Lactobacillus acidophilus versus placebo in the symptomatic treatment of irritable bowel syndrome: the LAPIBSS randomized trial

Irritable bowel syndrome is a chronic functional gastrointestinal disorder characterized by abdominal pain/discomfort and altered bowel habits. The use of Lactobacilli as probiotics during irritable bowel syndrome is based on their interesting mechanisms of action and their excellent safety profile but little is known about their clinical efficacy due to the lack of adequately designed clinical trials. The current clinical trial protocol aims to determine the effects of a mixture of Lactobacillus acidophilus NCFM and LAFTI L10 as probiotics to improve irritable bowel syndrome symptoms (LAPIBSS). Eighty patients with a positive diagnosis of irritable bowel syndrome according to Rome III criteria were recruited to a multicentre, double-blinded, in parallel groups, placebo-controlled randomized trial. Patients were provided with a daily dose of two capsules with two strains of Lactobacilli (5x109cfu/capsule) or placebo for 8 weeks on a 1:1 ratio. The primary outcome is to obtain scores of abdominal pain/discomfort assessed with a 100-mm visual analogue scale. The secondary outcome is to obtain scores of bloating, flatus and rumbling tested with a 100-mm visual analogue scale, composite score, stool frequency and stool consistency/appearance assessed with the Bristol Stool Form scale. According to the hypothesis that abdominal pain is mainly the result of a visceral hypersensitivity, the current study protocol aims to provide high quality proof of concept data to elucidate the efficacy of a consumption of a mixture of Lactobacillus acidophilus probiotic strains after 8 weeks, for decreasing abdominal pain. Ethical approval was given by ethics committee French Consultative Committee for the Protection of Individuals in Biomedical Research of the South West (Number CPP08-014a) and ANSM (French National Agency for Medicines and Health Products Safety - Number B80623-40). The findings from LAPBISS will be disseminated through peer-reviewed publications and at scientific conferences.

TRIAL REGISTRATION

EudraCT N°2008-A00844-51.

Short communication: Ischemia increases cortical Na⁺,K⁺-ATPase activity (K-Pase) in a model of kidney auto-transplantation in the large white pig

Acute renal failure (ARF) induced by Ischemia-Reperfusion (I-R) is associated with a significant impairment of tubular sodium reabsorption. Na⁺,K⁺-ATPase has a crucial role in tubular sodium reabsorption and maintenance of water and ion homeostasis. In this study, we examined whether renal I-R affects Na⁺,K⁺-ATPase activity in a renal auto graft model (Large White Pig) with controlateral nephrectomy. Kidney samples were obtained from medulla (n = 4) and cortex (n = 3) after one hour of warm ischemia in autotransplanted models. These experimental groups were compared with a controlateral nephrectomy group (Control). Na⁺,K⁺-ATPase activity in purified membrane fractions was measured as ouabain-sensitive K⁺ -stimulated paranitrophenyl phosphatase (pNPPase) activity. The Na⁺,K⁺-ATPase activities of control, ischemia and ischemia -reperfusion were significantly higher in the medulla than in the cortex, irrespective of the experimental group (P<0.05). In cortices, Na⁺,K⁺-ATPase activity increased significantly (P<0.05) by 35% after ischemia compared to control group. In medullae, there was only a trend toward an activation of Na⁺,K⁺-ATPase activity after Ischemia (increased by 25%) and after Ischemia-Reperfusion (increased by 30%) compared to control group, and these differences did not reach statistical significance. These data suggest that renal ischemia induces a significant alteration of Na⁺,K⁺-ATPase by increasing its ouabain-sensitive K⁺-stimulated paranitrophenyl phosphatase (pNPPase) activity in isolated membrane from cortical renal tissues after one hour of ischemia. This change of activity seems to be a new regulation mechanism of an important membrane ion transporter during renal I-R in the large pig model of renal transplantation.

Docosahexaenoic acid (DHA) injection in spinal cord transection stimulates Na⁺,K⁺-ATPase in skeletal muscle via β 1 subunit

Spinal cord injuries (SCI) induce a loss of skeletal muscle mass and functional capacity. The muscle excitability and contractility depend on the plasma membrane potential, regulated by transmembrane ion gradients, and thus necessarily on the Na⁺,K⁺-ATPase activity. The aim of this work was to evaluate the consequences of a spinal cord transection (SCT) on the skeletal muscle Na⁺,K⁺-ATPase and the impact of collateral GlyceroPhosphoLipids enriched in DocosaHexaenoic Acid (GPL-DHA) administration. The Na⁺,K⁺-ATPase activity and membrane expression of Na⁺,K⁺-ATPase α1, α2 and β1 isoforms were assessed by K⁺-stimulated paranitrophenyl phosphatase (pNPPase) measurements and Western Blotting, respectively. The results show that spinal cord transection increased significantly (p<0.05) Na⁺,K⁺-ATPase activity in muscle by 25% and decreased the amounts of α1 isoform and α2 isoform expressions by 50% (p<0.05) respectively compared to controls. The results also show that early injection of GPL-DHA after SCT decreases in membrane skeletal muscle the α1 and α2 isoforms expression but increases the membrane Na⁺,K⁺-ATPase activity. This treament partially restores the membrane expression of the β1 subunit of the Na⁺,K⁺-ATPase. These data suggest that the increase of β1 subunit expression is probably the main trigger to the membrane Na⁺,K⁺-ATPase activation following a trans-synaptic denervation.

Vitamin D metabolism, functions and needs: from science to health claims

BACKGROUND

Vitamin D is a nutrient long considered as essential for skeletal health but is now attracting interest from medical and nutritional communities as knowledge emerges of its biological function and its association with decreased risk of many chronic diseases.

RESULTS

A question emerges: How much more vitamin D do we need for these new functions of vitamin D? This review discusses vitamin D physiology and hypovitaminosis D and presents two vitamin D dietary policies: that according to regulatory authorities and that of nutrition scientists. Scientific evidence suggests that 25(OH)D serum levels should be over 75 nmol/L; otherwise, there is no beneficial effect of vitamin D on long-latency diseases. Current regulatory authority recommendations are insufficient to reach this level of adequacy. Observational and some prospective data show that vitamin D has a role in the prevention of cancer as well as immunity, diabetes and cardiovascular and muscle disorders, which supports the actions of 1α,25(OH)2D at cellular and molecular levels. The recent assessments done by the European Food Safety Authority should lead to new health claims.

CONCLUSIONS

Vitamin D, through food fortification and supplementation, is a promising new health strategy and thus provides opportunities for food industry and nutrition researchers to work together towards determining how to achieve this potential health benefit.

ω6/ω3 Polyunsaturated fatty acid supplementations in renal cell model lead to a particular regulation through lipidome for preserved ω6/ω3 ratios

Polyunsaturated fatty acids (PUFA) supplementations modify cell lipid composition leading to a change in cell function. However, the effect of PUFA supplementations in renal model cell on the kidney epithelial cells membrane fatty acid profile is not known. Therefore, the purpose of this study was to determine the effects of PUFAs with different ω6/ω3 ratios supplementations in the kidney epithelial cells and the type of supplementation that can be used as cellular protection during kidney transplantation. For that, we used as model the LLCPK1 cell and determined their membrane fatty acid (FA) composition after supplementation with three different commercial food supplements. These supplements consist of S1: docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) with ω6/ω3 ratio = 0.1, S2: DHA, EPA, linoleic acid (LA) and γ-linoleic acid (GLA) with ω6/ω3 ratio = 2.5, or S3: α-linolenic acid (ALA) and LA with ω6/ω3 ratio near 1. Cells were incubated for 24 hr with 30 μM of ω3 fatty acids from each supplement. Fatty acid composition of control and experimental groups was analysed by gas chromatography after extraction of lipids and fatty acids methylation. The efficiency of cell PUFA supplementation was achieved by showing 2 to 4 fold increases in cell PUFA incorporation. Whatever the supplementation used, the cell saturated fatty acids (SFA) were decreased by 50% following the three supplementations used (p<0.001) as compared to control group. These decreases in SFA were compensated in part by increasing monounsaturated fatty acid levels. All these changes were observed with constant of cell ω6/ω3 ratio whatever the supplementations used. These data suggest that the supplements, with long chain polyunsaturated fatty acids or their precursors, lead to important regulation in the lipidome (desaturases and elongases) associated to preserved ω6/ω3 ratios. The fatty acids remodeling may represent an interesting new mechanism by which renal FA homoestasis could occurred.

Opinion paper food supplements: the European regulation and its application in France. Thoughts on safety of food supplements

The first definition of food supplements in France was established by decree 96-307 of April 10th 1996. In 2002, the European Community adopted a regulation for food supplements (European Directive 2002/46/CE June 10th). This was an important event in the regulation of food supplements. The European regulation was adopted in France, with some modifications, by decree 2006-352 of March 20th 2006. The European Regulation on food supplements is more defined than those for any other food types and is exemplary. The Regulation on addition of vitamins and minerals to food differs from the regulation on the addition of other substances such as amino acids, essential fatty acids, fibers, carbohydrates, various plant, and herbal extracts. While the Regulation includes vitamins and minerals to the positive list of supplements, other substances are included in the negative list of supplements. According to the Regulation, substances added to food supplements must have a nutritional or physiological effect. The increased use of food supplements led to the creation of a department specialized in the safety of food supplement. The safety of food supplements is a permanent concern for sanitary authorities. These authorities have recently combined scientific methodological approaches and a collective expertise to implement and monitor simple and useful rules that insure consumer's safety. Safety laws aim to protect the consumers of food supplements.

Relation between α-isoform and phosphatase activity of Na+,K+-ATPase in rat skeletal muscle fiber types

In skeletal muscle the relationship between Na+,K+-ATPase activity and isoform content remains controversial (9,6). It could be due to the fiber-type content, membrane isolation and analytical methods. We investigated the distribution of subunit α1 and α2 Na+,K+-ATPase catalytic isoforms and the Na+,K+-ATPase activity in isolated membranes from white ( type I and glycolitic fibers) and red (type II and oxidative fibers) skeletal muscles. Red Gastrocnemius and White Gastrocnemius muscles were sampled from 8 week-old female Wistar rats and crude membranes were performed. The Na+,K+-ATPase activity and membrane distribution of Na+,K+-ATPase α1 and α2 isoforms were assessed by ouabain sensitive K-phosphatase (Kpase) measurements and Western Blot respectively. The Na+,K+-ATPase activity was 6 fold lower in White Gastrocnemius membranes than in Red Gastrocnemius membranes. The α1 and α2-isoform levels are higher in RG than in White Gastrocnemius. The α1 and α2-subunit Red Gastrocnemius content was significantly higher than in WG. The correlation between crude membrane Kpase activity and both catalytic α-subunit of the Na+,K+-ATPase exist.These data suggest that the Na+,K+-ATPase phosphatase activity correlates with the α1 and α2 isoforms levels in Red Gastrocnemius and White Gastrocnemius and confirms the fiber-specific Na+,K+-ATPase catalytic α-subunits and α2-isoform as the major catalytic isoform in rat skeletal muscle.

7-ketocholesterol inhibits Na,K-ATPase activity by decreasing expression of its α1-subunit and membrane fluidity in human endothelial cells

As cholesterol, oxysterols, can insert the cell membrane and thereby modify the functions of membrane-bound proteins. The Na,K-ATPase is very sensitive to its lipid environment, seems to be involved in important endothelial functions as the regulation of nitric oxide (NO) release. The effects of 7-ketocholesterol , an oxysterol present in oxidized LDL, was investigated on Na,K-ATPase in isolated human endothelial cells. Cells were incubated 24h with lecithin-, cholesterol- or 7-ketocholesterol liposomes (6 μg/ml). K+-stimulated paranitrophenyl phosphatase activity, reflecting Na,K-ATPase activity, was evaluated as well as cell viability and lipoperoxidation. The expression of Na,K-ATPase subunits mRNAs and membrane fluidity were also investigated. As Na,K-ATPase and nitric oxide seem to be related, we determined the production of NO and the expression of endothelial NO synthase mRNAs. Na,K-ATPase activity was strongly decreased by 7-ketocholesterol. This decrease, not related to lipoperoxidation, was correlated with a decreased expression of the Na,K-ATPase α1-subunit messengers and with rigidity of plasma membranes. Cholesterol induced similar effects but was less potent than 7-ketocholesterol. Basal NO production and expression of endothelial NO synthase mRNAs were not modified by 7-ketocholesterol. Our new findings demonstrate that 7-ketocholesterol, used at non toxic doses, was very potent to disrupt the transport of ions by Na,K-ATPase and perturb membrane structure. These data demonstrate that 7-ketocholesterol induces endothelial dysfunction without cell death that may contribute to early events in atherosclerosis.

Effect of a novel Omegacoeur®/Doluperine® nutritional combination on human embryonic kidney cell viability

Holistica Laboratories (Eguilles, France) developed the nutritional supplements Omegacoeur® and Doluperine® based on two of the most ancient and unique dietary health traditions. Omegacoeur® is formulated to supply key active components of Mediterranean diet (omega 3,6,9 fatty acids, garlic, and basil) and the formulation of Doluperine® was based on the Ayurvedic tradition (curcuma, pepper, ginger extracts). Interestingly, recent studies suggest that an combination of the ingredients supplied by these two supplements could provide additional and previously unanticipated benefit through synergistic actions of some of their key components. However, the effect of such combination on human cell viability has not been investigated. In this present article, a review of the various effects of the individual compounds of the new combination and the reported active doses, and the result of a study of an combination of Omegacoeur® / Dolupérine® on Human Embryonic Kidney (HEK 293) cells. Incremental doses of 4 Omegacoeur® / Dolupérine® combinations prepared so that the molar ratio DHA (Docosahexaenoic acid) in Omegacoeur® / curcumin in Dolupérine® was kept constant, at 2.5 DHA / 1 curcumin, were added to the culture media. After 24h of incubation, cell viability was assessed by the trypan blue exclusion method. The data suggest that the combination of Omegacoeur® with Dolupérine® does not affect HEK 293 cells viability in the range of doses that have demonstrated beneficial effects in earlier studies.

The Na, K-ATPase alpha3-isoform specifically localizes in the Schmidt-Lanterman incisures of human nerve

INTRODUCTION

To our knowledge, there is little reference in literature with regards to alpha3-isoform of Na+,K+-ATPase in human peripheral nerves. The aim of this study was to determine the expression of the neuronal alpha3-isoform of Na+,K+-ATPase in human sural nerves from patients with a permanent medullary central nervous system injury.

MATERIALS AND METHODS

We studied the immunolocalization of alpha3-isoform of Na+,K+-ATPase using a polyclonal antibody against the amino sequence near the phosphorylation site of the alpha3-isoforms of Na+,K+-ATPase using immunohistochemistry and confocal laser scanning microscopy. An antibody specific for alpha2-isoform of Na+,K+-ATPase was used to label the Schwann cells.

RESULTS

Morphometric analysis of longitudinal section of human sural nerves showed that the alpha3-isoform of Na+,K+-ATPase was distributed along the length of axolemma. The myelin sheath of the Schwann cells showed clearly a distribution of alpha3- but not alpha2-isoforms of Na+,K+-ATPase at the level of Schmidt-Lanterman incisures.

CONCLUSION

The human sural nerve shows a specific localization of the Na+,K+-ATPase alpha3-isoform in the Schmidt-Lanterman incisures of Schwann cells in addition to its localization in axonal membranes.

A high calorie diet induces type 2 diabetes in the desert sand rat (Psammomys obesus)

Diabetes mellitus type 2 is a major factor for cardiovascular diseases. The toxic effects of chronic hyperglycemia involve many alterations in the vascular tissue, including atherosclerosis. The pathogenesis of atherosclerosis in the diabetic syndrome (DS-II) has not been fully elucidated. A better understanding of the progress of DS-II at the level of the aorta could help us to identify inhibitors of atherosclerosis. Studies have shown that obesity and high calorie diet (HCD) are associated with the development of DS-II, however the lack of naturally occurring experimental models of DS-II have impaired to directly address these issues. We hypothesize that a HCD induces DS-II. This study (15 months duration) is designed to determine if HCD induces DS-II in the desert sand rat (Psammomys obesus; P. obesus). We also evaluated the histopathology of the aorta in animals fed with a laboratory chow pellets ad libitum (hypercaloric) and in control (animals fed with the naturally occurring hypocaloric diet; halophile plants). The weight and blood chemistry (glucose, lipids, and insulin levels) were evaluated periodically (once per week), and the histology of the aortas of these animals were assessed every 3 months for up to 12 months, during the development of DS-II. This study demonstrates that 40% of the animals in HCD develop DS-II at 3 months. Histological characterization demonstrates the typical alterations observed in atherosclerosis, i.e., alteration of the elastic fibers of the media layer and enrichment in collagen and glucosaminoglycans. This study demonstrates that P. obesus is an excellent animal model to study the progression of DS-II and the development of atherosclerosis.

Anti-arrhythmic effects of I (Na), I (Kr), and combined I (Kr)-I (CaL) blockade in an experimental model of acute stretch-related atrial fibrillation

INTRODUCTION

Atrial dilatation is commonly associated with atrial fibrillation (AF), but the electrophysiological mechanisms and the implications for anti-arrhythmic therapy are poorly understood. In a model of acute stretch-related AF in isolated rabbit hearts, we evaluated the electrophysiological effects of three different anti-arrhythmic drugs: dofetilide, flecainide and BRL-32872 (associating I (Kr) and I (CaL) blocking properties).

METHODS

After 30 min of sustained stretch-related AF, we perfused BRL 10-7 M, BRL 3.10-7 M, BRL 10-6 M, flecainide 2.4 10-6 M and dofetilide 10-7 M and iteratively measured atrial effective refractory periods (ERPs), AF inducibility and AF cycle length (AFCL) 15, 30 and 60 min after drug perfusion, respectively.

RESULTS

After a significant shortening of the ERPs by acute atrial stretch in the five groups individually (p < 0.001, stretch vs baseline for each group individually), drug perfusion led to a strong lengthening of AFCL, a very significant prolongation of ERPs (p < 0.001 vs stretch) and a reduction of AF inducibility (p < 0.01 vs control group) for each of the five experimental groups. The relative ERP increase was comparable in all groups, whereas a significantly lower AF inducibility was observed in the BRL 10-6 M group (p < 0.05 vs other BRL concentrations).

CONCLUSION

In a model of acute stretch-related AF, dofetilide, flecainide and BRL-32872 terminated AF and prevented its immediate reinduction after having comparatively prolonged AFCL and ERPs. These comparative results suggest that those drugs are equally efficacious, albeit with different mechanisms, in the setting of acute atrial stretch.

Protective effect of a low K+ cardioplegic solution on myocardial Na,K-ATPase activity

Long duration ischemia in hypothermic conditions followed by reperfusion alters membrane transport function and in particular Na,K-ATPase. We compared the protective effect of two well-described cardioplegic solutions on cardiac Na,K-ATPase activity during reperfusion after hypothermic ischemia. Isolated perfused rat hearts (n = 10) were arrested with CRMBM or UW cardioplegic solutions and submitted to 12 hr of ischemia at 4 degrees C in the same solution followed by 60 min of reperfusion. Functional recovery and Na,K-ATPase activity were measured at the end of reperfusion and compared with control hearts and hearts submitted to severe ischemia (30 min at 37 degrees C) followed by reflow. Na,K-ATPase activity was not altered after 12 hr of ischemia and 1 hr reflow when the CRMBM solution was used for preservation (55 +/- 2 micromolPi/mg prot/hr) compared to control (53 +/- 2 micromol Pi/mg prot/hr) while it was significantly altered with UW solution (44 +/- 2 micromol Pi/mg prot/hr, p < 0.05 vs control and CRMBM). Better preservation of Na,K-ATPase activity with the CRMBM solution was associated with higher functional recovery compared to UW as represented by the recovery of RPP, 52 +/- 12% vs 8 +/- 5%, p < 0.05 and coronary flow (70 +/- 2% vs 50 +/- 8%, p < 0.05). The enhanced protection provided by CRMBM compared to UW may be related to its lower K+ content.

Protective effect of cicletanine on renal function in diabetic spontaneously hypertensive rats

Hypertension and diabetes are commonly associated and strongly predispose to renal injuries. In general, antihypertensive therapies protect from these damages, but the effect of cicletanine, a new type of antihypertensive drug, is unknown. This study examines the effects of cicletanine on renal failure in spontaneously hypertensive rats with diabetes (SHRD). Diabetes mellitus was induced with streptozotocin in uninephrectomized SHR. Rats received the vehicle, 10 mg or 50 mg/kg per day of cicletanine for 6 weeks. Age-matched untreated Wistar-Kyoto rats were used as controls. Systolic blood pressure (SBP), microalbuminuria and proteinuria were assessed throughout the treatment. At the end of the study, creatinine clearance measurements and histological analysis of kidneys were performed. Cicletanine did not affect SBP but decreased the elevated albuminuria of diabetic SHR in a dose-dependent manner. Similar results were obtained for proteinuria. Treatment with the high dose of cicletanine also normalized the altered creatinine clearance of diabetic SHR. These results indicate that cicletanine has a renal-protective action, probably blood pressure-independent, in a model combining hypertension and diabetes. The mechanism of renal-protection of cicletanine is not clearly established but may be due to the stimulation of arterial prostacyclin synthesis and/or to the reduction of intraglomerular capillary pressure.

Peripheral diabetic neuropathy and polyunsaturated fatty acid supplementations: natural sources or biotechnological needs?

The two essential fatty acids linoleic and alpha-linolenic acids, precursors of the n-6 and n-3 PUFA family, respectively, are known to play a strong regulatory function on cells via their incorporation into membrane phospholipids, and also on microcirculation by the production of eicosanoids. Moreover, diabetes mellitus induces impairment in PUFA metabolism due to an inhibition of desaturases, the enzymes involved in their synthesis. The decrease in PUFA bioavailability will conduct to marked alterations in membranes as well as impairment of the microcirculation. Those metabolic perturbations are involved in part in the degenerative complications of diabetes such as neuropathy. Nutritional supplementations with PUFA have given very interesting results in experimental diabetic neuropathy but also in human diabetic neuropathy. The gamma linolenic and arachidonic acids, members of the n-6 family, prevent the physiological abnormalities associated to neuropathy. The results obtained with the n-3 family PUFA are more discordant, probably because of the simultaneous use of eicosapentaenoic and docosahexaenoic acids. Nevertheless, the use of docosahexaenoic acid-enriched phospholipids produced positive results in the treatment of experimental diabetic neuropathy. These PUFA are available from natural sources but a biotechnological demand exists to provide these PUFA in different structural forms.

Dose dependent accretion of docosahexaenoic acid (DHA) in cardiac membranes of rats fed egg yolk powder enriched in DHA

We tested the hypothesis that enrichment of the diet with docosahexaenoic acid (DHA) enriched egg yolk powder could modify specifically the (n-3) fatty acids content of rat plasma, red blood cells and heart membranes. Dose-dependent effect of DHA was studied in rats supplemented during 4 weeks. Three groups of adult male rats, DHA10, DHA35 and DHA60 (n = 5 each), had their diet supplemented with 10 mg, 35 mg or 60 mg DHA/kg body weight/day, respectively. Fatty acid composition of membranes and plasma lipids were determined. A significant dose-dependent increase in DHA was observed in all three types of samples. Arachidonic acid (AA) levels did not change in heart and red blood cell membranes whereas it increased significantly in plasma with the DHA35 diet. These results contrast with that previously reported for fish oil supplementation where a decrease in AA levels was reported. Hence, DHA enriched egg yolk supplementation leads to a specific accretion of DHA without competition on AA status.

RT-PCR detection of Na,K-ATPase subunit isoforms in human umbilical vein endothelial cells (HUVEC): evidence for the presence of alpha1 and beta3

The endothelial Na,K-ATPase is an active component in maintaining a variety of normal vascular functions. The enzyme is characterized by a complex molecular heterogeneity that results from differential expression and association of multiple isoforms of both its alpha- and beta-subunits. The aim of the present study was to determine which isoforms of the Na,K-ATPase are expressed in human endothelial cells. HUVEC (human umbilical vein endothelial cells) were used as a model of well known human endothelial cells. The high sensitive method RT-PCR was used with primers specific for the various isoforms of the alpha- and beta-subunits of the Na,K-ATPase. The results show that HUVEC express alpha1-, but not alpha2-, alpha3- or alpha4-isoforms of the catalytic subunit and that beta3- but not beta2- or beta1-isoforms is present in these cells. These findings are in contradiction with our previous detection of Na,K-ATPase isoforms in HUVEC using antibodies (14). Such results raise the technical problem of the specificity of the available antibodies directed against the different isoforms as well as the question of the physiological relevance of the diversity of the Na,K-ATPase isoforms.

RT-PCR detection of the Na,K-ATPase beta3-isoform in human heart

The Na,K-ATPase is a heterodimer composed of an alpha-catalytic and a beta-glycoprotein subunit. At present, three different alpha-polypeptides (alpha1, alpha2, alpha3) and two distinct beta-isoforms (beta1 and beta2) have been detected in human heart. The aim of the present study was to determine whether or not the beta3-isoform of the Na,K-ATPase can be detected in human heart. Using the highly sensitive method of RT-PCR, we here show that human heart expresses the beta3-isoform of the Na,K-ATPase. Given the differences in pharmacological properties of the nine different Na,K-ATPase isoenzymes (containing all combinations of the subunit isoforms), the study of beta3-isoform regulation in human heart may be of interest in understanding the altered response of human myocardium to digitalis therapy during heart failure.

Altered erythrocyte n-3 fatty acids in Mediterranean patients with coronary artery disease

A low frequency of ischaemic heart diseases in Eskimos has been related to polyunsaturated fatty acids. We therefore studied fatty acid patterns associated with coronary artery disease (CAD) for a possible relationship between fatty acid profile and CAD diagnosis in Mediterranean patients. The gas chromatography method was used to analyze the membranes of patients' erythrocytes. The patients without coronary stenosis were used as controls. Patients with CAD showed increased percentages of saturated fatty acids (35.8 vs. 34.2%, P<0.001) and monounsaturated fatty acids (14.6 vs. 13.6%, P<0.01), as well as reduced percentages of polyunsaturated fatty acids (38.5 vs. 41.3%, P<0.001). The decrease in polyunsaturated fatty acids percentages was due to the series of n-3 fatty acids (9.2 vs. 11.4%, P<0.001), mainly at the expense of docosahexaenoic acid [C22:6 (n-3)] (4.9+/-0.25% vs. 6.4+/-0.23%, P<0.001) and docosapentaenoic acid [C22:5 (n-3)] (3.0+/-0.19% vs. 3.9+/-0.12%, P<0.001). The study shows altered n-3 fatty acids in Mediterranean patients with CAD. Our data suggest that the percentage of docosahexaenoic and docosapentaenoic acids in erythrocytes could be used as indicators of an independent risk factor for coronary artery disease.

Omegacoeur, a Mediterranean nutritional complement, stimulates Na,K-ATPase activity in human endothelial cells

Fatty acids are known as modulators of the vasoactive properties of the vessel wall and can influence the physical and functional properties of cell membrane. The membrane-bound enzyme Na,K-ATPase plays a central role in endothelial function such as vasoconstriction. In a previous study, we have shown that omega3 fatty acids inhibited Na,K-ATPase activity in human endothelial cells. As Mediterranean diet is known to protect from cardiovascular diseases, we have investigated the effects of Omegacoeur, a Mediterranean nutritional complement consisting of omega3, omega6, omega9 fatty acids, garlic and basil, on Na,K-ATPase activity in human endothelial cells (HUVECs). Cells were incubated for 18 hr with pure lecithin liposomes or Omegacoeur-enriched emulsions (4 mg lecithin/ml). Na,K-ATPase and 5'-nucleotidase activities were determined using coupled assay methods on microsomal fractions obtained from HUVECs. Cell fatty acid composition was evaluated by gas chromatography after extraction of lipids and fatty acids methylation. The results showed that Omegacoeur (0.1 mM) increased Na,K-ATPase activity by 40% without changes in 5'-nucleotidase activity. Cells incubated with Omegacoeur preferentially incorporated linoleic acid. Therefore, linoleic acid or others constituents of Omegacoeur could be responsible of the stimulation of the Na,K-ATPase activity that might be related to changes in endothelial membrane fluidity.

Effects of digoxin on chemoreflex in patients with chronic heart failure

The effects of digitalis on the baroreflexes in human chronic heart failure have been well studied. Similarly, since it has been recently shown that chemoregulation remains generally effective during cardiac failure, the goal of this study was to evaluate the effects of a chronic administration of digoxin on the chemoreflexes. Hemodynamic and blood gas parameters were assessed in 7 patients with chronic congestive heart failure before and after chronic administration for 10 days of digoxin therapy (0.25 mg daily). In both situations measurements were performed 1/ in baseline conditions at room air and, 2/ after inhalation of pure O2 for 30 min, in order to inhibit the activation of the chemoreflexes. At room air, acute O2 inhalation resulted in a significant decrease in heart rate and cardiac output. After digoxin therapy, comparatively to pre-treatment values, cardiac output, stroke volume and PaO2 were significantly higher while heart rate, systemic resistance and pulmonary wedge pressure were lower. Furthermore, acute O2 inhalation did not modify heart rate or any hemodynamic variables. These results suggest that after digoxin therapy chemoreflex was no more activated in these patients. This effect may be related to the sympatho-inhibitory and to the positive inotropic effects of digoxin: improving hemodynamic and blood gas parameters may result in the inactivation of the reflex.

[Tolerance and efficacy of carvedilol prescription in patients with mild to moderated chronic heart failure]

The current treatment for heart failure, i.e., carvedilol administration, has brought about a significant reduction in cardiovascular morbidity and mortality. The European Cardiology Association task-force has recently recalled that the treatment for heart failure should be considered differently according to the regions within Europe. However, most studies have involved North American or Australasian subjects. The results of these studies have shown that carvedilol improves the symptomatic status of patients with mild to moderate chronic heart failure, but their extrapolation to the situation in Europe is questionable. In the present study, the authors have reported on the use of this beta-blocker over a 6-month period in 48 European subjects (an older patient population, and more frequently given digitalis treatment) with mild to moderate stage II and III chronic heart failure (mean NYHA functional stage = 2.75 +/- 0.2; mean left ventricular ejection fraction = 32.4 +/- 3.4). Six patients (12.5%) were obliged to withdraw from the study due to adverse reactions to carvedilol, i.e., 2 subjects during the test-dose (4.2%) and 4 others who were subsequently unable to withstand the progressive stepping up of drug dosage (8.3%). In the remaining 42 patients, the mean NYHA scores dropped significantly from 2.75 +/- 0.2 to 1.8 +/- 0.1 (p < 0.05) at the end of the study period, indicating an increase in symptomatic improvement with a favorable hemodynamic tolerance profile, even in cases of combined therapy with digitalis. This study confirms the positive action of carvedilol on functional symptomatology in southern European patients presenting with mild to moderate chronic heart failure. However, it should be emphasized that this beta-blocker should only be administered under strict and specialized medical surveillance as its effect of significantly slowing down the heart rate could also result in cardiac insufficiency.

Specific up-regulation of mitochondrial F0F1-ATPase activity after short episodes of atrial fibrillation in sheep

INTRODUCTION

Ventricular fibrillation induced by either digitalis intoxication or electrical stimulation is reported to alter myocardial energy by impairing the sarcolemmal Na,K-ATPase or the receptor for digitalis and the mitochondrial ATPase synthase or F0F1-ATPase. However, little is known about these membrane functions during atrial fibrillation (AF).

METHODS AND RESULTS

We analyzed the effects of electrically induced AF on biochemical activities of atrial F0F1-ATPase and Na,K-ATPase in sheep. A group of six sheep was subjected to direct short electrical stimulation of the right atrium to induce AF. Sham-operated sheep served as a control group. Microsomal and mitochondrial membranes of atrial muscle were isolated and tested for enzymatic activity. All paced sheep developed multiple episodes of sustained AF, with a mean total duration of 110 minutes over a 2-hour period. Data showed that short-term pacing-induced AF significantly activated membrane F0F1-ATPase activity (P < 0.05) without changes in cytochrome-c oxidase activity, Na,K-ATPase activity, ouabain sensitivity, and alpha1-subunit expression.

CONCLUSION

Specific activation of F0F1-ATPase activity is an early molecular consequence of sustained AF in sheep.

Inhibition of Na,K-ATPase by external electrical cardioversion in a sheep model of atrial fibrillation

INTRODUCTION

Electrical external cardioversion commonly used to treat atrial fibrillation (AF) is associated with myocardial membrane damage and disturbances in ionic homeostasis (hemodynamically unstable). The present study was designed to investigate whether alterations in ionic homeostasis observed were due in part to changes in the myocardial activity of Na,K-ATPase.

METHODS AND RESULTS

AF was induced by pacing in ten anesthetized sheep divided into two groups. Group I (n = 4) received a single external countershock of 360 J after three episodes of AF lasting 10 minutes. Group II (n = 6) served as controls. Activity, responsiveness to ouabain, and membrane expression of catalytic alpha and beta subunits of Na,K-ATPase in sarcolemmal myocardial membrane fractions were investigated. Membrane fluidity and fatty acid composition, and plasma levels of atrial natriuretic factor (ANF) also were measured. One shock after episodes of AF significantly decreased ventricular Na,K-ATPase activity up to 50% (P < 0.001) without modification of atrial activity at the membrane level. Sites with low affinity to ouabain showed a fivefold lower affinity for ouabain in the cardioversion group than in the control group (IC50 = 7.9 micromol/L vs 40 micromol/L ouabain, P < 0.05). Plasma levels of ANF were significantly increased in the cardioversion group compared with the control group. These changes were independent of membrane modulation in terms of expression of Na,K-ATPase, membrane fluidity, and fatty acid composition.

CONCLUSION

This study suggests that left ventricular perturbation of ionic homeostasis subsequent to transthoracic cardioversion could result from inactivation of Na,K-ATPase activity.

Effect of streptozotocin-induced diabetes on rat liver Na+/K+-ATPase

Na+/K+-ATPase during diabetes may be regulated by synthesis of its alpha and beta subunits and by changes in membrane fluidity and lipid composition. As these mechanisms were unknown in liver, we studied in rats the effect of streptozotocin-induced diabetes on liver Na+/K+-ATPase. We then evaluated whether fish oil treatment prevented the diabetes-induced changes. Diabetes mellitus induced an increased Na+/K+-ATPase activity and an enhanced expression of the beta1 subunit; there was no change in the amount of the alpha1 and beta3 isoenzymes. Biphasic ouabain inhibition curves were obtained for diabetic groups indicating the presence of low and high affinity sites. No alpha2 and alpha3 isoenzymes could be detected. Diabetes mellitus led to a decrease in membrane fluidity and a change in membrane lipid composition. The diabetes-induced changes are not prevented by fish oil treatment. The results suggest that the increase of Na+/K+-ATPase activity can be associated with the enhanced expression of the beta1 subunit in the diabetic state, but cannot be attributed to changes in membrane fluidity as typically this enzyme will increase in response to an enhancement of membrane fluidity. The presence of a high-affinity site for ouabain (IC50 = 10-7 M) could be explained by the presence of (alphabeta)2 diprotomeric structure of Na+/K+-ATPase or an as yet unknown alpha subunit isoform that may exist in diabetes mellitus. These stimulations might be related, in part, to the modification of fatty acid content during diabetes.

Dietary fish oil promotes positive inotropy of ouabain in the rat heart

We tested the hypothesis that a fish oil (FO) diet promotes positive inotropy of ouabain without increased toxicity. For 2 mo, two groups of adult male rats were fed 1) a regular food diet supplemented with dietary long-chain polyunsaturated fatty acid from FO or 2) a regular food diet (control). The responsiveness to ouabain was evaluated for the two groups in Langendorff-perfused hearts, by (31)P nuclear magnetic resonance spectroscopy, and on purified membrane-bound Na-K-ATPase. The maximum positive inotropy achieved with ouabain was nearly two times higher in the FO than in the control group and was not associated with significant changes in energetics. Alteration of function and energetic metabolism and inhibition of Na-K-ATPase in response to 3 x 10(-4) M ouabain were delayed in the FO group. This study demonstrates that dietary FO, by a cardiac membrane incorporation of n-3 polyunsaturated fatty acid, promotes positive inotropy of ouabain without toxicity and changes in cardiac metabolism.

Localization of Na,K-ATPase alpha/beta isoforms in rat sciatic nerves: effect of diabetes and fish oil treatment

The localization of the Na,K-ATPase isoenzymes in sciatic nerve remains controversial, as well as diabetes-induced changes in Na,K-ATPase isoforms. Some of these changes could be prevented by fish oil therapy. The aim of this study was to determine by confocal microscopy the distribution of Na,K-ATPase isoforms (alpha1, alpha2, alpha3, beta1, and beta2) in the sciatic nerve, the changes induced by diabetes, and the preventive effect of fish oil in diabetic neuropathy. This study was performed in three groups of rats. In the first two groups, diabetes was induced by streptozotocin and rats were supplemented daily with fish oil or olive oil at a dosage of 0.5 g/kg of body weight. The third one was a control group that was supplemented with olive oil. Five antibodies against specific epitopes of Na,K-ATPase isoenzymes were applied to stained dissociated nerve fibers with fluorescent secondary antibodies. The five isoenzymes were documented in nonspecific regions, Schwann cells (myelin), and the node of Ranvier. The localization of the alpha1, alpha2, and beta1 isoenzymes was not affected by diabetes. In contrast, diabetes induced a decrease of the alpha2 subunit (p < 0.05) and an up-regulation of the beta2 subunit (p < 0.05). These modifications were noted in both regions for alpha2 and were localized at the myelin domain only for the beta2. Fish oil supplementation prevented the diabetes-induced changes in the alpha2 subunit with an additional up-regulation. The beta2 subunit was not modified. A phenotypic change similar to nerve injury was induced by diabetes. Fish oil supplementation partially prevented some of these changes.

Relationship of plasminogen activator inhibitor-1 levels following thrombolytic therapy with rt-PA as compared to streptokinase and patency of infarct related coronary artery

BACKGROUND

Type 1 plasminogen activator inhibitor (PAI-1) is considered to be risk factor for acute myocardial infarction (AMI). A rebound of circulating PAI-1 has been reported after rt-PA administration. We investigated the relationships between PAI-1 levels before and after thrombolytic therapy with streptokinase (SK) as compared to rt-PA and the patency of infarct-related arteries.

METHODS AND RESULTS

Fifty five consecutive patients with acute MI were randomized to streptokinase or rt-PA. The plasma PAI-1 levels were studied before and serially within 24 h after thrombolytic administration. Vessel patency was assessed by an angiogram at 5+/-1days. The PAI-1 levels increased significantly with both rt-PA and SK as shown by the levels obtained from a control group of 10 patients treated with coronary angioplasty alone. However, the area under the PAI-1 curve was significantly higher with SK than with rt-PA (p<0.01) and the plasma PAI-1 levels peaked later with SK than with rt-PA (18 h versus 3 h respectively). Conversely to PAI-1 levels on admission, the PAI-1 levels after thrombolysis were related to vessel patency. Plasma PAI-1 levels 6 and 18 h after SK therapy and the area under the PAI-1 curve were significantly higher in patients with occluded arteries (p<0.002, p<0.04 and p<0.05 respectively). The same tendency was observed in the t-PA group without reaching significance.

CONCLUSIONS

This study showed that the PAI-1 level increase is more pronounced after SK treatment than after t-PA treatment. There is a relationship between increased PAI-1 levels after thrombolytic therapy and poor patency. Therapeutic approaches aimed at quenching PAI-1 activity after thrombolysis might be of interest to improve the efficacy of thrombolytic therapy for acute myocardial infarction.

A quantitative immunocytochemical study of Na+,K+-ATPase in rat hepatocytes after STZ-induced diabetes and dietary fish oil supplementation

Because diabetes causes alterations in hepatic membrane fatty acid content, these changes may affect the Na+,K+-ATPase. In this study we documented the effects of streptozotocin (STZ)-induced diabetes on hepatic Na+,K+-ATPase catalytic alpha1-subunit and evaluated whether these changes could be normalized by fish oil supplementation. Two groups of diabetic rats received fish oil or olive oil supplementation. Both groups had a respective control group. We studied the localization of catalytic alpha1-subunit on bile canalicular and basolateral membranes using immunocytochemical methods and confocal laser scanning microscopy, and the Na+, K+-ATPase activity, membrane fluidity, and fatty acid composition on isolated hepatic membranes. A decrease in the alpha1-subunit was observed with diabetes in the bile canalicular membranes, without changes in basolateral membranes. This decrease was partially prevented by dietary fish oil. Diabetes induces significant changes as documented by enzymatic Na+,K+-ATPase activity, membrane fluidity, and fatty acid content, whereas little change in these parameters was observed after a fish oil diet. In conclusion, STZ-induced diabetes appears to modify bile canalicular membrane integrity and dietary fish oil partly prevents the diabetes-induced alterations.

Diet deficient in alpha-linolenic acid alters fatty acid composition and enzymatic properties of Na+, K+-ATPase isoenzymes of brain membranes in the adult rat

The effects of dietary (n-6)/(n-3) polyunsaturated fatty acid balance on fatty acid composition, ouabain inhibition, and Na(+) dependence of Na(+), K(+)-ATPase isoenzymes of whole brain membranes were studied in 60-day-old rats fed over two generations a diet either devoid of alpha-linolenic acid [18:3(n-3)] (sunflower oil diet) or rich in 18:3(n-3) (soybean oil diet). In the brain membranes, the sunflower oil diet led to a dramatic decrease in docosahexaenoic acid [22:6(n-3)] membrane content. The activities of Na(+), K(+)-ATPase isoenzymes were discriminated on the basis of their differential affinities for ouabain and their sensitivity to sodium concentration. The ouabain titration curve of Na(+), K(+)-ATPase activity displayed three inhibitory processes with markedly different affinity [i.e., low (alpha1), high (alpha2), and very high (alpha3)] for brain membranes of rats fed the sunflower oil diet, whereas the brain membranes of rats fed the soybean oil diet exhibited only two inhibitory processes, low (alpha1) and high (alpha2' = alpha2 + alpha3). Regardless of the diet, on the basis of the Na(+) dependence of Na(+), K(+)-ATPase activity, three isoenzymes were found: alpha1 form displaying an affinity 1.5- to 2-fold higher that of than alpha2 and 3-fold higher that of alpha3. In rats fed the sunflower oil diet, alpha2 isoenzyme exhibited higher affinity for sodium (Ka = 8.8 mmol/L) than that of rats fed the soybean oil diet (Ka = 11.7 mmol/L). These results suggest that the membrane lipid environment modulates the functional properties of Na(+), K(+)-ATPase isoenzymes of high ouabain affinity (alpha2).

Fatty acid-induced modulation of ouabain responsiveness of rat Na, K-ATPase isoforms

Membrane phospholipids represent a potential influence on the enzymatic properties of the Na,K-ATPase. Little is known concerning the effects of the fatty acid environment surrounding the enzyme on the kinetic properties of the Na,K-ATPase. We used the most obvious difference among the alpha isoforms of rat, their affinities for digitalis glycosides, to examine the relationship between the lipid environment and the Na,K-ATPase. Specific membrane environments that differ in their fatty acid composition were produced by drug-induced diabetes, as well as variations in diet. The alpha1 isoforms in various tissues were then characterized by their resistance to ouabain in Na,K-ATPase-enriched membrane microsomal fractions. The Na,K-ATPase activity in nerves and hearts were altered by diabetes and partially restored in nerves after a fish oil diet. Evaluation of enzyme kinetics (dose-response curves for ouabain) in membrane preparations allowed us to correlate the ouabain affinity of alpha1 isoform with fatty acid composition. The affinity of the alpha1 isoform for ouabain was significantly increased with accretions in the total amount of fatty acids of the n-6 series (P < 0.0001). Our observations provide a partial explanation for the observed difference in isoform properties among tissues. Moreover, these results underline the interaction between membrane fatty acids and the glycoside binding site of the Na,K-ATPase alpha1 subunit.

Focal cerebral ischaemia induces a decrease in activity and a shift in ouabain affinity of Na+, K+-ATPase isoforms without modifications in mRNA and protein expression

In a mouse model of focal cerebral ischaemia, we observed after 1 h of ischaemia, that the total Na+, K+-ATPase activity was decreased by 39.4%, and then did not vary significantly up to 6 h post-occlusion. In the sham group, the dose-response curves for ouabain disclosed three inhibitory sites of low (LA), high (HA) and very high (VHA) affinity. In ischaemic animals, we detected the presence of only two inhibitory sites for ouabain. After 1 h of permanent occlusion, the first site exhibited a low affinity while the second site presented an affinity intermediate between those of HA and VHA sites, which evolved after 3 h and 6 h of occlusion towards that of the VHA site. The presence of only two ouabain sites for Na+, K+-ATPase after ischaemia could result from a change in ouabain affinity of both HA and VHA sites (alpha2 and alpha3 isoforms, respectively) to form a unique component. Irrespective of the duration of ischaemia, the smaller activity of this second site accounted entirely for the loss in total activity. Surprisingly, no modifications in protein and mRNA expression of any alpha or beta isoforms of the enzyme were observed, thus suggesting that ischaemia could induce intrinsic modifications of the Na+, K+-ATPase.

Cholesterol and omega-3 fatty acids inhibit Na, K-ATPase activity in human endothelial cells

We have investigated the effects of cholesterol and omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexenoic acid (DHA) on Na, K-ATPase activity in human endothelial cells (HUVEC). Cultured HUVEC were incubated for 18 h with pure egg phosphatidylcholine (PC), or cholesterol-enriched liposomes (4 mg PC/ml). EPA and DHA alpha-tocopherol-acetate were emulsified with PC and incubated with HUVEC (10 mM). Na, K-ATPase and 5'-nucleotidase activities were determined using the coupled assay method on microsomal fractions obtained from cultured cells using non treated cells as control. Cholesterol enrichment significantly reduced both Na, K-ATPase and 5'-nucleotidase activities by a similar level (- 40%), whereas pure phospholipid liposomes inhibited this activity only by 22%. The dose-response curves of Na, K-ATPase activity were all biphasic assuming the presence of two independent sites exhibiting different affinities for ouabain of nM and microM respectively. The cholesterol induced inhibitory effect was greater for low affinity sites (-54%) as compared to that of the high affinity sites (-24%) whereas omega-3 fatty acids reduced the activity of both sites by 22%. Short term effects of EPA and DHA on Na, K-ATPase activity were determined by incubating microsomal fractions from untreated cells with various concentrations of free fatty acids (from 1 to 200 microM) for 20 min. Both EPA and DHA significantly reduced Na, K-ATPase activity but inhibition by EPA seems to be more effective than DHA. These results suggest that cholesterol and omega-3 fatty acids reduce Na, K-ATPase activity in HUVEC.

Ginkgo biloba extract (EGb 761) protects Na,K-ATPase activity during cerebral ischemia in mice

Neuroprotective drugs such as Ginkgo biloba extract (EGb 761) could prevent the ischemia-induced impairment of the Na,K-ATPase activity. In this study, Na,K-ATPase activity and expression, contents in fatty acids and malondialdehyde, an index of lipoperoxidation, were compared in the ipsilateral (ischemic) and the contralateral (unlesioned) cortices after 1 h of unilateral focal cortices cerebral ischemia in the mouse. EGb 761 (110 mg/kg) was administered daily to half of the animals for 10 days before ischemia. Ischemia significantly reduced Na,K-ATPase activity by about 40% and increased malondialdehyde content; EGb 761 pretreatment abolished these effects. The free radical scavenger properties of EGb 761 are a potential mechanism by which Na,K-ATPase injury and lipoperoxidation are prevented.

Fish oil supplementation prevents diabetes-induced nerve conduction velocity and neuroanatomical changes in rats

Diabetic neuropathy has been associated with a decrease in nerve conduction velocity, Na,K-ATPase activity and characteristic histological damage of the sciatic nerve. The aim of this study was to evaluate the potential effect of a dietary supplementation with fish oil [(n-3) fatty acids] on the sciatic nerve of diabetic rats. Diabetes was induced by intravenous streptozotocin injection. Diabetic animals (n = 20) were fed a nonpurified diet supplemented with either olive oil (DO) or fish oil (DM), and control animals (n = 10) were fed a nonpurified diet supplemented with olive oil at a daily dose of 0.5 g/kg by gavage for 8 wk. Nerves were characterized by their conduction velocity, morphometric analysis and membrane Na, K-ATPase activity. Nerve conduction velocity, as well as Na,K-ATPase activity, was improved by fish oil treatment. A correlation was found between these two variables (R = 0.999, P < 0.05). Moreover, a preventive effect of fish oil was observed on nerve histological damage [endoneurial edema, axonal degeneration (by 10-15%) with demyelination]. Moreover, the normal bimodal distribution of the internal diameter of myelinated fibers was absent in the DO group and was restored in the DM group. These data suggest that fish oil therapy may be effective in the prevention of diabetic neuropathy.

Mechanism underlying the strong positive inotropic effects of LND-623: specific inhibition of Na, K-ATPase isoforms and exclusion of cellular sites of contractile control

LND-623 is a new aminosteroid analog of ouabain, with a greater separation between efficacy and toxicity than ouabain. To determine its mechanism of action, we studied its biochemical and physiological effects on human red blood cell sodium transports on different cellular structures regarded as sites of contractile control, and we compared its relative efficacy to ouabain in rat heart preparations and membrane-bound Na, K-ATPase isoenzymes. The response to ouabain was evaluated in Langendorff-perfused hearts and on purified membrane-bound Na, K-ATPase. LND-623 is 6.8-fold more efficient than ouabain in inhibiting the human Na+ pump (IC50 = 0.098 +/- 0.001 microM vs. 0.67 +/- 0.02 microM); (P < 0.0001). LND-623 had no effect on the following cellular functions: Na-Ca exchange, Na-K cotransport, Ca-ATPase, slow calcium channels, adenylate cyclase system, phosphodiesterase, and calcium sensitivity of the contractile protein system. The dose-response curve for the positive inotropic and inhibitory effects on rat cardiac isoenzymes produced by LND-623 were clearly biphasic. The amplitude of the maximum inotropic effect, without any toxic effect, was up to three-fold higher with LND-623 than with the same maximum dose of ouabain used. The strong positive inotropic effect of LND-623 in rats could be related to a specific inhibition of the two rat cardiac isoforms of the Na, K-ATPase.

Alterations of Na,K-ATPase isoenzymes in the rat diabetic neuropathy: protective effect of dietary supplementation with n-3 fatty acids

Diabetic neuropathy is a degenerative complication of diabetes accompanied by an alteration of nerve conduction velocity (NCV) and Na,K-ATPase activity. The present study in rats was designed first to measure diabetes-induced abnormalities in Na,K-ATPase activity, isoenzyme expression, fatty acid content in sciatic nerve membranes, and NCV and second to assess the preventive ability of a fish oil-rich diet (rich in n-3 fatty acids) on these abnormalities. Diabetes was induced by intravenous streptozotocin injection. Diabetic animals (D) and nondiabetic control animals (C) were fed the standard rat chow either without supplementation or supplemented with either fish oil (DM, CM) or olive oil (DO, CO) at a daily dose of 0.5 g/kg by gavage during 8 weeks. Analysis of the fatty acid composition of purified sciatic nerve membranes from diabetic animals showed a decreased incorporation of C16:1(n-7) fatty acids and arachidonic acids. Fish oil supplementation changed the fatty acid content of sciatic nerve membranes, decreasing C18:2(n-6) fatty acids and preventing the decreases of arachidonic acids and C18:1(n-9) fatty acids. Protein expression of Na,K-ATPase alpha subunits, Na,K-ATPase activity, and ouabain affinity were assayed in purified sciatic nerve membranes from CO, DO, and DM. Na,K-ATPase activity was significantly lower in sciatic nerve membranes of diabetic rats and significantly restored in diabetic animals that received fish oil supplementation. Diabetes induced a specific decrease of alpha1- and alpha3-isoform activity and protein expression in sciatic nerve membranes. Fish oil supplementation restored partial activity and expression to varying degrees depending on the isoenzyme. These effects were associated with a significant beneficial effect on NCV. This study indicates that fish oil has beneficial effects on diabetes-induced alterations in sciatic nerve Na,K-ATPase activity and function.

Antibodies against myosin in sera of patients with idiopathic paroxysmal atrial fibrillation

INTRODUCTION

Circulating autoantibodies against myosin heavy chain have been detected in patients with ventricular myocarditis and in patients with dilated cardiomyopathy. This study investigated the presence of antibodies against myosin in sera of healthy control persons as compared with patients with idiopathic paroxysmal atrial fibrillation refractory to antiarrhythmic therapy.

METHODS AND RESULTS

An SDS-PAGE (sodium dodecylsulfate polyacrylamide gel electrophoresis) procedure, followed by Western blotting with homogenates and membrane fractions of human left ventricular and atrial specimen as antigens, was used to analyze sera of 10 patients with idiopathic paroxysmal atrial fibrillation and 10 age-matched healthy control subjects. Circulating immunoglobulin G reactivity against cardiac myosin heavy chain was detected in 6 patients (60%) as compared with 1 control subject (10%). This difference was statistically significant (P < 0.05). All patients with idiopathic paroxysmal atrial fibrillation who showed reactivity against myosin heavy chain also had specific reactivity in their sera that exhibited reactivities to both ventricular and atrial cardiac myosin heavy chain isoforms.

CONCLUSION

This study demonstrates the presence of circulating autoantibodies against myosin heavy chain in a significant percentage of patients with idiopathic paroxysmal atrial fibrillation and raises the possibility of an autoimmune process in some patients with paroxysmal atrial fibrillation.

Evidence that human endothelial cells express different isoforms of Na,K-ATPase

BACKGROUND

The catalytic alpha and smaller beta subunits of the plasma membrane Na,K-ATPase occur in various molecular forms (alpha1, alpha2, alpha3, beta1 and beta2). The alpha isoforms of the enzyme have varying affinities for ouabain and exist in different tissues with particular distribution patterns.

OBJECTIVE

To document the existence of isoforms of the Na,K-ATPase in cultured human umbilical vein endothelial cells.

METHODS

Microsomal fractions were prepared by differential ultracentrifugation from primary cultures of human umbilical vein endothelial cells and from such cells obtained after three passages. Na,K-ATPase activity was assayed using the coupled assay method and sensitivity to ouabain was determined in the presence of varying concentrations of ouabain. Specific antibodies for the various Na,K-ATPase isoforms were used to label these different proteins by immunocytochemistry in endothelial cells and by Western blotting in isolated membranes.

RESULTS

In plotting the dose-response curves for Na,K-ATPase activity in response to ouabain we assumed the existence of two independent sites exhibiting different affinities for ouabain (in the micromol/l and the nmol/l ranges). The contribution of low-affinity sites was threefold that of high-affinity sites. After three passages in culture, a specific increase in Na,K-ATPase activity of the high-affinity sites was observed compared with that of cells from primary cultures. Confocal microscopy revealed the existence of beta1, beta2, and alpha1 subunit proteins in human umbilical endothelial cells. Staining for alpha3 isoform was less pronounced and no obvious alpha2 was detected.

CONCLUSION

These findings suggest that human umbilical vein endothelial cells contain beta1, beta2, a large amount of alpha1 isoform with an apparently low affinity for ouabain, and a lesser amount of high-affinity sites, which may correspond to the alpha3 protein.

Changes in ouabain affinity of Na+, K+-ATPase during focal cerebral ischaemia in the mouse

We investigated the effect of focal cerebral ischaemia on the activity and the affinity of the ouabain sites of Na+,K+-ATPase in the mouse. The Na+,K+-ATPase activity was decreased by 38% as early as 30 min following ischaemia. In the sham group, the dose-response curves for ouabain disclosed three inhibitory states which contribute, respectively, 24.9 +/- 6.7%, 39.1 +/- 7.5% and 36.0% of the total activity (low affinity, LA; high affinity, HA and very high affinity, VHA, respectively). Their computed IC50 values are, respectively: 1.3 X 10(-3) M, 4.5 X 10(-6) M and 2.9 X 10(-9) M. Surprisingly, in ischaemic cortices, only two sites for ouabain were detected. The first site exhibits a LA (IC50 = 2.0 X 10[-4] M) but its relative contribution to the total activity (46.1 +/- 5.2%) is twice that noted for the LA site in non-ischaemic tissues. The second site presents an affinity intermediate between those of HA and VHA sites of the sham group (IC50 = 1.7 X 10[-7] M) and contributes 53.9% to the total activity. Loss in the specific activity of the second site explains that of the total activity. The most likely explanation in the presence of only two ouabain sites of Na+,K+-ATPase following ischaemia may be a change in ouabain affinity of alpha2 and/or alpha3 isoforms, as the presence of all three alpha isoforms has been observed by Western blotting. These results suggest that ischaemia induces intrinsic modifications in Na+,K+-ATPase which result from perturbations in membrane integrity and/or association of the alpha isoforms of this enzyme.

Alteration of Na,K-ATPase isoenzymes in diabetic cardiomyopathy: effect of dietary supplementation with fish oil (n-3 fatty acids) in rats

Diabetic cardiomyopathy has been associated with a decrease in Na,K-ATPase activity and expression, as well as alterations in membrane lipid composition. The aim of this study was twofold: 1) to document in rats the effect of streptozotocin-induced diabetes on myocardial Na,K-ATPase and fatty acids, and 2) to evaluate the potential effect of a dietary supplementation with fish oil (n-3 fatty acids) on the streptozotocin-induced changes. Assays were performed in purified cardiac plasma membranes to determine Na,K-ATPase activity, expression of the different alpha- and beta-subunits of Na,K-ATPase, and the fatty acid content of total phospholipids. Relative abundance of the mRNAs encoding the alpha 1, alpha 2 and beta 1 isoforms was studied by Northern blot analysis. Results demonstrated that diabetes significantly decreased activities of alpha 1 and alpha 2 isoforms and mRNA levels of alpha 2 and beta 1 isoforms, and, at the protein level, increased alpha 1-isoforms and decreased both alpha 2- and beta 1-isoforms. Changes in fatty acid content of the membrane were consistent with inhibition of desaturase. Fish-oil supplementation produced an increase in membrane incorporation of eicosapentaenoic acid. It also increased the level of beta 1-isoforms and restored the activity of the alpha 2-isoenzyme without significant changes in the level of alpha 1- and alpha 2-isoforms. Northern blot analysis showed no effect of fish oil supplementation. Experimental diabetes and prevention by the fish oil rich (n-3 fatty acids) diet induced specific effects on the activity and expression of alpha and beta Na,K-ATPase subunit isoforms. These studies suggest that fish oil therapy may be effective in preventing some of the adverse consequences of diabetes.

Specific modulation of two neuronal digitalis receptors by anaesthesia

Three isoenzymes of digitalis receptors (alpha 1, alpha 2, alpha 3) in the brain and only one in the kidney (alpha 1) can be distinguished by their ouabain affinities and their responsiveness to sodium. Since we have reported modulations for these digitalis receptors by their fatty acid membrane environment, anaesthesics could bind on and modulate either directly these receptors or indirectly by disturbing membrane lipids. The aim of this study was to evaluate this anaesthetic action on apparent ouabain affinities and sodium dependence of cerebral and renal Na+, K(+)-ATPase isoenzymes activities. Rat brain and kidney membrane fractions with pentobarbital-induced anaesthetized state were compared to an unanaesthetized state for their (1) fatty acid composition of total membrane phospholipids, (2) responsiveness to ouabain and (3) Na+ dependence of digitalis receptors. An anaesthesia period of 10 minutes induced (1) a fatty acid modification of brain membranes and (2) a significant sensibilization to ouabain for the alpha 2 and alpha 3 isoforms of digitalis receptors (alpha 2, IC50; 8.2 +/- 0.5 x 10(-7) mol/l vs 4.5 +/- 0.2 x 10(-7) mol/l; alpha 3, IC50; 6.0 +/- 0.3 x 10(-8) mol/l vs 2.5 +/- 0.1 x 10(-8). In contrast, the ouabain affinity of the alpha 1 subunit expressed in kidney and brain membranes was unaltered. No anaesthetic effect was observed on the Na+ dependence of the alpha 1 isoenzyme in the brain (4 mmol/l) and the kidney (8 mmol/l). Pentobarbital induced a desensibilization for alpha 2-receptors (8.3 +/- 0.5 vs 16.0 +/- 1.4 mmol/l Na+) and a sensibilization for alpha 3-receptors (14.4 +/- 0.8 vs 10 +/- 1.3 mmol/l Na+). These altered properties could be related to a selective modification of the fatty acid composition and/or to the presence of a specific binding site for pentobarbital on these two neuronal digitalis receptors.

Canine cardiac digitalis receptors are preserved in congestive heart failure induced by rapid ventricular pacing

In dogs, it has been reported that acute ischemia or severe and terminal heart failure results in a selective reduction of myocardial alpha 3 isoform of Na, K-ATPase activity. The aim of this study was to evaluate if a similar change in the two canine digitalis receptor isoforms occurs following 4 weeks of rapid ventricular pacing-induced heart failure without profound necrosis. Heart failure was induced in dogs by rapid ventricular pacing (240 beats x min-1). Digitalis receptors were quantitated by [3H]-ouabain binding with isolated microsomal membranes from sham-operated (n = 3) and heart failure dogs (n = 4) and by Western blot analysis using specific alpha 1 and alpha 3 polyclonal antibodies. In kinetic studies, similar dissociation rates of 19 to 22 x 10(-4) s-1 and 1.3 to 2.4 x 10(-4) s-1 corresponding to high and low affinity sites respectively, were found in sham-operated and CHF dogs. Immunoblotting showed similar abundance of alpha 1 isoform in the two groups; however, levels of alpha 3 were increased by at least 50% in pacing-induced heart failure animals. In conclusion, heart failure selectively modulates the expression of cardiac alpha 3 isoform in dogs.

Modulation of mouse cerebral Na+,K(+)-ATPase activity by oxygen free radicals

There is increasing evidence that oxygen free radicals (OFR) are involved in cerebral ischaemia-reperfusion injury, possibly via a modulation of Na+,K(+)-ATPase activity, one of the major membrane pumps responsible for ionic homeostasis. We measured OFR-mediated modulation of this enzymatic activity and examined the roles of lipid and/or protein alterations. Using mouse brain microsomes exposed to UV-C irradiation, our results show a good correlation between activity inhibition and lipoperoxidation estimated by PUFA loss as well as malondialdehyde production. The protective effect of thiourea (OH scavenger) and the lack of effect noted with DTT (thiol protector) suggest that the functionality of the Na+,K(+)-ATPase is altered by perturbation of membrane integrity rather than by a structural alteration of the protein itself.

Inotropic effects of ouabain and Na, K-ATPase activity in failing rabbit hearts

Left ventricular (LV) function and Na+, K(+)-ATPase activity were studied in rabbit failing heart (FH) obtained by a double pressure plus volume overload which increased LV/body weight ratio by 58%. Ouabain (10(-6) M) increased peak dP/dt by 69% in control hearts (CH) but not in FH. Na+, K(+)-ATPase activity was similar in FH and in CH but the affinity of Na+, K(+)-ATPase for ouabain was significantly higher in CH than in FH (IC50: 2 microM vs 90 microM). The blunted LV contractile response to ouabain in FH is attributed to a decreased Na+, K(+)-ATPase affinity to ouabain and not to a decreased receptor density.

Immunodetection and enzymatic characterization of the alpha 3-isoform of Na,K-ATPase in dog heart

The expression of the canine alpha 2 and 3 subunit isoenzymes of NA,K-ATPase has been investigated in plasma membranes isolated from dog heart, brain and kidney by immunoblotting, employing polyclonal anti rat fusion protein, and enzymological techniques. Western blot analysis revealed with purified dog membrane Na,K-ATPase preparations, one immunoreactive signal with rat specific alpha 3 antisera in cardiac tissues, and two immunoreactive signals with rat alpha 2 and alpha 3 antisera in cerebral tissues. These findings suggested the specific expression of alpha 3 polypeptide in dog heart (99 kDa), whereas dog brain expressed the alpha 2 and 3 polypeptides. The stained bands were superimposed. The antibody to rat brain alpha 1 fusion protein did not cross-react with dog antigens whatever the three tissues tested. Expression of the alpha 3-subunit isoform in dog heart membranes was consistent with a high affinity digitoxigenin-sensitive class of Na,K-ATPase (IC50 = 7 +/- 2 nM). A single component with low affinity to digitoxigenin (IC50 = 110 +/- 10 nM) characterized the alpha 1 kidney form. The mixture of alpha 2 and alpha 3 isoforms in dog brain exhibited an apparent affinity for digitoxigenin (IC50 = 17 +/- 5 nM) lower than the heart. The sodium dependences of the high affinity digitoxigenin sites were for the cardiac alpha 3 form (K0.5 = 10 +/- 1.9 mM) and for the cerebral alpha 2 and alpha 3 mixture (K0.5 19.6 +/- 4.9 mM). The sensitivities for Na+ of the low affinity sites (alpha 1) were: 6.7 +/- 1.4 mM, 6.3 +/- 1.2 mM and 11.6 +/- 2.9 mM in heart, brain and kidney respectively. This is the first report of the catalytic characteristics of the alpha 3 subunit isoenzyme in canine cardiac plasma membranes.