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Biomedical subjects

A White

Publications and source records attributed to A White.

At least 19 recordsLinked to original sources
PubMed1999

Modification of plasma insulin-like growth factors and binding proteins during oral contraceptive use and the normal menstrual cycle.

OBJECTIVE: Sex steroid regulation of the insulin-like growth factor axis is a subject of contention. We examined the effect of combined oral contraceptives and investigated the cyclic variations in the insulin-like growth factor axis. STUDY DESIGN: Fasting blood samples were taken from 9 women receiving oral contraceptives, 10 women receiving no medication, and 10 male subjects. RESULTS: In women receiving oral contraceptives, insulin-like growth factor binding protein 1 remained highly phosphorylated and levels were acutely increased by sex steroid treatment (305 +/- 110 microg/L on day 14 of the cycle [medication phase] vs 118 +/- 70 microg/L during the medication-free period, P <.03). In women receiving no medication, insulin-like growth factor binding protein 1 levels were significantly lower (69 +/- 50 microg/L on day 14 of the menstrual cycle, P <.001) and varied cyclically, with a rise in the late-secretory phase that coincided with the appearance of nonphosphorylated and less phosphorylated insulin-like growth factor binding protein 1 isoforms. Compared with those in untreated women and in men, insulin-like growth factor I levels were decreased in women receiving oral contraceptives (405 +/- 104 ng/mL in untreated women and 330 +/- 28 ng/mL in men vs 287 +/- 73 ng/mL in women receiving oral contraceptives, P <.004). Oral contraceptive use had no effect on insulin-like growth factor II levels, and neither insulin-like growth factor I nor insulin-like growth factor II showed cyclic variation. CONCLUSION: The bioavailability of insulin-like growth factor I is reduced in users of oral contraceptives. This may contribute to the metabolic changes observed in such subjects.

Adult↗
PubMed1998

Characterization of human and rat brain myristoyl-CoA:protein N-myristoyltransferase: evidence for an alternative splice variant of the enzyme.

Using 5'-rapid amplification of cDNA ends, we have identified an extended 5'-end of mRNA coding for human myristoyl-CoA:protein N-myristoyltransferase (NMT). PCR using primers based on this new 5'-sequence and reverse primers within the currently accepted coding sequence of the enzyme resulted in the identification of a novel splice variant of NMT. In vitro translation of these cDNAs resulted in the production of proteins with apparent molecular masses of 63 kDa and 48 kDa. Immunoprecipitation of NMT from human cell lines and immunoblotting of a range of rat tissues has identified proteins with molecular masses corresponding to those derived from these cDNAs, and provided evidence that their relative abundance differs among tissues. Our results provide evidence that this enzyme exists in different forms resulting from alternative splicing of the mRNA.

Acyltransferases↗
PubMed1998

Structure of the metal-ion-activated diphtheria toxin repressor/tox operator complex.

The virulent phenotype of the pathogenic bacterium Corynebacterium diphtheriae is conferred by diphtheria toxin, whose expression is an adaptive response to low concentrations of iron. The expression of the toxin gene (tox) is regulated by the repressor DtxR, which is activated by transition metal ions. X-ray crystal structures of DtxR with and without (apo-form) its coordinated transition metal ion have established the general architecture of the repressor, identified the location of the metal-binding sites, and revealed a metal-ion-triggered subunit-subunit 'caliper-like' conformational change. Here we report the three-dimensional crystal structure of the complex between a biologically active Ni(II)-bound DtxR(C102D) mutant, in which a cysteine is replaced by an aspartate at residue 102, and a 33-base-pair DNA segment containing the toxin operator toxO. This structure shows that DNA interacts with two dimeric repressor proteins bound to opposite sides of the tox operator. We propose that a metal-ion-induced helix-to-coil structural transition in the amino-terminal region of the protein is partly responsible for the unique mode of repressor activation by transition metal ions.

Bacterial Proteins↗
PubMed1998

Procorticotrophin-releasing hormone: endoproteolytic processing and differential release of its derived peptides within AtT20 cells.

Procorticotrophin-releasing hormone (proCRH) is expressed mainly in the hypothalamus and in the placenta, where it undergoes tissue-specific endoproteolysis. Our results show that within stably transfected AtT20/D16V cells proCRH is cleaved to generate two fragments of approximately 8 and 3 kDa which could account for proCRH(125-194) and proCRH(125-151), respectively, and a 4.5 kDa product which could account for mature IR-CRH(1-41). The immunofluorescence staining patterns for IR-CRH and IR-ACTH and their response of secretagogues indicate targeting of proCRH and POMC to the secretory pathway in transfected AtT20 cells. In this work, we have used a unique set of specific RIAs and IRMAs to the full length POMC and proCRH molecules and several products of endoproteolytic processing to assess if they could be released differentially in response to stimulation. Although the release of both IR-ACTH and IR-CRH peptides from transfected AtT20 cells is stimulated in response to exposure to high potassium stimulation (51 mM KCl/SmM CaCl2), the sorting index (SI) suggests that mature ACTH is sorted to the regulated secretory pathway 2.1-fold more efficiently than mature CRH(1-41). Mature ACTH is also sorted to the regulated secretory pathway 9-fold more efficiently than IR-proCRH(125-151). Also, mature CRH(1-41) is sorted to the regulated secretory pathway 3-fold more efficiently than IR-proCRH(125-151). These results therefore indicate that the intracellular mechanisms for the storage and release of POMC, proCRH and their endoproteolytic products differ and would sustain the hypothesis that within mammalian peptidergic cells, different biologically active peptides originating from the same or different precursor molecules, could be differentially released in response to specific stimuli. This would give these cells the capacity to finely regulate neurotransmitter release in response to environmental and physiological demands.

Adrenocorticotropic Hormone↗
PubMed1998

Frequent downregulation of the KAI1(CD82) metastasis suppressor protein in human cancer cell lines.

KAI1 is a metastasis suppressor gene on human chromosome 11p11.2 that encodes a glycoprotein of the transmembrane four superfamily. Reduced KAI1 expression associates with malignant progression of human prostatic, lung and pancreatic cancers, but the role of KAI1 protein in the malignant progression of other human cancers remains to be elucidated. We analysed KAI1 protein in normal and cancer cells of the prostate, ovary, bladder, endometrium, lung and melanocytes by Western blot to determine if KAI1 may be involved in multiple cancers. We also investigated the relationship of KAI1 expression and two other transmembrane four superfamily proteins, CD81 and CD9, in the cells. We found that KAI1 protein was downregulated in 31/42 of the cancer cell lines analysed. Alternatively, some ovarian, bladder and endometrial cells had distinct, heterogeneous KAI1 protein band patterns in Western blots that were due primarily to N-linked glycosylation. Most of the cancer cells expressed two other transmembrane four superfamily proteins, CD81 and CD9. Downregulation of KAI1 protein may be an indicator of metastatic potential in cancers of urogenital, gynecological, and pulmonary origin and in melanomas. KAI1 may also have post-translational modifications specific to tissue type or malignant progression.

Antigens, CD↗
PubMed1998

Serum autoantibodies to neurofilament proteins in sporadic amyotrophic lateral sclerosis.

Anti-neurofilament (NF) autoantibodies were searched for by enzyme-linked immunosorbent assays (ELISA) in the serum from 85 sporadic amyotrophic lateral sclerosis (ALS) patients, 98 healthy controls and 79 patients with unrelated immunological diseases (Guillain-Barré syndrome, myasthenia gravis and multiple sclerosis). ELISA cutoff value was determined as mean control levels +2 SD and it corresponded to a specificity of 94%. Such high level antibodies were detected in 24.7% of ALS patients contrasting with 12.6% of neurological controls (P<0.05) and only 6.1% of healthy subjects (P<5.10[-4]). In ALS, anti-NF antibodies were significantly associated with a slow evolution, as measured by the mean time spent in the initial functional states. They did not relate with age, sex and clinical form. The predominant isotype of the anti-NF antibodies was IgM lambda by ELISA. In contrast to negative sera, indirect immunohistochemical studies demonstrated that most sera positive for anti-NF antibodies reacted with axons with predominant isotypes restricted to IgM lambda. By using Western blotting, small amounts of serum monoclonal IgM were found with a high frequency in anti-NF antibody-positive patients. These results suggest the possible involvement of anti-NF antibodies in an autoimmune process in a subgroup of ALS patients.

Aged↗
PubMed1998

The oestrogen receptor regulates NFkappaB and AP-1 activity in a cell-specific manner.

Oestrogens regulate the expression of genes both positively and negatively in a range of cell types. These effects are mediated via the oestrogen receptor (ER) and involve direct interactions between the ER and DNA response elements, as well as interactions between the ER and other nuclear proteins. We have examined the potential of the ERalpha to regulate the expression of reporter genes under the control of oestrogen response elements (EREs), NFkappaB response elements (NREs) or AP-1/TPA response elements (TREs) in HeLa cells and in human embryonic kidney (HEK-293) cells. Transiently transfected ERalpha was able to activate expression of beta-galactosidase under the control of EREs in an oestradiol (E2)-dependent manner in both HeLa and HEK-293 cells. The ERalpha was able to repress by 80% the TNF-mediated expression of beta-galactosidase under the control of NREs in an E2-dependent manner in HeLa cells but not in HEK-293 cells. ERalpha/E2 also induced a two-fold potentiation of TPA-mediated expression of beta-galactosidase under the control of TREs in HeLa cells but not in HEK-293 cells. These results suggest that the ERalpha is capable of regulating gene expression in a cell-specific manner. We further investigated the mechanisms by which the ERalpha regulates gene expression in these systems by co-expressing the ERalpha and the reporter gene constructs with known cofactors of the ERalpha. We have shown that expression of steroid receptor coactivator-1 alpha (SRC-1alpha) and receptor interacting protein-140 (RIP-140) have no effect on the capacity of the ERalpha to modulate NFkappaB reporter gene activity in HeLa cells. Furthermore, the expression of SRC-1alpha or RIP-140 does not enable the ERalpha to repress NFkappaB or to potentiate an AP-1 response in HEK-293 cells. This suggests that factors other than SRC-1alpha or RIP-140 are responsible for the cell-specific effects seen with ERalpha.

Dexamethasone↗
PubMed1998

Potentiation of anti-cancer agent cytotoxicity by the potent poly(ADP-ribose) polymerase inhibitors NU1025 and NU1064.

The ability of the potent poly(ADP-ribose) polymerase (PARP) inhibitor, NU1025 (8-hydroxy-2-methyl-quinazolin-4-[3H]one) to potentiate the cytotoxicity of a panel of mechanistically diverse anti-cancer agents was evaluated in L1210 cells. NU1025 enhanced the cytotoxicity of the DNA-methylating agent MTIC, gamma-irradiation and bleomycin 3.5-, 1.4- and 2-fold respectively. The cytotoxicities of the thymidylate synthase inhibitor, nolatrexed, and the cytotoxic nucleoside, gemcitabine, were not increased. Potentiation of MTIC cytotoxicity by a delayed exposure to NU1025 was equally effective as by a simultaneous exposure to NU1025, indicating that the effects of NU1025 were mediated by an inhibition of the cellular recovery. The recovery from potentially lethal gamma-irradiation damage cytotoxicity in plateau-phase cells was also inhibited by NU1025. Investigation of DNA strand breakage and repair in gamma-irradiated cells by alkaline elution demonstrated that NU1025 caused a marked retardation of DNA repair. A structurally different PARP inhibitor, NU1064 (2-methylbenzimidazole-4-carboxamide), also potentiated the cytotoxicity of MTIC, to a similar extent to NU1025. NU1064 potentiated a sublethal concentration of a DNA methylating agent in a concentration-dependent manner. Collectively, these data suggest that the most suitable cytotoxic agents for use in combination with PARP inhibitors are methylating agents, bleomycin and ionizing radiation, but not anti-metabolites.

Amides↗
PubMed1998

Differential effects of three radiographic contrast media on platelet aggregation and degranulation: implications for clinical practice?

We have determined the effects of three radiographic contrast media on platelet aggregation and degranulation in vitro. Aggregation was measured as loss of single platelets, and degranulation was measured as P-selectin expression using flow cytometry. Iopamidol added to hirudinized blood induced aggregation directly and also potentiated that induced by weak platelet agonists such as adenosine diphosphate (ADP). Iodixanol also potentiated platelet aggregation, but ioxaglate inhibited it. Iopamidol also caused marked platelet degranulation. The pro-aggregatory effect of iopamidol was evident in non-anticoagulated blood as well as in hirudinized blood, but not in citrated blood. In platelet-rich plasma (PRP) prepared from hirudinized blood neither iopamidol nor iodixanol directly induced platelet aggregation, but they rendered platelets hypersensitive to ADP. ADP antagonists inhibited the platelet aggregation and degranulation induced by iopamidol in whole blood, whereas aspirin, an inhibitor of thromborane A2 synthesis, did not. These data are consistent with clinical reports of increased thromboembolic risk with non-ionic low-osmolar media, and raise concerns about the routine use of these contrast media during diagnostic and interventional arteriographic procedures. Routine use of citrate in previous experiments may have masked a pro-aggregatory effect of some contrast media.

Adenosine Diphosphate↗
PubMed1998

The comparative anatomy of the pig middle ear cavity: a model for middle ear inflammation in the human?

This study was undertaken to develop a functional model of otitis media with effusion (OME) in the pig (Sus scrofa), with the purpose of investigating the origin of lymphocytes populating the middle ear during the course of an inflammatory process. The relevance of the model to the human condition of OME is to a large extent dependent on the anatomical and physiological similarities between the middle ear cavity and the pharyngeal lymphoid tissue of the pig and man. Anatomical specimens were collected from 7 young Large White pigs to determine the gross anatomy of the middle ear cavity and the histological characteristics of the middle ear mucosa. It was found that the anatomy of the 3 parts of the middle ear cavity in man and in the pig is broadly similar, although some minor differences were observed. The porcine eustachian tube was seen to be cartilaginous throughout its length in contrast to the part osseous, part cartilaginous structure found in man; the porcine ossicles were slightly different in shape to those of man and the air cell system was situated inferior to the tympanic cavity in the pig as opposed to posteriorly in man. This paper describes the structure and morphology of the pig middle ear cavity and compares and contrasts it with that of man. The minor differences observed are of anatomical importance but do not diminish the usefulness of the pig middle ear cleft as a potential model for human middle ear disorders.

Animals↗
PubMed1998

Axillary granular parakeratosis.

A 54-year-old woman had a 3 year history of a recurrent bilateral axillary rash during the summer months. Both axillae showed hyperkeratotic, fissured and cobblestone plaques. Skin biopsy showed the histology previously defined as axillary granular parakeratosis. This finding may indeed represent an unusual contact reaction to anti-perspirants interfering with epidermal keratinization.

Axilla↗
PubMed1998

Effect of exercise on erythrocyte beta-adrenergic receptors and plasma concentrations of catecholamines and thyroid hormones in Thoroughbred horses.

The effects of exercise stress on erythrocyte beta-adrenergic receptor characteristics and plasma concentrations of adrenaline, noradrenaline and thyroid hormones were studied in Thoroughbred racehorses during rest and after exercise. Five minutes after a maximal speed race of 1200 +/- 200 m (mean +/- s.d.), both plasma adrenaline and noradrenaline concentrations increased with respect to basal values (from 2.48 +/- 0.15 to 3.83 +/- 0.27 and from 2.13 +/- 0.11 to 3.53 +/- 0.27 nmol/l respectively). The increment of adrenaline was greater in high performance (HP) as compared to low performance (LP) horses (76.9 vs. 43.5%), in accordance with the contribution of the adrenal medulla in the sympathoadrenal response to exercise. Triiodothyronine (T3), but not thyroxine (T4) levels increased 5 min after exercise (from 55.6 +/- 2.9 to 81 +/- 3.7 ng/dl and from 0.67 +/- 0.04 to 0.70 +/- 0.05 micrograms/dl respectively). No differences were observed in basal values of thyroid hormones or in the percentage of T3 increment, when comparing HP vs. LP horses. Erythrocyte membranes obtained 5 min after racing showed decreased concentrations of beta-adrenergic receptors (beta-AR) and dissociation constant as compared to basal values (50.1 +/- 7.0 vs. 95.7 +/- 12.0 fmol/mg protein and 0.97 +/- 0.24 vs. 2.04 +/- 0.3 nmol/l respectively). This temporal pattern suggest that the observed changes in beta-AR characteristics could be mediated by catecholamines, but not by thyroid hormones, in this model. This down regulation of beta-AR may act as a protecting mechanism preventing the erythrocytes from the decrease in membrane fluidity known to be provoked by adrenergic agonists. The accomplished study showed that, in the Thoroughbred horse, there is a homeostatic response to race stress, characterised by a sudden increase in plasma catecholamines and T3 and a parallel decrease in beta-AR concentration on the erythrocyte membrane. In this way the racing horse could rapidly adjust its metabolism to the exercise stress, but at the same time override one possible undesirable side-effect caused by these hormonal changes. Further studies will be required to establish performance-related differences occurring in endocrine changes.

Animals↗
PubMed1998

Relative abundance of organochlorine pesticides and polychlorinated biphenyls in adipose tissue and serum of women in Long Island, New York.

Some organochlorine pesticides (OCPs) and PCBs are under investigation as possible risk factors for breast cancer because of their estrogenic properties and widespread presence in the environment. It is important to know whether adipose tissue used by some investigators and serum assays used by others can provide comparable information on body burden. Concentrations of seven OCPs or their breakdown products as well as 14 PCB congeners were measured in the adipose tissue and serum of 293 women enrolled as controls in a case-control study of environmental factors for breast cancer in Long Island, New York, a high-risk region. Adipose OCP/PCB levels were measured using a supercritical fluid extraction method developed by the authors. 1,1-Dichloro-2,2-di(4-chlorophenyl)ethylene (p,p'-DDE) was detected in all adipose and serum samples; two chlordane derivatives, beta-hexachlorocyclohexane (a lindane isomer) and hexachlorobenzene, were detected in at least 92% of adipose samples. The di-ortho hexachlorinated PCB congeners 2,4,5,2',4',5'-hexachlorobiphenyl and 2,3,4,2',4',5'-hexachlorobiphenyl were detected in all adipose and over 98% of serum samples. 1,1-Dichloro-2,2-di(4-chlorophenyl)ethylene comprised 77% of total pesticide residues in adipose and 71% in serum. 2,4,5,2',4',5'-Hexachlorobiphenyl comprised 24% of adipose and 21% of serum PCBs. The relative concentration patterns of the 14 PCB congeners were similar to those reported in other human studies and were also typical of patterns reported in environmental samples from various biota, including mammals and birds, but differed substantially from patterns reported in occupationally exposed workers. All adipose-serum correlations for pesticides and most PCBs were statistically significant. Either serum or adipose OCP/PCB levels of a variety of environmental organochlorine compounds may serve as useful biomarkers of body burden.

Adipose Tissue↗