Pathways of intracellular trafficking and release of ferritin by the liver in vivo: the effect of chloroquine and cytochalasin D.
We have previously shown that the clearance of exogenous ferritin and the release of endogenous ferritin into both serum and bile are altered by the microtubular inhibitor colchicine. In this study we further examined the role of the lysosome-endosome pathway in ferritin metabolism. We examined the effect of the lysosomotropic agent chloroquine and the microtubular inhibitor cytochalasin D on the uptake and release of ferritin by normal and iron-loaded rats under basal conditions and in the presence of an exogenous tissue ferritin load. Either chloroquine (50 mg/kg body wt) or cytochalasin D (0.9 microgram/100 gm body wt/min) was administered to normal and iron-loaded rats at zero time. Rats were also infused with either saline solution or rat liver ferritin containing a trace amount of 125I-ferritin. The clearance of 125I-ferritin from the circulation was not affected by chloroquine or cytochalasin D either in normal or in iron-loaded rats; however, both chloroquine and cytochalasin D decreased the serum ferritin concentration in normal rats to 39% +/- 9% and 22% +/- 7% of the baseline serum ferritin levels, respectively, implying that both drugs inhibited the release of endogenous ferritin in normal rats. In iron-loaded rats both chloroquine and cytochalasin D decreased the biliary ferritin concentration to 11% +/- 1% and 37% +/- 4% of the baseline ferritin levels, respectively, and the 125I protein-bound counts per minute in the bile to 50% of the control result. This finding is consistent with an inhibitory effect of both drugs on the biliary excretion of endogenous ferritin and the intracellular transport of exogenous ferritin, respectively. In the presence of an exogenous tissue ferritin load, there was no detectable inhibitory effect of either drug on the biliary excretion of either endogenous or exogenous ferritin. These results provide the following evidence: (a) the receptor-mediated endocytosis of ferritin is not dependent on functioning lysosomes or microfilaments; (b) the release of endogenous ferritin into the serum of normal rats and the bile of iron-loaded rats is a chloroquine-sensitive, microfilament-dependent process; (c) the biliary excretion of trace amounts of exogenous ferritin is dependent on both chloroquine-sensitive vesicles and microfilaments; and (d) increased levels of exogenous ferritin are excreted directly into the bile by way of a second microfilament-independent, chloroquine-insensitive pathway. This study provides support for a physiological mechanism for the release of ferritin from the liver.
Ramm
G A
GA
Liver Unit, Queensland Institute of Medical Research, Brisbane, Australia.
Powell
L W
LW
Halliday
J W
JW
D000410:Alanine Transaminase / Q000097:blood; D000818:Animals; D002738:Chloroquine / Q000494:pharmacology*; D015638:Cytochalasin D / Q000494:pharmacology*; D005293:Ferritins / Q000378:metabolism* / Q000493:pharmacokinetics; D007501:Iron / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D008247:Lysosomes / Q000502:physiology; D008297:Male; D051381:Rats
D015638:Cytochalasin D; D002738:Chloroquine; D005293:Ferritins; D007501:Iron; D000410:Alanine Transaminase