Evaluation of phenylmethanesulfonyl fluoride (PMSF) as a tracer candidate mapping acetylcholinesterase in vivo

Electrochemical Biosensor for Markers of Neurological Esterase Inhibition

A novel, integrated experimental and modeling framework was applied to an inhibition-based bi-enzyme (IBE) electrochemical biosensor to detect acetylcholinesterase (AChE) inhibitors that may trigger neurological diseases. The biosensor was fabricated by co-immobilizing AChE and tyrosinase (Tyr) on the gold working electrode of a screen-printed electrode (SPE) array. The reaction chemistry included a redox-recycle amplification mechanism to improve the biosensor's current output and sensitivity. A mechanistic mathematical model of the biosensor was used to simulate key diffusion and reaction steps, including diffusion of AChE's reactant (phenylacetate) and inhibitor, the reaction kinetics of the two enzymes, and electrochemical reaction kinetics at the SPE's working electrode. The model was validated by showing that it could reproduce a steady-state biosensor current as a function of the inhibitor (PMSF) concentration and unsteady-state dynamics of the biosensor current following the addition of a reactant (phenylacetate) and inhibitor phenylmethylsulfonylfluoride). The model's utility for characterizing and optimizing biosensor performance was then demonstrated. It was used to calculate the sensitivity of the biosensor's current output and the redox-recycle amplification factor as a function of experimental variables. It was used to calculate dimensionless Damkohler numbers and current-control coefficients that indicated the degree to which individual diffusion and reaction steps limited the biosensor's output current. Finally, the model's utility in designing IBE biosensors and operating conditions that achieve specific performance criteria was discussed.

Reduced clearance of proteins labeled with diisopropylfluorophosphate in portacaval-shunted rats

Portacaval shunting is a model for hepatic encephalopathy that causes chronic hyperammonemia, disruption of metabolic, signaling, and neurotransmitter systems, and progressive morphological changes. Exposure of cultured cells to ammonia raises intralysosomal pH and inhibits proteolysis, and the present study tested the hypothesis that proteolytic capacity is diminished in portacaval-shunted rats. Proteins were labeled in vivo with tracer doses of diisopropylfluorophosphate (DFP) and clearance of label was assayed. This approach labeled proteins independent of protein synthesis, which is reported to be altered in shunted rats, and avoided complications arising from re-utilization of labeled amino acids that causes underestimation of degradation rate. Characterization of DFP labeling showed that protein labeling was fast, about 50% of the label was released during a 24 h interval, labeling by DFP metabolites was negligible, inhibition of brain acetylcholinesterase was not detectable, and labeling by [(3)H]- and [(14)C]DFP was equivalent. To assay degradative capacity, proteins were first labeled with [(3)H]DFP, followed by labeling with [(14)C]DFP that was given 24 or 72 h later. The (3)H/(14)C ratio in each animal was used as a relative measure of removal of (3)H-labeled proteins. (3)H/(14)C ratios were generally significantly higher in portacaval-shunted rats than in controls, consistent with reduced proteolytic capacity. Assays of amino acid incorporation into brain protein generally replicated literature reports, supporting the conclusion that protein synthesis unlikely to be markedly inhibited and amino acid recycling influences calculated protein synthesis rates in shunted rats. Therapeutic strategies to reduce ammonia level would help normalize lysosomal functions and protein and lipid turnover.