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PHM142 UNIT 9A

Mitochondrial Diseases and the Brain

Instructions and materials:

Read ONLY sections in paper by Chaturvedi and Beal, 2013 (included in lecture material) highlighted in yellow, plus Figures 1 and 3 and Table 1 in this paper.

Be prepared to discuss these topics in class.

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PHM142 UNIT 9BMitochondrial Function and hepatic

detoxification of a) monoamines, alcohol, toluene

b) heme & bilirubin

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a) Detoxification of monoamines catalysed by mitochondrial outer membrane MAO

R-CHNH2

O2

H2O2

R-CH=NH

NH3

R-CHO

R-COOH-oxidation

CO2

ATP, HCO3

-

UREAurea cycle

MONOAMINE OXIDASEFlavin-containing amine oxidase

(imine)

inner membrane

outer membrane

e.g.,dopaminenorepinephrinetyraminephenethylamineoctylamineserotonin

aldehyde dehydrogenase

NAD+

NADH

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Amine specificity for the two isoforms (A & B) in humansMAO A preferentially metabolizes serotonin.MAO B preferentially metabolizes phenethylamine, dopamine.

MAO inhibitor + dietary amines or proprietary drugs

MAOB inhibitor deprenyl (selegiline) similar to phenethylamine and increases brain dopamine levels. This is used to treat Parkinson’s disease.

But “Hypertensive crisis” is a hyperadrenergic state induced by MAO inhibitors + pressor amines (e.g., tyramine in cheese,beer,wine or soya sauce) or proprietary drugs (e.g., L-DOPA, ephedrine, etc).

Cheese Tyramine (g/g)

English Stilton 1157

Blue 998

Mozzarella 158

Feta 76

Processed cheese slice nil

Cheese Tyramine (g/g)

Cheddar cheese, old 1530

Beer 2-11

Sherry Wine 3

Chianti Wine 25

Perry, 1996. http://www.vh.org/adult/provider/psychiatry/CPS/19.html

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b) Detoxification of alcohols by matrix ALDH2

ETHANOL acetaldehyde

cytosolic alcoholdehydrogenase

NAD+NADHMethylpyrazole

Covalently binds to protein-NH2

NAD+

NADH

aldehydedehydrogenase

acetate ATP

CoASHacetylCoA

CO2

TCAcycle

ANTABUSE (disulfiram) or cyanamide

ADH ALDH Suscept. to alcoholism Appearance social drinking

Chromosome # 4 9, 12, 17

Caucasians 99% normal 90% normal 10% (>) --

Japanese 90% atypicial 40% deficient < 10% flushing

(ADH)

(ALDH)

CONHCH2COOH

Hippuric acid

URINE

glycine

CH3 CH2OH CHO

COOH

Toluene Benzyl alcohol Benzaldehyde

Benzoic acid

ADH

ALDH1/ALDH2

Cyt P-450

Teratogen Update: Toluene teratology. 55, 145-51, (1997)

Benzoyl-CoA synthetase

ATPCoA

Benzoyl-CoA

N-acyltransferase

c) Benzoic acidosis induced by toluene glue sniffing

ER CYTOSOL

MITOCHONDRIA

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Cytochrome Heme Synthesis - Overall picture

Heme synthesis

• Heme required for synthesis of mitochondrial cytochromes and endoplasmic reticular P450s.

• Heme required for bone marrow synthesis of hemoglobin and muscle myoglobin

• STEP 1 for heme synthesis is the synthesis of aminolevulinic acid (ALA) from succinyl CoA of the citric acid cycle and glycine

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Heme biosynthesis in bone marrow (hemoglobin) and liver (cytochromes)

R.L.S. ALA synthetaseCOO

CH2

CH2

C

O

S CoA

Succinyl CoA

COO

CH2

COO

COO

CH2

CH2

C CH2

NH3

O

H+ CO2 + CoA

Feedback inhibition by heme(also induces heme oxygenase) Aminolevulinate

(ALA)

Glycine

HEME BIOSYNTHESISSTEP II

(CYTOSOL)

Fe, O2

COO

CH2

CH2

C CH

O

O

4,5-dioxovaleric acid (DOVA)

1) Brain Neuropsychiatric problems in acute porphyria, 2) Liver necrosis / cancer particularly if Fe overload

1) HEME arginate2) High carbohydrate

+

glucose-6-P NADPH

GSH reductaseGSH peroxidase

H2O2

-ketoglutaratesuccinate

citricacidcycle

CO2 + CoA

dehydrogenasecomplex

Therefore ANAPLEROTICreaction required to replacesuccinyl CoA in citric acidcycle.

ALA synthetase induced by:1) Heme deficiency due to excess P450 synthesis/induction e.g., by barbiturates Sulfonamides: Therefore an increase in urine porphyrins2) ERYTHROPOIETIN (formed by kidneys) improves quality of life of patients on kidney dialysis.3) Acute intermittent porphyria or ALA dehydratase deficiency.4) LEAD

Mitochondrial Matrix

pyridoxal

-ketoglutarateALA toxicity

Arch Biochem Biophys. 373, 368-74, (2000)

ALA SYNTHESIS AND TOXICITY

ALA accumulatesa) Acute intermittent porphyriab) Lead

NH4+, O2

ROS

DNA strand breaks

DNA ADDUCTSLIVER CANCER

Therapy

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or leadNH2

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Erythropoietin synthesised by kidney induces hemoglobin synthesis in bone marrow (replaces blood transfusion!)

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Heme Biosynthesis - STEP 2 in the cytosol (4 enzymes 2-5)

NH HN

NH HN

COOH

COOH

COOH

COOH

HOOC

HOOC

HOOC

coproporphyrinogen I

CYP1A2

NH HN

N HN

PA

PA

A

P P

A

NH HN

NH HN

HO

COOH

COOH

COOH

COOH

HOOC

HOOC

HOOC

non-enzymatic

COOH

COOH

NH

HOOC

HOOC NH2

COOH

H2N

O

NH HN

NH HN

COOH

COOH

COOH

HOOC

HOOC

HOOC

COOH

COOHUroporphyrinogen III synthase

NH HN

NH HN

COOH

COOH

COOHCOOH

CYP1A2

LIVER/BONE MARROW cytosol

ALA

Uroporphyrin

Coproporphyrinogen III

Uroporphoryrinogen decarboxylase

-4CO2

Uroporphyrinogen I

Symmetrical

Porphobilinogen (PBG)

PBGSYNTHASE

r.l.s polymorphism

Hydroxymethylbilane

ALA DehydrataseDeficiencyPorphryia *

phosphobilinogendeaminase

Acute IntermittentPorphyria*

CongenitalErythropoieticPorphyria

PorphyriaCutaneaTarda

PorphyriaCutaneaTarda

(UROPORPHYRIA)

Cutaneous Porphyria

* Acute Porphyria

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3

4

5

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STEP 1

STEP 3

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Heme Biosynthesis - STEP 3 - mitochondrial final steps (3 enzymes)

NH N

N HN

COOHCOOH

NH HN

NH HN

COOHCOOH

N N

N N

COOHCOOH

Fe2+

MITOCHONDRIA

O2 CO2 mitochondrialintermembrane space

Protoporphyrinogen IX

Protoporphyrinogen oxidase

i.m.

O2

Protoporphyrin IX

Ferrochelatase

i.m.r.l.s

HEME

Coproporphyrinogen oxidase

NH HN

NH HN

COOH

COOH

COOHCOOH

Coproporphyrinogen III

HereditaryCoproporphyria *

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78

VariegatePorphyria *

Protoporphyria

Acute Porphyria

* Cutaneous Porphyria

STEP 2

Fe

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OXIDATIVE DEGRADATION OF HEME TO BILIRUBIN

(a brain neurotoxin in babies)

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Detoxification function of the livera) heme toxin oxidation to bilirubinb) detoxification of bilirubin by glucuronidation or albumin

phagosomeHemeoxygenase

albumin LIVER

CO

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Degradation of heme STAGE 1Hemoglobin of old erythrocyte trappedin spleen

NH

NH

N NH

CH

CH

CH

OO

NH

NH

NH

NH

CH

CH2

CH

OO

M V M P P M M V

VMMPPMVM

BiliverdinNADPH + H+

NADP+

Biliverdin Reductase

Excreted by Reptilesand birds

HEMEO2 + NADPH

H2O + NADP+

Fe3+

BILIRUBIN(Neurotoxin to babies)

Bone marrow

transferrin

Plasma Serum Albumin Complex LIVER

Modified fromFig. 28-31 Stryer4th Ed.

NEONATAL JAUNDICEBilirubin accumulates in newborns.(destroy with sunlight).

Heme oxygenase (ER)

CO

H2O soluble

exhaled

ANTIOXIDANT

Fat soluble

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STAGE II - ligandin in hepatocyte surface membrane traps bilirubinfrom plasma and helps transport it into the liver where it is glucuronidated

Albumin- bilirubin

(a GSH transferase)

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*mutated gene in Gilbert’s disease(carried by 15% ofpopulation)

NH

NH

NH

NH

CH

CH2

CH

OO

VMMMVM

COOCOO

OH

OH

H

UDP

H

OHH

OH

COO

UDP-glucuronate

+

Bilirubin

Endoplasmic reticulumUDP-glucuronosyltransferase (UGT 1A1*)

NH

NH

NH

NH

CH

CH2

CH

OO

VMMMVM

COOC

OH

OH

H

O

H

OHH

OH

COO

O

BILIRUBIN DIGLUCURONIDE (Soluble bilirubin diglucuronide secreted

into the bile)

BILIRUBIN MONOGLUCURONIDE

UDP

UDP gluc. + UGT 1A1