Boron Homeostasis

Limited evidence is available regarding the molecular mechanism of boron homeostasis. Based on analysis of plasma boron concentrations in seven sibships, Barr et al. (1996) observed smaller variances within than between families and hypothesized that boron levels in humans are under genetic control. The data presented by Barr et al. (1996) need to be interpreted with caution as the blood samples were collected from individuals living in a rural region of northern Chile, and their dietary intakes were not determined. Also, the study was retrospective aud utilized blood samples that had been stored for over 20 years. More recent evidence suggests the involvemeut of a sodium-coupled boron transporter in animal cells, expressed in the basolateral manbrane, which determines the steady-state concentration of borate in the cytoplasm and hence maintains borate homeostasis (Park et al., 2004). 

Studies under controlled metabolic-ward conditions and in free-living subjects show that the urinary excretion of boron is a reflection of its intake. In addition, preliminary evidence suggests that boron may interact with other micronutrients depending on the physiological or nutritional status of the host individual. It has been suggested that such interactions can be danonstrated more clearly in the presence of metabolic stress. 

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Park, M., Li, Q., Shcheynikov, N., Zeng, W., Muallem, S. NaBCl is a ubiquitous electrogenic Na-r -coupled borate transporter essential for cellular boron homeostasis and cell growth and proliferation. Mol. Cell. 2004 16 331-341. 

Iron chelators can also be used to selectively bind iron in areas where oxidative stress is observed, thereby preventing the iron from taking part in Fenton reactions without interfering with normal iron homeostasis. Charkoudian et al. have developed boronic acid and boronic ester masked prochelators, which do not bind metals unless exposed to hydrogen peroxide (237,238). The binding of these chelators to iron(III) prevents redox cycling. Similar studies of these systems have been performed by a separate group (239,240). 

From evidence published so far, it appears that soil conditions and agricultural methods have limited effect on the boron composition of plant foods. This suggests that plants have effective mechanisms for maintaining homeostasis of boron, possibly mediated by specific boron transporters (Takano et al., 2002). The lack of a clear effect of agricultural methods on the plant composition of boron is consistent with the limited impact of agricultural methods on other nutrients (Dangour et al., 2009), and may well reflect the essentiality of boron for the integrity of the cell wall in plants (O Neill et al., 1996). 

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