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

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

AFRICA

higher in RUF. This is consistent with previous findings showing

that the amount of aspalathin can decrease by 98% during

fermentation.

However, in the present study, the antioxidant and free-

radical scavenger ferulic acid was found to be present in

RF, but not RUF. Ferulic acid is a potent antioxidant and

free-radical scavenger,

which also possesses blood pressure-

lowering effects.

It has also been suggested that ferulic acid

has multifactorial vasodilating effects, involving reduction of

angiotensin II and activation of eNOS, leading to an increase

in NO levels.

The presence of ferulic acid could therefore help

to explain the modulatory capacity of RF in this experimental

setting of nicotine-induced vascular injury.

The modulatory capabilities of melatonin were expected,

since melatonin is a known antioxidant and free-radical

scavenger and the effects of melatonin to reduce or abolish

vascular injury have previously been demonstrated. Our findings

support previous data by showing that melatonin was capable of

decreasing contraction and enhancing relaxation in the aortas of

nicotine-treated animals. The pro-relaxation action of melatonin

in aortic ring studies was first demonstrated in the rabbit

aorta,

and it has been suggested that melatonin could enhance

endothelium-dependent vasodilation, which could be explained

by the enhancement of the vascular NOS pathway.

A four-week melatonin treatment period has previously been

shown to increase SOD activity in liver tissue of nicotine-treated

rats,

while an eight-week treatment period increased SOD

activity in liver tissue in a fructose-induced model of the metabolic

syndrome.

In a rat model of renovascular hypertension, a nine-

week treatment period with melatonin led to an increase in SOD

and CAT activity in kidney and heart tissue.

Even though both melatonin and rooibos exerted beneficial

effects on the vascular system and increased antioxidant activity

in nicotine-exposed rats, it is possible that melatonin and rooibos

exert their effects through different mechanisms. It is, however,

possible that these mechanisms result in a restoration of vascular

homeostasis and, in particular, the function of NO.

The addition of Western blotting analysis of aortic rings

could provide more information on the underlying cellular

mechanisms of the different treatment groups. Proteins of

interest that would add value to our understanding of the

underlying mechanisms include eNOS, the main enzyme

responsible for vascular production of NO, and protein kinase

B (PKB)/AKT, a cell growth and survival protein and upstream

activator of eNOS and an important anti-apoptosis protein.

Furthermore, investigating the role of p22phox, a marker

of NADPH-oxidase activity, which is an important vascular

source of ROS and oxidative stress, may also further elucidate

the cellular mechanism involved. Proteomic analysis of aortic

rings to explore large-scale protein expression patterns and

differential protein regulation could greatly contribute to a better

understanding and identification of novel cellular pathways and

mechanisms involved in vascular injury and protection.

Limitations of the study include the absence of blood pressure

measurements in the rodent model, which would have provided

clinically relevant data relating to vascular function, and should

be considered in future studies. In addition,

in vitro

investigations

into the effect of melatonin on nicotine-injured rat AECs would

have supplied valuable insights into cellular mechanisms and are

worth exploring.

Conclusions

Nicotine administration resulted in significant vascular and

endothelial injury, associated with increased oxidative stress

and reduced antioxidant activity. In a novel finding, our data

showed that rooibos, specifically RF, exerted beneficial effects

on the vascular and endothelial system of nicotine-exposed

rats, and increased liver antioxidant enzyme activity. The results

shown with RF are similar to those observed with melatonin,

whose protective actions in the cardiovascular system are well

established. However, RUF did not exert beneficial effects to the

same extent as RF and melatonin, and was capable of reducing

contractility in aortic rings of nicotine-treated animals only.

It is plausible that both RF and Mel exerted their beneficial

vascular effects through their antioxidant properties, although

other mechanisms cannot be ruled out. Restoration of vascular

homeostasis, underscored by eNOS activation and subsequent

increased release of NO, as shown in the cultured cell experiments,

may also underlie the protective actions of both rooibos and

melatonin. Based on the data presented in this study, fermented

rooibos may show promise as a future cost-effective therapeutic

option on its own or as adjuvant therapy in combatting the

harmful effects of nicotine exposure on the vasculature system,

endothelium and redox status.

This research was supported by the Harry Crossley Foundation, and fund-

ing was awarded to SW and MSvS by the Faculty of Medicine and Health

Sciences, Stellenbosch University, South Africa. MSvS was supported by a

bursary awarded by the National Research Foundation of South Africa.

We thank Dr Dee Blackhurst (University of Cape Town, South Africa) for

performing the lipid peroxidation experiments (TBARS). The rooibos was a

gift to SW by Prof Wentzel Gelderblom, formerly of the Promec Unit of the

South African Medical Research Council.

References

Global Burden of Disease 2010. Institute of Health Metrics and

Evaluation, University of Washington, 2013. Available online: http://

www.healthdata.org/gbd

(accessed on 07/09/2018)

Mendis S,

et al

. Global atlas on cardiovascular disease prevention

and control 2011. Policies, strategies and interventions. World Health

Organization 2011. Available online:

http://www.who.int/cardiovascu-

lar_diseases/publications/atlas_cvd/en/ (accessed on 07/09/2018)

Cipollone F, Fazia ML, Mezzetti A. Oxidative stress, inflammation and

atherosclerotic plaque development

. Int Congress Ser

2007; 35–40.

Lusis AJ. Atherosclerosis.

Nature

2000;

407

: 233–241.

Naseem KM. The role of nitric oxide in cardiovascular diseases.

Mol

Aspects Med

2005;

: 33–65.

Barua RS, Ambrose JA, Srivastava S, DeVoe MC, Eales-Reynolds L.

Reactive oxygen species are involved in smoking-induced dysfunction

of nitric oxide biosynthesis and upregulation of endothelial nitric oxide

synthase: an

in vitro

demonstration in human coronary artery endothe-

lial cells.

Circulation

2003;

107

: 2342–2347.

Ambrose JA and Barua RS. The pathophysiology of cigarette smoking

and cardiovascular disease: An update.

J Am Coll Cardiol

2004;

1731–1737.

Sies H. Strategies of antioxidant defense.

Eur J Biochem

1993;

215

213–219.

Bonomini F, Tengattini S, Fabiano A, Bianchi R, Rezzani R.

Atherosclerosis and oxidative stress.

Histol Histopathol

2008;

381–390.