An update on the treatment options for focal segmental glomerulosclerosis

Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a leading cause of kidney disease worldwide. The presumed etiology of primary FSGS is a plasma factor with responsiveness to immunosuppressive therapy and a risk of recurrence after kidney transplant-important disease characteristics. In contrast, adaptive FSGS is associated with excessive nephron workload due to increased body size, reduced nephron capacity, or single glomerular hyperfiltration associated with certain diseases. Additional etiologies are now recognized as drivers of FSGS: high-penetrance genetic FSGS due to mutations in one of nearly 40 genes, virus-associated FSGS, and medication-associated FSGS. Emerging data support the identification of a sixth category: APOL1 risk allele-associated FSGS in individuals with sub-Saharan ancestry. The classification of a particular patient with FSGS relies on integration of findings from clinical history, laboratory testing, kidney biopsy, and in some patients, genetic testing. The kidney biopsy can be helpful, with clues provided by features on light microscopy (e.g, glomerular size, histologic variant of FSGS, microcystic tubular changes, and tubular hypertrophy), immunofluorescence (e.g, to rule out other primary glomerulopathies), and electron microscopy (e.g., extent of podocyte foot process effacement, podocyte microvillous transformation, and tubuloreticular inclusions). A complete assessment of renal histology is important for establishing the parenchymal setting of segmental glomerulosclerosis, distinguishing FSGS associated with one of many other glomerular diseases from the clinical-pathologic syndrome of FSGS. Genetic testing is beneficial in particular clinical settings. Identifying the etiology of FSGS guides selection of therapy and provides prognostic insight. Much progress has been made in our understanding of FSGS, but important outstanding issues remain, including the identity of the plasma factor believed to be responsible for primary FSGS, the value of routine implementation of genetic testing, and the identification of more effective and less toxic therapeutic interventions for FSGS.

Circulating and urinary microRNA profile in focal segmental glomerulosclerosis: a pilot study

BACKGROUND

MicroRNAs (miRNAs) are noncoding RNA molecules that play important roles in the pathogenesis of various kidney diseases. We investigated whether patients with minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) have distinct circulating and urinary miRNA expression profiles that could lead to potential development of noninvasive biomarkers of the disease.

MATERIALS AND METHODS

Exosome miRNAs were extracted from plasma and urine samples of patients with primary FSGS (n = 16) or MCD (n = 5) and healthy controls (n = 5). Differences in miRNA abundance were examined using Affymetrix GeneChip miRNA 3.0 arrays. QRT-PCR was used to validate the findings from the array.

RESULTS

Comparison analysis of FSGS versus MCD revealed 126 and 155 differentially expressed miRNAs in plasma and in urine, respectively. Only 38 of these miRNAs were previously cited, whereas the remaining miRNAs have not been described. Comparison analysis showed that a significant number of miRNAs were downregulated in both plasma and urine samples of patients with FSGS compared to those with MCD. Plasma levels of miR-30b, miR-30c, miR-34b, miR-34c and miR-342 and urine levels of mir-1225-5p were upregulated in patients with MCD compared to patients with FSGS and controls (P < 0.001). Urinary levels of mir-1915 and miR-663 were downregulated in patients with FSGS compared to MCD and controls (P < 0.001), whereas the urinary levels of miR-155 were upregulated in patients with FSGS when compared to patients with MCD and controls (P < 0.005).

CONCLUSIONS

Patients with FSGS and MCD have a unique circulating and urinary miRNA profile. The diagnostic and prognostic potential of miRNAs in FSGS and MCD warrants further studies.

Epithelial cell foot process effacement in podocytes in focal and segmental glomerulosclerosis: a quantitative analysis

BACKGROUND/AIM

Effacement of the epithelial cell foot processes of glomerular podocytes are thought to be diffuse in the primary form of focal and segmental glomerulosclerosis (FSGS). In contrast, effacements that occur in the secondary form of FSGS are thought to be focal. To evaluate this theory, the extent of epithelial cell foot process effacement was analyzed and compared in podocytes from cases of primary and secondary FSGS.

METHODS

Consecutive cases of adult primary and secondary FSGS that were diagnosed between January 1997 and December 2010 were retrospectively retrieved and analyzed. The electron microscopy materials of all specimens were reviewed. Glomerular podocytes from each sample were counted, recorded and analyzed for the percentage of diffuse versus focal epithelial foot process effacement.

RESULTS

Seventeen primary and 16 secondary FSGS specimens were reviewed. In the 17 primary FSGS cases, 35.1% of the podocytes were focally fused, and 64.9% were diffusely fused. In the 16 secondary FSGS cases, 72.1% of the podocytes were focally fused. There were significantly more focally fused podocytes in secondary FSGS than in primary FSGS. In contrast, significantly more diffusely fused podocytes were observed in primary FSGS than in secondary FSGS.

CONCLUSION

This is the first study to perform a quantitative analysis of the extent of epithelial cell foot process effacement in podocytes in primary and secondary FSGS. This study also confirms that the electron microscopic characteristics of the podocyte effacement process can be used to facilitate the diagnosis of primary versus secondary FSGS.

Urinary IgG and α2-macroglobulin are powerful predictors of outcome and responsiveness to steroids and cyclophosphamide in idiopathic focal segmental glomerulosclerosis with nephrotic syndrome

Objective. To assess whether high-molecular-weight proteins excretion predicts outcome and therapy-responsiveness in patients with FSGS and nephrotic syndrome. Research Design and Methods. Thirty-eight patients measured at biopsy fractional excretion of IgG (FEIgG) and urinary α2-macroglobulin/creatinine ratio (α2m/C). Low and high risk groups were defined by cutoffs assessed by ROC analysis. In all patients first-line therapy was with steroids alone or in combination with cyclophosphamide. Results. α2m/C and FEIgG were correlated with segmental sclerosis (r = 0.546; r = 0.522). Twenty-three patients (61%) entered Remission and 9 (24%) progressed to ESRD. Comparing low and high risk groups, by univariate analysis remission was predicted by FEIgG (77% versus 25%, P = 0.016) and α2m/C (81% versus 17%, P = 0.007) and ESRD at best by FEIgG (0% versus 75%, P < 0.0001) and α2m/C (4% versus 67%, P < 0.0001). By multivariate analysis FEIgG was the only independent predictor of remission and α2m/C the most powerful predictor of ESRD. Low and high risk groups of FEIgG and α2m/C in combination had very high predictive value of sustained remission and ESRD in response to therapy. Conclusions. FEIgG and α2m/C are powerful predictors of outcome and responsiveness to steroids and cyclophosphamide; their predictive value, if validated in prospective studies, may be useful in clinical practice suggesting first-line alternative treatments in high risk patients.

Tacrolimus versus cyclophosphamide in steroid-dependent or steroid-resistant focal segmental glomerulosclerosis: a randomized controlled trial

BACKGROUND

The efficacy and safety of tacrolimus (TAC) and cyclophosphamide (CTX) were prospectively examined in steroid-dependent or steroid-resistant primary focal segmental glomerulosclerosis (FSGS).

METHODS

Patients with biopsy-proven FSGS were enrolled and randomly divided into two groups: CTX and TAC. Patients treated with CTX (0.5-0.75 g/m(2)·month, i.v.) received prednisone at 0.8 mg/kg·day, while patients treated with TAC (0.1 mg/kg·day) received prednisone at 0.5 mg/kg·day. The plasma concentration of TAC was monitored and maintained at 5-10 ng/ml. After a 6-month treatment the patients were evaluated. Patients with complete remission (CR) and partial remission (PR) continued the treatment for 12 months with the dose tapered, whereas the patients with no response were excluded from the study and underwent an alternative treatment.

RESULTS

A total of 33 patients were recruited and 27 completed the 12-month follow-up. The TAC-treated patients (n = 15) showed a quick remission. The initial remission time averaged 1.23 ± 0.21 versus 2.21 ± 0.77 months in the CTX group (n = 18), but no significant difference was achieved (p > 0.05). At 6 months, the two groups showed a similar outcome. Ten patients from each group showed remission (7 CR and 3 PR). At 12 months, the CTX group had 9 CR and 3 PR while the TAC group had 6 CR and 5 PR. Remission rates in TAC tended to be higher than that in CTX, but there was no difference. CTX patients had a high prevalence of infections (50.0 vs. 13.3% in TAC, p < 0.05). In contrast, TAC-treated patients showed a high incidence of hyperglycemia (26.7 vs. 0.0% in CTX, p < 0.05).

CONCLUSION

These results suggest that CTX and TAC had a similar efficacy in steroid-dependent and steroid-resistant FSGS as manifested by reduced proteinuria, improved serum albumin level and renal function.

Is the antiproteinuric effect of cyclosporine a independent of its immunosuppressive function in T cells?

The antiproteinuric effect of cyclosporine A(CsA) has been believed to result from its immunosuppressive effect on the transcription factor NFAT in T cells. However, current evidences supporting this hypothesis are missing. A recent study showed that CsA has a direct antiproteinuric effect on podocytes, suggesting a novel non-immunosuppressive mechanism for CsA's antiproteinuric effect. Conditional NFATc1 activation in podoyctes per se is sufficient to induce proteinuria in mice, indicating that NFAT activation in podocytes is a critical pathogenic molecular event leading to podocyte injury and proteinuria. Meanwhile, evidence showed that TRPC6-mediated Ca(2+) influx stimulates NFAT-dependent TRPC6 expression. Altogether, these advances in podocyte research indicate that calcineurin-NFAT signal or calcineurin-synaptopodin axis has a direct proteinuric effect on podocytes which raises the possibility of developing specific antiproteinuric drugs that lack the unwanted effects of calcineurin or NFAT inhibition.

Impact of glomerular kidney diseases on the clearance of drugs

Numerous physiologic variations, including urinary protein excretion, low serum albumin concentrations, and reductions in kidney function (clearance), exist in patients with glomerulonephritis. These factors could alter the disposition of numerous drugs. The purpose of the current article was to review the influence of glomerulonephritis on the pharmacokinetics of drugs used clinically or experimentally in the treatment of these conditions. Several articles or presentations were located that reported on the pharmacokinetics of immunosuppressant, cytotoxic, and therapeutic antibody drugs in populations with glomerulonephritis. Most publications reported an increase in systemic clearance in glomerulonephritis as compared with populations in whom the drugs were typically used and in patients with nonglomerular forms of chronic kidney disease. It appears that the increase in systemic clearance is predominantly through nonrenal clearance pathways, although enhancement of renal clearance has also been appreciated for some drugs. Available preliminary data suggest specific alterations in the activity of individual pathways of drug metabolism and transport. Recommendations are provided for the design of future studies of drugs in the glomerulonephritis population and for inclusion of patients with urinary protein excretion in studies that assess drug pharmacokinetics.

Endothelin and the podocyte

In the past decade, research has advanced our understanding how endothelin contributes to proteinuria and glomerulosclerosis. Data from pre-clinical and clinical studies now provide evidence that proteinuric diseases such as focal segmental glomerulosclerosis and diabetic nephropathy as well as hypertension nephropathy are sensitive to treatment with endothelin receptor antagonists (ERAs). Like blockade of the renin-angiotensin system, ERA treatment-under certain conditions-may even cause disease regression, effects that could be achieved on top of renin-angiotensin-aldosterone system blockade, suggesting independent therapeutic mechanisms by which ERAs convey nephroprotection. Beneficial effects of ERAs on podocyte function, which is essential to maintain the glomerular filtration barrier, have been identified as one of the key mechanisms by which inhibition of the endothelin ETA receptor ameliorates renal structure and function. In this article, we will review pre-clinical studies demonstrating a causal role for endothelin in proteinuric chronic kidney disease (with a particular focus on functional and structural integrity of podocytes in vitro and in vivo). We will also review the evidence suggesting a therapeutic benefit of ERA treatment on the functional integrity of podocytes in humans.

Focal and segmental glomerulosclerosis: multiple pathways are involved

Focal segmental glomerulosclerosis (FSGS) is not a disease but a clinicopathologic entity. The term FSGS itself is a misnomer because its lesions are not always focal, segmental, or sclerotic. Its clinical expression also widely varies and is nonspecific. Confronted with such diversity, one cannot but translate the title of this contribution into a unifying version focusing on the podocyte, initial culprit, or victim of multiple processes leading to FSGS. Some have been identified in human glomerulopathies and/or in animal or cell culture models, and are classified as secondary. Genetic forms, nonsyndromic or syndromic, have adduced a wealth of knowledge on the slit diaphragm architecture and explain the reason for their steroid resistance. Others, mostly expressed by a nephrotic syndrome, will be considered as idiopathic until the offending factor(s) that affect the molecular array of the slit diaphragm filtration barrier are identified and counteracted. Recent research has lead to suggesting that FSGS is not a T-cell-driven autoimmune glomerulopathy. Thus, treatments considered as etiologic, including glucocorticoids and calcineurin inhibitors, are in fact endowed with a mode of action on podocytes that suggests that drugs used such as immunosuppressors also might be considered as antiproteinuric agents.

Rituximab's new therapeutic target: the podocyte actin cytoskeleton

Therapeutic off-target activities are well recognized for small-molecule drugs. In contrast, monoclonal antibodies (mAbs) traditionally are believed to act specifically and lack off-target therapeutic effects. In this issue of Science Translational Medicine, Fornoni et al. show therapeutic benefit, through an off-target-mediated mechanism, of the mAb drug rituximab in recurrent focal segmental glomerulosclerosis (FSGS) after kidney transplantation. These data shed new light on FSGS pathogenesis and suggest new therapeutic interventions for proteinuric diseases.

Clinical trials treating focal segmental glomerulosclerosis should measure patient quality of life

Optimal therapy of patients with steroid-resistant primary focal segmental glomerulosclerosis (FSGS) remains controversial. This report describes the initial study design, baseline characteristics, and quality of life of patients enrolled in the FSGS Clinical Trial, a large multicenter randomized study of this glomerulopathy comparing a 12-month regimen of cyclosporine to the combination of mycophenolate mofetil and oral dexamethasone. Patients with age ranging 2-40 years, with an estimated glomerular filtration rate > 40 ml/min per 1.73 m², a first morning urine protein-to-creatinine ratio over one, and resistant to corticosteroids were eligible. The primary outcome was complete or partial remission of proteinuria over 52 weeks after randomization. In all, 192 patients were screened, of whom 138 were randomized for treatment. Ethnic distributions were 53 black, 78 white, and 7 other. By self- or parent-proxy reporting, 26 of the 138 patients were identified as Hispanic. The baseline glomerular filtration rate was 112.4 (76.5, 180.0) ml/min per 1.73 m², and urine protein was 4.0 (2.1, 5.3) g/g. Overall, the quality of life of the patients with FSGS was lower than healthy controls and similar to that of patients with end-stage renal disease. Thus, the impact of FSGS on quality of life is significant and this measurement should be included in all trials.

Enzymatic disease of the podocyte

Proteinuria is an early sign of kidney disease and has gained increasing attention over the past decade because of its close association with cardio-vascular and renal morbidity and mortality. Podocytes have emerged as the cell type that is critical in maintaining proper functioning of the kidney filter. A few genes have been identified that explain genetic glomerular failure and recent insights shed light on the pathogenesis of acquired proteinuric diseases. This review highlights the unique role of the cysteine protease cathepsin L as a regulatory rather than a digestive protease and its action on podocyte structure and function. We provide arguments why many glomerular diseases can be regarded as podocyte enzymatic disorders.

Treatment of focal segmental glomerulosclerosis with immunophilin modulation: when did we stop thinking about pathogenesis?

Nephrotic focal segmental glomerulosclerosis (FSGS) represents a difficult therapeutic challenge. FSGS has long been considered a subset of idiopathic nephrotic syndrome, lumping together FSGS and minimal change disease (MCD). The time-honored 'Shalhoub hypothesis' has led to treating FSGS as a T-cell-driven condition in which a lymphokine, considered without proof as being the 'glomerular permeability factor,' induces proteinuria and podocyte functional and structural derangement. This has led to trying, in addition to steroids, every new drug marketed in the field of organ transplantation, first cyclosporine (CsA) and then other immunophilin modulators. The fact that alkylating agents and mycophenolate mofetil have obtained a poor and inconstant favorable effect, and that rituximab may obtain remissions, although inconstantly, has not led to reconsidering the T-cell hypothesis. This wrong thinking has fostered innumerable, mostly uncontrolled, treatment trials with various immunosuppressive agents. In fact, clinicians have not considered the fact that some but not all immunophilin modulators may be effective as nonspecific antiproteinuric agents, rather than as immunosuppressive drugs, and that treatment success does not exclude a non-immunologic pathophysiology. Recent findings on the mode of action of CsA and FK-506 have lent support to this concept. This review should be considered as a plea to reconsider the pathogenesis of nephrotic FSGS, applying all efforts to the identification of the factor, or factors, responsible for nephrotic FSGS, and to fund treatment to counteract the 'factor,' rather than pursuing costly and non-evidence-based immunosuppressive therapeutic trials.