Sulbactam: A β-Lactam Compound with Neuroprotective Effects in Epilepsy

Abstract

Background: The pathophysiology of epilepsy is characterized by increased neuronal activity due to an excess of the excitatory neurotransmitter glutamate and a deficiency in the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Epilepsy presents with seizures, neuronal loss, and hyperactivity in the subthalamic nucleus (STN). Astrocytes play a crucial role by absorbing extracellular glutamate through glutamate transporter-1 (GLT-1), thereby reducing neuronal excitation. Upregulating the expression of astrocytic GLT-1 is a promising therapeutic strategy for epilepsy. Sulbactam (SUL), a β-lactam antibiotic, has been demonstrated to exert neuroprotective effects by upregulating GLT-1 expression. Objectives: This study investigated the impact of SUL on neuronal and behavioral changes in epilepsy by using a pentylenetetrazol (PTZ)-induced rat model of epilepsy. Methods: Rats were treated with saline, SUL (50 and 150 mg/kg), or a combination of SUL and the GLT-1 blocker dihydrokainate (DHK) for 20 days. Subsequently, behavioral tasks were conducted to assess recognition, anxiety, and memory. Results: Histological analyses revealed that SUL ameliorated neuronal deficits, increased astrocytic GLT-1 expression, and reduced hyperactivity in the STN. Additionally, SUL promoted astrocyte proliferation, indicating a new dimension of its neuroprotective properties. However, the beneficial effects of SUL were prevented by DHK. Conclusions: This pioneering study highlights multiple benefits of SUL, including seizure suppression, increased GLT-1 expression, and astrocyte proliferation, underscoring its high potential as a treatment for epilepsy.

Keywords: astrocyte; cognitive function; epilepsy; glutamate; seizure; sulbactam.

Figure 1

Experimental timeline of PTZ-induced epilepsy model and sulbactam intervention. The study spanned 45 days and included five major phases. From day 1 to day 35, rats received daily intraperitoneal injections of pentylenetetrazol (PTZ) to induce kindling. Sulbactam was administered from day 25 to day 44 to evaluate its potential neuroprotective effects. Behavioral assessments—including novel object recognition, elevated plus maze, and passive avoidance test—were conducted between day 36 and day 41. Bromodeoxyuridine (BrdU) was injected from day 43 to day 44 to label proliferating cells. On day 45, animals were sacrificed for tissue collection and subsequent histological assay.

Figure 2

Effects of sulbactam (SUL) on behavior in the object recognition test in the pentylenetetrazol (PTZ)-induced kindling epilepsy rat model. *** p < 0.001, compared with the percentage of time spent exploring the old object. Data are presented as mean ± standard error of the mean (SEM).

Figure 3

Effects of SUL on latency to enter the dark box in the passive avoidance test in the PTZ-induced kindling epilepsy rat model. * p < 0.05 and ** p < 0.01, compared with the control + saline group. # p < 0.05, compared with the seizure + saline group. Data are presented as mean ± SEM.

Figure 4

Effects of SUL on behavior in the elevated-plus maze test in the PTZ-induced kindling epilepsy rat model. (A) Open arm time. (B) Number of closed-arm activities. *** p < 0.001, compared with the control + saline group. ## p < 0.01, compared with the seizure + saline group. Data are presented as mean ± SEM.

Figure 5

Effects of SUL on neuronal density in the hippocampus in the PTZ-induced kindling epilepsy rat model. (A–E) Coronal sections depicting Nissl stained cells in the medial CA3 (m–CA3) of the hippocampus for each group. Magnification, 100×; scale bar, 100 μm. The square in (F) denotes the region of m–CA3 used for measuring pyramidal neuron density. (G) Quantitative results (No./mm²). ** p < 0.01 and *** p < 0.001, compared with the control + saline group; ## p < 0.01, compared with the seizure + saline group. Data are presented as mean ± SEM.

Figure 6

Effects of SUL on the concentration of cytochrome c oxidase (COX) in the subthalamic nucleus (STN) in the PTZ–induced kindling epilepsy rat model. (A–E) Depiction of COX staining in the STN through representative coronal sections for each group. Magnification, 50×; scale bar, 200 μm. The square in (F) marks the region of STN used for measuring COX concentration. (G) Quantitative results of optical density. * p < 0.05 and *** p < 0.001, compared with the control + saline group; ### p < 0.001, compared with the seizure + saline group. Data are presented as mean ± SEM.

Figure 7

Effects of SUL on BrdU-positive cells in the hippocampal dentate gyrus (DG) in the PTZ-induced kindling epilepsy rat model. (A–E) Newly generated cells are indicated by BrdU labeling in representative coronal sections of each group. Magnification, 200×; scale bar, 100 μm. High-magnification insets (1000×) display BrdU-positive cells. The square in (F) indicates the DG area used for quantification. (G) Quantitative results (no). The red arrows in the figure point to new born cells. * p < 0.05, *** p < 0.001, compared with the control + saline group. Data are presented as mean ± SEM.

Figure 8

Effect of SUL on the density of astrocytes, GFAP-positive and GLT–1 expression in the hilus hippocampus in the PTZ-induced kindling epilepsy rat model. (A–E) Astrocytes are indicated by green GFAP labeling in representative coronal sections of each group. GLT–1 and pyramidal cells are shown in red and blue, respectively. Magnification, 200×; scale bar, 100 μm. The square in (F) indicates the hilus area used for quantification of astrocytes. (G) Quantitative results of astrocytes and GLT–1-positive astrocytes (No./mm²), respectively. * p < 0.05 and ** p < 0.01, compared with the control + saline group; ### p < 0.001, compared with the seizure + saline group. Data are presented as mean ± SEM.