Glomerular hypertrophy in minimal change disease predicts subsequent progression to focal glomerular sclerosis

Hyperfiltration and conservation of renal function in hypertensive nephrosclerosis patients

Renal glomerular hyperfiltration has been proposed as an important contributing factor to the progression of hypertensive nephrosclerosis in rats with reduced renal mass. However, no clinical studies have assessed the role of glomerular hyperfiltration in the pathogenesis of hypertensive nephrosclerosis in humans. In a prospective, randomized, long-term blood pressure control study with up to 3 years follow-up, we showed that good blood pressure control with a mean diastolic blood pressure < or = 95 mm Hg preceded by a 2- to 4-month period of diastolic blood pressure < or = 80 mm Hg improved renal function in hypertensive nephrosclerosis patients. Patients treated with minoxidil, an angiotensin-converting enzyme inhibitor (enalapril), or a calcium entry blocker (nifedipine) had improvement in renal function, as indicated by a positive slope of the reciprocal serum-creatine concentration versus time and an increment in glomerular filtration rate. These results suggested that improvement in renal function occurred with these major types of antihypertensive drug treatment. To assess the renal hemodynamics of minoxidil, enalapril, and nifedipine, eight patients with hypertensive nephrosclerosis were admitted to the General Clinical Research Center for renal clearance studies on each drug while ingesting a fixed-calorie, 12% protein, 40% fat, and 100 mEq Na/d diet. Mean blood pressure, effective renal plasma flow, and renal vascular resistance did not change during the three phases of treatment. However, minoxidil treatment increased the glomerular filtration rate by 48% versus enalapril and by 79% versus nifedipine. Since minoxidil treatment improves renal function while causing a relative hyperfiltration, glomerular hyperfiltration per se is an unlikely mechanism for the progression of hypertensive nephrosclerosis in humans.

Rat glomerular mesangial cells synthesize basic fibroblast growth factor. Release, upregulated synthesis, and mitogenicity in mesangial proliferative glomerulonephritis

Mesangial injury and cell proliferation are frequent findings in various glomerular diseases in man. Previous studies have demonstrated that basic fibroblast growth factor (bFGF) is a potent mesangial cell mitogen in vitro. To further elucidate the role of bFGF in rat mesangial cell (RMC) proliferation, we examined whether RMC synthesize bFGF in vitro and whether bFGF is involved in mesangial proliferation in vivo. Cultured RMC expressed bFGF protein (23, 21.5, and 18 kD forms) and bFGF mRNA, and released biologically active bFGF into the culture medium after antibody- and complement-mediated injury. Normal rat glomeruli in vivo contained no detectable bFGF mRNA, but bFGF protein (23 and 21.5 kD) could be demonstrated, which immunolocalized to the mesangium. Glomerular bFGF decreased markedly during the acute phase of glomerulonephritis induced by anti-Thy 1.1 antibody, compatible with mesangial bFGF release after complement-mediated mesangiolysis. During the subsequent mesangial proliferative phase, glomerular bFGF protein and mRNA increased above normal. Intrarenal infusion of heparin did not affect the bFGF immunostaining of glomeruli at this stage, indicating a predominantly intracellular localization of the bFGF. The capability of bFGF to mediate proliferation in the anti-Thy 1.1 model was further supported by experiments in which intravenous bFGF given 24 h after a subnephritogenic dose of anti-Thy 1.1 antibody led to a 4.9- to 5.1-fold increase in glomerular cell proliferation (with > 60% of the cells identified as mesangial cells by double immunolabeling). No such increase was observed in normal rats injected with bFGF. These data show that mesangial cells produce and release bFGF after injury and that bFGF is mitogenic for injured mesangial cells in vivo. Release of mesangial cell bFGF thus may be an important mechanism involved in the initiation of mesangial cell proliferation in vivo.

Mesangial deposition of type I collagen in human glomerulosclerosis

The presence of type I collagen in both diffuse and nodular diabetic glomerular lesions has been examined using immunohistochemical and electron microscopic techniques. At the ultrastructural level, banded collagen fibrils were observed in the mesangium in all cases of nodular (Kimmelstiel-Wilson) sclerosis and in 60% of the diffuse sclerotic lesions. Antibodies against type I collagen were localized in the fibrotic interstitium and the mesangium in all cases examined. Staining with type I collagen antibodies occurred in glomeruli with intact Bowman's capsules, and was predominantly localized to areas immediately adjacent to mesangial cells. In cases of focal sclerosis of nondiabetic origin, banded collagen fibrils and staining with anti-type I collagen antibody were observed in all cases in which the segmental lesion was presented in the specimen. The pattern of antibody localization in both the diabetic lesions and focal sclerosis differed from that obtained using anti-type IV (basement membrane) collagen antibodies. These results demonstrate that type I collagen is among the extracellular matrix components that comprise the sclerotic glomerular lesions of both diabetic and nondiabetic origin. Furthermore, the spatial localization of this collagen type suggests mesangial cell origin.

Renal histology in polycystic kidney disease with incipient and advanced renal failure

Renal specimens were obtained at surgery or postmortem from patients with autosomal dominant polycystic kidney disease (ADPKD). Patients had either serum creatinine (SCr) below 350 mumol/liter (N = 12) or terminal renal failure (N = 50). Specimens were examined by two independent observers using a carefully validated score system. Mean glomerular diameters were similar in ADPKD patients with early renal failure (176 +/- 38 microns) and in victims of traffic accidents (177 +/- 23 microns), while they were significantly greater in diabetics with comparable renal function (205 +/- 16 microns). Glomerular diameters in ADPKD patients with terminal renal failure (191 +/- 45 microns) and with early renal failure were not significantly different. On average, 29% of glomeruli (17 to 62) were globally sclerosed in early renal failure, and 49% (19 to 93) in terminal renal failure. The proportion of glomeruli with segmental sclerosis was less than 4% in both groups. Marked vascular sclerosis, interstitial fibrosis, and tubular atrophy were present in early renal failure, and even more so in terminal renal failure. Interstitial infiltrates were scarce and consisted mainly of CD4 positive lymphocytes and CD68 positive macrophages. Immunestaining with monoclonal renin antibodies showed an increased juxtaglomerular index and expression of renin by arterioles adjacent to cysts, as well as by cyst wall epithelia. The data show more severe vascular and interstitial, but not glomerular, changes in ADPKD with advanced as compared to early renal failure.

Glomerular damage after uninephrectomy in young rats. II. Mechanical stress on podocytes as a pathway to sclerosis

In a preceding study [1], we showed that within six months after UNX in young rats, glomeruli in the remnant kidney undergo a sequence of serious changes which finally lead to focal segmental glomerulosclerosis (FGS). The formation of abnormally-shaped capillary channels was shown to result from local mesangial failure and is considered to be a nidus for the development of more severe lesions. In the present paper, the development of characteristic lesions in podocyte structure is described and analyzed. Concomitant with overall glomerular growth after UNX, a pronounced hypertrophy of podocytes was observed, while the mean number of podocytes per glomerulus did not change. It appears that podocytes cannot sustain the same degree of growth as the tuft as a whole; podocyte hypertrophy is soon followed by maladaptive changes which eventually lead to cell destruction. The following sequence of pathologic changes can be suggested: cell bodies enlarge in volume and area associated with a dramatic attenuation to cytoplasmic sheets. Primary processes are thinned out and frequently extend to remote capillaries. As a whole, the capillary area served by a single podocyte is dramatically enlarged. Furthermore, the expanding cytoplasmic sheets (derived from podocyte cell bodies) cover an increasingly large proportion of the outer capillary surface, that is, of the filtration area. Consequently, an increasing amount of filtrate is delivered into the subcellbody space. Obstruction of the efflux of this filtrate into the urinary space causes bulging of the overlying cytoplasmic sheets into pseudocysts. Podocytes overlying abnormally-shaped and dilated capillary channels are generally the most seriously affected. Tuft hypertrophy, pseudocyst formation and local capillary expansion cause wide-spread apposition of podocytes to Bowman's capsule. Appositions are a prerequisite for the development of tuft adhesion. Local detachment of a podocyte from the GBM in those areas allows access of parietal cells to the GBM. In early adhesions the connection of the tuft to Bowman's capsule is established by single parietal cells which attach to both the GBM and the basement membrane of Bowman's capsule. An adhesion is considered as a nidus for segmental sclerosis; as the adhesion progresses, the related tuft regions turn into sclerosis. In the present model FGS develops exclusively in areas of tuft adhesion.

Estimation of glomerular volume: a comparison of four methods

Methods for estimating glomerular volume were compared in Zenker-fixed, paraffin-embedded biopsies from 10 patients with insulin-dependent diabetes mellitus and 6 normal kidney donors. Two methods of measurement of individual glomerular volumes were used: the Cavalieri method (considered the "gold standard") and the maximal profile area (MPA) method. Also studied were the method of Weibel and Gomez and a method based on the disector principle; both estimate mean volume (VG). MPA and Cavalieri showed strong correlation (r = 0.93; P less than 0.001), although the MPA method consistently overestimated the true volume; six glomeruli were necessary for a reliable estimate of VG. The disector method did not correlate with VG determined by Cavalieri. Weibel-Gomez did correlate with Cavalieri (r = 0.68; P less than 0.05), but overestimated VG. At least 15 profiles were needed to provide a dependable estimate of VG by Weibel-Gomez. The Cavalieri, MPA, and Weibel-Gomez methods all can provide reliable estimates of VG, the latter two with appropriate correction factors. The individual glomerular volume methods, while more time consuming, provide information on variation and distribution of the glomerular population and are the methods of choice for studies of glomerular volume.

Glomerular cell proliferation and PDGF expression precede glomerulosclerosis in the remnant kidney model

Increasing evidence supports a role of glomerular cell proliferation in the development of focal or diffuse glomerulosclerosis. This study investigates the chronology and sequence of cellular events that precede glomerulosclerosis in 5/6 nephrectomized rats. Within three days of renal ablation, a phenotypic switch occurred in which some mesangial cells expressed alpha-smooth muscle actin. This was followed by proliferation of mesangial cells, and to a lesser degree endothelial cells from day 5 to week 4 as detected by immunostaining for the proliferating cell nuclear antigen (PCNA). Glomerular cell proliferation was accompanied by increased immunohistochemical expression of PDGF B-chain. In situ hybridization showed no glomerular PDGF B-chain mRNA expression at the induction of proliferation (day 5), and a marked increase between week 1 and 4 in operated rats. In parallel, increased expression of PDGF receptor beta-subunit protein and mRNA was demonstrated by immunohistochemistry and Northern analysis of total glomerular RNA. The onset of glomerular cell proliferation was also associated with mild glomerular platelet accumulation (as defined by 111In-labelled platelet studies) as well as with fibrinogen deposition. Proteinuria, glomerular sclerotic changes, and leukocyte infiltration all followed cell proliferation. The glomerular leukocyte infiltrate consisted of monocytes/macrophages and increased markedly at week 10 in rats with renal ablation. Thus, our results suggest that in the remnant kidney model: 1) proliferation of intrinsic glomerular cells precedes glomerulosclerosis; 2) proliferation may be initiated by degranulating platelets and sustained by PDGF released from intrinsic glomerular cells; and 3) glomerular monocyte/macrophage infiltration occurs after the proliferation, and may possibly contribute to the development of glomerular sclerotic changes.

Focal glomerulosclerosis in idiopathic membranous glomerulonephritis

The significance of the finding of focal glomerulosclerosis (FGS) in idiopathic membranous glomerulonephritis (MGN) is uncertain. Twenty-seven patients with mixed FGS and MGN (MGN-FGS) were compared to 25 patients with MGN alone (generally matched for age, sex and stage of glomerular lesion) with respect to pathology, presenting clinical and laboratory features, and course of disease. Biopsies from the MGN-FGS patients showed significantly more extensive tubulointerstitial disease (P less than 0.001) than did those with MGN alone. At the time of biopsy, the MGN-FGS group had a significantly higher proportion of patients with hypertension (P = 0.006) and microhematuria (P = 0.006), a marginally higher percentage of patients with the nephrotic syndrome (P = 0.051), and a greater mean 24-hour urinary protein excretion (P = 0.004). A similar proportion of patients in each group were treated with either prednisone alone or prednisone with an immunosuppressive. Forty-eight percent of MGN-FGS patients and 13% of the MGN patients developed established renal failure in the follow-up period (P = 0.008). The renal survival rate for the MGN-FGS group was significantly lower at 24 months (0.61 vs. 0.93, P less than 0.05), 60 months (0.48 vs. 0.88, P less than 0.025), and over the entire follow-up period (P less than 0.05). The results indicate that FGS in MGN is associated with a significantly poorer prognosis than MGN without this lesion.

Comparison of size of juxtamedullary and outer cortical glomeruli in normal adult kidney

Abnormally large glomeruli are susceptible to hyperfiltration-associated sclerosis. We used an established morphometric method to test the general belief that juxtamedullary glomeruli are larger than those in the outer cortex, in a population with no clinical or pathological evidence of renal disease. Overall, juxtamedullary glomeruli were significantly larger, but this varied according to the amount of global glomerulosclerosis present. Global sclerosis increased with age, particularly in the outer cortex, and the ratio of juxtamedullary to outer cortical glomerular size showed a positive correlation with overall, and outer cortical, global sclerosis. Thus in the truly normal adult kidney, juxtamedullary glomeruli are not significantly larger than outer cortical glomeruli. However, global sclerosis increases with age and is most marked in the outer cortex, and this leads to compensatory enlargement of predominantly the juxtamedullary glomeruli. These findings suggest that in single kidneys, or in conditions characterised by ischaemic glomerulosclerosis such as hypertension, morphological changes related to hyperfiltration may appear first, and therefore become most severe, in juxtamedullary glomeruli.

Histopathologic findings associated with a chronic, progressive decline in renal allograft function

The relationship between specific histopathologic findings of chronic rejection (CR) and the clinical course of renal transplant recipients with a chronic progressive decline in allograft function (CPDAF) is unknown. We used one or two hinged regression lines, fitted by least-squares to serial creatinine clearances, to define the onset and clinical course of CPDAF. Biopsies (N = 100) from patients transplanted from 1978 to 1982 were studied retrospectively. Interstitial fibrosis, tubular atrophy, and fibrointimal arterial narrowing were more pronounced in biopsies obtained after, but not before the onset of CPDAF. Interstitial hemorrhage, an infrequent finding in acute vascular rejection, preceded the onset of CPDAF, but the more common histologic findings of acute cellular rejection did not. The severity of histologic features of CR (as reflected by a score combining fibrointimal arterial narrowing, interstitial fibrosis, tubular atrophy, glomerular sclerosis, glomerular mesangial expansion, and glomerular basement membrane reduplication) correlated with the duration of subsequent allograft survival (r = -0.65, P less than 0.001). Glomerular size increased after transplantation, but was not different in patients with or without CPDAF, suggesting that mechanisms related to compensatory hypertrophy did not play a major role in the pathogenesis of CR. In summary, the histologic findings of CR did not predict the onset of CPDAF, did not distinguish whether the pathogenesis was mediated by immune or nonimmune events, but did correlate with the duration of subsequent allograft survival.

Renal arteriolar diameters in spontaneously hypertensive rats. Vascular cast study

The relation between the arteriolar diameters and hypertensive glomerulosclerosis was studied by using microvascular casts and histological evaluation. Spontaneously hypertensive rats 4 weeks of age were divided into three groups: nontreated, captopril (40 mg/kg/day)-treated, and trichlormethiazide (1 mg/kg/day) with hydralazine (20 mg/kg/day)-treated. Wistar-Kyoto rats served as controls. At 6 weeks old, the captopril-treated rats showed a lower blood pressure and a larger afferent arteriolar diameter compared with the control rats. At 20 weeks old, the nontreated group exhibited hypertension and a lower arteriolar diameter ratio (afferent to efferent, 0.89 versus 1.22 in control group) because of afferent constriction and efferent dilatation, seen equally in the outer and inner cortexes. Glomerulosclerosis was accentuated only in the inner cortex of the nontreated group (score, 63 versus 29 in control group). In the two treated rat groups, the blood pressure was reduced and arteriolar diameter ratios were similar to those in the control group (1.18 and 1.26). The sclerosis score in the trichlormethiazide with hydralazine-treated rats (score, 26) was lower than in the nontreated rats but not the captopril-treated rats (score, 36). These results indicated that 1) in the hypertensive rats, despite a reduced diameter ratio, glomerulosclerosis was more severe in the inner cortex; 2) two therapies reduced blood pressure and reversed the arteriolar changes, but a decrease in glomerulosclerosis was seen only in the trichlormethiazide with hydralazine-treated rats; and 3) for development of glomerulosclerosis, factors other than hemodynamics may be important in addition to intraglomerular pressure.

Renal pathology in rats bearing tumour-secreting growth hormone

The effects of growth hormone (GH) on renal structure and function were investigated in rats aged 10-16 weeks bearing a tumour secreting GH. Body weight gain, food intake, urine volume, and urinary excretion of creatinine and urea nitrogen were significantly greater in tumour-bearing rats than in controls. The tumour-bearing rats presented progressive proteinuria, hyperproteinaemia, and hyperlipidaemia. Creatinine clearance was significantly higher in experimental animals during the early experimental stage, but decreased as the glomerular lesions progressed, associated with a rise in serum creatinine levels. The glomeruli became progressively enlarged with degenerative changes of the visceral epithelial cells and capsular adhesions. In advanced stages proteinaceous material invaded the subcapsular space and the capillary lumen collapsed finally leading to glomerulosclerosis. Except for the presence of proteinaceous material and damaged epithelial cells the glomerular lesions resemble those observed experimentally after reduction of renal mass, and in diabetes mellitus. We speculate that the pathological features described are due to effects of persistently high levels of circulating GH on the glomerular cells.

Role of growth hormone in the development of experimental renal scarring

Recent experimental data has implicated growth hormone in the development of glomerular sclerosis. In this study, we have examined the development and progression of glomerular and tubulointerstitial scarring in Wistar and Dwarf rats, selectively growth hormone-deficient, following subtotal nephrectomy. Wistar rats showed progressive proteinuria, hypertension and renal failure as well as severe renal scarring 120 days after subtotal nephrectomy. In contrast, growth hormone-deficient Dwarf rats had minimal proteinuria, mild renal functional impairment and moderate renal histological scarring. The difference in these functional and structural parameters between the two strains is highly significant, although both experimental groups had comparable food consumption and systemic blood pressure. The significantly smaller glomeruli and limited kidney hypertrophy over 120 days observed in Dwarf rats may account for some of the protection against glomerular sclerosis and tubulointerstitial scarring observed in that strain.

Evidence for a pathogenic linkage between glomerular hypertrophy and sclerosis

Primary renal disease of immunologic or nonimmunologic mechanisms induces loss of substantial nephron population. It is presumed that the initial loss of functioning nephrons causes alterations of function and metabolism in remnant nephrons, which per se are self-inflictive, leading to further loss of nephrons. The ultimate outcome of this vicious cycle is the end-stage kidney. The potential role of various pathophysiologic mechanisms has been explored. These studies have shown a tight link between glomerular hypertrophy and sclerosis. Analysis of individual glomeruli show a biphasic pattern of these two parameters. Early development of glomerular sclerosis takes place along with the hypertrophy of the glomerulus, and further advancement of sclerosis occurs with shrinkage in glomerular size. Thus, we propose that, after initial nephron loss, the remnant glomeruli are exposed to increased growth-promoting factors, which are self-inflictive in nature due to their capacity to produce excessive amounts of extracellular matrix in the mesangial area. When the excessive matrix obliterates the glomerular capillary lumen, a typical sclerotic lesion appears. This is a vicious and accelerating process, since sclerosis induces further reduction in the nephron population, thereby imposing greater influence of growth-promoting factors even on glomeruli that are initially resistant.

Increased ammoniagenesis as a determinant of progressive renal injury

Loss of renal mass evokes increased ammoniagenesis in surviving nephrons, which in turn enables net acid excretion by the kidney. However, this compensatory increase in ammonia production in surviving nephrons triggers the alternative complement pathway, thereby instigating progressive tubulointerstitial injury. Ammonia has recently been identified as a stimulus to renal growth. Enhanced renal growth may serve as a forerunner for renal injury. The growth-promoting properties of ammonia may provide another mechanism through which augmented ammoniagenesis may underlie the enhancement of renal growth and injury observed in such models as the remnant kidney, hypokalemic nephropathy, high protein feeding, experimental diabetes nephropathy, and dietary deficiency of antioxidants.

Identifying acoustic scattering sources in normal renal parenchyma from the anisotropy in acoustic properties

Acoustical and histological properties of dog kidney parenchyma are examined in vitro to determine sources of acoustic scattering in the normal kidney. The speed of sound, attenuation, backscatter, effective scatterer size and scattering strength were measured within the frequency range 1-15 MHz and at eight angles of incidence with respect to the predominant nephron orientation. Significant angular dependence, or anisotropy, was observed in backscatter coefficient and scattering strength estimates; attenuation was found to be weakly anisotropic. All three parameters, each measured at 19 degrees C, exhibited values that were maximum for perpendicular incidence and minimum for parallel incidence. Speed of sound and scatterer size estimates were observed to be independent of scanning angle. Comparisons between these data for renal cortex and histological observations suggest that the glomerulus is the principal scatterer at low frequencies, and renal tubules and blood vessels at high frequencies.