The Impact of Acetazolamide and Methazolamide on Exercise Performance in Normoxia and Hypoxia.

Doherty, Connor J., Jou-Chung Chang, Benjamin P. Thompson, Erik R. Swenson, Glen E. Foster, and Paolo B. Dominelli. The impact of acetazolamide and methazolamide on exercise performance in normoxia and hypoxia. High Alt Med Biol. 24:7-18, 2023.-Carbonic anhydrase (CA) inhibitors are commonly prescribed for acute mountain sickness (AMS). In this review, we sought to examine how two CA inhibitors, acetazolamide (AZ) and methazolamide (MZ), affect exercise performance in normoxia and hypoxia. First, we briefly describe the role of CA inhibition in facilitating the increase in ventilation and arterial oxygenation in preventing and treating AMS. Next, we detail how AZ affects exercise performance in normoxia and hypoxia and this is followed by a discussion on MZ. We emphasize that the overarching focus of the review is how the two drugs potentially affect exercise performance, rather than their ability to prevent/treat AMS per se, their interrelationship will be discussed. Overall, we suggest that AZ hinders exercise performance in normoxia, but may be beneficial in hypoxia. Based upon head-to-head studies of AZ and MZ in humans on diaphragmatic and locomotor strength in normoxia, MZ may be a better CA inhibitor when exercise performance is crucial at high altitude.

Imatinib and methazolamide ameliorate COVID-19-induced metabolic complications via elevating ACE2 enzymatic activity and inhibiting viral entry.

Coronavirus disease 2019 (COVID-19) represents a systemic disease that may cause severe metabolic complications in multiple tissues including liver, kidney, and cardiovascular system. However, the underlying mechanisms and optimal treatment remain elusive. Our study shows that impairment of ACE2 pathway is a key factor linking virus infection to its secondary metabolic sequelae. By using structure-based high-throughput virtual screening and connectivity map database, followed with experimental validations, we identify imatinib, methazolamide, and harpagoside as direct enzymatic activators of ACE2. Imatinib and methazolamide remarkably improve metabolic perturbations in vivo in an ACE2-dependent manner under the insulin-resistant state and SARS-CoV-2-infected state. Moreover, viral entry is directly inhibited by these three compounds due to allosteric inhibition of ACE2 binding to spike protein on SARS-CoV-2. Taken together, our study shows that enzymatic activation of ACE2 via imatinib, methazolamide, or harpagoside may be a conceptually new strategy to treat metabolic sequelae of COVID-19.

Methazolamide Attenuates the Development of Diabetic Cardiomyopathy by Promoting ß-Catenin Degradation in Type 1 Diabetic Mice.

Methazolamide (MTZ), a carbonic anhydrase inhibitor, has been shown to inhibit cardiomyocyte hypertrophy and exert a hypoglycemic effect in patients with type 2 diabetes and diabetic db/db mice. However, whether MTZ has a cardioprotective effect in the setting of diabetic cardiomyopathy is not clear. We investigated the effects of MTZ in a mouse model of streptozotocin-induced type 1 diabetes mellitus (T1DM). Diabetic mice received MTZ by intragastric gavage (10, 25, or 50 mg/kg, daily for 16 weeks). In the diabetic group, MTZ significantly reduced both random and fasting blood glucose levels and improved glucose tolerance in a dose-dependent manner. MTZ ameliorated T1DM-induced changes in cardiac morphology and dysfunction. Mechanistic analysis revealed that MTZ blunted T1DM-induced enhanced expression of ß-catenin. Similar results were observed in neonatal rat cardiomyocytes (NRCMs) and adult mouse cardiomyocytes treated with high glucose or Wnt3a (a ß-catenin activator). There was no significant change in ß-catenin mRNA levels in cardiac tissues or NRCMs. MTZ-mediated ß-catenin downregulation was recovered by MG132, a proteasome inhibitor. Immunoprecipitation and immunofluorescence analyses showed augmentation of AXIN1-ß-catenin interaction by MTZ in T1DM hearts and in NRCMs treated with Wnt3a; thus, MTZ may potentiate AXIN1-ß-catenin linkage to increase ß-catenin degradation. Overall, MTZ may alleviate cardiac hypertrophy by mediating AXIN1-ß-catenin interaction to promote degradation and inhibition of ß-catenin activity. These findings may help inform novel therapeutic strategy to prevent heart failure in patients with diabetes.

Methazolamide in high-altitude illnesses.

As a carbonic anhydrase inhibitor and a methylated lipophilic analogue of acetazolamide, Methazolamide has higher lipid solubility, less plasma protein binding and renal excretion, and fewer side effects, compared to acetazolamide. Methazolamide can increase systemic metabolic acidosis and sequentially improve ventilation and oxygenation level. The increased oxygenation level leads to reduced reactive oxygen species (ROS) production, relived cerebral edema, mitigated hypoxic pulmonary vasoconstriction, abrogated hypoxic fatigue, and decreased excessive erythrocytosis. In addition to the effect as a carbonic anhydrase inhibitor, methazolamide directly activates the transcription factor anti-oxidative nuclear factor-related factor 2 (Nrf2) and inhibits interleukin-1ß (IL-1ß) release. These pharmacological functions of methazolamide are beneficial for the prevention and treatment of high-altitude illnesses. Besides, methazolamide causes less fatigue side effects than acetazolamide does. It is also worth noting that several studies suggested that a lower dose of methazolamide has similar prophylaxis and treatment efficacy in acute mountain sickness (AMS) to a higher dose of acetazolamide. Given methazolamide's advantages over acetazolamide, methazolamide may thus represent an alternative for acetazolamide when taken for high-altitude illnesses prophylaxis and treatment. However, more in-depth clinical trials are needed to fully evaluate this efficacy of methazolamide.

Visual Field Mean Deviation at Diagnosis of Idiopathic Intracranial Hypertension Predicts Visual Outcome.

BACKGROUND: A robust predictor of visual outcome in idiopathic intracranial hypertension (IIH) would be useful in management, but there is limited information on this point. The purpose of this study was to ascertain whether visual field mean deviation on standard static perimetry performed at diagnosis in a large patient cohort is a reliable predictor of visual outcome. METHODS: We retrospectively reviewed the automated visual field mean deviations at diagnosis and at final encounter in 79 patients with IIH examined in the neuro-ophthalmology clinics at a single academic medical center from 1999 to 2015. RESULTS: Of the 79 study patients, 66 (84%) entered with visual field mean deviations of -7 dB or better. Of those 66 patients, 59 (89%) had final mean deviations of -4 dB or better and 33 (56%) had final mean deviations of -2 dB or better. The single patient who had an initial mean deviation of -7 dB or better and a poor final mean deviation (-32 dB) was nonadherent to prescribed medication. Of the 13 (21%) patients who entered with mean deviations worse than -7 dB, 11 (85%) ended up with poor visual outcomes, their final mean deviations ranging from -5 dB to -32 dB. Over half of those 13 patients had required surgery for IIH, often within 3 weeks of diagnosis, owing to severe papilledema and visual dysfunction at the time of diagnosis. CONCLUSIONS: Based on this retrospective study, patients with IIH who have relatively mild visual dysfunction at diagnosis are likely to have a favorable visual outcome, provided they are adherent to recommended treatment. Many of those with poor visual function at diagnosis will have unfavorable visual outcomes despite aggressive treatment.

Therapeutic Efficacy of Methazolamide Against Intermittent Hypoxia-Induced Excessive Erythrocytosis in Rats.

Zhang, Zhiqing, Zhonghai Xiao, Bingnan Deng, Xiaohua Liu, Wei Liu, Hongjing Nie, Xi Li, Zhaoli Chen, Danfeng Yang, and Ruifeng Duan. Therapeutic efficacy of methazolamide against intermittent hypoxia-induced excessive erythrocytosis in rats. High Alt Med Biol 19:69-80, 2018.-This study aimed to determine whether methazolamide is effective for the treatment of chronic mountain sickness. Forty-eight male Wistar rats were randomly divided into eight groups: normoxia control, hypoxia control, hypoxia + acetazolamide (30 mg·kg-1·d-1), and five hypoxia + methazolamide groups (5, 10, 30, 90, and 120 mg·kg-1·d-1). Excessive erythrocytosis was induced through 4 weeks of hypobaric hypoxia (8 hours O2 10%/16 hours O2 21%). Rats were then treated for 4 weeks, and their body weight was measured. Hematological, hemorheological, and biochemical parameters were analyzed. Renal hypoxia-inducible factor-1alpha (HIF-1α) and vascular endothelial growth factor (VEGF) levels were detected by immunohistochemistry. Proteomic analysis of plasma was conducted to determine the most differentially expressed proteins. Methazolamide with doses lower than 30 mg·kg-1·d-1 had no significant effects on body weight compared with the hypoxia control group (p > 0.05). Methazolamide dose-dependently reduced the hemoglobin concentration, hematocrit (Hct), and blood viscosity. Hct/blood viscosity, an oxygen delivery index, dose-dependently increased after methazolamide treatment. A methazolamide dose of 10 mg·kg-1·d-1 showed similar efficacy to an acetazolamide dose of 30 mg·kg-1·d-1 for all the above parameters. Plasma levels of low-density lipoprotein cholesterol, total cholesterol, creatinine, and hemoglobin increased substantially after long-term hypoxia, but decreased after methazolamide treatment. HIF-1α and VEGF both increased substantially after long-term hypoxia and decreased in the kidney after methazolamide treatment. The most differentially expressed protein was haptoglobin, an endogenous protective factor, which was depleted in rats with excessive erythrocytosis and increased substantially after methazolamide treatment. In summary, methazolamide exhibits dose-dependent efficacy for the treatment of excessive erythrocytosis induced by long-term hypoxia. It also has beneficial effects on oxygen transport and lipid metabolism, which are encouraging with regard to the development of methazolamide-based chronic mountain sickness therapies.

The Metabolism of Methazolamide in Immortalized Human Keratinocytes, HaCaT Cells.

OBJECTIVE: Drug therapy is occasionally accompanied by an idiosyncratic severe toxicity, which occurs very rarely, but can lead to patient mortality. Methazolamide, an anti-glaucomatous agent, could cause severe skin eruptions called Stevens-Johnson syndrome/toxic epidermal necrolyis (SJS/TEN). Its precise etiology is still uncertain. In this study, the metabolism of methazolamide was investigated in immortalized human keratinocytes to reveal the possible mechanism which causes SJS/TEN. METHODS: The metabolism of methazolamide was studied using immortalized human keratinocytes, HaCaT cells. HPLC was used to isolate a metabolite from the culture medium. Mass spectrometry (LCMS/ MS) was employed for its characterization. Three typical chemical inducers were assessed for the inducibility of cytochrome P450, and methimazole was used as the inhibitor of flavin-containing monooxygenase (FMO). RESULTS: A sulfonic acid, N-[3-methyl-5-sulfo-1,3,4-thiadiazol-2(3H)-ylidene]acetamide (MSO) was identified as the final metabolite. Dexamethasone and ß-naphthoflavone behaved as an inducer of cytochrome P450 in the metabolism, but isoniazid did not. The effect of methimazole was not consistent. We did not detect any glucuronide nor any mercapturic acid (N-acetylcysteine conjugate). CONCLUSION: N-[3-methyl-5-sulfo-1,3,4-thiadiazol-2(3H)-ylidene]acetamide (MSO) is not considered to be a direct product of an enzymatic reaction, but rather an auto-oxidation product of N-[3-methyl-5- sulfe-1,3,4-thiadiazol-2(3H)-ylidene]acetamide, a chemically unstable sulfenic acid, which is produced by cytochrome P450 from the ß-lyase product of cysteine conjugate of methazolamide. MSO is considered to be susceptible to glutathione and to return to glutathione conjugate of methazolamide, forming a futile cycle. A hypothetical scenario is presented as to the onset of the disease.

Drug interaction considerations in the therapeutic use of carbonic anhydrase inhibitors.

INTRODUCTION: Carbonic anhydrase inhibitors (CAIs) of the sulfonamide and sulfamate type are clinically used drugs as diuretics, antiglaucoma, antiepileptic, antiobesity and anti-high altitude disease agents. Anticancer agents based on CAIs are also in clinical development for the management of hypoxic, metastatic tumors. Acetazolamide, methazolamide, dichlorophenamide, dorzolamide and brinzolamide are mainly used as antiglaucoma drugs, sulthiame, topiramate and zonisamide as antiepileptic/antiobesity agents, celecoxib and polmacoxib are dual carbonic anhydrase/cycloxygenase inhibitors. Girentuximab, a monoclonal antibody and SLC-0111, a sulfonamide inhibitor, are in clinical trials as anticancer agents. AREAS COVERED: The drug interactions with many classes of pharmacological agents are reviewed. Some of these drugs, such as acetazolamide, topiramate and celecoxib show a large number of interactions with non-steroidal anti-inflammatory drugs (NSAIDs), diuretics, antiepileptics, immunosupressants, anticholinesterase drugs, ß-blockers, anesthetics, oral contraceptives, anticancer agents, antifungals, anti-mycobacterials, lithium, metformin and clopidogrel. EXPERT OPINION: The multiple drug interactions in which CAIs are involved should be carefully considered when such drugs are used in combination with the drug classes mentioned above, as the risks of developing toxicity and serious side effects if the dosages are not adjusted are high. There are also synergistic effects between CAIs and some NSAIDs, anticancer agents and benzodiazepines for the management of cystoid macular edema, some tumor types and neuropathic pain, respectively.

Efficacy and safety of oral methazolamide in patients with type 2 diabetes: a 24-week, placebo-controlled, double-blind study.

OBJECTIVE: To evaluate the safety and efficacy of methazolamide as a potential therapy for type 2 diabetes. RESEARCH DESIGN AND METHODS: This double-blind, placebo-controlled study randomized 76 patients to oral methazolamide (40 mg b.i.d.) or placebo for 24 weeks. The primary efficacy end point for methazolamide treatment was a placebo-corrected reduction in HbA1c from baseline after 24 weeks (ΔHbA1c). RESULTS: Mean ± SD baseline HbA1c was 7.1 ± 0.7% (54 ± 5 mmol/mol; n = 37) and 7.4 ± 0.6% (57 ± 5 mmol/mol; n = 39) in the methazolamide and placebo groups, respectively. Methazolamide treatment was associated with a ΔHbA1c of -0.39% (95% CI -0.82, 0.04; P < 0.05) (-4.3 mmol/mol [-9.0, 0.4]), an increase in the proportion of patients achieving HbA1c ≤6.5% (48 mmol/mol) from 8 to 33%, a rapid reduction in alanine aminotransferase (∼10 units/L), and weight loss (2%) in metformin-cotreated patients. CONCLUSIONS: Methazolamide is the archetype for a new intervention in type 2 diabetes with clinical benefits beyond glucose control.

Next-generation sequencing revealed a novel mutation in the gene encoding the beta subunit of rod phosphodiesterase.

PURPOSE: To report the phenotypes caused by a novel mutation in the PDE6B gene in a family with two affected siblings and one affected cousin with a 2-year follow-up. DESIGN: Three patients from a family with a history of retinitis pigmentosa underwent clinical evaluations. The affected patients' DNA was analyzed using next-generation sequencing and segregation analyses were performed for the family. SETTING: Edward S. Harkness Eye Institute, New York Presbyterian Hospital. PARTICIPANTS: Two siblings, one cousin, and five unaffected family members. MAIN OUTCOME MEASURES: Macular appearance assessed by funduscopy, autofluorescence imaging, spectral-domain optical coherence tomography and visual function assessed by electroretinography. RESULTS: The proband, brother, and cousin had rod-cone degeneration with cystoid macular edema. Fundus autofluorescence showed hyperautofluorescent ring constriction over time. Spectral-domain optical coherence tomography revealed retinal pigment epithelium atrophy, loss of external limiting membrane, retinal layer thinning, and reduction in ellipsoid zone length over time. Next-generation whole exome sequencing revealed a homozygous c.1923_1969ins6del47 nonsense PDE6B mutation, which has not been previously described, that segregated with the disease in the family. CONCLUSIONS: The homozygous PDE6B mutation causes retinitis pigmentosa. Acetazolamide treatment improved visual acuity but rod degeneration continued. Despite having the same mutation and living in the same environment, the proband's brother progressed at a faster rate starting at a younger age, suggesting that gene modifiers may influence the expressivity of the phenotype. Next-generation sequencing, used to discover this mutation, is a practical new technology that can detect novel disease-causing alleles, where previous arrayed primer extension (APEX) technology could not.

Decreased macular thickness in nonproliferative macular telangiectasia type 2 with oral carbonic anhydrase inhibitors.

PURPOSE: To evaluate whether carbonic anhydrase inhibitors reduce the macular thickness and/or cystic spaces in patients with macular telangiectasia (MacTel) Type 2. METHODS: Retrospective review of patients with nonproliferative cystoid changes associated with MacTel seen at the University of Iowa between 2009 and 2012. Carbonic anhydrase inhibitors were used in 8 patients with MacTel Type 2. Five patients with MacTel Type 2 were observed during this period. Initial and final visual acuities were documented. The presence of cystic spaces and the retinal thickness were measured with spectral-domain optical coherence tomography. RESULTS: Patients treated with oral carbonic anhydrase inhibitors showed significant reduction in both the cystoid cavities and central macular thickness when compared with the patients who were observed (-12.2 µm; P = 0.020). The reduction in retinal thickness was more pronounced in patients receiving acetazolamide (-20.13 µm; P = 0.007) compared with methazolamide (-6.25 µm; P = 0.177). There was no significant change in visual acuity in patients receiving carbonic anhydrase inhibitors. Five patients with MacTel Type 2 did not receive treatment and demonstrated no change in visual acuity, cystoid cavities, or central macular thickness. CONCLUSION: Oral carbonic anhydrase inhibitors, particularly acetazolamide, may decrease macular cystic cavities and reduce central macular thickness but does not appear to improve visual acuity. These findings have yet to be confirmed with a prospective treatment trial.

A case of paclitaxel-induced maculopathy treated with methazolamide.

A 54-year-old female patient who had been undergoing anti-cancer chemotherapy and radiotherapy for seven years after surgery for left breast cancer visited our clinic for visual disturbance in the right eye at nine months after paclitaxel administration. The best-corrected visual acuity was 0.5 in the right eye and 1.0 in the left eye. The patient was diagnosed with maculopathy due to paclitaxel administration based on the finding of cystoid macular edema in the right eye on fundus examination and optical coherence tomography; however, no leakage was detected on fluorescein angiography. Thus, drug replacement was planned. On the other hand, no abnormal finding was observed in the left eye. However, as the anti-cancer effect of paclitaxel is significant, replacing paclitaxel with another agent was not warranted; therefore, maintenance therapy with methazolamide was performed before and after administering the anti-cancer agent. Aggravation of cystoid macular edema was prevented, and vision improvement was achieved by oral maintenance therapy with methazolamide. In addition, the same fundus findings as shown in the right eye were detected in the left eye at 16 months after paclitaxel administration. After administering methazolamide, macular thickness was reduced, and vision was improved in the left eye. Paclitaxel administration was discontinued due to cutaneous metastasis from the breast cancer, and another anti-cancer agent was then administered. No subsequent cystoid macular edema has occurred.

Methazolamide is a new hepatic insulin sensitizer that lowers blood glucose in vivo.

We previously used Gene Expression Signature technology to identify methazolamide (MTZ) and related compounds with insulin sensitizing activity in vitro. The effects of these compounds were investigated in diabetic db/db mice, insulin-resistant diet-induced obese (DIO) mice, and rats with streptozotocin (STZ)-induced diabetes. MTZ reduced fasting blood glucose and HbA(1c) levels in db/db mice, improved glucose tolerance in DIO mice, and enhanced the glucose-lowering effects of exogenous insulin administration in rats with STZ-induced diabetes. Hyperinsulinemic-euglycemic clamps in DIO mice revealed that MTZ increased glucose infusion rate and suppressed endogenous glucose production. Whole-body or cellular oxygen consumption rate was not altered, suggesting MTZ may inhibit glucose production by different mechanism(s) to metformin. In support of this, MTZ enhanced the glucose-lowering effects of metformin in db/db mice. MTZ is known to be a carbonic anhydrase inhibitor (CAI); however, CAIs acetazolamide, ethoxyzolamide, dichlorphenamide, chlorthalidone, and furosemide were not effective in vivo. Our results demonstrate that MTZ acts as an insulin sensitizer that suppresses hepatic glucose production in vivo. The antidiabetic effect of MTZ does not appear to be a function of its known activity as a CAI. The additive glucose-lowering effect of MTZ together with metformin highlights the potential utility for the management of type 2 diabetes.

A Case of Paclitaxel-induced Maculopathy Treated with Methazolamide

A 54-year-old female patient who had been undergoing anti-cancer chemotherapy and radiotherapy for seven years after surgery for left breast cancer visited our clinic for visual disturbance in the right eye at nine months after paclitaxel administration. The best-corrected visual acuity was 0.5 in the right eye and 1.0 in the left eye. The patient was diagnosed with maculopathy due to paclitaxel administration based on the finding of cystoid macular edema in the right eye on fundus examination and optical coherence tomography; however, no leakage was detected on fluorescein angiography. Thus, drug replacement was planned. On the other hand, no abnormal finding was observed in the left eye. However, as the anti-cancer effect of paclitaxel is significant, replacing paclitaxel with another agent was not warranted; therefore, maintenance therapy with methazolamide was performed before and after administering the anti-cancer agent. Aggravation of cystoid macular edema was prevented, and vision improvement was achieved by oral maintenance therapy with methazolamide. In addition, the same fundus findings as shown in the right eye were detected in the left eye at 16 months after paclitaxel administration. After administering methazolamide, macular thickness was reduced, and vision was improved in the left eye. Paclitaxel administration was discontinued due to cutaneous metastasis from the breast cancer, and another anti-cancer agent was then administered. No subsequent cystoid macular edema has occurred.

Treat ankylosing spondylitis with methazolamide.

BACKGROUND: Increased bone resorption and new bone information are two characteristics of ankylosing spondylitis (AS). Much evidence has shown that carbonic anhydrase inhibitors can restrain bone resorption. We had detected increased expression of carbonic anhydrase I (CA1) in synovium of patients with AS. This study aimed to evaluate the effectiveness and safety of methazolamide, an anti-carbonic anhydrase drug, for treating patients with AS. METHODS: Two patients, called as S and L, were diagnosed with active AS based on BASDAI and BASFI assessments, radiographic data and other clinical indices. They took methazolamide tablets at a dose of 25 mg twice every day. RESULTS: Patient S's BASDAI score fell from 5.4 to 4.4, while patient L's BASDAI fell from 2.4 to 2. Patient S's BASFI score change from 2.7 to 2.9, while patient L's BASFI score fell from 1.2 to 0.2. The ESR values of patient S were considerably reduced, while the ESR value of patient L remained unchanged and in the normal range. The calcium concentration of patient S decreased from 3.05 mmol/L to 2.39 mmol/L. The CT evidence indicates that the articular surfaces of the erosive sacroiliac joints became clearer and the area of the calcium deposits began decreased. No significant systemic side effects were observed in either patient. CONCLUSIONS: The above results indicate that methazolamide was effective for active AS. Methazolamide may improve AS symptoms by inhibiting carbonic anhydrase activity during the processes of bone reporption and new bone formation.

HLA-B*5901 is strongly associated with methazolamide-induced Stevens-Johnson syndrome/toxic epidermal necrolysis.

AIMS: The carbonic anhydrase inhibitor methazolamide infrequently causes Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). An association between these diseases and the HLA-B59 serotype has been suggested in case reports. This study examined the disease-associated B*59 allele and investigated the association of these diseases with other HLA class I alleles. METHODS: We performed high-resolution HLA-A, -B and -C genotyping in five patients with methazolamide-induced SJS/TEN using a PCR-sequencing-based typing method and analyzed the association between HLA-class I alleles and occurrence of methazolamide-induced SJS/TEN. RESULTS: B*5901 and Cw*0102 alleles were observed in all patients and A*2402 was observed in four patients. The B*5901 allele showed the strongest association with methazolamide-induced SJS/TEN (p < 0.001; odds ratio: 249.8; 95% CI: 13.4-4813.5), followed by Cw*0102 (p = 0.004; odds ratio: 22.1; 95% CI: 1.2-414.3), when compared with the general population as a control. The frequency of the patients carrying B*5901, Cw*0102 and A*2402 simultaneously was significantly higher than that in the general population (p < 0.001; odds ratio: 110.1; 95% CI: 11.7-1038.6). CONCLUSION: A strong association was observed between HLA-B*5901 and methazolamide-induced SJS/TEN in Korean patients. HLA-B*5901 may be a useful screening marker for predicting methazolamide-induced SJS/TEN in patients of Korean and Japanese ancestry.

Inhibitors of cytochrome c release with therapeutic potential for Huntington's disease.

Release of mitochondrial cytochrome c resulting in downstream activation of cell death pathways has been suggested to play a role in neurologic diseases featuring cell death. However, the specific biologic importance of cytochrome c release has not been demonstrated in Huntington's disease (HD). To evaluate the role of cytochrome c release, we screened a drug library to identify new inhibitors of cytochrome c release from mitochondria. Drugs effective at the level of purified mitochondria were evaluated in a cellular model of HD. As proof of principle, one drug was chosen for in depth evaluation in vitro and a transgenic mouse model of HD. Our findings demonstrate the utility of mitochondrial screening to identify inhibitors of cell death and provide further support for the important functional role of cytochrome c release in HD. Given that many of these compounds have been approved by the Food and Drug Administration for clinical usage and cross the blood-brain barrier, these drugs may lead to trials in patients.