Simultaneous measurement of mitochondrial and microsomal cytochrome levels in human liver biopsy

Digital Microfluidics-Enabled Analysis of Individual Variation in Liver Cytochrome P450 Activity

The superfamily of hepatic cytochrome P450 (CYP) enzymes is responsible for the intrinsic clearance of the majority of therapeutic drugs in humans. However, the kinetics of drug clearance via CYPs varies significantly among individuals due to both genetic and external factors, and the enzyme amount and function are also largely impacted by many liver diseases. In this study, we developed a new methodology, based on digital microfluidics (DMF), for rapid determination of individual alterations in CYP activity from human-derived liver samples in biopsy-scale. The assay employs human liver microsomes (HLMs), immobilized on magnetic beads to facilitate determination of the activity of microsomal CYP enzymes in a parallelized system at physiological temperature. The thermal control is achieved with the help of a custom-designed, inkjet-printed microheater array modularly integrated with the DMF platform. The CYP activities are determined with the help of prefluorescent, enzyme-selective model compounds by quantifying the respective fluorescent metabolites based on optical readout in situ. The selectivity and sensitivity of the assay was established for four different CYP model reactions, and the diagnostic concept was validated by determining the interindividual variation in one of the four model reaction activities, that is, ethoxyresorufin O-deethylation (CYP1A1/2), between five donors. Overall, the developed protocol consumes only about 15 μg microsomal protein per assay. It is thus technically adaptable to screening of individual differences in CYP enzyme function from biopsy-scale liver samples in an automated fashion, so as to support tailoring of medical therapies, for example, in the context of liver disease diagnosis.

Central role of mitochondria in metabolic regulation of liver pathophysiology

Mitochondria play a central role in cellular energy metabolism. Oxidative phosphorylation occurs in the electron transport system of the inner mitochondrial membrane. Cytochrome aa3, b and c1 are encoded by mitochondrial DNA whereas cytochrome c is encoded by the nuclear gene, and these mitochondrial-DNA dependent cytochromes are decreased and electron transport at complex II, III and IV is disturbed in liver carcinomas and during carcinogenesis. The more the decreased cytochrome and oxidase activity are seen, the more significant is the increase in reactive oxygen species (ROS) production. ROS produced in mitochondria may be the main cause of nuclear-gene mutation in carcinogenesis. The mitochondrial dysfunction and overproduction of ROS plays a key role in progression of chronic hepatitis C and ethanol-induced liver injury. Ethanol also causes bacterial translocation in the intestine and the resulting lipopolysaccharides (LPS) activates Kupffer cells to produce pro-inflammatory cytokines. We suspect that non-alcoholic steatohepatitis (NASH) also is the result of increased ROS production in Kupffer cells and hepatocytes.

Estimated hepatic oxygen consumption in patients with chronic liver diseases as assessed by organ reflectance spectrophotometry

We investigated the estimated hepatic oxygen consumption by reflectance spectrophotometry during peritoneoscopy and the rate of in vitro oxygen consumption of liver slices obtained by liver biopsy using the oxygen electrode apparatus in patients with chronic liver diseases. The estimated hepatic oxygen consumption decreased concomitantly with the decrease in blood supply, expressed as the regional hepatic blood hemoglobin concentration, and it was significantly decreased in cirrhosis compared to chronic hepatitis. The estimated hepatic oxygen consumption also was significantly correlated with the serum albumin level, 15-min retention rate of indocyanine green, and prothrombin time. There was no correlation between the estimated hepatic oxygen consumption calculated from the reflectance spectra and the rate of in vitro oxygen consumption measured by the oxygen electrode apparatus. Most cirrhotic liver slices had a respiratory rate comparable to that in chronic hepatitis. Thus, it is concluded that the reduction of estimated hepatic oxygen consumption in cirrhosis of the liver is mainly due to the reduction of oxygen supply secondary to the decrease of hepatic blood flow.

Influence of liver disease and environmental factors on hepatic monooxygenase activity in vitro

The effects of liver disease and environmental factors on hepatic microsomal cytochrome P-450 content, NADPH-cytochrome c reductase (reductase) activity and aryl hydrocarbon hydroxylase (AHH) activity have been simultaneously investigated in 70 patients undergoing diagnostic liver biopsy. The activity of reductase was not significantly affected by the presence of liver disease or any of the environmental factors studied. Cytochrome P-450 content decreased with increasing severity of liver disease whereas AHH activity was only significantly reduced in biopsies showing hepatocellular destruction. None of the parameters of monooxygenase activity varied significantly with the age or sex of the patients. Alcohol excess was associated with decreased cytochrome P-450 content and AHH activity and this effect was independent of the histological status of the biopsy. Both high caffeine intake and cigarette smoking increased AHH activity in the absence of any change in cytochrome P-450 content. There was a positive correlation between the number of meat meals eaten per week and cytochrome P-450 content. Chronic treatment with enzyme-inducing anticonvulsants appeared to increase both cytochrome P-450 content and AHH activity. Despite differential effects of liver disease and environmental influences on cytochrome P-450 content and AHH activity there was a highly significant correlation between the two parameters. The results of the present study correlate well with the known effects of disease and environment on drug metabolism in vivo.

Hemoperfusion, rate of oxygen consumption and redox levels of mitochondrial cytochrome c (+c1) in liver in situ of anesthetized rat measured by reflectance spectrophotometry

Utilizing reflectance spectrophotometry, hemoperfusion, rate of oxygen consumption and redox level of mitochondrial cytochrome c (+c1) in livers in situ of anesthetized rats were measured. The transition to the anoxic state was induced by raising the pressure on the liver surface to more than the hepatic blood pressure by pressing with the tip of the optical guide of the reflectance spectrophotometer. During this transition, the average oxygen saturation of hemoglobin in the liver in situ decreased linearly with time until it became 10--20% of the total. This was followed by reduction of mitochondrial cytochrome c (+c1), which reached completion in 10--20 s. The measured O2 consumption rate remained constant until the percentage of oxyhemoglobin in situ decreased to a critical level. There was then a decrease in the rate of O2 consumption which was accompanied by a progressive reduction of cytochrome c (+c1). It was shown that amounts of hemoglobin and mitochondrial respiratory chain cytochromes in the liver in situ could be measured non-invasively and could provide important signals for vital cellular functions. The changes in hemoperfusion and rate of O2 consumption of the liver in situ following ethanol ingestion were also shown in rats, and are briefly discussed with respect to possible application of this method to study the pathophysiology of tissues.

Monooxygenase activity of human liver in microsomal fractions of needle biopsy specimens

1 Methods are described for the determination of mixed function oxidase activity in microsomal fractions from percutaneous needle biopsies of human liver. 2 Activities of needle biopsy samples were comparable with those of wedge biopsy sample obtained at laparotomy from different subjects. 3 Although cytochrome P-450 content of liver from rat and man was similar, human AHH activity was only 10% of that in the rat. 4 In biopsies with preserved hepatic architecture, AHH activity and cytochrome P-450 content showed a significant positive correlation. 5 Cigarette smoking significantly increased both AHH activity and turnover number, but not cytochrome P-450 content, of biopsies with normal architecture. 6 The presence of liver disease caused a significant decrease in AHH activity and cytochrome P-450 content.