BDNF increases with behavioral enrichment and an antioxidant diet in the aged dog.

The aged canine (dog) is an excellent model for investigating the neurobiological changes that underlie cognitive impairment and neurodegeneration in humans, as canines and humans undergo similar pathological and behavioral changes with aging. Recent evidence indicates that a combination of environmental enrichment and antioxidant-fortified diet can be used to reduce the rate of age-dependent neuropathology and cognitive decline in aged dogs, although the mechanisms underlying these changes have not been established. We examined the hypothesis that an increase in levels of brain-derived neurotrophic factor (BDNF) is one of the factors underlying improvements in learning and memory. Old, cognitively impaired animals that did not receive any treatment showed a significant decrease in BDNF mRNA in the temporal cortex when compared with the young group. Animals receiving either an antioxidant diet or environmental enrichment displayed intermediate levels of BDNF mRNA. However, dogs receiving both an antioxidant diet and environmental enrichment showed increased levels of BDNF mRNA when compared with untreated aged dogs, approaching levels measured in young animals. BDNF receptor TrkB mRNA levels did not differ between groups. BDNF mRNA levels were positively correlated with improved cognitive performance and inversely correlated with cortical Aß((1-42)) and Aß((1-40)) levels. These findings suggest that environmental enrichment and antioxidant diet interact to maintain brain levels of BDNF, which may lead to improved cognitive performance. This is the first demonstration in a higher animal that nonpharmacological changes in lifestyle in advanced age can upregulate BDNF to levels approaching those in the young brain.

Delivery of recombinant gene product to canine brain with the use of microencapsulation.

An alternative approach to somatic gene therapy is to deliver a therapeutic protein by implanting "universal" recombinant cells that are immunologically protected from graft rejection with alginate microcapsules. This strategy has proved successful in reversing pathologic conditions in several rodent models of human disease (dwarfism, lysosomal storage disease, hemophilia, cancer). In particular, neurologic disease and behavioral deficit in the mouse model of a neurodegenerative disease (mucopolysaccharidosis [MPS] VII) were significantly improved through the intraventricular implantation of the recombinant encapsulated cells. Here we report the feasibility of delivering recombinant gene products to the central nervous systems (CNSs) of dogs, first using human growth hormone as a marker for delivery in normal dogs and then using alpha-iduronidase as a therapeutic product for delivery in the MPS I dog that is genetically deficient in this lysosomal enzyme. Madin-Darby canine kidney cells were genetically modified to express either human growth hormone or canine alpha-iduronidase, then enclosed in alginate-poly-l-lysine-alginate microcapsules of about 500 microm in diameter. The encapsulated cells were implanted into the brain under steoreotaxic guidance. The brains were monitored with computed tomographic scans before and after surgery and examined biochemically and histologically. Delivery of gene products, as measured in the plasma and cerebrospinal fluid sampled periodically through 21 days or in various regions of the brain after death showed that the delivery of both gene products was extremely low but detectable. However, we noted extensive inflammatory reactions, both at the sites of implantation and in the immediate vicinity of the implanted microcapsules. Hence for this technology to be applicable to the CNSs of larger animals and human beings, a more accurate and less invasive neurosurgical procedure, more biocompatible microcapsule-recombinant cell combinations, and higher output of recombinant products must be developed.