Animal models of renal disease.

Mice have become a favored species to model disease. Many mouse strains have proven relatively resistant to some manipulations that have generated renal disease in other species. Kirchhoff et al. describe a means of producing hypertension, proteinuria, and glomerular sclerosis in a mouse strain.

Gene expression profiles of human proximal tubular epithelial cells in proteinuric nephropathies.

In kidney disease renal proximal tubular epithelial cells (RPTEC) actively contribute to the progression of tubulointerstitial fibrosis by mediating both an inflammatory response and via epithelial-to-mesenchymal transition. Using laser capture microdissection we specifically isolated RPTEC from cryosections of the healthy parts of kidneys removed owing to renal cell carcinoma and from kidney biopsies from patients with proteinuric nephropathies. RNA was extracted and hybridized to complementary DNA microarrays after linear RNA amplification. Statistical analysis identified 168 unique genes with known gene ontology association, which separated patients from controls. Besides distinct alterations in signal-transduction pathways (e.g. Wnt signalling), functional annotation revealed a significant upregulation of genes involved in cell proliferation and cell cycle control (like insulin-like growth factor 1 or cell division cycle 34), cell differentiation (e.g. bone morphogenetic protein 7), immune response, intracellular transport and metabolism in RPTEC from patients. On the contrary we found differential expression of a number of genes responsible for cell adhesion (like BH-protocadherin) with a marked downregulation of most of these transcripts. In summary, our results obtained from RPTEC revealed a differential regulation of genes, which are likely to be involved in either pro-fibrotic or tubulo-protective mechanisms in proteinuric patients at an early stage of kidney disease.

Downloadable computer models for renal replacement therapy.

Mathematical models can predict solute clearances and solute concentrations during renal replacement therapy. At present, however, most nephrologists cannot use these models because they require mathematical software. In this report, we describe models of solute transport by convection and diffusion adapted to run on the commonly available software program Excel for Macintosh computers and PCs running Windows. Two programs have been created that can be downloaded from http://www.stanford.edu/~twmeyer/ or http://dev.satellitehealth.com/research/journal.asp. The first, called 'Dr Addis Clearance Calculator', calculates clearance values from inputs including the blood flow Q(b), the hematocrit, the ultrafiltration rate Q(f), the dialysate flow rate Q(d), the reflection coefficient sigma and the mass transfer area coefficient K(o)A for the solute of interest, and the free fraction f if the solute is protein bound. Solute concentration profiles along the length of the artificial kidney are displayed graphically. The second program, called 'Dr Coplon Dialysis Simulator', calculates plasma solute concentrations from the clearance values obtained by the first program and from additional input values including the number of treatments per week, the duration of the treatments, and the solute's production rate and volumes of distribution. The program calculates the time-averaged solute concentration and provides a graphic display of the solute concentration profile through a week-long interval.

The development of clearance methods for measurement of glomerular filtration and tubular reabsorption.

This essay looks at the historical significance of four APS classic papers that are freely available online: Jolliffe N, Shannon JA, and Smith HW. The excretion of urine in the dog. III. The use of non-metabolized sugars in the measurement of the glomerular filtrate. Am J Physiol 100: 301-312, 1932 (http://ajplegacy.physiology.org/cgi/reprint/100/2/301). Shannon JA. The excretion of inulin by the dog. Am J Physiol 112: 405-413, 1935 (http://ajplegacy.physiology.org/cgi/reprint/112/3/405). Shannon JA and Fisher S. The renal tubular reabsorption of glucose in the normal dog. Am J Physiol 122: 765-774, 1938 (http://ajplegacy.physiology.org/cgi/reprint/122/3/765). Shannon JA, Farber S, and Troast L. The measurement of glucose Tm in the normal dog. Am J Physiol 133: 752-761, 1941 (http://ajplegacy.physiology.org/cgi/reprint/133/3/752).

Regulation of renal tubular cell apoptosis and proliferation after ischemic injury to a solitary kidney.

The time course and regulation of apoptosis and cellular regeneration after 30 minutes of acute ischemic injury to a single kidney was elucidated in rats at five time points over 20 weeks. The fraction of apoptotic cells was most prominent at 1 day after the insult in the distal tubule (8% +/- 4% vs 0% +/- 0%, acute renal failure [ARF] vs sham, respectively) and was still elevated at 7 days (2% +/- 2% vs 0% +/- 0%). At that time, the whole kidney mRNA expression of the apoptosis inhibitory genes bcl-xL and bcl-2, as well as that of the apoptosis promotor bax, was significantly reduced. Immunohistochemistry of kidney specimen showed suppression of bcl-2 in the distal tubule but up-regulation in the proximal tubule, whereas bax protein was more strongly expressed in the distal tubule. Cellular proliferation started at day 1 and continued over the following 20 weeks, leading to severe tubular dilation and kidney failure. These data indicate that differential regulation of bcl-2 family members contributes to the early apoptotic clearance of lethally injured tubular epithelial cells after ischemic injury to a solitary kidney.

Intrarenal angiotensin and bradykinin peptide levels in the remnant kidney model of renal insufficiency.

BACKGROUND: The remnant kidney model of renal failure is associated with normal or suppressed plasma renin and angiotensin (Ang) II levels when hypertension is established. However, the hypertension responds to angiotensin-converting enzyme (ACE) inhibition and Ang II receptor antagonism, suggesting a role for Ang II in the hypertensive process. Bradykinin (BK) is a potent vasoactive peptide that may also participate in this model. METHODS: Ang II and BK peptides were measured in the ischemic peri-infarct portion and the intact portion of the remnant kidney at two, five, and seven weeks after surgery. Plasma Ang II, renin, angiotensinogen, and aldosterone levels were also measured. RESULTS: Ang II levels in the peri-infarct portion were higher than in the intact portion at all time points and were higher than in sham-operated kidney at two weeks. Ang II levels in the intact portion were similar to the levels in kidneys of sham-operated rats at two and five weeks and were suppressed at seven weeks. BK levels were increased in the peri-infarct portion at all time points and in the intact portion at two and five weeks. Plasma Ang II and aldosterone levels were also elevated at two weeks. CONCLUSIONS: Peri-infarct renal tissue Ang II levels and plasma Ang II and aldosterone levels increase transiently during the evolution of hypertension in the remnant kidney model. Sustained hypertension is associated with an increase in intrarenal BK levels but not with persistent increases in intrarenal or circulating Ang II levels.

Effect of angiotensin II blockade on renal injury in mineralocorticoid-salt hypertension.

Kidney function and structure were compared in control rats (group 1) and in 3 groups of rats made hypertensive by administration of aldosterone and saline for 8 weeks (groups 2, 3, and 4). Group 2 rats received only aldosterone and saline, while group 3 also received losartan and group 4 also received enalapril. Rats in all groups were subjected to uninephrectomy before beginning the experiment. Hypertension and proteinuria in rats given aldosterone and saline were not affected by losartan or enalapril (8-week values for blood pressure in mm Hg: 135+/-3 group 1, 193+/-4 group 2, 189+/-4 group 3, 189+/-5 group 4; P<0.05 groups 2, 3, and 4 versus 1; 8-week values for proteinuria in mg/d: 44+/-8 group 1, 278+/-34 group 2, 267+/-37 group 3, 289+/-36 group 4; P<0.05 groups 2, 3, and 4 versus 1). Vascular, glomerular, and tubulointerstitial injury accompanied hypertension and proteinuria at 8 weeks. Losartan and enalapril did not prevent vascular injury, which was characterized by thickening of arterial and arteriolar walls and by fibrinoid necrosis and thrombotic microangiopathy. Likewise, losartan and enalapril did not reduce the prevalence of glomerular segmental sclerosis (1+/-1% group 1, 10+/-2% group 2, 11+/-2% group 3, 13+/-2% group 4; P<0.05 groups 2, 3, and 4 versus 1) or limit tubulointerstitial injury as reflected by the volume fraction of the cortical interstitium (15+/-1% group 1, 20+/-1% group 2, 21+/-1% group 3, 21+/-1% group 4; P<0.05 groups 2, 3, and 4 versus 1). These findings suggest that local angiotensin II activity does not contribute to the development of renal injury in mineralocorticoid-salt hypertension.

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.

Methods for estimating the volume of individual glomeruli.

UNLABELLED: Methods for estimating the volume of individual glomeruli. BACKGROUND: The Cavalieri and maximal planar area (MPA) methods are commonly used to measure the volume of individual glomeruli. Previous studies have suggested that the MPA method, which is less laborious, yields values that are much greater than those obtained by the Cavalieri method. The current study re-examined the relationship of MPA and Cavalieri values for glomerular volume in humans and rats. METHODS: Both methods were used to measure the volume of 1201 glomeruli from 58 humans and 281 glomeruli from 15 rats. Tissue was embedded in Epon. Further mathematical analysis was performed to assess the extent to which deviation of glomeruli from spherical shape affects the relationship of values obtained by the MPA and Cavalieri methods. RESULTS: MPA values exceeded Cavalieri values by an average of only 14 +/- 22% in humans and 6 +/- 16% in rats. The relationship of MPA to Cavalieri values was similar in individual humans and rats, with widely varying values for average glomerular volume. Neither the development of sclerosis nor the loss of any connection to a tubule affected the relationship of the MPA and Cavalieri values for the volume of individual glomeruli. Mathematical analysis showed that MPA values would not exceed Cavalieri values if glomeruli had ellipsoidal rather than spherical shape. CONCLUSION: Similar values for glomerular volume are obtained using the Cavalieri and MPA methods in humans and rats.

Transplant glomerulopathy as a cause of late graft loss.

Several pathophysiological processes contribute to chronic kidney transplant rejection. Among the most distinctive is transplant glomerulopathy, characterized by widening of the subendothelial space with accumulation of flocculent material and duplication of the basement membrane. The current study assessed the course of graft loss in patients with and without this form of injury. Twenty-five patients with prominent transplant glomerulopathy were identified from biopsies performed at a single center during 4 years. These patients were compared with control patients with a similar degree of renal dysfunction in whom biopsies showed chronic rejection without transplant glomerulopathy. Patients with transplant glomerulopathy showed an increased rate of graft loss after biopsy. Biopsies were performed longer after transplantation in these patients, however, than in control patients with an equal degree of graft dysfunction. Graft survival from the time of transplantation was therefore not different between the two groups. Morphological studies showed that transplant glomerulopathy was not associated with increased severity of chronic vascular injury characterized by arterial and arteriolar intimal thickening or hyalinosis. These findings show that transplant glomerulopathy may develop late after transplantation and separately from chronic vascular rejection. The appearance of transplant glomerulopathy on a biopsy specimen is followed by accelerated graft loss.

Podocyte number predicts long-term urinary albumin excretion in Pima Indians with Type II diabetes and microalbuminuria.

AIMS/HYPOTHESIS: The predictive value of glomerular structure on progression of renal disease was examined in patients with Type II (non-insulin-dependent) diabetes and microalbuminuria (urinary albumin-to-creatinine ratio = 30-299 mg/g). METHODS: Kidney biopsy specimens were obtained from 16 diabetic Pima Indians (6 men, 10 women). Progression of renal disease was assessed by measuring urinary albumin excretion 4 years after the biopsy (UAE(4 years)) and by computing the change in urinary albumin excretion during the study (Delta UAE). RESULTS: At baseline, the duration of diabetes averaged 13.3 years (range = 4.0-23.8 years) and the mean glomerular filtration rate was 159 ml x min(-1) x 1.73 m(-2) (range = 98 - 239 ml x min(-1) x 1.73 m(-2)). Median urinary albumin excretion was 67 mg/g (range = 25-136 mg/g) and it increased to 625 mg/g (range = 9-13471 mg/g) after 4 years; 10 subjects (63 %; 4 men, 6 women) developed macroalbuminuria (urinary albumin-to-creatinine ratio >/= 300 mg/g). Neither mean arterial pressure nor HbA(1 c) changed substantially during follow-up. Among the glomerular morphologic characteristics, the number of visceral epithelial cells, or podocytes, per glomerulus was the strongest predictor of renal disease progression (UAE(4 years), r = -0.49, p = 0.05; DeltaUAE, r = -0.57, p = 0.02), with fewer cells predicting more rapid progression. Glomerular basement membrane thickness did not predict progression (UAE(4 years), r = 0.11, p = 0.67; DeltaUAE, r = 0.09, p = 0.73) and mesangial volume fraction had only a modest effect (UAE(4 years,) r = 0.42, p = 0.11; DeltaUAE, r = 0.48, p = 0.06). CONCLUSION/INTERPRETATION: Whether lower epithelial cell number per glomerulus among those that progressed was due to cellular destruction, a reduced complement of epithelial cells, or both is uncertain. Nevertheless, these findings suggest that podocytes play an important part in the development and progression of diabetic renal disease. [Diabetologia (1999) 42: 1341-1344]

Effects of eprosartan on glomerular injury in rats with reduced renal mass.

The effects of the selective angiotensin AT1 receptor antagonist, eprosartan, were evaluated in experimental renal disease. Five-sixth nephrectomy in male Munich-Wistar rats led to the development of hypertension, proteinuria and remnant glomerulosclerosis. Administration of the AT1 receptor antagonist, eprosartan, for 4 weeks resulted in inhibition of angiotensin II activity as confirmed by a reduced blood pressure response to exogenous angiotensin II challenge. Compared to vehicle treatment, eprosartan normalized blood pressure, reduced proteinuria and limited remnant glomerulosclerosis. These data suggest that eprosartan may provide a new tool in the treatment of progressive renal disease.

Influence of donor factors on early function of graft kidneys.

Factors which influence graft function can be divided into donor factors that affect both kidneys from the same donor equally and postdonor factors that affect each kidney individually. This study assessed the influence of donor factors on graft function early after transplantation. Sixty-one donors who provided kidneys that were transplanted locally into two separate recipients were identified. Recipient creatinine clearance values were estimated from serum creatinine concentrations using a computer model. Pairwise ANOVA showed that donor factors accounted for 35 to 45% of the variation in recipient creatinine clearance from 2 d to 2 wk posttransplantation. Although donor factors had a large aggregate effect during this period, individual factors that influenced graft function could not be identified from analysis of donor medical records. At 6 mo after transplantation, the effect of donor factors on graft function was no longer discernible. These results show that the condition of the donor exerts an important influence on graft function early after transplantation. More detailed study is required to identify individual factors that contribute to this effect.

Late consequences of acute ischemic injury to a solitary kidney.

The sequelae of acute ischemic injury to a solitary kidney were assessed in rats subjected to right nephrectomy and transient occlusion of the left renal artery; control rats underwent right nephrectomy alone. Incomplete recovery from ischemic injury at 2 wk (serum creatinine levels of 1.1 +/- 0.2 versus 0.5 +/- 0.1 mg/dl, P < 0.05 for ischemia versus control) was followed by deterioration of renal function at 20 wk (serum creatinine levels of 1.7 +/- 0.4 versus 0.7 +/- 0.1 mg/dl, P < 0.05 for ischemia versus control). Morphologic studies showed that impairment of function after ischemic injury was associated with widespread tubulointerstitial disease. Some tubule segments were atrophic and others exhibited cystic dilation, so that the tubular cell volume fraction was reduced (37 +/- 4 versus 53 +/- 2%, P < 0.05), while the tubular lumen and interstitial volume fractions were increased (31 +/- 4 versus 23 +/- 2% and 29 +/- 2 versus 20 +/- 1%, respectively, both P < 0.05). Many glomeruli retained open capillary loops but were no longer connected to normal tubule segments (63 +/- 8 versus 15 +/- 7% of glomeruli, P < 0.05). There was a strong inverse correlation between the prevalence of such glomeruli and the GFR at 20 wk after ischemia (r2 = 0.79, P < 0.001). Tubulointerstitial disease at that time was accompanied by proteinuria and widespread segmental glomerular tuft injury. The occurrence of similar processes in human patients could contribute to the loss of graft kidneys that suffer ischemic injury during transplantation.

Contribution of tubular injury to loss of remnant kidney function.

BACKGROUND: The remnant kidney model has been widely used to identify mechanisms responsible for the progression of renal disease. However, the structural changes associated with progressive loss of function in this model have not been well characterized. METHODS: Kidney function and structure were assessed at 10 weeks (REM 10) and 25 weeks (REM 25) after five-sixths renal ablation and in control rats (Control). Serial sections were examined to relate glomerular and tubular structure in individual nephrons. RESULTS: Remnant kidney function declined between 10 and 25 weeks after ablation (GFR 0.90 +/- 0.34 vs. 0.23 +/- 0.07 ml/min, REM 10 vs. REM 25, P < 0.05). This decline in function was associated with an increase in the prevalence of globally sclerotic glomeruli (14 +/- 10 vs. 0 +/- 0 vs. 0 +/- 0%, REM 25 vs. REM 10 vs. Control, P < 0.05 REM 25 vs. REM 10 and Control). The decline in remnant kidney function between 10 and 25 weeks was also associated with the appearance of glomeruli that were atubular (48 +/- 14 vs. 9 +/- 8 vs. 3 +/- 5%, REM 25 vs. REM 10 vs. Control, P < 0.05 REM 25 vs. REM 10 and Control) or connected to atrophic proximal tubule segments (26 +/- 10 vs. 11 +/- 6 vs. 1 +/- 2%, REM 25 vs. REM 10 vs. Control, P < 0.05 all comparisons). Atubular glomeruli, which usually had open capillary loops available for filtration, were more numerous than globally sclerotic glomeruli at 25 weeks after ablation. CONCLUSIONS: These findings indicate that tubular injury contributes to progressive loss of renal function following reduction in nephron number.

Natriuretic effect of adenosine A1-receptor blockade in rats.

BACKGROUND: Many effects of adenosine on renal function have been identified. The development of adenosine receptor blockers has made it possible to identify which of these effects are exerted by endogenous adenosine. At least four adenosine receptor subtypes, denoted A1, A2a, A2b, and A3 are currently known. In the present study the selective A1 receptor blocker 1,3-dipropyl-8[2-(5,6-epoxy) norbanyl] xanthine (CVT-117) was used to assess the effect of A1 activation by endogenous adenosine on renal function in rats. METHODS: Clearance studies were performed before and after administration of 0.1 mg/kg and 0.8 mg/kg of CVT-117 in separate groups of rats and before and after administration of vehicle in time-control rats. Measurements of heart rate before and after administration of exogenous adenosine confirmed effective A1 receptor blockade. RESULTS: At both the lower and higher doses, A1 receptor blockade with CVT-117 increased fractional sodium excretion and urine flow rate without altering GFR. The increase in sodium excretion following A1 blockade was not accompanied by increases in the excretion of phosphate or potassium. CONCLUSION: These results show that endogenous adenosine promotes sodium retention by activation of A1 receptors.

Clinical and pathological course of renal disease in non-insulin-dependent diabetes mellitus: the Pima Indian experience.

Non-insulin-dependent diabetes mellitus (NIDDM) and the renal disease attributable to it have been characterized extensively in the Pima Indians, a group of American Indians who form the Gila River Indian Community in Arizona. Both of these diseases are common in this community, and their onset and duration are known with greater certainty than in other populations because research examinations, which include oral glucose tolerance tests and measures of urinary protein excretion, have been performed frequently on most members of the population for the past 30 years. Studies of glomerular structure and hemodynamic function in diabetic Pima Indians indicate that glomerular hyperfiltration often develops at the onset of NIDDM and remains elevated until after overt nephropathy appears. Structurally, the glomeruli in subjects with microalbuminuria are not clearly distinguishable from those in subjects with normoalbuminuria, but macroalbuminuria is characterized by extensive glomerular sclerosis, mesangial expansion, and widening of epithelial cell foot processes that together lead to a rapid decline in the glomerular filtration rate. The decline in glomerular function in subjects with macroalbuminuria is due both to a loss of ultrafiltration surface area and to reduction in glomerular hydraulic permeability.

Podocyte loss and progressive glomerular injury in type II diabetes.

Kidney biopsies from Pima Indians with type II diabetes were analyzed. Subjects were classified clinically as having early diabetes (n = 10), microalbuminuria (n = 17), normoalbuminuria, despite a duration of diabetes equal to that of the subjects with microalbuminuria (n = 12), or clinical nephropathy (n = 12). Subjects with microalbuminuria exhibited moderate increases in glomerular and mesangial volume when compared with those with early diabetes, but could not be distinguished from subjects who remained normoalbuminuric after an equal duration of diabetes. Subjects with clinical nephropathy exhibited global glomerular sclerosis and more prominent structural abnormalities in nonsclerosed glomeruli. Marked mesangial expansion was accompanied by a further increase in total glomerular volume. Glomerular capillary surface area remained stable, but the glomerular basement membrane thickness was increased and podocyte foot processes were broadened. Broadening of podocyte foot processes was associated with a reduction in the number of podocytes per glomerulus and an increase in the surface area covered by remaining podocytes. These findings suggest that podocyte loss contributes to the progression of diabetic nephropathy.