Hydrofluoric acid poisoning

A case of suicidal ingestion of hydrofluoric acid is presented. Death of the victim while in police custody was one of the more unique aspects of the case. This is the sixth case of poisoning of this type reported in Dade County. Clinical, pathological, and toxicological aspects of fluoride poisoning are discussed.

Receptor-mediated endocytosis of epidermal growth factor by hepatocytes in the perfused rat liver: ligand and receptor dynamics

We have used biochemical and morphological techniques to demonstrate that hepatocytes in the perfused liver bind, internalize, and degrade substantial amounts of murine epidermal growth factor (EGF) via a receptor-mediated process. Before ligand exposure, about 300,000 high-affinity receptors were detectable per cell, displayed no latency, and co-distributed with conventional plasma membrane markers. Cytochemical localization using EGF coupled to horseradish peroxidase (EGF-HRP) revealed that the receptors were distributed along the entire sinusoidal and lateral surfaces of hepatocytes. When saturating concentrations of EGF were perfused through a liver at 35 degrees C, ligand clearance was biphasic with a rapid primary phase of 20,000 molecules/min per cell that dramatically changed at 15-20 min to a slower secondary phase of 2,500 molecules/min per cell. During the primary phase of uptake, approximately 250,000 molecules of EGF and 80% of the total functional receptors were internalized into endocytic vesicles which could be separated from enzyme markers for plasma membranes and lysosomes on sucrose gradients. The ligand pathway was visualized cytochemically 2-25 min after EGF-HRP internalization and a rapid transport from endosomes at the periphery to those in the Golgi apparatus-lysosome region was observed (t 1/2 approximately equal to 7 min). However, no 125I-EGF degradation was detected for at least 20 min. Within 30 min after EGF addition, a steady state was reached which lasted up to 4 h such that (a) the rate of EGF clearance equaled the rate of ligand degradation (2,500 molecules/min per cell); (b) a constant pool of undegraded ligand was maintained in endosomes; and (c) the number of accessible (i.e., cell surface) receptors remained constant at 20% of initial values. By 4 h hepatocytes had internalized and degraded 3 and 2.3 times more EGF, respectively, than the initial number of available receptors, even in the presence of cycloheximide and without substantial loss of receptors. All of these results suggest that EGF receptors are internalized and that their rate of recycling to the surface from intracellular sites is governed by the rate of entry of ligand and/or receptor into lysosomes.

The effects of 1-amino-D-proline on the production of carnitine from exogenous protein-bound trimethyllysine by the perfused rat liver

Following receptor-mediated endocytosis of trimethyllysine-labeled asialofetuin and agalacto-orosomucoid by liver parenchymal and nonparenchymal cells, respectively, the glycoproteins are degraded and the methylated lysine residues released. The free intracellular trimethyllysine is then converted, in addition to 2-N-acetyl-6-N-trimethyllysine, to 4-N-trimethylaminobutyrate, carnitine, and acetylcarnitine. In the presence of 1-amino-D-proline, a vitamin B6 antagonist, the total production from protein-bound trimethyllysine of 4-N-trimethylaminobutyrate, the immediate precursor of carnitine, carnitine, and its acetylated derivative was depressed by as much as 60-80% in perfused rat liver. The decreased synthesis of carnitine was accompanied by an accumulation of 3-hydroxy-6-N-trimethyllysine, and intermediate in the carnitine biosynthetic pathway. The extent of 3-hydroxy-6-N-trimethyllysine accumulation, which was not evident in the absence of added 1-amino-D-proline, depended on the dose of 1-amino-D-proline perfused through the liver. In addition, those effects of 1-amino-D-proline were almost completely reversed by inclusion of pyridoxine in the perfusing medium. These results support the suggestion of a requirement for pyridoxal 5'-phosphate in the biosynthesis of carnitine by the liver.

Low temperature selectively inhibits fusion between pinocytic vesicles and lysosomes during heterophagy of 125I-asialofetuin by the perfused rat liver

Galactose-terminating ligands are specifically recognized by mammalian hepatocytes, internalized, and degraded within lysosomes. We have studied the effects of temperature on this process using 125I-asialofetuin and the perfused rat liver. Uptake and catabolism of 125I-asialofetuin continued but were progressively slowed as the temperature decreased from 35 degrees C to 20 degrees C. At 20 degrees C, lysosomal degradation completely stopped. Results of subcellular fractionation experiments and in situ electron microscopic autoradiography revealed that fusion between pinocytic vesicles and lysosomes did not occur below 20 degrees C, despite the continued endocytosis of 125I-asialofetuin and movement of pinocytic vesicles into the lysosome-Golgi region of the cell. Below 10 degrees C, endocytosis essentially stopped. Inhibition of the fusion step was reversed upon rewarming the liver to physiological temperature. By examining the reversal process the half-time for fusion between pinocytic vesicles and lysosomes was determined to be 7 min. This is the slowest metabolic event involved in the catabolism of asialofetuin by the liver both in the perfused organ and in vivo.

Hepatic synthesis of carnitine from protein-bound trimethyl-lysine. Lysosomal digestion of methyl-lysine-labelled asialo-fetuin

The biosynthesis of carnitine in the rat was studied by following the metabolism of two radioactive derivatives of asialo-fetuin. The first contained 14C-labelled methyl groups covalently bound to the 6-N-amino fraction of its lysine residues as 6-N-monomethyl- and dimethyl-lysine. By treating this protein with iodomethane, a second derivative was produced in which the radioactivity was preferentially incorporated as 6-N-[Me-14C]-trimethyl-lysine. These desialylated glycoproteins, like other asialo-proteins, were immediately cleared from the blood by rat liver. Within hepatocyte lysosomes, the 14C-labelled proteins were rapidly hydrolysed, producing free amino acids containing the various 6-N-[Me-14C]methylated lysine residues. The radioactive amino acids crossed the lysosomal membrane and were further metabolized in the cytosol. Carnitine was the major radioactive metabolite detected in extracts of the rat carcass and liver after intravenous injection of 6-N-[Me-14C]trimethyl-lysine-labelled asialo-fetuin. Within 3h, at least 34.6% of the trimethyl-lysine in the administered protein was converted into carnitine. Similarly, an isolated perfused rat liver converted 30% of the added peptide-bound trimethyl-lysine into carnitine within 90 min. On the other hand, in numerous attempts we failed to detect radioactive carnitine in both rat liver and carcass between 20 min and 22 h after injection of 6-N-[Me-14C]-monomethyl- and -dimethyl-lysine-labelled asialo-fetuin. These data provide evidence for a pathway of carnitine biosynthesis that involves trimethyl-lysine as a peptide-bound precursor as proposed by R.A. Cox & C.L. Hoppel [(1973) Biochem. J. 136, 1083-1090] and V. Tanphaichitr & H.P. Broquist [(1973) J. Biol. Chem. 248, 2176-2181]. The findings also show that rat liver can synthesize carnitine without the aid of other tissues, but cannot convert free partially methylated lysines into trimethyl-lysine.