Cardiovascular Journal of Africa: Vol 31 No 2 (March/April 2020)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 31, No 2, March/April 2020

AFRICA

only, as indicated by DAF-2/DA fluorescence (Fig. 4). However,

pre-treatment with 0.015 mg/ml RF was not able to significantly

reduce necrosis in nicotine-injured cells, as indicated by PI

fluorescence (Fig. 5).

Discussion

To the best of our knowledge, this is the first study to investigate

the effects of rooibos, both fermented and unfermented, in a

rat model of nicotine-induced vascular changes and oxidative

stress. The protective effects of RF and RUF were compared to

the known beneficial effects of the potent antioxidant and free-

radical scavenger, melatonin.

Exposure to 5mg/kg bw/day nicotine over a six-week treatment

period resulted in increased vascular contractility in aortic rings

and a reduction in antioxidant enzyme activity (SOD and CAT)

in liver tissue. Lipid peroxidation, as indicated by TBARS

levels, was increased in serum samples of nicotine-exposed rats,

therefore indicating that nicotine increases oxidative stress. The

harmful vascular endothelial effects of nicotine were further

characterised in a model of cultured rat AECs, where nicotine

treatment (100 nM; 24 hours) was associated with reduced NO

production and reduced cell viability.

In vascular studies, when RF (2%) and melatonin (4 mg/

kg bw/day) were co-administered with nicotine, the harmful

pro-contractile effects observed in aortic rings from rats treated

with nicotine only were attenuated. Additionally, endothelium-

dependent vasorelaxation was significantly enhanced in groups

co-treated with RF and melatonin. The effects of RUF were

limited to reducing contractility in aortic rings of nicotine-treated

animals. Furthermore, co-administration of RF and melatonin

with nicotine resulted in increased SOD and CAT activity in

liver tissue of rats compared to those treated with nicotine only,

whereas co-administration of RUF with nicotine did not result

in any significant increase in SOD or CAT activity. Co-treatment

with melatonin additionally decreased lipid peroxidation. In the

nicotine-injured AECs, pre-treatment with RF (0.015 mg/ml)

significantly increased NO production.

Nicotine-induced vascular changes and oxidative stress have

previously been demonstrated by others. Nicotine exposure

resulted in pro-contractile responses in the aortic rings of rats,

where aortic rings were challenged with Phe

or KCl

44,45

elicit contractile responses. Furthermore, exposure to nicotine

resulted in decreased SOD activity in the liver and increased lipid

peroxidation in Sprague-Dawley rats,

as well as decreased CAT

activity, when compared to untreated controls in Wistar rats.

these studies, oxidative damage, resulting in impaired integrity

of the vascular endothelium, was suggested as a possible

mechanism of action.

43-45

It is, to the best of our knowledge, the first time that

oral ingestion of RF over a period of six weeks has been

demonstrated to improve vascular endothelial function,

associated with increased activity of important antioxidant

enzymes, in a rat model of nicotine-induced injury. The potential

of rooibos to enhance antioxidant defences, including SOD and

CAT activity, has previously been demonstrated in rat brain

extracts in an immobilisation stress model,

while SOD levels

were significantly higher in RUF-treated animals in a rat colitis

model.

These actions have been attributed to the flavonoid content

in rooibos

and the potential ability of rooibos to reduce

DNA damage caused by oxidative reactions.

Epidemiological

evidence suggests that dietary-derived antioxidants have the

potential for disease prevention,

and it has been shown that

dietary polyphenols can increase endothelium-dependent NO

generation by modulating cellular sensors for oxidative stress.

NO is capable of reacting with O

•-

to form peroxynitrite,

which can lead to the nuclear accumulation of nuclear factor

erythroid 2-related factor (Nrf2).

Nrf2 is a redox-sensitive

transcription factor, involved in antioxidant response element

(

ARE

)-dependent gene expression,

and under conditions of

oxidative stress, Nrf2 is capable of activating

ARE-

dependent

transcription of phase II and antioxidant defence enzymes, such

as glutathione-

-transferase, GPx and heme-oxygenase-1.

Although the beneficial effects of RF on vascular endothelial

function and oxidative stress were comparable to those observed

with melatonin, the effects of RUF treatment were more modest

and limited to vascular contractility only. The difference in

the effects of RF and RUF is particularly interesting, since

the phytochemical content of rooibos changes considerably

during the fermentation process. The main difference was in the

aspalathin and nothofagin contents, which were considerably

Control

100

nicotine

0.015 mg/ml

Nicotine + RF

% DAF 2/DA fluorescence

150

100

Fig. 4.

The effects of RF pre-treatment on NO-production

as measured by DAF-2/DA fluorescence. *

0.05

vs control;

0.05 vs 100

M nicotine (

= 6– 8 per

group).

Control

100

nicotine

0.015 mg/ml

Nicotine + RF

Propidium iodide % change from controls

200

150

100

Fig. 5.

The effects of RF pre-treatment on cell viability.

Percentage change in necrosis indicated by PI fluo-

rescence. *

0.05 compared to control.

0.05

compared to 0.015 mg/ml RF; (

= 6–8 per group).