Research Article Volume 6 Issue 1
1Department of Genetics and Biotechnology, University of Calabar, Nigeria
2Department of Zoology and Environmental Biology, University of Calabar, Nigeria
3Department of plant Science and Biotechnology, Abia state University, Nigeria
4National Biotechnology Development Agency of Nigeria, Nigeria
5Department of Soil Science, University of Calabar, Nigeria
Correspondence: Godwin M Ubi, Department of Genetics and Biotechnology, Faculty of Biological Sciences, University of Calabar, PMB 1115, Calabar, Nigeria, Tel +2348064499332
Received: October 11, 2022 | Published: October 28, 2022
Citation: Godwin MU, Edu N, Eyogor, et al. Genotoxicity and metabolic pathway of aflatoxin isolate in contaminated poultry feed. Int J Avian & Wildlife Biol. 2022;6(1):41-46. DOI: 10.15406/ijawb.2022.06.00182
Aflatoxin is a nephrotoxic mycotoxin found in stale food which when consumed has some carcinogenic potentials. Aflatoxin presence has been identified in many foodstuffs all over the globe and with significantly higher frequency and concentrations coming from poultry feeds especially the locally formulated ones as a result of high cost of poultry feedstuff. Though foodstuffs are often contaminated with more than one mycotoxin, the focus of most research had centred on aflatoxin due to its wide occurrence and toxicology effect on the agro-morphometric parameters of poultry. The present studies reveals the major genes affected by aflatoxin ingestion in contaminated feed to include Tumour protein gene (TP53), Albumin protein gene (Alb), Spermatogenesis associated protein 5 (SPATA5), cytochrome p450 subfamily 3 polypeptide 4 and 7 protein genes (CYP3A4 and CYP3A7), glutathione s-transferase mu-1 protein gene (GSMU1) and minor genes such as the epoxide hydrolase 1 gene (EPHX 1), LACE 1 gene, XRCC1gene and cyclin 2 gene (CCGN2) whose expressions and functionality in the poultry has been silenced or activated leading to genotoxicity, highlights the biosynthesis and metabolic pathway of aflatoxins in poultry system and the toxin–protein interactions of aflatoxin ingested through contaminated poultry feed stuff as well as its co-occurrence with other mycotoxins in organisms as well on their combined toxicity. The metabolic pathway of aflatoxins B1, B2, G1 and G2 ingestion of aflatoxin in contaminated poultry feeds begins with the production of methyl-sterigmatocystin enzyme which pave the way for the complex, Sterigmatocystin which upon dimethylation produces versicolonin A (an enzyme which disrupts the colon) and versicolonin. The two enzymes reacts to form versiconial hemiactal acetate and producing 1‘5 Hydroxyaverantin both of which distorts the expression and functionality of Mycotoxin mixtures involving aflatoxin produced additive and synergistic effects in poultry birds suggesting that aflatoxins represent a significant health hazard. Hence, special attention should be given to poultry feedstuff screening and purification to prevent the associated toxicity that includes genotoxicity and the production of cancer-promoting mycotoxins.
Keywords: tumour protein gene, albumin protein gene, CYP3A4 & CYP3A7, Aspergillusflavus, Aspergilusparasiticus
TP53, Tumour protein gene; Alb, Albumin protein gene; SPATA5, Spermatogenesis associated protein 5; CYP3A4 and CYP3A7, cytochrome p450 subfamily 3 polypeptide 4 and 7 protein genes; GSMU1, glutathione s-transferase mu-1 protein gene; EPHX 1, epoxide hydrolase 1 gene
The livestock industry is an important subsector of the agricultural sector of Nigeria's economy. The role of this sector cannot be over-emphasized considering the importance of animal protein in the diet of people and contribution from this sector to the gross domestic product. Livestock types found in Nigeria include cattle, sheep, goats, pigs, poultry, horses, donkeys and camel.1 These animals are spread throughout various ecological zones in the country determined by environmental factors such as temperature, rainfall, humidity, light intensity etc. these factors determine whether an animal can or cannot survive within a specific environment. Livestock rearing is often considered a secondary occupation of many farmers in developing countries. Nevertheless, the importance of livestock in the livelihoods of the rural people cannot be underestimated. Households live on subsistent farming, often integrating crop production with livestock rearing, yielding multipurpose products and uses.2 The increasing cost of keeping livestock have entrenched the art and science of local feed formulation and the use of low quality or substandard prepared feeds which attract contamination by microorganisms notably among which are mycotoxins expressed in forms of aflatoxins, ochratoxin, fumonisin, patulin and many others bacterial. Mycotoxins are toxic metabolites produced by certain fungi. They are always hazardous to man and domestic animals and had come to public interest since the past 30years. Mycotoxins are secondary toxic metabolites growing on food products, such as corn, peanuts, and wheat, among others. Exposure occurs predominantly by the ingestion of contaminated feeds.
When contaminated cereal such as corn, wheat, peanuts and sorghum, as well as other raw materials, are used in the preparation of animal feed. Among them, aflatoxin is a class of potent Mycotoxins produced mainly by Aspergillusflavus, Aspergilusparasiticus and occasionally by other Aspergilus species.3 Aflatoxin constitutes a great threat to the health of animals and humans due to their teratogenic, carcinogenic, mutagenic and immunosuppressive effects.4,5 Additionally, in terms of the livestock industry, aflatoxin causes a huge economic loss by retarding animal growth, increasing feed consumption and reduced meat production.6,7 Among the various types of aflatoxins, aflatoxin B1 (AFB1) is known to be the most biologically active component. Aflatoxin, in the late 1950s and 1960s, were identified to be the cause of the turkey X disease in Great Britain.8–10 Aflatoxin was identified as carcinogenic in rainbow trout.11,12 In the United States, studies have implicated aflatoxin as the cause of epizootic hepatitis in dogs and as the cause of mouldy corn poisoning in pigs.13 The immune system of the poultry is the first target to be influenced by the Mycotoxins. Immunosupression can be observed in poultry ingesting aflatoxins at levels below those that cause over symptomatology, and explained in parts, by atrophy of the bursa of fabricius, thymus, and spleen.14
Aflatoxin are resistant to food processing and therefore, could be found both in animal feed and foodstuff for direct consumption or processed foods, posing a risk for human health. All bird species are sensitive to aflatoxin toxicity and although they do not receive relatively high concentration of the feed and end lethally, low levels could also be deleterious after continuous intake. Growing birds, especially ducklings and turkey poultry are extremely sensitive to the toxic effect of aflatoxin. The total aflatoxin content in feed should not exceed 20ug/kg feed. Nevertheless, levels lower than 20ug/kg feed also induce lower resistance to diseases and stress.15 The toxic effects of aflatoxin in domestic fowls are studied in detail with regards to their carcinogenic, teratogenic, mutagenic and growth inhibiting effects. The occurring haematological, biochemical (decreased serum, total protein, albumin, inorganic phosphorous, uric acid and total cholesterol and the values of heamatocrit, red blood cell counts, mean copuscular volume, haemoglobin, thrombocyte counts, percentage of monocyte counts, increased values of white blood cell and heterophils counts) Oguz, immunological depression in anti-bruscellaabortus antibodies) qureshi and morphological (hydropic generation in liver, significantly reduced in size and bursa of epithelium, intraepithelial cysts oedema in the intraepithelial areas and heterophil infiltrations: slightly lymphoid depletion of periateriolar lymphoid tissues in spleen; pale kidney with degeneration and/or necrosis of tubular epithelium. There are also grave effects of aflatoxins on the major and minor protein genes in poultry which further creates room for genetic disorders.
The morphological changes in the spleen are characterized with lymphatic degeneration, fatty dystrophy and haemorrhagic foci, cognitive event in the red pulp, reduction of lymphocytes, vascular dystrophy, and depletion of lymphoid cells, reticular cell hyperplasia, lymph cytolysis and increased germinal cell counts. A number of strategies for detoxification of Mycotoxins contaminated feeds are proposed and have included physical separation, heat inactivation, irradiation, microbial degradation, treatment with chemicals. Regardless of that, some of them reduce also the bioavailability of amino acids and/or minerals in the poultry birds. The importance of aflatoxin in poultry production cannot be overemphasized and thus created the heightened need for this research.
Potato dextrose agar plate was prepared and collected. Moulded poultry feed (growers mash) was serially diluted in saline solution. The samples were then inoculated into the agar plates. The plates (plate 1) were further inoculated at 28+20C for 3-5days. After incubation, the total numbers of fungal population per gram of the feed were estimated and fungal species identified.
The Mycotoxin from Aspergillus flavus called Aflatoxin was isolated from collected moulded poultry growers mash. Other materials used for the isolation process included potato dextrose agar, saline solution, chloroform, sodium bicarbonate solution, ethyl acetate, formic acid, toluene, 1% p-dimethyl aminobenaldehyde, petri dishes, incubator, microscope, pH scale, conical flask, Whatmann No. 1 filter paper, water bath, evaporator and silica gel.
The concentrated culture filtrate was shaken repeatedly with 100ml volume of chloroform and the extraction repeated 2 or 3 times. The chloroform extracts was combined and filtered through Whatmann No.1 filter paper. From the filtered chloroform extract, the toxins were extracted with sodium bicarbonate solution by shaking the chloroform extract several times with 0.5M sodium bicarbonate solution. All lipid materials were separated by filtration after keeping the sodium bicarbonate overnight in a separating funnel. Finally, the pH of the solution was brought down to 2.0 and the toxins were extracted from the concentrates into chloroform by repeated extraction with aliquots of chloroform. The extracts were cooled and concentrated and the crude toxins isolated.
Metabolic pathway and genotoxicity prediction was performed using Toxtree 2.6. and the Chembi KEGG online programme resources. The associated effect of aflatoxins on the target major and minor genes in terms of absorption, metabolism, distribution, excretion and toxicity. The expasy.org, click2drug, pathway databases stitch online resource programme was used to determine the aflatoxin genome (genotoxicty) interactions for the associated genetic, molecular, biological and cellular processes.
Aflatoxins are a group of closely related toxic metabolites that are designated mycotoxins. They are produced by Aspergillus flavus and Aspergillus parasiticus. Members of the group include aflatoxin B1, aflatoxin b2, aflatoxin G1, aflatoxin G2, aflatoxin M1 and aflatoxin M2 (MeSH) (328.3g/mol).
Functional analysis of the gene sets |
Set of genes involved |
False discovery rate |
Genes that are involve in the metabolism of xenobiotics using Cytochrome P450. |
3 |
0.000678 |
Genes associated with chemical carcinogenesis. |
3 |
0.000678 |
Genes that plays crucial role in drug metabolism and Cytochrome P450 activities |
2 |
0.0276 |
Genes that establishes the P53 signalling pathway |
2 |
0.0276 |
Genes that plays critical role in bile secretion. |
2 |
0.0276 |
Table 1 Functional analysis of the gene sets
Control of mycotoxicosis depends on the safeguarding of mycelial growth in the feedstuff, and on removing toxin contaminated feed. Unfortunately, aflatoxin is most likely and always found in contaminated feeds and foodstuff. The food and agriculture organisation (FAO) had posited that not less than 25% of global cereals are contaminated with aflatoxins. Hence, researching for procedures for detoxification becomes imminent.16 Though such processes should be able to detoxify aflatoxins to below regulatory limits and also prevent the production of additional compound from aflatoxin metabolism, and as well as maintaining the nutritional composition of the detoxified feedstuff. A good toxin binder should restore the nutritional values of aflatoxin contaminated feed. The quality of a good toxin binder is expressed in several means including, knowledge of their binding capacity, the absorption efficacy, the activation time and rate of Inclusion of aflatoxin contaminant in the feedstuff.17,18
Several methods have been developed in pursuant to their ability to inactivate aflatoxin in contaminated feedstuffs, with the sole aim of either removing or destroying the toxin and which may take the forms of physical, biological and chemical approaches. The approach adopted fully depends on the available know-how.
The general decrease in PCV, RBC, WBC, and Hb of broilers fed diets that contained graded levels of AFB1 particularly as the level increases from 25% to 35% to 45% to 55% shows that the toxin may contain blood diminishing factors that may have stimulated the shortage of blood production by the broilers.19 demonstrated decrease in Hb, RBC and PCV due to decreased mineral content of feed which is an indispensible factor of erythropoesis. The gradual drop in WBC as the inclusion levels increased suggest that AFB has negative effect to the immune system of the broilers. These haematological parameters fall within the low physiological ranges as established by19,20
The commercial poultry in Nigeria is largely private sector driven. The government only provides policy support. Household poultry flock size appears to be larger on the average than in the previous decade probably because of some elements of commercial poultry being introduced into it. In other to increased and maximize profit, most farmers and practitioners go into feed formulation with a resultant aflatoxin contamination. Organic acid is considered one of the most widely used food additives, which is commonly used as a preservative, acidulant, pH control agent, flavour enhancer and antioxidant in many foods. Organic acid is one of the important factors responsible for the characteristics smell and sour taste revealing its antibacterial and antifungal properties.21 Organic acids have been used to decrease the growth of aflatoxins and reduce secretion of harmful fungi. In addition, they have many effect on poultry health, including growth performance, decrease feed conversion ratio, and in haematological and pathological indices through the detoxification of aflatoxin.22
The use of mycotoxin binders such as biological methods, the microorganisms and their metabolites to be tailored to eliminate aflatoxins. This can be a good promising strategy due to its specificity, efficiency, and environmentally friendly method of detoxification.22 Some microbes including fungal and bacterial isolate, such as live yeast, Sacchromyces cerevisiae.19,22 Flavo bacterium aurantiacum,20 Stenotrophomonas Maltophilia,21 Myxococus fulvus16 and Aspergilus Niger17,22 were reported to effectively biodegrade aflatoxin in vitro. However, little is known about their efficiency in the biodegradation of aflatoxin and effect of aflatoxicosis in vivo. As a biological product, several studies have revealed that esterified glucomannan derieved from cell wall of Sachromyces cerevisiae20,22 have shown considerable promise in countering aflatoxins. Studies of using biological Mycotoxins based on S. Cerevisae, showed that using that binder in contaminated feeds was responsible for reducing liver residual aflatoxin levels,21,22 and in ameliorating the negative effect of aflatoxin on Newcastle antibody production.22,23
The study concludes that the major genes affected (genotoxicity) by aflatoxin ingestion in contaminated feed are the Tumour protein gene (TP53), Albumin protein gene (Alb), Spermatogenesis associated protein 5 (SPATA5), cytochrome p450 subfamily 3 polypeptide 4 and 7 protein genes (CYP3A4 and CYP3A7), glutathione s-transferase mu-1 protein gene (GSMU1) and minor genes such as the epoxide hydrolase 1 gene (EPHX 1), LACE 1 gene, XRCC1gene and cyclin 2 gene (CCGN2) whose expressions and functionality in the poultry has been silenced or activated leading to genotoxicity.
Highlights of the biosynthesis and metabolic pathway of aflatoxins B1, B2, G1 and G2 ingestion in contaminated poultry feeds induces the production of methyl-sterigmatocystin enzyme which pave the way for the complex, Sterigmatocystin which upon dimethylation produces versicolonin A (an enzyme which disrupts the colon) and versicolonin. The two enzymes reacts to form versiconial hemiactal acetate and producing 1‘5 Hydroxyaverantin both of which are cancer promoting substances and also distorts the expression and functionality of SPATA5, CYP3A4 and GSMU1 genes. Hence, there is urgent need for special attention to be given to poultry feedstuff screening and purification to prevent the associated toxicity that includes genotoxicity and the production of cancer-promoting mycotoxins. Considering the numerous practitioners of rural poultry in Nigeria, a special and urgent attention is needed for an effective control of Aflatoxin contamination of poultry feed to minimize the implications for the economy and public health.
Re-evaluate the options for the control of Aflatoxin with a view to determining which of the two options of either eradication or vaccination that will provide more comprehensive and long lasting solutions. Adequate poultry feed storage strategies should be developed and adopted to avoid the contamination of these feed by aflatoxin which could also affect human health as well as the health of the birds.
None.
Authors declared no conflicts of interest.
None.
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