The Potential of ANGPTL8 Antagonism to Simultaneously Reduce Triglyceride and Increase HDL-Cholesterol Plasma Levels

Inhibition of the ANGPTL3/8 Complex for the Prevention and Treatment of Atherosclerotic Cardiovascular Disease

PURPOSE OF REVIEW

Dyslipidemia is a casual risk factor for atherosclerotic cardiovascular disease (ASCVD). There is an unmet need for more effective treatments for patients with dyslipidemias. Angiopoietin-like protein 3 (ANGPTL3) and ANGPTL8 play key roles in triglyceride trafficking and energy balance in humans. We review the functional role of these ANGPTL proteins in the regulation of lipoprotein metabolism, and recent clinical trials targeting ANGPTL3 and ANGPTL3/8 with monoclonal antibody and/or nucleic acid therapies, including antisense oligonucleotides and small interfering RNA.

RECENT FINDINGS

Cumulative evidence supports the roles of ANGPTL3 and ANGPTL8 in lipid metabolism through inhibition of lipoprotein lipase and endothelial lipase activity. ANGPTL3 and ANGPTL3/8 inhibitors are effective in lowering plasma triglycerides and low-density lipoprotein (LDL)-cholesterol, with the possible advantage of raising high-density lipoprotein (HDL)-cholesterol with the inhibition of ANGPTL3/8. Therapeutic inhibition of ANGPTL3 and ANGPTL3/8 can lower plasma triglyceride and LDL-cholesterol levels possibly by lowering production and upregulating catabolism of triglyceride-rich lipoprotein and LDL particles. However, the effect of these novel agents on HDL metabolism remains unclear. The cardiovascular benefits of ANGPTL3 and ABGPTL3/8 inhibitors may also include improvement in vascular inflammation, but this requires further investigation.

Angiopoietin-like protein 8: a multifaceted protein instrumental in regulating triglyceride metabolism

PURPOSE OF REVIEW

The angiopoietin-like (ANGPTL) proteins ANGPTL3 and ANGPTL4 are critical lipoprotein lipase (LPL) inhibitors. This review discusses the unique ability of the insulin-responsive protein ANGPTL8 to regulate triglyceride (TG) metabolism by forming ANGPTL3/8 and ANGPTL4/8 complexes that control tissue-specific LPL activities.

RECENT FINDINGS

After feeding, ANGPTL4/8 acts locally in adipose tissue, has decreased LPL-inhibitory activity compared to ANGPTL4, and binds tissue plasminogen activator (tPA) and plasminogen to generate plasmin, which cleaves ANGPTL4/8 and other LPL inhibitors. This enables LPL to be fully active postprandially to promote efficient fatty acid (FA) uptake and minimize ectopic fat deposition. In contrast, liver-derived ANGPTL3/8 acts in an endocrine manner, has markedly increased LPL-inhibitory activity compared to ANGPTL3, and potently inhibits LPL in oxidative tissues to direct TG toward adipose tissue for storage. Circulating ANGPTL3/8 levels are strongly correlated with serum TG, and the ANGPTL3/8 LPL-inhibitory epitope is blocked by the TG-lowering protein apolipoprotein A5 (ApoA5).

SUMMARY

ANGPTL8 plays a crucial role in TG metabolism by forming ANGPTL3/8 and ANGPTL4/8 complexes that differentially modulate LPL activities in oxidative and adipose tissues respectively. Selective ANGPTL8 inhibition in the context of the ANGPTL3/8 complex has the potential to be a promising strategy for treating dyslipidemia.

Circumventing Cardiovascular Calamities: The Dawn of ANGPTL3 Blockade in Severe Dyslipidemia Management

The landscape of severe dyslipidemia treatment is undergoing a remarkable transformation with the advent of angiopoietin-like 3 (ANGPTL3) inhibitors. ANGPTL3, a pivotal regulator of lipoprotein lipase and endothelial lipase, orchestrates the catabolism of triglyceride-rich and high-density lipoproteins, thus playing a critical role in lipid homeostasis. This review article examines the therapeutic potential of ANGPTL3 blockade and its implications for patients with severe dyslipidemias, particularly those unresponsive to traditional lipid-lowering regimens. We delve into the molecular mechanisms by which ANGPTL3 influences lipid metabolism and appraise the clinical utility of emerging therapeutics, such as monoclonal antibodies and antisense oligonucleotides. Moreover, we discuss the impact of ANGPTL3 inhibition on cardiovascular risk factors and project its promising role in reducing cardiovascular morbidity and mortality. The narrative synthesizes data from recent clinical trials, including the efficacy and safety profiles of ANGPTL3 inhibitors, and forecasts the potential of these agents to revolutionize the management of dyslipidemic conditions. The advent of ANGPTL3-targeted therapies signifies a potential breakthrough in the therapeutic armamentarium against complex lipid disorders, heralding a new era of precision medicine in cardiovascular risk mitigation.

Adolescent obesity and ANGPTL8: correlations with high sensitivity C-reactive protein, leptin, and chemerin

Angiopoietin-like proteins (ANGPTLs) mediate many metabolic functions. We had recently reported increased plasma levels of ANGPTL8 in obese adults of Arab ethnicity. However, data on ANGPTL8 levels in adolescent obesity is lacking. Arab population is characterized by a rapid transition, due to sudden wealth seen in the post-oil era, in lifestyle, food habits and extent of physical activity. We adopted a cross-sectional study on Arab adolescents from Kuwait to examine the role of ANGPTL8 in adolescent obesity. The study cohort included 452 adolescents, aged 11-14 years, recruited from Middle Schools across Kuwait. BMI-for-age growth charts were used to categorize adolescents as normal-weight, overweight, and obese. ELISA and bead-based multiplexing assays were used to measure plasma levels of ANGPTL8 and other inflammation and obesity-related biomarkers. Data analysis showed significant differences in the plasma levels of ANGPTL8 among the three subgroups, with a significant increase in overweight and obese children compared to normal-weight children. This observation persisted even when the analysis was stratified by sex. Multinomial logistic regression analysis illustrated that adolescents with higher levels of ANGPTL8 were 7 times more likely to become obese and twice as likely to be overweight. ANGPTL8 levels were correlated with those of hsCRP, leptin and chemerin. ANGPTL8 level had a reasonable prognostic power for obesity with an AUC of 0.703 (95%-CI=0.648-0.759). These observations relating to increased ANGPTL8 levels corresponding to increased BMI-for-age z-scores indicate that ANGPTL8, along with hsCRP, leptin and chemerin, could play a role in the early stages of obesity development in children. ANGPTL8 is a potential early marker for adolescent obesity and is associated with well-known obesity and inflammatory markers.

Targeting ANGPTL3 by GalNAc-conjugated siRNA ANGsiR10 lowers blood lipids with long-lasting and potent efficacy in mice and monkeys

Angiopoietin-like protein 3 (ANGPTL3) is an important regulator of lipoproteins by inhibiting both lipoprotein and endothelial lipases. It has been intensively investigated as a drug target for the treatment of dyslipidemia. In the present study, a modified small interfering RNA (siRNA) conjugated with GalNAc ANGsiR10 was characterized by in vivo and in vitro studies for its effect on ANGPTL3 silencing, the reduction of plasma triglycerides (TGs), and cholesterol levels in disease models. The results showed that ANGsiR10 displayed a significant and long-lasting efficacy in reducing blood TG and cholesterol levels in both mice and monkeys. Remarkably, the maximal reductions of plasma TG levels in the hApoC3-Tg mice, a model with high TG levels, and the spontaneous dyslipidemia model of rhesus monkey were 96.3% and 67.7%, respectively, after a single dose of ANGsiR10, with long-lasting effects up to 15 weeks. The cholesterol levels were also reduced in response to treatment, especially the non-HDL-c level, without altering the ApoA/ApoB ratio. This study showed that ANGsiR10 is effective in treating dyslipidemia and is worth further development.

The Regulation of Triacylglycerol Metabolism and Lipoprotein Lipase Activity

Triacylglycerol (TG) metabolism is tightly regulated to maintain a pool of TG within circulating lipoproteins that can be hydrolyzed in a tissue-specific manner by lipoprotein lipase (LPL) to enable the delivery of fatty acids to adipose or oxidative tissues as needed. Elevated serum TG concentrations, which result from a deficiency of LPL activity or, more commonly, an imbalance in the regulation of tissue-specific LPL activities, have been associated with an increased risk of atherosclerotic cardiovascular disease through multiple studies. Among the most critical LPL regulators are the angiopoietin-like (ANGPTL) proteins ANGPTL3, ANGPTL4, and ANGPTL8, and a number of different apolipoproteins including apolipoprotein A5 (ApoA5), apolipoprotein C2 (ApoC2), and apolipoprotein C3 (ApoC3). These ANGPTLs and apolipoproteins work together to orchestrate LPL activity and therefore play pivotal roles in TG partitioning, hydrolysis, and utilization. This review summarizes the mechanisms of action, epidemiological findings, and genetic data most relevant to these ANGPTLs and apolipoproteins. The interplay between these important regulators of TG metabolism in both fasted and fed states is highlighted with a holistic view toward understanding key concepts and interactions. Strategies for developing safe and effective therapeutics to reduce circulating TG by selectively targeting these ANGPTLs and apolipoproteins are also discussed.

ANGPTL3 Is Involved in the Post-prandial Response in Triglyceride-Rich Lipoproteins and HDL Components in Patients With Coronary Artery Disease

It is well-established that there exists an inverse relationship between high-density lipoprotein (HDL) cholesterol and triglyceride (TG) levels in the plasma. However, information is lacking on the impact of post-prandial triglyceride-rich lipoproteins (TRLs) on the structure of HDL subclasses in patients with coronary artery disease (CAD). In this study, the data of 49 patients with CAD were analyzed to evaluate dynamic alterations in post-prandial lipid profiles using nuclear magnetic resonance-based methods. An enzyme-linked immunosorbent assay was used to quantify the serum angiopoietin-like protein 3 (ANGPTL3). After glucose supplementation, the expression of hepatic ANGPTL3 was evaluated both in vitro and in vivo. Compared to fasting levels, the post-prandial serum TG level of all participants was considerably increased. Although post-prandial total cholesterol in HDL (HDL-C) remained unchanged, free cholesterol in HDL particles (HDL-FC) was significantly reduced after a meal. Furthermore, the post-prandial decrease in the HDL-FC level corresponded to the increase in remnant cholesterol (RC), indicating the possible exchange of free cholesterol between HDL and TRLs after a meal. Moreover, CAD patients with exaggerated TG response to diet, defined as TG increase >30%, tend to have a greater post-prandial increase of RC and decrease of HDL-FC compared to those with TG increase ≤30%. Mechanistically, the fasting and post-prandial serum ANGPTL3 levels were significantly lower in those with TG increase ≤30% than those with TG increase >30%, suggesting that ANGPTL3, the key lipolysis regulator, may be responsible for the different post-prandial responses of TG, RC, and HDL-FC.

An anti-ANGPTL3/8 antibody decreases circulating triglycerides by binding to a LPL-inhibitory leucine zipper-like motif

Triglycerides (TG) are required for fatty acid transport and storage and are essential for human health. Angiopoietin-like-protein 8 (ANGPTL8) has previously been shown to form a complex with ANGPTL3 that increases circulating TG by potently inhibiting LPL. We also recently showed that the TG-lowering apolipoprotein A5 (ApoA5) decreases TG levels by suppressing ANGPTL3/8-mediated LPL inhibition. To understand how LPL binds ANGPTL3/8 and ApoA5 blocks this interaction, we used hydrogen-deuterium exchange mass-spectrometry and molecular modeling to map binding sites of LPL and ApoA5 on ANGPTL3/8. Remarkably, we found that LPL and ApoA5 both bound a unique ANGPTL3/8 epitope consisting of N-terminal regions of ANGPTL3 and ANGPTL8 that are unmasked upon formation of the ANGPTL3/8 complex. We further used ANGPTL3/8 as an immunogen to develop an antibody targeting this same epitope. After refocusing on antibodies that bound ANGPTL3/8, as opposed to ANGPTL3 or ANGPTL8 alone, we utilized bio-layer interferometry to select an antibody exhibiting high-affinity binding to the desired epitope. We revealed an ANGPTL3/8 leucine zipper-like motif within the anti-ANGPTL3/8 epitope, the LPL-inhibitory region, and the ApoA5-interacting region, suggesting the mechanism by which ApoA5 lowers TG is via competition with LPL for the same ANGPTL3/8-binding site. Supporting this hypothesis, we demonstrate that the anti-ANGPTL3/8 antibody potently blocked ANGPTL3/8-mediated LPL inhibition in vitro and dramatically lowered TG levels in vivo. Together, these data show that an anti-ANGPTL3/8 antibody targeting the same leucine zipper-containing epitope recognized by LPL and ApoA5 markedly decreases TG by suppressing ANGPTL3/8-mediated LPL inhibition.

An updated ANGPTL3-4-8 model as a mechanism of triglyceride partitioning between fat and oxidative tissues

In mammals, triglyceride (TG), the main form of lipids for storing and providing energy, is stored in white adipose tissue (WAT) after food intake, while during fasting it is routed to oxidative tissues (heart and skeletal muscle) for energy production, a process referred to as TG partitioning. Lipoprotein lipase (LPL), a rate-limiting enzyme in this fundamental physiological process, hydrolyzes circulating TG to generate free fatty acids that are taken up by peripheral tissues. The postprandial activity of LPL declines in oxidative tissues but rises in WAT, directing TG to WAT; the reverse is true during fasting. However, the molecular mechanism in regulating tissue-specific LPL activity during the fed-fast cycle has not been completely understood. Research on angiopoietin-like (ANGPTL) proteins (A3, A4, and A8) has resulted in an ANGPTL3-4-8 model to explain the TG partitioning between WAT and oxidative tissues. Food intake induces A8 expression in the liver and WAT. Liver A8 activates A3 by forming the A3-8 complex, which is then secreted into the circulation. The A3-8 complex acts in an endocrine manner to inhibit LPL in oxidative tissues. WAT A8 forms the A4-8 complex, which acts locally to block A4's LPL-inhibiting activity. Therefore, the postprandial activity of LPL is low in oxidative tissues but high in WAT, directing circulating TG to WAT. Conversely, during fasting, reduced A8 expression in the liver and WAT disables A3 from inhibiting oxidative-tissue LPL and restores WAT A4's LPL-inhibiting activity, respectively. Thus, the fasting LPL activity is high in oxidative tissues but low in WAT, directing TG to the former. According to the model, we hypothesize that A8 antagonism has the potential to simultaneously reduce TG and increase HDL-cholesterol plasma levels. Future research on A3, A4, and A8 can hopefully provide more insights into human health, disease, and therapeutics.