Dietary Supplementation of Boron Differentially Alters Expression of Borate Transporter (NaBCl) mRNA by Jejunum and Kidney of Growing Pigs

Abstract

Inorganic boron (B), in the form of various borates, is readily absorbed across gastrointestinal epithelia. Although there is no stated B requirement, dietary B supplementation is thought to positively affect animal growth and metabolism, including promotion of bone strength and cell proliferation. Because of effective homeostatic control of plasma B levels, primarly by renal excretion, B toxicity in animals and humans is rare. The mechanisms responsible for improved animal performance and borate homeostasis are incompletely understood. Although a Na+-coupled borate transporter (NaBC1) has been identified, the effect of dietary B supplementation on expression of NaBCl has not been evaluated. An experiment was conducted with growing pigs to determine if NaBC1 mRNA was expressed by small intestinal epithelia and kidney of growing barrows and whether dietary B (as borate) supplementation would affect expression of NaBC1 mRNA. A concomitant objective was to test the hypothesis that B supplementation of a phosphorus (P)-deficient diet would improve calcium, phosphorus, or nitrogen retention. Twenty-four crossbred growing barrows (body weight=74.0±9.8 kg) were selected and used in a randomized complete block design experiment with a total of eight blocks and three B supplementation treatments (n=8/treatment). A typical corn-soybean meal basal diet (calculated to contain 41 mg intrinsic B/kg) was formulated to meet or exceed nutrient requirements, except for P, and fed to all pigs for 12 days. The basal diet plus 0, 50, or 100 mg/kg of B (prilled sodium borate pentahydrate, Na₂B₄O₇·5H₂O) was then fed for 18 more days. Feces and urine were collected during days 6 to 16 of the B supplementation, and pigs were killed for collection of jejunal and ileal epithelia and kidney tissue. Real-time reverse transcription-PCR analysis revealed that NaBC1 mRNA was expressed by these tissues, a novel finding for jejunal and ileal epithelia. Boron supplementation increased jejunal, but decreased, renal NaBC1 mRNA expression, relative to the 0 mg/kg treatment. The finding that NaBC1 mRNA is regulatable by dietary B is novel. That B supplementation evoked opposite effects on jejunal and kidney NaBC1 mRNA expression indicates that transcriptional regulation of NaBC1 expression may constitute a part of the homeostatic control of B metabolism. In contrast to its effect on NaBC1 mRNA expression, B supplementation did not affect total tract digestibility or retention of phosphorus, calcium, or nitrogen.

Borax induces osteogenesis by stimulating NaBC1 transporter via activation of BMP pathway

“…Although there is some evidence for the tissue ubiquity of NaBC1 38 , we confirmed its presence in our cellular system under the same experimental conditions (after 3 or 15 days of culture and under basal or differentiation media) used in subsequent differentiation studies. When MSCs NaBC1 mRNA were amplified by qPCR, the results showed that in all the conditions assessed, NaBC1 gene expression was upregulated exclusively by borax and that this upregulation was dose-dependent (Supplementary Fig.…”

Boron induces osteogenesis by stimulating NaBC1 in cooperation with BMPR1A

“…Although there is some evidence for the tissue ubiquity of NaBC1 [47] , we confirmed its presence in our cellular system under the same experimental conditions (after 3 or 15 days of culture and under basal or differentiation media) used in previous studies. When MSCs NaBC1 mRNA were amplified by qPCR, the results showed that in all the conditions assessed, NaBC1 gene expression was upregulated exclusively by boron and that this upregulation was dose-dependent ( Figure S6-a).…”

“…We also investigated the gene expression of the late expressed markers involved in osteogenic (osteopontin-OPN) and adipogenic (Lipoprotein lipase-LPL) [47] differentiation by qPCR after 15 days of culture. These results demonstrate that the simultaneous stimulation of NaBC1 and FN-binding integrins promotes osteogenesis (in basal conditions) and strongly inhibits adipogenesis, even in an adipogenic induction medium.…”

The Divergence, Actions, Roles, and Relatives of Sodium-Coupled Bicarbonate Transporters

“…In the same study of pigs as was mentioned above, a doubling of dietary boron content, maintained over 18 days, resulted in a twofold decrease (rather than the increase observed in the jejunum) in renal BTR1 transcript abundance (583). A quadrupling of normal dietary boron intake had no greater effect on renal BTR1 transcript abundance (583). The consequence of the downregulation is not known, but is consistent with a role of renal BTR1 in boron homeostasis.…”

“…I) Increased transcript abundance following dietary boron supplementation. In a study of pigs, a doubling of dietary boron content, maintained over 18 days, resulted in a threefold increase in BTR1 transcript abundance in jejunal preparations but no increase in ileal preparations (583). A quadrupling of normal dietary boron intake had no greater effect on BTR1 transcript abundance in either the ileum or jejunum (583).…”