Modulation of Adverse Health Effects of Environmental Cadmium Exposure by Zinc and Its Transporters

Zinc (Zn) is the second most abundant metal in the human body and is essential for the function of 10% of all proteins. As metals cannot be synthesized or degraded, they must be assimilated from the diet by specialized transport proteins, which unfortunately also provide an entry route for the toxic metal pollutant cadmium (Cd). The intestinal absorption of Zn depends on the composition of food that is consumed, firstly the amount of Zn itself and then the quantity of other food constituents such as phytate, protein, and calcium (Ca). In cells, Zn is involved in the regulation of intermediary metabolism, gene expression, cell growth, differentiation, apoptosis, and antioxidant defense mechanisms. The cellular influx, efflux, subcellular compartmentalization, and trafficking of Zn are coordinated by transporter proteins, solute-linked carriers 30A and 39A (SLC30A and SLC39A), known as the ZnT and Zrt/Irt-like protein (ZIP). Because of its chemical similarity with Zn and Ca, Cd disrupts the physiological functions of both. The concurrent induction of a Zn efflux transporter ZnT1 (SLC30A1) and metallothionein by Cd disrupts the homeostasis and reduces the bioavailability of Zn. The present review highlights the increased mortality and the severity of various diseases among Cd-exposed persons and the roles of Zn and other transport proteins in the manifestation of Cd cytotoxicity. Special emphasis is given to Zn intake levels that may lower the risk of vision loss and bone fracture associated with Cd exposure. The difficult challenge of determining a permissible intake level of Cd is discussed in relation to the recommended dietary Zn intake levels.

Nitration of Flavonoids and Tocopherols as Potential Modulators of Nitrosative Stress—A Study Based on Their Conformational Structures and Energy Content

Vitamin E and dietary flavonoids are natural substances with antioxidant and anti-inflammatory activities, showing little or no side effects. Fruit and vegetable diets based on flavonoids and vitamin E provide a benefit to hypertensive subjects by regulating blood pressure. However, the exact mechanism of their anti-inflammatory properties has not been chemically explained. It has been proposed that their anti-oxidant and anti-inflammatory properties may be related to their ability to scavenge free radicals. We here describe the chemical considerations that flavonoids and tocopherols required to act as potential scavengers of the •NO2 radical, a key radical in the cellular oxidative process. Moreover, we provide a theoretical study of the energy content of the nitrated compounds in the different possible positions. With this analysis, it was predicted that five flavonoids from different families (quercetin (flavanol), naringenin (flavanone), luteolin (flavone), catechin (flavanol) and aurantinidin (anthocyanin)) and three tocopherols (β-, γ-, and δ-tocopherol, but not α-tocopherol) could act as potential scavengers of the harmful •NO2 radical. These results may help to explain their beneficial effect on cardiovascular health through its antioxidant role. To validate our theoretical considerations, we also examined uric acid, a well-known •NO2-scavenger. We hope this study could help to elucidate the potential scavenging activity of other dietary antioxidants.