The protective effect of 1-methyltryptophan isomers in renal ischemia-reperfusion injury is not exclusively dependent on indolamine 2,3-dioxygenase inhibition.

BACKGROUND AND PURPOSE: Indolamine 2,3-dioxygenase (IDO), an enzyme that catalyses the metabolism of tryptophan, may play a detrimental role in ischemia-reperfusion injury (IRI). IDO can be inhibited by 1-methyl-tryptophan, which exists in a D (D-MT) or L (L-MT) isomer. These forms show different pharmacological effects besides IDO inhibition. Therefore, we sought to investigate whether these isomers can play a protective role in renal IRI, either IDO-dependent or independent. EXPERIMENTAL APPROACH: We studied the effect of both isomers in a rat renal IRI model with a focus on IDO-dependent and independent effects. KEY RESULTS: Both MT isomers reduced creatinine and BUN levels, with D-MT having a faster onset of action but shorter duration and L-MT a slower onset but longer duration (24 h and 48 h vs 48 h and 96 h reperfusion time). Interestingly, this effect was not exclusively dependent on IDO inhibition, but rather from decreased TLR4 signalling, mimicking changes in renal function. Additionally, L-MT increased the overall survival of rats. Moreover, both MT isomers interfered with TGF-ß signalling and epithelial-mesenchymal transition. In order to study the effect of isomers in all mechanisms involved in IRI, a series of in vitro experiments was performed. The isomers affected signalling pathways in NK cells and tubular epithelial cells, as well as in dendritic cells and T cells. CONCLUSION AND IMPLICATIONS: This study shows that both MT isomers have a renoprotective effect after ischemia-reperfusion injury, mostly independent of IDO inhibition, involving mutually different mechanisms. We bring novel findings in the pharmacological properties and mechanism of action of MT isomers, which could become a novel therapeutic target of renal IRI.

Effect of N-Feruloylserotonin and Methotrexate on Severity of Experimental Arthritis and on Messenger RNA Expression of Key Proinflammatory Markers in Liver.

Rheumatoid arthritis (RA) is a chronic inflammatory disease, leading to progressive destruction of joints and extra-articular tissues, including organs such as liver and spleen. The purpose of this study was to compare the effects of a potential immunomodulator, natural polyphenol N-feruloylserotonin (N-f-5HT), with methotrexate (MTX), the standard in RA therapy, in the chronic phase of adjuvant-induced arthritis (AA) in male Lewis rats. The experiment included healthy controls (CO), arthritic animals (AA), AA given N-f-5HT (AA-N-f-5HT), and AA given MTX (AA-MTX). N-f-5HT did not affect the body weight change and clinical parameters until the 14th experimental day. Its positive effect was rising during the 28-day experiment, indicating a delayed onset of N-f-5HT action. Administration of either N-f-5HT or MTX caused reduction of inflammation measured as the level of CRP in plasma and the activity of LOX in the liver. mRNA transcription of TNF-α and iNOS in the liver was significantly attenuated in both MTX and N-f-5HT treated groups of arthritic rats. Interestingly, in contrast to MTX, N-f-5HT significantly lowered the level of IL-1ß in plasma and IL-1ß mRNA expression in the liver and spleen of arthritic rats. This speaks for future investigations of N-f-5HT as an agent in the treatment of RA in combination therapy with MTX.

Extension and Justification of Quasi-Steady-State Approximation for Reversible Bimolecular Binding.

The quasi-steady-state approximation (QSSA) is commonly applied in chemical kinetics without rigorous justification. We provide details of such a justification in the ubiquitous case of reversible two-step bimolecular binding in which molecules as an intermediate step of the reaction form a transient complex. First, we justify QSSA in the regime that agrees with the results in the literature and is characterized by max{R0, L0} ≪ K(m). Here, R0 and L0 are the initial concentrations of reacting receptor and ligand, respectively, and K(m) is the Michaelis constant. We also validate QSSA under an alternative condition that can be viewed as partially irreversible binding, and it does not require a tight bound on R0 and L0 but rather requires k2 + k₋2 ≪ k₋1. Here, k₋1 is the rate constant of decomposition of the transient complex to the ligand and the receptor, and k2 and k₋2 are the forward and the reverse rate constants of transformation of the complex to the product, respectively. Furthermore, we provide arguments that QSSA can also be accurate in a regime when max{R0, L0} ≈ K(m) and k2 + k₋2 ≈ k₋1 if |R0 - L0| ≪ K(m). The derived conditions may be of practical use as they provide weaker requirements for the validity of QSSA compared to the existing results.