Effects of cannabis and its components on the retina: a systematic review

Abstract

Purpose: Cannabis is the most prevalent drug in the world and its consumption is growing. Cannabinoid receptors are present in the human central nervous system. Recent studies show evidence of the effects of cannabinoids on the retina, and synthesising the results of these studies may be relevant for ophthalmologists. Thus, this review adopts standardised, systematic review methodology to investigate the effects of exposure to cannabis and components on the retina.

Methods: We searched five online databases for the combined terms for outcome (“retina”) and exposure (“cannabis”). Eligibility of studies were conducted by two independent reviewers, and risk of bias was assessed.

Results: We retrieved 495 studies, screened 229 studies, assessed 52 studies for eligibility, and included 16 studies for qualitative analysis. The cannabinoids most frequently investigated were delta-9-tetrahydrocannabinol (THC), abnormal cannabidiol, synthetic cannabinoid, and cannabidiol (CDB). The outcomes most studied were neuroretinal dysfunction, followed by vascular effects. The studies also included investigation of neuroprotective and anti-inflammatory effects and teratogenic effects.

Conclusions: This review suggests that cannabinoids may have an important role in retinal processing and function.     

Hippo/YAP信号通路在眼部作用的研究进展

Hippo-YAP通路在机体发育和疾病发生中均具有重要作用。Hippo-YAP通路的调节紊乱可能导致病理组织过度生长和肿瘤的进展；近年来研究发现，Hippo-YAP信号通路的异常调节可能与眼部疾病相关，如圆锥角膜、Sveinsson 脉络膜视网膜萎缩和视网膜变性等，本文就Hippo/YAP 在眼部作用的研究进展进行系统综述，为眼部疾病的治疗提供理论基础。     

补肾利水方联合玻璃体腔注射雷珠单抗治疗湿性年龄相关性黄斑变性临床研究

目的:观察补肾利水方联合玻璃体腔注射雷珠单抗治疗湿性年龄相关性黄斑变性(AMD)的临床疗效。方法:选取60例湿性AMD患者,按照随机数字表法分为治疗组和对照组,每组30例(眼数30只)。治疗组给予补肾利水方联合玻璃体腔注射雷珠单抗治疗,对照组单纯给予玻璃体腔注射雷珠单抗治疗。观察2组治疗前后最佳矫正视力、黄斑中心凹视网膜厚度和中医证候积分的变化。结果:治疗后,2组最佳矫正视力均较治疗前提高(P<0.05)。治疗组治疗3个月后最佳矫正视力优于对照组(P<0.05)。治疗后,2组黄斑中心凹视网膜厚度均较治疗前缩小(P<0.05);治疗组治疗3个月后黄斑中心凹视网膜厚度小于对照组(P<0.05)。治疗3个月后,2组各项中医证候积分均较治疗前降低(P<0.05),治疗组视物昏朦、视物变形、腰膝无力积分均比对照组降低更明显(P<0.05)。结论:补肾利水方联合玻璃体腔注射雷珠单抗治疗湿性AMD,可以提高患者的视力,缩小黄斑中心凹视网膜厚度,改善中医证候,疗效优于单纯玻璃体腔注射雷珠单抗治疗。     

Inhibition of inflammatory cells delays retinal degeneration in experimental retinal vein occlusion in mice

The role of microglia in retinal inflammation is still ambiguous. Branch retinal vein occlusion initiates an inflammatory response whereby resident microglia cells are activated. They trigger infiltration of neutrophils that exacerbate blood–retina barrier damage, regulate postischemic inflammation and irreversible loss of neuroretina. Suppression of microglia-mediated inflammation might bear potential for mitigating functional impairment after retinal vein occlusion (RVO). To test this hypothesis, we depleted microglia by PLX5622 (a selective tyrosine kinase inhibitor that targets the colony-stimulating factor-1 receptor) in fractalkine receptor reporter mice (Cx3cr1^gfp/+) subjected to various regimens of PLX5622 treatment and experimental RVO. Effectiveness of microglia suppression and retinal outcomes including retinal thickness as well as ganglion cell survival were compared to a control group of mice with experimental vein occlusion only. PLX5622 caused dramatic suppression of microglia. Despite vein occlusion, reappearance of green fluorescent protein positive cells was strongly impeded with continuous PLX5622 treatment and significantly delayed after its cessation. In depleted mice, retinal proinflammatory cytokine signaling was diminished and retinal ganglion cell survival improved by almost 50% compared to nondepleted animals 3 weeks after vein occlusion. Optical coherence tomography suggested delayed retinal degeneration in depleted mice. In summary, findings indicate that suppression of cells bearing the colony-stimulating factor-1 receptor, mainly microglia and monocytes, mitigates ischemic damage and salvages retinal ganglion cells. Blood–retina barrier breakdown seems central in the disease mechanism, and complex interactions between different cell types composing the blood–retina barrier as well as sustained hypoxia might explain why the protective effect was only partial.     

Physiological assessment of high glucose neurotoxicity in mouse and rat retinal explants

One of the tissues of the central nervous system most affected by diabetes is the retina. Despite a growing understanding of the biochemical processes involved in glucose toxicity, little is known about the physiological consequences of chronic high glucose (HG) on individual neurons and neuronal circuits. Electroretinogram recordings suggest that retinal bipolar cells (BCs), which filter and transmit photoreceptor output to the inner retina, are among the first cells affected by diabetic conditions, and may therefore serve as sensitive early biomarkers for incipient neuronal damage caused in diabetes. Here, we comparatively assessed retinal integrity, calcium responses, and the electrophysiological profiles of specific BC types of mouse and rat organotypic retinal explants after 1 to 3 weeks in tissue culture, under moderate glucose (MG) and HG conditions. While the retinal layers of both rodent species displayed a progressively reduced thickness in culture, BCs retained their electrophysiological profiles and remained morphologically identifiable for up to 2 weeks. Responses to glutamate and endogenous inhibitory responses were routinely observed, indicating that the retinal circuitry remained intact during this period. Significant physiological differences between MG and HG conditions were evident in calcium signals and in the time course of responses to glutamate, but the voltage-gated current profiles of BCs displayed only minor variations. Overall, rat retina appeared slightly more sensitive to HG levels compared with mouse. In conclusion, electrophysiological analysis of neuronal function in rodent retinal explants is useful for the study of early damage due to HG neurotoxicity.     

Systematic spatiotemporal mapping reveals divergent cell death pathways in three mouse models of hereditary retinal degeneration

Calcium (Ca²⁺) dysregulation has been linked to neuronal cell death, including in hereditary retinal degeneration. Ca²⁺ dysregulation is thought to cause rod and cone photoreceptor cell death. Spatial and temporal heterogeneities in retinal disease models have hampered validation of this hypothesis. We examined the role of Ca²⁺ in photoreceptor degeneration, assessing the activation pattern of Ca²⁺-dependent calpain proteases, generating spatiotemporal maps of the entire retina in the cpfl1 mouse model for primary cone degeneration, and in the rd1 and rd10 models for primary rod degeneration. We used Gaussian process models to distinguish the temporal sequences of degenerative molecular processes from other variability sources.In the rd1 and rd10 models, spatiotemporal pattern of increased calpain activity matched the progression of primary rod degeneration. High calpain activity coincided with activation of the calpain-2 isoform but not with calpain-1, suggesting differential roles for both calpain isoforms. Primary rod loss was linked to upregulation of apoptosis-inducing factor, although only a minute fraction of cells showed activity of the apoptotic marker caspase-3. After primary rod degeneration concluded, caspase-3 activation appeared in cones, suggesting apoptosis as the dominant mechanism for secondary cone loss. Gaussian process models highlighted calpain activity as a key event during primary rod photoreceptor cell death. Our data suggest a causal link between Ca²⁺ dysregulation and primary, nonapoptotic degeneration of photoreceptors and a role for apoptosis in secondary degeneration of cones, highlighting the importance of the spatial and temporal location of key molecular events, which may guide the evaluation of new therapies.