Adeno-associated virus type 6 is retrogradely transported in the non-human primate brain

We recently demonstrated that axonal transport of adeno-associated virus (AAV) is serotype-dependent. Thus, AAV2 is anterogradely transported (e.g., from cell bodies to nerve terminals) in both rat and non-human primate (NHP) brain. In contrast, AAV6 is retrogradely transported from terminals to neuronal cells bodies in the rat brain. However, the directionality of axonal transport of AAV6 in the NHP brain has not been determined. In this study, two Cynomolgus macaques received an infusion of AAV6 harboring green fluorescent protein (GFP) into the striatum (caudate and putamen) by magnetic resonance (MR)-guided convection-enhanced delivery. One month after infusion, immunohistochemical staining of brain sections revealed a striatal GFP expression that corresponded well with MR signal observed during gene delivery. As shown previously in rats, GFP expression was detected throughout the prefrontal, frontal, and parietal cortex, as well as substantia nigra pars compacta and thalamus, indicating retrograde transport of the vector in NHP. AAV6-GFP preferentially transduced neurons, although a few astrocytes were also transduced. Transduction of non-neuronal cells in the brain was associated with upregulation of the major histocompatibility complex-II (MHC-II) and lymphocytic infiltration as previously observed with AAV1 and AAV9. This contrasts with highly specific neuronal transduction in the rat brain. Retrograde axonal transport of AAV6 from a single striatal infusion permits efficient transduction of cortical neurons in significant tissue volumes that otherwise would difficult to achieve.

Yohimbine co-treatment during chronic morphine administration attenuates naloxone-precipitated withdrawal without diminishing tail-flick analgesia in rats

Noradrenergic neuronal hyperactivity following chronic morphine administration has been postulated to cause withdrawal signs and symptoms. Suppression of this hyperactivity, for example, by clonidine attenuates withdrawal. It might follow, therefore, that the prevention of suppression of noradrenergic systems during chronic morphine administration might diminish hyperactivity and prevent withdrawal. If the normalization of noradrenergic activity during opioid administration did not also suppress analgesia, it might be of medical and theoretical interest. To test this hypothesis, we gave the alpha-2-antagonist yohimbine to rats in order to increase noradrenergic activity during morphine treatment and then subsequently precipitated morphine withdrawal with naloxone. Six groups were examined: saline controls (N = 11), morphine (N = 11), morphine + 2.0 mg/kg/day yohimbine (N = 15), morphine + 3.0 mg/kg/day yohimbine (N = 5), 2.0 mg/kg/day yohimbine (N = 11) and 3.0 mg/kg/day yohimbine (N = 5). Subjects received 75 mg morphine pellets implanted on day 1,4 and 6 of the treatment or sham implantation. Yohimbine was delivered throughout the morphine treatment by subcutaneously implanted osmotic pumps. On day 7, all subjects were given 1.0 mg/kg naloxone and rated for behavioral signs of withdrawal. Analgesia was measured by observing tail flick latencies (TFL) before and after chronic drug treatments. Naloxone-precipitated withdrawal was characterized by irritability, ptosis, penile erection, diarrhea, rhinorrhea, abnormal posture, wet-dog shakes, jumping, and teeth chattering, none of which were observed in groups receiving only saline or yohimbine. Withdrawal behavior was attenuated in a dose-dependent manner when yohimbine was administered during morphine treatment but analgesia was not attenuated.(ABSTRACT TRUNCATED AT 250 WORDS)

Grafting genetically engineered cells into the striatum of nonhuman primates

An emerging new technology based on genetic engineering of viral vectors that can insert genes into the cells of living organisms may play a significant role in treating disorders of the central nervous system (CNS). Most neurodegenerative disorders affect focal regions of the brain. Preventive and/ or palliative treatment strategies need to be targeted only to the diseased parts of the brain without affecting other regions. Administration of therapeutic genes specifically to the disease-affected regions of the brain may be more beneficial than current treatment strategies, which are largely based on systemically administering small molecules. The latter can result not only in peripheral side effects but also CNS side effects since the drugs can affect both targeted and nontargeted brain sites. In addition, many therapeutic agents are prevented from entering the brain by the blood-brain barrier (BBB). For these reasons, many otherwise potentially useful proteins, such as trophic factors, cannot be administered systemically (1).

Tremor is associated with PET measures of nigrostriatal dopamine function in MPTP-lesioned monkeys

Unilateral intracarotid artery (ICA) MPTP infusion, along with sequential systemic doses of MPTP, produces near complete degeneration of the nigrostriatal pathway on the side of infusion (ipsilateral) and variable levels of damage in the contralateral hemisphere accompanied by varying levels of parkinsonism (overlesioned hemiparkinsonian model). Positron emission tomography and the dopamine (DA) metabolism tracer [(18)F]6-fluoro-l-m-tyrosine (FMT) were used to evaluate the relationship between DA metabolism and clinical features of parkinsonism in 14 overlesioned hemiparkinsonian monkeys. Monkeys were rated on a parkinsonian scale that included ratings of bradykinesia, fine motor skills (FMS), and rest tremor. Because the monkeys tended to show more severe clinical signs on the side of the body contralateral to ICA MPTP infusion, we calculated asymmetry scores for each of the clinical features as well as for FMT uptake (K(i)) in the caudate and putamen. Tremor asymmetry was associated with FMT uptake asymmetry in the putamen. No such relationship was observed for FMS or bradykinesia. The overall severity of tremor (mild, moderate/severe) was associated with FMT uptake in the caudate and putamen. Postmortem biochemical analysis for a subset of monkeys showed that the monkeys with moderate/severe tremor had significantly lower DA levels in both caudate and putamen than those with mild tremor. In addition, K(i) values were significantly correlated with DA levels in both caudate and putamen. These findings support the idea that nigrostriatal degeneration contributes to rest tremor.

Technique for bilateral intracranial implantation of cells in monkeys using an automated delivery system

Intracerebral grafting combined with gene transfer may provide a powerful technique for local delivery of therapeutic agents into the CNS. The present study was undertaken to: (i) develop a reliable and reproducible automated cell implantation system, (ii) determine optimal implantation parameters of cells into the striatum, (iii) determine upper safe limits of cellular implantation into the neostriatum of monkeys. Autologous fibroblasts were infused into six sites of the striatum in nonhuman primates (Macaca mulatta, n = 11). Twenty-six-gauge cannulae were inserted vertically through cortical entry sites into the striatum (two sites in the caudate nucleus and four sites in the putamen) at predefined coordinates based on magnetic resonance imaging (MRI). The cannulae were guided by an electronically operated, hydraulic micropositioner and withdrawn at controlled rates, while cells (5, 10, 20, 40, or 80 microl/site) were infused simultaneously. Varying infusion rates and cell concentrations were also evaluated. Visualization and evaluation of graft placement were performed using contrast MRI at 3-5 days postsurgery. Animals were monitored for signs of clinical complications and sacrificed 2 weeks following surgery. Postimplantation MRI revealed a tissue mass effect of the implant with shifting of midline, edema, and infiltration of the white tracts at 40 and 80 microl/site. In addition, these animals developed transient hemiparesis contralateral to the implant site. MRI of animals grafted with 20 microl/site exhibited columnar-shaped implants and evidence of infiltration into white matter tracts possibly due to a volume effect. No clinical side effects were seen in this group. At 14 days postsurgery, MRI scans showed consistent columnar grafts (measuring approximately 5 mm in height) throughout the striatum in animals implanted with 5 or 10 microl/site. No signs of clinical side effects were associated with these volumes and postmortem histological examination confirmed MRI observations. Optimal surgical parameters for delivery of cells into the striatum consist of a graft volume of 10 microl/site, an infusion rate of 1.6 microl/min, a cell concentration of 2.0 x 10(5) cells/microl, and a cannula withdrawal rate of 0.75 mm/min. These results show that infusion of cells into the striatum can be done in a safe and routine manner.

Convection-enhanced delivery of AAV vector in parkinsonian monkeys; in vivo detection of gene expression and restoration of dopaminergic function using pro-drug approach

Using an approach that combines gene therapy with aromatic l-amino acid decarboxylase (AADC) gene and a pro-drug (l-dopa), dopamine, the neurotransmitter involved in Parkinson's disease, can be synthesized and regulated. Striatal neurons infected with the AADC gene by an adeno-associated viral vector can convert peripheral l-dopa to dopamine and may therefore provide a buffer for unmetabolized l-dopa. This approach to treating Parkinson's disease may reduce the need for l-dopa/carbidopa, thus providing a better clinical response with fewer side effects. In addition, the imbalance in dopamine production between the nigrostriatal and mesolimbic dopaminergic systems can be corrected by using AADC gene delivery to the striatum. We have also demonstrated that a fundamental obstacle in the gene therapy approach to the central nervous system, i.e., the ability to deliver viral vectors in sufficient quantities to the whole brain, can be overcome by using convection-enhanced delivery. Finally, this study demonstrates that positron emission tomography and the AADC tracer, 6-[(18)F]fluoro-l-m-tyrosine, can be used to monitor gene therapy in vivo. Our therapeutic approach has the potential to restore dopamine production, even late in the disease process, at levels that can be maintained during continued nigrostriatal degeneration.

Dopamine transporter loss and clinical changes in MPTP-lesioned primates

Single photon emission computed tomography (SPECT) and the dopamine (DA) transporter tracer, 2 beta-carboxymethoxy-3 beta-(4-iodophenyl)tropane ([123I]beta-CIT), were used to determine DA transporter density in 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-lesioned monkeys with varying degrees of parkinsonism. The clinical stage of parkinsonism corresponded to SPECT measures of striatal DA transporter density suggesting that more severe parkinsonism was associated with a greater degree of dopaminergic terminal degeneration. These findings are similar to those reported earlier using positron emission tomography (PET) and the DA metabolism tracer, 6-[18F]fluoro-L-m-tyrosine (FMT), indicating that both are good methods for evaluating nigrostriatal degeneration in MPTP primate models.

A novel MPTP primate model of Parkinson's disease: neurochemical and clinical changes

Positron emission tomography (PET) and the dopamine (DA) metabolism tracer, [18F]6-fluoro-L-m-tyrosine (FMT) were used to evaluate the relationship between DA metabolism and the clinical stage of parkinsonism monkeys following either unilateral ICA MPTP infusion or unilateral ICA MPTP infusion and subsequent varying sequential systemic doses of MPTP. Clinical stage corresponded to PET measures of striatal DA metabolism, showing the usefulness of the overlesioned hemiparkinsonian monkey as a stable model of various stages of Parkinson's disease (PD).