Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Enzymes
Problems in Medical Enzymology

The achievements of enzymology are finding increasingly broad Applications in medicine, particularly in disease Prevention, Diagnostics, and Treatment. A new branch of enzymology—medical enzymology—is developing successfully, with its own Goals and Objectives, specific methodological approaches, and Research Methods. Medical enzymology develops along three main directions, although the potential for applying scientific breakthroughs of enzymology in medicine is theoretically limitless, specifically in the fields of enzymopathology, enzymodiagnostics, and enzymotherapy.

The field of enzymopathology represents the theoretical, fundamental pillar of pathology. It is designed to study the molecular foundations of pathological processes, grounded in data concerning impaired mechanisms of regulation regarding the activity or synthesis of an individual enzyme or a group of Enzymes. Possessing high catalytic activity and pronounced organotropism, Enzymes can be employed as the most delicate and selective tools for targeted intervention in pathological processes. As is well known, out of more than 5,000 human Hereditary diseases, the Molecular Mechanism of development has been elucidated for only 2 to 3 dozen. It is believed that the onset of a disease is most frequently associated with the hereditary deficiency or complete absence of the synthesis of a single specific enzyme within the patient's body. Sometimes these disorders are also referred to as enzymopathies. For instance, galactosemia is a hereditary condition characterized by an abnormally high concentration of galactose in the Blood. The disease develops As a result of a hereditary defect in the Synthesis of the enzyme hexose-1-phosphate uridylyltransferase, which catalyzes The conversion of galactose into easily metabolizable glucose. The cause of another hereditary disorder—phenylketonuria, which is accompanied by impaired mental function—is the loss by Liver Cells of The ability to synthesize the enzyme that catalyzes the conversion of phenylalanine into Tyrosine (see Chapter 12).

Enzymopathology also successfully addresses problems concerning the Pathogenesis of somatic diseases. Major scientific centers and research institutes have been established to investigate the molecular foundations of atherosclerosis, malignant growth, rheumatoid Arthritis, and other conditions. It is easy to appreciate the immense role played by enzyme systems, or even individual enzymes, whose dysregulated activity and synthesis drive the formation and progression of pathological processes.

The second direction of medical enzymology—enzymodiagnostics—develops along two distinct paths. One path involves using enzymes as selective Reagents for the detection and Quantitative determination of normal or abnormal chemical substances in blood serum, urine, gastric juice, and other fluids (for example, using enzymes to detect glucose, protein, or other substances in urine that are not normally present). The other path involves the detection and quantitative Determination of the enzymes themselves in biological fluids during pathology. It has been found that A number of enzymes appear in blood serum upon Cell disintegration (hence their designation as "necrotic enzymes"). For the Diagnosis of organic and functional lesions of Organs and Tissues, specific enzyme tests are widely used; they compare favorably with other chemical diagnostic tests utilized in clinical practice due to their high sensitivity and Specificity. Approximately 20 tests are known that are based on the quantitative DETERMINATION OF ENZYME (and isoenzyme) activity, primarily in blood (less frequently in urine) as well as in biopsy specimens (tissue fragments obtained via biopsy). It should be noted that out of the vast number of enzymes (over 3,500) discovered in nature (and partially in The Human Body), only a limited set of enzymes is utilized in diagnostic enzymology for a very restricted number of diseases (hepatitis, myocardial infarction, organic lesions of the Kidneys, Pancreas, liver, etc.). For instance, blood levels of lipase, amylase, Trypsin, and Chymotrypsin are sharply elevated in Diabetes Mellitus, malignant pancreatic lesions, and liver diseases. The levels of two aminotransferases, creatine kinase (and its isoforms), and Lactate dehydrogenase (and its isoforms) increase drastically in blood serum during myocardial infarction, while their content is moderately elevated in cases of Brain and liver tissue damage. Additionally, researchers determine The activity of acid phosphatase (levels elevated in prostate carcinoma), alkaline phosphatase, cholinesterase, and certain other organ-specific enzymes (such as histidase, Urocanase, and glycinamidinotransferase) in blood serum during disorders of Bone tissue, the liver, metastatic carcinomas, etc. It has been proven that human organs and tissues are characterized by specific enzymatic and isoenzymatic spectra, which are subject not only to individual variations but also to diurnal rhythms. A large concentration gradient exists between the intracellular and extracellular compartments of the body. Therefore, any cellular damage—even minor (and occasionally functional disorders)—leads to the release of enzymes into the extracellular space, from which they enter the bloodstream. The mechanism underlying hyperenzymemia (elevated enzyme levels in the blood) has not yet been fully elucidated. The rise of intracellular enzymes in Blood Plasma directly depends on The Nature of the damaging agent, the duration of exposure, and the degree of injury to the Introduction/36.html">Biological Membranes of cells and the Subcellular structures of organs. In evaluating enzyme tests for diagnostic purposes, knowing the half-life of each diagnostic enzyme in blood plasma is of paramount importance, as it dictates the precise timing required for blood enzyme analysis. Equally vital is an understanding of the distribution patterns (topography) of enzymes within individual organs and tissues, as well as their intracellular localization.

Recently, restriction enzymes—specific endonucleases (see Chapter 13) that catalyze the Cleavage of DNA inter-nucleotide bonds—have begun to be applied in the diagnosis of phenylketonuria, α- and β-thalassemias, and other human hereditary diseases. This method is based on restriction fragment length polymorphism (RFLP) of DNA.

It follows from the presented data that diagnostic enzymology can serve as a foundation not only for establishing a correct and timely diagnosis of a disease, but also for assessing the efficacy of the treatment regimen applied.

The further development of diagnostic enzymology proceeds predominantly along two promising paths of medical enzymology: simplifying and rationally modifying already proven methods, and searching for novel organ-specific (tissue-specific) enzymes and Isoenzymes.

The third direction of medical enzymology—enzymotherapy, i.e., The Use of enzymes and modulators (activators and inhibitors) of enzyme action as therapeutic agents—has a relatively brief history thus far. To date, work in this area has scarcely extended beyond the experimental stage. An exception is represented by certain proteinases: Pepsin, trypsin, chymotrypsin, and their mixtures (abomin, chymopsin), which are used to treat a number of digestive tract disorders. Alongside proteinases, a series of Other Enzymes—specifically RNase, DNase, hyaluronidase, collagenases, and elastases, either individually or mixed with proteinases—are utilized in cases of Burns, wound management, inflammatory foci, edema reduction, hematomas, keloid scars, and cavernous processes in Pulmonary Tuberculosis, among others. Enzymes are also employed in the Treatment of cardiovascular diseases and for dissolving blood clots. The world's first immobilized streptokinase preparation, recommended for the treatment of myocardial infarction, was developed in our country. Kallikreins, which are Enzymes of the kinin system, are used to lower blood pressure.

An important and highly promising area of enzymotherapy is the application of Enzyme Inhibitors. For example, natural proteinase inhibitors (α₁-antitrypsin, α₁-chymotrypsin, α₂-macroglobulin) have found application in the treatment of acute pancreatitis, arthritis, and allergic conditions characterized by enhanced proteolysis and Fibrinolysis, which are accompanied by the generation of vasoactive kinins.

In recent years, the clinical use of bacterial enzymes as therapeutic agents in oncology has gained recognition. L-asparaginase (produced on an industrial scale) and L-glutamine(asparagine)ase are widely used for the treatment of acute and chronic forms of leukemias and lymphogranulomatosis. More than a dozen bacterial enzymes described in literature have been tested primarily on animals bearing transplantable tumors or on Human and Animal Cancer cells grown in tissue culture. The core postulates governing the Application of Enzymes in oncology rely on differences in the METABOLISM of tumor cells compared to that of normal, healthy cells. Specifically, modern strategies and tactics in the enzymotherapy of tumors take into account the differential sensitivity of normal versus tumor cells to a shortage (deficiency) of essential growth factors. Such growth-promoting factors include not only nutritional components (Vitamins, Essential Amino acids, macro- and microelements) but also a number of so-called non-essential substances, including non-essential amino acids, toward whose deficiency tumor cells prove more sensitive due to their metabolic peculiarities. The therapeutic effect of L-asparaginase and L-glutamine(asparagine)ase in leukemias is most likely explained by the irreversible breakdown of both glutamine and asparagine. It turned out that tumor cells require amino acids from the host Organism for their growth and proliferation, as they lack the ability to synthesize amino acid amides themselves, whereas normal cells possess this capability. It was concluded that the amide nitrogen of glutamine and asparagine fulfills several unique Functions within cells, which are best understood for glutamine (see Chapter 12). In particular, the amide nitrogen of glutamine proved to be an absolute requirement—unreplaceable by Other Amino Acids—serving as the source of the nitrogen atom in at least ten synthetic reactions, such as those forming purine and pyrimidine NUCLEOTIDES (for DNA and RNA, respectively), ATP, hexosamines, Histidine, and others. Thus, the hypothesis is not without foundation that any enzyme or agent catalyzing the irreversible cleavage of a nutritional factor indispensable to a tumor cell (including amino acids) could, in principle, be applied in tumor enzymotherapy, provided that limitations related to the protein Nature of the enzyme are overcome. The evaluation of enzyme efficacy in experimental and clinical oncology contains numerous contradictions and vast gaps. The positive outcomes observed in several instances inspire hope that The production of standard enzyme preparations (including the creation of immobilized forms) on an industrial scale, coupled with their rational clinical application organized on a rigorous scientific basis, will undoubtedly provide physicians with yet another valuable weapon in the fight against human neoplastic diseases.

The idea of employing enzymes as medications (enzyme pharmacology) has always seemed alluring. However, their instability, short half-life, undesirable antigenic properties linked to the protein nature of enzymes and the risk of allergic reactions, alongside the difficulties of delivery to affected target organs and tissues, severely constrained the PRACTICAL USE OF enzyme preparations. Recent developments in Enzyme Immobilization methods (see above) have outlined concrete pathways for overcoming these hurdles: the utilization of Water-soluble, biocompatible carriers such as polylactic acid (which readily degrades within the body), the application of chemical modification and microencapsulation techniques, the preparation of mono- and polyclonal Antibodies, and enzyme-containing Liposomes, among others.

Recently, intensive research has been dedicated to Methods for the targeted transport of enzymes encapsulated within unique microcontainers (such as erythrocyte ghosts and liposomes), onto the outer surface of which targeted (vector) protein molecules can be attached (e.g., IMMUNOGLOBULINS—antibodies directed against specific components of a target organ or tissue, such as a tumor). Immobilized enzymes have begun to be used as therapeutic agents within specialized columns for extracorporeal blood perfusion (resembling artificial kidneys). Such treatment completely eliminates adverse systemic effects from foreign Proteins and can be administered over extended periods.

Thus, the spheres of application for enzymes in medicine are truly boundless. The Examples examined clearly demonstrate the remarkable and promising Prospects that medical enzymology already opens up today for future physicians.