Clinical and Pathology Findings Associate Consistently with Larger Glomerular Volume

Morphometric analysis of chronicity on kidney biopsy: a useful prognostic exercise

Chronic changes on kidney biopsy specimens include increasing amounts of arteriosclerosis, glomerulosclerosis, interstitial fibrosis and tubular atrophy, enlarged nephron size, and reduced nephron number. These chronic changes are difficult to accurately assess by visual inspection but are reasonably quantified using morphometry. This review describes the various patient populations that have undergone morphometric analysis of kidney biopsies. The common approaches to morphometric analysis are described. The chronic kidney disease outcomes associated with various chronic changes by morphometry are also summarized. Morphometry enriches the characterization of chronicity on a kidney biopsy and this can supplement the pathologist's diagnosis. Artificial intelligence image processing tools are needed to automate the annotations needed for practical morphometric analysis of kidney biopsy specimens in routine clinical care.

Capillary rarefaction: a missing link in renal and cardiovascular disease?

Patients with chronic kidney disease (CKD) have an increased risk for cardiovascular morbidity and mortality. Capillary rarefaction may be both one of the causes as well as a consequence of CKD and cardiovascular disease. We reviewed the published literature on human biopsy studies and conclude that renal capillary rarefaction occurs independently of the cause of renal function decline. Moreover, glomerular hypertrophy may be an early sign of generalized endothelial dysfunction, while peritubular capillary loss occurs in advanced renal disease. Recent studies with non-invasive measurements show that capillary rarefaction is detected systemically (e.g., in the skin) in individuals with albuminuria, as sign of early CKD and/or generalized endothelial dysfunction. Decreased capillary density is found in omental fat, muscle and heart biopsies of patients with advanced CKD as well as in skin, fat, muscle, brain and heart biopsies of individuals with cardiovascular risk factors. No biopsy studies have yet been performed on capillary rarefaction in individuals with early CKD. At present it is unknown whether individuals with CKD and cardiovascular disease merely share the same risk factors for capillary rarefaction, or whether there is a causal relationship between rarefaction in renal and systemic capillaries. Further studies on renal and systemic capillary rarefaction, including their temporal relationship and underlying mechanisms are needed. This review stresses the importance of preserving and maintaining capillary integrity and homeostasis in the prevention and management of renal and cardiovascular disease.

Podocyte Senescence and Aging

As the population in many industrial countries is aging, the risk, incidence, and prevalence of CKD increases. In the kidney, advancing age results in a progressive decrease in nephron number and an increase in glomerulosclerosis. In this review, we focus on the effect of aging on glomerular podocytes, the post-mitotic epithelial cells critical for the normal integrity and function of the glomerular filtration barrier. The podocytes undergo senescence and transition to a senescence-associated secretory phenotype typified by the production and secretion of inflammatory cytokines that can influence neighboring glomerular cells by paracrine signaling. In addition to senescence, the aging podocyte phenotype is characterized by ultrastructural and functional changes; hypertrophy; cellular, oxidative, and endoplasmic reticulum stress; reduced autophagy; and increased expression of aging genes. This results in a reduced podocyte health span and a shortened life span. Importantly, these changes in the pathways/processes characteristic of healthy podocyte aging are also often similar to pathways in the disease-induced injured podocyte. Finally, the better understanding of podocyte aging and senescence opens therapeutic options to slow the rate of podocyte aging and promote kidney health.

Spatial Heterogeneity of Glomerular Phenotypes Affects Kidney Biopsy Findings

Key Points

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.

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.

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.

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.

Changes in Glomerular Volume, Sclerosis, and Ischemia at 5 Years after Kidney Transplantation: Incidence and Correlation with Late Graft Failure

SIGNIFICANCE STATEMENT

Glomerular volume, ischemic glomeruli, and global glomerulosclerosis are not consistently assessed on kidney transplant biopsies. The authors evaluated morphometric measures of glomerular volume, the percentage of global glomerulosclerosis, and the percentage of ischemic glomeruli and assessed changes in these measures over time to determine whether such changes predict late allograft failure. All three features increased from transplant to five-year biopsy. Kidneys with smaller glomeruli at 5 years had more global glomerulosclerosis and a higher percentage of ischemic-appearing glomeruli. Smaller glomeruli and increasing percentages of global glomerulosclerosis and ischemic glomeruli at 5 years predicted allograft failure. Only increased percentage of ischemic glomeruli predicted allograft failure at 5 years independent of all Banff scores. Glomerular changes reflect pathologic processes that predicted allograft loss; measuring them quantitatively might enhance the current Banff system and provide biomarkers for intervention trials.

BACKGROUND

Histology can provide insight into the biology of renal allograft loss. However, studies are lacking that use quantitative morphometry to simultaneously assess changes in mean glomerular volume and in the percentages of globally sclerosed glomeruli (GSG) and ischemic-appearing glomeruli in surveillance biopsies over time to determine whether such changes are correlated with late graft failure.

METHODS

We used digital scans of surveillance biopsies (at implantation and at 1 and 5 years after transplantation) to morphometrically quantify glomerular volume and the percentages of GSG and ischemic-appearing glomeruli in a cohort of 835 kidney transplants. Cox proportional hazards models assessed the risk of allograft failure with these three glomerular features.

RESULTS

From implantation to 5 years, mean glomerular volume increased by nearly 30% (from 2.8×10 6 to 3.6×10 6 µm 3 ), mean percentage of GSG increased from 3.2% to 13.2%, and mean percentage of ischemic-appearing glomeruli increased from 0.8% to 9.5%. Higher percentages of GSG and ischemic-appearing glomeruli at 5-year biopsy predicted allograft loss. The three glomerular features at 5-year biopsy were related; the percentage of GSG and the percentage of ischemic glomeruli were positively correlated, and both were inversely correlated to glomerular volume. At 5 years, only 5.3% of biopsies had ≥40% ischemic glomeruli, but 45% of these grafts failed (versus 11.6% for <40% ischemic glomeruli). Higher Banff scores were more common with increasing percentages of GSG and ischemia, but at 5 years, only the percentage of ischemic glomeruli added to predictive models adjusted for Banff scores.

CONCLUSIONS

Glomerular changes reflect important pathologic processes that predict graft loss. Measuring glomerular changes quantitatively on surveillance biopsies, especially the proportion of ischemic-appearing glomeruli, may enhance the current Banff system and be a useful surrogate end point for clinical intervention trials.

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The Association Between Adult Height and Stroke Incidence in Japanese Men and Women: A Population-based Case-Control Study

BACKGROUND

No studies have examined the associations between adult height and ischemic stroke subtypes.

METHODS

We conducted a population-based case-control study that included 2,451 thrombotic and 687 embolic stroke cases, as well as 1,623 intracerebral and 768 subarachnoid hemorrhage cases without history of stroke aged 40-79 years, and the same number of sex- and age-matched controls. Cases and controls were grouped according to the quintile cut-off values of height in controls, and the third quintile, which was approximately the average height group, was used as the reference group. Height divided by one standard deviation of height in controls was also examined as a continuous variable. The analyses were carried out separately for participants aged 40-59 years and 60-79 years.

RESULTS

In both younger and older men, height was linearly inversely associated with total and thrombotic strokes, and the shortest quintile compared to the reference group was associated with increased risks of these strokes. Although height was linearly inversely associated with embolic stroke and intracerebral hemorrhage in younger men, the shortest quintile did not show increased risks of these strokes. Height did not seem to be associated with total stroke and any stroke subtypes in younger women. In contrast, the tallest quintile was significantly associated with increased risks of total stroke and intracerebral hemorrhage, and height tended to be positively associated with these strokes in older women.

CONCLUSION

We reported the associations between adult height and ischemic stroke subtypes for the first time, which differed according to sex and age group.

Relationships among Non-Neoplastic Histopathological Features, Kidney Function, Proteinuria, and Other Clinical Factors in Patients Undergoing Nephrectomy

Introduction

The non-neoplastic kidney parenchyma from nephrectomies is often overlooked in routine examinations. We aimed to evaluate the associations between global glomerulosclerosis (GS), interstitial fibrosis (IF), or arteriosclerosis (AS) and estimated glomerular filtration rate (eGFR), dipstick proteinuria, and other clinical factors.

Methods

We performed a cross-sectional analysis of 781 patients with nephrectomy. We used regression models with and without interaction factors. The tested exposures were GS, IF, or AS, and the outcome measures were GFR and dipstick proteinuria.

Results

In multivariable analyses, increasing degrees of GS, IF, or AS were significantly associated with lower eGFR and proteinuria (p < 0.05 for each). Obesity and hypertension (HTN) modified the association between eGFR and degrees of GS, whereas proteinuria and cardiovascular disease (CVD) modified the association between eGFR and degrees of AS (p for interaction <0.05). Compared with GS <10%, GS >50% was associated with lower eGFR in patients with (-45 mL/min/1.73 m2) than without (-19 mL/min/1.73 m2) obesity, and GS >50% was associated with lower eGFR in patients with (-31 mL/min/1.73 m2) than without (-16 mL/min/1.73 m2) HTN. Compared with AS <26%, AS >50% was associated with lower eGFR in patients with (-11 mL/min/1.73 m2) than without (-6 mL/min/1.73 m2) proteinuria, and AS >50% was associated with lower eGFR in patients with (-23 mL/min/1.73 m2) than without (-7 mL/min/1.73 m2) CVD.

Conclusion

Greater degrees of each GS, IF, and AS are independently associated with proteinuria and lower eGFR. Obesity, HTN, proteinuria, and CVD modify the relationship between eGFR and specific histopathological features of nephrosclerosis.

Associations between nephron number and podometrics in human kidneys

Podocyte loss and resultant nephron loss are common processes in the development of glomerulosclerosis and chronic kidney disease. While the cortical distribution of glomerulosclerosis is known to be non-uniform, the relationship between the numbers of non-sclerotic glomeruli (NSG), podometrics and zonal differences in podometrics remain incompletely understood. To help define this, we studied autopsy kidneys from 50 adults with median age 68 years and median eGFR 73.5 mL/min/1.73m² without apparent glomerular disease in a cross-sectional analysis. The number of NSG per kidney was estimated using the physical dissector/fractionator combination, while podometrics were estimated using model-based stereology. The number of NSG per kidney was directly correlated with podocyte number per tuft and podocyte density. Each additional 100,000 NSG per kidney was associated with 26 more podocytes per glomerulus and 16 podocytes per 10⁶ μm³ increase in podocyte density. These associations were independent of clinical factors and cortical zone. While podocyte number per glomerulus was similar in the three zones, superficial glomeruli were the smallest and had the highest podocyte density but smallest podocytes. Increasing age and hypertension were associated with lower podocyte number, with age mostly affecting superficial glomeruli, and hypertension mostly affecting juxtamedullary glomeruli. Thus, in this first study to report a direct correlation between the number of NSG and podometrics, we suggest that podocyte number is decreasing in NSG of individuals losing nephrons. However, another possible interpretation may be that more nephrons might protect against further podocyte loss.

Prognostic Implications of a Morphometric Evaluation for Chronic Changes on All Diagnostic Native Kidney Biopsies

BACKGROUND

Semiquantitative visual inspection for glomerulosclerosis, interstitial fibrosis, and arteriosclerosis is often used to assess chronic changes in native kidney biopsies. Morphometric evaluation of these and other chronic changes may improve the prognostic assessment.

METHODS

We studied a historical cohort of patients who underwent a native kidney biopsy between 1993 and 2015 and were followed through 2021 for ESKD and for progressive CKD (defined as experiencing 50% eGFR decline, temporary dialysis, or ESKD). Pathologist scores for the percentages of globally sclerosed glomeruli (GSG), interstitial fibrosis and tubular atrophy (IFTA), and arteriosclerosis (luminal stenosis) were available. We scanned biopsy sections into high-resolution images to trace microstructures. Morphometry measures were percentage of GSG; percentage of glomerulosclerosis (percentage of GSG, ischemic-appearing glomeruli, or segmentally sclerosed glomeruli); percentage of IFTA; IFTA foci density; percentage of artery luminal stenosis; arteriolar hyalinosis counts; and measures of nephron size. Models assessed risk of ESKD or progressive CKD with biopsy measures adjusted for age, hypertension, diabetes, body mass index, eGFR, and proteinuria.

RESULTS

Of 353 patients (followed for a median 7.5 years), 75 developed ESKD and 139 experienced progressive CKD events. Visually estimated scores by pathologists versus morphometry measures for percentages of GSG, IFTA, and luminal stenosis did not substantively differ in predicting outcomes. However, adding percentage of glomerulosclerosis, IFTA foci density, and arteriolar hyalinosis improved outcome prediction. A 10-point score using percentage of glomerulosclerosis, percentage of IFTA, IFTA foci density, and any arteriolar hyalinosis outperformed a 10-point score based on percentages of GSG, IFTA, and luminal stenosis >50% in discriminating risk of ESKD or progressive CKD.

CONCLUSION

Morphometric characterization of glomerulosclerosis, IFTA, and arteriolar hyalinosis on kidney biopsy improves prediction of long-term kidney outcomes.

Non-Immunologic Causes of Late Death-Censored Kidney Graft Failure: A Personalized Approach

Despite continuous advances in surgical and immunosuppressive protocols, the long-term survival of transplanted kidneys is still far from being satisfactory. Antibody-mediated rejection, recurrent autoimmune diseases, and death with functioning graft are the most frequent causes of late-kidney allograft failure. However, in addition to these complications, a number of other non-immunologic events may impair the function of transplanted kidneys and directly or indirectly lead to their failure. In this narrative review, we will list and discuss the most important nonimmune causes of late death-censored kidney graft failure, including quality of the donated kidney, adherence to prescriptions, drug toxicities, arterial hypertension, dyslipidemia, new onset diabetes mellitus, hyperuricemia, and lifestyle of the renal transplant recipient. For each of these risk factors, we will report the etiopathogenesis and the potential consequences on graft function, keeping in mind that in many cases, two or more risk factors may negatively interact together.

Kidney glomerular filtration rate plasticity after transplantation

Since the first living donor kidney transplantation about six decades ago, significant progress has been made in terms of extending allograft survival. However, to date, only a small number of studies have compared the functional changes of the donated kidney to that of the remaining kidney. Although relatively small, the study by Gonzalez Rinne et al. demonstrated the adaptive capacity of the transplanted kidney in 30 donor-recipient pairs. The glomerular filtration rate (GFR) in both donors and recipients was obtained 12 months after transplantation and the authors identified three scenarios: (i) where donors had a higher GFR than recipients; (ii) where donors had a lower GFR than recipients; and (iii) where donors had a similar GFR to recipients. The mechanisms mediating GFR adaptability after kidney transplantation seem to be associated with body surface area (including sex differences in body surface area). Microstructural analysis of human and animal models of renal physiology provides some clues to the physiological adaptation of the transplanted organ. The nephron number from endowment and age-related loss and the adaptive ability for compensatory glomerular hyperfiltration likely play a major role.

Healthy and unhealthy aging on kidney structure and function: human studies

PURPOSE OF REVIEW

This review is intended to provide an up-to-date analysis of the structural and functional alterations of the kidneys that accompany healthy and unhealthy aging in humans. Macro- and micro- structural changes and glomerular filtration rate (whole kidney and single nephron) accompanying aging will be stressed.

RECENT FINDINGS

Comparative findings concerning distribution of anatomic changes of the kidney healthy and unhealthy aging are reviewed. Challenges concerning definition of chronic kidney disease (CKD) in otherwise healthy aging patients are discussed. The complex interactions of CKD and aging are discussed. The role of podocyte dysbiosis in kidney aging is reviewed.

SUMMARY

Kidney aging is a complex phenomenon often difficult to distinguish from CKD. Nonetheless, phenotypes of healthy and unhealthy aging are evident. Much more information concerning the molecular characteristics of normal kidney aging and its relevance to chronic kidney disease is needed.

Chronic Kidney Disease from Polyvinylpyrrolidone Deposition in Persons with Intravenous Drug Use

BACKGROUND AND OBJECTIVES

Persons with intravenous drug use have a higher risk of developing CKD compared with the general population. In Norway, deposits of polyvinylpyrrolidone have been observed in kidney biopsies taken from persons with opioid addiction and intravenous drug use since 2009. Polyvinylpyrrolidone is an excipient commonly used in pharmaceuticals, and the polyvinylpyrrolidone deposits observed in these patients were caused by intravenous injection of a specific oral methadone syrup containing very high molecular weight polyvinylpyrrolidone. Here, we present the clinicopathologic findings from 28 patients with CKD associated with polyvinylpyrrolidone deposition in the kidney.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The 28 patients and their kidney biopsies were included when polyvinylpyrrolidone deposition was recognized, either retrospectively or at the time of diagnostic evaluation. Biopsies were taken between 2009 and 2016. We collected laboratory parameters and clinical data from digital patient charts. For each kidney biopsy, the glomerular volume, extent of polyvinylpyrrolidone deposition, and tubulointerstitial area with tubular atrophy were assessed quantitatively.

RESULTS

All patients (mean age: 37 years) had CKD (mean eGFR: 33 ml/min per 1.73 m²) and normal urine protein or non-nephrotic-range proteinuria. Biopsies showed moderate to severe tubular atrophy (mean extent: 65%) and interstitial infiltrates of vacuolated macrophages containing polyvinylpyrrolidone (mean share of biopsy area: 1.5%). Underperfused and ischemic glomeruli were common findings. In 22 samples, ultrastructural investigation revealed polyvinylpyrrolidone-containing vacuoles in the mesangial or endothelial cells of glomeruli. At the last follow-up, most patients had stable or improved eGFR. Two patients had developed kidney failure and underwent hemodialysis.

CONCLUSIONS

Intravenous injection of a specific oral methadone syrup caused polyvinylpyrrolidone deposition in the kidney in persons with opioid addiction and intravenous drug use. Kidney biopsy findings suggested an association between polyvinylpyrrolidone deposition and tubular atrophy.

Inflammatory Cells in Nephrectomy Tissue from Patients without and with a History of Urinary Stone Disease

BACKGROUND AND OBJECTIVES

Urinary stone disease has been associated with inflammation, but the specific cell interactions that mediate events remain poorly defined. This study compared calcification and inflammatory cell patterns in kidney tissue from radical nephrectomy specimens of patients without and with a history of urinary stone disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Nontumor parenchyma of biobanked radical nephrectomy specimens from age- and sex-matched stone formers (n=44) and nonstone formers (n=82) were compared. Calcification was detected by Yasue staining and inflammatory cell populations by immunohistochemistry for CD68 (proinflammatory M1 macrophages), CD163 and CD206 (anti-inflammatory M2 macrophages), CD3 (T lymphocytes), and tryptase (mast cells). Calcifications and inflammatory cells were quantified in cortex and medulla using Image-Pro analysis software.

RESULTS

Calcification in the medulla of stone formers was higher than in nonstone formers (P<0.001). M1 macrophages in the cortex and medulla of stone formers were greater than in nonstone formers (P<0.001), and greater in stone former medulla than stone former cortex (P=0.02). There were no differences in age, sex, body mass index, tumor characteristics (size, stage, or thrombus), vascular disease status, or eGFR between the groups. M2 macrophages, T lymphocytes, and mast cells did not differ by stone former status. There was a correlation between M1 macrophages and calcification in the medulla of stone formers (rho=0.48; P=0.001) and between M2 macrophages and calcification in the medulla of nonstone formers (rho=0.35; P=0.001). T lymphocytes were correlated with calcification in the cortex of both nonstone formers (rho=0.27; P=0.01) and stone formers (rho=0.42; P=0.004), whereas mast cells and calcification were correlated only in the cortex of stone formers (rho=0.35; P=0.02).

CONCLUSIONS

Higher medullary calcification stimulated accumulation of proinflammatory rather than anti-inflammatory macrophages in stone formers.

Nephron overload as a therapeutic target to maximize kidney lifespan

Kidney lifespan is a patient-oriented outcome that provides much needed context for understanding chronic kidney disease (CKD). Nephron endowment, age-associated decline in nephron number, kidney injury history and the intrinsic capacity of nephrons to adapt to haemodynamic and metabolic overload vary widely within the population. Defining percentiles of kidney function might therefore help to predict individual kidney lifespan and distinguish healthy ageing from progressive forms of CKD. In response to nephron loss, the remaining nephrons undergo functional and structural adaptations to meet the ongoing haemodynamic and metabolic demands of the organism. When these changes are no longer sufficient to maintain kidney cell homeostasis, remnant nephron demise occurs and CKD progression ensues. An individual's trajectory of glomerular filtration rate and albuminuria reflects the extent of nephron loss and adaptation of the remaining nephrons. Nephron overload represents the final common pathway of CKD progression and is largely independent of upstream disease mechanisms. Thus, interventions that efficiently attenuate nephron overload in early disease stages can protect remnant kidney cells and nephrons, and delay CKD progression. This Review provides a conceptual framework for individualized diagnosis, monitoring and treatment of CKD with the goal of maximizing kidney lifespan.

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.

Causal linkage between adult height and kidney function: An integrated population-scale observational analysis and Mendelian randomization study

As adult height is linked to various health outcomes, further investigation of its causal effects on kidney function later in life is warranted. This study involved a cross-sectional observational analysis and summary-level Mendelian randomization (MR) analysis. First, the observational association between height and estimated GFR determined by creatinine (eGFRcreatinine) or cystatin C (eGFRcystatinC) was investigated in 467,182 individuals aged 40-69 using UK Biobank. Second, the genetic instrument for adult height, as reported by the GIANT consortium, was implemented, and summary-level MR of eGFRcreatinine and CKDcreatinine in a CKDGen genome-wide association study was performed (N = 567,460), with multivariable MR being adjusted for the effects of genetic predisposition on body mass index. To replicate the findings, additional two-sample MR using the summary statistics of eGFRcystatinC and CKDcystatinC in UK Biobank was performed (N = 321,405). In observational analysis, adult height was inversely associated with both eGFRcreatinine (per 1 SD, adjusted beta -1.039, standard error 0.129, P < 0.001) and eGFRcystatinC (adjusted beta -1.769, standard error 0.161, P < 0.001) in a multivariable model adjusted for clinicodemographic, anthropometric, metabolic, and social factors. Moreover, multivariable summary-level MR showed that a taller genetically predicted adult height was causally linked to a lower log-eGFRcreatinine (adjusted beta -0.007, standard error 0.001, P < 0.001) and a higher risk of CKDcreatinine (adjusted beta 0.083, standard error 0.019, P < 0.001). Other pleiotropy-robust sensitivity MR analysis results supported the findings. In addition, similar results were obtained by two-sample MR of eGFRcystatinC (adjusted beta -1.303, standard error 0.140, P < 0.001) and CKDcystatinC (adjusted beta 0.153, standard error 0.025, P < 0.001) in UK Biobank. In conclusion, the results of this study suggest that a taller adult height is causally linked to worse kidney function in middle-aged to elderly individuals, independent of the effect of body mass index.

The Association between Glomerular Diameter and Secondary Focal Segmental Glomerulosclerosis in Chronic Kidney Disease

INTRODUCTION

When nephron loss occurs, the glomerular filtration rate (GFR) is suggested to be maintained by glomerular hypertrophy, but excessive hypertrophy can rather lead to the formation of focal segmental glomerulosclerosis (FSGS), thereby causing progressive kidney damage. However, it is not clear how much glomerular hypertrophy leads to the formation of FSGS. We examined the association between glomerular diameter and FSGS lesions in chronic kidney disease (CKD) patients.

METHODS

We recruited 77 patients who underwent renal biopsy during 2016-2017; however, those identified with primary FSGS and glomerulonephritis with active glomerular lesion were excluded. We evaluated the maximal glomerular diameter (Max GD), an indicator of glomerular size, in each renal biopsy specimen and examined its association with FSGS lesion.

RESULTS

The median age, blood pressure, and estimated GFR of the patients were 53 years, 122/70 mm Hg, and 65 mL/min/1.73 m2, respectively. The optimal cutoff threshold of Max GD for predicting the presence of FSGS lesions, assessed by receiver operating characteristic curve analysis, was determined to be at 224 μm (area under the curve, 0.81; sensitivity, 81%; specificity, 72%). Multivariate logistic regression analyses demonstrated that Max GD ≥224 μm was significantly associated with the presence of FSGS lesions, independent of other confounding factors (odds ratio, 11.70; 95% confidence interval, 1.93-70.84).

DISCUSSION/CONCLUSION

Glomerular hypertrophy (Max GD ≥224 μm) has been associated with FSGS lesions in CKD patients and may reflect the limits of the compensatory process.

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.

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.

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.

Histopathologic Correlates of Kidney Function: Insights From Nephrectomy Specimens

RATIONALE & OBJECTIVE

Existing data sets correlating kidney histopathologic findings with kidney function have low proportions of elderly patients (and those with a family history of kidney failure are over-represented), which limits their generalizability. Our objective was to use non-neoplastic tissue from nephrectomy specimens to examine the association between degree of histopathologic changes and estimated glomerular filtration rate (eGFR) and determine whether the association differed by age.

STUDY DESIGN

Cross-sectional study.

EXPOSURES

Glomerulosclerosis (GS), interstitial fibrosis/tubular atrophy (IFTA), and arterial sclerosis/arteriosclerosis (AS).

OUTCOME

eGFR.

ANALYTICAL APPROACH

We retrospectively reviewed kidney pathology reports (of non-neoplastic tissue) from 1,347 patients who underwent nephrectomy (1999-2018) for any indication but most commonly due to kidney cancer. We evaluated the association between degree of GS, IFTA, and AS with eGFR at the time of nephrectomy and whether this was modified by age.

RESULTS

Among the participants (aged 17-91 years), 42% and 57.8% had>10% GS and IFTA, respectively, and 81.8% had moderate or severe AS. We found that greater degrees of GS, IFTA, and AS were associated with lower eGFR after multivariable adjustment. Although there was a greater prevalence of more severe degrees of GS and IFTA in older individuals, the association between various histopathologic features and eGFR was not modified by age.

LIMITATIONS

Retrospective cross-sectional study.

CONCLUSIONS

Our study demonstrates differences in the histologic appearance of the kidneys across levels of eGFR. Although the prevalence of advanced changes was higher in the oldest group of patients, a subset had excellent kidney function and limited histologic changes.

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.

One-stop assessment of renal function and renal artery in hypertensive patients with suspected renal dysfunction: non-enhanced MRI using spatial labeling with multiple inversion pulses

OBJECTIVES

To assess whether spatial labeling with multiple inversion pulses (SLEEK) sequence can be employed as a one-stop assessment method for evaluating renal function and displaying renal artery in hypertensive patients with suspected renal dysfunction.

METHODS

A total of 78 patients with suspected hypertensive renal damage were enrolled in this retrospective study. All patients underwent MRI examinations, and both SLEEK and DWI sequences were performed simultaneously. According to estimated glomerular filtration rate (eGFR), patients were divided into three groups (Group 1, eGFR> 90; Group 2, eGFR = 60-90; Group 3, eGFR< 60). Twenty-two of these patients also underwent CT angiography (CTA) examination. Comparison between CTA, DWI, and eGFR was performed to assess the value of SLEEK in evaluating renal function and displaying renal artery.

RESULTS

The performance of SLEEK to display renal artery was highly consistent with the results of CTA (kappa = 0.713). The corticomedullary contrast ratio positively correlated with eGFR (p = 0.004, r = 0.322) and was significantly higher in SLEEK images than in DWI images in all three groups (p < 0.001). There was no significant difference in corticomedullary contrast ratio in SLEEK images between Group 1 and Group 2 (p = 0.285). However, the minimal renal cortical thickness, which significantly correlated with eGFR (p < 0.001, r = 0.866), was significantly different between Group 1 and Group 2 (p < 0.001). ROC analysis showed good diagnostic performance when differentiating patients with eGFR> 60 from those with eGFR< 60.

CONCLUSIONS

The SLEEK sequence could evaluate simultaneously renal function through corticomedullary differentiation and renal arteries, enabling one-stop assessment in hypertensive patients with suspected renal dysfunction.

KEY POINTS

• Spatial labeling with multiple inversion pulses (SLEEK) improves renal corticomedullary differentiation in hypertensive patients with renal dysfunction compared with DWI. • SLEEK clearly displays renal artery in hypertensive patients with renal dysfunction. • SLEEK could be utilized as a one-stop assessment method for evaluating renal function and renal artery in hypertensive patients.

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).

Glomerular Volume and Glomerulosclerosis at Different Depths within the Human Kidney

BACKGROUND

Age, CKD risk factors, and kidney function are associated with larger glomerular volume and a higher percentage of globally sclerotic glomeruli. Knowledge of how these associations may differ by cortical depth is limited.

METHODS

To investigate glomerular volume and glomerulosclerosis across different depths of cortex, we studied wedge sections of the renal parenchyma from 812 patients who underwent a radical nephrectomy (for a tumor), separately characterizing glomeruli in the superficial (subcapsular), middle, and deep (juxtamedullary) regions. We compared the association of mean nonsclerotic glomerular volume and of glomerulosclerosis (measured as the percentage of globally sclerotic glomeruli) with age, obesity, diabetes, smoking, kidney function, and structural pathology in the superficial, middle, and deep regions.

RESULTS

The superficial, middle, and deep regions showed significant differences in glomerular volume (0.0025, 0.0031, and 0.0028 µm³, respectively) and in glomerulosclerosis (18%, 7%, and 11%, respectively). There was a marked increase in glomerulosclerosis with age in the superficial region, but larger glomerular volume was not associated with age at any cortical depth. Glomerulosclerosis associated more strongly with arteriosclerosis and ischemic-appearing glomeruli in the superficial region. Hypertension, lower eGFR, and interstitial fibrosis associated with glomerulosclerosis and glomerular volume to a similar extent at any depth. Diabetes and proteinuria more strongly associated with glomerulosclerosis in the deep and middle regions, respectively, but neither associated with glomerular volume differently by depth. Obesity associated more strongly with glomerular volume in the superficial cortex.

CONCLUSIONS

Most clinical characteristic show similar associations with glomerulosclerosis and glomerulomegaly at different cortical depths. Exceptions include age-related glomerulosclerosis, which appears to be an ischemic process and is more predominant in the superficial region.

Aging Vs. Hypertension: An Autopsy Study of Sclerotic Renal Histopathological Lesions in Adults With Normal Renal Function

BACKGROUND AND AIMS

Arterial hypertension and glomerular ischemia coexist in elderly patients with hypertension. Thus, 2 conflicting therapeutic purposes, i.e., reduction of pressure overload and maintenance of renal arterial perfusion, must be considered in elderly patients with hypertension. This study examined this issue from the perspective of renal histopathology.

METHODS

Adult autopsied kidneys without apparent renal disease were analyzed for histopathological features that might be related to aging or hypertension. Mean glomerular volume (GV), global glomerulosclerosis (GGS), arteriosclerotic lesions (AL), arteriolar hyalinosis (AH), and interstitial fibrosis/tubular atrophy (IF/TA) were evaluated.

RESULTS

This study included 59 Japanese autopsy patients, of whom 28 (47%) were hypertensive. Overall, GGS, IF/TA, and AL, but not GV or AH, tended to increase with aging. Multivariate analysis revealed that age, but not hypertension, was an independent factor associated with GGS, IF/TA, and AL. In contrast, hypertension was independently associated with GV. AH was not associated with age or hypertension in this autopsy series. Of note, in the late elderly group (≥75 years), GGS was significantly lower in hypertensives than in normotensives. No such trend was found in the non-elderly (<65 years) or early elderly groups (65-74 years).

CONCLUSIONS

Normal aging has a major impact on the development of renal sclerotic lesions compared to hypertension in adults with no apparent renal disease. Hypertension may play a role in maintaining downstream glomerular perfusion in the aging kidney.

How Do Kidneys Adapt to a Deficit or Loss in Nephron Number?

A deficit or loss in the number of nephrons, the functional unit of the kidney, can induce compensatory growth and hyperfunction of remaining nephrons. An increase in single nephron glomerular filtration rate (SNGFR) aims to compensate but may be deleterious in the long term. The increase in SNGFR is determined by the dynamics of nephron loss, total remaining GFR, the body's excretory demand, and the functional capacity to sustain single nephron hyperfunction.