Dietary Cholesterol Is Highly Associated with Severity of Hyperlipidemia and Atherosclerotic Lesions in Heterozygous LDLR-Deficient Hamsters

L-carnitine and Ginkgo biloba Supplementation In Vivo Ameliorates HCD-Induced Steatohepatitis and Dyslipidemia by Regulating Hepatic Metabolism

Treatment strategies for steatohepatitis are of special interest given the high prevalence of obesity and fatty liver disease worldwide. This study aimed to investigate the potential therapeutic mechanism of L-carnitine (LC) and Ginkgo biloba leaf extract (GB) supplementation in ameliorating the adverse effects of hyperlipidemia and hepatosteatosis induced by a high-cholesterol diet (HCD) in an animal model. The study involved 50 rats divided into five groups, including a control group, a group receiving only an HCD, and three groups receiving an HCD along with either LC (300 mg LC/kg bw), GB (100 mg GB/kg bw), or both. After eight weeks, various parameters related to lipid and glucose metabolism, antioxidant capacity, histopathology, immune reactivity, and liver ultrastructure were measured. LC + GB supplementation reduced serum total cholesterol, triglyceride, low-density lipoprotein cholesterol, glucose, insulin, HOMA-IR, alanine transaminase, and aspartate transaminase levels and increased high-density lipoprotein cholesterol levels compared with those in the HCD group. Additionally, treatment with both supplements improved antioxidant ability and reduced lipid peroxidation. The histological examination confirmed that the combination therapy reduced liver steatosis and fibrosis while also improving the appearance of cell organelles in the ultrastructural hepatocytes. Finally, the immunohistochemical analysis indicated that cotreatment with LC + GB upregulated the immune expression of GLP-1 and β-Cat in liver sections that were similar to those of the control animals. Mono-treatment with LC or GB alone substantially but not completely protected the liver tissue, while the combined use of LC and GB may be more effective in treating liver damage caused by high cholesterol than either supplement alone by regulating hepatic oxidative stress and the protein expression of GLP-1 and β-Cat.

A Review of Progress on Targeting LDL Receptor-Dependent and -Independent Pathways for the Treatment of Hypercholesterolemia, a Major Risk Factor of ASCVD

Since the discovery of the LDL receptor in 1973 by Brown and Goldstein as a causative protein in hypercholesterolemia, tremendous amounts of effort have gone into finding ways to manage high LDL cholesterol in familial hypercholesterolemic (HoFH and HeFH) individuals with loss-of-function mutations in the LDL receptor (LDLR) gene. Statins proved to be the first blockbuster drug, helping both HoFH and HeFH individuals by inhibiting the cholesterol synthesis pathway rate-limiting enzyme HMG-CoA reductase and inducing the LDL receptor. However, statins could not achieve the therapeutic goal of LDL. Other therapies targeting LDLR include PCSK9, which lowers LDLR by promoting LDLR degradation. Inducible degrader of LDLR (IDOL) also controls the LDLR protein, but an IDOL-based therapy is yet to be developed. Among the LDLR-independent pathways, such as angiopoietin-like 3 (ANGPTL3), apolipoprotein (apo) B, apoC-III and CETP, only ANGPTL3 offers the advantage of treating both HoFH and HeFH patients and showing relatively better preclinical and clinical efficacy in animal models and hypercholesterolemic individuals, respectively. While loss-of-LDLR-function mutations have been known for decades, gain-of-LDLR-function mutations have recently been identified in some individuals. The new information on gain of LDLR function, together with CRISPR-Cas9 genome/base editing technology to target LDLR and ANGPTL3, offers promise to HoFH and HeFH individuals who are at a higher risk of developing atherosclerotic cardiovascular disease (ASCVD).

Non-Mouse Models of Atherosclerosis: Approaches to Exploring the Translational Potential of New Therapies

Cardiovascular disease is the largest single cause of disease-related mortality worldwide and the major underlying pathology is atherosclerosis. Atherosclerosis develops as a complex process of vascular lipid deposition and retention by modified proteoglycans, endothelial dysfunction and unresolved chronic inflammation. There are a multitude of current therapeutic agents, most based on lowering plasma lipid levels, but, overall, they have a lower than optimum level of efficacy and many deaths continue to arise from cardiovascular disease world-wide. To identify and evaluate potential novel cardiovascular drugs, suitable animal models that reproduce human atherosclerosis with a high degree of fidelity are required as essential pre-clinical research tools. Commonly used animal models of atherosclerosis include mice (ApoE-/-, LDLR-/- mice and others), rabbits (WHHL rabbits and others), rats, pigs, hamster, zebrafish and non-human primates. Models based on various wild-type and genetically modified mice have been extensively reviewed but mice may not always be appropriate. Thus, here, we provide an overview of the advantages and shortcomings of various non-mouse animal models of atherosclerotic plaque formation, and plaque rupture, as well as commonly used interventional strategies. Taken together, the combinatorial selection of suitable animal models readily facilitates reproducible and rigorous translational research in discovering and validating novel anti-atherosclerotic drugs.

Ablation of Plasma Prekallikrein Decreases LDL Cholesterol by Stabilizing LDL Receptor and Protects against Atherosclerosis

Background: High blood cholesterol accelerates the progression of atherosclerosis that is an asymptomatic process lasting for decades. Rupture of atherosclerotic plaques induces thrombosis that results in myocardial infarction or stroke. Lowering cholesterol levels is beneficial for preventing atherosclerotic cardiovascular disease (ASCVD). Methods: Low-density lipoprotein (LDL) receptor (LDLR) was used as the bait to identify its binding proteins in the plasma, and the coagulation factor prekallikrein (PK, encoded by the KLKB1 gene) was revealed. The correlation between serum PK protein content and lipid levels in young Chinese Han was then analyzed. To investigate the effects of PK ablation on LDLR and lipid levels in vivo, we genetically deleted Klkb1 in hamsters and heterozygous Ldlr knockout mice, as well as knocked Klkb1 down using adeno-associated virus-mediated shRNA in rats. The additive effect of PK and PCSK9 inhibition was evaluated as well. We also applied the anti-PK neutralizing antibody that blocked PK and LDLR interaction to mice. Mice lacking both PK and Apolipoprotein e (Klkb1^-/-Apoe^-/-) were generated to assess the role of PK in atherosclerosis. Results: PK directly bound LDLR and induced its lysosomal degradation. The serum PK concentrations positively correlated with LDL cholesterol levels in 198 young Chinese Han adults. Genetic depletion of Klkb1 increased hepatic LDLR and decreased circulating cholesterol in multiple rodent models. Inhibition of PCSK9 with Evolocumab further decreased plasma LDL cholesterol levels in Klkb1-deficient hamsters. The anti-PK neutralizing antibody could similarly lower plasma lipids through upregulating hepatic LDLR. Ablation of Klkb1 slowed down the progression of atherosclerosis in mice on Apoe-deficient background. Conclusions: PK regulates circulating cholesterol levels through binding to LDLR and inducing its lysosomal degradation. Ablation of PK stabilizes LDLR, decreases LDL cholesterol and prevents atherosclerotic plaque development. This study suggests that PK is a promising therapeutic target to treat ASCVD.

Genetically Engineered Hamster Models of Dyslipidemia and Atherosclerosis

Animal models of human diseases play an extremely important role in biomedical research. Among them, mice are widely used animal models for translational research, especially because of ease of generation of genetically engineered mice. However, because of the great differences in biology between mice and humans, translation of findings to humans remains a major issue. Therefore, the exploration of models with biological and metabolic characteristics closer to those of humans has never stopped.Although pig and nonhuman primates are biologically similar to humans, their genetic engineering is technically difficult, the cost of breeding is high, and the experimental time is long. As a result, the application of these species as model animals, especially genetically engineered model animals, in biomedical research is greatly limited.In terms of lipid metabolism and cardiovascular diseases, hamsters have several characteristics different from rats and mice, but similar to those in humans. The hamster is therefore an ideal animal model for studying lipid metabolism and cardiovascular disease because of its small size and short reproduction period. However, the phenomenon of zygote division, which was unexpectedly blocked during the manipulation of hamster embryos for some unknown reasons, had plagued researchers for decades and no genetically engineered hamsters have therefore been generated as animal models of human diseases for a long time. After solving the problem of in vitro development of hamster zygotes, we successfully prepared enhanced green fluorescent protein (eGFP) transgenic hamsters by microinjection of lentiviral vectors into the zona pellucida space of zygotes. On this basis, we started the development of cardiovascular disease models using the hamster embryo culture system combined with the novel genome editing technique of clustered regularly interspaced short palindromic repeats (CRISPR )/CRISPR associated protein 9 (Cas9). In this chapter, we will introduce some of the genetically engineered hamster models with dyslipidemia and the corresponding characteristics of these models. We hope that the genetically engineered hamster models can be further recognized and complement other genetically engineered animal models such as mice, rats, and rabbits. This will lead to new avenues and pathways for the study of lipid metabolism and its related diseases.

Dietary-Induced Elevations of Triglyceride-Rich Lipoproteins Promote Atherosclerosis in the Low-Density Lipoprotein Receptor Knockout Syrian Golden Hamster

Elevated triglycerides are associated with an increased risk of cardiovascular disease (CVD). Therefore, it is very important to understand the metabolism of triglyceride-rich lipoproteins (TRLs) and their atherogenic role in animal models. Using low-density lipoprotein receptor knockout (LDLR^-/-) Syrian golden hamsters, this study showed that unlike LDLR^-/- mice, when LDLR^-/- hamsters were fed a high cholesterol high-fat diet (HFD), they had very high plasma levels of triglycerides and cholesterol. We found that LDLR^-/- hamsters exhibited increased serum TRLs and the ApoB100 and 48 in these particles after being fed with HFD. Treatment with ezetimibe for 2 weeks decreased these large particles but not the LDL. In addition, ezetimibe simultaneously reduced ApoB48 and ApoE in plasma and TRLs. The expression of LRP1 did not change in the liver. These findings suggested that the significantly reduced large particles were mainly chylomicron remnants, and further, the remnants were mainly cleared by the LDL receptor in hamsters. After 40 days on an HFD, LDLR^-/- hamsters had accelerated aortic atherosclerosis, accompanied by severe fatty liver, and ezetimibe treatment reduced the consequences of hyperlipidemia. Compared with the serum from LDLR^-/- hamsters, that from ezetimibe-treated LDLR^-/- hamsters decreased the expression of vascular adhesion factors in vascular endothelial cells and lipid uptake by macrophages. Our results suggested that in the LDLR^-/- hamster model, intestinally-derived lipoprotein remnants are highly atherogenic and the inflammatory response of the endothelium and foam cells from macrophages triggered atherosclerosis. The LDL receptor might be very important for chylomicrons remnant clearance in the Syrian golden hamster, and this may not be compensated by another pathway. We suggest that the LDLR^-/- hamster is a good model for the study of TRLs-related diseases as it mimics more complex hyperlipidemia.

Sterols and Sterol Oxidation Products: Effect of Dietary Intake on Tissue Distribution in ApoE-Deficient Mice

Sterols and sterol oxidation products (SOPs) are well-known dietary factors influencing atherosclerosis; however, their distribution in vivo after dietary sterol/SOP intake is still unclear. Here, we investigated the tissue distribution of sterols and SOPs in ApoE^-/- mice after dietary exposure to diets supplemented with phytosterols (PS), phytosterol oxidation products (POPs), or cholesterol oxidation products (COPs). The results showed that PS intake reduced cholesterol in serum and the liver but increased cholesterol in the brain. PS intake increased the levels of PS in vivo and the levels of 7-keto- and triol-POPs in serum and the liver. COP intake elevated the level of all COPs in serum but did not change the 7-keto-cholesterol level in the liver and brain. All POPs in serum and parts of POPs in the liver and brain increased after dietary POP exposure. Our study indicated that dietary PS and SOPs accumulated in vivo with varying degrees and influenced cerebral cholesterol metabolism.

Genetically-engineered hamster models: applications and perspective in dyslipidemia and atherosclerosis-related cardiovascular disease

Cardiovascular disease is the leading cause of morbidity and mortality in both developed and developing countries, in which atherosclerosis triggered by dyslipidemia is the major pathological basis. Over the past 40 years, small rodent animals, such as mice, have been widely used for understanding of human atherosclerosis-related cardiovascular disease (ASCVD) with the advantages of low cost and ease of maintenance and manipulation. However, based on the concept of precision medicine and high demand of translational research, the applications of mouse models for human ASCVD study would be limited due to the natural differences in metabolic features between mice and humans even though they are still the most powerful tools in this research field, indicating that other species with biological similarity to humans need to be considered for studying ASCVD in future. With the development and breakthrough of novel gene editing technology, Syrian golden hamster, a small rodent animal replicating the metabolic characteristics of humans, has been genetically modified, suggesting that gene-targeted hamster models will provide new insights into the precision medicine and translational research of ASCVD. The purpose of this review was to summarize the genetically-modified hamster models with dyslipidemia to date, and their potential applications and perspective for ASCVD.

Dietary Sterols and Sterol Oxidation Products on Atherosclerosis: An Insight Provided by Liver Proteomic and Lipidomic

SCOPE

The development of atherosclerosis is closely associated with disorder of lipid metabolism. Dietary sterols and their oxidation products play a role in the pathogenesis of atherosclerosis. However, their effects on liver lipid metabolism during the atherosclerosis remain unknown.

METHODS AND RESULTS

Here, we apply lipidomic and proteomic analysis on liver of ApoE^-/- mice feed with phytosterols, cholesterol oxidation products (COPs), or phytosterol oxidation products (POPs) to profile lipid species and reveal the underlying mechanism. Dietary exposure of phytosterols, COPs, and POPs all reduce the accumulation of liver triglyceride (TG), but COPs and POPs accelerate the fibrosis of liver. Lipidomic analysis reveals that phytosterols mainly decrease the levels of phosphatidylinositol (PI), while COPs and POPs both increase the level of digalactosyldiacylglycerol (DGDG) and reduce TG with long-chain polyunsaturated fatty acids. Besides, COPs up-regulated levels of lipids associate with atherosclerosis risk, such as phosphatidylcholines (PC), phosphatidylethanolamine (PE) and ceramides (Cer). POPs down-regulate the level of acyl carnitine (AcCa). Furthermore, proteomic analysis shows that COPs promote oxidative phosphorylation and POPs inhibit the beta oxidation of fatty acids.

CONCLUSIONS

This study reveals that phytosterols, COPs, and POPs differently change the composition and metabolism of glycerophospholipids, sphingolipids, and glycerolipids in liver of ApoE^-/- mice.

Spontaneous Atherosclerosis in Aged LCAT-Deficient Hamsters With Enhanced Oxidative Stress-Brief Report

OBJECTIVE

LCAT (lecithin cholesterol acyltransferase) deficiency results in severe low HDL (high-density lipoprotein). Although whether LCAT is pro- or antiatherosclerosis was in debate in mouse studies, our previous study clearly shows that LCAT deficiency (LCAT^-/-) in hamster accelerates atherosclerotic development on high-fat diet. However, unlike in hypercholesterolemia and hypertriglyceridemia, whether LCAT deficiency could lead to spontaneous atherosclerosis has not been studied yet in animal models. We, therefore, sought to investigate the atherosclerosis in LCAT^-/- hamsters on standard laboratory diet and explore the potential underlying mechanisms. Approach and Results: Young (<8 months) and aged (>16 months) male and female wild-type and LCAT^-/- hamsters on standard laboratory diet were used. Compared with age- and sex-matched wild-type hamsters, LCAT^-/- hamsters showed a complete loss of plasma HDL and an increase in triglyceride by 2- to 8-fold at different stages of age. In aged LCAT^-/- hamsters, the lesion areas at the aortic roots were ≈40×10⁴ μm³ in males and 18×10⁴ μm³ in females, respectively, which were consistent with the en face plaques observed in male (1.2%) and (1.5%) female groups, respectively. The results of plasma malondialdehyde measurement showed that malondialdehyde concentrations were markedly elevated to 54.4 μmol/L in males and 30 μmol/L in females, which are significantly associated with the atherosclerotic lesions.

CONCLUSIONS

Our study demonstrates the development of spontaneous atherosclerotic lesions in aged male and female LCAT^-/- hamsters with higher plasma oxidative lipid levels independent of plasma total cholesterol levels, further confirming the antiatherosclerotic role of LCAT.

Clerodendrum volubile Ethanol Leaf Extract: A Potential Antidote to Doxorubicin-Induced Cardiotoxicity in Rats

Doxorubicin is widely applied in hematological and solid tumor treatment but limited by its off-target cardiotoxicity. Thus, cardioprotective potential and mechanism(s) of CVE in DOX-induced cardiotoxicity were investigated using cardiac and oxidative stress markers and histopathological endpoints. 50–400 mg/kg/day CVE in 5% DMSO in distilled water were investigated in Wistar rats intraperitoneally injected with 2.5 mg/kg DOX on alternate days for 14 days, using serum troponin I and LDH, complete lipid profile, cardiac tissue oxidative stress marker assays, and histopathological examination of DOX-treated cardiac tissue. Preliminary qualitative and quantitative assays of CVE's secondary metabolites were also conducted. Phytochemical analyses revealed the presence of flavonoids (34.79 ± 0.37 mg/100 mg dry extract), alkaloids (36.73 ± 0.27 mg/100 mg dry extract), reducing sugars (07.78 ± 0.09 mg/100 mg dry extract), and cardiac glycosides (24.55 ± 0.12 mg/100 mg dry extract). 50–400 mg/kg/day CVE significantly attenuated increases in the serum LDH and troponin I levels. Similarly, the CVE dose unrelatedly decreased serum TG and VLDL-c levels without significant alterations in the serum TC, HDL-c, and LDL-c levels. Also, CVE profoundly attenuated alterations in the cardiac tissue oxidative stress markers' activities while improving DOX-associated cardiac histological lesions that were possibly mediated via free radical scavenging and/or antioxidant mechanisms. Overall, CVE may play a significant therapeutic role in the management of DOX-induced cardiotoxicity in humans.

Anti‑glycolipid disorder effect of epigallocatechin‑3‑gallate on high‑fat diet and STZ‑induced T2DM in mice

Epigallocatechin-3-gallate (EGCG) is beneficial for inhibiting dyslipidemia and reducing hyperlipidemic risk. The purpose of the present study was to investigate the glycolipid regulatory effects and potential mechanisms of EGCG in a high-fat diet and streptozotocin-induced type 2 diabetes mellitus (T2DM) mouse model. The results demonstrated that EGCG can decrease blood glucose levels and increase insulin resistance in T2DM mice. In addition, EGCG can regulate serum lipid levels, including those of total cholesterol, triglyceride and low-density lipoprotein receptor (LDL-r), and reduce lipid deposition in vascular endothelial cells in a dose-dependent manner. In addition, the gene and protein expression of related scavenger receptors, including cluster of differentiation 36, sterol regulatory element binding protein 2 (SREBP), SREBP cleavage-activating protein and LDL-r, were downregulated in a dose-dependent manner. The present study noted that EGCG possesses potential as a natural product for preventing and treating metabolic hyperlipidemia syndrome, probably by reducing the blood lipid levels, alleviating vascular endothelial cell damage, maintaining normal lipid metabolism in blood vessels and ameliorating glycolipid disorders.

Ezetimibe promotes CYP7A1 and modulates PPARs as a compensatory mechanism in LDL receptor-deficient hamsters

Background

The LDL-C lowering effect of ezetimibe has been attributed primarily to increased catabolism of LDL-C via up-regulation of LDL receptor (LDLR) and decreased cholesterol absorption. Recently, ezetimibe has been demonstrated to have reverse cholesterol transport (RCT) promoting effects in mice, hamsters and humans. However, the underlying mechanisms are still not clear. The aim of this study is to investigate whether ezetimibe improves RCT-related protein expression in LDLR^−/− hamsters.

Methods

A high-fat diet was used to induce a human-like hyperlipidemia in LDLR^−/− hamsters. Lipid profiles were assayed by commercially available kits, and the effects of ezetimibe on lipid metabolism-related protein expression were carried out via western blot.

Results

Our data demonstrated that ezetimibe administration significantly reduced plasma total cholesterol (~ 51.6% reduction, P < 0.01) and triglyceride (from ~ 884.1 mg/dL to ~ 277.3 mg/dL) levels in LDLR^−/− hamsters fed a high-fat diet. Ezetimibe administration (25 mg/kg/d) significantly promoted the protein expression of cholesterol 7 alpha-hydroxylase A1 (CYP7A1), LXRβ and peroxisome proliferator-activated receptor (PPAR) γ; and down-regulated the protein expression of PPARα and PPARβ. However, it showed no significant effect on sterol regulatory element-binding protein (SREBP)-1c, SREBP-2, proprotein convertase subtilisin/kexin type 9 (PCSK9), Niemann-Pick C1-like 1 (NPC1L1), and ATP-biding cassette (ABC) G5/G8.

Conclusion

Ezetimibe may accelerate the transformation from cholesterol to bile acid via promoting CYP7A1 and thereby enhance RCT. As a compensatory mechanism of TG lowering, ezetimibe promoted the protein expression of PPARγ and decreased PPARα and β. These results are helpful in explaining the lipid-lowering effects of ezetimibe and the potential compensatory mechanisms.

Heterozygous Ldlr-Deficient Hamster as a Model to Evaluate the Efficacy of PCSK9 Antibody in Hyperlipidemia and Atherosclerosis

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a key role in cholesterol homeostasis and atherogenesis. However, there are only limited rodent models, with a functional low-density lipoprotein receptor (LDLR) pathway and cholesteryl ester transfer protein (CETP) to evaluate the drug candidates targeting the PCSK9/LDLR pathway, that are translatable to humans. Here, by using our recently generated LDLR heterozygote (Ldlr+/−) hamster model with functional LDLR pathway and CETP function, we seek to evaluate the effect of a PCSK9 antibody, evolocumab, on dyslipidemia and atherosclerosis compared with ezetimibe, an effective inhibitor of cholesterol absorption, as a positive therapeutic control. We show that the plasma levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) were significantly increased in Ldlr+/− hamsters fed a high-fat high-cholesterol (HFHC) diet; therefore, areas of atherosclerotic lesion in the aorta were obviously increased and positively correlated with plasma LDL-C and TC. Circulating free PCSK9 was downregulated by the HFHC diet and was undetectable in the evolocumab treated group, as expected. Most importantly, either evolocumab or ezetimibe treatment prevented HFHC diet-induced hyperlipidemia and subsequent atherosclerotic plaque formation. The results indicate that Ldlr+/− hamsters fed an HFHC diet represent an ideal rodent model to evaluate drug candidates that affect LDLR pathways.