Jing Zhao,Zhiguang Duan,Xiaoxuan Ma,Yannan Liu,Daidi Fan

1 Shaanxi Key Laboratory of Degradable Biomedical Materials,School of Chemical Engineering,Northwest University,Xi’an 710069,China

2 Shaanxi R&D Center of Biomaterials and Fermentation Engineering,School of Chemical Engineering,Northwest University,Xi’an 710069,China

3 Biotech.&Biomed.Research Institute,Northwest University,Xi’an 710069,China

ABSTRACT Ginsenosides are the main pharmacologically active constituents of ginseng which have been used in East Asian countries for centuries to modulate blood pressure,metabolism and immune function.Following the technological advances in isolation,purification and mass production,their mechanisms of action are gradually elucidated,providing solid basis for clinical applications.Ginseng extracts (total ginsenosides)and ginsenoside Rg3,CK,Rd have been marketed or entered clinical trials as drugs or dietary supplements.Despite the proven safety and efficacy of some ginsenosides,their applications are hindered by inferior pharmacokinetics such as low solubility,poor membrane permeability and metabolic instability.Nanoparticle formulation of drugs and implantable drug depots are effective strategies to improve the pharmacokinetics of therapeutic agents by enhancing solubility,providing protection,facilitating intracellular transport,and enabling sustained and controlled release.This mini-review summarizes the recent advances in systemic delivery of ginsenosides using liposomes,micelles,albumin-based nanoparticles,and inorganic nanoparticles,as well as local delivery of ginsenosides by electronspun fibrous membranes and hydrogels.

Keywords:Ginsenosides Nanoparticles Nanofibers Drug delivery

1.Introduction

Natural products from plants and animals are historically the predominant source of medicine for the treatment of a wide spectrum of diseases,and continue to enter clinical trials and provide structural basis for the design of synthetic molecules in highthroughput screening[1].It has been reported by US NIH that from 1946 to 2019,among the 259 small molecule anticancer drugs approved by the US FDA,39%are natural products(N)or direct natural product derivatives(ND);and around 79%are N,ND,botanical“defined mixtures”,and molecules related to natural product (i.e.inspired at one level or another by natural product structures)[2].Traditional Chinese Medicine(TCM)has been extensively documented for centuries with verified safety and bioactivity,hence provides an abundant source and structures for the discovery of therapeutic agents.Panax Ginsengis the most widely used and acclaimed herb in ancient Asian countries for the modulation of blood pressure,metabolism and immune function;and nowadays,its cancer prevention and treatment effects have been shown in multiple clinical studies [3].

1.1.Ginsenosides

Ginseng is widely consumed as dietary supplements,food products,personal care products,pharmaceuticals,and oral care products [4,5].The global ginseng market size was reported to be US$622.9 million in 2019,and is expected to rise at a compound annual growth rate (CAGR) of 4.8% between 2019 and 2027(futuremarketinsights.com).Ginsenosides are the key pharmacologically active constituents of ginseng.Since the isolation of ginsenosides in 1963,their structure,function and molecular mechanisms are gradually elucidated [6].Ginsenosides are triterpene saponins that consist of a dammarane or oleanolane skeleton and various attached sugar moieties.The majority of ginsenosides are dammarane-type and can be classified into protopanaxadiol(PPD) and protopanaxatriol (PPT),which differs by the position of sugar attachment.For PPD-type ginsenosides,the sugar moieties are attached to the C-3 and C-20 of the dammarane ring;while for PPT-type ginsenosides,the sugars are attached to C-6 and C-20[7](Fig.1).Based on the difference in C-20 chiral carbon substitution,PPD and PPT can be further categorized into 20S and 20R type.The pharmacological characteristic of ginseng is determined by its unique ginsenoside profile.The major ginsenosides inpanax ginsengare Rb1、Rg1 and Rd;the major ginsenosides inpanax quinquefoliumare Rb1,Re and Rd;and the major ginsenosides inpanax notoginsengare Rb1,Rg1,Ra and R1[8].In addition to these major ginsenosides,some rare ginsenosides which constitute an extremely small proportion of the total ginsenosides or obtained by de-glycosylation or dehydration of major ginsenosides via chemical or bio-transformations,have stronger efficacies for a large variety of biological activities including anti-inflammation[9],anti-tumor [10,11],anti-diabetes [12,13],anti-anemia [14],anti-insomnia [15],etc.

Fig.1.The chemical structures of representative PPD-type and PPT-type ginsenosides.(A)PPD-type major ginsenosides Rb1,Rb2,Rc,Rd and rare ginsenosides;(B)PPT-type major ginsenosides Re,R1,Rf and rare ginsenosides.Rare ginsenosides can be obtained from major ginsenosides by de-glycosylation and dehydration.

Rare ginsenoside Rg3 (Shenyi Capsule) and Rh2 (Jinxing Capsule) have been approved by the Chinese national medical products administration (NMPA) as oral therapeutic adjuvants to improve the immunity of patients undergoing chemotherapy[16].Currently,there are 26 clinical trials related to ginsenosides,16 of which are listed as drugs and 10 are dietary supplements(clinicaltrials.gov).Majority of the subjects examined are total ginseng extracts or mixed herbals,and only ginsenoside Rg3,Rd and CK are tested as single agent or in combination with first-line chemotherapeutic drugs for the treatment of cancer,ischemic stroke and rheumatoid arthritis.The synergistic effects between ginsenosides and conventional chemotherapeutic agents are widely investigated in preclinical settings.For example,ginsenoside Rg3 has been shown to sensitize cisplatin,paclitaxel,docetaxel,and reduce the side-effects of cyclophosphamide [17–19].Rd has been shown to ameliorate cisplatin resistance for the treatment of non-small-cell lung cancer via the nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway [20].Ginsenoside CK has been demonstrated to function synergistically with γ-ray radiation,cisplatin,and TRAIL for the treatment of cancer [21–23].

1.2.Pharmacokinetics of ginsenosides

Despite the proven safety and efficacy of some ginsenosides,their applications are hindered by inferior pharmacokinetic (PK)characteristics such as low solubility,poor membrane permeability and metabolic instability.Pharmacokinetic studies of ginsenosides using rats and dogs as animal models revealed that the oral bioavailability is generally below 5%[24].Rg3 is currently the most well developed ginsenoside that have entered clinic,hence it is the most popular choice of ginsenoside in PK studies.Wonet al.conducted PK study of Rg3 using rats and found that the bioavailability of orally administered Rg3 (10 mg·kg-1) was only 2.63% and the level of Rh2 and PDD,the major metabolites of Rg3,are undetectable due to the extremely low exposure to the systemic circulation [25].The low bioavailability could be attributed to low solubility,poor membrane permeability and metabolic instability.The solubilities of ginsenosides positively correlate with the number of sugar moieties,however,the anti-tumor activities generally increase with the decrease of sugar content.Membrane permeability is related to molecular size and lipid-water partition coefficient.The“rule of 5”proposed by Lipinski and colleagues that set guidelines for drug candidates pointed out that poor absorption or permeation is usually associated with molecules that have more than 5-H-bond donors,10-H bond acceptors,molecular weight greater than 500,and the calculated lgP(ClgP) greater than 5 [26,27].The molecular weight of ginsenosides usually exceeds 500,and have more than 5H-bond donors in their structures which limit their absorption according to the “rule of 5”[28].In addition,the drug efflux pumps such as P-glycoprotein(P-gp)cause the efflux of ginsenosides and lower their absorption [24].Besides,ginsenosides experience complex biotransformation in the GI track by intestinal microorganisms and enzymes,resulting in a reduction in concentration [29].Except low bioavailability,fast clearance is another reason that affects the therapeutic efficacy of ginsenosides.Qianet al.[30]found that Rg3 was not detectable in rat plasma and urine 1.5 h after oral administration largely due to the rapid clearance of Rg3 from the body.Penget al.[31]investigated the PK of 20(S)-Rg3 and 20(R)-Rg3 in rats and showed that after intravenous administration,the plasma concentrations of the two epimers rapidly decreased from 2 to 30 min and became undetectable after 1 h.

The bioavailability can be increased by changing the administration route and using absorption enhancing agents[6].Although oral administration is still the mainstream for ginseng-derived pharmaceuticals,intravenous administration of ginseng extracts such aspanax notoginsengandGinseng radix et rhizoma rubraandOphiopogonis radix(ShenMai Injection,SMI) have also been approved by the NMPA for the treatment of heart and cerebrovascular diseases,and were shown to have higher bioavailabilities than their oral formulations [32–35].Besides,intranasal administration of ginsenoside Rg3 and total ginsenosides ofpanax notoginsenghave also been tested on mice to circumvent the first-pass elimination [36,37].The use of absorption enhancer is another strategy to improve the bioavailability of ginsenosides.Xionget al.[38]found that adrenaline increased the Caco-2 cell uptake of Rg1 and the bioavailability of orally taken Rg1 in mice model.Chenet al.[39]discovered that ginsenoside Rg1 can be absorbed through the nasal mucous and borneol can enhance the absorption without causing damage to the nasal mucosa of rats.In addition,azone was found to improve the transdermal absorption efficiency of Rg1,and imidazole type-ionic liquid [BMIM][Cl]was shown to promote thein vitropercutaneous absorption of ginsenoside Rh1[40,41].These strategies improved the absorption,but have less effect on distribution,metabolism and excretion of ginsenosides.

1.3.Nanoparticles and implantable drug depots

In comparison to the aforementioned strategies,nanoparticle delivery systems have potential to improve absorption,distribution,metabolism and excretion of therapeutic agents by enhancing solubility,providing protection,facilitating intracellular transport,enabling sustained and controlled release and escaping immune recognition.Liposome and albumin have been used in clinic for decades and their safety and effectiveness in altering the PK of loaded drugs have been proven.Polymeric micelles and inorganic nanoparticles such as gold and iron oxide nanoparticles have also entered clinical trials for cancer treatment.Hence,nanoparticle formulations hold great promise in solving the PK issues of ginsenosides similar to what they did for plant-derived chemotherapeutic agents such as doxorubicin and paclitaxel.In addition to nanoparticles,implantable drug depots(i.e.local drug delivery systems)such as electrospun nanofibers and hydrogels are also effective drug delivery vehicles for sustained,controlled and sequential release of therapeutics and have been applied as wound dressings and tissue engineering scaffolds.This mini-review will provide an update on the systemic and local delivery of ginsenosides using nanoparticles and nanofiber-based drug depots with focuses on cancer treatment and wound healing(see Tables 1 and 2).Ginsenosides delivery using microparticles and microemulsions are summarized elsewhere [24].

2.Systemic Ginsenoside Delivery– Nanoparticles

2.1.Liposome

Liposome is a lipid-based vesicle that consists of an aqueous core enclosed by a photospholipid bilayer.Cholesterol is usually inserted into the lipid membrane to improve the colloidal stability and to prevent drug leaking.Ginsenosides which have steroid structures similar to that of cholesterol have been shown to stabilize phospholipid bilayers [64,65].Based on the anticancer activities and physiochemical properties of ginsenosides,Honget al.developed ginsenoside-based liposomes for the targeted delivery of chemotherapeutic drug paclitaxel[65].In the liposome formulations,ginsenoside Rg3/Rh2/Rg5 functioned as both liposome membrane stabilizers and chemotherapy adjuvants (Fig.2(A)),which worked synergistically with paclitaxel in suppressing gastric tumor growth that outperformed most reported paclitaxel formulations,including Lipusu?and Abraxane?.Liposomes mimic the structure of cell membranes and are generally safe,however,they have very short plasma half-life and drug retention time after administration[42].PEGylation provides steric hindrance to prevent surface protein adsorption and is an effective way to prolong the circulation half-life of liposomes (e.g.Doxil?),however polyethylene glycol(PEG) was shown to hinder tumor cell uptake of nanocarriers due to the same reason.Current solutions include surface modifications of targeting moieties and the use of detachable PEG shell that can be removed by intrinsic or external stimuli to expose the cellinternalization promotive surfaces.Ginsenoside CK is the intestinal bacterial metabolite of other PPD-type ginsenosides.It has remarkable anti-carcinogenic and anti-inflammatory activities and outperforms its parent ginsenosides.However,ginsenoside CK has only one sugar and has low aqueous solubility and serious drug efflux problem.Jinet al.[43]co-delivered two antitumor natural products parthenolide and ginsenoside CK in tumor homing peptide tLyp-1 modified liposome which was demonstrated to have synergistic antitumor effects and reduced toxicity to vital organs(Fig.2(B)).The tumor homing peptide,tLyp-1 was demonstrated to assist tissue penetration and cancer cell internalization.Yanget al.[44]synthesized d-α-tocopheryl polyethylene glycol 1000 succinate(TPGS)-modified liposome for the delivery of ginsenoside CK(Fig.2(C)).TPGS is a FDA approved drug excipient that can confer liposome stealth effect and may improve CK efficacy by inhibiting the P-gp drug efflux pumps.

Table 1 Representative systemic nanoparticle delivery systems for ginsenosides

2.2.Micelles

Micelles are formed by the self-assembly of amphiphilic molecules in aqueous solutions.The hydrophobic core enables the entrapment of hydrophobic drugs and the hydrophilic corona provides a favorable surface for protection,long-circulation and targeting.Ginsenosides contain hydrophobic dammarane or oleanolane and hydrophilic glucosyl groups,hence can selfassemble in aqueous environment into micelles.Xionget al.found thatpanax notoginsengextracts can form micelles with a critical micellar concentration of 0.339 mg·ml-1[45].Liet al.[66]have discovered that ginsenoside Rb1 could self-assemble into ultrasmall micelles (<8 nm) for the encapsulation of diclofenac to relief eye irritation.Rb1 micelle formulation was shown to significantly improve corneal permeation and anti-inflammatory efficacy of diclofenac compared to commercial diclofenac eye drops on rabbit model.Daiet al.[46]used self-assembled ginsenoside Rb1 micelles for the delivery of other low-solubility natural anticancer compounds,and increased their circulation half-life by 5–6 fold,leading to enhanced antitumor activities (Fig.3(A) and Fig.4).Except self-assembly,ginsenosides have also been delivered or codelivered with other therapy agents by lipids and emulsifiers such as F127 and TPGS.The benefits of ginsenoside self-assembly and the use of FDA approved pharmaceutical excipients (e.g.F127,TPGS)are the proven safety and high drug load.However,micelles formed by self-assembled ginsenosides,lipids and emulsifiers may suffer fromin vivoinstability and premature drug release due to the disassembly after dilution in blood circulation below CMC and fast recognition by macrophages.

In order to improve stability and prevent pre-mature release,strategies such as drug conjugation and the use of block copolymers,the hydrophobic part of which can form entanglement during micelle formation,are employed.It has been reported that the esterification of CK will not negatively affect the pharmacological activities of CK and the modification of CK with polyethylene glycol (PEG)viaester bond can effectively improve its solubility and PK [67,68].Liet al.[47]conjugated both celastrol and ginsenoside Rh2 to PEGviaester bonds which can then form micelles spontaneously in aqueous solution (Fig.3(B)).The two anticancer natural products could be released in physiological environment by hydrolysis and functioned synergistically for the treatment of non-small cell lung carcinoma(NSCLC).Amphiphilic block copolymer such as PEG-PLGA and PEG-PCL that contain hydrophilic PEG and lipophilic poly(lactic-co-glycolic acid) (PLGA) or poly(εcaprolactone) (PCL) can assemble into micelles with considerable colloidal stability[69,70].Their safety and delivery efficiency have been verified in animal models and some of them(e.g.GenexolPM,NK-105,CRLX-101,BIND-014) have been investigated in clinicalstudies [71].Yanget al.[48]developed TPGS/PEG-PCL mixed micelles for the delivery of CK;in the nanocarrier,TPGS inhibited P-gp and alleviated the efflux of CK,and PEG-PCL improved drug loading and facilitated sustained release.Suet al.[49]synthesized angiopep-2 modified PEG-PCL micelles for targeted delivery of ginsenoside Rg3 (ANG-Rg3-NP) (Fig.3(C)).Angiopep-2 which targets the low-density lipoprotein receptor-related protein-1 (LRP-1)over-expressed on blood–brain barrier and malignant astrocytomas,was shown to improve C6 glioma cell uptake of the Rg3 loaded micelles.

Table 2 Representative local delivery systems for ginsenosides

Fig.2.Schematic illustration of liposome formulations of ginsenosides.(A) ginsenosides Rg3,Rh2 and Rg5 functioned as both the membrane stabilizers and therapy adjuvants;(B) co-delivery of ginsenoside CK and other hydrophobic drugs using targeting ligand modified stealth liposomes;(C) delivery of ginsenoside CK using D-αtocopheryl polyethylene glycol 1000 succinate (Vitamin E-TPGS).

In addition to synthetic polymers,natural polysaccharide chitosan has also been used for the delivery of ginsenosides.Chitosan is biocompatible,biodegradable and mucoadhesive that can improve oral drug bioavailability.Zhanget al.[72]synthesized amphipathic deoxycholic acid-O carboxymethyl chitosan (DAOCMC) which could self-assemble into micelles around 170–190 nm in diameter.Ginsenoside CK was encapsulated into the core of the micelles for sustained release and enhanced cancer cell uptake and cytotoxicity.The same group further modified this delivery system with liver targeting peptide A54 using PEG as tethering molecule,resulting in enhanced hepatic cancer cell uptake and cytotoxicity (Fig.3(D)) [50].

2.3.Albumin-based nanoparticles

Fig.3.Schematic illustration of micelle formulations of ginsenosides.(A)co-delivery of ginsenoside Rb1 and other hydrophobic drugs using Rb1 self-assembled micelles;(B)co-delivery of celastrol and Rh2 using celastrol-PEG-Rh2 micelle;(C)ginsenoside CK delivery using targeting ligand modified amphiphilic block copolymer PCL-PEG micelle;(D) Rg3 delivery using amphipathic deoxycholic acid-O carboxymethyl chitosan micelle.

Fig.4.(A)Schematic illustration of self-assembled ginsenoside Rb1 nanoparticle loaded with anticancer drugs;(B)Blood circulation data of free drugs(BA,DHA,HCPT)and Rb1 micelle formulated drugs (Rb1/BA NP,Rb1/DHA NP and Rb1/HCPT NP) in C57BL/6 mice;(C) Antitumor efficacy in terms of relative tumor volumes and survival percentage of tumor bearing mice treated with free drugs(BA,DHA,HCPT)and drug loaded micelles(Rb1/BA NP,Rb1/DHA NP and Rb1/HCPT NP).Adapted from Ref.[46]with permission from RSC.ID means injected dose.

Albumin is the most abundant plasma protein involved in transport of nutrients in the body facilitated by its multiple hydrophobic binding pockets and long circulation half-life [73].Beside its nanosize and solubility,albumin can interact with cellular receptors including Gp60,a secreted protein acidic and rich in cysteine (SPARC),the Megalin/Cubilin complex,and the neonatal Fc receptor (FcRn) to facilitate vascular transcytosis and active organ/tumor targeting [74].Albumin formulation of drugs have achieved clinical benefits and been approved for the treatment of cancer and diabetes [75].This clinically relevant nanocarrier has been developed for the delivery of ginsenosides.Our group developed a bovine serum albumin (BSA) formulation of rare ginsenoside Rg5 which had anticancer potency for a wide spectrum of carcinoma using desolvation method and further modified the nanocarrier with folic acid (FA) for tumor targeting [51].The synthesized FA-Rg5-BSA has very high size uniformity (PDI:0.081)and a PH-dependent drug release.FA-BSA nanocarrier delivery effectively improved the PK and antitumor activity of Rg5 in mice.Yanget al.[52]used human serum albumin for the co-delivery of ginsenoside Rg3 and Fe3O4nanoparticle for combination of chemotherapy and magnetic hyperthermia therapy.The results demonstrated that the combination therapy has significantly higher cytotoxicity to Hela cells.The author discussed in the article that heating may increase blood flow and tumor cell membrane lipid fluidity to improve tumor accumulation and cellular uptake of drugs,hence it would be beneficial if anin vivostudy that explored how Rg3 and hyperthermia therapy functioned synergistically had been conducted.

2.4.Inorganic nanoparticles

Inorganic nanoparticles such as gold,iron oxide and silica nanoparticles have also been widely investigated for drug and gene delivery.Gold nanoparticles with proper sizes are biologically inert and generally considered safe.They have size and morphology related optical and thermal properties,as well as versatile surface chemistries.Gold nanoshell (AuroLase?) and recombinant human tumor necrosis factor (rhTNF) bound colloidal gold nanosphere(CYT-6091) have been tested on human as photothermal and immunotherapy agents respectively [75].Parket al.[53]conjugated ginsenoside Rg3 to gold nanospheres using a bifunctional heptaethylene glycol linker,of which the sulfhydryl group was anchored on gold nanoparticlesviaAu-S bond,and the carboxylic acid end was bond to a hydroxyl group of Rg3viaester bond.Kimet al.[54]synthesized CK absorbed gold nanospheres(DCY51T-AuCKNps) by lactic acid producing bacteria lactobacillus kimchicus DCY51Tand demonstrated itsin vitroanticancer activity.Although gold nanoparticles were shown not to cause acute toxicity,their long-term accumulation in metabolic organs such as liver and spleen still raised concerns [76].AuNPs with radium smaller than 6 nm could be excreted through renal clearance,however,the catalytic activity increased significantly when the sizes dropped below 5 nm [77].Hence for AuNP-based drug delivery systems,the biodistribution and clearance need to be carefully examined.In addition to gold,iron oxide nanoparticles have also been clinically tested for iron replacement therapy,magnetic resonance imaging,and tumor hyperthermia therapy [75].Renet al.[55]conjugated ginsenoside Rg3 onto Fe@Fe3O4nanoparticles using (3-aminopropyl) trimethoxysilane (APTMS) and disuccinimidyl suberate(DSS)as crosslinkers.The nanoparticle formulation of Rg3 (NpRg3) was shown to significantly prolong the survival of mice with hepatocellular carcinoma (HCC) and eliminated metastasis to the lung.Also,it was found that NpRg3 delayed DENinduced ileocecal morphology and gut microbial alterations,suggesting that NpRg3 has lower side-effects than conventional chemotherapeutic agents.

3.Local Ginsenoside Delivery– Implantable Drug Depots

Local drug delivery using implantable drug depots enhances drug dosage at targeted site,prevents off-target effect,and facilitates sustained,controlled and sequential delivery of therapy agents.Nanofibers and hydrogels have been used for local delivery of ginsenosides to treat hypertrophic scar (HS).HS which often occurs following deep trauma,severe burn,and surgical incision is a great concern for patients and a challenging problem for clinicians.Ginsenoside Rg3 has been shown to inhibit the formation of HS and later HS hyperplasia by inducing the apoptosis of fibroblasts,inhibiting inflammation and down-regulating vascular endothelial growth factor (VEGF) expression [78].Rg3 loaded wound dressings and skin tissue engineering scaffolds have potential to accelerate wound healing and prevent HS formation.

Electrospinning is a versatile and viable technique that relies on electric field for the generation of nanofibers for various application including tissue regeneration and drug delivery [79].Cui’s group synthesized Rg3 loaded PLGA electrospun nanofiber scaffolds with different surface modifications such as hyaluronic acid(Fig.5),chitosan,PEG,RGD peptide and bFGF growth factor for skin regeneration and HS prevention [56–58].Rg3 was loaded into nanofibers by co-solvent electrospinning method.A sustained release of Rg3 for more than one month has been observed,and the release rate can be adjusted to match the wound healing process by varying the polymer composition.The extracellular matrix mimicking scaffold structure and surface modifications improved cell adhesion and proliferation.Xuet al.[59]fabricated Rg3 loaded poly(γ-glutamic acid) (γ-PGA) electrospun photocrosslinkable hydrogel fibrous scaffold for tissue repair and wound treatment.γ-PGA is a strong hydrophilic polypeptide that can provide desirable microenvironment with high water content and simulates the biofunction of glycosaminoglycans.It contains abundant carboxyl groups hence can be easily functionalized.Rg3 was released sustainably for 16 days and inhibited HS formation.The combination of Rg3 and biomimetic scaffold promoted fast and scarless tissue repair.

In addition to electrospun fibrous membranes,Rg3 and its metabolite Rh2 loaded hydrogels have also been used for transdermal drug delivery and tissue regeneration.Hydrogels are crosslinked polymeric 3D network with high water content.Zhenget al.[60]developed a film-hydrogel-film multilayer wound dressing in which silver nanoparticles were loaded in basement for antisepsis,vascular endothelial growth factor (VEGF) was loaded in middle hydrogel for wound healing,and ginsenoside Rg3 was loaded in top for anti-scar effect.The sandwich-like structure enabled sequential drug release that might match the wound healing process.Sequential release of multiple agents can also be realized using the microsphere/hydrogel systems.Sunet al.[61]constructed a microsphere/hydrogel composite from ciprofloxacin(Cip)-loaded PLGA microspheres and ginsenoside Rh2 dispersed thermo-sensitive hydrogel.Ginsenoside Rh2 was released at first to inhibit the NorA efflux pumps and could prevent antibiotic resistance,followed by a sustained and long-term release of antibiotic Cip to treat antibiotic-resistant skin infections.Similarly,microemulsions and microspheres have also been loaded into or crosslinked to form hydrogels for sustained topical delivery of ginsenosides [62,63].

4.Conclusions and Future Perspectives

Technical advancement enables mass production and purification of ginsenosides and elucidation of their functioning mechanisms.These ginsenosides are valuable drug candidates,especially for complex diseases such as cancer,diabetes and cardiovascular diseases.Despite the proven safety and efficacy of some ginsenosides,their applications are hindered by inferior pharmacokinetics such as low solubility,poor membrane permeability and metabolic instability.In order to improve the pharmacokinetics of ginsenosides,nanoparticles made of lipids,polymers,inorganic nanoparticles,and electrospun nanofibers have been used for systemic and local delivery of ginsenosides.Apart from being considered solely as drugs,ginsenosides which are amphiphilic and share structural similarities with cholesterol,have also been used as emulsifier or stabilizer for the construction of nanoparticles.

Fig.5.(A) SEM image of PLGA electrospun nanofibers loaded with ginsenoside Rg3 and coated with hyaluronic acid (HA);(B) In vitro cumulative release of Rg3 from Rg3/PLGA (squares) and Rg3/PLGA/HA (circles) electrospun fibers;(C) Scar elevation index (SEI) for evaluating dermal hypertrophy;(D) Photographic imaging of the status of wound healing;(E) The wound healing time of different groups.Adapted from Ref.[56]with permission from RSC.

Researches have shown that ginsenosides such as Rg3 and CK functioned synergistically with conventional chemotherapeutic agents including paclitaxel,cisplatin and cyclophosphamide.In addition to anti-proliferative effects,ginsenosides can also inhibit metastasis,angiogenesis and epithelial-to-mesenchymal transition;hence hold great promise as chemotherapy adjuvants.Codelivery of ginsenosides and conventional cancer therapeutic agents enables precise spatiotemporal control of the ratio of combination to maximize the additive or synergistic efficacies.In addition,the concern of nanotoxicity hinders the clinical translation of nanoparticle drug formulations,especially when the carrier materials are non-biodegradable.Hence,the pharmacokinetics,biodistribution and toxicity to major organs should be carefully examined for nanocarriers drug delivery systems of ginsenosides.Moreover,orally taken ginsenosides suffer from first-pass elimination which limits their bioavailability.Nanoparticle delivery systems that are designed with unique rheological and mucoadhesive properties,or modified with ligands that bind specific receptors expressed on enterocytes or M cells can assist ginsenosides in penetrating the mucus barrier,extending the residence time in GI tract,releasing drugs in a sustained and controlled manner,hence improving absorption and bioavailability of ginsenosides.Furthermore,in current literature,the local delivery of ginsenosides for wound healing are pre-casted electrospun nanofiber membranes and hydrogels.In addition to these strategies,injectable and selfhealing hydrogel wound dressing or skin grafts loaded with ginsenosides can be developed to better fit wounds with complex shapes and simplify the operation procedures.In sum,the current research efforts in the delivery of ginsenosides using nanoparticles and nanofibers laid the foundation for further development of more sophisticated delivery systems.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Grant Nos.22078264,21978235,21776227 and 21706211),the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No.2019JQ259),and Northwest University Graduate Innovation Project (Grant No.YZZ17128).