The influence of preconditioning on metabolic changes in the pig liver before, during, and after warm liver ischemia measured by microdialysis

Glycerol-weighted chemical exchange saturation transfer nanoprobes allow 19F/1H dual-modality magnetic resonance imaging-guided cancer radiotherapy

Recently, radiotherapy (RT) has entered a new realm of precision cancer therapy with the introduction of magnetic resonance (MR) imaging guided radiotherapy systems into the clinic. Nonetheless, identifying an optimized radiotherapy time window (ORTW) is still critical for the best therapeutic efficacy of RT. Here we describe pH and O2 dual-sensitive, perfluorooctylbromide (PFOB)-based and glycerol-weighted chemical exchange saturation transfer (CEST) nano-molecular imaging probes (Gly-PFOBs) with dual fluorine and hydrogen proton based CEST MR imaging properties (19F/1H-CEST). Oxygenated Gly-PFOBs ameliorate tumor hypoxia and improve O2-dependent radiotherapy. Moreover, the pH and O2 dual-sensitive properties of Gly-PFOBs could be quantitatively, spatially, and temporally monitored by 19F/1H-CEST imaging to optimize ORTW. In this study, we describe the CEST signal characteristics exhibited by the glycerol components of Gly-PFOBs. The pH and O2 dual-sensitive Gly-PFOBs with19F/1H-CEST MR dual-modality imaging properties, with superior therapeutic efficacy and biosafety, are employed for sensitive imaging-guided lung cancer RT, illustrating the potential of multi-functional imaging to noninvasively monitor and enhance RT-integrated effectiveness.

Real-time histology in liver disease using multiphoton microscopy with fluorescence lifetime imaging

Conventional histology with light microscopy is essential in the diagnosis of most liver diseases. Recently, a concept of real-time histology with optical biopsy has been advocated. In this study, live mice livers (normal, with fibrosis, steatosis, hepatocellular carcinoma and ischemia-reperfusion injury) were imaged by MPM-FLIM for stain-free real-time histology. The acquired MPM-FLIM images were compared with conventional histological images. MPM-FLIM imaged subsurface cellular and subcellular histopathological hallmarks of live liver in mice models at high resolution. Additional information such as distribution of stellate cell associated autofluorescence and fluorescence lifetime changes was also gathered by MPM-FLIM simultaneously, which cannot be obtained from conventional histology. MPM-FLIM could simultaneously image and quantify the cellular morphology and microenvironment of live livers without conventional biopsy or fluorescent dyes. We anticipate that in the near future MPM-FLIM will be evaluated from bench to bedside, leading to real-time histology and dynamic monitoring of human liver diseases.

Ischemic injury of the liver in a porcine model of cardiac death assessed by in vivo microdialysis

This study aims to evaluate the ischemic injury of the liver in a porcine model of cardiac death assessed by in vivo microdialysis. A porcine model of cardiac death was established by the suffocation method. Metabolic indicators were monitored using the microdialysis technique during warm ischemia time (WIT) and cold ischemia time (CIT). Pathological changes in ischemic-injured livers were observed by haematoxylin-eosin staining. The predictive values of biochemical parameters regarding the liver donor were evaluated by receiver operating characteristic curve analysis. All statistical analyses were conducted using the SPSS 18.0 software (SPSS Inc, Chicago, Illinois, USA). The degree of warm ischemic injury of the livers increased with prolonged WIT. Serum glucose, glycerol, pyruvate, lactic acid levels and lactate-to-pyruvate (L/P) ratio increased gradually during WIT. Results from Pearson correlation analyses indicated that serum lactate level and L/P ratio were positively associated with the degree of warm ischemic injury of the livers. The degree of cold ischemic injury of the livers gradually increased after 12 h CIT. Serum glucose, lactic acid and L/P ratio achieved a peak after 6-8 h of CIT, but gradually decreased with prolonged CIT. The peak of glycerol occurred after 8 h of CIT, while no changes were found with prolonged CIT. Serum pyruvate level exhibited an increasing trend after 12 h CIT. Our results confirmed that serum glucose and lactate levels were negatively correlated with cold ischemic injury of the liver. However, serum glycerol and pyruvate levels showed positive correlations with cold ischemic injury of the liver. The liver donor was unavailable after 30 min WIT and 24 h CIT. The cut-off value of serum lactate level for warm ischemic injury of the livers was 2.374 with a sensitivity (Sen) of 90 % and specificity (Spe) of 95 %; while the L/P radio was 0.026 (Sen = 80 %, Spe = 83 %). In addition, the cut-off values of serum glucose, lactate, glycerol and pyruvate levels for cold ischemic injury of the livers were 0.339 (Sen = 100 %, Spe = 77 %), 1.172 (Sen = 100 %, Spe = 61 %), 56.359 (Sen = 100 %, Spe = 65 %) and 0.020 (Sen = 100 %, Spe = 67 %), respectively. Our findings provide empirical evidences that serum glucose, lactate levels and L/P ratio may be good indicators for the degree of warm ischemic injury of the livers after cardiac death; while serum glucose, lactate, glycerol and pyruvate levels may be important in predicting cold ischemic injury.

N-acetyl cysteine improves glycogenesis after segmental liver ischemia and reperfusion injury in pigs

OBJECTIVE

N-acetylcysteine (NAC) is an antioxidative molecule known to protect liver tissue from oxygen radical species generated during ischemia and reperfusion (IR). Nutritional and toxicology studies have shown that NAC also improves glucose metabolism and glycogen stores. We hypothesized that NAC improves glycogenesis and that impaired glycogenesis is a key element in IR injury.

MATERIAL AND METHODS

In an experimental model, 80 min of segmental liver ischemia was induced in 16 pigs and the reperfusion was followed for 360 min. Eight animals received NAC 150 mg/kg as a bolus injection followed by an infusion of NAC 50 mg/kg/h intravenously.

RESULTS

AST and leukocyte density were lower in the NAC-treated animals, unrelated to the glutathione levels or apoptosis. Glycogen stores returned to a higher degree in the NAC-treated animals and microdialysis revealed lower levels of lactate during the reperfusion phase. Nitrite/Nitrate levels in the NAC group were lower in both serum and microdialysates, indicating that NAC scavenges radical nitrosative species.

CONCLUSIONS

NAC treatment improves glycogenesis after liver IR injury and reduces the level of intraparenchymal lactate during reperfusion, possibly due to the scavenging of radical nitrosative species.

Multiphoton microscopy can visualize zonal damage and decreased cellular metabolic activity in hepatic ischemia-reperfusion injury in rats

Ischemia-reperfusion (I/R) injury is a common occurrence in liver surgery. In orthotopic transplantation, the donor liver is exposed to periods of ischemia and when oxygenated blood is reintroduced to the liver, oxidative stress may develop and lead to graft failure. The aim of this project was to investigate whether noninvasive multiphoton and fluorescence lifetime imaging microscopy, without external markers, were useful in detecting early liver damage caused by I/R injury. Localized hepatic ischemia was induced in rats for 1 h followed by 4 h reperfusion. Multiphoton and fluorescence lifetime imaging microscopy was conducted prior to ischemia and up to 4 h of reperfusion and compared to morphological and biochemical assessment of liver damage. Liver function was significantly impaired at 2 and 4 h of reperfusion. Multiphoton microscopy detected liver damage at 1 h of reperfusion, manifested by vacuolated cells and heterogeneous spread of damage over the liver. The damage was mainly localized in the midzonal region of the liver acinus. In addition, fluorescence lifetime imaging showed a decrease in cellular metabolic activity. Multiphoton and fluorescence lifetime imaging microscopy detected evidence of early I/R injury both structurally and functionally. This provides a simple noninvasive technique useful for following progressive liver injury without external markers.

Remote or conventional ischemic preconditioning--local liver metabolism in rats studied with microdialysis

BACKGROUND

Ischemic preconditioning (IPC) of the liver decreases liver injury secondary to ischemia and reperfusion. An attractive alternative to IPC is remote ischemic preconditioning (R-IPC), but these two methods have not previously been compared.

MATERIAL AND METHODS

Eighty-seven rats were randomized into four groups: sham operated (n = 15), 1 h segmental ischemia (IRI, n = 24), preceded by IPC (n = 24), or R-IPC (n = 24) (to the left hindleg). IPC and R-IPC were performed with 10 min ischemia and 10 min of reperfusion. Analyses of liver microdialysate (MD), serum transaminase levels, and liver histology were made.

RESULTS

Rats treated with IPC and R-IPC had significantly lower AST, 71.5 (19.6) IU/L respective 96.6 (12.4) at 4 h reperfusion than those subjected to IRI alone, 155 (20.9), P = 0.0004 and P = 0.04 respectively. IPC also had lower ALT levels, 41.6 (11.3) IU/L than had IRI 107.4 (15.5), P = 0.003. The MD glycerol was significantly higher during ischemia in the R-IPC [759 (84) μM] and the IRI [732 (67)] groups than in the IPC 514 (70) group, P = 0.022 and P = 0.046 respectively. The MD glucose after ischemia was lower in the IPC group 7.1 (1.2) than in the IRI group 12.7 (1.6), P = 0.005. Preconditioning to the liver caused an direct increase in lactate, glucose and glycerol in the ischemic segment compared with the control segment an effect not seen in the R-IPC and IRI groups.

CONCLUSIONS

IPC affects glucose metabolism in the rat liver, observed with MD. IPC reduces liver cell injury during ischemic and reperfusion in rats. R-IPC performed over the same length of time as IPC does not have the same effect as the latter on ALT levels and MD glycerol; this may suggest that R-IPC does not offer the same protection as IPC in this setting of rat liver IRI.

In vivo proton magnetic resonance spectroscopy of hepatic ischemia/reperfusion injury in an experimental model

RATIONALE AND OBJECTIVES

Hepatic ischemia/reperfusion injury (IRI) occurs during certain hepatobiliary surgeries, hemorrhagic shock, and veno-occlusive disease. Biochemical changes caused by hepatic IRI lead to hepatocellular remodeling, including cellular regeneration or irreversible apoptosis. This study aims to characterize and monitor the metabolic changes in hepatic IRI using proton magnetic resonance spectroscopy (¹H MRS).

MATERIALS AND METHODS

Sprague-Dawley rats (n = 8) were scanned with ¹H MRS using 5.0 × 5.0 × 5.0 mm³ voxel over a homogeneous liver parenchyma at 7 Tesla with a respiratory-gated point-resolved spectroscopy sequence at 1 day before, 6 hours, 1 day, and 1 week after 30 minutes total hepatic IRI. Signal integral ratios of choline-containing compounds (CCC), glycogen and glucose complex (Glyu), methylene proton ((-CH₂-)(n)), and methene proton (-CH=CH-) to lipid (integral sum of methyl proton (-CH₃), (-CH₂-)(n) and -CH=CH-) were quantified by areas under peaks longitudinally.

RESULTS

The CCC-to-lipid and Glyu-to-lipid ratios at 6 hours after IRI were significantly higher than those at 1 day before, 1 day, and 1 week after injury. The (-CH₂-)(n)-to-lipid, and -CH=CH-to-lipid ratios showed no significant differences over different time points. Hepatocellular regeneration was observed at 6 hours after IRI in histology with immunohistochemical technique.

CONCLUSIONS

Changes in CCC-to-lipid and Glyu-to-lipid ratios likely reflect the hepatocellular remodeling and impaired glucose utilization upon hepatic IRI, respectively. The experimental findings in the current study demonstrated that ¹H MRS is a valuable tool for characterizing either global or regional metabolic changes in liver noninvasively and longitudinally. Such capability has the potential to lead to early diagnosis and detection of impaired liver function.

Perioperative inflammatory response in total knee arthroplasty patients: impact of limb preconditioning

BACKGROUND AND OBJECTIVES

Ischemic preconditioning of tissue that is to undergo procedure-induced underperfusion has been used in a number of surgical settings to reduce the subsequent inflammatory response and its sequelae. The objective of this prospective, randomized study was to evaluate the effect of ischemic preconditioning on the systemic inflammatory response, degree of lung catabolism, and postoperative-pain associated with total knee arthroplasty (TKA).

MATERIALS

Thirty-four patients undergoing unilateral TKA under tourniquet ischemia were enrolled with half (n = 17) being randomized to an episode of limb preconditioning before induction of ischemia for surgery. Markers of inflammation (interleukin 6 [IL-6], C-reactive protein,tumor necrosis factor >, and leukocyte count) and elastin catabolism(desmosine) were measured at baseline and various points postoperatively.Pain scores and length of stay were recorded.

RESULTS

A significant increase in the levels of IL-6, C-reactive protein,tumor necrosis factor >, and white blood cell count was observed after surgery in both groups. Despite trends toward decrease in the IL-6 level in the preconditioning group, no significant difference between groups was observed for all markers at any given time point. Urine desmosine-creatinine-ratios did not differ between groups, and no significant-changes from baseline were seen postoperatively. However, median pain scores and length of hospital stay were lower in the treatment group.

CONCLUSIONS

Preconditioning of the lower extremity in the setting of TKA under regional anesthesia may have limited value in reducing the systemic inflammatory response and level of lung injury. However, preconditioning may be associated with beneficial effects such as reduction in postoperative pain levels, and thus, further investigations are warranted.