Faculty Bibliography

BACKGROUND:ANGPTL3 plays a key part in lipoprotein metabolism. Zodasiran, a liver-targeted RNA interference therapeutic, inhibits ANGPTL3 expression and reduces atherogenic lipoproteins through mechanisms independent of the LDL receptor (LDLR). This approach is relevant to patients with homozygous familial hypercholesterolaemia (HoFH) who have extreme elevations of LDL cholesterol due to markedly impaired LDLR function and, as a result, very high risk of premature adverse cardiovascular events. We aimed to evaluate the long-term safety and efficacy of zodasiran in patients with HoFH. METHODS:GATEWAY was an open-label, randomised, phase 2 study done at seven clinical sites in Australia, Canada, South Africa, and the USA. Patients aged 16 years or older with documented HoFH who were receiving stable lipid-lowering therapy, were on a low-fat diet, had a screening LDL cholesterol of 2·6 mmol/L (100 mg/dL) or higher, and had triglycerides less than 3·4 mmol/L (300 mg/dL) were randomly assigned (1:1) using a block design to receive subcutaneous injections of 200 mg or 300 mg zodasiran on day 1 and month 3. When a majority of patients completed 6 months of treatment, an interim, non-binding, aggregate analysis of efficacy and safety data was conducted according to an adaptive study design to decide whether a single dose could be used for longer-term evaluation. After 9 months of follow-up, patients could opt for long-term open-label extension for an additional 24 months of subcutaneous zodasiran 200 mg injections every 3 months, as established following the planned interim analysis. The primary endpoint was percentage change from baseline to month 6 in fasting LDL cholesterol and was assessed in all randomly assigned patients who received at least one dose of study drug. Safety was assessed in all patients who received one dose of study drug. This trial is registered with ClinicalTrials.gov, NCT05217667, and is ongoing (recruitment has now ended). FINDINGS/RESULTS:Between April 1 and Nov 12, 2022, 18 patients (mean age 43·0 years [SD 19·4] and 14 [78%] White) were randomly assigned to receive zodasiran 200 mg (n=9) or 300 mg (n=9). Mean baseline LDL cholesterol concentration was 9·8 mmol/L (SD 5·7) despite background lipid-lowering therapy. At month 6, patients showed substantial dose-responsive reductions in fasting LDL cholesterol (mean -35·7% [SD 28·6; 95% CI -57·6 to -13·7] with 200 mg and -39·9% [18·1; -53·9 to -26·0]) with 300 mg, which was consistent with the interim results of more than 40% reduction in both groups. Following partial washout, all patients entered the open-label extension, in which zodasiran showed evidence of continued effect, with reductions in fasting LDL cholesterol (mean -40·7% [SD 22·3] for the pooled doses) observed for an additional 12 months, as the study was stopped early for business reasons. Reductions were greater in a subset of patients in whom lipid-lowering therapy included a PCSK9 inhibitor (mean -55·8% [SD 19·1] at month 6 of the randomised treatment period and -51·9% [11·6] at month 12 of the open-label extension). There were no drug discontinuations, drug-related severe adverse events, or deaths. In the randomised treatment period, treatment-emergent adverse events occurred in six (67%) of nine patients in the zodasiran 200 mg group and six (67%) of nine patients in the zodasiran 300 mg group, with the most frequent adverse events being nasopharyngitis (two [22%] vs two [22%]), dizziness (two [22%] vs one [11%]), and upper respiratory tract infections (one [11%] vs one [11%]). Adverse events occurred in 11 (61%) of 18 patients in the open-label extension, and the most frequent adverse events were COVID-19 (five [28%]) and nasopharyngitis (five [28%]). INTERPRETATION/CONCLUSIONS:Quarterly dosed zodasiran shows evidence of reductions in LDL cholesterol with a favourable safety profile, in patients with HoFH receiving background lipid-lowering therapy. Further investigation in phase 3 trials is warranted. FUNDING/BACKGROUND:Arrowhead Pharmaceuticals.

Long-chain fatty acids in the blood are prevented from unfettered movement into nonfenestrated tissues or the arterial wall. During fasting, nonesterified FAs are released from adipose tissue into the circulation and bind to albumin, forming a complex >65 kDa, with limited ability to efficiently cross endothelial cell (EC) barriers without a specific receptor. For this reason, nonhepatic tissue distribution of circulating FA parallels EC expression of the FA-binding protein CD36 (cluster of differentiation 36). The deletion of CD36 in ECs reduces nonesterified FA uptake by the heart, muscle, and brown adipose tissue. The other major transport system for FAs is via lipoproteins. Circulating FAs are contained within TRLs (triglyceride-rich lipoproteins), chylomicrons during the postprandial period, and VLDL (very low-density lipoprotein) both postprandially and during fasting. LPL (lipoprotein lipase) on capillary ECs releases FAs from TRLs and likely allows their passage into tissues, in part, via a CD36-independent process. ECs can also internalize lipoprotein particles, followed by the transendothelial movement of lipids. In this review, we will discuss the pathways of EC uptake of FAs from circulation, how this process affects both EC and tissue biology, and the importance of these processes for systemic metabolism and vascular health. We will conclude with speculations on methods to modulate EC FA uptake and their implications for human health.

Despite major advances in medical therapies and prevention strategies, the risk of cardiovascular complications in patients with both type I and type II diabetes remains substantially elevated. In 2019, the American Heart Association sought applications for a Strategically Focused Research Network on Cardiometabolic Health and Type 2 Diabetes. In 2020, 4 centers were named, including Brigham and Women's Hospital, Johns Hopkins University, New York University, and the University of Iowa. These centers performed basic, translational, and clinical studies to provide insights to explain the over 2-fold risk of cardiovascular complications in diabetes. Clinical studies and studies in cells and animals aimed to uncover new mechanisms responsible for disease development. Studies using human populations sought to uncover new biomarkers to prognosticate risk. In this review, we discuss several key issues and current and developing methods to understand why diabetes drives atherosclerotic cardiovascular disease and heart failure. Both human data and experimental models are considered. We integrate a review of these topics with work from the Strategically Focused Research Network and conclude with suggestions for identifying novel risk factors and future experimental research.

BACKGROUND/UNASSIGNED:Movement of circulating lipids into tissues and arteries requires transfer across the endothelial cell (EC) barrier. This process allows the heart to obtain fatty acids, its chief source of energy, and apoB-containing lipoproteins to cross the arterial endothelial barrier, leading to cholesterol accumulation in the subendothelial space. Multiple studies have established elevated postprandial TRLs (triglyceride-rich lipoproteins) as an independent risk factor for cardiovascular disease. We explored how chylomicrons affect ECs and transfer their fatty acids across the EC barrier. METHODS/UNASSIGNED:C]oleate, we studied the uptake and release of this labeled by ECs. RESULTS/UNASSIGNED:]C labeled chylomicron triglycerides exited ECs primarily in phospholipids. EVs from chylomicron-treated versus untreated ECs were larger, more abundant, and contained specific microRNAs. Treatment of macrophages and naive ECs with media from chylomicron-treated ECs increased expression of inflammatory genes. CONCLUSIONS/UNASSIGNED:EC chylomicron metabolism produces EVs that increase macrophage inflammation and create LDs. Media containing these EVs also increases EC inflammation, illustrating an autocrine inflammatory process. Fatty acids within chylomicron triglycerides are converted to phospholipids within EVs. Thus, EC uptake of chylomicrons constitutes an important pathway for vascular inflammation and tissue lipid acquisition.

BACKGROUND & AIM/UNASSIGNED:Metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing health issue. Identifying factors that prevent hepatic lipid accumulation could inform new MASLD prevention or treatment strategies. We previously demonstrated that adipocyte microsomal triglyceride transfer protein (MTP) regulates intracellular lipolysis by inhibiting adipose triglyceride lipase activity. The aim of this study was to investigate the impact of adipose MTP deficiency on MASLD. METHODS/UNASSIGNED: RESULTS/UNASSIGNED: CONCLUSION/UNASSIGNED:These findings highlight the importance of regulated FA flux from adipose tissue to the liver and the liver's adaptive capacity to utilize adipose-derived FAs in maintaining hepatic health. Modulation of adipocyte FA release may represent a therapeutic strategy to reduce hepatic steatosis. IMPACT AND IMPLICATIONS/UNASSIGNED:This study provides significant insights into the role of adipose-specific microsomal triglyceride transfer protein in regulating hepatic lipid metabolism and its potential implications for treating metabolic dysfunction-associated steatotic liver disease. By demonstrating that microsomal triglyceride transfer protein deficiency in adipose tissue leads to increased fatty acid oxidation and reduced hepatic steatosis through enhanced PPARα activation, the research underscores the importance of adipose-liver crosstalk in maintaining liver health. These findings suggest that targeting adipocyte fatty acid release could be a promising therapeutic strategy to mitigate hepatic lipid accumulation and combat metabolic dysfunction-associated steatotic liver disease, offering a novel approach to addressing this growing health issue.

Excessive accumulation of lipids within cardiomyocytes can sometimes initiate cardiomyopathy, while in other situations excess lipids do not cause harm. To understand how pathologic and non-pathologic lipid accumulation differ, we isolated lipid droplets (LDs) from two genetically altered mouse lines and from wild-type (WT) mice after an overnight fast. The LDs from MHC-peroxisomal proliferator-activated receptor γ1(MHC-Pparg1) transgenic mice were threefold larger than those from either fasted WT or non-cardiomyopathy MHC-diacylglycerol acyl transferase 1 (MHC-Dgat1) transgenic mice. Proteomic analysis of the LD-associated membrane proteins (LDAMPs) showed that MHC-Pparg1 LDs had less perilipin (PLIN). Proteins associated with lipolysis and LD formation (CIDEs and MTP), lipid synthesis, and Pparg signaling pathways were increased in MHC-Pparg1 LDAMPs. Unlike in MHC-Pparg1, MHC-Dgat1 LDAMPs exhibited increased mitochondrial peroxidative proteins with reduced adipose triglyceride lipase (Pnpla2), and Pparg coactivator 1 alpha (Pgc1A). Cardiomyocytes from MHC-Pparg1 hearts had transmission electron microscopy (TEM) images of ongoing lipolysis and greater amounts of lipolytic proteins. In contrast, images from MHC-Dgat1 cardiomyocytes showed more lipophagy. Consistent with the proteomic study and EM images, cardiac immunofluorescence staining showed that PLIN5 protein, thought to block LD lipolysis, was markedly reduced with MHC-Pparg1 overexpression, while hormone-sensitive lipase was increased. The autophagosome marker protein LC3B was increased in MHC-Dgat1 but not in MHC-Pparg1 hearts. Potentially toxic lipids like diacylglycerols and ceramides were increased in hearts but not LDs from MHC-Pparg1 mice. Our data indicate that cardiomyocyte LDs vary in size, composition, and metabolism. Cardiotoxicity was associated with greater LD lipolysis, which we postulate leads to intracellular release of toxic lipids.

AIMS/OBJECTIVE:Activation of the transcriptional factor Krüppel-like factor 5 (KLF5) is detrimental to chronic heart failure. We explored the involvement of KLF5 in myocardial ischemia/reperfusion injury. METHODS AND RESULTS/RESULTS:Yorkshire pigs underwent 75΄ of ischemia, followed by 3h or 24h of reperfusion. C57BL/6J mice underwent 30΄ of ischemia, followed by 10', 2h, 12h, 24h, or 4 weeks of reperfusion. Hearts and isolated cardiomyocytes were analyzed for gene expression. We assessed cardiac function, infarct size (IS), oxidative stress, and fibrosis in mice subjected to pharmacologic or genetic KLF5 inhibition, as well as pharmacologic inhibition of NADPH oxidases or Glucose Transporter (GLUT)1 and GLUT4. Bulk RNA sequencing, untargeted 1H-NMR metabolomics and LC-MS lipidomics were performed. Isolated primary murine cardiomyocytes were infected with recombinant adenovirus expressing KLF5. During reperfusion, cardiοmyocyte KLF5 expression was increased in porcine and murine hearts. Pharmacologic or cardiomyocyte-specific genetic inhibition of KLF5 reduced IS and improved cardiac function in mice. Importantly, acute KLF5 inhibition during early reperfusion suppressed fibrosis and preserved systolic cardiac function 4 weeks post-ischemia/reperfusion. This improvement was associated with lower NOX4 expression, less oxidative stress, and suppressed inflammation and cell apoptosis. Pharmacologic inhibition of NOX4 conferred the same benefit. Metabolomic analysis indicated that KLF5 inhibition lowered glucose-derived metabolites (UDP-Glucose and Lactate) at early reperfusion. Accordingly, cardiac GLUT1 and GLUT4 levels were increased with ischemia/reperfusion, which was reverted by KLF5 inhibition. Pharmacologic inhibition of both GLUT1/4 reduced IS. Finally, myocardial KLF5 overexpression increased GLUT1 mRNA levels and mouse mortality. CONCLUSIONS:Ischemia/reperfusion increases cardiomyocyte KLF5 expression in pigs and mice. This constitutes a central element of myocardial injury pathophysiology and is associated with stimulation of GLUT1 and GLUT4 expression, activation of NOX4, oxidative stress, inflammation and apoptosis. Acute KLF5 inhibition during reperfusion constitutes a novel therapeutic approach against myocardial ischemia/reperfusion injury.

Angiopoietin-like 3 (ANGPTL3) inhibits lipases that hydrolyze triglycerides (TGs) in TG-rich lipoproteins (TRLs). We evaluated TRL-TGs, TRL particle (apolipoprotein B), palmitate, and glucose kinetics during a mixed-meal test that included intravenous and oral tracer administrations in people with extremely rare compound heterozygous ANGTPL3 loss-of-function mutations (ANGPTL3^-/- group, n = 3) and matched control participants (n = 7). Multi-organ (liver, muscle, and adipose tissue) insulin sensitivity was evaluated with a two-step hyperinsulinemic-euglycemic clamp procedure and glucose and palmitate tracer infusions. We find that plasma TG and TRL particle concentrations are more than 10-fold lower in the ANGPTL3^-/- than in the control group due to both markedly reduced liver-derived TRL particle and TG secretion rates combined with increased plasma clearance of both liver- and gut-derived TRLs. Palmitate and glucose kinetics during the meal test are not different between the groups. We conclude that the biological function of ANGPTL3 reaches beyond inhibiting intravascular lipase activity.

AIMS/HYPOTHESIS/OBJECTIVE:Microvascular dysfunction contributes to insulin resistance. CD36, a fatty acid transporter and modulator of insulin signalling, is abundant in microvascular endothelial cells. Humans carrying the minor allele (G) of CD36 coding variant rs3211938 have 50% reduced CD36 expression and show endothelial dysfunction. We aimed to determine whether G allele carriers have microvascular resistance to insulin and, if so, how this affects glucose disposal. METHODS:and wild-type mice, and in individuals with 50% CD36 deficiency, together with control counterparts, in addition to primary human-derived microvascular endothelial cells with/without CD36 depletion. RESULTS:mice have enhanced insulin-stimulated glucose disposal but reduced vascular compliance and capillary perfusion. Intravital microscopy of the gastrocnemius showed unaltered transcapillary insulin flux. CD36-deficient humans had better insulin-stimulated glucose disposal but insulin-unresponsive microvascular blood volume (MBV). Human microvascular cells depleted of CD36 showed impaired insulin activation of Akt, endothelial NO synthase and NO generation. Thus, in CD36 deficiency, microvascular insulin resistance paradoxically associated with enhanced insulin sensitivity of glucose disposal. CONCLUSIONS/INTERPRETATION/CONCLUSIONS:CD36 deficiency was previously shown to reduce muscle/heart fatty acid uptake, whereas here we showed that it reduced vascular compliance and the ability of insulin to increase MBV for optimising glucose and oxygen delivery. The muscle and heart respond to these energy challenges by transcriptional remodelling priming the tissue for insulin-stimulated glycolytic flux. Reduced oxygen delivery activating hypoxia-induced factors, endothelial release of growth factors or small intracellular vesicles might mediate this adaptation. Targeting NO bioavailability in CD36 deficiency could benefit the microvasculature and muscle/heart metabolism. TRIAL REGISTRATION/BACKGROUND:Clinicaltrials.gov NCT03012386 DATA AVAILABILITY: The RNAseq data generated in this study have been deposited in the NCBI Gene Expression Omnibus ( www.ncbi.nlm.nih.gov/geo/ ) under accession code GSE235988 ( https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE235988 ).