Jinan Zhuocheng Bio-Tech Co., Ltd.

Porcine reproductive and respiratory syndrome (PRRS), commonly known as “Blue Ear Disease,” is one of the major infectious diseases affecting the global swine industry. Caused by porcine reproductive and respiratory syndrome virus (PRRSV), the disease is characterized by a high mutation rate and complex circulating viral strains and lineages. Limited cross-protection provided by existing vaccines, combined with the lack of specific antiviral drugs, continues to pose significant challenges to PRRS prevention and control.

Recently, a research team led by Professor Yingfeng Sun of Tianjin Agricultural University published an important study online in the Journal of Virology entitled “Tylvalosin tartrate inhibits PRRSV replication by suppressing cellular pyroptosis through the TLR4/NF-κB signaling pathway.”

The study provides new evidence that tylvalosin tartrate can inhibit PRRSV replication by suppressing activation of the TLR4/NF-κB signaling pathway and blocking GSDMD-mediated cellular pyroptosis. The inhibitory effects were observed against multiple PRRSV lineages, including L1-like, L8.1-like and L8.3-like strains.

The findings provide a new scientific basis for the potential repurposing of tylvalosin tartrate and offer a new direction for PRRS clinical prevention and antiviral intervention.

1. A New Antiviral Mechanism Identified

The research team found that the antiviral activity of tylvalosin tartrate against PRRSV may extend beyond its conventional antimicrobial properties and involve the regulation of host-cell signaling pathways.

The study demonstrated that tylvalosin tartrate can target the TLR4/NF-κB/pyroptosis signaling axis, suppress PRRSV-induced cellular pyroptosis, and consequently restrict viral replication.

This discovery provides a new perspective on the biological activity of tylvalosin tartrate and expands the understanding of its potential antiviral mechanisms.

2. Inhibitory Activity Against Multiple PRRSV Lineages

In vitro experiments using porcine alveolar macrophages (PAMs) identified 3.125 μM as the maximum safe concentration of tylvalosin tartrate under the experimental conditions.

At this concentration, tylvalosin tartrate significantly inhibited the replication of the L1-like PRRSV TJ-C6 strain. It also demonstrated significant inhibitory effects against other major PRRSV strains, including:

• L5-like (VR2332-like)
• L8.1-like (CH-1a-like)
• L8.3-like (JXA1-like)

Western blot and immunofluorescence assay (IFA) results further showed a significant reduction in PRRSV N-protein expression following drug treatment.

These findings suggest that tylvalosin tartrate may have broad-spectrum inhibitory activity against multiple circulating PRRSV lineages.

3. Clinical Study Shows Reduced Lung Injury and Inflammation

The research team subsequently conducted a clinical treatment study in pigs naturally infected with an L1-like PRRSV strain.

In the study, tylvalosin tartrate was administered orally through feed at a dose of 1,000 mg/kg for 14 consecutive days.

Serum viral RNA levels in the treatment group were significantly lower than those in the untreated group on both day 12 and day 21.

Histopathological analysis of lung tissue showed that treatment with tylvalosin tartrate improved the integrity of alveolar structures, reduced pulmonary congestion and significantly lowered lung lesion scores.

At the same time, levels of inflammatory cytokines, including IL-1β, IL-6 and IL-18, were substantially reduced.

These findings indicate that tylvalosin tartrate may not only affect viral replication but may also help alleviate PRRSV-associated inflammation and tissue damage.

4. Cellular Pyroptosis Identified as a Key Mechanism

To further investigate the underlying mechanism, the research team conducted transcriptomic analysis.

The results showed that tylvalosin tartrate treatment significantly regulated several pathways associated with cellular pyroptosis, including key molecules such as NLRP3, CASP1, GSDMD, IL-1β and IL-18.

Further experiments demonstrated that PRRSV infection induced significant cellular pyroptosis in PAM cells.

Researchers subsequently used the CASP1 inhibitor VX765 and the GSDMD inhibitor LDC7559 to interfere with the pyroptosis pathway. When key proteins involved in pyroptosis were inhibited, PRRSV N-protein levels decreased substantially and viral replication was suppressed.

The results were highly consistent with those observed following tylvalosin tartrate treatment, providing further evidence that tylvalosin tartrate may restrict PRRSV replication by suppressing CASP1/GSDMD-mediated cellular pyroptosis.

5. TLR4/NF-κB Signaling Identified as an Upstream Target

Further investigation identified the TLR4/NF-κB signaling pathway as a potentially important upstream mechanism.

The researchers found that PRRSV infection induced increased TLR4 expression and promoted phosphorylation and nuclear translocation of NF-κB p65.

Tylvalosin tartrate significantly suppressed these changes.

The team then used the TLR4-specific inhibitor resatorvid and TLR4 siRNA for further validation. The results showed that inhibition or knockdown of TLR4 produced effects similar to those of tylvalosin tartrate, including suppression of cellular pyroptosis and PRRSV replication.

The study therefore suggests that the TLR4/NF-κB signaling pathway may serve as an important upstream target through which tylvalosin tartrate exerts its anti-pyroptotic and anti-PRRSV effects.

Overall, the research proposes a potential regulatory pathway linking TLR4/NF-κB signaling, CASP1/GSDMD-mediated pyroptosis and PRRSV replication, providing a new theoretical framework for understanding the antiviral activity of tylvalosin tartrate.

6. Drug Repurposing Offers a New Approach to PRRS Control

Tylvalosin tartrate is already an established veterinary pharmaceutical used in clinical practice. The latest findings expand the understanding of its potential biological activities and provide a new direction for the functional repurposing of existing veterinary medicines.

Compared with developing an entirely new antiviral compound from scratch, repurposing established veterinary drugs may offer advantages in terms of existing production technologies, manufacturing experience and clinical application history.

However, it should be emphasized that the current study primarily demonstrates the potential antiviral mechanism and application value of tylvalosin tartrate against PRRSV. Further large-scale clinical trials, pharmacodynamic studies and safety evaluations will be required before these findings can be translated into standardized clinical treatment protocols for PRRS.

7. Research Team and Funding

The research team led by Professor Yingfeng Sun at Tianjin Agricultural University has long focused on the pathogenesis, epidemiology, molecular mechanisms, vaccine development and evaluation of major infectious diseases in pigs.

Professor Yingfeng Sun and Associate Professor Xiaoxue Yu are the corresponding authors of the study, while Shiqin Zhang and Xinlei Li are co-first authors.

The research was supported by the Tianjin Science and Technology Plan, the Tianjin Human Resources and Social Security Bureau Youth Science and Technology Talent Program, and Zhejiang Ecom Bio-Tech Co., Ltd.

Conclusion

The high mutation rate and complex lineage distribution of PRRSV have long presented major challenges for the prevention and control of PRRS. By investigating the role of cellular pyroptosis and the TLR4/NF-κB signaling pathway, this study provides new insights into the antiviral activity of tylvalosin tartrate and offers a potential new direction for integrated PRRS management.

For the veterinary pharmaceutical and animal health industries, the study also highlights an important trend: re-examining the mechanisms of established veterinary drugs and exploring host-targeted drug repurposing may become an increasingly valuable strategy in the development of therapeutics for viral diseases in livestock.