Macro and microdistribution of boric acid in compact bone

The biodistribution of boronophenylalanine (BPA), a widely used compound for Boron Neutron Capture Therapy (BNCT), is well characterized. In contrast, data on boric acid (BA) biodistribution remain limited. Given previously observed high boron levels in calcified tissues following BA administration, we conducted a comparative study to evaluate its accumulation and retention in bone. Wistar rats were infused with: (a) BA at 40 ppm boron, (b) BPA at 40 ppm, and (c) BA at 200 ppm. Animals were euthanized under anesthesia at various time points post-injection (15 min-6 h). Boron concentrations in the diaphysis, knee joint, liver, kidney, skin, and blood were quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES). We also optimized neutron autoradiography to study boron microdistribution in compact bone. A novel sample preparation method was developed to prevent boron loss and improve the quality of the tissue sections. Samples from diaphysis, collected 3 h post-infusion, were sliced with a diamond saw and polished to the desired thickness using multiple double-sided diamond disks. Both ICP-OES and neutron autoradiography revealed high boron concentrations in bone regions, suggesting preferential accumulation in the mineral matrix. These findings highlight the potential relevance of BA not only for therapeutic purposes but also in evaluating possible radiotoxic effects during BNCT.