Preliminary study of the ameliorative effects of melatonin on cadmium‐induced morphological and biochemical alterations in the rat Harderian gland

Abstract

Herein is reported, for the first time in the rat Harderian gland (HG), the counteractive action of melatonin (Mlt), a well-known antioxidant radical scavenger, on the increased oxidative stress damages induced by a pro-oxidant substance, cadmium (Cd), an environmental pollutant also considered as endocrine disruptor.HG, an infraorbital gland present in almost all terrestrial vertebrates, produces a lipid secretion to lubricate the eyeball, as well as porphyrin/Mlt as light transducers.Moreover, HG is an extra-gonadal source of steroid sex hormones. Via ex vivo experiments lasting for 24 h, we verified the increased lipid peroxidation in Cd-treated glands, producing morphological alteration of the glandular epithelium, as well as an increased porphyrins accumulation. Moreover, Cd also induced a decreased protein level of the steroidogenic enzymes steroidogenic acute regulatory (StAR) and 3βHSD, and an increased mast cell number. Results obtained with Mlt cotreatment demonstrated that it decreased the levels of Cd-induced oxidative damage, with reversal of all the observed modification. Furthermore, the TUNEL assay showed that the increased number of apoptotic cells in Cd-treated HG was counteracted by the contemporaneous Mlt administration. Results confirmed that Mlt treatment restored the levels of two autophagy markers, LC3 and p62, counteracting the autophagy Cd-induced. Interestingly, the positive effects of Mlt alone were highlighted by the decreased rate of lipid peroxidation as compared with the control, confirming its antioxidant action. Combined data further confirmed the antioxidant action of Mlt in counteracting the degeneration provoked by reactive oxygen species (ROS) in the rat HG, a tissue extremely susceptible to oxidative stress condition.

Morphological and molecular changes in the Harderian gland of streptozotocin‐induced diabetic rats

“…We also demonstrated that melatonin, because of its antioxidant properties, was able to counteract the stressful condition provoked by Cd exposure on the analyzed parameters. Finally, all the combined results confirmed that HG is susceptible to exogenous stimuli (Romano et al, 2022).…”

“…In a previous work, we demonstrated that OS resulting from ROS overproduction induced an increase in connective-type interstitial MCN in the HG of rats treated with Cd (Romano et al, 2022), a wellknown prooxidant agent Venditti et al, 2021). In Figure 3, using the toluidine blue staining we evaluated the difference in MCN between control and T1D HG (Figure 3a).…”

“…In contrast, several experiments demonstrated that testosterone correlated negatively with MCN (Dias et al, 2022). We recently observed an increase in MCN in the HG of Cd‐treated rats, and this might be due to the characteristic of the metal being considered an endocrine disruptor, which by mimicking estrogen activates its receptors (Romano et al, 2022). In the light of these considerations, it should be noted that diabetes alters the balance of sex hormones through a reduction in plasma testosterone and an increase in E2 (Xu et al, 2008; Ziller et al, 2020).…”

“…It should be mentioned that the rat HG is located in the medial corner of the orbit, and it is continuously exposed to light, therefore the porphyrins produced can absorb UV light generating ROS via photo-oxidation (Hugo et al, 1987;Spike et al, 1990) 2021) demonstrated that in the hamster HG, autophagy and selective autophagy are activated as a protective response to OS induced by elevated intake of fructose, a nutritional element which plays a fundamental role in the developing disorders associated with metabolic syndrome. Because of this evidence, rodent HG is used as a model to have more insights and a better understanding of OS and its effects (Chieffi Baccari et al, 2022;Coto-Montes & Tomas-Zapico, 2006;Coto-Montes et al, 2001;Kong et al, 2021;Romano et al, 2022;Tomás-Zapico et al, 2005).…”

“…In this regard, in our previous work (Romano et al, 2022), we showed for the first time on the rat HG, the harmful effects of cadmium (Cd) which, producing OS, induced morphological, and biochemical changes, particularly the increase of lipid peroxidation, the induction of apoptosis and autophagy pathways and the reduction in the expression of steroidogenic enzymes. We also demonstrated that melatonin, because of its antioxidant properties, was able to counteract the stressful condition provoked by Cd exposure on the analyzed parameters.…”