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|Title:||DEVELOPMENT OF THERAPEUTIC CANDIDATES TO TREAT DIABETIC SENSORY NEUROPATHY|
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|Authors/Affiliations:||1 Randy Van der Ploeg; 2 Paul Fernyhough*; |
1 St Boniface Hospital Research Centre; 2 St Boniface Hospital Research Centre and dept of Pharmacology & Therapeutics, University of Manitoba; Canada
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|Content:||Objectives. The symmetrical sensory polyneuropathy exhibited by persons with type 1 and type 2 diabetes is the most common form of peripheral neuropathy and has an increasingly detrimental impact on human disease and associated health costs - there is no effective treatment. Though etiology remains poorly understood a dying back of distal axons from the peripheral target and a failure of axonal sprouting and/or regeneration are key features of this neurodegenerative disease. The heterogeneous nature of this neurodegenerative disease has confounded attempts based upon hypothesis-driven research to generate an effective therapy. Therefore, we elected to test the therapeutic potential of a group of pre-screened small molecule FDA-approved compounds for efficacy in rodent models of type 1 diabetes exhibiting diabetic sensory neuropathy. As part of a Juvenile Diabetes Research Foundation (JDRF)-funded drug screen we assessed 500 compounds from an NINDS drug library for the ability to significantly raise axon outgrowth in an in vitro assay consisting of cultured adult rat dorsal root ganglia (DRG) sensory neurons.|
Materials and methods. The assay comprised cultured adult rat sensory neurons and the ability of drugs to enhance total axonal outgrowth by at least 2-fold (P<0.05). The rationale was that axon outgrowth in this in vitro model was homologous to axon plasticity, growth and regeneration occurring in the epidermis of the skin. In diabetic sensory neuropathy the distal dying-back of axons is a key pathological feature and to this date not a single compound has proved efficacious in reversing axonal loss in the epidermis (in animal models or humans). Adult neurons were isolated from age matched control animals, or 3 month streptozotocin (STZ) diabetic rats (type 1 model) or 4 month Zucker diabetic fatty (ZDF) rats (type 2 model). DRG sensory neurons were cultured in Hams F-12 media under defined conditions in a sub-saturating cocktail of neurotrophic factors and exposed to drugs for 24 hr before being assessed for total levels of axon outgrowth and cell survival using a morphometric approach (a Weibel grid approach to be specific).
Results. Data have been generated from primary, secondary and tertiary screening of 18 promising drugs that increased axon outgrowth by 2-fold (P<0.05) in normal neurons. In the secondary and tertiary screens these 18 compounds were screened against adult cultures derived from STZ-diabetic rats and ZDF rats. In the STZ-diabetic rat screen guaifenesin, guanethidine sulphate and pirenzepine HCl elevated axonal outgrowth by at least 2-fold at certain doses. Interestingly, the same 3 compounds were effective in the cultures derived from ZDF rats. Therefore, at this stage the most promising compounds we have identified for further testing are guaifenesin, pirenzepine HCl and guanethidine sulphate, in addition ethopropazine HCl was effective against cultures from ZDF rats.
Conclusions. The four promising compounds noted above are now being exposed to medicinal chemistry to generate novel compounds for further in vitro and in vivo testing.
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