Partial Renal Ablation Research Articles

Inverse correlation between vascular endothelial growth factor back-filtration and capillary filtration pressures

Vascular endothelial growth factor A (VEGF) is an essential growth factor during glomerular development and postnatal homeostasis. VEGF is secreted in high amounts by podocytes into the primary urine, back-filtered across the glomerular capillary wall to act on endothelial cells. So far it has been assumed that VEGF back-filtration is driven at a constant rate exclusively by diffusion. In the present work, glomerular VEGF back-filtration was investigated in vivo using a novel extended model based on endothelial fenestrations as surrogate marker for local VEGF concentrations. Single nephron glomerular filtration rate (SNGFR) and/or local filtration flux were manipulated by partial renal mass ablation, tubular ablation, and in transgenic mouse models of systemic or podocytic VEGF overexpression or reduction. Our study shows positive correlations between VEGF back-filtration and SNGFR as well as effective filtration rate under physiological conditions along individual glomerular capillaries in rodents and humans. Our results suggest that an additional force drives VEGF back-filtration, potentially regulated by SNGFR.

Repair after nephron ablation reveals limitations of neonatal neonephrogenesis.

The neonatal mouse kidney retains nephron progenitor cells in a nephrogenic zone for 3 days after birth. We evaluated whether de novo nephrogenesis can be induced postnatally beyond 3 days. Given the long-term implications of nephron number for kidney health, it would be useful to enhance nephrogenesis in the neonate. We induced nephron reduction by cryoinjury with or without contralateral nephrectomy during the neonatal period or after 1 week of age. There was no detectable compensatory de novo nephrogenesis, as determined by glomerular counting and lineage tracing. Contralateral nephrectomy resulted in additional adaptive healing, with little or no fibrosis, but did not also stimulate de novo nephrogenesis. In contrast, injury initiated at 1 week of age led to healing with fibrosis. Thus, despite the presence of progenitor cells and ongoing nephron maturation in the newborn mouse kidney, de novo nephrogenesis is not inducible by acute nephron reduction. This indicates that additional nephron progenitors cannot be recruited after birth despite partial renal ablation providing a reparative stimulus and suggests that nephron number in the mouse is predetermined at birth.

Discoidin domain receptor 1 kinase activity is required for regulating collagen IV synthesis

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase that binds to and is activated by collagens. DDR1 expression increases following kidney injury and accumulating evidence suggests that it contributes to the progression of injury. To this end, deletion of DDR1 is beneficial in ameliorating kidney injury induced by angiotensin infusion, unilateral ureteral obstruction, or nephrotoxic nephritis. Most of the beneficial effects observed in the DDR1-null mice are attributed to reduced inflammatory cell infiltration to the site of injury, suggesting that DDR1 plays a pro-inflammatory effect. The goal of this study was to determine whether, in addition to its pro-inflammatory effect, DDR1 plays a deleterious effect in kidney injury by directly regulating extracellular matrix production. We show that DDR1-null mice have reduced deposition of glomerular collagens I and IV as well as decreased proteinuria following the partial renal ablation model of kidney injury. Using mesangial cells isolated from DDR1-null mice, we show that these cells produce significantly less collagen compared to DDR1-null cells reconstituted with wild type DDR1. Moreover, mutagenesis analysis revealed that mutations in the collagen binding site or in the kinase domain significantly reduce DDR1-mediated collagen production. Finally, we provide evidence that blocking DDR1 kinase activity with an ATP-competitive small molecule inhibitor reduces collagen production. In conclusion, our studies indicate that the kinase activity of DDR1 plays a key role in DDR1-induced collagen synthesis and suggest that blocking collagen-mediated DDR1 activation may be beneficial in fibrotic diseases.

Regression of Renal Disease by Angiotensin II Antagonism Is Caused by Regeneration of Kidney Vasculature

Chronic renal insufficiency inexorably progresses in patients, such as it does after partial renal ablation in rats. However, the progression of renal diseases can be delayed by angiotensin II blockers that stabilize renal function or increase GFR, even in advanced phases of the disease. Regression of glomerulosclerosis can be induced by angiotensin II antagonism, but the effect of these treatments on the entire vascular tree is unclear. Here, using microcomputed tomography and scanning electron microscopy, we compared the size and extension of kidney blood vessels in untreated Wistar rats with those in untreated and angiotensin II antagonist-treated Munich Wistar Frömter (MWF) rats that spontaneously develop kidney disease with age. The kidney vasculature underwent progressive rarefaction in untreated MWF rats, substantially affecting intermediate and small vessels. Microarray analysis showed increased Tgf-β and endothelin-1 gene expression with age. Notably, 10-week inhibition of the renin-angiotensin system regenerated kidney vasculature and normalized Tgf-β and endothelin-1 gene expression in aged MWF rats. These changes were associated with reduced apoptosis, increased endothelial cell proliferation, and restoration of Nrf2 expression, suggesting mechanisms by which angiotensin II antagonism mediates regeneration of capillary segments. These results have important implications in the clinical setting of chronic renal insufficiency.

P47phox contributes to albuminuria and kidney fibrosis in mice

Reactive oxygen species (ROS) play an important pathogenic role in the development of many diseases, including kidney disease. Major ROS generators in the glomerulus of the kidney are the p47phox-containing NAPDH oxidases NOX1 and NOX2. The cytosolic p47phox subunit is a key regulator of the assembly and function of NOX1 and NOX2 and its expression and phosphorylation are up-regulated in the course of renal injury, and have been shown to exacerbate diabetic nephropathy. However, its role in non-diabetic-mediated glomerular injury is unclear. To address this, we subjected p47phox-null mice to either adriamycin-mediated or partial renal ablation-mediated glomerular injury. Deletion of p47phox protected the mice from albuminuria and glomerulosclerosis in both injury models. Integrin α1-null mice develop more severe glomerulosclerosis than wild type mice in response to glomerular injury mainly due to increased production of ROS. Interestingly, the protective effects of p47phox knockout were more profound in p47phox/integrin α1 double knockout mice. In vitro analysis of primary mesangial cells showed that deletion of p47phox led to reduced basal levels of superoxide and collagen IV production. Thus, p47phox-dependent NADPH oxidases are a major glomerular source of ROS, contribute to kidney injury, and are potential targets for antioxidant therapy in fibrotic disease.

Pharmacokinetics and Pharmacodynamics of Recombinant Human EPO-Fc Fusion Protein In Vivo

In this study, the in vivo pharmacokinetics and pharmacodynamics of a novel recombinant human erythropoietin (rhEPO) Fc fusion protein, rhEPO-Fc, were studied in both rodents and rhesus monkeys. Animal models of anemia induced by irradiation, cyclophosphamide and partial renal ablation were used to evaluate therapeutic effects of rhEPO-Fc. We have demonstrated that serum half-life of rhEPO-Fc was 29.5 to 38.9 h at doses of 8, 25, 80 µg/kg in rhesus monkeys and 35.5 to 43.5 h at doses of 16, 50, 160 µg/kg in rats. In anemia animal models, rhEPO-Fc dose-dependently (7.5–30.0 µg/kg in mice, 5.4–21.4 µg/kg in rats and 5.0–10.0 µg/kg in rhesus monkeys) increased reticulocyte level, followed by an increase of RBC count, hemoglobin and hematocrit levels. At reduced intervention frequency of weekly treatments, rhEPO-Fc showed similar hematopoietic effects as compared with rhEPO given three times a week. These results indicated that rhEPO-Fc could potentially be used in treatment of anemia and warrants future clinical trials.

Inhibition of Integrin α2β1 Ameliorates Glomerular Injury

Mesangial cells and podocytes express integrins α1β1 and α2β1, which are the two major collagen receptors that regulate multiple cellular functions, including extracellular matrix homeostasis. Integrin α1β1 protects from glomerular injury by negatively regulating collagen production, but the role of integrin α2β1 in renal injury is unclear. Here, we subjected wild-type and integrin α2-null mice to injury with adriamycin or partial renal ablation. In both of these models, integrin α2-null mice developed significantly less proteinuria and glomerulosclerosis. In addition, selective pharmacological inhibition of integrin α2β1 significantly reduced adriamycin-induced proteinuria, glomerular injury, and collagen deposition in wild-type mice. This inhibitor significantly reduced collagen synthesis in wild-type, but not integrin α2-null, mesangial cells in vitro, demonstrating that its effects are integrin α2β1-dependent. Taken together, these results indicate that integrin α2β1 contributes to glomerular injury by positively regulating collagen synthesis and suggest that its inhibition may be a promising strategy to reduce glomerular injury and proteinuria.

Elastin Degradation and Vascular Smooth Muscle Cell Phenotype Change Precede Cell Loss and Arterial Medial Calcification in a Uremic Mouse Model of Chronic Kidney Disease

Arterial medial calcification (AMC), a hallmark of vascular disease in uremic patients, is highly correlated with serum phosphate levels and cardiovascular mortality. To determine the mechanisms of AMC, mice were made uremic by partial right-side renal ablation (week 0), followed by left-side nephrectomy at week 2. At 3 weeks, mice were switched to a high-phosphate diet, and various parameters of disease progression were examined over time. Serum phosphate, calcium, and fibroblast growth factor 23 (FGF-23) were up-regulated as early as week 4. Whereas serum phosphate and calcium levels declined to normal by 10 weeks, FGF-23 levels remained elevated through 16 weeks, consistent with an increased phosphate load. Elastin turnover and vascular smooth muscle cell (VSMC) phenotype change were early events, detected by week 4 and before AMC. Both AMC and VSMC loss were significantly elevated by week 8. Matrix metalloprotease 2 (MMP-2) and cathepsin S were present at baseline and were significantly elevated at weeks 8 and 12. In contrast, MMP-9 was not up-regulated until week 12. These findings over time suggest that VSMC phenotype change and VSMC loss (early phosphate-dependent events) may be necessary and sufficient to promote AMC in uremic mice fed a high-phosphate diet, whereas elastin degradation might be necessary but is not sufficient to induce AMC (because elastin degradation occurred also in uremic mice on a normal-phosphate diet, but they did not develop AMC).

Atherosclerosis in chronic kidney disease: the role of macrophages

Patients with chronic kidney disease (CKD) are at increased risk of atherosclerotic cardiovascular disease and loss of renal parenchyma accelerates atherosclerosis in animal models. Macrophages are central to atherogenesis because they regulate cholesterol traffic and inflammation in the arterial wall. CKD influences macrophage behavior at multiple levels, rendering them proatherogenic. Even at normal creatinine levels, macrophages from uninephrectomized Apoe(-/-) mice are enriched in cholesterol owing to downregulation of cholesterol transporter ATP-binding cassette subfamily A member 1 levels and activation of nuclear factor κB, which leads to impaired cholesterol efflux. Interestingly, treatment with an angiotensin-II-receptor blocker (ARB) improves these effects. Moreover, atherosclerotic aortas from Apoe(-/-) mice transplanted into renal-ablated normocholesterolemic recipients show plaque progression and increased macrophage content instead of the substantial regression seen in recipient mice with intact kidneys. ARBs reduce atherosclerosis development in mice with partial renal ablation. These results, combined with the clinical benefits of angiotensin-converting-enzyme (ACE) inhibitors and ARBs in patients with CKD, suggest an important role for the angiotensin system in the enhanced susceptibility to atherosclerosis seen across the spectrum of CKD. The role of macrophages could explain why these therapies may be effective in end-stage renal disease, one of the few conditions in which statins show no clinical benefit.

Long-term outcomes of kidney donors

Partial renal ablation in laboratory animals leads initially to compensatory glomerular hyperfiltration and progressive, sclerotic kidney disease. In addition, modest declines in kidney function are associated with premature mortality in epidemiological studies. Hence, the long-term safety of living-kidney donation is an important issue. The purpose of this review was to examine existing research on outcomes among living-kidney transplant donors, with a focus on longer term outcomes. Although studies with sibling controls are unavailable, the current evidence base suggests that kidney donors have mortality and end-stage renal disease risks that are equivalent to similar individuals in the general population. Although findings for albuminuria and hypertension vary between studies, risks may be acceptable if donors receive optimal follow-up and care. Parenthetically, viewed as an experimental model of kidney-function loss, the neutrality of outcomes among donors may have major implications for the population at large: the robust associations between modest declines in kidney function and mortality seen in the general population suggest a confounded relationship and finding these confounders could have major implications for future research directions and for public health. Long-term outcomes suggest that kidney donation is not a major threat to longevity.

Characterization of mandibular bone in a mouse model of chronic kidney disease.

Chronic kidney disease (CKD) is a worldwide health problem with increasing prevalence and poor outcomes, including severe cardiovascular disease and renal osteodystrophy. With advances in medical treatment, patients with CKD are living longer and require oral care. The aim of this study is to determine the effects of CKD and dietary phosphate on mandibular bone structure using a uremic mouse model. Uremia (U) was induced in female dilute brown agouti/2 mice by partial renal ablation. Uremic mice received a normal-phosphate (NP) or a high-phosphate (HP) diet. sham surgeries were performed in a control group of mice; half received an NP diet, and the other half was fed an HP diet. At termination, animals were sacrificed, and mandibles were collected for microcomputed tomography (micro-CT) and histologic analysis. Sera levels of blood urea nitrogen, parathyroid hormone, and alkaline phosphatase were significantly increased in U/NP and U/HP mice versus sham controls, whereas serum calcium was increased in the U/HP group, and no differences were noted in serum phosphate levels among groups. Micro-CT analyses revealed a significant reduction in cortical bone thickness and an increase in trabecular thickness and trabecular bone volume/tissue volume in U/NP and U/HP groups compared to the sham/NP group. A significant reduction in cortical bone thickness was also found in the sham/HP group versus the sham/NP group. Histologic evaluation confirmed increased trabeculation in the U groups. CKD in mice, especially under conditions of HP feeding, results in marked effects on alveolar bone homeostasis.

Regulation of amino acid transporters in the rat remnant kidney

Partial renal ablation is associated with compensatory renal growth, significant azotaemia, a significant increase in fractional excretion of sodium and changes in solute transport. The present study evaluated the occurrence of adaptations in the remnant kidney, especially in renal amino acid transporters and sodium transporters and their putative role in sodium handling in the early stages (24 h and 1 week) after uninephrectomy. Wistar rats aged 8 weeks old were submitted to renal ablation of the right kidney--Unx rats (n = 10). 24 hours (n = 5) and 1 week (n = 5) after surgery, rats were anesthetized and the left kidney was removed. Urinary and plasmatic levels of catecholamines, sodium, urea and creatinine were measured. Gene expression of the amino acid and sodium transporters was determined by Real-time reverse transcription PCR. Protein expression was evaluated by Western blot using specific antibodies for the amino acid and sodium transporters. Uninephrectomized (Unx) rats for 24 h showed a lower urinary excretion of L-DOPA, dopamine and DOPAC than the corresponding Sham rats, accompanied by an increase in the expression of the Na(+)-K(+)-ATPase protein (64% increase). Unx rats for 1 week presented a hypertrophied remnant kidney, higher urine outflow and a approximately 2-fold increase in the fractional excretion of sodium. The NHE3 mRNA expression was significantly decreased in Unx rats throughout the study (approximately 20% decrease). LAT1 transcript and protein were consistently overexpressed at both 24 h and 1 week after uninephrectomy. In contrast, 4F2hc and LAT2 transcript abundance was lower in 24-h Unx rats than in Sham rats (a 36% decrease in both cases). These results provide evidence that the renal expression of the amino acid transporters LAT1, LAT2 and 4F2hc and the sodium transporters Na(+)-K(+)-ATPase and NHE3 is differently regulated following unilateral nephrectomy. In conclusion, this study allowed us to characterize the renal adaptations in the early stages after uninephrectomy, which showed a combined interaction of multiple mechanisms regulating sodium homeostasis including the renal dopaminergic system, and the abundance of amino acid transporters and sodium transporters.

Laparoscopic partial kidney ablation with high intensity focused ultrasound.

High intensity focused ultrasound has been performed for transrectal and extracorporeal thermal ablation of tissues. We developed and tested a laparoscopic probe that allows real-time ultrasound imaging during partial renal ablation using high intensity focused ultrasound. A Sonablate 200 (Focus Surgery, Indianapolis, Indiana) high intensity focused ultrasound system with a modified 18 mm. laparoscopic probe was used in all experiments. In 13 Yucatan mini-pigs a 5Fr ureteral catheter was inserted into the renal pelvis and 10 cc air were instilled into the collecting system. The kidney was laparoscopically dissected, the high intensity focused ultrasound probe was inserted through a 33 mm. laparoscopic port and the targeted renal pole was treated. Renal lesions were created in 12 of 13 treated kidneys under real-time ultrasound visualization. Median operative time was 180 minutes, average high intensity focused ultrasound activation time was 18.3 minutes and lesion size was 23 x 17 x 11 mm. At 4 and 14 days 4 (acute group) and 6 (subacute group) animals were available for renal functional and anatomical evaluation, respectively. No difference in renal function was seen in treated and untreated kidneys. Pathological examination at 14 days revealed homogenous and complete tissue necrosis throughout the whole volume of the lesion with sharp demarcation from adjacent normal tissue. We were able to refine a probe for laparoscopic high intensity focused ultrasound delivery capable of simultaneous ultrasound imaging. Partial renal ablation using this probe is feasible and safe, and resulted in homogenous, complete and reproducible lesions.

Essential Hypertension: Defending the Contribution of a Congenital Nephron Deficit

To the Editor: We read the recent review by Johnson et al in the March 2005 edition of Hypertension 1 with great interest. The authors scrutinized the various hypotheses put forward to explain the mechanism responsible for the defect in sodium handling generally accepted to underlie the renal origins of hypertension. This was a timely and thorough review of the literature, but we write to defend one of the potential mechanisms we feel was undervalued: a congenital reduction in nephron number. It has become apparent that the timing of partial renal ablation is critical in determining its long-term effects. As stated by Johnson et al, uninephrectomy in adult life (ie, once nephrogenesis is complete) does not necessarily lead to the development of hypertension. However, interruption of nephron formation during nephrogenesis, either surgically or pharmacologically in animal models or in the case of unilateral renal agenesis in humans, clearly does result in the onset of hypertension in later life.2 While nephron number, per se, may not program hypertension, a maladaptation …

Laparoscopic Partial Kidney Ablation With High Intensity Focused Ultrasound

High intensity focused ultrasound has been performed for transrectal and extracorporeal thermal ablation of tissues. We developed and tested a laparoscopic probe that allows real-time ultrasound imaging during partial renal ablation using high intensity focused ultrasound. A Sonablate 200 (Focus Surgery, Indianapolis, Indiana) high intensity focused ultrasound system with a modified 18 mm. laparoscopic probe was used in all experiments. In 13 Yucatan mini-pigs a 5Fr ureteral catheter was inserted into the renal pelvis and 10 cc air were instilled into the collecting system. The kidney was laparoscopically dissected, the high intensity focused ultrasound probe was inserted through a 33 mm. laparoscopic port and the targeted renal pole was treated. Renal lesions were created in 12 of 13 treated kidneys under real-time ultrasound visualization. Median operative time was 180 minutes, average high intensity focused ultrasound activation time was 18.3 minutes and lesion size was 23 x 17 x 11 mm. At 4 and 14 days 4 (acute group) and 6 (subacute group) animals were available for renal functional and anatomical evaluation, respectively. No difference in renal function was seen in treated and untreated kidneys. Pathological examination at 14 days revealed homogenous and complete tissue necrosis throughout the whole volume of the lesion with sharp demarcation from adjacent normal tissue. We were able to refine a probe for laparoscopic high intensity focused ultrasound delivery capable of simultaneous ultrasound imaging. Partial renal ablation using this probe is feasible and safe, and resulted in homogenous, complete and reproducible lesions.

Effect of antioxidant therapy with dl-α-tocopherol on cardiovascular structure in experimental renal failure

Chronic renal failure is characterized by remodeling of the structure of the heart and the vasculature, for example, left ventricular hypertrophy, myocardial fibrosis, capillary/myocyte mismatch, as well as thickening of intramyocardial arteries and of peripheral arteries and veins. Furthermore, uremia is a state of increased oxygen stress. It was the purpose of this study to examine whether these findings are interrelated. To investigate whether antioxidative therapy with dl-alpha-tocopherol (Toco; vitamin E) interferes with the development of abnormal cardiovascular structure in experimental renal failure, 28 male Sprague-Dawley rats were subjected to partial renal ablation (subtotal nephrectomy, SNX) or to sham operation (sham). SNX were either left untreated or received the antioxidant Toco (2 x 1500 IE/kg BW/week in the pellets). Blood pressure was measured using tail plethysmography. The experiment was terminated after 12 weeks. Heart and left ventricular weight were determined and the following parameters were measured using morphometry and stereology: volume densities of cardiomyocytes, capillaries and non-vascular interstitium; length density and total length of cardiac capillaries, wall thickness of intramyocardial arterioles and of the aorta. Systolic blood pressure and body weight were comparable in all groups. Treatment with Toco led to significantly increased plasma concentrations of Toco. Left ventricular weight and wall thickness of intramyocardial arteries were significantly higher in both SNX groups compared to sham controls. Volume density of the cardiac interstitial tissue was significantly higher in untreated SNX than in Toco treated SNX and sham control rats. Length density of capillaries was significantly lower in untreated SNX than in control rats; however, the values were significantly higher, and even higher than in sham controls, when SNX were treated with Toco. Treatment with the antioxidant dl-alpha-tocopherol prevented cardiomyocyte/capillary mismatch, and to some extent also myocardial fibrosis in rats with renal failure. The results point to a role of oxidative stress in the genesis of myocardial interstitial fibrosis and capillary deficit of the heart.

Impaired JAK-STAT signal transduction contributes to growth hormone resistance in chronic uremia

Chronic renal failure (CRF) is associated with resistance to the growth-promoting and anabolic actions of growth hormone (GH). In rats with CRF induced by partial renal ablation, 7 days of GH treatment had a diminished effect on weight gain and hepatic IGF-1 and IGFBP-1 mRNA levels, compared with sham-operated pair-fed controls. To assess whether GH resistance might be due to altered signal transduction, activation of the JAK-STAT pathway was studied 10 or 15 minutes after intravenous injection of 5 mg/kg GH or vehicle. Hepatic GH receptor (GHR) mRNA levels were significantly decreased in CRF, but GHR protein abundance and GH binding to microsomal and plasma membranes was unaltered. JAK2, STAT1, STAT3, and STAT5 protein abundance was also unchanged. However, GH-induced tyrosine phosphorylation of JAK2, STAT5, and STAT3 was 75% lower in the CRF animals. Phosphorylated STAT5 and STAT3 were also diminished in nuclear extracts. The expression of the suppressor of cytokine signaling-2 (SOCS-2) was increased twofold in GH-treated CRF animals, and SOCS-3 mRNA levels were elevated by 60% in CRF, independent of GH treatment. In conclusion, CRF causes a postreceptor defect in GH signal transduction characterized by impaired phosphorylation and nuclear translocation of GH-activated STAT proteins, which is possibly mediated, at least in part, by overexpression of SOCS proteins.

Impaired JAK-STAT signal transduction contributes to growth hormone resistance in chronic uremia

Chronic renal failure (CRF) is associated with resistance to the growth-promoting and anabolic actions of growth hormone (GH). In rats with CRF induced by partial renal ablation, 7 days of GH treatment had a diminished effect on weight gain and hepatic IGF-1 and IGFBP-1 mRNA levels, compared with sham-operated pair-fed controls. To assess whether GH resistance might be due to altered signal transduction, activation of the JAK-STAT pathway was studied 10 or 15 minutes after intravenous injection of 5 mg/kg GH or vehicle. Hepatic GH receptor (GHR) mRNA levels were significantly decreased in CRF, but GHR protein abundance and GH binding to microsomal and plasma membranes was unaltered. JAK2, STAT1, STAT3, and STAT5 protein abundance was also unchanged. However, GH-induced tyrosine phosphorylation of JAK2, STAT5, and STAT3 was 75% lower in the CRF animals. Phosphorylated STAT5 and STAT3 were also diminished in nuclear extracts. The expression of the suppressor of cytokine signaling-2 (SOCS-2) was increased twofold in GH-treated CRF animals, and SOCS-3 mRNA levels were elevated by 60% in CRF, independent of GH treatment. In conclusion, CRF causes a postreceptor defect in GH signal transduction characterized by impaired phosphorylation and nuclear translocation of GH-activated STAT proteins, which is possibly mediated, at least in part, by overexpression of SOCS proteins.

Laparoscopic partial kidney ablation using high-intensity focused ultrasound

A laparoscopic ultrasound probe was developed for image-guided high-intensity focused ultrasound (HIFU) ablation of renal tissue. The probe expands the application of a commercially available HIFU system (SonablateTM) to laparascopic operations. It consists of a 4-MHz focused rectangular HIFU piezoceramic transducer (30×10 mm, FL=30 mm) confocally coupled with a circular central element (8 mm in diameter) used for real-time pulse-echo imaging during treatment. Precise mechanical movements of the transducer enable it to treat targeted tissue volumes. The probe was fully characterized by measuring its electrical impedance, acoustic field, and total acoustic power output. Moreover, the acoustic field was simulated using an analytical model. The laparoscopic probe was able to generate acoustic power levels up to 35 W that correspond to focal intensities over 2200 W/cm2 in tissue, sufficient for tissue ablation through rapid temperature rise (>90<th>°C) and cavitation mechanisms. The probe was tested in an in vivo animal study in which 15 pigs were treated through a sterile laparoscopic procedure. A lesion with dimensions of 23×17×11 mm ±1 mm was successfully generated in the left kidney of each pig during a treatment time of less than 30 min. Histology results demonstrated homogeneous well-delineated lesions generated in the target region.

Interleukin-2-Dependent Mechanisms Are Involved in the Development of Glomerulosclerosis after Partial Renal Ablation in Rats

Background: Glomerulosclerosis is a common feature of many end-stage renal diseases. The contribution of cellular immune mechanisms has been implicated in the development of glomerulosclerosis. We investigated whether the inhibition of lymphocyte activation influences this process in an established rat model of renal hyperfiltration. Methods: After removal of two-thirds of their respective kidney mass, rats were treated with either tacrolimus (0.08 mg/kg/day) or vehicle until the end of the study (n = 10/group). The rats were pair-fed and proteinuria was assessed regularly. Twenty weeks after nephrectomy, creatinine clearance and systemic blood pressure were determined, and kidneys were harvested for morphological, immunohistological and PCR analysis. Results: In control animals, renal function started to decline from week 12, as indicated by an elevated proteinuria. Interleukin (IL)-2 and IL-2 receptor synthesis was upregulated in control animals and inhibited by tacrolimus treatment. Transforming growth factor-β (TGF-β₁), platelet-derived growth factor-AA (PDGF-AA) and macrophage chemoattractant protein-1 (MCP-1) mRNA levels were upregulated in control animals, but were significantly lower in immunosuppressed hosts. Additionally, tacrolimus treatment resulted in a significant reduction of proteinuria. Morphological analysis supported these functional results; glomerular sclerosis, tubular atrophy and intimal proliferation were more pronounced in controls than in the tacrolimus group. These morphological parameters were accompanied by reduced infiltration of CD5+ (rat T-cell marker) T cells, ED1+ (rat macrophage marker) macrophages, and less intense staining for laminin and fibronectin. Conclusion: A continuous treatment with tacrolimus – an inhibitor of lymphocyte proliferation – reduced the pace of glomerulosclerosis in the remnant kidney.