Reduced nephron number and glomerulomegaly in Australian Aborigines: a group at high risk for renal disease and hypertension

Regional hotspots for chronic kidney disease: A multinational study from the ISN-GKHA

Chronic kidney disease (CKD) disproportionately affects certain populations as demonstrated by well-established subnational geographic hotspots of CKD in Central America and South Asia. Using data from the third iteration of the International Society of Nephrology Global Kidney Health Atlas (ISN-GKHA), we aimed to systematically identify sub-national geographic or population clusters with high prevalence of CKD. The ISN-GKHA survey was conducted from July to September 2022, and included questions regarding whether a regional CKD hotspot existed in the respondents' country and possible contributors. A CKD hotspot was defined as a population cluster with a high risk of kidney failure requiring dialysis or transplant, or people dying from kidney failure. Overall, 46 out of 162 responding countries reported subnational hotspots for CKD within their country. Hotspots were reported across all regions, except for the Middle East. Latin America had the highest percentage (12 of 21, 57%) of countries reporting a regional CKD hotspot followed by the regions of North and East Asia, and Western Europe. Adults aged 18 to 44 years and rural populations were most commonly identified as the primary groups affected. Clinical factors were most commonly identified as contributors to CKD (hypertension in 74% and diabetes in 72%), followed by cultural (e.g., diet and herbal medications in 67%), and environmental (e.g., polluted water in 43%) factors. Latin American countries more commonly reported climate, cultural, and environmental factors as contributors compared to other regions. Across the world, there are a number of subnational regions where in-country experts identify a disproportionately higher burden of CKD, commonly occurring among younger age groups with clinical, cultural, and environmental contributors specific to these geographic regions. In-depth studies, starting with systematic epidemiology efforts, are needed to investigate the aetiopathogenesis of these CKD hotspots around the world so that tailored interventions can be offered.

Systemic lupus erythematosus in Aboriginal and Torres Strait Islander peoples in Australia: addressing disparities and barriers to optimising patient care

The first inhabitants of Australia and the traditional owners of Australian lands are the Aboriginal and Torres Strait Islander peoples. Aboriginal and Torres Strait Islander peoples are two to four times more likely to have systemic lupus erythematosus (SLE) than the general Australian population. Phenotypically, SLE appears distinctive in Aboriginal and Torres Strait Islander peoples and its severity is substantially increased, with mortality rates up to six times higher than in the general Australian population with SLE. In particular, Aboriginal and Torres Strait Islander peoples with SLE have increased prevalence of lupus nephritis and increased rates of progression to end-stage kidney disease. The reasons for the increased prevalence and severity of SLE in this population are unclear, but socioeconomic, environmental, and biological factors are all likely to be implicated, although there are no published studies investigating these factors in Aboriginal and Torres Strait Islander peoples with SLE specifically, indicating an important knowledge gap. In this Review, we summarise the data on the incidence, prevalence, and clinical and biological findings relating to SLE in Aboriginal and Torres Strait Islander peoples and explore potential factors contributing to its increased prevalence and severity in this population. Importantly, we identify health disparities and deficiencies in health-care provision that limit optimal care and outcomes for many Aboriginal and Torres Strait Islander peoples with SLE and highlight potentially addressable goals to improve outcomes.

Ultrasound and magnetic resonance imaging features of fetal urogenital anomalies: A pictorial essay

This pictorial essay focuses on ultrasound (US) and magnetic resonance imaging (MRI) features of fetal urogenital anomalies. Fetal urogenital malformations account for 30%-50% of all anomalies discovered during pregnancy or at birth. They are usually detected by fetal ultrasound exams. However, when ultrasound data on their characteristics is insufficient, MRI is the best option for detecting other associated anomalies. The prognosis highly depends on their type and whether they are associated with other fetal abnormalities.

Oligonephronia: another piece in the CKDu jigsaw?

Rates of chronic kidney disease of unknown etiology are high in Aguascalientes, Mexico. Kidneys of adolescents are small by ultrasonography, compatible with oligonephronia, whereas proteinuria and higher estimated glomerular filtration rates and blood pressures among those with relatively higher kidney volumes probably flag relatively greater degrees of compensatory hypertrophy. Glomerulomegaly and podocytopathy, and later segmental glomerulosclerosis in biopsies, suggest a cascade driven by nephron deficiency. Better measures of glomerular number and volume should improve understanding, facilitate risk assessment, and guide interventions.

Association of linear growth velocities between 0 and 6 years with kidney function and size at 10 years: A birth cohort study in Ethiopia

BACKGROUND

Risk of noncommunicable diseases accrues from fetal life, with early childhood growth having an important role in adult disease risk. There is a need to understand how early-life growth relates to kidney function and size.

OBJECTIVES

This study aimed to assess the association of linear growth velocities among children between 0 and 6 y with kidney function and size among children aged 10 y.

METHODS

The Ethiopian Anthropometric and Body Composition birth cohort recruited infants born at term to mothers living in Jimma with a birth weight of ≥1500 g and without congenital malformations. Participants were followed up with 13 measurements between birth and 6 y of age. The latest follow-up was at ages 7-12 y with measurement of serum cystatin C as a marker of kidney function and ultrasound assessment of kidney dimensions. Kidney volume was computed using an ellipsoid formula. Linear-spline multilevel modeling was used to compute linear growth velocities between 0 and 6 y. Multiple linear regression modeling was used to examine the associations of linear growth velocities in selected age periods with cystatin C and kidney size.

RESULTS

Data were captured from 355 children, at a mean age of 10 (range 7-12) y. The linear growth velocity was high between 0 and 3 mo and then decreased with age. There was no evidence of an association of growth velocity ≤24 mo with cystatin C at 10 y. Between 24 and 48 and 48 and 76 mo, serum cystatin C was higher by 2.3% [95% confidence interval (CI): 0.6, 4.2] and 2.1% (95% CI: 0.3, 4.0) for 1 SD higher linear growth velocity, respectively. We found a positive association between linear growth velocities at all intervals between 0 and 6 y and kidney volume.

CONCLUSIONS

Greater linear growth between 0 and 6 y of development was positively associated with kidney size, and greater growth velocity after 2 y was associated with higher serum cystatin C concentrations.

Deletion of NuRD component Mta2 in nephron progenitor cells causes developmentally programmed FSGS

Low nephron endowment at birth is a risk factor for chronic kidney disease. The prevalence of this condition is increasing due to higher survival rates of preterm infants and children with multi- organ birth defect syndromes that affect the kidney and urinary tract. We created a mouse model of congenital low nephron number due to deletion of Mta2 in nephron progenitor cells. Mta2 is a core component of the Nucleosome Remodeling and Deacetylase (NuRD) chromatin remodeling complex. These mice developed albuminuria at 4 weeks of age followed by focal segmental glomerulosclerosis (FSGS) at 8 weeks, with progressive kidney injury and fibrosis. Our studies reveal that altered mitochondrial metabolism in the post-natal period leads to accumulation of neutral lipids in glomeruli at 4 weeks of age followed by reduced mitochondrial oxygen consumption. We found that NuRD cooperated with Zbtb7a/7b to regulate a large number of metabolic genes required for fatty acid oxidation and oxidative phosphorylation. Analysis of human kidney tissue also supported a role for reduced mitochondrial lipid metabolism and ZBTB7A/7B in FSGS and CKD. We propose that an inability to meet the physiological and metabolic demands of post-natal somatic growth of the kidney promotes the transition to CKD in the setting of glomerular hypertrophy due to low nephron endowment.

Evaluation of ceftriaxone pharmacokinetics in hospitalized Egyptian pediatric patients

This study aimed to evaluate ceftriaxone pharmacokinetics that affects the achievement of targets in the treatment of critically ill children (meningitis, pneumonia, urinary tract infection, peritonitis, and infective endocarditis( who were admitted to Zagazig University Pediatric hospital in Egypt to monitor for the drug adverse effects.Blood samples were obtained from 24 hospitalized pediatric patients (ages ranging from 2.5 months to 12 years) after administering the calculated dose of ceftriaxone via intravenous bolus route. Then, ceftriaxone plasma concentrations were measured using a validated HPLC method with ultraviolet detection. The pharmacokinetic analysis was conducted using Phoenix Winnonlin Program® software.Data for total and free ceftriaxone best fitted on a one-compartment model with the first-order elimination process. Clearance of ceftriaxone is reduced for patients with reduced kidney function and increased with those with augmented renal clearance. The volume of distribution and the free fraction are increased in these patients, especially those with hypoalbuminemia with a shorter half-life time were detected. A slight increase in total bilirubin and liver enzymes has been observed after treatment with ceftriaxone in these patients.   Conclusion: In most critically ill pediatric patients, the current ceftriaxone treatment regimen (50 to 100 mg/kg) offers adequate pathogenic coverage. The clearance of free ceftriaxone in all patients correlates well with their renal function (eGFR), with r2 = 0.7252. During therapy with ceftriaxone at all doses ranging from 50 to 100 mg/kg, a rise in total bilirubin was observed in these patients. Moreover, liver enzymes (ALT and AST) increased moderately (p 0.0001). So, it is recommended to monitor total bilirubin and liver enzymes during the treatment with ceftriaxone, especially for a long duration (more than 5 days) or use another agent in patients with high baseline values. What is Known: • The dosing regimen of ceftriaxone (50 to 100 mg/kg) provided optimum therapeutic outcomes. • Some studies show data for total and free Ceftriaxone best fitted on a one-compartment model while other studies show data for total and free Ceftriaxone best fitted on a two-compartment model. What is New: • Up to my knowledge this is the first study ,considering individual pharmacokinetic analysis, conducted on hospitalized Egyptian pediatric population most of them with reduced kidney function with ages ranging from 2.5 months to 12 years. Data for total and free Ceftriaxone best fitted on a one-compartment model with linear clearance of the free ceftriaxone. • In all patients, total bilirubin and liver function tests were mildly increased, making them at risk for cholestasis or ceftriaxone-induced cholestatic hepatitis.

An Improved Method for Estimating Nephron Number and the Association of Resulting Nephron Number Estimates with Chronic Kidney Disease Outcomes

SIGNIFICANCE STATEMENT

Nephron number currently can be estimated only from glomerular density on a kidney biopsy combined with cortical volume from kidney imaging. Because of measurement biases, refinement of this approach and validation across different patient populations have been needed. The prognostic importance of nephron number also has been unclear. The authors present an improved method of estimating nephron number that corrects for several biases, resulting in a 27% higher nephron number estimate for donor kidneys compared with a prior method. After accounting for comorbidities, the new nephron number estimate does not differ between kidney donors and kidney patients with tumor and shows consistent associations with clinical characteristics across these two populations. The findings also indicate that low nephron number predicts CKD independent of biopsy and clinical characteristics in both populations.

BACKGROUND

Nephron number can be estimated from glomerular density and cortical volume. However, because of measurement biases, this approach needs refinement, comparison between disparate populations, and evaluation as a predictor of CKD outcomes.

METHODS

We studied 3020 living kidney donors and 1354 patients who underwent radical nephrectomy for tumor. We determined cortex volume of the retained kidney from presurgical imaging and glomerular density by morphometric analysis of needle core biopsy of the donated kidney and wedge sections of the removed kidney. Glomerular density was corrected for missing glomerular tufts, absence of the kidney capsule, and then tissue shrinkage on the basis of analysis of 30 autopsy kidneys. We used logistic regression (in donors) and Cox proportional hazard models (in patients with tumor) to assess the risk of CKD outcomes associated with nephron number.

RESULTS

Donors had 1.17 million nephrons per kidney; patients with tumor had 0.99 million nephrons per kidney. A lower nephron number was associated with older age, female sex, shorter height, hypertension, family history of ESKD, lower GFR, and proteinuria. After adjusting for these characteristics, nephron number did not differ between donors and patients with tumor. Low nephron number (defined by <5th or <10th percentile by age and sex in a healthy subset) in both populations predicted future risk of CKD outcomes independent of biopsy and clinical characteristics.

CONCLUSIONS

Compared with an older method for estimating nephron number, a new method that addresses several sources of bias results in nephron number estimates that are 27% higher in donors and 1% higher in patients with tumor and shows consistency between two populations. Low nephron number independently predicts CKD in both populations.

Excellent clinical outcomes of renal transplant from pediatric deceased donors with acute kidney injury

BACKGROUND

The use of kidneys from deceased donors with acute kidney injury (AKI) to expand the donor pool is an ongoing trend. Prior research on the utilization of AKI donor kidneys, especially from pediatric AKI donors, was limited and has been subject to small sample sizes. In this study, we aimed to evaluate the safety and effectiveness of early post-transplantation outcomes in pediatric deceased donors with AKI.

METHODS

This retrospective study compared the clinical results (including delayed graft function [DGF], acute rejection, patient and death-censored graft survival rates and renal function post-transplant) of kidney transplantation from deceased donors who were categorized as pediatric donors and adult donors with or without AKI, as defined by the Kidney Disease: Improving Global Outcomes (KIDGO) criteria, at our center between January 2018 and December 2020.

RESULTS

Of the 740 patients, 154 received kidneys from pediatric donors (with AKI group [n = 41]; without AKI group [n = 113]), and 586 received kidneys from adult donors (with AKI group [n = 218]; without AKI group [n = 368]). The baseline characteristics were similar in both cohorts. No significant difference was observed in 1-year patient survival, death-censored graft survival, or acute rejection between the AKI and non-AKI groups in both the pediatric and adult cohorts. However, compared with those transplanted with adult AKI kidneys, those transplanted with pediatric AKI kidneys showed a superior recovery of allograft function. In pediatric cohorts, no significant difference was found in serum creatinine/estimated glomerular filtration rate (SCr/eGFR) between the AKI and non-AKI groups, even in the first week post-transplant. In contrast, the post-transplant SCr/eGFR level of the AKI group recipients in adult cohorts did not recover to a level statistically similar to that of non-AKI recipients, even at 6-months post-transplant. Nonetheless, AKI kidney recipients were at an increased risk of DGF in both pediatric (34.1% vs. 16.8%) and adult (38.5% vs. 17.4%) cohorts.

CONCLUSIONS

Kidney transplantation from deceased donors with AKI has short-term clinical outcomes comparable to those of non-AKI kidney transplantation. Pediatric AKI kidneys have a superior recovery of allograft function. The transplant community should utilize this donor pool to minimize waiting-list-related mortalities.

Risk of kidney disease following a pregnancy complicated by diabetes: a longitudinal, population-based data-linkage study among Aboriginal women in the Northern Territory, Australia

AIMS/HYPOTHESIS

The aim of this work was to investigate the risk of developing chronic kidney disease (CKD) or end-stage kidney disease (ESKD) following a pregnancy complicated by gestational diabetes mellitus (GDM) or pre-existing diabetes among Aboriginal women in the Northern Territory (NT), Australia.

METHODS

We undertook a longitudinal study of linked healthcare datasets. All Aboriginal women who gave birth between 2000 and 2016 were eligible for inclusion. Diabetes status in the index pregnancy was as recorded in the NT Perinatal Data Collection. Outcomes included any stage of CKD and ESKD as defined by ICD-10 coding in the NT Hospital Inpatient Activity dataset between 2000 and 2018. Risk was compared using Cox proportional hazards regression.

RESULTS

Among 10,508 Aboriginal women, the mean age was 23.1 (SD 6.1) years; 731 (7.0%) had GDM and 239 (2.3%) had pre-existing diabetes in pregnancy. Median follow-up was 12.1 years. Compared with women with no diabetes during pregnancy, women with GDM had increased risk of CKD (9.2% vs 2.2%, adjusted HR 5.2 [95% CI 3.9, 7.1]) and ESKD (2.4% vs 0.4%, adjusted HR 10.8 [95% CI 5.6, 20.8]). Among women with pre-existing diabetes in pregnancy, 29.1% developed CKD (adjusted HR 10.9 [95% CI 7.7, 15.4]) and 9.9% developed ESKD (adjusted HR 28.0 [95% CI 13.4, 58.6]).

CONCLUSIONS/INTERPRETATION

Aboriginal women in the NT with GDM or pre-existing diabetes during pregnancy are at high risk of developing CKD and ESKD. Pregnancy presents an important opportunity to identify kidney disease risk. Strategies to prevent kidney disease and address the social determinants of health are needed.

Nephrons, podocytes and chronic kidney disease: Strategic antihypertensive therapy for renoprotection

Chronic kidney disease (CKD) is one of the strongest risk factors for hypertension, and hypertension can exacerbate the progression of CKD. Thus, the management of CKD and antihypertensive therapy are inextricably linked. Research over the past decades has shown that the human kidney is more diverse than initially thought. Subjects with low nephron endowment are at increased risk of developing CKD and hypertension, which is consistent with the theory of the developmental origins of health and disease. Combined with other lifetime risks of CKD, hypertension may lead to a vicious cycle consisting of podocyte injury, glomerulosclerosis and further loss of nephrons. Of note, recent studies have shown that the number of nephrons correlates well with the number of podocytes, suggesting that these two components are intrinsically linked and may influence each other. Both nephrons and podocytes have no or very limited regenerative capacity and are destined to decrease throughout life. Therefore, one of the best strategies to slow the progression of CKD is to maintain the "numbers" of these essential components necessary to preserve renal function. To this end, both the achievement of an optimal blood pressure and a maximum reduction in urinary protein excretion are essential. Lifestyle modifications and antihypertensive drug therapy must be carefully individualized to address the potential diversity of the kidneys.

Low glomerular number at birth can lead to the development of chronic kidney disease

Chronic kidney disease (CKD) prevalence is increasing worldwide, and reducing the number of patients with CKD is of utmost importance. The environment during the fetal, perinatal, and early childhood stages may influence CKD development (developmental origins of health and disease). Under conditions of maternal malnutrition, the glomerular number of infants reduces, and the risk of developing CKD may increase. Nephron progenitor cells and ureteric buds interact with each other to form glomeruli at the tip of the ureteric bud. Thus, the number of glomeruli is determined by the number of ureteric bud branches, which are reportedly decreased due to maternal malnutrition, in turn reducing the glomerular number. Four possible mechanisms can explain the low glomerular number resulting from maternal malnutrition: 1) suppression of c-Ret expression, 2) suppression of nephron formation by renin-angiotensin-aldosterone system inhibition, 3) exposure to excess glucocorticoids, and 4) promotion of apoptosis. Additionally, nephron formation does not continue after birth in humans. Therefore, a low glomerular number at birth is a lifelong burden on the glomeruli and increases the risk of developing CKD. Therefore, it is important to maintain the glomerular number at birth. Accurate glomerular counts are essential for conducting studies on the glomerular number. The dissector/fractionator method is the gold standard; however, it can only be performed at some institutions. Recently, methods have been developed to measure the glomerular number by combining computed tomography and pathological examination and measure the glomerular count using magnetic resonance imaging. Models of decreased and increased glomerular numbers have been developed. Moreover, research regarding the causes of decreased glomerular number and its relationship with development of lifestyle-related diseases and renal dysfunction has significantly progressed, furthering our understanding of the importance of glomerular number.

Low birth weight, nephron number and chronic kidney disease

Chronic kidney diseases have a significant impact on morbidity and mortality worldwide. Low birth weight, fetal growth restriction and prematurity are indicators of fetal growth and development disorders associated with a congenital reduction in nephron number, which predisposes to an increased risk for chronic kidney disease. On an individual basis, a small nephron number at birth is not always enough to determine the onset of chronic kidney disease, but it decreases the ability of the kidneys to resist any insults to renal tissue that may occur later in life, such as exposure to nephrotoxic drugs or episodes of acute kidney injury. The high incidence of low birth weight and preterm birth globally suggests that, at the population level, the impact of alterations in fetal development on the subsequent onset of chronic kidney disease could be significant. The implementation of strategies aimed at reducing the incidence of prematurity, fetal growth restriction, as well as other conditions that lead to low birth weight and a reduced nephron number at birth, provides an opportunity to prevent the development of chronic kidney disease in adulthood. For these purposes the coordinated intervention of several specialists, including obstetricians, gynecologists, neonatologists, nephrologists, and family doctors, is necessary. Such strategies can be particularly useful in resource-poor countries, which are simultaneously burdened by maternal, fetal and child malnutrition; poor health; epidemics caused by communicable diseases; and little access to screening and primary care.

Acute kidney injury and the compensation of kidney function after nephrectomy in living donation

Acute kidney injury (AKI) incidence is growing rapidly, and AKI is one of the predictors of inpatient mortality. After nephrectomy, all the patients have decreased kidney function with AKI and recover from AKI. However, the characteristic and behavior of AKI is different from usual AKI and compensatory kidney function has been well known in the postoperative setting, especially in living donors. In this review, we have focused on the compensation of kidney function after nephrectomy in living donors. We discuss factors that have been identified as being associated with kidney recovery in donors including age, sex, body mass index, remnant kidney volume, estimated glomerular filtration rate, and various comorbidities.

Effects of Prematurity and Growth Restriction on Adult Blood Pressure and Kidney Volume

Gaining insight into the complex cycle of renal programming and its early-life clinical associations is essential to understand the origins of kidney disease. Prematurity and intrauterine growth restriction are associated with low nephron endowment. This increases the risk of developing hypertension and chronic kidney disease later in life. There is appreciable evidence to support mechanistic links between low nephron endowment secondary to intrauterine events and kidney size, kidney function, and blood pressure in postnatal life. A clear understanding of the cycle of developmental programming and consequences of fetal insults on the kidney is critical. In addition, the impact of events in the early postnatal period (accelerated postnatal growth, development of obesity, exposure to nephrotoxins) on the cardiovascular system and blood pressure of individuals born prematurely or with low birth weight is discussed. In summary, this review draws attention to the concepts of renal programming and nephron endowment and underscores the associations between intrauterine growth restriction, prematurity, and its clinical consequences in adult life.

Sociodemographic determinants of chronic kidney disease in Indigenous children

Rates of chronic kidney disease (CKD) are disproportionately increased in Indigenous peoples. The focus has traditionally been on adults, as they experience the highest rates of kidney failure requiring kidney replacement therapy. The impacts of colonization, systemic racism, and sociodemographic marginalization however impact the health of Indigenous peoples across the lifespan. This review presents the social context within which Indigenous children develop and the impact relevant to kidney health across the developmental stages. In utero exposures impact nephron endowment which can manifest in glomerular hyperfiltration and sclerosis as well as an increased risk of congenital anomalies of the kidney and urinary tract. Young children are at increased risk of autoimmune conditions, secondary to infectious and environmental exposures, and are also exposed to the impacts of a Western lifestyle manifesting early onset overweight/obesity. Adolescents begin to manifest more severe metabolic complications such as type 2 diabetes. The impacts of early onset diabetes are associated with aggressive kidney complications and high rates of kidney failure in young adulthood. Finally, the key elements of successful prevention and treatment strategies are discussed including the importance of screening for asymptomatic, modifiable early disease, linked with clinical primary and tertiary care follow-up, and culturally relevant and safe care.

The developmental origins of health and chronic kidney disease: Current status and practices in Japan

The concept of the developmental origins of health and disease (DOHaD) views unfavorable perinatal circumstances as contributing to the development of diseases in later life. It is well known that such unfavorable circumstances play an important role as a risk factor for chronic kidney disease (CKD) in infants born with prematurity. Low birthweight (LBW) is believed to be a potential contributor to CKD in adulthood. Preterm and/or LBW infants are born with incomplete nephrogenesis. As a result, the number of nephrons is low. The poor intrauterine environment also causes epigenetic changes that adversely affect postnatal renal function. After birth, hyperfiltration of individual nephrons due to low nephron numbers causes proteinuria and secondary glomerulosclerosis. Furthermore, the risk of CKD increases as renal damage takes a second hit from exposure to nephrotoxic substances and acquired insults such as acute kidney injury after birth among infants in neonatal intensive care. Meanwhile, unfortunately, recent studies have shown that the number of nephrons in healthy Japanese individuals is approximately two-thirds lower than that in previous reports. This means that Japanese premature infants are clearly at a high risk of developing CKD in later life. Recently, several DOHaD-related CKD studies from Japanese researchers have been reported. Here, we summarize the relevance of CKD in conjunction with DOHaD and review recent studies that have examined the impact of the upward LBW trend in Japan on renal health.

Single-cell RNA sequencing reveals differential cell cycle activity in key cell populations during nephrogenesis

The kidney is a complex organ composed of more than 30 terminally differentiated cell types that all are required to perform its numerous homeostatic functions. Defects in kidney development are a significant cause of chronic kidney disease in children, which can lead to kidney failure that can only be treated by transplant or dialysis. A better understanding of molecular mechanisms that drive kidney development is important for designing strategies to enhance renal repair and regeneration. In this study, we profiled gene expression in the developing mouse kidney at embryonic day 14.5 at single-cell resolution. Consistent with previous studies, clusters with distinct transcriptional signatures clearly identify major compartments and cell types of the developing kidney. Cell cycle activity distinguishes between the "primed" and "self-renewing" sub-populations of nephron progenitors, with increased expression of the cell cycle-related genes Birc5, Cdca3, Smc2 and Smc4 in "primed" nephron progenitors. In addition, augmented expression of cell cycle related genes Birc5, Cks2, Ccnb1, Ccnd1 and Tuba1a/b was detected in immature distal tubules, suggesting cell cycle regulation may be required for early events of nephron patterning and tubular fusion between the distal nephron and collecting duct epithelia.

Birthweight and the Prevalence, Progression, and Incidence of CKD in a Multideterminant Model in a High-Risk Australian Aboriginal Community

INTRODUCTION

We have previously showed that albuminuria was associated with low birthweight in young adults in a remote Australian Aboriginal community that has high rates of kidney disease. Here we describe the association of birthweight with incidence and progression of kidney disease over time.

METHODS

Among 695 members of an Aboriginal community with recorded birthweights, urine albumin creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) were measured at ages 5 to 40 years, and follow-up values were measured or imputed again a median of 11.6 years later. Prevalence of markers on each occasion and change over time were evaluated in the context of birthweights and other potentially significant factors.

RESULTS

On the second screen, ACR was inversely and significantly correlated with birthweight and eGFR was directly correlated with birthweight. Increases in ACR and in proportions of persons who developed new-onset (incident) albuminuria between screens were higher in those of lower birthweights (<2.5 kg). Proportions of persons who lost ≥20% of their baseline eGFR were higher in the lower birthweight groups. Lower birthweights also amplified elevations of ACR associated with other risk factors, specifically higher body mass indexes (BMIs) and a prior history of poststreptococcal glomerulonephritis (PSGN). At both screens, progressively higher levels of ACR beyond the mid-microalbuminuria range were correlated with lower levels of eGFR.

CONCLUSIONS

Lower birthweight contributes to an excess of kidney disease and its progression in this population. Because an excess of low birthweight and episodes of PSGN are eminently preventable, substantial containment of kidney disease is feasible.

Variations in clinical presentation and biomarkers amongst biopsy-proven Lupus Nephritis patients: a Top-End retrospective cohort study

BACKGROUND

Lupus nephritis (LN) is common feature of Systemic Lupus Erythematosus (SLE) and affects 50% of patients with SLE. Racial differences in incidence and prevalence have been well documented worldwide. In Australia, higher incidence and prevalence of SLE had been previously reported in Aboriginal and Torres Strait Australians compared to non-Indigenous Australians.

AIM

to describe the differences in clinical features and lupus biomarkers between Aboriginal and Torres Strait Islander Australian and non-Indigenous Australian LN patients.

METHODS

We retrospectively identified all consecutive biopsy-proven LN patients in our institution and compared the clinical features and lupus biomarkers between Aboriginal and Torres Strait Islander Australians and non-indigenous Australians.

RESULTS

Of the thirty-three consecutive biopsy proven LN patients, twenty-six self-identified as of Aboriginal and Torres Strait Islander descent. The estimated incidence of lupus nephritis in Aboriginal and Torres Strait Islander Australian and non-Indigenous Australians were 5.08 and 0.47 per 100,000 patient years respectively. Neurological manifestations (23.08% vs 0%), haematological manifestations (46.50 % vs 16.67) and right heart catheter proven pulmonary arterial hypertension (23.08% vs 0%) were more frequently observed amongst Indigenous Australian patients compared to non-Indigenous Australian patients. The incidence of positive Extractable Nuclear Antigen (ENA) was also higher among Indigenous Australian patients (84.62% vs 57.14%).

CONCLUSION

Our study further supports the observation that lupus in Aboriginal and Torres Strait Islander Australians were of a 'distinct phenotype' compared to non-Indigenous Australians. Future research should be aimed at delineating the reason for this observed difference. This article is protected by copyright. All rights reserved.

The number of glomeruli and pyruvate metabolism is not strongly coupled in the healthy rat kidney

PURPOSE

The number of glomeruli is different in men and women, as they also present different prevalence and progression of chronic kidney disease. A recent study has demonstrated a potential difference in renal metabolism between sexes, and a potential explanation could be the differences in glomeruli number. This study investigates the potential correlation between glomerular number and pyruvate metabolism in healthy kidneys.

METHODS

This study is an experimental study with rats (N = 12). We used cationized-ferritin MRI to visualize and count glomeruli and hyperpolarized [1-¹³ C]pyruvate to map the metabolism. Dynamic contrast-enhanced MRI was used to analyze kidney hemodynamics using gadolinium tracer.

RESULTS

Data showed no or subtle correlation between the number of glomeruli and the pyruvate metabolism. Minor differences were observed in the number of glomeruli (female = 24,509 vs. male = 26 350; p = .16), renal plasma flow (female = 606.6 vs. male= 455.7 ml/min/100 g; p = .18), and volume of distribution (female = 87.44 vs. male = 76.61 ml/100 ml; p = .54) between sexes. Mean transit time was significantly prolonged in males compared with females (female = 8.868 s vs. male = 10.63 s; p = .04).

CONCLUSION

No strong statistically significant correlation between the number of glomeruli and the pyruvate metabolism was found in healthy rat kidneys.

Assessment of nephron number and single-nephron glomerular filtration rate in a clinical setting

Total nephron counts vary widely between individuals and may affect susceptibility to certain diseases, including hypertension and chronic kidney disease. Detailed analyses of whole kidneys collected from autopsy patients remain the only method for accurately counting nephrons in humans, with no equivalent option in living subjects. Current technological advances have enabled estimations of nephron numbers in vivo, particularly the use of total nephron number and whole-kidney glomerular filtration rate to estimate the mean single-nephron glomerular filtration rate. The use of this method would allow physicians to detect dynamic changes in filtration function at the single-nephron level rather than to simply count the number of nephrons that appear to be functioning. Currently available methods for estimating total nephron number in clinical practice have the potential to overcome limitations associated with autopsy analyses and may therefore pave the way for new therapeutic interventions and improved clinical outcomes.

Arterial hypertension and cystatin C during neonatal physiologic dehydration

A reduced nephron number may play a role in the pathogenesis of arterial hypertension (AH), and it is well recognized that individual nephron endowment is widely variable. However, nephrons count is technically impossible in vivo. Based on the observation that subjects with a reduced nephron mass exhibit an increase in renal functional biomarkers during acute dehydration, we hypothesized that cystatin C concentration during neonatal physiological dehydration could identify subjects with reduced nephron endowment. This is a prospective, observational, cohort study enrolling healthy, caucasian, term neonates born after an uneventful pregnancy. Two groups of newborns were compared: neonates born to fathers on antihypertensive treatment (HF) versus those born to proven normotensive fathers older than 40 years of age (NF). Enrolled newborns underwent cystatin C determination at the time of newborn screening. Forty newborns with HF and 80 with NF were enrolled. No differences in baseline characteristics were observed between the two groups except for the number of hypertensive grandparents higher among newborns to HF (47.8% vs. 21.1%; p: 0.001). Cystatin C was significantly higher in newborns with HF (1.62 ± 0.30 mg/L vs 1.41 ± 0.27 mg/L; p < 0.001). Linear regression analysis corrected for confounders confirmed that paternal hypertension was the only variable significantly associated with high cystatin C level during post-natal dehydration. Besides offering new insights on the pathogenesis of familial hypertension, our results support the specific role of nephron endowment and suggest the possibility of identifying subjects at risk for reduced nephron endowment as early as at birth.

Rising Incidence of End-Stage Kidney Disease and Poorer Access to Kidney Transplant Among Australian Aboriginal and Torres Strait Islander Children and Young Adults

Introduction

Details of the pediatric population with end-stage kidney disease (ESKD) in Australia and New Zealand have been published previously. There is, however, a paucity of studies exploring the trends in incidence, etiology, renal replacement therapy (RRT) modality, and transplant access among the Aboriginal and Torres Strait Islander children and young adults (ATCYAs) residing in Australia.

Methods

An observational study was undertaken and data on Australian patients who commenced RRT at ≤24 years of age between 1963 and 2017 were extracted from the Australian and New Zealand Dialysis and Transplant Registry (ANZDATA). The incidence and prevalence rates were restricted from 1997 to 2017 because of the unavailability of Aboriginal– and Torres Strait Islander status–specific census data before 1997.

Results

A total of 3629 children and young adults received RRT during the observation period, including 178 (4.9%) who identified as ATCYAs and 3451 (95.1%) other children and young adults (OCYAs). Compared with OCYAs, incident rates have risen among ATCYAs since 2000, with the biggest rise for young adults 20 to 24 years of age. Fewer ATCYAs received a kidney transplant compared with OCYAs (56.2% vs. 89.3%, P < 0.001). Pre-emptive kidney transplants were less common in ATCYAs compared with OCYAs (3.4% vs. 16.8%, P < 0.001). Living related donor transplants were less common among ATCYAs than OCYAs (10.7% vs. 35.9%, P < 0.001).

Conclusions

Our study shows rising incident rates and poorer access to kidney transplantation among ATCYAs in Australia. The reasons for this health care disparity and barriers to transplantation need to be explored further and must be addressed.

Maternal Diet Influences Fetal Growth but Not Fetal Kidney Volume in an Australian Indigenous Pregnancy Cohort

Suboptimal nutrition during pregnancy is recognised as a significant modifiable determinant in the development of chronic disease in offspring in later life. The current study aimed: (i) to assess the dietary intakes of pregnant Indigenous Australian women against national recommendations and (ii) to investigate the associations between maternal nutrition during pregnancy and the growth of the offspring, including kidney development in late gestation in the Gomeroi gaaynggal cohort (n = 103). Maternal dietary intake in the third trimester was assessed using the Australian Eating Survey Food Frequency Questionnaire. Estimated fetal weight (EFW) and kidney size were obtained by ultrasound. Birth weight was retrieved from hospital birth records. Of the five key nutrients for optimal reproductive health (folate, iron, calcium, zinc and fibre), the nutrients with the highest percentage of pregnant women achieving the nutrient reference values (NRVs) were zinc (75.7%) and folate (57.3%), whereas iron was the lowest. Only four people achieved all NRVs (folate, iron, calcium, zinc and fibre) important in pregnancy. Sodium and saturated fat intake exceeded recommended levels and diet quality was low, with a median score of 28 out of 73 points. After adjusting for smoking and pre-pregnancy body mass index, only maternal intake of retinol equivalents and the proportion of energy from nutrient-dense or energy-dense, nutrient-poor (EDNP) foods were associated with fetal growth. EFW decreased by 0.13 g and birth weight decreased by 0.24 g for every µg increase in maternal dietary retinol intake. Interestingly, EFW, but not actual birth weight, was positively associated with percentage energy from nutrient dense foods and negatively associated with percentage energy from EDNP foods. Dietary supplement usage was associated with increased birthweight, most significantly iron and folate supplementation. Current dietary intakes of pregnant Australian women from this cohort do not align with national guidelines. Furthermore, current findings show that maternal retinol intake and diet composition during pregnancy can influence fetal growth, but not fetal kidney growth in late gestation. Strategies that aim to support and optimise nutrient intakes of Indigenous pregnant women are urgently needed. Future studies with long-term follow-up of the children in the current cohort to assess renal damage and blood pressure are imperative.

Multiscale three-dimensional imaging of intact human organs down to the cellular scale using hierarchical phase-contrast tomography

Human organs are complex, three-dimensional and multiscale systems. Spatially mapping the human body down through its hierarchy, from entire organs to their individual functional units and specialised cells, is a major obstacle to fully understanding health and disease. To meet this challenge, we developed hierarchical phase-contrast tomography (HiP-CT), an X-ray phase propagation technique utilising the European Synchrotron Radiation Facility's Extremely Brilliant Source: the world's first high-energy 4 th generation X-ray source. HiP-CT enabled three-dimensional and non-destructive imaging at near-micron resolution in soft tissues at one hundred thousand times the voxel size whilst maintaining the organ's structure. We applied HiP-CT to image five intact human parenchymal organs: brain, lung, heart, kidney and spleen. These were hierarchically assessed with HiP-CT, providing a structural overview of the whole organ alongside detail of the organ's individual functional units and cells. The potential applications of HiP-CT were demonstrated through quantification and morphometry of glomeruli in an intact human kidney, and identification of regional changes to the architecture of the air-tissue interface and alveolar morphology in the lung of a deceased COVID-19 patient. Overall, we show that HiP-CT is a powerful tool which can provide a comprehensive picture of structural information for whole intact human organs, encompassing precise details on functional units and their constituent cells to better understand human health and disease.

Evolutionary genetics and acclimatization in nephrology

Evolutionary processes, including mutation, migration and natural selection, have influenced the prevalence and distribution of various disorders in humans. However, despite a few well-known examples, such as the APOL1 variants - which have undergone positive genetic selection for their ability to confer resistance to Trypanosoma brucei infection but confer a higher risk of chronic kidney disease - little is known about the effects of evolutionary processes that have shaped genetic variation on kidney disease. An understanding of basic concepts in evolutionary genetics provides an opportunity to consider how findings from ancient and archaic genomes could inform our knowledge of evolution and provide insights into how population migration and genetic admixture have shaped the current distribution and landscape of human kidney-associated diseases. Differences in exposures to infectious agents, environmental toxins, dietary components and climate also have the potential to influence the evolutionary genetics of kidneys. Of note, selective pressure on loci associated with kidney disease is often from non-kidney diseases, and thus it is important to understand how the link between genome-wide selected loci and kidney disease occurs in relation to secondary nephropathies.

Comparison of high glomerular filtration rate thresholds for identifying hyperfiltration

BACKGROUND

High glomerular filtration rate (GFR) is often used as a surrogate for single-nephron hyperfiltration. Our objective was to determine the definition for high GFR that best reflects clinical and structural characteristics of hyperfiltration.

METHODS

We studied living kidney donors at the Mayo Clinic and Cleveland Clinic. Potential donors underwent evaluations that included measured GFR (mGFR) by iothalamate clearance and estimated GFR (eGFR) by the serum creatinine-based Chronic Kidney Disease-Epidemiology collaboration (CKD-EPI) equation. High GFR was defined by the 95th percentile for each method (mGFR or eGFR) using either overall or age-specific thresholds. High mGFR was defined as both corrected and uncorrected for body surface area. The association of high GFR by each definition with clinical characteristics and radiologic findings (kidney volume) was assessed. In the subset that donated, the association of high GFR with kidney biopsy findings (nephron number and glomerular volume) and single-nephron GFR was assessed.

RESULTS

We studied 3317 potential donors, including 2125 actual donors. The overall 95th percentile for corrected mGFR was 134 mL/min/1.73 m2 and for eGFR was 118 mL/min/1.73 m2. The age-based threshold for uncorrected mGFR was 198 mL/min - 0.943×Age, for corrected mGFR it was 164 mL/min/1.73 m2 - 0.730×Age and for eGFR it was 146 mL/min/1.73 m2 - 0.813×Age. High age-based uncorrected mGFR had the strongest associations with higher single-nephron GFR, larger glomerular volume, larger kidney volume, male gender, higher body mass index and higher 24-h urine albumin, but also had the strongest association with high nephron number. A high age-height-gender-based uncorrected mGFR definition performed almost as well but had a weaker association with nephron number and did not associate with male gender.

CONCLUSIONS

High age-based uncorrected mGFR showed the most consistent associations reflective of hyperfiltration. However, high age-based uncorrected mGFR has limited clinical utility because it does not distinguish between hyperfiltration and high nephron number.

Short adult height increases the risk of end-stage renal disease in type 2 diabetes

OBJECTIVE

Although short adult height has been associated with an increasing variety of diseases and all-cause death, no reliable data exist on the association between adult height and end-stage renal disease (ESRD) in diabetic patients. We investigated the relationship between short adult height, development of ESRD, and mortality in type 2 diabetes mellitus (DM).

METHODS

This nationwide population-based cohort study analyzed clinical data from a total of 2,621,907 subjects aged ≥30 years with type 2 DM between January 1, 2009 and December 31, 2012, using the National Health Insurance Database in Korea.

RESULTS

During a 6.9-year follow-up period, 220,457 subjects (8.4%) died, and 28,704 subjects (1.1%) started dialysis. Short adult height significantly increased the incidence of ESRD and all-cause mortality in the overall cohort analysis. In multivariable Cox models, hazard ratios (HR) for the development of ESRD comparing the highest and lowest quartiles of adult height were 0.86 (95% CI 0.83-0.89). All-cause mortality also decreased with the highest height compared to patients with the lowest height, after fully adjusting for confounding variables (HR 0.79, 95% CI 0.78-0.81). Adult height had an inverse relationship to newly diagnosed ESRD (male: HR 0.86, 95% CI 0.83-0.90, female: HR 0.84, 95% CI 0.79-0.90) and all-cause mortality (male: HR 0.81, 95% CI 0.79-0.82, female: HR 0.80, 95% CI 0.78-0.82).

CONCLUSIONS

Short adult height is strongly associated with the increased risk of ESRD development and all-cause mortality in type 2 DM.

Performance of cardiovascular risk prediction equations in Indigenous Australians

OBJECTIVE

To assess the performance of cardiovascular disease (CVD) risk equations in Indigenous Australians.

METHODS

We conducted an individual participant meta-analysis using longitudinal data of 3618 Indigenous Australians (55% women) aged 30-74 years without CVD from population-based cohorts of the Cardiovascular Risk in IndigenouS People(CRISP) consortium. Predicted risk was calculated using: 1991 and 2008 Framingham Heart Study (FHS), the Pooled Cohorts (PC), GloboRisk and the Central Australian Rural Practitioners Association (CARPA) modification of the FHS equation. Calibration, discrimination and diagnostic accuracy were evaluated. Risks were calculated with and without the use of clinical criteria to identify high-risk individuals.

RESULTS

When applied without clinical criteria, all equations, except the CARPA-adjusted FHS, underestimated CVD risk (range of percentage difference between observed and predicted CVD risks: -55% to -14%), with underestimation greater in women (-63% to -13%) than men (-47% to -18%) and in younger age groups. Discrimination ranged from 0.66 to 0.72. The CARPA-adjusted FHS equation showed good calibration but overestimated risk in younger people, those without diabetes and those not at high clinical risk. When clinical criteria were used with risk equations, the CARPA-adjusted FHS algorithm scored 64% of those who had CVD events as high risk; corresponding figures for the 1991-FHS were 58% and were 87% for the PC equation for non-Hispanic whites. However, specificity fell.

CONCLUSION

The CARPA-adjusted FHS CVD risk equation and clinical criteria performed the best, achieving higher combined sensitivity and specificity than other equations. However, future research should investigate whether modifications to this algorithm combination might lead to improved risk prediction.

Programming of Renal Development and Chronic Disease in Adult Life

Chronic kidney disease (CKD) can have an insidious onset because there is a gradual decline in nephron number throughout life. There may be no overt symptoms of renal dysfunction until about two thirds or more of the nephrons have been destroyed and glomerular filtration rate (GFR) falls to below 25% of normal (often in mid-late life) (Martinez-Maldonaldo et al., 1992). Once End Stage Renal Disease (ESRD) has been reached, survival depends on renal replacement therapy (RRT). CKD causes hypertension and cardiovascular disease; and hypertension causes CKD. Albuminuria is also a risk factor for cardiovascular disease. The age of onset of CKD is partly determined during fetal life. This review describes the mechanisms underlying the development of CKD in adult life that results from abnormal renal development caused by an adverse intrauterine environment. The basis of this form of CKD is thought to be mainly due to a reduction in the number of nephrons formed in utero which impacts on the age dependent decline in glomerular function. Factors that affect the risk of reduced nephron formation during intrauterine life are discussed and include maternal nutrition (malnutrition and obesity, micronutrients), smoking and alcohol, use of drugs that block the maternal renin-angiotensin system, glucocorticoid excess and maternal renal dysfunction and prematurity. Since CKD, hypertension and cardiovascular disease add to the disease burden in the community we recommend that kidney size at birth should be recorded using ultrasound and those individuals who are born premature or who have small kidneys at this time should be monitored regularly by determining GFR and albumin:creatinine clearance ratio. Furthermore, public health measures aimed at limiting the prevalence of obesity and diabetes mellitus as well as providing advice on limiting the amount of protein ingested during a single meal, because they are all associated with increased glomerular hyperfiltration and subsequent glomerulosclerosis would be beneficial.

Analysis of structure and gene expression in developing kidneys of male and female rats exposed to low protein diets in utero

A maternal low protein (LP) diet in rodents often results in low nephron endowment and renal pathophysiology in adult life, with outcomes often differing between male and female offspring. Precisely how a maternal LP diet results in low nephron endowment is unknown. We conducted morphological and molecular studies of branching morphogenesis and nephrogenesis to identify mechanisms and timepoints that might give rise to low nephron endowment. Sprague-Dawley rats were fed a normal protein (19.4% protein, NP) or LP (9% protein) diet for 3 weeks prior to mating and throughout gestation. Embryonic day 14.25 (E14.25) kidneys from males and females were either cultured for 2 days after which branching morphogenesis was quantified, or frozen for gene expression analysis. Real-time PCR was used to quantify expression of key nephrogenesis and branching morphogenesis genes at E14.25 and 17.25. At E17.25, nephron number was determined in fixed tissue. There was no effect of either maternal diet or sex on branching morphogenesis. Nephron number at E17.25 was 14% lower in male and female LP offspring than in NP controls. At E14.25 expression levels of genes involved in branching morphogenesis (Gfrα1, Bmp4, Gdnf) and nephrogenesis (Hnf4a, Pax2, Wnt4) were similar in the dietary groups, but significant differences between sexes were identified. At E17.25, expression of Gfrα1, Gdnf, Bmp4, Pax2 and Six2 was lower in LP offspring than NP offspring, in both male and female offspring. These findings provide new insights into how a LP diet leads to low nephron endowment and renal sexual dimorphism.

The core SWI/SNF catalytic subunit Brg1 regulates nephron progenitor cell proliferation and differentiation

Chromatin-remodeling complexes play critical roles in establishing gene expression patterns in response to developmental signals. How these epigenetic regulators determine the fate of progenitor cells during development of specific organs is not well understood. We found that genetic deletion of Brg1 (Smarca4), the core enzymatic protein in SWI/SNF, in nephron progenitor cells leads to severe renal hypoplasia. Nephron progenitor cells were depleted in Six2-Cre, Brg1^flx/flx mice due to reduced cell proliferation. This defect in self-renewal, together with impaired differentiation resulted in a profound nephron deficit in Brg1 mutant kidneys. Sall1, a transcription factor that is required for expansion and maintenance of nephron progenitors, associates with SWI/SNF. Brg1 and Sall1 bind promoters of many progenitor cell genes and regulate expression of key targets that promote their proliferation.

Low birth weight trends: possible impacts on the prevalences of hypertension and chronic kidney disease

Worldwide, hypertension and chronic kidney disease (CKD) are highly prevalent disorders and are strong risk factors for cardiovascular disease and end-stage renal disease (ESRD). The developmental origins of health and disease (DOHAD) concept suggests that undesirable perinatal environmental conditions, such as malnutrition, contribute to disease development in adults. Among the known hypertension and CKD risk factors, DOHAD plays a potential role in determining susceptibility to the onset of these diseases in later adulthood. Since low birth weight (LBW) is a surrogate marker for adverse fetal environmental conditions, the high incidence of LBW in developing countries and its increasing incidence in most developed countries (attributed to multiple pregnancies and prepregnancy maternal factors, such as undernutrition, advanced maternal age, and smoking) is concerning. Thus, LBW is an important public health problem not only because of the associated infant mortality and morbidity but also because it is a risk factor for adult-onset hypertension/CKD. During their reproductive years, pregnant women who were born with LBWs have an increased risk of hypertensive disorders of pregnancy, which contribute to the risk of developing cardiovascular disease and ESRD. The offspring of LBW females are also likely to be LBW, which suggests that susceptibility to hypertension/CKD may reflect transgenerational inheritance. Therefore, there is global concern about the increasing prevalence of LBW-related diseases. This review summarizes the relevance of hypertension and CKD in conjunction with DOHAD and discusses recent studies that have examined the impact of the upward LBW trend on renal function and blood pressure.

In-vivo techniques for determining nephron number

PURPOSE OF REVIEW

Many studies have suggested low nephron endowment at birth contributes to the risk of developing hypertension and chronic kidney disease (CKD) later in life. Loss of nephrons with age and disease is largely a subclinical process. New technologies are needed to count nephrons as glomerular filtration rate (GFR) is a poor surrogate for nephron number.

RECENT FINDINGS

Cortical volume, glomerular density, and percent globally sclerotic glomeruli are imperfect surrogates for nephron number. The disector-fractionator method is the most accurate method to count nephrons but is limited to autopsy settings. Glomerular density combined with kidney imaging and ultrafiltration coefficient-based methods require a kidney biopsy, and have been applied in living humans (kidney donors). Low nephron number predicts a higher postdonation urine albumin. Contrast-enhanced MRI has detected glomeruli without a biopsy, but so far, not in living humans.

SUMMARY

Currently, there is no accurate and well tolerated method for determining nephron number in living humans. A clinically useful method may allow GFR to be replaced by its more relevant determinants: nephron number and single nephron GFR. This could revolutionize nephrology by separating the measurement of chronic disease (nephron loss) from more reversible hemodynamic effects (nephron hyperfiltration/hypofiltration).

Acute kidney injury in Indigenous intensive care patients

BACKGROUND

Patients presenting to intensive care units (ICUs) report high rates of acute kidney injury (AKI) requiring renal replacement therapy (RRT). Globally, Indigenous populations report higher rates of renal disease than their non-Indigenous counterparts.

OBJECTIVES

This study reports the prevalence, presenting features, and outcomes of Indigenous ICU admissions with AKI (who require RRT) within an Australian ICU setting and compares these with those of Indigenous patients without AKI.

METHOD

A retrospective database review examined all Indigenous patients older than 18 years admitted to a regional Australian ICU between June 2013 and June 2016, excluding patients with chronic kidney disease requiring dialysis. We report patient demography, presenting clinical and physiological characteristics, ICU length of stay, hospital outcome, and renal requirements at three months after discharge, on Indigenous patients with AKI requiring RRT.

RESULTS

AKI requiring RRT was identified in 15.9% of ICU Indigenous patients. On univariate analysis, it was found that these patients were older and had a higher body mass index, lower urine output, and higher levels of creatinine and urea upon presentation than patients who did not have AKI. Patients with AKI reported longer ICU stays and a higher mortality rate (30%, p < 0.05), and 10% of these required ongoing RRT at 3 months. Multivariate analysis found significant associations with AKI were only found for presenting urine outputs, urea and creatinine levels.

CONCLUSIONS

This study reports higher rates of AKI requiring RRT for Indigenous adults than non-Indigenous adults, as has been previously published. Benefits arising from this study are as follows: these reported findings may initiate early targeted clinical management and can assist managing expectations, as some patients may require ongoing RRT after discharge.

Temporal Expression and Cellular Localization of PAPPA2 in the Developing Kidney of Rat

PAPPA2 is a metalloproteinase which cleaves insulin-like growth factor binding protein (IGFBP)-3 and IGFBP-5, and its role in pregnancy and postnatal growth is primarily studied. Using exclusion mapping, we reported a subcongenic (26-P) rat where a 0.71-Mbp region containing the pregnancy-associated plasma protein a2 (Pappa2) allele of salt-insensitive Brown Norway (BN) was introgressed into Dahl saltsensitive (SS) genetic background, resulting in the reduction of salt sensitivity. Pappa2 was differentially expressed in the adult kidney of 26-P and SS rats. Here, the expression and cellular localization of Pappa2 in embryonic and postnatal kidneys of 26-P and SS rats were examined. Pappa2 mRNA expression was 5-fold higher in the embryonic kidney (day 20.5) of the 26-P rat compared with the SS rat. Pappa2 mRNA expression progressively increased with the development of kidney, reaching a peak at postnatal day 5 before trending downward in subsequent stages of development in both strains. At all tested time points, Pappa2 remained higher in the 26-P compared with the SS rat kidney. Immunohistochemistry studies localized PAPPA2 in the ureteric bud (UB) and distal part of S-shaped body. PAPPA2 was colocalized with IGFBP-5 in the UB and Na⁺/K⁺/2Cl^- cotransporter-stained tubules, respectively. Future studies are needed to determine the role of Pappa2 in kidney development and mechanistic pathways involved in this process.

Moderate prenatal ethanol exposure in the rat promotes kidney cell apoptosis, nephron deficits, and sex-specific kidney dysfunction in adult offspring

Alcohol during pregnancy can impair fetal development and result in offspring with neurodevelopmental deficits. Less is known about how low to moderate alcohol exposure can affect other organs, such as the kidney. Here, the effects of moderate ethanol exposure throughout pregnancy on kidney development were examined using a rat model. Rats were fed a liquid diet containing 6% ethanol (vol/vol) or control (0% ethanol) throughout pregnancy. Kidneys were collected at embryonic day (E) 20 or postnatal day (PN) 30 and total glomerular (nephron) number determined using unbiased stereology. Kidney function was examined in offspring at 8 and 19 months. At E20, fetuses exposed to ethanol had fewer nephrons with increased apoptosis. Alcohol exposure caused kidney dysregulation of pro- (Bax) and anti- (Bcl-2) apoptotic factors, and reduced expression of the cell proliferation marker, Ki67. Prenatal alcohol decreased expression of Gdnf and Tgfb1, important regulators of branching morphogenesis, in male fetuses. At PN30, kidney volume and nephron number were lower in offspring exposed to prenatal alcohol. Urine flow and osmolality were normal in offspring exposed to alcohol however sodium excretion tended to be lower in females prenatally exposed to alcohol. Findings suggest exposure to moderate levels of alcohol during pregnancy results in impaired kidney development and leads to a permanent nephron deficit. Although the impact on adult kidney function was relatively minor, these data highlight that even at moderate levels, alcohol consumption during pregnancy can have deleterious long-term outcomes and should be avoided.

Human nephron number, hypertension, and renal pathology

Recent studies have reported that total nephron number varies widely in human kidneys and some racial groups with low nephron number have a higher incidence of hypertension and kidney disease. Importantly, nephrogenesis normally reaches completion at about 34-36 weeks gestation, with no new nephrons formed for the lifetime in humans after this time. Although the loss of glomeruli varies among individuals due to aging, blood pressure, or additional inducers of kidney injury, much of the variation in nephron number is nowadays thought to be present at birth. According to the hyperfiltration hypothesis, this subsequent nephron loss results in compensatory hyperfiltration and/or hypertension of remaining glomeruli, thereby contributing to increased susceptibility to systemic hypertension. However, recent studies have suggested that the association between a low nephron number and systemic hypertension is not a universal finding. In most studies to date, nephron counts were performed on kidneys obtained at autopsy. Several recent studies have attempted to estimate nephron number in living human subjects, but further work is required to obtain accurate and precise estimates of nephron number using these noninvasive methods. Longitudinal studies in living humans have the potential to reveal associations between nephron number and hypertension/renal pathology.

Renal dysfunction is already evident within the first month of life in Australian Indigenous infants born preterm

Antecedents of the high rates of chronic kidney disease in Australian Indigenous peoples may originate early in life. Fourteen percent of Australian Indigenous infants are born preterm (under 37 weeks gestation) and, therefore, at risk. Here, our observational cohort study sought to determine the impact of preterm birth on renal function in Australian Indigenous and non-Indigenous infants. Renal function was assessed between 4-29 days postnatally in 60 Indigenous and 42 non-Indigenous infants born at 24-36 weeks gestation. Indigenous ethnicity was associated with impaired renal function, with significantly higher serum creatinine (geometric mean ratio (GMR) 1.15 [1.06, 1.25]), fractional excretion of sodium (GMR 1.21 [1.04, 1.39]), and urine albumin (GMR 1.57 [1.05, 2.34]), β-2 microglobulin (GMR 1.82 [1.11, 2.98]) and cystatin C (GMR 3.27 [1.54, 6.95]) when controlling for gestational/postnatal age, sex and birth weight Z-score. Renal injury, as indicated by high urine neutrophil gelatinase-associated lipocalin levels, was associated with maternal smoking and postnatal antibiotic exposure. Indigenous infants appeared to be most susceptible to the adverse impact of antibiotics. These findings show that preterm Australian Indigenous infants are highly vulnerable to renal dysfunction. Preterm birth may contribute to their increased risk of chronic kidney disease. Thus, we recommended that renal function should be closely monitored life-long in Indigenous children born preterm.

Progressive Nephron Loss in Aging Kidneys: Clinical–Structural Associations Investigated by Two Anatomical Methods

Two major studies of structural changes associated with aging in human kidneys are reviewed and new information presented. The studies are the Monash University stereologically analyzed series of 319 autopsy kidneys from the United States in which 44% were white and the Mayo Clinic CT angiogram/biopsy analysis of 1,388 US kidney donors in which 97% were white. Hypertension rates in the Monash series were 48% and included moderate and severe hypertension. In the Mayo Clinic study, 12% had mild hypertension. The studies showed no relationship between glomerular number and hypertension except for a weak relationship with older white women in the Monash series. An inverse relationship was present between glomerular number and glomerular volume, a reciprocity that tended to enhance glomerular mass and by inference filtration capacity with lower nephron numbers. This relationship seemed to be present whether low nephron numbers were intrinsic or acquired. In the Mayo Clinic studies, pretransplant iothalamate clearances demonstrated that single nephron (SN) glomerular filtration rates (GFR) were similar throughout the range of glomerular number in subjects younger than 70 years, but that increased SNGFR correlated with nephron hypertrophy and increased nephrosclerosis particularly at 70 years of age and over. Hypertension at least through middle age cannot be related to a deficiency of glomeruli, but glomeruli are lost with later aging in association with adaptive nephron hypertrophy that can maintain GFR near normal. These studies help define an age‐related nephropathy that overlaps with hypertension as a potential cause of end‐stage renal disease when glomerulosclerosis is advanced.

Estimation of nephron number in living humans by combining unenhanced computed tomography with biopsy-based stereology

Methods for estimating nephron number in a clinical setting may be useful for predicting renal outcomes. This study aimed to establish such a method using unenhanced computed tomography (CT) and biopsy-based stereology. Patients or living kidney donors simultaneously subjected to enhanced and unenhanced CT examinations were randomly assigned to development and validation groups. The enhanced CT-measured arterial phase and the venous phase images of kidneys were regarded as the true values for cortical volume and parenchymal volume, respectively. Linear multiple regression analysis was used to create models for estimating cortical volume using explanatory variables including unenhanced CT-measured parenchymal volume. Nephron number was determined as the product of cortical volume and the glomerular density in biopsies of donors. Five equations for estimating cortical volume were created and verified. In donors, estimated nephron number by unenhanced CT was consistent with that by enhanced CT, with minimal errors in all models (636–655 ± 210–219 vs. 648 ± 224 × 10³/kidney). Clinical characteristics combined with parenchymal volume did not improve the equation over parenchymal volume alone. These results support the feasibility of estimating nephron number by a combination of unenhanced CT and biopsy-based stereology, with a possible application for renal disease patients who are often not suitable for contrast media.

Clinical consequences of developmental programming of low nephron number

Nephron number in humans varies up to 13-fold, likely reflecting the impact of multiple factors on kidney development, including inherited body size and ethnicity, as well as maternal health and nutrition, fetal exposure to gestational diabetes or preeclampsia and other environmental factors, which may potentially be modifiable. Such conditions predispose to low or high offspring birth weight, growth restriction or preterm birth, which have all been associated with increased risks of higher blood pressures and/or kidney dysfunction in later life. Low birth weight, preterm birth, and intrauterine growth restriction are associated with reduced nephron numbers. Humans with hypertension and chronic kidney disease tend to have fewer nephrons than their counterparts with normal blood pressures or kidney function. A developmentally programmed reduction in nephron number therefore enhances an individual's susceptibility to hypertension and kidney disease in later life. A low nephron number at birth may not lead to kidney dysfunction alone except when severe, but in the face of superimposed acute or chronic kidney injury, a kidney endowed with fewer nephrons may be less able to adapt, and overt kidney disease may develop. Given that millions of babies are born either too small, too big or too soon each year, the population impact of altered renal programming is likely to be significant. Many gestational exposures are modifiable, therefore urgent attention is required to implement public health measures to optimize maternal, fetal, and child health, to prevent or mitigate the consequences of developmental programming, to improve the health future generations.

The relationship between maternal adiposity during pregnancy and fetal kidney development and kidney function in infants: the Gomeroi gaaynggal study

Maternal obesity during pregnancy has a detrimental impact on offspring renal development and function. This is pertinent to Indigenous Australians as they are twice as likely as non-Indigenous Australians to develop chronic kidney disease (CKD). The aim of this study was to examine whether there was an association between maternal adiposity and fetal kidney growth in late gestation (>28 weeks) and kidney function in infants, <2.5 years of age, from the Gomeroi gaaynggal cohort. Pre-pregnancy body mass index (BMI) was recorded at the first prenatal visit and maternal adiposity indicators (percent body fat and visceral fat area) measured at >28 weeks gestation by bioelectrical impedance analysis. Fetal kidney structure was assessed by ultrasound. Renal function indicators (urinary albumin:creatinine and protein:creatinine) were measured in infants from a spot urine collection from nappies. Multiple linear regression and multi-level mixed effects linear regression models with clustering were used to account for repeated measures of urine. 147 mother-child pairs were examined. Estimated fetal weight (EFW), but not fetal kidney size, was positively associated with maternal adiposity and pre-pregnancy BMI. When adjusted for smoking, combined kidney volume relative to EFW was negatively associated with maternal percentage body fat. Infant kidney function was not influenced by maternal adiposity and pre-pregnancy BMI (n = 84 observations). Current findings show that Indigenous babies born to obese mothers have reduced kidney size relative to EFW. We suggest that these babies are experiencing a degree of glomerular hyperfiltration in utero, and therefore are at risk of developing CKD in later life, especially if their propensity for obesity is maintained. Although no impact on renal function was observed at <2.5 years of age, long-term follow-up of offspring is required to evaluate potential later life impacts.

Female preterm indigenous Australian infants have lower renal volumes than males: A predisposing factor for end-stage renal disease?

AIM

Indigenous Australians have an increased risk of developing chronic kidney disease (CKD). Indigenous women have a higher rate of CKD than men. In a cohort of Indigenous and non-Indigenous preterm neonates, we assessed total renal volume (TRV) (a proxy indicator for nephron number). We hypothesized that there would be no difference in renal volume between these two groups at term corrected (37 weeks gestation).

METHODS

Normally grown preterm neonates less than 32 weeks of gestation were recruited and at term corrected dates, the neonates underwent renal ultrasonography (TRV measurements), urine microalbumin-creatinine ratio and serum analysis for Cystatin C measurement for estimated glomerular filtration rate (eGFR) calculation.

RESULTS

One hundred and five neonates (38 Indigenous; 67 non-Indigenous) were recruited. Indigenous neonates were significantly more premature and of lower birth weight. At term corrected age, Indigenous neonates had a significantly smaller TRV (18.5 (4.2) vs 21.4 (5.1) cm3 ; P = 0.027) despite no significant difference in body weight. Despite having a smaller TRV, there was no significant difference in eGFR between Indigenous and Non-indigenous neonates (47.8 [43.2-50.4] vs 46.2 [42.6-53.3] ml/min per 1.73 m2 ; P = 0.986). These infants achieve similar eGFR through hyperfiltration, which likely increases their future risk of CKD. There was no difference in microalbumin-creatinine ratio. Female Indigenous neonates, however, had significantly smaller TRV compared with Indigenous male neonates (15.9 (3.6) vs 20.6 (3.6) cm3 ; P = 0.006), despite no difference in eGFR, birth weight, gestational age, and weight at term corrected.

CONCLUSION

The difference in TRV is likely to be an important risk factor for the difference in morbidity and mortality from renal disease reported between male and female Indigenous adults.

Low Birth Weight, Blood Pressure and Renal Susceptibility

PURPOSE OF THE REVIEW

The purpose of this review is to highlight the clinical significance of increased renal risk that has its origins in fetal life. This review will also discuss the critical need to identify therapeutic interventions for use in a pregnancy complicated by placental dysfunction and intrauterine growth restriction that can mitigate the developmental origins of kidney disease without inflicting additional harm on the developing fetus.

RECENT FINDINGS

A reduction in nephron number is a contributory factor in the pathogenesis of hypertension and kidney disease in low birth weight individuals. Reduced nephron number may heighten susceptibility to a secondary renal insult, and recent studies suggest that perinatal history including birth weight should be considered in the assessment of renal risk in kidney donors. This review highlights current findings related to placental dysfunction, intrauterine growth restriction, increased risk for renal injury and disease, and potential therapeutic interventions.

Growing a new human kidney

There are 3 reasons to generate a new human kidney. The first is to learn more about the biology of the developing and mature organ. The second is to generate tissues with which to model congenital and acquired kidney diseases. In particular, growing human kidneys in this manner ultimately should help us understand the mechanisms of common chronic kidney diseases such as diabetic nephropathy and others featuring fibrosis, as well as nephrotoxicity. The third reason is to provide functional kidney tissues that can be used directly in regenerative medicine therapies. The second and third reasons to grow new human kidneys are especially compelling given the millions of persons worldwide whose lives depend on a functioning kidney transplant or long-term dialysis, as well as those with end-stage renal disease who die prematurely because they are unable to access these treatments. As shown in this review, the aim to create healthy human kidney tissues has been partially realized. Moreover, the technology shows promise in terms of modeling genetic disease. In contrast, barely the first steps have been taken toward modeling nongenetic chronic kidney diseases or using newly grown human kidney tissue for regenerative medicine therapies.

Cat Kidney Glomeruli and Tubules Evaluated by Design-Based Stereology

Renal function is related to its structure and three-dimensional structural parameters correlate better with the kidney function than two-dimensional structural parameters. Stereology is the current gold-standard technique for the morphometrical evaluation of kidney structures. This study describes morphometric features of the kidney of the cat using design-based stereological techniques aimed to introduce the cat as a translational model in nephrology and provide basic findings for diagnosis and treatment of kidney diseases in this species. Left kidneys of four cats were included in the present study. The kidney volume, volume fraction of cortex and medulla, glomerular volume, glomerular mean volume, glomerular number, and proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) length were estimated. The kidney volume was estimated to 11.4 ± 1.3 cm³ . The volume fraction of cortex and medulla was 65.6 ± 2% and 34.2 ± 2%, respectively. The total number of glomeruli was estimated to be 186 ± 11 × 10³ using the physical disector/fractionator method. The mean glomerular volume was estimated to be 1.54 ± 0.06 × 10⁶ μm³ and the glomerular volume was covering 2.13 ± 0.34% of the whole kidney. The total length of PCT and DCT was estimated to be 2.26 ± 0.48 km and 505 ± 43 m, respectively. Our data might contribute to the knowledge of kidneys in mammals and provide a comparison with available data on human and other mammals. Anat Rec, 302:1846-1854, 2019. © 2019 American Association for Anatomy.