Effects of selenoprotein P on the contraction and relaxation of the airway smooth muscle.

Selenoprotein P (SeP) not only represents the major selenoprotein in plasma, but also provides more than 50% of the total plasma selenium. However, there is no report concerning the direct action of selenium or selenium-containing compounds on the contraction and relaxation of the airway smooth muscle. Therefore, we investigated the effects of SeP and sodium selenite (SS) on the indirectly induced contraction and relaxation of the cat bronchi, and gel contraction of cultured bovine tracheal smooth muscle cells (BTSMC) induced by ATP. In the present results, SeP or SS suppressed the amplitude of twitch-like contractions of cat bronchiole without affecting the non-adrenergic and non-cholinergic (NANC) relaxations evoked by electrical field stimulation. SeP also suppressed the ATP-induced gel contraction of BTSMC. These results suggest that SeP suppresses the amplitude of twitch-like contraction of cat bronchiole by acting directly on the bronchiolar smooth muscle.

The protective effect of selenoprotein P on injury in rat liver transplantation.

BACKGROUND/AIMS: Selenoprotein P (SeP), a plasma protein, is considered to have a protective effect against various organ damages. We investigated whether addition of SeP to storage solution could attenuate cold ischemia/reperfusion injury (IRI) in rat liver transplantation. METHODOLOGY: After 24 hrs cold preservation in either University of Wisconsin (UW) solution with or without SeP (1 micromol/L or 10 micromol/L), the liver was flushed with warm lactated Ringer's solution. Alanine aminotransferase (ALT) level in the venous effluent was measured. Orthotopic liver transplantation (OLTx) was then performed after the same preservation as above. Blood biochemical features and tissue lipid peroxide levels were measured after OLTx, and morphometric changes analyzed by hematoxylin and eosin, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) staining. RESULTS: ALT levels in effluent in the SeP 10 group were significantly lower than those in other groups. Serum aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) were significantly decreased in the SeP 10 group. Histological examinations showed amelioration of sinusoidal damage in the SeP 10 group at 1 hr after OLTx. Percentages of necrotic areas and apoptotic sinusoidal endothelial cells were decreased in the SeP 10 group. CONCLUSIONS: The addition of SeP to UW solution attenuates injury in OLTx.

Selenoprotein P protects endothelial cells from oxidative damage by stimulation of glutathione peroxidase expression and activity.

A major fraction of the essential trace element selenium circulating in human blood plasma is present as selenoprotein P (SeP). As SeP associates with endothelial membranes, the participation of SeP in selenium-mediated protection against oxidative damage was investigated, using the human endothelial cell line Ea.hy926 as a model system. Hepatocyte-derived SeP prevented tert-butylhydroperoxide (t-BHP)-induced oxidative cell death of Ea.hy926 cells in a similar manner as did sodium selenite, counteracting a t-BHP-induced loss of cellular membrane integrity. Protection was detected after at least 10 h of SeP supplementation and it peaked at 24 h. SeP time-dependently stimulated the expression of cytosolic glutathione peroxidase (cGPx) and increased the enzymatic activities of glutathione peroxidase (GPx) and thioredoxin reductase (TR). The cGPx inhibitor mercaptosuccinate as well as the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine counteracted the SeP-mediated protection, while the TR inhibitors cisplatin and auranofin had no effect. The presented data suggest that selenium supplementation by SeP prevents oxidative damage of human endothelial cells by restoring expression and enzymatic activity of GPx.

Involvement of selenoprotein P in protection of human astrocytes from oxidative damage.

Selenoprotein P (SeP) is a highly glycosylated, selenium-rich plasma protein. Aside from its role as selenium carrier protein, an antioxidative function of SeP has been suggested. Astrocytes, which detoxify reactive oxygen species in the brain, were described as potential target cells of SeP. We investigated the expression of SeP in human astrocytes and its involvement in the protection of these cells against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage. We show that primary human astrocytes and the human astrocytoma cell line MOG-G-CCM express SeP as an unglycosylated protein, which is not secreted. SeP expression in astrocytes is constitutive. Preincubation of astrocytes with hepatocyte-derived SeP mimicks the protective effect of low-molecular-weight selenocompounds such as sodium selenite or selenomethionine against oxidative damage, shielding astrocytes from t-BHP-induced cytotoxicity. Selenium supplementation of astrocytes counteracts oxidative stress via an increase in expression and activity of the selenoenzyme cytosolic glutathione peroxidase (cGPx). Furthermore, specific downregulation of SeP expression by small interfering RNA decreases cell viability of human astrocytes and makes them more susceptible to t-BHP-induced cytotoxicity. Our results implicate an antioxidant activity of constitutively expressed SeP in selenium-deficient astrocytes, while during adequate selenium supply the enhanced protection against oxidative stress is exerted by cGPx.