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Evaluation of Dimebon in cellular model of Huntington's disease.

Wu J, Li Q, Bezprozvanny I - Mol Neurodegener (2008)

Bottom Line: Lower concentrations of Dimebon (5 muM and 10 muM) did not stabilize glutamate-induced Ca2+ signals and did not exert neuroprotective effects in experiments with YAC128 MSN.Dimebon also had significant effect on a number of additional receptors.Our results suggest that Ca2+ and mitochondria stabilizing effects may, in part, be responsible for beneficial clinical effects of Dimebon.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology, UT Southwestern Medical Center at Dallas, TX 75390, USA. Ilya.Bezprozvanny@UTSouthwestern.edu.

ABSTRACT

Background: Dimebon is an antihistamine compound with a long history of clinical use in Russia. Recently, Dimebon has been proposed to be useful for treating neurodegenerative disorders. It has demonstrated efficacy in phase II Alzheimer's disease (AD) and Huntington's disease (HD) clinical trials. The mechanisms responsible for the beneficial actions of Dimebon in AD and HD remain unclear. It has been suggested that Dimebon may act by blocking NMDA receptors or voltage-gated Ca2+ channels and by preventing mitochondrial permeability pore transition.

Results: We evaluated the effects of Dimebon in experiments with primary striatal neuronal cultures (MSN) from wild type (WT) mice and YAC128 HD transgenic mice. We found that Dimebon acts as an inhibitor of NMDA receptors (IC50 = 10 muM) and voltage-gated calcium channels (IC50 = 50 muM) in WT and YAC128 MSN. We further found that application of 50 muM Dimebon stabilized glutamate-induced Ca2+ signals in YAC128 MSN and protected cultured YAC128 MSN from glutamate-induced apoptosis. Lower concentrations of Dimebon (5 muM and 10 muM) did not stabilize glutamate-induced Ca2+ signals and did not exert neuroprotective effects in experiments with YAC128 MSN. Evaluation of Dimebon against a set of biochemical targets indicated that Dimebon inhibits alpha-Adrenergic receptors (alpha1A, alpha1B, alpha1D, and alpha2A), Histamine H1 and H2 receptors and Serotonin 5-HT2c, 5-HT5A, 5-HT6 receptors with high affinity. Dimebon also had significant effect on a number of additional receptors.

Conclusion: Our results suggest that Ca2+ and mitochondria stabilizing effects may, in part, be responsible for beneficial clinical effects of Dimebon. However, the high concentrations of Dimebon required to achieve Ca2+ stabilizing and neuroprotective effects in our in vitro studies (50 muM) indicate that properties of Dimebon as cognitive enhancer are most likely due to potent inhibition of H1 histamine receptors. It is also possible that Dimebon acts on novel high affinity targets not present in cultured MSN preparation. Unbiased evaluation of Dimebon against a set of biochemical targets indicated that Dimebon efficiently inhibited a number of additional receptors. Potential interactions with these receptors need to be considered in interpretation of results obtained with Dimebon in clinical trials.

No MeSH data available.


Related in: MedlinePlus

Effects of Dimebon on glutamate-induced Ca2+signals. (A-B), Repetitive application of 20 μM glutamate induces Ca2+ signals in MSN from the WT (A) and YAC128 (B) mice. (C-D), The same experiment as in (A) and (B) was performed in the presence of 10 μM Dimebon with WT (C) and YAC128 (D) MSN. (E-F), The same experiment as in (A) and (B) was performed in the presence of 50 μM Dimebon with WT (E) and YAC128 (F) MSN. The traces shown on panels (A-F) are average traces from all MSN for each experimental group. (G) The average increase of basal Ca2+ level (mean ± SE, n is the number of MSN analyzed) after 20 pulses of glutamate are shown for WT MSN (n = 16), YAC128 MSN (n = 21), WT MSN in the presence of 10 μM Dimebon (n = 44), YAC128 MSN in the presence of 10 μM Dimebon (n = 41), WT MSN in the presence of 50 μM Dimebon (n = 17) and YAC128 MSN in the presence of 50 μM Dimebon (n = 44).
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Figure 2: Effects of Dimebon on glutamate-induced Ca2+signals. (A-B), Repetitive application of 20 μM glutamate induces Ca2+ signals in MSN from the WT (A) and YAC128 (B) mice. (C-D), The same experiment as in (A) and (B) was performed in the presence of 10 μM Dimebon with WT (C) and YAC128 (D) MSN. (E-F), The same experiment as in (A) and (B) was performed in the presence of 50 μM Dimebon with WT (E) and YAC128 (F) MSN. The traces shown on panels (A-F) are average traces from all MSN for each experimental group. (G) The average increase of basal Ca2+ level (mean ± SE, n is the number of MSN analyzed) after 20 pulses of glutamate are shown for WT MSN (n = 16), YAC128 MSN (n = 21), WT MSN in the presence of 10 μM Dimebon (n = 44), YAC128 MSN in the presence of 10 μM Dimebon (n = 41), WT MSN in the presence of 50 μM Dimebon (n = 17) and YAC128 MSN in the presence of 50 μM Dimebon (n = 44).

Mentions: To test the postulated "Ca2+ stabilizing" effects of Dimebon, in the first series of experiments, we compared Ca2+ responses induced by glutamate application to wild type (WT) and YAC128 MSN at 13–14 DIV. In our previous studies, we found that repetitive pulses of 20 μM glutamate resulted in a bigger elevation of cytosolic Ca2+ levels in the YAC128 MSN compared with that in WT MSN [12,14,15]. To test effects of Dimebon on glutamate-induced Ca2+ signals, we applied 20 pulses of 20 μM glutamate (each pulse 1 min in duration, followed by a 1 min washout) in the presence of 10 μM or 50 μM Dimebon. Control experiments were performed in the absence of Dimebon. The intracellular Ca2+ concentration in the experiments was continuously monitored by Fura-2 imaging and the 340/380 ratio was used to quantitatively determine the concentration of the intracellular Ca2+ ([Ca2+]i). The increase in Ca2+ was calculated as a difference between basal values of Ca2+ prior to glutamate application and at completion of "20 glutamate pulses" protocol in the same cell. On average, the increase in Ca2+ was 0.250 ± 0.029 for WT MSN and 0.403 ± 0.046 for YAC128 MSN (Figs 2A, B, G). Thus, in agreement with our previous findings [12,14,15], the increase in Ca2+ was significantly higher in YAC128 MSN than in WT MSN. In the presence of 10 μM Dimebon, the increase in Ca2+ was 0.236 ± 0.021 for WT MSN and 0.461 ± 0.034 for YAC128 MSN (Figs 2C, D, G). Thus, incubation with 10 μM Dimebon had no significant effect on the glutamate-induced Ca2+ increase in WT or YAC128 MSN. In the presence of 50 μM Dimebon, the increase in Ca2+ was 0.290 ± 0.027 for WT MSN and 0.234 ± 0.022 for YAC128 MSN (Figs 2E, F, G). Thus, 50 μM Dimebon significantly reduced the glutamate-induced Ca2+ increase of YAC128 MSN without affecting the Ca2+ signals in WT MSN. These results indicate that Dimebon exerts "Ca2+ stabilizing" effects in YAC128 MSN at 50 μM but not at 10 μM concentration.


Evaluation of Dimebon in cellular model of Huntington's disease.

Wu J, Li Q, Bezprozvanny I - Mol Neurodegener (2008)

Effects of Dimebon on glutamate-induced Ca2+signals. (A-B), Repetitive application of 20 μM glutamate induces Ca2+ signals in MSN from the WT (A) and YAC128 (B) mice. (C-D), The same experiment as in (A) and (B) was performed in the presence of 10 μM Dimebon with WT (C) and YAC128 (D) MSN. (E-F), The same experiment as in (A) and (B) was performed in the presence of 50 μM Dimebon with WT (E) and YAC128 (F) MSN. The traces shown on panels (A-F) are average traces from all MSN for each experimental group. (G) The average increase of basal Ca2+ level (mean ± SE, n is the number of MSN analyzed) after 20 pulses of glutamate are shown for WT MSN (n = 16), YAC128 MSN (n = 21), WT MSN in the presence of 10 μM Dimebon (n = 44), YAC128 MSN in the presence of 10 μM Dimebon (n = 41), WT MSN in the presence of 50 μM Dimebon (n = 17) and YAC128 MSN in the presence of 50 μM Dimebon (n = 44).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2577671&req=5

Figure 2: Effects of Dimebon on glutamate-induced Ca2+signals. (A-B), Repetitive application of 20 μM glutamate induces Ca2+ signals in MSN from the WT (A) and YAC128 (B) mice. (C-D), The same experiment as in (A) and (B) was performed in the presence of 10 μM Dimebon with WT (C) and YAC128 (D) MSN. (E-F), The same experiment as in (A) and (B) was performed in the presence of 50 μM Dimebon with WT (E) and YAC128 (F) MSN. The traces shown on panels (A-F) are average traces from all MSN for each experimental group. (G) The average increase of basal Ca2+ level (mean ± SE, n is the number of MSN analyzed) after 20 pulses of glutamate are shown for WT MSN (n = 16), YAC128 MSN (n = 21), WT MSN in the presence of 10 μM Dimebon (n = 44), YAC128 MSN in the presence of 10 μM Dimebon (n = 41), WT MSN in the presence of 50 μM Dimebon (n = 17) and YAC128 MSN in the presence of 50 μM Dimebon (n = 44).
Mentions: To test the postulated "Ca2+ stabilizing" effects of Dimebon, in the first series of experiments, we compared Ca2+ responses induced by glutamate application to wild type (WT) and YAC128 MSN at 13–14 DIV. In our previous studies, we found that repetitive pulses of 20 μM glutamate resulted in a bigger elevation of cytosolic Ca2+ levels in the YAC128 MSN compared with that in WT MSN [12,14,15]. To test effects of Dimebon on glutamate-induced Ca2+ signals, we applied 20 pulses of 20 μM glutamate (each pulse 1 min in duration, followed by a 1 min washout) in the presence of 10 μM or 50 μM Dimebon. Control experiments were performed in the absence of Dimebon. The intracellular Ca2+ concentration in the experiments was continuously monitored by Fura-2 imaging and the 340/380 ratio was used to quantitatively determine the concentration of the intracellular Ca2+ ([Ca2+]i). The increase in Ca2+ was calculated as a difference between basal values of Ca2+ prior to glutamate application and at completion of "20 glutamate pulses" protocol in the same cell. On average, the increase in Ca2+ was 0.250 ± 0.029 for WT MSN and 0.403 ± 0.046 for YAC128 MSN (Figs 2A, B, G). Thus, in agreement with our previous findings [12,14,15], the increase in Ca2+ was significantly higher in YAC128 MSN than in WT MSN. In the presence of 10 μM Dimebon, the increase in Ca2+ was 0.236 ± 0.021 for WT MSN and 0.461 ± 0.034 for YAC128 MSN (Figs 2C, D, G). Thus, incubation with 10 μM Dimebon had no significant effect on the glutamate-induced Ca2+ increase in WT or YAC128 MSN. In the presence of 50 μM Dimebon, the increase in Ca2+ was 0.290 ± 0.027 for WT MSN and 0.234 ± 0.022 for YAC128 MSN (Figs 2E, F, G). Thus, 50 μM Dimebon significantly reduced the glutamate-induced Ca2+ increase of YAC128 MSN without affecting the Ca2+ signals in WT MSN. These results indicate that Dimebon exerts "Ca2+ stabilizing" effects in YAC128 MSN at 50 μM but not at 10 μM concentration.

Bottom Line: Lower concentrations of Dimebon (5 muM and 10 muM) did not stabilize glutamate-induced Ca2+ signals and did not exert neuroprotective effects in experiments with YAC128 MSN.Dimebon also had significant effect on a number of additional receptors.Our results suggest that Ca2+ and mitochondria stabilizing effects may, in part, be responsible for beneficial clinical effects of Dimebon.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology, UT Southwestern Medical Center at Dallas, TX 75390, USA. Ilya.Bezprozvanny@UTSouthwestern.edu.

ABSTRACT

Background: Dimebon is an antihistamine compound with a long history of clinical use in Russia. Recently, Dimebon has been proposed to be useful for treating neurodegenerative disorders. It has demonstrated efficacy in phase II Alzheimer's disease (AD) and Huntington's disease (HD) clinical trials. The mechanisms responsible for the beneficial actions of Dimebon in AD and HD remain unclear. It has been suggested that Dimebon may act by blocking NMDA receptors or voltage-gated Ca2+ channels and by preventing mitochondrial permeability pore transition.

Results: We evaluated the effects of Dimebon in experiments with primary striatal neuronal cultures (MSN) from wild type (WT) mice and YAC128 HD transgenic mice. We found that Dimebon acts as an inhibitor of NMDA receptors (IC50 = 10 muM) and voltage-gated calcium channels (IC50 = 50 muM) in WT and YAC128 MSN. We further found that application of 50 muM Dimebon stabilized glutamate-induced Ca2+ signals in YAC128 MSN and protected cultured YAC128 MSN from glutamate-induced apoptosis. Lower concentrations of Dimebon (5 muM and 10 muM) did not stabilize glutamate-induced Ca2+ signals and did not exert neuroprotective effects in experiments with YAC128 MSN. Evaluation of Dimebon against a set of biochemical targets indicated that Dimebon inhibits alpha-Adrenergic receptors (alpha1A, alpha1B, alpha1D, and alpha2A), Histamine H1 and H2 receptors and Serotonin 5-HT2c, 5-HT5A, 5-HT6 receptors with high affinity. Dimebon also had significant effect on a number of additional receptors.

Conclusion: Our results suggest that Ca2+ and mitochondria stabilizing effects may, in part, be responsible for beneficial clinical effects of Dimebon. However, the high concentrations of Dimebon required to achieve Ca2+ stabilizing and neuroprotective effects in our in vitro studies (50 muM) indicate that properties of Dimebon as cognitive enhancer are most likely due to potent inhibition of H1 histamine receptors. It is also possible that Dimebon acts on novel high affinity targets not present in cultured MSN preparation. Unbiased evaluation of Dimebon against a set of biochemical targets indicated that Dimebon efficiently inhibited a number of additional receptors. Potential interactions with these receptors need to be considered in interpretation of results obtained with Dimebon in clinical trials.

No MeSH data available.


Related in: MedlinePlus