1. محاضرات ما قبل النصفي

2. Phenylketonuria (PKU)
Phenylalanine hydroxylase is an enzyme which converts phenylalanine to tyrosine.
A deficiency of this enzyme leads to a buildup of phenylalanine which results in severe mental retardation.
Phenylalanine accumulates and is metabolized by alternate degradative pathway into phenylpyruvic acid and others leading to mental retardation.

3. Tyrosinemia
There are three types of tyrosinemia. Each has distinctive symptoms and is caused by the deficiency of a different enzyme.
Type I tyrosinemia, the most severe form of this disorder, is caused by a shortage of the enzyme fumarylacetoacetate hydrolase.
Type II tyrosinemia is caused by a deficiency of the enzyme tyrosine aminotransferase.
Diagnostic criteria include an elevated tyrosine level using MS/MS coupled with a confirmatory test for an elevated level of the abnormal metabolite succinylacetone

4. Cystinuria
It is caused by a defect in the amino acid transport system rather than a metabolic enzyme deficiency.
Normally, amino acids are free filtered by the glomerulus and then actively reabsorbed in the proximal renal tubules.
In cystinuria, there is a fold increase in the urinary excretion of cystine due to a genetic defect in the renal resorptive mechanism.
Because cystine is relatively insoluble, it tends to precipitate in the kidney tubules and form urinary calculi.
Cystinuria can be tested by cyanide-nitroprusside test.
Ion exchange chromatography can be used for quantitative analysis of amino acids in urine or plasma.

5. Enzyme classification
Plasma vs. non-plasma specific enzymes
Plasma specific enzymes have a very definite/specific function in the plasma
1) Plasma is normal site of action
2) Concentration in plasma is greater than in most tissues
3) Often are liver synthesized
4) Examples: cholinesterase, plasmin, thrombin
cholinesterase is an enzyme that catalyzes the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation.
M. Zaharna Clin. Chem. 2015

6. Enzyme classification
Non-plasma specific enzymes have no known physiological function in the plasma
1) Some are secreted into the plasma
2) A number of enzymes associated with cell metabolism normally found in the plasma only in low concentrations.
An increased plasma concentration of these enzymes is associated with cell disruption or death
M. Zaharna Clin. Chem. 2015

7. Factors Affecting Enzyme Levels in Blood
Entry of enzymes into the blood
Leakage from cells
Altered production of enzymes
E.g. increased osteoblastic activity results in increase in enzymes in bone disease
Clearance of enzymes
Half life vary from few hours to several days
M. Zaharna Clin. Chem. 2015

8. Measuring enzyme activity
Enzyme activity can be tested by measuring
Increase of product
Decrease of substrate
Decrease of co-enzyme
Increase of altered co-enzyme
If substrate and co-enzyme are in excess concentration, the reaction rate is controlled by the enzyme activity.
M. Zaharna Clin. Chem. 2015

9. Haptoglobin (α2) Synthesized in the liver
Considered an acute-phase protein
Binds free hemoglobin
Prevents loss of Hemoglobin & Iron into urine
Used to detect and evaluate hemolytic anemia and to distinguish it from anemia due to other causes
Haptoglobin
Reticulocytes 1
Decreased
Increased
Hemolytic anemia 2
Normal
RBC destruction may be occurring in organs such as the spleen and liver 3
Anemia present is not due to RBC breakdown
When the haptoglobin and hemoglobin attach, the reticuloendothelial cells (mainly in the spleen) remove the haptoglobin–hemoglobin complex from circulation
2- Because the freed hemoglobin is not released into the bloodstream, the haptoglobin is not used up and so is normal.

10. Ceruloplasmin (α2) Synthesized in the liver acute-phase reactant
Copper carrying protein
90% of serum copper is bound to it
Ordered along with blood and/or urine copper tests to help diagnose Wilson's disease,
decreased levels of ceruloplasmin and excess storage of copper in the liver, brain, and other organs resulting in hepatic cirrhosis and neurologic damage.
Wilson's disease, an autosomal recessive inherited disorder

11. α2 Macroglobulin Tetramer of four identical subunits
Synthesized by liver
major component of the α2 band in protein electrophoresis
Primarily intravascular spaces due to size
Inhibits proteases trypsin, pepsin & plasmin

12. Transferrin (Siderophilin)
The major component of the -globulin.
Glycoprotein synthesized by liver
Carries 2 ferric iron molecules
Normally 33% saturated
Prevents loss of iron through kidneys
Transports to storage sites where Iron is transferred to ferritin
Transports to bone marrow for RBC synthesis
Negative acute-phase protein

13. Hemopexin Beta globulin acute-phase reactant
Purpose is to remove circulating Heme
Breakdown product of Hemoglobin & myoglobin
Carried to liver – broken down
Increased in
pregnancy,
Some malignancies
Low hemopexin levels are diagnostic of a hemolytic anemia
Hemopexin can be determined by radial immunodiffusion

14. Disease Correlations Azotemia: elevated conc. of urea in blood
Very high plasma urea concentration accompanied by renal failure is called uremia, or the uremic syndrome
Causes of urea plasma elevations are:
Prerenal
Renal
and postrenal

15. Pre-Renal Azotemia
Reduced renal blood flow Less blood is delivered to the kidney less urea filtered
Anything that produces a decrease in functional blood volume, include:
Congestive heart failure,
shock,
hemorrhage,
dehydration
High protein diet or increased catabolism (Fever, major illness, stress)

16. Renal Azotemia
Decreased renal function causes increased blood urea due to poor excretion
Acute & Chronic renal failure
Glomerular nephritis
Tubular necrosis
caused by a lack of oxygen to the kidney tissues (ischemia of the kidneys).
& other Intrinsic renal disease
Glomerulonephritis, also known as glomerular nephritis, abbreviated GN, is a renal disease characterized by inflammation of the glomeruli, or small blood vessels in the kidneys

17. Post-Renal Azotemia Obstruction of urine flow
Renal calculi
Tumors of bladder or prostate
Severe infections

18. Uric Acid
Uric acid is a final breakdown product of purine metabolism (adenosine/guanine) in liver
Most other mammals degrade it further to allantoin
Uric acid is transported to kidney and filtered (Renal excretion accounts for about 70% of uric acid elimination)
98% reabsorbed in proximal convoluted tubule (PCT)
Some secreted by distal convoluted tubule (DCT)
Net amount 6-12% of filtered amount
Remaining 30% by GIT
PCT= proximal convoluted tubule
DCT= distal

19. Uric Acid Present in plasma as monosodium urate
At plasma pH → relatively insoluble
Conc. > 6.8 mg/dl → plasma saturated → urate crystals may form & precipitate in tissue
Uric acid is measured to:
assess inherited disorders of purine metabolism,
to confirm diagnosis and monitor treatment of gout,
to assist in the diagnosis of renal calculi,
to prevent uric acid nephropathy during chemotherapeutic treatment,
and to detect kidney dysfunction