Bilirubin as protective factor against the development of chronic degenerative disease: serum biomarker and potential for pharmacological modulation
Bilirubin is present in various chemical forms in the blood, namely, conjugated with glucuronic acid (direct bilirubin), unconjugated bound to serum albumin (indirect bilirubin) and unconjugated-unbound (free bilirubin). The bioactive form is the free bilirubin, which is not measured routinely in the clinical setting, but has been recently identified to be around 10 nM in serum. Importantly, nanomolar concentrations of bilirubin can protect cells from the 10,000-fold molar excess of oxidants when both substances are added exogenously to cell culture. This remarkable effect has been explained that bilirubin acting as antioxidant, is itself oxidized to biliverdin, and then recycled by biliverdin reductase back to bilirubin. All in all, bilirubin is an endogenous antioxidant with anti‑inflammatory and anti-thrombotic activity, and is inversely correlated with disease risk of the cardiovascular system, such as ischemic heart disease, hypertension, diabetes type II, metabolic syndrome, obesity, among others. Importantly, some positive lifestyle modifications, e.g. weight loss or cessation of smoking, lead to higher levels of serum bilirubin. We hypothesise that bilirubin has the potential to be used as a biomarker for cardiovascular pre‑disease states and that serum bilirubin levels can be modulated.
In this project we will include a large sample of healthy volunteers and volunteer-patients and measure in their serum all forms of bilirubin, including free bilirubin and free biliverdin. We will introduce a new parameter B / B (ratio of free bilirubin / biliverdin free) as a potential biomarker for development of chronicdegenerative diseases, especially cardiovascular and neurodegenerative, which involve in its aetiology increased oxidative stress and chronic inflammation. Importantly, in this project we will also study the potential of pharmacological modulation of serum bilirubin levels. We aim to identify drug compunds that interfere with protein targets, which are involved in bilirubin homeostasis, by in silico experiments (computer modelling), in vitro (cell culture) and in vivo (whole animal) experiments.
The aim of the project is to determine how to moderatley increase serum bilirubin levels, in order to enhance its protective activity. Namely, we will investigate the following hypotheses:
- positive lifestyle changes (due to lower consumption of bilirubin due to reduced oxidative stress and reduces inflammation) – a prospective study in volunteers, which will decide for at least one substantial amendment in their lives:
- smoking cessation;
- loss of excess weight;
- an increase in physical activity;
- improvement in diet;
- reduction of psychosocial stress.
- pharmacological interventions (increase in serum bilirubin) by increasing the synthesis of bilirubin (induction biliverdin reductase (BVR) and heme oxidase-1 (HO-1), which are responsible for the synthesis of bilirubin), inhibition of uptake in liver cells (inhibition of organic anion transporters (OATP) and bilitranslocase (BTL), inhibition of its metabolism in liver cells (inhibition of UDP-glucuronosyltransferase (UGT1A1), or through displacement from albumin (the interaction of the active substance with bilirubin bound to albumin). These studies will take place in the computer models (in silico), in cell culture (in vitro) and animal models (in vivo). The aim is to identify new clinical indications for drugs that are already registered in the market with an established safety profile (drug repurposing).
Project partners: University of Ljubljana, Faculty of Medicine (coordinator); National Institute of Chemistry; Universita del Litorale, Facolta di Scienze della Salute; University of Nova Gorica.
Duration of project: 01.05.2017 – 30.04.2020
Link to official project web page: Bilirubin