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Biomedical subjects

N J Miller

Publications and source records attributed to N J Miller.

At least 19 recordsLinked to original sources
PubMed2006

Absence of genetic divergence between western corn rootworms (Coleoptera: Chrysomelidae) resistant and susceptible to control by crop rotation.

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of corn, Zea mays L., in North America that has recently invaded Europe. A loss of ovipositional fidelity to cornfields has allowed the species to circumvent crop rotation as a means of control in part of its range in the United States. Analyses of variation at eight microsatellite loci provided no evidence for general genetic differentiation between samples of western corn rootworm collected in soybean, Glycine max (L.) Merr., fields and those collected in cornfields both inside and outside the rotation-resistance problem area. This result suggests that few or no barriers to gene flow exist between rotation-resistant and -susceptible rootworm populations. The implications of this result for the management of western corn rootworm in North America and Europe are discussed.

Animals↗
PubMed2005

Host-associated populations in the lettuce root aphid, Pemphigus bursarius (L.).

Pemphigus bursarius is a host-alternating aphid in which annual rounds of sexual reproduction on its primary host, Populus nigra, are interspersed with parthenogenesis on a range of secondary hosts. Evidence was sought for the existence of genetically distinct populations, associated with different secondary hosts, in P. bursarius. Microsatellite markers revealed that genetically distinct populations were present on three different secondary host species. Microsatellites were also used, in conjunction with mitochondrial DNA sequence variation, to investigate the relationships between aphids on Populus, following sexual reproduction, and those on the secondary hosts. Evidence was found for a distinct, cyclically parthenogenetic population that exploited Lactuca sativa as its secondary host. In contrast, populations associated with Matricaria inodora appeared to be largely composed of obligate parthenogens or may even have been another species of Pemphigus. Populations on Lapsana communis appeared to be a mixture of cyclical and obligate parthenogens and were more genetically heterogeneous than those on other secondary hosts, possibly due to founder effects. Experiments to measure the performance of P. bursarius clones on different secondary hosts were inconclusive, failing to demonstrate either the presence or absence of adaptations to secondary hosts.

Animals↗
PubMed2004

The molecular epidemiology of Streptococcus pneumoniae with quinolone resistance mutations.

BACKGROUND: The purpose of this study was to determine the prevalence of fluoroquinolone resistance and quinolone resistance-determining region (QRDR) mutations among Streptococcus pneumoniae isolates in the United States during the period of 2001-2002. A second objective was to examine the genetic relatedness of pneumococcal isolates with parC and/or gyrA mutations during the period of 1994-2002. METHODS: Susceptibility testing was performed for 1902 S. pneumoniae isolates collected in the United States during the period of 2001-2002. On the basis of the minimum inhibitory concentration (MIC) of ciprofloxacin, 146 isolates were selected from the 2001-2002 study for QRDR analysis of parC, parE, gyrA, and gyrB genes. The genetic relatedness of isolates with parC and/or gyrA mutations from 2001-2002 (n=55) and from 3 US surveillance studies conducted during 1994-2000 (n=56) was determined by pulsed-field gel electrophoresis (PFGE). RESULTS: Between 1999-2000 and 2001-2002, there was a 2-fold increase in the rate of ciprofloxacin resistance (MIC, >or=4 micro g/mL), from 1.2% to 2.7%, and in the rate of levofloxacin nonsusceptibility (MIC, >or=4 micro g/mL), from 0.6% to 1.3%. The 111 isolates with parC and/or gyrA mutations were assigned to 48 different PFGE types. Forty-four isolates (40%) belonged to 8 PFGE types that were closely related to widespread clones. Fifteen of the 43 levofloxacin-nonsusceptible pneumococci (LNSP) belonged to 4 PFGE types that were closely related to major clones (Spain(23F)-1 [n=6]; Spain(6B)-2 [n=5], Taiwan(19F)-14 [n=2], and Tennessee(23F)-4 [n=2]). CONCLUSION: The population of fluoroquinolone-resistant S. pneumoniae in the United States has increased but remains genetically diverse. However, 35% of LNSP were related to widespread pneumococcal clones, increasing the potential for the rapid spread of quinolone resistance in this species.

Anti-Bacterial Agents↗
PubMed2003

Population genetic structure of the lettuce root aphid, Pemphigus bursarius (L.), in relation to geographic distance, gene flow and host plant usage.

Microsatellite markers were used to examine the population structure of Pemphigus bursarius, a cyclically parthenogenetic aphid. Substantial allele frequency differences were observed between populations on the primary host plant (collected shortly after sexual reproduction) separated by distances as low as 14 km. This suggested that migratory movements occur over relatively short distances in this species. However, the degree of allele frequency divergence between populations was not correlated with their geographical separation, indicating that isolation by distance was not the sole cause of spatial genetic structuring. Significant excesses of homozygotes were observed in several populations. Substantial allele frequency differences were also found between aphids on the primary host and those sampled from a secondary host plant after several parthenogenetic generations at the same location in two successive years. This could have been due to the existence of obligately parthenogenetic lineages living on the secondary host or genetically divergent populations confined to different secondary host plant species but sharing a common primary host.

Animals↗
PubMed2001

Postnatal development and control of the pulmonary surfactant system in the tammar wallaby Macropus eugenii.

Marsupials are born at an early stage of development and are adapted for future development inside the pouch. Whether the pulmonary surfactant system is fully established at this altricial stage is unknown. This study correlates the presence of surfactant proteins (SP-A, SP-B and SP-D), using immunohistochemistry, with the ex-utero development of the lung in the tammar wallaby Macropus eugenii and also investigates the control of phosphatidylcholine (PC) secretion from developing alveolar type II cells. All three surfactant proteins were found at the site of gas exchange in the lungs of joeys at all ages, even at birth when the lungs are in the early stages of the terminal air-sac phase. Co-cultures of alveolar type II cells and fibroblasts were isolated from the lungs of 30- and 70-day-old joeys and incubated with the hormones dexamethasone (10 micromol l(-1)), prolactin (1 micromol l(-1)) or triiodothyronine (100 micromol l(-1)) or with the autonomic secretagogues isoproterenol (100 micromol l(-1)) or carbamylcholine chloride (100 micromol l(-1)). Basal secretion of PC was greater at 30 days of age than at 70 days. Co-cultures responded to all five agonists at 30 days of age, but only the autonomic secretagogues caused a significant increase in PC secretion at 70 days of age. This demonstrates that, as the cells mature, their activity and responsiveness are reduced. The presence of the surfactant proteins at the site of gas exchange at birth suggests that the system is fully functional. It appears that surfactant development is coupled with the terminal air-sac phase of lung development rather than with birth, the length of gestation or the onset of air-breathing.

Animals↗
PubMed2000

Antioxidant activities of estrogens against aqueous and lipophilic radicals; differences between phenol and catechol estrogens.

Natural estrogens have much greater radical-scavenging antioxidant activity than has previously been demonstrated, with activities up to 2.5 times those of vitamin C and vitamin E. The biological significance of this finding remains to be elucidated. In this work the antioxidant activity of a range of estrogens (phenolic, catecholic and stilbene-derived) has been studied. The activity of these substances as hydrogen-donating scavengers of free radicals in an aqueous solution has been determined by monitoring their relative abilities to quench the chromogenic radical cation 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS*+). The results show that the order of reactivity in scavenging this radical in the aqueous phase is dependent on the precise estrogenic structure, with phenolic estrogens being more potent antioxidants than catecholestrogens or diethylstilbestrol. The ability of the same estrogens to scavenge lipid phase radicals has also been assessed, determined by the ex vivo enhancement of the resistance of low-density lipoprotein (LDL) to oxidation; the order of efficacy is different from that in the aqueous phase, with the phenolic estrogens estriol, estrone and 17beta-estradiol being less potent than 2-hydroxyestradiol, 4-hydroxyestradiol, or diethylstilbestrol. In this lipid-based system, phenolic estrogens were found to be unable to regenerate alpha-tocopherol from LDL subjected to oxidative stress, while at the same time 2- and 4-hydroxyestradiol significantly delayed alpha-tocopherol loss. These results indicate that the various estrogens are good scavengers of free radicals generated in both the aqueous and the lipophilic phases. The antioxidant activity of an estrogen depends not only on the hydrophilic or lipophilic nature of the scavenged radical, but also on the phenol and catechol structures of the estrogen compound.

Antioxidants↗
PubMed2000

Complement-mediated killing of Borrelia burgdorferi by nonimmune sera from sika deer.

Various species of cervid deer are the preferred hosts for adult, black-legged ticks (Ixodes scapularis and Ixodes pacificus) in the United States. Although frequently exposed to the agent of Lyme disease (Borrelia burgdorferi), these animals, for the most part, are incompetent as transmission reservoirs. We examined the borreliacidal activity of normal and B. burgdorferi-immune sera from sika deer (Cervus nippon) maintained in a laboratory setting and compared it to that of similar sera from reservoir-competent mice and rabbits. All normal deer sera (NDS) tested killed > 90% of B. burgdorferi cells. In contrast, normal mouse and rabbit sera killed < or = 22% of the Borrelia. Anti-B. burgdorferi antibodies could not be detected in any normal sera by indirect fluorescent antibody assay (IFA). Sera collected from deer 6 wk after exposure to B. burgdorferi by tick feeding exhibited IFA titers of 1:256, whereas sera from mice and rabbits similarly exposed had titers of > 1:1,024. Heat treatment (56 C, 30 min) of NDS reduced borreliacidal activity, with < 20% of the B. burgdorferi cells killed, suggesting complement-mediated killing. The chelators EGTA and EDTA were used to block the classical or both the classical and alternative complement pathways, respectively. Addition of 10 mM EGTA to NDS had a negligible effect on borreliacidal activity, with > 90% of the cells killed. Addition of 10 mM EDTA reduced the killing to approximately 30%, whereas the addition of Mg2+ (10 mM) restored borreliacidal activity to NDS. The addition of zymosan A, an activator of the alternative pathway, increased the survival of B. burgdorferi cells to approximately 80% in NDS. These data suggest that the alternative complement activation pathway plays a major role in the borreliacidal activity of NDS. Additionally, 10 mM EGTA had almost no effect on the killing activity of B. burgdorferi-exposed deer sera, suggesting that the classical pathway is not involved in Borrelia killing, even in sera from B. burgdorferi-exposed deer.

Animals↗
PubMed1998

Could antioxidants play a role in high rates of coronary heart disease in the Czech Republic?

OBJECTIVES: To compare plasma levels of antioxidant vitamins in the Czech population with those in a western European population, and to investigate whether plasma levels of antioxidant vitamins in Czech population are related to risk of MI. DESIGN: The study has two parts: a cross-sectional survey and a population based case-control study. SETTING: Adult population in two districts of the Czech Republic, and London based civil servants group as the comparison. SUBJECTS: A random sample of men and women aged 25-64y resident in two districts were selected for the cross- sectional survey. Subjects in the age group 40-49 y were compared to a sample of British civil servants of the same age enrolled in the Whitehall II Study. Men in the Czech sample served as controls to 52 male cases of first non-fatal myocardial infarction (MI) which occurred in the same population. Plasma samples were obtained from venepuncture during an interview in hospital in the population sample and immediately after hospitalization in the MI cases. MAIN OUTCOME MEASURES: Plasma levels of beta-carotene and alpha-tocopherol, and the event of MI. Identical protocol and one laboratory was used for all analyses. RESULTS: The mean plasma levels of beta-carotene and alpha-tocopherol in healthy Czech men and women were substantially lower than in a subsample of British civil servants examined in the same laboratory. Smoking was strongly related to beta-carotene in both populations but differences between Czechs and Brits were present in both smokers and non-smokers. In the case-control study among Czech men, low levels of the vitamins were strongly related to an increases risk of MI. Age-adjusted odds ratios for concentrations below the median were 3.33 (95% confidence interval 1.43-8.33) for beta-carotene and 1.89 (0.94-3.45) for alpha-tocopherol; further adjustment for a range of variables reduced these estimates only slightly. CONCLUSIONS: Plasma concentrations of antioxidants in the Czech population appeared to be very low, and men with low levels of these substances are at increased risk of MI. This indicates that sub-optimal intake of antioxidants or related dietary factors may have played a role in the high rates of coronary heart disease in this population.

Adult↗
PubMed1997

Serum total antioxidant activity after myocardial infarction.

Serum total antioxidant activity (TAA), albumin and uric acid were measured on admission, and for the next 2 days in 56 patients suffering myocardial infarction, 20 of whom received streptokinase. The 'antioxidant gap', the difference between the serum TAA and the sum of the serum albumin and uric acid activity, was calculated. No significant changes in serum total antioxidant activity were observed in either group of patients between admission, day 1 and day 2. However, a decline in the 'antioxidant gap' after myocardial infarction was associated with a significantly higher mortality.

Adult↗
PubMed1997

Antioxidant activity of phytoestrogenic isoflavones.

The aim of this work was to determine the antioxidant activities of a range of phytoestrogenic isoflavones. The antioxidant activity in the aqueous phase was determined by means of the ABTS.+ total antioxidant activity assay. The results show that the order of reactivity in scavenging the radical in the aqueous phase is genistein > daidzein = genistin approximately equal to biochanin A = daidzin > formononetin approximately equal to ononin, the latter displaying no antioxidant activity. The importance of the single 4'-hydroxyl group in the reactivity of the isoflavones, as scavengers of aqueous phase radicals, as well as the 5'7-dihydroxy structure is demonstrated. Examination of their abilities to enhance the resistance of low density lipoproteins to oxidation supports the observation that genistein is the most potent antioxidant among this family of compound studied, both in the aqueous and in the lipophilic phases.

Antioxidants↗
PubMed1997

Factors influencing the antioxidant activity determined by the ABTS.+ radical cation assay.

This study introduces a simple direct antioxidant assay, based on the reduction of the ABTS.+ radical cation, and compares it with the myoglobin/ABTS.+ assay. The methods give closely similar results, establishing that the antioxidants studied to date in the latter assay act by scavenging the ABTS.+ radical cation and not by inhibiting its formation through reduction of ferryl myoglobin or reaction with H2O2.

Antioxidants↗
PubMed1997

Reference values for alpha-tocopherol and beta-carotene in the Whitehall II Study.

Plasma alpha-tocopherol, beta-carotene, serum lipids and their derived ratios were determined in British Civil Servants (n = 7177) at the second medical examination of the Whitehall II Study, a longitudinal study of cardiovascular disease. For plasma alpha-tocopherol the non-parametric 95% reference interval (90% confidence limits) for the total population was: 11.1 (10.9-11.3)-51.5 (50.6-52.7) mumol/l. For plasma beta-carotene the non-parametric reference interval for the total population was: 0.05 (0.05-0.05)-2.14 (2.08-2.21) mumol/l. The latter interval was wider than those previously published with a higher mean (0.61 mumol/l) and median (0.75 mumol/l). Plasma beta-carotene concentrations were higher in women than men with age-adjusted means of 0.70 and 0.57 mumol/l respectively (p < 0.001). This may reflect differences in diet, lifestyle and metabolism between the sexes. The alpha-tocopherol/cholesterol ratio, as in other surveys, did not vary with age. Among men, current- and ex-smokers had a higher alpha-tocopherol/cholesterol ratio than never-smokers with age-adjusted means of 4.18, 4.19 mumol/mmol and 4.05 mumol/mmol respectively. This difference is as yet unexplained. Follow-up of these subjects will help to clarify the role of antioxidant nutrients as protective factors for cardiovascular disease and cancer.

Adult↗
PubMed1997

Isolation of Cryptosporidium parvum and Cyclospora cayetanensis from vegetables collected in markets of an endemic region in Peru.

Cryptosporidium parvum and Cyclospora cayetanensis are protozoan pathogens that cause prolonged diarrhea in both immunocompetent and immunocompromised hosts. Cryptosporidium parvum can be transmitted via the fecal-oral route, while the exact mechanisms of transmission of Cyclospora cayetanensis have not been fully determined. Humans appear to be the sole host for the latter and a distinct seasonality has been observed in endemic areas around the world. Samples of vegetables were collected at several small markets in a periurban slum in Peru during the seasons of high and low incidence. The vegetables were washed, the supernatants were collected and centrifuged, and the pellets were resuspended in a solution of 2.5% potassium dichromate. Pellets were examined using direct microscopic observation, acid-fast staining, and immunofluorescent assays for C. parvum and Cyclospora cayetanensis oocysts. Samples were collected during three time periods: the season of low incidence, the beginning of the season of high incidence, and end of the season of high incidence. Of the total vegetables examined, 14.5% contained C. parvum oocysts and 1.8% had Cyclospora oocysts. Thus, market vegetables may provide a route by which Cryptosporidium and Cyclospora can be transmitted. Our study also suggests that washing vegetables does not completely remove Cryptosporidium and Cyclospora oocysts.

Animals↗