Effects of green tea, black tea and Rooibos tea on angiotensin-converting enzyme and nitric oxide in healthy volunteers

Abstract

Objective: Tea has been reported to reduce cardiovascular mortality, but the underlying mechanisms are largely unknown. The aim of the current project was to investigate the effect of green tea (Japanese Sencha), black tea (Indian Assam B.O.P.) and Rooibos tea (South Africa) on angiotensin-converting enzyme (ACE) and nitric oxide (NO). Design: Seventeen healthy volunteers received a single oral dose of 400 ml green tea, black tea or Rooibos tea in a randomized, three-phase, crossover study. ACE activity and NO concentration were measured (at 0, 30, 60 and 180 min) in all phases. ACE activity was analysed by means of a commercial radioenzymatic assay. Nitrite was analysed as a marker of NO concentration. In addition, ACE genotype was determined using a PCR method. Results: Oral intake of a single dose of Rooibos tea significantly inhibited ACE activity after 30 min (P , 0?01) and after 60 min (P , 0?05). A significant inhibition of ACE activity was seen with green tea for the ACE II genotype 30 min after intake of the tea (P , 0?05) and for the ACE ID genotype 60 min after intake (P , 0?05). A significant inhibition of ACE activity was also seen with Rooibos tea for the ACE II genotype 60 min after intake (P , 0?05). No significant effect on NO concentration was seen. Conclusions: These results suggest that green tea and Rooibos tea may have cardiovascular effects through inhibition of ACE activity.

The influence of Aspalathus linearis (Rooibos) and dihydrochalcones on adrenal steroidogenesis: Quantification of steroid intermediates and end products in H295R cells

“…Rooibos consumption has been shown to significantly improve the lipid profiles and redox status in humans at risk for developing cardiovascular disease [34]. In addition, it has been shown by Persson et al [35] that Rooibos significantly inhibits angiotensin-converting enzyme (ACE) activity after an oral intake of a single dose of Rooibos tea, supporting the potential role of Rooibos in the overall management of cardiovascular and metabolic-related diseases. Rooibos has been shown to have beneficial effects on glucose homeostasis and type 2 diabetes, with aspalathin stimulating glucose uptake in muscle tissues as well as insulin secretion from pancreatic ␤-cells [36].…”

Processed dietary plants demonstrate broad capacity for angiotensin converting enzyme and angiotensin II receptor binding inhibition in vitro

“…Finally, green tea was the only plant type included in this study for which an IC 50 could be determined in both ACE and AngII-AT 1 R in vitro assay methods. Cardiovascular protection attributed to tea flavonoids has been widely reported and shown to involve a range of possible mechanisms (Stangl, Lorenz, & Stangl, 2006) including via RAS (Persson et al, 2010), however the link to AngII receptor binding inhibition has not previously been noted. angiotensin II (AngII) to angiotensin type 1 receptor (AT 1 R) competitive inhibition measured under standard assay conditions, at a final nominal concentration of 5 mg/mL total solids, versus total polyphenolics (TPP) content reported in gallic acid equivalents (mg per 100 mg sample), for a selection of 24 individual Stage 1-processed plant products, representing 11 taxonomic families.…”

“…ACE inhibition by tea extracts has been recently shown to depend strongly on processing due to effects on polyphenolics (Dong, Xu, Liang, Head, & Bennett, 2011;Murakami et al, 2011;Ranilla, Kwon, Apostolidis, & Shetty, 2010) and supports data showing in vitro bioactivity of enzyme and heat-modified black tea (prior to application of Stage 1 processing) was lower than green tea (Table 2). Catechin 3-O-gallate from green tea was shown to inhibit ACE by noncompetitive kinetics (Liu et al, 2003) with other mechanisms of BP regulation shown by tea polyphenolics including via NO-mediated vasodilation (Negishi et al, 2004;Persson, Persson, Hagg, & Andersson, 2010). However, the capacity for in vivo regulation of RAS by tea polyphenolics was supported by studies with normotensive (Persson et al, 2010) and mildly hypertensive subjects (Kurita, Maeda-Yamamoto, Tachibana, & Kamei, 2010) where BP lowering correlated with ACE inhibition.…”

“…Catechin 3-O-gallate from green tea was shown to inhibit ACE by noncompetitive kinetics (Liu et al, 2003) with other mechanisms of BP regulation shown by tea polyphenolics including via NO-mediated vasodilation (Negishi et al, 2004;Persson, Persson, Hagg, & Andersson, 2010). However, the capacity for in vivo regulation of RAS by tea polyphenolics was supported by studies with normotensive (Persson et al, 2010) and mildly hypertensive subjects (Kurita, Maeda-Yamamoto, Tachibana, & Kamei, 2010) where BP lowering correlated with ACE inhibition. Recent studies in SHR showed green tea-mediated a lowering of BP and plasma AngII and were linked with ACE inhibition (Liang et al, 2010).…”

Evaluation of the Taste of Tea with Different Degrees of Fermentation Using a Taste Sensing System

“…It is well known that tea is very useful for health, (1)(2)(3)(4) but few people know that many types of tea, such as black tea, green tea, and oolong tea, come from the same plant and their taste depends on the manufacturing process. One of the key steps in the tea manufacturing process, which is a factor in determining the types of tea, is the degree of fermentation.…”