[ZN] is one of the most important trace elements in the body and its deficiencies accompany many diseases as well as some types of cancer. . With a US (40 mg) and EU (25 mg) safe upper limit, zinc is included as zinc oxide, acetate, gluconate or zinc amino acid chelate. Although sulfate is a commonly used form of zinc, zinc citrate, zinc gluconate, and zinc picolinate are better absorbed than zinc oxide. More than 300 enzymes and 1000 transcription factors require ZN as a catalyst [its presence in nature does not exceed 0.02%].
In humans, [after iron] it occurs in all classes of enzymes. In proteins, zinc ions are coordinated to amino acids [such as aspartic acid, glutamic acid, cysteine and histidine], stored and transported to metallothioneins. About 10% of human proteins (~3000) bind zinc. Most zinc is found in the brain, muscles, bones, kidneys and liver, with the highest concentrations in the prostate and parts of the eye. Semen is particularly rich in zinc, which is why it is said to be the sperm’s fuel.
Zinc homeostasis is primarily controlled by the gut.ZN is present in many proteins, peptides, enzymes, hormones, transcription factors and cytokines, essential components for maintaining body homeostasis.
ZN is required to maintain nitric oxide[NO] synthase activity, does it regulate the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs)?
α2 macroglobulin and 13-amyloid precursor protein. Changes in the balance between MMPs and TIMPs or α2 macroglobulin have been observed in cancer, infections and aging.
The importance of ZN is strictly linked to special proteins called metallothioneins (MTs) that [act as antioxidants and transfer ZN to other proteins [via redox]. The redox properties of MTs are crucial in transient stress, but are detrimental in aging due to persistent oxidative damage. MTs bind ZN and prevent transfer to other proteins during aging.
Reduced endocrine activity, NK cells and cytokine production, were observed with ZN-free diets. MTs have a central role in ZN-related cellular homeostasis [due to high affinity to ZN] for the effectiveness of the entire immune system [NK cells, etc. ] ZN-gene interaction also affects certain cytokines (IL-6 and TNF-α) and Hsp70 in aging, atherosclerosis and infections. Some regulatory or inhibitory transcription factors regulated by ZN (NF-κB, STAT, HSF-1), are involved in the regulation of pro-inflammatory cytokines (IL-6 and TNF-α) and Hsp70 during inflammation and in the presence of antigenic stimuli.
Zinc homeostasis also plays a critical role in the functional regulation of the central nervous system. Zinc has been identified as a messenger that activates signaling pathways and many of them are associated with cancer development.
It plays a structural role in zinc finger proteins [ZINC FINGER…ZINFs] that are part of some transcription factors that recognize DNA base sequences during replication and transcription.
In plasma, it is bound and transported by albumin (60%) and transferrin (10%). Cells in the salivary gland, prostate, immune system and intestine use zinc to communicate with other cells. The dopamine transporter contains a zinc binding site which, upon binding, inhibits dopamine reuptake.
SOURCE: International Journal of Gerontology 2007
