Tanzania Journal of Health Research Health User's Trust Fund (HRUTF) ISSN: 1821-6404 Vol. 12, Num. 1, 2011

Tanzania Journal of Health Research, Vol. 12, No. 1, January, 2010

Brine shrimp toxicity of some plants used as traditional medicines in Kagera Region, north western Tanzania

M.J.MOSHI¹*, E. INNOCENT¹, J.J. MAGADULA¹, D.F. OTIENO², A. WEISHEIT³, P.K. MBABAZI³ and R.S.O.NONDO¹

¹Department of Biological and Preclinical Studies, Institute of Traditional Medicine, Muhimbili University of Health and Allied Sciences, Box 65001, Dar es Salaam, Tanzania.
²Department of Biological Sciences, Moi University, Eldoret, Kenya
³Faculty of Development Studies,  Mbarara University of Science & Technology, Mbarara, Uganda

* Correspondence: Prof. Mainen J. Moshi; E-mail: mmoshi@muhas.ac.tz

Received 27 October 2009
Revised 30 November 2009
Accepted 3 December 2009

Code Number: th10007

Abstract

Dichloromethane and/or ethanol extracts of 30 plants used as traditional medicines in Bukoba district, northwestern Tanzania were evaluated for brine shrimp toxicity. Among the 50 extracts tested, 32 extracts (64%) showed very low toxicity with LC₅₀ values above 100 μg/ml. Among these 12 (24%) which had LC₅₀ >500 μg /ml can be categorized as being  practically non-toxic.  Among the remaining extracts 19 (38%) which showed LC₅₀ >100 < 500 μg /ml are also considered to be non-toxic. Extracts that showed LC₅₀ results between 30-100 μg/ml have been categorized as mildly toxic; these include ethanol extracts of Lantana trifolia (LC₅₀ 32.3 μg/ml), Vernonia bradycalyx (LC₅₀ 33.9 μg/ml), Antiaris toxicaria (LC₅₀ 38.2 μg /ml) and Rubus rigidus (LC₅₀ 41.7 μg /ml) and the dichloromethane extracts of Gynura scandens (LC₅₀ 36.5 μg /ml) and Bridelia micrantha (LC₅₀ 32.0 μg /ml). The dichloromethane extracts of Picralima nitida (LC₅₀ 18.3 μg/ml) and Rubus rigidus (LC₅₀ 19.8 μg /ml), were only moderately toxic. Picralima nitida and Rubus rigidus extracts are only 1.1 and 1.2 less toxic than the standard drug, cyclophosphamide (LC₅₀ 16.3 μg /ml). In conclusion, the results indicate that among the 30 plants used as traditional medicines, 28 are safe for short term use. Picralima nitida and Rubus rigidus extracts are mildly toxic, but by comparison have a remote possibility to yield active anticancer compounds.

Keywords: Traditional medicines; Brine shrimp toxicity; safety evaluation

Introduction

Traditional medicines support well over 60% of the rural Tanzanian population (Kisangau et al., 2007). Available evidence suggests that even in urban areas which are well served by modern healthcare facilities a good number of patients rely on traditional healers to meet some of their healthcare needs (Kilima et al., 2003). The Kagera region of northwestern Tanzania is one of places where traditional medicines are widely used and thus play a significant role in the provision of health care. According to Medicine du Monde, a French non-governmental organization in Kagera Region, five out of every six HIV patients receive their medical attention from a traditional healer rather than from a hospital or primary health care facility (Anonymous, 1996). Due to good rains and vegetation cover in the region, there is a rich diversity of medicinal plants present. However most of these are yet to be documented and evaluated for safety and efficacy.

Current efforts therefore aim at documenting these plants and in addition evaluate them for safety and efficacy. Two recent studies in Bukoba rural district (Kisangau et al., 2007; Moshi et al., 2009) have set the pace and more studies are ongoing. This study reports on brine shrimp toxicity tests of extracts from some of the plants reported from Bugabo Ward in Kagera region by Moshi et al. (2009). These tests are normally conducted so as to draw some inferences on the safety of plant extracts, and to depict trends of their biological activities (Harwig & Scott, 1971; Meyer et al., 1982).

Materials and Methods

Materials

Ethanol was bought from Fisher Scientific UK Ltd. (Loughborough, Leicestershire, UK),  Dimethyl sulphoxide (DMSO) from Sigma (Poole, Dorset, UK and Brine shrimp eggs from O.S.I. Marine Lab. Inc., Hayward, CA 94545, USA..  Sea salt was prepared by evaporating water collected from the Indian Ocean along the Dar es Salaam coast.

The plants used in this study are among plants recently reported as being used in traditional medicine in Bukoba rural district (Moshi et al., 2009). The material for this study was collected from Bukoba district in November, 2008 by Mr. Didas Ngemera, a traditional healer participating in the study. The collected material was dried in shade until completely dry and then transported to the Institute of Traditional Medicine in Dar es Salaam where it was ground into powder using a milling machine.

Preparation of extracts brine shrimp lethality test

Powdered plant material was soaked sequentially in dichloromethane (99 %) and then ethanol (96 %), each for 48 h. However, extracts were obtained from some of the plants using ethanol only. The extracts were filtered and solvents removed using a rotary evaporator at a temperature of 40° C. The extracts were further dried in a freeze dryer to remove any residual water and then stored in a freezer at -20° C until the day of use.

Solutions of the extracts were made in DMSO, at varying concentrations, and incubated in duplicate vials with the brine shrimp larvae in a total volume of 5 ml. Ten brine shrimp larvae were then placed in each of the duplicate vials. Others were placed in a mixture of DMSO (30 µl) and seawater to serve as a negative control. Cyclophosphamide, an anticancer drug, was used as a positive control. After 24 h the nauplii were examined against a lighted background, with a magnifying glass and the average number of survived larvae was determined. The mean percentage mortality was plotted against the logarithm of concentrations and the concentration killing fifty percent of the larvae (LC₅₀) was determined from the graph.

Data analysis

The mean results of brine shrimp mortality against the logarithms of concentrations were plotted using the Fig P computer program (Biosoft Inc, USA), which also gives regression equations. The regression equations were used to calculate LC₁₆, LC₅₀ and LC₈₄ values. Confidence intervals (95% CI) were calculated according to a previously reported method (Litchfield and Wilcoxon, 1949).

Results

The yield of extracts from plants used ranged between 1.04 - 4.02 %. Of the fifty (50) plant extracts tested, 8 showed little to no toxicity to brine shrimps (Table 1). These included the dichloromethane extracts of Antiaris toxicaria, Asystasia gangetica, and Bersama abyssinica and the ethanol extracts of Anthocleista grandiflora, Canna indica, Gynura scandens and Oxalis latifolia which had LC₅₀ values above 1000 μg/ml.  Dichloromethane extracts of Cratispermum schweinfurthii and Lantana trifolia and the ethanol extracts of Blumea auriculata and Pseudospondius microcarpa were also practically non-toxic to brine shrimps with LC₅₀ values of between 500 and 800 μg/ml.  Dichloromethane extracts of eight plants and ethanol extracts of twelve plants gave LC₅₀ values between 100 and 500 μg/ml (Table 1).  The extracts which have potential for toxicity with LC₅₀ values below 100 μg/ml can be categorized into those with LC₅₀ values of 30–100 μg/ml and those whose LC₅₀ values were below 30 μg/ml. In the former category are dichloromethane extracts of Blumea auriculata, Boerhavia diffusa, Clausena anisata, Teclea nobilis and Vernonia bradycalyx, and ethanol extracts of Clausena anisata, Garcinia buchanannii, Hibiscus cannabinus, Hugonia castenifolia, Lantana trifolia, Vernonia bradycalyx, Antiaris toxicaria, Bidens shimperi and Bridelia micrantha, ethanol extract of Rubus rigidus and dichloromethane extract of Gynura scanden. In the second category are dichloromethane extracts of Picralima nitida (LC₅₀ 18.3 μg/ml) and Rubus rigidus (LC₅₀ 19.8 μg/ml) which were almost as toxic as cyclophosphamide (LC₅₀ 16.3 μg/ml).

Table 1: Brine shrimp toxicity of plant extracts

Key: - = not done; L = leaves; AP = aerial parts; SB = stem bark; R = roots; WP = whole plant; DCMex = dichloromethane extract, EToHex = ethanol extract, CPMD = Cyclophosphamide

Discussion

The brine shrimp results in this study are interpreted as follows: LC₅₀ <1.0 µg/ml – highly toxic; LC₅₀ 1.0-10.0 µg/ml – toxic; LC₅₀ 10.0-30.0 µg/ml – moderately toxic; LC₅₀ >30 <100 µg/ml – mildly toxic, and > 100μg/ml as non-toxic. Cyclophosphamide (LC₅₀ 16.3 μg/ml) was used as a standard so that it can allow some inference to be made for potential to yield anticancer compounds.

The brine shrimp test results indicate that 64% of the plant extracts tested had LC₅₀ values above 100 μg/ml which suggests that they are practically non-toxic. As traditional medicines, most of the extracts are prepared as decoctions, which, in a way is mirrored on the ethanol extracts, the results of which suggest that the way they are used poses no threat of acute toxicity.  Some of the extracts, including Antiaris toxicaria ( LC₅₀ 38.2 μg/ml), Bidens shimperi (LC₅₀ 46.9 μg/ml), Bridelia micrantha (LC₅₀ 32.0 μg/ml), Lantana trifolia (LC₅₀ 32.3 μg/ml), Rubus rigidus (LC₅₀ 41.7 μg/ml) and Vernonia bradycalyx (LC₅₀ 33.9 μg/ml), are mildly toxic and probably have no obvious danger of outright toxicity during acute exposure. 

Dichloromethane extracts for Picralima nitida (LC₅₀ 18.3 μg/ml) and Rubus rigidus (LC₅₀ 19.8 μg/ml) were the most toxic. However extracts from these two plants used as traditional medicines are unlikely to have any ill effects on patients as they are not on the highly toxic category.

Some brine shrimp results that are already available (Moshi et al., 2006; 2004) provide a circumstantial evidence that plant extracts with LC₅₀ values below 20 μg/ml have a likelihood of yielding anticancer compounds.  This corroboration is demonstrated by Bridelia cathartica (Moshi et al., 2004; Suffness et al., 1988), Croton macrostachys (Moshi et al., 2004; Kupchan et al., 1969), Maytenus putterlickioides (Moshi et al., 2004; Shibuta, 1984), Ozoroa insignis (Moshi et al., 2004; Abreu et al., 1999), Psorospermum febrifugum (Moshi et al., 2006; Abou-Shoer et al., 1988; Kupchan et al., 1980), Phyllanthus engleri (Moshi et al., 2006; Ratnayake et al., 2009) and Ximenia americana (Moshi et al., 2004; Asres et al., 2001.  This cut-off point has also been suggested elsewhere (Geran et al., 1972). In the 2004 study using brine shrimps, Phyllanthus engleri gave an LC₅₀ of 0.47 μg/ml (Moshi et al., 2004), and recently the plant yielded englerin A, a selective anti-cancer compound against kidney cancer cells (Ratnayake et al., 2009), which provides further corroborative evidence on the potential of the brine shrimp test to predict the presence of anti-cancer compounds in plant extracts. It is therefore possible that in this study, dichloromethane extracts of Picralima nitida (LC₅₀ 18.3 μg/ml) and Rubus rigidus (LC₅₀ 19.8 μg/ml) may have potential to yield compounds active against cancer cell lines, and is consistent with the results of cyclophosphamide (LC₅₀ 16.3 μg/ml) and the criterion set by Geran et al. (1972.  As compared to cyclophosphamide the two LC₅₀ values are only 1.1 and 1.2 times higher, and probably not too far fetched to speculate of their possibility to yield cancer cell line active compounds. 

In conclusion most of the extracts of the plants tested seem to be innocuous on short term use. Dichloromethane extracts of Picralima nitida and Rubus rigidus which were the most toxic among the tested extracts have LC₅₀ values that suggest a remote possibility that they may yield cancer cell line active compounds.

Acknowledgements

This work would not have been possible without the co-operation of Mr. Didas Ngemera and his family together with their village members who accepted to give us information on their medicinal plants. We thank the NAPRALERT Data base of the University of Illinois at Chicago for allowing us access and literature retrieval. We also thank Mr. Selemani Haji for identifying the plants; Mr. Superatus Chuma and Mr. Daniel Kamala for their contribution to this work. This collaborative Lake Victoria Research  (VicRes) was financially supported by SIDA-SAREC through the Inter-University Council of East Africa. The project is VicRes Project No. 31 (see (http://www.vicres.net).

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