Spectroscopic studies of lipids and biological membranes: carbon-13 and proton magic-angle sample-spinning nuclear magnetic resonance study of glycolipid-water systems

We have obtained 1H and 13C magic-angle sample-spinning (MAS) nuclear magnetic resonance (NMR) spectra of three glycosyldiacylglycerol-water (1:1, weight ratio) mesophases, at 11.7 T, as a function of temperature, in order to probe lipid headgroup, backbone, and acyl chain dynamics by using natural-abundance NMR probes. The systems investigated were monogalactosyldiacyldiglyceride [MGDG; primarily 1,2-di[(9Z,12Z,15Z)octadec-9,12,15-trienoyl++ +]-3-beta-D-galactopyranosyl- sn-glycerol]; digalactosyldiacyldiglyceride [DGDG; primarily 1,2-di[(9Z,12Z,15Z)octadec-9,12,15-trienoyl++ +]-3- (alpha-D-galactopyranosyl-1-6-beta-D-glactopyranosyl)-sn-glycerol] ; and sulfoquinovosyldiacyldiglyceride [SQDG; primarily 1-[(9Z,12Z,15Z)octadec-9,12,15-trienoyl]-2 -hexadecanoyl-3-(6-deoxyl-6- sulfono-alpha-D-glucopyranosyl)-sn-glycerol]. At approximately 22 degrees C, all three lipid-water systems give well-resoled 13C and 1H MAS NMR spectra, characteristic of fluid, liquid-crystalline mesophases. 13C spin-lattice relaxation times of the headgroup and glycerol backbone carbons of all three materials give, within experimental error, the same NT1 values (approximately 400 ms), implying similar high-frequency motions, independent of headgroup size and charge. Upon cooling, pronounced line broadenings are observed, due to an increase in slow motional behavior. For each lipid, the onset of line broadening is seen with the glycosyl headgroup, glycerol backbone, and the first two or three carbons of the acyl chains. By approximately -20 degrees, all headgroup carbon resonances are broadened beyond detection. Both galactose moieties in DGDG "freeze out" together, implying a rigid-body motion of the disaccharide unit. Upon further cooling, the bulk polymethylene chain resonances in all three systems (in both 13C and 1H MAS) broaden greatly, followed by the olefinic and allylic carbon resonances.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon-13 nuclear magnetic resonance spectroscopy of lipids: differential line broadening due to cross-correlation effects as a probe of membrane structure

We have obtained proton-coupled carbon-13 nuclear magnetic resonance (NMR) spectra of a variety of lipid-water and lipid-drug-water systems, at 11.7 T, as a function of temperature, using the "magic-angle" sample-spinning (MAS) NMR technique. The resulting spectra show a wide range of line shapes, due to interferences between dipole-dipole and dipole-chemical shielding anisotropy interactions. The differential line-broadening effects observed are particularly large for aromatic and olefinic (sp2) carbon atom sites. Coupled spectra of the tricyclic antidepressants desipramine and imipramine, in 1,2-dimyristoyl-sn-glycero-3-phosphocholine-water mesophases, show well-resolved doublets having different line shapes for each of the four aromatic methine groups, due to selective averaging of the four C-H dipolar interactions due to rapid motion about the director (or drug C2) axis. 2H NMR spectra of [2,4,6,8-2H4]desipramine (and imipramine) in the same 1,2-dimyristoyl-sn-glycero-3-phosphocholine-water mesophase exhibit quadrupole splittings of approximately 0-2 and approximately 20 kHz, indicating an approximate magic-angle orientation of the C2-2H(1H) and C8-2H(1H) vectors with respect to an axis of motional averaging, in accord with the 13C NMR results. Selective deuteration of imipramine confirms these ideas. Spectra of digalactosyl diglyceride [primarily 1,2-di[(9Z,12Z,15Z)-octadeca-9,12,15-trienoyl ]-3- (alpha-D-galactopyranosyl-1-6-beta-D-galactopyranosyl)-sn-glycerol]-H2O (in the L alpha phase) show a large differential line broadening for C9 but a reduced effect for C10, consistent with the results of 2H NMR of specifically 2H-labeled phospholipids [Seelig, J., & Waespe-Saracevic, N. (1978) Biochemistry 17, 3310-3315].(ABSTRACT TRUNCATED AT 250 WORDS)

Epidural sufentanil for postoperative analgesia: dose-response in patients recovering from major gynecologic surgery

To determine the lowest effective dose of epidural sufentanil given for analgesia, 41 patients undergoing elective abdominal gynecologic surgery during continuous epidural anesthesia (lidocaine 2%) were randomly assigned to one of four postoperative treatment groups. Patients received an epidural bolus of either 25 (group A), 40 (group B), 55 (group C), or 70 micrograms (group D) sufentanil in 10 mL of saline. They were evaluated for the next 8 h using a 10-cm visual analogue scale. Except for two individuals in group A, all patients achieved a visual analogue scale score of 1 cm or less during the study interval. The onset of analgesia was most rapid in the two higher dose groups (A vs C and D; P less than 0.05). Pairwise comparison between groups showed a significant difference in the time needed to achieve maximum pain relief between the lowest and highest treatment groups (A vs D; P less than 0.05). Duration of analgesia was also significantly longer in groups C and D than in group A (208.0 +/- 21.1 and 224.0 +/- 14.7 vs 140.0 +/- 10.7 min; P less than 0.05). There were no differences among groups with regard to mean respiratory rate, level of sedation, 24-h narcotic requirements, or incidence of nausea, vomiting, and pruritus (P = NS). A single patient in group D suffered profound respiratory depression within seconds of administration. We conclude that, in patients recovering from lower abdominal surgery, a single 40-55-micrograms epidural bolus of sufentanil provides 3-3.5 h of effective analgesia, and that larger doses are not warranted.

In vitro and in vivo analysis of the c-myc RNA polymerase III promoter

The c-myc promoter has the unusual property of displaying both RNA polymerase II (Pol II) and RNA polymerase III (Pol III) activities. Both Pol II and Pol III utilize the same transcription initiation site. We have now examined the effects of mutations in crucial regions of the c-myc promoter to assess their effects on both transcriptional activities. In doing this we show that both Pol II and Pol III activities require sequences that are located within the stronger of the two principal c-myc promoter regions (P2). Further, we show that the Pol III activity using this initiation site does not require an A box or distal upstream sequences. Like the Pol II activity, it does require an intact TATA sequence and alterations at this site result in the simultaneous loss of both Pol II and Pol III activities. The superimposition of two apparently inseparable promoter activities makes it possible to consider common features, possible common protein elements in each holoenzyme complex, as well as a potential role for each enzyme in the regulated expression of the c-myc gene.

Heat shock induces two distinct S6 protein kinase activities in quiescent mammalian fibroblasts

The regulation of S6 kinase activity was used to monitor perturbations of intracellular signaling activity during heat shock of quiescent murine and human fibroblasts. Previous reports on exponentially growing insect and plant cells had indicated that 40S ribosomal protein S6 is dephosphorylated during heat shock; thus inhibition of S6 kinase activity by heat shock was anticipated in NIH 3T3 fibroblasts and human cells (HeLa, diploid embryonic fibroblasts MRC-5, and skin-derived fibroblasts). Unexpectedly, two distinct S6 protein kinases were activated in quiescent fibroblasts after heat exposure. One of the enzymes was partially purified by sequential column chromatography and was determined to be equivalent to the enzyme activated by serum and other growth factors, referred to here as pp70-S6 protein kinase. The other protein S6 kinase, pp90rsk, was identified by a specific immunoprecipitation assay. Monitoring both enzymatic activities during heat shock revealed a temporal pattern of activation that was reversed when compared to non-stressed, mitogen-stimulated cells. Finally, heat shock stimulated protein S6 phosphorylation in cultured, quiescent mammalian cells. These data demonstrate that specific protein kinases can be activated during heat shock, and that some early mitogenic signals may also participate in the response of cells to physiologic stress.

Mitogen-activated Swiss mouse 3T3 RSK kinases I and II are related to pp44mpk from sea star oocytes and participate in the regulation of pp90rsk activity

Using a recombinant rsk gene product as a substrate for in vitro kinase assays, we have identified two mitogen-activated Swiss 3T3 RSK protein kinase activities (referred to as RSK kinase I and RSK kinase II, based on their order of elution from phenyl-Sepharose). Polyclonal antisera prepared against maturation-regulated 44-kDa myelin basic protein (MBP) kinase (pp44mpk) purified from sea star oocytes demonstrated immunocrossreactivity with polypeptides of approximately 44 kDa in the RSK kinase I preparation and approximately 42 kDa in the RSK kinase II preparation, respectively. These polypeptides were also recognized by anti-phosphotyrosine antibodies, and either phosphatase 1B or 2A (tyrosine- and serine/threonine-specific phosphatases, respectively) separately inactivated RSK phosphotransferase activity supporting the notion that tyrosine and serine/threonine phosphorylation are required for activity. In vitro, both RSK kinases and MBP kinase phosphorylated recombinant RSK and generated nearly identical two-dimensional tryptic phosphopeptide maps. They also phosphorylated MBP and microtubule-associated protein 2 but not 40S ribosomal protein S6. Furthermore, these protein kinases phosphorylated and partially activated pp90rsk in immune complexes obtained from quiescent cells.

Distinct mechanisms for the activation of the RSK kinases/MAP2 kinase/pp90rsk and pp70-S6 kinase signaling systems are indicated by inhibition of protein synthesis

Previous studies demonstrated that addition of protein synthesis inhibitors to quiescent cells resulted in the stimulation of S6 kinase activity. The present characterization of several growth factor- and oncogene-regulated protein-serine/threonine kinases demonstrated that pp70-S6 protein kinase and not pp90rsk, RSK kinase, or MAP2 kinase activities were rapidly stimulated. Dose-response experiments revealed a close correlation between the extent of protein synthesis inhibition and the level of activation of pp70-S6 kinase activity. Analysis of S6 phosphorylation suggests that activation of pp90rsk S6 phosphotransferase activity, whose Xenopus homologues appear to be responsible for S6 phosphorylation during oocyte maturation, may participate in, but is not essential for, the increase in S6 phosphorylation observed in growth-stimulated somatic animal cells. These studies provide additional evidence for the existence of two distinct, independently regulated protein phosphorylation cascades activated in the early G1 phase of the cell cycle.

Coordinate regulation of pp90rsk and a distinct protein-serine/threonine kinase activity that phosphorylates recombinant pp90rsk in vitro

Protein kinase assays that use recombinant pp90rsk as a substrate were developed in an attempt to identify growth-regulated enzymes responsible for the phosphorylation and activation of pp90rsk S6 phosphotransferase activity. With this assay we have ientified a pp60v-src-, growth factor-, phorbol ester-, and vanadate-regulated serine/threonine protein kinase activity that is not related to two other cofactor-independent, growth-regulated protein kinases, pp70-S6 protein kinase and pp90rsk. The pp90rsk-protein kinase activity (referred to as rsk-kinase) is also not related to cofactor-dependent signal transducing protein kinases such as the cyclic AMP-dependent protein kinases, members of the protein kinase C family, or other Ca2(+)-dependent protein kinases. In vitro, partially purified rsk-kinase phosphorylates several of the sites (serine and threonine) that are phosphorylated in growth-stimulated cultured cells. A detailed examination of the mitogen-regulated activation kinetics of rsk-kinase and pp90rsk activities demonstrated that they are coordinately regulated. In addition, protein kinase C is not absolutely required for epidermal and fibroblast growth factor-stimulated activation of rsk-kinase, whereas, like pp90rsk, platelet-derived growth factor- and vanadate-stimulated rsk-kinase activity exhibits a greater dependence on protein kinase C-mediated signal transduction. The characterization and future purification of the rsk-kinase(s) will improve our understanding of the early signaling events regulating cell growth.

Regulation of pp90rsk phosphorylation and S6 phosphotransferase activity in Swiss 3T3 cells by growth factor-, phorbol ester-, and cyclic AMP-mediated signal transduction

Somatic cell homologs to the Xenopus laevis S6 protein kinases (referred to collectively as pp90rsk) have recently been identified and partially characterized. Here we examine alterations in pp90rsk phosphorylation and S6 phosphotransferase activity in response to regulators of multiple signal transduction systems: purified growth factors, phorbol ester, changes in cyclic AMP (cAMP) levels, and sodium vanadate. All reagents tested increased pp90rsk serine and threonine phosphorylation, but only those agents that regulate cell proliferation and sodium vanadate activated its S6 kinase activity. In addition to the cAMP-stimulated phosphorylation of pp90rsk, a simple correlation between the extent of growth-regulated pp90rsk phosphorylation and S6 phosphotransferase activity was not observed. Quantitative phosphorylation of pp90rsk continued to increase after its S6 kinase activity began its return towards basal levels. However, a close correlation between the appearance and disappearance of a slow-mobility form of phosphorylated pp90rsk (by electrophoresis) and pp90rsk activity was observed. In addition, pp90rsk was regulated by both protein kinase C-independent and -dependent signaling mechanisms. The extent of protein kinase C participation, however, varied depending on which growth factor receptor was activated. Furthermore, growth factor-specific differences in the temporal regulation of pp90rsk S6 phosphotransferase activity were also observed. These results support the notion that the complex regulation of the rsk gene product constitutes one of the primary responses of animal cells to mitogenic signals.

An evaluation of morphine and oxymorphone administered via patient-controlled analgesia (PCA) or PCA plus basal infusion in postcesarean-delivery patients

The analgesic efficacy and adverse effects of morphine and oxymorphone in 32 patients who received traditional patient-controlled analgesia (PCA) following cesarean delivery were compared with those in 32 other patients receiving the same agents via PCA plus basal opioid infusion (PCA + BI). All patients were operated upon during epidural anesthesia with 2% lidocaine and 1:200,000 epinephrine to achieve a T4 sensory level. Upon first complaint of pain in the recovery room, patients were given a titrated iv loading dose of the assigned opioid until comfortable and were then provided with a programmable PCA device. Group I (PCA) consisted of two subsets in which incremental boluses of morphine (1.8 mg, n = 16) or oxymorphone (0.3 mg, n = 16) could be self-administered via conventional PCA. Patients in group II (PCA + BI) received a basal infusion of morphine (0.6 mg/hour, n = 16) or oxymorphone (0.1 mg/hour, n = 16) in addition to self-administered boluses of 1.8 and 0.3 mg, respectively. Patients were evaluated for 24 h following initiation of analgesic therapy, and 10-cm visual analog scales (VAS) were utilized at selected intervals to assess pain at rest, pain during movement, and satisfaction with therapy. The level of sedation and incidence of nausea/vomiting and pruritus were also recorded. Patients utilizing PCA + BI noted significant reductions in resting pain scores with oxymorphone and decreased pain during movement with both opioids when compared with individuals using PCA alone (P less than 0.05). There were no significant differences between treatment groups in 24-h dose requirements or patient satisfaction with therapy (P = ns).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of surfactant-associated protein-A (SP-A) on the activity of lipid extract surfactant

The properties of natural bovine surfactant and its lipid extract have been examined with a pulsating bubble surfactometer which assesses the ability of surfactant lipids to adsorb to the air/liquid interface and reduce the surface tension to near 0 dynes/cm during dynamic compression. Studies conducted at 1 mg/ml phospholipid revealed that the surface activity (i.e., the ability to produce low surface tensions) of lipid extracts could be enhanced by incubating the sample at 37 degrees C for 120 min or by addition of CaCl2. In contrast, incubation at 37 degrees C only slightly improved the biophysical activity of natural surfactant and the addition of CaCl2 had a more modest effect than with lipid extracts. With 20 mM CaCl2, the surfactant activity of lipid extract surfactant was similar to that of natural surfactant. Incubation with EDTA reduced the biophysical activity of natural surfactant. Experiments in which increasing amounts of lipid extract were replaced by natural surfactant revealed that small amounts of natural surfactant enhanced the surfactant activity of lipid extract. The biophysical activity of lipid extract surfactant was also increased by the addition of soluble surfactant-associated protein-A (SP-A) (28-36 kDa) purified from natural bovine surfactant. These results indicate that SP-A (28-36 kDa) improves the surfactant activity of lipid extracts by enhancing the rate of adsorption and/or spreading of phospholipid at the air/liquid interface resulting in the formation of a stable lipid monolayer at lower bulk concentrations of either phospholipid or calcium.

Expression of the gene for main intrinsic polypeptide (MIP): separate spatial distributions of MIP and beta-crystallin gene transcripts in rat lens development

The main intrinsic polypeptide (MIP) is the major protein present in the lens fiber cell membrane and is the product of a gene which, as far as is known, is expressed only in the lens. We have used in situ hybridization and immunofluorescence microscopy to characterize the expression of this gene during the course of development in the rat. At progressive stages of lens morphogenesis, we find that synthesis of the protein is closely tied to the accumulation of MIP mRNA in cells that are committed to terminal differentiation, first in the elongating presumptive primary lens fibers and later in the secondary fibers as they differentiate from the anterior epithelial cells. The transcripts accumulate in the basal cytoplasm of the primary fibers and in the cytoplasm which surrounds the cell nucleus in the secondary fibers. We have compared this pattern of expression with that of a gene for a cytoplasmic protein, beta-crystallin beta-A1/A3. In sharp contrast to the localized concentrations seen for the MIP mRNA, beta-A1/A3 transcripts are relatively uniformly distributed throughout the cytoplasm. Neither MIP nor crystallin gene appears to be transcriptionally active in the undifferentiated epithelial cell, but transcripts from the beta-A1/A3 gene appear earlier in fiber cell differentiation than do those from the gene for MIP.

The c-myc gene encodes superimposed RNA polymerase II and III promoters

The first exon of the c-myc gene has unusual properties that suggest some further role in gene regulation. It encodes a large, evolutionarily conserved leader exon that is transcribed more frequently than the remaining exons of the c-myc gene. In what follows, we provide a possible explanation for these observations. We find that the major promoter of the c-myc gene is bifunctional; that is, it supports transcription by RNA polymerases II and III (pol II and III). Both enzymes initiate in vitro transcription from the major c-myc initiation site (P2), but pol III is completely blocked near the 3' end of the first exon while pol II, though partially blocked, transcribes through this region. These superimposed transcriptional activities suggest a potential regulatory mechanism by which one polymerase system could influence the activity of another.

Protein sequence analysis studies on the low molecular weight hydrophobic proteins associated with bovine pulmonary surfactant

Lipid extracts of bovine pulmonary surfactant, which exhibit biophysical and biological activity, contain two hydrophobic proteins which have been designated surfactant protein-B (SP-B) and SP-C. Amino terminal amino acid sequence analysis of whole lipid extracts and partially purified protein fractions gave rise to three sequences, two major and one minor. The first sequence, identified as a member of the SP-B family, extended for 60 amino acids beginning with an amino terminal phe. The second polypeptide, identified as a member of the SP-C family, sequenced for 35 amino acids and had a leu amino terminus. The third minor sequence corresponded to amino acids 2-9 of SP-C (N-leu) and was designated SP-C (N-ile). Sequence analysis of cyanogen bromide peptides derived from methyl isocyanate-blocked lipid extract material produced two peptides which extended the amino acid sequence of SP-B to residue 79, which appears to be a glycine.

The production of tumor necrosis factor by mouse bone marrow-derived macrophages in response to bacterial lipopolysaccharide and a chemically synthesized monosaccharide precursor

Lipid X, a monosaccharide biosynthetic precursor of lipid A, has been chemically synthesized and was shown to induce bone marrow-derived macrophages to release tumor necrosis factor (TNF) in vitro. However, relatively high amounts of lipid X were necessary for induction, and the levels of TNF were much less than those induced by small amounts of lipid A itself or LPS. Lipid X prepared by extraction of Escherichia coli mutants induced higher levels of TNF than the chemically synthesized material, but this is probably partially due to amounts of impurities in the extracted material. Pretreatment of macrophages with IFN-gamma resulted in the release of higher amounts of TNF on subsequent induction with either LPS or lipid X. In contrast, pretreatment of macrophages with LPS induced hyporesponsiveness for TNF production on subsequent rechallenge with LPS. Lipid X, on the other hand, was incapable of making macrophages hyporesponsive for TNF production.

The production of tumor necrosis factor by mouse bone marrow-derived macrophages in response to bacterial lipopolysaccharide and a chemically synthesized monosaccharide precursor

Lipid X, a monosaccharide biosynthetic precursor of lipid A, has been chemically synthesized and was shown to induce bone marrow-derived macrophages to release tumor necrosis factor (TNF) in vitro. However, relatively high amounts of lipid X were necessary for induction, and the levels of TNF were much less than those induced by small amounts of lipid A itself or LPS. Lipid X prepared by extraction of Escherichia coli mutants induced higher levels of TNF than the chemically synthesized material, but this is probably partially due to amounts of impurities in the extracted material. Pretreatment of macrophages with IFN-gamma resulted in the release of higher amounts of TNF on subsequent induction with either LPS or lipid X. In contrast, pretreatment of macrophages with LPS induced hyporesponsiveness for TNF production on subsequent rechallenge with LPS. Lipid X, on the other hand, was incapable of making macrophages hyporesponsive for TNF production.

Trans-acting elements modulate expression of the human c-myc gene in Burkitt lymphoma cells

We have used a competition assay to identify the targets of trans-acting elements that modulate the expression of the human c-myc gene (designated MYC in human gene nomenclature). For this purpose, a c-myc hybrid indicator gene was formed by joining the c-myc promoter region, first noncoding exon, and intron to the bacterial gene for chloramphenicol acetyltransferase (CAT). The test assay consisted of cotransfecting the indicator gene with competing fragments of DNA derived from suspected control regions of the c-myc gene. Such experiments test the hypothesis that control regions are often targets for the binding of trans-acting regulatory factors that can be diverted to competing fragments of DNA. A negatively acting element will be diverted from the indicator gene, allowing the gene's enhanced expression, whereas a positively acting element will behave oppositely. Control indicator genes driven by non-myc promoters assess the specificity of the effect. Using this approach, we find three c-myc regions that are capable of enhancing the expression of the indicator gene in competition assays (i.e., putative sites of negative modulation). In addition, we find sequences near the c-myc promoters that suppress expression in competition assays (i.e., putative binding sites of positively acting factors). These results, with appropriate controls, suggest the existence of target sites near the c-myc gene that specifically modulate its expression both positively and negatively. Their locations fit well with regions damaged or lost in many Burkitt lymphoma and murine plasmacytoma translocations.

Metallothionein levels in liver and kidney of Canadians--a potential indicator of environmental exposure to cadmium

Liver and kidney cortex samples were obtained from 89 human autopsies for the determination of metallothionein (MT), cadmium (Cd), zinc (Zn), and copper (Cu). An age-dependent increase of Cd, Zn, and Cd/Zn was observed in the kidney; increases peaked at mid-age and were followed by a decline. Cadmium was present at a low constant level in the liver at all ages. The mean concentrations of Cd and Zn were 18.0 and 40.1 micrograms/g wet weight, respectively, in the kidney, and for the liver the values for Cd and Zn were 2.0 and 79.0 micrograms/g wet weight, respectively. A positive linear relationship was observed between Cd or Zn and MT in the kidney and between Zn and MT in the liver. No other correlation was found between Cu and MT in either organs. Similar values were obtained for MT when estimated by Ag-hem and Cd-hem methods.

In vivo activation of murine natural killer cell functions by human recombinant DNA interleukin 2

Intraperitoneal (i.p.) injections of purified human recombinant DNA (rDNA)-interleukin 2 (IL 2) resulted in in vivo activation of local natural killer (NK) cell activities in wild-type and congenitally athymic mice. NK cells were identified by short-term cytotoxicity assays against YAC tumor targets and by cell-surface phenotyping. The magnitude of the cytolytic responses was dependent on the IL 2 dose (greater than or equal to 0.1 microgram per injection) and the time period of treatment (the maximum response was on days 3 to 4 after daily treatment). In vivo application of antisera against the murine NK marker asialo GM1 (asGM1) and against interferon-alpha/beta and -gamma (IFN) significantly inhibited NK cell activation. Limiting dilution analysis revealed high frequencies (up to 1 in 1.8 X 10(3)) of in vitro IL 2 reactive mononuclear cells among the peritoneal exudate cells (PEC) of normal mice. rDNA-IL 2 activated non-adherent PEC to proliferate. The majority of these cultures also displayed cytotoxicity against YAC targets. No exogenous IFN was required for either response. Endogenous IFN production did not appear to play an important role for induction of cytotoxicity in this system either. Only a minority of cultures produced measurable levels of IFN without showing excessive cytotoxic activity. In vivo IL 2 treatment resulted in a rapid increase of the total numbers and frequencies of the IL 2 reactive PEC. Hence, IL 2 alone was apparently sufficient for in vitro activation of NK-like activities, whereas IFN-induction by IL 2 was required for in vivo elicitation of similar responses in perhaps the same cell populations.

In vitro mass: activity distribution of lecithin--cholesterol acyltransferase among human plasma lipoproteins

In order to compare the mass-activity distribution of lecithin-cholesterol acyltransferase (LCAT) among plasma lipoproteins separated by various ultracentrifugal or chromatographic procedures, we have quantified the enzyme by an electroimmunoassay technique using a specific antibody raised in the rabbit. This antibody, when added to whole serum, inhibited all of the enzyme activity present in it. The percent mass distribution of the enzyme among the lipoproteins isolated by rate-zonal ultracentrifugation (d 1.00-1.36 g/ml, SW 40 rotor, 37 000 rpm, 16 h) was as follows: very low density lipoproteins (VLDL), 0; low density lipoproteins (LDL), 6.2; HDL2, 6.5; HDL3, 12 and d greater than 1.21 g/ml fraction, 75. Measurement of LCAT activity of each lipoprotein fraction against mixed single bilayer lecithin-cholesterol vesicles (molar ratio, 4:1) containing apo A-I, indicated that VLDL, LDL and HDL2 were inactive or minimally active under the experimental conditions used, whereas HDL3 and the d greater than 1.21 g/ml fraction contained 17.5 and 79.9% of the total enzyme activity. Prolonged ultracentrifugation of the LCAT-containing lipoproteins resulted in the recovery of activity in the lipoprotein-free infranatant. In studies with lipoproteins linked to Sepharose 4B, LCAT was found to bind LDL, HDL2, and HDL3. It is concluded that LCAT is present in all the major lipoproteins except for VLDL. The activity appears to be dependent, at least in part, on the type of lipoproteins to which the enzyme is associated with.

Neutrophils are required for the DNA synthetic response of human lymphocytes to mevalonic acid: evidence suggesting that a nonsterol product of mevalonate is involved

Human peripheral blood lymphocytes, in the presence of human neutrophils, initiate DNA synthesis and cell cycling when exposed to mevalonic acid. The ability of lymphocytes to respond in this manner is a radiosensitive property of cells, whereas the help provided by neutrophils is maintained despite their exposure to x-irradiation. Other organic acid anions, including precursors of mevalonic acid biosynthesis and a variety of products of mevalonate metabolism, fail to initiate DNA synthesis when added to human lymphocytes. Because only the metabolically active R(--) enantiomer of mevalonic acid initiates lymphocyte DNA synthesis, we presume that physiological pathways of mevalonate metabolism are involved. The response to mevalonic acid of ML-236B (compactin)-inhibited lymphocytes is increased, and the threshold concentration of meyalonate at which lymphocyte DNA synthesis first appears is decreased, when the cells are cultured in lipoprotein-containing (as opposed to lipoprotein-depleted) medium. The response to mevalonic acid of lymphocytes cultured in lipoprotein-depleted medium can be enhanced by addition to the cultures of low density lipoprotein but not by addition of high density lipoprotein. Based upon the flux diversion hypothesis of mevalonate metabolism, these observations suggest that a nonsterol product of mevalonate metabolism may be responsible for the initiation of lymphocyte DNA synthesis by mevalonic acid.

Properties and metabolic fate of two very low density lipoprotein subfractions from rhesus monkey serum

Physical, chemical and physiological approaches were used to examine the properties of two very low density lipoproteins, VLDL-I (slow-beta), and VLDL-II (pre-beta), which were isolated by agarose column chromatography from the serum of rhesus monkeys fed either Purina Chow or one of four hyperlipidemic diets containing 0.5-20% cholesterol suspended in either coconut oil, peanut oil, mixed coconut oil and butter fat or lard. In the coconut oil-fed hyperlipidemic animals, the majority of the apolar lipids of VLDL-I was represented by cholesteryl esters. The small percentage of triacylglycerol (15%) had a fatty acid composition which resembled that of the fatty acid in each of the diets. In turn, VLDL-II had a triacylglycerol-rich core and differed from VLDL-I in apolipoprotein distribution (VLDL-I: low molecular weight apolipoprotein B, 36%; apolipoprotein E, 64%; and VLDL-II: high molecular weight apolipoprotein B, 38%; apolipoprotein E, 3%; and apolipoprotein C, 65%). Both VLDLs were hydrolyzed in vitro by milk lipoprotein lipase by first-order kinetics although VLDL-I exhibited a slightly slower reaction rate. When an oral dose of [3H]retinol was given to one of the animals, both VLDLs became labeled but the specific activity of VLDL-I was six times higher than that of VLDL-II and the other lipoproteins. We conclude that VLDL-I represents a cholesteryl ester-rich lipoprotein probably of intestinal origin, whereas VLDL-II may be a particle of hepatic derivation modified by its interaction with the other plasma lipoproteins.

Serum lipoproteins modulate oxygenated sterol insertion into human red cell membranes

The insertion of oxygenated sterol compounds into human red blood cell membranes as well as the consequent transformation of the red cells to an echinocyte shape and the expansion of the membranes are impeded by the presence of serum lipoproteins in the incubation medium. All density classes of human serum lipoproteins bind oxygenated sterol compounds, and lipoproteins can act as acceptors of oxygenated sterols previously inserted into red cells. Since oxygenated sterols have been reported to be atherogenic, the modulating and possibly protective effects of serum lipoproteins on oxygenated sterol-induced derangement of cell membrane structure and function may provide a useful model for further study.

Effect of oxygenated sterol compounds on human bone marrow granulocytic progenitor cells

Oxygenated sterol compounds are potent inhibitors of sterol and DNA synthesis in mammalian cells. We studied the effects of oxygenated sterols on human marrow granulocytic progenitor cells in vitro (CFU-C). 25-Hydroxycholesterol was found to be a potent inhibitor of sterol synthesis in marrow mononuclear cells, with 50% inhibition occurring at approximately 10(-7) M. This compound, as well as 6-ketocholestanol, 7-ketocholesterol, and 20 alpha-hydroxycholesterol, also demonstrated marked inhibition of CFU-C proliferation. The latter effect, which was not a result of direct cytoxicity of the compounds, was reversible by cholesterol, but not by mevalonic acid. We conclude that inhibition of sterol synthesis by oxygenated sterol compounds may be insufficient to explain their suppression of CFU-C proliferation.

Inhibition of human lymphocyte E-rosette formation by oxygenated sterols

25-Hydroxycholesterol, 20 alpha-hydroxycholesterol, 7 alpha-hydroxycholesterol, and 5 alpha-hydroxy-6-ketocholestanol, when added to cultures of human lymphocytes in lipoprotein-depleted medium (LPDM) at a concentration of 2.5 x 10(-6) M, inhibit E-rosette formation with sheep red blood cells. 20 alpha-Hydroxycholesterol, 7 alpha-hydroxycholesterol, and 5 alpha-hydroxy-6-ketocholestanol are more potent inhibitors than 25-hydroxycholesterol. The inhibitory effect of 5 alpha-hydroxy-6-ketocholestanol on E-rosette formation appears after 15 min of exposure; with the other three compounds, an exposure time of 18 hr is necessary. The inhibitory effect of E-rosette formation can be abolished by addition of free cholesterol, low-density lipoprotein, or high-density lipoprotein to the LPDM or by incubation of the cells in normal AB serum, but not by the addition of mevalonic acid to the LPDM. These observations suggest that the capacity of oxygenated sterol compounds (OSC) to inhibit E-rosette formation is independent of their inhibitory effect on sterol synthesis. It is possible that OSC inhibit E-rosette formation as a consequence of their insertion into the lymphocyte membrane as cholesterol analogues.

Apoproteins of human serum high density lipoproteins. Isolation and characterization of the peptides of Sephadex fraction V from normal subjects and patients with abeta-lipoproteinemia

1. Sephadex fraction V, obtained from human serum high density lipoprotein apoprotein (HDL apoprotein) of normal subjects and of patients with abetalipoproteinemia, was resolved by DEAE-cellulose ion exchange column chromatography into several fractions which were defined in terms of amino acid composition, NH2- and COOH-terminsls, sialic acid content, immunologic and electrophoretic properties, and in vitro activation of purified lipoprotein lipase from rat adipose tissue. 2. Fraction V of HDL apoprotein of both normal and abetalipoproteinemic subjects was found to contain polypeptides corresponding to apolipoproteins C-I, C-II, C-III-1, and C-III-2, which had been described previously in very low-density lipoproteins (VLDL). The content of apo C-III-1 in abetalipoproteinemia-HDL was very low, whereas the percentage, by weight, of apo C-I was about twice as high as that in the normal subjects studied. Furthermore, both normal and abetalipoproteinemia-HDL apoprotein contained a previously unreported peptide which had a molecular weight of about 7 000 and electrophoretic, chemical, and immunological properties distinct from those of the known C apolipoproteins. Of all of the peptides comprising fraction V, only apo C-II activated a purified preparation of rat adipose tissue lipoprotein lipase. This was the case for both normal and abetalipoproteinemic subjects.

Effect of anti-inflammatory compounds on -irradiation induced radiodermatitis

The effect of several anti-inflammatory agents given <i>per os</i>, intraperitoneally, or topically to alleviate acute radiodermatitis in guinea pig skin following 3,000 or 4,000 rep β-irradiation was studied. Up to the 21st day post-irradiation, there was pronounced suppression of the acute inflammatory response observed with chloroquine diphosphate, or meclofenamic acid (Cl-583). Chloroquine diphosphate given systemically was most potent among the single drugs tested. Qualitatively, combinations of the drugs given <i>per os</i> were somewhat more effective in suppression of the second erythema and late skin reactions. Topical application of 50% DMSO or of anti-inflammatory drugs dissolved in this solvent resulted in increased inflammatory reactions. Triamcinolone acetonide appeared to be the only active compound when applied topically. The effective anti-inflammatory agents decreased the frequency but did not prevent the onset of ulcers. Ulceration was delayed by about 10 days in the drug-treated animals (as compared with its appearance by the 20th day in controls) and the ulcerated area was smaller and healed more rapidly.

Dissociation of low density lipoprotein-antibody precipitates at alkaline pH

The effect of alkaline pH on the dissociation of immunoprecipitates of low density lipoproteins (LDL) of the S(f) 0-10 class was studied by immunological and ultracentrifugal methods. The precipitates prepared at the equivalence point were dissolved and centrifuged in sodium chloride solutions of density 1.063 and pH's between 10.25 and 11.5. Analytical centrifugation of the top fraction, which floated at density 1.063, after dialysis against 0.9% sodium chloride of pH 7.4 revealed the presence of LDL and of soluble LDL-antibody complex. The amount of soluble complex was greater for the preparations obtained at lower pH than those obtained at higher pH and was undetectable at pH 11.5. The yield of immunoglobulin from the bottom fractions was maximal when the pH of the centrifugation medium was 11.0. Below pH 11.0, the greatly reduced yield of immunoglobulin was due partly to incomplete dissociation and partly to aggregation of soluble complex, while above pH 11.0 the decreased yield was possibly due to alkaline denaturation of the globulin. The immunoglobulin separated at pH 11.0 and dialyzed to pH 7.4 was reprecipitatable by LDL, and the reactivity did not seem to be appreciably influenced by the alkaline treatment.