Effect of intracerebral hydroxytyrosol and its nitroderivatives on striatal dopamine metabolism: A study by in vivo microdialysis

Nerve Injury Triggers Time-dependent Activation of the Locus Coeruleus, Influencing Spontaneous Pain-like Behavior in Rats

BACKGROUND

Dynamic changes in neuronal activity and in noradrenergic locus coeruleus (LC) projections have been proposed during the transition from acute to chronic pain. Thus, the authors explored the cellular cFos activity of the LC and its projections in conjunction with spontaneous pain-like behavior in neuropathic rats.

METHODS

Tyrosine hydroxylase:Cre and wild-type Long-Evans rats, males and females, were subjected to chronic constriction injury (CCI) for 2 (short-term, CCI-ST) or 30 days (long-term, CCI-LT), evaluating cFos and Fluoro-Gold expression in the LC, and its projections to the spinal cord (SC) and rostral anterior cingulate cortex (rACC). These tests were carried out under basal conditions (unstimulated) and after noxious mechanical stimulation. LC activity was evaluated through chemogenetic and pharmacologic approaches, as were its projections, in association with spontaneous pain-like behaviors.

RESULTS

CCI-ST enhanced basal cFos expression in the LC and in its projection to the SC, which increased further after noxious stimulation. Similar basal activation was found in the neurons projecting to the rACC, although this was not modified by stimulation. Strong basal cFos expression was found in CCI-LT, specifically in the projection to the rACC, which was again not modified by stimulation. No cFos expression was found in the CCI-LT LCipsilateral (ipsi)/contralateral (contra)→SC. Chemogenetics showed that CCI-ST is associated with greater spontaneous pain-like behavior when the LCipsi is blocked, or by selectively blocking the LCipsi→SC projection. Activation of the LCipsi or LCipsi/contra→SC dampened pain-like behavior. Moreover, Designer Receptor Exclusively Activated by Designer Drugs (DREADDs)-mediated inactivation of the CCI-ST LCipsi→rACC or CCI-LT LCipsi/contra→rACC pathway, or intra-rACC antagonism of α-adrenoreceptors, also dampens pain-like behavior.

CONCLUSIONS

In the short term, activation of the LC after CCI attenuates spontaneous pain-like behaviors via projections to the SC while increasing nociception via projections to the rACC. In the long term, only the projections from the LC to the rACC contribute to modulate pain-like behaviors in this model.

EDITOR’S PERSPECTIVE

Effect of Hydroxytyrosol Derivatives of Donepezil on the Activity of Enzymes Involved in Neurodegenerative Diseases and Oxidative Damage

Monoamine oxidase and xanthine oxidase inhibitors represent useful multi-target drugs for the prevention, attenuation, and treatment of oxidative damage and neurodegenerative disorders. Chimeric molecules, constituted by naturally derived compounds linked to drugs, represent lead compounds to be explored for the discovery of new synthetic drugs acting as enzyme inhibitors. We have previously reported that seven hydroxytyrosol-donepezil hybrid compounds play a protective role in an in vitro neuronal cell model of Alzheimer's disease. In this work, we analyzed the effects exerted by the hybrid compounds on the activity of monoamine oxidase A (MAO-A) and B (MAO-B), as well as on xanthine oxidase (XO), enzymes involved in both neurodegenerative disorders and oxidative stress. The results pointed to the identification, among the compounds tested, of selective inhibitors between the two classes of enzymes. While the 4-hydroxy-3-methoxyphenethyl 1-benzylpiperidine-4-carboxylate- (HT3) and the 4-hydroxyphenethyl 1-benzylpiperidine-4-carboxylate- donepezil derivatives (HT4) represented the best inhibitors of MAO-A, with a scarce effect on MAO-B, they were almost ineffective on XO. On the other hand, the 4,5-dihydroxy-2-nitrophenethyl 1-benzylpiperidine-4-carboxylate donepezil derivative (HT2), the least efficient MAO inhibitor, acted like the best XO inhibitor. Therefore, the differential enzymatic targets identified among the hybrid compounds synthesized enhance the possible applications of these polyphenol-donepezil hybrids in neurodegenerative disorders and oxidative stress.

Comparative Cytotoxic Activity of Hydroxytyrosol and Its Semisynthetic Lipophilic Derivatives in Prostate Cancer Cells

A high adherence to a Mediterranean diet has been related to numerous beneficial effects in human health, including a lower incidence and mortality of prostate cancer (PCa). Olive oil is an important source of phenolic bioactive compounds, mainly hydroxytyrosol (HT), of this diet. Because of the growing interest of this compound and its derivatives as a cancer chemopreventive agent, we aimed to compare the in vitro effect of HT isolated from olive mill wastewaters and five semisynthetic alkyl ether, ester, and nitro-derivatives against prostate cancer (PCa) cell lines. The effect in cell proliferation was determined in RWPE-1, LNCaP, 22Rv1, and PC-3 cells by resazurin assay, the effect in cell migration by wound healing assay, and tumorsphere and colony formation were evaluated. The changes in key signaling pathways involved in carcinogenesis were assessed by using a phosphorylation pathway profiling array and by Western blotting. Antiproliferative effects of HT and two lipophilic derivatives [hydroxytyrosyl acetate (HT-Ac)/ethyl hydroxytyrosyl ether (HT-Et)] were significantly higher in cancerous PC-3 and 22Rv1 cells than in non-malignant RWPE-1 cells. HT/HT-Ac/HT-Et significantly reduced migration capacity in RWPE-1 and PC-3 and prostatosphere size and colony formation in 22Rv1, whereas only HT-Ac and HT-Et reduced these functional parameters in PC-3. The cytotoxic effect in 22Rv1 cells was correlated with modifications in the phosphorylation pattern of key proteins, including ERK1/2 and AKT. Consistently, HT-Ac and HT-Et decreased p-AKT levels in PC-3. In sum, our results suggest that HT and its lipophilic derivatives could be considered as potential therapeutic tools in PCa.

Polyphenols and IUGR Pregnancies: Effects of the Antioxidant Hydroxytyrosol on Brain Neurochemistry and Development in a Porcine Model

Supplementation of a mother’s diet with antioxidants, such as hydroxytyrosol (HTX), has been proposed to ameliorate the adverse phenotypes of fetuses at risk of intrauterine growth restriction. In the present study, sows were treated daily with or without 1.5 mg of HTX per kilogram of feed from day 35 of pregnancy (at 30% of total gestational period), and individuals were sampled at three different ages: 100-day-old fetuses and 1-month- and 6-month-old piglets. After euthanasia, the brain was removed and the hippocampus, amygdala, and prefrontal cortex were dissected. The profile of the catecholaminergic and serotoninergic neurotransmitters (NTs) was characterized and an immunohistochemical study of the hippocampus was performed. The results indicated that maternal supplementation with HTX during pregnancy affected the NT profile in a brain-area-dependant mode and it modified the process of neuron differentiation in the hippocampal CA1 and GD areas, indicating that cell differentiation occurred more rapidly in the HTX group. These effects were specific to the fetal period, concomitantly with HTX maternal supplementation, since no major differences remained between the control and treated groups in 1-month- and 6-month-old pigs.

Low Molecular Weight (poly)Phenol Metabolites Across the Blood-Brain Barrier: The Underexplored Journey

The world of (poly)phenols arising from dietary sources has been significantly amplified with the discovery of low molecular weight (LMW) (poly)phenol metabolites resulting from phase I and phase II metabolism and microbiota transformations. These metabolites, which are known to reach human circulation have been studied to further explore their interesting properties, especially regarding neuroprotection. Nevertheless, once in circulation, their distribution to target tissues, such as the brain, relies on their ability to cross the blood-brain barrier (BBB), one of the most controlled barriers present in humans. This represents a key step of an underexplored journey towards the brain. Present review highlights the main findings related to the ability of LMW (poly)phenol metabolites to reach the brain, considering different studies: in silico, in vitro, and in vivo. The mechanisms associated with the transport of these LMW (poly)phenol metabolites across the BBB and possible transporters will be discussed. Overall, the transport of these LMW (poly)phenol metabolites is crucial to elucidate which compounds may exert direct neuroprotective effects, so it is imperative to continue dissecting their potential to cross the BBB and the mechanisms behind their permeation.

Behavioral and Neurochemical Effects of Extra Virgin Olive Oil Total Phenolic Content and Sideritis Extract in Female Mice

The aim of this study was to determine the cognitive and behavioral effects of extra virgin olive oil total phenolic content (TPC) and Sideritis (SID) extracts in female mice, and identify the associated neurochemical changes in the hippocampus and the prefrontal cortex. All animals received intraperitoneal low or high doses of TPC, SID or vehicle treatment for 7 days and were subjected to the Open Field (OF), Novel Object Recognition (NOR) and Tail Suspension Test (TST). The prefrontal cortex and hippocampus were dissected for analysis of neurotransmitters and aminoacids with high performance liquid chromatography with electrochemical detection (HPLC-ED). Both TPC doses enhanced vertical activity and center entries in the OF, which could indicate an anxiolytic-like effect. In addition, TPC enhanced non-spatial working memory and, in high doses, exerted antidepressant effects. On the other hand, high SID doses remarkably decreased the animals’ overall activity. Locomotor and exploratory activities were closely associated with cortical increases in serotonin turnover induced by both treatments. Cognitive performance was linked to glutamate level changes. Furthermore, TPC reduced cortical taurine levels, while SID reduced cortical aspartate levels. TPC seems to have promising cognitive, anxiolytic and antidepressant effects, whereas SID has sedative effects in high doses. Both extracts act in the brain, but their specific actions and properties merit further exploration.

Addressing the instability issue of dopamine during microdialysis: the determination of dopamine, serotonin, methamphetamine and its metabolites in rat brain

Dopamine is a catecholamine neurotransmitter that degrades rapidly in aqueous solutions; hence, its analysis following brain microdialysis is challenging. The aim of the current study was to develop and validate a new microdialysis coupled LC-MS/MS system with improved accuracy, precision, simplicity and turnaround time for dopamine, serotonin, methamphetamine, amphetamine, 4-hydroxymethamphetamine and 4-hydroxyamphetamine analysis in the brain. Dopamine degradation was studied with different stabilizing agents under different storage conditions. The modified microdialysis system was tested in vitro, and was optimized for best probe recovery, assessed by %gain. LC-MS/MS assay was developed and validated for the targeted compounds. Stabilizing agents (ascorbic acid, EDTA and acetic acid) as well as internal and cold standards were added on-line to the dialysate flow. Assay linearity range was 0.01-100 ng/mL, precision and accuracy passed criteria, and LOQ and LLOQ were 0.2 and 1.0 pg, respectively. The new microdialysis coupled LC-MS/MS system was used in Wistar rats striatum after 4 mg/kg subcutaneous methamphetamine. Methamphetamine rapidly distributed to rat striatum reaching an average ~200 ng/mL maximum, ~82.5 min post-dose. Amphetamine, followed by 4-hydroxymethamphetamine, was the most abundant metabolite. Dopamine was released following methamphetamine injection, while serotonin was not altered. In conclusion, we proposed and tested an innovative and simplified solution to improve stability, accuracy and turnover time to monitor unstable molecules, such as dopamine, by microdialysis.

Physiological linkage of gender, bioavailable hydroxytyrosol derivatives, and their metabolites with systemic catecholamine metabolism

Despite extensive characterization of hydroxytyrosol (HT), there is a gap in the knowledge about its capacity to modulate catecholamine pathways. This study deals with the evaluation of the effects of HT, hydroxytyrosol acetate (HTA), and 3,4-dihydroxyphenylacetic acid (DOPAC), as well as their microbial metabolites (homovanillyl alcohol and tyrosol), on the excretion of catecholamines by UHPLC-ESI-QqQ-MS/MS upon administration at 1 and 5 mg kg^-1 to male and female rats. The evaluation of urinary dopamine, norepinephrine, normetanephrine, and 3-methoxytyramine demonstrated 12.0- and 1.5-fold augmented excretions in males and females, respectively, due to the intake of HT derivatives. In addition, specific interconnections were identified between HT, HTA, DOPAC, and tyrosol and 3-methoxytyramine; between HTA and dopamine, norepinephrine, and normetanephrine; between HT, HTA, HVA, and tyrosol and dopamine, norepinephrine, and normetanephrine; and between HT, DOPAC, and HVA and dopamine and 3-methoxytyramine. Hence, a lack of linear relationships was observed between the oral administration of HT, HTA, and DOPAC and their plasma concentrations or urinary excretion levels after they were absorbed and distributed systemically. HT derivatives increase the synthesis of catecholamines in a derivative-, dosage-, and gender-dependent way.

Laccase-Mediated Enhancement of the Antioxidant Activity of Propolis and Poplar Bud Exudates

The treatment of propolis and poplar bud exudates with laccase from Trametes versicolor and 2,2,6,6-tetramethyl-1-piperidinyloxy free radical increased the antioxidant activity, as evaluated by the 2,2'-diphenyl picrylhydrazyl (DPPH)- and t-butyl-OOH-induced DNA breakage comet assay analyses. The effect was highest for shorter reaction times. Propolis showed the highest antioxidant activity in the DPPH test, whereas poplar bud exudates were more active in reducing the t-butyl-OOH-induced lesions in the Chinese hamster ovary cell line. Even if the concentration of polyphenols decreased during the oxidation, the formation of low-molecular-weight phenols phloroglucinol 4 (1,3,5-trihydroxy benzene), hydroquinone 5 (1,4-dihydroxy benzene), and catechol 6 (1,2-dihydroxy benzene), characterized by the radical-scavenging activity, can account for the observed increase in the antioxidant activity.

Hydroxytyrosol targets extracellular matrix remodeling by endothelial cells and inhibits both ex vivo and in vivo angiogenesis

The health benefits of olive oil are attributed to their bioactive compounds, such as hydroxytyrosol. Previously, we demonstrated that hydroxytyrosol inhibits angiogenesis in vitro. The present study aimed to: i) get further insight into the effects of hydroxytyrosol on extracellular matrix remodeling; and ii) test whether hydroxytyrosol is able to inhibit angiogenesis ex vivo and in vivo. Hydroxytyrosol induced a shift toward inhibition of proteolysis in endothelial cells, with decreased expression of extracellular matrix remodeling-enzyme coding genes and increased levels of some of their inhibitors. Furthermore, this work demonstrated that hydroxytyrosol, at concentrations within the range of its content in virgin olive oil that can be absorbed from moderate and sustained virgin olive oil consumption, is a strong inhibitor of angiogenesis ex vivo and in vivo. These results suggest the need for translational studies to evaluate the potential use of hydroxytyrosol for angio-prevention and angiogenesis inhibition in clinical setting.

Synthesis and Antioxidant Activity of Alkyl Nitroderivatives of Hydroxytyrosol

A series of alkyl nitrohydroxytyrosyl ether derivatives has been synthesized from free hydroxytyrosol (HT), the natural olive oil phenol, in order to increase the assortment of compounds with potential neuroprotective activity in Parkinson’s disease. In this work, the antioxidant activity of these novel compounds has been evaluated using Ferric Reducing Antioxidant Power (FRAP), 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), and Oxygen Radical Scavenging Capacity (ORAC) assays compared to that of nitrohydroxytyrosol (NO₂HT) and free HT. New compounds showed variable antioxidant activity depending on the alkyl side chain length; compounds with short chains (2–4 carbon atoms) maintained or even improved the antioxidant activity compared to NO₂HT and/or HT, whereas those with longer side chains (6–8 carbon atoms) showed lower activity than NO₂HT but higher than HT.

Evaluation of the Bioavailability and Metabolism of Nitroderivatives of Hydroxytyrosol Using Caco-2 and HepG2 Human Cell Models

Considering that nitrocatechols present putative effects against Parkinson's disease, the absorption and metabolism of nitroderivatives of hydroxytyrosol (HT) were assessed using human cell model systems. The test compounds nitrohydroxytyrosol (NO2HT), nitrohydroxytyrosyl acetate (NO2HT-A), and ethyl nitrohydroxytyrosyl ether (NO2HT-E) were efficiently transferred across human Caco-2 cell monolayers as an intestinal barrier model, NO2HT-A and NO2HT-E being better (p < 0.05) absorbed (absorption rate (AR) = 1.4 ± 0.1 and 1.5 ± 0.2, respectively) than their precursor, NO2HT (AR = 1.1 ± 0.1). A significant amount of the absorbed compounds remained unconjugated (81, 70, and 33% for NO2HT, NO2HT-A, and NO2HT-E, respectively) after incubation in Caco-2 cells, being available for hepatic metabolism. Nitrocatechols were extensively taken up and metabolized by human hepatoma HepG2 cells as a model of the human liver. Both studies revealed extensive hydrolysis of NO2HT-A into NO2HT, whereas NO2HT-E was not hydrolyzed. Glucuronide (75-55%), methylglucuronide (25-33%), and methyl derivatives (0-12%) were the main nitrocatechol metabolites detected after metabolism in Caco-2 and HepG2 cells. In conclusion, NO2HT, NO2HT-A, and NO2HT-E show high in vitro bioavailability and are extensively metabolized by hepatic cells.