Determination of succinylcholine hydrolytic enzyme activity in human plasma

Simultaneous determination of pancuronium, vecuronium and their related compounds using LC–ESI-MS

A simultaneous determination method of quaternary amino steroidal muscle relaxants, pancuronium (PAN), vecuronium (VEC), and 17-monodesacetyl pancuronium (17-OH-PAN), 3,17-bisdesacetyl pancuronium (3,17-OH-PAN), 3-monodesacetyl vecuronium (3-OH-VEC), 3,17-bisdesacetyl vecuronium (3,17-OH-VEC) in human serum was developed using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). The weak cation exchange cartridge was useful for the extraction of these compounds. Under optimized LC-ESI-MS conditions, these compounds were almost fully separated within 6.5 min. Linear responses over the concentration range 0.25-50.0 ng/mL were demonstrated for each compound. The developed method successfully detected VEC, 3-OH-VEC and 3,17-OH-VEC in serum intravenously administered with VEC. The level of 3-OH-VEC was higher than other compounds. This suggested that 3-OH-VEC was useful as a forensic probe in VEC administration.

In vitro succinylcholine hydrolysis in plasma of the African elephant (Loxodonta africana) and impala (Aepyceros melampus)

In elephants the time lapsed from i.m. injection of an overdose of the muscle relaxant succinylcholine (SuCh) until death, is significantly longer than in impala. To determine a difference in the rate of SuCh hydrolysis, once the drug enters the circulation, contributes to this phenomenon we have measured the rate of hydrolysis of SuCh in elephant and impala plasma, and by elephant erythrocytes. Rate of hydrolysis was determined by incubating SuCh in plasma or erythrocyte lysate at 37 degrees C and quantifying the choline produced. Plasma SuCh hydrolytic activity in elephant plasma (12.1+/-1.7 Ul(-1) mean+/-S.D.; n=9) was significantly higher than it was in impala plasma (6.6+/-0.6 Ul(-1); n=5), but were approximately 12 and 21 times lower, respectively, than in human plasma. Elephant erythrocyte lysate had no SuCh hydrolytic activity. Applying this data to previous studies, we can show that the ratio of SuCh absorption to SuCh hydrolysis is expected to be 1.25:1 and 1.41:1 for elephants and impala respectively. It will thus take at least 1.7 times longer for elephant to achieve a plasma SuCh concentration similar to that in impala. We conclude that a more rapid hydrolysis of SuCh in elephant plasma is one factor that contributes to the longer time to death compared to impala.

Determination of succinylcholine in plasma by high-pressure liquid chromatography with electrochemical detection

The plasma concentration of the neuromuscular blocking drug, succinylcholine, is difficult to measure. We have measured concentrations of the breakdown product of succinylcholine, choline, to assess whether choline concentration gives an accurate measure of succinylcholine concentration. Choline concentration was measured by HPLC and electrochemical detection in two blood or plasma samples, one in which succinylcholine hydrolysis was inhibited by 10(-5) M physostigmine and another in which succinylcholine was completely hydrolysed in 20 min by 200 mU butyrylcholinesterase at 37 degrees C. The difference in choline content between the two samples gives the succinylcholine concentration. Ninety-five per cent recovery of choline was achieved. Choline standard curves were linear from 156 pmol ml-1 to 200 nmol ml-1. Within-day and between-day mean coefficients of variation for succinylcholine hydrolysis were small (mean (SD) 3.7% (1.2%) and 3.8% (1.6%), respectively). We conclude that this method of measuring succinylcholine concentration in blood is accurate, repeatable and relatively easy.

Role of aspartate 70 and tryptophan 82 in binding of succinyldithiocholine to human butyrylcholinesterase

The atypical variant of human butyrylcholinesterase has Gly in place of Asp 70. Patients with this D70G mutation respond abnormally to the muscle relaxant succinyldicholine, experiencing hours of apnea rather than the intended 3 min. Asp 70 is at the rim of the active site gorge 12 A from the active site Ser 198. An unanswered question in the literature is why the atypical variant has a 10-fold increase in Km for compounds with a single positive charge but a 100-fold increase in Km for compounds with two positive charges. We mutated residues Asp 70, Trp 82, Trp 231, Glu 197, and Tyr 332 and expressed mutant enzymes in mammalian cells. Steady-state kinetic parameters for hydrolysis of butyrylthiocholine, benzoylcholine, succinyldithiocholine, and o-nitrophenyl butyrate were determined. The wild type and the D70G mutant had identical k(cat) values for all substrates. Molecular modeling and molecular dynamics suggested that succinyldicholine could bind in two consecutive orientations in the active site gorge; formation of one complex caused a conformational change in the omega loop involving Asp 70 and Trp 82. We propose the formation of three enzyme-substrate intermediates preceding the acyl-enzyme intermediate; kinetic data support this contention. Substrates with a single positive charge interact with Asp 70 just once, whereas substrates with two positive charges, for example succinyldithiocholine, interact with Asp 70 in two complexes, thus explaining the 10- and 100-fold increases in Km in the D70G mutant.

Enzymic determinations with rotating bioreactors and continuous-flow-stopped-flow processing. Determination of choline esters in pharmaceuticals

The neuromuscular blocking agent, succinylcholine, and the neurotransmitter, acetylcholine, have been determined in pharmaceutical preparations utilizing a sensing unit comprised of a rotating bioreactor and an amperometric detector. The bioreactor consisted of a rotating disk made of Teflon (1 cm id) with cholinesterase (EC 3.1.1.8) and choline oxidase (EC 1.1.3.17) co-immobilized on the top surface of the disk. Amperometric detection of H2O2 and initial rate measurements were employed for quantification.