Improving contact area between the peritoneum and intraperitoneal therapeutic solutions

Is the Peritoneum a Significant Transport Barrier in Peritoneal Dialysis?

Objectives

The anatomic peritoneum is often considered equivalent to the barrier between the dialysate and the blood, and is also called “the peritoneal membrane.” Our hypothesis is that the normal peritoneum is not a significant barrier to solute or water flow. The goal of this study was to explore the effects of alteration of the anatomic peritoneum on the transperitoneal transport of water and solute.

Design

In vivo transport experiments were carried out in control and treated rats. Treatments consisted of frequent mixing of the peritoneal solution versus no mixing, drying the peritoneum prior to the experiment, or selective removal of the entire peritoneum. Transport experiments were carried out via a plastic chamber affixed to the parietal peritoneum. After measuring solute transport or osmotically induced filtration, the tissue underlying the chamber was collected and stained for histology.

Results

Mixing the chamber solution every 5 minutes versus no mixing over 90 minutes did not result in a significant change in the mass transfer coefficient for mannitol (MTCmannitol, n = 14, p > 0.25). Drying the peritoneum prior to the transport experiment did not significantly alter the MTC of albumin or mannitol ( n = 17, p > 0.6; n = 19, p > 0.1, respectively). Manual drying did not remove or significantly alter the apparent peritoneal coating on the surface of the mesothelium. Removal of the entire peritoneum did not significantly alter the osmotically induced volume flux from the tissue, nor did it change the MTCmannitol( n = 9, p > 0.9; n = 9, p > 0.4, respectively).

Conclusions

Mixing of the solution directly over the tissue, manual drying of the peritoneum, or removal of the entire peritoneum does not result in significant alterations in transport. We conclude that the anatomic peritoneum is relatively unimportant as a physical transport barrier in peritoneal dialysis.

In Vivo Peritoneal Surface Area Measurement in Rats by Micro-Computed Tomography (μCT)

Peritoneal dialysis (PD) uses the dynamic dialysis properties of the peritoneal membrane. The fraction of the anatomic peritoneal surface area (PSA) recruited is of importance for maximizing exchanges and is potentially impacted by parameters such as fill volume.

We describe an in vivo assessment of the contact surface area by micro-computed tomography (μCT) using an iodinated contrast medium added to the PD fluid, a contrast agent presumed without surfactant property. In the isotropic volume (reconstructed voxel size 186 μm x 186 μm x 186 μm), the iodinated PD fluid is automatically selected, thanks to its contrast difference with soft tissues, and its surface area is computed. The method was first tested on phantoms showing the ability to select the PD fluid volume and to measure its surface area. In vivo experiments in rat consisted of μCT acquisition of rat abdomen directly after intraperitoneal administration (10 mL/100 g rat body weight) of a dialysis fluid containing 10% by volume iodinated contrast agent. Fluorescein isothiocyanate albumin was used as dilution marker.

We found a strong linear relationship ( R2= 0.98) between recruited PSA (cm2) and rat weight (g) in the range of 235 to 435 g: recruited PSA = (1.61 weight + 40.5) cm2. Applying μCT with a fill volume of 10 mL/100 g rat body weight, the in vivo measured PSA was in the order of magnitude of the ex vivo anatomic PSA as determined by Kuzlan's formula, considered in most instances as the maximal surface area that can be recruited by PD fluid.

This new methodology was the first to give an in vivo high-resolution isotropic three-dimensional (3-D) determination of the PSA in contact with dialysate. Its sensitivity allows us to take into account the recruitment of fine 3-D structures of the PSA membrane that were not accessible to previous 2-D-based imaging methodologies. Its in vivo application also integrates the physiological natural tensile stress of tissues.

Physiological Properties of the Peritoneum in an Adult Peritoneal Dialysis Population over a Three-Year Period

Objectives

To describe the physiological properties of the peritoneal membrane in adult patients treated with peritoneal dialysis (PD) and to analyze the effects of patient characteristics and time.

Design

Observational study.

Setting

Department of Nephrology at the Sahlgrenska University Hospital.

Method

Peritoneal function was analyzed by the Personal Dialysis Capacity (PDC) test, based on the three-pore theory of capillary transport. The functional PDC variables are absorption, large-pore flow, and the area parameter (A0/Δx), which determines the diffusion of small solutes. The ultra-filtration (UF) coefficient is determined mainly by A0/Δx.

Patients

All patients ( n = 280) who had at least one PDC test done between September 1990 and August 1999.

Results

In 249 patients examined soon after start of PD, area was 19000 (SD 7100) cm2/cm/1.73 m2, large-pore flow 0.112 (SD 0.052) mL/min/1.73 m2, and the UF coefficient 0.071 (SD 0.032) mL/minute/mmHg/1.73 m2. Absorption was 1.54 (SD +2.64, –0.97) mL/min/1.73 m2. Large-pore flow was greater in patients with severe comorbidity than in patients with fewer comorbid conditions. Elderly patients had a lower UF coefficient than did younger patients ( p < 0.05). Repeated PDC tests were performed in 208 patients during a mean observation time of 18.4 months. There was a slight increase in the slope of the area-versus-time curve of 54 cm2/cm/1.73 m2 per month (approximately 10% after 3 years, p < 0.01); all other parameters remained constant.

Conclusion

Patient characteristics have an impact on peritoneal performance already at the start of dialysis. Peritoneal function can remain essentially stable during medium long-term PD.

Vasoactive Components of Dialysis Solution

Background

Conventional peritoneal dialysis (PD) solutions elicit vasodilation, which is implicated in the variable rate of solute transport during the dwell. The components causing such vasoactivity are still controversial. This study was conducted to define the vasoactive components of conventional and new PD solutions.

Methods

Three visceral peritoneal microvascular levels were visualized by intravital video microscopy of the terminal ileum of anesthetized rats. Anesthesia-free decerebrate conscious rats served as control. Microvascular diameter and blood flow by Doppler measurements were conducted after topical peritoneal exposure to 4 clinical PD solutions and 6 prepared solutions designed to isolate potential vasoactive components of the PD solution.

Results

All clinically available PD solutions produced a rapid and generalized vasodilation at all intestinal microvascular levels, regardless of the osmotic solute. The pattern and magnitude of this dilation was not affected by anesthesia but was determined by arteriolar size, the osmotic solute, and the solution's buffer anion system. The greatest dilation occurred in the small precapillary arterioles and was elicited by conventional PD solution and heat re-sterilized solution containing low glucose degradation products (GDPs). Hypertonic mannitol solutions produced a dilation that was approximately 50% less than the dilation obtained with glucose solutions with identical osmolarity and buffer. Increasing a solution's osmolarity did not produce a parallel increase in the magnitude of dilation, suggesting a nonlinear relationship between the two variables. Lactate dissolved in an isotonic solution was completely non-vasoactive unless the solution's H+concentration was increased. At low pH, isotonic lactate produced a rapid but transient vasodilation. This vascular reactivity was similar in magnitude and pattern to that obtained with the isotonic 7.5% icodextrin solution (Extraneal; Baxter Healthcare, Deerfield, Illinois, USA).

Conclusions

( 1 ) Hyperosmolarity is the major vasoactive component of PD solution. ( 2 ) Hyperosmolarity and active intracellular glucose uptake account together for approximately 75% of PD solution-induced dilation, whereas GDPs contribute to approximately 25%. ( 3 ) Lactate is vasoactive only at low pH (high [H+]). ( 4 ) The magnitude of PD solution-mediated vasodilation is partially dependent on the nature of the osmotic solute, the GDP contents, and the [H+], which determine the vasoactivity of the lactate-buffer anion system. Studies are required to define the molecular mechanisms of PD-induced vasodilation and to determine the vasoactive properties of these solutions after chronic infusion.

Pulmonary arterial hypertension induced by a novel method: Twice-intraperitoneal injection of monocrotaline

Pulmonary arterial hypertension (PAH) in humans manifests as a chronic process. However, PAH induced by high-dose monocrotaline (MCT) in animals occurs as a subacute process. To establish a chronic PAH model, rats were randomly divided into three groups, control (ctrl), single injection (SI), and twice injection (TI) groups. Rats in the SI group received a single intraperitoneal injection of 40 mg/kg MCT on day 0. Rats in the TI group received twice injections of 20 mg/kg MCT on days 0 and 7. Survival percentage, characteristic changes of pulmonary arterial variables, and right ventricular features were evaluated. Thirty-five days after the first MCT injection, survival percentage in TI group was higher than that in the SI group. The mean pulmonary arterial pressure (mPAP), right ventricular hypertrophy index (RVHI), pulmonary vascular remodeling, serum tumor necrosis factor α (TNFα), and interleukin-6 (IL-6) were higher either in SI or in TI 28 and 35 days after the first MCT injection. The rats in the SI and TI groups exhibited higher right ventricle end diastolic diameter (RVEDD) and lower adjusted pulmonary artery acceleration time (PAAT/HR), tricuspid annular plane systolic excursion (TAPSE), cardiac output (CO) and right ventricle fractional shortening (RVFS) when compared with controls. However, mPAP, RVHI, TAPSE, PAAT/HR, CO, TNFα, and IL-6 were lower and RVEDD were higher in the TI group than in the SI group. Pulmonary macrophage infiltration and right ventricle (RV) fibrosis were lower in TI than SI groups. The cardiomyocyte cross-sectional area and the beta myosin heavy chain (MYH7) mRNA level of RV were lower in TI than SI, whereas alpha myosin heavy chain (MYH6) was increased. These results show that two intraperitoneal injections of 20 mg/kg MCT with seven days interval could induce a model similar to chronic PAH with increased survival percentage in rats. Impact statement We demonstrated previously that a single intraperitoneal injection of 40 mg/kg MCT produced a subacute, not chronic, PAH model in rats, and the short survival periods of these rats did not represent adequately the chronic PAH seen in humans. To overcome this limitation, in this study, the single dose of 40 mg/kg MCT was divided into twice injections of 20 mg/kg with an interval of seven days. This modified administration of MCT produced an animal model much more similar to chronic PAH with prolonged survival and characteristic changes of structures and function in pulmonary arteries and right ventricles.

Intraoperative Incident Dark Field Imaging of the Human Peritoneal Microcirculation

BACKGROUND/AIMS

This study describes the peritoneal microcirculation, compares quantitative parameters and angioarchitecture to the standard of sublingual microcirculatory assessment, and determines the practical feasibility of this method.

METHODS

Incident dark field imaging was performed of the peritoneum and sublingually to determine angioarchitecture, total and perfused vessel density (TVD and PVD), the proportion of perfused vessels (PPV), the microvascular flow index (MFI) and image acquisition time.

RESULTS

Peritoneal angioarchitecture was characterized by a quadrangular network of longitudinally oriented capillaries, often flanked by fat cells. Differences between peritoneal and sublingual microcirculation were observed with regard to TVD (peritoneum 12 mm/mm2 [95% CI 10-14] vs. sublingual 23 mm/mm2 [95% CI 21-25]; p < 0.0001), PVD (peritoneum 11 mm/mm2 [95% CI 9-13] vs. sublingual 23 mm/mm2 [95% CI 21-25]; p < 0.0001), PPV (peritoneum 88% [95% CI 79-97] vs. sublingual 99% [95% CI 99-100]; p = 0.014), and MFI (peritoneum 3 [IQR 2.3-3.0] vs. sublingual 3 [IQR 3.0-3.0]; p = 0.012). There was no difference in image acquisition time (peritoneum 2: 34 min [95% CI 1: 49-3: 19] vs. sublingual 2: 38 [95% CI 1: 37-3: 32]; p = 0.916).

CONCLUSION

The peritoneal microcirculation was characterized by a low capillary density and a distinctive angioarchitecture. The possibility of peri-toneal microcirculatory assessment offers promise for the study of peritoneal (patho-)physiology and (monitoring or detection of) associated diseases.

Mouse model of foreign body reaction that alters the submesothelium and transperitoneal transport

To address the hypothesis that sterile intraperitoneal (ip) catheters alone promote a progressive foreign body reaction (FBR), silicone catheters were surgically implanted in C57BL mice. Controls (CON) underwent sham operations. After 1-5 wk (E1-E5 for catheter-bearing mice), catheters were recovered, and the adherent cell layer (ACL) was separated and cultured to demonstrate sterility. Transperitoneal transport experiments were performed to determine the mass transfer coefficients of mannitol (MTCM) and albumin (MTCA) and the osmotic filtration flux (Josm). After euthanasia, tissue samples were analyzed for submesothelial thickness, angiogenesis, and cytokine immunohistochemistry (IHC). Progressive increases with time were observed in submesothelial thickness (μm: CON, 18.8±12.3; E1, 46.1±20.0; E2, 72.0±17.9; E4, 97.3±20.0; E5, 131.7±10.3; P<0.003), angiogenesis (no. of vessels/mm of peritoneum: CON, 10.7±9.4; E1, 15.4±15.6; E2, 27.0±14.0; E4, 39.8±15.7; E5, 90.1±8.1; P<0.0003), MTCA (6.5±1.5×10(-5) cm/min, mean CON; 18.0±1.1×10(-5) cm/min, mean E1-E5, P<0.0001), Josm (0.0013±0.0001 cm/min, mean CON; 0.0017±0.0001 cm/min, mean E1-E5, P<0.01). No significant differences were found for MTCM. IHC demonstrated strong staining for all treated animals and correlated with the ACL. This mouse model demonstrates that ip silicone catheters result in progressive FBR, altering the submesothelial anatomy and transperitoneal transport, and will form the basis for mechanistic studies in genetically-altered animals.

Peritoneal membrane recruitment in rats: a micro-computerized tomography (muCT) study

The peritoneal contact surface area (PCSA), which represents the area parameter in the mass transfer area coefficient (MTAC), is a crucial marker in the evaluation of peritoneal dialysis effectiveness. However, the capacity to recruit a larger PCSA has only been rarely demonstrated in vivo and, in most cases, changes in MTAC are interpreted as permeability changes and not as surface area variations. Here, we report the use of micro-computerized tomography (muCT) for the measurement of PCSA changes to various fill volumes. Using this three-dimensional imaging method, PCSA was measured in vivo in 26 healthy Wistar rats receiving intraperitoneally increasing fill volumes of peritoneal dialysis solutions: 5 mL (group 1, n = 8), 10 mL (group 2, n = 8) and 15 mL (group 3, n = 10) per 100 g of body weight. A non-ionic iodinated contrast agent was added to the dialysis solution in order to distinguish the intraperitoneal dialysis solutions from soft tissues. The normalized PCSA/weight ratio (cm(2)/g) increased with fill volume: 1.12 +/- 0.10 cm(2)/g (range 0.98-1.25) in group 1; 1.74 +/- 0.08 cm(2)/g (range 1.64-1.87) in group 2; 2.13 +/- 0.09 cm(2)/g(range 1.90-2.30) in group 3. With this muCT method, PCSA recruited in vivo with a 10 mL/100 g fill volume was in the range 94-107%) of ex vivo total peritoneal surface area (evPSA), as calculated with the Kuzlan's formula. With a 15 mL/100 g fill volume, the in vivo-measured PCSA, the exchange surface area, surpassed the evPSA (range 113-139%).

Systematic review of cytoreductive surgery and heated intraoperative intraperitoneal chemotherapy for treatment of peritoneal carcinomatosis in primary and recurrent ovarian cancer

The aim of this systematic review is to critically evaluate cytoreductive surgery combined with heated intraoperative intraperitoneal chemotherapy in the treatment of ovarian cancer. A systematic review of all manuscripts published in the English literature that met predetermined inclusion criteria was carried out. Data concerning cytoreductive surgery, method and agents for administration of heated intraoperative intraperitoneal chemotherapy, morbidity, mortality, hospital stay and survival were extracted, critically reviewed and tabulated. Fourteen studies were analyzed. A wide variety of drug doses, methods of intraperitoneal chemotherapy administration and volume of chemotherapy solution were used. Seven studies showed that patients with complete cytoreduction had the greatest benefit. The median overall survival for primary and recurrent disease ranged from 22 to 54 months and the median disease-free survival from 10 to 26 months. The rates of significant morbidity associated with this combined treatment were low, ranging from 5% to 36%. The median mortality was 3% (range 0%-10%). Cytoreductive surgery combined with heated intraoperative intraperitoneal chemotherapy is a treatment option for patients with ovarian cancer that is worthy of further investigation. Selection criteria for patients most likely to benefit need to be defined.

Peritoneal changes after exposure to sterile solutions by catheter

Most current animal models that are used to study effects of long-term peritoneal exposure to dialysis solutions use an indwelling catheter for daily injections. It was hypothesized that the presence of a foreign body in the peritoneal cavity (PC) might alter the inflammatory response to the solutions and that the response would depend on exposure duration. For addressing these, long-term injections were carried out for 2 to 8 wk in 90 Sprague-Dawley rats: 40 via a subcutaneous port connected to a silicone catheter tunneled to the PC, 40 via direct needle injection, and 10 noninjected, age-control rats. Daily volumes were 30 to 40 ml of filter-sterilized, bicarbonate-buffered solutions that contained 4% dextrose. After 2, 4, 6, and 8 wk, anesthetized rats underwent transport experiments with a chamber affixed to the abdominal wall to determine mass transfer coefficients of mannitol (MTC(mannitol)) and albumin (MTC(BSA)), osmotic filtration flux (J(osm)), and hydrostatic pressure-driven flux. After the rats were killed, tissues were collected for measurement of peritoneal thickness, vascular density, and immunohistochemical staining. ANOVA demonstrated significant (P < 0.01) differences in thickness, vessel density, MTC(mannitol), and MTC(BSA) among the groups at the various time intervals and in overall means. Differences among the groups were less pronounced for hydrostatic pressure-driven flux and J(osm). Vessel density, MTC(mannitol), MTC(BSA), and J(osm) were dependent on injection duration (P < 0.01). There were marked differences between the needle injection and catheter injection groups at various intervals in the expression of three cytokines. It is concluded that the histologic and functional response depends on the duration of injection with animals that are exposed for as little as 2 wk demonstrating alterations. These findings confirm the hypothesis that the presence of a PC catheter increases inflammatory response to sterile solutions as evidenced by the structural and functional changes in the peritoneal barrier.

Similitude of transperitoneal permeability in different rodent species

Transgenic mice facilitate mechanistic studies of altered peritoneal transport, but the majority of transport studies have been carried out in rats. We hypothesized that mouse transport parameters, normalized to the peritoneal contact area, would be similar to those of the rat. To address this, we affixed small (∼10-mm diameter) plastic chambers to the serosa of the abdominal wall of anesthetized CD1 and C57BL mice. The chamber constrained transfer across the area of the chamber base and facilitated mixing, volumetric, and concentration measurements vs. time for mannitol, serum albumin, and osmotic and hydrostatic pressure-driven convection. The mass transfer coefficient of mannitol (MTCM) and of serum albumin (MTCBSA), hydrostatic pressure-driven flux ( JP), and osmotic filtration ( Josm) were calculated from the time-dependent volume and concentration data. The units of all parameters (μl·min−1·cm−2) were compared with previously derived parameters from SD rats with a one-way ANOVA. Results indicated small but significant differences in MTCBSA(x102): CD1, 9.72 ± 1.97, n = 6; C57BL, 7.13 ± 1.52, n = 10; rat, 12.5 ± 1.6, n = 17 ( P = 0.03). ANOVAs of all other parameters were not significant and confirmed our hypothesis: MTCM(CD1, 3.20 ± 0.38, n = 7; C57BL, 2.34 ± 0.41, n = 6; rat, 2.72 ± 0.23 n = 19), JP(CD1, 0.77 ± 0.15, n = 10; C57BL, 0.33 ± 0.13, n = 15; rat, 0.51 ± 0.16, n = 9), or Josm(CD1, 0.92 ± 0.35, n = 6; C57BL, 0.49 ± 0.35, n = 6; rat 1.72 ± 0.35, n = 6). We conclude that elimination of the variable peritoneal transfer area normalizes calculated transport characteristics and facilitates comparison between species.

In vivo determination of diffusive transport parameters in a superfused tissue

To address the hypothesis that functional changes in tissue transport can be related to structural alterations, we combined mathematical modeling with in vivo experimentation. The model concept includes interstitial diffusion and removal by a distributed microvasculature. Transport of solute and water across the peritoneum is measured via a plastic chamber affixed to the abdominal wall of anesthetized Sprague-Dawley rats. Solutions containing [14C]mannitol, with or without vasoactive compounds [control (C; n = 10), C + nitroprusside (NP; n = 10), C + norepinephrine (NE; n = 10)], were infused into the chamber, and the volume and tracer concentrations were determined over 60 min to calculate the mass transfer coefficient (MTC) and the water flux. At 60 min, FITC-dextran (500 kDa) was given to mark the perfused vasculature. After euthanasia, the tissue under the chamber was frozen, dried, sliced with a cryomicrotome, and examined with fluorescent microscopy and quantitative autoradiography. The microvessel density (×103/cm2: NE, 50 ± 10; C, 180 ± 7.0; NP, 225 ± 15) resulted in marked differences ( P < 0.05) in water flux (μl·min−1·cm−2: NE, 0.1 ± 0.1; C, 1.6 ± 0.4; NP, 1.0 ± 0.2) and in mannitol MTC (×103cm/min: NE, 0.9 ± 0.3; C, 3.8 ± 0.3; NP, 3.6 ± 0.6). Concentration profiles and calculated capillary permeability and tissue diffusivity were significantly different among the groups. These results demonstrate a direct correlation of mass transfer, diffusion, capillary permeability, and water flux with peritoneal vascular density and validate a method by which mechanistic changes in transport may be measured.

Distributed model of peritoneal fluid absorption

The process of water reabsorption from the peritoneal cavity into the surrounding tissue substantially decreases the net ultrafiltration in patients on peritoneal dialysis. The goal of this study was to propose a mathematical model based on data from clinical studies and animal experiments to describe the changes in absorption rate, interstitial hydrostatic pressure, and tissue hydration caused by increased intraperitoneal pressure after the initiation of peritoneal dialysis. The model describes water transport through a deformable, porous tissue after infusion of isotonic solution into the peritoneal cavity. Blood capillary and lymphatic vessels are assumed to be uniformly distributed within the tissue. Starling's law is applied for a description of fluid transport through the capillary wall, and the transport within the interstitium is modeled by Darcy's law. Transport parameters such as interstitial fluid volume ratio, tissue hydraulic conductance, and lymphatic absorption in the tissue are dependent on local interstitial pressure. Numerical simulations show the strong dependence of fluid absorption and tissue hydration on the values of intraperitoneal pressure. Our results predict that in the steady state only ∼20–40% of the fluid that flows into the tissue from the peritoneal cavity is absorbed by the lymphatics situated in the tissue, whereas the larger (60–80%) part of the fluid is absorbed by the blood capillaries.

Disparity in osmolarity-induced vascular reactivity

Conventional peritoneal dialysis solutions (PDS) are vasoactive. This study was conducted to identify vasoactive components of PDS and to describe quantitatively such vasoactivity. Anesthetized nonheparinized rats were monitored continuously for hemodynamics while the microvasculature of the jejunum was studied with in vivo intravital microscopy. In separate experiments, vascular reactivity of rat endothelium-intact and -denuded aortic rings (2 mm) was studied ex vivo in a standard tissue bath. In both studies, suffusion of the vessels was performed with filter-sterilized isotonic and hypertonic solutions that contained glucose or mannitol as osmotic agents. PDS served as a control (Delflex 2.25%). Hypertonic glucose and mannitol solutions produced a significant vascular reactivity in aortic rings and instantaneous and sustained vascular relaxation at all levels of the intestinal microvasculature. Similarly, lactate that was dissolved in a low-pH isotonic physiologic salt solution produced significant force generation in aortic rings. Whereas isotonic glucose and mannitol solutions had no vasoactivity in aortic rings, isotonic glucose produced a selective, insidious, and time-dependent vasodilation in the intestinal premucosal arterioles (18 +/- 0.2% of baseline), which was not observed in the larger inflow arterioles (100 mum). This isotonic glucose-mediated vascular relaxation can be attenuated by approximately 50% with combined adenosine A(2a) and A(2b) receptor antagonists and completely abolished by adenosine A(1) receptor inhibition. By using two different experimental techniques, this study demonstrates that hyperosmolality and lactate are the major vasoactive components of clinical peritoneal dialysis solutions. The pattern and the magnitude of such reactivity are dependent on vessel size and on the solutes' metabolic activity. Low pH of conventional PDS is not a vasoactive component by itself but renders lactate vasoactive. Energy-dependent transport of glucose into cells mediates vasodilation of small visceral arterioles by an adenosine receptor-mediated mechanism and constitutes a significant fraction of PDS-mediated vascular reactivity in the visceral microvasculature.

Resistance of tumor interstitial pressure to the penetration of intraperitoneally delivered antibodies into metastatic ovarian tumors

PURPOSE

Despite evidence that regional chemotherapy improves the treatment of metastatic peritoneal ovarian carcinoma, monoclonal antibodies have not shown significant success in i.p. delivery. The present study was designed to address the hypothesis that convective penetration of macromolecular antineoplastic agents depends on a positive pressure difference between the i.p. therapeutic solution and the tumor.

EXPERIMENTAL DESIGN

Nude rats with human ovarian xenografts implanted in the abdominal wall were used in experiments to facilitate in vivo measurement of tumor pressure and the treatment of the tumor with i.p. solutions at high pressures. Penetration of (125)I-labeled trastuzumab was measured with quantitative autoradiography.

RESULTS

Tumor pressure profiles showed peak pressures of 32 mm Hg with mean pressures (+/- SD, mm Hg) in 12 SKOV3 tumors of 9.7 +/- 8.3 and in 15 OVCAR3 tumors of 12.5 +/- 7.0. I.p. therapeutic dwells at 6 to 8 mm Hg (maximum feasible pressure) showed significantly less penetration of trastuzumab than in adjacent normal muscle. To establish a driving force for convection into the tumor, various maneuvers were attempted to reduce tumor pressure, including treatment with taxanes or prostaglandin E(1), elimination of tumor circulation, and removal of the tumor capsule. Tumor decapsulation decreased the pressure to zero but did not enhance the penetration of antibody. Binding to specific trastuzumab receptors on each tumor was shown to be not a significant barrier to antibody penetration.

CONCLUSIONS

The results only partially support our hypothesis and imply that the microenvironment of the tumor is in itself a major barrier to delivery of charged macromolecules.

Correlating structure with solute and water transport in a chronic model of peritoneal inflammation

To study the process of chronic peritoneal inflammation from sterile solutions, we established an animal model to link structural changes with solute and water transport. Filtered solutions containing 4% N-acetylglucosamine (NAG) or 4% glucose (G) were injected intraperitoneally daily in 200- to 300-g rats and compared with controls (C). After 2 mo, each animal underwent transport studies using a chamber affixed to the parietal peritoneum to determine small-solute and protein mass transfer, osmotic filtration, and hydraulic flow. After euthanasia, parietal tissues were sampled for histological analysis, which demonstrated significant differences in peritoneal thickness (microm; C, 42.6 +/- 7.5; G, 80.4 +/- 22.3; NAG, 450 +/- 104; P < 0.05). Staining for VEGF correlated with CD-31 vessel counts (no./mm2: C, 53.1 +/- 16.1; G, 166 +/- 32; NAG, 183 +/- 32; P < 0.05). Tissue analysis showed treatment effects on tissue hyaluronan (micro/g: C, 962 +/- 73; G, 1,169 +/- 69; NAG, 1,428 +/- 69; P < 0.05) and collagen (microg/g: C, 56.9 +/- 12.0; G, 107 +/- 12; NAG, 97.6 +/- 11.4; P < 0.05) but not sulfated glycosaminoglycan. Transport experiments revealed no significant differences in mannitol transfer or osmotic flow. Changes were seen in hydrostatic pressure-driven flux (microl x min(-1) x cm(-2): C, 0.676 +/- 0.133; G, 0.317 +/- 0.124; NAG, 0.284 +/- 0.117; P < 0.05) and albumin transfer (microl x min(-1) x cm(-2): C, 0.331 +/- 0.028; G, 0.286 +/- 0.026; NAG, 0.229 +/- 0.025; P < 0.04). We conclude that alteration of the interstitial matrix correlates with diminished hydraulic conductivity and macromolecular transport.

Transdiaphragmatic transport of tracer albumin from peritoneal to pleural liquid measured in rats

In conscious Wistar-Kyoto rats, we studied the uptake of radioactive tracer (125)I-albumin into the pleural space and circulation after intraperitoneal (IP) injections with 1 or 5 ml of Ringer solution (3 g/dl albumin). Postmortem, we sampled pleural liquid, peritoneal liquid, and blood plasma 2-48 h after IP injection and measured their radioactivity and protein concentration. Tracer concentration was greater in pleural liquid than in plasma approximately 3 h after injection with both IP injection volumes. This behavior indicated transport of tracer through the diaphragm into the pleural space. A dynamic analysis of the tracer uptake with 5-ml IP injections showed that at least 50% of the total pleural flow was via the diaphragm. A similar estimate was derived from an analysis of total protein concentrations. Both estimates were based on restricted pleural capillary filtration and unrestricted transdiaphragmatic transport. The 5-ml IP injections did not change plasma protein concentration but increased pleural and peritoneal protein concentrations from control values by 22 and 30%, respectively. These changes were consistent with a small (approximately 8%) increase in capillary filtration and a small (approximately 20%) reduction in transdiaphragmatic flow from control values, consistent with the small (3%) decrease in hydration measured in diaphragm muscle. Thus the pleural uptake of tracer via the diaphragm with the IP injections occurred by the near-normal transport of liquid and protein.

Peritoneal Dialysis: A Viable Renal Replacement Therapy Option

The number of patients with end-stage renal disease requiring dialysis has increased markedly over the last decade and continues to grow at an alarming rate in the United States. Of the currently available dialysis options for end-stage renal disease (hemodialysis and peritoneal dialysis), peritoneal dialysis (PD) is underutilized in the United States for nonmedical reasons. In fact, PD is the less expensive dialysis modality and may provide a survival advantage over hemodialysis in first 2 to 4 years of treatment, but that advantage is not as robust with increasing age and with the presence of diabetes. Moreover, the initial survival advantage is lost in long-term PD, mainly owing to changes in the peritoneal membrane from the use of conventional bio-incompatible PD solutions. Current data suggest that not many patients continue on PD beyond 10 years. The recent development of a more biocompatible PD solution should help to preserve membrane function, promote ultrafiltration, improve nutritional status, and, it is hoped, prolong the survival advantage of PD. Identification of molecular mechanisms involved in cellular responses leading to peritoneal fibrosis and angiogenesis evokes new therapeutic strategies that might protect the peritoneal membrane against the consequences of long-term PD.

The transport barrier in intraperitoneal therapy

The peritoneal cavity is important in clinical medicine because of its use as a portal of entry for drugs utilized in regional chemotherapy and as a means of dialysis for anephric patients. The barrier between the therapeutic solution in the cavity and the plasma does not correspond to the classic semipermeable membrane but instead is a complex structure of cells, extracellular matrix, and blood microvessels in the surrounding tissue. New research on the nature of the capillary barrier and on the orderly array of extracellular matrix molecules has provided insights into the physiological basis of osmosis and the alterations in transport that result from infusion of large volumes of fluid. The anatomic peritoneum is highly permeable to water, small solutes, and proteins and therefore is not a physical barrier. However, the cells of the mesothelium play an essential role in the immune response in the cavity and produce cytokines and chemokines in response to contact with noncompatible solutions. The process of inflammation, which depends on the interaction of mesothelial, interstitial, and endothelial cells, ultimately leads to angiogenesis and fibrosis and the functional alteration of the barrier. New animal models, such as the transgenic mouse, will accelerate the discovery of methods to preserve the functional peritoneal barrier.

A novel method of peritoneal resuscitation improves organ perfusion after hemorrhagic shock

BACKGROUND

After resuscitation from hemorrhagic shock, intestinal microvessels constrict leading to impairment of blood flow. This occurs despite restoration and maintenance of central hemodynamics. Our recent studies have demonstrated that topical and continuous exposure of the gut microvasculature to a clinical solution (Delflex; Fresenius Medical Care), as a technique of direct peritoneal resuscitation (DPR), reverses the postresuscitation vasoconstriction and hypoperfusion to a sustained dilation and hyperperfusion. We hypothesize that initiation of DPR simultaneously with resuscitation from hemorrhagic shock enhance organ blood flow to all tissues surrounding the peritoneal cavity as well as distant organs.

METHODS

Male Sprague-Dawley rats were anesthetized, intubated and cannulated for monitoring of hemodynamics and for withdrawal of blood. Rats were hemorrhaged to 50% of mean blood pressure for 60 minutes prior to resuscitation with shed blood plus 2 volumes of saline. Animals were randomized for intraperitoneal therapy with 30 mL saline (group 1, n = 9), or Delflex (group 2, n = 9). Whole organ blood flow was measured by colorimetric microsphere technique with phantom organ at baseline, after completion of resuscitation, and at 120 minutes postresuscitation. Replenishment of the dwelling intraperitoneal saline or Delflex was performed in (group 3, n = 8), and (group 4, n = 8), respectively at 90 minutes postresuscitation, and a single whole organ blood flow was performed at 120 minutes postresuscitation.

RESULTS

Direct peritoneal resuscitation caused a significant increase in blood flow to the jejunum (35%), ileum (33%), spleen (48%), and pancreas (57%), whereas a marked increase in blood flow was detected in the lung (111%), psoas major muscle (115%), and diaphragm (132%), as compared with the saline treated animals in group 1. At 120 minutes postresuscitation, organ blood flow returned to the prehemorrhagic shock baseline level in all organs irrespective of peritoneal therapy. Replenishment of the intraperitoneal solution in group 3 and 4, enhanced blood flow to the liver, kidneys, and diaphragm.

CONCLUSIONS

Direct peritoneal resuscitation enhanced blood flow to organs incited in the pathogenesis of multiple organ failure that follows hemorrhagic shock.

Development of a formulation that enhances gene expression and efficacy following intraperitoneal administration in rabbits and mice

We conducted a series of experiments to determine if intraperitoneal (IP) delivery of recombinant adenovirus (rAd)-based therapies is improved through carrier vehicle selection, and compared an icodextrin solution (a high molecular weight dextrin with a prolonged peritoneal cavity residence time) with a standardized phosphate buffered saline (PBS) delivery solution. In vitro, comparative adenovirus particle concentration determination (27 h) and bioactivity assay (24h) indicated equivalent compatibility with icodextrin or PBS. In vivo, rabbits treated IP (100 ml) with rAd-betagal 1 x 10(9) P/ml in icodextrin showed improved transgene expression throughout the peritoneal wall compared to rAd-betagal in PBS. In PC-3 tumor-bearing mice treated IP with 5 x 10(9) P/0.5 ml or 1 x 10(10) P/0.5 ml rAd-betagal, transgene expression was significantly enhanced (p < 0.01) with icodextrin compared to PBS in both tumor specimens and peritoneal wall. In subsequent studies we compared prolongation of survival in intraperitoneal PC-3 and MDAH-2774 human xenograft tumor models in nude mice using rAd-p53 in icodextrin or PBS in multi-dose ranging (1 x 10(8) to 1 x 10(10) P) experiments. The icodextrin formulation alone significantly increased rAd-p53 mediated survival (p < 0.05). In animals, these results show that IP rAd gene therapy can be improved with the use of icodextrin, and suggest that prolonged retention and distribution in the peritoneal cavity is an important factor.

Effect of increased dialysate volume on peritoneal surface area among peritoneal dialysis patients

Large dialysate volumes are often required to increase solute clearance for peritoneal dialysis patients. The resulting increase in solute clearance might be attributable to an increased plasma-to-dialysate concentration gradient and/or to an increased effective peritoneal surface area. One of the factors affecting the latter is the peritoneal surface area in contact with dialysate (PSA-CD). The aim of this study was to estimate the change in PSA-CD after a 50% increase in the instilled dialysate volume for patients undergoing peritoneal dialysis. PSA-CD was estimated by using a method applying stereologic techniques to computed tomographic (CT) scans of the peritoneal space. The peritoneal cavity of 10 peritoneal dialysis patients was filled with a solution containing dialysate, half-isotonic saline solution, and contrast medium. Peritoneal function tests and CT scanning of the abdomen were performed twice for each patient (with an interval of 1 wk), after instillation of a 2- or 3-L solution. Scanning of thin helical CT sections was performed, and 36 random sections of the abdomen were obtained after reconstruction. A grid was superimposed on the sections. The surface area was estimated by using stereologic methods. After instillation of the 2-L solution, the volume of the peritoneal solution at the time of CT scanning was 2.32 +/- 0.05 L. The PSA-CD was 0.57 +/- 0.03 m(2), ranging from 0.41 to 0.76 m(2). The use of the 3-L solution increased the peritoneal volume by 46 +/- 2%. PSA-CD increased by 18 +/- 2.3% to 0.67 +/- 0.04 m(2) (range, 0.49 to 0.84 m(2); P < 0.01). Creatinine mass transfer increased from 112 +/- 10 mg to 142 +/- 11 mg (P < 0.0001). The slope of the change of the plasma-to-dialysate creatinine concentration gradient with time decreased from -2.26 +/- 0.23 x 10(-2) to -1.97 +/- 0.16 x 10(-2) (P = 0.01). K(BD-0) (permeability-surface area product or mass area transfer coefficient at time 0 of the dwell) increased from 10.6 +/- 0.7 to 13.6 +/- 1.2 ml/min (P < 0.02). These data demonstrate that increasing the instilled dialysate volume by 50% for peritoneal dialysis patients results in significant increases in the PSA-CD and K(BD).

Solute Transport Across the Peritoneal Membrane

ABSTRACT. The current understanding of the transport pathways that govern solute removal during peritoneal dialysis is reviewed. Diffusive transport rates across the peritoneal membrane for small solutes are slow. Even though the rate of diffusive solute transport decreases with increasing molecular size, large molecules (e.g., albumin) are nevertheless removed from the patient during routine peritoneal dialysis. Recent work has confirmed a previous suggestion that diffusive solute transport is limited by the small area of the peritoneal membrane that participates in the transport process. This small functional area is due to either poor contact of the peritoneal membrane with dialysis solution bathing the peritoneal cavity or to the limited surface area of capillaries that perfuse peritoneal tissues. Convective solute transport during peritoneal dialysis is proportional to the transperitoneal ultrafiltration rate but is less than that expected, because of low solute sieving by the peritoneal membrane and fluid absorption from the peritoneal cavity. Low solute sieving across the peritoneal membrane was first identified in 1966, a phenomenon that is now attributed to the presence of water-only transport pathways mediated by aquaporin-1. Fluid absorption from the peritoneal cavity occurs at the same time as transperitoneal ultrafiltration, but the pathways by which these two processes occur simultaneously remain speculative. This review proposes a novel hypothesis, whereby fluid absorption occurs in areas of the peritoneal membrane that are governed by different physical forces than those governing transperitoneal ultrafiltration. Further understanding of the pathways for fluid and solute transport during peritoneal dialysis will permit improvements in the adequacy of the dialysis dose and the more efficacious use of peritoneal dialysis to treat patients with end-stage renal disease.

Increasing peritoneal contact area during dialysis improves mass transfer

Previous studies in mice demonstrated that relatively large volumes in the peritoneal cavity made contact with only 40% of the anatomic peritoneum and that this contact area (A(contact)) could be increased with use of a surfactant, dioctyl sodium sulfosuccinate (DSS). To investigate the hypothesis that mass transfer rates during peritoneal dialysis are dependent on the area of peritoneum in contact with the dialysis solution, rats were dialyzed for 2 h with a solution that contained (14)C-mannitol, with or without 0.02% DSS. The mass transfer-area coefficients (MTAC) were determined to be (mean +/- SEM, ml/min): no DSS, 0.163 +/- 0.008; with DSS, 0.247 +/- 0.006 (P < 0.002). DSS also caused an increase in total protein loss over 2 h (mean +/- SEM, mg): no DSS, 83.8 +/- 15.8; DSS, 159.5 +/- 6.3 (P < 0.001). In a separate set of animals, the ratio (R) of A(contact) to anatomic area in each plane was measured as in the previous study R(mean) (mean +/- SEM) and equaled 0.466 +/- 0.075, no DSS; 0.837 +/- 0.074, with DSS. The ratio of MTAC (1.52) and protein loss (1.90) approximate the ratio of R(mean(S)) (1.78). Because MTAC = mass transfer coefficient (MTC) x A(contact), small peritoneal transport chambers were used to determine MTC for (14)C-mannitol and fluorescein isothiocyanate-albumin. MTC(mannitol) did not change significantly with the addition of DSS. MTC(albumin) (cm/min x 10(4), mean +/- SEM) equaled 1.47 +/- 0.45 without DSS and 1.78 +/- 0.52 with DSS (P < 0.04). It was concluded that DSS increases the mass transfer rates of mannitol and protein by increasing A(contact), whereas protein transport is further augmented by an apparent increase in the barrier permeability to protein.