Cell protection, immunomodulation and virus inhibition by an endogenous substance
TWINCORE research team describes previously unknown effects of citraconic acid
The endogenous molecule itaconic acid has antiviral and anti-inflammatory effects, as researchers from TWINCORE have recently shown. In cooperation with scientists from the Helmholtz Centre for Infection Research in Braunschweig and the Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), they have now investigated the closely related substance citraconic acid. The result: Citraconic acid protects cells through antioxidant and anti-inflammatory properties. It also inhibits the release of flu viruses from human cells. They published these results in the journal Nature Metabolism.
"Itaconic acid has two isomers, natural relatives that differ only slightly in chemical structure, mesaconic and citraconic acid," says PD Dr. Frank Pessler, head of the working group "Biomarkers for Infectious Diseases" at the Institute for Experimental Infection Research at TWINCORE - Centre for Experimental and Clinical Infection Research in Hannover, a joint facility of the Helmholtz Centre for Infection Research (HZI) in Braunschweig and the Hannover Medical School. All three substances occur naturally in higher organisms and Pessler's research group had first detected all three in lymph nodes and spleen, important organs of the immune system, in 2021. "We then characterised these isomers further. Here, the results with citraconic acid were the most promising for drug development."
The researchers found that citraconic acid has several positive effects for the immune system at once. "We discovered that citraconic acid activates an important signalling pathway in the immune system," says Pessler. "The so-called NRF2 pathway controls antioxidative and anti-inflammatory processes that can protect cells from harmful influences." The effect of citraconic acid here is many times stronger than that of itaconic and mesaconic acid.
When the researchers infected human cells with flu viruses and simultaneously treated them with citraconic acid, they observed a strong inhibition of messenger substances that trigger inflammation. "It inhibits the signalling cascades of type 1 interferons, thereby reducing proinflammatory cytokines and chemokines," says Pessler. "These are signalling molecules that initiate and amplify processes in the immune system." In the same experiments, the researchers also tested the effect of the three isomers on the replication of flu viruses. They found that citraconic acid in particular nearly completely suppressed the release of virus particles from infected cells. Citraconic acid was also stronger than itaconic and mesaconic acid in this area. Through this simultaneous inhibition of viral replication, messenger substances and cell-damaging oxidising molecules, Pessler hopes that drugs based on citraconic acid will help patients with severe viral infections such as influenza, but also COVID-19. Such inhibitors could find clinically important applications.
Pessler and his team also found that itaconic acid and citraconic acid interact directly. Here, the mitochondrial enzyme ACOD1 plays a central role. ACOD1 mediates the synthesis of itaconic acid in inflamed tissues. "Citraconic acid prevents the production of itaconic acid by binding directly to the active site of the enzyme. Such inhibitors were previously unknown," says Dr Fangfang Chen. The biotechnologist did most of the experimental work as part of her doctoral thesis "Too much itaconic acid can weaken the immune system. Therefore, the administration of citraconic acid could lead to an increase in the performance of the immune system. This could help with advanced sepsis, or blood poisoning, or in people whose immune systems respond poorly to vaccinations."
"Other research groups have shown that itaconic acid can promote the growth of certain tumours," says Pessler. Again, citraconic acid could prevent the formation of itaconic acid. "ACOD1 inhibitors based on citraconic acid could therefore form a new class of anti-cancer drugs."
"We have already applied for a patent for medical applications of citraconic acid," says Pessler. "However, we still have a lot of work ahead of us before we know whether and how drugs based on citraconic acid can best be used."
Citraconate inhibits ACOD1 (IRG1) catalysis, reduces interferon responses and oxidative stress, and modulates inflammation and cell metabolism. F. Chen, W. A. M. Elgaher, M. Winterhoff, K. Büssow, F. H. Waqas, E. Graner, Y. Pires-Afonso, L. Casares Perez, L. de la Vega, N. Sahini, L. Czichon, W. Zobl, T. Zillinger, M. Shehata, S. Pleschka, H. Bähre, C. Falk, A. Michelucci, S. Schuchardt, W. Blankenfeldt, A. K. H. Hirsch & F. Pessler. Nature Metabolism (2022)