In vitro drug-herb interaction potential of African medicinal plant products used by Type II diabetics
- Authors: Fang, Yuan Yuan
- Date: 2011
- Subjects: Materia medica, Vegetable -- South Africa , Drugs -- Therapeutic use , Drug-herb interactions -- South Africa , Non-insulin-dependent diabetes -- South Africa , Non-insulin-dependent diabetes -- Treatment -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10317 , http://hdl.handle.net/10948/1341 , Materia medica, Vegetable -- South Africa , Drugs -- Therapeutic use , Drug-herb interactions -- South Africa , Non-insulin-dependent diabetes -- South Africa , Non-insulin-dependent diabetes -- Treatment -- South Africa
- Description: In Africa, use of medicinal plants for the treatment of diabetes is very common. However, efficacy on co-administering of medicinal plants with therapeutic drugs hasn't been fully determined, especially for African medicinal plants. The current study focused on assessing the in vitro modulation effects of three popular African medicinal plants, namely: Aloe ferox, Sutherlandia frutescens and Prunus africana (including five commercial preparations containing these medicinal plants) on two of the most important anti-diabetic drug metabolising enzymes, Cytochrome P450 (CYP450) 2C9 and CYP3A4 and a key drug efflux transporter, P-glycoprotein (P-gp). Vivid® microsome-based screening kits were used to assess inhibitory potency of plants preparations on CYP2C9 and CYP3A4 enzymes activities. The study showed that P. africana was a more potent inhibitor of CYP2C9 and CYP3A4 activity than the corresponding positive controls Ginkgo biloba and St. John's wort, which are known to cause clinically significant drug-herb interactions. S. frutescens leaf extract demonstrated potent to moderate inhibition on both the tested CYP activities, while its commercial products (Promune® and Probetix®) possessed moderate to mild inhibitory effects on the activities of both CYPs. Potent inhibitory effect on CYP2C9 and CYP3A4 was seen with Aloe Ferox®. Prosit® and Aloes powder® showed potent to moderate inhibition on CYP2C9 activity and moderate to mild inhibition on CYP3A4 activity. In addition to CYP450 activity, the present study also investigated the effects of the selected medicinal plant products on the activity of the main drug efflux protein, P-gp. A screening assay was specifically developed to assess the potential for herbal remedies to interact with P-gp mediated drug absorption. The assay is based on the principle of the reversal of drug resistance in modified Caco-2 cells specifically altered to express high iv efflux protein activity. These cells display a multidrug resistance phenotype and the addition of a plant extract containing a P-gp inhibitor or substrate will inhibit or compete with any cytotoxic drug and consequently reverse the drug resistance. The suitability of the assay was confirmed using a known P-gp inhibitor. The study observed that the anti-proliferation effect of vinblastine was significantly enhanced in vinblastine-resistant Caco-2 cells, which have high P-gp expression, when they were exposed to the selected African herbal preparations. This observation indicates that the studied plant preparations may alter P-gp functionality and therefore lead to interference with the absorption of co-administered drugs. The outcomes of this study provide useful information on whether there are any potential drug-herb interactions between the commonly used African medicinal plants and oral anti-diabetic drugs, at the level of CYP and P-gp drug metabolism and could contribute to better therapeutic management of Type II diabetics. However these predicted interactions will need to be verified in a clinical setting.
- Full Text:
- Date Issued: 2011
- Authors: Fang, Yuan Yuan
- Date: 2011
- Subjects: Materia medica, Vegetable -- South Africa , Drugs -- Therapeutic use , Drug-herb interactions -- South Africa , Non-insulin-dependent diabetes -- South Africa , Non-insulin-dependent diabetes -- Treatment -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10317 , http://hdl.handle.net/10948/1341 , Materia medica, Vegetable -- South Africa , Drugs -- Therapeutic use , Drug-herb interactions -- South Africa , Non-insulin-dependent diabetes -- South Africa , Non-insulin-dependent diabetes -- Treatment -- South Africa
- Description: In Africa, use of medicinal plants for the treatment of diabetes is very common. However, efficacy on co-administering of medicinal plants with therapeutic drugs hasn't been fully determined, especially for African medicinal plants. The current study focused on assessing the in vitro modulation effects of three popular African medicinal plants, namely: Aloe ferox, Sutherlandia frutescens and Prunus africana (including five commercial preparations containing these medicinal plants) on two of the most important anti-diabetic drug metabolising enzymes, Cytochrome P450 (CYP450) 2C9 and CYP3A4 and a key drug efflux transporter, P-glycoprotein (P-gp). Vivid® microsome-based screening kits were used to assess inhibitory potency of plants preparations on CYP2C9 and CYP3A4 enzymes activities. The study showed that P. africana was a more potent inhibitor of CYP2C9 and CYP3A4 activity than the corresponding positive controls Ginkgo biloba and St. John's wort, which are known to cause clinically significant drug-herb interactions. S. frutescens leaf extract demonstrated potent to moderate inhibition on both the tested CYP activities, while its commercial products (Promune® and Probetix®) possessed moderate to mild inhibitory effects on the activities of both CYPs. Potent inhibitory effect on CYP2C9 and CYP3A4 was seen with Aloe Ferox®. Prosit® and Aloes powder® showed potent to moderate inhibition on CYP2C9 activity and moderate to mild inhibition on CYP3A4 activity. In addition to CYP450 activity, the present study also investigated the effects of the selected medicinal plant products on the activity of the main drug efflux protein, P-gp. A screening assay was specifically developed to assess the potential for herbal remedies to interact with P-gp mediated drug absorption. The assay is based on the principle of the reversal of drug resistance in modified Caco-2 cells specifically altered to express high iv efflux protein activity. These cells display a multidrug resistance phenotype and the addition of a plant extract containing a P-gp inhibitor or substrate will inhibit or compete with any cytotoxic drug and consequently reverse the drug resistance. The suitability of the assay was confirmed using a known P-gp inhibitor. The study observed that the anti-proliferation effect of vinblastine was significantly enhanced in vinblastine-resistant Caco-2 cells, which have high P-gp expression, when they were exposed to the selected African herbal preparations. This observation indicates that the studied plant preparations may alter P-gp functionality and therefore lead to interference with the absorption of co-administered drugs. The outcomes of this study provide useful information on whether there are any potential drug-herb interactions between the commonly used African medicinal plants and oral anti-diabetic drugs, at the level of CYP and P-gp drug metabolism and could contribute to better therapeutic management of Type II diabetics. However these predicted interactions will need to be verified in a clinical setting.
- Full Text:
- Date Issued: 2011
Implementation of novel flow cytometric methods to assess the in vitro antidiabetic mechanism of a Sutherlandia Frutescens extract
- Authors: Elliot, Gayle Pamela
- Date: 2010
- Subjects: Insulin resistance -- South Africa , Insulin -- Therapeutic use -- South Africa , Medicinal plants -- South Africa , Non-insulin-dependent diabetes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10304 , http://hdl.handle.net/10948/1439 , Insulin resistance -- South Africa , Insulin -- Therapeutic use -- South Africa , Medicinal plants -- South Africa , Non-insulin-dependent diabetes -- South Africa
- Description: The ability of insulin to stimulate glucose uptake into muscle and adipose tissue is central to the maintenance of whole-body glucose homeostasis. Deregulation of insulin action manifests itself as insulin resistance, a key component of type 2 diabetes. Insulin resistance is also observed in HIV patients receiving protease inhibitors. An agent that can reversibly induce an insulin-resistant state would be a very useful tool in developing model systems that mimic the pathogenesis of type 2 diabetes. Insulin resistance can arise from defects in insulin signal transduction, changes in the expression of proteins or genes that are targets of insulin action, cross talk from other hormonal systems or metabolic abnormalities. Deterioration of the insulin-receptor-signalling pathway at different levels leading to decreased levels of signalling pathway intermediates and/or decreased activation through phosphorylation accounts for the evolution from an insulin-resistant state to type 2 diabetes. In addition, defects in GLUT4 glucose transporter translocation are observed, further fuelling impairments in skeletal muscle glucose uptake. Levels of insulin-induced GLUT4 translocation in the skeletal muscle of type 2 diabetic patients are typically reduced by 90%. Many cellular pathways & their intermediates are in some way or another linked to insulin signalling. This study focused on three of these namely the PI3-kinase/Akt pathway, the Mitogen Activated Protein Kinase (MAPK) cascade and the AMP Kinase pathway, with successful monitoring of the PI3-K pathway. Investigations involved observing and evaluating the effects of various compounds as well as an indigenous medicinal plant, Sutherlandia frutescens on the activities of key insulin signalling pathway intermediates within the three fore mentioned pathways including Akt, AMPK and MEK1/2 as well as membrane surface GLUT4 levels. Scientific research has in the past leant heavily on Western blotting as the method of choice for gaining vital information relating to signal transduction pathways, however for research into cellular mechanisms the negatives of this method outweigh the positives. The drawbacks include a need for large amount of cells, multiple washing steps which may be disadvantageous to any weak and transient interactions as well as lysing of cells which may interfere with the maintenance of the subcellular localisation of a specific signalling event. Based on these, the need for a better method in terms of speed & reliability to monitor phosphorylation states of signal transduction pathway intermediates & GLUT4 translocation was evident and was one VII of the main aims & successes of this study. The method created used the mouse muscle cell line C2C12 in conjunction with the quick, sensitive method of flow cytometry which allowed us to monitor these processes in these cells through immune-labelling. Adherent cell cultures such as the C2C12 cell line pose the problem of possible damage to plasma membrane receptors (including insulin receptors) during harvesting to obtain a cell suspension for flow cytometry. We however used C2C12 mouse myocytes to optimize a method yielding insulin responsive cells in suspension that were successfully used for flow cytometry after immunelabelling of insulin signalling intermediates. Insulin (0.1μM) significantly raised the levels of both P-Akt and GLUT4 above basal levels. This effect was shown to be dose dependent. At a concentration of 50μg/ml, Sutherlandia frutescens was able to act as an insulin-mimetic in terms of its ability to increase P-Akt levels, GLUT4 translocation and glucose utilisation in an acute manner. These increases could be reduced with the addition of wortmannin, a PI3-K inhibitor. Therefore, these results suggest the mechanism of the plant extract’s insulin-like activity may be in part due to the activation of the insulin signalling pathway leading to GLUT4 translocation, which involves the phosphorylation of insulin receptor- and subsequent PI3-K activity, leading to P-Akt activity. These results provide further evidence of this plant extract’s anti-diabetic potential. The effect of Sutherlandia frutescens on insulin secretion, calcium signalling and proliferation in INS-1 rat pancreatic cells was also investigated and it was found to increase the activities of all of these processes. However no change in the levels of GLUT2 glucose transporter was seen. Ritonavir is prescribed by the South African Department of Health in co-formulation with other protease inhibitors within its second regime in the treatment of HIV and AIDS. Using C2C12 cells, ritonavir decreased glucose uptake acutely and had no effect on GLUT4 translocation however surprisingly increased P-Akt levels. In conclusion, it was found that Sutherlandia frutescens has antidiabetic benefits, diverse in nature depending on tissue type as well as length of time administered. The establishment of novel flow cytometry techniques to assess antidiabetic properties using in vitro cell culture was achieved. These methods will be useful in the future for the assessment of insulin sensitivity and in the identification of novel compounds that stimulate the insulin signalling pathways.
- Full Text:
- Date Issued: 2010
- Authors: Elliot, Gayle Pamela
- Date: 2010
- Subjects: Insulin resistance -- South Africa , Insulin -- Therapeutic use -- South Africa , Medicinal plants -- South Africa , Non-insulin-dependent diabetes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10304 , http://hdl.handle.net/10948/1439 , Insulin resistance -- South Africa , Insulin -- Therapeutic use -- South Africa , Medicinal plants -- South Africa , Non-insulin-dependent diabetes -- South Africa
- Description: The ability of insulin to stimulate glucose uptake into muscle and adipose tissue is central to the maintenance of whole-body glucose homeostasis. Deregulation of insulin action manifests itself as insulin resistance, a key component of type 2 diabetes. Insulin resistance is also observed in HIV patients receiving protease inhibitors. An agent that can reversibly induce an insulin-resistant state would be a very useful tool in developing model systems that mimic the pathogenesis of type 2 diabetes. Insulin resistance can arise from defects in insulin signal transduction, changes in the expression of proteins or genes that are targets of insulin action, cross talk from other hormonal systems or metabolic abnormalities. Deterioration of the insulin-receptor-signalling pathway at different levels leading to decreased levels of signalling pathway intermediates and/or decreased activation through phosphorylation accounts for the evolution from an insulin-resistant state to type 2 diabetes. In addition, defects in GLUT4 glucose transporter translocation are observed, further fuelling impairments in skeletal muscle glucose uptake. Levels of insulin-induced GLUT4 translocation in the skeletal muscle of type 2 diabetic patients are typically reduced by 90%. Many cellular pathways & their intermediates are in some way or another linked to insulin signalling. This study focused on three of these namely the PI3-kinase/Akt pathway, the Mitogen Activated Protein Kinase (MAPK) cascade and the AMP Kinase pathway, with successful monitoring of the PI3-K pathway. Investigations involved observing and evaluating the effects of various compounds as well as an indigenous medicinal plant, Sutherlandia frutescens on the activities of key insulin signalling pathway intermediates within the three fore mentioned pathways including Akt, AMPK and MEK1/2 as well as membrane surface GLUT4 levels. Scientific research has in the past leant heavily on Western blotting as the method of choice for gaining vital information relating to signal transduction pathways, however for research into cellular mechanisms the negatives of this method outweigh the positives. The drawbacks include a need for large amount of cells, multiple washing steps which may be disadvantageous to any weak and transient interactions as well as lysing of cells which may interfere with the maintenance of the subcellular localisation of a specific signalling event. Based on these, the need for a better method in terms of speed & reliability to monitor phosphorylation states of signal transduction pathway intermediates & GLUT4 translocation was evident and was one VII of the main aims & successes of this study. The method created used the mouse muscle cell line C2C12 in conjunction with the quick, sensitive method of flow cytometry which allowed us to monitor these processes in these cells through immune-labelling. Adherent cell cultures such as the C2C12 cell line pose the problem of possible damage to plasma membrane receptors (including insulin receptors) during harvesting to obtain a cell suspension for flow cytometry. We however used C2C12 mouse myocytes to optimize a method yielding insulin responsive cells in suspension that were successfully used for flow cytometry after immunelabelling of insulin signalling intermediates. Insulin (0.1μM) significantly raised the levels of both P-Akt and GLUT4 above basal levels. This effect was shown to be dose dependent. At a concentration of 50μg/ml, Sutherlandia frutescens was able to act as an insulin-mimetic in terms of its ability to increase P-Akt levels, GLUT4 translocation and glucose utilisation in an acute manner. These increases could be reduced with the addition of wortmannin, a PI3-K inhibitor. Therefore, these results suggest the mechanism of the plant extract’s insulin-like activity may be in part due to the activation of the insulin signalling pathway leading to GLUT4 translocation, which involves the phosphorylation of insulin receptor- and subsequent PI3-K activity, leading to P-Akt activity. These results provide further evidence of this plant extract’s anti-diabetic potential. The effect of Sutherlandia frutescens on insulin secretion, calcium signalling and proliferation in INS-1 rat pancreatic cells was also investigated and it was found to increase the activities of all of these processes. However no change in the levels of GLUT2 glucose transporter was seen. Ritonavir is prescribed by the South African Department of Health in co-formulation with other protease inhibitors within its second regime in the treatment of HIV and AIDS. Using C2C12 cells, ritonavir decreased glucose uptake acutely and had no effect on GLUT4 translocation however surprisingly increased P-Akt levels. In conclusion, it was found that Sutherlandia frutescens has antidiabetic benefits, diverse in nature depending on tissue type as well as length of time administered. The establishment of novel flow cytometry techniques to assess antidiabetic properties using in vitro cell culture was achieved. These methods will be useful in the future for the assessment of insulin sensitivity and in the identification of novel compounds that stimulate the insulin signalling pathways.
- Full Text:
- Date Issued: 2010
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