International Journal of Applied Pharmaceutics ISSN - 0975 - 7058 Vol 13, Special Issue 1, 2021 KINETIC PARAMETER ANALYSIS OF MYELOPEROXIDASE IN THE PRESENCE OF SOME COSUSBTRATES IN SALIVA OF NEWBORN AT RISK OF SEPSIS ARI YUNANTO 1 , EDI HARTOYO 1 , ISKANDAR THALIB 1 *, NIARSARI ANUGRAHING PUTRI 1 , EKO SUHARTONO 2 1 Department of Child Health, Faculty of Medicine, Lambung Mangkurat University, Banjarmasin, Indonesia. 2 Department of Medical Chemistry/Biochemistry, Faculty of Medicine, Lambung Mangkurat University, Banjarbaru, Indonesia. Email: iskandarthalib@gmail.com Objective: During infection like sepsis, myeloperoxidase (MPO) enzyme will be generated from the neutrophil. This enzyme will catalyze the oxidation of halide or pseudohalide (Cl, I - , SCN, and Br - ) using hydrogen peroxide (H 2 O 2 ). However, the mechanism by which oxidation of these several cosubstrates in neonatal sepsis is unknown. Here, we have compared the kinetic parameter of MPO in saliva of newborn at risk of sepsis with or without the presence of these several cosubstrates. Methods: In this experiment, saliva samples were taken from newborn in health (n = 20) and risk of sepsis (n = 20). Saliva samples from each group then homogenized and divided into four groups. Group 1 served as control which contains saliva+H 2 O 2 ; Group 2 contains saliva+H 2 O 2 +Cl − ; Group 3 contains saliva+H 2 O 2 +I − ; and Group 4 contains saliva+H 2 O 2 +SCN − . After 1 h incubation, the kinetic parameters (Km and Vmax) were analyzed. Results: The result shows that in sepsis condition, compared without the presence of some cosubstrates, it seems the addition of some cosubstrate will increase the affinity between MPO, H 2 O 2 , and the cosubstrate. Between these three cosubstrates, it seems in sepsis condition MPO will oxidize Cl − . Conclusion: In sepsis condition, MPO works by a common mechanism, that is, oxidizing Cl − to hypochlorous acid than another cosubstrate. Keywords: Myeloperoxidase, Neonatal Sepsis, Saliva INTRODUCTION Neonatal sepsis (NS) is still a problem in the worldwide because it is one of the leading causes of neonatal death. It is estimated that more than 40% death of children under-5 years old occur in neonates, and each year there are 3.1 million neonates who die in the world [1]. The death of the neonate is mostly caused by NS. NS is responsible for 30–50% of all total neonatal deaths, especially in developing countries [2]. NS is a clinical syndrome which is characterized by a hemodynamic, respiratory, and metabolic disturbance process due to systemic infection that can trigger an abnormal systemic inflammatory response syndrome in infants [3,4]. The signs and symptoms of NS are varied and not specific. This causes the diagnosis of NS to be difficult. Until now, only blood culture can be a definitive diagnosis for NS, but as it is known, blood culture takes a long time and is quite expensive. The difficulties of this diagnosis make some of clinicians used “Suspected sepsis” to diagnoses NS before the blood culture results [5]. The pathomechanism of NS is still unclear, but several studies have suggested that myeloperoxidase (MPO) enzyme was involved in these pathomechanism. Our previous result study shows that the level of MPO was significantly higher in saliva of newborn with risk of sepsis compared to healthy newborn [6]. The MPO level elevation in NS is thought to be caused by an immune and inflammatory response during NS. This response was important in these time, because it plays an important role in killing invading parasites and pathogens [5]. MPO is a heme-containing enzyme which is produced by neutrophils during phagocytosis. MPO plays an important role in killing pathogens through the formation of reactive oxidants which acts as an antimicrobial [7,8]. Furthermore, because MPO is one of the peroxidases family enzyme, it also can act as a catalyst of hydrogen peroxide (H 2 O 2 ) removal, depending on the conditions under which it operates. If the MPO plays a role in the defense mechanism against the pathogen, MPO will use H 2 O 2 and halide (iodide, bromide, chloride, and thiocyanate; I, Br, Cl, and SCN) to produce pseudo-halide such as hypoiodous acid (HOI), hypobromous acid, hypochlorous acid (HOCl), and hypothiocyanite acid (HOSCN). Conversely, if the MPO plays a role for H 2 O 2 removal, then the MPO will catalyze the change of H 2 O 2 into water (H 2 O) and oxygen (O 2 ) [9,10]. Study of kinetics parameters of an enzyme is important to explain the work mechanism of the enzyme. From this point of view, it is important to know the kinetic parameters of the MPO in NS considering that many reactions catalyzed by MPO. Due to important role of MPO in NS, the work mechanism in these diseases has attracted much attention. In this regard and for better understanding of the possible mechanisms of MPO with the presence of some cosubstrates (I, Cl, and SCN) in NS, changes in the kinetic parameters of MPO on interaction with those cosubstrates were studied. MATERIALS AND METHODS Participants This was a prospective study conducted from December 2016 to June 2017. Ethical approval was obtained from the Ethics Commission of the Faculty of Medicine, Lambung Mangkurat University, Banjarmasin, South Kalimantan, Indonesia (approval number: 2010019). Written informed consent was obtained from all guardians on behalf of the newborn participants involved in the study. Patients who were participated in this study are newborn with risk of SN (n = 15) based on The American Congress of Obstetricians and Gynaecologist guidelines criteria for NS. Patients who were participated must at least have 1 major criterion or 2 minor criteria according to these criteria. Healthy newborns (n = 15) were included as controls. Full Proceeding Paper © 2021 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open access article under the CC BY license (http://creativecommons. org/ licenses/by/4.0/) DOI: http://dx.doi.org/10.22159/ijap.2021.v13s1.Y0072. Journal homepage: https://innovareacademics.in/journals/index.php/ijap Received: 21 November 2019, Revised and Accepted: 24 January 2020 ABSTRACT 5 th International Conference on Pharmacy and Pharmaceutical Science (ICPPS) 2020