Efficacy of picroliv in combination with miltefosine, an orally effective antileishmanial drug against experimental visceral leishmaniasis

Revisiting nature: a review of iridoids as a potential antileishmanial class

Leishmaniasis still stands as one of the most prevalent neglected tropical diseases in the least developed and emerging countries. The recommended therapeutic arsenal to treat leishmaniasis is characterized by several shortcomings, and resistance has already been reported. Hence, this dramatic background highlights the pressing need to develop novel, affordable, and safe antileishmanial drugs. Multiple classes of natural compounds have been reported to possess antileishmanial activity. Among these classes, iridoids stand out as a special type of monoterpenoids with diverse biological properties-including their antileishmanial potential. This review aims to discuss the available literature between 1991 and 2020 related to the antileishmanial activity of the iridoid class. Throughout the past decades, various investigations attributed antileishmanial action to assorted iridoid types, including inhibitory potential towards validated drug targets and immunomodulatory activity. The latter deserves special attention due to the ability of some iridoids to improve the host's immune response against parasites. It opens the possibility of iridoids become adjuncts in leishmaniasis treatments by improving the efficacy of currently employed drugs. Furthermore, the present study intends to provide a convenient visual representation of which iridoids and Leishmania spp. species have been most investigated as a guide for further researches.

Herb-drug interactions: a mechanistic approach

In India, traditional herbal medicines have been an essential part of therapy for the last centuries. However, a large portion of the general populace is using these therapies in combination with allopathy lacking a proper understanding of possible interactions (synergistic or antagonistic) between the herbal product and the allopathic drug. This is based on the assumption that herbal drugs are relatively safe, i.e. without side effects. We have established a comprehensive understanding of the possible herb-drug interactions and identified interaction patterns between the most common herbs and drugs currently in use in the Indian market. For this purpose, we listed common interactors (herbs and allopathic drugs) using available scientific literature. Drugs were then categorized into therapeutic classes and aligned to produce a recognizable pattern present only if interactions were observed between a drug class and herb in the scientific literature. Interestingly, the top three categories (with highest interactors), antibiotics, oral hypoglycemics, and anticonvulsants, displayed synergistic interactions only. Another major interactor category was CYP450 enzymes, a natural component of our metabolism. Both activation and inhibition of CYP450 enzymes were observed. As many allopathic drugs are known CYP substrates, inhibitors or inducers, ingestion of an interacting herb could result in interaction with the co-administered drug. This information is largely unavailable for the Indian population and should be studied in greater detail to avoid such interactions. Although this information is not absolute, the systematic literature review proves the existence of herb-drug interactions in the literature and studies where no interaction was detected are equally important.

An overview of azoles targeting sterol 14α-demethylase for antileishmanial therapy

The azole antifungal drugs are an important class of chemotherapeutic agents with broad-spectrum of activity against yeasts and filamentous fungi, act in the ergosterol biosynthetic pathway through inhibition of the cytochrome P450-dependent enzyme sterol 14α-demethylase. Azole antifungals have also been repurposed for treatment of tropical protozoan infections including human leishmaniasis. Recent advances in molecular biology and computational chemistry areas have increased our knowledge about sterol biochemical pathway in Leishmania parasites. Based on the importance of sterol biosynthetic pathway in Leishmania parasites, we reviewed all studies reported on azoles for potential antileishmanial therapy along their structural and biological aspects. This review may help medicinal chemists for design of new azole-derived antileishmanial drugs.

Nanotized Curcumin and Miltefosine, a Potential Combination for Treatment of Experimental Visceral Leishmaniasis

Leishmaniasis chemotherapy remains very challenging due to high cost of the drug and its associated toxicity and drug resistance, which develops over a period of time. Combination therapies (CT) are now in use to treat many diseases, such as cancer and malaria, since it is more effective and affordable than monotherapy. CT are believed to represent a new explorable strategy for leishmaniasis, a neglected tropical disease caused by the obligate intracellular parasite Leishmania In the present study, we investigated the effect of a combination of a traditional Indian medicine (ayurveda), a natural product curcumin and miltefosine, the only oral drug for visceral leishmaniasis (VL) using a Leishmania donovani-hamster model. We developed an oral nanoparticle-based formulation of curcumin. Nanoformulation of curcumin alone exhibited significant leishmanicidal activity both in vitro and in vivo In combination with miltefosine, it exhibited a synergistic effect on both promastigotes and amastigotes under in vitro conditions. The combination of these two agents also demonstrated increased in vivo leishmanicidal activity accompanied by increased production of toxic reactive oxygen/nitrogen metabolites and enhanced phagocytic activity. The combination also exhibited increased lymphocyte proliferation. The present study thus establishes the possible use of nanocurcumin as an adjunct to antileishmanial chemotherapy.

Cross reactive molecules of human lymphatic filaria Brugia malayi inhibit Leishmania donovani infection in hamsters

Coinfections are common in natural populations and the outcome of their interactions depends on the immune responses of the host elicited by the parasites. Earlier we showed that immunization with BmAFII (Sephadex G-200 eluted) fraction of human lymphatic filaria Brugia malayi inhibited progression of Leishmania donovani infection in golden hamsters. In the present study we identified cross reactive molecules of B. malayi, and investigated their effect on L. donovani infection and associated immune responses in the host. The sequence alignment and sharing of linear T- and B-cell epitopes in protein molecules of B. malayi and L. donovani counterparts were studied in silico. Hamsters were immunized with robustly cross reactive SDS-PAGE resolved fractions F6 (54.2-67.8kDa) and F9 (41.3-45.0kDa) of B. malayi and subsequently inoculated with amastigotes of L. donovani intracardially. F6 inhibited (∼72%) L. donovani infection and upregulated Th1 cytokine expression, lymphoproliferation, IgG2, IgG2/3 levels and NO production, and downregulated Th2 cytokine expression. Sequences in HSP60 and EF-2 of F6 and L. donovani counterparts were conserved and B- and T-cell epitopes in the proteins shared antigenic regions. In conclusion, leishmania-cross reactive molecules of filarial parasite considerably inhibited leishmanial infection via Th1-mediated immune responses and NO production. Common B- and T-cell epitope regions in HSP60 and EF-2 of the parasites might have contributed to the inhibitory effect on the L. donovani infection. Thus, leishmania-cross reactive filarial parasite molecules may help in designing prophylactic(s) against L. donovani.

Discovery of a new class of natural product-inspired quinazolinone hybrid as potent antileishmanial agents

The high potential of quinazolinone containing natural products and their derivatives in medicinal chemistry led us to discover four novel series of 53 compounds of quinazolinone based on the concept of molecular hybridization. Most of the synthesized analogues exhibited potent leishmanicidal activity against intracellular amastigotes (IC50 from 0.65 ± 0.2 to 7.76 ± 2.1 μM) as compared to miltefosine (IC50 = 8.4 ± 2.1 μM) and nontoxic toward the J-774A.1 cell line and Vero cells. Moreover, activation of Th1 type and suppression of Th2 type immune responses and induction in nitric oxide generation proved that 8a and 8g induce murine macrophages to prevent survival of parasites. Compounds 8a and 8g exhibited significant in vivo inhibition of parasite 73.15 ± 12.69% and 80.93 ± 10.50% against Leishmania donovani /hamster model. Our results indicate that compounds 8a, 8g, and 9f represent a new structural lead for this serious and neglected disease.

Interactions of antileishmanial drugs with monolayers of lipids used in the development of amphotericin B-miltefosine-loaded nanocochleates

The emergence of strains of Leishmania resistant to existing drugs complicates the treatment of life-threatening visceral leishmaniasis. The development of new lipid formulation (nanocochleates), containing two active drugs: amphotericin B (AmB) and miltefosine (hexadecylphosphocholine, HePC), could increase effectiveness, decrease toxicity and reduce the risk of appearance of resistance. Nanocochleates are cigar-shaped structures of rolled negatively charged lipid bilayers bridged by calcium, prepared from dioleoylphosphatidylserine (DOPS) and cholesterol (Cho) and able to accommodate drugs. To determine the interaction, the orientation and the stability of the amphiphilic drugs in the lipid mixture and the optimal drugs/lipids ratio, the Langmuir film balance and BAM (Brewster angle microscopy) were used. The drugs were mixed with the lipids (DOPS or 9DOPS/1Cho) and spread at the air-water interface. A stability study showed that DOPS maintained HePC at the interface at low molar fraction of HePC; this effect became more marked in the presence of Cho. The fact that HePC can be stably associated with the monolayer at low molar fraction (below 10%) suggests that in the nanocochleates HePC is inserted between the lipid molecules rather than between the bilayers. Phase diagrams and BAM images showed that, even at low pressure, DOPS maintains AmB at low molar fraction (below 10%) in the "erect" rather than the horizontal form at the interface and that the presence of Cho reinforces this effect. These results allowed us to predict the organization and the orientation of these drugs in the nanocochleates and to determine the optimal drugs/lipids ratio.

Enhancement in therapeutic efficacy of miltefosine in combination with synthetic bacterial lipopeptide, Pam3Cys against experimental Visceral Leishmaniasis

Existing drugs for visceral leishmaniasis (VL) are partially effective, toxic, having high cost and long term treatment. Their efficacies are also compromised due to suppression of immune function associated during the course of infection. Combination therapy including a potential and safe immunostimulant with lower doses of effective drug has proven as a significant approach which is more effective than immunotherapy or drug therapy alone. In the present study, we have used the combination of Pam3Cys (an in-built immunoadjuvant and TLR2 ligand) and miltefosine. Initially dose optimization of both the agents was carried out and after that, antileishmanial effect of their combination was evaluated. All experiments were done in BALB/c mouse model. The immunomodulatory role of Pam3Cys on the immune functions of the host receiving combination treatment was also determined using immunological and biochemical parameters viz. phagocytosis, Th1/Th2 cytokines and production of ROS, RNS and H(2)O(2). Combination group showed significant enhancement in parasitic inhibition as compared to groups receiving miltefosine and Pam3Cys separately. Enhanced production of Th1 cytokines as well as ROS, RNS and H(2)O(2) was witnessed during the study of immunological alterations. Remarkable increase in phagocytosis index was also observed. Thus, the risk of development of drug resistance against miltefosine can be resolved through using low doses of it and Pam3Cys (single-dose) in combination and also provide a promising alternative for cure of leishmaniasis, with a pronounced transformation of the host immune response.

Effect of Pam3Cys induced protection on the therapeutic efficacy of miltefosine against experimental visceral leishmaniasis

Prophylactic potential of synthetic bacterial lipopeptide and a TLR2 agonist, Pam3Cys was first evaluated against experimental visceral leishmaniasis in rodent model. After establishing the potential its effect on therapeutic efficacy of miltefosine was also studied. Pam3Cys showed 74.64% inhibition in parasitic establishment when administered by ip route at a dose of 100 μg/animal spaced at two weeks, i.e. on day -7 and +7 of challenge with Leishmania donovani amastigotes. However, when aforesaid dose of Pam3Cys was given with sub-curative dose of miltefosine (2.5 mg/kg for 5 days) its efficacy enhanced from 49.80% to 92.25%. These findings revealed that this lipopeptide has potential protective efficacy which significantly enhanced the therapeutic efficacy of miltefosine used at low dose against Leishmania infection and warrants detailed investigations on its possible immunopotentiatory actions.

Plant derived therapeutics for the treatment of Leishmaniasis

Diseases caused by insect borne trypanosomatid parasites are significant, yet remain a neglected public health problem. Leishmania, a unicellular protozoan parasite is the causative organism of Leishmaniasis and is transmitted by female phlebotamine sandflies affecting millions of people worldwide. In the wake of resistance to pentavalent antimonial drugs, new therapeutic alternatives are desirable. The plant kingdom has in the past provided several affordable compounds and this review aims to provide an overview of the current status of available leishmanicidal plant derived compounds that are effective singly or in combination with conventional anti-leishmanial drugs, yet are non toxic to mammalian host cells. Furthermore, delineation of the contributory biochemical mechanisms involved in mediating their effect would help develop new chemotherapeutic approaches.

Improved treatment of visceral leishmaniasis (kala-azar) by using combination of ketoconazole, miltefosine with an immunomodulator-Picroliv

Visceral leishmaniasis (VL) caused by the parasite Leishmania donovani, is a potentially fatal disease. It is characterized by prolonged fever, enlarged spleen and liver, substantial weight loss and progressive anemia. Available drugs are toxic, costly and require prolonged treatment duration viz; 28 days of oral treatment with miltefosine, 30 days infusion with Amphotericin B and 21 days intramascular with paromomycin sulfate. Drug combination for VL clinically proved to shorten the duration of treatment. The efficacy of drugs is also compromised due to suppression of immune function during the course of infection. To combat this situation leishmanicidal efficacy of already marketed standard antifungal drug, ketoconazole under the approach of 'therapeutic switching' in combination with standard antileishmanial drug, miltefosine and a potent immunomodulator agent, picroliv were evaluated in L. donovani/hamsters model. Animals treated with combination of ketoconazole (50 mg/kg, 5 days, po)+miltefosine (5 mg/kg, 5 days, po) showed augmentation in efficacy against leishmania parasite (72%) in comparison to those treated with ketoconazole (54.67%) and miltefosine (54.77%) separately. Co-administration of picroliv (10 mg/kg, 12 days, po) has further enhanced antileishmanial efficacy from 72% to 82%. Significant generation of ROS, RNS and H(2)O(2) and increased phagocytosis was observed in animals treated with ketoconazole+miltefosine; however, addition of picroliv to this combination did not alter the level of metabolites and phagocytosis due to its antioxidative and nonleishmanicidal characteristics, respectively. Significant rise in cell mediated immunity witnessed in this group reveals the role played by the immunomodulator, picroliv and justifies the significance of enhanced cell mediated immunity in the therapy. These findings suggest a new strategy for leishmanial chemotherapy at reduced cost and toxicity.

Use of antimony in the treatment of leishmaniasis: current status and future directions

In the recent past the standard treatment of kala-azar involved the use of pentavalent antimonials Sb(V). Because of progressive rise in treatment failure to Sb(V) was limited its use in the treatment program in the Indian subcontinent. Until now the mechanism of action of Sb(V) is not very clear. Recent studies indicated that both parasite and hosts contribute to the antimony efflux mechanism. Interestingly, antimonials show strong immunostimulatory abilities as evident from the upregulation of transplantation antigens and enhanced T cell stimulating ability of normal antigen presenting cells when treated with Sb(V) in vitro. Recently, it has been shown that some of the peroxovanadium compounds have Sb(V)-resistance modifying ability in experimental infection with Sb(V) resistant Leishmania donovani isolates in murine model. Thus, vanadium compounds may be used in combination with Sb(V) in the treatment of Sb(V) resistance cases of kala-azar.

CpG oligodeoxynucleotide 2006 and miltefosine, a potential combination for treatment of experimental visceral leishmaniasis

In view of the severe immunosuppression in visceral leishmaniasis (VL), a rational approach to effectively combat the parasitic scourge would be to enhance the immune status of the host. Use of CpG oligodeoxynucleotide (CpG-ODN) against leishmaniasis has previously been reported, especially as an immunomodulator and adjuvant with various immunogens. In the present study, experiments were carried out with BALB/c mice and hamsters infected with Leishmania donovani. Immunostimulating class B bacterial CpG-ODN namely, ODN-2006, was administered at various doses by the intraperitoneal (i.p.) route. The dose of CpG-ODN-2006 (1 nM/single dose) showing the most antileishmanial activity was given as free and liposomal forms with different doses of miltefosine, namely, 5 and 10 mg/kg of body weight, for 5 days in mice and hamsters, respectively. Among the various groups, mice coadministered liposomal CpG-ODN and miltefosine (5 mg/kg) showed the best inhibitory effect (97% parasite inhibition) compared with free CpG-ODN plus miltefosine and miltefosine, free CpG-ODN, and liposomal CpG-ODN given separately. Similar responses were observed in the case of hamsters, where the combination of liposomal CpG-ODN with miltefosine (10 mg/kg) gave 96% parasite inhibition. Promising antileishmanial efficacy was observed in animals treated with liposomal CpG-ODN and miltefosine.

Antileishmanial efficacy of fluconazole and miltefosine in combination with an immunomodulator--picroliv

The chemotherapy of visceral leishmaniasis (VL) has several limitations including resistance and toxicity of the existing drugs. Downregulation of immune system further aggravates the problems. To combat this situation, leishmanicidal efficacy of already marketed standard antifungal drug, fluconazole under the approach of "therapeutic switching" in combination with standard antileishmanial drug, miltefosine, and a potent immunomodulator agent, picroliv, were evaluated in hamsters infected with Leishmania donovani. Animals treated with fluconazole (50 mg/kg × 5 days, oral (p.o.)) + miltefosine (5 mg/kg × 5 days, p.o.) showed enhancement in antileishmanial efficacy (77%), reactive nitrogen species, reactive oxygen species, hydrogen peroxide, and phagocytosis index as compared to those treated with individual drugs. Addition of picroliv to this combination further increased the antileishmanial efficacy from 77% to 88%. Upregulation of cell-mediated immunity was also observed in animals of this group which strengthens the immunomodulatory role of picroliv. These findings suggest a new option for antileishmanial chemotherapy at lower cost and toxicity.

Immunomodulatory effect of picroliv on the efficacy of paromomycin and miltefosine in combination in experimental visceral leishmaniasis

Combination therapy for the treatment of visceral leishmaniasis has increasingly been advocated as a way to increase treatment efficacy and tolerance, to reduce treatment duration and cost, and to limit the emergence of drug resistance. In the present work, we have adopted a rational approach, which can modulate the immune response to overcome the negative control systems and to boost the positive killing responses. This study was designed to investigate the immunomodulatory effect of picroliv (standardized fraction from the alcoholic extract of root and rhizome of Picrorhiza kurroa) on a combination of paromomycin and miltefosine using Leishmania donovani/hamster model. Picroliv has significantly enhanced antileishmanial efficacy and lymphocyte proliferation when given in combination with paromomycin and miltefosine. Increased toxic oxygen metabolite generation and phagocytosis were also witnessed. Present study thus establishes the possible use of picroliv as adjunct to antileishmanial chemotherapy.

CpG oligodeoxynucleotide augments the antileishmanial activity of miltefosine against experimental visceral leishmaniasis

OBJECTIVES

To evaluate the combination of CpG oligodeoxynucleotide (CpG ODN) and miltefosine for the treatment of experimental visceral leishmaniasis (VL).

METHODS

The experiments were carried out using BALB/c mice and hamsters, infected with Leishmania donovani. CpG ODN was administered at various doses by the intraperitoneal (ip) route. The dose of CpG ODN (1 nM/single dose) showing best antileishmanial activity was given as free and liposomal forms with a subcurative dose of miltefosine, namely 2.5 and 5 mg/kg x 5 days in mice and hamsters, respectively.

RESULTS

Among the various groups of mice, co-administered liposomal CpG ODN and miltefosine showed the best inhibitory effect (85% inhibition) compared with free CpG ODN and miltefosine, and miltefosine, free CpG ODN and liposomal CpG ODN separately. Production of Th1 cytokines, nitric oxide (NO), reactive oxygen species (ROS) and H(2)O(2) was enhanced. A remarkable increase in the phagocytosis index was also observed, indicating overall immunological support to antileishmanial activity of miltefosine by CpG ODN. Similar responses were observed in hamsters.

CONCLUSIONS

Promising antileishmanial efficacy was observed in animals treated with liposomal CpG ODN and miltefosine, strongly supported by enhancement of Th1 cytokines as well as NO, ROS and H(2)O(2) levels. The correlation of experimental findings in both the models (mouse and hamster) strengthens the potential of CpG ODN as an immunomodulator in combination with miltefosine against VL.

Drug resistance in visceral leishmaniasis

Visceral leishmaniasis remains a public health problem worldwide. This illness was included by the World Health Organization in the list of neglected tropical diseases targeted for elimination by 2015. The widespread emergence of resistance to pentavalent antimonials in India where half cases occur globally and the unavailability of a vaccine in clinical use constitute major obstacles in achieving of this goal. The last decade new antileishmanials became available, including the oral agent miltefosine. However, in poor endemic countries their wide use was curtailed because of the high costs, and also due to concerns of toxicity and emergence of resistance. Various mechanisms of antileishmanial resistance were identified recently in field isolates. Their elucidation will boost the design of new drugs and the molecular surveillance of resistance. Combination regimens should be evaluated in large trials. Overall, the development of antileishmanials has been generally slow; new drugs are needed. In order to control visceral leishmaniasis worldwide, treatment advances should become affordable in the poorest countries, where they are needed most.

Immunomodulator effect of picroliv and its potential in treatment against resistant Plasmodium yoelii (MDR) infection in mice

PURPOSE

The present study was envisaged to evaluate potential of combination therapy comprising of immunomodulator picroliv and antimalarial chloroquine against drug resistant Plasmodium yoelii (P. yoelii) infection in BALB/c mice.

METHODS

The immunomodulatory potential of picroliv was established by immunizing animals with model antigen along with picroliv. Immune response was assessed using T-cell proliferation assay and also by determining the antibody isotype-profile induced in the immunized mice. In the next set of experiment, prophylactic potential of picroliv to strengthen antimalarial properties of chloroquine against P. yoelii (MDR) infection in BALB/c mice was assessed.

RESULTS

T-cell proliferation as well as antibody production study reveals that picroliv helps in evoking strong immuno-potentiating response against model antigen in the immunized mice. Co-administration of picroliv enhances efficacy of CHQ against experimental murine malaria.

CONCLUSION

The activation of host immune system can increase the efficacy of chloroquine for suppression of drug resistant malaria infection in BALB/c mice.

Influence of Brugia malayi life stages and BmAFII fraction on experimental Leishmania donovani infection in hamsters

The influence of live Brugia malayi parasites and a Sephadex G-200 fraction of the adult parasite extract (BmAFII) on the progression of Leishmania donovani infection was studied. Inbred hamsters were first infected with B. malayi infective 3rd stage larvae (L3), adult worms or microfilariae (mf), and then with L. donovani amastigotes (Ld), or vice versa or received both the infections simultaneously; a group of animals were first immunized with BmAFII and then infected with Ld. L. donovani parasite burden was determined between 17 and 19 days post amastigote challenge (p.a.c.) and, in case of immunized animals, between 32 and 35 days p.a.c also. Nitric oxide (NO) release from peritoneal macrophages and cellular proliferative responses of lymphnode cells were assessed in BmAFII-immunized animals given leishmania infection or no infection. Leishmanial parasite burden was significantly reduced in animals exposed to filarial L3 before amastigote inoculation and in animals given filarial adult worms after or together with amastigotes. Prior immunization of leishmania-infected animals with BmAFII also reduced the leishmanial parasite burden (17-19 days p.a.c.: >90%; 32-35 days p.a.c.: 60%). These animals showed upregulation of NO release and cellular proliferative responses to promastigote antigen or BmAFII stimulation in vitro. The findings show, for the first time, that B. malayi L3/adult worms or immunization with BmAFII inhibits progression of L. donovani infection in hamsters and this is associated with upregulation of NO and lymphocyte proliferative responses indicating that Th1 response might be responsible for this.