Effect of diabetes mellitus on the recovery of changes in renal functions and glomerular permeability following reversible 24-hour unilateral ureteral obstruction

Shrunken pore syndrome in heart transplantation: a pore ready to close?

Background: A newly discovered renal syndrome, shrunken pore syndrome (SPS), has been shown to increase mortality regardless of renal function. SPS is defined as an estimated glomerular filtration rate (eGFR) of cystatin C ≤ 60% than eGFRcreatinine. We set out to study SPS in relation to the survival of heart transplantation patients with a follow-up of up to 12 years. Methods. This was a single-center cohort study including 253 consecutive patients undergoing heart transplantation. The prevalence of SPS at different time points post-transplantation and its effect on survival was evaluated using Kaplan-Meier's analysis and multivariable Cox proportional hazards regression. Results. The prevalence of SPS was 7.5% the day after transplantation (D1), which rose to 71% week 4 after surgery. There was no difference in survival for patients with SPS D1 compared to patients without SPS D1. Patients with SPS 4 weeks compared to patients without SPS 4 weeks after transplantation showed a 5- and 10-year survival of 73% vs. 93% (p = .02) and 63% vs. 90% (p = .005), respectively. SPS developed during the postoperative period was also found to be an independent predictor of mortality (HR 4.65; 95% CI 1.36-15.8). Discussion. SPS that developed in the postoperative course after heart transplantation was found to be an independent predictor of mortality with a severe negative impact on 5- and 10-year survival.

Selective glomerular hypofiltration syndrome

The estimated glomerular filtration rate (eGFR) provides insight into cardiovascular disease (CVD) risk stratification and proactive management. Accumulating evidence suggests that combining eGFR calculated from serum cystatin C (eGFRcys) and from serum creatinine (eGFRcrea) improves CVD risk stratification over eGFRcrea alone. The term selective glomerular hypofiltration syndrome (SGHS) or shrunken pore syndrome has been proposed to define an eGFRcys:eGFRcrea ratio <1, which is hypothesized to result from a reduced glomerular filtration of 5- to 30-kDa molecules as compared with smaller molecules. SGHS may be identified in people with normal or reduced measured GFR, but the prevalence depends on the cut-off value of the eGFRcys:eGFRcrea ratio used, which is not yet standardized. SGHS is strongly associated with increased CVD and mortality risks and it may offer an opportunity to expand our understanding of the mechanisms linking GFR disorders with CVD risk (e.g. an altered plasma proteome), which may guide treatment decisions. However, muscle wasting may also contribute to a reduced eGFRcys:eGFRcrea ratio and there are open questions regarding the pathophysiology of a reduced eGFRcys:eGFRcrea ratio, the reference cut-off values of the ratio to define the syndrome and its clinical implications. We now critically review the SGHS concept, its pathophysiological basis and links to CVD and the potential consequences for clinical practice and propose a research agenda.

The Effect of Hypertension on the Recovery of Renal Dysfunction following Reversal of Unilateral Ureteral Obstruction in the Rat

Both ureteral obstruction (UO) and hypertension are common conditions that affect kidney functions. Hypertension and chronic kidney disease are closely associated with an overlapping and intermingled cause-and-effect relationship. The effect of hypertension on the renal dysfunction following reversible UO has not been studied previously. To study this effect, spontaneously hypertensive (G-HT, n = 10) and normotensive Wistar (G-NT, n = 10) rats underwent 48-h reversible left unilateral UO (UUO), and the effect of UUO was studied 96 h following UUO reversal. The glomerular filtration rate, renal blood flow, and renal tubular functions such as the fractional excretion of sodium in the post-obstructed left kidney (POK) in both groups were significantly altered compared with the non-obstructed right kidney (NOK). However, the alterations in the G-HT were significantly more exaggerated when compared with the G-NT. Similar findings were observed with the histological features, gene expression of kidney injury markers, pro-inflammatory, pro-fibrotic and pro-apoptotic cytokines, and pro-collagen, as well as tissue levels of apoptotic markers. We conclude that hypertension has significantly exaggerated the alterations in renal functions and other parameters of renal injury associated with UUO.

The complexity of kidney disease and diagnosing it - cystatin C, selective glomerular hypofiltration syndromes and proteome regulation

Estimation of kidney function is often part of daily clinical practice, mostly done by using the endogenous glomerular filtration rate (GFR)-markers creatinine or cystatin C. A recommendation to use both markers in parallel in 2010 has resulted in new knowledge concerning the pathophysiology of kidney disorders by the identification of a new set of kidney disorders, selective glomerular hypofiltration syndromes. These syndromes, connected to strong increases in mortality and morbidity, are characterized by a selective reduction in the glomerular filtration of 5-30 kDa molecules, such as cystatin C, compared to the filtration of small molecules <1 kDa dominating the glomerular filtrate, for example water, urea and creatinine. At least two types of such disorders, shrunken or elongated pore syndrome, are possible according to the pore model for glomerular filtration. Selective glomerular hypofiltration syndromes are prevalent in investigated populations, and patients with these syndromes often display normal measured GFR or creatinine-based GFR-estimates. The syndromes are characterized by proteomic changes promoting the development of atherosclerosis, indicating antibodies and specific receptor-blocking substances as possible new treatment modalities. Presently, the KDIGO guidelines for diagnosing kidney disorders do not recommend cystatin C as a general marker of kidney function and will therefore not allow the identification of a considerable number of patients with selective glomerular hypofiltration syndromes. Furthermore, as cystatin C is uninfluenced by muscle mass, diet or variations in tubular secretion and cystatin C-based GFR-estimation equations do not require controversial race or sex terms, it is obvious that cystatin C should be a part of future KDIGO guidelines.

Effect of angiotensin II on diabetic glomerular hyperpermeability: an in vivo permeability study in rats

Angiotensin II drives the pathogenesis of diabetic kidney disease, and its systemic administration induces glomerular hyperpermeability in normal rats. However, the response of diabetic glomerular permeability to angiotensin II is largely unknown. In the present study, we investigated the impact of extended systemic administration of angiotensin II on the glomerular permeability of streptozotocin (STZ)-induced late diabetes in rats. We examined the changes in the glomerular permeability after subcutaneous infusion of angiotensin II at 200 ng·kg^-1·min^-1 for 7 days in male Wistar diabetic rats with 3 mo of STZ-induced diabetes (i.e., blood glucose of ∼20 mmol/L). We also compared these changes with the effects on nondiabetic rats. The sieving coefficients (θ) for inert polydisperse Ficoll molecules, which had a radius of 10-90 Å (Ficoll_{70-90 Å}), were measured in vivo. The θ for large Ficoll molecules was selectively enhanced after infusion of extended angiotensin II in both diabetic (θ for Ficoll_{70-90 Å} = 0.00244 vs. 0.00079, P < 0.001) and nondiabetic animals (θ for Ficoll_{70-90 Å} = 0.00029 vs. 0.00006, P < 0.001). These changes were compatible with the more than twofold increase in the macromolecular glomerular transport through the large-pore pathways after infusion of angiotensin II in both diabetic and nondiabetic animals. Angiotensin II infusion enhanced the large shunt-like glomerular transport pathway of STZ-induced late diabetes. Such defects can account for the large-molecular-weight IgM-uria that is observed in severe diabetic kidney disease.

Despite initial recovery of GFR, long-term renal functions deteriorate following short periods of unilateral ureteral obstruction

Following the release of short periods of unilateral ureteral obstruction (UUO), glomerular filtration rate (GFR) recovers by time. However, research in experimental animal models has demonstrated the presence of an ongoing element of renal interstitial fibrosis a few weeks following UUO reversal. Interstitial fibrosis can cause deterioration in GFR, and it is not known whether it leads to an ongoing slow deterioration in other renal functions despite the apparent initial recovery postreversal. To investigate this, rats underwent a 72-h reversible UUO. Renal functions of nonobstructed and previously obstructed kidneys were measured 1, 4, and 18 mo postreversal. GFR in nonobstructed and previously obstructed kidneys was similar up to 18 mo postreversal. However, there was ongoing tubulointerstitial fibrosis, and the degree of tubular atrophy and dilatation deteriorated by time. This was associated with an increase in urinary albumin leakage and alterations in renal injury markers, proinflammatory and profibrotic cytokines, and p53 from 4 mo onward despite the recovery in GFR. In conclusion, several aspects of renal functions continue to deteriorate following reversal of relatively short periods of UUO despite the initial recovery in GFR. This might stimulate further research in this area and might have clinical implications in terms of determining the best time for intervention following acute ureteral obstruction and long-term monitoring of these individuals.