Acetylcholinesterase in lumbar and ventricular cerebrospinal fluid

Effect of bupivacaine application on cholinesterase activities, total protein- and albumin concentration in serum and cerebrospinal fluid

The rationale of this study was to determine whether Bupivacaine used for spinal anesthesia alters the specific secretory activity of nerve cells and/or the function of the blood/cerebrospinal fluid barrier. Four groups were assessed: (1) patients undergoing spinal anesthesia using Bupivacaine for lower limb surgery, (2) spinal Bupivacaine anesthesia without subsequent surgery, (3) local facet joint infiltration using Bupivacaine, and (4) general anesthesia for lower limb surgery without Bupivacaine application. Cholinesterase activities, total protein- and albumin concentrations in serum as well as in cerebrospinal fluid were significantly decreased after surgical intervention under spinal Bupivacaine anesthesia but remained unchanged following spinal Bupivacaine application without surgery. No significant correlation was found between Bupivacaine dosage and parameter alteration. There was no influence of intrathecal Bupivacaine application on the albumin ratio cerebrospinal fluid/serum, nor was there any significant alteration of total protein- or albumin concentrations and butyrylcholinesterase activity in the serum as a result of local injection of Bupivacaine to facet joints. These serum parameters were reduced after surgery under general anesthesia. Alterations of serum- and cerebrospinal fluid parameters investigated after surgery are not related to Bupivacaine application but to effects linked to operative treatment, i.e. suppressed secretory cell activity or protein depletion owing to blood loss. We conclude that the secretory function of cholinesterase-releasing nerve cells is not affected by spinal application of Bupivacaine. The blood/cerebrospinal fluid barrier remains intact.

Acetylcholinesterase assay for cerebrospinal fluid using bupivacaine to inhibit butyrylcholinesterase

BACKGROUND

Most test systems for acetylcholinesterase activity (E.C.3.1.1.7.) are using toxic inhibitors (BW284c51 and iso-OMPA) to distinguish the enzyme from butyrylcholinesterase (E.C.3.1.1.8.) which occurs simultaneously in the cerebrospinal fluid. Applying Ellman's colorimetric method, we were looking for a non-toxic inhibitor to restrain butyrylcholinesterase activity. Based on results of previous in vitro studies bupivacaine emerged to be a suitable inhibitor.

RESULTS

Pharmacokinetic investigations with purified cholinesterases have shown maximum inhibition of butyrylcholinesterase activity and minimal interference with acetylcholinesterase activity at bupivacaine final concentrations between 0.1 and 0.5 mmol/l. Based on detailed analysis of pharmacokinetic data we developed three equations representing enzyme inhibition at bupivacaine concentrations of 0.1, 0.2 and 0.5 mmol/l. These equations allow us to calculate the acetylcholinesterase activity in solutions containing both cholinesterases utilizing the extinction differences measured spectrophotometrically in samples with and without bupivacaine. The accuracy of the bupivacaine-inhibition test could be confirmed by investigations on solutions of both purified cholinesterases and on samples of human cerebrospinal fluid. If butyrylcholinesterase activity has to be assessed simultaneously an independent test using butyrylthiocholine iodide as substrate (final concentration 5 mmol/l) has to be conducted.

CONCLUSIONS

The bupivacaine-inhibition test is a reliable method using spectrophotometrical techniques to measure acetylcholinesterase activity in cerebrospinal fluid. It avoids the use of toxic inhibitors for differentiation of acetylcholinesterase from butyrylcholinesterase in fluids containing both enzymes. Our investigations suggest that bupivacaine concentrations of 0.1, 0.2 or 0.5 mmol/l can be applied with the same effect using 1 mmol/l acetylthiocholine iodide as substrate.