Pharmacokinetics, toxicities, and efficacies of sodium stibogluconate formulations after intravenous administration in animals

Alternative Non-Drug Treatment Options of the Most Neglected Parasitic Disease Cutaneous Leishmaniasis: A Narrative Review

With more than 12 million cases worldwide, leishmaniasis is one of the top 10 neglected tropical diseases. According to the WHO, there are approximately 2 million new cases each year in foci in around 90 countries, of which 1.5 million are cutaneous leishmaniasis (CL). Cutaneous leishmaniasis (CL) is a complex cutaneous condition that is caused by a variety of Leishmania species, including L. (Leishmania) major, L. (L) tropica, L. (L) aethiopica, L. (L) mexicana, L. (Viannia) braziliensis, and L. (L) amazonensis. The disease imposes a significant burden on those who are affected since it typically results in disfiguring scars and extreme social stigma. There are no vaccines or preventive treatments available, and chemotherapeutic medications, including antimonials, amphotericin B, miltefosine, paromomycin, pentamidine, and antifungal medications, have a high price tag, a significant risk of developing drug resistance, and a variety of systemic toxicities. To work around these limitations, researchers are continuously looking for brand-new medications and other forms of therapy. To avoid toxicity with systemic medication use, high cure rates have been observed using local therapy techniques such as cryotherapy, photodynamic therapy, and thermotherapy, in addition to some forms of traditional therapies, including leech and cauterization therapies. These CL therapeutic strategies are emphasized and assessed in this review to help with the process of locating the appropriate species-specific medicines with fewer side effects, lower costs, and elevated cure rates.

Krebs cycle enzymes for targeted therapeutics and immunotherapy for anti-leishmanial drug development using: Pathways, potential targets, and future perspectives

Leishmaniasis is a parasitic and neglected tropical disease which majorly impacts poor and developing nations. One of the significant factors that impacts the severity of the pathological condition includes the socioeconomic background of the affected region. The rise of drug-resistant Leishmania is a serious concern for the effectiveness of the present treatment. As a result, the drug options need to be relooked immediately. Leishmania employs Krebs cycle intermediates for its needs after infection for establishing various defense mechanisms to escape the host immune responses. Nevertheless, a variety of immunological reactions are also seen during infection, which clear the parasites. One of the more promising strategies in this regard would involve combining targeted therapy and immunotherapy. The targeted treatments work by obstructing vital pathways that are required for Leishmania to grow and survive. The mechanism of action of immunotherapy is the control of the host immune response, which entails the blockage of molecular pathways essential for the growth and maintenance of the parasite. The Krebs cycle intermediates have important biochemical roles. Additionally, in macrophages and dendritic cells, they play roles as signalling molecules for controlling inflammatory responses. The review brings together the available literature about the importance of Krebs cycle metabolites as potential treatment targets for leishmaniasis.

Nanotechnology based solutions for anti-leishmanial impediments: a detailed insight

As a neglected tropical disease, Leishmaniasis is significantly instigating morbidity and mortality across the globe. Its clinical spectrum varies from ulcerative cutaneous lesions to systemic immersion causing hyperthermic hepato-splenomegaly. Curbing leishmanial parasite is toughly attributable to the myriad obstacles in existing chemotherapy and immunization. Since the 1990s, extensive research has been conducted for ameliorating disease prognosis, by resolving certain obstacles of conventional therapeutics viz. poor efficacy, systemic toxicity, inadequate drug accumulation inside the macrophage, scarce antigenic presentation to body's immune cells, protracted length and cost of the treatment. Mentioned hurdles can be restricted by designing nano-drug delivery system (nano-DDS) of extant anti-leishmanials, phyto-nano-DDS, surface modified-mannosylated and thiolated nano-DDS. Likewise, antigen delivery with co-transportation of suitable adjuvants would be achievable through nano-vaccines. In the past decade, researchers have engineered nano-DDS to improve the safety profile of existing drugs by restricting their release parameters. Polymerically-derived nano-DDS were found as a suitable option for oral delivery as well as SLNs due to pharmacokinetic re-modeling of drugs. Mannosylated nano-DDS have upgraded macrophage internalizing of nanosystem and the entrapped drug, provided with minimal toxicity. Cutaneous Leishmaniasis (CL) was tackling by the utilization of nano-DDS designed for topical delivery including niosomes, liposomes, and transfersomes. Transfersomes, however, appears to be superior for this purpose. The nanotechnology-based solution to prevent parasitic resistance is the use of Thiolated drug-loaded and multiple drugs loaded nano-DDS. These surfaces amended nano-DDS possess augmented IC50 values in comparison to conventional drugs and un-modified nano-DDS. Phyto-nano-DDS, another obscure horizon, have also been evaluated for their anti-leishmanial response, however, more intense assessment is a prerequisite. Impoverished Cytotoxic T-cells response followed by Leishmanial antigen proteins delivery have also been vanquished using nano-adjuvants. The eminence of nano-DDS for curtailment of anti-leishmanial chemotherapy and immunization associated challenges are extensively summed up in this review. This expedited approach is ameliorating the Leishmaniasis management successfully. Alongside, total to partial eradication of this disease can be sought along with associated co-morbidities.

Antileishmanial efficacy and tolerability of combined treatment with non-ionic surfactant vesicle formulations of sodium stibogluconate and paromomycin in dogs

Infection with Leishmania infantum causes the disease visceral leishmaniasis (VL), which is a serious clinical and veterinary problem. The drugs used to treat canine leishmaniasis (CanL) do not cause complete parasite clearance; they can be toxic, and emerging drug resistance in parasite populations limits their clinical utility. Therefore, in this study we have evaluated the toxicity and efficacy of joint treatment with a 1:1 mixture of sodium stibogluconate-NIV (SSG-NIV, 10 mg Sb^v/day) and paromomycin-NIV (PMM-NIV, 10 mg PMM/kg/day), given intravenously daily for seven days from day 270 post-infection, to nine-month-old female beagle dogs (n = 6) experimentally infected with Leishmania infantum. Treatment significantly improved the clinical symptoms of VL infection in all the treated dogs, reduced parasite burdens in lymph nodes and bone marrow, and all symptomatic treated dogs, were asymptomatic at 90 days post-treatment. Treatment was associated with a progressive and significant decrease in specific IgG anti-Leishmania antibodies using parasite soluble antigen (p < 0.01) or rK39 (p < 0.01) as the target antigen. In addition, all dogs were classified as parasite negative based on Leishmania nested PCR and quantitative real time PCR tests and as well as an inability to culture of promastigote parasites from lymph nodes and bone marrow tissue samples taken at day 90 post-treatment. However, treatment did not cure the dogs as parasites were detected at 10 months post-treatment, indicating that a different dosing regimen is required to cause long term cure or prevent relapse.

Low-level laser therapy for the treatment of early stage cutaneous leishmaniasis: A pilot study

Low-Level Laser Therapy (LLLT) has been investigated for the treatment of various dermatological disorders. Here, we investigate the efficacy of LLLT for the treatment of cutaneous leishmaniasis (CL). This study comprised of 53 patients (total 123 lesions) with a confirmed diagnosis of CL via positive smear of LD-bodies. The CL lesions were classified in Grade I (ie, papule of size ≤1 cm) to Grade V (ie, vesicle formation, ulceration, and superadded infection of size >4 cm). All the patients were divided into group 1 with low grade (ie, Grade I and II) CL lesions and group 2 with high-grade disease (ie, Grade III-V). Red laser light (wavelength = 635 nm) was used for the lesion irradiation, with a light dose of 75 J/cm2 and at a low power of 300 mW. The treatment was divided into four sessions, one session per week. Disease assessment at 10 months follow-up revealed complete response in 91% and partial response in 9% patients of group 1, while no response was observed in patients of group 2. LLLT offers a promising treatment modality for patients presenting with early-stage (ie, Grade I and II) CL lesions.

Exploiting knowledge on pharmacodynamics-pharmacokinetics for accelerated anti-leishmanial drug discovery/development

Introduction: Being on the top list of neglected tropical diseases, leishmaniasis has been marked for elimination by 2020. In the light of small armamentarium of drugs and their associated drawbacks, the understanding of pharmacodynamics and/or pharmacokinetics becomes a priority to achieve and sustain disease elimination. Areas covered: The authors have looked into pharmacological aspects of existing and emerging drugs for treatment of leishmaniasis. An in-depth understanding of pharmacodynamics and pharmacokinetics (PKPD) provides a rationale for drug designing and optimizing the treatment strategies. It forms a key to prevent drug resistance and avoid drug-associated adverse effects. The authors have compiled the researches on the PKPD of different anti-leishmanial formulations that have the potential for improved and/or effective disease intervention. Expert opinion: Understanding the pharmacological aspects of drugs forms the basis for the clinical application of novel drugs. Tailoring drug dosage and individualized treatment can avoid the adverse events and bridge gap between the in vitro models and their clinical application. An integrated approach, with pragmatic use of technological advances can improve phenotypic screening and physiochemical properties of novel drugs. Concomitantly, this can serve to improve clinical efficacies, reduce the incidence of relapse and accelerate the drug discovery/development process for leishmaniasis elimination.

Sodium stibogluconate loaded nano-deformable liposomes for topical treatment of leishmaniasis: macrophage as a target cell

Topical drug delivery against cutaneous leishmaniasis (CL) signifies an effective alternate for improving the availability and reducing the toxicity associated with the parenteral administration of conventional sodium stibogluconate (SSG) injection. The basic aim of the study was to develop nano-deformable liposomes (NDLs) for the dermal delivery of SSG against CL. NDLs were formulated by a modified thin film hydration method and optimized via Box–Behnken statistical design. The physicochemical properties of SSG-NDLs were established in terms of vesicle size (195.1 nm), polydispersity index (0.158), zeta potential (−32.8 mV), and entrapment efficiency (35.26%). Moreover, deformability index, in vitro release, and macrophage uptake studies were also accomplished. SSG-NDLs were entrapped within Carbopol gel network for the ease of skin application. The ex vivo skin permeation study revealed that SSG-NDLs gel provided 10-fold higher skin retention towards the deeper skin layers, attained without use of classical permeation enhancers. Moreover, in vivo skin irritation and histopathological studies verified safety of the topically applied formulation. Interestingly, the cytotoxic potential of SSG-NDLs (1.3 mg/ml) was higher than plain SSG (1.65 mg/ml). The anti-leishmanial activity on intramacrophage amastigote model of Leishmania tropica showed that IC₅₀ value of the SSG-NDLs was ∼ fourfold lower than the plain drug solution with marked increase in the selectivity index. The in vivo results displayed higher anti-leishmanial activity by efficiently healing lesion and successfully reducing parasite burden. Concisely, the outcomes indicated that the targeted delivery of SSG could be accomplished by using topically applied NDLs for the effective treatment of CL.

Evaluation of minor groove binders (MGBs) as novel anti-mycobacterial agents and the effect of using non-ionic surfactant vesicles as a delivery system to improve their efficacy

OBJECTIVES

The slow development of major advances in drug discovery for the treatment of Mycobacterium tuberculosis (Mtb) infection suggests a compelling need for evaluation of more effective drug therapies against TB. New classes of drugs are constantly being evaluated for anti-mycobacterial activity with currently a very limited number of new drugs approved for TB treatment. Minor groove binders (MGBs) have previously revealed promising antimicrobial activity against various infectious agents; however, they have not yet been screened against Mtb.

METHODS

The mycobactericidal activity of 96 MGB compounds against Mtb was determined using an H37Rv-GFP microplate assay. MGB hits were screened for their intracellular mycobactericidal efficacy against the clinical Beijing Mtb strain HN878 in bone-marrow-derived macrophages using standard cfu counting. Cell viability was assessed by CellTiter-Blue assays. Selected MGBs were encapsulated into non-ionic surfactant vesicles (NIVs) for drug delivery system evaluation.

RESULTS

H37Rv-GFP screening yielded a hit-list of seven compounds at an MIC99 of between 0.39 and 1.56 μM. MGB-362 and MGB-364 displayed intracellular mycobactericidal activity against Mtb HN878 at an MIC50 of 4.09 and 4.19 μM, respectively, whilst being non-toxic. Subsequent encapsulation into NIVs demonstrated a 1.6- and 2.1-fold increased intracellular mycobacterial activity, similar to that of rifampicin when compared with MGB-alone formulation.

CONCLUSIONS

MGB anti-mycobacterial activities together with non-toxic properties indicate that MGB compounds constitute an important new class of drug/chemical entity, which holds promise in future anti-TB therapy. Furthermore, the ability of NIVs to better deliver entrapped MGB compounds to an intracellular Mtb infection suggests further preclinical evaluation is warranted.

Current status on prevention and treatment of canine leishmaniasis

Canine leishmaniasis (CanL) is a parasite-borne disease mainly induced by Leishmania infantum in the Old World and Leishmania chagasi (infantum) in the New World. CanL is a zoonosis transmitted by the bite of infected Phlebotominae flies that act as vectors. CanL is a very serious disease that usually produces death when remains untreated and can be a focus of transmission to other dogs or humans. Infected dogs and other domestic and wild animals act as reservoirs and are a real threat to uninfected/healthy dogs and humans in endemic areas where the sand flies are present. Prevention of new infections in dogs can help to stop the current increase of the disease in humans, reinforcing the concept of "One Health" approach. The management of CanL is being performed using prophylactic measures in healthy dogs - insecticides impregnated in collars or immunostimulants applied by spot-on devices - and chemotherapy in animals that suffer from the disease. Antimonials as first-line monotherapy have proven efficacy in reducing most of the clinical signs of CanL, but they need to be administered during several days, and no complete parasite clearance is achieved, favouring the presence of relapses among treated dogs. Therefore, new drugs, such as miltefosine, or combinations of this drug or antimonials with allopurinol are in the pipeline of clinical treatment of CanL. Recently, there has been an emergence of protective - prophylactic - and curative - autogenous vaccines - immunotherapy tools to face CanL, whose results are still under study. This review highlights the current use of preventive and eradicative weapons to fight against this disease, which is a scourge for dogs and a continuous threat to human beings.

Inhibition of Src homology 2 domain-containing phosphatase 1 increases insulin sensitivity in high-fat diet-induced insulin-resistant mice

Insulin resistance plays a crucial role in the development of type 2 diabetes. Insulin receptor signalling is antagonized and tightly controlled by protein tyrosine phosphatases (PTPs). However, the precise role of the PTP src homology 2 domain‐containing phosphatase 1 (SHP‐1) in insulin resistance has not been explored. Male C57BL/6J mice were fed a high‐fat diet (HFD, 60% kcal from fat), to induce insulin resistance, or a low‐fat diet (LFD, 10% kcal from fat) for 10 weeks. Afterwards, HFD‐fed mice were pharmacologically treated with the SHP‐1 (Ptpn6) inhibitor sodium stibogluconate and the broad spectrum pan‐PTP inhibitor bis(maltolato)oxovanadium(IV) (BMOV). Both inhibitors ameliorated the metabolic phenotype, as evidenced by reduced body weight, improved insulin sensitivity and glucose tolerance, which was not due to altered PTP gene expression. In parallel, phosphorylation of the insulin receptor and of the insulin signalling key intermediate Akt was enhanced, and both PTP inhibitors and siRNA‐mediated SHP‐1 downregulation resulted in an increased glucose uptake in vitro. Finally, recombinant SHP‐1 was capable of dephosphorylating the ligand‐induced tyrosine‐phosphorylated insulin receptor. These results indicate a central role of SHP‐1 in insulin signalling during obesity, and SHP‐1 inhibition as a potential therapeutic approach in metabolic diseases.

Tissue distribution of residual antimony in rats treated with multiple doses of meglumine antimoniate

Meglumine antimoniate (MA) and sodium stibogluconate are pentavalent antimony (Sb^V) drugs used since the mid-1940s. Notwithstanding the fact that they are first-choice drugs for the treatment of leishmaniases, there are gaps in our knowledge of their toxicological profile, mode of action and kinetics. Little is known about the distribution of antimony in tissues after Sb^V administration. In this study, we evaluated the Sb content of tissues from male rats 24 h and three weeks after a 21-day course of treatment with MA (300 mg Sb^V/kg body wt/d, subcutaneous). Sb concentrations in the blood and organs were determined by inductively coupled plasma-mass spectrometry. In rats, as with in humans, the Sb blood levels after MA dosing can be described by a two-compartment model with a fast (t1/2 = 0.6 h) and a slow (t1/2 >> 24 h) elimination phase. The spleen was the organ that accumulated the highest amount of Sb, while bone and thyroid ranked second in descending order of tissues according to Sb levels (spleen >> bone, thyroid, kidneys > liver, epididymis, lungs, adrenals > prostate > thymus, pancreas, heart, small intestines > skeletal muscle, testes, stomach > brain). The pathophysiological consequences of Sb accumulation in the thyroid and Sb speciation in the liver, thyroid, spleen and bone warrant further studies.

Investigational drugs for visceral leishmaniasis

Introduction: The armamentarium of antileishmanial drugs is small. It is further being threatened by the development of resistance and decreasing sensitivity to the available drugs. The development of newer drugs is sorely needed. Areas covered: The authors have based their review on a literature search performed using PubMed. The article specifically looks at investigational drugs, which have demonstrated, at the very least, in vitro and in vivo activities against the leishmania species that cause visceral leishmaniasis. Specifically, the authors review the nitroimidazole compound fexinidazole, which is one of the few drugs which have reached Phase II trials. The article also discusses the R enantiomer of (S)-PA-824, which has shown good antileishmanial activity. Finally, the article also highlights the many novel delivery systems and oral formulations of amphotericin B, which are both cheap and less toxic and are currently under investigation. Expert opinion: Very few new drugs have reached the clinic for this neglected tropical disease and there is an urgent need for new efficacious therapeutics. The authors believe that support from public-private partnerships would help in enabling the prompt development of drug candidates that could potentially make the clinic.

A potential link among antioxidant enzymes, histopathology and trace elements in canine visceral leishmaniasis

Canine visceral leishmaniasis (CVL) is a severe and fatal systemic chronic inflammatory disease. We investigated the alterations in, and potential associations among, antioxidant enzymes, trace elements and histopathology in CVL. Blood and tissue levels of Cu-Zn superoxide dismutase, catalase and glutathione peroxidase were measured in mixed-breed dogs naturally infected with Leishmania infantum chagasi, symptomatic (n = 19) and asymptomatic (n = 11). Serum levels of copper, iron, zinc, selenium and nitric oxide, and plasma lipid peroxidation were measured. Histological and morphometric analyses were conducted of lesions in liver, spleen and lymph nodes. We found lower blood catalase and glutathione peroxidase activity to be correlated with lower iron and selenium respectively. However, higher activity of Cu-Zn superoxide dismutase was not correlated with the increase in copper and decreased in zinc observed in infected animals compared to controls. Organ tissue was characterized by lower enzyme activity in infected dogs than in controls, but this was not correlated with trace elements. Lipid peroxidation was higher in symptomatic than in asymptomatic and control dogs and was associated with lesions such as chronic inflammatory reaction, congestion, haemosiderin and fibrosis. Systemic iron deposition was observed primarily in the symptomatic dogs showing a higher tissue parasite load. Dogs with symptomatic CVL displayed enhanced LPO and Fe tissue deposition associated with decreased levels of antioxidant enzymes. These results showed new points in the pathology of CVL and might open new treatment perspectives associated with antioxidants and the role of iron in the pathogenesis of CVL.

Complement activation-related pseudoallergy in dogs following intravenous administration of a liposomal formulation of meglumine antimoniate

The increasing use of nanotechnologies in advanced therapies has allowed the observation of specific adverse reactions related to nanostructures. The toxicity of a novel liposome formulation of meglumine antimoniate in dogs with visceral leishmaniasis after single dose has been investigated. Groups of 12 animals received by the intravenous route a single dose of liposomal meglumine antimoniate (group I [GI], 6.5 mg Sb/kg), empty liposomes (GII) or isotonic saline (GIII). Evaluation of hematological and biochemical parameters showed no significant changes 4 days after administration. No undesired effects were registered in the GIII. However, adverse reactions were observed in 67.7% of dogs from both groups that received liposomal formulations. The side effects began moments after bolus administration and disappeared during the first 15 minutes after treatment. Prostation, sialorrhea and defecation were the most frequent clinical signs, registered in 33.3% and 41.6 % of animals from the groups GI and GII, respectively. Tachypnea, mydriasis, miosis, vomiting and cyanosis were also registered in both groups. The adverse reactions observed in this study were attributed to the activation of the complement system by lipid vesicles in a phenomenon known as Complement Activation-Related Pseudoallergy (CARPA). The influence of the physical-chemical characteristics of liposomal formulation in the triggering of CARPA is discussed.

Strategies for the design of orally bioavailable antileishmanial treatments

Leishmaniasis is one of the six major tropical diseases targeted by the World Health Organization. The most serious, life-threatening form is visceral leishmaniasis (VL). No vaccine is yet available for human use and chemotherapy is the main mean of dealing with this disease. This review focuses on the development of drug delivery systems (DDS) for treatment of leishmaniasis. After an overview of the significance of leishmaniasis in 2013, current chemotherapy and its limitations are considered, leading to possible strategies to improve the treatment of VL: new drugs, combinations of existing drugs and DDS, particularly for oral administration. Nanostructured biomaterials such as lipid-based or polymeric nanoparticles have unique physicochemical properties, ultra-small and controllable size, large surface area to mass ratio and the possibility of surface modification which can be used to advantage for the oral administration of antileishmanial drugs. They can improve the rate of dissolution of poorly water-soluble drugs, increase intestinal residence time by bioadhesion and, especially when lipid additives are used, influence the route and efficiency of absorption. These recent advances in this very active field should lead to better management of this serious disease.

Disposition of antimony in rhesus monkeys infected with Leishmania braziliensis and treated with meglumine antimoniate

Antimony (Sb) disposition and toxicity was evaluated in Leishmania braziliensis-infected monkeys (Macaca mulatta) treated with a 21-d course of low (LOW) or standard (STD) meglumine antimoniate (MA) dosage regimens (5 or 20 mg Sb(V)/kg body weight/d im). Antimony levels in biological matrices were determined by inductively coupled plasma mass spectrometry (ICPMS), while on-line ion chromatography coupled to ICPMS was used to separate and quantify Sb species in plasma. Nadir Sb levels rose steadily from 19.6 ± 4 and 65.1 ± 17.4 ng/g, 24 h after the first injection, up to 27.4 ± 5.8 and 95.7 ± 6.6 ng/g, 24 h after the 21st dose in LOW and SDT groups, respectively. Subsequently, Sb plasma levels gradually declined with a terminal elimination phase half-life of 35.8 d. Antimony speciation in plasma on posttreatment days 1-9 indicated that as total Sb levels declined, proportion of Sb(V) remained nearly constant (11-20%), while proportion of Sb(III) rose from 5% (d 1) to 50% (d 9). Plasma [Sb]/erythrocyte [Sb] ratio was >1 until 12 h after dosing and reversed thereafter. Tissue Sb concentrations (posttreatment days 55 and 95) were as follows: >1000 ng/g in thyroid, nails, liver, gall bladder and spleen; >200 and <1000 ng/g in lymph nodes, kidneys, adrenals, bones, skeletal muscles, heart and skin; and <200 ng/g in various brain structures, thymus, stomach, colon, pancreas. and teeth. Results from this study are therefore consistent with view that Sb(V) is reduced to Sb(III), the active form, within cells from where it is slowly eliminated. Localization of Sb active forms in the thyroid gland and liver and the pathophysiological consequences of marked Sb accumulation in these tissues warrant further studies.

Drug delivery strategies for therapy of visceral leishmaniasis

IMPORTANCE OF THE FIELD

Visceral leishmaniasis (VL) is the most overwhelming type of leishmaniasis associated with the poverty of developing countries and usually mortal if untreated. Most of the conventionally used dosage forms offer us the shortcomings of toxic side effects and emergence of drug resistance. Several efforts have been made to overcome the barriers involved in the treatment of VL. Colloidal carriers extensively represent the drug delivery systems (DDSs) for intracellular localization of antileishmanial compounds in macrophage-rich organs such as liver, spleen and bone marrow. These DDSs offer superior therapeutic efficacy over the conventional treatment in terms of site-specific drug delivery with reduced side effects. However, after 35 years of research in the field, AmBisome (Amphotericin B liposome for injection, Astellas Pharma US, Inc.) is the only DDS used against the VL.

AREAS COVERED IN THIS REVIEW

A literature search was performed (for drugs and DDSs against VL) on PubMed and through Google.

WHAT THE READER WILL GAIN

This review aims to describe the pathophysiology of VL and its current conventional treatment with special reference to DDSs designed against VL.

TAKE HOME MESSAGE

On reviewing the conventional drugs and DDSs developed against VL, it is concluded that advances in the field of targeted drug delivery can result in more efficient strategies for the therapy of VL.

Pentavalent antimonials: new perspectives for old drugs

Pentavalent antimonials, including meglumine antimoniate and sodium stibogluconate, have been used for more than half a century in the therapy of the parasitic disease leishmaniasis. Even though antimonials are still the first-line drugs, they exhibit several limitations, including severe side effects, the need for daily parenteral administration and drug resistance. The molecular structure of antimonials, their metabolism and mechanism of action are still being investigated. Some recent studies suggest that pentavalent antimony acts as a prodrug that is converted to active and more toxic trivalent antimony. Other works support the direct involvement of pentavalent antimony. Recent data suggest that the biomolecules, thiols and ribonucleosides, may mediate the actions of these drugs. This review will summarize the progress to date on the chemistry and biochemistry of pentavalent antimony. It will also present the most recent works being done to improve antimonial chemotherapy. These works include the development of simple synthetic methods for pentavalent antimonials, liposome-based formulations for targeting the Leishmania parasites responsible for visceral leishmaniasis and cyclodextrin-based formulations to promote the oral delivery of antimony.

Reduced Tissue Parasitic Load and Infectivity to Sand Flies in Dogs Naturally Infected by Leishmania ( Leishmania ) chagasi following Treatment with a Liposome Formulation of Meglumine Antimoniate

The toxicity and antileishmanial effectiveness of a novel liposome formulation of meglumine antimoniate in mongrel dogs with visceral leishmaniasis (VL) obtained from a region where VL is endemic in Brazil have been investigated. Groups of 12 animals received by the intravenous route four doses (with 4-day intervals) of either liposomal meglumine antimoniate (group I [GI], 6.5 mg Sb/kg of body weight/dose), empty liposomes (GII), or isotonic saline (GIII). Evaluation of markers of hematopoietic, hepatic, and renal functions before and just after treatment showed no significant change. On the other hand, transitory adverse reactions, including prostration, defecation, tachypnea, and sialorrhea, were observed during the first 15 min after injections in GI and GII. Parasitological evaluation of sternal bone marrow 4 days after the last dose showed a significant reduction of parasite burden in GI, compared to the other groups. Immunocytochemical evaluations of the skin, bone marrow, cervical lymph nodes, livers, and spleens of dogs for parasites, 150 days after treatment, indicated significant parasite suppression (higher than 95.7%) in the lymph nodes, livers, and spleens of GI, compared to control groups. Feeding of Lutzomyia longipalpis phlebotomines on dogs from GI, 150 days after treatment, resulted in a significant reduction of sand fly infection efficiency, compared to feeding on animals from GII and GIII. This is the first report of both long-term parasite suppression and reduction of infectivity to sand flies in naturally infected dogs following treatment with a liposome-encapsulated drug. Importantly, this was achieved using a 20-fold-lower cumulative dose of Sb than is used for conventional antimonial treatment.

Improved targeting of antimony to the bone marrow of dogs using liposomes of reduced size

A novel liposomal formulation of meglumine antimoniate (MA), consisting of vesicles of reduced size, has been evaluated in dogs with visceral leishmaniasis to determine its pharmacokinetics as well as the impact of vesicle size on the targeting of antimony to the bone marrow. Encapsulation of MA in liposomes was achieved through freeze-drying of empty liposomes in the presence of sucrose and rehydration with a solution of MA. The resulting formulation, with a mean vesicle diameter of about 400 nm, was given to mongrel dogs with visceral leishmaniasis as an i.v. bolus injection at 4.2 mgSb/kg of body weight. The pharmacokinetics of antimony were assessed in the blood and in organs of the mononuclear phagocyte system and compared to those achieved with the free drug and the drug encapsulated in large sized liposomes (mean diameter of 1200 nm). The targeting of antimony to the bone marrow was improved (approximately three-fold) with the novel liposomal formulation, when compared to the formulation of MA in large sized liposomes. This study provides the first direct experimental evidence that passive targeting of liposomes to the bone marrow of dogs is improved by the reduction of vesicle size from the micron to the nanometer scale.

In vitro and in vivo interactions between miltefosine and other antileishmanial drugs

The interaction of miltefosine with amphotericin B, sodium stibogluconate, paromomycin, and sitamaquine was assessed in vitro and additionally for the first three combinations in vivo. In vitro interactions were indifferent for miltefosine combined with amphotericin B (mean sums of fractional inhibitory concentrations [mean summation operatorFICs] ranging from 1.22 to 1.51 at the 50% effective concentration [EC50] level and 1.08 to 1.38 at the EC90 level), sitamaquine (mean summation operatorFICs from 1.33 to 1.38 and 1.0 to 1.02, respectively), and paromomycin (mean summation operatorFICs from 0.79 to 0.93 at the EC50 and 0.77 to 1.35 at the EC90 level). Some synergy was observed for miltefosine combined with sodium stibogluconate (mean summation operatorFICs from 0.61 to 0.75 at EC50 and 0.49 to 0.97 at EC90). Different interactions were found in vivo, where the highest potentiation of miltefosine activity was achieved with amphotericin B (activity enhancement index [AEI] of up to 11.3). No significant interaction was observed when miltefosine was combined with sodium stibogluconate (AEI of up to 2.38). The potentiation of miltefosine in vivo was also achieved with the combination of miltefosine and paromomycin (AEI of up to 7.22).

Inhibition of hepatitis C virus replication by antimonial compounds

Chronic hepatitis C virus (HCV) infection is a worldwide health problem causing serious complications, such as liver cirrhosis and hepatoma. Alpha interferon (IFN-alpha) or its polyethylene glycol-modified form combined with ribavirin is the only recommended therapy. However, an alternative therapy is needed due to the unsatisfactory cure rate of the IFN-based therapy. Using a modified reporter assay based on the HCV subgenomic-replicon system, we found that sodium stibogluconate (SSG), a compound used for leishmania treatment, suppressed HCV replication. We have previously reported that SSG is effective at inhibiting HCV replication in a cell line permissive for HCV infection/replication and in an ex vivo assay using fresh human liver slices obtained from patients infected with HCV (26). In this study, we show that the SSG 50% inhibitory dose for HCV replication is 0.2 to 0.3 mg/ml (equivalent to 345 to 517 microM of Sb) in the HCV subgenomic-replicon system. We also found that SSG and IFN-alpha exert a strong synergistic anti-HCV effect in both the traditional isobologram analysis and the median effect principle (CalcuSyn analysis). The combination of SSG and IFN-alpha could sustain the antiviral response better than SSG or IFN-alpha alone. The results suggest that SSG may be a good drug candidate for use in combination with other therapeutics, such as IFN-alpha and ribavirin, to treat HCV infection.

Canine Leishmaniasis

Canine leishmaniasis is caused by Leishmania infantum (syn. L. chagasi, in America) and is transmitted by the bite of phlebotomine sand flies. Infected dogs constitute the main domestic reservoir of the parasite and play a key role in transmission to humans, in which the parasite produces visceral leishmaniasis. The increasing awareness that control of the human disease depends on effective control of canine leishmaniasis has promoted, in the last few years, research into leishmanial infection in dogs. Newly available specific reagents and molecular tools have been applied to the detailed investigation of canine leishmaniasis and important advances have been made in elucidating the epidemiology and pathology of the disease. These new findings have led to better understanding of the disease, and have also helped in the development of new diagnostic methods and control measures against the infection, such as insecticide-impregnated collars for dogs, new drugs and treatment protocols, and second generation vaccines, with the hope of not only reducing the heavy burden of the disease among dogs but also reducing the incidence of human visceral leishmaniasis.