RESUMO
Novel potent and selective 5,6,5- and 5,5,6-tricyclic pyrrolidine dipeptidyl peptidase IV (DPP-4) inhibitors were identified. Structure-activity relationship (SAR) efforts focused on improving the intrinsic DPP-4 inhibition potency, increasing protease selectivity, and demonstrating clean ion channel and cytochrome P450 profiles while trying to achieve a pharmacokinetic profile suitable for once weekly dosing in humans.
Assuntos
Dipeptidil Peptidase 4/metabolismo , Inibidores da Dipeptidil Peptidase IV/farmacologia , Descoberta de Drogas , Pirrolidinas/farmacologia , Animais , Cristalografia por Raios X , Inibidores da Dipeptidil Peptidase IV/síntese química , Inibidores da Dipeptidil Peptidase IV/química , Cães , Relação Dose-Resposta a Droga , Humanos , Modelos Moleculares , Estrutura Molecular , Pirrolidinas/síntese química , Pirrolidinas/química , Ratos , Relação Estrutura-AtividadeRESUMO
A series of novel substituted-[(3R)-amino-2-(2,5-difluorophenyl)]tetrahydro-2H-pyran analogs have been prepared and evaluated as potent, selective and orally active DPP-4 inhibitors. These efforts lead to the discovery of a long acting DPP-4 inhibitor, omarigliptin (MK-3102), which recently completed phase III clinical development and has been approved in Japan.
Assuntos
Amidas/química , Inibidores da Dipeptidil Peptidase IV/química , Compostos Heterocíclicos com 2 Anéis/química , Piranos/química , Sulfonamidas/química , Animais , Sítios de Ligação , Dipeptidil Peptidase 4/química , Dipeptidil Peptidase 4/metabolismo , Inibidores da Dipeptidil Peptidase IV/síntese química , Inibidores da Dipeptidil Peptidase IV/farmacocinética , Cães , Meia-Vida , Compostos Heterocíclicos com 2 Anéis/síntese química , Compostos Heterocíclicos com 2 Anéis/farmacocinética , Simulação de Acoplamento Molecular , Estrutura Terciária de Proteína , Piranos/síntese química , Piranos/farmacocinética , Ratos , Relação Estrutura-AtividadeRESUMO
A series of benzazepinones were synthesized and evaluated for block of Nav1.7 sodium channels. Compound 30 from this series displayed potent channel block, good selectivity versus other targets, and dose-dependent oral efficacy in a rat model of neuropathic pain.
Assuntos
Benzazepinas/farmacologia , Neuralgia/tratamento farmacológico , Bloqueadores dos Canais de Sódio/farmacologia , Animais , Modelos Animais de Doenças , RatosRESUMO
Understanding whether regulation of tryptophan metabolites can ameliorate neurodegeneration is of high interest to investigators. A recent publication describes 3,4-dimethoxy-N-(4-(3-nitrophenyl)-5-(piperidin-1-ylmethyl)thiazol-2-yl)benzenesulfonamide (JM6) as a novel prodrug for the kynurenine 3-monooxygenase (KMO) inhibitor 3,4-dimethoxy-N-(4-(3-nitrophenyl)thiazol-2-yl)benzenesulfonamide (Ro-61-8048) that elicits therapeutic effects in mouse models of Huntington's and Alzheimer's diseases (Cell 145:863-874, 2011). Our evaluation of the metabolism and pharmacokinetics of JM6 and Ro-61-8048 indicate instead that Ro-61-8048 concentrations in mouse plasma after JM6 administration originate from a Ro-61-8048 impurity (<0.1%) in JM6. After a 0.05 mg/kg Ro-61-8048 oral dose alone or coadministered with 10 mg/kg JM6 to mice, the Ro-61-8048 areas under the concentration-time curves (AUCs) from 0 to infinity were similar (4300 and 4900 nM × h, respectively), indicating no detectable contributions of JM6 metabolism to the Ro-61-8048 AUCs. JM6 was stable in incubations under acidic conditions and Ro-61-8048 was not a product of JM6 metabolism in vitro (plasma, blood, or hepatic models). Species differences in the quantitative rate of oxidative metabolism indicate that major circulating JM6 metabolite(s) in mice are unlikely to be major in humans: JM6 is rapidly metabolized via the piperidyl moiety in mouse (forming an iminium ion reactive intermediate) but is slowly metabolized in human (in vitro), primarily via O-dealkylation at the phenyl ring. Our data indicate that JM6 is not a prodrug for Ro-61-8048 and is not a potent KMO inhibitor.
Assuntos
Pró-Fármacos/farmacocinética , Sulfonamidas/farmacocinética , Tiazóis/farmacocinética , Animais , Área Sob a Curva , Linhagem Celular , Cães , Hepatócitos/enzimologia , Hepatócitos/metabolismo , Humanos , Células Madin Darby de Rim Canino , Masculino , Desintoxicação Metabólica Fase I , Camundongos , Camundongos Endogâmicos C57BL , Microssomos Hepáticos/enzimologia , Microssomos Hepáticos/metabolismo , Ratos , Sulfonamidas/administração & dosagem , Tiazóis/administração & dosagemRESUMO
A series of 4-amino cyclohexanes and 4-substituted piperidines were prepared and evaluated for inhibition of DPP-4. Analog 20q displayed both good DPP-4 potency and selectivity against other proteases, while derivative 20k displayed long half life and modest oral bioavailability in rat. The most potent analog, 3-(5-aminocarbonylpyridyl piperidine 53j, displayed excellent DPP-4 activity with good selectivity versus other proline enzymes.
Assuntos
Cicloexanos/síntese química , Cicloexanos/farmacologia , Inibidores da Dipeptidil Peptidase IV/síntese química , Inibidores da Dipeptidil Peptidase IV/farmacologia , Piperidinas/síntese química , Piperidinas/farmacologia , Animais , Disponibilidade Biológica , Cicloexanos/farmacocinética , Inibidores da Dipeptidil Peptidase IV/farmacocinética , Meia-Vida , Piperidinas/farmacocinética , RatosRESUMO
Bombesin receptor subtype-3 (BRS-3) is an orphan G-protein coupled receptor belonging to the subfamily of bombesin-like receptors. BRS-3 is implicated in the development of obesity and diabetes. We report here small-molecule agonists that are based on a 4-(alkylamino)pyridine-3-sulfonamide core. We describe the discovery of 2a, which has mid-nanomolar potency, selectivity for human BRS-3 versus the other bombesin-like receptors, and good bioavailability.
Assuntos
Piridinas/química , Receptores da Bombesina/agonistas , Sulfonamidas/farmacologia , Compostos de Sulfonilureia/farmacologia , Animais , Disponibilidade Biológica , Ligação de Hidrogênio , Masculino , Ratos , Ratos Sprague-Dawley , Sulfonamidas/química , Sulfonamidas/farmacocinética , Compostos de Sulfonilureia/química , Compostos de Sulfonilureia/farmacocinéticaRESUMO
N-type calcium channels (Ca(v)2.2) have been shown to play a critical role in pain. A series of low molecular weight 2-aryl indoles were identified as potent Ca(v)2.2 blockers with good in vitro and in vivo potency.
Assuntos
Bloqueadores dos Canais de Cálcio/uso terapêutico , Canais de Cálcio Tipo N/metabolismo , Indóis/uso terapêutico , Dor/tratamento farmacológico , Animais , Bloqueadores dos Canais de Cálcio/farmacocinética , Bloqueadores dos Canais de Cálcio/farmacologia , Cães , Haplorrinos , Humanos , Indóis/farmacocinética , Indóis/farmacologia , RatosRESUMO
Voltage-gated calcium channel (Ca(v))2.2 (N-type calcium channels) are key components in nociceptive transmission pathways. Ziconotide, a state-independent peptide inhibitor of Ca(v)2.2 channels, is efficacious in treating refractory pain but exhibits a narrow therapeutic window and must be administered intrathecally. We have discovered an N-triazole oxindole, (3R)-5-(3-chloro-4-fluorophenyl)-3-methyl-3-(pyrimidin-5-ylmethyl)-1-(1H-1,2,4-triazol-3-yl)-1,3-dihydro-2H-indol-2-one (TROX-1), as a small-molecule, state-dependent blocker of Ca(v)2 channels, and we investigated the therapeutic advantages of this compound for analgesia. TROX-1 preferentially inhibited potassium-triggered calcium influx through recombinant Ca(v)2.2 channels under depolarized conditions (IC(50) = 0.27 microM) compared with hyperpolarized conditions (IC(50) > 20 microM). In rat dorsal root ganglion (DRG) neurons, TROX-1 inhibited omega-conotoxin GVIA-sensitive calcium currents (Ca(v)2.2 channel currents), with greater potency under depolarized conditions (IC(50) = 0.4 microM) than under hyperpolarized conditions (IC(50) = 2.6 microM), indicating state-dependent Ca(v)2.2 channel block of native as well as recombinant channels. TROX-1 fully blocked calcium influx mediated by a mixture of Ca(v)2 channels in calcium imaging experiments in rat DRG neurons, indicating additional block of all Ca(v)2 family channels. TROX-1 reversed inflammatory-induced hyperalgesia with maximal effects equivalent to nonsteroidal anti-inflammatory drugs, and it reversed nerve injury-induced allodynia to the same extent as pregabalin and duloxetine. In contrast, no significant reversal of hyperalgesia was observed in Ca(v)2.2 gene-deleted mice. Mild impairment of motor function in the Rotarod test and cardiovascular functions were observed at 20- to 40-fold higher plasma concentrations than required for analgesic activities. TROX-1 demonstrates that an orally available state-dependent Ca(v)2 channel blocker may achieve a therapeutic window suitable for the treatment of chronic pain.
Assuntos
Analgésicos/farmacologia , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio Tipo N/fisiologia , Indóis/farmacologia , Triazóis/farmacologia , Analgésicos/efeitos adversos , Analgésicos/farmacocinética , Animais , Barorreflexo/efeitos dos fármacos , Disponibilidade Biológica , Bloqueadores dos Canais de Cálcio/efeitos adversos , Bloqueadores dos Canais de Cálcio/farmacocinética , Canais de Cálcio Tipo N/genética , Canais de Cálcio Tipo R/fisiologia , Proteínas de Transporte de Cátions/fisiologia , Linhagem Celular , Cães , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/fisiologia , Hiperalgesia/tratamento farmacológico , Hipotensão Ortostática/induzido quimicamente , Indóis/efeitos adversos , Indóis/farmacocinética , Masculino , Camundongos , Camundongos Knockout , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Dor/tratamento farmacológico , Dor/etiologia , Técnicas de Patch-Clamp , Ratos , Ratos Sprague-Dawley , Triazóis/efeitos adversos , Triazóis/farmacocinéticaRESUMO
The original structure of a high-throughput screening hit obtained from an external vendor was revised based on multiple NMR studies. The active compound was re-synthesized via a novel route and its structure and biological activity as a BRS-3 agonist were unambiguously confirmed. Multi-gram quantities of the hit were prepared for pharmacokinetic and efficacy studies. The synthetic strategy allowed for the preparation of multiple analogs for SAR exploration.
Assuntos
Fármacos Antiobesidade/síntese química , Naftiridinas/síntese química , Pirazóis/síntese química , Receptores da Bombesina/agonistas , Animais , Fármacos Antiobesidade/química , Fármacos Antiobesidade/farmacocinética , Ensaios de Triagem em Larga Escala , Humanos , Naftiridinas/química , Naftiridinas/farmacocinética , Pirazóis/química , Pirazóis/farmacocinética , Ratos , Receptores da Bombesina/metabolismo , Relação Estrutura-AtividadeRESUMO
A series of novel biphenyl pyrazole dicarboxamides were identified as potential sodium channel blockers for treatment of neuropathic pain. Compound 20 had outstanding efficacy in the Chung rat spinal nerve ligation (SNL) model of neuropathic pain.
Assuntos
Compostos de Bifenilo/química , Neuralgia/tratamento farmacológico , Pirazóis/química , Bloqueadores dos Canais de Sódio/química , Canais de Sódio/química , Animais , Compostos de Bifenilo/síntese química , Compostos de Bifenilo/uso terapêutico , Cães , Avaliação Pré-Clínica de Medicamentos , Humanos , Camundongos , Microssomos Hepáticos/metabolismo , Atividade Motora/efeitos dos fármacos , Pirazóis/farmacocinética , Pirazóis/uso terapêutico , Ratos , Bloqueadores dos Canais de Sódio/farmacocinética , Bloqueadores dos Canais de Sódio/uso terapêutico , Canais de Sódio/metabolismoRESUMO
A series of novel isoxazole voltage gated sodium channel blockers have been synthesized and evaluated. Substitutions on the benzylic position of benzamide were investigated to determine their effect on Na(v)1.7 inhibitory potency. The spirocyclobutyl substitution had the most significant enhancement on Na(v)1.7 inhibitory activity.
Assuntos
Isoxazóis/uso terapêutico , Dor/tratamento farmacológico , Bloqueadores dos Canais de Sódio/uso terapêutico , Canais de Sódio/metabolismo , Animais , Linhagem Celular , Doença Crônica , Humanos , Isoxazóis/química , Isoxazóis/farmacologia , Dor/imunologia , Ratos , Bloqueadores dos Canais de Sódio/química , Bloqueadores dos Canais de Sódio/farmacologia , Nervos Espinhais/efeitos dos fármacos , Relação Estrutura-AtividadeRESUMO
Analogs of the previously reported voltage gated sodium channel blocker CDA54 were prepared in which one of the amide functions was replaced with aromatic and non-aromatic heterocycles. Replacement of the amide with an aromatic heterocycle resulted in significant loss of sodium channel blocking activity, while non-aromatic heterocycle replacements were well tolerated.
Assuntos
Isoxazóis/química , Isoxazóis/farmacologia , Bloqueadores dos Canais de Sódio/química , Bloqueadores dos Canais de Sódio/farmacologia , Animais , Isoxazóis/uso terapêutico , Modelos Moleculares , Estrutura Molecular , Dor/tratamento farmacológico , Ratos , Ratos Sprague-Dawley , Bloqueadores dos Canais de Sódio/uso terapêutico , Nervos Espinhais/efeitos dos fármacos , Relação Estrutura-AtividadeRESUMO
A new series of DPP-4 inhibitors derived from piperidine-fused benzimidazoles and imidazopyridines is described. Optimization of this class of DPP-4 inhibitors led to the discovery of imidazopyridine 34. The potency, selectivity, cross-species DMPK profiles, and in vivo efficacy of 34 is reported.
Assuntos
Química Farmacêutica/métodos , Inibidores da Dipeptidil Peptidase IV/síntese química , Imidazóis/síntese química , Piperidinas/química , Piperidinas/síntese química , Animais , Benzimidazóis/síntese química , Benzimidazóis/farmacologia , Cristalografia por Raios X/métodos , Inibidores da Dipeptidil Peptidase IV/farmacologia , Cães , Desenho de Fármacos , Peptídeo 1 Semelhante ao Glucagon/química , Humanos , Hidrólise , Imidazóis/farmacologia , Concentração Inibidora 50 , Macaca mulatta , Camundongos , Piperidinas/farmacologia , Pirazinas/síntese química , Pirazinas/farmacologia , Piridinas/síntese química , Piridinas/farmacologia , Ratos , Fosfato de Sitagliptina , Triazóis/síntese química , Triazóis/farmacologiaRESUMO
BACKGROUND: Voltage-gated sodium channels (Na(v)1) are expressed in primary sensory neurons where they influence excitability via their role in the generation and propagation of action potentials. Recently, human genetic data have shown that one sodium channel subtype, Na(v)1.7, plays a major role in pain. We performed these studies to characterize the antinociceptive effects of N-[(R)-1-((R)-7-chloro-1-isopropyl-2-oxo-2,3,4,5-tetrahydro-1H-benzo[b]azepin-3-ylcarbamoyl)-2-(2-fluorophenyl)-ethyl]-4-fluoro-2-trifluoromethyl-benzamide (BZP), a non-central nervous system (CNS) penetrant small molecule with high affinity and preferential selectivity for Na(v)1.7 over Na(v)1.8 and Na(v)1.5. METHODS: BZP was evaluated in rat preclinical models of inflammatory and neuropathic pain and compared with standard analgesics. Two models were used: the complete Freund's adjuvant model of inflammatory pain and the spinal nerve ligation model of neuropathic pain. BZP was also evaluated in a motor coordination assay to assess its propensity for CNS side effects. RESULTS: In preclinical models of chronic pain, BZP displayed efficacy comparable with that of leading analgesics. In the complete Freund's adjuvant model, BZP produced reversal of hyperalgesia comparable with nonsteroidal antiinflammatory drugs, and in the spinal nerve ligation model, BZP produced reversal of allodynia comparable with gabapentin and mexiletine. Unlike the CNS penetrant compounds gabapentin and mexiletine, BZP did not induce any impairment of motor coordination. CONCLUSIONS: These data suggest that a peripherally acting sodium channel blocker, preferentially acting through Na(v)1.7, could provide clinical relief of chronic pain without the CNS side effects typical of many existing pain treatments.
Assuntos
Benzamidas/farmacologia , Inflamação , Canais de Sódio/metabolismo , Analgésicos/farmacologia , Animais , Linhagem Celular , Humanos , Hiperalgesia/patologia , Masculino , Canal de Sódio Disparado por Voltagem NAV1.7 , Degeneração Neural/patologia , Dor , Ratos , Ratos Sprague-Dawley , Nervos Espinhais/patologiaRESUMO
A series of beta-aminoamides bearing triazolopiperazines have been discovered as potent, selective, and orally active dipeptidyl peptidase IV (DPP-4) inhibitors by extensive structure-activity relationship (SAR) studies around the triazolopiperazine moiety. Among these, compound 34b with excellent in vitro potency (IC50 = 4.3 nM) against DPP-4, high selectivity over other enzymes, and good pharmacokinetic profiles exhibited pronounced in vivo efficacy in an oral glucose tolerance test (OGTT) in lean mice. On the basis of these properties, compound 34b has been profiled in detail. Further refinement of the triazolopiperazines resulted in the discovery of a series of extremely potent compounds with subnanomolar activity against DPP-4 (42b- 49b), that is, 4-fluorobenzyl-substituted compound 46b, which is notable for its superior potency (IC50 = 0.18 nM). X-ray crystal structure determination of compounds 34b and 46b in complex with DPP-4 enzyme revealed that (R)-stereochemistry at the 8-position of triazolopiperazines is strongly preferred over (S) with respect to DPP-4 inhibition.
Assuntos
Amidas/síntese química , Inibidores da Dipeptidil Peptidase IV , Piperazinas/síntese química , Pirazinas/síntese química , Triazóis/síntese química , Amidas/farmacocinética , Amidas/farmacologia , Animais , Cristalografia por Raios X , Dipeptidil Peptidase 4/química , Cães , Teste de Tolerância a Glucose , Haplorrinos , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Piperazinas/farmacocinética , Piperazinas/farmacologia , Pirazinas/farmacocinética , Pirazinas/farmacologia , Ratos , Estereoisomerismo , Relação Estrutura-Atividade , Triazóis/farmacocinética , Triazóis/farmacologiaRESUMO
A series of imidazopyridines were evaluated as potential sodium channel blockers for the treatment of neuropathic pain. Several members were identified with good hNa(v)1.7 potency and excellent rat pharmacokinetic profiles. Compound 4 had good efficacy (52% and 41% reversal of allodynia at 2 and 4h post-dose, respectively) in the Chung rat spinal nerve ligation (SNL) model of neuropathic pain when dosed orally at 10mg/kg.
Assuntos
Piridinas/química , Piridinas/farmacologia , Bloqueadores dos Canais de Sódio/química , Bloqueadores dos Canais de Sódio/farmacologia , Canais de Sódio/metabolismo , Analgésicos/química , Analgésicos/farmacologia , Animais , Inflamação/tratamento farmacológico , Estrutura Molecular , Canal de Sódio Disparado por Voltagem NAV1.7 , Dor/tratamento farmacológico , Ratos , Bloqueadores dos Canais de Sódio/farmacocinética , Relação Estrutura-AtividadeRESUMO
The synthesis, selectivity, rat pharmacokinetic profile, and drug metabolism profiles of a series of potent fluoroolefin-derived DPP-4 inhibitors (4) are reported. A radiolabeled fluoroolefin 33 was shown to possess a high propensity to form reactive metabolites, thus revealing a potential liability for this class of DPP-4 inhibitors.
Assuntos
Alcenos/farmacocinética , Amidas/química , Inibidores da Dipeptidil Peptidase IV/farmacocinética , Hidrocarbonetos Fluorados/farmacocinética , Hipoglicemiantes/farmacocinética , Microssomos Hepáticos/efeitos dos fármacos , Alcenos/síntese química , Animais , Inibidores da Dipeptidil Peptidase IV/síntese química , Hidrocarbonetos Fluorados/síntese química , Hipoglicemiantes/síntese química , Microssomos Hepáticos/patologia , Modelos Químicos , Mimetismo Molecular , Ratos , Estereoisomerismo , Relação Estrutura-Atividade , Especificidade por SubstratoRESUMO
A series of 3-amino-1,5-benzodiazepinones were synthesized and evaluated as potential sodium channel blockers in a functional, membrane potential-based assay. One member of this series displayed subnanomolar, state-dependent sodium channel block, and was orally efficacious in a mouse model of epilepsy.
Assuntos
Anticonvulsivantes/farmacologia , Benzodiazepinonas/farmacologia , Epilepsia/tratamento farmacológico , Canais de Potássio Éter-A-Go-Go/antagonistas & inibidores , Bloqueadores dos Canais de Sódio/farmacologia , Animais , Anticonvulsivantes/síntese química , Anticonvulsivantes/farmacocinética , Benzodiazepinonas/síntese química , Benzodiazepinonas/farmacocinética , Eletrofisiologia , Eletrochoque , Epilepsia/metabolismo , Canais de Potássio Éter-A-Go-Go/metabolismo , Transferência Ressonante de Energia de Fluorescência , Humanos , Camundongos , Estrutura Molecular , Ratos , Bloqueadores dos Canais de Sódio/síntese química , Bloqueadores dos Canais de Sódio/farmacocinéticaRESUMO
Decoding facial expressions of emotion is an important aspect of social communication that is often impaired following psychiatric or neurological illness. However, little is known of the cognitive components involved in perceiving emotional expressions. Three dual task studies explored the role of verbal working memory in decoding emotions. Concurrent working memory load substantially interfered with choosing which emotional label described a facial expression (Experiment 1). A key factor in the magnitude of interference was the number of emotion labels from which to choose (Experiment 2). In contrast the ability to decide that two faces represented the same emotion in a discrimination task was relatively unaffected by concurrent working memory load (Experiment 3). Different methods of assessing emotion perception make substantially different demands on working memory. Implications for clinical disorders which affect both working memory and emotion perception are considered.
Assuntos
Tomada de Decisões , Emoções , Expressão Facial , Memória de Curto Prazo , Adolescente , Adulto , Atenção , Aprendizagem por Discriminação , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Semântica , Aprendizagem Seriada , Percepção da FalaRESUMO
In cells, phosphorylation of pantothenic acid to generate phosphopantothenic acid by the pantothenate kinase enzymes is the first step in coenzyme A synthesis. Pantothenate kinase 2, the isoform localized in neuronal cell mitochondria, is dysfunctional in patients with pantothenate kinase-associated neurodegeneration. Fosmetpantotenate is a phosphopantothenic acid prodrug in clinical development for treatment of pantothenate kinase-associated neurodegeneration, which aims to replenish phosphopantothenic acid in patients. Fosmetpantotenate restored coenzyme A in short-hairpin RNA pantothenate kinase 2 gene-silenced neuroblastoma cells and was permeable in a blood-brain barrier model. The rate of fosmetpantotenate metabolism in blood is species-dependent. Following up to 700 mg/kg orally, blood exposure to fosmetpantotenate was negligible in rat and mouse, but measurable in monkey. Consistent with the difference in whole blood half-life, fosmetpantotenate dosed orally was found in the brains of the monkey (striatal dialysate) but was absent in mice. Following administration of isotopically labeled-fosmetpantotenate to mice, ~40% of liver coenzyme A (after 500 mg/kg orally) and ~50% of brain coenzyme A (after 125 µg intrastriatally) originated from isotopically labeled-fosmetpantotenate. Additionally, 10-day dosing of isotopically labeled-fosmetpantotenate, 12.5 µg, intracerebroventricularly in mice led to ~30% of brain coenzyme A containing the stable isotopic labels. This work supports the hypothesis that fosmetpantotenate acts to replace reduced phosphopantothenic acid in pantothenate kinase 2-deficient tissues.