5 phenylketonuria, homocystinuria, oxidants and oxidative stress

Phenylketonia defective enzymes

phenylalanine to tyrosine. phenylalanine hydroxylase

why does PKU increase serum phenylalanine and production of phenylpyruvate

defective phenylalanine hydroxylase dietary phenylalanine cannot be degraded. enters transamination pathway to produce phenylpyruvate

phenylketonuria why in urine

defective phenylalanine hydroxylase dietary phenylalanine cannot be degraded. therefore it accumulates in the blood until it exceeds the renal threshold

phenylalanine + a-ketoglutarate

phenylpyruvate and glutamate

clinical consequences of PKU and why should it be diagnosed ASAP

inhibition of brain development as phenylpyruvate inhibits uptake of pyruvate into mit so disturbs energy metabolism and disturbs neurotransmitter synth. irreversible build up so must be diagnosed asap to prevent intake

treatment of pt with PKU

diet low in phenylalanine. essential AA so monitoring of blood conc. avoid aspartame (sweetner)

why pt dietary source of tyrosine

produced in first step of disposal of xtra phenylalanine. pt with PKU cannot produce tyrosine therefore dietary source required

most common mutation in PKU

many. classic PKU is single base pair (g>A) resulting in premature stop codon and unstable mRNA transcript

Homocystinuria

Cystathione synthase deficiency

Lens subluxation, thrombosis, marfanoid, intellectual disabiliity

Tx: pyridoxine

why homocysteine in urine

plasma conc of homocysteine exceeds renal threshold so excreted in urine.

why methione not found in urine of homocysteineuria

renal tubular reabsorption of methione is highly efficient so may not appear in urine which is

HomocystEine vs HomocystIne

homocystine is oxidised to form homocysteine which is in urine

biochemical basis of high methionine and homocysteine in blood

not being metabolised. sulphur containing AA usually interconvertible. methionine and homocysteine not being broken down.

why does homocytinuria resemble marfan syndrome and what is the diff

marfan conditon of connective tissue. homocytinuria has similar clinical presentations (lens dislocation and skeletal deformities). homocysteine in excess damages collagen and elastic fibres in CT as it binds lysine residues in the prt. methionine toxic to neurones and cause neurological symptoms in homocystinuria which is not seen in marfan

why homocystinuria associated with increased risk of early onset CVD

high plasma levels of homocysteine is prothrombotic and pro-atherosclerotic

treatment for homocystinuria

no cure.

low methionine diet (low animal prt).

- high dose pyridoxine (VB6) (co factor required by CBS enzyme if present).

-betiane (methyl donor) adjunct to dietary B12

-folic acid (conversion to methionine and added cysteine (for glutathione)

glucogenic amino acids

can be converted into intermediates (glutamic, aspartic, serine) that feed into gluconeogenesis for glucose synth.

ketogenic amino acids

produce acetyl CoA. lysine and leucine

how can AA converted to glucose

removal of amino group (NH2) converted to urea (co(NH2)2) and excreted as urine. C-skeletons converted to pyruvate,oxaloacetate, fumarate, a-ketoglutamate, succinatem acetyl CoA.

ketogenic and glucogenic amino acids

Isoleucine

Phenylalanine

Threonine

Tryptophan

Tyrosine. larger. give rise to both acetyl CoA and other organic precursors

Which set of clinical findings in a blood sample is more suggestive of liver disease? A.) Increased ALT, AST and bilirubin, or B.), increased ALT, no change in AST or bilirubin

ALT and AST leak into blood when liver cells are damaged. increased bilirubin means hepatic metabolism problem

in general terms how AA degraded in the body and list the products

deamination or trans amination. in liver n atoms converted to urea for excretion or to ammonia to be converted glutamine (purines and pyrimidines). c atoms converted to intermediates of carb metabolism (glucogenic aa) or lipid (ketogenic aa).

products urea, pyruvate, acetyl coA, a-ketoglutarate, oxaloacetate, succinate, fumarate

urea cycle

1) mitochondria nh3+co2+2ATP->carbamoyl phosphate

2) carbomyl phosph. + orrnithine -> citrulline

3) citrulline leaves mit to cytoplasm.

4) citrulline and aspartate -> arginino succinate via synthetase

5) arginino succinate -> fumate and arginine via lyase

6) arginine -> ornithine and urea and h2o via arginase (cleavage)

7.

where do the Ns, C come from for urea

first N comes from ammonia; second from aspartate; c from co2

glutamate dehydrogenase

glutamate + NAD + H2O -> a-ketoglutarate + NH4 + NADH + H*

glutamate dehydrogenase importance

glutamate and alpha-ketoglutarate synthesis

Explain why blood ammonia levels are normally kept low

ammonia toxic to CNS as it removes a-ketoglutarate (forming glutamate) from krebs which interferes with ATP production and inhibits brain function. ammonia reacts with water to produce ammonium and hydroxyl ions and can cause pH changes

what processes involved in removing ammonia

conversion to urea. conversion to glutamine using glutamate and used for purine and pyrimidine synth. excretion as ammonium ion in urine

how superoxide radicals produced by mit

during OP some electrons do not reach end of electron transport chain and prematurely reduce oxygen to superoxide radicals

agents in cells which protect against reactive oxygen

superoxide mutase, catalase, glutathione, nadph, antioxidant vit (c,E) and antioxidants in diet (polyphenols)

relationship between glutathione and nadph

recycling between NADPH glutathione. NADPH reduces oxidised glutathione via GSH reductase. reduced glutathione available to be oxidised by reactive oxidative species therefore removing ROS

antioxidant vitamins

A- retinol

c- asorbic acid water sol

e- a-tocopherol lipid soluble

oxidative stress

when production of ROS is excessive and antioxidant levels are low so balance shifted in favour of ros. normally cells have sufficient antioxidants to cope

A 9 month old boy was admitted to hospital following chronic vomiting and a developmental delay. Lab results showed elevated levels of ammonia, glutamine alanine and ornithine. Citrulline was low. Which urea cycle enzyme is deficient in this child?

mitochondrial X linked OTC. elevated ammonia, ornithine which are substrates for the cycle. elevated level of ammonia causes a rise in glutamine and alanine which which transport nitrogen from aa catabolism . citrulline the product OTC decreases

OTC

ornithine carbomoyl transferase. carbamoyl phosphate to citrulline

OTC deficiency

X-linked

urea cycle disorder

vomitting, seizures, hypotonia

high ammonia (CHECK FOR HYPERAMMONIA IN MOM)

respiratory alkalosis

poor feeding

can be activated by extreme stress in adult onset

cerebral edema, papilledema, lethargy, coma

OTC deficiency treatment

low prt diet, AA suplements essential

essential amino acids

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

The patient was a 7-month old baby boy. He had developed normally until he was weaned at 6 months. Following the introduction of a high protein diet he had become irritable, lethargic and less alert and had begun to vomit. He was admitted to hospital where he had episodes of screaming, listlessness and ataxia (uncontrolled limb movements) especially after a protein rich meal. His urine was persistently alkaline and contained a lower urea concentration than normal. His blood NH4 + and glutamine concentrations were increased but fell to normal when his protein intake was reduced. He was put on a special low-protein diet and his subsequent development was normal. 1. Explain the biochemical basis of this patient's symptoms.

symp and signs began when high prt diet and disappeared when removed. so aa metabolism defect. high blood nh4 and glutamine with low urine urea conc therefore inability to convert NH4 to urea. therefore enzymes of urea cycle deficient. CNS symptoms as NH4 interferes with energy metabolism of CNS

positive nitrogen balance

state in which the body retains more nitrogen than it loses

negative nitrogen balance

body loses more nitrogen than it retains. abnormal. muscle wasting

positive nitrogen balance in 7mnth old

normal in growing child as dietary prt increase total body prt.

glutamine synthetase

ammonia and glutamate to glutamine in peripheral tissues. glutamine to liver and kidneys in blood

urea cycle genetic defects mode of inheritence

autosomal recessive manner. 1/5 enzymes in urea cycle

urea cycle enzyme deficiency treatment

low prt diet. replace aa with keto acids

Some of the enzymes of the Urea cycle are inducible. How is this relevant when refeeding a patient who is known to have long history of anorexia nervosa?

states of low prt intake enzyme activity are down regulated. when pt increases prt intake, enzyme activity of urea cycle not enough (enzymes have been down regulated) to deal with the ammonia therefore there is a risk of hyperammonia. reintroduction of food needs to be carefully managed with assistance of dieticians and careful biochemical monitering

Some enzymes are inducible. What is meant by this

enzymes whose activity can be repressed or increased according to demand

what is urea soluble in

water soluble. eliminated in urine by kidneys.

renal failure and urea. what does plasma urea indicate

plasma urea will increase. relation to renal function, state of hydration, nitrogen balance.

Why is Plasma Urea less accurate than Creatinine as indicator

urea indicator of hydration, nitrogen balance.

cortisol and prt metabolism

increase prt breakdown

cortisol and cushing's syndrome

loss of muscle, reduced bone density, weakened skin, poor wound healing, increased infection

cortisol actions in body

protein breakdown, insulin resistence, enhances adrenaline action, affects androgen metabolism. mineralcorticoid activity involved in water, sodium, k hoeostasis

acetoacetate

1 of 2 Ketone Bodies (β-Hydroxybutyrate) Produced in liver (mitochondria) from fatty acids in prolonged starvation, diabetic ketoacidosis, alcoholism.

Brain can use Ketone Bodies during starvation but RBCs can NOT

Rate limiting enzyme: HMG-CoA Synthase

Spontaneously becomes acetone which causes the fruity breath one can smell.

Urine test for ketones does not detect β-Hydroxybutyrate

polyuria diabetes

glucose in urine means increase osmorality, water diffuses by osmosis to urine and urine volume ^. produce more vol of urine. more drinking polydipsia. urine output excess of fluid intake so will be thirsty all the time. lose weight from dehydration

Kwashiorkor Disease

protein deficiency with appropriate caloric intake

transamination

during transamination catalysed by ALT, alanine amine group from a-ketoglutarate transferred to a-ketaglutarate to form glutamate and initial acid becomes ketoacid

most common and safe form of ammonia transported from tissue via blood to liver

glutamate

most common enzyme defect in urea cycle

ornithine transcarbamylase

free radical

any atom/mol/ion contains one or more unpaired electrons and can exist independently. very reactive and aquire electrons from other mol causing cellular damage

ROS in body

superoxide radical, hydroxy radical, hydrogen peroxide

which cellular component most affected by ROS

mitochondria

enzyme catalyses conversion of superoxide to hydrogen peroxide and oxygen

superoxide dismutase

oxidative stress from lack of enzyme

glucose 6phosphatase deficiency

ALT

alanine and a-ketoglutarate to pyruvate and glutamate

AST

aspartate and a-ketoglutamate to make oxaloacetate and glutamate

aminotransferase co-factor

pryidozal phosphate (VB)

deamination enzyme glutaminase

glutsmate + NAD+ + H2O to a-krtoglutarate + NH4+ + NADH + H+

deamination enzymes

glutaminase, AA oxidases, glutamine DHs

ammonia effects

pH, interacts acts with a-ketoglutarate to form glutamate, blood:brain, interferes with neurotransmitters (glutamate and aspartate),

main pathway of transport of ammonia

NH3 in tissues to glutamate to glutamine by (GS), glutamine to blood to liver to glutaminase to glutamate and deaminated by GDH

autosomal recessive disorders caused by loss of which enzymes in urea cyce. hyperammmonaemia and accumulation of urea cycle intermediates

carbomoyl phosphate synthetase, orthinin transcarbamylase, argininosuccinate synthetase and acid lyase, arginase

OCT deficiency

vomiting, lethargy, irritability, mental retardation. low protien diet and replace with ketoacids.

PKU

phenylalanine hydroxylase deficiency. accumulation of phenylalanine in tissues, plasma and urine along with phenylkeyones. phenylketones oxidised to give musty smell

pathophysiology of PKU autosomal recessive

pheynylalanine cannot be converted to tyrosine. therefore is instead deaminated to produce phenylpyruvate. then oxidised to produce phenyacetate and phenylactate. siezures, hypopigmentation, developmental delay

homocystinuria pathophysiology autosomal recessive

defect in CBS. excess homocystine (oxidised form of homocysteine). accumulation of methionine and homocysteine.

methione will be transformed to homocysteine. but homocysteine cannot produce cystathione to cysteine as CBS would transform homocysteine to cystathione. so without CBS, homocysteine accumulates .

causes dislocation of long limbs and fingers and intellectual disability

tyrosine

melanin, thyroid hormones, catecholamines

cysteine

hydrogen sulphide, glutathione

tryptophan

nicotinoamide, serotonin, melatonin

histidine

histamine

glutamate

GABA

glycine

purines, glutathione, haem, creatine

arginine

NO

serine

sphingoside

formation of ROS and RNs

oxygen: add electron to produce superoxide

superoxide: add an electron and 2H to produce hydrogen peroxide

hydrogen peroxide: react with Fe to produce free radicals. add e- and H to produce water and hydroxy radical

hydroxyradical: most reactive and damaging free radical. add H and e- to produce water

free radicals from electron transport chain

e- escape chain and react with dissolved o2 to form superoxide

endogenous sorces of biological oxidants

electron transport chain, peroxidases, NO synthases, lipoxygenases, NADPH pxidases

ROS and DNA

ROS reacts with base causing mispairing and mutation

ROS reacts with sugar and can cause break and mutation as result of repair

ROS damage to protein

side chain: carbonyls, hydroxylated adducts, ring opened species

backbone: fragmentation, degredation

any change in protein will cause either loss or gain of function which will then be degraded

ROS damage to lipids

unsaturated with ROS termed peroxidation. lipid peroxides are formed. causes damage to PM

nitric oxide synthase

arginine -> nitric oxide

release citrulline by nirtic oxide sythase.

nitric oxide synthase types:

inducible: produces high NO concentrations in phagocytosis

endothelial: signalling

neural: signalling

superoxide dismutase

converts superoxide radicals to h2o2. catalase converts H2O2 to h2o and h2o

NADPH and GLutathione

glutathione: thiol group of Cys donate e- to ROS. GSH reacts with another GSH to produce GSSG. GSSG reduced back to GSH by glutathione reductase which catalyses the transfer of electrons from NADPH to disulphide bond.

vitamin E

lipid soluble antioxidant against lipid peroxidation.

vitamin C

water soluble antioxidant. regenerates reduced form of VE

Free radical scavengers

reduce radical damage by donating H atom and its e- to free radicals in non enzymatic reaction

respiratory burst

neutrophils, monocytes produce ROS. cell is destroyed but surronding area with pathogen os destroyed.

membrane bound complex including phagosomes.: NADPH oxidase

transfers e- from NADPH from across membrane to couple with molecular O2 to produce O + NO which produces ONOO- to attack bacteria or O2* combined with H2O2 and Cl- to produce myelooperoxidase which produces HOCL- which also attacks bacteria