Experimental Guillain-Barre syndrome induced by immunization with gangliosides: Keyhole limpet hemocyanin is required for disease triggering.

An experimental model of Guillain-Barré Syndrome has been established in recent years. Rabbits develop disease upon immunization with a single dose of an emulsion containing bovine brain gangliosides, KLH and complete Freund's adjuvant. Within a period of four to ten weeks after immunization, they began to produce anti-ganglioside IgG-antibodies first, and to show clinical signs of neuropathy afterwards. In addition to gangliosides, KLH is a requirement for antibody production and disease triggering. Although KLH is commonly used as an immunological carrier protein, an anti-KLH-specific immune response was necessary for induction of both events. KLH is a glycoprotein carrying most of the immunogenicity in its glycan moiety. Between 20% to 80% of anti-ganglioside IgG-antibodies present in sick rabbit sera cross-reacted with KLH, indicating that both immune responses are related. The terminal Gal-ß(1,3)-GalNAc glycan (present in gangliosides and KLH) is proposed as "key" antigenic determinant involved in inducing the anti-ganglioside immune response. These results are discussed in the context of the "binding site drift" hypothesis.

The Inhibitory Activity of Plants from Central Argentina on p-Hydroxyphenylpyruvate Dioxygenase. Isolation and Mechanism of Inhibition of a Flavanone from Flourensia oolepis.

The enzyme 4-hydroxyphenylpyruvate dioxygenase catalyzes the second step in the tyrosine degradation pathway. In mammals, this enzyme is the molecular target of drugs used for the treatment of metabolic disorders associated with defects in the tyrosine catabolism, mainly the fatal hereditary disease tyrosinemia type 1. This study evaluated the inhibitory effect of 91 extracts on 4-hydroxyphenylpyruvate dioxygenase from mostly native plants from central Argentina. Flourensia oolepis ethanol extract showed itself to be the most effective, and bioguided fractionation yielded pinocembrin (1) as its active principle. This flavanone, with an IC50 value of 73.1 µM and a KI of 13.7 µM, behaved as a reversible inhibitor of the enzyme and as a noncompetitive inhibitor. Molecular modeling studies confirmed the inhibitory potency of 1 and explained its activity by means of in silico determination of its binding mode in comparison to inhibitors of known activity, cocrystallized with 4-hydroxyphenylpyruvate dioxygenase. The main structural determinants that confer its potency are discussed. Analysis of the binding mode of the flavanone 1 with 4-hydroxyphenylpyruvate dioxygenase revealed the basis of the noncompetitive reversible mechanism of inhibition at the molecular level, which seems to be a common feature in this ubiquitous family of natural compounds. The resulting information may establish the basis for obtaining novel 4-hydroxyphenylpyruvate dioxygenase inhibitors for the treatment of tyrosinemia type 1 and other disorders associated with tyrosinase catabolism.

Tyrosinase inhibitory activity of a 6-isoprenoid-substituted flavanone isolated from Dalea elegans.

To aid the pharmaceutical and cosmetic industry in the development of alternatives to prevent melanin-related hyperpigmentation disorders, the plant Dalea elegans was submitted to fractionation with the aim of obtaining its anti-tyrosinase principle. Bioguided fractionation of D. elegans led to the isolation of 5,2',4'-trihydroxy-2″,2″-dimethylchromene-(6,7:5″,6″)-flavanone (1) as the active compound. This novel flavanone, named as dalenin, showed notable activity at inhibiting tyrosinase using l-tyrosine or l-DOPA as substrates with IC(50) values of 0.26 and 18.61 µM, respectively. This meant that the flavanone was 52 and 495 times more effective as a monophenolase inhibitor than hydroquinone and kojic acid, respectively. With l-DOPA as a substrate, compound 1 showed itself 59 times more effective at inhibiting the enzyme than hydroquinone and showed the same level of effectiveness as that of kojic acid. It was found that the flavanone behaved as a reversible inhibitor of the enzyme and that it was a mixed-I type or a non-competitive inhibitor with l-tyrosine or l-DOPA as substrates, respectively. Molecular modeling studies were conducted confirming the inhibitory potency of dalenin and showing that the 2',4'-dihydroxy substituents are important for the interaction with the enzyme. The results suggest that compound 1 has great potential to be further developed as a pharmaceutical and cosmetic agent for use in dermatological disorders associated with melanin.