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Yang M, Lennikov A, Chang K, Ashok A, Lee C, Cho KS, Utheim TP, Dartt DA, Chen DF. Transcorneal but not transpalpebral electrical stimulation disrupts mucin homeostasis of the ocular surface. BMC Ophthalmol 2022; 22:490. [PMID: 36522696 PMCID: PMC9756492 DOI: 10.1186/s12886-022-02717-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 11/29/2022] [Indexed: 12/23/2022] Open
Abstract
PURPOSE Transcorneal electrical stimulation (TcES) is increasingly applied as a therapy for preserving and improving vision in retinal neurodegenerative and ischemic disorders. However, a common complaint about TcES is its induction of eye pain and dryness in the clinic, while the mechanisms remain unknown. METHOD TcES or transpalpebral ES (TpES) was conducted in C57BL6j mice for 14 days. The contralateral eyes were used as non-stimulated controls. Levels of intracellular [Ca2+] ([Ca2+]i) were assessed by Fura-2AM. The conductance resistances of the eye under various ES conditions were measured in vivo by an oscilloscope. RESULTS Although TcES did not affect tear production, it significantly induced damage to the ocular surface, as revealed by corneal fluorescein staining that was accompanied by significantly decreased mucin (MUC) 4 expression compared to the control. Similar effects of ES were detected in cultured primary corneal epithelium cells, showing decreased MUC4 and ZO-1 levels after the ES in vitro. In addition, TcES decreased secretion of MUC5AC from the conjunctiva in vivo, which was also corroborated in goblet cell cultures, where ES significantly attenuated carbachol-induced [Ca2+]i increase. In contrast to TcES, transpalpebral ES (TpES) did not induce corneal fluorescein staining while significantly increasing tear production. Importantly, the conductive resistance from orbital skin to the TpES was significantly smaller than that from the cornea to the retina in TcES. CONCLUSION TcES, but not TpES, induces corneal epithelial damage in mice by disrupting mucin homeostasis. TpES thus may represent a safer and more effective ES approach for treating retinal neurodegeneration clinically.
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Affiliation(s)
- Menglu Yang
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
| | - Anton Lennikov
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
- Department of Medical Biochemistry, Oslo University Hospital, University of Oslo, Kirkeveien 166, Oslo, 0450 Norway
| | - Karen Chang
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
- Department of Medical Biochemistry, Oslo University Hospital, University of Oslo, Kirkeveien 166, Oslo, 0450 Norway
| | - Ajay Ashok
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
- Department of Medical Biochemistry, Oslo University Hospital, University of Oslo, Kirkeveien 166, Oslo, 0450 Norway
| | - Cherin Lee
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
| | - Kin-Sang Cho
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
| | - Tor Paaske Utheim
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
- Department of Medical Biochemistry, Oslo University Hospital, University of Oslo, Kirkeveien 166, Oslo, 0450 Norway
| | - Darlene A. Dartt
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
| | - Dong Feng Chen
- Department of Ophthalmology, Harvard Medical School, Schepens Eye Research Institute of Massachusetts Eye and Ear, 20 Staniford St, Boston, MA 02114 USA
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Zakaria NF, Hamid M, Khayat ME. Amino Acid-Induced Impairment of Insulin Signaling and Involvement of G-Protein Coupling Receptor. Nutrients 2021; 13:nu13072229. [PMID: 34209599 PMCID: PMC8308393 DOI: 10.3390/nu13072229] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 06/18/2021] [Accepted: 06/24/2021] [Indexed: 12/12/2022] Open
Abstract
Amino acids are needed for general bodily function and well-being. Despite their importance, augmentation in their serum concentration is closely related to metabolic disorder, insulin resistance (IR), or worse, diabetes mellitus. Essential amino acids such as the branched-chain amino acids (BCAAs) have been heavily studied as a plausible biomarker or even a cause of IR. Although there is a long list of benefits, in subjects with abnormal amino acids profiles, some amino acids are correlated with a higher risk of IR. Metabolic dysfunction, upregulation of the mammalian target of the rapamycin (mTOR) pathway, the gut microbiome, 3-hydroxyisobutyrate, inflammation, and the collusion of G-protein coupled receptors (GPCRs) are among the indicators and causes of metabolic disorders generating from amino acids that contribute to IR and the onset of type 2 diabetes mellitus (T2DM). This review summarizes the current understanding of the true involvement of amino acids with IR. Additionally, the involvement of GPCRs in IR will be further discussed in this review.
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Affiliation(s)
- Nur Fatini Zakaria
- Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia;
| | - Muhajir Hamid
- Department of Microbiology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia;
| | - Mohd Ezuan Khayat
- Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia;
- Correspondence:
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