Neuroprotective effects of saxagliptin against radiation-induced cognitive impairment: Insights on Akt/CREB/SIRT1/BDNF signaling pathway

Radiation-induced cognitive impairment has recently fueled scientific interest with an increasing prevalence of cancer patients requiring whole brain irradiation (WBI) in their treatment algorithm. Saxagliptin (SAXA), a dipeptidyl peptidase-IV (DPP-IV) inhibitor, has exhibited competent neuroprotective effects against varied neurodegenerative disorders. Hence, this study aimed at examining the efficacy of SAXA in alleviating WBI-induced cognitive deficits. Male Sprague Dawley rats were distributed into control group, WBI group exposed to 20 Gy ϒ-radiation, SAXA group treated for three weeks with SAXA (10 mg/kg. orally, once daily), and WBI/SAXA group exposed to 20 Gy ϒ-radiation then treated with SAXA (10 mg/kg. orally, once daily). SAXA effectively reversed memory deterioration and motor dysfunction induced by 20 Gy WBI during behavioural tests and preserved normal histological architecture of the hippocampal tissues of irradiated rats. Mechanistically, SAXA inhibited WBI-induced hippocampal oxidative stress via decreasing lipid peroxidation while restoring catalase antioxidant activity. Moreover, SAXA abrogated radiation-induced hippocampal neuronal apoptosis through downregulating proapoptotic Bcl-2 Associated X-protein (Bax) and upregulating antiapoptotic B-cell lymphoma 2 (Bcl-2) expressions and eventually diminishing expression of cleaved caspase 3. Furthermore, SAXA boosted hippocampal neurogenesis by upregulating brain-derived neurotrophic factor (BDNF) expression. These valuable neuroprotective capabilities of SAXA were linked to activating protein kinase B (Akt), and cAMP-response element-binding protein (CREB) along with elevating the expression of sirtuin 1 (SIRT-1). SAXA successfully mitigated cognitive dysfunction triggered by WBI, attenuated oxidative injury, and neuronal apoptosis, and enhanced neurogenesis through switching on Akt/CREB/BDNF/SIRT-1 signaling axes. Such fruitful neurorestorative effects of SAXA provide an innovative therapeutic strategy for improving the cognitive capacity of cancer patients exposed to radiotherapy.

Glucagon-like peptide-1 attenuates diabetes-associated osteoporosis in ZDF rat, possibly through the RAGE pathway

Background

Diabetes-associated osteoporosis are partly caused by accumulation of advanced glycation endproducts (AGEs). Glucagon-like peptide-1 (GLP-1) has been shown to regulate bone turnover. Here we explore whether GLP-1 receptor agonist (GLP1RA) can have a beneficial effect on bone in diabetes by ameliorating AGEs.

Methods

In the present study, we evaluated the effects of the GLP-1 receptor agonist liraglutide, insulin and dipeptidyl peptidase-4 inhibitor saxagliptin on Zucker diabetic fatty rats. Meanwhile, we observed the effect of GLP-1 on AGEs-mediated osteoblast proliferation and differentiation and the signal pathway.

Results

Liraglutide prevented the deterioration of trabecular microarchitecture and enhanced bone strength. Moreover, it increased serum Alpl, Ocn and P1NP levels and decreased serum CTX. In vitro we confirmed that GLP-1 could attenuate AGEs-mediated damage in osteogenic proliferation and differentiation. Besides, GLP-1 down-regulated the ROS that caused by AGEs and the mRNA and protein expression of Rage .

Conclusions

Altogether, our findings suggest that GLP-1 receptor agonist promotes osteoblastogenesis and suppresses bone resorption on obese type 2 diabetic rats to a certain degree. The mechanism of these effects may be partly mediated by AGEs-RAGE-ROS pathway via the interaction with GLP-1 receptor.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05396-5.

ER Stress Amelioration by Saxagliptin Protects the Liver Against Fructose-induced Insulin Resistance

BACKGROUND/AIM

The study is aimed to demonstrate whether saxagliptin treatment may reduce endoplasmic reticulum (ER) stress, oxidative damage, and inflammation in the liver of fructose-induced insulin resistance (IR) rats.

MATERIAL AND METHODS

Twenty-eight rats were divided as control, IR, saxagliptin treatment (ST) and IR+ST groups. IR caused by fructose (10%) administration for 10 weeks and, ST was administered for 15 d. The liver tissues were obtained from rats. ER stress markers were analyzed using Real-Time PCR. Oxidative stress was measured. The inflammation in the liver was detected by the streptavidin-biotin immunostaining method.

RESULTS

The values of total oxidant/antioxidant status were the same between control and IR rats. The numbers of IL-6, NF-κB and PPARγ immune⁺ cells showed significant changes in the liver among four groups. The increased mRNA expression levels of ER stress and apoptosis markers as GRP78, PERK, IRE1α, ATF-4 and -6, CHOP, Caspase-3, -8, -9 and -12 in IR reduced with ST.

CONCLUSION

These findings indicate that saxagliptin treatment may ameliorate IR by reducing ER stress rather than inflammation and oxidative stress in the liver.

The protective effects of saxagliptin against lipopolysaccharide (LPS)-induced inflammation and damage in human dental pulp cells

Bacteria play a pivotal role in the pathological initiation and progression of pulpitis. Lipopolysaccharide (LPS) is recognized as a major component of the outer wall of Gram-negative bacteria. Saxagliptin, a potent inhibitor of dipeptidyl peptidase-4 (DPP-4), has been licensed for the treatment of type 2 diabetes. In this study, we aimed to evaluate the protective effects of saxagliptin against LPS-induced intracellular insults in human dental pulp cells (HDPCs). We found that DPP-4 is expressed in HDPCs. Interestingly, the expression of DPP-4 was increased in response to LPS treatment. We also found that saxagliptin ameliorated LPS-induced production of ROS and reduction of glutathione (GSH). Additionally, saxagliptin prevented LPS-induced mitochondrial dysfunction by increasing the levels of mitochondrial membrane potential (MMP) and the production of adenosine triphosphate (ATP). Importantly, saxagliptin ameliorated LPS-induced reduction of cell viability and lactate dehydrogenase (LDH) release. Our results indicate that saxagliptin significantly inhibited LPS-induced expression and secretions of tumour necrosis factor alpha (TNF-α), interleukin (IL)-1β and IL-6 in HDPCs. Mechanistically, we found that saxagliptin inhibited the phosphorylation of p38 and the activation of NF-κB. Our findings suggest that saxagliptin might have a potential therapeutic capacity for the treatment of pulpitis through mitigating inflammatory signalling in dental pulp cells.

Proteomic analysis of oxidized proteins in the brain and liver of the Nile tilapia (Oreochromis niloticus) exposed to a water-accommodated fraction of Maya crude oil

Crude oil (CO) is a super mixture of chemical compounds whose toxic effects are reported in fish species according to international guidelines. In the current study a proteomic analysis of oxidized proteins (ox) was performed on the brain and liver of Nile tilapia exposed to WAF obtained from relevant environmental loads (0.01, 0.1 and 1.0 g/L) of Maya CO. Results have shown that oxidation of specific proteins was a newly discovered organ-dependent process able to disrupt key functions in Nile tilapia. In control fish, enzymes involved on aerobic metabolism (liver aldehyde dehydrogenase and brain dihydrofolate reductase) and liver tryptophan--tRNA ligase were oxidized. In WAF-treated liver specimens, fructose-bisphosphate aldolase (FBA), β-galactosidase (β-GAL) and dipeptidyl peptidase 9 (DPP-9) were detected in oxidized form. oxDPP-9 could be favorable by reducing the risk associated with altered glucose metabolism, the opposite effects elicited by oxFBA and oxβ-GAL. oxTrypsin showed a clear adverse effect by reducing probably the hepatocyte capacity to achieve proteolysis of oxidized proteins as well as for performing the proper digestive function. Additionally, enzyme implicated in purine metabolism adenosine (deaminase) was oxidized. Cerebral enzymes of mitochondrial respiratory chain complex (COX IV, COX5B), of glycosphingolipid biosynthesis (β-N-acetylhexosaminidase), involved in catecholamines degradation (catechol O-methyltransferase), and microtubule cytoskeleton (stathmin) were oxidized in WAF-treated specimens. This response suggests, in the brain, an adverse scenario for the mitochondrial respiration process and for ATP provision as for ischemia/reoxygenation challenges. Proteomic analysis of oxidized proteins is a promising tool for monitoring environmental quality influenced by hydrocarbons dissolved in water.