gIsolation and purification of acetylshikonin and β-acetoxyisovalerylshikonin from cell suspension cultures ofArnebia euchroma(Royle) Johnston using rapid preparative HPLC*

Naphthoquinones and triterpenoids from Arnebia euchroma (Royle) Johnst and their hypoglycemic and lipid-lowering effects

A new pentacyclic triterpenoid, 2-hydroxy-1-ene-hydroxyhopanone (19), and a new benzoxepin-5-one, 3-(4-methyl-3-penten-1-yl)-6-hydroxy-9-methoxy-2H-1-benzoxepin-5-one (25), along with 26 known compounds (1-18, 20-24, 26-28), were isolated from the roots of Arnebia euchroma (Royle) Johnst. The structures of the new compounds were elucidated by extensive spectroscopic analyses. The absolute configurations of shikonofurans 9-13 were determined by quantum chemical ECD calculations and CD spectra comparison for the first time. Pharmacological study revealed that naphthoquinones 1-5, 7, and 8 had obvious cytotoxicity toward human lung adenocarcinoma A549 cell line. Meanwhile, the hypoglycemic and lipid-lowering effects of isolated compounds were assessed by checking their inhibitory effects on key enzymes regulating glucose and lipid metabolism. Results showed that compounds 1, 3, 5, 6, 8, 18, and 19 could inhibit the activity of ATP-citrate lyase (ACL); compound 7 could inhibit the activity of acetyl-CoA carboxylase (ACC1); while compounds 8 and 19 showed inhibitory effects on protein tyrosine phosphatase 1B (PTP1B). Among them, the naphthoquinone 6, steroid 18, and triterpenoid 19 showed moderate inhibitory effects on ACL and PTP1B, but didn't exhibit obvious cytotoxicity. This study demonstrated that compounds 6, 18, and 19 show great promising for the development of new agents for the treatment of metabolic diseases.

Cytotoxic naphthoquinones from Arnebia densiflora (Nordm.) Ledeb and determining new apoptosis inducers

In this study, phytochemical composition of Arnebia densiflora (AD) was determined and cytotoxic effects of the n-hexane extract and compounds isolated from this species on various cell lines were investigated. By means of serial chromatographic studies, 6 naphthoquinone derivatives were yielded, which are isovalerylalkannin, α-methyl-n-butyl alkannin, acetylalkannin, β-acetoxy isovalerylalkannin, alkannin and a new compound: 4-hydroxy 4-methyl valeryl alkannin. Structures of the isolated compounds were elucidated using UV, IR, 1D-2D NMR, MS and CD methods. Cytotoxic effects of the extract and isolated alkannins were investigated on L929, HeLa, HEp-2 cells. AD and the isolated compounds demonstrated moderate to strong cytotoxic effects (IC₅₀ range: 4.92-172.35 µg/ml). The results of DNA fragmentation and caspase-3 activity studies on HeLa cells exhibited that AD and the naphthoquinones isolated from it caused cytotoxicity through induction of apoptosis.[Formula: see text].

Concurrent NP-HPTLC Determination of Shikonin and β,β-Dimethylacryl Shikonin in Arnebia benthamii

Naphthoquinones are important class of molecules found as a natural red color pigments in roots of Arnebia benthamii (Wall. ex G. Don) L M. Johnston. The aim of present investigation is to develop and validates a simple, cost-effective and reliable method for quantification of these compounds. Therefore, a normal phase-high performance thin-layer chromatography (NP-HPTLC) method for concurrent determination of shikonin and β,β-dimethylacryl shikonin in A. benthamii was established. Method development of naphthoquinones in the methanol extract was done using hexane-ethyl acetate-methanol (40:7.5:2.5, v/v/v) solvent system at 520 nm. The developed method showed good band separation for shikonin (Rf, 0.37) and β,β-dimethylacryl shikonin (Rf, 0.58). The linearity ranged between 100 and 8,000 ng spot(-1) with an average recovery of >97% in both cases. The results showed reproducible intraday and interday precision (<2.0% RSD) in quantification of naphthoquinones. The limits of detection are 12.96 and 14.65 ng spot(-1) while the limits of quantification are 39.27 and 44.39 ng spot(-1) for shikonin and β,β-dimethylacryl shikonin, respectively. The developed method is reliable, fast, easy to follow and economic in concurrent assessment of shikonin and β,β-dimethylacryl shikonin in A. benthamii root samples. In addition, it seems to be first report for identification and quantification of β,β-dimethylacryl shikonin from the A. benthamii.

Biotechnological approaches to the production of shikonins: a critical review with recent updates

Shikonins are commercially important secondary compounds, known for array of biological activities such as antimicrobial, insecticidal, antitumor, antioxidants, etc. These compounds are usually colored and therefore have application in food, textiles and cosmetics. Shikonin and its derivatives, which are commercially most important of the naphthoquinone pigments, are distributed among members of the family Boraginaceae. These include different species of Lithospermum, Arnebia, Alkanna, Anchusa, Echium and Onosma. The growing demand for plant-based natural products has made this group of compounds one of the enthralling targets for their in vitro production. The aim of this review is to highlight the recent progress in production of shikonins by various biotechnological means. Different methods of increasing the levels of shikonins in plant cells such as selection of cell lines, optimization of culture conditions, elicitation, in situ product removal, genetic transformation and metabolic engineering are discussed. The experience of different researchers working worldwide on this aspect is also considered. Further, to meet market demand, the needs for continuous and reliable production systems, as well as future prospects, are included.

Enhanced production of napthoquinone metabolite (shikonin) from cell suspension culture of Arnebia sp. and its up-scaling through bioreactor

Cell culture in shake flask and air-lift bioreactor was carried out to exploit the potential of Arnebia sp. for napthoquinone metabolite production. Cell suspension cultures of Arnebia were established from friable callus in liquid MS medium supplemented with 6-benzylaminopurine (BAP) (10 μM) and indole-3-butyric acid (IBA) (5 μM). Growth kinetic studies were done by using settled cell volume and fresh/dry cell weight method. Suspension cultures were maintained by sub-culturing at 10 days interval. A two-stage culture system is employed using growth medium (GM) and modified M9 medium (production medium) for cell biomass and naphthoquinone pigment production, respectively. Results showed that cultivation of cells under dark conditions at room temperature (25 ± 2 °C) enhanced the cell biomass from 100 to 625 g l⁻¹. The pigment production was also found to be increased in dark conditions at room temperature. Alkaline pH found to have positive effect on pigment yield. In case of M9 medium constituents, absence of Na₂SO₄ does not affect the pigment yield. The current approaches have the cumulative effect to meet an increased level of (25.5 μg/ml) metabolite production in air-lift bioreactor.

Liquid perfluorodecalin application for in situ extraction and enhanced naphthoquinones production in Arnebia euchroma cell suspension cultures

Suspension cultures of Arnebia euchroma supported with liquid perfluorodecalin (PFD) degassed, aerated, or ethylene-saturated were investigated as a novel in situ extraction system for enhanced alkannin/shikonin production. Simultaneously, the effect of PFD applied as the liquid gas carrier on the growth of A. euchroma biomass was studied. The similar dry (4-fold) and fresh (7-fold) biomass increase was observed in the control (without PFD addition) and supplemented with PFD-degassed or PFD-aerated cultures while PFD-ethylene application impeded cell growth. The highest total of alkannin/shikonin production (23.23 mg flask⁻¹) was observed when PFD-aerated has been used and it resulted in about 50 % higher yield of alkannin/shikonin compared with the control culture. Chiral HPLC analysis revealed that in cultures supported with PFD, both alkannin and shikonin were produced. Their mutual ratio varied depending on culture conditions, and the accumulation of alkannin prevailed under almost all culture conditions. PFD has proved to be exceptionally efficient and cell-safe solvent for the in situ extraction of naphthoquinone red pigments without exerting any detrimental effects on cell growth. Extracellularly secreted red naphthoquinones were easily dissolved and extracted from the PFD phase, which can be regenerated and reused (e.g., in continuous culture system).

Callus culture of Echium italicum L. towards production of a shikonin derivative

Callus induction and proliferation of Echium italicum L. (Boraginaceae) were investigated using cotyledon, hypocotyl and root explants. Calli were initiated and established using B5, LS, 1/2LS and White media supplemented with different auxins, including 2,4-dichlorophenoxyacetic acid (2,4-D), indole-3-acetic acid (IAA) and 1-naphthaleneacetic acid (NAA) in combination with kinetin. The maximum pigmented callus induction (100%) was observed in the White medium. The n-hexane extract of proliferated callus tissues were analysed by TLC and HPLC. The major secondary metabolite was separated by preparative HPLC and its structure was elucidated by UV, ¹H and ¹³C-NMR spectroscopy. As a result, shikonin acetate was identified by various spectroscopic methods from callus culture of E. italicum. These findings highlight the shikonin production potential of the E. italicum callus, which may be considered as a new source for the production of shikonin and its derivatives for industrial use.

Identification of shikonin and its ester derivatives from the roots of Echium italicum L

Nine shikonin pigments: shikonin (S), acetylshikonin (AS), propionylshikonin (PS), isobutyrylshikonin (IBS), tiglylshikonin (TS), 3,3-dimethylacrylshikonin (DAS), angelylshikonin (ANS), 2-methyl-n-butyrylshikonin (MBS) and isovalerylshikonin (IVS) were identified in the root epidermis of Echium italicum L. for the first time. A new thin-layer chromatographic (TLC) method for the separation of enantiomers alkannin and shikonin proved only shikonin after saponification of the root extract, and was afterwards esterified with the corresponding acyl chloride to acquire seven standard compounds (all except ANS). The developed isocratic high-peformance liquid chromatographic (HPLC) methods with VIS and mass spectrometry (MS) detection, allowed for the first time simultaneous separation of all nine compounds with similar structures including positional and geometric isomers in a short time. Structures of the main five compounds (AS, IBS, ANS, MBS, IVS) isolated from the extract by a new semi-preparative HPLC on C18 have additionally been confirmed by (1)H and (13)C nuclear magnetic resonance spectra, which were reported for AS and MBS for the first time.