Nuclear magnetic resonance studies of lipoproteins

Breast Tissue Chemistry Measured In Vivo In Healthy Women Correlate with Breast Density and Breast Cancer Risk

BACKGROUND

The relationship of tissue chemistry to breast density and cancer risk has not been documented despite breast density being a known risk factor.

PURPOSE

To investigate whether distinct chemical profiles associated with breast density and cancer risk are identified in healthy breast tissue using in vivo two-dimensional correlated spectroscopy (2D COSY).

STUDY TYPE

Prospective.

POPULATION

One-hundred-seven participants including 55 at low risk and 52 at high risk of developing breast cancer.

FIELD STRENGTH/SEQUENCE

3 T/ axial/ T1, T2, 2D COSY.

ASSESSMENT

Two radiologists defined breast density on T2. Interobserver variability assessed. Peak volumes normalized to methylene at (1.30, 1.30) ppm as internal shift reference.

STATISTICAL TESTS

Chi-squared/Mann-Whitney/Kappa statistics/Kruskal Wallis/pairwise analyses. Significance level 0.05.

RESULTS

Ten percentage were fatty breasts, 39% scattered fibroglandular, 35% heterogeneously dense, and 16% extremely dense. Interobserver variability was excellent (kappa = 0.817). Sixty percentage (64/107) were premenopausal. Four distinct tissue chemistry categories were identified: low-density (LD)/premenopausal, high-density (HD)/premenopausal, LD/postmenopausal, and HD/postmenopausal. Compared to LD, HD breast chemistry showed significant increases of cholesterol (235%) and lipid unsaturation (33%). In the low-risk category, postmenopausal women with dense breasts recorded the largest significant changes including cholesterol methyl 540%, lipid unsaturation 207%, glutamine/glutamate 900%, and choline/phosphocholine 800%. In the high-risk cohort, premenopausal women with HD recorded a more active chemical profile with significant increases in choline/phosphocholine 1100%, taurine/glucose 550% and cholesterol sterol 250%.

DATA CONCLUSION

Four distinct chemical profiles were identified in healthy breast tissue based on breast density and menopausal status in participants at low and high risk. Gradual increase in neutral lipid content and metabolites was noted in both risk groups across categories in different order. In low risk, the HD postmenopausal category exhibited the highest metabolic activity, while women at high risk exhibited the highest lipid content and metabolic activity in the HD premenopausal category.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 3.

Compact NMR relaxometry of human blood and blood components

Nuclear magnetic resonance relaxometry is a uniquely practical and versatile implementation of NMR technology. Because it does not depend on chemical shift resolution, it can be performed using low-field compact instruments deployed in atypical settings. Early relaxometry studies of human blood were focused on developing a diagnostic test for cancer. Those efforts were misplaced, as the measurements were not specific to cancer. However, important lessons were learned about the factors that drive the water longitudinal (T1) and transverse (T2) relaxation times. One key factor is the overall distribution of proteins and lipoproteins. Plasma water T2 can detect shifts in the blood proteome resulting from inflammation, insulin resistance and dyslipidemia. In whole blood, T2 is sensitive to hemoglobin content and oxygenation, although the latter can be suppressed by manipulating the static and applied magnetic fields. Current applications of compact NMR relaxometry include blood tests for candidiasis, hemostasis, malaria and insulin resistance.

Nanofluidity of fatty acid hydrocarbon chains as monitored by benchtop time-domain nuclear magnetic resonance

The functional properties of lipid-rich assemblies such as serum lipoproteins, cell membranes, and intracellular lipid droplets are modulated by the fluidity of the hydrocarbon chain environment. Existing methods for monitoring hydrocarbon chain fluidity include fluorescence, electron spin resonance, and nuclear magnetic resonance (NMR) spectroscopy; each possesses advantages and limitations. Here we introduce a new approach based on benchtop time-domain (1)H NMR relaxometry (TD-NMR). Unlike conventional NMR spectroscopy, TD-NMR does not rely on the chemical shift resolution made possible by homogeneous, high-field magnets and Fourier transforms. Rather, it focuses on a multiexponential analysis of the time decay signal. In this study, we investigated a series of single-phase fatty acid oils, which allowed us to correlate (1)H spin-spin relaxation time constants (T2) with experimental measures of sample fluidity, as obtained using a viscometer. Remarkably, benchtop TD-NMR at 40 MHz was able to resolve two to four T2 components in biologically relevant fatty acids, assigned to nanometer-scale domains in different segments of the hydrocarbon chain. The T2 values for each domain were exquisitely sensitive to hydrocarbon chain structure; the largest values were observed for pure fatty acids or mixtures with the highest cis-double bond content. Moreover, the T2 values for each domain exhibited positive linear correlations with fluidity. The TD-NMR T2 and fluidity measurements appear to be monitoring the same underlying phenomenon: variations in hydrocarbon chain packing. The results from this study validate the use of benchtop TD-NMR T2 as a nanofluidity meter and demonstrate its potential for probing nanofluidity in other systems of biological interest.

Novel mono-, di-, and trimethylornithine membrane lipids in northern wetland planctomycetes

Northern peatlands represent a significant global carbon store and commonly originate from Sphagnum moss-dominated wetlands. These ombrotrophic ecosystems are rain fed, resulting in nutrient-poor, acidic conditions. Members of the bacterial phylum Planctomycetes are highly abundant and appear to play an important role in the decomposition of Sphagnum-derived litter in these ecosystems. High-performance liquid chromatography coupled to high-resolution accurate-mass mass spectrometry (HPLC-HRAM/MS) analysis of lipid extracts of four isolated planctomycetes from wetlands of European north Russia revealed novel ornithine membrane lipids (OLs) that are mono-, di-, and trimethylated at the ε-nitrogen position of the ornithine head group. Nuclear magnetic resonance (NMR) analysis of the isolated trimethylornithine lipid confirmed the structural identification. Similar fatty acid distributions between mono-, di-, and trimethylornithine lipids suggest that the three lipid classes are biosynthetically linked, as in the sequential methylation of the terminal nitrogen in phosphatidylethanolamine to produce phosphatidylcholine. The mono-, di-, and trimethylornithine lipids described here represent the first report of methylation of the ornithine head groups in biological membranes. Various bacteria are known to produce OLs under phosphorus limitation or fatty-acid-hydroxylated OLs under thermal or acid stress. The sequential methylation of OLs, leading to a charged choline-like moiety in the trimethylornithine lipid head group, may be an adaptation to provide membrane stability under acidic conditions without the use of scarce phosphate in nutrient-poor ombrotrophic wetlands.

1H NMR at 800MHz facilitates detailed phospholipid follow-up during atherogenic modifications in low density lipoproteins

The structure of low density lipoprotein (LDL) particles and, particularly, the enzymatic and oxidative modifications of their surface is crucial in the initiation of atherosclerosis. Due to the structural complexity of LDL, there is a lack of suitable methods for dynamic follow-up studies of the molecular mechanisms in native and modified particles in physiological conditions. Here, we report that phosphatidylcholine (PC), lysophosphatidylcholine (lyso-PC), and sphingomyelin (SM) can all be identified and quantified in LDL particles by (1)H NMR spectroscopy at 800 MHz. The signal assignment for the lyso-PC is novel and we illustrate the applicability of the methodology in the case of lipid peroxidation that is generally considered as one of the key proatherogenic modifications of LDL. It was found, somewhat surprisingly, that the LDL-associated phospholipase A(2) is activated in the very beginning of the formation of PC-hydroperoxides. The (patho)physiological rationale of the resulting lyso-PC generation is also briefly discussed.

Identification of cholesteryl esters in human carotid atherosclerosis by ex vivo image-guided proton MRS

Vulnerable atherosclerotic plaques may be identified by their large lipid component, particularly liquid cholesteryl ester (CE), covered by a fibrous cap. We hypothesized that image-guided 1H proton magnetic resonance spectroscopy (MRS) would identify mobile CE in discrete, preselected regions of atherosclerotic plaque. Human carotid endarterectomy specimens (n = 10) were imaged ex vivo by magnetic resonance imaging (MRI) at high field (11.7 T) utilizing standard T1- and T2-weighted spin echo protocols. MRS spectra were acquired from 1 mm3 voxels, localized to plaque regions that we judged by MRI to be lipid rich or lipid poor. The spectra revealed methyl and methylene resonances of fatty acyl chains with relative intensities and linewidths characteristic of pure CE, by comparison with lipid standards. Regions judged to be lipid rich by MRI showed much more intense CE resonances than did lipid-poor regions. The integrated intensities of lipid peaks were 5.5 +/- 2.0% (lipid-rich regions) versus 0.9 +/- 0.6% (lipid-poor regions) of the unsuppressed water peak (P < 0.0001). Lipid distribution by histology, MRS, and MRI showed strong correlation. Image-guided proton MRS accurately identified CE in selected regions of atherosclerotic plaque as small as 1 mm3 in an ex vivo setting. This procedure may permit the noninvasive detection and quantification of CE in atherosclerotic plaque in vivo.

Integral apolipoproteins increase surface-located triacylglycerol in intact native apoB-100-containing lipoproteins

High-resolution NMR was used to measure the presence and quantity of triacylglycerol (TAG) in the surface of intact native apolipoprotein B-100-containing lipoprotein particles that are made by chickens in response to estrogen treatment and that in hens are deposited in yolk follicles (VLDLy). Integration of 13C NMR resonances shows that intact VLDLy particles contain more surface TAG (5.1 +/- 0.6 mol%, 6.7 +/- 0.8 weight %) than predicted by apolipoprotein-free models using similarly acyl-heterogenous TAG. Change in downfield chemical shift values of surface to core TAG in VLDLy was 0.8 ppm compared with 1.3 ppm in vesicles prepared with purified egg phosphatidylcholine and TAG isolated from the VLDLy, indicating that reduced surface TAG hydration may contribute to the resistance to lipase hydrolysis characteristic of this lipoprotein species. Apolipoprotein-mediated changes in surface lipid composition and lipid hydration provide possible general mechanisms for selectivity in lipoprotein substrate characteristics.

1H NMR spectroscopic evidence of interaction between ibuprofen and lipoproteins in human blood plasma

Recent studies have suggested that ibuprofen inhibits low-density lipoprotein oxidation in a high dose-dependent manner and is a promising drug for treatment of the conditions associated with atherosclerosis. In this article, we present the NMR spectroscopic evidence for the interaction between ibuprofen and phospholipids in lipoprotein particles in intact human plasma. Ibuprofen caused chemical shift upfield drifts for the protons of -N(+)(CH(3))(3) moieties of phosphatidylcholine and sphingomyelin, olefinic chains (-CH[double bond]CH[bond], [bond]CH[triple bond]CHCH(2)CH[triple bond]CH[bond], [bond](CH(2))(n)CH(2)CH[double bond]), and (CH(2))(n) and CH(3) groups, from unsaturated lipids in lipoprotein particles. The ibuprofen may interact directly with the above-mentioned groups of phospholipids or induce structural changes in the lipoproteins. This may shed light on the mechanism by which the drug protects against oxidative modification of lipoproteins.

1H-NMR and 13C-NMR lipid profiles of human renal tissues

Lipids from human renal tissues are studied by means of (1)H- and (13)C-NMR spectroscopy. The total lipid fractions obtained from healthy kidneys, malignant renal cell carcinomas, and benign oncocytomas are characterized and analyzed to elucidate the main differences between the functional and neoplastic tissues. In all cases the lipid components are well identified. The healthy kidney is characterized by high amounts of triglycerides and the presence of cholesterol in its free form. On the contrary, renal cell carcinomas contain high amounts of cholesterol that are almost completely esterified as oleate, suggesting an intracellular localization of the cholesteryl esters synthesis. Cholesteryl esters are considered markers of renal cell carcinomas, thus supporting recent theories that these compounds play a leading role in cell proliferation. Oncocytomas are particularly rich in phosphatidylcholine and, analogous to the healthy kidney, are completely lacking in cholesteryl esters. Healthy kidneys and oncocytomas appear to have other similarities if compared with renal cell carcinomas: a very high fatty acyl/cholesterol ratio, the presence of dolichols, and a higher grade of unsaturation. The (13)C data suggest a new method for the direct evaluation of the saturated/unsaturated fatty acyl ratio.

NMR studies of lipoprotein structure

Early NMR structural studies of serum lipoproteins were based on (1)H, (13)C, (31)P, and (2)H studies of lipid components. From the early studies information on composition, lipid chain dynamics and order parameters, and monolayer organization resulted. More recently, selective or complete isotopic labeling techniques, combined with multidimensional NMR spectroscopy, have resulted in structural information of apoprotein fragments. Finally, use of heteronuclear three- and four-dimensional experiments have yielded solution structures and protein-lipid interactions of intact apolipoproteins C-I, C-II, and A-I.

Effects of lipid interaction on the lysine microenvironments in apolipoprotein E

Lysines in apolipoprotein (apo) E are key factors in the binding of apoE to the low density lipoprotein receptor, and high affinity binding requires that apoE be associated with lipid. To gain insight into this effect, we examined the microenvironments of the eight lysines in the 22-kDa fragment of apoE3 (residues 1-191) in the lipid-free and lipid-associated states. As shown by (1)H,(13)C heteronuclear single quantum coherence nuclear magnetic resonance, lysine resonances in the lipid-free fragment were poorly resolved over a wide pH range, whereas in apoE3.dimyristoyl phosphatidylcholine (DMPC) discs, the lysine microenvironments and protein conformation were significantly altered. Sequence-specific assignments of the lysine resonances in the spectrum of the lipidated 22-kDa fragment were made. In the lipid-free protein, six lysines could be resolved, and all had pK(a) values above 10. In apoE3.DMPC complexes, however, all eight lysines were resolved, and the pK(a) values were 9.2-11.1. Lys-143 and Lys-146, both in the receptor binding region in helix 4, had unusually low pK(a) values of 9.5 and 9.2, respectively, likely as a result of local increases in positive electrostatic potential with lipid association. Shift reagent experiments with potassium ferricyanide showed that Lys-143 and Lys-146 were much more accessible to the ferricyanide anion in the apoE3.DMPC complex than in the lipid-free state. The angle of the nonpolar face of helix 4 is smaller than the angles of helices 1, 2, and 3, suggesting that helix 4 cannot penetrate as deeply into the DMPC acyl chains at the edge of the complex and that its polar face protrudes from the edge of the disc. This increased exposure and the greater positive electrostatic potential created by interaction with DMPC may explain why lipid association is required for high affinity binding of apoE to the low density lipoprotein receptor.

Evidence for distinct behaviour of phosphatidylcholine and sphingomyelin at the low density lipoprotein surface

This study demonstrates that the use of high field 1H NMR spectroscopy permits individual detection of phosphatidylcholine and sphingomyelin molecules at the surface of native low density lipoprotein (LDL) particles. Distinct behaviour was observed for the choline head group -N(CH3)3 resonances of these different phospholipids revealing preferential immobilisation for phosphatidylcholine. This suggests the existence of reversible and irreversible phosphatidylcholine-apolipoprotein B interactions and is consistent with microdomain formation at the surface monolayer of LDL. The novel resonance assignment and results show that 1H NMR can provide efficient and practical means for future studies on the structure and dynamics at the LDL surface.

Changes in organic solutes, volume, energy state, and metabolism associated with osmotic stress in a glial cell line: a multinuclear NMR study

Diffusion-weighted in vivo 1H-NMR spectroscopy of F98 glioma cells embedded in basement membrane gel threads showed that the initial cell swelling to about 180% of the original volume induced under hypotonic stress was followed by a regulatory volume decrease to nearly 100% of the control volume in Dulbecco's modified Eagle's medium (DMEM) but only to 130% in Krebs-Henseleit buffer (KHB, containing only glucose as a substrate) after 7 h. The initial cell shrinkage to approx. 70% induced by the hypertonic stress was compensated by a regulatory volume increase which after 7 h reached almost 100% of the control value in KHB and 75% in DMEM. 1H-, 13C- and 31P-NMR spectroscopy of perchloric acid extracts showed that these volume regulatory processes were accompanied by pronounced changes in the content of organic osmolytes. Adaptation of intra- to extracellular osmolarity was preferentially mediated by a decrease in the cytosolic taurine level under hypotonic stress and by an intracellular accumulation of amino acids under hypertonic stress. If these solutes were not available in sufficient quantities (as in KHB), the osmolarity of the cytosol was increasingly modified by biosynthesis of products and intermediates of essential metabolic pathways, such as alanine, glutamate and glycerophosphocholine in addition to ethanolamine. The cellular nucleoside triphosphate level measured by in vivo 31P-NMR spectroscopy indicated that the energy state of the cells was more easily sustained under hypotonic than hypertonic conditions.

Identification and localization of two distinct microenvironments for the diacylglycerol component of lipophorin particles by 13C NMR

13C nuclear magnetic resonance spectroscopy of lipoproteins, isolated from the insect Manduca sexta, has been employed to probe the microenvironment of diacylglycerol (DG), their major neutral lipid component. Natural abundance 13C NMR spectra of high density lipophorin exhibited several well-separated resonances derived from its lipid moiety, including those for the carbonyl carbon atoms of phospholipid and DG fatty acyl chains in the region of 175-180 ppm. To verify the assignment of the DG acyl chain carbonyl carbon resonances, di[1-13C]oleoylglycerol high density lipophorin was isolated after instilling a bolus of tri[1-13C]oleoylglycerol into the midgut of larvae fed a fat-free diet. 13C NMR spectra of the isolated lipoprotein revealed a specific and dramatic enrichment of resonances at 175.5 ppm. Expansion of this region revealed two resonances separated by 0.08 ppm. These were assigned as 1,2- and 1,3- isomers of DG, the latter presumably arising from spontaneous acyl chain migration of 1,2-DG following lipoprotein isolation. On the basis of compositional and structural analysis of this lipoprotein, it is postulated that these DG species are localized predominantly in the hydrophobic core of the particle. By contrast, natural abundance 13C NMR spectra of the DG-rich, low density lipophorin (LDLp) subspecies revealed two additional resonances, separated by 0.2 ppm, that were tentatively assigned as 1,2- and 1,3-DG present at the surface of the particle. The verify this assignment, experiments employing phospholipase C, to convert lipophorin surface associated phospholipid into DG, were performed.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of native and drug-loaded human low density lipoproteins

Low-density lipoproteins (LDLs), the physiological vehicles for lipids, are potentially useful drug delivery devices for (hydrophobic) drugs. The physicochemical characteristics of LDL loaded with the adriamycin derivative AD 32 or the N-mustard derivative WB 4291 were compared to that of native and reconstituted LDL at different temperatures. X-ray solution scattering indicates that loading with AD 32 has no detectable effect on the particle structure at room temperature, in contrast to WB 4291. According to 19F NMR data, AD 32 molecules are located in two distinct chemical environments with restricted motional freedom of the CF3 groups in samples stored as lyophilisates. 1H NMR signals from AD 32 were not observed, while those from WB 4291 could be distinguished from those of LDL constituents. WB 4291 molecules are in an environment with a higher motional freedom than AD 32 molecules. 1H NMR data suggest a higher fluidity of the core components for the WB-loaded LDLs compared to the other LDL preparations. While the motional freedom of the phospholipid head groups seems to be temperature independent, there is an increase in the mobility of the lipid components in the core region of the LDL particles with temperature.

13C-NMR spectroscopy of human atherosclerotic lesions. Relation between fatty acid saturation, cholesteryl ester content, and luminal obstruction

Previous investigations have used 13C-nuclear magnetic resonance (NMR) spectroscopy to demonstrate the similarities between lipoproteins and the mobile lipids of atheroma. In this study, we tested the hypothesis that 13C-NMR changes are related to indices of histological severity. We classified 20 human arteries according to their obstruction ratio (OR), defined as the ratio of the plaque area to the area delimited by the external elastic lamina. In group A, OR was < 40%, and in group B, OR was > 40%. We analyzed at 9.4 T the resonances of unsaturated (UFA) and polyunsaturated (PUFA) carbons, the resonances of the carbons 19 and 21 (C19, C21) of cholesteryl esters (CE), the methine carbon peak of fatty acids (CH2)n, the choline peak from phospholipids (PL), and the glycerol peak from triglyceride (TG). The UFA/PUFA, UFA/(CH2)n, and PUFA/(CH2)n ratios are markers of fatty acid saturation. (C19, C21)/(CH2)n, choline/(CH2)n, and glycerol/(CH2)n are indices of CE, PL, and TG content, respectively. UFA/PUFA in group A is 1.15 +/- 0.34 versus 1.63 +/- 0.32 in group B (P = .005). PUFA/(CH2)n is 0.26 +/- 0.10 in group A versus 0.16 +/- 0.04 in group B (P = .049). C19, C21/(CH2)n in group A is 0.32 +/- 0.15 versus 0.63 +/- 0.23 for group B (P = .003). No significant difference was found in UFA/(CH2)n or in the TG or PL ratios. 13C spectral examination of human atherosclerosis demonstrates decreased resonances for polyunsaturated fatty acyl chains and cholesteryl esters with increasing obstruction.

Regulation of intracellular pH in neuronal and glial tumour cells, studied by multinuclear NMR spectroscopy

The effect of extracellular pH (pHe) on intracellular pH (pHi) and cellular metabolism was examined by multinuclear NMR spectroscopy of cells in vivo and in vitro. A decrease in pHe from 7.4 to 6.4 led to a significant drop in pHi, in both neuronal and glial tumour cells, as detected by in vivo 31P NMR of cells embedded in basement membrane gel threads. A more than 50% decrease in both the phosphocreatine (PCr) level and derivatives of glycolysis (i.e., glycerol 3-phosphate) was observed, concomitantly to the fall in pHi. A 50% decrease in intracellular lactate levels was seen in in vivo 1H NMR spectra under these conditions. Reperfusion with fresh medium (pHe 7.4) resulted in the full recovery of pHi, simultaneously with an increase in both PCr and intracellular lactate back to their control levels. Perchloric acid and lipid extract measurements confirmed the observations made by in vivo 31P and 1H NMR spectroscopy and further showed a decrease both in tricarboxylic acid cycle activity and phospholipid synthesis. The data revealed no significant differences between the neuronal and glial tumour cells investigated. pHi measurements in the presence of inhibitors of the various pH regulatory mechanisms showed that the Na+/H+ exchanger, the carbonic anhydrase and at least one of the bicarbonate-transport systems are involved in pH regulation of both cell types. The results suggest that Na+/H+ exchange is the preferred mechanism by which both neuronal and glial cells regulate their pHi after extracellular acidification.

Esterified cholesterol and triglyceride are present in plasma membranes of Chinese hamster ovary cells

The chemical composition of highly purified plasma membrane preparations from a series of malignant Chinese hamster ovary (CHO) cell lines were undertaken to ascertain if neutral lipid, including cholesteryl ester and triacylglycerol, were present. Triacylglycerols (33-41 nmol/mg total lipid) and cholesteryl ester (226-271 nmol/mg) were measured in the plasma membranes and differences in the chemical composition of these membranes recorded. The most significant difference was a gradual decrease in the level of free cholesterol from wild type (312 +/- 7 nmol/mg total plasma membrane lipid), Pod RII-6 (268 +/- 64 nmol/mg total plasma membrane lipid), Col R-22 (243 +/- 39 nmol/mg total plasma membrane lipid) to EOT (204 +/- 20 nmol/mg total plasma membrane lipid), with a concomitant increase in the degree of saturation of the cholesteryl ester fatty acids, particularly palmitic acid. No statistically significant differences were apparent in the chemical composition of the whole cells in this series. The one-dimensional (1D) 1H-NMR spectra of the four malignant cell lines showed a gradation in intensity of lipid resonances, in the order of wild type, Pod RII-6, Col R-22 and EOT, with EOT having the strongest lipid spectrum. Interestingly, the increase in acyl-chain signal intensities in the 1H-NMR spectra of this series of CHO cells and emergence of signals from cholesterol and/or cholesteryl ester, coincide with alterations in the amount of free cholesterol and the degree of saturation of the fatty-acyl chain of the esterified cholesterol in the plasma membranes. It is our hypothesis that, together, cholesteryl ester and triacylglycerol form domains in the plasma membrane and that when the cholesteryl ester has a largely saturated fatty acid content, the lipids are in isotropic liquid phase and hence visible by NMR.

Free radicals promote modifications in plasma high-density lipoprotein: nuclear magnetic resonance analysis

The behavior of high-density lipoprotein (HDL) after free-radical-mediated oxidation was studied by incubating plasma HDL with chemical oxidizing systems (Cu++) in conditions similar to those used for low-density lipoprotein (LDL) chemical oxidation. Nuclear magnetic resonance (NMR) spectroscopy (1H and 31P) was used to evaluate the degree of oxidation and to characterize the oxidized products. The almost complete loss of polyunsaturated systems together with an appreciable decrease in choline peak demonstrates large-scale HDL-lipid degradation. The appearance of epoxide systems on fatty chains and the identification of oxidized cholesterol derivatives as cholesterol 5 alpha,6 alpha-epoxide, 5 beta,6 beta-epoxide, 7-keto, and 25-hydroxy confirm this picture. Phospholipid analysis indicates an alteration of the phospholipid profile in lyso-phosphatidylcholine (Lyso-PC) production and the disappearance of phosphatidylethanolamine (PE). This study shows that HDL is extensively degraded although there are no large variations in the classical oxidative monitors, lipid hydroperoxide (LPO) and thiobarbituric acid reactive substance (TBARS). Our results suggest that HDL is significantly modified when submitted to an oxidative process.

NMR analysis of low-density lipoprotein oxidatively-modified in vitro

Human plasma low density lipoprotein has been oxidized at different stages in vitro and analysed by 1H, 13C, and 31P NMR spectroscopy and by biochemical methods. Information was obtained on: a) structure mobilities of lipids and on lipid-protein interactions; b) conjugated and oxo-dienes; c) polyunsaturated/monounsaturated fatty acid chains; d) lysophosphatidylcholine production. The results show that the NMR approach is particularly useful for the assessment of structural modification in oxidized LDL.

Proton nuclear magnetic resonance methyl and methylene linewidths from plasma decrease during postprandial lipemia

Narrow proton nuclear magnetic resonance (1H-NMR) linewidths from plasma have been associated with the presence of malignancy (Fossel et al., New Engl. J. Med. (1986) 315, 1369-1376). In that study, subjects and controls were not fasted. In the present study, 1H-NMR methyl and methylene linewidths were measured in plasma from normolipemic individuals without cancer both during fasting and every 90 min after eating a fat meal. Plasma lipoprotein levels were measured in order to relate results to postprandial lipemia. Methyl, methylene, and average 1H-NMR linewidths were strongly positively correlated with high-density lipoprotein levels and inversely correlated with triacylglycerol-rich lipoprotein levels in both the fasting and postprandial states. Linewidths decreased postprandially, reaching a nadir at the peak of plasma triacylglycerol levels. This study demonstrated that postprandial lipemia can lead to narrowing of plasma methyl and methylene resonances comparable to that reported for subjects with cancer.

NMR studies of body fluids

High resolution, high frequency, in vitro, proton NMR spectra of various body fluids, including urine, sweat, aqueous humour, amniotic fluid, seminal plasma, cerebrospinal fluid, synovial fluid and blood plasma are described and discussed. Applications include the detection of metabolic disorders, investigations of the biochemical basis of drug and xenobiotic metabolism, organ damage, and diagnoses for sick babies. The determination of metabolite concentrations is straightforward for fluids with a low protein content such as urine. In fluids with a high protein content such as blood plasma, it is possible to detect not only small molecules but also mobile regions of macromolecules, and to demonstrate the interaction of anions such as lactate with proteins. It seems likely that these methods will soon become established in modern pathology laboratories.

H and 13C n.m.r. studies of serum from normal and Echinococcus multilocularis infected jirds

The major components of the 13C and high field region of the 1H nuclear magnetic resonance (n.m.r.) spectra of normal and Echinococcus multilocularis infected jirds were identified and compared. Substantial depletion of the glucose and fatty acid chains from lower density lipoproteins was detected in sera from infected animals. In addition, this proliferating metacestode markedly changed the appearance of the spectral region recently assigned to N-acetyl protons of carbohydrate side chains of N-acetylated glycoproteins.

Assessing the value of identifying the presence of malignant disease in human plasma by proton nuclear magnetic resonance spectroscopy

PURPOSE

This study was performed to assess the ability of the average linewidths of the methyl and methylene resonances from the proton nuclear magnetic resonance (NMR) spectrum of human plasma to distinguish reliably between a normal, apparently healthy population and untreated patients with cancer as was suggested by a recent report (Fossel et al, N Engl J Med 1986; 315: 1369-1376). In that report, the absence of overlap between the two populations suggested that the technique had great diagnostic potential.

SUBJECTS AND METHODS

Blood samples were collected from healthy hospital personnel and patients with biopsy proven cancer who had not yet undergone chemotherapy or radiotherapy. NMR measurements were obtained on decanted plasma samples. In addition, to determine whether the distributions obtained were sensitive to experimental conditions, we varied a number of experimental parameters. These were storage temperature, observation temperature, NMR observation technique, and magnetic field inhomogeneity.

RESULTS

In our hands, the distributions substantially overlapped, although the means of the average linewidths of the normal (35.0 +/- 5.3 Hz, range = 24 to 48 Hz) and patient (31.6 +/- 5.7 Hz, range 20 to 44 Hz) populations were significantly different, delta = 3.4 Hz, p = 0.023. The degree of overlap corresponded to 74 percent sensitivity and 59 percent specificity. The distributions were independent of the experimental conditions except for observation temperature. In this case, there was insufficient difference between our experimental conditions and those of Fossel et al (25 degrees C versus 22 degrees C) to explain the difference in results.

CONCLUSION

Our findings suggest that wide variations exist among normal, apparently healthy persons and emphasize the need for carefully matched control subjects. We conclude that this measurement is, as of now, unsuitable as a method for identifying malignant disease.

1H and 13C nuclear magnetic resonance studies of plasma from patients with primary intracranial neoplasms

Plasma from patients with malignant and benign primary intracranial neoplasms and from healthy control subjects has been examined using proton (1H) and carbon-13 nuclear magnetic resonance (NMR) spectroscopy. Some features in the spectra of plasma from patients with malignant tumors differ significantly (p less than 0.01) from the corresponding features in the spectra of plasma from control subjects and from patients with benign tumors. The NMR spectral parameters vary consistently with the Kernohan grade of astrocytoma, which may suggest that they give a measure of tumor growth kinetics. The observed spectral differences are shown to be due to elevated levels of monounsaturated and polyunsaturated fatty acid residues in the plasma of cancer patients. It is proposed that these lipid residues arise from cell membranes shed from cells in growing tumors. The ability to follow tumor growth kinetics directly may be of considerable importance in elucidating the effects of primary intracranial neoplasm therapy.