Influence of the injection of mannan on rat liver lysosomes

Abstract

As has been recently described, yeast invertase, injected at a sufficiently high dose, causes an increase in density of the liver lysosomes in which it accumulates. These lysosomes mainly originate from non-parenchymal cells (Jadot et al . , 1985). As yeast invertase is a glycoprotein rich in mannose (Neumann & Lampen, 1967), we were interested to see if mannan, which chiefly consists of mannose and is quasi devoid of protein, can also induce a density change of the sinusoidal cell lysosomes. Rats were intravenously injected with mannan (Sigma) and killed at selected times after injection. Total mitochondrial fractions (M + L ofde Duve et al . , 1955) were isolated from the liver and analysed by isopycnic centrifugation in sucrose gradients. Fig. 1 illustrates the distribution of several reference enzymes after injecting 10 mg of mannan, the animal being killed 15 h after injection. The distributions were compared with those observed with a non-injected rat. Injection of mannan does not change the distribution of cytochrome oxidase (mitochondria) and of catalase (peroxisomes). On the other hand, a change of arylsulphatase distribution is clearly visible. It consists of the shift of a proportion of that enzyme to higher density regions of the gradient; a slight effect is also observed for cathepsin C, another lysosomal enzyme. We have found that the effect of mannan on liver lysosomes has the following characteristics: ( I ) the density shift of lysosomal enzyme in a sucrose gradient depends on the amount of injected mannan; (2) the proportion of acid hydrolase activity affected by mannan is different for each enzyme and is particularly striking for arylsulfatase; (3) most of the lysosomes, whose density is increased by mannan injection, are recovered in the M fraction (heavy mitochondrial fraction); (4) mannan treatment causes a distribution shift of invertase while only slightly affecting the distribution of '251-asialofetuin, when these two substances have been injected 3 h before killing the animal. These results can be explained by supposing that mannan, like invertase, reaches a distinct population of lysosomes, originating from non-parenchymal cells of the liver; as it is probably a poor substrate for lysosomal hydrolases, it accumulates in these lysosomes and causes a specific increase in their density. Like invertase, mannan could be used in analytical and preparative centrifugation, to individualize two lysosomes populations in rat liver, one belonging to parenchymal cells, the other to non-parenchymal cells.