X-ray structures of Torpedo californica acetylcholinesterase complexed with (+)-huperzine A and (-)-huperzine B: structural evidence for an active site rearrangement

Kinetic and structural data are presented on the interaction with Torpedo californica acetylcholinesterase (TcAChE) of (+)-huperzine A, a synthetic enantiomer of the anti-Alzheimer drug, (-)-huperzine A, and of its natural homologue (-)-huperzine B. (+)-Huperzine A and (-)-huperzine B bind to the enzyme with dissociation constants of 4.30 and 0.33 microM, respectively, compared to 0.18 microM for (-)-huperzine A. The X-ray structures of the complexes of (+)-huperzine A and (-)-huperzine B with TcAChE were determined to 2.1 and 2.35 A resolution, respectively, and compared to the previously determined structure of the (-)-huperzine A complex. All three interact with the "anionic" subsite of the active site, primarily through pi-pi stacking and through van der Waals or C-H.pi interactions with Trp84 and Phe330. Since their alpha-pyridone moieties are responsible for their key interactions with the active site via hydrogen bonding, and possibly via C-H.pi interactions, all three maintain similar positions and orientations with respect to it. The carbonyl oxygens of all three appear to repel the carbonyl oxygen of Gly117, thus causing the peptide bond between Gly117 and Gly118 to undergo a peptide flip. As a consequence, the position of the main chain nitrogen of Gly118 in the "oxyanion" hole in the native enzyme becomes occupied by the carbonyl of Gly117. Furthermore, the flipped conformation is stabilized by hydrogen bonding of Gly117O to Gly119N and Ala201N, the other two functional elements of the three-pronged "oxyanion hole" characteristic of cholinesterases. All three inhibitors thus would be expected to abolish hydrolysis of all ester substrates, whether charged or neutral.

Similar potency of the enantiomers of huperzine A in inhibition of [(3)H]dizocilpine (MK-801) binding in rat cerebral cortex

The inhibition of huperzine A, a potential therapeutic agent to treat Alzheimer's disease, on rat cortical acetylcholinesterase was found to be highly stereospecific. In the present study the effect of the enantiomers of huperzine A on [(3)H]dizocilpine (MK-801) binding to synaptic membrane of rat cerebral cortex was compared. The natural (-)-huperzine A and the synthetic (+)-huperzine A inhibited the specific binding of [(3)H]MK-801 with a similar potency. The IC(50) values were 65+/-7 and 82+/-12 microM (n=5 for each enantiomer, P=0.248), respectively. The result indicates that huperzine A inhibits N-methyl-D-aspartate (NMDA) receptor in rat cerebral cortex without stereoselectivity.

Huperzine A, a potential therapeutic agent for treatment of Alzheimer's disease

HupA is a potent, reversible and selective inhibitor of AChE with a rapid absorption and penetration into the brain in animal tests. It exhibits memory-enhancing activities in animal and clinical trials. Compared to tacrine and donepezil, HupA possesses a longer duration of action and higher therapeutic index, and the peripheral cholinergic side effects are minimal at therapeutic doses. This review article deals with a comprehensive survey of the progress in chemical and pharmacological studies of HupA including the isolation and structure elucidation, pharmacological actions, total synthesis, SAR studies and the future development of HupA. Recently, it has been reported that HupA could reduce neuronal cell death caused by glutamate. The dual bio-activities of HupA would further enhance its value and potentiality as the therapeutic agent for Alzheimer s disease.

Effects of synthetic (-)-huperzine A on cholinesterase activities and mouse water maze performance

AIM

To compare the effects of synthetic and natural (-)-huperzine A (Hup A) on cholinesterase and mouse water maze performance.

METHODS

Spectrophotometry was used to determine cholinesterase activity. Mouse water maze was used to evaluate nootropic effect.

RESULTS

The IC50 of synthetic Hup A for acetylcholinesterase (AChE) of rat cortex and rat erythrocyte membrane determined in vitro were 64.7 (52.6-79.5) and 53.9 (43.6-66.6) nmol.L-1, respectively, and for butyrylcholinesterase of rat serum was 53.6 (44.9-63.8) mumol.L-1. Synthetic Hup A 0.12-0.48 mg.kg-1 ig produced a dose-dependent inhibition of brain AChE in mice. Synthetic Hup A 0.05 mg.kg-1 ig attenuated scopolamine-induced impairment of spatial memory. The efficacy of synthetic Hup A was the same as natural Hup A.

CONCLUSION

Synthetic Hup A yielded an in vitro and in vivo pharmacological profile of activities similar to that of natural Hup A.

Perception-action coupling in the development of visual control of posture

In this investigation of developmental changes in the coordination of perceived optical flow and postural responses, 4 age groups of infants (5-, 7-, 9-, and 13-month-olds) were tested while seated on a force plate in a "moving room." During each trial the walls oscillated in an anteroposterior direction for 12 s, and the postural sway of the infant was measured. The results revealed that infants perceived the frequency and amplitude of the optical flow and scaled their postural responses to the visual information. This scaling was present even before infants could sit without support, but it showed considerable improvement during the period when infants learn to sit. Taken together, these results suggest that the visuomotor coordination necessary for controlling sitting is functional prior to the onset of independent sitting but becomes more finely tuned with experience.

Perception-action coupling in the development of visual control of posture

In this investigation of developmental changes in the coordination of perceived optical flow and postural responses, 4 age groups of infants (5-, 7-, 9-, and 13-month-olds) were tested while seated on a force plate in a "moving room." During each trial the walls oscillated in an anteroposterior direction for 12 s, and the postural sway of the infant was measured. The results revealed that infants perceived the frequency and amplitude of the optical flow and scaled their postural responses to the visual information. This scaling was present even before infants could sit without support, but it showed considerable improvement during the period when infants learn to sit. Taken together, these results suggest that the visuomotor coordination necessary for controlling sitting is functional prior to the onset of independent sitting but becomes more finely tuned with experience.

Locomotor status and the development of spatial search skills

The principal objective of this experiment was to investigate whether previous reports of a relation between locomotor status and stage 4 object permanence performance generalized to performance on a different object localization task. A secondary objective was to evaluate the contribution of visual tracking as a mediating variable in the relation between locomotor experience and search performance. Precrawling (n = 20), crawling (n = 10), and creeping (n = 18) infants (M = 33 weeks old) were tested using a search task in which either they or the hiding containers were rotated 180 degrees before search was permitted. The results revealed that locomotor status was related to search performance following a displacement of the infant, but not following a displacement of the containers. Moreover, visual tracking of the correct container was not related to locomotor status, even though it was related to search performance. These findings suggest that the effects of locomotor experience on infants' search performance are quite specific and are mediated by a variety of factors that do not necessarily generalize across search tasks.

Traditional Chinese materia medica--a retrospect and prospect

For thousands of years, traditional medicine and remedies have been practiced and used in the fight against disease in China. They have proved to be valuable and the distillate of vast historical experience based on field-tested human experiments, long-term observations and clinical trials. The Chinese people believe that traditional medicine is consistent with their own culture. Endowed with a unique theoretical system and provided outstanding clinical results, traditional Chinese medicine continues to play an important role in helping the Chinese nation flourish.