Self-assembled nano-vesicles based on mPEG-NH2 modified carboxymethyl chitosan-graft-eleostearic acid conjugates for delivery of spinosad for Helicoverpa armigera
Introduction
Insect pests not only cause serious damage to crop products, but also bring about considerable economic losses. Helicoverpa armigera, a polyphagous pest, can dramatically reduce the yield of cotton, peanuts, okra, tomatoes, wheat and so on. At present, Helicoverpa armigera has developed resistance to commonly used synthetic insecticides, so it is very important to find biological pesticide instead of synthetic insecticides. However, the active ingredients of biological pesticides are easily degraded by sunlight and ultraviolet radiation and cannot be widely used. Recently, significant progress has been made in the research and development of polymeric nanomaterials and agricultural nanotechnology [1], which have high pesticide utilization efficiency and low environmental side effects, and can effectively protect the active ingredients of pesticides from degradation by external conditions [2,3].
Chitosan (CS) [[4], [5], [6]], a nature polymeric materials, is widely used and recognized in the fileds of medicine [[7], [8], [9]], biochemistry [10,11], chemical industries [[12], [13], [14]] and agriculture [[15], [16], [17]] due to their favorable properties of biodegradability [18], renewability and biocompatibility [19]. However, the water solubility of CS is poor because of its rigid linear molecule structure, and the application of CS is restricted. Therefore, various methods were developed to increase the water solubility of CS, including grafting functional groups onto the molecular chain of chitosan [20,21]. Carboxymethyl chitosan (CMCS) [[22], [23], [24]], a water soluble chitosan derivative by introducing the CH2-COOH functional group into chitosan, not only maintains the merits of chitosan, but also can be dissolved in an aqueous solution with a broad range of pH. In particular, fatty acid (such as stearic acid and eleostearic acid), an endogenous long-chain fatty acid, is widely accepted for pharmaceutical use [25]. As a main composition of fat, fatty acid is hydrophobic and biocompatible with low cytotoxicity. Thus, it is expected that the introduction of fatty acid into CMCS would induce self-association to form nanoparticles with good biocompatibility. In recent years, the amphipathic modification of CMCS has been extremely active and has become a research focus in the field of drug carriers [26,27]. Cong [28] constructed clarithromycin loaded ureido-modified carboxymethyl chitosan-graft-stearic acid polymeric nano-micelles by self-assembly method, which showed a superior anti-H. pylori effect in vitro. Guo [29] prepared galactosylated O-carboxymethyl chitosan-graft-stearic acid conjugates and constructed Gal-OCMC-g-SA/DOX nanoparticles, which had a sustained and pH-dependent drug release manner and could be applied in cancer therapy.
Poly(ethylene glycol) (PEG), a highly hydrophilic and biocompatible polymer, has been widely used in chemical fiber [30], medicine [31,32], carrier [33], pesticide [34] and so on. The polymers and materials modified with PEG were found to be better hemocompatibility, due to the flexibility of the backbone and hydrophilicity of the polymer. PEG modified chitosan and its derivatives increase the solubility and improve the biocompatibility of chitosan [[35], [36], [37]]. Dong [38] prepared an amphiphilic chitosan derivative by grafting methoxypolyethylene glycols (mPEG) and N-acetyl-l-isoleucine (NAI) onto chitosan and embedded spinosad, with a superior control of Fusarium oxysporum and the grafted large molecular weight of mPEG was beneficial to reduce the particle size of micelles.
Hence, in this work, carboxymethyl chitosan-graft-eleostearic acid (CMCS-g-EA) conjugates and mPEG-NH2 modified carboxymethyl chitosan-graft-eleostearic acid (mPEG-CMCS-g-EA) conjugates were synthesized through the amide reaction. The self-aggregation behavior of the conjugates was investigated using pyrene as fluorescent probe. Then spinosad loaded CMCS-g-EA and mPEH-CMCS-g-EA nano-vesicles were prepared by a dialysis-ultrasound method and the physicochemical properties of the drug-loaded nano-vesicles including encapsulation efficiency (EE), loading capacity (LC), partical size, morphology, the in vitro drug release and photostability were investigated. In addition, the toxicity of the drug-loaded nano-vesicles on Helicoverpa armigera was also researched. This work demonstrated that mPEG-CMCS-g-EA could be used as an effective carrier to improve the toxicity of spinosad to Helicoverpa armigera.
Section snippets
Materials
Carboxymethyl chitosan (CMCS, Mw = 1.0–2.0 × 104, degree of deacetylation ≥85%, degree of carboxymethylation ≥80%) was purchased from Shanghai Macklin Biochemical Co., Ltd., China. 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) N-hydroxysuccinimide (NHS) and amino-terminated mPEG (mPEG-NH2) (Mw = 2000) were purchased from Aladdin Reagent Co. Ltd., China. Eleostearic acid (EA) was obtained from Sinopharm Chemical Reagent Co., Ltd., China, and the purity was 95.6%. Spinosad
Characteristics of CMCS-g-EA and mPEG-CMCS-g-EA conjugates
The FT-IR spectra of CMCS, EA, CMCS-g-EA and mPEG-CMCS-g-EA co-polymers were shown in Fig. 1(A). For CMCS, the peak at 3439 cm−1 was attributed to the stretching vibrations of the OH and NH2 groups, and the peaks at 2928 cm−1 and 2856 cm−1 were assigned to the stretching vibrations of CH (methylene), and the peak at 1710 cm−1 was related to the CO stretching vibrations in amide linkages. While the peaks at about 1643 and 1594 cm−1 were ascribed to the amide I and II band stretching vibration of
Conclusions
In this work, a novel conjugate, mPEG-NH2 modified carboxymethyl chitosan-graft-eleostearic acid (mPEG-CMCS-g-EA), was synthesized as an effective drug delivery carrier for embedding spinosad. And the chemical structures of mPEG-CMCS-g-EA were confirmed by FT-IR and NMR spectra. The amphiphilic conjugates could self-assemble into nano-vesicles in aqueous solution with a low critical aggregation concentration. The EE and LC of SSD@mPEG-CMCS-g-EA nano-vesicles were 42.00%, 23.07%, respectively.
Data availability
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.
Author statement
This publication is approved by all authors and tacitly or explicitly by my institute where this work was carried out. If it were accepted, it will not be published elsewhere in the same form in English or in any other language, without the written consent of the publisher.
Declaration of Competing Interest
We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
Acknowledgements
This work was supported by National Key R&D Program of China (2018YFD0201100), the Natural Science Foundation of Hainan Province (219QN294, 319QN297), the Central Public-interest Scientific Institution Basal Research Fund for Chinese Academy of Tropical Agricultural Sciences (1630122019012, 1630122019011, 1630122017009), the Natural Science Foundation of Guangdong Province (2019A1515010714, 2018A030313109, 2018A030307015) and the Science and technology projects of Zhanjiang (No.2018A02015).
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2023, Carbohydrate PolymersCitation Excerpt :Fig. 2a showed the FT-IR spectra of CS, CMCS and CMCS-g-CA. In the spectrum of CMCS, the characteristic peak at 3416 cm−1 was attributed to the stretching vibrations of the OH group (Alhwaige, Ishida, & Qutubuddin, 2019), and the peaks at 2923 cm−1 was assigned to the stretching vibrations of methylene (Zhou et al., 2020). While, the peaks at 1425 and 1312 cm−1 ascribed to the antisymmetric and symmetric vibrations of COO group appeared in the spectrum of CMCS (Abu El-Soad et al., 2022), confirming that CS was carboxymethylated and CMCS was synthesized.
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2022, International Journal of Biological MacromoleculesCitation Excerpt :Many scholars have prepared amphiphilic chitosan by grafting hydrophilic and hydrophobic groups on the molecular chain of CMCS as the hydrophobic group carriers [20,21]. Zhou et al. [22] synthesized a mPEG-NH2 modified carboxymethyl chitosan-graft-eleostearic acid conjugate and prepared drug-loaded nano-vesicles with a pH responsive and superior inhibitory property of Helicoverpa armigera. Cong et al. [23] constructed clarithromycin loaded ureido-modified carboxymethyl chitosan-graft-stearic acid polymeric nano-micelles by self-assembly method, which showed a superior anti-H.
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2020, Carbohydrate PolymersCitation Excerpt :Chitosan alone has also been used to synthesize the spinosad nanoparticles by Sharma, Sood, Kaur, and Khatri (2019) using ion gelation method, with toxicity and residual effect checked. Particularly, pH-responsive spinosad nanoformulations based on the carrier of chitosan-isoleucine-polyethylene glycol methyl ether copolymer (Dong et al., 2019) or mPEG-NH2 modified carboxymethyl chitosan-graft-eleostearic acid conjugate have been reported (Zhou et al., 2020). Despite these investigations, few researches have been conducted on stimuli-responsive formulation of spinosad.