Functional and morphologic evaluation of kidney proximal tubuli and correlation with renal allograft prognosis

The renoprotective effects of hesperidin on kidney injury induced by exposure to severe chronic dust storm particulate matter through inhibiting the Smads/TGF-β1 signaling in rat

Exposure to dust storm particulate matter (PM) is detrimental to kidney tissue. In this study, the impacts of chronic intake of dusty PM were explored as a major objective in a specified compartment to make a real-like dust storm (DS) model, and the role of hesperidin (HSP) as an antioxidant on kidney tissue was assessed in rats. Thirty-two male Wistar rats (200-220 g) were randomly allocated into 4 groups: CA+NS: (clean air and normal saline as a vehicle of HSP). Dusty PM and NS (DS+NS). HSP+ CA: rats received 200 mg/kg of HSP by gavage for 28 days, once daily in addition to exposure to clean air. HSP+DS: HSP plus DS. In DS groups, the animals were exposed to dust storms at a concentration of 5000-8000 μg/m3 in the chamber for 1 h daily, for 4 consecutive weeks, except Thursdays and Fridays. At the end of the experiment, the animals were sacrificed for biochemical, inflammatory, oxidative stress, molecular parameters, and histological evaluation. DS significantly enhanced blood urea nitrogen and creatinine, inflammatory (tumor necrosis factor-α, and interleukin-1β), and oxidative stress indexes. Likewise, a significant increase was seen in mRNA Smads, collagen-I, and transforming growth factor-β1 (TGF-β1) expressions in the kidney. Histological findings showed contracted glomeruli and kidney structure disorder. In addition, Masson's trichrome staining demonstrated renal fibrosis. Nevertheless, HSP could significantly reverse these changes. Our data confirmed that DS results in kidney fibrosis through enhancing Smads/TGF-β1 signaling. However, HSP was able to inhibit these changes as confirmed by histological findings.

Gentisic acid mitigates gentamicin-induced nephrotoxicity in rats

The current investigation was considered to evaluate the beneficial effects of gentisic acid (GA) on gentamicin (GEN)-induced nephrotoxicity in rat kidneys through assessment of oxidative stress, inflammatory cytokines, and histopathological changes. Rats were split into five equal groups. Rats were treated with GA (25, 50, and 100 mg/kg/day, p.o.) for 14 consecutive days and GEN (100 mg/kg, i.p.) was administrated from day 8 to day 14 of the experiment. On the 15th day, blood samples were collected to determine neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), blood urea nitrogen (BUN), and creatinine (Cr) levels. Malondialdehyde (MDA), glutathione (GSH), tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β), and nitric oxide (NO) levels and the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were assessed in the renal tissue. Histopathological evaluations were done to confirm the biochemical results. GEN increased the levels of NGAL, KIM-1, BUN, and Cr in serum as well as MDA, NO, GSH, TNF-α, and IL-1β in renal tissue. Moreover, GEN administration reduced the activity of CAT, SOD, and GPx in renal tissue. Nonetheless, the administration of GA before and alongside GEN mitigated these deleterious effects. In conclusion, GA has a beneficial effect on biochemical, inflammatory, and oxidative stress indices against GEN-induced nephrotoxicity.

Tubular maximum phosphate reabsorption capacity in living kidney donors is independently associated with one-year recipient GFR

The donor glomerular filtration rate (GFR) measured before kidney donation is a strong determinant of recipient graft outcome. No tubular function markers have been identified that can similarly be used in donors to predict recipient outcomes. In the present study we investigated whether the pre-donation tubular maximum reabsorption capacity of phosphate (TmP-GFR), which may be considered a functional tubular marker in healthy kidney donors, is associated with recipient GFR at 1 yr after transplantation, a key determinant of long-term outcome. We calculated the pre-donation TmP-GFR from serum and 24-h urine phosphate and creatinine levels in 165 kidney donors, and recipient ¹²⁵I-iothalamate GFR and eGFR (CKD-EPI) at 12 mo after transplantation. Kidney donors were 51 ± 10 yr old, 47% were men, and mean GFR was 118 ± 26 ml/min. The donor TmP-GFR was associated with recipient GFR 12 mo after transplantation (GFR 6.0 ml/min lower per 1 mg/dl decrement of TmP-GFR), which persisted after multivariable adjustment for donor age, sex, pre-donation GFR, and blood pressure and other potential confounders. Results were highly similar when eGFR at 12 mo was taken as the outcome. Tubular damage markers kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin were low and not associated with recipient GFR. A lower donor TmP-GFR before donation, which may be considered to represent a functional measure of tubular phosphate reabsorption capacity, is independently associated with a lower recipient GFR 1 yr after transplantation. These data are the first to link donor tubular phosphate reabsorption with recipient GFR post-transplantation.

Post-Transplant Hypophosphatemia and the Risk of Death-Censored Graft Failure and Mortality after Kidney Transplantation

BACKGROUND AND OBJECTIVES

Hypophosphatemia is common in the first year after kidney transplantation, but its clinical implications are unclear. We investigated the relationship between the severity of post-transplant hypophosphatemia and mortality or death-censored graft failure in a large cohort of renal transplant recipients with long-term follow-up.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a longitudinal cohort study in 957 renal transplant recipients who were transplanted between 1993 and 2008 at a single center. We used a large real-life dataset containing 28,178 phosphate measurements (median of 27; first to third quartiles, 23-34) serial measurements per patient) and selected the lowest intraindividual phosphate level during the first year after transplantation. The primary outcomes were all-cause mortality, cardiovascular mortality, and death-censored graft failure.

RESULTS

The median (interquartile range) intraindividual lowest phosphate level was 1.58 (1.30-1.95) mg/dl, and it was reached at 33 (21-51) days post-transplant. eGFR was the main correlate of the lowest serum phosphate level (model R2 =0.32). During 9 (5-12) years of follow-up, 181 (19%) patients developed graft failure, and 295 (35%) patients died, of which 94 (32%) deaths were due to cardiovascular disease. In multivariable Cox regression analysis, more severe hypophosphatemia was associated with a lower risk of death-censored graft failure (fully adjusted hazard ratio, 0.61; 95% confidence interval, 0.43 to 0.88 per 1 mg/dl lower serum phosphate) and cardiovascular mortality (fully adjusted hazard ratio, 0.37; 95% confidence interval, 0.22 to 0.62) but not noncardiovascular mortality (fully adjusted hazard ratio, 1.33; 95% confidence interval, 0.9 to 1.96) or all-cause mortality (fully adjusted hazard ratio, 1.15; 95% confidence interval, 0.81 to 1.61).

CONCLUSIONS

Post-transplant hypophosphatemia develops early after transplantation. These data connect post-transplant hypophosphatemia with favorable long-term graft and patient outcomes.

The proximal tubule is the primary target of injury and progression of kidney disease: role of the glomerulotubular junction

There is an alarming global increase in the incidence of end-stage kidney disease, for which early biomarkers and effective treatment options are lacking. Largely based on the histology of the end-stage kidney and on the model of unilateral ureteral obstruction, current investigation is focused on the pathogenesis of renal interstitial fibrosis as a central mechanism in the progression of chronic kidney disease (CKD). It is now recognized that cumulative episodes of acute kidney injury (AKI) can lead to CKD, and, conversely, CKD is a risk factor for AKI. Based on recent and historic studies, this review shifts attention from the glomerulus and interstitium to the proximal tubule as the primary sensor and effector in the progression of CKD as well as AKI. Packed with mitochondria and dependent on oxidative phosphorylation, the proximal tubule is particularly vulnerable to injury (obstructive, ischemic, hypoxic, oxidative, metabolic), resulting in cell death and ultimately in the formation of atubular glomeruli. Animal models of human glomerular and tubular disorders have provided evidence for a broad repertoire of morphological and functional responses of the proximal tubule, revealing processes of degeneration and repair that may lead to new therapeutic strategies. Most promising are studies that encompass the entire life cycle from fetus to senescence, recognizing epigenetic factors. The application of techniques in molecular characterization of tubule segments and the development of human kidney organoids may provide new insights into the mammalian kidney subjected to stress or injury, leading to biomarkers of early CKD and new therapies.

Intragraft transcriptional profiling of renal transplant patients with tubular dysfunction reveals mechanisms underlying graft injury and recovery

Background

Proximal tubular dysfunction (PTD) is associated with a decreased long-term graft survival in renal transplant patients and can be detected by the elevation of urinary tubular proteins. This study investigated transcriptional changes in biopsies from renal transplant patients with PTD to disclose molecular mechanisms underlying graft injury and functional recovery.

Methods

Thirty-three renal transplant patients with high urinary levels of retinol-binding protein, a biomarker of PTD, were enrolled in the study. The initial immunosuppressive scheme included azathioprine, cyclosporine, and steroids. After randomization, 18 patients (group 2) had their treatment modified by reducing cyclosporine dosage and substituting azathioprine for mycophenolate mofetil, while the other 15 patients (group 1) remained under the initial scheme. Patients were biopsied at enrollment and after 12 months of follow-up, and paired comparisons were performed between their intragraft gene expression profiles. The differential transcriptome profiles were analyzed by constructing gene co-expression networks and identifying enriched functions and central nodes in each network.

Results

Only the alternative immunosuppressive scheme used in group 2 ameliorated renal function and tubular proteinuria after 12 months of follow-up. Intragraft molecular changes observed in group 2 were linked to autophagy, extracellular matrix, and adaptive immunity. Conversely, gene expression changes in group 1 were related to fibrosis, endocytosis, ubiquitination, and endoplasmic reticulum stress.

Conclusion

These results suggest that molecular networks associated with the control of endocytosis, autophagy, protein overload, fibrosis, and adaptive immunity may be involved in improvement of graft function.

Electronic supplementary material

The online version of this article (doi:10.1186/s40246-015-0059-6) contains supplementary material, which is available to authorized users.

Does graft mass impact on pediatric kidney transplant outcomes?

BACKGROUND

The aim of this study is to assess the evolution of renal size and function in pediatric transplant patients according to the graft mass/recipient size ratio.

METHODS

Fifty pediatric renal transplant recipients were followed over 2 years. Grafts were weighed, and three different graft mass/m(2) ratios were determined: (1) low graft mass (58 g/m(2), range 31-57 g/m(2)), (2) median (142 g/m(2), range 59-141 g/m(2)) and high (267 g/m(2), range 143-353 g/m(2)). Patients underwent repeated ultrasound Doppler scans and repeated measurements of estimated glomerular filtration rate (eGFR; 1 week and 1, 6, 12 and 24 months), urinary retinol-binding protein (RBP) and proteinuria (1 week and 6, 12 and 24 months).

RESULTS

The volume of renal tissue increased by 12 ± 5.6 cm(3) at 24 months (p = 0.035) in the low graft mass and decreased by -14 ± 7 cm(3) (p = 0.046) in the high graft mass. The eGFR increased when either low (30 ± 5 ml/min/1.73 m(2), p < 0.001) or median (19 ± 4 ml/min/1.73 m(2), p < 0.001) graft mass was transplanted but remained stable when high graft mass was transplanted. The resistive index (RI) presented a significant decrease throughout early follow-up in the transplants involving low and median graft mass, whereas a slight rise was observed in those involving high graft mass. A significant difference was apparent 6 months post-transplant. Transplants of low and median graft mass were associated with an initial higher urinary RBP. No significant differences in proteinuria were detected.

CONCLUSIONS

Small kidneys undergo increases in volume and function without escalation of either proteinuria or urinary RBP, characterizing an adequate adaptation to the recipient. Children receiving larger kidneys present a reduction in volume, stable GFR and higher RI at 6 months.

Urine high and low molecular weight proteins one-year post-kidney transplant: relationship to histology and graft survival

Increased urinary protein excretion is common after renal transplantation and portends worse outcome. In this study we assessed the prognostic contribution of several urinary proteins. Urinary total protein, albumin, retinol binding protein (RBP), α-1-microglobulin, IgG and IgM were measured in banked urine samples from 221 individuals 1 year after renal transplantation (age 52 ± 13 years, 55% male, 93% Caucasian and 82% living donor). Levels of all proteins measured were higher than in normal nontransplant populations. Patients with glomerular lesions had higher urinary albumin than those with normal histology, while those with interstitial fibrosis and tubular atrophy plus inflammation (ci>0, cg = 0, i>0) had higher levels of IgG, IgM, α-1-microglobulin and RBP. Concomitant normal levels of urinary albumin, IgM and RBP identified normal histology (specificity 91%, sensitivity 15%,). Urinary levels of the specific proteins were highly correlated, could not differentiate among the histologic groups, and appeared to result from tubulointerstitial damage. Increased urinary excretion of the low molecular weight protein RBP was a sensitive marker of allografts at risk, predicting long-term graft loss independent of histology and urinary albumin. This study highlights the prognostic importance of tubulointerstitial disease for long-term graft loss.

Identifying biomarkers as diagnostic tools in kidney transplantation

There is a critical need for biomarkers for early diagnosis, treatment response, and surrogate end point and outcome prediction in organ transplantation, leading to a tailored and individualized treatment. Genomic and proteomic platforms have provided multiple promising new biomarkers during the last few years. However, there is still no routine application of any of these markers in clinical transplantation. This article will discuss the existing gap between biomarker discovery and clinical application in the kidney transplant setting. Approaches to implementing biomarker monitoring into clinical practice will also be discussed.