Biomedical subjects
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This article focuses on people from India, Pakistan, Sri Lanka, Bangladesh, Laos, Cambodia, Vietnam, China, and the Pacific Islands. Health care providers must be aware of cultural differences, language obstacles, poverty, social isolation, and genetic conditions when treating these ethnic groups.
Polysialic acid (PSA) is an unusual homopolymer of sialic acid (Sia) found on a limited number of animal glycoproteins and in the capsules of certain pathogenic bacteria. The biological properties of PSA are known to vary markedly with the length of the polymer. We confirm here that while the primary linkage unit of PSA (Sia alpha 2-8Sia) is more stable than commoner Sia linkages, PSA with > 3 Sia units is substantially more labile. A "limit digest" of PSA yields fragments of degree of polymerization (DP) = 2 and 3 and little monomeric Sia. In keeping with this, the fragmentation of PSA of DP 4 is non-random, with the internal glycosidic bond being more labile than those at the two ends. The accelerated breakdown of PSA involves an intramolecular mechanism that is not explained by lactone formation, cation effects, or specific secondary structural features. However, it is dependent upon the intactness of internal carboxyl groups, which have an anomalously high pKa. Thus, the instability of PSA appears to result from intramolecular self-cleavage of the glycosidic bonds of internal Sia units, in which the adjacent carboxyl group with a high pKa acts as a proton donor for general acid catalysis. This lability of PSA is seen under mildly acidic conditions that can be encountered in various physiological and pathological situations and thus has potential implications for neuronal adhesion, embryogenesis, and bacterial pathogenicity.
The carbohydrate-deficient glycoprotein syndrome (CDGS) is a developmental disease associated with an abnormally high isoelectric point of serum transferrin. Carbohydrate analyses of this glycoprotein initially suggested a defect in N-linked oligosaccharide processing, although more recent studies indicate a defect in the attachment of these sugar chains to the protein. We studied both serum glycoproteins and fibroblast-derived [2-3H]mannose-labeled oligosaccharides from CDGS patients and normal controls. While there was a decrease in the glycosylation of serum glycoproteins of affected individuals, differences were not seen in either monosaccharide composition or oligosaccharide structures. The lectin-binding profiles of glycopeptides from [2-3H]-mannose-labeled fibroblasts were likewise indistinguishable. However, the incorporation of [2-3H]mannose into both glycoproteins and the dolichol-linked oligosaccharide precursor was significantly reduced. Thus, at least in some patients, CDGS is not due to a defect in processing of N-linked oligosaccharides, but rather to defective synthesis and transfer of nascent dolichol-linked oligosaccharide precursors. This abnormality could result in both a failure to glycosylate some sites on some proteins, as well as secondary abnormalities in overall glycoprotein processing and/or function.
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Delta-9-tetrahydrocannabinol (THC), the major psychoactive component of marijuana, is known to inhibit a variety of immune functions. However, the mechanisms of action of THC-induced immunosuppression are unclear. Because THC is known to affect arachidonic acid metabolism in non-lymphoid cells and because arachidonic acid metabolites are important regulators of the immune response, a detailed examination of the effects of THC on arachidonic acid metabolism in human peripheral blood mononuclear cells (PBMC) was performed. THC increased the amount of label released from PBMC prelabeled with [3H]-arachidonic acid. Further studies were performed using RP-HPLC to determine whether the increase in label release from cell membranes was due to the release of free [3H]-arachidonic acid or metabolites. Our results indicated that THC increases the production of the eicosanoid 12-HETE from PBMC. To determine whether other metabolites, such as the leukotrienes, were also affected by THC, leukotriene B4 (LTB4) was measured by enzyme immunoassay. THC was shown to increase markedly the production of LTB4 from PBMC stimulated with the calcium ionophore A23187. These results indicate that THC alters arachidonic acid metabolism in lymphocytes by increasing the production of lipoxygenase products.
Lectin-carbohydrate recognition between the selectins and their ligands are among the earliest events in leukocyte recirculation, leukocyte recruitment into inflamed areas, and abnormal egress of leukocytes in diseases. Previously, we have described a dimeric sialoglycoprotein from myeloid cells with subunits of molecular mass = 120 kDa, which is selectively recognized by P-selectin (Moore, K.L., Stults, N.L., Diaz, S., Smith, D.F., Cummings, R.D., Varki, A., and McEver, R.P. (1992) J. Cell Biol. 188, 445-456). Here, we demonstrate that this P-selectin ligand carries alpha 2-3-linked sialic acids and the sialyl-Lewisx (SLex) tetrasaccharide motif. This glycoprotein contains < 1% of the total membrane-bound sialic acids and a very small fraction of the total SLex on neutrophil membranes. In spite of a relative resistance to sialidase digestion, the predominant form of sialic acid on the ligand is N-acetylneuraminic acid. Selective periodate oxidation of the side chain of sialic acids does not affect P-selectin binding and allows the introduction of tritium label into the truncated sialic acids. beta-Elimination with alkaline borohydride releases labeled O-linked oligosaccharides both from the labeled neutrophil ligand and from the ligand purified from HL-60 cells metabolically labeled with [3H]glucosamine. The ligand from both neutrophils and HL-60 cells is also susceptible to cleavage by the enzyme O-sialoglycoprotease from Pasteurella hemolytica. Analysis of the specificity of this enzyme suggests that the P-selectin ligand carries large numbers of closely spaced sialylated O-linked oligosaccharides. O-Sialoglycoprotease abolishes both direct binding of P-selectin to HL-60 cells and the adhesion of HL-60 cells to immobilized P-selectin, without significantly decreasing overall cell surface SLex expression. This indicates that the 120-kDa ligand may be the major determinant of P-selectin:myeloid cell interaction in vivo. Finally, based on the current and previous data, we hypothesize that the high affinity recognition site(s) of this P-selectin ligand may be derived from a "clustered saccharide patch" of sialylated fucosylated O-linked oligosaccharide sequences.
O-Acetylation of sialic acids has previously been considered an uncommon modification found on certain salivary mucins and neural gangliosides. We show here that glycosidically bound sialic acids from total membranes of rat liver have surprisingly high levels (approximately 20%) of O-acetylation at the 7- or 9-position. This O-acetylation is further enriched in N-linked oligosaccharides but is barely detectable in ganglioside fractions from the same tissue. The position of O-acetylation on the sialic acid side chain varies between different subcellular fractions. In particular, 7-O-acetylation was enriched in lysosomal membranes and 9-O-acetylation in plasma membranes, whereas Golgi membranes contained both types. This distribution fits with the ability of the rat liver sialate: O-acetyltransferase(s) to synthesize both 7- and 9-O-acetyl esters (Diaz, S., Higa, H. H., Hayes, B. K., and Varki, A. (1989) J. Biol. Chem. 264, 19416-19426) and the fact that 7-O-acetyl esters can migrate to the 9-position at physiological temperature but only under neutral or mildly alkaline conditions. Subcellular fractionation shows that sialate:O-acetyltransferase activity directed toward endogenous acceptors is enriched in Golgi fractions, whereas an intralumenal sialic acid-specific O-acetylesterase activity is not. The O-acetyltransferase is labile and difficult to solubilize in the intact state and cannot be assayed with exogenous acceptors. However, a prelabeled [3H]acetyl intermediate can be solubilized from Golgi membranes with Triton X-100 and is stable for a prolonged time in the cold. In contrast to the transferase, the lumenal esterase is easily released in a stable and water-soluble form from membrane fractions by saponin permeabilization or repeated freeze-thaw. In keeping with this finding, differential subcellular fractionation and continuous sucrose gradients indicate that this enzyme is enriched in lysosomal fractions (see also the accompanying paper (Butor, C., Higa, H. H., and Varki, A. (1993) J. Biol. Chem. 268, 10207-10213). Based upon findings reported in this and previous studies, a model is proposed for the biosynthesis, maturation, and turnover of 7- and 9-O-acetyl esters on the sialic acids of N-linked oligosaccharides that are attached to membrane-bound proteins in the rat liver.
Human neutrophils were activated by the bacterial chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) to produce superoxide (O2-) and to release the primary granule enzyme beta-glucuronidase and the predominantly secondary granule enzyme lysozyme. Pretreatment with granulocyte-macrophage colony-stimulating factor (GM-CSF) increased the secretion of all three substances upon addition of fMLP. The augmentation by GM-CSF was significantly attenuated by the 5-lipoxygenase inhibitor AA861 and by the guanylate cyclase inhibitor LY83583. The secretion induced by fMLP alone was much less affected by either of the two inhibitors. AA861 inhibited leukotriene B4 production in neutrophils primed with GM-CSF and stimulated with fMLP, and LY83583 inhibited GM-CSF-evoked increases of 3',5'-guanosine monophosphate. The data suggest that activation of lipoxygenase and guanylate cyclase is not critical to the fMLP stimulation pathway, but they may be important components of the pathway by which GM-CSF augments neutrophil responses to fMLP. However, AA861 and LY83583 may have important actions in addition to inhibition of 5-lipoxygenase and guanylate cyclase.
Quality of care means that the needs of the clients in the context of their personal life should be the major determinant of the behavior of the providers and the goal of the programs. Since family planning has been recognized as a right of individuals and couples, quality of care can be focused as a right of the client. Ten rights of family planning clients have been outlined by the International Planned Parenthood Federation (IPPF) as follows. Rights to: information, access, choice, safety, privacy, confidentiality, dignity, comfort, continuity, and opinion. The responsibilities for quality of care, and therefore fulfilling the rights of the clients, are distributed throughout the whole family planning program, but those who are actually seen as most responsible are the ones who are in direct contact with the clients--the service providers. A strategy for quality of care cannot be realistic without recognising that service providers have their own needs which can be outlined as: training, information infrastructure, supplies, guidance, back-up, respect, encouragement, feedback, and self-expression. When fulfilling the rights of the clients and needs of the service providers, both technical and human aspects should be taken into account.
Performance of the Slimline and Standard models of the Gyne T 380 were measured through four years in a comparative study initially involving 996 women, seventy percent of whom were randomized to the Slimline device. Cumulative pregnancy rates of Slimline users were 0.3 +/- 0.2 per 100 both at three and at four years, as compared with rates of 1.5 +/- 0.9 and 3.8 +/- 1.7 at the same intervals for users of the Standard model (P > .05). The four-year explusion rate of the Slimline, 8.6 +/- 1.3 per 100, was significantly higher than the comparable rate of the Standard model, 4.4 +/- 1.6 (P < .05). The two Gyne T* models did not differ in continuation rates. First time IUD users, however, had substantially lower continuation rates than did former users (P < .001), in consequence of their relative youth and desire to have additional children. Other performance measures did not differ importantly by device.
Delta-9-tetrahydrocannabinol (THC) is the major psychoactive component of marijuana. Suppression of mitogen-stimulated blastogenesis of human lymphocytes in vitro by THC was previously demonstrated. This effect was shown to be concentration dependent with the non-toxic concentrations 5, 7.5, and 10 micrograms THC/ml showing the greatest suppression. However, the mechanism(s) by which THC induces suppression are still unclear. The current study examines the effect of THC on the adenosine 3':5'-cyclic monophosphate (cAMP) pathway second messenger system, which is involved in activation of human peripheral blood lymphocytes. Lymphocyte cAMP levels were stimulated using three hormone receptor stimulators, isoproterenol, histamine, or 5'-N-ethylcarboxamide adenosine (NECA), each of which utilizes a different receptor to enhance cAMP production. THC suppressed cAMP levels independently of the hormone and receptor utilized. Levels of cAMP in non-mitogen-stimulated peripheral blood mononuclear cells and plastic non-adherent lymphocytes, as well as cells stimulated with phytohemmagglutinin, were suppressed by THC. Suppression of cAMP production by THC was further examined to determine whether inhibition involved a GTP-binding protein (Gi), which is known to down-regulate cAMP production. Cells were pre-treated with pertussis toxin to inhibit Gi activity; this blocked the THC-induced suppression of cAMP production. These results suggest that THC can exert its effects on second messenger systems at the lymphocyte membrane level, and that a pertussis toxin-sensitive Gi protein may be involved. Thus, second messenger regulated pathways may be involved in THC-induced immune suppression. However, the relationship between alteration of cAMP production and suppression of lymphocyte function due to the presence of THC in the medium remains to be established.
A new method is described for the extraction of aflatoxins from milk and milk products based on a diphasic dialysis technique, followed by detection and quantification of aflatoxins by TLC. Recovery was 65 to 99% for aflatoxins B1, G1, and M1, and the detection limit in milk and yogurt was .01 to .02 ppb for all aflatoxins studied. In cheese, the detection limit was .03 to .04 ppb for aflatoxins B1 and G1 and .1 ppb for aflatoxin M1. The main advantages of this technique are its simplicity; sensitivity; very economical use of reagents, thereby minimizing environmental pollution; efficiency, allowing the quick processing of a high number of samples; use by laboratories with little equipment; and a sensitivity comparable with that of much more sophisticated techniques.
OBJECTIVES: The objectives were to measure rates of planned pregnancy and factors affecting these rates after use of very-long-acting contraceptive methods (Norplant or Norplant II implants, a levonorgestrel-releasing intrauterine contraceptive device, or the copper T (model TCu 380Ag) intrauterine contraceptive device. STUDY DESIGN: The design was a concurrent, multicenter prospective study of 372 women who stopped contraception for planned pregnancy. Analysis was by life-table, log-rank, and standard chi 2 methods. RESULTS: Pregnancy rates 12 and 24 months after cessation of contraceptive use were 82 and 89 per 100, respectively. Age at removal and family planning intentions at initiation of contraception were both significantly correlated with pregnancy rates (p less than 0.05), but former contraceptive regimen and duration of contraceptive use were not. Pregnancy outcomes did not deviate from normal limits and did not differ by contraceptive formerly used. CONCLUSION: Contraceptive implants releasing 30 micrograms/day of levonorgestrel or intrauterine contraceptive devices releasing 20 micrograms/day of levonorgestrel or having copper surface areas of 380 mm2 are associated with normal fertility after use for women seeking pregnancy at termination. Durations of use do not affect pregnancy rates.
P-selectin (CD62, GMP-140, PADGEM), a Ca(2+)-dependent lectin on activated platelets and endothelium, functions as a receptor for myeloid cells by interacting with sialylated, fucosylated lactosaminoglycans. P-selectin binds to a limited number of protease-sensitive sites on myeloid cells, but the protein(s) that carry the glycans recognized by P-selectin are unknown. Blotting of neutrophil or HL-60 cell membrane extracts with [125I]P-selectin and affinity chromatography of [3H]glucosamine-labeled HL-60 cell extracts were used to identify P-selectin ligands. A major ligand was identified with an approximately 250,000 M(r) under nonreducing conditions and approximately 120,000 under reducing conditions. Binding of P-selectin to the ligand was Ca2+ dependent and was blocked by mAbs to P-selectin. Brief sialidase digestion of the ligand increased its apparent molecular weight; however, prolonged digestion abolished binding of P-selectin. Peptide:N-glycosidase F treatment reduced the apparent molecular weight of the ligand by approximately 3,000 but did not affect P-selectin binding. Western blot and immunodepletion experiments indicated that the ligand was not lamp-1, lamp-2, or L-selectin, which carry sialyl Le(x), nor was it leukosialin, a heavily sialylated glycoprotein of similar molecular weight. The preferential interaction of the ligand with P-selectin suggests that it may play a role in adhesion of myeloid cells to activated platelets and endothelial cells.
9-O-acetylation of sialic acids is tissue specific and developmentally regulated. We have selectively destroyed these O-acetyl groups during murine embryogenesis by expressing the 9-O-acetyl-sialic acid-specific esterase of influenza C. DNA constructs driven by the metallothionein promoter arrested development at the 2-cell stage and gave a markedly decreased yield of live mice. A similar construct driven by the phenylethanolamine-N-methyltransferase promoter did not cause this block, but gave transgenic mice with selective expression of esterase in the retina and the adrenal gland. These organs showed variable abnormalities in organization, while all other tissues examined appeared normal. The ganglioside 9-O-acetyl-GD3 was selectively destroyed in target tissues. Thus, 9-O-acetylated sialic acids may play an role in murine development at the 2-cell stage and in certain differentiated tissues.
A levonorgestrel-releasing IUD and the Copper T 380Ag IUD were in randomized comparison for seven years in five clinics. In two other clinics the randomized study was truncated at five years, but use of the Copper T continued. No pregnancies occurred to users of either device in years 6 and 7. Cumulative pregnancy rates were 1.1 per 100 at seven years for the steroid-releasing and 1.4 per 100 for the copper-releasing IUDs. Cumulative rates of PID did not differ between devices. Infection rates appeared to be lowest during the sixth and seventh years of the study. Termination attributable to amenorrhea was the principal contributor to differences in cumulative continuation rates between devices. At the five clinics that carried the comparative study to seven years, cumulative continuation rates were 24.9 per 100 for LNg20 IUD users and 29.4 per 100 for TCu 380Ag users. Women who used either method for periods of five to seven years experienced, on average, marked to mild increases in hemoglobin as compared with levels at admission. The Copper T380 family and the LNg20 IUDs represent the most effective reversible contraceptive methods yet studied in long-term randomized trials.
In a randomized trial of the Gyne T* 380 Slimline, the-two year pregnancy rate was 0.3 per 100 and the continuation rate was 65 per 100. These rates did not differ statistically from those of the standard Gyne T* 380, nor did other performance parameters differ between devices by the log-rank test. Women under age 30 had lower continuation rates using either device than did women age 30 or older at admission because of removals for planned pregnancy. Conception rates among those who desired pregnancy were 35 per 100 at one month and 86 per 100 at one year.