INHERITED DISORDERS OF BILIRUBIN GLUCURONIDATION

Project: Research project

Project Details

Description

Bilirubin and many other non-polar endogenous metabolites or
exogenous carcinogens, toxins and drugs are converted to polar
conjugates, primarily in the liver, by UDP-glucuronosyltransferase
(UDPGT)-mediated glucuronidation prior to excretion in the bile
or urine. UDPGT is a principal enzyme-system in conjugative
detoxification. Inherited disorders with defective UDPGT
function are associated with unconjugated hyperbilirubinemia; in
severe cases (e.g. Crigler-Najjar syndrome, Type I), patients die in
infancy or around the age of puberty from bilirubin induced brain
damage. Gunn rats are an animal model of Crigler-Najjar
syndrome, Type I. Our studies indicate that in rat liver, UDPGT
exists as multiple distinct but structurally related isoforms. Two
of these isoforms catalyze the glucuronidation of bilirubin, others
mediate the conjugation of phenolic, steroidal, N- and S-
substrates. In Gunn rats, two UDPGT isoforms, Isoform V
(normally active toward bilirubin), and Isoform I (normally active
toward 4-nitrophenol), are present in immunoreactive but
functionally defective forms. UDPGT activities toward various
substrates develop at different periods of perinatal life, are
specifically inducible and are expressed differentially during
hepatocellular proliferation. Molecular mechanisms of
multiplicity, ontogenic development, induction, and inherited
functional defects of UDPGT are not known. As a part of this
project during the last two years we have purified normal and
functionally defective UDPGT isoforms from Gunn and normal
rats and developed a series of UDPGT-specific cDNA clones from
rat liver. Specific aims of this continuation application are to use
these clones for development of UDPGT isoform-specific cDNA
probes, which will be used for (a) the study the molecular
mechanism of development and induction of UDPGTs and (b)
determination of whether individual UDPGT isoforms are products
of distinct genes; and (b) full-length cDNA clones for UDPGT
Isoforms I and V, which will be used to define the structural basis
for defective UDPGT function in Gunn rats by nucleotide
sequence determination. We also wish to introduce the normal
cDNA sequences for Isoforms I and V into isolated Gunn rat
hepatocytes for correction of the inherited disorder of bilirubin
glucuronidation; these cells will be subsequently transplanted into
syngeneic Gunn rat recipients by a method which was also
developed in our laboratory during execution of this project. This
system represents the application of recently developed
technology in the investigation of these biologically important
protein that have multiple isoforms, are differentially regulated,
have defective function in mutants and are of low abundance
indicating tight control.
StatusFinished
Effective start/end date7/1/846/30/92

Funding

  • National Institutes of Health: $229,891.00

ASJC

  • Medicine(all)
  • Drug Discovery
  • Molecular Biology
  • Developmental Neuroscience
  • Biochemistry
  • Toxicology

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