DEVELOPMENT OF AN ANTIGEN HETEROLOGOUS ENZYME LINKED IMMUNOSORBENT ASSAY FOR MEASUREMENT OF CORTICOSTERONE IN RAT SERUM

Impact of bridge heterology on functional parameters of ELISA for 17α-methyltestosterone

In this study, we have developed bridge heterologous ELISA for the detection of 17α- Methyltestosterone by incorporating aromatic spacers between 17α-Methyltestosterone-3-Carboxymethyloxime and Horseradish peroxidase label through N-hydroxysuccinimide mediated carbodiimide reaction method. The immunogen 17α-Methyltestosterone-3-Carboxymethyloxime-Bovine serum albumin used to generate the antibody was also prepared by the N-hydroxysuccinimide mediated carbodiimide reaction without using any spacer. We have studied the impact of bridge/aromatic spacers on functional parameters i.e. sensitivity, affinity and ED50 of the bridge heterologous assay and compared it with homologous assay. The five combinations of bridge heterologous assay using 17α-Methyl testosterone-3-CMO-BSA antiserum and 17α-MT-3-CMO-4,4'-Diaminodiphenyl sulphide-HRP, 17α MT-3-CMO-4,4'-Oxydianiline-HRP, 17α-MT-3-CMO-Benzidine-HRP, 17α- MT-3-CMO-p-Phenylenediamine-HRP and 17α-MT-3-CMO-Dapson-HRP enzyme conjugates were evaluated. Out of these five combinations, the combination 17α-MT-3-CMO-BSA with 17α-MT-3-CMO-Benzidine-HRP showed the best results. Sensitivity, affinity and ED50 were improved and found to be 0.02 ng/mL, 0.086 × 10-8 L/mol and 2.95 ng/mL than homologous assay where Sensitivity, affinity and ED50 were 0.11 ng/mL, 0.02 × 10-8 L/mol and 5.78 ng/mL respectively. The cross-reactivity for this bridge heterologous assay combination was seen with only 4 steroids (6-hydrotestosterone- 6%, Testosterone-5.14%, Danazol-0.9% and Nandrolone-0.85%) instead of eight steroids (6-hydrotestosterone-43.75%, Testosterone-38.3%, Danazol-25.14%, Androstenediol-19.16%, Nandrolone-19%, Metandienone-5%, Androstenedione-3.52%, and 17α dimethyltestosterone-2%) as in homologous assay out of 59 structurally related steroids. Thus, the results of this study conclude that the incorporation of aromatic spacer (bridge) in enzyme conjugate has a crucial role in improving sensitivity, specificity, ED50 and affinity of the developed assay. The assay was then studied for parameters such as recovery (97.4%-108.6%), precision (Inter and Intra-assay coefficient of variation <10%), correlation coefficient (R2 = 0.96) by comparing with the commercial kit and validated by measuring levels of 17α- methyltestosterone in rat serum after administering them.

Experimentally induced stress, oxidative load and changes in immunity in a tropical wild bird, Perdicula asiatica: involvement of melatonin and glucocorticoid receptors

Throughout the year, birds encounter various environmental challenges such as extreme temperatures, rainfall and shortage of food. Here we report on the effect of stress on the general immunity of wild birds as measured by several assays including melatonin, an anti-stress hormone. We selected Perdicula asiatica, a wild tropical bird, and exposed them to experimental stressors such as water deprivation, food deprivation and immobilization, i.e., stressors that they would encounter in a natural environment. We measured the oxidative load in the spleen in terms of superoxide dismutase (SOD), catalase activity and thiobarbituric acid-reactive substance (TBARS) levels. The immune status was judged by total leukocyte count (TLC), heterophil/lymphocyte ratios (H/L) and percent stimulation ratio of splenocytes (%SR). The peripheral levels of melatonin and corticosterone were also determined and correlated with the expression of melatonin (Mel(1a)/Mel(1b)) and glucocorticoid receptors. Our results showed a significant (p < 0.05) decrease in splenic SOD and catalase activity, while a significant (p < 0.05) increase in TBARS and a corticosterone level was observed. Stressful conditions also decreased the immune status as reflected by the low values of H/L ratios, TLC and %SR. In contrast, melatonin pretreatment significantly (p < 0.05) reduced the oxidative stress and improved the immune parameters when compared to untreated control birds. This suggests that melatonin prevents/alleviates oxidative damage and suppresses the immune status induced by stressful conditions via its membrane receptor expression (Mel(1a) and Mel(1b)) in P. asiatica.