Npt2a as a target for treating hyperphosphatemia

Hyperphosphatemia results from an imbalance in phosphate (Pi) homeostasis. In patients with and without reduced kidney function, hyperphosphatemia is associated with cardiovascular complications. The current mainstays in the management of hyperphosphatemia are oral Pi binder and dietary Pi restriction. Although these options are employed in patients with chronic kidney disease (CKD), they seem inadequate to correct elevated plasma Pi levels. In addition, a paradoxical increase in expression of intestinal Pi transporter and uptake may occur. Recently, studies in rodents targeting the renal Na+/Pi cotransporter 2a (Npt2a), responsible for ∼70% of Pi reabsorption, have been proposed as a potential treatment option. Two compounds (PF-06869206 and BAY-767) have been developed which are selective for Npt2a. These Npt2a inhibitors significantly increased urinary Pi excretion consequently lowering plasma Pi and PTH levels. Additionally, increases in urinary excretions of Na+, Cl− and Ca2+ have been observed. Some of these results are also seen in models of reduced kidney function. Responses of FGF23, a phosphaturic hormone that has been linked to the development of left ventricular hypertrophy in CKD, are ambiguous. In this review, we discuss the recent advances on the role of Npt2a inhibition on Pi homeostasis as well as other pleiotropic effects observed with Npt2a inhibition.

Kidney trajectory charts to assist general practitioners in the assessment of patients with reduced kidney function: a randomised vignette study

ObjectiveTo investigate the decisional impact of an age-based chart of kidney function decline to support general practitioners (GPs) to appropriately interpret estimated glomerular filtration rate (eGFR) and identify patients with a clinically relevant kidney problem.Design and settingRandomised vignette studyParticipants372 Australian GPs from August 2018 to November 2018.InterventionGPs were given two patient case scenarios: (1) an older woman with reduced but stable renal function and (2) a younger Aboriginal man with declining kidney function still in the normal range. One group was given an age-based chart of kidney function to assist their assessment of the patient (initial chart group); the second group was asked to assess the patients without the chart, and then again using the chart (delayed chart group).Main outcome measuresGPs’ assessment of the likelihood—on a Likert scale—that the patients had chronic kidney disease (CKD) according to the usual definition or a clinical problem with their kidneys.ResultsPrior to viewing the age-based chart GPs were evenly distributed as to whether they thought case 1—the older woman—had CKD or a clinically relevant kidney problem. GPs who had initial access to the chart were less likely to think that the older woman had CKD, and less likely to think she had a clinically relevant problem with her kidneys than GPs who had not viewed the chart. After subsequently viewing the chart, 14% of GPs in the delayed chart group changed their opinion, to indicate she was unlikely to have a clinically relevant problem with her kidneys.Prior to viewing the chart, the majority of GPs (66%) thought case 2—the younger man—did not have CKD, and were evenly distributed as to whether they thought he had a clinically relevant kidney problem. In contrast, GPs who had initial access to the chart were more likely to think he had CKD and the majority (72%) thought he had a clinically relevant kidney problem. After subsequently viewing the chart, 37% of GPs in the delayed chart group changed their opinion to indicate he likely had a clinically relevant problem with his kidneys.ConclusionsUse of the chart changed GPs interpretation of eGFR, with increased recognition of the younger male patient’s clinically relevant kidney problem, and increased numbers classifying the older female patient’s kidney function as normal for her age. This study has shown the potential of an age-based kidney function chart to reduce both overdiagnosis and underdiagnosis.

Mitochondrial Bioenergetic and Proteomic Phenotyping Reveals Organ-Specific Consequences of Chronic Kidney Disease in Mice

Chronic kidney disease (CKD) results in reduced kidney function, uremia, and accumulation of uremic metabolites. Mitochondrial alterations have been suggested to play a role in the disease pathology within various tissues. The purpose of this study was to perform a comprehensive bioenergetic and proteomic phenotyping of mitochondria from skeletal muscle (SkM), cardiac muscle (CM), and renal tissue from mice with CKD. The 5-month-old C57BL/6J male mice were fed a casein control or adenine-supplemented diet for 6 months. CKD was confirmed by blood urea nitrogen. A mitochondrial diagnostic workflow was employed to examine respiratory function, membrane and redox potential, reactive oxygen species production, and maximal activities of matrix dehydrogenases and electron transport system (ETS) protein complexes. Additionally, tandem-mass-tag-assisted proteomic analyses were performed to uncover possible differences in mitochondrial protein abundance. CKD negatively impacted mitochondrial energy transduction (all p < 0.05) in SkM, CM, and renal mitochondria, when assessed at physiologically relevant cellular energy demands (ΔGATP) and revealed the tissue-specific impact of CKD on mitochondrial health. Proteomic analyses indicated significant abundance changes in CM and renal mitochondria (115 and 164 proteins, p < 0.05), but no differences in SkM. Taken together, these findings reveal the tissue-specific impact of chronic renal insufficiency on mitochondrial health.

Body Composition, Anemia, and Kidney Function among Guatemalan Sugarcane Workers

Rates of anemia among agricultural workers, who are also at risk for kidney injury and chronic kidney disease of unknown cause (CKDu), are unknown. We evaluated body composition through the sum of three skinfolds among 203 male sugarcane cutters and assessed the relationship of variables related to nutrition, anemia (hemoglobin < 13 g/dL), and elevated hemoglobin A1c (HbA1c ≥ 5.7%) with estimated glomerular filtration rate (eGFR) using linear regression. Eleven percent of workers were at the level of essential body fat (2–5%). Anemia was present among 13% of workers, 70% of which were normochromic normocytic, a type of anemia suggesting potential underlying chronic disease. Anemia was more common among those with lower BMI and fat free mass. The prevalence of elevated HbA1c was 21%. A moderate negative correlation was found between hemoglobin and HbA1c (Pearson’s r = −0.32, p < 0.01) which suggests that HbA1c values should be interpreted with caution in populations that have high rates of anemia. Twelve percent of workers had reduced kidney function with an eGFR < 90 mL/min/1.73 m2. On average, the eGFR was 18 mL/min per 1.73 m2 lower [(95% CI:−24, −12), p < 0.01)] for those with anemia than those without, and 8 mL/min per 1.73 m2 lower among those with elevated HbA1c [(95% CI: −13, −2), p < 0.01]. Results will inform future studies examining the role of anemia in the evaluation of CKDu and interventions to improve nutrition for workers in low-resource settings.

TP5.2.18 Should follow up to bariatric surgery be extended beyond 2 years for patients with concurrent renal disease?

Aims Following bariatric surgery, all patients must be offered a minimum follow up period of 2 years to support patients with potential early and long-term post-operative complications. Patients with end-stage renal disease may need extra support for extended period as micronutrient homeostasis may be impaired long term due to reduced kidney function. This study aims to analyse micronutrient homeostasis of patients with concurrent renal disease and post-op bariatric surgery, to determine need for an extended minimum follow up period. Methods The study was performed in a single referral centre between 2009-2021 and the data was collated from a prospectively collected database. All patients included must have concurrent renal disease and bariatric surgery and followed up for at least 3 years. In addition to clinical variables, micronutrient and metabolic data were collected and analysed. Results A total of 35 patients were included in this study. Micronutrient homeostasis difficulties were recorded in 32 of the 35 patients. Specific micronutrients that were affected includes: vitamin A, B12, folate, ferritin, copper, zinc, selenium, calcium and magnesium. All micronutrient instabilities lasted a period of at least 3 years without a renal transplant. Conclusion Data from this study suggests that patients post bariatric surgery with concurrent renal disease have difficulties maintaining micronutrient homeostasis. This suggests that extending the minimum follow up period and may be necessary to avoid pathological sequalae from micronutrient excess and or deficiency.

Adverse outcomes after partner bereavement in people with reduced kidney function: Parallel cohort studies in England and Denmark

Objectives To investigate whether partner bereavement is associated with adverse cardiovascular and kidney-related events in people with reduced kidney function. Design Two parallel matched cohort studies using linked routinely collected health data. Setting England (general practices and hospitals using linked Clinical Practice Research Datalink, Hospital Episode Statistics, and Office of National Statistics) and Denmark (hospitals and community pharmacies using the Danish National Patient, Prescription and Education Registries and the Civil Registration System). Participants Bereaved people with reduced kidney function (estimated glomerular filtration rate (eGFR) <60mL/min/1.73m2 (England) or hospital-coded chronic kidney disease (Denmark)) and non-bereaved people with reduced kidney function similarly defined, matched on age, sex, general practice (England), and county of residence (Denmark) and followed-up from the bereavement date of the exposed person. Main outcome measures Cardiovascular disease (CVD) or acute kidney injury (AKI) hospitalization, or death. Results In people with reduced kidney function, we identified 19,820 (England) and 5,408 (Denmark) bereaved individuals and matched them with 134,828 (England) and 35,741 (Denmark) non-bereaved individuals. Among the bereaved, the rates of hospitalizations (per 1000 person-years) with CVD were 31.7 (95%-CI: 30.5–32.9) in England and 78.8 (95%-CI: 74.9–82.9) in Denmark; the rates of hospitalizations with AKI were 13.2 (95%-CI: 12.5–14.0) in England and 11.2 (95%-CI: 9.9–12.7) in Denmark; and the rates of death were 70.2 (95%-CI: 68.5–72.0) in England and 126.4 (95%-CI: 121.8–131.1) in Denmark. After adjusting for confounders, we found increased rates of CVD (England, HR 1.06 [95%-CI: 1.01–1.12]; Denmark, HR 1.10 [95%-CI: 1.04–1.17]), of AKI (England, HR 1.20 [95%-CI: 1.10–1.31]; Denmark HR 1.36 [95%-CI: 1.17–1.58]), and of death (England, HR 1.10 [95%-CI: 1.05–1.14]; Denmark HR 1.20 [95%-CI: 1.15–1.25]) in bereaved compared with non-bereaved people. Conclusions Partner bereavement is associated with an increased rate of CVD and AKI hospitalization, and death in people with reduced kidney function. Additional supportive care for this at-risk population may help prevent serious adverse events.

Estimation of kidney function in patients with primary neuromuscular diseases: is serum cystatin C a better marker of kidney function than creatinine?

Background Using serum creatinine leads to an overestimation of kidney function in patients with primary neuromuscular disorders, and reduced kidney function may remain undetected. Cystatin C (CysC) could provide a better estimation. Aim To evaluate the precision, accuracy, and bias of two creatinine-, one cystatin C-based and one combined equation to estimate glomerular filtration rate (eGFR) in patients with primary neuromuscular disease. Patients and methods Of the 418 patients initially identified at the out-patient clinic, data on kidney function was obtained for 145 adult patients (age 46 ± 14 years, BMI 26 ± 6 kg/m2) with primary neuromuscular disease. Kidney function was measured by iohexol clearance, and blood samples for serum creatinine and CysC were drawn simultaneously. Bias was defined as the mean difference between eGFR and measured iohexol clearance, and accuracy as the proportion of eGFRs within ± 10% (P10) of measured clearance. Results Kidney function (iohexol clearance) was 81 ± 19 (38–134) ml/min/1.73m2. All equations overestimated kidney function by 22–60 ml/min/1.73m2. eGFR CysC had the lowest bias overall 22 (95% CI 20–26) ml/min/1.73m2 also at all levels of kidney function we evaluated (at 30–59 ml/min/1.73m2 bias was 27 (95% CI 21–35), at 60–89 it was 25 (95% CI 20–28) and at ≥ 90 it was 12 (95% CI 7–22)). eGFR CysC also had the best accuracy in patients with reduced kidney function (P10 was 5.9% at 30–59 ml/min/1.73m2). Conclusions Cystatin C-based estimations of kidney function performed better than creatinine-based ones in patients with primary neuromuscular disease, but most importantly, all evaluated equations overestimated kidney function, especially in patients with reduced kidney function. Therefore, kidney function should be measured by gold-standard methods when precision and accuracy are needed. Graphic abstract

Nintedanib-Induced Renal Thrombotic Microangiopathy

Nintedanib is a unique tyrosine kinase inhibitor used to suppress fibrosis in patients with idiopathic pulmonary fibrosis (IPF). Nintedanib has been shown to suppress multiple processes of fibrosis, thereby reducing the rate of lung function decline in patients with IPF. Since vascular endothelial growth factor is one of this agent’s targets, nephrotoxicity, including renal thrombotic microangiopathy (TMA), is a possible major adverse effect. However, only 2 previous cases of nintedanib-induced renal TMA have been published. Our patient was an 83-year-old man with IPF. As adverse effects including liver enzyme level elevation, diarrhoea, anorexia, and nephrotoxicity developed, the nintedanib dosage was reduced after 9 months. The digestive symptoms resolved promptly, but the proteinuria and reduced kidney function remained. Although the kidney injury had improved to some extent, we performed a percutaneous renal biopsy. The biopsy revealed typical TMA findings such as microaneurysms filled with pale material, segmental double contours of glomerular basement membranes, and intracapillary foam cells. After discontinuation of nintedanib, the patient’s nephrotoxicity improved. Nintedanib-induced renal TMA is reversible and is possibly dose-dependent. Here, we report the clinical course of our case and review the characteristics of nintedanib-induced renal TMA.