Pharmacokinetics and effects after intravenous administration of high-dose boron to rat

Subchronic and genetic safety evaluation of a calcium fructoborate in rats

A branded calcium fructoborate product, a nature-identical calcium salt of bis (fructose) ester of boric acid found in plants and a natural source of boron in the human diet and sold under the trade name FruiteX-B(®) Brand Calcium Fructoborate ("FrxB"), was evaluated in a 90-day dietary toxicity study and two genotoxicity studies. In the 90-day study, four groups of 10 male and 10 female Crl:SD CD(®) IGS rats were fed diets with FrxB admixtures of 0.56, 1.12, and 1.68% dietary concentration, providing mean overall daily intakes of FrxB in male rats of 385.8, 774.9, and 1161.3 mg/kg bw/day, and 392.1, 784.4, and 1171.1 mg/kg bw/day in female rats. There were no mortalities, no clinical or ophthalmologic signs, body weight, body weight gain, food consumption, food efficiency, Functional Observational Battery (FOB), or Motor Activity (MA) findings associated with the administration of FrxB. There were no adverse changes in hematology, coagulation, clinical chemistry, or urinalysis parameters in male or female rats considered the result of test substance administration. At necropsy, there were no macroscopic, histopathological findings, or organ weight changes deemed related to administration of the test substance. Under the conditions of this study, based on the toxicological endpoints evaluated, the no-observed-adverse-effect level (NOAEL) for FrxB in the diet was 1161.3 and 1171.1 mg/kg bw/day in male and female rats, respectively. Bacterial mutagenicity studies and a micronucleus test using Chinese hamster V79 cells demonstrated no mutagenic or genotoxic potential of the tested brand of calcium fructoborate.

Boric acid inhibits embryonic histone deacetylases: a suggested mechanism to explain boric acid-related teratogenicity

Histone deacetylases (HDAC) control gene expression by changing histonic as well as non histonic protein conformation. HDAC inhibitors (HDACi) are considered to be among the most promising drugs for epigenetic treatment for cancer. Recently a strict relationship between histone hyperacetylation in specific tissues of mouse embryos exposed to two HDACi (valproic acid and trichostatin A) and specific axial skeleton malformations has been demonstrated. The aim of this study is to verify if boric acid (BA), that induces in rodents malformations similar to those valproic acid and trichostatin A-related, acts through similar mechanisms: HDAC inhibition and histone hyperacetylation. Pregnant mice were treated intraperitoneally with a teratogenic dose of BA (1000 mg/kg, day 8 of gestation). Western blot analysis and immunostaining were performed with anti hyperacetylated histone 4 (H4) antibody on embryos explanted 1, 3 or 4 h after treatment and revealed H4 hyperacetylation at the level of somites. HDAC enzyme assay was performed on embryonic nuclear extracts. A significant HDAC inhibition activity (compatible with a mixed type partial inhibition mechanism) was evident with BA. Kinetic analyses indicate that BA modifies substrate affinity by a factor alpha=0.51 and maximum velocity by a factor beta=0.70. This work provides the first evidence for HDAC inhibition by BA and suggests such a molecular mechanism for the induction of BA-related malformations.