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IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

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342<br />

<strong>IARC</strong> <strong>M<strong>ON</strong>OGRAPHS</strong> VOLUME 82<br />

Figure 6. Proposed biochemical effects and cellular responses associated with fumonisin<br />

B 1 (FB 1)-induced alterations in delta 6 (Δ6) desaturase, sphingomyelinase<br />

(SMase), and ceramide synthase activity and biosynthesis of phosphotidylcholine<br />

(PC) and phosphatidylethanolamine (PE)<br />

(−)<br />

(+)<br />

(+)<br />

MITO-INHIBITI<strong>ON</strong> APOPTOSIS<br />

GF<br />

PLA2<br />

PGE 1<br />

PGE 2<br />

C18:2ω6<br />

delta 6 desaturase<br />

C18:3ω6<br />

C20:3ω6<br />

C20:4ω6<br />

(+)<br />

(+)<br />

(−)<br />

(+)<br />

PC/PE<br />

Abbreviations: PLA 2, phospholipase A 2; LP, products of lipid peroxidation; GF, growth factors; PGE 1 and<br />

PGE 2, prostaglandin E 1 and E 2; Sa, free sphinganine; So, free sphingosine; +, stimulatory; –, inhibitory or<br />

decreased; ?, response may be either increased or decreased (see Section 4.5.1); SM, sphingomyelin<br />

Modified from Gelderblom et al. (2001a)<br />

c-myc and oxidative damage could further enhance apoptosis and alter cell growth in<br />

affected hepatocytes (Gelderblom et al., 2001a; WHO, 2002).<br />

(g) Hypothesized cellular mechanism<br />

Fumonisin B 1 has been shown to alter cell proliferation both in vitro and in vivo. The<br />

fumonisin B 1-induced effects on membrane lipids and the resultant effects on signalling<br />

pathways that involve lipid mediators could create an environment in which the growth<br />

of normal cells is impaired. Differential inhibition of cell proliferation is a possible<br />

mechanism by which hepatocytes resistant to fumonisin B 1-induced inhibition of cell<br />

growth are selectively stimulated, while growth of normal hepatocytes is inhibited. This<br />

selective inhibition of normal cell growth could increase the chances of survival of DNAdamaged<br />

hepatocytes, resulting in an increased likelihood of cancer development<br />

(Gelderblom et al., 2001a; WHO, 2002).<br />

FB 1<br />

(+)<br />

(−)<br />

SM<br />

(−)<br />

FB 1<br />

( +− )<br />

PROLIFERATI<strong>ON</strong><br />

LP<br />

(−)<br />

SMase<br />

(−)<br />

c-myc/TGF-α<br />

Sa<br />

Ceramide synthase<br />

CERAMIDE<br />

Ceramide synthase<br />

?<br />

So<br />

?<br />

(+)<br />

?

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