New application of a subcellular fractionation method to kidney and testis for the determination of conjugated linoleic acid in selected cell organelles of healthy and cancerous human tissues

To clarify the mechanism of the anticarcinogenic effect of conjugated linoleic acid (CLA), its intracellular distribution needs to be determined. Subcellular fractionation using centrifugation techniques is a method that is frequently used for isolation of cell organelles from different tissues. But as the size and density of the organelles differ, the method needs to be optimised for every type of tissue. The novelty of this study is the application of a subcellular fractionation method to human healthy and cancerous renal and testicular tissue. Separation of total tissue homogenate into nuclei, cytosol, and a mixture of mitochondria and plasma membranes was achieved by differential centrifugation. As mitochondria and plasma membranes seemed to be too similar in size and weight to be separated by differential centrifugation, discontinuous density-gradient centrifugation was carried out successfully. The purity of the subcellular fractions was checked by measuring the activity of marker enzymes. All fractions were highly enriched in their corresponding marker enzyme. However, the nuclear fractions of kidney and renal cell carcinoma were slightly contaminated with mitochondria and plasma membrane fractions of all tissues with lysosomes. The fraction designated the cytosolic fraction contained not only cytosol, but also microsomes and lysosomes. The CLA contents of the subcellular fractions were in the range 0.13–0.37% of total fatty acids and were lowest in the plasma membrane fractions of all types of tissue studied. C16:0, C18:0, C18:1 c9, C18:2 n-6, and C20:4 n-6 were found to be the major fatty acids in all the subcellular fractions studied. However, marked variations in fatty acid content between subcellular fractions and between types of tissue were detectable. Because of these differences between tissues, no general statement on characteristic fatty acid profiles of single subcellular fractions is possible.