Lysophosphatidylinositols Are Upregulated After Human β-Cell Loss and Potentiate Insulin Release

In this study, we identified new lipid species associated with the loss of pancreatic β-cells triggering diabetes. We performed lipidomics measurements on serum from prediabetic mice lacking β-cell prohibitin-2 (a model of monogenic diabetes) patients without previous history of diabetes but scheduled for pancreaticoduodenectomy resulting in the acute reduction of their β-cell mass (∼50%), and patients with type 2 diabetes (T2D). We found lysophosphatidylinositols (lysoPIs) were the main circulating lipid species altered in prediabetic mice. The changes were confirmed in the patients with acute reduction of their β-cell mass and in those with T2D. Increased lysoPIs significantly correlated with HbA1c (reflecting glycemic control), fasting glycemia, and disposition index, and did not correlate with insulin resistance or obesity in human patients with T2D. INS-1E β-cells as well as pancreatic islets isolated from nondiabetic mice and human donors exposed to exogenous lysoPIs showed potentiated glucose-stimulated and basal insulin secretion. Finally, addition of exogenous lysoPIs partially rescued impaired glucose-stimulated insulin secretion in islets from mice and humans in the diabetic state. Overall, lysoPIs appear to be lipid species upregulated in the prediabetic stage associated with the loss of β-cells and that support the secretory function of the remaining β-cells.

ARTICLE HIGHLIGHTS

Circulating lysophosphatidylinositols (lysoPIs) are increased in situations associated with β-cell loss in mice and humans such as (pre-)diabetes, and hemipancreatectomy. Pancreatic islets isolated from nondiabetic mice and human donors, as well as INS-1E β-cells, exposed to exogenous lysoPIs exhibited potentiated glucose-stimulated and basal insulin secretion. Addition of exogenous lysoPIs partially rescued impaired glucose-stimulated insulin secretion in islets from mice and humans in the diabetic state. LysoPIs appear as lipid species being upregulated already in the prediabetic stage associated with the loss of β-cells and supporting the function of the remaining β-cells.

Circadian organization of lipid landscape is perturbed in type 2 diabetic patients

Lipid homeostasis in humans follows a diurnal pattern in muscle and pancreatic islets, altered upon metabolic dysregulation. We employ tandem and liquid-chromatography mass spectrometry to investigate daily regulation of lipid metabolism in subcutaneous white adipose tissue (SAT) and serum of type 2 diabetic (T2D) and non-diabetic (ND) human volunteers (n = 12). Around 8% of ≈440 lipid metabolites exhibit diurnal rhythmicity in serum and SAT from ND and T2D subjects. The spectrum of rhythmic lipids differs between ND and T2D individuals, with the most substantial changes observed early morning, as confirmed by lipidomics in an independent cohort of ND and T2D subjects (n = 32) conducted at a single morning time point. Strikingly, metabolites identified as daily rhythmic in both serum and SAT from T2D subjects exhibit phase differences. Our study reveals massive temporal and tissue-specific alterations of human lipid homeostasis in T2D, providing essential clues for the development of lipid biomarkers in a temporal manner.

Inactivation mechanisms of influenza A virus under pH conditions encountered in aerosol particles as revealed by whole-virus HDX-MS

Multiple respiratory viruses, including influenza A virus (IAV), can be transmitted via expiratory aerosol particles, and aerosol pH was recently identified as a major factor influencing airborne virus infectivity. Indoors, small exhaled aerosols undergo rapid acidification to pH ~4. IAV is known to be sensitive to mildly acidic conditions encountered within host endosomes; however, it is unknown whether the same mechanisms could mediate viral inactivation within the more acidic aerosol micro-environment. Here, we identified that transient exposure to pH 4 caused IAV inactivation by a two-stage process, with an initial sharp decline in infectious titers mainly attributed to premature attainment of the post-fusion conformation of viral protein haemagglutinin (HA). Protein changes were observed by hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) as early as 10 s post-exposure to acidic conditions. Our HDX-MS data are in agreement with other more labor-intensive structural analysis techniques, such as X-ray crystallography, highlighting the ease and usefulness of whole-virus HDX-MS for multiplexed protein analyses, even within enveloped viruses such as IAV. Additionally, virion integrity was partially but irreversibly affected by acidic conditions, with a progressive unfolding of the internal matrix protein 1 (M1) that aligned with a more gradual decline in viral infectivity with time. In contrast, no acid-mediated changes to the genome or lipid envelope were detected. Improved understanding of respiratory virus fate within exhaled aerosols constitutes a global public health priority, and information gained here could aid the development of novel strategies to control the airborne persistence of seasonal and/or pandemic influenza in the future. IMPORTANCE It is well established that COVID-19, influenza, and many other respiratory diseases can be transmitted by the inhalation of aerosolized viruses. Many studies have shown that the survival time of these airborne viruses is limited, but it remains an open question as to what drives their infectivity loss. Here, we address this question for influenza A virus by investigating structural protein changes incurred by the virus under conditions relevant to respiratory aerosol particles. From prior work, we know that expelled aerosols can become highly acidic due to equilibration with indoor room air, and our results indicate that two viral proteins are affected by these acidic conditions at multiple sites, leading to virus inactivation. Our findings suggest that the development of air treatments to quicken the speed of aerosol acidification would be a major strategy to control infectious bioburdens in the air.

Type 2 diabetes disrupts circadian orchestration of lipid metabolism and membrane fluidity in human pancreatic islets

Recent evidence suggests that circadian clocks ensure temporal orchestration of lipid homeostasis and play a role in pathophysiology of metabolic diseases in humans, including type 2 diabetes (T2D). Nevertheless, circadian regulation of lipid metabolism in human pancreatic islets has not been explored. Employing lipidomic analyses, we conducted temporal profiling in human pancreatic islets derived from 10 nondiabetic (ND) and 6 T2D donors. Among 329 detected lipid species across 8 major lipid classes, 5% exhibited circadian rhythmicity in ND human islets synchronized in vitro. Two-time point-based lipidomic analyses in T2D human islets revealed global and temporal alterations in phospho- and sphingolipids. Key enzymes regulating turnover of sphingolipids were rhythmically expressed in ND islets and exhibited altered levels in ND islets bearing disrupted clocks and in T2D islets. Strikingly, cellular membrane fluidity, measured by a Nile Red derivative NR12S, was reduced in plasma membrane of T2D diabetic human islets, in ND donors’ islets with disrupted circadian clockwork, or treated with sphingolipid pathway modulators. Moreover, inhibiting the glycosphingolipid biosynthesis led to strong reduction of insulin secretion triggered by glucose or KCl, whereas inhibiting earlier steps of de novo ceramide synthesis resulted in milder inhibitory effect on insulin secretion by ND islets. Our data suggest that circadian clocks operative in human pancreatic islets are required for temporal orchestration of lipid homeostasis, and that perturbation of temporal regulation of the islet lipid metabolism upon T2D leads to altered insulin secretion and membrane fluidity. These phenotypes were recapitulated in ND islets bearing disrupted clocks.

Sphingolipids control dermal fibroblast heterogeneity

Human cells produce thousands of lipids that change during cell differentiation and can vary across individual cells of the same type. However, we are only starting to characterize the function of these cell-to-cell differences in lipid composition. Here, we measured the lipidomes and transcriptomes of individual human dermal fibroblasts by coupling high-resolution mass spectrometry imaging with single-cell transcriptomics. We found that the cell-to-cell variations of specific lipid metabolic pathways contribute to the establishment of cell states involved in the organization of skin architecture. Sphingolipid composition is shown to define fibroblast subpopulations, with sphingolipid metabolic rewiring driving cell-state transitions. Therefore, cell-to-cell lipid heterogeneity affects the determination of cell states, adding a new regulatory component to the self-organization of multicellular systems.

S-acylation controls SARS-CoV-2 membrane lipid organization and enhances infectivity

SARS-CoV-2 virions are surrounded by a lipid bilayer that contains membrane proteins such as spike, responsible for target-cell binding and virus fusion. We found that during SARS-CoV-2 infection, spike becomes lipid modified, through the sequential action of the S-acyltransferases ZDHHC20 and 9. Particularly striking is the rapid acylation of spike on 10 cytosolic cysteines within the ER and Golgi. Using a combination of computational, lipidomics, and biochemical approaches, we show that this massive lipidation controls spike biogenesis and degradation, and drives the formation of localized ordered cholesterol and sphingolipid-rich lipid nanodomains in the early Golgi, where viral budding occurs. Finally, S-acylation of spike allows the formation of viruses with enhanced fusion capacity. Our study points toward S-acylating enzymes and lipid biosynthesis enzymes as novel therapeutic anti-viral targets.

Ether lipids, sphingolipids and toxic 1-deoxyceramides as hallmarks for lean and obese type 2 diabetic patients

AIM

The worldwide increase in obesity and type 2 diabetes (T2D) represents a major health challenge. Chronically altered lipids induced by obesity further promote the development of T2D, and the accumulation of toxic lipid metabolites in serum and peripheral organs may contribute to the diabetic phenotype.

METHODS

To better understand the complex metabolic pattern of lean and obese T2D and non-T2D individuals, we analysed the lipid profile of human serum, skeletal muscle and visceral adipose tissue of two cohorts by systematic mass spectrometry-based lipid analysis.

RESULTS

Lipid homeostasis was strongly altered in a disease- and tissue-specific manner, allowing us to define T2D signatures associated with obesity from those that were obesity independent. Lipid changes encompassed lyso-, diacyl- and ether-phospholipids. Moreover, strong changes in sphingolipids included cytotoxic 1-deoxyceramide accumulation in a disease-specific manner in serum and visceral adipose tissue. The high amounts of non-canonical 1-deoxyceramide present in human adipose tissue most likely come from cell-autonomous synthesis because 1-deoxyceramide production increased upon differentiation to adipocytes in mouse cell culture experiments.

CONCLUSION

Taken together, the observed lipidome changes in obesity and T2D will facilitate the identification of T2D patient subgroups and represent an important step towards personalized medicine in diabetes.

A high resolution LC-MS targeted method for the concomitant analysis of 11 contraceptive progestins and 4 steroids

In the context of hormonal contraception and hormone replacement therapy (HRT), many women are exposed to exogenous hormones. Current use of hormonal contraception with combined ethinyl estradiol and different progestins bestows a breast cancer relative risk (RR) of 1.2- while combined HRT has a RR of 2. Although these exposures present an important public health issue, little is known about the effects of individual progestins on the breast and other tissues. Increasing availability of large scale biobanks, high throughput analyses and data management tools enable ever expanding, sophisticated population studies. In order to address the impact of distinct progestins on various health indicators, it is desirable to accurately quantify progestins in clinical samples. Here we have developed and validated a high resolution liquid chromatography mass spectrometry (LC-MS) targeted method for the simultaneous quantification of 11 synthetic progestins widely used in oral contraceptives, gestodene, levonorgestrel, etonogestrel, chlormadinone acetate, cyproterone acetate, drospirenone, desacetyl norgestimate, medroxyprogesterone acetate, norethindrone, dienogest, nomegestrol acetate, and 4 endogenous steroid hormones, progesterone, testosterone, androstenedione, and cortisol in blood samples. This highly specific quantitative analysis with high resolution Orbitrap technology detects and quantifies 15 compounds using their internal standard counterparts in a single 12 min LC-MS run. Sensitivity is attained by the use of the instrument in targeted selected ion monitoring mode. Lower limit of quantitation ranges from 2.4 pg/ml for drospirenone to 78.1 pg/ml for chlormadinone acetate. The method provides comprehensive progestin panel measurements with as little as 50 μl of murine or human plasma.

Drug-induced increase in lysobisphosphatidic acid reduces the cholesterol overload in Niemann-Pick type C cells and mice

Most cells acquire cholesterol by endocytosis of circulating low-density lipoproteins (LDLs). After cholesteryl ester de-esterification in endosomes, free cholesterol is redistributed to intracellular membranes via unclear mechanisms. Our previous work suggested that the unconventional phospholipid lysobisphosphatidic acid (LBPA) may play a role in modulating the cholesterol flux through endosomes. In this study, we used the Prestwick library of FDA-approved compounds in a high-content, image-based screen of the endosomal lipids, lysobisphosphatidic acid and LDL-derived cholesterol. We report that thioperamide maleate, an inverse agonist of the histamine H3 receptor HRH3, increases highly selectively the levels of lysobisphosphatidic acid, without affecting any endosomal protein or function that we tested. Our data also show that thioperamide significantly reduces the endosome cholesterol overload in fibroblasts from patients with the cholesterol storage disorder Niemann-Pick type C (NPC), as well as in liver of Npc1-/- mice. We conclude that LBPA controls endosomal cholesterol mobilization and export to cellular destinations, perhaps by fluidifying or buffering cholesterol in endosomal membranes, and that thioperamide has repurposing potential for the treatment of NPC.

Cyclodextrin triggers MCOLN1-dependent endo-lysosome secretion in Niemann-Pick type C cells

In specialized cell types, lysosome-related organelles support regulated secretory pathways, whereas in nonspecialized cells, lysosomes can undergo fusion with the plasma membrane in response to a transient rise in cytosolic calcium. Recent evidence also indicates that lysosome secretion can be controlled transcriptionally and promote clearance in lysosome storage diseases. In addition, evidence is also accumulating that low concentrations of cyclodextrins reduce the cholesterol-storage phenotype in cells and animals with the cholesterol storage disease Niemann-Pick type C, via an unknown mechanism. Here, we report that cyclodextrin triggers the secretion of the endo/lysosomal content in nonspecialized cells and that this mechanism is responsible for the decreased cholesterol overload in Niemann-Pick type C cells. We also find that the secretion of the endo/lysosome content occurs via a mechanism dependent on the endosomal calcium channel mucolipin-1, as well as FYCO1, the AP1 adaptor, and its partner Gadkin. We conclude that endo-lysosomes in nonspecialized cells can acquire secretory functions elicited by cyclodextrin and that this pathway is responsible for the decrease in cholesterol storage in Niemann-Pick C cells.

Oxidation of virus proteins during UV(254) and singlet oxygen mediated inactivation

Despite the widespread use of UV(254) irradiation and solar disinfection for water treatment, little is known about the photochemical pathways that lead to virus inactivation by these treatments. The goal of this study was to identify reactions that occur in virus capsid proteins upon treatment by UV(254) irradiation and (1)O(2), an important oxidant involved in sunlight-mediated disinfection. Bacteriophage MS2 was inactivated via UV(254) irradiation and exposure to (1)O(2) in buffered water, and their capsid proteins were then analyzed with MALDI-TOF-TOF and ESI-TOF before and after digestion with protease enzymes. The results demonstrate that chemical modifications occur in the MS2 major capsid protein with both treatments. One oxidation event was detected following (1)O(2) treatment in an amino acid residue located on the capsid outer surface. UV(254) treatment caused three chemical reactions in the capsid proteins, two of which were oxidation reactions with residues on the capsid outer surface. A site-specific cleavage also occurred with UV(254) irradiation at a protein chain location on the inside face of the capsid shell. We attribute this UV(254) induced protein scission, which is nearly unprecedented in the literature, to a close association between the affected residues and viral RNA, an efficient UV(254) absorber. These results suggest that viral protein oxidation by UV(254) and (1)O(2) may play a role in virus inactivation and that viral inactivation may be tracked with mass spectrometric measurements.

A Simple, High-Precision, High-Sensitivity Tracer Assay for N(inf2) Fixation

We describe a simple, precise, and sensitive experimental protocol for direct measurement of N(inf2) fixation using the conversion of (sup15)N(inf2) to organic N. Our protocol greatly reduces the limit of detection for N(inf2) fixation by taking advantage of the high sensitivity of a modern, multiple-collector isotope ratio mass spectrometer. This instrument allowed measurement of N(inf2) fixation by natural assemblages of plankton in incubations lasting several hours in the presence of relatively low-level (ca. 10 atom%) tracer additions of (sup15)N(inf2) to the ambient pool of N(inf2). The sensitivity and precision of this tracer method are comparable to or better than those associated with the C(inf2)H(inf2) reduction assay. Data obtained in a series of experiments in the Gotland Basin of the Baltic Sea showed excellent agreement between (sup15)N(inf2) tracer and C(inf2)H(inf2) reduction measurements, with the largest discrepancies between the methods occurring at very low fixation rates. The ratio of C(inf2)H(inf2) reduced to N(inf2) fixed was 4.68 (plusmn) 0.11 (mean (plusmn) standard error, n = 39). In these experiments, the rate of C(inf2)H(inf2) reduction was relatively insensitive to assay volume. Our results, the first for planktonic diazotroph populations of the Baltic, confirm the validity of the C(inf2)H(inf2) reduction method as a quantitative measure of N(inf2) fixation in this system. Our (sup15)N(inf2) protocols are comparable to standard C(inf2)H(inf2) reduction procedures, which should promote use of direct (sup15)N(inf2) fixation measurements in other systems.

Vertical distribution of nitrogen-fixing phylotypes in a meromictic, hypersaline lake

We investigated the diversity of nitrogenase genes in the alkaline, moderately hypersaline Mono Lake, California to determine (1) whether nitrogen-fixing (diazotrophic) populations were similar to those in other aquatic environments and (2) if there was a pattern of distribution of phylotypes that reflected redox conditions, as well as (3) to identify populations that could be important in N dynamics in this nitrogen-limited lake. Mono Lake has been meromictic for almost a decade and has steep gradients in oxygen and reduced compounds that provide a wide range of aerobic and anaerobic habitats. We amplified a fragment of the nitrogenase gene (nifH) from planktonic DNA samples collected at three depths representing oxygenated surface waters, the oxycline, and anoxic, ammonium-rich deep waters. Forty-three percent of the 90 sequences grouped in nifH Cluster I. The majority of clones (57%) grouped in Cluster III, which contains many known anaerobic bacteria. Cluster I and Cluster III sequences were retrieved at every depth indicating little vertical zonation in sequence types related to the prominent gradients in oxygen and ammonia. One group in Cluster I was found most often at every depth and accounted for 29% of all the clones. These sequences formed a subcluster that contained other environmental clones, but no cultivated representatives. No significant nitrogen fixation was detected by the 15N2 method after 48 h of incubation of surface, oxycline, or deep waters, suggesting that pelagic diazotrophs were contributing little to nitrogen fluxes in the lake. The failure to measure any significant nitrogen fixation, despite the detection of diverse and novel nitrogenase genes throughout the water column, raises interesting questions about the ecological controls on diazotrophy in Mono Lake and the distribution of functional genes in the environment.

Unicellular cyanobacteria fix N2 in the subtropical North Pacific Ocean

Fixed nitrogen (N) often limits the growth of organisms in terrestrial and aquatic biomes, and N availability has been important in controlling the CO2 balance of modern and ancient oceans. The fixation of atmospheric dinitrogen gas (N2) to ammonia is catalysed by nitrogenase and provides a fixed N for N-limited environments. The filamentous cyanobacterium Trichodesmium has been assumed to be the predominant oceanic N2-fixing microorganism since the discovery of N2 fixation in Trichodesmium in 1961 (ref. 6). Attention has recently focused on oceanic N2 fixation because nitrogen availability is generally limiting in many oceans, and attempts to constrain the global atmosphere-ocean fluxes of CO2 are based on basin-scale N balances. Biogeochemical studies and models have suggested that total N2-fixation rates may be substantially greater than previously believed but cannot be reconciled with observed Trichodesmium abundances. It is curious that there are so few known N2-fixing microorganisms in oligotrophic oceans when it is clearly ecologically advantageous. Here we show that there are unicellular cyanobacteria in the open ocean that are expressing nitrogenase, and are abundant enough to potentially have a significant role in N dynamics.

Hemodynamic effect of a low-resistance artificial lung in series with the native lungs of sheep

BACKGROUND

An artificial lung with 1 to 6 month work life could act as a bridge to transplantation. A pumpless artificial lung has been developed.

METHODS

The artificial lung was placed in series with the native lungs of adult sheep. Hemodynamics were observed, as the right ventricle generated flow through the device. Through a left thoracotomy, two 20-mm grafts were anastomosed in an end-to-side fashion to the pulmonary artery. The grafts were externalized, and directed flow through the chest wall, to the extracorporeal lung. The animals were recovered, weaned from the ventilator, and when standing, flow was diverted through the device.

RESULTS

Five of 7 animals survived 24 hours with 75% to 100% of the cardiac output diverted through the device. All animals were active, with interest in food and water, and able to stand.

CONCLUSIONS

The right ventricle perfused the artificial lung with 75% to 100% of the cardiac output for 24 hours. This device demonstrates the feasibility of a pumpless pulmonary assist device relying on the right ventricle for perfusion.

Steady-state nitrogen isotope effects of N2 and N2O production in Paracoccus denitrificans

Nitrogen stable-isotope compositions (delta15N) can help track denitrification and N2O production in the environment, as can knowledge of the isotopic discrimination, or isotope effect, inherent to denitrification. However, the isotope effects associated with denitrification as a function of dissolved-oxygen concentration and their influence on the isotopic composition of N2O are not known. We developed a simple steady-state reactor to allow the measurement of denitrification isotope effects in Paracoccus denitrificans. With [dO2] between 0 and 1.2 microM, the N stable-isotope effects of NO3- and N2O reduction were constant at 28.6 per thousand +/- 1.9 per thousand and 12.9 per thousand +/- 2.6 per thousand, respectively (mean +/- standard error, n = 5). This estimate of the isotope effect of N2O reduction is the first in an axenic denitrifying culture and places the delta15N of denitrification-produced N2O midway between those of the nitrogenous oxide substrates and the product N2 in steady-state systems. Application of both isotope effects to N2O cycling studies is discussed.

Effects of static pressure on red blood cells on removal of the air interface

Previous studies investigated the effects of pressure on red blood cells, but did not address the presence of an air interface. It has been established that an air interface promotes damage to blood. This study was designed to allow for the isolation of the blood-air interface during pressurization. Fresh human blood was divided into 2 ml samples in polypropylene tubes and exposed to either negative or positive pressure for 5 min at 37 degrees C. The plasma free hemoglobin was measured and compared to controls (0 mmHg) exposed to the same environment. This procedure was duplicated with a 1 ml layer of mineral oil on each sample, to remove the air interface. The sample size for each pressure was 15. Results from this study demonstrate that blood is resistant to positive pressures (1,000 mmHg), even on removal of the air interface. However, hemolysis previously attributed to negative pressures was not seen when the air interface was removed by mineral oil. Removal of the air interface halted cavitation, which occurred at pressures equal to or below -680 mmHg in the presence of the air interface. It is the authors' belief that hemolysis is not correlated with negative pressure, but rather with the susceptibility of blood to cavitation.

Significant safety advantages gained with an improved pressure-regulated blood pump

A prototype of a non-occlusive pressure-regulated blood pump (M-pump) was evaluated in-vitro for safety in a comparative study with the roller and centrifugal pumps. The M-pump consists of collapsible tubing of unique design wrapped under tension around a rotor without a stator. The prototype M-pumps were tested in vitro to evaluate performance with respect to flow/ pressure characteristics, hemolysis, bubble generation (cavitation) and durability. The M-pump and centrifugal pump did not overpressurize at any RPM when the pump outlet was occluded, but the roller pump reached pressures in excess of 1000 mmHg. The M-pump did not generate negative pressures upon occlusion of the inlet, whereas the roller and centrifugal pumps produced near-vacuum pressures. Furthermore, the M-pump was unable to empty a blood reservoir when the height of the pump inlet was placed slightly above the reservoir outlet. The levels of microbubbles in the M-pump were significantly lower than the roller and centrifugal pumps upon sudden restriction of the pump inlet as determined with an ultrasonic bubble detector. The results of our in-vitro evaluation of the M-pump have shown it to have lower hemolysis than the centrifugal pump and lower or comparable hemolysis to roller pumps at flowrates of 0.1, 0.5, 4.0 and 6 L/min. We determined that the M-pump design possesses important safety advantages over roller and centrifugal pumps for cardiopulmonary bypass applications.

Development and application of a simplified liquid ventilator

OBJECTIVE

Perfluorocarbon liquid ventilation has been shown to have advantages over conventional gas ventilation in premature newborn and lung-injured animals. To simplify the process of liquid ventilation, we adapted an extra-corporeal life-support circuit as a time-cycled, volume-limited liquid ventilator.

DESIGN

Laboratory study that involved sequential application of gas and liquid ventilation in normal cats and in lung-injured sheep.

SETTING

A research laboratory at a university medical center.

SUBJECTS

Eight normal cats weighing 2.7 to 3.8 kg (mean 3.1 +/- 0.5), and four lung-injured young sheep weighing 10.4 to 22.5 kg (mean 15.9 +/- 5.0).

INTERVENTIONS

Normal cats were supported with traditional gas ventilation for 1 hr (respiratory rate 20 breaths/min, peak inspiratory pressure 12 cm H2O, positive end-expiratory pressure 4 cm H2O, and FIO2 1.0). The lungs were then filled with perfluorocarbon (30 mL/kg) and tidal volume liquid ventilation was instituted, utilizing a newly developed liquid ventilation device. Liquid ventilatory settings were 4 secs for inspiration time, 8 secs for expiration time, 5 breaths/min for respiratory rate, and 15 to 20 mL/kg for tidal volume. Liquid ventilation utilizing this device was also applied to sheep after induction of severe lung injury by right atrial injection of 0.07 mL/kg of oleic acid, followed by saline pulmonary lavage. Extracorporeal life support was instituted to provide a stable model of lung injury. For the first 30 mins of extracorporeal support, all animals were ventilated with gas. Animals were then ventilated with 15 mL/kg of perfluorocarbon over the ensuing 2.5 hrs.

MEASUREMENTS AND MAIN RESULTS

In normal cats, mean PaO2 values after 1 hr of liquid or gas ventilation were 275 +/- 90 (SD) torr (36.7 +/- 10.4 kPa) in the liquid-ventilated animals and 332 +/- 78 torr (44.3 +/- 10.4 kPa) in the gas-ventilated animals (NS). Mean PaCO2 values were 40.5 +/- 5.7 torr (5.39 +/- 0.31 kPa) in the liquid-ventilated animals and 37.6 +/- 2.3 torr (5.01 +/- 0.31 kPa) in the gas-ventilated animals (NS). Mean arterial pH values were 7.35 +/- 0.07 in the liquid-ventilated animals and 7.34 +/- 0.04 in the gas-ventilated animals (NS). No significant changes in heart rate, mean arterial pressure, lung compliance, or right atrial venous oxygen saturation were observed during liquid ventilation when compared with gas ventilation. In the lung-injured sheep, an increase in physiologic shunt from 15 +/- 7% to 66 +/- 9% was observed with induction of lung injury during gas ventilation. Liquid ventilation resulted in a significant reduction in physiologic shunt to 31 +/- 10% (p < .001). In addition, the extracorporeal blood flow rate required to maintain the PaO2 in the 50 to 80 torr (6.7 to 10.7 kPa) range was substantially and significantly (p < .001) lower during liquid ventilation than during gas ventilation (liquid ventilation 15 +/- 5 vs. gas ventilation 87 +/- 15 mL/min/kg).

CONCLUSIONS

Liquid ventilation can be performed successfully utilizing this simple adaptation of an extracorporeal life-support circuit. This modification to an existing extracorporeal circuit may allow other centers to apply this new investigational method of ventilation in the laboratory or clinical setting.

An intrapleural lung prosthesis: rationale, design, and testing

Extracorporeal life support (ECLS or ECMO) is standard treatment for severe respiratory failure but poses many contraindications to future lung transplantation. The solution to this dilemma is the implantable gas exchange device (IGED) or artificial lung. Preliminary efforts to create such an artificial lung have been made since 1970 and include designs involving single devices, intravascular devices (i.e., IVOX), and combination heart-lung devices. Stringent requirements govern the design of such a device, the most important of which are high gas exchange efficiency, low resistance to blood flow, and size. This paper describes such a device. It incorporates large diameter inflow and outflow ports in close proximity and a low resistance wound hollow fiber core encapsulated in a compliant outer shell which conserves the work of the right ventricle. In a large animal model (adult sheep) this device was connected in line with the main pulmonary artery in series with the native lungs. This configuration has the advantages of using the lungs as an embolic filter, perfusing the lungs with fully oxygenated blood, and maintaining the integrity of the anatomy necessary for transplant. Laboratory experiments have run > 8 h. Preliminary data show that the animals have remained hemodynamically stable while the devices have supported the animals completely by supplying 100% O2 saturation with PO2 values ranging from 250-350 mm Hg. Additionally, this model makes possible the study of respiratory failure without introducing other variables such as extracorporeal circuits or pumps. The other metabolic, endocrine, and reticuloendothelial functions of normal and injured lungs can now be studied more precisely by excluding these variables.(ABSTRACT TRUNCATED AT 250 WORDS)

The development of an implantable artificial lung

This report describes the development of an implantable gas exchange device. The device is composed of hollow fiber elements wound around a central open core enclosed in a compliant outer casing, offering very low resistance to blood while providing adequate gas exchange. The purpose of this study was to determine if this device design can completely support the gas exchange requirements of a large animal when the device is placed in series with the main pulmonary artery (PA). Six 40-80 kg adult sheep were used. The device was placed with vascular grafts anastomosed end to side on the proximal and distal main PA. The study began with the entire right ventricular blood flow being diverted through the device by occlusion of a snare around the PA between the vascular grafts. Total gas exchange then was provided by the device and the endotracheal tube was clamped. Results showed that this pumpless potentially implantable device is capable of completely supporting the gas exchange requirements of the experimental animals for up to 8 hours in the acute setting without significant change in cardiac index (CI) and oxygen consumption (VO2) compared with baseline. CI = 55.0 +/- 17.0 cc/min/kg versus 45.0 +/- 17.3 cc/min/kg. VO2 = 1.90 +/- 0.96 cc O2/min/kg versus 2.08 +/- 0.54 cc O2/min/kg.

Laboratory experience with a novel, non-occlusive, pressure-regulated peristaltic blood pump

Current blood pumps have potential safety problems, including the ability to generate extreme positive and negative pressures. These problems were addressed in the design and testing of a non-occlusive, peristaltic blood pump. The pump consists of a tubing of unique design (pump chamber) wrapped under tension around a rotor with rollers. The pump chamber design is such that the pump is passively filling; flow is dependent upon the pressure of the blood supply and the size of the pump chamber. Thus, negative pressures cannot be generated. With the outlet occluded, the pump produces the maximum attainable pressure, which can be set by adjusting the tension of the pump chamber around the rollers. The design characteristics make the pump suitable for prolonged use. The pump was tested in vitro for pressure safety, hemolysis, and durability. The pump prototype was used in 25 experiments involving extracorporeal circulation on sheep, with an average duration of approximately 6 hr and bypass flow rates between 0.5 and 2.0 L/min. No pump related complications occurred in any of these experiments. The pump described here is suitable for short- and long-term perfusion applications, and does not require additional pressure regulation, as do current blood pumps.

Plasma leakage through microporous membranes. Role of phospholipids

Plasma leakage through microporous membrane oxygenators is a well known complication of prolonged extracorporeal circulation. The authors hypothesized that adsorption of bipolar plasma molecules, such as phospholipids on the microporous membrane, results in formation of a hydrophilic layer over the hydrophobic surface of the membrane; this, in turn, leads to plasma leakage at normal surface tensions. A lipid phosphorus assay was used to measure phospholipid adsorption onto the fibers of microporous membrane oxygenators tested under a variety of experimental conditions. Adsorption of phospholipids on the microporous membrane was concentration dependent. Reproducible plasma leakage occurred both in vitro and in vivo, and the time to leakage was dependent on the concentration of phospholipids adsorbed upon the microporous membrane. Based upon these results, the authors conclude that adsorption of phospholipids contributes to the development of plasma leakage through microporous membrane oxygenators.

New method for describing the performance of cardiac surgery cannulas

Cardiac surgery cannulas are characterized by external diameter only, which provides little information about the pressure-flow characteristics of a cannula. A system has been developed to describe pressure-flow characteristics with a single, unitless number, M, which is patterned after a Reynolds friction factor correlation. A cannula with a lower M number has a more favorable pressure-flow relationship. The M number was determined for 16 arterials cannulas ranging in size from 10F to 26F and 27 venous cannulas sized 12F to 36F. Pressure-flow characteristics vary considerably among cannulas from different manufacturers despite having similar French sizes. Clinical decisions regarding choice of cannula can be simplified by using the M number, which gives a more accurate description of the performance characteristics of a cannula than the French size designation.

Evaluation of extracorporeal perfusion catheters using a standardized measurement technique--the M-number

Cannulas used for extracorporeal circulating devices are made in many shapes and sizes. Side hole placement, length, and wall thickness can make the pressure-flow characteristics of catheters with similar French sizes quite different in their actual performance. A single value, the M-number, has been developed that describes the pressure-flow characteristics of an individual cannula. This number can be used to compare catheters and assess their potential utility for given bypass requirements. The M-numbers for commonly used catheters that are placed by extrathoracic dissections are determined. Clinical situations are presented that demonstrate applications of the M-number.

A standardized system for describing flow/pressure relationships in vascular access devices

Catheters are usually characterized by length and external diameter only. We developed a system to describe flow-pressure characteristics with a single number, M, patterned after a Reynolds number-friction factor correlation. A simple alignment chart was constructed that can be used to determine M for catheters of regular internal diameter and given length. If tapers, side holes, or integral connectors are present, M can be determined in-vitro with water by measuring pressure drop at various flows. The chart describes flow pressure functions for blood (Hct = 0.41) if M is known. Using this system, any catheter, needle, valve seat, extracorporeal tubing, or vascular graft can be assigned a single number that describes hydrodynamic performance characteristics.