Carbon monoxide and cultured rat heart cells. I. Inhibition of cell growth and maintenance of beating rate

Carbon monoxide cardiotoxicity

Cardiac dysfunction including arrhythmias and myocardial ischemia have often been reported in carbon monoxide poisoning; scattered punctiform hemorrhages throughout the heart have been documented in autopsy samples. An appropriate diagnostic approach is crucial to assess carbon monoxide cardiac damage. This evaluation may be confounded by several factors, including the absence of overt symptoms and of specific ischemic changes in the electrocardiogram. In experimental studies, laboratory animals can develop cardiac changes similar to those seen in humans and therefore proved to be useful models to study the effects and the mechanisms of cardiac damage due to carbon monoxide. These investigations, as well as others performed in vitro, provide support for a direct action of carbon monoxide on the heart, in addition to systemic hypoxia produced by carboxyhemoglobin formation. This review focuses on the diagnostic aspects of carbon monoxide cardiotoxicity. Experimental results obtained in animals and in vitro models are also discussed.

Developmental effects of boric acid in rats related to maternal blood boron concentrations

Timed-mated Sprague-Dawley rats (60/group) were exposed to boric acid (BA) from gestational days (gd) 0 to 20. BA added to the diet (0, 0.025, 0.050, 0.075, 0.1, or 0.2%) yielded boron (B) intakes of <0.35 (control), 3, 6, 10, 13, or 25 mg B/kg body wt/d. Approximately one-half of the dams/group were terminated on gd 20, maternal whole blood collected and frozen, and prenatal outcome (fetal growth, viability, and morphology) evaluated. Remaining dams received control diet beginning on gd 20, and litters were monitored throughout lactation. Blood samples were prepared by a high-temperature alkaline ashing method and analyzed for B by inductively coupled plasma (ICP) optical emission spectrometry. On gd 20, blood B concentrations of 1.27 +/- 0.298 and 1.53 +/- 0.546 microg B/g were associated with the no-observed-adverse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) (10 and 13 mg B/kg/d, respectively) for developmental toxicity. Developmental toxicity persisted postnatally only at 25 mg B/kg/d, a dose associated with >10-fold increase in maternal blood B (2.82 +/- 0.987 vs. 0.229 +/- 0.143 microg B/g for controls). Maternal blood B concentrations were: 1. Significantly elevated in all BA-exposed groups. 2. Positively correlated with maternal BA intake. 3. Inversely correlated with fetal body weight at doses above the NOAEL.

Effects of carbon monoxide on cardiac muscle cells in culture

Embryonic rat cardiac muscle cells grown in the presence of various tensions of CO (5-95%) without the presence of O2 survived and exhibited reduced cell growth, which was concentration dependent. When cardiac muscle cells were grown in the presence of a mixture of CO (10-20%) and O2 (10-20%), the growth rate of these cells was comparable to that of the control cells. Cardiac myocytes continued to beat when exposed to varying tensions of CO, except in the case of 95% CO. The cells exposed to different concentrations of CO contained fewer myofibrils of different stages of differentiation compared with the control and the culture exposed to a mixture of 20% O2 and 20% CO, with cells that contained abundant, highly differentiated myofibrils. There was no significant difference in the structural organization of mitochondria between the control and the surviving experimental cells. It is evident from the present studies that O2 is required for the optimum in vitro cellular growth of cardiac muscle. Furthermore, CO in combination with O2 at a concentration of 10 or 20% can produce optimal growth of cardiac muscle cells in culture.

An in vitro approach to the study of target organ toxicity of drugs and chemicals

A major goal of our laboratory has been the development of primary culture systems that retain differentiated functions and responses characteristic of intact tissues in vivo. Specifically, we have developed cellular models of primary cultures of rat heart, liver, and kidney cells to explore the mechanisms by which drugs or chemicals may be toxic to key organs of the body and to develop new techniques by which xenobiotics may be evaluated or identified as potential toxicants to living systems. The purpose of this paper is to describe our rationale and approach to the study of target organ toxicology with in vitro cellular systems.

Reduction of cell injury in hypoxic cultures of rat myocardial cells by methylprednisolone

An in vitro model to study myocardial cell injury was developed with primary monolayer cultures of rat myocardial cells. Two important conditions associated with myocardial ischemia were simulated by depriving the cultures of oxygen and glucose for a specified period of time. Cellular injury caused by hypoxia and glucose deprivation resulted in significant leakage of lactate dehydrogenase (LDH) from the cells into the culture medium. The cells were not lethally injured by treatments as reflected by a lack of change in cell viability and protein content when compared to controls. Pretreatment of cultures with methylprednisolone for 24 hr provided protection to the cells when challenged by hypoxia and glucose deprivation. Methylprednisolone exhibited a dose-response effect in reducing LDH leakage in cultures, which were subsequently deprived of oxygen and glucose for 4 hr. Similar pretreatment with hydrocortisone had no effect in limiting cellular injury in hypoxic and glucose-deprived cultures.

Injury to primary cultures of rat heart endothelial cells by hypoxia and glucose deprivation

Primary cultures of rat heart endothelial cells were subjected to simulated conditions of ischemia: hyposia and glucose deprivation for 4 and 24 hr. Cellular injury was evaluated by measuring changes in viability, total protein, cellular morphology, and leakage of cytoplasmic enzymes from the cells into the culture medium. Deprivation of oxygen and glucose for 4 or 24 hr did not lethally injure the cells as noted by no change in cell viability, morphology, and total protein when compared to controls. However, reversible or non-lethal cellular injury was produced as reflected by a significant release of lactate dehydrogenase (LDH) from the cells into the medium after treatment with hypoxia and glucose deprivation for 4 or 24 hr. When the cultures were deprived of glucose, but were oxygenated, cellular injury was not evident after 24 hr. Deprivation of oxygen but not glucose resulted in significant loss of LDH after 4 or 24 hr. When the cultures were allowed to recover after oxygen and glucose deprivation in complete medium containing 1000 mg glucose per 1 and a normal atmosphere of 20% O2, they had levels of LDH leakage comparable to those of control cultures.

Acute mitochondrial toxicity of caffeine in cultured heart cells

The cytotoxic effect of caffeine on heart cells was evaluated in primary cultures of rat heart muscle (M) and endothelioid (E) cells. The cultures were exposed to 5, 10, or 20 mM caffeine for 6, 12, or 24 hours. As an index of cytotoxicity produced by the treatments, in situ changes in mitochondrial membrane fragility were measured by a sensitive cytochemical technique. The 24 hr treatment with 20 mM caffeine was lethal to both E and M cell cultures; only the 12 hr treatment of M cell cultures with 20 mM caffeine produced significant labilization of mitochondrial membranes. The results of tests with other concentrations and durations of treatment were not statistically significant.

Cardiotoxicity of diazepam in cultured heart cells

The responses of primary cultures of rat myocardial cells to diazepam (Valium) were evaluated. The cells were exposed to 4, 16 or 32 microgram/ml of diazepam for 1, 4 or 24 h. The cultures were evaluated for changes in beating activity and morphology and for cytotoxic effects. After the 1-h treatment exposure, the cultures exhibited tachycardia which was dose-dependent. The longer durations of treatment either produced arrhythmias or caused a loss of beating. Major morphological alterations observed were the formation pseudopodia and increased cytoplasmic granulation. Cytotoxicity was measured quantitatively by leakage of lactic dehydrogenase (LDH) from the cells into the media and by cell viability. Moderate amounts of LDH were leaked from the cells after exposure to diazepam for 4 h. After 24 h of treatment with the higher concentrations of diazepam, cell viability was greatly reduced.

Ischemic myocardial injury in cultured heart cells: preliminary observations on morphology and beating activity

An in vitro model of myocardial ischemia has been established with primary monolayer cultures of neonatal rat heart cells. Ischemic conditions were simulated in vitro by subjecting the heart cell cultures to various levels of oxygen and glucose deprivation. After the ischemic treatments, cultures of beating muscle (M) cells were evaluated for functional and morphological changes. The experimental protocol consisted of treatment with 20% or 0% O2 and 1000, 500 or 0 mg glucose per 1 of medium for 4, 12 or 24 hr. Control cultures were treated with 20% O2 and 1000 mg glucose. The morphological alterations induced by the deficiency of O2 and glucose in the medium were the formation of pseudopodia and cytoplasmic vacuoles; increased cytoplasmic granulation; and the formation of abnormal cell shapes, such as long, spindly shaped M cells. There was a time-dependent decrease in beating activity as the M cells were exposed to longer durations of ischemic conditions. However, if the cultures were replenished with complete medium (1000 mg glucose) and 20% O2, the cells regained their ability to beat.

Cytotoxicity of caffeine in cultured heart cells

The cytotoxic effect of caffeine on myocardial cells was evaluated in primary cultures of rat heart muscle (M) and endothelioid (E) cells. The cells were exposed to 5, 10, or 20 mM caffeine for 6, 12, or 24 h. As an index of cell injury produced by the treatments, in situ changes in lysosomal membrane permeability were measured by a sensitive cytochemical technique. The highest concentration of caffeine (20 mM) produced such toxic signs as reduced cell viability, increased vacuolization, and pseudopod formation. At the lower concentrations, caffeine labilized lysosomal membranes of M cells more easily than those of E cells. Pretreatment with hydrocortisone prior to exposure to caffeine protected E and M cell lysosomes from the labilizing effects of caffeine.