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Biomedical subjects

G R Castro

Publications and source records attributed to G R Castro.

28 records · Page 2Linked to original sources
PubMed1993

Apolipoprotein A-I conformation in discoidal particles: evidence for alternate structures.

To define the conformation of apolipoprotein A-I in discoidal particles, the immunoreactivity of a series of epitopes distributed along the apoA-I sequence has been evaluated in lipid-free apoA-I and in lipid-bound form. To this end, reconstituted discoidal lipoproteins, here called LpA-I, and defined by number of apoA-I per particle (e.g., Lp2A-I), have been prepared with palmitoyloleoylphosphatidylcholine, cholesterol, and apoA-I. Four LpA-I have been obtained and studied: two in the Lp2A-I class, 7.8 and 9.6 nm in diameter, and two in the Lp3A-I class, 10.8 and 13.4 nm. The immunoreactivity of all the epitopes tested was significantly different in LpA-I particles compared to lipid-free apoA-I, demonstrating that binding to lipids produces a drastic change in apoA-I conformation. Specific domains in the primary sequence become highly exposed while others are masked. Although the variation in immunoreactivity of the epitopes between various LpA-I was not drastic, significant differences in the calculated ED50 values were observed for a number of antibodies in small versus large particles within each class (Lp2A-I or Lp3A-I), indicating that particle size can modulate apoA-I conformation. In addition, when the competition between pairs of mAbs was analyzed in order to understand the relative position of epitopes, highly significant differences were observed as a function of particle size within each class. In particular, the competition between mAbs recognizing epitopes in the central region of apoA-I was greater in the larger particles than in their small counterparts.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗
PubMed1993

Cholesterol esters selectively delivered in vivo by high-density-lipoprotein subclass LpA-I to rat liver are processed faster into bile acids than are LpA-I/A-II-derived cholesterol esters.

High-density lipoprotein (HDL) subclass LpA-I has been reported to promote cholesterol efflux from mouse adipose cells in vitro, whereas subclass LpA-I/A-II has no effect. To investigate whether the apolipoprotein composition of HDL plays a role in the selective delivery of cholesterol esters to the liver in vivo, we labelled HDL in its cholesterol ester moiety and separated [3H]cholesterol oleate-labelled HDL into subclasses LpA-I and LpA-I/A-II by immuno-affinity chromatography. Serum decay and liver association of LpA-I and LpA-I/A-II were compared for the apoprotein and cholesterol ester moieties. Both LpA-I and LpA-I/A-II selectively delivered cholesterol esters to the liver with similar kinetics. The kinetics of biliary secretion of processed cholesterol esters, initially associated with LpA-I or LpA-I/A-II, were studied in rats equipped with permanent catheters in bile, duodenum and heart. For both LpA-I and LpA-I/A-II, liver association was coupled to bile acid synthesis, with an increase in secretion rate during the night. During the first night period, the biliary secretion of LpA-I-derived radio-activity was significantly greater than for LpA-I/A-II. The data indicate that with both LpA-I and LpA-I/A-II selective delivery of cholesterol esters from HDL to the liver occurs, but that cholesterol esters delivered by LpA-I are more efficiently coupled to bile acid synthesis.

Animals↗
PubMed1993

Antimicrobial activity determined in strains of Bacillus circulans cluster.

Wild-type strains of the genus Bacillus were screened for antimicrobial activity. Two strains exhibited antimicrobial activity against Micrococcus luteus and were identified as Bacillus polymyxa MIR-23 and Bacillus circulans MIR-13. Bacillus polymyxa MIR-23 was active against Escherichia coli, Pseudomonas aeruginosa and Aspergillus niger, whereas Bacillus circulans MIR-13 did not show activity against these microorganisms. Bacillus subtilis ATCC 6633 and B. polymyxa ATCC 10401 were used as standard antibiotic-producer strain and showed different antimicrobial profiles and yields from B. polymyxa MIR-23. The different antimicrobial profile of the two selected strains could possibly be used as a taxonomic marker.

Anti-Bacterial Agents↗
PubMed1992

Production of antimicrobials by Bacillus subtilis MIR 15.

We report the isolation and characterization of a strain of Bacillus, designed MIR 15, which appears to produce and excrete antimicrobials active against Gram-negative bacteria, but not against fungi. B. subtilis MIR 15 varied its antimicrobial profiles and production with the cultivation temperature.

Anti-Bacterial Agents↗
PubMed1989

Cutaneous xanthoma in association with paraproteinemia in the absence of hyperlipidemia.

In the present report we describe a patient with multiple myeloma and long-standing paraproteinemia who developed xanthoma in the absence of an elevation in plasma cholesterol or triglyceride concentrations. Studies demonstrated that our patient's monoclonal IgG antibody interacted with apoprotein B-100. The LDL-antibody complex isolated from our patient did not affect the degradation of LDL by human fibroblasts, indicating that while IgG derived from our patient interacted with LDL it did not alter the metabolism of this lipoprotein by the LDL receptor pathway. Since the LDL receptor pathway is the major route of LDL metabolism, this probably explains why our patient was not hyperlipidemic. In contrast to an absence of effect on the LDL receptor, our patient's LDL-antibody complex stimulated cholesterol esterification within macrophages indicating the uptake and degradation of the LDL-antibody complex. The LDL-antibody complex inhibited the degradation of acetyl LDL by macrophages (scavenger pathway), demonstrating that our patient's LDL-antibody complex was recognized as a modified LDL. Moreover, mixing Ig from our patient with normal LDL also resulted in the normal LDL increasing the esterification of cholesterol by macrophages. One can hypothesize that our patient's monoclonal IgG-LDL complex interacted with the macrophage scavenger receptor, thereby resulting in the occurrence of xanthoma in the absence of hyperlipidemia.

Acetylation↗
PubMed1988

Early incorporation of cell-derived cholesterol into pre-beta-migrating high-density lipoprotein.

Cultures of human skin fibroblasts were labeled to high cholesterol specific activity with [3H]cholesterol and incubated briefly (1-3 min) with normal human plasma. The plasma was fractionated by two-dimensional agarose-polyacrylamide gel electrophoresis and the early appearance of cholesterol label among plasma lipoproteins determined. A major part of the label at 1-min incubation was in a pre-beta-migrating apo A-I lipoprotein fraction with a molecular weight of ca. 70,000. Label was enriched about 30-fold in this fraction relative to its content of apo A-I (1-2% of total apo A-I). The proportion of label in this lipoprotein was strongly correlated with its concentration in plasma. Further incubation (2 min) in the presence of unlabeled cells demonstrated transfer of label from this fraction to a higher molecular weight pre-beta apo A-I species, to low-density lipoprotein, and to the alpha-migrating apo A-I that made up the bulk (96%) of total apo A-I in plasma. The data suggest that a significant part of cell-derived cholesterol is transferred specifically to a pre-beta-migrating lipoprotein A-I species as part of a cholesterol transport transfer sequence in plasma.

Apolipoprotein A-I↗
PubMed1986

Distribution of apolipoprotein E in the plasma of insulin-dependent and noninsulin-dependent diabetics and its relation to cholesterol net transport.

Noninsulin-dependent diabetics, whose plasma contained no detectable beta-VLDL (very low density lipoprotein), had a proportion (0.23 +/- 0.04) of plasma apolipoprotein E in the form of an abnormal lipoprotein not recognized by antibodies to apoB-100 from LDL (low density lipoprotein) or apoA-I from HDL (high density lipoprotein). This lipoprotein, abnormally rich in free cholesterol and apoE, had a calculated particle density within the low density lipoprotein range. It competed with LDL at the apoB,E receptor of normal fibroblasts and stimulated cholesteryl ester accumulation in mouse peritoneal macrophages. However, it did not compete with the binding of labeled rabbit beta-VLDL to macrophages. A much lower proportion of apoE (0.04 +/- 0.03) was in this form in the plasma of patients with insulin-dependent diabetes who had a comparable degree of hyperglycemia. The diabetic lipoprotein was absent in normoglycemic control subjects. The net transport of cholesterol from cell membranes to the plasma of noninsulin-dependent diabetics (and to a lesser extent, insulin-dependent diabetics) was inhibited relative to control values, and the magnitude of this inhibition was well correlated with the concentration of the abnormal lipoprotein of diabetes in plasma (r = 0.66 and 0.75, respectively). These findings suggest that diabetic plasma contains an abnormal and novel low density lipoprotein that mediates the abnormal cholesterol transport characteristic of human diabetes mellitus.

Apolipoproteins↗
PubMed1985

Effects of postprandial lipemia on plasma cholesterol metabolism.

Cholesterol net transport, esterification, and cholesteryl ester transfer have been determined in plasma during fasting, and postprandially, after a high fat-cholesterol meal. Significant rises in plasma triglyceride, phospholipid, and free cholesterol were associated with increases in cholesterol net transport, esterification, and transfer (all P less than 0.005), which were well correlated in individual subjects (r greater than 0.60). Essentially, the whole of free cholesterol required for such increased esterification was derived from cell membranes, when cultured fibroblasts were present, despite the increased level of free cholesterol in postprandial plasma; most of the additional cholesteryl ester generated was transferred to the low and very low density lipoproteins (LDL and VLDL) of plasma. Postprandial LDL (the major carrier of free and ester cholesterol and phospholipids among the acceptor lipoproteins) contained significantly decreased ratios of free cholesterol to phospholipid (P less than 0.001), which may modulate the increased transfer of cholesteryl ester to VLDL and LDL. These data suggest that the presence of postprandial acceptor lipoproteins in plasma may play an important role in stimulating the "reverse" transport of cholesterol from peripheral cells for hepatic degradation, which is effective even after the ingestion of dietary cholesterol.

Adult↗
PubMed1984

Evidence for the distribution of apolipoprotein E between lipoprotein classes in human normocholesterolemic plasma and for the origin of unassociated apolipoprotein E (Lp-E).

The distribution of apoE between the major lipoprotein classes of normocholesterolemic plasma has been determined by molecular sieve chromatography, immunoaffinity chromatography, preparative ultracentrifugation, and polyanionic precipitation. Highly comparable values were obtained for the first two procedures (correlation coefficient (r) = 0.958), while the other procedures gave recoveries of apoE in high density lipoprotein that were respectively higher and lower, although total recoveries of apoE were essentially complete in each case. Immunoaffinity chromatography under the conditions described was not accompanied by detectable dissociation or redistribution of apoE. By immunoaffinity chromatography, all the apoE of native plasma was present in the form of complexes also containing either apoA-I or apoB. However, both ultracentrifugation and polyanionic precipitation methods of lipoprotein fractionation dissociated substantial proportions of apoE into both lipid-rich and lipid-poor forms that were unassociated with other apolipoproteins. These forms were derived mainly or exclusively from the dissociation of apoE from lipoproteins containing apoB, while apoE bound to apoA-I was dissociated by neither procedure. When lipoproteins were adsorbed on immobilized antibodies to apoA-I or apoB and dissociated with 3 M NaCNS, the apoE and apoA-I remained associated while the complex of apoB and apoE was substantially dissociated. These results suggest that immunoaffinity chromatography accurately determines apoE distribution in plasma. The results on the in vitro generation of unassociated apoE (Lp-E) are discussed in terms of the "family" concept of lipoprotein structure.

Apolipoprotein A-I↗