Clinical Outcomes of Patients With Newly Diagnosed Acute Lymphoblastic Leukemia in a County Hospital System

BACKGROUND

Major advances in the treatment of acute lymphoblastic leukemia (ALL) over the past decade have resulted in 5-year overall survival (OS) rates of 80% in mature B cell ALL, 50% in precursor B cell ALL, 50% to 60% in T cell ALL, and 60% to 70% in Philadelphia chromosome-positive (Ph+) ALL, as reported in studies from large, specialized centers. However, many patients treated in the community have limited access to novel therapies and stem cell transplantation (HSCT).

PATIENTS AND METHODS

The purpose of this retrospective cohort analysis was to evaluate the clinical outcomes of patients ≥ 16 years with newly diagnosed ALL treated from October 2007 to June 2019 in the Harris County Health System, Houston, TX.

RESULTS

One hundred forty-six patients were included, with newly diagnosed pre-B-ALL (n = 127), T-ALL (n = 18), and chronic myeloid leukemia and/or lymphoid blast crisis (n = 1). Median age was 35 years (16-82) at diagnosis, and 81(55%) were male. The majority of patients with pre-B ALL identified as Hispanic (n = 118, or 92%). Ninety-eight (67%) of patients were uninsured or indigent, receiving care under the county's financial assistance programs. Hyper-CVAD-based induction chemotherapy was administered in 134 (92%) of patients, while 9 (6%) were treated on different protocols, and 3 (2%) were not treated due to early death, or patient refusal. Imatinib was the most common TKI used in 17 of 30 or 57% of patients with Ph+ disease. Out of 137 evaluable for response patients, 117 (85%) achieved complete remission (CR + CRi), 19 (14%) had refractory disease, and 1 (1%) died within 4 weeks of diagnosis. Median follow-up time was 50 months (1.5-135). For the entire study cohort, the median duration of CR/CRi was 15.4 months. Out of 62 patients who were eligible for consolidative HSCT at first CR, 52 (89%) did not receive it, with lack of insurance being the most common reason (n = 29, or 56%). Barriers to utilization of novel therapies such as blinatumomab or CAR-T were also observed. Patient-caused delays in administration of chemotherapy and treatment interruptions of at least 30 days were seen in 31(23%) patients. At 1, 2, and 5 years, relapse rates were 37%, 56%, and 70%. Recurrent and/or refractory disease was the cause of death in most patients (n = 69 [85%]). Five-year EFS and OS rates were 22% and 38% for patients with pre-B ALL, 24% and 44% for patients with T ALL, and 13% and 27% for patients with Ph+ ALL. Median OS was significantly increased (not reached [NR] vs. 24 months; P = .00088) in patients with an indication for HSCT in first CR due to high-risk features who underwent HSCT, versus those who did not.

CONCLUSION

Addressing barriers raised by socioeconomic disparities, increasing access to effective therapies, and including patients with ALL treated in the community in clinical trials may improve survival for underserved populations.

Methionine-Homocysteine Pathway in African-American Prostate Cancer

African American (AA) men have a 60% higher incidence and two times greater risk of dying of prostate cancer (PCa) than European American men, yet there is limited insight into the molecular mechanisms driving this difference. To our knowledge, metabolic alterations, a cancer-associated hallmark, have not been reported in AA PCa, despite their importance in tumor biology. Therefore, we measured 190 metabolites across ancestry-verified AA PCa/benign adjacent tissue pairs (n = 33 each) and identified alterations in the methionine-homocysteine pathway utilizing two-sided statistical tests for all comparisons. Consistent with this finding, methionine and homocysteine were elevated in plasma from AA PCa patients using case-control (AA PCa vs AA control, methionine: P = .0007 and homocysteine: P < .0001), biopsy cohorts (AA biopsy positive vs AA biopsy negative, methionine: P = .0002 and homocysteine: P < .0001), and race assignments based on either self-report (AA PCa vs European American PCa, methionine: P = .001, homocysteine: P < .0001) or West African ancestry (upper tertile vs middle tertile, homocysteine: P < .0001; upper tertile vs low tertile, homocysteine: P = .002). These findings demonstrate reprogrammed metabolism in AA PCa patients and provide a potential biological basis for PCa disparities.

Structure-function relationship of lipoprotein lipase-mediated enhancement of very low density lipoprotein binding and catabolism by the low density lipoprotein receptor. Functional importance of a properly folded surface loop covering the catalytic center

We examined the structure-function relationship of human lipoprotein lipase (hLPL) in its ability to enhance the binding and catabolism of very low density lipoproteins (VLDL) in COS cells. Untransfected COS cells did not bind to or catabolize normal VLDL. Expression of wild-type hLPL by transient transfection enhanced binding, uptake, and degradation of the VLDL (a property of LPL that we call bridge function). Heparin pretreatment and a monoclonal antibody ID7 that blocks LDL receptor-binding domain of apoE both inhibited binding, and apoE2/E2 VLDL from a Type III hyperlipidemic subject did not bind. However, LDL did not reduce 125I-VLDL binding to the hLPL-expressing cells, whereas rabbit beta-VLDL was an effective competitor. By contrast, LDL reduced uptake and degradation of 125I-VLDL to the same extent as excess unlabeled VLDL or beta-VLDL. These data suggest that binding occurs by direct interaction of VLDL with LPL but the subsequent catabolism of the VLDL is mediated by the LDL receptor. Mutant hLPLs that were catalytically inactive, S132A, S132D, as well as the partially active mutant, S251T, and S172G, gave normal enhancement of VLDL binding and catabolism, whereas the partially active mutant S172D had markedly impaired capacity for the process; thus, there is no correlation between bridge function and lipolytic activity. A naturally occurring genetic variant hLPL, S447-->Ter, has normal bridge function. The catalytic center of LPL is covered by a 21-amino acid loop that must be repositioned before a lipid substrate can gain access to the active site for catalysis. We studied three hLPL loop mutants (LPL-cH, an enzymatically active mutant with the loop replaced by a hepatic lipase loop; LPL-cP, an enzymatically inactive mutant with the loop replaced by a pancreatic lipase loop; and C216S/C239S, an enzymatically inactive mutant with the pair of Cys residues delimiting the loop substituted by Ser residues) and a control double Cys mutant, C418S/C438S. Two of the loop mutants (LPL-cH and LPL-cP) and the control double Cys mutant C418S/C438S gave normal enhancement of VLDL binding and catabolism, whereas the third loop mutant, C216S/C239S, was completely inactive. We conclude that although catalytic activity and the actual primary sequence of the loop of LPL are relatively unimportant (wild-type LPL loop and pancreatic lipase loops have little sequence similarity), the intact folding of the loop, flanked by disulfide bonds, must be maintained for LPL to express its bridge function.

A novel DNA-peptide complex for efficient gene transfer and expression in mammalian cells

To develop a nonviral gene delivery system for treatment of diseases, our strategy is to construct DNA complexes with short synthetic peptides that mimic the functions of viral proteins. We have designed and synthesized two peptides which emulate viral functions - a DNA condensing agent, YKAK(8)WK, and an amphipathic, pH-dependent endosomal releasing agent, GLFEALLELLESLWELLLEA. The active gene delivery complex was constructed step-wise through a spontaneous self-assembly process involving oppositely charged, electrostatic interactions. To assemble DNA-peptide complexes with different overall net charges, only the negative charges of DNA phosphate, the positive charges of the 10 epsilon-amino groups of YKAK(8)WK and the negative charges of the 5 gamma-carboxyl groups of GLFEALLELLESLWELLLEA were considered. In the first step, negatively charged DNA was rapidly-mixed with an excess of YKAK(8)WK to form positively charged DNA-YKAK(8)WK complexes, which gave little gene transfer. In the second step and to form the active complex,the cationic DNA complex was rapidly mixed with spontaneously incorporated through electrostatic interactions. Transfection using these complexes of CMV-luc, YKAK(8)WK and GLFEALLELLESLWELLLEA gave high-levels of gene expression in a variety of cell lines. These simple DNA complexes, which contain only three molecularly defined components, have general utility for gene delivery and can replace viral vectors and cationic lipids for some applications in gene therapy.

In vivo gene therapy for hyperlipidemia: phenotypic correction in Watanabe rabbits by hepatic delivery of the rabbit LDL receptor gene

Elevations of plasma total or LDL cholesterol are major risk factors for cardiovascular disease. Efforts directed at preventing and treating cardiovascular disease have often focused on reducing the levels of these substances in the blood. The Watanabe Heritable Hyperlipidemic Rabbit, which has exceedingly high plasma cholesterol levels resulting from an LDL receptor deficiency, provides an excellent animal model for testing new treatments. A recombinant adenoviral vector containing the rabbit LDL receptor cDNA was administered to Watanabe rabbits. Plasma total cholesterol levels in the treated animals were reduced from 825.5 +/- 69.8 (mean +/- SD) to 247.3 +/- 61.5 mg/dl 6 d after infusion. These animals also demonstrated a 300-400% increase in plasma levels of HDL cholesterol and apo AI 10 d after treatment. As a result, the LDL:HDL ratio exhibited a dramatic decrease. Because only the rabbit LDL receptor gene was used for treatment, the results strongly suggest that the elevations of plasma HDL cholesterol and apo AI were secondary to a reduction in plasma total cholesterol in the treated animals. These results suggest an inverse relationship between plasma LDL and HDL cholesterol levels and imply that reduction of LDL cholesterol levels may have a beneficial effect on plasma HDL cholesterol.

Murine VCAM-1. Molecular cloning, mapping, and analysis of a truncated form

Vascular cell adhesion molecule-1 (VCAM-1) is a member of the Ig superfamily that shows increased expression in a number of pathologic conditions. The role of VCAM-1 in human disease remains undefined and murine models are being extensively studied to help define the importance of VCAM-1 in inflammatory disorders. We have cloned and characterized the murine Vcam1 gene including 3 kb of 5'-flanking sequences and mapped the gene to chromosome 3 near Amy1. cDNA clones isolated from a stimulated hepatic library were found to encode a truncated form of VCAM-1 (T-VCAM-1) which contains Ig domains 1 through 3 and has a unique alternative carboxyl terminus. This form arises by alternative splicing. High level expression of T-VCAM-1 in transfected L cells was sufficient to support adhesion of lymphocytes, and this adhesion was blocked by Abs to VCAM-1. Treatment of transfected COS cells with phospholipase C led to reduced levels of T-VCAM-1 on the cell surface consistent with glycosylphosphatidylinositol linkage. Northern blot analysis showed that mRNA for T-VCAM-1 is inducible in multiple tissues after stimulation with endotoxin. Both forms of VCAM-1 were expressed in cultured endothelial, fibroblast, and aortic smooth muscle cells, whereas neither form was observed in monocyte- and lymphocyte-derived lines. Differential regulation of both forms of VCAM-1 was observed in the three different cell types that are present in the vessel wall. Thus, expression of VCAM-1 is restricted and controlled at the level of transcription and by alternative splicing.

Murine VCAM-1. Molecular cloning, mapping, and analysis of a truncated form

Vascular cell adhesion molecule-1 (VCAM-1) is a member of the Ig superfamily that shows increased expression in a number of pathologic conditions. The role of VCAM-1 in human disease remains undefined and murine models are being extensively studied to help define the importance of VCAM-1 in inflammatory disorders. We have cloned and characterized the murine Vcam1 gene including 3 kb of 5'-flanking sequences and mapped the gene to chromosome 3 near Amy1. cDNA clones isolated from a stimulated hepatic library were found to encode a truncated form of VCAM-1 (T-VCAM-1) which contains Ig domains 1 through 3 and has a unique alternative carboxyl terminus. This form arises by alternative splicing. High level expression of T-VCAM-1 in transfected L cells was sufficient to support adhesion of lymphocytes, and this adhesion was blocked by Abs to VCAM-1. Treatment of transfected COS cells with phospholipase C led to reduced levels of T-VCAM-1 on the cell surface consistent with glycosylphosphatidylinositol linkage. Northern blot analysis showed that mRNA for T-VCAM-1 is inducible in multiple tissues after stimulation with endotoxin. Both forms of VCAM-1 were expressed in cultured endothelial, fibroblast, and aortic smooth muscle cells, whereas neither form was observed in monocyte- and lymphocyte-derived lines. Differential regulation of both forms of VCAM-1 was observed in the three different cell types that are present in the vessel wall. Thus, expression of VCAM-1 is restricted and controlled at the level of transcription and by alternative splicing.

A nonexchangeable apolipoprotein E peptide that mediates binding to the low density lipoprotein receptor

ApoE is a 34-kDa apoprotein that mediates lipoprotein binding to the low density lipoprotein (LDL) receptor and to the LDL receptor-related protein. Receptor binding is mediated by a highly basic, alpha-helical sequence of approximately 15 amino acids that interacts with cysteine-rich repeat regions of the receptor. To determine the relationship between the receptor binding and lipid associating properties of apoE, we have synthesized a series of apoE peptides containing all (residues 129-169) or part (residues 139-169, 144-169, and 148-169) of the receptor-binding domain. The lipophilicity of these peptides was increased by modification of their N termini by acylation with either palmitic acid (C16-apoE peptide) or the N,N-distearyl derivative of glycine (diC18-Gly-apoE peptide). The unmodified peptides demonstrated low affinity for lipid surfaces (Kd > 10(-5) M) and moderate alpha-helicity in the presence of lipid (40%) and had no effect on LDL uptake by fibroblasts. N-Palmitoyl peptides had increased affinity for lipid (Kd approximately 10(-6) M) and increased alpha-helicity (55%) in the presence of lipid. The addition of the C16-apoE-(129-169)-peptide to 125I-LDL enhanced its uptake and degradation by fibroblasts 8-10-fold; however, < 50% of the degradation was mediated by the LDL receptor. By contrast, the diC18-Gly-apoE-(129-169)-peptide was essentially nonexchangeable (Kd < or = 10(-9) M) and highly helical (78%) in the presence of lipid. The addition of the diC18-Gly-apoE-(129-169)-peptide to 125I-LDL enhanced the specific uptake and degradation of LDL by both LDL receptor-mediated and non-LDL receptor-mediated mechanisms. Uptake and degradation of methylated LDL containing diC18-Gly-apoE-(129-169) revealed that the lipoprotein-bound peptide is the active agent. In agreement with this finding, a mutant diC18-Gly-apoE peptide (Arg142-->Gln) was much less effective than the wild-type peptide in potentiating binding, uptake, and degradation of 125I-LDL. Complexes of diC18-Gly-apoE-(129-169), apoA-I, and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine containing four to six copies of the peptide/particle displayed an affinity for the LDL receptor similar to that of apoE-L-alpha-dimyristoylphosphatidylcholine discs containing four copies of apoE.(ABSTRACT TRUNCATED AT 400 WORDS)

Attenuation of the neurotoxic effect of A beta amyloid peptide by apolipoprotein E

Alzheimer's disease patients have increased frequency of apolipoprotein E allele c4, suggesting apoE4 is a risk factor determining disease. ApoE binds A beta amyloid peptide with great avidity in vitro and in the neuritic plaque. Potentially, binding of A beta to apolipoprotein E could increase A beta neurotoxicity. However, in hippocampal cultures, 0.1 microM apolipoprotein E eliminated the neurotoxicity of 10 microM A beta. Neuronal rescue was dose-dependent and occurred even after 48 hours exposure to A beta, but was overwhelmed by excess A beta. Thus, interaction between these proteins does not directly increase A beta neurotoxicity, and the role of ApoE in Alzheimer's disease remains to be elucidated.

Recent advances in lipoprotein and atherosclerosis research at Baylor College of Medicine. Apolipoprotein B, lipoprotein[a], and transplantation arteriopathy

A multidisciplinary team approach with focused objectives characterizes research at Baylor College of Medicine into the causes, prevention, and treatment of atherosclerotic disease. Current clinical activities range from programs to modify lifestyle for the primary prevention of coronary artery disease to a large, angiographically monitored lipid-lowering trial. In basic research, much attention has been focused on the plasma lipoproteins and their roles in atherogenesis. The current review highlights recent advances in ongoing basic research involving 1) apolipoprotein (apo) B, whose form apo B-100 serves as a ligand for the low-density lipoprotein receptor; 2) lipoprotein[a], elevated plasma levels of which are predictive of atherosclerotic disease; and 3) transplantation arteriopathy, which impedes long-term survival of cardiac transplant recipients.

Interaction of LDL and Lp[a] with human skin fibroblasts

We have studied the interaction of LDL and Lp[a] with fibroblasts. Our studies suggest that Lp[a] does not effectively compete with LDL for binding to the LDL receptor, and does not efficiently suppress the activity of the intracellular enzyme HMG-CoA reductase. However, Lp[a-], formed by reduction of the disulfide bond between apo[a] and apoB, behaves much like homologous LDL, whether or not apo[a] is removed from the mixture, and in spite of the fact that one or more apoB disulfides may also have been cleaved. In our studies we also noted that Lp[a] often enhanced binding of 125I-LDL by fibroblasts. Further investigation has suggested that this interaction is time-dependent. Experiments in receptor-negative fibroblasts indicate that the enhancement is not related to the presence of the LDL receptor; however, it is inhibited by the removal of calcium from the medium. The presence of sialic acid at millimolar concentrations in the medium inhibits much of the Lp[a]-enhanced binding of 125I-LDL to the cells. These studies suggest that Lp[] may in some way enhance LDL binding to cells, perhaps via interaction with cell surface glycosaminoglycans or proteoglycans or with collagen.

Acrylodan can label amino as well as sulfhydryl groups: results with low-density lipoprotein, lipoprotein[a], and lipid-free proteins

Human plasma lipoprotein[a] and autologous low-density lipoprotein were reacted with the fluorescent probe 6-acryloyl-2-(dimethylamino)naphthalene (acrylodan) previously reported to be specific for sulfhydryl groups. Reaction kinetics were biphasic in both cases. The reaction of bovine serum albumin with acrylodan was also biphasic. Monophasic kinetics were observed when protein free sulfhydryl groups were blocked by carboxamidomethylation prior to acrylodan reaction. A significant increase in total fluorescence was observed in the reaction of acrylodan with proteins containing no free sulfhydryl groups and with polylysine. The rates of these reactions were highly sensitive to pH. Fluorescence changes due to dissolution of probe into hydrophobic protein or lipid domains were minimal as was reaction of probe with phospholipid head groups. When isolated from acrylodan-labeled Lp[a], apo[a], which contains no free sulfhydryl groups, contained covalently bound acrylodan. These results suggest that acrylodan can modify the lysine residues of lipid-free proteins and may modify not only the free sulfhydryl groups of low-density lipoprotein and lipoprotein[a] but also reactive amino groups. We conclude that under these conditions, the use of this probe to quantify free sulfhydryl groups in these lipoproteins is infeasible.

Triglyceride metabolism in 3T3-L1 cells. An in vivo 13C NMR study

13C nuclear magnetic resonance spectroscopy has been used to study triglyceride metabolism in 3T3-L1 cells incubated with [1-13/14C] acetate, myristate, palmitate, stearate, or oleate. Labeled cells embedded in agarose filaments were perfused in a specially fitted NMR tube within the spectrometer magnet. Incubation of 3T3-L1 cells with a specific fatty acid enriched the cellular triglycerides with that fatty acid; the NMR signal observed in the carbonyl region of the cell spectrum was due in large part to that fatty acid. NMR data demonstrated that cellular enzymes preferentially esterified saturated fatty acids at the glyceride sn-1,3 position and unsaturated fatty acids at the sn-2 position. cellular triglyceride hydrolysis by hormone-sensitive lipase was monitored by measuring the decrease in the integrated intensities of resonances arising from fatty acyl carbonyls esterified at glycerol carbons sn-1,3 and sn-2. Under basal conditions, the time courses were first-order, and the average rates were 0.14% of signal/min at both carbonyl positions. Under isoproterenol stimulated conditions, these rates were still first-order and increased 6.4-fold at the sn-1,3 position and 2.4-fold at the sn-2 position. The observation that the hydrolysis time courses were first-order suggested that only a small amount of cellular triglyceride was available to hormone-sensitive lipase, supporting the view that lipolytic enzymes operate at lipid surfaces where only small amounts of neutral lipid may be soluble. Attempts to correlate the measured rates with the rates of hydrolysis at the sn-1,3 and sn-2 positions were hindered by the fact that the chemical shifts of the carbonyl carbons of the diglyceride hydrolysis product did not overlie those of the triglyceride. Analysis of hydrolysis kinetics revealed that hormone-sensitive lipase exhibited little preference for a particular esterified fatty acid under basal conditions; however, under stimulated conditions, the enzyme exhibited a preference for certain triglyceride species.

Altered ultrastructural morphology of self-aggregated low density lipoproteins: coalescence of lipid domains forming droplets and vesicles

Lipid droplets and vesicles can presumably be formed directly from lipoproteins in the extracellular space in atherosclerosis, but an in vitro demonstration of the phenomenon in the absence of cellular pathways has been lacking. Low density lipoproteins (LDL) are known to undergo self-aggregation after brief vortexing in vitro. In the present study, LDL aggregates were examined by electron microscopy, using new mordant techniques for lipid visualization, and by chemical analysis. Aggregation of LDL by vortexing is regularly accompanied by the formation of comparatively large lipid droplets (up to 600 nm diameter) and vesicles. Aggregates containing droplets and vesicles were formed after as little as 5 sec of vortexing, and LDL protein and cholesteryl ester were almost completely (95%) incorporated into aggregates after 4 min vortexing. Substantial fractions of phospholipid and unesterified cholesterol from the original LDL remained in solution even after 4 min vortexing, forming large multilamellar vesicles that did not adhere to the aggregated material. Spontaneous aggregates retrieved from LDL solutions after prolonged storage were also examined by electron microscopy, revealing similar lipid droplets and vesicles. The ultrastructural appearance of LDL aggregated in vitro is remarkably similar to the appearance of extracellular lipid deposits in atherosclerosis, lending credence to the hypothesis of direct extracellular formation of these deposits from lipoproteins.

Amino acid sequence of rabbit apolipoprotein E

The complete amino acid sequence of rabbit apolipoprotein E (apoE) was determined by generating three sets of peptides using cyanogen bromide, endoproteinase AspN, and Staphylococcus aureus V8 protease to cleave the protein. Through twenty cycles of sequence analysis on the whole protein, glutamic acid was identified as the N-terminal residue of rabbit apoE; the C-terminus of the protein was identified as glutamine. Based on the sequence of 294 amino acid residues determined by protein structure analysis, the molecular weight of rabbit apoE was determined to be 33,684. The protein sequence differed from the cDNA inferred sequence in 19 positions, only one of which could be attributed to microheterogeneity. The corrected amino acid sequence of rabbit apoE shares 80% homology with the human apoE sequence, 4% greater homology than that inferred from the cDNA sequence. The great similarity in the amino acid sequences of human and rabbit apoE suggests that their physical and physiological properties may also be similar. This homology and the relative ease with which apoE is isolated from rabbit plasma make it possible to conduct some in vitro experiments with the rabbit apoprotein that would have direct relevance to human apoE, but would be difficult or impossible with the human counterpart because of the quantity of protein required.

Effect of particle size and temperature on the conformation and physiological behavior of apolipoprotein E bound to model lipoprotein particles

The effect of particle size and structural order/disorder of the lipid domain on the conformation and physiological behavior of lipid-associated apolipoprotein E (apoE) was evaluated. Circular dichroic (CD) spectra of apoE bound to large (LME) and small (SME) microemulsion particles, composed of dimyristoylphosphatidylcholine (DMPC) and cholesteryl oleate (CO), and to DMPC disks revealed that at 4 degrees C, where all of the lipid constituents were in an ordered state, apoE bound to LME displayed approximately 60% alpha-helicity, while apoE bound to SME and DMPC disks displayed 73% and 95% helicity, respectively. Over the temperature range 4-50 degrees C, encompassing the lipid thermal transitions, only apoE bound to LME demonstrated an abrupt change in its CD spectrum (decrease in alpha-helicity) in response to temperature. To determine the source of the abrupt CD change, the constants for dissociation (Kd) of apoE from the surface of the large and small microemulsion particles were determined at 4, 25, and 37 degrees C. These results demonstrated that at 4 degrees C, the KdS for binding of apoE to the LME and SME were approximately equal; however, between 4 and 25 degrees C, there was a 5-fold increase in the Kd for binding of apoE to the LME, whereas the Kd for binding to the SME remained constant. The physiological effects of these differences in apoE secondary structure and equilibrium binding were examined by measuring the capacity of each apoE-containing particle to complete with LDL for binding to human fibroblasts, and by measuring the capacity of the apoE-microemulsion particles to suppress HMG-CoA reductase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of triglyceride levels on methyl and methylene envelope line widths in proton nuclear magnetic resonance spectroscopy of human plasma

Recent studies have described a relation between the line widths of the methyl and methylene resonance envelopes in the proton nuclear magnetic resonance spectrum of human plasma and the occurrence of cancer. An average line width of less than 33 Hz has been reported to correlate with the presence of cancer, whereas greater line widths have not. In 26 normal volunteers, we found a significant inverse correlation between fasting triglyceride level and plasma spectral line width. We also observed that dietary lipids have measurable effects on spectral line widths. In another sample of seven normal persons (three of whom had elevated plasma triglyceride levels), the line widths of whole plasma varied widely (mean, 35.6 +/- 8.8 Hz); however, the mean line widths of the lipoprotein fractions isolated from those samples differed greatly, but the variance within each fraction was small (very-low-density lipoprotein, 22.0 +/- 1.9 Hz; low-density lipoprotein, 35.0 +/- 2.8; high-density lipoprotein, 28.8 +/- 1.9). The results of this study indicate that the plasma triglyceride level has a profound effect on the average spectral line width of plasma. This effect can be explained by the relative amounts of lipoprotein fractions in whole plasma. Plasma triglyceride concentrations of more than 1.24 mmol per liter (greater than 110 mg per deciliter), whatever the source, produce average plasma methyl and methylene line widths of less than 33 Hz.

Lipolysis of phospholipids in model cholesteryl ester rich lipoproteins and related systems: effect of core and surface lipid phase state

Porcine pancreatic phospholipase A2 (PL A2) was used as a probe to study the structure of phospholipid domains of dimyristoylphosphatidylcholine (DMPC) vesicles +/- 2% cholesteryl oleate (CO), of discoidal structures formed by the interaction of apolipoprotein E (apoE) with these vesicles, and of large CO/DMPC microemulsion particles +/- apoE. Results of phospholipid hydrolysis over a range of temperatures were compared with the thermal transitions of the lipid components of the particles as measured by differential scanning calorimetry. These studies revealed that DMPC vesicles were most susceptible to digestion at or near the transition temperature. A similar result was obtained with DMPC/apoE disks; however, these particles were hydrolyzed over a broader temperature range than the vesicles. DMPC/CO vesicles were resistant to hydrolysis at every temperature tested; however, discoidal structures formed by interaction of apoE with these vesicles were hydrolyzed maximally above their thermal transition. Large microemulsion particles of CO and DMPC were poor substrates for the enzyme at every temperature; binding of apoE to these particles improved the ability of PL A2 to hydrolyze the phospholipid. These results suggest that the curvature of the surface, the presence of dissolved cholesteryl ester, and the binding of protein have profound effects on the temperature and breadth of the phospholipid phase transition and on the accessibility of the phospholipid to hydrolysis by PL A2.

Motion and surface accessibility of spin-labeled lipids in a model lipoprotein containing cholesteryl oleate, dimyristoylphosphatidylcholine, and apolipoprotein E

A series of spin-labeled phosphatidylcholines (PCs) and cholesteryl esters (CEs) bearing the paramagnetic 2,2-dimethyloxazolidinyl-1-oxy (doxyl) group at fatty acyl carbon C5', C12', or C16' were used to study acyl chain motions in the polar surface shell and hydrophobic core domains of microemulsion (ME) particles containing cholesteryl oleate and dimyristoylphosphatidylcholine (DMPC), and of particles with apolipoprotein E (apoE) bound to their surfaces. Electron paramagnetic resonance data obtained with the doxyl-labeled PCs indicated a gradient of motion in the ME surface monolayer similar to that observed with the same probes in a bilayer. The 5- and 12-doxyl-CEs clearly demonstrated a higher degree of order for the cholesteryl ester rich core than the corresponding doxyl-PCs showed for the phospholipid-rich surface over the entire range 10-60 degrees C. The temperature dependencies of spectra of the 16-doxyl-CE in the core and PC in the surface of the ME were almost identical, suggesting that there was no sharp boundary between core and surface domains. None of the probes detected either the surface phospholipid transition (31 degrees C) or the cholesteryl ester core transition (46 degrees C) measured previously by differential scanning calorimetry and 13C nuclear magnetic resonance. Binding of apoE to spin-labeled DMPC vesicles increased the order of the 5'-position of the sn-2 acyl chain over the range 15-33 degrees C; the thermal transition was broadened and its midpoint elevated. The effect of protein binding was not as striking for the ME particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Microemulsions of cholesteryl oleate and dimyristoylphosphatidylcholine: a model for cholesteryl ester rich very low density lipoproteins

This study describes the preparation, purification, and characterization of a cholesteryl oleate/dimyristoylphosphatidylcholine microemulsion as a model for the interaction of lipid domains in cholesteryl ester rich very low density lipoproteins. These lipids were chosen specifically because their thermal transitions were distinct from each other, and their differences in chemical structure permitted the motion(s) of each lipid component to be monitored independently by 13C nuclear magnetic resonance (NMR). The model particles were formed by cosonication of cholesteryl oleate and dimyristoylphosphatidylcholine in a 4:1 molar ratio for 45 min at 55-60 degrees C (above both lipid phase transition temperatures). The crude microemulsion was fractionated by low-speed centrifugation and Sepharose CL-2B chromatography. Microemulsion particles which eluted from the column at a volume similar to that of cholesteryl ester rich very low density lipoproteins had high cholesteryl ester:phospholipid ratios (2.5:1----6:1). Electron micrographs of negatively stained particles showed them to be large spheres devoid of multilamellar or unilamellar vesicle structures. Particle size calculated from a simple compositional model correlated well with sizes determined by electron microscopy (500-1000 A) for various column fractions. Differential scanning calorimetry studies of the microemulsion revealed two thermal transitions for the model particles, at 31.0 and 46.6 degrees C, which were tentatively assigned to the surface phospholipid and core cholesteryl ester domains, respectively. These assignments were confirmed by 13C NMR which demonstrated that, at temperatures near the lower thermotropic transition, only resonances derived from carbon atoms of dimyristoylphosphatidylcholine (DMPC) were observable. As the temperature was raised to 38.6 degrees C, resonances from the olefinic carbons in the cholesteryl ester acyl chain appeared in the spectrum. At 46.6 degrees C, the center of the higher temperature endotherm, resonances from both the steroid ring and remaining acyl chain carbons of cholesteryl oleate became observable in the spectrum. Further increases in temperature did not result in the appearance of new resonances; however, those that were present narrowed and increased in intensity. The elevation in transition temperature for DMPC in these particles (31 degrees C) as compared to that for DMPC in small unilamellar (18 degrees C) and large multilamellar (23 degrees C) vesicles suggested a stabilization of the phospholipid monolayer, possibly by interaction with the nonpolar core lipids.(ABSTRACT TRUNCATED AT 400 WORDS)

Ligand binding to heme proteins. An evaluation of distal effects

The O2, CO, and alkyl isocyanide-binding properties of a variety of vertebrate and invertebrate heme proteins have been compared in detail to those of protoheme mono-3-(1-imidazoyl)-propylamide monomethyl ester in aqueous suspensions of soap micelles. The proteins examined include: cytochrome P-450cam from Pseudomonas putida, beef heart cytochrome c oxidase, yeast cytochrome c peroxidase, alpha and beta subunits of human hemoglobin, sheep hemoglobin, carp hemoglobin, sperm whale myoglobin, horse heart myoglobin, a monomeric hemoglobin from Glycera dibranchiata, erythrocruorin from Chironomusthummii, soybean leghemoglobin, and several hemoglobins that lack distal histidines. The smallest bimolecular rates were observed for cytochrome P-450 containing bound camphor, cytochrome c oxidase, and cytochrome c peroxidase. In the case of P-450, the extremely low isonitrile binding rates (approximately 1 M-1 S-1 at 20 degrees C) are due to steric exclusion by bound camphor molecules. For the oxidase and peroxidase, inhibition of CO and isonitrile binding appears to be due to the polar nature of the active sites. In the cases of animal hemoglobins and myoglobins, the sixth coordination positions appear to be designed to accommodate diatomic molecules with no steric hindrance by distal protein residues. Protein resistance to the diffusion of CO and O2 does not limit the observed association rate constants. In contrast, ligands containing three or more atoms are sterically hindered both in their final bound positions and during diffusion to the active site. The magnitude of this hindrance (greater than or equal to 2 kcal/mol) exhibits a complex dependence on ligand size and shape. The most important protein residue appears to be His E7. In addition to restricting the size of the sixth coordination position, the distal histidine is also capable of forming a hydrogen bond with bound oxygen molecules. The strength of this hydrogen bond was estimated to be -2 and -1 kcal/mol for mammalian myoglobins and hemoglobins, respectively, and accounts for the smaller CO/O2 partition constants (M values) observed for these proteins in comparison to the constants observed for pentacoordinate model heme compounds.

Proton nuclear magnetic resonance studies of isonitrile-heme protein complexes

Steric interactions between bound ligand molecules and the valine E11 methyl groups of human hemoglobin and sperm whale myoglobin have been examined directly by high resolution NMR techniques. The methyl proton resonances of this amino acid are shifted markedly upfield and away from the bulk of the protein resonances by the shielding effect of circulating pi electrons in the porphyrin ring. We have monitored the valine resonance in the presence of CO and a series of isonitriles and found considerable shifts in its position, both between the various protein complexes and among the different liganded states. The ring current shifts of the gamma 1-methyl group of Val E11 in the CO forms of isolated alpha and beta chains and myoglobin are -2.70, -2.91, and -3.30 ppm, respectively. In all the proteins, these positions show little change in going from bound CO to bound methyl and ethyl isocyanide. In alpha subunits and myoglobin, n-propyl and n-butyl isocyanide binding produces marked decreases in the magnitude of these shifts, indicating that the valine residue has been forced away from the center of ring by the presence of these large ligand molecules. In the case of beta subunits, however, only tert-butyl isocyanide produces a marked decrease (from -2.91 to -1.99 ppm) in the ring current shift of the valine methyl protons. New peaks were observed in the isonitrile-protein spectra and identified as ligand proton resonances by comparing the spectra of normal and totally deuterated isonitrile complexes. The magnitudes of the ring current shifts for the terminal methyl protons of ethyl isocyanide suggest a linear geometry for the Fe equal to C equal to N - C bonds in beta chains and a bent geometry for alpha chains. The bent geometry in alpha subunits appears to be dictated by the position of the Val E11 methyl group which is located further up from the heme plane but closer to the heme center than the corresponding position of the beta subunit residue. The free energy changes for ethyl isocyanide binding to the two chains are nearly identical, suggesting that the linear and bent geometries are energetically equivalent. Myoglobin ethyl isocyanide complexes exhibit ligand ring current shifts intermediate to those observed for the hemoglobin subunits. Assignment of resonances and positions to the alkyl protons of the longer isonitriles is more difficult.