Drug delivery to tumors. A problem requiring microscopic resolution

One factor in the effectiveness of chemotherapy for both primary tumors and their metastases is the delivery of the drug to the cancer cells within the tumor. The uptake of Adriamycin, assayed in 8 cu mm samples from primary tumors, lung metastases and "normal" lung tissue (unaffected by the metastases) in mice, showed wide variations between different tumors, between primary tumors and their metastases and between different metastases. The heterogeneity of uptake was greater in tumors than in normal lung tissues, whose uptake was in the range of the metastases, i.e., higher than in the tumor itself. Studies of Adriamycin uptake within individual tumors showed a wide range of values; this variability was statistically significantly increased as compared with the variation in normal lung tissues. Since the lower levels found in some tumor areas were below the cytotoxic level, those areas may represent "drug-resistant" cells from which tumor recurrence could ensue. In a three-dimensional reconstruction, the areas of lowest uptake were found at both peripheral and internal regions, a finding not in accord with the concentric zonal concentration expected on the basis of considerations of tumor vascularity. It is suggested that the problem of drug delivery to tumors needs further study at the microscopic level and that automated microscopic image analysis and three-dimensional reconstructions of serial sections could greatly extend the macroscopic findings of this study.     

The effect of N-acetylcysteine in combination with vitamin C on the activity of ornithine decarboxylase of lung carcinoma cells--In vitro

Ornithine decarboxylase (ODC) is a marker of lung cancer and is a key enzyme in the synthesis of polyamines, which are necessary for the promotion of the growth of malignant cells. This study assesses the dose-dependent effect of N-acetylcysteine (NAC), a chemopreventive agent, in combination with vitamin C (VC) on the activity of ODC in lung carcinoma cell line, NCI-H82. The cells were subjected to supplementation of NAC and VC both individually and in combination at different dosages for 24 h as well as 48 h. The cells were incubated with radiolabeled L-ornithine (14C) after the supplementation of NAC and VC individually as well as in combination. A microprocedure was carried out to estimate the activity of ODC in cells after 24 and 48 h of incubation. The activity which was found to be elevated in control cells was decreased significantly on drug supplementation in dose-dependent fashion. The content of nucleic acids also exhibited similar result and [3H]-thymidine incorporation was also affected by the supplementation.     

Significant antitumor effect of a synthetic lipid A analogue,DT-5461, on murine syngeneic tumor models

Summary The antitumor effect of a synthetic lipid A analogue, DT-5461, was investigated using syngeneic tumor models in mice. Intravenous injection of DT-5461 into mice transplanted with solid tumors of MethA fibrosarcoma, MH134 hepatoma, MM46 mammary carcinoma, Lewis lung carcinoma (3LL), and colon adenocarcinomas 26 and 38 resulted in significant reductions in the weight of all tumors except Colon 26, with marked hemorrhagic necrosis of tumor tissues. Efficacy was almost equal to that of anEscherichia coli-type synthetic lipid A (compound 506), and also to those of some chemotherapeutics including Adriamycin, mitomycin C, fluorouracil and cisplatin. Furthermore, DT-5461 was more effective than other immunotherapeutics, including picibanil (OK-432) and lentinan. However, its antitumor effects were inferior to those of Adriamycin or OK-432 against the malignant ascites caused by intraperitoneal inoculation with MethA or with MH134 cells; life span was not prolonged by either intraperitoneal or intravenous administration. In addition, although DT-5461 showed direct inhibitory effects on the in vitro growth of MethA or MH134, these were much weaker than those of Adriamycin. These findings clearly indicated that DT-5461 with systemic administration is a highly effective antitumor agent on solid tumors, and suggest that the antitumor effect of DT-5461 with potent necrotizing activity might derive from indirect mechanisms related to the activation of host immune systems and not to the weak direct cytotoxicity.     

Hemodynamics and the vascular endothelial cytoskeleton

Although there is considerable evidence to suggest that hemodynamics play an important role in vascular disease processes, the exact mechanisms are unknown. With this in mind, we have designed a pulsatile perfusion apparatus which reproducibly delivers pulsatile hemodynamics upon freshly excised canine carotid arteries in vitro. Quantifiable simulations included normotension with normal or lowered flow rates (120/80 mmHg, 120 and 40 ml/min), normotension with lowered or elevated transmural pressures (40-170 mmHg), and elevated pulse pressure (120 and 80 mmHg) with normal (150 ml/min) or elevated rates of flow (300 and 270 ml/min). Arterial biomechanical stresses and cellular behaviors were characterized biochemically and morphologically under all these stimulations which continued for 2-24 h. We found that increased pulse pressure alone had little effect on the total amount of radiolabeled [4-14C]cholesterol present within the medial compartment. However, normotension when coupled with altered transmural pressure yielded a three- to fourfold increase. Combinations of increased pulse pressure and flow potentiated cholesterol uptake by a factor of 10 when compared with normotension control values. Simulations that enhanced carotid arterial cholesterol uptake also influenced the endothelial cytoskeletal array of actin. Stress fibers were not present within the carotid endothelial cells of either the sham controls or the normotension and increased pulse pressure (normal flow) simulations. Endothelial cells lining carotids exposed to elevations in flow or those present within vessels perfused as per simulation b above assembled stress fibers (x = 4 and 10 per cell, respectively) within the time course of these studies. When endothelial cells were subjected to hemodynamic conditions that potentiated maximally cholesterol transport, no diffuse or stress fiber staining could be seen, but the cortical array of actin was intact. These results suggest that those biomechanical stresses that alter endothelial permeability and intimal integrity may do so via cytoskeletal actin signaling.     

Aerosolized Pseudomonas elastase and lung fluid balance in anesthetized sheep.

The role of the lung epithelium in lung fluid balance was studied by ventilating anesthetized sheep with an aerosol of 20 mg of elastase from Pseudomonas aeruginosa (Ps. elastase) to increase lung epithelial permeability without affecting lung endothelial permeability or lung vascular pressures. Ps. elastase had no effect on the lung vascular pressures, the alveolar-arterial PO2 gradient (A-aPO2), the flow or protein concentration of the lung lymph, or the postmortem water volume of the lungs. The morphological alveolar flooding score in these sheep was 2.5 times the control level, but this was only marginally significant. Elevation of the left atrial pressure by 20 cmH2O alone increased the postmortem lung water volume but had no effect on A-aPO2, the alveolar flooding score, or the lung epithelial permeability assessed by the clearance of 99mTc-labeled human serum albumin. Addition of aerosolized Ps. elastase to these sheep had no effect on the total lung water volume, but it caused a redistribution of water into the air spaces, as evidenced by significant increases in the alveolar flooding score and A-aPO2 (P less than 0.01). Elevation of the left atrial pressure by 40 cmH2O without elastase caused the same response as elevation of the left atrial pressure by 20 cmH2O with elastase, except the higher pressure caused a greater increase in the total lung water volume. We conclude that alteration of the integrity of the lung epithelium with aerosolized Ps. elastase causes a redistribution of lung water into the alveoli without affecting the total lung water volume.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spontaneous resolution of pulmonary edema caused by short periods of cyclic overinflation.

Mechanical ventilation with high or even moderate peak inspiratory pressure produces pulmonary permeability edema. Besides the level of overinflation, duration may affect both severity and type of edema. We studied the effect of 2 min of 35-mmHg peak pressure mechanical ventilation (HV) on microvascular permeability and deep lung fluid balance in rats. It resulted in increased extravascular lung water (+50%), bloodless dry lung weight (+25%), and albumin uptake in lungs (+450%). The increase in dry lung weight and albumin uptake compared with that of lung water suggested major permeability alterations. Ultrastructural examination showed the presence of numerous endothelial blebs. Epithelial lining fluid (ELF) volume, its potassium and protein concentrations, and cellular composition were assessed by bronchoalveolar lavage. There was an increase in ELF volume (+180%), a decrease in ELF potassium concentration (-50%), and an increase in ELF protein content (+76%). A few blood cells were recovered, suggesting the presence of a few large epithelial breaks. Some animals were allowed to recover for periods less than or equal to 180 min after HV. Extravascular lung water, dry lung weight, and albumin distribution space returned to control levels within 45 min. ELF volume diminished but remained larger than in controls, and ELF protein concentration increased probably because of alveolar fluid resorption. No further hemorrhage was observed. These results indicate that periods of HV as short as 2 min transiently alter microvascular permeability in rats.     

Somatic hybrids of normal and tumor Djzungarian hamster cells. I. Preferential elimination of chromosomes of the normal partner

Normal Djungarian hamster lymphoid cells were fused with SV40 transformed malignant fibroblasts. The resulting 11 hybrid clones were subjected to the chromosome analysis. The karyotype of hybrids proved to be unstable. In some cases the total tetraploid number of chromosomes in hybrids drastically decreased up to the near-diploid level close to that of the malignant parent cells. The G-band chromosome analysis showed that as a rule morphologically unchanged chromosomes were preferentially lost from the hybrid cells, the markers of the malignant partner being retained. On the basis of these data it is assumed than the hybrids between normal and tumour cells of Djungarian hamster preferentially lose the chromosomes of the normal parent cells during cultivation in vitro.     

In vitro cytotoxic drug sensitivity of human normal and malignant lymphocyte-clone-forming cells

Cytotoxic drug sensitivity of normal human lymphocytes and malignant lymphocytes was estimated by a clonogenic method. Malignant T and B lymphocytes were relatively more sensitive than normal T lymphocytes to vincristine and Adriamycin. Since no plateau was observed in the clone survival with associated increasing drug concentration, spontaneous mutants could not be detected. It is suggested that the resistance to "natural product" drugs such as vincristine arises from induced mutations and not from the selection of already existing spontaneous mutants.     

Pulmonary microvascular response to LTB4: effects of perfusate composition

We examined the effects of leukotriene B4 (LTB4) on pulmonary hemodynamics and vascular permeability using isolated perfused guinea pig lungs and cultured monolayers of pulmonary arterial endothelial cells. In lungs perfused with Ringer solution, containing 0.5 g/100 ml albumin (R-alb), LTB4 (4 micrograms) transiently increased pulmonary arterial pressure (Ppa) and capillary pressure (Pcap). Pulmonary edema developed within 70 min after LTB4 injection despite a normal Pcap. The LTB4 metabolite, 20-COOH-LTB4 (4 micrograms), did not induce hemodynamic and lung weight changes. In lungs perfused with autologous blood hematocrit = 12 +/- 1%; protein concentration = 1.5 +/- 0.2 g/100 ml), the increases in Ppa and Pcap were greater, and both pressures remained elevated. The lung weight did not increase in blood-perfused lungs. In lungs perfused with R-alb (1.5 g/100 ml albumin) to match the blood perfusate protein concentration, LTB4 induced similar hemodynamic changes as R-alb (0.5 g/100 ml) perfusate, but the additional albumin prevented the pulmonary edema. LTB4 (10(-11)-10(-6) M) with or without the addition of neutrophils to the monolayer did not increase endothelial 125I-albumin permeability. Therefore LTB4 induces pulmonary edema when the perfusate contains a low albumin concentration, but increasing the albumin concentration or adding blood cells prevents the edema. The edema is not due to increased endothelial permeability to protein and is independent of hemodynamic alterations. Protection at higher protein-concentration may be the result of LTB4 binding to albumin.     

Effect of prolonged renal dysfunction on intravascular and extravascular pulmonary fluid volumes during left atrial hypertension

To examine the development of pulmonary edema during experimental renal dysfunction, left atrial pressure was altered in 14 mongrel dogs divided into two groups. Group 1 was composed of seven control animals, and Group 2 was composed of seven animals with surgically induced renal failure (1 week of bilateral ureteral ligation). Data were obtained at two levels of matched transmural pulmonary vascular pressure (defined as mean left atrial pressure less serum protein osmotic pressure). In the animals with renal dysfunction, extravascular lung water (EVLW) (thermal-green dye technique) was higher at moderately (-1 to -2 mm Hg) and severely elevated (11 to 12 mm Hg) vascular driving pressures (11.5 +/- 1.2 cc/kg vs 10.6 +/- 0.8 cc/kg and 14.8 +/- 1.3 cc/kg vs 13.0 +/- 1.9 cc/kg, respectively, both P less than 0.05 vs control). Because protein osmotic pressure was lower in the renal failure group (15.0 +/- 1.8 mm Hg vs 18.4 +/- 1.4 mm Hg, P less than 0.05), greater accumulations of extravascular lung water occurred at lower levels of left atrial pressure (14.2 +/- 1.4 mm Hg vs 17.1 +/- 1.2 mm Hg, P less than 0.05; 26.8 +/- 2.6 mm Hg vs 29.5 +/- 2.3 mm Hg, P less than 0.01). In addition, when the ratio of EVLW/PBV (pulmonary blood volume) was examined in both groups at each stage of the experiment, the ratio was greater in the Group 2 animals at each elevated pressure, suggesting increased permeability with renal dysfunction. In conclusion, pulmonary edema formation occurs at lower left atrial pressures in the setting of sustained renal dysfunction, this phenomenon can be partially explained by lower protein osmotic pressure though altered pulmonary microvascular permeability may contribute to edema formation.     

Effects of Hydrostatic Pressure on Carcinogenic Properties of Epithelia

The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma.     

Regulatory role for nucleosome assembly protein-1 in the proliferative and vasculogenic phenotype of pulmonary endothelium

Mediators of angiogenesis such as VEGFs and angiopoietins may regulate pulmonary vascular permeability under normal and pathological conditions. Ephrin family receptor tyrosine kinases are expressed in the vasculature and also regulate angiogenesis under some circumstances, but whether they also modulate lung vascular permeability is unknown. We hypothesized that stimulation of lung endothelial EphA receptors with ephrin-a1 ligand would alter pulmonary vascular permeability and tested this idea in vivo and in vitro. We found that ephrin-a1 ligand and EphA2 receptors are expressed in distal normal lung vasculature and that their expression is increased in injured lung, suggesting a link to mechanisms of increased permeability. Intravenous injection of ephrin-a1 caused a large increase in the leakage of labeled albumin into the lungs of rats within 30 min (293 +/- 27 vs. 150 +/- 6 ng/mg dry lung, P < 0.01), along with histological evidence of the formation of endothelial disruptions. In cultured lung vascular endothelial cells, stimulation with ephrin-a1 increased monolayer permeability by 44% (P < 0.01), a permeability change similar to that seen with VEGF stimulation of the same cells. Ephrin-a1 stimulation in vivo and in vitro was associated with histological evidence for disruptions of tight and adherens junctions. These observations describe a novel role for ephrin-a1 and EphA receptors in the regulation of vascular permeability in the lung.     

siRNA干扰MMP-9和FAK双基因抑制小鼠黑色素瘤生长和在体迁移

目的:观察干扰MMP-9和FAK双基因对恶性黑色素瘤高转移细胞B16F10体内转移的影响。方法:构建PGV102-MMP9-siRNA、PGV102-FAK-siRNA重组质粒载体,脂质体^TM2000介导转染小鼠黑色素瘤B16F10细胞,RT-PCR检测基因的干扰效果;建立C57BL/6小鼠皮下移植瘤模型观察细胞在体成瘤和肿瘤的生长情况,常规组织切片,H&E染色观察肿瘤组织病理学特征;经C57BL/6小鼠尾静脉注射细胞5×10⁵个/只,24天后计数小鼠肺转移结节数评价肿瘤细胞在体迁移能力。结果:RT-PCR结果表明,重组质粒转染细胞组的MMP-9和FAK的mRNA水平显著低于正常细胞组(P<0.01),转染细胞组C57BL/6小鼠皮下成瘤的肿瘤生长速率、黑色素瘤肺转移结节数明显低于正常细胞组(P<0.01)。结论:干扰B16F10细胞MMP-9和FAK双基因可明显抑制小鼠体内恶性肿瘤的生长和迁移。     

The influence of culture conditions on cell morphology and tyrosine aminotransferase levels in rat liver epithelial cell lines

Experimental conditions known to alter the shape, permeability and organization of cells were used to find out their effects on tyrosine aminotransferase (TAT) in rat liver epithelial cell lines. To produce a more spheroidal morphology for non-malignant cells than that obtainable on plastic, floating collagen and poly(2-hydroxyethylmethacrylate) (poly(HEMA)), were used as substrata. Under these experimental conditions the basal level of TAT activity increased 1.5–2.5-fold. When monolayer cultures were permeabilized by the use of a hypertonic salt solution, the basal activity increased 4–5-fold. TAT activity was also elevated in hepatoma cells cultured in anchorage-independent conditions. The enzyme was not inducible by dexamethasone (DEX) under any of these culture conditions, and the lack of induction was not due to the absence of receptors for this hormone. These studies have shown that the production of TAT, one of the characteristics of adult liver, has persisted in a number of rat epithelial cell lines derived from normal, malignant or regenerating liver and its activity was influenced by the different culture conditions employed.     

The effect of saffron on intracellular DNA, RNA and protein synthesis in malignant and non-malignant human cells.

Extract of saffron (Crocus sativis) has previously been shown to inhibit colony formation and cellular DNA and RNA synthesis by HeLa cells in vitro. In order to compare the sensitivity of malignant and non-malignant cells to saffron, we examined the effect of the extract on macromolecular synthesis in three human cell lines: A549 cells (derived from a lung tumor), WI-38 cells (normal lung fibroblasts) and VA-13 cells (WI-38 cells transformed in vitro by SV40 tumor virus). We found that the malignant cells were more sensitive than the normal cells to the inhibitory effects of saffron on both DNA and RNA synthesis. There was no effect on protein synthesis in any of the cells.     

Preferential elevation of Prx I and Trx expression in lung cancer cells following hypoxia and in human lung cancer tissues

Transient/chronic microenvironmental hypoxia that exists within a majority of solid tumors has been suggested to have a profound influence on tumor growth and therapeutic outcome. Since the functions of novel antioxidant proteins, peroxiredoxin I (Prx I) and II, have been implicated in regulating cell proliferation, differentiation, and apoptosis, it was of our special interest to probe a possible role of Prx I and II in the context of hypoxic tumor microenvironment. Since both Prx I and II use thioredoxin (Trx) as an electron donor and Trx is a substrate for thioredoxin reductase (TrxR), we investigated the regulation of Trx and TrxR as well as Prx expression following hypoxia. Here we show a dynamic change of glutathione homeostasis in lung cancer A549 cells and an up-regulation of Prx I and Trx following hypoxia. Western blot analysis of 10 human lung cancer and paired normal lung tissues also revealed an elevated expression of Prx I and Trx proteins in lung cancer tissues. Immunohistochemical analysis of the lung cancer tissues confirmed an augmented Prx I and Trx expression in cancer cells with respect to the parenchymal cells in adjacent normal lung tissue. Based on these results, we suggest that the redox changes in lung tumor microenvironment could have acted as a trigger for the up-regulation of Prx I and Trx in lung cancer cells. Although the clinical significance of our finding awaits more rigorous future study, preferential augmentation of the Prx I and Trx in lung cancer cells may well represent an attempt of cancer cells to manipulate a dynamic redox change in tumor microenvironment in a manner that is beneficial for their proliferation and malignant progression.     

Increased pulmonary microvasuclar permeability induced by alpha-naphthylthiourea

The effects of alpha-naphthylthiourea (ANTU) on lung microvascular permeability to plasma proteins were studied in anesthetized open-chest dogs. Lymph flow (Jv) was recorded, and total protein in plasma and lymph was analyzed after cannulating a small prenodal lung lymphatic. The protocol involved four experimental periods. Period 1. During this base-line period the preparation stabilized and steady states were reached in Jv, lymph total protein, pulmonary arterial pressure (Ppa), and left atrial pressure (Pla). Period 2. Pla was increased to approximately 20 cmH2O and maintained at that level until Jv and protein measurements attained a new steady state. Period 3. After Pla was lowered to control levels, ANTU (5 mg/kg body wt) was infused intravenously and parameters were measured for 3 h. Period 4 Pla was again raised to the pre-ANTU levels of period 2 and maintained for an additional 2-3 h. The lymphatic total protein clearance increased 8.6-fold for an equivalent increase in pulmonary capillary pressure after ANTU. Vascular permeability was assessed by estimating the osmotic reflection coefficient (sigma d) for total protein at the pulmonary capillary membrane. Sigma d decreased from 0.65 to 0.40 following ANTU. From plasma protein fractions in four experiments, equivalent pore radii for the capillary membrane of 95 and 280 A were calculated after ANTU compared with 80 and 200 A for normal lung capillaries. In addition, extravascular lung water increased from 3.8 +/- 0.16 to 5.87 +/- 0.25 following ANTU and to 7.55 +/- 0.55 (g/g blood-free dry wt) when Pla was elevated with ANTU. The experimental design allowed quantitative assessment of the vascular permeability increase after ANTU by use of lymph protein fluxes that had minimal errors due to changes in surface area or lymph contamination from nonpulmonary structures.     

Cathelicidin LL-37 increases lung epithelial cell stiffness, decreases transepithelial permeability, and prevents epithelial invasion by Pseudomonas aeruginosa

In addition to its antibacterial activity, the cathelicidin-derived LL-37 peptide induces multiple immunomodulatory effects on host cells. Atomic force microscopy, F-actin staining with phalloidin, passage of FITC-conjugated dextran through a monolayer of lung epithelial cells, and assessment of bacterial outgrowth from cells subjected to Pseudomonas aeruginosa infection were used to determine LL-37's effect on epithelial cell mechanical properties, permeability, and bacteria uptake. A concentration-dependent increase in stiffness and F-actin content in the cortical region of A549 cells and primary human lung epithelial cells was observed after treatment with LL-37 (0.5-5 μM), sphingosine 1-phosphate (1 μM), or LPS (1 μg/ml) or infection with PAO1 bacteria. Other cationic peptides, such as RK-31, KR-20, or WLBU2, and the antibacterial cationic steroid CSA-13 did not reproduce the effect of LL-37. A549 cell pretreatment with WRW4, an antagonist of the transmembrane formyl peptide receptor-like 1 protein attenuated LL-37's ability to increase cell stiffness. The LL-37-mediated increase in cell stiffness was accompanied by a decrease in permeability and P. aeruginosa uptake by a confluent monolayer of polarized normal human bronchial epithelial cells. These results suggested that the antibacterial effect of LL-37 involves an LL-37-dependent increase in cell stiffness that prevents epithelial invasion by bacteria.     

Redox regulation of endothelial barrier integrity

Intestinal ischemia-reperfusion is associated with the generation of reactive oxygen metabolites as well as remote, oxidant-mediated lung injury. Oxidants elicit endothelial redox imbalance and loss of vascular integrity by disorganizing several junctional proteins that contribute to the maintenance and regulation of the endothelial barrier. To determine the specific effect of redox imbalance on pulmonary vascular barrier integrity, microvascular permeability was determined in lungs of animals subjected to chemically induced redox imbalance. The effect of redox imbalance on microvascular permeability and endothelial junctional integrity in cultured lung microvascular cells was also determined. Whole lung and cultured pulmonary endothelial cell permeability both increased significantly in response to chemical redox imbalance. Thiol depletion also resulted in decreased endothelial cadherin content and disruption of the endothelial barrier. These deleterious effects of intracellular redox imbalance were blocked by pretreatment with exogenous glutathione. The results of this study suggest that redox imbalance contributes to pulmonary microvascular dysfunction by altering the content and/or spatial distribution of endothelial junctional proteins.     

Effects of mechanical ventilation at low lung volume on respiratory mechanics and nitric oxide exhalation in normal rabbits.

Lung mechanics, exhaled NO (NOe), and TNF-alpha in serum and bronchoalveolar lavage fluid were assessed in eight closed and eight open chest, normal anesthetized rabbits undergoing prolonged (3-4 h) mechanical ventilation (MV) at low volume with physiological tidal volumes (10 ml/kg). Relative to initial MV on positive end-expiratory pressure (PEEP), MV at low volume increased lung quasi-static elastance (+267 and +281%), airway (+471 and +382%) and viscolelastic resistance (+480 and +294%), and decreased NOe (-42 and -25%) in closed and open chest rabbits, respectively. After restoration of PEEP, viscoelastic resistance returned to control, whereas airway resistance remained elevated (+120 and +31%) and NOe low (-25 and -20%) in both groups of rabbits. Elastance remained elevated (+23%) only in closed-chest animals, being associated with interstitial pulmonary edema, as reflected by increased lung wet-to-dry weight ratio with normal albumin concentration in bronchoalveolar lavage fluid. In contrast, in 16 additional closed- and open-chest rabbits, there were no changes of lung mechanics or NOe after prolonged MV on PEEP only. At the end of prolonged MV, TNF-alpha was practically undetectable in serum, whereas its concentration in bronchoalveolar lavage fluid was low and similar in animals subjected or not subjected to ventilation at low volume (62 vs. 43 pg/ml). These results indicate that mechanical injury of peripheral airways due to their cyclic opening and closing during ventilation at low volume results in changes in lung mechanics and reduction in NOe and that these alterations are not mediated by a proinflammatory process, since this is expressed by TNF-alpha levels.