Comparison of the effects of extracts from three Vitex plant species on Anopheles gambiae s.s. (Diptera: Culicidae) larvae

A comprehensive review of ethnomedicinal approaches, phytochemical analysis, and pharmacological potential of Vitex trifolia L

Plants, renowned for their rich reservoir of metabolites, play a pivotal role in addressing health-related issues. The Verbenaceae family stands out, showcasing immense potential in preventing and treating chronic diseases. Vitex trifolia L. (V. trifolia), a shrub with a rich history in traditional medicine, particularly in Eastern Asia, has garnered attention for its diverse therapeutic applications. This comprehensive review aims to bridge traditional knowledge and contemporary insights by investigating ethnopharmacology, phytochemistry, and pharmacological effects of V. trifolia. The keyword "V. trifolia" and its synonyms were searched within the main scientific databases including PubMed, Web of Science, ScienceDirect, Google Scholar, and Baidu Scholar (from 1974 to 2022, last search: 21.10.2023). Phytochemical analyses reveal a spectrum of secondary metabolites in V. trifolia, including terpenoids, flavonoids, lignans, phytosterols, anthraquinones, and fatty acids. Notably, terpenoids and flavonoids emerge as the main bioactive metabolites. Pharmacological studies validate its therapeutic potential, demonstrating significant antioxidant, anti-inflammatory, hepatoprotective, anticancer, anti-amnesic, antimicrobial, antiviral, anti-malaria, antispasmodic activities, and reported insecticidal effects. Despite existing literature exploring pharmacological attributes and secondary metabolites of related species, a conspicuous gap exists, specifically focusing on the pharmacological activities and novel methods of purification of pure metabolites from V. trifolia. This review aimed to fill this gap by delving into traditional medicinal applications, exploring secondary metabolites comprehensively, and providing an in-depth analysis of pharmacological effects of pure metabolites. Combining traditional uses with contemporary pharmacological insights, this article sought to serve as a crucial reference for future research and practical application of V. trifolia. This approach contributes substantially to understanding the plant, fostering scientific inquiry, and facilitating its broader application in healthcare.

Traditional use, phytochemistry and pharmacology of Viticis Fructus

Ethnopharmacological relevance

Viticis Fructus (called Manjingzi in China) is the dried ripe fruits of the plant species Vitex trifolia subsp. litoralis Steenis and Vitex trifolia L. in the family Lamiaceae. Viticis Fructus has been used as a traditional Chinese medicine for thousands of years to treat illness such as colds, headache, vertigo, anesthesia, and hyperkinesias. More chemical constituents and medicinal effects have been discovered in Viticis Fructus with the development of modern technology.The aim of the review: This review aims to analyze the research progress of Viticis Fructus from the aspects of botany, ethnopharmacology, phytochemistry, and pharmacological activity, as well as to provide an outlook on the research and use prospects of Viticis Fructus.

Material and methods

A comprehensive literature search using online databases such Science Direct, CNKI, Wiley online library, Spring Link, Web of Science, PubMed, Wanfang Data and SCI-Finder. In addition, information was obtained from local and foreign books on ethnobotany and ethnomedicine.

Results

The application of Viticis Fructus as a medicine can be traced back to around 480 AD. So far, more than 190 compounds have been isolated from Viticis Fructus, including flavonoids, sterols, cyclic enol ether terpenoids, and diterpenoids. Modern pharmacological studies have shown that the extracts of Viticis Fructus have various pharmacological effects, such as anti-allergic, antioxidant, anti-inflammatory, anti-cancer, and anti-bacterial effects.

Conclusion

As a widely used traditional medicine, Viticis Fructus is rich in chemical compositions and has an obvious biological activity. However, the application and pharmacological activity of Viticis Fructus have not been scientifically evaluated or convincing due to poor methodology, unclear results and lack of clinical data. Systematic and comprehensive research evaluations are needed to verify its pharmaceutical activity, clinical therapeutic efficacy and safety. As an important herbal medicine, it should be further explored to facilitate the development of new medicines and treatments for a variety of diseases.

Vitex rotundifolia L. f. and Vitex trifolia L.: A review on their traditional medicine, phytochemistry, pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Vitex rotundifolia L. f. and Vitex trifolia L. belong to the genus Vitex, and Vitex rotundifolia L. f. evolved from Vitex trifolia L. Both are essential ethnic medicinal plants with a long history, commonly used to treat headaches, fever, diarrhea, hair loss, wound recovery, and other diseases.

AIM OF THE REVIEW

The research status of Vitex trifolia L. and its relative species Vitex rotundifolia L. f. were reviewed from the aspects of traditional medicinal use, phytochemistry, and pharmacological activities, to provide a reference for the further development and utilization of Vitex rotundifolia L. f. and Vitex trifolia L.

MATERIALS AND METHODS

In this paper, a comprehensive search of published literature was conducted through various books and online databases to obtain relevant information on Vitex rotundifolia L. f. and Vitex trifolia L. The search terms "(Vitex rotundifolia) OR (Vitex trifolia) OR (Fructus viticis)" were entered in PubMed, Web of Science, China national knowledge infrastructure (CNKI), Wanfang Data, Baidu Scholar, respectively. In addition to setting the year threshold of "2018-2022" on Baidu Scholar, other databases searched all fields and found 889, 283, 1263, 1023, and 147 articles, respectively. Among them, review, repetition, overlapping data, and other reasons were excluded, and finally, a total of 164 articles were included in the review study.

RESULTS

A total of 369 compounds have been identified, including 159 terpenoids, 51 flavonoids, 83 phenylpropanoids, and 76 other compounds. Pharmacological studies have shown that Vitex rotundifolia L. f. and Vitex trifolia L. have a variety of pharmacological activities, such as anti-tumor, analgesic, antipyretic, anti-inflammatory, antioxidant, antibacterial, and estrogen-like activity. Modern clinical use for treating cold headaches, diarrhea dysentery, irregular menstruation, and other diseases.

CONCLUSIONS

As traditional medicinal plants, Vitex rotundifolia L. f. and Vitex trifolia L. have wealthy chemical constituents and extensive pharmacological activities and are widely used in clinical practice from traditional to modern times. However, the research on the pharmacological activities of Vitex rotundifolia L. f. and Vitex trifolia L. is not in-depth, and the potential active components still need to be explored.

Transcriptomic response of Anopheles gambiae sensu stricto mosquito larvae to Curry tree (Murraya koenigii) phytochemicals

BACKGROUND

Insect growth regulators (IGRs) can control insect vector populations by disrupting growth and development in juvenile stages of the vectors. We previously identified and described the curry tree (Murraya koenigii (L.) Spreng) phytochemical leaf extract composition (neplanocin A, 3-(1-naphthyl)-L-alanine, lumiflavine, terezine C, agelaspongin and murrayazolinol), which disrupted growth and development in Anopheles gambiae sensu stricto mosquito larvae by inducing morphogenetic abnormalities, reducing locomotion and delaying pupation in the mosquito. Here, we attempted to establish the transcriptional process in the larvae that underpins these phenotypes in the mosquito.

METHODS

We first exposed third-fourth instar larvae of the mosquito to the leaf extract and consequently the inherent phytochemicals (and corresponding non-exposed controls) in two independent biological replicates. We collected the larvae for our experiments sampled 24 h before peak pupation, which was 7 and 18 days post-exposure for controls and exposed larvae, respectively. The differences in duration to peak pupation were due to extract-induced growth delay in the larvae. The two study groups (exposed vs control) were consequently not age-matched. We then sequentially (i) isolated RNA (whole larvae) from each replicate treatment, (ii) sequenced the RNA on Illumina HiSeq platform, (iii) performed differential bioinformatics analyses between libraries (exposed vs control) and (iv) independently validated the transcriptome expression profiles through RT-qPCR.

RESULTS

Our analyses revealed significant induction of transcripts predominantly associated with hard cuticular proteins, juvenile hormone esterases, immunity and detoxification in the larvae samples exposed to the extract relative to the non-exposed control samples. Our analysis also revealed alteration of pathways functionally associated with putrescine metabolism and structural constituents of the cuticle in the extract-exposed larvae relative to the non-exposed control, putatively linked to the exoskeleton and immune response in the larvae. The extract-exposed larvae also appeared to have suppressed pathways functionally associated with molting, cell division and growth in the larvae. However, given the age mismatch between the extract-exposed and non-exposed larvae, we can attribute the modulation of innate immune, detoxification, cuticular and associated transcripts and pathways we observed to effects of age differences among the larvae samples (exposed vs control) and to exposures of the larvae to the extract.

CONCLUSIONS

The exposure treatment appears to disrupt cuticular development, immune response and oxidative stress pathways in Anopheles gambiae s.s larvae. These pathways can potentially be targeted in development of more efficacious curry tree phytochemical-based IGRs against An. gambiae s.s mosquito larvae.

Plant extracts for developing mosquito larvicides: From laboratory to the field, with insights on the modes of action

In the last decades, major research efforts have been done to investigate the insecticidal activity of plant-based products against mosquitoes. This is a modern and timely challenge in parasitology, aimed to reduce the frequent overuse of synthetic pesticides boosting resistance development in mosquitoes and causing serious threats to human health and environment. This review covers the huge amount of literature available on plant extracts tested as mosquito larvicides, particularly aqueous and alcoholic ones, due to their easy formulation in water without using surfactants. We analysed results obtained on more than 400 plant species, outlining that 29 of them have outstanding larvicidal activity (i.e., LC₅₀ values below 10 ppm) against major vectors belonging to the genera Anopheles, Aedes and Culex, among others. Furthermore, synergistic and antagonistic effects between plant extracts and conventional pesticides, as well as among selected plant extracts are discussed. The efficacy of pure compounds isolated from the most effective plant extracts and - when available - their mechanism of action, as well as the impact on non-target species, is also covered. These belong to the following class of secondary metabolites: alkaloids, alkamides, sesquiterpenes, triterpenes, sterols, flavonoids, coumarins, anthraquinones, xanthones, acetogenonins and aliphatics. Their mode of action on mosquito larvae ranges from neurotoxic effects to inhibition of detoxificant enzymes and larval development and/or midugut damages. In the final section, current drawbacks as well as key challenges for future research, including technologies to synergize efficacy and improve stability - thus field performances - of the selected plant extracts, are outlined. Unfortunately, despite the huge amount of laboratory evidences about their efficacy, only a limited number of studies was aimed to validate their efficacy in the field, nor the epidemiological impact potentially arising from these vector control operations has been assessed. This strongly limits the development of commercial mosquito larvicides of botanical origin, at variance with plant-borne products developed in the latest decades to kill or repel other key arthropod species of medical and veterinary importance (e.g., ticks and lice), as well as mosquito adults. Further research on these issues is urgently needed.

Growth-disrupting Murraya koenigii leaf extracts on Anopheles gambiae larvae and identification of associated candidate bioactive constituents

Plant-based constituents have been proposed as eco-friendly alternatives to synthetic insecticides for control of mosquito vectors of malaria. In this study, we first screened the effects of methanolic leaf extracts of curry tree (Murraya koenigii) growing in tropical (Mombasa, Malindi) and semi-arid (Kibwezi, and Makindu) ecological zones of Kenya on third instar An. gambiae s.s. larvae. Extracts of the plant from the semi-arid region, and particularly from Kibwezi, led to high mortality of the larvae. Bioassay-guided fractionation of the methanolic extract of the leaves of the plants from Kibwezi was then undertaken and the most active fraction (20 fold more potent than the crude extract) was then analyzed by Liquid chromatography quadruple time of flight coupled with mass spectrometry (LC-QtoF-MS) and a number of constituents were identified, including a major alkaloid constituent, Neplanocin A (5). Exposure of the third instar larvae to a sub-lethal dose (4.43 ppm) of this fraction over 7-day periods induced gross morphogenetic abnormalities in the larvae, with reduced locomotion, and delayed pupation. Moreover, the few adults that emerged from some pupae failed to fly from the water surface, unlike in the untreated control group. These results demonstrate subtle growth-disrupting effects of the phytochemical blend from M. koenigii leaves on aquatic stages An. gambiae mosquito. The study lays down some useful groundwork for the downstream development of phytochemical blends that can be evaluated for integration into eco-friendly control of An. gambiae vector population targeting the often overlooked but important immature stages of the malaria vector.

Prospects for malaria control through manipulation of mosquito larval habitats and olfactory-mediated behavioural responses using plant-derived compounds

Malaria presents an overwhelming public health challenge, particularly in sub-Saharan Africa where vector favourable conditions and poverty prevail, potentiating the disease burden. Behavioural variability of malaria vectors poses a great challenge to existing vector control programmes with insecticide resistance already acquired to nearly all available chemical compounds. Thus, approaches incorporating plant-derived compounds to manipulate semiochemical-mediated behaviours through disruption of mosquito olfactory sensory system have considerably gained interests to interrupt malaria transmission cycle. The combination of push-pull methods and larval control have the potential to reduce malaria vector populations, thus minimising the risk of contracting malaria especially in resource-constrained communities where access to synthetic insecticides is a challenge. In this review, we have compiled information regarding the current status of knowledge on manipulation of larval ecology and chemical-mediated behaviour of adult mosquitoes with plant-derived compounds for controlling mosquito populations. Further, an update on the current advancements in technologies to improve longevity and efficiency of these compounds for field applications has been provided.

Methanolic extract of Agerantum conyzoides exhibited toxicity and growth disruption activities against Anopheles gambiae sensu stricto and Anopheles arabiensis larvae

Background

Vector control remains the mainstay to effective malaria management. The negative implications following persistent application of synthetic insecticides geared towards regulation of mosquito populations have necessitated prospection for ecofriendly effective chemistries. Plant-derived compounds have the potential to control malaria-transmitting mosquito populations. Previously, Agerantum conyzoides extracts have demonstrated toxicity effects on disease-transmitting mosquitoes. However, their efficacy in controlling Afrotropical malaria vectors remains unclear. Herein, the toxicity and growth disruption activities of crude methanolic leaf extract of A. conyzoides on Anopheles gambiae sensu stricto and An. arabiensis larvae were assessed.

Methods

Late third (L3) instars of An. gambiae s.s and An. arabiensis larvae were challenged with increasing doses of crude methanolic extract of A. conyzoides. The larval mortality rates were recorded every 24 h and the LC₅₀ values determined at their associated 95% confidence levels. ANOVA followed by Post-hoc Student-Newman-Keuls (SNK) test was used to compare results between treatment and control groups. Phytochemical profiling of the extract was performed using standard chemical procedures.

Results

Treatment of larvae with the methanolic extract depicted dose-dependent effects with highest mortality percentages of ≥ 69% observed when exposed with 250 ppm and 500 ppm for 48 h while growth disruption effects were induced by sublethal doses of between 50–100 ppm for both species. Relative to experimental controls, the extract significantly reduced larval survival in both mosquito species (ANOVA, F_(8,126) = 43.16776, P < 0.001). The LC₅₀ values of the extract against An. gambiae s.s ranged between 84.71–232.70 ppm (95% CI 81.17–239.20), while against An. arabiensis the values ranged between 133.46–406.35 ppm (95% CI 131.51–411.25). The development of the juvenile stages was arrested at pupal-larval intermediates and adult emergence. The presence of alkaloids, aglycone flavonoids, triterpenoids, tannins and coumarins can partly be associated with the observed effects.

Conclusion

The extract displayed considerable larvicidal activity and inhibited emergence of adult mosquitoes relative to experimental controls, a phenomenon probably associated with induced developmental hormone imbalance. Optimization of the bioactive compounds could open pathways into vector control programmes for improved mosquito control and reduced malaria transmission rates.