Present state and future development of the therapy of Alzheimer disease

Effects of a memory enhancing peptide on cognitive abilities of brain-lesioned mice: additivity with huperzine A and relative potency to tacrine

Alzheimer's disease (AD) and related dementing disorders having cognitive manifestations represent an increasing threat to public health. In the present study, the effects of a memory enhancing NLPR tetra-peptide (MEP), huperzine A (Hup A), or a combination of the two on the cognitive abilities of brain-lesioned mice were evaluated and compared with tacrine in the passive avoidance and Y-water maze tests for the acquisition and retention aspects of cognitive functions. MEP at microg kg(-1) doses, and Hup A or tacrine at mg kg(-1) doses significantly reversed the cognition deficits induced by scopolamine. For acquisition ability, it was observed that mice administered with MEP (4.0 microg kg(-1)) spent less time escaping onto the platform in the water maze than those treated with tacrine (1.5 mg kg(-1)); whereas for memory retention, tacrine-administration resulted in a higher step-through latency in mice at the tested dose regime. In addition, co-administration of MEP (2.0 microg kg(-1)) and Hup A (0.1 mg kg(-1)) exhibited an additive effect resulting in considerable improvements in both acquisition and retention abilities of brain-lesioned mice. The results demonstrated that MEP was highly efficient in the rescue of cognitive abilities of brain-lesioned mice and in particular, the effective doses of MEP were about two orders of magnitude lower than that of tacrine, a therapeutic currently used in the treatment of AD. Moreover, MEP and Hup A were effective at reduced doses when the two were co-administered, providing a rationale for their combined usage in the treatment of cognitive deficits.

Some blood biochemistry parameters during the cholinergic treatment of Alzheimer's disease

Acetylcholinesterase (ACE) activity and lipid peroxidation (LPO) parameters were measured in the blood of patients with Alzheimer's disease (AD) during treatment with amiridine and gliatiline. Treatment was accompanied by inhibition of ACE. There was a statistically significant relationship between clinical efficacy and changes in ACE activity. AD was charactefized by significant changes in LPO parameters, with a three-fold increase in the level of primary oxidation products on the background of a sharp (seven-fold) increase in total lipid desaturatedness. There was a statistically significant relationship between ACE activity and the levels of primary oxidation products in the RBC of patients with AD before and after treatment with amiridine and gliatiline.

Age-associated memory impairment. Assessing the role of nitric oxide

Several neurotransmitter systems have been investigated to assess hypothesized mechanisms underlying the decline in recent memory abilities in normal aging and in Alzheimer's disease. Examining the performance of F344 rats in a 14-unit T-maze (Stone maze), we have focused on the muscarinic cholinergic (mACh) and the N-methyl-D-aspartate (NMDA) glutamate (Glu) systems and their interactions. Maze learning is impaired by antagonists to mACh or NMDA receptors. We have also shown that stimulation of mACh receptors can overcome a maze learning deficit induced by NMDA blockade, and stimulation of the NMDA receptor can overcome a similar blockade of mACh receptors. No consistent evidence in rats has been produced from our laboratory to reveal significant age-related declines in mACh or NMDA receptor binding in the hippocampus (HC), a brain region that is greatly involved in processing of recent memory. Thus, we have directed attention to the possibility of a common signal transduction pathway, the nitric oxide (NO) system. Activated by calcium influx through the NMDA receptor, NO is hypothesized to be a retrograde messenger that enhances presynaptic Glu release. Maze learning can be impaired by inhibiting the synthetic enzyme for NO, nitric oxide synthase (NOS), or enhanced by stimulating NO release. However, we have found no age-related loss of NOS-containing HC neurons or fibers in rats. Additionally, other laboratories have reported no evidence of an age-related loss of HC NOS activity. In a microdialysis study we have found preliminary evidence of reduced NO production following NMDA stimulation. We are currently working to identify the parameters of this phenomenon as well as testing various strategies for safely stimulating the NO system to improve memory function in aged rats.

Phenserine: a physostigmine derivative that is a long-acting inhibitor of cholinesterase and demonstrates a wide dose range for attenuating a scopolamine-induced learning impairment of rats in a 14-unit T-maze

Phenserine ((-)-N-phenylcarbamoyl eseroline), a carbamate analog of physostigmine (Phy), is a long-acting inhibitor of cholinesterase. We have assessed the potential clinical value of phenserine for cholinomimetic therapy of cognitive impairments associated with aging and Alzheimer's disease by evaluating its duration of in vivo activity against rat plasma acetylcholinesterase (AChE) and its effect on attenuating a scopolamine-induced impairment in learning performance of young rats in a shock-motivated 14-unit T-maze. Phenserine achieved maximum AChE inhibition of 73.5% at 5 min and maintained a high and relatively constant inhibition for more than 8 h. For analysis of effects on learning performance, 69, 3-month-old male Fischer-344 rats were pretrained in a straight runway to avoid electric footshock. On the following day, each animal received 15 trials in the 14-unit T-maze. Sixty minutes prior to the maze training, each rat received the first IP injection of either vehicle (Tween 80, ethanol and 0.9% NaCl) or phenserine at 1.5, 3.0, 4.0, 5.0, 7.5, or 10.0 mg/kg. Then 30 min prior to the training, each animal received a second IP injection of either 0.9% NaCl or scopolamine hydrochloride (0.75 mg/kg; SCOP). Compared to the vehicle-SCOP group, all but the 7.5 mg/kg dose of phenserine significantly ameliorated error performance, runtime, shock frequency and shock duration in SCOP-treated rats at the final block of three trials. Appearing to have a long effect and a wide therapeutic window, phenserine deserves further study as a cognitive enhancer.

Preferential inhibition of acetylcholinesterase molecular forms in rat brain

The effect of eight different acetylcholinesterase inhibitors (AChEIs) on the activity of acetylcholinesterase (AChE) molecular forms was investigated. Aqueous-soluble and detergent-soluble AChE molecular forms were separated from rat brain homogenate by sucrose density sedimentation. The bulk of soluble AChE corresponds to globular tetrameric (G4), and monomeric (G1) forms. Heptylphysostigmine (HEP) and diisopropylfluorophosphate were more selective for the G1 than for the G4 form in aqueous-soluble extract. Neostigmine showed slightly more selectivity for the G1 form both in aqueous- and detergent-soluble extracts. Other drugs such as physostigmine, echothiophate, BW284C51, tetrahydroaminoacridine, and metrifonate inhibited both aqueous- and detergent-soluble AChE molecular forms with similar potency. Inhibition of aqueous-soluble AChE by HEP was highly competitive with Triton X-100 in a gradient, indicating that HEP may bind to a detergent-sensitive non-catalytic site of AChE. These results suggest a differential sensitivity among AChE molecular forms to inhibition by drugs through an allosteric mechanism. The application of these properties in developing AChEIs for treatment of Alzheimer disease is considered.