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Recently, we reported a pH-responsive nanoparticle (NP) system shelled with chitosan (CS), which could effectively increase the oral absorption of insulin and produce a hypoglycemic effect, presumably due to the CS-mediated tight junction (TJ) opening. It has been often questioned whether CS can also enhance the absorption of endotoxins present in the small intestine. To address this concern, we studied the effect of CS NPs on the absorption of lipopolysaccharide (LPS), the most commonly found toxin in the gastrointestinal tract. To follow their biodistribution by the single-photon emission computed tomography/computed tomography, LPS and insulin were labeled with ^99mTc-pertechnetate (^99mTc-LPS) and ¹²³iodine (¹²³I-insulin), respectively. The ^99mTc-LPS was ingested 1 h prior to the administration of the ¹²³I-insulin-loaded NPs to mimic the physiological conditions. The confocal and TEM micrographs …