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Fulltext King Cobra and snakebite envenomation: on the natural history, human-snake relationship and medical importance of Ophiophagus hannah

Tan CH, Bourges A, Tan KY

J Venom Anim Toxins Incl Trop Dis, 2021;27:e20210051.
PMID: 35069710 DOI: 10.1590/1678-9199-JVATITD-2021-0051

King Cobra (Ophiophagus hannah) has a significant place in many cultures, and is a medically important venomous snake in the world. Envenomation by this snake is highly lethal, manifested mainly by neurotoxicity and local tissue damage. King Cobra may be part of a larger species complex, and is widely distributed across Southeast Asia, southern China, northern and eastern regions as well as the Western Ghats of India, indicating potential geographical variation in venom composition. There is, however, only one species-specific King Cobra antivenom available worldwide that is produced in Thailand, using venom from the snake of Thai origin. Issues relating to the management of King Cobra envenomation (e.g., variation in the composition and toxicity of the venom, limited availability and efficacy of antivenom), and challenges faced in the research of venom (in particular proteomics), are rarely addressed. This article reviews the natural history and sociocultural importance of King Cobra, cases of snakebite envenomation caused by this species, current practice of management (preclinical and clinical), and major toxinological studies of the venom with a focus on venom proteomics, toxicity and neutralization. Unfortunately, epidemiological data of King Cobra bite is scarce, and venom proteomes reported in various studies revealed marked discrepancies in details. Challenges, such as inconsistency in snake venom sampling, varying methodology of proteomic analysis, lack of mechanistic and antivenomic studies, and controversy surrounding antivenom use in treating King Cobra envenomation are herein discussed. Future directions are proposed, including the effort to establish a standard, comprehensive Pan-Asian proteomic database of King Cobra venom, from which the venom variation can be determined. Research should be undertaken to characterize the toxin antigenicity, and to develop an antivenom with improved efficacy and wider geographical utility. The endeavors are aligned with the WHO´s roadmap that aims to reduce the disease burden of snakebite by 50% before 2030.
Fulltext Snake Venom Proteomics, Immunoreactivity and Toxicity Neutralization Studies for the Asiatic Mountain Pit Vipers, Ovophis convictus, Ovophis tonkinensis, and Hime Habu, Ovophis okinavensis

Tan CH, Palasuberniam P, Tan KY

Toxins (Basel), 2021 07 23;13(8).
PMID: 34437385 DOI: 10.3390/toxins13080514

Snakebite envenomation is a serious neglected tropical disease, and its management is often complicated by the diversity of snake venoms. In Asia, pit vipers of the Ovophis species complex are medically important venomous snakes whose venom properties have not been investigated in depth. This study characterized the venom proteomes of Ovophis convictus (West Malaysia), Ovophis tonkinensis (northern Vietnam, southern China), and Ovophis okinavensis (Okinawa, Japan) by applying liquid chromatography-tandem mass spectrometry, which detected a high abundance of snake venom serine proteases (SVSP, constituting 40-60% of total venom proteins), followed by phospholipases A2, snake venom metalloproteinases of mainly P-III class, L-amino acid oxidases, and toxins from other protein families which were less abundant. The venoms exhibited different procoagulant activities in human plasma, with potency decreasing from O. tonkinensis > O. okinavensis > O. convictus. The procoagulant nature of venom confirms that consumptive coagulopathy underlies the pathophysiology of Ovophis pit viper envenomation. The hetero-specific antivenoms Gloydius brevicaudus monovalent antivenom (GbMAV) and Trimeresurus albolabris monovalent antivenom (TaMAV) were immunoreactive toward the venoms, and cross-neutralized their procoagulant activities, albeit at variably limited efficacy. In the absence of species-specific antivenom, these hetero-specific antivenoms may be useful in treating coagulotoxic envenomation caused by the different snakes in their respective regions.
Snake venom proteomics and antivenomics of two Sundaic lance-headed pit vipers: Trimeresurus wiroti (Malaysia) and Trimeresurus puniceus (Indonesia)

Lee LP, Tan KY, Tan CH

Comp Biochem Physiol Part D Genomics Proteomics, 2021 12;40:100875.
PMID: 34311411 DOI: 10.1016/j.cbd.2021.100875

Envenomation by two medically important Sundaic pit vipers, Trimeresurus wiroti (Malaysia) and Trimeresurus puniceus (Indonesia), causes hemotoxic syndrome with a potentially fatal outcome. Research on the compositions and antigenicity of these pit viper venoms is however lacking, limiting our understanding of the pathophysiology and treatment of envenomation. This study investigated the venom proteomes of both species through a protein decomplexation strategy, applying C18 reverse-phase high-performance liquid chromatography followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and protein identification through nano-electrospray ionization liquid chromatography-tandem mass spectrometry (nano-ESI-LCMS/MS) of trypsin-digested peptides. The venom antigenicity was profiled against the Thai Green Pit Viper Antivenom (GPVAV, a hetero-specific antivenom), using indirect enzyme-linked immunosorbent assay (ELISA). The venom proteomes of T. wiroti and T. puniceus consisted of 10 and 12 toxin families, respectively. The major proteins were of diverse snake venom serine proteases (19-30% of total venom proteins), snake venom metalloproteinases (17-26%), disintegrins (9-16%), phospholipases A2 (8-28%) and C-type lectins (~8%). These were putative snake toxins implicated in hemorrhage and coagulopathy, consistent with clinical hemotoxicity. GPVAV showed strong immunorecognition toward high and medium molecular weight proteins (e.g., SVMP and PLA2) in both venoms, while a lower binding activity was observed toward small proteins such as disintegrins. Conserved antigenicity in the major hemotoxins supported toxicity cross-neutralization by GPVAV and indicated that the immunorecognition of low molecular weight toxins may be optimized for improved binding efficacy. Taken together, the study provides insights into the pathophysiology and antivenom treatment of envenomation caused by T. wiroti and T. puniceus in the region.
Fulltext Rhinoscleroma: a case series

Tan SL, Neoh CY, Tan HH

Singapore Med J, 2012 Feb;53(2):e24-7.
PMID: 22337196

Rhinoscleroma is a chronic, slowly progressive, inflammatory disease of the upper respiratory tract. It is associated with Klebsiella rhinoscleromatis infection. We present the clinical and pathological features of four patients diagnosed with rhinoscleroma at the National Skin Centre, Singapore between 1997 and 2010. All four patients presented with only cutaneous involvement, and the diagnosis was clinched via histological examination. The patients were treated with a combination of antibiotics. Two patients who were on follow-up at the time of this writing responded positively to the antibiotic treatment, while two were lost to follow-up. Rhinoscleroma is a diagnostic challenge, as it is an uncommon disease in Singapore and Malaysia. We highlight this condition to raise awareness of the disease in order to aid in early diagnosis of patients. Without treatment, this condition can result in significant complications, including involvement of the lower airways. Early diagnosis and appropriate treatment help to reduce morbidity.
Fulltext Antenatal HIV screening--knowledge, attitudes and practices of obstetricians in KKH

Tan TY, Teo KP, Tan KH

Singapore Med J, 1999 Dec;40(12):733-7.
PMID: 10709422

To determine the knowledge, attitudes and practices of obstetricians with regards to HIV screening in pregnant women.
Fulltext Occupational Safety & Health Management and Corporate Sustainability: The Mediating Role of Affective Commitment

Tan ZC, Tan CE, Choong YO

Saf Health Work, 2023 Dec;14(4):415-424.
PMID: 38187210 DOI: 10.1016/j.shaw.2023.10.006

BACKGROUND: Occupational safety & health management (OSH) has garnered greater attention for its significance in promoting corporate sustainability for organizations in recent decades. The construction industry, in particular, is a major contributor to Malaysia's thirst for corporate sustainability in order to provide long-term support for the country. Thus, the main tenet of this study is to examine the mediating effect of employee affective commitment on the relationship between OSH and corporate sustainability.
METHODS: A questionnaire was administered to 273 full-time employees of listed construction companies in Malaysia. Smart PLS software version 3 was used to test the proposed model and hypotheses. Both the measurement model and the structural model were evaluated.
RESULTS: According to the findings, OSH and its dimensions are positively related to employee affective commitment. Employee affective commitment, on the other hand, has been found to be significantly related to corporate sustainability and its dimensions: economic, social, and environmental sustainability. Apart from this, the prominent results reveal that employee affective commitment partially mediates the relationship between OSH and corporate sustainability and its dimensions: economic, social, and environmental sustainability.
CONCLUSION: This empirical finding adds to the existing literature in explaining how OSH and affective commitment led to corporate sustainability. Several implications are offered to various stakeholders, such as construction companies, policymakers, and relevant regulators.
Immunoreactivity and neutralization efficacy of Pakistani Viper Antivenom (PVAV) against venoms of Saw-scaled Vipers (Echis carinatus subspp.) and Western Russell's Vipers (Daboia russelii) from the Indian subcontinent

Lim ASS, Tan KY, Tan CH

Acta Trop, 2024 Feb;250:107099.
PMID: 38097152 DOI: 10.1016/j.actatropica.2023.107099

Snakebite envenoming (SBE) is a priority Neglected Tropical Disease listed by the World Health Organization. South Asia is heavily affected, and virtually all countries in the region import polyvalent antivenom products from India for clinical use. The imported antivenoms, however, have suboptimal effectiveness due to geographical venom variation. Recently, a domestic bivalent product, named Pakistani Viper Antivenom (PVAV) has been developed specifically for Pakistani vipers, Echis carinatus sochureki and Daboia russelii. As a bivalent viperid antivenom, it is unknown yet if PVAV exhibits higher immunological binding and neutralization activities against viper venoms from distant locales compared with polyvalent antivenoms manufactured in India. This study thus examined the preclinical efficacy of PVAV against venoms of Western Russell's Vipers and Saw-scaled Viper subspecies from selected locales in the Indian subcontinent. PVAV generally outperformed the commonly used VINS polyvalent antivenom (VPAV, manufactured in India) in binding toward venoms, and showed superior or comparable neutralization efficacy against the venom procoagulant and hemorrhagic effects of Saw-scaled Vipers as well as Russell's Vipers from Pakistan and Sri Lanka. Based on normalized potency values, PVAV is far more potent than VPAV in neutralizing the lethality of all viper venoms, except that of the Indian Russell's Viper. The study shows conserved antigenicity of toxins responsible for major toxicity across these viperid venoms, and suggests the feasible production of a viper-specific antivenom with higher potency and broader geographical utility for the region.
Appendiceal Tie Syndrome

Ng ZQ, Tan HCL, Tan JH

J Gastrointest Surg, 2023 Apr;27(4):836-837.
PMID: 36658386 DOI: 10.1007/s11605-023-05597-w
Floral phenylpropanoid cocktail and architecture of Bulbophyllum vinaceum orchid in attracting fruit flies for pollination

Tan KH, Tan LT, Nishida R

J Chem Ecol, 2006 Nov;32(11):2429-41.
PMID: 17082990 DOI: 10.1007/s10886-006-9154-4

It is widely believed that most orchid flowers attract insects by using deception or chemical rewards in the form of nectar. Flowers of Bulbophyllum vinaceum produce a large array of phenylpropanoids that lure tephritid fruit fly males and also act as floral reward, which the flies subsequently convert to pheromone components. The major floral volatile components identified are methyl eugenol (ME), trans-coniferyl alcohol (CF), 2-allyl-4,5-dimethoxphenol (DMP), and trans-3,4-dimethoxycinnamyl acetate, whereas the minor components are eugenol, euasarone, trans-3,4-dimethoxy cinnamyl alcohol, and cis-coniferyl alcohol. Among the various floral parts, the lip (which is held in a closed position up against the sexual organs) has the highest concentration of the major compounds. An attracted male fly normally lands on one of the petals before climbing up onto and forcing the "spring loaded" floral lip into the open position, hence exposing the floral sexual organs. The architecture and location of chemical attractants of the lip compel the fly to align itself along the lip's longitudinal axis in a precise manner. As the fly laps up the compounds and moves towards the base of the lip, it passes the point of imbalance causing the lip to spring back to its normal closed position. The fly is catapulted headfirst into the column cavity, and its dorsum strikes the protruding sticky base of the hamulus and adheres to it. The momentum of the fly and the structural morphology of the long stiff hamulus act to pry out the pollinia from its anther cover. Hence, the pollinarium (pollinia + hamulus) is detached from the flower and adhered to the fly's dorsum. In this unique mutualistic association, both species receive direct reproductive benefits--the flower's pollinarium is transported for cross pollination, and the fly is offered a bouquet of phenylpropanoids (synomone) that it consumes, converts, and/or sequesters as sex pheromonal components, thus enhancing sexual attraction and mating success.
Well-Differentiated Papillary Mesothelioma of the Tunica Vaginalis: Case Report and Systematic Review of Literature

Tan WK, Tan MY, Tan WS, Gan SC, Pathmanathan R, Tan HM, et al.

Clin Genitourin Cancer, 2016 Aug;14(4):e435-9.
PMID: 27067374 DOI: 10.1016/j.clgc.2016.03.007
Venomics, lethality and neutralization of Naja kaouthia (monocled cobra) venoms from three different geographical regions of Southeast Asia

Tan KY, Tan CH, Fung SY, Tan NH

J Proteomics, 2015 Apr 29;120:105-25.
PMID: 25748141 DOI: 10.1016/j.jprot.2015.02.012

Previous studies showed that venoms of the monocled cobra, Naja kaouthia from Thailand and Malaysia are substantially different in their median lethal doses. The intraspecific venom variations of N. kaouthia, however, have not been fully elucidated. Here we investigated the venom proteomes of N. kaouthia from Malaysia (NK-M), Thailand (NK-T) and Vietnam (NK-V) through reverse-phase HPLC, SDS-PAGE and tandem mass spectrometry. The venom proteins comprise 13 toxin families, with three-finger toxins being the most abundant (63-77%) and the most varied (11-18 isoforms) among the three populations. NK-T has the highest content of neurotoxins (50%, predominantly long neurotoxins), followed by NK-V (29%, predominantly weak neurotoxins and some short neurotoxins), while NK-M has the least (18%, some weak neurotoxins but less short and long neurotoxins). On the other hand, cytotoxins constitute the main bulk of toxins in NK-M and NK-V venoms (up to 45% each), but less in NK-T venom (27%). The three venoms show different lethal potencies that generally reflect the proteomic findings. Despite the proteomic variations, the use of Thai monovalent and Neuro polyvalent antivenoms for N. kaouthia envenomation in the three regions is appropriate as the different venoms were neutralized by the antivenoms albeit at different degrees of effectiveness.
Fulltext Antivenom cross-neutralization of the venoms of Hydrophis schistosus and Hydrophis curtus, two common sea snakes in Malaysian waters

Tan CH, Tan NH, Tan KY, Kwong KO

Toxins (Basel), 2015 Feb;7(2):572-81.
PMID: 25690691 DOI: 10.3390/toxins7020572

Sea snake envenomation is a serious occupational hazard in tropical waters. In Malaysia, the beaked sea snake (Hydrophis schistosus, formerly known as Enhydrina schistosa) and the spine-bellied sea snake (Hydrophis curtus, formerly known as Lapemis curtus or Lapemis hardwickii) are two commonly encountered species. Australian CSL sea snake antivenom is the definitive treatment for sea snake envenomation; it is unfortunately extremely costly locally and is not widely available or adequately stocked in local hospitals. This study investigated the cross-neutralizing potential of three regionally produced anti-cobra antivenoms against the venoms of Malaysian H. schistosus and H. curtus. All three antivenoms conferred paraspecific protection from sea snake venom lethality in mice, with potency increasing in the following order: Taiwan bivalent antivenom < Thai monocled cobra monovalent antivenom < Thai neuro polyvalent antivenom (NPAV). NPAV demonstrated cross-neutralizing potencies of 0.4 mg/vial for H. schistosus venom and 0.8 mg/vial for H. curtus, which translates to a dose of less than 20 vials of NPAV to neutralize an average amount of sea snake venom per bite (inferred from venom milking). The cross-neutralization activity was supported by ELISA cross-reactivity between NPAV and the venoms of H. schistosus (58.4%) and H. curtus (70.4%). These findings revealed the potential of NPAV as a second-line treatment for sea snake envenomation in the region. Further profiling of the cross-neutralization activity should address the antivenomic basis using purified toxin-based assays.
Fulltext Venom-gland transcriptome and venom proteome of the Malaysian king cobra (Ophiophagus hannah)

Tan CH, Tan KY, Fung SY, Tan NH

BMC Genomics, 2015;16:687.
PMID: 26358635 DOI: 10.1186/s12864-015-1828-2

The king cobra (Ophiophagus hannah) is widely distributed throughout many parts of Asia. This study aims to investigate the complexity of Malaysian Ophiophagus hannah (MOh) venom for a better understanding of king cobra venom variation and its envenoming pathophysiology. The venom gland transcriptome was investigated using the Illumina HiSeq™ platform, while the venom proteome was profiled by 1D-SDS-PAGE-nano-ESI-LCMS/MS.
Venomics of the beaked sea snake, Hydrophis schistosus: A minimalist toxin arsenal and its cross-neutralization by heterologous antivenoms

Tan CH, Tan KY, Lim SE, Tan NH

J Proteomics, 2015 Aug 3;126:121-30.
PMID: 26047715 DOI: 10.1016/j.jprot.2015.05.035

The venom proteome of Hydrophis schistosus (syn: Enhydrina schistosa) captured in Malaysian waters was investigated using reverse-phase HPLC, SDS-PAGE and high-resolution liquid chromatography-tandem mass spectrometry. The findings revealed a minimalist profile with only 18 venom proteins. These proteins belong to 5 toxin families: three-finger toxin (3FTx), phospholipase A2 (PLA2), cysteine-rich secretory protein (CRISP), snake venom metalloprotease (SVMP) and L-amino acid oxidase (LAAO). The 3FTxs (3 short neurotoxins and 4 long neurotoxins) constitute 70.5% of total venom protein, 55.8% being short neurotoxins and 14.7% long neurotoxins. The PLA2 family consists of four basic (21.4%) and three acidic (6.1%) isoforms. The minor proteins include one CRISP (1.3%), two SVMPs (0.5%) and one LAAO (0.2%). This is the first report of the presence of long neurotoxins, CRISP and LAAO in H. schistosus venom. The neurotoxins and the basic PLA2 are highly lethal in mice with an intravenous median lethal dose of <0.2 μg/g. Cross-neutralization by heterologous elapid antivenoms (Naja kaouthia monovalent antivenom and Neuro polyvalent antivenom) was moderate against the long neurotoxin and basic PLA2, but weak against the short neurotoxin, indicating that the latter is the limiting factor to be overcome for improving the antivenom cross-neutralization efficacy.
Case series of retained rectal foreign body. A Malaysian experience

Pang WS, Tan JH, Tan HCL, Tan JKG

Malays Fam Physician, 2021 Jul 22;16(2):78-82.
PMID: 34386169 DOI: 10.51866/cr1087

Retained rectal foreign body, with its associated social stigma, is a medical condition that is infrequently reported in Malaysia. We report the surgical management of five cases of retained foreign objects in the rectum seen over a one-year period. There were three young and two elderly male patients. One of the elderly patients presented with altered bowel habits and an abdominal mass that mimicked a symptomatic colonic tumor. All patients had an abdominal radiograph which clinched the diagnosis of a retained foreign rectal body. Successfully retrieved objects included two bottles, one bidet device, and two sex toys. Open surgery for retrieval of the impacted rectal foreign body was required in one patient. All underwent successful retrievals without any adverse postoperative complications. In our case series, retained rectal foreign bodies were observed only in the male gender. The age presentation was bimodal, with age groups in the twenties and sixties. The treatment options used for the retrieval of these impacted foreign bodies included transanal extraction or explorative laparotomy. Proximal migration and delayed presentation are possible indications for the latter approach.
Fulltext A Neurotoxic Snake Venom without Phospholipase A2: Proteomics and Cross-Neutralization of the Venom from Senegalese Cobra, Naja senegalensis (Subgenus: Uraeus)

Wong KY, Tan KY, Tan NH, Tan CH

Toxins (Basel), 2021 01 14;13(1).
PMID: 33466660 DOI: 10.3390/toxins13010060

The Senegalese cobra, Naja senegalensis, is a non-spitting cobra species newly erected from the Naja haje complex. Naja senegalensis causes neurotoxic envenomation in Western Africa but its venom properties remain underexplored. Applying a protein decomplexation proteomic approach, this study unveiled the unique complexity of the venom composition. Three-finger toxins constituted the major component, accounting for 75.91% of total venom proteins. Of these, cardiotoxin/cytotoxin (~53%) and alpha-neurotoxins (~23%) predominated in the venom proteome. Phospholipase A2, however, was not present in the venom, suggesting a unique snake venom phenotype found in this species. The venom, despite the absence of PLA2, is highly lethal with an intravenous LD50 of 0.39 µg/g in mice, consistent with the high abundance of alpha-neurotoxins (predominating long neurotoxins) in the venom. The hetero-specific VINS African Polyvalent Antivenom (VAPAV) was immunoreactive to the venom, implying conserved protein antigenicity in the venoms of N. senegalensis and N. haje. Furthermore, VAPAV was able to cross-neutralize the lethal effect of N. senegalensis venom but the potency was limited (0.59 mg venom completely neutralized per mL antivenom, or ~82 LD50 per ml of antivenom). The efficacy of antivenom should be further improved to optimize the treatment of cobra bite envenomation in Africa.
Insights into the evolutionary and medical significance of unique alpha-neurotoxin and phospholipase A2 compositions in Naja SPP. (cobra) venoms

Tan CH, Tan KY, Tan NH, Wong KY

Toxicon, 2020 Apr 20;177 Suppl 1:S28-S29.
PMID: 32634978 DOI: 10.1016/j.toxicon.2019.12.027
Insights into the evolutionary and medical significance of unique alpha-neurotoxin and phospholipase A2 compositions in Naja spp. (cobra) venoms

Tan CH, Tan KY, Tan NH, Wong KY

Toxicon, 2020 Apr 20;177 Suppl 1:S11-S12.
PMID: 32634912 DOI: 10.1016/j.toxicon.2019.10.052
Proteomics and neutralization of Bungarus multicinctus (Many-banded Krait) venom: Intra-specific comparisons between specimens from China and Taiwan

Oh AMF, Tan KY, Tan NH, Tan CH

Comp Biochem Physiol C Toxicol Pharmacol, 2021 Sep;247:109063.
PMID: 33910092 DOI: 10.1016/j.cbpc.2021.109063

The Many-banded Krait (Bungarus multicinctus) is a medically important venomous snake in East Asia. This study investigated the venom proteomes of B. multicinctus from Guangdong, southern China (BM-China) and insular Taiwan (BM-Taiwan), and the neutralization activities of two antivenom products (produced separately in China and Taiwan) against the lethal effect of the venoms. The venom proteomes of both specimens contained similar toxin families, notwithstanding small variations in the subtypes and abundances of minor components. More than 90% of the total venom proteins belong to three-finger toxins (3FTx, including alpha-neurotoxins) and phospholipases A2 (PLA2, including beta-bungarotoxins), supporting their key involvement in the pathophysiology of krait envenomation which manifests as pre- and post-synaptic neurotoxicity. The venoms exhibited potent neurotoxic and lethal effects with extremely low i.v. LD50 of 0.027 μg/g (Bm-China) and 0.087 μg/g (Bm-Taiwan), respectively, in mice. Bungarus multicinctus monovalent antivenom (BMMAV) produced in China and Neuro bivalent antivenom (NBAV) produced in Taiwan were immunoreactive toward both venoms and their toxin fractions. The antivenoms neutralized the venom lethality variably, with BMMAV being more efficacious than NBAV by approximately two-fold. Findings suggest that the monovalent antivenom has a higher potency presumably due to its species-specificity toward the krait venom.
Genus Calliophis of Asiatic coral snakes: A deficiency of venom cross-reactivity and neutralization against seven regional elapid antivenoms

Tan CH, Liew JL, Tan KY, Tan NH

Toxicon, 2016 Oct;121:130-133.
PMID: 27616455 DOI: 10.1016/j.toxicon.2016.09.003

Venoms of Calliophis bivirgata and Calliophis intestinalis exhibited moderate binding activities toward Neuro Bivalent Antivenom (Taiwan) but not the other six elapid monovalent or bivalent antivenoms available in the region. All antivenoms failed to neutralize C. bivirgata venom lethality in mice. The findings indicate the need to validate antivenom cross-reactivity with in vivo cross-neutralization, and imply that distinct antigens of Calliophis venoms should be incorporated in the production of a pan-regional poly-specific antivenom.

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