PubMed Health⌕ Search

Biomedical subjects

S M Miller

Publications and source records attributed to S M Miller.

At least 55 records · Page 3Linked to original sources
PubMed2000

Carbon monoxide and nitric oxide as coneurotransmitters in the enteric nervous system: evidence from genomic deletion of biosynthetic enzymes.

Nitric oxide (NO) and carbon monoxide (CO) seem to be neurotransmitters in the brain. The colocalization of their respective biosynthetic enzymes, neuronal NO synthase (nNOS) and heme oxygenase-2 (HO2), in enteric neurons and altered intestinal function in mice with genomic deletion of the enzymes (nNOS(Delta/Delta) and HO2(Delta/Delta)) suggest neurotransmitter roles for NO and CO in the enteric nervous system. We now establish that NO and CO are both neurotransmitters that interact as cotransmitters. Small intestinal smooth muscle cells from nNOS(Delta/Delta) and HO2(Delta/Delta) mice are depolarized, with apparent additive effects in the double knockouts (HO2(Delta/Delta)/nNOS(Delta/Delta)). Muscle relaxation and inhibitory neurotransmission are reduced in the mutant mice. In HO2(Delta/Delta) preparations, responses to electrical field stimulation are nearly abolished despite persistent nNOS expression, whereas exogenous CO restores normal responses, indicating that the NO system does not function in the absence of CO generation.

Animals↗
PubMed2000

Chemistry and insulin-mimetic properties of bis(acetylacetonate)oxovanadium(IV) and derivatives.

The syntheses and the solid state structural and spectroscopic solution characterizations of VO(Me-acac)2 and VO(Et-acac)2 (where Me-acac is 3-methyl-2,4-pentanedionato and Et-acac is 3-ethyl-2,4-pentanedionato) have been conducted since both VO(acac)2 and VO(Et-acac)2 have long-term in vivo insulin-mimetic effects in streptozotocin-induced diabetic Wistar rats. X-ray structural characterizations of VO(Me-acac)2 and VO(Et-acac)2 show that both contain five-coordinate vanadium similar to the parent VO(acac)2. The unit cells for VO(Et-acac)2 and VO(Me-acac)2 are both triclinic, P1, with a = 9.29970(10) A, b = 13.6117(2) A, c = 13.6642(2) A, alpha = 94.1770(10) degrees, beta = 106.4770(10) degrees, gamma = 106.6350(10) degrees for VO(Et-acac)2 and a = 7.72969(4) A, b = 8.1856(5) A, c = 11.9029(6) A, alpha = 79.927(2) degrees, beta = 73.988(2)degrees, gamma = 65.1790(10)degrees for VO(Me-acac)2. The total concentration of EPR-observable vanadium(IV) species for VO(acac)2 and derivatives in water solution at 20 degreesC was determined by double integration of the EPR spectra and apportioned between individual species on the basis of computer simulations of the spectra. Three species were observed, and the concentrations were found to be time, pH, temperature, and salt dependent. The three complexes are assigned as the trans-VO(acac)2.H2O adduct, cis-VO(acac)2.H2O adduct, and a hydrolysis product containing one vanadium atom and one R-acac- group. The reaction rate for conversion of species was slower for VO(acac)2 than for VO(malto)2, VO(Et-acac)2, and VO(Me-acac)2; however, in aqueous solution the rates for all of these species are slow compared to those of other vanadium species. The concentration of vanadium(V) species was determined by 51V NMR. The visible spectra were time dependent, consistent with the changes in species concentrations that were observed in the EPR and NMR spectra. EPR and visible spectroscopic studies of solutions prepared as for administration to diabetic rats documented both a salt effect on speciation and formation of a new halogen-containing complex. Compound efficacy with respect to long-term lowering of plasma glucose levels in diabetic rats traces the concentration of the hydrolysis product in the administration solution.

Animals↗
PubMed2000

Random distribution of mixed species malaria infections in Papua New Guinea.

Plasmodium falciparum (Pf), P. vivax (Pv), P. malariae (Pm), and P. ovale (Po) infections are endemic in coastal areas of Papua New Guinea. Here 2,162 individuals living near Dreikikir, East Sepik Province, have been analyzed for complexity of malaria infection by blood smear and polymerase chain reaction (PCR) diagnoses. According to blood smear, the overall prevalence of Plasmodium infection was 0.320. Most individuals (0.283) were infected with a single species only. The prevalence of mixed species infections was low (0.037). Further analysis of a 173-sample subset by nested PCR of small subunit ribosomal DNA resulted in an overall 3.0-fold increase in prevalence of infection, with a 17.5-fold increase in the frequency of mixed species infections. Among mixed species infections detected by PCR, the frequency of double species was 0.364, and that of triple species was 0.237. Nine individuals (0.052) were infected with all 4 species. To determine if infection status (uninfected, single, and multiple infections) deviates from an independent random distribution (null hypothesis), observed versus expected frequencies of all combinations of Plasmodium species infections, or assemblages (Pf-, Pv-, Pm-, Po-, to Pf+, Pv+, Pm+, Po+), were compared using a multiple-kind lottery model. All 4 species were randomly distributed whether diagnosed by blood smear or PCR in the overall population and when divided into age group categories. These findings suggest that mixed species malaria infections are common, and that Plasmodium species appear to establish infection independent of one another.

Animals↗
PubMed1999

Emergence of FY*A(null) in a Plasmodium vivax-endemic region of Papua New Guinea.

In Papua New Guinea (PNG), numerous blood group polymorphisms and hemoglobinopathies characterize the human population. Human genetic polymorphisms of this nature are common in malarious regions, and all four human malaria parasites are holoendemic below 1500 meters in PNG. At this elevation, a prominent condition characterizing Melanesians is alpha(+)-thalassemia. Interestingly, recent epidemiological surveys have demonstrated that alpha(+)-thalassemia is associated with increased susceptibility to uncomplicated malaria among young children. It is further proposed that alpha(+)-thalassemia may facilitate so-called "benign" Plasmodium vivax infection to act later in life as a "natural vaccine" against severe Plasmodium falciparum malaria. Here, in a P. vivax-endemic region of PNG where the resident Abelam-speaking population is characterized by a frequency of alpha(+)-thalassemia >/=0.98, we have discovered the mutation responsible for erythrocyte Duffy antigen-negativity (Fy[a-b-]) on the FY*A allele. In this study population there were 23 heterozygous and no homozygous individuals bearing this new allele (allele frequency, 23/1062 = 0.022). Flow cytometric analysis illustrated a 2-fold difference in erythroid-specific Fy-antigen expression between heterozygous (FY*A/FY*A(null)) and homozygous (FY*A/FY*A) individuals, suggesting a gene-dosage effect. In further comparisons, we observed a higher prevalence of P. vivax infection in FY*A/FY*A (83/508 = 0.163) compared with FY*A/FY*A(null) (2/23 = 0.087) individuals (odds ratio = 2.05, 95% confidence interval = 0.47-8.91). Emergence of FY*A(null) in this population suggests that P. vivax is involved in selection of this erythroid polymorphism. This mutation would ultimately compromise alpha(+)-thalassemia/P. vivax-mediated protection against severe P. falciparum malaria.

Animals↗
PubMed1999

Complement-mediated lesion of sympathetic ganglia in vitro with acetylcholinesterase antibodies.

When administered to rats, antibodies against acetylcholinesterase (AChE) selectively destroy presynaptic inputs to sympathetic ganglia. To investigate the mechanism of this immunolesion, we created an in vitro system in which relevant components could be manipulated. Freshly dissected rat superior cervical ganglia (SCG) were incubated 15-20 h at 37 degrees C in fresh human serum (a potent source of complement) with continuous oxygenation. More than 96% of neurons in six control ganglia retained synaptic inputs, as defined by action potentials or excitatory postsynaptic potentials (EPSP) upon stimulation of the preganglionic trunk. However, when anti-AChE antibodies were present (0.16 mg/ml), none of 61 neurons from six incubated ganglia showed synaptic responses although membrane potential and input resistance remained normal. Staining for AChE and synaptophysin (a synaptic vesicle marker) was also disrupted in ganglia exposed to AChE antibodies in complement-sufficient serum. When complement was eliminated by substituting serum that was heat-inactivated or deficient in C3, synaptic input was retained in 60-90% of neurons incubated with AChE antibodies. Choline acetyltransferase activity (ChAT), an enzymatic marker of cholinergic cytoplasm in sympathetic ganglia, was largely lost after incubation with AChE antibodies and serum. However, incubation with AChE antibodies in heat-inactivated serum, or serum that was deficient in C3 or C8, caused no measurable loss of ganglionic ChAT activity. These findings strongly implicate the complement cascade in the destruction of preganglionic sympathetic terminals that follows binding of AChE antibodies.

Acetylcholinesterase↗
PubMed1999

No metal cofactor in orotidine 5'-monophosphate decarboxylase.

Orotidine 5'-monophosphate decarboxylase (OMP decarboxylase, ODCase) is an important enzyme that catalyzes the final step of de novo pyrimidine nucleotide biosynthesis. The mechanism of this unique enzyme and whether metal ions play any role in catalysis have been topics of intense research interest. In this report, the role of Zn in ODCase was reexamined. Atomic absorption (AA) and X-ray absorption (XAS) spectroscopic studies did not detect zinc in active enzyme samples at high concentration. The XAS results also indicated the absence of other transition metal ions in ODCase.

Catalysis↗
PubMed1999

Investigation of the kinetic mechanism of cytidine 5'-monophosphate N-acetylneuraminic acid synthetase from Haemophilus ducreyi with new insights on rate-limiting steps from product inhibition analysis.

The presence of sialic acid as a component of cell surface lipooligosaccharides or capsular polysaccharides has been shown to be correlated with the virulence of a number of Gram-negative mucosal pathogens, including several Haemophilus and Neisseria spp. As part of our efforts to evaluate the role of sialic acid in the pathobiology of these organisms, we have initiated studies of the enzymes from Haemophilus ducreyi (the infectious agent of chancroid) responsible for the activation and attachment of sialic acid to the lipooligosaccharide. In this report, we describe results of an investigation of the steady-state kinetic mechanism of the activating enzyme, cytidine 5'-monophosphate N-acetylneuraminic acid (CMP-NeuAc) synthetase. Using a combination of initial velocity, product inhibition, and dead-end inhibition studies, the reaction is shown to be freely reversible and to proceed through an ordered bi-bi kinetic mechanism in which CTP binds first and CMP-NeuAc dissociates last. In addition, a detailed analysis of the kinetic expressions for the observable constants is presented showing how the variation in apparent product inhibition constants (Kii) can be used to predict the rate-limiting step in kcat, which appears to be dissociation of CMP-NeuAc in this enzyme. To our knowledge, this relationship has not been previously recognized.

Binding, Competitive↗
PubMed1999

Leptin receptor immunoreactivity in sympathetic prevertebral ganglion neurons of mouse and rat.

Prevertebral ganglia, comprising the inferior mesenteric, superior mesenteric and celiac ganglia, contain the cell bodies of sympathetic neurons that regulate gastrointestinal motility, visceral blood flow, secretion and absorption. In the present study, we report the presence of leptin receptor-like immunoreactivity in the superior mesenteric and celiac ganglia of mice and rats. Ganglion neurons were immunopositive for leptin receptor. Confocal microscopy and three-dimensional (3-D) reconstruction of ganglion neurons filled with Lucifer yellow and then immunostained for leptin receptor showed that leptin receptor immunoreactivity was intracellular and that it was present on structures encircling the nucleus. These results raise the possibility that leptin may affect gastrointestinal function by acting on leptin receptors located in prevertebral ganglion neurons.

Animals↗
PubMed1999

Alternative routes for entry of HgX2 into the active site of mercuric ion reductase depend on the nature of the X ligands.

Wild-type mercuric ion reductase (CCCC enzyme) possesses four cysteines in each of its Hg(II) binding sites, a redox-active pair and a C-terminal pair. Mutation of the C-terminal cysteines to alanines (CCAA enzyme) leads to a loss of steady-state mercuric ion reductase activity using Hg(SR)2 substrates. However, CCCC and CCAA enzymes exhibit an equally high rate of binding and turnover using HgBr2 as substrate under pre-steady-state conditions [Engst and Miller (1998) Biochemistry 37, 11496-11507.]. Since the ligands in these HgX2 substrates differ both in size and in affinity for Hg(II), one or both of these properties may contribute to their different reactivities with CCAA enzyme. To further explore the importance of these two properties, we have examined the pre-steady-state reactions of CCCC and CCAA with Hg(CN)2, which has small, high-affinity ligands, and with Hg(Cys)2, which has bulky, high-affinity ligands. The results indicate that HgX2 substrates with small ligands can rapidly access the redox-active cysteines in the absence of the C-terminal cysteines, but those with large ligands require the C-terminal cysteines for rapid access. In addition, it is concluded that the C-terminal cysteines play a critical role in removing the high-affinity ligands before Hg(II) reaches the redox-active cysteines in the inner active site, since direct access of HgX2 substrates with high-affinity ligands leads to formation of an inhibited complex. Consistent with the results, both a narrow channel leading directly to the redox-active cysteines and a wider channel leading to the redox-active cysteines via initial contact with the C-terminal cysteines can be identified in the structure of the enzyme from Bacillus sp. RC607.

Binding Sites↗
PubMed1999

Decision making about prophylactic oophorectomy among at-risk women: psychological influences and implications.

OBJECTIVE: Women with a family history of ovarian cancer are confronted with difficult decisions regarding the management of their risk status. Currently, the main preventive option available is prophylactic oophorectomy. The objective of the present paper is to review research and theory on psychological factors that influence decision making about preventive surgery and discuss the implications for patient management. METHODS: Guided by a cognitive-social framework, the literature on decision making about preventive surgery is reviewed and integrated. RESULTS: The available studies show that women are more likely to opt for surgery if they feel more vulnerable to cancer, believe that surgery will prevent cancer, and are worried about developing cancer. Further, the response to ovarian risk is influenced by the individual's characteristic psychological style: monitors (who typically scan for and amplify threatening cues) tend to feel more vulnerable to cancer and more distressed about their cancer risk than blunters (who typically distract from threatening cues) do. CONCLUSION: On the basis of prior research, monitors may be more likely to choose surgical intervention to reduce their distress, without fully anticipating the psychological and medical consequences of that decision. In order to facilitate informed decision making, counseling protocols should be designed to enable the patient to understand and take account of the psychological consequences of the available medical options. Future studies are needed to systematically extend and explore the proposed theory-based relationships.

Affect↗
PubMed1999

[Reconstructive surgery of the efferent urinary tract in pelvic exenteration of gynecological tumors].

In locally advanced or recurrent tumors of the female genital tract anterior or total exenteration may be mandatory in case of tumor invasion into the lower urinary tract or if a second course of radiation therapy is not feasible. The management of resection and reconstruction of the affected lower urinary tract has to be well integrated into the gynecological therapeutic concept. In 11/32 patients the reconstruction of the partially resected lower urinary tract was feasible with preservation of a functionally intact urinary bladder. Urinary diversion following pelvic exenteration was achieved in 13/17 patients with a continent urinary reservoir and in 4/17 patients with an ileal conduit. Operative reinterventions were needed only in patients with continent urinary diversion in 5 cases. All these patients had a past history of primary radiation therapy of their gynecological tumor. In the remaining other 11 patients with a history of primary radiation therapy no complications occurred. 9 of 32 patients survived the operative procedure 40.8 (25-57) month with no evidence of recurrent tumor. Continent urinary diversion represents an excellent therapeutic option for replacement of function lost due to exenterative pelvic surgery. Stringent selection of patients is mandatory to consider the presented therapeutic concept a reasonable tool in the management of the described clinical situations.

Adult↗
PubMed1999

Specific worry about breast cancer predicts mammography use in women at risk for breast and ovarian cancer.

This longitudinal study examined predictors of mammography use among women with a family history of breast cancer participating in a risk assessment and surveillance program (N = 213). Assessed were background variables (age, prior mammography utilization), cognitive variables (perceived vulnerability), and affective variables (cancer worry and general distress). Results of logistic regression analyses predicting adherence 1 year after baseline contact, in which variables of prior utilization, feelings of vulnerability, and general distress were controlled for, indicated that cancer worry and age were significant predictors of mammography adherence. Results suggest that moderate levels of cancer worry facilitate, rather than undermine, adherence. The results have implications for the construction of educational messages that should be designed to acknowledge feelings of cancer-specific worry and to provide guidance in health protective behaviors.

Adult↗
PubMed1999

Bacterial detoxification of Hg(II) and organomercurials.

The most common bacterial mechanism for resistance to mercuric-ion species involves intracellular reduction of Hg(II) to Hg(0). Key proteins of the pathway typically include: MerR, which regulates pathway expression; MerP, which protects the external environment; MerT or MerC, which transport Hg(II) species across the inner membrane; MerA, which catalyses reduction of Hg(II); and sometimes MerB, which catalyses cleavage of C-Hg bonds in organomercurials. Cysteine residues of varying number are arranged in each of the key proteins to optimize their unique roles in sensing (high affinity), transporting (exchangeability), and reducing (redox accessibility) Hg(II). Nature's regulator of this pathway, MerR, is an exquisitely sensitive, Hg(II)-binding, DNA-binding protein that holds the system primed for immediate transcription at the slightest influx of Hg(II).

Bacteria↗
PubMed1999

regA, a Volvox gene that plays a central role in germ-soma differentiation, encodes a novel regulatory protein.

Volvox has two cell types: mortal somatic cells and immortal germ cells. Here we describe the transposon-tagging, cloning and characterization of regA, which plays a central role as a master regulatory gene in Volvox germ-soma differentiation by suppressing reproductive activities in somatic cells. The 12.5 kb regA transcription unit generates a 6,725 nucleotide mRNA that appears at the beginning of somatic cell differentiation, and that encodes a 111 kDa RegA protein that localizes to the nucleus, and has an unusual abundance of alanine, glutamine and proline. This is a compositional feature shared by functional domains of many 'active' repressors. These findings are consistent with the hypothesis that RegA acts in somatic cells to repress transcription of genes required for growth and reproduction, including 13 genes whose products are required for chloroplast biogenesis.

Algal Proteins↗
PubMed1999

glsA, a Volvox gene required for asymmetric division and germ cell specification, encodes a chaperone-like protein.

The gls genes of Volvox are required for the asymmetric divisions that set apart cells of the germ and somatic lineages during embryogenesis. Here we used transposon tagging to clone glsA, and then showed that it is expressed maximally in asymmetrically dividing embryos, and that it encodes a 748-amino acid protein with two potential protein-binding domains. Site-directed mutagenesis of one of these, the J domain (by which Hsp40-class chaperones bind to and activate specific Hsp70 partners) abolishes the capacity of glsA to rescue mutants. Based on this and other considerations, including the fact that the GlsA protein is associated with the mitotic spindle, we discuss how it might function, in conjunction with an Hsp70-type partner, to shift the division plane in asymmetrically dividing cells.

Algal Proteins↗
PubMed1998

A 'sticky' interhemispheric switch in bipolar disorder?

Despite years of research into bipolar disorder (manic depression), its underlying pathophysiology remains elusive. It is widely acknowledged that the disorder is strongly heritable, but the genetics are complex with less than full concordance in monozygotic twins and at least four susceptibility loci identified. We propose that bipolar disorder is the result of a genetic propensity for slow interhemispheric switching mechanisms that become 'stuck' in one or the other state. Because slow switches are also 'sticky' when compared with fast switches, the clinical manifestations of bipolar disorder may be explained by hemispheric activation being 'stuck' on the left (mania) or on the right (depression). Support for this 'sticky' interhemispheric switching hypothesis stems from our recent observation that the rate of perceptual alternation in binocular rivalry is slow in euthymic subjects with bipolar disorder (n = 18, median = 0.27 Hz) compared with normal controls (n = 49, median = 0.60 Hz, p < 0.0005). We have presented evidence elsewhere that binocular rivalry is itself an interhemispheric switching phenomenon. The rivalry alternation rate (putative interhemispheric switch rate) is robust in a given individual, with a test-retest correlation of more than 0.8, making it suitable for genetic studies. The interhemispheric switch rate may provide a trait-dependent biological marker for bipolar disorder.

Adult↗
PubMed1998

Binding and reactivity of Candida albicans estrogen binding protein with steroid and other substrates.

In this report recombinant estrogen binding protein (EBP1), isolated originally from Candida albicans as a result of its high affinity for 17beta-estradiol, has been purified extensively using a modified affinity purification scheme originally developed for a homolog of EBP1, old yellow enzyme (OYE). It is shown that like OYE, the protein binds a variety of compounds with a phenolic structure, including 17beta-estradiol, and compounds with an alpha, beta-unsaturated keto or aldehyde structure. In addition, EBP1 exhibits an NADPH oxidoreductase activity, transferring electrons from NADPH to all alpha,beta-unsaturated ketones and aldehydes tested via the tightly bound FMN cofactor. Analysis of the steady-state kinetics of these reactions indicate a tetra uni ping-pong mechanism. Inhibition of the steady-state reaction by 17beta-estradiol gives a Ki = 10 +/- 2 nM, and indicates exclusive binding of this steroid to the enzyme in its oxidized state. In contrast, 19-nortestosterone binds to both oxidized and reduced forms of the enzyme with dissociation constants of 600 +/- 100 and 650 +/- 90 nM, respectively. EBP1 also catalyzes a disproportionation reaction with certain compounds, in which two molecules of a cylic alpha,beta-unsaturated ketone, including the steroid 19-nortestosterone, are individually aromatized and reduced to the corresponding saturated ketone. Despite the extensive similarity in sequence and enzymic activity, notable differences between EBP1 and the OYE family of proteins exist with regard to the binding behavior and reactivity with the two steroids tested here, estradiol and 19-nortestosterone.

Binding, Competitive↗