Glucocorticoid pharmacogenetics in pediatric idiopathic nephrotic syndrome

Optimizing the corticosteroid dose in steroid-sensitive nephrotic syndrome

The use of corticosteroids in the treatment of steroid-sensitive nephrotic (SSNS) syndrome in children has evolved surprisingly slowly since the ISKDC consensus over 50 years ago. From a move towards longer courses of corticosteroid to treat the first episode in the 1990s and 2000s, more recent large, well-designed randomized controlled trials (RCTs) have unequivocally shown no benefit from an extended course, although doubt remains whether this applies across all age groups. With regard to prevention of relapses, daily ultra-low-dose prednisolone has recently been shown to be more effective than low-dose alternate-day prednisolone. Daily low-dose prednisolone for a week at the time of acute viral infection seems to be effective in the prevention of relapses but the results of a larger RCT are awaited. Recently, corticosteroid dosing to treat relapses has been questioned, with data suggesting lower doses may be as effective. The need for large RCTs to address the question of whether corticosteroid doses can be reduced was the conclusion of the authors of the recent corticosteroid therapy for nephrotic syndrome in children Cochrane update. This review summarizes development in thinking on corticosteroid use in SSNS and makes suggestions for areas that merit further scrutiny.

Steroid-resistant Nephrotic Syndrome in Children: A Mini-review on Genetic Mechanisms, Predictive Biomarkers and Pharmacotherapy Strategies

Steroid-resistant nephrotic syndrome (SRNS) constitutes the second most frequent cause of chronic kidney disease in childhood. The etiology of SRNS remains largely unknown and no standardized treatment exists. Recent advances in genomics have helped to build understanding of the molecular mechanisms and pathogenesis of the disease. The genetic polymorphisms in genes encoding proteins which are involved in the pharmacokinetics and pharmacodynamics of glucocorticoids (GCs) partially account for the different responses between patients with nephrotic syndrome. More importantly, single-gene causation in podocytes-associated proteins was found in approximately 30% of SRNS patients. Some potential biomarkers have been tested for their abilities to discriminate against pediatric patients who are sensitive to GCs treatment and patients who are resistant to the same therapy. This article reviews the recent findings on genetic mechanisms, predictive biomarkers and current therapies for SRNS with the goal to improve the management of children with this syndrome.

Osteoclasts protect bone blood vessels against senescence through the angiogenin/plexin-B2 axis

Synthetic glucocorticoids (GCs), one of the most effective treatments for chronic inflammatory and autoimmune conditions in children, have adverse effects on the growing skeleton. GCs inhibit angiogenesis in growing bone, but the underlying mechanisms remain unclear. Here, we show that GC treatment in young mice induces vascular endothelial cell senescence in metaphysis of long bone, and that inhibition of endothelial cell senescence improves GC-impaired bone angiogenesis with coupled osteogenesis. We identify angiogenin (ANG), a ribonuclease with pro-angiogenic activity, secreted by osteoclasts as a key factor for protecting the neighboring vascular cells against senescence. ANG maintains the proliferative activity of endothelial cells through plexin-B2 (PLXNB2)-mediated transcription of ribosomal RNA (rRNA). GC treatment inhibits ANG production by suppressing osteoclast formation in metaphysis, resulting in impaired endothelial cell rRNA transcription and subsequent cellular senescence. These findings reveal the role of metaphyseal blood vessel senescence in mediating the action of GCs on growing skeleton and establish the ANG/PLXNB2 axis as a molecular basis for the osteoclast-vascular interplay in skeletal angiogenesis.

Glucocorticoid receptors and their upstream epigenetic regulators in adults with steroid-resistant nephrotic syndrome

Steroid-resistant nephrotic syndrome (SRNS) is a clinical challenge with variable clinical outcomes. In patients with SRNS, unsuccessful anti-inflammatory and anti-proteinuric effects of steroids lead to end-stage renal disease (ESRD). Our objective was to define the expression pattern of the glucocorticoid receptors (GR) α and β and their epigenetic regulators (miR-24, miR-30a, and miR-370) in a group of adults with SRNS. In this regard, sixty primary NS patients with focal segmental glomerulosclerosis (FSGS, N = 30) and membranous glomerulonephritis (MGN, N = 30) and also healthy volunteers (N = 24) were enrolled. Real-time PCR was performed to evaluate the expression levels of the aforementioned genes in peripheral blood mononuclear cell (PBMC) samples. Furthermore, an in-silico analysis was performed to understand the signaling pathways and biological procedures that may be targeted by these microRNAs in NS. The decreased and increased levels of GRα and GRβ were not significant, respectively. Statistically significant reduced miR-24 levels were observed between control/MGN (p = .022) and MGN/FSGS (p = .032) groups. Additionally, a decrease was detected in miR-30a between MGN and FSGS (p = .049) groups. There was a significant increase in miR-370 expression level between control and NS groups (p = .029), as well as control/MGN (p = .008), and MGN/FSGS (p = .046). Bioinformatics analysis predicted the possible targets of the studied genes including genes involved in TGF-β, Notch1, and p53 signaling pathways, regulation of gene expression, intracellular signal transduction, negative regulation of response to the stimulus, cell-cell signaling, and cell activation in the pathogenesis of SRNS. Taken all together, dysregulated levels of GRα, GRβ were not attributed to SRNS in our patients. It seems that pharmacokinetics and the genetic variations in podocyte-related genes may be associated with the steroid-resistance in our adult patients with NS rather than GR expression.

The impact of steroids on the injured podocytes in nephrotic syndrome

Nephrotic syndrome (NS), a common chronic kidney disease, embraces a variety of kidney disorders. Though Glucocorticoids (GCs) are generally used in the treatment of NS, their mechanism of action is poorly understood. A plethora of evidence indicates that podocytes are considered as the main target cells for the therapeutic strategies to prevent NS. GCs regulate the transactivation and transrepression of genes in podocytes that affect their morphological and cytoskeletal features, motility, apoptosis and survival rate. Moreover, they prevent protein leakage through the glomerular barrier membrane by affecting the synthesis, trafficking and posttranslational modifications of slit diaphragms components, podocytes' intercellular junctions. The response to the treatment is variable among different ethnics and populations and resistance to the steroids is detected in almost 50% of adult patients. Not only do pharmacokinetics and pharmacogenetics of steroids play a role in GC resistance but also the genetic variations in one or more podocyte related genes are connected with the steroid resistance in cases with NS. The focus of this review is to explain the underlying cellular and molecular mechanisms of GCs in podocytes. Understanding the mechanisms by which the GCs and GCs receptors in podocytes regulate the gene expression network and crosstalk with other molecular pathways would guarantee an optimum therapeutic benefit of steroid treatment.

Compositional alterations of gut microbiota in children with primary nephrotic syndrome after initial therapy

Background

Primary nephrotic syndrome (PNS) is a common glomerular disease in children. T cell dysfunction plays a crucial role in the pathogenesis of PNS. Moreover, dysbiosis of gut microbiota contributes to immunological disorders. Whether the initial therapy of PNS affects gut microbiota remains an important question. Our study investigated compositional changes of gut microbiota after initial therapy.

Methods

Fecal samples of 20 children with PNS were collected before and after 4-week initial therapy. Total bacteria DNA were extracted and the V3-V4 regions of bacteria 16S ribosomal RNA gene were sequenced. The composition of gut microbiota before and after initial therapy was analyzed by bioinformatics methods. The function of altered gut microbiota was predicted with PICRUSt method.

Results

The richness and diversity of gut microbiota were similar before and after 4-week initial therapy. Gut microbiota at the phylum level was dominated by four phyla including Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria, but the increased relative abundance after initial therapy was found in Deinococcus-Thermus and Acidobacteria. At the genus level, the increased abundance of gut microbiota after initial therapy was observed in short chain fat acids (SCFA)-producing bacteria including Romboutsia, Stomatobaculum and Cloacibacillus (p < 0.05). Moreover, the predicted functional profile of gut microbiota showed that selenocompound metabolism, isoflavonoid biosynthesis and phosphatidylinositol signaling system weakened after initial therapy of PNS.

Conclusions

Initial therapy of PNS increased SCFA-producing gut microbiota, but might diminish selenocompound metabolism, isoflavonoid biosynthesis and phosphatidylinositol signaling system in children.

MIF plasma level as a possible tool to predict steroid responsiveness in children with idiopathic nephrotic syndrome

PURPOSE

Idiopathic nephrotic syndrome (INS) is the most frequent form of childhood nephrotic syndrome. Steroids represent the best therapeutic option; however, inter-individual differences in their efficacy and side effects have been reported. To date, there is no way to predict patients' resistance and/or dependence. Alterations in the cytokine profile of INS patients might contribute to proteinuria and glomerular damage and affect drug sensitivity.

METHODS

The cytokine plasma levels were measured in 21 INS children at diagnosis to investigate the association among cytokines pattern and clinical response. Patients were selected on the basis of their clinical response: 7 steroid sensitive (SS), 7 dependent (SD), and 7 resistant (SR). Significant results were then analyzed in 41 additional pediatric INS patients.

RESULTS

Within the 48 cytokines analyzed, macrophage migration inhibitory factor (MIF) was a good predictor of steroid response. Indeed, SR patients showed significantly higher MIF plasma levels compared with all others (p = 0.022; OR = 4.3, 95%CI = 1.2-25.4): a cutoff concentration of MIF > 501 pg/ml significantly discriminated SR patients (sensitivity = 85.7%, specificity = 71.4%). On the contrary, SD patients showed lower MIF plasma levels compared with others (p = 0.010; OR = 0.12, 95%CI = 9.2 × 10^-3-6.7 × 10^-1). Significant results were confirmed in the entire cohort.

CONCLUSIONS

Our comprehensive cytokine analysis indicates that assessing MIF plasma levels at diagnosis could predict response to glucocorticoids in children with INS.

Reciprocal Relationship Between HDAC2 and P-Glycoprotein/MRP-1 and Their Role in Steroid Resistance in Childhood Nephrotic Syndrome

Background: Reduced HDACs levels have been reported in steroid resistant chronic obstructive pulmonary disease and bronchial asthma patients. P-glycoprotein (P-gp) over expression in peripheral blood mononuclear cells (PBMCs) has been reported in patients with steroid resistant nephrotic syndrome (NS). Whether and how HDACs and P-gp are linked with each other is not clear, especially in NS patients. Aim: To evaluate mRNA expression of P-gp/MRP-1 and HDAC2 in PBMCs of steroid sensitive (SSNS) and steroid resistant nephrotic syndrome (SRNS) patients, and determine the relationship between expression of HDAC2 and P-gp/ MRP-1in NS patients. Methods: Twenty subjects (10 in each group), SSNS (mean age 7.54 ± 3.5 years), and SRNS (mean age 8.43 ± 3.8 years) were recruited. mRNA expression of HDAC2 and P-gp/MRP-1 was studied by quantitative real time PCR. PBMCs were treated with Theophylline, 1 μM, and Trichostatin A, 0.8 μM, for 48 h for induction and suppression of HDAC2, respectively. Results: At baseline, expression of P-gp (4.79 ± 0.10 vs. 2.13 ± 0.12, p < 0.0001) and MRP-1 (3.99 ± 0.08 vs. 1.99 ±0.11, p < 0.0001) on PBMCs were increased whereas, HDAC2 mRNA levels (2.97 ± 0.15 vs. 6.02 ± 0.13, p < 0.0001) were significantly decreased in SRNS as compared to that of SSNS patients. Compared to baseline, theophylline reduced mRNA expression of P-gp and MRP-1 (fold change 2.65 and 2.21, ^* p < 0.0001 in SRNS) (fold change 1.25, 1.24, ^* p < 0.0001 in SSNS), respectively. However, it increased the expression of HDAC2 (fold change 5.67, ^* p < 0.0001 in SRNS) (fold change 6.93, ^* p < 0.0001 in SSNS). Compared to baseline, TSA treatment increased mRNA levels of P-gp and MRP-1 (fold change 7.51, 7.31, ^* p < 0.0001 in SRNS) and (fold change 3.49, 3.35, ^* p < 0.0001 in SSNS), respectively. It significantly decreased the level of HDAC2 (fold change 1.50, ^* p < 0.0001 in SRNS) (fold change 2.53, ^* p < 0.0001 in SSNS) patients. Conclusion: Reduced HDAC2 and increased P-gp/MRP-1 activity may play a role in response to steroids in childhood NS. HDAC2 and P-gp/MRP-1 are in reciprocal relationship with each other.

Pharmacology and pharmacogenetics of prednisone and prednisolone in patients with nephrotic syndrome

Nephrotic syndrome is one of the most common glomerular disorders in childhood. Glucocorticoids have been the cornerstone of the treatment of childhood nephrotic syndrome for several decades, as the majority of children achieves complete remission after prednisone or prednisolone treatment. Currently, treatment guidelines for the first manifestation and relapse of nephrotic syndrome are mostly standardized, while large inter-individual variation is present in the clinical course of disease and side effects of glucocorticoid treatment. This review describes the mechanisms of glucocorticoid action and clinical pharmacokinetics and pharmacodynamics of prednisone and prednisolone in nephrotic syndrome patients. However, these mechanisms do not account for the large inter-individual variability in the response to glucocorticoid treatment. Previous research has shown that genetic factors can have a major influence on the pharmacokinetic and dynamic profile of the individual patient. Therefore, pharmacogenetics may have a promising role in personalized medicine for patients with nephrotic syndrome. Currently, little is known about the impact of genetic polymorphisms on glucocorticoid response and steroid-related toxicities in children with nephrotic syndrome. Although the evidence is limited, the data summarized in this study do suggest a role for pharmacogenetics to improve individualization of glucocorticoid therapy. Therefore, studies in larger cohorts with nephrotic syndrome patients are necessary to draw final conclusions about the influence of genetic polymorphisms on the glucocorticoid response and steroid-related toxicities to ultimately implement pharmacogenetics in clinical practice.

NR3C1 gene polymorphisms are associated with steroid resistance in patients with primary nephrotic syndrome

Aim: The aim of this study was to investigate the role of SNPs of genes involved in the glucocorticoid pathway in the development of steroid resistance in patients with primary nephrotic syndrome. Methods: Sequenom MassARRAY method was used to sequence 25 SNP genotypes in 154 patients. The frequency distribution of the genotypes was compared between patients with steroid-sensitive nephrotic syndrome and those with steroid-resistant nephrotic syndrome. Results: NR3C1 rs6196 G allele carriers had a decreased risk of steroid resistance compared with that of the A allele carriers. The presence of rs10052957 and rs258751 A alleles could reduce the incidence of steroid resistance compared with that with G allele. Haplotype analysis showed AAG and GGA haplotypes that contain NR3C1 rs10052957, rs258751 and rs6196 were associated with steroid resistance. Conclusion: NR3C1 gene polymorphisms are significantly associated with the response to glucocorticoids in patients with primary nephrotic syndrome.

Single-Gene Congenic Strain Reveals the Effect of Zbtb16 on Dexamethasone-Induced Insulin Resistance

BACKGROUND

Glucocorticoids (GCs) are potent therapeutic agents frequently used for treatment of number of conditions, including hematologic, inflammatory, and allergic diseases. Both their therapeutic and adverse effects display significant interindividual variation, partially attributable to genetic factors. We have previously isolated a seven-gene region of rat chromosome 8 sensitizing to dexamethasone (DEX)-induced dyslipidemia and insulin resistance (IR) of skeletal muscle. Using two newly derived congenic strains, we aimed to investigate the effect of one of the prime candidates for this pharmacogenetic interaction, the Zbtb16 gene.

METHODS

Adult male rats of SHR-Lx.PD5^PD-Zbtb16 (n = 9) and SHR-Lx.PD5^SHR-Zbtb16 (n = 8) were fed standard diet (STD) and subsequently treated with DEX in drinking water (2.6 µg/ml) for 3 days. The morphometric and metabolic profiles of both strains including oral glucose tolerance test, triacylglycerols (TGs), free fatty acids, insulin, and C-reactive protein levels were assessed before and after the DEX treatment. Insulin sensitivity of skeletal muscle and visceral adipose tissue was determined by incorporation of radioactively labeled glucose.

RESULTS

The differential segment of SHR-Lx.PD5^SHR-Zbtb16 rat strain spans 563 kb and contains six genes: Htr3a, Htr3b, Usp28, Zw10, Tmprss5, and part of Drd2. The SHR-Lx.PD5^PD-Zbtb16 minimal congenic strain contains only Zbtb16 gene on SHR genomic background and its differential segment spans 254 kb. Total body weight was significantly increased in SHR-Lx.PD5^PD-Zbtb16 strain compared with SHR-Lx.PD5^SHR-Zbtb16 , however, no differences in the weights of adipose tissue depots were observed. While STD-fed rats of both strains did not show major differences in their metabolic profiles, after DEX treatment the SHR-Lx.PD5^PD-Zbtb16 congenic strain showed increased levels of TGs, glucose, and blunted inhibition of lipolysis by insulin. Both basal and insulin-stimulated incorporation of radioactively labeled glucose into skeletal muscle glycogen were significantly reduced in SHR-Lx.PD5^PD-Zbtb16 strain, but the insulin sensitivity of adipose tissue was comparable between the two strains.

CONCLUSION

The metabolic disturbances including impaired glucose tolerance, dyslipidemia, and IR of skeletal muscle observed after DEX treatment in the congenic SHR-Lx.PD5^PD-Zbtb16 reveal the Zbtb16 locus as a possible sensitizing factor for side effects of GC therapy.