Caeruloplasmin isoforms in Wilson's disease in neonates

Diagnosis and clinical biochemistry of inherited tubulopathies

Epithelial ion channels and transporter proteins have physiologically important roles throughout the length of the nephron. Discovering the molecular identities of tubular epithelial cell proteins and their functional roles has increased understanding of both renal physiology and tubular diseases. Defects in tubular handling of solutes may present with nephrocalcinosis or nephrolithiasis, rickets, acid base, electrolyte or blood pressure disturbances. Biochemical analysis of both serum and urine, together with clinical history and examination, remain fundamental for their diagnosis, whilst understanding of underlying molecular mechanisms allows appropriate management.

Specific oxidase activity of cord serum ceruloplasmin in the newborn

In a study of 50 full-term newborns, we found serum levels of ceruloplasmin, its oxidase activity and specific oxidase activity (activity per unit mass of enzyme protein) which were significantly lower than in adult subjects (p<0.001). A significant correlation was obtained between the specific oxidase activity of the neonatal ceruloplasmin and the transferrin/alpha-fetoprotein ratio (p<0.01), which reflects the maturity of the fetal hepatocyte through its ability to synthesise fetal- and non-fetal-associated proteins. The lower specific oxidase activity of the ceruloplasmin in newborns would be due to a higher relative proportion of apoprotein, and/or other molecular forms with a poor copper content in the oxidase sites. This could be due to an inability to transfer copper into a common intracellular pool for holoceruloplasmin synthesis and biliary copper excretion. A high interindividual variability was found for the specific oxidase activity of the neonatal ceruloplasmin, and in the newborns with higher levels of ceruloplasmin this, from a catalytic point of view, is more similar to the adult form.

Biological functions of ceruloplasmin and their deficiency caused by mutation in genes regulating copper and iron metabolism

Ceruloplasmin, a multicopper ferroxidase, is involved in iron and copper homeostasis and integrates these metabolic pathways. Impaired biosynthesis of ceruloplasmin caused by gene mutations disturbs iron metabolism with iron deposition in different organs, especially in the basal ganglia, and severe neuronal damage. Dysfunction of ATP7B, a copper-transporting ATPase leads to the development of Wilson's disease, i.e., multiple abnormalities in copper metabolism associated with reduced synthesis of holoceruloplasmin and biliary copper excretion controlled by both proteins. The lowest content of serum ceruloplasmin is observed in the most grave early neurological form of Wilson's disease (according to N. V. Konovalov's classification), which confirms the important role of ceruloplasmin in the striatal metabolism of catecholamines.