Microquantification of cholesterol and cholesteryl esters in rat peritoneal macrophages by reverse-phase high-performance liquid chromatography

A simple and rapid method for the microquantification of cholesterol and cholesteryl esters by reverse-phase high performance liquid chromatography has been established. Comparison of elution patterns of authentic cholesterol and cholesteryl esters revealed that a mu Bondasphere reverse-phase C8 (300-A) column was more suitable than a corresponding reverse-phase C4 or C18 column in terms of rapidity and sensitivity. Recovery of cholesterol and cholesteryl esters from a C8 column was greater than 98% when determined either by radioactive cholesterol and cholesteryl oleate or by cholesteryl heptadecanoate. The sensitivity of the quantification ranged from 5 ng to 50 micrograms for both cholesterol and cholesteryl esters. This method was applied to determination of cellular cholesterol and cholesteryl esters of rat peritoneal macrophages. Lipid extracts of these cells were found to contain 38.01 +/- 2.60 micrograms of cholesterol and 3.18 +/- 0.36 micrograms of cholesteryl esters per milligram of cell protein. When the cells were loaded with cholesteryl esters by incubation for 24 h with various concentrations of acetylated low-density lipoprotein, a cellular level of cholesteryl esters showed a dose-dependent increase and reached a maximal level of 106.60 +/- 3.05 micrograms/mg cell protein. Thus, the present method is useful for the microquantification of cholesterol and cholesteryl esters from lipid extracts of biological samples.

Inhibition of ischemia and reflow-induced liver injury by an SOD derivative that circulates bound to albumin

Ischemia followed by reflow often results in tissue injury. Although reactive oxygens seem to play an important role in the pathogenesis of postischemic reflow-induced tissue injury, the mechanism and an efficient way to inhibit oxidative injury are not known. We studied the mechanism by which hepatic transport function was inhibited by a transient occlusion followed by reflow of the portal vein and hepatic artery by using a superoxide dismutase (SOD) derivative (SM-SOD) which circulates bound to albumin with a half-life of 6 h. Occlusion of the hepatic vessels for 20 min followed by reflow for 60 min significantly inhibited transhepatic transport of cholephilic ligands, such as bromosulfophthalein (BSP) and taurocholic acid. Intravenous administration of SM-SOD markedly inhibited the reflow-induced decrease in transhepatic transport of these ligands. Thiobarbituric acid - reactive metabolites (TBAR) in the liver and plasma remained unchanged during occlusion and reflow, while TBAR in the bile increased significantly. Intravenous injection of SM-SOD inhibited the reflow-induced increase in biliary TBAR. Xanthine oxidase activity in plasma also increased during occlusion and reflow by an SM-SOD-inhibitable mechanism. Polymorphonuclear leukocyte-dependent chemiluminescence of the peripheral blood remained unchanged during occlusion, but increased markedly with time after reflow. SM-SOD also inhibited the increase in chemiluminescence almost completely. These and other results suggested that the superoxide radical and/or its metabolite(s) might play an important role in the pathogenesis of the reflow-induced liver injury and that SM-SOD might be useful for studying the mechanism for tissue injury caused by oxygen toxicity.

Effect of obstructive jaundice on the fate of a nephrophilic organic anion in the rat

Renal transtubular transport of phenolsulfophthalein (PSP), a nephrophilic organic anion that circulates bound to albumin, was studied in normal and bile-duct-ligated rats. Intravenously injected PSP disappeared from the circulation more rapidly in bile-duct-ligated jaundiced rats than in intact animals. However, urinary excretion of PSP was significantly lower in the former than in the latter. Kinetic analysis revealed that binding of PSP to plasma protein(s) was significantly lower with jaundiced rats than with intact animals. Addition of albumin to plasma samples from bile-duct-ligated rats markedly increased PSP binding. The decreased PSP binding returned to normal levels after treating the jaundiced plasma with bilirubin oxidase, an enzyme that degrades amphiphilic bilirubin to water soluble metabolites. These results suggest that bilirubin might be the major metabolite that occupied the PSP binding site(s) on albumin in jaundiced rats. When PSP was injected bound to equimolar amount of albumin, the rate of PSP disappearance from the circulation decreased and urinary excretion of the ligand increased markedly; urinary excretion of PSP was significantly larger in bile-duct-ligated rats than in intact animals. These results suggest that the renal transport capacity for amphiphilic organic anions, such as PSP, might be increased compensatively in bile-duct-ligated animals, and that the apparent decrease in renal secretory transport for PSP might result from, at least in part, random distribution of the ligand to extrarenal tissues due to decrease in the binding activity of albumin.

[Relationship between clinical findings and subgingival microbial flora in periodontitis (2)]

The purpose of this study was to examine the relationship between clinical findings and subgingival relationship between clinical findings and subgingival microbial flora in periodontitis at the first medical examination and after initial preparation. The results obtained were as follows: 1. Clinical findings with the exception of plaque index showed improvement after initial preparation in comparison with the first medical examination. 2. In phase contrast microscopy, both total bacteria and incidence of spirochetes and motile rods decreased after initial preparation in comparison with the first medical examination. 3. Clinical findings with the exception of plaque index were related to the total bacteria and proportional distribution of spirochetes and motile rods in periodontal pockets, observed in phase contrast microscopy. 4. Total bacteria and proportional distribution of black-pigmented Bacteroides in periodontal pockets decreased after initial preparation in comparison with the first medical examination.

Scavenger receptor of human monocytic leukemia cell line (THP-1) and murine macrophages for nonenzymatically glycosylated proteins

Long-term incubation of proteins with glucose undergo a series of nonenzymatic reactions to form advanced glycosylation end product (AGE) with fluorescence and brown color. The receptor for AGE-proteins was demonstrated in murine macrophages (Vlassara et al. (1985) Proc. Natl. Acad. Sci. USA 82. 5588). Our recent study with rat macrophages revealed that the receptor also recognized proteins modified with aliphatic aldehydes such as formaldehyde or glycolaldehyde, indicating its close identity to a scavenger receptor for aldehyde-modified proteins (Takata, K. et al. (1988) J. Biol. Chem. 263. 14819). This notion was tested in the present study with human monocytic leukemia cell line (THP-1 cells), human monocyte macrophages and murine peritoneal macrophages. Endocytic uptake of AGE-proteins and aldehyde-modified proteins was inhibited in a cross-competitive fashion. The receptor activities of THP-1 cells for AGE-albumin and aldehyde-modified proteins were induced synchronously by phorbol 12-myristate 13-acetate. Furthermore, upon reduction by NaBH4 of the Schiff base formed between proteins and glucose or aldehydes, no ligand activity was generated. However, once the ligand activity was generated, NaBH4 was no longer effective for the ligand activity. Thus, a structure in common between AGE-proteins and aldehyde-modified proteins may be crucial for recognition by the human macrophage receptor.

Protective effect of lipoproteins containing apoprotein A-I on Cu2+-catalyzed oxidation of human low density lipoprotein

Two apoprotein A-I (apoA-I)-containing lipoproteins, one containing apoA-I and apoA-II (LpA-I/A-II) and the other containing only apoA-I (LpA-I), were examined for their effect on Cu2+-mediated oxidation of low density lipoprotein (LDL). The presence of LpA-I or LpA-I/A-II prevented LDL oxidation when assessed by the electrophoretic mobility, apoprotein B fragmentation and amounts of thiobarbituric acid-reactive substances. The protection of LDL oxidation by these lipoproteins was effective for up to 6 h, with LpA-I being more active than LpA-I/A-II. Results from these in vitro model experiments raise a possibility that LpA-I may play a role in protecting LDL from Cu2+-mediated oxidation.

Inhibition of postischemic reperfusion arrhythmias by an SOD derivative that circulates bound to albumin with prolonged in vivo half-life

Intravenously administered superoxide dismutase (SOD) rapidly disappeared from the circulation and often failed to prevent oxidative tissue injury. Thus, although superoxide radicals have been postulated to play an important role in the pathogenesis of postischemic reflow-induced tissue injury, conclusive evidence supporting this concept is lacking. We have synthesized an SOD derivative (SM-SOD) that circulated bound to albumin and accumulated in injured tissues whose local pH was decreased. Transient occlusion followed by reperfusion of the coronary artery elicited severe ventricular arrhythmias in rats. Intravenous administration of SM-SOD markedly inhibited the reflow-induced arrhythmias. SOD did not show such inhibitory effect. Kinetic analysis revealed that SM-SOD accumulated in the acidic lesion of the injured heart soon after reflow and returned to the circulation thereafter. These and other results suggest that superoxide radical and/or its metabolites would play a critical role in the pathogenesis of reperfusion arrhythmias and that SM-SOD may be useful for protecting acute myocardial injury induced by such hazardous oxygen metabolites.

Partial purification and characterization of CA19-9 antigen from the ascitic fluid of a patient with pancreatic cancer

CA19-9 immunoreactive protein was partially purified from the ascitic fluid of a patient with pancreatic cancer by perchloric acid fractionation, gel chromatography and Affi-gel Blue column chromatography, resulting in a purified sample of 5.0 x 10(6) CA19-9 units per milligram of protein (3700-fold purification). Western blotting analysis of this purified sample revealed a single band of molecular weight 210 kDa. Although the original ascitic fluid showed a high CA125 immunoreactivity, this purified sample had no CA125 immunoreactivity. The elution pattern for CA19-9 activity on Affi-gel Blue column is quite distinct from that for CA125. These results suggest that CA19-9 antigen in carcinoma patients may be identical or very similar to that recently purified from the culture media of the colorectal cell line SW1116 and is distinct from CA125 antigen.

Role of variant prealbumin in the pathogenesis of familial amyloidotic polyneuropathy: fate of normal and variant prealbumin in the circulation

According to recent studies on protein chemistry and genetic engineering, replacement of the Val30 residue of prealbumin by methionine is believed to play a critical role in the formation of amyloid deposit and the pathogenesis of familial amyloidotic polyneuropathy (FAP). However, only limited information is available concerning the behavior of prealbumin in the circulation. To obtain the molecular insight into the mechanism of amyloid deposition, it is indispensable to know the fates of normal and variant prealbumin in vivo. Thus, the fates of prealbumin samples from normal and FAP patients were studied in normal rats as well as in animals that were challenged with acute inflammation induced by turpentine. The effect of in vitro photooxidation of prealbumin samples on their behavior was also examined in vivo. Kinetic analysis revealed no appreciable difference between prealbumin samples from normal and FAP patients. These results suggest that factors other than the rate of transfer of the variant form prealbumin from plasma to an extravascular compartment may play a critical role in the pathogenesis of amyloid deposition in FAP patients.

Inhibition of stress-induced gastric injury in the rat by glutathione

Glutathione metabolism occurs via interorgan cycles in which hepatic synthesis of reduced glutathione and its transfer to extrahepatic tissues play an important role. To elucidate the physiologic significance of the cycles and tissue thiol status during stress-induced gastric mucosal injury, dynamic aspects of glutathione metabolism were analyzed in rats that were treated with water-immersion restraint. This treatment induced gastric mucosal lesion with concomitant decrease in the levels of perchloric acid-soluble thiols in various tissues, particularly in the liver and stomach. During the treatment, glutathione levels markedly decreased in the liver but not in other tissues. Depletion of hepatic glutathione by buthionine sulfoximine, a specific inhibitor for gamma-glutamyl cysteine synthetase, markedly decreased hepatic glutathione levels and increased the gastric injury. Intraperitoneal injection of reduced glutathione significantly increased plasma levels of glutathione and inhibited the occurrence of gastric injury without affecting intracellular glutathione levels. These results indicate that extracellular glutathione and its interorgan metabolism might play a critical role in the protection of gastric mucosa particularly when animals were challenged with various stress.

Scavenger receptor-mediated recognition of maleylated albumin and its relation to subsequent endocytic degradation

Rat sinusoidal liver cells take up maleylated bovine serum albumin (maleyl-BSA) and its demaleylated form (demaleyl-BSA) by scavenger receptor-mediated endocytosis. Cellular binding of maleyl-BSA and demaleyl-BSA and its quantitative relation to subsequent intracellular degradation were investigated. The binding affinities of these ligands were almost equal whereas the number of binding sites for maleyl-BSA was more than twice as large than that for demaleyl-BSA. However, no difference was observed in their endocytic degradation. The amounts of maleyl-BSA degraded were proportional to those bound to the cell surface up to a certain level. However, a further increase in cell-bound ligands did not affect the degradation of maleyl-BSA. Several polyanions such as fucoidin and dextran sulfate of Mr = 5000 inhibited the binding of maleyl-BSA but did not affect its degradation. In contrast, acetylated or oxidized low density lipoprotein had virtually no effect on cellular binding of maleyl-BSA but exhibited profound effects on its intracellular degradation. Similar results were obtained with rat peritoneal macrophages. Based on these data, we would propose that two binding sites are involved in the receptor-mediated ligand recognition; one is coupled to subsequent endocytic degradation, and the other serves as a binding site for polyanionic compounds.

Regional ligand domain is involved in scavenger receptor-mediated recognition of maleyl-albumin by rat sinusoidal liver cells

Scavenger receptor-mediated endocytosis of maleyl-albumin was studied with rat sinusoidal liver cells. Upon maleylation of greater than 28 mol lysine residues per protein, bovine serum albumin became an active ligand. Further modification of up to 37 mol lysine residues per protein resulted in a sharp increase in the ligand activity, reaching a maximum level thereafter. Removal of maleyl moieties from maleyl-albumin (demaleylation) from 53 mol to 14 mol lysine residues per protein did not affect the ligand activity. However, further demaleylation to less than 5 mol lysine residues per protein led to complete loss of the ligand activity. Thus, the covalently incorporated maleyl moieties are needed for the ligand activity. The ligand activity was also generated when two peptides (Frag N and Frag C) from cyanogen bromide-cleaved albumin were maleylated, indicating that the formation of an active ligand would not require a whole albumin molecule. Maleyl Frag C was further separated into three peptides; maleyl Frag C-1 (261 amino acid residues), maleyl Frag C-2 (102 residues) and maleyl Frag C-3 (36 residues). The cellular binding and endocytic degradation of maleyl-albumin or acetylated low density lipoprotein were effectively competed for by maleyl Frag C-1 and maleyl Frag C-2 but not by maleyl Frag C-3. Thus, regional domains might be involved in the ligand recognition by the scavenger receptor.

Endocytic pathway of high density lipoprotein via trans-Golgi system in rat resident peritoneal macrophages

Interaction of high density lipoprotein (HDL) with rat resident peritoneal macrophages was investigated by morphological and biochemical approaches. Binding studies at 0 degree C demonstrated saturable binding sites for 125I-HDL on the surface membrane. When cells were incubated with 125I-HDL at 37 degrees C, the cell-associated radioactivity increased with time, but intracellular degradation of HDL did not occur. Rather, the cell-associated 125I-HDL was released intact into the medium. Two morphological probes were employed to visualize the post-binding fate of HDL. Horseradish peroxidase and ferritin conjugates of HDL showed specific bindings to the coated pits of the plasma membranes and were internalized and delivered through receptosomes to a trans-Golgi system. They were then resecreted as secretory vesicles from the cells. Parallel experiments with transferrin-horseradish peroxidase conjugates revealed an endocytic pathway identical or very similar to that observed with HDL. These results provide evidence that internalization and subsequent nonlysosomal pathway via the trans-Golgi system are involved in receptor-mediated endocytosis of HDL by macrophages.

Synthesis of a superoxide dismutase derivative that circulates bound to albumin and accumulates in tissues whose pH is decreased

Protection of tissues from oxidative stress is one of the major prerequisites for aerobic life. Since intravenously injected Cu2+/Zn2+-type superoxide dismutase (SOD) disappears from the circulation with a short half-life of 5 min, its clinical use as a scavenger for superoxide radical is limited. We synthesized a human erythrocyte type SOD derivative (SM-SOD) by linking 2 mol of hydrophobic organic anion, alpha-4-[( 6-(N-maleimido)hexanoyloxymethyl]cumyl]half-butyl-esterified poly(styrene-co-maleic acid) (SM), to the cysteinyl residues of the dimeric enzyme without decreasing enzymic activity. SM-SOD, but not SOD, bound to an albumin-Sepharose column; the bound SM-SOD was eluted by a buffer solution containing 0.5% sodium dodecyl sulfate or 10 mM warfarin, suggesting that SM-SOD reversibly binds to the warfarin site on albumin. Due to the amphipathic nature of the SMI moiety, SM-SOD bound also to cell membranes particularly when the pH was decreased. In vivo analysis in the rat revealed that intravenously injected SM-SOD circulated bound to albumin with a half-life of 6 h. Postischemic reperfusion arrhythmias were almost completely prevented by a single dose of SM-SOD, but not SOD. Thus, the prolonged half-life of SM-SOD in the circulation and its preferential accumulation in an injured site with decreased pH appeared to be responsible for preventing myocardial injury. These results suggest that superoxide radical and/or its metabolite(s) would play an important role in the pathogenesis of postischemic reperfusion arrhythmias and that SM-SOD may be useful for decreasing tissue injury in ischemic heart disease.

Degradation of plasma bilirubin by a bilirubin oxidase derivative which has a relatively long half-life in the circulation

To enhance degradation of unconjugated bilirubin in hyperbilirubinemic subjects, we synthesized a bilirubin oxidase (EC 1.3.3.5) (BO) derivative (PEGBO) by covalently linking (2,4-bis[O-methoxy(polyethyleneglycol)]-6-chloro-s-triazine) (PEG) to the enzyme. Intravenously injected BO in rats disappeared from the circulation with a half-life of 2.5 min; the half-life of PEGBO was 190 min. Intravenously injected BO minimally and transiently decreased plasma bilirubin levels in jaundiced Gunn rats and in bile-duct-ligated jaundiced rats. In contrast, PEGBO rapidly and substantially decreased plasma bilirubin levels and the effect persisted for longer than 3 h. Renal dysfunction often occurs in patients with liver diseases. To study the role of bilirubin toxicity for the kidney, functions of transtubular transport for organic anions was measured in bile-duct-ligated jaundiced animals before and after treatment with PEGBO. Bile duct ligation decreased urinary excretion of phenolsulfophthalein (PSP), an organic anion used for renal function test. Treatment of the jaundiced animals with PEGBO increased the rate of PSP disappearance from the circulation and normalized its urinary excretion. Thus, PEGBO might be useful for the study of bilirubin toxicity in jaundiced animals.

Substitution of a lysyl residue for arginine 386 of Escherichia coli aspartate aminotransferase

Substitution of a lysyl residue for Arg-386 of Escherichia coli aspartate aminotransferase resulted in an extensive decrease in Vmax values (0.8% with the aspartate-2-oxoglutarate pair and 0.2% with the glutamate-oxalacetate pair, compared with the corresponding values for the wild-type enzyme). Kinetic analysis of the four sets of half-reactions, the pyridoxal form of the enzyme with aspartate or glutamate and the pyridoxamine form with 2-oxoglutarate or oxalacetate, allowed us to define the independent effect of the mutation on the reactivity of each substrate. Decrease in the first order rate constant (kmax) was more pronounced in the reactions with five-carbon substrates (glutamate and 2-oxoglutarate) than in those with four-carbon substrates (aspartate and oxalacetate), while the increase in the apparent dissociation constant (Kd) was greater for four-carbon substrates than for five-carbon substrates. The decrease of overall catalytic efficiency as judged by the values, kmax/Kd, was more pronounced in the reactions with five-carbon substrates than in those with four-carbon substrates. Affinities for substrate analogs such as succinate, glutarate, 2-methylaspartate, and erythro-3-hydroxyaspartate, were also considerably decreased by the mutation of the enzyme. These findings indicate that the side chain of the lysyl residue, although it bears a positive charge similar to that of the arginyl residue, is not structurally adequate for the productive binding of a substrate during catalysis.

Intracellular accumulation of cholesteryl esters suppresses production of lipopolysaccharide-induced interleukin 1 by rat peritoneal macrophages

Interleukin 1 (IL-1) is a major cytokine of macrophages secreted by several stimulants such as lipopolysaccharide (LPS). Macrophages are known to possess the scavenger receptor for acetylated low density lipoprotein (acetyl-LDL) and maleylated albumin. In the present study we determined effects of these ligands on LPS-induced IL-1 production by rat peritoneal macrophages. These ligands themselves did not induce IL-1 production. However, upon short incubation with acetyl-LDL, LPS-induced IL-1 production was significantly suppressed. The extent of the suppression was proportional to cellular cholesteryl esters. Thus, intracellular accumulation of cholesteryl esters might be responsible for suppression of LPS-induced IL-1 production.

Import and processing of precursor to mitochondrial aspartate aminotransferase. Structure-function relationships of the presequence

The precursor protein of pig mitochondrial aspartate aminotransferase (pre-mAspAT) contains a 29-residue presequence (Joh, T., Nomiyama, H., Maeda, S., Shimada, K., and Morino, Y. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 1-5). Pre-mAspAT produced in an in vitro transcription and translation system was avidly imported into pig and rat liver mitochondria to be processed to the mature form of the enzyme. The pre-mAspAT was also processed to the mature form upon incubation with mitochondrial extracts. We synthesized precursor proteins with alterations within the presequence and compared quantitatively the effects of these mutations on the rates of both import and processing. Single and multiple substitutions of four basic residues with neutral amino acids at positions 5, 8, 18, and 28 showed that each residue contributes differentially to import and processing. Substitutions of His5 and Arg8 with glycines abolished the import activity but did not appreciably affect the rate of processing. Substitution of Arg28 with leucine at the position adjacent to the cleavage site seriously impaired the processing without appreciably affecting the rate of import. Analysis of deletions revealed that the amino-terminal region from position 2 to 8 was essential for both the import and processing. Thus the positive charges in the amino-terminal region are critical for import while the amino-terminal peptide segment and the cleavage site region appear to be requisite for recognition by a processing protease.

[Arg292----Val] or [Arg292----Leu] mutation enhances the reactivity of Escherichia coli aspartate aminotransferase with aromatic amino acids

Arg292 of E. coli aspartate aminotransferase was substituted with valine or leucine by site-directed mutagenesis. In comparison with the wild-type enzyme, either of the mutant enzymes showed a decrease by over 5 orders of magnitude of kcat/km values for aspartate and glutamate. This supports the contention that Arg292 is important for determining the specificity of this enzyme for dicarboxylic substrates. In contrast, mutant enzymes displayed a 5- to 10-fold increase in kcat/Km values for aromatic amino acids as substrates. Thus, introduction of an uncharged, hydrophobic side chain into position 292 leads to a striking alteration in substrate specificity of this enzyme, thereby improving catalytic efficiency toward aromatic amino acids.

cDNA cloning and expression of pig cytosolic aspartate aminotransferase in Escherichia coli: amino-terminal heterogeneity of expressed products and lack of its correlation with enzyme function

A full-length cDNA encoding the pig cytosolic aspartate aminotransferase (EC 2.6.1.1) (cAspAT) was constructed from two overlapping cDNA clones. One clone (Lm pcAAT-8) isolated from a lambda gt10 pig heart cDNA library contained a 3' untranslated sequence, a poly(A) segment, and a part of the coding region for amino acid positions 127-412. Another clone (Lm pcAAT-107) isolated from a lambda gt10 primer extension library contained the coding region for amino acid positions 1-148 and a 5' untranslated sequence. Rejoining of the cDNA inserts of the two clones and recloning into pUC18 gave rise to a cDNA covering an entire coding sequence for pig cAspAT mRNA. Insertion into pKK223-3 yielded an expression plasmid, ppcAAT200. Escherichia coli JM105 cells transfected with ppcAAT200 overproduced pig cAspAT to an extent of about 3% of the total cellular soluble proteins. The expressed product was indistinguishable from the alpha subform of cAspAT isolated from pig heart in terms of specific activity, absorption spectra, molecular size, crystalline form, and immunological reactivity with anti pig cAspAT antibody. Compared with the amino-terminal sequence (Ala-Pro-Pro-) reported for pig heart cAspAT, the recombinant pig cAspAT showed heterogeneity in the amino-terminal sequence: Ala 1 (26%), Pro2 (54%), and Pro3 (19%). Construction of a mutant cAspAT with deletion of residues 1-3 and its comparison with the wild-type enzyme revealed that loss of the three amino-terminal residues does not affect the catalytic activity and structural integrity of the enzyme.