Hepatic processing of recombinant human renin: mechanisms of uptake and degradation.
Biologically active 125I-Bolton-Hunter-labeled recombinant human renin (BH-renin) was used to study hepatic processing of renin both in vivo in bile fistula rats and in vitro in isolated perfused rat livers. BH-renin was composed mainly (80%) of a form that bound to concanavalin A-agarose (CB-renin). Twenty minutes after femoral venous injection of CB-renin in vivo, 47% of injected radiolabel was present in liver. Hepatic uptake of CB-renin was inhibited in a dose-dependent manner by mannosylated bovine serum albumin (MBSA) and mannan, but was unaffected by asialofetuin and mannose 6-phosphate. MBSA also significantly inhibited the plasma disappearance of endogenous renin in kidney-ligated rats. Cell separation techniques and light microscopic autoradiography showed that CB-renin was preferentially cleared by hepatic nonparenchymal cells via the mannose receptor, but was also cleared by hepatocytes via an unidentified mechanism. Tissue fractionation demonstrated that after injection of CB-renin, radiolabel was concentrated in lysosome-enriched liver fractions. In the liver, CB-renin was rapidly degraded to trichloroacetic acid-soluble fragments, which accumulated in urine and bile. Leupeptin, an inhibitor of lysosomal proteases, decreased degradation of CB-renin by 60%; vinblastine and colchicine, microtubule binding agents, each inhibited CB-renin degradation by 40%. Our results show that the liver plays a major role in the regulation of plasma renin levels via clearance by the mannose receptor on nonparenchymal cells and subsequent degradation in lysosomes.
Marks
D L
DL
Center for Basic Research in Digestive Diseases, Mayo Medical School, Rochester, Minnesota 55905.
Kost
L J
LJ
Kuntz
S M
SM
Romero
J C
JC
LaRusso
N F
NF
D000818:Animals; D001345:Autoradiography; D005591:Chemical Fractionation; D003208:Concanavalin A; D006023:Glycoproteins / Q000494:pharmacology; D006801:Humans; D007668:Kidney / Q000502:physiology; D037181:Lectins, C-Type; D008026:Ligation; D008099:Liver / Q000378:metabolism*; D008297:Male; D008358:Mannose / Q000378:metabolism / Q000494:pharmacology; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000037:antagonists & inhibitors; D011994:Recombinant Proteins; D012083:Renin / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D012709:Serum Albumin; D012710:Serum Albumin, Bovine / Q000494:pharmacology
D006023:Glycoproteins; D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; D012709:Serum Albumin; C023840:mannose-bovine serum albumin conjugate; D003208:Concanavalin A; D012710:Serum Albumin, Bovine; D012083:Renin; D008358:Mannose