The growing popularity of novel psychoactive substances (NPS) has aroused the concerns of public health specialists. The pyrovalerone derivatives are a branch of synthetic cathinones, a very popular group of psychostimulant NPS. Despite numerous case reports of fatal intoxications, little is known about the cytotoxicity of these substances. Therefore, this study was aimed to evaluate the toxic properties of pyrovalerone, its highly prevalent derivative 3,4-methylenedioxypyrovalerone (3,4-MDPV) with its two major metabolites (catechol-MDPV and methylcatechol-MDPV) and the structural isomer 2,3-MDPV, together with newer members of the group, i.e., α-pyrrolidinovalerothiophenone (α-PVT) and α-pyrrolidinooctanophenone (PV9), using model human cell lines for neurons (SH-SY5Y), hepatocytes (Hep G2), and upper airway epithelium (RPMI 2650). We found that the first generation pyrovalerones (pyrovalerone, 3,4-MDPV, and 2,3-MDPV) produced a modest decrease of mitochondrial activity in the three examined cell lines, but were active in lower concentrations than methamphetamine used as a reference psychostimulant compound. Since catechol-MDPV displayed greater toxic potential than the parent compound, we suggest that the toxicity of 3,4-MDPV could be attributed to activity of this metabolite. Strikingly, the two new generation pyrovalerones, α-PVT and PV9, seem to be the most potent cytotoxic compounds: both induced highly pronounced mitochondrial dysfunction; the latter also demonstrated significant damage to cell membranes. The reported in vitro toxic activity of pyrovalerone cathinones against different cell types reinforces existing concerns regarding the health risks associated with the intake of these drugs.

Orexins A and B are newly discovered neuropeptides with pleiotropic activity. They signal through two G protein-coupled receptors: OX1 and OX2. In this study, we examined the expression of orexin receptors and effects of the receptors’ activation on cyclic AMP formation in the primary neuronal cell cultures from rat cerebral cortex. Both types of orexin receptors were expressed in rat cortical neurons; the level of OX2R was markedly higher compared to OX1R. Orexin A (an agonist of OX1R and OX2R) and [Ala11-D-Leu15]orexin B (a selective agonist of OX2R) did not affect basal cyclic AMP formation in the primary neuronal cell cultures. Both peptides (0.001–1 μM) inhibited, in a concentration-dependent manner and IC50 values in low nanomolar range, the increase in the nucleotide production evoked by forskolin (1 μM; a direct activator of adenylyl cyclase), pituitary adenylate cyclase-activating polypeptide (PACAP27; 0.1 μM), and vasoactive intestinal peptide (VIP; 3 μM). Effects of orexin A on forskolin-, PACAP27-, and VIP-stimulated cyclic AMP synthesis were blocked by TCS OX2 29 (a selective antagonist of OX2R), and unaffected by SB 408124 (a selective antagonist of OX1R). Pretreatment of neuronal cell cultures with pertussis toxin (PTX) abolished the inhibitory action of orexin A on forskolin- and PACAP-stimulated cyclic AMP accumulation. It is suggested that in cultured rat cortical neurons orexins, acting at OX2 receptors coupled to PTX-sensitive Gi protein, inhibit cyclic AMP synthesis.

The effects of orexins, which are also named hypocretins, on cAMP formation were examined in primary cultures of rat astrocytes. Orexin A, an agonist of OX₁ and OX₂ receptors, stimulated cAMP production with an EC₅₀ value of 0.68 μM and potentiated the forskolin-induced increase in the nucleotide synthesis. [Ala¹¹-D-Leu¹⁵]orexin B, an agonist of OX₂ receptors, was inactive. The effects of orexin A were antagonized by SB 408124, a selective blocker of OX₁ receptors, but were not affected by TCS OX2 29, a selective antagonist of OX₃ receptors. We hypothesized that the activation of OX₁ receptors stimulated cAMP synthesis in primary rat astrocyte cultures.

Effects of white and monochromatic (blue-434 nm, green-548 nm, and red-614 nm) lights on the nighttime retinal and pineal NAT activity were examined in chicks. The potency of the tested lights to suppress NAT activity was similar for the retina and pineal gland, with a following rank order: white > green > blue > or = red. The studied tissues of chick were far less sensitive to pulses of monochromatic light than the rat pineal gland. The potency of light to decrease pineal NAT activity of rat was: white > green >> blue > red. In chicks, the suppression of the nocturnal NAT activity produced by a short 5-min pulse of monochromatic light was completely reversible in the pineal gland, and partially reversible in the retina. Our data suggest the existence of some differences between birds and mammals in terms of sensitivity and mechanisms involved in the light-induced suppression of melatonin biosynthesis.

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