Johan Louw

Assessment of the Antidiabetic Potential of an Aqueous Extract of Honeybush (Cyclopia intermedia) in Streptozotocin and Obese Insulin Resistant Wistar Rats

Christo J.F. Muller1, Elizabeth Joubert2,3, Kwazi Gabuza1, Dalene de Beer2, Stephen J. Fey4 and Johan Louw1 1Diabetes Discovery Platform, Medical Research Council (MRC), Cape Town, 2Post-Harvest and Wine Technology Division, Agricultural Research Council (ARC), Infruitec-Nietvoorbij, Stellenbosch, 3Department of Food Science, Stellenbosch University, Stellenbosch, 4Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, 1,2,3South Africa 4Denmark

Hyperglycemia-induced oxidative stress and heart disease-cardioprotective effects of rooibos flavonoids and phenylpyruvic acid-2-O-β-D-glucoside

Diabetic patients are at an increased risk of developing heart failure when compared to their non-diabetic counter parts. Accumulative evidence suggests chronic hyperglycemia to be central in the development of myocardial infarction in these patients. At present, there are limited therapies aimed at specifically protecting the diabetic heart at risk from hyperglycemia-induced injury. Oxidative stress, through over production of free radical species, has been hypothesized to alter mitochondrial function and abnormally augment the activity of the NADPH oxidase enzyme system resulting in accelerated myocardial injury within a diabetic state. This has led to a dramatic increase in the exploration of plant-derived materials known to possess antioxidative properties. Several edible plants contain various natural constituents, including polyphenols that may counteract oxidative-induced tissue damage through their modulatory effects of intracellular signaling pathways. Rooibos, an indigenous South African plant, well-known for its use as herbal tea, is increasingly studied for its metabolic benefits. Prospective studies linking diet rich in polyphenols from rooibos to reduced diabetes associated cardiovascular complications have not been extensively assessed. Aspalathin, a flavonoid, and phenylpyruvic acid-2-O-β-D-glucoside, a phenolic precursor, are some of the major compounds found in rooibos that can ameliorate hyperglycemia-induced cardiomyocyte damage in vitro. While the latter has demonstrated potential to protect against cell apoptosis, the proposed mechanism of action of aspalathin is linked to its capacity to enhance the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression, an intracellular antioxidant response element. Thus, here we review literature on the potential cardioprotective properties of flavonoids and a phenylpropenoic acid found in rooibos against diabetes-induced oxidative injury.

Polyphenols, autophagy and doxorubicin-induced cardiotoxicity

Doxorubicin is a highly effective, first line chemotherapeutic agent used in the management of hematological and solid tumors. The effective use of doxorubicin in cancer therapy has been severely limited owing to its well-documented cardiotoxic side effect. Oxidative stress, lipid peroxidation, apoptosis as well as dysregulation of autophagy, has been implicated as a major contributor associated with doxorubicin-induced cardiotoxicity. Increased oxidative stress and lipid peroxidation are known to enhance the production of reactive oxygen species, while autophagy has been reported to protect the cell from stress stimuli or, alternatively, contribute to cell death. Nonetheless, to date, no single chemical synthesized drug is available to prevent the harmful action of doxorubicin without reducing its anti-cancer efficacy. Therefore, the search for an effective and safe antagonist of doxorubicin-induced cardiotoxicity remains a challenge. In recent years, there has been much interest in the role plant-derived polyphenols play in the regulation of oxidative stress and autophagy. Therefore, the present review renders a concise overview of the mechanism associated with doxorubicin-induced cardiotoxicity as well as giving insight into the role plant-derived phytochemical play as a possible adjunctive therapy against the development of doxorubicin-induced cardiotoxicity.

Recommendations for Short Term Culturing of Viable Rod Shaped Rat Cardiomyocytes

In vitro primary cultures of isolated adult rat cardiomyocytes are becoming an increasingly popular model to study heart muscle stressors. This model can easily be manipulated in a controlled environment and results obtained can provide valuable insights into the pathophysiology of heart disease. Over the past years several improved methodologies have been described in the development of a robust technique to help maintain cardiomyocytes in culture. However, despite these advances, culturing of primary cardiomyocytes remains a challenge. In this study, we present a simple yet reproducible method for isolation and culture of viable rod shaped cardiomyocytes. Cardiomyocytes were maintained in supplemented Media 199 with or without foetal bovine serum. Their viability was assessed using trypan blue while the metabolic activity was measured using an Adenosine 5’-triphosphate assay. Results obtained in this study were used to provide general guidelines to evade pitfalls related to low cardiomyocyte yields and subsequent poor culturability of cardiomyocytes. Isolated cardiomyocytes cultured in the presence of foetal bovine serum maintained their in vitro striated rod shaped morphology for 72 hours in culture, after which, they flattened and spread out. Whereas, cardiomyocytes cultured in the absence of foetal bovine serum remained rod shaped for up to 120 hours.

Age-dependent development of left ventricular wall thickness in type 2 diabetic (db/db) mice is associated with elevated low-density lipoprotein and triglyceride serum levels

Diabetic cardiomyopathy (DCM) is a disease of heart muscle that remains one of the leading causes of death in diabetic individuals. Shifts in substrate preference resulting in aberrant serum lipid content and enlarged left ventricular wall thickness are well-established characteristics associated with the development of DCM. As underlying mechanisms driving the onset of the DCM remain relatively unclear, this study sought to characterize age-dependent development of left ventricular (LV) wall thickness in diabetic (db/db) mice. Such data were compared with low-density lipoprotein (LDL) and triglyceride serum levels to assess whether any correlation exists between the parameters here investigated. For methods, db/db mice together with nondiabetic controls (nxa0=xa0six per group) were monitored from the age of 6–16xa0weeks. Mice were terminated each week to measure body weights, heart weights, liver weights, tibia length, and fasting plasma glucose levels. Heart tissues were stained with haematoxylin and eosin to measure LV wall and interventricular septum thickness together with an assessment of myocardial remodeling. Serum was collected weekly and used to measure LDL and triglyceride levels. Results showed that db/db mice presented significantly increased body weights, liver/body weight, and fasting plasma glucose levels from the age of 6–16xa0weeks. They further displayed a marked enlargement of LV wall and interventricular septum thickness from the age of 11xa0weeks, while increased heart weight/tibia length was recorded only from week 16. From week 11, the LV wall and interventricular septum thickness results corresponded with cardiac remodeling and raised LDL and triglyceride serum levels. In summary, age-dependent development of LV wall thickness in db/db mice is partially associated with increased LDL and triglyceride levels, elucidating a potential pathophysiological mechanism.

A Systematic Review on the Protective Effect of N-Acetyl Cysteine Against Diabetes-Associated Cardiovascular Complications

IntroductionHeart failure is the leading cause of death in patients with diabetes. No treatment currently exists to specifically protect these patients at risk of developing cardiovascular complications. Accelerated oxidative stress-induced tissue damage due to persistent hyperglycemia is one of the major factors implicated in deteriorated cardiac function within a diabetic state. N-acetyl cysteine (NAC), through its enhanced capacity to endogenously synthesize glutathione, a potent antioxidant, has displayed abundant health-promoting properties and has a favorable safety profile.ObjectiveAn increasing number of experimental studies have reported on the strong ameliorative properties of NAC. We systematically reviewed the data on the cardioprotective potential of this compound to provide an informative summary.MethodsTwo independent reviewers systematically searched major databases, including PubMed, Cochrane Library, Google scholar, and Embase for available studies reporting on the ameliorative effects of NAC as a monotherapy or in combination with other therapies against diabetes-associated cardiovascular complications. We used the ARRIVE and JBI appraisal guidelines to assess the quality of individual studies included in the review. A meta-analysis could not be performed because the included studies were heterogeneous and data from randomized clinical trials were unavailable.ResultsMost studies support the ameliorative potential of NAC against a number of diabetes-associated complications, including oxidative stress. We discuss future prospects, such as identification of additional molecular mechanisms implicated in diabetes-induced cardiac damage, and highlight limitations, such as insufficient studies reporting on the comparative effect of NAC with common glucose-lowering therapies. Information on the comparative analysis of NAC, in terms of dose selection, administration mode, and its effect on different cardiovascular-related markers is important for translation into clinical studies.ConclusionsNAC exhibits strong potential for the protection of the diabetic heart at risk of myocardial infarction through inhibition of oxidative stress. The effect of NAC in preventing both ischemia and non-ischemic-associated cardiac damage is also of interest. Consistency in dose selection in most studies reported remains important in dose translation for clinical relevance.

Polyphenol-Enriched Fractions of Cyclopia intermedia Selectively Affect Lipogenesis and Lipolysis in 3T3-L1 Adipocytes

Cyclopia species are increasingly investigated as sources of phenolic compounds with potential as therapeutic agents. Recently, we demonstrated that a crude polyphenol-enriched organic fraction (CPEF) of Cyclopia intermedia, currently forming the bulk of commercial production, decreased lipid content in 3T3-L1 adipocytes and inhibited body weight gain in obese db/db mice. The aim of the present study was to determine whether a more effective product and/or one with higher specificity could be obtained by fractionation of the CPEF by purposely increasing xanthone and benzophenone levels. Fractionation of the CPEF using high performance counter-current chromatography (HPCCC) resulted in four fractions (F1-F4), predominantly containing iriflophenone-3-C-β-D-glucoside-4-O-β-D-glucoside (benzophenone: F1), hesperidin (flavanone: F2), mangiferin (xanthone: F3), and neoponcirin (flavone: F4), as quantified by high-performance liquid chromatography with diode array detection (HPLC-DAD), and confirmed by LC-DAD with mass spectrometric (MS) and tandem MS (MSE) detection. All fractions inhibited lipid accumulation in 3T3-L1 pre-adipocytes and decreased lipid content in mature 3T3-L1 adipocytes, although their effects were concentration-dependent. F1-F3 stimulated lipolysis in mature adipocytes. Treatment of mature adipocytes with F1 and F2 increased the messenger RNA expression of hormone sensitive lipase, while treatment with F1 and F4 increased uncoupling protein 3 expression. In conclusion, HPCCC resulted in fractions with different phenolic compounds and varying anti-obesity effects. The activities of fractions were lower than the CPEF; thus, fractionation did not enhance activity within a single fraction worthwhile for exploitation as a nutraceutical product, which illustrates the importance of considering synergistic effects in plant extracts.

Altered microRNA expression during Impaired Glucose Tolerance and High-fat Diet Feeding

OBJECTIVEnMicroRNAs (miRNAs) play a critical role in metabolic regulation. Recently, we identified novel miRNAs in the whole blood of South African women of mixed ethnic ancestry. The aim of this study was to investigate whether five of these novel miRNAs are expressed in serum and whether their expression is altered during metabolic dysregulation.nnnMETHODSnExpression levels of the five novel miRNAs (MYN08, MYNO22, MYN059, MYNO66 and MYNO95) were measured in the serum of women with Impaired Glucose Tolerance (IGT) and Normoglycemia (NGT) (n=24), and in the whole blood of vervet monkeys fed a high-fat or standard diet (n=16) using quantitative real-time PCR.nnnRESULTSnOnly three of the selected novel miRNAs (MYNO8, MYNO22 and MYNO66) were expressed in serum. The expression of MYN08 and MYNO22 were associated with fasting glucose and insulin concentrations, decreased during IGT and able to predict IGT. The expression of these miRNAs were similarly decreased in vervet monkeys fed a high-fat diet. In silico analysis identified a total of 291 putative messenger RNA targets for MYNO8 and MYNO22, including genes involved in gluconeogenesis, carbohydrate metabolism, glucose homeostasis and lipid transport.nnnCONCLUSIONnTwo novel miRNAs, MYNO8 and MYNO22, are associated with metabolic dysregulation in South African women of mixed ethnic ancestry and with high-fat diet feeding in vervet monkeys. Furthermore, putative gene targets were enriched in biological processes involved in key aspects of glucose regulation, which strengthens the candidacy of these miRNAs as biomarkers for dysglycemia, and warranting further studies to assess their clinical applicability.