Structural changes in femoral bone microstructure of female rabbits after intramuscular administration of quercetin

Background

Quercetin is one of the best known flavonoids being present in a variety of fruits and vegetables. It has cardioprotective, anticarcinogenic, antioxidant, anti-inflammatory and antiapoptotic properties. Some studies suggest that quercetin has protective effects on bone. However, its influence on qualitative and quantitative histological characteristics of compact bone is still unknown. In our study, 12 clinically healthy five-month-old female rabbits were divided into four groups of three animals each. Quercetin was applied intramuscularly in various concentrations; 10 µg/kg body weight (bw) in the E1 group, 100 µg/kg bw in the E2 group, and 1000 µg/kg bw in the E3 group for 90 days, 3 times per week. Three rabbits without exposure to quercetin served as a control (C) group. Differences in femoral bone microstructure among groups were evaluated.

Results

Qualitative histological characteristics of compact bone differed between rabbits from the E1 and E2 groups. Primary vascular longitudinal bone tissue was not found in some areas near the endosteal surface due to increased endocortical bone resorption. In addition, periosteal border of rabbits from the E1 group was composed of a thicker layer of primary vascular longitudinal bone tissue than in the other groups. In all groups of rabbits administered quercetin, a lower density of secondary osteons was observed. Histomorphometrical evaluations showed significantly decreased sizes of the primary osteons’ vascular canals in individuals from the E1 and E2 groups. Secondary osteons were significantly smaller in rabbits from the E1, E2, E3 groups when compared to the C group. Cortical bone thickness was significantly increased in females from the E1 and E2 groups.

Conclusions

The results indicate that quercetin has not only a positive dose–response on qualitative and quantitative histological characteristics of the compact bone of female rabbits as it would be expected.

Quercetin-induced changes in femoral bone microstructure of adult male rabbits

Flavonoids are a group of plant metabolites with antioxidant effects. One of the most abundant flavonoids in the human diet is quercetin. It is found widely in fruits, vegetables and has a lot of beneficial effects on human health. Quercetin has a positive pharmacological effect on bone metabolism and it prevents the organism against bone loss. However, its impact on the size of basic structural units of the compact bone is still unknown. Therefore, the aim of present study was to investigate the impact of the quercetin on femoral bone microstructure in 5-month-old male rabbits. Five rabbits of Californian broiler line were randomly divided into two groups. In the experimental group (E group; n=3), animals were intramuscularly injected with quercetin at dose 1000 μg.kg-1 body weight (bw) for 90 days, 3 times per week. Two rabbits without quercetin administration served as a control group (C group). According to our results, intramuscular application of quercetin had an insignificant effect on cortical bone thickness in male rabbits. In these rabbits, changes in qualitative histological characteristics were present in the middle part of the compacta, where primary vascular longitudinal bone tissue was present and expanded there from the periosteum. Also, a lower number of secondary osteons was found in these animals. From the histomorphometrical point of view, significantly decreased sizes of primary osteons' vascular canals and secondary osteons (p <0.05) were found in rabbits administered by quercetin. Our findings indicate that subchronic administration of quercetin at the dose used in our study had considerable impact on both qualitative and quantitative histological characteristics of the compact bone in adult male rabbits.

Discovery of biaryl-4-carbonitriles as antihyperglycemic agents that may act through AMPK-p38 MAPK pathway

A series of functionalized biaryl-4-carbonitriles was synthesized in three steps and evaluated for PTP-1B inhibitory activity. Among the synthesized compounds, four biaryls 6a-d showed inhibition (IC50 58-75 μM) against in vitro PTP-1B assay possibly due to interaction with amino acid residues Lys120, Tyr46 through hydrogen bonding and aromatic-aromatic interactions, respectively. Two biaryl-4-carbonitriles 6b and 6c showed improved glucose tolerance, fasting as well as postprandial blood glucose, serum total triglycerides, and increased high-density lipoprotein-cholesterol in SLM, STZ, STZ-S and C57BL/KsJ-db/db animal models. The bioanalysis of 4'-bromo-2,3-dimethyl-5-(piperidin-1-yl)biphenyl-4-carbonitrile (6b) revealed that like insulin, it increased 2-deoxyglucose uptake in skeletal muscle cells (L6 and C2C12 myotubes). The compound 6b significantly up-regulated the genes related to the insulin signaling pathways like AMPK, MAPK including glucose transporter-4 (GLUT-4) gene in muscle tissue of C57BL/KsJ-db/db mice. Furthermore, it was observed that the compound 6b up-regulated PPARα, UCP2 and HNF4α, which are key regulator of glucose, lipid, and fatty acid metabolism. Western blot analysis of the compound 6b showed that it significantly increased the phosphorylation of AMPK and p38 MAPK and ameliorated glucose uptake in C57BL/KsJ-db/db mice through the AMPK-p38 MAPK pathway.