Phthalate mono-2-ethylhexyl

MEHP Mono(2-ethylhexyl)phthalate (2) Proton affinity... 

The metabolism of C-DEHP by rainbow trout liver subcell-ular fractions and serum was studied by Melancon and Lech (14). The data in Table VI show that without added NADPH, the major metabolite produced was mono-2-ethylhexyl phthalate. When NADPH was added to liver homogenates or the mitochondrial or microsomal fractions, two unidentified metabolites more polar than the monoester were produced. Additional studies showed that the metabolism of DEHP by the mitochondrial and the microsomal fractions were very similar (Figure 1). Both fractions show an increased production of metabolites of DEHP resulting from addition of NADPH and the shift from production of monoester to that of more polar metabolites. The reduced accumulation of monoester which accompanied this NADPH mediated production of more polar metabolites may help in interpreting the pathway of DEHP metabolism in trout liver. This decreased accumulation of monoester could be explained either by metabolism of the monoester to more polar metabolites or the shift of DEHP from the hydrolytic route to a different, oxidative pathway. The latter explanation is unlikely because in these experiments less than 20% of the DEHP was metabolized. 

Rock, G. and Viau, A., Drug Metab. Disp. (1978) 6, Metabolism and Tissue Distribution of Mono-2-Ethylhexyl Phthalate in the Rat, 146-149. 

Di-2-ethylhexyl phthalate DEHP Mono-(2-ethylhexyl) phthalate MEHP... 

Eor example, in the intestinal tract and liver of both humans and animals DEHP is rapidly hydrolyzed by esterases to yield mono-(2-ethylhexyl) phthalate (MEHP) and 2-ethylhexanol [25]. The latter metabolite is subsequently oxidized enzymatically to 2-ethyl hexanoic acid (2-EHXA) [26]. MEHP, 2-hethylhexanol, and/or their metabolites are the immediate inducers of the majority of enzymes known to be affected by exposure of DEHP [27]. Due to the high importance of the primary and secondary PAE metabolites in the human exposure smdies, during the last years a big number of smdies have been conducted to prove that some of them are appropriate biomarkers to calculate human PAE intake [28-30] and that their determination is easier than calculate it through food intake, which are more time consuming and subjects to several error sources. 

Kleinsasser NH, Harreus UA, Kastenbauer ER, Wallner BC, Sassen AW, Staudenmaier R, Rettenmeier AW (2004) Mono(2-ethylhexyl) phthalate exhibits genotoxic effects in human lymphocytes and mucosal cells of the upper aerodigestive tract in the comet assay. Toxicol Lett 148 83-90... 

Boruchoff SA. Hypotension and cardiac arrest in rats after infusion of mono(2-ethylhexyl)phthalate (MEHP), a contaminant of stored blood. N Engl J Med 1987 316 1218-19. 

Williams J, Foster PM. 1989. The effects of 1,3-dinitrobenzene and mono-(2-ethylhexyl) phthalate on hormonally stimulated lactate and pyruvate production by rat Sertoli cell cultures. Toxicol Lett 47 249-257. 

Di(2-ethylhexyl) phthalate was found at concentrations ranging from 0.8 to 4.2 mg/L serum in 17 haemodialysis patients after dialysis and 0.1-0.9 mg/L in four of seven continuous ambulatory peritoneal dialysis (CAPD) patients. In three of the CAPD patients and in all of the predialysis patients, di(2-ethylhexyl) phthalate was not detected (< 0.1 mg/L) in no case could the hydrolysis product mono(2-ethylhexyl) phthalate be detected (< 0.4 mg/L) (Nassbeiger et al., 1987). 

Because distribution studies have monitored total radioactivity, our understanding of the distribution of intact di(2-ethylhexyl) phthalate is limited. Chu et al. (1978) studied the metabolism and distribution of mono(2-ethylhexyl) phthalate in rats after oral dosing and found that the intestine contained the highest tissues levels after 24 h. The liver, heart, lung and muscle each contained approximately half the level in the intestine. They also reported that 80% of the I C-dose of mono(2-ethylhexyl) phthalate was eliminated 24 h after oral administration, 72% in the urine and 8% in the faeces. Twenty minutes after the administration of an intravenous dose of [ C]mono(2-ethyl-hexyl) phthalate, Chu et al. (1978) found comparable levels in the liver, kidney and bladder, with other organs containing approximately 10-25% of the level of the liver. 

Species differences in the metabolism of di(2-ethylhexyl) phthalate have been reported and attempts have been made to explain the susceptibility of animals to di(2-ethylhexyl) phthalate-induced hepatic peroxisome proliferation based on their metabolic profiles (Doull et al., 1999). As mentioned above, the bulk of a di(2-ethylhexyl) phthalate dose is absorbed as the mono-ester, mono(2-ethylhexyl) phthalate, and following absorption this metabolite is subjected to extensive oxidative metabolism mediated by cytochrome P450 enzymes (Albro Lavenhar, 1989 Astill, 1989 Huber et al., 1996 Doull et al., 1999). The metabolism of mono(2-ethylhexyl) phthalate has been summarized by Doull et al. (1999) as follows (see Figure 1) ... 

Radiolabelled di(2-ethylhexyl) phthalate (10 mL/kg) was administered by oral gavage to ddY-SLC mice on gestation day 8. Three and 12 h after exposure, levels of di(2-ethylhexyl) phthalate in the fetuses were 522 pg/g and 426 pg/g, respectively. The level of mono(2-ethylhexyl) phthalate in the fetus was approximately 1% that of di(2-ethylhexyl) phthalate (Tomitaeta/., 1986). 

Mettang et al. (1996b) investigated the relationship between di(2-ethylhexyl) phthalate exposure and uraemic pruritus in dialysis patients. There was no relationship between severity of pmritus and post-dialysis serum concentrations of di(2-ethylhexyl) phthalate, mono(2-ethylhexyl) phthalate, phthalic acid or 2-ethylhexanol. Furthermore, serum concentrations of di(2-ethylhexyl) phthalate and these related compounds were not significantly different between patients with or without uraemic pmritus. 

Young male Wistar rats were given 2000 mg/kg bw di(2-ethylhexyl) phthalate per day by gavage for periods of 3-21 days (Lake et al, 1975). Treatment caused increases in relative liver weight and in microsomal cytochrome P450 content. Ultra-structural examination revealed marked peroxisome proliferation and a dilation of the smooth and rough endoplasmic reticulum. Rats were also treated with mono(2-ethyl-hexyl) phthalate, 2-ethylhexanol and phthalic acid at doses equimolar to 2000 mg/kg bw per day di(2-ethylhexyl) phthalate for seven days. While phthalic acid had no effect, both mono(2-ethylhexyl) phthalate and 2-ethylhexanol increased relative liver weight and produced hepatic peroxisome proliferation. 

In non-hepatocytic systems in vitro, addition of mono(2-ethylhexyl) phthalate results in activation of PPARa (Issemann Green, 1990 Isseman et al, 1993). Such... 

Hepatocytes isolated from male Wistar rats (180-250 g) were treated with 0.2 mM mono(2-ethylhexyl) phthalate or 1 mM 2-ethylhexanol for 48 h (Gray et al., 1982). Both di(2-ethylhexyl) phthalate metabolites increased carnitine acetyltransferase activity about nine-fold. In studies with hepatocytes from male Sprague-Dawley rats (180-220 g), treatment with 0.2 mM mono(2-ethylhexyl) phthalate and 1.0 mM 2-ethylhexanol for 48 h resulted in induction of carnitine acetyltransferase activity about 15-fold and six-fold, respectively (Gray et al., 1983). Mono(2-ethylhexyl) phthalate was also shown to induce cyanide-insensitive palmitoyl-CoA oxidation and, by ultra-structural examination, to increase numbers of peroxisomes. Hepatocytes were isolated from Wistar-derived rats (180-220 g) and treated for 72 h with 0-0.5 mM mono(2-ethylhexyl) phthalate and some mono(2-ethylhexyl) phthalate metabolites (Mitchell etal., 1985). Treatment with mono(2-ethylhexyl) phthalate and metabolites VI and IX (see Figure 1) resulted in a concentration-dependent induction of cyanide-insensitive palmitoyl-CoA oxidation. In addition, 0-0.5 mM mono(2-ethylhexyl) phthalate and 0-1.0 mM metabolite VI produced concentration-dependent increases in lauric acid hydroxylation. Treatment with metabolites I and V resulted in only small effects on the enzymatic markers of peroxisome proliferation. In another study with hepatocytes from Wistar-derived rats (180-220 g), metabolite VI was shown by subjective ultrastructural examination to cause proliferation of peroxisomes (Elcombe Mitchell, 1986). 

Primary hepatocyte cultures may also be employed to study species differences in hepatic peroxisome proliferation (lARC, 1995 Doull et al, 1999). Hepatocytes were isolated from male Sprague-Dawley rats (180-220 g), male Syrian hamsters (70-80 g) and male Dunkin-Hartley guinea-pigs (400-450 g). Treatment with 20-200 0,M mono(2-ethylhexyl) phthalate for 70 h caused strong induction of cyanide-insensitive palmitoyl-CoA oxidation activity in rat hepatocytes (up to 600% of control levels), while no marked effect was observed in Syrian hamster (up to 120% of control) or guinea-pig (down to 80% of control) hepatocytes (Lake et al., 1986). 

Species comparisons of hepatic peroxisomal proliferation have also included studies of human and non-human primate primary hepatocyte cultures. Hepatocytes isolated from Wistar-derived rats (180-220 g), male Alderley Park guinea-pigs (400-500 g), male marmosets (350-500 g) and three human liver samples (renal transplant donors) were treated with 0-0.5 mM mono(2-ethylhexyl) phthalate for 72 h (Elcombe Mitchell, 1986). While there was a concentration-dependent induction of cyanide-insensitive palmitoyl-CoA oxidation in rat hepatocytes, no induction was observed in guinea-pig or human hepatocytes and only small non-concentration-dependent effects were observed in marmoset hepatocytes. Metabolite VI induced cyanide-insensitive palmitoyl-CoA oxidation and lauric acid hydroxylation in cultured... 

Hepatocytes were isolated from male Fischer 344 rats and from two human liver samples (liver surgery patients). Treatment with 200 pM mono(2-ethylhexyl) phthalate for either 48 or 72 h induced carnitine acetyltransferase activity in cultured rat but not human hepatocytes (Butterworth et al, 1989). 

Peroxisome proliferators have also been shown to induce replicative DNA synthesis in cultured rodent hepatocytes (lARC, 1995). In contrast, several peroxisome proliferators have failed to induce replicative DNA s mthesis in human hepatocyte cultures (Doull et al., 1999). Hepatocytes were isolated from male Wistar-derived rats and from three human liver samples (liver transplantation donors) and treated with 2-ethylhexanoic acid and some other peroxisome proliferators for 72 h (Elcombe et al, 1996). While 2-ethylhexanoic acid induced replicative DNA s5mthesis in cultured rat hepatocytes, no effect was observed in human hepatocytes. Hepatocytes were isolated from male Fischer 344 rats and three humans and treated in culture with 250-2000 pM mono(2-ethylhexyl) phthalate (Hasmall et al, 1999). Increased peroxisomal (O-oxi-dation (at 250-750 pM), replicative DNA s mthesis (at 500-1000 pM), and inhibition of apoptosis (at 250-1000 pM) were observed in rat hepatocytes. None of these parameters was affected by mono(2-ethylhexyl) phthalate in human hepatocytes. 

---