Bacterial responses to plant antimicrobials: the case of alkannin and shikonin derivatives

Alkannin, shikonin and their derivatives (A/S) are secondary metabolites produced in the roots of certain plants of the Boraginaceae family such as Lithospermum erythrorhizon Siebold & Zucc. and Alkanna tinctoria (L.) Tausch. These naphthoquinones express anti-cancer, wound healing, and antimicrobial activities. To study the interactions between endophytic bacteria isolated from A. tinctoria and the antimicrobials A/S, endophytic bacteria known to be resistant to the compounds were screened for their effect on A/S in liquid medium. Thereafter, the strain Pseudomonas sp. R-72008, was selected and tested for its ability to modify A/S in nutrient medium and minimal medium with A/S as sole carbon source. Bacterial growth was recorded, and high performance liquid chromatography-diode array and ultra-high performance liquid chromatography-electrospray ionization-mass spectrometry analyses were performed to detect and quantify metabolites. In nutrient medium inoculated with R-72008, a decrease in the amount of A/S monomers initially present was observed and correlated with an increase of A/S oligomers. Moreover, a significant decrease of initial A/S monomers in minimal medium was correlated with bacterial growth, showing for the first time that a bacterial strain, Pseudomonas sp. R-72008, was able to use the naphthoquinones A/S as sole carbon source. This study opens new perspectives on the interactions between bacteria and plant antimicrobials.

Expanding the Biological Properties of Alkannins and Shikonins: Their Impact on Adipogenesis and Life Expectancy in Nematodes

Alkannin, shikonin (A/S) and their derivatives are naturally occurring hydroxynaphthoquinones biosynthesized in some species of the Boraginaceae family. These natural compounds have been extensively investigated for their biological properties over the last 40 years, demonstrating a plethora of activities, such as wound healing, regenerative, anti-inflammatory, antitumor, antimicrobial and antioxidant. This study aims to extend the current knowledge by investigating the effects of various A/S compounds on two model systems, namely on 3T3-L1 pre-adipocytes and the nematode Caenorhabditis elegans. The former constitutes an established in vitro model for investigating anti-obesity and insulin-mimetic properties, while the latter has been widely used as a model organism for studying fat accumulation, lifespan and the anthelmintic potential. A set of chemically well-defined A/S derivatives were screened for their effect on pre-adipocytes to assess cell toxicity, cell morphology, and cell differentiation. The differentiation of pre-adipocytes into mature adipocytes was examined upon treatment with A/S compounds in the presence/absence of insulin, aiming to establish a structure-activity relationship. The majority of A/S compounds induced cell proliferation at sub-micromolar concentrations. The ester derivatives exhibited higher IC₅₀ values, and thus, proved to be less toxic to 3T3-L1 cells. The parent molecules, A and S tested at 1 μM resulted in a truncated differentiation with a reduced number of forming lipids, whereas compounds lacking the side chain hydroxyl group projected higher populations of mature adipocytes. In C. elegans mutant strain SS104, A/S enriched extracts were not able to inhibit the fat accumulation but resulted in a drastic shortage of survival. Thus, the set of A/S compounds were tested at 15 and 60 μg/ml in the wild-type strain N2 for their nematocidal activity, which is of relevance for the discovery of anthelmintic drugs. The most pronounced nematocidal activity was observed for naphthazarin and β,β-dimethyl-acryl-shikonin, followed by isovaleryl-shikonin. The latter 2 A/S esters were identified as the most abundant constituents in the mixture of A/S derivatives isolated from Alkanna tinctoria (L.) Tausch. Taken together, the findings show that the structural variations in the moiety of A/S compounds significantly impact the modulation of their biological activities in both model systems investigated in this study.

Electrospun wound dressings containing bioactive natural products: physico-chemical characterization and biological assessment

Background

Current research on skin tissue engineering has been focusing on novel therapies for the effective management of chronic wounds. A critical aspect is to develop matrices that promote growth and uniform distribution of cells across the wound area, and at the same time offer protection, as well as deliver drugs that help wound healing and tissue regeneration. In this context, we aimed at developing electrospun scaffolds that could serve as carriers for the bioactive natural products alkannin and shikonin (A/S).

Methods

A series of polymeric nanofibers composed of cellulose acetate (CA) or poly(ε-caprolactone) (PCL) and varying ratios of a mixture of A/S derivatives, has been successfully fabricated and their physico-chemical and biological properties have been explored.

Results

Scanning electron microscopy revealed a uniform and bead-free morphology for CA scaffolds, while for PCL beads along the fibers were observed. The average diameters for all nanofibers ranged between 361 ± 47 and 487 ± 88 nm. During the assessment of physicochemical characteristics, CA fiber mats exhibited a more favored profile, while the assessment of the biological properties of the scaffolds showed that CA samples containing A/S mixture up to 1 wt.% achieved to facilitate attachment, survival and migration of Hs27 fibroblasts. With respect to the antimicrobial properties of the scaffolds, higher drug-loaded (1 and 5 wt.%) samples succeeded in inhibiting the growth of Staphylococcus epidermidis and S. aureus around the edges of the fiber mats. Finally, carrying out a structure-activity relationship study regarding the biological activities (fibroblast toxicity/proliferation and antibacterial activity) of pure A/S compounds – present in the A/S mixture – we concluded that A/S ester derivatives and the dimeric A/S augmented cell proliferation after 3 days, whereas shikonin proved to be toxic at 500 nM and 1 μM and alkannin only at 1 μM. Additionally, alkannin, shikonin and acetyl-shikonin showed more pronounced antibacterial properties than the other esters, the dimeric derivative and the A/S mixture itself.

Conclusions

Taken together, these findings indicate that embedding A/S derivatives into CA nanofibers might be an advantageous drug delivery system that could also serve as a potential candidate for biomedical applications in the field of skin tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-021-00223-9.

Novel electrospun poly-hydroxybutyrate scaffolds as carriers for the wound healing agents alkannins and shikonins

The aim of this study was to investigate the potential of novel electrospun fiber mats loaded with alkannin and shikonin (A/S) derivatives, using as carrier a highly biocompatible, bio-derived, eco-friendly polymer such as poly[(R)-3-hydroxybutyric acid] (PHB). PHB fibers containing a mixture of A/S derivatives at different ratios were successfully fabricated via electrospinning. Αs evidenced by scanning electron microscopy, the fibers formed a bead-free mesh with average diameters from 1.25 to 1.47 μm. Spectroscopic measurements suggest that electrospinning marginally increases the amorphous content of the predominantly crystalline PHB in the fibers, while a significant drug amount lies near the fiber surface for samples of high total A/S content. All scaffolds displayed satisfactory characteristics, with the lower concentrations of A/S mixture-loaded PHB fiber mats achieving higher porosity, water uptake ratios, and entrapment efficiencies. The in vitro dissolution studies revealed that all samples released more than 70% of the encapsulated drug after 72 h. All PHB scaffolds tested by cell viability assay were proven non-toxic for Hs27 fibroblasts, with the 0.15 wt.% sample favoring cell attachment, spreading onto the scaffold surface, as well as cell proliferation. Finally, the antimicrobial activity of PHB meshes loaded with A/S mixture was documented for Staphylococcus epidermidis and S. aureus.

Endophytic Bacteria From the Roots of the Medicinal Plant Alkanna tinctoria Tausch (Boraginaceae): Exploration of Plant Growth Promoting Properties and Potential Role in the Production of Plant Secondary Metabolites

Alkannin and shikonin (A/S) are enantiomeric naphthoquinones produced in the roots of certain plants from the Boraginaceae family such as Lithospermum spp. and Alkanna spp. They possess antimicrobial, anti-tumoral and wound healing properties. The production of secondary metabolites by Alkanna tinctoria might be influenced by its endomicrobiome. To study the interaction between this medicinal plant and its bacterial endophytes, we isolated bacteria from the roots of wild growing Alkanna tinctoria collected near to Athens and Thessaloniki in Greece. Representative strains selected by MALDI-TOF mass spectrometry were identified by partial 16S rRNA gene sequence analysis. In total, 197 distinct phylotypes of endophytic bacteria were detected. The most abundant genera recovered were Pseudomonas, Xanthomonas, Variovorax, Bacillus, Inquilinus, Pantoea, and Stenotrophomonas. Several bacteria were then tested in vitro for their plant growth promoting activity and the production of cell-wall degrading enzymes. Strains of Pseudomonas, Pantoea, Bacillus and Inquilinus showed positive plant growth properties whereas those of Bacteroidetes and Rhizobiaceae showed pectinase and cellulase activity in vitro. In addition, bacterial responses to alkannin and shikonin were investigated through resistance assays. Gram negative bacteria were found to be resistant to the antimicrobial properties of A/S, whereas the Gram positives were sensitive. A selection of bacteria was then tested for the ability to induce A/S production in hairy roots culture of A. tinctoria. Four strains belonging to Chitinophaga sp., Allorhizobium sp., Duganella sp., and Micromonospora sp., resulted in significantly more A/S in the hairy roots than the uninoculated control. As these bacteria can produce cell-wall degrading enzymes, we hypothesize that the A/S induction may be related with the plant-bacteria interaction during colonization.

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

Drug delivery is considered a mature scientific and technological platform for producing innovative medicines with nanosystems composed of intelligent bio-materials that carry active pharmaceutical ingredients forming advanced drug delivery nanosystems (aDDnSs). Shikonin and its enantiomer alkannin are natural products that have been extensively studied in vitro and in vivo for, among others, their antitumor activity, and various efforts have been made to prepare shikonin-loaded drug delivery systems. This study is focused on chimeric aDDnSs and specifically on liposomal formulations combining three lipids (egg-phosphatidylcholine; dipalmitoyl phosphatidylcholine; and distearoyl phosphatidylcholine) and a hyperbranched polymer (PFH-64-OH). Furthermore, PEGylated liposomal formulations of all samples were also prepared. Calorimetric techniques and electron paramagnetic resonance were used to explore and evaluate the interactions and stability of the liposomal formulations, showing that the presence of hyperbranched polymers promote the overall stability of the chimeric aDDnSs based on the drug release profile enhancement. Furthermore, results showed that polyethylene glycol enhances drug stabilization inside the liposomes, forming a stable and promising carrier for shikonin with improved characteristics.

Metabolic profiling study of shikonin's cytotoxic activity in the Huh7 human hepatoma cell line

Shikonin and its enantiomer alkannin, which are natural products, have been extensively studied in vitro and in vivo for, among others, their antitumor activity. The investigation of the molecular pathways involved in their action is of interest, since they are not yet clearly defined. Metabolic profiling in cells can provide a picture of a cell's phenotype upon intervention, assisting in the elucidation of the mechanism of action. In this study, the cytotoxic effect of shikonin on a human hepatocarcinoma cell line was studied. Huh7 cells were treated with shikonin at 5 μM, and it was found that shikonin markedly inhibited cell growth. Metabolic profiling indicated alterations in the metabolic content of the cells and the culture media upon treatment, detecting the metabolic response of the cells. This study demonstrates the potential of metabolomics to improve knowledge on the mechanisms involved in shikonin's antitumor action.

Inhibition of c-MYC with involvement of ERK/JNK/MAPK and AKT pathways as a novel mechanism for shikonin and its derivatives in killing leukemia cells

Leukemia remains life-threatening despite remarkable advances in chemotherapy. The poor prognosis and drug resistance are challenging treatment. Novel drugs are urgently needed. Shikonin, a natural naphthoquinone, has been previously shown by us to be particularly effective towards various leukemia cell lines compared to solid tumors. However, the underlying mechanisms are still poorly understood. Here, we investigated shikonin and 14 derivatives on U937 leukemia cells. Four derivatives (isobutyrylshikonin, 2-methylbutyrylshikonin, isovalerylshikonin and β,β-dimethylacrylshikonin) were more active than shikonin. AnnexinV-PI analysis revealed that shikonins induced apoptosis. Cell cycle G1/S check point regulation and the transcription factor c-MYC, which plays a vital role in cell cycle regulation and proliferation, were identified as the most commonly down-regulated mechanisms upon treatment with shikonins in mRNA microarray hybridizations. Western blotting and DNA-binding assays confirmed the inhibition of c-MYC expression and transcriptional activity by shikonins. Reduction of c-MYC expression was closely associated with deregulated ERK, JNK MAPK and AKT activity, indicating their involvement in shikonin-triggered c-MYC inactivation. Molecular docking studies revealed that shikonin and its derivatives bind to the same DNA-binding domain of c-MYC as the known c-MYC inhibitors 10058-F4 and 10074-G5. This finding indicates that shikonins bind to c-MYC. The effect of shikonin on U937 cells was confirmed in other leukemia cell lines (Jurkat, Molt4, CCRF-CEM, and multidrug-resistant CEM/ADR5000), where shikonin also inhibited c-MYC expression and influenced phosphorylation of AKT, ERK1/2, and SAPK/JNK. In summary, inhibition of c-MYC and related pathways represents a novel mechanism of shikonin and its derivatives to explain their anti-leukemic activity.

Pistacia lentiscus Oleoresin: Virtual Screening and Identification of Masticadienonic and Isomasticadienonic Acids as Inhibitors of 11β-Hydroxysteroid Dehydrogenase 1

In traditional medicine, the oleoresinous gum of Pistacia lentiscus var. chia, so-called mastic gum, has been used to treat multiple conditions such as coughs, sore throats, eczema, dyslipidemia, and diabetes. Mastic gum is rich in triterpenes, which have been postulated to exert antidiabetic effects and improve lipid metabolism. In fact, there is evidence of oleanonic acid, a constituent of mastic gum, acting as a peroxisome proliferator-activated receptor γ agonist, and mastic gum being antidiabetic in mice in vivo. Despite these findings, the exact antidiabetic mechanism of mastic gum remains unknown. Glucocorticoids play a key role in regulating glucose and fatty acid metabolism, and inhibition of 11β-hydroxysteroid dehydrogenase 1 that converts inactive cortisone to active cortisol has been proposed as a promising approach to combat metabolic disturbances including diabetes. In this study, a pharmacophore-based virtual screening was applied to filter a natural product database for possible 11β-hydroxysteroid dehydrogenase 1 inhibitors. The hit list analysis was especially focused on the triterpenoids present in Pistacia species. Multiple triterpenoids, such as masticadienonic acid and isomasticadienonic acid, main constituents of mastic gum, were identified. Indeed, masticadienonic acid and isomasticadienonic acid selectively inhibited 11β-hydroxysteroid dehydrogenase 1 over 11β-hydroxysteroid dehydrogenase 2 at low micromolar concentrations. These findings suggest that inhibition of 11β-hydroxysteroid dehydrogenase 1 contributes to the antidiabetic activity of mastic gum.

Quantitative determination of alkannins and shikonins in endemic Mediterranean Alkanna species

The optical antipodes alkannin/shikonin (A/S) and their esters are potent pharmaceutical substances found in the roots of 150 Boraginaceous species. This study estimated and compared total and free A/S content and A/S enantiomeric ratio in roots of 11 Alkanna species (A. corcyrensis, A. tinctoria, A. pindicola, A. orientalis, A. methanaea, A. calliensis, A. graeca, A. primuliflora, A. stribrnyi, A. sieberi and A. noneiformis) growing wild in various Greek regions, to compare with cultivated species. It also re-characterized the chirality of A/S commercial samples, since most of them were misnamed by the providers. Several Alkanna species were collected (groups 1 and 3) and botanically identified, whereas some Alkanna species were cultivated from collected seeds (group 2). Free A/S and derivatives were extracted from the dried roots of Alkanna species and analyzed by high performance liquid chromatography-diode array detection (HPLC-DAD). For total A/S content the hexane extracts of Alkanna roots were hydrolyzed and analyzed by HPLC-DAD. Chirality determination and A/S enantiomeric ratio estimation was performed for several commercial samples by polarimetry,chiral LC-DAD and circular dichroism studies. Quantitative analysis revealed that A/S content varied from one region to another even within the same species. Most of the cultivated samples contained greater amounts of free and total A/S compared with the wild ones, wheras no difference was observed in A/S enantiomeric ratio. All the Alkanna samples tested contain mainly alkannin derivatives. Some of the examined Alkanna species of the Greek flora that are endemic to the Mediterranean area could serve as alternative sources for medicinally valuable A/S derivatives. Most of the commercial A/S samples tested were misnamed in terms of chirality and re-characterized.

Solid-phase extraction for purification of alkannin/shikonin samples and isolation of monomeric and dimeric fractions

Isohexenylnaphthazarins (IHN), commonly known as alkannins and shikonins (A/S), are potent pharmaceutical substances with a wide spectrum of wound healing, antimicrobial, anti-inflammatory, and antitumor activity. Purification of A/S is crucial for their use in pharmaceuticals and for biological experimentation. Dimeric and oligomeric A/S derivatives co-exist with the active monomeric ones in most of the samples produced either by (semi)-synthesis or biotechnologically or isolated from natural products. Oligomeric A/S derivatives have not been studied for biological activity hitherto and a method to isolate them is essential.In the present study, solid-phase extraction (SPE) was applied for purification of commercial samples and isolation of monomeric and oligomeric A/S fractions, testing several stationary phases. Sephadex LH-20 cartridges achieved efficient purification for commercial samples containing both monomeric and dimeric A/S derivatives and also separation and isolation of both pure monomeric and dimeric A/S fractions for biological experiments. A high-performance liquid chromatography-diode array detection method was applied for detection, identification and quantification of monomeric and oligomeric shikonin fractions.

Naturally Occurring Isohexenylnaphthazarins and Wound Healing: Experimental Study in Dogs

Background:

The healing efficacy of isohexenylnaphthazarins (IHN) has been well proved on chronic or contaminated wounds.

Objective:

To evaluate the wound healing activity of an experimental ointment containing IHN on acute and noncontaminated wounds in dogs. Methods: In each of six beagle dogs, four full-thickness skin defects were created bilaterally: one 2 × 2 cm defect on the lateral aspect of each arm for subjective evaluation, laser Doppler flowmetry (LDF), and planimetry and three 1.5 × 1.5 cm defects on opposite sides of the dorsal midline for histologic evaluation. Wounds on the left were treated with an ointment based on IHN and on the right with another based on petroleum jelly (Vaseline) and beeswax.

Results:

Wound size decreased significantly in both sides. The significantly increased percentage of epithelialization was higher ( p = .0274) in the petroleum jelly–treated wounds on day 20. Tissue perfusion (LDF) increased significantly bilaterally in the center of the wound but only in the IHN-treated side cranial to the wound. Histologically, angiogenesis was significantly higher ( p = .0431) on day 5 in the IHN-treated wounds compared with the petroleum jelly–treated wounds. Collagen production increased significantly bilaterally.

Conclusion:

The IHN-based ointment promoted some of the proliferative processes, but it did not enhance the overall wound healing of acute, surgically created wounds in dogs.

Preparative isolation and purification of alkannin/shikonin derivatives from natural products by high-speed counter-current chromatography

Alkannin and shikonin (A/S) and their derivatives have been found in the roots of several Boraginaceous species and are also produced through plant tissue cultures. The chiral compounds A/S are potent pharmaceutical substances with a wide spectrum of biological and pharmacological activities like wound healing, antimicrobial, anti-inflammatory, anticancer and antioxidant activity. High-speed counter-current chromatography (HSCCC) was applied for the first time to the separation, preparative isolation and purification of A/S and their esters from extracts of Alkanna tinctoria roots, as well as commercial samples. The constituents of HSCCC fractions and their purity were determined by high-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS), since DAD cannot detect oligomeric A/S derivatives that are present in most of the samples containing the respective monomeric derivatives. The purity of HSCCC fractions was compared with the one of fractions isolated by column chromatography (CC) using as stationary phases silica gel and Sephadex LH-20. As shown, the purity of monomeric alkannin/shikonin was greater by HSCCC than CC separation of commercial A/S samples.

Alkannins and shikonins: a new class of wound healing agents

Alkannins and Shikonins (A/S) are chiral-pairs of naturally occurring isohexenylnaphthazarins. They are found in the external layer of the roots of at least a hundred and fifty species that belong mainly to the genera Alkanna, Lithospermum, Echium, Onosma and Arnebia of the Boraginaceae family. Their occurrence in Jatropha glandulifera, a member of the Euphorbiaceae, should be considered as an exception. Pharmaceutical formulations with wound healing properties based on A/S have been in the market for many years. Although their wound-healing, anti-inflammatory, antimicrobial, antioxidant, antithrombotic and antitumor properties have been extensively documented, significant insight into their specific molecular pathways and mechanisms was hindered until recently. With the establishment of viable synthetic and biosynthetic routes of A/S and the synthesis of specific derivatives that were discovered the last few years, the effects of those compounds in the molecular-cell biology of human tissues in health and disease have just started being explored in depth, revealing a new class of drugs that hold promise as the basis for many valuable therapeutic targets. In the recent years, a wealth of new information arising from research efforts, on the wound healing properties of A/S has been accumulated. In this paper we review the findings and advances on the molecular and biological properties of A/S that promote wound healing.

Preparation and release studies of alkannin-containing microcapsules

Microcapsules containing the pharmaceutical substance alkannin were prepared by the solvent evaporation method to enhance alkannin stability (reduce photo-oxidation, polymerization), to decrease its hydrophobicity and to control its release rate. The effect of various parameters, such as the type of polymeric matrix, the type of surfactant used for microcapsules preparation and the addition of Pistacia lentiscus resin in the core, on the characteristics of the produced microcapsules and the release rate of alkannin were investigated experimentally. Among the polymers tested for matrix, ethylcellulose of viscosity 46cp was the most successful, while ethylcellulose 10cp gave microcapsules with good morphological characteristics but high release rate. Beeswax resulted in flocculation and P. lentiscus resin with or without colophony as the matrix resulted in compact particles with no pores and much slower release, but did not allow alkannin to release easily from the matrix. Sodium dodecyl sulfate resulted in microcapsules with desirable morphological and physicochemical characteristics, while acacia and tragacanth gums were not indicated as surfactants in alkannin microencapsulation since they gave a high release rate and a great extent of particle size, respectively. The incorporation of Pistacia lentiscus resin in the capsule core increased loading and microencapsulation efficiency. Ethylcellulose of 46cp viscosity with sodium dodecyl sulfate as surfactant had the best characteristics studied for alkannin microencapsulation. Finally, the dissolution rate of alkannin from microcapsules was studied in a simulated intestinal and gastric environment and an external environment. Alkannin-containing microcapsules with improved properties can be used internally and externally as a new drug-delivery system.

Simultaneous determination of monomeric and oligomeric alkannins and shikonins by high-performance liquid chromatography-diode array detection-mass spectrometry

Alkannin and shikonin (A/S) derivatives have been found in the roots of several Boraginaceous species and are produced through plant tissue cultures. The chiral compounds alkannins and shikonins are potent pharmaceutical substances with a wide spectrum of pharmacological activities such as wound healing, antimicrobial, anti-inflammatory, anticancer and antioxidant. Although oligomeric A/S derivatives have been detected in root extracts and commercial samples their detection and determination through high-performance liquid chromatography has not been reported. Therefore, in the present study a rapid, simple high-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) method was developed to detect, separate and determine monomeric and oligomeric/polymeric derivatives of alkannin/shikonin simultaneously for the first time. An optimization of HPLC-DAD parameters was performed. Both atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) modes were applied, in order to compare detection of monomeric and oligomeric A/S. Additionally, oligomeric A/S constituents in several samples were identified and the mode of A/S polymerization was proposed.

Analysis of alkannin derivatives from Alkanna species by high-performance liquid chromatography/photodiode array/mass spectrometry

Alkannin, shikonin (A/S) and their derivatives are enantiomeric hydroxynaphthoquinone red pigments found in the roots of almost 150 species of the Boraginaceae family. A/S have been shown to exhibit strong wound healing, antimicrobial, anti-inflammatory and antioxidant activities and recent extensive research has well established their antitumor properties. A/S and their derivatives comprise the active ingredients of several pharmaceutical and cosmetic preparations. Although A/S have been efficiently synthesized and have been produced by cell tissue cultures in high yield, most of the pharmaceutical preparations worldwide contain A/S extracted from the roots of Boraginaceous species, found in nature. In the present study, a high-performance liquid chromatography/photodiode array/mass spectrometry (HPLC/PDA/MS) method was established to identify monomeric hydroxynaphthoquinones of the alkannin series and other metabolites from Boraginaceous root extracts. This method can be applied for the identification of alkannin derivatives and other metabolites from Boraginaceous cell cultures, and also to determine active ingredients in pharmaceutical preparations containing A/S derivatives. A phytochemical investigation of the Alkanna genus grown in Greece was also performed. Fifty-three root samples belonging to 10 species of the genus Alkanna (A. calliensis, A. corcyrensis, A. graeca, A. methanaea, A. orientalis, A. pindicola, A. primuliflora, A. sieberi, A. stribrnyi and A. tinctoria) were collected from several regions of the Greek flora and analyzed for their constituent hydroxynaphthoquinones and other metabolites. In most of the above Alkanna samples tested, the main hydroxynaphthoquinones were determined to be beta,beta-dimethylacrylalkannin, isovalerylalkannin + alpha-methyl-n-butylalkannin and acetylalkannin. The hydroxynaphthoquinone constituents and their proportions were found to vary among Alkanna species. Unknown metabolites (not monomeric hydroxynaphthoquinones) were detected by HPLC-PDA-MS, while in several Alkanna species hydroxynaphthoquinones were detected for the first time.

Radical scavenging activity of Crocus sativus L. extract and its bioactive constituents

Radical scavenging activity is involved in aging processes, antiinflammatory, anticancer and wound healing activity. Hence, in the present study the DPPH radical scavenging activity of a natural product that possesses biological properties, an extract of Crocus sativus L. (saffron), grown in Crocos, Kozani (Greece), and some of its bioactive constituents (crocin, safranal) was studied. It was shown that a methanol extract of Crocus sativus exhibited high antioxidant activity, although it contains several active and inactive constituents. In trying to approximate a structure-activity relationship, two bioactive constituents of saffron extract were tested, namely crocin and safranal. Crocin showed high radical scavenging activity (50% and 65% for 500 and 1,000 ppm solution in methanol, respectively), followed by safranal (34% for 500 ppm solution). All the tested samples showed high radical scavenging activity, probably due to the ability to donate a hydrogen atom to the DPPH radical.Thus, saffron grown in Greece can be used promisingly in functional foods, drinks with antioxidant activity, in pharmaceutical and cosmetic preparations for their antioxidant activity and probably for their antiaging activity. Saffron can also be used internally in the form of powder or other pharmacotechnical formulae as a food supplement with antioxidant properties.

GC-MS analysis of penta- and tetra-cyclic triterpenes from resins of Pistacia species. Part I. Pistacia lentiscus var. Chia

Pistacia species contain oleoresins with bioactive triterpenes. In this study triterpenes, including minor components, were identified and quantified in both neutral and acidic fraction of Pistacia lentiscus var. Chia resin, grown exclusively in Chios island (Greece), collected traditionally, as well as by the use of stimulating agents (liquid collection). It was proved that these two resin samples were composed of several different minor triterpenes. In the traditional collection of the resin, 36 triterpenes were identified, 23 of which are new minor compounds (five in the acidic and eighteen in the neutral fraction). In the liquid collection resin eight compounds were identified in the acidic and 11 in the neutral fraction, while seven compounds were not contained in resin traditionally collected. The main triterpenes in both resin samples collected traditionally and by use of stimulating agents were in the following order: isomasticadienonic acid (24 and 22.5% w/w of triterpenic fraction respectively), masticadienonic acid (9.3 and 14.7% w/w of triterpenic fraction) and 28-norolean-17-en-3-one (19 and 36% w/w of triterpenic fraction respectively). The aim of this study was to compare the qualitative and quantitative composition of triterpenes in the resin samples collected using the traditional and new liquid techniques, and examine whether the collection technique influences the contained triterpenes in P. lentiscus var. Chia resin samples. Finally, since there is confusion on interpreting mass spectra of triterpenes we present an analytical review on the base peaks, main fragments and fragmentation mechanism/pattern of several skeleton penta- and tetra- cyclic triterpenes reported in P. lentiscus resin. Also, a biosynthetic route for triterpene skeletons contained in P. lentiscus resin was approached.

Analysis of antioxidant compounds in sweet orange peel by HPLC-diode array detection-electrospray ionization mass spectrometry

HPLC-diode array detection-electrospray ionization mass spectrometry was used to determine qualitatively and quantitatively the flavonoid content of several fractions and residues of extracts of Greek navel sweet orange peel (Citrus sinensis) from the region of southern Greece (Leonidi-Tripoli). The main groups of flavonoids found according to HPLC retention times, spectral data and literature references were polymethoxylated flavones, C-glycosylated flavones, O-glycosylated flavones, O-glycosylated flavanones, flavonols and phenolic acids and their derivatives. The ethyl acetate fraction which has been shown in previous work to possess the best radical scavenging activity among the others was found to contain C-glycosylated flavones, polymethoxylated flavones, O-glycosylated flavones, O-glycosylated flavanones, two phenolic acid derivatives and two unknown compounds, all in low concentrations. The group of C-glycosylated flavones was reported for the first time in the peel of Navel sweet orange. The C-glycosylated flavones found according to their spectral characteristics and literature were 6-C-beta-glucosyldiosmin, 6,8-di-C-glucopyranosylapigenin, 6,8-di-C-beta-glucosyldiosmin and two unknown. The results suggest that the ethyl acetate fraction of navel Citrus sinensis peel consists of significant antioxidant compounds and can be used as a food additive of natural origin or a pharmaceutical supplement using as a source of peel the byproducts of the orange juice industry.

Radical scavenging activity ofAlkanna tinctoria root extracts and their main constituents, hydroxynaphthoquinones

Alkannin and shikonin (A[sol ]S) are pharmaceutical substances with a wide spectrum of biological properties. Radical scavenging activity is involved in aging processes, antiinssammatory, anticancer and wound healing activities. Hence, in the present study the DPPH radical scavenging activity of alkannin and shikonin, both monomeric and oligomeric, and extracts of Alkanna tinctoria roots were studied and a structure-activity relationship was approximated. It was shown that both monomeric and oligomeric alkannin and shikonin and also A[sol ]S esters exhibited extremely high radical scavenging activity. The presence of the naphthoquinone moiety seems to be essential for that activity, while the side chain of A[sol ]S possibly plays a minor role. Esterification of A[sol ]S on the side chain hydroxyl group does not affect radical scavenging activity. Organic solvents and olive oil (extracted at room temperature) extracts of Alkanna tinctoria roots, which contain as active ingredients A[sol ]S esters, exhibited very good antiradical activity. Alkannin and shikonin and their esters and also extracts of Alkanna tinctoria roots could be used promisingly in pharmaceutical and cosmetic preparations for their radical scavenging activity and probably for their antiaging activity.

Structure determination of oligomeric alkannin and shikonin derivatives

Monomeric alkannin and shikonin (A/S) are potent pharmaceutical substances with a wide spectrum of biological activity and comprise the active ingredients for several pharmaceutical preparations. Therefore, the determination of the impurities, degradation products or byproducts in alkannin and shikonin samples is of great importance. Oligomeric alkannin and shikonin are formed during biosynthesis of these bioactive secondary metabolites in Boraginaceaous root plants, during tissue culture production of A/S, during alkaline hydrolysis of A/S esters and also thermal treatment of A/S. In the present study, a dimeric alkannin/shikonin compound was isolated by size exclusion chromatography from alkannin and shikonin commercial samples and its structure was determined by one- and two-dimensional NMR spectroscopy. The structure of the most abundant oligomeric species in these samples, a dimeric naphthoquinone, was established for the fi rst time, indicating that coupling of the side chain of one naphthoquinone unit with the aromatic ring of a second naphthoquinone leads to dimer formation. This type of coupling allows further oligomerization by leaving one isohexenyl side chain available at the second monomer unit.

GC-MS analysis of penta- and tetra-cyclic triterpenes from resins ofPistacia species. Part II.Pistacia terebinthus var. Chia

Pistacia species contain oleoresins with bioactive triterpenes. In this study triterpenes, including minor components, were identified and quantified in both neutral and acidic fractions of Pistacia terebinthus var. Chia resin, grown exclusively in Chios island (Greece), collected traditionally, as well as using stimulating agents (liquid collection). It was proved that these two resin samples were composed of several different minor triterpenes, while major constituents were similar but in different proportions. Compounds that differentiated two resin samples of P. lentiscus and P. terebinthus var. Chia, both traditionally collected, were detected, in order to identify the nature of resins present in archaeological materials. In the traditionally collected resin, 37 triterpenes were identified, 12 in the acidic and 25 in the neutral fraction. In the liquid collection resin 10 compounds were identified in the acidic and 23 in the neutral fraction, while 16 compounds were not contained in the traditionally collected resin. The main triterpenes in both resin samples collected traditionally and using stimulating agents were: isomasticadienonic acid (23.6 and 26.3% w[sol ]w of the triterpenic fraction, respectively), 28-norolean-17-en-3-one (16.3 and 17.5% w[sol ]w of the triterpenic fraction, respectively) and masticadienonic acid (5.8 and 6.0% w[sol ]w of the triterpenic fraction). In this study the qualitative and quantitative composition of triterpenes was compared in the Pistacia lentiscus and P. terebinthus var. Chia resin samples collected with the traditional and new liquid techniques, and also triterpenes in resins of P. terebinthus obtained by the traditional technique and using stimulating agents. The aim of the study was also to examine whether the collection technique influenced the triterpenes contained in P. terebinthus var. Chia resin samples.

Encapsulation of isohexenylnaphthazarins in cyclodextrins

Naturally occurring isohexenylnaphthazarins (IHN), such as Alkannin, Shikonin (A/S) and their derivatives, are potent pharmaceutical substances with a wide spectrum of biological activity. In the present study, inclusion complexes of alkannin and shikonin commercial samples and IHN derivatives in the form of an oily extract of Alkanna tinctoria roots were formed with beta-cyclodextrin (CD) and beta-HPCD. These complexes were investigated to evaluate the effect of complexation on their aqueous solubility, decoloration, and also the percentage of polymeric A/S and IHN derivatives enclosed in the CDs cavity, since these decrease the active monomeric IHN. Both beta-CD and beta-HPCD increased the aqueous solubility of A/S and IHN derivatives and thus inclusion complexes can be used as drug delivery systems for A/S in both internal (capsules, tablets) and external hydrophilic pharmaceutical and cosmetic preparations (creams, gels, sprays) with enhanced bioavailability. The inclusion complexes formed had a pale purple colour, contributing to the partial decoloration of the A/S and thus of the fi nal pharmaceutical preparations. Finally, CDs selectively included more monomeric and less polymeric IHN, compared with the initial each time sample that is encapsulated; thus inclusion complexes may present enhanced biological activity.

Study on isohexenylnaphthazarins polymerization in alkaline media

The chiral pair alkannin and shikonin (A/S) and their isohexenylnaphthazarin (IHN) esters, which are naturally occurring hydroxynaphthoquinones (HNQ), are potent pharmaceutical substances with a wide spectrum of biological activity. The stability of A/S and their derivatives during process and storage is crucial to their use as drugs, cosmetics and food additives. The influence of alkaline media and of IHN esters hydrolysis was experimentally investigated on IHN polymerization by size exclusion chromatography (SEC). It was proved that during IHN esters hydrolysis, polymeric A/S and IHN are formed. An optimization of the hydrolysis conditions of IHN esters was also approached in terms of polymerization. Hydrolysis of IHN from a pure mixture of pigments proved preferable to that of preliminary root extracts by means of IHN polymerization, even for analytical determination; non-polar solvents are proposed for the extraction of IHN from roots, followed by hydrolysis, aiming to minimize the polymeric IHN and A/S formed. It was also proved that polymerization of IHN in alkaline media and during hydrolysis of IHN esters proceeds through the intermediate formation of semiquinones; after acidification, coupling of semiquinones with phenoxyl radicals results in polymeric IHN structures.

Study on polymerization of the pharmaceutical substances isohexenylnaphthazarins

Polymerization of naturally occurring isohexenylnaphthazarins (IHN), such as alkannin, shikonin (A/S) and their derivatives, which are potent pharmaceutical substances, significantly affects their use in pharmaceuticals, cosmetics and as food colorants, because it leads to reduction of the lustre of their red coloration, a decrease in their solubility and reduces the active monomeric IHN derivatives. In the present study, the influence of several crucial variables (processing and storage) was experimentally investigated on IHN polymerization by size exclusion chromatography (SEC). Temperature and solvent polarity increased significantly the concentration of hydroxynaphthoquinone (HNQ) polymers, while air and light exposure conditions did not significantly affect IHN polymerization. Low temperatures are proposed for all processes of industrial production of pharmaceutical preparations containing IHN and HNQ. An optimization of the industrial conditions used for the preparation of pharmaceutical and cosmetic preparations containing IHN, maximizing the active monomeric IHN fraction, was performed.

Study on the enantiomeric ratio of the pharmaceutical substances alkannin and shikonin

The chiral pair alkannin and shikonin (A/S) are potent pharmaceutical substances with a wide spectrum of biological activity; their enantiomeric ratio does not influence the major biological activity studied hitherto. Nevertheless, in pharmaceutical development and approval of chiral drugs from the Health and Regulatory Authorities, full documentation of methods of analysis of enantiomeric drugs, is required in order to evaluate the enantiomeric purity of starting materials and final products and to control the stability of enantiomers in pharmaceutical formulations under several experimental conditions. In the present study, the enantiomeric ratio of A/S was determined in several commercial samples of alkannin and shikonin and also the proportion of A/S derivatives in several Alkanna root samples, which are all used as active ingredients in pharmaceuticals. Light and air proved not to influence the enantiomeric ratio of A/S on a shikonin commercial sample, and temperature also did not alter the A/S ratio on shikonin and alkannin commercial samples. Microencapsulation of alkannin and shikonin commercial samples in ethylcellulose microspheres and also molecular inclusion of a shikonin commercial sample in beta-hydroxypropyl-cyclodextrin, which are used as drug delivery systems, did not alter the A/S enantiomeric ratio.

Synthesis and release studies of shikonin-containing microcapsules prepared by the solvent evaporation method

Microcapsules, containing the pharmaceutical substance shikonin, were prepared by the solvent evaporation method in order to enhance shikonin stability (reduce photo-oxidation, polymerization), decrease its hydrophobicity and control its release rate. The effect of various parameters, such as type of polymer, type and concentration of surfactant, solvent volume and mastic gum (Pistacia lentiscus resin) content/concentration as core additive, on the characteristics of the produced microcapsules and the release rate of shikonin, were experimentally investigated. Among the polymers tested for matrix, ethylcellulose (EC) of viscosity 10 cp was the most successful; EC 100 cp and mastic gum result in larger/compact particles with no pores and much slower release. Sodium dodecyl sulphate (SDS) results in microcapsules with desirable morphological and physicochemical characteristics, while polyethylene glycol (PEG) and polyvinyl alcohol (PVA) are not indicated as surfactants in shikonin microencapsulation. Decreasing the solvent volume (dichloromethane) results in increased mean particle size and, thus, in slower release rate of shikonin, while the incorporation of mastic gum in the capsule core results in better control of shikonin release. Finally, the combination of EC 10 cp as matrix, mastic gum as core additive, low dichloromethane (DCM) volume and low SDS concentration results in microcapsules with the best characteristics in terms of efficiency, loading, release and particle size distribution.

Lipids of the hexane extract from the roots of medicinal boraginaceous species

The chemical compositions of hexane extracts of the lipid fraction of the roots of the medicinal Boraginaceous species Alkanna tinctoria, Onosma heterophylla, Macrotomia densiflora and Onosma hispidium are presented and their phytochemical relevance evaluated. The predominating fatty acids in all of the root lipids were stearic, palmitic, oleic, linoleic and gamma-linolenic acids, while the latter and stearidonic acid predominated in the seeds and leaves of various Boraginaceous species. The indigenous presence of methyl, ethyl and isopropyl esters of fatty acids, reported for the first time in the roots of higher plants, is considered to be of particular importance in the biosynthesis of fatty substances. The results suggest the use of fatty acids as chemotaxonomic markers for Boraginaceous species and the utilisation of Boraginaceous species as new commercial sources for fatty acids with valuable medicinal and nutritional properties.

Inhibitory activity of minor polyphenolic and nonpolyphenolic constituents of olive oil against in vitro low-density lipoprotein oxidation

The minor polyphenolic and nonpolyphenolic constituents of olive oil were examined, in various doses, against copper ion-induced low-density lipoprotein (LDL) oxidation and were found, in optimal doses (final concentration, 10 microM or 20 microM), to have remarkable biological activity, contributing to that previously reported for the major phenolic compounds. The main phytosterols, beta-sitosterol, campesterol, and stigmasterol, were found to have 43.8%, 37.3%, and 33.4% LDL mean protection (MP) activity, respectively, while free cholesterol exhibited 43.2% MP. The triterpenoid derivative compounds, ursolic acid, uvaol, and oleanolic acid, had similar MP activities of 50.5%, 46.8%, and 46.0%, respectively. Tocopherol (Toc) isomers exhibited an increasing effect in the following order: alpha-Toc (33.6%) < beta-Toc (36.1%) < gamma-Toc (42.9%) < delta-Toc (46.0%). The flavonoid polyphenols, quercetin, luteolin, and rutin, exhibited the highest activities--46.8%, 49.5%, and 53.7% MP, respectively, comparable to the 49.0% MP activity found for oleuropein. These findings indicate the relative independence of LDL protection activity in regard to structural differences among the involved compounds. A relation to the Mediterranean diet is also demonstrated.

Alkannin and shikonin: effect on free radical processes and on inflammation - a preliminary pharmacochemical investigation

Alkannin and shikonin, two natural products from Alkanna tinctoria and Lithospermum erhythrorhizon (Boraginaceae), are used in folk medicine where they are claimed to possess, among other properties, wound healing and anti-inflammatory activity. We investigated, together with the structurally related naphthazarin, their in vitro antioxidant and hydroxyl radical scavenging activity as well as their in vivo antiinflammatory activity. I was found that all examined compounds significantly inhibited in vitro lipid peroxidation of ra hepatic microsomal membranes, competed with DMSO for free hydroxyl radicals, and reduced inflammation (mouse paw edema induced by FCA) very efficiently. The examined compounds proved equal or superior to the common reference compounds for each of these properties. I is concluded that the claimed and/or proven actions of alkannin and shikonin are attributable at least partly to their intervention in free radical processes.

A new efficient route for multigram asymmetric synthesis of alkannin and shikonin

A short and convergent approach for the synthesis of alkannin, shikonin and shikalkin is presented. A Hauser-type annulation of cyanophthalide 26 with enone 7 affords the complete aromatic system in just one step with concomitant attachment of the entire side chain. Subsequent Corey's oxazaborolidine mediated asymmetric reduction of the above advanced intermediate, leads to the required isomer in high enantiomeric excess. Finally, a selective and high yielding deprotection protocol furnishes the title compounds as pure crystalline precipitates. Thus, a multigram synthesis of shikonin, alkannin and shikalkin is achieved in high yield and enantioselectivity.

Synthesis and cytogenetic effects of aminoquinone derivatives with a di- and a tripeptide

Quinones are of significant interest due to their important role in specific cellular functions. Quinoproteins are a big class of oxyreductive agents occurring in bacteria and other organisms. In this investigation derivatives of 2-amino-1,4-benzoquinone, 2-amino-1,4-naphthoquinone and 2-amino-5,8-dihydroxy-1,4-naphthoquinone with a di- and a tripeptide were prepared for first time. The effect of the synthesized compounds on sister chomatid exchange (SCE) rates and human lymphocyte proliferation kinetics on a molar basis was studied. Among these coupled products the most effective in inducing SCEs and depressing proliferation rate indices is the coupling product of 2-amino-1,4-naphthoquinone with the tripeptide GHK (10). Next in order of magnitude in inducing cytogenetic effects is 2-amino-1,4-naphthoquinone (2) and its coupling products with glycine and serine (4 and 5), while the rest displayed marginal activity.

The Chemistry and Biology of Alkannin, Shikonin, and Related Naphthazarin Natural Products

Wound healing properties of plant extracts that contain the naphthoquinone natural products alkannin (1) and shikonin (2) have been known for many centuries. More recently, the biological properties of 1, 2, and related derivatives have been demonstrated experimentally, and their production both by cell cultures and chemical synthesis has been studied extensively.

Inhibition of topoisomerase I by naphthoquinone derivatives

Alkannin and shikonin are naturally occurring naphthoquinones. We have tested several derivatives of the title compounds and we have found that naphthoquinones bearing at least one phenolic hydroxyl group are potent inhibitors of topoisomerase I. The ability of the tested compounds to complex Zn++ parallels with a few exceptions their topoisomerase I inhibition properties while their intercalation and redox properties do not.

Efficient Synthesis of Aminonaphthoquinones and Azidobenzohydroquinones: Mechanistic Considerations of the Reaction of Hydrazoic Acid with Quinones. An Overview

Parameters useful to predict and control the reaction outcome of conjugate addition of hydrazoic acid to quinones have been studied, and the optimum conditions for the efficient synthesis of aminonaphthoquinones and azidobenzohydroquinones are reported. The application of this reaction for the efficient formal synthesis of dephostatin is also presented.

A General Procedure for the Efficient Synthesis of (Alkylamino)naphthoquinones

Alkylamino derivatives of naphthazarine, juglone, and naphthoquinone have been synthesized via their corresponding bromo-analogues, in high yields, especially in the case of naphthazarins.