UTP UV
CHAPTER 2 Literature Review
2.23 HUMAN STUDIES
When culture material of F. verticillioides (MRC 826) was fed to horses, pigs, sheep, rats and baboons; lung oedema occurred only in pigs. Clinical signs ofPPO typically occur two to seven days after pigs consume diets containing large amounts of fumonisins over a short period of time. Clinical signs include dyspnoea, weakness, cyanosis and death (Kriek et aI., 1981; Osweiler et aI., 1992; Casteel et aI., 1993; 1994; Diaz and Boermans, 1994; Rotter et al., 1996; Fazekas et aI., 1998; Gumprecht et aI., 1998). At necropsy, the animals exhibit varying degrees of interstitial and interlobular oedema, with pulmonary oedema and hydrothorax (Colvin and Harrison, 1992; Colvin et aI., 1993). It has been hypothesised that cardiovascular alterations are a consequence of sphingoid base induced inhibition of L-type calcium channels (Smith et aI., 1996), and that cardiovascular dysfunction in pigs, subsequent to increased free sphingoid base concentration in the heart, is the cause of PPO (Haschek et aI., 1995; Smith et aI., 1996; 1999;
Haschek-Hock et aI., 1998).
2.22.3 Vervet monkeys
Riley et al. (1996) recommended that quantitative detection of high concentrations of free Sa in urine, serum or tissues be used in conjunction with other clinical tools in situations where toxicity to animals resulting from exposure to fumonisins is suspected.
Shephard et al. (1996b) studied the Sa:So ratio in serum of Vervet monkeys over 60 weeks.
These animals consumed diets such that their total daily fumonisin intake was -0.3 and 0.8 mg. kg-l bodyweight per day of F. moniliforme culture material. Serum Sa levels in the experimental groups (mean of 219nM and 325nM, respectively) were significantly elevated above the levels in controls (mean 46nM; p=O.02). The Sa:So ratio was significantly elevated from a mean of 0.43 in the control group to 1.72 and 2.57 in the experimental groups, respectively (p=0.003). Hence, the disruption of sphingolipid biosynthesis in vervet monkeys induced by fumonisins in their diet, can effectively be monitored in the serum as an elevation of the Sa: So ratio (Shephard et aI., 1996b).
for biochemical reactions involving one carbon metabolism, such as the biosynthesis of purines and thymidine, the regeneration of methionine from homocysteine and histidine metabolism. The folate receptor is found in membrane domains enriched in cholesterol and sphingolipid, and IS a glycosylphosphatidylinositol (GPI) anchored protein (Lacey et aI., 1989). This receptor is responsible for transport of folate into cells with elevated folate requirements, such as placenta, kidney and breast. By the time of organogenesis, the foetus is dependent on maternally derived folic acid. This continuous requirement for folic acid is not usually a problem because the placenta concentrates this water-soluble vitamin 3: 1 in favour of the foetus (Henderson et aI., 1995). It has been shown that treatment of Caco-2 cells with FB I inhibits folate receptor mediated transport of 5-methyltetrahydrofolate in both a time and concentration dependent fashion (Stevens and Tang, 1997). It is not unreasonable to assume that blocking the placental uptake of this water-soluble vitamin for a few critical days might induce a NTD.
Coumi (2000) dealt with the possible role of FBI in pre-eclampsia, and immunolocalised FBI in placental tissue obtained from normotensive and pre-eclamptic patients. Image analysis indicated that the intensity of staining for FBI was higher in the pre-eclamptic group than in the normotensive group. Serum obtained from both maternal and cord blood samples taken from the same patients as the placental samples were analysed for FBI presence using high performance liquid chromatography (HPLC). Fumonisin BI was detected in the maternal and cord blood serum samples of the pre-eclamptic group.
Fumonisin BI was also detected in three normotensive maternal serum samples, but was not detected in any of the cord serum samples of those pregnancies. In utero exposure to FBI is suggested by the presence of this mycotoxin in the placental samples, and in the maternal and cord serum samples obtained from pre-eclamptic pregnancies (Coumi, 2000).
Chelule et al. (2000) analysed 20 stool samples of rural school children of Vulamehlo in SA for FBI, as well as 23 urban control stool samples obtained from various households within the Durban metropolitan area. The rural (35%) and urban samples (9%) showed the presence of FB I ranging from 790 to 19 560ng per gram of freeze dried stool. Clearly, the rural population have greater exposure as they consume locally produced maize that is often contaminated with FBI. Considering the losses due to degradation during digestion, recovery, dilution effects and the time interval to when food was consumed, the quantities detected might be equivalent to considerable amounts offumonisins in food. Children from
rural areas, who were not regarded as suffering from any disease, are clearly routinely exposed to FBI which is resident in their gastrointestinal tract (GIT) for considerable periods of time, depending upon personal habits. If positive results were found, it was initially predicted these would be from the rural population where maize is the staple food.
However, two volunteers from Durban were positive at levels in the higher range of contamination (3.5 and 16.2 mg.g- I respectively). Fischer's exact test showed that the rural population was six times more at risk to FBI exposure than the urban group. It is usual however for urbanized black people to eat maize products, presumably from urban stores, and therefore may be complacent about its quality (Chelule et al., 2000).
Subsequently, Chelule et al. (2001) surveyed households in rural (in villages of Mphise and Ngcolisis) and urban (Durban Metro) areas of KZN, SA. Analysing stored maize, plate ready food and faeces enabled assessment of the exposure of the inhabitants to FB I.
Of the 50 rural maize samples examined 32% had levels of FBI ranging from 0.1-22.2 mg. kg-I , whereas 29% of the 28 cooked maize (phutu) samples contained FBI ranging from 0.1-0.4 mg.kg-I. The incidence and levels of FBI in faeces were 33% and 0.5-39 mg. kg-I respectively. Of the 49 urban maize samples analysed, 6.1% had a range of 0.2-0.5 mg.kg-I FBI, whereas 3 of 44 faecal samples (6%) ranged between 0.6-16.2mg.kg-l. No FBI was detected in urban phutu samples. Because these levels are lower than those published from regions in SA with high incidence of oesophageal cancer (OC), it may be concluded that the risk ofOC from FBI exposure is lower in the KZN region (Chelule et al., 2001).
Several possibilities present themselves; either FB I is highly potent or its absorption is aided by other dietary factors such as alcohol or fat. Previous data indicates that it is improbable that in the digestive tract toxin is modified into a more accessible form e.g., by esterification, or that there are transport systems that assist in passage, either present in an active or latent form. An alternative approach is to measure Sa and So levels, which are elevated, however, hold out some hope for exposure studies. However detailed work will be needed to correlate exposure levels with dose and time periods.