TNF-alpha inhibition as a treatment strategy for neurodegenerative disorders: new drug candidates and targets.

As the average ages of North Americans and Europeans continue to rise; similarly the incidence of "old age" associated illnesses likewise increases. Most notably among these ailments are conditions linked to dementia-related neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD) and stroke. While in the early stages, these conditions are associated with cellular dysfunction in distinctly different brain regions, thus affecting different neuronal cell types; it is most likely that the final stages share similar cellular and molecular processes leading to neuronal death and ultimately overt clinical symptoms. In this regard, different environmental and genetic triggers ranging from head trauma to protein mutations and toxicological exposure may instigate a cascade of intracellular events that ultimately lead to neuronal death. One strong candidate trigger protein, and thus a potential target for therapeutic manipulation is the potent pro-inflammatory / pro-apoptotic cytokine, tumor necrosis factor-alpha (TNF-alpha). TNF-alpha is secreted by the brain resident marcophage (the microglial cell) in response to various stimuli. It has been demonstrated to play a major role in central nervous system (CNS) neuroinflammation-mediated cell death in AD, PD and amyotrophic lateral sclerosis (ALS) as well as several other CNS complications. Recently, agents that modulate the levels of circulating peripheral TNF-alpha protein have been shown to be worthwhile therapeutic agents with the use of Enbrel (Etanercept) and Remicade (Infliximab), both of which display beneficial properties against rheumatoid arthritis and other peripheral inflammatory diseases. Unfortunately, these agents are largely unable to penetrate the blood-brain barrier, which severely limits their use in the setting of neuroinflammation in the CNS. However, thalidomide, a small molecule drug, can inhibit TNF-alpha protein synthesis and, unlike larger molecules, is readily capable of crossing the blood-brain barrier. Thus thalidomide and its analogs are excellent candidate agents for use in determining the potential value of anti-TNF-alpha therapies in a variety of diseases underpinned by inflammation within the nervous system. Consequently, we have chosen to discuss the relevance of unregulated TNF-alpha expression in illnesses of the CNS and, to an extent, the peripheral nervous system. Additionally, we consider the utilization of thalidomide-derived agents as anti-TNF-alpha therapeutics in the setting of neuroinflammation.