Functional roles of phenylalanine(7) of thymic humoral factor-gamma 2 in the impaired blastogenic response of uremic T-lymphocytes

Degradation of thymic humoral factor γ2 in human, rat and mouse blood: An experimental and theoretical study

The degradation of the immunomodulatory octapeptide, thymic humoral factor γ2 (THF-γ2, thymoctonan) has been studied in whole blood samples from human, rat and mouse. The peptide, Leu-Glu-Asp-Gly-Pro-Lys-Phe-Leu, was shown to be rapidly degraded by peptidases. The half-life of the intact peptide was less than 6 min at 37 °C in blood from the three species tested. The main fragments formed from THF-γ2 were found to be Glu-Asp-Gly-Pro-Lys-Phe-Leu (2–8), Asp-Gly-Pro-Lys-Phe-Leu (3–8) and Glu-Asp-Gly-Pro-Lys (2–6) in human and in rat blood and 2–8 and 2–6 in mouse blood. Analysis of the time course of degradation revealed a sequential removal of single amino acids from the N-terminus (aminopeptidase activities) in a process that was apparently unable to cleave the Gly-Pro bond (positions 4–5 in the peptide) together with an independent cleavage of the Lys-Phe bond (positions 6–7 in the peptide) to release the dipeptide Phe-Leu. This behaviour and the effects of inhibitors showed the involvement of metallo-exopeptidases in the N-terminal digestion and a phosphoramidon-sensitive metallo-endopeptidase in the cleavage of the Lys-Phe bond. The degradation patterns in human blood were modelled in terms of the competing pathways involved approximating to first-order kinetics, and an analytical solution obtained via the method of Laplace Transforms. The half-life of THF degradation in whole rat blood sample was found to be significantly lower than in human or mouse.

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The immunomodulatory octapeptide THF-γ2 is rapidly degraded in human and rodent blood.

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The half-life of the intact peptide was <6 min in all species.

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The nature of the peptidases involved was determined by the use of specific inhibitors.

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Laplace transforms were used to model the degradation patterns in human blood.

Synthesis of [I-NaI3]] thymopoietin II and examination of its immunological effect on the uremic T-lymphocytes

A TP II analogue, [1-Nal3] TP II, was synthesized by a conventional solution method, followed by deprotection with 1M TFMSA-thioanisole (molar ratio 1:1) in TFA in the presence of Me2Se and m-cresol as scavengers. The synthetic [1-Nal3] TP II, TP II and [Phe (4 F)3] TP II were tested for comparative effect on the impaired T-lymphocyte transformation by PHA in uremic patients suffering from recurrent infectious diseases. The synthetic analogue was found to have stronger restorative activity than those of our synthetic TP II and [Phe (4F)3] TP II.