No effect of anti-leprosy drugs in the prevention of Alzheimer's disease and beta-amyloid neurotoxicity.

There is continuing controversy as to whether or not anti-leprosy drugs prevent Alzheimer's disease (AD). Therefore, we examined the effect of anti-leprosy drugs on the prevalence of AD in leprosy patients, and also investigated the effect of anti-leprosy drugs on amyloid beta-protein (Abeta)-induced neurotoxicity in vitro. The present study suggests that anti-leprosy treatments do not prevent the onset of AD. None of our data found anti-leprosy drugs (dapsone, rifampicin, clofazimine, minomycin or ofloxacin) had any effect on Abeta neurotoxicity. It is now important to examine the infection of Mycobacterium leprae in the central nervous system to clarify the reason for the low prevalence of senile dementia, and low frequency of Abeta deposition in leprosy patients.

Role of electrostatic interactions in defining the potency of neurotoxin B-IV from Cerebratulus lacteus.

Chemical modification implicates arginine residues of the Cerebratulus lacteus neurotoxin B-IV in biological activity. In the present study, we used site-directed mutagenesis to assess the functional contributions of each of these residues. Panels of mutants at each site have been constructed by polymerase chain reaction and recombinant proteins expressed and purified to homogeneity using an Escherichia coli expression system developed in this laboratory. All substitutions for Arg-17 (Gln, Ala, or Lys) yield proteins having undetectable levels of activity, while charge neutralizing replacement of Arg-25 (R25Q) causes a 400-fold reduction in specific toxicity. However, the R25K mutein is almost as active as natural toxin. Circular dichroism spectroscopy indicates that there are no major conformational changes in any of these muteins. These results therefore demonstrate the requirement for a guanidinium group at position 17, and a positive charge at position 25. NMR analyses (Hansen, P. E., Kem, W. R., Bieber, A. L., and Norton, R. S. (1992) Eur. J. Biochem. 210, 231-240) reveal neurotoxin B-IV to contain two antiparallel alpha-helices, which together include 57% of the sequence. Both Arg-17 and Arg-25 lie on the same face of the N-terminal helix (residues 13-26), as do the carboxyl groups of Glu-13 and Asp-21. However, charge neutralizing mutations of the latter two sites have no effects on biological activity. Arg-34, situated near the N terminus of helix 2 (residues 33-49) is also important for activity, as its replacement by Gln or Ala diminishes activity by 20- and 80-fold, respectively. However, unlike Arg-17 and Arg-25, thermal denaturation experiments suggest that R34Q may be structurally destabilized relative to wild-type B-IV.

Rifampicin prevents the aggregation and neurotoxicity of amyloid beta protein in vitro.

The aggregation and cerebral deposition of amyloid beta protein (A beta), which is a major component of senile plaques in Alzheimer's disease (AD) brains, is believed to be involved in the pathogenesis of AD. Inhibition of A beta aggregation would seem to be a promising strategy for the treatment of AD. Here, we show that rifampicin, which is an antibiotic widely used in the treatment of tuberculosis and leprosy, inhibited the aggregation and fibril formation of synthetic A beta 1-40 peptide in a dose-dependent manner at reasonable concentrations. Furthermore, rifampicin was found to prevent A beta 1-40-induced neurotoxicity on rat pheochromocytoma PC12 cells. Rifampicin may have therapeutic potential as an agent for inhibiting the initial step of amyloid formation in AD.