Investigation of the thermal and tissue injury behaviour in microwave thermal therapy using a porcine kidney model

Minimally invasive microwave thermal therapies are being developed for the treatment of small renal cell carcinomas (RCC, d<3 cm). This study assessed the thermal history and corresponding tissue injury patterns resulting from microwave treatment of the porcine renal cortex. Three groups of kidneys were evaluated: (1) in vitro treated, (2) in vivo with 2-h post-treatment perfusion (acute) and (3) in vivo with 7-day post-treatment perfusion (chronic). The kidneys were treated with an interstitial water-cooled microwave probe (Urologix, Plymouth, MN) that created a lesion centered in the renal cortex (50 W for 10 min). The thermal histories were recorded at 0.5 cm radial intervals from the probe axis for correlation with the histologic cellular and vascular injury. The kidneys showed a reproducible 2 cm chronic lesion with distinct histologic injury zones identified. The thermal histories at the edge of these zones were found using Lagrangian interpolation. The threshold thermal histories for microvascular injury and stasis appeared to be lower than that for renal epithelial cell injury. The Arrhenius kinetic injury models were fit to the thermal histories and injury data to determine the kinetic parameters (i.e. activation energy and frequency factor) for the thermal injury processes. The resultant activation energies are consistent in magnitude with those for thermally induced protein denaturation. A 3-D finite element thermal model based on the Pennes bioheat equation was developed and solved using ANSYS (V7.0). The real geometry of the kidneys studied and temperature dependent thermal properties were used in this model. The specific absorption rate (SAR) of the microwave probe required for the thermal modelling was experimentally determined. The results from the thermal modelling suggest that the complicated change of local renal blood perfusion with temperature and time during microwave thermal therapy can be predicted, although a first order kinetic model may be insufficient to capture blood flow changes. The local blood perfusion was found to be a complicated function of temperature and time. A non-linear model based on the degree of vascular stasis was introduced to predict the blood perfusion. In conclusion, interstitial microwave thermal therapy in the normal porcine kidney results in predictable thermal and tissue injury behaviour. Future work in human kidney tissue will be necessary to confirm the clinical significance of these results.

The repeated extracorporeal shock waves and the renal parenchyma injury on normal and diabetic rats

PURPOSE

To assess the effect of repeated extracorporeal shock waves (ESW) on renal parenchyma of normal and diabetic rats.

METHODS

40 normal rats (A) and 40 diabetic rats (B) were assigned for ESW (Direx Tripter X1 - 14 KVA) as follow: A1/B1 and A3/B3 no ESW; A2/B2 one ESW (2,000 SW); A4/B4 two ESW (4,000 SW) in an elapsed 14 days. All the animals were sacrificed 3 days after the ESW and samples of renal parenchyma were histological prepared, stained by H&E. For each animal the frequency of hemorrhage focus (HF) in the subcapsular, interstitial and glomerulus area was calculated (percentage) on 20 randomly histological sections.

RESULTS

No one HF was identified in all normal or diabetic animals without ESW (A1, A3 and B1, B3). In the normal rats the HF frequency was similar to one ESW (subcapsular =15%; interstitial =20% and glomerular =10%) or repeated ESW (subcapsular =25%; interstitial =20%; glomerular=10%). In diabetic rats the occurrence of HF with repeated ESW was more frequent (subcapsular =40%; interstitial =30% and glomerular =10%) than with a single ESW (subcapsular =25%; interstitial =15% and glomerular =15%).

CONCLUSION

A single ESW or a repeated ESW caused a mild and similar damage on renal cortex of normal rats. In diabetic rats the repeated ESW may result in an accumulated damage, especially with focus of hemorrhage in subcapsular and interstitial tissue and glomerulus edema.

Morphological changes induced in the pig kidney by extracorporeal shock wave lithotripsy: nephron injury

While shock wave lithotripsy (SWL) is known to cause significant damage to the kidney, little is known about the initial injury to cells along the nephron. In this study, one kidney in each of six juvenile pigs (6-7 weeks old) was treated with 1,000 shock waves (at 24 kV) directed at a lower pole calyx with an unmodified HM-3 lithotripter. Three pigs were utilized as sham-controls. Kidneys were fixed by vascular perfusion immediately after SWL or sham-SWL. Three of the treated kidneys were used to quantitate lesion size. Cortical and medullary samples for light (LM) and transmission electron microscopy (TEM) were taken from the focal zone for the shock waves (F2), the contralateral kidney, and the kidneys of sham-SWL pigs. Because preservation of the tissue occurred within minutes of SWL, the initial injury caused by the shock waves could be separated from secondary changes. No tissue damage was observed in contralateral sham-SWL kidneys, but treated kidneys showed signs of injury, with a lesion of 0.2% +/- 0.1% of renal volume. Intraparenchymal hemorrhage and injury to tubules was found at F2 in both the cortex and medulla of SWL-treated kidneys. Tubular injury was always associated with intraparenchymal bleeding, and the range of tissue injury included total destruction of tubules, focal cellular fragmentation, necrosis, cell vacuolization, and membrane blebbing. The initial injury caused by SWL was cellular fragmentation and necrosis. Cellular vacuolization, membrane blebbing, and disorganization of apical brush borders appear to be secondary changes related to hypoxia.

The role of endothelin in early renal cortical reperfusionin renal transplantation

The role of specific endothelin receptors in the early renal reperfusion and long-term survival in renal transplantation was investigated in Lewis rats. Left renal transplantation was performed following 2 h cold ischaemia without and with ET(A) receptor antagonism and following 16 h cold ischaemia with no treatment, with ET(A) receptor antagonism and with ET(B) receptor antagonism. The ET(A) and ET(B) receptor antagonists, BQ-610 and A-192621 respectively, were added to the preservation solution. Renal cortical perfusion (RCP) was measured postoperatively using laser Doppler flowmetry. All rats in the 2-hour groups survived for 15 days. Animals in the untreated 16-hour group or in the A-192621-treated group died between days 3 and 6 after surgery. Fifty percent of the rats in the 16-hour and BQ-610-treated group died between days 4 and 7 after surgery while the other 50% survived for 15 days. Survival rates correlated well with both the postoperative serum creatinine and the recovery of RCP. We conclude that addition of an ET(A) receptor antagonist to the preservation solution improves renal reperfusion and long-term survival following prolonged ischaemia, whereas ET(B) receptor antagonism does neither.

Cholesterol ester accumulation: an immediate consequence of acute in vivo ischemic renal injury

BACKGROUND

Cholesterol is a major constituent of plasma membranes, and recent evidence indicates that it is up-regulated during the maintenance phase of acute renal failure (ARF). However, cholesterol's fate and that of the cholesterol ester (CE) cycle [shuttling between free cholesterol (FC) and CEs] during the induction phase of ARF have not been well defined. The present studies sought to provide initial insights into these issues.

METHODS

FC and CE were measured in mouse renal cortex after in vivo ischemia (15 and 45 minutes)/reperfusion (0 to 120 minutes) and glycerol-induced myoglobinuria (1 to 2 hours). FC/CE were also measured in (1) cultured human proximal tubule (HK-2) cells three hours after ATP depletion and in (2) isolated mouse proximal tubule segments (PTSs) subjected to plasma membrane damage (with cholesterol oxidase, sphingomyelinase, phospholipase A2, or cytoskeletal disruption with cytochalasin B). The impact of cholesterol synthesis inhibition (with mevastatin) and FC traffic blockade (with progesterone) on injury-evoked FC/CE changes was also assessed.

RESULTS

In vivo ischemia caused approximately threefold to fourfold CE elevations, but not FC elevations, that persisted for at least two hours of reperfusion. Conversely, myoglobinuria had no effect. Isolated CE increments were observed in ATP-depleted HK-2 cells. Neither mevastatin nor progesterone blocked this CE accumulation. Plasma membrane injury induced with sphingomyelinase or cholesterol oxidase, but not with phospholipase A(2) or cytochalasin B, increased tubule CE content. High CE levels, induced with cholesterol oxidase, partially blocked hypoxic PTS attack.

CONCLUSIONS

In vivo ischemia/reperfusion acutely increases renal cortical CE, but not FC, content, indicating perturbed CE/FC cycling. The available data suggest that this could stem from specific types of plasma membrane damage, which then increase FC flux via aberrant pathways to the endoplasmic reticulum, where CE formation occurs. That CE levels are known to inversely correlate with both renal and nonrenal cell injury suggests the potential relevance of these observations to the induction phase of ischemic ARF.

Modulation by cyclic AMP and phorbol myristate acetate of cephaloridine-induced injury in rat renal cortical slices

Intracellular signaling pathways of cAMP and protein kinase C (PKC) have been suggested to modulate the generation of free radicals. We investigated the effects of cAMP and phorbol myristate acetate (PMA), a PKC activator, on cephaloridine (CER)-induced renal cell injury, which has been reported to be due to the generation of free radicals. Incubation of rat renal cortical slices with CER resulted in increases in lipid peroxidation and lactate dehydrogenase (LDH) release and in decreases in gluconeogenesis and p-aminohippurate (PAH) accumulation in rat renal cortical slices, suggesting free radical-induced injury in slices exposed to CER. A derivative of cAMP ameliorated not only the increase in lipid peroxidation but also the renal cell damage induced by CER. This amelioration by a cAMP derivative of lipid peroxidation and renal cell damage caused by CER was blocked by KT 5720, a protein kinase A (PKA) inhibitor. Lipid peroxidation and the indices of cell injury were increased by PMA. PMA also enhanced CER-induced lipid peroxidation and cell damage in the slices. This enhancement by PMA of CER-induced injury was blocked by H-7, a PKC inhibitor. These results indicated that intracellular signaling pathways of cAMP and PKC modulate free radical-mediated nephrotoxicity induced by CER.

Material characterization of the pig kidney in relation with the biomechanical analysis of renal trauma

The objective of this study was an investigation of the material properties of the fresh pig kidney and parametric characterization of its elastic and inelastic material behavior. The material investigation included density measurements, uniaxial as well as three-dimensional compression tests, tensile tests. and shear tests on the samples extracted from the fresh pig kidney. For comparison, density measurements on a number of soft synthetic materials were also performed. Compression tests on the radial and the tangential specimens from the cortex tissue were performed at various loading rates. Three-axial compression tests were performed on the cortex tissues placed in a compression chamber. Shear tests were performed by punching a cylinder into a slice of the cortex. Tensile tests were carried out on the outer capsule. For characterization of the material behavior, a non-linear theoretical simulation based on a two parameter Blatz model was used. For characterization of the time-dependent behavior of the pig kidney cortex, a four-parameter linear viscoelastic model was employed. From the present experimental and theoretical studies, a number of conclusions were derived: (1) The general behavior of the pig kidney cortex samples under compression showed the general non-linear features typical of the soft tissues; the stress strain diagram was composed of a very flat part at very low stress level to about 30% relative deformation which was followed by a steeply rising stiffening leading to the radial rupture of samples marked by a maximum nominal rupture strain of about 50%. (2) The uniaxial compression tests on the radial and the tangential samples from the cortex tissue showed an increase of the rupture stress with the increase in the loading rate, but a decrease in the related rupture strain. (3) The long-term uniaxial compression tests on the cortex specimens under sustained constant load showed an instantaneous deformation followed by a creep response which eventually approached an asymptote. (4) Simulation of the non-linear material behavior of the cortex tissue under uniaxial compression by the Blatz model gave two pairs of material parameters for the cortex in the radial and the tangential directions. Furthermore, fitting of the assumed four-parameter linear viscoelastic model with the experimental data resulted in the viscoelastic material parameters.

Attempted nonoperative management of blunt renal lacerations extending through the corticomedullary junction: the short-term and long-term sequelae

A total of 50 patients who sustained a renal laceration extending through the corticomedullary junction following blunt trauma underwent an attempt at nonoperative (expectant) management of the urological injury. Of the patients 18% could not be stabilized and they subsequently underwent emergency laparotomy. Among our stabilized patients 2 major categories existed: 1) 30 patients with vascularized renal fragments and 2) 11 in whom a fragment of the kidney was devascularized. A statistically significant difference in the length of hospital stay (p equals 0.01) and the need for delayed surgical intervention (p less than 0.001) was noted between the 2 groups. We recommend that the physician must have a heightened awareness of probable complications in patients with major renal lacerations associated with devitalized fragments and suggest that early surgical management should be considered.

Dosimetry study of Nd:YAG laser damage to canine renal cortex

A dosimetry study of factors affecting the extent of tissue damage inflicted upon the canine renal cortex by the Neodymium:Yttrium Aluminum Garnet (Nd:YAG) laser was undertaken. Laser parameters and renal tissue conditions were varied independently in duplicate in the following manner: (1) power - 5, 10, 20, 50, 75, 100 watts with a spot size of 1.2 mm; (2) exposure duration - 1, 2, and 4 seconds; (3) kidney perfusion and temperature--renal artery unclamped (perfused) without cooling; renal artery clamped (non-perfused) without cooling; and renal artery clamped with cooling. Five days following application of the laser, the animals were sacrificed and serial sections of the renal cortex were examined for maximum depth and width of tissue damage and ablation. Multiple linear regression analysis of the data indicated a direct linear relationship between the joules (watts X seconds) of energy delivered to the renal cortex and the depth and width of tissue damage and ablation (p less than 0.001 for joule regression coefficient for each variable). Seconds and/or watts alone were not major predictors of the outcome after accounting for joules. Clamping the main renal artery significantly reduced the depth and width of laser damage when compared to the perfused kidney (p less than 0.001 for each variable). The depth of damage was similar in the cooled and the non-cooled non-perfused kidney. These data suggest that increased laser energy and kidney perfusion significantly increase renal cortical laser induced damage. Adjustment of these parameters may permit controlled tumor ablation or tissue incision with minimal damage to adjacent normal tissue.

Comparative studies of cellular reactions to injuries between the inner medulla and the cortex of rat kidneys

The inner medulla and the cortex of the rat kidney were surgically traumatized or threaded with a silk suture, and the sequence of morphologic events occurring in these two topographic locations were studied by light microscopy on Days 7, 14, and 28. On Days 7, 14, and 28 following the infliction of the surgical trauma, such cellular reactions as mononuclear cell infiltration and fibroblastic proliferation were less intense in the injured site of the inner medulla than in the cortex. Numerous foreign body type giant cells appeared about the suture material in the cortex as early as Day 7 and were persistently present on Days 14 and 28. A similar type of foreign body giant cells did not appear about the suture material within the inner medulla throughout the experiment. Our results suggest that there is a difference in cellular reaction to injury or to a foreign body between the inner medulla and the cortex of rat kidneys.