Browsing Pathways

Fondaparinux, also known as Arixtra, is an anticoagulant medication. It is part of a class of antithrombotic drugs, the first of this new class. In the blood capillary bed, Fondaparinux sodium activates antithrombin III. Then zooming in even further to the endoplasmic reticulum within the liver, vitamin K1 2,3-epoxide uses vitamin K epoxide reductase complex subunit 1 to become reduced vitamin K (phylloquinone), and then back to vitamin K1 2,3-epoxide continually through vitamin K-dependent gamma-carboxylase. This enzyme also catalyzes precursors of prothrombin and coagulation factors VII, IX and X to prothrombin and coagulation factors VII, IX and X. From there, these precursors and factors leave the liver cell and enter into the blood capillary bed. Once there, prothrombin is catalyzed into the protein complex prothrombinase complex which is made up of coagulation factor Xa/coagulation factor Va (platelet factor 3). These factors are joined by coagulation factor V and prothrombin. Through the two factors coagulation factor Xa and coagulation factor Va, thrombin is produced, which then uses fibrinogen alphabet, and gamma chains to create fibrin (loose). This is then turned into coagulation factor XIIIa, which is activated through coagulation factor XIII A and B chains. From here, fibrin (mesh) is produced which interacts with endothelial cells to cause coagulation. Plasmin is then created from fibrin (mesh), then joined by tissue-type plasminogen activator through plasminogen and creates fibrin degradation products. These are enzymes that stay in your blood after your body has dissolved a blood clot. Coming back to the factors transported from the liver, coagulation factor X is catalyzed into a group of enzymes called the tenase complex: coagulation factor IX and coagulation factor VIIIa (platelet factor 3). This protein complex is also contributed to by coagulation factor VIII, which through prothrombin is catalyzed into coagulation factor VIIIa. From there, this protein complex is catalyzed into prothrombinase complex, the group of proteins mentioned above, contributing to the above process ending in fibrin degradation products. Another enzyme transported from the liver is coagulation factor IX which becomes coagulation factor IXa, part of the tense complex, through coagulation factor XIa. Coagulation factor XIa is produced through coagulation factor XIIa which converts coagulation XI to become coagulation factor XIa. Coagulation factor XIIa is introduced through chain of activation starting in the endothelial cell with collagen alpha-1 (I) chain, which paired with coagulation factor XII activates coagulation factor XIIa. It is also activated through plasma prekallikrein and coagulation factor XIIa which activate plasma kallikrein, which then pairs with coagulation factor XII simultaneously with the previous collagen chain pairing to activate coagulation XIIa. Lastly, the previously transported coagulation factor VII and tissue factor coming from a vascular injury work together to activate tissue factor: coagulation factor VIIa. This enzyme helps coagulation factor X catalyze into coagulation factor Xa, to contribute to the prothrombinase complex and complete the pathway.

Tyrosinemia type I, also known as fumarylacetoacetase or FAH deficiency, is the most severe type of tyrosinemia, a buildup of tyrosine in the body. It is caused by an autosomal recessive mutation in the the FAH gene that encodes for fumarylacetoacetase, an enzyme that is responsible for the last of five steps that are involved in the metabolic breakdown of tyrosine in the liver and kidneys. The lack of this enzyme's function leads to a buildup of 4-fumarylacetoacetic acid as it couldn't be broken down to fumaric acid and acetoacetic acid. This also leads to an increased concentration of maleylacetoacetic acid. This eventually leads to the increased concentration of L-tyrosine in the body. Symptoms of tyrosinemia type I include jaundice and an enlarged liver, kidney dysfunction, as well as a failure to grow, as foods with high protein and amino acids lead to increased symptoms. Additionally, individuals are more at risk for future liver cancer.

Tyrosinemia II also known as Richner-Hanhart syndrome is an autosomal recessive disorder caused by a mutation in the TAT gene the encodes for tyrosine aminotransferase. A defect in this enzyme causes excess tyrosine to accumulate in the blood and urine, tyrosine crystals to form in the cornea, and increased excretion in the urine of 4-hydroxyphenylpyruvic acid, hydroxyphenyllactic acid, and p-hydroxyphenylacetic acid. Symptoms commonly appear in early childhood and include: mental retardation, photophobia (increased sensitivity to light), excessive tearing, eye redness and pain and skin lesions of the palms and soles. The patient is treated with restriction of dietary phenylalanine and tyrosine. Sometimes a tyrosine degradation inhibitor is also used to prevents the formation of fumarylacetoacetate from tyrosine. Trosinemia II is commonly misdiagnosed as herpes simplex keratitis.

Segawa syndrome is a condition in which the affected individual has a clumsy or unusual gait, and experiences involuntary muscle contractions and uncontrolled movements (dystonia). Some cases are mild, while others can be severe. The beginning signs of this condition are dystonia in the legs, and clubfeet. The cause of this condition is a mutation in the GCH1 gene. Tetrahydrobiopterin is an important compound in the production of neurotransmitters, specifically dopamine and serotonin, and the processing of quite a few amino acids, The mutation on GCH1 causes GTP cyclohydrase 1 production to be reduced or absent which causes the first three steps of tetrahydrobiopterin biosynthesis to be compromised. Dopamine is imperative in maintaining smooth muscle movements, which is why patients with Segawa syndrome experience movement problems and an unusual gait.

Lovastatin (also known as Mevacor or Mevinolin) is a statin drug (hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors) that can be used for lowering cholesterol, treating hypercholesterolemia and preventing myocardial infarction and stroke. Lovastatin is produced by fermentation of Aspergillus terreus. HMG-CoA catalyzes the conversion of HMG-CoA to mevalonic acid, the rate-limiting step of cholesterol biosynthesis. Lovastatin, like simvastin, is a prodrug. These prodrugs are converted to their active form by in vivo hydrolysis of the lactone ring. The hydrolyzed lactone ring resembles the tetrahedral reaction intermediate produced by HMG-CoA reductase and the bicyclic portions of these compounds bind to the coenzyme A site of the enzyme. The active drug concentrates in the liver during first-pass circulation. Cholesterol biosynthesis accounts for approximately 80% of cholesterol in the body; thus, inhibiting this process can significantly lower cholesterol levels.

Alendronate (also known as alendronic acid) is a type of bisphosphonate medication with nitrogen that can inhibit FPP synthase, which can block the pathway that produce geranyl-PP and farnesyl pyrophosphate. Geranyl-PP and farnesyl pyrophosphate are the compounds that are required for small GTPase signalling proteins undergo post-translational farnesylation and geranylgeranylation. Therefore, lack the formation of geranyl-PP and farnesyl pyrophosphate can prevent osteoclast activity, which lead to prevention of reduced bone resorption and turnover.

Hyperimmunoglobulinemia D syndrome, or HIDS, is a condition characterized by fevers that come and go, usually lasting 3-7 days, and other various symptoms such as rashes, vomiting, diarrhea and aphthous ulcers. These are usually noticed within the first year of a patient's life, and the highest frequency of HIDS usually occurs during childhood/adolescence. It occurs due to a mevalonate kinase deficiency inherited from both parents. In patients with this condition, the MVK gene is mutated, resulting in a lack of mevalonate kinase. Although globally this condition is rare, there are much higher instances in The Netherlands, about 1 in 350 Dutch nationals carry this mutation.

Cerivastatin inhibits cholesterol synthesis via the mevalonate pathway by inhibiting 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. HMG-CoA reductase is the enzyme responsible for the conversion of HMG-CoA to mevalonic acid, the rate-limiting step of cholesterol synthesis by this pathway. Cerivastatin bears a chemical resemblance to the reduced HMG-CoA reaction intermediate that is formed during catalysis. Cerivastatin, like fluvastatin, atorvastatin and rosuvastatin, is one of the synthetically derived statins. Cholesterol biosynthesis accounts for approximately 80% of cholesterol in the body; thus, inhibiting this process can significantly lower cholesterol levels.

Hypercholesterolemia, also called elevated cholesterol, is an autosomal dominant disorder caused by a defective LDLR gene. The LDLR gene codes for a receptor that binds to low-density lipoprotein which are carriers of cholesterol in the blood. The mutation on the LDLR gene causes the removal of cholesterol from the bloodstream to be limited, resulting in a buildup of cholesterol in the blood. This disorder is characterized by a large accumulation of cholesterol in the blood. Symptoms of the disorder include angina, tendon xanthomas increased risk of cardiac arrest. Treatment with atorvastatin, simvastatin or rosuvastatin, in combination with a heart healthy diet and regular exercise is very effective. It is estimated that hypercholesterolemia affects 1 in 500 individuals in most countries.

Porphyria variegata (PV) is a rare inborn error of metabolism (IEM) which arises from a defective gene called PPOX. PPOX is responsible for protoporphyrinogen oxidase. A defect in this enzyme results in the build up of several compounds, including porphobilinogen, 5-aminolevulinic acid, and in feces and urine, porphyrin and coproporphyrin. Of the wide range of symptoms which present themselves in affected individuals, some include abdominal pain, vomiting, and diarrhea. As well as seizures, hallucinations and skin sensitivity to light. Indeed, the skin sensitivity can be so extreme that skin pigmentation changes, scarring and blistering and even hair growth can ensue on exposed areas.