Lipid accumulation in isolated perfused rat hearts has no apparent effect on mechanical function or energy metabolism as measured by 31P NMR

Short-term caloric restriction induces accumulation of myocardial triglycerides and decreases left ventricular diastolic function in healthy subjects

OBJECTIVE

Diabetes and obesity are associated with increased plasma nonesterified fatty acid (NEFA) levels, myocardial triglyceride accumulation, and myocardial dysfunction. Because a very low-calorie diet (VLCD) also increases plasma NEFA levels, we studied the effect of a VLCD on myocardial triglyceride content and cardiac function in healthy subjects.

RESEARCH DESIGN AND METHODS

Fourteen healthy nonobese men underwent (1)H-magnetic resonance spectroscopy (MRS) to determine myocardial and hepatic triglyceride content, (31)P-MRS to assess myocardial high-energy phosphate (HEP) metabolism (phosphocreatine/ATP), and magnetic resonance imaging of myocardial function at baseline and after a 3-day VLCD.

RESULTS

After the dietary intervention, plasma NEFA levels increased compared with those at baseline (from 0.5 +/- 0.1 to 1.1 +/- 0.1 mmol/l, P < 0.05). Concomitantly, myocardial triglyceride content increased by approximately 55% compared with that at baseline (from 0.38 +/- 0.05 to 0.59 +/- 0.06%, P < 0.05), whereas liver triglyceride content decreased by approximately 32% (from 2.2 +/- 0.5 to 1.5 +/- 0.4%, P < 0.05). The VLCD did not change myocardial phosphocreatine-to-ATP ratio (2.33 +/- 0.15 vs. 2.33 +/- 0.08, P > 0.05) or systolic function. Interestingly, deceleration of the early diastolic flow across the mitral valve decreased after the VLCD (from 3.37 +/- 0.20 to 2.91 +/- 0.16 ml/s(2) x 10(-3), P < 0.05). This decrease in diastolic function was significantly correlated with the increase in myocardial triglyceride content.

CONCLUSIONS

Short-term VLCD induces accumulation of myocardial triglycerides. In addition, VLCD decreases left ventricular diastolic function, without alterations in myocardial HEP metabolism. This study documents diet-dependent physiological variations in myocardial triglyceride content and diastolic function in healthy subjects.

Expression of large genomic clones in transgenic mice: new insights into apolipoprotein B structure, function and regulation

Extensive manipulation of the apolipoprotein B gene in yeast and bacterial artificial chromosome clones and subsequent expression of these clones in transgenic mice have provided fresh insights into several aspects of apolipoprotein B biology, including the identification of sequences important for lipoprotein (a) assembly, the demonstration that intestinal expression of apolipoprotein B is controlled by DNA sequences > 50 kb from the gene, and the extraordinary finding that apolipoprotein B is expressed in the heart.

Simultaneous measurement of both lipid and lactate in isolated rat hearts by 1H NMR spectroscopy

Myocardial lipid and lactate levels are sensitive indicators of biochemical status: lipid levels have been shown to increase in response to high fat diets, disease or metabolic stress and elevated lactate levels are indicative of reduced oxygen supply. Selective measurement of lactate or lipid levels by 1H NMR is not straightforward since both the lactate methyl group and lipid methylene groups resonate at 1.3 ppm. We have overcome this difficulty by employing spectral editing techniques to observe both lipid methylene and lactate methyl resonances, and have measured lipid and lactate levels in perfused rat hearts during control perfusion and in response to metabolic stress. Lactate increased during ischemia and decreased during reperfusion, and the ischemia-induced increase is inhibited by iodoacetate, as expected. In contrast, lipid levels increased during ischemia and remained elevated during reperfusion. Hearts from rats fed high fat diet show elevated lipid levels during control perfusion. Data obtained by 1H NMR are consistent with biochemical data, validating the technique.