Assay using succinyldithiocholine as substrate: the method of choice for the measurement of cholinesterase catalytic activity in serum to diagnose succinyldicholine sensitivity

No comparative information is available concerning the ability of various cholinesterase (ChE) methods to identify succinyldicholine-sensitive patients, purely on the basis of the enzyme activity recorded in serum. Here, we evaluated six different methods for the measurement of ChE activity; 131 subjects were subdivided according to ChE phenotype and, therefore, to succinyldicholine sensitivity. ChE phenotype was determined by measuring dibucaine and fluoride numbers. DNA analysis was also performed to confirm correlation between the phenotype classification used in the study and the ChE genotype. The tested methods were significantly different in their ability to discriminate between the subjects with and without succinyldicholine-sensitive phenotypes. The succinyldithiocholine/5,5'-dithio-bis(2-nitrobenzoate) (DTNB) method showed the highest accuracy (area under the receiver operating characteristic (ROC) curve 0.97) followed by the propionylthiocholine/DTNB method (area under the ROC curve 0.94). On the other hand, the two methods using butyrylthiocholine as substrate and that employing benzoylcholine showed limited clinical utility in discriminating subjects at risk of prolonged apnea (area under the ROC curve < or = 0.9). Using the succinyldithiocholine method, a value < or = 23 U/l was approximately five times as likely to occur in a sensitive individual as in a normal one.

[Emergency from anesthesia in small children. From laryngospasm to prolonged apnea]

Postoperative laryngospasm during emergence from anaesthesia represents a potentially life-threatening complication. Even if this is successfully overcome using drug therapy, new, serious problems may develop. We report the case of a 3 1/2 -year-old boy of African descent weighing 15 kg who developed a laryngospasm during emergence from anaesthesia. Because the airway obstruction could not be controlled by deepening the anaesthesia again and administering anti-obstructive drugs, the boy was given 15 mg succinylcholine. Thereafter prolonged apnea developed such that the patient had to be admitted to the pediatric intensive care unit. The child was extubated 6 h later and the further course was normal so that he could be released from the hospital the following day. Further diagnostic study revealed a dibucaine-sensitive, fluoride-resistant pseudocholinesterase in the plasma, which is a rare form of atypical pseudocholinesterase, explaining the prolonged arousal phase after the administration of succinylcholine. Three significant aspects of this case are discussed: 1. risk factors and treatment of perioperative airway obstruction 2. factors and treatment of prolonged apnea, and 3. delayed arousal reactions and their management in an outpatient setting.

Neonatal hepatic steatosis by disruption of the adenosine kinase gene

Neonatal hepatic steatosis (OMIM 228100) is a fatal condition of unknown etiology characterized by a pale and yellow liver and early postnatal mortality. In the present study, a deficit in adenosine-dependent metabolism is proposed as a causative factor. Physiologically, adenosine is efficiently metabolized to AMP by adenosine kinase (ADK), an enzyme highly expressed in liver. ADK not only ensures normal adenine nucleotide levels but also is essential for maintaining S-adenosylmethionine-dependent transmethylation processes, where adenosine, an obligatory product, has to be constantly removed. Homozygous Adk(-/-) mutants developed normally during embryogenesis. However, within 4 days after birth they displayed microvesicular hepatic steatosis and died within 14 days with fatty liver. Adenine nucleotides were decreased and S-adenosylhomocysteine, a potent inhibitor of transmethylation reactions, was increased in the mutant liver. Thus, a deficiency in adenosine metabolism is identified as a powerful contributor to the development of neonatal hepatic steatosis, providing a model for the rapid development of postnatally lethal fatty liver.

An explanation for the different inhibitory characteristics of human serum butyrylcholinesterase phenotypes deriving from inhibition of atypical heterozygotes

The time course of inhibition of butyrylcholinesterase (EC 3.1.1.8) by the dimethylcarbamate Ro 02-0683 in sera taken from patients heterozygous for the usual (U), atypical (A), K or J variants was followed using propionylthiocholine as substrate. Data obtained were used to determine rate constants of inhibition together with the contribution made by each variant to total enzyme activity. The findings substantiate earlier reports that J and K mutations lead to quantitative changes in the concentration of usual enzyme in contrast to the qualitative changes of the atypical variant. The contribution of the atypical enzyme to the total activity in serum from UA, AK and AJ heterozygotes was respectively 17-20, 24-31 and 34-53%. The altered ratios of atypical to usual, K or J enzyme in UA, AK and AJ together with the constants on the usual enzyme alone, explain the differences in observed inhibitor numbers which enable these heterozygotes to be identified.

[3-hydroxy-3-methylglutaric aciduria and recurrent Reye-like syndrome]

INTRODUCTION

3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is an inborn error of ketogenesis and Leucine catabolism. HMG-CoA lyase catalyses the final step in leucine degradation, converting HMG-CoA to acetyl-CoA and acetoacetic acid. Clinical manifestations include hepatomegaly, lethargy or coma and apnoea. Biochemically there is a characteristic absence of ketosis with hypoglycemia, acidosis, hipertransaminasemia and variable hyperammoniemia. The urinary organic acid profile includes elevated concentrations of 3-hydroxy-3-isovaleric, 3-hydroxy-3-methylglutaric, 3-methylglutaconic and 3-methylglutaric acids.

CLINICAL CASE

Here, we report the case of a 17-year-old girl who presented in both ten months and five years of age a clinical picture characterized by lethargy leading to apnea and coma, hepatomegaly, hypoglycemia, metabolic acidosis, hyperammoniemia, elevated serum transaminases and absence of ketonuria. Diagnostic of Reye syndrome was suggested by hystopathologic finding of hepatic steatosis and clinical and biochemical data. As of 11 years old, laboratory investigations revealed carnitine deficiency and characteristic aciduria. Confirmatory enzyme diagnosis revealing deficiency of HMG-CoA lyase was made in cultured fibroblasts.

CONCLUSION

Our report constitutes an example of the presentation of HMG-CoA lyase deficiency as recurrent Reye-like syndrome.

[Prolonged neuromuscular block caused by succinylcholine in a patient with normal cholinesterase activity]

The authors describe a case of prolonged neuromuscular blockade following suxamethonlum in a patient with a normal cholinesterase activity and dibucaine number > or = 75%. In this case a peripheral nerve stimulator and capnography allowed neuromuscular blockade evaluation and fresh frozen plasma infusion led to a normal recovery from suxamethonium neuromuscular blockade. This report suggests a case of abnormal cholinesterase activity described as "silent variant".

Reversal of prolonged suxamethonium apnoea with fresh frozen plasma in a 6-week-old infant

A period of apnoea lasting 480 minutes following suxamethonium in a 6-week-old male infant is described. Neuromuscular function recovered following the administration of fresh frozen plasma. The infant was found to be homozygous for atypical cholinesterase (E1a E1a). This is believed to be the youngest reported case of suxamethonium apnoea.

[Procedure for identifying atypical variants of pseudocholinesterase for the prevention of prolonged apnea induced by succinylcholine]

The simple Sclavo test based on succinyldicholine hydrolysis and on the following reaction with 5,5'-dithio-bis-2-nitrobenzoic acid for detection of the atypical patterns of serum cholinesterase has been investigated. A yellow staining appears but in presence of the atypical forms of the enzyme. Analysis of 4055 serum samples by the 430 Selective Analyzer Sclavo allowed the identification of one atypical homozygous patient. Prolonged apnoea induced by use of succinyldicholine as a neuromuscular blocking agent during anaesthesia may be avoided by use of this test.

[Phenotype of plasma cholinesterase in prolonged apnea and sensitivity to succinylcholine]

90% of the injected dose of succinylcholine is hydrolysed by serum cholinesterase (E.C.3.I.I.8) Abnormal variants of serum cholinesterase lead to prolonged apnea. This report presents the results of 62 serum cholinesterase phenotyping including 12 cases of prolonged apneas. One clinical case of prolonged apnea in a patient homozygous for the atypical cholinesterase gene is presented with a study of his genealogy. The phenotypes were established on the basis of dibucaïne, fluorure, chloride and propranolol differential inhibition. The frequency and significance of the various phenotypes is discussed.

Is succinyldicholine the substrate of choice for the measurement of cholinesterase activity?

We have developed a succinyldicholine-based assay for serum cholinesterase (EC 3.1.1.8) to help establish whether patients with suspected sensitivity to drugs of this type have enzyme abnormalities that cannot be detected by conventional laboratory techniques. Although the method discriminates between cholinesterase activities of drug-sensitive and nonsensitive people as well as an assay involving propionylthiocholine does, it has not revealed cholinesterase abnormalities in patients who experienced prolonged apnea after succinyldicholine, in whom no enzyme defect could be demonstrated by other procedures. Of 50 individuals who were apneic for between 20 and 180 min, only one had a cholinesterase activity less than the mean for E1u homozygotes by more than 2.5 SD. We conclude that the number of patients who experience clinical problems due to enzyme abnormalities that at present go unrecognized is small. Consequently, although succinyldicholine might eventually become the substrate of choice for cholinesterase, its advantages over propionylthiocholine are not yet sufficient to encourage its use.

Heterozygotes for atypical cholinesterase

Three hundred and thirty-two patients undergoing electroconvulsive therapy received thiopentone and suxamethonium. In 31 the duration of the apnoea was greater than an assumed upper limit of normal of 240 s. Eight of these patients proved, on biochemical grounds, to be heterozygotes for the atypical gene. The reason why the heterozygous state is rarely present in those who have prolonged apnoea is that the vast majority of those who suffer from this abnormality are only slightly more sensitive to suxamethonium than are normal individuals.

A family segregating for E1j and E1k at cholinesterase locus 1

A family segregating for the A, J, and K alleles at cholinesterase locus 1 is described. Several further examples of the AJ and AK phenotypes occur in this family, and one member of the family, by genetic analysis, is phenotype JK. In relation to possible succinylcholine apnoea, phenotypes AJ, AK, and JK should all be considered vulnerable.

Suxamethonium apnoea associated with plasmaphoresis

A patient is reported who developed suxamethonium apnoea as a result of reduction in serum cholinesterase activity secondary to both pregnancy and plasmaphoresis. Had the enzyme studies been carried out before operation, regional rather than general, anaesthesia would have been used. In order to avoid the problems associated with prolonged paralysis we recommend the measurement of cholinesterase activity in all patients who have undergone plasmaphoresis and in whom anaesthesia involving the use of suxamethonium is contemplated.

Prolonged apnoea after suxamethonium: an analysis of the first 225 cases reported to the Danish Cholinesterase Research Unit

During the last 4 years, 225 patients have been referred to the Danish Cholinesterase Research Unit following an episode of prolonged apnoea after suxamethonium. Fourteen patients (6.2%) were found to have a low serum cholinesterase activity due to an acquired deficiency (for instance, liver disease, chronic debilitating disease or carcinoma). One hundred and forty-eight patients (65.8%) had an inherited abnormal serum cholinesterase, and 105 of these patients (46.7%) were homozygous for the atypical enzyme (E1 Ea1). The mean period of apnoea in this latter group was 92 min (range: 25--240). Seventeen patients (7.6%) were heterozygous for the normal and the atypical enzyme (Eu1 Ea1), with a mean apnoea period of 25 min (range: 7--60 min). Twelve patients were found to be heterozygous for the atypical and the silent gene (E(a)1 E(s)1). The mean period of apnoea was 126 min (range: 45--210 min). Fourteen patients had other rare genotypes. The longest mean period of apnoea (170 min, range: 70--330) was found in patients homozygous for the silent gene (Es1 Es1). The silent gene and the fluoride-resistant gene were found in 8.9% and 2.7% of the patients, respectively. In 63 patients (28.1%) both the type and quantity of serum cholinesterase were normal. In 34 of these patients (15.2%), the prolonged apnoea was due to other causes; for example, suxamethonium overdose, hyperventilation and central as well as peripheral respiratory depression. However, in the other 29 patients (12.9%), the reason for the prolonged apnoea could not be established. The possibility therefore exists that these cases represent unknown genotypes.

Incidence of suxamethonium apnoea in patients undergoing E.C.T

Plasma cholinesterase variants have been examined in blood samples obtained from 23 patients who, after an intravenous injection of suxamethonium 30 mg before e.c.t., had prolonged apnoea. Attempts have been made to screen the relatives of all patients shown to have an unusual plasma cholinesterase. The present study indicates an increased frequency of the fluoride-resistant variants in those psychiatric patients sensitive to suxamethonium.

[A spectrophotometric method for the determination of serum cholinesterase variants with succinyl choline as substrate (author's transl)]

A simple and rapid method for the estimation of the hydrolysis of succinyl choline by serum cholinesterase variants is described. Succinyl choline, as substrate for the enzyme assay, has many advantages over other substrates (acetyl choline, benzoyl choline and butyryl choline) which have no clinical application. Choline, the hydrolytic product of succinyl choline, is oxidized to betaine aldehyde by choline oxidase (EC 1.1.99.1), a rat liver mitochondrial preparation; this is coupled to the reduction of cytochrome c which is measured at 550 nm. Fifty normal sera (UU), 17 heterozygous (UA) and 8 atypical (AA) were tested with this method, and on the basis of resistance to dibucaine (Cinchocain; Kalow, W. & Genest, K. (1957) Canad. J. Biochem. Physiol. 35, 339-346) inhibition, three distinct groups could be established using succinyl choline as substrate. These results are comparable with the standard optical method of Kalow & Genest (cf. above) using benzoyl choline as substrate.

The temperature activity relationships of serum cholinesterases

A study has been made of the temperature activity relationships of the serum cholinesterase variants differentiated by means of dibucaine and fluoride inhibition. Using benzoylcholine as substrate, there is a characteristic temperature activity curve for each phenotype, and, for those most sensitive to succinyldicholine, this differs radically from that of the normal enzyme.A true index of serum cholinesterase activity is obtained only at 37 degrees C, as at other temperatures various assumptions and correction factors have to be made, and the results could be misleading.