Pathways

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, which is also known LCHADD, is a rare inherited inborn error of metabolism (IEM) of long-chain fatty acid metabolism. The estimated birth prevalence of LCHADD is 1 in 62 000 in Northern European individuals. The worldwide birth prevalence is estimated at 1 in 250 000. MCADD is an autosomal recessive disorder associated with a mutation in the enzyme known as hydroxyacyl-CoA dehydrogenase (HADHA). HADHA catalyzes the last three steps of mitochondrial beta-oxidation of long chain fatty acids. HADHA converts medium- and long-chain 2-enoyl-CoA compounds into the corresponding 3-ketoacyl-CoA compounds when NAD is present, and acetyl-CoA when NAD and CoASH are present. Deficiencies in this enzyme prevent the body from converting certain fats to energy, particularly during periods without food (fasting). Signs and symptoms of LCHAD deficiency typically manifest during infancy or early childhood and can include feeding difficulties, hypoglycemia, hypotonia, lethargy, liver problems, and retinal abnormalities. During late childhood, people may experience muscle pain and peripheral neuropathy. LCHAD-deficiency individuals are also at risk for breathing difficulties, serious heart problems, coma, and sudden death. Fasting or illnesses (e.g. viral infections) can trigger related problems. LCHADD is associated with some pregnancy-specific disorders, including preeclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), hyperemesis gravidarum, acute fatty liver of pregnancy, and maternal floor infarction of the placenta.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, which is also known LCHADD, is a rare inherited inborn error of metabolism (IEM) of long-chain fatty acid metabolism. The estimated birth prevalence of LCHADD is 1 in 62 000 in Northern European individuals. The worldwide birth prevalence is estimated at 1 in 250 000. MCADD is an autosomal recessive disorder associated with a mutation in the enzyme known as hydroxyacyl-CoA dehydrogenase (HADHA). HADHA catalyzes the last three steps of mitochondrial beta-oxidation of long chain fatty acids. HADHA converts medium- and long-chain 2-enoyl-CoA compounds into the corresponding 3-ketoacyl-CoA compounds when NAD is present, and acetyl-CoA when NAD and CoASH are present. Deficiencies in this enzyme prevent the body from converting certain fats to energy, particularly during periods without food (fasting). Signs and symptoms of LCHAD deficiency typically manifest during infancy or early childhood and can include feeding difficulties, hypoglycemia, hypotonia, lethargy, liver problems, and retinal abnormalities. During late childhood, people may experience muscle pain and peripheral neuropathy. LCHAD-deficiency individuals are also at risk for breathing difficulties, serious heart problems, coma, and sudden death. Fasting or illnesses (e.g. viral infections) can trigger related problems. LCHADD is associated with some pregnancy-specific disorders, including preeclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), hyperemesis gravidarum, acute fatty liver of pregnancy, and maternal floor infarction of the placenta.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, which is also known LCHADD, is a rare inherited inborn error of metabolism (IEM) of long-chain fatty acid metabolism. The estimated birth prevalence of LCHADD is 1 in 62 000 in Northern European individuals. The worldwide birth prevalence is estimated at 1 in 250 000. MCADD is an autosomal recessive disorder associated with a mutation in the enzyme known as hydroxyacyl-CoA dehydrogenase (HADHA). HADHA catalyzes the last three steps of mitochondrial beta-oxidation of long chain fatty acids. HADHA converts medium- and long-chain 2-enoyl-CoA compounds into the corresponding 3-ketoacyl-CoA compounds when NAD is present, and acetyl-CoA when NAD and CoASH are present. Deficiencies in this enzyme prevent the body from converting certain fats to energy, particularly during periods without food (fasting). Signs and symptoms of LCHAD deficiency typically manifest during infancy or early childhood and can include feeding difficulties, hypoglycemia, hypotonia, lethargy, liver problems, and retinal abnormalities. During late childhood, people may experience muscle pain and peripheral neuropathy. LCHAD-deficiency individuals are also at risk for breathing difficulties, serious heart problems, coma, and sudden death. Fasting or illnesses (e.g. viral infections) can trigger related problems. LCHADD is associated with some pregnancy-specific disorders, including preeclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), hyperemesis gravidarum, acute fatty liver of pregnancy, and maternal floor infarction of the placenta.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, which is also known LCHADD, is a rare inherited inborn error of metabolism (IEM) of long-chain fatty acid metabolism. The estimated birth prevalence of LCHADD is 1 in 62 000 in Northern European individuals. The worldwide birth prevalence is estimated at 1 in 250 000. MCADD is an autosomal recessive disorder associated with a mutation in the enzyme known as hydroxyacyl-CoA dehydrogenase (HADHA). HADHA catalyzes the last three steps of mitochondrial beta-oxidation of long chain fatty acids. HADHA converts medium- and long-chain 2-enoyl-CoA compounds into the corresponding 3-ketoacyl-CoA compounds when NAD is present, and acetyl-CoA when NAD and CoASH are present. Deficiencies in this enzyme prevent the body from converting certain fats to energy, particularly during periods without food (fasting). Signs and symptoms of LCHAD deficiency typically manifest during infancy or early childhood and can include feeding difficulties, hypoglycemia, hypotonia, lethargy, liver problems, and retinal abnormalities. During late childhood, people may experience muscle pain and peripheral neuropathy. LCHAD-deficiency individuals are also at risk for breathing difficulties, serious heart problems, coma, and sudden death. Fasting or illnesses (e.g. viral infections) can trigger related problems. LCHADD is associated with some pregnancy-specific disorders, including preeclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), hyperemesis gravidarum, acute fatty liver of pregnancy, and maternal floor infarction of the placenta.

Lonoctocog alfa also known as Afstyla is a recombinant coagulation factor VIII that is used in the treatment of hemophilia A. Once administered intravenously it binds to the coagulation factor IXa to convert coagulation factor X to its active form Xa to carry on the reactions of the clotting cascade.

Loperamide is an antidiarrheal opioid that cannot cross the blood-brain barrier so it does not act on the central nervous system like other opioids do. Loperamide is taken orally and travels to the myenteric plexus, which is a plexus of neurons that is located between the longitudinal and circular muscle layers of the intestine. Here it activates the mu-opioid receptors which is coupled with G-protein receptors. Binding of Loperamide stimulates the exchange of GTP for GDP on the G-protein complex. The G-protein system inhibits adenylate cyclase which prevents ATP from being synthesized into cAMP which causes a decrease in intracellular cAMP. The activated G-proteins also close N-type voltage-operated calcium channels which prevents calcium from entering the neuron, and it opens calcium-dependent inwardly rectifying potassium channels which causes sodium to leave the neuron. This results in hyperpolarization and reduced neuronal excitability. Subsequently this prevents acetylcholine and other excitatory neurons from being released into the synapse. The low concentration of acetylcholine means it cannot activate muscarinic acetylcholine (M2 and M3) receptors located on the circular muscles of the instestine. Muscarinic acetylcholine receptors M3 are coupled to the Gq signaling cascade. The activation of this leads to the acitvation of phospholipase C, which converts Phosphatidylinositol (3,4,5)-trisphosphate to inositol (3,4,5)-trisphosphate (IP3) and diacylglycerol (DAG). IP3 activates IP3 receptors on the sarcoplasmic reticulum leading to the release of stored calcium into the cytosol. DAG activates protein kinase C (PKC). One of the downstream effects of PKC include activation of calcium channels on the membrane, leading to influx of calcium ions into the cytosol. Both IP3 and DAG increase cytosolic levels of calcium which then binds to calmodulin to create a calcium-calmodulin complex. Muscle contraction and relaxation are controlled by the enzymes myosin kinase and myosin phosphatase. Myosin kinase phosphorylates myosin light chain, leading to interaction between actin and myosin, producing muscle contraction. The calcium-calmodulin activates myosin kinase, leading to increased phosphorylation of myosin light chain and more muscle contraction. With acetylcholine in low concentrations, myosin light chain kinase is activated less which means contraction of the muscle occurs less often. Nitric oxide is synthesized in the epithelial cells as well as many other places near the intestine. It is lipid soluble so it can enter the myocyte and activate guanalyl cyclase which catalyzes GTP into cGMP. CGMP activates Myosin light chain phosphatase which dephosphorylates the phosphorylated myosin light chain, preventing interaction with actin, producing muscle relaxation. This keeps the myocyte relaxed for longer and slows the cyclic muscle contractions caused by action potential in the cyclic myocytes of the intestine. This keeps the substances in the intestine for longer, allowing the intestine to absorb more water from the substances.This also suppresses the gastrocolic reflex.

Loperamide is an antidiarrheal used for general diarrhea and chronic diarrhea. Loperamide is taken orally as a pill. It is transported from the intestine into the intestinal epithelial cell possibly via solute carrier family 15 member 1, one of 3 drug transporters into epithelial cells. It is then transported into blood vessels via ATP-binding cassette sub-family C member 3. In the blood it travels to the target cells via the loperamide pathway as well as to the liver where it is transported into the liver hepatic cell vis P-glycoprotein. On the endoplasmic reticulum membrane loperamide is metabolized by Cytochrome P450 3A4, Cytochrome P450 2D6, Cytochrome P450 2C8, or Cytochrome P450 2B6 into N-Desmethyloperamide. The majority of loperamide is metabolized, but some leaves the liver with the metabolite N-Desmethyloperamide. They are transported into the bile ducts through the P-glycoprotein transporter. In the bile ducts they are then transported to the intestines where they are both excreted through the feces.

Lopinavir is an antiretroviral HIV-1 protease inhibitor used in combination with ritonavir to treat human immunodeficiency virus (HIV) infection. Lopinavir is marketed and administered exclusively in combination with ritonavir. This combination is necessary due to lopinavir's poor oral bioavailability and extensive biotransformation. The HIV virus binds and penetrates the host cell. Viral RNA is transcribed into viral DNA via reverse transcriptase. Viral DNA enters the host nucleus and is integrated into the host DNA via integrase. The DNA is then transcribed, creating viral mRNA. Viral mRNA is translater into the gag-pol polyprotein. HIV protease is synthesized as part of the Gag-pol polyprotein, where Gag encodes for the capsid and matrix protein to form the outer protein shell, and Pol encodes for the reverse transcriptase and integrase protein to synthesize and incorporate its genome into host cells. HIV-1 protease cleaves the Gag-pol polyprotein into 66 molecular species, including HIV-1 protease, integrase, and reverse transcriptase. Lopinavir inhibits HIV-1 protease. This inhibition prevents the HIV virion from fully maturing and becoming infective. Using the lipid bilayer of the host cell, a virus is formed and released. The inhibition of HIV-1 protease prevents the necessary molecular species from forming, therefore preventing maturation and activation of viral particles. This forms immature, non-infectious viral particles, therefore, Lopinavir prevents the virus from reproducing.