Without keyword UDC 591.151 S.L. MOROZOV 1, 2 , V.V. LONG 1 1 Scientific Research Clinical Institute of Pediatrics. acad. Yu.E. Veltishchev RNIMU them. N.I. Pirogov Ministry of Health of the Russian Federation, Moscow

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UDC 591.151

S.L. MOROZOV 1, 2 , V.V. LENGTH 1

1 Research Clinical Institute of Pediatrics named after acad. Yu.E. Veltishchev RNIMU them. N.I. Pirogov Ministry of Health of the Russian Federation, Moscow

2 Russian National Research Medical University named after N.N. N.I. Pirogov Ministry of Health of the Russian Federation, Moscow

Contact Information:

Morozov Sergey Leonidovich ― Candidate of Medical Sciences, Senior Researcher of the Department of Hereditary and Acquired Kidney Diseases, Associate Professor of the Department of Hospital Pediatrics No.

The address: 125412, Moscow, st. Taldomskaya, 2, tel. +7-903-138-77-32, e-mail: [email protected]

The article published data on the principles of steroid therapy for primary nephrotic syndrome in children. Unfortunately, to date, modern guidelines for the treatment of nephrotic syndrome are based on empirical recommendations, and among doctors there is a large variability of opinions on the treatment of nephrotic syndrome, especially relapses, and the choice of immunosuppressive therapy. The article presents data on the molecular basis of the action of steroids in nephrotic syndrome and evaluates the prospects for a personalized approach to therapy.

Keywords: children, primary nephrotic syndrome, glucocorticosteroids, polymorphisms, personalized therapy.

S.L. MOROZOV 1, 2 , V.V. DLIN 1

1 Scientific-research Clinical Institute for Pediatrics named after Acad. Yu.E. Veltishchev, Moscow

2 Russian Scientific-research Medical University named after N.I. Pirogov, Moscow

On steroid therapy of primary nephrotic syndrome in children

contact:

Morozov S.L. ― PhD (medicine), Senior Researcher of the Department of Inherited and Acquired Kidney Diseases, Associate Professor of the Department of Hospital Pediatrics No. 2 of Pediatrics Faculty

address: 2 Taldomskaya Str., 125412, Moscow, Russian Federation, tel. +7-903-138-77-32, e-mail: [email protected]

The article presents data on steroid therapy of primary nephrotic syndrome in children. Unfortunately, to date, modern guidelines for the treatment of nephrotic syndrome are based on empirical recommendations, and among doctors there is great variability in the treatment of nephrotic syndrome, especially relapses and the choice of immunosuppressive therapy. The article provides data on the molecular basis of the steroids action in nephrotic syndrome and assesses the prospects for a personalized approach to therapy.

key words: withhildren, primary nephrotic syndrome, glucocorticosteroids, polymorphisms, personalized therapy.

One of the most common glomerular diseases in childhood is nephrotic syndrome (NS), the prevalence of which is 1-7 cases per 100,000 children per year [1, 2]. The disease is characterized by the classic triad of nephrotic proteinuria, hypoalbuminemia, and edema. For more than 60 years, glucocorticoids have been the main drugs in the treatment of nephrotic syndrome. This is primarily due to the high efficacy of steroid drugs, since more than 80% of patients achieve remission on prednisolone therapy and only about 20% of patients are not sensitive to standard steroid therapy [1]. Despite the high efficacy of prednisolone, approximately 80% of patients have relapses of the disease. Currently, recommendations for the treatment of the onset of nephrotic syndrome and relapses of steroid-sensitive NS are standardized and presented in clinical guidelines [3].

Despite the effectiveness of glucocorticosteroid therapy regimens in children, in clinical practice there is currently no unambiguous approach among physicians to the management of patients with nephrotic syndrome, especially when it comes to relapses of the disease and further choice of immunosuppressive drugs. Often this is due only to the preferences of the doctor, and not to the individual characteristics of the disease. A cohort study conducted in the Netherlands demonstrated that the duration of steroid therapy at the onset of the disease did not affect the frequency of subsequent relapses. The same conclusions were obtained by British researchers, who also demonstrated the absence of a significant effect of long-term steroid therapy on the onset of nephrotic syndrome [4, 5].

It has long been noted that the course of nephrotic syndrome in children has pronounced individual differences, which manifest themselves in the form of varying degrees of NS activity and a wide range of side effects of steroid therapy. In most cases, morphologically, nephrotic syndrome is represented by damage to the legs of podocytes in the form of their "spreading", which leads to a violation of the filtration barrier.

Currently, there is an active discussion of the causes leading to the development of the disease, which are associated primarily with the state of the proteins of the slit membrane of podocytes, namely, the identification of mutations in the genes encoding these proteins, which made it possible to establish a number of causes for the development of NS. More than 70 genes are known whose mutations are associated with the development of nephrotic syndrome [6–8]. In addition, in a number of patients, the development of the disease is due to impaired immune regulation, which can also lead to steroid-resistant nephrotic syndrome [9, 10]. The presence of immune complexes explains the recurrence of nephrotic syndrome in the graft [11]. In addition, in favor of defects in the immune system is the fact that infectious and allergic factors act as triggers for both the onset and relapses of nephrotic syndrome, and treatment with NS glucocorticoids is effective.

Research data of recent decades have shown that the immune response to foreign and self antigens is different depending on the activation of T-helpers of the 1st or 2nd type (which way the immune reaction will go). In the pathogenesis of nephrotic syndrome, the significant role of B-lymphocytes is also taken into account. That is why rituximab began to be used in the treatment of NS, which ensures complete depletion of CD-19 and, in most cases, leads to the development of stable remission of NS [12].

In the vast majority of children with nephrotic syndrome, the disease is based on minimal changes that are manifested by "spreading" of podocytes, which cannot fully explain the clinical variability of patients.Recently, much attention has been paid not only to search for monogenic forms of the disease, but also pharmacogenesis factors that affect the pharmacokinetics and pharmacodynamics of immunosuppressive drugs in a particular patient [6, 9, 13].

According to various authors, genetic factors affecting the individual pharmacodynamic and pharmacokinetic profile can be from 20 to 95% of the variability of the efficiency and development of undesirable phenomena from drugs used for the treatment of nephrotic syndrome [1, 6, 9, 14].

The study of pharmacokinetics, pharmacodynamic and genetic aspects of immunosuppressive drugs used for the treatment of nephrotic syndrome, as well as the possibility of genotyping patients prior to treatment, in the future will prevent the emergence of many unwanted phenomena, and the active development of methods of molecular diagnosis of kidney disease opens a large section of medicine that can be called like "molecular nephropathology". Further study of kidney diseases from the position of molecular biology will re-look at the pathogenesis of many diseases and solve a number of problems from the standpoint of "personalized therapy", which takes into account the genetic features of the patient [6].

Glucocorticoids (GC) have a pronounced anti-inflammatory and immunosuppressive effect. The effects of the Civil Code are due both genomic and negative mechanisms. Genomic mechanisms are mediated by the active replication of specific genes encoding anti and pro-inflammatory proteins. A feature is a long-term translation and transcription of mRNA than the slow start of the answer is due. If we consider non-combat mechanisms, they do not affect gene expression and have a quick start and relatively short duration of action.

Figure 1. Molecular mechanisms of glucocorticoids

AR-1 ― Activator 1 protein; IκB. ― Inhibitor κB; IPO13 – Importin-13 (transport protein); NF-κB. ― nuclear factor κB; GRE (transactivation).

Figure 1. Molecular Mechanisms of Glucocorticoids

AR-1 ― Activator Protein 1; I.κB- κB inhibitor; IPO13 – Importin-13 (Transporting Protein); NF-κB. ― κB nucleus factor; GRE (Transactivation).

Like all steroid hormones, glucocorticosteroids are lipophilic structures that easily penetrate the cell membrane and are associated with glucocorticosteroid receptors (GR) [15]. All inactive receptors are associated with the Schperon protein complex, this connection ensures the stability of receptors and prevents the penetration of GR through the nuclear membrane. When glucocorticosteroids fall into the cage, they are binding to GR in the cytoplasm, forming a hormone / receptor complex (GR / GC), then it is transferred to the cell core through special transport proteins Importin-13 (IPO13) [16]. In the nucleus, the GR / GC complex communicates with DNA or interacts with co-activator complexes. Anti-inflammatory and immunosuppressive effect is achieved by the increased expression of anti-inflammatory genes (transactivation) and reduce the expression of pro-inflammatory genes (transparency) [17].In addition, the GR/GC complex can, directly or indirectly, interact with pro-inflammatory transcription factors, nuclear factor κB (NF-κB) and activator protein 1 (AP-1), and thus reduce their activity [18] (Fig. . one).

Non-genomic mechanisms are largely unknown, the only thing that is certain is that steroids affect the physicochemical properties of cell membranes directly or indirectly through transmembrane bonds. Their effects lead to inhibition of inflammatory function in cells, and it is also believed that the protein complexes "chaperones" that are released during hormone/receptor binding play the role of signal proteins/molecules responsible for the rapid reactions of glucocorticosteroids [14].

One of the main drugs for the treatment of nephrotic syndrome is prednisolone, which is well absorbed and has a high bioavailability (99±8%) [19]. It should be noted the peculiarity of the distribution of prednisolone in patients with nephrotic syndrome. Upon entering the body, the prednisolone molecule binds to transcortin (i.e., corticosteroid-binding globulin) and to albumin. In the active phase of NS, the level of serum albumin and transcortin in patients decreases, which ultimately leads to a decrease in the binding of proteins to prednisolone, thereby free molecules are removed from the body faster, which ultimately leads to a decrease in the total concentration of the drug (Fig. 2). ) [20].

Figure 2. Unbound prednisolone molecules in patients with nephrotic syndrome.

Figure 2. Unbound molecules of prednisolone in patients with nephritic syndrome

Intracellular metabolism is controlled by the enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD), which binds the prednisolone molecule to glucocorticoid and mineralocorticoid receptors. There are two types of 11β-HSD receptors. Thus, 11β-HSD-1 acts as a reductase, converting prednisolone to its active form, while 11β-HSD-2 acts mainly as an oxidase and converts prednisolone to prednisone, thereby protecting the mineralocorticoid receptor from capture by cortisol and prednisolone. It is believed that the pronounced mineralocorticoid effects will depend on the activity of 11β-HSD-2.

Excretion from the body of prednisolone is mainly provided by the enzymatic system of the liver cytochrome P450. However, with respect to the metabolism of prednisolone, the extent to which specific cytochrome P450 (CYP) 3A isoenzymes are involved has not yet been fully elucidated. However, co-administration of the strong CYP3A4 inhibitor ketoconazole has been shown to increase total and unbound plasma concentrations of prednisolone by approximately 50% due to a decrease in its clearance [21]. This feature should be taken into account when using prednisolone together with enzyme inducers, which leads to an increase in clearance and a decrease in the half-life of prednisolone [22]. In addition to liver enzymes, it has been shown that prednisolone is a substrate of P-glycoprotein, which is an ATP-dependent membrane transporter "Efflux" (energy-dependent transporter through cell membranes), which is found in large quantities in the small intestine and kidneys.Expression of P-glycoprotein in the intestinal epithelium limits the absorption of drug substrates from the gastrointestinal tract. Therefore, theoretically, the co-administration of P-glycoprotein inhibitors can increase the absorption of glucocorticoids and oral bioavailability, which, ultimately, can affect the distribution of glucocorticoids, one such inhibitor is cyclosporine [23].

Based on the metabolism of prednisolone in patients with nephrotic syndrome, various dosing regimens have been studied. It has been shown that a single single use of prednisolone is fully effective, as is its repeated use, however, the frequency of side effects, such as obesity, arterial hypertension, Cushing's syndrome, was significantly less with the once a day dosing regimen compared with patients who received separate doses, which is associated with a change in the activity of 11β-HSD-2 in the case of multiple daily intake of high doses of steroids [24].

Although glucocorticosteroids have been used in the treatment of nephrotic syndrome for more than fifty years, the mechanisms of its effect in patients with nephrotic syndrome are not well understood. A striking example is the high variability in efficacy and adverse events in patients with NS. Also, the molecular mechanisms of the development of resistance to steroid therapy are not fully understood. Currently, there are a number of hypotheses that explain these mechanisms. Thus, Xing et al showed that dexamethasone enhances the expression of nephrin, which is one of the key components of the glomerular slit diaphragm. The study suggested that glucocorticosteroids act directly on podocytes by stimulating repair with an increase in the formation process and activation of nephrin [25]. In addition, podocyte processes at the base consist of cortical actin filaments and actin-associated proteins that provide dynamic maintenance and reorganization of the cytoskeleton [26]. In vitro studies have shown a direct effect of glucocorticoids on podocytes by protecting cultured podocytes by stabilizing actin filaments and preventing apoptosis. The effect on apoptosis and nephrin activation appeared to be dependent on the doses of glucocorticoids used, which may explain the observed differences in the variability in clinical responses. It was shown that GR expression in glomeruli was significantly higher with minimal changes. In addition, patients with steroid-resistant nephrotic syndrome, on the contrary, had low expression of GR in the glomeruli and, therefore, the assessment of glomerular GR expression at the time of diagnosis can help predict the response to steroid therapy.

A number of studies are aimed at studying the genes encoding glucocorticoid receptors.It is now well known that different splicing variants and modifications lead to the formation of different polypeptides, and therefore the glucocorticoid receptor has several different isoforms, such as: GRα, GRβ, GRγ, GRA and GRP, of which the last two are believed to be associated with steroid resistance [27-28]. These data showed that the predominance of receptor isoforms GRβ due to overexpression GRβ can lead to imbalance GRα/GRβ, which ultimately is the cause of the development of hormone resistance in patients with nephrotic syndrome. A striking example is the study of the expression of the multidrug resistance gene MDR1 in steroid-resistant nephrotic syndrome (SRNS). The study and prediction of drug resistance in patients with nephrotic syndrome is particularly important.

Since the mechanism of action of glucocorticoids includes numerous receptors, enzymes and proteins, there are many variants of polymorphism that determine the effects of glucocorticoid therapy. Table 1 shows just a few of them.

Table 1. Effects of gene polymorphisms affecting glucocorticoid targets in patients with nephrotic syndrome [29-33]

Table 1. Effects of gene polymorphisms influencing glucocorticoid targets in patients with nephritic syndrome [29–33]