Change in renal parenchymal volume in living kidney transplant donors

Renal transplants increase in size and function in keeping with compensatory renal hypertrophy

AIM

To evaluate changes in allograft kidney length in renal transplant recipients and the relationship with estimated glomerular filtration rate (eGFR).

METHODS

This single-centre retrospective study of renal transplant recipients was conducted at Flinders Medical Centre (FMC) from January 2007 to June 2020. Donor and recipient details, renal allograft length from transplant ultrasounds at 0, 1, 3, 6 and 12 months were collected. The association between compensatory renal hypertrophy (CRH) and eGFR and its magnitude was analysed using multivariate multilevel mixed-effects linear regression models.

RESULTS

A total of 183 renal transplant recipients were studied. 100 of 175 recipients (62.9%) demonstrated an increase in renal length defined as any increase in maximal longitudinal diameter on serial ultrasounds. Twenty-three recipients (13.1%) had no change in transplant length and 42 recipients (24%) had a decrease in length. The mean increase in kidney length over the first 12 months was 0.57 cm. Ninety of 156 (57.7%) recipients with a renal ultrasound within a month post-transplant demonstrated a mean increase kidney length of 0.3 cm. Multivariate analysis demonstrated that eGFR increased by 2.5 mL/min/1.73 m2 (95% CI 0.72- 4.4; p = .006) with every 1 cm increase in kidney length. Absolute changes in kidney length did not demonstrate any statistically significant correlation with eGFR in both complete case and multiple imputation analysis.

CONCLUSION

An increase in transplant kidney length is common in renal transplant recipients and is associated with enhanced eGFR. However, further studies need to be performed to study the association of absolute change in kidney length and eGFR.

Age and Pre-operative HbA1c levels affect renal function compensation in living kidney donors

OBJECTIVES

About 90% of Japanese kidney transplantations are conducted from living donors, and their safety and the maintenance of their renal function are critical. This study aims to identify factors that affect the compensation of renal function in living kidney donors after donor nephrectomy.

METHOD

In a retrospective cohort study, we reviewed data from 120 patients who underwent nephrectomy as living kidney transplant donors in our department from 2012 to 2021. Univariable and multivariable linear regression analyses were performed for donor factors affecting renal function after donor nephrectomy.

RESULT

The multivariable linear regression model revealed that the donor's age (p = 0.025), preoperative estimated Glomerular Filtration Rate (eGFR) (p < 0.001), and hemoglobin A1c (HbA1c) (p = 0.043) were independent risk factors for eGFR at six months after nephrectomy. The eGFR deterioration was more strongly associated with age in females than in males, whereas higher HbA1c values were more strongly associated with eGFR deterioration in males. Higher donor age and higher HbA1c each enhance the deterioration of eGFR six months after living donor nephrectomy. The data suggest that old age in especially female donors and preoperative higher HbA1c in male donors have a harmful impact on their renal function compensation.

Compensatory Hypertrophy in Paediatric Patients with a Unilateral Ureteropelvic Junction Obstruction

Background

Compensatory hypertrophy is common in children with solitary functioning kidney, but it is unknown whether it also develops in children with unilateral partial reduction of kidney function.

Objective

The aim of this study was to assess whether children with a unilateral ureteropelvic junction obstruction (UPJO) show compensatory growth of the unaffected kidney. Furthermore, we investigated whether the length of the unaffected kidney was related to the degree of split kidney function lost and other possible risk factors. Lastly, we studied a possible relationship with signs of kidney injury.

Design, setting, and participants

We retrospectively analysed clinical information from 194 children with a unilateral UPJO who participated in the Aetiologic research into Genetic and Occupational/environmental Risk factors for Anomalies in children (AGORA) data- and biobank. Data on kidney length, split kidney function, and other factors possibly associated with kidney length were extracted from electronic patient records.

Outcome measurements and statistical analysis

Pearson’s correlation coefficients between the split kidney function and unaffected kidney length were calculated. Multivariable logistic regression analyses were performed to identify factors associated with kidney length and signs of kidney injury.

Results and limitations

Most children with a UPJO had an unaffected kidney length above the reference for age at the end of follow-up (median age 6.5 yr). A correlation with split kidney function was present only in children with a split kidney function of ≥60% in the unaffected kidney (r = 0.41). Aside from split kidney function, UPJO side was the only determinant of kidney length, while no associations between kidney length and kidney injury were identified.

Conclusions

Compensatory growth was visible in most children with a UPJO after sufficient follow-up time and was correlated with split kidney function in children with a severe UPJO. Contralateral kidney length provided no clear prognostic value for developing kidney injury. Studies with more patients and additional biomarkers of kidney injury are needed to further personalise care.

Patient summary

Children with obstruction of urine outflow in one kidney often had a larger contralateral kidney. However, the size of this kidney could not be used to predict which children would develop kidney injury.

Living kidney donor assessment: Kidney length vs differential function

BACKGROUND

The key question in living kidney donor assessment is how best to determine the contribution of each kidney to overall renal function and guide selection of which kidney to donate, ensuring safety of procedure and good outcome for both recipient and donor. It is thought that a length difference > 2 cm may indicate significant difference in function and therefore need for measurement of differential function.

AIM

To determine the effect of using kidney length to decide which kidney to donate in a retrospective cohort of potential donors.

METHODS

All 333 potential living kidney donors between January 2009 and August 2018 who completed assessment were retrospectively evaluated. Donor assessment was performed as per United Kingdom guidelines. Data included age, sex, kidney length (cranio-caudal) obtained by computed tomography/ultrasono-graphy,51-chromium ethylenediamine tetraacetatic acid measured glomerular filtration rate, mercapto acetyl tri glycine split function and vascular anatomy. There were 48 exclusions due to inadequate data or incomplete investigations. Statistical analysis was performed using Excel pivot tables and GraphPad Prism. Correlation between kidney length and differential function was determined with Pearson's correlation coefficient.

RESULTS

Of 285 potential donors included in the study, there were 144 males (mean age 49.9 ± 14.75) and 141 females (mean age 51.2 ± 11.23). Overall, the Pearson's correlation between differences in length and divided function of kidney pairs was 0.1630, P = 0.0058. Of 73 with significant difference (> 10%) in divided function, 18 (24.7%) had no difference in kidney length; 54 (74%) had a difference of < 2 cm and only one of > 2 cm. Using a length difference of > 1 cm would only predict significant difference in divided function in 8/34 (23.5%) of cases. Using a difference of > 2 cm as cut off for performing split function would lead to false reassurance in 72 patients (6 had > 20% difference in divided function whereas 66 had 10%-20% difference).

CONCLUSION

Length difference between kidney pairs alone is not sufficient to replace measurement of divided function. This issue requires a randomised controlled trial to resolve it.

Compensatory renal hypertrophy following nephrectomy: When and how?

Following surgical removal of one kidney, the other enlarges and increases its function. The mechanism for the sensing of this change and the growth is incompletely understood but begins within days and compensatory renal hypertrophy (CRH) is the dominant contributor to the growth. In many individuals undergoing nephrectomy for cancer or kidney donation this produces a substantial and helpful increase in renal function. Two main mechanisms have been proposed, one in which increased activity by the remaining kidney leads to hypertrophy, the second in which there is release of a kidney specific factor in response to a unilateral nephrectomy that initiates CRH. Whilst multiple growth factors and pathways such as the mTORC pathway have been implicated in experimental studies, their roles and the precise mechanism of CRH are not defined. Unrestrained hypoxia inducible factor activation in renal cancer promotes growth and may play an important role in driving CRH.

Assessment of Perfusion and Oxygenation of the Human Renal Cortex and Medulla by Quantitative MRI during Handgrip Exercise

BACKGROUND

Renal flow abnormalities are believed to play a central role in the pathogenesis of nephropathy and in primary and secondary hypertension, but are difficult to measure in humans. Handgrip exercise is known to reduce renal arterial flow (RAF) by means of increased renal sympathetic nerve activity.

METHODS

To monitor medullary and cortical oxygenation under handgrip exercise-reduced perfusion, we used contrast- and radiation-free magnetic resonance imaging (MRI) to measure regional changes in renal perfusion and blood oxygenation in ten healthy normotensive individuals during handgrip exercise. We used phase-contrast MRI to measure RAF, arterial spin labeling to measure perfusion, and both changes in transverse relaxation time (T₂*) and dynamic blood oxygenation level-dependent imaging to measure blood oxygenation.

RESULTS

Handgrip exercise induced a significant decrease in RAF. In the renal medulla, this was accompanied by an increase of oxygenation (reflected by an increase in T₂*) despite a significant drop in medullary perfusion; the renal cortex showed a significant decrease in both perfusion and oxygenation. We also found a significant correlation (R²=0.8) between resting systolic BP and the decrease in RAF during handgrip exercise.

CONCLUSIONS

Renal MRI measurements in response to handgrip exercise were consistent with a sympathetically mediated decrease in RAF. In the renal medulla, oxygenation increased despite a reduction in perfusion, which we interpreted as the result of decreased GFR and a subsequently reduced reabsorptive workload. Our results further indicate that the renal flow response's sensitivity to sympathetic activation is correlated with resting BP, even within a normotensive range.

Donor Nephrectomy May Compromise the Cardiovascular System: A Retrospective, Single-Center Study

OBJECTIVES

Our goal was to determine the short-term effects of donor nephrectomy on the cardiovascular system and to gain a better understanding of the recently recognized long-term increased risk of end-stage renal disease and cardiovascular mortality.

MATERIALS AND METHODS

Living kidney donors who underwent donor nephrectomy between January 2010 and January 2015 at the Hacettepe University Transplantation Unit were retrospectively screened. Echocardiographic parameters, kidney volumes, and renal functions before nephrectomy were compared with measurements after nephrectomy. Flow-mediated dilatation values of living kidney donors were compared with healthy individuals.

RESULTS

The study included 73 female and 31 male living kidney donors with a mean age of 46.1 ± 10.8 years. In the comparative analysis of donors versus 35 healthy individuals, the changes in flow-mediated dilatation were 12.3 ± 5.7% and 15.4 ± 6.3%, respectively (P = .016). In the comparative analysis of preoperative versus the last visit transthoracic echocardiographic results, left ventricular end-systolic and end-diastolic diameters decreased and left ventricular posterior wall thickness and septum thickness increased (P = .025, P = .002, P = .026, and P = .019, respectively).

CONCLUSIONS

Nephrectomy may cause several hemodynamic changes in living kidney donors, which may exacerbate cardiovascular risks in this population.

Benign and tumor parenchyma metabolomic profiles affect compensatory renal growth in renal cell carcinoma surgical patients

BACKGROUND AND OBJECTIVES

Pre-operative kidney volume is an independent predictor of glomerular filtration rate in renal cell carcinoma patients. Compensatory renal growth (CRG) can ensue prior to nephrectomy in parallel to tumor growth and benign parenchyma loss. We aimed to test whether renal metabolite abundances significantly associate with CRG, suggesting a causative relationship.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Tissue metabolomics data from 49 patients, with a median age of 60 years, were previously collected and the pre-operative fold-change of their contra to ipsi-lateral benign kidney volume served as a surrogate for their CRG. Contra-lateral kidney volume fold-change within a 3.3 +/- 2.1 years follow-up interval was used as a surrogate for long-term CRG. Using a multivariable statistical model, we identified metabolites whose abundances significantly associate with CRG.

RESULTS

Our analysis found 13 metabolites in the benign (e.g. L-urobilin, Variable Influence in Projection, VIP, score = 3.02, adjusted p = 0.017) and 163 metabolites in the malignant (e.g. 3-indoxyl-sulfate, VIP score = 1.3, adjusted p = 0.044) tissues that significantly associate with CRG. Benign/tumor fold change in metabolite abundances revealed three additional metabolites with that significantly positively associate with CRG (e.g. p-cresol sulfate, VIP score = 2.945, adjusted p = 0.033). At the pathway level, we show that fatty-acid oxidation is highly enriched with metabolites whose benign tissue abundances strongly positively associate with CRG, both pre-operatively and long term, whereas in the tumor tissue significant enrichment of dipeptides and benzoate (positive association), glycolysis/gluconeogenesis, lysolipid and nucleotide sugar pentose (negative associations) sub-pathways, were observed.

CONCLUSION

These data suggest that specific biological processes in the benign as well as in the tumor parenchyma strongly influence compensatory renal growth.

Does size matter? Kidney transplant donor size determines kidney function among living donors

BACKGROUND

Kidney donor outcomes are gaining attention, particularly as donor eligibility criteria continue to expand. Kidney size, a useful predictor of recipient kidney function, also likely correlates with donor outcomes. Although donor evaluation includes donor kidney size measurements, the association between kidney size and outcomes are poorly defined.

METHODS

We examined the relationship between kidney size (body surface area-adjusted total volume, cortical volume and length) and renal outcomes (post-operative recovery and longer-term kidney function) among 85 kidney donors using general linear models and time-to-chronic kidney disease data.

RESULTS

Donors with the largest adjusted cortical volume were more likely to achieve an estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 over a median 24-month follow-up than those with smaller cortical volumes (P <0.001), had a shorter duration of renal recovery (1.3-2.2 versus 32.5 days) and started with a higher eGFR at pre-donation (107-110 versus 91 mL/min/1.73 m2) and immediately post-nephrectomy (∼63 versus 50-51 mL/min/1.73 m2). Similar findings were seen with adjusted total volume and length.

CONCLUSIONS

Larger kidney donors were more likely to achieve an eGFR ≥60 mL/min/1.73 m2 with renal recovery over a shorter duration due to higher pre-donation and initial post-nephrectomy eGFRs.

Risk Factors Associated with Decreased Renal Function after Hand-Assisted Laparoscopic Donor Nephrectomy: A Multivariate Analysis of a Single Surgeon Experience

Background: Hand-assisted laparoscopic donor nephrectomy is a minimally invasive procedure for living kidney donation. The surgeon operative volume is associated with postoperative morbidity and mortality. We evaluated the risk factors associated with decreased renal function after hand-assisted laparoscopic donor nephrectomy performed by a single experienced surgeon. Methods: We included living renal donors who underwent hand-assisted laparoscopic donor nephrectomy by a single experienced surgeon between 2006 and 2013. Decreased renal function was defined as an estimated glomerular filtration rate (eGFR) of < 60 mL/min/1.73 m² on postoperative day 4. The donors were categorized into groups with postoperative eGFR < 60 mL/min/1.73 m² or ≥ 60 mL/min/1.73 m². Univariate and multivariate logistic regression analyses were performed to evaluate the risk factors associated with decreased renal function after hand-assisted laparoscopic donor nephrectomy. The hospital stay duration, intensive care unit admission rate, and eGFR at postoperative year 1 were evaluated. Results: Of 643 patients, 166 (25.8%) exhibited a postoperative eGFR of < 60 mL/min/1.73 m². Multivariate logistic regression analysis demonstrated that the risk factors for decreased renal function were age [odds ratio (95% confidence interval), 1.062 (1.035-1.089), P < 0.001], male sex [odds ratio (95% confidence interval), 3.436 (2.123-5.561), P < 0.001], body mass index (BMI) [odds ratio (95% confidence interval), 1.093 (1.016-1.177), P = 0.018], and preoperative eGFR [odds ratio (95% confidence interval), 0.902 (0.881-0.924), P < 0.001]. There were no significant differences in postoperative hospital stay duration and intensive care unit admission rate between the two groups. In addition, 383 of 643 donors were analyzed at postoperative year 1. Sixty donors consisting of 14 (5.0%) from the group of 279 donors in eGFR ≥ 60 mL/min/1.73 m², and 46 (44.2%) from the group of 104 donors in eGFR < 60 mL/min/1.73 m² had eGFR < 60 mL/min/1.73 m² at postoperative year 1 (P < 0.001). Conclusions: Increased age, male sex, higher BMI, and decreased preoperative eGFR were risk factors for decreased renal function after hand-assisted laparoscopic donor nephrectomy by a single experienced surgeon. These results provide important evidence for the safe perioperative management of living renal donors.

Impact of remaining kidney volume to body weight ratio on renal function in living kidney donors

To investigate whether the ratio of remnant kidney volume to body weight (V/W ratio) can impact renal function in donors, 45 living kidney donors were enrolled. Kidney volume was analyzed by magnetic resonance imaging. Renal function was compared between donors with a V/W ratio of < 2.0 mL/kg (n = 23) or ≥ 2.0 mL/kg (n = 22). Donors in both V/W groups showed similar serum creatinine levels and estimated glomerular filtration rates (eGFRs) at 7 days and 1 year, whereas donors with a V/W ratio of < 2.0 mL/kg had significantly higher 24-hour urine protein levels at 1 year (0.54 ± 0.23 g/d vs. 0.33 ± 0.19 g/d, p = 0.028). Multivariate analysis revealed no correlation between the V/W ratio and eGFR at 7 days or 1 year, and a V/W ratio of < 2 mL/kg was not associated with an increased incidence of eGFR < 60 mL/min/1.73 m(2) at 1 year (risk ratio 1.73, 95% confidence interval 0.10-29.47). The V/W ratio correlated inversely with 24-hour urine protein (r = -0.377, p = 0.021) at 1 year, and donors with a V/W ratio of < 2.0 mL/kg were more likely to show 24-hour urine protein >300 mg (risk ratio 1.70, 95% confidence interval 1.08-2.67) at 1 year. Donors with lower V/W ratios have higher 24-hour urinary protein levels at 1 year after transplantation. These findings suggest that the V/W ratio may be useful for kidney selection.

Podometrics as a Potential Clinical Tool for Glomerular Disease Management

Chronic kidney disease culminating in end-stage kidney disease is a major public health problem costing in excess of $40 billion per year with high morbidity and mortality. Current tools for glomerular disease monitoring lack precision and contribute to poor outcome. The podocyte depletion hypothesis describes the major mechanisms underlying the progression of glomerular diseases, which are responsible for more than 80% of cases of end-stage kidney disease. The question arises of whether this new knowledge can be used to improve outcomes and reduce costs. Podocytes have unique characteristics that make them an attractive monitoring tool. Methodologies for estimating podocyte number, size, density, glomerular volume and other parameters in routine kidney biopsies, and the rate of podocyte detachment from glomeruli into urine (podometrics) now have been developed and validated. They potentially fill important gaps in the glomerular disease monitoring toolbox. The application of these tools to glomerular disease groups shows good correlation with outcome, although data validating their use for individual decision making is not yet available. Given the urgency of the clinical problem, we argue that the time has come to focus on testing these tools for application to individualized clinical decision making toward more effective progression prevention.

Comparison of preoperative adaptive enlargement of the contralateral normal kidney in patients nephrectomized for benign non-functioning kidney versus renal cell carcinoma

OBJECTIVES

To investigate the potential effects of preoperative volumetric compensation of the contralateral normal kidney on renal function after simple nephrectomy or radical nephrectomy.

METHODS

A total of 306 patients (80 simple nephrectomy patients and 226 radical nephrectomy patients) with 1:3 propensity score matching were included between October 1996 and December 2013. Preoperative three-dimensional kidney volume was estimated from computed tomography images using a specialized volumetric program. Glomerular filtration rate assessed using the Chronic Kidney Disease Epidemiology Collaboration equations was checked preoperatively, 1 week, 3 months and 1 year after nephrectomy.

RESULTS

Preoperative mean Chronic Kidney Disease Epidemiology Collaboration glomerular filtration rate was 76.5 mL/min/1.73 m(2) in the simple nephrectomy group and 89.2 mL/min/1.73 m(2) in the radical nephrectomy group. In simple nephrectomy patients, mean Chronic Kidney Disease Epidemiology Collaboration glomerular filtration rate showed a stable pattern up to 3 months (75.5 mL/min/1.73 m(2) at 7 days and 76.2 mL/min/1.73 m(2) at 3 months), and decreased slightly to 72.6 mL/min/1.73 m(2) at 1 year. However, in radical nephrectomy patients, mean Chronic Kidney Disease Epidemiology Collaboration glomerular filtration rate decreased immediately to 63.4 mL/min/1.73 m(2) at 7 days after surgery, and then increased gradually to 64.6 mL/min/1.73 m(2) at 3 months and 65.9 mL/min/1.73 m(2) at 1 year. Preoperative mean contralateral normal kidney volume was 225.7 mL in the simple nephrectomy group and 180.1 mL in the radical nephrectomy group (P < 0.001). The contralateral normal kidney volume to total normal kidney volume ratio was 0.74 in the simple nephrectomy group and 0.51 in the radical nephrectomy group (P < 0.001).

CONCLUSIONS

Preoperative volumetric compensation of the contralateral normal kidney is important to maintain postoperative renal function in patients undergoing nephrectomy.

Podocyte Regeneration Driven by Renal Progenitors Determines Glomerular Disease Remission and Can Be Pharmacologically Enhanced

Podocyte loss is a general mechanism of glomerular dysfunction that initiates and drives the progression of chronic kidney disease, which affects 10% of the world population. Here, we evaluate whether the regenerative response to podocyte injury influences chronic kidney disease outcome. In models of focal segmental glomerulosclerosis performed in inducible transgenic mice where podocytes are tagged, remission or progression of disease was determined by the amount of regenerated podocytes. When the same model was established in inducible transgenic mice where renal progenitors are tagged, the disease remitted if renal progenitors successfully differentiated into podocytes, while it persisted if differentiation was ineffective, resulting in glomerulosclerosis. Treatment with BIO, a GSK3s inhibitor, significantly increased disease remission by enhancing renal progenitor sensitivity to the differentiation effect of endogenous retinoic acid. These results establish renal progenitors as critical determinants of glomerular disease outcome and a pharmacological enhancement of their differentiation as a possible therapeutic strategy.

The two kidney to one kidney transition and transplant glomerulopathy: a podocyte perspective

The attrition rate of functioning allografts beyond the first year has not improved despite improved immunosuppression, suggesting that nonimmune mechanisms could be involved. Notably, glomerulopathies may account for about 40% of failed kidney allografts beyond the first year of engraftment, and glomerulosclerosis and progression to ESRD are caused by podocyte depletion. Model systems demonstrate that nephrectomy can precipitate hypertrophic podocyte stress that triggers progressive podocyte depletion leading to ESRD, and that this process is accompanied by accelerated podocyte detachment that can be measured in urine. Here, we show that kidney transplantation "reverse nephrectomy" is also associated with podocyte hypertrophy and increased podocyte detachment. Patients with stable normal allograft function and no proteinuria had levels of podocyte detachment similar to levels in two-kidney controls as measured by urine podocyte assay. By contrast, patients who developed transplant glomerulopathy had 10- to 20-fold increased levels of podocyte detachment. Morphometric studies showed that a subset of these patients developed reduced glomerular podocyte density within 2 years of transplantation due to reduced podocyte number per glomerulus. A second subset developed glomerulopathy by an average of 10 years after transplantation due to reduced glomerular podocyte number and glomerular tuft enlargement. Reduced podocyte density was associated with reduced eGFR, glomerulosclerosis, and proteinuria. These data are compatible with the hypothesis that podocyte depletion contributes to allograft failure and reduced allograft half-life. Mechanisms may include immune-driven processes affecting the podocyte or other cells and/or hypertrophy-induced podocyte stress causing accelerated podocyte detachment, which would be amenable to nonimmune therapeutic targeting.