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Biomedical subjects

A W Johnson

Publications and source records attributed to A W Johnson.

At least 19 recordsLinked to original sources
PubMed1998

A method for the quantitation of conjugated bile acids in dried blood spots using electrospray ionization-mass spectrometry.

Bile acid concentrations are elevated in the blood of neonates with cholestatic hepatobiliary disorders providing a possible means of screening for treatable conditions including biliary atresia. A method is described for the determination of concentrations of conjugated bile acids in dried blood spots using electrospray ionization mass spectrometry. Bile acids were eluted from the blood spots using methanol containing, as internal standards, the taurine and glycine conjugates of D4-chenodeoxycholic acid and D4-cholic acid. The samples were then reconstituted in acetonitrile/water and injected by autosampler into the electrospray source operating in negative ion mode. Optimal conditions were determined for both single quadrupole and tandem mass spectrometry analysis. Blood spot bile acid profiles were studied in two groups of infants (< 1 y), a cholestatic group (conjugated bilirubin > 25 mumol/L; n = 49), and a control group (n = 96). The best discrimination between the two groups was provided by measurements of taurodihydroxycholanoates (normal < 5 mumol/L; cholestatic group 18-94 mumol/L) and glycodihydroxycholanoates (normal < 5 mumol/L; cholestatic group 11-66 mumol/L). The method can also be adapted to detect unusual bile acids which are diagnostic of inborn errors of bile acid synthesis and peroxisomal disorders. The method is fast, reliable, reproducible, and relatively cheap; however, much more work is required to determine whether it can be used for mass screening for cholestasis. It will be necessary to show that measurement of bile acid concentrations in blood spots obtained at 7-10 d can be used to detect infants who currently present with jaundice, pale stools, and dark urine during the first 6 mo of life.

Bile Acids and Salts↗
PubMed1997

Solitary adenocarcinoma metastasis mimicking sarcomatous degeneration in Paget's disease.

A rare case of mucinous adenocarcinoma presented as a solitary, metastatic deposit to a region of Paget's disease within the peripheral skeleton. Historical, physical, radiographic, and scintigraphic findings were indistinguishable from those of sarcomatous degeneration arising from pagetoid bone. This case supports the idea that when a painful, osteolytic lesion is discovered within a region of Paget's disease, bone scintigraphy has greater value of disclosing potential multifocal or multicentric disease than for providing etiologic specificity for the principal lesion.

Adenocarcinoma, Mucinous↗
PubMed1997

Rat1p and Xrn1p are functionally interchangeable exoribonucleases that are restricted to and required in the nucleus and cytoplasm, respectively.

XRN1 encodes an abundant cytoplasmic exoribonuclease, Xrn1p, responsible for mRNA turnover in yeast. A screen for bypass suppressors of the inviability of xrn1 ski2 double mutants identified dominant alleles of RAT1, encoding an exoribonuclease homologous with Xrn1p. These RAT1 alleles restored XRN1-like functions, including cytoplasmic RNA turnover, wild-type sensitivity to the microtubule-destabilizing drug benomyl, and sporulation. The mutations were localized to a region of the RAT1 gene encoding a putative bipartite nuclear localization sequence (NLS). Fusions to green fluorescent protein were used to demonstrate that wild-type Rat1p is localized to the nucleus and that the mutant alleles result in mislocalization of Rat1p to the cytoplasm. Conversely, targeting Xrn1p to the nucleus by the addition of the simian virus 40 large-T-antigen NLS resulted in complementation of the temperature sensitivity of a rat1-1 strain. These results indicate that Xrn1p and Rat1p are functionally interchangeable exoribonucleases that function in and are restricted to the cytoplasm and nucleus, respectively. It is likely that the higher eukaryotic homologs of these proteins will function similarly in the cytoplasm and nucleus.

Amino Acid Sequence↗
PubMed1996

Acute bronchiolitis in tropical Africa: a hospital-based perspective in Ibadan, Nigeria.

In a 30-month prospective study of severe acute lower respiratory infections in hospitalized pre-school Nigerian children, acute bronchiolitis was diagnosed in 67 cases; 19 (28.4%) and 2 (3.0%) of these had concomitant pneumonia or croup, respectively. The peak prevalence was in the wet (rainy) season (May-October). The male/female (M:F) ratio in infants < or = 6 months was 2.9:1, differing significantly from the 1.1:1 in older subjects (P = 0.04). None of the subjects had severe malnutrition. Neither a high fever (> or = 39 degrees C), nor tachypnea on admission was significantly correlated with co-existing pneumonia. Of the 29 subjects in whom it was possible to explore viral immunofluorescence studies and/or serodiagnosis, we identified 26 viral identifications in 18 (62.1%) cases; 6 (20.7%) had > or = 2 viruses. Respiratory syncytial virus was identified in 11 (38.0%) of the 29 cases, and parainfluenza virus (PIV) types 1, 2, and 3 in 10 (34.5%). PIV type 3 accounted for 7 cases, including 3 with bacteremia. Bacterial isolates were made in 9 (21.4%) of 42 blood cultures and in the only lung aspirate; Staphylococcus epidermidis and Staphylococcus aureus accounted for 4 and 3 cases, respectively. Although bacteremia was 2.9 times more common in cases with co-existing pneumonia or croup, the respective frequency of virus-positive cases and that of bacteremia was not significantly different between cases with bronchiolitis alone and those with associated pneumonia or croup. No deaths were recorded, but subjects aged > 6 months had a significantly shorter hospital stay than those < 6 months old (P = 0.02). Despite the limited sample size, our findings reflect the etiological importance of the paramyxoviruses and the seasonal pattern of bronchiolitis in tropical Africa.

Acute Disease↗
PubMed1996

Ataxia associated with increased plasma concentrations of pristanic acid, phytanic acid and C27 bile acids but normal fibroblast branched-chain fatty acid oxidation.

Investigations of peroxisomal function were undertaken in an 8-year-old girl who developed motor difficulties at the age of 3.5 years and went on to develop a progressive ataxia and dysarthria. There were no other neurological abnormalities and she was of normal intelligence. Analysis of plasma very long-chain fatty acids revealed a normal C26 concentration and normal C24/C22 and C26/C22 ratios. Analysis of branched-chain fatty acids showed an elevated plasma phytanic acid concentration of 60 mumol/L (normal < 15) and a considerably elevated pristanic acid concentration of 50 mumol/L (normal < 2). Plasma concentrations of the C27 bile acids 3 alpha, 7 alpha-dihydroxycholestanoic acid (DHCA) and 3 alpha, 7 alpha, 12 alpha-trihydroxycholestanoic acid (THCA) and of the C29-dicarboxylic acid were also increased. We postulated that these results might be due to deficiency of the peroxisomal branched-chain acyl-CoA oxidase, but when oxidation of branched-chain fatty acids was studied in cultured skin fibroblasts it was found to be normal. Alternative explanations for the accumulation of branched-chain substrates for peroxisomal beta-oxidation are discussed. Treatment with a low-phytanic acid diet arrested the progression of the ataxia and led to a slight improvement.

Ataxia↗
PubMed1996

Delta 4-3-oxosteroid 5 beta-reductase deficiency: failure of ursodeoxycholic acid treatment and response to chenodeoxycholic acid plus cholic acid.

BACKGROUND: In some infants with liver disease, 3-oxo-delta 4 bile acids are the major bile acids in urine, a phenomenon attributed to reduced activity of the delta 4-3-oxosteroid 5 beta-reductase required for synthesis of chenodeoxycholic acid and cholic acid. These patients form a heterogeneous group. Many have a known cause of hepatic dysfunction and plasma concentrations of chenodeoxycholic acid and cholic acid that are actually greater than those of the 3-oxo-delta 4 bile acids. It is unlikely that these patients have a primary genetic deficiency of the 5 beta-reductase enzyme. AIMS: To document the bile acid profile, clinical phenotype, and response to treatment of an infant with cholestasis, increased plasma concentrations of 3-oxo-delta 4 bile acids, low plasma concentrations of chenodeoxycholic acid and cholic acid, and no other identifiable cause of liver disease. PATIENTS: This infant was compared with normal infants and infants with cholestasis of known cause. METHODS: Analysis of bile acids by liquid secondary ionisation mass spectrometry and gas chromatography-mass spectrometry. RESULTS: The plasma bile acid profile of the patient was unique. She had chronic cholestatic liver disease associated with malabsorption of vitamins D and E and a normal gamma-glutamyltranspeptidase when the transaminases were increased. The liver disease failed to improve with ursodeoxycholic acid but responded to a combination of chenodeoxycholic acid and cholic acid. CONCLUSION: Treatment of primary 5 beta-reductase deficiency requires the use of bile acids that inhibit cholesterol 7 alpha-hydroxylase.

Bile Acids and Salts↗
PubMed1995

Low doses of repetitive ultraviolet A induce morphologic changes in human skin.

Repetitive exposure of skin to sunlight is known to result in dermatoheliosis, characterized by photoaging and carcinogenesis. It has been demonstrated previously that relatively large amounts of ultraviolet (UV) A can produce photodamage and it is believed that UVB plays a major role in the induction of photodamage and photocarcinogenesis. The study reported here determines the cutaneous effects of minimal erythemal amounts of solar-simulated UV radiation as well as suberythemal and minimal erythemal doses of UVA. Previously non-sunexposed human skin was irradiated twice weekly for 24 weeks. Biopsies were obtained 12, 24 and 36 weeks after the initial irradiation and assessed for both epidermal and dermal alterations. Dermal elastic tissue content was measured via computerized image analysis. All UV treatment regimens produced observable epidermal and dermal changes. These alterations were observed after only 12 weeks of twice-weekly irradiation and were still evident 12 weeks after the final irradiation. Interestingly, UVA irradiation produced a decrease in elastic tissue content whereas solar-simulated UV produced a slight increase. Most notable were the changes produced by the suberythemal dose of UVA. Surprisingly, this relatively low UVA dose produced a reduction in elastic tissue content. The results of this investigation demonstrate that small amounts of UVA or solar-simulated UV are capable of producing cutaneous photodamage. These findings suggest that even suberythemal doses of repetitive UVA may lead to photoaging of the skin and that there is a need for daily broad spectrum UV protection.

Adult↗
PubMed1995

Synthetic lethality of sep1 (xrn1) ski2 and sep1 (xrn1) ski3 mutants of Saccharomyces cerevisiae is independent of killer virus and suggests a general role for these genes in translation control.

Strand exchange protein 1 (Sep1) (also referred to as exoribonuclease I [Xrn1]) from Saccharomyces cerevisiae has been implicated in DNA recombination, RNA turnover, karyogamy, and G4 DNA pairing among other disparate cellular processes. Using a genetic approach to study the role of SEP1/XRN1 in mitotic yeast cells, we identified mutations in the genes superkiller 2 (SKI2) and superkiller 3 (SKI3) as synthetically lethal with an sep1 null mutation. The SKI genes are thought to comprise an intracellular antiviral system controlling the expression of killer toxin from double-stranded RNA virus found in many yeast strains. However, the lethality of sep1 ski2 and sep1 ski3 mutants was independent of the L-A and M viruses, suggesting that the SKI genes act in a general cellular process in addition to virus control. We propose that Sep1/Xrn1 and Ski2 both act to block translation on transcripts targeted for degradation. Using a temperature-sensitive allele of SEP1/XRN1, we show that double mutants display a synthetic cell cycle arrest in late G1 at Start.

Base Sequence↗
PubMed1995

Regulation and intracellular localization of Saccharomyces cerevisiae strand exchange protein 1 (Sep1/Xrn1/Kem1), a multifunctional exonuclease.

The Saccharomyces cerevisiae strand exchange protein 1 (Sep1; also referred to as Xrn1, Kem1, Rar5, or Stp beta) catalyzes the formation of hybrid DNA from model substrates in vitro. The protein is also a 5'-to-3' exonuclease active on DNA and RNA. Multiple roles for the in vivo function of Sep1, ranging from DNA recombination and cytoskeleton to RNA turnover, have been proposed. We show that Sep1 is an abundant protein in vegetative S. cerevisiae cells, present at about 80,000 molecules per diploid cell. Protein levels were not changed during the cell cycle or in response to DNA-damaging agents but increased twofold during meiosis. Cell fractionation and indirect immunofluorescence studies indicated that > 90% of Sep1 was cytoplasmic in vegetative cells, and indirect immunofluorescence indicated a cytoplasmic localization in meiotic cells as well. The localization supports the proposal that Sep1 has a role in cytoplasmic RNA metabolism. Anti-Sep1 monoclonal antibodies detected cross-reacting antigens in the fission yeast Schizosccharomyces pombe, in Drosophila melanogaster embryos, in Xenopus laevis, and in a mouse pre-B-cell line.

Animals↗
PubMed1995

Microbial inciters of acute asthma in urban Nigerian children.

BACKGROUND: In tropical Africa the role of microbial agents of acute respiratory infections in acute exacerbations of bronchial asthma remains largely unexplored. However, empirical antibacterial therapy is frequently initiated in moderate to severe cases of acute asthma with symptoms of acute respiratory infection. A study was set up to determine how often acute respiratory infection is associated with acute asthma, to identify the associated pathogens, and to proffer appropriate therapeutic suggestions. METHODS: Over a 16 month period, 86 episodes of acute asthma were studied for clinical and laboratory features of acute respiratory infection at the University College Hospital (UCH), Ibadan. Virological diagnosis was based on immunofluorescence studies of nasopharyngeal aspirates and/or serological tests using the microtitre complement fixation technique. Throat swabs and blood were cultured for bacterial agents. RESULTS: Of the 64 cases who presented with rhinorrhoea, 51 (79.7%) were pyrexial (T > or = 37.6 degrees C). Inflammatory changes (frequently interstitial streakiness) were identified in 10 (19.6%) of the 51 chest radiographs; only two of these had lobar shadowing. Significant bacterial isolates were made in only three (3.5%) of the throat swabs and two (2.4%) of the blood cultures from the 86 cases; none had clinical septicaemia. On the other hand, 55 viral agents were identified from 39 (53%) of the 74 subjects studied; 16 (41.0%) had dual viral identifications. Respiratory syncytial virus (RSV) accounted for 20 (36.4%) identifications, parainfluenza virus (PIV) type 3 for 15 (27.3%), and influenza type A (Flu A) for 12 (21.8%). Viral identifications were significantly higher in infants and preschool subjects (< 5 years) and in those presenting with either rhinorrhoea or pyrexia. CONCLUSIONS: The results of this study underscore the importance of viral upper respiratory infections in asthma exacerbations in a tropical setting. The paucity of clinical and investigative features of bacterial acute respiratory infection suggests that there is little rationale for routine antibiotic cover in children with acute exacerbations of asthma in the tropics.

Acute Disease↗
PubMed1994

The activity of the Saccharomyces cerevisiae strand exchange protein 1 intrinsic exonuclease during joint molecule formation.

Strand exchange protein 1 (Sep1) from Saccharomyces cerevisiae catalyzes the formation of heteroduplex DNA from single-stranded and homologous linear duplex DNA. The initial pairing reaction requires limited exonucleolytic digestion of the double-stranded DNA (dsDNA) by the intrinsic 5' to 3' exonuclease of Sep1 or by an exogenous exonuclease. Subsequent strand exchange proceeds without the need for exonuclease activity. Sep1 degrades linear dsDNA at a rate of 20 nucleotides/min with an average processivity of 45 nucleotides. During strand exchange reactions joint molecules are first observed after 1-2 min, suggesting that only limited digestion is necessary for pairing. The linear dsDNA was found to pair with single-stranded DNA (ssDNA) when it was resected by only 22 nucleotides, and linear dsDNA digested by more than 22 nucleotides was observed only in joint molecules. Approximately 20 nucleotides were also the minimum extent of digestion that could support pairing. In the absence of exonuclease activity, Sep1-promoted pairing requires dsDNA molecules with single-stranded tails homologous to the circular ssDNA. These results suggest that Sep1-promoted strand exchange requires a single-strand annealing event prior to the strand displacement phase of the reaction.

Bacteriophage M13↗
PubMed1993

Tuberculous laryngitis in a Nigerian child.

A 12.5-year-old Nigerian child presented with progressively worsening hoarseness of 9 months duration, without overt features of chronic ill health. Superficial discrete cervical adenitis, radiological evidence of miliary tuberculosis and hilar adenopathy were identified on admission. The laryngoscopic findings comprised fully mobile but 'beefy' red, oedematous vocal cords and interarytenoid region. The diagnosis of tuberculous laryngitis was made on the basis of the laryngoscopic, radiological and clinical improvement that followed antituberculous therapy. The possible pathogeneses of tuberculous laryngitis are discussed. We emphasize the importance of considering tuberculous laryngitis in a child with persistent hoarseness.

Child↗
PubMed1993

Bacterial aetiology of acute lower respiratory infections in pre-school Nigerian children and comparative predictive features of bacteraemic and non-bacteraemic illnesses.

In a 9-month surveillance of the microbial agents causing acute lower respiratory infections (ALRI) in hospitalized preschool Nigerian children, 24 bacterial isolates were made from 22 (33 per cent) out of 66 blood cultures, including seven (70 per cent) of the 10 cultures from subjects with pleural effusion. Of the 24 positive isolates, Staphylococcus aureus accounted for 14 (58 per cent), Klebsiella pneumoniae for four (17 per cent), Streptococcus pneumoniae and Staphylococcus albus for two (8 per cent) each, and Haemophilus influenzae for only one case. Seven subjects had a mixed aetiology, comprising one bacteraemic case with measles and six with concomitant viral identifications. Sixteen cases, 10 (63 per cent) of whom were malnourished, had two or more pathogens, including 10 with multiple viruses. Bacterial isolates from the throat, were not significantly predictive of the ALRI aetiology. Overt malnutrition, empyema, and anaemia, were significantly commoner in bacteraemic cases (P < 0.03, 0.01, and 0.05), while rhinorrhoea and crepitations were each associated with the non-bacteraemic ones. (P = 0.05 and < 0.05). A similar association was shown between rhinorrhoea, wheezing/rhonchi and the mixed aetiological group (P < 0.05 and 0.05, respectively). The case-fatality in bacteraemic subjects, was 9 per cent and was 2.1 times higher than that for non-bacteraemic cases, in whom a shorter mean duration of admission was recorded. In developing countries, the need for periodic local surveillance of ALRI pathogens, as a prerequisite for evolving rational antimicrobial policies, is emphasized. Our findings underscore the predictive importance of malnutrition as a risk-factor of severe bacteraemic ALRI, frequently associated with multiple pathogens. The relative usefulness of blood culture in identifying bacterial agents of ALRI is discussed.

Acute Disease↗
PubMed1992

The association of household pollutants and socio-economic risk factors with the short-term outcome of acute lower respiratory infections in hospitalized pre-school Nigerian children.

In a 9-month study of acute lower respiratory infections (ALRI), the short-term prognostic implications of socio-economic and household risk factors were examined in 103 hospitalized pre-school Nigerian children. Seventy-nine (77%) subjects were potentially exposed to the combustion products of kerosene stoves, 16 (16%) to wood smoke and five (5%) to the products of cooking gas combustion. Only 17 subjects (17%) were exposed to household cigarette smoke. A highly significant association (p < 0.005) was shown between household cooking fuel and the outcome of hospitalization: five (63%) of the eight who died were potentially exposed to wood smoke. The duration of hospitalization was only significantly associated with paternal income (p < 0.05). None of the other domestic risk factors was significantly related to outcome or duration of admission. These findings suggest an association between an adverse outcome of ALRI and domestic exposure to wood smoke. While the hospital-based source will not allow definite conclusions, the present findings underscore the need for community-based studies. The implications for future strategies of ARI control are discussed, with suggestions.

Acute Disease↗