Alterations in plasma triglycerides and ceramides: links with cardiac function in humans with type 2 diabetes.

Cardiac dysfunction in T2D is associated with excessive FA uptake, oxidation, and generation of toxic lipid species by the heart. It is not known whether decreasing lipid delivery to the heart can effect improvement in cardiac function in humans with T2D. Thus, our objective was to test the hypothesis that lowering lipid delivery to the heart would result in evidence of decreased "lipotoxicity," improved cardiac function, and salutary effects on plasma biomarkers of cardiovascular risk. Thus, we performed a double-blind randomized placebo-controlled parallel design study of the effects of 12 weeks of fenofibrate-induced lipid lowering on cardiac function, inflammation, and oxidation biomarkers, and on the ratio of two plasma ceramides, Cer d18:1 (4E) (1OH, 3OH)/24:0 and Cer d18:1 (4E) (1OH, 3OH)/16:0 (i.e., "C24:0/C16:0"), which is associated with decreased risk of cardiac dysfunction and heart failure. Fenofibrate lowered plasma TG and cholesterol but did not improve heart systolic or diastolic function. Fenofibrate treatment lowered the plasma C24:0/C16:0 ceramide ratio and minimally altered oxidative stress markers but did not alter measures of inflammation. Overall, plasma TG lowering correlated with improvement of cardiac relaxation (diastolic function) as measured by tissue Doppler-derived parameter e'. Moreover, lowering the plasma C24:0/C16:0 ceramide ratio was correlated with worse diastolic function. These findings indicate that fenofibrate treatment per se is not sufficient to effect changes in cardiac function; however, decreases in plasma TG may be linked to improved diastolic function. In contrast, decreases in plasma C24:0/C16:0 are linked with worsening cardiac function.

Development and validation of LC-MS/MS method for determination of very long acyl chain (C22:0 and C24:0) ceramides in human plasma.

Ceramide is a key metabolite in both anabolic and catabolic pathways of sphingolipids. The very long fatty acyl chain ceramides N-(docosanoyl)-sphing-4-enine (Cer(22:0)) and N-(tetracosanoyl)-sphing-4-enine (Cer(24:0)) are associated with multiple biological functions. Elevated levels of these sphingolipids in tissues and in the circulation have been associated with insulin resistance and diabetes. To facilitate quantification of these very long chain ceramides in clinical samples from human subjects, we have developed a sensitive, accurate, and high-throughput assay for determination of Cer(22:0) and Cer(24:0) in human plasma. Cer(22:0) and Cer(24:0) and their deuterated internal standards were extracted by protein precipitation and chromatographically separated by HPLC. The analytes and their internal standards were ionized using positive-ion electrospray mass spectrometry, then detected by multiple-reaction monitoring with a tandem mass spectrometer. Total liquid chromatography-tandem mass spectrometry (LC-MS/MS) runtime was 5 min. The assay exhibited a linear dynamic range of 0.02-4 and 0.08-16 µg/ml for Cer(22:0) and Cer(24:0), respectively, in human plasma with corresponding absolute recoveries from plasma at 109 and 114 %, respectively. The lower limit of quantifications were 0.02 and 0.08 µg/ml for Cer(22:0) and Cer(24:0), respectively. Acceptable precision and accuracy were obtained for concentrations over the calibration curve ranges. With the semi-automated format and short LC runtime for the assay, a throughput of ∼200 samples/day can easily be achieved.

Quantitative analysis of the magnitude and time delay of cyclic variation of myocardial backscatter from asymptomatic type 2 diabetes mellitus subjects.

Early detection of diabetic patients at high risk for developing diabetic cardiomyopathy may permit effective intervention. The goal of this work is to determine whether measurements of the magnitude and time delay of cyclic variation of myocardial backscatter, individually and in combination, can be used to discriminate between subgroups of individuals including normal controls and asymptomatic type 2 diabetes subjects. Two-dimensional parasternal long-axis echocardiographic images of 104 type 2 diabetic patients and 44 normal volunteers were acquired. Cyclic variation data were produced by measuring the mean myocardial backscatter level within a region-of-interest in the posterior wall, and characterized in terms of the magnitude and normalized time delay. The cyclic variation parameters were analyzed using Bayes classification and a nonparametric estimate of the area under the receiver operating characteristic (ROC) curve to illustrate the relative effectiveness of using one or two features to segregate subgroups of individuals. The subjects were grouped based on glycated hemoglobin (HbA1c), the homeostasis model assessment for insulin resistance (HOMA-IR) and the ratio of triglyceride to high-density lipoprotein cholesterol (TG/HDL-C). Analyses comparing the cyclic variation measurements of subjects in the highest and lowest quartiles of HbA1c, HOMA-IR and TG/HDL-C showed substantial differences in the mean magnitude and normalized time delay of cyclic variation. Results show that analyses of the cyclic variation of backscatter in young asymptomatic type 2 diabetics may be an early indicator for the development of diabetic cardiomyopathy.