Research makes ground on treating antibiotic-resistant infection

A collaborative study involving researchers at Duke Kunshan University’s Global Health Research Center and Wang-Cai Biochemistry Laboratory has made important ground in understanding Clostridioides difficile infection, an antibiotic resistant pathogen that can cause severe diarrhoea, belly pain, fever and potentially lead to death.

The research, published in the American Society for Microbiology journal mBio, sheds light on key genes that are involved in tissue damage caused by the infection, which is a growing problem across the globe, and could help with the development of medicines to treat it.

Clostridioides difficile infection (C. diff) is a “significant threat to public health,” said Linfeng Huang, associate professor of biology at DKU, who led the research. “As a global health care problem, there is an urgent need to understand the infection mechanism and develop efficient therapeutics.”

Linfeng Huang, associate professor of biology (left) and Yingxue Li, biology lab instructor in the Division of Natural and Applied Sciences (right) (Photo by Tom Zhang)

C. diff bacteria enter the human body through the mouth and remain dormant until they reach the large intestine, where they release tissue-damaging toxins. Those toxins kill cells, which leads to diarrhoea, belly pain, fever and in extreme cases can cause death. The bacteria are resistant to antibiotics and extremely resilient in the environment, passing between people in a tough structure called a spore.

According to statistics from the Center for Disease Control and Prevention in the United States, C. diff is the leading cause of antibiotic-associated intestinal disease there, with around 230,000 cases of it in 2017, costing about $100 million in treatment, of which 12,800 resulted in death. Its rise has been caused by the increasing use of antibiotics which has boosted C. diff and other resistant bacterial species, as well as weakening natural defences against infection in older people.

“The aim of our research was to understand key genes that are involved in tissue damage caused by the infection,” said Huang. “We also want to develop medicines that can precisely target those genes to rescue the damage.”

They did this by modelling the infection process using human cells adapted to grow in the laboratory that could mimic the gut system and the toxins produced by C. diff, which are the major cause of cell damage.

Yingxue Li, biology lab instructor at DKU’s Division of Natural and Applied Sciences and researchers at a host of other academic institutions including Cornell University in the United States, worked on the project with Huang. Together they spearheaded the setup of a “novel genetic screen method, using bacterial cells to make thousands of precise gene targeting molecules, called small interfering RNAs (siRNAs),” said Li.

“We then tested those siRNA molecules using a high throughput method and looked for their functions in toxin-induced cell death using biochemical assays and microscopy. Finally, we found a few very promising candidate genes and confirmed their involvement in toxin-induced cell damage by various lab techniques,” Li added.

Yingxue Li, biology lab instructor in DKU’s Division of Natural and Applied Sciences, working the in the laboratory (Photo by Tom Zhang)

They discovered several novel genes that are important in initiating C. diff induced cell death, including plakoglobin, a gene previously known for its role in cell-to-cell attachment, and demonstrated that by using small molecules and siRNAs to block specific gene functions, they could potentially treat the infection.

“It is plausible that blocking gene functions may alleviate cell death caused by the bacterial toxins,” said Huang.

“Glycyrrhizin, a Chinese medicine compound, which is capable of blocking one of the candidate genes, HMGB1, was tested in cell culture and animal models and demonstrated potent protection effects against C. diff toxin-induced cell and tissue damage,” he added.

“Glycyrrhizin is an approved drug for treating liver diseases in China and our research shows that it might be repurposed to treat C. diff infection,” he said.

While the research is promising, there is a “long road” ahead before any treatments are approved, added Huang, as drugs will have to be tested vigorously for safety and efficacy in animal models and then in clinical trials first.

While those tests are done, Huang’s research team at DKU’s Global Health Research Center and Wang-Cai Biochemistry Laboratory is also focused on new research using their novel siRNA-based genetic screen approach to study other important diseases including metabolic diseases and cancers in hope of developing more candidates for gene-targeted precision medicine.

Author: John Butcher

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