Advanced Drug Delivery Nanosystems for Shikonin: A Calorimetric and Electron Paramagnetic Resonance Study

Promising Nanomedicines of Shikonin for Cancer Therapy

Malignant tumor, the leading cause of death worldwide, poses a serious threat to human health. For decades, natural product has been proven to be an essential source for novel anticancer drug discovery. Shikonin (SHK), a natural molecule separated from the root of Lithospermum erythrorhizon, shows great potential in anticancer therapy. However, its further clinical application is significantly restricted by poor bioavailability, adverse effects, and non-selective toxicity. With the development of nanotechnology, nano drug delivery systems have emerged as promising strategies to improve bioavailability and enhance the therapeutic efficacy of drugs. To overcome the shortcoming of SHK, various nano drug delivery systems such as liposomes, polymeric micelles, nanoparticles, nanogels, and nanoemulsions, were developed to achieve efficient delivery for enhanced antitumor effects. Herein, this review summarizes the anticancer pharmacological activities and pharmacokinetics of SHK. Additionally, the latest progress of SHK nanomedicines in cancer therapy is outlined, focusing on long circulation, tumor targeting ability, tumor microenvironment responsive drug release, and nanosystem-mediated combination therapy. Finally, the challenges and prospects of SHK nanomedicines in the future clinical application are spotlighted.

Shikonin, a naphthalene ingredient: Therapeutic actions, pharmacokinetics, toxicology, clinical trials and pharmaceutical researches

BACKGROUND

Shikonin is one of the major phytochemical components of Lithospermum erythrorhizon (Purple Cromwell), which is a type of medicinal herb broadly utilized in traditional Chinese medicine. It is well established that shikonin possesses remarkable therapeutic actions on various diseases, with the underlying mechanisms, pharmacokinetics and toxicological effects elusive. Also, the clinical trial and pharmaceutical study of shikonin remain to be comprehensively delineated.

PURPOSE

The present review aimed to systematically summarize the updated knowledge regarding the therapeutic actions, pharmacokinetics, toxicological effects, clinical trial and pharmaceutical study of shikonin.

METHODS

The information contained in this review article were retrieved from some authoritative databases including Web of Science, PubMed, Google scholar, Chinese National Knowledge Infrastructure (CNKI), Wanfang Database and so on, till August 2021.

RESULTS

Shikonin exerts multiple therapeutic efficacies, such as anti-inflammation, anti-cancer, cardiovascular protection, anti-microbiomes, analgesia, anti-obesity, brain protection, and so on, mainly by regulating the NF-κB, PI3K/Akt/MAPKs, Akt/mTOR, TGF-β, GSK3β, TLR4/Akt signaling pathways, NLRP3 inflammasome, reactive oxygen stress, Bax/Bcl-2, etc. In terms of pharmacokinetics, shikonin has an unfavorable oral bioavailability, 64.6% of the binding rate of plasma protein, and enhances some metabolic enzymes, particularly including cytochrome P450. In regard to the toxicological effects, shikonin may potentially cause nephrotoxicity and skin allergy. The above pharmacodynamics and pharmacokinetics of shikonin have been validated by few clinical trials. In addition, pharmaceutical innovation of shikonin with novel drug delivery system such as nanoparticles, liposomes, microemulsions, nanogel, cyclodextrin complexes, micelles and polymers are beneficial to the development of shikonin-based drugs.

CONCLUSIONS

Shikonin is a promising phytochemical for drug candidates. Extensive and intensive explorations on shikonin are warranted to expedite the utilization of shikonin-based drugs in the clinical setting.

Grapevine stilbenoids as natural food preservatives: calorimetric and spectroscopic insights into the interaction with model cell membranes

Food contamination with pathogenic microorganisms, such as Listeria monocytogenes, Salmonella enterica, Staphylococcus aureus and Bacillus cereus, is a common health concern. Natural products, which have been the main source of antimicrobials for centuries, may represent a turning point in alleviating the antibiotic crisis, and plant polyphenolic compounds are considered a promising source for new antibacterial agents. Resveratrol and resveratrol-derived monomers and oligomers (stilbenoids) have been shown to exert a variegated pattern of efficacy as antimicrobials depending on both the polyphenols' structure and the nature of the microorganisms, and the bacterial cell membrane seems to be one of their primary targets.In this scenario and based on the thermodynamic information reported in the literature about cell membranes, this study aimed at the investigation of the direct interaction of selected stilbenoids with a simple but informative model cell membrane. Three complete stilbenoid "monomer/dimer/dehydro-dimer" sets were chosen according to different geometries and substitution patterns. Micro-DSC was performed on 2 : 3 DPPC : DSPC small unilamellar vesicles with incorporated polyphenols at physiological pH and the results were integrated using complementary NMR data. The study highlighted the molecular determinants and mechanisms involved in the stilbenoid-membrane interaction, and the results were well correlated with the microbiological evidence previously assessed.

Build-Up of a 3D Organogel Network within the Bilayer Shell of Nanoliposomes. A Novel Delivery System for Vitamin D3: Preparation, Characterization, and Physicochemical Stability

The inherent thermodynamic instability of liposomes during production and storage has limited their widespread applications. Therefore, a novel structure of food-grade nanoliposomes stabilized by a 3D organogel network within the bilayer shell was developed through the extrusion process and successfully applied to encapsulate vitamin D₃. A huge flocculation and a significant reduction of zeta potential (-17 mV) were observed in control nanoliposomes (without the organogel shell) after 2 months of storage at 4 °C, while the sample with a gelled bilayer showed excellent stability with a particle diameter of 105 nm and a high negative zeta potential (-63.4 mV), even after 3 months. The development of spherical vesicles was confirmed by TEM. Interestingly, the gelled bilayer shell led to improved stability against osmotically active divalent salt ions. Electron paramagnetic resonance confirmed the higher rigidity of the shell bilayer upon gelation. The novel liposome offered a dramatic increase in encapsulation efficiency and loading of vitamin D₃ compared to those of control.

Structure, thermotropic phase behavior and membrane interaction of N-acyl-β-alaninols. Homologs of stress-combating N-acylethanolamines

β-Alaninol and its derivatives were reported to exhibit interesting biological and pharmacological activities and showed potential application in formulating drug delivery vehicles. In the present study, we report the synthesis and characterization of N-acyl-β-alaninols (NABAOHs) bearing saturated acyl chains (n = 8-20) with respect to thermotropic phase behavior, supramolecular organization and interaction with diacylphosphatidylcholine, a major membrane lipid. Results obtained from DSC and powder XRD studies revealed that the transition temperatures (T_t), transition enthalpies (ΔH_t), transition entropies (ΔS_t) and d-spacings of NABAOHs show odd-even alteration. A linear dependence was observed in the values of ΔH_t and ΔS_t on the acyl chain length, independently for even and odd acyl chains in both dry and hydrated states; further, the even chainlength molecules exhibited higher values than the odd chainlength series. The crystals structures of N-lauroyl-β-alaninol and N-palmitoyl-β-alaninol, solved in monoclinic system in the P21/c space group, show that the NABAOHs adopt a tilted bilayer structure. A number of NH⋯O, O-H⋯O, and C-H⋯O hydrogen bonds between the hydroxyl and amide moieties of the head groups of NABAOH molecules belonging to adjacent and opposite layers stabilize the overall supramolecular organization of the self-assembled bilayer system. DSC studies on the interaction of N-myristoyl-β-alaninol (NMBAOH) with dimyristoylphosphatidylcholine (DMPC) indicate that these two lipids mix well up to 45 mol% NMBAOH, whereas phase separation was observed at higher contents of NMBAOH. Transmission electron microscopic studies reveal that mixtures containing 20-50 mol% NMBAOH form stable ULVs of 90-150 nm diameter, suitable for use in drug delivery applications.

Influence of Free Fatty Acids on Lipid Membrane-Nisin Interaction

The influence of free fatty acids (FFAs) on the nisin-membrane interaction was investigated through micro-DSC and fluorescence spectroscopy. A simple but informative model membrane was prepared (5.7 DMPC:3.8 DPPS:0.5 DOPC molar ratio) by considering the presence of different phospholipid headgroups in charge and size and different phospholipid tails in length and unsaturation level, allowing the discrimination of the combined interaction of nisin and FFAs with the single phospholipid constituents. The effects of six FFAs on membrane stability were evaluated, namely two saturated FFAs (palmitic acid and stearic acid), two monounsaturated FFAs (cis-unsaturated oleic acid and trans-unsaturated elaidic acid) and two cis-polyunsaturated FFAs (ω-6 linoleic acid and ω-3 docosahexaenoic acid). The results permitted assessment of a thermodynamic picture of such interactions which indicates that the peptide-membrane interaction does not overlook the presence of FFAs within the lipid bilayer since both FFAs and nisin are able to selectively promote thermodynamic phase separations as well as a general lipid reorganization within the host membrane. Furthermore, the magnitude of the effects may be different depending on the FFA chemical structure as well as the membrane lipid composition.

DOTA Glycodendrimers as Cu(II) Complexing Agents and Their Dynamic Interaction Characteristics toward Liposomes

Copper (Cu)(II) ions, mainly an excess amount, play a negative role in the course of several diseases, like cancers, neurodegenerative diseases, and the so-called Wilson disease. On the contrary, Cu(II) ions are also capable of improving anticancer drug efficiency. For this reason, it is of great interest to study the interacting ability of Cu(II)-nanodrug and Cu(II)-nanocarrier complexes with cell membranes for their potential use as nanotherapeutics. In this study, the complex interaction between 1,4,7,10-tetraazacyclododecan-N,N',N'',N'''-tetraacetic acid (DOTA)-functionalized poly(propyleneimine) (PPI) glycodendrimers and Cu(II) ions and/or neutral and anionic lipid membrane models using different liposomes is described. These interactions were investigated via dynamic light scattering (DLS), ζ-potential (ZP), electron paramagnetic resonance (EPR), fluorescence anisotropy, and cryogenic transmission electron microscopy (cryo-TEM). Structural and dynamic information about the PPI glycodendrimer and its Cu(II) complexes toward liposomes was obtained via EPR. At the binding site Cu-N₂O₂ coordination prevails, while at the external interface, this coordination partially weakens due to competitive dendrimer-liposome interactions, with only small liposome structural perturbation. Fluorescence anisotropy was used to evaluate the membrane fluidity of both the hydrophobic and hydrophilic parts of the lipid bilayer, while DLS and ZP allowed us to determine the distribution profile of the nanoparticle (PPI glycodendrimer and liposomes) size and surface charge, respectively. From this multitechnique approach, it is deduced that DOTA-PPI glycodendrimers selectively extract Cu(II) ions from the bioenvironment, while these complexes interact with the liposome surface, preferentially with even more negatively charged liposomes. However, these complexes are not able to cross the cell membrane model and poorly perturb the membrane structure, showing their potential for biomedical use.

Physical interactions between marine phytoplankton and PET plastics in seawater

Plastics are the most abundant marine debris globally dispersed in the oceans and its production is rising with documented negative impacts in marine ecosystems. However, the chemical-physical and biological interactions occurring between plastic and planktonic communities of different types of microorganisms are poorly understood. In these respects, it is of paramount importance to understand, on a molecular level on the surface, what happens to plastic fragments when dispersed in the ocean and directly interacting with phytoplankton assemblages. This study presents a computer-aided analysis of electron paramagnetic resonance (EPR) spectra of selected spin probes able to enter the phyoplanktonic cell interface and interact with the plastic surface. Two different marine phytoplankton species were analyzed, such as the diatom Skeletonema marinoi and dinoflagellate Lingulodinium polyedrum, in absence and presence of polyethylene terephthalate (PET) fragments in synthetic seawater (ASPM), in order to in-situ characterize the interactions occurring between the microalgal cells and plastic surfaces. The analysis was performed at increasing incubation times. The cellular growth and adhesion rates of microalgae in batch culture medium and on the plastic fragments were also evaluated. The data agreed with the EPR results, which showed a significant difference in terms of surface properties between the diatom and dinoflagellate species. Low-polar interactions of lipid aggregates with the plastic surface sites were mainly responsible for the cell-plastic adhesion by S. marinoi, which is exponentially growing on the plastic surface over the incubation time.

Micro-characterization of modified microemulsions loaded with gossypol, pure and extracted from cottonseed

Microemulsions (MEs) have gained increasing interest as carriers of hydrophobic bioactives in the last decades. However, it is still difficult to control the uptake and the release of bioactives directly extracted from plants. In this study, modified ME nanodroplets (nano-sized self-assembled liquids, NSSLs) were employed as extraction medium of gossypol, a toxic component of cottonseed. Loading was performed using both pure gossypol, and gossypol obtained by extraction from cottonseed. We achieved two goals: i) remove gossypol from cottonseed to obtain cotton-oil free of gossypol; and ii) extract gossypol directly into a nano-delivery vehicle for biomedical purposes. Structural and dynamical information on the unloaded and gossypol-loaded NSSL systems were obtained by self-diffusion nuclear magnetic resonance, SD-NMR, and spin-probe electron paramagnetic resonance (EPR) studies. The results showed that NSSL formed fluid water-in-oil (W/O) nano domains at the lowest water contents; a more viscous bicontinuous structure at comparable oil and water contents, and, finally, oil-in-water (O/W, micellar-like) at the higher concentration of water. These micellar-like structures were more fluid at the external hydrated surface, as demonstrated by SD-NMR, while the lipidic region tested by EPR revealed an increasing packing. In all these structures, gossypol mainly localized in the lipophilic region close to the water interface. Overall, SD-NMR and EPR provided complementary information, helping to clarify the structural properties of NSSLs formed at different water contents and their ability to incorporate gossypol also directly from cottonseed-NSSL mixtures.

Insight into the antitumor activity of carbosilane Cu(ii)-metallodendrimers through their interaction with biological membrane models

Current cancer therapies present serious drawbacks including severe side-effects and development of drug resistance. Strategies based on nanosized metallodrugs combine the structural diversity and non-classical modes of action of metal complexes with the selectivity arising from the unique interaction of nanoparticles with biological membranes. A new family of water-soluble copper(ii) carbosilane metallodendrimers was synthesized and characterized as a nanotechnological alternative to current therapies. The interactions occurring over time between the dendrimers, at different generations (G₀ to G₂) and with different Cu(ii) counter-ions (nitrate vs. chloride), and cell-membrane models (cethyl-trimethylammonium bromide (CTAB) micelles and lecithin liposomes) were investigated using a computer-aided analysis of the electron paramagnetic resonance (EPR) spectra. The EPR analysis provided structural and dynamical information on the systems indicating that the increase in generation and the change of the Cu(ii) contra-ion - from nitrate to chloride - produce an increased relative amount and strength of interaction of the dendrimer with the model membranes. Interestingly, the stabilization effect produced a lower toxicity towards cancer cells. The cytotoxic effect of Cu(ii) metallodendrimers was verified by an in vitro screening in a selection of tumor cell lines, revealing the impact of multivalency on the effectivity and selectivity of the metallodrugs. As a proof-of-concept, first-generation dendrimer G₁-Cu(ONO₂)₂ was selected for in-depth in vitro and in vivo antitumor evaluation towards resistant prostate cancer. The Cu(ii)-metallodendrimers produced a significant tumor size reduction with no signs of toxicity during the experiment, confirming their promising potential as anticancer metallodrugs.

Structural Characterization of Reconstituted Bioactive-Loaded Nanodomains after Embedding in Films Using Electron Paramagnetic Resonance and Self-Diffusion Nuclear Magnetic Resonance Techniques

Pharmaceutical applications of microemulsions (MEs) as drug delivery vehicles are recently gaining scientific and practical interests. Most MEs are able to solubilize bioactive molecules, but, at present, they cannot guarantee either controlled release of the drugs or significant advantage in the bioavailability of the bioactives. This study proposes to incorporate the modified ME structures, or nanodomains, into a natural polymeric film, to be used as a stable and capacious reservoir of drug-loaded nanodomains. These nanodomain-loaded films may release the nanodroplets along with the drug molecules in a slow and controlled way. Gellan gum, an anionic polysaccharide, was used in aqueous solution as the film former, and curcumin, hydrophobic polyphenol, served as the guest molecule in the loaded systems. Films were prepared by using empty and curcumin-loaded MEs. It is imperative to verify the persistence of the ME structure upon the dissolution of the film mimicking its behavior when in contact with a human physiological aqueous environment via reaching the cell membranes. For this purpose, the films were dissolved, and the reconstituted ME structure was compared with the ME structure before film formation. Characterization of these structures, before and after dissolution, was achieved using electron paramagnetic resonance (EPR) and self-diffusion nuclear magnetic resonance (SD-NMR) techniques. Specific spin probes were inserted in the system, and a computer-aided analysis of the EPR spectra was performed to provide information on nanodomain microstructure assemblies. In addition, the SD-NMR profile of each component was analyzed to extract information on the diffusivity of the ME components before film formation and after ME reconstitution. The EPR and SD-NMR results were in good agreement to each other. The most important finding was that, after film dissolution, the ME nanodomains were reversibly and spontaneously reformed. It was also found that the film did not perturb the ME-nanodomain structure embedded in it. The film remained transparent and the bioactive curcumin was easily solubilized into the ME-droplet/water interface even after film dissolution. The combined techniques confirmed that the film constituted by bioactive-loaded MEs can serve as novel drug delivery vehicles.

Electron Paramagnetic Resonance and Small-Angle X-ray Scattering Characterization of Solid Lipid Nanoparticles and Nanostructured Lipid Carriers for Dibucaine Encapsulation

Dibucaine (DBC) is one of the most potent long-acting local anesthetics, but it also has significant toxic side effects and low water solubility. Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) have been proposed as drug-delivery systems to increase the bioavailability of local anesthetics. The purpose of the present study was to characterize SLNs and NLCs composed of cetyl palmitate or myristyl myristate, a mixture of capric and caprylic acids (for NLCs only) plus Pluronic F68 prepared for the encapsulation of DBC. We intended to provide a careful structural characterization of the nanoparticles to identify the relevant architectural parameters that lead to the desirable biological response. Initially, SLNs and NLCs were assessed in terms of their size distribution, morphology, surface charge, and drug loading. Spectroscopic techniques (infrared spectroscopy and electron paramagnetic resonance, EPR) plus small-angle X-ray scattering (SAXS) provided information on the interactions between nanoparticle components and their structural organization. The sizes of nanoparticles were in the 180 nm range with low polydispersity and negative zeta values (-25 to -46 mV). The partition coefficient of DBC between nanoparticles and water at pH 8.2 was very high (>10⁴). EPR (with doxyl-stearate spin labels) data revealed the existence of lamellar arrangements inside the lipid nanoparticles, which was also confirmed by SAXS experiments. Moreover, the addition of DBC increased the molecular packing of both SLN and NLC lipids, indicative of DBC insertion between the lipids, in the milieu assessed by spin labels. Such structural information brings insights into understanding the molecular organization of these versatile drug-delivery systems which have already demonstrated their potential for therapeutic applications in pain control.