Cardiac Steatosis and Left Ventricular Hypertrophy in Patients With Generalized Lipodystrophy as Determined by Magnetic Resonance Spectroscopy and Imaging

Generalized lipodystrophy is a rare disorder characterized by marked loss of adipose tissue with reduced triglyceride storage capacity, leading to a severe form of metabolic syndrome including hypertriglyceridemia, insulin resistance, type 2 diabetes mellitus, and hepatic steatosis. Recent echocardiographic studies suggest that concentric left ventricular (LV) hypertrophy is another characteristic feature of this syndrome, but the mechanism remains unknown. It has recently been hypothesized that the LV hypertrophy could be an extreme clinical example of “lipotoxic cardiomyopathy”: excessive myocyte accumulation of triglyceride leading to adverse hypertrophic signaling. To test this hypothesis, the first cardiac magnetic resonance study of patients with generalized lipodystrophy was performed, using magnetic resonance imaging and localized proton spectroscopy to detect excessive triglyceride content in the hypertrophied myocytes. Six patients with generalized lipodystrophy and 6 healthy controls matched for age, gender, and body mass index were studied. As hypothesized, myocardial triglyceride content was threefold higher in patients than controls: 0.6 ± 0.2% versus 0.2 ± 0.1% (p = 0.004). The presence of pericardial fat was also found, representing a previously undescribed adipose depot in generalized lipodystrophy. Patients with generalized lipodystrophy, compared with controls, also had a striking degree of concentric LV hypertrophy, independent of blood pressure: LV mass index 101.0 ± 18.3 versus 69.0 ± 17.7 g/m2, respectively (p = 0.02), and LV concentricity 1.3 ± 0.3 versus 0.99 ± 0.1 g/ml, respectively (p = 0.04). In conclusion, these findings advance the lipotoxicity hypothesis as a putative underlying mechanism for the dramatic concentric LV hypertrophy found in generalized lipodystrophy. Generalized lipodystrophy is a rare disorder characterized by marked loss of adipose tissue with reduced triglyceride storage capacity, leading to a severe form of metabolic syndrome including hypertriglyceridemia, insulin resistance, type 2 diabetes mellitus, and hepatic steatosis. Recent echocardiographic studies suggest that concentric left ventricular (LV) hypertrophy is another characteristic feature of this syndrome, but the mechanism remains unknown. It has recently been hypothesized that the LV hypertrophy could be an extreme clinical example of “lipotoxic cardiomyopathy”: excessive myocyte accumulation of triglyceride leading to adverse hypertrophic signaling. To test this hypothesis, the first cardiac magnetic resonance study of patients with generalized lipodystrophy was performed, using magnetic resonance imaging and localized proton spectroscopy to detect excessive triglyceride content in the hypertrophied myocytes. Six patients with generalized lipodystrophy and 6 healthy controls matched for age, gender, and body mass index were studied. As hypothesized, myocardial triglyceride content was threefold higher in patients than controls: 0.6 ± 0.2% versus 0.2 ± 0.1% (p = 0.004). The presence of pericardial fat was also found, representing a previously undescribed adipose depot in generalized lipodystrophy. Patients with generalized lipodystrophy, compared with controls, also had a striking degree of concentric LV hypertrophy, independent of blood pressure: LV mass index 101.0 ± 18.3 versus 69.0 ± 17.7 g/m2, respectively (p = 0.02), and LV concentricity 1.3 ± 0.3 versus 0.99 ± 0.1 g/ml, respectively (p = 0.04). In conclusion, these findings advance the lipotoxicity hypothesis as a putative underlying mechanism for the dramatic concentric LV hypertrophy found in generalized lipodystrophy. Lipodystrophy is an extremely rare disorder characterized by loss of body fat and thus deficiency of the adipocytokines, such as leptin and adiponectin.1Garg A. Lipodystrophies: genetic and acquired body fat disorders.J Clin Endocrinol Metab. 2011; 96: 3313-3325Crossref PubMed Scopus (373) Google Scholar The cause can be either inherited or acquired, and the loss of body fat may be generalized or partial. Patients with generalized lipodystrophy are markedly leptin deficient and are severely hyperphagic, but they have no adipose tissue to store the excess energy, leading to ectopic deposition of triglyceride in nonadipose tissue, most notably the parenchymal cells of the liver and skeletal muscle.2Szczepaniak L.S. Babcock E.E. Schick F. Dobbins R.L. Garg A. Burns D.K. McGarry J.D. Stein D.T. Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo.Am J Physiol Endocrinol Metab. 1999; 276: E977-E989Google Scholar, 3Simha V. Szczepaniak L.S. Wagner A.J. DePaoli A.M. Garg A. Effect of leptin replacement on intrahepatic and intramyocellular lipid content in patients with generalized lipodystrophy.Diabetes Care. 2003; 26: 30-35Crossref PubMed Scopus (104) Google Scholar Consequently, they develop a severe form of metabolic syndrome with insulin resistance, type 2 diabetes mellitus, hypertriglyceridemia, and nonalcoholic fatty liver disease.4Garg A. Misra A. Lipodystrophies: rare disorders causing metabolic syndrome.Endocrinol Metab Clin of North Am. 2004; 33: 305-331Abstract Full Text Full Text PDF PubMed Scopus (108) Google Scholar Recent echocardiographic studies suggest that concentric left ventricular (LV) hypertrophy constitutes another common feature of patients with either congenital or acquired generalized lipodystrophy.5Lupsa B.C. Sachdev V. Lungu A.O. Rosing D.R. Gorden P. Cardiomyopathy in congenital and acquired generalized lipodystrophy: a clinical assessment.Medicine. 2010; 89: 245-250Crossref PubMed Scopus (63) Google Scholar Although the precise underlying mechanism remains unknown, an attractive hypothesis is that the LV hypertrophy could be an extreme clinical example of “lipotoxic cardiomyopathy”: excessive myocyte accumulation of triglyceride (i.e., “cardiac steatosis”) leading to adverse hypertrophic signaling. However, myocardial triglyceride content has not previously been measured in these patients. We therefore used magnetic resonance imaging (MRI) and localized proton magnetic resonance spectroscopy (MRS) to determine if there was a relation between myocardial hypertrophy and triglyceride content in patients with generalized lipodystrophy. Six patients with generalized lipodystrophy (2 with congenital generalized lipodystrophy type 1 due to acylglycerol phosphate acyltransferase isoform 2 gene mutations, 3 with type 2 congenital generalized lipodystrophy due to Berardinelli-Seip congenital lipodystrophy 2 gene mutations, and 1 with acquired generalized lipodystrophy) were recruited for the present investigation. For cross-sectional comparison, 6 healthy control subjects, matched for age, gender, and body mass index, without metabolic disease, were selected from an existing database. The study was approved by the Institutional Review Board of the University of Texas Southwestern Medical Center, and all participants provided written informed consent before the study. Body mass index was calculated as weight in kilograms divided by the square of height in meters. Body surface area was calculated according to the formula of DuBois and DuBois.6DuBois D. DuBois E. A formula to estimate the approximate surface area if height and weight be known.Arch Intern Med. 1916; 17: 863-871Crossref Scopus (4131) Google Scholar Blood pressure was measured in the seated position, with a validated oscillometric sphygmomanometer (series 52000; Welch Allyn, Inc., Arden, North Carolina), with an appropriately sized cuff placed on the upper left arm. Venous blood samples were obtained from all participants and processed according to standard laboratory procedures.7Ahmad Z. Subramanyam L. Szczepaniak L. Simha V. Adams-Huet B. Garg A. Cholic acid for hepatic steatosis in patients with lipodystrophy: a randomized, controlled trial.Eur J Endocrinol. 2013; 168: 771-778Crossref PubMed Scopus (15) Google Scholar All cardiac magnetic resonance experiments were performed using a 1.5-T Gyroscan Intera whole-body magnetic resonance system (Philips Medical Systems, Best, The Netherlands). Cardiac MRI was used to assess LV morphology, as previously described.8McGavock J.M. Lingvay I. Zib I. Tillery T. Salas N. Unger R. Levine B.D. Raskin P. Victor R.G. Szczepaniak L.S. Cardiac steatosis in diabetes mellitus: a 1H-magnetic resonance spectroscopy study.Circulation. 2007; 116: 1170-1175Crossref PubMed Scopus (485) Google Scholar, 9Riley-Hagan M. Peshock R.M. Stray-Gundersen J. Katz J. Ryschon T.W. Mitchell J.H. Left ventricular dimensions and mass using magnetic resonance imaging in female endurance athletes.Am J Cardiol. 1992; 69: 1067-1074Abstract Full Text PDF PubMed Scopus (52) Google Scholar Cardiac MRS was used for the noninvasive quantification of cardiac triglyceride content, as described in detail elsewhere.2Szczepaniak L.S. Babcock E.E. Schick F. Dobbins R.L. Garg A. Burns D.K. McGarry J.D. Stein D.T. Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo.Am J Physiol Endocrinol Metab. 1999; 276: E977-E989Google Scholar, 3Simha V. Szczepaniak L.S. Wagner A.J. DePaoli A.M. Garg A. Effect of leptin replacement on intrahepatic and intramyocellular lipid content in patients with generalized lipodystrophy.Diabetes Care. 2003; 26: 30-35Crossref PubMed Scopus (104) Google Scholar, 10Szczepaniak L.S. Dobbins R.L. Stein D.T. McGarry J.D. Bulk magnetic susceptibility effects on the assessment of intra- and extramyocellular lipids in vivo.Magn Reson Med. 2002; 47: 607-610Crossref PubMed Scopus (66) Google Scholar, 11Szczepaniak L.S. Nurenberg P. Leonard D. Browning J.D. Reingold J.S. Grundy S. Hobbs H.H. Dobbins R.L. Magnetic resonance spectroscopy to measure hepatic triglyceride content: prevalence of hepatic steatosis in the general population.Am J Physiol Endocrinol Metab. 2005; 288: E462-E468Crossref PubMed Scopus (1231) Google Scholar Briefly, image-guided MRS was performed with the following imaging parameters: repetition time 4 seconds, echo time 25 ms, and 1,024 data points over a 1,000-kHz spectral width. The volume of interest (voxel) was centered over the intraventricular septum at end-systole to avoid vascular structures and gross adipose tissue deposits and to ensure consistent orientation of muscle fibers along the magnetic field (Figure 1). Spectra were processed and resonances quantified using a standard analysis package (NUTS; ACORNNMR, Fremont, California). Myocardial triglyceride content is expressed as a percentage of the intensity of the water resonance peak. Cross-sectional comparisons (patients vs controls) were performed using independent-samples Student's t tests. The level of significance was set a priori at p ≤0.05. Data are reported as mean ± SE, unless otherwise specified. Patient-specific characteristics are listed in Table 1. Patients and controls were well matched for age, height, and weight, and therefore no differences in body surface area or body mass index were found. As expected, patients had elevated circulating triglycerides and fasting glucose, with 4 of the 6 patients being treated with insulin (patients from pairs 1, 3, 4, and 6; Table 1). One patient (pair 6) was being treated with a lipid-lowering medication at the time of the study. No difference in serum cholesterol level was found, whereas high-density lipoprotein cholesterol was significantly lower in patients compared with controls. Blood pressure was similar between the 2 groups and in the normotensive range, except for 2 patients with lipodystrophy (pairs 3 and 6) whose blood pressures were elevated at the time of the study.Table 1Cross-sectional participant characteristics: patients versus controlsVariablePair 1Pair 2Pair 3Pair 4Pair 5Pair 6Mean ± SDp ValuePatientControlPatientControlPatientControlPatientControlPatientControlPatientControlPatientControlAnthropometrics Age (yrs)16231833201921222323302721 ± 524 ± 50.288 GenderFFFFMMMMFFFF—— Height (cm)160158162160175173163184176160171168168 ± 7167 ± 0.10.941 Weight (kg)5051474683.48666817255.971.365.864.9 ± 14.064.3 ± 16.30.897 Body mass index (kg/m2)19.520.417.918.027.228.724.823.923.221.824.423.322.9 ± 3.522.7 ± 3.60.944 Body surface area (m2)1.51.51.51.52.02.01.72.01.91.61.81.81.7 ± 0.21.7 ± 0.30.924Hemodynamics Systolic blood pressure (mm Hg)120112106118142141125122122106166136130 ± 21122 ± 140.470 Diastolic blood pressure (mm Hg)76746069717178677663988677 ± 1272 ± 80.440 Mean arterial pressure (mm Hg)9187758595949485917712110294 ± 14589 ± 90.427 Heart rate (beats/min)858480868267855675601057885 ± 1069 ± 120.038LV morphology End-diastolic volume (ml)120111.6103.477.7178.1141142.6169.5137.9121.2127.593.6135.0 ± 25.3119.1 ± 33.00.372 End-systolic volume (ml)45.351.733.527.276.553.250.644.556.546.551.927.952.4 ± 14.241.8 ± 11.50.188 Stroke volume (ml)75.16069.950.5101.687.892125.081.474.775.665.782.6 ± 12.077.3 ± 26.60.665 Ejection fraction (%)625467.76757626573.75961.7597062 ± 465 ± 70.372 Mass (g)147.599.5110.765.4212.0140.4196195163.4126.3229.198.6176.4 ± 44.2120.9 ± 44.60.055 Mass index (g/m2)98.266.375.045.1106.570.2114.595.68780.3125.156.4101.0 ± 18.369.0 ± 17.70.012 Concentricity (g/ml)1.20.91.10.81.21.01.41.21.21.01.81.01.3 ± 0.30.99 ± 0.10.023Blood chemistry Glucose (mg/dl)2378981863039918290818010594164.8 ± 91.989.7 ± 6.50.07 Triglycerides (mg/dl)1,42012366.3722,27019390426633470282968.0 ± 765.191.0 ± 59.20.02 Cholesterol (mg/dl)291192196167448204129129196137203180243.8 ± 112.6168.2 ± 30.00.143 High-density lipoproteins (mg/dl)32.461.3276246.034.528.1352749.426.456.731.2 ± 7.649.8 ± 12.50.01 Open table in a new tab The major novel finding of our study is that intramyocardial triglyceride content was threefold higher in patients with lipodystrophy compared with controls (p = 0.004; Figure 1). Unexpectedly, cardiac MRI also detected pericardial adipose tissue in the patients, despite their general lack of adipose tissue elsewhere in the body (Figure 2). Last, LV mass indexed to body surface area and LV concentricity were dramatically increased in patients compared with controls (Table 1), regardless of whether the 2 patients with elevated blood pressure were excluded from analysis (Figure 3). No group differences were found in LV end-diastolic volume, end-systolic volume, stroke volume, or ejection fraction between groups (Table 1).Figure 3LV concentricity and LV mass are independent of arterial blood pressure. Note that with the 2 patients with the highest blood pressure removed, systolic blood pressure (A) decreases to less than that of controls, but LV mass indexed to body surface area (BSA) (B) and LV concentricity (C) remain elevated above controls. Subject-specific data are presented (solid circle, patient 1, pair 1; solid square, patient 2, pair 2; open circle, patient 3, pair 3; open square, patient 4, pair 4; solid triangle, patient 5, pair 5; open triangle, patient 6; pair 6), along with the mean and SE (open bars). ∗p <0.05.View Large Image Figure ViewerDownload Hi-res image Download (PPT) This is the first cardiac MRI study of patients with generalized lipodystrophy. The MRI data confirm a high degree of concentric LV hypertrophy, as suggested by previous echocardiographic studies, and document 2 major new findings. First, consistent with the lipotoxicity hypothesis, we found that myocardial triglyceride content was markedly elevated in the patients' hypertrophied cardiomyocytes. Second, we unexpectedly found pericardial fat to be present in all the patients, representing a previously undescribed depot of adipocytes preserved in generalized lipodystrophy. Generalized lipodystrophy has been associated with ectopic accumulation of triglyceride in the parenchymal cells of the liver and skeletal muscle.2Szczepaniak L.S. Babcock E.E. Schick F. Dobbins R.L. Garg A. Burns D.K. McGarry J.D. Stein D.T. Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo.Am J Physiol Endocrinol Metab. 1999; 276: E977-E989Google Scholar, 3Simha V. Szczepaniak L.S. Wagner A.J. DePaoli A.M. Garg A. Effect of leptin replacement on intrahepatic and intramyocellular lipid content in patients with generalized lipodystrophy.Diabetes Care. 2003; 26: 30-35Crossref PubMed Scopus (104) Google Scholar The threefold elevation in myocardial triglyceride content in our patients shows that the heart is another steatotic target organ in this disease. From a mechanistic standpoint, generalized lipodystrophy is a perfect storm for cardiac steatosis. In patients with congenital generalized lipodystrophy, widespread failure of adipogenesis causes leptin deficiency and a greatly reduced adipocyte pool to store triglyceride. In patients with acquired generalized lipodystrophy, autoimmune or other unknown mechanisms cause loss of adipose tissue. These patients therefore lack the central neural action of leptin, which suppresses appetite, and the peripheral antisteatotic action of leptin, which upregulates fatty acid oxidation of nonadipose tissue, so as to oxidize any lipid spillover that may have occurred because of overnutrition.12Lee Y. Wang M.Y. Kakuma T. Wang Z.W. Babcock E. McCorkle K. Higa M. Zhou Y.T. Unger R.H. Liporegulation in diet-induced obesity: the antisteatotic role of hyperleptinemia.J Biol Chem. 2001; 276: 5629-5635Crossref PubMed Scopus (238) Google Scholar Furthermore, secondary insulin resistance would also be expected to disrupt the balance of cardiac substrate utilization, favoring greater uptake of fatty acids.13Finck B.N. Kelly D.P. Peroxisome proliferator-activated Receptor alpha (PPARalpha) signaling in the gene regulatory control of energy metabolism in the normal and diseased heart.J Mol Cell Cardiol. 2002; 34: 1249-1257Abstract Full Text PDF PubMed Google Scholar, 14Finck B.N. Lehman J.J. Leone T.C. Welch M.J. Bennett M.J. Kovacs A. Han X. Gross R.W. Kozak R. Lopaschuk G.D. Kelly D.P. The cardiac phenotype induced by PPARalpha overexpression mimics that caused by diabetes mellitus.J Clin Invest. 2002; 109: 121-130Crossref PubMed Scopus (807) Google Scholar In addition to the new spectroscopy data, our imaging data not only confirm a dramatic degree of concentric LV hypertrophy in generalized lipodystrophy but also document the consistent presence of pericardial fat. The latter finding was quite unexpected because pericardial fat represents a protected pool of adipocytes in a disease characterized by widespread failure of adipogenesis. This in vivo cardiac MRI finding differs from autopsy studies concluding that patients with generalized lipodystrophy have no pericardial fat.15Arky R.A. McCully K.S. Case 1–1975.N Engl J Med. 1975; 292: 35-41Crossref PubMed Scopus (7) Google Scholar, 16Chandalia M. Garg A. Vuitch F. Nizzi F. Postmortem findings in congenital generalized lipodystrophy.J Clin Endocrinol Metab. 1995; 80: 3077-3081Crossref PubMed Google Scholar We interpret our data to suggest that the beating heart produces repetitive stimulation of mechanosensitive transcriptional elements of genes involved in adipogenesis. Mechanosensitive adipogenesis is indeed an accepted explanation for the residual adipose tissue patients with congenital generalized lipodystrophy type 1 have in the intraorbital region, palms, and soles.17Garg A. Fleckenstein J.L. Peshock R.M. Grundy S.M. Peculiar distribution of adipose tissue in patients with congenital generalized lipodystrophy.J Clin Endocrinol Metab. 1992; 75: 358-361Crossref PubMed Scopus (62) Google Scholar Thus, although generalized lipodystrophy results in poor growth and development of metabolically active adipose tissue, “mechanical adipose tissue” (reducing friction) appears preserved with pericardial fat, constituting yet another example. The major strength of this study is the application of cardiac MRI and MRS in an extremely rare human disease that provides a unique experiment of nature to study cardiac lipotoxicity in the absence of generalized obesity. Although these data in patients with generalized lipodystrophy are entirely consistent with the concentric LV hypertrophy being an extreme human example of lipotoxic cardiomyopathy, the major limitation of this work is that these cross-sectional data cannot prove causal attribution. Importantly, our patients' LV hypertrophy appears to have been independent of hypertension and thus was not pressure overload hypertrophy. Likewise, none of the patients was actively engaged in regular exercise training, excluding the possibility of exercise-induced cardiac remodeling. We also did not observe a systematic relation between those with impaired glucose tolerance, who were receiving insulin injections, and the development of LV hypertrophy, suggesting that the hypertrophy observed in our patients may have been independent of insulin. Last, pericardial fat has recently been implicated in the pathogenesis of LV hypertrophy,18Corradi D. Maestri R. Callegari S. P. M. The ventricular fat is to the myocardial mass in and hypertrophic 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, A. F. between adipose tissue and left ventricular J Cardiol. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, N. S. A.M. in fat weight loss in severely PubMed Scopus Google Scholar but the of pericardial fat in our patients no higher than Thus, is to that the development of LV hypertrophy in patients with generalized lipodystrophy is to their dramatic cardiac steatosis. in overexpression of fatty acid or involved in triglyceride produces severe cardiac with the excess fatty acid causing concentric LV Kovacs A. R. P. A novel of lipotoxic Clin Invest. 2001; PubMed Scopus Google Scholar, Wang F. M. Y. Y. Y. A of cardiac steatosis to 2011; PubMed Scopus Google Scholar Thus, in addition to a mechanistic explanation for the described in generalized lipodystrophy, the present results may also the development of The have no of interest to