**4. Biomonitoring of mycotoxins**

#### **4.1 Biomonitoring of aflatoxins**

The introduction of methods for biomonitoring individual members of the population is a major development which will make a significant contribution towards confirming the perceived linkage between mycotoxin exposure and human diseases. Biomarkers for the

Mycotoxins: Quality Management, Prevention, Metabolism, Toxicity and Biomonitoring 135

aflatoxin-DNA adduct reflects exposure to aflatoxin on the previous day, the level of aflatoxin-albumin adduct is a measure of chronic exposure to aflatoxin, over the previous 2- 3 months (Hall and Wild, 1994). Secondly, the collection of fingerprick samples of peripheral

The aflatoxin-albumin adduct has been measured in children and adults from a variety of African, and other countries. In Africa, between 12 and 100% of the samples contained the adduct, whereas samples from Thailand were contaminated at lower levels and incidence. An estimate of the average daily intake of aflatoxin B1 was performed by determining the aflatoxin-albumin adduct in blood samples collected from population of 100 persons attending health screening at the Bangladesh Institute of Research and Rehabillitation in Diabetes, Endocrine and Metabolic Disorders, BIRDEM) and United Kingdom. A comprehensive studies of the major foods showed that the main staples such as rice, pulses and wheat, were relatively free of mycotoxin contamination, whereas maize and groundnuts were significantly contaminated. Over 60% of the groundnut samples contained aflatoxin, with some samples containing levels of toxin which were 40 times greater than the maximal level permitted in the European Union, EU. About 70% of maize were contaminated, and 17% of these contained more than one mycotoxin; one sample contained five different mycotoxins. Since the use of maize, both as an animal feed and as human food, is being activiely encourage in Bangladesh, it is essential that every effort is made to alleviate the

Studies in the field of molecular biology have led to a better understanding of the generic alterations which occur during the progression from initiation to tumour formation, and to

The p53 tumour suppression gene is mutated in more than 50% of all human tumours (Hollstein et al., 1991). The number and type of mutations in this gene (the mutation spectrum) are not equally distributed, but occur in specific hot-spots which vary with the

In vitro studies using the human p53 gene have shown that codon 249 is the preferential site for the formation of aflatoxin-N7-guanine adducts (Pusieux et al., 1991). Exposure of cultured human liver cells to aflatoxin B1 has produced codon 249 mutations. Although the link between aflatoxin exposure and specific p53 gene mutations in human populations has still to be confirmed, the gene mutation spectrum has considerable potential as a marker for

Susceptibility to a particular agent will be influenced by the ability of individuals to absorb, distribute and metabolize the agent, and the nature of the metabolic process. The ability of individuals to repair damage inflicted by the agent will also contribute to the level of susceptibility. Studies with human liver microsomes have shown that the cytochrome P450s involved in the activation (epoxidation) of aflatoxin B1 vary with the level of exposure. The activation of high levels of aflatoxin B1, for example, is performed by cytochrome P450 3A4

blood is a far more convenient operation than the collected urine.

**4.2.6 Aflatoxin-albumin adduct in blood serum** 

occurrence of mycotoxin in this commodity.

exposure to, and damage from, the aflatoxins.

**4.4.1 Measures of genetic variation in metabolism** 

the development of sensitivity tests for the diagnosis of tumours.

**4.3 Markers of early biological effect 4.3.1 Measures of mutation spectra** 

etiology of tumour formation.

**4.4 Markers of susceptibility** 

aflatoxin, in humans, will now be discussed in terms of their role as markers of internal dose, biologically affective dose, early biological effect and susceptibility.

#### **4.2 Markers of internal dose 4.2.1 Markers in urine**

Aflatoxin M1 is a predominant metabolite in human urine. The presence of aflatoxin M1 in urine may be detected by TLC, HPLC and ELIZA methods. Immunoaffinity columns have also been used to clean-up the samples prior to quantification.

Zhu et al. (1987) have compared dietary exposure to the aflatoxins with the urinary excretion of aflatoxin M1, over a 3-day period, by analysing 252 urine samples in Guangxi Region of China. Between 1.2 and 2.2% of the dietary aflatoxin B1 appeared in the urine as aflatoxin M1, with a good correlation between the ingestion and excreted toxins.

### **4.2.2 Markers in milk**

The occurrence of aflatoxin M1 in human breast milk is both an indicator of exposure of individual mothers to aflatoxin in food, and of the exposure of their infants to this toxin. However, no studies have reported a good correlation between levels of ingested aflatoxin B1 and levels of aflatoxin M1 in human breast milk. The occurrence of aflatoxin M1 in human breast milk has been studied in Zimbabwe and France (Wild et al., 1987). In Zimbabwe , 11% of 54 samples of milk contained up to 0.05ug/L) aflatoxin M1, whereas none of the 42 samples collected in France was contaminated.

#### **4.2.3 Markers in blood**

Unmetabolised aflatoxin B1 in human blood serum has been used as an indicator of recent exposure to aflatoxins in food. Aflatoxin B1 has been detected (Tsuboi et al., 1984; Denning et al., 1988), for examples, in serum samples collected in Japan, Nigeria and Sudan. The detection methods used were ELIZA and HPLC; up to 3ug/kg B1 were detected.

The aflatoxin M1, B1, B2, G1 and G2 have been detected in cord sera from Ghana (34% of 188 samples); and aflatoxin M1, M2 and in B2 cord sera collected in Nigeria (12% of 78 samples) (Lamplugh et al., 1988).

#### **4.2.4 Markers of biologically effective dose**

Two biomarkers of biologically effective dose have been developed. The first marker is a urinary aflatoxin B1 -DNA adduct whereas the second is an adduct between aflatoxin B1 and serum protein.

#### **4.2.5 Aflatoxin B1-DNA adduct in urine**

Studies in rats have examined the urinary excretion kinetics of specific metabolites after a single exposure to aflatoxin B1-N7-guanine (the primary B1-DNA adduct (Figure 8) accounted for 7.5% of the total detectable aflatoxins, whereas the aflatoxins P1, Q1, M1 and B1 accounted for 31.5, 3,0, 2.2 and 0.3% of total aflatoxins, respectively (Groopman et al., 1992). Over the 24 hours after exposure, an excellent correlation existed between the oral dose of aflatoxin B1 and the urinary aflatoxin-N7-guanine adduct. The other metabolites showed no such relationship.

The use of the aflatoxin-albumin adduct as a marker of the biologically effective does offers two advantages over the measurement of the aflatoxin-DNA adduct. Firstly, whereas the aflatoxin-DNA adduct reflects exposure to aflatoxin on the previous day, the level of aflatoxin-albumin adduct is a measure of chronic exposure to aflatoxin, over the previous 2- 3 months (Hall and Wild, 1994). Secondly, the collection of fingerprick samples of peripheral blood is a far more convenient operation than the collected urine.
