Advancements in the use of xenopus oocytes for modelling neurological disease for novel drug discovery

INTRODUCTION

Introduced about 50 years ago, the model of Xenopus oocytes for the expression of recombinant proteins has gained a broad spectrum of applications. The authors herein review the benefits brought from using this model system, with a focus on modeling neurological disease mechanisms and application to drug discovery.

AREAS COVERED

Using multiple examples spanning from ligand gated ion channels to transporters, this review presents, in the light of the latest publications, the benefits offered from using Xenopus oocytes. Studies range from the characterization of gene mutations to the discovery of novel treatments for disorders of the central nervous system (CNS).

EXPERT OPINION

Development of new drugs targeting CNS disorders has been marked by failures in the translation from preclinical to clinical studies. As progress in genetics and molecular biology highlights large functional differences arising from a single to a few amino acid exchanges, the need for drug screening and functional testing against human proteins is increasing. The use of Xenopus oocytes to enable precise modeling and characterization of clinically relevant genetic variants constitutes a powerful model system that can be used to inform various aspects of CNS drug discovery and development.

The importance of ligand gated ion channels in sleep and sleep disorders

On average, humans spend about 26 years of their life sleeping. Increased sleep duration and quality has been linked to reduced disease risk; however, the cellular and molecular underpinnings of sleep remain open questions. It has been known for some time that pharmacological modulation of neurotransmission in the brain can promote either sleep or wakefulness thereby providing some clues about the molecular mechanisms at play. However, the field of sleep research has developed an increasingly detailed understanding of the requisite neuronal circuitry and key neurotransmitter receptor subtypes, suggesting that it may be possible to identify next generation pharmacological interventions to treat sleep disorders within this same space. The aim of this work is to examine the latest physiological and pharmacological findings highlighting the contribution of ligand gated ion channels including the inhibitory GABA_A and glycine receptors and excitatory nicotinic acetylcholine receptors and glutamate receptors in the sleep-wake cycle regulation. Overall, a better understanding of ligand gated ion channels in sleep will help determine if these highly druggable targets could facilitate a better night's sleep.

The molecular mechanism of snake short-chain α-neurotoxin binding to muscle-type nicotinic acetylcholine receptors

Bites by elapid snakes (e.g. cobras) can result in life-threatening paralysis caused by venom neurotoxins blocking neuromuscular nicotinic acetylcholine receptors. Here, we determine the cryo-EM structure of the muscle-type Torpedo receptor in complex with ScNtx, a recombinant short-chain α-neurotoxin. ScNtx is pinched between loop C on the principal subunit and a unique hairpin in loop F on the complementary subunit, thereby blocking access to the neurotransmitter binding site. ScNtx adopts a binding mode that is tilted toward the complementary subunit, forming a wider network of interactions than those seen in the long-chain α-Bungarotoxin complex. Certain mutations in ScNtx at the toxin-receptor interface eliminate inhibition of neuronal α7 nAChRs, but not of human muscle-type receptors. These observations explain why ScNtx binds more tightly to muscle-type receptors than neuronal receptors. Together, these data offer a framework for understanding subtype-specific actions of short-chain α-neurotoxins and inspire strategies for design of new snake antivenoms.

Bites by elapid snakes can result in life-threatening paralysis caused by α-neurotoxins blocking the neuromuscular nicotinic acetylcholine receptor. Here, the authors determine the cryo-EM structure of this receptor in complex with a short-chain α-neurotoxin.

Regulation of a pentameric ligand-gated ion channel by a semiconserved cationic lipid-binding site

Pentameric ligand-gated ion channels (pLGICs) are crucial mediators of electrochemical signal transduction in various organisms from bacteria to humans. Lipids play an important role in regulating pLGIC function, yet the structural bases for specific pLGIC-lipid interactions remain poorly understood. The bacterial channel ELIC recapitulates several properties of eukaryotic pLGICs, including activation by the neurotransmitter GABA and binding and modulation by lipids, offering a simplified model system for structure-function relationship studies. In this study, functional effects of noncanonical amino acid substitution of a potential lipid-interacting residue (W206) at the top of the M1-helix, combined with detergent interactions observed in recent X-ray structures, are consistent with this region being the location of a lipid-binding site on the outward face of the ELIC transmembrane domain. Coarse-grained and atomistic molecular dynamics simulations revealed preferential binding of lipids containing a positive charge, particularly involving interactions with residue W206, consistent with cation-π binding. Polar contacts from other regions of the protein, particularly M3 residue Q264, further support lipid binding via headgroup ester linkages. Aromatic residues were identified at analogous sites in a handful of eukaryotic family members, including the human GABAA receptor ε subunit, suggesting conservation of relevant interactions in other evolutionary branches. Further mutagenesis experiments indicated that mutations at this site in ε-containing GABAA receptors can change the apparent affinity of the agonist response to GABA, suggesting a potential role of this site in channel gating. In conclusion, this work details type-specific lipid interactions, which adds to our growing understanding of how lipids modulate pLGICs.

Ligand gated receptor interactions: A key to the power of neuronal networks

The discovery of the chemical synapse was a seminal finding in Neurobiology but the large body of microscopic interactions involved in synaptic transmission could hardly have been foreseen at the time of these first discoveries. Characterization of the molecular players at work at synapses and the increased granularity at which we can now analyze electrical and chemical signal processing that occur in even the simplest neuronal system are shining a new light on receptor interactions. The aim of this review is to discuss the complexity of some representative interactions between excitatory and inhibitory ligand-gated ion channels and/or G protein coupled receptors, as well as other key machinery that can impact neurotransmission and to explain how such mechanisms can be an important determinant of nervous system function.

Modulation of the Erwinia ligand-gated ion channel (ELIC) and the 5-HT3 receptor via a common vestibule site

Pentameric ligand-gated ion channels (pLGICs) or Cys-loop receptors are involved in fast synaptic signaling in the nervous system. Allosteric modulators bind to sites that are remote from the neurotransmitter binding site, but modify coupling of ligand binding to channel opening. In this study, we developed nanobodies (single domain antibodies), which are functionally active as allosteric modulators, and solved co-crystal structures of the prokaryote (Erwinia) channel ELIC bound either to a positive or a negative allosteric modulator. The allosteric nanobody binding sites partially overlap with those of small molecule modulators, including a vestibule binding site that is not accessible in some pLGICs. Using mutagenesis, we extrapolate the functional importance of the vestibule binding site to the human 5-HT3 receptor, suggesting a common mechanism of modulation in this protein and ELIC. Thus we identify key elements of allosteric binding sites, and extend drug design possibilities in pLGICs with an accessible vestibule site.

Receptor variants and the development of centrally acting medications

The progressive changes in research paradigms observed in the largest pharmaceutical companies and the burgeoning of biotechnology startups over the last 10 years have generated a need for outsourcing research facilities. In parallel, progress made in the fields of genomics, protein expression in recombinant systems, and electrophysiological recording methods have offered new possibilities for the development of contract research organizations (CROs). Successful partnering between pharmaceutical companies and CROs largely depends upon the competences and scientific quality on offer for the discovery of novel active molecules and targets. Thus, it is critical to review the knowledge in the field of neuroscience research, how genetic approaches are augmenting our knowledge, and how they can be applied in the translation from the identification of potential molecules up to the first clinical trials. Taking these together, it is apparent that CROs have an important role to play in the neuroscience of drug discovery.


Cyclic-β-glucans of Rhizobium (Sinorhizobium) sp. strain NGR234 are required for hypo-osmotic adaptation, motility, and efficient symbiosis with host plants

Cyclic-β-glucans (CβG) consist of cyclic homo-polymers of glucose that are present in the periplasmic space of many Gram-negative bacteria. A number of studies have demonstrated their importance for bacterial infection of plant and animal cells. In this study, a mutant of Rhizobium (Sinorhizobium) sp. strain NGR234 (NGR234) was generated in the cyclic glucan synthase (ndvB)-encoding gene. The great majority of CβG produced by wild-type NGR234 are negatively charged and substituted. The ndvB mutation abolished CβG biosynthesis. We found that, in NGR234, a functional ndvB gene is essential for hypo-osmotic adaptation and swimming, attachment to the roots, and efficient infection of Vigna unguiculata and Leucaena leucocephala.

Rhizobia utilize pathogen-like effector proteins during symbiosis

A type III protein secretion system (T3SS) is an important host range determinant for the infection of legumes by Rhizobium sp. NGR234. Although a functional T3SS can have either beneficial or detrimental effects on nodule formation, only the rhizobial-specific positively acting effector proteins, NopL and NopP, have been characterized. NGR234 possesses three open reading frames potentially encoding homologues of effector proteins from pathogenic bacteria. NopJ, NopM and NopT are secreted by the T3SS of NGR234. All three can have negative effects on the interaction with legumes, but NopM and NopT also stimulate nodulation on certain plants. NopT belongs to a family of pathogenic effector proteases, typified by the avirulence protein, AvrPphB. The protease domain of NopT is required for its recognition and a subsequent strong inhibition in infection of Crotalaria juncea. In contrast, the negative effects of NopJ are relatively minor when compared with those induced by its Avr homologues. Thus NGR234 uses a mixture of rhizobial-specific and pathogen-derived effector proteins. Whereas some legumes recognize an effector as potentially pathogen-derived, leading to a block in the infection process, others perceive both the negative- and positive-acting effectors concomitantly. It is this equilibrium of effector action that leads to modulation of symbiotic development.

TtsI regulates symbiotic genes in Rhizobium species NGR234 by binding to tts boxes

Infection of legumes by Rhizobium sp. NGR234 and subsequent development of nitrogen-fixing nodules are dependent on the coordinated actions of Nod factors, proteins secreted by a type III secretion system (T3SS) and modifications to surface polysaccharides. The production of these signal molecules is dependent on plant flavonoids which trigger a regulatory cascade controlled by the transcriptional activators NodD1, NodD2, SyrM2 and TtsI. TtsI is known to control the genes responsible for T3SS function and synthesis of a symbiotically important rhamnose-rich lipo-polysaccharide, most probably by binding to cis elements termed tts boxes. Eleven tts boxes were identified in the promoter regions of target genes on the symbiotic plasmid of NGR234. Expression profiles of lacZ fusions to these tts boxes showed that they are part of a TtsI-dependent regulon induced by plant-derived flavonoids. TtsI was purified and demonstrated to bind directly to two of these tts boxes. DNase I footprinting revealed that TtsI occupied not only the tts box consensus sequence, but also upstream and downstream regions in a concentration-dependent manner. Highly conserved bases of the consensus tts box were mutated and, although TtsI binding was still observed in vitro, gfp fusions were no longer transcribed in vivo. Random mutagenesis of a tts box-containing promoter revealed more nucleotides critical for transcriptional activity outside of the consensus.

An efficient method for purifying high quality RNA from wheat pistils

Many methods are available for total RNA extraction from plants, except the floral organs like wheat pistils containing high levels of polysaccharides that bind/or co-precipitate with RNA. In this protocol, a simple and effective method for extracting total RNA from small and feathery wheat pistils has been developed. Lithium chloride (LiCl) and phenol:chloroform:isoamylalcohol (PCI) were employed and the samples were ground in microcentrifuge tube using plastic pestle. A jacket of liquid nitrogen and simplified procedures were applied to ensure thorough grinding of the pistils and to minimize the samples loss. These measures substantially increased the recovery of total RNA (approximately 50%) in the extraction process. Reliable differential display by cDNA-AFLP was successfully achieved with the total RNA after DNase treatment and reverse transcription. This method is also practicable for gene expression and gene regulation studies in floral parts of other plants.

Clinical and radiographic evaluation of disc excision for lumbar disc herniation with and without posterolateral fusion

STUDY DESIGN

A prospective study evaluating the clinical and radiographic results in 95 patients with lumbar disc herniation.

OBJECTIVES

To evaluate the results of disc excision, with and without posterolateral fusion.

SUMMARY OF BACKGROUND DATA

The effect of posterolateral fusion on the outcomes and radiologic changes in patients with lumbar disc herniation has rarely been reported.

METHODS

Forty-four patients underwent disc excision, and 51 patients underwent disc excision and fusion. Clinical symptoms were evaluated using the Japanese Orthopaedic Association Back scores. All medical and surgical records were examined with regard to intraoperative blood loss, operation time, and other data. Preoperative and follow-up radiographs were analyzed to determine the spinal motion and disc height.

RESULTS

Clinical outcome was excellent or good in 73% of the nonfusion group and in 82% of the fusion group (P = 0.31). The reduction in lower back pain after surgery was greater in the fusion group. The rate of recurrent disc herniation at the surgical level in the nonfusion group increased, but intraoperative blood loss, operation time, length of hospital stay, and total cost of procedure were all significantly less in the patients undergoing disc excision alone than in the fusion group. The radiologic analysis provided evidence that the disc height at the level of disc excision and posterolateral fusion in the fusion group decreased with time, as in the nonfusion group. The changes in disc height and spinal motion were not related to the clinical results.

CONCLUSIONS

Although there is still controversy regarding the pros and cons of fusion in association with disc excision, there is seldom an indication for primary fusion for lumbar disc herniation.

Apoptosis in microvascular endothelial cells of perfused rabbit lungs with acute hydrostatic edema

We test the hypothesis that microvascular endothelial cells may undergo apoptosis in response to acute pulmonary venous hypertension. The isolated rabbit lungs were perfused in situ for 4 h with left atrial pressure of 0, 10, or 20 mmHg at a constant blood flow. Edema formation was monitored by lung weight gain. To assay for apoptosis, we performed agarose gel electrophoresis of DNA, in situ nick end labeling of DNA strand breaks, and electron microscopy. We also examined the levels of expression of Bcl-2, a suppressor of apoptosis, in microvascular endothelial cells using an immunohistochemical technique. In a vascular pressure-dependent fashion, we found apoptosis in endothelial cells of alveolar septal capillaries, as well as expression of Bcl-2 in arteriolar and venular endothelial cells. We conclude that acute pulmonary venous hypertension induces apoptosis in capillary endothelial cells but not in arteriolar and venular endothelial cells, suggesting that microvascular endothelial cell apoptosis is dependent on the levels of Bcl-2 expression and influences the formation or resolution of acute hydrostatic lung edema.

Effects of low-dose Beraprost sodium, a stable prostaglandin I2 analogue, on reperfusion injury to rabbit lungs

We investigated the effects of low-dose Beraprost sodium (BPS), a stable prostaglandin I2 (PGI2) analogue, on microvascular permeability and the plasma concentrations of thromboxane and adenosine 3',5'-cyclic monophosphate (cAMP) in blood-perfused rabbit lungs subjected to ischemia-reperfusion (I/R). After an ischemic insult for 2 h, saline as a vehicle, 3 pmol/L of BPS (BPS-1), 150 to 300 pmol/L of BPS (BPS-2), 900 pmol/L of BPS (BPS-3), or 60 micromol/L of indomethacin (IND) was administered into the reservoir, then the lungs were reperfused and reventilated for 1 h. Vascular permeability was assessed by determining the microvascular filtration coefficient (Kf, ml/min/mm Hg/100 g wet lung). I/R resulted in increases in vascular resistance, Kf, and thromboxane. BPS-2, BPS-3, and IND inhibited the increase in vascular resistance, and BPS-3 and IND attenuated the increases in Kf and thromboxane. BPS-3 increased, but IND decreased, the concentrations of cAMP in the perfusate. Perfusate thromboxane released after reperfusion was significantly correlated with Kf. We conclude that cyclooxygenase products play a critical role in I/R-induced lung vascular injury and that 900 pmol/L of BPS inhibits the production of thromboxane and enhances the permeability barrier via a cAMP-elevating effect. However, vasodilatory action of BPS may exacerbate the reperfused lung injury by increasing the flow through injured capillaries via inhibition of thromboxane-induced vasoconstriction.

Effects of ventilation and pleural effusion on measurements of airway thermal volume and blood flow in dog lungs

We studied the effects of ventilation and pleural effusion on measurements of airway thermal volume (ATV) and pulmonary blood flow (PBF) by using the airway gas thermometry method of V. B. Serikov, M. S. Rumm, K. Kambara, M. I. Bootomo, A. R. Osmack, and N. C. Staub (J. Appl. Physiol. 72: 944-953, 1992) in 39 anesthetized dogs with or without lung edema or pleural effusion. To examine the differential effects of increased-pressure and increased-permeability lung edema on accuracy and sensitivity of ATV and PBF, two models of lung edema were induced by intravenous infusion of a Dextran 70 solution and alloxan monohydrate, respectively. Dogs were hyperventilated for 3 min by using a wide range of minute ventilation (VE) to produce two steady-state conditions of airway temperature. Higher levels of VE increased an estimated amount of ATV. The ATV produced by hyperventilation at VE values of 559, 158, and 72 ml.min-1.kg-1 was consistent with the gravimetric total lung mass, the blood-free wet lung weight, and the extravascular lung water volume, respectively. The coefficient of lung thermal conductivity, a practical index of the rate of heat conduction through tissue from lung vessels, was related to the ratio of the decrease in expired air temperature to VE, and estimated PBF was consistent with the thermodilution cardiac output. Pleural effusion had little effect on measurements of ATV and PBF. However, ATV and PBF showed increased variation in dogs with dextran-induced lung edema.

Alternations in atrial natriuretic peptide release after DC cardioversion of non-valvular chronic atrial fibrillation

The response of atrial natriuretic peptide (ANP) release to haemodynamic influences after cardioversion of atrial fibrillation has not been fully examined. We measured plasma concentrations of ANP and assessed haemodynamic changes 60-120 min after DC cardioversion in 22 patients with non-valvular chronic atrial fibrillation. Passive leg elevation to enhance volume expansion was performed 60 min after DC cardioversion. Sinus rhythm was restored in 18 of the 22 patients (successful DC cardioversion group). The control group consisted of seven patients with non-valvular chronic atrial fibrillation who did not undergo DC cardioversion (atrial fibrillation control group). In the successful DC cardioversion group, the mean pulmonary artery wedge pressure decreased significantly 15 min after cardioversion (P < 0.05) and then remained unchanged. Plasma concentrations of ANP also decreased significantly 15 min after cardioversion (P < 0.05). Furthermore, there was an additional significant decrease in ANP levels for up to 60 min after cardioversion (P < 0.05 from 15 min). Passive leg elevation for 15 min led to an increase in the mean pulmonary artery wedge pressure (P < 0.01) and right atrial pressure (P < 0.05), but did not result in increased plasma concentrations of ANP (47.1 +/- 27.6 vs 43.9 +/- 34.4 pg.ml-1, mean +/- SD, P = ns). In the atrial fibrillation control group, passive leg elevation increased the mean pulmonary artery wedge pressure (P < 0.01), the mean right atrial pressure (P < 0.05) and plasma concentrations of ANP (139.9 +/- 85.8 vs 168.1 +/- 108.2, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

[Bone union after lumbar postero-lateral fusion: comparative evaluation by x-ray and CT]

As yet there has been no report on a uniform and precise method for evaluating bone union after lumbar postero-lateral fusion (PLF). Here we report and compare the roentgenogram (X-P) and computerized tomography (CT) methods to evaluate the union and non-union of PLF. PLF without internal fixation was undertaken in 252 patients between 1978 and 1991. Of these, 125 patients underwent both X-P and CT scanning and were followed up for more than one year (mean 4 years and 2 months, range 1 to 14 years). In the cases of complete union, X-P demonstrated that the solid fusion mass showed a continuous trabecular pattern along the grafted segment, while CT demonstrated that the solid fusion mass appeared as a long bone with the mass incorporated into the transverse process and the superior facet. In such cases, there was no micromotion on stress roentgenograms. In the cases of incomplete union, the status of the non-union was classified into three types as; Type I showing atrophy and resorption of the grafted bone, Type II showing a lack in trabecular continuity of the fusion mass, and Type III showing a gap either cranially or caudally between the fusion mass and lumbar matrix (which includes the transverse process and superior facet). X-P could easily diagnose Type I and Type II, but could not clearly diagnose Type III. CT, however, could easily diagnose Type III. Therefore, the use of only X-P might lead to a misdiagnosis in cases of Type III. The application of CT was more uniform and precise method to evaluate the state of PLF in the lumbosacral spine.

Usefulness of the pulmonary vein flow velocity-time profile as an estimate of left atrial storage fraction

During ventricular systole, the left atrium (LA) stores a certain amount of ventricular stroke volume; this is defined as an LA storage volume. From cineangiocardiograms, an LA storage fraction is obtained as the ratio of the LA storage volume to left ventricular stroke volume. From the pulmonary vein (PV) flow velocity-time profile, the LA storage fraction may be estimated as a ratio of the PV flow velocity-time integral during systole (Sa) to a sum of that during systole and diastole (Sa+Da), namely, Sa/(Sa+Da), provided that the PV cross-sectional area remains relatively unchanged during one cardiac cycle and that the PV flow velocity-time profile is similar in any of the PVs draining to the LA. To evaluate usefulness of Doppler echocardiographic method of estimating the LA storage fraction, the authors measured the LA storage fraction from the left upper PV flow velocity-time profile by transesophageal Doppler echocardiography and compared it with the LA storage fraction from conventional cineangiocardiographic volumes. Subjects were 23 patients with a variety of cardiac diseases in normal sinus rhythm, ranging from eighteen to seventy-four years of age. The LA storage fraction was 0.58 +/- 0.12 (mean +/- SD) from cineangiocardiography and 0.64 +/- 0.08 from Doppler echocardiography larger than that from cineangiocardiography (P < 0.01), the correlation was good (r = 0.643). The authors conclude that the left upper PV flow velocity-time profile appears to provide a better correlation with that by cineangiography and may be used as a reliable quantitative estimate of the LA storage fraction.

[A patient with Legionella pneumonia diagnosed early by the PCR method]

A 72-year-old man was admitted to our hospital because of acute respiratory failure. Initially he had been diagnosed as having pneumonia in the lower left lung field and treated with cephem antibiotics by a local physician. Chest X-ray photograph revealed wide-spread infiltrates throughout both lungs, and chest CT scan revealed pleural effusions. The partial pressure of oxygen in arterial blood was 45.8 Torr. In the bronchoalveolar lavage fluid (BALF) specimen, legionella DNA was detected by the polymerase chain reaction (PCR) method. Thus, we were able to diagnose Legionella pneumonia immediately, and to treat the patient successfully.

Effects of acetylsalicylic acid on pulmonary vascular tone and membrane permeability in blood-perfused dog lung

We studied the effects of acetylsalicylic acid (ASA) on pressor response, microvascular filtration coefficient (Kf), extravascular lung water, and plasma concentrations of cyclooxygenase- and 5-lipoxygenase-derived products in 21 blood-perfused dog lungs with constant flow. The lungs were perfused for 1 h with an intrapulmonary injection of saline as vehicle (n = 5), a low dose of ASA [136 +/- 25 (SD) micrograms/ml perfusate; n = 5], a high dose of ASA (1,006 +/- 278 micrograms/ml perfusate; n = 6), or alloxan (1,000 mg; n = 5). Alloxan significantly increased Kf and extravascular lung water, whereas neither the low nor high dose of ASA increased Kf or extravascular lung water. The ASA-induced increase in vascular resistance did not correlate with the extent of the decrease in perfusate 6-keto-prostaglandin F1 alpha or the ratio of perfusate 6-ketoprostaglandin F1 alpha to thromboxane B2. Moreover, ASA did not enhance the generation of perfusate leukotrienes B4, D4, or E4. We conclude that pulmonary microvascular permeability is unaltered by ASA and that neither the decrease in plasma prostacyclin nor the increase in plasma sulfidopeptide leukotrienes may account for ASA-induced pulmonary vasoconstriction.

Usefulness of sodium chloride as a nondiffusible indicator in the measurement of extravascular lung thermal volume in dogs

The authors examined the usefulness of sodium chloride as a nondiffusible indicator during the first passage through dogs' lungs, before and after increased-permeability pulmonary oedema produced by an intravenous injection of alloxan. With an injection of a mixture of ice-cold 3 per cent sodium chloride and indocyanine green dye (a nondiffusible reference indicator), the authors simultaneously recorded three dilution curves from the aortic root: dye dilution, thermal and blood electrical conductivity dilution curves in six dogs. The mean transit time of sodium chloride in the conductivity dilution curve was significantly different from, but fairly equal to, that of indocyanine green dye (6.2 +/- 1.4 s (mean +/- SD) against 6.5 +/- 1.4 s (p < 0.01) in the baseline period, and 7.6 +/- 1.9 s against 8.4 +/- 2.1 s (p < 0.01) in the oedema period, respectively). The calculated extravascular lung thermal volume with the thermal and conductivity dilution method (Y, ml kg-1) correlated well with the gravimetrically determined extravascular lung mass in a total of 12 dogs, including six other dogs without intervention (x, g kg-1) (y = 0.72 x +3.03, r = 0.96). The authors conclude that sodium chloride is useful as a nondiffusible indicator in the first passage through the lungs, and that the thermal and conductivity dilution method is also useful for measuring extravascular lung water mass.

Ultrastructural substrates for increased lung water content in experimental pulmonary edema

We examined the relationship between the incidence of ultrastructural changes in the alveolar septum and the extravascular lung water content. Pulmonary edema was induced in 18 mongrel dogs by either dextran (n = 12) or alloxan (n = 6) administration. Six other dogs served as controls. Extravascular lung water content was measured by the thermal-dye double indicator dilution method. Specimens of lung tissue were examined with an electron microscope, and the incidence of 13 types of pathological changes in the alveolar septum was studied. For each type of pathological change, the incidence was correlated with the magnitude of lung water content. The following results were obtained. The incidence of edematous changes in the alveolar interstitium (widening of the interstitial space, and dispersion and disarray of collagen fibres in the interstitial space) was well correlated with lung water content (r = 0.78, p < 0.01, and r = 0.84, p < 0.01, respectively). The correlation was not significant in the remaining types of changes. We conclude that the incidence of the pathological changes in the alveolar septum is increased along with the increase in the content of lung water in both dextran- and alloxan-induced experimental pulmonary edema in dogs.

Correction for apparent prolongation of mean transit time resulting from response time in a thermodilution system

We investigated a method of correcting an apparent prolongation in the measured mean transit time (MTT), resulting from the response time of the thermodilution system. We measured the mean response times (MRT) for five commercially available thermistor-tipped catheters by recording their step function response curves. MRT is the sum of the time from the point of step change to the point of the first detection of change in temperature (latency time) plus the time from the first detection to the point of 63.2% of full response (time constant). By using a flow loop model filled with saline through a mixing chamber, we recorded pairs of thermodilution curves simultaneously with pairs of catheters, and studied the influence of MRT on MTT over the constant flow rates of 1-6 L/min. The difference in MRT's (delta MRT, second) between a pair of thermodilution systems correlated with the difference in MTT's (delta MTT, second) between a corresponding pair of thermodilution curves, yielding an equation: delta MTT = 1.07 delta MRT = 0.04 (n = 72, r = 0.95), delta MTT/delta MRT = 1.02 +/- 0.18 (mean +/- SD). We conclude that an apparent prolongation of MTT due to response time is removable by subtracting MRT from measured MTT.

Reliability of extravascular lung thermal volume measurements by thermal conductivity technique in sheep

We tested the accuracy, sensitivity, and reproducibility of a new lung water computer, based on the thermal conductivity technique, in 22 anesthetized closed-chest ventilated sheep with different treatments: 1) controls (n = 8), 2) 0.05 ml/kg of oleic acid + 100 ml/kg of lactated Ringer solution (n = 6), and 3) airway instillation of saline [3.1 +/- 1.3 (SD) g/kg, n = 8]. After 4 h, we determined the extravascular lung water gravimetrically. We found a significant overall correlation between the final extravascular lung thermal volume and the gravimetric extravascular lung mass (P < 0.001). Although the average ratio of extravascular lung thermal volume to extravascular lung mass was 0.97 +/- 0.25 ml/g for all groups, the computer overestimated extravascular lung mass in controls by 10% (17 g) and underestimated it in sheep with oleic acid by 15% (95 g) and in sheep with airway instillation by 8% (37 g). The computer also underestimated the small quantities of saline placed via the airway in the alveolar space by 75% (61 g). Reproducibility of three consecutive measurements was 4.3% (SE). We conclude that the thermal conductivity technique has an ability to detect the baseline extravascular lung mass but has a poor ability to detect an accurate increment of the extravascular lung water under poor tissue perfusion in anesthetized ventilated sheep.

Pretreatment with catalase or dimethyl sulfoxide protects alloxan-induced acute lung edema in dogs

We tested the preventive effects of catalase, an enzymatic scavenger of hydrogen peroxide, or dimethyl sulfoxide (DMSO), a hydroxyl radical scavenger, on intravenous alloxan-induced lung edema in four groups of pentobarbital sodium-anesthetized, ventilated dogs for 3 h: saline (20 ml.kg-1.h-1) infusion alone (n = 5), alloxan (75 mg/kg) + saline infusion (n = 5), catalase (150,000 U/kg) + alloxan + saline infusion (n = 5), or DMSO (4 mg/kg) + alloxan + saline infusion (n = 5). Catalase or DMSO significantly prevented the increase in plasma thromboxane B2 and 6-keto-prostaglandin F1 alpha over 3 h after alloxan and the accumulation of extravascular lung water after 3 h [3.95 +/- 0.52 (SE) g/g with catalase, 3.06 +/- 0.42 g/g with DMSO] but not early pulmonary arterial pressor response. An electron microscopic study indicated that catalase or DMSO significantly reduced the endothelial cellular damages after alloxan. These findings strongly suggest that hydrogen peroxide and hydroxyl radical are major mediators responsible for intravenous alloxan-induced edematous lung injury in anesthetized ventilated dogs.

Effects of ulinastatin, an antiprotease, on alloxan-induced lung injury in dogs

To determine if alloxan-induced lung injury could be prevented by an antiprotease, ulinastatin, we used three groups of five anesthetized, ventilated dogs. They were given saline (20 ml/kg/hr) infusion alone (saline group), alloxan (75 mg/kg) + saline infusion (alloxan group), or ulinastatin (50,000 U/kg) + alloxan + saline infusion (ulinastatin group). The course of all dogs was followed for three hours. In the saline group, extravascular lung water to blood-free dry weight (Qwl/dQl) was 3.22 +/- 0.31 g/g (mean +/- SE). The alloxan group presented the following significant findings: a decrease in white blood cell and platelet counts (44.2% and 68.2% of control, respectively) at five minutes; an increase in thromboxane B2 and 6-keto-prostaglandin F1 alpha (731.6% and 476.6% of control, respectively) at 15 minutes; an increase in beta-glucuronidase (124.8% of control) at 30 minutes; and an increase in Qwl/dQl (8.84 +/- 1.82 g/g) at the end of experiment. The addition of ulinastatin significantly reduced most alloxan-induced effects: differences in white blood cell counts, thromboxane B2, 6-keto-prostaglandin F1 alpha, and Qwl/dQl between the saline and ulinastatin groups were small. We conclude that ulinastatin significantly reduces the extent of lung water accumulation in alloxan-induced lung injury.

Effect of interstitial edema on lung lymph flow in goats in the absence of filtration

We tested the effect of interstitial edema on lung lymph flow when no filtration occurred. In 16 anesthetized open-thorax ventilated supine goats, we set pulmonary arterial and left atrial pressures to nearly zero and measured lymph flow for 3 h from six lungs without edema and ten with edema. Lymph flow decreased exponentially in all experiments as soon as filtration ceased. In the normal lungs the mean half time of the lymph flow decrease was 12.7 +/- 4.8 (SD) min, which was significantly shorter (P less than 0.05) than the 29.1 +/- 14.8 min half time in the edematous lungs. When ventilation was stopped, lymph flow in the edematous lungs decreased as rapidly as in the normal lungs. The total quantity of lymph after filtration ceased was 2.7 +/- 0.8 ml in normal lungs and 9.5 +/- 6.3 ml in edematous lungs, even though extravascular lung water was doubled in the latter (8.4 +/- 2.4 vs. 3.3 +/- 0.4 g/g dry lung, P less than 0.01). Thus the maximum possible clearance of the interstitial edema liquid by the lymphatics was 6.3 +/- 4.8%. When we restarted pulmonary blood flow after 1-2 h in four additional goats, lymph flow recovered within 30 min to the baseline level. These findings support the hypothesis that lung lymph flow originates mainly from alveolar wall perimicrovascular interstitial liquid and that the contribution of the lung lymphatic system to the clearance of interstitial edema (bronchovascular cuffs, interlobular septa) is small.

Application of respiratory heat exchange for the measurement of lung water

A noninvasive method for measuring pulmonary blood flow and lung mass (called airway thermal volume), based on the measurements of lung heat exchange with environment, is described. The lungs function as a steady-state heat exchange system, having an inner heat source (pulmonary blood flow) and an external heat sink (ventilation). Sudden changes in the steady-state condition, such as caused by hyperventilation of dry air, lead to a new steady state after a few minutes. The expired air temperature difference between the initial and final steady states is proportional to pulmonary blood flow, whereas the rate at which the new steady state is achieved is proportional to airway thermal volume. The method was tested in 20 isolated dogs lungs, 9 perfused goat lungs, and 27 anesthetized sheep. The expired air temperature fall during hyperventilation was inversely proportional to the perfusion rate of the isolated lungs, and half-time of the temperature fall was proportional to the lung tissue mass. Experiments in anesthetized sheep showed that the measured airway thermal volume is close to the total mass of the excised lungs, including its residual blood (r = 0.98). Pulmonary edema and fluid instillation into the bronchial tree increased in the measured lung mass.

Increases in Urinary Enzyme Excretion in Rats Depleted of Glutathione Inhibited by Scavenger of Oxygen Free Radicals

Urinary excretion of enzymes by rats was assessed after glutathione (GSH) was depleted by treatment with a mixture of the GSH depletors D,L-buthionine-S,R-sulfoximine (BSO) and diethylmaleate (DEM). Renal GSH was low 2 h after treatment and later returned to the control level. The urinary excretion of gamma-glutamyltranspeptidase (gamma-GTP) and N-acetyl-beta-D-glucosaminidase (NAG) remained high for at least 3 d after the injection of BSO (100 mg/kg) and DEM (0.5 ml/kg), with no effect on the blood urea nitrogen level. N,N'-Dimethylthiourea (DMTU), a scavenger of oxygen free radicals, inhibited this increase in the urinary excretion of gamma-GTP. DMTU also inhibited the increase in cisplatin-induced NAG excretion caused by the GSH depletors. These results suggested that the urinary excretion of these enzymes is an index of renal tubular injury caused by short-term depletion of renal GSH, and that the generation of free radicals may be involved in renal tubular injury during GSH depletion or caused by cisplatin together with GSH depletors.

Effect of superior vena caval hypertension on alloxan-induced lung injury in dogs

To investigate how fast and to what extent superior vena caval hypertension (SVCH) increases lung water in acute increased-permeability state, we studied the time course of lung water accumulation for 3 h in anesthetized dogs under different treatments: 1) controls without intervention (5 dogs), 2) SVCH alone (5 dogs), 3) mild lung microvascular injury induced by low-dose alloxan (75 mg/kg) alone (5 dogs), and 4) SVCH coupled with low-dose alloxan (5 dogs). Neither low-dose alloxan alone nor SVCH alone [superior vena caval pressure (Psvc) = 11.0 +/- 3.1 (SD) mmHg] increased lung water significantly. The SVCH coupled with low-dose alloxan (Psvc = 11.3 +/- 2.7 mmHg) doubled extravascular lung thermal volume measured by the thermal-dye dilution technique within 1 h (5.3 +/- 0.9 ml/kg at base line and 10.9 +/- 4.7 ml/kg at 1 h), then remained unchanged (12.5 +/- 5.7 ml/kg at 3 h). This increase in lung water was confirmed by gravimetric method (5.69 +/- 1.71 g/g blood-free dry wt). We conclude that SVCH is one of the factors that may promote lung water accumulation in increased-permeability state.

Intermittent oversensing due to internal insulation damage of temperature sensing rate responsive pacemaker lead in subclavian venipuncture method

A 49-year-old male patient developed sensing failure (oversensing) 6 months after the implantation of a temperature sensing rate responsive pacemaker by the subclavian venipuncture method. Intermittent oversensing appeared in the sitting position, but did not appear in the supine position. Temperature telemetry showed an excessive fluctuation of the temperature data points while sitting and while doing a treadmill exercise test. Internal insulation damage was found approximately 31 cm from the distal tip of the explanted lead. The electrical resistance between one thermistor coil and the pacing coil changed from 9 kiloohms to 40 ohms when moderate pressure was applied to the outside lead in the fault area. This electrical shunt resulted from internal insulation damage that resulted from compression of the pacemaker lead between the first rib and the clavicle.

Electron microscopic pathological patterns of alveolar septum in acute dextran-induced and alloxan-induced pulmonary edema in dogs

We studied the incidence of electron microscopic pathological patterns of the alveolar septum observed 30 min after induction of pulmonary edema by dextran-70 infusion (6 dogs, dextran group) and by alloxan injection (6 dogs, alloxan group). For comparable amounts of extravascular lung water in both dextran and alloxan groups, which were twice as much as control group (6 dogs), we characterized the pathological changes. The incidence of the electron microscopic pathological patterns that appeared in dextran group compared with that in control group was significantly high in terms of the widening of the interstitial space, dispersion and disarray of collagen fibrils, and erythrocytes in the interstitial space. The incidence in alloxan group compared with that in control group was significantly high in terms of the swelling of epithelial cells and endothelial cells as well as the widening of the interstitial space, and dispersion and disarray of collagen fibrils. We conclude that dextran causes interstitial changes exclusively and alloxan causes cellular changes primarily coupled with secondary interstitial changes in acute pulmonary edema.

Intracytoplasmic crystalloid structures in a malignant fibrous histiocytoma: ultrastructural and cytochemical study

Crystalloid structures were frequently observed in the cytoplasm of the tumor cells of a malignant fibrous histiocytoma arising in the left leg of a 71-year-old female. These structures were located in the cytoplasm of the fibroblastlike and histiocyte-like tumor cells. The structures consisted of an aggregate of dense granules without unit membrane. Neither glycoproteins nor polysaccharides were detected in these structures on sections stained with chromic acid-phosphotungstic acid or periodic acid-thiocarbohydrazide-silver proteinate. On sections from acrylate-embedded specimens, the structures were easily digested by trypsin and protease but were not sensitive to RNase. Although the significance and origin of these structures remain obscure, the results indicate that the crystalloid structures in the present study are mainly composed of proteinaceous substance.

Exponential increases in pulmonary intravascular and extravascular fluid volumes by overperfusion with dextran 70 in anesthetized dogs

In the lung overperfused by dextran 70, it is not known how intravascular blood volume and extravascular water volume increase as a function of pulmonary microvascular pressure. To determine their characteristics, we produced an overperfusion state (high pressure and high blood flow) by infusing dextran 70 (100 ml/kg over 30 min) into 15 anesthetized dogs. Using the thermal and dye dilution technique, we simultaneously estimated the pulmonary blood volume (PBV) and the extravascular lung thermal volume (EVLTV), and correlated mathematically these variables with pulmonary artery end-diastolic pressure (PAEDP). Here, we defined PAEDP as the pulmonary microvascular pressure. From the values determined before, during and after dextran 70 infusion, we obtained the following exponential relations. PBV(ml/kg) = 30[1-0.902(e-0.021PAEDP(mmHg)) EVLTV(ml/kg) = 5.15(e0.027PAEDP (mmHg)) From these mathematical relations, we conclude that: (1) the pulmonary blood volume increases rapidly at low pressure and slowly at high pressure; and (2) the pulmonary extravascular water volume increases slowly at low pressure and then increases rapidly at high pressure. In addition, this equation indicates that the critical pressure from which the pulmonary extravascular water volume exceeds the upper limit of its normal volume is about 17 mmHg in PAEDP. Infusion of dextran 70 increased plasma macromolecular osmotic pressure from 20.8 +/- 0.6 (mean +/- SD) mmHg before infusion to 43.7 +/- 1.4 mmHg after infusion. Therefore, dextran 70 does not change the critical microvascular pressure against pulmonary edema.

Pressure-volume relationships in the pulmonary "venous" system in living dogs

In this study, we examined the pressure-volume (P-V) relationships of the pulmonary "venous" (P'V') system in anesthetized living dogs, and assessed compliance by fitting the derived data of the P-V relationships to the exponential function. By definition, the P'V' system consists of the pulmonary veins and the left atrium. The pulmonary "venous" volume (P'V'V) was determined with our modified double indicator dilution method using a single injection and double sampling technique. The mean left atrial pressure (PLA) was measured directly. To observe sequential changes over a wide range of the P-V relationships, dogs were studied from the control state through the volume-loaded state with dextran. The P'V'V ranged from 3.4 to 12.2 ml X kg-1 and the PLA from 3.2 to 40.6 mmHg. We fitted the data of the P-V relationships (n = 24) to the exponential function, yielding an equation: P'V'V (ml X kg-1) = 19(1-0.833(e-0.017PLA(mmHg)). We then differentiated an above equation to estimate the slope of this curve (static compliance), giving the equation: dV/dP (ml X mmHg-1 X kg-1) = 0.269(e-0.017PLA(mmHg)). Therefore, at PLA of 10 mmHg (normal level), the compliance is 0.227 ml X mmHg-1 X kg-1. The compliance, obtained with an application of the present results in dogs to man, (disregarding expected species differences), coincides well with that in man determined with our indirect method.

Fluid volume balance between pulmonary intravascular space and extravascular space in dogs

We aimed to study the agreement of estimates of the pulmonary blood volume by the double indicator dilution method and the direct destructive method and the fluid volume balance between the pulmonary intravascular and extravascular spaces. We employed the double indicator dilution method using heat and indocyanine green, with a single injection (into the right atrium) and double sampling technique, that is from the pulmonary artery trunk (PAT) and the aortic root (Ao). With this method, we simultaneously determined the pulmonary extravascular water volume (PEWV), defined as the extravascular lung thermal volume estimated in Ao (LTVAo), and the pulmonary blood volume (PBV) from PAT to the left atrium (LA) (PBVPAT-LA). Dogs were divided into groups: a group without intervention (n = 16), a group loaded with dextran (n = 12) and a group loaded with alloxan (n = 7). When all groups were included, PBVPAT-LA (ml/kg) = 1.02 X PBVdirect(g/kg) + 0.96, n = 35, r = 0.83 where PBVdirect means the blood contents from the pulmonary artery bifurcation to the pulmonary vein measured by the direct destructive method. We substantiated the validity of the use of the double indicator dilution method. In studying the fluid volume balance, based on the results of the direct destructive method, the pulmonary intravascular-extravascular fluid volume ratio (intra/extra) was 1.3 +/- 0.3 (mean +/- SD) in the control state, implying that the interstitium in the lung is relatively "dry". As overt pulmonary edema developed by dextran infusion, the ratio exponentially decreased to 1.0 +/- 0.1 (p less than 0.01). The behavior of the fluid volume balance in question (intra/extra), studied with the double indicator dilution method, was essentially similar to that analyzed by the direct destructive method.

Pulmonary blood volume and pulmonary extravascular water volume in men

In order to estimate the pulmonary blood volume between the pulmonary artery trunk and the left atrium (PBV PAT-LA), simultaneously with the pulmonary extravascular water volume (PEWV) in the chronically stable cardiac patients, we employed the double indicator dilution method using heat as a diffusible indicator and indocyanine green as a non-diffusible indicator. The PEWV was obtained as the extravascular lung thermal volume estimated in the aortic root (LTVAo). In the group of hemodynamically normal patients, in spite of ischemic heart disease (G-N, n = 22), the mean pulmonary artery wedge (PAW) pressure was 9.3 +/- 3.9 mmHg (mean +/- SD), PBVPAT-LA was 8.95 +/- 1.71 ml/kg, LTVAo was 5.71 +/- 1.37 ml/kg and PBVPAT-LA/LTVAo ratio was 1.64 +/- 0.44. In the group of hemodynamically slightly compromised patients with mitral stenosis (G-MS, n = 13), the mean PAW pressure was 14.2 +/- 2.6 mmHg, PBVPAT-LA was 11.12 +/- 2.86 ml/kg, LTVAo was 5.68 +/- 1.41 ml/kg and PBVPAT-LA/LTVAo ratio was 2.02 +/- 0.58. Between the two groups, LTVAo was not statistically significant, whereas the mean PAW pressure, PBVPAT-LA and PBVPAT-LA/LTVAo ratio were all significantly increased in G-MS (p less than 0.05). Neither PBVPAT-LA nor LTVAo correlated with the mean PAW pressure in both groups. From PBVPAT-LA/LTVAo ratio, fluid volume in the intravascular space was greater than that in the extravascular space in both groups. From LTVAo, PEWV in G-MS was identical with that in G-N, in spite of the elevated mean PAW pressure. Therefore, even in the patients with mitral stenosis, the interstitium in the lung is kept "dry" under conditions of the mean PAW pressure below 20 mmHg. The safety factors that prevent pulmonary edema, as evidenced in animal studies, seem to operate effectively in man.

A problem intrinsic to the measurements of the pulmonary extravascular water volume by the thermal-dye technic with the sampling site in the bifurcation of the aorta. Thermal equilibrium with the aortic wall

When estimating the pulmonary extravascular water volume (PEWV) as the lung thermal volume (LTV), by the double indicator dilution technic using heat and indocyanine green (ICG), a part of the left ventricular wall comes to the thermal equilibrium, and this leads to an overestimation of PEWV, when the samplings are made in the aortic root. In a previous study from this laboratory, this overestimation was approximately 10% of the measured LTV in the aortic root. In the present study, we evaluated the extent to which the thermal equilibrium with the aortic wall would cause LTV to slightly overestimate PEWV. For this purpose, we injected a mixture of the indicators into the right atrium, and recorded the indicator dilution curves at the bifurcation of the aorta (AB). We then compared this LTV with the one calculated from the indicator dilution curves recorded simultaneously in the aortic root (Ao). We obtained the following results: Firstly, the values of cardiac output (CO) from the dye dilution curve and from the thermodilution curve at two sites, Ao and AB, were all in agreement. Secondly, LTV estimated in Ao (LTVAo) and LTV estimated in AB (LTVAB) were not the same, and their relationships were: LTVAB = 1.21 X LTVAo + 0.44 (ml/kg), n = 32, (r = 0.98, p less than 0.001) A close agreement of CO determined at two sites indicated that there was virtually no loss of heat between the two sampling sites, Ao and AB. An excess of LTVAB over LTVAo came to about 20%, and this excess appeared to be ascribable to the incorporation of the thermally equilibrated "volume" of the aortic wall. This finding appeared to be a challenge to the validity of estimating LTV when sampling the indicators in the distal abdominal aorta.

A problem in the measurements of pulmonary extravascular water volume by double indicator dilution method, using heat and dye--thermal diffusion into the left ventricular wall

Pulmonary extravascular water volume was obtained as the lung thermal volume (LTV) in mongrel dogs (n = 31) by double indicator dilution method, using negative heat and indocyanine green. We used a technic of one injection site (right atrium) and two sampling sites, i.e., pulmonary artery trunk and aortic root. In 13 dogs, cardiac outputs determined simultaneously from thermodilution curves in pulmonary artery trunk, aortic root and from dye dilution curve in aortic root, were in a good agreement with a coefficient of variation of +/- 12%. Lung thermal volume measured twice within a period of 5 minutes in 17 dogs, gave closely similar values with a coefficient of variation of +/- 9%. Lung thermal volume was 5.7 +/- 1.1 ml/kg (mean +/- SD) and corresponding "weighed lung water" (WLW), which was measured by destructive, direct method, was 5.0 +/- 1.0 ml/kg, the ratio of LTV to WLW (LTV/WLW) being 1.2 +/- 0.2 in control state. LTV/WLW ratio was 1.2 +/- 0.2 in 11 dogs loaded with dextran, and 1.1 +/- 0.1 in 6 dogs loaded with alloxan. Thus the lung thermal volume slightly exceeded WLW. In order to evaluate the extent to which the thermal diffusion into the left ventricular wall would cause LTV to slightly overestimate the pulmonary extravascular water volume, dye dilution curves and thermodilution curves were recorded simultaneously in the left atrium (LA) and aortic root (Ao) in a total of 25 runs in 5 dogs. The ratio of LTV obtained in LA to that in Ao was 0.9 +/- 0.1 (mean +/- SD). It was concluded that the pulmonary extravascular water volume was overestimated, by about 10% due to the thermal diffusion into the left ventricular wall.