Plants as sources of antimalarial drugs. Part 7. Activity of some species of meliaceae plants and their constituent limonoids

A comprehensive review of antimalarial medicinal plants used by Tanzanians

CONTEXT

Tanzania has rich medicinal plant (MP) resources, and most rural inhabitants rely on traditional healing practices for their primary healthcare needs. However, available research evidence on antimalarial MPs is highly fragmented in the country.

OBJECTIVE

This systematic review compiles ethnomedicinal research evidence on MPs used by Tanzanians as antimalarials.

MATERIALS AND METHODS

A systematic web search was conducted using various electronic databases and grey materials to gather relevant information on antimalarial MPs utilized by Tanzanians. The review was per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The data were collected from 25 articles, and MS Excel software was used to analyse relevant ethnobotanical information using descriptive statistics.

RESULTS

A total of 227 MPs belonging to 67 botanical families and 180 genera were identified. Fabaceae (15.9%) is the most frequently utilized family. The ethnobotanical recipes analysis indicated leaves (40%) and trees (44%) are the preferred MPs part and life form, respectively. Decoctions (67%) are the dominant preparation method of remedies. Of the recorded MPs, 25.9% have been scientifically investigated for antimalarial activities with positive results. However, 74.1% of MPs have no scientific records on antimalarial activities, but they could be potential sources of remedies.

CONCLUSIONS

The study discloses a wealth of antimalarial MPs possessed by Tanzanians and suggests a need for research to authenticate the healing potential of antimalarial compounds from the unstudied MPs. Additionally, it indicates that some of the presented MPs are potential sources for developing safe, effective and affordable antimalarial drugs.

Limonoids from neem (Azadirachta indica A. Juss.) are potential anticancer drug candidates

Neem (Azadirachta indica A. Juss.), a versatile evergreen tree recognized for its ethnopharmacological value, is a rich source of limonoids of the triterpenoid class, endowed with potent medicinal properties. Extracts of neem have been documented to display anticancer effects in diverse malignant cell lines as well as in preclinical animal models that has largely been attributed to the constituent limonoids. Of late, neem limonoids have become the cynosure of research attention as potential candidate agents for cancer prevention and therapy. Among the various limonoids found in neem, azadirachtin, epoxyazadiradione, gedunin, and nimbolide, have been extensively investigated for anticancer activity. Azadirachtin, a potent biodegradable pesticide, exhibits profound antiproliferative effects by preventing mitotic spindle formation and cell division. The antiproliferative activity of gedunin has been demonstrated to be mediated primarily via inhibition of heat shock protein90 and its client proteins. Epoxyazadiradione inhibits pro-inflammatory and kinase-driven signaling pathways to block tumorigenesis. Nimbolide, the most potent cytotoxic neem limonoid, inhibits the growth of cancer cells by regulating the phosphorylation of keystone kinases that drive oncogenic signaling besides modulating the epigenome. There is overwhelming evidence to indicate that neem limonoids exert anticancer effects by preventing the acquisition of hallmark traits of cancer, such as cell proliferation, apoptosis evasion, inflammation, invasion, angiogenesis, and drug resistance. Neem limonoids are value additions to the armamentarium of natural compounds that target aberrant oncogenic signaling to inhibit cancer development and progression.

Ethnomedicinal plants used for malaria treatment in Rukungiri District, Western Uganda

BACKGROUND

Malaria remains a major global health challenge and a serious cause of morbidity and mortality in sub-Saharan Africa. In Uganda, limited access to medical facilities has perpetuated the reliance of indigenous communities on herbal medicine for the prevention and management of malaria. This study was undertaken to document ethnobotanical knowledge on medicinal plants prescribed for managing malaria in Rukungiri District, a meso-endemic malaria region of Western Uganda.

METHODS

An ethnobotanical survey was carried out between May 2022 and December 2022 in Bwambara Sub-County, Rukungiri District, Western Uganda using semi-structured questionnaire. A total of 125 respondents (81 females and 44 males) were randomly selected and seven (7) key informants were engaged in open interviews. In all cases, awareness of herbalists on malaria, treatment-seeking behaviour and herbal treatment practices were obtained. The ethnobotanical data were analyzed using descriptive statistics, informant consensus factor and preference ranking.

RESULTS

The study identified 48 medicinal plants belonging to 47 genera and 23 families used in the treatment of malaria and its symptoms in the study area. The most frequently cited species were Vernonia amygdalina, Aloe vera and Azadirachta indica. Leaves (74%) was the most used plant organ, mostly for preparation of decoctions (41.8%) and infusions (23.6%) which are administered orally (89.6%) or used for bathing (10.4%).

CONCLUSIONS

Indigenous knowledge of medicinal plants used as prophylaxis and for treatment of malaria still exist among the local communities of Bwambara Sub-County. However, there is a need to investigate the antimalarial efficacy, phytochemical composition and safety of species (such as Digitaria abyssinica and Berkheya barbata) with high percentage use values to validate their use.

Medicinal plants used for treatment of malaria by indigenous communities of Tororo District, Eastern Uganda

BACKGROUND

Malaria remains the leading cause of death in sub-Saharan Africa. Although recent developments such as malaria vaccine trials inspire optimism, the search for novel antimalarial drugs is urgently needed to control the mounting resistance of Plasmodium species to the available therapies. The present study was conducted to document ethnobotanical knowledge on the plants used to treat symptoms of malaria in Tororo district, a malaria-endemic region of Eastern Uganda.

METHODS

An ethnobotanical study was carried out between February 2020 and September 2020 in 12 randomly selected villages of Tororo district. In total, 151 respondents (21 herbalists and 130 non-herbalists) were selected using multistage random sampling method. Their awareness of malaria, treatment-seeking behaviour and herbal treatment practices were obtained using semi-structured questionnaires and focus group discussions. Data were analysed using descriptive statistics, paired comparison, preference ranking and informant consensus factor.

RESULTS

A total of 45 plant species belonging to 26 families and 44 genera were used in the preparation of herbal medicines for management of malaria and its symptoms. The most frequently mentioned plant species were Vernonia amygdalina, Chamaecrista nigricans, Aloe nobilis, Warburgia ugandensis, Abrus precatorius, Kedrostis foetidissima, Senna occidentalis, Azadirachta indica and Mangifera indica. Leaves (67.3%) were the most used plant part while maceration (56%) was the major method of herbal remedy preparation. Oral route was the predominant mode of administration with inconsistencies in the posology prescribed.

CONCLUSION

This study showed that the identified medicinal plants in Tororo district, Uganda, are potential sources of new antimalarial drugs. This provides a basis for investigating the antimalarial efficacy, phytochemistry and toxicity of the unstudied species with high percentage use values to validate their use in the management of malaria.

Phytochemistry and Biological Activities of Guarea Genus (Meliaceae)

Guarea is one of the largest genera of the American Meliaceae family, consisting of over 69 species which are widely distributed in Mexico, Argentina, and Africa and are used in traditional medicine for several diseases. Previous studies reported that the Guarea species produce secondary metabolites such as sesquiterpenoid, diterpenoid, triterpenoid, limonoid, steroid, and aromatic compounds. The preliminary chemical investigation commenced by isolating the limonoid compound, dihydrogedunin, in 1962; then, 240 compounds were obtained from the isolation and hydrodistillation process. Meanwhile, sesquiterpenoid is a significant compound with 52% of Guarea species. The extract and compounds were evaluated for their anti-inflammation, antimalarial, antiparasitic, antiprotozoal, antiviral, antimicrobial, insecticidal, antioxidant, phosphorylation inhibitor, and cytotoxic biological activities. The Guarea genus has also been reported as one of the sources of active compounds for medicinal chemistry. This review summarizes some descriptions regarding the types of Guarea species, especially ethnobotany and ethnopharmacology, such as the compounds isolated from the part of this genus, various isolation methods, and their bioactivities. The information can be used in further investigations to obtain more bioactive compounds and their reaction mechanisms.

A novel gedunin-2-hydroxypropyl-β-cyclodextrin inclusion complex improves anti-nociceptive and anti-inflammatory activities of gedunin in rodents

Gedunin is a bioactive compound, obtained from Entandrophragma angolense (EA), which has limited therapeutic usefulness due to poor aqueous solubility and first-pass effects. Cyclodextrins are cyclic oligosaccharides that form complexes with poorly soluble compounds, thus enhancing their pharmacological activity. In this article, we evaluated the pharmacological activities of gedunin-2-hydroxypropyl-β-cyclodextrin complex (GCD) in rodents. The antinociceptive activity of GCD (50, 100, 200 mg/kg) and Gedunin (50mg/kg) was tested in acetic acid-induced writhing and formalin-induced paw licking in mice. The anti-inflammatory activity was investigated in carrageenan-induced paw oedema and air pouch inflammation models in rats. Leucocytes counts, Tumour Necrosis Factor-alpha (TNF-α) level, nitric oxide, malondialdehyde, reduced glutathione, and myeloperoxidase enzyme activities were assessed in the air pouch exudate. The GCD (200mg/kg) significantly decreased writhing response, reduced licking duration and decreased oedema compared with gedunin and control. Exudate volume and leucocyte count were significantly reduced by GCD (200 mg/kg), it decreased myeloperoxidase activity and inhibited TNF-α release. The carrageenan-induced GSH depletion, increased malondialdehyde and nitrite levels were significantly reversed by GCD (200 mg/kg) relative to gedunin and control.  The GCD complex demonstrated significant antinociceptive and anti-inflammatory activities relative to gedunin alone via mechanisms associated with inhibition of oxidative stress and inflammation in rodents.

Contribution of Meliaceous plants in furnishing lead compounds for antiplasmodial and insecticidal drug development

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria remains one of the greatest threats to human life especially in the tropical and sub-tropical regions where it claims hundreds of thousands of lives of young children every year. Meliaceae represent a large family of trees and shrubs, which are widely used in African traditional medicine for the treatment of several ailments including fever due to malaria. The in vitro and in vivo antiplasmodial as well as insecticidal investigations of their extracts or isolated compounds have led to promising results but to the best of our knowledge, no specific review on the traditional uses, phytochemistry of the antiplasmodial, insecticidal and cytotoxic lead compounds and extracts of Meliaceae plants has been compiled.

AIMS

To review the literature up to 2021 on the Meliaceae family with antiplasmodial, insecticidal and cytotoxic activity.

MATERIALS AND METHODS

A number of online libraries including PubMed, Scifinder, Google Scholar and Web of Science were used in searching for information on antiplasmodial metabolites from Meliaceous plants. The keywords Meliaceae, malaria, Plasmodium, Anopheles and antiplasmodial were used to monitor and refine our search without language restriction.

RESULTS

The phytochemical investigations of genera of the family Meliaceae led to the isolation and characterization of a wide range of structural diversity of compounds, 124 of which have been evaluated for their antiplasmodial potency against 11 chloroquine-sensitive and chloroquine-resistant Plasmodium falciparum strains. A total of 45 compounds were reported with promising insecticidal potentials against two efficient vector species, Anopheles stephensi Liston and A. gambiae Giles. Limonoids were the most abundant (51.6%) reported compounds and they exhibited the most promising antiplasmodial activity such as gedunin (3) which demonstrated an activity equal to quinine or azadirachtin (1) displaying promising larvicidal, pupicidal and adulticidal effects on different larval instars of A. stephensi with almost 100% larval mortality at 1 ppm concentration.

CONCLUSION

Studies performed so far on Meliaceae plants have reported compounds with significant antiplasmodial and insecticidal activity, lending support to the use of species of this family in folk medicine, for the treatment of malaria. Moreover, results qualified several of these species as important sources of compounds for the development of eco-friendly pesticides to control mosquito vectors. However, more in vitro, in vivo and full ADMET studies are still required to provide additional data that could guide in developing novel drugs and insecticides.

Antimalarial Plants Used across Kenyan Communities

Malaria is one of the serious health problems in Africa, Asia, and Latin America. Its treatment has been met with chronic failure due to pathogenic resistance to the currently available drugs. This review attempts to compile phytotherapeutical information on antimalarial plants in Kenya based on electronic data. A comprehensive web search was conducted in multidisciplinary databases, and a total of 286 plant species from 75 families, distributed among 192 genera, were retrieved. Globally, about 139 (48.6%) of the species have been investigated for antiplasmodial (18%) or antimalarial activities (97.1%) with promising results. However, there is no record on the antimalarial activity of about 51.4% of the species used although they could be potential sources of antimalarial remedies. Analysis of ethnomedicinal recipes indicated that mainly leaves (27.7%) and roots (19.4%) of shrubs (33.2%), trees (30.1%), and herbs (29.7%) are used for preparation of antimalarial decoctions (70.5%) and infusions (5.4%) in Kenya. The study highlighted a rich diversity of indigenous antimalarial plants with equally divergent herbal remedy preparation and use pattern. Further research is required to validate the therapeutic potential of antimalarial compounds from the unstudied claimed species. Although some species were investigated for their antimalarial efficacies, their toxicity and safety aspects need to be further investigated.

Biological Activities of Gedunin-A Limonoid from the Meliaceae Family

Gedunin is an important limonoid present in several genera of the Meliaceae family, mainly in seeds. Several biological activities have been attributed to gedunin, including antibacterial, insecticidal, antimalarial, antiallergic, anti-inflammatory, anticancer, and neuroprotective effects. The discovery of gedunin as a heat shock protein (Hsp) inhibitor represented a very important landmark for its application as a biological therapeutic agent. The current study is a critical literature review based on the several biological activities so far described for gedunin, its therapeutic effect on some human diseases, and future directions of research for this natural compound.

In vivo Anti-Plasmodium Activity and Toxicity of Afzelia bipindensis and Senna Siamea Extracts: A Murine Model

Background:

Malaria, a parasitosis affecting man, remains a public health problem in developing countries where morbidity and mortality are very high. Afzelia bipindensis and Senna siamea are two plants used in the treatment of malaria in different African countries including Cameroon.

Objective:

The aim of the present study was to evaluate the antiplasmodial activity of hydroethanolic leaves extracts of Afzelia bipindensis and Senna siamea, from Northern Cameron using Plasmodium berghei and to investigate the acute and sub-acute toxicity of leaves extracts in a rodent model.

Methods:

The four days Peter’s suppressive test was used to evaluate the antiplasmodial activity and the OCDE 423 and 412 guidelines were applied to evaluate acute and sub-acute toxicity. Biochemical tests related to hepatic, cardiac and renal toxicity were also assessed.

Results:

The leaves’ extracts of Afzelia bipindensis at doses 180, 360, 720 mg/kg and Senna siamea at doses of 100, 200, 400 mg/kg have shown significant antiplasmodial activity (P) with parasite reduction ≈ 50%. No mortality of rats was observed at the tested doses. The biochemical analysis did not reveal any statistically significant difference when compared with control. However, ALT was statistically increased at a higher dose (720 mg/kg) of Afzelia bipindensis leaves extract. On the other hand, there was a significant decrease in triglycerides at 360 mg/kg and 720 mg/kg

Conclusion:

It is concluded that daily consumption of leaves extract of Afzelia bipindensis and Senna siamea are without significant risks to human health, favoring the use of these products in the treatment of malaria.

Non-nitrogenous Plant-derived Constituents with Antiplasmodial Activity

The paper is a compilation of the studies reported in the literature concerning non-nitrogenous natural constituents that have shown antiplasmodial activity and aims to provide a basis for further in vivo studies as well as for clinical trials to develop new antimalarial agents. Due to the increasingly unsatisfactory outcomes for N-heterocyclic drugs, coupled with the rising incidence of the deadly falciparum malaria, the advent of non-nitrogenous lead compounds is timely, signaling a new era of antimalarial chemotherapy. Currently a few non-nitrogenous molecules are used in therapy, but many promising molecules of plant origin are under study, such as peroxide sesquiterpenes, quinoid triterpenes, quassinoids, gallic acid derivatives, lignans, flavonoids and biflavonoids, xanthones, naphthoquinones and phenylanthraquinones. Many of these constituents are isolated from plants used traditionally to treat malaria and fever. Ethnopharmacology can still be considered as a rich source of lead molecules.

Effects of Azadirachta indica seed kernel extracts on early erythrocytic schizogony of Plasmodium berghei and pro-inflammatory response in inbred mice

BACKGROUND

Medicinal plant research may contribute to develop new pharmacological control tools for vector borne diseases, such as malaria.

METHODS

The effects of methanol extracts (ME) obtained from seed kernel of ripe and unripe Azadirachta indica fruits were studied on erythrocytic proliferation of the rodent malaria parasite Plasmodium berghei strain ANKA and on mice pro-inflammatory response, as evaluated by measuring the matrix-metalloproteinase-9 (MMP-9) and tumour necrosis factor (TNF) plasma levels, in two mouse strains (C57BL/6 and BALB/c) which are considered as prototypical of Th1 and Th2 immune response, respectively.

RESULTS

ME obtained from seed kernel of unripe Azadirachta indica fruits decreased by about 30% the proportion of erythrocytes infected with the malaria parasite in C57BL/6 mice in the 4 days suppressive test. In this treatment group, MMP-9 and TNF levels were notably higher than those measured in the same mouse strain treated with the anti-malarial drug artesunate, Azadirachta indica kernel extracts from ripe fruits or solvent. In BALB/c mice, treatment with kernel extracts did not influence parasitaemia. MMP-9 and TNF levels measured in this mouse strain were notably lower than those recorded in C57BL/6 mice and did not vary among treatment groups.

CONCLUSIONS

The effects of the ME on the parasite-host interactions appeared to be mouse strain-dependent, but also related to the ripening stage of the neem fruits, as only the unripe fruit seed kernel extracts displayed appreciable bioactivity.

Hydroethanolic Extracts of Erigeron floribundus and Azadirachta indica Reduced Plasmodium berghei Parasitemia in Balb/c Mice

Malaria is one of the most important infectious diseases in Africa especially in Cameroon. The nonaccessibility to current treatments for poor people and the appearance of drug-resistant Plasmodium falciparum parasites stimulate the search for alternative treatments. The aim of this study was to evaluate the antimalarial activity and the safety of hydroethanolic extracts from Erigeron floribundus and Azadirachta indica. The crude hydroethanolic extracts of E. floribundus (HEEF) and A. indica (HEAI) were prepared via maceration of the whole plant powder of E. floribundus and the leaves of A. indica in 70% ethanol. The antimalarial activity was determined according to Peter's 4-day suppressive test using the murine model Plasmodium berghei/Balb C mice, while the acute and subacute toxicity tests were assessed according to the OECD 425 and 407 guidelines, respectively. The results indicate a reduction of parasitemia ranging from 49.75 ± 3.64 to 69.28 ± 1.36% for HEAI and from 30.46 ± 4.30 to 62.36 ± 2.32% for HEEI. Overall, HEEF and HEAI at doses of 60, 120, and 240 mg/kg b.w. and 75, 150, and 300 mg/kg b.w., respectively, showed a significant (p≤0.001) parasitemia reduction on P. berghei infecting BALB/c mice. HEEF and HEAI caused a significant (p<0.001) attenuation of body temperature drop in mice compared to negative control, except for the 150 mg/kg b.w. dose in the female group. Moreover, there was no mice mortality observed with these extracts even at 5000 mg/kg, while the aspartate amino transferase (ASAT) level of mice treated with 300 mg/kg b.w. of HEAI extract increased when compared with the control. The results of this study support the traditional use of these plants species extracts against malaria infection in rural zones of Northern Cameroon, therefore confirming their potential as sources for the development of efficient phytomedicines for malaria-poverty disease alleviation.

Medicinal plants used by the people of Nsukka Local Government Area, south-eastern Nigeria for the treatment of malaria: An ethnobotanical survey

ETHNOBOTANICAL RELEVANCE

Malaria is a serious public health problem especially in sub-Saharan African countries such as Nigeria. The causative parasite is increasingly developing resistance to the existing drugs. There is urgent need for alternative and affordable therapy from medicinal plants which have been used by the indigenous people for many years.

AIM OF STUDY

This study was conducted to document the medicinal plant species traditionally used by the people of Nsukka Local Government Area in south-eastern Nigeria for the treatment of malaria.

METHODS

A total of 213 respondents, represented by women (59.2%) and men (40.8%), were interviewed using a semi-structured questionnaire. The results were analysed and discussed in the context of previously published information on anti-malarial and phytochemical studies of the identified plants.

RESULTS

The survey revealed that 50 plant species belonging to 30 botanical families were used in this region for the treatment of malaria. The most cited families were Apocynaceae (13.3%), Annonaceae (10.0%), Asteraceae (10.0%), Lamiaceae (10.0%), Poaceae (10.0%), Rubiaceae (10.0%) and Rutaceae (10.0%). The most cited plant species were Azadirachta indica (11.3%), Mangifera indica (9.1%), Carica papaya (8.5%), Cymbopogon citratus (8.5%) and Psidium guajava (8.5%).

CONCLUSION

The present findings showed that the people of Nsukka use a large variety of plants for the treatment of malaria. The identified plants are currently undergoing screening for anti-malarial, toxicity and chemical studies in our laboratory.

Treatment of malaria and related symptoms using traditional herbal medicine in Ethiopia

ETHNOPHARMACOLOGICAL RELEVANCE

Medicinal plants have always been an integral part of different cultures in Ethiopia in the treatment of different illnesses including malaria and related symptoms. However, due to lack of proper documentation, urbanization, drought, acculturation and deforestation, there is an increased risk of losing this traditional knowledge. Hence, the use of the indigenous knowledge should be well documented and validated for potential future use.

AIM OF THE STUDY

To gather and document information on medicinal plants which are used in the traditional treatment of malaria and related symptoms in Ethiopia.

MATERIALS AND METHODS

First, an ethnomedicinal survey of plants was conducted in 17 districts of Jimma zone, the Oromia national regional state of Ethiopia. Jimma zone is malarious and rich in natural flora. A total of 115 traditional healers were interviewed using a semi-structured questionnaire containing personal data of the respondents, and information on medicinal plants used to treat malaria and related symptoms. In addition, a literature search using Medline/PubMed, Google Scholar, ScienceDirect and HINARI was conducted on the indigenous use, in-vitro/in-vivo anti-malarial activity reports, and the chemical characterization of medicinal plants of Ethiopia used against malaria.

RESULTS

From ethnomedicinal survey, a total of 28 species of plants used in the traditional treatment of malaria and related symptoms in Jimma Zone were collected, identified and documented. In addition, the literature search revealed that 124 medicinal plant species were reported to be traditionally used in the treatment of malaria in Ethiopia. From both ethnomedicinal survey and the literature search, Asteraceae and Fabaceae were the most represented families and Allium sativum L., Carica papaya L., Vernonia amygdalina Del., Lepidium sativum L. and Croton macrostachyus Del. were the most frequently reported plant species for their anti-malarial use. The dominant plant parts used in the preparation of remedies were leaves. About 54% of the medicinal plants documented in the survey have been reported as an anti-malarial plant in the literature search. Furthermore, the in-vitro and in-vivo anti-plasmodial activity reports of extracts from some of plant species were found to support the traditional claim of the documented plants. Moreover, literatures indicate that several secondary metabolites isolated from certain plant species that are traditionally used for the treatment of malaria and related symptoms in Ethiopia demonstrate strong anti-plasmodial activity.

CONCLUSIONS

The result of the current study showed that traditional knowledge is still playing an important role in the management of malaria and related symptoms in Ethiopia. Allium sativum L., Carica papaya L., Vernonia amygdalina Del., and Lepidium sativum L. are the most commonly reported species as anti-malarial plants and the traditional claim of some species was supported by known anti-plasmodial activity and bioactivity reports. The finding of this study is important in the rational prioritization of plant species which are potentially used for investigating new compounds, which could be efficacious for malaria treatment.

Gaining Synthetic Appreciation for the Gedunin ABC Ring System

Gedunin, first isolated in 1960, displays a remarkable range of biological activity, but has yet to receive dedicated synthetic attention from a ground up construction perspective. Presented herein is a successfully executed approach to the fully functionalized ABC ring system of this challengingly complex natural product.

Transmission blocking effects of neem (Azadirachta indica) seed kernel limonoids on Plasmodium berghei early sporogonic development

Azadirachta indica, known as neem tree and traditionally called "nature's drug store" makes part of several African pharmacopeias and is widely used for the preparation of homemade remedies and commercial preparations against various illnesses, including malaria. Employing a bio-guided fractionation approach, molecules obtained from A. indica ripe and green fruit kernels were tested for activity against early sporogonic stages of Plasmodium berghei, the parasite stages that develop in the mosquito mid gut after an infective blood meal. The limonoid deacetylnimbin (3) was identified as one the most active compounds of the extract, with a considerably higher activity compared to that of the close analogue nimbin (2). Pure deacetylnimbin (3) appeared to interfere with transmissible Plasmodium stages at a similar potency as azadirachtin A. Considering its higher thermal and chemical stability, deacetylnimbin could represent a suitable alternative to azadirachtin A for the preparation of transmission blocking antimalarials.

In vitro and in vivo anti-malarial activity of limonoids isolated from the residual seed biomass from Carapa guianensis (andiroba) oil production

BACKGROUND

Carapa guianensis is a cultivable tree used by traditional health practitioners in the Amazon region to treat several diseases and particularly symptoms related to malaria. Abundant residual pressed seed material (RPSM) results as a by-product of carapa or andiroba oil production. The objective of this study was to evaluate the in vitro and in vivo anti-malarial activity and cytotoxicity of limonoids isolated from C. guaianensis RPSM.

METHODS

6α-acetoxyepoxyazadiradione (1), andirobin (2), 6α-acetoxygedunin (3) and 7-deacetoxy-7-oxogedunin (4) (all isolated from RPSM using extraction and chromatography techniques) and 6α-hydroxy-deacetylgedunin (5) (prepared from 3) were evaluated using the micro test on the multi-drug-resistant Plasmodium falciparum K1 strain. The efficacy of limonoids 3 and 4 was then evaluated orally and subcutaneously in BALB/c mice infected with chloroquine-sensitive Plasmodium berghei NK65 strain in the 4-day suppressive test.

RESULTS

In vitro, limonoids 1-5 exhibited median inhibition concentrations (IC50) of 20.7-5.0 μM, respectively. In general, these limonoids were not toxic to normal cells (MRC-5 human fibroblasts). In vivo, 3 was more active than 4. At oral doses of 50 and 100 mg/kg/day, 3 suppressed parasitaemia versus untreated controls by 40 and 66%, respectively, evidencing a clear dose-response.

CONCLUSION

6α-acetoxygedunin is an abundant natural product present in C. guianensis residual seed materials that exhibits significant in vivo anti-malarial properties.

Transmission blocking activity of Azadirachta indica and Guiera senegalensis extracts on the sporogonic development of Plasmodium falciparum field isolates in Anopheles coluzzii mosquitoes

BACKGROUND

Targeting the stages of the malaria parasites responsible for transmission from the human host to the mosquito vector is a key pharmacological strategy for malaria control. Research efforts to identify compounds that are active against these stages have significantly increased in recent years. However, at present, only two drugs are available, namely primaquine and artesunate, which reportedly act on late stage gametocytes.

METHODS

In this study, we assessed the antiplasmodial effects of 5 extracts obtained from the neem tree Azadirachta indica and Guiera senegalensis against the early vector stages of Plasmodium falciparum, using field isolates. In an ex vivo assay gametocytaemic blood was supplemented with the plant extracts and offered to Anopheles coluzzii females by membrane feeding. Transmission blocking activity was evaluated by assessing oocyst prevalence and density on the mosquito midguts.

RESULTS

Initial screening of the 5 plant extracts at 250 ppm revealed transmission blocking activity in two neem preparations. Up to a concentration of 70 ppm the commercial extract NeemAzal completely blocked transmission and at 60 ppm mosquitoes of 4 out of 5 replicate groups remained uninfected. Mosquitoes fed on the ethyl acetate phase of neem leaves at 250 ppm showed a reduction in oocyst prevalence of 59.0% (CI₉₅ 12.0 - 79.0; p < 10-4) and in oocyst density of 90.5% (CI₉₅ 86.0 - 93.5; p < 10-4 ), while the ethanol extract from the same plant part did not exhibit any activity. No evidence of transmission blocking activity was found using G. senegalensis ethyl acetate extract from stem galls.

CONCLUSIONS

The results of this study highlight the potential of antimalarial plants for the discovery of novel transmission blocking molecules, and open up the potential of developing standardized transmission blocking herbal formulations as malaria control tools to complement currently used antimalarial drugs and combination treatments.

Synthesis of the B-seco limonoid core scaffold

Synthetic investigations towards the structurally complex and highly decorated framework of B-seco limonoid natural products by means of a [3,3]-sigmatropic rearrangement are described. Detailed model studies reveal, that an Ireland-Claisen rearrangement can be employed to construct the central C9-C10 bond thereby giving access to the B-seco limonoid scaffold. However, application of the developed strategy ended up failing in more complex and sterically demanding systems.

Ceramicine B, a limonoid with anti-lipid droplets accumulation activity from Chisocheton ceramicus

The Meliaceae family of plants has been shown to contain a vast number of compounds with the potential to be developed for medicinal purposes. We have previously reported the isolation of limonoids from a plant in the Meliaceae family named Chisocheton ceramicus. Ceramicine B was identified as an active compound in inhibiting lipid droplets accumulation (LDA) in the mouse preadipocyte cell line MC3T3-G2/PA6. The presence of ceramicine B was found to inhibit the expression of glucose transporter type 4, lipoprotein lipase, and 11-beta hydroxysteroid dehydrogenase mRNA, and also adipogenic master regulator, peroxisome proliferator-activated receptor-γ, and CCAAT-enhancer-binding protein-α (C/EBPα) mRNA. However, for early adipogenic regulators, such as C/EBPβ and C/EBPδ, and intermediary adipogenic regulators, Krüppel-like factors were unaffected. Western blot analysis showed that ceramicine B was found to inhibit the phosphorylation of Forkhead box O1 (Foxo1), a key process in the insulin signaling pathway. This suggested that the mechanism of anti-LDA activity of ceramicine B was partly via the inhibition of Foxo1 phosphorylation.

Antimalarial plant remedies from Burkina Faso: their potential for prophylactic use

ETHNOPHARMACOLOGICAL RELEVANCE

Saye, a combination remedy prepared from Cochlospermum planchonii Hook.f. (Cochlospermaceae), Cassia alata L. (Fabaceae) and Phyllanthus amarus Schumach. et Thonn. (Euphorbiaceae), N'Dribala, a Cochlospermum planchonii root decoction, and a fruit preparation of Azadirachta indica A. Juss. (Meliaceae) are plant remedies of the folk medicine in Burkina Faso and are commonly used by traditional healers for the treatment of malaria.

AIM OF THE STUDY

This study aimed at validating the antiplasmodial activity of the preparations and at estimating their potential for prophylaxis, using the murine malaria system Plasmodium berghei/Anopheles stephensi.

MATERIALS AND METHODS

Aqueous extracts were orally administered to mice (6 animals per treatment group) at a daily dose of 200mg/kg body weight for nine days, applying protocols that mimic as much as possible traditional recipes and treatment schemes.

RESULTS

Saye, N'Dribala and Azadirachta indica preparations revealed prophylactic activity, reducing parasitaemia in treated mice, with respect to controls, by 52.0% (CI(95) 46.1-57.9), 45.5% (CI(95) 44.5-46.5) and 45.0% (CI(95) 41.1-48.9), respectively. No evidence of transmission blocking effects was detected with any of the tested remedies.

CONCLUSIONS

This study confirms, in the murine malaria system, the antiplasmodial properties of the examined remedies on the Plasmodium stages developing in the vertebrate host, thus encouraging studies aiming at identifying the active fractions and compounds responsible for the described activity and to develop standardized prophylactic remedies.

Ceramicines J-L, new limonoids from Chisocheton ceramicus

Three new limonoids, ceramicines J (1), K (2), and L (3), were isolated from the hexane layer of Chisocheton ceramicus bark extract. Their structures were elucidated from 1D and 2D NMR data. Ceramicines J-L (1-3) exhibited dose-dependent moderate cytotoxicity against the HL-60 cell line.

Potential of a Khaya ivorensis -Alstonia boonei extract combination as antimalarial prophylactic remedy

ETHNOPHARMACOLOGICAL RELEVANCE

The decoction of the combined stem barks of Khaya ivorensis A. Chev. (Meliaceae) and Alstonia boonei De Wild (Apocynaceae) has a history of use in traditional medicine of central Cameroon for malaria treatment but also for the prevention of the disease.

AIM OF THE STUDY

The purpose of this investigation was to determine the antiplasmodial activity of Khaya ivorensis (K) and Alstonia boonei (A) preparations in the murine malaria model Plasmodium berghei/Anopheles stephensi, to estimate their prophylactic potential and to assess acute and sub-acute toxicity of the formulations prepared according to the traditional recipes.

MATERIALS AND METHODS

Aqueous extracts from the stem-bark of the two plants were prepared and tested separately and in combination. BALB/c mice were treated for 9 days and challenged on day 3 by exposure to mosquitoes infected with Plasmodium berghei. Treatment doses ranged between 200 and 400mg/kg/day, corresponding approximately to the dosage applied by traditional healers to cure malaria patients or prevent the disease. Parasitemia reduction in treated animals was calculated from Giemsa smear counts, of two replicate experiments. To estimate acute toxicity in terms of median lethal dose (LD50), geometrically increasing doses were administered to mice. Sub-acute toxicity of the herbal combination (KA) was investigated by administering the same doses as in the antiplasmodial activity test for a period of 14 days, followed by 14 days of recovery observation. Locomotor activity (Open Field Test), body weight, liver and kidney morphology were monitored.

RESULTS

The combination KA was found to exhibit antiplasmodial activity in the murine malaria model. In mice treated with the combination remedy at a dosage of 200mg/kg/day, parasitemia values of 6.2% ± 1.7 and 6.5% ± 0.8 were recorded, compared to 10.8% ± 1.3 and 12.0% ± 4.0 in controls (p<0.01). Doubling the dosage of the extracts did not significantly increase parasite suppression. When extracts of K and A were administered separately at a dosage of 400mg/kg, a reduction in parasitemia was still obtained, but it did not reach statistical significance. Toxicity studies yielded comforting results: the LD50 was estimated to be greater than 2779.5mg/kg. Moreover, mice exposed to the fourteen-day repeated-dose toxicity test (sub-acute toxicity test) did not display weight loss, liver or kidney morphological modifications, significant alterations in locomotor activity or any other sign of illness.

CONCLUSION

The antiplasmodial activity and the wide dose interval between the therapeutic dosage and the toxic dosage exhibited by the KA herbal combination in the murine malaria model argue in favor of its use as an antimalarial prophylactic remedy. It remains to be demonstrated by human clinical trials whether the combination remedy, when taken by inhabitants during malaria transmission season, can reduce parasite density and lead to a reduction of malaria episodes in the community.

Chisomicines A-C, limonoids from Chisocheton ceramicus

Three new limonoids, chisomicines A-C (1-3), have been isolated from the bark of Chisocheton ceramicus. Their structures were determined by 2D NMR, CD spectroscopic methods, and X-ray analysis. Chisomicine A (1) exhibited NO production inhibitory activity in J774.1 cells stimulated by LPS dose-dependently at high cell viability.

Cytotoxic and apoptosis-inducing activities of limonoids from the seeds of Azadirachta indica (neem)

Thirty-five limonoids, including 15 of the azadiradione type (1-15), five of the gedunin type (16-20), four of the azadirachtin type (21-24), nine of the nimbin type (25-33), and two degraded limonoids (34, 35), isolated from Azadirachta indica seed extracts, were evaluated for their cytotoxic activities against five human cancer cell lines. Seven compounds (3, 6, 7, 16, 18, 28, and 29) exhibited cytotoxic activity against one or more cell lines. Among these compounds, 7-deacetyl-7-benzoylepoxyazadiradione (7), 7-deacetyl-7-benzoylgeduin (18), and 28-deoxonimbolide (28) exhibited potent cytotoxic activity against HL60 leukemia cells with IC(50) values in the range 2.7-3.1 μM. Compounds 7, 18, and 28 induced early apoptosis in HL60 cells, observed by flow cytometry. Western blot analysis showed that compounds 7, 18, and 28 activated caspases-3, -8, and -9 in HL60 cells. This suggested that compounds 7, 18, and 28 induced apoptotic cell death in HL60 cells via both the mitochondrial- and the death receptor-mediated pathways. Futhermore, compound 7 was shown to possess high selective cytotoxicity for leukemia cells since it exhibited only weak cytotoxicity against a normal lymphocyte cell line (RPMI 1788).

In vitro antiplasmodial activity and cytotoxicity of crude extracts and compounds from the stem bark of Kigelia africana (Lam.) Benth (Bignoniaceae)

In order to assess the potential of the stem bark of Kigelia africana (Lam.) Benth as source of new anti-malarial leads, n-hexane and ethyl acetate (EtOAc) extracts and four compounds isolated from the stem bark were screened in vitro against the chloroquine-resistant W-2 and two field isolates of Plasmodium falciparum using lactate dehydrogenase assay. The products were also tested for their cytotoxicity on LLC/MK2 monkey kidney cells. The EtOAc extract exhibited a significant antiplasmodial activity (IC(50) = 11.15 μg/mL on W-2; 3.91 and 4.74 μg/mL on field CAM10 and SHF4 isolates, respectively), whereas the n-hexane fraction showed a weak activity (IC(50) = 73.78 μg/mL on W-2 and 21.85 μg/mL on SHF4). Three out of the four compounds showed good activity against all the three different parasite strains (IC(50) <5 μM). Specicoside exhibited the highest activity on W-2 (IC(50) = 1.54 μM) followed by 2β, 3β, 19α-trihydroxy-urs-12-en-28-oic acid (IC(50) = 1.60 μM) and atranorin (IC(50) = 4.41 μM), while p-hydroxycinnamic acid was the least active (IC(50) =53.84 μM). The EtOAc extract and its isolated compounds (specicoside and p-hydroxycinnamic acid) were non-cytotoxic (CC(50) > 30 μg/mL), whereas the n-hexane extract and two of its products, atranorin and 2β, 3β, 19α-trihydroxy-urs-12-en-28-oic acid showed cytotoxicity at high concentrations, with the last one being the most toxic (CC(50) = 9.37 μg/mL). These findings justify the use of K. africana stem bark as antimalaria by traditional healers of Western Cameroon, and could constitute a good basis for further studies towards development of new leads or natural drugs for malaria.

Traditional herbal antimalarial therapy in Kilifi district, Kenya

AIM OF STUDY

To identify plant species used by the traditional health practitioners (THPs) in treatment of malaria, carry out cytotoxicity and efficacy evaluation of the identified plants and to evaluate combination effects.

MATERIALS AND METHODS

Thirteen plants were selected through interviews with traditional healers. In vitro antiplasmodial testing was done by measuring ability of the test sample to inhibit the incorporation of radio-labelled hypoxanthine into the malaria parasite. The extracts were tested singly and then in combination using the standard fixed ratio analysis to evaluate synergism. In vivo bioassay was done in mice using Peter's 4-days suppressive test and cytotoxicity evaluated in vitro using Vero E6 cells.

RESULTS

Of the plants tested in vitro, 25% were highly active (IC(50)<10 μg/ml), 46% moderately active (IC(50) 10-50 μg/ml), 16% had weak activity of 50-100 μg/ml while 13% were not active IC(50) >100 μg/ml. Methanolic extracts of Azadirachta indica, Premna chrysoclada and Uvaria acuminata were the most active (IC(50)<10μg/ml) against both the chloroquine (CQ) sensitive (D6) and the CQ resistant (W2) Plasmodium falciparum clones. When tested in vivo in a mouse model, Azadirachta indica, Rhus natalensis and Grewia plagiophylla depicted the highest percent parasite clearance and chemo suppression of 89%, 82% and 78%, respectively. Evaluating effect of combining some of these extracts with one another against a multi-drug resistant Plasmodium falciparum (W2) clone revealed synergism among some combinations. The highest synergy was between Uvaria acuminata and Premna chrysoclada. The interaction between Grewia plagiophylla and Combretum illairii was largely antagonistic. Impressive cytotoxicity results were obtained with most of the plants tested revealing high selectivity indices an indication of enabling achievement of therapeutic doses at safe concentrations. Uvaria acuminata was, however, toxic to the cultured cells. Mild cytotoxicity was also observed in Hoslundia opposita and Lannea schweinfurthii (CC(50) 37 and 76 μg/ml, respectively).

CONCLUSIONS

This study identified plants with low IC(50) values, high percent chemo suppression and low cytotoxicity thus potential sources for novel antiplasmodial agents. The findings remotely justify use of combined medicinal plants in traditional medicine practices as synergy among some plant species was demonstrated.

Potential antimalarials from Nigerian plants: a review

Malaria, caused by parasites of the genus Plasmodium, is one of the leading infectious diseases in many tropical regions, including Nigeria, a West African country where transmission occurs all year round. Many of the inhabitants use plants as remedies against fever and other symptoms of acute malaria, as reported herein. Some of these plants have their antimalarial efficacies scientifically demonstrated and the active compounds isolated with their probable mechanisms of action studied. Medicinal plants are used to treat diseases also where the biodiversity of plants occur in parallel with endemic transmission of malaria. This review focuses on medicinal plants which are used to treat malaria in Nigeria, and on antimalarial testing of extracts and purified compounds from plants. Some show intense activity against malaria parasites in vitro and in experimentally infected mice. The search for new drugs based on plants is important due to the emergence and widespread of chloroquine-resistant and multiple drug-resistant malaria parasites, which require the development of new antimalarials. An acquaintance with antimalarial plants may be a springboard for new phytotherapies that could be affordable to treat malaria, especially among the less privileged native people living in endemic areas of the tropics, mostly at risk of this devastating disease.

Blocking Plasmodium falciparum Malaria Transmission with Drugs: The Gametocytocidal and Sporontocidal Properties of Current and Prospective Antimalarials

Drugs that kill or inhibit the sexual stages of Plasmodium could potentially amplify or synergize the impact of other interventions by blocking transmission to mosquitoes. Primaquine and other 8-aminoquinolines have long offered such potential, but safety and other concerns have limited their use. Although transmission-blocking properties are not often a priority of drug discovery efforts, a number of interesting gametocytocidal and/or sporontocidal drug candidates have emerged in recent years. Some still bear significant technical and safety concerns, while others have passed clinical trials and are on the verge of entering the antimalarial armamentarium. Recent advances in our knowledge of gametocyte differentiation, gametogenesis and sporogony have also led to the identification of a large array of potential new targets for drugs that might interfere with malaria transmission. This review examines the properties of existing and prospective drugs, mechanisms of action, counter-indications and their potential role in regional malaria elimination efforts.

Traditional antimalarial phytotherapy remedies used by the South Coast community, Kenya

AIM OF THE STUDY

This study was conducted to document herbal medicines used in the treatment of malaria as well as the existing knowledge, attitudes and practices related to malaria recognition, control and treatment in South Coast, Kenya.

METHODS

Data was collected using semistructured questionnaires and interviews. A focused group discussion held with the community members, one in each of the study villages supplemented the interview and questionnaire survey.

RESULTS

The respondents were found to have a good understanding of malaria and could distinguish it from other fever types. They were also aware that malaria was spread by mosquitoes. Malaria prevalence was high, and affected individuals an average of four times a year. Community members avoided mosquito bites by using mosquito nets, clearing bushes around their homesteads and burning plant parts to generate smoke. They prevented and treated malaria by taking decoctions or concoctions of traditional herbal remedies. Forty plant species in thirty-five genera distributed in twenty-four families were used as antimalarials in the study area. Five plant species, namely; Heeria insignis Del. (Anacardiaceae), Rottboelia exaltata L.F (Gramineae), Pentanisia ouranogyne S. Moore (Rubiaceae), Agathisanthenum globosum (A. Rich) Hiern (Rubiaceae), and Grewia trichocarpa Hochst ex A. Rich (Tiliaceae) are documented for the first time in South Coast, Kenya, for the treatment of malaria.

CONCLUSIONS

The plants documented in the current study are a potential source for new bioactive compounds of therapeutic value in malaria treatment. The results provide data for further pharmacological and toxicological studies and development of commercial antimalarial phytotherapy products.

Antimalarial herbal remedies of Msambweni, Kenya

Malaria is a serious cause of mortality globally. The disease is of regional concern in Africa and of national interest in Kenya due to its high morbidity and mortality as a result of development of resistant strains of Plasmodium falciparum to many existing drugs such as chloroquine. Alternative medicine using herbal remedies are commonly used to treat malaria in Kenya. However, plants used in some rural areas in Kenya are not documented. Many antimalarial drugs have been derived from plants. This study was conducted to document medicinal plants that are traditionally used by the Msambweni community of Kenyan South Coast to treat malaria, where the disease is endemic. Herbalists were interviewed by administration of semistructured questionnaires in order to obtain information on medicinal plants traditionally used for the treatment of malaria. Focused group discussions held with the herbalists supplemented the interview and questionnaire survey. Twenty-seven species of plants in 24 genera distributed in 20 families were reported to be used in this region for the treatment of malaria. Labiatae, Rutaceae and Liliaceae families had each eleven percent of the plant species reported and represented the species that are most commonly used. Thirteen plant species, namely; Aloe deserti Berger (Liliaceae), Launea cornuta (Oliv and Hiern) C. Jeffrey (Compositae), Ocimum bacilicum L. (Labiatae), Teclea simplicifolia (Eng) Verdoon (Rutaceae), Gerranthus lobatus (Cogn.) Jeffrey (Cucurbitaceae), Grewia hexaminta Burret. (Tiliaceae), Canthium glaucum Hiern. (Rubiaceae), Amaranthus hybridus L. (Amaranthaceae), Combretum padoides Engl and Diels. (Combretaceae), Senecio syringitolius O. Hoffman. (Compositae), Ocimum suave Willd (Labiatae), Aloe macrosiphon Bak. (Liliaceae) and Laudolphia buchananii (Hall.f) Stapf. (Apocynaceae) are documented from this region for the first time for the treatment of malaria. These results become a basis for selection of plants for further pharmacological, toxicological and phytochemical studies in developing new plant based antimalarial drugs.

Transmission blocking activity of a standardized neem (Azadirachta indica) seed extract on the rodent malaria parasite Plasmodium berghei in its vector Anopheles stephensi

Background

The wide use of gametocytocidal artemisinin-based combination therapy (ACT) lead to a reduction of Plasmodium falciparum transmission in several African endemic settings. An increased impact on malaria burden may be achieved through the development of improved transmission-blocking formulations, including molecules complementing the gametocytocidal effects of artemisinin derivatives and/or acting on Plasmodium stages developing in the vector. Azadirachtin, a limonoid (tetranortriterpenoid) abundant in neem (Azadirachta indica, Meliaceae) seeds, is a promising candidate, inhibiting Plasmodium exflagellation in vitro at low concentrations. This work aimed at assessing the transmission-blocking potential of NeemAzal^®, an azadirachtin-enriched extract of neem seeds, using the rodent malaria in vivo model Plasmodium berghei/Anopheles stephensi.

Methods

Anopheles stephensi females were offered a blood-meal on P. berghei infected, gametocytaemic BALB/c mice, treated intraperitoneally with NeemAzal, one hour before feeding. The transmission-blocking activity of the product was evaluated by assessing oocyst prevalence, oocyst density and capacity to infect healthy mice. To characterize the anti-plasmodial effects of NeemAzal^® on early midgut stages, i.e. zygotes and ookinetes, Giemsa-stained mosquito midgut smears were examined.

Results

NeemAzal^® completely blocked P. berghei development in the vector, at an azadirachtin dose of 50 mg/kg mouse body weight. The totally 138 examined, treated mosquitoes (three experimental replications) did not reveal any oocyst and none of the healthy mice exposed to their bites developed parasitaemia. The examination of midgut content smears revealed a reduced number of zygotes and post-zygotic forms and the absence of mature ookinetes in treated mosquitoes. Post-zygotic forms showed several morphological alterations, compatible with the hypothesis of an azadirachtin interference with the functionality of the microtubule organizing centres and with the assembly of cytoskeletal microtubules, which are both fundamental processes in Plasmodium gametogenesis and ookinete formation.

Conclusions

This work demonstrated in vivo transmission blocking activity of an azadirachtin-enriched neem seed extract at an azadirachtin dose compatible with 'druggability' requisites. These results and evidence of anti-plasmodial activity of neem products accumulated over the last years encourage to convey neem compounds into the drug discovery & development pipeline and to evaluate their potential for the design of novel or improved transmission-blocking remedies.

Therapeutic effect of meliacine, an antiviral derived from Melia azedarach L., in mice genital herpetic infection

Since natural products are considered powerful sources of novel drug discovery, a partially purified extract (meliacine) from the leaves of Melia azedarach L., a plant used in traditional medicine in India for the treatment of several diseases, has been studied. Meliacine exhibits a potent antiviral effect against several viruses without displaying cytotoxicity. The purpose of the present study was to evaluate the therapeutic effect of intravaginal administration of meliacine in a mouse model of genital herpetic infection. BALB/c female mice were infected with MS or G strains of Herpes Simplex Virus type 2 and then treated with meliacine topically. An overall protective effect was observed. Animal survival increased, the severity of the disease was reduced, life span was extended and virus shedding in vagina fluids was diminished. In addition, meliacine reduced the amount of virus that migrated to the brain and vaginal fluids presented higher levels of IFN-gamma and TNF-alpha than untreated infected mice. These results indicate that meliacine could be an alternative therapeutic compound against HSV-2 genital infection.