Nanocrystals as an effective strategy to improve Pomalidomide bioavailability in rodent

Pomalidomide (POM) is an FDA-approved immunomodulatory imide drug (IMiDs) an it is effectively used in the treatment of multiple myeloma. IMiDs are analogs of the drug thalidomide and they have been repurposed for the treatment of several diseases such as psoriatic arthritis and Kaposi Sarcoma. In recent years, IMiDs have been also evaluated as a new treatment for neurological disorders with an inflammatory and neuroinflammatory component. POM draws particular interest for its potent anti-TNF-α activity at significantly lower concentrations than the parent compound thalidomide. However, POM's low water solubility underpins its low gastrointestinal permeability resulting in irregular and poor absorption. The purpose of this work was to prepare a POM nanocrystal-based formulation that could efficiently improve POM's plasma and brain concentration after intraperitoneal injection. POM nanocrystals prepared as a nanosuspension by the media milling method showed a mean diameter of 219 nm and a polydispersity index of 0.21. POM's nanocrystal solubility value (22.97 µg/mL) in phosphate buffer was about 1.58 folds higher than the POM raw powder. Finally, in vivo studies conducted in adult Male Sprague-Dawley rats indicated that POM nanocrystal ensured higher and longer-lasting drug levels in plasma and brain when compared with POM coarse suspension.

Trimethyl Chitosan Hydrogel Nanoparticles for Progesterone Delivery in Neurodegenerative Disorders

Progesterone is a sex hormone which shows neuroprotective effects in different neurodegenerative disorders, including Parkinson’s disease, stroke, and Alzheimer’s disease. However, the pharmacokinetic limitations associated with the peripheral administration of this molecule highlight the need for more efficient delivery approaches to increase brain progesterone levels. Since the nose-to-brain administration of mucoadhesive hydrogel nanoparticles is a non-invasive and convenient strategy for the delivery of therapeutics to the central nervous system, in this work, progesterone-loaded hydrogel nanoparticle formulations have been prepared, characterized, and tested in vivo. Nanoparticles, loaded with different progesterone concentrations, have been obtained by polyelectrolyte complex formation between trimethyl chitosan and sodium alginate, followed by ionotropic gelation with sodium tripolyphosphate as a cross-linking agent. All formulations showed a mean diameter ranging from 200 nm to 236 nm, a polydispersity index smaller than 0.23, and a high progesterone encapsulation efficiency (83–95%). The zeta potential values were all positive and greater than 28 mV, thus ensuring nanoparticles stability against aggregation phenomena as well as interaction with negative sialic residues of the nasal mucosa. Finally, in vivo studies on Sprague–Dawley male rats demonstrated a 5-fold increase in brain progesterone concentrations compared to basal progesterone level after 30 min of hydrogel nanoparticle inhalation.

Neuroprotective and anti-inflammatory properties of a novel non-thiazolidinedione PPARγ agonist in vitro and in MPTP-treated mice

Peroxisome proliferator-activated receptor (PPAR)γ is a potential pharmacological target for disease-modification in Parkinson's disease (PD), mainly acting by modulating the neuroinflammatory response. However, currently available agonists thiazolidinediones (TZDs) present limitations due to safety concerns. We evaluated a novel thiobarbituric-like compound MDG548, which acts as a functional PPARγ agonist displaying higher and selective binding affinity as compared to TZDs. Neuroprotection by MDG548 was tested in vitro and in a mouse MPTP model of PD, and neuroinflammation was investigated as a putative underlying mechanism. Viability assay on rat cortical neurons showed lack of cytotoxic effect in the dose-range of 100 nM-10 μM, which was therefore used for testing in vitro protection against H2O2 and MPP+ neurotoxicity. MDG548 dose-dependently increased cell viability of rat cortical neurons co-treated with H2O2 or pre-exposed to MDG548 prior to H2O2. Moreover, MDG548 induced neuroprotection in MPP+-treated PC12 cells. NF-kB activation was investigated to assess anti-inflammatory activity. MDG548 dose-dependently decreased NF-kB activation induced by LPS (100 ng/100ml) in HEK-Blue-hTLR4 cells. Given the supposed cancer risk of other PPARγ agonists, Ames test for genotoxicity was performed in Salmonella typhimurium TA100 and TA98 strains, showing that MDG548 was not genotoxic. In vivo, BL/6J mice were treated with MPTP (20mg/kg i.p. once/day for 4 days) in association with saline or MDG548 (2, 5, 10 mg/kg i.p.). Stereological counting showed that MDG548 prevented the MPTP-induced reduction in TH-positive cells in the substantia nigra compacta (SNc) at all doses tested. Moreover, MDG548 reduced reactive microglia and iNOS induction in the SNc. MDG548, being a non-TZD compound with high PPARγ affinity, void of genotoxicity, and with in vitro as well as in vivo neuroprotective properties, provides a promising alternative in the search for safer PPARγ agonists to be tested as potential disease-modifying drugs in PD.

Activation of PPAR gamma receptors reduces levodopa-induced dyskinesias in 6-OHDA-lesioned rats

Long-term administration of l-3,4-dihydroxyphenylalanine (levodopa), the mainstay treatment for Parkinson's disease (PD), is accompanied by fluctuations in its duration of action and motor complications (dyskinesia) that dramatically affect the quality of life of patients. Levodopa-induced dyskinesias (LID) can be modeled in rats with unilateral 6-OHDA lesions via chronic administration of levodopa, which causes increasingly severe axial, limb, and orofacial abnormal involuntary movements (AIMs) over time. In previous studies, we showed that the direct activation of CB1 cannabinoid receptors alleviated rat AIMs. Interestingly, elevation of the endocannabinoid anandamide by URB597 (URB), an inhibitor of endocannabinoid catabolism, produced an anti-dyskinetic response that was only partially mediated via CB1 receptors and required the concomitant blockade of transient receptor potential vanilloid type-1 (TRPV1) channels by capsazepine (CPZ) (Morgese et al., 2007). In this study, we showed that the stimulation of peroxisome proliferator-activated receptors (PPAR), a family of transcription factors activated by anandamide, contributes to the anti-dyskinetic effects of URB+CPZ, and that the direct activation of the PPARγ subtype by rosiglitazone (RGZ) alleviates levodopa-induced AIMs in 6-OHDA rats. AIM reduction was associated with an attenuation of levodopa-induced increase of dynorphin, zif-268, and of ERK phosphorylation in the denervated striatum. RGZ treatment did not decrease striatal levodopa and dopamine bioavailability, nor did it affect levodopa anti-parkinsonian activity. Collectively, these data indicate that PPARγ may represent a new pharmacological target for the treatment of LID.

Different responsiveness of striatonigral and striatopallidal neurons to L-DOPA after a subchronic intermittent L-DOPA treatment

Early gene induction by L-DOPA in the striatum of dopamine denervated rats represents a useful way to study long-term modifications produced by this drug. The effects of acute and subchronic L-DOPA administration on zif-268 mRNA expression were compared in 6-hydroxydopamine-lesioned rats. Rats received a subchronic intermittent L-DOPA (6 mg/kg) treatment, which produces behavioural sensitization, a correlate of dyskinetic movements. Three days after interruption of subchronic treatment, zif-268 mRNA was evaluated after an L-DOPA challenge. Zif-268 mRNA levels increased in the lesioned dorsolateral striatum after either acute or subchronic L-DOPA administration. Double labelling of striatal cells with zif-268 and enkephalin or dynorphin mRNA probes was performed to assess neuronal activation in the indirect and direct output pathway. Single acute L-DOPA significantly increased zif-268 in all striatal neurons reflecting a hyperresponsiveness of dopamine-depleted striatum. After subchronic L-DOPA, zif-268 mRNA labelling was still increased in the striatonigral pathway, limited to dynorphin(+) neurons, whereas in all other neurons it was similar to the control value. Results suggest that striatal neurons responding to acute L-DOPA differ from those responding to subchronic L-DOPA. L-DOPA-induced behavioural sensitization was associated to a down-regulation in the responsiveness of striatopallidal and striatonigral dynorphin(-) neurons, whereas in striatonigral neurons containing dynorphin a hyperresponsiveness to L-DOPA was observed. High levels of zif-268, together with a persistent hyperresponsiveness of striatonigral dymorphinergic neurons and hyporesponsiveness of striatopallidal neurons, by creating an unbalanced state of striatal efferent neurons, may be implicated in dyskinetic movements observed in Parkinson's disease (PD).

Selective modifications in GAD67 mRNA levels in striatonigral and striatopallidal pathways correlate to dopamine agonist priming in 6-hydroxydopamine-lesioned rats

The present study investigated long-term alterations in striatal gene expression after single exposure of unilaterally 6-hydroxydopamine-lesioned rats to different dopamine agonists (priming). Rats were primed with the D1 agonist SKF38393 (10 mg/kg), the D2/D3 agonist quinpirole (0.2 mg/kg), the dopamine precursor L-DOPA (50 mg/kg) or with vehicle (drug-naive), and GAD67, dynorphin and enkephalin mRNAs were evaluated in the striatum by in situ hybridization, 3 days after priming. To evaluate GAD67 mRNA in striatonigral and striatopallidal neurons, identified as enkephalin (-) and (+) neurons, double-labelling in situ hybridization was used. Drug-naive lesioned rats showed an increase in GAD67 mRNA in enkephalin (-) and (+) neurons, an increase in enkephalin and a decrease in dynorphin mRNAs. Priming with either SKF38393 or quinpirole further increased GAD67 mRNA in enkephalin (-) and (+) neurons, however, while SKF38393 produced a high and unbalanced activation toward enkephalin (-) neurons, after quinpirole the increase was of low intensity and similar in the two pathways. Dynorphin mRNA was increased by SKF38393 but not by quinpirole, whereas enkephalin mRNA was not changed by either priming. L-DOPA produced a high and similar increase in GAD67 mRNA in enkephalin (-) and (+) neurons. Priming differentially affected peptides and GAD67 mRNA in striatopallidal and striatonigral neurons depending on the dopamine agonist used. The degree of enduring overactivity of the striatopallidal and striatonigral pathways may be related to the ability of L-DOPA and D1 or D2/D3 receptor agonists to prime motor behavioural responses and to produce dyskinetic side-effects.

Modification of adenosine extracellular levels and adenosine A(2A) receptor mRNA by dopamine denervation

Adenosine A(2A) receptor antagonists have been proposed as an effective therapy in the treatment of Parkinson's disease. To explore the possibility that dopamine denervation may produce modifications in adenosine A(2A) transmission, we measured the extracellular concentration of adenosine and adenosine A(2A) receptor mRNA in the striatum of rats infused unilaterally with 6-hydroxydopamine in the medial forebrain bundle. Fifteen days after 6-hydroxydopamine infusion, extracellular adenosine levels, measured by in vivo microdialysis, were significantly lower (-35%) in the dopamine-denervated striatum. At the time of the decrease in adenosine levels, an increase in striatal adenosine A(2A) receptor mRNA levels (+20%), measured by in situ hybridization, was observed. Modifications in adenosine A(2A) transmission, following nigrostriatal dopamine neuron degeneration, establish a potential neural basis for the effectiveness of adenosine A(2A) receptor antagonists in the treatment of Parkinson's disease.

Cocaine effects on gene regulation in the striatum and behavior: increased sensitivity in D3 dopamine receptor-deficient mice

Central effects of psychostimulants such as cocaine are predominantly mediated by dopamine receptors. We have used mice with a targeted deletion of the D3 dopamine receptor subtype to investigate the role of this receptor in the regulation of gene expression in striatal neurons and behavior by acute and repeated treatment with cocaine (25 mg/kg). In mice lacking D3 receptors, acute administration of cocaine has more pronounced stimulatory effects on c-fos and dynorphin expression in the dorsal and ventral striatum. The behavioral response to cocaine is also increased in these mice. These findings indicate that the D3 receptor plays an inhibitory role in the action of cocaine on behavior and gene regulation in the striatum.

Expression of functional leptin receptors in rodent Leydig cells

Several studies indicate that the size of body fat stores and the circulating levels of the adipocyte-derived hormone leptin are able to influence the activity of the hypothalamic-pituitary-gonadal axis. The leptin-hypothalamic-pituitary-gonadal interactions have been mainly studied at the level of the central nervous system. In this study, we investigated the possibility that leptin may have direct effects on the rodent Leydig cell function. To probe this hypothesis, we first analyzed the expression of leptin receptors (OB-R) in rodent Leydig cells in culture. RT-PCR studies showed that rat Leydig cells express both the long (OB-Rb) and short isoform (OB-Ra) of leptin receptor, whereas MLTC-1 cells (a murine Leydig tumor cell line) express only the long isoform. Short-term (30-90 min) incubation of rat Leydig cells with increasing concentrations ofleptin (2-500 ng/ml) led to a significant and dose-dependent inhibition of human (h)CG-stimulated testosterone (T) production (approximately 60% reduction, IC50 = 20 ng/ml) but no change in basal androgen release. Also, leptin (150 ng/ml) amplified hCG-induced intracellular cAMP formation (1- to 2-fold) without modifying basal cAMP levels. Subsequent experiments showed that leptin inhibited 8Br-cAMP-stimulated T production, indicating that leptin's effect is exerted beyond cAMP. The inhibitory effect of leptin on hCG-induced T secretion was accompanied by a significant reduction of androstenedione and a concomitant rise of the precursor metabolites pregnenolone, progesterone, and 17-OH-progesterone, conceivable with a leptin-induced lesion of 17,20 lyase activity. Separate experiments performed with the MLTC-1 cells (not expressing cytochrome P450-17alpha) showed that leptin, though amplifying hCG-stimulated cAMP production, did not modify hCG-stimulated pregnenolone and progesterone release. These results further indicate that leptin action on steroidogenesis occurs downstream of progesterone synthesis. Northern Blot experiments showed no acute effect of leptin on cytochrome P450-17alpha messenger RNA accumulation in rat Leydig cells in basal and hCG-stimulated conditions, excluding that the rapid changes observed were caused by messenger RNA degradation. In conclusion, these findings, for the first time, show that leptin has direct, receptor-mediated actions on rodent Leydig cells in culture, at concentrations within the range of obese men.

Lack of a role for the D3 receptor in clozapine induction of c-fos demonstrated in D3 dopamine receptor-deficient mice

The role of the D3 dopamine receptor in mediating the effects of clozapine was analysed using in situ hybridization histochemistry to measure the induction of the immediate early gene c-fos in different brain areas of mice lacking a functional D3 dopamine receptor compared to wild type mice. Clozapine treatment (15 and 30 mg/kg, s.c.) resulted in a dose-dependent pattern of induction of c-fos messenger RNA in the striatum, accumbens and septal area, with a non-significant increase in the prefrontal cortex. There was no difference detected in any of these areas in the level of induction between mice lacking the D3 receptor (D3-/-) and wild type (D3+/+). To determine which types of neurons in the striatum and accumbens displayed clozapine (30 mg/kg) induction of c-fos messenger RNA, a double-labeling experiment was performed using a radioactive c-fos messenger RNA probe and a digoxigenin-labeled enkephalin messenger RNA probe, the latter used as a marker of D2-containing neurons. Clozapine-induced c-fos was detected in 20% of enkephalin-positive striatal neurons and 15% of enkephalin-positive accumbens neurons, and in both areas in about 10% of enkephalin-negative, putative D1 neurons, in both D3+/+ and D3-/- mice. These results demonstrate that clozapine induction of c-fos messenger RNA is not dependent on the D3 dopamine receptor subtype in the striatum or nucleus accumbens.