Fluorescence of neutrophil granulocytes as a biomarker for clozapine use

Describing Characteristics and Differences of Neutrophils in Sepsis, Trauma, and Control Patients in Routinely Measured Hematology Data

Neutrophils have an important role in the immune response. These cells can be subjected to an impaired function and a shift in population depending on disease states. In sepsis, this shift is recognized and flagged by automated hematology analyzers, including the presence of band neutrophils, while these cells, although present, appear not to be detected in trauma patients. To better understand this suspected error in flagging, we set out to distinguish neutrophil populations of these two patient groups and compared these with controls. Different data-driven methods were used compared to standard algorithms used by the software of the analyzers. Using K-means clustering, we extracted neutrophils from raw hematology analyzer datafiles, and compared characteristics of these clusters between the patient groups. We observed an increased neutrophil size for both sepsis and trauma patients, but trauma patients had a smaller increase. Trauma patients also had a high proportion of cells with relatively high nuclear segmentation, which is contradictory with the presence of band neutrophils. This, in combination with the smaller size increase, might explain the inability to flag band neutrophils in trauma.

Neutrophil fluorescence in clozapine users is attributable to a 14kDa secretable protein

Clozapine is the only antipsychotic agent with demonstrated efficacy in refractory schizophrenia. However, use of clozapine is hampered by its adverse effects, including potentially fatal agranulocytosis. Recently, we showed an association between neutrophil autofluorescence and clozapine use. In this study, we evaluated the subcellular localization of clozapine-associated fluorescence and tried to elucidate its source. Neutrophils of clozapine users were analyzed with fluorescence microscopy to determine the emission spectrum and localization of the fluorescence signal. Next, these neutrophils were stimulated with different degranulation agents to determine the localization of fluorescence. Lastly, isolated neutrophil lysates of clozapine users were separated by SDS-PAGE and evaluated. Clozapine-associated fluorescence ranged from 420 nm to 720 nm, peaking at 500-550 nm. Fluorescence was localized in a large number of small loci, suggesting granular localization of the signal. Neutrophil degranulation induced by Cytochalasin B/fMLF reduced fluorescence, whereas platelet-activating factor (PAF)/fMLF induced degranulation did not, indicating that the fluorescence originates from a secretable substance in azurophilic granules. SDS-PAGE of isolated neutrophil lysates revealed a fluorescent 14kDa band, suggesting that neutrophil fluorescence is likely to be originated from a 14kDa protein/peptide fragment. We conclude that clozapine-associated fluorescence in neutrophils is originating from a 14kDa soluble protein (fragment) present in azurophilic granules of neutrophils. This protein could be an autofluorescent protein already present in the cell and upregulated by clozapine, or a protein altered by clozapine to express fluorescence. Future studies should further explore the identity of this protein and its potential role in the pathophysiology of clozapine-induced agranulocytosis.

Fragile neutrophils in surgical patients: A phenomenon associated with critical illness

Leukocyte viability (determined by e.g. propidium iodide [PI] staining) is automatically measured by hematology analyzers to check for delayed bench time. Incidental findings in fresh blood samples revealed the existence of leukocytes with decreased viability in critically ill surgical patients. Not much is known about these cells and their functional and/or clinical implications. Therefore, we investigated the incidence of decreased leukocyte viability, the implications for leukocyte functioning and its relation with clinical outcomes. An automated alarm was set in a routine hematology analyzer (Cell-Dyn Sapphire) for the presence of non-viable leukocytes characterized by increased fluorescence in the PI-channel (FL3:630±30nm). Patients with non-viable leukocytes were prospectively included and blood samples were drawn to investigate leukocyte viability in detail and to investigate leukocyte functioning (phagocytosis and responsiveness to a bacterial stimulus). Then, a retrospective analysis was conducted to investigate the incidence of fragile neutrophils in the circulation and clinical outcomes of surgical patients with fragile neutrophils hospitalized between 2013–2017. A high FL3 signal was either caused by 1) neutrophil autofluorescence which was considered false positive, or by 2) actual non-viable PI-positive neutrophils in the blood sample. These two causes could be distinguished using automatically generated data from the hematology analyzer. The non-viable (PI-positive) neutrophils proved to be viable (PI-negative) in non-lysed blood samples, and were therefore referred to as ‘fragile neutrophils’. Overall leukocyte functioning was not impaired in patients with fragile neutrophils. Of the 11 872 retrospectively included surgical patients, 75 (0.63%) were identified to have fragile neutrophils during hospitalization. Of all patients with fragile neutrophils, 75.7% developed an infection, 70.3% were admitted to the ICU and 31.3% died during hospitalization. In conclusion, fragile neutrophils occur in the circulation of critically ill surgical patients. These cells can be automatically detected during routine blood analyses and are an indicator of critical illness.

Assessment of adherence to oral antipsychotic medications: What has changed over the past decade?

INTRODUCTION

In a previous review, spanning 3 decades, we found that self-report and other non-objective measures were the primary means of assessing adherence to oral antipsychotic medications for individuals with schizophrenia. Moreover, consensus regarding the definition of adherence was completely lacking. Here, we examined the next decade of studies to determine what may have changed.

METHOD

We searched the peer reviewed literature published between January 1, 2007 and December 31, 2017 using Google scholar, Science Direct, CINAHL, PsychINFO, PsychARTICLES and Medline. Search terms were medication adherence or medication compliance or medication acceptance or medication follow-through or medication concordance or medication persistence AND schizophrenia. We included articles that assessed adherence behavior.

RESULTS

The search yielded 663 articles, 363 of these were eliminated. Included studies represent over 560,000 individuals. Definitions of adherence remain variable with cutoffs from 67% to 95%. Subjective measures of adherence remain the most commonly used. However, the use of objective measures has significantly increased, as has the use of electronic claims data. However, the absolute number of studies using objective measures remains low and very few approaches identify the amount of medication actually taken.

CONCLUSIONS

Some movement toward more standardization and the use of more objective measures of adherence has been made over the past decade. However, objective measures continue to be underutilized and definitions remain variable. Assessing adherence in less than optimal ways calls into question the results of studies purporting to identify reasons for problem adherence and to elucidate the relationships among adherence and other variables.

Development of a nomogram for the estimation of long-term adherence to clozapine therapy using neutrophil fluorescence

AIMS

Previously, we have reported an association between clozapine use and elevated FL3 neutrophil fluorescence, a flow-cytometric parameter for cell viability. Here, we developed and evaluated a pharmacokinetic-pharmacodynamic model relating FL3-fluorescence to clozapine exposure and derived a nomogram for estimation of long-term adherence.

METHODS

Data from 27 patients initiating clozapine were analysed using nonlinear mixed effects modelling. A previously described pharmacokinetic model for clozapine was coupled to a FL3 fluorescence model. For this, an effect compartment with clozapine concentrations as input and a first order decay rate as output was linked with an E_max model to FL3-fluorescence. FL3-fluorescence was simulated for clozapine doses of 50, 150 and 400 mg daily (n = 10 000) to establish the nomogram. Finally, true simulated adherence (% of daily doses taken over 100 days) was compared to nomogram-estimated adherence to evaluate the performance of the nomogram.

RESULTS

The half-life of FL3-fluorescence was estimated at 228 h (coefficient of variation 35%). Median absolute prediction errors of the nomogram in case of fully random adherence for 50, 150 and 400 mg ranged from -0.193% to -0.525%. The nomogram performed slightly worse in case of nonrandom adherence (median prediction error up to 5.19%), but was still clinically acceptable. Compliance patterns containing longer drug holidays revealed that the nomogram adequately estimates compliance over approximately the last 3 weeks prior to FL3-measurement.

CONCLUSION

Our nomogram could provide information regarding long-term adherence based on prescribed clozapine dose and FL3-fluorescence. Future studies should further explore the clinical value of this biomarker and nomogram.