Investigation into potential endocrine disruptive effects of Sceletium tortuosum

Louw, Letitia (2018-03)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Depression has been recognised by the World Health Organisation (WHO) as the leading cause of disability, affecting an estimated 300 million people globally. To date antidepressants are prescribed as the first step in the treatment strategy. However, finding the appropriate antidepressant is often a lengthy process and is usually accompanied by side effects. A major and often unexpected side effect is reduced sexual function, which has been reported to aggravate depression and could possibly lead to poor compliance to medication. Sceletium tortuosum is a native South African plant, which has exhibited both antidepressant and anxiolytic properties. Although the exact mechanism of action remains to be elucidated, there are currently two hypotheses which attempt to explain it’s mechanism of action. Firstly, it has been reported to act in the same manner as a selective serotonin reuptake inhibitor (SSRI), binding to the serotonin transporter and preventing the reuptake of serotonin (5-HT) and thus leading to an increase of 5-HT in the synaptic cleft. On the other hand, it has been reported to act as a monoamine releasing agent (MRA) which assists with the release of monoamine vesicles from the presynaptic neuron, also resulting in an increase of 5-HT in the synaptic cleft. A strong correlation exists between depression and the hyper-activation of the hypothalamus-pituitary-adrenal (HPA) axis. On the other hand, antidepressants and MRA’s have been associated with endocrine disruption. Although a human safety study has illustrated that S.tortuosum is safe for consumption, it was recently reported to decrease sex steroid hormone levels including androstenedione (A4) and testosterone (T) in the H295R cell line, but conclusive remarks could not be formulated. The objective of this thesis was to establish whether Trimesemine™ (Tri; a mesembrine-rich S.tortuosum) could adversely affect gonadal steroid synthesis. HEK293 cells were transfected with 17βHSD type 5 (17βHSD5) cDNA, resulting in the overexpression of the 17βHSD5 enzyme, which is responsible for the conversion of A4 to T. Previous studies within our group used Trimesemine™ at doses ranging from 0.0001 mg/ml to 1 mg/ml. For this study narrower ranges were chosen. The cells were treated with Tri™ at proven effective dose (0.01 mg/ml) and high (0.5 mg/ml) dose, the supernatant was removed after 24 hours and the samples were analysed by UPC2-MS/MS. Routinely euthanized mice were accessed immediately after the culling to obtain viable tissue for primary cultures. Testes were removed, decapsulated and a mixed culture was plated. After 24 hours the cells were treated with lower and high doses of Tri™, following another 24 hours the supernatant was removed and the samples were analysed with UPLC-MS/MS. Ovaries were collected, dissociated and plated. The mixed culture was allowed to stabilise for 24 hours. This was followed by treatment with Tri™ at lower and high doses for a period of 24 hours, the supernatant was removed and the samples were analysed with UPLC-MS/MS. At the lower dose Tri™ did not appear to have any effect on A4, T and estradiol (E2). However, the high dose of Tri™ appeared to decrease A4 (mixed testicular culture) and T (HEK293 cells), possibly via inhibition of the 3βHSD or 17βHSD enzymes. In contrast no there did not appear to be estrogenic effects. In conclusion, low dose Tri™ did not appear to exhibit endocrine disruptive properties in vitro. These doses are comparable to those recommended for consumer use. The adverse effect elicited by the high dose Tri™ could be used as a marker for overdose, provided that basal levels of the hormones are known. These positive results indicates endocrine safety in vitro, but in vivo data is required for conclusive confirmation.

AFRIKAANSE OPSOMMING: Depressie word deur die Wêreldgesondheidsorganisasie (WHO) erken as die grootste oorsaak van ongeskiktheid, wat wêreldwyd sowat 300 miljoen mense raak. Tot op datum word antidepressante as die eerste stap in die behandelingstrategie voorgeskryf. Om ‘n toepaslike antidepressant te vind is dikwels 'n langdurige proses en gaan gewoonlik gepaard met newe-effekte. ‘n Meestal onverwagte newe-effek is verminderde seksuele funksie, wat moontlik die depressie kan vererger, of die pasiënt ‘n rede gee om hul medikasie minder as voorgeskryf te gebruik. Sceletium tortuosum is 'n inheemse Suid-Afrikaanse plant, wat beide antidepressante en teen-angstigheid eienskappe het. Alhoewel die meganisme(s) van aksie van die plant nog nie geheel bekend is nie, is daar twee modelle wat dit probeer verduidelik. Dit word beweer dat S.tortuosum aan die serotonien reseptor bind om die heropname van serotonien te verhoed, en werk dus soos ‘n selektiewe serotonien heropname inhibeerder (SSRI) . Die tweede model beweer dat S.tortuosum help met die vrystelling van die monoamien neuroseinoordraer uit die presinaptiese neuron, en dus soos 'n monoamien vrystellingsagent (MRA) werk. Daar is 'n sterk verband tussen depressie en die hiperaktivering van die hipotalamus-pituïtêre-adrenale (HPA) as. Beide antidepressante en MRA's word geassosieer met endokriene ontwrigting. Hoewel ʼn veiligheidstudie bevind het dat S.tortuosum veilig is vir menslike gebruik, is dit onlangs gerapporteer dat daar ‘n moontlikheid is dat dit sekere steroïedhormone, soos androstenedioon (A4) en testosteroon (T), kan verminder, maar beslissende opmerkings kon nie geformuleer word nie. Die doel van hierdie proefskrif was om vas te stel of Trimesemine™ (Tri; mesembrine ryk S.tortuosum) moontlik ʼn nadelige effek op steroïedsintese in die testis en/of ovarium het. HEK293 selle is getransfekteer met 17βHSD tipe 5 (17βHSD5) cDNA, wat lei tot die ooruitdrukking van die 17βHSD5 ensiem, wat verantwoordelik is vir die omskakeling van A4 na T. Die selle is voorafbehandel met Tri™ teen 'n bewese effektiewe dosis (0.01 mg / ml) en hoë (0.5 mg / ml) dosis. Na 24 uur was die supernatant verwyder en die monsters was ontleed deur gebruik te maak van UPC2-MS/MS. In ʼn opvolgeksperiment is primêre gemengde muistestis kulture opgestel. Testisse is verwyder, ontkapsel en 'n gemengde kultuur was uitgeplaat. Na 24 uur is die selle behandel met lae en hoë dosisse Tri™. 24 uur later is die supernatant verwyder en die monsters was geanaliseer deur behulp van UPLC-MS / MS. Die ovaria is verwyder, fyngemaak en uitgeplaat. Na 24 uur is die selle behandel met effektiewe en hoë dosisse Tri™. 24 uur later is die supernatant verwyder en die monsters was geanaliseer deur behulp van UPC2-MS / MS. By die laer dosis was daar geen nadelige effek op A4, T en estradiool (E2) nie. Die hoë dosis Tri™ het egter vlakke van A4 (testikulêre gemengde kultuur) en T (HEK293 selle) verminder, moontlik deur inhibisie van 3βHSD of 17βHSD ensieme. Daar was geen verandering in die vlakke van E2 gesien nie. Ten slotte blyk dit dat laer dosis Tri™ nie in vitro endokriene ontwrigtende eienskappe vertoon nie. Hierdie dosisse is vergelykbaar met dié wat aanbeveel word vir verbruikersgebruik. Die nadelige effek wat deur verhoogde dosisse van Tri™ verkry word, kan moontlik as 'n merker vir oordosis gebruik word, indien die basale vlakke van die hormone bekend is. Alhoewel die huidige studie dui op endokriene veiligheid in vitro, is in vivo data nodig vir voldoende bevestiging hiervan.

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