A breakthrough in understanding how a single-celled parasite produces ergosterol (its version of cholesterol) could lead to more effective drugs for human leishmaniasis, a parasitic disease that affects about 1 million people and kills about 30,000 people worldwide. world every year.
The findings, reported in Nature CommunicationsThey also solve a decades-old scientific conundrum that has prevented drug makers from successfully using azole antifungal drugs to treat visceral leishmaniasis, or VL.
About 30 years ago, scientists discovered that the two species of single-celled parasites that cause VL, Leishmania donovani and Leishmania infantum, produced the same lipid sterol, called ergosterol, as fungi that had been shown to be susceptible to azole antifungals. These azole antifungals target an enzyme crucial for sterol biosynthesis, called CYP51.
While not fungi, both Leishmania species have biochemical similarities to fungi in their plasma membrane, where ergosterol helps maintain cellular integrity and supports a number of biological functions, much like cholesterol does in humans.
“People looked at the sterol profile of the parasites and found that they mainly have ergosterol,” said the study’s corresponding author, Michael Zhuo Wang, a professor of pharmaceutical chemistry at the University of Kansas School of Pharmacy. “This sterol is the main sterol component of their plasma membranes. A similar case can be observed in fungi. Fungal organisms also have a large amount of ergosterol in their membranes. There was an original instinct to use antifungal azoles to try block it. way.”
However, scientists were unable to use effective antifungals against viral leukoencephalopathy.
“In the research laboratory and in some of the clinical trials, some azoles worked a little and some didn’t work at all,” Wang said. “I finally focused on this sterol pathway, a scientific question: whether this parasite also uses ergosterol, you would think that all antifungal azoles would work against this parasite.”
Along these lines, Wang began his independent research career as part of a group at the University of North Carolina-Chapel Hill called the Parasitic Drug Development Consortium.
“We were interested in developing new drugs against neglected tropical diseases,” he said. “One of these diseases is leishmaniasis. The other is African sleeping sickness. Leishmaniasis, transmitted by a sand fly vector in warmer climates, can cause a truly devastating infection of internal organs such as the liver and spleen, as well as the bone marrow.”
In their new academic paper, Wang and his collaborators have largely resolved that long-standing scientific question. They show that the parasites that cause leishmaniasis are vulnerable through a different pathway for the biosynthesis of their ergosterol, known as the CYP5122A1 enzyme. Therefore, azole antifungals targeting the CYP5122A1 enzyme, as well as the traditional CYP51 pathway, should be much more effective in the treatment of leishmaniasis.
“So those azoles don’t work very well against leishmania unless you have an azole that also inhibits the new pathway, CYP5122A1,” Wang said. “Then all of a sudden, they’re much more active against leishmania. That’s the main discovery of this study: we discovered the true target of the drug in leishmania. It is really necessary to attack this new enzyme, 22A1, to be able to stop the parasites.”
Wang’s laboratory at KU demonstrated that the CYP5122A1 gene encodes an essential sterol C4-methyl oxidase in the leishmania parasite, through extensive biochemical characterization.
“This involved defining its biochemical function: what this enzyme does in terms of sterol biosynthesis,” he said. “We determined its biochemical function and clarified its role in the ergosterol biosynthesis pathway.”
The researchers are already publishing follow-up studies and discoveries based on their new breakthrough in understanding the sterol synthesis pathway in parasites. They said drug makers and researchers should develop therapies targeting CYP5122A1. These should be more effective in helping people survive leishmaniasis, Wang said.
“This tells us how we should repurpose these existing antifungal azoles by detecting this new target,” said the KU researcher. “Those that actually inhibit this new target should have a better chance of acting against leishmania infection.”
Wang’s co-authors at the KU School of Pharmacy were doctoral students Yiru Jin and Mei Feng, who were the lead authors, and doctoral student Lingli Qin as a co-author in the Department of Pharmaceutical Chemistry; director Chamani Perera and PhD student Indeewara Munasinghe from KU’s Central Laboratory for Synthetic Chemical Biology; Philip Gao, director of the KU Protein Production Group; and Judy Qiju Wu, associate professor of pharmacy practice.
The KU researchers were joined by Kai Zhang, Somrita Basu, Yu Ning, Robert Madden, Hannah Burks and Salma Waheed Sheikh from Texas Tech University; and Karl Werbovetz, Arline Joachim, Junan Li and April Joice of Ohio State University.
This study was supported in part by the US National Institute of Allergy and Infectious Diseases, the US Department of Defense, and the KU Centers of Biomedical Research Excellence (COBRE).