Regulation of sodium channel gene expression by class I antiarrhythmic drugs and n - 3 polyunsaturated fatty acids in cultured neonatal rat cardiac myocytes

Pharmacological and nutritional targeting of voltage-gated sodium channels in the treatment of cancers

Voltage-gated sodium (NaV) channels, initially characterized in excitable cells, have been shown to be aberrantly expressed in non-excitable cancer tissues and cells from epithelial origins such as in breast, lung, prostate, colon, and cervix, whereas they are not expressed in cognate non-cancer tissues. Their activity was demonstrated to promote aggressive and invasive potencies of cancer cells, both in vitro and in vivo, whereas their deregulated expression in cancer tissues has been associated with metastatic progression and cancer-related death. This review proposes NaV channels as pharmacological targets for anticancer treatments providing opportunities for repurposing existing NaV-inhibitors or developing new pharmacological and nutritional interventions.

Structures Illuminate Cardiac Ion Channel Functions in Health and in Long QT Syndrome

The cardiac action potential is critical to the production of a synchronized heartbeat. This electrical impulse is governed by the intricate activity of cardiac ion channels, among them the cardiac voltage-gated potassium (Kv) channels KCNQ1 and hERG as well as the voltage-gated sodium (Nav) channel encoded by SCN5A. Each channel performs a highly distinct function, despite sharing a common topology and structural components. These three channels are also the primary proteins mutated in congenital long QT syndrome (LQTS), a genetic condition that predisposes to cardiac arrhythmia and sudden cardiac death due to impaired repolarization of the action potential and has a particular proclivity for reentrant ventricular arrhythmias. Recent cryo-electron microscopy structures of human KCNQ1 and hERG, along with the rat homolog of SCN5A and other mammalian sodium channels, provide atomic-level insight into the structure and function of these proteins that advance our understanding of their distinct functions in the cardiac action potential, as well as the molecular basis of LQTS. In this review, the gating, regulation, LQTS mechanisms, and pharmacological properties of KCNQ1, hERG, and SCN5A are discussed in light of these recent structural findings.

Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels

Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (Na_V), potassium (K_V), calcium (Ca_V), and proton (H_V) channels, as well as calcium-activated potassium (K_Ca), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1: The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2: The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3: The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4: The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5: The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels.

Lipid Regulation of Sodium Channels

The lipid landscapes of cellular membranes are complex and dynamic, are tissue dependent, and can change with the age and the development of a variety of diseases. Researchers are now gaining new appreciation for the regulation of ion channel proteins by the membrane lipids in which they are embedded. Thus, as membrane lipids change, for example, during the development of disease, it is likely that the ionic currents that conduct through the ion channels embedded in these membranes will also be altered. This chapter provides an overview of the complex regulation of prokaryotic and eukaryotic voltage-dependent sodium (Nav) channels by fatty acids, sterols, glycerophospholipids, sphingolipids, and cannabinoids. The impact of lipid regulation on channel gating kinetics, voltage-dependence, trafficking, toxin binding, and structure are explored for Nav channels that have been examined in heterologous expression systems, native tissue, and reconstituted into artificial membranes. Putative mechanisms for Nav regulation by lipids are also discussed.

Use of in vivo magnetic resonance spectroscopy for studying metabolic diseases

Owing to the worldwide obesity epidemic and the sedentary lifestyle in industrialized countries, the number of people with metabolic diseases is explosively increasing. Magnetic resonance spectroscopy (MRS), which is fundamentally similar to magnetic resonance imaging, can detect metabolic changes in vivo noninvasively. With its noninvasive nature, (1)H, (13)C and (31)P MRS are being actively utilized in clinical and biomedical metabolic studies to detect lipids and important metabolites without ionizing radiation. (1)H MRS can quantify lipid content in liver and muscle and can detect other metabolites, such as 2-hydroxyglutarate, in vivo. Of interest, many studies have indicated that hepatic and intramyocellular lipid content is inversely correlated with insulin sensitivity in humans. Thus, lipid content can be utilized as an in vivo biomarker for detecting early insulin resistance. Employing (13)C MRS, hepatic glycogen synthesis and breakdown can be directly detected, whereas (31)P MRS provides in vivo adenosine triphosphate (ATP) synthesis rates by saturation transfer methods in addition to ATP content. These in vivo data can be very difficult to assess by other methods and offer a critical piece of metabolic information. To aid the reader in understanding these new methods, fundamentals of MRS are described in this review in addition to promising future applications of MRS and its limitations.

Mitochondrial basis of the anti-arrhythmic action of lidocaine and modulation by the n-6 to n-3 PUFA ratio of cardiac phospholipids

The aim of this study was to evaluate the involvement of mitochondria in the mechanism of the anti-arrhythmic lidocaine. Rats were fed with a diet containing either n-6 polyunsaturated fatty acids (PUFAs, SSO group) or an equimolecular mixture of n-3 and n-6 PUFAs (FO group) for 8 weeks. The hearts were perfused according to the working mode using a medium with or without lidocaine 5 μm. They were then subjected to local ischemia (20 min) and reperfusion (30 min). Dietary n-3 PUFAs triggered the expected decrease in the n-6/n-3 PUFA ratio of cardiac phospholipids. Reperfusing the ischemic area favored the incidence of severe arrhythmias. Lidocaine treatment abolished almost completely reperfusion arrhythmias in the FO group, but did not display anti-arrhythmic properties in the SSO group. As it was indicated by measurements of the mitochondrial function, lidocaine seemed to favor mitochondrial calcium retention in the FO group, which might prevent cytosolic calcium spikes and reperfusion arrhythmias. In the SSO group, the resistance to lidocaine was associated with an aggravation of cellular damages. The mitochondrial calcium retention capacities were saturated, and lidocaine was unable to increase them, making the drug inefficient in preventing reperfusion arrhythmias.

Chronic administration of KB-R7943 induces up-regulation of cardiac NCX1

The NCX1 (sodium-calcium exchanger) is up-regulated in human heart failure and in many animal models of heart failure. The potential benefits and risks of therapeutically blocking NCX1 in heart failure and during ischemia-reperfusion are being actively investigated. In this study, we demonstrate that prolonged administration of the NCX1 inhibitor KB-R7943 resulted in the up-regulation of Ncx1 gene expression in both isolated adult cardiomyocytes and intact mouse hearts. Ncx1 up-regulation is mediated by the activation of p38. Importantly, p38 is not activated by KB-R7943 treatment in heart tubes from Ncx1(-/-) mice at 9.5 days postcoitum but is activated in heart tubes from Ncx1(+/+) mice. p38 activation does not appear to be in response to changes in cytosolic calcium concentration, [Ca(2+)](i). Interestingly, chronic KB-R7943 treatment in mice leads to the formation of an NCX1-p38 complex. Our study demonstrates for the first time that the electrogenic sarcolemma membrane cardiac NCX1 can act as a regulator of "activity-dependent signal transduction" leading to changes in gene expression.

Eicosapentaenoic acid inhibits voltage-gated sodium channels and invasiveness in prostate cancer cells

BACKGROUND AND PURPOSE

The voltage-gated Na(+) channels (Na(v)) and their corresponding current (I(Na)) are involved in several cellular processes, crucial to metastasis of cancer cells. We investigated the effects of eicosapentaenoic (EPA), an omega-3 polyunsaturated fatty acid, on I(Na) and metastatic functions (cell proliferation, endocytosis and invasion) in human and rat prostate cancer cell lines (PC-3 and Mat-LyLu cells).

EXPERIMENTAL APPROACH

The whole-cell voltage clamp technique and conventional/quantitative real-time reverse transcriptase polymerase chain reaction analysis were used. The presence of Na(v) proteins was shown by immunohistochemical methods. Alterations in the fatty acid composition of phospholipids after treatment with EPA and metastatic functions were also examined.

KEY RESULTS

A transient inward Na(+) current (I(Na)), highly sensitive to tetrodotoxin, and Na(V) proteins were found in these cells. Expression of Na(V)1.6 and Na(V)1.7 transcripts (SCN8A and SCN9A) was predominant in PC-3 cells, while Na(V)1.7 transcript (SCN9A) was the major component in Mat-LyLu cells. Tetrodotoxin or synthetic small interfering RNA targeted for SCN8A and SCN9A inhibited metastatic functions (endocytosis and invasion), but failed to inhibit proliferation in PC-3 cells. Exposure to EPA produced a rapid and concentration-dependent suppression of I(Na). In cells chronically treated (up to 72h) with EPA, the EPA content of cell lipids increased time-dependently, while arachidonic acid content decreased. Treatment of PC-3 cells with EPA decreased levels of mRNA for SCN9A and SCN8A, cell proliferation, invasion and endocytosis.

CONCLUSION AND IMPLICATIONS

Treatment with EPA inhibited I(Na) directly and also indirectly, by down-regulation of Na(v) mRNA expression in prostate cancer cells, thus inhibiting their metastatic potential.

Inhibition of delayed rectifier potassium channels and induction of arrhythmia: a novel effect of celecoxib and the mechanism underlying it

Selective inhibitors of cyclooxygenase-2 (COX-2), such as rofecoxib (Vioxx), celecoxib (Celebrex), and valdecoxib (Bextra), have been developed for treating arthritis and other musculoskeletal complaints. Selective inhibition of COX-2 over COX-1 results in preferential decrease in prostacyclin production over thromboxane A2 production, thus leading to less gastric effects than those seen with nonselective COX inhibitors such as acetylsalicylic acid (aspirin). Here we show a novel effect of celecoxib via a mechanism that is independent of COX-2 inhibition. The drug inhibited the delayed rectifier (Kv2) potassium channels from Drosophila, rats, and humans and led to pronounced arrhythmia in Drosophila heart and arrhythmic beating of rat heart cells in culture. These effects occurred despite the genomic absence of cyclooxygenases in Drosophila and the failure of acetylsalicylic acid, a potent inhibitor of both COX-1 and COX-2, to inhibit rat Kv2.1 channels. A genetically null mutant of Drosophila Shab (Kv2) channels reproduced the cardiac effect of celecoxib, and the drug was unable to further enhance the effect of the mutation. These observations reveal an unanticipated effect of celecoxib on Drosophila hearts and on heart cells from rats, implicating the inhibition of Kv2 channels as the mechanism underlying this effect.

n-3 PUFAs-From dietary supplements to medicines

Although there has been a great progress in the prevention of cardiovascular diseases, the mortality of patients with acute myocardial infarction (AMI) still remains high. One of the most important underlying causes explaining this phenomenon is the sudden cardiac death. Nearly half of all cardiovascular deaths in the USA each year is attributed to this unpredictable and unexpected complication of AMI. Hence, there is an urgent medical need for a targeted therapy to reduce the incidence of sudden cardiac death. Since 1980 there have been several epidemiological and other studies concerning the benefits of n-3 polyunsaturated fatty acids (n-3 PUFAs) in cardiovascular health and prevention. Results from one of the largest studies, GISSI Prevenzione Trial show that adding the n-3 PUFAs to standard therapy of patients who survived AMI reduces sudden cardiac death (44% risk reduction, p=0.0006). In addition, significant decline in all-cause cardiovascular mortality (21% risk reduction, p=0.0064) further emphasizes the role of n-3 PUFA in cardiovascular prevention. To date, beneficial effects of n-3 PUFA are attributed to their antiarrhythmic, lipid lowering, antithrombotic and anti-inflammatory properties. To conclude, EPA and DHA improve the prognosis of cardiovascular patients in the secondary prevention of sudden cardiac death without any documented side effects.

Prevention of sudden cardiac death by n-3 polyunsaturated fatty acids

There were already several epidemiologic studies that showed eating fish frequently seemed to reduce deaths from coronary heart disease. There were also observational and clinical trials, which more specifically showed that the reduction in cardiovascular deaths from eating fish were largely the result of n-3 polyunsaturated fatty acids in fish oil for the prevention of sudden cardiac death (SCD). This led me to perform a clinical trial in which all subjects had an implanted cardioverter-defibrillator and were at very high risk of SCD. The results of this study and the mechanisms by which the n-3 fish oil fatty acids prevent fatal cardiac arrhythmias will be the subject of this review.

Effects of Mexiletine on Electrical Field Stimulation-Induced Contractile Responses in the Ipsilateral and Contralateral Vasa Deferentia after Unilateral Testicular Torsion/Detorsion

AIM

To investigate testicular torsion-induced changes on the electrical field stimulation (EFS)-induced contractions in rabbit vasa deferentia and to evaluate the effect of mexiletine.

METHODS

18 male New Zealand albino rabbits were used in this experiment. Rabbits were divided into three groups: (1) control group (n = 6); (2) torsion group (n = 6), and (3) mexiletine group (n = 6). In the control group, vasa deferentia on both sides were harvested. In the torsion and mexiletine groups, the left testes of the rabbits were subjected to 720 degrees of clockwise torsion for 2 h and then detorsion was performed. In the mexiletine group, 50 mg/kg i.p. mexiletine was administered 1 h before detorsion. Following 24 h of the torsion, vasa deferentia on both sides were harvested and 2-cm strips including both the prostatic and epididymal portions were prepared to record EFS-induced contractions.

RESULTS

Testicular torsion caused a significant inhibition in both phases of EFS-induced biphasic contractions of the ipsi- and contralateral vasa deferentia. Mexiletine treatment did not affect these inhibitory responses. Torsion/detorsion of the spermatic cord did not alter exogenously applied noradrenaline-induced contractions in both vasa deferentia. However, KCl-induced contractions diminished significantly in ipsilateral vas deferens of the torsion group and mexiletine restored this inhibition.

CONCLUSIONS

Unilateral testicular torsion/detorsion leads to inhibition in both phases of EFS-induced biphasic contractions of the ipsi- and contralateral vasa deferentia by causing a defect in presynaptic nerve transmission. However, mexiletine has no effect on this inhibition. Inhibition of the KCl-induced contractions in the ipsilateral vas deferens, which indicates postsynaptic tissue damage, is restored by administering mexiletine 1 h prior to detorsion.

Antiarrhythmic effects of omega-3 fatty acids

Fish oil, and omega-3 fatty acids in particular, have been found to reduce plasma levels of triglycerides and increase levels of high-density lipoprotein in patients with marked hypertriglyceridemia, and a pharmaceutical-grade preparation has recently received approval from the US Food and Drug Administration to market for this purpose. However, in both bench research studies and clinical trials, evidence for clinically significant antiarrhythmic properties has also been detected in association with omega-3 fatty acid intake. Arguably the most significant finding in this data set was the reduction in the incidence of sudden death in survivors of myocardial infarction in the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico (GISSI)-Prevenzione trial and the subsequent recommendation for administration of fish oil as part of the postinfarction regimen in Europe. This article reviews in detail the basic and clinical research studies of fish oil as an antiarrhythmic entity, the forms of preparation and/or administration that appear to possess these properties and those that do not, the types of arrhythmias (ventricular ectopy and atrial fibrillation as well as ventricular tachyarrhythmias) that have been beneficially affected by fish oil administration, and the presumed and known mechanisms by which the beneficial actions are exerted.

Effects of n-3 polyunsaturated fatty acid on upper limit of vulnerability shocks

BACKGROUND

Ventricular fibrillation (VF) can be induced when a strong shock is delivered during the vulnerable period of a cardiac cycle. VF, however, cannot be induced if the shock strength is increased to the "upper limit of vulnerability" (ULV) level. Docosahexaenoic acid (DHA) has been shown to prevent the occurrence of VF after coronary occlusion. However, its effects on the ULV have not been verified. We tested the hypothesis that ULV shock strength is decreased after DHA administration.

METHODS

In 10 pigs, 10 S1s (square, 5-ms) were delivered from the RV apex electrode at 300 ms cycle length. Shocks (S2, biphasic) were delivered from the RV-SVC electrodes after the last S1. The ULV was determined using an up/down protocol. In group 1 (n = 5), after the control ULV was determined at the beginning of the study, a solution containing 1.0 gm of DHA was infused intravenously within 90 min. The ULV (DHA-ULV) was determined again after the end of infusion. In group 2 (n = 5), the vehicle for DHA was infused instead of DHA to confirm that the vehicle did not have an effect on the ULV.

RESULTS

DHA-ULV (412 +/- 58 V, 12 +/- 3 J) was significantly decreased (P < 0.04) compared to the control ULV (478 +/- 32 V, 16 +/- 3 J). The ULV before (483 +/- 28 V, 16 +/- 1 J) and after (463 +/- 28 V, 15 +/- 2 J) the vehicle infusion was not different (P = 0.4). There was no change in the systolic blood pressure as well as heart rate in both groups.

CONCLUSION

DHA significantly decreases the ULV (13% by voltage and 25% by energy), suggesting that DHA can help to prevent VF induced by a strong stimulus delivered during the vulnerable period.

Docosahexaenoic acid (omega−3) blocks voltage-gated sodium channel activity and migration of MDA-MB-231 human breast cancer cells

Omega-3 polyunsaturated fatty acids have been suggested to play an important role in cancer prevention/progression, on the one hand, and in modulation of membrane ion channels on the other. We investigated whether docosahexaenoic acid would influence the in vitro migration of MDA-MB-231 human breast cancer cells. An important follow-up question was whether any effect would involve voltage-gated Na(+) channels, shown previously to occur in human breast cancer in vitro and in vivo and to correlate with metastatic potential. Short-term (acute) and long-term (24-72 h) application of docosahexaenoic acid suppressed the activity of the channel activity in a dose-dependent manner. At the working concentrations of docosahexaenoic acid used (0.05-0.5 microM), there was no effect on proliferation. Long-term treatment with docosahexaenoic acid down-regulated mRNA and protein (total and plasma membrane) levels of neonatal Nav1.5 voltage-gated Na(+) channel, known to be predominant in these cells. Docosahexaenoic acid suppressed migration of the MDA-MB-231 cells to the same extent as tetrodotoxin, a highly specific blocker of voltage-gated Na(+) channels, but the two effects were not additive. It was concluded that the docosahexaenoic acid-induced suppression of cellular migration occurred primarily via down-regulation of voltage-gated Na(+) channel (neonatal Nav1.5) mRNA and functional protein expression.

Acute and chronic effects of eicosapentaenoic acid on voltage-gated sodium channel expressed in cultured human bronchial smooth muscle cells

This study investigated acute and chronic effects of eicosapentaenoic acid (EPA) on voltage-gated Na+ current (I(Na)) expressed in cultured human bronchial smooth muscle cells (hBSMCs). The whole-cell voltage clamp technique and quantitative real-time RT-PCR analysis were applied. The alterations in the fatty acid composition of phospholipids after treatment with EPA were also examined. Extracellular application of EPA produced a rapid and concentration-dependent suppression of tetrodotoxin-sensitive I(Na) with the half-maximal inhibitory concentration of 2 microM. After washing out EPA with albumin, I(Na) returned to the control level. Similar inhibitory effects were observed regarding other fatty acids (docosahexaenoic, arachidonic, stearic, and oleic acids), but EPA was the most potent inhibitor. The effect of EPA on I(Na) was not blocked by nordihydroguaiaretic acid and indometacin, and was accompanied by a significant shift of the steady-state inactivation curve to more negative potentials. In cells chronically treated with EPA, the EPA content of the cell lipid fraction (mol%) increased time-dependently, while arachidonic acid (AA) decreased, resulting in an increase of EPA to AA ratio. Then, the level of mRNA (SCN9A) encoding I(Na) decreased significantly. These results provide novel evidence that EPA not only rapidly inhibits I(Na), but also reduces the mRNA levels of the Na+ channel after cellular incorporation of EPA in cultured hBSMCs.

Membrane Effects of the n-3 Fish Oil Fatty Acids, which Prevent Fatal Ventricular Arrhythmias

Fish oil fatty acids are known to exert beneficial effects on the heart and vascular systems. We have studied the membrane effects on ion channel conductance by the n-3 fish oil fatty acids that account for these beneficial effects. We have confirmed that these fatty acids prevent fatal cardiac arrhythmias in a reliable dog model of sudden cardiac death. This finding was followed by experiments indicating that the n-3 fatty acids electrically stabilize heart cells and do so largely through modulation of the fast voltage-dependent Na(+) currents and the L-type Ca(2+) channels in a manner, which makes the heart cells resistant to arrhythmias. Others and we have demonstrated that these membrane effects on the heart can prevent fatal cardiac arrhythmias in humans.

Tandem Promoters and Developmentally Regulated 5′- and 3′-mRNA Untranslated Regions of the Mouse Scn5a Cardiac Sodium Channel

The SCN5A gene encodes a voltage-sensitive sodium channel expressed in cardiac and skeletal muscle. Coding region mutations cause cardiac sudden death syndromes and conduction system failure. Polymorphisms in the 5'-sequence adjacent to the SCN5A gene have been linked to cardiac arrhythmias. We identified three alternative 5'-splice variants (1A, 1B, and 1C) of the untranslated exon 1 and two 3'-variants in the murine Scn5a mRNA. Two of the exon 1 isoforms (1B and 1C) were novel when compared with the published human and rat SCN5A sequences. Quantitative real time PCR results showed that the abundance of the isoforms varied during cardiac development. The 1A, 1B, and 1C mRNA splice variants increased 7.8 +/- 1.7-fold (E1A), 6.0 +/- 1.0-fold (E1B), and 20.6 +/- 3.7-fold (E1C) from fetal to adult heart, respectively. Promoter deletion and luciferase reporter gene analysis using cardiac and skeletal muscle cell lines demonstrated a pattern of distinct cardiac-specific enhancer elements associated with exons 1A and 1C. In the case of exon 1C, the enhancer element appeared to be within the exon. A 5'-repressor preceded each cardiac enhancer element. We concluded that the murine Na(+) channel has both 5'- and 3'-untranslated region mRNA variants that are developmentally regulated and that the promoter region contains two distinct cardiac-specific enhancer regions. The presence of homologous human splicing suggests that that these regions may be fruitful new areas of study in understanding cardiac sodium channel regulation and the genetic susceptibility to sudden death.

Modulation of epithelial Na+ channel activity by long-chain n-3 fatty acids

The epithelial sodium channel is found in apical membranes of a variety of native epithelial tissues, where it regulates sodium and fluid balance. In vivo, a number of hormones and other endogenous factors, including polyunsaturated fatty acids (PUFAs), regulate these channels. We tested the effects of essential n-3 and n-6 PUFAs on amiloride-sensitive sodium transport in A6 epithelial cells. Eicosapentaenoic acid [EPA; C20:5(n-3)] transiently stimulated amiloride-sensitive open-circuit current (I(Na)) from 4.0 +/- 0.3 to 7.7 +/- 0.3 microA/cm2 within 30 min (P < 0.001). No activation was seen in the presence of 10 microM amiloride. In cell-attached but not in cell-excised patches, EPA acutely increased the open probability of sodium channels from 0.45 +/- 0.08 to 0.63 +/- 0.10 (P = 0.02, paired t-test). n-6 PUFAs, including linoleic acid (C18:2), eicosatetraynoic acid (C20:4), and docosapentanoic acid (C22:5) had no effect, whereas n-3 docosahexanoic acid (C22:6) activated amiloride-sensitive I(Na) in a manner similar to EPA. Activation of I(Na) by EPA was prevented by H-89, a PKA inhibitor. Similarly, PKA activity was stimulated by EPA. Nonspecific stimulation of phosphodiesterase activity by CoCl2 completely prevented the effect of EPA on sodium transport. We conclude that n-3 PUFAs activate epithelial sodium channels downstream of cAMP in a cAMP-dependent pathway also involving PKA.

Effect of hypo- and hyperthyroid states on phospholipid composition in developing rat heart

The aim of this study was to examine the effect of hypo- and hyperthyroidism on the phospholipid composition in developing rat heart. The hypothyroid state (PTU) was induced by 0.05% 6-n-propyl-2-thiouracil in drinking water given to nursing mothers from the postnatal day 2-21. The hyperthyroidism (T3) was made by daily injection of 3,3',5-triiodo-L-thyronine (10 microg/100 g body wt) to newborns in the same time period. Age matched intact littermates were taken as euthyroid controls. PTU decreased the concentration of total phospholipids (PL), choline phosphoglycerides (PC), ethanolamine phosphoglycerides (PE) and diphosphatidylglycerol (DPG) and increased the proportion of plasmalogen component of PE (PLPE). T3 increased the concentration of PL, PC, PE, DPG and decreased PLPE in comparison with euthyroid controls. The ratio of saturated/unsaturated fatty acids (FA) in PE was decreased in PTU and increased in T3 group. The ratio of n-6/n-3 polyunsaturated FA in PC, PE and phosphatidylinositol (PI) was increased in PTU due to increase of 18:2n-6 and decrease of 22:6n-3 proportion. T3 decreased this ratio because of decline in 20:4n-6 and rise in 22:6n-3 proportion. Both hypo- and hyperthyroidism decreased the ratio of 20:4n-6/18:2n-6 in the majority of phospholipids. PTU decreased the unsaturation index in PC, PI and phosphatidylserine. It is concluded that thyroid state plays an essential role in the development of membrane phospholipid components in cardiac membranes during the early postnatal period.

Prevention of sudden cardiac death by n-3 polyunsaturated fatty acids

This is a review of our present understanding of the mechanism by which the n-3 polyunsaturated fatty acids (PUFA) in fish oils prevent fatal ventricular arrhythmias in animals and cultured heart cells. A brief review of three clinical trials that suggest that these PUFAs prevent sudden cardiac death is also included in order to emphasize the potential importance of these fatty acids in human nutrition. The PUFAs act by stabilizing electrically every cardiac myocyte by modulating conductance of ion channels in the sarcolemma, particularly the fast, voltage-dependent sodium current and the L-type calcium currents, though other ion currents are also affected. Work in progress suggests that the primary site of action of the PUFAs may be on the phospholipid bilayer of the heart cells in the microdomains through which the ion channels penetrate the membrane bilayer in juxtaposition with the ion channels rather than directly on the channel protein itself. These PUFAs then allosterically alter the conformation and conductance of the channels. Both potential benefits and possible adverse effects of the PUFAs in man will be discussed. Knowing that the ion channels have been structurally conserved among all excitable tissues, we tested their effects on the electrophysiology of rat hippocampal CA1 neurons and found that the sodium and calcium ion channels in these neurons were also affected by PUFAs. An attempt to show the place of the PUFAs in human nutrition during the 2-4 million years of our evolution will conclude the review.

In vivo characterization of fatty acids in human adipose tissue using natural abundance 1H decoupled 13C MRS at 1.5 T: clinical applications to dietary therapy

Natural abundance proton-decoupled (13)C magnetic resonance spectroscopy was used to establish the in vivo lipid composition of normal adipose tissue and the corresponding effects of altered lipid diets. Experiments were performed on a standard 1.5 T clinical MR scanner using a double-tuned (1)H-(13)C coil. Peaks from double-bonded and methylene carbons were analyzed. Normal lipid composition was established in 20 control subjects. For comparison, five subjects on altered lipid diets were studied. Four subjects were on a fish oil supplement diet or predominantly seafood diet (polyunsaturated fatty acids), and one subject was on a Lorenzo's oil diet (monounsaturated fatty acids). Well-resolved (13)C spectra were obtained from the calf adipose tissue with a total acquisition time of 10 min. Model oil solutions were used to identify specific (13)C resonances. Subjects on lipid diets showed significantly elevated levels of monounsaturated and polyunsaturated fatty acids for Lorenzo's and fish oil diets, respectively. We conclude that (13)C MR spectroscopy can readily detect changes in lipid composition due to medium- and long-term therapeutic lipid diets. Since the examination is rapid, robust and noninvasive, opportunities arise for large clinical trials of preventive or therapeutic diets to be performed with (13)C MRS on a clinical MR scanner.

Differential effects of bupivacaine enantiomers, ropivacaine and lidocaine on up-regulation of cell surface voltage-dependent sodium channels in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, (+/-)-bupivacaine inhibited veratridine-induced 22Na(+) influx (IC(50) 6.8 microM). The IC(50) of (+)-bupivacaine (2.8 microM) was 6.2-, 7.4-, and 17.1-fold lower than those of (-)-bupivacaine (17.3 microM), (-)-ropivacaine (20.6 microM), and lidocaine (47.8 microM). Chronic (i.e. 3-h) treatment of cells with (+/-)-bupivacaine increased cell surface [3H]saxitoxin ([3H]STX) binding capacity by 48% (EC(50) of 233 microM; t(1/2)=7.4 h), without changing the K(d) value. Treatment for 24 h with either (+)- or (-)-bupivacaine, or (-)-ropivacaine elevated [3H]STX binding, whereas 24-h treatment with lidocaine had no effect. The rise of [3H]STX binding by (+/-)-bupivacaine was prevented by cycloheximide, an inhibitor of protein synthesis, or brefeldin A, an inhibitor of cell surface vesicular exit from the trans-Golgi network; however, (+/-)-bupivacaine did not increase Na(+) channel alpha- and beta(1)-subunit mRNA levels. In cells subjected to (+/-)-bupivacaine treatment (1 mM for 24 h) followed by 3-h washout, veratridine-induced 22Na(+) influx was enhanced, even when measured in the presence of ouabain, an inhibitor of Na(+),K(+)-ATPase. Ptychodiscus brevis toxin-3 potentiated veratridine-induced 22Na(+) influx by 2.3-fold in the (+/-)-bupivacaine-treated cells, as in non-treated cells. These results suggest that lipophilic bupivacaine enantiomers or (-)-ropivacaine acutely inhibit Na(+) channel gating, whereas its chronic treatment up-regulates cell surface expression of Na(+) channels via translational and externalization events.

Could n-3 polyunsaturated fatty acids reduce pathological pain by direct actions on the nervous system?

The intake of n-3 polyunsaturated fatty acids (PUFAs) in many industrialized countries is relatively low and its increased consumption has protective and modifying effects on such diverse conditions as atherosclerosis, ventricular arrhythmias, multiple sclerosis, major depression and inflammatory and autoimmune diseases. In addition, n-3 PUFAs have been shown to alleviate pain in patients with rheumatoid arthritis, inflammatory bowel disease and in a number of other painful conditions. This has been attributed to the inhibition of pro-inflammatory eicosanoid and cytokine production by peripheral tissues. n-3 PUFAs have also been shown to inhibit eicosanoid production in glial cells, block voltage-gated sodium channels (VGSCs), inhibit neuronal protein kinases and modulate gene expression. They also appear to have mood-stabilizing and sympatholytic effects. The present article explores the possibility that, based on what is known about their neural and non-neural effects, n-3 PUFAs directly attenuate the neuronal and glial processes that underlie neuropathic and inflammatory pain.

Fatty acid augmentation of the cardiac slowly activating delayed rectifier current (IKs) is conferred by hminK

The mechanism by which dietary fatty acids confer protection against cardiac arrhythmias and sudden cardiac death is not resolved. Here, we study the effects of several known cardio-protective and arrhythmogenic fatty acids on the slowly activating delayed rectifier potassium current (IKs), which is responsible for the repolarization phase of the cardiac action potential. cRNAs encoding either or both of the two subunits, KvLQT1 and hminK, that together produce IKs, were injected into Xenopus oocytes, and the effects of various fatty acids were determined. Docosahexaenoic acid (DHA) significantly augmented IKs as did the short-chained fully saturated lauric acid, and to a lesser extent the cis-unsaturated oleic acid. Eicosapentaenoic acid (EPA) was without significant effect on current magnitude, although it reduced the rate of activation. These results suggest that not all "antiarrhythmic" fatty acids target the same channel. To examine the role of hminK in this response, KvLQT1 was expressed alone. In this case, DHA, lauric acid, and oleic acid did not augment current, suggesting that hminK confers fatty acid sensitivity to IKs.

Heat acclimation in rats: modulation via lipid polyunsaturation

Heat acclimation of rats has been shown to enhance endurance of rat hearts to ischemic insult and acute heat stress. Common protective features have been shown to be operative during both these stress-inducing conditions. To explore the role of membrane lipid composition in the adaptive response, we analyzed two major parameters that impact membrane dynamics and order, the nonesterified cholesterol levels and the acyl chain composition of phospholipids, in rat heart and salivary glands, both major thermoregulatory organs, in short- and long-term heat-acclimated rats. Before exposure to heat, control salivary gland tissue has a higher cholesterol-to-phospholipid mole ratio (0.32 +/- 0.02) than heart (0.14 +/- 0.01), and the acyl chains of its phospholipids are 50% more saturated. The remodeling strategies of the tissues after exposure to heat differed. Heart cholesterol levels increased after short-term heat acclimation (approximately 50%), whereas salivary gland cholesterol levels decreased in acute heat stress and long-term heat acclimation (approximately 32%). Remodeling of phospholipid acyl chains, particularly an increase in docosahexaenoic acid, was a protective strategy in both tissues (57% in heart and >100% in salivary glands). Modifying membrane lipid composition by treating rats with liposomes composed of egg phosphatidylcholine (PC) before exposure to heat resulted in a 38% increase in endurance to thermal stress. The density and affinity of muscarinic receptors of submaxillary salivary glands, involved in the acclimation response, were measured in control and PC liposome-treated rats, and then both groups were subjected to short-term heat acclimation. After PC treatment the well-established compensatory upregulation of the muscarinic receptors and concomitant decrease in their affinity was blunted. The substantial increase in the thermal endurance of heat-challenged intact rats after treatment with PC liposomes (600 vs. 200 min) suggests that membrane lipid composition plays a role in the ability of these tissues to respond to heat stress.

Short- and long-term differential effects of neuroprotective drug NS-7 on voltage-dependent sodium channels in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride], a newly-synthesized neuroprotective drug, inhibited veratridine-induced (22)Na(+) influx via voltage-dependent Na(+) channels (IC(50)=11.4 microM). The inhibition by NS-7 occurred in the presence of ouabain, an inhibitor of Na(+),K(+) ATPase, but disappeared at higher concentration of veratridine, and upon the washout of NS-7. NS-7 attenuated veratridine-induced (45)Ca(2+) influx via voltage-dependent Ca(2+) channels (IC(50)=20.0 microM) and catecholamine secretion (IC(50)=25.8 microM). Chronic (>/=12 h) treatment of cells with NS-7 increased cell surface [(3)H]-STX binding by 86% (EC(50)=10.5 microM; t(1/2)=27 h), but did not alter the K(D) value; it was prevented by cycloheximide, an inhibitor of protein synthesis, or brefeldin A, an inhibitor of vesicular transport from the trans-Golgi network, but was not associated with increased levels of Na(+) channel alpha- and beta(1)-subunit mRNAs. In cells subjected to chronic NS-7 treatment, (22)Na(+) influx caused by veratridine (site 2 toxin), alpha-scorpion venom (site 3 toxin) or beta-scorpion venom (site 4 toxin) was suppressed even after the extensive washout of NS-7, and veratridine-induced (22)Na(+) influx remained depressed even at higher concentration of veratridine; however, either alpha- or beta-scorpion venom, or Ptychodiscus brevis toxin-3 (site 5 toxin) enhanced veratridine-induced (22)Na(+) influx as in nontreated cells. These results suggest that in the acute treatment, NS-7 binds to the site 2 and reversibly inhibits Na(+) channels, thereby reducing Ca(2+) channel gating and catecholamine secretion. Chronic treatment with NS-7 up-regulates cell surface Na(+) channels via translational and externalization events, but persistently inhibits Na(+) channel gating without impairing the cooperative interaction between the functional domains of Na(+) channels.

Gene targets related to phospholipid and fatty acid metabolism in schizophrenia and other psychiatric disorders: an update

Phospholipids make up about 60% of the brain's dry weight and play key roles in many brain signal tranduction mechanisms. A recent review(1)identified the increasing evidence that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. This current paper reviews the main pathways of phospholipid metabolism, emphasizing the role of phospholipases of the A2 in signal tranduction processes. It also updates the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.

New gene targets related to schizophrenia and other psychiatric disorders: enzymes, binding proteins and transport proteins involved in phospholipid and fatty acid metabolism

Phospholipids make up about 60% of the brain's dry weight. In spite of this, phospholipid metabolism has received relatively little attention from those seeking genetic factors involved in psychiatric and neurological disorders. However, there is now increasing evidence from many quarters that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. To date the possible specific proteins and genes involved have been relatively ill-defined. This paper reviews the main pathways of phospholipid metabolism, emphasizing the roles of phospholipases of the A2 and C series in signal transduction processes. It identifies some likely protein candidates for involvement in psychiatric and neurological disorders. It also reviews the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.

Prevention of ischemia-induced cardiac sudden death by n-3 polyunsaturated fatty acids in dogs

The objective of this study was to obtain functional information associated with the prevention by n-3 polyunsaturated fatty acids (PUFA) of ischemia-induced fatal cardiac ventricular arrhythmias in the intact, conscious, exercising dog. Thirteen dogs susceptible to ischemia-induced ventricular fibrillation were prepared surgically by ligation of their anterior descending left coronary artery and placement of an inflatable cuff around their left circumflex artery. After 4 wk of recovery, exercise-plus-ischemia tests were performed without and then with an intravenous infusion of an emulsion of free n-3 PUFA just prior to occluding the left circumflex artery while the animals were running on a treadmill. One week later the exercise-plus-ischemia test was repeated but with a control infusion replacing the emulsion of n-3 PUFA. The infusion of the free n-3 PUFA in quantities of 1.0 to 10 g prevented ventricular fibrillation in 10 of the 13 dogs tested (P < 0.005), apparently without esterification of the PUFA into membrane phospholipids. The antiarrhythmic effect of the n-3 PUFA was associated with slowing of the heart rate, shortening of the QT-interval (electrical action potential duration), reduction of left ventricular systolic pressure, and prolongation of the electrocardiographic atrial-ventricular conduction time (P-R interval). These effects are comparable with those we have reported in studies with cultured neonatal rat cardiac myocytes.