A review on heavy metal pollution, toxicity and remedial measures: Current trends and future perspectives

The use of medicinal plants as a fundamental component of the African traditional healthcare system is perhaps the oldest and the most assorted of all therapeutic systems. In many parts of rural Africa, traditional healers prescribing medicinal plants are the most easily accessible and affordable health resource available to the local community and at times the only therapy that subsists. Nonetheless, there is still a paucity of updated comprehensive compilation of promising medicinal plants from the African continent. The major focus of the present review is to provide an updated overview of 10 promising medicinal plants from the African biodiversity which have short- as well as long-term potential to be developed as future phytopharmaceuticals to treat and/or manage panoply of infectious and chronic conditions. In this endeavour, key scientific databases have been probed to investigate trends in the rapidly increasing number of scientific publications on African traditional medicinal plants. Within the framework of enhancing the significance of traditional African medicinal plants, aspects such as traditional use, phytochemical profile, in vitro, in vivo, and clinical studies and also future challenges pertaining to the use of these plants have been explored.

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Traditional Medicines in Africa: An Appraisal of Ten Potent African Medicinal Plants

The sesquiterpene (E)-b-caryophyllene is emitted by maize (Zea mays) leaves in response to attack by lepidopteran larvae like Spodoptera littoralis and released from roots after damage by larvae of the coleopteran Diabrotica virgifera virgifera. We identified a maize terpene synthase, Terpene Synthase 23 (TPS23), that produces (E)-b-caryophyllene from farnesyl diphosphate. The expression of TPS23 is controlled at the transcript level and induced independently by D. v. virgifera damage in roots and S. littoralis damage in leaves. We demonstrate that (E)-b-caryophyllene can attract natural enemies of both herbivores: entomopathogenic nematodes below ground and parasitic wasps, after an initial learning experience, above ground. The biochemical properties of TPS23 are similar to those of (E)-b-caryophyllene synthases from dicotyledons but are the result of repeated evolution. The sequence of TPS23 is maintained by positive selection in maize and its closest wild relatives, teosinte (Zea sp) species. The gene encoding TPS23 is active in teosinte species and European maize lines, but decreased transcription in most North American lines resulted in the loss of (E)-b-caryophyllene production. We argue that the (E)-b-caryophyllene defense signal was lost during breeding of the North American lines and that its restoration might help to increase the resistance of these lines against agronomically important pests.

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A Maize (E)-β-Caryophyllene Synthase Implicated in Indirect Defense Responses against Herbivores Is Not Expressed in Most American Maize Varieties

Flowers have a high risk of pathogen attack because of their rich nutrient and moisture content, and high frequency of insect visitors. We investigated the role of (E)-β-caryophyllene in floral defense against a microbial pathogen. This sesquiterpene is a common volatile compound emitted from flowers, and is a major volatile released from the stigma of Arabidopsis thaliana flowers. Arabidopsis thaliana lines lacking a functional (E)-β-caryophyllene synthase or constitutively overexpressing this gene were challenged with Pseudomonas syringae pv. tomato DC3000, which is a bacterial pathogen of brassicaceous plants. Flowers of plant lines lacking (E)-β-caryophyllene emission showed greater bacterial growth on their stigmas than did wild-type flowers, and their seeds were lighter and misshapen. By contrast, plant lines with ectopic (E)-β-caryophyllene emission from vegetative parts were more resistant than wild-type plants to pathogen infection of leaves, and showed reduced cell damage and higher seed production. Based on in vitro experiments, (E)-β-caryophyllene seems to act by direct inhibition of bacterial growth, rather than by triggering defense signaling pathways. (E)-β-Caryophyllene thus appears to serve as a defense against pathogens that invade floral tissues and, like other floral volatiles, may play multiple roles in defense and pollinator attraction.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2011.04001.x

The major volatile organic compound emitted from Arabidopsis thaliana flowers, the sesquiterpene (E)-β-caryophyllene, is a defense against a bacterial pathogen.

Natural bicyclic sesquiterpenes, β‐caryophyllene (BCP) and β‐caryophyllene oxide (BCPO), are present in a large number of plants worldwide. Both BCP and BCPO (BCP(O)) possess significant anticancer activities, affecting growth and proliferation of numerous cancer cells. Nevertheless, their antineoplastic effects have hardly been investigated in vivo. In addition, both compounds potentiate the classical drug efficacy by augmenting their concentrations inside the cells. The mechanisms underlying the anticancer activities of these sesquiterpenes are poorly described. BCP is a phytocannabinoid with strong affinity to cannabinoid receptor type 2 (CB 2), but not cannabinoid receptor type 1 (CB 1). In opposite, BCP oxidation derivative, BCPO, does not exhibit CB 1/2 binding, thus the mechanism of its action is not related to endocannabinoid system (ECS) machinery. It is known that BCPO alters several key pathways for cancer development, such as mitogen‐activated protein kinase (MAPK), PI3K/AKT/mTOR/S6K1 and STAT3 pathways. In addition, treatment with this compound reduces the expression of procancer genes/proteins, while increases the levels of those with proapoptotic properties. The selective activation of CB 2 may be considered a novel strategy in pain treatment, devoid of psychoactive side effects associated with CB 1 stimulation. Thus, BCP as selective CB 2 activator may be taken into account as potential natural analgesic drug. Moreover, due to the fact that chronic pain is often an element of cancer disease, the double activity of BCP, anticancer and analgesic, as well as its beneficial influence on the efficacy of classical chemotherapeutics, is particularly valuable in oncology. This review is focused on anticancer and analgesic activities of BCP and BCPO, the mechanisms of their actions, and potential therapeutic utility.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cam4.816

β‐caryophyllene and β‐caryophyllene oxide—natural compounds of anticancer and analgesic properties

Caryophyllene-rich rhizome oil of Zingiber nimmonii from South India: Chemical characterization and antimicrobial activity

Citrus peels prevent cancer

Mucuna pruriens is the best known natural source of L-dopa, the gold standard for treatment of Parkinsonism. M. pruriens varieties are protein rich supplements, and are used as food and fodder worldwide. Here, we report L-dopa contents in seeds of fifty six accessions of four M. pruriens varieties, M. pruriens var. pruriens, M. pruriens var. hirsuta, M. pruriens var. utilis and M. pruriens var. thekkadiensis, quantified by HPTLC-densitometry. L-dopa contents varied between 0.58 to 6.42 (%, dr. wt.). High and low L-dopa yielding genotypes/chemotypes of M. pruriens could be multiplied for medicinal and nutritional purposes, respectively. HPTLC profiles of M. pruriens seeds on repeated extraction (24 h) in 1:1 formic acid-alcohol followed by development in butanol:acetic acid:water (4:1:1, v/v) showed consistent degradation of L-dopa (Rf 0.34 ± 0.02) into a second peak (Rf 0.41 ± 0.02). An average of 52.11% degradation of L-dopa was found in seeds of M. pruriens varieties. Since M. pruriens seeds and/or L-dopa are used for treatment of Parkinson's disease and as an aphrodisiac both in modern and/or traditional systems of medicine, the finding of high level of L-dopa degradation (in pure form and in M. pruriens extracts) into damaging quinones and ROS is very significant.

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Levodopa in Mucuna pruriens and its degradation

Carnivorous plants acquire most of their nutrients by capturing ants, insects and other arthropods through their leaf-evolved biological traps. So far, the best-known attractants in carnivorous prey traps are nectar, colour and olfactory cues. Here, fresh prey traps of 14 Nepenthes, five Sarracenia, five Drosera, two Pinguicula species/hybrids, Dionaea muscipula and Utricularia stellaris were scanned at UV 366 nm. Fluorescence emissions of major isolates of fresh Nepenthes khasiana pitcher peristomes were recorded at an excitation wavelength of 366 nm. N. khasiana field pitcher peristomes were masked by its slippery zone extract, and prey capture rates were compared with control pitchers. We found the existence of distinct blue fluorescence emissions at the capture spots of Nepenthes, Sarracenia and Dionaea prey traps at UV 366 nm. These alluring blue emissions gradually developed with the growth of the prey traps and diminished towards their death. On excitation at 366 nm, N. khasiana peristome 3:1 CHCl3–MeOH extract and its two major blue bands showed strong fluorescence emissions at 430–480 nm. Masking of blue emissions on peristomes drastically reduced prey capture in N. khasiana pitchers. We propose these molecular emissions as a critical factor attracting arthropods and other visitors to these carnivorous traps. Drosera, Pinguicula and Utricularia prey traps showed only red chlorophyll emissions at 366 nm.

Fluorescent prey traps in carnivorous plants

Zerumbone is a sesquiterpene phytochemical with potential anticancer, anti-inflammatory, anti-HIV and other biological activities, most abundantly found in Zingiber zerumbet (L.) Smith. Previous studies reported 12.6–73.1% of zerumbone in Z. zerumbet rhizome oils from various geographical locations. In a careful review of the literature, we found that most of the previous gas chromatographic profiling studies on volatile oils of Z. zerumbet were inadequate, since they were based on poor identification and quantification procedures and also on single-sample data. In this study, we report the chemical profiles of volatile oils of Z. zerumbet rhizomes from six locations in the southern Indian state of Kerala and also from Penang in Malaysia. Chemical profiling of volatiles was carried out by extensive GC–FID, GC–MS and associated techniques, supported by 1H-NMR, 13C-NMR, FABMS and HPTLC. The full chemical profiles of rhizome oils of these seven accessions of Z. zerumbet were elucidated. The south Indian accessions of Z. zerumbet reported 76.3–84.8% zerumbone content in their rhizome oils. The Malaysian accession recorded the lowest content of zerumbone (68.9%). This study reveals the high content of the bioactive compound zerumbone in Z. zerumbet from Kerala. Copyright © 2009 John Wiley & Sons, Ltd.

Rajani Kurup

Papers

Caryophyllene-rich rhizome oil of Zingiber nimmonii from South India: Chemical characterization and antimicrobial activity

Citrus peels prevent cancer

Levodopa in Mucuna pruriens and its degradation

Fluorescent prey traps in carnivorous plants

High content of zerumbone in volatile oils of Zingiber zerumbet from southern India and Malaysia