Fumonisins in Fish
Fumonisins are a group of recently discovered mycotoxins which belong to the family of Fusarium toxins. The contamination of feedstuffs with mycotoxins poses a serious threat to the health and productivity of animals and cause great economic losses. Fumonisins are mainly produced by Fusarium verticillioides (syn. moniliforme) as well as by Fusarium proliferatum and they occur predominately in maize and maize-based feeds (Ross et al. 1992).
In 1988 they were first identified and isolated and so far there are 28 fumonisin analogues known (Gelderblom et al. 1988; Rheeder et al. 2002). Fumonisins are divided into four groups: Serial A, B, C and G. With regard to their toxicity the B-type fumonisins represent the most important ones (Marasas 1996). In naturally contaminated food and feed fumonisin B1 represents about 70% - 80% of the total fumonisin content (Krska et al. 2007).
Fumonisins are very polar and water soluble compounds. Unlike other mycotoxins, they have a long chain structure. Chemically, they are polyhydroxyl alkylamines esterified with two carbon acids, i.e. tricarballylic acid (TCA). The four common members of the type B fumonisins differ by presence and position of the free hydroxyl groups respectively (ApSimon 2001). The one-sided or bilateral elimination of TCA results in partial hydrolyzed fumonisin or hydrolyzed fumonisin (HFB1). Fungal colonization and growth and/or mycotoxin production are influenced by a variety of factors. Optimum conditions for fumonisin production are temperatures between 10°C and 30°C with a water activity (amount of free available water) of 0.93 aw (Marin et al. 1999).
A published survey about the occurrence of mycotoxins in Asia initiated by Biomin GmbH together with Romer® laboratories in Singapore reported that 58% out of 960 feed raw material samples were contaminated with fumonisins. In this report the highest level of fumonisins detected was 21.5 mg/kg in a corn sample from China (Rodrigues and Wegleitner 2008). In Europe, levels up to 250 mg/kg were reported in maize from Italy (Bottalico et al. 1995) . Table 1 gives examples on high concentrations of fumonisins found in maize samples around the world.
Table 1: Examples on high concentrations of fumonisins in maize samples
|250||Italy||Bottalico et al. 1995|
|160||Korea||Seo and Lee 1999|
|155||China||Chu and Li 1994|
|122||USA||Wilson et al. 1990|
|117||South Africa||Rheeder and Marasas 1998|
|75||Hungrey||Fazekas et al. 1998|
|21.5||China||Rodrigues and Wegleitner, 2008|
|10.6||China||Chin and Tan, 2006|
The toxicity of fumonisin is based on the structural similarity to the sphingoid bases; sphingosine and sphinganine (Figure 1). They are inhibitors of sphinganine (sphingosine) N-acyltransferase (ceramide synthase), a key enzyme in the lipid metabolism, resulting in a disruption of this pathway. This enzyme catalyzes the acylation of sphinganine in the biosynthesis of sphingolipids and also the deacylation of dietary sphingosine and the sphingosine that is released by the degradation of complex sphingolipids (ceramid, sphingomyelin and glycosphingolipide) (Wang et al. 1991). Sphingolipids are basically important for the membrane and lipoprotein structure and also for cell regulations and communications (second messenger for growth factors) (Berg et al. 2003).
Figure 1: Structures of sphinganine, sphingosine and fumonisin B1
As a consequence of this disruption many bioactive intermediates are elevated, others reduced. The main points are:
- Rapid increase of sphinganine (sometimes sphingosine).
- Increase of sphinganine degradation products like sphinganine 1-phosphate.
- Decrease of complex sphingolipids.
Free sphingoid bases are toxic to most cells by affecting cell proliferation and inducing apoptosis or necrotic cell death (Riley et al. 1996; Stevens et al. 1990). The accumulation of sphinganine is associated with hepato- and nephrotoxic effects (Riley et al. 1994). Complex sphingolipids are important for cell growth regulation and also cell-cell interactions. The accumulation of free sphingoid bases in the serum and urine are a useful biomarker for the exposure of fumonisins (Riley et al. 1993).
Toxicity in fish
This is still poorly understood in fish as there have been only a few studies published. However several experiments have documented fumonisins to be toxic for fish.
In an experiment, one-year and two-year channel catfish were fed diets containing Fusarium moniliforme from maize to contain FB1 at 20, 80, 320, and 720 mg/kg for 10 weeks and 14 weeks, respectively (Lumlertdacha et al. 1995). It was reported that dietary levels of FB1 of 20 ppm or above are toxic to one-year and two-year channel catfish fish fed with 20 mg/kg. FB1 did not show differences in mortalities but weight gain was significantly decreased by 15 % compared to the control group. Additionally, liver lesions were noted.
In another study with catfish consuming Fusarium moniliforme maize containing fumonisins, an increase of the free sphinganine and free sphingosine ratios (Sa:So ratio) in serum, liver, kidney and muscle were found at ?10 mg FB1/kg after 12 weeks (Voss 2007). Catfish were also fed with FB1 from Fusarium cultured maize (EFSA, 2005). Eight groups of 20 catfishes were fed 0, 0.7, 2.5, 5.0, 10.0, 20.0, 40.0 or 240.0 mg FB1/kg feed, respectively, for 12 weeks. At concentrations of 40 mg FB1/kg feed, weight gain and feed consumption were decreased and histological changes were detected.
Tuan et al. (2003) demonstrated that feeding FB1 at levels of 10, 40, 70 and 150 mg/kg feed for 8 weeks affected growth performance of Nile tilapia fingerlings. In this experiment the mortality was low and histopathological lesions were not observed. Fish fed diets containing FB1 at levels of 40 mg/kg or higher had decreased average weight gain. Haematocrit was decreased only in tilapia fed diets containing 150 mg FB1/kg. The Sa:So ratio in liver increased at a 150 mg FB1/kg in the fish feed.
Although research studies revealed that FB1 is toxic to tilapia and channel catfish by suppressing growth and/or causing histopathological lesions, this fish survived mycotoxins levels up to 150 ppm. Reduction on the percentage of survival of channel catfish was observed for diets containing 240 ppm FB1 (Li et al. 1994).
Adverse effects of fumonisin contaminated diets were reported in carps. Signs of toxicity can be observed with 10 mg FB1/kg feed (Petrinec et al. 2004) in one-year old carps. In these experiments scattered lesions in the exocrine and endocrine pancreas and inter-renal tissue, probably due to ischemia and/or increased endothelial permeability were reported. In one-year old carp, consumption of pellets contaminated with 0.5 and 5.0 mg FB1 per kg body weight resulted in a loss of body weight. Alterations of haematological and biochemical parameters, indicating) were target organs (Pepeljnjak et al. 2003).
Preventive measurements describe all the steps to counteract mycotoxins during the growth of the grain as well as during harvesting or storage. In the field, all management practices which maximize plant performance and reduce plant stress can substantially decrease mycotoxin contamination. However, all these prevention measures can only reduce but not eliminate the risk of mycotoxin contamination. Therefore successful detoxification procedures after harvest are essential. They are classified into three categories: physical, chemical and biological methods.
The efficacy of physical treatments depends on the level of contamination and the distribution of the mycotoxins in the grain. Additionally, the results obtained are often uncertain and associated with high losses. Various chemicals (bases, oxidizing agents, different gases etc) have been tested for their ability to detoxify mycotoxins but only a limited number of them are shown to be effective against them without reducing nutritive value, palatability of the feed or producing toxic by-products. In achieving adequate decontamination results, several parameters such as reaction time, temperature and moisture have to be monitored. Due to their uncertain and uneconomic results, the practical application of physical and chemical treatments is very limited.
Adsorbent agents are added to the feed and bind mycotoxins during digestion in the gastrointestinal tract resulting in a reduction of toxin bioavailability. Adsorption of mycotoxins requires molecule polarity and also a suitable position of the functional groups. Due to this, only a few mycotoxins can be adsorbed efficiently without affecting essential feed ingredients.
This method is especially used to counteract aflatoxins, however in the case of fumonisins there has been partially successful. In a study, different adsorbents were tested for their potential to bind FB1. An effective adsorption of FB1 was described with activated charcoal and cholestyramin in vitro. However, activated charcoal is a very unspecific adsorbent and binds valuable nutrients as well; therefore these results could only be confirmed for cholestyramin in vivo (Solfrizzo 2001). Avantaggiato et al. (2005) from the Institute of Science of Food Production (ISPA) and the National Research Council (CNR), Bari, Italy, found out that among the commercially available feed additives Mycofix® Plus ( BIOMIN GmbH) showed good results with adsorption rates of 100% and 77% of 2 µg/ml and 20 µg/ml FB1, respectively. Recently a research project on adsorption efficiency was performed by the Christian Doppler Laboratory of Mycotoxin Research Tulln in cooperation with the University of Agricultural Sciences in Vienna and with BIOMIN GmbH. In the course of the research project about 60 different minerals were examined to obtain information concerning adsorption efficacy, specificity and the mechanism of the adsorption process. From this 2 year research project a new product (Mycofix®Secure) was developed which exhibits high adsortion specificity for aflatoxin B1 but is also capable of adsorbe and eliminate up to 90 % of FB1 (Figure 2).
Figure 2 – Adsorption curve of fumonisins in gastrointestinal juice by Mycofix® Secure
Fumonisins are natural toxins and therefore they are biodegradable. Compared to adsorption of mycotoxins by clay, microbial biodegradation has the advantages of being highly specific and irreversible. Several microbial strains which are capable of fumonisin biodegradation were previously isolated, and the genes encoding fumonisin detoxification enzymes were identified (Blackwell et al. 1999: Duvick et al. 1998a; Duvick et al. 1998b).
Recently, BIOMIN GmbH scientists isolated and characterized new fumonisin-metabolizing bacterial strains (Schatzmayr et al. 2007). Some of these isolates were found to be active in the gastrointestinal tract of animals. One of the strains with the highest technological potential belongs to the family of the Sphingomonadaceae and was called MTA144. It degrades fumonisins by first cleaving off tricarballylic acid side chains and subsequently catabolising the rest of the molecule into non-toxic products. Development of a novel feed additive for fumonisin detoxification based on this strain - whose efficacy was proven in vitro - is in progress. Nevertheless in vivo trials are necessary to prove its efficacy in the animals.
A number of experiments have reported that fumonisins are toxic for fish and the main target organs are the liver and kidney. Although there can be a careful selection of raw materials, maintaining good storage conditions for feeds and raw materials, there is still a potential risk of mycotoxin contamination. As a result of their different structures mycotoxins can cause various toxic effects in animals. Therefore, there is a need to reduce the negative impact of mycotoxins in aqua species. Amounting evidence shows that there cannot be only one effective strategy against mycotoxins. Through its intensive research in mycotoxin risk management Biomin has developed effective solutions to counteract the negative effects of mycotoxins combining adsorption and biotransformation strategies.
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