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Chronic Liver Disease
Published in Praveen S. Goday, Cassandra L. S. Walia, Pediatric Nutrition for Dietitians, 2022
Julia M. Boster, Kelly A. Klaczkiewicz, Shikha S. Sundaram
Vitamin A deficiency can manifest as night blindness, xerophthalmia (dry eyes), Bitot spots (white plaques on the conjunctiva), and follicular hyperkeratosis (a rough, raised rash located on the extremities). Ideally, the serum retinol level and retinol to retinol-binding protein molar ratio (retinol:RBP) are used to assess vitamin A status. Serum retinol of <20 μg/dL with a molar ratio of <0.8 indicates vitamin A deficiency.
Extrahepatic Synthesis of Acute Phase Proteins
Published in Andrzej Mackiewicz, Irving Kushner, Heinz Baumann, Acute Phase Proteins, 2020
Gerhard Schreiber, Angela R. Aldred
Retinol is transported in the blood stream bound to retinol-binding protein. Retinolbinding protein is, itself, bound to transthyretin. Using a genomic DNA fragment containing the exons coding for retinol-binding protein as a probe, extrahepatic expression of the gene for retinol-binding protein was demonstrated95 for choroid plexus, other areas of the brain, and liver by Northern analysis of RNA extracts, as illustrated in Figure 17.
Transport of Protein-Bound Radiotracers Into Tissues*
Published in Lelio G. Colombetti, Biological Transport of Radiotracers, 2020
Retinol-binding protein is a 14,000 mol wt protein secreted by the liver and transported in the circulation bound to TBPA.80 The KD of TBPA-binding of RBP is about 5 μM,80 a figure which approximates the normal plasma level of TBPA.81 The function of TBPA binding of RBP is believed to be the restriction of RBP clearance by glomerular capillaries, which are fenestrated and are permeable to small proteins such as RBP. However, the question then arises as to how RBP dissociates from TBPA to traverse the fenestrated choroidal capillaries of the eye. The choroidal capillaries are permeable to proteins such as myoglobulin (extraction = 8%, mol wt — 18,000) and presumably, RBP, but not to albumin (extraction = 0%, mol wt 68,000) or presumably, TBPA (mol wt 50,000).82 However, if the KD in vivo of TBPA binding of RBP is comparable to the in vitro KD of 5 μM, then given Equation 15 and TBPA = 7 μM, then the percent free RBP = 42%. Therefore, free RBP would normally represent a large part of the total plasma RBP pool and would be cleared in part by choroidal and, presumably, glomerular capillaries.
All-Trans Retinoic Acid Prevents the Progression of Gastric Precancerous Lesions by Regulating Disordered Retinoic Acid Metabolism
Published in Nutrition and Cancer, 2022
Hanhan Wu, Didi Zhao, Chen Wang, Daoming Zhang, Min Tang, Shiqing Qian, Lina Xu, Tao Xia, Juanyan Zhou, Guangjun Wang, Yue He, Lei Gao, Wenjun Chen, Li Li, Wanshui Yang, Qihong Zhao, Chuanlai Hu, Anla Hu
As the most biologically active metabolite of vitamin A, retinoic acid (RA) cannot be obtained directly from food but only vitamin A (retinol, retinyl ester, or carotenoids) from food that is metabolized in the body (11). Retinol is delivered to target cells bound to plasma retinol-binding protein (RBP). HoloRBP binds to RBP receptor, stimulated by retinoic acid gene 6 (STRA6) (12, 13). Cellular retinol-binding protein 1 (CRBP1) accepts retinol from STRA6 in the cytoplasm and delivers retinol to membranes, where retinol is either esterified by lecithin retinol acyltransferase (LRAT) to inactive retinyl ester or oxidized by retinol dehydrogenases (RDH) to retinal (14, 15). Retinal is oxidized further to RA by aldehyde dehydrogenases (ALDH) in the cytoplasm or is reduced back to retinol by retinal dehydrogenases in the membranes (14, 16). RA binds to cellular retinol acid-binding protein (CRABP1/2). Most RA is transferred by holoCRABP2 to the nucleus for binding to heterodimers of RA receptors (RARs) and retinoid X receptors (RXRs) in the target nucleus and thereafter triggers the downstream signaling pathways. The remainder is delivered to enzymes by holoCRABP1 for degradation. The clearance of RA is mediated predominantly by cytochrome P450 family 26 enzymes (CYP26). The family consists of three highly conserved enzymes, CYP26A1, CYP26B1, and CYP26C1 (17, 18). In addition, β-carotene is taken up by the cells and cleaved into retinal by β-carotene 15-15′-oxygenase (BCO1). Retinals derived from β-carotene may be oxidized to RA or converted to retinol (19).
Combination of podophyllotoxin and rutin modulate radiation-induced alterations of jejunal proteome in mice
Published in International Journal of Radiation Biology, 2020
Sania Bajaj, Syed Imteyaz Alam, Basir Ahmad, Humaira Farooqi, Manju Lata Gupta
Exposure to 9 Gy radiation resulted in upregulation of bimolecular transportation and metabolic pathway related proteins such as alcohol dehydrogenase 6 A (class V), ribonuclease inhibitor, and UMP-CMP kinase in mice jejunum. Retinol-binding protein 2 of the same category upregulated immediately after radiation exposure but decreased significantly at 216 h. It was found upregulated at initial time-points even with G-003M pretreatment but its expression gradually returned to normal at 840 h post-experimentation. Cytoskeleton proteins like tropomyosin alpha-4 chain, tropomyosin alpha-3 chain, gamma-actin, and cofilin-1 were also observed to downregulate after 9 gray IR exposures. Cofilin-1 drastically decreased post 1 h radiation exposure, but tropomyosin alpha chain 3 and 4 showed a gradual decrease till death of the animal. Myosin regulatory light polypeptide 9 (MYL9) increased initially (24 h) but a gradual decrease was observed thereafter to 0.66 ± 0.3-fold post-IR. Radiation mediated decrease in expression of these proteins not just affects the rearrangement of cellular cytoskeleton but also destabilizes their dynamics which severely disbalances cellular homeostasis. The pre-administration of G-003M expressed a positive modulation over these proteins. The tropomyosin proteins and MYL9 revealed a non-significant change in expression even post-IR but cofilin-1 declined initially to 0.57 ± 0.13-fold till 120 h but later enhanced to control level by 840 h.
Serum RBP4 positively correlates with triglyceride level but not with BMI, fat mass and insulin resistance in healthy obese and non-obese individuals
Published in Biomarkers, 2018
Emilia Korek, Magdalena Gibas-Dorna, Zuzanna Chęcińska-Maciejewska, Hanna Krauss, Małgorzata Łagiedo-Żelazowska, Barbara Kołodziejczak, Paweł Bogdański
Retinol-binding protein 4 (RBP4) is a globular protein with a molecular weight of 21 kDa, mainly produced by the liver and adipose tissue (Kotnik et al. 2011). The primary role of this molecule is to transport vitamin A (retinol) in the circulation (Blaner 1989). RBP4 has recently been proposed to be implicated in the pathophysiology of the metabolic consequences of obesity (Yang et al. 2005, Rabe et al.2008). For example, RBP4 was described as a protein associated with markers of lipid metabolism, pathogenesis of arteriosclerosis and nonalcoholic fatty liver disease (Junjun et al. 2013, Rocha et al. 2013, Liu et al. 2016). Additionally, elevated RBP4 levels were observed in subjects with obesity, impaired glucose tolerance, or type 2 diabetes as well as in non-obese insulin-resistant subjects (Graham et al. 2006, Gavi et al. 2007). Contrary to these results, a number of studies reported no associations between RBP4 and obesity-related insulin resistance (Erikstrup et al. 2006, Takashima et al. 2006, Broch et al. 2007, Gavi et al. 2007). Therefore, the current data cannot bring a clear evidence demonstrating that RBP4 itself directly affects insulin sensitivity and may be considered as a predictive marker for obesity-related disorders.