Displaying publications 1 - 20 of 34 in total

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  1. Chye SM, Hseu YC, Liang SH, Chen CH, Chen SC
    Bull Environ Contam Toxicol, 2008 Jan;80(1):58-62.
    PMID: 18058049
    Para-Phenylenediamine (PPD), the main aromatic amines used in the hair dye formation, and its four derivatives (2-chloro-p-phenylenediamine, 4-chloro-o-phenylenediamine, 2-nitro-p-phenylenediamine, and 4-nitro-o-phenylenediamine) were examined for their potential to produce single strand DNA breaks in human lymphocytes using the alkaline comet assay. Results revealed that all the tested chemicals within the range of doses from 100 microM to 500 microM showed the genotoxicity in a dose-dependent manner after the incubation of lymphocytes with these chemicals for 2 h. In this study, we first reported that PPD and its four derivatives can elicit the type of single strand breaks in human lymphocytes.
  2. Chye SM, Tiong YL, Yip WK, Koh RY, Len YW, Seow HF, et al.
    Environ Toxicol, 2014 Sep;29(9):981-90.
    PMID: 23172806 DOI: 10.1002/tox.21828
    para-Phenylenediamine (p-PD) is a suspected carcinogen, but it has been widely used as a component in permanent hair dyes. In this study, the mechanism of p-PD-induced cell death in normal Chang liver cells was investigated. The results demonstrated that p-PD decreased cell viability in a dose-dependent manner. Cell death via apoptosis was confirmed by enhanced DNA damage and increased cell number in the sub-G1 phase of the cell cycle, using Hoechst 33258 dye staining and flow cytometry analysis. Apoptosis via reactive oxygen species generation was detected by the dichlorofluorescin diacetate staining method. Mitogen-activated protein kinase (MAPK) activation was assessed by western blot analysis and revealed that p-PD activated not only stress-activated protein kinase (SAPK)/c-Jun N-terminal kinases (JNK) and p38 MAPK but also extracellular signal-regulated kinase (ERK). Cytotoxicity and apoptosis induced by p-PD were markedly enhanced by ERK activation and selectively inhibited by ERK inhibitor PD98059, thus indicating a negative role of ERK. In contrast, inhibition of p38 MAPK activity with the p38-specific inhibitor SB203580 moderately inhibited cytotoxicity and apoptosis induction by p-PD. Similarly, SP600125, an inhibitor of SAPK/JNK, moderately inhibited cytotoxicity and apoptosis induced by p-PD, thus implying that p38 MAPK and SAPK/JNK had a partial role in p-PD-induced apoptosis. Western blot analysis revealed that p-PD significantly increased phosphorylation of p38 and SAPK/JNK and decreased phosphorylation of ERK. In conclusion, the results demonstrated that SAPK/JNK and p38 cooperatively participate in apoptosis induced by p-PD and that a decreased ERK signal contributes to growth inhibition or apoptosis.
  3. Tan HY, Ng KY, Koh RY, Chye SM
    Cell Mol Neurobiol, 2020 Jan;40(1):25-51.
    PMID: 31435851 DOI: 10.1007/s10571-019-00724-1
    The progressive loss of structure and functions of neurons, including neuronal death, is one of the main factors leading to poor quality of life. Promotion of functional recovery of neuron after injury is a great challenge in neuroregenerative studies. Melatonin, a hormone is secreted by pineal gland and has antioxidative, anti-inflammatory, and anti-apoptotic properties. Besides that, melatonin has high cell permeability and is able to cross the blood-brain barrier. Apart from that, there are no reported side effects associated with long-term usage of melatonin at both physiological and pharmacological doses. Thus, in this review article, we summarize the pharmacological effects of melatonin as neuroprotectant in central nervous system injury, ischemic-reperfusion injury, optic nerve injury, peripheral nerve injury, neurotmesis, axonotmesis, scar formation, cell degeneration, and apoptosis in rodent models.
  4. Chong FP, Ng KY, Koh RY, Chye SM
    Cell Mol Neurobiol, 2018 Jul;38(5):965-980.
    PMID: 29299792 DOI: 10.1007/s10571-017-0574-1
    Alzheimer's disease (AD) is characterized by progressive memory loss and cognitive function deficits. There are two major pathological hallmarks that contribute to the pathogenesis of AD which are the presence of extracellular amyloid plaques composed of amyloid-β (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau. Despite extensive research that has been done on Aβ in the last two decades, therapies targeting Aβ were not very fruitful at treating AD as the efficacy of Aβ therapies observed in animal models is not reflected in human clinical trials. Hence, tau-directed therapies have received tremendous attention as the potential treatments for AD. Tauopathies are closely correlated with dementia and immunotherapy has been effective at reducing tau pathology and improving cognitive deficits in animal models. Thus, in this review article, we discussed the pathological mechanism of tau proteins, the key factors contributing to tauopathies, and therapeutic approaches for tauopathies in AD based on the recent progress in tau-based research.
  5. Ng PY, Chang IS, Koh RY, Chye SM
    Metab Brain Dis, 2020 10;35(7):1049-1066.
    PMID: 32632666 DOI: 10.1007/s11011-020-00591-6
    Alzheimer's disease (AD) has been a worldwide concern for many years now. This is due to the fact that AD is an irreversible and progressive neurodegenerative disease that affects quality of life. Failure of some Phase II/III clinical trials in AD targeting accumulation of β-amyloid in the brain has led to an increase in interest in studying alternative treatments against tubulin-associated unit (Tau) pathology. These alternative treatments include active and passive immunisation. Based on numerous studies, Tau is reported as a potential immunotherapeutic target for tauopathy-related diseases including AD. Accumulation and aggregation of hyperphosphorylated Tau as neuropil threads and neurofibrillary tangles (NFT) are pathological hallmarks of AD. Both active and passive immunisation targeting Tau protein have shown the capabilities to decrease or prevent Tau pathology and improve either motor or cognitive impairment in various animal models. In this review, we summarise recent advances in active and passive immunisation targeting pathological Tau protein, and will discuss with data obtained from both animal and human trials. Together, we give a brief overview about problems being encountered in these immunotherapies.
  6. Reena K, Ng KY, Koh RY, Gnanajothy P, Chye SM
    Environ Toxicol, 2017 Jan;32(1):265-277.
    PMID: 26784575 DOI: 10.1002/tox.22233
    para-Phenylenediamine (PPD) has long been used in two-thirds of permanent oxidative hair dye formulations. Epidemiological studies and in vivo studies have shown that hair dye is a suspected carcinogen of bladder cancer. However, the toxicity effects of PPD to human bladder remains elusive. In this study, the effects of PPD and its involvement in the apoptosis pathways in human urothelial cells (UROtsa) was investigated. It was demonstrated that PPD decreased cell viability and increased the number of sub-G1 hypodiploid cells in UROtsa cells. Cell death due to apoptosis was detected using Annexin V binding assay. Further analysis showed PPD generated reactive oxygen species (ROS), induced mitochondrial dysfunction through the loss of mitochondrial membrane potential and increased caspase-3 level in UROtsa cells. Western blot analysis of PPD-treated UROtsa cells showed down-regulation of phosphorylated proteins from NF-κB, mTOR, and Wnt pathways. In conclusion, PPD induced apoptosis via activation of ROS-mediated mitochondrial pathway, and possibly through inhibition of NF-κB, mTOR, and Wnt pathways. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 265-277, 2017.
  7. Chok KC, Koh RY, Ng MG, Ng PY, Chye SM
    Molecules, 2021 Aug 20;26(16).
    PMID: 34443626 DOI: 10.3390/molecules26165038
    Even though an increasing number of anticancer treatments have been discovered, the mortality rates of colorectal cancer (CRC) have still been high in the past few years. It has been discovered that melatonin has pro-apoptotic properties and counteracts inflammation, proliferation, angiogenesis, cell invasion, and cell migration. In previous studies, melatonin has been shown to have an anticancer effect in multiple tumors, including CRC, but the underlying mechanisms of melatonin action on CRC have not been fully explored. Thus, in this study, we investigated the role of autophagy pathways in CRC cells treated with melatonin. In vitro CRC cell models, HT-29, SW48, and Caco-2, were treated with melatonin. CRC cell death, oxidative stress, and autophagic vacuoles formation were induced by melatonin in a dose-dependent manner. Several autophagy pathways were examined, including the endoplasmic reticulum (ER) stress, 5'-adenosine monophosphate-activated protein kinase (AMPK), phosphoinositide 3-kinase (PI3K), serine/threonine-specific protein kinase (Akt), and mammalian target of rapamycin (mTOR) signaling pathways. Our results showed that melatonin significantly induced autophagy via the ER stress pathway in CRC cells. In conclusion, melatonin demonstrated a potential as an anticancer drug for CRC.
  8. Tiong YL, Ng KY, Koh RY, Ponnudurai G, Chye SM
    Horm Mol Biol Clin Investig, 2020 Jun 29;41(4).
    PMID: 32598308 DOI: 10.1515/hmbci-2020-0009
    BACKGROUND: Cardiovascular disease (CVD) is one of the major cause of mortality in diabetic patients. Evidence suggests that hyperglycemia in diabetic patients contributes to increased risk of CVD. This study is to investigate the therapeutic effects of melatonin on glucose-treated human umbilical vein endothelial cells (HUVEC) and provide insights on the underlying mechanisms.

    MATERIALS AND METHODS: Cell viability was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Reactive oxygen species (ROS) and membrane potential was detected using 2',7'-dichlorofluorescein diacetate and 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1) dye staining, respectively. While, cell apoptosis was determined by Annexin-V staining and protein expression was measured using Western blot.

    RESULTS: Our results suggested that melatonin inhibited glucose-induced ROS elevation, mitochondria dysfunction and apoptosis on HUVEC. Melatonin inhibited glucose-induced HUVEC apoptosis via PI3K/Akt signaling pathway. Activation of Akt further activated BcL-2 pathway through upregulation of Mcl-1 expression and downregulation Bax expression in order to inhibit glucose-induced HUVEC apoptosis. Besides that, melatonin promoted downregulation of oxLDL/LOX-1 in order to inhibit glucose-induced HUVEC apoptosis.

    CONCLUSIONS: In conclusion, our results suggested that melatonin exerted vasculoprotective effects against glucose-induced apoptosis in HUVEC through PI3K/Akt, Bcl-2 and oxLDL/LOX-1 signaling pathways.

  9. Ng MG, Ng KY, Koh RY, Chye SM
    Horm Mol Biol Clin Investig, 2021 Aug 06;42(4):445-461.
    PMID: 34355548 DOI: 10.1515/hmbci-2021-0009
    Leukaemia is a haematological malignancy originated from the bone marrow. Studies have shown that shift work could disrupt the melatonin secretion and eventually increase leukaemia incidence risk. Melatonin, a pineal hormone, has shown promising oncostatic properties on a wide range of cancers, including leukaemia. We first reviewed the relationship between shift work and the incidence rate of leukaemia and then discussed the role of melatonin receptors (MT1 and MT2) and their functions in leukaemia. Moreover, the connection between inflammation and leukaemia, and melatonin-induced anti-leukaemia mechanisms including anti-proliferation, apoptosis induction and immunomodulation are comprehensively discussed. Apart from that, the synergistic effects of melatonin with other anticancer compounds are also included. In short, this review article has compiled the evidence of anti-leukaemia properties displayed by melatonin and discuss its potential to act as adjunct for anti-leukaemia treatment. This review may serve as a reference for future studies or experimental research to explore the possibility of melatonin serving as a novel therapeutic agent for leukaemia.
  10. Chok KC, Ng KY, Koh RY, Chye SM
    Rev Neurosci, 2021 11 25;32(7):767-789.
    PMID: 33725748 DOI: 10.1515/revneuro-2020-0122
    Alzheimer's disease (AD) is the most common form of dementia, affecting millions of individuals each year and this number is expected to significantly increase. The complicated microorganisms residing in human gut are closely associated with our health. Emerging evidence has suggested possible involvement of human gut microbiome in AD. Symbiotic gut microbiomes are known to maintain brain health by modulating host's barriers integrity, metabolic system, immune system, nervous system and endocrine system. However, in the event of gut dysbiosis and barriers disruption, gut pathobionts disrupt homeostasis of the metabolic system, immune system, nervous system, and endocrine system, resulting in deterioration of neurological functions and subsequently promoting development of AD. Multiple therapeutic approaches, such as fecal microbiome transplant, antibiotics, prebiotics, probiotics, symbiotic, and diet are discussed as potential treatment options for AD by manipulating the gut microbiome to reverse pathological alteration in the systems above.
  11. Lai SSM, Ng KY, Koh RY, Chok KC, Chye SM
    Metab Brain Dis, 2021 08;36(6):1087-1100.
    PMID: 33881723 DOI: 10.1007/s11011-021-00737-0
    The endosomal-lysosomal system mediates the process of protein degradation through endocytic pathway. This system consists of early endosomes, late endosomes, recycling endosomes and lysosomes. Each component in the endosomal-lysosomal system plays individual crucial role and they work concordantly to ensure protein degradation can be carried out functionally. Dysregulation in the endosomal-lysosomal system can contribute to the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). In AD endosomal-lysosomal abnormalities are the earliest pathological features to note and hence it is important to understand the involvement of endosomal-lysosomal dysfunction in the pathogenesis of AD. In-depth understanding of this dysfunction can allow development of new therapeutic intervention to prevent and treat AD.
  12. Chia KY, Ng KY, Koh RY, Chye SM
    CNS Neurol Disord Drug Targets, 2018;17(9):671-679.
    PMID: 29546836 DOI: 10.2174/1871527317666180315161626
    BACKGROUND & OBJECTIVE: Protein misfolding and aggregation have been considered the common pathological hallmarks for a number of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). These abnormal proteins aggregates damage mitochondria and induce oxidative stress, resulting in neuronal cell death. Prolonged neuronal damage activates microglia and astrocytes, development of inflammation reaction and further promotes neurodegeneration. Thus, elimination of abnormal protein aggregates without eliciting any adverse effects are the main treatment strategies. To overcome this, recent studies have deployed single- chain fragment variable antibodies (scFvs) to target the pathological protein aggregates, such as amyloid-beta (Aβ) peptides, α-synuclein (α-syn) and Huntingtin (Htt). To date scFv has been effective at inhibiting abnormal protein aggregates formation in both in vitro and in vivo model system of AD, PD and HD.

    CONCLUSION: Currently active research is still ongoing to improve the scFv gene delivery technology, to further enhance brain penetration, intracellular stability, solubility and efficacy of scFv intrabody.

  13. Ngai ZN, Chok KC, Ng KY, Koh RY, Chye SM
    Horm Mol Biol Clin Investig, 2022 Dec 01;43(4):485-503.
    PMID: 35728260 DOI: 10.1515/hmbci-2022-0018
    Lung cancer is the second most common cancer and the most lethal cancer worldwide. Melatonin, an indoleamine produced in the pineal gland, shows anticancer effects on a variety of cancers, especially lung cancer. Herein, we clarify the pathophysiology of lung cancer, the association of circadian rhythm with lung, and the relationship between shift work and the incidence of lung cancer. Special focus is placed on the role of melatonin receptors in lung cancer, the relationship between inflammation and lung cancer, control of cell proliferation, apoptosis, autophagy, and immunomodulation in lung cancer by melatonin. A review of the drug synergy of melatonin with other anticancer drugs suggests its usefulness in combination therapy. In summary, the information compiled may serve as a comprehensive reference for the various mechanisms of action of melatonin against lung cancer, as a guide for the design of future experimental research and for advancing melatonin as a therapeutic agent for lung cancer.
  14. Ko Y, Ngai ZN, Koh RY, Chye SM
    Tuberc Respir Dis (Seoul), 2023 Apr;86(2):102-110.
    PMID: 36597582 DOI: 10.4046/trd.2022.0125
    Coronavirus disease 2019 (COVID-19) has become a major health burden worldwide, with over 600 million confirmed cases and 6 million deaths by 15 December 2022. Although the acute phase of COVID-19 management has been established, the long-term clinical course and complications due to the relatively short outbreak is yet to be assessed. The current COVID-19 pandemic is causing significant morbidity and mortality around the world. Interestingly, epidemiological studies have shown that fatality rates vary considerably across different countries, and men and elderly patients are at higher risk of developing severe diseases. There is increasing evidence that COVID-19 infection causes neurological deficits in a substantial proportion to patients suffering from acute respiratory distress syndrome. Furthermore, lack of physical activity and smoking are associated with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) susceptibility. We should therefore explore why lack of physical activity, smoking, etc causing a population more susceptible to SARS-CoV-2 infection, and mechanism involved. Thus, in this review article, we summarize epidemiological evidence related to risk factors and lifestyle that affect COVID-19 severity and the mechanism involved. These risk factors or lifestyle interventions include smoking, cardiovascular health, obesity, exercise, environmental pollution, psychosocial social stress, and diet.
  15. Ng MG, Chan BJL, Koh RY, Ng KY, Chye SM
    PMID: 37326115 DOI: 10.2174/1871527322666230616092054
    Parkinson's disease (PD) is a debilitating neurological disorder characterized by progressively worsening motor dysfunction. Currently, available therapies merely alleviate symptoms, and there are no cures. Consequently, some researchers have now shifted their attention to identifying the modifiable risk factors of PD, with the intention of possibly implementing early interventions to prevent the development of PD. Four primary risk factors for PD are discussed including environmental factors (pesticides and heavy metals), lifestyle (physical activity and dietary intake), drug abuse, and individual comorbidities. Additionally, clinical biomarkers, neuroimaging, biochemical biomarkers, and genetic biomarkers could also help to detect prodromal PD. This review compiled available evidence that illustrates the relationship between modifiable risk factors, biomarkers, and PD. In summary, we raise the distinct possibility of preventing PD via early interventions of the modifiable risk factors and early diagnosis.
  16. Salem HMA, Chok KC, Koh RY, Ng PY, Tiong YL, Chye SM
    Int J Biochem Mol Biol, 2023;14(3):25-31.
    PMID: 37456910
    Diabetic neuropathy (DN) is a condition in which nerve fibers are continually exposed to high glucose-induced free radicals. Recent discoveries demonstrated that melatonin is an indole hormone that contributes to neuroprotection through the modulation of autophagy. Herein, this study aims to examine the neuroprotective effects of melatonin on Schwann cells under high glucose conditions. 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay was used to measure cell viability. The activation of autophagosomes was determined using acridine orange staining (AO). Western blot assay was used to measure the expression of proteins involved in autophagy and endoplasmic reticulum (ER) stress. Our results demonstrated that melatonin at 1 µM has the highest protective effects on high glucose-induced cell death. Melatonin concentrations of 5 and 10 µM were found to be the most effective in reducing autophagy induced by high glucose. Under high glucose conditions, the protein expressions of LC3, ATF4, ATF6, CHOP, PERK and eIF2-α were up-regulated in Schwann cells. However, melatonin attenuated these changes by downregulating LC3 and the ER stress markers ATF4, ATF6, CHOP, PERK and eIF2-α protein expressions in Schwann cells. In conclusion, melatonin alleviates high glucose-induced autophagy in Schwann cells through PERK-eIF2α-ATF4-CHOP signaling pathways.
  17. Tiong YL, Ng KY, Koh RY, Ponnudurai G, Chye SM
    Exp Ther Med, 2020 Nov;20(5):16.
    PMID: 32934681 DOI: 10.3892/etm.2020.9143
    Upon peripheral nerve injury (PNI), continuous proliferation of Schwann cells is critical for axon regeneration and tubular reconstruction for nerve regeneration. Melatonin is a hormone that is able to induce proliferation in various cell types. In the present study, the effects of melatonin on promoting Schwann cell proliferation and the molecular mechanism involved were investigated. The present results showed that melatonin enhanced the melatonin receptors (MT1 and MT2) expression in Schwann cells. Melatonin induced Schwann cell dedifferentiation into progenitor-like Schwann cells, as observed by immunofluorescence staining, which showed Sox2 marker expression. In addition, melatonin enhanced Schwann cell proliferation, mediated by the upregulation of glial cell-derived neurotropic factor (GNDF) and protein kinase C (PKC). Furthermore, the Ras/Raf/ERK and MAPK signaling pathways were also involved in Schwann cell dedifferentiation and proliferation. In conclusion, melatonin induced Schwann cell dedifferentiation and proliferation via the Ras/Raf/ERK, MAPK and GDNF/PKC pathways. The present results suggested that melatonin could be used to enhance the recovery of PNI.
  18. Khor SLQ, Ng KY, Koh RY, Chye SM
    CNS Neurol Disord Drug Targets, 2024;23(3):315-330.
    PMID: 36999187 DOI: 10.2174/1871527322666230330093829
    The blood-brain barrier (BBB) plays a crucial role in the central nervous system by tightly regulating the influx and efflux of biological substances between the brain parenchyma and peripheral circulation. Its restrictive nature acts as an obstacle to protect the brain from potentially noxious substances such as blood-borne toxins, immune cells, and pathogens. Thus, the maintenance of its structural and functional integrity is vital in the preservation of neuronal function and cellular homeostasis in the brain microenvironment. However, the barrier's foundation can become compromised during neurological or pathological conditions, which can result in dysregulated ionic homeostasis, impaired transport of nutrients, and accumulation of neurotoxins that eventually lead to irreversible neuronal loss. Initially, the BBB is thought to remain intact during neurodegenerative diseases, but accumulating evidence as of late has suggested the possible association of BBB dysfunction with Parkinson's disease (PD) pathology. The neurodegeneration occurring in PD is believed to stem from a myriad of pathogenic mechanisms, including tight junction alterations, abnormal angiogenesis, and dysfunctional BBB transporter mechanism, which ultimately causes altered BBB permeability. In this review, the major elements of the neurovascular unit (NVU) comprising the BBB are discussed, along with their role in the maintenance of barrier integrity and PD pathogenesis. We also elaborated on how the neuroendocrine system can influence the regulation of BBB function and PD pathogenesis. Several novel therapeutic approaches targeting the NVU components are explored to provide a fresh outlook on treatment options for PD.
  19. Woon SM, Seng YW, Ling AP, Chye SM, Koh RY
    J Zhejiang Univ Sci B, 2014 Mar;15(3):295-302.
    PMID: 24599694 DOI: 10.1631/jzus.B1300123
    This study examined the anti-adipogenic effects of extracts of Ficus deltoidea var. deltoidia and var. angustifolia, a natural slimming aid, on 3T3-L1 adipocytes.
  20. Chua LK, Lim CL, Ling APK, Chye SM, Koh RY
    Plant Foods Hum Nutr, 2019 Mar;74(1):18-27.
    PMID: 30535971 DOI: 10.1007/s11130-018-0704-z
    Cancer is a preventable and treatable disease, however, the incidence rates are on the rise. Classical treatment modalities for cancer include surgery, radiotherapy and chemotherapy. However, these are associated with detrimental side effects such as nausea and emesis. Therefore, researchers currently vest interest in complementary and alternative medicines for cancer treatment and prevention. Plants such as Syzygium sp. are a common basis of complementary medicines due to its abundance of bioactive phytochemicals. Numerous natural compounds derived from Syzygium sp., such as phenolics, oleanolic acids, and betulinic acids, and dimethyl cardamonins, were reported to have anticancer effects. Many possess the ability to inhibit cell proliferation and induce apoptosis. In this review, we discuss the vast potential Syzygium sp. harbours as a source of anticancer natural compounds due to its abundance, easy acceptability, affordability and safety for regular consumption.
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