Melatonin resistance
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Melatonin Resistance in Insulin Resistance and Metabolic Disorders
Melatonin Supplementation and Insulin Resistance Improvement
Research shows that melatonin supplementation can help reduce insulin resistance in both animal and human studies. Most studies found that melatonin lowers fasting insulin levels and HOMA-IR (a measure of insulin resistance), and increases insulin sensitivity as measured by QUICKI. However, melatonin does not consistently lower fasting plasma glucose levels. These effects have been observed in people with various health conditions, suggesting melatonin may be broadly beneficial for improving insulin sensitivity, though not all individuals may respond equally, hinting at possible melatonin resistance in some cases .
Mechanisms of Melatonin Action in Insulin Resistance
Melatonin improves insulin resistance by acting on several molecular pathways. In ovarian granulosa cells from women with polycystic ovary syndrome (PCOS), melatonin increases the expression of insulin receptor substrate (IRS-1) and glucose transporter (GLUT4), and enhances the PI3K/Akt signaling pathway, which is crucial for insulin action. This leads to better glucose uptake and reduced insulin resistance in these cells . In the liver, melatonin reduces the expression of fetuin-A (a protein linked to insulin resistance) and decreases endoplasmic reticulum (ER) stress, further improving insulin sensitivity and reducing fat accumulation in the liver . In the brain, melatonin restores insulin signaling disrupted by a high-fat diet, reduces inflammation and oxidative stress, and improves cognitive function, all of which are negatively affected by insulin resistance .
Melatonin Resistance: When Melatonin Fails to Improve Insulin Sensitivity
Some studies suggest that melatonin’s ability to improve insulin resistance depends on certain conditions. For example, if fetuin-A is overexpressed in liver cells, melatonin cannot improve insulin resistance, indicating that high levels of this protein may cause resistance to melatonin’s beneficial effects . This suggests that melatonin resistance may occur when specific molecular pathways are disrupted or overwhelmed.
Melatonin Resistance in Cancer and Multidrug Resistance
Melatonin and Cancer Drug Resistance
Melatonin has been studied for its ability to overcome drug resistance in cancer therapy. It can make cancer cells more sensitive to chemotherapy by affecting key signaling pathways (such as Akt and MAPK), reducing drug clearance, altering DNA repair, and promoting cell death through apoptosis and autophagy. These effects have been observed in various cancers, including breast, lung, liver, colon, and leukemia . Melatonin also helps regulate the tumor microenvironment, which can influence how cancer cells respond to treatment and develop resistance .
Mechanisms of Melatonin’s Action Against Multidrug Resistance
Melatonin may counteract multidrug resistance by modulating oxidative stress, reversing pH changes in the tumor environment, and protecting cell membrane structures. It can also regulate prion proteins, which are involved in cancer cell adaptation and resistance to therapy. By targeting these mechanisms, melatonin may help prevent or reverse resistance to cancer drugs 678.
Melatonin Resistance in Plants
Melatonin and Plant Disease Resistance
In plants, melatonin can enhance resistance to viral and fungal infections by activating defense-related genes and signaling pathways. However, if certain pathways (like the salicylic acid pathway) are disrupted, melatonin treatment does not improve resistance, indicating a form of melatonin resistance in plants as well 24.
Conclusion
Melatonin generally improves insulin sensitivity, reduces drug resistance in cancer, and enhances disease resistance in plants. However, its effectiveness can be limited by specific molecular or environmental factors, leading to melatonin resistance. Understanding these mechanisms is important for optimizing melatonin’s use in treating metabolic disorders, cancer, and plant diseases 1567+3 MORE.
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