At A Glance
- Use of proton pump inhibitors (PPIs) in the elderly population to treat GERD can increase incidence of osteoporosis, infections, and electrolyte abnormalities.
Use of PPIs to treat GERD in patients with AMD has potential risk and should be used cautiously.
Other drug classes, such as H2 receptor antagonists, should also be considered as adjunct treatment for GERD and as a means to reduce PPI exposure burden.
As average life expectancy continues to increase, the number of people with age-related macular degeneration (AMD) is predicted to more than double by 2050.1 AMD is the leading cause of irreversible central vision loss and affects more than 2 million Americans.2 As people age, they are also more susceptible to acid-related gastrointestinal disorders such as gastroesophageal reflux disease (GERD),3 which is typically treated with a proton pump inhibitor (PPI). However, use of PPIs in the elderly population has been shown to be problematic because they can increase the incidence of osteoporosis, infections, and electrolyte abnormalities. Some small studies have shown that use of PPIs in patients with advanced AMD can cause development of Charles Bonnet syndrome (CBS), a condition leading to visual hallucinations (see Charles Bonnet Syndrome Quick Facts).4 Other literature has shown that PPIs can interfere with the function of lysosomes,5 which are organelles responsible for waste product degradation in the retinal pigment epithelium (RPE).6 Disruption in functions of the RPE can contribute to the formation of yellow deposits called drusen that are associated with increased risk of developing AMD.7
The pathophysiology of PPIs in patients with AMD, however, is still unclear. This article attempts to raise awareness of the potential complications associated with PPI use in patients with AMD.
SPOTLIGHT ON LYSOSOMES
The retina contains photoreceptors, rods and cones, which are responsible for vision in low light and color vision, respectively.8 These photoreceptors are structured as stacked membranes, with the distal tips of their outer segments contacting the RPE. One of the functions of the RPE is to phagocytose the photoreceptor outer segments and break them down through lysosomes.6,7 These organelles maintain an acidic environment, with a pH value around 4.5 to 5.9,10
Aging is associated with a decline in lysosomal degradation.6 Additionally, the RPE is highly metabolically active; therefore, a high rate of autophagy is expected.6 As people age, not only will they have fewer lysosomes, but the existing lysosomes will have a higher work burden,7 which can lead to a buildup of excess biologic waste, such as lipofuscin and other undigested proteins. For this reason, the dysfunction in the lysosomal pathway is thought to be a risk factor for AMD.6
Sparrow et al found that lipofuscin and its component bis-retinoid N-retinylidene-N-retinylethanolamine (A2E) accumulated in the macula as residue from lysosomal degradation.10 A2E has been shown to cause cellular toxicity and is associated with blinding retinal diseases such as AMD. Sparrow and colleagues found that A2E had an affinity for acidic organelles (eg, lysosomes) and exhibited a detergent-like effect that disrupted the organelle’s membrane. De and Sakmar reported similar effects, in that A2E was detrimental to cells once above a critical concentration.11 These studies determined that A2E affected liposomal function, but the mechanism was unclear.
In 2004, a study by Bergmann et al revealed that lysosomes had severely impaired function due to reduced lysosomal acidification subsequent to inhibition of the H+ ATPase pump by A2E.12 The increase in intraliposomal pH leads to inhibition of lysosomal hydrolases and results in intracellular accumulation of undegraded material. The study was performed by loading cultured human RPE cells with various levels of A2E and measuring lysosomal phagocytic action on exogenous iodinated photoreceptor outer segments added to the culture medium.
PPIs and Lysosomal Function
PPIs may also interfere with the pH gradient needed for lysosomal function. Lysosomes use H+ ATPases to create a proton gradient, while proton pumps normally target H+/K+ ATPases in the parietal cells.13 However, research in oncology has found that H+/K+ ATPases aren’t completely specific for parietal cells only. A study by Liu et al found that PPIs also inhibit lysosomal enzyme function in other organs such as the spleen.5 This means that, through systemic absorption, PPIs may be able to reach RPE cells and contribute to the inhibition of lysosomal function there as well, although this requires further study.
The morbidity effects of long-term PPI use in other conditions is well known. For example, Yepuri et al found that esomeprazole impaired lysosomal function by increasing lysosomal pH.4 This led to accumulation of protein aggregates, which promoted vascular senescence in their experiment and may explain why PPI use increased cardiovascular morbidity and mortality.
A Connection to Alzheimer Disease?
The inhibition of lysosomal function by PPIs is also being studied as a risk factor that predisposes patients to Alzheimer disease. In fact, Fallahzadek et al hypothesize that the increase in pH has an effect on the degradation of fibrillar A beta.14
RISK OF CBS
Aside from the lysosomal inhibition by PPIs, there is another reason that PPIs should be avoided in patients with AMD. There have been studies that indicated an association with PPI use and CBS in patients who had AMD. Leandro et al found that, among patients with AMD, PPIs doubled the risk (15%) of CBS compared with patients who were not taking PPIs (7%) in a total population of 471 patients.15 The researchers believe that PPIs may block horizontal cell feedback to photoreceptors, which can lead to hallucinatory activity.
BETTER SAFE THAN SORRY
It is now known that inhibition of lysosomal pumps, whether through A2E or PPIs, leads to accumulation of intracellular waste.16 Because there is no treatment to prevent the buildup of A2E, we should not add to the burden by prescribing PPIs to patients with AMD to increase intraliposomal pH. In addition to the lysosomal pump inhibition, PPIs may also increase the risk of visual hallucinations in patients who already have AMD. For these reasons, it is important that over-the-counter PPIs not be used for more than 14 consecutive days. Further, this 14-day regimen should not be repeated more frequently than every 4 months. Other drug classes, such as H2 receptor antagonists, should also be considered in this patient population. Despite this knowledge, additional research is needed, specifically regarding how PPIs affect lysosomes in the RPE, to improve our understanding and to help clinicians be better informed in our recommendations.
- 1. Facts about age-related macular degeneration. National Eye Institute. nei.nih.gov/eyedata/amd. Accessed January 14, 2019.
- 2. Facts about age-related macular degeneration. National Eye Institute. September 2015. nei.nih.gov/health/maculardegen/armd_facts. Accessed January 14, 2019.
- 3. Zagaria M. PPIs: Consideration and resources for deprescribing in older adults. US Pharm. 2016;12(41):7-10. uspharmacist.com/article/ppis-considerations-and-resources-for-deprescribing-in-older-adults. Published December 16, 2016. Accessed January 14, 2019.
- 4. Yepuri G, Sukhovershin R, Nazari-Shafti TZ, Petrascheck M, Ghebre YT, Cooke JP. Proton pump inhibitors accelerate endothelial senescence. Circ Res. 2016;118(12):e36-42.
- 5. Liu W, Baker SS, Trinidad J, et al. Inhibition of lysosomal enzyme activities by proton pump inhibitors. J Gastroenterol. 2013;48(12):1343-1352.
- 6. Sinha D, Valapala M, Shang P, et al. Lysosomes: regulators of autophagy in the retinal pigmented epithelium. Exp Eye Res. 2016;144:46-53.
- 7. Wang AL, Lukas TJ, Yuan M, Du N, Tso MO, Neufeld AH. Autophagy and exosomes in the aged retinal pigment epithelium: possible relevance to drusen formation and age-related macular degeneration. PLoS One. 2009;4(1):e4160.
- 8. Mitchell C, Laties, A. Method for treatment of macular degeneration by modulating P2Y12 or P2X7 receptors. 2018. US Grant US8828966B2.
- 9. Spugnini EP, Citro G, Fais S. Proton pump inhibitors as anti vacuolar-ATPases drugs: a novel anticancer strategy. J Exp Clin Cancer Res. 2010;29:44.
- 10. Sparrow JR, Parish CA, Hashimoto M, Nakanishi K. A2E, a lipofuscin fluorophore, in human retinal pigmented epithelial cells in culture. Invest Ophthalmol Vis Sci. 1999;40(12):2988-2995.
- 11. De S, Sakmar TP. Interaction of A2E with model membranes. Implications to the pathogenesis of age-related macular degeneration. J Gen Physiol. 2002;120(2):147-157.
- 12. Bergmann M, Schütt F, Holz FG, Kopitz J. Inhibition of the ATP-driven proton pump in RPE lysosomes by the major lipofuscin fluorophore A2-E may contribute to the pathogenesis of age-related macular degeneration. FASEB J. 2004;18(3):562-564.
- 13. Strand DS, Kim D, Peura DA. 25 Years of proton pump inhibitors: a comprehensive review. Gut Liver. 2016;11(1):27-37.
- 14. Fallahzadek M, Borhani H, Namazi M. Proton pump inhibitors: predisposers to Alzheimer disease? J Clin Pharm Ther. 2010;35(2):125-126.
- 15. Leandro J, Beato J, Pedrosa A, et al. The Charles Bonnet syndrome in patients with neovascular age-related macular degeneration: association with proton pump inhibitors. Invest Ophthalmol Vis Sci. 2017;58(10):4138-4142.
- 16. Settembre C, Fraldi A, Medina DL, Ballabio A. Signals from the lysososome: a control centre for cellular clearance and energy metabolsim. Nat Rev Mol Cell Biol. 2013;14(5):283-296.