Development and validation of a reversed-phase HPLC method for the determination of γ-tocotrienol in rat and human plasma

Extraction of Vitamin E Isomers from Palm Oil: Methodology, Characterization, and in Vitro Anti-Tumor Activity

Vitamin E refers to a family of eight tocopherols (T) and tocotrienol (T3) isomers. Due to the unique pharmacological and anticancer activity of the individual isomers, there is a need to extract and separate the individual T3 isomers from T/T3 rich fractions of palm oil. The objective of the present study was to present a detailed protocol for the extraction of gram quantities of vitamin E isomers from a T3 rich fraction (Tocotrol™) that was obtained from palm oil, by column chromatography using a binary hexane:EtOAc (1-12%) phase system. The chemical integrity and identity of the extracted isomers was confirmed by TLC, HPLC, ¹H-NMR, and Raman analysis. To evaluate their anticancer activity, vitamin E isomers were first entrapped into nanoemulsions and then tested against a panel of breast and pancreatic cancer cell lines. Nanoemulsions were prepared by the solvent evaporation technique. They had an average droplet size between 156-200 nm. In confirmation to what has been reported in the literature, γ-T3 and δ-T3 isomers were found to be significantly more active against tumor cells than the α-T and α-T3 isomers. The current study has demonstrated the feasibility of extracting the individual vitamin E isomers at high yields from natural sources while maintaining their chemical integrity and pharmacological activity.

Validation of a HPLC/FLD Method for Quantification of Tocotrienols in Human Plasma

Quantification of tocotrienols in human plasma is critical when the attention towards tocotrienols on its distinctive properties is arising. We aim to develop a simple and practical normal-phase high performance liquid chromatography method to quantify the amount of four tocotrienol homologues in human plasma. Using both the external and internal standards, tocotrienol homologues were quantified via a normal-phase high performance liquid chromatography with fluorescence detector maintained at the excitation wavelength of 295 nm and the emission wavelength of 325 nm. The four tocotrienol homologues were well separated within 30 minutes. A large interindividual variation between subjects was observed as the absorption of tocotrienols is dependent on food matrix and gut lipolysis. The accuracies of lower and upper limit of quantification ranged between 92% and 109% for intraday assays and 90% and 112% for interday assays. This method was successfully applied to quantify the total amount of four tocotrienol homologues in human plasma.

PEGylated γ-tocotrienol isomer of vitamin E: Synthesis, characterization, in vitro cytotoxicity, and oral bioavailability

Vitamin E refers to a family of eight isomers divided into two subgroups, tocopherols and the therapeutically active tocotrienols (T3). The PEGylated α-tocopherol isomer of vitamin E (vitamin E TPGS) has been extensively investigated for its solubilizing capacity as a nonionic surfactant in various drug delivery systems. Limited information, however, is available about the PEG conjugates of the tocotrienol isomers of vitamin E. In this study two PEGylated γ-T3 variants with mPEG molecular weights of 350 (γ-T3PGS 350) and 1000 (γ-T3PGS 1000) were synthesized by a two-step reaction procedure and characterized by (1)H NMR, HPLC, and mass spectroscopy. The physical properties of their self-assemblies in water were characterized by zeta, CMC, and size analysis. Similar physical properties were found between the PEGylated T3 and vitamin E TPGS. PEGylated T3 were also found to retain the in vitro cytotoxic activity of the free T3 against the MCF-7 and the triple-negative MDA-MB-231 breast cancer cells. PEGylated γ-T3 also increased the oral bioavailability of γ-T3 by threefolds when compared to the bioavailability of γ-T3 formulated into a self-emulsified drug delivery system. No significant differences in biological activity were found between the PEG 350 and 100 conjugates. Results from this study suggest that PEGylation of γ-T3 represents a viable platform for the oral and parenteral delivery of γ-T3 for potential use in the prevention of breast cancer.

Gamma-tocotrienol attenuates high-fat diet-induced obesity and insulin resistance by inhibiting adipose inflammation and M1 macrophage recruitment

BACKGROUND AND OBJECTIVE

We have previously demonstrated that gamma tocotrienol (γT3) potently inhibits adipocyte hyperplasia in human adipose-derived stem cells (hASCs). In this study, our objective was to investigate the γT3 effects on early-onset obesity, inflammation and insulin resistance in vivo.

METHODS

Young C57BL/6J mice were fed a high-fat (HF) diet supplemented with 0.05% γT3 for 4 weeks. The concentrations of γT3 in plasma and adipose tissue were measured using high-performance liquid chromatography. Effects of γT3 on body weight gain, adipose volume, plasma levels of fasting glucose, insulin (enzyme-linked immunosorbent assay (ELISA)), proinflammatory cytokines (mouse cytokine array), insulin signaling (western blotting) and gene expression (quantitative real-time PCR, qPCR) in the liver and adipose tissue were examined. Influences of γT3 on [3H]-2-deoxyglucose uptake and lipopolysaccharide (LPS)-mediated NFκB signaling (western blotting) were assessed in hASCs. Effects of γT3 on macrophage M1/M2 activation were investigated using qPCR in mouse bone marrow-derived macrophages.

RESULTS

After a 4-week treatment, γT3 accumulated in adipose tissue and reduced HF diet-induced weight gain in epididymal fat, mesenteric fat and the liver. Compared with HF diet-fed mice, HF+γT3-fed mice were associated with (1) decreased plasma levels of fasting glucose, insulin and proinflammatory cytokines, (2) improved glucose tolerance and (3) enhanced insulin signaling in adipose tissue. There were substantial decreases in macrophage specific markers, and monocyte chemoattractant protein-1, indicating that γT3 reduced the recruitment of adipose tissue macrophages (ATMs). In addition, γT3 treatment in human adipocytes resulted in (1) activation of insulin-stimulated glucose uptake and (2) a significant suppression of MAP kinase and NFκB activation. In parallel, γT3 treatment led to a reduction of LPS-mediated M1 macrophage polarization.

CONCLUSION

Our results demonstrated that γT3 ameliorates HF diet-mediated obesity and insulin resistance by inhibiting systemic and adipose inflammation, as well as ATM recruitment.

Enhanced solubility and oral bioavailability of γ-tocotrienol using a self-emulsifying drug delivery system (SEDDS)

The aim of this study was to evaluate the in vitro and in vivo performance of γ-tocotrienol (γ-T3) incorporated in a self-emulsifying drug delivery system (SEDDS) and to compare its enhanced performance to a commercially available product, namely Tocovid Suprabio™ (hereafter Tocovid), containing tocotrienols. The solubilization of γ-T3 was tested in a dynamic in vitro lipolysis model followed by in vitro cellular uptake study for the lipolysis products. In addition, in vitro uptake studies using Caco2 cells were conducted at different concentrations of γ-T3 prepared as SEDDS, Tocovid, or mixed micelles. γ-T3 incorporated in SEDDS or Tocovid was orally administered to rats at different doses and absolute oral bioavailability from both formulations were determined. The dynamic in vitro lipolysis experiment showed about two fold increase in the solubilization of γ-T3 prepared as SEDDS compared to Tocovid, which correlated with higher cellular uptake in the subsequent uptake studies. In vitro cellular uptake and in vivo oral bioavailability studies have shown a twofold increase in the cellular uptake and oral bioavailability of γ-T3 incorporated in SEDDS compared to Tocovid as a result of improvement in its solubility and passive uptake as confirmed by in vitro studies. In conclusion, incorporation of γ-T3 in SEDDS formulation enhanced γ-T3 solubilization and passive permeability, thus its cellular uptake and oral bioavailability when compared to Tocovid.

Effect of PEG surface conformation on anticancer activity and blood circulation of nanoemulsions loaded with tocotrienol-rich fraction of palm oil

Tocotrienol-rich fraction of palm oil, which contains the isomers of vitamin E, was shown to possess potent anticancer activity against mammary adenocarcinoma cell lines. Its clinical use, however, is limited by poor oral bioavailability and short half-life. Previously, we developed tocotrienol-rich lipid nanoemulsions for intravenous administration. The objective of this study was to investigate the effect of surface grafted polyethylene glycol (PEG) on the properties of the nanoemulsions. PEGylation was achieved by the addition of equimolar PEG groups using poloxamer or 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)2000] (PEG2000-DSPE). The effect of PEG surface topography on the antiproliferative activity of nanoemulsions against mammary adenocarcinoma cells, their susceptibility to protein adsorption, and its effect on blood hemolysis and circulation time was investigated. Nanoemulsions PEGylated with poloxamer or PEG2000-DSPE were stable under physical stress. Poloxamer nanoemulsion, however, displayed higher uptake and potency against MCF-7 tumor cells in 2D and 3D culture and increased hemolytic effect and susceptibility to IgG adsorption, which was reflected in its rapid clearance and short circulation half-life (1.7 h). Conversely, PEGylation with PEG2000-DSPE led to a 7-fold increase in mean residence time (12.3 h) after IV injection in rats. Reduced activity in vitro and improved circulation time suggested strong shielding of plasma proteins from the droplets. Differences between the nanoemulsions were attributed to polymer imbibitions and the differences in PEG conformation and density on the surface of the droplets.

Nonlinear absorption kinetics of self-emulsifying drug delivery systems (SEDDS) containing tocotrienols as lipophilic molecules: in vivo and in vitro studies

Self-emulsifying drug delivery systems (SEDDS) have been broadly used to promote the oral absorption of poorly water-soluble drugs. The purpose of the current study was to evaluate the in vivo oral bioavailability of vitamin E isoforms, δ-tocotrienol (δ-T3) and γ-tocotrienol (γ-T3) administered as SEDDS, as compared to commercially available UNIQUE E® Tocotrienols capsules. Results from studies in rats showed that low dose treatment with δ-T3 (90%) and γ-T3 (10%) formulated SEDDS showed bioavailability of 31.5% and 332%, respectively. However, bioavailability showed a progressive decrease with increased treatment dose that displayed nonlinear absorption kinetics. Additional in vitro studies examining cellular uptake studies in Caco 2 cells revealed that the SEDDS formulation increased passive permeability of δ-T3 and γ-T3 by threefold as compared to the commercial capsule formulation. These studies also showed that free surfactants decreased δ-T3 and γ-T3 absorption. Specifically, combined treatment cremophor EL or labrasol with tocotrienols caused a 60-85% reduction in the cellular uptake of δ-T3 and γ-T3 and these effects appear to result from surfactant-induced inhibition of the δ-T3 and γ-T3 transport protein Niemann-Pick C1-like 1 (NPC1L1). In summary, results showed that SEDDS formulation significantly increases the absorption and bioavailability δ-T3 and γ-T3. However, this effect is self-limiting because treatment with increasing doses of SEDDS appears to be associated with a corresponding increase in free surfactants levels that directly and negatively impact tocotrienol transport protein function and results in nonlinear absorption kinetics and a progressive decrease in δ-T3 and γ-T3 absorption and bioavailability.

Concurrent delivery of tocotrienols and simvastatin by lipid nanoemulsions potentiates their antitumor activity against human mammary adenocarcenoma cells

Tocotrienol rich fraction (TRF) of vitamin E was previously shown to have anticancer activity against murine tumor cells in vitro. TRF was also shown to potentiate the anticancer activity of statins. The objectives of this study were therefore (a) to prepare and characterize stable parenteral lipid nanoemulsions as a novel platform for the concurrent delivery of TRF and simvastatin for subsequent use in combination chemotherapy, and (b) to evaluate the antiproliferative activity of the nanoemulsions against MCF-7 and MDA-MB-231 human mammary tumor cells. Nanoemulsions were prepared by the high-pressure homogenization technique using a viscous 70/30 blend of TRF and medium chain triglycerides as the oil phase in which simvastatin was dissolved at 9%w/w loading. Nanoemulsion droplets were about 200 nm in size and had surface potential of -45 mV. In a dissolution study, approximately 20% of simvastatin was released in sink conditions after 24h. The stability of the nanoemulsions was monitored over 6 months of storage. No oxidation or degradation products were detected and no loss in simvastatin loading was observed during this period. The antiproliferative activity of the nanoemulsions was also retained after storage. The IC50 of the TRF nanoemulsions against MCF-7 and MDA-MB-231 was 14 and 7 μM, respectively, which decreased to 10 μM and 4.8 μM when simvastatin was added to the nanoemulsions. Nanoemulsions prepared with tocopherol had no anticancer activity and were used as negative control. This study demonstrated that parenteral lipid nanoemulsions are viable delivery platform for potential use in cancer chemotherapy.

Comparison of the intestinal absorption and bioavailability of γ-tocotrienol and α-tocopherol: in vitro, in situ and in vivo studies

The aim of this work was to compare the intestinal absorption kinetics and the bioavailability of γ-tocotrienol (γ-T3) and α-tocopherol (α-Tph) administered separately as oil solutions to rats in vivo. Also, to explain the significant difference in the oral bioavailability of the compounds: (1) the release profiles using the dynamic in vitro lipolysis model, (2) the intestinal permeability and (3) carrier-mediated uptake by Niemann-Pick C1-like 1 (NPC1L1) transporter were examined. Absolute bioavailability studies were conducted after oral administration of γ-T3 or α-Tph prepared in corn oil to rats. In situ rat intestinal perfusion with ezetimibe (a NPC1L1 inhibitor) was performed to compare intestinal permeability. The in vitro interaction kinetics with NPC1L1 was examined in NPC1L1 transfected cells. While the in vitro release studies demonstrated a significantly higher release rate of γ-T3 in the aqueous phase, the oral bioavailability of α-Tph (36%) was significantly higher than γ-T3 (9%). Consequent in situ studies revealed significantly higher intestinal permeability for α-Tph compared with γ-T3 in rats. Moreover, the NPC1L1 kinetic studies demonstrated higher Vmax and Km values for α-Tph compared with γ-T3. Collectively, these results indicate that intestinal permeability is the main contributing factor for the higher bioavailability of α-Tph. Also, these results emphasize the potentially important role of intestinal permeability in the bioavailability of γ-T3, suggesting that enhancing its permeability would increase its oral bioavailability.

Development and validation of a sensitive LC/MS/MS method for the determination of γ-tocotrienol in rat plasma: application to pharmacokinetic studies

γ-Tocotrienol has attracted much attention owing to its multiple health benefits. This study developed and validated a simple, specific, sensitive and reliable LC/MS/MS method to analyze γ-tocotrienol in rat plasma. Plasma samples (50 μL) were extracted with internal standard solution (25 ng/mL of itraconazole) in acetonitrile (200 μL) with an average recovery of 44.7% and an average matrix effect of -2.9%. The separation of γ-tocotrienol and internal standard from the plasma components was achieved with a Waters XTerra® MS C(18) column with acetonitrile-water as mobile phase. Analysis was performed under positive ionization electrospray mass spectrometer via the multiple reaction monitoring. The standard curve was linear over a concentration range of 10-1000 ng/mL with correlation coefficient values >0.997. The method was validated with intra- and inter-day accuracy (relative error) ranging from 1.79 to 9.17% and from 2.16 to 9.66%, respectively, and precision (coefficient of variation) ranged from 1.94 to 9.25% and from 2.37 to 10.08%, respectively. Short-term stability, freeze-thaw stability and the processed sample stability tests were performed. This method was further applied to analyze γ-tocotrienol plasma concentrations in rats at various time points after administration of a 2 mg/kg single intravenous dose, and a pharmacokinetic profile was successfully obtained.