Determination of gossypol enantiomer ratio in cotton plants by chiral higher-performance liquid chromatography

Gossypol and Its Natural Derivatives: Multitargeted Phytochemicals as Potential Drug Candidates for Oncologic Diseases

Despite the vast amounts of research and remarkable discoveries that have been made in recent decades, cancer remains a leading cause of death and a major public health concern worldwide. Gossypol, a natural polyphenolic compound derived from the seeds, roots, and stems of cotton (Gossypium hirsutum L.), was first used as a male contraceptive agent. Due to its diverse biological properties, including antifertility, antiviral, antioxidant, antibacterial, antimalarial, and most notably antitumor activities, gossypol has been the subject of numerous studies. Nevertheless, no systematic review has been performed that analyzes the antineoplastic potential of gossypol and related natural compounds in an organ-specific manner while delineating the molecular mechanisms of action. Hence, we have performed an extensive literature search for anticancer properties of gossypol and their natural derivatives against various types of cancer cells utilizing PubMed, ScienceDirect, Google Scholar, and Scopus. The sources, distribution, chemical structure, and toxicity of gossypol and its constituents are briefly reviewed. Based on emerging evidence, gossypol and related compounds exhibit significant antineoplastic effects against various cancer types through the modulation of different cancer hallmarks and signaling pathways. Additionally, the synergistic activity of gossypol and its derivatives with chemotherapeutic agents has been observed. Our evaluation of the current literature suggests the potential of gossypol and its derivatives as multitargeting drug candidates to combat multiple human malignancies.

NMR-based metabolomics reveals tissue metabolic responses to tetramethoxy gossypol in cottonseed oil

BACKGROUND

Cottonseed oil is one of the most widely consumed cooking oils because of its high nutritional benefits and relatively low price. The present study evaluated the effects of tetramethoxy gossypol (TMG), a rarely reported degradation product of free gossypol produced in crudely extracted cottonseed oil, on the metabolic responses of liver, heart, spleen, kidney and lung tissues in rats using proton nuclear magnetic resonance (¹ H NMR) spectroscopy combined with chemometric and bioinformatics techniques.

RESULTS

Endogenous low-molecular-weight metabolites in rat liver, heart, spleen, kidney and lung tissues were profiled by ¹ H NMR spectroscopy. The unsupervised principal components analysis and the supervised orthogonal partial least squares discriminant analysis revealed that the metabolic profiles in liver samples were greatly changed after TMG administration. Twenty significantly changed liver metabolites were screened out and further evaluated by receiver operating characteristic curve analysis, which were closely related to amino acid, glutathione, energy and lipid metabolism.

CONCLUSION

Concerning the potential chronic exposure to TMG in cottonseed oil and other cottonseed products, the cumulative effects of dietary TMG on tissues, especially the liver, should be noted when improving the quality control standard of cottonseed oil. © 2022 Society of Chemical Industry.

Natural Product Gossypol and its Derivatives in Precision Cancer Medicine

Gossypol, a natural product extracted from the seed, roots, and stem of cotton, was initially used as a male contraceptive but was subsequently investigated as a novel antitumor agent. This review depicts the current status of gossypol and its derivatives as novel antitumor agents as well as presents their preparation and characteristics, especially of some gossypol Schiff bases, through quantitative and structural analysis. The main attractive target sites of gossypol and its derivatives are Bcl-2 family proteins containing the anti-apoptosis proteins Bcl-2 and Bcl-XL. The molecular mechanism of gossypol analogs not only involves cell apoptosis but also autophagy, cell cycle arrest, and other abnormal cellular phenomena. Gossypol and its derivatives exert antitumor effects on different cancer types in vitro and in vivo, and demonstrate synergistic effects with other chemo- and radio- therapeutic treatments. In addition, several nanocarriers have been designed to load gossypol or its derivatives in order to expand the range of their applications and evaluate their combination effects with other anti-tumor agents. This review may serve as a reference for the rational application of gossypol analogs as anti-tumor agents.

Pharmacokinetic comparison of gossypol isomers in cattle: transfer from diet to plasma and degradation by rumen microbes*#

A pharmacokinetic comparison of gossypol isomers in cattle was made by investigating their transfer from ingested food to plasma and their degradation by rumen microbes. The gossypol isomers in whole cottonseed, plasma, and rumen fluid were determined by high-performance liquid chromatography (HPLC). The intakes of (+)-and (−)-gossypol by cows on three farms were about 5.6–8.5 and 3.8–5.9 g/(d·herd), respectively. The plasma gossypol concentrations increased as ingestion increased and ranged from 0.31 to 0.48 μg/ml for the (+) form and from 0.39 to 0.59 μg/ml for the (−) form. The (+) form was slightly predominant (58.8%–59.8%) in the gossypol ingested by the cows, whereas the (−) form predominated (54.6%–55.9%) in the plasma. An in vitro study showed that at 6 h, 67.4% and 85.7% of the (−)-gossypol were degraded in 500 and 1000 μg/g treatment groups, respectively, and these increased to 83.6% and 92.5%, respectively, at 12 h. The regularity of the degradation of (+)-gossypol was similar to that of (−)-gossypol. These results showed that (−)-gossypol may be more persistent than (+)-gossypol in plasma, and that the degradation of the gossypol isomers in the rumen is rapid and not enantioselective in cattle.

Enantiomeric Mixtures in Natural Product Chemistry: Separation and Absolute Configuration Assignment

Chiral natural product molecules are generally assumed to be biosynthesized in an enantiomerically pure or enriched fashion. Nevertheless, a significant amount of racemates or enantiomerically enriched mixtures has been reported from natural sources. This number is estimated to be even larger since the enantiomeric purity of secondary metabolites is rarely checked in the natural product isolation pipeline. This latter fact may have drastic effects on the evaluation of the biological activity of chiral natural products. A second bottleneck is the determination of their absolute configurations. Despite the widespread use of optical rotation and electronic circular dichroism, most of the stereochemical assignments are based on empirical correlations with similar compounds reported in the literature. As an alternative, the combination of vibrational circular dichroism and quantum chemical calculations has emerged as a powerful and reliable tool for both conformational and configurational analysis of natural products, even for those lacking UV-Vis chromophores. In this review, we aim to provide the reader with a critical overview of the occurrence of enantiomeric mixtures of secondary metabolites in nature as well the best practices for their detection, enantioselective separation using liquid chromatography, and determination of absolute configuration by means of vibrational circular dichroism and density functional theory calculations.

Expression in Pichia pastoris and characterization of two novel dirigent proteins for atropselective formation of gossypol

We established an efficient fed-batch fermentation process for two novel dirigent proteins from cotton plants, GbDIR2 from Gossypium barbadense and GhDIR3 from G. hirsutum, using the engineered Pichia pastoris GlycoSwitch® SuperMan₅ strain to prevent hyperglycosylation. The two (His)₆-tagged proteins were purified by metal-chelate affinity chromatography and obtained in quantities of 12 and 15 mg L^-1 of culture volume, respectively. Glycosylation sites were identified for the native and for the enzymatically deglycosylated proteins by mass spectrometry, confirming five to six of the seven predicted glycosylation sites in the NxS/T sequence context. The predominant glycan structure was Man₅GlcNAc₂ with, however, a significant contribution of Man_4-10GlcNAc₂. Both dirigent proteins (DIRs) mediated the formation of (+)-gossypol by atropselective coupling of hemigossypol radicals. Similar to previously characterized DIRs, GbDIR2 and GhDIR3 lacked oxidizing activity and depended on an oxidizing system (laccase/O₂) for the generation of substrate radicals. In contrast to DIRs involved in the biosynthesis of lignans, glycosylation was not essential for function. Quantitative enzymatic deglycosylation yielded active GbDIR2 and GhDIR3 in excellent purity. The described fermentation process in combination with enzymatic deglycosylation will pave the way for mechanistic and structural studies and, eventually, the application of cotton DIRs in a biomimetic approach towards atropselective biaryl synthesis.

Gossypol: phytoalexin of cotton

Sesquiterpenoids are a class of 15-carbon secondary metabolites that play diverse roles in plant adaptation to environment. Cotton plants accumulate a large amount of sesquiterpene aldehydes (including gossypol) as phytoalexins against pathogens and herbivores. They are stored in pigment glands of aerial organs and in epidermal layers of roots. Several enzymes of gossypol biosynthesis pathway have been characterized, including 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and farnesyl diphosphate synthase (FPS) that catalyze the formation of the precursor farnesyl diphosphate (FPP), (+)-δ-cadinene synthase (CDN) which is the first enzyme committed to gossypol biosynthesis, and the downstream enzymes of CYP706B1 and methyltransferase. Expressions of these genes are tightly regulated during cotton plants development and induced by jasmonate and fungi elicitors. The transcription factor GaWRKY1 has been shown to be involved in gossypol pathway regulation. Recent development of new genomic platforms and methods and releases of diploid and tetraploid cotton genome sequences will greatly facilitate the elucidation of gossypol biosynthetic pathway and its regulation.

Transcriptional responses underlying the hormetic and detrimental effects of the plant secondary metabolite gossypol on the generalist herbivore Helicoverpa armigera

BACKGROUND

Hormesis is a biphasic biological response characterized by the stimulatory effect at relatively low amounts of chemical compounds which are otherwise detrimental at higher concentrations. A hormetic response in larval growth rates has been observed in cotton-feeding insects in response to increasing concentrations of gossypol, a toxic metabolite found in the pigment glands of some plants in the family Malvaceae. We investigated the developmental effect of gossypol in the cotton bollworm, Helicoverpa armigera, an important heliothine pest species, by exposing larvae to different doses of this metabolite in their diet. In addition, we sought to determine the underlying transcriptional responses to different gossypol doses.

RESULTS

Larval weight gain, pupal weight and larval development time were measured in feeding experiments and a hormetic response was seen for the first two characters. On the basis of net larval weight gain responses to gossypol, three concentrations (0%, 0.016% and 0.16%) were selected for transcript profiling in the gut and the rest of the body in a two-color double reference design microarray experiment. Hormesis could be observed at the transcript level, since at the low gossypol dose, genes involved in energy acquisition such as β-fructofuranosidases were up-regulated in the gut, and genes involved in cell adhesion were down-regulated in the body. Genes with products predicted to be integral to the membrane or associated with the proteasome core complex were significantly affected by the detrimental dose treatment in the body. Oxidoreductase activity-related genes were observed to be significantly altered in both tissues at the highest gossypol dose.

CONCLUSIONS

This study represents the first transcriptional profiling approach investigating the effects of different concentrations of gossypol in a lepidopteran species. H. armigera's transcriptional response to gossypol feeding is tissue- and dose-dependent and involves diverse detoxifying mechanisms not only to alleviate direct effects of gossypol but also indirect damage such as pH disturbance and oxygen radical formation. Genes discovered through this transcriptional approach may be additional candidates for understanding gossypol detoxification and coping with gossypol-induced stress. In a generalist herbivore that has evolved transcriptionally-regulated responses to a variety of different plant compounds, hormesis may be due to a lower induction threshold of growth-promoting, stress-coping responses and a higher induction threshold of detoxification pathways that are costly and cause collateral damage to the cell.

Identification of differentially expressed genes associated with semigamy in Pima cotton (Gossypium barbadense L.) through comparative microarray analysis

BACKGROUND

Semigamy in cotton is a type of facultative apomixis controlled by an incompletely dominant autosomal gene (Se). During semigamy, the sperm and egg cells undergo cellular fusion, but the sperm and egg nucleus fail to fuse in the embryo sac, giving rise to diploid, haploid, or chimeric embryos composed of sectors of paternal and maternal origin. In this study we sought to identify differentially expressed genes related to the semigamy genotype by implementing a comparative microarray analysis of anthers and ovules between a non-semigametic Pima S-1 cotton and its doubled haploid natural isogenic mutant semigametic 57-4. Selected differentially expressed genes identified by the microarray results were then confirmed using quantitative reverse transcription PCR (qRT-PCR).

RESULTS

The comparative analysis between isogenic 57-4 and Pima S-1 identified 284 genes in anthers and 1,864 genes in ovules as being differentially expressed in the semigametic genotype 57-4. Based on gene functions, 127 differentially expressed genes were common to both semigametic anthers and ovules, with 115 being consistently differentially expressed in both tissues. Nine of those genes were selected for qRT-PCR analysis, seven of which were confirmed. Furthermore, several well characterized metabolic pathways including glycolysis/gluconeogenesis, carbon fixation in photosynthetic organisms, sesquiterpenoid biosynthesis, and the biosynthesis of and response to plant hormones were shown to be affected by differentially expressed genes in the semigametic tissues.

CONCLUSION

As the first report using microarray analysis, several important metabolic pathways affected by differentially expressed genes in the semigametic cotton genotype have been identified and described in detail. While these genes are unlikely to be the semigamy gene itself, the effects associated with expression changes in those genes do mimic phenotypic traits observed in semigametic plants. A more in-depth analysis of semigamy is necessary to understand its expression and regulation at the genetic and molecular level.

One- and two-dimensional direct chiral liquid chromatographic determination of mixtures of diclofop-Acid and diclofop-methyl herbicides

Simple one- and two-dimensional high-performance liquid chromatography (HPLC) methods for the simultaneous enantiomeric determination of alkyloxyphenoxypropionic acid herbicides is presented. Compounds studied were ( R, S)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionic acid (diclofop-acid) and ( R, S)-2-[4-(2,4-dichlorophenoxy)]methyl propionate (diclofop-methyl). Mobile phases necessary to separate their enantiomers on an alpha1-acid glycoprotein chiral stationary phase are different; therefore, the simultaneous separation by an isocratic mode is not possible. The chiral separation method proposed involves a one-step gradient allowing for the simultaneous determination of both racemic enantiomers. Detection limits of the method were 0.03 mg/L for both diclofop-acid enantiomers and 0.14 and 0.15 mg/L for diclofop-methyl enantiomers, respectively. The two-dimensional method involves the use of two chromatographs in one achiral-chiral coupling. The LC-LC method is more suitable for complex samples because it involves an online cleanup effect. Detection limits were 1.25 and 1.87 mg/L for diclofop-acid and 2.70 and 3.02 mg/L for diclofop-methyl enantiomers, respectively. Accuracy, repeatability, and reproducibility have been studied in standard samples and a technical product.

Combining HPLC-PDA-MS-SPE-NMR with circular dichroism for complete natural product characterization in crude extracts: levorotatory gossypol in Thespesia danis

Despite recent demonstration of the power of HPLC-PDA-MS-SPE-NMR (high-performance liquid chromatography-photodiode-array detection-mass spectrometry-solid-phase extraction-nuclear magnetic resonance) in structure determination of natural products directly from minute amounts of crude extracts, this technique leaves chirality of the compounds uncharacterized. In this work we demonstrate that postcolumn SPE is a useful method of analyte concentration and accumulation not only for NMR but also for CD (circular dichroism) spectroscopy. Thus, use of HPLC-PDA-MS-SPE-NMR in combination with CD allowed rapid detection of ( R)-(-)-gossypol [( R)- 1] in Thespesia danis, providing a very rare example of the predominance of the levorotatory enantiomer of gossypol. Enantioselectivity of the in vitro antiplasmodial activity of gossypol was also demonstrated; the IC50 value of ( R)- 1 was 4.5 +/- 0.2 microM, with the eudismic ratio of about 2.5. No gossypol was detected in Gossypioides kirkii.