Effect of dietary di-2-ethylhexyl phthalate on lipid biosynthesis in selected tissues from the rat,in vitro

Di-2-ethylhexyl phthalate (DEHP), a plasticizer commonly used in the production of polyvinyl chloride plastics, has become an environmental pollutant. At the present time, the biological significance of phthalates in the environment is unknown. In the present studies, we observed that addition of DEHP to a stock diet of rats resulted in marked effects on incorporation of¹⁴C-acetate into lipid by liver and kidney slices; other organs, such as heart, testes, and aorta were unaffected. Incorporation of¹⁴C-acetate into total lipid of liver (dpm/mg wet wt) from rats, fed 0.5% or 1.0% DEHP for 10 or 18 days, respectively, was decreased to ca. 50% of control values. The decreased incorporation into liver lipid is not attributable to any one lipid fraction, inasmuch as incorporation into the phospholipid, sterol+diglyceride, free fatty acid, triglyceride, and sterol ester+hydrocarbon fractions was decreased 30–70% with respect to controls. In addition, the percent distribution of¹⁴C-acetate among the individual phospholipids was ca. 25% lower in phosphatidyl choline of the DEHP-fed rats. In rats fed 0.5% DEHP, incorporation of¹⁴C-acetate into total lipid of kidney was similar to control values, but incorporation into the triglyceride and sterol ester+hydrocarbon fraction was decreased 30–40%, whereas incorporation into the sterol+diglyceride fraction was increased 38%. Livers from DEHP-fed rats were ca. 20% larger than livers from control rats and, at the 0.%% level of DEHP feeding, testes wts were elevated; no significant changes were noted in wts of spleen, heart, aorta, kidney, or body wt gains in rats fed DEHP. These studies emphasize a subtle toxicity of phthalate esters not previously reported and emphasize the need for further biochemical studies to evaluate the effect of phthalates on biological systems.     

Inhibition of hepatic sterol and squalene biosynthesis in rats fed di-2-ethylhexyl phthalate

Di-2-ethylhexyl phthalate (DEHP), a commonly used plasticizer, was found to be an inhibitor of the biosynthesis of hepatic nonsaponifiable lipids in the rat. The addition of DEHP at levels of 0.5% or 1.0% to a stock diet of rats resulted in a decreased conversion of acetate-1-¹⁴C and mevalonate-5-³H into squalene, C₃₀ sterols, and C₂₇ sterols by liver minces or slices, in vitro. In studies conducted with 0.5% DEHP feeding from 2 to 11 days, the degree of inhibition was found to increase with the duration of DEHP feeding; the inhibition of³H-mevalonate conversion to squalene and sterols developed more slowly, being reduced to ca. 70% of control values in 11 days, whereas¹⁴C-acetate conversion was reduced to ca. 35% of control values during the same period.³H-mevalonate conversion to sterols and squalene was, however, found to be suppressable to the same extent as¹⁴C-acetate conversion when diets containing 1.0% DEHP were fed for 18 days. The inhibitory effect of dietary DEHP on sterol and squalene biosynthesis from¹⁴C-acetate and³H-mevalonate by rat liver preparations is unlikely to be accounted for by the negative feedback of cholesterol secondary to hepatic sterol accumulation since, in these studies, hepatic total lipid and hepatic total sterol levels were simialr in control and DEHP-fed rats.     

Effect of phthalate esters on serum cholesterol and lipid biosynthesis in liver,testes, and epididymal fat in the rat and rabbit

Lipid biosynthesis was studied in vitro in liver, testes, and epididymal fat obtained from rats and rabbits fed di-(2-ethylhexyl)phthalate for 4 weeks at levels of 0.5% and 1.0%, respectively. Several differences in response of the two species to DEHP feeding were observed. In rats, but not in rabbits, DEHP feeding significantly reduced the incorporation of labeled mevalonic acid into total sterols (p <0.02), digitonin-precipitable sterols (p<0.01), and squalene (p<0.05). Inhibition of hepatic sterologenesis previously observed with DEHP feeding in the rat was also observed in the rabbit. In liver minces from the DEHP-fed rabbits, incorporation of³H-mevalonic acid into C₂₇ sterols (cholesterol) and C₃₀ sterols (lanosterol) was significantly reduced by about 40% (p<0.05 and p<0.01, respectively), whereas the incorporation of¹⁴C-glycerol 3-phosphate into phospholipids, and the combined fraction of monoglyceride + diglyceride, was significantly increased (p<0.001 and p<0.01, respectively). In studies with epididymal fat, DEHP feeding did not affect the total incorporation of¹⁴C-acetate or³H-mevalonate into total saponifiable and nonsaponifiable lipids of either the rat or rabbit. However, in the rat, significantly less of the¹⁴C-acetate (p<0.02) and³H-mevalonate (p<0.01) that was incorporated appeared in the combined fraction of cholesteryl ester + squalene. In addition, DEHP feeding significantly reduced serum cholesterol (p<0.01) in the rat but not in the rabbit. The results of this study indicate that DEHP feeding is associated with alterations in tissue lipid metabolism and that there are species differences in the response of tissues to DEHP.     

Inhibition of sterologenesis in brain and liver of fetal and suckling rats from dams fed di-2-ethylhexyl phthalate plasticizer

The effect of di-2-ethylhexyl phthalate (DEHP) on lipid metabolism was studied in liver and brain from fetal rats taken 3 days before parturition from dams receiving dietary DEHP during gestation. In fetuses from rats receiving 0.5% or 1.0% DEHP in a stock diet, the incorporation of¹⁴C-acetate and labeled mevalonate (³H or¹⁴C) into the C₂₇ sterols, C₃₀ sterols, and squalene fractions of brain tissue incubated in vitro was significantly reduced between the confidence limits P<0.05 to P<0.001. When liver from fetuses was incubated with labeled mevalonate, incorporation of label into the C₂₇ sterol and C₃₀ sterol fractions was significantly reduced as well (P<0.02 to P<0.001), whereas incorporation of labeled mevalonate into the squalene fraction was not significantly altered. The incorporation of¹⁴C-acetate into total hepatic lipids of the fetal rats was also studied, and statistically significant reductions in incorporation were observed in the lanosterol fraction (P<0.001), the combined fraction of sterol esters + squalene (P<0.02), and the combined fraction of cholesterol + diglycerides (P<0.01). No significant changes were observed in the incorporation of¹⁴C-acetate into phospholipids, free fatty acids, or triglycerides. In 8-day old suckling rats delivered from dams fed 0.5% DEHP for the last 16 days of gestation and maintained on the same diet during the nursing period, the incorporation of¹⁴C-mevalonate into hepatic C₂₇ sterols, in vitro, was significantly depressed (P<0.05) whereas in corporation into C₃₀ sterols and squalene was similar to control values. In these same suckling rats, body weights were significantly lower in the control group (21.7 vs. 18.8 g, P<0.01), whereas liver weight as a % of body weight was significantly higher (P<0.01) in rats nursing from the DEHP-fed dams. The results indicate that the inhibitory effect of dietary DEHP on lipid metabolism in the mature rat is transmitted across the placental barrier to the developing fetus and that the abnormal pattern of lipid metabolism in rats delivered from DEHP-fed females is only partially restored to normal during the suckling periods.     

气相色谱法测定6种邻苯二甲酸酯痕量组分的固相萃取条件研究

利用固相萃取技术富集了水中6种邻苯二甲酸酯类:邻苯二甲酸二(2-乙基己基)酯(DEHP)、邻苯二甲酸二甲酯(DMP)、邻苯二甲酸二乙酯(DEP)、邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二辛酯(DOP)、邻苯二甲酸丁基苄基酯(BBP)。借助均匀设计法及计算机回归建模优化技术对6种邻苯二甲酸酯类的固相萃取条件进行了设计与优化,得到最佳固相萃取条件为:洗脱剂配比(正己烷与丙酮的体积比)30∶1,洗脱体积2 mL,洗脱速率为4 mL/min,上样速率8 mL/min。富集后的样品用带电子捕获器的毛细管气相色谱检测,方法的线性范围为1~1 000μg/L(DMP、DEP、DOP),0.2~100μg/L(DBP、DEHP),0.1~100μg/L(BBP);线性回归方程的相关系数为0.997 0~1.000,检测限为0.01~0.4μg/L,方法回收率为69.0%~117.0%,相对标准偏差为2.2%~9.5%。     

Effect of dietary di-2-ethylhexyl phthalate on oxidation of14C-palmitoyl CoA by mitochondria from mammalian heart and liver

Oxidation of [1-¹⁴C] palmitoyl CoA by heart and liver mitochondria from rats fed dietary di-2-ethylhexyl phthalate (DEHP) was investigated in vitro. Oxidation of¹⁴C-palmitoyl CoA to¹⁴CO₂ increased two- to threefold in hepatic mitochondria from rats fed 0.1% DEHP for 2 to 3 days; this increase appeared to be a maximum response since similar data were obtained using hepatic mitochondria from rats receiving 0.5% or 1.0% DEHP in the diet. The response of hepatic mitochondria to DEHP was found to continue throughout the duration of 35-day trials in which 1.0% DEHP was fed. In contrast to hepatic mitochondria, the oxidation of¹⁴C-palmitoyl CoA by heart mitochondria decreased ca. 40% upon addition of 0.1% or 0.5% DEHP to the diet; this effect of DEHP on heart mitochondria was not sustained beyond ca. 8 days of DEHP feeding. Limited studies were also performed in rabbits and pigs. Oxidation of¹⁴C-palmitoyl CoA was increased ca. twofold in hepatic mitochondria from rabbits fed 1% dietary DEHP for 12 days and in hepatic mitochondria from pigs that received 5 doses of DEHP (0.8g/kg) at 12-hr intervals; the oxidation¹⁴C-palmitoyl CoA by heart mitochondria from these same animals was unchanged in the rabbit but increased an average of 37% in the pig. DEHP feeding to rats was associated with increased yields of hepatic mitochondrial protein; standardized preparations of heart mitochondria were not similarly affected.     

Sorption of Phthalates on Molecularly Imprinted Polymers

Porous beads of styrene divinylbenzene copolymer, S-co-DVB, imprinted with dimethyl phthalate, DMP, were obtained. Two solvents were applied for the formation of pores: n-hexane and n-octane. The sorbents were prepared by membrane emulsification of monomer mixtures containing DMP followed by suspension polymerization. The average diameters of the synthesized beads were 40 µm for beads obtained from mixtures with n-octane, and 30 µm for preparations with n-hexane as solvent. It was shown that almost all monodispersive sorbents were obtained; their SPAN parameter was as small as 0.7–0.9. Sorption properties of evaluated samples varied in relation to the kind of applied reaction mixture. Generally, imprinted materials showed higher sorption capacity towards DMP than their off-template analogues. For the sorbent obtained in the presence of n-octane and with 3 wt.% of DMP, sorption of dimethyl phthalate took the highest value - 89 mg/g. The sorbents imprinted with DMP were checked for sorption of diethyl phthalate, DEP, and dibuthyl phthalate, DBP also. It was shown that sorbability of synthesized materials towards other phthalates was much smaller than for DMP and was not related to the presence of dimethyl phthalate foot prints.     

Additives for the preparation of polysulfone-based ultrafiltration membranes,especially for hemodialysis and hemo-osmometer

Using various phthalates such as DMP, DBP, DAP, and DOP as so-called “rejection additives” to casting solutions of Polysulfone (PS) membranes, PS membranes were prepared exhibiting up to nearly 100% rejection for higher molecular weight substances (e.g. ? 99%, 82%, 77% and 73% average rejection for bovine serum albumin (BSA)]. The casting conditions were similar to those described in a previous paper, e.g. room temperature, 70–95% relative humidity, water of 25 ± 5°C as precipitation bath, and 0–5s evaporation time.     

SPE-GC/MS法快速检测水体中多组分内分泌干扰物

采用固相萃取-气相色谱/质谱法(SPE-GC/MS)研究了温州8个水体中邻苯二甲酸二甲酯、西玛津、莠去津、甲草胺、邻苯二甲酸二丁酯、双酚A、邻苯二甲酸二(2-乙基己基)酯七种内分泌干扰物的残留。水样用C18柱固相萃取进行富集、3mL10%的甲醇水溶液淋洗、10mL丙酮洗脱;并采用GC-MS法对七种内分泌干扰素进行分析。本实验建立的方法定性定量准确、可靠,适用于水体中多组分内分泌干扰物的快速检测,在所有测定的水样中,邻苯二甲酸二丁酯、双酚A、邻苯二甲酸二(2-乙基己基)酯是主要残留物,最高残留邻苯二甲酸二丁酯、双酚A、邻苯二甲酸二(2-乙基己基)酯分别为0.82、3.16、1.50ng/L。     

Cholesterol metabolism in the baboon

Studies on the transport of exogenous and endogenous cholesterol in the baboon have been carried out using¹⁴C-acetate,¹⁴C-mevalonic acid, or³H-cholesterol. The results suggest the following characteristics of cholesterol metabolism in the baboon: the serum α- and β-lipoproteins show no preference in the transport of exogenous or endogenous cholesterol; the half-life (t_1/2) of disappearance of cholesterol from the whole animal varied between 31 and 50 days; the daily rate of whole body cholesterol biosynthesis in the baboon (47 mg/kg/day) is comparable with that rate observed in the human being (18–41 mg/kg/day); after administration of¹⁴C-acetate,¹⁴C-mevalonic acid, or³H-cholesterol to baboons, newly synthesized cholesterol esters appear to be incorporated to a greater extent into the serum α-lipoproteins.     

邻环己烷二甲酸二丁酯合成与分离的流程模拟

实验研究了在金属Ni催化剂上邻苯二甲酸二丁酯（DBP）加氢合成邻环己烷二甲酸二丁酯和邻苯二甲酸二异丁酯（DIBP）加氢合成邻环己烷二甲酸二异丁酯的反应。根据实验结果确定了DBP加氢反应的适宜条件为：温度130℃,压力6.1 MPa,空速1 h^-1。相应的反应转化率为99.93%,选择性为92.47%。DIBP加氢反应的适宜条件为：温度100℃,压力6.1 MPa,空速0.5 h^-1。相应的反应转化率为99.70%,选择性为90.42%。将反应转化率和选择性作为Aspen Plus中反应模型的参数,建立了邻环己烷二甲酸二丁酯和邻环己烷二甲酸二异丁酯合成与分离的流程,所得产品纯度可达99%（质量分数）以上。模拟得到的工艺参数对邻环己烷二甲酸二丁酯和邻环己烷二甲酸二异丁酯合成与分离流程的工业化具有指导意义。     

Cholesterol metabolism and vitamin B6: II. Intestinal cholesterogenesis in vitamin B6 deficient rats

The in vitro incorporation of 1-¹⁴C-acetate into cholesterol by vitamin B₆ deficient and pair-fed rat intestinal tissue was assayed. It was found that vitamin B₆ deficiency increases, by a twofold factor, the incorporation of 1-¹⁴C-acetate into the cholesterol biosynthetic chain, when using a segment of the ileum, and on the other hand no increase was observed when using a segment from the jejunum. The production of¹⁴CO₂ from 1-¹⁴C-acetate was not found altered by a vitamin B₆ deficiency when using segments from the jejunum or the ileum. The effect of sodium cholate and sodium chenodeoxycholate on the incorporation of radioactivity into cholesterol and on the production of radioactive CO₂, with 1-¹⁴C-acetate as a substrate, was assayed with the two groups of animals. The significance of these findings and the posible relationships between these factors are discussed.     

Relative incorporation of acetate and glucose into glycerides ofGlomerella cingulata

Cultures of the fungusGlomerella cingulata were pulse-labeled for 30 min with 1-¹⁴C-acetate at ages from 2 to 12 days old. The greatest incorporation into triglycerides and phosphoglycerides occurred in the youngest cultures, but more of the radioactive acetate was diverted to the phosphoglycerides than to the triglycerides in these cultures. In another series of experiments the incorporation of 1-¹⁴C-acetate or 2-¹⁴C-glucose into the triglycerides and phosphoglycerides of the fungus was investigated at 15-minute intervals for 1 hr. Hydrolysis of the two classes of glycerides revealed some labeling of glycerol from acetate; but, not surprisingly, acetate was incorporated into the fatty acid moieties to a greater extent than into the glycerol moieties, and there was relatively greater incorporation of 2-¹⁴C-glucose into glycerol than into fatty acids. Some relationships of these results to the growth and development ofG. cingulata are suggested, and implications relative to control mechanisms are pointed out.     

Transformation of phthalic acid diesters in an anaerobic/anoxic/oxic leachate treatment process

Transformations of di-n-butyl phthalate(DBP) and di(2-ethylhexyl) phthalate(DEHP) have been investigated in anaerobic/anoxic/oxic(A/A/O) leachate treatment processes. Although the DBP removal processes are different when the DBP initial concentration is different, the overall system DBP removal efficiencies are high(N 94%).DEHP is much more difficult to remove than DBP. The removal efficiency of DEHP is approximately 75%–78%.The results of mass balance calculations indicate that approximately 33.7%–50.7% of the DBP is degraded by the activated sludge, 48.9%–64.9% accumulates in the system, and 0.4%–1.4% is contained in the final effluent. Approximately 15.0%–19.0% of the DEHP is degraded by activated microcosms, 75.8%–79.0% accumulates in the system, and 5.2%–6.0% is contained in the final effluent. Biodegradation and adsorption to the activated sludge are the main mechanisms for DBP removal and adsorption to the activated sludge is the main mechanism for DEHP removal. The different removal mechanisms of the two PAEs may be related to their different molecular structures. However, PAEs are not really removed when they adsorb onto the sludge. Therefore, methods for decreasing PAEs adsorption and increasing the biodegradation efficiencies of the leachate treatment processes should be further investigated.     

Stimulation of bile acid synthesis by dibutyryl cyclic AMP in isolated rat hepatocytes

Freshly isolated rat hepatocytes were used to examine the effects of dibutyryl cyclic AMP on the incorporation of¹⁴C-acetate and¹⁴C-cholesterol into bile acids. After an initial lag period, both precursors were incorporated into cholic and chenodeoxycholic acids at a linear rate for the subsequent 60 min. An apparent stimulation of bile acid formation from¹⁴C-acetate by dibutyryl cyclic AMP was complicated by the concomitant inhibition of cholesterol synthesis. In experiments with¹⁴C-cholesterol, dibutyryl cyclic AMP (1 mM) increased the labeled cholic and chenodeoxycholic acids in the medium by 83 and 224%, respectively, but cellular levels of labeled bile acids were unchanged. As a result, the nucleotide stimulated the overall incorporation of¹⁴C-cholesterol into cholic acid by 39% and into chenodeoxycholic acid by 123%. The mean ratio of labeled cholic to chenodeoxycholic acid declined from 55∶45 in control cells to 41∶59 in cells incubated with dibutyryl cyclic AMP. The results demonstrate that label incorporation can be used to study the regulation of bile acid synthesis in isolated hepatocytes. We propose that dibutyryl cyclic AMP enhances bile acid production by phosphorylating, and thus stimulating the activity of, cholesterol 7α-hydroxylase, the rate-limiting enzyme in bile acid synthesis.     

The effect of feeding di-(2-ethylhexyl) phthalate (DEHP) on the lipid metabolism of laying hens

Di-(2-ethylhexyl)phthalate (DEHP), a commonly used plasticizer, is now seen as an environmental pollutant. DEHP has been found to inhibit lipid and sterol synthesis in rats and mice. The effects of DEHP on various aspects of lipid metabolism were examined in chickens. White Leghorn laying hens were fed either a standard laying mash control diet (C) or the control diet containing 1% DEHP (DEHP) or 1% DEHP and 5% tallow (DEHP-T) for 28 days. DEHP and DEHP-T lowered feed consumption 10% but did not significantly affect body weight. After 3 weeks on the diets, egg production was 15–20% less in DEHP-T than in C and DEHP hens. No differences were observed in egg weight, percent shell, white or yolk among the groups. DEHP and DEHP-T did not alter egg lipid or egg cholesterol concentrations. DEHP and DEHP-T lowered plasma lipid concentration about 20% and free and total cholesterol 20–30%. Liver weights increased, being 30, 34 and 39 g for C, DEHP and DEHP-T hens, respectively, after 28 days. Total liver lipid and cholesterol increased 19% and 26% in DEHP hens and 54% and 79% in DEHP-T hens when compared to controls. In contrast, the fat content of pectoralis major muscle decreased significantly in DEHP and DEHP-T hens. These results, in showing that DEHP alters plasma and tissue cholesterol but not yolk cholesterol, demonstrate again that egg cholesterol is remarkably resistant to alteration by dietary means.     

Diurnal variation of plasma methyl sterols and cholesterol in the rat: Relation to hepatic cholesterol synthesis

Free cholesterol of plasma low density lipoproteins (LDL) and high density lipoproteins (HDL) of the rat was high and that of plasma very low density lipoproteins (VLDL) was low during the dark period of the diurnal cycle. Variations in the esterified plasma sterols were inconsistent. Free methyl sterols were high in all lipoproteins during the dark phase. Simultaneously, the incorporation of¹⁴C-acetate into nonsaponifiable sterols and the concentrations of free methyl sterols and cholesterol in the liver were elevated.     

手机涂料及涂膜中邻苯二甲酸酯类有害物质的测定

涂料经溶剂提取或涂膜经索氏提取后,提出液中邻苯二甲酸酯类单体DEHP、DBP、BBP、DNOP可用DB-130.0m×φ0.25mm×0.5μm色谱柱同时分离,GC-FID或GC-MSD全扫描测定,DINP、DIDP宜采用GC-MSD选择离子扫描单独测定。采用GC-MSD测定时,方法的回收率不低于95%,DEHP、DBP、BBP、DNOP的最小检出限(LODs)均为0.04μg/mL,最低定量限(LOQ)均为0.35μg/mL。选择扫描时,DINP、DIDP的LODs、LOQ分别为0.4μg/mL、3.5μg/mL。实验结果表明:某些丙烯酸树脂涂料以及手机外壳涂层含有高含量生殖致癌物PAEs类单体,应为制定手机涂料中邻苯二甲酸酯类有害物质最高允许限量进行评价。     

Dietary fatty acids regulate cholesterol induction of liver CYP7α1 expression and bile acid production

In the present study we investigated the effects of dietary fats containing predominantly PUFA, monounsaturated FA (MUFA), or saturated FA (SFA) on lipid profile and liver cholesterol 7α-hydroxylase (CYP7α1) mRNA expression and bile acid production in C57BL/6J mice. The animals (n=75) were randomly divided into five groups and fed a basic chow diet (AIN-93G) (BC diet), a chow diet with 1g/100g of cholesterol (Chol diet), a chow diet with 1g/100g of cholesterol and 14g/100g of safflower oil (Chol+PUFA diet), a chow diet with 1g/100g of cholesterol and olive oil (Chol+MUFA diet), or a chow diet with 1g/100g of cholesterol and myristic acid (Chol+SFA diet) for 6 wk. The results showed that the Chol+SFA diet decreased CYP7α1 gene expression and bile acid pool size, resulting in increased blood and liver cholesterol levels. Addition of PUFA and MUFA to a 1% cholesterol diet increased the bile acid pool production or bile acid excretion and simultaneously decreased liver cholesterol accumulation despite decreased CYP7α1 mRNA expression. The results indicate that the decreased bile acid pool size induced by the SFA diet is related to inhibition of the liver CYP7α1 gene expression, but an increased bile acid pool size and improved cholesterol homeostasis are disassociated from the liver CYP7α1 gene expression.     

Effects of su-13437, a new hypolipidemic drug,upon synthesis in vivo of hepatic and carcass total fatty acids and total cholesterol

The present study is directed toward obtaining information on the metabolic effects and on the mode of action of CIBA-Su-13437, a new hypolipidemic phenolic ether structurally related to clofibrate. The ability of Su-13437 to affect the net formation of lipids in vivo was studied by measuring the total incorporation of intraperitoneally injected 1,2-¹⁴C-sodium acetate and uniformly labeled¹⁴C-glucose into total fatty acids and total cholesterol by the liver and carcass of control and Su-13437-treated mice. Treated mice received Su-13437 orally at 25, 100 or 250 mg/kg/day for 14 or 15 consecutive days. Treatment with Su-13437 resulted in pronounced enlargement of the liver and significant reductions in the plasma levels of triglycerides and total cholesterol. Essentially all of the observed metabolic effects of Su-13437 were confined to the liver. At all doses studied, in addition to liver enlargement, there were large increases in incorporation of both¹⁴C-acetate and¹⁴C-glucose carbon into hepatic total fatty acids; marked increases in hepatic total fatty acid content; and decreases in the liver’s relative cholesterol content of up to 30% with little or no effect upon the net synthesis of cholesterol per gram of liver. These observations are interpreted as indicating that Su-13437 lowers plasma triglyceride and cholesterol levels by means other than net inhibition of fatty acid and cholesterol formation by either hepatic or extrahepatic tissues.