9-cis-retinoic acid improves sensitivity to platelet-derived growth factor-BB via RXRα and SHP-1 in diabetic retinopathy

Vitamin A and Diabetes

Recently, research data have shown that vitamin A (VA, retinol) as a micronutrient participates in the regulation of glucose and lipid metabolism. Since diabetes is a metabolic disease, it is imperative to reveal the relationship of VA and diabetes. This review was aimed to summarize the current understanding of VA and its metabolites in diabetes. Since April of 2020, the authors have searched the PubMed using key words and retrieved articles that focused on diabetes and VA or its metabolites. Based on the published data, it appears that the development of type 1 diabetes leads to reduction of blood VA level in human and animals, and increase of hepatic VA store in experimental animals. On the other hand, the mutual impacts of type 2 diabetes and VA intake and blood VA level on each other appear to be uncertain. Retinoic acid, the active metabolite of VA, has been studied extensively for the treatment of diabetic complications. The current data appear to indicate that the development of diabetes is associated with changes of VA metabolism. More carefully designed clinical and laboratory experiments are needed to reveal the impacts of diabetes on VA metabolism and the role of VA in the development and treatment of diabetes.

Role of platelet-derived growth factor in type II diabetes mellitus and its complications

Type 2 diabetes mellitus is a type of metabolic disorder characterized by hyperglycaemia with multiple serious complications, such as diabetic neuropathies, diabetic nephropathy, diabetic retinopathy, and diabetic foot. Platelet-derived growth factors are growth factors that regulate cell growth and division, playing a critical role in diabetes and its harmful complications. This review focused on the cellular mechanism of platelet-derived growth factors and their receptors on diabetes development. Furthermore, we raise some proper therapeutic molecular targets for the treatment of diabetes and its complications.

The relationship between mean platelet volume and diabetic retinopathy: a systematic review and meta-analysis

BACKGROUND

Diabetic retinopathy (DR) is one of the most common diseases causing blindness in the world, and most patients are already in advanced stage. Recent years, many studies reported mean platelet volume (MPV) may be associated with development of DR, but there was no consistent conclusion reached.

METHODS

Literature was retrieved by formally searching PubMed, Embase, Cochrane library and Scopus and by hand searching of reference lists of related articles. Finally, a total of 14 literatures included, and Review manager 5.3 and STATA 14.0 statistical software were utilized for processing.

RESULTS

Meta-analysis showed that MPV values in DR were significantly higher than health controls [SMD (95% CI) = 0.92 (0.60-1.24)] and type 2 diabetes mellitus without diabetic retinopathy (T2DM without DR) [SMD (95% CI) = 0.36 (0.19-0.53)]. Subgroup analysis indicated that MPV level in proliferative diabetic retinopathy (PDR) patients was higher than T2DM without DR patients [SMD (95% CI) = 0.48 (0.28, 0.68)], but this difference didn't appear in non-proliferative diabetic retinopathy (NPDR).

CONCLUSIONS

The study demonstrated that increased MPV level was significant associated with the development of DR, and it might reflect the severity of DR, which could be provided to monitor development and progression of DR clinically.

9-cis-retinoic acid elevates MRP3 expression by inhibiting sumoylation of RXRα to alleviate cholestatic liver injury

AIMS

Vitamin A and its metabolites has been found to be protective against cholestatic liver injury, but the exact underlying mechanisms involved in cholestatic liver injury remain unclear. The objective of this study was to determine the function and mechanisms of 9-cis-retinoic acid, the metabolite of vitamin A, in cholestatic liver injury.

METHODS

The bile duct ligated (BDL) mice were treated with 9-cis-retinoic acid by intravenous injection through the tail for 10 days. The liver function and histology were assessed in the matched group and experimental group. The expression of MRP3 in liver tissue was tested by qRT-PCR, Western blotting, and IHC. Effect of RXRα sumoylation on MRP3 expression was investigated at a cellular level. Influence of 9-cis-retinoic acid on RXRα sumoylation was also tested in cells.

RESULTS

Our findings showed that 9-cis-retinoic acid significantly decreases the serum ALT and AST level, alleviates hepatic necrosis of the BDL-mice. We also identified MRP3, an important protective hepatobiliary transporter in cholestasis, was elevated by 9-cis-retinoic acid in vivo and in vitro. 9-cis-retinoic acid weakened the sumoylation of RXRα, which promotes the cytoplasmic location of RXRα and lightens the interaction of RXRα and RARα. Inhibition of RXRα and RARα interaction increased MRP3 expression.

CONCLUSIONS

9-cis-retinoic acid alleviates cholestatic liver injury by elevating MRP3 expression through its mechanism of inhibiting sumoylation of RXRα.

Improvement of Human-Oral-Epithelial-Barrier Function and of Tight Junctions by Micronutrients

The oral epithelium represents a major interface between an organism and its external environment. Improving this barrier at the molecular level can provide an organism added protection from microbial-based diseases. Barrier function of the Gie-3B11-human-gingival-epithelial-cell-culture model is enhanced by the micronutrients zinc, quercetin, retinoic acid, and acetyl-11-keto-β-boswellic acid, as observed by a concentration-dependent increase in transepithelial electrical resistance and a decrease in transepithelial ¹⁴C-d-mannitol permeability. With this improvement of tight-junction (TJ)-barrier function (reduced leak) comes a pattern of micronutrient-induced changes in TJ claudin abundance that is specific to each individual micronutrient, along with changes in claudin subcellular localization. These micronutrients were effective not only when administered to both cell surfaces simultaneously but also when administered to the apical surface alone, the surface to which the micronutrients would be presented in routine clinical use. The biomedical implications of micronutrient enhancement of the oral-epithelial barrier are discussed.