Ticlopidine prevents renal disease progression in rats with reduced renal mass

Crocetin ameliorative effect on diabetic nephropathy in rats through a decrease in transforming growth factor-β and an increase in glyoxalase-I activity

BACKGROUND & AIMS

Glycation, oxidative stress, and inflammation due to the elevation of transforming growth factor-β1 (TGF-β1) participate in diabetic nephropathy (DN). Thus, we investigated for the first time the effect of crocetin (Crt) on the renal histopathological parameters, TGF-β1 and glycation, oxidative stress, as well as inflammatory markers in the DN rat model.

METHODS

Forty male Wistar rats were randomly divided into 4 equal groups: normal (N), N + Crt, DN, and DN + Crt. DN was induced in rats with a combination of nephrectomy and streptozotocin. Treated groups received 100 mg/kg of Crt via intraperitoneal injection monthly for 3 months. Different glycation (glycated albumin, glycated LDL, Methylglyoxal, and pentosidine), oxidative stress (advanced oxidation protein products, malondialdehyde, glutathione, and paraoxonase-I (PON-1)), and inflammatory markers (tumor necrosis factor-α, myeloperoxidase, and TGF-β1), blood glucose, insulin, lipid profile, creatinine in the serum, and proteinuria, as well as the glyoxalase-1 (GLO-1) activity, was determined.

RESULTS

Crt decreased renal biochemical (Cre and PU) and histopathological (glomerulosclerosis) renal dysfunction parameters, diverse glycation, oxidative stress, and inflammatory markers in the DN rats. Furthermore, the treatment corrected glycemia, insulin resistance, and dyslipidemia as well as induced the activities of GLO-1 and PON-1. Over and above, the treatment decreased TGF-β1 in their serum (p > 0.001).

CONCLUSIONS

Crocetin improved DN owing to an advantageous effect on metabolic profile. Further, the treatment with a reducing effect on TGF-β1, oxidative stress, glycation, and inflammation markers along with an increase in Glo-1 activity showed multiple protective effects on kidney tissue.

The Role of Platelets in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is among the most common microvascular complications in patients with diabetes, and it currently accounts for the majority of end-stage kidney disease cases worldwide. The pathogenesis of DKD is complex and multifactorial, including systemic and intra-renal inflammatory and coagulation processes. Activated platelets play a pivotal role in inflammation, coagulation, and fibrosis. Mounting evidence shows that platelets play a role in the pathogenesis and progression of DKD. The potentially beneficial effects of antiplatelet agents in preventing progression of DKD has been studied in animal models and clinical trials. This review summarizes the current knowledge on the role of platelets in DKD, including the potential therapeutic effects of antiplatelet therapies.

Up-regulation of the kinin B2 receptor pathway modulates the TGF-β/Smad signaling cascade to reduce renal fibrosis induced by albumin

The presence of high protein levels in the glomerular filtrate plays an important role in renal fibrosis, a disorder that justifies the use of animal models of experimental proteinuria. Such models have proved useful as tools in the study of the pathogenesis of chronic, progressive renal disease. Since bradykinin and the kinin B2 receptor (B2R) belong to a renoprotective system with mechanisms still unclarified, we investigated its anti-fibrotic role in the in vivo rat model of overload proteinuria. Upon up-regulating the kinin system by a high potassium diet we observed reduction of tubulointerstitial fibrosis, decreased renal expression of α-smooth muscle actin (α-SMA) and vimentin, reduced Smad3 phosphorylation and increase of Smad7. These cellular and molecular effects were reversed by HOE-140, a specific B2R antagonist. In vitro experiments, performed on a cell line of proximal tubular epithelial cells, showed that high concentrations of albumin induced expression of mesenchymal biomarkers, in concomitance with increases in TGF-β1 mRNA and its functionally active peptide, TGF-β1. Stimulation of the tubule cells by bradykinin inhibited the albumin-induced changes, namely α-SMA and vimentin were reduced, and cytokeratin recovered together with increase in Smad7 levels and decrease in type II TGF-β1 receptor, TGF-β1 mRNA and its active fragment. The protective changes produced by bradykinin in vitro were blocked by HOE-140. The development of stable bradykinin analogues and/or up-regulation of the B2R signaling pathway may prove value in the management of chronic renal fibrosis in progressive proteinuric renal diseases.

Antihypertensive and renoprotective effect of the kinin pathway activated by potassium in a model of salt sensitivity following overload proteinuria

The albumin overload model induces proteinuria and tubulointersitial damage, followed by hypertension when rats are exposed to a hypersodic diet. To understand the effect of kinin system stimulation on salt-sensitive hypertension and to explore its potential renoprotective effects, the model was induced in Sprague-Dawley rats that had previously received a high-potassium diet to enhance activity of the kinin pathway, followed with/without administration of icatibant to block the kinin B₂ receptor (B₂R). A disease control group received albumin but not potassium or icatibant, and all groups were exposed to a hypersodic diet to induce salt-sensitive hypertension. Potassium treatment increased the synthesis and excretion of tissue kallikrein (Klk1/rKLK1) accompanied by a significant reduction in blood pressure and renal fibrosis and with downregulation of renal transforming growth factor-β (TGF-β) mRNA and protein compared with rats that did not receive potassium. Participation of the B₂R was evidenced by the fact that all beneficial effects were lost in the presence of the B₂R antagonist. In vitro experiments using the HK-2 proximal tubule cell line showed that treatment of tubular cells with 10 nM bradykinin reduced the epithelial-mesenchymal transdifferentiation and albumin-induced production of TGF-β, and the effects produced by bradykinin were prevented by pretreatment with the B₂R antagonist. These experiments support not only the pathogenic role of the kinin pathway in salt sensitivity but also sustain its role as a renoprotective, antifibrotic paracrine system that modulates renal levels of TGF-β.

Microsomal prostaglandin E synthase 1 deletion retards renal disease progression but exacerbates anemia in mice with renal mass reduction

Microsomal prostaglandin E synthase 1 (mPGES-1) is a cytokine-inducible enzyme responsible for generation of prostaglandin E(2) (PGE(2)) during the inflammatory response. In the present study, we investigated the role of mPGES-1 in the development of chronic renal failure in mice with 5/6 nephrectomy (Nx). After 4 weeks of Nx, wild-type mice with renal mass reduction exhibited increased blood urea nitrogen, plasma creatinine and phosphorus concentrations, and defective urine concentrating capability, all of which were significantly attenuated by mPGES-1 deletion. The Nx wild-type mice developed a 2.6-fold increase in urinary albumin excretion, accompanied by glomerulosclerosis and reduction of nephrin and wild-type 1 expression in the remnant kidney. In contrast, the Nx KO mice had normal albuminuria with improvement of glomerular injury. Nx-induced increases in circulating and renal tumor necrosis factor 1α and renal interleukin 1β and monocyte chemoattractant protein 1 expressions were all remarkably attenuated or abolished by mPGES-1 deletion. Paradoxically, the Nx knockout mice developed worsened anemia, accompanied by impaired erythropoietin synthesis. The coinduction of mPGES-1 and cyclooxygenase 2 but not cyclooxygenase 1 mRNA expressions, along with increased PGE(2) synthesis, was demonstrated in the remnant kidney of wild-type mice. mPGES-1 deletion remarkably reduced renal PGE(2) content and urinary PGE(2) excretion after renal ablation but had a limited effect on the baseline PGE(2) production. We conclude that mPGES-1 deletion ameliorates chronic renal failure in the mouse model of renal mass reduction, and mPGES-1 deletion paradoxically exacerbates anemia in this model likely via suppression of erythropoietin synthesis.

Purinergic receptors contribute to early mesangial cell transformation and renal vessel hypertrophy during angiotensin II-induced hypertension

Chronic ANG II infusions lead to increases in intrarenal ANG II levels, hypertension, and tissue injury. Increased blood pressure also elicits increases in renal interstitial fluid (RIF) ATP concentrations that stimulate cell proliferation. We evaluated the contribution of purinergic receptor activation to ANG II-induced renal injury in rats by treating with clopidogrel, a P2Y12 receptor blocker, or with PPADS, a nonselective P2 receptor blocker. alpha-Actin expression in mesangial cells, afferent arteriolar wall thickness (AAWT), cortical cell proliferation, and macrophage infiltration were used as early markers of renal injury. Clopidogrel and PPADS did not alter blood pressure, renin or kidney ANG II content. alpha-Actin expression increased from control of 0.6 +/- 0.4% of mesangial area to 6.3 +/- 1.9% in ANG II-infused rats and this response was prevented by clopidogrel (0.4 +/- 0.2%) and PPADS. The increase in AAWT from 4.7 +/- 0.1 to 6.0 +/- 0.1 mm in ANG II rats was also prevented by clopidogrel (4.8 +/- 0.1 mm) and PPADS. ANG II infusion led to interstitial macrophage infiltration (105 +/- 16 vs. 62 +/- 4 cell/mm(2)) and tubular proliferation (71 +/- 15 vs. 20 +/- 4 cell/mm(2)) and these effects were prevented by clopidogrel (52 +/- 4 and 36 +/- 3 cell/mm(2)) and PPADS. RIF ATP levels were higher in ANG II-infused rats than in control rats (11.8 +/- 1.9 vs. 5.6 +/- 0.6 nmol/l, P < 0.05). The results suggest that activation of vascular and glomerular purinergic P2 receptors may contribute to the mesangial cell transformation, renal inflammation, and vascular hypertrophy observed in ANG II-dependent hypertension.

Anti-inflammatory renoprotective effect of clopidogrel and irbesartan in chronic renal injury

Recent evidence suggests that platelet activation and angiotensin II may each contribute to glomerular inflammation and fibrosis. Clopidogrel inhibits platelet activation and may also reduce inflammation. This study investigated the anti-inflammatory and renoprotective effects of clopidogrel and irbesartan in the five-sixths nephrectomy rat model of chronic kidney disease. After 8 wk of treatment, 24-h proteinuria, serum creatinine, and histologic scores of glomerular sclerosis and tubulointerstitial damage were significantly lower in treated compared with untreated rats. Clopidogrel/irbesartan combination therapy had greater effects than either drug alone. Rats that underwent five-sixths nephrectomy had higher markers of platelet activation (plasma GMP-140 and renal cortical fibrin deposition) than sham-operated rats, and clopidogrel attenuated these effects. Clopidogrel and irbesartan similarly reduced the accumulation of ED-1-expressing macrophages in the cortical glomeruli and the interstitium. Combination therapy almost completely abolished macrophage infiltration and attenuated the expression of monocyte chemoattractant protein-1, intercellular adhesion molecule-1, TGF-beta(1), and connective tissue growth factor. In conclusion, combination treatment with clopidogrel and irbesartan, more so than either alone, decreases early renal injury induced by five-sixths nephrectomy by inhibiting renal inflammation.

Modulation of renal kallikrein by a high potassium diet in rats with intense proteinuria

Injury of the renal tubulointerstitial compartment is recognized to play an important role in hypertension. Its damage may in turn, impair the activity of vasodepressor systems, like the kallikrein-kinin, in blood pressure regulation. The overload proteinuria model induces tubulointerstitial injury with activation of the renin-angiotensin system, but renal kallikrein and the development of hypertension have not received special attention. Sprague-Dawley rats received seven intraperitoneal doses of bovine serum albumin (BSA) 2 g/day under normosodic diet and were hydrated ad libitum. A second group received a high potassium diet to stimulate kallikrein production during the previous four weeks and while under BSA administration. A third one received potassium and BSA in the same schedule, but with the kinin B2 receptor antagonist, HOE140, added during the protein load phase. A control group received seven saline injections. Kallikrein protein was detected by immune labeling on renal sections and enzymatic activity in the urine. The BSA group showed massive proteinuria followed by intense tubulointerstitial damage. Blood pressure increased after the third dose in BSA animals, remaining elevated throughout the experiment, associated with significant reductions in renal expression and urinary activity of kallikrein, compared with controls. An inverse correlation was found between blood pressure and immunohistochemistry and urinary activity of kallikrein. Potassium induced a significant increase in both urinary activity and renal kallikrein expression, associated with significant reduction in blood pressure. The HOE140 antagonist blunted the antihypertensive effect of kallikrein stimulation in proteinuric rats. Loss of renal kallikrein, produced by tubulointerstitial injury, may participate in the pathogenesis of the hypertension observed in this model.

Platelet inhibition limits TGF-β overexpression and matrix expansion after induction of anti-thy1 glomerulonephritis

BACKGROUND

Although a role of platelets is well established in atherosclerosis, only little is known about their contribution to pathologic renal matrix expansion. The present study analyzes the effect of the platelet inhibitor clopidogrel on the early injury and subsequent repair phase of experimental anti-thy1 glomerulonephritis.

METHODS

In male Sprague-Dawley rats, acute anti-thy1 glomerulonephritis was induced by intravenous injection of OX-7 antibody. In protocol 1 (injury), clopidogrel was given starting 5 days before antibody injection. One day after disease induction, parameters of mesangial cell injury (glomerular cell number, inducible NO synthesis, and macrophage infiltration) were analyzed. In protocol 2 (repair), clopidogrel treatment was started one day after antibody injection. On day 6, parameters of glomerular repair [glomerular matrix score, expression of transforming growth factor (TGF)-beta 1, fibronectin, and plasminogen activator inhibitor (PAI)-1] and thrombosis (aneurysm formation and fibrinogen deposition) were determined. In both protocols, an additional group of rats was treated with the angiotensin-converting enzyme (ACE) inhibitor enalapril.

RESULTS

In the injury protocol, platelet inhibition did not affect mesangial cell lysis, glomerular NO production, and macrophage infiltration, while ACE inhibition was protective. In the repair protocol, clopidogrel significantly limited aneurysm formation and fibrinogen deposition, as well as glomerular matrix expansion, TGF-beta 1, fibronectin, and PAI-1 expression. In comparison, enalapril was less effective in preventing glomerular thrombosis, but was significantly superior to clopidogrel in limiting matrix protein expression and accumulation.

CONCLUSION

The present study shows that platelets play a significant role in the sequence from mesangial cell injury to renal matrix expansion in anti-thy1 glomerulonephritis. The results, directly comparing renin-angiotensin-system and platelet inhibition, suggest that platelets contribute less than angiotensin II to TGF-beta overexpression and matrix accumulation in this model of acute glomerular wound repair.

Cellular and molecular mediators in common pathway mechanisms of chronic renal disease progression

Injury mechanisms activated by the hemodynamic adaptations to nephron loss are considered to represent a final common pathway that underlies the progressive nature of chronic renal disease. In this article, we review experimental evidence that the induction of cell adhesion molecule, cytokine and profibrotic growth factor gene expression and the resultant renal infiltration by inflammatory cells, especially macrophages, are important components of these common pathway mechanisms. Interventions aimed at inhibiting these mechanisms may offer new treatments for slowing or arresting the progression of chronic renal disease.

Role of ticlopidine on adriamycin-induced nephropathy

The effect of ticlopidine on rats with adriamycin nephropathy was observed during 26 weeks. In the ticlopidine-treated nephrotic animals (TNG), proteinuria was less than in the untreated nephrotic animals (NG), but this difference was significant only at week 6 (TNG = 47.27 +/- 16.52 versus NG = 100.08 +/- 13.83 mg/24 h, p < 0.01) and week 26 (TNG = 157.00 +/- 28.73 versus NG = 217.00 +/- 21.73 mg/24 h, p < 0.01) after ADR injection. NG presented severe tubulointerstitial abnormalities with a tubulointerstitial lesion index of 3+. No difference in glomerular lesions was observed among the groups (NG median = 6%, TNG median = 4% and TCG median = 2%). The tubulointerstitial lesion index of TNG was less intense (median = 2+) but not different from those of the control groups (CG median = 1+; TCG median = 0+) nor NG (median = 3+). We concluded that the treatment with ticlopidine produced some partially beneficial effects but did not prevent the development of adriamycin-induced nephropathy.

Mycophenolate mofetil prevents the progressive renal failure induced by 5/6 renal ablation in rats

BACKGROUND

Extensive renal ablation is associated with progressive sclerosis of the remnant kidney. Because lymphocytes and monocytes accumulate in the remnant kidney, it is likely that they play a role in the renal scarring. Therefore, we treated rats with 5/6 nephrectomy (5/6Nx) with mycophenolate mofetil (MMF), a drug that has an antiproliferative effect and that suppresses the expression of intercellular adhesion molecules.

METHODS

Sprague-Dawley rats with 5/6Nx received MMF (30 mg. kg-1. day-1 by daily gastric gavage, N = 15) or vehicle (N = 16). Ten additional rats were sham operated. All rats were fed a 30% protein diet. Body weight, serum creatinine, and urinary protein excretion were determined weekly. Lipid peroxidation, as a measure of oxidative stress observed by urinary malondialdehyde determinations, was performed every two weeks. Histologic studies were done in the remnant kidney four weeks (9 rats from the vehicle-treated group, 7 rats from the MMF group, and 5 sham-operated rats) and eight weeks after surgery (the remaining rats). Glomerular volume, sclerosis in glomeruli (segmental and global) and interstitium (semiquantitative scale), infiltrating lymphocytes and macrophages (CD43- and ED1-positive cells), and expression of adhesion molecules (CD54, CD18, and CD11b) were analyzed.

RESULTS

MMF treatment prevented the progressive increment in serum creatinine and the proteinuria observed in the 5/6 nephrectomized rats during the eight weeks of observation (P < 0.01). Weight gain was comparable in the MMF-treated and sham-operated rats, whereas weight gain was decreased in untreated 5/6 nephrectomized rats. Excretion of malondialdehyde increased after surgery but returned sooner to control levels in the MMF-treated rats. Increments in glomerular size and mean arterial blood pressure induced by renal ablation were not modified by MMF treatment. Eight weeks after surgery, segmental sclerosis was present in 48.4 +/- 8.35% (+/- sd) glomeruli in the vehicle-treated group versus 25 +/- 10.5% in the MMF-treated group (P < 0.001). Interstitial fibrosis was reduced significantly with MMF treatment (P < 0.001). Infiltration with CD43- and ED1-positive cells in glomeruli and interstitium was two to five times lower in MMF-treated rats (P < 0.01). Expression of adhesion molecules CD18 and CD11b was similarly reduced.

CONCLUSION

MMF ameliorates the progressive renal damage in the remnant kidney after 5/6Nx. This effect is associated with a reduction in the infiltration of lymphocytes and monocytes, whereas glomerular hypertrophy and systemic hypertension are unchanged.

Pharmacokinetics and effect of ticlopidine on platelet aggregation in subjects with normal and impaired renal function

The pharmacokinetics and the effect of ticlopidine on platelet aggregation were determined in patients with chronic renal failure (n = 6), who were not on dialysis and had glomerular filtration of 16.9 +/- 4.4 mL/min, and were matched with the pharmacokinetics and effects in healthy volunteers (n = 7). Participants were studied after acute oral administration of ticlopidine at the beginning of the study and after 36 days of treatment with 250 mg twice daily. For unchanged ticlopidine there were no significant differences between the concentration profiles for the two study groups. By day 36 the minimum concentrations in plasma were identical (0.35 +/- 0.22 mg/L and 0.36 +/- 0.21 mg/L, respectively). Using 14C-labeled ticlopidine, the concentration profiles of radioactivity on day 1 were similar to those on day 36 for both groups. However, maximum concentrations and area under the concentration-time curve at 72 hours were both higher in patients with renal failure than in healthy volunteers. Treatment with ticlopidine progressively decreased sensitivity to adenosine diphosphate-induced platelet aggregation. At day 36, the concentration of adenosine diphosphate required to achieve 50% platelet aggregation was approximately 2.5 times greater than before treatment. Both patients and healthy volunteers exhibited closely comparable changes. The response to collagen-induced platelet aggregation was not changed in patients by treatment with ticlopidine. In contrast, volunteers required a three- to fourfold increase in collagen concentration to achieve 50% platelet aggregation after 36 days of therapy. Although some differences in both pharmacokinetics and pharmacodynamics of ticlopidine have been demonstrated between patients and and healthy volunteers, results in this study demonstrated that a change of dosage is not required in renal failure.

Abnormal permeability to proteins and glomerular lesions: a meta-analysis of experimental and human studies

Whether abnormal protein traffic through the glomerular capillary is one of the possible causes of glomerular injury has been a matter of considerable controversy. Experimental and clinical evidence indicate an association between the two, and several explanations of potential pathophysiologic pathways are available that may explain protein-dependent forms of renal injury. However, none of the mechanisms suggested thus far have been definitely proven. A meta-analytic review was used to further explore the relationship between urinary protein excretion and glomerular injury in experimental and human proteinuric nephropathies. In experimental models a definite positive association (P < 0.0001) was found between urinary protein excretion and glomerulosclerosis. The overall effect size d for this relationship was 2.36 (95% confidence interval, 2.13 to 2.60), corresponding to a correlation coefficient of r = 0.76. Similarly, the correlation between albuminuria and glomerular sclerotic lesions was highly significant (overall d = 2.88; 95% confidence interval, 2.33 to 3.42; P < 0.0001; correlation coefficient, r = 0.82). In humans the meta-analytic correlation yielded analogous, although less striking, results (overall d = 0.58; 95% confidence interval, 0.43 to 0.73; P < 0.0001; correlation coefficient, r = 0.28). In conclusion, meta-analysis of data from studies examining urinary protein excretion revealed a significant positive correlation with glomerular sclerosis in both experimental models and human diseases. This study supports the role of abnormal protein traffic through the glomerular capillary as one of the possible causes of renal injury. However, the strong relationship found does not necessary establish a cause-and-effect relationship.

Role of platelets in progressive glomerular diseases

There is increasing evidence that platelets are involved in the pathogenesis of glomerulonephritis. Intraglomerular platelets or their degradation products are observed in biopsies from patients with lupus nephritis, mesangioproliferative, membranous or IgA nephropathy. Moreover shortened platelet survival in patients with various glomerular diseases has also been described. In models of experimental glomerulonephritis, platelets may participate in glomerular injury, together with other mediators, by complex mechanisms. As extensively documented, platelets release within the glomerulus vasoactive, chemotactic and mitogenic substance that interact with a number of soluble mediators generated by renal resident or inflammatory cells and contribute to amplify glomerular injury. Thus platelet-activating factor and other platelet secretory products, polycationic macromolecules, platelet factor 4 and beta-thromboglobulin, alter glomerular permeability to proteins and enhance immune-mediated glomerular injury. Platelet-derived factors, like platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF beta) mediate renal disease progression in experimental and human glomerulonephritis via their chemotactic activity for infiltrating leucocytes and their effect of promoting extracellular matrix synthesis by resident renal cells. In these settings increased renal expression of PDGF and TGF beta has correlated with clinical features. Specific PDGF and TGF beta inhibitors ameliorated experimental glomerular disease. A wide variety of therapies to inhibit platelet function have been employed over the years, however the results of clinical studies are controversial and do not allow conclusions to be drawn about the efficacy of anti-platelet agents in progressive renal disease. Identification of specific platelet inhibitors or interventions specific for platelet secretory products and their target cells will be crucial for understanding the exact role of platelets and their products in glomerular disease.

Antiplatelet therapy and development of hypertension induced by recombinant human erythropoietin in uremic patients

The pathogenesis of hypertension induced by recombinant human erythropoietin (rHuEPO) remains a subject of intense interest. The observation that patients treated with antiplatelet drugs never developed hypertension following rHuEPO therapy prompted us to study retrospectively the incidence and risk factors associated with the development of hypertension in 91 patients on renal replacement therapy who had commenced rHuEPO therapy in the last three years. Logistic regression analysis was used to determine the risk factors associated with the development or aggravation of hypertension during the first six months on rHuEPO therapy. The predictors were: age, gender, number of months on dialysis, antecedent of hypertension, use of antiplatelet drugs, and those parameters related with dose, route and magnitude of the hematological response to rHuEPO. Of the 91 patients studied, 34 developed hypertension (37%). Of the 34 patients who were on antiplatelet treatment, 2 (5.8%) developed hypertension, whereas among 57 who did not receive antiplatelet drugs, 32 (56%) developed it. By multiple logistic regression analysis, the best predictive variables over the development of hypertension were: age (odds ratio: 0.959, P = 0.02), antecedent of hypertension (odds ratio: 6.52, P = 0.002), and use of antiplatelet therapy (odds ratio: 0.030, P < 0.0001). The rest of the studied variables failed to explain the development of hypertension. Antiplatelet therapy may prevent the development of hypertension in patients treated with rHuEPO. Since the antiplatelet drugs used in this study did not have a significant hemodynamic effect, we infer that changes in platelet aggregability induced by rHuEPO may be involved in the pathogenesis of hypertension induced by this hormone.

Thromboxane synthesis and action within the kidney

PGH2 and TxA2 exert their actions via tissue specific, receptor isoforms. PGH2/TxA2-dependent platelet aggregation and contraction of vascular and bronchial smooth muscle and of glomerular mesangial cells occur via receptors linked to activation of phospholipase C. Although PGH2/TxA2 appear to be of little importance in the maintenance of renal function under physiological circumstances, increased renal TxA2 biosynthesis has been documented in a variety of animal models of renal disease and in some clinical disorders (Table 2). The effects of this eicosanoid on renal tissues in vitro and of pharmacological manipulation of TxA2 synthesis and action in vivo suggest that such interventions will provide new drugs for the treatment of human kidney disease.

Thromboxane mediates glomerular haemodynamics in a model of chronic glomerular disease

In order to evaluate a possible haemodynamic role of cyclooxygenase products in chronic renal disease, a model of chronic glomerular injury was induced in nephritic rats by unilateral nephrectomy and high dietary protein intake. Eight weeks after induction of an in situ immune complex glomerulonephritis (CGN), rats subjected to high protein (HP) intake (42% protein) and uninephrectomy revealed a significantly lower glomerular filtration rate (GFR; 485 +/- 53 microliters min-1 100 g-1 body weight (BW)) compared with uninephrectomized rats with ICGN which were on low protein (LP) diet (6% protein) (825 +/- 155 microliters min-1 100 g-1 BW) (P less than 0.01). The glomerular thromboxane B2 (TxB2) formation in uninephrectomized rats with ICGN on either LP or HP intake was not significantly different (HP: 473 +/- 61; LP: 493 +/- 63 pg mg-1 min-1), but was significantly higher when compared with non-nephritic controls on either diet. Glomerular prostaglandin E2 (PGE2) production in rats on HP diet was higher compared with rats with LP intake (HP: 617 +/- 67; LP: 351 +/- 76 pg mg-1 min-1) (P less than 0.01). The thromboxane receptor blocker daltroban significantly elevated suppressed GFR in ICGN rats on HP diet (ICGN+vehicle: 426 +/- 69; ICGN+daltro: 689 +/- 66 microliters min-1 100 g-1 BW) (P less than 0.01). Thromboxane receptor blockade had no effect on glomerular haemodynamics in ICGN animals receiving LP diet (ICGN+vehicle: 771 +/- 24; ICGN+daltro: 684 +/- 85 microliters min-1 100 g-1 BW).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

The beta-blocker acebutolol down modulates the spontaneous polyclonal activation of lymphocytes in NZB X NZW lupus mice

Acebutolol is a beta blocking agent that induces in C57Bl/6 mice a polyclonal activation of lymphocytes (PAL). In this study, its effect on cellular parameters of spontaneous PAL and lupus disease in NZB x NZW female mice is investigated. A significant reduction of PAL is found in 10-week-old mice after only five injections of 50 mg/kg/day of acebutolol. This effect is also observed in 7- and 9-month-old mice after 12 weeks of treatment. In these chronically treated mice, a significant decrease in incidence and levels of proteinuria as compared with untreated mice is found. No statistically significant increase in survival is observed. In conclusion, acebutolol down modulates the spontaneous PAL which characterizes the NZB x NZW mouse lupus disease and might prevent to some extent the development of nephritis.

Role of endothelium-derived nitric oxide in the bleeding tendency of uremia

Endothelium-derived relaxing factor, now identified as nitric oxide (NO), is a labile humoral agent formed by vascular endothelial cells from L-arginine. NO mediates the action of substances that induce endothelium-dependent relaxation and plays a role in regulating blood pressure. In this study we investigated whether NO is involved in the pathogenesis of the bleeding tendency associated with renal failure. Rats with extensive surgical ablation of renal mass develop renal insufficiency due to progressive glomerulosclerosis. Like uremic humans, rats with renal mass reduction and uremia have a bleeding tendency that manifests itself by a prolonged bleeding time. We found that N-monomethyl-L-arginine (L-NMMA), a specific inhibitor of NO formation from L-arginine, completely normalized bleeding time when given to uremic rats. L-NMMA injection also increased ex vivo platelet adhesion but did not affect ex vivo platelet aggregation induced by adenosine diphosphate, arachidonic acid, and calcium ionophore A23187. The shortening effect of L-NMMA on bleeding time was completely reversed by giving the animals the NO precursor L-arginine, but not D-arginine, which is not a precursor of NO. It thus appears that NO is a mediator of the bleeding tendency of uremia.