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Ahmet Hoke

Publications and source records attributed to Ahmet Hoke.

18 recordsLinked to original sources
PubMed2006

Neuroimmunophilin ligands protect cavernous nerves after crush injury in the rat: new experimental paradigms.

OBJECTIVES: We investigated the effects of the orally bioavailable non-immunosuppressive immunophilin ligand GPI 1046 (GPI) on erectile function and cavernous nerve (CN) histology following unilateral or bilateral crush injury (UCI, BCI, respectively) of the CNs. METHODS: Adult male Sprague-Dawley rats were administered GPI 15 mg/kg intraperitoneally (ip) or 30 mg/kg orally (po), FK506 1 mg/kg, ip, or vehicle controls for each route of administration just prior to UCI or BCI and daily up to 7 d following injury. At day 1 or 7 of treatment, erectile function induced by CN electrical stimulation was measured, and electron microscopic analysis of the injured CN was performed. RESULTS: Intraperitoneal administration of GPI to rats with injured CN protected erectile function, in a fashion similar to the prototypic immunophilin ligand FK506, compared with vehicle-treated animals (93%+/-9% vs. 70%+/-5% vs. 45%+/-1%, p<0.01, respectively). Oral administration of GPI elicited the same level of significant protection from CN injury. GPI administered po at 30 mg/kg/d, dosing either once daily or four times daily with 7.5 mg/kg, provided nearly complete protection of erectile function. In a more severe BCI model, po administration of GPI maintained erectile function at 24 h after CN injury. Ultrastructural analysis of injured CNs indicated that GPI administered at the time of CN injury prevents degeneration of about 83% of the unmyelinated axons at 7 d after CN injury. CONCLUSIONS: The orally administered immunophilin ligand GPI neuroprotects CNs and maintains erectile function in rats under various conditions of CN crush injury.

Administration, Oral↗
PubMed2006

Sensory neuropathy in human immunodeficiency virus/acquired immunodeficiency syndrome patients: protease inhibitor-mediated neurotoxicity.

OBJECTIVE: Human immunodeficiency virus-associated sensory neuropathy (HIV-SN) is a common and disabling disorder, often associated with antiretroviral therapy (ART) use. We investigated the clinical features and associated pathogenic determinants of HIV-SN in a neurological cohort of HIV-infected patients, together with a novel model of HIV-SN. METHODS: HIV-infected patients with neurological disease were investigated in terms of clinical and laboratory aspects together with ART exposure focusing on symptomatic HIV-SN. Rat-derived dorsal root ganglion (DRG) cultures, transgenic for human CD4 and CCR5 treated with ARTs or HIV infected, or both, were studied with respect to quantitative neuronal injury. RESULTS: Among 221 patients assessed from 1998 to 2004, 120 had no sensory neuropathy, whereas 101 displayed HIV-SN, including 64 with distal sensory neuropathy and 37 with antiretroviral toxic neuropathy. HIV-SN patients exhibited significantly greater mean age, peak plasma viral loads, and exposure to neurotoxic dideoxynucleosides and protease inhibitors, including indinavir, saquinavir, or ritonavir. HIV-infected DRG cultures exposed to indinavir or didanosine showed significant neuronal atrophy, neurite retraction, and process loss, compared with controls. Indinavir was selectively cytotoxic to DRG macrophages compared with other ARTs. INTERPRETATION: Protease inhibitor exposure is an unrecognized risk factor for the development of HIV-SN, which may potentiate neuronal damage in HIV-infected DRGs, possibly through the loss of macrophage-derived trophic factors.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Recovery from paralysis in adult rats using embryonic stem cells.

OBJECTIVE: We explored the potential of embryonic stem cell-derived motor neurons to functionally replace those cells destroyed in paralyzed adult rats. METHODS: We administered a phosphodiesterase type 4 inhibitor and dibutyryl cyclic adenosine monophosphate to overcome myelin-mediated repulsion and provided glial cell-derived neurotrophic factor within the sciatic nerve to attract transplanted embryonic stem cell-derived axons toward skeletal muscle targets. RESULTS: We found that these strategies significantly increased the success of transplanted axons extending out of the spinal cord into ventral roots. Furthermore, transplant-derived axons reached muscle, formed neuromuscular junctions, were physiologically active, and mediated partial recovery from paralysis. INTERPRETATION: We conclude that restoration of functional motor units by embryonic stem cells is possible and represents a potential therapeutic strategy for patients with paralysis. To our knowledge, this is the first report of the anatomical and functional replacement of a motor neuron circuit within the adult mammalian host.

Age Factors↗
PubMed2006

Recent advances in HIV neuropathy.

PURPOSE OF REVIEW: To describe recent advances in HIV neuropathy. RECENT FINDINGS: Epidemiologic studies since highly active antiretroviral therapy was introduced have shown that the incidence of HIV-associated distal sensory polyneuropathy is reduced. Studies have also shown the relationship between distal sensory polyneuropathy and the use of neurotoxic antiretroviral drugs. Skin punch biopsy for assessment of epidermal nerve fiber density is valuable both for diagnosis of distal sensory polyneuropathy and as a predictor of the condition occurring in the future. An in-vitro model of antiretroviral toxic neuropathy showed that dideoxynucleoside analogues that cause neuropathy exert direct mitochondrial toxicity that is not mediated indirectly through the inhibition of DNA polymerase-gamma. HIV envelope protein gp120 exerts axonal toxicity directly or indirectly via perineuronal Schwann cells. A feline model of HIV, infection of neonatal cats with the feline immunodeficiency virus, showed development of peripheral neuropathy characterized by loss of epidermal innervation. SUMMARY: While epidemiological studies of HIV-associated peripheral neuropathy continue to provide useful information, pathogenic studies are moving forward. Animal models of the disease will allow researchers to 'manipulate' the system. It is hoped that these types of studies will translate to an improved understanding of the pathogenesis of HIV-associated neuropathies leading to better treatments.

Antiretroviral Therapy, Highly Active↗
PubMed2005

Loss of ALS2 function is insufficient to trigger motor neuron degeneration in knock-out mice but predisposes neurons to oxidative stress.

Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease, is caused by a selective loss of motor neurons in the CNS. Mutations in the ALS2 gene have been linked to one form of autosomal recessive juvenile onset ALS (ALS2). To investigate the pathogenic mechanisms of ALS2, we generated ALS2 knock-out (ALS2(-/-)) mice. Although ALS2(-/-) mice lacked obvious developmental abnormalities, they exhibited age-dependent deficits in motor coordination and motor learning. Moreover, ALS2(-/-) mice showed a higher anxiety response in the open-field and elevated plus-maze tasks. Although they failed to recapitulate clinical or neuropathological phenotypes consistent with motor neuron disease by 20 months of age, ALS2(-/-) mice or primary cultured neurons derived from these mice were more susceptible to oxidative stress compared with wild-type controls. These observations suggest that loss of ALS2 function is insufficient to cause major motor deficits or motor neuron degeneration in a mouse model but predisposes neurons to oxidative stress.

Amyotrophic Lateral Sclerosis↗
PubMed2005

Hydroxychloroquine causes severe vacuolar myopathy in a patient with chronic graft-versus-host disease.

A 51-year-old man developed progressive debilitating limb and respiratory muscle weakness while undergoing treatment for chronic graft-versus-host disease secondary to allogeneic bone marrow transplant for mantle cell lymphoma. He had a normal serum creatine kinase level and acetylcholine receptor antibodies were negative. Electromyography showed a severe, nonirritable myopathy and a sensory motor axonal polyneuropathy. A muscle biopsy showed a necrotizing, vacuolar myopathy with many fibers containing autophagic and red-rimmed vacuoles, suggestive of an amphiphilic drug myopathy. The patient's strength and function improved significantly after discontinuation of hydroxychloroquine.

Biopsy↗
PubMed2005

Erythropoietin promotes the recovery of erectile function following cavernous nerve injury.

PURPOSE: We investigated the effects of recombinant human (rh) erythropoietin (EPO) on erectile function recovery in a rat model of cavernous nerve (CN) injury. MATERIALS AND METHODS: Male rats underwent unilateral CN transection and excision of a 5 mm segment of the contralateral CN. One group received rhEPO (5,000 U/kg) subcutaneously daily for 14 days, while another received rhEPO 1 day and 1 hour prior to nerve injury. An additional group of animals was pretreated with 1 dose of darbepoetin (25 microg/kg). At 14 days following CN injury rats underwent erection physiology studies. Axonal regeneration was evaluated by electron microscopy. EPO receptor expression in the penis and major pelvic ganglion was evaluated immunohistochemically and by real-time polymerase chain reaction. RESULTS: Daily rhEPO effectively recovered erections after CN injury compared with saline treatment. Maximal intracavernous pressure area under the curve normalized to mean arterial pressure was significantly greater in EPO treated vs saline treated animals (p < 0.05). rhEPO and darbepoetin pretreatment was as effective as continuous 14-day therapy. EPO receptor expression was localized to neuronal cell bodies of the major pelvic ganglion, penile nerves and endothelial cells in the penis. Electron microscopy revealed significant improvement in axonal regeneration in rhEPO treated animals 14 days following injury compared to controls. CONCLUSIONS: EPO receptors are expressed in local neuronal and vascular tissues. Exogenous administration of rhEPO or darbepoetin in the setting of CN injury promotes erectile function recovery. This occurs through axonal regeneration of the injured nerve and possible penile protection.

Analysis of Variance↗
PubMed2004

Erythropoietin is neuroprotective in models of HIV sensory neuropathy.

HIV-associated sensory neuropathy (HIV-SN) is the most common neurological complication of HIV infection. Presently, there are no effective therapies for this painful neuropathy. The pathology of HIV-SN is characterized by 'dying back' sensory axonal degeneration and a more modest loss of dorsal root ganglion (DRG) sensory neurons. It has been hypothesized that HIV-SN results from neurotoxicity by secreted viral proteins, such as the HIV envelope glycoprotein gp120. Furthermore, neurotoxicity by dideoxynucleoside (DDX) agents, results in the observed higher incidence of HIV-SN in HIV-infected patients taking these antiretroviral drugs. In this study we show that administration of picomolar amounts of the hormone erythropoietin (EPO) prevents sensory axonal degeneration and in vitro DRG neuronal death by both gp120 and ddC (a neurotoxic DDX drug). Our results suggest that EPO may be useful in the treatment of HIV-SN.

Animals↗
PubMed2004

The use of GAP-43 mRNA quantification in high throughput screening of putative neuroprotective agents in dorsal root ganglion cultures.

Large scale screening for neuroprotective drugs for peripheral neuropathies requires development of a high throughput system that is reliable and reproducible. Currently most accurate outcome measures of axonal degeneration are based on time-consuming, laborious measurement of morphological changes in neurites. In order to improve on the scalability of the screening procedure we developed a real-time RT-PCR based method of gene expression that correlates very well with morphological measures of neuritic degeneration. We examined the changes in GAP-43 expression in primary dorsal root ganglion (DRG) neurons in vitro with exposure to a zalcitabine (ddC), an antiretroviral drug that causes neuropathy in human immunodeficiency virus (HIV)-infected individuals, with and without FK506, an immunophilin ligand with neuroprotective and neuroregenerative properties. Similar to morphological measures of neuritic degeneration, in ddC-treated cultures there was a reduction in the expression of GAP-43 mRNA. This was prevented, in a dose-dependent manner, by co-administration of FK506. This assay, performed in a 96-well format, can easily be scaled for high throughput screening (HTS) using robotic systems.

Animals↗
PubMed2004

Peripheral neuropathy in lentivirus infection: evidence of inflammation and axonal injury.

OBJECTIVE: As distal sensory polyneuropathy (DSP) is a major neurological complication of HIV-1 infection, we investigated the extent of peripheral nervous system disease in animals infected with the lentivirus, feline immunodeficiency virus (FIV), because it causes neurological disease and immunosuppression in cats similar to HIV-1 in humans. METHODS: After infection with a neurovirulent FIV molecular clone, neurobehavioral testing, nerve morphology, viral detection and load measurements were performed. RESULTS: Neurobehavioral studies showed delayed withdrawal in response to a noxious stimulus among FIV-infected animals compared with sham-infected controls (P < 0.05). Dorsal root ganglia and sciatic nerves from FIV-infected ammals showed activated macrophages that were increased in number and size compared with controls. In addition, TNF-alpha messenger RNA was detectable in most nerves and spinal cords from the FIV-infected group, but was infrequently detected in controls. Viral RNA copy numbers in plasma and sciatic nerves were detectable in all FIV-infected animals at high levels. Studies of sural nerves identified myelinated fiber atrophy in 12-week FIV-infected animals compared with age-matched control animals, which was accompanied by reduced myelin sheath thickness (P < 0.05). The footpads of FIV-infected animals displayed reduced intraepidermal fiber density compared with control animals (P < 0.01). CONCLUSION: FIV infection results in the rapid onset of peripheral neuropathy, defined by axonal injury and macrophage activation, together with abundant virus within the nerve, indicating that it may serve as a model of HIV-related DSP.

Animals↗
PubMed2004

Differences between human and mouse embryonic stem cells.

We compared gene expression profiles of mouse and human ES cells by immunocytochemistry, RT-PCR, and membrane-based focused cDNA array analysis. Several markers that in concert could distinguish undifferentiated ES cells from their differentiated progeny were identified. These included known markers such as SSEA antigens, OCT3/4, SOX-2, REX-1 and TERT, as well as additional markers such as UTF-1, TRF1, TRF2, connexin43, and connexin45, FGFR-4, ABCG-2, and Glut-1. A set of negative markers that confirm the absence of differentiation was also developed. These include genes characteristic of trophoectoderm, markers of germ layers, and of more specialized progenitor cells. While the expression of many of the markers was similar in mouse and human cells, significant differences were found in the expression of vimentin, beta-III tubulin, alpha-fetoprotein, eomesodermin, HEB, ARNT, and FoxD3 as well as in the expression of the LIF receptor complex LIFR/IL6ST (gp130). Profound differences in cell cycle regulation, control of apoptosis, and cytokine expression were uncovered using focused microarrays. The profile of gene expression observed in H1 cells was similar to that of two other human ES cell lines tested (line I-6 and clonal line-H9.2) and to feeder-free subclones of H1, H7, and H9, indicating that the observed differences between human and mouse ES cells were species-specific rather than arising from differences in culture conditions.

Animals↗
PubMed2004

A novel endogenous erythropoietin mediated pathway prevents axonal degeneration.

Clinically relevant peripheral neuropathies (such as diabetic and human immunodeficiency virus sensory neuropathies) are characterized by distal axonal degeneration, rather than neuronal death. Here, we describe a novel, endogenous pathway that prevents axonal degeneration. We show that in response to axonal injury, periaxonal Schwann cells release erythropoietin (EPO), which via EPO receptor binding on neurons, prevents axonal degeneration. We demonstrate that the relevant axonal injury signal that stimulates EPO production from surrounding glial cells is nitric oxide. In addition, we show that this endogenous pathway can be therapeutically exploited by administering exogenous EPO. In an animal model of distal axonopathy, systemic EPO administration prevents axonal degeneration, and this is associated with a reduction in limb weakness and neuropathic pain behavior. Our in vivo and in vitro data suggest that EPO prevents axonal degeneration and therefore may be therapeutically useful in a wide variety of human neurological diseases characterized by axonopathy.

Animals↗
PubMed2003

FK506 is neuroprotective in a model of antiretroviral toxic neuropathy.

Antiretroviral toxic neuropathy is the most common neurological complication of human immunodeficiency virus infection. This painful neuropathy not only affects the quality of life of human immunodeficiency virus-infected patients but also severely limits viral suppression strategies. We have developed an in vitro model of this toxic neuropathy to better understand the mechanism of neurotoxicity and to test potential neuroprotective compounds. We show that among the dideoxynucleosides, ddC appears to be the most neurotoxic, followed by ddI and then d4T. This reflects their potency in causing neuropathy. AZT, which does not cause a peripheral neuropathy in patients, does not cause significant neurotoxicity in our model. Furthermore, in this model, we show that the immunophilin ligand FK506 but not cyclosporin A prevents the development of neurotoxicity by ddC, as judged by amelioration of ddC-induced "neuritic pruning," neuronal mitochondrial depolarization, and neuronal necrotic death. This finding suggests a calcineurin-independent mechanism of neuroprotection. As calcineurin inhibition underlies the immunosuppressive properties of these clinically used immunophilin ligands, this holds promise for the neuroprotective efficacy of nonimmunosuppressive analogs of FK506 in the prevention or treatment of antiretroviral toxic neuropathy.

Animals↗
PubMed2003

Schwann cell chemokine receptors mediate HIV-1 gp120 toxicity to sensory neurons.

Human immunodeficiency virus (HIV)-associated sensory neuropathy (HIV-SN) is the most common neurological complication of HIV infection. Currently, the pathogenesis of HIV-SN is unknown. Because there is no convincing evidence of neuronal infection, HIV neurotoxicity is likely to be effected either by secreted viral proteins such as the envelope glycoprotein gp120 or by neurotoxic cytokines released from infected/activated glial cells. We describe a model of gp120 toxicity to primary sensory neurons, in which gp120 induces neuritic degeneration and neuronal apoptosis. We show that Schwann cells, the cells that ensheath peripheral nerve axons, and which traditionally have been viewed as having a passive, supporting role, mediate this neurotoxicity. Ligation of the chemokine receptor CXCR4 on Schwann cells by gp120 resulted in the release of RANTES, which induced dorsal root ganglion neurons to produce tumor necrosis factor-alpha and subsequent TNFR1-mediated neurotoxicity in an autocrine fashion. This newly described Schwann cell-neuron interaction may be pathogenically relevant not only in HIV-SN but also in other peripheral neuropathies.

Animals↗
PubMed2003

Designing, testing, and validating a focused stem cell microarray for characterization of neural stem cells and progenitor cells.

Fetal neural stem cells (NSCs) have received great attention not only for their roles in normal development but also for their potential use in the treatment of neurodegenerative disorders. To develop a robust method of assessing the state of stem cells, we have designed, tested, and validated a rodent NSC array. This array consists of 260 genes that include cell type-specific markers for embryonic stem (ES) cells and neural progenitor cells as well as growth factors, cell cycle-related genes, and extracellular matrix molecules known to regulate NSC biology. The 500-bp polymerase chain reaction products amplified and validated by using gene-specific primers were arrayed along with positive controls. Blanks were included for quality control, and some genes were arrayed in duplicate. No cross-hybridization was detected. The quality of the arrays and their sensitivity were also examined by using probes prepared by conventional reverse transcriptase or by using amplified probes prepared by linear polymerase replication (LPR). Both methods showed good reproducibility, and probes prepared by LPR labeling appeared to detect expression of a larger proportion of expressed genes. Expression detected by either method could be verified by RT-PCR with high reproducibility. Using these stem cell chips, we have profiled liver, ES, and neural cells. The cell types could be readily distinguished from each other. Nine markers specific to mouse ES cells and 17 markers found in neural cells were verified as robust markers of the stem cell state. Thus, this focused neural stem array provides a convenient and useful tool for detection and assessment of NSCs and progenitor cells and can reliably distinguish them from other cell populations.

Animals↗