Nephron hypertrophy and glomerulosclerosis and their association with kidney function and risk factors among living kidney donors

Evaluation of self-monitoring of blood pressure in the PERHIT study and the impact on glomerular function

BACKGROUND

Although intensive blood pressure (BP) control has not been shown to slow the progression of chronic kidney disease (CKD), intensive BP control has been shown to reduce the risk for adverse cardiovascular outcomes in the CKD population. The aim of this post-hoc study was to study the interplay between a self-monitoring BP system and glomerular function.

METHODS

In all, 949 participants with hypertension underwent visits at baseline, after eight weeks and 12 months. Half of the participants received a BP monitor and installed a program on their mobile phone. During eight weeks, they measured daily and reported their BP values.

RESULTS

Within the intervention group, BP and systolic BP (SBP) decreased from baseline to eight weeks and 12 months (p < .001). Pulse pressure (PP) and mean arterial blood pressure (MAP) decreased from baseline to eight weeks (p = .021 and p = .004) vs 12 months (p = .035 and p = .008). Within the control group, a decrease was observed from baseline to 12 months for SBP, diastolic BP (DBP) and PP (p = .025, p = .023 and p = .036). In the intervention group, we observed an association between a decrease in SBP, DBP, PP and MAP and a decrease in eGFR (estimated glomerular filtration rate), (p < .001, p < .001, p = .013 and p < .001). In the control group, similar results were observed for PP only (p = .027). Within the intervention group, eGFR decreased (p < .001) but within the control group, the decrease was non-significant (p = .051).

CONCLUSION

We observed an association between a decrease in all BP components and eGFR decline within the normal range in the intervention group but not in the controls.

TRIAL REGISTRATION

The study was registered with ClinicalTrials.gov [NCT03554382].

SGLT2 inhibition to target kidney aging

Anti-aging therapy is the latest frontier in the world of medical science, especially for widespread diseases such as chronic kidney disease (CKD). Both renal aging and CKD are characterized by increased cellular senescence, inflammation and oxidative stress. A variety of cellular signalling mechanisms are involved in these processes, which provide new potential targets for therapeutic strategies aimed at counteracting the onset and progression of CKD. At the same time, sodium-glucose co-transporter 2 inhibitors (SGLT2is) continuously demonstrate large beneficial effects at all stages of the cardiorenal metabolic continuum. The broad-spectrum benefits of SGLT2is have led to changes in several treatment guidelines and to growing scientific interest in the underlying working principles. Multiple mechanisms have been studied to explain these great renal benefits, but many things remain to be solved. With this in mind, we provide an overview of the experimental evidence for the effects of SGLT2is on the molecular pathway's ability to modulate senescence, aging and parenchymal damage, especially at the kidney level. We propose to shed some light on the role of SGLT2is in kidney care by focusing on their potential to reduce the progression of kidney disease across the spectrum of aging and dysregulation of senescence.

Urine albumin-to-creatinine ratio diurnal variation rate predicts outcomes in idiopathic membranous nephropathy

BACKGROUND

Idiopathic membranous nephropathy (IMN) is a leading cause of end-stage renal disease (ESRD). The purpose of this study was to evaluate whether urinary albumin-to-creatinine ratio (UACR) diurnal variation rate calculated by spot urinary protein test predicts 1-year nephrotic outcomes as a biomarker of proteinuria severity in patients with IMN.

METHODS

Patients' baseline demographics, blood and urinary biomarkers, and clinical and pathological characteristics were collected retrospectively. Urine samples were collected at 7:00 (before breakfast) and 19:00 (after dinner) to calculate the UACR diurnal variation rate. A prediction model for no remission (NR) was developed statistically based on differences between prognosis groups. Receiver operating characteristic curve (ROC) analysis was performed to evaluate prediction abilities and determine optimal cut-off points of the model and UACR diurnal variation rate alone.

RESULTS

The formula for calculating the probability of NR was exp(L)/(1 + exp(L)), where the linear predictor L =  - 22.038 + 0.134 × Age (years) + 0.457 × 24-h urinary protein + 0.511 × blood urea nitrogen (BUN) + 0.014 × serum uric acid (SUA) + 2.411 if glomerular sclerosis + 0.816 × fasting blood glucose (FBG)-0.039 × UACR diurnal variation rate (%). Optimal cut-off points for NR prediction by the final model and UACR diurnal variation rate alone were 0.331 and 58.5%, respectively. Sensitivity and specificity were 0.889 and 0.859 for the final model, and 0.926 and 0.676 for UACR diurnal variation rate alone.

CONCLUSION

UACR diurnal variation using spot urinary protein is a simpler way to predict nephrotic outcomes and is a highly sensitive screening tool for identifying patients who should undergo further comprehensive risk assessment.

Association of Implantation Biopsy Findings in Living Donor Kidneys With Donor and Recipient Outcomes

RATIONALE & OBJECTIVE

Some living donor kidneys are found to have biopsy evidence of chronic scarring and/or glomerular disease at implantation, but it is unclear if these biopsy findings help predict donor kidney recovery or allograft outcomes. Our objective was to identify the prevalence of chronic histological changes and glomerular disease in donor kidneys, and their association with donor and recipient outcomes.

STUDY DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

Single center, living donor kidney transplants from January 2010 to July 2022.

EXPOSURE

Chronic histological changes, glomerular disease in donor kidney implantation biopsies.

OUTCOME

For donors, single-kidney estimated glomerular filtration rate (eGFR) increase, percent total eGFR loss, ≥40% eGFR decline from predonation baseline, and eGFR<60mL/min/1.73m2 at 6 months after donation; for recipients, death-censored allograft survival.

ANALYTICAL APPROACH

Biopsies were classified as having possible glomerular disease by pathologist diagnosis or chronic changes based on the percentage of glomerulosclerosis, interstitial fibrosis/tubular atrophy, and vascular disease. We used logistic regression to identify factors associated with the presence of chronic changes, linear regression to identify the association between chronic changes and single-kidney estimated glomerular filtration rate (eGFR) recovery, and time-to-event analyses to identify the relationship between abnormal biopsy findings and allograft outcomes.

RESULTS

Among 1,104 living donor kidneys, 155 (14%) had advanced chronic changes on implantation biopsy, and 12 (1%) had findings suggestive of possible donor glomerular disease. Adjusted logistic regression showed that age (odds ratio [OR], 2.44 per 10 years [95% CI, 1.98-3.01), Hispanic ethnicity (OR, 1.87 [95% CI, 1.15-3.05), and hypertension (OR, 1.92 [95% CI, 1.01-3.64), were associated with higher odds of chronic changes on implantation biopsy. Adjusted linear regression showed no association of advanced chronic changes with single-kidney eGFR increase or relative risk of eGFR<60mL/min/1.73m2. There were no differences in time-to-death-censored allograft failure in unadjusted or adjusted Cox proportional hazards models when comparing kidneys with chronic changes to kidneys without histological abnormalities.

LIMITATIONS

Retrospective, absence of measured GFR.

CONCLUSIONS

Approximately 1 in 7 living donor kidneys had chronic changes on implantation biopsy, primarily in the form of moderate vascular disease, and 1% had possible donor glomerular disease. Abnormal implantation biopsy findings were not significantly associated with 6-month donor eGFR outcomes or allograft survival.

PLAIN-LANGUAGE SUMMARY

Kidney biopsies are the gold standard test to identify the presence or absence of kidney disease. However, kidneys donated by healthy living donors-who are extensively screened for any evidence of kidney disease before donation-occasionally show findings that might be considered "abnormal," including the presence of scarring in the kidney or findings suggestive of a primary kidney disease. We studied the frequency of abnormal kidney biopsy findings among living donors at our center. We found that about 14% of kidneys had chronic abnormalities and 1% had findings suggesting possible glomerular kidney disease, but the presence of abnormal biopsy findings was not associated with worse outcomes for the donors or their recipients.

Kidney function assessment in the geriatric population

PURPOSE OF REVIEW

Kidney function declines with normal aging. But it also declines with the progression of some diseases. This review calls for a more nuanced interpretation of kidney function in the geriatric population, who may have frailty and comorbidities.

RECENT FINDINGS

GFR declines with healthy aging kidneys. Aging kidney changes include decreased cortical volume, senescent global glomerulosclerosis, and reduced nephron numbers. Yet normal aging is not associated with increased glomerular volume or single-nephron GFR. The prevalence of GFR less than 60 ml/min/1.73 m 2 in the geriatric population is high. However, the decline in GFR with normal aging may not reflect true CKD without albuminuria. Although the risk of ESKD and mortality increases in all age groups when eGFR less than 45 ml/min/m 2 , there is no significant increased relative risk of ESKD and mortality in the geriatric population when eGFR 45-59 ml/min/m 2 in the absence of albuminuria. Innovative approaches are needed to better estimate GFR and define CKD in the geriatric population.

SUMMARY

The expected GFR decline in the geriatric population is consistent with normal aging kidney changes. To avoid CKD overdiagnosis and unnecessary referrals to nephrology for possible CKD, age-adapted definitions of CKD in the absence of albuminuria are needed.

Why is chronic kidney disease progressive? Evolutionary adaptations and maladaptations

Despite significant advances in renal physiology, the global prevalence of chronic kidney disease (CKD) continues to increase. The emergence of multicellular organisms gave rise to increasing complexity of life resulting in trade-offs reflecting ancestral adaptations to changing environments. Three evolutionary traits shape CKD over the lifespan: 1) variation in nephron number at birth, 2) progressive nephron loss with aging, and 3) adaptive kidney growth in response to decreased nephron number. Although providing plasticity in adaptation to changing environments, the cell cycle must function within constraints dictated by available energy. Prioritized allocation of energy available through the placenta can restrict fetal nephrogenesis, a risk factor for CKD. Moreover, nephron loss with aging is a consequence of cell senescence, a pathway accelerated by adaptive nephron hypertrophy that maintains metabolic homeostasis at the expense of increased vulnerability to stressors. Driven by reproductive fitness, natural selection operates in early life but diminishes thereafter, leading to an exponential increase in CKD with aging, a product of antagonistic pleiotropy. A deeper understanding of the evolutionary constraints on the cell cycle may lead to manipulation of the balance between progenitor cell renewal and differentiation, regulation of cell senescence, and modulation of the balance between cell proliferation and hypertrophy. Application of an evolutionary perspective may enhance understanding of adaptation and maladaptation by nephrons in the progression of CKD, leading to new therapeutic advances.

Spatial Heterogeneity of Glomerular Phenotypes Affects Kidney Biopsy Findings

Key Points

Glomeruli with pathologic changes are not homogeneously distributed throughout the kidney cortex. Biopsies that do not include the kidney capsule may underdetect glomeruli with pathologic changes. Location of glomeruli with pathologic changes may be related to underlying clinical characteristics.

Background

Detection of rare glomerular phenotypes can affect diagnosis in indication kidney biopsies and in kidney tissue used for research studies. Nephropathologists are aware of potential sampling error when assessing needle biopsy cores, but quantitative data are lacking.

Methods

Kidney tissue from patients undergoing total nephrectomy enrolled in an observational, cross-sectional cohort study was used to characterize glomeruli as typical or atypical, which included globally sclerotic glomeruli (GSGs), segmentally sclerotic glomeruli, ischemic-like, and imploding. A 2D map of the glomerular annotations was generated. Spatial centrality of atypical glomeruli using the L2 metric and differences in pairwise distances between typical or atypical glomeruli were calculated. To determine how the yield of capturing atypical glomerular phenotype was affected by biopsy depth (i.e. , not including the renal capsule), simulated kidney biopsies were generated from the 2D map.

Results

The mean number of glomeruli in a nephrectomy specimen was 209 (SD 143), and GSGs were the most common type of atypical glomeruli (median: 13% [interquartile range: 5,31]). Typical glomeruli were more likely to be surrounded by other glomeruli (i.e. , centrally located in the kidney cortex) than GSGs, segmentally sclerosed glomeruli, ischemic-like glomeruli, and imploding glomeruli. Atypical glomeruli were 7.3% (95% confidence interval, 4.1 to 10.4) closer together than typical glomeruli and were more likely to be closer together in older patients or those with hypertension. In simulated kidney biopsies, failure to capture the capsule was associated with underdetection of GSGs, ischemic-like glomeruli, and imploding glomeruli.

Conclusions

Spatial analysis of large sections of kidney tissue provided quantitative evidence of spatial heterogeneity of glomerular phenotypes including clustering of atypical glomeruli in individuals with hypertension or older age. Most importantly, deep kidney biopsies that lack subcapsular area underdetect atypical glomerular phenotypes, suggesting that capturing the renal capsule is an important quality control measure for kidney biopsies.

Living Donors' Age Modifies the Impact of Pre-Donation Estimated Glomerular Filtration Rate on Graft Survival

BACKGROUND

The global scarcity of organs for kidney transplants (KTs) has led to the increased acceptance of living donors (LDs) with minor abnormalities to increase the donor pool.. We sought to evaluate the effects of some of these LDs' clinical characteristics (older age, borderline renal function, hypertension, dyslipidemia, smoking, and obesity) on graft outcomes.

METHODS

We studied 352 recipients of LDKTs (1998-2020). Firstly, considering the recipients and KT variables, we identified relevant predictors of overall and censored graft failure (GF). Then, adjusting for these predictors, we explored LD variables as predictors of overall and censored GF in a multivariable Cox model.

RESULTS

The recipients from LD with higher eGFR (≥90 mL/min/1.73 m2) had significantly better overall and censored graft survival GS) at 15 y after KT (respectively, 67 and 75% vs. 46 and 46%, p < 0.001). Importantly, none of the remaining LD factors which were evaluated (hypertension, dyslipidemia, smoking, proteinuria, and obesity) were independent predictors of GF. In recipients from LDs < 50 y, having an eGFR < 90 was an independent predictor of overall GF [adjusted HR (95%CI) of 2.578 (1.120-5.795)] and censored GF [adjusted HR (95%CI) of 3.216 (1.300-7.959)], compared to recipients from LDs with eGFR ≥ 90. Contrarily, when donors were older, no difference in the risk of GF was observed between eGFR categories.

CONCLUSION

In our cohort, lower pre-donation eGFR had an impact on GS only in younger LDs. An age-adjusted eGFR cutoff may be pursued for improved donor admissibility.

The relationship of peritubular capillary density with glomerular volume and kidney function in living kidney donors

BACKGROUND

Peritubular capillary rarefaction plays an important role in the progression of chronic kidney disease. Little is known about the relation between peritubular capillary density, glomerular volume and filtration rate in the healthy kidney.

METHODS

In this single-center study, we included 69 living kidney donors who donated between 2005 and 2008 and had representative renal biopsies available. In all donors, glomerular filtration rate was measured using 125I-Iothalamate before donation and at five years after donation. Before donation, the increase in glomerular filtration rate after dopamine stimulation was measured. Glomerular volume and peritubular capillary density were determined in biopsies taken at the time of transplantation. Pearson's correlation coefficient and linear regression were used to assess relations between parameters.

RESULTS

Mean donor age was 52 ± 11 years and mean measured glomerular filtration rate was 119 ± 22 mL/min before donation and 82 ± 15 mL/min at five years after donation. While peritubular capillary density (measured by either number of peritubular capillaries/50,000 μm2 or number of peritubular capillaries/tubule) was not associated with measured glomerular filtration rate before or after donation, number of peritubular capillaries/tubule was associated with the increase in measured glomerular filtration rate after dopamine stimulation (St.β = 0.33, p = 0.004), and correlated positively with glomerular volume (R = 0.24, p = 0.047). Glomerular volume was associated with unstimulated measured glomerular filtration rate before donation (St.β = 0.31, p = 0.01) and at five years (St.β = 0.30, p = 0.01) after donation, independent of age.

CONCLUSIONS

In summary, peritubular capillary density was not related to unstimulated kidney function before or after kidney donation, in contrast to glomerular volume. However, number of peritubular capillaries/tubule correlated with the increase in glomerular filtration rate after dopamine stimulation in healthy kidneys, and with glomerular volume. These findings suggest that peritubular capillary density and glomerular volume differentially affect kidney function in healthy living kidney donors.

Tubular and Glomerular Size by Cortex Depth as Predictor of Progressive CKD after Radical Nephrectomy for Tumor

SIGNIFICANCE STATEMENT

Glomerular size differs by cortex depth. Larger nephrons are prognostic of progressive kidney disease, but it is unknown whether this risk differs by cortex depth or by glomeruli versus proximal or distal tubule size. We studied the average minor axis diameter in oval proximal and distal tubules separately and by cortex depth in patients who had radical nephrectomy to remove a tumor from 2019 to 2020. In adjusted analyses, larger glomerular volume in the middle and deep cortex predicted progressive kidney disease. Wider proximal tubular diameter did not predict progressive kidney disease independent of glomerular volume. Wider distal tubular diameter showed a gradient of strength of prediction of progressive kidney disease in the more superficial cortex than in the deep cortex.

BACKGROUND

Larger nephrons are prognostic of progressive kidney disease, but whether this risk differs by nephron segments or by depth in the cortex is unclear.

METHODS

We studied patients who underwent radical nephrectomy for a tumor between 2000 and 2019. Large wedge kidney sections were scanned into digital images. We estimated the diameters of proximal and distal tubules by the minor axis of oval tubular profiles and estimated glomerular volume with the Weibel-Gomez stereological model. Analyses were performed separately in the superficial, middle, and deep cortex. Cox proportional hazard models assessed the risk of progressive CKD (dialysis, kidney transplantation, sustained eGFR <10 ml/min per 1.73 m 2 , or a sustained 40% decline from the postnephrectomy baseline eGFR) with glomerular volume or tubule diameters. At each cortical depth, models were unadjusted, adjusted for glomerular volume or tubular diameter, and further adjusted for clinical characteristics (age, sex, body mass index, hypertension, diabetes, postnephrectomy baseline eGFR, and proteinuria).

RESULTS

Among 1367 patients were 62 progressive CKD events during a median follow-up of 4.5 years. Glomerular volume predicted CKD outcomes at all depths, but only in the middle and deep cortex after adjusted analyses. Proximal tubular diameter also predicted progressive CKD at any depth but not after adjusted analyses. Distal tubular diameter showed a gradient of more strongly predicting progressive CKD in the superficial than deep cortex, even in adjusted analysis.

CONCLUSIONS

Larger glomeruli are independent predictors of progressive CKD in the deeper cortex, whereas in the superficial cortex, wider distal tubular diameters are an independent predictor of progressive CKD.

Sex differences in long-term kidney fibrosis following neonatal nephron loss during ongoing nephrogenesis

BACKGROUND

Clinical studies suggest that female sex plays a protective role in the development and progression of kidney disease. Recent experimental studies indicate that in male rats early nephron loss under ongoing nephrogenesis is accompanied by severe long-term sequelae. In humans, nephron formation occurs mainly in the third trimester, ceasing with 36 weeks of gestation. Due to perinatal complications, preterm infants delivered during this vulnerable period may undergo acute nephron loss. In rats nephrogenesis persists until postnatal day 10, reflecting the situation of human preterms with persisting nephrogenesis. In our animal model of neonatal uninephrectomy, female and male rats were uninephrectomized at day 1 of life. Hypothesizing sex-dependent differences, long-term renal outcome was assessed after 1 year.

RESULTS

In both sexes, neonatal uninephrectomy was not followed by arterial hypertension at 1 year of age. Compensatory weight gain and glomerular hypertrophy of the remaining kidney occurred in uninephrectomized female and male animals. Selected markers of interstitial inflammation and fibrosis were regulated sex-dependently. The expression of monocyte chemoattractant protein-1 was increased in females, while tubulointerstitial infiltration by M1 macrophages was significantly higher in males after neonatal uninephrectomy. Neonatally uninephrectomized male rats had more glomerulosclerosis and podocyte damage compared to females, which was assessed by a semiquantitative score and desmin staining. RT-PCR revealed that after neonatal uninephrectomy in the remaining contralateral kidney of female rats the expression of candidate genes of renal development and function, i.e., wt-1, nephrin, synaptopodin, gdnf, and itga8 was higher than in males.

CONCLUSIONS

Based on these observations we conclude that female sex is protective in the long-term response of the kidney to acute nephron loss under active nephrogenesis.

Pathological and clinical characteristics of late-onset oligomeganephronia based on a histomorphometric study

BACKGROUND

Late-onset oligomeganephronia (OMN) is a rare chronic kidney disease and has no quantitative criteria for diagnosis yet. The current study aimed to explore its clinicopathological features by histomorphometric analysis.

METHODS

We retrospectively re-reviewed all patients with enlarged and sparse glomeruli by light microscopy at Peking University First Hospital from 2012 to 2021, excluding those with any factor known to contribute to similar changes. Age- and sex-matched patients with thin basement membrane nephropathy were selected as control to establish the cut-off values for glomerulomegaly and rarity. Late-onset OMN cases were then confirmed and the clinicopathological characteristics were summarized.

RESULTS

Mean diameter and density of cortical glomeruli in control was 156.53 ± 27.50 μm and 4.07 ± 0.63 /mm², giving a lower limit of 211.53 μm for glomerulomegaly and an upper of 2.81 /mm² for rarity. Seven adults of three females and four males were finally diagnosed as late-onset OMN with a mean age of 26.57 years. They showed mild to moderate proteinuria and/or renal dysfunction at biopsy with the mean proteinuria, serum creatinine (Scr) level, and estimated glomerular filtration rate of 0.50 g/d (0.10-0.95 g/d), 140.9 µmol/L (95.1-227.1 µmol/L), and 58.7 mL/min/1.73m² (21.3-98.0 mL/min/1.73m²), respectively. Four patients (57.1%) had normal Scr at diagnosis. Six patients with available data showed renal tubular injury with increased urinary microalbumin in all, elevated N-acetyl-β-glucosaminidase in two, and elevated α1 microglobulin in five. Kidney size was normal or slightly reduced. The mean density and glomerular diameter of the seven cases was 0.86 mm² (0.55-1.41 /mm²) and 229.73 μm (211.88-260.66 μm). Segmental glomerular sclerosis was observed in six (85.7%) with four (66.7%) of perihilar type. Proximal tubule dilation was observed in all, focal to diffuse, lining with enlarged epithelial cells. The mean foot process width was 634.02 nm, wider than 472.54 nm of the control (P = 0.0002).

CONCLUSION

Late-onset OMN should be considered a special entity with relatively slow clinical progress characterized by hypertrophy of the sparsely distributed nephron.

Prediction of Renal Function in Living Kidney Donors and Recipients of Living Donor Kidneys Using Quantitative Histology

BACKGROUND

Living kidney donors (LKDs) are at increased risk of chronic kidney disease, whereas transplant recipients experience progressive reduction of graft function. We examined the predictive value of quantitative stereology on renal function in LKDs and recipients of living donor kidneys, based on perioperative biopsies from the donated kidney.

METHODS

Cortex volume of both donor kidneys was determined by contrast-enhanced computed tomography and single-kidney glomerular filtration rate (GFR) by 51 chrome-EDTA clearance together with renography. Glomerular density was used to estimate total glomeruli number in addition to glomerular volume, glomerular sclerosis, kidney fibrosis, and arteriole dimensions. GFR measurements were repeated 1 y after transplantation in both LKDs and recipients. Associations between GFR at follow-up and cortex volume and histomorphometric parameters after adjustment of age, gender, body mass index, smoking status, 24-h blood pressure, and single-kidney GFR were examined.

RESULTS

We included 49 LKDs (age, 51 ± 12 y) and 51 recipients (age, 44 ± 13 y). At follow-up, GFR was 71 ± 16 mL/min in LKDs and 61 ± 18 mL/min in recipients with hyperfiltration being more prominent in LKDs (30.4%) as compared to recipients (16.4%; P < 0.05). One-year GFR in donors correlated to cortex volume ( P < 0.001) but not to any histological parameters, whereas GFR in recipients correlated to the amount of interstitial fibrosis ( P < 0.01) but not to other histological parameters or cortex volume.

CONCLUSIONS

Kidney cortex volume, but not renal histology parameters, predicts 1-y renal outcome in LKDs. In contrast, the amount of interstitial fibrosis, but not cortex volume, predicts 1-y graft function in recipients.

Long-term dietary restriction ameliorates ageing-related renal fibrosis in male mice by normalizing mitochondrial functions and autophagy

As the kidneys age, gradual changes in the structures and functions of mitochondria occur. Dietary restriction (DR) can play a protective role in ageing-associated renal decline, however the exact mechanisms involved are still unclear. This study aims to clarify the beneficial effects of long-term DR on renal ageing and to explore the potential mechanisms of mitochondrial homeostasis. Eight-week-old C57BL/6 male mice (n = 30) were randomly divided into three groups, Young-AL (AL, ad libitum), Aged-AL, and Aged-DR (60% intake of AL). Mice were sacrificed at age of 7 months (Young) or 22 months (Aged). Heavier body and kidney weights were associated with ageing, but DR reduced these increases in aged mice. Ageing caused extensive tubulointerstitial fibrosis and glomerulosclerosis in the kidney. Giant mitochondria with looser and irregular crista were observed in Aged-AL kidneys. DR retarded these morphological alterations in aged kidneys. In addition, DR reversed the increase of MDA caused by ageing. Renal ATP level was elevated by DR treatment. Mitochondrial-related proteins were analysed to elucidate this association. Ageing downregulated the renal levels of VDAC, FOXO1, SOD2, LC3I and II, and upregulated the renal levels of MFN2 and PINK1. In contrast, DR elevated the levels of VDAC, FOXO1, and LC3I and reduced the ratio of LC3II to LC3I in aged kidneys. To conclude, impaired mitochondria, increased oxidative stress, and severe fibrosis were noticed in the aged kidneys, and DR improved these changes by increasing functional mitochondria and promoting autophagic clearance.

Molecular programs associated with glomerular hyperfiltration in early diabetic kidney disease

Hyperfiltration is a state of high glomerular filtration rate (GFR) observed in early diabetes that damages glomeruli, resulting in an iterative process of increasing filtration load on fewer and fewer remaining functional glomeruli. To delineate underlying cellular mechanisms of damage associated with hyperfiltration, transcriptional profiles of kidney biopsies from Pima Indians with type 2 diabetes with or without early-stage diabetic kidney disease were grouped into two hyperfiltration categories based on annual iothalamate GFR measurements. Twenty-six participants with a peak GFR measurement within two years of biopsy were categorized as the hyperfiltration group, and 26 in whom biopsy preceded peak GFR by over two years were considered pre-hyperfiltration. The hyperfiltration group had higher hemoglobin A1c, higher urine albumin-to-creatinine ratio, increased glomerular basement membrane width and lower podocyte density compared to the pre-hyperfiltration group. A glomerular 1240-gene transcriptional signature identified in the hyperfiltration group was enriched for endothelial stress response signaling genes, including endothelin-1, tec-kinase and transforming growth factor-β1 pathways, with the majority of the transcripts mapped to endothelial and inflammatory cell clusters in kidney single cell transcriptional data. Thus, our analysis reveals molecular pathomechanisms associated with hyperfiltration in early diabetic kidney disease involving putative ligand-receptor pairs with downstream intracellular targets linked to cellular crosstalk between endothelial and mesangial cells.

Birth Weight Is Associated With Kidney Size in Middle-Aged Women

Introduction

Low birth weight (LBW) is associated with increased risk of kidney disease due to lower nephron endowment leading to hyperfiltration and subsequent nephron loss. Kidney size is commonly used as a proxy for nephron number. We compared kidney volume measured by magnetic resonance imaging (MRI) with measured glomerular filtration rate (mGFR) in adults with either normal birth weight (NBW) or low birth weight (LBW).

Methods

Healthy individuals aged 42 to 52 years with LBW (1100−2300 g) and NBW (3500 −4000 g) were invited to participate. The GFR was measured using plasma clearance of iohexol. Kidney volume was measured on magnetic resonance images using axial T2 images and coronal T1 images with fat saturation without contrast enhancement; calculations were performed according to the ellipsoid formula π/6 × length × width × depth.

Results

We included 102 individuals (54 LBW and 48 NBW). Total kidney volume was 302 ± 51 ml for female NBW vs 258 ± 48 ml for female LBW individuals (P = 0.002). For male individuals, total kidney volume was 347 ± 51 ml vs. 340 ± 65 ml (P = 0.7). The mGFR was significantly associated with kidney volume, with r = 0.52 (P < 0.001) for women and r = 0.39 (P = 0.007) for men. A mediation analysis showed that the association between birth weight and mGFR (significant in total sample and women) was mediated by kidney volume.

Conclusion

Healthy female individuals born with LBW have smaller kidneys than healthy females born with NBW. The previously shown associations between LBW and lower mGFR in adult women might be explained by smaller kidney volume.

A Higher Foci Density of Interstitial Fibrosis and Tubular Atrophy Predicts Progressive CKD after a Radical Nephrectomy for Tumor

BACKGROUND

Chronic tubulointerstitial injury on kidney biopsy is usually quantified by the percentage of cortex with interstitial fibrosis/tubular atrophy (IF/TA). Whether other patterns of IF/TA or inflammation in the tubulointerstitium have prognostic importance beyond percentage IF/TA is unclear.

METHODS

We obtained, stained, and digitally scanned full cortical thickness wedge sections of renal parenchyma from patients who underwent a radical nephrectomy for a tumor over 2000-2015, and morphometrically analyzed the tubulointerstitium of the cortex for percentage IF/TA, IF/TA density (foci per mm² cortex), percentage subcapsular IF/TA, striped IF/TA, percentage inflammation (both within and outside IF/TA regions), and percentage subcapsular inflammation. Patients were followed with visits every 6-12 months. Progressive CKD was defined as dialysis, kidney transplantation, or 40% decline from the postnephrectomy eGFR. Cox models assessed the risk of CKD or noncancer mortality with morphometric measures of tubulointerstitial injury after adjustment for the percentage IF/TA and clinical characteristics.

RESULTS

Among 936 patients (mean age, 64 years; postnephrectomy baseline eGFR, 48 ml/min per 1.73m²), 117 progressive CKD events and 183 noncancer deaths occurred over a median 6.4 years. Higher IF/TA density predicted both progressive CKD and noncancer mortality after adjustment for percentage IF/TA and predicted progressive CKD after further adjustment for clinical characteristics. Independent of percentage IF/TA, age, and sex, higher IF/TA density correlated with lower eGFR, smaller nonsclerosed glomeruli, more global glomerulosclerosis, and smaller total cortical volume.

CONCLUSIONS

Higher density of IF/TA foci (a more scattered pattern with more and smaller foci) predicts higher risk of progressive CKD after radical nephrectomy compared with the same percentage of IF/TA but with fewer and larger foci.

Chronic exposure to PM2.5 aggravates SLE manifestations in lupus-prone mice

Background

Air pollution causes negative impacts on health. Systemic lupus erythematosus (SLE) is an autoimmune disease with diverse clinical manifestations and multifactorial etiology. Recent studies suggest that air pollution can trigger SLE and induce disease activity. However, this association has not been deeply investigated. Thus, the aim of this study was to evaluate whether exposure to fine particulate matter (PM2.5) exacerbates SLE manifestations, focusing on renal complications, in a lupus-prone animal model. Female NZBWF1 mice were exposed daily to 600 μg/m³ of inhaled concentrated ambient particles (CAP) or filtered air (FA). Survival rate, body weight, weight of organs (kidney, spleen, thymus, liver and heart), blood cell count, proteinuria, kidney stereology, renal histopathology, gene expression and oxidative stress were analyzed.

Results

Female NZBW mice exposed to CAP showed decreased survival, increased circulating neutrophils, early onset of proteinuria and increased kidney weight with renal cortex enlargement when compared to NZBW mice exposed to FA.

Conclusions

This work shows that air pollution aggravates some SLE manifestations in lupus-prone mice. These results reinforce the need of reducing air pollutant levels in order to promote a better quality of life for individuals diagnosed with SLE.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00407-0.

Factors Associated With Residual Kidney Function and Proteinuria After Living Kidney Donation in the United States

BACKGROUND

Living kidney donors are carefully screened, but despite overall good health, long-term donor outcomes have been shown to vary by predonation demographics. Since 2013, the United Network for Organ Sharing has mandated 2-year postdonation follow-up with measurements of kidney function and proteinuria.

METHODS

Using data from the Scientific Registry of Transplant Recipients, we sought to analyze donor factors associated with the percent change of kidney function from baseline (predonation) to 2-year postdonation, along with incidence of proteinuria reported within the same follow-up period.

RESULTS

Older donor age, male gender, black race, and body mass index >25 kg/m2 were independently associated with a greater percent decline in estimated glomerular filtration rate (eGFR). Male gender, black race, and higher body mass index were also independently associated with incident proteinuria. In contrast, younger donor age was associated with proteinuria, but proteinuria did not correlate with greater decline in eGFR in the overall cohort.

CONCLUSIONS

Donor factors associated with lower eGFR at 2-year postdonation were similar to those previously found to be associated with long-term risk for end-stage renal disease. Early postdonation assessment of kidney function and proteinuria may help to identify donors who are at greater risk of end-stage renal disease and who may benefit from more intense long-term monitoring.

Kidney Microstructural Features at the Time of Donation Predict Long-term Risk of Chronic Kidney Disease in Living Kidney Donors

OBJECTIVE

To determine whether microstructural features on a kidney biopsy specimen obtained during kidney transplant surgery predict long-term risk of chronic kidney disease in the donor.

PATIENTS AND METHODS

We studied kidney donors from May 1, 1999, through December 31, 2018, with a follow-up survey for the results of recent blood pressure and kidney function tests (estimated glomerular filtration rate [eGFR] and proteinuria). If not recently available, blood pressure and eGFRs were requested from a local clinic. Microstructural features on kidney biopsy at the time of donation were assessed as predictors of hypertension and kidney function after adjusting for years of follow-up, baseline age, sex, and clinical predictors.

RESULTS

There were 807 donors surveyed a mean 10.5 years after donation. An eGFR less than 45 mL/min/1.73 m2 in 6.4% (43/673) of donors was predicted by larger glomerular volume per standard deviation (odds ratio [OR], 1.48; 95% CI, 1.08 to 2.04) and nephron number below the age-specific 5th percentile (OR, 3.38; 95% CI, 1.31 to 8.72). An eGFR less than 60 mL/min/1.73 m2 in 42.5% (286/673) of donors was not predicted by any microstructural feature. Residual eGFR (postdonation/predonation eGFR) was predicted by nephron number below the age-specific 5th percentile (difference, -6.07%; 95% CI, -10.24% to -1.89%). Self-reported proteinuria in 5.1% (40/786) of donors was predicted by larger glomerular volume (OR, 1.42; 95% CI, 1.08 to 1.86). Incident hypertension in 18.8% (119/633) of donors was not predicted by any microstructural features.

CONCLUSION

Low nephron number for age and larger glomeruli are important microstructural predictors for long-term risk of chronic kidney disease after living kidney donation.

Low birthweight is associated with lower glomerular filtration rate in middle-aged mainly healthy women

Background

Low birthweight (LBW) has been shown to increase the risk of severe kidney disease. Studies have also shown associations between LBW and lower estimated glomerular filtration rate (GFR) in young adults. In this study we investigated whether LBW associates with measured GFR (mGFR) in middle-aged mainly healthy adults.

Methods

We invited individuals with LBW (1100–2300 g) and individuals with normal BW (NBW; 3500–4000 g) ages 41–52 years. GFR was measured using plasma clearance of iohexol. BW and BW for gestational age (BWGA) were obtained from the Medical Birth Registry of Norway and tested as main predictors. GFR was the main outcome.

Results

We included 105 individuals (57 LBW and 48 NBW). The mean GFR was 95 ± 14 mL/min/1.73 m² in the LBW group and 100 ± 13 mL/min/1.73 m² in the NBW group (P = 0.04). There was a significant sex difference: in women the mean GFR was 90 ± 12 versus 101 ± 14 mL/min/1.73 m² in the LBW and NBW groups, respectively (P = 0.006), whereas corresponding values for men were 101 ± 15 versus 100 ± 11 mL/min/1.73 m² (P = 0.7). Using linear regression, we found the GFR was 4.5 mL/min/1.73 m² higher per 1 kg higher BW for women (P = 0.02), with a non-significant 1.2 mL/min/1.73 m² lower GFR for men (P = 0.6). In analyses of BWGA, there was also a significant association for women, but not for men.

Conclusions

Middle-aged mainly healthy women with LBW had lower mGFR as compared with women with NBW. No such difference was found for men.

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.

Larger Nephron Size and Nephrosclerosis Predict Progressive CKD and Mortality after Radical Nephrectomy for Tumor and Independent of Kidney Function

BACKGROUND

Nephron hypertrophy and nephrosclerosis may be important determinants of CKD and mortality. However, studies of outcomes associated with these microstructural features have been limited to small tissue specimens from patients selected for either good kidney health or known kidney disease.

METHODS

To determine whether microstructural features are predictive of progressive CKD and mortality outcomes, we studied patients who underwent a radical nephrectomy for a tumor. Large wedge sections of renal parenchyma distal to the tumor were stained and scanned into high-resolution images; we annotated the cortex and all glomeruli to calculate glomerular volume, cortex volume per glomerulus, and percentage of globally sclerotic glomeruli. Morphometric measurements also included percentages of artery luminal stenosis and interstitial fibrosis/tubular atrophy (IF/TA) of the cortex. At follow-up visits every 6-12 months, we determined which patients experienced progressive CKD (defined as dialysis, kidney transplantation, or a 40% decline from postnephrectomy eGFR). Cox models for these outcomes were adjusted for age, sex, body mass index, hypertension, diabetes, smoking, eGFR, and proteinuria.

RESULTS

Among 936 patients (mean age, 64 years; postnephrectomy baseline eGFR, 48 ml/min per 1.73 m²), 117 progressive CKD events, 183 noncancer deaths, and 116 cancer deaths occurred during a median follow-up of 6.4 years. Larger glomerular volume, larger cortex per glomerulus, and higher percentage of globally sclerotic glomeruli or IF/TA predicted progressive CKD. Higher percentage IF/TA also predicted noncancer mortality. Microstructural features did not predict cancer mortality or recurrence.

CONCLUSIONS

After a radical nephrectomy, larger nephrons and nephrosclerosis predicted progressive CKD, and IF/TA predicted noncancer mortality. Morphometric analysis of renal parenchyma can predict noncancer clinical events in patients long after their radical nephrectomy.

Understanding the Link between Neighborhoods and Kidney Disease

Neighborhoods are where we live, learn, work, pray, and play. Growing evidence indicates that neighborhoods are an important determinant of health. The built features of our neighborhoods, such as the ways in which the streets are designed and connected and the availability of green spaces and transit stops, as well as the social features, such as the trust among neighbors and the perceptions of safety, may influence health through multiple pathways, such as access to important resources, psychosocial stress, and health behaviors. In particular, the extant literature consistently documents an association between neighborhood features and renal-associated conditions, such as cardiovascular disease, hypertension, diabetes, and obesity. There is also some evidence suggesting an association between neighborhood poverty and ESKD. The link between neighborhood and earlier stages of CKD, however, has been less clear, with most studies documenting no association. It may be that the neighborhood measures used in previous studies do not capture features of the neighborhood important for earlier stages of disease development and progression. It may also be that our current biomarkers (e.g., eGFR) and urine protein are not able to pick up very early forms of renal damage because of the kidney's overall high reserve capacity. This paper critically reviews the state of the literature on neighborhood and renal disease, with recommendations for neighborhood measures in future research. Neighborhoods are designed, built, and informed by policy, and thus, they are amenable to intervention, making them a potentially powerful way to improve renal health and reduce health inequalities at the population level.

Rethinking toxicity testing: Influence of aging on the outcome of long-term toxicity testing and possible remediation

Traditionally, toxicity testing is conducted at fixed dose rates (i.e., mg/kg/day) without considering life-changing events, e.g., stress, sickness, aging- and/or pregnancy-related changes in physical, physiological and biochemical parameters. In humans, life-changing events may cause systemic dose non-proportionality requiring modulation of drug dosage; similar changes occur in animals altering systemic dose during chronic/carcinogenic testing leading to "late-occurring" effects in some studies. For example, propylene monomethyl ether, an industrial chemical, initially induced sedation in rats and mice with recovery upon induction of hepatic CYPs after ~1 week. Sedation reappeared in rats but not in mice after ~12 months of exposure due to decreased CYP activity in rats, elderly mice were able to maintain slightly higher CYP activity avoiding recurrence of sedation. The systemic dose of two pharmaceuticals (doxazosin and brimonidine tartrate) increased up to 6-fold in ≥12-month old rats with no toxicity. In a rat reproductive toxicity study, systemic dose of 2,4-D, an herbicide, rapidly increased due to increased consumption of 2,4-D-fortified diet during pregnancy, lactation and neonatal growth, requiring adjustment to maintain the targeted systemic dose. Ideally, toxicological studies should be based on systemic dose with the option of modulating external dose rates to maintain the targeted systemic dose. Systemic dose can easily be monitored in selected core study animals at desired intervals considering recent developments in sampling and analysis at a fraction of the overall cost of a study.

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).

Kidney structural characteristics based on a kidney biopsy and contrast-enhanced computed tomography in healthy living kidney donors

The demands for kidney transplantations are increasing, and so is the number of live kidney donors (LKDs). Recent studies show that LKDs have an increased risk of developing end-stage renal disease compared with healthy non-donors. However, the knowledge about factors predicting renal disease in kidney donors is sparse. Some evidence points to increased glomerular sclerosis and kidney fibrosis, as well as a low number of glomeruli as associated with a worse renal outcome. This methodological study investigated that which estimates are obtainable with a standard kidney biopsy taken from the donated kidney during the transplantation, and a standard contrast-enhanced computed tomography (CT) in kidney donors. CT-scans were used to obtain total volume of the kidney and kidney cortex using the Cavalieri estimator and 2D-nucleator. Glomerular number density in the biopsies was estimated by a model-based method, and was multiplied by total cortex volume in order to estimate the total number of glomeruli in the kidney. Glomerular volume was estimated by the 2D-nucleator and a model-based stereological technique. Kidney fibrosis (point-counting), glomerular sclerosis (evaluation of glomerular profiles), and arteriole dimensions (2D-nucleator) were also estimated in the biopsy sections from the donated kidney. Various studies have attempted to identify predictors of renal outcome in LKDs. There is no consensus yet, and further studies are needed to elucidate if and how the estimates described in this study are associated with renal outcome in LKDs.

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.

Synergistic Impact of Diabetes and Hypertension on the Progression and Distribution of Glomerular Histopathological Lesions

BACKGROUND

Diabetes and hypertension share renal histopathological features, such as arterial lesions and glomerular hypertrophy, that have not been investigated in relation to the blood pressure status of diabetic subjects. The severity of glomerular lesions varies across locations of the renal cortex, which may be further affected by diabetes and/or hypertension.

METHODS

Histopathological lesions in different parts of the renal cortex of autopsy kidneys were evaluated and analyzed based on medical histories of diabetes and hypertension.

RESULTS

This study included a total of 82 Japanese autopsies composed of normotensive nondiabetics (n = 31), hypertensive nondiabetics (n = 28), normotensive diabetics (n = 14), and hypertensive diabetics (n = 9). There were no differences in age, sex, renal function, or body size among groups. In both the superficial and juxtamedullary cortices, increased glomerular volume (GV) was significantly associated with either diabetes or hypertension. In addition, diabetes and hypertension showed a significant interaction with GV regardless of the cortical location. Values for global glomerulosclerosis (GGS) and arteriolar hyalinosis (AH) were associated with diabetes but not with hypertension. Only values for GGS consistently showed cortical surface superiority. The zonal distribution of AH, GV, or other diabetic glomerular lesions differed among the lesions depending on the presence or absence of hypertension.

CONCLUSIONS

These results imply that diabetes and hypertension synergistically enhance glomerular hypertrophy across all layers of the human renal cortex. The process is closely associated with the severity of GGS and AH predominantly associated with diabetes.

In vivo measurements of kidney glomerular number and size in healthy and Os/+ mice using MRI

The development of chronic kidney disease (CKD) is associated with the loss of functional nephrons. However, there are no methods to directly measure nephron number in living subjects. Thus, there are no methods to track the early stages of progressive CKD before changes in total renal function. In this work, we used cationic ferritin-enhanced magnetic resonance imaging (CFE-MRI) to enable measurements of glomerular number (N_glom) and apparent glomerular volume (aV_glom) in vivo in healthy wild-type (WT) mice (n = 4) and mice with oligosyndactylism (Os^/+; n = 4), a model of congenital renal hypoplasia leading to nephron reduction. We validated in vivo measurements of N_glom and aV_glom by high-resolution ex vivo MRI. CFE-MRI measured a mean N_glom of 12,220 ± 2,028 and 6,848 ± 1,676 (means ± SD) for WT and Os^/+ mouse kidneys in vivo, respectively. N_glom measured in all mice in vivo using CFE-MRI varied by an average 15% from N_glom measured ex vivo in the same kidney (α = 0.05, P = 0.67). To confirm that CFE-MRI can also be used to track nephron endowment longitudinally, a WT mouse was imaged three times by CFE-MRI over 2 wk. Values of N_glom measured in vivo in the same kidney varied within ~3%. Values of aV_glom calculated from CFE-MRI in vivo were significantly different (~15% on average, P < 0.01) from those measured ex vivo, warranting further investigation. This is the first report of direct measurements of N_glom and aV_glom in healthy and diseased mice in vivo.

Larger nephron size, low nephron number, and nephrosclerosis on biopsy as predictors of kidney function after donating a kidney

It is unclear whether structural findings in the kidneys of living kidney donors predict postdonation kidney function. We studied living kidney donors who had a kidney biopsy during donation. Nephron size was measured by glomerular volume, cortex volume per glomerulus, and mean cross-sectional tubular area. Age-specific thresholds were defined for low nephron number (calculated from CT and biopsy measures) and nephrosclerosis (global glomerulosclerosis, interstitial fibrosis/tubular atrophy, and arteriosclerosis). These structural measures were assessed as predictors of postdonation measured GFR, 24-hour urine albumin, and hypertension. Analyses were adjusted for baseline age, gender, body mass index, systolic and diastolic blood pressure, hypertension, measured GFR, urine albumin, living related donor status, and time since donation. Of 2673 donors, 1334 returned for a follow-up visit at a median 4.4 months after donation, with measured GFR <60 mL/min/1.73 m² in 34%, urine albumin >5 mg/24 h in 13%, and hypertension in 5.3%. Larger glomerular volume and interstitial fibrosis/tubular atrophy predicted follow-up measured GFR <60 mL/min/1.73 m² . Larger cortex volume per glomerulus and low nephron number predicted follow-up urine albumin >5 mg/24 h. Arteriosclerosis predicted hypertension. Microstructural findings predict GFR <60 mL/min/1.73 m² , modest increases in urine albumin, and hypertension shortly after kidney donation.

Diagnostic Performance of Blood Pressure Measurement Modalities in Living Kidney Donor Candidates

BACKGROUND AND OBJECTIVES

Precise BP measurement to exclude hypertension is critical in evaluating potential living kidney donors. Ambulatory BP monitoring is considered the gold standard method for diagnosing hypertension, but it is cumbersome to perform. We sought to determine whether lower BP cutoffs using office and automated BP would reduce the rate of missed hypertension in potential living donors.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We measured BP in 578 prospective donors using three modalities: (1) single office BP, (2) office automated BP (average of five consecutive automated readings separated by 1 minute), and (3) ambulatory BP. Daytime ambulatory BP was considered the gold standard for diagnosing hypertension. We assessed both the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-7) and the American College of Cardiology/American Heart Association (ACC/AHA) definitions of hypertension in the cohort. Empirical thresholds of office BP and automated BP for the detection of ambulatory BP-diagnosed hypertension were derived using Youden index, which maximizes the sum of sensitivity and specificity and gives equal weight to false positive and false negative values.

RESULTS

Hypertension was diagnosed in 90 (16%) prospective donors by JNC-7 criteria and 198 (34%) prospective donors by ACC/AHA criteria. Masked hypertension was found in 3% of the total cohort by JNC-7 using the combination of office or automated BP, and it was seen in 24% by ACC/AHA guidelines. Using Youden index, cutoffs were derived for both office and automated BP using JNC-7 (<123/82 and <120/78 mm Hg) and ACC/AHA (<119/79 and <116/76 mm Hg) definitions. Using these lower cutoffs, the sensitivity for detecting hypertension improved from 79% to 87% for JNC-7 and from 32% to 87% by ACC/AHA definition, with negative predictive values of 95% and 87%, respectively. Missed (masked) hypertension was reduced to 2% and 4% of the entire cohort by JNC-7and ACC/AHA, respectively.

CONCLUSIONS

The prevalence of hypertension was higher in living donor candidates using ACC/AHA compared JNC-7 definitions. Lower BP cutoffs in the clinic improved sensitivity and led to a low overall prevalence of missed hypertension in prospective living kidney donors.

Pathologic glomerular characteristics and glomerular basement membrane alterations in biopsy-proven thin basement membrane nephropathy

BACKGROUND

Thin basement membrane nephropathy (TBMN) is diagnosed by diffuse thinning of the glomerular basement membrane (GBM) without any clinical and pathologic findings of Alport syndrome and the other renal diseases. TBMN is characterized clinically by benign familial hematuria but rarely develops into end-stage renal disease.

METHODS

In 27 cases of biopsy-proven TBMN, we evaluated the pathologic characteristics of TBMN, and examined the correlation between these pathologic characterizations and renal dysfunction.

RESULTS

All patients had hematuria, and 21 patients (77.8%) had proteinuria. In six patients (28.6%) who were more than 50 years of age, the estimated glomerular filtration rate (eGFR) decreased from G3a to G4 in the chronic kidney disease stage. Pathologically, an irregular decrease in intensity of type IV collagen α5(IV) chain was seen in GBM, and irregular thinning with diffuse rough etched images was observed on the GBM surface with several sizes of holes by low-vacuum scanning electron microscopy. The glomerular morphology of TBMN was characterized by an increased number of small glomerular capillaries with an increased extracellular matrix (ECM). These characteristic morphologic alterations were evident from a young age in patients with TBMN, but were not correlated directly with the decrease of eGFR, the degree of hematuria, and proteinuria. The decrease of eGFR in patients with TBMN who were more than 50 years of age might be primarily mediated by arteriolosclerosis-associated glomerulosclerosis and interstitial fibrosis.

CONCLUSION

Characteristic pathological glomerular findings and GBM alterations occurred from a young age but were not associated directly with renal impairment in biopsy-proven TBMN.

Predictive Value of Cortical Thickness Measured by Ultrasonography for Renal Impairment: A Longitudinal Study in Chronic Kidney Disease

Background: Kidney size is associated with renal function, however it is not elucidated whether kidney size is a risk for the progression of chronic kidney disease. The aim of this study was to investigate the predictive value of morphological evaluation of kidney size by ultrasonography for the progression of renal dysfunction. Methods: Morphological parameters including kidney length, volume, cortical thickness, and medullary thickness were measured by ultrasonography in 87 patients with chronic kidney disease, and adjusted by body size. Renal functions at baseline and after 2 years were measured and the associations of morphological parameters to decline in renal function over 2 years were analyzed. Results: Height-adjusted cortical thickness was correlated to decline in renal function (r = 0.426, p < 0.001). Height-adjusted cortical thickness could predict renal dysfunction with the area under the curve of 0.786, and height-adjusted cortical thickness of 4.0 mm/cm was a cut off value with a sensitivity of 72.5% and a specificity of 80.0% for the risk of a more than 30% decline in renal function or initiation of dialysis. Conclusions: We provide new insights into the utility of measuring cortical thickness by ultrasonography for predict future renal impairment.

Living donor postnephrectomy kidney function and recipient graft loss: A dose-response relationship

Development of end-stage renal disease (ESRD) in living kidney donors is associated with increased graft loss in the recipients of their kidneys. Our goal was to investigate if this relationship was reflected at an earlier stage postdonation, possibly early enough for recipient risk prediction based on donor response to nephrectomy. Using national registry data, we studied 29 464 recipients and their donors from 2008-2016 to determine the association between donor 6-month postnephrectomy estimated GFR (eGFR) and recipient death-censored graft failure (DCGF). We explored donor BMI as an effect modifier, given the association between obesity and hyperfiltration. On average, risk of DCGF increased with each 10 mL/min decrement in postdonation eGFR (adjusted hazard ratio [aHR] 1.06, 95% confidence interval [CI] 1.02-1.10, P = .007). The association was attenuated with higher donor BMI (interaction P = .049): recipients from donors with BMI = 20 (aHR 1.12, 95% CI 1.04-1.19, P = .002) and BMI = 25 (aHR 1.07, 95% CI 1.03-1.12, P = .001) had a higher risk of DCGF with each 10 mL/min decrement in postdonation eGFR, whereas recipients from donors with BMI = 30 and BMI = 35 did not have a higher risk. The relationship between postdonation eGFR, donor BMI, and recipient graft loss can inform counseling and management of living donor kidney transplant recipients.

The expression of two isoforms of matrix metalloproteinase-2 in aged mouse models of diabetes mellitus and chronic kidney disease

Background

This study was undertaken to explore the effects of aging on the kidneys in mouse models of diabetes and chronic kidney disease (CKD), and to compare the expression of two isoforms of matrix metalloproteinase-2 (MMP-2)–secretory full-length MMP-2 and intracellular N-terminal truncated MMP-2 (NTT-MMP-2)–in these models.

Methods

Two experimental ICR mouse models were used: a streptozotocin (STZ)-induced type 1 diabetes mellitus model and a 5/6 nephrectomized (5/6Nx) CKD model. The abundance of each isoform of MMP-2 was determined by quantitative polymerase chain reaction (qPCR), and functional analyses were conducted. Moreover, the protein levels of the two MMP-2 isoforms were determined semi-quantitatively by immunohistochemical staining, and their association with tissue damage was assessed.

Results

Both isoforms of MMP-2 were upregulated in the kidney tissues of STZ-induced diabetic mice and 5/6Nx mice, irrespective of age. Characteristically, NTT-MMP-2 protein expression was elevated in old control mice, in line with the qPCR results. NTT-MMP-2 expression was limited to the renal cortex, and to the tubulointerstitial area rather than the glomerular area. In terms of tissue damage, tubulointerstitial fibrosis was more severe in old 5/6Nx mice than in their young counterparts, whereas glomerulosclerosis was comparable in old and young 5/6Nx mice.

Conclusion

The intracellular isoform of MMP-2 was induced by ageing, irrespective of the presence of diabetes or CKD, and its induction may be related to tubulointerstitial fibrosis in chronic kidney disease.

Clinical and Pathology Findings Associate Consistently with Larger Glomerular Volume

Background Glomerular volume increases when demand exceeds nephron supply, which may lead to glomerulosclerosis. It is unclear if determinants of glomerular volume are consistent between populations that differ by severity of comorbidities.Methods We studied kidney biopsy specimens from living kidney donors (n=2453) and patients who underwent radical nephrectomy for a renal tumor (n=780). We scanned specimen sections into high-resolution digital images, manually traced glomerular profiles, and calculated mean glomerular volumes using the Weibel-Gomez stereologic formula (separately for nonsclerosed glomeruli and globally sclerosed glomeruli). We then assessed the relationship of glomerular volume with age, clinical characteristics, and nephrosclerosis on biopsy specimen.Results Compared with kidney donors, patients with tumors were older and more frequently men, obese, diabetic, or hypertensive, had more glomerulosclerosis and interstitial fibrosis on biopsy specimen, and had 12% larger nonsclerosed glomeruli (P<0.001). In both populations, male sex, taller height, obesity, hypertension, and proteinuria associated with larger nonsclerosed glomeruli to a similar extent. In patients with tumors, diabetes, glomerulosclerosis >25%, and interstitial fibrosis >25% also associated with larger nonsclerosed glomeruli. Independent clinical predictors of larger nonsclerotic glomeruli were family history of ESRD, male sex, taller height, obesity, diabetes, and proteinuria. After adjustment for these characteristics, nonsclerotic glomerular volume did not differ between populations and was stable up to age 75 years, after which it decreased with age. Many of these findings were also evident with globally sclerotic glomerular volume.Conclusions Characteristics associated with glomerular volume are consistent between patient populations with low and high levels of comorbidity.

Clinical associations of total kidney volume: the Framingham Heart Study

Background

Total kidney volume (TKV) is an imaging biomarker that may have diagnostic and prognostic utility. The relationships between kidney volume, renal function and cardiovascular disease (CVD) have not been characterized in a large community-dwelling population. This information is needed to advance the clinical application of TKV.

Methods

We measured TKV in 1852 Framingham Heart Study participants (mean age 64.1 ± 9.2 years, 53% women) using magnetic resonance imaging. A healthy sample was used to define reference values. The associations between TKV, renal function and CVD risk factors were determined using multivariable logistic regression analysis.

Results

Overall, mean TKV was 278 ± 54 cm3 for women and 365 ± 66 cm3 for men. Risk factors for high TKV (>90% healthy referent size) were body surface area (BSA), diabetes, smoking and albuminuria, while age, female and estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 were protective. Participants with high TKV had higher odds of diabetes [odds ratio (OR) 2.15, P < 0.001] and lower odds of eGFR <60 mL/min/1.73 m2 (OR 0.32, P = 0.007). Risk factors for low TKV (<10% healthy referent size) were age, female and eGFR <60 mL/min/1.73 m2, while BSA and diabetes were protective. Participants with low TKV had higher odds of eGFR <60 mL/min/1.73 m2 (OR 6.12, P < 0.001) and albuminuria (OR 1.56, P = 0.03).

Conclusions

Low TKV is associated with markers of kidney damage including albuminuria and eGFR <60 mL/min/1.73 m2, while high TKV is associated with diabetes and decreased odds of eGFR <60 mL/min/1.73 m2. Prospective studies are needed to characterize the natural progression and clinical consequences of TKV.

Renal shear wave elastography for the assessment of nephron hypertrophy: a cross-sectional study in chronic kidney disease

PURPOSE

To investigate the association of renal elasticity to microscopic findings of nephron hypertrophy and nephrosclerosis.

METHODS

Patients who underwent renal biopsy were enrolled. Renal elasticity was measured by acoustic radiation force impulse, and nephron size (glomerular volume, non-sclerotic glomerular density, and mean profile tubular area) and nephrosclerosis (globally sclerotic glomeruli and interstitial fibrosis) were estimated. Nephron hypertrophy was indicated by larger glomerular volume, larger tubular area, and lower non-sclerotic glomerular density. Nephrosclerosis was indicated by a higher percentage of globally sclerotic glomeruli and higher severity of fibrosis.

RESULTS

Renal elasticity was negatively correlated with glomerular volume (r = - 0.480, P = 0.024) and mean tubular area (r = - 0.469, P = 0.028), but it was not correlated with non-sclerotic glomerular density (r = 0.205, P = 0.359), percentage of globally sclerotic glomeruli (r = 0.057, P = 0.800), and severity of fibrosis (r = 0.014, P = 0.950). In a multiple linear regression analysis, glomerular volume and mean tubular area were independently associated with renal elasticity (std β = - 0.454, P = 0.015 and std β = - 0.577, P = 0.007, respectively).

CONCLUSION

Renal elasticity was correlated with microstructural findings of nephron hypertrophy. Measuring renal elasticity could help in detecting kidney disease.

New insights on glomerular hyperfiltration: a Japanese autopsy study

It has been suggested that low nephron number contributes to glomerular hypertension and hyperperfusion injury in progressive chronic kidney disease (CKD). The incidence of CKD in Japan is among the highest in the world, but the reasons remain unclear. We estimated total nephron (glomerular) number (NglomTOTAL) as well as numbers of nonsclerosed (NglomNSG) and globally sclerosed glomeruli (NglomGSG), and the mean volume of nonsclerosed glomeruli (VglomNSG) in Japanese normotensive, hypertensive, and CKD subjects and investigated associations between these parameters and estimated glomerular filtration rate (eGFR). Autopsy kidneys from age-matched Japanese men (9 normotensives, 9 hypertensives, 9 CKD) had nephron number and VglomNSG estimated using disector/fractionator stereology. Subject eGFR, single-nephron eGFR (SNeGFR), and the ratio SNeGFR/VglomNSG were calculated. NglomNSG in Japanese with hypertension (392,108 ± 87,605; P < 0.001) and CKD (268,043 ± 106,968; P < 0.001) was less than in normotensives (640,399 ± 160,016). eGFR was directly correlated with NglomNSG (r = 0.70, P < 0.001) and inversely correlated with VglomNSG (r = -0.53, P < 0.01). SNeGFR was higher in hypertensives than normotensives (P = 0.03), but was similar in normotensives and CKD, while the ratio SNeGFR/VglomNSG was similar in normotensives and hypertensives but markedly reduced in CKD. Nephron number in Japanese with hypertension or CKD was low. This results in a higher SNeGFR in hypertensives compared with normotensive and CKD subjects, but lowered SNeGFR/VglomNSG in CKD subjects, suggesting that changes in GFR are accommodated by glomerular hypertrophy rather than glomerular hypertension. These findings suggest glomerular hypertrophy is a dominant factor in maintenance of GFR under conditions of low nephron number.

Structural and Functional Changes in Human Kidneys with Healthy Aging

Aging is associated with significant changes in structure and function of the kidney, even in the absence of age-related comorbidities. On the macrostructural level, kidney cortical volume decreases, surface roughness increases, and the number and size of simple renal cysts increase with age. On the microstructural level, the histologic signs of nephrosclerosis (arteriosclerosis/arteriolosclerosis, global glomerulosclerosis, interstitial fibrosis, and tubular atrophy) all increase with age. The decline of nephron number is accompanied by a comparable reduction in measured whole-kidney GFR. However, single-nephron GFR remains relatively constant with healthy aging as does glomerular volume. Only when glomerulosclerosis and arteriosclerosis exceed that expected for age is there an increase in single-nephron GFR. In the absence of albuminuria, age-related reduction in GFR with the corresponding increase in CKD (defined by an eGFR<60 ml/min per 1.73 m²) has been shown to associate with a very modest to no increase in age-standardized mortality risk or ESRD. These findings raise the question of whether disease labeling of an age-related decline in GFR is appropriate. These findings also emphasize the need for a different management approach for many elderly individuals considered to have CKD by current criteria.

Single-Nephron Glomerular Filtration Rate in Healthy Adults

BACKGROUND

The glomerular filtration rate (GFR) assesses the function of all nephrons, and the single-nephron GFR assesses the function of individual nephrons. How the single-nephron GFR relates to demographic and clinical characteristics and kidney-biopsy findings in humans is unknown.

METHODS

We identified 1388 living kidney donors at the Mayo Clinic and the Cleveland Clinic who underwent a computed tomographic (CT) scan of the kidney with the use of contrast material and an iothalamate-based measurement of the GFR during donor evaluation and who underwent a kidney biopsy at donation. The mean single-nephron GFR was calculated as the GFR divided by the number of nephrons (calculated as the cortical volume of both kidneys as assessed on CT times the biopsy-determined glomerular density). Demographic and clinical characteristics and biopsy findings were correlated with the single-nephron GFR.

RESULTS

A total of 58% of the donors were women, and the mean (±SD) age of the donors was 44±12 years. The mean GFR was 115±24 ml per minute, the mean number of nephrons was 860,000±370,000 per kidney, and the mean single-nephron GFR was 80±40 nl per minute. The single-nephron GFR did not vary significantly according to age (among donors <70 years of age), sex, or height (among donors ≤190 cm tall). A higher single-nephron GFR was independently associated with larger nephrons on biopsy and more glomerulosclerosis and arteriosclerosis than would be expected for age. A higher single-nephron GFR was associated with a height of more than 190 cm, obesity, and a family history of end-stage renal disease.

CONCLUSIONS

Among healthy adult kidney donors, the single-nephron GFR was fairly constant with regard to age, sex, and height (if ≤190 cm). A higher single-nephron GFR was associated with certain risk factors for chronic kidney disease and certain kidney-biopsy findings. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases.).