31P NMR of tissue phospholipids: competition for Mg2+, Ca2+, Na+ and K+ cations

Subclinical Cardiovascular Disease Markers in Relation to Serum and Dietary Magnesium in Individuals from the General Population: The KORA-MRI Study

Several studies have implied a role of magnesium in the development of cardiovascular disease (CVD). Thus, magnesium might serve as a potential risk marker for early CVD. Therefore, we investigated the association of serum magnesium and dietary magnesium intake with markers of subclinical CVD in a population-based study. We used cross-sectional data from the sub-study of the Cooperative Health Research in the Region of Augsburg (KORA-FF4). Markers of subclinical CVD, namely, left and right ventricular structure and function and carotid plaque and carotid wall thickness, were derived by magnetic resonance imaging (MRI). Multivariable-adjusted regression models were applied to assess the relationship between serum and dietary magnesium and MRI-derived subclinical CVD markers. Among 396 included participants (mean age: 56.3 ± 9.2 years; 57.8% male), 181 (45.7%) had low serum magnesium levels (<2.07 mg/dL). Among 311 subjects with complete dietary data (mean age: 56.3 ± 9.1 years; 56.3% male), 154 (49.5%) had low dietary magnesium intake (≤155.2 mg/1000 kcal/day). Serum and dietary magnesium were not correlated (p-value = 0.5). Serum magnesium was significantly associated with presence of carotid plaque (OR 1.62, p-value 0.033). Dietary magnesium was associated with higher left ventricular end-systolic and end-diastolic volume (0.04 mL/m2, 0.06 mL/m2; p-value 0.011, 0.013, respectively), and also with a decrease in left ventricular remodeling index and mean diastolic wall thickness (−0.001 g/mL/m2, −0.002 mm/m2; p-value 0.004, 0.029, respectively). In summary, there was no consistent association of serum and dietary magnesium with imaging markers of subclinical CVD.

Promotion of plasmalogen biosynthesis reverse lipid changes in a Barth Syndrome cell model

In Barth syndrome (BTHS) mutations in tafazzin leads to changes in both the quantities and the molecular species of cardiolipin (CL), which are the hallmarks of BTHS. Contrary to the well-established alterations in CL associated with BTHS; recently a marked decrease in the plasmalogen levels in Barth specimens has been identified. To restore the plasmalogen levels, the present study reports the effect of promotion of plasmalogen biosynthesis on the lipidome of lymphoblasts derived from Barth patients as well as on cell viability, mitochondria biogenesis, and mitochondrial membrane potential. High resolution ³¹P NMR phospholipidomic analysis showed an increase in the levels of plasmenylethanolamine (the major plasmalogen in lymphoblasts), which reached values comparable to the control and a compensatory decrease in the levels of its diacyl-PE counterpart. Importantly, ³¹P NMR showed a significant increase in the levels of CL, while not altering the levels of monolysocardiolipin. Mass spectrometry measurements showed that the promotion of plasmalogen biosynthesis did not change the molecular species profile of targeted phospholipids. In addition, promotion of plasmalogen biosynthesis did not impact on cellular viability, although it significantly decrease mitochondria copy number and restored mitochondrial membrane potential. Overall, the results showed the efficacy of the promotion of plasmalogen biosynthesis on increasing the CL levels in a BTHS cell model and highlight the potential beneficial effect of a diet supplemented with plasmalogen precursors to BTHS patients.

Plasmalogen loss caused by remodeling deficiency in mitochondria

Lipid homeostasis is crucial in human health. Barth syndrome (BTHS), a life-threatening disease typically diagnosed with cardiomyopathy and neutropenia, is caused by mutations in the mitochondrial transacylase tafazzin. By high-resolution 31P nuclear magnetic resonance (NMR) with cryoprobe technology, recently we found a dramatic loss of choline plasmalogen in the tafazzin-knockdown (TAZ-KD) mouse heart, besides observing characteristic cardiolipin (CL) alterations in BTHS. In inner mitochondrial membrane where tafazzin locates, CL and diacyl phosphatidylethanolamine are known to be essential via lipid-protein interactions reflecting their cone shape for integrity of respiratory chain supercomplexes and cristae ultrastructure. Here, we investigate the TAZ-KD brain, liver, kidney, and lymphoblast from patients compared with controls. We identified common yet markedly cell type-dependent losses of ethanolamine plasmalogen as the dominant plasmalogen class therein. Tafazzin function thus critically relates to homeostasis of plasmalogen, which in the ethanolamine class has conceivably analogous and more potent molecular functions in mitochondria than diacyl phosphatidylethanolamine. The present discussion of a loss of plasmalogen-protein interaction applies to other diseases with mitochondrial plasmalogen loss and aberrant forms of this organelle, including Alzheimer's disease.

Substantial Decrease in Plasmalogen in the Heart Associated with Tafazzin Deficiency

Tafazzin is the mitochondrial enzyme that catalyzes transacylation between a phospholipid and a lysophospholipid in remodeling. Mutations in tafazzin cause Barth syndrome, a potentially life-threatening disease with the major symptom being cardiomyopathy. In the tafazzin-deficient heart, cardiolipin (CL) acyl chains become abnormally heterogeneous unlike those in the normal heart with a single dominant linoleoyl species, tetralinoleoyl CL. In addition, the amount of CL decreases and monolysocardiolipin (MLCL) accumulates. Here we determine using high-resolution 31P nuclear magnetic resonance with cryoprobe technology the fundamental phospholipid composition, including the major but oxidation-labile plasmalogens, in the tafazzin-knockdown (TAZ-KD) mouse heart as a model of Barth syndrome. In addition to confirming a lower level of CL (6.4 ± 0.1 → 2.0 ± 0.4 mol % of the total phospholipid) and accumulation of MLCL (not detected → 3.3 ± 0.5 mol %) in the TAZ-KD, we found a substantial reduction in the level of plasmenylcholine (30.8 ± 2.8 → 18.1 ± 3.1 mol %), the most abundant phospholipid in the control wild type. A quantitative Western blot revealed that while the level of peroxisomes, where early steps of plasmalogen synthesis take place, was normal in the TAZ-KD model, expression of Far1 as a rate-determining enzyme in plasmalogen synthesis was dramatically upregulated by 8.3 (±1.6)-fold to accelerate the synthesis in response to the reduced level of plasmalogen. We confirmed lyso-plasmenylcholine or plasmenylcholine is a substrate of purified tafazzin for transacylation with CL or MLCL, respectively. Our results suggest that plasmenylcholine, abundant in linoleoyl species, is important in remodeling CL in the heart. Tafazzin deficiency thus has a major impact on the cardiac plasmenylcholine level and thereby its functions.

Association of magnesium in serum and urine with carotid intima-media thickness and serum lipids in middle-aged and elderly Chinese: a community-based cross-sectional study

OBJECTIVE

Previous studies suggested that magnesium (Mg) might protect against atherosclerosis, but data were scarce in an Asian population. We examined the association of Mg levels in serum and urine with carotid intima-media thickness (cIMT) and serum lipids in Chinese adults.

METHODS

This community-based cross-sectional study recruited 2,837 participants aged 40-75 years in Guangzhou, China. General information, lifestyle factors, serum and urinary concentrations of Mg and cardiometabolic factors were determined. The cIMTs of the common carotid artery (CCA) and the carotid bifurcation (BIF) were measured ultrasonographically.

RESULTS

The mean (SD) concentration of serum Mg was 0.85 (0.07) mmol/L and median (IQR) for urinary Mg excretion was 2.29 (1.56-3.51) mmol/L. After adjustment for potential covariates, both serum and the urinary concentrations of Mg were inversely associated with CCA-IMT, but not with BIF-IMT. The regression coefficients (standard errors) were -100 (29) µm (total), -86 (34) µm (women) and -117 (52) µm (men) CCA-IMT per 1 mmol/L of serum Mg, and -41 (8) µm (total), -41 (10) µm (women) and -44 (15) µm (men) CCA-IMT per 1 unit of urinary Mg/creatinine (log mmol/mmol) (all p < 0.05), respectively. Higher serum Mg levels were associated with higher total cholesterol, HDLc, LDLc and triglyceride, but lower non-HDLc/HDLc in total population (all p < 0.05). Similar relationships of urinary Mg with lipoproteins were also found in total population (all p < 0.05).

CONCLUSION

Higher levels of serum and urinary Mg are associated with lower CCA-IMTs, and the role of Mg in lipid metabolism needs further investigation.

Cations as switches of amyloid-mediated membrane disruption mechanisms: calcium and IAPP

Disruption of the integrity of the plasma membrane by amyloidogenic proteins is linked to the pathogenesis of a number of common age-related diseases. Although accumulating evidence suggests that adverse environmental stressors such as unbalanced levels of metal ions may trigger amyloid-mediated membrane damage, many features of the molecular mechanisms underlying these events are unknown. Using human islet amyloid polypeptide (hIAPP, aka amylin), an amyloidogenic peptide associated with β-cell death in type 2 diabetes, we demonstrate that the presence of Ca(2+) ions inhibits membrane damage occurring immediately after the interaction of freshly dissolved hIAPP with the membrane, but significantly enhances fiber-dependent membrane disruption. In particular, dye leakage, quartz crystal microbalance, atomic force microscopy, and NMR experiments show that Ca(2+) ions promote a shallow membrane insertion of hIAPP, which leads to the removal of lipids from the bilayer through a detergent-like mechanism triggered by fiber growth. Because both types of membrane-damage mechanisms are common to amyloid toxicity by most amyloidogenic proteins, it is likely that unregulated ion homeostasis, amyloid aggregation, and membrane disruption are all parts of a self-perpetuating cycle that fuels amyloid cytotoxicity.

Clustered Conserved Cysteines in Hyaluronan Synthase Mediate Cooperative Activation by Mg2+ Ions and Severe Inhibitory Effects of Divalent Cations

Hyaluronan synthase (HAS) uses UDP-GlcUA and UDP-GlcNAc to make hyaluronan (HA). Streptococcus equisimilis HAS (SeHAS) contains four conserved cysteines clustered near the membrane, and requires phospholipids and Mg²⁺ for activity. Activity of membrane-bound or purified enzyme displayed a sigmoidal saturation profile for Mg²⁺ with a Hill coefficient of 2. To assess if Cys residues are important for cooperativity we examined the Mg²⁺ dependence of mutants with various combinations of Cys-to-Ala mutations. All Cys-mutants lost the cooperative response to Mg²⁺. In the presence of Mg²⁺, other divalent cations inhibited SeHAS with different potencies (Cu²⁺~Zn²⁺ >Co²⁺ >Ni²⁺ >Mn²⁺ >Ba²⁺ Sr²⁺ Ca²⁺). Some divalent metal ions likely inhibit by displacement of Mg²⁺-UDP-Sugar complexes (e.g. Ca²⁺, Sr²⁺ and Ba²⁺ had apparent K_i values of 2-5 mM). In contrast, Zn²⁺ and Cu²⁺ inhibited more potently (apparent K_i ≤ 0.2 mM). Inhibition of Cys-null SeHAS by Cu²⁺, but not Zn²⁺, was greatly attenuated compared to wildtype. Double and triple Cys-mutants showed differing sensitivities to Zn²⁺ or Cu²⁺. Wildtype SeHAS allowed to make HA prior to exposure to Zn²⁺ or Cu²⁺ was protected from inhibition, indicating that access of metal ions to sensitive functional groups was hindered in processively acting HA•HAS complexes. We conclude that clustered Cys residues mediate cooperative interactions with Mg²⁺ and that transition metal ions inhibit SeHAS very potently by interacting with one or more of these -SH groups.

Multiparametric optimization of (31)P NMR spectroscopic analysis of phospholipids in crude tissue extracts. 2. Line width and spectral resolution

The quality of NMR spectra in general and of spectra to be used for analysis of compound mixtures in particular is essentially defined by two basic parameters: signal-to-noise ratio and spectral resolution. The latter is determined by signal dispersion (chemical shift differences) and line widths. The present study focuses on multiparametric optimization of spectral resolution in (31)P NMR spectra of phospholipids from brain tissue extracts. This report presents, for the first time, a systematic and comprehensive study of phospholipid (31)P NMR line widths as a function of four experimental parameters: (i) extract concentration, (ii) concentration of a chelating agent, (iii) pH of the aqueous component of the solvent system, and (iv) temperature of the NMR measurement. Theoretical underpinnings of observed line width variations (transversal relaxation effects) are briefly discussed. In conjunction with an analogous, concurrently published report on chemical shift effects in the same tissue extract system, this multiparametric line width study provides a complete set of methodological guidelines for (i) generating well-defined tissue extracts, and (ii) choosing matched and optimized measurement conditions for highly reproducible and well-resolved (31)P NMR spectra of brain phospholipids. This study also offers a comprehensive database and a strategy for rational and efficient optimization of phospholipid spectra from other tissue extracts.

Relationship between serum magnesium values, lipids and anthropometric risk factors

Serum magnesium (SMg) has been reported to negatively correlate with an atherogenic lipid profile in individuals with diabetes mellitus (DM) and metabolic syndrome. This study examines whether the relationships between SMg levels and biochemical and anthropometric risk factors for these conditions are also present in the general adult population.

DESIGN AND METHODS

Biochemical parameters and anthropometric variables were assessed in 1318 healthy adult subjects recruited from the Newfoundland population.

RESULTS

SMg positively correlated with age, and serum phosphate, calcium, albumin, total cholesterol, HDL-cholesterol, LDL-cholesterol and triglyceride levels. SMg negatively correlated with HOMA-beta and percent body fat measured by DEXA. On sub-grouping subjects according to sex, menopausal status or after excluding subjects with DM, only a significant correlation of SMg with albumin, calcium, phosphate, and total cholesterol was common to all. Stepwise linear regression analysis revealed albumin, phosphate, age, total cholesterol, glucose, and body mass index as independent predictors of SMg levels.

CONCLUSIONS

These results indicate that SMg levels positively correlate with total cholesterol and possibly all lipoproteins in a large adult study population which suggests that variation of SMg with serum lipid levels may be different in healthy individuals compared with those with DM. We speculate on a possible binding interaction.

Effect of temperature and pH on 31P nuclear magnetic resonances of phospholipids in cholate micelles

Accurate and precise determination of phospholipid composition by 31P NMR spectroscopy requires correct assignments and adequate spectral resolution. Because temperature and pH may affect chemical shifts (delta), our first aim was to establish the temperature coefficient (Deltadelta/DeltaT) of common phospholipid classes when using sodium cholate as detergent. This parameter can then be used to aid in resonance assignments. The second goal was to investigate the pH dependence of delta so that, in addition to temperature, pH control can be used to minimize spectral overlap. For phosphatidylcholine, sphingomyelin, dihydrosphingomyelin and phosphatidylglycerol, delta values were invariant with pH and temperature. Whereas the Deltadelta/DeltaT for phosphatidylinositol was 4 x 10(-3)ppm/ degrees C, regardless of pH, these coefficients were highly pH-dependent for phosphatidic acid, phosphatidylethanolamine and phosphatidylserine, exhibiting maximal variations with the deprotonation of the headgroup, particularly for phosphatidic acid. These trends indicate the importance of H-bonding on delta and Deltadelta/DeltaT for phospholipid resonances.

Malignant breast tumor phospholipid profiles using (31)P magnetic resonance

Biochemical markers improve the classification and staging of breast cancer and may refine management decisions if it can be shown that they correlate with accepted prognostic factors or patient outcome. Using phosphorus-31 magnetic resonance spectroscopy ((31)P MRS), we determined the phospholipid content of 43 malignant breast tumors, correlating the profiles with specific histopathologic and clinical features and hormone receptor status. Among the 14 phospholipids identified, the mean mole percentage of sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidic acid, phosphatidylglycerol, and alkylacylphosphatidylcholine predicted cellular infiltration, infiltration type, elastosis, lymphatic invasion, perineural invasion, necrosis, and estrogen receptor positivity. (31)P MRS phospholipid profile data provide statistical correlations among histologic features and molecules known to play important roles in cellular communication, regulation, and processes unique to malignant tissues.

Final report on the safety assessment of Lecithin and Hydrogenated Lecithin

Lecithin is a naturally occurring mixture of the diglycerides of stearic, palmitic, and oleic acids, linked to the choline ester of phosphoric acid, commonly called phosphatidylcholine. Hydrogenated Lecithin is the product of controlled hydrogenation of Lecithin. Bilayers of these phospholipids in water may form liposomes, a spherical structure in which the acyl chains are inside and not exposed to the aqueous phase. Lecithin and Hydrogenated Lecithin are used in a large number of cosmetic formulations as skin conditioning agents-miscellaneous and as surfactant-emulsifying agents. Hydrogenated Lecithin is also used as a suspending agent-nonsurfactant. Historical data on concentration of use of Lecithin reveals that 0.1% to 1.0% is the concentration range most frequently seen, with concentrations up to 50% reported for two moisturizing products. A solution of 65% Lecithin is currently reported to be used at concentrations up to 3% in cosmetics. Nonocclusive application of Lecithin-containing liposomes to murine skin resulted in 30% penetration to the subdermis. In piglet skin, the same application resulted in 99% accumulating in the stratum corneum. In general, liposomes are considered effective in capturing other compounds inside their spherical structure and delivering any such captured compound through the skin barrier. As a result, caution should be exhibited in formulating cosmetic products that contain these ingredients in combination with other ingredients whose safety is based on their lack of absorption or where dermal absorption is a concern. Lecithin is virtually nontoxic in acute oral studies, short-term oral studies, and subchronic dermal studies in animals. Lecithin is not a reproductive toxicant, nor is it mutagenic in several assays. In an oral carcinogenicity study, brain neoplasms were found in mice exposed to Lecithin. In a subcutaneous carcinogenicity study, no neoplasms were found in mice and rats exposed to Lecithin. Adverse reactions to Lecithin in a metered-dose inhaler have been reported. Lecithin and Hydrogenated Lecithin were generally nonirritating and nonsensitizing in animal and human skin. Based on the available data, Lecithin and Hydrogenated Lecithin are safe as used in rinse-off cosmetic products; they may be safely used in leave-on products at concentrations up to 15%, the highest concentration tested in clinical irritation and sensitization studies; but the safety of use could not be substantiated in cosmetic products likely to be inhaled. Because of the possibility of formation of nitrosamines, these ingredients should not be used in cosmetic products in which N-nitroso compounds may be formed.

Chronic myo-inositol increases rat brain phosphatidylethanolamine plasmalogen

BACKGROUND

Oral myo-inositol (12--18 g/day) has shown beneficial effect in placebo-controlled studies of major depression, panic disorder, and obsessive compulsive disorder, and preliminary data suggest it also may be effective in bipolar depression. Evidence linking antidepressant activity to membrane phospholipid alterations suggested the examination of acute and chronic myo-inositol effects on rat brain membrane phospholipid metabolism.

METHODS

With both (31)P nuclear magnetic resonance (NMR) and quantitative high-performance thin-layer chromatography (HPTLC; hydrolysis) methods, rat brain phospholipid levels were measured after acute (n = 20, each group) and chronic myo-inositol administration (n = 10, each group). With (31)P NMR, we measured myo-inositol rat brain levels after acute and chronic myo-inositol administration.

RESULTS

Brain myo-inositol increased by 17% after acute myo-inositol administration and by 5% after chronic administration, as compared with the control groups. Chronic myo-inositol administration increased brain phosphatidylethanolamine (PtdEtn) plasmalogen by 10% and decreased brain PtdEtn by 5%, thus increasing the ratio PtdEtn plasmalogen (PtdEtn-Plas)/PtdEtn by 15%. Phosphatidylethanolamine plasmalogen levels quantified by (31)P NMR and HPTLC were highly correlated. The validity and reliability of the (31)P NMR method for phospholipid analysis were demonstrated with phospholipid standards.

CONCLUSIONS

The observed alteration in the PtdEtn-Plas/PtdEtn ratio could provide insights into the therapeutic effect of myo-inositol in affective disorders.

Activation of ion-conducting pathways in the inner mitochondrial membrane - an unrecognized activity of fatty acid?

The effect of non-esterified myristate (C14:0) or dodecyl sulfate was studied on passive swelling of rat liver mitochondria suspended in hypotonic alkaline KCl medium in the absence of the potassium ionophore valinomycin. Both compounds rapidly initiated large-amplitude swelling. However, they failed to initiate swelling when the mitochondria were suspended in hypotonic alkaline sucrose medium. In contrast to myristate or dodecyl sulfate, the non-ionic detergent Triton X-100 initiated swelling of mitochondria in both of the media. The following findings indicate that the inner mitochondrial membrane (IMM) is permeabilized by myristate to K+ and Cl- in a specific manner. (i) Swelling initiated by myristate did not respond to cyclosporin A, (ii) the protonophoric uncoupler FCCP was unable to mimic the myristate effect on swelling, and (iii) myristate-induced Cl- -permeation (measured with KCl medium plus valinomycin) was inhibited by N,N'-dicyclohexylcarbodiimide, quinine or ATP. Myristate- or dodecyl sulfate-initiated swelling was paralleled by the lowering of endogenous Mg2+ content. Both effects, stimulation of swelling and depletion of endogenous Mg2+ are correlated with each other. Similar effects have been reported previously for the carboxylic divalent cation ionophore calcimycin (A23187). The A23187-induced swelling has identical inhibiting characteristics on Cl- -permeation with respect to N,N'-dicyclohexylcarbodiimide, quinine and ATP as the myristate-stimulated swelling. Therefore, we conclude that non-esterified fatty acids increase the permeability of mitochondria to K+ and Cl- at alkaline pH by activating Mg2+-dependent ion-conducting pathways in IMM.

Static and magic angle spinning (31)P NMR spectroscopy of two natural plasma membranes

Static and magic angle spinning (31)P NMR spectroscopy was used for the first time in natural plasma membranes from erythrocytes and skeletal muscle to study phospholipid arrangement and composition. Typical static powder-like spectra were obtained showing that phospholipids were in a bilayer arrangement. Magic angle spinning narrowed spectra into two components. The first one corresponded to phosphatidylcholine and the second one to the other phospholipids with intensities in agreement with the known phospholipid composition. These findings show that NMR data previously acquired using model membranes can be transposed to studies on phospholipids in their natural environment.

Competition between Li+ and Mg2+ for red blood cell membrane phospholipids: A 31P, 7Li, and 6Li nuclear magnetic resonance study

The mode of action of the lithium ion (Li+) in the treatment of manic depression or bipolar illness is still under investigation, although this inorganic drug has been in clinical use for 50 yr. Several research reports have provided evidence for Li+/Mg2+ competition in biomolecules. We carried out this study to characterize the interactions of Li+ and Mg2+ with red blood cell (RBC) membrane components to see whether Li+/Mg2+ competition occurs. 31P nuclear magnetic resonance chemical shift measurements of the phospholipids extracted from the RBC membranes indicated that the anionic phospholipids, phosphatidylserine and phosphatidylinositol, bind Li+ and Mg2+ most strongly. From 6Li relaxation measurements, the Li+ binding constant to the phospholipid extract was found to be 45 +/- 5 M(-1). Thus, these studies showed that the phospholipids play a major role in metal ion binding. 7Li spin-lattice relaxation measurements conducted on unsealed and cytoskeleton-depleted RBC membrane in the presence of magnesium indicated that the removal of the cytoskeleton increases lithium binding to the more exposed anionic phospholipids (357 +/- 24 M(-1)) when compared to lithium binding in the unsealed RBC membrane (221 +/- 21 M(-1)). Therefore, it can be seen that the cytoskeleton does not play a major role in Li+ binding or in Li+/Mg2+ competition.

Alterations in heart and kidney membrane phospholipids in hypertension as observed by 31P nuclear magnetic resonance

Abnormalities of phospholipids in hypertension have previously been described in human erythrocyte, platelet, and plasma lipoproteins. Since the heart and kidney are adversely affected by hypertension, we investigated possible alterations in their membrane phospholipids, which could play a role in the derangement of intracellular ion balance widely observed in hypertension. The phospholipid compositions of heart and kidney from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were determined by using 31P nuclear magnetic resonance (NMR) spectroscopy. Absolute contents of all phospholipids in hypertensive hearts and kidneys were significantly higher than in normotensive hearts and kidneys. Expressed as a fraction of total phospholipid, cardiolipin (CL) and phosphatidylethanolamine plasmalogen (PEp) were significantly increased in SHR hearts compared to WKY hearts (CL and PEp were 7.95+/-0.22% and 13.16+/-0.35% in SHR vs. 7.01+/-0.20% and 11.19+/-0.42% in WKY rats, P< or =0.05), but phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were significantly decreased in SHR (PE and PC were 22.46+/-0.37% and 44.81+/-0.43% in SHR vs. 24.02+/-0.44% and 46.01+/-0.50% in WKY rats, P< or =0.05). In the phospholipids extracted from rat kidneys, the percentage of PE was significantly higher for SHR than for WKY rats (20.37+/-0.60% vs. 18.43+/-0.37%, P< or =0.05), while PEp and phosphatidylserine (PS) were significantly lower for SHR (PEp and PS were 10.22+/-0.36% and 8.42+/-0.28% in SHRs vs. 11.29+/-0.36% and 9.71+/-0.40% in WKY rats, P< or =0.05). The above alterations in phospholipid composition might contribute to the higher oxygen consumption in the hypertensive heart and abnormal intracellular ion concentrations and ion transport in the heart and the kidney in hypertension.

Meibomian gland phospholipids

The content of the meibomian gland lipid exprimate is known, but little is known about the phospholipids that comprise the glandular cells. The purpose of the present study is to identify and quantitate the phospholipid complement of the meibomian gland cells that produce the lipid secretion of meibomian oil and which is vital to tear film stability. Eyelids (n = 50) were excised from rabbits, and after surgical removal of surrounding tissues, the tarsal plates with and without expressing meibomian oil were extracted and phospholipids of the plates quantified by 31P nuclear magnetic resonance (NMR). Seventeen phospholipids were quantified from tarsal plates expressed of oil and tarsal plates containing meibomian oil: alkylacylphosphatidylcholine (AAPC), dihydrosphingomyelin (DHSM), dimethylphosphatidylethanolamine, diphosphatidylglycerol (cardiolipin), ethanolamine plasmalogen (EPLAS), lysoethanolamine plasmalogen, lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylserine, phosphatidic acid, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, sphingomyelin (SM), sphingosylphosphorylcholine. The six zwitterionic and neutral phospholipids, DHSM, EPLAS, PE, SM, AAPC, and PC together comprise 79.5% of the total meibomian gland phospholipid profile (in meibomian oil this value is 84.2%). The zwitterionic and neutral phospholipids dominate meibomian gland phospholipid profiles. Since the meibomian gland cells undergo holocrine secretion and form the meibomian glad secretion, such a composition is consistent with the hypothesis that a chemically stable lamellar surfactant layer phospholipids bind non-polar meibomian oil to the aqueous layer of the tear film.

Correlations of Na+-Li+ exchange activity with Na+ and Li+ binding and phospholipid composition in erythrocyte membranes of white hypertensive and normotensive individuals: a nuclear magnetic resonance investigation

Enhanced Na+-Li+ exchange activity has been reported in red blood cells (RBCs) of white patients with essential hypertension compared with RBCs of normotensive individuals. To understand the factors responsible for this finding, we applied novel and conventional spectroscopic and kinetic methods to blood samples from 10 hypertensive and 10 normotensive individuals. We measured the kinetic parameters (V std, V max, and K m) for RBC Na+-Li+ exchange by atomic absorption spectrophotometry and used 23Na and 7Li nuclear magnetic resonance relaxation methods to measure Na+ and Li+ binding to RBC membranes as well as 31P nuclear magnetic resonance spectroscopy to measure membrane phospholipid compositions. We found significant differences between the two groups for the affinity of Na+ for the RBC membrane (0.202 +/- 0.054 mmol/L-1 for hypertensive patients versus 0.296 +/- 0.071 mmol/L-1 for normotensive subjects, P<.005). The kinetic parameters of RBC Na+-Li+ exchange (V std, V max, and K m) were 0.32 +/- 0.09 and 0.66 +/- 0.17 mmol Li+/L cell.h and 160 +/- 62 mmol/L, respectively, for hypertensive patients versus 0.21 +/- 0.06 and 0.32 +/- 0.14 mmol Li+/L cell.h and 86 +/- 69 mmol/L for normotensive subjects (P<.05). The fractions of phosphatidylserine and phosphatidylethanolamine were 0.153 +/- 0.009 and 0.294 +/- 0.016 for hypertensive patients versus 0.138 +/- 0.013 and 0.325 +/- 0.018 for normotensive subjects (P<.05). The Na+ binding constants were negatively correlated with the Km values for both the hypertensive (r=-.61, P=.01) and normotensive (r=-.43, P=.04) groups. Changes in lipid-protein interactions in the RBC membranes of hypertensive patients appear to be responsible for weaker Na+ binding to the membrane and for the faster rates of RBC Na+-Li+ exchange.

Phospholipid profiling of sediments using phosphorus-31 nuclear magnetic resonance

A phosphorus-31 nuclear magnetic resonance method has been developed for the determination of aquatic sediment phospholipid profiles that may be generally applied to all soils and deposits containing viable cellular material. A method of scrubbing chloroform/methanol extracts with potassium acid phosphate overcomes adverse signal broadening from the mineral component, permitting eleven sediment phospholipids to be determined at the quantitative level.

Algal phospholipids by 31P NMR: comparing isopropanol pretreatment with simple chloroform/methanol extraction

1. A modified Folch procedure [potassium (ethylenedinitrilo)-tetraacetic acid at pH 6 substituted for KCl] is suitable for the extraction of marine algae. 2. The quantitative 31P nuclear magnetic resonance phospholipid profiles of four marine algae, Gracilaria verrucosa, Bryothamnion triquetrum, Padina gymnospora, and Caulerpa sertularioides, were obtained from Folch and Nichols extractions of both fresh and dried algae, and essentially identical results were obtained using either extraction procedure. 3. Extracts of air-dried algae are statistically different when compared to extracts of living algae, suggesting that tissue handling is a critical factor in phospholipid extractions.

Esophageal cancer phospholipid characterization by 31P NMR

Phospholipid extracts of surgical tissue specimens from 18 patients, consisting of normal esophagus, distal esophageal tumor and normal stomach, were analyzed using 31P NMR. The prominent phospholipids detected in these tissues included cardiolipin (CL), phosphatidylethanolamine plasmalogen, phosphatidylethanolamine (PE), phosphatidylserine (PS), sphingomyelin (SPH), phosphatidylinositol (PI), phosphatidylcholine plasmalogen and phosphatidylcholine (PC). Very small quantities of the phospholipids lysophosphatidylcholine, phosphatidic acid, phosphatidylglycerol, and an uncharacterized phospholipid at -0.13 delta also were detected in some of the 54 tissue specimens analyzed. The mean relative concentrations of these phospholipids, in mole percentages of total detected phosphorus, were determined from the acquired spectra and used to differentiate among the three tissue groups. The relative concentrations of the following phospholipids differed significantly (p < 0.001) among the respective tissue groups: normal esophagus vs esophageal tumor, PS, SPH, PI, PC; normal esophagus vs normal stomach, CL, PE, PS, SPH; esophageal tumor vs normal stomach, CL, PE. Membrane phospholipids implicated in modulating the growth and metastases of tumors of epithelial origin can be profiled to discriminate among normal esophagus, distal esophageal tumor and normal stomach using 31P NMR.

Effects of exercise training and anabolic steroids on plantaris and soleus phospholipids: a 31P nuclear magnetic resonance study

1. The purpose of this study was to examine the effect of exercise, anabolic steroid treatment, and a combination of both treatments on the phospholipid composition of predominantly fast twitch (plantaris) and slow twitch (soleus) skeletal muscles. The 4 experimental groups analyzed were sedentary control (C), steroid-treated (S), exercise-trained (E), and exercise plus steroid-treated (ES). 2. Among the 11 phospholipids quantitated, for the plantaris muscle, phosphatidylcholine was reduced in ES relative to C, while phosphatidylethanolamine and phosphatidylethanolamine plasmalogen were elevated in E and ES relative to C. For the soleus muscle, phosphatidylserine was reduced in S and E relative to C, and cardiolipin was elevated in E relative to C. 3. Of the 27 metabolic indices calculated for the plantaris, 15 changed significantly among E and ES relative to S and C, while for the soleus, only three indices changed among the four groups, two among E and ES relative to S and C and one between S and C. 4. For the plantaris muscle, the results are consistent with an exercise-induced alteration of membrane phospholipid composition that increases ion translocation activity. For the soleus muscle, this membrane alteration essentially does not take place. 5. Steroid treatment had little to no statistically significant effect on plantaris and soleus muscle phospholipid systems, regardless of the imposed regimen.