How reliable are in vitro IC50 values? Values vary with cytotoxicity assays in human glioblastoma cells.

Increasing evidence shows that discrepancies exist among in vitro cytotoxicity methods resulting in unreliable drug toxicity profiles. This is particularly criticial for cell lines such as gliomas which are histologically and genetically heterogeneous. The high level of variation in these cells makes comparative analysis difficult and is a severe limitation for the usefulness of high-throughput screening methods. Here we examine variations between four conventional in vitro cytotoxicity assays (MTT, Alamar Blue, Acid Phosphatase and Trypan Blue) for assessing the viable cell number following treatment of two human glioblastoma cell lines (U87MG and U373MG) with different chemical agents (carboplatin, etoposide, paraquat). The variations in IC50 values between the four assays suggest that even when combining several endpoints such as mitochondrial function, lysosomal activity, and membrane integrity, a reliable and uniform toxicity profile was not achieved. Because of these variations between cytotoxicity assays using compounds with varying mechanisms of cytotoxicity, then it is possible that the true IC50 value of valuable and beneficial compounds for glioblastoma may have been missed through over/underestimation. This highlights the importance of reliability and accuracy in pre-animal models such as in vitro models of cytotoxicity for better predictive in vivo responses.

The efficacy of the appetite suppressant, diethylpropion, is dependent on both when it is given (day vs. night) and under conditions of high fat dietary restriction.

Obesity is a public health problem caused by excessive consumption of high caloric diets and/or lack of physical activity. Although treatments for obesity include low caloric diets and exercise programs, these activities frequently are supplemented with appetite suppressants. For the short-term treatment of weight loss, diethylpropion (DEP) is a commonly used appetite suppressant. However, little is known with regard to how to improve its weight loss efficacy. We therefore evaluated, in rats, two administration protocols where the animals received daily injections of DEP. First, when these nocturnal animals were normally active (at night) and when they were normally inactive (daytime), and second, with or without high fat dietary restriction (HFDR). We observed that DEP induced a greater weight-loss administered when the animals were in their active phase than in their inactive phase. Moreover, DEP's administration during the inactive phase (and to a lesser degree in the active phase) promotes the consumption of food during normal sleeping time. In addition, we found that DEP-induced weight loss under ad libitum access to a HF diet, but its efficacy significantly improved under conditions of HFDR. In summary, the efficacy of DEP, and presumably other like appetite suppressants, is enhanced by carefully controlling the time it is administered and under dietary restriction of HF diets.

D1 and D2 antagonists reverse the effects of appetite suppressants on weight loss, food intake, locomotion, and rebalance spiking inhibition in the rat NAc shell.

Obesity is a worldwide health problem that has reached epidemic proportions. To ameliorate this problem, one approach is the use of appetite suppressants. These compounds are frequently amphetamine congeners such as diethylpropion (DEP), phentermine (PHEN), and bupropion (BUP), whose effects are mediated through serotonin, norepinephrine, and dopaminergic pathways. The nucleus accumbens (NAc) shell receives dopaminergic inputs and is involved in feeding and motor activity. However, little is known about how appetite suppressants modulate its activity. Therefore, we characterized behavioral and neuronal NAc shell responses to short-term treatments of DEP, PHEN, and BUP. These compounds caused a transient decrease in weight and food intake while increasing locomotion, stereotypy, and insomnia. They evoked a large inhibitory imbalance in NAc shell spiking activity that correlated with the onset of locomotion and stereotypy. Analysis of the local field potentials (LFPs) showed that all three drugs modulated beta, theta, and delta oscillations. These oscillations do not reflect an aversive-malaise brain state, as ascertained from taste aversion experiments, but tracked both the initial decrease in weight and food intake and the subsequent tolerance to these drugs. Importantly, the appetite suppressant-induced weight loss and locomotion were markedly reduced by intragastric (and intra-NAc shell) infusions of dopamine antagonists SCH-23390 (D1 receptor) or raclopride (D2 receptor). Furthermore, both antagonists attenuated appetite suppressant-induced LFP oscillations and partially restored the imbalance in NAc shell activity. These data reveal that appetite suppressant-induced behavioral and neuronal activity recorded in the NAc shell depend, to various extents, on dopaminergic activation and thus point to an important role for D1/D2-like receptors (in the NAc shell) in the mechanism of action for these anorexic compounds.