Brazilin Inhibits Prostatic Acidic Phosphatase Fibrillogenesis and Decreases its Cytotoxicity.

A 39-amino acid peptide fragment that is derived from prostatic acidic phosphatase (PAP), PAP248-286 , is secreted in large amounts in human semen and forms amyloid fibrils. These fibrils can capture HIV virions and increase the attachment of virions to target cells; as such, they are called a "semen-derived enhancer of virus infection" (SEVI). Therefore, the inhibition of the formation of PAP248-286 amyloid fibrils is of great significance. Herein, we demonstrate that brazilin effectively inhibits PAP248-286 aggregation. The inhibitory effect increases with increasing brazilin concentration. Thioflavin T fluorescence assays and TEM observations confirmed that a few fibrils formed when brazilin was present with PAP248-286 in an equimolar concentration. Circular dichroism spectroscopy indicated that brazilin inhibited the secondary structural transitions from α-helices and random coils into ß-sheets. Cytotoxicity assays showed that brazilin significantly decreased the cytotoxicity of the fibrils at 0.01 mmol L-1 . Isothermal titration calorimetry revealed that hydrophobic interactions were the main driving force for the binding of brazilin to the PAP248-286 monomer (dissociation constant, 4.03 µmol L-1 ), and that the binding affinity of brazilin for the fibrils was at least three orders of magnitude lower than that for the monomer. These results indicate that brazilin holds great potential as a small-molecule agent against SEVIs.

The pharmacological role of phosphatases (acid and alkaline phosphomonoesterases) in snake venoms related to release of purines - a multitoxin.

Snake venom components, acting in concert in the prey, cause their immobilization and initiate digestion. To achieve this, several hydrolytic enzymes of snake venom have evolved to interfere in various physiological processes, which are well defined. However, hydrolytic enzymes such as phosphatases (acid and alkaline phosphomonoesterases) are less studied and their pharmacological role in venoms is not clearly defined. Also, they show overlapping substrate specificities and have other common biochemical properties causing uncertainty about their identity in venoms. The near-ubiquitous distribution of these enzymes in venoms, suggests a significant role for these enzymes in envenomation. It appears that these enzymes may play a central role in liberating purines (mainly adenosine) - a multitoxin and through the action of purines help in prey immobilization. However, apart from this, these enzymes could also possess other pharmacological activities as venom enzymes have been evolved to interfere in diverse physiological processes. This has not been verified by pharmacological studies using purified enzymes. Further research is needed to biologically characterize these enzymes in snake venoms, such that their role in venom is clearly established.