aerochamber) and ultrasonic nebuliser (Pentasonic) was assessed using sodium cromoglycate. The mean proportion of a known intratracheal dose of sodium cromoglycate excreted in the urine of four intubated infants was 37.5%. After assuming that 38% of the sodium cromoglycate aerosol reaching the neonatal lung will be excreted in the urine, three puffs (15 mg) delivered by metered dose inhaler and spacer resulted in a pulmonary dose of 258 micrograms (1.7%, n = 7). A dose of 20 mg (4 ml) sodium cromoglycate ultrasonically nebulised over five minutes into the inspiratory limb of a standard ventilator circuit produced a pulmonary dose of 257 micrograms (1.3%, n = 7). Of two in vitro lung models assessed, a combination of filter and neonatal test lung was superior to a multistage impactor in estimating the in vivo pulmonary sodium cromoglycate dose delivered by metered dose inhaler and spacer (243 micrograms v 1740 micrograms).

Exogenous surfactant treatment for the adult respiratory distress syndrome? A historical perspective

Images

The delivery of therapeutic aerosols through endotracheal tubes

We used an in vitro model system to examine the sites of deposition of aqueous therapeutic aerosols administered through 3-mm, 6-mm, and 9-mm endotracheal tubes (commonly used in infants, children, and adults) at clinically relevant inspiratory flow rates. Aerosol was delivered to the endotracheal tube via a "T" piece and a 90 degree elbow. Aerosol exiting the endotracheal tube passed through an appropriately sized Plexiglas model of the trachea and mainstem bronchi, and then into an 80-liter bag. Aerosol deposited in the "T" and elbow, endotracheal tube, large airway model, and collection bag was quantitated separately using 0.1% uranine as a tracer. Study of a conventional aerosol typical of those in common clinical use (aerodynamic mass median diameter = 3.95 microns) showed that most of the aerosol delivered into each endotracheal tube was deposited before leaving the mainstem bronchi. Substitution of an alternative nebulizer that produced a much smaller aerosol particle size (aerodynamic mass median diameter = 0.54 micron) dramatically decreased aerosol deposition in the "T" and elbow, endotracheal tube, and large airway model, and increased the quantity of aerosol penetrating beyond the mainstem bronchi up to ninefold. The mass median particle diameter of the conventional aerosol was reduced during endotracheal tube and large airway passage by poorly defined aerodynamic mechanisms that selectively removed larger particles. The smaller submicron aerosol was not similarly affected. Thus, conventional therapeutic aerosols appear to penetrate poorly through endotracheal tubes. Use of smaller particle size aerosols in treatment of intubated patients may be an effective way to circumvent this problem.