Wilmar de Graaf

Physiological and biochemical basis of clinical liver function tests: a review

Objective:To review the literature on the most clinically relevant and novel liver function tests used for the assessment of hepatic function before liver surgery. Background:Postoperative liver failure is the major cause of mortality and morbidity after partial liver resection and develops as a result of insufficient remnant liver function. Therefore, accurate preoperative assessment of the future remnant liver function is mandatory in the selection of candidates for safe partial liver resection. Methods:A MEDLINE search was performed using the key words “liver function tests,” “functional studies in the liver,” “compromised liver,” “physiological basis,” and “mechanistic background,” with and without Boolean operators. Results:Passive liver function tests, including biochemical parameters and clinical grading systems, are not accurate enough in predicting outcome after liver surgery. Dynamic quantitative liver function tests, such as the indocyanine green test and galactose elimination capacity, are more accurate as they measure the elimination process of a substance that is cleared and/or metabolized almost exclusively by the liver. However, these tests only measure global liver function. Nuclear imaging techniques (99mTc-galactosyl serum albumin scintigraphy and 99mTc-mebrofenin hepatobiliary scintigraphy) can measure both total and future remnant liver function and potentially identify patients at risk for postresectional liver failure. Conclusions:Because of the complexity of liver function, one single test does not represent overall liver function. In addition to computed tomography volumetry, quantitative liver function tests should be used to determine whether a safe resection can be performed. Presently, 99mTc-mebrofenin hepatobiliary scintigraphy seems to be the most valuable quantitative liver function test, as it can measure multiple aspects of liver function in, specifically, the future remnant liver.

Transporters involved in the hepatic uptake of 99mTc-mebrofenin and indocyanine green

BACKGROUND & AIMS (99m)Tc-mebrofenin hepatobiliary scintigraphy (HBS) and the indocyanine green (ICG) clearance test are used for the assessment of hepatic function before and after liver surgery. The hepatic uptake of (99m)Tc-mebrofenin and ICG is considered similar to the uptake of organic anions such as bilirubin and bile acids. Little is known about hepatic uptake mechanisms of both compounds and recent evidence suggests that the hepatic transporters for ICG and (99m)Tc-mebrofenin are distinct. The aim of this study was to identify the specific human hepatic transporters of (99m)Tc-mebrofenin and ICG. METHODS The uptake of (99m)Tc-mebrofenin was investigated in cRNA-injected Xenopus laevis oocytes expressing human OATP1B1, OATP1B3, OATP2B1, or NTCP. Chinese hamster ovary (CHO) cells stably expressing OATP1B1, OATP1B3, OATP2B1, or NTCP were used as a mammalian expression system. ICG transport into CHO cells was additionally imaged with confocal microscopy. RESULTS We demonstrated that OATP1B1 and OATP1B3 are involved in the transport of (99m)Tc-mebrofenin. OATP1B1 showed an approximately 1.5-fold higher affinity for (99m)Tc-mebrofenin compared to OATP1B3. ICG is transported by OATP1B3 and NTCP. CONCLUSIONS The transporter specificity of (99m)Tc-mebrofenin and ICG partially overlaps as both compounds are transported by OATP1B3. (99m)Tc-mebrofenin is also taken up by OATP1B1, whereas ICG is additionally transported by NTCP.

Induction of tumor growth after preoperative portal vein embolization: is it a real problem?

Although preoperative portal vein embolization (PVE) is an effective means to increase future remnant liver (FRL) volume, little has been published on possible adverse effects. This review discusses the clinical and experimental evidence regarding the effect of PVE on tumor growth in both embolized and nonembolized liver lobes, as well as potential strategies to control tumor progression after PVE. A literature review was performed using MEDLINE with keywords related to experimental and clinical studies concerning PVE, portal vein ligation (PVL), and tumor growth. Cross-references and references from reviews were also checked. Clinical and experimental data suggest that tumor progression can occur after preoperative PVE in embolized and nonembolized liver segments. Clinical evidence indicating possible tumor progression in patients with colorectal metastases or with primary liver tumors is based on studies with small sample size. Although multiple studies demonstrated tumor progression, evidence concerning a direct increase in tumor growth rate as a result of PVE is circumstantial. Three possible mechanisms influencing tumor growth after PVE can be recognized, namely changes in cytokines or growth factors, alteration in hepatic blood supply and an enhanced cellular host response promoting local tumor growth after PVE. Post-PVE chemotherapy and sequential transcatheter arterial chemoembolization (TACE) before PVE have been proposed to reduce tumor mass after PVE. We conclude that tumor progression can occur after PVE in patients with colorectal metastases as well as in patients with primary liver tumors. However, further research is needed in order to rate this risk of tumor progression after PVE.Although preoperative portal vein embolization (PVE) is an effective means to increase future remnant liver (FRL) volume, little has been published on possible adverse effects. This review discusses the clinical and experimental evidence regarding the effect of PVE on tumor growth in both embolized and nonembolized liver lobes, as well as potential strategies to control tumor progression after PVE. A literature review was performed using MEDLINE with keywords related to experimental and clinical studies concerning PVE, portal vein ligation (PVL), and tumor growth. Cross-references and references from reviews were also checked. Clinical and experimental data suggest that tumor progression can occur after preoperative PVE in embolized and nonembolized liver segments. Clinical evidence indicating possible tumor progression in patients with colorectal metastases or with primary liver tumors is based on studies with small sample size. Although multiple studies demonstrated tumor progression, evidence concerning a direct increase in tumor growth rate as a result of PVE is circumstantial. Three possible mechanisms influencing tumor growth after PVE can be recognized, namely changes in cytokines or growth factors, alteration in hepatic blood supply and an enhanced cellular host response promoting local tumor growth after PVE. Post-PVE chemotherapy and sequential transcatheter arterial chemoembolization (TACE) before PVE have been proposed to reduce tumor mass after PVE. We conclude that tumor progression can occur after PVE in patients with colorectal metastases as well as in patients with primary liver tumors. However, further research is needed in order to rate this risk of tumor progression after PVE.

Assessment of Future Remnant Liver Function Using Hepatobiliary Scintigraphy in Patients Undergoing Major Liver Resection

Background99mTc-mebrofenin hepatobiliary scintigraphy (HBS) was used as a quantitative method to evaluate liver function. The aim of this study was to compare future remnant liver function assessed by 99mTc-mebrofenin hepatobiliary scintigraphy with future remnant liver volume in the prediction of liver failure after major liver resection.MethodsComputed tomography (CT) volumetry and 99mTc-mebrofenin hepatobiliary scintigraphy were performed prior to major resection in 55 high-risk patients, including 30 patients with parenchymal liver disease. Liver volume was expressed as percentage of total liver volume or as standardized future remnant liver volume. Receiver operating characteristic (ROC) curve analysis was performed to identify a cutoff value for future remnant liver function in predicting postoperative liver failure.ResultsPostoperative liver failure occurred in nine patients. A liver function cutoff value of 2.69%/min/m2 was calculated by ROC curve analysis. 99mTc-mebrofenin hepatobiliary scintigraphy demonstrated better sensitivity, specificity, and positive and negative predictive value compared to future remnant liver volume. Using 99mTc-mebrofenin hepatobiliary scintigraphy, one cutoff value suffices in both compromised and noncompromised patients.ConclusionPreoperative 99mTc-mebrofenin hepatobiliary scintigraphy is a valuable technique to estimate the risk of postoperative liver failure. Especially in patients with uncertain quality of the liver parenchyma, 99mTc-mebrofenin HBS proved of more value than CT volumetry.

Risk Assessment of Posthepatectomy Liver Failure Using Hepatobiliary Scintigraphy and CT Volumetry

A major part of morbidity and mortality after liver resections is caused by inadequate remnant liver function leading to liver failure. It is therefore important to develop accurate diagnostic tools that can predict the risk of liver resection–related morbidity and mortality. In this study, preoperative hepatobiliary scintigraphy of the future remnant liver and CT volumetric measurement of the future remnant liver were performed on patients who were to undergo liver resection. The accuracy of risk assessment for postoperative morbidity, liver failure, and mortality was evaluated. Methods: Forty-six patients who were scheduled for liver resection because of hepatobiliary tumors, including 17 patients with parenchymal disease (37%) and 13 patients with hilar cholangiocarcinoma (28%), were assessed preoperatively. Hepatobiliary scintigraphy was performed by drawing regions of interest around the future remnant to calculate 99mTc-mebrofenin uptake in it. CT volumetry was used to measure the volume of the total liver, the tumors, and the future remnant. Receiver-operating-characteristic analysis was performed to assess cutoff values for risk assessment of morbidity, liver failure, and mortality. Furthermore, univariate and multivariate analyses were performed to determine factors related to morbidity and mortality. Results: Morbidity and mortality rates were 61% and 11%, respectively. Liver failure occurred in 6 patients (13%). Significantly decreased uptake in the future remnant was found in patients in whom liver failure and liver failure–related mortality developed (P = 0.003 and 0.02, respectively). The volume of the future remnant was not significantly associated with any of the outcome parameters. In receiver-operating-characteristic analysis, uptake cutoff values for liver failure and liver failure–related mortality were 2.5%/min/body surface area and 2.2%/min/body surface area, respectively. In multivariate analysis, uptake was the only significant factor associated with liver failure. Conclusion: Preoperative measurement of 99mTc-mebrofenin uptake in the future remnant liver on hepatobiliary scintigraphy proved more valuable than measurement of the volume of the future remnant on CT in assessing the risk of liver failure and liver failure–related mortality after partial liver resection.

Nuclear Imaging Techniques for the Assessment of Hepatic Function in Liver Surgery and Transplantation

This review describes the application of 2 nuclear imaging techniques for assessment of hepatic function in the setting of liver surgery and transplantation. The biochemical and technical background, as well as the clinical applications, of 99mTc-labeled diethylenetriaminepentaacetic acid galactosyl human serum albumin (GSA) scintigraphy and hepatobiliary scintigraphy (HBS) with 99mTc-labeled iminodiacetic acid derivates is discussed. 99mTc-mebrofenin is considered the most suitable iminodiacetic acid agent for 99mTc-HBS. 99mTc-GSA scintigraphy and 99mTc-mebrofenin HBS are based on 2 different principles. 99mTc-GSA scintigraphy is a receptor-mediated technique whereas HBS represents hepatic uptake and excretion function. Both techniques are noninvasive and provide visual and quantitative information on both total and regional liver function. They can be used for preoperative assessment of future remnant liver function, follow-up after preoperative portal vein embolization, and evaluation of postoperative liver regeneration. In liver transplantation, these methods are used to assess graft function and biliary complications.

Controversies in the Use of Portal Vein Embolization

Background/Aims: Portal vein embolization (PVE) has reached worldwide acceptance to increase future remnant liver (FRL) volume before undertaking major liver resection. The aim of this overview is to point out and discuss current controversies in the application of PVE. Methods: Review of literature pertaining to techniques of PVE, complications, tumor proliferation, timing of resection, and hypertrophy response after PVE. Results: Procedure-related complications after PVE include hematoma, hemobilia, overflow of embolization material, and thrombosis of portal vein branch(es) of the non-embolized lobe. Persistence of the embolized, atrophic lobe is usually not harmful. Embolization of the portal branches to segment 4 in addition to embolization of the right portal trunk is controversial and is advised only in selected cases. It remains undecided whether embolization of the portal venous system is more effective in inducing hypertrophy of the FRL than ligation of the portal vein. Accelerated tumor growth after PVE is a major concern and requires consideration of post-PVE chemotherapy. A waiting time of 3 weeks between PVE and liver resection is advised. Post-hepatectomy regeneration is not hampered after preoperative PVE. Conclusion: PVE is a useful preoperative intervention to increase volume and function of the FRL. Further progress awaits clarification of the mechanisms of the hypertrophy response induced by PVE in conjunction with new embolization materials and protective chemotherapy.

Vascular Occlusion Techniques during Liver Resection

Control of bleeding from the transected liver basically consists of vascular inflow occlusion and control of hepatic venous backflow from the caval vein. Central venous pressure determines the pressure in the hepatic veins and is an extremely important factor in controlling blood loss through venous backflow. Vascular inflow occlusion (Pringle maneuver) involves clamping of the portal vein and the hepatic artery in the hepatic pedicle and gives rise to postischemic, reperfusion injury. Several strategies have been devised to reduce reperfusion injury (pharmacological interventions) or to increase ischemic tolerance of the liver (ischemic preconditioning). Intermittent clamping is recommended in complex liver resections or in patients with diseased livers. The combination of occlusion of vascular inflow and outflow of the liver results in total hepatic vascular exclusion (THVE) and is mainly used in tumors invading the caval vein. During THVE the liver can be cooled by hypothermic perfusion allowing for extended ischemia times. Selective THVE entails clamping of the main hepatic veins in their extrahepatic course, thus preserving caval flow. Safe liver surgery requires knowledge of the regular techniques of vascular occlusion for ‘on demand’ use when necessitated to reduce blood loss.

99mTc-GSA Scintigraphy with SPECT for Assessment of Hepatic Function and Functional Volume During Liver Regeneration in a Rat Model of Partial Hepatectomy

Small-animal models are crucial to gain insights in the complex recovery mechanisms of liver function during liver regeneration. 99mTc-Mebrofenin hepatobiliary scintigraphy (HBS) has been introduced for noninvasive assessment of liver function in the clinical setting as well as in experimental research. However, HBS is restricted to planar modalities in small animals because hepatic kinetics are generally too fast for SPECT acquisition. 99mTc-DTPA-galactosyl serum albumin (where DTPA is diethylenetriaminepentaacetic acid) (99mTc-GSA) scintigraphy is an alternative, receptor-mediated, noninvasive liver function test. After hepatic uptake, 99mTc-GSA remains trapped in the liver, which readily enables additional SPECT for the assessment of both liver function and liver functional volume within one test. In this study we evaluated the use of 99mTc-GSA scintigraphy combined with SPECT for the assessment of liver function and liver functional volume in normal and regenerating rat livers. Methods: The reproducibility of 99mTc-GSA scintigraphy and SPECT was investigated by repeated measurements within the same rat. For the assessment in a regenerating liver, 99mTc-GSA scintigraphy with SPECT was performed on 1, 3, 5, and 7 d (n = 6 rats per time point) after 70% partial hepatectomy (PH). Results: The correlation between repeated 99mTc-GSA measurements was strong (r = 0.75, P = 0.019). In normal rat livers, there was a strong, significant correlation between liver functional volume and conventional liver volume (r = 0.93; < 0.0001). The correlation between 99mTc-GSA uptake and liver volume was moderate (r = 0.62, P = 0.043). During the regeneration process, 99mTc-GSA uptake was significantly lower compared with both liver volume (P < 0.001) and liver functional volume (P < 0.001), when expressed as a percentage of baseline levels. There was a strong correlation between liver functional volume and conventional liver volume in the regenerating liver (r = 0.92, P < 0.0001). Conclusion: 99mTc-GSA scintigraphy combined with SPECT is a feasible, noninvasive method to assess hepatic functional volume in normal rat liver as well as in the regenerating rat liver. However, the hepatic 99mTc-GSA uptake as a liver function test seems to underestimate hepatic regeneration in comparison to liver volume.

Portal vein embolization induces more liver regeneration than portal vein ligation in a standardized rabbit model

BACKGROUND Portal vein ligation (PVL) and portal vein embolization (PVE) are used to induce hypertrophy of the future remnant liver before major liver resection. The aim of our study was to compare the hypertrophy response of the liver after PVL versus PVE in a rabbit model. METHODS Twenty rabbits were divided into an embolization group (n = 10) and a ligation group (n = 10). Both groups were divided in 2 subgroups of 5 rabbits that were humanely killed after days 7 and 14. The portal vein branches to the 3 cranial liver lobes (80% of the liver) were occluded. Regeneration of the caudal liver lobe was measured using volumetry based on computed tomography on days 3, 7, 10, and 14. Immunohistochemistry for Ki-67 and RAM11 was performed to quantify proliferating cells and macrophages. In addition, tissue tumor necrosis factor-α and interleukin-6 were assessed. RESULTS The caudal liver volume increased over time in both groups (P < .001), but this increase was greater after PVE than after PVL (P = .001) with a mean degree of hypertrophy of 15% ± 4% and 20% ± 2%, respectively. When comparing the groups on the separate time points, a difference was found on days 10 and 14 (P = .008 and P = .016, respectively). These data were confirmed by Ki-67 staining, which showed a greater number of proliferating hepatocytes on day 7 after embolization (P = .016). Cytokine analysis of liver tissue did not show significant differences between the ligation and embolization groups on days 7 and 14. CONCLUSION PVE is superior to PVL in terms of the extent of the hypertrophy response in this rabbit model.