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Glutathione
Published in Ruth G. Alscher, John L. Hess, Antioxidants in Higher Plants, 2017
Alfred Hausladen, Ruth G. Alscher
Enzymatic and HPLC methods for the determination of GSH have recently been reviewed by Anderson11 and Fahey.12 Enzymatic determination in a coupled assay system containing glutathione reductase and dithiobis(2-nitrobenzoic acid) (DTNB) is a convenient, inexpensive method which is highly sensitive and specific. After removal of GSH from extracts by 2-vinylpyridine, the same assay can be used to measure GSSG. It should be cautioned, however, that this assay shows twofold higher reaction rates with hGSH than with GSH, which can lead to erroneous results when investigating hGSH-containing plants.2 A second widely used method is HPLC separation with fluorometric detection after derivatization of thiols with monobromobimane. The method has the advantage of simultaneously measuring other low-molecular weight thiols, such as cysteine, γ-glutamylcysteine, or cys-teinylglycine, and has been adapted for the separation of hGSH from GSH.2 However, the determination of GSSG by this method is less reliable, since it can only be measured as the difference in GSH content before and after dithiothreitol (DTT) reduction of extracts. GSH can be up to 95% of the total glutathione pool;6 the reduction of GSSG will, therefore, only slightly increase the value obtained for GSH.
Polymer–Silver Nanocomposites: Preparation, Characterisation and Antibacterial Mechanism
Published in Huiliang Cao, Silver Nanoparticles for Antibacterial Devices, 2017
Among the stabilisers, polymers are the preferred choice because of their special configuration, physicochemical properties and structural characteristics for grafting onto metal nanoparticles with good dispersion. In addition, the functional groups on polymers can be used as the binding sites of targeting reaction to control the oriented synthesis of the nanocomposites (Chen et al. 2005; Ijeri et al. 2010; Zhang et al. 2006). To obtain polymer–metal nanocomposites with excellent antibacterial activity, the polymers, such as polyethylene glycols (Popa et al. 2007), poly(vinylalcohols) (Chou et al. 2000), poly(vinylpyrrolidons) (Choi et al. 2008; Greulich et al. 2012; Heckel et al. 2009; Huang et al. 1996), poly(acrylamides) (Chen et al. 2006, 2013), polyurethanes (Chou et al. 2006), poly(methyl methacrylate) (Kong and Jang 2008), poly(bisphosphonate-b-2-vinylpyridine) (Zhang et al. 2014), poly(d,l-lactide-co-glycolide) (Fortunati et al. 2013), poly(styrene–divinylbenzene) (Kumar et al. 2013), polysaccharide (Cheng et al. 2013; Lu et al. 2015), protein (Fei et al. 2013; Zimoch-Korzycka and Jarmoluk 2015) and peptide (Liu et al. 2013; Regiel-Futyra et al. 2015), have been commonly employed as substrates for Ag NPs. The aim of this chapter is to offer a rather comprehensive survey of the well-established and newly developed polymer–Ag nanocomposites having anti-infective activity.
Engineered Nanoparticles for Drug Delivery in Cancer Therapy *
Published in Valerio Voliani, Nanomaterials and Neoplasms, 2021
Tianmeng Sun, Yu Shrike Zhang, Pang Bo, Dong Choon Hyun, Miaoxin Yang, Younan Xia
Figure 2.3 schematically illustrates how the polymer chains either extend or collapse in response to the variation in pH value and thereby cause changes to the electrostatic interactions, allowing for pH-dependent release of drug molecules [93d,93e]. For example, micelles derived from block copolymers can release the preloaded drug when the pH value is varied (Fig. 2.3a). One way to trigger the release is to reduce electrostatic interactions between a positively charged drug (such as doxorubicin) and an oppositely charged block copolymer by protonating the carboxylate groups of the block copolymer [94]. Polymer chains sensitive to the pH value can also be incorporated into liposome to make the permeability of the phospholipid bilayers dependent on pH value (Fig. 2.3b) [93e]. For example, the protonation of poly-2-vinylpyridine (P2VP) blocks at pH 4.9 induced rupture of the membrane of PEG-b-P2VP polymersomes, triggering the release of the encapsulated drug [95]. Hydrogel nanoparticles can be employed for pH-sensitive release as well, where changes to the degree of protonation/deprotonation lead to swelling and/or shrinking, triggering the release of drug molecules (Fig. 2.3c) [96]. For example, Bae and coworkers demonstrated the synthesis of a self-assembled, pH-responsive hydrogel. When loaded with doxorubicin, this system showed an enhancement in toxicity at pH 6.8, which is similar to the pH level inside the tumor tissue [97]. Another approach is to incorporate cleavable bonds into the nanoparticle carrier. The cleavable bonds can be broken to directly release the drug molecules conjugated to or encapsulated in the carrier [69e, 98]. Figure 2.4 shows a partial list of cleavable bonds that can be incorporated into polymer carriers. In the case of polymer–drug conjugates, pH-sensitive linkages such as hydrazone, hydrazide, and acetal have been used to directly attach drug molecules to polymers. To this end, Rihova and coworkers synthesized N-(2-hydroxypropyl) methacrylamide (HPMA), a polymer conjugated with hydrazone groups for the attachment of doxorubicin. The drug was released from the conjugates at pH 5 [99]. Similarly, doxorubicin conjugated to a hydrazone-linked dendrimer was released in a pH-sensitive manner. The release was rapidly completed at pH 5, reaching 100% release within 48 h [100]. Kratz and coworkers developed an acid-cleavable doxorubicin prodrug derived from dendritic polyglycerol. Use of the hydrazone linker led to a dramatic change in drug release between pH 5 and 6 [101]. A polymer containing an acid-degradable backbone was obtained through terpolymerization of PEG, divinyl ether, and serinol. The pendant amino groups can be used for the conjugation of doxorubicin to the polymer backbone [102]. In another demonstration, acid-degradable linkers such as the pH-labile hydrazone bond was exploited to trigger the release of a drug. Such a linker allows the attachment of doxorubicin to the hydrophobic block of an amphiphilic polymer [103].
3D printing for enhanced drug delivery: current state-of-the-art and challenges
Published in Drug Development and Industrial Pharmacy, 2020
Melissa Wallis, Zaisam Al-Dulimi, Deck Khong Tan, Mohammed Maniruzzaman, Ali Nokhodchi
There are many pH-sensitive polymers on the market and some of them such as cellulose acetate phthalate (CAP), cellulose acetate trimellitate (CAT), hydroxypropyl methylcellulose phthalate (HPMCP), and Eudragit L and S were used in the preparation of drug/polymer matrix tablets [71]. In addition, chitosan and alginate have also been employed to make pH-sensitive formulations [72]. Among these polymers, polymethacrylates such as Eudragit® L100-55 and Eudragit® S100 are polymers that can be used for the fabrication of filaments which are suitable for 3D printing and their solubility is pH-dependent [73]. The study by Gioumouxouzis et al. produced pH-responsive chitosan-coated alginate beads loaded with 5-Fluorouracil. The beads were then placed in a 3D printed tablet that is made of PLA and Eudragit. The Eudragit layer of the 3D printed drug is only soluble when pH value corresponds to the colonic environment, ensuring a colon-specific drug delivery. Poly(2-vinylpyridine) (P2VP) is also a pH-responsive polymer which can be used for 3D printing [74]. In addition, hydrogels such as Poloxamers and Pluronics exhibit pH-responsive properties and can also be used for the 3D printing of scaffolds [75].
Multi-fractal modeling of curcumin release mechanism from polymeric nanomicelles
Published in Drug Delivery, 2022
Camelia E. Iurciuc (Tincu), Marcel Popa, Leonard I. Atanase, Ovidiu Popa, Lacramioara Ochiuz, Paraschiva Postolache, Vlad Ghizdovat, Stefan A. Irimiciuc, Maricel Agop, Constantin Volovat, Simona Volovat
Poly(2-vinylpyridine)-b-poly(ethylene oxide), P2VP-b-PEO, diblock copolymers were synthesized by living anionic polymerization in THF in the presence of phenylisopropyl potassium as initiator (Atanase & Riess, 2013). For decreasing the reactivity of the initiator and stopping the transfer reactions, a unit of 1,1-diphenylethylene is recommended. First the 2-vinylpyridine is polymerized at −75 °C for 2.5 h. The ethylene oxide is added and the temperature is increased to 20 °C. The copolymer was recovered by precipitation in heptane, followed by drying in vacuum.
Neuro-protective potential of quercetin during chlorpyrifos induced neurotoxicity in rats
Published in Drug and Chemical Toxicology, 2019
Simranjeet Kaur, Neha Singla, D. K. Dhawan
The oxidized glutathione content was measured using the spectrophotometric method of Tietze (Tietze 1969). In this assay, 5-sulfosalicylic acid was mixed with 2-vinylpyridine and the mixture was adjusted to pH 6.8 with triethanolamine that was further incubated at 25 °C for 20 min. Brain samples were mixed with 0.6 mM DTNB, 0.2 mM NADPH, and 5 mM EDTA in 0.1 M sodium phosphate buffer (pH 7.5) and the reaction was initiated by adding GR (1.3 units/ml). The contents of GSH were expressed as micromoles of GSH produced/mg protein.