Vitamin A and Daucus carota root extract mitigate STZ-induced diabetic retinal degeneration in Wistar albino rats by modulating neurotransmission and downregulation of apoptotic pathways

The Protective Effect of Topical PACAP38 in Retinal Morphology and Function of Type 2 Diabetic Retinopathy

The continuously growing diabetes population is a significant concern with type 2 diabetic retinal disease (T2DRD), which is a leading cause of permanent blindness. However, the underlying pathophysiological mechanism of T2DRD has not yet been fully understood. Pituitary adenylate cyclase-activating polypeptide (PACAP) was first isolated from the ovine hypothalamus based on its stimulating effect on the adenylate cyclase enzyme in anterior pituitary cells. PACAP38 (PACAP with 38 amino acids) activates anti-apoptotic pathways, inhibits pro-apoptotic signaling, and creates an anti-inflammatory environment in the retina. The aim of the present study was to test the possible retinoprotective effect of the topical administration of PACAP38 in a type 2 diabetic animal model induced by a high-fat diet and the intraperitoneally injected low-dose streptozotocin (STZ). Wistar rats were divided into four groups: the control, control + PACAP38, diabetes, and diabetes + PACAP38 groups randomly. Type 2 diabetes was induced with the combination of STZ (30 mg/kg) and a high-fat diet. All rats were treated topically two times a day for 16 weeks: the control + PACAP38 and diabetes + PACAP38 groups were applied with PACAP38 eye drops (1 µg/drop), while the control and diabetes groups were administered using vehicles (artificial tears). The diabetes model was validated by a fasting oral glucose tolerance test (OGTT) and C-peptide ELISA test. Animals were monitored during the whole experiment for the progression of the disease using electroretinography (ERG) and optical coherence tomography (OCT). Post-mortem immunohistochemistry and a vessel analysis were performed in the retina samples after 16 weeks. An OGTT, a C-peptide ELISA test, and the investigation of blood parameters proved the development of type 2 diabetes. Significant differences could be detected in visual function between the two diabetic groups at week 16 (in the a-wave, b-wave, and OP amplitudes), where the diabetes PACAP38-treated group was similar to the control ones. OCT measurements correlated with ERG data, where the total retinal thickness was preserved in the diabetes + PACAP38 group. PACAP38 also protected the microvascular structure in the retina. Topically administered PACAP38 has potent neuroprotective effects against type 2 diabetic retinal disease; therefore, it could be a promising therapeutic approach for the treatment of T2DRD.

Effect of madecassic acid on retinal oxidative stress, inflammation and Growth Factors in streptozotocin-induced diabetic rats

Diabetic retinopathy (DR) is the leading cause of blindness and visual loss in people with diabetes. It has been suggested that the progression of DR is associated with chronic inflammation and oxidative stress. The aim of the present work was to evaluate the ability of the natural compound madecassic acid (MEA) to reverse the negative impact of streptozotocin (STZ) on retinal injury in rats. Diabetic rats induced by STZ were treated with MEA at the doses of 10 and 20 mg/kg bw for 8 weeks. The study compared the efficacy of the drug in controlling high blood sugar levels and its impact on therapeutic targets such as SOD, CAT, GPx, NF-κB, TNF-α, IL-6, IL-1β, VEGF, IGF, bFGF and Keap1/Nrf-2 pathway. The results showed that the treatment with MEA significantly restored the retinal SOD, CAT, and GPx levels in diabetic rats to the near-normal levels. Moreover, the level of inflammatory mediators (TNF-α, IL-1β, IL-6) and growth factors (VEGF, IGF, bFGF) was significantly lower in retinas of animals treated with MEA as compared to retinas of diabetic animals. The study also established that MEA administration reduced the NF-κB protein and altered the Nrf-2/Keap1 pathway thereby reducing oxidative stress and inflammation. Furthermore, the use of MEA prevented the progression of the retinal capillary basement membrane thickening. It has been found that MEA offers significant protection to the retina and therefore, the compound may be useful in the treatment of DR in humans.

Medicinal Plants Used for Eye Conditions in Mexico-A Review

Medicinal plants have been historically significant for treating common human diseases in Mexico. Although some ethnobotanical research exists, limited ethnomedicinal data has documented medicinal plants employed for eye health. This review focuses on ethnomedicinal information and preclinical and clinical studies regarding medicinal plants used in Mexico for treating symptoms associated with eye conditions. An electronic database search was conducted by consulting scientific articles, books about Mexican herbal medicine, and academic theses. This work recorded 69 plant species belonging to 26 plant families, especially plants from the Crassulaceae family, which are used as remedies for irritation and infections in the eye. Eight of these medicinal plants have been the subject of preclinical studies using ocular models, and one medicinal plant has been tested in clinical trials. The evidence of pharmacological effects indicates the promising therapeutic potential of these medicinal plants for developing new treatments for eye conditions. However, toxicological studies are necessary to ensure safe application to the eye, particularly as traditional medicine continues to be relied upon worldwide. In addition, this review highlights the need to perform ethnobotanical and phytochemical studies in Mexico regarding the medicinal flora used as remedies for eye conditions.

18F-FP-CIT dopamine transporter PET findings in the striatum and retina of type 1 diabetic rats

PURPOSE

Noninvasive methods used in clinic to accurately detect DA neuron loss in diabetic brain injury and diabetic retinopathy have not been reported up to now. ¹⁸F-FP-CIT is a promising dopamine transporter (DAT) targeted probe. Our study first applies ¹⁸F-FP-CIT PET imaging to assess DA neuron loss in the striatum and retina of T1DM rat model.

METHODS

T1DM rat model was induced by a single intraperitoneal injection of streptozotocin (STZ) (65 mg kg^-1, ip). ¹⁸F-FP-CIT uptake in the striatum and retina was evaluated at 4 weeks, 8 weeks and 12 weeks after STZ injection. The mean standardized uptake value (SUVmean) and the maximum standardized uptake value (SUVmax) were analyzed. Western blot was performed to confirm the DAT protein levels in the striatum and retina.

RESULTS

PET/CT results showed that the SUV of ¹⁸F-FP-CIT was significantly reduced in the diabetic striatum and retina compared with the normal one from 4-week to 12-week (p < 0.0001). Western blots showed that DAT was significantly lower in the diabetic striatum and retina compared to the normal one for all three time points (p < 0.05). The results from Western blots confirmed the findings in PET imaging studies.

CONCLUSIONS

DA neuron loss in the striatum and retina of T1DM rat model can be non-invasively detected with PET imaging using ¹⁸F-FP-CIT targeting DAT. ¹⁸F-FP-CIT PET imaging may be a useful tool used in clinic for DR and diabetic brain injury diagnosis in future. The expression level of DAT in striatum and retina may act as a new biomarker for DR and diabetic brain injury diagnosis.

Redoxisome and diabetic retinopathy: Pathophysiology and therapeutic interventions

Diabetic retinopathy (DR) is a chronic microvascular complication of diabetes mellitus (DM). It is a worldwide growing epidemic disease considered to be the leading cause of vision-loss and blindness in people with DM. Redox reactions occurring at the extra- and intracellular levels are essential for the maintenance of cellular homeostasis. Dysregulation of redox homeostasis are implicated in the onset and development of DR. Thioredoxin1 (TRX1) and Thioredoxin2 (TRX2) are cytoplasmic and mitochondrially localized antioxidant proteins ubiquitously expressed in various cells and control cellular reactive oxygen species (ROS) by reducing the disulfides into thiol groups. Thioredoxin-interacting protein (TXNIP) binds to TRX system and inhibits the active reduced form of TRX through disulfide exchange reaction. Recent studies indicate the association of TRX/TXNIP with redox signal transduction pathways including activation of Nod-like receptor pyrin domain containing protein-3 (NLRP3) inflammasome, apoptosis, autophagy/mitophagy, epigenetic modifications in a redox-dependent manner. Thus, it is important to gain a more in-depth understanding about the cellular and molecular mechanisms that links redoxisome and ER/Mitochondrial dysfunction to drive the progression of DR. The purpose of this review is to provide a mechanistic understanding of the complex molecular mechanisms and pathophysiological roles associated with redoxisome, the TRX/TXNIP redox signaling complex under oxidative stress in the development of DR. Also, the molecular targets of FDA approved drugs and clinical trials in addition to effective antioxidant strategies for the treatment of diabetic retinopathy are reviewed.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.