Inhibition of Na,K-ATPase and sodium pump by protein kinase C regulators sphingosine, lysophosphatidylcholine, and oleic acid

Brain lipid sensing and the neural control of energy balance

The central nervous system continuously detects circulating concentrations of lipids such as fatty acids and troglycerides. Once information has been detected, the central nervous system can in turn participate in the control of energy balance and blood sugar levels and in particular regulate the secretion and action of insulin. Neurons capable of detecting circulating lipid variations are located in the hypothalamus and in other regions such as the nucleus accumbens, the striatum or the hippocampus. An excess of lipids will have deleterious effects and may induce central lipotoxicity, in particular following local production of ceramides and the appearance of neuroinflammation which may lead to metabolic diseases such as obesity and type 2 diabetes.

The Effectiveness of Myo-Inositol in Women With Polycystic Ovary Syndrome: A Prospective Clinical Study

Background Polycystic ovarian syndrome (PCOS) is a multifaceted complex endocrine disorder showing an alarming rise in women worldwide. Insulin resistance is the chief driving force in the pathogenesis of PCOS. Myo-inositol is an upcoming insulin-sensitizing agent, which is a second messenger responsible for insulin-mediated intracellular glucose transport. This study aims to evaluate the efficacy of myo-inositol and its clinical, hormonal, and metabolic profile in treating women with PCOS. Methodology A prospective clinical study was conducted over 18 months in the Department of Obstetrics and Gynecology at Sree Balaji Medical College and Hospital, Chennai, after obtaining permission from the Institutional Ethical Committee. A total of 90 women diagnosed with PCOS, according to Rotterdam's criteria, were included in the study. They received tablet myo-inositol 1 g BD for six months. Before the start of the therapy, detailed history and baseline investigations were recorded and subsequently re-assessed at the end of six months. Results Around 68% of patients restored menstrual cycle regularity. There was a statistically significant decrease in luteinizing hormone (LH) (10.31 ± 7.92 to 7.42 ± 6.25; p = 0.002), LH/follicle-stimulating hormone ratio (2.34 ± 0.34 to 1.91 ± 0.32; p = 0.000), fasting serum insulin levels (16.71 ± 13.92 to 13.18 ± 9.41; p = 0.041), and homeostatic model assessment for insulin resistance (4.52 ± 1.34 to 2.74 ± 1.28; p = 0.041). Conclusions According to our study, it was observed that myo-inositol led to a statistically significant improvement in the hormonal and metabolic profile of PCOS patients. Moreover, it is safe and has good compliance. Hence, we can justify the addition of myo-inositol to the armamentarium for PCOS management.

The effects of acarbose treatment on cardiovascular risk factors in impaired glucose tolerance and diabetic patients: a systematic review and dose-response meta-analysis of randomized clinical trials

Acarbose (ACB) seems to be an effective drug in the management of cardiovascular risk factors. However, no previous meta-analysis of randomized controlled trials (RCTs) has been done to evaluate the effects of ACB on cardiovascular risk factors on impaired glucose tolerance (IGT), type 2 diabetes mellitus (T2D), and type 1 diabetes mellitus (T1D). We comprehensively searched electronic databases including Scopus, Web of Science, and PubMed for RCTs for related keywords up to September 2022. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% confidence interval (CI). The pooled analysis demonstrated that ACB treatment had a significant effect on fasting blood glucose (FBG) (WMD = -3.55 mg/dL; 95%CI: -6.29, -0.81; p = 0.011), fasting insulin (WMD = -6.73 pmoL/L; 95%CI: -10.37, -3.10; p < 0.001), HbA1c [WMD = -0.32%; 95%CI: -0.45, -0.20; p < 0.001], body weight (WMD = -1.25 kg; 95%CI: -1.79, -0.75; p < 0.001), body mass index (BMI) (WMD = -0.64 kg/m2; 95%CI: -0.92, -0.37; p < 0.001), tumor necrosis factor-alpha (TNF-α) (WMD = -2.70 pg/mL, 95%CI: -5.25, -0.16; p = 0.037), leptin (WMD = -1.58 ng/mL; 95%CI: -2.82, -0.35; p = 0.012), alanine transaminase (ALT) (WMD = 0.71 U/L; 95%CI: -0.31, 1.85; p = 0.164), triglyceride (TG) (WMD = -13.89 mg/dL; 95%CI: -20.69, -7.09; p < 0.001), total cholesterol (TC) (WMD = -2.26 mg/dL; 95%CI: -4.18, -0.34; p = 0.021), systolic blood pressure (SBP) (WMD = -1.29 mmHg; 95%CI: -2.44, -0.15; p = 0.027), and diastolic blood pressure (DBP) (WMD = 0.02 mmHg; 95%CI: -0.41, 0.45; p = 0.925) in an intervention group, compared with a placebo group. The non-linear dose-response analysis showed that ACB reduces the TC in trial duration by >50 weeks, and 180 mg/day is more effective for the decrement of CRP. ACB can improve lipid profiles, glycemic indices, anthropometric indices, and inflammatory markers in T2D, T1D, and IGT patients.

The relationship of oleic acid/albumin molar ratio and clinical outcomes in leptospirosis

Human leptospirosis is an acute infectious zoonosis presenting specific lipid disorders. Previous in vitro studies showed both leptospira glycolipoprotein endotoxin, and high oleic acid levels were associated with Na/K-ATPase inhibition that is amplified by the reduction of circulating albumin levels. In this study, we aimed to investigate the relationship of oleic acid/albumin (OA/A) molar ratio and clinical outcomes in Leptospirosis. Through a prospective observational cohort study employing high-performance liquid chromatography (HPLC) we sequentially determined serum concentrations of nonesterified fatty acids (NEFA) and albumin in twenty-eight patients with severe leptospirosis since their hospital admission. Twenty patients recovered, and eight died. Data was distributed in two groups according to clinical outcomes. Oleic acid/albumin molar ratios (OA/A), initial samples, were higher than those in healthy donors. The ratio OA/A, however, persisted high in dying patients, whereas patients who survived had a reduction matching to healthy donors. Biochemical alterations suggest that cure is correlated to the reestablishment of the OA/A molar ratio, while fatal outcomes related to persisting OA/A imbalances. Analysis by receiver operating characteristic (ROC) showed the area under the curve of 0.864 and the cutoff value of 0.715 being associated with a high odds ratio. Lipid analysis from patients with leptospirosis had an acute high serum OA/A molar ratio, and sustained imbalance has a high odds ratio and strong correlation with mortality.

Early Postnatal Exposure to a Low Dose of Nanoparticulate Silver Induces Alterations in Glutamate Transporters in Brain of Immature Rats

Due to strong antimicrobial properties, silver nanoparticles (AgNPs) are used in a wide range of medical and consumer products, including those dedicated for infants and children. While AgNPs are known to exert neurotoxic effects, current knowledge concerning their impact on the developing brain is scarce. During investigations of mechanisms of neurotoxicity in immature rats, we studied the influence of AgNPs on glutamate transporter systems which are involved in regulation of extracellular concentration of glutamate, an excitotoxic amino acid, and compared it with positive control—Ag citrate. We identified significant deposition of AgNPs in brain tissue of exposed rats over the post-exposure time. Ultrastructural alterations in endoplasmic reticulum (ER) and Golgi complexes were observed in neurons of AgNP-exposed rats, which are characteristics of ER stress. These changes presumably underlie substantial long-lasting downregulation of neuronal glutamate transporter EAAC1, which was noted in AgNP-exposed rats. Conversely, the expression of astroglial glutamate transporters GLT-1 and GLAST was not affected by exposure to AgNPs, but the activity of the transporters was diminished. These results indicate that even low doses of AgNPs administered during an early stage of life create a substantial risk for health of immature organisms. Hence, the safety of AgNP-containing products for infants and children should be carefully considered.

Docosahexaenoic acid prevents palmitate-induced insulin-dependent impairments of neuronal health

The importance of fatty acids (FAs) for healthy brain development and function has become more evident in the past decades. However, most studies focus on the hypothalamus as an important FA-sensing brain region involved in energy homeostasis. Less work has been done to evaluate the effects of FAs on brain regions such as the hippocampus or cortex, two important centres of learning, memory formation, and cognition. Furthermore, the mechanisms of how FAs modulate the neuronal development and function are incompletely understood. Therefore, this study examined the effects of the saturated FA palmitic acid (PA) and the polyunsaturated FA docosahexaenoic acid (DHA) on primary hippocampal and cortical cultures isolated from P0/P1 Sprague Dawley rat pups. Exposure to PA, but not DHA, resulted in severe morphological changes in primary neurons such as cell body swelling, axonal and dendritic blebbing, and a reduction in synaptic innervation, compromising healthy cell function and excitability. Pharmacological assessment revealed that the PA-mediated alterations were caused by overactivation of neuronal insulin signaling, demonstrated by insulin stimulation and phosphoinositide 3-kinase inhibition. Remarkably, co-exposure to DHA prevented all PA-induced morphological changes. This work provides new insights into how FAs can affect the cytoskeletal rearrangements and neuronal function via modulation of insulin signaling.

Myo-inositol: its metabolism and potential implications for poultry nutrition-a review

Myo-inositol (MI) has gained relevance in physiology research during the last decade. As a constituent of animal cells, MI was proven to be crucial in several metabolic and regulatory processes. Myo-inositol is involved in lipid signaling, osmolarity, glucose, and insulin metabolism. In humans and rodents, dietary MI was assessed to be important for health so that MI supplementation appeared to be a valuable alternative for treatment of several diseases as well as for improvements in metabolic performance. In poultry, there is a lack of evidence not only related to specific species-linked metabolic processes but also about the effects of dietary MI on performance and health. This review intends to provide information about the meaning of dietary MI in animal metabolism as well as to discuss potential implications of dietary MI in poultry health and performance with the aim to identify open questions in poultry research.

Metabonomic Analysis of the Therapeutic Effects of Chinese Medicine Sanqi Oral Solution on Rats With Exhaustive Exercise

Exhaustive exercise has emerged as an important health issue nowadays. This study was designed to assess the metabolite abnormalities of rats after exhaustive exercise and the holistic efficacy of Chinese medicine Sanqi oral solution (SQ). Through exhaustive swimming, the exhaustive exercise model in rats was established. Thirty male Sprague–Dawley rats were randomly divided into control, model, and treatment groups. SQ (12 mL·kg⁻¹·d⁻¹) or 0.9% saline solution was administrated orally by gastric gavage. After 4 weeks, serum samples were collected for biochemical measurements and ultra performance liquid chromatography (UPLC)/quadrupole time-of-flight mass spectrometry (Q-TOF-MS)-based metabonomic study. It was found that rats with SQ intervention showed longer exhaustive swimming time (P < 0.05) than model rats, with an average of 1,160.36 ± 123.89 s in SQ group and 906.57 ± 172.11 s in model group. Among the biochemical indices, the levels of creatine kinase isoenzyme, lactate dehydrogenase, and glucose of exhaustive exercise rats increased, whereas levels of creatine kinase, urea, triglyceride, and total cholesterol decreased. These biochemical indices came normal after SQ administration, except for triglyceride. Twenty-seven potential biomarkers belonging to sphingolipids, phospholipids, fatty acids, amino acid, and other classes were identified in serum. This study indicated that SQ exerted protective effects on exhaustive exercise by significantly prolonging the swimming endurance time. The metabonomic-based findings of the metabolic state and analysis of potential biomarkers in serum well correlated with biochemical assessment, confirming that SQ had a definite efficacy. Moreover, the shifts in lipid-related metabolites and glycolytic pathway suggested that SQ may serve as a potential supplementation in sports nutrition for its pharmacological effect of regulating energy metabolism as well as improving signal transduction and muscle-cell physiological functions.

Renoprotective effect of Zhenwu decoction against renal fibrosis by regulation of oxidative damage and energy metabolism disorder

Zhenwu decoction (ZWD) is a promising traditional Chinese prescription against renal fibrosis, while its underlying mechanism remains unclear. Rat model of renal fibrosis were established and divided into control group, model group, ZWD treatment group and enalapril maleate treatment group. Metabolic profiles on serum samples from each group were acquired by using ultra performance liquid chromatography coupled with quadrupole time-of-flight high-resolution mass spectrometry. Metabolomics combined with molecular biology were comparatively conducted on samples of various groups. Fifteen potential biomarkers were identified and these biomarkers are mainly phospholipids and fatty acids. The results showed renal fibrosis was associated with oxidative damage and energy metabolism disorder. The results of histopathology, biochemistry and metabolomics demonstrated that ZWD exhibited an efficient renoprotective effect by alleviating oxidative stress, increasing energy metabolism and regulating fibrotic cytokines. This study provided scientific support for the research and development of new drugs from traditional Chinese medicine.

Inhibitory effect of several sphingolipid metabolites on calcineurin

Neurons have well-developed membrane microdomains called "rafts" that are recovered as a detergent-resistant membrane microdomain fraction (DRM). NAP-22 is one of the major protein components of neuronal DRM. In a previous study, we showed that DRM-derived NAP-22 binds ganglioside and the inhibitory effect of ganglioside to calcineurin (CaN), a neuron-enriched calmodulin-regulated phosphoprotein phosphatase. Considering the important roles of CaN in neurons, identification of other cellular regulators of CaN could be a good clue to understand the molecular background of neuronal function. In this study, we screened the effect of several membrane lipid-derived molecules on the CaN activity and found sphingosine and some sphingosine-derived metabolites such as sphingosylphosphorylcholine, galactosylsphingosine (psychosine), and glucosylsphingosine, have inhibitory effect on CaN through the interaction with calmodulin.

Cardiovascular Risk in Patients with Prehypertension and the Metabolic Syndrome

Prehypertension (pHTN) and metabolic syndrome (MetS) are both lifestyle diseases that are potentiated by increased adiposity, as both disease processes are closely related to weight. In the case of pHTN, increased adiposity causes dysregulation of the renin-angiotensin-aldosterone-system (RAAS) as well as adipokine- and leptin-associated increases in adrenergic tone. In MetS, excess weight potentiates hyperglycemia and insulin resistance which causes positive feedback into the RAAS system, activates an inflammatory cascade that potentiates atherosclerosis, and causes lipid dysregulation which together contribute to cardiovascular disease, especially coronary heart disease (CHD) and heart failure (HF). The relationship with all-cause mortality is not as clear-cut in part because of some protective effects associated with the obesity paradox in chronic diseases such as CHD and HF. However, in healthy populations, the absence of excess weight and its associated effects on prehypertension and MetS are associated with a longer absolute and disease-free lifespan.

Lipid signaling to membrane proteins: From second messengers to membrane domains and adapter-free endocytosis

Hilgemann et al. explain how lipid signaling to membrane proteins involves a hierarchy of mechanisms from lipid binding to membrane domain coalescence.

Lipids influence powerfully the function of ion channels and transporters in two well-documented ways. A few lipids act as bona fide second messengers by binding to specific sites that control channel and transporter gating. Other lipids act nonspecifically by modifying the physical environment of channels and transporters, in particular the protein–membrane interface. In this short review, we first consider lipid signaling from this traditional viewpoint, highlighting innumerable Journal of General Physiology publications that have contributed to our present understanding. We then switch to our own emerging view that much important lipid signaling occurs via the formation of membrane domains that influence the function of channels and transporters within them, promote selected protein–protein interactions, and control the turnover of surface membrane.

Regional changes in CNS and retinal glycerophospholipid profiles with age: a molecular blueprint

We present here a quantitative molecular blueprint of the three major glycerophospholipid (GPL) classes, phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE), in retina and six regions of the brain in C57Bl6 mice at 2, 10, and 26 months of age. We found an age-related increase in molecular species containing saturated and monoenoic FAs and an overall decrease in the longer-chain PUFA molecular species across brain regions, with loss of DHA-containing molecular species as the most consistent and dramatic finding. Although we found very-long-chain PUFAs (VLC-PUFAs) (C28) in PC in the retina, no detectable levels were found in any brain region at any of the ages examined. All brain regions (except hippocampus and retina) showed a significant increase with age in PE plasmalogens. All three retina GPLs had di-PUFA molecular species (predominantly 44:12), which were most abundant in PS (∼30%). In contrast, low levels of di-PUFA GPL (1-2%) were found in all regions of the brain. This study provides a regional and age-related assessment of the brain's lipidome with a level of detail, inclusion, and quantification that has not heretofore been published.

Obesity and hypertension

The imbalance between energy intake and expenditure is the main cause of excessive overweight and obesity. Technically, obesity is defined as the abnormal accumulation of ≥20% of body fat, over the individual's ideal body weight. The latter constitutes the maximal healthful value for an individual that is calculated based chiefly on the height, age, build and degree of muscular development. However, obesity is diagnosed by measuring the weight in relation to the height of an individual, thereby determining or calculating the body mass index. The National Institutes of Health have defined 30 kg/m² as the limit over which an individual is qualified as obese. Accordingly, the prevalence of obesity in on the increase in children and adults worldwide, despite World Health Organization warnings. The growth of obesity and the scale of associated health issues induce serious consequences for individuals and governmental health systems. Excessive overweight remains among the most neglected public health issues worldwide, while obesity is associated with increasing risks of disability, illness and death. Cardiovascular diseases, the leading cause of mortality worldwide, particularly hypertension and diabetes, are the main illnesses associated with obesity. Nevertheless, the mechanisms underlying obesity-associated hypertension or other associated metabolic diseases remains to be adequately investigated. In the present review, we addressed the association between obesity and cardiovascular disease, particularly the biological mechanisms linking obesity and hypertension.

Brain lipid sensing and the neural control of energy balance

Fatty acid (FA) -sensitive neurons are present in the brain, especially the hypothalamus, and play a key role in the neural control of energy and glucose homeostasis including feeding behavior, secretion insulin and action. Subpopulations of neurons in the arcuate and ventromedial hypothalamic nuclei are selectively either activated or inhibited by FA. Molecular effectors of these FA effects include ion channels such as chloride, potassium or calcium. In addition, at least half of the responses in the hypothalamic ventromedial FA neurons are mediated through interaction with the FA translocator/receptor, FAT/CD36, that does not require metabolism to activate intracellular signaling downstream. Recently, an important role of lipoprotein lipase in FA detection has also been demonstrated not only in the hypothalamus, but also in the hippocampus and striatum. Finally, FA could overload energy homeostasis via increased hypothalamic ceramide synthesis which could, in turn, contribute to the pathogenesis of diabetes of obesity and/or type 2 in predisposed individuals by disrupting the endocrine signaling pathways of insulin and/or leptin.

[Role of fatty acids in the nervous control of energy balance]

Fatty acid (FA)-sensitive neurons are present in the brain, especially the hypothalamus, and play a key role in the neural control of energy and glucose homeostasis including feeding behavior, insulin secretion and action. Subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FA. Molecular effectors of these FA effects include ion channels such as chloride, potassium or calcium. In addition at least half of the FA responses in ventromedial hypothalamic neurons are mediated by interaction with FAT/CD36, a FA translocator/receptor that does not require intracellular metabolism to activate downstream signaling. Recently, an important role of lipoprotein lipase in FA sensing has also been demonstrated not only in hypothalamus, but also in the hippocampus and striatum. Finally, FA overload might impair neural control of energy homeostasis through enhanced ceramide synthesis and may contribute to obesity and/or type 2 diabetes pathogenesis in predisposed subjects.

Physiological and pathophysiological implications of lipid sensing in the brain

Fatty acid (FA)-sensitive neurons are present in the brain, especially the hypothalamus, and play a key role in the neural control of energy homeostasis. Through neuronal output, FA may modulate feeding behaviour as well as insulin secretion and action. Subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FA. Molecular effectors of these FA effects probably include chloride or potassium ion channels. While intracellular metabolism and activation of the ATP-sensitive K⁺ channel appear to be necessary for some of the signalling effects of FA, at least half of the FA responses in ventromedial hypothalamic neurons are mediated by interaction with FAT/CD36, an FA transporter/receptor that does not require intracellular metabolism to activate downstream signalling. Thus, FA or their metabolites can modulate neuronal activity as a means of directly monitoring ongoing fuel availability by brain nutrient-sensing neurons involved in the regulation of energy and glucose homeostasis. Recently, the role of lipoprotein lipase in FA sensing has also been shown in animal models not only in hypothalamus, but also in hippocampus and striatum. Finally, FA overload might impair neural control of energy homeostasis through enhanced ceramide synthesis and may contribute to obesity and/or type 2 diabetes pathogenesis in predisposed subjects.

Effects of obesity and estradiol on Na+/K+-ATPase and their relevance to cardiovascular diseases

Obesity is associated with aberrant sodium/potassium-ATPase (Na(+)/K(+)-ATPase) activity, apparently linked to hyperglycemic hyperinsulinemia, which may repress or inactivate the enzyme. The reduction of Na(+)/K(+)-ATPase activity in cardiac tissue induces myocyte death and cardiac dysfunction, leading to the development of myocardial dilation in animal models; this has also been documented in patients with heart failure (HF). During several pathological situations (cardiac insufficiency and HF) and in experimental models (obesity), the heart becomes more sensitive to the effect of cardiac glycosides, due to a decrease in Na(+)/K(+)-ATPase levels. The primary female sex steroid estradiol has long been recognized to be important in a wide variety of physiological processes. Numerous studies, including ours, have shown that estradiol is one of the major factors controlling the activity and expression of Na(+)/K(+)-ATPase in the cardiovascular (CV) system. However, the effects of estradiol on Na(+)/K(+)-ATPase in both normal and pathological conditions, such as obesity, remain unclear. Increasing our understanding of the molecular mechanisms by which estradiol mediates its effects on Na(+)/K(+)-ATPase function may help to develop new strategies for the treatment of CV diseases. Herein, we discuss the latest data from animal and clinical studies that have examined how pathophysiological conditions such as obesity and the action of estradiol regulate Na(+)/K(+)-ATPase activity.

Potential role and therapeutic interests of myo-inositol in metabolic diseases

Several inositol isomers and in particular myo-inositol (MI) and D-chiro-inositol (DCI), were shown to possess insulin-mimetic properties and to be efficient in lowering post-prandial blood glucose. In addition, abnormalities in inositol metabolism are associated with insulin resistance and with long term microvascular complications of diabetes, supporting a role of inositol or its derivatives in glucose metabolism. The aim of this review is to focus on the potential benefits of a dietary supplement of myo-inositol, by far the most common inositol isomer in foodstuffs, in human disorders associated with insulin resistance (polycystic ovary syndrome, gestational diabetes mellitus or metabolic syndrome) or in prevention or treatment of some diabetic complications (neuropathy, nephropathy, cataract). The relevance of such a nutritional strategy will be discussed for each context on the basis of the clinical and/or animal studies. The dietary sources of myo-inositol and its metabolism from its dietary uptake to its renal excretion will be also covered in this review. Finally, the actual insights into inositol insulin-sensitizing effects will be addressed and in particular the possible role of inositol glycans as insulin second messengers.

Purification and characterization of a second type of neutral ceramidase from rat brain: a second more hydrophobic form of rat brain ceramidase

Ceramidases (CDase) are enzymes that catalyze the hydrolysis of N-acyl linkage of ceramide (Cer) to generate sphingosine and free fatty acids. In this study we report the purification and characterization of a novel second type of neutral ceramidase from rat brain (RBCDase II). Triton X-100 protein extract from rat brain membrane was purified sequentially using Q-Sepharose, HiLoad16/60 Superdex 200pg, heparin-Sepharose, phenyl-Sepharose HP, and Mono Q columns. After Mono Q, the specific activity of the enzyme increased by ~15,000-fold over that of the rat brain homogenate. This enzyme has pH optima of 7.5, and it has a larger apparent molecular weight (110kDa) than the previously purified (90kDa) and characterized neutral rat brain CDase (RBCDase I). De-glycosylation experiments show that the differences in molecular mass of RBCDase I and II on SDS-PAGE are not due to the heterogeneity with N-glycan. RBCDase II is partially stimulated by Ca(2+) and is inhibited by pyrimidine mono nucleotides such as TMP and UMP. This finding is significant as it demonstrates for the first time an effect by nucleotides on a CDase activity. The enzyme was also inhibited by both oxidized and reduced GSH. The effects of metal ions were examined, and we found that the enzyme is very sensitive to Hg(2+) and Fe(3+), while it is not affected by Mn(2+). EDTA was somewhat inhibitory at a 20mM concentration.

Brain lipid sensing and nervous control of energy balance

Nutrient sensitive neurons (glucose and fatty acids (FA)) are present in many sites throughout the brain, including the hypothalamus and brainstem, and play a key role in the neural control of energy and glucose homeostasis. Through neuronal output, FA may modulate feeding behaviour as well as both insulin secretion and action. For example, central administration of oleate inhibits food intake and glucose production in rats. This suggests that daily variations in plasma FA concentrations might be detected by the central nervous system as a signal which contributes to the regulation of energy balance. At the cellular level, subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FA. Possible molecular effectors of these FA effects likely include chloride or potassium ion channels. While intracellular metabolism and activation of the ATP-sensitive K(+) channel appear to be necessary for some of the signaling effects of FA, at least half of the FA responses in ventromedial hypothalamic neurons are mediated by interaction with FAT/CD36, a FA transporter/receptor that does not require intracellular metabolism to activate downstream signaling. Thus, FA or their metabolites can modulate neuronal activity as a means of directly monitoring ongoing fuel availability by brain nutrient-sensing neurons involved in the regulation of energy and glucose homeostasis. Besides these physiological effects, FA overload or metabolic dysfunction might impair neural control of energy homeostasis and contribute to obesity and/or type 2 diabetes in predisposed subjects.

Sensing the fuels: glucose and lipid signaling in the CNS controlling energy homeostasis

The central nervous system (CNS) is capable of gathering information on the body's nutritional state and it implements appropriate behavioral and metabolic responses to changes in fuel availability. This feedback signaling of peripheral tissues ensures the maintenance of energy homeostasis. The hypothalamus is a primary site of convergence and integration for these nutrient-related feedback signals, which include central and peripheral neuronal inputs as well as hormonal signals. Increasing evidence indicates that glucose and lipids are detected by specialized fuel-sensing neurons that are integrated in these hypothalamic neuronal circuits. The purpose of this review is to outline the current understanding of fuel-sensing mechanisms in the hypothalamus, to integrate the recent findings in this field, and to address the potential role of dysregulation in these pathways in the development of obesity and type 2 diabetes mellitus.

GPR55-dependent and -independent ion signalling in response to lysophosphatidylinositol in endothelial cells

BACKGROUND AND PURPOSE

The glycerol-based lysophospholipid lysophosphatidylinositol (LPI) is an endogenous agonist of the G-protein-coupled receptor 55 (GPR55) exhibiting cannabinoid receptor-like properties in endothelial cells. To estimate the contribution of GPR55 to the physiological effects of LPI, the GPR55-dependent and -independent electrical responses in this cell type were investigated.

EXPERIMENTAL APPROACH

Applying small interference RNA-mediated knock-down and transient overexpression, GPR55-dependent and -independent effects of LPI on cytosolic free Ca(2+) concentration, membrane potential and transmembrane ion currents were studied in EA.hy296 cells.

KEY RESULTS

In a GPR55-dependent, GDPbetaS and U73122-sensitive manner, LPI induced rapid and transient intracellular Ca(2+) release that was associated with activation of charybdotoxin-sensitive, large conductance, Ca(2+)-activated, K(+) channels (BK(Ca)) and temporary membrane hyperpolarization. Following these initial electrical reactions, LPI elicited GPR55-independent long-lasting Na(+) loading and a non-selective inward current causing sustained membrane depolarization that depended on extracellular Ca(2+) and Na(+) and was partially inhibited by Ni(2+) and La(3+). This inward current was due to the activation of a voltage-independent non-selective cation current. The Ni(2+) and La(3+)-insensitive depolarization with LPI was prevented by inhibition of the Na/K-ATPase by ouabain.

CONCLUSIONS AND IMPLICATIONS

LPI elicited a biphasic response in endothelial cells of which the immediate Ca(2+) signalling depends on GPR55 while the subsequent depolarization is due to Na(+) loading via non-selective cation channels and an inhibition of the Na/K-ATPase. Thus, LPI is a potent signalling molecule that affects endothelial functions by modulating several cellular electrical responses that are only partially linked to GPR55.

Mechanisms of obesity-induced hypertension

The relationship between obesity and hypertension is well established both in children and adults. The mechanisms through which obesity directly causes hypertension are still an area of research. Activation of the sympathetic nervous system has been considered to have an important function in the pathogenesis of obesity-related hypertension. The arterial-pressure control mechanism of diuresis and natriuresis, according to the principle of infinite feedback gain, seems to be shifted toward higher blood-pressure levels in obese individuals. During the early phases of obesity, primary sodium retention exists as a result of increase in renal tubular reabsorption. Extracellular-fluid volume is expanded and the kidney-fluid apparatus is resetted to a hypertensive level, consistent with a model of hypertension because of volume overload. Plasma renin activity, angiotensinogen, angiotensin II and aldosterone values display significant increase during obesity. Insulin resistance and inflammation may promote an altered profile of vascular function and consequently hypertension. Leptin and other neuropeptides are possible links between obesity and the development of hypertension. Obesity should be considered as a chronic medical condition, which is likely to require long-term treatment. Understanding of the mechanisms associated with obesity-related hypertension is essential for successful treatment strategies.

Pharmacological stimulation of brain carnitine palmitoyl-transferase-1 decreases food intake and body weight

Inhibition of brain carnitine palmitoyl-transferase-1 (CPT-1) is reported to decrease food intake and body weight in rats. Yet, the fatty acid synthase (FAS) inhibitor and CPT-1 stimulator C75 produces hypophagia and weight loss when given to rodents intracerebroventricularly (icv). Thus roles and relative contributions of altered brain CPT-1 activity and fatty acid oxidation in these phenomena remain unclarified. We administered compounds that target FAS or CPT-1 to mice by single icv bolus and examined acute and prolonged effects on feeding and body weight. C75 decreased food intake rapidly and potently at all doses (1-56 nmol) and dose dependently inhibited intake on day 1. Dose-dependent weight loss on day 1 persisted through 4 days of postinjection monitoring. The FAS inhibitor cerulenin produced dose-dependent (560 nmol) hypophagia for 1 day, weight loss for 2 days, and weight regain to vehicle control by day 3. The CPT-1 inhibitor etomoxir (32, 320 nmol) did not alter overall day 1 feeding. However, etomoxir attenuated the hypophagia produced by C75, indicating that CPT-1 stimulation is important for C75's effect. A novel compound, C89b, was characterized in vitro as a selective stimulator of CPT-1 that does not affect fatty acid synthesis. C89b (100, 320 nmol) decreased feeding in mice for 3 days and produced persistent weight loss for 6 days without producing conditioned taste aversion. Similarly, intraperitoneal administration decreased feeding and body weight without producing conditioned taste aversion. These results suggest a role for brain CPT-1 in the regulation of energy balance and implicate CPT-1 stimulation as a pharmacological approach to weight loss.

A novel method to quantify H+-ATPase-dependent Na+ transport across plasma membrane vesicles

To prevent sodium toxicity in plants, Na(+) is excluded from the cytosol to the apoplast or the vacuole by Na(+)/H(+) antiporters. The secondary active transport of Na(+) to apoplast against its electrochemical gradient is driven by plasma membrane H(+)-ATPases that hydrolyze ATP and pump H(+) across the plasma membrane. Current methods to determine Na(+) flux rely either on the use of Na-isotopes ((22)Na) which require special working permission or sophisticated equipment or on indirect methods estimating changes in the H(+) gradient due to H(+)-ATPase in the presence or absence of Na(+) by pH-sensitive probes. To date, there are no methods that can directly quantify H(+)-ATPase-dependent Na(+) transport in plasma membrane vesicles. We developed a method to measure bidirectional H(+)-ATPase-dependent Na(+) transport in isolated membrane vesicle systems using atomic absorption spectrometry (AAS). The experiments were performed using plasma membrane-enriched vesicles isolated by aqueous two-phase partitioning from leaves of Populus tomentosa. Since most of the plasma membrane vesicles have a sealed right-side-out orientation after repeated aqueous two-phase partitioning, the ATP-binding sites of H(+)-ATPases are exposed towards inner side. Leaky vesicles were preloaded with Na(+) sealed for the study of H(+)-ATPase-dependent Na(+) transport. Our data implicate that Na(+) movement across vesicle membranes is highly dependent on H(+)-ATPase activity requiring ATP and Mg(2+) and displays optimum rates of 2.50 microM Na(+) mg(-1) membrane protein min(-1) at pH 6.5 and 25 degrees C. In this study, for the first time, we establish new protocols for the preparation of sealed preloaded right-side-out vesicles for the study of H(+)-ATPase-dependent Na(+) transport. The results demonstrate that the Na(+) content of various types of plasma membrane vesicle can be directly quantified by AAS, and the results measured using AAS method were consistent with those determined by the previous established fluorescence probe method. The method is a convenient system for the study of bidirectional H(+)-ATPase-dependent Na(+) transport with membrane vesicles.

Fatty acid sensing and nervous control of energy homeostasis

Nutrient sensitive neurons (glucose and fatty acids, FA) are present in both the hypothalamus and the brainstem and play a key role in nervous control of energy homeostasis. Through neuronal output, especially the autonomic nervous system, it is now evidenced that FA may modulate food behaviour and both insulin secretion and action. For example, central administration of oleate inhibits both food intake and hepatic glucose production in rats. This suggests that a slight increase in plasma FA concentrations in the postprandial state might be detected by the central nervous system as a satiety signal. At cellular levels, subpopulations of FA-sensitive neurons (either excited or inhibited by FA) are now identified within the hypothalamus. However molecular effectors of FA effects remain unclear. They probably include ionic channels such as chloride or potassium. FA metabolism seems also required to induce neuronal response. Thus, FA per se or their metabolites modulate neuronal activity, as a mean of directly monitoring ongoing fuel availability by CNS nutrient-sensing neurons involved in the regulation of insulin secretion. Beside these physiological effects, FA overload or dysfunction of their metabolism could impair nervous control of energy homeostasis and contribute to development of obesity and/or type 2 diabetes in predisposed subjects.

Regulation of membrane protein function by lipid bilayer elasticity-a single molecule technology to measure the bilayer properties experienced by an embedded protein

Membrane protein function is generally regulated by the molecular composition of the host lipid bilayer. The underlying mechanisms have long remained enigmatic. Some cases involve specific molecular interactions, but very often lipids and other amphiphiles, which are adsorbed to lipid bilayers, regulate a number of structurally unrelated proteins in an apparently non-specific manner. It is well known that changes in the physical properties of a lipid bilayer (e.g., thickness or monolayer spontaneous curvature) can affect the function of an embedded protein. However, the role of such changes, in the general regulation of membrane protein function, is unclear. This is to a large extent due to lack of a generally accepted framework in which to understand the many observations. The present review summarizes studies which have demonstrated that the hydrophobic interactions between a membrane protein and the host lipid bilayer provide an energetic coupling, whereby protein function can be regulated by the bilayer elasticity. The feasibility of this 'hydrophobic coupling mechanism' has been demonstrated using the gramicidin channel, a model membrane protein, in planar lipid bilayers. Using voltage-dependent sodium channels, N-type calcium channels and GABA(A) receptors, it has been shown that membrane protein function in living cells can be regulated by amphiphile induced changes in bilayer elasticity. Using the gramicidin channel as a molecular force transducer, a nanotechnology to measure the elastic properties experienced by an embedded protein has been developed. A theoretical and technological framework, to study the regulation of membrane protein function by lipid bilayer elasticity, has been established.

Basis of rise in intracellular sodium in airway hyperresponsiveness and asthma

The aim of this study was to investigate the basis of disturbances in sodium transport in asthma and in airway hyperresponsiveness without symptoms of asthma (asymptomatic AHR). We measured the intracellular sodium (Na(i)); activity of Na(+)/K(+)-ATPase in unstimulated cells (resting activity) and in cell homogenate under optimal conditions (maximal activity); and sodium influx, in mixed leukocytes of 15 normal subjects, 12 subjects with asymptomatic AHR, and 26 asthmatics with or without active symptoms. Resting Na(+)/K(+)-ATPase activity was the same as sodium influx, consistent with homeostasis. Compared with normal subjects, those with asymptomatic AHR or asthma with controlled symptoms had a twofold increase in sodium influx and Na(i). Symptomatic asthmatics also had a twofold increase in sodium influx but a fourfold elevation of Na(i). Maximal Na(+)/K(+)-ATPase activity was reduced by half in symptomatic asthmatics compared with normal subjects. The reduction of maximal Na(+)/K(+)-ATPase activity was associated with a significant decrease in ATP turnover per Na(+)/K(+)-ATPase molecule but not number of Na(+)/K(+)-ATPase molecules per cell. In summary, airway hyperresponsiveness with or without asthma is associated with increased sodium influx and Na in leukocytes. Resting activity of Na(+)/K(+)-ATPase is also increased as a compensatory response to the increased sodium influx, but it is achieved at the expense of higher Na(i). Symptomatic asthma is additionally associated with reduction in maximal activity of Na(+)/K(+)-ATPase, resulting in reduced capacity to handle the increase in sodium influx and consequent severe elevations in Na(i).

Effects of Oleic Acid on Distinct Populations of Neurons in the Hypothalamic Arcuate Nucleus Are Dependent on Extracellular Glucose Levels

Pharmacological manipulation of fatty acid metabolism in the hypothalamic arcuate nucleus (ARC) alters energy balance and glucose homeostasis. Thus, we tested the hypotheses that distinctive populations of ARC neurons are oleic acid (OA) sensors that exhibit a glucose dependency, independent of whether some of these OA sensors are also glucose-sensing neurons. We used patch-clamp recordings to investigate the effects of OA on ARC neurons in brain slices from 14- to 21-day-old Sprague–Dawley (SD) rats. Additionally, we recorded spontaneous discharge rate in ARC neurons in 8-wk-old fed and fasted SD rats in vivo. Patch-clamp studies showed that in 2.5 mM glucose 12 of 94 (13%) ARC neurons were excited by 2 μM OA (OA-excited or OAE neurons), whereas six of 94 (6%) were inhibited (OA-inhibited2.5or OAI2.5neurons). In contrast, in 0.1 mM glucose, OA inhibited six of 20 (30%) ARC neurons (OAI0.1neurons); none was excited. None of the OAI0.1neurons responded to OA in 2.5 mM glucose. Thus OAI2.5and OAI0.1neurons are distinct. Similarly, in seven of 20 fed rats (35%) the overall response was OAE-like, whereas in three of 20 (15%) it was OAI-like. In contrast, in fasted rats only OAI-like response were observed (three of 15; 20%). There was minimal overlap between OA-sensing neurons and glucose-sensing neurons. In conclusion, OA regulated three distinct subpopulations of ARC neurons in a glucose-dependent fashion. These data suggest that an interaction between glucose and fatty acids regulates OA sensing in ARC neurons.

Fumonisin B1, a sphingoid toxin, is a potent inhibitor of the plasma membrane H+-ATPase

Fumonisin B(1) (FB(1)) is an amphipathic toxin produced by the pathogenic fungus Fusarium verticillioides which causes stem, root and ear rot in maize (Zea mays L.). In this work, we studied the action of FB(1) on the plasma membrane H(+)-ATPase (EC 3.6.1.34) from germinating maize embryos, and on the fluidity and lipid peroxidation of these membranes. In maize embryos the toxin at 40 microM inhibited root elongation by 50% and at 30 microM decreased medium acidification by about 80%. Irrespective of the presence and absence of FB(1), the H(+)-ATPase in plasma membrane vesicles exhibited non-hyperbolic saturation kinetics by ATPH-Mg, with Hill number of 0.67. Initial velocity studies revealed that FB(1) is a total uncompetitive inhibitor of this enzyme with an inhibition constant value of 17.5+/-1 microM. Thus FB(1) decreased V(max) and increased the apparent affinity of the enzyme for ATP-Mg to the same extent. Although FB(1) increased the fluidity at the hydrophobic region of the membrane, no correlation was found with its effect on enzyme activity, since both effects showed different FB(1)-concentration dependence. Peroxidation of membrane lipids was not affected by the toxin. Our results suggest that, under in vivo conditions, the plasma membrane H(+)-ATPase is a potentially important target of the toxin, as it is inhibited not only by FB(1) but also by its structural analogs, the sphingoid intermediates, which accumulate upon the inhibition of sphinganine N-acyltransferase by this toxin.

Omega-3 fatty acids modulate ATPases involved in duodenal Ca absorption

Dietary supplementation with fish oil that contains omega-3 polyunsaturated fatty acids has been shown to enhance bone density as well as duodenal calcium uptake in rats. The latter process is supported by membrane ATPases. The present in vitro study was undertaken to test the effect of omega-3 fatty acids on ATPase activity in isolated basolateral membranes from rat duodenal enterocytes. Ca-ATPase in calmodulin-stripped membranes was activated in a biphasic manner by docosahexanoic acid (DHA) (10-30 microg/ml) but not by eicosapentanoic acid (EPA). This effect was blocked partially by 0.5 microM calphostin (a protein kinase C blocker). DHA inhibited Na,K-ATPase (-49% of basal activity, [DHA]=30 microg/ml, P <0.01). This effect could be reversed partially by 50 microM genistein, a tyrosine kinase blocker. EPA also inhibited Na,K-ATPase: (-47% of basal activity, [EPA]=30 microg/ml, P <0.01), this effect was partially reversed by 100 microM indomethacin, a cyclo-oxygenase blocker. Omega-3 fatty acids are thus involved in multiple signalling effects that effect ATPases in BLM.

Platelet-activating factor and lyso-PAF possess direct antimicrobial properties in vitro

The effects of platelet-activating factor (PAF) and lyso-platelet-activating factor (L-PAF) at concentrations of 0.25-20 microg/ml on potassium transport and growth of gram-positive and gram-negative bacteria have been investigated in vitro and compared with those of lysophosphatidylcholine (LPC). Potassium transport was determined using 86Rb+ as tracer, while growth was measured according to the extent of uptake of radiolabeled amino acids. All of the test phospholipids caused dose-related inhibition of 86Rb+-uptake and growth of gram-positive bacteria, the order of potency being PAF>LPC>L-PAF. Gram-negative bacteria, on the other hand, were less sensitive to the inhibitory effects of the phospholipids on K+ transport and growth. Some, but not all, of the gram-positive and gram-negative bacteria were able to degrade LPC, but not PAF or L-PAF, demonstrating that enzymatic degradation of phospholipids does not explain the differential sensitivity to these agents. The bioactive phospholipids LPC, PAF and L-PAF may represent an oxygen-independent antimicrobial host defense system operative primarily against gram-positive bacteria.

Effect of arachidonic acid on duodenal enterocyte ATPases

Duodenal ion transport processes are supported by ATPase enzymes in basolateral membranes of the enterocyte. In vivo studies have shown that long term n-6 poly-unsaturated fatty acid (PUFA) supplementation in rats causes increases in intestinal Ca absorption, coupled with a higher total calcium balance and bone calcium content. The present in vitro study was undertaken to test the effect of arachidonic acid (AA), a highly unsaturated (and thus physiologically potent) member of the n-6 PUFA family, on ATPases in enterocyte basolateral membranes isolated with a sorbitol density gradient procedure. This paper presents results which show that AA inhibits Na+,K+-ATPase in a dose-dependent manner (-67% of basal activity at a concentration of 30 microg/ml, P < 0.005) but that this effect is not mediated by protein kinase C, as shown by the use of the protein kinase C blocker calphostin (0.5 microM). Indomethacin (IDM) at 0.1 mM, a cyclo-oxygenase blocker, could also not reverse the inhibitory effect of AA on Na+,K+-ATPase. Ca2+-ATPase, on the other hand, is not affected significantly (-10%, P > 0.05) by arachidonic acid at 30 microg/ml.

Upregulation of duodenal calcium absorption by poly-unsaturated fatty acids: events at the basolateral membrane

Poly-unsaturated fatty acids, especially of the n-3 series, have a beneficial effect in treatment of osteoporosis in the elderly. Duodenal calcium absorption is a particularly vulnerable aspect of the development of this disease. It has been shown that the process of calcium transport through the rat duodenal enterocyte takes place in essentially three steps: entry of calcium through channels in the brush border (apical membrane), transcellular transport through the cytoplasm by calbindin and extrusion at the basolateral membrane by Ca(2+)-ATPase and a Ca(2+)-Na(+)exchanger which is driven by Na(+), K(+)-ATPase. This paper presents a hypothesis that poly-unsaturated fatty acids can modulate both Ca(2+)-ATPase and Na(+), K(+)-ATPase activity either by a direct action on the enzyme or by phosphorylation processes via protein kinases A and C and thus exert their positive influence on calcium absorption in this manner.

Bee venom phospholipase A2 induces stage-specific growth arrest of the intraerythrocytic Plasmodium falciparum via modifications of human serum components

Secreted phospholipases A(2) (sPLA(2)s) from snake and insect venoms and from mammalian pancreas are structurally related enzymes that have been associated with several toxic, pathological, or physiological processes. We addressed the issue of whether toxic sPLA(2)s might exert specific effects on the Plasmodium falciparum intraerythrocytic development. We showed that both toxic and non-toxic sPLA(2)s are lethal to P. falciparum grown in vitro, with large discrepancies between respective IC(50) values; IC(50) values from toxic PLA(2)s ranged from 1.1 to 200 pm, and IC(50) values from non-toxic PLA(2)s ranged from 0.14 to 1 microm. Analysis of the molecular mechanisms responsible for cytotoxicity of bee venom PLA(2) (toxic) and hog pancreas PLA(2) (non-toxic) demonstrated that, in both cases, enzymatic hydrolysis of serum phospholipids present in the culture medium was responsible for parasite growth arrest. However, bee PLA(2)-lipolyzed serum induced stage-specific inhibition of P. falciparum development, whereas hog PLA(2)-lipolyzed serum killed parasites at either stage. Sensitivity to bee PLA(2)-treated serum appeared restricted to the 19-26-h period of the 48 h parasite cycle. Analysis of the respective role of the different lipoprotein classes as substrates of bee PLA(2) showed that enzyme treatment of high density lipoproteins, low density lipoproteins, and very low density lipoproteins/chylomicrons fractions induces cytotoxicity of either fraction. In conclusion, our results demonstrate that toxic and non-toxic PLA(2)s 1) are cytotoxic to P. falciparum via hydrolysis of lipoprotein phospholipids and 2) display different killing processes presumably involving lipoprotein by-products recognizing different targets on the infected red blood cell.

Mechanisms of sodium pump regulation

The Na(+)-K(+)-ATPase, or sodium pump, is the membrane-bound enzyme that maintains the Na(+) and K(+) gradients across the plasma membrane of animal cells. Because of its importance in many basic and specialized cellular functions, this enzyme must be able to adapt to changing cellular and physiological stimuli. This review presents an overview of the many mechanisms in place to regulate sodium pump activity in a tissue-specific manner. These mechanisms include regulation by substrates, membrane-associated components such as cytoskeletal elements and the gamma-subunit, and circulating endogenous inhibitors as well as a variety of hormones, including corticosteroids, peptide hormones, and catecholamines. In addition, the review considers the effects of a range of specific intracellular signaling pathways involved in the regulation of pump activity and subcellular distribution, with particular consideration given to the effects of protein kinases and phosphatases.

Diverse effects of sphingosine on calcium mobilization and influx in differentiated HL-60 cells

Sphingosine induces a biphasic increase in cytosolic-free Ca(2+)([Ca(2+)](i)) with an initial peak followed by a sustained increase in HL-60 cells differentiated into neutrophil-like cells. The initial peak is not affected by the presence of ethylene glycol bis (beta-aminoethyl ether) N, N, N', N-tetraacetic acid (EGTA) in the buffer and appears to be dependent on conversion of sphingosine to sphingosine -1-phosphate (S1P) by sphingosine kinase, since it is blocked by the presence of N, N-dimethylsphingosine (DMS), which, like sphingosine, causes a sustained increase itself. The sustained increase that is elicited by sphingosine or DMS is abolished by the presence of EGTA in the buffer. The sustained sphingosine-induced Ca(2+)influx does not appear due to Ca(2+)influx through store-operated Ca(2+)(SOC) channels, since the influx is not inhibited by SKF 96365, nor is it augmented by loperamide. In addition, sphingosine and DMS attenuate the Ca(2+)influx through SOC channels that occurs after depletion of intracellular stores by ATP or thapsigargin. Both the initial peak and the sustained increase in [Ca(2+)](i)elicited by sphingosine can be blocked by phorbol 12-myristate 13-acetate (PMA)-elicited activation of protein kinase C. Thus, in HL-60 cells sphingosine causes a mobilization of Ca(2+)from intracellular Ca(2+)stores, which requires conversion to S1P, while both sphingosine and DMS elicit a Ca(2+)influx through an undefined Ca(2+)channel and cause a blockade of SOC channels.

Inhibition of duodenal enterocyte Mg2+-ATPase by arachidonic acid is not mediated by an effect on protein kinase C

Active absorption processes in the duodenal enterocyte are driven by various ATPases. It is known that the activity of Na+,K+-ATPase, Ca2+-ATPase and Mg2+-ATPase can be modulated by polyunsaturated fatty acids of the n-6 series, for example by linoleic and gamma-linolenic acids. These effects may be achieved by protein phosphorylation via protein kinase C. The present study was undertaken to determine the effect of arachidonic acid on Mg2+-ATPase (measured colorimetrically) activity in basolateral membranes prepared from rat duodenum. It shows, for the first time, significant dose-dependent inhibition of Mg2+-ATPase (26-62%) by arachidonic acid (10-50 microg/ml) which already takes place after one minute of exposure, indicating involvement of a rapid signal transduction mechanism. Addition of the protein kinase C inhibitors bisimidolylmaleimide (2.5 microM) and calphostin (0.5 microM) did not influence the action of arachidonic acid on Mg2+-ATPase; protein kinase C involvement in this process is thus not indicated.

Molecular cloning, sequencing, and expression of the gene encoding alkaline ceramidase from Pseudomonas aeruginosa. Cloning of a ceramidase homologue from Mycobacterium tuberculosis

We previously reported the purification and characterization of a novel type of alkaline ceramidase from Pseudomonas aeruginosa strain AN17 (Okino, N., Tani, M., Imayama, S., and Ito, M. (1998) J. Biol. Chem. 273, 14368-14373). Here, we report the molecular cloning, sequencing, and expression of the gene encoding the ceramidase of this strain. Specific oligonucleotide primers were synthesized using the peptide sequences of the purified ceramidase obtained by digestion with lysylendopeptidase and used for polymerase chain reaction. DNA fragments thus amplified were used as probes to clone the gene encoding the ceramidase from a genomic library of strain AN17. The open reading frame of 2,010 nucleotides encoded a polypeptide of 670 amino acids including a signal sequence of 24 residues, 64 residues of which matched the amino acid sequence determined for the purified enzyme. The molecular weight of the mature enzyme was estimated to be 70,767 from the deduced amino acid sequence. Expression of the ceramidase gene in Escherichia coli, resulted in production of a soluble enzyme with the identical N-terminal amino acid sequence. Recombinant ceramidase was purified to homogeneity from the lysate of E. coli cells and confirmed to be identical to the Pseudomonas enzyme in its specificity and other enzymatic properties. No significant sequence similarities were found in other known functional proteins including human acid ceramidase. However, we found a sequence homologous to the ceramidase in hypothetical proteins encoded in Mycobacterium tuberculosis, Dictyostelium discoideum, and Arabidopsis thaliana. The homologue of the ceramidase gene was thus cloned from an M. tuberculosis cosmid and expressed in E. coli, and the gene was demonstrated to encode an alkaline ceramidase. This is the first report for the cloning of an alkaline ceramidase.

Inhibition of potassium transport and growth of mycobacteria exposed to clofazimine and B669 is associated with a calcium-independent increase in microbial phospholipase A2 activity

Altered phospholipase A2 (PLA2) activity and its relationship to cation (K+, Ca2+) uptake and growth were investigated in mycobacteria exposed to the riminophenazine antimicrobial agents, clofazimine and B669 (0.15-2.5 mg/L). Microbial PLA2 activity was measured using a radiometric thin-layer chromatography procedure, whereas K+ and Ca2+ transport were measured using 86Rb+ or 42K+ and 45Ca2+, respectively. Short-term exposure (15-30 min) of Mycobacterium aurum A+ or the virulent and avirulent isolates of Mycobacterium tuberculosis H37R to the riminophenazines resulted in dose-related enhancement of microbial PLA2 activity, which was associated with inhibition of K+ influx and growth. Uptake of Ca2+ by mycobacteria was unaffected, or minimally affected, by the riminophenazines at concentrations of < or = 0.6 mg/L, whereas higher concentrations resulted in increased uptake of the cation in the setting of decreased microbial ATP concentrations. The results of kinetic studies using a fixed concentration (2.5 mg/L) of B669 demonstrated that riminophenazine-mediated enhancement of PLA2 activity and inhibition of K+ uptake in mycobacteria are rapid and probably related events that precede, by several minutes, any detectable effects on microbial ATP concentrations and uptake of Ca2+. Inclusion of the extracellular and intracellular Ca2+-chelating agents EGTA (0.2-7.2 g/L) and BAPTA/FURA-2 (0.2-9.5 mg/L), individually or in combination, did not prevent the effects of B669 on mycobacterial PLA2 activity or K+ transport, whereas alpha-tocopherol, which neutralizes PLA2 primary hydrolysis products, antagonized the inhibitory effects of the riminophenazines on microbial K+ uptake and growth. These results demonstrate that the antimycobacterial activities of clofazimine and B669 are related to a Ca2+-independent increase in mycobacterial PLA2, leading to interference with microbial K+ transport.

Polyunsaturated fatty acids inhibit Mg2+ -ATPase in basolateral membranes from rat enterocytes

It is known that certain polyunsaturated fatty acids of the n-6 family, for example linoleic and arachidonic acids, can activate both Na+, K+-ATPase and Ca2+-ATPase. These enzymes drive active absorption processes in the duodenal enterocyte. This study presents data which show a 30-50% inhibition of Mg2+-ATPase activity in enterocyte basolateral membrane preparations by linoleic and gamma-linolenic acids (also a member of the n-6 family.) Mg2+-ATPase activity has several possible roles in the enterocyte: involvement in Mg2+ and Ca2+ absorption (as part of Ca2+-ATPase and also myosin I activity) as well as control of phospholipid distribution in the membrane by a class of Mg2+-ATPases called 'flippases'. The action of linoleic and gamma-linolenic acids on basolateral membrane Mg2+-ATPase may thus modulate several cellular transport processes.

Lysophosphatidylcholine modulates catalytically important motions of the Ca-ATPase phosphorylation domain

Catalytically important motions of the Ca-ATPase, modulated by the physical properties of surrounding membrane phospholipids, have been suggested to be rate-limiting under physiological conditions. To identify the nature of the structural coupling between the Ca-ATPase and membrane phospholipids, we have investigated the functional and structural effects resulting from the incorporation of the lysophospholipid 1-myristoyl-2-hydroxy-sn-glycerol-3-phosphocholine (LPC) into native sarcoplasmic reticulum (SR) membranes. Nonsolubilizing concentrations of LPC abolish changes in fluorescence signals associated with either intrinsic or extrinsic chromophores that monitor normal conformational transitions accompanying calcium activation of the Ca-ATPase. There are corresponding decreases in the rates of calcium transport coupled to ATP hydrolysis, suggesting that LPC may increase conformational barriers associated with catalytic function. Fluorescence anisotropy measurements of the lipid analogue 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) partitioned into SR membranes indicate that LPC does not significantly modify lipid acyl chain rotational dynamics, suggesting differences in headgroup conformation between LPC and diacylglycerol phosphatidylcholines. Complementary measurements using phosphorescence anisotropy of erythrosin isothiocyanate at Lys464 on the Ca-ATPase provide a measure of the dynamic structure of the phosphorylation domain, and indicate that LPC restricts the amplitude of rotational motion. These results suggest a structural linkage between the cytosolic phosphorylation domain and the conformation of membrane phospholipid headgroups. Thus, changes in membrane phospholipid composition can modulate membrane surface properties and affect catalytically important motions of the Ca-ATPase in a manner that suggests a role for LPC generated during signal transduction.

Influence of probes for calcium-calmodulin and protein kinase C signalling on the plasma membrane Ca2+-ATPase activity of rat synaptosomes and leukocyte membranes

The influence of selected inhibitors of calcium signalling on the plasma membrane Ca2+-ATPase activity of rat synaptosomes and peritoneal leukocyte membranes was studied. The calmodulin inhibitor calmidazolium was an efficient inhibitor (50%) of the synaptosomal Ca2+-ATPase activity in a manner competitive with phosphatidylserine. The inhibition by CGS 9343B (30%) was not counteracted by phosphatidylserine. The intracellular calcium antagonist TMB-8 and the protein kinase inhibitor staurosporine and the derivatives CGP 41251 and CGP 42700 hardly affected the synaptosomal Ca2+-ATPase activity. The flavonoid quercetin was a more effective inhibitor of the ATPase activity of synaptosomal than of leukocyte membranes. Phloretin, at relatively high concentrations, caused only a modest inhibition of synaptosomes. The protein kinase C inhibitor sphingosine was a weak inhibitor of the synaptosomal but an effective inhibitor of the leukocyte membrane Ca2+-ATPase activity. The antineoplastic ether phospholipids BM 41.440 (ilmofosine) and ET-18-OCH3 (edelfosine) effectively inhibited the leukocyte membranes whereas the ATPase activity of synaptosomes was significantly increased by 20 microM and slightly inhibited by higher concentrations of these agents. The analogue hexadecylphosphocholine (miltefosine) did not affect the ATPase activity of the synaptosomes and only inhibited that of the leukocyte membranes at concentrations above 20 microM. These results show that several test substances of current interest affect the activity of the plasma membrane Ca2+-ATPase. The effects depend on the origin of the membranes. The investigation does not permit a distinction between direct effects on the enzyme and an interference with its membrane environment although the latter is indicated for the ether phospholipids.

Dietary borage oil alters plasma, hepatic and vascular tissue fatty acid composition in spontaneously hypertensive rats

Dietary borage oil rich in gamma-linolenic acid (GLA) has been shown to lower blood pressure in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). A potential mechanism for this effect may be attributed to changes in metabolism of GLA to dihomogamma-linolenic (DGLA) and arachidonic acids (AA). We investigated the effects of dietary borage oil on fatty acid composition in the plasma, liver and vascular tissue in WKY and SHR. The diet significantly increased the levels of omega-6 polyunsaturated fatty acids. GLA and DGLA levels in the plasma, liver, aorta and renal artery tissues increased in SHR (P < 0.001) and WKY (P < 0.001). AA levels were also increased in both plasma and liver of SHR (P < 0.05) and WKY (P < 0.05) fed the borage oil enriched diet. The results demonstrate that dietary borage oil produces marked changes in the metabolism of GLA which may contribute to its blood pressure lowering effect in WKY and SHR.

Lysophosphatidylcholine and Cellular Potassium Loss in Isolated Rabbit Ventricle

BACKGROUND: Lysophospholipids such as lysophosphatidylcholine (LPC) have many direct electrophysiological effects on cardiac muscle and have been implicated as a cause of lethal ventricular arrhythmias during acute myocardial ischemia. Because extracellular K(+) accumulation is also a key arrhythmogenic factor during acute ischemia, we examined the effects of LPC on cellular K(+) balance, including its interaction with adenosine triphosphate-sensitive K(+) (K(ATP)) channels. METHODS AND RESULTS: Isolated rabbit interventricular septa paced at 75 beats/min were loaded with (42)K(+) to measure unidirectional K(+) efflux rate (in (42)K(+) washout experiments) or tissue K(+) content ((42)K(+) uptake experiments) and action potential duration (APD) during exposure to 20 µM LPC for 30 minutes. LPC caused tissue K(+) content to decrease by 15 +/- 2% (n = 4) at a steady rate over 30 minutes, associated with gradual APD shortening and a delayed increase in unidirectional K(+) efflux rate. Pretreatment with 12 µM cromakalim to selectively activate K(ATP) channels shortened APD by 44 +/- 66% and had no effect on net tissue K(+) content during control aerobic perfusion. However, cromakalim increased net K(+) loss during exposure to LPC to 22 +/- 4%, a 47% increase. CONCLUSIONS: LPC induced net K(+) loss in heart, which was potentiated by the K(ATP) channel agonist cromakalim. This ATP finding suggests that if LPC accumulates to similar levels during myocardial ischemia and hypoxia, it may be an important mechanism in net K(+) loss.