Browsing by Author "Pretorius, Lesha"

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    The effect of altered trace aminergic signalling and estrogen on intestinal inflammation, within an IBS context
    (Stellenbosch : Stellenbosch University, 2022-12) Pretorius, Lesha; Smith, Carine; Van Staden, Anton du Preez; Stellenbosch University. Faculty of Science. Dept. of Physiological Sciences.
    ENGLISH ABSTRACT: Irritable bowel syndrome (IBS) is a widespread (≈10% global prevalence) female predominant functional gastrointestinal (GI) disorder. While it is known that IBS is underpinned by relative microbial dysbiosis and chronic microinflammation, current therapeutic strategies often only provide transient symptomatic relief (with relative neglect of inflammation) and are thus unsatisfactory in many cases. As such, the development of targeted therapeutics to alleviate GI inflammation and consequential symptomologies are required. We suggest that the trace aminergic system, which connects several IBS risk factors (sex, dysbiosis, diet, inflammation and anxiety), may be a pretermitted regulatory system that could be manipulated as a therapeutic target. In addition, existing data supports an interpretation of sex dependence in trace aminergic signalling. As such, fluctuations of female reproductive hormones, such as 17β-estradiol (E2), may alter subsequent signalling cascades. Therefore, this thesis aimed to investigate the GI modulatory effects of selected trace amines (TAs), with consideration of the context of female predominance. To elucidate mechanisms at play, a multidisciplinary approach was necessitated. As such, multiple model systems were utilised, including both in vitro (microbial cultures and human tissue cultures) and in vivo (zebrafish larval) models. In this regard, microbial (probiotic and commensal strains) culturing techniques, coupled with the development of a novel multianalyte mass spectrometry methodology, allowed for the accurate assessment of microbial TA generation. Indeed, data generated in these studies highlighted firstly, the dependence of probiotic secretome profile on host hormonal status, and secondly, that specific rooibos supplementation strategies may be able to negate E2-induced alterations in secretome TA profiles, both of which have important implications in TA-associated symptom management in females with GI disorders. Data generated in vitro in HT-29 colon adenocarcinoma cells and in vivo in zebrafish larvae, in which the effects of increased TA load were assessed, demonstrated potential differences in the mechanisms of actions between TYR and AGM in particular. In this regard, extensive occludin redistribution was observed following TYR-exposure, which was associated with increased reactive oxygen species and pro-inflammatory cytokine levels, as well as tight junction disruption – an outcome prevented by E2 treatment. In contrast, AGM administration promoted the colocalization of ZO-1 and occludin to promote tight junction integrity but was also associated with risk of pro-oxidant damage when AGM metabolism was insufficient. In conclusion, this dissertation contributes significantly to our understanding of the role of TAs in GI physiology, consistently illustrating (across in vitro and in vivo models), that while some TAs may promote disease symptomology, others may have therapeutic benefit when responsibly administered. From a therapeutics standpoint, data presented here crucially highlights the importance of dosage and administration optimisation to achieve benefit and minimize adverse side effects when targeting TA signalling in the context of functional GI disease. In addition, potential mechanistic insights by which E2 - or rather the transient cyclic lack thereof - is associated with trace aminergic signalling, was elucidated.
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    Platelet activity and hypercoagulation in type 2 diabetes
    (BMC (part of Springer Nature), 2018-11-02) Pretorius, Lesha; Thomson, Greig J. A.; Adams, Rozanne C. M.; Nell, Theo A.; Laubscher, Willem A.; Pretorius, Etheresia
    Background: A strong correlation exists between type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD), with CVD and the presence of atherosclerosis being the prevailing cause of morbidity and mortality in diabetic populations. T2DM is accompanied by various coagulopathies, including anomalous clot formation or amyloid fibrin(ogen), the presence of dysregulated inflammatory molecules. Platelets are intimately involved in thrombus formation and particularly vulnerable to inflammatory cytokines. Methods: The aim of this current study was therefore to assess whole blood (hyper)coagulability, platelet ultrastructure and receptor expression, as well as the levels of IL-1β, IL-6, IL-8 and sP-selectin in healthy and diabetic individuals. Platelet morphology was assessed through scanning electron microscopy (SEM), while assessment of GPIIb/IIIa receptor expression was performed with confocal microscopy and flow cytometry with the addition of FITC-PAC-1 and CD41-PE antibodies. IL-1β, IL-6 and IL-8 and sP-selectin levels were assessed using a multiplex assay. Results: In T2DM there is significant upregulation of circulating inflammatory markers, hypercoagulation and platelet activation, with increased GPIIb/IIIa receptor expression, as seen with flow cytometry and confocal microscopy. Analyses showed that these receptors were additionally shed onto microparticles, which was confirmed with SEM. Conclusions: Cumulatively, this provides mechanistic evidence that pathological states of platelets together with amyloid fibrin(ogen) in T2DM, might underpin an increased risk for cardiovascular events.
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    The trace aminergic system : a gender-sensitive therapeutic target for IBS?
    (BioMed Central, 2020-09-28) Pretorius, Lesha; Smith, Carine
    Due to a lack of specific or sensitive biomarkers, drug discovery advances have been limited for individuals suffering from irritable bowel syndrome (IBS). While current therapies provide symptomatic relief, inflammation itself is relatively neglected, despite the presence of chronic immune activation and innate immune system dysfunction. Moreover, considering the microgenderome concept, gender is a significant aetiological risk factor. We believe that we have pinpointed a “missing link” that connects gender, dysbiosis, diet, and inflammation in the context of IBS, which may be manipulated as therapeutic target. The trace aminergic system is conveniently positioned at the interface of the gut microbiome, dietary nutrients and by-products, and mucosal immunity. Almost all leukocyte populations express trace amine associated receptors and significant amounts of trace amines originate from both food and the gut microbiota. Additionally, although IBS-specific data are sparse, existing data supports an interpretation in favour of a gender dependence in trace aminergic signalling. As such, trace aminergic signalling may be altered by fluctuations of especially female reproductive hormones. Utilizing a multidisciplinary approach, this review discusses potential mechanisms of actions, which include hyperreactivity of the immune system and aberrant serotonin signalling, and links outcomes to the symptomology clinically prevalent in IBS. Taken together, it is feasible that the additional level of regulation by the trace aminergic system in IBS has been overlooked, until now. As such, we suggest that components of the trace aminergic system be considered targets for future therapeutic action, with the specific focus of reducing oxidative stress and inflammation.