Leflunomide alleviates obesity via activation of the TAK1-AMPK pathway and induction of lipophagy

Lipophagy is a subset of selective autophagy that specifically degrades lipid droplets and plays an important role in obesity. Leflunomide treatment in rheumatoid arthritis (RA) patients has been associated with weight loss and decreased blood glucose levels, which cannot be attributed to its known side effects. Our prior studies showed that A77 1726, the active metabolite of leflunomide, acts as an inhibitor of S6K1 to sensitize the insulin receptor and control hyperglycemia. Whether the anti-obesity effect of leflunomide is mediated by targeting S6K1 and its underlying mechanisms remain unclear. Here, we report that A77 1726 induced LC3 lipidation and increased the formation of autophagosomes and lipoautolysosomes in 3T3-L1 adipocytes by activating TGF-β-activated kinase 1 (TAK1), AMP-activated kinase (AMPK), and Unc-51 like autophagy-activated kinase 1 (ULK1). A77 1726 reduced the content of lipid droplets in 3T3-L1 adipocytes, which was blocked by bafilomycin or by beclin-1 knockdown. Similar observations were made in murine adipocytes differentiated from S6K1-/- embryonic fibroblasts (MEFs). Leflunomide treatment restricted bodyweight gains in ob/ob mice and reduced the visceral fat deposit and the size of adipocytes. Leflunomide treatment induced autophagy in adipose and liver tissues and reduced hepatic lipid contents. Consistently, S6K1 knockout increased the levels of LC3 lipidation in the liver, muscle, and fat of S6K-/- mice. Leflunomide treatment and S6K1 deficiency both induced TAK1, AMPK, and ULK1 phosphorylation in these tissues. These observations collectively suggest that leflunomide controls obesity in part by activating AMPK and inducing lipophagy. Our study provides insights into the mechanisms of leflunomide-mediated anti-obesity activity.

Restriction of intracellular Salmonella typhimurium growth by the small-molecule autophagy inducer A77 1726 through the activation of the AMPK-ULK1 axis

Autophagy plays an important role in restricting the growth of invading intracellular microbes. Salmonella (S) Typhimurium, an intracellular pathogen that causes gastroenteritis and food poisoning in humans, evades autophagic detection by multiple mechanisms. There has been growing interest in developing autophagy inducers as novel antimicrobial agents for treating intracellular bacterial infections. We recently reported that A77 1726, the active metabolite of the anti-inflammatory drug leflunomide, induces autophagy by activating AMP-activated protein kinase (AMPK) and Unc-51 like autophagy activating kinase 1 (ULK1). Our present study aims to determine if A77 1726 was able to restrict intracellular Salmonella growth by inducing autophagy. We first confirmed the ability of A77 1726 to induce autophagy by activating the AMPK-ULK1 axis in uninfected RAW264.7 (a murine macrophage cell line) and HeLa cells (a human cervical carcinoma cell line). A77 1726 enhanced autophagy in S. Typhimurium-infected cells, as evidenced by increased levels of LC3 lipidation and increased numbers of autophagosomes and autolysosomes. Confocal microscopy revealed that A77 1726 induced xenophagy in macrophages, as evidenced by an increased number of LC3-coated bacteria in the cytoplasm. A77 1726 significantly decreased the number of intracellular S. Typhimurium in macrophages. Taken together, our study has demonstrated the ability of A77 1726 to restrict intracellular S. Typhimurium growth in vitro by enhancing xenophagy.

Inhibition of canine distemper virus replication by blocking pyrimidine nucleotide synthesis with A77 1726, the active metabolite of the anti-inflammatory drug leflunomide

Canine distemper virus (CDV) is the aetiological agent that causes canine distemper (CD). Currently, no antiviral drugs have been approved for CD treatment. A77 1726 is the active metabolite of the anti-rheumatoid arthritis (RA) drug leflunomide. It inhibits the activity of Janus kinases (JAKs) and dihydroorotate dehydrogenase (DHO-DHase), a rate-limiting enzyme in de novo pyrimidine nucleotide synthesis. A77 1726 also inhibits the activity of p70 S6 kinase (S6K1), a serine/threonine kinase that phosphorylates and activates carbamoyl-phosphate synthetase (CAD), a second rate-limiting enzyme in the de novo pathway of pyrimidine nucleotide synthesis. Our present study focuses on the ability of A77 1726 to inhibit CDV replication and its underlying mechanisms. Here we report that A77 1726 decreased the levels of the N and M proteins of CDV and lowered the virus titres in the conditioned media of CDV-infected Vero cells. CDV replication was not inhibited by Ruxolitinib (Rux), a JAK-specific inhibitor, but by brequinar sodium (BQR), a DHO-DHase-specific inhibitor, and PF-4708671, an S6K1-specific inhibitor. Addition of exogenous uridine, which restores intracellular pyrimidine nucleotide levels, blocked the antiviral activity of A77 1726, BQR and PF-4708671. A77 1726 and PF-4708671 inhibited the activity of S6K1 in CDV-infected Vero cells, as evidenced by the decreased levels of CAD and S6 phosphorylation. S6K1 knockdown suppressed CDV replication and enhanced the antiviral activity of A77 1726. These observations collectively suggest that the antiviral activity of A77 1726 against CDV is mediated by targeting pyrimidine nucleotide synthesis via inhibiting DHO-DHase activity and S6K1-mediated CAD activation.

A77 1726, the active metabolite of the anti-rheumatoid arthritis drug leflunomide, inhibits influenza A virus replication in vitro and in vivo by inhibiting the activity of Janus kinases

The newly reassorted IAV subtypes from zoonotic reservoirs respond poorly to current vaccines and antiviral therapy. There is an unmet need in developing novel antiviral drugs for better control of IAV infection. The cellular factors that are crucial for virus replication have been sought as novel molecular targets for antiviral therapy. Recent studies have shown that Janus kinases (JAK), JAK1, and JAK2, play an important role in IAV replication. Leflunomide is an anti-inflammatory drug primarily used for treating rheumatoid arthritis (RA). Prior studies suggest that A77 1726, the active metabolite of leflunomide, inhibits the activity of JAK1 and JAK3. Our current study aims to determine if A77 1726 can function as a JAK inhibitor to control IAV infection. Here, we report that A77 1726 inhibited the replication of three IAV subtypes（H5N1, H1N1, H9N2）in three cell types (chicken embryonic fibroblasts, A549, and MDCK). A77 1726 inhibited JAK1, JAK2, and STAT3 tyrosine phosphorylation. Similar observations were made with Ruxolitinib (Rux), a JAK-specific inhibitor. JAK2 overexpression enhanced H5N1 virus replication and compromised the antiviral activity of A77 1726. Leflunomide inhibited virus replication in the lungs of IAV-infected mice, alleviated their body weight loss, and prolonged their survival. Our study demonstrates for the first time the ability of A77 1726 to inhibit JAK2 activity and suggests that inhibition of JAK activity contributes to its antiviral activity.

Inhibition of porcine epidemic diarrhea virus (PEDV) replication by A77 1726 through targeting JAK and Src tyrosine kinases

Porcine epidemic diarrhea (PED) virus (PEDV) is a coronavirus that primarily infects porcine intestinal epithelial cells and causes severe diarrhea and high fatality in piglets. A77 1726 is the active metabolite of leflunomide, a clinically approved anti-rheumatoid arthritis (RA) drug. A77 1726 inhibits the activity of protein tyrosine kinases (PTKs), p70 S6 kinase (S6K1), and dihydroorotate dehydrogenase (DHO-DHase). Whether A77 1726 can control coronavirus infections has not been investigated. Here we report that A77 1726 effectively restricted PEDV replication by inhibiting Janus kinases (JAKs) and Src kinase activities but not by inhibiting DHO-DHase and S6K1 activities. Overexpression of Src, JAK2 or its substrate STAT3 enhanced PEDV replication and attenuated the antiviral activity of A77 1726. Our study demonstrates for the first time the ability of A77 1726 to control coronavirus replication by inhibiting PTK activities. Leflunomide has potential therapeutic value for the control of PEDV and other coronavirus infections.

Phytophthora infestans Dihydroorotate Dehydrogenase Is a Potential Target for Chemical Control - A Comparison With the Enzyme From Solanum tuberosum

The oomycete Phytophthora infestans is the causal agent of tomato and potato late blight, a disease that causes tremendous economic losses in the production of solanaceous crops. The similarities between oomycetes and the apicomplexa led us to hypothesize that dihydroorotate dehydrogenase (DHODH), the enzyme catalyzing the fourth step in pyrimidine biosynthetic pathway, and a validated drug target in treatment of malaria, could be a potential target for controlling P. infestans growth. In eukaryotes, class 2 DHODHs are mitochondrially associated ubiquinone-linked enzymes that catalyze the fourth, and only redox step of de novo pyrimidine biosynthesis. We characterized the enzymes from both the pathogen and a host, Solanum tuberosum. Plant DHODHs are known to be class 2 enzymes. Sequence analysis suggested that the pathogen enzyme (PiDHODHs) also belongs to this class. We confirmed the mitochondrial localization of GFP-PiDHODH showing colocalization with mCherry-labeled ATPase in a transgenic pathogen. N-terminally truncated versions of the two DHODHs were overproduced in E. coli, purified, and kinetically characterized. StDHODH exhibited a apparent specific activity of 41 ± 1 μmol min^-1 mg^-1, a k_cat^app of 30 ± 1 s^-1, and a K_m^app of 20 ± 1 μM for L-dihydroorotate, and a K_m^app= 30 ± 3 μM for decylubiquinone (Qd). PiDHODH exhibited an apparent specific activity of 104 ± 1 μmol min^-1 mg^-1, a k_cat^app of 75 ± 1 s^-1, and a K_m^app of 57 ± 3 μM for L-dihydroorotate, and a K_m^app of 15 ± 1 μM for Qd. The two enzymes exhibited different activities with different quinones and napthoquinone derivatives, and different sensitivities to compounds known to cause inhibition of DHODHs from other organisms. The IC₅₀ for A77 1726, a nanomolar inhibitor of human DHODH, was 2.9 ± 0.6 mM for StDHODH, and 79 ± 1 μM for PiDHODH. In vivo, 0.5 mM A77 1726 decreased mycelial growth by approximately 50%, after 92 h. Collectively, our findings suggest that the PiDHODH could be a target for selective inhibitors and we provide a biochemical background for the development of compounds that could be helpful for the control of the pathogen, opening the way to protein crystallization.