Steady state pharmacokinetics of oral treatment with 13-cis-retinoic acid or all-trans-retinoic acid in male and female adult rats.

Male and female Sprague-Dawley rats were orally gavaged with 13-cis-retinoic acid (7.5 or 15 mg/kg) or all-trans-retinoic acid (10 or 15 mg/kg) for 7 consecutive days. Blood was collected out to 8 hr after the last gavage on day 7. HPLC serum concentrations of 13-cis-retinoic acid, all-trans-retinoic acid, and 13-cis-4-oxo-retinoic acid were subjected to model independent pharmacokinetic analyses. Peak serum levels of 563 to 1640 ng/ml were observed for rats treated with 13-cis-retinoic acid at 1.5-2 hr after gavage. Peak serum levels of 183 to 267 ng/ml at 1.5 hr after gavage were observed for all-trans-retinoic acids. The elimination half-life of 13-cis-retinoic acid was about 1.5 hr while the elimination half-life of all-trans-retinoic acid was slightly longer. There were no sex differences for any parameter. Serum levels resulting from the 7.5 mg/kg 13-cis-retinoic acid were similar to those of human Accutane users.

Four weeks of oral isotretinoin treatment causes few signs of general toxicity in male and female Sprague-Dawley rats.

Despite widespread use of isotretinoin for its anti-acne effects and its current evaluation in clinical trials as a cancer treatment, little is known about its general toxicity in adult nonpregnant animals, particularly after oral administration which mimics the human route. Here, adult male and female Sprague-Dawley rats were gavaged daily with 0 (soy oil), 7.5, or 15 mg/kg isotretinoin for 28 days during which time body weight, food/water intake, and estrous phase were measured. At sacrifice, organ weights were collected and concentrations of dopamine (DA), serotonin and metabolites were measured in frontal cortex, striatum, hippocampus, and diencephalon. Food intake was mildly decreased in both treated groups (approximately 15% in males and 7% in females); however, body weight and water consumption were unaffected. The estrous cycle appeared slightly affected (i.e., lengthened by 15 mg/kg, and both treated groups appeared to have less time in diestrus and more time in estrus). Kidney/body weight ratio was decreased by 7.5 and 15 mg/kg isotretinoin and spleen/body weight ratio was increased in the 7.5 mg/kg group. Males of the 7.5 mg/kg group exhibited significantly higher gonad/body weight ratios than did same-sex controls. Concentrations of monoamine and metabolites in the frontal cortex and diencephalon were unaffected. Nor were striatal DA and DOPAC concentrations affected; however, there were isolated effects on striatal HVA and 5-HIAA. Hippocampal DA concentrations were marginally increased. These data indicate mild effects resulting from oral isotretinoin treatment at doses which likely produce serum levels within the range of humans.

Iron Oxide Nanoparticles Induce Dopaminergic Damage: In vitro Pathways and In Vivo Imaging Reveals Mechanism of Neuronal Damage.

Various iron-oxide nanoparticles have been in use for a long time as therapeutic and imaging agents and for supplemental delivery in cases of iron-deficiency. While all of these products have a specified size range of ∼ 40 nm and above, efforts are underway to produce smaller particles, down to ∼ 1 nm. Here, we show that after a 24-h exposure of SHSY-5Y human neuroblastoma cells to 10 µg/ml of 10 and 30 nm ferric oxide nanoparticles (Fe-NPs), cellular dopamine content was depleted by 68 and 52 %, respectively. Increases in activated tyrosine kinase c-Abl, a molecular switch induced by oxidative stress, and neuronal α-synuclein expression, a protein marker associated with neuronal injury, were also observed (55 and 38 % percent increases, respectively). Inhibition of cell-proliferation, significant reductions in the number of active mitochondria, and a dose-dependent increase in reactive oxygen species (ROS) were observed in neuronal cells. Additionally, using a rat in vitro blood-brain barrier (BBB) model, a dose-dependent increase in ROS accompanied by increased fluorescein efflux demonstrated compromised BBB integrity. To assess translational implications, in vivo Fe-NP-induced neurotoxicity was determined using in vivo MRI and post-mortem neurochemical and neuropathological correlates in adult male rats after exposure to 50 mg/kg of 10 nm Fe-NPs. Significant decrease in T 2 values was observed. Dynamic observations suggested transfer and retention of Fe-NPs from brain vasculature into brain ventricles. A significant decrease in striatal dopamine and its metabolites was also observed, and neuropathological correlates provided additional evidence of significant nerve cell body and dopaminergic terminal damage as well as damage to neuronal vasculature after exposure to 10 nm Fe-NPs. These data demonstrate a neurotoxic potential of very small size iron nanoparticles and suggest that use of these ferric oxide nanoparticles may result in neurotoxicity, thereby limiting their clinical application.

Comparative effects of substituted amphetamines (PMA, MDMA, and METH) on monoamines in rat caudate: a microdialysis study.

Paramethoxyamphetamine (PMA) is a methoxylated phenethylamine derivative that has been used illicitly in Australia since 1994. PMA is also becoming popular at rave parties in the United States. PMA raised concern when a series of fatalities resulted after its use in South Australia, where it was marketed as "ecstasy," which is the colloquial name for MDMA. In the present study, we evaluated the comparative neurotoxicity of substituted amphetamines in rats. Extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were assayed in the caudate of freely moving rats using microdialysis and HPLC-EC. Dialysates were assayed every 20 minutes for 4 hours after an intraperitoneal (i.p.) injection of PMA (2.5, 5, 10, 20 mg/kg), MDMA (10 and 20 mg/kg), or METH (2.5 mg/kg). METH produced a significant increase in extracellular DA (700%), and significant decreases in extracellular DOPAC and HVA (30% and 50%), with no detectable changes in either 5-HT or 5-HIAA. MDMA produced significant increases in DA (700% at 10 mg/kg and 950% at 20 mg/kg) and decreases in DOPAC (15% for both 10 and 20 mg/kg), and HVA (50% at 10 mg/kg and 35% at 20 mg/kg). MDMA also increased 5-HT (350% at 10, and 575% at 20 mg/kg), and decreased 5-HIAA to 60% for both dose levels. PMA produced no detectable increases in DA at dose levels of 2.5, 5, or 10 mg/kg, but significantly increased DA (975%) at a dose of 20 mg/kg. However, PMA significantly decreased DOPAC at all dose levels (75% at 2.5; 40% at 5; 30% at 10; 10% at 20 mg/kg), with comparable decreases in HVA at all dose levels. PMA also produced significant increases in 5-HT at 10 and 20 mg/kg (350% for both dose levels), with no detectable changes in 5-HT at 2.5 or 5 mg/kg. All dose levels of PMA significantly decreased 5-HIAA (50 to 70%). These data suggest that PMA, like MDMA and METH, is capable of producing dopaminergic and serotonergic neurotoxicity.

In vivo basal and amphetamine-induced striatal dopamine and metabolite levels are similar in the spontaneously hypertensive, Wistar-Kyoto and Sprague-Dawley male rats.

Nigrostriatal alterations are proposed to partially underlie the hypertension and hyperactivity exhibited by the spontaneously hypertensive rat (SHR). Here, in vivo microdialysis was used to measure baseline and d-amphetamine (AMPH)-stimulated striatal dopamine (DA) and metabolite levels in adult male SHR, Wistar-Kyoto (WKY), and Sprague-Dawley (SD) rats. At approximately 19 weeks of age, baseline levels of DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were measured after which time, each rat was injected intraperitoneally with 2 mg/kg AMPH and samples were collected for the subsequent 200 min. There were no significant strain differences in baseline levels of DA, HVA, and 5-HIAA. The baseline level of DOPAC was decreased in the WKY relative to the SD. AMPH treatment altered DA, DOPAC, HVA, and 5-HIAA to a similar extent in all strains; thus, there were no significant strain differences, nor did the area under the curve (AUC) for DA levels differ between strains. AUC for DOPAC was significantly smaller for the WKY relative to the SD strain, likely due to the lower baseline level. At the single dose of amphetamine used here, the results indicate that in vivo DA levels in the SHR are similar to the WKY and SD strains.

Effects of lifelong dietary exposure to genistein or nonylphenol on amphetamine-stimulated striatal dopamine release in male and female rats.

Estrogen modulates baseline and amphetamine-stimulated dopamine (DA) release in the adult female rat striatum. The isoflavone found in soybeans, genistein, is a phytoestrogen and may have comparable effects on striatal DA levels. Similarly, the industrial intermediate and potential endocrine disrupter, para-nonylphenol, has estrogen-like effects. Here, Sprague-Dawley rats were continuously exposed to phytoestrogen-free diets containing 0, 100, or 500 ppm genistein (Experiment 1) or 0 or 200, or 750 ppm nonylphenol (Experiment 2) beginning at conception and continuing throughout. To eliminate estrous cycle influences on DA levels, females were ovariectomized at adulthood. As adults, striatal levels of DA and its metabolites [3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)] were measured in unanesthetized male and female rats via cerebral microdialysis before and for 200 min after an intraperitoneal injection of 2 mg/kg D-amphetamine. Although baseline 5-hydroxyindoleacetic acid (5-HIAA) levels indicated an isolated effect in genistein-treated females, there were no meaningful differences among treatment groups in baseline levels of DA, DOPAC, or HVA. However, dietary exposure to 500 ppm genistein significantly potentiated amphetamine-stimulated DA release in males and a similar trend was apparent, but not statistically significant, in females. Dietary exposure to 200 or 750 ppm nonylphenol had no significant effects in males or females. These results suggest that dietary genistein exposure may act similarly to estradiol in augmenting amphetamine-stimulated DA release.

Chronic exposure to rotenone, a dopaminergic toxin, results in peripheral neuropathy associated with dopaminergic damage.

Rotenone, a widely used pesticide, causes a syndrome in rats that replicates, both pathologically and behaviorally, the symptoms of Parkinson's disease (PD). In the present study, we sought to determine if a chronic exposure to rotenone, resulting in dopaminergic loss, could also lead to peripheral neuronal damage related to motor dysfunction. Adult male Sprague-Dawley rats (n=14) were treated with rotenone (1 or 2mg/kg, s.c., once daily) on days 1, 3, 6, 8, 10, 13, 15, 17, 21, 22, and 27 to minimize mortality. Control rats received vehicle (DMSO) injections. Animals were weighed on the days of injection and monitored daily. A mortality of 21% was observed in rotenone treated rats. The motor nerve conduction velocity (MCV) was assessed using action potentials detected from the tail muscle through surface receiver electrodes installed around the distal portion of the tail. Rats exposed to rotenone often developed hind limb paresis with a significant decrease in MCV as detected in tail nerves (p<0.05). Animals were then sacrificed, either 24h after rotenone exposure on day 6 or 24h after the last dose of rotenone on day 27. The striatum and sciatic nerves were dissected on dry ice and flash-frozen and kept at -80°C until further analysis. Striatal dopamine (DA) was analyzed using HPLC-ECD and sciatic nerve pathology was analyzed for neurodegeneration. A time-dependent rotenone-induced striatal depletion of DA (60% after 7 days and 80% after 27 days) was observed. Furthermore, Neurofilament-neurofilament B, Flouro-Jade C and myelin basic protein analyses suggested a time-dependent rotenone-induced neurodegeneration in sciatic nerves. These data, for the first time, indicate an association between dopaminergic damage and peripheral motor nerve degeneration in an animal model of dopaminergic toxicity. Peripheral motor nerve dysfunction in rats following a chronic exposure to rotenone may serve not only as a relevant experimental model of motor neuropathy but also as a peripheral marker of dopaminergic neuronal damage to the central nervous system.

Buprenorphine modulates methamphetamine-induced dopamine dynamics in the rat caudate nucleus.

Methamphetamine (METH) abuse and addiction present a major problem in the United States and globally. Oxidative stress associated with exposure to METH mediates to the large extent METH-evoked neurotoxicity. While there are currently no medications approved for treating METH addiction, its pharmacology provides opportunities for potential pharmacotherapeutic adjuncts to behavioral therapy in the treatment of METH addiction. Opioid receptor agonists can modulate the activity of dopamine neurons and could, therefore, modify the pharmacodynamic effects of METH in the dopaminergic system. Efficacy of the adjunctive medication with buprenorphine has been demonstrated in the treatment of cocaine addiction extending beyond opiate addiction. We investigated the interactions of morphine (10 mg/kg) and buprenorphine (0.01 and 10 mg/kg) with METH (2 mg/kg) affecting striatal dopaminergic transmission. The extracellular concentration of dopamine (DA) and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were determined using brain microdialysis coupled with high performance liquid chromatography with electrochemical detection (HPLC-ED) in the caudate nucleus of adult, awake, male Sprague-Dawley rats. Compared to METH alone, extracellular DA release was prolonged for 140 min without changes in DA peak-effect by combined treatment with morphine/METH. Morphine did not change DOPAC efflux evoked by METH. On the other hand, both buprenorphine doses attenuated the METH-induced DA peak-effect. However, whereas high buprenorphine dose extended DA outflow for 190 min, the low-dose abbreviated DA release. High buprenorphine dose also shortened METH-induced decrease in DOPAC efflux. Data confirm that opiates modulate dopaminergic neurotransmission evoked by METH. Alteration of dopaminergic response to METH challenge under buprenorphine may suggest effectiveness of buprenorphine treatment in METH addiction.

Assessment of 3-nitropropionic acid-evoked peripheral neuropathy in rats: neuroprotective effects of acetyl-l-carnitine and resveratrol.

Oxidative stress and secondary excitotoxicity, due to cellular energy deficit, are major factors playing roles in 3-nitropropionic acid (3-NPA) induced mitochondrial dysfunction. Acute or chronic exposure to 3-NPA also leads to neuronal degeneration in different brain regions. The present study quantitatively assessed peripheral neuropathy induced by chronic exposure to 3-NPA in rats. The neuroprotective abilities of two antioxidants, acetyl-l-carnitine and resveratrol, were investigated as well. Rats were exposed for up to four weeks to 3-NPA alone or 3-NPA combined with acetyl-l-carnitine or resveratrol, administered peripherally. The experimental outcome was evaluated by neurophysiological, histological, and morphometric analyses. Rats exposed to 3-NPA developed hind limb paresis. Furthermore, a significant decrease in motor nerve conduction velocity (MCV) was detected in tail nerves and axonal degeneration in sciatic nerves (p<0.05). Treatment with resveratrol prevented the functional effects of 3-NPA exposure, whereas treatment with acetyl-l-carnitine, preventing paresis, was not effective to MCV and morphological changes. These data suggest that resveratrol is a good candidate for treatment of metabolic neuropathy. The experimental outcome of this study shows that chronic treatment with 3-NPA in rats is relevant in development of an experimental model of toxic neuropathy.