Biomedical subjects
Publications and source records attributed to A Ma.
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This study was intended to address the mechanism of the degradation for the bioabsorbable materials poly(epsilon-caprolactone) (PCL) in vitro and in vivo by measurement of changes in intrinsic viscosity, number average molecular weight and crystalliniy. The test demonstrated that the degradation in rabbit was quicker than that in vitro. This illustrates that the mechanism of bioerosion in vivo is as important as the nonenzymatic random hydrolytic cleavage of ester linkages. Regardless of the initial Mn of the sample, a linear relationship between ln[eta] and time was observed until the Mn decreased to about 5000. Before this decrease of Mn, the main mechanism of degradation is hydrolytic cleavage of ester groups, with an accompanying enzymatic surface erosion, but after this decrease of Mn, the bioerosion with weight loss plays a role more significant than that the hydrolytic reaction plays in the degradation. The morphological characteristics of PCL materials after and before erosion were also compared by means of Scanning Electron Microscopy.
As a model for studying the generation of antibody diversity, a gene-targeted mouse was produced that is hemizygous for a rearranged V(D)J segment at the immunoglobulin (Ig) heavy chain locus, the other allele being nonfunctional. The mouse also has no functional kappa light chain allele. The heavy chain, when paired with any lambda light chain, is specific for the hapten (4-hydroxy-3-nitrophenyl) acetyl (NP). The primary repertoire of this quasi-monoclonal mouse is monospecific, but somatic hypermutation and secondary rearrangements change the specificity of 20 percent of the antigen receptors on B cells. The serum concentrations of the Ig isotypes are similar to those in nontransgenic littermates, but less than half of the serum IgM binds to NP, and none of the other isotypes do. Thus, neither network interactions nor random activation of a small fraction of the B cell population can account for serum Ig concentrations.
The association between high intake of fruit and vegetables and low incidence of certain cancers is well established. Dietary antioxidants present in these foods are thought to decrease free radical attack on DNA and hence to protect against mutations that cause cancer, but this causal mechanism remains conjectural. We have adopted a molecular epidemiological approach to this question, based on a modified alkaline single-cell gel electrophoresis assay ("comet assay") which specifically detects oxidation of pyrimidines in the DNA of human lymphocytes. In a survey of men 50-59 years of age living in the northeast of Scotland, smokers initially showed significantly more base damage than nonsmokers. Correlations between oxidative base damage and plasma concentrations of various antioxidants were generally negative but not statistically significant. Supplementation of the diet for 20 weeks with vitamin C (100 mg/day), vitamin E (280 mg/day), and beta-carotene (25 mg/day) resulted in a highly significant (P < 0.002) decrease in endogenous oxidative base damage in the lymphocyte DNA of both smokers and nonsmokers. In addition, lymphocytes of antioxidant-supplemented subjects showed an increased resistance to oxidative damage when challenged in vitro with H2O2. These findings strongly support the hypothesis that fruit and vegetables exert a cancer-protective effect via a decrease in oxidative damage to DNA.
The rat sperm surface antigen, 2B1, that has been proposed to play a key role in sperm adhesion to the zona pellucida, has been cloned and its entire cDNA sequenced. Northern blot analysis indicates that 2B1 is encoded by a 2.2-kb RNA transcript that is abundantly expressed in the testis. The deduced protein sequence contains 512 amino-acid residues with a strong candidate signal sequence and C-terminal transmembrane domain. Data base searches reveal a high degree of sequence similarity to guinea pig, rabbit, monkey, and human PH20 sperm surface antigens, and a lower degree of similarity to honey bee and whiteface hornet venom hyaluronidases. Rat 2B1 antigen also possesses hyaluronidase activity, suggesting that it is a bifunctional protein with putative roles in the dispersion of cumulus oophorus cells as well as zona adhesion. However, while it would appear that 2B1 is the rat homologue of the guinea pig PH20 antigen, they differ in a number of important biochemical respects (including their mode of attachment to the sperm membrane and distribution between soluble and membrane-bound fractions), as well as in their localization on the sperm membrane. Expression of regions of the 2B1 protein in recombinant bacterial cells has allowed a preliminary mapping of the 2B1 epitope, and has provided more definitive information on the endoproteolytic processing of 2B1 during epididymal transit.
Binding of mammalian spermatozoa to the zona pellucida of homologous eggs is mediated by specific molecules on their surface membranes. In the present investigation we describe the biogenesis, epididymal processing and cellular distribution of a plasma membrane antigen (2B1) on rat spermatozoa that has a potential role in mediating zona binding. 2B1 is expressed postmeiotically in the testis as a precursor glycoprotein (approximately 60 kDa) that first appears on the plasma membrane of stage 6 to 8 round spermatids. Northern and western blot analyses show that there is a close correlation between the timing of transcription and expression of the glycoprotein on the cell surface. During spermatid elongation 2B1 is excluded from the head domain and is sequestered onto the sperm tail. As spermatozoa pass through the caput epididymidis 2B1 is endoproteolytically cleaved at a specific arginine residue (Arg 312) to produce a heterodimeric glycoprotein (approximately 40 kDa and approximately 19 kDa) containing intramolecular disulphide bridges. Endoproteolysis at Arg 312 also takes place during culture of washed testicular or caput spermatozoa in vitro and can be prevented by serine proteinase inhibitors or enhanced by trypsinisation. However, neither processing in vivo or in vitro has any effect on the domain organisation of 2B1 antigen i.e. it remains localised to the tail. These results support the hypothesis that sperm antigens that are important for fertilization are synthesized as precursor molecules in the testis and are then "activated' during epididymal maturation and capacitation, thereby ensuring that they only become fully functional at the site of fertilization.
We have already proved that the mitochondrial membrane-phospholipid (MMP) injury changes of peripheral lymphocytes in patients with heart failure can be used as an injury indicator of myocardia, and are related to the long-term prognosis. In the present study, MMP localization of the peripheral lymphocytes was performed by modified Demer's tricomplex flocculation method, and we compared the changes, after classification, between the pre-treatment and the 12-week post-treatment, of coenzyme Q10 (Co.Q10) and captopril in 61 hospitalized patients with dilated cardiomyopathy (DCM). They were followed up for 16.1 +/- 7.8 months (mean). The results showed that compared with the placebo, Co.Q10 and captopril could significantly protect against and repair MMP injury and improve the heart function of patients with DCM after 12 weeks, and the 2-year survival rate rose significantly by 72.7% for Co.Q10, and 64.0% for captopril, vs 24.7% for placebo. As for Longrank test, X2 equals 4.660 and 6.318, respectively, with both p < 0.05. The aforementioned results indicate that MMP injury of peripheral lymphocytes can predict the prognosis of the patients with DCM, thus the protection and repairment of MMP injury can improve the life-quality and prolong the life-span of the patients.
Coexpression of the proto-oncogenes c-myc and bcl-2 under the control of the immunoglobulin enhancer E mu provokes the rapid development of primitive lymphoid tumors in transgenic mice. In the present study we show that the myc family members N-myc and L-myc also cooperate with bcl-2 in oncogenesis and can provoke the development of more mature pre-B, B and T cell type lymphomas. The analysis of prelymphomatous B-cells from single E mu N-myc and bcl-2-Ig transgenic animals and from young, tumor free, double transgenic E mu N-myc/bcl-2-Ig mice revealed that E mu directed expression of N-myc leads to very rapid apoptosis after explantation and culturing compared to B-cells from normal mice. As expected, B-cells from bcl-2-Ig transgenics were protected to a certain degree from apoptosis. Strikingly however, B-cells from E mu N-myc/bcl-2-Ig double transgenic animals were found to be almost completely resistant towards a number of different apoptotic stimuli. Furthermore, after treatment with H2O2, which can trigger apoptosis, B-cells from E mu N-myc animals reach levels of intracellular free Ca2+ concentrations that are comparable to B-cells from normal mice, whereas B-cells from bcl-2-Ig or E mu N-myc/bcl-2-Ig double transgenic mice show no increase in intracellular Ca2+ concentrations after stimulation with H2O2. These findings suggest that the prevention of apoptosis conferred by bcl-2 correlates with the inhibition of intracellular Ca2+ fluxes whereas induction of apoptosis mediated by N-myc requires normal Ca2+ levels. We hypothesize therefore that the regulation of intracellular Ca2+ concentrations represent one important parameter in the oncogenic cooperation between bcl-2 and N-myc.
Interleukin-2 (IL-2)-deficient (IL-2-/-) mice develop anemia and colonic inflammatory bowel disease. To elucidate the mechanism of this disease, we have bred IL-2-/- mice to two strains of immunodeficient mice, RAG-2-deficient (RAG-2-/-, lacking B and T cells) and JH-deficient mice (JH-/-, lacking B cells). IL-2-/-, RAG-2-/- double-mutant mice are disease free, while IL-2-/-, JH-/- double-mutant mice succumb to bowel disease at the same rate as IL-2-/- littermates. IL-2-/-, JH-/- mice do not, however, succumb to anemia. Thus, spontaneous intestinal inflammation in IL-2-/- mice requires mature T cells, not B cells, while anemia is dependent on B cells.
The bclx gene has been shown to regulate programmed cell death in vitro. We now show that Bclx expression increases dramatically when T cells differentiate from CD4- CD8- (double negative) thymocytes to CD4+ CD8+ [double positive (DP)] thymocytes. In contrast single-positive (SP) thymocytes express negligible amounts of Bclx protein. This expression pattern contrasts with that of Bcl2, which is present in double-negative thymocytes, down-regulated in DP thymocytes, and reinduced upon maturation to SP thymocytes. Elimination of Bclx by gene targeting dramatically shortens the survival of DP thymocytes but not the survival of SP thymocytes or peripheral SP T cells. These data suggest that the induction of Bclx during thymic maturation plays a critical role in regulating the length of time DP thymocytes survive in the absence of selection.
To determine whether CD3 epsilon and CD3 zeta proteins have unique roles in TCR-dependent functions, chimeric genes encoding the extracellular and transmembrane domains of the human IL-2 receptor alpha chain (Tac) fused to a cytoplasmic domain of either the CD3 epsilon or CD3 zeta chain were introduced as transgenes into both normal and RAG2-deficient (RAG2-/-) mice. Developmental arrest of T lineage cells at the CD4, CD8 double-negative stage in the transgenic RAG2-/- thymus was released to the CD4, CD8 double-positive (DP) stage by in vivo cross-linking of TT epsilon or TT zeta with anti-Tac antibody. In TT epsilon + or TT zeta +, RAG2-/- mice, in vitro cross-linking of TT epsilon and TT zeta induced DP thymocyte cell death and proliferation of mature single-positive T cells. Overall, no qualitative differences were observed between TT epsilon- and TT zeta-mediated functions, suggesting that different CD3 components deliver qualitatively similar signals in inducing TCR-dependent functions.
Interleukin-2 receptor alpha chain (IL-2R alpha) expression occurs at specific stages of early T and B lymphocyte development and is induced upon activation of mature lymphocytes. Young mice that lack IL-2R alpha have phenotypically normal development of T and B cells. However, as adults, these mice develop massive enlargement of peripheral lymphoid organs associated with polyclonal T and B cell expansion, which, for T cells, is correlated with impaired activation-induced cell death in vivo. Older IL-2R alpha-deficient mice also develop autoimmune disorders, including hemolytic anemia and inflammatory bowel disease. Thus, IL-2R alpha is essential for regulation of both the size and content of the peripheral lymphoid compartment, probably by influencing the balance between clonal expansion and cell death following lymphocyte activation.
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The content of lymphocytic and erythrocytic K+, Na+, Ca++, Mg++ changed in patients with congestive heart failure, related to clinical treatment and prognosis. The longer the course of disease, the more significant the changes, with no relation to the etiology of heart disease. The changes were partially improved after treatment of the heart failure. The content of electrolytes is not significantly different in patients in NYHA Class III, compared to those in NYHA Class IV. The metabolic changes of electrolytes occur on the myocardial cells, skeletal muscle cells and peripheral erythrocytes in patients with congestive heart failure. However, serum electrolyte content does not reflect precisely overall electrolyte metabolism in the body. Whether similar changes of electrolyte content occur in the peripheral lymphocytes is rarely reported. We studied the lymphocytic and erythrocytic electrolyte content in patients with congestive heart failure, to provide some reference in the clinical treatment and prognosis of congestive heart failure.
The IL-2/IL-2 receptor (IL-2R) has been studied intensively because of its potential function in the development and regulation of the immune system. The IL-2R alpha chain has been shown to be expressed on CD4-CD8- thymocytes and activated T and B cells. In this report, we show that IL-2R alpha is also expressed on precursor B cells in the bone marrow. Its expression is initiated by functional rearrangement and expression of Ig mu heavy chain gene and is down-regulated when immature B cells mature and express IgD. Its potential function in early B cell differentiation is discussed in comparison with its role in thymocyte differentiation.
Catheter balloon valvulotomy (CBV) is useful in the relief of rheumatic mitral stenosis. Morphologic scoring of the mitral valve by transthoracic echocardiography is predictive of success with CBV. Horizontal plane transesophageal echocardiography can obtain high quality images of the mitral valve and left atrium, but its value with routine use in the pre and post CBV setting is unknown. We prospectively examined 14 patients with mitral stenosis, pre and post CBV, noting scores, complications of mitral stenosis, and complications of CBV. Mitral valve scoring was similar by TTE and TEE pre and post CBV, but TEE did tend to underestimate scores pre CBV. There was a single thrombus, it was detected only by TEE. Post CBV, both TTE and TEE detected one of two torn chordae. Of three patients with ASD's by colour flow mapping, TTE and TEE each detected two. Increases in mitral insufficiency post CBV were seen equally frequently by TTE and TEE. The increases appeared to be of a higher grade (NS) by TEE. TTE and TEE yielded complementary findings, pre and post CBV. Other than for the detection of thrombi through, the net clinical contribution of routine use of TEE appears small, and large series would be needed to establish its contribution.
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Using an in vitro binding-site selection assay, we have demonstrated that c-Myc-Max complexes bind not only to canonical CACGTG or CATGTG motifs that are flanked by variable sequences but also to noncanonical sites that consist of an internal CG or TG dinucleotide in the context of particular variations in the CA--TG consensus. None of the selected sites contain an internal TA dinucleotide, suggesting that Myc proteins necessarily bind asymmetrically in the context of a CAT half-site. The noncanonical sites can all be bound by proteins of the Myc-Max family but not necessarily by the related CACGTG- and CATGTG-binding proteins USF and TFE3. Substitution of an arginine that is conserved in these proteins into MyoD (MyoD-R) changes its binding specificity so that it recognizes CACGTG instead of the MyoD cognate sequence (CAGCTG). However, like USF and TFE3, MyoD-R does not bind to all of the noncanonical c-Myc-Max sites. Although this R substitution changes the internal dinucleotide specificity of MyoD, it does not significantly alter its wild-type binding sequence preferences at positions outside of the CA--TG motif, suggesting that it does not dramatically change other important amino acid-DNA contacts; this observation has important implications for models of basic-helix-loop-helix protein-DNA binding.