1
|
Bejarano E, Weinberg J, Clark M, Taylor A, Rowan S, Whitcomb EA. Redox Regulation in Age-Related Cataracts: Roles for Glutathione, Vitamin C, and the NRF2 Signaling Pathway. Nutrients 2023; 15:3375. [PMID: 37571310 PMCID: PMC10421530 DOI: 10.3390/nu15153375] [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: 06/29/2023] [Revised: 07/19/2023] [Accepted: 07/26/2023] [Indexed: 08/13/2023] Open
Abstract
Age is the biggest risk factor for cataracts, and aberrant oxidative modifications are correlated with age-related cataracts, suggesting that proper redox regulation is important for lens clarity. The lens has very high levels of antioxidants, including ascorbate and glutathione that aid in keeping the lens clear, at least in young animals and humans. We summarize current functional and genetic data supporting the hypothesis that impaired regulation of oxidative stress leads to redox dysregulation and cataract. We will focus on the essential endogenous antioxidant glutathione and the exogenous antioxidant vitamin C/ascorbate. Additionally, gene expression in response to oxidative stress is regulated in part by the transcription factor NRF2 (nuclear factor erythroid 2-related factor 2 [NFE2L2]), thus we will summarize our data regarding cataracts in Nrf2-/- mice. In this work, we discuss the function and integration of these capacities with the objective of maintaining lens clarity.
Collapse
Affiliation(s)
- Eloy Bejarano
- JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA; (E.B.); (J.W.); (M.C.); (A.T.); (S.R.)
- School of Health Sciences and Veterinary, Universidad CEU Cardenal Herrera, CEU Universities, 46113 Valencia, Spain
| | - Jasper Weinberg
- JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA; (E.B.); (J.W.); (M.C.); (A.T.); (S.R.)
| | - Madison Clark
- JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA; (E.B.); (J.W.); (M.C.); (A.T.); (S.R.)
| | - Allen Taylor
- JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA; (E.B.); (J.W.); (M.C.); (A.T.); (S.R.)
- Friedman School of Nutrition Science and Policy, Tufts University, Boston, MA 02111, USA
- Department of Ophthalmology, School of Medicine, Tufts University, Boston, MA 02111, USA
- Department of Developmental, Chemical and Molecular Biology, Tufts University, Boston, MA 02111, USA
| | - Sheldon Rowan
- JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA; (E.B.); (J.W.); (M.C.); (A.T.); (S.R.)
- Friedman School of Nutrition Science and Policy, Tufts University, Boston, MA 02111, USA
- Department of Ophthalmology, School of Medicine, Tufts University, Boston, MA 02111, USA
| | - Elizabeth A. Whitcomb
- JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA; (E.B.); (J.W.); (M.C.); (A.T.); (S.R.)
| |
Collapse
|
2
|
Lou MF. Glutathione and Glutaredoxin in Redox Regulation and Cell Signaling of the Lens. Antioxidants (Basel) 2022; 11:1973. [PMID: 36290696 PMCID: PMC9598519 DOI: 10.3390/antiox11101973] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 09/20/2022] [Accepted: 09/23/2022] [Indexed: 11/16/2022] Open
Abstract
The ocular lens has a very high content of the antioxidant glutathione (GSH) and the enzymes that can recycle its oxidized form, glutathione disulfide (GSSG), for further use. It can be synthesized in the lens and, in part, transported from the neighboring anterior aqueous humor and posterior vitreous body. GSH is known to protect the thiols of the structural lens crystallin proteins from oxidation by reactive oxygen species (ROS) so the lens can maintain its transparency for proper visual function. Age-related lens opacity or senile cataract is the major visual impairment in the general population, and its cause is closely associated with aging and a constant exposure to environmental oxidative stress, such as ultraviolet light and the metabolic end product, H2O2. The mechanism for senile cataractogenesis has been hypothesized as the results of oxidation-induced protein-thiol mixed disulfide formation, such as protein-S-S-glutathione and protein-S-S-cysteine mixed disulfides, which if not reduced in time, can change the protein conformation to allow cascading modifications of various kinds leading to protein-protein aggregation and insolubilization. The consequence of such changes in lens structural proteins is lens opacity. Besides GSH, the lens has several antioxidation defense enzymes that can repair oxidation damage. One of the specific redox regulating enzymes that has been recently identified is thioltransferase (glutaredoxin 1), which works in concert with GSH, to reduce the oxidative stress as well as to regulate thiol/disulfide redox balance by preventing protein-thiol mixed disulfide accumulation in the lens. This oxidation-resistant and inducible enzyme has multiple physiological functions. In addition to protecting structural proteins and metabolic enzymes, it is able to regulate the redox signaling of the cells during growth factor-stimulated cell proliferation and other cellular functions. This review article focuses on describing the redox regulating functions of GSH and the thioltransferase enzyme in the ocular lens.
Collapse
Affiliation(s)
- Marjorie F. Lou
- School of Veterinary Medicine and Biomedical Sciences, Redox Biology Center, University of Nebraska-Lincoln, Lincoln, NE 68583, USA;
- Department of Ophthalmology, University of Nebraska Medical Center, Omaha, NE 68198, USA
- Department of Pharmaceutical Sciences, System College of Pharmacy, University of North Texas Health Science Center, Fort Worth, TX 76107, USA
| |
Collapse
|
3
|
Quan Y, Du Y, Wu C, Gu S, Jiang JX. Connexin hemichannels regulate redox potential via metabolite exchange and protect lens against cellular oxidative damage. Redox Biol 2021; 46:102102. [PMID: 34474393 PMCID: PMC8408634 DOI: 10.1016/j.redox.2021.102102] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Revised: 08/10/2021] [Accepted: 08/11/2021] [Indexed: 11/23/2022] Open
Abstract
Increased oxidative stress contributes to cataract formation during aging. Anterior epithelial cells are a frontline antioxidant defense system with powerful capacities to maintain redox homeostasis and lens transparency. In this study, we report a new molecular mechanism of connexin (Cx) hemichannels (HCs) in lens epithelial cells to protect lens against oxidative stress. Our results showed haploinsufficiency of Cx43 elevated oxidative stress and susceptibility to cataracts in the mouse lens. Cx43 HCs opened in response to hydrogen peroxide (H2O2) or ultraviolet radiation (UVR) in human lens epithelium HLE-B3 cells, and this activation contributed to a cellular protective mechanism against oxidative stress-induced apoptotic cell death. Furthermore, we found that Cx43 HCs mediated the exchange of oxidants and antioxidants in lens epithelial cells undergoing oxidative stress. These transporting activities facilitated a reduction of intracellular reactive oxygen species (ROS) accumulation and maintained the intracellular glutathione (GSH) level through the exchange of redox metabolites and change of anti-oxidative gene expression. In addition, we show that Cx43 HCs can be regulated by the intracellular redox state and this regulation is mediated by residue Cys260 located at the Cx43 C-terminus. Together, our results demonstrate that Cx43 HCs activated by oxidative stress in the lens epithelial cells play a key role in maintaining redox homeostasis in lens under oxidative stress. Our findings contribute to advancing our understanding of oxidative stress induced lens disorders, such as age-related non-congenital cataracts.
Collapse
Affiliation(s)
- Yumeng Quan
- Department of Ophthalmology, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi, China; Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Yu Du
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Changrui Wu
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Sumin Gu
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Jean X Jiang
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, USA.
| |
Collapse
|
4
|
Lim JC, Grey AC, Zahraei A, Donaldson PJ. Age‐dependent changes in glutathione metabolism pathways in the lens: New insights into therapeutic strategies to prevent cataract formation—A review. Clin Exp Ophthalmol 2020; 48:1031-1042. [DOI: 10.1111/ceo.13801] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 05/15/2020] [Accepted: 05/22/2020] [Indexed: 12/29/2022]
Affiliation(s)
- Julie C. Lim
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center University of Auckland Auckland New Zealand
| | - Angus C. Grey
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center University of Auckland Auckland New Zealand
| | - Ali Zahraei
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center University of Auckland Auckland New Zealand
| | - Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center University of Auckland Auckland New Zealand
| |
Collapse
|
5
|
Whitson JA, Sell DR, Goodman MC, Monnier VM, Fan X. Evidence of Dual Mechanisms of Glutathione Uptake in the Rodent Lens: A Novel Role for Vitreous Humor in Lens Glutathione Homeostasis. Invest Ophthalmol Vis Sci 2017; 57:3914-25. [PMID: 27472077 PMCID: PMC4998144 DOI: 10.1167/iovs.16-19592] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Purpose Lens glutathione synthesis knockout (LEGSKO) mouse lenses lack de novo glutathione (GSH) synthesis but still maintain >1 mM GSH. We sought to determine the source of this residual GSH and the mechanism by which it accumulates in the lens. Methods Levels of GSH, glutathione disulfide (GSSG), and GSH-related compounds were measured in vitro and in vivo using isotope standards and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Results Wild-type (WT) lenses could accumulate GSH from γ-glutamylcysteine and glycine or from intact GSH, but LEGSKO lenses could only accumulate GSH from intact GSH, indicating that LEGSKO lens GSH content is not due to synthesis by a salvage pathway. Uptake of GSH in cultured lenses occurred at the same rate for LEGSKO and WT lenses, could not be inhibited, and occurred primarily through cortical fiber cells. In contrast, uptake of GSH from aqueous humor could be competitively inhibited and showed an enhanced Km in LEGSKO lenses. Mouse vitreous had >1 mM GSH, whereas aqueous had <20 μM GSH. Testing physiologically relevant GSH concentrations for uptake in vivo, we found that both LEGSKO and WT lenses could obtain GSH from the vitreous but not from the aqueous. Vitreous rapidly accumulated GSH from the circulation, and depletion of circulating GSH reduced vitreous but not aqueous GSH. Conclusions The above data provide, for the first time, evidence for the existence of dual mechanisms of GSH uptake into the lens, one mechanism being a passive, high-flux transport through the vitreous exposed side of the lens versus an active, carrier-mediated uptake mechanism at the anterior of the lens.
Collapse
Affiliation(s)
- Jeremy A Whitson
- Department of Pathology Case Western Reserve University, Cleveland, Ohio, United States
| | - David R Sell
- Department of Pathology Case Western Reserve University, Cleveland, Ohio, United States
| | - Michael C Goodman
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee, United States
| | - Vincent M Monnier
- Department of Pathology Case Western Reserve University, Cleveland, Ohio, United States 3Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, United States
| | - Xingjun Fan
- Department of Pathology Case Western Reserve University, Cleveland, Ohio, United States
| |
Collapse
|
6
|
Fan X, Monnier VM, Whitson J. Lens glutathione homeostasis: Discrepancies and gaps in knowledge standing in the way of novel therapeutic approaches. Exp Eye Res 2016; 156:103-111. [PMID: 27373973 DOI: 10.1016/j.exer.2016.06.018] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 03/10/2016] [Accepted: 06/25/2016] [Indexed: 01/18/2023]
Abstract
Cataract is the major cause of blindness worldwide. The WHO has estimated around 20 million people have bilateral blindness from cataract, and that number is expected to reach 50 million in 2050. The cataract surgery is currently the main treatment approach, though often associated with complications, such as Posterior Capsule Opacification (PCO)-also known as secondary cataract. The lens is an avascular ocular structure equipped with an unusually high level of glutathione (GSH), which plays a vital role in maintaining lens transparency by regulating lenticular redox state. The lens epithelium and outer cortex are thought to be responsible for providing the majority of lens GSH via GSH de novo synthesis, assisted by a continuous supply of constituent amino acids from the aqueous humor, as well as extracellular GSH recycling from the gamma-glutamyl cycle. However, when de novo synthesis is impaired, in the presence of low GSH levels, as in the aging human lens, compensatory mechanisms exist, suggesting that the lens is able to uptake GSH from the surrounding ocular tissues. However, these uptake mechanisms, and the GSH source and its origin, are largely unknown. The lens nucleus does not have the ability to synthesize its own GSH and fully relies on transport from the outer cortex by yet unknown mechanisms. Understanding how aging reduces GSH levels, particularly in the lens nucleus, how it is associated with age-related nuclear cataract (ARNC), and how the lens compensates for GSH loss via external uptake should be a major research priority. The intent of this review, which is dedicated to the memory of David C. Beebe, is to summarize our current understanding of lens GSH homeostasis and highlight discrepancies and gaps in knowledge that stand in the way of pharmacologically minimizing the impact of declining GSH content in the prevention of age-related cataract.
Collapse
Affiliation(s)
- Xingjun Fan
- Department of Pathology, Case Western Reserve University, USA.
| | - Vincent M Monnier
- Department of Pathology, Case Western Reserve University, USA; Department of Biochemistry, Case Western Reserve University, USA
| | - Jeremy Whitson
- Department of Pathology, Case Western Reserve University, USA
| |
Collapse
|
7
|
Presbyopia. Emerging from a blur towards an understanding of the molecular basis for this most common eye condition. Exp Eye Res 2008; 88:241-7. [PMID: 18675268 DOI: 10.1016/j.exer.2008.07.003] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2008] [Revised: 07/04/2008] [Accepted: 07/08/2008] [Indexed: 11/24/2022]
Abstract
All people will be presbyopic by age 50, and we now understand something of the basis for this condition. It turns out to be a direct consequence of two features; first the design of the transparent lens and the way it must change shape to enable focussing by the human eye, and second the instability of proteins over a very long time period. The incremental changes that take place in the lens to render the central region inflexible by middle age and, as a consequence the person presbyopic, may also promote the subsequent development of cataract. Based on the most recent data, heat-induced denaturation of proteins in the lens appears to be a worthy topic for future investigation. Understanding such processes may allow us to glimpse the origin both of presbyopia and age-related nuclear cataract.
Collapse
|
8
|
Younan C, Mitchell P, Cumming R, Rochtchina E, Panchapakesan J, Tumuluri K. Cardiovascular disease, vascular risk factors and the incidence of cataract and cataract surgery: the Blue Mountains Eye Study. Ophthalmic Epidemiol 2004; 10:227-40. [PMID: 14628965 DOI: 10.1076/opep.10.4.227.15905] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
PURPOSE To assess whether an association exists between cardiovascular disease, vascular risk factors and incident cataract and cataract surgery. METHODS The Blue Mountains Eye Study examined 3654 participants > or = 49 years of age during 1992-4, then 2335 survivors (75.1%) after five years. Trained interviewers administered a vascular history questionnaire; height, weight and blood pressure were measured. Lens photographs from both examinations were graded for presence of cortical, nuclear or posterior subcapsular cataract. RESULTS Obesity (body mass index > or = 30 kg/m2) was significantly associated with increased incidence of both cortical [odds ratio (OR) 1.6, 95% confidence interval (CI) 1.2-2.2] and posterior subcapsular cataract (OR 2.1, CI 1.2-3.7). Hypertensive participants using medication and aged less than 65 years at baseline had a higher incidence of posterior subcapsular cataract (OR 3.4, 95% CI 1.3-8.4) than normotensive subjects. A history of angina was associated with higher cataract surgery incidence (OR 2.1, 95% CI 1.3-3-5). CONCLUSIONS These longitudinal data provide some evidence supporting a relationship between cardiovascular disease, vascular risk factors and incident cataract and cataract surgery. The findings confirm a number of associations previously documented in cross-sectional data.
Collapse
Affiliation(s)
- Christine Younan
- Department of Ophthalmology and the Westmead Millennium and Save Sight Institutes, University of Sydney, NSW, Australia
| | | | | | | | | | | |
Collapse
|
9
|
Lash LH. Measurement of glutathione transport. CURRENT PROTOCOLS IN TOXICOLOGY 2001; Chapter 6:Unit6.3. [PMID: 23045055 DOI: 10.1002/0471140856.tx0603s00] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
This unit provides methods for analyzing uptake in rat kidney proximal tubule cells and rat kidney cortical mitochondria, preparation of proximal tubule cells and cortical mitochondria, and HPLC analysis of glutathione and related compounds.
Collapse
Affiliation(s)
- L H Lash
- Wayne State University School of Medicine, Detroit, Michigan, USA
| |
Collapse
|
10
|
Kannan R, Bao Y, Wang Y, Sarthy VP, Kaplowitz N. Protection from oxidant injury by sodium-dependent GSH uptake in retinal Müller cells. Exp Eye Res 1999; 68:609-16. [PMID: 10328975 DOI: 10.1006/exer.1998.0639] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Glutathione (GSH) is known to play an important role in regulating oxidative damage to cells. The present study was initiated to examine the effect of exogenous GSH on oxidative injury in a retinal Müller cell line and to characterize GSH transport in these cells. Rat Müller cells (rMC-1) were incubated with varying concentrations of t-butylhydroperoxide (t-BHP) to induce oxidative stress, and cell viability was measured after addition of GSH. In other studies, kinetics of GSH uptake and Na+-dependency were examined by incubating cells with35S-GSH in Na+-containing and Na+-free buffers. GSH uptake was studied with GSH at concentrations varying from 0. 05-10 m m in NaCl buffer. In the presence of sodium, extracellular GSH provided protection against t-BHP-induced oxidant injury to rMC-1 cells; in contrast, the amino acid precursors of GSH did not have any effect on cell viability. GSH was taken up by rMC-1 cells in a concentration- and sodium-dependent manner. Kinetic studies revealed both a high affinity (Km approximately 0.31 m m) and low affinity Km( approximately 4.2 m m) component. Furthermore, GSH depletion had no significant effect on the rate of GSH uptake. The results show that physiological concentrations of GSH can protect Müller cells from oxidative injury. Both Na+-dependent and Na+-independent transport systems for GSH exist in Müller cells, and the Na+-dependent GSH transporter may be involved in the protective role of GSH.
Collapse
Affiliation(s)
- R Kannan
- Division of Gastrointestinal and Liver Diseases, University of Southern California School of Medicine, Los Angeles, CA, USA
| | | | | | | | | |
Collapse
|
11
|
Redzic ZB, Markovic ID, Vidovic VP, Vranic VP, Gasic JM, Duricic BM, Pokrajac M, Dordevic JB, Segal MB, Rakic LM. Endogenous nucleosides in the guinea-pig eye: analysis of transport and metabolites. Exp Eye Res 1998; 66:315-25. [PMID: 9533859 DOI: 10.1006/exer.1997.0424] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigates the transport of endogenous nucleosides and deoxynucleosides from the capillaries of the eye into the aqueous humour and the lens using the in situ vascular eye perfusion technique in the guinea-pig. The transport of [3H] adenosine and [3H] thymidine across the blood-aqueous barrier proved to be very rapid with a volume of distribution after 4 minutes perfusion reaching 11.9+/-3.0% and 9.93+/-1.1%, respectively. However, the transport of [3H] guanosine and [3H] cytidine was slower, with volumes of distribution reaching only 3.38+/-0.58% and 4.8+/-1.41%. The values for the entry of deoxyadenosine and deoxyguanosine were not significantly different from the values obtained for corresponding ribonucleosides (adenosine and guanosine) so that a change in the pentose sugar does not change the affinity of the nucleoside for the transport protein. Perfusion with a low sodium medium inhibited the transport of [3H] adenosine and [3H] thymidine into the aqueous humour. The presence of 800 nM NBTI also caused a decrease in adenosine transport into the aqueous humour, so that the volume of distribution after 2 minutes reached only 3.78+/-1.87%. These findings suggest that the transfer of adenosine across the blood-aqueous barrier has both concentrative and equilibrative components. The presence of 0.1 mM thymidine had no effect on the [3H] adenosine transport, whereas 0.1 mM of adenosine resulted in a marked decrease on the [3H] thymidine transport which suggests that the concentrative nucleotide transport is probably mediated by both cif and cit transport systems. The cellular uptake of nucleosides into the lens was very rapid and the volume of distribution of purine nucleosides was within the range of 30-50% whereas that for thymidine uptake was somewhat lower, reaching 20-30%. HPLC analysis of the eye structures in the guinea-pig showed that lens, vitreous body and the rest of the eye do not contain either free nucleosides or purine bases in detectable quantities, except for xanthine which was detected in aqueous humour at a concentration of 2.51+/-0.51 mM. However, serum of the anaesthetised guinea-pig did not contain xanthine in detectable amount so it seems that the metabolic degradation of the nucleosides in the guinea-pig eye progresses as far as xanthine, which is then accumulated in the aqueous humour.
Collapse
Affiliation(s)
- Z B Redzic
- Institute of Biochemistry, Faculty of Medicine, Belgrade, Yugoslavia
| | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Kannan R, Fernández-Checa JC, García-Ruiz C, Mackic JB, Zlokovic BV. Liver and lens glutathione and cysteine regulation in galactose-fed guinea pigs. Curr Eye Res 1997; 16:365-71. [PMID: 9134326 DOI: 10.1076/ceyr.16.4.365.10688] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
PURPOSE To study the mechanism of lenticular glutathione (GSH) depletion in galactose-fed guinea pigs, with particular reference to correlations between liver and lens GSH, precursor (cysteine) status and GSH synthetic capacities. METHODS Guinea pigs in the ad libitum-fed state were fed powdered guinea pig chow containing 50% galactose for 3 and 14-16 days. Plasma GSH and GSH levels in lens, liver and freshly isolated hepatocytes were determined. Maximal rates of GSH synthesis in liver and lens as well as steady state levels of precursor cysteine were also determined. In separate experiments, linear rate of 35S-cysteine uptake was studied in isolated hepatocytes from control and galactose-fed animals. Lens and liver GSH decreased significantly with galactose feeding. Hepatic GSH showed a dramatic decrease (approximately 83%) as early as day 3 whereas approximately 43% decrease was observed in lens. The maximal GSH synthetic rates (GSH-SR) in the whole lens and liver on days 3 and 14-16 were not different from those of controls. Steady-state levels of cysteine also decreased in both tissues with galactose feeding, and the magnitude of decrease was higher in the liver as compared to the lens. The rate of cysteine uptake in hepatocytes isolated from galactose-fed guinea pigs was significantly lower for the cysteine concentrations studied (10 microM to 1 mM) as compared to control uptake. The decreased steady-state liver GSH and cysteine levels in galactose-fed guinea pigs caused a significant decrease in plasma (and aqueous) GSH concentrations. CONCLUSIONS We concluded that the decrease in lens GSH due to galactose occurs without alterations in the capacity of GSH synthesis, in either lens or liver. It is suggested that decreased hepatic GSH, resulting in reduced plasma GSH levels due to decreased GSH efflux into plasma, may contribute to impairment in plasma to lens GSH transport with galactose. Thus, the functional role of recently identified lens GSH transporters, particularly that of Na(+)-dependent GSH transporter, in galactose-induced cataract formation will be worthy of investigation.
Collapse
Affiliation(s)
- R Kannan
- Division of Gastrointestinal and Liver Diseases, University of Southern California School of Medicine 90033, USA
| | | | | | | | | |
Collapse
|
13
|
Elliot PJ, Bartus RT, Mackic JB, Zlokovic BV. Intravenous infusion of RMP-7 increases ocular uptake of ganciclovir. Pharm Res 1997; 14:80-5. [PMID: 9034225 DOI: 10.1023/a:1012011618785] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
PURPOSE The ability of intravenous (i.v.) infusions of the bradykinin agonist, RMP-7, to permeabilize the blood-ocular barriers (BOB) to the antiviral agent ganciclovir was investigated in guinea-pigs. METHODS Different i.v. dosing regimens included pre-treatment with RMP-7 (0.2 microg/kg/min for 5 min) followed by either [3H]-ganciclovir (1 microCi/0.2 ml/min) alone, and/or co-infusion with RMP-7 and [3H]-ganciclovir. At specific times the animals were sacrificed, their eyes removed, and the retina and lens epithelium dissected and analyzed for the amount of radioactivity. RESULTS Using the ratio of tissue vs. integrated plasma radioactivity concentration, a two-fold increase in ganciclovir steady-state levels were observed in the retina as well as lens epithelium following RMP-7 pretreatment. Peak uptake effects were achieved with a 4.5 min ganciclovir infusion. Neither longer infusions of ganciclovir alone, nor co-infusions of RMP-7 and ganciclovir further enhanced the uptake effects. Kinetic analysis indicated that RMP-7 increased the rate of ganciclovir entry (K(IN)) in studied ocular tissues, while the efflux of drug (K(OUT)) was not affected by this treatment. Finally, ganciclovir retina:plasma ratios elevated by RMP-7 pre-treatment, remained higher than control ratios within 60 min following cessation of 4.5 min ganciclovir infusion. CONCLUSIONS These data offer further evidence that BOB and in particular the blood-retinal barrier can be permeabilized via bradykinin receptor stimulation. As the i.v. infusions of RMP-7 enhanced the retinal uptake of ganciclovir, it is suggested that a combination of RMP-7 and ganciclovir may provide a novel approach for treating cytomegalovirus retinis.
Collapse
Affiliation(s)
- P J Elliot
- Alkermes Inc., Cambridge, Massachusetts 02139, USA
| | | | | | | |
Collapse
|
14
|
Kaplowitz N, Fernández-Checa JC, Kannan R, Garcia-Ruiz C, Ookhtens M, Yi JR. GSH transporters: molecular characterization and role in GSH homeostasis. BIOLOGICAL CHEMISTRY HOPPE-SEYLER 1996; 377:267-73. [PMID: 8828817 DOI: 10.1515/bchm3.1996.377.5.267] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Considerable progress has been made in the last few years in the molecular identification and characterization of hepatic GSH transporter-associated polypeptides. We are now poised to determine their precise mechanisms of action and regulation at the transcriptional and post-translational level. It is also anticipated that molecular characterization of the mitochondrial GSH transporter and sodium GSH co-transporters will be accomplished in the near future. With this information, a more complete understanding of GSH/cysteine homeostasis can be achieved which can be applied to furthering the prevention and treatment of the diseases of oxidative stress, such as aging, HIV, cataract, atherosclerosis, cancer and alcoholic liver disease.
Collapse
Affiliation(s)
- N Kaplowitz
- USC Center for Liver Diseases, USC School of Medicine, Los Angeles, 90033-4581, USA
| | | | | | | | | | | |
Collapse
|