Histological evidence for dissociation of lipid peroxidation and cell necrosis in bromotrichloromethane hepatotoxicity in the perfused rat liver

Chromophore-Modified Highly Selective Ratiometric Upconversion Nanoprobes for Detection of ONOO- -Related Hepatotoxicity In Vivo

Acute hepatitis is a major problem affecting public health and has attracted more and more attention. Generally, as the standard means, blood tests are taken for evaluating hepatitis. However, such tests fail to accurately reflect the level of hepatitis in vivo. Herein, two highly selective ratiometric fluorescent probes are designed to track peroxynitrite (ONOO^- ) as the hepatitis indicator, and further evaluate acute liver injury in vivo through dye-grafted upconversion nanoparticles (UCNPs). Specifically, upconversion luminescence of nanoprobes at 540 or 660 nm can be quenched by the designed and synthesized chromophore E-CC or H-CC, that can be destroyed by ONOO^- via energy transfer (ET) process, while the upconversion luminescence intensity at 810 nm remains the same. Thus, the developed nanoprobes can be used for ratiometric detection (I₅₄₀ /I₆₆₀ or I₆₆₀ /I₈₁₀ ) of ONOO^- . Moreover, the developed near infrared ratiometric nanoprobes can highly selectively detect ONOO^- , which can eliminate the interference of HOCl and SO₃^2- . Finally, it is demonstrated that this highly selective ratiometric nanosystem can achieve effective detection of ONOO^- in living cells and CCl₄ -induced acute liver injury models. It provides some reference value for clinical detection of hepatotoxicity.

Computational experiments reveal plausible mechanisms for changing patterns of hepatic zonation of xenobiotic clearance and hepatotoxicity

No concrete, causal, mechanistic theory is available to explain how different hepatic zonation patterns of P450 isozyme levels and hepatotoxicity emerge following dosing with different compounds. We used the synthetic method of modeling and simulation to discover, explore, and experimentally challenge concrete mechanisms that show how and why biomimetic zonation patterns can emerge and change within agent-based analogues, expecting that those mechanisms may have counterparts in rats. Mobile objects map to compounds. One analogue represents a cross-section through a lobule. It is comprised of 460 identical, quasi-autonomous functional units called sinusoidal segments (SSs). SSs detect and respond to compound-generated response signals and the local level of an endogenous gradient. Each SS adapts by using those signals to adjust (or not) the probability that it will clear a detected compound during the next simulation cycle. The adjustment decision is based on the value of a biomimetic algorithm that is based on an assumed, evolution imposed, genetic mandate that normal hepatocytes resist increasing the cost of their actions. The algorithm estimates the long-term, discounted cost to a given SS of continuing to use its current clearance effort. Upon compound exposure, lobular analogues developed a variety of clearance and hepatotoxicity patterns that were strikingly similar to those reported in the literature. A degree of quantitative validation was achieved against data on hepatic zonation of CYP1A2 mRNA expression caused by three different doses of TCDD (2,3,7,8-tetracholorodibenzo-p-dioxone).

[Learning toxicology from carbon tetrachloride-induced hepatotoxicity]

The mechanism of carbon tetrachloride (CCl4)-induced hepatotoxicity, especially necrosis and fatty liver, has long been a challenging subject of many researchers from various fields over the past 50 years. Even though the mechanisms of tissue damages are different among chemicals and affected tissues, CCl4 has played a role as a key substance of tissue injury. A number of studies have been conducted and various hypotheses have been raised. As a result, several important basic mechanisms of tissue damages have emerged, involving metabolic activation, reactive free radical metabolites, lipid peroxidation, covalent binding and disturbance of calcium homeostasis. Recent studies also revealed inflammation and regeneration as important modification factors in the tissue injury. The author attempted to summarize the history of CCl4 research with some emphasis on the experiments done by the author and his colleagues. Their studies with isolated perfused rat liver suggest that covalent binding of CCl4 metabolites rather than lipid peroxidation has a significant role in the production of centrilobular necrosis following CCl4 administration. Further studies are necessary to unveil detailed mechanisms of hepatocyte necrosis induced by CCl4.

Histochemical visualization of oxidant stress

Free radicals induce oxidative modification in distinct components of the living matter (lipid, proteins, and DNA). For qualitative and quantitative determination of free radical-induced modifications, different, more or less sensitive biochemical methods are available. Because of the high reactivity and short life of free radicals, ongoing oxidative damage is generally analyzed by measurement of secondary products-such as H(2)O(2), oxidized proteins, peroxidized lipids, and their breakdown products, oxidized DNA-or by fluorographic analysis in combination with fluorescent dyes such as dichlorofluorescin (DCFH). In addition, the determination of free radical-related oxidation products is usually carried out in plasma, urine, or, less frequently, in bioptic material. Consequently, biochemical data seldom reflect the effects of free radical insults in situ. The histochemical visualization of selected molecular markers of oxidative damage can often provide more valuable information concerning the in vivo distribution of oxidative processes. This review summarizes the methods currently available for histochemical detection and indirect visualization of free radical-induced alterations in tissues and isolated cells.

Development of a small-scale bioreactor for drug metabolism studies maintaining hepatospecific functions

1. The aim of the study was the development of a small-scale liver cell bioreactor maintaining tissue monoxygenase activity and hepatospecific activities over at least 2 weeks. 2. For characterization the antihypertensive drug urapidil was used as a model compound to study maintenance of metabolic activity. Tissue-specific parameters assessed included urea and albumin secretion as well as cellular integrity. The problem of the use of serum in bioreactor cultures is addressed. 3. Bioreactor runs could be performed in serum- and lactate-free cultures with a joint recovery of oxidative biotransformation capacity for urapidil as well as tissue-specific markers. LDH release was reduced with older cultures. Fibronectin was shown as a contributing factor for cell attachment. 4. In the present study the design and function of a modular, small-scale-type bioartificial liver cell culture model is thus described lending itself for drug metabolism studies but maintaining also typical hepatospecific properties.

Carbon tetrachloride-induced cell death in perfused livers from phenobarbital-pretreated rats under hypoxic conditions and various ionic milieu. Further evidence for calcium-dependent irreversible changes

The role of Ca2+ in the initiation of carbon tetrachloride (CCl4) hepatotoxicity was studied using perfused livers isolated from phenobarbital-pretreated rats in a single-pass system. Krebs-Henseleit bicarbonate buffer containing 1.3 mM CaCl2 (KHB) was the regular ionic milieu. In the liver perfused with fructose-supplemented regular KHB equilibrated with 95% N2-5% CO2, infusion of 0.5 mM CCl4 caused an early uptake of Ca2+ coupled with K+ leakage and Na+ uptake within the infusion time of 30 min, which was followed by a marked lactic dehydrogenase (LDH) leakage into the effluent perfusate and further Ca2+ uptake by the liver. With Ca(2+)-free medium, the prenecrotic K+ leakage and the successive LDH leakage were suppressed markedly. However, a perfusate exchange from regular to Ca(2+)-free KHB at the end of the prenecrotic stage did not protect against the LDH leakage, and the perfusate exchange conversely did not produce LDH leakage. Perfusion of the liver with high K+(Cl-) medium under 20% O2 markedly suppressed CCl4-induced LDH leakage even in the presence of Ca2+, whereas once CCl4 had acted under regular KHB perfusion, changing the medium to high K+ did not further prevent the LDH leakage. High K(+)-lactobionic acid medium containing Ca2+ and supplemented with fructose also suppressed LDH leakage under 95% N2 without the accompanying prenecrotic Ca2+ uptake. However, a change of the medium after CCl4 infusion to regular KHB containing Ca2+ caused LDH leakage and K+ leakage, with Ca2+ uptake. The prevention of LDH leakage in a different ionic milieu may not be due to suppression of CCl4 bioactivation, since the liver cytochrome P450 content decreased to a similar extent. These findings suggest that entry of extracellular Ca2+ into hepatocytes coupled with K+ leakage and Na+ entry is a prerequisite for CCl4-induced hepatocyte death and that association of Ca2+ with a CCl4-derived radical-mediated process may be necessary for early and irreversible plasma membrane damage.