Heterogeneous distribution of glomerular size in adult kidneys with normal renal function

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

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

Total Nephron Number and Single-Nephron Parameters in Patients with IgA Nephropathy

Background

Single-nephron dynamics in progressive IgA nephropathy (IgAN) have not been studied. We applied novel methodology to explore single-nephron parameters in IgAN.

Methods

Nonglobally sclerotic glomeruli (NSG) and globally sclerotic glomeruli (GSG) per kidney were estimated using cortical volume assessment via unenhanced computed tomography and biopsy-based stereology. Estimated single-nephron GFR (eSNGFR) and single-nephron urine protein excretion (SNUPE) were calculated by dividing eGFR and UPE by the number of NSG. Associations with CKD stage and clinicopathologic findings were cross-sectionally investigated.

Results

This study included 245 patients with IgAN (mean age 43 years, 62% male, 45% on renin-angiotensin aldosterone system [RAAS] inhibitors prebiopsy) evaluated at kidney biopsy. CKD stages were 10% CKD1, 43% CKD2, 19% CKD3a, 14% CKD3b, and 14% CKD4-5. With advancing CKD stage, NSG decreased from mean 992,000 to 300,000 per kidney, whereas GSG increased from median 64,000 to 202,000 per kidney. In multivariable models, advancing CKD stage associated with lower numbers of NSG, higher numbers of GSG, and lower numbers of GSG + NSG, indicating potential resorption of sclerosed glomeruli. In contrast to the higher mean glomerular volume and markedly elevated SNUPE in advanced CKD, the eSNGFR was largely unaffected by CKD stage. Lower SNGFR associated with Oxford scores for endocapillary hypercellularity and crescents, whereas higher SNUPE associated with segmental glomerulosclerosis and tubulointerstitial scarring.

Conclusions

SNUPE emerged as a sensitive biomarker of advancing IgAN. The failure of eSNGFR to increase in response to reduced number of functioning nephrons suggests limited capacity for compensatory hyperfiltration by diseased glomeruli with intrinsic lesions.

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.