Recombinant DNA Technology and Gene Therapy Using Viruses
Patricia G. Melloy in Viruses and Society, 2023
Although a small number of gene therapy products have been approved in the United States, many are being tested right now, including potential treatment for monogenic disorders that have been studied for many years. As mentioned earlier, both cystic fibrosis (CF) and sickle cell disease (SCD) are well-known monogenic disorders. Cystic fibrosis involves a defective chloride ion transporter causing mucus buildup in the lungs, making patients prone to infections, among other issues. Other organs, such as parts of the digestive system, are also affected in CF. Physicians and scientists have been working on gene therapy approaches to treat CF for many years. So far, there are no approved gene therapy treatments, although several approaches are being tested in clinical trials. Since CF can affect more than one organ, determining where to deliver the therapy is one challenge, in addition to providing a treatment that is long lasting (Foundation 2022; Colavito 2007). Sickle cell disease (also known as sickle cell anemia) involves the loss of functional adult hemoglobin for oxygen transport in the blood due to a defective beta-globin gene. Clinical trials in SCD patients are underway to use a lentivirus-based vector to restore a normal copy of the beta-globin gene. A second treatment approach for SCD involves using gene therapy to reactivate expression of the gamma-globin gene, a component of fetal hemoglobin, to substitute for the defective beta-globin in the adult hemoglobin form (Eisenstein 2021; Kunz and Kulozik 2020).
Genetic Counseling in Assisted Reproductive Technology
Carlos Simón, Carmen Rubio in Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Alpha-thalassemia major, or Hb Bart disease, is a hemoglobinopathy that can cause fetal loss. Hemoglobin is formed by a tetramer of α-globin and β-globin molecules. Changes in the stoichiometric ratios of α-globin and β-globin molecules impact the formation of hemoglobin and the delivery of oxygen to the fetus during pregnancy. The α-globin gene region contains two tandem α-globin genes on each allele, for a total of four copies in a typical individual. Hb Bart disease, caused by deletions in all four α-globin copies (−/−), results in severe intrauterine hypoxia and hydrops fetalis. The α-thalassemia trait genotype −/αα is common among Southeast Asians and is associated with a 25% risk of passing on Hb Bart disease if both members of the reproductive couple are carriers. Reproductive genetic counseling should be recommended for couples with a family history of thalassemia.
Phylogeny of Normal and Abnormal Hemoglobin Genes
S. K. Dutta in DNA Systematics, 2019
Human globin chains all consist of a single polypeptide of slightly over 140 amino acids. The a chains contain 141 while the non-α chains have 146. All globin chains, including myoglobin, the oxygen-binding protein found in muscle, share a common tertiary structure and all exist under similar structural constraints. The proteins are made up primarily of α helical segments connected by short random coil segments. There is no β structure. There are eight helical regions designated A to H. Perutz1 and others have shown that the function of hemoglobin requires a series of concerted shifts in tertiary structure which place stringent limitations on the amino acids which can occupy a given location in the molecule. This is especially true in the region of the G and H helices and at the terminal regions. Other structural restrictions include the portions of the E and F helices that form the heme binding site which must be hydrophobic and those portions of each chain which contribute to the interchain contacts that characterize the quaternary structure. A more detailed review of hemoglobin structure and function may be found in the excellent book by Dickerson and Geis.2
Hb Santa Juana (β 108(G10) Asn > Ser): a low oxygen affinity hemoglobin variant in a family of Bosnian background
Published in Hematology, 2023
N. P. Wildenberg, C. Rossi, A. E. Kulozik, J. B. Kunz
Hemoglobin is a heterotetramer composed of two α- and two β-globin chains, with a total of four heme groups as oxygen binding sites. According to the allosteric two-state-model [2], the heterotetramer can exist in a relaxed R state with high oxygen affinity and a strained T state with low oxygen affinity. Binding of an oxygen molecule to one heme group increases the oxygen affinity of the other subunits. This effect explains the sigmoidal shape of the oxygen binding curve. Hemoglobin variants with decreased oxygen affinity stabilize the T-state and result in increased oxygen delivery to the tissues, while oxygen uptake in the lungs is decreased. The oxygen dissociation curve is right-shifted and characterized by a higher oxygen tension required to reach 50% saturation (p50). However, additional factors contribute to oxygen release into the tissue, such as the concentration of 2,3-bisphosphoglycerate, pH, and CO2 tension. Weak oxygen binding to hemoglobin favors oxygen release into the tissue, suppressing erythropoietin secretion and causing normocytic anemia. Although some patients expressing hemoglobin variants with decreased oxygen affinity present with cyanosis, most are asymptomatic. A low oxygen affinity hemoglobin variant may be suggested by otherwise unexplained reduced pulse oximetry measurements and normocytic anemia.
The state of the art of fetal hemoglobin-inducing agents
Published in Expert Opinion on Drug Discovery, 2022
Aline Renata Pavan, Juliana Romano Lopes, Jean Leandro Dos Santos
Another pathway that regulates γ-globin gene expression is the guanylate cyclase and the ⋅NO/cGMP signaling pathway. Soluble guanylate cyclase (sGC) converts guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP), which is an important second messenger that mediates several physiological processes, such as smooth muscle relaxation and platelet adhesion [86]. To demonstrate the role of sGC in γ-globin gene expression, researchers evaluated the level of expression of the subunits (α and β) that compose the enzyme in K562 cells. The results demonstrated that these cells expressed high levels of the α and β subunits, comparable to the levels found in the lungs and the brain cells. Also, a positive correlation was found between the expression of the α subunit and the expression of γ-globin. Furthermore, an sGC activator increased the γ-globin mRNA levels by five-fold to six-fold, and this effect disappeared when the cells were pre-treated with an sGC inhibitor. Similar results were found after the treatment of K562 cells and primary erythroblasts from healthy individuals and β-thalassemic patients with a cGMP analog (8-Br-cGMP), which indicated that modulation of sGC might be performed to regulate γ-globin gene expression and HbF induction [87].
Role of Oxidative Stress and the Protective Effect of Fermented Papaya Preparation in Sickle Cell Disease
Published in Hemoglobin, 2022
Prashant P. Warang, Nikhil S. Shinde, Vinod D. Umare, Prajyot V. Deshmukh, Kanjaksha Ghosh, Manisha R. Madkaikar, Roshan B. Colah, Malay B. Mukherjee
Sickle cell disease is hereditary hemolytic anemia due to a mutation in the β-globin gene that encodes for an abortive globin and hemoglobin (Hb). Sickle cell disease, like other hemoglobinopathies, was reported to be associated with oxidative stress. Oxidative stress is the result of imbalance between the enhanced generation of reactive oxygen species (ROS) and low levels of antioxidants, which triggers a series of oxidative reactions damaging lipids, proteins, and DNA ultimately leading to hemolysis of red blood cells (RBCs). Oxidative stress in sickle cell disease patients leads to multiple pathophysiologic mechanisms, such as hemolysis, endothelial damage, reduced nitric oxide (NO) bioavailability, and vaso-occlusion leading to chronic organ damage [1]. Fermented papaya preparation (FPP) is a health product with anti-oxidative properties, resulting from yeast fermentation of carica papaya. It has previously been shown that FPP is efficient in limiting oxidative stress in β-thalassemia (β-thal), Hb E (HBB: c.79G > A)/β-thal, hereditary spherocytosis and paroxysmal nocturnal hemoglobinuria [2]. To the best of our knowledge, anti-oxidative effects of FPP in sickle cell disease patients have not yet been studied.
Related Knowledge Centers
- Alpha Helix
- Globular Protein
- Heme
- Oxygen
- Protein Tertiary Structure
- Myoglobin
- Hemoglobin
- Protein Superfamily
- Molecular Binding
- Protein Fold Class