Distribution and characterization of neurosteroid sulfatase from the bovine brain

Do Dehydroepiandrosterone (DHEA) and Its Sulfate (DHEAS) Play a Role in the Stress Response in Domestic Animals?

In animal husbandry, stress is often associated with poor health and welfare. Stress occurs when a physiological control system detects a state of real or presumptive threat to the animal's homeostasis or a failure to control a fitness-critical variable. The definition of stress has mostly relied on glucocorticoids measurement, even though glucocorticoids represent one stress-response system, the hypothalamus-pituitary-adrenocortical axis, which is not precise enough as it is also related to metabolic regulation and activated in non-stressful situations (pleasure, excitement, and arousal). The mammal adrenal can synthesize the androgenic steroid dehydroepiandrosterone (DHEA) and its sulfate metabolite (DHEAS), which have been associated to the stress response in several studies performed mostly in humans and laboratory animals. Although the functions of these steroids are not fully understood, available data suggest their antagonistic effects on glucocorticoids and, in humans, their secretion is affected by stress. This review explores the scientific literature on DHEA and DHEAS release in domestic animals in response to stressors of different nature (inflammatory, physical, or social) and duration, and the extra-adrenal contribution to circulating DHEA. Then, the potential use of DHEA in conjunction with cortisol to improve the definition of the stress phenotype in farmed animals is discussed. Although the focus of this review is on farmed animals, examples from other species are reported when available.

Steroid sulfatase is a potential modifier of cognition in attention deficit hyperactivity disorder

Deletions encompassing the X-linked STS gene (encoding steroid sulfatase) have been observed in subjects with neurodevelopmental disorders, including attention deficit hyperactivity disorder (ADHD). Recently, two single nucleotide polymorphisms (SNPs) within STS (rs12861247 and rs17268988) have been reported to be associated with ADHD risk and inattentive symptoms in ADHD, respectively. Using a UK sample of ADHD subjects (aged 5-18 years), we tested the hypothesis that rs12861247 is associated with ADHD risk using a case-control approach (comparing 327 ADHD cases with 358 male controls from the Wellcome Trust Case Control Consortium). Using a subset of males from the ADHD sample, we also examined whether variation within STS is associated with symptomatology/cognitive function in ADHD. We then tested whether SNPs associated with cognitive function in ADHD were also associated with cognitive function in healthy male subjects using a German sample (n = 143, aged 18-30 years), and whether STS was expressed in brain regions pertinent to ADHD pathology during development. We did not replicate the previously identified association with rs12861247. However, in ADHD males, variation at rs17268988 was associated with inattentive symptoms, while variation within STS was significantly associated with performance on three cognitive measures. Three SNPs associated with cognitive function in ADHD males were not associated with cognitive function in healthy males. STS was highly expressed in the developing cerebellar neuroepithelium, basal ganglia, thalamus, pituitary gland, hypothalamus and choroid plexus. These data suggest that genetic variants affecting STS expression and/or activity could influence the function of brain regions perturbed in ADHD.

Pregnenolone sulfate potentiates the inwardly rectifying K channel Kir2.3

Background

Neurosteroids have various physiological and neuropsychopharmacological effects. In addition to the genomic effects of steroids, some neurosteroids modulate several neurotransmitter receptors and channels, such as N-methyl-D-aspartate receptors, γ-aminobutyric acid type A (GABA_A) receptors, and σ₁ receptors, and voltage-gated Ca²⁺ and K⁺ channels. However, the molecular mechanisms underlying the various effects of neurosteroids have not yet been sufficiently clarified. In the nervous system, inwardly rectifying K⁺ (Kir) channels also play important roles in the control of resting membrane potential, cellular excitability and K⁺ homeostasis. Among constitutively active Kir2 channels in a major Kir subfamily, Kir2.3 channels are expressed predominantly in the forebrain, a brain area related to cognition, memory, emotion, and neuropsychiatric disorders.

Methodology/Principal Findings

The present study examined the effects of various neurosteroids on Kir2.3 channels using the Xenopus oocyte expression assay. In oocytes injected with Kir2.3 mRNA, only pregnenolone sulfate (PREGS), among nine neurosteroids tested, reversibly potentiated Kir2.3 currents. The potentiation effect was concentration-dependent in the micromolar range, and the current-voltage relationship showed inward rectification. However, the potentiation effect of PREGS was not observed when PREGS was applied intracellularly and was not affected by extracellular pH conditions. Furthermore, although Kir1.1, Kir2.1, Kir2.2, and Kir3 channels were insensitive to PREGS, in oocytes injected with Kir2.1/Kir2.3 or Kir2.2/Kir2.3 mRNA, but not Kir2.1/Kir2.2 mRNA, PREGS potentiated Kir currents. These potentiation properties in the concentration-response relationships were less potent than for Kir2.3 channels, suggesting action of PREGS on Kir2.3-containing Kir2 heteromeric channels.

Conclusions/Significance

The present results suggest that PREGS acts as a positive modulator of Kir2.3 channels. Kir2.3 channel potentiation may provide novel insights into the various effects of PREGS.

Sulfated steroids as endogenous neuromodulators

Central nervous system function is critically dependent upon an exquisitely tuned balance between excitatory synaptic transmission, mediated primarily by glutamate, and inhibitory synaptic transmission, mediated primarily by GABA. Modulation of either excitation or inhibition would be expected to result in altered functionality of finely tuned synaptic pathways and global neural systems, leading to altered nervous system function. Administration of positive or negative modulators of ligand-gated ion channels has been used extensively and successfully in CNS therapeutics, particularly for the induction of sedation and treatment of anxiety, seizures, insomnia, and pain. Excessive activation of excitatory glutamate receptors, such as in cerebral ischemia, can result in neuronal damage via excitotoxic mechanisms. The discovery that neuroactive steroids exert rapid, direct effects upon the function of both excitatory and inhibitory neurotransmitter receptors has raised the possibility that endogenous neurosteroids may play a regulatory role in synaptic transmission by modulating the balance between excitatory and inhibitory neurotransmission. The sites to which neuroactive steroids bind may also serve as targets for the discovery of therapeutic neuromodulators.

Steroid sulfatase and sulfuryl transferase activity in monkey brain tissue

Dehydroepiandrosterone and its sulfated form are commonly known as modulators of gamma-aminobutyrate A and N-methyl-D-aspartate receptors. In spite of poor permeability of the blood-brain barrier for sulfated steroids, high concentrations of dehydroepiandrosterone and also its sulfate have been found in brain tissue. Physiological concentrations of these neuromodulators are maintained by two enzymes present in the blood and many peripheral tissues, including the brain, namely, steroid sulfatase and neurosteroid sulfuryl transferase (NSST). This prompted us to investigate activities of these enzymes in primate brain tissue. Rather low neurosteroid sulfuryl transferase activity was detectable in in vitro incubations of cytosol fractions from male and female Macaca mulatta brains, dissected to cerebral cortex, subcortex, and cerebellum. In male monkeys, the highest activity was found in the cerebellum followed by cortex and subcortex. On the other hand, in female monkeys, the highest activity was determined in the cortex followed by subcortex and cerebellum. Steroid sulfatase activity was determined in in vitro microsomal samples from each of the above-mentioned brain regions. Specific activities in female cerebral regions declined in the order: cerebellum, cortex, and subcortex. In male monkeys, no significant difference among the studied regions was observed. Using dehydroepiandrosterone sulfate as a substrate, the apparent kinetic characteristics of steroid sulfatase were determined as follows: K(M) 36.10 +/- 8.33 microM, V(max) 8.38 +/- 1.68 nmol/h/mg protein. These results will serve as a basis for further studies concerning the pathophysiology of human brain tumors.

Dehydroepiandrosterone (DHEA) and the aging brain: flipping a coin in the "fountain of youth"

The physiological role of dehydroepiandrosterone (DHEA) and its sulphated ester DHEA(S) has been studied for nearly 2 decades and still eludes final clarification. The major interest in DHEA derives from its unique pattern of activity. Its levels exhibit a dramatic age-related decline that supports significant involvement of DHEA(S) in the aging process. Particularly relevant to the aging process is the functional decline that involves memory and cognitive abilities. DHEA is derived mainly from synthesis in the adrenal glands and gonads. It can also be detected in the brain where it is derived from a synthesis that is independent from peripheral steroid sources. For this reason DHEA and other steroid molecules have been named "neurosteroids." Pharmacological studies on animals provided evidence that neurosteroids could be involved in learning and memory processes because they can display memory-enhancing properties in aged rodents. However, human studies have reported contradictory results that so far do not directly support the use of DHEA in aging-related conditions. As such, it is important to remember that plasma levels of DHEA(S) may not reflect levels in the central nervous system (CNS), due to intrinsic ability of the brain to produce neurosteroids. Thus, the importance of neurosteroids in the memory process and in age-related cognitive impairment should not be dismissed. Furthermore, the fact that the compound is sold in most countries as a health food supplement is hampering the rigorous scientific evaluation of its potential. We will describe the effect of neurosteroids, in particular DHEA, on neurochemical mechanism involved in memory and learning. We will focus on a novel effect on a signal transduction mechanism involving a classical "cognitive kinase" such as protein kinase C. The final objective is to provide additional tools to understand the physiological role and therapeutic potentials of neurosteroids in normal and/or pathological aging, such as Alzheimer's disease.

Characterization of iodothyronine sulfatase activities in human and rat liver and placenta

In conditions associated with high serum iodothyronine sulfate concentrations, e.g. during fetal development, desulfation of these conjugates may be important in the regulation of thyroid hormone homeostasis. However, little is known about which sulfatases are involved in this process. Therefore, we investigated the hydrolysis of iodothyronine sulfates by homogenates of V79 cells expressing the human arylsulfatases A (ARSA), B (ARSB), or C (ARSC; steroid sulfatase), as well as tissue fractions of human and rat liver and placenta. We found that only the microsomal fraction from liver and placenta hydrolyzed iodothyronine sulfates. Among the recombinant enzymes only the endoplasmic reticulum-associated ARSC showed activity toward iodothyronine sulfates; the soluble lysosomal ARSA and ARSB were inactive. Recombinant ARSC as well as human placenta microsomes hydrolyzed iodothyronine sulfates with a substrate preference for 3,3'-diiodothyronine sulfate (3,3'-T(2)S) approximately T(3) sulfate (T(3)S) >> rT(3)S approximately T(4)S, whereas human and rat liver microsomes showed a preference for 3,3'-T(2)S > T(3)S >> rT(3)S approximately T(4)S. ARSC and the tissue microsomal sulfatases were all characterized by high apparent K(m) values (>50 microM) for 3,3'-T(2)S and T(3)S. Iodothyronine sulfatase activity determined using 3,3'-T(2)S as a substrate was much higher in human liver microsomes than in human placenta microsomes, although ARSC is expressed at higher levels in human placenta than in human liver. The ratio of estrone sulfate to T(2)S hydrolysis in human liver microsomes (0.2) differed largely from that in ARSC homogenate (80) and human placenta microsomes (150). These results suggest that ARSC accounts for the relatively low iodothyronine sulfatase activity of human placenta, and that additional arylsulfatase(s) contributes to the high iodothyronine sulfatase activity in human liver. Further research is needed to identify these iodothyronine sulfatases, and to study the physiological importance of the reversible sulfation of iodothyronines in thyroid hormone metabolism.

Aggressive behavior induced by the steroid sulfatase inhibitor COUMATE and by DHEAS in CBA/H mice

The steroid sulfatase enzyme (STS) regulates the formation of dehydroepiandrosterone (DHEA) from dehydroepiandrosterone-sulfate (DHEAS). DHEAS is a well-known negative allosteric modulator of the GABA(A) receptor-gated chloride channels. It is classified as an excitatory neurosteroid. The implication of GABA(A) receptor activity in aggressive behavior in rodents is well-documented. In addition a genetic correlation between STS level in the liver and aggressive behavior across 12 strains of mice suggest that STS activity could be involved in aggression in mice. We assessed herein whether COUMATE (an STS inhibitor) and DHEAS modulate aggression in CBA/H mice. We hypothesized that inhibiting STS activity in vivo followed by DHEAS injections which increase the level of sulfated steroid that cross the blood-brain barrier and then modulate neurotransmitter receptors could modify the attack behavior in mice. COUMATE (10 mg/kg) was administrated p.o. alone or in combination with the neurosteroid DHEAS (0-50 mg/kg) i.p. Animals were thereafter tested for aggression. A single dose of COUMATE significantly inhibited STS activity both in the brain (70.57%) and in the liver (87%) 24 h following administration. Behavioral tests showed that the inhibitor and DHEAS enhanced aggressive behavior when animals were simultaneously subjected to both molecules. These results confirm the correlation between aggressive behavior and STS concentration in mice. In addition, we confirm that the steroid metabolism can modulate the behavior in rodents.

Subunits of neurosteroid sulfatase from bovine brain

We have purified the neurosteroid sulfatase (NSS) from Triton X-100 solubilized microsomes of bovine brain about 100-fold. The purified enzyme is composed of two catalytic units (MW: 57 kDa) and two regulatory units (MW: 38 kDa), making it an alpha(2)beta(2) heterotetramer, whose apparent molecular weight was 180 kDa by gel filtration in the presence of Triton X-100.

Actions of dehydroepiandrosterone and its sulfate in the central nervous system: effects on cognition and emotion in animals and humans

Dehydroepiandrosterone (DHEA) and its sulfate ester, DHEAS, exert multiple effects in the rodent central nervous system (CNS). Most of them seem to be mediated through their non-genomic action on several neurotransmitter receptors. DHEA(S) increases neuronal excitability, enhances neuronal plasticity and also has neuroprotective properties. In line with these observations DHEA(S) treatment in rodents enhances memory in several paradigms. Even more studies show antiamnestic effects of the steroids. However, DHEA(S) has also anxiolytic and anti-aggressive properties. In humans cross-sectional and longitudinal studies suggest that DHEAS might be associated with global measures of well-being and functioning; however, a relationship with cognition could not be detected to date. Moreover, studies investigating DHEAS levels in neurodegenerative diseases have produced conflicting results. Experimental studies in elderly humans have revealed preliminary evidence for mood enhancing and antidepressant effects of DHEA treatment, while positive effects on measures of memory and attention could not be found. However, electrophysiological studies demonstrated that DHEA treatment has effects on the human CNS. Several reasons for the discrepancy between data obtained in rodents and humans are discussed and research perspectives are outlined which might help to improve interpretation of results obtained in the two species.

The length of the polyoxyethylene chain in the Triton X detergents modulates the apparent activation of neurosteroid sulfatase in bovine brain

The effect of the Triton X series on the solubilization and enzyme activity of neurosteroid sulfatase (NSS) in the bovine midbrain was investigated. Triton X-100 and X165 stimulated NSS activity in the bovine midbrain, while Triton X-305 did not. This apparent activation was attributed to the action of the detergents, and not to the latency of the enzyme or the removal of some inhibitory substance from the microsomes. The maximum stimulation was obtained when the length of the polyoxyethylene chain of the detergent was 16.