Relationship between aldose reductase enzyme and the signaling pathway of protein kinase C in an in vitro diabetic retinopathy model

Natural plant medications for the treatment of retinal diseases: The blood-retinal barrier as a clue

BACKGROUND

Retinal diseases significantly contribute to the global burden of visual impairment and blindness. The occurrence of retinal diseases is often accompanied by destruction of the blood‒retinal barrier, a vital physiological structure responsible for maintaining the stability of the retinal microenvironment. However, detailed summaries of the factors damage the blood‒retinal barrier and treatment methods involving natural plant medications are lacking.

PURPOSE

To comprehensively summarize and analyze the protective effects of active substances in natural plant medications on damage to the blood-retina barrier that occurs when retinal illnesses, particularly diabetic retinopathy, and examine their medicinal value and future development prospects.

METHODS

In this study, we searched for studies published in the ScienceDirect, PubMed, and Web of Science databases. The keywords used included natural plant medications, plants, natural herbs, blood retinal barrier, retinal diseases, diabetic retinopathy, age-related macular degeneration, and uveitis. Chinese herbal compound articles, non-English articles, warning journals, and duplicates were excluded from the analysis.

RESULTS

The blood‒retinal barrier is susceptible to high glucose, aging, immune responses, and other factors that destroy retinal homeostasis, resulting in pathological changes such as apoptosis and increased vascular permeability. Existing studies have shown that the active compounds or extracts of many natural plants have the effect of repairing blood-retinal barrier dysfunction. Notably, berberine, puerarin, and Lycium barbarum polysaccharides exhibited remarkable therapeutic effects. Additionally, curcumin, astragaloside IV, hesperidin, resveratrol, ginsenoside Rb1, luteolin, and Panax notoginseng saponins can effectively protect the blood‒retinal barrier by interfering with distinct pathways. The active ingredients found in natural plant medications primarily repair the blood‒retinal barrier by modulating pathological factors such as oxidative stress, inflammation, pyroptosis, and autophagy, thereby alleviating retinal diseases.

CONCLUSION

This review summarizes a series of plant extracts and plant active compounds that can treat retinal diseases by preventing and treating blood‒retinal barrier damage and provides reference for the research of new drugs for treating retinal diseases.

Relationship between Biochemical Pathways and Non-Coding RNAs Involved in the Progression of Diabetic Retinopathy

Diabetic retinopathy (DR) is a progressive blinding disease, which affects the vision and quality of life of patients, and it severely impacts the society. This complication, caused by abnormal glucose metabolism, leads to structural, functional, molecular, and biochemical abnormalities in the retina. Oxidative stress and inflammation also play pivotal roles in the pathogenic process of DR, leading to mitochondrial damage and a decrease in mitochondrial function. DR causes retinal degeneration in glial and neural cells, while the disappearance of pericytes in retinal blood vessels leads to alterations in vascular regulation and stability. Clinical changes include dilatation and blood flow changes in response to the decrease in retinal perfusion in retinal blood vessels, leading to vascular leakage, neovascularization, and neurodegeneration. The loss of vascular cells in the retina results in capillary occlusion and ischemia. Thus, DR is a highly complex disease with various biological factors, which contribute to its pathogenesis. The interplay between biochemical pathways and non-coding RNAs (ncRNAs) is essential for understanding the development and progression of DR. Abnormal expression of ncRNAs has been confirmed to promote the development of DR, suggesting that ncRNAs such as miRNAs, lncRNAs, and circRNAs have potential as diagnostic biomarkers and theranostic targets in DR. This review provides an overview of the interactions between abnormal biochemical pathways and dysregulated expression of ncRNAs under the influence of hyperglycemic environment in DR.

Key Therapeutic Targets to Treat Hyperglycemia-Induced Atherosclerosis Analyzed Using a Petri Net-Based Model

Chronic superphysiological glucose concentration is a hallmark of diabetes mellitus (DM) and a cause of damage to many types of cells. Atherosclerosis coexists with glucose metabolism disturbances, constituting a significant problem and exacerbating its complications. Atherosclerosis in DM is accelerated, so it is vital to slow its progression. However, from the complex network of interdependencies, molecules, and processes involved, choosing which ones should be inhibited without blocking the pathways crucial for the organism's functioning is challenging. To conduct this type of analysis, in silicotesting comes in handy. In our study, to identify sites in the network that need to be blocked to have an inhibitory effect on atherosclerosis in hyperglycemia, which is toxic for the human organism, we created a model using Petri net theory and performed analyses. We have found that blocking isoforms of protein kinase C (PKC)-PKCβ and PKCγ-in diabetic patients can contribute to the inhibition of atherosclerosis progression. In addition, we have discovered that aldose reductase inhibition can slow down atherosclerosis progression, and this has been shown to reduce PKC (β and γ) expression in DM. It has also been observed that diminishing oxidative stress through the inhibitory effect on the AGE-RAGE axis may be a promising therapeutic approach in treating hyperglycemia-induced atherosclerosis. Moreover, the blockade of NADPH oxidase, the key enzyme responsible for the formation of reactive oxygen species (ROS) in blood vessels, only moderately slowed down atherosclerosis development. However, unlike aldose reductase blockade, or direct PKC (β and γ), the increased production of mitochondrial ROS associated with mitochondrial dysfunction effectively stopped after NADPH oxidase blockade. The results obtained may constitute the basis for further in-depth research.

Rapid identification of chemical components in Xuelian granule by UHPLC-Q-orbitrap-HRMS based on enzyme activity in vitro

BACKGROUND

Xuelian granule (XL), a traditional Chinese medicine (TCM) formula, has been used for the treatment of diabetic nephropathy for a long time as a hospital preparation. Because the active ingredients in the XL that can help to treat diabetic nephropathy are still unclear, which limits the interpretation for its pharmacological mechanism, further development and subsequent study on the material basis of its efficacy.

METHODS

In this study, a screening method based on inhibition activity against aldose reductase (AR) was employed for activity-directed chemical analysis of XL using ultra-high performance liquid chromatography combined with quadrupole-orbitrap high resolution mass spectrometry (UHPLC-Q-orbitrap-HRMS) technique.

RESULTS

A total of 178 compounds, including 46 terpenes, 47 organic acids, 25 flavonoids, 29 phenylethanoid glycosides, and 31 other types, were tentatively identified from XL which might responsible for its AR inhibition activity.

CONCLUSION

This is the first study for a systematic, rapid, and accurate qualitative analysis of XL. This research provides a scientific and experimental basis for further researches on pharmacodynamics material basis and quality control of XL.

The role of ferroptosis in metabolic diseases

The annual incidence of metabolic diseases such as diabetes, non-alcoholic fatty liver disease (NAFLD), osteoporosis, and atherosclerosis (AS) is increasing, resulting in a heavy burden on human health and the social economy. Ferroptosis is a novel form of programmed cell death driven by iron-dependent lipid peroxidation, which was discovered in recent years. Emerging evidence has suggested that ferroptosis contributes to the development of metabolic diseases. Here, we summarize the mechanisms and molecular signaling pathways involved in ferroptosis. Then we discuss the role of ferroptosis in metabolic diseases. Finally, we analyze the potential of targeting ferroptosis as a promising therapeutic approach for metabolic diseases.

Response of a Human Lens Epithelial Cell Line to Hyperglycemic and Oxidative Stress: The Role of Aldose Reductase

A common feature of different types of diabetes is the high blood glucose levels, which are known to induce a series of metabolic alterations, leading to damaging events in different tissues. Among these alterations, both increased polyol pathway flux and oxidative stress are considered to play relevant roles in the response of different cells. In this work, the effect on a human lens epithelial cell line of stress conditions, consisting of exposure to either high glucose levels or to the lipid peroxidation product 4-hydroxy-2-nonenal, is reported. The occurrence of osmotic imbalance, alterations of glutathione levels, and expression of inflammatory markers was monitored. A common feature of the two stress conditions was the expression of COX-2, which, only in the case of hyperglycemic stress, occurred through NF-κB activation. In our cell model, aldose reductase activity, which is confirmed as the only activity responsible for the osmotic imbalance occurring in hyperglycemic conditions, seemed to have no role in controlling the onset of the inflammatory phenomena. However, it played a relevant role in cellular detoxification against lipid peroxidation products. These results, in confirming the multifactorial nature of the inflammatory phenomena, highlight the dual role of aldose reductase as having both damaging but also protecting activity, depending on stress conditions.

VEGF promotes diabetic retinopathy by upregulating the PKC/ET/NF-κB/ICAM-1 signaling pathway

Diabetic retinopathy (DR) is a common microvascular complication in patients with diabetes mellitus. DR is caused by chronic hyperglycemia and is characterized by progressive loss of vision because of damage to the retinal microvasculature. In this study, we investigated the regulatory role and clinical significance of the vascular endothelial growth factor (VEGF)/protein kinase C (PKC)/endothelin (ET)/nuclear factor-κB (NF-κB)/intercellular adhesion molecule 1 (ICAM-1) signaling pathway in DR using a rat model. Intraperitoneal injections of the VEGF agonist, streptozotocin (STZ) were used to generate the DR model rats. DR rats treated with the VEGF inhibitor (DR+VEGF inhibitor) were used to study the specific effects of VEGF on DR pathology and the underlying mechanisms. DR and DR+VEGF agonist rats were injected with the PKCβ2 inhibitor, GF109203X to determine the therapeutic potential of blocking the VEGF/PKC/ET/NF-κB/ICAM-1 signaling pathway. The body weights and blood glucose levels of the rats in all groups were evaluated at 16 weeks. DR-related retinal histopathology was analyzed by hematoxylin and eosin staining. ELISA assay was used to estimate the PKC activity in the retinal tissues. Western blotting and RT-qPCR assays were used to analyze the expression levels of PKC-β2, VEGF, ETs, NF-κB, and ICAM-1 in the retinal tissues. Immunohistochemistry was used to analyze VEGF and ICAM-1 expression in the rat retinal tissues. Our results showed that VEGF, ICAM-1, PKCβ2, ET, and NF-κB expression levels as well as PKC activity were significantly increased in the retinal tissues of the DR and DR+VEGF agonist rat groups compared to the control and DR+VEGF inhibitor rat groups. DR and DR+VEGF agonist rats showed significantly lower body weight and significantly higher retinal histopathology scores and blood glucose levels compared to the control and DR+VEGF inhibitor group rats. However, treatment of DR and DR+VEGF agonist rats with GF109203X partially alleviated DR pathology by inhibiting the VEGF/ PKC/ET/NF-κB/ICAM-1 signaling pathway. In summary, our data demonstrated that inhibition of the VEGF/ PKC/ET/NF-κB/ICAM-1 signaling pathway significantly alleviated DR-related pathology in the rat model. Therefore, VEGF/PKC/ET/NF-κB/ICAM-1 signaling axis is a promising therapeutic target for DR.

Genetic variants of ALR (-106C → T /-12C → G) and serum PKC-δ are associated with peripheral neuropathy in Egyptian diabetic patients with impaired handwriting

Purpose

Diabetic peripheral neuropathy can injure the hand median nerve and cause extensive nerve damage. PKC and ALR are associated with progression of diabetic complications. We hypothesized a genetic association between the ALR polymorphisms (-106C → T/-12C → G) and elevated serum PKC-δ levels in diabetic neuropathy and its adverse effects on handwriting in Egyptian population.

Methods

One hundred DPN were compared with 100 DP and 100 healthy volunteers. ALR -106C → T/-12C → G variants were studied using the PCR-RFLP method. A routine set of standard laboratory markers was determined. Serum PKC-δ concentration was determined by ELISA. Logistic regression analysis and areas under the receiver characteristic curves (AUCs) were evaluated to investigate the predictors of diabetic neuropathy. Arabic handwriting was analyzed based on the recognition of functional features, word shape, and ascending/descending parts of letters.

Results

Individuals carrying ALR-106C → C and -12G → G had a significantly higher risk of developing diabetic neuropathy than individuals with -106C → T and -12C → G genotypes (P = 0.01, P = 0.02). Carriers of the (-106C → T) CC and (-12C → G) GG genotypes had significantly increased serum levels of PKC-δ, FBG, TC, and LDL-c. PKC- δ serum levels were significantly correlated with glycemic and lipid indicators (P < 0.001). PKC-δ is a significant predictor of diabetes with or without neuropathy at a cutoff value of 16.6, sensitivity was 89%, and specificity 100%. All DPN showed complete deterioration of handwriting after the onset of diabetic neuropathy.

Conclusion

The genetic variants ALR-106C → C / -12G → G and PKC-δ in serum may help in the detection and treatment of diabetic neuropathy in Egyptian population before writing performance is affected.

Aldose Reductase: a cause and a potential target for the treatment of diabetic complications

Diabetes mellitus, a disorder of metabolism, results in the elevation of glucose level in the blood. In this hyperglycaemic condition, aldose reductase overexpresses and leads to further complications of diabetes through the polyol pathway. Glucose metabolism-related disorders are the accumulation of sorbitol, overproduction of NADH and fructose, reduction in NAD⁺, and excessive NADPH usage, leading to diabetic pathogenesis and its complications such as retinopathy, neuropathy, and nephropathy. Accumulation of sorbitol results in the alteration of osmotic pressure and leads to osmotic stress. The overproduction of NADH causes an increase in reactive oxygen species production which leads to oxidative stress. The overproduction of fructose causes cell death and non-alcoholic fatty liver disease. Apart from these disorders, many other complications have also been discussed in the literature. Therefore, the article overviews the aldose reductase as the causative agent and a potential target for the treatment of diabetic complications. So, aldose reductase inhibitors have gained much importance worldwide right now. Several inhibitors, like derivatives of carboxylic acid, spirohydantoin, phenolic derivatives, etc. could prevent diabetic complications are discussed in this article.

Potential effect of tropical fruits Phyllanthus emblica L. for the prevention and management of type 2 diabetic complications: a systematic review of recent advances

Phyllanthus emblica is a fruit widely consumed in subtropical areas, which is rich in polyphenols and other nutrients. There are increasing evidences that as a daily and nutritious fruit, it may have a positive role in controlling diabetic complications. According to the new study, its mechanisms include enhancing the functioning of insulin, reducing insulin resistance, activating the insulin-signaling pathway, protecting β-cells, scavenging free radicals, alleviating inflammatory reactions, and reducing the accumulation of advanced glycation end products. Owing to its few side effects, and low price, it should be easily accepted by patients and has potential for preventing diabetes. Taken together, Phyllanthus emblica may be an ideal fruit for controlling diabetic complications. This review highlights the latest findings of the role of Phyllanthus emblica in anti-diabetes and its complications, especially clarifies the molecular mechanism of the chemical components related to this effect, and prospects some existing problems and future research directions.