Hypoxis Hemerocallidea)
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Pharmaceutical Analysis and Drug Interaction Studies: African Potato (Hypoxis hemerocallidea) A Thesis Submitted in Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY of RHODES UNIVERSITY By VIPIN DEVI PRASAD PURUSHOTHAMAN NAIR January 2006 Abstract In order for a medicinal product to produce a consistent and reliable therapeutic response, it is essential that the final composition of the product is invariable and that the active ingredient/s is/are present in appropriate, non-toxic amounts. However, due to the complexity involved in the standardization of natural products, quality control (QC) criteria and procedures for the registration and market approval of such products are conspicuously absent in most countries around the world. African Potato (AP) is of great medical interest and this particular plant has gained tremendous popularity following the endorsement by the South African Minister of Health as a remedy for HIV/ AIDS patients. Very little information has appeared in the literature to describe methods for the quantitative analysis of hypoxoside, an important component in AP. It has also been claimed that sterols and sterolins present in AP are responsible for its medicinal property but is yet to be proven scientifically. To-date, no QC methods have been reported for the simultaneous quantitative analysis of the combination, β- sitosterol (BSS)/ stigmasterol (STG)/ stigmastanol (STN), purported to be present in preparations containing AP. The effect of concomitant administration of AP and other herbal medicines on the safety and efficacy of conventional medicines has not yet been fully determined. Amongst the objectives of this study was to develop and validate quantitative analytical methods that are suitable for the assay and quality control of plant material, extracts and commercial formulations containing AP. ii Hypoxoside was isolated from AP and characterized for use as a reference standard for the quality control of AP products and a stability-indicating HPLC/ UV assay method for the quantitative determination of hypoxoside was developed. In addition, a quantitative capillary zone electrophoretic (CZE) method was developed to determine hypoxoside, specifically for its advantages over HPLC. A HPLC method was also developed and validated for the quantitative analysis of BSS, STG and STN in commercially available oral dosage forms containing AP material or extracts thereof. The antioxidant activity of an aqueous extract of lyophilized corms of AP along with hypoxoside and rooperol were investigated. In comparison with the AP extracts and also with hypoxoside, rooperol showed significant antioxidant activity. The capacity of AP, (extracts, formulations, hypoxoside and rooperol as well as sterols to inhibit in vitro metabolism of drug substrates by human cytochrome P450 (CYP) enzymes such as CYP 3A4, 3A5 and CYP19 were investigated. Samples were also assessed for their effect on drug transport proteins such as P-glycoprotein (P-gp). Various extracts of AP, AP formulations, stigmasterol and the norlignans, in particular the aglycone rooperol, exhibited inhibitory effects on CYP 3A4, 3A5 and CYP19 mediated metabolism.These results suggest that concurrent therapy with AP and other medicines, in particular antiretroviral drugs, can have important implications for safety and efficacy. Large discrepancies in marker content between AP products were found. Dissolution testing of AP products was investigated as a QC tool and the results also revealed inconsistencies between different AP products. iii Acknowledgements With the blessings of my parents and the Almighty, I would like to dedicate this thesis to my supervisor, Prof. I. Kanfer, who commands my great respect. I am indebted to him for the patience and care with which he has nurtured my research, and for the invaluable opportunities he has provided me that have stimulated my growth. I convey my deepest thanks to him for ensuring that I have adequate financial resources to complete this research. I would also like to thank the following people: Dr. BC Foster, Prof. JT Arnason, (Centre for Research in Biopharmaceuticals and Biotechnology, University of Ottawa, Ottawa, Ontario, Canada) and Mr. Ed J Mills (The Canadian College of Naturopathic Medicine, Toronto, Ontario, Canada), for providing me with excellent facilities and opportunities at the Department of Cellular and Molecular Medicine, University of Ottawa, Canada. The time spent in their lab has been pivotal in my research. Mr. Andy Soper, Dr. Denzil Beukes and Dr. Vikash Sewram, for their expertise regarding NMR and LC-MS. Prof. Santy Daya and Dr. Mike Skinner for their constant encouragement. Mr. Leon Purdon, Sheena, Linda and Dave, for always promptly attending to my laboratory requirements and thus ensuring that I have been able to conduct my research timeously. Mr. Tich Samkhange, for his excellent technical support. Prof. Rod Walker for his constructive criticism which has been helpful throughout my studies. iv To Rhodes University and the Medical Research Council, South Africa for their financial aid, without which this research would not have been possible. Dr. Carl Albrecht, for the generous donation of phytochemicals that were essential to my work. I extend my sincerest gratitude to my lab colleagues, especially Ami Dairam, Mary Jean, Sandile, Dr. Ali Mohammadhi and Layla Cassim, for their support and constant encouragement. My dear friends Syd Ramdhani, Srinivas Patnala, Sunitha Srinivas, as well as their families, to whom I owe so much. They have been a constant source of support and laughter, and have helped me to feel at home in Grahamstown and to overcome the challenges of being so far away from my family. I wish to express my deepest gratitude to my sister, parents and family, for being my pillar of strength, an unending source of wisdom and love, and for inspiring every step that I have taken in my life. Above all, I thank God for being with me, and for blessing me with a lovely fiancée, Lekshmi H Nair, who has been incredibly supportive and understanding throughout the period of my studies. v TABLE OF CONTENTS ABSTRACT ii ACKNOWLEGEMENTS iv TABLE OF CONTENTS vi LIST OF FIGURES xiv LIST OF TABLES xviii LIST OF ABBREVIATIONS xix LIST OF UNITS xxv CHAPTER 1 Introduction 1 1.1 Quality, Safety and Efficacy of Natural Products 3 1.1.1 Quality of Natural Products 3 1.1.2 Safety of Natural Products 5 1.1.2.1 Adverse Effects 6 1.1.2.2 Adulteration and Contamination of Natural Products 7 1.1.2.3 Interactions with Orthodox Medicines 8 1.1.3 Efficacy of Natural Products 9 1.2 Regulatory Aspects and Alternative Medicines 10 1.2.1 Definitions 10 1.2.2 Regulatory Situation of Complementary and Alternative Medicine (CAM) in Several Countries 17 1.2.2.1 The United States of America (USA) 17 1.2.2.2 Canada 18 1.2.2.3 Europe 20 1.2.2.4 United Kingdom (UK) 22 1.2.2.5 Asia 23 1.2.2.6 Australia 25 1.2.2.6.1 Pre-market Assessment 26 1.2.2.6.2 Licensing of Manufacturers 26 1.2.2.6.3 Post-market Vigilance 26 1.2.2.7 South Africa 27 1.3 Conclusions 29 vi CHAPTER 2 African Potato (Hypoxis hemerocallidea) 32 2.1 Background 32 2.1.1 Vernacular Names 32 2.2 Introduction 33 2.2.2 Prominent Species of the Genus Hypoxis 34 2.2.2.1 List of Prominent Species 35 2.2.3 Traditional Use of the Plants under the Genus Hypoxis 38 2.2.4 Extracts of Hypoxis Genus and Biological Activity 39 2.2.4.1 The Extracts of Hypoxis 40 2.3 Phytochemical Constituents in Hypoxis Species 43 2.3.1 Chemical Properties of Hypoxoside, Rooperol, Sterols, Stanols and Sterolins 49 2.4 Pharmacological Properties of Hypoxoside, Rooperol, Sterols, Stanols and Sterolins 53 2.4.1 Sterols, Stanols and Sterolins 53 2.4.2 Hypoxoside and Rooperol 56 2.4.2.1 Inhibitory Activity on Cell Growth (Cytotoxicity) 56 2.4.2.1.1 Mechanism of Cytotoxic Activity 57 2.4.2.2 Antioxidant Activity 58 2.4.2.3 Anti-HIV Activity 59 2.4.2.4 Analgesic Activity 60 2.4.2.5 Cardiovascular Effects 60 2.4.2.6 Miscellaneous Activities and Effects 61 2.5 Pharmacokinetics 61 2.5.1 Animal Studies 61 2.6 Clinical Studies 63 2.7 Patents 65 2.8 Formulations and Marketing of AP Products 68 CHAPTER 3 Extraction, Isolation and Characterization of Hypoxoside 90 3.1 Introduction 90 3.2 Material and Methods 91 3.2.1 Reagents 91 3.2.2 Instrumentation 92 3.3 Experimental 92 vii 3.3.1 Raw Material Collection 92 3.3.2 Extraction 93 3.3.3 Isolation 94 3.4 Characterization 95 3.4.1 Appearance 95 3.4.2 Determination of Melting Point 96 3.4.3 Fourier Transform Infrared (FTIR) Spectroscopy 97 3.4.4 UV Absorption Spectroscopy 100 3.4.5 Chromatographic Purity 101 3.4.6 LC-MS Analysis 101 3.4.7 Nuclear Magnetic Resonance (1H and 13C NMR) 105 3.5 Conclusions 109 CHAPTER 4 High-Performance Liquid Chromatography (HPLC) 110 4.1 Introduction 110 4.2 Background and Objectives 112 4.3 Stability Studies 113 4.4 Materials and Methods 114 4.4.1 Instrumentation 114 4.4.2 Reagents 114 4.5 Experimental 115 4.5.1 Method Development 115 4.5.2 Method Validation 119 4.5.2.1 Sample Treatment 119 4.5.2.2 Hypoxoside Reference Standard 120 4.5.2.3 Preparation and Standard Solutions 120 4.5.2.4 Sample Extraction 120 4.5.2.5 Stability of Hypoxoside Solutions 122 4.5.3 Forced Degradation Studies 122 4.5.3.1 Stress Testing of Hypoxoside 122 4.5.3.2 Stress Conditions 125 4.6 Results and Discussion 126 4.6.1 Method Validation 126 4.6.1.1 Linearity 126 4.6.1.2 Limits of Detection (LOD) and Quantification (LOQ) 126 4.6.1.3 Accuracy and Precision 126 4.6.1.4 Recovery 128 viii 4.6.2 Analysis of Samples 129 4.6.2.1 Extraction