Stigmasterol as a potential biomarker for amphotericin B resistance in Leishmania donovani

Isolation and antimicrobial activity of secondary metabolites of pothos tener wall

The Pothos genus is extensively utilised in traditional medicine in China and India. An underexplored species of Pothos tener Wall was identified in Sulawesi, Indonesia. Antimicrobial activity was assessed using microdilutions and streak plates against Staphylococcus aureus, Eschericia coli, Aeromonas hydrophila, Aspergillus niger, and Candida albicans. Significant effectiveness was observed in the methanol extract, as indicated by the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values for three different extracts (methanol, ethyl acetate, and n-hexane) of P. tener. The isolates obtained were structurally analysed using Ultraviolet (UV)-spectroscopy, Fourier-transform Infra Red-Spectroscopy (FT-IR), Mass Spectroscopy (MS), Nuclear Magnetic Resonance (NMR), and antimicrobial testing after undergoing fractionation and subfractionation. The isolate obtained was stigmasterol with moderate antimicrobial activity against A. niger and A. hydrophila, with MIC equivalent to MBC of 500 µg/ml. The first report of stigmasterol from P. tener has potent antimicrobial properties, bolstering empirical data in this field.

Sterol 14-alpha demethylase (CYP51) activity in Leishmania donovani is likely dependent upon cytochrome P450 reductase 1

Liposomal amphotericin B is an important frontline drug for the treatment of visceral leishmaniasis, a neglected disease of poverty. The mechanism of action of amphotericin B (AmB) is thought to involve interaction with ergosterol and other ergostane sterols, resulting in disruption of the integrity and key functions of the plasma membrane. Emergence of clinically refractory isolates of Leishmania donovani and L. infantum is an ongoing issue and knowledge of potential resistance mechanisms can help to alleviate this problem. Here we report the characterisation of four independently selected L. donovani clones that are resistant to AmB. Whole genome sequencing revealed that in three of the moderately resistant clones, resistance was due solely to the deletion of a gene encoding C24-sterol methyltransferase (SMT1). The fourth, hyper-resistant resistant clone (>60-fold) was found to have a 24 bp deletion in both alleles of a gene encoding a putative cytochrome P450 reductase (P450R1). Metabolic profiling indicated these parasites were virtually devoid of ergosterol (0.2% versus 18% of total sterols in wild-type) and had a marked accumulation of 14-methylfecosterol (75% versus 0.1% of total sterols in wild-type) and other 14-alpha methylcholestanes. These are substrates for sterol 14-alpha demethylase (CYP51) suggesting that this enzyme may be a bona fide P450R specifically involved in electron transfer from NADPH to CYP51 during catalysis. Deletion of P450R1 in wild-type cells phenocopied the metabolic changes observed in our AmB hyper-resistant clone as well as in CYP51 nulls. Likewise, addition of a wild type P450R1 gene restored sterol profiles to wild type. Our studies indicate that P450R1 is essential for L. donovani amastigote viability, thus loss of this gene is unlikely to be a driver of clinical resistance. Nevertheless, investigating the mechanisms underpinning AmB resistance in these cells provided insights that refine our understanding of the L. donovani sterol biosynthetic pathway.

Amphotericin B resistance in Leishmania amazonensis: In vitro and in vivo characterization of a Brazilian clinical isolate

In Brazil, Leishmania amazonensis is the etiological agent of cutaneous and diffuse cutaneous leishmaniasis. The state of Maranhão in the Northeast of Brazil is prevalent for these clinical forms of the disease and also has high rates of HIV infection. Here, we characterized the drug susceptibility of a L. amazonensis clinical isolate from a 46-year-old man with diffuse cutaneous leishmaniasis coinfected with HIV from this endemic area. This patient underwent several therapeutic regimens with meglumine antimoniate, liposomal amphotericin B, and pentamidine, without success. In vitro susceptibility assays against promastigotes and intracellular amastigotes demonstrated that this isolate had low susceptibility to amphotericin B, when compared with the reference strain of this species that is considered susceptible to antileishmanial drugs. Additionally, we investigated whether the low in vitro susceptibility would affect the in vivo response to amphotericin B treatment. The drug was effective in reducing the lesion size and parasite burden in mice infected with the reference strain, whereas those infected with the clinical isolate and a resistant line (generated experimentally by stepwise selection) were refractory to amphotericin B treatment. To evaluate whether the isolate was intrinsically resistant to amphotericin B in animals, infected mice were treated with other drugs that had not been used in the treatment of the patient (miltefosine, paromomycin, and a combination of both). Our findings demonstrated that all drug schemes were able to reduce lesion size and parasite burden in animals infected with the clinical isolate, confirming the amphotericin B-resistance phenotype. These findings indicate that the treatment failure observed in the patient may be associated with amphotericin B resistance, and demonstrate the potential emergence of amphotericin B-resistant L. amazonensis isolates in an area of Brazil endemic for cutaneous leishmaniasis.

Epithelial homelessness: an atypical form of anoikis triggered by Leishmania interaction with epithelial cells

Aim: Leishmaniasis is characterized by a spectrum of diseases with two main clinical forms, cutaneous and visceral, caused by Leishmania tropica and Leishmania donovani, respectively. Studying Leishmania's interaction with the epithelial barrier at the initial site of a bite is crucial to understanding the establishment of the disease. Materials & methods: To discern parasite-host epithelial interaction, we developed in vitro cellular models involving co-cultures of Leishmania and MDCK epithelial cells. Results: Both L. donovani-MDCK and L. tropica-MDCK co-culture models demonstrated a phenomenon known as atypical anoikis apoptosis, typically identified by distinctive 'flipping in' of cell membranes and disordered cytoskeletal frameworks. Conclusion: This study bridges the gap in the fundamental understanding of the intricate latticework involving vector-Leishmania-host and may inform drug development strategies.

A Comprehensive Update on Phytochemistry, Analytical Aspects, Medicinal Attributes, Specifications and Stability of Stigmasterol

Phytosterols are bioactive substances naturally found in plant cell membranes, and their chemical structure is comparable to cholesterol found in mammalian cells. They are widely distributed in plant foods like olive oil, nuts, seeds, and legumes. Amongst the variety of phytosterols, stigmasterol is the vital compound found abundantly in plants. Numerous hormones, including estrogen, progesterone, corticoids and androgen, are synthesized by stigmasterol. Multiple in-vitro and in-vivo investigations have shown that stigmasterol has various biological effects, including antioxidant, anticancer, antidiabetic, respiratory diseases, and lipid-lowering effects. Experimental research on stigmasterol provides indisputable proof that this phytosterol has the potential to be employed in supplements used to treat the illnesses mentioned above. This substance has a high potential, making it a noteworthy medication in the future. Although several researchers have investigated this phytosterol to assess its prospective qualities, it has not yet attained therapeutic levels, necessitating additional clinical studies. This review offers a comprehensive update on stigmasterol, including chemical framework, biosynthesis, synthetic derivatives, extraction and isolation, analytical aspects, pharmacological profile, patent status, clinical trials, stability and specifications as per regulatory bodies.

Advances in Stigmasterol on its anti-tumor effect and mechanism of action

Stigmasterol is a phytosterol derived from multiple herbaceous plants such as herbs, soybean and tobacco, and it has received much attention for its various pharmacological effects including anti-inflammation, anti-diabetes, anti-oxidization, and lowering blood cholesterol. Multiple studies have revealed that stigmasterol holds promise as a potentially beneficial therapeutic agent for malignant tumors because of its significant anti-tumor bioactivity. It is reported that stigmasterol has anti-tumor effect in a variety of malignancies (e.g., breast, lung, liver and ovarian cancers) by promoting apoptosis, inhibiting proliferation, metastasis and invasion, and inducing autophagy in tumor cells. Mechanistic study shows that stigmasterol triggers apoptosis in tumor cells by regulating the PI3K/Akt signaling pathway and the generation of mitochondrial reactive oxygen species, while its anti-proliferative activity is mainly dependent on its modulatory effect on cyclin proteins and cyclin-dependent kinase (CDK). There have been multiple mechanisms underlying the anti-tumor effect of stigmasterol, which make stigmasterol promising as a new anti-tumor agent and provide insights into research on its anti-tumor role. Presently, stigmasterol has been poorly understood, and there is a paucity of systemic review on the mechanism underlying its anti-tumor effect. The current study attempts to conduct a literature review on stigmasterol for its anti-tumor effect to provide reference for researchers and clinical workers.

Amphotericin B resistance in Leishmania mexicana: Alterations to sterol metabolism and oxidative stress response

Amphotericin B is increasingly used in treatment of leishmaniasis. Here, fourteen independent lines of Leishmania mexicana and one L. infantum line were selected for resistance to either amphotericin B or the related polyene antimicrobial, nystatin. Sterol profiling revealed that, in each resistant line, the predominant wild-type sterol, ergosta-5,7,24-trienol, was replaced by other sterol intermediates. Broadly, two different profiles emerged among the resistant lines. Whole genome sequencing then showed that these distinct profiles were due either to mutations in the sterol methyl transferase (C24SMT) gene locus or the sterol C5 desaturase (C5DS) gene. In three lines an additional deletion of the miltefosine transporter gene was found. Differences in sensitivity to amphotericin B were apparent, depending on whether cells were grown in HOMEM, supplemented with foetal bovine serum, or a serum free defined medium (DM). Metabolomic analysis after exposure to AmB showed that a large increase in glucose flux via the pentose phosphate pathway preceded cell death in cells sustained in HOMEM but not DM, indicating the oxidative stress was more significantly induced under HOMEM conditions. Several of the lines were tested for their ability to infect macrophages and replicate as amastigote forms, alongside their ability to establish infections in mice. While several AmB resistant lines showed reduced virulence, at least two lines displayed heightened virulence in mice whilst retaining their resistance phenotype, emphasising the risks of resistance emerging to this critical drug.

Biomembrane lipids: When physics and chemistry join to shape biological activity

Biomembranes constitute the first lines of defense of cells. While small molecules can often permeate cell walls in bacteria and plants, they are generally unable to penetrate the barrier constituted by the double layer of phospholipids, unless specific receptors or channels are present. Antimicrobial or cell-penetrating peptides are in fact highly specialized molecules able to bypass this barrier and even discriminate among different cell types. This capacity is made possible by the intrinsic properties of its phospholipids, their distribution between the internal and external leaflet, and their ability to mutually interact, modulating the membrane fluidity and the exposition of key headgroups. Although common phospholipids can be found in the membranes of most organisms, some are characteristic of specific cell types. Here, we review the properties of the most common lipids and describe how they interact with each other in biomembrane. We then discuss how their assembly in bilayers determines some key physical-chemical properties such as permeability, potential and phase status. Finally, we describe how the exposition of specific phospholipids determines the recognition of cell types by membrane-targeting molecules.

Tackling Drug Resistance and Other Causes of Treatment Failure in Leishmaniasis

Leishmaniasis is a tropical infectious disease caused by the protozoan Leishmania parasite. The disease is transmitted by female sand flies and, depending on the infecting parasite species, causes either cutaneous (stigmatizing skin lesions), mucocutaneous (destruction of mucous membranes of nose, mouth and throat) or visceral disease (a potentially fatal infection of liver, spleen and bone marrow). Although more than 1 million new cases occur annually, chemotherapeutic options are limited and their efficacy is jeopardized by increasing treatment failure rates and growing drug resistance. To delay the emergence of resistance to existing and new drugs, elucidating the currently unknown causes of variable drug efficacy (related to parasite susceptibility, host immunity and drug pharmacokinetics) and improved use of genotypic and phenotypic tools to define, measure and monitor resistance in the field are critical. This review highlights recent progress in our understanding of drug action and resistance in Leishmania, ongoing challenges (including setbacks related to the COVID-19 pandemic) and provides an overview of possible strategies to tackle this public health challenge.

In vitro leishmanicidal activity of two cholesterol derivatives

We evaluated the leishmanicidal activity of commercially available 5α-cholest-7-en-3β-ol [5α-chol], (+)-4-cholesten-3-one [(+)-4-chol] and the equimolar mixture of the two of them in promastigotes and amastigotes of two different strains of Leishmania mexicana (LCL) and (DCL). The leishmanicidal effectiveness of these sterols was determined by promastigote growth-kinetic experiments and promastigote viability using the propidium iodide staining procedure. The proliferation test was performed using the CFSE (5-Carboxyfluorescein N-succinimidyl ester) staining of parasites at different time points. To determine the leishmanicidal effectiveness of these sterols in amastigotes, we evaluated parasite killing inside of macrophages at different time points. The trypan blue exclusion test was used to determine cytotoxicity of sterols in uninfected macrophages. We included in all experiments a control group of parasites treated with 2% DMSO (Dimethyl Sulfoxide) and another one treated with the reference drug sodium stibogluconate (Sb). Our results showed that the equimolar mixture at 2000 times lower concentration presented similar leishmanicidal activity as Sb. This mixture was similarly effective at 100 times lower concentration than individual sterols tested separately indicating the existence of a synergistic effect against LCL and DCL parasites. The therapeutic index of the equimolar mixture was 10,000-16,000 times higher than the one recorded by Sb and was not cytotoxic to macrophages. Therefore, the equimolar mixture of 5α-Chol and (+)-4-chol may represent a potential alternative for the treatment of cutaneous leishmaniasis.

Nanotechnological approaches for pentamidine delivery

Pentamidine (PTM), which is a diamine that is widely known for its antimicrobial activity, is a very interesting drug whose mechanism of action is not fully understood. In recent years, PTM has been proposed as a novel potential drug candidate for the treatment of mental illnesses, myotonic dystrophy, diabetes, and tumors. Nevertheless, the systemic administration of PTM causes severe side effects, especially nephrotoxicity. In order to efficiently deliver PTM and reduce its side effects, several nanosystems that take advantage of the chemical characteristics of PTM, such as the presence of two positively charged amidine groups at physiological pH, have been proposed as useful delivery tools. Polymeric, lipidic, inorganic, and other types of nanocarriers have been reported in the literature for PTM delivery, and they are all in different development phases. The available approaches for the design of PTM nanoparticulate delivery systems are reported in this review, with a particular emphasis on formulation strategies and in vitro/in vivo applications. Furthermore, a critical view of the future developments of nanomedicine for PTM applications, based on recent repurposing studies, is provided. Created with BioRender.com.

Drug combinations as effective anti-leishmanials against drug resistant Leishmania mexicana

Leishmania is a parasite that causes the disease leishmaniasis, and 700 000 to 1 million new cases occur each year. There are few drugs that treat the disease and drug resistance in the parasite limits the clinical utility of existing drugs. One way to combat drug resistance is to use combination therapy rather than monotherapy. In this study we have compared the effect of single and combination treatments with four different compounds, i.e. alkylphosphocholine analogues APC12 and APC14, miltefosine (MIL), ketoconazole (KTZ), and amphotericin B (AmpB), on the survival of Leishmania mexicana wild-type promastigotes and a cell line derived from the WT with induced resistance to APC12 (C12Rx). The combination treatment with APC14 and APC16 had a synergistic effect in killing the WT while the combination treatment with KTZ and APC12 or APC14 or APC12 and APC14 had a synergistic effect against C12Rx. More than 90% killing efficiency was obtained using APC12 alone at >1 mg ml^-1 against the C12Rx strain; however, combinations with APC14 produced a similar killing efficiency using APC12 at 0.063-0.25 mg ml^-1 and APC14 at 0.003-0.5 mg ml^-1. These results show that combination therapy can negate induced drug resistance in L. mexicana and that the use of this type of screening system could accelerate the development of drug combinations for clinical use.