No abstract

In this work, a curcumin-diglutaric acid (CurDG) prodrug was synthesized by conjugation of curcumin with glutaric acid via an ester linkage. The water solubility, partition coefficient, release characteristics, and antinociceptive activity of CurDG were compared to those of curcumin. The aqueous solubility of CurDG (7.48 μg/mL) is significantly greater than that of curcumin (0.068 μg/mL). A study in human plasma showed that the CurDG completely releases curcumin within 2 h, suggesting the ability of CurDG to serve as a prodrug of curcumin. A hot plate test in mice showed the highest antinociceptive effect dose of curcumin at 200 mg/kg p.o., whereas CurDG showed the same effect at an effective dose of 100 mg/kg p.o., indicating that CurDG significantly enhanced the antinociceptive effect compared to curcumin. The enhanced antinociceptive effect of CurDG may be due to improved water solubility and increased oral bioavailability compared to curcumin.

Silk sericin was found to suppress the production of pro-inflammatory cytokines, which are related to the inflammatory reaction. The objectives of this study were to investigate the anti-inflammatory effect of sericin in vivo using the carrageenan-induced rat edema model and changes in the histology of tissues. The effects of sericin on the expression of COX-2 and iNOS were also evaluated. Sericin solutions at 0.004-0.080 mg/mL were applied topically to the top of the hind paw and carrageenan (1.0 mg) was injected subcutaneously to the plantar surface of the right hind paw. Our results indicated that sericin significantly reduced the inflammation in rats' paw compared with the negative control (water and acetone) and its effect at 0.080 mg/mL was only slightly lower than that of 1.0% w/v indomethacin. Similar numbers of polymorphonuclear and macrophage cells were found in rats' tissue treated with indomethacin and sericin solution, while the numbers were significantly higher in their absence. The gene expression results by RT-PCR showed that the COX-2 and iNOS genes were down-regulated in samples treated with sericin in a dose dependent manner. These data indicated that the anti-inflammatory properties of sericin may be partly attributable to the suppression of the COX-2 enzyme and nitric oxide production.

Curcumin diethyl disuccinate did not significantly improve the oral bioavailability of curcumin due to first pass metabolism in the gastrointestinal tract. Further studies on reduction of first pass metabolism are required to optimise delivery of curcumin using a prodrug approach.

The use of endotoxin, such as lipopolysaccharide (LPS) as a model of sickness behavior, has attracted recent attention. To objectively investigate sickness behavior along with its pain-like behaviors in LPS-treated mice, the behavioral measurement requires accurate methods, which reflects clinical relevance. While reflexive pain response tests have been used for decades for pain assessment, its accuracy and clinical relevance remain problematic. Hence, we used automated home-cage monitoring LABORAS to evaluate spontaneous locomotive behaviors in LPS-induced mice. LPS-treated mice displayed sickness behaviors including pain-like behaviors in automated home-cage monitoring characterized by decreased mobile behaviors (climbing, locomotion, rearing) and increased immobility compared to that of the control group in both short- and long-term locomotive assessments. Here, in short-term measurement, both in the open-field test and automated home-cage monitoring, mice demonstrated impaired locomotive behaviors. We also assessed 24 h long-term locomotor activity in the home-cage system, which profiled the diurnal behaviors of LPS-stimulated mice. The results demonstrated significant behavioral impairment in LPS-stimulated mice compared to the control mice in both light and dark phases. However, the difference is more evident in the dark phase compared to the light phase owing to the nocturnal activity of mice. In addition, the administration of indomethacin as a pharmacological intervention improved sickness behaviors in the open-field test as well as automated home-cage monitoring, confirming that automated home-cage monitoring could be potentially useful in pharmacological screening. Together, our results demonstrate that automated home-cage monitoring could be a feasible alternative to conventional methods, such as the open-field test and combining several behavioral assessments may provide a better understanding of sickness behavior and pain-like behaviors in LPS-treated mice.