The role of DHEA in the aetiology of modern chronic disease

Powrie, Yigael Samuel Louis (2020-04)

Thesis (PhD)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Dehydroepiandrosterone (DHEA) is an androgenic steroid predominantly viewed as the main precursor to androgen and estrogen hormones in the human body. DHEA exists as a sulphated ester known as DHEAS, which is also the most predominant steroid hormone in human circulation. A decline in circulating DHEA concentrations is associated with age, inflammatory disease, as well as neurodegenerative pathologies. It has numerous demonstrated neuroprotective, anti-inflammatory and anti-glucocorticoid effects. The human adrenal glands and gonads are the main sites for DHEA biosynthesis in the periphery, but historical evidence has suggested that central steroid biosynthesis, termed neurosteroidogenesis, is responsible for the presence of DHEA in the brain. The process of neurosteroidogenesis has to date proven to be an elusive process, as only a handful of relatively dated studies have provided evidence for its existence. Furthermore, clear differences are apparent in systemic rodent steroidogenesis and human steroidogenesis, the latter of which most the evidence of neurosteroidogenesis is formulated upon. In order to exploit the numerous reported beneficial effects of DHEA in the brain, it is pertinent that we understand how it is synthesised, how it may exert its effects centrally and whether species differences will affect the function thereof. Utilising the sensitivity and specificity of Ultra-Performance Convergence Chromatography (UPC2)-tandem mass spectrometry we comprehensively assessed the ability of primary human astrocytes (pHAs) and primary rat brain ex vivo mixed cell cultures (pRBMCs) to synthesise DHEA from a known substrate, pregnenolone, in the presence or absence of steroidogenic modulators. Additionally, we also sought to elucidate the ability of the cells to metabolise DHEA, in either the presence or absence of steroidogenic modulators. Both pHAs and pRBMCs were unable to synthesise DHEA from pregnenolone as the substrate in the absence or presence of steroidogenic modulators. pHAs and pRBMCs were able to convert pregnenolone in progesterone, demonstrating 3β-HSD activity. Additionally, although both cell populations were unable to demonstrate DHEA biosynthesis, they were able to convert exogenous DHEA into androstenedione and androstenediol, demonstrating not only 3β-HSD, but17β-HSD activity as well. This is the first study demonstrating androstendiol biosynthesis by human glial cells. The inability of pHAs and pRBMCs to synthesise DHEA from pregnenolone as a substrate contradicts available literature. The metabolism of exogenous DHEA into downstream metabolites suggests that the numerous beneficial effects of DHEA are not due to the steroids itself, but rather its metabolites. This current characterisation of DHEA metabolism both questions our current understanding of DHEA biosynthesis in the brain and holds promise for new therapeutic development in modern chronic disease and specifically neurodegeneration.

AFRIKAANSE OPSOMMING: Dehydroepiandrosterone (DHEA) is ‘n androgeniese steroïedhormoon wat hoofsaaklik as die belangrikste voorloper vir androgeen en estrogeen hormone in die menslike liggaam beskou word. DHEA bestaan ook as 'n gesulfateerde ester, bekend as DHEAS, wat ook die volopste steroïedhormoon in die menslike bloedsomloop is. 'n Afname in die sirkulerende DHEA konsentrasies word geassosieer met ouderdom, inflammatoriese siektes, sowel as neurodegeneratiewe patologieë. Dit het talle neurobeskermende, anti-inflammatoriese en anti-glukokortikoïede effekte. Die menslike byniere en gonades is die belangrikste organe vir DHEA-biosintese in die periferie, maar historiese bewyse dui aan dat sentrale steroïedbiosintese, wat neurosteroïedgenese genoem word, verantwoordelik is vir die teenwoordigheid van DHEA in die brein is. Die proses van neurosteroïedgenese is tot dusver 'n ontwykende proses, aangesien slegs 'n handjievol relatief verouderde studies bewys lewer dat dit bestaan. Verder is daar duidelike verskille in sistemiese knaagdiersteroïedgenese en menslike steroïedgenese, waarvan laasgenoemde die bewys van neurosteroïedgenese is. Om die talle gerapporteerde voordelige gevolge van DHEA in die brein te benut, is dit pertinent dat ons verstaan hoe dit gesintetiseer word, hoe DHEA sy effekte sentraal kan uitoefen en of spesieverskille die funksie daarvan sal beïnvloed. Deur gebruik te maak van die sensitiwiteit en spesifisiteit van ultra werkverrigting konvergensie-chromatografie (UPC2)-tandem-massaspektrometrie, het ons die vermoë van primêre menslike astrosiete (pHA's) en primêre rotbrein ex vivo gemengde selkulture (pRBMC's) om DHEA vanaf die bekende substraat pregnenoloon te sintetiseer, in die teenwoordigheid of afwesigheid van moduleerders van steroïedgenese. Daarbenewens het ons ook probeer om die vermoë van hierdie selle om DHEA te metaboliseer, onder dieselfde toestande, toe te lig. Beide pHA's en pRBMC's kon nie DHEA van pregnenoloon as substraat sintetiseer nie. Die afwesigheid of teenwoordigheid van moduleerders van steroïedgenese het ook nie hierdie bevinding beïnvloed nie. pHA's en pRBMC's het 3β-HSD-aktiwiteit getoon deur pregnenoloon na progesteroon om te skakel. Alhoewel beide selpreparate nie DHEA-biosintese kon demonstreer nie, kon hulle wel eksogene DHEA in androsteendioon en androsteendiol omskakel, wat nie net 3β -HSD, maar ook 17β-HSD aktiwiteit demonstreer. Dit is die eerste studie wat die biosintese van androsteendiol deur menslike glanselle demonstreer. Die onvermoë van pHA's en pRBMC's om DHEA vanaf pregnenoloon as substraat te sintetiseer stem nie ooreen met die beskikbare literatuur nie. Die metabolisme van eksogene DHEA na stroom-af metaboliete dui daarop dat die talle voordelige effekte van DHEA nie te wyte is aan dié steroïed spesifiek nie, maar eerder die metaboliete daarvan. Hierdie huidige karakterisering van DHEA-metabolisme bevraagteken ons huidige begrip van DHEA-biosintese in die brein, maar hou ook belofte in vir nuwe terapeutiese ontwikkeling in moderne chroniese siektes en spesifiek neurodegenerasie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107887
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