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Trypanosomiasis and leishmaniasis are among the major neglected diseases that affect poor people, mainly in developing countries. In Ethiopia, the latex of Aloe rugosifolia Gilbert & Sebsebe is traditionally used for the treatment of protozoal diseases, among others. In this study, the in vitro antitrypanosomal activity of the leaf latex of A. rugosifolia was evaluated against Trypanosoma congolense field isolate using in vitro motility and in vivo infectivity tests. The latex was also tested against the promastigotes of Leishmania aethiopica and L. donovani clinical isolates using alamar blue assay. Preparative thin-layer chromatography of the latex afforded a naphthalene derivative identified as plicataloside (2,8- O , O -di-(β-D-glucopyranosyl)-1,2,8-trihydroxy-3-methyl-naphthalene) by means of spectroscopic techniques (HRESI-MS, 1 H, 13 C-NMR). Results of the study demonstrated that at 4.0 mg/mL concentration plicataloside arrested mobility of trypanosomes within 30 min of incubation period. Furthermore, plicataloside completely eliminated subsequent infectivity in mice for 30 days at concentrations of 4.0 and 2.0 mg/mL. Plicataloside also displayed antileishmanial activity against the promastigotes of L. aethopica and L. donovani with IC 50 values 14.22 ± 0.41 µg/mL (27.66 ± 0.80 µM) and 18.86 ± 0.03 µg/mL (36.69 ± 0.06 µM), respectively. Thus, plicataloside may be used as a scaffold for the development of novel drugs effective against trypanosomiasis and leishmaniasis.

Aloesin ( 1 ) and 7- O -methyl-6'- O- coumaroylaloesin ( 2 ) were isolated from the leaf latex of Aloe monticola Reynolds, and their structures determined on the basis of NMR and mass spectroscopic analyses. The antimicrobial activities of the isolated chromones were evaluated against 21 bacterial and 4 fungal strains. Both compounds displayed antibacterial and antifungal effects against most bacterial and fungal strains tested, but their action was more prominent against Salmonella typhi , Shigella dysentery and Staphylococcus aureus (MIC = 10 μg/ml). Acute toxicity tests on mice revealed that neither the latex nor the isolated compounds possess toxicity up to a dose of 2000 mg/kg, signifying an oral LD 50 greater than 2000 mg/kg. The results indicate that A. monticola possesses genuine in vitro antimicrobial effect attributed in full or in part to the presence of the isolated chromones in the latex.

The leaf latex of Aloe yavellana Reynolds is traditionally used for the treatment of various illnesses of humans and domestic animals in Ethiopia. In the present study, the latex and two major compounds isolated from it, namely, aloin A/B and microdontin A/B were assessed for their larvicidal activity against Amblyomma variegatum tick larvae using a larval packet test (LPT). The LC 50 and LC 99 of the latex were found to be 35.82 ± 2.27 and 83.48 ± 3.95 mg/ml, respectively. Although microdontin A/B showed better larvicidal activity (LC 50 = 89.40 ± 4.45 mg/ml) than aloin A/B (LC 50 = 257.69 ± 6.31 mg/ml), neither of the isolated compounds was as active as the latex suggesting that the compounds acted synergistically or minor compounds with potent larvicidal activity may exist in the latex. The results confirmed that the leaf latex of A. yavellana and its isolated compounds could have the potential to be used as larvicidal against A. variegatum ticks., (Copyright © 2018. Published by Elsevier B.V.)

Malaria is one of the three major global public health threats due to a wide spread resistance of the parasites to the standard antimalarial drugs. Considering this growing problem, the ethnomedicinal approach in the search for new antimalarial drugs from plant sources has proven to be more effective and inexpensive. The leaves of Aloe pulcherrima Gilbert and Sebsebe, an endemic Ethiopian plant, are locally used for the treatment of malaria and other infectious diseases. Application of the leaf latex of A. pulcherrima on preparative silica gel TLC led to the isolation of two C -glycosylated anthrones, identified as nataloin ( 1 ) and 7-hydroxyaloin ( 2 ) by spectroscopic techniques (UV, IR, ¹H- and 13 C-NMR, HR-ESIMS). Both the latex and isolated compounds displayed antimalarial activity in a dose-independent manner using a four-day suppressive test, with the highest percent suppression of 56.2% achieved at 200 mg/kg/day for 2 . The results indicate that both the leaf latex of A. pulcherrima and its two major constituents are endowed with antiplasmodial activities, which support the traditional use of the leaves of the plant for the treatment of malaria.

Background: The incidents of drug resistant microorganisms and the need of treatments for newly emerging pathogens are of great concern to the global community. Our ability to treat infectious diseases is dependent on the development of new pharmaceuticals, and one potential source being medicinal plants with traditional claims. The leaves of Aloe trigonantha L.C. Leach, an endemic Ethiopian plant, are locally used for the treatment of infectious and inflammatory diseases. This study explores the potential of the latex of this plant and compounds isolated thereof for their in vitro antibacterial and antifungal properties., Methods: Analytical RP-HPLC and silica gel preparative TLC were used for identification and isolation of active constituents, respectively. Characterization of the compounds was based on UV, IR, HR-ESIMS, (1)H and (13)C NMR, and 2D-NMR spectral assignments. Antimicrobial activity studies were carried out against 21 pathogenic bacterial and 4 fungal strains using the disk diffusion method. Minimum inhibitory concentrations (MICs) were determined by the broth dilution method., Results: A C-glycosylated chromone identified as aloesin, and three C-glycosylated anthrones characterized as 8-O-methy-7-hydroxyaloin A/B, aloin A/B and aloin-6'-O-acetate A/B were isolated. The latex and isolated compounds exhibited in vitro antibacterial activity against the tested pathogens. In some cases the activity of the isolated compounds (MIC = 10 μg/mL) was comparable with that of the standard drug ciprofloxacin, particularly against some of the Gram-negative bacterial strains tested. However, their activity towards the fungal pathogens tested was relatively weaker showing maximum activity against Candida albicans with MIC value of 400 μg/mL., Conclusion: The present findings can be used for further research aimed at the development of new antibacterial agents, and may also justify the ethnomedicinal claim of the plant for the treatment of infectious diseases.

Leishmaniasis is a major protozoal disease threatening the lives of 350 million people throughout the world. However, the therapeutic options for the disease are limited. In the present study, the antiprotozoal activity of the latex obtained from the Ethiopian plant Aloe calidophila Reynolds was evaluated by in vitro testing against Leishmania aethiopica and Leishmania major. It was found that the latex possesses moderate activity against both parasites with IC50 values of 64.05 and 82.29 µg/mL, respectively. Phytochemical investigation resulted in the isolation of three anthrones identified as aloinoside, aloin, and microdontin on the basis of IR, MS, (1) H NMR, and (13) C NMR spectral data. The isolated compounds showed strong antileishmanial activity with IC50 values ranging from 1.76 to 6.32 µg/mL against L. aethiopica and from 2.09 to 8.85 µg/mL against L. major. Although these values were higher than those of amphotericin B (IC50  = 0.109 and 0.067 µg/mL), the selectivity indices (813.35 and 694.90, respectively, against L. aethiopica and L. major) of aloinoside were much better than those of the standard drug (423.49 and 688.96). The results indicate that the isolated compounds have the potential to be used as a scaffold for the development of safe and cost-effective antileishmanial agents., (Copyright © 2014 John Wiley & Sons, Ltd.)

Phytochemical investigation of the leaf latex of Aloe trichosantha by preparative TLC gave two closely related anthrones, aloin A/B (1) and aloin-6'-O-acetate A/B (2). The identity of the compounds was established from HRESI-MS, 1H, 13C, DEPT, HMQC and HMBC spectral and chemical data. Whilst aloin A/B occurs in several Aloe species, aloin-6'-O-acetate A/B was isolated for the first time. The isolated compounds inhibited growth of several bacterial and fungal pathogens with minimum inhibitory concentration (MIC) from 10 to 400 microg/mL and 800 to 1000 microg/mL, respectively.

In the search for new antimicrobial and antioxidant compounds from plants, the latex of the medicinal plant Aloe harlana Reynolds from Ethiopia was subjected to bioassay-guided fractionation, which led to the isolation of two known compounds, anthrone (aloin) and chromone (7-O-methylaloeresin A). The latex and its two constituents were assessed for their possible antimicrobial activities against 23 bacterial and four fungal strains using the disc diffusion method and their antioxidant activity by two complementary test systems, namely 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2-deoxyribose degradation assay methods. The isolated compounds showed promising results against various pathogenic bacterial and fungal strains in comparison with standard drugs. Moreover, 7-O-methylaloeresin A exhibited good activity against multiple drug resistant Staphylococcus aureus (NCTC 11994) and Salmonella typhimurium (ATCC 1255) with MIC values of 0.72 and 0.18 mm, respectively. Among the fungal strains tested, Candida albicans (ATCC 10231) was the most susceptible organism to the latex and the two isolated compounds. The latex and isolated compounds also showed significant activities on both antioxidant assays with the highest activity being observed for 7-O-methylaloeresin A, which gave IC(50) values of 0.026 mm and 0.021 mm for DPPH and 2-deoxyribose degradation assay, respectively. These findings support the traditional uses of the plant for the treatment of various infectious and inflammatory diseases., (Copyright © 2011 John Wiley & Sons, Ltd.)

The currently available antileishmanial drugs are either toxic or too expensive for routine use in developing countries where the disease is most common. Local people in the Somalia region of Ethiopia use the leaves of Aloe macrocarpa Todaro for the treatment of malaria, jaundice, and skin diseases. In our ongoing search for new, efficient, and safe antileishmanial drugs, we investigated the leaf latex of Aloe macrocarpa and its acid-hydrolyzed product aloin A/B (1), as well as the semisynthesized derivatives of aloin A/B, namely, aloe-emodin (2) and rhein (3) against promastigotes and axenically cultured amastigotes of Leishmania aethiopica and L. donovani clinical isolates. Activity study was carried out based on the fluorescence characteristic of resazurin added to drug-treated cultures. Oxidative hydrolysis of aloin A/B by ferric chloride and concentrated hydrochloric acid afforded aloe-emodin (2), which was further oxidized using sodium nitrite and concentrated sulfuric acid to furnish rhein (3). Cytotoxicity study of test substances was performed against human monocytic cell line THP-1 using Alamar Blue and cell viability was measured fluorometrically. The test compounds showed lower activity (IC50 = 6.7 to 12.1 μM for promastigotes and IC50 = 3.6 to 10.2 μM for axenic amastigotes) than the reference drug amphotericin B (IC50 = 1.3 to 2.7 μM). However, amphotericin B (LC50 = 11.1 μM) was much more toxic than the test compounds (LC50 = 369.2 – 611.6 μM) towards human monocytic cell line (THP-1) despite its efficiency. As demonstrated in the current study, high selectivity indices (SIs) of the test compounds represent a remarkable advantage over the reference drug and highlight their potential use as templates for further development of safe leishmanicidal drugs. [ABSTRACT FROM AUTHOR]

Background: Malaria is one of the major obstacles to the socioeconomic development of several developing countries. Adequate treatment of the disease is becoming increasingly difficult due to the worsening problems of drug resistance in many parts of the world. Therefore, increased efforts in antimalarial drug discovery are urgently needed. Objectives: This study was designed to evaluate the antimalarial activity of the leaf latex of Aloe citrina Carter and Brandham and its major constituent. Materials and Methods: The leaf latex of A.citrina was dissolved in methanol and subjected to preparative thin layer chromatography. Structure of the isolated compound was determined on the basis of its electrospray-ionization tandem mass spectrometry, ¹H, 13C NMR and DEPT spectral data. The latex and its isolated compound were tested for their in vivo antimalarial activity using a 4-day suppressive test against chloroquine sensitive ANKA strain of Plasmodium berghei in mice. Results: Homonataloin A/B was isolated as a major component of the latex. Both the latex and isolated compound exhibited significant (P < 0.001) antimalarial activity at a dose of 400 mg/kg with parasite suppression of 60.59% and 67.52%, respectively. No significant adverse signs of toxicity were observed in mice treated with the leaf latex up to the highest dose (5000 mg/kg). Conclusion: The results of this study indicate that the antimalarial activity of the plant is attributed in part or in full to the presence of homonataloin A/B in the latex. It also validates the traditional use of the plant as an antimalarial agent. [ABSTRACT FROM AUTHOR]