Therapeutic developments in peroxisome biogenesis disorders

Molecular basis of peroxisomal biogenesis disorders caused by defects in peroxisomal matrix protein import

Peroxisomal biogenesis disorders (PBDs) represent a spectrum of autosomal recessive metabolic disorders that are collectively characterized by abnormal peroxisome assembly and impaired peroxisomal function. The importance of this ubiquitous organelle for human health is highlighted by the fact that PBDs are multisystemic disorders that often cause death in early infancy. Peroxisomes contribute to central metabolic pathways. Most enzymes in the peroxisomal matrix are linked to lipid metabolism and detoxification of reactive oxygen species. Proper assembly of peroxisomes and thus also import of their enzymes relies on specific peroxisomal biogenesis factors, so called peroxins with PEX being the gene acronym. To date, 13 PEX genes are known to cause PBDs when mutated. Studies of the cellular and molecular defects in cells derived from PBD patients have significantly contributed to the understanding of the functional role of the corresponding peroxins in peroxisome assembly. In this review, we discuss recent data derived from both human cell culture as well as model organisms like yeasts and present an overview on the molecular mechanism underlying peroxisomal biogenesis disorders with emphasis on disorders caused by defects in the peroxisomal matrix protein import machinery.

Hypergonadotropic hypogonadism, progressive early-onset spinocerebellar ataxia, and late-onset sensorineural hearing loss: case report and literature review

The association of ataxia, hypergonadotropic hypogonadism and hearing loss is extremely rare. Considerable heterogeneity exists in the literature of the neurological manifestations, age of onset, clinical severity and associated abnormalities. We describe a 24-year-old woman with secondary hypergonadotropic amenorrhea, early-onset progressive spinocerebellar ataxia (SCA), late-onset sensorineural hearing loss and normal intelligence and compare it with reported cases.

A novel fluorescent sensor protein for visualization of redox states in the cytoplasm and in peroxisomes

Reactive oxygen species are generated within peroxisomes during peroxisomal metabolism. However, due to technological difficulties, the intraperoxisomal redox state remain elusive, and the effect of peroxisome deficiency on the intracellular redox state is controversial. A newly developed, genetically encoded fluorescence resonance energy transfer (FRET) probe, Redoxfluor, senses the physiological redox state via its internal disulfide bonds, resulting in a change in the conformation of the protein leading to a FRET response. We made use of Redoxfluor to measure the redox states at the subcellular level in yeast and Chinese hamster ovary (CHO) cells. In wild-type peroxisomes harboring an intact fatty acid beta-oxidation system, the redox state within the peroxisomes was more reductive than that in the cytosol, despite the fact that reactive oxygen species were generated within the peroxisomes. Interestingly, we observed that the redox state of the cytosol of cell mutants for peroxisome assembly, regarded as models for a neurological metabolic disorder, was more reductive than that of the wild-type cells in yeast and CHO cells. Furthermore, Redoxfluor was utilized to develop an efficient system for the screening of drugs that moderate the abnormal cytosolic redox state in the mutant CHO cell lines for peroxisome assembly without affecting the redox state of normal cells.

Modulation of lipid rafts by Omega-3 fatty acids in inflammation and cancer: implications for use of lipids during nutrition support

Current understanding of biologic membrane structure and function is largely based on the concept of lipid rafts. Lipid rafts are composed primarily of tightly packed, liquid-ordered sphingolipids/cholesterol/saturated phospholipids that float in a sea of more unsaturated and loosely packed, liquid-disordered lipids. Lipid rafts have important clinical implications because many important membrane-signaling proteins are located within the raft regions of the membrane, and alterations in raft structure can alter activity of these signaling proteins. Because rafts are lipid-based, their composition, structure, and function are susceptible to manipulation by dietary components such as omega-3 polyunsaturated fatty acids and by cholesterol depletion. We review how alteration of raft lipids affects the raft/nonraft localization and hence the function of several proteins involved in cell signaling. We focus our discussion of raft-signaling proteins on inflammation and cancer.

Peroxisome biogenesis disorders

Defects in PEX genes impair peroxisome assembly and multiple metabolic pathways confined to this organelle, thus providing the biochemical and molecular bases of the peroxisome biogenesis disorders (PBD). PBD are divided into two types--Zellweger syndrome spectrum (ZSS) and rhizomelic chondrodysplasia punctata (RCDP). Biochemical studies performed in blood and urine are used to screen for the PBD. DNA testing is possible for all of the disorders, but is more challenging for the ZSS since 12 PEX genes are known to be associated with this spectrum of PBD. In contrast, PBD-RCDP is associated with defects in the PEX7 gene alone. Studies of the cellular and molecular defects in PBD patients have contributed significantly to our understanding of the role of each PEX gene in peroxisome assembly.

Phenylbutyrate inhibits growth of cervical carcinoma cells independent of HPV type and copy number

PURPOSE

Inhibitors of histone deacetylase, such as sodium butyrate, block proliferation of cervical carcinoma cells by inhibiting the G1 to S transition of the cell cycle. The derivative phenylbutyrate (PB), characterized by its higher pharmacological half-life, and its metabolite phenylacetate (PA) were tested for their growth-inhibitory function on cervical cancer cells differing in their HPV type, copy number, and integration sites.

METHODS AND RESULTS

Using flow cytometric and Western blot analyses, we show that a 24-h incubation period with PB, but not with PA, was already sufficient to cause a dose-dependent growth arrest by increasing the G1 fraction with a concomitant drop in the S-phase. Consistent with the cell cycle block, only PB, but not PA, induced the cyclin-dependent kinase inhibitors p21(CIP1) and p27(KIP1). The inhibitory effect was not the result of a non-specific cytotoxic effect of PB, since cessation of cellular growth was already completely reversible 5 h after drug removal.

CONCLUSIONS

Due to its broad growth inhibitory properties on different cervical carcinoma cells in vitro, and its low toxic profile demonstrated in preceding clinical studies, PB may serve as an effective drug in handling pre-cancerous lesions and cervical cancer in patients.

Identification of phenylbutyrylglutamine, a new metabolite of phenylbutyrate metabolism in humans

Phenylbutyrate is used in humans for treating inborn errors of ureagenesis, certain forms of cancer, cystic fibrosis and thalassemia. The known metabolism of phenylbutyrate leads to phenylacetylglutamine, which is excreted in urine. We have identified phenylbutyrylglutamine as a new metabolite of phenylbutyrate in human plasma and urine. We describe the synthesis of phenylbutyrylglutamine and its assay by gas chromatography/mass spectrometry as a tert-butyldimethylsilyl or methyl derivative, using standards of [(2)H(5)]phenylbutyrylglutamine and phenylpropionylglutamine. After administration of phenylbutyrate to normal humans, the cumulative urinary excretion of phenylacetate, phenylbutyrate, phenylacetylglutamine and phenylbutyrylglutamine amounts to about half of the dose of phenylbutyrate. Thus, additional metabolites of phenylbutyrate are yet to be identified.