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Premium member Presentation Transcript HEME,PORPHYRIN AND BILIRUBIN: HEME,PORPHYRIN AND BILIRUBIN Dr.Gogoi , University of Fiji PORPHYRINS: PORPHYRINS NOMENCLATURE Types of substituents Symmetry I or III Oxidation between rings Methylene -CH2- Methene -CH= PORPHYRIN AND HEME METABOLISM: PORPHYRIN AND HEME METABOLISM Porphyrins metal and protein Hemoproteins Heme Hemoglobin Iron Globin chains Protoporphyrin III (IX) PowerPoint Presentation: Heme Fig.44.2 Page 836 Protoporphyrin III Reactions for Protoporphyrin IX Fig. 44.3 Page 837: Reactions for Protoporphyrin IX Fig. 44.3 Page 837 PowerPoint Presentation: Step 1 Synthesis of d -amino levulinic acid Fig. 44.4 837 Mitochondrial location Rate limiting Pyridoxal phosphate (decarboxylase) Regulation of enzyme levels by iron and protohemin PowerPoint Presentation: Step 2 Synthesis of porphobilinogen Fig. 44.5 Page 838 Also called porphobilinogen synthase Zinc-dependent Site of lead toxicity Further Reactions: Further Reactions Step 3 Tetrapyrrole formation synthesis of hydroxymethylbilane synthesis of uroporphyrinogen III Step 4 Conversion to protoporphyrin III uro to copro copro to proto porphyrinogen to porphyrin Step 5 Protoheme synthesis insertion of ferrous iron site of lead toxicity PowerPoint Presentation: 1 2 3 3 4 4 5 Heme Proteins : Heme Proteins Protoheme (or heme) + globin ~ hemoglobin Protohemin formation -- formation of superoxide Variations in heme Fe ligands 4, 5, or 6 Ferrous or Ferric Protoporphyrin III attachment to protein PowerPoint Presentation: Iron-IRE Defects in Heme Biosynthesis: Defects in Heme Biosynthesis Most animals synthesize their own heme Mutations or mis-regulaton of enzymes in heme biosynthesis pathway lead to porphyrias Accumulation of uroporphyrinogen I causes urine to become red teeth to fluoresce under UV light skin to be sensitive to UV light desire to obtain heme with diet PowerPoint Presentation: Porphyrias Treatment Hematin (hemin hydroxide) PowerPoint Presentation: 1 2 3 3 4 4 5 Bilirubin synthesis: Bilirubin synthesis 80% bilirubin originates from senescent RBCs 1-2 х 10*8 RBCs destroyed/hour 6g hb produced in body/day 250-300 mg bilirubin produced/day Pathway for RBC Scavenging: Pathway for RBC Scavenging Liver, Spleen & Bone marrow Hemoglobin Globin Amino acids Amino acid pool Heme Bilirubin Fe 2+ Excreted Phagocytosis & Lysis Through Liver 20 PowerPoint Presentation: Bilirubin synthesis PowerPoint Presentation: Fog J, Jellum E. Structure of bilirubin. SUMMARY OF BILIRUBIN METABOLISM IN LIVER: SUMMARY OF BILIRUBIN METABOLISM IN LIVER BILIRUBIN CONJUGATION: BILIRUBIN CONJUGATION Essential for biliary excretion of bilirubin Glucuronic acid – major conjugating sugar in bile Glucosyl,xylosyl conjugates-traces Catalyzed by UDP-glucuronosyltransferase(UGT ) UGT ENZYME SYSTEM: UGT ENZYME SYSTEM 2 Major families UGT 1: Major bilirubin conjugating form in human UGT 2: Conjugation of steroids,other endogenous and exogenous substrates Multiple isoforms present One isoform of UGT 2 family: inducible by phenobarbital Significance: UGT 1A locus abnormalities- disorders of bilirubin conjugation phenobarbital used as enzyme inducer in some conditions of hyperbilirubinemia UGT 1 COMPLEX: UGT 1 COMPLEX Chromosome 2q37 Exons 2,3,4,5- used in all isoforms expressed from this locus,so mutations affect all isoforms Exons 1A1-12 : variable ; each exon has different promoter region and differently regulated,mutation affects only the corresponding isoform PowerPoint Presentation: A TATATATATATA TAA A TATATA (TA) TATATA TAA BILIRUBIN EXCRETION: BILIRUBIN EXCRETION The rate limiting step in bilirubin metabolism Excreted across canalicular membrane into bile MRP( Multidrug resistant protein) family – efflux pumps MRP 2- essential for bilirubin excretion Significance: Deficiency of MRP 2: DUBIN JOHNSON SYNDROME MRP 2- downregulated in cholestasis BILIRUBIN IN INTESTINE: BILIRUBIN IN INTESTINE 30 BILIRUBIN HANDLING IN KIDNEY: BILIRUBIN HANDLING IN KIDNEY 31 INHERITED DISORDERS OF BILIRUBIN METABOLISM: INHERITED DISORDERS OF BILIRUBIN METABOLISM UNCONJUGATED HYPERBILIRUBINEMIA CRIGLER NAJJAR SYN. TYPE 1 CRIGLER NAJJAR SYN. TYPE 2 (ARIAS SYN.) GILBERT SYNDROME CONJUGATED HYPERBILIRUBINEMIA DUBIN JOHNSON SYNDROME ROTOR SYNDROME GILBERT SYNDROME: GILBERT SYNDROME pronounced 'zheel-BAYR', often shortened to GS , also called Gilbert-Meulengrachts syndrome Described by Gilbert in 1901 Most common inherited disorder of bilirubin metabolism Males > females; Prevalence 8-10% Presentation: Bilirubin levels remain < 3mg/dL; may increase during intercurrent illness or stress Jaundice is the only positive finding often Routine lab tests are normal PowerPoint Presentation: Molecular mechanism: A TATATATATATA TAA A TATATA (TA) TATATA TAA Promoter-reporter studies show that an increased TATAA box length reduces UGT1A1 expression Bosma PJ, Roy Chowdhury J, Bakker C, et al. The genetic basis of the reduced expression of bilirubin UDP- glucuronosyltransferase 1 in Gilbert’s syndrome. N Engl J Med 1995; 333:1171. UGT 1A1*28 PowerPoint Presentation: DIAGNOSIS: Presumptive diagnosis made if: Mild unconjugated hyperbilirubinemia on several occasions Serum GGT,ALP,fasting and postcibal bile acids normal Confirmation : Estimate relative concentrations of bilirubin monoglucuronide to diglucuronide Genetic analysis CRIGLER NAJJAR SYNDROME TYPE 1: CRIGLER NAJJAR SYNDROME TYPE 1 Described by Crigler and Najjar in 1952. Autosomal recessive inheritance Incidence 0.6-1.0/ million; occurs in all races Characterised by striking unconjugated hyperbilirubinemia 20-45 mg/dL (340-765 µmol/L) Jaundice Appears in neonatal period ; persists for life MOLECULAR MECHANISM : MOLECULAR MECHANISM TYPE 1A : Defect in conjugation of various drugs and xenobiotics in addition to bilirubin Constitutes majority of cases; mutations in exons 2-5 TYPE 1B : Defect limited to bilirubin conjugation Small subset of patients; mutations in exon A1 CLINICAL FEATURES: CLINICAL FEATURES Severe unconjugated hyperbilirubinemia at birth Prior to phototherapy: Kernicterus Death in infancy PowerPoint Presentation: With phototherapy: Child may survive infancy Jaundice persists throught life Prone to kernicterus throught life PowerPoint Presentation: LAB FEATURES: High serum bilirubin 18-30 mg, no evidence of hemolysis Other parameters within normal limits Bilirubin not present in urine; bile lacks glucuronides Liver biopsy shows normal histology Molecular diagnostics for gene sequence abnormalities for diagnosis PowerPoint Presentation: TREATMENT : Aims at reducing bilirubin levels Exchange tranfusion: in immediate neonatal period Phototherapy: Main stay of treatment Special blue lamps used;wavelength 450-500 nm PowerPoint Presentation: Phototherpy for infants PowerPoint Presentation: Becomes less effective near puberty Plasmapheresis: Effective in emergencies Orthotopic liver transplantation: Standard treatment for CN-1 CRIGLER NAJJAR SYN.2: CRIGLER NAJJAR SYN.2 ARIAS Syndrome Milder variant Autosomal recessive Differs from CN 1 by: Average bilirubin concentrations low Infrequently associated with kenicterus Bile deeply coloured; bilirubin monoglucuronides present UGT1A activity reduced;not absent totally Bilirubin concentration falls by >25% with phenobarbital administration PowerPoint Presentation: Molecular mechanisms: Characterised by aminoacid substitutions – reduce UGT1A1 activity, not abolish it Clinical features: Asymptomatic in most cases Treatment: Similar to CN-1 DUBIN JOHNSON SYNDROME: DUBIN JOHNSON SYNDROME First described by DUBIN & JOHNSON in 1954 Characterised by chronic non-hemolytic jaundice with accumulation of conjugated bilirubin in serum Dark pigmented liver- dark liver jaundice Autosomal recessive ; both sex affected Clinical features: Mild icterus Asymptomatic Hyperbilirubinemia during illness, pregnancy PowerPoint Presentation: PATHOGENESIS: Defeciency of MRP 2 protein on canalicular membrane. Tm reduced; storage normal ROTOR SYNDROME: ROTOR SYNDROME First described by ROTOR in 1948 Rare disorder autosomal recessive inheritance Predominantly conjugated hyperbilirubinemia ctd..: ctd.. Shares many features with DJS. Liver not pigmented. Both Tm and storage reduced Abnormality: not known PowerPoint Presentation: ?Defect in bilirubin uptake: decreased clearance may also be related to defective uptake Effect of fasting: 2-3 fold increase in s.bilirubin observed on reducing caloric intake to 400 cal. For 48 hours. Limited use in diagnosis BILIRUBIN- FRIEND OR FOE??: BILIRUBIN- FRIEND OR FOE?? Function as natural antioxidants in newborns Attenuates graft rejection in cardiac transplant models Inverse relation between bilirubin and coronary artery disease Inverse relation between bilirubin and colorectal cancer You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.