Imaging and elemental mapping of biological specimens with a dual-EDS dedicated scanning transmission electron microscope.

A dedicated analytical scanning transmission electron microscope (STEM) with dual energy dispersive spectroscopy (EDS) detectors has been designed for complementary high performance imaging as well as high sensitivity elemental analysis and mapping of biological structures. The performance of this new design, based on a Hitachi HD-2300A model, was evaluated using a variety of biological specimens. With three imaging detectors, both the surface and internal structure of cells can be examined simultaneously. The whole-cell elemental mapping, especially of heavier metal species that have low cross-section for electron energy loss spectroscopy (EELS), can be faithfully obtained. Optimization of STEM imaging conditions is applied to thick sections as well as thin sections of biological cells under low-dose conditions at room and cryogenic temperatures. Such multimodal capabilities applied to soft/biological structures usher a new era for analytical studies in biological systems.

Serum relaxin levels and kidney function in late pregnancy with or without preeclampsia.

OBJECTIVE: Relaxin, a potent pregnancy-related hormone, has been proposed to be a major mediator of renal physiology in normal pregnancy. We wished to test relaxin levels in pregnancy and preeclampsia. METHODS: We performed precise physiologic measurements of kidney function in 38 normal peripartum women and 58 women with preeclampsia. We measured serum relaxin levels prior to delivery and over the first 4 postpartum weeks utilizing a modern, validated ELISA. Results were compared to those of 18 normal women of childbearing age. RESULTS: Relaxin levels were substantially elevated in women prior to delivery (364 ± 268 vs. 15 ± 16 pg/ml) and fell rapidly over the first postpartum week reaching normal non pregnant levels by Week 2 (32 ± 64 vs. 15 ± 16 pg/ml). No differences were seen between relaxin levels in normal pregnancy as compared to preeclampsia (364 ± 268 vs. 376 ± 241 pg/ml) despite substantial and persistent abnormalities in GFR (149 ± 33 vs. 89 ± 25 ml/min), albuminuria (14 vs. 687 mg/g) and mean arterial pressure (80 ± 8 vs. 111 ± 18). Furthermore no correlation could be established between physiologic measures (GFR, MAP, RBF, RVR) and relaxin levels (p > 0.3), either in the overall population or any of the subgroups. CONCLUSION: Relaxin is indeed significantly elevated in the serum of women during late pregnancy and the early puerperium. However, serum relaxin does not appear to influence BP, renal vascular resistance, renal blood flow or GFR in late pregnancy or in women with preeclampsia.

Course of preeclamptic glomerular injury after delivery.

We evaluated the early postpartum recovery of glomerular function over 4 wk in 57 women with preeclampsia. We used physiological techniques to measure glomerular filtration rate (GFR), renal plasma flow, and oncotic pressure (pi(A)) and computed a value for the two-kidney ultrafiltration coefficient (K(f)). Compared with healthy, postpartum controls, GFR was depressed by 40% on postpartum day 1, but by only 19% and 8% in the second and fourth postpartum weeks, respectively. Hypofiltration was attributable solely to depression, at corresponding postpartum times, of K(f) by 55%, 30%, and 18%, respectively. Improvement in glomerular filtration capacity was accompanied by recovery of hypertension to near-normal levels and significant improvement in albuminuria. We conclude that the functional manifestations of the glomerular endothelial injury of preeclampsia largely resolve within the first postpartum month.

Effect of L-arginine therapy on the glomerular injury of preeclampsia: a randomized controlled trial.

OBJECTIVE: To assess the benefit of l-arginine, the precursor to nitric oxide, on blood pressure and recovery of the glomerular lesion in preeclampsia. METHODS: Forty-five women with preeclampsia were randomized to receive either l-arginine or placebo until day 10 postpartum. Primary outcome measures including mean arterial pressure, glomerular filtration rate, and proteinuria were assessed on the third and 10th days postpartum by inulin clearance and albumin-to-creatinine ratio. Nitric oxide, cyclic guanosine 3'5' monophosphate, endothelin-1, and asymmetric-dimethyl-arginine and arginine levels were assayed before delivery and on the third and 10th days postpartum. Healthy gravid women provided control values. Assuming a standard deviation of 10 mm Hg, the study was powered to detect a 10-mm Hg difference in mean arterial pressure (alpha .05, beta .20) between the study groups. RESULTS: No significant differences existed between the groups with preeclampsia before randomization. Compared with the gravid control group, women with preeclampsia exhibited significantly increased serum levels of endothelin-1, cyclic guanosine 3'5' monophosphate, and asymmetric-dimethyl-arginine before delivery. Despite a significant increase in postpartum serum arginine levels due to treatment, no differences were found in the corresponding levels of nitric oxide, endothelin-1, cyclic guanosine 3'5' monophosphate, or asymmetric-dimethyl-arginine between the two groups with preeclampsia. Further, there were no significant differences in any of the primary outcome measures with both groups demonstrating similar levels in glomerular filtration rate and equivalent improvements in both blood pressure and proteinuria. CONCLUSION: Blood pressure and kidney function improve markedly in preeclampsia by the 10th day postpartum. Supplementation with l-arginine does not hasten this recovery. LEVEL OF EVIDENCE: I.

The dynamics of glomerular filtration in the puerperium.

We evaluated the glomerular filtration rate (GFR) during the second postpartum week in 22 healthy women who had completed an uncomplicated pregnancy. We used physiological techniques to measure GFR, renal plasma flow, and oncotic pressure and computed a value for the two-kidney ultrafiltration coefficient (K(f)). We compared these findings with those in pregnant women previously studied on the first postpartum day as well as nongravid women of reproductive age. Healthy female transplant donors of reproductive age permitted the morphometric analysis of glomeruli and computation of the single-nephron K(f). The aforementioned physiological and morphometric measurements were utilized to estimate transcapillary hydraulic pressure (Delta P) from a mathematical model of glomerular ultrafiltration. We conclude that postpartum day 1 is associated with marked glomerular hyperfiltration (+41%). A theoretical analysis of GFR determinants suggests that depression of glomerular capillary oncotic pressure, the force opposing the formation of filtrate, is the predominant determinant of early elevation of postpartum GFR. A reversal of the gestational hypervolemia and hemodilution, still evident on postpartum day 1, eventuates by postpartum week 2. An elevation of oncotic pressure in the plasma that flows axially along the glomerular capillaries to supernormal levels ensues; however, GFR remains modestly elevated (+20%) above nongravid levels. An analysis of filtration dynamics at this time suggests that a significant increase in Delta P by up to 16%, an approximately 50% increase in K(f), or a combination of smaller increments in both must be invoked to account for the persistent hyperfiltration.

Determinants of GFR depression in early membranous nephropathy.

We evaluated the glomerular filtration rate (GFR) in 34 subjects with membranous nephropathy (MN) of new onset. We used physiological techniques to measure GFR, renal plasma flow, and oncotic pressure and computed a value for the two-kidney ultrafiltration coefficient (K(f)). A morphometric analysis of glomeruli in the diagnostic biopsy permitted computation of the single-nephron ultrafiltration coefficient (SNK(f)). MN subjects were divided into two groups: moderate or severe, according to whether GFR was depressed by less or more than 50%. SNK(f) was subnormal but similar in moderate and severe MN. In contrast, two-kidney K(f) was significantly more depressed in severe than in moderate MN. We estimated the total number of functioning glomeruli (N(g)) by dividing two-kidney K(f) by SNK(f). Whereas mean N(g) was similar in controls and moderate MN (1.5 and 1.4-1.7 x 10(6), respectively), it was significantly lower in severe MN (0.5 x 10(6)). This degree of glomerulopenia was not reflected in the rate of global sclerosis. We conclude that a combination of depressed SNK(f) (due to foot process broadening) and profound glomerulopenia accounts for GFR depression of >50% early in the course of MN. The cause of the glomerulopenia remains to be elucidated.

Structural determinants of glomerular permeability.

Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular basement membrane (GBM), and epithelial filtration slits form a series arrangement in which the flow diverges as it enters the GBM from the fenestrae and converges again at the filtration slits. A hydrodynamic model that combines morphometric findings with water flow data in isolated GBM has predicted overall hydraulic permeabilities that are consistent with measurements in vivo. The resistance of the GBM to water flow, which accounts for roughly half that of the capillary wall, is strongly dependent on the extent to which the GBM surfaces are blocked by cells. The spatial frequency of filtration slits is predicted to be a very important determinant of the overall hydraulic permeability, in keeping with observations in several glomerular diseases in humans. Whereas the hydraulic resistances of the cell layers and GBM are additive, the overall sieving coefficient for a macromolecule (its concentration in Bowman's space divided by that in plasma) is the product of the sieving coefficients for the individual layers. Models for macromolecule filtration reveal that the individual sieving coefficients are influenced by one another and by the filtrate velocity, requiring great care in extrapolating in vitro observations to the living animal. The size selectivity of the glomerular capillary has been shown to be determined largely by the cellular layers, rather than the GBM. Controversial findings concerning glomerular charge selectivity are reviewed, and it is concluded that there is good evidence for a role of charge in restricting the transmural movement of albumin. Also discussed is an effect of albumin that has received little attention, namely, its tendency to increase the sieving coefficients of test macromolecules via steric interactions. Among the unresolved issues are the specific contributions of the endothelial glycocalyx and epithelial slit diaphragm to the overall hydraulic resistance and macromolecule selectivity and the nanostructural basis for the observed permeability properties of the GBM.

Glomerular permselectivity in early stages of overt diabetic nephropathy.

BACKGROUND: Impairment of glomerular size selectivity has been demonstrated by the dextran-sieving technique in nephropathic diabetics with heavy, but not mild proteinuria. The purpose of the present study was to determine whether such a barrier defect could be demonstrated with mild proteinuria by substituting Ficoll 70, a polysucrose, for dextran as a probe of the filtration barrier. METHODS: Differential solute clearances were performed in 12 individuals with early diabetic nephropathy on two occasions: after 60 days of treatment with losartan 50 mg daily or a placebo. An uncharged preparation of nonreabsorbable Ficoll 70 was infused along with inulin. Fractional clearance (theta) of Ficoll of discrete size was determined after separating molecules in urine and plasma in narrow 2 A fractions over a 20 to 60 A radius interval by size exclusion high-performance liquid chromatography (HPLC). A hydrodynamic theory of hindered ficoll transport through water-filled pores was used to characterize the pore size distribution of the glomerular barrier. RESULTS: The theta for Ficoll molecules with radii> 50 A was selectively enhanced in placebo-treated diabetic nephropathy versus corresponding theta in healthy control subjects (N = 12). Computations revealed a lower distribution of glomerular pores that was unaltered in nephropathic diabetics. However, an upper distribution of large, shunt-like pores was more prominent, exceeding healthy controls by one order of magnitude in diabetic nephropathy (P = 0.01). A trend to lower theta for Ficoll in the 56 to 60 A radius range during losartan therapy is computed to have lowered the fraction of shunted filtrate by 26 to 44%, depending on whether glomerular pressure declined. The corresponding reduction in theta for endogenous albumin, IgG, and IgG4 was by 19 to 23% (P < 0.05). CONCLUSION: Our findings suggest that shunt-like defects, partially reversible by angiotensin II blockade, are present early in the course of diabetic nephropathy. We estimate that such defects can account for immunoglobulinuria in this disorder. Additional impairment of either charge- or shape-selectivity must be invoked to explain the observed level of albuminuria, however.

Evolution of incipient nephropathy in type 2 diabetes mellitus.

BACKGROUND: We examined the course of glomerular injury in 12 Pima Indians with long-standing (>8 years) type 2 diabetes mellitus, normal serum creatinine, and microalbuminuria. They were compared with a group of 10 Pima Indians in Arizona with new-onset (<5 years) type 2 diabetes, normal renal function, and normoalbuminuria (<30 mg albumin/g creatinine on random urine specimens). METHODS: A combination of physiological and morphological techniques was used to evaluate glomerular function and structure serially on two occasions separated by a 48-month interval. Clearances of iothalamate and p-aminohippuric acid were used to determine glomerular filtration rate (GFR) and renal plasma flow, respectively. Afferent oncotic pressure was determined by membrane osmometry. The single nephron ultrafiltration coefficient (Kf) was determined by morphometric analysis of glomeruli and mathematical modeling. RESULTS: The urinary albumin-to-creatinine ratio (median + range) increased from 84 (28 to 415) to 260 (31 to 2232) mg/g between the two examinations (P = 0.01), and 6 of 12 patients advanced from incipient (ratio = 30 to 299 mg/g) to overt nephropathy (>/=300 mg/g). A 17% decline in GFR between the two examinations from 186 +/- 41 to 155 +/- 50 mL/min (mean +/- SD; P = 0.06) was accompanied by a 17% decline in renal plasma flow (P = 0.003) and a 6% increase in plasma oncotic pressure (P = 0.02). Computed glomerular hydraulic permeability was depressed by 13% below control values at both examinations, a result of a widened basement membrane and a reduction in frequency of epithelial filtration slits. The filtration surface area declined significantly, however, from 6.96 +/- 2.53 to 5.51 +/- 1.62 x 105 mm2 (P = 0.01), a change that was accompanied by a significant decline in the number of mesangial cells (P = 0.001), endothelial cells (P = 0.038), and podocytes (P = 0.0005). These changes lowered single nephron Kf by 20% from 16.5 +/- 6.0 to 13.2 +/- 3.6 nL/(minutes + mm Hg) between the two examinations (P = 0.02). Multiple linear regression analysis revealed that among the determinants of GFR, only the change in single nephron Kf was related to the corresponding change in GFR. CONCLUSION: We conclude that a reduction in Kf is the major determinant of a decline in GFR from an elevated toward a normal range as nephropathy in type 2 diabetes advances from an incipient to an overt stage.

Severe glomerular sclerosis is not associated with poor outcome after kidney transplantation.

BACKGROUND: The increased utilization of expanded criteria kidney donors has necessitated the reevaluation of multiple donor risk factors to insure the best outcome from this valuable resource. Reports of decreased graft survival in recipients of kidneys from donors with > or =20% glomerular sclerosis (GS) have led many transplant centers to refuse these donor kidneys. The purpose of this study is to compare outcome in recipients of cadaveric donor kidneys with > or =20% GS versus those with <20% or no GS at our center. METHODS: We retrospectively reviewed 18 donor and 19 recipient and outcome variables in 89 recipients of kidneys, which were biopsied at the time of transplantation, between February 1995 and November 1998. We evaluated outcome based upon the percent of GS and the degree of vasculopathy. RESULTS: Donors with > or =20% GS were older and had more hypertension. Recipients of kidneys with > or =20% GS were older, had higher serum creatinine values at 1 and 2 years, but similar rates of delayed graft function and 2-year graft survival. Vasculopathy did not correlate to any important donor criteria except the percent GS. However, serum creatinine was significantly higher in recipients of kidneys with moderate vasculopathy versus none, up to 2 years after transplantation. There was no significant difference in graft loss based upon vasculopathy. CONCLUSION: Kidneys from donors with > or =20% GS provide excellent outcome similar to kidneys from donors with no GS.

PAH extraction and estimation of plasma flow in human postischemic acute renal failure.

We determined the effect of postischemic injury to the human renal allograft on p-aminohippurate (PAH) extraction (E(PAH)) and renal blood flow. We evaluated renal function in 44 allograft recipients on two occasions: 1-3 h after reperfusion (day 0) and again on postoperative day 7. On day 0 subsets underwent intraoperative determination of renal blood flow (n = 35) by Doppler flow meter and E(PAH) (n = 25) by renal venous assay. Blood flow was also determined in another subset of 16 recipients on postoperative day 7 by phase contrast-cine-magnetic resonance imaging, and E(PAH) was computed from the simultaneous PAH clearance. Glomerular filtration rate (GFR) on day 7 was used to divide subjects into recovering (n = 23) and sustained (n = 21) acute renal failure (ARF) groups, respectively. Despite profound depression of GFR in the sustained ARF group, renal plasma flow was only slightly depressed, averaging 296 +/- 162 ml. min(-1). 1.73 m(-2) on day 0 and 202 +/- 72 ml. min(-1). 1.73 m(-2) on day 7, respectively. These values did not differ from corresponding values in the recovering ARF group: 252 +/- 133 and 280 +/- 109 ml. min(-1). 1.73 m(-2), respectively. E(PAH) was profoundly depressed on day 0, averaging 18 +/- 14 and 10 +/- 7% in recovering and sustained ARF groups, respectively, vs. 86 +/- 6% in normal controls (P < 0.001). Corresponding values on day 7 remained significantly depressed at 65 +/- 20 and 11 +/- 22%, respectively. We conclude that postischemic injury to the renal allograft results in profound impairment of E(PAH) that persists for at least 7 days, even after the onset of recovery. An ensuing reduction in urinary PAH clearance results in a gross underestimate of renal plasma flow, which is close to the normal range in the initiation, maintenance, and recovery stages of this injury.

The dynamics of glomerular filtration after Caesarean section.

The objective of this study was to determine whether the glomerular hyperfiltration of pregnancy is maintained even after Caesarean section and, if so, to define the responsible hemodynamics. The dynamics of glomerular filtration were evaluated in 12 healthy women who had just completed an uncomplicated pregnancy and were delivered by Caesarean section. Age-matched but non-gravid female volunteers (n = 22) served as control subjects. GFR in postpartum women was elevated above control values by 41%; 149+/-10 versus 106+/-3 ml/min per 1.73 m2, respectively (P < 0.001). In contrast, corresponding renal plasma flow was the same in the two groups, such that the postpartum filtration fraction was significantly elevated by 20%. Computation of glomerular intracapillary oncotic pressure (piGC) from knowledge of plasma oncotic pressure and the filtration fraction revealed this quantity to be significantly reduced in postpartum women, 20.6+/-1.7 versus 26.1+/-2.0 mmHg in control subjects (P < 0.001). A theoretical analysis of glomerular ultrafiltration suggests that depression of piGC, the force opposing the formation of filtrate, is predominantly or uniquely responsible for the observed postpartum hyperfiltration.

Changing glomerular filtration with progression from impaired glucose tolerance to Type II diabetes mellitus.

Glomerular filtration rate (iothalamate clearance) was measured serially for 48 months in 26 Pima Indians with impaired glucose tolerance and 27 with normal glucose tolerance. At baseline, the mean glomerular filtration rate (SEM) was 133+/-8 ml/min in subjects with impaired glucose tolerance and 123+/-5 ml/min in those with normal glucose tolerance (p = 0.12). In the 12 subjects with impaired glucose tolerance who progressed to Type II (non-insulin-dependent) diabetes during follow-up, mean glomerular filtration rate increased by 30% (p = 0.011). Among the remaining 14 subjects with impaired glucose tolerance, 12 reverted to normoglycaemia. The glomerular filtration rate both at baseline and after 48 months in this subgroup exceeded the values of subjects with normal glucose tolerance by 20 % (p = 0.008) and 14% (p=0.013), respectively. A pronounced rise in the glomerular filtration rate occurs at the onset of Type II diabetes but a trend to hyperfiltration is also present in those with impaired glucose tolerance.

Sodium reabsorption and distribution of Na+/K+-ATPase during postischemic injury to the renal allograft.

BACKGROUND: A loss of proximal tubule cell polarity is thought to activate tubuloglomerular feedback, thereby contributing to glomerular filtration rate depression in postischemic acute renal failure (ARF). METHODS: We used immunomicroscopy to evaluate the segmental distribution of Na+/K+-ATPase in tubules of recipients of cadaveric renal allografts. Fractional excretion (FE) of sodium and lithium was determined simultaneously. Observations were made on two occasions: one to three hours after graft reperfusion (day 0) and again on post-transplant day 7. An inulin clearance below or above 25 ml/min on day 7 was used to divide subjects into groups with sustained (N = 15) or recovering (N = 16) ARF, respectively. RESULTS: In sustained ARF, the fractional excretion of sodium (FENa) was 40 +/- 6% and 11 +/- 5%, and the fractional excretion of lithium (FELi) was 76 +/- 5% and 70 +/- 2% on days 0 and 7, respectively. Corresponding findings in recovering ARF were 28 +/- 2% and 6 +/- 2% for the FENa and 77 +/- 4% and 55 +/- 3% (P < 0.05 vs. sustained) for FELi. Na+/K+-ATPase distribution in both groups was mainly basolateral in distal straight and convoluted tubule segments and collecting ducts. However, Na+/K+-ATPase was poorly retained in the basolateral membrane of proximal convoluted and straight tubule segments in sustained and recovering ARF on both days 0 and 7. CONCLUSIONS: We conclude that loss of proximal tubule cell polarity for Na+/K+-ATPase distribution is associated with enhanced delivery of filtered Na+ to the macula densa for seven days after allograft reperfusion. Whether an ensuing activation of tubuloglomerular feedback is an important cause of glomerular filtration rate depression in this form of ARF remains to be determined.

Distribution of cell membrane-associated proteins along the human nephron.

Cytoskeletal proteins associate with specific cell adhesion complexes and membrane proteins and influence the structural and functional organization of polarized epithelial cells in the kidney. Among such proteins that have been studied in cultured cell lines and in animals are the tight junction complex (ZO-1 and occludin), the adherens cell-cell adhesion complex (alpha-, beta-catenin and plakoglobin), and Na+,K+-ATPase, with its associated membrane skeleton proteins ankyrin and fodrin. Although abnormal distribution of these proteins has been implicated in the pathogenesis of various renal diseases, the relevance of these findings to corresponding disease of the human kidney remains to be established. As a first step towards elucidating a role for such proteins in human kidney disease, we undertook a histochemical analysis of the distribution of these proteins in biopsy specimens of human kidney taken from healthy kidney transplant donors. We found each protein to have a characteristic subcellular localization and an intensity of staining that varied among different segments of the nephron in a manner that is consistent with discrete, segmental nephron function.

Nature of glomerular dysfunction in pre-eclampsia.

BACKGROUND: Pre-eclampsia is characterized by hypertension, proteinuria and edema. Simultaneous studies of kidney function and structure have not been reported. We wished to explore the degree and nature of glomerular dysfunction in pre-eclampsia. METHODS: Physiologic techniques were used to estimate glomerular filtration rate (GFR), renal plasma flow and afferent oncotic pressure immediately after delivery in consecutive patients with pre-eclampsia (PET; N = 13). Healthy mothers completing an uncomplicated pregnancy served as functional controls (N = 12). A morphometric analysis of glomeruli obtained by biopsy and mathematical modeling were used to estimate the glomerular ultrafiltration coefficient (Kf). Glomeruli from healthy female kidney transplant donors served as structural controls (N = 8). RESULTS: The GFR in PET was depressed below the control level, 91 +/- 23 versus 149 +/- 34 ml/min/1.73 m2, respectively (P < 0.0001). In contrast, renal plasma flow and oncotic pressure were similar in the two groups (P = NS). A reduction in the density and size of endothelial fenestrae and subendothelial accumulation of fibrinoid deposits lowered glomerular hydraulic permeability in PET compared to controls, 1.81 versus 2.58 x 10(-9) m/sec/PA. Mesangial cell interposition also curtailed effective filtration surface area. Together, these changes lowered the computed single nephron Kf in PET below control, 4.26 versus 6.78 nl/min x mm Hg, respectively. CONCLUSION: The proportionate (approximately 40%) depression of Kf for single nephrons and GFR suggests that hypofiltration in PET does not have a hemodynamic basis, but is a consequence of structural changes that lead to impairment of intrinsic glomerular ultrafiltration capacity.

Mechanisms of progressive glomerular injury in membranous nephropathy.

Glomerular function and structure were serially evaluated in 15 patients with membranous nephropathy who exhibited relapsing nephrosis and chronic depression of GFR. GFR declined from 56+/-8 (mean+/-SEM) at onset to 31+/-4 ml/min per 1.73 m2 after a 2- to 5-yr period of observation (P < 0.05). An analysis of filtration dynamics suggested persistent elevation of net ultrafiltration pressure. To examine a possible role for declining intrinsic glomerular filtration capacity as the basis for the observed hypofiltration, glomeruli in the baseline and a repeat biopsy (performed after a median of 28 mo) were subjected to morphometric analysis and mathematical modeling. Analysis of the baseline biopsy revealed a reduction in filtration slit frequency and thickening of the glomerular basement membrane, lowering computed hydraulic permeability by 66% compared with normal kidney donors. In contrast, filtration surface area was increased by 37% as a result of glomerular hypertrophy. The repeat biopsy revealed persistent depression of hydraulic permeability, primarily owing to foot process broadening. An additional finding was a decrease in filtration surface area from baseline in patent glomeruli, possibly due to encroachment on the capillary lumen of an increasingly widened basement membrane. Also, a striking increase in the prevalence of global glomerulosclerosis from 7+/-2% to 23+/-4% was found between the two biopsies, suggesting a significant loss of functioning nephrons. It is concluded that hypofiltration in membranous nephropathy is the consequence of a biphasic loss of glomerular ultrafiltration capacity, initially owing to impaired hydraulic permeability that is later exacerbated by a superimposed loss of functioning glomeruli and of filtration surface area.

Backleak, tight junctions, and cell- cell adhesion in postischemic injury to the renal allograft.

Postischemic injury in recipients of 3-7-d-old renal allografts was classified into sustained (n = 19) or recovering (n = 20) acute renal failure (ARF) according to the prevailing inulin clearance. Recipients of optimally functioning, long-standing allografts and living donors undergoing nephrectomy served as functional (n = 14) and structural controls (n = 10), respectively. Marked elevation above control of fractional clearance of dextrans of graded size was consistent with transtubular backleak of 57% of filtrate (inulin) in sustained ARF. No backleak was detected in recovering ARF. To explore a structural basis for backleak, allograft biopsies were taken intraoperatively, 1 h after reperfusion in all recipients, and again on day 7 after transplant in a subset (n = 10). Electron microscopy revealed disruption of both apical and basolateral membranes of proximal tubule cells in both sustained and recovering ARF, but cell exfoliation and tubule basement membrane denudation were negligible. Histochemical analysis of membrane-associated adhesion complexes confirmed an abnormality of proximal but not distal tubule cells, marked in sustained ARF but not in recovering ARF. Staining for the zonula occludens complex (ZO-1) and adherens complex (alpha, beta, and gamma catenins) revealed diminished intensity and redistribution of each cytoskeletal protein from the apico-lateral membrane boundary. We conclude that impaired integrity of tight junctions and cell-cell adhesion in the proximal tubule provides a paracellular pathway through which filtrate leaks back in sustained allograft ARF.

Angiotensin-converting enzyme inhibitor for slowing progression of diabetic and nondiabetic kidney disease.

A growing body of evidence suggests that agents that inhibit the angiotensin-converting enzyme are renoprotective. In experimental animal models of chronic renal injury, such renoprotection can virtually eliminate progression of the renal injury, provided that therapy is started at the time of injury. In humans with chronic renal injury, renoprotection has been successfully demonstrated only late in the course of the renal disease. The rate of progression to end-stage renal failure can be delayed, but progression continues at a slower pace. Further study is required to determine whether earlier intervention can better preserve nephron structure and function. A strategy for future trials is recommended. It emphasizes more sensitive outcome measures so as to achieve greater statistical power.