Utility of Drug Depletion-Time Profiles in Isolated Hepatocytes for Accessing Hepatic Uptake Clearance: Identifying Rate-Limiting Steps and Role of Passive Processes

2012 ◽  
Vol 40 (8) ◽  
pp. 1596-1602 ◽  
Author(s):  
Emilie Jigorel ◽  
J. Brian Houston
1985 ◽  
Vol 249 (6) ◽  
pp. G711-G718 ◽  
Author(s):  
M. S. Anwer ◽  
L. M. Clayton

The role of extracellular Ca2+ in hepatic bile formation, biliary membrane permeability, and taurocholate (TC) transport was studied in isolated perfused rat livers and in isolated rat hepatocytes to determine the functional importance of paracellular permeability in biliary bile acid excretion. Each liver was perfused for 1 h with perfusate containing 1.3 mM Ca2+ (control period) followed by another hour with 1.3, 0.5, 0.1, 0.05, 0.03, or 0.01 mM Ca2+ (experimental period). Basal bile flow and biliary excretion of added TC declined significantly only at and below 0.05 mM perfusate Ca2+ and was associated with an increase in bile-to-perfusate concentration ratio of [3H]inulin (B/P inulin ratio). A twofold increase in the diffusional permeability coefficient at 0.05 mM and a sixfold increase at 0.03 and 0.01 mM perfusate Ca2+ could explain the increased in B/P inulin ratios. Time-dependent increases in cell-to-medium concentration ratios of inulin were less in the absence than in the presence of Ca2+. Hepatic uptake rates of TC determined in isolated hepatocytes and from perfusate disappearance of added TC and efflux rates of TC from preloaded hepatocytes were not significantly affected by Ca2+ removal. It is possible that the observed decline in biliary TC excretion at low perfusate Ca2+ is due to regurgitation of secreted TC back into the perfusate followed by reuptake. This was supported by an accumulation of perfusate radioactivity when TC uptake inhibitors (furosemide and bumetanide) were added to the perfusate (0.03 mM Ca2+) 60 min after the addition of [14C]TC.(ABSTRACT TRUNCATED AT 250 WORDS)


1997 ◽  
Vol 273 (5) ◽  
pp. G1023-G1030 ◽  
Author(s):  
Gert Fricker ◽  
Ralph Wössner ◽  
Jürgen Drewe ◽  
Ruth Fricker ◽  
James L. Boyer

The sulfated bile alcohol scymnol sulfate (ScyS), 3α,7α,12α,24ξ,26,27-hexahydroxy-5β-cholestane-26(27)-sulfate, is the major bile salt in bile of an elasmobranch, the little skate. To investigate hepatic transport of bile alcohols in skate liver, [3H]ScyS and a potential precursor, 3α,7α,12α-trihydroxy-5β-cholestane (chtriol), were used as model compounds. Their transport into isolated hepatocytes was partially saturable, temperature sensitive, and Na+ independent. The uptake of ScyS was inhibited by cholyltaurine, and uptake of cholyltaurine was inhibited by ScyS in a competitive manner. In contrast, uptake of chtriol was not inhibited by cholyltaurine, suggesting separate transport systems. ScyS and chtriol showed a choleretic effect in isolated perfused livers. When ScyS was added to the perfusate of isolated perfused livers, >25% was found in bile within 7 h. When chtriol was added to the perfusate, 10% of the dose was secreted into the bile mainly in the form of polar metabolites, whereas only nonmetabolized chtriol remained in the livers. The slow bile flow of 40–50 μl/h and the high recovery in the liver suggest that metabolism may be the rate-limiting step in the hepatic elimination of chtriol. The major metabolites secreted into bile were identified by mass spectrometry and chromatography as scymnol and ScyS. To study the enterohepatic circulation, [3H]ScyS or [3H]chtriol was administered into the duodenum of free-swimming skates, and bile was collected through exteriorized indwelling cannulas over a 4-day period. More than 90% of the radioactivity was recovered from bile, indicating that there was a highly effective absorption in the intestinal epithelium, as well as specific transport mechanisms for hepatic uptake and biliary secretion of these compounds. This is the first direct demonstration of an enterohepatic circulation for a bile alcohol sulfate in fish liver.


2021 ◽  
Vol 22 (15) ◽  
pp. 7765
Author(s):  
Youichirou Higashi ◽  
Takaaki Aratake ◽  
Takahiro Shimizu ◽  
Shogo Shimizu ◽  
Motoaki Saito

Stroke is a major cause of death worldwide, leading to serious disability. Post-ischemic injury, especially in the cerebral ischemia-prone hippocampus, is a serious problem, as it contributes to vascular dementia. Many studies have shown that in the hippocampus, ischemia/reperfusion induces neuronal death through oxidative stress and neuronal zinc (Zn2+) dyshomeostasis. Glutathione (GSH) plays an important role in protecting neurons against oxidative stress as a major intracellular antioxidant. In addition, the thiol group of GSH can function as a principal Zn2+ chelator for the maintenance of Zn2+ homeostasis in neurons. These lines of evidence suggest that neuronal GSH levels could be a key factor in post-stroke neuronal survival. In neurons, excitatory amino acid carrier 1 (EAAC1) is involved in the influx of cysteine, and intracellular cysteine is the rate-limiting substrate for the synthesis of GSH. Recently, several studies have indicated that cysteine uptake through EAAC1 suppresses ischemia-induced neuronal death via the promotion of hippocampal GSH synthesis in ischemic animal models. In this article, we aimed to review and describe the role of GSH in hippocampal neuroprotection after ischemia/reperfusion, focusing on EAAC1.


Cancers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 909
Author(s):  
Krzysztof Kotowski ◽  
Jakub Rosik ◽  
Filip Machaj ◽  
Stanisław Supplitt ◽  
Daniel Wiczew ◽  
...  

Glycolysis is a crucial metabolic process in rapidly proliferating cells such as cancer cells. Phosphofructokinase-1 (PFK-1) is a key rate-limiting enzyme of glycolysis. Its efficiency is allosterically regulated by numerous substances occurring in the cytoplasm. However, the most potent regulator of PFK-1 is fructose-2,6-bisphosphate (F-2,6-BP), the level of which is strongly associated with 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase activity (PFK-2/FBPase-2, PFKFB). PFK-2/FBPase-2 is a bifunctional enzyme responsible for F-2,6-BP synthesis and degradation. Four isozymes of PFKFB (PFKFB1, PFKFB2, PFKFB3, and PFKFB4) have been identified. Alterations in the levels of all PFK-2/FBPase-2 isozymes have been reported in different diseases. However, most recent studies have focused on an increased expression of PFKFB3 and PFKFB4 in cancer tissues and their role in carcinogenesis. In this review, we summarize our current knowledge on all PFKFB genes and protein structures, and emphasize important differences between the isoenzymes, which likely affect their kinase/phosphatase activities. The main focus is on the latest reports in this field of cancer research, and in particular the impact of PFKFB3 and PFKFB4 on tumor progression, metastasis, angiogenesis, and autophagy. We also present the most recent achievements in the development of new drugs targeting these isozymes. Finally, we discuss potential combination therapies using PFKFB3 inhibitors, which may represent important future cancer treatment options.


Biochemistry ◽  
2021 ◽  
Vol 60 (4) ◽  
pp. 259-273
Author(s):  
Margarita A. Tararina ◽  
Katie K. Dam ◽  
Manaswni Dhingra ◽  
Kim D. Janda ◽  
Bruce A. Palfey ◽  
...  

1989 ◽  
Vol 2 (1) ◽  
pp. 46-50 ◽  
Author(s):  
Pierluigi Nicotera ◽  
Mats Rundgren ◽  
David J. Porubek ◽  
Ian Cotgreave ◽  
Peter Moldeus ◽  
...  
Keyword(s):  

2001 ◽  
Vol 155 (3) ◽  
pp. 369-380 ◽  
Author(s):  
Hein Sprong ◽  
Sophie Degroote ◽  
Tijs Claessens ◽  
Judith van Drunen ◽  
Viola Oorschot ◽  
...  

A;lthough glycosphingolipids are ubiquitously expressed and essential for multicellular organisms, surprisingly little is known about their intracellular functions. To explore the role of glycosphingolipids in membrane transport, we used the glycosphingolipid-deficient GM95 mouse melanoma cell line. We found that GM95 cells do not make melanin pigment because tyrosinase, the first and rate-limiting enzyme in melanin synthesis, was not targeted to melanosomes but accumulated in the Golgi complex. However, tyrosinase-related protein 1 still reached melanosomal structures via the plasma membrane instead of the direct pathway from the Golgi. Delivery of lysosomal enzymes from the Golgi complex to endosomes was normal, suggesting that this pathway is not affected by the absence of glycosphingolipids. Loss of pigmentation was due to tyrosinase mislocalization, since transfection of tyrosinase with an extended transmembrane domain, which bypassed the transport block, restored pigmentation. Transfection of ceramide glucosyltransferase or addition of glucosylsphingosine restored tyrosinase transport and pigmentation. We conclude that protein transport from Golgi to melanosomes via the direct pathway requires glycosphingolipids.


1984 ◽  
Vol 50 (3) ◽  
pp. 255-265 ◽  
Author(s):  
E. Albano ◽  
G. Poli ◽  
A. Tomasi ◽  
A. Bini ◽  
V. Vannini ◽  
...  

Author(s):  
Mohammed Yousif Rashid ◽  
Anupa Gnawali

AbstractAcute pancreatitis is the most common iatrogenic dilemma of endoscopic retrograde cholangiopancreatography, and it is associated with significant morbidity and mortality. Several factors have been implicated in the pathogenesis of post-endoscopic retrograde cholangiopancreatography pancreatitis, and preventive measures were practiced accordingly. This study aims to refine the potential mechanisms that trigger post-endoscopic retrograde cholangiopancreatography pancreatitis and define the role of enteropeptidase in the pathogenesis of post-endoscopic retrograde cholangiopancreatography pancreatitis. Furthermore, address the role of a new novel medication known as SCO-792, a potent enteropeptidase inhibitor, in the prevention of post-endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis.Post-endoscopic retrograde cholangiopancreatography pancreatitis is caused by premature activation of the pancreatic enzymes within the pancreatic parenchyma. This activation is either an autoactivation due to direct provocation of intra-acinar enzymes as a result of the procedure or due to activation by enterpeptidase, a rate-limiting enzyme. Endoscopic retrograde cholangiopancreatography interjects duodenal juice that is rich in enterokinase into the pancreatic-biliary tract, which in turn leads to intra-ductal activation of trypsinogen and subsequent enzymes. Given the vital role of enterokinase in initiating the pathogenesis of pancreatitis, enteropeptidase inhibition may prevent and reduce the severity of post-endoscopic retrograde cholangiopancreatography pancreatitis.SCO-792, a novel enteropeptidase inhibitor, is developed by SCOHIA Pharma, and pre-clinical trials confirmed its efficacy in inhibiting enteropeptidase. Studies are needed to confirm the efficacy of enteropeptidase inhibitors in preventing post-endoscopic retrograde cholangiopancreatography pancreatitis.


2021 ◽  
Author(s):  
Alexandros Adamis ◽  
Astrid Veronig ◽  
Tatiana Podladchikova ◽  
Karin Dissauer ◽  
Rositsa Miteva ◽  
...  

<p><strong>We present a statistical study on the early evolution of coronal mass ejections (CMEs), to better understand the effect of CME (over)- expansion and how it relates to the production of Solar Energetic Particle (SEP) events. We study the kinematic CME characteristics in terms of their radial and lateral expansion, from their early evolution in the Sun’s atmosphere as observed in EUV imagers and coronagraphs. The data covers 72 CMEs that occurred in the time range of July 2010 to September 2012, where the twin STEREO spacecraft where in quasiquadrature </strong><strong>to the Sun-Earth line. From the STEREO point-of-view, the CMEs under study were observed close to the limb. We calculated the radial and lateral height (width) versus time profiles and derived the corresponding peak and mean velocities, accelerations, and angular expansion rates, with particular emphasis on the role of potential lateral overexpansion in the early CME evolution. We find high correlations between the radial and lateral CME velocities and accelerations. CMEs that are associated tend to be located at the high-value end of the distributions of velocities, widths, and expansion rates compared to nonSEP associated events.<br></strong></p>


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