Analysis of serum undercarboxylated osteocalcin level in rats with type 2 diabetes mellitus and the correlation with cognitive impairment

Roles of osteocalcin in the central nervous system

BACKGROUND

Bone-derived protein osteocalcin, which has beneficial effects on brain function, may be a future research direction for neurological disorders. A growing body of evidence suggests a link between osteocalcin and neurological disorders, but the exact relationship is contradictory and unclear.

SCOPE OF REVIEW

The aim of this review is to summarize the current research on the interaction between osteocalcin and the central nervous system and to propose some speculative future research directions.

MAJOR CONCLUSIONS

In the normal central nervous system, osteocalcin is involved in neuronal structure, neuroprotection, and the regulation of cognition and anxiety. Studies on osteocalcin-related abnormalities in the central nervous system are divided into animal model studies and human studies, depending on the subject. In humans, the link between osteocalcin and brain function is inconsistent. These conflicting data may be due to methodological inconsistencies. By reviewing the related literature on osteocalcin, some comorbidities of the bone and nervous system and future research directions related to osteocalcin are proposed.

Study on Undercarboxylated Osteocalcin in Improving Cognitive Function of Rats with Type 2 Diabetes Mellitus by Regulating PI3K-AKT-GSK/3β Signaling Pathwaythrough medical images

This paper aims to clarify the effect of Undercarboxylated osteocalcin (ucOC) on cognitive function in rats with type 2 diabetes mellitus (T2DM). This research reviewed the cognitive function of 35 diabetic patients, 33 non-diabetic patients and the serum levels of Undercarboxylated osteocalcin (ucOC) in patients. What's more, we analyzed the correlation between serum ucOC levels and cognitive function. Diabetic rats were treated with high (30 μg·kg^-1·d^-1) and low (10 μg·kg^-1·d^-1) doses of ucOC to investigate its effects in regulating ucOC on blood lipid, blood glucose and cognitive function. We systematically detected the phosphorylation levels of cognitive level-related proteins (PI3K, AKT, and GSK/3β) in the hippocampus by Western Blot. Finally, PI3K-Akt pathway involved in regulating cognitive function in diabetic rats by ucOC was verified with AKT pathway inhibitor LY294002. MoCA score and serum ucOC levels were significantly reduced in patients with diabetes mellitus. ucOC could concentration-dose-dependently decrease the blood glucose and lipid levels, and improve glucose metabolism and weaken insulin resistance in diabetic rats (P < 0.001). In addition, escape latency in diabetic rats was significantly higher than that of normal rats in the Morris maze test, and ucOC dose-dependently shortened the escape latency in diabetic rats (all with P < 0.05). After using AKT pathway inhibitor, ucOC failed to shorten the escape latency in diabetic rats. In conclusion, this study explored the relevant mechanisms in inducing cognitive dysfunction of T2DM, suggesting the potential value of ucOC as a drug to improve cognitive dysfunction in patients with T2DM in clinical.

Role of NOD-Like Receptors in a Miniature Pig Model of Diabetic Renal Injuries

Activation of NOD-like receptor (NLR) signaling pathway can promote downstream cytokine and proinflammatory cytokines release, and inflammation induced by excess nutrients leads to renal metabolic injury. How the NLRs influence metabolic progress and then lead to the renal injury remains poorly investigated. Compared with rodents, minipigs are more similar to humans and are more ideal animal models for human disease research. In this study, we established a diabetic minipig model through a high-sugar and high-fat diet combined with streptozotocin (STZ) injection. Blood biological markers and renal pathological markers, expression of NLRP subfamily members (NLRP1 and NLRP3) and their downstream cytokines (precursors of IL-1β and IL-18 and mature forms of IL-1β and IL-18), expression of NLRC subfamily members (NLRC1, NLRC2, and NLRC5) and their downstream nuclear factor-κB (NF-κB) signaling pathway molecules (IKKβ, IκBα, and NF-κB p65), and inflammatory cytokines (TNF-α and interleukin-6 (IL-6)) were systematically evaluated. The expression of NLRP3 and its downstream cytokine signaling molecules, the precursors of IL-1β and IL-18, and the mature forms of IL-1β and IL-18 was significantly upregulated. The expression levels of NLRC1, NLRC2, and NLRC5 and activation of the downstream NF-κB pathway molecules phospho-IKKβ, phospho-IκBα, NF-κB p65, and phospho-NF-κB p65 were significantly increased. The TNF-α and IL-6 levels were significantly increased in diabetic pig kidneys. The TGF-β/Smad signaling molecules, TGF-β and P-SMAD2/3, were also increased. These results suggested that the metabolic inflammation activated by NLRs might play an important role in diabetic renal injuries.

Effect of visfatin on KATP channel upregulation in colonic smooth muscle cells in diabetic colon dysmotility

The mechanisms of diabetes-related gastrointestinal dysmotility remains unclear. This study aimed to investigate the effect and mechanisms of proinflammatory adipokine visfatin (VF) in the contractile dysfunction of diabetic rat colonic smooth muscle. Twenty Sprague-Dawley rats were randomly divided into control and type 2 diabetes mellitus groups. VF levels in the serum and colonic muscle tissues were tested, the time of the bead ejection and contractility of colonic smooth muscle strips were measured, and the expression of ATP-sensitive potassium (K_ATP) channels in the colonic muscle tissues was analyzed. In vitro, we tested VF's effects on intracellular reactive oxygen species (ROS) levels, NF-κB's nuclear transcription, K_ATP channel expression, intracellular Ca²⁺ concentrations, and myosin light chain (MLC) phosphorylation in colonic smooth muscle cells (CSMCs). The effects of NAC (ROS inhibitor) and BAY 11-7082 (NF-κB inhibitor) on K_ATP expression were also tested. Diabetic rats showed elevated VF levels in serum and colonic muscle tissues, a delayed distal colon ejection response time, weakened contractility of colonic smooth muscle strips, and increased K_ATP channel expression in colonic muscle tissues. VF significantly inhibited the contractility of colonic smooth muscle strips from normal rats. In cultured CSMCs, VF caused ROS overload, increased NF-κB nuclear transcription activity and increased expression of Kir6.1, eventually reducing intracellular Ca²⁺ levels and MLC phosphorylation. NAC and BAY 11-7082 inhibited the VF-induced Kir6.1 upregulation. In conclusion, VF may cause contractile dysfunction of CSMCs by upregulating the expression of the Kir6.1 subunit of K_ATP channels via the ROS/NF-κB pathway and interfering with Ca²⁺ signaling.

Mogroside IIe Ameliorates Cardiomyopathy by Suppressing Cardiomyocyte Apoptosis in a Type 2 Diabetic Model

Mogroside II_e is primarily present in the unripe fruit of Siraitia grosvenorii (Swingle) C. Jeffrey, and it is the predominant saponin component. The purpose of this study was to investigate the effects of mogroside IIe (MGE IIe) on myocardial cell apoptosis in diabetic cardiomyopathy (DCM) rats by establishing a high-sugar and high-fat diet–induced model of type 2 diabetes (T2D) in SD rats and a homocysteine (Hcy)-induced apoptotic model in rat H9c2 cardiomyocytes. The results showed that MGE IIe decreased the levels of fasting blood glucose (FBG), total cholesterol (TC), triglyceride (TG), and low-density lipoprotein (LDL) levels, but increased the levels of high-density lipoprotein (HDL) in the SD rat model. Furthermore, MGE IIe decreased the levels of lactate dehydrogenase 2 (LDH2), creatine phosphokinase isoenzyme (CKMB), and creatine kinase (CK), and improved heart function. Additionally, MGE IIe inhibited the secretion of interleukin-1 (IL-1), IL-6, and tumor necrosis factor-α (TNF-α), improved myocardial morphology, and reduced myocardial apoptosis in the SD rat model. Furthermore, MGE IIe inhibited the mRNA and protein expression of active-caspase-3, -8, -9, -12, and Bax and Cyt-C, and promoted the mRNA and protein expression of Bcl-2 in the SD rat model. Furthermore, MGE IIe suppressed homocysteine-induced apoptosis of H9c2 cells by inhibiting the activity of caspases-3, -8, -9, and -12. In conclusion, MGE IIe inhibits the apoptotic pathway, thereby relieving DCM in vivo and in vitro.

Improvement of cognitive function, glucose and lipid homeostasis and serum osteocalcin levels by liraglutide in diabetic rats

BACKGROUND

Glucose and lipid abnormalities, oxidative stress (OXS) and reduced brain-derived neurotrophic factor (BDNF) are involved in cognitive dysfunction in diabetes. Glucagon like peptide 1 (GLP1) receptors modulate glucose and lipid metabolism, cognitive function and serum osteocalcin. On the other hand, osteocalcin modulates cognitive function and glucose and lipid metabolism. This study investigated whether the GLP 1 agonist liraglutide improves cognitive function via modulation of serum osteocalcin and glucose and lipid metabolism.

METHODS

Effects of 4 weeks liraglutide treatment (100 µg/Kg/d and 300 µg/Kg/d) on changes in cognitive function and bone homeostasis, induced by high fat diet/low-dose streptozotocin (HFD-STZ), were determined in rats. Cognitive function was assessed using Morris water maze (MWM) test. Serum and bone biochemical parameters were determined.

RESULTS

Liraglutide dose-dependently improved cognitive function in diabetic rats (reduced escape latency, and increased time spent in target quadrant in MWM test, compared to diabetic control). Glucose and lipid abnormalities and the associated changes in serum BDNF and oxidative stress makers were improved. Serum BDNF and glutathione were significantly increased, whereas malondialdehyde level was reduced. Serum osteocalcin was significantly increased and correlated with improvement in cognitive dysfunction. Serum and bone receptor activator of nuclear factor κB ligand (RANKL)/osteoprotegerin ratios were significantly reduced by liraglutide treatment.

CONCLUSION

Improvement of cognitive dysfunction by liraglutide involves modulation of glucose and lipid metabolism and serum osteocalcin. GLP1 agonists may provide an alternative metabolic approach for cognitive dysfunction in diabetes.

Under-carboxylated osteocalcin regulates glucose and lipid metabolism during pregnancy and lactation in rats

PURPOSE

Under-carboxylated osteocalcin (UcOC), a bone-released hormone is suggested to regulate energy metabolism. Pregnancy and lactation physiological conditions that require high levels of energy. The current study attempts to examine whether UcOC is involved in regulating energy metabolism during these conditions using adult Wistar rats.

METHODS AND RESULTS

Insulin tolerance tests indicated insulin resistance during late pregnancy (day 19 of pregnancy; P19) and insulin sensitivity during early lactation (day 6 of lactation; L6). Gene expression analyses suggested that muscle glucose metabolism was downregulated during P19 and enhanced during L6. Concomitantly, circulatory UcOC levels were lower during pregnancy but higher during early lactation; the rise in UcOC levels was tightly linked to the lactation process. Altering endogenous UcOC levels pharmacologically with warfarin and alendronate in P19 and L6 rats changed whole-body insulin response and muscle glucose transporter (Glut4) expression. Glut4 expression can be increased by either UcOC or estrogen receptors (ERs), both of which act independent of each other. A high fat diet decreased UcOC levels and insulin sensitivity in lactating rats, suggesting that diet can compromise UcOC-established energy homeostasis. Gene expression of lipid metabolism markers and triglyceride levels suggested that UcOC suppression during early pregnancy is an essential step in maternal lipid storage.

CONCLUSION

Taken together, we found that UcOC plays an important role in energy homeostasis via regulation of glucose and lipid metabolism during pregnancy and lactation.