In vivo assessment of nodularin-induced hepatotoxicity in the rat using magnetic resonance techniques (MRI, MRS and EPR oximetry)

Comprehensive insights into the occurrence and toxicological issues of nodularins

The occurrence of cyanobacterial toxins is being increasingly reported. Nodularins (NODs) are one of the cyanotoxins group mainly produced by Nodularia spumigena throughout the world. NODs may exert adverse effects on animal and human health, and NOD-R variant is the most widely investigated. However, research focused on them is still limited. In order to understand the realistic risk well, the aim of this review is to compile the available information in the scientific literature regarding NODs, including their sources, distribution, structural characteristics, physicochemical properties, biosynthesis and degradation, adverse effects in vitro and vivo, and toxicokinetics. More data is urgently needed to integrate the cumulative or synergistic effects of NODs on different species and various cells to better understand, anticipate and aggressively manage their potential toxicity after both short- and long-term exposure in ecosystem, and to minimize or prevent the adverse effects on human health, environment and the economy.

Cyanobacterial Toxins in Freshwater and Food: Important Sources of Exposure to Humans

A recent ecological study demonstrated a significant association between an increased risk of nonalcoholic liver disease mortality and freshwater cyanobacterial blooms. Moreover, previous epidemiology studies highlighted a relationship between cyanotoxins in drinking water with liver cancer and damage and colorectal cancer. These associations identified cyanobacterial blooms as a global public health and environmental problem, affecting freshwater bodies that are important sources for drinking water, agriculture, and aquafarms. Furthermore, as a result of climate change, it is expected that our freshwater environments will become more favorable for producing harmful blooms that produce various cyanotoxins. Food is an important source of cyanotoxin exposure to humans, but it has been less addressed. This paper synthesizes information from the studies that have investigated cyanotoxins in freshwater and food on a global scale. We also review and summarize the health effects and exposure routes of cyanotoxins and candidates for cyanotoxin treatment methods that can be applied to food.

Application of Electron Paramagnetic Resonance (EPR) Oximetry to Monitor Oxygen in Wounds in Diabetic Models

A lack of oxygen is classically described as a major cause of impaired wound healing in diabetic patients. Even if the role of oxygen in the wound healing process is well recognized, measurement of oxygen levels in a wound remains challenging. The purpose of the present study was to assess the value of electron paramagnetic resonance (EPR) oximetry to monitor pO2 in wounds during the healing process in diabetic mouse models. Kinetics of wound closure were carried out in streptozotocin (STZ)-treated and db/db mice. The pO2 was followed repeatedly during the healing process by 1 GHz EPR spectroscopy with lithium phthalocyanine (LiPc) crystals used as oxygen sensor in two different wound models: a full-thickness excisional skin wound and a pedicled skin flap. Wound closure kinetics were dramatically slower in 12-week-old db/db compared to control (db/+) mice, whereas kinetics were not statistically different in STZ-treated compared to control mice. At the center of excisional wounds, measurements were highly influenced by atmospheric oxygen early in the healing process. In pedicled flaps, hypoxia was observed early after wounding. While reoxygenation occurred over time in db/+ mice, hypoxia was prolonged in the diabetic db/db model. This observation was consistent with impaired healing and microangiopathies observed using intravital microscopy. In conclusion, EPR oximetry using LiPc crystals as the oxygen sensor is an appropriate technique to follow wound oxygenation in acute and chronic wounds, in normal and diabetic animals. Nevertheless, the technique is limited for measurements in pedicled skin flaps and cannot be applied to excisional wounds in which diffusion of atmospheric oxygen significantly affects the measurements.

Magnetic resonance imaging for rapid screening for the nephrotoxic and hepatotoxic effects of microcystins

In vivo visualization of kidney and liver damage by Magnetic Resonance Imaging (MRI) may offer an advantage when there is a need for a simple, non-invasive and rapid method for screening of the effects of potential nephrotoxic and hepatotoxic substances in chronic experiments. Here, we used MRI for monitoring chronic intoxication with microcystins (MCs) in rat. Male adult Wistar rats were treated every other day for eight months, either with MC-LR (10 μg/kg i.p.) or MC-YR (10 μg/kg i.p.). Control groups were treated with vehicle solutions. T1-weighted MR-images were acquired before and at the end of the eight months experimental period. Kidney injury induced by the MCs presented with the increased intensity of T1-weighted MR-signal of the kidneys and liver as compared to these organs from the control animals treated for eight months, either with the vehicle solution or with saline. The intensification of the T1-weighted MR-signal correlated with the increased volume density of heavily injured tubuli (R2 = 0.77), with heavily damaged glomeruli (R2 = 0.84) and with volume density of connective tissue (R2 = 0.72). The changes in the MR signal intensity probably reflect the presence of an abundant proteinaceous material within the dilated nephrons and proliferation of the connective tissue. T1-weighted MRI-is a valuable method for the in vivo screening of kidney and liver damage in rat models of intoxication with hepatotoxic and nephrotoxic agents, such as microcystins.

Application of in vivo EPR for tissue pO2 and redox measurements

The technique of electron paramagnetic resonance (EPR) spectroscopy is more than 50 years old, but only recently it has been used for in vivo studies. Its limited application in the past was due to the problem of high nonresonant dielectric loss of the exciting frequency because of high water content in biological samples. However, with the development of spectrometers working at lower frequencies (1,200 MHz and below) during the last 15 years, it is now possible to conduct in vivo measurements on a variety of animals and isolated organs. This is further facilitated by the development of new resonators with high sensitivity and appropriate stability for in vivo applications. It now has become feasible to obtain new insights into the complex aspects of physiology and pathophysiology using in vivo EPR. Among several important applications of this technique, the in vivo tissue pO(2) (partial pressure of oxygen) and redox measurements seem to be the most extensive use of this technique. In this chapter, we describe the procedure for in vivo pO(2) and redox measurements in animal models.

Repetitive tissue pO2 measurements by electron paramagnetic resonance oximetry: current status and future potential for experimental and clinical studies

Tissue oxygen plays a crucial role in maintaining tissue viability and in various diseases, including responses to therapy. Useful knowledge has been gained by methods that can give limited snapshots of tissue oxygen (e.g., oxygen electrodes) or evidence of a history of tissue hypoxia (e.g., EF5) or even indirect evidence by monitoring oxygen availability in the circulatory system (e.g., NMR methods). Each of these methods has advantages and significant limitations. EPR oximetry is a technique for direct measurement of tissue pO2, which has several advantages over the other existing methods for applications in which the parameter of interest is the pO2 of tissues, and information is needed over a time course of minutes to hours, and/or for repetitive measurements over days or weeks or years. The aim of this article is to provide an overview of EPR oximetry using particulates to readers who are not familiar with this technique and its potential in vivo and clinical applications. The data presented here are from the experiments currently being carried out in our laboratory. We are confident that in vivo EPR oximetry will play a crucial role in the understanding and clinical management of various pathologies in the years to come.

High-resolution visualization of oxygen distribution in the liver in vivo

Microcirculatory failure after stress events results in mismatch in oxygen supply and demand. Determination of tissue oxygen distribution in vivo may help elucidate mechanisms of injury, but present methods have limited resolution. Male Sprague-Dawley rats were anesthetized, prepared for intravital microscopy, and received intravenously the oxygen-sensitive fluorescent dye Tris(1,10-phenanthroline)ruthenium(II) chloride hydrate [Ru(phen)3(2+)]. An impaired hepatic oxygen distribution was induced by either phenylephrine or hemorrhage. Intensity of Ru(phen)3(2+) fluorescence was compared with NADH autofluorescence indicating changes in the mitochondrial redox potential. Ethanol was injected to affect the NADH-to-NAD+ ratio without altering the P(O2). Infusion of Ru(phen)3(2+) resulted in a heterogeneous fluorescence under baseline conditions reflecting the physiological acinar P(O2) distribution. A decrease in oxygen supply due to phenylephrine or hemorrhage was paralleled by an increase in Ru(phen)3(2+) and NADH fluorescence reflecting an impaired mitochondrial redox state. Ethanol did not alter Ru(phen)3(2+) fluorescence but increased NADH fluorescence indicating independence of P(O2) and redox state imaging. Intravenous administration of Ru(phen)3(2+) for intravital videomicroscopy represents a new method to visualize the hepatic tissue P(O2). Combined with NADH autofluorescence, it provides additional information regarding the tissue redox state.