Blood Component Factors and Antiaging Medicine: Parabiosis and Antiaging

Parabiosis (parabiosis) is derived from the Greek words para (next, close) and bios (life) and refers to a state where two living animals are surgically connected and share a single circulatory system. It is often likened to conjoined twins that naturally occur as parabiosis. The experimental technique of parabiosis was established in rats by French physiologist Paul Bert in the 1860s. It was centrally used for the functional analysis of liquid factors exchanged between connected animals, contributing to the development of endocrine physiology research [1]. For example, it was widely used for hormone function analysis. However, the number of papers rapidly decreased with the peak in the 1960s and 80s, and it was temporarily forgotten as a research method. However, since the beginning of this century, the number of applications in fields such as immunology, stem cells, organ interrelationships, aging, and regeneration has rapidly increased. It is widely known not only for distinguishing the contribution of the circulatory and nervous systems by comparing cells and molecules transmitted through the bloodstream with local cells and molecules in tissues, but also as an experimental method that brings innovative hypotheses. Currently, mice are mainly used for parabiosis experiments. An incision is made in the skin of the flank, and the skin flaps of the two animals are sutured together [2]. Nowadays, it is common to make a long incision on the entire side of the body and connect it, and sometimes an incision is made in the peritoneum to connect the abdominal cavity. With the angiogenesis associated with wound healing at the connection site, the blood vessels of the two animals connect and they start to share a circulatory system. When inbred animals are used, rejection does not occur, and they can survive for a long time as a pair. An example of the presence of physiologically active substances in the blood suggested by parabiosis is the identification of leptin. Coleman found that by connecting a db/db mouse, a model of diabetes and obesity, with a wild-type mouse, the wild-type mouse stopped eating and starved to death [3]. From this result, Coleman thought that there might be a factor in the blood of the db/db mouse that conveys a sense of fullness and strongly suppresses the appetite of the wild-type mouse. Later, Friedman and others identified leptin.