In the exploration into new therapeutic agents for human disease, medicinal herbs offer an enormous resource due to their wide range of biologically active components. However, because of these biologically active components, medicinal herbs can also have toxic side effects. The focus of this thesis is the effect of herbal therapies, both good and bad, on chronic kidney disease (CKD) and tubulointerstitial fibrosis. Tubulointerstitial fibrosis is considered one of the defining characteristics of CKD. In Chapter 1, the literature regarding the pathogenesis of tubulointerstitial fibrosis is reviewed, beginning with the mechanisms of its development, the main structural and functional features, and the molecular mediators. The structural features include activation of resident fibroblasts and transition of tubular epithelial cells into myofibroblasts, deposition of extracellular matrix proteins, increased apoptosis of normal cells of the renal nephron and development of tubular atrophy, increased renal oxidative stress, and hypoxia of renal tissues. Molecular mediators that are explored include angiotensin II, transforming growth factor-ß1 and numerous other cytokines and growth factors. Pharmacological manipulation of these features and their molecular mediators for regression of tubulointerstitial fibrosis is then discussed. Currently, the gold standard of therapy for people with CKD is blockade of the renin-angiotensin-aldosterone system with angiotensin converting enzyme inhibitors (ACEIs) and/or angiotensin receptor blockers (ARBs). Because of the complexity of the pathogenesis of renal fibrosis and the multiple mechanisms by which ACEIs and ARBs work, this portion of the thesis focuses on the qualities that additional agents should have to complement their actions. These additional agents could work by decreasing oxidative damage, by decreasing fibroblast numbers through apoptosis, through the interruption of inflammatory, fibrotic mediators, by increasing anti-inflammatory mediators or through other mechanisms. The literature review therefore continues with a discussion of the historical use of medicinal herbs in genitourinary pathologies and the known contributions that medicinal herbs can make to the treatment or development of tubulointerstitial fibrosis and CKD. From this review, a large number of herbs were identified as having traditional use in renal disorders or as being of interest, currently, to researchers of renal pathologies. However, much information is lacking regarding the mechanisms by which the hypothesised benefits occur, making it impossible to assess which herb(s) may offer valuable additive support or alternative treatments to the therapies currently given to people with CKD. Furthermore, there is a lack of information regarding toxicity of these herbs; many herbs have never been assessed in cell culture or in animal toxicity studies. It was apparent that preliminary in vitro work was necessary before in vivo pharmacological work could be undertaken. This thesis, therefore, aimed to test the following hypotheses: (1) That medicinal herbs used currently for treatment of renal dysfunction have high anti-oxidant properties that can be further enhanced by specific extraction processes; (2) That the in vitro testing of selected extracts from medicinal herbs, identified in (1), will reveal some anti-oxidant benefits or indications of toxicity that need careful analysis in animal studies; (3) That careful in vivo testing of specific toxic medicinal herbs identified in these leadup studies will define specific pathological processes that predict an outcome of CKD; and (4) That careful in vivo testing of selected medicinal herbs, used in conjunction with more conventional medicines for CKD, will show an additive benefit when used to ameliorate development of CKD induced using an established animal model. The subsequent laboratory work was designed to test the validity of these hypotheses and the results are then presented in Chapters that each comprise a publication. The aim of Chapter 2 was to present a systematic analysis of the oxidant properties of 55 medicinal herbs that have been used traditionally to treat kidney and urinary disorders or have been of recent interest to researchers of renal disorders. Since different extraction processes yield different constituents, each of the herbs was sequentially extracted with three solvents of decreasing polarity. An assay was performed on each of the fractions to determine the oxygen radical absorbance capacity. The aim of Chapter 3 was to test the benefit or otherwise of each of the three extracts of the chosen herbs using an in vitro cell study. Each extract was tested for potential toxic, apoptotic, mutagenic and antioxidant activity on normal mammalian renal tubular epithelial cells (NRK-52E). The effect of the extracts on renal fibroblasts (NRK-49F) was also analysed. Several specific hypotheses arose from the combination of the systematic analyses and the literature review regarding benefits and toxicities of a number of the extracts. The subsequent in vivo work was designed to test the validity of two of these hypotheses. The aim of Chapter 4 was to test the hypotheses developed from the results of the previous Chapter. The herb Dioscorea villosa had demonstrated extreme cytotoxicity to mammalian renal epithelial cells and had caused transdifferentiation of epithelial cells into fibroblasts. An in vivo rodent model was used to test chronic dosage with this herb and its toxicity and predisposition for induction of CKD verified. The aim of Chapter 5 was to determine whether a herbal preparation (Angelica sinensis and Astragalus membranaceus) that had some support from the literature and the results from Chapters 2 and 3, could complement the actions of ACEIs in a rodent model of renal fibrosis (unilateral ureteral obstruction). The combination of herbal medicines and the ACEI was significantly more effective than the ACEI alone in ameliorating several characteristics of CKD development. To conclude the thesis, Chapter 6 provides an overview discussion of the results and a critical analysis of the methods used. Further, Chapter 6 looks towards future experiments that are planned to further resolve issues of concern about effects on renal health from use of medicinal herbs. .
| Identifer | oai:union.ndltd.org:ADTP/279261 |
| Creators | Kenneth Wojcikowski |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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