Biphasic effects of chlorpromazine on cell viability in a neuroblastoma cell line

Establishing a Mouse Model of Chlorpromazine-Induced Corneal Trigeminal Denervation

Purpose

This study aimed to establish a mouse model of chlorpromazine-induced corneal trigeminal denervation (CCTD).

Methods

Retrobulbar chlorpromazine injections were administered to 6- to 8-week-old C57BL/6j mice to induce corneal denervation. Additionally, apoptosis was assessed in isolated primary trigeminal ganglion cells after culturing in a conditioned medium containing chlorpromazine. Finally, the success rate of model generation, mortality and complication rates, and model-preparation learning curves were compared between the CCTD model and the electrocoagulation and axotomy models.

Results

Chlorpromazine retrobulbar injections resulted in trigeminal denervation, leading to a reduced blink reflex, corneal nerve density, and corneal epithelium thickness. Furthermore, 90% (9/10) of the mice developed epithelial defects, accompanied by increased apoptosis and inhibited proliferation of corneal epithelial cells. In vitro, trigeminal ganglion cell apoptosis increased after culturing in a conditioned medium containing chlorpromazine. Moreover, the CCTD model exhibited a higher success rate, longer survival rate, and lower complication rate compared to the electrocoagulation and axotomy models. Crucially, the learning curve demonstrated that the method used to generate the CCTD model was easy to learn.

Conclusions

The CCTD model is a user-friendly mouse model for studying corneal trigeminal denervation that offers a less invasive alternative to existing models.

Translational Relevance

The CCTD model serves as a valuable tool for investigating the functional mechanisms of corneal trigeminal nerves and their interactions with corneal cells.

Endocytic pathways mediating oligomeric Abeta42 neurotoxicity

BACKGROUND

One pathological hallmark of Alzheimer's disease (AD) is amyloid plaques, composed primarily of amyloid-beta peptide (Abeta). Over-production or diminished clearance of the 42 amino acid form of Abeta (Abeta42) in the brain leads to accumulation of soluble Abeta and plaque formation. Soluble oligomeric Abeta (oAbeta) has recently emerged to be as a likely proximal cause of AD.

RESULTS

Here we demonstrate that endocytosis is critical in mediating oAbeta42-induced neurotoxicity and intraneuronal accumulation of Abeta. Inhibition of clathrin function either with a pharmacological inhibitor, knock-down of clathrin heavy chain expression, or expression of the dominant-negative mutant of clathrin-assembly protein AP180 did not block oAbeta42-induced neurotoxicity or intraneuronal accumulation of Abeta. However, inhibition of dynamin and RhoA by expression of dominant negative mutants reduced neurotoxicity and intraneuronal Abeta accumulation. Pharmacologic inhibition of the dynamin-mediated endocytic pathway by genistein also reduced neurotoxicity.

CONCLUSIONS

These data suggest that dynamin-mediated and RhoA-regulated endocytosis are integral steps for oligomeric Abeta42-induced neurotoxicity and intraneuronal Abeta accumulation.

Cancer biology and hormesis: human tumor cell lines commonly display hormetic (biphasic) dose responses

This article assesses the nature of the dose-response relationship of human tumor cell lines with a wide range of agents including antineoplastics, toxic substances (i.e., environmental pollutants), nonneoplastic drugs, endogenous agonists, and phyto-compounds. Hormetic-like biphasic dose responses were commonly reported and demonstrated in 136 tumor cell lines from over 30 tissue types for over 120 different agents. Quantitative features of these hormetic dose responses were similar, regardless of tumor cell line or agent tested. That is, the magnitude of the responses was generally modest, with maximum stimulatory responses typically not greater than twice the control, while the width of the stimulatory concentration range was usually less than 100-fold. Particular attention was directed to possible molecular mechanisms of the biphasic nature of the dose response, as well as clinical implications in which a low concentration of chemotherapeutic agent may stimulate tumor cell proliferation. Finally, these findings further support the conclusion that hormetic dose responses are broadly generalizable, being independent of biological model, endpoint measured, and stressor agent, and represent a basic feature of biological responsiveness to chemical and physical stressors.

Chemotherapeutics and hormesis

This article represents the first comprehensive assessment of hormetic effects of chemotherapeutic agents. Hormetic dose-response relationships were reported for a wide range of chemotherapeutics, including antibiotics, antiviral, and antitumor agents as well as substances that affect hair growth, prostate function, cognitive performance, and numerous other endpoints. Particular attention was given to assessing the quantitative features of the dose response, the underlying mechanistic features of the biphasic nature of the dose response, and the clinical implications of hormetic responses. Recognition of the hormetic-like biphasic nature of the dose response is expected to have an important impact on the design of experiments to assess chemotherapeutics and how such agents may be employed more successfully in clinical applications.

Hypothermia inhibits pentylenetetrazol kindling and prevents kindling-induced deficit in shuttle-box avoidance

In this study, we evaluated the effects of hypothermic exposure on pentylenetetrazol (PTZ) kindling and the resulting deficit of shuttle-box avoidance learning in rats. Additionally, to acknowledge neuronal cell loss, we estimated the number of toluidine blue-positive cells in different brain regions after PTZ kindling and hypothermia exposure in comparison to different normothermic and hypothermic controls. To obtain hypothermic conditions over a period of up to about 3 h, 30 min after PTZ application the animals were treated with 5 mg/kg chlorpromazine (CP) and 25 min later exposed to 15 degrees C cold water for 5 min. Under these conditions the rectal and the striatal temperature were reduced up to a maximum of 5 degrees C. The additional injection of CP did not influence the development of PTZ kindling. Animals treated with PTZ/CP and exposed to hypothermia did not reach the criterion for kindling. Furthermore, this group of animals did not demonstrate any learning deficit. Forty-eight hours after the last kindling application the number of toluidine blue-stained cells was decreased in the investigated brain regions (hippocampal CA1 and CA3 sector, hilus, and cingular cortex) of kindled rats. Hypothermia protected from cell damage in the hippocampal CA3 sector and in the hilus. Results suggest that the inhibiting effect of hypothermia on the development of kindling and the following learning deficit possibly resulted from the suppression of cell damage in distinct brain structures on PTZ-kindled rats.

Chlorpromazine protection against Ca(2+)-dependent and oxidative cell injury. Limitations due to depressed mitochondrial function

Chlorpromazine (CPZ), a phenothiazine, demonstrated both cytoprotective and toxic effects on cardiomyocytes. CPZ markedly reduced cytotoxicity caused by two toxic challenges, each with a distinct cytotoxic mechanism. Lethal cell injury was induced in cultured neonatal cardiomyocytes by either: (1) ionomycin, a Ca2+ ionophore that caused Ca(2+)-dependent cell injury; or (2) ethacrynic acid (EA), a glutathione (GSH) depletor that killed cells primarily via peroxidative damage. Pretreatment with 50 microM CPZ reduced the extent of ionomycin-induced cell death, as measured by lactate dehydrogenase (LDH) leakage, but enhanced the loss of intracellular ATP and collapsed the mitochondrial transmembrane potential (delta psi). In EA-treated cultures, 50 microM CPZ also lowered LDH leakage and diminished the peroxidative damage responsible for the cytotoxicity, but again enhanced the loss of intracellular ATP and collapsed the delta psi. CPZ protection was incomplete and limited to a narrow concentration range that was essentially identical for both toxic challenges. Maximum protection was observed with 50 microM CPZ, yet the amount of residual damage was similar to the degree of injury caused by a mitochondrial uncoupler, carbonylcyanide-m-chlorophenylhydrazone alone. In the absence of either challenge, 50 microM CPZ did not affect cellular energy status or kill the cells, but a higher concentration of CPZ (150 microM) did deenergize unchallenged cardiomyocytes. These data demonstrate that CPZ can reduce cytotoxicity caused by either Ca(2+)-dependent events or oxidative stress. However, even at an optimally protective level, CPZ in combination with either ionomycin or EA deenergized the cells, although neither toxic challenge nor 50 microM CPZ alone seriously affected delta psi. It would appear that intracellular perturbations induced by either challenge promote a depression of mitochondrial function by CPZ, which limits the protective action of the drug. Since both of the challenges used contain toxicologic features exhibited by a wide variety of toxic insults, results of this study have both mechanistic and clinical implications.

Chemical radiosensitizers in cancer therapy

The development of effective low-LET radiation therapy for cancer has been hindered by the lack of consistent differential responses to radiation between tumor and normal tissues. One major difference between many solid tumors and the surrounding normal stroma is the presence of hypoxic foci in solid tumors due to the inadequate supply of nutritional needs as a result of the breakdown of microvasculature. Consequently, failure of conventional radiotherapy and local recurrences are in part attributed to the radioresistant hypoxic cell populations, present in the tumor. Local cure/control rates of a tumor can be increased only by an effective increase in the radiation dose. At the same time, an increase in such a dose would damage the oxic normal stroma, more than the hypoxic tumor cells. Hence, specific modification of tumor radiosensitivity by the use of chemical radiosensitizers, in combination with conventional radiotherapy, is an attractive alternative. Many clinicians and radiotherapists are skeptical about the outcome of using radiosensitizers in patients. Nevertheless, a vast amount of information is currently available regarding the first- and second-generation radiosensitizers both in murine and in human tumors. As a result, it is hoped that eventually a radiosensitizing drug would be discovered/synthesized that will overcome the drawbacks so far encountered in their use in the clinic. In this article, the development of chemical radiosensitizers since the early sixties, the basis for their selection, their mechanism(s) of action, and the results obtained with the various groups of radiosensitizers are reviewed.

Recovery from calcium-induced damage in a neuroblastoma cell line

Calcium may act as a second messenger in normal cellular signal transduction systems. However, an excessive influx of calcium into the cytoplasm is well known to be a final common pathway causing cell death under various pathological conditions. The purpose of this study was to investigate the effect of a transient treatment with the calcium ionophore A23187 on the recovery process of cell viability, energy metabolism, amino acid incorporation and calcium uptake in a neuroblastoma cell line. When neuroblastoma cells were treated with 20 microM of the calcium ionophore A23187 in combination with extracellular calcium, rapid energy failure and marked inhibition of amino acid incorporation by the cells occurred together with a massive influx of calcium, and finally resulted in cell death. Recovery from this calcium-induced damage with regards to energy metabolism and prognosis of cell viability was better after a 10-min treatment than after a 30-min treatment with A23187. After a 10-min treatment, the viability was higher in calcium-free medium than in calcium-containing medium in contrast with the cases after treatment for 30 min. The above difference in viability after treatment for 10 min had a very significant correlation with the degree of exclusion of excessive calcium and the recovery of CTP, indicating that the recovery of CTP and the rate of calcium exclusion may be final markers of the recovery of cells from calcium-induced damage rather than the recovery of ATP or amino acid incorporation. Amino acid incorporation was restricted to a level lower than that of the control long after the recovery of GTP and the GTP/GDP ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of an increase in susceptibility to calcium in a neuroblastoma cell line

An increase in susceptibility of neuroblastoma cells to calcium was inhibited when the cells were treated with hypothermia, diphenylhydantoin, chlorpromazine or pentobarbital; all of these treatments affect membrane permeability to calcium or membrane-associated cell metabolism. Diphenylhydantoin and chlorpromazine were found to have positive effects only when they were administered before the addition of calcium. This was in contrast to flunarizine, which showed a protective effect only in combination with calcium. However, leupeptin did not show any positive effect, indicating that calcium-activated neutral protease may be only slightly involved in this type of calcium-induced cell damage.