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Biomedical subjects

R B Hill

Publications and source records attributed to R B Hill.

At least 19 recordsLinked to original sources
PubMed2001

Bcl-xL promotes the open configuration of the voltage-dependent anion channel and metabolite passage through the outer mitochondrial membrane.

The diffusion of metabolites across the outer mitochondrial membrane is essential for coupled cellular respiration. The outer membrane of mitochondria isolated from growth factor-deprived cells is impaired in its ability to exchange metabolic anions. When added to mitochondria, recombinant Bcl-x(L) restores metabolite exchange across the outer membrane without inducing the loss of cytochrome c from the intermembrane space. Restoration of outer membrane permeability to anionic metabolites does not occur directly through Bcl-x(L) ion channels. Instead, recombinant Bcl-x(L) maintains the outer mitochondrial membrane channel, VDAC, in an open configuration. Consistent with these findings, when ADP-induced oxidative phosphorylation is limited by exogenous beta-NADH, recombinant Bcl-x(L) can sustain outer mitochondrial membrane permeability to ADP. beta-NADH limits respiration by promoting the closed configuration of VDAC. Together these results demonstrate that following an apoptotic signal, Bcl-x(L) can maintain metabolite exchange across the outer mitochondrial membrane by inhibiting VDAC closure.

Adenosine Diphosphate↗
PubMed2001

Suppression of spontaneous and hydrogen peroxide-induced mutagenesis by the antioxidant ascorbate in mismatch repair-deficient human colon cancer cells.

Genomic instability associated with deficiencies in mismatch repair (MMR) plays a critical role in tumorigenesis. Here we have investigated the contribution of oxidative damage to this instability in MMR-defective cells. Treatment with H(2)O(2) produced less cytotoxicity in MMR-deficient cells than in those proficient in MMR, supporting a role for MMR in the recognition and/or processing of oxidative damage. Additionally, growth of MMR-defective cells in the presence of the antioxidant ascorbate (500 microM) reduced the spontaneous mutation rate at the hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus by up to 50% and reduced microsatellite instability by 30%. Induction of HPRT mutants by exogenously added H(2)O(2) was also significantly suppressed by ascorbate. Collectively, these results suggest that (i) oxidative damage contributes significantly to the spontaneous mutator phenotype in MMR-defective cells, (ii) this damage may select for MMR-deficient cells due to their increased resistance to cell killing and (iii) dietary antioxidants may help to suppress the mutator phenotype and resulting carcinogenesis in individuals with compromised MMR.

Antimetabolites, Antineoplastic↗
PubMed2001

Role of Ca(2+) in excitation-contraction coupling in echinoderm muscle: comparison with role in other tissues.

The longitudinal muscle of the body wall of Isostichopus badionotus may be considered a model for excitation-contraction coupling in echinoderm muscle. Other echinoderm muscles are reviewed by comparison with the model. Echinoderm muscle is also of interest as a model for 'mutable collagenous tissue'; however, in that tissue, Ca(2+) has been proposed to function both in living control systems and in regulation of non-living interstitial substance.

Animals↗
PubMed2000

A polar, solvent-exposed residue can be essential for native protein structure.

BACKGROUND: A large energy gap between the native state and the non-native folded states is required for folding into a unique three-dimensional structure. The features that define this energy gap are not well understood, but can be addressed using de novo protein design. Previously, alpha(2)D, a dimeric four-helix bundle, was designed and shown to adopt a native-like conformation. The high-resolution solution structure revealed that this protein adopted a bisecting U motif. Glu7, a solvent-exposed residue that adopts many conformations in solution, might be involved in defining the unique three-dimensional structure of alpha(2)D. RESULTS: A variety of hydrophobic and polar residues were substituted for Glu7 and the dynamic and thermodynamic properties of the resulting proteins were characterized by analytical ultracentrifugation, circular dichroism spectroscopy, and nuclear magnetic resonance spectroscopy. The majority of substitutions at this solvent-exposed position had little affect on the ability to fold into a dimeric four-helix bundle. The ability to adopt a unique conformation, however, was profoundly modulated by the residue at this position despite the similar free energies of folding of each variant. CONCLUSIONS: Although Glu7 is not involved directly in stabilizing the native state of alpha(2)D, it is involved indirectly in specifying the observed fold by modulating the energy gap between the native state and the non-native folded states. These results provide experimental support for hypothetical models arising from lattice simulations of protein folding, and underscore the importance of polar interfacial residues in defining the native conformations of proteins.

Dimerization↗
PubMed2000

Sexual behaviour and contraception among unmarried adolescents and young adults in Greater Accra and Eastern regions of Ghana.

A fertility survey of unmarried adolescents and young adults (953 males and 829 females) in Greater Accra and Eastern regions of Ghana revealed that a substantial proportion of the respondents were sexually experienced. Overall, 66.8% of the males and 78.4% of the females were sexually experienced. The mean ages (+/- SD) of the males and females were 15.5 +/- 2.5 and 16.2 +/- 2.0 years, respectively. Most respondents claimed to have received adequate information on reproductive health and sexually transmitted diseases (STDs), including AIDS. However, 20% and 30% of the respondents in peri-urban and rural areas, respectively, did not know that a girl could get pregnant the first time she has sexual intercourse. The incidence of pregnancy among the unmarried female respondents was relatively high (37%), and was higher in urban than in rural areas. Approximately 47% of those who had ever been pregnant reported that they had had an abortion. Levels of contraceptive awareness were high (98.2% among males and 95.5% among females) but many still engaged in unprotected sexual relations. The most commonly used methods were the condom and the pill. The main reasons given for non-use were that they did not think about contraception, were concerned about the safety of contraceptives, and partner objection. These findings point to the need for targeting of unmarried adolescents and young adults with information on reproductive health and family planning to increase their awareness of the risks of pregnancy, STDs and HIV infection.

Abortion, Induced↗
PubMed2000

De novo design of helical bundles as models for understanding protein folding and function.

De novo protein design has proven to be a powerful tool for understanding protein folding, structure, and function. In this Account, we highlight aspects of our research on the design of dimeric, four-helix bundles. Dimeric, four-helix bundles are found throughout nature, and the history of their design in our laboratory illustrates our hierarchic approach to protein design. This approach has been successfully applied to create a completely native-like protein. Structural and mutational analysis allowed us to explore the determinants of native protein structure. These determinants were then applied to the design of a dinuclear metal-binding protein that can now serve as a model for this important class of proteins.

Chemical Phenomena↗
PubMed1999

Serum concentrations of insulin, insulin-like growth factor-I and insulin-like growth factor binding proteins are different between white and African American girls.

OBJECTIVES: To determine whether serum insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP) concentrations are different between African American and white girls. STUDY DESIGN: Serum glucose and hormone concentrations were measured in blood samples collected after a 12-hour fast from 79 white and 57 African American healthy girls between 9 and 17 years of age. Tanner stages of pubic hair development were evaluated by physical examination, and body composition by dual energy x-ray absorptiometry. RESULTS: The African American girls were older and sexually more mature and had higher fat mass, higher serum insulin and free IGF-I concentrations, higher serum free IGF-I to total IGF-I ratio, but lower serum IGFBP-1 concentrations than the white girls. After controlling for sexual maturation and fat mass, the serum concentrations of total IGF-I, bound IGF-I, and IGFBP-3 in the white girls became significantly higher than those in the African American girls. The higher concentrations of total IGF-I in the white girls were due to a proportional increase in the concentrations of bound IGF-I that coincided with a similar increase in serum IGFBP-3 concentrations. CONCLUSIONS: Higher serum insulin concentrations in the African American girls are associated with lower serum IGFBP-1 concentrations and increased bioavailability of free IGF-I, which may contribute to their accelerated growth compared with their white counterparts.

Absorptiometry, Photon↗
PubMed1999

The interaction between RTX toxins and target cells.

RTX toxins are important virulence factors produced by a wide range of Gram-negative bacteria. They fall into two categories: the hemolysins, which affect a variety of cell types, and the leukotoxins, which are cell-type- and species-specific. These toxins offer interesting models for targeting, insertion and translocation of aqueous proteins into lipid membranes.

Animals↗
PubMed1999

Validity of self-assessment of pubertal maturation in African American and European American adolescents.

PURPOSE: To evaluate interobserver reliability of physician assessments of pubertal maturation and to evaluate the validity of self-assessment compared to physician assessments of pubertal maturation by girls in a multiethnic sample. METHODS: The study design is descriptive. A total of 107 8-17-year-old healthy volunteers from settings with large minority populations in the Houston metropolitan area were recruited for a study on adolescents' energy needs. The two outcome measures were interobserver reliability between two physicians' assessments of breast and pubic hair, and the self-assessment of breast and pubic hair maturation compared to physicians' assessments. RESULTS: The kappa coefficient for physician interobserver agreement for breast maturation was 0.5. The kappa coefficient for physician interobserver agreement for assessment of pubic hair was 0.79. The kappa coefficient for the validity of self-assessment of breast development was 0.34, and that for self-assessment of pubic hair was 0.37. CONCLUSION: Interobserver agreement for physician assessment of breast maturation was low and self-assessment of breast maturation was not reliable in this group of adolescent girls. However, whereas physician interobserver agreement for pubic hair was good, self-assessment of pubic hair maturation was not reliable in this group of adolescent girls.

Adolescent↗
PubMed1999

Pubertal African-American girls expend less energy at rest and during physical activity than Caucasian girls.

Between 1963 and 1991, the most dramatic increases in the prevalence of overweight in the United States have been reported in African-American girls. Lower basal energy expenditure and lack of physical activity are believed to be risk factors for excessive weight gain. We hypothesized that energy expenditure at rest and during physical activity are lower in pubertal African-American girls than in Caucasian girls. Basal metabolic rate and sleeping energy expenditure of 40 Caucasian and 41 African-American pubertal girls (matched for age, physical characteristics, body fat, and energy intake) were measured by whole-room calorimetry, energy expended for physical activity by the doubly labeled water method, sexual maturity by physical examination, body composition by dual-energy x-ray absorptiometry, physical fitness by treadmill testing, and energy intake by 3-day food record. After adjusting for soft lean tissue mass, the basal energy expenditure (1333 +/- 132 vs. 1412 +/- 132 kcal/day, P = 0.01) and energy expended for physical activity (809 +/- 637 vs. 1271 +/- 162 kcal/day, P < 0.01) were significantly lower in the African-American girls than in the Caucasian girls. The differences remained the same after controlling for differences in sexual maturity and/or physical fitness. The lower energy expenditure of the pubertal African-American girls suggests that they are at a higher risk of becoming overweight than their Caucasian counterparts.

Adolescent↗
PubMed1999

Teachers' personalities and students' behavior in referrals for special education.

84 regular classroom teachers completed four self-report personality scales (self-concept, tolerance, locus of control, and teachers' efficacy) and reviewed hypothetical records of three types of students (withdrawn, acting-out, and neutral) and made decisions for referral for each student to special education. Scores for self-concept, tolerance, locus of control, and teachers' efficacy were not related to their decisions to refer across types of students.

Adult↗
PubMed1998

Fewer chromosome aberrations and earlier apoptosis induced by DNA synthesis inhibitors, a topoisomerase II inhibitor or alkylating agents in human cells with normal compared with mutant p53.

The human lymphoblastoid cell lines TK6 (normal p53) and WI-L2-NS or WTK1 (mutant p53) differ in sensitivity to killing and induction of gene mutations and chromosome aberrations by ionizing radiation. This may be related to decreased apoptosis in the cells with mutated p53, such that more damaged cells survive. We compared the response of the two cell types to various chemicals. First, to ensure that the thymidine kinase deficiency does not increase the sensitivity of TK6 tk+/- cells to mutagens, we demonstrated that they were not hypersensitive to aberration induction by altered DNA precursor pools or DNA synthesis inhibition, by aphidicolin (APC), methotrexate, hydroxyurea (HU), cytosine arabinoside and thymidine. TK6 cells were then compared with WI-L2-NS or WTK1 cells. With APC, HU, methyl methanesulfonate (MMS), ethyl nitrosourea (ENU) and etoposide (etop), TK6 cells had more apoptosis in the first two days after treatment. Fewer aberrations were seen in normal p53 TK6 cells than the mutant p53 WI-L2-NS cells, ranging from very little difference between the two cell types with MMS to very large differences with ENU and etop. For MMS and ENU we followed cultures for several days, and found that WI-L2-NS cells underwent delayed apoptosis 3 to 5 days after treatment, in parallel with published observations with ionizing radiation. WI-L2-NS cells also had a delayed increase in aberrations (up to 5 days post-treatment) when no aberrations remained in TK6 cells. Colony forming efficiency was measured for APC, MMS and ENU, and was greater in the p53 mutant cells. Our results show that normal p53 function is required for rapid and efficient apoptosis in these lymphoblastoid cells with DNA synthesis inhibitors, alkylating agents and a topoisomerase II inhibitor, and support the hypothesis that induced levels of aberrations are higher in p53 mutant cells because of a failure to remove damaged cells by apoptosis.

Alkylating Agents↗
PubMed1998

Serum leptin concentrations in Caucasian and African-American girls.

Because African-American girls are heavier, taller, and mature earlier than Caucasian girls, we hypothesized that the serum leptin concentration differs between the two groups. Serum leptin concentrations were measured by immunoassay in 12-h fasted blood samples collected from 79 Caucasian and 57 African-American girls between 8 and 17 yr of age. Body composition was measured by dual-energy x-ray absorptiometry, sexual maturity by physical examination, and physical fitness by treadmill testing. Serum leptin concentrations were positively correlated (P < 0.01) with maturation, body fatness, and insulin and were higher (6.6 ng/mL, P < 0.01) in the African-American girls after adjusting for age. The difference remained significant (P < 0.01) but was reduced to 3.2 ng/mL after controlling for differences in maturation, fat mass, and physical fitness. The higher serum leptin levels might play an important role in the accelerated growth and sexual maturation of African-American girls.

Adolescent↗
PubMed1998

Chromosome aberrations in vitro related to cytotoxicity of nonmutagenic chemicals and metabolic poisons.

Chromosome aberrations can occur by secondary mechanism(s) associated with cytotoxicity, induced by chemicals that do not attack DNA. Aberrations are formed from DNA double-strand breaks, and DSBs are known to be induced by nonmutagenic (Ames test negative) noncarcinogens at toxic levels [Storer et al. (1996): Mutat Res 368:59-101]. Here, 8 of 12 of these chemicals caused aberrations in CHO cells at cytotoxic doses, and often only when cell counts (survival) at 20 hr approached < or =50% of controls. Five of eight noncarcinogens (2,4,-dichlorophenol, dithiocarb, menthol, phthalic anhydride, and ethionamide) and one of two equivocal carcinogens (bisphenol A) caused aberrations, usually over a narrow dose range with steeply increasing cytotoxicity. Phthalic anhydride and ethionamide were positive only at doses with precipitate. Phenformin was negative even at toxic doses and ephedrine and phenylephrine were negative and gave little toxicity. Aberrations were also induced by metabolic poisons, 2,4-dinitrophenol, (uncouples oxidative phosphorylation), and sodium iodoacetate, (Nal; blocks ATP production). Five of the chemicals that induced aberrations in CHO cells were tested in human TK6 cells and four were positive, the fifth being equivocal. Stable aberrations (translocations) were induced in human cells by Nal. Clearly, chemicals can give "false-positive" results in the chromosome aberration assay at cytotoxic levels, though cytotoxicity does not always produce aberrations, so that further information (e.g., DNA reactivity) is needed to determine whether a result is a "false-positive." Primary DNA-damaging chemicals such as alkylators are also cytotoxic, but give strong increases in aberrations without marked initial toxicity by the measures used here, although the aberrations they induce do reduce long-term survival in colony-forming assays.

Animals↗
PubMed1997

Thalidomide: lack of mutagenic activity across phyla and genetic endpoints.

The human and rabbit teratogen thalidomide has been tested for mutagenicity in a wide range of assays, ranging from bacterial gene mutation assays conducted in vitro to in vivo cytogenetic assays conducted using rabbits, and including a variety of human-derived tissues. Thalidomide was not mutagenic to 6 strains of Salmonella when tested both in the presence and absence of Aroclor-induced rat liver S9 mix. This inactivity was confirmed in strains TA98 and TA100 using a 1-h pre-incubation assay protocol with the same S9 mix (10% S9), and additionally, in strain TA98 using 3 concentrations of S9 (4%, 10% and 30% S9 in S9 mix). Thalidomide was not clastogenic either to cultured human lymphocytes (whole blood cultures, minus S9 mix) or to Chinese hamster ovary (CHO) cells treated in vitro. Further, no cytotoxicity was observed in purified human lymphocytes when exposed to thalidomide up to the limit of its solubility in the medium in the presence and absence of liver S9 from Aroclor-induced pregnant rabbit. The CHO assays were conducted without metabolic activation and in the presence of a variety of sources of auxiliary metabolic activation (PB/beta NP-induced rat liver S9 mix, pooled male and female human liver S9 mix, uninduced and Aroclor-induced pregnant rabbit liver S9 mix and foetal rabbit S9 mix). Thalidomide did not induce micronuclei in isolated human lymphocytes (minus S9 mix) and it was non-mutagenic to mouse lymphoma L5178Y TK+/- cells when tested to the limits of its solubility in the culture medium (+/- S9 mix). No indication of recombinogenic or clastogenic activity was observed for thalidomide when tested in Drosophila. In addition, it failed to induce chromosome aberrations in grasshopper neuroblasts when tested in the presence and absence of Aroclor-induced rat liver S9 mix. Some unusual chromosome morphologies were observed in the grasshopper cytogenetic preparations indicating a potential of thalidomide to interact with chromosomal proteins. However, this potential was not evident in the human lymphocyte micronucleus assay, and thalidomide was apparently not reactive to the proteins of the mouse skin, as it gave negative results in a mouse local lymph node assay for skin sensitizing agents. Thalidomide was inactive in bone marrow micronucleus assays conducted using males and females from two strains of mice, and female New Zealand white rabbits. It is concluded that thalidomide is neither a mutagen nor an aneugen. This conclusion is discussed within the context of the results of earlier mutagenicity studies, the recent claim that thalidomide may be a heritable germ cell mutagen to humans, and the current interest in thalidomide for the treatment of immune system-related diseases.

Abnormalities, Drug-Induced↗
PubMed1997

Alpha-1 acid glycoprotein is an immunosuppressive factor found in ascites from ovaria carcinoma.

BACKGROUND: Although the ascites of patients with ovarian carcinoma has been reported to contain immunosuppressive factors, the identity and source of this activity has not been fully elucidated. The objective of this study was to describe the purification of a single immunosuppressive protein, alpha-1 acid glycoprotein, from ovarian carcinoma ascites, identify its site of production, and describe a possible mechanism by which it inhibits lymphocytes. METHODS: Ascites from proteins from five patients with epithelial ovarian carcinoma first were differentially precipitated by size with different concentrations of polyethylene glycol and then separated on the basis of isoelectric focusing. The protein factions then were placed in a lymphocyte proliferation assay to determine immunosuppressive activity. Western blot analysis was used to identify alpha-1 acid glycoprotein as an immunosuppressive protein in ascites. Total RNA was extracted from ovarian and hepatic cell lines as well as primary and recurrent ovarian tumor samples. Reverse-transcriptase polymerase chain reaction then was utilized to identify the site of production of this protein. Purified alpha-1 acid glycoprotein was placed in lymphocyte culture and its effects on lymphocyte interleukin-2 (IL-2) production were measured by enzyme-linked immunoadsorbent assay. RESULTS: Addition of purified alpha-1 acid glycoprotein to the lymphocyte assay resulted in a 60% decrease in lymphocyte proliferation (P < 0.05). Alpha-1 acid glycoprotein transcript was not identified in ovarian tumor cells. The addition of purified alpha-1 acid glycoprotein to the lymphocyte culture resulted in a 65% decrease in IL-2 secretion into the media (P < 0.05). CONCLUSIONS: Alpha-1 acid glycoprotein is an immunosuppressive protein purified from ovarian carcinoma ascites. It is not expressed primarily by ovarian carcinoma cells. It appears to inhibit IL-2 secretion by lymphocytes.

Ascites↗
PubMed1997

The in vitro effect on T cell function of soluble IL-2Ralpha from advanced ovarian cancer ascites.

Activated T cells not only secrete interleukin-2 (IL-2) and express cell surface interleukin 2 receptor alpha (IL-2R alpha), but also shed IL-2R alpha. This soluble receptor is a truncated form of the membrane-bound p55 receptor with a similar binding affinity. It has been proposed that soluble IL-2R alpha (sIL-2R alpha) could negatively modulate local immune response. High levels of sIL-2R alpha have been found in the serum and ascites of ovarian cancer patients. The purpose of this investigation is to determine the amount of in vitro T cell inhibition seen in ovarian cancer ascites that is attributable to high levels of sIL-2R alpha. Purified sIL-2R alpha at levels up to 100,000 pg/ml was placed in lymphocyte proliferation assays. Soluble IL-2R alpha was removed from the ascites of three patients with advanced ovarian cancer. Lymphocyte proliferation assays utilizing phytohemaglutin (PHA) stimulation were carried out with this ascites. Untreated ascites from each patient served as control. Addition of purified sIL-2R alpha to lymphocyte proliferation assays failed to demonstrate significant lymphocyte suppression. Addition of ascites to the lymphocyte assays resulted in up to an 80% decrease in lymphocyte proliferation. Neutralization of ascites sIL-2R alpha as well as removal of sIL-2R alpha via a protein G column failed to reverse any of the observed lymphocyte suppression. We conclude that although sIL2R alpha is elevated in ascites of patients with ovarian cancer, it does not account for the profound ascites-induced T cell suppression observed in vitro.

Adult↗