In vitro anti-Leishmania activity of 8-hydroxyquinoline and its synergistic effect with amphotericin B deoxycholate against Leishmania martiniquensis

Leishmania (Mundinia) martiniquensis is responsible for visceral leishmaniasis in patients with no known underlying immunodeficiency, and visceral or disseminated cutaneous leishmaniasis in HIV-infected patients. The available anti-Leishmania drugs for treatment have limitations such as high toxicity and variable efficacy. To improve the therapeutic index of anti-Leishmania drugs, the search for a new drug or a new natural compound in combination therapy instead of using monotherapy to reduce drug side effect and have high efficacy is required. In this study, anti-Leishmania activity of 8-hydroxyquinoline (8HQN) and its synergistic effect with amphotericin B (AmB) against L. martiniquensis were evaluated in vitro for the first time. These results showed that 8HQN presented anti-Leishmania activity against L. martiniquensis with IC₅₀ 1.60 ± 0.28 and 1.56 ± 0.02 µg/mL for promastigotes and intracellular amastigotes, respectively. The selectivity index (SI) value of 8HQN was 79.84 for promastigotes and 82.40 for intracellular amastigotes, which highlight promising results for the use of 8HQN in the treatment of L. martiniquensis-infected host cells. Interestingly, four combinations of 8HQN and AmB provided synergistic effects for intracellular amastigotes and showed no toxic effects to host cells. These results provided information of using a combination therapy in treating this Leishmania species leads to further development of therapy and can be considered as an alternative treatment for leishmaniasis.

Experimental infection of Leishmania (Mundinia) martiniquensis in BALB/c mice and Syrian golden hamsters

Our objective was to investigate clinical progression, presence of parasites and DNAs, parasite loads, and histological alterations in BALB/c mice and Syrian golden hamsters after intraperitoneal inoculation with Leishmania (Mundinia) martiniquensis promastigotes with a goal to choosing an appropriate animal model for visceral leishmaniasis. Infections were monitored for 16 weeks. Infected BALB/c mice were asymptomatic during the infection course. Parasite DNAs were detected in the liver at week 8 of infection, followed by clearance in most animals at week 16; whereas in the spleen, parasite DNAs were detected until week 16. These results are correlated to those obtained measuring parasite loads in both organs. No parasite DNA and no alteration in the bone marrow were observed indicating that no dissemination occurred. These results suggest the control of visceralization of L. martiniquensis by BALB/c mice. In hamsters, weight loss, cachexia, and fatigue were observed after week 11. Leishmania martiniquensis parasites were observed in tissue smears of the liver, spleen, and bone marrow by week 16. Parasite loads correlated with those from the presence of parasites and DNAs in the examined tissues. Alterations in the liver with nuclear destruction and cytoplasmic degeneration of infected hepatocytes, presence of inflammatory infiltrates, necrosis of hepatocytes, and changes in splenic architecture and reduction and deformation of white pulp in the spleen were noted. These results indicate a chronic form of visceral leishmaniasis indicating that the hamster is a suitable animal model for the study of pathological features of chronic visceral leishmaniasis caused by L. martiniquensis.

Development of Leishmania (Mundinia) in guinea pigs

BACKGROUND

Leishmaniasis is a human and animal disease caused by parasites of the genus Leishmania, which is now divided into four subgenera, Leishmania, Viannia, Sauroleishmania and Mundinia. Subgenus Mundinia, established in 2016, is geographically widely dispersed, its distribution covers all continents, except Antarctica. It consists of 5 species; L. enriettii and L. macropodum are parasites of wild mammals while L. martiniquensis, L. orientalis and an unnamed Leishmania sp. from Ghana are infectious to humans. There is very little information on natural reservoir hosts and vectors for any Mundinia species.

METHODS

Experimental infections of guinea pigs with all five Mundinia species were performed. Animals were injected intradermally with 10⁷ culture-derived promastigotes into both ear pinnae. The courses of infections were monitored weekly; xenodiagnoses were performed at weeks 4 and 8 post-infection using Lutzomyia migonei. The distribution of parasites in different tissues was determined post-mortem by conventional PCR.

RESULTS

No significant differences in weight were observed between infected animals and the control group. Animals infected with L. enriettii developed temporary lesions at the site of inoculation and were infectious to Lu. migonei in xenodiagnoses. Animals infected with L. martiniquensis and L. orientalis developed temporary erythema and dry lesions at the site of inoculation, respectively, but were not infectious to sand flies. Guinea pigs infected by L. macropodum and Leishmania sp. from Ghana showed no signs of infection during experiments, were not infectious to sand flies and leishmanial DNA was not detected in their tissue samples at the end of experiments at week 12 post-inoculation.

CONCLUSIONS

According to our results, guinea pigs are not an appropriate model organism for studying Mundinia species other than L. enriettii. We suggest that for better understanding of L. (Mundinia) biology it is necessary to focus on other model organisms.

Antileishmanial Activity and Synergistic Effects of Amphotericin B Deoxycholate with Allicin and Andrographolide against Leishmania martiniquensis In Vitro

Leishmania (Mundinia) martiniquensis is a causative agent of visceral leishmaniasis, but in HIV-infected patients both visceral and disseminated cutaneous leishmaniasis are presented. Recurrence of the disease after treatment has been reported in some cases indicating that improved chemotherapy is required. In this study, the susceptibility of L. martiniquensis to Amphotericin B deoxycholate (AmB), allicin, and andrographolide was evaluated and the synergistic effects of allicin or andrographolide combined with AmB against L. martiniquensis intracellular amastigotes in mouse peritoneal exudate macrophages (PEMs) were investigated in vitro for the first time. The results showed that L. martiniquensis was highly susceptible to AmB as expected, but allicin and andrographolide had selectivity index (SI) values greater than 10, indicating promise in both compounds for treatment of host cells infected with L. martiniquensis. Four AmB/allicin combinations presented combination index (CI) values less than 1 (0.58–0.68) for intracellular amastigotes indicating synergistic effects. The combination with the highest dose reduction index (DRI) allowed an approximately four-fold reduction of AmB use in that combination. No synergistic effects were observed in AmB/andrographolide combinations. The data provided in this study leads for further study to develop novel therapeutic agents and improve the treatment outcome for leishmaniasis caused by this Leishmania species.

Host competence of the African rodents Arvicanthis neumanni, A. niloticus and Mastomys natalensis for Leishmania donovani from Ethiopia and L. (Mundinia) sp. from Ghana

Visceral leishmaniasis caused by Leishmania donovani is regarded as mostly anthroponotic, but a role for animal reservoir hosts in transmission has been suggested in East Africa. Field studies in this region have shown the presence of this parasite in several mammalian species, including rodents of the genera Arvicanthis and Mastomys. Further, the natural reservoirs of Leishmania (Mundinia) sp. causing human cutaneous disease in Ghana, West Africa, are unknown. This study assessed the potential role of the Sub-Saharan rodents Arvicanthis neumanni, A. niloticus and Mastomys natalensis as hosts of L. donovani and L. sp. from Ghana, based on experimental infections of animals and xenodiagnoses. The distribution and load of parasites were determined post mortem using qPCR from the blood, skin and viscera samples. The attractiveness of Arvicanthis and Mastomys to Phlebotomus orientalis was tested by pair-wise comparisons. None of the animals inoculated with L. donovani were infectious to P. orientalis females, although, in some animals, parasites were detected by PCR even 30 weeks post infection. Skin infections were characterized by low numbers of parasites while high parasite burdens were present in spleen, liver and lymph nodes only. Therefore, wild Arvicanthis and Mastomys found infected with L. donovani, should be considered parasite sinks rather than parasite reservoirs. This is indirectly supported also by results of host choice experiments with P. orientalis in which females preferred humans over both Arvicanthis and Mastomys, and their feeding rates on rodents ranged from 1.4 to 5.8% only. Therefore, the involvement of these rodents in transmission of L. donovani by P. orientalis is very unlikely. Similarly, poor survival of Leishmania parasites in the studied rodents and negative results of xenodiagnostic experiments do not support the involvement of Arvicanthis and Mastomys spp. in the transmission cycle of L. sp. from Ghana.

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Three species of Sub-Saharan rodents were infected and xenodiagnosed.

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Skin infections in Arvicanthis and Mastomys were characterized by low parasite loads.

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None of animals inoculated with leishmania were infectious to sand flies.

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Phlebotomus orientalis females significantly preferred man over rodents.

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Rodents are unlikely to be involved in the circulation of the two studied Leishmania in nature.

Development of Leishmania orientalis in the sand fly Lutzomyia longipalpis (Diptera: Psychodidae) and the biting midge Culicoides soronensis (Diptera: Ceratopogonidae)

Leishmania (Mundinia) orientalis is a newly described species causing human leishmaniasis in Thailand whose natural vector is unknown. L. orientalis infections in sand flies and/or biting midges under laboratory conditions have not been previously investigated. In this study, the development of L. orientalis in two experimental vectors, Lutzomyia longipalpis sand flies and Culicoides sonorensis biting midges was investigated for the first time using light microscopy, scanning electron microscopy, and histological examination. The results showed that L. orientalis was unable to establish infection in Lu. longipalpis. No parasites were found in the sand fly gut 4 days post-infected blood meal (PIBM). In contrast, the parasite successfully established infection in C. sonorensis. The parasites differentiated from amastigotes to procyclic promastigotes in the abdominal midgut (AMG) on day 1 PIBM. On day 2 PIBM, nectomonad promastigotes were observed in the AMG and migrated to the thoracic midgut (TMG). Leptomonad promastigotes appeared at the TMG on day 3 PIBM. Clusters of leptomonad promastigotes and metacyclic promastigotes colonized around the stomodeal valve with the accumulation of a promastigote secretory gel-like material from day 3 PIBM onwards. Haptomonad-like promastigotes were observed from day 5 PIBM, and the proportion of metacyclic promastigotes reached 23% on day 7 PIBM. The results suggest that biting midges or other sand fly genera or species might be vectors of L. orientalis.

Leishmania (Mundinia) orientalis n. sp. (Trypanosomatidae), a parasite from Thailand responsible for localised cutaneous leishmaniasis

BACKGROUND

Leishmaniasis is an emerging disease in Thailand with an unknown incidence or prevalence. Although the number of properly characterized and clinically confirmed cases is about 20, it is suspected that this low number masks a potentially high prevalence, with clinical disease typically manifesting itself against an immunocompromised background, but with a substantial number of subclinical or cured cases of infection. To date leishmaniasis in Thailand has been mainly ascribed to two taxa within the recently erected subgenus Mundinia Shaw, Camargo & Teixeira, 2016, Leishmania (Mundinia) martiniquensis Desbois, Pratlong & Dedet, 2014 and a species that has not been formally described prior to this study.

RESULTS

A case of simple cutaneous leishmaniasis was diagnosed in a patient from Nan Province, Thailand. Molecular analysis of parasites derived from a biopsy sample revealed this to be a new species of Leishmania Ross, 1908, which has been named as Leishmania (Mundinia) orientalis Bates & Jariyapan n. sp. A formal description is provided, and this new taxon supercedes some isolates from the invalid taxon "Leishmania siamensis". A summary of all known cases of leishmaniasis with a corrected species identification is provided.

CONCLUSIONS

Three species of parasites are now known to cause leishmaniasis is Thailand, L. martiniquensis and L. orientalis n. sp. in the subgenus Mundinia, which contains the type-species Leishmania enriettii Muniz & Medina, 1948, and a single case of Leishmania infantum Nicolle, 1908. This study now enables epidemiological and other investigations into the biology of these unusual parasites to be conducted. It is recommended that the use of the taxonomically invalid name "L. siamensis" should be discontinued.