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Park JW, Piknova B, Tunau-Spencer KJ, Thomas SM, Cai H, Walter PJ, Jenkins A, Hellinga D, Parver LM, Schechter AN. Dietary Nitrate Metabolism in Porcine Ocular Tissues Determined Using 15N-Labeled Sodium Nitrate Supplementation. Nutrients 2024; 16:1154. [PMID: 38674845 PMCID: PMC11054199 DOI: 10.3390/nu16081154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 04/11/2024] [Accepted: 04/12/2024] [Indexed: 04/28/2024] Open
Abstract
Nitrate (NO3-) obtained from the diet is converted to nitrite (NO2-) and subsequently to nitric oxide (NO) within the body. Previously, we showed that porcine eye components contain substantial amounts of nitrate and nitrite that are similar to those in blood. Notably, cornea and sclera exhibited the capability to reduce nitrate to nitrite. To gain deeper insights into nitrate metabolism in porcine eyes, our current study involved feeding pigs either NaCl or Na15NO3 and assessing the levels of total and 15N-labeled NO3-/NO2- in various ocular tissues. Three hours after Na15NO3 ingestion, a marked increase in 15NO3- and 15NO2- was observed in all parts of the eye; in particular, the aqueous and vitreous humor showed a high 15NO3- enrichment (77.5 and 74.5%, respectively), similar to that of plasma (77.1%) and showed an even higher 15NO2- enrichment (39.9 and 35.3%, respectively) than that of plasma (19.8%). The total amounts of NO3- and NO2- exhibited patterns consistent with those observed in 15N analysis. Next, to investigate whether nitrate or nitrite accumulate proportionally after multiple nitrate treatments, we measured nitrate and nitrite contents after supplementing pigs with Na15NO3 for five consecutive days. In both 15N-labeled and total nitrate and nitrite analysis, we did not observe further accumulation of these ions after multiple treatments, compared to a single treatment. These findings suggest that dietary nitrate supplementation exerts a significant influence on nitrate and nitrite levels and potentially NO levels in the eye and opens up the possibility for the therapeutic use of dietary nitrate/nitrite to enhance or restore NO levels in ocular tissues.
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Affiliation(s)
- Ji Won Park
- Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA; (J.W.P.); (B.P.); (K.J.T.-S.); (S.M.T.)
- Molecular Medicine Branch, National Institutes of Health, Bethesda, MD 20892, USA
| | - Barbora Piknova
- Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA; (J.W.P.); (B.P.); (K.J.T.-S.); (S.M.T.)
- Molecular Medicine Branch, National Institutes of Health, Bethesda, MD 20892, USA
| | - Khalid J. Tunau-Spencer
- Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA; (J.W.P.); (B.P.); (K.J.T.-S.); (S.M.T.)
- Molecular Medicine Branch, National Institutes of Health, Bethesda, MD 20892, USA
| | - Samantha M. Thomas
- Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA; (J.W.P.); (B.P.); (K.J.T.-S.); (S.M.T.)
- Molecular Medicine Branch, National Institutes of Health, Bethesda, MD 20892, USA
| | - Hongyi Cai
- Clinical Mass Spectrometry Core, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA; (H.C.); (P.J.W.)
- Clinical Mass Spectrometry Core, National Institutes of Health, Bethesda, MD 20892, USA
| | - Peter J. Walter
- Clinical Mass Spectrometry Core, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA; (H.C.); (P.J.W.)
- Clinical Mass Spectrometry Core, National Institutes of Health, Bethesda, MD 20892, USA
| | - Audrey Jenkins
- MedStar Health Research Institute, Washington, DC 20010, USA; (A.J.); (D.H.)
| | - David Hellinga
- MedStar Health Research Institute, Washington, DC 20010, USA; (A.J.); (D.H.)
| | - Leonard M. Parver
- Department of Ophthalmology, Medstar Georgetown University Hospital, Washington, DC 20007, USA
| | - Alan N. Schechter
- Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA; (J.W.P.); (B.P.); (K.J.T.-S.); (S.M.T.)
- Molecular Medicine Branch, National Institutes of Health, Bethesda, MD 20892, USA
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Tsao Y, Wu W, Chen K, Yeh L, Hwang Y, Hsueh Y, Chen H, Cheng C. Analysis of aqueous humor total antioxidant capacity and its correlation with corneal endothelial health. Bioeng Transl Med 2021; 6:e10199. [PMID: 34027088 PMCID: PMC8126826 DOI: 10.1002/btm2.10199] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Revised: 10/11/2020] [Accepted: 10/29/2020] [Indexed: 02/04/2023] Open
Abstract
Corneal endothelial decompensation is a serious condition that frequently requires treatment via corneal transplantation which contributes to a global shortage in donor corneas. Therefore, the purpose of this study was to analyze the influence of aqueous humor total antioxidant capacity (TAC) on corneal endothelial health. There is an urgent need for discovering protective factors to combat corneal endothelial cell (CEC) loss. For methods, we developed a cupric ion-based TAC (CuTAC) assay to analyze TAC level in a small volume of aqueous humor, that is, 10 μL per test, and examined the influences of ascorbic acid (AA) and antioxidant proteins on aqueous humor TAC. To broaden the investigation, we conducted a case-control study with patients classified into two groups, an insufficient endothelial cell density (ECD < 2100 cells/mm2) group, and a control group. These groups were formed based on baseline ECD values and were used to evaluate the influence of aqueous humor TAC and AA on overall corneal endothelial health. A CuTAC assay was used to accurately measure aqueous humor TAC without the need for sample dilution. After analyzing a total of 164 human aqueous humor samples, we found that AA was the major contributor to aqueous humor TAC (73.2%). In addition, TAC and AA levels in the IECD and control groups were both found to be significantly different (1.168 vs. 1.592 mM, p = 0.009 and 0.856 vs. 1.178 mM, p = 0.016). TAC and AA were considered independent protective factors against IECD with adjusted odds ratios of 0.02 (p = 0.017) and 0.023 (p = 0.033), respectively. In conclusion, aqueous humor TAC and AA contribute to the maintenance of sufficient corneal ECD, and our CuTAC assay can be a useful tool for analyzing TAC using only a small aqueous humor sample volume.
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Affiliation(s)
- Yu‐Ting Tsao
- Institute of Biomedical Engineering, National Tsing Hua UniversityHsinchuTaiwan
- Department of EducationChang Gung Memorial HospitalLinkouTaiwan
| | - Wei‐Chi Wu
- Department of OphthalmologyChang Gung Memorial HospitalLinkouTaiwan
- Department of MedicineChang Gung University College of MedicineTaoyuanTaiwan
| | - Kuan‐Jen Chen
- Department of OphthalmologyChang Gung Memorial HospitalLinkouTaiwan
- Department of MedicineChang Gung University College of MedicineTaoyuanTaiwan
| | - Lung‐Kun Yeh
- Department of OphthalmologyChang Gung Memorial HospitalLinkouTaiwan
- Department of MedicineChang Gung University College of MedicineTaoyuanTaiwan
| | - Yih‐Shiou Hwang
- Department of OphthalmologyChang Gung Memorial HospitalLinkouTaiwan
- Department of MedicineChang Gung University College of MedicineTaoyuanTaiwan
| | - Yi‐Jen Hsueh
- Department of OphthalmologyChang Gung Memorial HospitalLinkouTaiwan
- Center for Tissue EngineeringChang Gung Memorial HospitalLinkouTaiwan
| | - Hung‐Chi Chen
- Department of OphthalmologyChang Gung Memorial HospitalLinkouTaiwan
- Department of MedicineChang Gung University College of MedicineTaoyuanTaiwan
- Center for Tissue EngineeringChang Gung Memorial HospitalLinkouTaiwan
| | - Chao‐Min Cheng
- Institute of Biomedical Engineering and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua UniversityHsinchuTaiwan
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