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.

Allylamine-induced vascular toxicity in vitro: prevention by semicarbazide-sensitive amine oxidase inhibitors

The present studies were designed to evaluate the role that metabolic activation plays in allylamine (AAM)-induced vascular toxicity. The effects of AAM were evaluated in primary cultures of rat vascular endothelial (VEC) and smooth muscle cells (SMC). Semicarbazide (SC) and diethyldithiocarbamate (DDC) were used as inhibitors of semicarbazide-sensitive amine oxidase (SSAO). Clorgyline and pargyline were used as inhibitors of monoamine oxidase (MAO) A and B, respectively. The effect of catalase, a hydrogen peroxide scavenger, on AAM-induced cytotoxicity was also evaluated. Lactate dehydrogenase (LDH) release and morphological alterations were chosen as indicators of cytotoxicity. Confluent cultures of VEC and SMC were exposed to various concentrations of AAM (2-200 microM) in the absence and presence of serum for 4, 12, or 24 hr. High concentrations of AAM (200 microM) alone produced a time-dependent increase in LDH release and morphologic alterations in cultures of both cell types. Lower concentrations of AAM did not compromise the structural integrity of the cells. Semicarbazide (200 microM) or DDC (2 mM), but not clorgyline (10 microM) or pargyline (10 microM), prevented the toxicity of AAM (200 microM). Allylamine-induced cytotoxicity was partially prevented by catalase (2500 U/ml). The presence of fetal bovine serum in the medium was not essential for the manifestation of cytotoxicity. Single cell suspensions of VEC or SMC formed acrolein (ACR) when incubated in the presence of AAM. The formation of ACR mediated by SMC was inhibited by SC (20 microM), but not clorgyline (10 microM). These results support the concept that AAM is oxidatively deaminated by an SSAO present in vascular cells to generate toxic metabolic by-products capable of causing extensive cellular injury.

Primary cultures of rat aortic endothelial and smooth muscle cells: I. An in vitro model to study xenobiotic-induced vascular cytotoxicity

Primary cultures of rat vascular endothelial and smooth muscle cells were developed as models to study xenobiotic-induced cytotoxicity. Endothelial and smooth muscle cells were isolated by enzymatic digestion and mechanical dissociation of rat thoracic aortae. Optimal cell growth and minimal fibroblast contamination in cultures of both cell types were obtained in Medium 199 supplemented with 10% fetal bovine serum. Cultured cells were characterized by distinctive morphologic features and growth patterns. Intercellular endothelial cell junctions were selectively stained with silver nitrate. Endothelial cells also exhibited a nonthrombogenic surface, as reflected by platelet-binding studies. Confluent cultures of smooth muscle cells, but not endothelial cells, contracted in response to norepinephrine (10 microM). Cultures of both cell types were exposed to acrolein (2, 5 or 50 ppm), an environmental pollutant, for 4 and 24 h. Morphologic damage, lactate dehydrogenase release, and cellular thiol content were used as indices of cytotoxicity. Acrolein-induced enzyme leakage and morphologic alterations were dose- and time-dependent and more pronounced in cultures of smooth muscle cells than in endothelial cells. The total thiol content of endothelial cells exposed to acrolein (50 ppm) for 24 h was not significantly different from that of respective controls. In contrast, the content of treated smooth muscle cells was higher than that of controls. These observations show that primary cultures of vascular cells provide a useful model to evaluate xenobiotic-induced cytotoxicity. The information obtained using a cell culture system may be complemented by the use of other in vivo and in vitro models to determine the mechanisms by which xenobiotics cause vascular cell injury.

Alterations of rabbit aortic smooth muscle cell proliferation in diabetes mellitus

OBJECTIVE

Diabetes mellitus is a known risk factor for atherosclerosis. Because initiation and/or progression of the atherosclerotic process is associated with alterations in vascular smooth muscle cell growth and differentiation, the present studies were conducted to evaluate the effect of diabetes mellitus on the proliferative behaviour of cultured aortic smooth muscle cells.

METHODS

Male New Zealand White rabbits were made diabetic with a single intravenous injection of alloxan monohydrate (100 mg.kg-1) in saline. Primary cultures of smooth muscle cells were established from thoracic aortic segments of control and diabetic rabbits and used to develop multiple cell strains. The proliferative capability of secondary cultures was determined by measurements of [3H]-thymidine incorporation into DNA, cell counts, and protein content in control and diabetic cultures. The serum dependence of cellular growth was evaluated by incubation of cultured cells in growth medium supplemented with various fetal calf serum concentrations.

RESULTS

Cultures of diabetic origin incorporated thymidine to a greater extent than control cultures. Although the efficiency of cell attachment was not different between control and diabetic cells, diabetic cells had a shorter population doubling time than control cells [41.08(SEM 4.15) h v 58.08(6.79) h] and achieved higher final densities than control cultures. The serum dependence of smooth muscle cell cultures for viability and growth was different between the two groups.

CONCLUSIONS

These findings support the hypothesis that diabetes induces changes in vascular smooth muscle cell proliferation which may be associated with the onset or progression of the atherogenic process observed in diabetes.

Cardiotoxicity of tricyclic antidepressants in primary cultures of rat myocardial cells

Primary cultures of myocardial cells were used to evaluate the cardiotoxic potential of various tricyclic antidepressants (TCAs). Lactate dehydrogenase (LDH) leakage, cellular viability, and beating rates were measured to compare the cardiotoxicity of amitriptyline, desipramine, imipramine, and nortriptyline. Tricyclic antidepressants were added to the cultures to give final concentrations of 1 X 10(-5), 1 X 10(-4), and 1 X 10(-3) M. Treatments lasted 1 and 4 h. All TCAs tested caused significant release of LDH and decreased cellular viability when added at 1 X 10(-3) M for 1 and 4 h. Amitriptyline was the only compound that caused significant LDH release 4 h after exposure to lower doses. Decreased viability was observed 4 h after exposure to all TCAs at a concentration of 1 X 10(-4) and 1 X 10(-3) M. Arrhythmias were observed 1 h after exposure to 1 X 10(-5) and 1 X 10(-4) M amitriptyline. All doses of amitriptyline inhibited beating 4 h after exposure. Imipramine, desipramine, and nortriptyline at a concentration of 1 X 10(-5) M decreased the beating rates of cultured myocytes 1 and 4 h after exposure. Arrhythmias and/or total inhibition of beating were observed when the cultures were exposed to higher concentrations of these compounds. Based on these data, the rank order of cardiotoxicity was amitriptyline greater than imipramine = desipramine greater than nortriptyline.

Cocaine-induced cardiotoxicity in vitro

A growing number of reports have related cocaine use with the onset of myocardial infarction in young otherwise healthy individuals. Although the cardiac effects of cocaine have traditionally been attributed to sympathomimetic stimulation, several studies have suggested that cocaine may be directly cardiotoxic. The purpose of this study was to evaluate the cardiotoxic effects of cocaine in an in vitro preparation devoid of sympathetic innervation. Primary cultures of rat cardiac muscle and non-muscle cells were prepared from hearts excised from 3-5-day-old Sprague-Dawley rats. Cultures were exposed to various cocaine concentrations (1 x 10(-7)-1 x 10(-3)m) for 1-24 hr. Beating activity, morphological status and lactate dehydrogenase (LDH) leakage were evaluated following cocaine exposure. A decrease in the beating activity of cultured muscle cells was observed 1 hr after exposure to the highest cocaine concentrations (1 x 10(-5)-1 x 10(-3)m) tested. Similar results were obtained 24 hr after exposure. Morphological alterations in muscle cells were evident only after exposure to the highest concentration (1 x 10(-3)m). Vacuoles appeared 1 hr after cocaine exposure and were replaced by dark granules within 24 hr. LDH release was significantly elevated in the muscle cell cultures exposed to 1 x 10(-3)m cocaine for 24 hr. The pattern of cocaine-induced morphological alterations and enzyme leakage was similar in non-muscle cells. These data suggest that cocaine induces direct toxic effects on both cardiac muscle and non-muscle cells maintained in an environment free of neuronal and hormonal influences.

Role of calcium in isoproterenol cytotoxicity to cultured myocardial cells

Primary cultures of rat myocardial cells were used to evaluate the cellular dynamics of calcium accumulation after exposure to isoproterenol (ISO). Non-toxic concentrations of ISO (2.4 X 10(-7) M) caused a gradual increase in myocyte calcium uptake. These effects peaked 3 min after exposure and returned to control levels within 2 min. Toxic concentrations of ISO caused a biphasic increase in calcium uptake. The initial phase peaked 1 min after exposure and returned to control levels by 3 min. A second phase was characterized by a progressive increase in calcium uptake that plateaued 10 min after exposure. Ascorbic acid (AA, 5 X 10(-3) M) and sodium bisulfite (SB, 9.6 X 10(-4) M) did not modify the calcium uptake of the initial phase, whereas propranolol (1 X 10(-6) M) and verapamil (1 X 10(-5) M) prevented the initial rise in calcium uptake. In contrast, the antioxidants prevented the the second phase of ISO-induced calcium uptake, whereas verapamil and propranolol did not. The toxic accumulation of calcium induced by ISO may be due to oxidative damage of the sarcolemma. Antioxidants may prevent the formation of oxidative metabolites from ISO and the subsequent calcium overload. Our results show that agents which modify slow calcium-channel transport do not prevent ISO-induced calcium overload in our cell culture system.

Modulation of phosphoinositide metabolism in aortic smooth muscle cells by allylamine

Aortic smooth muscle cells (SMC) modulate from a contractile to a proliferative phenotype upon subchronic exposure to allylamine. The present studies were designed to determine if this phenotypic modulation is associated with alterations in the metabolism of membrane phosphoinositides. 32P incorporation into phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), and phosphatidic acid (PA) was lower by 31, 35, and 22%, respectively, in SMC from allylamine-treated animals relative to controls. In contrast, incorporation of [3H]myoinositol into inositol phosphates did not differ in allylamine cells relative to control cells. Exposure to dibutyryl (db) cAMP (0.2 mM) and theophylline (0.1 mM) reduced 32P incorporation into PIP and PIP2 in SMC from both experimental groups. Under these conditions, a decrease in [3H]myoinositol incorporation into inositol 1-phosphate was only observed in allylamine cells. The effects of db cAMP and theophylline in allylamine and control SMC correlated with a marked decrease in cellular proliferation. These results suggest that alterations in phosphoinositide synthesis and/or degradation contribute to the enhanced proliferation of SMC induced by allylamine. To further examine this concept, the effects of agents which modulate protein kinase C (PKC) activity were evaluated. Sphingosine (125-500 ng/ml), a PKC inhibitor, decreased SMC proliferation in allylamine, but not control cells. 12-O-Tetradecanoylphorbol-13-acetate (1-100 ng/ml), a PKC agonist, stimulated proliferation in control cells, but inhibited proliferation in cells from allylamine-treated animals. We conclude that allylamine-induced phenotypic modulation of SMC is associated with alterations in phosphoinositide metabolism.

Cytotoxicity of isoproterenol to cultured heart cells: effects of antioxidants on modifying membrane damage

Primary cultures of rat myocytes were used to study the cardiac damage induced by toxic doses of L-isoproterenol (ISO). Cultures were exposed to varying concentrations of ISO (2.4 X 10(-5), 1 X 10(-4), and 5 X 10(-4) M) for 0.5, 1.5, 4, and 12 hr. Mitochondrial membrane fragility, myocyte potassium content (as an index of sarcolemmal damage), and cellular glutathione content were used to evaluate cellular injury. A significant increase in mitochondrial fragility was observed 0.5 hr after treatment with 5 X 10(-4) M ISO. Lower doses caused an increase in mitochondrial fragility 1.5 hr after exposure. Longer durations of ISO exposure (4 and 12 hr) were necessary to decrease cellular potassium content. Glutathione levels were minimally affected by ISO. L-Ascorbic acid (5 X 10(-3) M) or sodium bisulfite (9.6 X 10(-4) M) were added to the cultures to determine if antioxidants prevent the toxicity caused by ISO. The presence of L-ascorbic acid or sodium bisulfite in ISO-treated myocyte cultures prevented the toxic changes in mitochondrial fragility and myocyte potassium content. The data indicate that antioxidants may be useful in reducing injury induced by toxic doses of ISO. Furthermore, mitochondrial injury may be involved significantly with the development of ISO-induced cardiotoxicity.

Prevention by L(-) ascorbic acid of isoproterenol-induced cardiotoxicity in primary cultures of rat myocytes

Primary cultures of rat myocytes were exposed to various doses of L-isoproterenol (ISO) for 4, 12 and 24 h. L-ascorbic acid (AA) was added to some cultures immediately after exposure to ISO to determine if antioxidants reduce the toxicity caused by ISO. Leakage of lactate dehydrogenase (LDH) and cell viability were used as indices of cell injury. A significant increase in LDH release was found 24 h after exposure to 1 X 10(-4) M ISO alone. Higher doses (5 X 10(-4) and 1 X 10(-3) M) caused significant enzyme release 4, 12 and 24 h after exposure. The viability of cultures exposed to toxic doses of ISO for 4 h was not affected. A dose-dependent decrease in cell viability was observed 12 h and 24 h after exposure to ISO. L-ascorbic acid (5 X 10(-3) and 1.5 X 10(-2) M) significantly reduced the LDH release caused by ISO. The enzyme release from cultures exposed to 5 X 10(-4) and 5 X 10(-3) M AA alone was similar to that of control cultures. However, 1.5 X 10(-2) and 3 X 10(-2) M AA caused marked LDH release. The viability of cultures subjected to ISO in the presence of 5 X 10(-3) M AA was similar to that of controls. Our results show that AA protects against the LDH release and decreased cellular viability caused by toxic doses of ISO.

Rabbit aortic smooth muscle cell culture. A model for the pharmacological study of diabetes-induced alterations in cell proliferation

Atherosclerotic vascular disease is the most common complication of diabetes mellitus. Enhanced vascular smooth muscle cell proliferation plays a central role in atherosclerotic lesion formation. Studies using explant cultures have demonstrated that aortic smooth muscle cells from rats with experimental or genetic diabetes have enhanced rates of proliferation when compared to controls. However, this method of culture may select for cells with enhanced migratory potential. In the present studies, aortic smooth muscle cells were successfully cultured from control and diabetic rabbits after enzymatic and mechanical dispersion from thoracic aortic segments. The proliferative patterns of control cells were characterized and growth rates of diabetic cells were compared to controls. Primary cultures from control rabbits grew after an initial 5-day lag period to achieve threefold increases in cell number by 9 days. Subcultures of aortic smooth muscle cells entered the logarithmic phase of growth after 2 days, reaching the plateau phase of growth in 5-7 days and achieving three to fourfold increases in cell number. The final density to which cultures grew was not affected by the number of cells attached on day 1 for the range studied. Cells from diabetic rabbits displayed shorter doubling times and reached greater densities at confluence than did cells from controls. These data support the hypothesis that diabetes induces an atherogenic response. The dissociated rabbit aortic smooth muscle cell culture provides a model in which to study diabetes-induced modulation of cell proliferation that is amenable to pharmacological manipulation to investigate agonist and growth factor-induced responses.

Comparative angiotoxic responses of avian and rodent species in vivo: implications in atherogenesis

As the intrinsic susceptibility to atherosclerosis differs among several taxonomic groups, the present studies were conducted to compare the angiotoxic responses of atherosclerosis-susceptible (quail) and -resistant (rat) animals to allylamine, a selective cardiovascular toxin. Japanese quail (125-150 g) and Sprague-Dawley rats (175-200 g) were gavaged daily for 1, 7, or 20 d with allylamine HCl (0.7, 7, and 70 mg/kg) or tap water. At the ultrastructural level, subchronic exposure of quail and rats to allylamine was associated with dose- and time-dependent disruption of the structural integrity of aortas. These alterations correlated with fluctuations in the nonprotein thiol content of avian and rodent vessels. Angiotoxicity was not associated with alterations in serum cholesterol content. At all times and doses tested, quail were more susceptible than rats to the angiotoxic effects of allylamine. Although the avian sensitivity to toxic insult was greater than that of rodents, quail aortic homogenates bioactivated allylamine to a lesser extent than rat homogenates. Collectively, these results suggest that the aortic sensitivity to toxic insult in avian and rodent species correlates with their intrinsic susceptibility to vascular injury.

Cell injury of cultured rat myocardial cells after reoxygenation of hypoxic cultures in the presence and absence of calcium

Primary cultures of rat myocytes were deprived of oxygen (approximately 5 mm Hg, pO2) for 2 h in the presence or absence of calcium and were subsequently incubated for different time periods under normoxic (approximately 120 mm Hg, pO2) conditions. Myocyte calcium content was determined at the end of the oxygen-free period and after repletion of oxygen. Lactate dehydrogenase (LDH) release from the cells into the medium was used as an index of cell injury. Cultures deprived of oxygen in the absence of calcium showed a significant decrease in myocyte calcium content at the end of the oxygen-free period. However, the calcium content of myocyte cultures deprived of oxygen in the presence of calcium did not change significantly. The enzyme release of both groups of oxygen-deprived cultures was similar to that of controls. A progressive increase in myocyte calcium content was observed 5, 10, 15, and 30 min after repletion of oxygen in both groups. Reoxygenation of cultures subjected to hypoxia in the presence of calcium caused minimal LDH leakage. However, major enzyme release was observed 30 min after oxygen repletion in cultures previously subjected to hypoxia in a calcium-free environment. The present study shows that reoxygenation injury is more severe in myocyte cultures previously deprived of both oxygen and calcium than in cultures deprived of oxygen in the presence of calcium.

Modulation by retinoic acid of spontaneous and benzo(a)pyrene-induced c-Ha-ras expression

The effects of retinoic acid on the expression of the Ha-ras gene were studied in transformed rat hepatoma cells (H4IIE) and in rat aortic smooth muscle cells (ASMC) treated with benzo(a)pyrene (30 microM) in vitro. In H4IIE cells, a dose-dependent increase in steady state Ha-ras mRNA levels was observed upon exposure to retinoic acid for 24 hr. Exposure of ASMC to 10 microM retinoic acid under similar experimental conditions was also associated with increased Ha-ras expression. In contrast, retinoic acid (1 and 10 microM) inhibited benzo(a)pyrene-induced expression of Ha-ras in ASMC. These results suggest that retinoic acid modulates spontaneous and carcinogen-induced expression of Ha-ras in a differential manner.

Cellular injury of primary cultures of rat myocytes incubated in calcium-free medium followed by recovery in calcium

Primary monolayer cultures of rat myocardial cells were used to study the cellular injury that occurs when calcium is reintroduced after a period of calcium depletion. Cultures were treated with a calcium-free balanced salt solution (BSS) for 2 h and were then incubated for different time periods in the presence of normocalcemic BSS (2.5 mM CaCl2). Myocyte calcium content was determined after the calcium-free period and after incubation in the presence of calcium. Leakage of cytoplasmic lactate dehydrogenase (LDH) into the medium was used as an index of cell injury. At the end of the calcium-free period there was a significant decrease in the total cellular content of calcium, and LDH release was minimal. After incubation in normocalcemic BSS, the myocyte calcium content increased progressively with time and cellular injury was manifested by significant leakage of LDH. The calcium content of treated cells reached control levels 10 min after calcium repletion. Maximal leakage of LDH was observed 60 min after the restoration of calcium. The calcium content of treated cultures was higher than that of control cultures 120 min after incubation in normocalcemic BSS.

Attenuation by antioxidants of Na+/K+ ATPase inhibition by toxic concentrations of isoproterenol in cultured rat myocardial cells

We have reported previously that toxic concentrations of isoproterenol caused severe alterations in the structural integrity of the sarcolemma and mitochondria found in primary cultures of rat myocardial cells [8, 9]. Mitochondrial injury was observed 1.5 h after exposure to isoproterenol, whereas leakage of intracellular ions and enzymes was observed only after prolonged exposures (greater than 4 h). Ascorbic acid and sodium bisulfite prevented the cytotoxic effects of isoproterenol in our cell culture system. Takeo et al. [13] suggested that adrenochrome (an oxidative metabolite of epinephrine) specifically inhibits the activity of the sodium/potassium ATPase. Other investigators have shown that an indole metabolite of epinephrine inhibited actomyosin ATPase [1, 4]. These inhibitory actions may result from an interaction between the oxidative metabolites and sulfhydryl groups present in the enzyme [13]. Inhibition of the sodium/potassium ATPase is associated with an increase in the intracellular concentration of Na+ and Ca2+ and a decrease in intracellular K+. Changes in the intracellular concentration of these ions are commonly seen in heart cell damage and contractile failure [2]. The present study was designed to determine if isoproterenol, a synthetic catecholamine, inhibits the sodium/potassium ATPase activity in a primary culture system of rat myocardial cells.

Using digital chatbots to close gaps in healthcare access during the COVID-19 pandemic

INTRODUCTION

Chatbots have emerged as a first link to care in recent years. The COVID-19 pandemic, and consequent health system disruptions, expanded their use. Socios En Salud (SES) introduced chatbots in Peru, which experienced one of the highest excess COVID mortalities in the world.

METHODS

SES and the government identified unmet population health needs, which could be amenable to virtual interventions. Chatbots were developed to screen individuals for these conditions; we describe the period of deployment, number of screenings, and number of people who received services.

RESULTS

Between April 2020 and May 2021, SES deployed nine ChatBots: four for mental health, two for maternal and child health, and three for chronic diseases: breast cancer, hypertension, diabetes mellitus, and obesity. Mental health services were provided to 42,932 people, 99.99% of those offered services. The other ChatBots reached fewer people. Overall, more than 50% of eligible people accepted chatbot-based services.

DISCUSSION

ChatBot use was highest for mental health. Chatbots may increase connections between a vulnerable population and health services; this is likely dependent on several factors, including condition, population, and penetration of smart phones. Future research will be critical to understand user experience and preferences and to ensure that chatbots link vulnerable populations to appropriate, high-quality care.