Citrus p-Synephrine Improves Energy Homeostasis by Regulating Amino Acid Metabolism in HFD-Induced Mice.

p-Synephrine is a common alkaloid widely distributed in citrus fruits. However, the effects of p-synephrine on the metabolic profiles of individuals with energy abnormalities are still unclear. In the study, we investigated the effect of p-synephrine on energy homeostasis and metabolic profiles using a high fat diet (HFD)-induced mouse model. We found that p-synephrine inhibited the gain in body weight, liver weight and white adipose tissues weight induced by HFD. p-Synephrine supplementation also reduced levels of serum total cholesterol (TC), triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C) but not to a statistically significant degree. Histological analysis showed that HFD induced excessive lipid accumulation and glycogen loss in the liver and adipocyte enlargement in perirenal fat tissue, while p-synephrine supplementation reversed the changes induced by HFD. Moreover, HFD feeding significantly increased mRNA expression levels of tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß) and reduced the mRNA expression level of interleukin-10 (IL-10) compared to the control group, while p-synephrine supplementation significantly reversed these HFD-induced changes. Liver and serum metabolomic analysis showed that p-synephrine supplementation significantly altered small molecule metabolites in liver and serum in HFD mice and that the changes were closely associated with improvement of energy homeostasis. Notably, amino acid metabolism pathways, both in liver and serum samples, were significantly enriched. Our study suggests that p-synephrine improves energy homeostasis probably by regulating amino acid metabolism in HFD mice, which provides a novel insight into the action mechanism of p-synephrine modulating energy homeostasis.

Stachydrine, a Bioactive Equilibrist for Synephrine, Identified from Four Citrus Chinese Herbs.

Four Chinese herbs from the Citrus genus, namely Aurantii Fructus Immaturus (Zhishi), Aurantii Fructus (Zhiqiao), Citri Reticulatae Pericarpium Viride (Qingpi) and Citri Reticulatae Pericarpium (Chenpi), are widely used for treating various cardiovascular and gastrointestinal diseases. Many ingredients have already been identified from these herbs, and their various bioactivities provide some interpretations for the pharmacological functions of these herbs. However, the complex functions of these herbs imply undisclosed cholinergic activity. To discover some ingredients with cholinergic activity and further clarify possible reasons for the complex pharmacological functions presented by these herbs, depending on the extended structure-activity relationships of cholinergic and anti-cholinergic agents, a simple method was established here for quickly discovering possible choline analogs using a specific TLC method, and then stachydrine and choline were first identified from these Citrus herb decoctions based on their NMR and HRMS data. After this, two TLC scanning (TLCS) methods were first established for the quantitative analyses of stachydrine and choline, and the contents of the two ingredients and synephrine in 39 samples were determined using the valid TLCS and HPLC methods, respectively. The results showed that the contents of stachydrine (3.04‱) were 2.4 times greater than those of synephrine (1.25‱) in Zhiqiao and about one-third to two-thirds of those of Zhishi, Qingpi and Chenpi. Simultaneously, the contents of stachydrine, choline and synephrine in these herbs present similar decreasing trends with the delay of harvest time; e.g., those of stachydrine decrease from 5.16‱ (Zhishi) to 3.04‱ (Zhike) and from 1.98‱ (Qingpi) to 1.68‱ (Chenpi). Differently, the contents of synephrine decrease the fastest, while those of stachydrine decrease the slowest. Based on these results, compared with the pharmacological activities and pharmacokinetics reported for stachydrine and synephrine, it is indicated that stachydrine can be considered as a bioactive equilibrist for synephrine, especially in the cardio-cerebrovascular protection from these citrus herbs. Additionally, the results confirmed that stachydrine plays an important role in the pharmacological functions of these citrus herbs, especially in dual-directionally regulating the uterus, and in various beneficial effects on the cardio-cerebrovascular system, kidneys and liver.

The Safety and Efficacy of Citrus aurantium (Bitter Orange) Extracts and p-Synephrine: A Systematic Review and Meta-Analysis.

Synephrine has been used to promote weight loss; however, its safety and efficacy have not been fully established. The goals of our study were to give an overview of the safety and efficacy of p-synephrine, to systematically evaluate its efficacy regarding weight loss and to assess its safety, focusing on its cardiovascular side effects in a meta-analysis. PubMed, the Cochrane Library, Web of Science and Embase were searched for relevant studies. Only placebo-controlled, human clinical trials with synephrine intervention were included in the meta-analysis. The meta-analysis was reported according to the PRISMA guidelines using the PICOS format and taking into account the CONSORT recommendations. Altogether, 18 articles were included in the meta-analysis. Both systolic and diastolic blood pressure (DBP) increased significantly after prolonged use (6.37 mmHg, 95% CI: 1.02-11.72, p = 0.02 and 4.33 mmHg, 95% CI: 0.48-8.18, p = 0.03, respectively). The weight loss in the synephrine group was non-significant after prolonged treatment, and it did not influence body composition parameters. Based on the analyzed clinical studies, synephrine tends to raise blood pressure and heart rate, and there is no evidence that synephrine can facilitate weight loss. Further studies are needed to confirm evidence of its safety and efficacy.

Effect of p-Synephrine on Fat Oxidation Rate during Exercise of Increasing Intensity in Healthy Active Women.

p-Synephrine is the principal alkaloid of bitter orange (Citrus aurantium). Several recent investigations have found that the intake of 2-3 mg/kg of p-synephrine raises fat oxidation rate during exercise of low-to-moderate intensity. However, these investigations have been carried out only with samples of male participants or mixed men/women samples. Therefore, the aim of this investigation was to study the effect of p-synephrine intake on fat oxidation during exercise of increasing intensity in healthy women. Using a double-blind, randomized experiment, 18 healthy recreationally active women performed two identical exercise trials after the ingestion of (a) 3 mg/kg of p-synephrine and (b) 3 mg/kg of a placebo (cellulose). The exercise trials consisted of a ramp test (from 30 to 80% of maximal oxygen uptake; VO2max) on a cycle ergometer while substrate oxidation rates were measured at each workload by indirect calorimetry. In comparison to the placebo, the intake of p-synephrine increased resting tympanic temperature (36.1 ± 0.5 vs. 36.4 ± 0.4 °C p = 0.033, d = 0.87) with no effect on resting heart rate (p = 0.111) and systolic (p = 0.994) and diastolic blood pressure (p = 0.751). During exercise, there was no significant effect of p-synephrine on fat oxidation rate (F = 0.517; p = 0.484), carbohydrate oxidation rate (F = 0.730; p = 0.795), energy expenditure rate (F = 0.480; p = 0.833), heart rate (F = 4.269; p = 0.068) and participant's perceived exertion (F = 0.337; p = 0.580). The maximal rate of fat oxidation with placebo was 0.26 ± 0.10 g/min and it was similar with p-synephrine (0.28 ± 0.08 g/min, p = 0.449, d = 0.21). An acute intake of 3 mg/kg of p-synephrine before exercise did not modify energy expenditure and substrate oxidation during submaximal aerobic exercise in healthy active women. It is likely that the increase in resting tympanic temperature induced by p-synephrine hindered the effect of this substance on fat utilization during exercise in healthy active women.

Combined Anti-Adipogenic Effects of Hispidulin and p-Synephrine on 3T3-L1 Adipocytes.

Hispidulin is abundant in Arrabidaea chica, Crossostephium chinense, and Grindelia argentina, among others. p-Synephrine is the main phytochemical constituent of Citrus aurantium. It has been used in combination with various other phytochemicals to determine synergistic effects in studies involving human participants. However, there have been no reports comparing the anti-adipogenic effects of the combination of hispidulin and p-synephrine. The current study explores the anti-adipogenic effects of hispidulin alone and in combination with p-synephrine in a murine preadipocyte cell line, 3T3-L1. Co-treatment resulted in a greater inhibition of the formation of red-labeled lipid droplets than the hispidulin or p-synephrine-alone treatments. Co-treatment with hispidulin and p-synephrine also significantly inhibited adipogenic marker proteins, including Akt, mitogen-activated protein kinases, peroxisome proliferator-activated receptor gamma, CCAAT/enhancer-binding protein alpha, glucocorticoid receptor, and CCAAT/enhancer-binding protein ß. Although further studies are required to assess the effects of each drug on pharmacokinetic parameters, a combination treatment with hispidulin and p-synephrine may be a potential alternative strategy for developing novel anti-obesity drugs.

Synephrine and caffeine combination promotes cytotoxicity, DNA damage and transcriptional modulation of apoptosis-related genes in human HepG2 cells.

The abusive consumption of thermogenic supplements occurs worldwide and deserves special attention due to their use to stimulate weight loss and prevent obesity. Thermogenic formulations usually contain Synephrine (SN) and Caffeine (CAF), stimulating compounds extracted from natural sources, but no genetic toxicology studies have predicted this hazardous combination potential. This study examined the toxicogenomic responses induced by SN and CAF, either alone or in combination, in the human hepatic cell line HepG2 in vitro. SN (0.03-30 µM) and CAF (0.6-600 µM) alone did neither decrease cell viability nor induce DNA damage, as assessed using the MTT and comet assays, respectively. SN (3 µM) and CAF (30-600 µM) were combined at concentrations similar to those found in commercial dietary supplements. SN/CAF at 3:90 and 3:600 µM ratios significantly decreased cell viability and increased DNA damage levels in HepG2 cells. CAF (600 µM) and the SN/CAF association at 3:60, 3:90, and 3:600 µM ratios promoted cell death by apoptosis, as demonstrated by flow cytometry. Similar results were observed in gene expression (RT-qPCR): SN/CAF up-regulated the expression of apoptosis- (BCL-2 and CASP9) and DNA repair-related (XPC) genes. SN/CAF at 3:90 µM also downregulated the expression of cell cycle control (CDKN1A) genes. In conclusion, the SN/CAF combination reduces cell viability by inducing apoptosis, damages DNA, and modulates the transcriptional expression of apoptosis-, cell cycle-, and DNA repair-related genes in human hepatic (HepG2) cells in vitro. These effects can be worrisome to consumers of thermogenic supplements.

Renal artery responses to trace amines: Multiple and differential mechanisms of action.

PURPOSE: The rise in consumption of dietary supplements containing the trace amines p-tyramine, p-synephrine and p-octopamine has been associated with cardiovascular side effects. Since renal blood flow plays an important role in blood pressure regulation, this study investigated the mechanisms of action of these trace amines on isolated porcine renal arteries. MAIN METHODS: Contractile responses to amines were investigated in noradrenaline-depleted rings of porcine main renal arteries in the absence and presence of the α1-adrenoceptor antagonist, prazosin (1 µM), ß-adrenoceptor antagonist, propranolol (1 µM), or the trace amine-associated receptor (TAAR-1) antagonist, EPPTB (RO-5212773; 100 nM or 100 µM). KEY FINDINGS: All three amines induced constrictor responses of similar magnitude and potency. However, their mechanisms of action on the renal artery appeared to differ. Depleting endogenous noradrenaline stores significantly reduced maximum responses to tyramine and synephrine, but less for octopamine. When direct responses were examined after depleting tissues of noradrenaline, responses to synephrine and octopamine, but not tyramine, were reduced in the presence of prazosin(1 µM) and potentiated in the presence of propranolol (1 µM) or L-NNA (100 µM). Generally, vasoconstrictor responses remaining after noradrenaline-depletion and α-adrenoceptor blockade were not affected by the TAAR-1 antagonist EPPTB (0.1-100 µM), although responses to low concentration of synephrine and octopamine were enhanced by this antagonist. SIGNIFICANCE: Tyramine appears to mediate constriction of the renal artery mainly via an indirect sympathomimetic mechanism, whereas synephrine and octopamine exert additional direct effects on α1-adrenoceptors and possibly contractile TAAR (not TAAR-1). The two amines also activate simultaneous inhibitory responses via ß-adrenoceptors, TAAR-1 and nitric oxide release.

Deciphering the synergistic network regulation of active components from SiNiSan against irritable bowel syndrome via a comprehensive strategy: Combined effects of synephrine, paeoniflorin and naringin.

BACKGROUND: SiNiSan (SNS) is an ancient Chinese herbal prescription, and the current clinical treatment of irritable bowel syndrome (IBS) is effective. In the previous study of the research team, the multi-functional co-synergism of SNS against IBS was presented. Some potential drug targets and candidate ligands were predicted. PURPOSE: This study attempts to explore the crucial ingredient combinations from SNS formula and reveal their synergistic mechanism for IBS therapy. MATERIALS AND METHODS: In present study, a comprehensive strategy was performed to reveal IBS related pathways and biological modules, and explore synergistic effects of the ingredients, including ADME (absorption, distribution, metabolism, excretion) screening, Text mining, Venn analysis, Gene ontology (GO) analysis, Pathway cluster analysis, Molecular docking, Network construction and Experimental verification in visceral hypersensitivity (VHS) rats. RESULTS: Three compressed IBS signal pathways were derived from ClueGO KEGG analysis of 63 IBS genes, including Neuroactive ligand-receptor interaction, Inflammatory mediator regulation of TRP (transient receptor potential) channels and Serotonergic synapse. A multi-module network, composed of four IBS therapeutic modules (psychological, inflammation, neuroendocrine and cross-talk modules), was revealed by Target-Pathway network. Nine kernel targets were considered closely associated with the IBS pathways, including ADRA2A, HTR2A, F2RL1, F2RL3, TRPV1, PKC, PKA, IL-1Β and NGF. In silico analysis revealed that three crucial ingredients (synephrine, paeoniflorin and naringin) were assumed to coordinate the network of those IBS therapeutic modules by acting on these kernel targets in the important pathways. In vivo experimental results showed that the crucial ingredient combinations synergistically affected the expressions of the kernel biological molecules, and improved the minimum capacity threshold of AWR in VHS rats. CONCLUSION: The study proposes the important IBS associated pathways and the network regulation mechanisms of the crucial ingredients. It reveals the multi-target synergistic effect of the crucial ingredient combinations for the novel therapy on IBS.

Effects of p-Synephrine during Exercise: A Brief Narrative Review.

The p-synephrine is the principal phytochemical found in bitter orange (Citrus aurantium). This substance is widely included in dietary supplements for weight loss/body fat reduction due to its potential benefits of increasing fat oxidation. For years, p-synephrine-containing dietary supplements have been marketed without proper knowledge of their true effectiveness to enhance fat utilization, especially when combined with exercise. However, the effects of p-synephrine on fat oxidation during exercise have been investigated in the last few years. The aim of the current discussion is to summarize the evidence on the effects of p-synephrine intake on fat oxidation and performance during exercise. Previous investigations have demonstrated that the acute intake of p-synephrine does not modify running sprint performance, jumping capacity, or aerobic capacity. However, the acute intake of p-synephrine, in a dose of 2-3 mg/kg of body mass, has been effective to enhance the rate of fat oxidation during incremental and continuous exercise. This effect has been observed in a range of exercise workloads between 30% and 80% of peak oxygen uptake (VO2peak). The p-synephrine has the ability to increase the maximal rate of fat oxidation during exercise of increasing intensity without affecting the workload at which maximal fat oxidation is obtained (Fatmax). The effect of p-synephrine on fat oxidation is normally accompanied by a concomitant reduction of carbohydrate utilization during exercise, without modifying the energy expended during exercise. The shifting in substrate oxidation is obtained without any effect on heart rate during exercise and the prevalence of adverse effects is negligible. Thus, the acute use of p-synephrine, or p-synephrine-containing products, might offer some benefits for those individuals seeking higher fat utilization during exercise at low to moderate intensities. However, more research is still necessary to determine if the effect of p-synephrine on fat oxidation during exercise is maintained with chronic ingestion, in order to ascertain the utility of this substance in conjunction with exercise programs to produce an effective body fat/weight loss reduction.

p-Synephrine, ephedrine, p-octopamine and m-synephrine: Comparative mechanistic, physiological and pharmacological properties.

Confusion and misunderstanding exist regarding the lack of cardiovascular and other adverse health effects of p-synephrine and p-octopamine relative to ephedrine and m-synephrine (phenylephrine) which are known for their effects on the cardiovascular system. These four molecules have some structural similarities. However, the structural and stereochemical differences of p-synephrine and p-octopamine as related to ephedrine and m-synephrine result in markedly different adrenergic receptor binding characteristics as well as other mechanistic differences which are reviewed. p-Synephrine and p-octopamine exhibit little binding to α-1, α-2, ß-1 and ß-2 adrenergic receptors, nor are they known to exhibit indirect actions leading to an increase in available levels of endogenous norepinephrine and epinephrine at commonly used doses. The relative absence of these mechanistic actions provides an explanation for their lack of production of cardiovascular effects at commonly used oral doses as compared to ephedrine and m-synephrine. As a consequence, the effects of ephedrine and m-synephrine cannot be directly extrapolated to p-synephrine and p-octopamine which exhibit significantly different pharmacokinetic, and physiological/pharmacological properties. These conclusions are supported by human, animal and in vitro studies that are discussed.

Acute p-synephrine ingestion increases whole-body fat oxidation during 1-h of cycling at Fatmax.

PURPOSE: p-Synephrine, the principal alkaloid of bitter orange (Citrus aurantium), is widely used in dietary supplements for weight loss due to its purported effect of increasing fat oxidation. However, there is a paucity of scientific information about its effectiveness in enhancing fat oxidation during exercise. The aim of this investigation was to determine the effect of an acute dose of p-synephrine on substrate oxidation during prolonged and constant intensity exercise. METHODS: In a double-blind and randomized experiment, 14 healthy subjects performed two acute experimental trials after ingesting either p-synephrine (3 mg kg-1) or a placebo (cellulose). Energy expenditure and fat oxidation rates were continuously measured by indirect calorimetry during 1 h of continuous cycling at Fatmax, the intensity that induces maximal fat oxidation rate. RESULTS: In comparison to the placebo, energy expenditure during 1 h of cycling remained unchanged with p-synephrine (698 ± 129 vs. 686 ± 123 kcal, P = 0.08). However, p-synephrine increased whole-body fat oxidation (33.6 ± 10.4 vs. 37.3 ± 9.8 g, P < 0.01) while also reducing carbohydrate oxidation (99.5 ± 30.4 vs. 85.0 ± 28.4 g, P < 0.01). However, the magnitude of the shift on substrate oxidation induced by p-synephrine was small. CONCLUSION: Acute ingestion of p-synephrine augments fat oxidation during prolonged and constant-intensity exercise.

p-Synephrine exhibits anti-adipogenic activity by activating the Akt/GSK3ß signaling pathway in 3T3-L1 adipocytes.

This work aimed to investigate the effects of p-synephrine on the differentiation of adipocyte and explore the underlying mechanism. We found that p-synephrine suppressed the 3T3-L1 cell adipogenesis by reducing the expression level of CCAAT/enhancer-binding protein α (C/EBPα) and peroxisome proliferator-activated receptor γ (PPARγ), which subsequently led to a reduction in the fatty acid-binding protein 4 (aP2) expression. p-Synephrine treatment markedly activated the protein kinase B (PKB/Akt) pathway and sequentially inhibited glycogen synthase kinase 3ß (GSK3ß) activity. Inhibition of GSK3ß activity by LiCl was found to partially ameliorate the above-mentioned effects. All these data suggested that p-synephrine exhibited the anti-adipogenic effects via the regulation of Akt signaling pathway and the suppression of adipogenesis-related proteins. PRACTICAL APPLICATIONS: Citrus aurantium often uses as herbal or dietary supplement in various countries around the world, including in Seville, Spain and South Africa. In traditional Chinese herbs, it is referred to as "Fructus aurantii immaturus," "Zhi shi," or "Zhi ke," and has been used for hundreds of years for various digestive problems. Its primary protoalkaloid, p-synephrine, exhibited lipolytic effects and energy expenditure, which has rapidly replaced ephedrine as an "ephedra-free" alternative dietary supplement. The current study firstly demonstrated the anti-adipogenic effects of p-synephrine in 3T3-L1 preadipocytes, which was due to the regulation of Akt signaling pathway and the subsequent suppression of adipogenesis-related proteins. The present study may offer invaluable opinions into the mechanisms of body weight/fat-losing activities of p-synephrine in theory, and scientific experimental evidence on dietary supplement in practice. p-Synephrine could be utilized for the preventive and therapeutic uses against metabolic syndrome.

Differential mechanisms of action of the trace amines octopamine, synephrine and tyramine on the porcine coronary and mesenteric artery.

Trace amines such as p-tyramine, p-octopamine and p-synephrine are found in low concentrations in animals and plants. Consumption of pre-workout supplements containing these plant-derived amines has been associated with cardiovascular side effects. The aim of this study was to determine the mechanisms of action of these trace amines on porcine isolated coronary and mesenteric arteries. Noradrenaline caused contraction of mesenteric arteries and relaxation of coronary arteries. In both tissues, all three trace amines induced contractions with similar potencies and responses were unaffected by the ß-adrenoceptor antagonist propranolol (1 µM), the nitric oxide synthase inhibitor L-NNA (100 µM), or the TAAR-1 antagonist, EPPTB (100 nM). However, the contractile responses of mesenteric arteries, but not coronary arteries, were significantly reduced by depletion of endogenous noradrenaline. Mesenteric responses to all three amines were abolished in the presence of prazosin (1 µM) whereas residual contractile responses remained in the coronary artery which were inhibited by a high concentration (100 µM) of EPPTB. The results suggest complex responses of the coronary artery to the trace amines, with activity at α1-adrenoceptors and potentially TAARs other than TAAR-1. In contrast the actions of the amines on the mesenteric artery appeared to involve indirect sympathomimetic actions and direct actions on α1-adrenoceptors.

Co-Existence of Hypertensive and Anti-Hypertensive Constituents, Synephrine, and Nobiletin in Citrus unshiu Peel.

A single herb can contain multiple constituents with diverse bioactivities. We found that the extract of Citrus unshiu peel (CUP), induced abnormal vasoconstriction responses on the freshly isolated rat aortic rings in vitro. CUP stimulated the vasoconstriction alone, and it suppressed the phenylephrine-stimulated vasoconstriction. We studied the reasons behind this abnormal vasoconstriction pattern. Major constituents of CUP were determined and evaluated for their vaso-activities. Notably, synephrine, a contractile agonist, and nobiletin, newly identified to have anti-contractile activity co-existed in CUP. Synephrine and nobiletin competitively blocked or activated the same contractile targets resulting in contradicting and abnormal vasoconstriction responses. Accordingly, the vasoconstriction pattern varies significantly depending on the relative contents of synephrine and nobiletin in CUP. Interestingly, this response pattern could be observed with another plant extract, Acorus gramineus Sol. Collectively, we demonstrated that active ingredients with contradicting bioactivities could co-exist in a single plant extract, interact and produce abnormal response patterns in bioassay, which would give an important insight into the interpretation of unusual activity patterns induced by plant extracts.

Study to Probe Subsistence of Host-Guest Inclusion Complexes of α and ß-Cyclodextrins with Biologically Potent Drugs for Safety Regulatory Dischargement.

Host-guest interaction of two significant drugs, phenylephrine hydrochloride and synephrine with α and ß-cyclodextrins were studied systematically. Initially two simple but reliable physicochemical techniques namely conductance and surface tension were employed to find out saturation concentration for the inclusion and its stoichiometry. The obtained 1:1 stoichiometry was further confirmed by two spectrometric methods, UV-Vis study and spectrofluorimetry. Significant shifts in IR stretching frequency also support the inclusion process. Relative stabilities of the inclusion complexes were established by the association constants obtained from UV-Vis spectroscopic measurements, program based mathematical calculation of conductivity data. Calculations of the thermodynamic parameters dictates thermodynamic feasibility of the inclusion process. Spectrofluorometric measurement scaffolds the UV-Vis spectroscopic measurement validating stability of the ICs once again. Mass spectroscopic measurement gives the molecular ion peaks corresponding to the inclusion complex of 1:1 molar ratio of host and guest molecules. The mechanism of inclusion was drawn by 1H-NMR and 2D ROESY spectroscopic analysis. Surface texture of the inclusion complexes was studied by SEM. Finally, the cytotoxic activities of the inclusion complexes were analyzed and found, Cell viability also balances for non-toxic behavior of the ICs. Moreover, all the studies reveal the formation of inclusion complexes of two ephedra free, alternatively emerging drugs (after their banned product having ephedra) SNP, PEH with α and ß-CD which enriches the drug delivery system with their regulatory release without any chemical modification.

Induction of beige adipocytes by naturally occurring ß3-adrenoceptor agonist p-synephrine.

The prevalence of obesity and its associated diseases is increasing worldwide, and the therapeutic potential of increasing energy expenditure through differentiation or activation of beige adipocytes has attracted much interest. Therefore, we explored naturally occurring compounds that induce beige adipocytes by screening for activity to induce mRNA expression of uncoupling protein 1 (UCP1) in stromal vascular fraction (SVF) cells cultured in beige adipocyte differentiation medium. Through screening, p-synephrine, a compound isolated from Citrus unshiu Marcov., was found to be an active compound that increased UCP1 mRNA expression in a dose-dependent manner from a concentration of 3.12 µM, which induced morphological changes specific for beige adipocytes. Similar effects were also observed in SVF cells prepared from db/db obese mice. While investigating the underlying mechanism of p-synephrine-induced beige adipocyte differentiation, we found that the effects of p-synephrine were abolished by the ß3-adrenoceptor antagonist SR58894. Intriguingly, p-synephrine increased UCP1 mRNA levels in SVF cells cultured in beige adipocyte differentiation medium lacking insulin to an extent different from those by the ß-agonist isoprenaline. Furthermore, phosphatidylinositol 3-kinase inhibitor LY294002 decreased isoprenaline-induced UCP1 mRNA levels in the early phase of beige adipocyte differentiation and p-synephrine-induced UCP1 mRNA levels in fully differentiated beige adipocytes. Thus, p-synephrine appears to elicit signals via ß3-adrenoceptor combined with some part of the insulin signaling pathway, finally resulting in efficient stimulation of beige adipocyte differentiation with the support of certain beige adipocyte differentiation-inducing factors. The present results suggest the potential of p-synephrine for prophylaxis and treatment of obesity and its associated diseases.

An Overview on Citrus aurantium L.: Its Functions as Food Ingredient and Therapeutic Agent.

Citrus aurantium L. (Rutaceae), commonly known as bitter orange, possesses multiple therapeutic potentials. These biological credentials include anticancer, antianxiety, antiobesity, antibacterial, antioxidant, pesticidal, and antidiabetic activities. The essential oil of C. aurantium was reported to display marked pharmacological effects and great variation in chemical composition depending on growing locations but mostly contained limonene, linalool, and ß-myrcene. Phytochemically, C. aurantium is rich in p-synephrine, an alkaloid, and many health-giving secondary metabolites such as flavonoids. Animal studies have demonstrated a low affinity of p-synephrine for adrenergic receptors and an even lower affinity in human models. The present review focuses on the different biological activities of the C. aurantium in animal and human models in the form of extract and its pure secondary metabolites. Finally, it is concluded that both the extract and isolated compounds have no unwanted effects in human at therapeutic doses and, therefore, can confidently be used in various dietary formulations.

Effects of p-Synephrine and Caffeine Ingestion on Substrate Oxidation during Exercise.

PURPOSE: Caffeine and p-synephrine are substances usually included in commercially available products for weight loss because of their purported thermogenic effects. However, scientific information is lacking about the effects of combining these substances on substrate oxidation during exercise. The purpose of this investigation was to determine the isolated and combined effects of p-synephrine and caffeine on fat oxidation rate during exercise. METHODS: In a double-blind randomized experiment, 13 healthy subjects participated in four experimental trials after the ingestion of a capsule containing a placebo, 3 mg·kg of caffeine, 3 mg·kg of p-synephrine, or the combination of these doses of caffeine and p-synephrine. Energy expenditure and substrate oxidation rates were measured by indirect calorimetry during a cycle ergometer ramp test from 30% to 90% of V˙O2max. RESULTS: In comparison with the placebo, the ingestion of caffeine, p-synephrine, or p-synephrine + caffeine did not alter total energy expenditure or heart rate during the whole exercise test. However, the ingestion of caffeine (0.44 ± 0.15 g·min, P = 0.03), p-synephrine (0.43 ± 0.19 g·min, P < 0.01), and p-synephrine + caffeine (0.45 ± 0.15 g·min, P = 0.02) increased the maximal rate of fat oxidation during exercise when compared with the placebo (0.30 ± 0.12 g·min). The exercise intensity that elicited maximal fat oxidation was similar in all trials (~46.2% ± 10.2% of V˙O2max). CONCLUSION: Caffeine, p-synephrine, and p-synephrine + caffeine increased the maximal rate of fat oxidation during exercise compared with a placebo, without modifying energy expenditure or heart rate. However, the coingestion of p-synephrine and caffeine did not present an additive effect to further increase fat oxidation during exercise.

Acute hematological and mood perception effects of bitter orange extract (p-synephrine) consumed alone and in combination with caffeine: A placebo-controlled, double-blind study.

The purpose of this study was to examine acute hematological and mood perception responses to supplementation with p-synephrine alone and in combination with caffeine during quiet sitting. Sixteen subjects visited the laboratory on 6 occasions and were given (in randomized double-blind manner) 103-mg p-synephrine (S), 233-mg caffeine + 104-mg p-synephrine, 240-mg caffeine, 337-mg caffeine + 46-mg p-synephrine, 325-mg caffeine, or a placebo (PL). The subjects sat quietly for 3 hr while completing mood state questionnaires every 30 min. Venous blood samples were collected at baseline (pre) and 3 hr (post) to determine immune, lipid, and chemistry panels. Compared with PL, no significant supplement differences were observed during the S trial with the exception of differential time effects seen in hematocrit (decrease in PL, no change in S), triglycerides and very low-density lipoproteins (no changes in PL, significant decreases in S), and iron (no change in PL, significant elevation in S). Supplements containing caffeine showed increased feelings of attention, excitement, energy, and vigor. These data indicate that consumption of 103-mg p-synephrine does not negatively impact acute blood parameters, does not augment the effects of caffeine, or produce stimulant-like perceptual mood effects.

Actions of p-synephrine on hepatic enzyme activities linked to carbohydrate metabolism and ATP levels in vivo and in the perfused rat liver.

p-Synephrine is one of the main active components of the fruit of Citrus aurantium (bitter orange). Extracts of the bitter orange and other preparations containing p-synephrine have been used worldwide to promote weight loss and for sports performance. The purpose of the study was to measure the action of p-synephrine on hepatic enzyme activities linked to carbohydrate and energy metabolism and the levels of adenine mononucleotides. Enzymes and adenine mononucleotides were measured in the isolated perfused rat liver and in vivo after oral administration of the drug (50 and 300 mg/kg) by using standard techniques. p-Synephrine increased the activity of glycogen phosphorylase in vivo and in the perfused liver. It decreased, however, the activities of pyruvate kinase and pyruvate dehydrogenase also in vivo and in the perfused liver. p-Synephrine increased the hepatic pools of adenosine diphosphate and adenosine triphosphate. Stimulation of glycogen phosphorylase is consistent with the reported increased glycogenolysis in the perfused liver and increased glycemia in rats. The decrease in the pyruvate dehydrogenase activity indicates that p-synephrine is potentially capable of inhibiting the transformation of carbohydrates into lipids. The capability of increasing the adenosine triphosphate-adenosine diphosphate pool indicates a beneficial effect of p-synephrine on the cellular energetics.