John L. Bowers

Hepatic microcirculatory changes after reperfusion in fatty and normal liver transplantation in the rat

The hepatic microcirculation in fatty and normal liver grafts in ACI rats was investigated using in vivo microscopy. Six groups were studied. They were: normal and fatty control livers (sham operated), 6-hr cold University of Wisconsin solution (UW)-preserved fatty and normal liver grafts (survival conditions, fatty and normal liver grafts), 18-hr cold UW-preserved fatty livers (nonsurvival conditions, fatty liver graft), and 24-hr cold UW-preserved normal livers (nonsurvival conditions, normal liver grafts). Fatty livers in all groups were found to have narrow and irregular sinusoids with blood cell adhesions to endothelial cells. The number of adhesions increased as the preservation time increased. Sinusoidal blood flow area decreased as the preservation time increased and was correlated with survival in both normal and fatty liver grafts. The phagocytic activity of Kupffer cells (corrected for flow) increased as the preservation time increased. The phagocytic Kupffer cell activity of the 18-hr preserved fatty liver group was greater than the activity of any other group. These features may cause liver cell death and contribute to primary graft nonfunction after transplantation of a fatty liver.

A rat fatty liver transplant model

A rat model of fatty liver transplantation has been developed to study primary nonfunction in fatty liver grafts. ACI rats were fed with a diet deficient in choline and methionine for 7, 14, 28, and 42 days. Fat content in the pretransplant livers was examined by gas chromatography and histology. The main constituent of the fatty droplets was determined to be triglyceride. The triglyceride concentration reached a maximum by day 14 and remained constant for an additional 28 days. Histology revealed an absence of necrosis in 14- and 28-day fatty livers but scattered hepatocytic necrosis and inflammation in 42-day fatty livers. After being given cold (UW stored, 4 degrees C) or warm (37 degrees C) ischemia, the fatty liver was orthotopically transplanted into normal ACI rats. The one-week survival of fatty liver grafts after 6, 12, 18, and 24 hr cold preservation was 5/5, 5/6, 3/8, 0/6 for 14-day fatty liver and 5/5, 4/6, 0/8, 0/6 for 42-day fatty livers. The survival of normal liver grafts was 5/5, 6/6, 5/9, 2/8, respectively. Increased survival rate was correlated with the absence of hepatocytic necrosis. The survival after 15 and 30 min warm ischemia prior to transplant was 5/5, 2/6 for normal liver grafts and 4/7, 0/6 for 28-day fatty liver graft, respectively. Fatty livers were less resistant to damage induced by cold or warm ischemia.

In vivo bone marrow lipid characterization with line scan Carr-Purcell-Meiboom-Gill proton spectroscopic imaging

Line scan Carr-Purcell-Meiboom-Gill spectroscopic imaging sequences have been used to extract lipid chemical composition indices in healthy adult bone marrow in the knee at 1.5 T. Since several spectroscopic echo readouts follow each excitation, the information acquired reflects a balance between spectral T2 decay processes and spectral resolution. To examine this balance in detail, data sets with two different echo spacings and spectral resolutions have been acquired to compare the information available from each in studies of bone marrow. Oils for which high field (7 T) proton spectra were recorded were used to evaluate the accuracy of lipid chemical composition indices extracted from the line scan Carr-Purcell-Meiboom-Gill spectroscopic imaging methods at 1.5 T. The extension of the method to fast spectroscopic imaging of bone marrow with multiple echoes is demonstrated.

Response to and Control of Destructive Energy by Magnetic Resonance

Magnetic resonance imaging techniques can be used to control and monitor the deposition of destructive energy. The authors evaluated the feasibility of phosphorus-31 magnetic resonance spectroscopy for the control, monitoring, and prediction of the three-dimensional extent of tissue destruction during interstitial laser surgery. Characteristic metabolic changes were demonstrated within the lesion and in the adjacent normal tissue during the deposition of thermal energy.

31P NMR ASSESSMENT OF ORTHOTOPIC RAT LIVER TRANSPLANT VIABILITY THE EFFECT OF WARM ISCHEMIA1,2

The relationship between NMR visible high energy phosphates and transplant outcome for the case of liver damage by warm ischemia was investigated. In vivo 31P nuclear magnetic resonance (NMR) spectroscopy of rat liver was performed before the induction of warm ischemia in the donor and 20 min after reestablishment of portal blood flow in the recipient. Pretransplant damage was varied by subjecting the livers to 0, 15, 30, or 60 min of warm ischemia prior to harvesting. In the controls (0 min warm ischemia), 4 of 4 rats survived transplantation (one week survival end-point) and the mean NTP recovery was 94± 8%; 3 of 6 rats survived in the 15 min warm ischemia group. Mean NTP recovery was 77±20% in the 15 min survival subgroup and 32± 20% in the nonsurvival subgroup. Of 6 rats, 1 survived in the 30 min group. NTP recovery was 44% for the 30 min survivor and 37±5% in the nonsurvival subgroup. Of 4 rats, 1 survived in the 60 min warm ischemia group. NTP recovery was 56% for the 60 min survivor and 28±7% in the nonsurvival subgroup. Overall, there was a significant difference between the mean NTP recovery of the survival and nonsurvival subgroups (78±21% versus 31±18%, P< 0.001). The dividing line between the survival and nonsurvival groups was approximately 50% NTP recovery. Of 9 rats with liver NTP recovery greater than 50%, 8 survived while 10 of 11 rats with less than 50% recovery died. NMR visible NTP recovery 20 min after the reestablishment of portal blood flow was a good indicator of transplant outcome in the case of rat liver damage by warm ischemia.

In vivo microscopic assessment of hepatic microcirculation during liver allograft rejection in the rat

The hemodynamic alterations in hepatic microvasculature during acute rejection of rat liver allografts was studied using in vivo fluorescence microscopy. ACI rat livers were transplanted into Lewis (allograft) or ACI (isograft) recipients. Microscopy was performed on days 3 (n=7) and 6 (n=7) in allografts, and on day 6 (n=7) in isografts. Naive ACI livers (n=7) served as nontransplant controls. Changes in sinusoidal blood perfusion, microvascular structure, and leukocyte-endothelial interactions were observed and quantitated. Six days after transplantation, acinar perfusion was markedly impaired in allografts and was accompanied by a lower percentage of perfused sinusoids (59±8%, mean ± SEM, P<0.01) relative to isografts (89±3%) and nontransplant controls (100±0%). The hepatic cord width in allografts was significantly greater than in isografts or in nontransplant controls, indicating swelling of parenchymal and sinusoidal lining cells. Furthermore, the number of leukocytes adhering to the sinusoidal endothelium significantly increased in allografts. Adherence to postsinusoidal venules was more prominent in allograft livers (4025±1400/mm2 of vascular endothelial surface) compared with that in isografts (574±77/mm2) and nontransplant controls (185±28/mm2). These microcirculatory alterations in allografts were significant even on day 3. The results show extensive abnormalities of the microcirculatory hemodynamics in rejecting liver allografts which were associated with increased leukocyte adherence to microvascular endothelium. Our findings may provide strategic information for the prevention and treatment of allograft rejection.

Multiecho Approaches to Spectroscopic Imaging of the Braina

Spectroscopic imaging (SI) with nuclear magnetic resonance (NMR) is one of the most powerful tools available for studying brain chemistry in vivo. Both proton (1H) and phosphorus (31P) NMR offer valuable biochemical information that can in principle be mapped throughout the entire brain, thereby enhancing our understanding of brain function. With the exception of protons from tissue water and the triglycerides of adipose tissue, however, nuclei contributing to the NMR signals of living tissue are in relatively small (millimolar) concentrations. The low concentration of metabolite nuclei reduces the overall sensitivity of conventional SI techniques, making high-quality metabolite mapping a lengthy procedure. This problem has led to the development and testing of nonconventional methods for reducing SI scan times, including techniques based on the collection of multiple spin-echoes. The extent to which multiecho methods can be used to decrease SI scan times and maintain high-quality metabolite mapping depends on several factors. These include the spectral transverse relaxation times, the spectral resolution required, and J-coupling interactions. We have discussed these various technical aspects of multiecho SI methods as applied to 1H and 31P spectroscopic imaging of the living brain.

Biliary complications after orthotopic liver transplantation in rats

We recently experienced a high frequency of biliary complications after orthotopic liver transplantation in rats (22 of 25 cases (88%): biloma, 20 cases; biliary peritonitis, 2 cases). These complications seemed to be rare in general, but some researchers reported such cases and addressed them mainly through rearterialization. The biliary complications we encountered were found to be associated with necrosis of the donor bile duct and an opportunistic infection of Enterobacteriaceae. After administering appropriate antibiotics, the complications significantly diminished (2 of 25 cases (8%),P=0.0001). The nonarterialized bile duct, which becomes ischemic soon after liver transplantation, appears to be susceptible to infections. Such opportunistic infections may prevent the development of arterial collaterals, causing bile duct necrosis and the subsequent leakage of bile juice. When biliary complications frequently occur after nonarterialized liver transplantation in rats, the possibility of an opportunistic infection should thus be considered.

31P nuclear magnetic resonance spectroscopic evaluation of liver preservation solutions

The individual effects of verapamil and 2 antioxidants on perfused rat liver nucleoside triphosphate (NTP) recovery following cold storage in University of Wisconsin (UW) solution was assessed using 31P nuclear magnetic resonance spectroscopy. The pharmacological agents were added to UW solution and were present only during organ storage. NTP recovery was significantly higher for the 24-hr UW + 40 μM verapamil group as compared with the 24-hr UW group. None of the other pharmacological agents caused a significant increase in NTP recovery. These findings suggest that addition of verapamil to UW organ preservation solution may result in better poststorage liver function.