CREATINE AND GLUTATHIONE METABOLISM, STEPS AND CLINICAL ASPECTS

FOR MBBS, BDS STUDENTS

1. Formation of Creatine, Glutathione, Gamma Glutamyl Cycle Dr. Apeksha Niraula Assistant Professor Clinical Biochemistry Institute of Medicine

2. Contents Formation of Glutathione Formation of Creatine Gamma-Glutamyl Cycle Importance Hyperammonemia

3. Amino Acids : 1) Building Block of Proteins 2) Precursors of many Nitrogenous containing compounds These molecules include: Porphyrins Neurotransmitters Hormones Creatine Purines, Pyrimidines Glutathione

4. L- α Amino Acids Alanine Arginine Cysteine Glycine Histidine Methionine Serine Tryptophan Tyrosine Non- α Amino Acids β- Alanine β - AminoIsobutyrate β - Alanyl Dipeptides γ - Aminobutyrate

5. Glycine Many drugs, drug metabolites, and other compounds with carboxyl groups are excreted in the urine as glycine conjugates. Specialized Products : Glycine Conjugates: Glycocholic Acid, Taurocholic Acid Heme Glutathione Purines Creatine

6. Metabolites and pharmaceuticals excreted as water-soluble glycine conjugates include Glycocholic acid and hippuric acid formed from the food additive benzoate

7. Glutathione (GSH) , present in plants, animals, and some bacteria, often at high levels, act as a redox buffer Derived from Glycine, Glutamate, and Cysteine Carboxyl group of glutamate is activated by ATP to form an acyl phosphate intermediate, which is then attacked by the α-amino group of cysteine Glutathione (GSH)

8. A second condensation reaction follows, with the - carboxyl group of cysteine activated to an acyl phosphate to permit a reaction with Glycine The oxidized form of glutathione (GSSG), produced in the course of its redox activities, contains two glutathione molecules linked by a disulfide bond Glutathione probably helps maintain the sulfhydryl groups of proteins in the reduced state and the iron of heme in the Ferrous (Fe 2+ ) state

9. Glutathione (GSH) Reduced

10. Glutathione serves as a Reductant ; is conjugated to drugs to make them more water-soluble (Detoxification). Its redox function is also used to remove toxic peroxides formed in the normal course of growth and metabolism under aerobic conditions Reaction catalyzed by Glutathione Peroxidase

11. In the intestines, kidney tubules, and the brain, the absorption of neutral amino acids is affected by the gamma-glutamyl cycle The main role is played by the tripeptide glutathione (GSH) (gamma-glutamyl-cysteinyl glycine) It reacts with the amino acid to form gamma-glutamyl amino acid- Catalysed by Gamma-Glutamyl Transferase The glutamyl amino acid is then cleaved to give the free amino acid The net result is the transfer of an amino acid across the membrane The transport of one molecule of amino acid and regeneration of GSH requires 3 molecules of ATP Importance of GGT Cycle

12. Creatine phosphate/ Phosphocreatine Found in muscle, a high-energy compound that can reversibly donate a phosphate group to adenosine diphosphate to form ATP. Provides a small but rapidly mobilized reserve of high-energy phosphates used to maintain the intracellular level of Adenosine triphosphate (ATP) during the first few minutes of intense muscular contraction. Creatine

13. Creatine is synthesized from Glycine and the Guanidino group of Arginine, plus a methyl group from S-adenosylmethionine Creatine is reversibly phosphorylated to creatine phosphate by Creatine kinase, using ATP as the phosphate donor Synthesis of Creatine:

14. The amount of creatinine produced is related to muscle mass The level of creatinine excretion (clearance rate) is a measure of renal function

15. Creatine and Creatine phosphate spontaneously cyclize at a slow but constant rate to form creatinine, which is excreted in the urine The amount of creatinine excreted is proportional to the total creatine phosphate content of the body and thus can be used to estimate muscle mass Any rise in blood creatinine is a sensitive indicator of kidney malfunction. An Adult male excretes 15mmol of Creatinine per day Degradation of Creatine

16. Hyperammonemia  is a  metabolic disturbance characterized by an excess of  ammonia in the  blood It is a dangerous condition that may lead to brain injury and death M ay be Primary or Secondary Measurement of ammonia levels is a very critical parameter for the assessment of a variety of genetic and acquired conditions The most important genetic causes of hyperammonemia are urea cycle disorders and organic acidurias Organic acidurias usually present with life-threatening metabolic acidosis and hyperammonemia; whereas urea cycle disorders often have metabolic alkalosis along with hyperammonemia Hyperammonemia

17. Types: Primary vs. S econdary Primary hyperammonemia is caused by several  inborn errors of metabolism that are characterized by reduced activity of any of the  enzymes  in the  urea cycle M ost common example is: Ornithine Transcarbamoylase Deficiency: X-linked inherited; Propionic Acidemia and  M ethylmalonic acidemia Secondary hyperammonemia: caused by inborn errors of intermediary metabolism which are characterized by reduced activity of enzymes that are not part of the urea cycle or dysfunction of cells that make major contributions to metabolism Examples: A cute liver failure and  hepatic cirrhosis with liver failure

18. Hepatic encephalopathy (HE) or portosystemic encephalopathy (PSE): reversible syndrome of impaired brain function occurring in patients with advanced liver failure D efined as an alteration in mental status and cognitive function occurring in the presence of liver failure M ore c ommonly seen in patients with chronic liver disease Gut-derived neurotoxins that are not removed by the liver because of vascular shunting and decreased hepatic mass get to the brain and cause the symptoms like hepatic encephalopathy Ammonia levels are typically elevated in patients with hepatic en c ephalopathy Other compounds and metabolites that may contribute to the development of encephalopathy include certain false neurotransmitters and mercaptans Hepatic Encephalopathy

19. In acute liver failure, changes in mental status can occur within weeks to months Brain edema can be seen in these patients , with severe encephalopathy associated with swelling of the gray matter Cerebral herniation is a feared complication of brain edema in acute liver failure and treatment is meant to decrease edema with mannitol and judicious use of intravenous fluids They may actually be quite violent and difficult to manage; alternatively, patients may be very sleepy and difficult to rouse Clinical Features

20. Ammonia levels may be elevated in hepatic coma (Hepatic Encephalopathy) In this condition liver function tests will also often be grossly abnormal Other conditions where ammonia is elevated include cor pulmonale, pulmonary emphysema, and renal failure A low-protein diet and bowel disinfection using antibiotics will reduce bacterial load Then, lactulose administration can reduce ammonia levels by reducing intestinal production of ammonia

21. Thank You