Sterculic Oil, a Natural SCD1 Inhibitor, Improves Glucose Tolerance in Obese ob/ob Mice

An insight into advances and challenges in the development of potential stearoyl Co-A desaturase 1 inhibitors

Stearoyl-CoA desaturase 1 (SCD1) is one of the key enzymes involved in lipid metabolism, plays a vital role in the synthesis of monounsaturated fatty acids (MUFAs) from saturated fatty acids (SFAs). Due to its promising therapeutic potential in treating metabolic disorders, cancers, and skin diseases there is an increasing interest in the development of novel inhibitors against SCD1. This review comprehensively explores the evolution of potential SCD1 inhibitors, focusing on systemic and liver-targeted inhibitors and discusses their structure-activity relationship (SAR) pattern. Among the various small molecules reported, natural products like sterculic acid have emerged as significant SCD1 inhibitors, highlighting the potential of naturally derived compounds in therapeutic development. This review also addresses the challenges in optimizing pharmacokinetic properties and reducing adverse effects, providing insights into the future directions for the development of potential novel SCD1 inhibitors with maximum therapeutic effect and minimum side effects.

Effect of Isoquercitrin on Free Fatty Acid-Induced Lipid Accumulation in HepG2 Cells

Liver metabolic disorders and oxidative stress are crucial factors in the development of nonalcoholic fatty liver disease (NAFLD); however, treatment strategies to combat NAFLD remain poorly established, presenting an important challenge that needs to be addressed. Herein, we aimed to examine the effect of isoquercitrin on lipid accumulation induced by exogenous free fatty acids (FFA) using HepG2 cells and elucidate the underlying molecular mechanism. The cells were exposed to 0.5 mM FFA to induce intracellular lipid accumulation, followed by co-treatment with isoquercitrin to confirm the potential inhibitory effect on FFA-induced lipid production. HepG2 cells exposed to FFA alone exhibited intracellular lipid accumulation, compromised endoplasmic reticulum (ER) stress, and enhanced expression of proteins and genes involved in lipid synthesis; however, co-treatment with isoquercitrin decreased the expression of these molecules in a dose-dependent manner. Furthermore, isoquercitrin could activate AMP-activated protein kinase (AMPK), a key regulatory protein of hepatic fatty acid oxidation, suppressing new lipid production by phosphorylating acetyl-CoA carboxylase (ACC) and inhibiting sterol regulatory element-binding transcription factor 1 (SREBP-1)/fatty acid synthase (FAS) signals. Overall, these findings suggest that isoquercitrin can be employed as a therapeutic agent to improve NAFLD via the regulation of lipid metabolism by targeting the AMPK/ACC and SREBP1/FAS pathways.

Voluntary exercise training improves body weight of leptin-deficient ob/ob mice by altering hepatic stearoyl-CoA desaturase 1 and deleted in breast cancer 1 protein levels

[Purpose]

Deleted in breast cancer 1 (DBC1) ablation causes obesity, and stearoyl-CoA desaturase 1 (SCD1) induces the biosynthesis of monounsaturated fatty acids. This study examined whether voluntary wheel running (VWR) alters SCD-1 and DBC1 protein levels in the liver of leptin-deficient ob/ob mice.

[Methods]

Twenty-five Ob/Ob mice were divided into two groups (ob/ob-Sed and ob/ob-Ex). The expression of DBC1 and SCD1 in the mouse liver was determined using western blotting.

[Results]

After 10 weeks, VWR significantly reduced body weight without affecting the fatty acid synthase and CD36 protein levels. The average daily running distance was 4.0±1.0 km/day. This improvement was associated with changes in the hepatic SCD1 and DBC1 levels. Hepatic SCD-1 protein levels increased significantly, and DBC1 protein levels decreased in ob/ob-Sed animals. On the other hand, VWR inhibited the obesity-induced increase in SCD1 expression and impaired the obesity-induced decrease in DBC1 expression in the liver of leptin-deficient ob/ob mice.

[Conclusion]

This is the first study showing that VWR has strong effects on hepatic SCD1 and DBC1 in ob/ob mice, and provides key insights into the effects of exercise on obesity.

Sterculic Acid Alters Adhesion Molecules Expression and Extracellular Matrix Compounds to Regulate Migration of Lung Cancer Cells

Sterculic acid (SA) is a cyclopropenoid fatty acid isolated from Sterculia foetida seeds. This molecule is a well-known inhibitor of SCD1 enzyme, also known as ∆9-desaturase, which main function is related to lipid metabolism. However, recent studies have demonstrated that it also modifies many other pathways and the underlying gene expression. SCD overexpression, or up-regulated activity, has been associated with tumor aggressiveness and poor prognosis in many cancer types. Scd1 down-regulation, with different inhibitors or molecular strategies, reduces tumor cell survival and cell proliferation, as well as the chemoresistance associated with cancer stem cell presence. However, SA effects over cancer cell migration and extracellular matrix or adhesion molecules have not been described in cancer cells up to now. We used different migration assays and qPCR gene expression analysis to evaluate the effects of SA treatment in cancer cells. The results reveal that SA induces tumoral cell death at high doses, but we also observed that lower SA-treatments induce cell adhesion-migration capacity reduction as a result of modifications in the expression of genes related to integrins and extracellular matrix compounds. Overall, the functional and transcriptomic findings suggest that SA could represent a new inhibitor activity of epithelial to mesenchymal transition.

Inhibition of Stearoyl-CoA Desaturase by Sterculic Oil Reduces Proliferation and Induces Apoptosis in Prostate Cancer Cell Lines

Prostate cancer (PCa) is a common type of cancer affecting male population. PCa treatments have side effects and are temporarily effective, so new therapeutic options are being investigated. Due to the high demand of energy for cell proliferation, an increase in the expression and activity of lipogenic enzymes such as the stearoyl-CoA desaturase (SCD) have been observed in PCa. Sterculic acid, contained in the seed's oil of Malvales, is a natural inhibitor of SCD. The objective of our investigation was to evaluate the effects of sterculic oil (SO) from Sterculia apetala seeds on proliferation, cell cycle and apoptosis in prostate cancer cells. SO was administered to PC3 and LNCaP cells, and to prostate normal cells; cell viability, cell cycle, apoptosis, SCD gene and protein expression and enzymatic activity were analyzed. SO administration (4 mM sterculic acid) diminished cell viability in LNCaP and PC3 cells, arrested cell cycle in G2 and promoted apoptosis. SO diminished SCD enzymatic activity with no effects on gene nor protein expression. Our results suggest that SO might offer benefits as an adjuvant in hormonal and chemotherapy prostate cancer treatments. This is the first study to analyze the effect of SO on cancer cells.

Anopheles coluzzii stearoyl-CoA desaturase is essential for adult female survival and reproduction upon blood feeding

Vitellogenesis and oocyte maturation require anautogenous female Anopheles mosquitoes to obtain a bloodmeal from a vertebrate host. The bloodmeal is rich in proteins that are readily broken down into amino acids in the midgut lumen and absorbed by the midgut epithelial cells where they are converted into lipids and then transported to other tissues including ovaries. The stearoyl-CoA desaturase (SCD) plays a pivotal role in this process by converting saturated (SFAs) to unsaturated (UFAs) fatty acids; the latter being essential for maintaining cell membrane fluidity amongst other housekeeping functions. Here, we report the functional and phenotypic characterization of SCD1 in the malaria vector mosquito Anopheles coluzzii. We show that RNA interference (RNAi) silencing of SCD1 and administration of sterculic acid (SA), a small molecule inhibitor of SCD1, significantly impact on the survival and reproduction of female mosquitoes following blood feeding. Microscopic observations reveal that the mosquito thorax is quickly filled with blood, a phenomenon likely caused by the collapse of midgut epithelial cell membranes, and that epithelial cells are depleted of lipid droplets and oocytes fail to mature. Transcriptional profiling shows that genes involved in protein, lipid and carbohydrate metabolism and immunity-related genes are the most affected by SCD1 knock down (KD) in blood-fed mosquitoes. Metabolic profiling reveals that these mosquitoes exhibit increased amounts of saturated fatty acids and TCA cycle intermediates, highlighting the biochemical framework by which the SCD1 KD phenotype manifests as a result of a detrimental metabolic syndrome. Accumulation of SFAs is also the likely cause of the potent immune response observed in the absence of infection, which resembles an auto-inflammatory condition. These data provide insights into mosquito bloodmeal metabolism and lipid homeostasis and could inform efforts to develop novel interventions against mosquito-borne diseases.

Female mosquitoes can become infected with malaria parasites upon ingestion of blood from an infected person and can transmit the disease when they bite another person some days later. The bloodmeal is rich in proteins which female mosquitoes use to develop their eggs after converting them first to saturated and then to unsaturated fatty acids inside their gut cells. Here, we present the characterization of the enzyme that mosquitoes use to convert saturated to unsaturated fatty acids and show that when this enzyme is eliminated or inhibited mosquitoes cannot produce eggs and die soon after they feed on blood. The mosquito death appears to be primarily associated with the collapse of their gut epithelial barrier due to the loss of cell membrane integrity, leading to their inner body cavity being filled with the ingested blood. These mosquitoes also suffer from an acute and detrimental auto-inflammatory condition due to mounting of a potent immune response in the absence of any infection. We conclude that this enzyme and the mechanism of converting blood-derived proteins to unsaturated fatty acids as a whole can be a good target of interventions aiming at limiting the mosquito abundance and blocking malaria transmission.

Effects of Dietary Cottonseed Oil and Cottonseed Meal Supplementation on Liver Lipid Content, Fatty Acid Profile and Hepatic Function in Laying Hens

Antinutrients, such as cyclopropene fatty acids (CPFAs) and free gossypol (FG), present together in cottonseed have caused numerous adverse effects on liver health and egg quality of laying hens, which are both likely to be related to a disturbance in lipid metabolism. This experiment employed a 3 × 3 factorial arrangement using corn-soybean-meal-based diets supplemented with different levels of cottonseed oil (0%, 2%, or 4% CSO) containing CPFAs and cottonseed meal (0%, 6%, or 12% CSM) containing FG to elucidate the effects of them or their interaction on fatty acid profile, lipid content, and liver health of laying hens. An overall increase in fatty acid saturation and an overall significant decrease (p < 0.05) in monounsaturated fatty acids (MUFAs) were shown in the livers of hens fed diets with either 2% or 4% CSO. Meanwhile, the concentration of liver cholesterol, serum cholesterol, and serum LDL-c of hens fed a diet supplemented with a high level of CSO (4%) were noticeably increased (p < 0.05). Even though the supplementation of 4% CSO in diets aroused beneficial influences on liver function, a high level of CSO inclusion in laying hens' diets is not recommended due to its hypercholesterolemia effect. In conclusion, supplementation of CSO, which contains 0.20% CPFAs, was the primary cause of alteration in fatty acid composition and cholesterol content in hens, while no interaction between CSM and CSO nor CSM effect was found for lipid profile and liver health in laying hen.

Flavonoid and Non-Flavonoid Compounds of Autumn Royal and Egnatia Grape Skin Extracts Affect Membrane PUFA's Profile and Cell Morphology in Human Colon Cancer Cell Lines

Grapes contain many flavonoid and non-flavonoid compounds with anticancer effects. In this work we fully characterized the polyphenolic profile of two grape skin extracts (GSEs), Autumn Royal and Egnatia, and assessed their effects on Polyunsaturated Fatty Acid (PUFA) membrane levels of Caco2 and SW480 human colon cancer cell lines. Gene expression of 15-lipoxygenase-1 (15-LOX-1), and peroxisome proliferator-activated receptor gamma (PPAR-γ), as well as cell morphology, were evaluated. The polyphenolic composition was analyzed by Ultra-High-Performance Liquid Chromatography/Quadrupole-Time of Flight mass spectrometry (UHPLC/QTOF) analysis. PUFA levels were evaluated by gas chromatography, and gene expression levels of 15-LOX-1 and PPAR-γ were analyzed by real-time Polymerase Chain Reaction (PCR). Morphological cell changes caused by GSEs were identified by field emission scanning electron microscope (FE-SEM) and photomicrograph examination. We detected a different profile of flavonoid and non-flavonoid compounds in Autumn Royal and Egnatia GSEs. Cultured cells showed an increase of total PUFA levels mainly after treatment with Autumn Royal grape, and were richer in flavonoids when compared with the Egnatia variety. Both GSEs were able to affect 15-LOX-1 and PPAR-γ gene expression and cell morphology. Our results highlighted a new antitumor mechanism of GSEs that involves membrane PUFAs and their downstream pathways.

Genome-Wide Transcriptomic Analysis Identifies Pathways Regulated by Sterculic Acid in Retinal Pigmented Epithelium Cells

In addition to its predominant role in lipid metabolism and body weight control, SCD1 has emerged recently as a potential new target for the treatment of various diseases. Sterculic acid (SA) is a cyclopropene fatty acid with numerous biological activities, generally attributed to its Stearoyl-CoA desaturase (SCD) inhibitory properties. Additional effects exerted by SA, independently of SCD inhibition, may be mediating anti-inflammatory and protective roles in retinal diseases such as age-related macular degeneration (AMD), but the mechanisms involved are poorly understood. In order to provide insights into those mechanisms, genome-wide transcriptomic analyses were carried out in mRPE cells exposed to SA for 24 h. Integrative functional enrichment analysis of genome-wide expression data provided biological insight about the protective mechanisms induced by SA. On the one hand, pivotal genes related to fatty acid biosynthesis, steroid biosynthesis, cell death, actin-cytoskeleton reorganization and extracellular matrix-receptor interaction were significantly downregulated by exposition to SA. On the other hand, genes related to fatty acid degradation and beta-oxidation were significantly upregulated. In conclusion, SA administration to RPE cells regulates crucial pathways related to cell proliferation, inflammation and cell death that may be of interest for the treatment of ocular diseases.

Sterculic Acid: The Mechanisms of Action beyond Stearoyl-CoA Desaturase Inhibition and Therapeutic Opportunities in Human Diseases

In many tissues, stearoyl-CoA desaturase 1 (SCD1) catalyzes the biosynthesis of monounsaturated fatty acids (MUFAS), (i.e., palmitoleate and oleate) from their saturated fatty acid (SFA) precursors (i.e., palmitate and stearate), influencing cellular membrane physiology and signaling, leading to broad effects on human physiology. In addition to its predominant role in lipid metabolism and body weight control, SCD1 has emerged recently as a potential new target for the treatment for various diseases, such as nonalcoholic steatohepatitis, Alzheimer’s disease, cancer, and skin disorders. Sterculic acid (SA) is a cyclopropene fatty acid originally found in the seeds of the plant Sterculia foetida with numerous biological activities. On the one hand, its ability to inhibit stearoyl-CoA desaturase (SCD) allows its use as a coadjuvant of several pathologies where this enzyme has been associated. On the other hand, additional effects independently of its SCD inhibitory properties, involve anti-inflammatory and protective roles in retinal diseases such as age-related macular degeneration (AMD). This review aims to summarize the mechanisms by which SA exerts its actions and to highlight the emerging areas where this natural compound may be of help for the development of new therapies for human diseases.

Impact of Blood or Erythrocyte Membrane Fatty Acids for Disease Risk Prediction: Focusing on Cardiovascular Disease and Chronic Kidney Disease

Fatty acids (FAs) are essential nutrients and main constituents of cell membranes that are involved in the signaling pathway and associated with health conditions. We investigated if blood or erythrocyte membrane FAs can predict the risk of cardiovascular disease (CVD), chronic kidney disease (CKD), and related complications. Omega-3 (n-3) FAs are important predictors for metabolic syndrome, diabetes, CVD, and CKD risks, and the n-3 index is also a good biomarker for sudden cardiac death in coronary artery disease. Linoleic acid, which is one of the major n-6 FAs reflecting recent dietary FA intake, may predict CVD risk and mortality in the general population and patients with CKD. Monounsaturated FAs (MUFAs) are also related to diabetes or diabetic nephropathy. Oleic acid, a major MUFA, is an emerging marker that is related to acute coronary syndrome, low glomerular filtration rate, and vascular calcification in patients with CKD, and can be modified by n-3 FA supplementation. Saturated FAs, trans-FAs, and FA desaturation/elongation are associated with CVD risk; however, few studies have been conducted on patients with CKD. In summary, blood or erythrocyte membrane FA measurements are important for CVD and CKD risk prediction and management. Further studies are needed to elucidate the FAs for their risk predictions.

Protein engineering: Regulatory perspectives of stearoyl CoA desaturase

Stearoyl Co A desaturase (SCD) is a rate-limiting lipogenic enzyme that plays an integral role in catalyzing the synthesis of monounsaturated fatty acids, chiefly oleate and palmitoleate. Both contribute a major part of the biological membrane. Numerous SCD isoforms exist in mouse and humans, i.e., SCD-1 to SCD-4 and SCD-1 and SCD-5, respectively. From the biological viewpoint, hyperexpression of SCD1 cause many metabolic disorders including obesity, insulin resistance, hypertension, and hypertriglyceridemia, etc. Herein, an effort has been made to highlight the value of protein engineering in controlling the SCD-1 expression with the involvement of different inhibitors as therapeutic agents. The first part of the review describes Stearoyl CoA desaturase index and different SCD isoforms. Various regulatory aspects of SCD are reviewed in four subsections, i.e., (1) hormonal regulation, (2) regulation by dietary carbohydrates, (3) regulation by green tea, and (4) regulation via polyunsaturated fatty acids (PUFAs). Moreover, the regulation of Stearoyl CoA desaturase expression in the metabolism of fats and carbohydrates is discussed. The third part mainly focuses on natural and synthetic inhibitors. Towards the end, information is also given on potential future considerations of SCD-1 inhibitors as metabolic syndrome therapeutics, yet additional work is required.

Effects of heat stress and insulin sensitizers on pig adipose tissue

Heat stress (HS) negatively impacts several swine production variables, including carcass fat quality and quantity. Pigs reared in HS have more adipose tissue than energetically predicted, explainable, in part, by HS-induced hyperinsulinemia. Study objectives were to evaluate insulin's role in altering fat characteristics during HS via feeding insulin-sensitizing compounds. Forty crossbred barrows (113 ± 9 kg BW) were randomly assigned to one of five environment by diet treatments: 1) thermoneutral (TN) fed ad libitum (TNAL), 2) TN and pair-fed (TNPF), 3) HS fed ad libitum (HSAL), 4) HS fed ad libitum with sterculic oil (SO) supplementation (HSSO; 13 g/d), and 5) HS fed ad libitum with dietary chromium (Cr) supplementation (HSCr; 0.5 mg/d; Kemin Industries, Des Moines, IA). The study consisted of three experimental periods (P). During P0 (2 d), all pigs were exposed to TN conditions (23 ± 3 °C, 68 ± 10% RH) and fed ad libitum. During P1 (7 d), all pigs received their respective dietary supplements, were maintained in TN conditions, and fed ad libitum. During P2 (21 d), HSAL, HSSO, and HSCr pigs were fed ad libitum and exposed to cyclical HS conditions (28 to 33 °C, 58 ± 10% RH). The TNAL and TNPF pigs remained in TN conditions and were fed ad libitum or pair-fed to their HSAL counterparts. Rectal temperature (TR), respiration rate (RR), and skin temperature (TS) were obtained daily at 0600 and 1800 h. At 1800 h, HS exposed pigs had increased TR, RR, and TS relative to TNAL controls (1.13 °C, 48 bpm, and 3.51 °C, respectively; P < 0.01). During wk 2 and 3 of P2, HSSO pigs had increased 1800 h TR relative to HSAL and HSCr (~0.40 and ~0.42 °C, respectively; P ≤ 0.05). Heat stress decreased ADFI and ADG compared to TNAL pigs (2.24 vs. 3.28 and 0.63 vs. 1.09 kg/d, respectively; P < 0.01) and neither variable was affected by SO or Cr supplementation. Heat stress increased or tended to increase moisture content of abdominal (7.7 vs. 5.9%; P = 0.07) and inner s.c. (11.4 vs. 9.8%; P < 0.05) adipose depots compared to TNAL controls. Interestingly, TNPF pigs also had increased adipose tissue moisture content and this was most pronounced in the outer s.c. depot (15.0 vs. 12.2%; P < 0.01) compared to TNAL pigs. Heat stress had little or no effect on fatty acid composition of abdominal, inner, and outer s.c. adipose tissue depots. In summary, the negative effects of HS on fat quality do not appear to be fatty acid composition related, but may be explained by increased adipose tissue moisture content.

Digital Cushion Fatty Acid Composition and Lipid Metabolism Gene Network Expression in Holstein Dairy Cows Fed a High-Energy Diet

The hoof digital cushion is a complex structure composed of adipose tissue beneath the distal phalanx, i.e. axial, middle and abaxial fat pad. The major role of these fat depots is dampening compression of the corium underneath the cushion. The study aimed to determine expression of target genes and fatty acid profiles in the hoof of non-pregnant dry Holstein cows fed low (CON) or high-energy (OVE) diets. The middle fat pad of the hoof digital cushion was collected soon after slaughter. Despite the lack of effect on expression of the transcription regulators SREBF1 and PPARG, the expression of the lipogenic enzymes ACACA, FASN, SCD, and DGAT2 was upregulated with OVE. Along with the upregulation of G6PD and IDH1, important for NADPH synthesis during lipogenesis, and the basal glucose transporter SLC2A1, these data indicated a pro-lipogenic response in the digital cushion with OVE. The expression of the lipid droplet-associated protein PLIN2 was upregulated while expression of lipolytic enzymes (ATGL, ABDH5, and LIPE) only tended to be upregulated with OVE. Therefore, OVE induced lipogenesis, lipid droplet formation, and lipolysis, albeit to different extents. Although concentration of monounsaturated fatty acids (MUFA) did not differ, among the polyunsaturated fatty acids (PUFA), the concentration of 20:5n3 was lower with OVE. Among the saturated fatty acids, 20:0 concentration was greater with OVE. Although data indicated that the hoof digital cushion metabolic transcriptome is responsive to higher-energy diets, this did not translate into marked differences in the fatty acid composition. The decrease in concentration of PUFA, which could contribute to synthesis of inflammatory molecules, in OVE-fed cows indicated that feeding higher-energy diets might be detrimental for the mediation of inflammation in digital cushion. This effect could be further exacerbated by physiologic and endocrine changes during the peripartal period that favor inflammation.

Serum phospholipid monounsaturated fatty acid composition and Δ-9-desaturase activity are associated with early alteration of fasting glycemic status

Because alterations in blood fatty acid (FA) composition by dietary lipids are associated with insulin resistance and related metabolic disorders, we hypothesized that serum phospholipid FA composition would reflect the early alteration of fasting glycemic status, even in people without metabolic syndrome (MetS). To examine this hypothesis, serum phospholipid FA, desaturase activities, fasting glycemic status, and cardiometabolic parameters were measured in study participants (n = 1022; 30-69 years; male, n = 527; female, n = 495; nondiabetics without disease) who were stratified into normal fasting glucose (NFG) and impaired fasting glucose (IFG) groups. Total monounsaturated FA (MUFA), oleic acid (OA; 18:1n-9), dihomo-γ-linolenic acid (DGLA; 20:3n-6), Δ-9-desaturase activity (D9D; 18:1n-9/18:0), and DGLA/linoleic acid (20:3n-6/18:2n-6) in serum phospholipids were significantly higher in IFG subjects than NFG controls. Study subjects were subdivided into 4 groups, based on fasting glucose levels and MetS status. Palmitoleic acid (16:1n-7) was highest in IFG-MetS and lowest in NFG-non-MetS subjects. Oleic acid and D9D were higher in IFG-MetS than in the other 3 groups. Dihomo-γ-linolenic acid and DGLA/linoleic acid were higher in MetS than in non-MetS, regardless of fasting glucose levels. The high-sensitivity C-reactive proteins (hs-CRPs) and 8-epi-prostaglandin-F2α were higher in IFG than in NFG, regardless of MetS status. Oxidized low-density lipoproteins were higher in IFG-MetS than in the other 3 groups. Total MUFAs, OA, and D9D were positively correlated with homeostasis model assessment of insulin resistance, fasting glucose, triglyceride, hs-CRP, and 8-epi-prostaglandin-F2α. Palmitoleic acid was positively correlated with triglyceride and hs-CRP. Lastly, total MUFA, OA, palmitoleic acid, and D9D were associated with early alteration of fasting glycemic status, therefore suggesting that these may be useful markers for predicting the risk of type 2 diabetes and cardiometabolic diseases.