Continuous infusion of oxalate by minipumps induces calcium oxalate nephrocalcinosis.

It is hypothesized that oxalate plays an active role in calcium oxalate (CaOx) nephrocalcinosis and oxalate driven nephrolithiasis by interacting with the kidney. We developed an adjustable, nonprecursor, continuous infusion model of hyperoxaluria and CaOx nephrocalcinosis to investigate this hypothesis. Minipumps containing PBS or KOx (60-360 micromol/day; n = 5-7/dose) were implanted subcutaneously in male Sprague-Dawley rats on D0 and D6. Rats were killed on D13. Oxalate excretion and CaOx crystalluria were monitored by 20+4 h urine collections. Localization and content of intrarenal crystals were determined on frozen sections using polarization and microFTIR. Oxalate excretion was significantly elevated in all KOx rats (P < or = 0.005). CaOx crystalluria was most persistent in the 240-360 micromol/day KOx rats, but even 60 micromol/day KOx rats showed sporadic crystalluria. One hundred percent of KOx rats had CaOx nephrocalcinosis as confirmed by microFTIR. Most crystals were localized to the lumens of the corticomedullary collecting ducts. A few crystals are localized just under the papillar urothelium. The minipump model is the first model of hyperoxaluria to provide continuous infusion of oxalate. It permits control of the levels of hyperoxaluria, crystalluria and CaOx nephrocalcinosis. The level of sustained hyperoxaluria and CaOx nephrocalcinosis induced by treatment with 360 micromol/day KOx for 13D models the conditions frequently observed in jejunoileal bypass patients. Adjustments in the length of treatment and level of hyperoxaluria may allow this model to also be used to study the oxalate driven CaOx-nephrolithiasis common in patients with hyperoxaluria due to other causes.

Local release of dexamethasone from polymer millirods effectively prevents fibrosis after radiofrequency ablation.

Recent studies show that after radiofrequency (RF) ablation, fibrosis occurs at the ablation boundary, hindering anticancer drug transport from a locally implanted polymer depot to the ablation margin, where tumors recur. The purpose of this study is to investigate strategies that can effectively deliver dexamethasone (DEX), an anti-inflammatory agent, to prevent fibrosis. Polymer millirods consisting of poly(D,L-lactide-co-glycolide) (PLGA) were loaded with either DEX complexed with hydroxypropyl beta-cyclodextrin (HPbeta-CD), or an NaCl and DEX mixture. In vitro release studies show that DEX complexed with HPbeta-CD released 95% of the drug after 4 days, compared to 14% from millirods containing NaCl and DEX. Rat livers underwent RF ablation and received either DEX-HPbeta-CD-loaded millirods, PLGA millirods with an intraperitoneal (i.p.) DEX injection, or control PLGA millirods alone. After 8 days in vivo, heightened inflammation and the appearance of a well-defined fibrous capsule can be observed in both the control experiments and those receiving a DEX injection (0.29 +/- 0.08 and 0.26 +/- 0.07 mm in thickness, respectively), with minimal inflammation and fibrosis present in livers receiving DEX millirods (0.04 +/- 0.01 mm). Results from this study show that local release of DEX prevents fibrosis more effectively than a systemic i.p. injection.

Combined tumor therapy by using radiofrequency ablation and 5-FU-laden polymer implants: evaluation in rats and rabbits.

PURPOSE: To evaluate the use of 5-fluorouracil (5-FU)-laden polymer implants as an adjunct to radiofrequency (RF) ablation for tumor treatment. MATERIALS AND METHODS: All animal studies were performed in compliance with the Case Western Reserve University Institutional Animal Care and Use Committee guidelines. Three studies were performed to investigate (a) in vitro dissolution of 5-FU-laden polymer implants in saline and bovine serum, (b) tissue distribution of 5-FU and its metabolite, 5-fluorouridine (5-FUrd), in the ablated liver tissue of rats (n = 4), and (c) efficacy of combined approach (n = 4) compared with that of ablation alone (n = 6) for VX2 liver tumor model in rabbits. Characterization of 5-FU release in vitro and distribution of 5-FU in rat liver tissue were analyzed by using high performance liquid chromatography; in vivo efficacy was assessed by using computed tomography and pathologic examination. RESULTS: Results of the in vitro dissolution study showed that a 75% release of 5-FU occurred in 2 days when exposed to bovine serum and in 9 days when exposed to phosphate-buffered saline. In the ablated rat liver, the 5-FU level was higher at the center and lower at the periphery of the tissue both at 24 hours (41.0 mg per kilogram tissue vs 15.0 mg per kilogram tissue, respectively) and at 48 hours (8.0 mg per kilogram tissue vs 2.0 mg per kilogram tissue, respectively). The 5-FUrd concentration was twofold higher peripherally than centrally and was higher at 48 hours than at 24 hours. In rabbits, local delivery of 5-FU immediately after RF ablation provided a significant (P < .05) reduction in tumor size compared with ablation alone (1.80 cm3 +/- 0.28 [standard error] vs 3.53 cm3 +/- 0.52, respectively; P = .034) and a more than 20-fold reduction in tumor size compared with the control (1.80 cm3 +/- 0.28 vs 41.95 cm3 +/- 11.58, respectively; P = .018). CONCLUSION: Combined treatment by using 5-FU polymer implants and RF ablation shows uniform sustained release of 5-FU for 48 hours at least 8 mm from the edge of the ablation zone and appears to be successful at controlling the growth of an experimental tumor in rabbits appreciably better than does ablation alone.

Quantitative computed tomography analysis of local chemotherapy in liver tissue after radiofrequency ablation.

RATIONALE AND OBJECTIVES: Computed tomography (CT) was used to noninvasively monitor local drug pharmacokinetics from polymer implants in rat livers before and following radiofrequency ablation. MATERIALS AND METHODS: Polymer matrixes containing carboplatin (a platinum-containing chemotherapeutic agent) were implanted into rat livers either immediately after radiofrequency ablation (n = 15) or without prior treatment (n = 15). The animals were divided into five subgroups (n = 3 per group) and subjected to a terminal CT scan at 6, 24, 48, 96, or 144 hours. Carboplatin concentration in tissue and within the implant matrix was correlated with CT intensity, and standard curves were produced for each environment. This correlation was used to evaluate the differences in drug transport properties between normal and ablated rat livers. A quantitative image analysis method was developed and used to evaluate the release rate and tissue distribution of carboplatin in normal and ablated liver tissue. The CT data were validated by previously reported atomic absorption spectroscopy measurement of implant and tissue drug levels. RESULTS: Correlation of carboplatin concentration and Hounsfield units results in a linear relationship with correlation coefficients (slopes) of 15 and 4 Hounsfield units/(mg/mL), for carboplatin in tissue and polymer, respectively. Noninvasive monitoring of local pharmacokinetics in normal and ablated tissues indicates that ablation before local carboplatin delivery increases the retention of carboplatin within the polymer matrix and drastically increases the drug retention in the ablated tissue volume (over 3-fold difference) resulting in a higher average dose to the surrounding tissue. At 1.6 mm from the implant boundary, carboplatin concentration is significantly higher in ablated tissue at 48, 96, and 144 hours (P <.05), and reaches 4.7 mg/mL in ablated tissue at 48 hours. In comparison, the concentration in normal liver at 1.6 mm reaches only 0.7 mg/mL at the same time point. The drug penetrates 3.1 mm in ablated liver compared with 2.3 mm in normal liver also at 48 hours. After 144 hours, the drug is still detected at 3.1 mm in ablated liver but not in normal liver. The differences are significant (P <.05) at both 48 and 144 hours. Correlation with chemical analysis suggests that CT data accurately predicts the drug pharmacokinetics in both ablated and normal livers. CONCLUSION: This work shows that X-ray CT imaging is a useful and promising technique for in vivo monitoring of the release kinetics of locally delivered radiopaque agents.

A feasibility study of high intensity focused ultrasound for liver biopsy hemostasis.

This study was conducted to demonstrate the feasibility of high intensity focused ultrasound (HIFU) application to control post-liver-biopsy hemorrhage. Anesthetized Yorkshire pigs (n = 3; mean weight = 23.0 kg) were used and the liver organ was exposed surgically by an open laparotomy. Core biopsies were performed on the hepatic parenchyma with 14-gauge (n = 41) and 18-gauge (n = 33) core biopsy needles. The focus of HIFU (4.23 MHz) field was applied for 15 to 45 s to the needle entry site in the liver immediately after needle retraction. Blood loss from a biopsy site was determined using surgical sponges as absorbent applied at the site. Mean blood loss for control sites was 6.16 g (14-gauge, n = 20) and 1.22 g (18-gauge, n = 10). Virtually no blood loss was measured for biopsies after HIFU application (n = 44) for using needles of both sizes. Our results indicate that intraoperative HIFU application could successfully induce hemostasis after liver biopsy in a porcine model.

Noninvasive monitoring of local drug release using X-ray computed tomography: optimization and in vitro/in vivo validation.

In vivo release profiles of drug-loaded biodegradable implants were noninvasively monitored and characterized using X-ray computed tomography (CT). The imaging method was adapted and optimized to quantitatively examine the release of an active agent from a model cylindrical PLGA device (the millirod) into rabbit livers over 48 h. Iohexol, a CT contrast agent, served as a model drug; optimization of CT acquisition parameters yielded a sensitivity of 0.21 mg/mL (or 95 microg iodine/mL) for this agent. In vitro validation of the method was carried out by tracking release of iohexol in gelatin gel phantoms. In vivo release in rabbit livers was characterized through quantitative analysis of CT images and compared with UV-Vis analysis of the explanted devices at three implantation times. After correction for respiratory motion, CT analysis correlates well with the extracted iohexol data at all time points. The percent error between the actual and experimental image data was below 10%. This study demonstrates the potential of using computed tomography to noninvasively quantify the rate of agent release from controlled delivery devices in vivo.

Noninvasive monitoring of local drug release in a rabbit radiofrequency (RF) ablation model using X-ray computed tomography.

In this study, X-ray computed tomography (CT) was utilized as a noninvasive method to directly examine local drug release kinetics in livers before and following radiofrequency thermal ablation. Iohexol, a CT contrast agent, was used as a drug-mimicking molecule. Release of iohexol in healthy and ablated rabbit livers over 48 h was quantified and correlated with the release profiles from phosphate-buffered saline (PBS) in vitro. The results show that iohexol release in ablated livers is significantly slower than both release in normal livers and in vitro. The time at which 50% of the drug was released (t(1/2)) into ablated liver (20.6+/-5.9 h) was 1.7 times longer than in normal liver (12.1+/-5.4 h) and approximately two times longer than that in PBS (10.1+/-1.2 h). The slower release in ablated livers is a result of severe tissue damage inflicted by thermal ablation, as supported by histological examination. This data suggests that a noninvasive imaging method provides a superior measurement over in vitro release studies in accurately quantifying the local release kinetics of an agent in an altered physiological system in vivo. Because the development of a successful local drug therapy is dependent on the understanding of the agent release kinetics at the implantation site, the noninvasive data may be indispensable in effectively predicting the implant behavior in a physiological system.