Role of peroxidase inhibition by insulin in the bovine thyroid cell proliferation mechanism

Abstract

Monolayer primary cultures of thyroid cells produce, in the presence of insulin, a cytosolic inhibitor of thyroid peroxidase (TPO), lacto peroxidase (LPO), horseradish peroxidase (HRPO) and glutathione peroxidase (GPX). The inhibitor, localized in the cytosol, is thermostable and hydrophylic. Its molecular mass is less than 2 kDa. The inhibitory activity, resistant to proteolytic and nucleolytic enzymes, disappears with sodium metaperiodate treatment, as an oxidant of carbohydrates, supporting its oligosaccharide structure. The presence of inositol, mannose, glucose, the specific inhibition of cyclic AMP-dependent protein kinase and the disappearance of peroxidase inhibition by alkaline phosphatase and a-mannosidase in purified samples confirms its chemical structure as inositol phosphoglycan-like. Purification by anionic interchange shows that the peroxidase inhibitor elutes like the two subtypes of inositol phosphoglycans (IPG)P and A, characterized as signal transducers of insulin action. Insulin significantly increases the concentration of the peroxidase inhibitor in a thyroid cell culture at 48 h. The addition of both isolated substances to a primary thyroid culture produces, after 30 min, a significant increase in hydrogen peroxide (H 2 O 2 ) concentration in the medium, concomitantly with the disappearance of the GPX activity in the same conditions. The presence of insulin or anyone of both products, during 48 h, induces cell proliferation of the thyroid cell culture. In conclusion, insulin stimulates thyroid cell division through the effect of a peroxidase inhibitor, as its second messenger. The inhibition of GPX by its action positively modulates the H 2 O 2 level, which would produce, as was demonstrated by other authors, the signal for cell proliferation.

Different effects of low- and high-dose insulin on ROS production and VEGF expression in bovine retinal microvascular endothelial cells in the presence of high glucose

“…In diabetes, the main sources of ROS generation in the vasculature include glucose auto-oxidation, the polyol pathway, AGE, mitochondrial electron transport chain (ETC), uncoupled eNOS, and NAd (P)H oxidases, with the latter enzymes arguably a major source of ROS generation in hypertension, atherosclerosis, and diabetes [26,29]. Recently, insulin has been reported to increase intracellular ROS production, possibly through phosphatidylinositol 3´-kinase-dependent mechanism and protein kinase C-dependent mechanism [5][6][7][8][9]. Our study demonstrated that insulin could increase intracellular ROS production in BRECs also through mitochondria and NADPH oxidase, as administration of NAd (P)H inhibitor apocynin can counteract insulin-induced overproduction of ROS.…”

“…Several possible mechanisms have been reported for the phenomenon: first, diabetes was severe at the early stage; however, randomized clinical trails have ruled out this possibility [4]; second, insulin reduced retinal blood flow and subsequently led to retinal hypoxia, increased vascular permeability, and edema; third, insulin could cause arthrosclerosis and promote mitosis, thrombosis formation; finally, vascular endothelial growth factor was also thought to be involved in insulin-induced deterioration of retinopathy. Recently, insulin has been reported to increase intracellular reactive oxygen species (ROS) production in HepG2 cells [5], 3T3L1 adipocytes [6], thyroid cells [7], and human fibroblasts [8,9].…”

Interferon-β lipofection II. Mechanisms involved in cell death and bystander effect induced by cationic lipid-mediated interferon-β gene transfer to human tumor cells

“…This increase in ROOH levels could be because of a higher production or lower activity of degrading enzymes (that is, CAT) or to a combination of both events. Preliminary results demonstrated that an unspecific inhibitor of peroxidases 34 was increased in the cytosolic compartment of hIFNb-expressing EW7 cells (data not shown). On the other hand, we found that hIFNb gene decreased the antioxidant capacity of EW7 cells (Figure 7d).…”

Inhibition of Peroxidase and Catalase Activities and Modulation of Hydrogen Peroxide Level by Inositol Phosphoglycan-like Compounds

“…ever, conversely, the mechanism of the production of IPGP from the membrane ' s GPI is not clear [6] . To date, the exact chemical structure of IPGs has not been elucidated and they are identifi ed by the methods reported by Krawiec et al [7] . The peroxidase inhibitor is termed an IPG-like product, considering its individual components.…”

“…The peroxidase inhibitor is termed an IPG-like product, considering its individual components. Krawiec et al [7] showed that insulin ' s promotion of thyroid cell proliferation may be attributed to the inhibition exerted by IPG on GPX and TPO activities. This inhibition enhances the H 2 O 2 level, which would be the signal for the induction of the mitogenic mechanism, acting on the oncogene c-jun, as was demonstrated by Lee et al [8] .…”