Bioengineered Cystinotic Kidney Tubules Recapitulate a Nephropathic Phenotype

Nephropathic cystinosis is a rare and severe disease caused by disruptions in the CTNS gene. Cystinosis is characterized by lysosomal cystine accumulation, vesicle trafficking impairment, oxidative stress, and apoptosis. Additionally, cystinotic patients exhibit weakening and leakage of the proximal tubular segment of the nephrons, leading to renal Fanconi syndrome and kidney failure early in life. Current in vitro cystinotic models cannot recapitulate all clinical features of the disease which limits their translational value. Therefore, the development of novel, complex in vitro models that better mimic the disease and exhibit characteristics not compatible with 2-dimensional cell culture is of crucial importance for novel therapies development. In this study, we developed a 3-dimensional bioengineered model of nephropathic cystinosis by culturing conditionally immortalized proximal tubule epithelial cells (ciPTECs) on hollow fiber membranes (HFM). Cystinotic kidney tubules showed lysosomal cystine accumulation, increased autophagy and vesicle trafficking deterioration, the impairment of several metabolic pathways, and the disruption of the epithelial monolayer tightness as compared to control kidney tubules. In particular, the loss of monolayer organization and leakage could be mimicked with the use of the cystinotic kidney tubules, which has not been possible before, using the standard 2-dimensional cell culture. Overall, bioengineered cystinotic kidney tubules recapitulate better the nephropathic phenotype at a molecular, structural, and functional proximal tubule level compared to 2-dimensional cell cultures.

Muscle and Bone Impairment in Infantile Nephropathic Cystinosis: New Concepts

Cystinosis Metabolic Bone Disease (CMBD) has emerged during the last decade as a well-recognized, long-term complication in patients suffering from infantile nephropathic cystinosis (INC), resulting in significant morbidity and impaired quality of life in teenagers and adults with INC. Its underlying pathophysiology is complex and multifactorial, associating complementary, albeit distinct entities, in addition to ordinary mineral and bone disorders observed in other types of chronic kidney disease. Amongst these long-term consequences are renal Fanconi syndrome, hypophosphatemic rickets, malnutrition, hormonal abnormalities, muscular impairment, and intrinsic cellular bone defects in bone cells, due to CTNS mutations. Recent research data in the field have demonstrated abnormal mineral regulation, intrinsic bone defects, cysteamine toxicity, muscle wasting and, likely interleukin-1-driven inflammation in the setting of CMBD. Here we summarize these new pathophysiological deregulations and discuss the crucial interplay between bone and muscle in INC. In future, vitamin D and/or biotherapies targeting the IL1β pathway may improve muscle wasting and subsequently CMBD, but this remains to be proven.

Distinct Mitochondrial Pathologies Caused by Mutations of the Proximal Tubular Enzymes EHHADH and GATM

The mitochondria of the proximal tubule are essential for providing energy in this nephron segment, whose ATP generation is almost exclusively oxygen dependent. In addition, mitochondria are involved in a variety of metabolic processes and complex signaling networks. Proximal tubular mitochondrial dysfunction can therefore affect renal function in very different ways. Two autosomal dominantly inherited forms of renal Fanconi syndrome illustrate how multifaceted mitochondrial pathology can be: Mutation of EHHADH, an enzyme in fatty acid metabolism, results in decreased ATP synthesis and a consecutive transport defect. In contrast, mutations of GATM, an enzyme in the creatine biosynthetic pathway, leave ATP synthesis unaffected but do lead to mitochondrial protein aggregates, inflammasome activation, and renal fibrosis with progressive renal failure. In this review article, the distinct pathophysiological mechanisms of these two diseases are presented, which are examples of the spectrum of proximal tubular mitochondrial diseases.

Serum Chitotriosidase level as a Novel Biomarker for Therapeutic Monitoring of Nephropathic Cystinosis among the Iraqi children

Background: Cystinosis is a rare autosomal recessive lysosomal storage disease with high morbidity and mortality. It is caused by mutations in the CTNS gene that encodes the cystine transporter, cystinosin, which leads to lysosomal cystine accumulation. It is the major cause of inherited Fanconi syndrome, and should be suspected in young children with failure to thrive and signs of renal proximal tubular damage. The diagnosis can be missed in infants, because not all signs of renal Fanconi syndrome are present during the first months of life. Elevated white blood cell cystine content is the cornerstone of the diagnosis. Since chitotriosidase (CHIT1 or chitinase-1) is mainly produced by activated macrophages both in normal and inflammatory conditions which suggest that cystinosis should be included within the differential diagnosis of disorders associated with increased plasma chitotriosidase activity. This study is aimed to estimate serum chitotriosidase level, as a screening marker and therapeutic monitor for cystinosis disease in Iraqi children with cystinosis.Subjects and Methods: The present study is a case-control study that included samples of 30 children with nephropathic cystinosis, compared to 25 healthy control children from those attending at The Genetic Rare Diseases Center / AL-Emamain AL-Kadhimain Teaching Hospital, Baghdad-Iraq.Results: Our results reported that cystinotic children had a marked elevation of serum chitotriosidase activity, compared to age-matched healthy children, besides a significant associated with leukocyte-cystine content for cystinotic patients.CHT1 as a Novel BiomarkerConclusion: Estimation of serum chitotriosidase activity might aid in monitoring the therapeutic benefits of cysteamine therapy, as well as the prognosis of the disease when WBC cystine assessment is not available.Key Words: Cystinosis, Cysteamine, Chitotriosidase.

Drug toxicity in the proximal tubule: new models, methods and mechanisms

The proximal tubule (PT) reabsorbs most of the glomerular filtrate and plays an important role in the uptake, metabolism and excretion of xenobiotics. Some therapeutic drugs are harmful to the PT, and resulting nephrotoxicity is thought to be responsible for approximately 1 in 6 of cases of children hospitalized with acute kidney injury (AKI). Clinically, PT dysfunction leads to urinary wasting of important solutes normally reabsorbed by this nephron segment, leading to systemic complications such as bone demineralization and a clinical scenario known as the renal Fanconi syndrome (RFS). While PT defects can be diagnosed using a combination of blood and urine markers, including urinary excretion of low molecular weight proteins (LMWP), standardized definitions of what constitutes clinically significant toxicity are lacking, and identifying which patients will go on to develop progressive loss of kidney function remains a major challenge. In addition, much of our understanding of cellular mechanisms of drug toxicity is still limited, partly due to the constraints of available cell and animal models. However, advances in new and more sophisticated in vitro models of the PT, along with the application of high-content analytical methods that can provide readouts more relevant to the clinical manifestations of nephrotoxicity, are beginning to extend our knowledge. Such technical progress should help in discovering new biomarkers that can better detect nephrotoxicity earlier and predict its long-term consequences, and herald a new era of more personalized medicine.

MO004PRIMARY BILIARY CHOLANGITIS PRESENTING WITH RENAL FANCONI SYNDROME: A FORGOTTEN PHENOTYPE

Background and Aims Primary biliary cholangitits (PBC) is an autoimmune liver disease, leading to liver fibrosis and cirrhosis. It is a rare disease affecting 1 in 3-4000 people and is more common in females. Symptoms may go unnoticed and include itch and fatigue. Most patients have anti-mitochondrial antibodies (AMA) as well as raised gamma-glutamyl transferase (GGT) and alkaline phosphatase (ALP) levels. First line treatment for PBC is ursodeoxycholic acid and is usually continued lifelong. It improves liver biochemistry, histological progression of liver disease and liver transplant-free survival. Renal complications of PBC include distal renal tubular acidosis (RTA), tubule-interstitial nephritis (TIN) and renal Fanconi syndrome. Method We reviewed a case of PBC presenting with renal Fanconi syndrome. Results A 48-year-old female was referred to the renal clinic due to progressive decline in renal function since she was diagnosed with type 2 diabetes in 2007. She was also known to have AMA (>1:640) and previously had transient transaminitis. She was clinically well with no major symptoms but reported that she had had a few episodes of urinary tract infection in the previous year. Her diabetes was managed with lifestyle modifications in the past until a few months ago when Metformin was introduced. However, her HbA1c level had never been greater than 55 mmol/mol. Urine dipstick in the clinic showed pH of 6, blood+, glucose+++, protein+++ and ketone trace. The severity of glycosuria was inconsistent with her glycaemic control. There was a disparity between her urine albumin/creatinine ration (ACR) of 18.8g/mol and protein/creatinine ratio (PCR) of 124mg/mmol. Myeloma screen was negative and further urine analysis showed generalised aminoaciduria. She also had hypouricaemia, intermittent hypophosphataemia and non-anion gap metabolic acidosis. These results are in keeping with renal Fanconi syndrome. Her eGFR was 48 ml/min/1.72m2 in 2007 and was 21 ml/min/1.72m at the time of review. A renal biopsy was undertaken, and the appearances were suggestive of mild tubulo-interstitial nephritis; the glomeruli were unremarkable; there was mild chronic tubulo-interstitial damage. She was started on oral steroid, sodium bicarbonate and ursodeoxycholic acid. The course of steroid had a slight transitory beneficial effect on the renal function. Conclusion Distal RTA is the usual renal feature of PBC, occurring in 1/3 of cases with advanced disease. In contrast, proximal RTA associating with renal Fanconi syndrome occurs rarely. Like our case, the cases that have been previously reported show that Fanconi syndrome occurred during the early phase of PBC in the absence of marked hepatic abnormalities, and were associated with CKD. Fanconi syndrome and TIN are renal features of mitochondrial cytopathies and are perhaps a forgotten association of PBC. Antimitochondrial antibodies may play a role in the onset of tubulo-interstitial nephritis and Fanconi syndrome.

MO142A SINGLE-CENTER CASE SERIES OF 150 PATIENTS WITH RENAL FANCONI SYNDROME

Background and Aims Renal Fanconi syndrome (RFS) is characterized by generalized dysfunctions of renal proximal tubular (PT) transport. The causes of FS can be inherited or acquired, the latter of which mostly includes drugs, heavy metals, monoclonal light chains (LC), and primary Sj gren’s syndrome (pSS). We intended to observe the clinico-pathological features of RFS with different etiologies. Method From January 2012 to September 2018, all the patients diagnosed as RFS in our hospital were enrolled. Their clinicopathological records were retrospectively reviewed. The diagnosis of RFS was defined as existence of ≥ 3 of the following five items alone or ≥ 2 items combined with an evidence of PT damages in kidney pathology: (I) normoglycemic glycosuria; (II) generalized aminoaciduria; (III) hypophosphatemia and hyperphosphaturia; (IV) hypouricemia and hyperuricosuria; (V) proximal RTA. Results: 1. Clinical characteristics We identified 150 RFS patients, with an average age of (45.9±14.2) years old and male: female ratio 1.3:1. They presented with different degrees of PT dysfunctions and the most common were hypophosphatemia (83.2%) and aminoaciduria (80.6%). Their mean eGFR levels were 76.3 (4.5-188.6) ml/min/1.73m2 with 73.5% had proteinuria. 2. Renal pathological features 47 RFS patients received kidney biopsy and the most common pathological diagnosis was interstitial nephritis. They all presented with different degrees of proximal tubule atrophy, defective brush border, interstitial edema and fibrosis. 3. Etiology-related clinicopathologic features The most common causes of our RFS were LC (14.0%), drugs (13.3%), and pSS (9.3%). Compared to pSS associated RFS, LC associated RFS patients showed a higher prevalence of bone involvement, more severe proteinuria and less severe hypokalemia (P < 0.05) despite similar eGFR levels. Specific renal pathological features were seen in different etiology groups, including crystalline formation and increased lysosomes in PT cells under electron microscope in LC associated RFS, and CD21 positive ectopic germinal center formation in renal interstitum in parts of the pSS associated RFS. Conclusion We identified 150 RFS with different etiologies and they showed etiology-specific patterns of PT dysfunctions and renal pathologic changes.

Transient generalized proximal tubular dysfunction in an infant with a urinary tract infection: the effect of maternal infliximab therapy?

Objectives Urinary tract infections (UTIs) are common in childhood. Distal tubular dysfunction during a UTI is relatively common, but proximal tubular involvement is a unique feature in humans. Case presentation We present the first case of transient generalized proximal tubular dysfunction (renal Fanconi syndrome) in an infant with an UTI. During pregnancy, his mother was treated for Crohn’s disease with infliximab (last dose at 28 weeks of gestation). He presented at the age of six weeks with a reduced intake, and was found to have amino-aciduria, glucosuria, and urinary loss of potassium, bicarbonate and low-molecular-weight proteins. Within a few weeks after antibiotic treatment for the UTI, no proximal tubular disorder remained and the boy is doing well. Conclusions We hypothesize that the inflammatory response caused by the UTI was more profoundly present due to the maternal infliximab therapy, and thereby included not only the distal but also the proximal tubules.