Human placental extract rescues hippocampal damage associated with cognitive impairment in diabetic male rats through antioxidative, anti-inflammatory, and neuromodulatory activities

Abstract

Memory and cognitive impairment have emerged as significant comorbidities associated with diabetes, yet effective treatment remains elusive. Various studies have shown that human placental extract (HPE) is rich in bioactive molecules that exhibit anti-inflammatory, antioxidant, anti-apoptotic, and immunomodulatory properties. However, the impact of HPE on memory and cognitive decline is not well understood. This study aimed to investigate the therapeutic effects of HPE on memory and cognitive dysfunction induced by streptozotocin (STZ) in rats, while also exploring the underlying mechanisms. To induce type 2 diabetes mellitus (T2DM), rats were first fed a high-fat diet for two weeks, followed by a single intraperitoneal injection of STZ (40 mg/kg body weight) and subsequently treated with HPE (20 mg/kg body weight per day) for 14 days. The results of our behavioral tests demonstrated that HPE significantly enhanced learning, memory, and cognitive function in rats subjected to STZ administration. Specifically, HPE increased the discrimination index in the novel object recognition test from a negative value in STZ rats to a positive value in treated rats and improved spontaneous alternation in the T-maze from 41.25 ± 8.25% to 74.50 ± 8.50%. Additionally, HPE notably improved serum levels of insulin, glucose, the homeostatic model assessment of insulin resistance (HOMA-IR), and lipid profiles compared to untreated diabetic rats. It also modulated oxidative stress markers, antioxidants, as well as pro-inflammatory cytokines and neurochemicals levels in hippocampal tissue, underscoring its antioxidant and anti-inflammatory properties. Notably, HPE treatment improved the neurological morphology of the hippocampus and reduced DNA damage. The percentage of tailed cells dropped from 25.67 ± 0.33 in diabetic rats to 13.67 ± 0.88 with HPE treatment. In summary, HPE exhibits neuroprotective effects and could serve as a promising therapeutic strategy for addressing neurodegenerative symptoms associated with T2DM in a rat model.

Keywords: Hippocampus; Natural therapeutic products; Neuroinflammation; Neurotransmitters; Oxidative stress; Type 2 diabetes mellitus.

Fig. 1

Behavioral assessment of cognitive function in different experimental groups (n = 4 rats/group). (A) Total exploration time (in seconds) of novel versus familiar object in the Novel Object Recognition Test (NORT). (B) Percentage of exploratory preference for the novel object. (C) Discrimination index indicating memory performance (negative values indicate impaired memory). (D) Percentage of spontaneous alternations in the T-maze test assessing spatial working memory. Data are expressed as mean ± SEM. Asterisks (*) in panel A indicate statistical significance at p ≤ 0.05. Different letters in panels B–D indicate statistically significant differences between groups (p < 0.05; ANOVA followed by LSD post hoc test). Groups sharing the same letter are not significantly different

Fig. 2

Metabolic parameters in different experimental groups (n = 4 rats/group). (A) Body weight. (B) Serum insulin levels. (C) Serum glucose levels. (D) HOMA-IR index. (E–H) Lipid profile including cholesterol, triglycerides, low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Values are presented as mean ± SEM. Different letters indicate statistically significant differences among groups within each parameter (p < 0.05; ANOVA with LSD post hoc test). Groups sharing the same letter are not significantly different

Fig. 3

Oxidative stress and inflammatory markers in the hippocampus across experimental groups (n = 4 rats/group). (A) Malondialdehyde (MDA). (B) Nitric oxide (NO). (C) Glutathione (GSH). (D–E) Antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). (F–H) Pro-inflammatory cytokines TNF-α, IL-1β, and IL-8. Data are expressed as mean ± SEM. Different letters indicate statistically significant differences between groups (p < 0.001; ANOVA with LSD post hoc test). Groups sharing the same letter are not significantly different

Fig. 4

Neurotransmitter levels and enzyme activities in the hippocampus (n = 4 rats/group). (A–D) Levels of acetylcholine (Ach), dopamine, GABA, and glutamate. (E–F) Activities of acetylcholinesterase (AchE) and monoamine oxidase (MAO). Values are shown as mean ± SEM. Different letters indicate statistically significant differences among groups (p < 0.001; ANOVA with LSD post hoc test). Groups sharing the same letter are not significantly different

Fig. 5

Evaluation of DNA damage in the hippocampus using the Comet assay (n = 3 rats/group). (A) Control group showing intact nuclei. (B) STZ group showing extensive DNA damage and comet tails. (C) STZ + HPE group showing reduced DNA damage. (D–E) Percentage of tailed versus untailed cells. (F–H) Quantification of DNA damage parameters (e.g., tail length, % DNA in tail, tail moment). Data are expressed as mean ± SEM. Statistical differences were determined using ANOVA followed by LSD post hoc test

Fig. 6

Histopathological changes in the rat hippocampus (n = 3 rats/group, H&E staining). (A–B) Normal hippocampal architecture in control group, the hippocampus consists of the Cornu Ammonis (CA) regions, including CA1, CA2, and CA3. The CA field is bordered on one side by the dentate gyrus (DG). The CA3 region displays three layers: the polymorphic layer (PM), pyramidal layer (PY), and molecular layer (M). Notably, both the M and PM layers contain sparsely distributed glial cells (indicated by red circles) and blood capillaries (bc), while the PY layer features large neurons with prominent vesicular nuclei (N) and nucleoli. (C–D) HPE group showing preserved the CA regions. (E–F) Diabetic group showing disrupted hippocampal architecture, pyknotic neurons (red arrows), and vacuolated cytoplasm. The M and PM layers contain an abundance of glial cells (red circles) and congested blood capillaries (bc). (G–H) STZ + HPE group showing improved structure with fewer abnormal cells. Few pyramidal cells display darkly stained nuclei and pericellular spaces (red arrows). Scale bars are defined within each panel