Blood-brain barrier to 6-hydroxydopamine: uptake by heart and brain

Neuroprotection of Truncated Peptide IIAVE from Isochrysis zhanjiangensis: Quantum Chemical, Molecular Docking, and Bioactivity Studies

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the elderly for which there is no cure or disease-modifying therapy. Mitochondrial dysfunction and oxidative stress play a central role in dopaminergic neurodegeneration in PD. Therefore, antioxidants are considered a promising neuroprotective approach. In in vivo activity studies, 6-OHDA-induced oxidative stress in SH-SY5Y cells was established as a model of PD for cellular experiments. IIAVE (Ile-Ile-Ala-Val-Glu) was derived from Isochrysis zhanjiangensis octapeptide (IIAVEAGC), which has a small molecular weight. The structure and antioxidant activity of IIAVE were tested in a previous study and proved to have good antioxidant potential. In this study, the chemical properties of IIAVE were calculated using quantum chemical methods, including frontier molecular orbital (FMO), molecular electrostatic potential (MEP), natural population analysis (NPA), and global reactivity properties. The interaction of IIAVE with Bcl-2 and DJ-1 was investigated using the molecular docking method. The results showed that IIAVE promoted the activation of the Keap1/Nrf2 pathway and up-regulated the expression of the superoxide dismutase 1 (SOD-1) protein by inhibiting the level of reactive oxygen species (ROS) in cells. In addition, IIAVE inhibits ROS production and prevents 6-OHDA-induced oxidative damage by restoring mitochondrial membrane potential. Furthermore, IIAVE inhibited cell apoptosis by increasing the Bcl-2/Bax ratio and inhibiting the activation of Caspase-9 and Caspase-3. Thus, IIAVE may become a potential drug for the treatment and prevention of PD.

Guanosine Protects Striatal Slices Against 6-OHDA-Induced Oxidative Damage, Mitochondrial Dysfunction, and ATP Depletion

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by loss of dopaminergic neurons in substantia nigra pars compacta which induces severe motor symptoms. 6-OHDA is a neurotoxin widely used in PD animal models due to its high affinity by dopamine transporter, its rapid non-enzymatic auto-oxidation which generates reactive oxygen species (ROS), oxidative stress, and for induced mitochondrial dysfunction. We previously reported an in vitro protocol of 6-OHDA-induced toxicity in brain regions slices, as a simple and sensitive assay to screen for protective compounds related to PD. Guanosine (GUO), a guanine-based purine nucleoside, is a neuroprotective molecule that is showing promising effects as an antiparkinsonian agent. To investigate the mechanisms involved on GUO-induced neuroprotection, slices of cortex, striatum, and hippocampus were incubated with GUO in the presence of 6-OHDA (100 μM). 6-OHDA promoted a decrease in cellular viability and increased ROS generation in all brain regions. Disruption of mitochondrial potential, depletion in intracellular ATP levels, and increase in cell membrane permeabilization were evidenced in striatal slices. GUO prevented the increase in ROS generation, disruption in mitochondrial potential, and depletion of intracellular ATP induced by 6-OHDA in striatal slices. In conclusion, GUO was effective to prevent oxidative events before cell damage, such as mitochondrial disruption, intracellular ATP levels depletion, and ROS generation in striatal slices subjected to in vitro 6-OHDA-induced toxicity.

Time-course of brain oxidative damage caused by intrastriatal administration of 6-hydroxydopamine in a rat model of Parkinson's disease

The unilateral and intrastriatal injection of 6-hydroxydopamine is commonly used to provide a partial lesion model of Parkinson's disease in the investigation of the molecular mechanisms involved in its pathogenesis and to assess new neuroprotective treatments. Its capacity to induce neurodegeneration has been related to its ability to undergo autoxidation in the presence of oxygen and consequently to generate oxidative stress. The aim of the present study was to investigate the time course of brain oxidative damage induced by 6-hydroxydopamine (6 microg in 5 microl of sterile saline containing 0.2% ascorbic acid) injection in the right striatum of the rat. The results of this study show that the indices of both lipid peroxidation (TBARS) and protein oxidation (carbonyl and free thiol contents) increase simultaneously in the ipsilateral striatum and ventral midbrain, reaching a peak value at 48-h post-injection for both TBARS and protein carbonyl content, and at 24 h for protein free thiol content. A lower but significant increase was also observed in the contralateral side (striatum and ventral midbrain). The indices of oxidative stress returned to values close to those found in controls at 7-day post-injection. These data show that the oxidative stress is a possible triggering factor for the neurodegenerative process and the retrograde neurodegeneration observed after 1-week post-injection is a consequence of the cell damage caused during the first days post-injection. The optimal time to assess brain indices of oxidative stress in this model is 48-h post-injection.

Density of the dopamine innervation in rat cerebral cortex after neonatal 6-hydroxydopamine or adult stage DSP-4 noradrenaline denervations: a quantitative radioautographic study

An in vitro radioautographic approach was used to count dopamine axon terminals (varicosities) of the mediofrontal and the supragenual cingulate cortex in 30-40-day-old rats treated with 6-hydroxydopamine at birth or with N(2-chloro-ethyl)N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) 7-10 days earlier. Compared to controls, there were no increases in the density of dopamine innervation in either region of the noradrenaline-denervated cortex after either treatment. The results, therefore, did not support the hypothesis of a sprouting of dopamine terminals reported to account for augmented cortical dopamine levels under these conditions. In line with earlier observations, such biochemical changes might rather be indicative of altered dopamine steady-state levels.

An investigation of the role of adrenergic innervation in the regulation of the extraneuronal uptake of [3H]-isoprenaline into rat vasa deferentia and atria

Destruction of adrenergic nerves by neonatal guanethidine treatment did not affect the extraneuronal accumulation of [3H]-isoprenaline by adult vasa deferentia or atria. Neither pre- nor post-ganglionic denervation of vasa deferentia resulted in a significant change in extraneuronal accumulation of [3H]-isoprenaline. The appearance and subsequent development of extraneuronal uptake in embryonic and newborn rats did not appear to be dependent on a fully developed or functional adrenergic innervation. Decreasing plasma catecholamine levels by adrenal demedullation did not have an effect on extraneuronal uptake. Chronic cold exposure (7 days) significantly increased plasma levels of adrenaline, and there was a significant decrease in the corticosterone-sensitive extraneuronal uptake of [3H]-isoprenaline into atria. After 14 days in the cold, plasma adrenaline levels had fallen, and were no longer significantly different from control levels. The extraneuronal uptake of [3H]-isoprenaline into atria after 14 days cold exposure was no longer different from that of control atria. There did not appear to be a direct correlation between plasma catecholamines and extraneuronal accumulation of [3H]-isoprenaline. Neither the presence of adrenergic nerves nor plasma catecholamines appear to play a major role in the regulation of extraneuronal uptake by atria and vasa deferentia of the rat.

Intraventricular 6-hydroxydopamine increases the adrenal cortex mitotic activity in rats

Effects of intraventricular injections of 6-hydroxydopamine (6-OHDA) on adrenocortical cell proliferation in rats have been investigated by means of the colchicine metaphase-arrest technique. In the group of animals receiving 6-OHDA alone, an increase of mean mitotic activity rate (MMAR) was observed at 96 h and 144 h after injection. This rise of MMAR was completely inhibited by pretreatment of animals with desmethylimipramine (DMI) - a blocker of norepinephrine uptake. It is concluded that enhancement of ACTH secretion is responsible for the above mentioned increase of mitotic activity after 6-OHDA administration. This phenomenon is related to abolition of the inhibitory noradrenergic effect on ACTH secretion by 6-OHDA treatment. Additionally, the results suggest little or no involvement of dopaminergic neurons in early changes of ACTH secretion after intraventricular 6-OHDA.

Neural contribution to renal hypertension following acute renal artery stenosis in conscious rats

To assess the hemodynamic changes during acute renal artery stenosis (RSt) and their dependence on alterations in the renin-angiotensin and sympathetic nervous systems, we studied conscious rats chronically instrumented with miniaturized pulsed-Doppler flow probes. Probes were implanted on the superior mesenteric and both renal arteries, and on the lower abdominal aorta for measurement of mesenteric (MR), renal (RR), and hindquarters (HQR) vascular resistance. Unilateral RSt, with a pneumatic cuff occluder that reduced flow by approximately 50%, increased mean arterial pressure (MAP) by 32%, reduced heart rate, and increased MR, nonstenotic (contralateral) RR and HQR. The hypertension was renin-dependent since plasma renin activity increased 6-fold and the angiotensin II (AII) antagonist, saralasin, significantly reduced MAP and regional resistances. The acute hypertension was also associated with increased neurogenic vasoconstrictor tone since hexamethonium markedly reduced MAP, MR, HQR and non-stenotic RR. Hexamethonium similarly decreased MAP during hypertension induced by AII infusion, whereas hypertension produced by the "pure" peripheral vasoconstrictor, phenylephrine, was unaffected by ganglionic blockade. In animals with peripheral sympathectomy produced by 6-hydroxydopamine, acute RSt produced hemodynamic changes similar in magnitude to intact animals; however, PRA increased 3-fold more than in intact rats. We conclude that hypertension induced by acute RSt in conscious rats is not only renin-dependent, but is also associated with inappropriately high neurogenic vasoconstrictor tone, presumably activated by indirect neural actions of AII.

Further studies on the effects of intravenously administered 6-hydroxydopamine on the median eminence of the rat

6-Hydroxydopamine (6-OHDA) given i.v. in a dose of 150 mg/kg to adult male Sprague-Dawley rats produces at 24 h a complete depletion of median eminence (ME) and neurointermediate lobe (NIL) catecholamines (CA), as judged by Falck-Hillarp fluorescence histochemistry, leaving the remainder of the hypothalamus substantially unaltered. Restoration of a normal fluorescence histochemical appearance took place over 35 days, apparently due to regeneration of CA-containing terminals. Administration of desipramine prior to 6-OHDA injection modified its effect; depletion was largely confined to the midline region of the external layer of the ME and to the NIL, suggesting that these regions contain dopaminergic terminals. Microspectrofluorometric methods were used in an attempt to verify this conclusion. It is suggested that this technique provides a model for establishing the role of ME and NIL CA-containing structures in control of pituitary gland function.

Diurnal rhythms in noradrenaline turnover and motility after reserpine and 6-hydroxydopamine

Experiments were performed in male Wistar rats synchronized by controlled conditions of light (0700--1900 hr) and of darkness (1900--0700 hr). Separately in each photo-period the effects of reserpine or 6-OHDA on the cardiac noradrenaline turnover. Whereas peripheral chemical sympathectomy did not greatly affect the diurnal rhythm in the motor activity were investigated. Initial depletion of the cardiac noradrenaline after acute application of either drug was significantly greater when injected at 2000 hr compared to 0800 hr. In both photo-periods the cardiac turnover of noradrenaline was increased after peripheral chemical sympathectomy with 6-OHDA as well as after amine depletion with reserpine. Inhibition of the protein synthesis had no effect, ganglionic blockade by chlorisondamine on the other hand abolished the rhythm in the motor activity, subacute treatment with reserpine differently affected motor activity in both photo-periods, depending on the time of drug application within 24 hr of a day. The results show that diurnal variations in the levels of neuronal and of motor activity are able to influence drug effects and have thus to be taken into account in animal studies.