Increased cholesterol biosynthesis and hypercholesterolemia in mice overexpressing squalene synthase in the liver

Unveiling the Therapeutic Potential of Squalene Synthase: Deciphering Its Biochemical Mechanism, Disease Implications, and Intriguing Ties to Ferroptosis

Squalene synthase (SQS) has emerged as a promising therapeutic target for various diseases, including cancers, owing to its pivotal role in the mevalonate pathway and the antioxidant properties of squalene. Primarily, SQS orchestrates the head-to-head condensation reaction, catalyzing the fusion of two farnesyl pyrophosphate molecules, leading to the formation of squalene, which has been depicted as a highly effective oxygen-scavenging agent in in vitro studies. Recent studies have depicted this isoprenoid as a protective layer against ferroptosis due to its potential regulation of lipid peroxidation, as well as its protection against oxidative damage. Therefore, beyond its fundamental function, recent investigations have unveiled additional roles for SQS as a regulator of lipid peroxidation and programmed cell death pathways, such as ferroptosis-a type of cell death characterized by elevated levels of lipid peroxide, one of the forms of reactive oxygen species (ROS), and intracellular iron concentration. Notably, thorough explorations have shed light on the distinctive features that set SQS apart from other members within the isoprenoid synthase superfamily. Its unique biochemical structure, intricately intertwined with its reaction mechanism, has garnered significant attention. Moreover, considerable evidence substantiates the significance of SQS in various disease contexts, and its intriguing association with ferroptosis and lipid peroxidation. The objective of this report is to analyze the existing literature comprehensively, corroborating these findings, and provide an up-to-date perspective on the current understanding of SQS as a prospective therapeutic target, as well as its intricate relationship with ferroptosis. This review aims to consolidate the knowledge surrounding SQS, thereby contributing to the broader comprehension of its potential implications in disease management and therapeutic interventions.

Roles of Farnesyl-Diphosphate Farnesyltransferase 1 in Tumour and Tumour Microenvironments

Farnesyl-diphosphate farnesyltransferase 1 (FDFT1, squalene synthase), a membrane-associated enzyme, synthesizes squalene via condensation of two molecules of farnesyl pyrophosphate. Accumulating evidence has noted that FDFT1 plays a critical role in cancer, particularly in metabolic reprogramming, cell proliferation, and invasion. Based on these advances in our knowledge, FDFT1 could be a potential target for cancer treatment. This review focuses on the contribution of FDFT1 to the hallmarks of cancer, and further, we discuss the applicability of FDFT1 as a cancer prognostic marker and target for anticancer therapy.

Critical Role of SREBP-1c Large-VLDL Pathway in Environment-Induced Hypertriglyceridemia of Apo AV Deficiency

Objective- APOA5 variants are strongly associated with hypertriglyceridemia, as well as increased risks of cardiovascular disease and acute pancreatitis. Hypertriglyceridemia in apo AV dysfunction often aggravates by environmental factors such as high-carbohydrate diets or aging. To date, the molecular mechanisms by which these environmental factors induce hypertriglyceridemia are poorly defined, leaving the high-risk hypertriglyceridemia condition undertreated. Previously, we reported that LXR (liver X receptor)-SREBP (sterol regulatory element-binding protein)-1c pathway regulates large-VLDL (very low-density lipoprotein) production induced by LXR agonist. However, the pathophysiological relevance of the finding remains unknown. Approach and Results- Here, we reconstitute the environment-induced hypertriglyceridemia phenotype of human APOA5 deficiency in Apoa5^-/- mice and delineate the role of SREBP-1c in vivo by generating Apoa5^-/- ;Srebp-1c^-/- mice. The Apoa5^-/- mice, which showed moderate hypertriglyceridemia on a chow diet, developed severe hypertriglyceridemia on high-carbohydrate feeding or aging as seen in patients with human apo AV deficiency. These responses were nearly completely abolished in the Apoa5^-/- ;Srebp-1c^-/- mice. Further mechanistic studies revealed that in response to these environmental factors, SREBP-1c was activated to increase triglyceride synthesis and to permit the incorporation of triglyceride into abnormally large-VLDL particles, which require apo AV for efficient clearance. Conclusions- Severe hypertriglyceridemia develops only when genetic factors (apo AV deficiency) and environmental effects (SREBP-1c activation) coexist. We demonstrate that the regulated production of large-sized VLDL particles via SREBP-1c determines plasma triglyceride levels in apo AV deficiency. Our findings explain the long-standing enigma of the late-onset hypertriglyceridemia phenotype of apo AV deficiency and suggest a new approach to treat hypertriglyceridemia by targeting genes that mediate environmental effects.

Fermented Garlic Ameliorates Hypercholesterolemia and Inhibits Platelet Activation

Dietary cholesterol augments the lipid profile and induces the production and activation of platelets, leading to the development of atherosclerosis with detrimental effects on cardiovascular health. Ethnomedicine and Mediterranean diets are natural and cost-effective approaches against several ailments including cardiovascular diseases. In addition, fermented foods have attracted interest due to their increased nutrient profile and enhanced bioavailability and efficacy. Garlic is known to reduce cholesterol and inhibit platelet activation. Therefore, we examined whether fermented garlic could effectively ameliorate the effects of hypercholesterolemia and platelet functions in rats. Male Sprague-Dawley rats were fed a hypercholesterolemic diet and treated with spirulina and fermented and nonfermented preparations of garlic for one month. Platelet aggregation and granule secretion were assessed to evaluate platelet activation. Analysis of the liver and kidney weights and lipid and enzymatic profiles of the serum and whole blood analysis was performed. The expression levels of SREBP-2, ACAT-2, and HMG-CoA were assessed by RT-PCR, while ACAT-1 and ACAT-2 were assessed by real-time PCR, and histological changes in the liver and adipose tissues were analyzed. Both fermented and nonfermented garlic inhibited platelet aggregation and granule secretion; however, fermented garlic exhibited a greater inhibitory effect. In comparison with nonfermented garlic, fermented garlic significantly reduced liver weight and triglyceride concentrations. Fermented garlic also markedly abrogated the detrimental effects of steatosis on liver and adipose tissues. We conclude that fermented garlic significantly improved the lipid profile and modulated platelet functions, thereby inhibiting atherosclerosis- and platelet-related cardiovascular disorders.

Genome-Wide Variation Patterns Uncover the Origin and Selection in Cultivated Ginseng (Panax ginseng Meyer)

Chinese ginseng (Panax ginseng Meyer) is a medicinally important herb and plays crucial roles in traditional Chinese medicine. Pharmacological analyses identified diverse bioactive components from Chinese ginseng. However, basic biological attributes including domestication and selection of the ginseng plant remain under-investigated. Here, we presented a genome-wide view of the domestication and selection of cultivated ginseng based on the whole genome data. A total of 8,660 protein-coding genes were selected for genome-wide scanning of the 30 wild and cultivated ginseng accessions. In complement, the 45s rDNA, chloroplast and mitochondrial genomes were included to perform phylogenetic and population genetic analyses. The observed spatial genetic structure between northern cultivated ginseng (NCG) and southern cultivated ginseng (SCG) accessions suggested multiple independent origins of cultivated ginseng. Genome-wide scanning further demonstrated that NCG and SCG have undergone distinct selection pressures during the domestication process, with more genes identified in the NCG (97 genes) than in the SCG group (5 genes). Functional analyses revealed that these genes are involved in diverse pathways, including DNA methylation, lignin biosynthesis, and cell differentiation. These findings suggested that the SCG and NCG groups have distinct demographic histories. Candidate genes identified are useful for future molecular breeding of cultivated ginseng.

Improvement of De Novo Cholesterol Biosynthesis Efficiently Promotes the Production of Human Immunodeficiency Virus Type 1-Derived Lentiviral Vectors

The use of lentiviral vectors (LVs) for gene transfer in research, technological, or clinical applications requires the production of large amounts of vector. Mass production of clinical-grade LVs remains a challenge and limits certain perspectives for therapeutic use. Some improvements in LV production protocols have been possible by acting on multiple steps of the production process. The addition of animal-derived cholesterol to the culture medium of producer cells is known to increase the infectivity of LVs. To avoid the use of this animal-derived product in clinical settings, an alternative approach is to increase de novo the production of cholesterol by overexpressing a crucial cholesterogenic enzyme, namely, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). This project evaluates the impact of such an approach on the production, infectivity, and stability of LVs. We demonstrated that the overexpression of human HMGCR isoform 1 (hHMGCR1) in LV producer cells efficiently increased de novo cholesterol biosynthesis and enhanced by 2- to 3-fold the physical and infectious titers of LVs. We also observed that LVs produced in hHMGCR1-overexpressing cells were comparable in stability to LVs produced under classical conditions and were capable of transducing human CD34⁺ hematopoietic stem/progenitor cells efficiently. Interestingly, we also showed that LV production in the absence of fetal calf serum (FCS) but under hHMGCR1-overexpressing conditions allowed a viral production yield comparable to that achieved under classical conditions in high FCS content, leading the way to the establishment of new LV production protocols on adherent cells without serum.

Plasma cholesterol-lowering and transient liver dysfunction in mice lacking squalene synthase in the liver

Squalene synthase (SS) catalyzes the biosynthesis of squalene, the first specific intermediate in the cholesterol biosynthetic pathway. To test the feasibility of lowering plasma cholesterol by inhibiting hepatic SS, we generated mice in which SS is specifically knocked out in the liver (L-SSKO) using Cre-loxP technology. Hepatic SS activity of L-SSKO mice was reduced by >90%. In addition, cholesterol biosynthesis in the liver slices was almost eliminated. Although the hepatic squalene contents were markedly reduced in L-SSKO mice, the hepatic contents of cholesterol and its precursors distal to squalene were indistinguishable from those of control mice, indicating the presence of sufficient centripetal flow of cholesterol and/or its precursors from the extrahepatic tissues. L-SSKO mice showed a transient liver dysfunction with moderate hepatomegaly presumably secondary to increased farnesol production. In a fed state, the plasma total cholesterol and triglyceride were significantly reduced in L-SSKO mice, primarily owing to reduced hepatic VLDL secretion. In a fasted state, the hypolipidemic effect was lost. mRNA expression of liver X receptor α target genes was reduced, while that of sterol-regulatory element binding protein 2 target genes was increased. In conclusion, liver-specific ablation of SS inhibits hepatic cholesterol biosynthesis and induces hypolipidemia without increasing significant mortality.

Metabolic syndrome in pediatrics

The ever growing prevalence of childhood obesity is being accompanied by an increase in the pediatric population of diseases once believed to be exclusive of the adulthood such as the metabolic syndrome (MS). The MS has been defined as the link between insulin resistance, hypertension, dyslipidemia, impaired glucose tolerance, and other metabolic abnormalities associated with an increased risk of atherosclerotic cardiovascular diseases in adults. In this review, we will discuss the peculiar aspects of the pediatric MS and the role of novel molecules and biomarkers in its pathogenesis.

The endoplasmic reticulum coat protein II transport machinery coordinates cellular lipid secretion and cholesterol biosynthesis

Triglycerides and cholesterol are essential for life in most organisms. Triglycerides serve as the principal energy storage depot and, where vascular systems exist, as a means of energy transport. Cholesterol is essential for the functional integrity of all cellular membrane systems. The endoplasmic reticulum is the site of secretory lipoprotein production and de novo cholesterol synthesis, yet little is known about how these activities are coordinated with each other or with the activity of the COPII machinery, which transports endoplasmic reticulum cargo to the Golgi. The Sar1B component of this machinery is mutated in chylomicron retention disorder, indicating that this Sar1 isoform secures delivery of dietary lipids into the circulation. However, it is not known why some patients with chylomicron retention disorder develop hepatic steatosis, despite impaired intestinal fat malabsorption, and why very severe hypocholesterolemia develops in this condition. Here, we show that Sar1B also promotes hepatic apolipoprotein (apo) B lipoprotein secretion and that this promoting activity is coordinated with the processes regulating apoB expression and the transfer of triglycerides/cholesterol moieties onto this large lipid transport protein. We also show that although Sar1A antagonizes the lipoprotein secretion-promoting activity of Sar1B, both isoforms modulate the expression of genes encoding cholesterol biosynthetic enzymes and the synthesis of cholesterol de novo. These results not only establish that Sar1B promotes the secretion of hepatic lipids but also adds regulation of cholesterol synthesis to Sar1B's repertoire of transport functions.

Recent Advances in Study of Ginsenoside Biosynthetic Pathway in Panax ginseng

Ginsenosides, the major bioactive ingredients of P. ginseng can improve the anti-disease abilities of human being, and generate significant social and economic benefits. However, along with gradually or rapidly or dramatically increasing demand of the ginsenosides, extensive studies have focused on regulating the ginsenoside biosynthetic pathway on a genetic level. This review provides the latest research progress on biosynthetic pathway of ginsenosides, including the mevalonate (MVA) and the methylerythritol phosphate (MEP) pathway, which is newly discovered and located in P. ginseng. Moreover, it also indicated lanosterol synthase metabolic flux present in P. ginseng.

Increase in the Contents of Ginsenosides in Raw Ginseng Roots in Response to Exposure to 450 and 470 nm Light from Light-Emitting Diodes

An light-emitting diode (LED)-based light source was used as a monochromatic light source to determine the responses of raw ginseng roots (Panax ginseng Meyer) to specific emission spectra with respect to the production of ginsenosides. The ginsenoside content in the ginseng roots changed in response to the LED light treatments at 25℃ relative to the levels in the control roots that were treated in the dark or at 4℃ for 7 d. Ginseng roots were exposed to LEDs with four different peak emission wavelengths, 380, 450, 470, and 660 nm, in closed compartments. Compared with the control 4℃-treated roots, roots that were treated with 450 and 470 nm light showed a significantly increased production of ginsenosides (p<0.05), with increases of 64.9% and 74.1%, respectively. The contents of the ginsenosides Rb₂, Rc, and Rg₁ were significantly higher (p<0.05) in the 450 and 470 nm-treated root samples. The ratio of protopanaxadiol ginsenosides (Rb₁, Rb₂, Rc, and Rd) to protopanaxatriol ginsenosides (Rg₁, Rg₂, Re, and Rf) was significantly higher (p<0.05) in the 450 and 470 nm-treated root samples than in the control 4℃-treated roots. This is the first report that demonstrates the increase and conversion of ginsenosides in raw ginseng roots in response to exposure to LED light.

The association between hepatic fat content and liver injury in obese children and adolescents: effects of ethnicity, insulin resistance, and common gene variants

OBJECTIVE

Nonalcoholic fatty liver disease and nonalcoholic steatohepatitis (NASH) are highly prevalent in obese youth. Herein, we aimed to study the association between hepatic fat accumulation as assessed by magnetic resonance imaging and circulating levels of cytokeratin-18 (CK-18) fragments, a robust NASH biomarker, and to explore the impact on this association of ethnicity, insulin resistance, and single nucleotide polymorphisms (SNPs) associated with steatosis (rs738409 in the PNPLA3, rs1260326 in the GCKR) or NASH severity (rs2645424 in the FDFT1).

RESEARCH DESIGN AND METHODS

Two-hundred twenty-nine obese youths (87 Caucasians, 61 African Americans, and 81 Hispanics; mean age, 12.8 ± 2.9 years; mean BMI, 31.4 ± 7.4) underwent magnetic resonance imaging, oral glucose tolerance test, and CK-18 levels measurement; 12 subjects underwent liver biopsy.

RESULTS

African Americans showed lower CK-18 levels than Hispanics (P < 0.001) and Caucasians (P = 0.004). Hepatic fat content (HFF%) and whole body insulin sensitivity index (WBISI) modulated CK-18 levels in Caucasians and Hispanics (P = 0.02 and P = 0.011), but not in African Americans; in fact, CK-18 was associated with HFF% and WBISI in Caucasians (P = 0.0018 and P < 0.0001) and Hispanics (P < 0.0001 and P = 0.02), but not in African Americans (both P = 0.5). The PNPLA3 SNP showed association in Caucasians (P = 0.02) and Hispanics (P = 0.05), and FDFT1 SNP showed an association in Caucasians (P = 0.05) and Hispanics (P = 0.02), with the same trend in African Americans (P = 0.07).

CONCLUSIONS

African Americans have lower levels of CK-18 than Caucasians and Hispanics irrespective of HFF% and insulin resistance. Moreover, SNPs in the PNPLA3 and FDFT1 may drive the individual predisposition to development of hepatic injury.

Energy Drinks: An Assessment of Their Market Size, Consumer Demographics, Ingredient Profile, Functionality, and Regulations in the United States

  The consumption of energy drinks is rapidly increasing, as demonstrated by their large market growth. The targeted demographic group is teenagers, young adults, 18 to 34 y old; although expansion into nontraditional markets is also occurring. It is claimed that energy drinks can offer an increased energy boost related to their ingredient profile of caffeine, taurine, herbal extracts, and vitamins. Research suggests that energy drink formulations, in addition to increasing energy utilization, may also improve mood, enhance physical endurance, reduce mental fatigue, and increase reaction time. However, in most cases, the corresponding mechanisms of action are not clear. In addition, concerns have been raised over their safety and with a currently weak regulatory environment, efforts need to be made to ensure consumer safety. The objective of this article is to review the current U.S. energy drink market with emphasis on its market size, target demographic, active ingredients, potential benefits, safety, and regulations.

Pharmacologic inhibition of squalene synthase and other downstream enzymes of the cholesterol synthesis pathway: a new therapeutic approach to treatment of hypercholesterolemia

Hypercholesterolemia is a major risk factor for the development of atherosclerotic vascular diseases. The most popular agents for cholesterol reduction are the statin drugs, which are competitive inhibitors of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase, the primary rate-limiting enzyme in the hepatic biosynthesis of cholesterol. Although relatively safe and effective, the available statins can cause elevations in liver enzymes and myopathy. Squalene synthase is another enzyme that is downstream to HMG-CoA reductase in the cholesterol synthesis pathway and modulates the first committed step of hepatic cholesterol biosynthesis at the final branch point of the cholesterol biosynthetic pathway. Squalene epoxidase and oxidosqualene cyclase are other enzymes that act distally to squalene synthase. Pharmacologic inhibitors of these downstream enzymes have been developed, which may reduce low-density lipoprotein cholesterol and reduce the myopathy side effect seen with upstream inhibition of HMG-CoA. At this juncture, one squalene synthase inhibitor, lapaquistat (TAK-475) is in active clinical trials as a monotherapy, but there have been suggestions of increased hepatotoxicity with the drug.

K45R variant of squalene synthase increases total cholesterol levels in two study samples from a French Canadian population

Squalene synthase is an important component of the cholesterol biosynthetic pathway, and inhibitors of this enzyme have been shown to lower plasma cholesterol levels. Previously, we sequenced the squalene synthase gene, FDFT1 (farnesyl-diphosphate farnesyltransferase), and identified several SNPs, including a nonsynonymous variant, rs11549147:A>G (K45R). To examine the possible association of K45R with plasma lipid traits, we tested 887 individuals from 149 families from the founder population of Saguenay-Lac St. Jean (SLSJ), Quebec. K45R was associated with increased total cholesterol (TC) (P=0.035) and non-high-density lipoprotein cholesterol (non-HDL-C) (P=0.01). These results were replicated in an independent sample of unrelated individuals (P=0.0008 for TC, P=0.004 for non-HDL-C). This SNP also influenced low-density lipoprotein cholesterol (P=0.042) and HDL-C (P=0.025) in the family-based sample, and triglycerides (TG) (P=0.007) in the unrelated subjects. The lysine (K) in codon 45 is conserved across 11 mammals and lies in a potential exonic splicing enhancer (ESE) site. These results suggest that this coding variant in the squalene synthase gene influences plasma cholesterol levels, possibly by affecting the intracellular production of cholesterol.

Progress in understanding of ginsenoside biosynthesis

Ginseng is an economically important medicinal plant. The major bioactive ingredients of ginseng are ginsenosides, which are triterpene saponins. Because of difficulties in ginseng cultivation and the low productivity of ginseng cell and tissue culture, it has become important to improve ginsenoside levels by using metabolic engineering based on the biosynthetic pathway of ginsenosides. During the last decade, substantial advances have been made in biosynthesis of ginsenosides. This review is concerned with recent developments in our understanding of the biosynthesis of ginsenosides.

Hepatic ABCG5/G8 overexpression reduces apoB-lipoproteins and atherosclerosis when cholesterol absorption is inhibited

We previously reported that liver-specific overexpression of ABCG5/G8 in mice is not atheroprotective, suggesting that increased biliary cholesterol secretion must be coupled with decreased intestinal cholesterol absorption to increase net sterol loss from the body and reduce atherosclerosis. To evaluate this hypothesis, we fed low density lipoprotein receptor-knockout (LDLr-KO) control and ABCG5/G8-transgenic (ABCG5/G8-Tg)xLDLr-KO mice, which overexpress ABCG5/G8 only in liver, a Western diet containing ezetimibe to reduce intestinal cholesterol absorption. On this dietary regimen, liver-specific ABCG5/G8 overexpression increased hepatobiliary cholesterol concentration and secretion rates (1.5-fold and 1.9-fold, respectively), resulting in 1.6-fold increased fecal cholesterol excretion, decreased hepatic cholesterol, and increased (4.4-fold) de novo hepatic cholesterol synthesis versus LDLr-KO mice. Plasma lipids decreased (total cholesterol, 32%; cholesteryl ester, 32%; free cholesterol, 30%), mostly as a result of reduced non-high density lipoprotein-cholesterol and apolipoprotein B (apoB; 36% and 25%, respectively). ApoB-containing lipoproteins were smaller and lipid-depleted in ABCG5/G8-TgxLDLr-KO mice. Kinetic studies revealed similar 125I-apoB intermediate density lipoprotein/LDL fractional catabolic rates, but apoB production rates were decreased 37% in ABCG5/G8-TgxLDLr-KO mice. Proximal aortic atherosclerosis decreased by 52% (male) and 59% (female) in ABCG5/G8-TgxLDLr-KO versus LDLr-KO mice fed the Western/ezetimibe diet. Thus, increased biliary secretion, resulting from hepatic ABCG5/G8 overexpression, reduces atherogenic risk in LDLr-KO mice fed a Western diet containing ezetimibe. These findings identify distinct roles for liver and intestinal ABCG5/G8 in modulating sterol metabolism and atherosclerosis.