Hello from Hanna:
"It is common knowledge that "cortisol it related to stress", which is correct: Cortisol is the body's main stress hormone. It is produced in the adrenal gland, which is the gland on top of each kidney.
Nobody enjoy being stressed all the time, and it is established that high levels of cortisol over an extended period of time is unfavorable: It causes an increase in reactive oxygen species (ROS), and these free radicals cause an oxidative stress reaction. This is a physical response. The same physical response anything living will have to stress. If we don't like stress, then neither does the fish. Probably.
Either way: Aiming to create a less stressful environment for fish will never be a bad thing!"
Oxidative stress happens inside the body when there is imbalance between free radicals and antioxidants. Free radicals are oxygen-containing, positively charged molecules, ready to steal electrons and cause chemical chain reactions. Antioxidants are molecules with the ability to donate electrons and remain stable afterwards. If the free radicals grab electrons from the wrong cells it can cause damage to DNA and break down cell walls. . Antioxidants will happily give away electrons and thus provide a stable chemical reaction within your body. (This is why you eat blueberries - To protect your DNA!)
The oxidative stress reaction is the process where free radicals are detoxified and stabilized. The number of free radicals can be increased directly by stress and/or indirectly by living with elevated cortisol levels. These free radicals want to stabilize, and they do so by stealing electrons from nearby molecules: Whether those electrons belong to a cell wall or an antioxidant doesn't matter to the free radical, but it does matter to your health!
The level of stress in a body can be measured by either directly measuring cortisol or measure biproducts made by changing levels of cortisol. We have sensors with the ability to do either. We have a total antioxidative status (TAS)-sensor which we use to measure antioxidants. This sensor is used to detect levels of nutrients in the fishes blood, and so its health status in regard to feed.
Glucose is a biproduct of being stressed: The body make lots of easy energy accessible throughout the body by increasing levels of glucose through glycogenesis. Since cortisol is a 'catalyst' for the glycogenesis, we decided a sensor measuring both cortisol and glucose would give the most accurate results.
During development of cortisol sensors we ran into a few challanges: 1.Limit of detection and sensitivity
140-690 nM is considered normal levels for humans throughout a day. In fish the concentration of cortisol in plasma is relativly lower: 23 nM in normal conditions, and a maximum of 534 nM under the introduction of the stressor.
2.Biocomponents such as antibodies were claimed to be able to detect the cortisol at low level, but the limitation is poor stability of these biomolecules.
3.Non enzymatic cortisol sensors face the drawback of poor selectivity. If the sensor reacts to another biomarker in addition to cortisol it will give inaccurate data regarding the cortisol.
Our cortisol sensors are using enzymatic mechanism that can detect cortisol at the clinical level above. We have avoided using the less stable antibodies and the sensors are selective to cortisol thanks to the specific enzyme. Thanks to this enzyme, our cortisol-team have been able to produce the results below.
Even though the results are good, (and amazingly much better than our first few tries) there is still more work to be done to further improve our wire sensors. Luckily we have a great team already on it.
Until next time,
Hanna T. Bråthen
Engineer at ZP
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