We aimed to improve the use of the human intestinal Caco-2 cell line for studying dietary lipid and cholesterol processing by using isolated pure clones (). Three clones (TC7, PD7 and PF11) were grown as monolayers on semi-permeable filters and compared for cell viability, fatty acid and cholesterol apical uptake or basolateral secretion, apolipoprotein B-48 basolateral secretion and 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase activity. The TC7 clone showed the best viability upon apical incubation with mixed micelles and should be preferred for routine work. Short-term (3·0 h) rates of apical uptake of cholesterol were not different with the three clones, whereas the rate of apical uptake of oleic acid (18 : 1) was lower (P<0·05) with PF11 (250·6 nmol/mg) and the basolateral secretion of cholesterol and oleic acid was lower with the TC7 clone (0·40 and 29·1 nmol/mg respectively). The secretion of apolipoprotein B-48 basolaterally was about 2-fold lower than from PD7 clone. The basal levels of HMG-CoA reductase activity were significantly different (P<0·05; TC7>PF11>PD7). The down-regulation of the enzyme activity was moderate (range 13·8–21·0 %) and comparable in the presence of apical micellar cholesterol, but was much marked upon basolateral incubation with LDL (range 34·0–53·6 %), especially for the PD7 clone. In conclusion, the Caco-2 clones characterized here proved to be particularly suitable for studying lipid nutrients processing. Because these three clones exhibit some different metabolic capabilities, they provide a new tool to study intestinal response to lipid nutrients.

We aimed to improve the use of the human intestinal Caco-2 cell line for studying dietary lipid and cholesterol processing by using isolated pure clones . Three clones (TC7, PD7 and PF11) were grown as monolayers on semi-permeable filters and compared for cell viability, fatty acid and cholesterol apical uptake or basolateral secretion, apolipoprotein B-48 basolateral secretion and 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase activity. The TC7 clone showed the best viability upon apical incubation with mixed micelles and should be preferred for routine work. Short-term (3·0 h) rates of apical uptake of cholesterol were not different with the three clones, whereas the rate of apical uptake of oleic acid (18 : 1) was lower (P,0·05) with PF11 (250·6 nmol/mg) and the basolateral secretion of cholesterol and oleic acid was lower with the TC7 clone (0·40 and 29·1 nmol/mg respectively). The secretion of apolipoprotein B-48 basolaterally was about 2-fold lower than from PD7 clone. The basal levels of HMG-CoA reductase activity were significantly different (P,0·05; TC7.PF11.PD7). The down-regulation of the enzyme activity was moderate (range 13·8 -21·0 %) and comparable in the presence of apical micellar cholesterol, but was much marked upon basolateral incubation with LDL (range 34·0 -53·6 %), especially for the PD7 clone. In conclusion, the Caco-2 clones characterized here proved to be particularly suitable for studying lipid nutrients processing. Because these three clones exhibit some different metabolic capabilities, they provide a new tool to study intestinal response to lipid nutrients.Cholesterol: Lipids: Absorption: Intestine * Corresponding author: Dr Denis Lairon, fax +33 491 75 15 62, email lairon@marseille.inserm.fr Abbreviations: Apo, apolipoprotein; HMG, 3-hydroxy-3-methylglutaryl; LDH, lactate dehydrogenase.

Open thyroid follicles were prepared by mechanical disruption of pig thyroid fragments through a metal sieve. This procedure allowed preparation of thyroid-cell material depleted of colloid thyroglobulin. Open thyroid follicles were used to prepared a crude particulate fraction, which contained lysosomes, mitochondria and endoplasmic reticulum. These organelles were subfractionated by isopycnic centrifugation on iso-osmotic Percoll gradients. (1) A lysosomal peak was identified by its content of acid hydrolases: acid phosphatase, cathepsin D, ,l-galactosidase and ,-glucuronidase. The lysosomal peak was well separated from mitochondria and endoplasmic reticulum. (2) The lysosomal peak, from which Percoll was removed by centrifugation, was taken as the purified lysosome fraction (L). Lysosomes of fraction L were purified 45-55-fold (as compared with the homogenate) and contained about 5% of the total thyroid acid hydrolase activities. (3) Electron microscopy showed that fraction L was composed of an approx. 90% pure population of lysosomes, with an average diameter of 220 nm. (4) Acid hydrolase activities were almost completely (80-90% ) released by an osmotic-pressure-dependent lysis. (5) Thyroglobulin was identified by polyacrylamide-gel electrophoresis as a soluble component of the lysosome fraction. In conclusion, a 50-fold purification of pig thyroid lysosomes was achieved by using a new tissue-disruption procedure and isopycnic centrifugation on Percoll gradient. The presence of thyroglobulin indicates that the lysosome population is probably composed of primary and secondary lysosomes. Isolated thyroid lysosomes should serve as an interesting model to study the reactions whereby thyroid hormones are generated from thyroglobulin and released into the thyroid cells.

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