Neuro- and immunomodulatory effects of Sceletium tortuosum

Bennett, Amber Clare (2018-03)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Chronic lifestyle stress translates to chronic physiological and psychological conditions. Continual stress-response activation plays a key role in the development of inflammatory diseases, such as diabetes, Alzheimer’s disease, anxiety and depression. It is known that inflammatory cytokines produced in the periphery can cross the blood-brain barrier, resulting in release of neurotoxins that can lead to demise of central nervous system integrity. Pro-inflammatory cytokines are also responsible for undesired modulation of serotonin signalling and receptor expression. Since two of the major systems implicated in the aetiology of neurodegeneration and psychological illness are central inflammation and maladaptations in serotonergic signalling, it is important to investigate potential therapeutic targets in this context. A high-mesembrine Sceletium tortuosum extract (Trimesemine™) was shown to possess cytoprotective and mild anti-inflammatory properties in human monocytes, and inhibitory effects on adrenal glucocorticoid synthesis. Additionally, it was recently confirmed that claimed selective serotonin reuptake inhibition (SSRI) properties of Sceletium tortuosum are, in fact, secondary to its monoamine-releasing agent (MRA) capacity. A high-Δ7-mesembrenone Sceletium extract has also shown promising anti-oxidant capacity and anti-cancer effects. In this thesis, two models were employed to further investigate the therapeutic potential of Sceletium tortuosum in maladaptations to chronic stress. Firstly, the central immunomodulatory effects of two Sceletium tortuosum extracts, high-mesembrine extract, Trimesemine™, and high-Δ7-mesembrenone extract, Delta-7, were investigated. Human astrocytes were pre-treated with each extract for 30 minutes, before exposure to Escherichia coli lipopolysaccharide for 23.5 hours (in the presence of treatment). Cytotoxicity, mitotoxicity and cytokine responses (basally and in response to inflammatory stimulus) were assessed. Total polyphenol content, antioxidant capacity and selected neural enzyme inhibition capacity were also assessed for both extracts. Trimesemine™ exerted cytoprotective (p<0.0001) and anti-inflammatory effects (p<0.05). In contrast, Delta-7 exhibited potent antioxidant effects (p<0.05), although with relatively higher risk of adverse effects with overdose. The second model employed was a platelet model of the central serotonergic system, to investigate the effects of high-mesembrine Sceletium on serotonin system parameters in anxious and non-anxious individuals. Modulators of the serotonergic system – an SSRI (citalopram) and a mild MRA (Trimesemine™) – were used to investigate the platelet model in anxiety. Isolated platelets from anxious and non-anxious subjects were exposed to a known activator (calcium ionophore A23187) and each modulator for 15 minutes. Cytokine secretion and changes in platelet serotonergic system activity were assessed. Serotonin transporter expression was down-regulated in state anxiety in response to citalopram, validating the platelet model in this context. Basal platelet serotonin levels in individuals exhibiting state/trait anxiety were lower than no-anxiety controls (p<0.05), while platelet activation state was increased (p<0.05). Trimesemine™ was again confirmed to have anti-inflammatory effect by its modulation of pro- and anti-inflammatory cytokine secretion. We conclude that both Sceletium tortuosum extracts may be employed as either a preventative supplement or complimentary treatment in the context of chronic immune-mediated disease. This study has also highlighted key differences between anxious and non-anxious individuals, and between anxiety type, in terms of serotonergic system parameters and inflammatory responses, suggesting diagnostic potential for the platelet model.

AFRKAANSE OPSOMMING: Chroniese leefstylstres lei to chroniese fisiologiese en sielkundige toestande. Voortdurende aktivering van die stress respons speel ‘n groot rol in die ontwikkeling van inflammatoriese siektes/toestande, soos diabetes, Alzheimer se siekte, angstigheid en depressie. Dit is bekend dat sitokiene wat in die periferie vervaardig word, die bloed-breinskans kan oorsteek en kan lei tot die afskeiding van neurotoksiene wat weer die integriteit van die sentrale senuweestelsel kan aftakel. Pro-inflammatoriese sitokiene is ook vir ongewenste veranderings in reseptor uitdrukking en serotonien seinoordrag verantwoordelik. Aangesien sentrale inflammasie en wanaangepaste serotonien seinoordrag sentraal staan tot die ontwikkelling van neurodegenerasie en psigologiese siektes, is dit bepaald belangrik om moontlike terapeutiese teikens in hierdie konteks te ondersoek. ‘n Sceletium tortuosum ekstrak met hoë mesembrien inhoud (Trimesemine™) het bewese sitobeskermende en ligte anti-inflammatoriese eienskappe, soos geïllustreer in monosiete, asook beperkende effekte op bynier glukokortikoïed sintese. Onlangse navorsing het ook bewys dat die selektiewe serotonien heropname inhibisie (SSRI) effek wat algemeen aanvaar word vir die ekstrak, eintlik sekondêr is tot ‘n mono-amien vrystellings (MRA) funksie. In voorlopige studies het ‘n Sceletium tortuosum ekstrak met hoë Δ7-mesembrenoon inhoud ook belowende anti-oksidant en teenkankereffekte getoon. In hierdie tesis word twee modelle gebruik om die terapeutiese potensiaal van Sceletium tortuosum in die konteks van wanaanpassings as gevolg van chroniese stres, verder toe te lig. Eerstens is die sentrale immuun-modulerende effekte van twee Sceletium tortuosum ekstrakte – een met hoë mesembrien inhoud, Trimesemine™, en een met hoë Δ7-mesembrenoon inhoud, Delta-7, ondersoek. Menslike astrosiete is vir 30 minute voorafbehandel met elke ekstrak, waarna dit vir 23.5 uur aan Escherichia coli lipopolisakkaried blootgestel is (in die teenwoordigheid van ekstrak). Sitotoksisiteit, mitotoksisiteit en sitokienreaksies (beide basal en in reaksie op die inflammatoriese stimulus) is bepaal. Totale polifenoolinhoud, anti-oksidant kapasiteit en inhibisie van relevante neurale ensieme is ook vir beide ekstrakte bepaal. Trimesemine™ het sitobeskermende (p<0.0001) en anti-inflammatoriese (p<0.05) effekte getoon. In kontras daarmee, het Delta-7 sterk anti-oksidant effekte getoon (p<0.05), alhoewel dit met ‘n relatiewe hoër risiko vir ongewenste effekte van oordosering verbind kan word. Die tweede model was ‘n plaatjie-model van die sentrale serotonergiese sisteem, waarmee die effek van hoë-mesembrien Sceletium op parameters van die serotonien sisteem in beide angstige en nie-angstige individue bepaal is. Moduleerders van die serotonergiese sisteem – ‘n SSRI (citalopram) en ‘n ligte MRA (Trimesemine™) – is aangewend om die plaatjiemodel in die konteks van angstigheid te toets. Plaatjies geïsoleer uit angstige en nie-angstige skenkers is vir 15 minute saam met ‘n bekende aktiveerder (calcium ionophore A23187) aan elke moduleerder blootgestel. Sitokien afskeiding en veranderinge in plaatjie parameters wat die serotonien sisteemaktiwiteit aandui, is bepaal. Serotonien vervoerreseptor (SERT) uitdrukking is afgereguleer na citalopram behandeling, in toestand-angstigheid, wat die plaatjie-model bekragtig. Basale plaatjie serotonienvlakke was laer in individue met beide toestand- en eienskap-angstigheid, in vergelyking met nie-angstige kontroles (p<0.05), terwyl plaatjie aktiveringstatus verhoog was (p<0.05). Anti-inflammatoriese effek van Trimesemine™ is weer bevestig met die modulering van pro- en anti-inflammatoriese sitokiene. Ten slotte bevind ons dat beide Sceletium tortuosum ekstrakte as voorkomende of komplimentêre behandeling in die konteks van chroniese siekte gebruik kan word. Hierdie studie lig ook belangrike verskille tussen angstige en nie-angstige individue, asoos tipes angstigheid, uit, in terme van parameters van die serotonien sisteem en inflammatoriese reaksies, wat diagnostiese potensiaal van die plaatjie-model mag aandui.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103396
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