Macrophages modulate liver cell function via tryptophan metabolites

Tryptophan alleviates lipopolysaccharide-induced liver injury and inflammation by modulating necroptosis and pyroptosis signaling pathways in piglets

The liver plays crucial roles in material metabolism and immune response. Bacterial endotoxin can cause various liver diseases, thereby causing significant economic losses to pig industry. Tryptophan is an essential amino acid in piglets. However, whether tryptophan can alleviate liver injury and inflammation by regulating necroptosis and pyroptosis has not been clarified. This study aimed to investigate whether dietary tryptophan can alleviate lipopolysaccharide (LPS)-induced liver injury in weaned piglets. 18 weaned piglets were randomly distributed to three treatments, each with 6 replicates: (1) control; (2) LPS-challenged control; (3) LPS + 0.2% tryptophan. After feeding with control or 0.2% tryptophan-supplemented diets for 35 d, pigs were intraperitoneally injected with saline or LPS (100 mg/kg body weight). At 4 h post-injection, blood samples and liver were collected. Results indicated that tryptophan reduced alanine aminotransferase, aspartate aminotransferase, decreased the mRNA expression and protein expression of 70-kDa heat shock proteins. Moreover, tryptophan increased the mRNA expression and protein expression of claudin-1, occludin and zonula occludens and decreased hydrogen peroxide and malondialdehyde contents, and increased catalase, glutathione peroxidase and total superoxide dismutase activities and proinflammatory cytokine levels in the liver. Meanwhile, tryptophan inhibited pyroptosis-related and necroptosis-related protein expression in liver. Collectively, tryptophan could relieve liver damage, increased the antioxidant capacity and reduced inflammation by inhibiting pyroptosis and necroptosis signaling pathways.

Kynurenine concentration of serum was increased by exercise

Kynurenine pathway of tryptophan makes a lot of physiological active substances, such as quinolinate, NAD and so on, suggesting that kynurenine itself may play a very important role physiologically. Therefore, we examined the influence of exercise on serum kynurenine concentration. At first, we assayed kynurenine concentration of students (n = 13) who took part in a rugby camp for three days. The mean value of kynurenine concentration of before and after training were 1.362 +/- 0.306 microM and 1.725 +/- 0.511 microM respectively. These data means that severe exercise rise the serum kynurenine concentration. Then we tried to examine the relationship between the level of exercise and serum kynurenine concentration. Serum kynurenine concentration had significantly increased immediately after the exercise from 1.869 +/- 0.285 microM to 2.138 +/- 0.248 microM of 24 hours later by loading of 65% heart rate max exercise for each subject. These results suggested that at least the severe exercise affect on the tryptophan metabolism. We will discuss the change of serum kynurenine concentration by another sports such as soccer game and 20 km run.

Cinnabarinic acid was formed in damaged mitochondria and its effect on mitochondrial respiration

Tryptophan administration aggravates experimental mouse liver injury caused by carbon tetrachloride when 3-hydroxyanthranilic acid concentration elevates in serum. Tryptophan metabolism is changed by macrophages in injured liver. 3-Hydroxyanthranilic acid may be oxidized to cinnabarinic acid by injured mitochondria in the liver aggravating the state of injured liver. Mitochondria prepared from the liver 24 hr after CCl4 treatment have lost their ability of respiratory control. In consequence, 3-hydroxyanthranilic acid is oxidized to cinnabarinic acid by incubation with these mitochondria, whereas 3-hydroxykynurenine is not. Thus, formed cinnabarinic acid is able to inhibit completely the mitochondrial respiratory control at concentration of 10 microM.