Pathogenic Connections in Post-COVID Conditions: What Do We Know in the Large Unknown? A Narrative Review.

The coronavirus 2019 (COVID-19) disease has long-term effects, known as post-COVID conditions (PCC) or long-COVID. Post-COVID-19 syndrome is defined by signs and symptoms that occur during or after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection which persist for more than 12 weeks and cannot be supported by an alternative diagnosis. The cardiovascular damage caused by COVID-19 in the severe forms of the disease is induced by severe systemic inflammation, considered to be one of the causes of myocardial lesions, with increased levels of circulating cytokines and toxic response mediators. We have focused on conditions that can induce long-COVID-19, or multisystem inflammatory syndrome in adults or children (MIS-C/MIS-A), with an emphasis on endocrinological and metabolic disorders. Although described less frequently in children than in adults, long-COVID syndrome should not be confused with MIS-C, which is an acute condition characterized by multisystem involvement and paraclinical evidence of inflammation in a pediatric patient who tested positive for SARS-CoV-2. At the same time, we mention that the MIS-A symptoms remit within a few weeks, while the duration of long-COVID is measured in months. Long-COVID syndrome, along with its complications, MIS-A and MIS-C, represents an important challenge in the medical community. Underlying comorbidities can expose both COVID-19 adult and pediatric patients to a higher risk of negative outcomes not only during, but in the aftermath of the SARS-CoV-2 infection as well.

Role of Irisin in Endocrine and Metabolic Disorders—Possible New Therapeutic Agent?

Irisin is a novel hormone that provides a possible solution for the treatment of metabolic disorders. Discovered in 2012 by Boström et al., irisin very quickly became an interesting subject in medical research. Irisin has been found in cerebrospinal fluid, the cerebellum, thyroid, pineal gland, liver, pancreas, testis, spleen, adult stomach, and human fetuses. Regarding the actions of irisin, both in animals and humans, the results are contradictory but interesting. Its capability to influence adipose tissue and glycemic homeostasis may be utilized in order to treat hypothyroidism, polycystic ovary syndrome, Prader–Willi syndrome, and other endocrine and metabolic disorders. Considering its osteogenic potential, irisin might be a therapeutic choice in diseases caused by a sedentary lifestyle. New data indicate that irisin treatment may serve in the treatment of severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) infection. Furthermore, several therapeutic agents, such as insulin, metformin, fenofibrate, exenatide, and melatonin, influence the concentrations of irisin in animal models or in humans. Nutritional factors including polyunsaturated fatty acids may also have an effect on irisin concentrations. While it may be “too good to be true,” irisin offers many opportunities for future research that would aim to find its optimal therapeutical role in endocrine and metabolic diseases.