Lipids of human myocardium

Micromethods for analysis of lipids in endomyocardial biopsy specimens

Triglycerides and phospholipids extracted from endomyocardial biopsy specimens were quantitated with sensitive photometric methods and the fatty acid composition of phospholipids was determined after separation of the methyl esters by gas chromatography. The degree of triglyceride accumulation was expressed as the molar ratio triglyceride/phospholipid since in most cases the phospholipid concentration is relatively constant. The representativity of the analysis of endomyocardial biopsy was investigated by comparing lipid analyses of large and small myocardial specimens obtained at necropsy. The methods described may be valuable tools in studies on metabolic disturbances in different cardiomyophaties.

Effects of fish-oil supplementation on myocardial fatty acids in humans

BACKGROUND

Increased fish or fish-oil consumption is associated with reduced risk of cardiac mortality, especially sudden death. This benefit putatively arises from the incorporation of the long-chain n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into cardiomyocyte phospholipids.

OBJECTIVE

The study examined the kinetics of incorporation of n-3 fatty acids into human myocardial membrane phospholipids during supplementation with fish oil and alpha-linolenic acid-rich flaxseed oil.

DESIGN

Patients with low self-reported fish intake (<1 fish meal/wk and no oil supplements) accepted for elective cardiac surgery involving cardiopulmonary bypass were randomly allocated to 1 of 6 groups: no supplement; fish oil (6 g EPA+DHA/d) for either 7, 14, or 21 d before surgery; flaxseed oil; or olive oil (both 10 mL/d for 21 d before surgery). Right atrial appendage tissue removed during surgery and blood collected at enrollment and before surgery were analyzed for phospholipid fatty acids.

RESULTS

Surgery rescheduling resulted in a range of treatment times from 7 to 118 d. In the fish-oil-treated subjects, accumulation of EPA and DHA in the right atrium was curvilinear with time and reached a maximum at approximately 30 d of treatment and displaced mainly arachidonic acid. Flaxseed oil supplementation yielded a small increase in atrial EPA but not DHA, whereas olive oil did not significantly change atrial n-3 fatty acids.

CONCLUSION

The results of the present study show that dietary n-3 fatty acids are rapidly incorporated into human myocardial phospholipids at the expense of arachidonic acid during high-dose fish-oil supplementation.

Prediction of pharmacokinetics prior to in vivo studies. 1. Mechanism-based prediction of volume of distribution

In drug discovery and nonclinical development the volume of distribution at steady state (V(ss)) of each novel drug candidate is commonly determined under in vivo conditions. Therefore, it is of interest to predict V(ss) without conducting in vivo studies. The traditional description of V(ss) corresponds to the sum of the products of each tissue:plasma partition coefficient (P(t:p)) and the respective tissue volume in addition to the plasma volume. Because data on volumes of tissues and plasma are available in the literature for mammals, the other input parameters needed to estimate V(ss) are the P(t:p)'s, which can potentially be predicted with established tissue composition-based equations. In vitro data on drug lipophilicity and plasma protein binding are the input parameters used in these equations. Such a mechanism-based approach would be particularly useful to provide first-cut estimates of V(ss) prior to any in vivo studies and to explore potential unexpected deviations between sets of predicted and in vivo V(ss) data, when the in vivo data become available during the drug development process. The objective of the present study was to use tissue composition-based equations to predict rat and human V(ss) prior to in vivo studies for 123 structurally unrelated compounds (acids, bases, and neutrals). The predicted data were compared with in vivo data obtained from the literature or at Roche. Overall, the average ratio of predicted-to-experimental rat and human V(ss) values was 1.06 (SD = 0.817, r = 0.78, n = 147). In fact, 80% of all predicted values were within a factor of two of the corresponding experimental values. The drugs can therefore be separated into two groups. The first group contains 98 drugs for which the predicted V(ss) were within a factor of two of those experimentally determined (average ratio of 1.01, SD = 0.39, r = 0.93, n = 118), and the second group includes 25 other drugs for which the predicted and experimental V(ss) differ by a factor larger than two (average ratio of 1.32, SD = 1.74, r = 0.42, n = 29). Thus, additional relevant distribution processes were neglected in predicting V(ss) of drugs of the second group. This was true especially in the case of some cationic-amphiphilic bases. The present study is the first attempt to develop and validate a mechanistic distribution model for predicting rat and human V(ss) of drugs prior to in vivo studies.

Lipid oxidation products in ischemic porcine heart tissue

Infarcted porcine heart tissue and surrounding tissue were investigated for the content of plasmalogens and oxidatively derived corresponding alpha-hydroxyaldehydes as well as for products of lipid peroxidation, e.g. malondialdehyde, glyoxal, 2-hydroxyheptanal and oxygenated fatty acids. Oxidation products of unsaturated fatty acids and plasmalogens were accumulated in infarcted tissue compared to the surrounding one. Their amounts increased with time of ischemia. In addition leukotoxins (9, 10-epoxy-12-octadecenoic acid and 12,13-epoxy-9-octadecenoic acid) as well as other epoxides of unsaturated fatty acids were identified. These compounds are absent in healthy heart tissue. Some of the monohydroxy fatty acids, found in comparable high yield, can not be derived from LPO processes. They are obviously generated from epoxides. Their distribution pattern indicates that they originate by an enzymic rather than by an autocatalytic process. We assume that the enzymes are activated by cell injury due to infarction. Linoleic acid seems to be an as equally well-suited substrate for enzymic attack as arachidonic acid.

An approach for incorporating tissue composition data into physiologically based pharmacokinetic models

The objective of this study was to develop an approach for incorporating tissue composition data into physiologically based pharmacokinetic (PBPK) models in order to facilitate "built-in" calculation of tissue: air partition coefficients (PCs) of volatile organic chemicals. The approach involved characterizing tissue compartments within PBPK models as a mixture of neutral lipids, phospholipids, and water (instead of using the conventional description of them as "empty" boxes). This approach enabled automated calculation of the tissue solubility of chemicals from n-octanol and water solubility data, since these data approximate those of solubility in tissue lipids and water. Tissue solubility was divided by the saturable vapor concentration at 37 degrees C to estimate the tissue: air PCs within PBPK models, according to the method of Poulin and Krishnan (1995c). The highest and lowest lipid and water levels for human muscle, liver, and adipose tissues were obtained from the literature and incorporated within the tissue composition-based PBPK model to calculate the tissue: air PCs of dichloromethane (DCM) and simulate the pharmacokinetics of DCM in humans. The PC values predicted for human tissues were comparable to those estimated using rat tissues in cases where the relative levels of lipids and water were comparable in both species. These results suggest that the default assumption of using rat tissue: air PCs in human PBPK models may be acceptable for certain tissues (liver, adipose tissues), but questionable for others (e.g., muscle). The PBPK modeling exercise indicated that the interindividual differences in tissue dose arising from variations of tissue: air PCs may not be reflected sufficiently by venous blood concentrations. Overall, the present approach of incorporating tissue composition data into PBPK models would not only enhance the biological basis of these models but also provide a means of evaluating the impact of interindividual and interspecies differences in tissue composition on the tissue dose surrogates used in PBPK-based risk assessments.

A biologically-based algorithm for predicting human tissue: blood partition coefficients of organic chemicals

A biologically-based algorithm for predicting the tissue: blood partition coefficients (PCs) of organic chemicals has been developed. The approach consisted of (i) describing tissues and blood in terms of their neutral lipid, phospholipid, and water contents, (ii) obtaining data on the solubility of chemicals in n-octanol and water, and (iii) calculating the tissue: blood PCs by assuming that the solubility of a chemical in n-octanol corresponds to its solubility in neutral lipids, the solubility in water corresponds to the solubility in tissue/blood water fraction, and the solubility in phospholipids is a function of solubility in water and n-octanol. The adequacy of this approach was verified by comparing the predicted values with previously published experimental data on human tissue (liver, lung, muscle, kidney, brain, adipose tissue): blood PCs for 23 organic chemicals. In the case of liver, lung, and muscle, the predicted PC values were in close agreement with the higher-end of the range of experimental PC values found in the literature. The predicted brain: and kidney: blood PCs were greater than the experimental PCs in most cases by approximately a factor of two. Whereas the adipose tissue: blood PCs of relatively less hydrophilic chemicals were adequately predicted, the predicted PCs for relatively more hydrophilic chemicals were much greater than the experimentally-determined values. There was a good agreement between the predicted and experimentally-determined blood solubility of the 23 chemicals chosen for this study, indicating that the over-estimation of tissue:blood PCs by the present method is not due to under-estimation of blood solubility of chemicals.(ABSTRACT TRUNCATED AT 250 WORDS)

Phospholipid content and fatty acid composition of human heart

Phospholipid content and fatty acid composition of human heart were determined on 36 biopsy specimens collected during open heart surgery. The main phospholipid classes, phosphatidylcholine (PC), phosphatidylethanolamine (PE), diphosphatidylglycerol (DPG), and sphingomyelin (SPH) were separated by HPLC, quantified, and converted to fatty acid methyl esters which were chromatographed on capillary GLC columns. Sex and age (mainly 40-70) of patients had no significant influence on the relative distribution of phospholipid classes and only a slight effect on fatty acid composition. Incorporation of trans 18:1 in phospholipid classes was low. cis and trans octadecenoic isomers seemed to be selectively incorporated, the delta 9 and delta 11 cis or trans isomers being predominant. Human and rat data were compared, and some species differences were noticed. In human PC, palmitic acid is higher and stearic acid much lower than in rat PC. Saturated dimethyl acetals (16:0 and 18:0) in PC and PE were greater for humans. Incorporation of 20:4 n-6 in human PE is higher than in rat PE.

Fatty acid composition of human heart phospholipids: data from 53 biopsy specimens

Fatty acid composition of human heart phospholipids was determined in 53 specimens of left ventricular myocardium collected during mitral valve replacement. Ages of the subjects (29 males and 24 females) ranged from 14 to 75 years (mean age = 54). Samples were immediately placed in chloroform-methanol 2/1, v/v to which antioxidant was added. Extracted phospholipids were converted to methyl esters which were analyzed by gas liquid chromatography on glass capillary columns. Morphological examination was also performed on 35 out of 53 samples. Age of the patients as well as the morphological state of the organ had no significant effect on major fatty acids in heart phospholipids. No difference by sex was detected. Trans-octadecenoic isomers were detected in all samples but they remained at a low level (0.4% to 1.2% of the total fatty acids).

Isolation and partial characterization of the neutral glycosphingolipids and gangliosides of the human heart

The glycosphingolipids (GSL) of the human heart muscle have been isolated from total lipids by column and thin layer chromatography and their sugars and fatty acids analyzed by gas liquid chromatography. Hearts from traffic victims were obtained at autopsy between 12 and 16 hr after death and dissected into parts (left and right ventricular walls, intraventricular septum and papillary muscle). The neutral GSL content for those parts of the hearts of two males aged 22 and one female aged 14 ranged from about 90 to 160 nmoles/g wet weight. Trihexosyl ceramide and globoside were the most abundant neutral GSL. Total ganglioside content was about 50 nmoles/g wet weight, and the most abundant gangliosides were partially characterized as GM3 and GM1; other mono-, di- and trisialogangliosides were also present. Differences in the content and composition of neutral GSL and gangliosides between the heart and other human tissues are discussed. It is concluded that the patterns of these two GSL fractions of the heart are more complex than those of the extraneural human tissues.

Evidence for cardiomyopathy in familial diabetes mellitus

Recent epidemiologic studies have suggested that cardiac disease in common in diabetics and may often have a noncoronary basis. To examine the status of the left ventricle, 17 adult-onset diabetics of familial type without hypertension or obesity underwent hemodynamic study and were compared to 9 controls of similar age. Of the 17, 12 subjects had no significant occlusive lesions by coronary angiography. From this group eight without heart failure had a modest, but significant, elevation of left ventricular end-diastolic pressure. End-diastolic and stroke volumes were reduced, but ejection fraction and mean rate of fiber shortening were within normal limits. The left ventricular end-diastolic pressure/volume ratio was significantly higher than controls. Afterload increments effected a significant increase of filling pressure compared to normals without a stroke volume response, consistent with a preclinical cardiomyopathy. Four patients with prior heart failure had similar but more extensive abnormalities. None had local dyskinesia by angiography, and lactate production was not observed during pacing-induced tachycardia. Left ventricular biopsy in two patients without ventricular decompensation showed interstitial collagen deposition with relatively normal muscle cells. These findings suggest a myopathic process without ischemia. Postmortem studies were performed in 11 uncomplicated diabetics. Nine were without significant obstructive disease of the proximal coronary arteries, and the majority succumbed with cardiac failure. On left ventricular sections, none had evident luminal narrowing of the intramural vessels. All nine exhibited periodic acid-Schiff-positive material in the interstitium. Collagen accumulation was present in perivascular loci, between myofibers, or as replacement fibrosis. Multiple samples of left ventricle and septum revealed enhanced triglyceride and cholesterol concentrations, as compared to controls. Thus, a diffuse extravascular abnormality may be a basis for cardiomyopathic features in diabetes.