MyMedR

The edema inducing activity of phospholipase A2 enzymes

Tan NH, Saifuddin MN, Yong WY

Biochem. Int., 1991 Jan;23(1):175-81.

The edema inducing activity of phospholipase A2 (PLA2) enzymes from snake venoms and porcine pancreas was investigated using mouse paw as experimental model. All ten PLA2 enzymes exhibited potent edema inducing activity. PLA2, however, is generally not the major edema inducing component of snake venom. Chemical modification studies indicated that enzymatic activity of PLA2 was required for its edema inducing activity. All PLA2 enzymes examined displayed a rapid onset edema which was suppressed by pretreatment of the mice with antihistamine. Dexamethasone pretreatment also inhibited edemas elicited by some PLA2 enzymes.

Electrophoretic profiles and biological activities: intraspecific variation in the venom of the Malayan pit viper (Calloselasma rhodostoma)

Daltry JC, Ponnudurai G, Shin CK, Tan NH, Thorpe RS, Wüster W

Toxicon, 1996 Jan;34(1):67-79.

PMID: 8835335

The Malayan pit viper (Calloselasma rhodostoma) is of major clinical significance both as a leading cause of snakebite and as the source of ancrod (Arvin). Although its venom has been extensively studied, the degree to which venom composition varies between individuals is poorly known. We individually analysed the venoms of over 100 C. rhodostoma using isoelectric focusing. In all populations, females produced an intense band that was absent from all males, and significant ontogenetic variation was detected. Principal components analysis of the banding profiles also revealed strong geographic variation, which was significantly congruent with variation in the biological activities of the venom (phosphodiesterase, alkalinephosphoesterase, L-amino acid oxidase, arginine ester hydrolase, 5'-nucleotidase, thrombin-like enzyme, haemorrhagic activity). Studies of captive-bred snakes indicate that the intraspecific variation in venom is genetically inherited rather than environmentally induced. The intraspecific variation in venom composition and biological activity could be of applied importance to snakebite therapy, both in correct diagnosis of the source of envenomation and in the development of a more effective antivenom. Greater attention should be given to the source of C. rhodostoma venom used in research to ensure reproducibility of results.

Purification and properties of the L-amino acid oxidase from Malayan pit viper (Calloselasma rhodostoma) venom

Ponnudurai G, Chung MC, Tan NH

Arch Biochem Biophys, 1994 Sep;313(2):373-8.

PMID: 8080286

The L-amino acid oxidase of Malayan pit viper (Calloselasma rhodostoma) venom was purified to electrophoretic homogeneity. The molecular weight of the enzyme was 132,000 as determined by Sephadex G-200 gel filtration chromatography and 66,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It is a glycoprotein, has an isoelectric point of 4.4, and contains 2 mol of flavin mononucleotide per mole of enzyme. The N-terminal amino acid sequence of the enzyme was A-D-D-R-N-P-L-A-E-E-F-Q-E-N-N-Y-E-E-F-L. Kinetic studies suggest the presence of a alkyl side-chain binding site in the enzyme and that the binding site comprises at least four hydrophobic subsites. The characteristics of the binding site differ slightly from those of cobra venom L-amino acid oxidases.

Six isoforms of cardiotoxin in malayan spitting cobra (Naja naja sputatrix) venom: cloning and characterization of cDNAs

Jeyaseelan K, Armugam A, Lachumanan R, Tan CH, Tan NH

Biochim. Biophys. Acta, 1998 Apr 10;1380(2):209-22.

PMID: 9565688

Cardiotoxins are the most abundant toxin components of cobra venom. Although many cardiotoxins have been purified and characterized by amino acid sequencing and other pharmacological and biochemical studies, to date only five cardiotoxin cDNAs from Taiwan cobra (Naja naja atra), three cDNAs from Chinese cobra (Naja atra) and two more of uncertain origin (either Chinese or Taiwan cobra) have been reported. In this paper we show the existence of four isoforms of cardiotoxin by protein analysis and nine cDNA sequences encoding six isoforms of cardiotoxins (CTX 1-3, 4a, 4b and 5) from N. n. sputatrix by cDNA cloning. This forms the first report on the cloning and characterization of several cardiotoxin genes from a single species of a spitting cobra. The cDNAs encoding these isoforms, obtained by reverse transcription-polymerase chain reaction (RT-PCR), were subsequently expressed in Escherichia coli. The native and recombinant cardiotoxins were first characterized by Western blotting and N-terminal protein sequencing. These proteins were also found to have different levels of cytolytic activity on cultured baby hamster kidney cells. Four of the isoforms (CTX 1, 2, 4 and 5) are unique to N. n. sputatrix, with CTX 2 being the most abundant species constituting about 50% of the total cardiotoxins. The isoform CTX 3 (20% constitution) is highly homologous to the cardiotoxins of N. n. atra and N. n. naja, indicating that it may be universally present in all Naja naja subspecies. Our studies suggest that the most hydrophilic isoform (CTX 5) could have evolved first followed by the hydrophobic isoforms (CTX 1, 2, 3 and 4). We also speculate that Asiatic cobras could be the modern descendants of the African and Egyptian counterparts.

Cardiotoxins from the venom of Malayan cobra (Naja naja sputatrix)

Tan NH

Arch Biochem Biophys, 1982 Oct 01;218(1):51-8.

PMID: 7149742

Isolation and characterization of a hemorrhagin from the venom of Calloselasma rhodostoma (Malayan pit viper)

Ponnudurai G, Chung MC, Tan NH

Toxicon, 1993 Aug;31(8):997-1005.

PMID: 8212052

The major hemorrhagin (termed rhodostoxin) of the venom of Calloselasma rhodostoma (Malayan pit viper) was purified to electrophoretic homogeneity by Sephadex G-200 gel filtration followed by high performance ion exchange chromatography. The purified hemorrhagin also yielded a single peak in reversed-phase HPLC. It had an isoelectric point of 5.3 and a mol. wt of 34,000. Rhodostoxin exhibited potent proteolytic, hemorrhagic and edema-inducing activities but was not lethal to mice at a dose of 6 microgram/g (i.v.). Treatment of rhodostoxin with EDTA eliminated both the proteolytic and hemorrhagic activities completely. The N-terminal sequence of rhodostoxin was determined to be NHEIKRHVDIVVVXDSRFCTK.

Achieving triple treatment goals in multi-ethnic Asian patients with type 2 diabetes mellitus in primary care

Goh CC, Koh KH, Goh S, Koh Y, Tan NC

Malays Fam Physician, 2018;13(2):10-18.

PMID: 30302178

Introduction: Achieving optimal glycated hemoglobin (HbA1c), blood pressure (BP), and LDL-Cholesterol (LDL-C) in patients mitigates macro- and micro-vascular complications, which is the key treatment goal in managing type 2 diabetes mellitus (T2DM). This study aimed to determine the proportion of patients in an urban community with T2DM and the above modifiable conditions attaining triple vascular treatment goals based on current practice guidelines.

Methods: A questionnaire was distributed to adult Asian patients with dyslipidemia at two primary care clinics (polyclinics) in northeastern Singapore. The demographic and clinical data for this sub-population with both T2DM and dyslipidemia were collated with laboratory and treatment information retrieved from their electronic health records. The combined data was then analyzed to determine the proportion of patients who attained triple treatment goals, and logistic regression analysis was used to identify factors associated with this outcome.

Results: 665 eligible patients [60.5% female, 30.5% Chinese, 35% Malays, and 34.4% Indians] with a mean age of 60.6 years were recruited. Of these patients, 71% achieved LDL-C ≤2.6 mmol/L, 70.4% had BP

Fulltext Intake of foods containing proteins of high biological value in families of low income groups in Singapore

Tan N

Singapore Med J, 1970 Jun;11(2):130-7.

PMID: 5505886

Comparison of combination therapy of high-dose oral N-acetylcysteine and intravenous sodium bicarbonate hydration with individual therapies in the reduction of Contrast-induced Nephropathy during Cardiac Catheterisation and Percutaneous Coronary Intervention (CONTRAST): A multi-centre, randomised, controlled trial

Chong E, Poh KK, Lu Q, Zhang JJ, Tan N, Hou XM, et al.

Int J Cardiol, 2015 Dec 15;201:237-42.

PMID: 26301645 DOI: 10.1016/j.ijcard.2015.07.108

N-acetylcysteine (NAC) and sodium bicarbonate (SOB) therapies may prevent contrast-induced nephropathy (CIN). However, the efficacy of using combination over individual therapies was not established, and there was no large randomised study comparing abbreviated SOB therapy with conventional sustained saline pre-hydration with oral NAC.

A comparative study of the enzymatic and toxic properties of venoms of the Asian lance-headed pit viper (Genus Trimeresurus)

Tan NH, Armugam A, Tan CS

Comp. Biochem. Physiol., B, 1989;93(4):757-62.

PMID: 2553329

1. The lethalities, anticoagulant effects, hermorrhagic, thrombin-like enzyme, hyaluronidase, protease, arginine ester hydrolase, 5'-nucleotidase, L-amino acid oxidase, alkaline phosphomonoesterase, phosphodiesterase and phospholipase A activities of twenty-three samples of venoms from twelve species of Asian lance-headed pit vipers (genus Trimeresurus) were examined. 2. The results indicate that notwithstanding individual variations in venom properties, the differences in biological properties of the Trimeresurus venoms can be used for the differentiation of venoms from different species of Trimeresurus. 3. The results also suggest that differences in the biological properties of snake venoms are useful parameters in the classification of snake species. 4. Our results indicate that venoms from the species T. okinavensis exhibited biological properties markedly different from other Trimeresurus venoms examined. This observation supports the recently proposed reclassification of T. okinavensis as a member of the genus Ovophis, rather than the genus Trimeresurus.

A comparative study of cobra (Naja) venom enzymes

Tan NH, Tan CS

Comp. Biochem. Physiol., B, 1988;90(4):745-50.

PMID: 2854766

1. The L-amino acid oxidase, hyaluronidase, alkaline phosphomonoesterase, protease, phosphodiesterase, acetylcholinesterase, phospholipase A and 5'-nucleotidase activities of 47 samples of venoms from all the six species of cobra (Naja), including five subspecies of Naja naja, were examined. 2. The results demonstrated interspecific differences in the venom contents of phospholipase A, acetylcholinesterase, hyaluronidase and phosphodiesterase. These differences in venom enzyme contents can be used for the differentiation of species of the genus Naja. 3. Thus, our results revealed a correlation between the enzyme composition of venom and the taxonomic status of the snake at the species level for the genus Naja.

Acidimetric assay for phospholipase A using egg yolk suspension as substrate

Tan NH, Tan CS

Anal Biochem, 1988 May 1;170(2):282-8.

PMID: 3394929

A convenient acidimetric assay for phospholipase A using egg yolk suspension as substrate has been developed. The substrate mixture consists of 1 part egg yolk, 1 part 8.1 mM sodium deoxycholate, and 1 part 18 mM calcium chloride. Phospholipase A activity is measured by following the initial rate of pH change, which is linear between pH 8.0 and 7.75 and is proportional to enzyme concentration over a wide range. The assay is highly reproducible, with a coefficient of variation of 3%, and as sensitive as most established assays for phospholipase A. The assay uses inexpensive and easily available substrate and is simple to perform. It is particularly useful for monitoring phospholipase A activity in chromatography fractions.

The enzymatic activities and lethal toxins of Trimeresurus wagleri (speckled pit viper) venom

Tan NH, Tan CS

Toxicon, 1989;27(3):349-57.

PMID: 2543103

Trimeresurus wagleri (speckled pit viper) venom exhibited the usual set of enzyme activities occurring in pit viper venoms but the content of alkaline phosphomonoesterase was unusually high, whereas the proportions of protease and arginine ester hydrolase were very low. The venom also exhibited weak thrombin-like activity but did not exhibit hemorrhagic or anticoagulant activity. Analysis of the Sephadex G-200 gel filtration fractions of the venom indicated that the lethal fraction was a low mol.wt protein, and that fractions exhibiting phosphodiesterase, phosphomonoesterase, arginine ester hydrolase, thrombin-like enzyme, L-amino acid oxidase and phospholipase A activities were not lethal. Two lethal toxins, designated as wagleri toxins 1 and 2, were isolated from the venom using Sephadex G-50 gel filtration chromatography followed by SP-Sephadex C-25 ion exchange chromatography. The mol.wts of the two toxins were 8900 by gel filtration. The LD50 (i.v.) values in mice for wagleri toxins 1 and 2 are 0.17 microgram/g and 0.19 microgram/g, respectively.

Partial purification of acetylcholinesterase from the venom of the shore pit viper (Trimeresurus purpureomaculatus)

Tan NH, Tan CS

Toxicon, 1988;26(5):505-8.

PMID: 3188057

Trimeresurus purpureomaculatus venom acetylcholinesterase has been partially purified by Sephadex G-200 gel filtration chromatography and DEAE Sephacel ion exchange chromatography. The enzyme has a mol. wt of 58,600. It was strongly inhibited by physostigmine salicylate and edrophonium chloride and exhibited substrate inhibition at high substrate concentration. The content of acetylcholinesterase in Trimeresurus purpureomaculatus venom was estimated to be much less than 0.3%.

Enzymatic activities of Malayan cobra (Naja naja sputatrix) venoms

Tan NH, Tan CS

Toxicon, 1987;25(11):1249-53.

PMID: 3433296

The enzymatic activities of four samples of Malayan cobra venom were investigated. There was significant variation in the contents of L-amino acid oxidase, alkaline phosphomonoesterase, acetylcholinesterase, phospholipase A, 5'-nucleotidase and hyaluronidase. The phosphodiesterase content was, however, constant. Storage of the lyophilized venom powder at 25 degrees C for 1 month did not affect the enzymatic activities. The venom enzymatic activities were generally also stable at 4 degrees C in 0.85% saline solution. After incubation at 37 degrees C for 39 days in 0.85% saline solution, the venom still retained considerable amounts of enzymatic activities. SP-Sephadex C-25 ion-exchange chromatography of the venom showed that the phospholipase A, L-amino acid oxidase, 5'-nucleotidase, phosphodiesterase and alkaline phosphomonoesterase exist in multiple forms.

The lethal and biochemical properties of Bungarus candidus (Malayan krait) venom and venom fractions

Tan NH, Poh CH, Tan CS

Toxicon, 1989;27(9):1065-70.

PMID: 2799837

Bungarus candidus venom exhibited high hyaluronidase, acetylcholinesterase and phospholipase A activities; low proteinase, 5'-nucleotidase, alkaline phosphomonoesterase and phosphodiesterase activities and moderately high L-amino acid oxidase activity. SP-Sephadex C-50 ion exchange chromatographic fractionation of the venom and Sephadex G-50 chromatography of the major lethal venom fractions indicate that the venom contains at least two highly lethal, basic phospholipases A with LD50 (i.v.) values of 0.02 micrograms/g (F6A) and 0.18 micrograms/g (F4A), respectively; as well as two polypeptide toxins with LD50 (i.v.) values of 0.17 micrograms/g and 0.83 micrograms/g, respectively. The major lethal toxin is the basic lethal phospholipase A, F6A, which accounts for approximately 13% of the venom protein and has a mol. wt of 21,000.

Fractionation of Sumatran pit viper (Trimeresurus sumatranus sumatranus) venom by DEAE-Sephacel ion exchange chromatography and some biological properties of the fractions

Tan NH, Tan CS

Toxicon, 1989;27(6):697-702.

PMID: 2749766

Sumatran pit viper (Trimeresurus sumatranus sumatranus) venom was fractionated by DEAE-Sephacel ion exchange chromatography into seven fractions. Fractions 4, 5 and 6 were lethal to mice and exhibited strong hemorrhagic activity, as well as some enzymatic activities. Fraction 6 also exhibited potent anticoagulant and thrombin-like activities. Analysis of the biological and enzymatic properties of the three lethal fractions suggests that the major lethal component of fractions 4 and 5 may be the hemorrhagic principle, and that the lethality of fraction 6 may be due to the hemorrhagic principle and/or the anticoagulant principle.

Inducing curricular change: Initial evaluation of outcomes

Azila NM, Tan NH, Tan CP

Med Educ, 2006 Nov;40(11):1125.

PMID: 17054624

The role of transvaginal sonography in the diagnosis of placenta praevia

Tan NH, Abu M, Woo JL, Tahir HM

Aust N Z J Obstet Gynaecol, 1995 Feb;35(1):42-5.

PMID: 7771998 DOI: 10.1111/j.1479-828x.1995.tb01828.x

Transvaginal sonography was performed in 70 patients diagnosed to have placenta praevia by transabdominal sonography. The diagnosis was confirmed either by digital examination in theatre at term or operative finding at delivery. Forty-nine cases (70%) were correctly diagnosed to have placenta praevia by both modes of sonography. Transvaginal sonography ruled out placenta praevia in 12 cases (17%) thought to be placenta praevia by transabdominal ultrasound. Both transabdominal and transvaginal sonography demonstrated 'placental migration' in 4 cases (6%) which were no longer praevia at delivery. Five patients (7%) were erroneously believed to have placenta praevia by both sonographic techniques. Overall, the diagnostic accuracy of transvaginal sonography was 92.8% compared with 75.7% for transabdominal sonography. None of the subjects experienced any exacerbation of bleeding or other complications. The results suggest that transvaginal sonographic localization of the placenta is safe and superior to the transabdominal route.

Purification and properties of the L-amino acid oxidase from monocellate cobra (Naja naja kaouthia) venom

Tan NH, Swaminathan S

Int. J. Biochem., 1992 Jun;24(6):967-73.

PMID: 1612186

1. The L-amino acid oxidase of the monocellate cobra (Naja naja kaouthia) venom was purified to electrophoretic homogeneity. The molecular weight of the enzyme was 112,200 as determined by Sephadex G-200 gel filtration chromatography, and 57,400 as determined by SDS-polyacrylamide gel electrophoresis. 2. The enzyme had an isoelectric point of 8.12 and a pH optimum of 8.5. It showed remarkable thermal stability, and, unlike many venom L-amino acid oxidase, was also stable in alkaline medium. The enzyme was partially inactivated by freezing. 3. The enzyme was very active against L-phenylalanine and L-tyrosine, moderately active against L-tryptophan, L-methionine, L-leucine, L-norleucine, L-arginine and L-norvaline. Other L-amino acids were oxidized slowly or not oxidized. 4. Kinetic studies suggest the presence of a side-chain binding site in the enzyme, and that the binding site comprises of at least four hydrophobic subsites.

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