Potential pitfalls in the nuclear medicine imaging: Experimental models to evaluate the effect of natural products on the radiolabeling of blood constituents, bioavailability of radiopharmaceutical and on the survival of Escherichia coli strains submitted

Single photon emission computed tomography (SPECT) allows studies of physiological or pathological processes. Red blood cells labeled with technetium-99m (99mTc-RBC) are used as a radiopharmaceutical in several evaluations. The radiolabeling efficiency and bioavailability of radiopharmaceuticals can be altered by natural/synthetic drugs and may induce pitfalls in the analysis of the nuclear medicine imaging. The labeling with 99mTc requires a reducing agent and stannous chloride (SnCl2) is widely utilized. However, SnCl2 presents a citotoxic and/or genotoxic potential in Escherichia coli (E. coli) strains. The aim of this work was to evaluate the influence of aqueous extracts of Baccharis genistelloides (BG), Terminalia chebula (TC), Maytenus ilicifolia (MI), Cassia angustifolia (CA) and Equisetum arvense (EA) on (i) radiolabeling of blood constituents, (ii) bioavailability of sodium pertechnetate(Na99mTcO4) radiopharmaceutical, (iii) survival of E. coli. In vitro labeling of RBC was performed with blood (Wistar rats) incubated with each extract, SnCl2 and Na99mTcO4. Plasma (P) and blood cells (BC) were isolated, another aliquots precipitated and soluble (SF) and insoluble (IF) fractions isolated and counted. In the bioavailability of Na99mTcO4, Wistar rats were treated (7 days) with aqueous extract or with 0.9%NaCl, the radiopharmaceutical was administered, the animals sacrificed, the organs isolated, weighted and radioactivity counted. To evaluate the effect on the bacterial survival, E. coli was treated with: (a) SnCl2; (b) 0.9% NaCl; (c) vegetal extract; or (d) SnCl2 and vegetal extract. Radiolabeling efficiency showed a significantly decrease (ANOVA/Tukey post-test, p<0.05) after treatment with BG, TC, MI and CA extracts. The bioavailability results showed that the uptake of Na99mTcO4 was altered significantly (unpaired t-student test, p<0.05) in blood, lungs (CA/TC extracts), bone, heart, ovary (EA/TC), spleen, kidney (TC), pancreas, thyroid (CA) and liver (all the extracts). The alterations promoted by TC extract could be related to cardiotonic, antidiabetes and renal toxicity. The alteration in liver in EA and CA extracts could be related to its hepatoprotective activities. The extracts (EA, MI, BG) were not capable to interfere in the survival of E. coli. Moreover, these extracts have protected the E. coli against the SnCl2 action and this fact can be related to the free radical scavenging properties of the chemical compounds of the extracts. In conclusion these findings could be worthwhile to try to understand and to avoid some pitfalls in the nuclear medicine.