Comparison of uptake kinetics in freshly isolated suspensions and short-term primary cultures of rat hepatocytes

The apparent kinetics of uptake of various model substrates were examined for hepatocytes in suspension and primary culture up to 72 h. The ability of hepatocytes to take up taurocholate and ouabain was decreased in culture. Vmax for uptake of both substrates diminished rapidly with increasing time in culture. An increase in Km was observed in cultures 6 h after plating, but there was no further change with prolongation of culture time. The decrease of uptake of taurocholate and ouabain during culture may be due to the reduction in the number of transport carriers plus a decrease of affinity of the carrier to substrates. The nonsaturable component of cadmium uptake was much reduced in cultured cells compared with the suspensions. The saturable process was lower in 6 h culture but increased to a level comparable with the fresh cells at longer culture time. No significant change was found in the Km between suspensions and cultures. Uptake of alpha-aminoisobutyric acid was greater in culture while that of 3-O-methyl-D-glucose was relatively stable but about one-half that found in cell suspension. Thus, uptake of two substrates, taurocholate and ouabain, is clearly compromised with increasing time in primary culture, while uptake of the other substrates does not reflect such a dramatic decrease. It is therefore apparent that the cell preparation of choice in uptake studies depends on the substrate and the nature of the experiments.     

N-acetyltransferase polymorphism in Thailand

A series of 222 individuals from the northeastern provinces of Thailand were studied with respect to acetylator phenotypes. Among individuals of pure Thai descent 55.5% were rapid acetylators. The corresponding figure for Chinese was 66.0%. There were no significant differences between Thais and Chinese. The result shows a lower frequency of rapid acetylators in Thais than in previous reports on Thais.     

Tetrahydrocurcumin Protects against Cadmium-Induced Hypertension,Raised Arterial Stiffness and Vascular Remodeling in Mice

Background

Cadmium (Cd) is a nonessential heavy metal, causing oxidative damage to various tissues and associated with hypertension. Tetrahydrocurcumin (THU), a major metabolite of curcumin, has been demonstrated to be an antioxidant, anti-diabetic, anti-hypertensive and anti-inflammatory agent. In this study, we investigated the protective effect of THU against Cd-induced hypertension, raised arterial stiffness and vascular remodeling in mice.

Methods

Male ICR mice received CdCl₂ (100 mg/l) via drinking water for 8 weeks. THU was administered intragastrically at dose of 50 or 100 mg/kg/day concurrently with Cd treatment.

Results

Administration of CdCl₂ significantly increased arterial blood pressure, blunted vascular responses to vasoactive agents, increased aortic stiffness, and induced hypertrophic aortic wall remodeling by increasing number of smooth muscle cells and collagen deposition, decreasing elastin, and increasing matrix metalloproteinase (MMP)-2 and MMP-9 levels in the aortic medial wall. Supplementation with THU significantly decreased blood pressure, improved vascular responsiveness, and reversed the structural and mechanical alterations of the aortas, including collagen and elastin deposition. The reduction on the adverse response of Cd treatment was associated with upregulated eNOS and downregulated iNOS protein expressions, increased nitrate/nitrite level, alleviated oxidative stress and enhanced antioxidant glutathione. Moreover, THU also reduced the accumulation of Cd in the blood and tissues.

Conclusions

Our results suggest that THU ameliorates cadmium-induced hypertension, vascular dysfunction, and arterial stiffness in mice through enhancing NO bioavailability, attenuating oxidative stress, improving vascular remodeling and decreasing Cd accumulation in other tissues. THU has a beneficial effect in moderating the vascular alterations associated with Cd exposure.     

Does vibration cause poststenotic dilatation in vivo and influence atherogenesis in cholesterol-fed rabbits?

Arterial post-stenotic dilatation (PSD) is a fusiform swelling immediately down-stream to a stenosis. It is characterized by the presence of turbulent blood flow and wall vibration which has been claimed by others to be causal by producing structural weakening. We tested the hypothesis that vibration causes PSD in vivo by attaching electromagnetic and pneumatic vibrators to the aortic wall in chronic rabbits. We also observed whether mechanical vibration of the aorta in vivo influenced the distribution of oil-red-O lesions during one percent dietary cholesterol feeding. Low mass vibration gauges were developed to measure the vibration. Electromechanical vibrators having a ceramic magnet slug within a coil supplied with 50 Hz were glued to the aorta of chronic rabbits and the vibration maintained for an average of 8 weeks. Despite greater amounts of energy imparted to the wall there was no dilatation or difference in oil-red-O staining from the controls. Five weeks vibration at 100 Hz and an amplitude equal to the normal diameter pulse also produced no dilatation. We conclude that vibration does not cause PSD in vivo and suggest that its cause is likely to involve the vascular muscle stimulated by the effect of turbulent flow on the endothelium.     

Protective effect of ascorbic acid on cadmium-induced hypertension and vascular dysfunction in mice

Cadmium (Cd) is one of the most important environmental pollutants that cause a number of adverse health effects in humans and animals. Recent studies have shown that Cd-induced oxidative damage within the vascular tissues results in vascular dysfunction. The current study was aimed to investigate whether ascorbic acid could protect against Cd-induced vascular dysfunction in mice. Male ICR mice were received CdCl₂ (100 mg/l) via drinking water for 8 weeks alone or received ascorbic acid supplementation at doses of 50 and 100 mg/kg/day for every other day. Results showed that Cd administration increased arterial blood pressure and blunted the vascular responses to vasoactive agents. These alterations were related to increased superoxide production in thoracic aorta, increased urinary nitrate/nitrite, increased plasma protein carbonyl, elevated malondialdehyde (MDA) concentrations in plasma and tissues, decreased blood glutathione (GSH), and increased Cd contents in blood and tissues. Ascorbic acid dose-dependently normalized the blood pressure, improved vascular reactivities to acetylcholine (ACh), phenylephrine (Phe) and sodium nitroprusside (SNP). These improvements were associated with significant suppression of oxidant formation, prevention of GSH depletion, and partial reduction of Cd contents in blood and tissues. The findings in this study provide the first evidence in pharmacological effects of ascorbic acid on alleviation of oxidative damage and improvement of vascular function in a mouse model of Cd-induced hypertension and vascular dysfunction. Moreover, our study suggests that dietary supplementation of ascorbic acid may provide beneficial effects by reversing the oxidative stress and vascular dysfunction in Cd-induced toxicity.     

Chemical-induced interference with hepatocellular transport. Role in cholestasis

Transport of endogenous chemicals both into (at the basolateral membrane) and out of (at the canalicular membrane) hepatocytes plays an important role in bile formation. Hence, interference with these processes, for example by chemicals, may result in reduced bile output. Several different systems are available for the study of transport and hence chemicals that may interfere with the process. These have been used to varying degrees with isolated hepatocytes probably being the most popular over recent years. It is likely that hepatocyte couplets and highly purified plasma membrane vesicles will be increasingly employed over the ensuing years. The inhibitory effects of several chemicals on the transport of bile acids have been demonstrated with indications that this may help to account for some aspects of chemical-induced hepatobiliary dysfunction. For example, the inhibition of transport of bile acids by cyclosporin A is consistent with the reported pattern of liver dysfunction in patients on high doses of this immunosuppressant. Investigation into chemical-induced interference with electrolyte transport has yet to receive the same degree of attention. This and other aspects have been suggested as deserving of and likely to be subjected to more intensive experimentation over the next few years.     

Crucial role of heme oxygenase-1 on the sensitivity of cholangiocarcinoma cells to chemotherapeutic agents

Cancer cells acquire drug resistance via various mechanisms including enhanced cellular cytoprotective and antioxidant activities. Heme oxygenase-1 (HO-1) is a key enzyme exerting potent cytoprotection, cell proliferation and drug resistance. We aimed to investigate roles of HO-1 in human cholangiocarcinoma (CCA) cells for cytoprotection against chemotherapeutic agents. KKU-100 and KKU-M214 CCA cell lines with high and low HO-1 expression levels, respectively, were used to evaluate the sensitivity to chemotherapeutic agents, gemcitabine (Gem) and doxorubicin. Inhibition of HO-1 by zinc protoporphyrin IX (ZnPP) sensitized both cell types to the cytotoxicity of chemotherapeutic agents. HO-1 gene silencing by siRNA validated the cytoprotective effect of HO-1 on CCA cells against Gem. Induction of HO-1 protein expression by stannous chloride enhanced the cytoprotection and suppression of apoptosis caused by anticancer agents. The sensitizing effect of ZnPP was associated with increased ROS formation and loss of mitochondrial transmembrane potential, while Gem alone did not show any effects. A ROS scavenger, Tempol, abolished the sensitizing effect of ZnPP on Gem. Combination of ZnPP and Gem enhanced the release of cytochrome c and increased p21 levels. The results show that HO-1 played a critical role in cytoprotection in CCA cells against chemotherapeutic agents. Targeted inhibition of HO-1 may be a strategy to overcome drug resistance in chemotherapy of bile duct cancer.     

Cellular adaptation mediated through Nrf2-induced glutamate cysteine ligase up-regulation against oxidative stress caused by iron overload in β-thalassemia/HbE patients

Oxidative stress caused as a result of iron overload is implicated in clinical manifestation of beta-thalassemia/haemoglobin E (β-Thal/HbE). In this study, we investigated the cellular adaptation against oxidative stress in β-Thal/HbE patients. Twenty-four paediatric β-Thal/HbE patients and 22 healthy controls were recruited in the study. Blood samples from patients exhibited iron overload, elevation of lipid peroxidation, and marked diminution in the reduced glutathione (GSH) level. However, expression of glutamate-cysteine ligase catalytic (GCLC) subunit, a key enzyme in GSH biosynthesis, was up-regulated when compared with that in controls. GCLC protein levels were correlated with serum iron. There was an enhanced binding activity of the oligonucleotide probe for Nrf2-driven antioxidant response element (ARE) to nuclear protein from blood mononuclear cells of thalassemia subjects. In conclusion, β-Thal/HbE patients exhibit elevated plasma levels of GCLC expression and Nrf2-ARE binding activity, which may account for their adaptive survival response to oxidative stress.