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John Knight

Publications and source records attributed to John Knight.

17 recordsLinked to original sources
PubMed2006

Glyoxylate reductase activity in blood mononuclear cells and the diagnosis of primary hyperoxaluria type 2.

BACKGROUND: Primary hyperoxaluria type 2 (PH2) is a rare monogenic disorder characterized by an elevated urinary excretion of oxalate. Increased oxalate excretion in PH2 patients can cause nephrolithiasis and nephrocalcinosis, and can, in some cases, result in renal failure and systemic oxalate deposition. The disease is due to a deficiency of glyoxylate reductase/hydroxypyruvate reductase (GRHPR) activity. A definitive diagnosis of PH2 is currently made by the analysis of GR activity in a liver biopsy. GRHPR is expressed in virtually every tissue in the body, suggesting that utilization of more readily available cells could be used to determine GRHPR deficiency. In this study, we have evaluated the potential of determining GR and d-glycerate dehydrogenase (DGDH) activity in blood mononuclear cells (BMC) as a diagnostic indicator of PH2. METHODS: Blood samples were obtained from 10 male and 10 female normal subjects, median age 31, range 21-63, at the Wake Forest University Medical Center and from primary hyperoxaluria patients at the Mayo Clinic. The BMC were isolated and GR and DGDH activities measured in cell lysates. RESULTS: An assay of 20 normal individuals indicated that BMC contained a DGDH and GR activity of 0.97+/-0.20 (range 0.62-1.45), and 10.6+/-3.3 (range 8.3-16.6) nmol/min/mg protein, respectively. The intra-assay coefficient of variation for DGDH and GR activity was 8.2 and 11.5%, respectively. The BMC lysates from normal adult subjects and patients with PH1 showed similar GR and DGDH activities. This was confirmed by the presence of immunoreactive GRHPR protein by western blot analysis. In contrast, PH2 BMC lysates did not exhibit DGDH or GR activity, and showed no immunoreactive GRHPR by western blot analysis. CONCLUSION: These results suggest that the assay of DGDH or GR activity in BMC could be used as a minimally invasive diagnostic test for PH2.

Adult↗
PubMed2006

Idazoxan increases perforant path-evoked EPSP slope paired pulse inhibition and reduces perforant path-evoked population spike paired pulse facilitation in rat dentate gyrus.

Norepinephrine, acting via beta-adrenoceptors, enhances the perforant path-evoked potential in dentate gyrus. Using systemic idazoxan to increase norepinephrine, and paired perforant path pulses to probe early inhibition, previous investigators reported that idazoxan increased initial spike amplitude and increased somatic feedback inhibition. Here, feedback inhibition was re-examined in idazoxan-treated (5 mg/kg) rats under urethane anesthesia. To control for initial increased spike amplitude after idazoxan, evoked potentials were matched, pre- and post-idazoxan, on initial population spike. Input-output current profiles were also compared pre- and post-idazoxan. Saline- and timolol-filled micropipettes permitted evaluation of a contribution of local beta-adrenoceptors. As previously observed, initial spike amplitude was potentiated by idazoxan. Comparable spike potentiation was not seen on the timolol micropipette. Paired pulse inhibition of spike amplitude apparently increased, but input-output curve comparisons revealed a loss of feedback facilitation rather than an increase in feedback inhibition. Initial EPSP slopes were depressed after idazoxan in input-output curve data. EPSP slope feedback ratios were significantly reduced following idazoxan. These data suggest idazoxan has multiple effects on perforant path input to the dentate gyrus. Spike potentiation following idazoxan has previously been shown to depend on intact norepinephrine input. Here, the reduction in spike potentiation on the timolol pipette is consistent with other evidence that norepinephrine-mediated potentiation of the perforant path-evoked potential is dependent on local beta-adrenoceptor activation. The input-output data suggest a decrease in feedback facilitation after idazoxan is likely to account for the apparent increase in feedback inhibition previously reported. Decreased EPSP slope ratios with similar paired pulse intervals have been reported in novel environments. Since exposure to novel environments activates locus coeruleus neurons, norepinephrine may mediate the change in EPSP slope inhibition reported in awake rats. In summary, these results are consistent with the hypothesis that idazoxan potentiates granule cell responses to perforant path input in the dentate gyrus via increases in norepinephrine that lead to beta-adrenoceptor activation, and, further, that idazoxan reduces paired pulse feedback spike facilitation and enhances EPSP slope, but not spike, feedback inhibition.

Adrenergic alpha-Antagonists↗
PubMed2005

Mitochondrial hydroxyproline metabolism: implications for primary hyperoxaluria.

BACKGROUND/AIMS: Primary hyperoxaluria results from an alteration in enzymes that metabolize glyoxylate. The metabolism that leads to glyoxylate synthesis is not well defined. The aim of this study was to investigate the production of glyoxylate in liver mitochondria when they metabolize hydroxyproline. METHODS: Mitochondria were isolated from mouse liver using Percoll gradient centrifugation. The metabolism of hydroxyproline was examined by a combination of HPLC and ion chromatography/mass spectrometry techniques. RESULTS: Glyoxylate production was substantially greater when mitochondria were incubated with hydroxyproline in comparison with proline. Inclusion of malate and glutamate with hydroxyproline resulted in a drop in glyoxylate and an increase in glycolate in the incubation mixture. This suggests an increased NAD(P)+ reduction which occurred with the inclusion of glutamate/malate and that the NAD(P)H production was required to stimulate the glyoxylate reductase-catalyzed conversion of glyoxylate to glycolate. The presence of glyoxylate reductase in these mitochondria was confirmed by measuring enzymatic activity and by Western blotting. CONCLUSION: These results indicate that studies on isolated mitochondria have the potential to help unravel the metabolism associated with glyoxylate and oxalate production and understand the metabolic function of glyoxylate reductase.

Animals↗
PubMed2005

Epoetin-associated pure red cell aplasia in patients with chronic kidney disease: solving the mystery.

A substantial increase in the incidence of pure red cell aplasia (PRCA) associated with recombinant human erythropoietin (epoetin) treatment occurred in 1998. The upsurge of antibody-mediated PRCA was almost exclusively associated with chronic kidney disease patients who received subcutaneous epoetin therapy and the formulation of epoetin-alpha distributed outside the USA (EPREX/ERYPO). A systematic programme of technical, immunological and epidemiological investigations was initiated to identify the possible causes. The potential causes were evaluated on the basis of the following criteria: temporal correlation with the increase in incidence of PRCA, significant difference between EPREX/ERYPO and other epoetin products, sufficient concentration in the product to elicit a weak immune response, evidence of immunogenic activity in animals supportive, and consistent with available clinical data. Organic compounds that were leached from rubber stoppers through the action of polysorbate 80 were detected in pre-filled syringes with uncoated rubber stoppers containing polysorbate 80-formulated EPREX/ERYPO (introduced outside the USA in 1998). The leachates were not present when the stoppers were coated, in the product formulated with human serum albumin or in other epoetin products. The adjuvant activity of the leachates was demonstrated in mice. The incidence of PRCA was significantly higher in patients exposed to the polysorbate 80 formulation of epoetin-alpha delivered from pre-filled syringes with uncoated rubber stoppers, which were recalled in 2003, than in patients exposed to the same formulation from syringes with coated rubber stoppers. In conclusion, these data strongly suggest that leachates were the critical contributory factor in the increased incidence of antibody-mediated PRCA attributed to EPREX/ERYPO.

Anemia↗
PubMed2005

Sensitive pepsin immunoassay for detection of laryngopharyngeal reflux.

OBJECTIVES/HYPOTHESIS: To determine whether measurement of pepsin in throat sputum by immunoassay could be used as a sensitive and reliable method for detecting laryngopharyngeal reflux (LPR) compared with 24-hour double-probe (esophageal and pharyngeal) pH monitoring. STUDY DESIGN: Patients with clinical LPR undergoing pH monitoring provided throat sputum samples during the reflux-testing period for pepsin measurement using enzyme-linked immunoadsorbent assay. RESULTS: Pepsin assay results from 63 throat sputum samples obtained from 23 study subjects were compared with their pH monitoring data. Twenty-two percent (14/63) of the sputum samples correlated the presence of pepsin with LPR (pH < or = 4 at the pharyngeal probe), of which the median concentration of pepsin was 0.18 microg/mL (range 0.003-22 microg/mL). Seventy-eight percent (49/63) of the samples unassociated with (pharyngeal) reflux contained no detectible pepsin. Mean pH values for pepsin-positive samples were significantly lower than negative samples at both esophageal probe (pH 2.2 vs. pH 5.0) (P < .01) and the pharyngeal probe (pH 4.4 vs. pH 5.8) (P < .01). When the pepsin assay results were compared with the pharyngeal pH data for detecting reflux (events pH < or = 4), the pepsin immunoassay was 100% sensitive and 89% specific for LPR. CONCLUSIONS: Detection of pepsin in throat sputum by immunoassay appears to provide a sensitive, noninvasive method to detect LPR.

Acid-Base Equilibrium↗
PubMed2005

The increased incidence of pure red cell aplasia with an Eprex formulation in uncoated rubber stopper syringes.

BACKGROUND: The incidence of pure red cell aplasia (PRCA) in chronic kidney disease patients treated with epoetins increased substantially in 1998, was shown to be antibody mediated, and was associated predominantly with subcutaneous administration of Eprex. A technical investigation identified organic compounds leached from uncoated rubber stoppers in prefilled syringes containing polysorbate 80 as the most probable cause of the increased immunogenicity. METHODS: This study investigated whether the incidence of PRCA was higher for exposure to the product form containing leachates than for leachate-free product forms. Antibody-mediated PRCA cases were classified according to indication, product form, and route of administration. Exposure estimates were obtained by country, indication, route of administration, and product form. RESULTS: For 2001 to 2003, the PRCA incidence rate for patients with subcutaneous exposure to Eprex in prefilled syringes with polysorbate 80 and uncoated rubber stoppers (leachates present) was 4.61/10,000 patient years (95% CI 3.88-5.43) versus 0.26/10,000 patient years (95% CI 0.007-1.44) for syringes with coated stoppers (leachates absent). The rate difference was 4.35/10,000 patient years (95% CI 3.44-5.26; P < 0.0001); the rate ratio was 17 (95% CI 3.14-707). A substantial rate difference remained in sensitivity analyses that adjusted for exposure to multiple product forms. CONCLUSION: The epidemiologic data, together with the chemical and immunologic data, support the hypothesis that leachates from uncoated rubber syringe stoppers caused the increased incidence of PRCA associated with Eprex. Currently, all Eprex prefilled syringes contain fluoro-resin coated stoppers, which has contributed to decreased incidence of PRCA with continued surveillance.

Chemistry, Pharmaceutical↗
PubMed2004

Pepsin and carbonic anhydrase isoenzyme III as diagnostic markers for laryngopharyngeal reflux disease.

OBJECTIVES/HYPOTHESIS: The objective was to investigate the potential use of pepsin and carbonic anhydrase isoenzyme III (CA-III) as diagnostic markers for laryngopharyngeal reflux disease. STUDY DESIGN: Prospective cell biological investigation was conducted of laryngeal biopsy specimens taken from 9 patients with laryngopharyngeal reflux disease and 12 normal control subjects using antibodies specific for human pepsin (produced in the authors' laboratory within the Department of Otolaryngology at Wake Forest University Health Sciences, Winston-Salem, NC) and CA-III. METHODS: Laryngeal biopsy specimens were frozen in liquid nitrogen for Western blot analysis and fixed in formalin for pepsin immunohistochemical study. Specimens between two groups (patients with laryngopharyngeal reflux disease and control subjects) were compared for the presence of pepsin. Further analyses investigated the correlation between pepsin, CA-III depletion, and pH testing data. RESULTS: Analysis revealed that the level of pepsin was significantly different between the two groups (P < .001). Secondary analyses demonstrated that presence of pepsin correlated with CA-III depletion in the laryngeal vocal fold and ventricle (P < .001) and with pH testing data in individuals with laryngopharyngeal reflux disease. CONCLUSION: Pepsin was detected in 8 of 9 patients with laryngopharyngeal reflux disease, but not in normal control subjects (0 of 12). The presence of pepsin was associated with CA-III depletion in the laryngeal vocal fold and ventricle. Given the correlation between laryngopharyngeal reflux disease and CA-III depletion, it is highly plausible that CA-III depletion, as a result of pepsin exposure during laryngopharyngeal reflux, predisposes laryngeal mucosa to reflux-related inflammatory damage.

Biomarkers↗
PubMed2004

A review of Internet-based home drug-testing products for parents.

OBJECTIVE: To review home drug-testing products and the Internet-based recommendations intended for parents. METHODS: A qualitative review of drug-testing products and structured analysis of information presented on company Internet sites were conducted. Eight Internet sites that sold home drug-testing products and contained a "parent's section" were identified by Ixquick using the search term "home drug testing." Description and prices of products sold by each Internet site and recommended indications for testing, consent, collection procedures, and follow-up of positive and negative test results were researched. RESULTS: A variety of drug-testing products were available, including breath and saliva tests for alcohol, a multidrug panel hair test, and a variety of laboratory and instant urine tests. Prices ranged from 2.75 dollars for a single alcohol test to 89.00 dollars for a multidrug combination urine/hair package. A total of 14 indications for home drug-testing were cited; all sites claimed that drug testing was a way to know with certainty whether a child has used drugs. Only 1 web site made a clear statement against testing an adolescent against his or her will. Little information was presented on valid specimen collection procedures and the risks of false-positive and false-negative tests. Only half of the sites recommended that parents consult a professional if a test is positive. CONCLUSIONS: Pediatricians should advise parents of the limitations and potential risks associated with home drug-testing products.

Adolescent↗
PubMed2004

Inhaler therapy. What it means for children with asthma.

OBJECTIVE: To investigate what inhaler therapy means for children with asthma and to identify problems and concerns children experience with inhalers. DESIGN: Qualitative research design. SETTING: A community-based family practice in rural Newfoundland. PARTICIPANTS: Seventeen children, aged 5 to 16, who had been diagnosed with mild or moderate asthma and were being prescribed inhaled steroids or bronchodilators. METHOD: Two in-depth interviews with each of a purposive sample of participants were analyzed by the selective or highlighting approach. MAIN FINDINGS: Common positive themes were identified: inhalers were easy to use, and medication was necessary for good quality of life. Common negative themes were simply forgetting, inconvenient and annoying, only-as-needed approach, medication does not work well anyway, and side effects. CONCLUSION: Inhaler therapy had both positive and negative meaning for children. Although inhaled medications were seen as very important for good quality of life when taken regularly, most children wanted to use them only as needed for symptom control. Children knew the importance of inhaler therapy but still complied poorly.

Adolescent↗
PubMed2003

Impact of sodium-hydrogen exchange inhibition by cariporide on death or myocardial infarction in high-risk CABG surgery patients: results of the CABG surgery cohort of the GUARDIAN study.

OBJECTIVES: To evaluate the effects of cariporide on all-cause mortality or myocardial infarction at 36 days in patients at risk of myocardial necrosis after coronary artery bypass graft surgery. METHODS: In the coronary artery bypass graft cohort of the GUARD During Ischemia Against Necrosis trial, patients > or =18 years who required urgent coronary artery bypass graft, repeat coronary artery bypass graft, or had a history of unstable angina and > or =2 risk factors (age >65 years, female gender, diabetes mellitus, ejection fraction <35%, or left main or 3-vessel disease) were randomized to placebo (n = 743) or cariporide 20 mg (n = 736), 80 mg (n = 705), or 120 mg (n = 734). A 1-hour intravenous infusion was initiated shortly before surgery and administered every 8 hours for 2 to 7 days. Patients were followed up for 6 months. A nonparametric covariance analysis was used to calculate the primary efficacy endpoint. RESULTS: Baseline characteristics were similar between treatment groups. The cariporide 20- and 80-mg groups had event rates similar to placebo. The endpoint of all-cause mortality or myocardial infarction at day 36 was significant with cariporide 120 mg versus placebo (event rate 12.2% vs 16.2%; P =.027). The risk reduction was evident on postoperative day 1 (3.3% vs 6.5%; P =.005) and was maintained at 6 months (event rate 15.0% vs 18.6%; P =.033). Cariporide was well tolerated, and most adverse events were mild and transient in this high-risk population. CONCLUSIONS: Clinical benefit with cariporide 120 mg was observed early after treatment initiation and continued for 6 months postsurgery, suggesting that sodium-hydrogen exchange inhibition with cariporide is cardioprotective in patients undergoing high-risk coronary artery bypass graft surgery.

Adolescent↗
PubMed2003

Attachment characteristics and behavioural problems in rural and urban juvenile delinquents.

Self-reported attachment characteristics, substance use and behavioural problems were assessed in 68 male juvenile delinquents from rural and urban areas. As was predicted, insecure attachment characteristics were related to behavioural problems, substance use, and poor family functioning. Urban delinquents reported more substance use and more interpersonal problems with peers and family members than their rural counterparts. Contextual influences on adolescent attachment relationships and adjustment problems may have implications for the administration and delivery of psychological treatments in youth correctional settings.

Adolescent↗
PubMed2003

Behavioural and substance use problems in rural and urban delinquent youths.

OBJECTIVE: To examine rates of behavioural and substance use problems in incarcerated young offenders and to explore rural and urban differences in the expression and severity of these problems. METHOD: We assessed a sample of 68 confined male young offenders (63.3% rural and 35.3% urban), using the Drug Use Screening Inventory (DUSI) and the Youth Self-Report (YSR). RESULTS: Based on clinical cut-offs, data showed high rates of externalizing behavioural problems (75.4%) and substance use problems (95.7%). Urban delinquent youths showed higher rates of attention problems, delinquent behaviours, and externalizing behaviours than those in rural communities. CONCLUSIONS: Incarcerated young offenders show elevated rates of psychological problems that require treatment. Rural and urban differences in the rates of these problems may reflect differences in community service availability in these areas or in environmental influences on the development of child behavioural problems.

Adolescent↗