A sensitive photochemical reaction-capacitively coupled contactless conductivity detection system for HPLC and its application in determination of Cyclosporin A.

High performance liquid chromatography (HPLC) post-column photochemical reaction (PR) coupled capacitively coupled contactless conductivity detector (C4D) was used for the first time in analysis of weak ultraviolet (UV)-absorbing, non-fluorescence and nonpolar compound. A series of conditions including the radiation power of light source, the length of the reaction tube and the thickness of detection tube were investigated. HPLC-PR-C4D system was successfully applied to the determination of Cyclosporin A (CsA). Consequently, under optimal conditions, the detection system exhibited a detection limit of 0.04 µg/mL and wide linear range from 0.5 µg/mL to 100 µg/mL for CsA detection. Application of the HPLC-PR- C4D system to pharmaceutical formulation and biological samples revealed the system developed maybe reliably applied to clinical studies.

Augmented photoswitching modulates immune signaling.

Reversible and non-invasive photoswitching of the immunosuppressive effect of a drug would be a very valuable tool for precisely regulating the immune system. Using a combination of protein borrowing and two-photon photoisomerization, we designed and synthesized derivatives of cyclosporin A. Here we demonstrate photoswitching of the local conformation within small molecules, which we used to modulate inhibitory potencies for cyclophilin, influence ternary and quaternary complex formations and regulate T-cell transcriptional activation in situ.

A new aspect of specific radiation damage: hydrogen abstraction from organic molecules.

Radiation damage is one of the major impediments in obtaining high-resolution structural information utilizing ionizing radiation. From electron microscopy it is known that electron irradiation of biological samples results in the formation of molecular hydrogen. In the present work radiation-induced structural changes of the polypeptide cyclosporine A were observed at a temperature of 100 K. Bond length changes are thought to be due to radiation-induced hydrogen abstraction which chemically modifies the molecules in an irreversible way. The resulting formation of molecular hydrogen might explain the observed increase of the crystal mosaicity, which has also been reported in many previous radiation damage studies.

Effects of sterilizing gamma irradiation on bloodspot newborn screening tests and whole blood cyclosporine and tacrolimus measurements.

Sterilizing irradiation of the US mail has been proposed as a method to prevent delivery of viable anthrax spores. Because newborn screening samples (bloodspots) and cyclosporine and tacrolimus specimens (whole blood) are delivered routinely through the mail, we studied whether sterilizing gamma irradiation could affect these test results. Specimens were exposed to 18 kGy gamma irradiation (100 hours x 18,000 rad/h), a "kill dose" for Bacillus pumilus spore strips. Irradiation had no significant effect on whole blood cyclosporine or tacrolimus results, but it had a degradative effect on bloodspot phenylalanine, hemoglobins, biotinidase, galactose-1-phosphate uridyltransferase, thyroxine, and thyrotropin. Such irradiation potentially could cause false-negative results for the detection of phenylketonuria and likely would lead to an increase in secondary testing for hemoglobin variants, but it is unlikely to lead to false-negative or false-positive results for the remaining newborn screening tests. These experiments cannot rule out possible greater effects by larger doses or other types of irradiation.