Rooibos Extract Research Articles

Antioxidant-induced reductive stress has untoward consequences on the brain microvasculature.

Antioxidant-induced reductive stress has untoward consequences on the brain microvasculature.

In Vitro Chemopreventive Properties of Green Tea, Rooibos and Honeybush Extracts in Skin Cells.

The chemopreventive properties of the herbal teas rooibos (Aspalathus linearis) and honeybush (Cyclopia spp.) have been demonstrated on mouse skin in vivo but the underlying mechanisms are not clear. The aim of the current study was to determine the anti-proliferative and pro-apoptotic activity of methanol and aqueous extracts of rooibos and two Cyclopia species in different skin cells, using green tea (Camellia sinensis) as a benchmark. Extracts were also characterised for their major individual polyphenols by high performance liquid chromatography and spectroscopically for the total polyphenol (TP) groups. The methanol extract of rooibos, containing higher levels of polyphenols than its aqueous extract, displayed similar activity to green tea as it selectively targeted premalignant cells by inhibiting cell proliferation at lower concentrations whilst inducing apoptosis via membrane depolarisation at higher concentrations. Specific roles of the major rooibos dihydrochalcones and flavanol/proanthocyanidin-type (FLAVA) compounds are likely to be involved. The aqueous extracts of the Cyclopia species were more active against cell proliferation and at inducing apoptosis which was associated with a higher FLAVA content and a reduced TP/FLAVA ratio. In contrast, their methanol extracts exhibited a cytoprotective effect against apoptosis which was related to their monomeric xanthone and flavanone content. The underlying chemopreventive properties of green tea and the herbal teas appear to be associated with diverse and complex monomeric/polymeric polyphenolic cell interactions.

Inhibitory Interactions of Aspalathus linearis (Rooibos) Extracts and Compounds, Aspalathin and Z-2-(β-d-Glucopyranosyloxy)-3-phenylpropenoic Acid, on Cytochromes Metabolizing Hypoglycemic and Hypolipidemic Drugs.

Rooibos extract, due to its glucose and lipid lowering effects, has potential as a nutraceutical for improvement of metabolic dysfunction. Potential herb-drug interactions as a result of the use of natural products are of increasing concern. Cytochrome P450 enzymes, CYP2C8, CYP2C9, and CYP3A4, are important in the metabolism of hypoglycemic drugs, such as thiazolidinediones (TZDs) and sulfonylureas, and hypocholesterolemic drugs, such as atorvastatin. This study investigated the effects of rooibos extracts, prepared from “unfermented” and “fermented” rooibos plant material and two of the major bioactive compounds, Z-2-(β-d-glucopyranosyloxy)-3-phenylpropenoic acid (PPAG) and aspalathin (ASP), on Vivid® recombinant CYP450 enzymes. Unfermented (GRT) and fermented (FRE) rooibos extracts inhibited the activity of CYP2C8 (7.69 ± 8.85 µg/mL and 8.93 ± 8.88 µg/mL, respectively) and CYP3A4 (31.33 ± 4.69 µg/mL and 51.44 ± 4.31 µg/mL, respectively) based on their respective IC50 concentrations. Both extracts dose- and time-dependently inhibited CYP2C8 activity, but only time-dependently inhibited CYP2C9. CYP3A4 showed concentration-dependent inhibition by ASP, GRT, and FRE at 25, 50, and 100 µg/mL concentrations. ASP, GRT, and FRE time-dependently inhibited CYP3A4 activity with GRT and FRE showing a more potent time-dependent inhibition, comparable to erythromycin. These findings suggest that herb-drug interactions may occur when nutraceuticals containing rooibos extracts are co-administered with hypoglycemic drugs such as TZDs, sulfonylureas, and dyslipidemic drug, atorvastatin.

Anti-Inflammatory Effects of Aspalathus linearis and Cyclopia spp. Extracts in a UVB/Keratinocyte (HaCaT) Model Utilising Interleukin-1α Accumulation as Biomarker

Ultraviolet B (UVB) radiation is one of the major predisposing risk factors of skin cancer. The anticancer and photoprotective effects of unoxidized rooibos (Aspalathus linearis) and honeybush (Cyclopia) herbal teas, containing high levels of dihydrochalones and xanthones, respectively, have been demonstrated in skin cancer models in vivo. In the current study, the anti-inflammatory effects of methanol and aqueous extracts of these herbal teas were investigated in a UVB/HaCaT keratinocyte model with intracellular interleukin-1α (icIL-1α) accumulation as a biomarker. Extracts of green tea (Camellia sinensis) served as benchmark. Both extracts of green tea and rooibos, as well as the aqueous extract of C. intermedia, enhanced UVB-induced inhibition of cell viability, proliferation and induction of apoptosis, facilitating the removal of icIL-1α. The underlying mechanisms may involve mitochondrial dysfunction exhibiting pro-oxidant responses via polyphenol-iron interactions. The methanol extracts of honeybush, however, protected against UVB-induced reduction of cell growth parameters, presumably via antioxidant mechanisms that prevented the removal of highly inflamed icIL-1α-containing keratinocytes via apoptosis. The dual antioxidant and/or pro-oxidant role of the polyphenolic herbal tea constituents should be considered in developing preventive strategies against UVB-induced skin carcinogenesis. The indirect removal of UVB damaged keratinocytes by herbal tea extracts via apoptosis may find application in the prevention of photo-induced inflammation.

Identification of broad-based sensory attributes driving consumer preference of ready-to-drink rooibos iced tea with increased aspalathin content

Traditional rooibos iced teas prepared using fermented rooibos extract contain a low concentration of the unique antioxidant, aspalathin, which also has anti-diabetic properties. In order to increase the aspalathin content an array of rooibos iced tea formulations containing aspalathin-enriched green rooibos extract or the same extract solubilised in nanomicelles in the presence of ascorbic acid (solubilisate), as well as a mixture of the solubilisate and fermented extract, were formulated with or without lemon flavour. Since sensory attributes are important from a consumer viewpoint, the broad-based sensory attributes of these formulations were compared with those of traditional fermented rooibos iced tea. The iced tea formulations containing green rooibos extract exhibited a “plant-like” character, which was reduced with the addition of a commercial lemon flavour. The formulations containing the solubilisate had a prominent “hay-like” flavour, which was reduced by the addition of both lemon flavour and fermented rooibos extract. The formulations containing fermented rooibos extract exhibited a prominent “rooibos-woody” flavour characteristic of fermented rooibos tea. The perceived intensity of this characteristic attribute decreased with addition of commercial lemon flavour and solubilisate. All the iced teas exhibited a measure of astringency, but the astringency of iced teas containing fermented extract was the greatest and was reduced by addition of lemon flavour. In order to gauge consumer acceptance, the four lemon flavoured variants of rooibos iced tea were evaluated by a consumer panel. Consumers preferred the iced teas with fermented rooibos extract and disliked those with green rooibos extract. Preference mapping showed that the presence of the “rooibos-woody” flavour and the absence of a “plant-like” flavour most likely drive the preference of rooibos iced teas amongst South African consumers. The presence of a slight “hay-like” character did not reduce the preference of rooibos iced teas. Despite the functional benefits associated with a higher aspalathin content of green rooibos iced tea compared to the traditional fermented rooibos iced tea, consumers disliked the product, because of its overt “plant-like” note. However, a green rooibos extract solubilised in nanomicelles in combination with the fermented extract can be used to produce an iced tea with enhanced aspalathin content that is still acceptable to consumers from a taste point of view.

루이보스 추출물이 중년 남성의 지루성 두피 개선에 미치는 효과

루이보스 추출물이 중년 남성의 지루성 두피 개선에 미치는 효과

Rooibos (Aspalathus linearis), honeybush (Cyclopia intermedia) and cancer bush (Sutherlandia frutescens subsp. microphylla) protect against tobacco-specific mutagenesis in vitro

Antimutagenesis studies against the tobacco-specific mutagens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N-oxide, 4 (methyl-nitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), were conducted using hot water aqueous extracts of rooibos (Aspalathus linearis), honeybush (Cyclopia intermedia), and cancer bush (Sutherlandia frutescens). Aqueous extracts of both “fermented” and “unfermented” (green) rooibos and honeybush were included, while extracts of green and black teas (Camellia sinensis) served as benchmarks. A polyphenol-enriched methanol extract of unfermented rooibos (RgM) was included to further elucidate the possible role of rooibos polyphenols. Studies were performed in the presence of the metabolic activation against Salmonella typhimurium tester strain TA1535, using the standard plate incorporation and micro-suspension, pre-incubation assays. The mutagenic effects of NNK against the strain TA1535 was best demonstrated using the standard plate incorporation assay, while a higher mutagenicity was demonstrated for NNAL using the micro-suspension, pre-incubation method. Black tea and RgM exhibited the highest protection against NNK-induced mutagenesis followed by the aqueous extracts of rooibos≥green tea≥honeybush≥cancer bush. Black tea, green tea, RgM and unfermented rooibos were the most effective against NNAL-induced mutagenesis, followed by fermented rooibos. The two honeybush extracts exhibited similar, but the weakest protective response. When considering the amount of total polyphenols (TPP) incorporated in the plate incorporation assay, cancer bush exhibited similar protection to that of fermented and unfermented honeybush against NNK mutagenesis. The involvement of specific polyphenol-cytochrome P450 (CYP450) interactions is likely to be involved in the protection against tobacco-related mutagenesis. Polyphenol constituents of rooibos, honeybush and cancer bush could play an important role in the protection against mutagenesis induced by the major tobacco-specific carcinogens.

Phenylpropenoic Acid Glucoside from Rooibos Protects Pancreatic Beta Cells against Cell Death Induced by Acute Injury.

ObjectivePrevious studies demonstrated that a phenylpropenoic acid glucoside (PPAG) from rooibos (Aspalathus linearis) extract had anti-hyperglycemic activity and significant protective effects on the pancreatic beta cell mass in a chronic diet-induced diabetes model. The present study evaluated the cytoprotective effect of the phytochemical on beta cells exposed to acute cell stress.MethodsSynthetically prepared PPAG was administered orally in mice treated with a single dose of streptozotocin to acutely induce beta cell death and hyperglycemia. Its effect was assessed on beta cell mass, proliferation and apoptotic cell death. Its cytoprotective effect was also studied in vitro on INS-1E beta cells and on human pancreatic islet cells.ResultsTreatment with the phytochemical PPAG protected beta cells during the first days after the insult against apoptotic cell death, as evidenced by TUNEL staining, and prevented loss of expression of anti-apoptotic protein BCL2 in vivo. In vitro, PPAG protected INS-1E beta cells from streptozotocin-induced apoptosis and necrosis in a BCL2-dependent and independent way, respectively, depending on glucose concentration. PPAG also protected human pancreatic islet cells against the cytotoxic action of the fatty acid palmitate.ConclusionsThese findings show the potential use of PPAG as phytomedicine which protects the beta cell mass exposed to acute diabetogenic stress.

PIXE and RBS analysis of serum specimens of rats fed with tea extracts to ascertain elemental absorption

Antioxidants are compounds that easily donate an electron to become oxidized, while oxidants readily accept these electrons. An antioxidant thus slows down or prevents the oxidation of other molecules. Enzymes normally counteract these effects. Various trace elements are incorporated into the structure of enzymes and are the center of activity. In this study, liquid herbal extracts of rooibos (Aspalathus linearis) and green tea were fed to male Wistar rats. The objective was to ascertain the effect of these extracts on the trace element absorption and to correlate these effects with the enzymes activities.

Hepatic, renal and endogenous antioxidant status modulatory effects of chronic co-supplementation of rooibos (<i>Aspalathus linearis</i>) and red palm oil (<i>Elaeis guineensis</i>) in male Wistar rats

Background: This study investigated the hepatic, renal and endogenous antioxidant status modulatory effects of chronic cosupplementation of rooibos and red palm oil (RPO) in male Wistar rats. Materials and Methods: Rats were randomized into four groups (n=10/group) and fed daily either standard rat chow (SRC) and water ( Group I ), SRC and the aqueous rooibos extract (2% w/v; ( Group II ), SRC and RPO (200 μL/day) with water ( Group III ), or SRC and RPO (200 μL/day) with rooibos (2% w/v; Group IV ) for 22 weeks. Results: Chronic feeding of rooibos, RPO or their combination did not induce any adverse hepatic or renal effects, as shown by serum levels of alkaline phosphatase, alanine- and aspartate aminotransferase, lactate dehydrogenase, albumin, creatinine, blood urea nitrogen and uric acid. Histopathology analyses showed that liver from the three supplementation groups displayed normal hepatic histoarchitecture. Chronic feeding of RPO did not influence the redox status in the blood and liver significantly. Supplementation of rooibos alone for 22 weeks significantly (P<0.05) increased the reduced glutathione (GSH) level, GSH/GSSG ratio and catalase (CAT) activity in the liver. Co supplementation of rooibos and RPO significantly (P<0.05) increased plasma total polyphenol content, trolox equivalent antioxidant capacity (TEAC), as well as blood GSH and GSH/GSSG ratio. Plasma conjugated dienes (CD) and hepatic malondialdehyde (MDA) levels were reduced significantly by the combination treatment, which also increased significantly the activity of CAT, glutathione reductase (GR), as well as the GSH/GSSG ratio in the liver. Conclusion: Our results suggest that chronic feeding of an aqueous fermented rooibos extract alone or in combination with RPO modulate the endogenous antioxidant system in rats. This modulation could be indicative of a threshold effect and/or an additive effect indicating a positive interaction between the bioactive components in the rooibos and RPO; however future studies are needed to elucidate the nature and specific mechanisms involved. Also, the health status of the individual/experimental animal should be considered before antioxidant supplementation, as it is suggested to affect the outcome. Keywords: endogenous antioxidant system; glutathione redox status; lipid peroxidation; rooibos; red palm oil

HEPATIC, RENAL AND ENDOGENOUS ANTIOXIDANT STATUS MODULATORY EFFECTS OF CHRONIC CO-SUPPLEMENTATION OF ROOIBOS (ASPALATHUS LINEARIS) AND RED PALM OIL (ELAEIS GUINEENSIS) IN MALE WISTAR RATS

Background: This study investigated the hepatic, renal and endogenous antioxidant status modulatory effects of chronic cosupplementation&#x0D; of rooibos and red palm oil (RPO) in male Wistar rats.&#x0D; Materials and Methods: Rats were randomized into four groups (n=10/group) and fed daily either standard rat chow (SRC) and water&#x0D; (Group I), SRC and the aqueous rooibos extract (2% w/v; Group II), SRC and RPO (200 μL/day) with water (Group III), or SRC and&#x0D; RPO (200 μL/day) with rooibos (2% w/v; Group IV) for 22 weeks.&#x0D; Results: Chronic feeding of rooibos, RPO or their combination did not induce any adverse hepatic or renal effects, as shown by serum&#x0D; levels of alkaline phosphatase, alanine- and aspartate aminotransferase, lactate dehydrogenase, albumin, creatinine, blood urea nitrogen&#x0D; and uric acid. Histopathology analyses showed that liver from the three supplementation groups displayed normal hepatic&#x0D; histoarchitecture. Chronic feeding of RPO did not influence the redox status in the blood and liver significantly. Supplementation of&#x0D; rooibos alone for 22 weeks significantly (P

Production of dihydrochalcone-rich green rooibos (Aspalathus linearis) extract taking into account seasonal and batch-to-batch variation in phenolic composition of plant material

Randomly selected rooibos plants from three plantations were harvested (a few branches per plant) at intervals from early summer to late spring. The aspalathin and nothofagin content of the plant material was highest at the first harvest date (3.76% and 0.54%, respectively) in summer whereafter their content decreased gradually to the lowest levels in winter and increased to 3.31% and 0.36%, respectively in mid-spring. Commercial green rooibos production batches (n=47), produced over a period of 49days (end of January until mid-March) from plant material harvested from one plantation were analysed to provide further insight into expected batch-to-batch variation in aspalathin, nothofagin, orientin and iso-orientin content. The aspalathin content of green rooibos varied between 2.50% and 4.49%, even though the plant material was harvested from the same plantation. The other compounds were present in the plant material in much lower quantities (<0.5%). The iso-orientin and orientin contents of the green rooibos samples did not vary substantially. The variation observed in the plant material was subsequently also observed in the freeze-dried hot water extracts prepared from the commercial green rooibos production batches, with the theoretical dried extract yield varying between 15.07% and 22.89%. The aspalathin content and total polyphenol content of the dried extract varied between 8.11% and 12.33% and between 29.7 and 43.5g gallic acid equivalents/100g, respectively. The mean content values for the other compounds were less than 1.2%. Combined these major dihydrochalcones and flavones comprised between 10.22% and 14.88% of the freeze-dried extract. Aspalathin contributed between 13.1% and 22.8% of the total antioxidant capacity (2873–4286μmol Trolox equivalents/g) of the dried extract as determined by the DPPH radical scavenging assay.

Short-Term and Sub-Chronic Dietary Exposure to Aspalathin-Enriched Green Rooibos (Aspalathus linearis) Extract Affects Rat Liver Function and Antioxidant Status.

An aspalathin-enriched green rooibos (Aspalathus linearis) extract (GRE) was fed to male Fischer rats in two independent studies for 28 and 90 days. The average dietary total polyphenol (TP) intake was 75.6 and 62.7 mg Gallic acid equivalents (GAE)/kg body weight (bw)/day over 28 and 90 days, respectively, equaling human equivalent doses (HEDs) of 12.3 and 10.2 GAE mg/kg bw/day. Aspalathin intake of 29.5 mg/kg bw/day represents a HED of 4.8 mg/kg bw/day (90 day study). Consumption of GRE increased feed intake significantly (p < 0.05) compared to the control after 90 days, but no effect on body and organ weight parameters was observed. GRE significantly (p < 0.05) reduced serum total cholesterol and iron levels, whilst significantly (p < 0.05) increasing alkaline phosphatase enzyme activity after 90 days. Endogenous antioxidant enzyme activity in the liver, i.e., catalase and superoxide dismutase activity, was not adversely affected. Glutathione reductase activity significantly (p < 0.05) increased after 28 days, while glutathione (GSH) content was decreased after 90 days, suggesting an altered glutathione redox cycle. Quantitative Real Time polymerase chain reaction (PCR) analysis showed altered expression of certain antioxidant defense and oxidative stress related genes, indicative, among others, of an underlying oxidative stress related to changes in the GSH redox pathway and possible biliary dysfunction.

Oxidative stability of blesbok, springbok and fallow deer droëwors with added rooibos extract

The addition of rooibos extract (RBE) (0%, 0.25%, 0.50%, 1.0% RBE) to improve the oxidative stability of blesbok, springbok and fallow deer droëwors (dried sausage) was studied. RBE treatments had no effects (p&gt;0.05) on the lipid and protein oxidation of the dried product. With the addition of RBE 0.25%, lipid stability after drying showed the malonaldehydes decreased considerably. Haem-iron concentration increased after drying and differed (p&lt;0.05) between RBE treatments within the dried stage within species. There were no differences (p&gt;0.05) between the moisture, protein and fat contents between treatments within a specific processing stage. With the high polyunsaturated fatty acid content of the sausages, a high level of oxidation occurred. Even though RBE addition did not reduce oxidation significantly during the drying process, it could be a successful addition to the traditional South African meat product if it is shown to impart positive flavour attributes.

Aspalathin improves glucose and lipid metabolism in 3T3-L1 adipocytes exposed to palmitate.

Saturated-free fatty acids, such as palmitate, are associated with insulin resistance. This study aimed to establish if an aspalathin-enriched green rooibos extract (GRE) and, its major flavanoid, aspalathin (ASP) could contribute significantly to the amelioration of experimentally induced insulin resistance in 3T3-L1 adipocytes. 3T3-L1 adipocytes were cultured in DMEM containing 0.75 mM palmitate for 16 h to induce insulin resistance before treatment for 3 h with GRE (10 μg/mL) or ASP (10 μM). GRE and ASP reversed the palmitate-induced insulin resistance. At a protein level GRE and ASP suppressed nuclear factor kappa beta (NF-κB), insulin receptor substrate one (serine 307) (IRS1 (Ser (307) )) and AMP-activated protein kinase phosphorylation and increased serine/threonine kinase AKT (AKT) activation, while only GRE increased glucose transporter four (Glut4) protein expression. Peroxisome proliferator-activated receptor alpha and gamma (PPARα and γ), and carnitine palmitoyltransferase one (CPT1) expression were increased by ASP alone. Together these effects offer a plausible explanation for the ameliorative effect of GRE and ASP on insulin-resistance, an underlying cause for obesity and type 2 diabetes.

Free radical scavenging ability of Aspalathus linearis in two in vitro models of diabetes and cancer

The free radical scavenging activity of Aspalathus linearis (Rooibos tea) and its effect on reactive oxygen species (ROS), catalase (CAT), and superoxide dismutase (SOD) were investigated in two in vitro disease models of cancer and diabetes. Although the antioxidant activity of this tea has been reported in several studies, its effects in disease models of ROS-induced oxidative stress have not been systematically evaluated to date. The oxygen radical absorbance capacity (ORAC) assay was used in this study to quantify the antioxidant capacity of the extract, whereas the ROS scavenging ability in hyperglycemia-induced human umbilical vein endothelial cells (HUVECs) and HeLa cells were investigated. The CAT and SOD assays were also carried out in the two disease models in order to evaluate the effect of the extract in the stimulation of these two enzyme activities. The extract was observed to have reduced ROS in a dose-dependent manner in both HUVECs and HeLa cells. The stimulation of the CAT and SOD enzyme activities were observed to be dose-dependent as well. The high ORAC value of the extract indicated the presence of antioxidant compounds which could directly quench ROS, whereby this mechanism of action could be hypothesized to have been further complemented through the stimulation of CAT and SOD. Overall, the Aspalathus linearis extract was observed to have increased the CAT and SOD activities in two in vitro disease models of cancer and hyperglycemia. Given the correlation between the ORAC values, the increases in CAT and SOD activities and the reduction in ROS in a dose-dependent manner, it could be hypothesized that the extract had a significant therapeutic potential for either the prevention of the onset of the two diseases or their progression because ROS has been identified as their root causes.

Effect of rooibos extract (Aspalathus linearis) on lipid oxidation over time and the sensory analysis of blesbok (Damaliscus pygargus phillipsi) and springbok (Antidorcas marsupialis) droëwors

The study objective was to investigate the addition of rooibos extract (RBE) in blesbok and springbok droëwors, a dried meat sausage with added beef fat, to improve oxidative stability. After a storage period of two weeks, inhibition of lipid oxidation showed to be successful with RBE 1.0% addition. No differences (P>0.05) in heme-iron results within the raw, dried or stored samples were seen. However, a positive correlation between lipid oxidation and heme-iron was noted. The fatty acid profiles suggest that after drying the decrease in polyunsaturated fats could be linked to the increase in lipid oxidation. Flavor and aroma differences between the varying RBE concentrations in the droëwors were detected by the sensory panel. A droëwors formulation using a combination of game meat and beef fat with the addition of RBE at a 1.0% concentration could be a successful addition to the processed meat market.

Green Rooibos Extract from &lt;i&gt;Aspalathus linearis&lt;/i&gt;, and its Component, Aspalathin, Suppress Elevation of Blood Glucose Levels in Mice and Inhibit α-amylase and α-glucosidase Activities &lt;i&gt;in vitro&lt;/i&gt;

Green Rooibos Extract from &lt;i&gt;Aspalathus linearis&lt;/i&gt;, and its Component, Aspalathin, Suppress Elevation of Blood Glucose Levels in Mice and Inhibit α-amylase and α-glucosidase Activities &lt;i&gt;in vitro&lt;/i&gt;

Polydisperse Low Diameter ‘Non-Toxic’ Silver Nanoparticles Encapsulated by Rooibos Tea Templates

This work reports the synthesis of ‘non-toxic’ polydisperse, low diameter silver nanoparticles (AgNPs). Rooibos extracts at temperatures 25 °C, 30 °C, 50 °C, 70 °C and 90 °C were used. The effect of different extraction temperature on the % yield and nature of the AgNPs were investigated. The characteristics of the ‘green synthesis’ processed AgNPs were evaluated through UV-Vis spectroscopy, high resolution tunnelling microscopy (HRTEM), X-ray diffraction (XRD) and EDX techniques. Results indicated an increase in extraction temperature leads to more polyphenol extraction, increase in the AgNP % yield and greater absorbance. A yellow to brown to dark brown colour change observed during the synthesis indicated AgNPs formation. UV-Vis results indicated the AgNPs surface plasmon peaks at 440, 447, 450, 460 and 489 nm for the 25 °C, 30 °C, 50 °C, 70 °C, 90 °C respectively. SEM results revealed spherical nanosized particles with dense cores and lighter outer region with mean diameters for AgNPs ranged between 4.4-5.8 nm. EDX results indicated prominent Ag peaks at 3.10 keV. XRD results showed vaguely defined amorphous polyol peaks at below 2θ = 27°. The sharp peaks at 2θ = 38°, 45°, 66° and 77° which were assigned as 111, 200, 220 and 321 corresponded to the face-centred cubic crystalline silver phase.

Antidiabetic effect of green rooibos (Aspalathus linearis) extract in cultured cells and type 2 diabetic model KK-A(y) mice.

Previous studies have demonstrated antidiabetic effects for rooibos (Aspalathus linearis) and aspalathin (ASP), one of its main polyphenols. Rooibos, an endemic plant of South Africa, is well-known for its use as herbal tea. Green ('unfermented') rooibos has been shown to contain more ASP than 'fermented' rooibos tea, currently the major product. In the present study, we investigated the antidiabetic effect of green rooibos extract (GRE) through studies on glucose uptake in L6 myotubes and on pancreatic β-cell protective ability from reactive oxygen species (ROS) in RIN-5F cells. Its in vivo effect was also examined using obese diabetic KK-A(y) mice. GRE increased glucose uptake under insulin absent condition and induced phosphorylation of 5'-adenosine monophosphate-activated protein kinase (AMPK) in L6 myotubes as previously demonstrated for ASP. In addition to AMPK, GRE also promoted phosphorylation of Akt, another promoter of glucose transporter 4 (GLUT4) translocation, in L6 myotubes unlike ASP, suggesting an involvement of GRE component(s) other than ASP in Akt phosphorylation. Promotion of GLUT4 translocation to the plasma membrane by GRE in L6 myotubes was demonstrated by Western blotting analysis. GRE suppressed the advanced glycation end products (AGEs)-induced increase in ROS levels in RIN-5F pancreatic β-cells. Subchronic feeding with GRE suppressed the increase in fasting blood glucose levels in type 2 diabetic model KK-A(y) mice. These in vitro and in vivo results strongly suggest that GRE has antidiabetic potential through multiple modes of action.