Prophylactic use of levosimendan in preoperative setting for surgical repair of congenital heart disease in children

Introduction

Low cardiac output syndrome (LCOS) is a significant cause of morbidity and the leading cause of mortality after pediatric cardiac surgery. Levosimendan has been shown safe and effective in pediatrics to treat LCOS. We aimed to review our local strategy with preoperative prophylactic Levosimendan infusion to minimize LCOS after heart surgery in identified high-risk patients.

Methods

Retrospective monocentric study. As there is no reliable cardiac output measurement in children, we recorded hemodynamic parameters as surrogates of cardiac output after extracorporeal circulation through an electronic patient survey system at different time points.

Results

Seventy-two children received Levosimendan before surgery between 2010 and 2019. As expected, most patients were newborns and infants with prolonged open-heart surgeries. Median cardiopulmonary bypass time was 182 [137-234] min, and aortic clamping time was 95 [64-126] min. The postoperative hemodynamic parameters, vasoactive-inotropic score, and urine output remained stable throughout the first 48 h. Only a tiny portion of the patients had combined surrogate markers of LCOS with a maximal median arterial lactate of 2.6 [1.9-3.5] mmol/L during the first six postoperative hours, which then progressively normalized. The median arterio-venous difference in oxygen saturation was 31 [23-38] % between 12 and 18 h post-surgery and gradually decreased. The median venous-to-arterial CO2 difference was the highest at 10 [7-12] mmHg between 12 and 18 h post-surgery. Nine patients (13%) required extracorporeal membrane oxygenation. No patient required dialysis or hemofiltration. Mortality was 0%.

Conclusion

Before congenital heart surgery, preoperative prophylactic administration of Levosimendan seems effective and safe for decreasing occurrence and duration of LCOS in high-risk children.

Complete and incomplete Kawasaki disease: Clinical differences and coronary artery outcome from a national prospective surveillance study in Switzerland

Introduction

The aim of this national prospective surveillance study was to compare the clinical presentation, laboratory findings, treatment, and coronary artery outcome in patients with incomplete and complete Kawasaki disease (KD).

Methods

Between March 2013 and February 2019, children with a diagnosis of complete and incomplete KD were reported by the Swiss Paediatric Surveillance Unit and prospectively enrolled. Clinical data, laboratory values, treatment, and echocardiographic features were collected at diagnosis and 1 year of follow-up. Data were compared between children with complete or incomplete KD.

Results

A total of 351 questionnaires were registered from children with a diagnosis of KD. Of them, 219 (62.4%) children had complete KD, and 132 (37.6%) children had incomplete KD. Children with incomplete KD were younger and had a longer-lasting fever; however, there were no differences in the level of C-reactive protein. All but four children received intravenous immunoglobulin treatment, whereas 14% of children were treated with corticosteroids. Children with incomplete KD were more often treated with corticosteroids than children with incomplete KD (p = 0.01). At diagnosis, 39 (11.1%) patients had only coronary artery dilation and 57 (16.2%) had at least one coronary artery aneurysm. There were no differences in coronary artery involvement between the two groups. At follow-up, 273 of 294 (92.8%) patients had no coronary artery involvement, with no difference between the two groups (p = 0.609). The overall incidence of coronary artery aneurysms at diagnosis was 16.2%. At follow-up, most coronary artery aneurysms had regressed, and coronary artery aneurysms were present in only 5.8% of the patients. Coronary artery aneurysms were slightly more frequent in patients with incomplete KD at follow-up (p = 0.039) but not at diagnosis (p = 0.208).

Conclusion

Although the clinical presentation in children with incomplete and complete KD differs, the absence of coronary artery involvement does not. The use of corticosteroids appears to be preventive against the development of coronary artery aneurysms in these patients. However, the results of this study suggest a lower rate of coronary artery aneurysm regression in patients with incomplete KD. Further studies on a larger scale are needed to assess the risk of non-regression of coronary artery aneurysms in this particular group of patients.

Laparoscopic surgery in a child with a failing Fontan circulation

A child with early failure of a Fontan circulation was listed for cardiac transplantation and then developed a subhepatic abscess. Surgical drainage was deemed necessary after the failure of an attempted percutaneous procedure. Following a multidisciplinary discussion, a laparoscopic technique was chosen to optimise postoperative recovery. To our knowledge, the literature does not describe any case of laparoscopic surgery in a patient with a failing Fontan circulation. This case report highlights the physiological variations involved with this management strategy, discusses the implications and risks, and offers some recommendations.

Maternal diabetes during pregnancy and carotid intima-media thickness in children

Background

Cardiovascular risk over the life course may be related to intrauterine risk factors, for instance, the exposure to maternal diabetes. Our objective was to systematically review studies that assessed the association of maternal diabetes during pregnancy and carotid-intima media thickness (CIMT), a marker of cardiovascular risk, in children.

Methods

We followed methods outlined in a published protocol for a systematic review on risk factors and determinants of CIMT in children (PROSPERO registration: CRD42017075169). Standardized mean differences in CIMT between offspring of women with and without diabetes during pregnancy were computed. Random effects meta-analyses were performed. The reliability of CIMT measurements was assessed.

Funding

SNSF 32003B-163240.

Results

Three observational studies involving 658 children were retained. Two studies were conducted in Europe and one in Australia. Age at CIMT assessment ranged from 2 days to 8 years. Two studies evaluated gestational diabetes during pregnancy and found no difference in CIMT among exposed children compared to controls (0.00 (95% CI: -0.41 to 0.41); 0.00 (95% CI; -0.28 to 0.28)). One study, that did not specify the type of diabetes evaluated, identified a higher CIMT (0.46 (95% CI; -0.07 to 1.00)). The pooled standardized mean difference in CIMT between offspring of women with and without diabetes during pregnancy was 0.08 (95% CI: -0.16 to 0.33; I2: 17.1%).

Conclusions

Overall, there is no clear association between maternal diabetes during pregnancy and offspring's CIMT. The degree of confidence in results is limited by the low number of studies, with relatively small sample sizes and a low number of participants exposed to maternal diabetes.

Key messages

Children exposed to maternal diabetes have no substantial alterations in vascular structure. More research is needed to inform primordial prevention of cardiovascular disease among these children.

[Congenital heart disease: from childhood to adulthood]

With the improvement of congenital heart surgery, most children with congenital heart disease will survive into adulthood with a good quality of life. Regular cardiac follow-up is recommended for all patients. The adolescent period coincides often with medium and long term consequences and complications and repeat surgery or catheter interventions might be needed. It is therefore of prime importance to begin the transition process early and to pursue it well into adulthood. We have elaborated a formal transition program adapted to youngsters with congenital heart disease.

[Malaria prevention: the general practitioners experience on the Reunion Island]

Malaria has been officially eradicated from the Reunion Island since 1979. However, a potentially active vector of the disease - Anopheles arabiensis - persists on the island. The risk of resurgence is quite significant. More than 90%of the patients presenting a malarial infection in Reunion Island after a stay in Madagascar or in the Comoros had followed a chemoprophylaxis that was not in accordance with the guidelines. A survey, that included 100 general practitioners, wasconducted in the Reunion Island regarding their practices concerning the malaria prevention. The upshot of all this is that these doctors themselves do not follow the optimal malaria prevention practices during journeys, and neglect their protection against mosquito bites. Travelers' consultations with the doctors before a journey represent only a modest part of their activity. However, the general practitioner is considered to be the interlocutor of choice for these patients. During these consultations, they do not refer enough to the national references which, according to a number of practitioners, are difficult to obtain. On the contrary, they refer too much to the information delivered by the pharmaceutical industry. With regard to the prescriptions of prophylactic treatments, only 40% of the doctors respect the official recommendations. This gap in the recommendations is sometimes deliberate and justified by the very high cost of a number of treatments. However, a lack of up-to-date knowledge cannot be excluded. Finally, the promotion of the protection against mosquito bites remains very poor. According to these data, it seems important to promote networking between the doctors and the reference centers, which would enhance optimal practices concerning chemoprophylaxis and protection against mosquito bites, especially targeting the "at risk" patients.

[A cause of dilated cardiomyopathy in a child: primary carnitine deficiency]

AIM

The aim of this case report was to show the importance to research metabolic etiology, especially a carnitine deficiency in dilated cardiomyopathy of children.

CASE REPORT

A three years old Togolese child presented muscular hypotonia, dyspnea. Examination showed left galop murmur and systolic murmur 2/6. Chest X-ray showed cardiomegaly (CTI: 0.66), electrocardiogram, a sinusal rythm, left ventricle hypertrophy and T wave abnormalities. Echocardiogram showed a markedly dilated left ventricle with reduced systolic function (EF: 0.43; reference range 0.55-0.80) and moderate mitral regurgitation. The inflammatory signs where negatives. Magnetic resonance imaging don't show signs of ischemic or myocarditis. The levels of free and total plasmatic carnitine decreased: 3μmol/L (N: 18-48μmol/L) and 5μmol/l (N: 29-70μmol/L) respectively. Mutation analysis of the gene SLC22A5 confirms the diagnosis of primary systemic carnitine deficiency. Treatment with oral carnitine was started at 200mg/kg per day. Within three weeks of treatment, we observed the decrease of all symptoms and the left ventricular size and function normalized (EF: 0.62). He has now been on oral carnitine for live.

CONCLUSION

Primary carnitine deficiency is a cause of dilated cardiomyopathy in child. It must systematically be suspected when a child presents a primitive cardiomyopathy. The treatment with oral carnitine for live is simple, with excellent prognosis.

[A rare cause of arterial hypertension in children: Takayasu arteritis]

Takayasu arteritis, a nonspecific inflammatory arteritis, is particularly rare in children. We report the case of a 6-year-old girl presenting with severe arterial hypertension in the upper segment associated with an inflammatory syndrome. Investigations showed coarctation of the abdominal aorta at different levels, due to Takayasu arteritis. The patient was treated with percutaneous dilatation and stent implantation as well as prolonged anti-inflammatory therapy. Arterial hypertension in children needs to be investigated until its cause, which may be rare, such as Takaysu arteritis, is determined.

[Stents valves for percutaneous valve replacement]

Stents have a long history in traditional valve surgery as both, porcine biological valves as well as pericardial valves are mounted on stents prior to implantation. Recently stent-mounted biological devices have been compressed up to the point, where they can be passed through a catheter. Various routes can be distinguished for implantation: open access, the trans-vascular route in antegrade or retrograde fashion, as well as direct trans-apical or trans-atrial access. Direct access has the potentialforvideo-endoscopic valve replacement. In theory, as well as in the experimental setting, valved stents have been implanted in tricuspid and caval position respectively, as well as in pulmonary, mitral and aortic locations. The largest clinical experience has been achieved in pulmonary position whereas current efforts target the aortic position.

[Hybrid procedures in congenital heart disease]

Increasing complexity in management of congenital heart disease imposes more frequent surgeries and interventions. Each technique has its own limitations, which could impair the anticipated result. Hybrid procedures join the advantages of cardiac surgery and interventions, creating a synergy in the management of these patients with cardiac anomalies. In our experience, hybrid procedures shorten cardiopulmonary bypass, reduce morbidity of surgery and reduce duration of stay in the intensive care unit. For some complex congenital heart diseases for which there are no ideal surgical or interventional options, hybrid procedures are becoming increasingly important in their management. Finally hybrid procedures allow surgeons and cardiologist to achieve complex procedures that could not be possible in another way.

[Pediatrics]

This article summarizes the medical progress achieved in 2 frequent and 2 rare pathologies: 1. Cryptorchidism should be operated around 12 months of age and hormonal treatment abandoned in order to maintain fertility and avoid development of testicular tumors. 2. For the treatment of streptococcal pharyngitis oral cephalosporins for 4 to 5 days are equivalent to a Penicillin treatment of 10 days. 3. Thanks to carvedilol (a beta-blocker agent), levosimendan (a calcium sensibiliser) and nesiritide (an analog to the natriuretic peptide) a new hormonal approach to cardiac failure is possible. 4. Corticosteroids allow to improve quality of live and life expectancy in Duchenne muscular dystrophy, provided treatment starts early and a multidisciplinary approach is assured.

[Transposition of the great arteries: long-term follow-up]

The management of transposition of the great arteries has changed importantly over the last decades. New techniques are employed for the diagnosis and surgical intervention has improved. This has lead to an increasing number of long-term survivors, who require specialised and focussed follow-up, depending on their type of surgical repair Mustard/Senning of arterial Switch. The long-term problems vary for each type of repair and require a specific approach, pharmacotherapy, catheter intervention or surgery. These complex sequellae implicate that transposition patients are never completely cured and probably will have a limited life span.

[Treatment of congential heart disease with interventional catheterization]

The development in pediatric interventional cardiology has changed the therapeutic strategy for many patients with congenital heart disease. Interventional catheterization became the first choice for valvuloplasty, angioplasty and collateral vessel occlusion. Effective and safe transcatheter interventions exist for closure of atrial or ventricular septal defects and for patent ductus arteriosus. The progress in the technology used in the catheterization laboratory will permit to continue the expansion of the range of interventions performed without surgery. Pediatric cardiologists and congenital heart surgeons must understand each other's interventional techniques and how they can be used in a coordinated fashion. This interaction is essential for the optimal management of patients with both simple and complex congenital heart disease.

[Pediatrics. Advantages of prenatal diagnosis in congenital cardiopathies]

The diagnosis of a congenital heart disease can be made by fetal ultrasound as soon as the 12th week of pregnancy. The main indications for fetal echocardiography are maternal and fetal. Sequential approach is necessary to precise the anatomy and to elaborate a therapeutic strategy for that patient. For severe heart lesions delivery and postnatal care can be programmed, avoiding thus severe hypoxia and acidosis after birth. The prognosis of these children are thus much improved.

Measurement of activated clotting time in children--comparison of the Celite i-STAT ACT with the Medtronic ACT II

BACKGROUND

To evaluate a recently introduced blood-saving method for the measurement of activated clotting time (ACT), the Celite i-STAT ACT, by comparing the values obtained with those from the widely used Medtronic ACT II device.

METHODS

In a prospective clinical study, we compared ACT values from the i-STAT device with the Medtronic ACT II device in 60 paediatric, interventional, cardiac catheterization procedures necessitating prophylactic heparinization. Blood samples were pair-analyzed using two i-STAT analyzers and one Medtronic ACT II device with double-tube-cartridges before and after heparinization. Data were compared using Bland-Altman bias analysis, Student's t-test and simple regression analysis.

RESULTS

Bias and precision between the Medtronic ACT II and the i-STAT ACT values was -5.4 +/- 26.3. The i-STAT and Medtronic ACT II values were similar before heparinization (P = 0.22), but i-STAT ACT values became significantly longer than Medtronic ACT II values after heparinization (P = 0.021). The increase of ACT after heparinization was greater (median 86.3; range 40-187 s) in the i-STAT analyzer than in the Medtronic ACT II analyzer (median 73.0; range 19-235.5 s). Increase in ACT values was inversely affected by intraoperative haemoglobin concentration in the Medtronic ACT II analyzer (P = 0.001) but not in the i-STAT analyzer.

CONCLUSION

Activated clotting times obtained from the Celite i-STAT ACT and the Medtronic ACT II demonstrated poor agreement. The technical principles are quite different and the two methods showed diverse susceptibility to intraoperative haemoglobin concentration. Users have to be aware of technique-specific ACT target ranges and their confounders, which need to be provided by the manufacturers.

Direct interaction between a membrane domain subunit and a connector subunit in the H(+)-translocating NADH-quinone oxidoreductase

When Paracoccus denitrificans membranes were treated with a crosslinker, m-maleimidobenzoyl-N-hydroxysuccinimide ester (MBS), a cross-linked product of M(r) approximately 31 kDa was found which reacted with antibodies against the hydrophobic subunit Nqo7 and the connector subunit Nqo6. NaI treatment of the Paracoccus membranes before, but not after, the crosslinking step prevented the formation of the 31 kDa band. When Nqo7 and Nqo6 were coexpressed in Escherichia coli, both subunits were located in the membrane fraction. MBS treatment of the E. coli membranes generated the 31 kDa band as in the Paracoccus membranes. These results indicate that Nqo7 interacts with probable N2-binding Nqo6.

NADH dehydrogenases: from basic science to biomedicine

This review article is concerned with two on-going research projects in our laboratory, both of which are related to the study of the NADH dehydrogenase enzyme complexes in the respiratory chain. The goal of the first project is to decipher the structure and mechanism of action of the proton-translocating NADH-quinone oxidoreductase (NDH-1) from two bacteria, Paracoccus denitrificans and Thermus thermophilus HB-8. These microorganisms are of particular interest because of the close resemblance of the former (P. denitrificans) to a mammalian mitochondria, and because of the thermostability of the enzymes of the latter (T. thermophilus). The NDH-1 enzyme complex of these and other bacteria is composed of 13 to 14 unlike subunits and has a relatively simple structure relative to the mitochondrial proton-translocating NADH-quinone oxidoreductase (complex I), which is composed of at least 42 different subunits. Therefore, the bacterial NDH-I is believed to be a useful model for studying the mitochondrial complex I, which is understood to have the most intricate structure of all the membrane-associated enzyme complexes. Recently, the study of the NADH dehydrogenase complex has taken on new urgency as a result of reports that complex I defects are involved in many human mitochondrial diseases. Thus the goal of the second project is to develop possible gene therapies for mitochondrial diseases caused by complex I defects. This project involves attempting to repair complex I defects in the mammalian system using Saccharomyces cerevisiae NDI1 genes, which code for the internal, rotenone-insensitive NADH-quinone oxidoreductase. In this review, we will discuss our progress and the data generated by these two projects to date. In addition, background information and the significance of various approaches employed to pursue these research objectives will be described.

[Acute respiratory distress syndrome in children]

The acute respiratory distress syndrome (ARDS) encountered in a child may be either due to a primary lung infection or may be secondary to a systemic inflammatory response of varying origin. Therapy is based on: 1) the mechanical ventilation strategy aimed at maintaining the functional residual capacity by alveolar recruitment using positive end expiratory pressure and to limit secondary pulmonary lesions by using small tidal volumes, 2) prone positioning as soon as sufficient stability is achieved; 3) optimizing tissue oxygen delivery by cardiac support; 4) correction of any other organ dysfunction. If this conventional approach is not sufficient experimental therapies may be tempted given the vital risk. For instance inhaled nitric oxide and high frequency oscillation ventilation may be a valuable support. Newer techniques, such as partial liquid ventilation, are being developed and could become useful therapeutic options. After the acute phase a close medical follow-up is mandatory. Because of the possibility of a chronic respiratory insufficiency with negative consequences on the right ventricular function, these patients may need long term oxygen therapy and diuretics. Cardiac echography helps orientation in maintaining or discontinuing this long term therapy by estimating the arterial pulmonary pressure.

Exploring the membrane domain of the reduced nicotinamide adenine dinucleotide-quinone oxidoreductase of Paracoccus denitrificans: characterization of the NQO7 subunit

The proton-translocating reduced nicotinamide adenine dinucleotide- (NADH-) quinone oxidoreductase (NDH-1) of Paracoccus denitrificans is composed of at least 14 different subunits (NQO1-14). In addition, this enzyme complex houses one flavin mononucleotide (FMN) and 7-8 iron-sulfur clusters as cofactors. The expression and partial characterization of the NQO7 subunit, one of the seven subunits that constitute the hydrophobic sector of the enzyme complex, have been performed and are reported here. Expression of the NQO7 subunit was achieved by use of the glutathione-S-transferase (GST) fusion system together with Escherichia coli strains BLR(DE3)pLysS and BL21(DE3)pLysS. The GST-fused NQO7 subunit was expressed in the membrane fraction of the host cells and was extracted from the membranes by nonionic detergents (Triton X-100, dodecyl maltoside). The extracted polypeptide was purified by glutathione affinity column chromatography and characterized. The isolated GST-fused NQO7 subunit (but not the GST alone) was determined to interact with phospholipid vesicles and suppress the membrane fluidity. Antibodies against both the N- and C-terminal regions of the deduced primary structure of the NQO7 subunit reacted with a single band (15 kDa) of the Paracoccus membranes. By use of immunochemical and cysteine residue modification techniques, the topology of the Paracoccus NQO7 subunit in the membranes has been examined. The data suggest that the Paracoccus NQO7 subunit contains three transmembrane segments and that its N- and C-terminal regions are directed toward the cytoplasmic and periplasmic phases of the membrane, respectively. The proposed topology of the GST-fused NQO7 subunit expressed in E. coli membranes is consistent with that of the NQO7 subunit in the Paracoccus membranes.

[Subtotal thrombosis of the juxta-ductal thoracic aorta in a premature 36-week-old infant. Alteplase therapy]

The authors report the case of a neonate, a premature 36 weeks gestation male child who presented with a spontaneous thrombosis of the juxtaduetal aorta at 3 days of age. The clinical presentation mimicked that of severe coarctation with cardiocirculatory failure. The diagnosis was ineffective, the introduction of low dose alteplase (plasma activator of human recombinant plasminogen) with continued anticoagulation resulted in near complete lysis of the clot and avoided surgery. Thromboembolic cerebral and renal complications were observed during treatment. However, 6 months after the acute episode, there were no clinical or echographic sequellae. Global renal function remained normal despite mild atrophy of the parenchyma of the left kidney. This combined treatment represents an alternative to high risk surgery. The follow-up of this form of management should be rigorous in view of the potential renal and cerebral complications.

NADH-quinone oxidoreductase: PSST subunit couples electron transfer from iron-sulfur cluster N2 to quinone

The proton-translocating NADH-quinone oxidoreductase (EC 1.6.99.3) is the largest and least understood enzyme complex of the respiratory chain. The mammalian mitochondrial enzyme (also called complex I) contains more than 40 subunits, whereas its structurally simpler bacterial counterpart (NDH-1) in Paracoccus denitrificans and Thermus thermophilus HB-8 consists of 14 subunits. A major unsolved question is the location and mechanism of the terminal electron transfer step from iron-sulfur cluster N2 to quinone. Potent inhibitors acting at this key region are candidate photoaffinity probes to dissect NADH-quinone oxidoreductases. Complex I and NDH-1 are very sensitive to inhibition by a variety of structurally diverse toxicants, including rotenone, piericidin A, bullatacin, and pyridaben. We designed (trifluoromethyl)diazirinyl[3H]pyridaben ([3H]TDP) as our photoaffinity ligand because it combines outstanding inhibitor potency, a suitable photoreactive group, and tritium at high specific activity. Photoaffinity labeling of mitochondrial electron transport particles was specific and saturable. Isolation, protein sequencing, and immunoprecipitation identified the high-affinity specifically labeled 23-kDa subunit as PSST of complex I. Immunoprecipitation of labeled membranes of P. denitrificans and T. thermophilus established photoaffinity labeling of the equivalent bacterial NQO6. Competitive binding and enzyme inhibition studies showed that photoaffinity labeling of the specific high-affinity binding site of PSST is exceptionally sensitive to each of the high-potency inhibitors mentioned above. These findings establish that the homologous PSST of mitochondria and NQO6 of bacteria have a conserved inhibitor-binding site and that this subunit plays a key role in electron transfer by functionally coupling iron-sulfur cluster N2 to quinone.

Localization and mobility of coenzyme Q in lipid bilayers and membranes

We have studied the mobility of coenzyme Q (CoQ) in lipid bilayers and mitochondrial membranes in relation to the control of electron transfer activities. A molecular dynamics computer simulation in the vacuum yielded a folded structure for CoQ10, with a length of only 21 A. Using this information we were able to calculate diffusion coefficients in the range of 10(-6) cm2/s in good agreement with those found experimentally by fluorescence quenching of pyrene derivatives. To investigate if CoQ diffusion may represent the rate-limiting step of electron transfer, we reconstituted complexes I and III and assayed the resulting NADH-cytochrome c reductase activity in presence of different CoQ10 levels and at different distances between complexes; the experimental turnovers were higher than the collision frequencies calculated using diffusion coefficients of 10(-9) cm2/s but compatible with values found by us by fluorescence quenching. Since the experimental turnovers are independent of the distance between complexes, we conclude that CoQ diffusion is not rate-limiting for electron transfer.

A high diffusion coefficient for coenzyme Q10 might be related to a folded structure

We measured the lateral diffusion of different coenzyme Q homologues and analogues in model lipid vesicles using the fluorescence collisional quenching technique with pyrene derivatives and found diffusion coefficients in the range of 10(-6) cm2/s. Theoretical diffusion coefficients for these highly hydrophobic components were calculated according to the free volume theory. An important parameter in the free volume theory is the relative dimension between diffusant and solvent: a molecular dynamics computer simulation of the coenzymes yielded their most probable geometries and volumes and revealed surprisingly similar sizes of the short and long homologues, due to a folded structure of the isoprenoid chain in the latter, with a length for coenzyme Q10 of 21 A. Using this information we were able to calculate diffusion coefficients in the range of 10(-6) cm2/s, in good agreement with those found experimentally.

Saturation kinetics of coenzyme Q in NADH oxidation: rate enhancement by incorporation of excess quinone

In beef heart mitochondria it has been found that the Km for coenzyme Q10 of the NADH oxidation system is in the range of the membrane concentration of the quinone; this is contrary to succinate oxidation which is in Vmax with respect to quinone content. The same proportional difference between the two systems is maintained in their affinities for the exogenous acceptor CoQ1 in non-extracted mitochondria. The Km of succinate- coenzyme Q reductase for CoQ1 is reversibly lowered in CoQ-depleted mitochondria; while in contrast the Km for NADH-coenzyme Q reductase is reversibly increased by CoQ extraction. Incorporation of exogenous quinones by co-sonication with submitochondrial particles, as evidenced by fluorescence quenching of pyrene, enhances NADH-cytochrome c reductase activity in accordance with the lack of saturation of the former system.

The role of DT-diaphorase in the maintenance of the reduced antioxidant form of coenzyme Q in membrane systems

The experiments reported here were designed to test the hypothesis that the two-electron quinone reductase DT-diaphorase [NAD(P)H:(quinone-acceptor) oxidoreductase, EC 1.6.99.2] functions to maintain membrane-bound coenzyme Q (CoQ) in its reduced antioxidant state, thereby providing protection from free radical damage. DT-diaphorase was isolated and purified from rat liver cytosol, and its ability to reduce several CoQ homologs incorporated into large unilamellar vesicles was demonstrated. Addition of NADH and DT-diaphorase to either large unilamellar or multilamellar vesicles containing homologs of CoQ, including CoQ9 and CoQ10, resulted in the essentially complete reduction of the CoQ. The ability of DT-diaphorase to maintain the reduced state of CoQ and protect membrane components from free radical damage as lipid peroxidation was tested by incorporating either reduced CoQ9 or CoQ10 and the lipophylic azoinitiator 2,2'-azobis(2,4-dimethylvaleronitrile) into multilamellar vesicles in the presence of NADH and DT-diaphorase. The presence of DT-diaphorase prevented the oxidation of reduced CoQ and inhibited lipid peroxidation. The interaction between DT-diaphorase and CoQ was also demonstrated in an isolated rat liver hepatocyte system. Incubation with adriamycin resulted in mitochondrial membrane damage as measured by membrane potential and the release of hydrogen peroxide. Incorporation of CoQ10 provided protection from adriamycin-induced mitochondrial membrane damage. The incorporation of dicoumarol, a potent inhibitor of DT-diaphorase, interfered with the protection provided by CoQ. The results of these experiments provide support for the hypothesis that DT-diaphorase functions as an antioxidant in both artificial membrane and natural membrane systems by acting as a two-electron CoQ reductase that forms and maintains the antioxidant form of CoQ. The suggestion is offered that DT-diaphorase was selected during evolution to perform this role and that its conversion of xenobiotics and other synthetic molecules is secondary and coincidental.

Steady-state kinetics of the reduction of coenzyme Q analogs by complex I (NADH:ubiquinone oxidoreductase) in bovine heart mitochondria and submitochondrial particles

The reduction kinetics of coenzyme Q (CoQ, ubiquinone) by NADH:ubiquinone oxidoreductase (complex I, EC 1.6.99.3) was investigated in bovine heart mitochondrial membranes using water-soluble homologs and analogs of the endogenous ubiquinone acceptor CoQ10 [the lower homologs from CoQ0 to CoQ3, the 6-pentyl (PB) and 6-decyl (DB) analogs, and duroquinone]. By far the best substrates in bovine heart submitochondrial particles are CoQ1 and PB. The kinetics of NADH-CoQ reductase was investigated in detail using CoQ1 and PB as acceptors. The kinetic pattern follows a ping-pong mechanism; the Km for CoQ1 is in the range of 20 microM but is reversibly increased to 60 microM by extraction of the endogenous CoQ10. The increased Km in CoQ10-depleted membranes indicates that endogenous ubiquinone not only does not exert significant product inhibition but rather is required for the appropriate structure of the acceptor site. The much lower Vmax with CoQ2 but not with DB as acceptor, associated with an almost identical Km, suggests that the sites for endogenous ubiquinone bind 6-isoprenyl- and 6-alkylubiquinones with similar affinity, but the mode of electron transfer is less efficient with CoQ2. The Kmin (kcat/Km) for CoQ1 is 4 orders of magnitude lower than the bimolecular collisional constant calculated from fluorescence quenching of membrane probes; moreover, the activation energy calculated from Arrhenius plots of kmin is much higher than that of the collisional quenching constants. These observations strongly suggest that the interaction of the exogenous quinones with the enzyme is not diffusion-controlled. Contrary to other systems, in bovine submitochondrial particles, CoQ1 usually appears to be able to support a rate approaching that of endogenous CoQ10, as shown by application of the "pool equation" [Kröger, A., & Klingenberg, M. (1973) Eur. J. Biochem. 39, 313-323] relating the rate of ubiquinone reduction to the rate of ubiquinol oxidation and the overall rate through the ubiquinone pool.

Characterization of 9-aminoacridine interaction with chromatophore membranes and modelling of the probe response to artificially induced transmembrane delta pH values

We analyze the adsorption of the fluorescent monoamine 9-aminoacridine to the membrane phase of photosynthetic chromatophores, in the physiological interval of pH values ranging from 5.5 to 8.5 and at ionic strengths of 0.005 and 0.150 M. The interaction of the probe with the membrane phase is described with S-shaped isotherms of the Hill type and is modulated by electrostatic effects as modelled with the Gouy-Chapman-Boltzman theory. This description is consistent with different values of the surface change density of the chromatophore membranes decreasing from about 1.3 x 10(-3) to about 0.5 x 10(-3) e-/A2, on changing the pH from 8.5/7.5 to 6.5/5.5, respectively. Furthermore we show that, when the free concentrations of the probe in the inner and outer vesicle compartments are computed from the adsorbing isotherms at the proper pH values, the model considering the equilibrium distribution of the neutral monoamine following the onset of a delta pH is sufficient to describe the dependence of the artificially induced transmembrane delta pH values on the observed quenching of the probe fluorescence.