Preventive potential of dietary inclusion of Brachystegia eurycoma (Harms) seeds on N-methyl-N-nitrosourea-induced colon carcinogenesis in Wistar rats

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Abstract

Ethnopharmacological relevance

Brachystegia eurycoma seed is used as dietary condiment and as part of recipes for treating colorectal disorders, while laboratory studies have established that it contains crude fiber and polyphenols which are important in cancer prevention.

Aim of the study

To establish the efficacy of a Nigerian diet in colon cancer prevention, a study was conducted to evaluate dietary inclusion of Brachystegia eurycoma seed in experimental colon carcinogenesis.

Methods

Rats undergoing intra-rectal instillations of N-Methyl-N-nitrosourea (MNU) were fed B. eurycoma included diets at 0%, 2.5%, 5% and 10% for a period of ten (10) weeks following which they were sacrificed; blood and tissues were monitored for biochemical, histological and immunohistochemical parameters.

Results

Brachystegia eurycoma significantly (P < 0.05) prevented MNU-induced elevation of malondialdehyde and carcinoembryonic antigen (CEA) as well as reduced activities of catalase and superoxide dismutase. The colon showed deep mucosal ulceration with moderate inter-glandular inflammation in the MNU control group, but only mild or no inflammation was observed in the colon of the MNU groups fed experimental diets. Similarly, colon immunohistochemistry assay showed that the dietary inclusion significantly prevented MNU-induced damage to mismatch repair gene (MutL homolog1). Positive relationship existed between fiber content of B. eurycoma seeds and MutL homolog1 protein expression while that between polyphenol/flavonoids contents of diets and CEA was negative.

Conclusion

These data suggest that both dietary fiber and polyphenol/flavonoids contribute synergistically or additively to the potential preventive effect of B. eurycoma seeds in colon carcinogenesis, presumably through mechanisms that involve limiting the extent of oxidative stress and preventing or delaying the onset of pro-carcinogenic inflammatory processes.

Introduction

Colorectal cancer (CRC) includes all cancer originating from the caecum to the anus, which commonly occurs sporadically, but inherited in about 5% of the cases (Mo'ez et al., 2009). Incidence rates of CRC in the West African Sub-region which was less than 3 per 100,000 populations in the last 40–50 years has been increasing steadily in recent times. For example, in 2018, age standardized incidence rate per 100,000 of CRC in Western Africa was 6.0 and 5.1 in male and female, respectively (Bray et al., 2018), while in 2000–2017, Nigeria had the incidence rate of 3.4/100,000 population (Irabor, 2017). According to World Health Organization (2014), out of 30,400 cancer deaths in Nigeria, colon cancer constitutes 5.3% in men and 3.8% in women. These statistics call for urgent concerted action to reverse the increasing trend in CRC. Population variations in colon cancer incidences suggest that environmental factors, specifically dietary trends, may play an important role in the etiology of this disease.

Many plants contain secondary metabolites that have therapeutic value for humans, especially the antioxidant polyphenols (Alam et al., 2018), while food with rich antioxidants play essential role in the prevention of disease caused by oxidative stress. Therefore, antioxidants-rich plants are now receiving special attention in the prevention of carcinogenesis, while plants already used as food will be a special class in this regards. One of such plants is Brachystegia eurycoma, known in the Igbo language of South Eastern Nigeria as “Achi”.

Brachystegia eurycoma is normally a dietary soup thickening agent that is also prescribed as part of recipes for treating colorectal disorders by traditional medical practitioners. It is believed to aid in maintaining heat within the body when consumed, and in softening bulky stools (Ndukwu, 2009), an important factor in the development of colon cancer. Carcinogenesis, being a multistage process can be effectively inhibited through processes that promote the onset of cancer. Dietary constituents like antioxidant polyphenols and fiber have been associated with colon cancer chemoprevention. The presence of specific cancer chemopreventive compounds have been reported in this seed, hence the purpose of this study was to explore to what extent, the total content of these phytochemicals could collectively contribute to indices of colon carcinogenesis chemoprevention using dietary inclusion of the seeds of B. eurycoma in experimental colon carcinogenesis. Since the major focus of the research is prevention of colon carcinogenesis through traditional medicinal recipes that are also important as dietary components, the animal model was adopted as the bottom line for easy recommendations and application, as it is practically impossible, at least in the target population in Africa, to have any dietary or medicinal plant component in its pure form for continuous consumption or administration in a sustainable campaign.

Section snippets

Plant sample collection and authentication

Dried seeds of B. eurycoma were collected from Anambra State, Nigeria and identified at the Herbarium Unit, Department of Botany, Ahmadu Bello University, Zaria, Nigeria with voucher number 424. The seeds were driedunder the sun to a relatively constant weight, pounded using laboratory mortar and pestle and stored in air-tight containers until required.

Experimental animals

Male Wistar rats weighing between 80 and 100 g were obtained from Animal House, Physiology Department, Ahmadu Bello University, Zaria. The

Total polyphenol, flavonoids and fiber content

The level of total polyphenols, flavonoids and fiber at different levels of dietary inclusion are shown in Table 1. There was increase in the level of crude fiber content as well as the levels of total polyphenols and flavonoids with increasing levels of B. eurycoma seed inclusion in the diet.

Effect of B. eurycoma seed-included diets on some oxidative stress, antioxidant enzymes and some indices of carcinogenesis

Assessment of the in vivo antioxidant effect of dietary inclusion of B. eurycoma seeds in diets on MNU intoxication showed a statistically significant (P < 0.05) increase in the level of malondialdehyde in

Discussion

Due to the increasing risk factors of humans to various deadly diseases, there has been a global trend towards the use of natural substance from medicinal plants and food plants as therapeutic antioxidants for disease prevention and management. Many studies have primarily focused on the potential benefits of the individual phytochemical compounds and their roles in early and late carcinogenesis prevention. However, a few studies have established that the cumulative synergistic effect of

Conclusion

That the seeds of Brachystegia eurycoma demonstrated high antioxidant potential in colon carcinogenesis model and protected the colon tissues from oxidative damage, prevented upregulation of carcinoembryonic antigen and guaranteed normal expression of one of the key DNA mismatch proteins (MLH-1), strongly suggest that B. eurycoma seeds could prevent or delay the process of carcinogenesis in the population where it is frequently consumed. Therefore, this study provides a basis for the folkloric

Author contributions

SEA contributed in the work by supervising the design, execution of the experiment and the analysis of the data, as well as well as in finalizing the writing of the manuscript, while UDI produced the design, carried out the laboratory investigations, performed the data analysis and produced the first draft of the manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors, but authors would like to thank Alexander von Humboldt Foundation (AvH) of Germany for partial funding of SEA's research on antioxidants.

Conflicts of interest

The authors hereby declare no conflicts of interest.

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