Comparative glycomic analysis of hawk ( <i>Rupornis magnirostris</i> ), caiman ( <i>Caiman latirostris</i> ) and sea turtle ( <i>Caretta caretta</i> ) tear films

Glycans are recognized as biomarkers and therapeutic targets. However, these molecules remain a critical blind spot in understanding post-translational modifications, particularly in vertebrate species inhabiting diverse habitats. The glycans present in tears play a crucial role in eye protection and may be one of the key factors in adapting to direct environmental contact. This study aimed to describe and compare the glycomic profiles of roadside hawk (<i>Rupornis magnirostris</i>), broad-snouted caiman (<i>Caiman latirostris</i>), and loggerhead sea turtle (<i>Caretta caretta</i>) tears, thereby one avian and two reptilian species. Samples were collected from 10 healthy roadside hawks, 70 broad-snouted caimans, and 10 loggerhead sea turtles to determine <i>N</i>- and <i>O</i>-glycan compounds. The compounds were released from tear glycoproteins and enriched by solid-phase extraction (SPE). Then, the glycans were eluted based on size and polarity. SPE fractions were analyzed using high-resolution mass spectrometry. 155 <i>N</i>-glycans (56% sialylated) and 259 <i>O</i>-glycans (37% sialylated) were detected in roadside hawk tears; 127 <i>N</i>-glycans (55% sialylated) and 263 <i>O</i>-glycans (35% sialofucosylated) in broad-snouted caiman tears; and 85 <i>N</i>-glycans (36% fucosylated) and 84 <i>O</i>-glycans (89% fucosylated) in loggerhead sea turtle tears. The marine habitat has a significant impact on the tear's glycans. The high presence of fucosylated glycans can represent a shield mechanism potentially related to its adhesion to glycocalyx, and interaction with the immune system, also serving as an environmental biomarker. Tears are composed of various biologically active substances, and this description can help in further studies on the identification of novel ocular surface biomarkers and in the differentiation of glycan profiles in healthy and non-healthy animals.