Discrimination of Baphicacanthis Cusiae Rhizoma et radix and its adulterant species and establishment of an assay method for quality control

BACKGROUND

Baphicacanthis Cusiae Rhizoma et Radix, commonly known as Nan-Ban-Lan-Gen (NBLG), is an essential traditional Chinese medicine that possesses diverse bioactivities, particularly noteworthy for its antiviral properties. Although NBLG has been listed in the Chinese Pharmacopoeia as an independent Chinese medicine, the establishment of a comprehensive quality standard for NBLG remains elusive. The absence of assay for marker compound in its quality standards has led to the lack of corresponding quality control measures for NBLG-containing preparations, and its discrimination from adulterant species in the market which thereby can significantly impact the efficacy and safety of NBLG-containing products.

METHODS

Ultra-high performance liquid chromatography (UHPLC) coupled with quadrupole-time-of-flight mass spectrometry (Q-TOF-MS) was employed for comprehensive profiling of the chemical constituents of NBLG, the stem of Baphicacanthus cusia (Nees) Bremek (NBLJ), and the roots of Isatis indigotica Fort. (Bei-Ban-Lan-Gen, BBLG). Additionally, multivariate analysis was conducted to compare the chemical components of NBLG with those of NBLJ and BBLG. Furthermore, we established an optimized and validated HPLC method to obtain the fingerprint of NBLG and quantify the content of 2-benzoxazolinone and acteoside in the samples.

RESULTS

A total of 73 compounds belonging to six classes were assigned in NBLG, with alkaloids being the most abundant and diverse species. High compositional similarities with significant differences in content were observed between NBLG and NBLJ. Moreover, the chemical profile of BBLG markedly differed from that of NBLG. An informative high performance liquid chromatography (HPLC) fingerprint of NBLG comprising seven characteristic peaks that can be used for quality assessment was established. Notably, we propose a quality control standard for NBLG, stipulating that the limit of content in dry weight for both 2-benzoxazolinone and acteoside should not be less than 0.010%.

CONCLUSION

This study provides the most comprehensive chemical information to date on NBLG, offering valuable insights into its authentication and quality control. Our findings highlight the importance of comprehensive chemical profiling to differentiate potential substitutions and adulterations of herbal medicines, particularly when the original source is scarce or unavailable. These results can aid in the development of quality control measures for NBLG-containing preparations, ensuring their safety and efficacy.

Comparative study of water-soluble polysaccharides isolated from leaves and roots of Isatis indigotica Fort

Water-soluble polysaccharides were isolated from the leaves and roots of Isatis indigotica Fort., and their structural features were studied and compared. One neutral polysaccharide fraction (WFIP-N) and three pectin fractions (WFIP-A-A, WFIP-A-B and WFIP-A-C) were obtained from the leaves, and one neutral polysaccharide fraction (WRIP-N) and two pectin fractions (WRIP-A-A and WRIP-A-B) were obtained from the roots. WFIP-A-B (Mw = 34.6 kDa) and WRIP-A-B (Mw = 29.9 kDa) were the major pectic polysaccharides. Monosaccharide composition, FT-IR, enzymatic hydrolysis, NMR and methylation analysis indicated that both WFIP-A-B and WRIP-A-B are composed of rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II) and homogalacturonan (HG) domains with mass ratios of 1.5:1.0:0.4 and 0.3:1.0:1.7, respectively. WFIP-A-B and WRIP-A-B were found to be rich in RG-I and HG domains, respectively, and mainly contained type II arabinogalactan (AG-II) and α-L-1,5-arabinan side chains, but those in WRIP-A-B were more numerous and longer. Our results provide structural features and differences between these polysaccharides which will help to elucidate their functional differences.

Polysaccharide Nanoparticles from Isatis indigotica Fort. Root Decoction: Diversity, Cytotoxicity, and Antiviral Activity

It has been revealed that numerous nanoparticles are formed during the boiling preparation of traditional Chinese medical decoctions and culinary soups. They may possess physiological effects different from those of constituent components and are worth paying attention to but are barely noticed and investigated as of yet. In this study, six groups of nanoparticles, whose size ranged from 57 to 300 nm, were successfully isolated from the decoction of Isatis indigotica Fort. root, according to their particle size by the means of size-exclusive chromatography. All of the obtained nanoparticles have a high content of polysaccharides, which distinguishes them from the disclosed BLG protein nanoparticles. They also have high similarities in other compositions, surface charge, and stimuli responses. However, four out of these six nanoparticles (F2, F3, F4, and F5) exhibited significant antiviral activity against influenza virus H1N1, and their antiviral activities and cytotoxicity towards MDCK cells varied with their sizes. It suggested that the antiviral efficacy of BLG decoction could also be from its nanoparticles besides its well-known antiviral phytochemicals. It also implied that the biological effects of these polysaccharide nanoparticles, including cytotoxicity and antiviral activity, may be correlative with the physicochemical properties, especially the particle size.

Identification of key gene networks controlling vernalization development characteristics of Isatis indigotica by full-length transcriptomes and gene expression profiles

Isatis indigotica Fort., as a common Chinese medicinal raw material, will lose its medicinal value if it blooms early, so it is highly valuable to clarify the induction mechanism of the vernalization of I. indigotica at low temperature. In this study, the concentrations of soluble sugar, proline, glutathione and zeatin in two germplasms of I. indigotica with different degrees of low temperature tolerance (Y1 and Y2) were determined at 10 days, 20 days and 30 days of low-temperature treatment, and the full-length transcriptome of 24 samples was sequenced by Nanopore sequencing with Oxford Nanopore Technologies (ONT). After that, the data of transcripts involved in the vernalization of I. indigotica at low temperature were obtained, and these transcripts were identified using weighted gene co-expression network analysis (WGCNA). The results revealed the massive accumulation of soluble sugar and proline in Y1 and Y2 after low temperature induction. A total of 18,385 new transcripts, 6168 transcription factors and 470 lncRNAs were obtained. Differential expression analysis showed that gibberellin, flavonoids, fatty acids and some processes related to low temperature response were significantly enriched. Eight key transcripts were identified by WGCNA, among which ONT.14640.1, ONT.9119.1, ONT.13080.2 and ONT.16007.1 encodes a flavonoid transporter, 9-cis-epoxycarotenoid dioxygenase 3 (NCED3), growth factor gene and L-aspartate oxidase in plants, respectively. It indicated that secondary metabolites such as hormones and flavonoids play an important role in the vernalization of I. indigotica. qRT-PCR proved the reliability of transcriptome results. These results provide important insights on the low-temperature vernalization of I. indigotica, and provide a research basis for analyzing the vernalization mechanism of I. indigotica.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01110-2.

Genome-Wide Identification and Analysis on YUCCA Gene Family in Isatis indigotica Fort. and IiYUCCA6-1 Functional Exploration

Auxin is one of the most critical hormones in plants. YUCCA (Tryptophan aminotransferase of Arabidopsis (TAA)/YUCCA) enzymes catalyze the key rate-limiting step of the tryptophan-dependent auxin biosynthesis pathway, from IPA (Indole-3-pyruvateacid) to IAA (Indole-3-acetic acid). Here, 13 YUCCA family genes were identified from Isatis indigotica, which were divided into four categories, distributing randomly on chromosomes (2n = 14). The typical and conservative motifs, including the flavin adenine dinucleotide (FAD)-binding motif and flavin-containing monooxygenases (FMO)-identifying sequence, existed in the gene structures. IiYUCCA genes were expressed differently in different organs (roots, stems, leaves, buds, flowers, and siliques) and developmental periods (7, 21, 60, and 150 days after germination). Taking IiYUCCA6-1 as an example, the YUCCA genes functions were discussed. The results showed that IiYUCCA6-1 was sensitive to PEG (polyethylene glycol), cold, wounding, and NaCl treatments. The over-expressed tobacco plants exhibited high auxin performances, and some early auxin response genes (NbIAA8, NbIAA16, NbGH3.1, and NbGH3.6) were upregulated with increased IAA content. In the dark, the contents of total chlorophyll and hydrogen peroxide in the transgenic lines were significantly lower than in the control group, with NbSAG12 downregulated and some delayed leaf senescence characteristics, which delayed the senescence process to a certain extent. The findings provide comprehensive insight into the phylogenetic relationships, chromosomal distributions, and expression patterns and functions of the YUCCA gene family in I. indigotica.

Erucic acid from Isatis indigotica Fort. suppresses influenza A virus replication and inflammation in vitro and in vivo through modulation of NF-κB and p38 MAPK pathway

Isatis indigotica Fort. (Ban-Lan-Gen) is an herbal medicine prescribed for influenza treatment. However, its active components and mode of action remain mostly unknown. In the present study, erucic acid was isolated from Isatis indigotica Fort., and subsequently its underlying mechanism against influenza A virus (IAV) infection was investigated in vitro and in vivo. Our results demonstrated that erucic acid exhibited broad-spectrum antiviral activity against IAV resulting from reduction of viral polymerase transcription activity. Erucic acid was found to exert inhibitory effects on IAV or viral (v) RNA-induced pro-inflammatory mediators as well as interferons (IFNs). The molecular mechanism by which erucic acid with antiviral and anti-inflammatory properties was attributed to inactivation of NF-κB and p38 MAPK signaling. Furthermore, the NF-κB and p38 MAPK inhibitory effect of erucic acid led to diminishing the transcriptional activity of interferon-stimulated gene factor 3 (ISGF-3), and thereby reducing IAV-triggered pro-inflammatory response amplification in IFN-β-sensitized cells. Additionally, IAV- or vRNA-triggered apoptosis of alveolar epithelial A549 cells was prevented by erucic acid. In vivo, erucic acid administration consistently displayed decreased lung viral load and viral antigens expression. Meanwhile, erucic acid markedly reduced CD8⁺ cytotoxic T lymphocyte (CTL) recruitment, pro-apoptotic signaling, hyperactivity of multiple signaling pathways, and exacerbated immune inflammation in the lung, which resulted in decreased lung injury and mortality in mice with a mouse-adapted A/FM/1/47-MA(H1N1) strain infection. Our findings provided a mechanistic basis for the action of erucic acid against IAV-mediated inflammation and injury, suggesting that erucic acid may have a therapeutic potential in the treatment of influenza.

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Erucic acid from Isatis indigotica Fort. exhibited broad-spectrum anti-influenza virus activity.

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Erucic acid reduced IAV polymerase transcription activity.

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Erucic acid suppressed IAV-triggered inflammation as well as pro-inflammatory amplification effects in IFN-sensitized cells.

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Erucic acid protected mice from lethal IAV infection.

Optimization of ultrasound-assisted extraction of indigo and indirubin from Isatis indigotica Fort. and their antioxidant capacities

An effective method for the ultrasound-assisted extraction of indigo and indirubin from Isatis indigotica Fort. was established and their antioxidant activities were investigated. Response surface methodology based on a three-level, four-factor Box-Behnken design was used to optimize the extraction conditions. Analysis of variance showed that the quadratic model was significant for the extraction of indigo and indirubin (112.72% ± 1.65% and 116.42% ± 1.27%, respectively) under the optimal conditions (methanol concentration, 80%; extraction time, 25 min; ratio of solid to liquid, 1:34 g/mL; and extraction temperature, 41 °C) and was in good agreement with the predicted value. Moreover, evaluation of the antioxidant activities suggested that indigo and indirubin presented better scavenging effects on 1,1-diphenyl-2-picrylhydrazyl free radical and superoxide radical than the extract and the extract revealed certain antioxidant activities in hydroxyl radical scavenging and reducing power, and indigo and indirubin could be used as natural antioxidants in the food or medicine industry.

Selection and Validation of Appropriate Reference Genes for qRT-PCR Analysis in Isatis indigotica Fort

Due to its sensitivity and specificity, real-time quantitative PCR (qRT-PCR) is a popular technique for investigating gene expression levels in plants. Based on the Minimum Information for Publication of Real-Time Quantitative PCR Experiments (MIQE) guidelines, it is necessary to select and validate putative appropriate reference genes for qRT-PCR normalization. In the current study, three algorithms, geNorm, NormFinder, and BestKeeper, were applied to assess the expression stability of 10 candidate reference genes across five different tissues and three different abiotic stresses in Isatis indigotica Fort. Additionally, the IiYUC6 gene associated with IAA biosynthesis was applied to validate the candidate reference genes. The analysis results of the geNorm, NormFinder, and BestKeeper algorithms indicated certain differences for the different sample sets and different experiment conditions. Considering all of the algorithms, PP2A-4 and TUB4 were recommended as the most stable reference genes for total and different tissue samples, respectively. Moreover, RPL15 and PP2A-4 were considered to be the most suitable reference genes for abiotic stress treatments. The obtained experimental results might contribute to improved accuracy and credibility for the expression levels of target genes by qRT-PCR normalization in I. indigotica.