Cornelius Knabbe

Publications (6)30.29 Total impact

• Article: Fully validated method for rapid and simultaneous measurement of six antiepileptic drugs in serum and plasma using ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry.

  Joachim Kuhn, Cornelius Knabbe
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  ABSTRACT: Therapeutic drug monitoring (TDM) may be very useful in the clinical management of antiepileptic drug therapy for multiple reasons, such as individual variability, metabolism, genetic factors or drug-drug or drug-food interactions. In addition, TDM is helpful to study the variation in pharmacokinetics that occurs between individuals. Here, we describe a rapid assay using ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry to measure the antiepileptic drugs lacosamide, lamotrigine, levetiracetam, primidone, topiramate, and zonisamide. After the addition of internal standards (ISs) and protein precipitation of serum or plasma, 1μl of sample was separated on a 2.1×50mm reverse phase column (Waters, Acquity UPLC BEH Phenyl, 1.7μm). Analytes were then ionized and detected by electrospray ionization mass spectrometry with multiple reaction monitoring. Runtime was 2.5min per injection. Matrix effects were investigated by systematical ion suppression and in-source fragmentation experiments. The calibration curves of the 6 antiepileptic drugs were linear over the working range between 0.05 and 50mg/L (r>0.99). The limit of detection (LOD) was <0.05mg/L, whereas the limit of quantification (LLOQ) was 0.10mg/L of all drugs measured in the assay. The intraassay and interassay coefficients of variation for all compounds were <15% for very low concentration (0.1mg/L) and <8% in the clinically relevant concentration range (>1.0mg/L). Mean recoveries were between 87.8 and 98.6% for all drugs. There were no significant ion suppressions detected at the elution times of the analytes. The mean differences between serum and heparinized plasma values were less than 6% for the 6 antiepileptic drugs. All drugs were stable in serum at -20°C, 4°C, and even at RT for at least 1 month. In summary, a specific and sensitive stable isotope dilution UPLC-MS/MS method was developed and validated for routine clinical monitoring of lacosamide, lamotrigine, levetiracetam, primidone, topiramate, and zonisamide.
  Talanta 06/2013; 110:71-80. · 3.79 Impact Factor
• Article: Vitamin D status and the risk of major adverse cardiac and cerebrovascular events in cardiac surgery.

  Armin Zittermann, Joachim Kuhn, Jens Dreier, Cornelius Knabbe, Jan F Gummert, Jochen Börgermann
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  ABSTRACT: AimsA significant proportion of cardiac surgical patients develop critical post-operative complications. We aimed to investigate the association of pre-operative 25-hydroxyvitamin D (25(OH)D) levels with major cardiac and cerebrovascular events (MACCE) in cardiac surgical patients.Methods and resultsFrom January 2010 to August 2011, we consecutively measured circulating 25(OH)D in 4418 operated patients. Of the study cohort, 38.0% had deficient 25(OH)D values (<30 nmol/L) and additional 32.3% had insufficient values (30-49.9 nmol/L), whereas only 3.1% had values >100 nmol/L. The incidence of MACCE was 11.5%. In multivariable-adjusted logistic regression models, the odds ratio of MACCE at deficient, inadequate, and high 25(OH)D levels was 2.23 [95% confidence interval (CI): 1.31-3.79], 1.73 (95% CI: 1.01-2.96) and 2.34 (95% CI: 1.12-4.89), respectively, compared with 25(OH)D levels of 75-100 nmol/L. A U-shaped association with circulating 25(OH)D was also present for duration of mechanical ventilatory support and intensive care unit stay. Multivariable-adjusted 6- and 12-month mortality were higher in patients with deficient 25(OH)D levels compared with patients with 25(OH)D levels of 75-100 nmol/L.Conclusion Deficient 25(OH)D levels are prevalent in cardiac surgical patients in Central Europe and are independently associated with the risk of MACCE. Further research should clarify the potential of vitamin D supplements in reducing cardiovascular risk in vitamin D-deficient patients and also the mechanisms leading to adverse effects on the cardiovascular system in the small group of patients with 25(OH)D levels >100 nmol/L.Trial registration information: Clinicaltrials.gov identifier number: NCT01552382.
  European Heart Journal 01/2013; · 10.48 Impact Factor
• Article: Comparison of three multiplex PCR assays for the detection of respiratory viral infections: evaluation of xTAG respiratory virus panel fast assay, RespiFinder 19 assay and RespiFinder SMART 22 assay.

  Mareike Dabisch-Ruthe, Tanja Vollmer, Ortwin Adams, Cornelius Knabbe, Jens Dreier
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  ABSTRACT: BACKGROUND: A broad spectrum of pathogens is causative for respiratory tract infections, but symptoms are mostly similar. Therefore, the identification of the causative viruses and bacteria is only feasible using multiplex PCR or several monoplex PCR tests in parallel. METHODS: The analytical sensitivity of three multiplex PCR assays, RespiFinder-19, RespiFinder- SMART-22 and xTAG-Respiratory-Virus-Panel-Fast-Assay (RVP), were compared to monoplex real-time PCR with quantified standardized control material. All assays include the most common respiratory pathogens. RESULTS: To compare the analytical sensitivity of the multiplex assays, samples were inoculated with 13 different quantified viruses in the range of 101 to 105 copies/ml. Concordant results were received for rhinovirus, whereas the RVP detected influenzavirus, RSV and hMPV more frequently in low concentrations. The RespiFinder-19 and the RespiFinder-SMART-22 showed a higher analytical sensitivity for adenoviruses and coronaviruses, whereas the RVP was incapable to detect adenovirus and coronavirus in concentrations of 104 copies/ml. The RespiFinder-19 and RespiFinder-SMART-22A did not detect influenzaviruses (104 copies/ml) and RSV (103 copies/ml). The detection of all 13 viruses in one sample was only achieved using monoplex PCR. To analyze possible competitive amplification reactions between the different viruses, samples were further inoculated with only 4 different viruses in one sample. Compared to the detection of 13 viruses in parallel, only a few differences were found. The incidence of respiratory viruses was compared in tracheal secretion (TS) samples (n = 100) of mechanically ventilated patients in winter (n = 50) and summer (n = 50). In winter, respiratory viruses were detected in 32 TS samples (64%) by RespiFinder-19, whereas the detection rate with RVP was only 22%. The most frequent viruses were adenovirus (32%) and PIV-2 (20%). Multiple infections were detected in 16 TS samples (32%) by RespiFinder-19. Fewer infections were found in summer (RespiFinder-19: 20%; RVP: 6%). All positive results were verified using monoplex PCR. CONCLUSIONS: Multiplex PCR tests have a broad spectrum of pathogens to test at a time. Analysis of multiple inoculated samples revealed a different focus of the detected virus types by the three assays. Analysis of clinical samples showed a high concordance of detected viruses by the RespiFinder-19 compared to monoplex tests.
  BMC Infectious Diseases 07/2012; 12(1):163. · 3.12 Impact Factor
• Article: 1,25-Dihydroxyvitamin D fluctuations in cardiac surgery are related to age and clinical outcome*.

  Jochen Börgermann, Kanstantsin Lazouski, Joachim Kuhn, Jens Dreier, Michael Schmidt, Thomas Gilis-Januszewski, Cornelius Knabbe, Jan F Gummert, Armin Zittermann
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  ABSTRACT: To investigate the interrelationship between cardiac surgery, age, circulating concentrations of the vitamin D hormone 1,25-dihydroxyvitamin D, and clinical outcome. Prospective, monocentric, two-arm parallel study. Tertiary Heart and Diabetes Center in the Federal State of North Rhine-Westphalia, Germany. Twenty-nine cardiac surgical patients aged ≤ 65 yrs and 30 patients ≥ 75 yrs. We assessed 1,25-dihydroxyvitamin D and other biochemical parameters of mineral metabolism (calcium, phosphate, 25-hydroxyvitamin D, and parathyroid hormone), various inflammatory markers (C-reactive protein, interleukin-6 and 8), and different immunological parameters (CD4 and CD8 cells, monocyte HLA-DR expression). We collected blood samples preoperatively, immediately after surgery, and on postoperative days 1, 5, and 30. In addition, we assessed adverse outcome until discharge as a composite of myocardial infarction, low cardiac output syndrome, infection, stroke, or in-hospital death. There were significant transient cardiac surgery-related fluctuations in 1,25-dihydroxyvitamin D and the aforementioned parameters of mineral metabolism, inflammation, and immune status. Compared to younger patients, older patients had consistently lower 1,25-dihydroxyvitamin D and phosphate levels (p = .013 and p = .036, respectively) and significantly higher interleukin 6 and 8 levels (p = .008 and p < .001, respectively). Circulating 1,25-dihydroxyvitamin D was directly related to glomerular filtration rate (R(2) = .227; p < .001) and inversely related to interleukin 6 (R(2) = .105; p = .012). The rate of adverse outcome tended to be higher in older than in younger patients (20.0% vs. 3.5%; p = .081). In risk score-adjusted logistic regression analysis, adverse outcome risk decreased by 7.7% (SE: 3.7%) for each pmol/L increment in 1,25-dihydroxyvitamin D (p = .037). Circulating 1,25-dihydroxyvitamin D levels fluctuate in relation to cardiac surgery. Low 1,25-dihydroxyvitamin D levels are associated with inflammatory processes and age-related differences in clinical outcome. Future studies should determine whether therapies aimed at treating low 1,25-dihydroxyvitamin D levels can improve the outcome in older cardiac surgery patients.
  Critical care medicine 05/2012; 40(7):2073-81. · 6.37 Impact Factor
• Article: Fast and sample cleanup-free measurement of nicotine and cotinine by stable isotope dilution ultra-performance liquid chromatography-tandem mass spectrometry.

  Joachim Kuhn, Tanja Vollmer, Claudia Martin, Doris Hendig, Cornelius Knabbe
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  ABSTRACT: We developed a stable isotope dilution ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry assay to measure nicotine and cotinine, the major oxidative and pharmacologically less active metabolite of nicotine, in human urine. A simple dilution step was used as sample preparation and the measurement of nicotine and cotinine was performed during a 1.5-min run-time using nicotine-D₄ and cotinine-D₄ as internal standards. Multiple calibration curves for the analysis of both nicotine and cotinine exhibited a consistent excellent linearity and reproducibility in the range of 5-35,000 μg/L (r>0.999). Limits of Detection were 0.7 μg/L for nicotine and 0.4 μg/L for cotinine, and Lower Limits of Quantification were 1.7 μg/L for nicotine and 1.1 μg/L for cotinine. The intraassay coefficients of variation (CVs) for nicotine and cotinine were <4% and <2%, respectively, the interassay CVs were <6% for nicotine and <4% for cotinine. The inaccuracy was <6% for both substances. The mean recovery was 103.2% (range 96.8-105.1%) for nicotine and 97.4% (range 94.3-99.2%) for cotinine. A method comparison showed that the values of nicotine metabolites in human urine samples (n=98) measured by a commercially available chemiluminescent immunoassay tested on analyzer IMMULITE 2000 were much higher than the cotinine concentration in the same urine samples measured by our UPLC-MS/MS assay. The Passing-Bablok regression line was: immunoassay=4.62 (UPLC-MS/MS)+3.64 [μg/L]; r=0.75. This robust, sensitive and interference-free UPLC-MS/MS assay permits rapid and accurate determination of nicotine and cotinine in human urine.
  Journal of pharmaceutical and biomedical analysis 05/2012; 67-68:137-43. · 2.45 Impact Factor
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  Available from: Jens Dreier

  Article: Complete genome and comparative analysis of Streptococcus gallolyticus subsp. gallolyticus, an emerging pathogen of infective endocarditis.

  Dennis Hinse, Tanja Vollmer, Christian Rückert, Jochen Blom, Jörn Kalinowski, Cornelius Knabbe, Jens Dreier
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  ABSTRACT: Streptococcus gallolyticus subsp. gallolyticus is an important causative agent of infectious endocarditis, while the pathogenicity of this species is widely unclear. To gain insight into the pathomechanisms and the underlying genetic elements for lateral gene transfer, we sequenced the entire genome of this pathogen. We sequenced the whole genome of S. gallolyticus subsp. gallolyticus strain ATCC BAA-2069, consisting of a 2,356,444 bp circular DNA molecule with a G+C-content of 37.65% and a novel 20,765 bp plasmid designated as pSGG1. Bioinformatic analysis predicted 2,309 ORFs and the presence of 80 tRNAs and 21 rRNAs in the chromosome. Furthermore, 21 ORFs were detected on the plasmid pSGG1, including tetracycline resistance genes telL and tet(O/W/32/O). Screening of 41 S. gallolyticus subsp. gallolyticus isolates revealed one plasmid (pSGG2) homologous to pSGG1. We further predicted 21 surface proteins containing the cell wall-sorting motif LPxTG, which were shown to play a functional role in the adhesion of bacteria to host cells. In addition, we performed a whole genome comparison to the recently sequenced S. gallolyticus subsp. gallolyticus strain UCN34, revealing significant differences. The analysis of the whole genome sequence of S. gallolyticus subsp. gallolyticus promotes understanding of genetic factors concerning the pathogenesis and adhesion to ECM of this pathogen. For the first time we detected the presence of the mobilizable pSGG1 plasmid, which may play a functional role in lateral gene transfer and promote a selective advantage due to a tetracycline resistance.
  BMC Genomics 08/2011; 12:400. · 4.07 Impact Factor