Torsten Hoffmann

Dipeptidyl peptidase IV (CD 26) and aminopeptidase N (CD 13) catalyzed hydrolysis of cytokines and peptides with N-terminal cytokine sequences.

A number of natural cytokines are characterized as having dipeptidyl peptidase (DP) IV susceptible N‐terminal peptide sequences. Here we demonstrate that oligopeptides with sequences analogous to the N‐terminal part of human IL‐1β, IL‐2, TNF‐β and murine IL‐6 were hydrolyzed by purified DP IV and aminopeptidase N (AP‐N). The rate of DP IV‐catalyzed hydrolysis of these peptides was negatively correlated with their chain length. In contrast to these results, no degradation was found under our conditions for the intact recombinant cytokines, IL‐1α, IL‐1β, IL‐2, G‐CSF and for natural IL‐2, independent of whether DP IV and AP‐N were used separately or in combination.

Inhibition of dipeptidyl peptidase IV (DP IV) by anti-DP IV antibodies and non-substrate X-X-Pro- oligopeptides ascertained by capillary electrophoresis

Dipeptidyl peptidase IV (DP IV)-catalyzed hydrolysis of the NH2-X-Pro-containing N-terminal dodecapeptide of IL-2 was studied using free zone capillary electrophoresis as an alternative peptidase assay. In contrast to the conventional DP IV substrate glycyl-prolyl-p-nitroanilide (Gly-Pro-pNA), the hydrolysis of this peptide by DP IV was found to be significantly inhibited by anti-DP IV antibodies. Inhibition of DP IV was also observed with a number of non-substrate oligopeptides containing an N-terminal X-X-Pro- structure, including the HIV Tat protein. For Met-IL-2(1-6), we determined a competitive inhibition with an inhibition constant of ca. 100 microM.

CD26 Mediates the Action of HIVA Tat Protein on DNA Synthesis and Cytokine Production in U937 Cells

The human immunodeficiency virus 1 (HIV-1) Tat protein is known to be capable of suppressing antigen- and CD3-induced activation of human T cells. Previously, it was shown that Tat can bind to the dipeptidyl peptidase IV (DP IV, CD26) and inhibit the degradation of the chromogenic substrate Gly-Pro-p-nitroanilide. Using the method of free zone capillary electrophoresis, here we have shown that the DP IV-catalyzed hydrolysis of the NH2-X-Pro-containing cytokine peptides IL-2(1-12), IL-1 beta(1-6), and IL-6(1-12) was also significantly inhibited by the Tat protein. Moreover, HIV-1 Tat at a concentration of 10 micrograms/ml was found to have a strong suppressive effect on DNA synthesis and IL-1 beta production, but stimulates secretion of IL-1 receptor antagonist (IL-1RA) and TNF-alpha of CD26-expressing U937-H cells. It did not impair neither DNA synthesis nor cytokine production of low CD26-expressing U937-L cells. Similar results have been found with synthetic DP IV/CD26 inhibitors (Immunobiol., 1994, vol. 192, pp. 121-136). These data strongly suggest that Tat protein is a potent natural inhibitor of DP IV/CD26, and they support the hypothesis that DPIV plays a role in Tats immunosuppressive activity.

Particle–Gas Mass Transfer in a Spouted Bed with Adjustable Air Inlet

Spouted bed equipment has the potential of producing high-quality particulate materials with reduced energy consumption and environment impact. Particle-to-gas mass transfer was investigated in a spouted bed with a novel design of two rotating drums placed symmetrically in the apparatus to create air inlet openings of adjustable width, so that fluidization can be adapted to the requirements of each product and process. The mass transfer coefficients between particle surface and gas were derived from first-period drying experiments with porous, nonhygroscopic material by assuming perfect back-mixing or, alternatively, ideal plug flow of the gas. Respective Sherwood numbers were empirically correlated and found to be superior to the Sherwood numbers of conventional fluidized beds or conventional spouted beds.

Prediction of Shell Porosities in Continuous Fluidized Bed Spray Layering

In this work, experimental results for a continuous fluidized bed spray layering process are used to identify product quality influencing process parameters, such as the shell porosity. The prediction of the shell porosity is based on an empirical relation established for fluidized bed layering in batch mode. It uses gas-side properties, which are represented by the drying potential of the gas. It is shown that the shell porosities forming in the continuous mode can be deduced from this relation by comparing experimental data and simulation results. Process stability and seed formation are also discussed using the obtained experimental data.