Elsevier

Epilepsy Research

Volume 54, Issue 1, April 2003, Pages 11-19
Epilepsy Research

Allopregnanolone serum levels and expression of 5α-reductase and 3α-hydroxysteroid dehydrogenase isoforms in hippocampal and temporal cortex of patients with epilepsy

https://doi.org/10.1016/S0920-1211(03)00036-6Get rights and content

Abstract

In the human central nervous system, progesterone is rapidly metabolised to 5α-dihydroprogesterone which subsequently is further reduced to allopregnanolone (AP). These conversions are catalysed by 5α-reductase and 3α-hydroxysteroid dehydrogenase (3α-HSD). Although different isoforms of both enzymes have been identified in the brain, our knowledge of their expression in the human brain remains limited. The aim of the present study was to investigate the mRNA expression of 5α-reductase 1 as well as 3α-HSD 1, 2, 3 and 20α-HSD in brain tissue from patients with pharmacoresistant temporal lobe epilepsy (TLE). Specimens were derived from either the hippocampus or the temporal lobe cortex and from the tumor-free approach corridor tissue of patients with brain tumors. Quantification of different mRNAs was achieved by real time PCR. In addition, we provide data on simultaneous evaluation of serum AP concentrations. We could demonstrate that 3α-HSD 1 was not expressed in the hippocampus and temporal lobe of patients with TLE. In the hippocampus and temporal lobe, the expression levels of 3α-HSD 2 were about 20% of that in liver tissue, those of 3α-HSD 3 about 7% and those of 20α-HSD about 2%, respectively. In patients with TLE, expression of 3α-HSD 2 was significantly higher in the hippocampus than in temporal lobe cortex tissue (P<0.006). AP concentrations did not correlate significantly with the mRNA expression levels of 5α-reductase 1, 3α-HSD 2 and 3 and 20α-HSD in any of the patient groups under investigation. In conclusion, the present study demonstrates mRNA expression of 5α-reductase 1 and 3α-HSD 2 and 3 and 20α-HSD in the hippocampus and temporal lobe of epileptic patients. These findings provide further molecular biological evidence for the formation and metabolism of neuroactive steroids in the human brain.

Introduction

Neurosteroids such as the progesterone metabolite allopregnanolone (AP; 3α-hydroxy-5α-pregnane-20-one or 3α,5α-THP) are potent positive modulators of the GABAA receptor with anticonvulsant, anxiolytic, and sedative properties (Lambert et al., 1995, Compagnone and Mellon, 2000, Beyenburg et al., 2001, Mellon and Griffin, 2002). There is now convincing evidence that AP synthesis can play a role in the suppression of seizures via progesterone (Beyenburg et al., 2001; Reddy and Rogawski, 2000, Reddy and Rogawski, 2001a, Reddy and Rogawski, 2001b). In animal models, withdrawal from AP enhances seizure susceptibility (Reddy and Rogawski, 2000, Reddy and Rogawski, 2001a, Reddy and Rogawski, 2001b; Smith, 2002). It has been suggested that, in patients with focal epilepsy, AP plays a role in the control of neuronal excitability and seizures (Galli et al., 1996, Beyenburg et al., 2001, Galli et al., 2001). One mechanism by which AP may alter seizure susceptibility is via modulation of GABAA receptor subunit composition. Animal studies have shown that changes in AP levels alter hippocampal subunit expression leading to altered GABAA receptor sensitivities (Smith et al., 1998).

In the human central nervous system, progesterone is rapidly metabolised to 5α-dihydroprogesterone (5α-DHP), which subsequently is further reduced to AP (Stoffel-Wagner, 2001, Mellon and Griffin, 2002). These reductive conversions are catalysed by 5α-reductase and 3α-hydroxysteroid dehydrogenase (3α-HSD) (Compagnone and Mellon, 2000), and it is now generally accepted that the 5α-reductase–3α-HSD complex plays a major role in the activation of neurosteroids in human and animal brain (Lephart, 1993, Compagnone and Mellon, 2000, Steckelbroeck et al., 2001, Stoffel-Wagner, 2001). Different isoformes of 5α-reductase and 3α-HSD have been identified in the human brain, notably in the human hippocampus (Stoffel-Wagner et al., 1998, Stoffel-Wagner et al., 2000, Steckelbroeck et al., 2001). However, information on steroidogenic enzymes in the human brain is still limited. In previous work, we demonstrated the exclusive expression of the 5α-reductase type 1 isoform mRNA in the human temporal lobe and hippocampus obtained from patients with pharmacoresistant temporal lobe epilepsy (TLE) (Stoffel-Wagner et al., 1998, Stoffel-Wagner et al., 2000). Recently, we further characterised the 5α-reductase–3α-HSD complex in the human brain (Steckelbroeck et al., 2001). The lack of sex-specific differences and the colocalisation of both steroidogenic enzymes at all life stages provide further evidence that 5α-reductase and 3α-HSD are important enzymes in the synthesis and metabolism of neurosteroids in the human brain. Here, we extend our previous studies and demonstrate—for the first time—the expression of all currently known human isoformes of 3α-HSD in the human brain. In addition, we provide data on simultaneous evaluation of serum AP concentrations.

Section snippets

Patients

In all patients suffering from medically intractable TLE who were included in the present study, the hippocampus or temporal lobe was removed to achieve seizure control. The study was approved by the local ethics committee and informed consent was obtained from all tissue donors. Following presurgical evaluation of the seizure focus, patients underwent epilepsy surgery. Hippocampal tissue specimens from 10 women (35.7±2.4 years, mean±S.E.M.) and 8 men (39.6±5.3 years) as well as temporal cortex

Expression of 5α-reductase 1, 3α-HSD 1, 2, 3 and 20α-HSD mRNA in reference tissue and brain tissue

In order to validate our mRNA quantification protocol, we determined the expression of 5α-reductase 1, 3α-HSD 1, 2 and 3 mRNA as well as 20α-HSD in liver tissue which served as reference tissue. As shown in Table 2, all of these mRNAs were expressed in liver tissue. In brain tissue, 3α-HSD 1 was not expressed. The expression levels of 3α-HSD 2 were about one-fifth of that in liver tissue, those of 3α-HSD 3 about 7% (≈1/15) of that in liver tissue, those of 20α-HSD about 2% (≈1/40) of that in

Discussion

In the present study, we investigated the mRNA expression of 5α-reductase 1 as well as 3α-HSD 1, 2, 3 and 20α-HSD in brain tissue from patients with pharmacoresistant TLE. Specimens derived from either hippocampus or temporal lobe cortex and from the tumor-free approach corridor tissue of patients with brain tumors. As the distribution of the 3α-HSD isoforms in the human brain with regard to hormonal state has not yet been examined, we additionally correlated the mRNA expression levels of the

Acknowledgements

This study was supported by the Herbert Reeck Stiftung Bonn. We thank Dr. Prof. M. Nuri, Waldkrankenhaus Bonn, Department of Urology, for supply of prostate tissue and Dr. M. Wolff, University of Bonn, Department of Surgery, for supply of liver tissue.

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