Imbalance of p75(NTR)/TrkB protein expression in Huntington's disease: implication for neuroprotective therapies.

Neuroprotective therapies based on brain-derived neurotrophic factor (BDNF) administration have been proposed for Huntington's disease (HD) treatment. However, our group has recently reported reduced levels of TrkB in HD mouse models and HD human brain suggesting that besides a decrease on BDNF levels a reduction of TrkB expression could also contribute to diminished neurotrophic support in HD. BDNF can also bind to p75 neurotrophin receptor (p75(NTR)) modulating TrkB signaling. Therefore, in this study we have analyzed the levels of p75(NTR) in several HD models, as well as in HD human brain. Our data demonstrates a p75(NTR)/TrkB imbalance in the striatum of two different HD mouse models, Hdh(Q111/111) homozygous knockin mice and R6/1 mice that was also manifested in the putamen of HD patients. The imbalance between TrkB and p75(NTR) levels in a HD cellular model did not affect BDNF-mediated TrkB activation of prosurvival pathways but induced activation of apoptotic cascades as demonstrated by increased JNK phosphorylation. Moreover, BDNF failed to protect mutant huntingtin striatal cells transfected with p75(NTR) against NMDA-mediated excitotoxicity, which was associated with decreased Akt phosphorylation. Interestingly, lack of Akt activation following BDNF and NMDA treatment correlated with increased PP1 levels. Accordingly, pharmacological inhibition of PP1 by okadaic acid (OA) prevented mutant huntingtin striatal cell death induced by NMDA and BDNF. Altogether, our findings demonstrate that the p75(NTR)/TrkB imbalance induced by mutant huntingtin in striatal cells associated with the aberrant activity of PP1 disturbs BDNF neuroprotection likely contributing to increasing striatal vulnerability in HD. On the basis of this data we hypothesize that normalization of p75(NTR) and/or TrkB expression or their signaling will improve BDNF neuroprotective therapies in HD.

The dopaminergic stabilizer, (-)-OSU6162, rescues striatal neurons with normal and expanded polyglutamine chains in huntingtin protein from exposure to free radicals and mitochondrial toxins.

Huntington's disease (HD) is a neurodegenerative disease characterized by progressive motor, cognitive and psychiatric deficits, associated with predominant loss of striatal neurons and caused by a polyglutamine expansion in the huntingtin protein. There is so far neither cure nor approved disease-slowing therapy for HD, though recent clinical studies have shown a beneficial long-term effect of pridopidine in patients with HD. The nature of this effect, purely symptomatic or, in addition, neuroprotective, is difficult to elucidate in clinical trials. Pridopidine and (-)-OSU6162 are members of a new family of compounds referred to as dopaminergic stabilizers, which normalize abnormal dopamine neurotransmission. We investigated the effects of (-)-OSU6162 on huntingtin knocked-in striatal neurons in culture. Control neurons had normal full-length huntingtin with 7 glutamines while "mutant" neurons had large expansions (Q=111). We studied the dose-effect curves of (-)-OSU6162 on mitochondrial activity, LDH levels, necrosis and apoptosis in untreated Q7 and Q111 cells. In addition, we investigated the effects of (-)-OSU6162 on Q7 and Q111 neurons challenged with different neurotoxins such as sodium glutamate, H(2)O(2), rotenone and 3-nitropropionic acid (3NP). As we found prevention of toxicity of some of these neurotoxins, we investigated the putative neuroprotective mechanisms of action of (-)-OSU6162 measuring the effects of this dopaminergic stabilizer on expression and release of BDNF, the ratios of Bcl2/Bax proteins and of p-ERK/ERK, the levels of chaperones and GSH, and the effects of (-)-OSU6162 on dopamine uptake and release. We found that (-)-OSU6162, 3-150 µM, produces a dose dependent increase of mitochondrial activity and a reduction of cell death. (-)-OSU6162 does not change glutamate toxicity, but it partially prevents that of H(2)O(2), rotenone and 3-nitropropionic acid. (-)-OSU6162 increases the intracellular levels of BDNF and Bcl2/Bax and decreases those of p-ERK/ERK and CHIP in Q111 cells. (-)-OSU6162 increased (3)H-dopamine uptake and amphetamine-induced (3)H-dopamine release in E13 mouse mid brain neurons. Our studies demonstrate that (-)-OSU6162 improves survival and mitochondrial function in striatal Q111 neurons and the resistance of these cells to several striatal neurotoxins, suggesting that (-)-OSU6162 and related compounds should be tested for neuroprotection in animal models and, eventually, in patients with HD.

Long-term memory deficits in Huntington's disease are associated with reduced CBP histone acetylase activity.

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder caused by an expanded CAG/polyglutamine repeat in the coding region of the huntingtin (htt) gene. Although HD is classically considered a motor disorder, there is now considerable evidence that early cognitive deficits appear in patients before the onset of motor disturbances. Here we demonstrate early impairment of long-term spatial and recognition memory in heterozygous HD knock-in mutant mice (Hdh(Q7/Q111)), a genetically accurate HD mouse model. Cognitive deficits are associated with reduced hippocampal expression of CREB-binding protein (CBP) and diminished levels of histone H3 acetylation. In agreement with reduced CBP, the expression of CREB/CBP target genes related to memory, such c-fos, Arc and Nr4a2, was significantly reduced in the hippocampus of Hdh(Q7/Q111) mice compared with wild-type mice. Finally, and consistent with a role of CBP in cognitive impairment in Hdh(Q7/Q111) mice, administration of the histone deacetylase inhibitor trichostatin A rescues recognition memory deficits and transcription of selective CREB/CBP target genes in Hdh(Q7/Q111) mice. These findings demonstrate an important role for CBP in cognitive dysfunction in HD and suggest the use of histone deacetylase inhibitors as a novel therapeutic strategy for the treatment of memory deficits in this disease.

[Sexual dysfunction with antidepressive agents. Effect of the change to amineptine in patients with sexual dysfunction secondary to SSRI]. / Disfunción sexual con antidepresivos. Efecto del cambio a amineptino en pacientes con disfunción sexual secundaria a ISRS.

UNLABELLED: Sexual dysfunction secondary to the use of antidepressants, especially clomipramine or SSRI's is an adverse effect that is often underestimated and according to earlier studies, this can affect approximately 60% of the patients. This presents as a decrease in libido, alterations in the ability to reach orgasm/ejaculation, and an erectile dysfunction or a decreased vaginal lubrication. This dysfunction appears to be related with the resulting increase in serotonin and with the stimulation of serotonin 5HT2 receptors. OBJECTIVES: 1) Evaluate the effect of amineptine, a drug with an increased dopamine transmission and scant serotonin transmission, on the sexual function of depressed patients who begin treatment, and 2) evaluate whether the change to amineptine improves the sexual function in patients who presented sexual dysfunction after beginning treatment with a SSRI. MATERIAL AND METHODS: Prospective, observational, open and multicentric design. 111 patients with an average age of 41.3 years (36 men, 75 women) were distributed into three groups: Group 1 (n= 26): patients with depression (DSM IV) who begin de novo treatment with amineptine 200 mg/day. Group 2 (n= 47): depressed patients undergoing treatment with a SSRI who show a favorable response and who present sexual dysfunction secondary to a poorly tolerated treatment, so the treatment is changed to 200 mg/day of amineptine. Group 3 (n= 38): patients with the same characteristics as those of group 2, but whose treatment was changed to 20 mg/day of paroxetine. The <> (Montejo et al, 1996) was used together with the Hamilton Depression Scale, the IGC Scale, and an adverse events scale, over a 6 months follow up period during which visits took place at: baseline, month 1, month 2, month 3, and month 6. RESULTS: In group 1, treated with amineptine from the beginning, of the 5 patients who showed a decrease in the libido at the beginning of the treatment, only one still presented this in the 6th month. The Hamilton Scale decreased from 23.12 (baseline) to 5.25 after 6 months. After substituting amineptine for SSRI's in patients with sexual dysfunction, the incidence of any type of sexual dysfunction decreased significantly from 100% (baseline) to 55.3% after 6 months. (P< 0.001). The incidence of delayed orgasm dropped to 15.8%, anorgasmia to 17.4%, and impotence dropped to 15.8% in this group, with the antidepressant effect that had already been achieved with the SSRI being maintained. However, in group 3 there was barely any improvement on the sexual function after changing to paroxetine (20 mg/day), with the baseline incidence being 100% and the incidence after 6 months being 89.7%. In this last group the antidepressant effect present at the baseline level, was maintained. CONCLUSIONS: Amineptine was shown to be an effective antidepressant in the patients studied, and did not cause secondary sexual dysfunction, and even improved the dysfunction that was present in some patients. In those patients previously treated with SSRI's, amineptine is able to significantly improve the sexual dysfunction and yet maintain the efficacy of the antidepressive treatment used before these 6 months. On the other hand, Paroxetine did not improve the sexual dysfunction of the people in whom this drug substituted another SSRI, as this is an adverse effect common to the entire group of selective serotonin re-uptake inhibiting drugs. Amineptine showed a good safety and tolerance profile. Its most common side effect (anxiety/restlessness) disappeared 2 months after the beginning of the treatment.