The steroid sulfatase inhibitor COUMATE attenuates rather than enhances access of dehydroepiandrosterone sulfate to the brain in the mouse

Abstract

Intraperitoneal injection of adult male mice with the neuroactive steroid dehydroepiandrosterone sulfate (DHEAS) at 1 and 40 mg/kg caused dose-dependent increases in the concentration of both this compound and its corresponding free steroid DHEA in brain within 1 h of injection. Pretreatment of these animals for 24 h with the steroid sulfatase inhibitor COUMATE at a dose (10 mg/kg, p.o.) shown previously to cause almost complete inhibition of this enzyme in liver and brain was expected to increase the amount of the DHEAS dose reaching the brain. Surprisingly however, the increases in brain concentrations of DHEAS and DHEA after injection of DHEAS i.p. were attenuated by pretreatment with COUMATE. The results suggest that the arylsulfamate based steroid sulfatase inhibitors such as COUMATE interfere with the influx of the DHEAS anion into the brain.

Introduction

Since the characterization of dehydroepiandrosterone sulfate (DHEAS) as a brain steroid (Corpéchot et al., 1981) there has been detailed investigation of the effects of this compound on neural function (see Gibbs et al., 2006). Of particular interest in view of the decline in plasma DHEAS of adrenal origin with human ageing is the ability of this steroid to improve retention of memory after subcutaneous or intracerebral injection in mice (Flood et al., 1988). Several studies have since shown DHEAS administered either systemically or directly into the brain to enhance the acquisition and consolidation of memory and reverse pharmacologically induced amnesia in a variety of species (see Wolf and Kirschbaum, 1999). Possible neural sites of action for the above effects of DHEAS include antagonism of GABA_A receptors (Majewska et al., 1990) and stimulation of sigma receptors, the latter underlying an enhancement of NMDA receptor function (Monnet et al., 1995; see also Maurice et al., 2006). Additional modes of action are likely for DHEAS and its corresponding free steroid dehydroepiandrosterone (DHEA), in particular to explain the antiglucocorticoid and neuroprotective effects of these compounds (see Wolf and Kirschbaum, 1999).

In addition to enhancement of memory, other behavioral effects of DHEAS in mice include anxiolysis on the elevated plus maze (Melchior and Ritzmann, 1994) and increased attack behavior against a conspecific male (Nicolas et al., 2001). The latter is correlated with the expression of liver steroid sulfatase (STS; Le Roy et al., 1999), an enzyme which is also present in brain (Mortaud et al., 1996) and which catalyzes the hydrolysis of 3β-hydroxysteroid sulfates such as DHEAS to liberate the free steroid DHEA. Several irreversible inhibitors of this enzyme have become available in recent years, all of which feature an arylsulfamate moiety (see Nussbaumer and Billich, 2004). Although developed primarily as potential therapeutic agents for the treatment of estrogen- and androgen-dependent disorders of peripheral tissues, these STS inhibitors would be expected to increase the potency of steroid sulfates, at least for their direct actions at the receptor sites in the brain described above. Indeed, a previous study by one of us (Nicolas et al., 2001) showed that prior treatment of mice with the STS inhibitor COUMATE (7-O-sulfamoyl-4-methylcoumarin) decreased the dose of intraperitoneally administered DHEAS needed to elicit aggressive behavior. At the time, this observation was interpreted as evidence for inhibition of STS allowing more of the circulating DHEAS to cross the blood–brain barrier. We now report that the opposite is the case and that pretreatment with the STS inhibitor COUMATE actually decreases the access of DHEAS to the brain in the mouse.