PARAMOUNT LEVELS OF ERGOTHIONEINE TRANSPORTER SLC22A4 MRNA IN BOAR SEMINAL VESICLES AND CROSS-SPECIES ANALYSIS OF ERGOTHIONEINE AND GLUTATHIONE IN SEMINAL PLASMA

Abstract

INTRODUCTION Ergothioneine (ET) is a natural antioxidant which is biosynthesized solely by fungi and mycobacteria (1). Chemically, ET is the betaine of histidine with a sulfur atom attached to the imidazole ring. It should not be considered a thiol compound, but rather a thione, a derivative of thiourea. As a consequence of the prevailing thione tautomer, ET is a very stable antioxidant with unique properties (2). Recently, we have discovered an ET transporter (ETT; gene symbol SLC22A4) (3). ETT from human (ETTh) has high affinity for ET (K m =21 µmol/l) and catalyzes cotransport of ET with Na + . Cells lacking ETT do not accumulate ET, since the plasma membrane is virtually impermeable for this compound. By contrast, cells with expression of ETT accumulate ET to high levels. In humans, ETT is strongly expressed in small intestine, kidney, erythrocyte progenitor cells in bone marrow, and monocytes (3). Much interest in ETT has been generated by casecontrol studies that suggest an association of polymorphisms in the SLC22A4 gene with susceptibility to chronic inflammatory diseases such as Crohn's disease (4-9), ulcerative colitis (10) and Type I diabetes (11). It is presently unknown how the mutation in the transporter gene promotes disease. The existence of a specific transporter suggests a beneficial role for ET. Most authors consider ET as an intracellular antioxidant. However, the precise physiological purpose of ET and the consequences of ET deficiency are still unclear. A particularly conspicuous site of ET accumulation is boar semen; in seminal plasma, 0.3-0.8 mmol/l ET has been measured (12, 13). Boar spermatozoa contain, if any at all, much less ET than seminal plasma (14). Thus, in boar semen ET is an extracellular constituent -unlike blood, where nearly all ET is contained within erythrocytes and specific leukocytes. ET apparently enters boar semen at the seminal vesicles. The isolated secretion of this gland contains amazingly high concentrations (average: 3.4 mmol/l; range: 1.3-11 mM; 29-256 mg/100 ml) (12); this level is 10 times higher than in the blood of pig (range: 0.13-1.2 mM; 3-27 mg/100 ml) or other specie