Sulfur-containing histidine compounds inhibit γ-glutamyl transpeptidase activity in human cancer cells

γ-Glutamyl transpeptidase (GGT) is an enzyme located on the surface of cellular membranes and involved in GSH metabolism and maintenance of redox homeostasis. High GGT expression on tumor cells is associated with increased cell proliferation and resistance against chemotherapy. GGT inhibitors evaluated so far in clinical trials are too toxic for human use. In this study, using enzyme kinetics analyses, we demonstrate that ovothiols, 5(Nπ)-methyl thiohistidines of marine origin, act as noncompetitive inhibitors of GGT, with an apparent K_i of 21 μm, when we fixed the concentrations of the donor substrate. We found that these compounds are more potent than the known GGT inhibitor 6-diazo-5-oxo-l-norleucine and are not toxic toward human embryonic cells. In particular, cellular process-specific fluorescence-based assays revealed that ovothiols induce a mixed cell-death phenotype of apoptosis and autophagy in GGT-overexpressing cell lines, including human liver cancer and chronic B leukemic cells. The findings of our study provide the basis for further development of 5-thiohistidines as therapeutics for GGT-positive tumors and highlight that GGT inhibition is involved in autophagy.

The estimation of post-transplant lymphocele origin using creatine kinase activity

INTRODUCTION

The aim of this research was to create a laboratory instrument for the estimation of post-transplant lymphocele origin. It is based on the enzymatic activity of creatine kinase (CK) in the lymphocele content.

MATERIAL AND METHODS

A total of 120 lymph samples from different retroperitoneal regions were obtained from non-transplanted patients; equal numbers from the iliac region, renal cysts, and the subdiaphragmatic retroperitoneum. Activities of creatine kinase (CK) and gamma-glutamyl transpeptidase (GGT) were determined in all samples and statistically analyzed against their activity in serum from patients without surgery.

RESULTS

Activities of CK in the pelvis, retroperitoneum, renal cysts, and serum were 5.06, 0.83, 6.48 (P<0.001), 2.50, 0.73, 3.60 (P<0.001), 0.02, 0.01, 0.05 (P<0.001), and 0.66, 0.41, 0.79 microkat/l, respectively. Activities of GGT in the same lymph samples were 0.26, 0.16, 0.36 (P=0.048), 0.41, 0.25, 0.48 (non-significant), 0.11, 0.07, 1.17 (P=0.003) and 0.34, 0.24, 0.55 microkat/l, respectively. A graph was constructed relating CK activity to lymph origin.

CONCLUSION

Significantly different CK enzyme activity was observed in different regions of the retroperitoneum. The presented graph is a simple instrument for the estimation of the lymphocele content origin. The method requires percutaneous aspiration of the lymphocele and evaluation of the CK and GGT activity in the sample. From the graph the estimated proportion of renal lymph in the lymphocele can be read directly. This instrument can provide better understanding of post-transplant lymphocele fluid source.