The influence of sutherlandia frutescens on adrenal steroid hormones and downstream receptor interactions

Sergeant, Catherine Anne (2017-12)

Thesis (PhD)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The study was aimed at: 1. linking anti-stress properties of Sutherlandia frutescens to its influence on adrenal steroid biosynthesis in terms of extracts, sutherlandioside (SU) compounds and gammaaminobutyric acid (GABA). 2. linking anti-inflammatory and anti-hypertension properties to steroid receptor interaction, the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). The influence of S. frutescens extracts, and SUs, on key steroidogenic enzymes was assayed in COS-1 cells and binding to adrenal P450-dependent enzymes was assayed in ovine adrenal mitochondrial and microsomal suspensions. The effects of the methanol extract and sutherlandioside B (SUB) were assayed on basal, forskolin and angiotensin II (Ang II) stimulated hormone levels in the adrenal H295R cell model. The effect of GABA on basal steroid production was investigated in H295R cells. Agonist activity of the methanolic extract and SUB, for both transactivation and transrepression of GR and MR mediated gene transcription, was subsequently investigated. S. frutescens extracts affected all the steroidogenic enzymes with inhibition being substrate specific. SUB had a greater effect on substrate binding to mitochondrial and microsomal P450 enzymes than sutherlandioside A (SUA). SUB inhibited the catalytic activity of CYP17A1, CYP11B2 and 3β-HSD2 while not affecting CYP21A2. In H295R cells, while the extract decreased total steroid production under basal and forskolin stimulated conditions, only cortisol and its precursor, deoxycortisol, and mineralocorticoid metabolites were decreased significantly in the presence of forskolin. A SU mixture did not influence steroid production, with only cortisol levels decreasing significantly with SUB decreasing cortisol, deoxycortisol, androstendione and 11-hydroxyandrostenedione significantly. The data show that the SU mixture was not able to elicit the same effects as SUB, suggesting that the compounds do not act synergistically. GABA significantly decreased adrenal steroid production in H295R cells with the greatest inhibitory effect observed in the production of adrenal androgens. S. frutescens extracts and SUB repressed NF-κB-driven gene expression without activating GREdriven gene expression while neither activated MR mediated gene transcription while both antagonized the effects of aldosterone via the MR. The results of this study provide evidence linking anti-stress, anti-inflammatory and antihypertensive properties of S. frutescens to the inhibition of steroidogenic enzymes and modulation of adrenal hormone biosynthesis. The findings suggesting that S. frutescens and SUB exhibit dissociated glucocorticoid characteristics underline potential therapeutic applications in the treatment of inflammation and hypertension.

AFRIKAANSE OPSOMMING: Die studie het ten doel gehad om: 1. die koppeling van die anti-stres eienskappe van ekstrakte van Sutherlandia frutescens, die sutherlandiosiede (SU) en gamma-aminobottersuur (GABA) aan die plant se invloed op adrenale steroïedbiosintese. 2. die koppeling van anti-inflammatoriese- en anti-hipertensie-eienskappe aan steroïedreseptor interaksie in terme van die glukokortikoïedreseptor (GR) en die mineralokortikoïedreseptor (MR). Die invloed van S. frutescens ekstrakte en SU op sleutel steroïedogenise ensieme is in COS-1-selle ondersoek. Die binding aan adrenale P450-afhanklike ensieme is ook ondersoek deur gebruik te maak van skaapbynier mitochondriale en -mikrosomale suspensies. Die invloed van ‘n metanol ekstrak en sutherlandiosied B (SUB) is op basale, forskolien en angiotensien II (Ang II) gestimuleerde hormoonvlakke in die H295R-bynierselmodel geassesseer. Die effek van GABA op basale steroïedproduksie in H295R-selle is ook ondersoek. Agonistiese aktiwiteit van die metanolekstrak en SUB, vir beide transaktivering en transrepresie van GR- en MR-gemedieerde geen transkripsie, is vervolgens ondersoek. S. frutescens ekstrakte het al die steroidogeniese ensieme beïnvloed en het substraatspesifieke inhibisie getoon. SUB het 'n groter effek as sutherlandioside A (SUA) op substraatbinding aan mitochondriale- en mikrosomale P450-afhanklike ensieme gehad. SUB inhibeer die katalitiese aktiwiteit van CYP17A1, CYP11B2 en 3β-HSD2 terwyl CYP21A2 nie deur hierdie verbinding ge-affekteer word nie. Die ekstrak het totale steroïedproduksie onder basale en forskoliengestimuleerde toestande in H295R-selle verlaag. Slegs kortisol-, sy voorloper deoksikortisol- en mineralokortikoïedmetabolietvlakke is egter beduidend verlaag in die teenwoordigheid van ekstrakte. Steroïedproduksie is nie deur 'n SU-mengsel beïnvloed nie en slegs kortisolvlakke het beduidend afgeneem. Daarenteen het SUB kortisol-, deoksikortisol-, androsteendioon en 11- hidroksi-androsteendioon vlakke beïnvloed. Die data toon dat die SU mengsel nie dieselfde effekte as SUB kon ontlok nie, wat daarop dui dat die verbindings nie sinergisties optree nie. GABA het 'n aansienlik afname in byniersteroïedproduksie in H295R-selle tot gevolg gehad, met die grootste inhibitoreise effek op die produksie van adrenale androgene. S. frutescens ekstrakte en SUB het NF-κB-gedrewe geenekspressie onderdruk sonder om GREgedrewe geenekspressie te aktiveer maar geen invloed getoon op die MR gemedieerde geentranskripsie getoon nie. Beide die ekstrak en SUB het as aldosteroon antagoniste via die MR opgetree. Die resultate van hierdie studie bied bewyse wat die anti-stres-, anti-inflammatoriese en antihipertensiewe eienskappe van S. frutescens verbind met die inhibisie van adrenale steroïedogeniese ensieme en gevolglike modulering van adrenale hormoonbiosintese. Die bevindinge dui duidelik daarop dat S. frutescens en SUB dissiatiewe glukokortikoïedeienskappe vertoon, en wys op moontlike terapeutiese toepassings in die behandeling van inflammasie en hipertensie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102758
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