Uptake of intact TPGS (d-alpha-tocopheryl polyethylene glycol 1000 succinate) a water-miscible form of vitamin E by human cells in vitro

Alpha-Tocopherol from people to plants is an essential cog in the metabolic machinery

SIGNIFICANCE

Protection from oxygen, a di-radical, became a necessity with the evolution of photosynthetic organisms about 2.7 billion years. α-Tocopherol plays an essential role in organisms from plants to people. An overview of human conditions that result in severe vitamin E (α-tocopherol) deficiency is provided.

RECENT ADVANCES

α-Tocopherol has a critical role in the oxygen protection system by stopping lipid peroxidation, its induced damage and cellular death by ferroptosis. Recent findings in bacteria and plants support the concept of why lipid peroxidation is so dangerous to life and why the family of tocochromanols are essential for aerobic organisms and for plants.

CRITICAL ISSUES

The hypothesis that prevention of the propagation of lipid peroxidation is the basis for the α-tocopherol requirement in vertebrates is proposed and further that its absence dysregulates energy metabolism, one-carbon metabolism and thiol homeostasis. By recruiting intermediate metabolites from adjacent pathways to sustain effective lipid hydroperoxide elimination, α-tocopherol function is linked not only to NADPH metabolism and its formation through the pentose phosphate pathway via glucose metabolism, but also to sulfur-containing amino acid metabolism, and to one-carbon metabolism.

FUTURE DIRECTIONS

Evidence from humans, animals and plants support the hypothesis but future studies are needed to assess the genetic sensors that detect lipid peroxidation and cause the ensuing metabolic dysregulation.

α-Tocopherol Pharmacokinetics in Adults with Cystic Fibrosis: Benefits of Supplemental Vitamin C Administration

BACKGROUND

Numerous abnormalities in cystic fibrosis (CF) could influence tocopherol absorption, transportation, storage, metabolism and excretion. We hypothesized that the oxidative distress due to inflammation in CF increases vitamin E utilization, which could be positively influenced by supplemental vitamin C administration.

METHODS

Immediately before and after receiving vitamin C (500 mg) twice daily for 3.5 weeks, adult CF patients (n = 6) with moderately advanced respiratory tract (RT) disease consumed a standardized breakfast with 30% fat and a capsule containing 50 mg each hexadeuterium (d₆)-α- and dideuterium (d₂)-γ-tocopheryl acetates. Blood samples were taken frequently up to 72 h; plasma tocopherol pharmacokinetics were determined. During both trials, d₆-α- and d₂-γ-tocopherols were similarly absorbed and reached similar maximal plasma concentrations ~18-20 h. As predicted, during vitamin C supplementation, the rates of plasma d₆-α-tocopherol decline were significantly slower.

CONCLUSIONS

The vitamin C-induced decrease in the plasma disappearance rate of α-tocopherol suggests that vitamin C recycled α-tocopherol, thereby augmenting its concentrations. We conclude that some attention should be paid to plasma ascorbic acid concentrations in CF patients, particularly to those individuals with more advanced RT inflammatory disease and including those with severe exacerbations.

Cyclosporine-loaded micelles for ocular delivery: Investigating the penetration mechanisms

Cyclosporine is an immunomodulatory drug commonly used for the treatment of mild-to-severe dry eye syndrome as well as intermediate and posterior segment diseases as uveitis. The ocular administration is however hampered by its relatively high molecular weight and poor permeability across biological barriers. The aim of this work was to identify a micellar formulation with the ability to solubilize a considerable amount of cyclosporine and promote its transport across ocular barriers. Non-ionic amphiphilic polymers used for micelles preparation were tocopherol polyethylene glycol 1000 succinate (TPGS) and Solutol® HS15. Furthermore, the addition of alpha-linolenic acid was assessed. A second aim was to evaluate micelles fate in the ocular tissues (cornea and sclera) to shed light on penetration mechanisms. This was possible by extracting and quantifying both drug and polymer in the tissues, by studying TPGS hydrolysis in a bio-relevant environment and by following micelles penetration with two-photon microscopy. Furthermore, TPGS role as permeation enhancer on the cornea, with possible irreversible modifications of tissue permeability, was analyzed. Results showed that TPGS micelles (approx. 13 nm in size), loaded with 5 mg/ml of cyclosporine, promoted drug retention in both the cornea and the sclera. Data demonstrated that micelles behavior strictly depends on the tissue: micelles disruption occurs in contact with the cornea, while intact micelles diffuse in the interfibrillar pores of the sclera and form a reservoir that can sustain over time drug delivery to the deeper tissues. Finally, cornea quickly restore the barrier properties after TPGS removal from the tissue, demonstrating its potential good tolerability for ocular application.

Biological fate and interaction with cytochromes P450 of the nanocarrier material, D-α-tocopheryl polyethylene glycol 1000 succinate

d-α-Tocopheryl polyethylene glycol 1000 succinate (TPGS, also known as vitamin E-TPGS) is a biodegradable amphiphilic polymer prepared by esterification of vitamin E with polyethylene glycol (PEG) 1000. It is approved by the US Food and Drug Administration (FDA) and has found wide application in nanocarrier drug delivery systems (NDDS). Fully characterizing the in vivo fate and pharmacokinetic behavior of TPGS is important to promote the further development of TPGS-based NDDS. However, to date, a bioassay for the simultaneous quantitation of TPGS and its metabolite, PEG1000, has not been reported. In the present study, we developed such an innovative bioassay and used it to investigate the pharmacokinetics, tissue distribution and excretion of TPGS and PEG1000 in rat after oral and intravenous dosing. In addition, we evaluated the interaction of TPGS with cytochromes P450 (CYP450s) in human liver microsomes. The results show that TPGS is poorly absorbed after oral administration with very low bioavailability and that, after intravenous administration, TPGS and PEG1000 are mainly distributed to the spleen, liver, lung and kidney before both being slowly eliminated in urine and feces as PEG1000. In vitro studies show the inhibition of human CYP450 enzymes by TPGS is limited to a weak inhibition of CYP3A4. Overall, our results provide a clear picture of the in vivo fate of TPGS which will be useful in evaluating the safety of TPGS-based NDDS in clinical use and in promoting their further development.

Vitamin E: How much is enough, too much and why!

α-Tocopherol (α-T) is a required dietary nutrient for humans and thus is a vitamin. This narrative review focuses on vitamin E structures, functions, biological determinants and its deficiency symptoms in humans. The mechanisms for the preferential α-T tissue enrichment in the human body include the α-T transfer protein (TTPA) and the preferential metabolism of non-α-T forms. Potential new α-T biomarkers, pharmacokinetic data, and whether there are better approaches to evaluate and set the α-T dietary requirement are discussed. Finally, the possible role of α-T supplements in delay of chronic diseases and the evaluation of vitamin E safety are considered.

Absorption, transportation, and distribution of vitamin E homologs

Vitamin E has eight different naturally occurring forms: four tocopherols and four tocotrienols. Because α-tocopherol has three asymmetric carbons, both natural α-tocopherol (RRR-α-tocopherol) and synthetic α-tocopherol (all-rac-α-tocopherol) are utilized in both pharmaceutical products and food additives. Therefore, determining the distribution of vitamin E in the body is very important. With regard to absorption, and transportation of vitamin E, it is suggested that the pathways mediated by three proteins (CD36, SR-BI, and NPC1L1) as well as passive diffusion affect absorption of vitamin E. Vitamin E homologs are mainly transported by very low-density lipoprotein (VLDL) with the α-tocopherol being recognized by the α-tocopherol transfer protein in liver. However, it is also suggested that chylomicrons (CMs) and high-density lipoprotein (HDL) are involved in transportation of vitamin E homologs from the small intestine to each section of peripheral tissue. In particular, it is speculated that vitamin E homologs transportation by CMs and HDL from enterocytes to peripheral tissues such as adipose tissue greatly affects the distribution of vitamin E homologs, excluding α-tocopherol. However, how lipoprotein lipase affects the incorporation of vitamin E homologs containing lipoprotein into peripheral tissues is unclear. Whether there is biodiscrimination when vitamin E homologs are incorporated into peripheral tissues from lipoprotein is an interesting question. It is likely that future research will reveal how individual vitamin E homologs are incorporated into peripheral tissue, especially the brain, adipose tissue, and skin.

Comparison of α-Tocopherol, α-Tocopherol Acetate, and α-Tocopheryl Polyethylene Glycol Succinate 1000 Absorption by Caco-2 TC7 Intestinal Cells

(1) Background: vitamin E is often supplemented in the form of tocopherol acetate, but it has poor bioavailability and can fail to correct blood tocopherol concentrations in some patients with severe cholestasis. In this context, α-tocopheryl polyethylene glycol succinate 1000 (TPGS) has been of value, but very little is known about the mechanisms of its absorption. The aim of our work was to evaluate the mechanisms of absorption/secretion of TPGS compared to tocopherol acetate (TAC) and α-tocopherol by human enterocyte-like Caco-2 TC7 cells. (2) Methods: two weeks post-confluence Caco-2 cells were incubated with tocopherol- or TAC- or TPGS-rich mixed micelles up to 24 h and, following lipid extraction, TAC and tocopherol amounts were measured by high performance liquid chromatography (HPLC) in apical, cellular, and basolateral compartments. (3) Results: at equivalent concentrations of tocopherol in the apical side, the amounts of tocopherol secreted at the basolateral pole of Caco-2 cells are (i) significantly greater when the tocopherol is in the free form in the micelles; (ii) intermediate when it is in the TAC form in the micelles (p < 0.001); and (iii) significantly lower with the TPGS form (p < 0.0001). Interestingly, our results show, for the first time, that Caco-2 cells secrete one or more esterified forms of the vitamin contained in TPGS at the basolateral side.

Iron Transport Tocopheryl Polyethylene Glycol Succinate in Animal Health and Diseases

Gut health is the starting place for maintaining the overall health of an animal. Strategies to maintain gut health are, thus, an important part in achieving the goal of improving animal health. A new strategy to do this involves two molecules: the iron transport protein ovotransferrin (IT) and α-tocopheryl polyethylene glycol succinate (TPGS), which result in the novel formulation of ITPGS. These molecules help reduce gut pathogens, while enhancing the absorption and bioavailability of therapeutic drugs, phytomedicines, and nanomedicines. This, in turn, helps to maintain normal health in animals. Maintaining the gastrointestinal tract (GIT) in its normal condition is key for successful absorption and efficacy of any nutrient. A compromised GIT, due to an imbalance (dysbiosis) in the GIT microbiome, can lead to an impaired GI barrier system with impaired absorption and overall health of the animal. The molecules in ITPGS may address the issue of poor absorption by keeping the GI system healthy by maintaining the normal microbiome and improving the absorption of nutrients through multiple mechanisms involving antioxidative, anti-inflammatory, immunomodulatory, and antimicrobial activities. The ITPGS technology can allow the dose of active pharmaceutical or herbal medicine to be significantly reduced in order to attain equal or better efficacy. With complimentary actions between IT and TPGS, ITPGS presents a novel approach to increase the bioavailability of drugs, phytoconstituents, nutrients, and nanomedicines by enhanced transport to the tissues at the site of action, while reducing gut pathogen load. The ITPGS approach appears to be a novel strategy for maintaining the health of animals by manipulation of microbiota.

Vitamin E d-α-Tocopheryl Polyethylene Glycol Succinate (TPGS) Provokes Cell Death in Human Neuroblastoma SK-N-SH Cells via a Pro-Oxidant Signaling Mechanism

Neuroblastoma (NB) is the most common neoplasm during infancy. Unfortunately, NB is still a lethal cancer. Therefore, innovative curative therapies are immediately required. In this study, we showed the prodeath activity of TPGS in human NB SK-N-SH cancer cells. NB cells were exposed to TPGS (10-80 μM). We report for the first time that TPGS induces cell death by apoptosis in NB cells via a pro-oxidant-mediated signaling pathway. Certainly, H₂O₂ directly oxidizes DJ-1 cysteine¹⁰⁶-thiolate into DJ-1 cysteine¹⁰⁶-sulfonate, indirectly activates the transcription factors NF-kappaB, p53, and c-JUN, induces the upregulation of mitochondria regulator proteins BAX/PUMA, and provokes the loss of mitochondrial membrane potential (ΔΨ_m) and the activation of caspase-3/AIF, leading to nuclear disintegration, demonstrated by cellular and biochemical techniques such as fluorescence microscopy, flow cytometry, and Western blot analysis. Since TPGS is a U.S. Food and Drug Administration (FDA)-approved pharmaceutical excipient, this molecule might be used in clinical trials for NB treatment.

Recent trends on gellan gum blends with natural and synthetic polymers: A review

Gellan gum (GG), a linear negatively charged exopolysaccharide,is biodegradable and non-toxic in nature. It produces hard and translucent gel in the presence of metallic ions which is stable at low pH. However, GG has poor mechanical strength, poor stability in physiological conditions, high gelling temperature and small temperature window.Therefore,it is blended with different polymers such as agar, chitosan, cellulose, sodium alginate, starch, pectin, polyanaline, pullulan, polyvinyl chloride, and xanthan gum. In this article, a comprehensive overview of combination of GG with natural and synthetic polymers/compounds and their applications in biomedical field involving drug delivery system, insulin delivery, wound healing and gene therapy, is presented. It also describes the utilization of GG based materials in food and petroleum industry. All the technical scientific issues have been addressed; highlighting the recent advancement.

Electrospun gelatin nanofibers loaded with vitamins A and E as antibacterial wound dressing materials

Illustration showing the fabrication process and test contents of electrospun gelatin nanofibers loaded with vitamins A and E as wound dressing materials in this paper.

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.

Drug Delivery Innovations for Enhancing the Anticancer Potential of Vitamin E Isoforms and Their Derivatives

Vitamin E isoforms have been extensively studied for their anticancer properties. Novel drug delivery systems (DDS) that include liposomes, nanoparticles, and micelles are actively being developed to improve Vitamin E delivery. Furthermore, several drug delivery systems that incorporate Vitamin E isoforms have been synthesized in order to increase the bioavailability of chemotherapeutic agents or to provide a synergistic effect. D-alpha-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) is a synthetic derivative of natural alpha-tocopherol which is gaining increasing interest in the development of drug delivery systems and has also shown promising anticancer effect as a single agent. This review provides a summary of the properties and anticancer effects of the most potent Vitamin E isoforms and an overview of the various formulations developed to improve their efficacy, with an emphasis on the use of TPGS in drug delivery approaches.

Novel in situ gel systems based on P123/TPGS mixed micelles and gellan gum for ophthalmic delivery of curcumin

Curcumin, a natural polyphenol compound, has been widely reported for diverse pharmacological effects and already been investigated for eye diseases. However, the water-insolubility of curcumin and the inherent penetration barriers in cornea make it difficult for curcumin to enter eye. This work aimed to develop ion-sensitive curcumin-loaded Pluronic P123 (P123)/D-a-tocopheryl polyethylene glycolsuccinate (TPGS) mixed micelle in situ gels (CUR-MM-ISGs) to prolong ocular retention time and improve cornea permeability. Central composite design-response surface methodology was applied for the optimization of curcumin-loaded P123/TPGS mixed micelles (CUR-MMs). Characterization tests showed that CUR-MMs were in spherical shape with small size and low critical micelle concentration. After dispersing the micelles in gellan gum solution (0.2%, w/w) at the ratio of 3:1 and 1:1 (v/v), respectively, CUR-MM-ISGs were formed and presented transparent appearance. Sustained release profile was obtained in vitro for both CUR-MM-ISGs (3:1 or 1:1, v/v). The irritation test proved that CUR-MM-ISGs as ophthalmic formulations were gentle and biocompatible towards ocular tissues. In addition, the ex vivo corneal penetration study indicated that the cumulative drug permeation amount of CUR-MM-ISGs (3:1, v/v) was respectively 1.16-fold and 1.32-fold higher than CUR-MM-ISGs (1:1, v/v) and curcumin solution. It can be concluded from these results that the developed ion-sensitive mixed micelle in situ gel system is a potential ophthalmic delivery carrier for curcumin as a poorly soluble drug.

Mechanisms for the prevention of vitamin E excess

The liver is at the nexus of the regulation of lipoprotein uptake, synthesis, and secretion, and it is the site of xenobiotic detoxification by cytochrome P450 oxidation systems (phase I), conjugation systems (phase II), and transporters (phase III). These two major liver systems control vitamin E status. The mechanisms for the preference for α-tocopherol relative to the eight naturally occurring vitamin E forms largely depend upon the liver and include both a preferential secretion of α-tocopherol from the liver into the plasma for its transport in circulating lipoproteins for subsequent uptake by tissues, as well as the preferential hepatic metabolism of non-α-tocopherol forms. These mechanisms are the focus of this review.

Vitamin E-loaded silk fibroin nanofibrous mats fabricated by green process for skin care application

In the present study, we reported fabrication and skin benefit of a novel vitamin E (VE)-loaded silk fibroin (SF) nanofibrous mats. RRR-α-Tocopherol polyethylene glycol 1000 succinate (VE TPGS), a water-soluble derivative of VE, was incorporated into SF nanofiber successfully by aqua solution electrospinning for the first time. Morphology of the composite nanofibers changed with the different amount of VE TPGS: a ribbon-like shape for lower loading dose of VE TPGS, while a round shape for higher loading dose (more than 4% (wt/wt) based on the weight of SF). After treated with 75% (v/v) ethanol vapor, the composite nanofibrous mats showed an excellent water-resistant ability. In vitro study disclosed a sustained release behavior of VE TPGS disassociated from the nanofibrous mats. The mouse skin fibroblasts (L929 cells) cultured on the VE-loaded SF nanofibrous mats spread and proliferated much better than on cover slips. Moreover, the incorporation of VE TPGS was found strengthening the ability of SF nanofibrous mats on protecting the cells against oxidation stress induced by tert-butyl hydroperoxide. Our data presented impressive skin benefits of this VE-loaded SF nanofibrous mats, suggesting a promising applicative potential of this novel product on personal skin care, tissue regeneration and other related area.

Water-soluble antioxidant derivative poly(triethylene glycol methyl acrylate-co-α-tocopheryl acrylate) as a potential prodrug to enable localized neuroprotection

Implantable microelectrode arrays (MEA) hold enormous hope for individuals with sensory or motor deficits. However, long-term function of MEA remains a critical hurdle. The objective of this study was to synthesize an antioxidant prodrug that can be delivered to the neural tissue around the implant and present a pharmacological depot to combat the injurious oxidative stress around the MEA. In this report, monomers of triethylene glycol methyl acrylate and α-tocopheryl acrylate, a synthetic derivative of the antioxidant α-tocopherol (vitamin E, Ve), were copolymerized to obtain poly(triethylene glycol methyl acrylate-co-α-tocopheryl acrylate) (PVT) with different compositions. In contrast to the poor water solubility of Ve, solubility of the PVT prodrug in water can reach as high as 3.1 mg ml(-1) (equivalent to 500 μM Ve) by tuning the copolymer composition. To demonstrate the applicability of the prodrug for MEA implants, PVT was successfully deposited on silicon substrates with poly(acrylic acid) (PAA) or tannic acid (TA) using the layer-by-layer technique mediated by hydrogen bonding. Ellipsometry and quartz crystal microbalance data showed that the multilayers of PAA/PVT were destructible at physiological pH. In contrast, multilayers of TA/PVT were stable. The PVT prodrug was non-cytotoxic toward A172 human astrocytes. Furthermore, PVT was able to protect astrocytes against oxidative stress exerted by H(2)O(2) in vitro. Using a free radical scavenging assay, the protection mechanism was attributed to the hydrolysis of the labile ester linkage and release of the active Ve.

Enhancement of corneal permeation of riboflavin-5'-phosphate through vitamin E TPGS: a promising approach in corneal trans-epithelial cross linking treatment

Corneal accumulation of riboflavin-5'-phosphate (riboflavin) is an essential step in the so called corneal cross-linking (CXL), an elective therapy for the treatment of progressive keratoconus, corneal ectasia and irregular astigmatism. CXL is usually performed after surgical debridement of corneal epithelium, since it impedes the stromal penetration of riboflavin in a relatively short time. d-Alpha-tocopheryl poly(ethylene glycol) 1000 succinate (VE-TPGS) is an effective permeation enhancer used to increase adsorption of drugs trough different biological barriers. Moreover, belonging to the group of tocopherol pro-drugs, VE-TPGS exerts a protective effect on biological membrane against free-radical damage. The aim of this work is the evaluation of VE-TPGS effects on riboflavin corneal permeability, and the assessment of its protective effect against free-radicals generated during CXL procedures. Different solutions containing riboflavin (0.125% w/w), dextran (20.0% w/w) and increasing concentration of VE-TPGS were tested. Corneal permeation was evaluated in vitro by the use of modified Franz-cell type diffusion cells and freshly excised porcine corneas as barrier. The effect of VE-TPGS on riboflavin corneal penetration was compared with a standard commercial solution of riboflavin in dextran at different times. Accumulation experiments were conducted both on epithelized and non-epithelized corneas. Moreover, epithelized porcine corneas, treated with the tested solutions, were subjected to an in vitro CXL procedure versus non-epithelized corneas, treated with a commercial solution of riboflavin. Differences were measured by means of corneal rigidity using Young's modulus. The photo-protective effect of tested solutions on corneal epithelium was, finally, evaluated. CXL treatment was applied, in vitro, on human explanted corneas and resulting morphology of corneal epithelium was investigated by scanning electron microscopy.

An in vitro study of osteoblast vitality influenced by the vitamins C and E

Vitamin C and vitamin E are known as important cellular antioxidants and are involved in several other non-antioxidant processes. Generally vitamin C and vitamin E are not synthesized by humans and therefore have to be applied by nutrition. The absence or deficiency of the vitamins can lead to several dysfunctions and even diseases (e.g. scurvy). The main interest in this study is that vitamin C and E are known to influence bone formation, e.g. vitamin C plays the key role in the synthesis of collagen, the major component of the extracellular bone matrix.

In the present study we evaluate the effect of ascorbic acid (vitamin C) and α-tocopherol (vitamin E) on the proliferation and differentiation of primary bovine osteoblasts in vitro. Starting from standard growth medium we minimized the foetal calf serum to reduce their stimulatory effect on proliferation.

An improved growth and an increased synthesis of the extracellular matrix proteins collagen type I, osteonectin and osteocalcin was observed while increasing the ascorbic acid concentration up to 200 μg/ml. Furthermore the effects of α-tocopherol on cell growth and cell differentiation were examined, whereby neither improved growth nor increased synthesis of the extracellular matrix proteins collagen type I, osteonectin and osteocalcin were detected.

Further investigations are necessary to target at better supportive effect of vitamins on bone regeneration, and healing.

Development of docetaxel-loaded vitamin E TPGS micelles: formulation optimization, effects on brain cancer cells and biodistribution in rats

Aim: This work aimed to develop docetaxel-loaded D-α-tocopheryl polyethylene glycol 1000 succinate (vitamin E TPGS or TPGS) micelles for brain cancer chemotherapy by taking advantage of polyethylene glycol for its long half-life in circulation and vitamin E for its high cellular uptake. Material & methods: TPGS micelles containing docetaxel or coumarin-6 were prepared by the solvent casting method and the direct dissolution method at high, moderate and low drug-loading levels. Results & discussion: The particle size of the docetaxel-loaded TPGS micelles ranged between 12 and 14 nm. Docetaxel formulated in the TPGS micelles of high, moderate and low drug-loading levels achieved lower IC50 values compared with Taxotere® after 24-h incubation with C6 glioma brain cancer cells. The TPGS has much lower critical micelle concentration than most phospholipids in micellar formulation, which can be an efficient drug carrier across the blood brain–barrier with high drug encapsulation efficiency, cell uptake, cytotoxicity and desired biodistribution of the formulated drug.

Original submitted: 21 March 2011; Revised submitted: 14th June 2011

In vivo evaluation of the biocompatibility of surface modified hemodialysis polysulfone hollow fibers in rat

Polysulfone (Psf) hollow fiber membranes (HFMs) have been widely used in blood purification but their biocompatibility remains a concern. To enhance their biocompatibility, Psf/TPGS (d-α-tocopheryl polyethylene glycol 1000 succinate) composite HFMs and 2-methacryloyloxyethyl phosphorylcholine (MPC) coated Psf HFMs have been prepared. They have been evaluated for in vivo biocompatibility and graft acceptance and compared with sham and commercial membranes by intra-peritoneal implantation in rats at day 7 and 21. Normal body weights, tissue formation and angiogenesis indicate acceptance of implants by the animals. Hematological observations show presence of post-surgical stress which subsides over time. Serum biochemistry results reveal normal organ function and elevated liver ALP levels at day 21. Histological studies exhibit fibroblast recruitment cells, angiogenesis and collagen deposition at the implant surface indicating new tissue formation. Immuno-histochemistry studies show non-activation of MHC molecules signifying biocompatibilty. Additionally, Psf/TPGS exhibit most favorable tissue response as compared with other HFMs making them the material of choice for HFM preparation for hemodialysis applications.

Direct quantification of mono- and di-D-α-tocopherol polyethylene glycol 1000 succinate by high performance liquid chromatography

A simple and direct reversed-phase high performance liquid chromatography (RP-HPLC) method with UV detection was developed and validated for the determination of mono- and di-D-α-tocopherol polyethylene glycol 1000 succinate (TPGS 1000) in TPGS mixture. Before the HPLC analysis, mono- and di-TPGS 1000 were separated by simulated moving bed (SMB) chromatography system and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The mass spectrometric results confirmed that the molar mass distribution of TPGS prepared in our laboratory was very close to that of the product of Eastman Chemical Company with similar n¯ (average polymerization degree), M(n)¯ (number-average molecular weight) and M(w)¯ (weight-average molecular weight). The HPLC analysis was carried out on a C30 analytical column with mobile phases comprised of acetonitrile (A) and isopropanol (B) in gradient conditions. Validation of the analytical method was done on the following parameters: system suitability, linearity, limits of detection and quantification, accuracy and precision, method robustness and solution stability. The linearity of the calibration curves for mono- and di-TPGS 1000 from both sources was found to be good (r(2)>0.9996). The recovery values were from 94.6% to 103.3% for mono-TPGS, and 93.5% to 103.3% for di-TPGS. This method could be successfully used in the direct quantification of mono- and di-TPGS in TPGS 1000 mixture using TPGS standards with similar molecular mass distributions although derived from different sources.

Impact of formulation excipients on human intestinal transit

The accelerating effect of polyethylene glycol 400 on small intestinal transit has been previously reported. The aim of this study was to investigate the influence of other solubility-enhancing excipient, propylene glycol, D-α-tocopheryl-polyethylene glycol-1000 succinate (VitE-TPGS) and Capmul MCM, on human intestinal transit. A 5-g dose of each excipient was administered to seven healthy male subjects. Propylene glycol and VitE-TPGS were administered dissolved in 150 mL water. Capmul MCM was administered in the form of four 000 hard gelatin capsules to mask its taste and then given with 150 mL water. On a separate occasion, 150 mL water was administered as the control. Each formulation was radiolabelled with technetium-99 m to follow its transit using a gamma camera. The mean small intestinal transit times were 234, 207, 241 and 209 min for the control, propylene glycol, VitE-TPGS and Capmul MCM treatments, respectively. Although there were differences in the small intestinal transit times for the excipients investigated compared with the control, none of the results were statistically significant. Unlike polyethylene glycol 400 at the same dose of 5g, the excipients tested (propylene glycol, VitE-TPGS and Capmul MCM) had little or no impact on small intestinal transit.

Polyoxyethylated nonionic surfactants and their applications in topical ocular drug delivery

Topical dosing of ophthalmic drugs to the eye is a widely accepted route of administration because of convenience, ease of use, and non-invasiveness. However, it has been well recognized that topical ocular delivery endures a low bioavailability due to the anatomical and physiological constraints of the eye which limit drug absorption from the pre-corneal surface. Nonionic surfactants as versatile functional agents in topical ocular drug delivery systems are uniquely suited to meet the challenges through their potential ability to increase bioavailability by increasing drug solubility, prolonging pre-corneal retention, and enhancing permeability. This review attempts to place in perspective the importance of polyoxyethylated nonionic surfactants in the design and development of topical ocular drug delivery systems by assessing their compatibility with common ophthalmic inactive ingredients, their impact on product stability, and their roles in facilitating ocular drugs to reach the target sites.

Effect of Tocopheryl Polyethylene Glycol Succinate on the Percutaneous Penetration of Minoxidil from Water/Ethanol/Polyethylene Glycol 400 Solutions

We described to achieve the local retention of minoxidil which has penetrated the skin with minimization of its absorption into the general circulation and elimination of local irritation induced by propylene glycol. The effect of tocopheryl polyethylene glycol succinate (TPGS) on the penetration flux of minoxidil and its retention in the skin from topical minoxidil formulations consisting of water, alcohol, and polyethylene glycol 400 was characterized by an experimental design of ten solvent formulations in this study. Results show that the addition of TPGS was only able to improve the solubility of minoxidil in those solvent systems containing higher proportions of water and PEG 400, and the extent of improvement was also more profound with the addition of TPGS at concentrations higher than 5%. For those solvent systems containing a higher fraction of alcohol, an insignificant change in minoxidil solubility with increasing added amounts of TPGS was noted even with the tendency to decrease the solubility of minoxidil with higher amounts of TPGS. Increasing the amount of TPGS added gradually increased the flux and the corrected flux from solvent formulations with a lower solubility parameter, but decreased those from solvent systems with a higher solubility parameter. With the addition of TPGS, solvent formulation F6 (alcohol:PEG 400 of 50:50) was demonstrated to be the optimal choice by having an improved local effect and a reduced systemic effect compared to the reference of 2% Regaine((R)). Tocopheryl polyethylene glycol succinate (TPGS) was mainly retained locally in the stratum corneum, and the amount was proportional to the increase in the amount of TPGS added to these ten solvent formulations.

Tocopheryl Polyethylene Glycol Succinate as a Safe, Antioxidant Surfactant for Processing Carbon Nanotubes and Fullerenes

This work investigates the physical interactions between carbon nanomaterials and tocopheryl polyethylene glycol succinate (TPGS). TPGS is a synthetic amphiphile that undergoes enzymatic cleavage to deliver the lipophilic antioxidant, alpha-tocopherol (vitamin E) to cell membranes, and is FDA approved as a water-soluble vitamin E nutritional supplement and drug delivery vehicle. Here we show that TPGS 1000 is capable of dispersing multi-wall and single-wall carbon nanotubes in aqueous media, and for multiwall tubes is more effective than the commonly used non-ionic surfactant Triton X-100. TPGS is also capable of solubilizing C(60) in aqueous phases by dissolving fullerene in the core of its spherical micelles. Drying of these solutions leads to fullerene/TPGS phase separation and the self-assembly of highly ordered asymmetric nanoparticles, with fullerene nanocrystals attached to the hydrophobic end of crystalline TPGS nanobrushes. The article discusses surface charge, colloidal stability, and the potential applications of TPGS as a safe surfactant for "green" processing of carbon nanomaterials.

Excipient effects on gastrointestinal transit and drug absorption in beagle dogs

Previous work has shown that polyethylene glycol 400 (PEG 400) has an accelerating effect on gastrointestinal transit and a modulating influence on drug absorption in humans. The aim of this study was to assess the impact of various excipients, PEG 400, propylene glycol, d-alpha-tocopheryl-polyethylene glycol-1000 succinate (TPGS) and Labrasol on gastrointestinal transit and drug absorption in four beagle dogs using scintigraphy. Each dog received, on five separate occasions, water (control) or a dose of excipient equivalent to 1 g PEG 400, 2 g propylene glycol, 1 g TPGS or 2 g Labrasol dissolved in water and administered in the form of two capsules. The model drugs ampicillin (200mg) and antipyrine (100mg) were co-administered in the capsules. The capsule solutions were radiolabelled with technetium-99m to follow their transit using a dual-headed gamma camera, and blood samples were collected to determine drug pharmacokinetics. On a separate occasion, the drugs were dissolved in saline and given intravenously. The capsules rapidly disintegrated in the stomach liberating their liquid contents. The mean small intestinal transit times for the different treatments (control, PEG 400, propylene glycol, TPGS and Labarasol) were 183, 179, 195, 168 and 154 min, respectively. The corresponding mean absolute oral bioavailability figures were 36, 32, 39, 42 and 32% for ampicillin and 76, 74, 85, 73 and 74% for antipyrine, respectively. The transit and bioavailability data for the excipient treatments were not significantly different from the control. In summary, these excipients, at the doses administered, have limited influence on gastrointestinal transit and drug in beagle dogs.

Can changes in hydrophobicity increase the bioavailability of α–tocopherol?

BACKGROUND

Bioavailability of fat-soluble vitamins from conventional oral supplements is insufficient in some conditions in which fat digestion and absorption are chronically impaired (e. g. cystic fibrosis).

AIM OF THE STUDY

We used a water-soluble form of fatsoluble vitamin E (AQUANOVA solubilisate) to create a nutritional supplement (NS) in the form of vitaminized gummi bears (with micellised water-soluble alpha-tocopheryl acetate (100 IU) and 400 mg crystalline vitamin C). We assessed the bioavailability of the NS in comparison to conventional preparations.

METHODS

The trial consisted of three study days (d0: NS sucked; d10: NS swallowed; d20: reference products swallowed). A total of 14 subjects (6 male/8 female), aged 25.3 (22.7-35.3) years, BMI 24.3 (19.0-31.7) kg/m(2) participated in the study. They had blood samples drawn after fasting for >or=12 hours and then 1, 5, 15, 30, 60, 120, 180, 240, 300 and 320 minutes after ingesting the vitamins. HPLC and a colorimetric method were used to determine vitamin E and vitamin C, respectively. Areas under the curve (AUC(0-320min)) and maximum increases in plasma concentrations (Delta concentration) were calculated to assess bioavailability.

RESULTS

The AUCs(0-320min) of alpha-tocopherol from d0 were significantly larger (p = 0.016) when compared to d20. Moreover, the maximum increase in alpha-tocopherol plasma concentrations was significantly higher for d0 (p = 0.023) and d10 (p = 0.002) when compared to d20.

CONCLUSIONS

Short-term bioavailability of AQUANOVA micellised fat-soluble vitamin E from our NS was significantly higher than from regular supplements. The NS will now be tested for its clinical efficacy in a randomized double-blind controlled intervention trial with CF patients.

Influence of micelle solubilization by tocopheryl polyethylene glycol succinate (TPGS) on solubility enhancement and percutaneous penetration of estradiol

The effect of micellar solubilization on the enhancement of the solubility and percutaneous penetration of estradiol by the surface-active agent, tocopheryl polyethylene glycol succinate (TPGS) was characterized in this study. Results show that the solubility of estradiol was improved in the presence of TPGS through micellar solubilization. The critical micelle concentration (CMC) of TPGS increased with increasing ethanol concentration in the medium. With the flux corrected to the saturated level (J(corrected)) of the free form of estradiol, an increase in the alcohol content of the medium resulted in an increase in J(corrected) for all levels of TPGS examined. For the same level of alcohol content, an increase in the TPGS concentration mostly led to a small extent of decrease in J(corrected). However, the extent of decrease was more obvious in media containing more than 60% alcohol. We also confirmed that only an insignificant amount of TPGS was transported across the skin (below the detection limit of 2 microg/ml). Permeabilities (P(eff)), which describe the overall effects (DK/H) on the stratum corneum (SC), decreased with increasing TPGS concentration for media containing 0, 40, 60, and 80% alcohol, whereas they increased then decreased with increasing TPGS concentration for media containing 10 and 20% alcohol. The enhancement ratios based on P(eff) assuming that the medium contained 0% TPGS and alcohol as unity did not increase accordingly with increases in TPGS concentration at the same level as alcohol. Likewise, the enhancement ratios for the same level of TPGS increased with low alcohol content, but then decreased with increasing alcohol content. We concluded that micellar solubilization by TPGS was able to improve the solubility of estradiol, but it only had an insignificant influence on the skin. Interfacial coverage of TPGS with increasing TPGS concentration and hindrance of the partitioning of estradiol by the increasing alcohol content might play a role in influencing the permeability of estradiol.

Approaches and agents for imaging the vascular system

Several classes of vascular imaging agents are described: (1) liposome-based blood cell mimetics; (2) plasma protein mimetics; (3) small molecules that bind to plasma proteins in the circulation. The characteristic features of the different agents are described and critically compared, including the advantages and potential pitfalls of each individual type.

Isolation of tocopherol-binding proteins from the cytosol of smooth muscle A7r5 cells

Cultured smooth muscle A7r5 cells were able to take up alpha-tocopherol (32 +/- 1.2 nmol/mg protein) the largest part of which (60%) was present in the cytosolic fraction. Using a tocopherol-based affinity chromatography and alpha-, beta-, gamma-, and delta-tocopherols as eluants, three polypeptides of molecular masses 81, 58 and 31 kDa were eluted. This preparation had alpha-[3H]tocopherol binding capability. The 58-kDa polypeptide could also be eluted by chromanol and the 81-kDa polypeptide could be eluted also by phytol. The 81-kDa polypeptide had the unique P-E-E-D-Q-X-Q-Y N-terminal sequence.

Plasma alpha-tocopherol profiles in sheep after oral administration of dl-alpha-tocopheryl acetate and d-alpha-tocopheryl polyethylene glycol-1000 succinate

Twenty-five yearling wethers, weighing 45 to 50 kg, were used in a trial designed to compare the bioavailability of dl-alpha-tocopheryl acetate (TA) and d-alpha-tocopheryl polyethylene glycol-1000 succinate (TPGS). The sheep, five per treatment, were each given a basal diet without vitamin E supplement (control) or with a daily oral supplement of 240 iu TA or TPGS, or of 480 iu TA or TPGS. Blood samples were obtained at zero time, and then twice daily for three weeks. The bioavailability was greater for TA than for TPGS. This was indicated by the significantly higher (P less than 0.01) plasma alpha-tocopherol concentrations during the three-week experimental period in sheep dosed with equivalent units of TA than in those dosed with TPGS. When administered at 480 iu, the TPGS produced plasma profiles similar to those found after administration of the lower (240 iu) dose of the TA.

Absorption, transport and metabolism of vitamin E

Vitamin E includes eight naturally occurring fat-soluble nutrients called tocopherols and dietary intake of vitamin E activity is essential in many species. alpha-Tocopherol has the highest biological activity and the highest molar concentration of lipid soluble antioxidant in man. Deficiency of vitamin E may cause neurological dysfunction, myopathies and diminished erythrocyte life span. alpha-Tocopherol is absorbed via the lymphatic pathway and transported in association with chylomicrons. In plasma alpha-tocopherol is found in all lipoprotein fractions, but mostly associated with apo B-containing lipoproteins in man. In rats approximately 50% of alpha-tocopherol is bound to high density lipoproteins (HDL). After intestinal absorption and transport with chylomicrons alpha-tocopherol is mostly transferred to parenchymal cells of the liver were most of the fat-soluble vitamin is stored. Little vitamin E is stored in the non-parenchymal cells (endothelial, stellate and Kupffer cells). alpha-Tocopherol is secreted in association with very low density lipoprotein (VLDL) from the liver. In the rat about 90% of total body mass of alpha-tocopherol is recovered in the liver, skeletal muscle and adipose tissue. Most alpha-tocopherol is located in the mitochondrial fractions and in the endoplasmic reticulum, whereas little is found in cytosol and peroxisomes. Clinical evidence from heavy drinkers and from experimental work in rats suggests that alcohol may increase oxidation of alpha-tocopherol, causing reduced tissue concentrations of alpha-tocopherol. Increased demand for vitamin E has also been observed in premature babies and patients with malabsorption, but there is little evidence that the well balanced diet of the healthy population would be improved by supplementation with vitamin E.

Comparative evaluation of the antioxidant activity of alpha-tocopherol, alpha-tocopherol polyethylene glycol 1000 succinate and alpha-tocopherol succinate in isolated hepatocytes and liver microsomal suspensions

The antioxidant activity of alpha-tocopherol polyethylene glycol 1000 succinate (TPGS) and of alpha-tocopherol succinate (TS) has been examined in isolated hepatocytes and microsomal fractions from rat liver. Both TPGS and TS require esterase activity to yield free alpha-tocopherol and, hence, antioxidant activity. TPGS and TS consistently exerted a more effective antioxidant protection than an equivalent amount of directly-added free alpha-tocopherol. The low antioxidant efficiency of directly added free alpha-tocopherol in such water-based experimental systems as used here seems to be due to its extreme hydrophobicity. TPGS, on the other hand, is an extremely hydrophilic compound that is being examined as a useful source of alpha-tocopherol in certain clinical situations and is here shown to be a convenient and effective source for experimental studies into lipid peroxidation and antioxidant mechanisms.