Untargeted NMR Metabolomics Reveals Alternative Biomarkers and Pathways in Alkaptonuria

Abstract

Alkaptonuria (AKU) is an ultra-rare metabolic disease caused by the accumulation of homogentisic acid (HGA), an intermediate product of phenylalanine and tyrosine degradation. AKU patients carry variants within the gene coding for homogentisate-1,2-dioxygenase (HGD), which are responsible for reducing the enzyme catalytic activity and the consequent accumulation of HGA and formation of a dark pigment called the ochronotic pigment. In individuals with alkaptonuria, ochronotic pigmentation of connective tissues occurs, leading to inflammation, degeneration, and eventually osteoarthritis. The molecular mechanisms underlying the multisystemic development of the disease severity are still not fully understood and are mostly limited to the metabolic pathway segment involving HGA. In this view, untargeted metabolomics of biofluids in metabolic diseases allows the direct investigation of molecular species involved in pathways alterations and their interplay. Here, we present the untargeted metabolomics study of AKU through the nuclear magnetic resonance of urine from a cohort of Italian patients; the study aims to unravel molecular species and mechanisms underlying the AKU metabolic disorder. Dysregulation of metabolic pathways other than the HGD route and new potential biomarkers beyond homogentisate are suggested, contributing to a more comprehensive molecular signature definition for AKU and the development of future adjuvant treatment.

A proximity complementation assay to identify small molecules that enhance the traffic of ABCA4 misfolding variants

“…Chemical chaperones or kosmotropes display a nonspecific mode of action, stabilising protein structure and assisting folding, or enabling the mutant proteins to escape the cell quality control systems [19][20][21] . Pharmacological chaperones are low molecular weight compounds that directly bind to the target protein, promoting thermodynamic stabilization and template-based induction of proper folding, correcting aberrant folding and thereby enhancing protein function 22,23 .…”

Pharmacological Chaperones and Protein Conformational Diseases: Approaches of Computational Structural Biology

“…Many people suffer from conformational diseases, significantly challenging human health [ 8 ]. The present review focuses on examples of rare types of conformational diseases, such as (with involved protein in parenthesis): Phenylketonuria (phenylalanine hydroxylase, PAH) [ 9 , 10 ], Alkaptonuria (1,2 homogentisate dioxygenase, HGD) [ 11 , 12 ], Transthyretin-related hereditary amyloidosis (transthyretin, TTR) [ 13 ], and the group of lysosomal storage diseases [ 14 ] including GM1-gangliosidosis (β-galactosidase), Tay-Sachs disease (β-hexosaminidase A), Sandhoff disease (β-hexosaminidases A and B), AB variant of GM2-gangliosidosis (GM2 activator protein), Fabry disease (α-galactosidase A), Gaucher disease (β-glucocerebrosidase), Pompe disease (α-glucosidase), mucopolysaccharidosis IIIC (heparan-α-glucosaminide N-acetyltransferase), and Batten disease (battenin).…”

Identification of Potential Inhibitors for the Treatment of Alkaptonuria Using an Integrated In Silico Computational Strategy

“…Furthermore, Boedeker suggested the name of AKU which was derived from the term Alkapton. The term Alkapton is of Greek origin that is kápton which means “to gulp down” [ 5 ]. It is characterized by high levels of serum and urine homogentisic acid (HGA) due to mutations in the nucleotide sequence of homogentisate 1,2-dioxygenase (HGD) [ 1 ].…”