Porphyrins & Bile PigmentsFY WIDODO

University of Wijaya Kusuma SurabayaMedical Faculty Department of Biochemistry

PORFIRINCyclic compounds formed by the linkage of four pyrrole rings through methyne (HC =) bridgesFormation of complexes with metal ions bound to the nitrogen atom of the pyrrole rings

Examples of Some Important Human HemoproteinsProteinFunctionHemoglobinTransport of oxygen in bloodMyoglobinStorage of oxygen in muscleCytochrome c Involvement in electron transport chainCytochrome P450Hydroxylation of xenobioticsCatalaseDegradation of hydrogen peroxideTryptophan pyrrolaseOxidation of tryptophan

A (acetate)P (propionate)M (methyl)Addition of iron to protoporphyrin to form heme. V (vinyl) = CHCH2.

Formation of HemeThe two starting materials are succinyl-CoA and glycine Pyridoxal phosphate "activate" glycineCondensation reaction between succinyl-CoA and glycine a-amino- b-ketoadipic acid d-aminolevulinate (ALA)

Enzyme: ALA synthase

decarboxilationMITOCHONDRIATwo molecules of ALA are condensed by the enzyme ALA dehydratase to form two molecules of water and one of porphobilinogen (PBG)ALA dehydratase is a zinc-containing enzyme and is sensitive to inhibition by lead, as can occur in lead poisoning.CYTOSOL

The formation of a cyclic tetrapyrroleie, a porphyrinoccurs by condensation of four molecules of PBG

These four molecules condense in a head-to-tail manner to form a linear tetrapyrrole, hydroxymethylbilane (HMB)

Enzyme: uroporphyrinogen I synthase = porphobilinogen (PBG) deaminase = HMB synthase cyclizes spontaneously uroporphyrinogen IHMB uroporphyrinogen III synthase uroporphyrinogen III

These compounds are colorless (porphyrinogens) auto-oxidized porphyrins (colored).

uroporphyrinogen I uroporphyrinogen decarboxylase coproporphyrinogen Iuroporphyrinogen III coproporphyrinogen IIIAcetate (A) methyle (M) : decarboxylated by uroporphyrinogen decarboxylase

coproporphyrinogen III coproporphyrinogen oxidase protoporphyrinogen III protoporphyrinogen III protoporphyrinogen oxidase protoporphyrin IIIRequires molecular oxygen.Protoporphyrin III + Fe2+ HemeEnzyme: ferrochelatase (heme synthase)cytosolmitochondria

Decarboxylation of uroporphyrinogens to coproporphyrinogens in cytosol. (A, acetyl; M, methyl; P, propionyl.)Heme biosynthesis occurs in most mammalian cells with the exception of mature erythrocytes, which do not contain mitochondria. However, approximately 85% of heme synthesis occurs in erythroid precursor cellsin the bone marrow and the majority of the remainder in hepatocytes.

Regulation in Biosynthesis of HemeALA synthase occurs in both hepatic (ALAS1) and erythroid (ALAS2) formsThe rate-limiting enzyme: ALAS1 feedback inhibitionHeme (-) ALAS1 Heme (+) ALAS1

Aporepressor molecule + Heme negative regulator of the synthesis of ALAS1

Drugs (eg, barbiturates, griseofulvin) increase in ALAS1. Most of these drugs are metabolized by a system in the liver that utilizes cytochrome P450

Glucose can prevent derepression of ALAS1 in liver as can the administration of hematin (an oxidized form of heme).

PORPHYRIASDisorders due to abnormalities in the pathway of biosynthesis of heme genetic or acquired

In general, the porphyrias described are inherited in an autosomal dominant manner, with the exception of congenital erythropoietic porphyria, which is inherited in a recessive modeThe signs and symptoms of porphyria result from either a deficiency of metabolic products beyond the enzymatic block or from an accumulation of metabolites behind the block.If the enzyme lesion occurs early in the pathway, clinically, patients complain of abdominal pain and neuropsychiatric symptoms relate to elevated levels of ALA or PBG or to a deficiency of hemeIf the enzyme blocks later in the pathway result in the accumulation of the porphyrinogens, their oxidation products, the corresponding porphyrin derivatives, cause photosensitivity, a reaction to visible light of about 400 nm The porphyrins, when exposed to light of this wavelength, are thought to become "excited" and then react with molecular oxygen to form oxygen radicals injure lysosomes and other organelles release their degradative enzymes skin damage, including scarring.The porphyrias can be classified on the basis of the organs or cells that are most affected: erythropoietic, hepatic & erythrohepatic

Barbiturates, griseofulvin cytochrome P450 heme ALAS1 porphyriaDiagnosis: clinical and family history, the physical examination, and appropriate laboratory testsTreatment:- symptomatic- to avoid drugs that cause induction of cytochrome P450.- glucose,hematin may repress ALAS1- photosensitivity : b-carotene free radicals Sunscreens

Katabolisme Heme12 x 108 erythrocytes are destroyed per hour in 1 day turns over approximately 6 g of hemoglobinglobin amino acids reused; iron poolEnzyme: complex enzyme system called heme oxygenase

METABOLISME BILIRUBINPENGAMBILAN BILIRUBIN OLEH HATIBilirubin hanya sedikit larut dalam plasma & terikat dengan albuminObat / antibiotika kompetisi untuk berikatan dg albuminLIVER: Bilirubin dilepas dari albumin diambil pada permukaan sinusoid hapatosit Sistem Transport Berfasilitas (facilitated transport system = carrier-mediated saturable system) masuk ke sel hati berikatan dengan cytosolic protein (ligandin, protein Y). Ikatan ini juga menjaga agar bilirubin tidak kembali ke aliran darah lagi.Aktivitas sistem ini menurun pada keadaan patologis

hijaukuning

KONJUGASI BILIRUBINLIVER: Bilirubin yang non-polar polarKonjugasi dengan GLUKORONAT Bilirubin diglukoronida (conjugated, "direct-reacting" bilirubin) polarEnzyme: glucuronosyltransferase (dlm retikulum endoplasma)Donor glukuronosil: UDP-glucuronic acidEnzim dapat diinduksi oleh PhenobarbitalBilirubin diglukoronida diekskresi melalui faeces when exist abnormally in human plasma (eg, in obstructive jaundice), they are predominantly monoglucuronidesObstructive jaundice bilirubin conjugates (predominan monoglukuronida)

Bilirubin diglukoronida

METABOLISME BILIRUBIN DALAM USUS Diglukoronida BilirubindiglukoronidaBilirubin

Bilirubin direduksi oleh flora usus UROBILINOGEN (tak berwarna) Sebagian kecil urobilinogen diabsorbsi & diresekresi melalui liver (SIKLUS ENTEROHEPATIK) Sebagian besar urobilinogen oksidasi UROBILIN (kuning) faeces Urobilinogen dlm urine abnormalb-glukoronidaseBakteri usus

Diagrammatic representation of the three major processes (uptake, conjugation, and secretion) involved in the transfer of bilirubin from blood to bile. Certain proteins of hepatocytes, such as ligandin (a member of the glutathione S-transferase family of enzymes) and Y protein, bind intracellular bilirubin and may prevent its efflux into the blood stream. The process affected in a number of conditions causing jaundice is also shown.

HIPERBILIRUBINEMIABilirubin dlm darah >1 mg/dl. Penyebab:- produksi bilirubin h tidak sebanding dg ekskresi hati- kegagalan ekskresi hati karena:- kerusakan hati- obstruksi saluran ekskresiBilirubin masuk ke jaringan Ehrlichs test dari van den Bergh: - reagen diazo + Bilirubin + etanol senyawa Azo (ungu-merah)INDIRECT REACTION BILI UNCONJUGATED (FREE) - reagen diazo + Bilirubin (tanpa etanol) senyawa Azo DIRECT REACTION BILI CONJUGATEDRetention hyperbilirubinemia: unconjugated hhRegurgitation hyperbilirubinemia : conjugated hhBili unconjugated dpt menembus blood-brain barrier encephalopathy Kern icterusKUNING / ICTERUS / JAUNDICE

Jaundice

UNCONJUGATED HYPERBILIRUBINEMIAHemolytic AnemiasBiasanya ringan (< 4 mg/dL; < 68.4 mmol/L) kapasitas hati besar utk mengelola bilirubin (uptake, konjugasi, ekskresi)

Neonatal Physiologic Jaundice- Hemolisis > metabolisme bilirubin dlm hati- aktivitas / sintesis UDP-glukoronosil transferase K- Dpt menyebabkan Kern icterus- Tx: Phenobarbital +

C. Crigler-Najjar Syndrome, Type I- = Congenital nonhemolytic jaundice- Autosomal resesif; mutasi pada gen pengkode enzim Bilirubin- UGT UDP-glukoronosil transferase K - Bilirubin bisa sd > 20 mg/dL bilirubin tdk bisa dikonjugasikan- Klinis: ikterus kongenital berat fatal dalam 15 bulan- Tx: , liver transplant. Phenobarbital tdk menolong.D. Crigler-Najjar Syndrome, Type II- Mutasi pada gen pengkode enzim Bilirubin-UGT, tdk seberat tipe I, bilirubin serum tdk sampai 20 mg/dL- Dapat di Tx dg Phenobarbital dosisi tinggiE. Gilbert Syndrome- Mutasi pada gen pengkode enzim Bilirubin-UGT, sering pada pria- Klinis tdk berat, aktivitas enzim masih ada sekitar 30 %F. Toxic Hyperbilirubinemia- chloroform, arsphenamine, CCl4, acetaminophen, virus hepatitis, chirrhosis, jamur beracun kerusakan parenkim hati

CONJUGATED HYPERBILIRUBINEMIAA. OBSTRUKSI SALURAN EMPEDU- Penyebab: baru empedu, ca. caput pankreas.- Bilirubin diglukoronida tidak bisa diekskresi regurgitasi ke vena- vena di liver dan saluran limfe bilirubin masuk ke aliran darah dan urine (choluric jaundice)- Cholestatic Jaundice: extrhepatic obstructive jaundiceB. DUBIN-JOHNSON SYNDROME- Autosomal resesif, mutasi gen MRP-2- Hepatosit pada area centrilobular mengandung pigmen hitam yang abnormal yang merupakan derivat epinephrine.C. ROTOR SYNDROME- Hiperbilirubinemia terkonjugasi yang kronis, histopatologi hepar tetap normal- Etiologi: tdk tahu

Laboratory Results in Normal Patients and Patients with Three Different Causes of Jaundice