Immunomodulatory effect of oxygen and pressure.

The immunomodulatory effect of hyperbaric oxygen, involving altered cytokine release by macrophages, is well described. Importantly, however, it is not known what the relative contribution is of the hyperbaric environment of the cells vs. increased oxygen tension on these hyperbaric oxygen-dependent effects. We compared, therefore, cytokine release by murine macrophages under hyperbaric oxygen, hyperpressure of normal air and normobaric conditions. We observed that hyperbaric oxygen enhanced cytokine release of both unstimulated as well as lipopolysaccharide (LPS)-challenged macrophages. Hyperpressure of normal air, however, enhanced LPS-induced cytokine production but did not elicit cytokine release in unstimulated macrophages. To further investigate the molecular details underlying the effects of hyperbaric oxygen, we investigated the effect of the p42/p44 mitogen-activated protein (MAP) kinase inhibitor PD98059 and the p38 MAP kinase inhibitor SB203580. Neither inhibitor, however, had a significant effect on the modulatory effects of hyperbaric oxygen on cytokine release. We concluded that the immunomodulatory effect of hyperbaric oxygen contains a component for which hyperpressure is sufficient and a component that apart from hyperpressure also requires hyperoxygenation.

Effects of hyperbaric oxygen and normobaric carbogen on the radiation response of the rat rhabdomyosarcoma R1H.

PURPOSE: Hypoxic tumor cells are an important factor of radioresistance. Hyperbaric oxygen (HBO) and normobaric carbogen (95% oxygen, 5% carbon dioxide) increase the oxygen delivery to tumors. This study was performed to explore changes of tumor oxygenation during a course of fractionated irradiation and to determine the effectiveness of normobaric carbogen and HBO during the final phase of the radiation treatment. METHODS AND MATERIALS: Experiments were performed on the rhabdomyosarcoma R1H growing on WAG/Rij rats. After 20 X-ray fractions of 2 Gy within 4 weeks, oxygen partial pressure (pO2) was measured using the Eppendorf oxygen electrode under ambient conditions, with normobaric carbogen or HBO at a pressure of 240 kPa. Following the 4-week radiation course, a top-up dose of 10-50 Gy was applied in 2-10 fractions of 5 Gy with or without hyperoxygenation. RESULTS: HBO but not carbogen significantly increased the median pO2 in irradiated tumors. The radiation doses to control 50% of tumors were 38.0 Gy, 29.5 Gy, and 25.0 Gy for air, carbogen, and HBO, respectively. Both high oxygen content gas inspirations led to significantly improved tumor responses with oxygen enhancement ratios (OERs) of 1.3 for normobaric carbogen and 1.5 for HBO (air vs. carbogen: p = 0.044; air vs. HBO: p = 0.02; carbogen vs. HBO: p = 0.048). CONCLUSION: Both normobaric carbogen and HBO significantly improved the radiation response of R1H tumors. HBO appeared to be more effective than normobaric carbogen, both with regard to tumor oxygenation and response to irradiation.

Radiosensitizing effect of carbogen breathing during pulsed irradiation of the rat R1H tumor.

The objective of the present study was to investigate the radiosensitizing effect of carbogen breathing during pulsed x-ray irradiation in an experimental tumor model. Rat R1H rhabdomyosarcoma tumors were irradiated with 36 Gy total dose in 1 Gy high dose rate pulses, either hourly repeated, or in an 'office hours' protocol with irradiation-free overnight intervals. With the hourly, pulsed irradiation scheme, tumor growth delay (TGD) was significantly increased from 24.4+/-0.7 days in air-breathing animals to 29.0+/-0.9 days in animals breathing carbogen during irradiation. With irradiation during office hours, the TGD was shortened, and carbogen was less effective. The data show that carbogen acts as a radiosensitizer when applied during pulsed irradiation. Translation of the experimental data to clinical practice indicates that hyperoxygenation of the tumor during pulsed dose rate (PDR) or high dose rate (HDR) brachytherapy might enhance the tumor response of patients.

Tumor hypoxia--a confounding or exploitable factor in interstitial brachytherapy? Effects of tissue trauma in an experimental rat tumor model.

PURPOSE: To evaluate the potential effects of tumor hypoxia induced by afterloading catheter implantation on the effectiveness of brachytherapy in a rat tumor model. METHODS AND MATERIALS: Afterloading catheters (4) were implanted in subcutaneously growing R1M rhabdomyosarcoma in female Wag/Rij rats. A MicroSelectron (Nucletron) was used for interstitial high-dose-rate irradiation ((192)Ir). Tumor oxygenation, perfusion, and cell survival were assessed by pO(2) histography (Eppendorf), Tc-99m injection, and excision assay, respectively. RESULTS: Tumor perfusion was markedly reduced at 1 h after catheter implantation (33.9 +/- 6.0% (SEM, n = 9) of control) and partly recovered after 5 h (61.5 +/- 12.2%). At 24 h, the perfusion level reached control values (100.6 +/- 25.7%), but was highly variable with some of the tumors showing hardly any recovery at all. Tumor oxygenation showed a similar pattern, but with less recovery. Median pO(2) readings were 13.5, 1.2, and 5.3 mm Hg before and at 1 and 24 h after implantation, respectively (7 tumors). The percentages of pO(2) readings

Intrahepatic tissue pO2 during continuous or intermittent vascular inflow occlusion in a pig liver resection model.

BACKGROUND: Temporary vascular inflow occlusion of the liver (clamping of the hepatic pedicle) can prevent massive blood loss during liver resections. In this study, intrahepatic tissue pO2 was assessed as parameter of microcirculatory disturbances induced by ischemia and reperfusion (I/R) in the liver following continuous (Cnt) or intermittent (Int) clamping in a hemihepatectomy model in the pig. METHODS: Pigs (20-34 kg) were divided into 2 groups: I/R without hemihepatectomy (-HH; n = 10) and I/R with hemihepatectomy (+HH; n = 8). Ischemia during 90 min was Cnt or Int (6 sequential periods of 12 min of ischemia and 3 min of reperfusion), followed by 120 min of reperfusion. Intrahepatic pO2 histograms (polarographic pO2 needle electrode) were constructed before ischemia, at the end of 90 min of ischemia and after 120 min of reperfusion, along with assessment of plasma AST, ALT and LDH. Bile production was monitored continuously. RESULTS: Cumulative frequency distribution curves (CFDC) after 120 min of reperfusion in the Cnt-HH group were not different from preischemic CFDC (means +/- SEM), whereas in the Int-HH group a left shift occurred indicating more hypo(non)perfused liver areas (pO2 < 10 mm Hg: 2.6 +/- 1.2 and 41.0 +/- 17.5% in Cnt-HH and Int-HH; p < 0.01). In the Cnt+HH group, a left shift in the CFDC occurred. In the Int+HH group, a left and a right shift occurred simultaneously, indicating both hypo(non)- and hyperperfused (shunting) liver areas (pO2 < 10 mm Hg: 4.0 +/- 2.7 and 9.6 +/- 8.5%, n.s., and pO2 > 60 mm Hg: 2.0 +/- 2.0 and 17.3 +/- 6.4%, p = 0.015, in Cnt+HH and Int+HH). Plasma AST, ALT and LDH levels were not increased after 120 min of reperfusion, except for AST in Cnt+HH and Int+HH (from 54.6 +/- 14.0 to 270.4 +/- 42.8 U/l, p < 0.01, and from 47.8 +/- 9.4 to 176.5 +/- 55.9 U/l, n.s.). Bile production (percentage of mean preischemic value) during 120 min of reperfusion was significantly reduced in the Int-HH group, as compared to the Cnt-HH group (57.0 and 117.0% after 120 min of reperfusion, p = 0.002). In Cnt+HH and Int+HH, bile production was significantly reduced (33.3 +/- 20.0%, p = 0.05, and 38.5 +/- 7.9%, p = 0.007); however it was not different between the two groups. CONCLUSIONS: (1) Intrahepatic tissue pO2 as indicator of microvascular perfusion is a parameter of early I/R injury; (2) continuous vascular inflow occlusion resulted in less microcirculatory disturbances, when compared to intermittent occlusion.

HBO and the uptake and retention of [125I] MIBG in human platelets and two neuroendocrine cell lines.

In this paper we report the effects of Hyperbaric Oxygen (HBO) exposure on the uptake and retention of meta-Iodobenzylguanidine (MIBG) in human platelets and two neuroendocrine cell lines. The combination of [131I] MIBG and HBO is used for therapy of neuroblastoma. Exposure to HBO can cause oxidative stress, which is potentially capable of affecting uptake and storage of MIBG in both neuroendocrine cells and platelets. Oxidative stress generated by menadione decreased both the uptake and retention of MIBG in the platelets and the cell lines. HBO did not affect these processes, indicating that the HBO induced oxidative stress is not high enough to affect the MIBG uptake and storage pathways in these cells. This suggests that the positive effects observed by the treatment of neuroblastoma patients with the combination of HBO and [131I] MIBG are most likely not due to improved uptake or retention of MIBG in the neuroblastoma. Neither can reduced cytotoxicity (trombocytopenia) be expected due to decreased uptake/retention of [131I] MIBG in platelets or their precursor cells.

Critical tissue oxygen tension defines tissue oxygen debt in the isolated hindlimb of the pig during progressive ischemia.

OBJECTIVE: To determine a critical skeletal muscle oxygen tension (PO2) value below which a tissue oxygen debt develops. DESIGN: Descriptive study of oxygen transport values in relation to skeletal muscle PO2 throughout progressive ischemia by means of arterial blood flow reductions in an isolated hindlimb model in the pig. SETTING: Surgical Research department of the University of Amsterdam. SUBJECTS: Six female Yorkshire pigs weighing 26 to 35 kg (average 33). INTERVENTIONS: Controlled blood flow to the isolated hindlimb was achieved by means of extracorporeal circulation. The hindlimb was studied during progressive flow reduction. MEASUREMENTS AND MAIN RESULTS: Oxygen delivery (DO2) and oxygen consumption were calculated as the product of extracorporeal blood flow and, respectively, arterial oxygen content and arterial-venous oxygen content difference. In this fashion, an oxygen supply dependency could be determined in all animals. A critical DO2 value was determined below which a tissue oxygen debt developed. Skeletal muscle PO2 was measured continuously, using a Clark-type polarographic oxygen sensor. Combining the critical DO2 value with the corresponding skeletal muscle PO2 value resulted in a critical skeletal muscle PO2 value of 15.2 +/- 0.4 torr (2.0 +/- 0.1 kPa). CONCLUSION: In this pig model, a critical skeletal muscle PO2 value could be determined below which a tissue oxygen debt presumably developed.

Clinical experience with radiation enhancement by hyperbaric oxygen in children with recurrent neuroblastoma stage IV.

The high risk group of patients with neuroblastoma are children over 1 year with stage IV disease. Most series report a maximum of 20% survival at 5 years. For recurrent neuroblastoma stage IV, cure rates are not reported in the literature, but they are nil. Any treatment for recurrent neuroblastoma stage IV remains a therapeutic dilemma. The outcome of radiation therapy is variable. A very important factor in tumour treatment remains tumour hypoxia, and others, such as metabolic factors, also play a role. Combined application of radiation modifiers may influence the final survival rate. In an attempt to improve the survival of recurrent neuroblastoma stage IV, hyperbaric oxygen and radioionated meta-Iodobenzylguanidine (MIBG) was used in a clinical setting. Although survival may not be used as a determinant of the usefulness of a treatment for stage IV neuroblastoma disease, a better one is not available. In this study, at 28 months, a cumulative probability of survival of 32% was recorded for patients treated with [131I]MIBG and hyperbaric oxygen compared to 12% for [131I]MIBG treatment alone. These preliminary results are promising but further studies are needed to reveal substantial therapeutic gain.