The African Green Monkey model for cutaneous and visceral leishmaniasis

Why do few drug delivery systems to combat neglected tropical diseases reach the market? An analysis from the technology's stages

INTRODUCTION

Many drugs used to combat schistosomiasis, Chagas disease, and leishmaniasis (SCL) have clinical limitations such as: high toxicity to the liver, kidneys and spleen; reproductive, gastrointestinal, and heart disorders; teratogenicity. In this sense, drug delivery systems (DDSs) have been described in the literature as a viable option for overcoming the limitations of these drugs. An analysis of the level of development (TRL) of patents can help in determine the steps that must be taken for promising technologies to reach the market.

AREAS COVERED

This study aimed to analyze the stage of development of DDSs for the treatment of SCL described in patents. In addition, we try to understand the main reasons why many DDSs do not reach the market. In this study, we examined DDSs for drugs indicated by WHO and treatment of SCL, by performing a search for patents.

EXPERT OPINION

In this present work we provide arguments that support the hypothesis that there is a lack of integration between academia and industry to finance and continue research, especially the development of clinical studies. We cite the translational research consortia as the potential alternative for developing DDSs to combat NTDs.

Research Relevant Conditions and Pathology in Nonhuman Primates

Biomedical research involving animal models continues to provide important insights into disease pathogenesis and treatment of diseases that impact human health. In particular, nonhuman primates (NHPs) have been used extensively in translational research due to their phylogenetic proximity to humans and similarities to disease pathogenesis and treatment responses as assessed in clinical trials. Microscopic changes in tissues remain a significant endpoint in studies involving these models. Spontaneous, expected (ie, incidental or background) histopathologic changes are commonly encountered and influenced by species, genetic variations, age, and geographical origin of animals, including exposure to infectious or parasitic agents. Often, the background findings confound study-related changes, because numbers of NHPs used in research are limited by animal welfare and other considerations. Moreover, background findings in NHPs can be exacerbated by experimental conditions such as treatment with xenobiotics (eg, infectious morphological changes related to immunosuppressive therapy). This review and summary of research-relevant conditions and pathology in rhesus and cynomolgus macaques, baboons, African green monkeys, common marmosets, tamarins, and squirrel and owl monkeys aims to improve the interpretation and validity of NHP studies.

The Demographic and Adaptive History of the African Green Monkey

Relatively little is known about the evolutionary history of the African green monkey (genus Chlorocebus) due to the lack of sampled polymorphism data from wild populations. Yet, this characterization of genetic diversity is not only critical for a better understanding of their own history, but also for human biomedical research given that they are one of the most widely used primate models. Here, I analyze the demographic and selective history of the African green monkey, utilizing one of the most comprehensive catalogs of wild genetic diversity to date, consisting of 1,795,643 autosomal single nucleotide polymorphisms in 25 individuals, representing all five major populations: C. a. aethiops, C. a. cynosurus, C. a. pygerythrus, C. a. sabaeus, and C. a tantalus. Assuming a mutation rate of 5.9 × 10-9 per base pair per generation and a generation time of 8.5 years, divergence time estimates range from 523 to 621 kya for the basal split of C. a. aethiops from the other four populations. Importantly, the resulting tree characterizing the relationship and split-times between these populations differs significantly from that presented in the original genome paper, owing to their neglect of within-population variation when calculating between population-divergence. In addition, I find that the demographic history of all five populations is well explained by a model of population fragmentation and isolation, rather than novel colonization events. Finally, utilizing these demographic models as a null, I investigate the selective history of the populations, identifying candidate regions potentially related to adaptation in response to pathogen exposure.

A Review: The Current In Vivo Models for the Discovery and Utility of New Anti-leishmanial Drugs Targeting Cutaneous Leishmaniasis

The current in vivo models for the utility and discovery of new potential anti-leishmanial drugs targeting Cutaneous Leishmaniasis (CL) differ vastly in their immunological responses to the disease and clinical presentation of symptoms. Animal models that show similarities to the human form of CL after infection with Leishmania should be more representative as to the effect of the parasite within a human. Thus, these models are used to evaluate the efficacy of new anti-leishmanial compounds before human clinical trials. Current animal models aim to investigate (i) host–parasite interactions, (ii) pathogenesis, (iii) biochemical changes/pathways, (iv) in vivo maintenance of parasites, and (v) clinical evaluation of drug candidates. This review focuses on the trends of infection observed between Leishmania parasites, the predictability of different strains, and the determination of parasite load. These factors were used to investigate the overall effectiveness of the current animal models. The main aim was to assess the efficacy and limitations of the various CL models and their potential for drug discovery and evaluation. In conclusion, we found that the following models are the most suitable for the assessment of anti-leishmanial drugs: L. major–C57BL/6 mice (or–vervet monkey, or–rhesus monkeys), L. tropica–CsS-16 mice, L. amazonensis–CBA mice, L. braziliensis–golden hamster (or–rhesus monkey). We also provide in-depth guidance for which models are not suitable for these investigations.

Susceptibility of peritoneal macrophage from different species of neotropical primates to ex vivo Leishmania (L.) infantum chagasi-infection

This study examined the susceptibility of peritoneal macrophage (PM) from the Neotropical primates: Callithrix jacchus, Callithrix penicillata, Saimiri sciureus, Aotus azarae infulatus and Callimico goeldii to ex vivo Leishmania (L.) infantum chagasi-infection, the etiological agent of American visceral leishmaniasis (AVL), as a screening assay for evaluating the potential of these non-human primates as experimental models for studying AVL. The PM-susceptibility to infection was accessed by the PM-infection index (PMI) at 24, 72 h and by the mean of these rates (FPMI), as well as by the TNF-α, IL-12 (Capture ELISA) and Nitric oxide (NO) responses (Griess method). At 24h, the PMI of A. azarae infulatus (128) was higher than those of C. penicillata (83), C. goeldii (78), S. sciureus (77) and C. jacchus (55). At 72h, there was a significant PMI decrease in four monkeys: A. azarae infulatus (128/37), C. penicillata (83/38), S. sciureus (77/38) and C. jacchus (55/12), with exception of C. goeldii (78/54). The FPMI of A. azarae infulatus (82.5) and C. goeldii (66) were higher than C. jacchus (33.5), but not higher than those of C. penicillata (60.5) and S. sciureus (57.5). The TNF-a response was more regular in those four primates which decreased their PMI at 24/72 h: C. jacchus (145/122 pg/mL), C. penicillata (154/130 pg/mL), S. sciureus (164/104 pg/mL) and A. azarae infulatus (154/104 pg/mL), with exception of C. goeldii (38/83 pg/mL). The IL-12 response was mainly prominent in A. infulatus and C. goeldii which presented the highest FPMI and, the NO response was higher in C. goeldii, mainly at 72 h. These findings strongly suggest that these New World primates have developed a resistant innate immune response mechanism capable of controlling the macrophage intracellular growth of L. (L.) i. chagasi-infection, which do not encourage their use as animal model for studying AVL.

Immunity to visceral leishmaniasis using genetically defined live-attenuated parasites

Leishmaniasis is a protozoan parasitic disease endemic to the tropical and subtropical regions of the world, with three major clinical forms, self-healing cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis (MCL), and visceral leishmaniasis (VL). Drug treatments are expensive and often result in the development of drug resistance. No vaccine is available against leishmaniasis. Subunit Leishmania vaccine immunization in animal models has shown some efficacy but little or none in humans. However, individuals who recover from natural infection are protected from reinfection and develop life-long protection, suggesting that infection may be a prerequisite for immunological memory. Thus, genetically altered live-attenuated parasites with controlled infectivity could achieve such memory. In this paper, we discuss development and characteristics of genetically altered, live-attenuated Leishmania donovani parasites and their possible use as vaccine candidates against VL. In addition, we discuss the challenges and other considerations in the use of live-attenuated parasites.

Susceptibility of Cebus apella monkey (Primates: Cebidae) to experimental Leishmania (L.) infantum chagasi-infection

In Amazonian Brazil, the Cebus apella monkey (Primates: Cebidae) has been associated with the enzootic cycle of Leishmania (V.) shawi, a dermotropic parasite causing American cutaneous leishmaniasis (ACL). It has also been successfully used as animal model for studying cutaneous leishmaniasis. In this work, there has been investigated its susceptibility to experimental Leishmania (L.) infantum chagasi-infection, the etiologic agent of American visceral leishmaniasis (AVL). There were used ten C. apella specimens, eight adult and two young, four males and six females, all born and raised in captivity. Two experimental infection protocols were performed: i) six monkeys were inoculated, intra-dermal via (ID), into the base of the tail with 2 x 10(6) promastigotes forms from the stationary phase culture medium; ii) other four monkeys were inoculated with 3 x 10(7) amastigotes forms from the visceral infection of infected hamsters by two different via: a) two by intravenous via (IV) and, b) other two by intra-peritoneal via (IP). The parameters of infection evaluation included: a) clinical: physical exam of abdomen, weigh and body temperature; b) parasitological: needle aspiration of the bone-marrow for searching of amastigotes (Giemsa-stained smears) and promastigotes forms (culture medium); c) immunological: Indirect fluorescence antibody test (IFAT) and, Delayed-type hypersensitivity (DTH). In the six monkeys ID inoculated (promastigotes forms) all parameters of infection evaluation were negative during the 12 months period of follow-up. Among the four monkeys inoculated with amastigotes forms, two IV inoculated showed the parasite in the bone-marrow from the first toward to the sixth month p.i. and following that they cleared the infection, whereas the other two IP inoculated were totally negative. These four monkeys showed specific IgG-antibody response since the third month p.i. (IP: 1/80 and IV: 1/320 IgG) toward to the 12th month (IP: 1/160 and IV: 1/5120). The DTH-conversion occurred in only one IV inoculated monkey with a strong (30 mm) skin reaction. Considering these results, we do not encourage the use of C. apella monkey as animal model for studying the AVL.

Prevalence of antibodies and cell mediated immune response against Leishmania major in feral nonhuman primates from Kenya

In Kenya, Leishmania major is responsible for human cutaneous leishmaniasis (CL). Natural infection with L. major of a vervet monkey and experimental susceptibility of some nonhuman primates (NHPs) from Kenya has been established. However, there has been no comprehensive study of the prevalence of zoonotic CL in Kenya. And also, no investigation has been done to assess whether NHPs could be potential reservoir hosts of L. major even when the involvement of reservoir animals is obligatory in transmission of this parasite. To achieve this, wild caught Chlorocebus aethiops (Vervet monkeys n=213), Papio cynocephalus anubis (olive baboons n=101) and Cercopithecus mitis (Syke's monkeys n=64) from five geographical locations in Kenya were screened for antibodies against L. major using enzyme linked immunosorbent assay (ELISA) and Western blot (WB) analysis. From the population of C. aethiops (n=213) captured, 57 were used in lymphocyte proliferation assay. ELISA revealed a high prevalence of leishmaniasis sero conversion in olive baboons 78/101 (77.2%), vervet monkeys 129/213 (60.6%) and Sykes' monkeys 43/64 (67.2%). WB detected anti-L. major antibodies in 48.5% (49/101) of the baboons, 48% (102/213) of vervet monkeys and 37.5% (24/64) of Sykes' monkey sera. Specific proliferation of peripheral blood mononuclear cells to L. major antigen was demonstrated in 17 of the 57 (29.8%) vervet monkeys. In conclusion, the results of serological assays provide strong circumstantial evidence that CL is prevalent in five Provinces of Kenya and that Kenyan NHPs could be could be a potential reservoir hosts of L. major.

Identification of a surrogate marker for infection in the African green monkey model of inhalation anthrax

In 2001, a bioterrorism attack involving Bacillus anthracis spore-laced letters resulted in 22 cases of inhalation anthrax, with five fatalities. This incident identified gaps in our health care system and precipitated a renewed interest in identifying both therapeutics and rapid diagnostic assays. To address those gaps, well-characterized animal models that resemble the human disease are needed. In addition, a rapid assay for a reliable diagnostic marker is key to the success of these efforts. In this study, we exposed African green monkeys to B. anthracis spores; examined clinical signs and physiological parameters, including fever, heart rate, complete blood count, and bacteremia; and evaluated the PCR assay and electrochemiluminescence (ECL) immunoassay for the biomarkers protective antigen and capsule. The results demonstrated that although there were neither objective clinical nor physiological signs that consistently identified either infection or the onset of clinical anthrax disease, the African green monkey is a suitable animal model exhibiting a disease course similar to that observed in the rhesus model and humans. We also demonstrated that detection of the biomarkers protective antigen and capsule correlated with bacterial loads in the blood of these nonhuman primates. The ECL immunoassay described here is simple and sensitive enough to provide results in one to two hours, making this assay a viable option for use in the diagnosis of anthrax, leading to timely initiation of treatment, which is a key component of B. anthracis therapeutic development.

Enzootic simian piroplasm (Entopolypoides macaci ) in wild-caught Kenyan non-human primates

BACKGROUND

Three species of non-human primates comprising African green monkeys (AGMs), (Cercopithecus aethiops, n = 89), Syke's monkeys (Cercopithecus mitis, n = 60) and olive baboons (Papio cynocephalus anubis, n = 30), were screened for Entopolypoides macaci.

METHODS

Observation of blood smears prepared from these animals revealed E. macaci infection rate of 42.7% in AGMs, 35% in Syke's monkeys and 33.3% in baboons.

RESULTS

Gender infection rate was 38.2% in females and 29% in males. Statistically, there was no significant difference in infection rates between the monkey species and sexes (P > 0.05). Subsequent indirect immuno fluorescent antibody test supported the morphological appearance of E. macaci observed by microscopy. Sera from infected animals reacted positively (1:625) with E. macaci antigen, but not to Babesia bigemina or B. bovis antigen at 1:125 titer.

CONCLUSION

This study has revealed high prevalence of E. macaci infection in all three widely distributed Kenyan non-human primates. With the continued use of these animals as models for human parasitic diseases, the presence of this highly enzootic parasite should be noted.

Pathology of inhalational anthrax infection in the african green monkey

There is a critical need for an alternative nonhuman primate model for inhalational anthrax infection because of the increasingly limited supply and cost of the current model. This report describes the pathology in 12 African green monkeys (AGMs) that succumbed to inhalational anthrax after exposure to a low dose (presented dose 200-2 x 10(4)colony-forming units [cfu]) or a high dose (presented dose 2 x 10(4)-1 x 10(7) cfu) of Bacillus anthracis (Ames strain) spores. Frequent gross lesions noted in the AGM were hemorrhage and edema in the lung, mediastinum, and mediastinal lymph nodes; pleural and pericardial effusions; meningitis; and gastrointestinal congestion and hemorrhage. Histopathologic findings included necrohemorrhagic lymphadenitis of mediastinal, axillary, inguinal, and mesenteric lymph nodes; mediastinal edema; necrotizing splenitis; meningitis; and congestion, hemorrhage, and edema of the lung, mesentery, mesenteric lymph nodes, gastrointestinal tract, and gonads. Pathologic changes in AGMs were remarkably similar to what has been reported in rhesus macaques and humans that succumbed to inhalational anthrax; thus, AGMs could serve as useful models for inhalation anthrax studies.

A genetic linkage map of the vervet monkey (Chlorocebus aethiops sabaeus)

The spectacular progress in genomics increasingly highlights the importance of comparative biology in biomedical research. In particular, nonhuman primates, as model systems, provide a crucial intermediate between humans and mice. The close similarities between humans and other primates are stimulating primate studies in virtually every area of biomedical research, including development, anatomy, physiology, immunology, and behavior. The vervet monkey (Chlorocebus aethiops sabaeus) is an important model for studying human diseases and complex traits, especially behavior. We have developed a vervet genetic linkage map to enable mapping complex traits in this model organism and facilitate comparative genomic analysis between vervet and other primates. Here we report construction of an initial genetic map built with about 360 human orthologous short tandem repeats (STRs) that were genotyped in 434 members of an extended vervet pedigree. The map includes 226 markers mapped in a unique order with a resolution of 9.8 Kosambi centimorgans (cM) in the vervet monkey genome, and with a total length (including all 360 markers) of 2726 cM. At least one complex and 11 simple rearrangements in marker order distinguish vervet chromosomes from human homologs. While inversions and insertions can explain a similar number of changes in marker order between vervet and rhesus homologs, mostly inversions are observed when vervet chromosome organization is compared to that in human and chimpanzee. Our results support the notion that large inversions played a less prominent role in the evolution within the group of the Old World monkeys compared to the human and chimpanzee lineages.

Design and synthesis of hydroxyferroquine derivatives with antimalarial and antiviral activities

Three ferroquine (FQ) derivatives, closely mimicking the antimalarial drug hydroxychloroquine (HCQ), have been prepared. Whereas these organometallic compounds provide the expected reduced cytotoxic effects compared to FQ, they inhibit in vitro growth of Plasmodium falciparum far better than chloroquine (CQ). Moreover, this new class of bioorganometallic compounds exert antiviral effects with some selectivity toward SARS-CoV infection. These new drugs may offer an interesting alternative for Asia where SARS originated and malaria has remained endemic.

Efficacy of Trypan: a diminazene based drug as antileishmanial agent

Trypan, a diamidine based drug, was tested as an antileishmanial agent. Duplicate cultures of both Leishmania major and Leishmania donovani promastigotes in M199 medium and Trypan at various concentrations were tested. The cultures were incubated at 25 degrees C and parasites counted at 48 h interval, and the data generated was used to establish growth inhibition curves. Drug-free cultures were included to serve as control. In the in vivo study, a total of 40 BALB/c mice were divided into five groups of 8 mice each. They were infected with 2 x 10(6) promastogotes on the left footpad. Two groups were treated with 70 microg/ml of Trypan, a total of 500 microl used immediately after infection, one group by topical application and the other administered intraperitoneally. The treatments were repeated for the two other groups 10 weeks post infection, one by topical application and the other administered intraperitoneally. One group was not treated and thus served as control. Footpad sizes were measured using Vernier calliper every 2 weeks for 21 weeks. In the in vitro studies, Trypan inhibited growth of either L. major or L. donovani promastigotes in all the concentrations tested with more dramatic inhibition in high concentrations. Based on the in vivo studies, it was evident that Trypan had effect on L. major infected lesions when applied topically immediately after infection. However, there was no effect when treatment commenced after the lesions were established. The data is discussed.