Low abdominal contribution to breathing as daytime predictor of nocturnal desaturation in adolescents and young adults with Duchenne Muscular Dystrophy

In the respiratory management of DMD patients it is still under debate what parameter should indicate the correct timing for institution of nocturnal non-invasive ventilation (NIV), in addition to forced vital capacity, which is generally considered as a prognostic marker of disease progression. The aim of this study was to determine if volume variations of rib cage and abdominal compartments measured by Opto-Electronic Plethysmography can be helpful to distinguish between those patients who are in the early stages of nocturnal oxygen desaturation development and those who do not yet. Pulmonary function, abdominal contribution to tidal volume and to inspiratory capacity (%Abd IC) and a set of breathing pattern indexes were assessed in 40 DMD patients older than 14 years and not yet under nocturnal NIV. ROC analysis revealed that among all the considered parameters, %Abd IC in supine position was the best discriminator between DeSat (at least 10% of the night time with SpO(2) < 95%) and NonDeSat patients, providing an area under the curve with 95%CI equal to 0.752. In conclusion, in adolescents and adults DMD patients who present either no sign or only mild nocturnal oxygen desaturation, a reduced abdominal contribution to inspiratory capacity is a marker of the onset of diaphragm weakness and should be considered to identify the correct timing for the institution of nocturnal NIV.

Effects of propofol anaesthesia on thoraco-abdominal volume variations during spontaneous breathing and mechanical ventilation

BACKGROUND

Anaesthesia based on inhalational agents has profound effects on chest wall configuration and breathing pattern. The effects of propofol are less well characterised. The aim of the current study was to evaluate the effects of propofol anaesthesia on chest wall motion during spontaneous breathing and positive pressure ventilation.

METHODS

We studied 16 subjects undergoing elective surgery requiring general anaesthesia. Chest wall volumes were continuously monitored by opto-electronic plethysmography during quiet breathing (QB) in the conscious state, induction of anaesthesia, spontaneous breathing during anaesthesia (SB), pressure support ventilation (PSV) and pressure control ventilation (PCV) after muscle paralysis.

RESULTS

The total chest wall volume decreased by 0.41 ± 0.08 l immediately after induction by equal reductions in the rib cage and abdominal volumes. An increase in the rib cage volume was then seen, resulting in total chest wall volumes 0.26 ± 0.09, 0.24 ± 0.10, 0.22 ± 0.10 l lower than baseline, during SB, PSV and PCV, respectively. During QB, rib cage volume displacement corresponded to 34.2 ± 5.3% of the tidal volume. During SB, PSV and PCV, this increased to 42.2 ± 4.9%, 48.2 ± 3.6% and 46.3 ± 3.2%, respectively, with a corresponding decrease in the abdominal contribution. Breathing was initiated by the rib cage muscles during SB.

CONCLUSION

Propofol anaesthesia decreases end-expiratory chest wall volume, with a more pronounced effect on the diaphragm than on the rib cage muscles, which initiate breathing after apnoea.

Respiratory and leg muscles perceived exertion during exercise at altitude

We compared the rate of perceived exertion for respiratory (RPE,resp) and leg (RPE,legs) muscles, using a 10-point Borg scale, to their specific power outputs in 10 healthy male subjects during incremental cycle exercise at sea level (SL) and high altitude (HA, 4559 m). Respiratory power output was calculated from breath-by-breath esophageal pressure and chest wall volume changes. At HA ventilation was increased at any leg power output by ∼ 54%. However, for any given ventilation, breathing pattern was unchanged in terms of tidal volume, respiratory rate and operational volumes of the different chest wall compartments. RPE,resp scaled uniquely with total respiratory power output, irrespectively of SL or HA, while RPE,legs for any leg power output was exacerbated at HA. With increasing respective power outputs, the rate of change of RPE,resp exponentially decreased, while that of RPE,legs increased. We conclude that RPE,resp uniquely relates to respiratory power output, while RPE,legs varies depending on muscle metabolic conditions.

Breathing pattern and chest wall volumes during exercise in patients with cystic fibrosis, pulmonary fibrosis and COPD before and after lung transplantation

BACKGROUND

Pulmonary fibrosis (PF), cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) often cause chronic respiratory failure (CRF).

METHODS

In order to investigate if there are different patterns of adaptation of the ventilatory pump in CRF, in three groups of lung transplant candidates with PF (n=9, forced expiratory volume in 1 s (FEV(1))=37+/-3% predicted, forced vital capacity (FVC)=32+/-2% predicted), CF (n=9, FEV(1)=22+/-3% predicted, FVC=30+/-3% predicted) and COPD (n=21, FEV(1)=21+/-1% predicted, FVC=46+/-2% predicted), 10 healthy controls and 16 transplanted patients, total and compartmental chest wall volumes were measured by opto-electronic plethysmography during rest and exercise.

RESULTS

Three different breathing patterns were found during CRF in PF, CF and COPD. Patients with COPD were characterised by a reduced duty cycle at rest and maximal exercise (34+/-1%, p<0.001), while patients with PF and CF showed an increased breathing frequency (49+/-6 and 34+/-2/min, respectively) and decreased tidal volume (0.75+/-0.10 and 0.79+/-0.07 litres) (p<0.05). During exercise, end-expiratory chest wall and rib cage volumes increased significantly in patients with COPD and CF but not in those with PF. End-inspiratory volumes did not increase in CF and PF. The breathing pattern of transplanted patients was similar to that of healthy controls.

CONCLUSIONS

There are three distinct patterns of CRF in patients with PF, CF and COPD adopted by the ventilatory pump to cope with the underlying lung disease that may explain why patients with PF and CF are prone to respiratory failure earlier than patients with COPD. After lung transplantation the chronic adaptations of the ventilatory pattern to advanced lung diseases are reversible and indicate that the main contributing factor is the lung itself rather than systemic effects of the disease.

Synthesis of human renalase1 in Escherichia coli and its purification as a FAD-containing holoprotein

Renalase is a protein ubiquitous in vertebrates, which has been proposed to modulate blood pressure and heart rate, and whose downregulation might result in hypertension. Despite its potential relevance for human health, the biochemical characterization of renalase is still lacking, possibly due to difficulties in obtaining it in recombinant form. By expressing two different gene constructs, we found that the major isoform of human renalase, renalase1, is mainly produced in Escherichia coli in inclusion bodies. However, by optimizing the expression conditions, significant amounts of soluble products were obtained. Both soluble renalase forms have been purified to homogeneity exploiting their N-terminal His-tag. Linking of the protein of interest to the SUMO protein did not improve solubility, but yielded untagged renalase1 after proteolytic processing of the fusion product. The two recombinant renalase forms displayed the same molecular properties. They bind equimolar amounts of FAD and appear to be correctly folded by various criteria. The procedures for the production and isolation of recombinant renalase1 here reported are expected to boost the much awaited biochemical studies on this remarkable protein.

Plasmodium falciparum ferredoxin-NADP+ reductase His286 plays a dual role in NADP(H) binding and catalysis

The NADP-binding site of Plasmodium falciparum ferredoxin-NADP(+) reductase contains two basic residues, His286 and Lys249, conserved within the Plasmodium genus, but not in other plant-type homologues. Previous crystal studies indicated that His286 interacts with the adenine ring and with the 5'-phosphate of 2'-P-AMP, a ligand that mimics the adenylate moiety of NADP(H). Here we show that replacement of His286 with aliphatic residues results both in a decrease in the affinity of the enzyme for NADPH and in a decrease in k(cat), due to a lowered hydride-transfer rate. Unexpectedly, the mutation to Gln produces an enzyme more active than the wild-type one, whereas the change to Lys destabilizes the nicotinamide-isoalloxazine interaction, decreasing k(cat). On the basis of the crystal structure of selected mutants complexed with 2'-P-AMP, we conclude that the His286 side chain plays a dual role in catalysis both by providing binding energy for NADPH and by favoring the catalytically competent orientation of its nicotinamide ring. For the latter function, the H-bonding potential rather than the positively charged state of the His286 imidazole seems sufficient. Furthermore, we show that the Lys249Ala mutation decreases K(m)(NADPH) and K(d) for NADP(+) or 2'-P-AMP by a factor of 10. We propose that the Lys249 side chain participates in substrate recognition by interacting with the 2'-phosphate of NADP(H) and that this interaction was not observed in the crystal form of the enzyme-2'-P-AMP complex due to a conformational perturbation of the substrate-binding loop induced by dimerization.

Abdominal volume contribution to tidal volume as an early indicator of respiratory impairment in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is characterised by progressive loss of muscular strength that leads to an increasingly restrictive pulmonary syndrome. However, it is still not clear whether this determines alterations in the breathing pattern. We studied: 66 DMD patients at different stages of the disease (mean+/- sem age 12.6+/-0.6 yrs, range 5-22 yrs of age), subdivided into four groups according to age; and 21 age-matched healthy male controls. Spirometry, lung volumes and nocturnal oxygen saturation were measured in all DMD patients. Ventilatory pattern and chest wall volume variations were assessed by optoelectronic plethysmography during spontaneous breathing both in seated and supine positions. Whilst in a seated position, no significant differences were found between patients and controls or between different age groups. In the supine position, the average contribution of abdominal volume change (DeltaV(AB)) to tidal volume progressively decreased with age (p<0.001). The patients who showed nocturnal hypoxaemia showed significantly lower Delta V(AB). In conclusion, chest wall motion during spontaneous breathing in awake conditions and in supine position is an important indicator of the degree of respiratory muscle impairment in DMD. DeltaV(AB) is not only an important marker of the progression of the disease but is also an early indicator of nocturnal hypoxaemia.

The ferredoxin-NADP+ reductase/ferredoxin electron transfer system of Plasmodium falciparum

In the apicoplast of apicomplexan parasites, plastidic-type ferredoxin and ferredoxin-NADP(+) reductase (FNR) form a short electron transport chain that provides reducing power for the synthesis of isoprenoid precursors. These proteins are attractive targets for the development of novel drugs against diseases such as malaria, toxoplasmosis, and coccidiosis. We have obtained ferredoxin and FNR of both Toxoplasma gondii and Plasmodium falciparum in recombinant form, and recently we solved the crystal structure of the P. falciparum reductase. Here we report on the functional properties of the latter enzyme, which differ markedly from those of homologous FNRs. In the physiological reaction, P. falciparum FNR displays a k(cat) five-fold lower than those usually determined for plastidic-type FNRs. By rapid kinetics, we found that hydride transfer between NADPH and protein-bound FAD is slower in the P. falciparum enzyme. The redox properties of the enzyme were determined, and showed that the FAD semiquinone species is highly destabilized. We propose that these two features, i.e. slow hydride transfer and unstable FAD semiquinone, are responsible for the poor catalytic efficiency of the P. falciparum enzyme. Another unprecedented feature of the malarial parasite FNR is its ability to yield, under oxidizing conditions, an inactive dimeric form stabilized by an intermolecular disulfide bond. Here we show that the monomerdimer interconversion can be controlled by oxidizing and reducing agents that are possibly present within the apicoplast, such as H(2)O(2), glutathione, and lipoate. This finding suggests that modulation of the quaternary structure of P. falciparum FNR might represent a regulatory mechanism, although this needs to be verified in vivo.

Non-invasive three-dimensional imaging of human diaphragm in-vivo

Three-dimensional reconstruction of human diaphragm provide useful information on the functional anatomy of the respiratory system by the analysis of its geometry. The aim of the current work is the development of a new method for the 3D analysis of diaphragm geometry by the combination of free-hand Ultrasound (US) scans with an optoelectronic system of movement analysis for the tracking of the probe. 6 healthy subjects (age=24+/-2), have been measured with a free-hand US scanning of the abdomen in supine (SP) and seated position (ST), during breath-holding at Functional Residual Capacity (FRC) and Total Lung Capacity (TLC). For one of them, measurements have been repeated in supine position in an MR scan for the validation of the method. Posture has different implications on diaphragm geometry depending on the respiratory volume. At FRC the ray of curvature (rho) in ST is 101.1+/-43.1 mm higher than in SP (p=0.006), while at TLC, posture influences the position of the diaphragm with a caudo-cranial displacement from SP to ST of 23.4+/-16.7mm (p=0.019). Diaphragm geometry at different lung volumes is influenced by the posture. In SP, rho increases of 105.9+/-48.3 mm (p=0.008) and there is a cranio-caudal displacement (Deltay) of 47.54+/-15 mm (p=0.002) shifting from FRC to TLC. In ST, Deltay=31.1+/-13.5 mm (p=0.006) while rho increases not significantly. Percentage errors between MR and US 3D reconstructions are 2.1% and 10.46% for Deltay and TLC/FRC rho ratio, respectively. US 3D reconstruction is a reliable method for the assessment of diaphragm functional anatomy. Posture directly influence diaphragm geometry and hence respiratory mechanics.

Paradoxical movement of the lower ribcage at rest and during exercise in COPD patients

Paradoxical inward displacement of the costal margin during inspiration is observed in many chronic obstructive pulmonary disease patients at rest but its importance is unclear. The current authors studied 20 patients (forced expiratory volume in one second 32.6+/-11.7, functional residual capacity 186+/-32% predicted) and 10 healthy controls at rest and during symptom-limited incremental exercise. With optoelectronic plethysmography, the phase shift between pulmonary and abdominal ribcage volumes and the percentage of inspiratory time the ribcage compartments moved in opposite directions were quantified, using control data to define the normal range of movement. Eight patients showed lower ribcage inspiratory paradox at rest (P+), while 12 patients did not (P-). This was unrelated to resting lung function or exercise tolerance. Total end-expiratory chest wall volume (EEV(cw)) increased immediately when exercise began in P+ patients, but later in exercise in P- patients. This difference in EEV(cw) was mainly due to a greater increase of end-expiratory pulmonary ribcage volume in P+ patients. During exercise, dyspnoea increased similarly in the two groups, while leg effort increased more markedly in the patients without paradox. In conclusion, lower ribcage paradox at rest is reproducible and associated with early-onset hyperinflation of the chest wall and predominant dyspnoea at end-exercise. When paradox is absent, the sense of leg effort becomes a more important symptom limiting exercise.

Effect of salt and pH on the reductive half-reaction of Mycobacterium tuberculosis FprA with NADPH

Despite a number of studies, the formation of the Michaelis complexes between ferredoxin-NADP (+) reductases and NADP(H) eluded detailed investigations by rapid kinetic techniques because of their high formation rates. Moreover, the reversible nature of the reaction of hydride ion transfer between these enzymes and NADPH prevented the obtainment of reliable estimates of the rate constant of the hydride transfer step. Here we show that by working at a high salt concentration, the mechanism of the reaction with NADPH of FprA, a Mycobacterium tuberculosis homologue of adrenodoxin reductase, is greatly simplified, making it amenable to investigation by rapid reaction techniques. The approach presented herein allowed for the first time the observation of the formation of the Michaelis complex between an adrenodoxin reductase-like enzyme and NADPH, and the determination of the related rate constants for association and dissociation. Furthermore, the rate constant for the reaction of hydride ion transfer between NADPH and FAD could be unambiguously assessed. It is proposed that the approach described should be applicable to other ferredoxin reductase enzymes, providing a valuable experimental tool for the study of their kinetic properties.

Structural and functional diversity of ferredoxin-NADP(+) reductases

Although all ferredoxin-NADP(+) reductases (FNRs) catalyze the same reaction, i.e. the transfer of reducing equivalents between NADP(H) and ferredoxin, they belong to two unrelated families of proteins: the plant-type and the glutathione reductase-type of FNRs. Aim of this review is to provide a general classification scheme for these enzymes, to be used as a framework for the comparison of their properties. Furthermore, we report on some recent findings, which significantly increased the understanding of the structure-function relationships of FNRs, i.e. the ability of adrenodoxin reductase and its homologs to catalyze the oxidation of NADP(+) to its 4-oxo derivative, and the properties of plant-type FNRs from non-photosynthetic organisms. Plant-type FNRs from bacteria and Apicomplexan parasites provide examples of novel ways of FAD- and NADP(H)-binding. The recent characterization of an FNR from Plasmodium falciparum brings these enzymes into the field of drug design.

The crucial step in ether phospholipid biosynthesis: structural basis of a noncanonical reaction associated with a peroxisomal disorder

Ether phospholipids are essential constituents of eukaryotic cell membranes. Rhizomelic chondrodysplasia punctata type 3 is a severe peroxisomal disorder caused by inborn deficiency of alkyldihydroxyacetonephosphate synthase (ADPS). The enzyme carries out the most characteristic step in ether phospholipid biosynthesis: formation of the ether bond. The crystal structure of ADPS from Dictyostelium discoideum shows a fatty-alcohol molecule bound in a narrow hydrophobic tunnel, specific for aliphatic chains of 16 carbons. Access to the tunnel is controlled by a flexible loop and a gating helix at the protein-membrane interface. Structural and mutagenesis investigations identify a cluster of hydrophilic catalytic residues, including an essential tyrosine, possibly involved in substrate proton abstraction, and the arginine that is mutated in ADPS-deficient patients. We propose that ether bond formation might be orchestrated through a covalent imine intermediate with the flavin, accounting for the noncanonical employment of a flavin cofactor in a nonredox reaction.

Enzymatic oxidation of NADP+ to its 4-oxo derivative is a side-reaction displayed only by the adrenodoxin reductase type of ferredoxin-NADP+ reductases

We have previously shown that Mycobacterium tuberculosis FprA, an NADPH-ferredoxin reductase homologous to mammalian adrenodoxin reductase, promotes the oxidation of NADP(+) to its 4-oxo derivative 3-carboxamide-4-pyridone adenine dinucleotide phosphate [Bossi RT, Aliverti A, Raimondi D, Fischer F, Zanetti G, Ferrari D, Tahallah N, Maier CS, Heck AJ, Rizzi M et al. (2002) Biochemistry41, 8807-8818]. Here, we provide a detailed study of this unusual enzyme reaction, showing that it occurs at a very slow rate (0.14 h(-1)), requires the participation of the enzyme-bound FAD, and is regiospecific in affecting only the C4 of the NADP nicotinamide ring. By protein engineering, we excluded the involvement in catalysis of residues Glu214 and His57, previously suggested to be implicated on the basis of their localization in the three-dimensional structure of the enzyme. Our results substantiate a catalytic mechanism for 3-carboxamide-4-pyridone adenine dinucleotide phosphate formation in which the initial and rate-determining step is the nucleophilic attack of the nicotinamide moiety by an active site water molecule. Whereas plant-type ferredoxin reductases were unable to oxidize NADP(+), the mammalian adrenodoxin reductase also catalyzed this unusual reaction. Thus, the 3-carboxamide-4-pyridone adenine dinucleotide phosphate formation reaction seems to be a peculiar feature of the mitochondrial type of ferredoxin reductases, possibly reflecting conserved properties of their active sites. Furthermore, we showed that 3-carboxamide-4-pyridone adenine dinucleotide phosphate is good ligand and a competitive inhibitor of various dehydrogenases, making this nucleotide analog a useful tool for the characterization of the cosubstrate-binding site of NADPH-dependent enzymes.

The crystal structure of FdxA, a 7Fe ferredoxin from Mycobacterium smegmatis

Mycobacterium smegmatis ferredoxin FdxA, which has an orthologue ferredoxin in Mycobacterium tuberculosis, FdxC, contains both one [3Fe-4S] and one [4Fe-4S] cluster. M. smegmatis FdxA has been shown to be a preferred ferredoxin substrate of FprA [F. Fischer, D. Raimondi, A. Aliverti, G. Zanetti, Mycobacterium tuberculosis FprA, a novel bacterial NADPH-ferredoxin reductase, Eur. J. Biochem. 269 (2002) 3005-3013], an adrenodoxin reductase-like flavoprotein of M. tuberculosis, suggesting that M. tuberculosis FdxC could be the physiological partner of the enzyme in providing reducing power to the cytochromes P450. We report here the crystal structure of FdxA at 1.6A resolution (R(factor) 16.5%, R(free) 20.2%). Besides providing an insight on protein architecture for this 106-residue ferredoxin, our crystallographic investigation highlights lability of the [4Fe-4S] center, which is shown to loose a Fe atom during crystal growth. Due to their high similarity (87% sequence identity), the structure here reported can be considered a valuable model for M. tuberculosis FdxC, thus representing a step forward in the study of the complex mycobacterial redox pathways.