Effects of nateglinide and repaglinide administered intracerebroventricularly on the CA3 hippocampal neuronal cell death and hyperglycemia induced by kainic acid in mice

Crosstalk between Alzheimer's disease and diabetes: a focus on anti-diabetic drugs

Alzheimer's disease (AD) and Type 2 diabetes mellitus (T2DM) are two of the most common age-related diseases. There is accumulating evidence of an overlap in the pathophysiological mechanisms of these two diseases. Studies have demonstrated insulin pathway alternation may interact with amyloid-β protein deposition and tau protein phosphorylation, two essential factors in AD. So attention to the use of anti-diabetic drugs in AD treatment has increased in recent years. In vitro, in vivo, and clinical studies have evaluated possible neuroprotective effects of anti-diabetic different medicines in AD, with some promising results. Here we review the evidence on the therapeutic potential of insulin, metformin, Glucagon-like peptide-1 receptor agonist (GLP1R), thiazolidinediones (TZDs), Dipeptidyl Peptidase IV (DPP IV) Inhibitors, Sulfonylureas, Sodium-glucose Cotransporter-2 (SGLT2) Inhibitors, Alpha-glucosidase inhibitors, and Amylin analog against AD. Given that many questions remain unanswered, further studies are required to confirm the positive effects of anti-diabetic drugs in AD treatment. So to date, no particular anti-diabetic drugs can be recommended to treat AD.

Repaglinide Elicits a Neuroprotective Effect in Rotenone-Induced Parkinson's Disease in Rats: Emphasis on Targeting the DREAM-ER Stress BiP/ATF6/CHOP Trajectory and Activation of Mitophagy

Repaglinide, a meglitinide insulinotropic antidiabetic, was unraveled as a promising therapeutic agent for Huntington's disease by targeting the neuronal calcium sensor downstream regulatory element antagonist modulator (DREAM). However, its mechanistic profile in Parkinson's disease (PD) especially its impact on endoplasmic reticulum (ER) stress, mitophagy, and their interconnections is poorly elucidated. This study is the first to examine the neuroprotective potential of repaglinide in rotenone-induced PD in rats by exploring its effects on DREAM, BiP/ATF6/CHOP ER stress pathway, apoptosis, mitophagy/autophagy, oxidative stress, astrogliosis/microgliosis, and neuroinflammation. Male Wistar rats were randomly assigned to four groups: groups 1 and 2 received the vehicle or repaglinide (0.5 mg/kg/day p.o). Groups 3 and 4 received rotenone (1.5 mg/kg/48 h s.c) for 21 days; meanwhile, group 4 additionally received repaglinide (0.5 mg/kg/day p.o) for 15 days starting from day 11. Interestingly, repaglinide lessened striatal ER stress and apoptosis as evidenced by reduced BiP/ATF6/CHOP and caspase-3 levels; however, it augmented striatal DREAM mRNA expression. Repaglinide triggered the expression of the mitophagy marker PINK1 and the autophagy protein beclin1 and alleviated striatal oxidative stress through escalating catalase activity. In addition, repaglinide halted astrocyte/microglial activation and neuroinflammation in the striatum as expressed by reducing glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor protein 1 (Iba1) immunostaining and decreasing interleukin (IL)-6 and IL-1β levels. Repaglinide restored striatum morphological alterations, intact neuron count, and neurobehavioral motor performance in rats examined by an open field, grip strength, and footprint gait analysis. Conclusively, repaglinide modulates the DREAM-ER stress BiP/ATF6/CHOP cascade, increases mitophagy/autophagy, inhibits apoptosis, and lessens oxidative stress, astrocyte/microglial activation, and neuroinflammation in PD.

Nateglinide Exerts Neuroprotective Effects via Downregulation of HIF-1α/TIM-3 Inflammatory Pathway and Promotion of Caveolin-1 Expression in the Rat's Hippocampus Subjected to Focal Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is a major cause of death and motor disabilities all over the world. It is a muti-factorial disorder associated with inflammatory, apoptotic, and oxidative responses. Nateglinide (NAT), an insulinotropic agent used for the treatment of type 2 diabetes mellitus, recently showed potential anti-inflammatory and anti-apoptotic effects. The aim of our study was to elucidate the unique neuroprotective role of NAT in the middle cerebral artery occlusion (MCAO)-induced stroke in rats. Fifty-six male rats were divided to 4 groups (n = 14 in each group): the sham-operated group, sham receiving NAT (50 mg/kg/day, p.o) group, ischemia/reperfusion (IR) group, and IR receiving NAT group (50 mg/kg/day, p.o). MCAO caused potent deficits in motor and behavioral functions of the rats. Significant increase in inflammatory and apoptotic biomarkers has been observed in rats' hippocampi. Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathway was significantly stimulated causing activation of series inflammatory biomarkers ending up neuro-inflammatory milieu. Pretreatment with NAT preserved rats' normal behavioral and motor functions. Moreover, NAT opposed the expression of hypoxia-inducible factor-1α (HIF-1α) resulting in downregulation of more inflammatory mediators namely, NF-κB, tumor necrosis factor-β (TNF-β), and the anti-survival gene PMAIP-1. NAT stimulated caveolin-1 (Cav-1) which prevented expression of oxidative biomarkers, nitric oxide (NO), and myeloperoxidase (MPO) and hamper the activation of apoptotic biomarker caspase-3. In conclusion, our work postulated that NAT exhibited its neuroprotective effects in rats with ischemic stroke via attenuation of different unique oxidative, apoptotic, and inflammatory pathways.

Intracerebroventricular Kainic Acid-Induced Damage Affects Blood Glucose Level in d-glucose-fed Mouse Model

We have previously reported that the intracerebroventricular (i.c.v.) administration of kainic acid (KA) results in significant neuronal damage on the hippocampal CA3 region. In this study, we examined possible changes in the blood glucose level after i.c.v. pretreatment with KA. The blood glucose level was elevated at 30 min, began to decrease at 60 min and returned to normal at 120 min after D-glucose-feeding. We found that the blood glucose level in the KA-pretreated group was higher than in the saline-pretreated group. The up-regulation of the blood glucose level in the KA-pretreated group was still present even after 1~4 weeks. The plasma corticosterone and insulin levels were slightly higher in the KA-treated group. Corticosterone levels decreased whereas insulin levels were elevated when mice were fed with D-glucose. The i.c.v. pretreatment with KA for 24 hr caused a significant reversal of D-glucose-induced down-regulation of corticosterone level. However, the insulin level was enhanced in the KA-pretreated group compared to the vehicle-treated group when mice were fed with D-glucose. These results suggest that KA-induced alterations of the blood glucose level are related to cell death in the CA3 region whereas the up-regulation of blood glucose level in the KA-pretreated group appears to be due to a reversal of D-glucose feeding-induced down-regulation of corticosterone level.