## 1 Introduction  
Poly (ADP-ribose) polymerase 1 (PARP-1) is the first and most abundant isoform of the PARP nuclear enzyme family which has a crucial role in the stabilization of DNA replication forks by repairing DNA strands in homeostatic conditions [1, 2]. After binding with DNA breaks, the activated PARP cleaves NAD+ into nicotinamide and ADP-ribose which polymerizes the nuclear acceptor proteins including transcription factors and histone. PARP1 initiates and modulates multiple DNA repair pathways and is thus important for maintaining genomic integrity [3]. Nevertheless, its overactivation in several pathological conditions induces a depletion of NAD+ and ATP that triggers cellular death and up-regulation of key inflammatory pathways [4, 5]. Therefore, loss of PARP1 activity by its inhibitor is an attractive strategy for treatment of malignancies, both as single agents and in combination to enhance the cytotoxic activity of DNA damaging agents [6]. Beneficial effects of some PARP inhibitors, e.g., nicotinamide and 3-aminobenzamide, have been previously reportedin various pathophysiological conditions [7], but they were not more potent and have poor permeability across cell membranes [8; 9]. 5-Aminoisoquinoline (5-AIQ) is a water-soluble, more potent and selective inhibitor of PARP-1 in human cells, being widely used as a biochemical and pharmacological tool to study the effects of inhibition of the PARPs [10; 11; 12]. 5-AIQ has also been proven to be useful in producing beneficial effects in various experimental models of ischemia-reperfusion injury for cerebral, cardiac splanchnic, renal and hepatic artery [13; 14; 15; 16]. Due to its anti-inflammatory and immunomodulatory properties, it has produced beneficial effects in experimental models of neuroimmune dysfunction, lungs injury, along with remarkable anti-angiogenic activity and anti-metastatic activity [17; 18; 19]. In a genotoxicity test, 5-AIQ was found to be non-mutagenic, suggesting that it has no role to play in DNA damage under normal conditions [20]. In addition, 5-AIQ can be a therapeutic alternative in depression, arthritis, asthma, Parkinson's disease, multiple sclerosis and hepatic disease due to its PARP1 antagonist potential [11]. 5-AIQ is also found to be the most active among the TRPV-1 (Transient Receptor Potential Varilloid-1) antagonists in the class of 1,3-disubstituted urea derivatives and is under development for varying indications including chronic pain [21].  
The quantitative detection of the active compounds is pivotal to obtain reliable results and to make critical decisions supporting safety and efficacy of compounds [22; 23]. In drug development, each compound must undergo metabolic fate and pharmacokinetic studies which enable decisions for optimal route of administration, dosing regimen and its biodistribution. A selective and reliable analytical method is required for determining the quantity of a compound in a biological matrix. In spite of having a broad therapeutic potential, no analytical assay has been reported for the quantitative determination of 5-AIQ in plasma or liver microsomes. Among the available techniques, ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) is considered the \"gold standard\" method for the determination of target analytes in biological fluids. This article presents the data on the development and validation of a method for quantitative detection of 5-AIQ in plasma using the UPLC-MS/MS method. Furthermore, the developed assay was successfully applied in metabolic stability studies in human liver microsomes. In silico, an absorption, distribution, metabolism and excretion (ADME) profile was also computed to predict the drug-like possibilities of 5-AIQ.