Lignans from the fruits of Schisandra chinensis (Turcz.) Baill inhibit proprotein convertase subtilisin/kexin type 9 expression

Dibenzocyclooctadiene lignans from the family Schisandraceae: A review of phytochemistry, structure-activity relationship, and hepatoprotective effects

Liver injury is a common pathological process characterized by massive degeneration and abnormal death of liver cells. With increase in dead cells and necrosis, liver injury eventually leads to nonalcoholic fatty liver disease (NAFLD), hepatic fibrosis, and even hepatocellular carcinoma (HCC). Consequently, it is necessary to treat liver injury and to prevent its progression. The drug Bicylol is widely employed in China to treat chronic hepatitis B virus (HBV) and has therapeutic potential for liver injury. It is the derivative of dibenzocyclooctadiene lignans extracted from Schisandra chinensis (SC). The Schisandraceae family is a rich source of dibenzocyclooctadiene lignans, which possesses potential liver protective activity. This study aimed to comprehensively summarize the phytochemistry, structure-activity relationship and molecular mechanisms underlying the liver protective activities of dibenzocyclooctadiene lignans from the Schisandraceae family. Here, we had discussed the analysis of absorption or permeation properties of 358 compounds based on Lipinski's rule of five. So far, 358 dibenzocyclooctadiene lignans have been reported, with 37 of them exhibited hepatoprotective effects. The molecular mechanism of the active compounds mainly involves antioxidative stress, anti-inflammation and autophagy through Kelch-like ECH-associating protein 1/nuclear factor erythroid 2 related factor 2/antioxidant response element (Keap1/Nrf2/ARE), nuclear factor kappa B (NF-кB), and transforming growth factor β (TGF-β)/Smad 2/3 signaling pathways. This review is expected to provide scientific ideas for future research related to developing and utilizing the dibenzocyclooctadiene lignans from Schisandraceae family.

Ultrasensitive Homogeneous Detection of PCSK9 and Efficacy Monitoring of the PCSK9 Inhibitor Based on Proximity Hybridization-Dependent Chemiluminescence Imaging Immunoassay

Accurate quantification of proprotein convertase subtilisin/kexin type 9 (PCSK9) in serum before and after the medication is helpful in grasping the evolution of PCSK9-related disease and evaluating the efficacy of PCSK9 inhibitors. Conventional approaches for PCSK9 quantification suffered from complicated operations and low sensitivity. By integrating stimuli-responsive mesoporous silica nanoparticles, dual-recognition proximity hybridization, and T7 exonuclease-assisted recycling amplification, a novel homogeneous chemiluminescence (CL) imaging approach was proposed for ultrasensitive and convenient immunoassay of PCSK9. Owing to the intelligent design and signal amplification property, the whole assay was conducted without separation and rinsing, significantly simplifying the procedure and eliminating the errors associated with the professional operation; meanwhile, it showed linear ranges over 5 orders of magnitude and detection limit as low as 0.7 pg mL^-1. Parallel testing was allowed due to the imaging readout, which brought a maximum throughput of 26 tests h^-1. The proposed CL approach was applied to analyze PCSK9 from hyperlipidemia mice before and after the intervention of the PCSK9 inhibitor. Serum PCSK9 levels in the model group and the intervention group could be distinguished efficiently. The results were reliable compared to commercial immunoassay results and histopathologic findings. Thus, it could facilitate the monitoring of the serum PCSK9 level and the lipid-lowering effect of the PCSK9 inhibitor, showing promising potential in bioanalysis and pharmaceuticals.

Isocoumarins and Benzoquinones with Their Proprotein Convertase Subtilisin/Kexin Type 9 Expression Inhibitory Activities from Dried Roots of Lysimachia vulgaris

A phytochemical investigation of the n-hexane-soluble chemical constituents of Lysimachia vulgaris roots allowed for selection using a proprotein convertase subtilisin-kexin type 9 (PCSK9) mRNA expression monitoring assay in HepG2 cells. This led to the isolation of two previously undescribed isocoumarins of natural origin, 8'Z,11'Z-octadecadienyl-6,8-dihydroxyisocoumarin (1) and 3-pentadecyl-6,8-dihydroxyisocoumarin (2), along with 20 previously reported compounds (3-22). All of the structures were established using NMR spectroscopic data and MS analysis. Of the isolates, 1 and 3 were found to inhibit PCSK9, inducible degrader of the low-density lipoprotein receptor (IDOL), and SREBP2 mRNA expression. Further computational dockings of both 1 and 3 to C-ring of IDOL E3 ubiquitin ligase predicted the mechanism behind the inhibitory effect of these compounds on the enzyme.

Chemical Constituents from the Roots and Rhizomes of Sophora tonkinensis and Their Effects on Proprotein Convertase Substilisin/Kexin Type 9 Expression

This study was conducted to further investigate bioactive molecules from Sophora tonkinensis that can inhibit proprotein convertase substilisin/kexin type 9 (PCSK9) expression. After interpreting NMR spectroscopic data and MS spectral data of all isolates, a new naturally occurring compound, 6-hydroxy-vitexin-2″-O-rhamnoside (7), was identified along with 30 known compounds. The calculation of the gauge-including atomic orbital (GAIO) and electronic circular dichroism (ECD) proposed the absolute configuration of 17 as (2S,3R)-methyl-2-(4-hydroxybenzyl)tartrate by comparing the calculated ECD with experimental data. All isolates were tested for their inhibitory effects on PCSK9 mRNA expression. Of the tested compounds, (+)-isolariciresinol (12) inhibited PCSK9 expression via downregulation of HNF1α and SREBPs.

Dammarane-type saponins with proprotein convertase subtilisin/kexin type 9 inhibitory activity from Gynostemma pentaphyllum

Seven undescribed dammarane-type saponins, gypenosides LXXXI-LXXXVII, together with four known compounds, were isolated from the whole herb of Gynostemma pentaphyllum. The chemical structures of these undescribed compounds were elucidated on the basis of physical and spectroscopic analysis and comparison with literature data. All the isolates were evaluated for their proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitory activities in HepG2 cells. Among them, gypenosides LXXXII-LXXXVII, gynosaponin II, IV and VI suppressed the expression of PCSK9 in LPDS-induced HepG2 cells at 20 μM; gypenosides LXXXII, LXXXV and LXXXVII showed inhibitory activities against PCSK9 at 10 μM; notably, gypenoside LXXXII still exhibited inhibitory activity against PCSK9 at 5 μM.

Acylated saponins and flavonoid glycosides from the fruits of Stewartia koreana

Three acylated saponins and three flavonoid glycosides, along with nine known flavonoids, were isolated from the fruits of Stewartia koreana Nakai ex Rehder (Theaceae) using relative mass defect filtering analysis. The structures of these compounds were determined by performing spectroscopic analyses and using chemical methods. Furthermore, all the isolates were evaluated for their effects on the mRNA expression of the genes for proprotein convertase subtilisin/kexin type 9 (PCSK9) and low-density lipoprotein receptor (LDLR) as well as their inhibitory activities on PCSK9 and LDLR binding. None of the isolates was deemed to be active in PCSK9-LDLR binding inhibition. However, (+)-catechin was found to inhibit PCSK9 expression and increase LDLR expression, suggesting the potential of (+)-catechin to lower cholesterol level via the downregulation of PCSK9 expression.

Schisandrin C Affects Glucose-Stimulated Insulin Secretion in Pancreatic β-Cells and Glucose Uptake in Skeletal Muscle Cells

The aim of our study was to investigate the effect of three lignans (schisandrol A, schisandrol B, and schisandrin C) on insulin secretion in rat INS-1 pancreatic β-cells and glucose uptake in mouse C2C12 skeletal muscle cells. Schisandrol A and schisandrin C enhanced insulin secretion in response to high glucose levels with no toxic effects on INS-1 cells. The effect of schisandrin C was superior to that of gliclazide (positive control), a drug commonly used to treat type 2 diabetes (T2D). In addition, western blot analysis showed that the expression of associated proteins, including peroxisome proliferator-activated receptor γ (PPARγ), pancreatic and duodenal homeobox 1 (PDX-1), phosphatidylinositol 3-kinase (PI3K), Akt, and insulin receptor substrate-2 (IRS-2), was increased in INS-1 cells after treatment with schisandrin C. In addition, insulin secretion effect of schisandrin C were enhanced by the Bay K 8644 (L-type Ca²⁺ channel agonist) and glibenclamide (K⁺ channel blocker), were abolished by the nifedipine (L-type Ca²⁺ channel blocker) and diazoxide (K⁺ channel activator). Moreover, schisandrin C enhanced glucose uptake with no toxic effects on C2C12 cells. Western blot analysis showed that the expression of associated proteins, including insulin receptor substrate-1 (IRS-1), AMP-activated protein kinase (AMPK), PI3K, Akt, glucose transporter type 4 (GLUT-4), was increased in C2C12 cells after treatment with schisandrin C. Schisandrin C may improve hyperglycemia by enhancing insulin secretion in pancreatic β-cells and improving glucose uptake into skeletal muscle cells. Our findings may provide evidence that schisandrin C may be beneficial in devising novel anti-T2D strategies.

Identification of neolignans with PCSK9 downregulatory and LDLR upregulatory activities from Penthorum chinense and the potential in cholesterol uptake by transcriptional regulation of LDLR via SREBP2

ETHNOPHARMACOLOGICAL RELEVANCE

Penthorum chinense has been used in East Asia for the treatment of cholecystitis, infectious hepatitis, jaundice and to treat liver problems. Recent evidences provided the potential for the clinical use of P. chinense in the treatment of metabolic disease.

AIM OF THE STUDY

Based on the traditional use and recent evidences, we investigated the effects of constituents from P. chinense with modulation on proprotein convertase subtilisin/kexin type 9 (PCSK9) and low-density lipoprotein receptor (LDLR) expression, and the effect of the most active substance on cholesterol uptake, and genes relevant to lipid metabolism.

MATERIALS AND METHODS

The isolation of compounds from the BuOH-soluble extract of 80% methanol extract of P. chinense was conducted using chromatographic methods and the structures were established by interpreting spectroscopic data. Quantitative real time-PCR, and Western blot analysis were performed to monitor the regulatory activity on PCSK9 and LDLR expression. PCSK9-LDLR binding interaction was also tested. The cholesterol uptake in hepatocyte was measured using 1,1-dioctadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate (DiI)-labeled LDL cholesterol. Additionally, gene network analysis of LDLR and responses of its target proteins were carried out to discover genes germane to the effect of active compound on HepG2 cells. Moreover, we performed protein-protein interaction analysis via String and constructed the compound target network using Cytoscape.

RESULTS

Two new neolignans and 37 known compounds were characterized from P. chinense. Of the isolated compounds, (7'E,8S)-2',4,8-trihydroxy-3-methoxy-2,4'-epoxy-8,5'-neolign-7'-en-7-one (3), penthorin A (4) and methyl gallate (25) were found to suppress PCSK9 mRNA expression with IC₅₀ values of 5.13, 15.56 and 11.66 μM, respectively. However, all the isolated compounds were found to be inactive in PCSK9-LDLR interaction assay. Additionally, a dibenzoxepine-type lignan analog, (7'E,8S)-2',4,8-trihydroxy-3-methoxy-2,4'-epoxy-8,5'-neolign-7'-en-7-one (3) demonstrated to upregulate LDLR mRNA and protein expression via transcriptional factor sterol regulatory element-binding protein 2 (SREBP2). Furthermore, (7'E,8S)-2',4,8-trihydroxy-3-methoxy-2,4'-epoxy-8,5'-neolign-7'-en-7-one (3) increase the LDL-cholesterol uptake in DiI-LDL assay.

CONCLUSION

(7'E,8S)-2',4,8-trihydroxy-3-methoxy-2,4'-epoxy-8,5'-neolign-7'-en-7-one (3) seemed to increase potentially cholesterol uptake via the downregulation of PCSK9 and the activation of LDLR in hepatocytes. Moreover, SREBP2 was found to play an important role in regulation of PCSK9 and LDLR by (7'E,8S)-2',4,8-trihydroxy-3-methoxy-2,4'-epoxy-8,5'-neolign-7'-en-7-one.

Sesquiterpenoids from the Aerial Parts of Salvia plebeia with Inhibitory Activities on Proprotein Convertase Subtilisin/Kexin Type 9 Expression

Phytochemical investigation of the methanol extract of the aerial parts of Salvia plebeia aided by a proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA expression screening assay in HepG2 cells led to the identification of 19 compounds including one new norsesquiterpene (1), six new eudesmane sesquiterpenoids (2-5, 8, and 11), and 12 known compounds. The structures of all compounds were elucidated by interpretation of their 1D and 2D NMR spectroscopic and MS data. Furthermore, computational prediction of ECD or chemical shifts was used to propose the absolute configurations of the new structures. All isolates were assessed for their inhibitory activities against PCSK9 mRNA expression and PCSK9-low-density lipoprotein receptor (LDLR) interactions. None of the isolated compounds inhibited PCSK9 and LDLR interactions. However, compounds 1, 9, and 10 downregulated PCSK9 mRNA expression.

Compounds Isolated From the Fruits of Xanthium strumarium, Including a New Neo-Lignan, and Their Anticancer Effects

A new neo-lignan, (7′ S,8 ′R)-4′,5′,9′-trihydroxy-4,6-dimethoxy-5,8′-oxyneolign-7-en-9-al (1), along with 5 known compounds (2-6), were isolated from the fruits of Xanthium strumarium. Their structures were elucidated by extensive spectroscopic methods. All the isolates were evaluated for in vitro cytotoxicities against the human cancer lines HepG2, A549, HCT-116, and SGC-7901. Compounds 1 and 3 showed potent antiproliferative effects against A549 cancer cells with half-maximal inhibitory concentration (IC50) values of 11.2 and 8.3 µM, respectively. In addition, compound 3 exhibited moderate cytotoxicity to SGC-7901 cancer cells, with an IC50 value of 12.9 µM.

Butein Synergizes with Statin to Upregulate Low-Density Lipoprotein Receptor Through HNF1α-Mediated PCSK9 Inhibition in HepG2 Cells

Downregulation of the low-density lipoprotein (LDL) receptor (LDLR) can lead to hypercholesterolemia and related conditions, including cardiovascular diseases. Statins are a class of LDL cholesterol-lowering agents and are best-selling medications for patients at high risk of developing cardiovascular diseases. Indeed, statins upregulate LDLR and proprotein convertase subtilisin/kexin type 9a (PCSK9), leading to LDLR lysosomal degradation, which interferes with the attenuation of hypercholesterolemia. In the present study, butein was found to decrease extracellular PCSK9 levels by reducing its mRNA expression, which was attributable to butein-mediated downregulation of HNF1α in HepG2 cells. Butein-mediated PCSK9 inhibition further reversed LDLR protein synthesis inhibition, which possibly occurred through butein-mediated inhibition of LDLR degradation. When treated as a combination of butein and a statin, butein reduced statin-mediated enhancement of PCSK9 protein expression. This resulted in a synergistic enhancement of LDLR protein expression, whereas butein alone marginally increased LDLR protein expression. These findings suggest that butein, a novel PCSK9 inhibitor, may be a potential alternative or adjunct to statin treatment.

A stilbene dimer and flavonoids from the aerial parts of Chromolaena odorata with proprotein convertase subtilisin/kexin type 9 expression inhibitory activity

Investigation of components of the chloroform-soluble and ethyl acetate-soluble extracts of the aerial parts of Chromolaena odorata L. selected by PCSK9 mRNA expression monitoring assay in HepG2 cells led to the isolation of a new stilbene dimer, (+)-8b-epi-ampelopsin A (1), and 30 known compounds (2-31). The structures of the isolates were established by interpretation of NMR spectroscopic data and the stereochemistry of the new stilbene (1) was proposed based on ECD and NMR calculations. Among the isolates, 1, 5,6,7,4'-tetramethoxyflavanone (6), 5,6,7,3',4'-pentamethoxyflavanone (7), acacetin (18), and uridine (21) were found to inhibit PCSK9 mRNA expression with IC₅₀ values of 20.6, 21.4, 31.7, 15.0, and 13.7 µM, respectively. Furthermore, the most abundant isolate among the selected compounds, 6, suppressed PCSK9 and low-density lipoprotein receptor protein expression in addition to downregulating the mRNA expression of HNF-1α.

Differential effects of red yeast rice, Berberis aristata and Morus alba extracts on PCSK9 and LDL uptake

BACKGROUND AND AIMS

The novel nutraceutical combination containing red yeast rice (monacolin K 3.3 mg), Berberis aristata cortex extract (Berberine 531.25 mg) and Morus alba leaves extract (1-deoxynojirimycin 4 mg) is effective in the management of elevated plasma low-density lipoprotein cholesterol (LDL-C) levels. The aim of the present study was to investigate the effects of the three components on proprotein convertase subtilisin/kexin type 9 (PCSK9), a key regulator of LDL receptor (LDLR) expression, in hepatocyte cell lines and to compare their effects on LDL cellular uptake.

METHODS AND RESULTS

HepG2 and Huh7 cells were incubated with B. aristata cortex extract (BCE), red yeast rice (RYR) and M. alba leaves extract (MLE) alone or in combination for 24 h. RYR (50 μg/mL) increased PCSK9 protein expression (Western blot analysis and ELISA), PCSK9 mRNA (qPCR) and its promoter activity (luciferase reporter assay). BCE (40 μg/mL) reduced instead PCSK9 expression, mRNA levels and promoter activity. MLE determined a concentration-dependent reduction of PCSK9 at the mRNA and protein levels, with a maximal reduction at 1 mg/mL, without significant changes of PCSK9 promoter activity. MLE also downregulated the expression of 3-hydroxy-3-methyl-3-glutaryl coenzyme A reductase and fatty acid synthase mRNA levels. The combination of RYR, BCE and MLE reduced the PCSK9 mRNA and protein levels, as well as the promoter activity. Finally, the single components and their combination induced LDL receptor and LDL uptake by the hepatocytes.

CONCLUSION

The positive effect of MLE on PCSK9 supports the rationale of using the nutraceutical combination of RYR, BCE and MLE to control hyperlipidemic conditions.

Design, synthesis, and biological evaluation of novel tetrahydroprotoberberine derivatives (THPBs) as proprotein convertase subtilisin/kexin type 9 (PCSK9) modulators for the treatment of hyperlipidemia

Proprotein convertase subtilisin/kexin type 9 (PCSK9) modulators may attenuate PCSK9-induced low-density lipoprotein receptor (LDLR) degradation in lysosome and promote the clearance of circulating low-density lipoprotein cholesterol (LDL-C). A novel series of tetrahydroprotoberberine derivatives (THPBs) were designed, synthesized, and evaluated as PCSK9 modulators for the treatment of hyperlipidemia. Among them, eight compounds exhibited excellent activities in downregulating hepatic PCSK9 expression better than berberine in HepG2 cells. In addition, five compounds 15, 18, 22, (R)-22, and (S)-22 showed better performance in the low-density lipoprotein, labeled with 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl-indocarbocyanine perchlorate (DiI-LDL) uptake assay, compared with berberine at the same concentration. Compound 22, selected for in vivo evaluation, demonstrated significant reductions of total cholesterol (TC) and LDL-C in hyperlipidemic hamsters with a good pharmacokinetic profile. Further exploring of the lipid-lowering mechanism showed that compound 22 promoted hepatic LDLR expression in a dose-dependent manner in HepG2 cells. Additional results of human ether-à-go-go related gene (hERG) inhibition assay indicated the potential druggability for compound 22, which is a promising lead compound for the development of PCSK9 modulator for the treatment of hyperlipidemia.

Discovery of 2,3'-diindolylmethanes as a novel class of PCSK9 modulators

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes the degradation of low density lipoprotein receptor (LDLR). Anti-PCSK9 agents have been approved for the treatment of hypercholesterolemia. We recently discovered a series of small-molecule PCSK9 modulators that contains a relatively small pharmacophore of 2,3'-diindolylmethane with molecular weights around only 250. These molecules can significantly lower the amount of PCSK9 protein in a cell-based phenotypic assay. Our SAR studies yielded compound 16 with a IC₅₀-value of 200 nM. No obvious cytotoxicity was observed at concentrations below 50 µM.

Lignans and Neolignans: Plant secondary metabolites as a reservoir of biologically active substances

Lignans and neolignans are plant secondary metabolites derived from the oxidative coupling of phenylpropanoids. Biological activity of these phenolic compounds ranges from antioxidant, antitumor (terminaloside P, IC₅₀ = 10 nM), anti-inflammatory, anti-neurodegenerative (schibitubin B, IC₅₀ = 3.2 nM) and antiviral (patentiflorin A, IC₅₀ = 14-23 nM) to antimicrobial. In addition, it was observed that several members of this group, namely enterolactone and its biochemical precursors also known as phytoestrogens, possess important protective properties. Most of these lignans and neolignans are presented in reasonable amounts in one's diet and thus the protection they provide against the colon and breast cancer, to name a few, is even more important to note. Similarly, neuroprotective properties were observed (schisanwilsonin G, IC₅₀ = 3.2 nM) These structural motives also serve as an important starting point in the development of anticancer drugs. Presumably the most famous members of this family, etoposide and teniposide, synthetic derivatives of podophyllotoxin, are used in the clinical treatment of lymphocytic leukemia, certain brain tumors, and lung tumors already for nearly 20 years. This review describes 413 lignans and neolignans which have been isolated between 2016 and mid-2018 being reported in more than 300 peer-reviewed articles. It covers their source, structure elucidation, and bioactivity. Within the review, the structure-based overview of compounds as well as the bioactivity-based overview of compounds are described.

Prenylated Flavonoids from the Roots and Rhizomes of Sophora tonkinensis and Their Effects on the Expression of Inflammatory Mediators and Proprotein Convertase Subtilisin/Kexin Type 9

Seven new prenylated flavonoids (1-7) and one new prenylated phenylpropiophenone (8) were isolated from roots and rhizomes of Sophora tonkinensis, along with nine known compounds (9-17). The structures 1-8 were elucidated by spectroscopic data analysis and comparison with reported values. Compounds 8 and 12 (7-methoxyebenosin) showed inhibitory activities against nitric oxide production in lipopolysaccharide-induced RAW264.7 cells, with IC₅₀ values of 8.1 and 6.2 μM, respectively. They also significantly lowered expression of CSF2, TNF, and IL-1β. Lonchocarpol A (10) and erybraedin D (16) at concentrations of 20 μM downregulated proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA expression in HepG2 cells. Moreover, erybraedin D (16) inhibited PCSK9 protein synthesis (IC₅₀ 7.8 μM), while simultaneously activating AMP-activated protein kinase and acetyl-CoA carboxylase.

Systematically identifying the hepatoprotective ingredients of schisandra lignan extract from pharmacokinetic and pharmacodynamic perspectives

BACKGROUND

Herbal medicines (HMs) have been proven to be productive sources of leads for the development of drugs. To date approximately 150 lignans have been identified from Schisandra sphenanthera. Hepatoprotective activity is a well-known characteristic of schisandra lignans, yet the authentic types of active lignans are still not well known.

PURPOSE

The present study aimed to develop a reliable and efficient strategy for identifying the hepatoprotective ingredients of schisandra lignan extract (SLE).

METHODS

SLEs were prepared by extracting Schisandra sphenanthera powder using 10%, 50% and 90% ethanol (w/w 1:10) combining 5-fold volume of ethyl acetate. The schisandra lignans in SLEs were qualitatively analyzed based on liquid chromatography hybrid ion trap time-of-flight mass spectrometry (LCMS-IT-TOF). Preparative liquid chromatography (PLC) was used to collect ingredient fractions. The hepatoprotective activity of schisandra lignans was systematically investigated on in vivo and in vitro models.

RESULTS

The SLE extracted by 50% ethanol and 5-fold volume of ethyl acetate (50%SLE) had the highest lignan content and exhibited significantly stronger hepatoprotective activity than other SLEs (P <  0.01). The hepatoprotective effect of 50%SLE mainly attributed to the SLE segment which collected from 12 to 22 min by PLC. Schisantherin A (Sth A) was confirmed as the most promising hepatoprotective drug in Schisandra sphenanthera due to high content in crude materials, high exposure level in vivo and high efficiency on APAP-induced hepatotoxicity.

CONCLUSION

The hepatoprotective ingredients of SLEs were systematically investigated based on the presently developed approach, and Sth A was identified as the optimum hepatoprotective candidate in Schisandra sphenanthera.

Small molecules as inhibitors of PCSK9: Current status and future challenges

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in regulating lipoprotein metabolism by binding to low-density lipoprotein receptors (LDLRs), leading to their degradation. LDL cholesterol (LDL-C) lowering drugs that operate through the inhibition of PCSK9 are being pursued for the management of hypercholesterolemia and reducing its associated atherosclerotic cardiovascular disease (CVD) risk. Two PCSK9-blocking monoclonal antibodies (mAbs), alirocumab and evolocumab, were approved in 2015. However, the high costs of PCSK9 antibody drugs impede their prior authorization practices and reduce their long-term adherence. Given the potential of small-molecule drugs, the development of small-molecule PCSK9 inhibitors has attracted considerable attention. This article provides an overview of the recent development of small-molecule PCSK9 inhibitors disclosed in the literature and patent applications, and different approaches that have been pursued to modulate the functional activity of PCSK9 using small molecules are described. Challenges and potential strategies in developing small-molecule PCSK9 inhibitors are also discussed.

Sauchinone controls hepatic cholesterol homeostasis by the negative regulation of PCSK9 transcriptional network

Whole-transcriptome analysis and western blotting of sauchinone-treated HepG2 cells demonstrated that sauchinone regulated genes relevant to cholesterol metabolism and synthesis. In particular, it was found that the expression of proprotein convertase subtilisin/kexin type 9 (PCSK9) was downregulated, and the expression of low density lipoprotein receptor (LDLR) was upregulated in sauchinone-treated HepG2 cells. Consequently, LDL-cholesterol (LDL-C) uptake was increased. As a transcriptional regulator of PCSK9 expression, sterol regulatory elements binding protein-2 (SREBP-2) was proposed by transcriptome analysis and western blotting. Oral administration of sauchinone increased hepatic LDLR through PCSK9 inhibition in obese mice and showed the reduced serum LDL-C levels and downstream targets of SREBP-2. Thus, it is evident that sauchinone reduces hepatic steatosis by downregulating the expression of hepatic PCSK9 via SREBP-2.

Discovery of Flavonoids from Scutellaria baicalensis with Inhibitory Activity Against PCSK 9 Expression: Isolation, Synthesis and Their Biological Evaluation

Nine flavonoids were isolated and identified from a chloroform-soluble fraction of the roots of Scutellaria baicalensis through a bioactivity-guided fractionation using a proprotein convertase subtilisin/kexin type 9 (PCSK9) monitoring assay in HepG2 cells. All structures were established by interpreting the corresponding spectroscopic data and comparing measured values from those in the literature. All compounds were assessed for their ability to inhibit PCSK9 mRNA expression; compounds 1 (3,7,2'-trihydroxy-5-methoxy-flavanone) and 4 (skullcapflavone II) were found to suppress PCSK9 mRNA via SREBP-1. Furthermore, compound 1 was found to increase low-density lipoprotein receptor protein expression. Also, synthesis of compound 1 as a racemic mixture form (1a) was completed for the first time. Natural compound 1 and synthetic racemic 1a were evaluated for their inhibitory activities against PCSK9 mRNA expression and the results confirmed the stereochemistry of 1 was important.