Curcumin ZnO and MgO Nanoparticles Confer Protective Effects Against Ketamine-Induced Bipolar Disorder in Mice: Role of Brain-Derived Neurotrophic Factor

Abstract

Background:

Bipolar disorder (BD), or bipolar disease, is a prevalent psychiatric condition. Current treatment options are often ineffective, with numerous side effects. Brain-derived neurotrophic factor (BDNF) may be a potential biomarker for BD.

Materials and Methods:

Synthesized curcumin-conjugated ZnO nanoparticles (Cur-ZnO NPs) and curcumin-conjugated MgO nanoparticles (Cur-MgO NPs) were characterized by Fourier transform infrared, field emission scanning electron microscopy, (energy dispersive X-ray analysis (EDX), and ultraviolet-visible spectrophotometry. Behavioral changes in an open field test and the level of hippocampal BDNF were evaluated in a ketamine-induced manic-depressive-like behavior mouse model. Mice were treated intraperitoneal daily for 14 days. Control mice received saline; positive control mice received 25 mg/kg ketamine. Lithium (45 mg/kg), 5 mg/kg magnesium oxide (MgO), 5 mg/kg zinc oxide (ZnO), or 40 mg/kg curcumin was administrated in separates groups simultaneously with ketamine (25 mg/kg). Mice in the treatment group were given ketamine (25 mg/kg) plus Cur-MgO NPs or Cur-ZnO NPs (10, 20, or 40 mg/kg).

Results:

Both nanoparticles were chemically characterized. Both nanoparticles increased central square entries, time spent in the center zone, the rearing frequency, and ambulation distance in the ketamine-treated mice in the OFT. The hippocampal BDNF levels were also increased compared to the ketamine-treated mice.

Conclusion:

Cur-ZnO NPs and Cur-MgO NPs may be potential candidates for treating manic-depressive-like disorders.

INTRODUCTION

Bipolar disorder (BD) is a prevalent psychiatric disease,[1,2] defined by manic, hypomanic, and depressive episodes.[1,3] BD has been categorized into (1) type I (depressive and manic episodes: diagnosed with a history of one or more manic episodes); (2) type II (depressive and hypomanic episodes); (3) cyclothymic disorder (hypomanic and depressive symptoms outside the criteria for depressive episodes); and form to the diagnostic criteria for other three conditions.).[1,4,5] Defining symptoms of a manic episode are sleeplessness, hallucinations, psychosis, grandiose delusions, and/or paranoid rage.[5] Depressive episodes are more complex and more challenging to treat in people who have never experienced manias or hypomania.[5,6]

Brain-derived neurotrophic factor (BDNF) has been suggested as a possible target for managing symptoms of BDs because BDNF has been reported to be altered in this disorder.[7,8] Although several treatments are available, none have been fully effective, and each has its own unique side effects.[9,10] For these reasons, newer treatments based on new pharmaceutical technologies, including nanotechnology and herbal compounds with neuroprotective properties, have received attention.[11,12]

Turmeric, a flowering plant of the ginger family, Curcuma longa, has been prescribed as an indigenous medicine in Middle-Eastern and Asian countries for centuries (48–50). The yellow-colored curcumin, the primary active ingredient in turmeric,[13,14] has significant medicinal and pharmacological value.[15,16,17] The biological effects of curcumin are related to its anti-oxidant, anti-inflammatory, anti-apoptotic, and immunomodulatory activity.[18] The protective effects of curcumin on neurodegenerative and neuropsychiatric disorders have been evaluated in clinical and experimental studies.[19,20,21,22]

Nanotechnology is the manipulation of matter on an atomic, molecular, and supramolecular scale[23] and can create novel effects and materials with a range of applications.[23,24] Nanotechnology can potentially improve curcumin’s therapeutic effects, including its pharmacokinetics and pharmacodynamics properties.[25,26,27,28] Nanotechnology has revolutionized drug delivery, and in the context of treatment with curcumin, it provides the possibility of delivering such a nanoparticle to specific cells and tissue, such as the brain.[24,29]

Metal oxides of curcumin enhance its efficacy by increasing the water solubility and bioavailability of curcumin, thereby boosting its effectiveness while potentially decreasing toxicity.[30,31] ZnO and MgO, as metal nanomaterials, can be combined with curcumin.[32,33,34] However, the outcome of a nano combination of curcumin and bivalent cations such as Mg²⁺ and Zn²⁺ in treating central nervous system diseases has not been reported.[35,36,37] Thus, the aims of this research were to 1) synthesize Cur-ZnO NPs and Cur-MgO NPs and 2) evaluate the effects of Cur-ZnO NPs and Cur-MgO NPs in a mouse model of mania by determining behavior in an open field test and by measuring the hippocampal levels of BDNF.

MATERIALS AND METHODS

Materials

Magnesium nitrate hexahydrate (Mg (NO₃) ₂·6H₂O) and zinc nitrate hexahydrate (Zn (NO₃) ₂·6H₂O) (98% purity) were acquired from Sigma-Aldrich (St. Louis, MO, USA). Curcumin hydroxide and ethanol (HPLC grade) were purchased from Merck (Darmstadt, Germany). Ketamine, lithium, and all other chemicals and reagents were acquired from Sigma-Aldrich (St. Louis, MO, USA) and were analytical grade. Double-distilled H₂O (ddH₂O) was used for all solutions except ketamine, lithium, Cur-ZnO, and Cur-MgO, which were dissolved in normal saline.

Synthesis of Cur-MgO NPs and Cur-ZnO NPs

First, 5 mL of 0.1 M KOH and 50 mL of 0.5 M Mg (NO₃)₂·6H₂O or 50 mL of 0.5 M Zn (NO₃)₂·6H₂O solutions were prepared in ddH₂0. Next, curcumin (0.075 g) was added to 250 mL of ddH₂0. The curcumin solution was mixed, heated to 80°C, and maintained at a neutral pH until the curcumin was solubilized. The Mg (NO₃)₂·6H₂O 0.5 M solution or Zn (NO₃)₂·6H₂O 0.5 M solution was added to the solubilized curcumin solution. The yellow solution was heated at 85°C–90°C for 1 h, cooled to 4°C in an ice bath, and adjusted to 8.3 pH with 5 mL of 0.1 M KOH. The orange-yellow Cur-ZnO or Cur-MgO NPs were harvested after vacuum drying at room temperature.

Characterization of nanoparticles

Open capillary and a BUCHI 510 melting point device (Buchi Labortechnik AG, Switzerland) (uncorrected) were used for measuring melting points. The morphology of both nanoparticles was analyzed in a Zeiss Merlin SEM. The KBr pellet technique was used to measure the transmission of the powdered solids. The sample was washed with acetone in an ultrasonic bath. The sample was dried using compressed gas on a hot plate to form the powder for testing. After mixing the powder sample with powdered potassium bromide (KBr), it was pressed into pellet form by using a pellet die and then inserted into a pellet hold. A blank KBr pellet containing no sample corrected for light scattering losses in the pellet and moisture absorbed by KBr. A thin film of a conducting material was added to the sample surface. The mid-IR (4,000–400 cm⁻¹) region is where powdered alkali halides become transparent.

A Philips Powder Diffractometer (PW1373 goniometer, Cu Ka = 1.5406 Å) was used for X-ray diffraction. The scanning rate was in the 2Ø range, and the temperature was 10°C–80°C. A double-beam ultraviolet (UV) spectrophotometer (Hitachi, U-2900) confirmed the formation of nanoparticles. Field-emission scanning electron microscopy (FE-SEM) (Cam scan MV2300) recorded morphology and particle dispersion. The chemical composition of the nanostructures was evaluated by energy dispersive spectroscopy using scanning electron microscopy. FESEM-EDX confirmed the correlation between elemental composition and morphological changes. The Fourier transform infrared (FTIR) spectra were determined with pressed KBr pellets by using a Perkin Elmer FTIR instrument (Perkin Elmer, USA).

Stability of Cur-ZnO and Cur-MgO NPs

Because stability had previously been verified at pH 8.3 (26, 27), both nanoparticles were maintained at pH 8.3. Next, 5 mg of each nanoparticle was incubated in a 50 mL buffer of pH values between 2.0 and 10.0 at 37°C. The degradation kinetic of curcumin and its conjugates were monitored for 0–120 min and 0–24 h, respectively, between 350 and 600 nm.

In vivo study

Animals

In total, 96 male BALB/c mice weighing 25–30 g were obtained from the University of Medical Sciences, Iran, and transferred to the animal unit laboratory for 7 days before being randomly placed into experimental and control groups. Animals were housed in groups of six and had free access to pellet feed (Parsfeed Co, Tehran, Iran) and water.[38] Animals were monitored for signs of toxicity at 24 h and continuously during weeks 1 and 2.

Anti-bipolar role of Cur-MgO NPs

Forty-eight mice were treated as follows. Group 1 mice received 0.2 mL saline intraperitoneal (ip) once daily for 14 days; group 2 animals were given 25 mg/kg ketamine ip once daily for 14 days; group 3 mice were given 40 mg/kg curcumin and 25 mg/kg ketamine ip once daily for 14 days; groups 4–6 received ketamine (25 mg/kg ip) and Cur-MgO NPs (10, 20, or 40 mg/kg, ip) once daily for 14 days; group 7 mice were given 5 mg/kg MgO and ketamine (25 mg/kg) ip daily for 14 days; and group 8 mice were dosed with ketamine (25/mg/kg) and lithium (45 mg/kg) ip daily for 14 days. Six mice were allotted to each group.

Anti-bipolar role of Cur-ZnO NPs

Forty-eight mice were treated as follows. Group 1 mice received 0.2 mL saline ip once daily for 14 days; group 2 animals were given 25 mg/kg ketamine ip once daily for 14 days; group 3 mice were given 40 mg/kg curcumin and 25 mg/kg ketamine ip once daily for 14 days; groups 4–6 received ketamine (25 mg/kg ip) and Cur-ZnO NPs (10, 20, or 40 mg/kg, ip) once daily for 14 days; group 7 mice were given 5 mg/kg ZnO and ketamine (25 mg/kg) ip daily for 14 days; and group 8 mice were dosed with ketamine (25/mg/kg) and lithium (45 mg/kg) ip daily for 14 days. Six mice were allotted to each group.

After the open field behavioral test, animals were anesthetized with thiopental (50 mg/kg, ip), euthanized, and necropsied. After the brains were removed, the hippocampus was carefully separated to determine BDNF levels.[39]

Open field test

On day 15, locomotor changes and manic-like behavior were assessed.[40,41] OFT consisted of a box with black walls (120 cm × 120 cm × 50 cm) (Bionic-Mobin, Tehran, Iran) located in the dark behavioral testing room. Sixteen equally spaced squares were marked by white lines and a central red square on the bottom. The test chamber’s upper surface was lit by a 100-W lamp 110 cm above the ground. To capture behavior activity, a video camcorder (Hitachi, VM-7500LA Tokyo, Japan) was placed 2.1 m above the apparatus. Naïve animals (treated and controlled) were positioned in the central area. The following behaviors were measured: rearing number, ambulatory distance, number of center square entries, and time spend in the center square.[40,41] Autovision software, version 1.3 (Noldus Information Technology, Wageningen, The Netherlands) and Windows X software (California, USA) were used to analyze the data. Normal animals preferred the central square, while anxious animals stayed close to the walls during the 5-minute test duration.[40,41]

Evaluation of brain-derived neurotrophic factor

On the 17^th day, animals were anesthetized with thiopental (50 mg/kg, ip), euthanized, and necropsied. The hippocampus was isolated after the removal of the brain.[39] BDNF was measured using a commercial enzyme-linked immunosorbent assay (ELISA) kit with a sensitivity of less than 2 pg BDNF/mL (My BioSource Co. Catalog number MBS355435, San Diego, USA). According to the manufacturer, the intra- and inter-assay coefficients of variation for the test were <4% and <7%, respectively. Based on previous studies and our laboratory protocol, several steps in the process were altered, and solutions and reagents were purchased from different suppliers. These changes are described below.

Hippocampal tissue homogenization was conducted in a cold buffer solution (25 mM 4-morpholine propane sulfonic acid, 400 mM sucrose, 4 mM magnesium chloride (MgCl₂), and 0.05 mM EGTA, pH 7.3) The homogenized hippocampal sample was initially centrifuged for 12 min at 450 g, followed by a second centrifugation was at 12,000 g for 12 min. Samples were kept at 0°C. The hippocampal tissue was mixed with 200 uL HCL-Tris buffer and homogenized to lyse the tissue. The homogenized solution was centrifuged at 14,000 g for 30 min at 4°C. Fifty µL of the supernatant fluid was added to wells of 96-well plates, and 50 µL of diluent solution was added to each well. Samples were incubated on a shaker at 4°C–8°C. The wells were emptied and washed four times with the diluted washing solution. The secondary antibody (0.1 mL, Sinabiotech, Tehran, Iran) was added to each well and incubated for 3 h on a shaker at room temperature. After incubation with the secondary antibody, the wells were washed four times with the diluted washing solution, and 100 µL of diluted horseradish peroxidase (HRP)-Strep enzyme (DNAbiotech, Tehran, Iran) was added. The 96-well plates were placed on a shaker at room temperature for 1 h. Wells were washed four additional times. Next, 100 µL TMB (3,3′ 5,5′-tetramethylbenzidine) enzyme substrate (DNAbiotech, Tehran, Iran) was added to each well, and the plate was placed on a shaker at room temperature for 15 min. After 15 min, 100 µL of stopping solution (Solution Stop, DNA Biotech, Tehran, Iran) was added to each well (the color of the solution turns from yellow to blue when the reaction is stopped), and absorption was read in a microplate spectrophotometer at 450 nm. The absorption rate is proportional to the BDNF concentration, and the concentration of BDNF was calculated based on a standard curve. All samples were assayed in duplicate.

To assess BDNF concentration, an ELISA kit (BDNF Sandwich ELISA Kit. Rat BDNF ELISA Kit (ab213899), Boston, USA) was used. Protein quantification was achieved through the preparation of a BSA (Bovine Serum Albumin) standard curve (0.1–1.0 mg/mL).[42,43] Using the Bradford method, the protein concentration was determined at 630 nm.[43] The concentration of BDNF is reported as pg/mL of tissue solution.[44,45]

Statistical analysis

Data were analyzed using GraphPad PRISM v. 6 software (2016) (Graph Pad Company, San Diego, USA). The difference between all experimental groups was evaluated using one-way analysis of variance (ANOVA), and differences among groups (group-by-group comparisons) were assessed using Bonferroni’s post-hoc-test. The Kolmogorov-Smirnov test was employed to verify the normal distribution of continuous variables. The homogeneity of variances between two or more groups was assessed using Leven’s or Bartlett’s test. Results showed the normality of data and indicated that there was homogeneity of variances among the tested groups. The data from all experiments were analyzed using a one-way ANOVA F-test, and the mean ± standard error of the means (SEM) was calculated. P < 0.05 or P < 0.001 was considered significant. The number in parentheses after each experimental parameter is the F ratio followed by the P value.

RESULTS

Synthesis of Cur-ZnO NPs and Cur-MgO NPs

FT-IR spectral analysis

FT-IR spectral analysis of curcumin [Figure 1a] showed absorption bands at 1618 cm⁻¹ related to the overlapping stretching vibrations of alkenes (C = C) and carbonyls (C = O), and the bands at 1273 cm⁻¹ and 3200–3500 cm⁻¹ are attributed to the bending vibration of the ν(C-O) phenolic band and OH groups, respectively. The peaks at 1427 cm⁻¹ can be related to stretching C = C aromatics ring vibration (48).

Figure 1.

FTIR spectrum of (a) curcumin, (b) Cur-ZnO NPs, and (c) Cur-MgO NPs

The ν(C = O) peak of the free curcumin shifted from 1618 cm⁻¹ to 1600 cm⁻¹ in the IR spectra of the Cur-ZnO NPs and Cur-MgO NPs [Figure 1b and c]. The υ (OH) of the two phenolic groups in curcumin showed several bonds in the 3500 cm⁻¹ regions, but in both the Cur-ZnO NPs and Cur-MgO NPs spectra, the bonds were limited to 3425 cm⁻¹ and 3422 cm⁻¹ as broad bands, respectively. Moreover, peaks at 800–400 cm⁻¹ are assigned to υ (M-O) stretching frequency related to the bonding of Zn²⁺ and Mg²⁺ with oxygen. The FT-IR analysis suggested that ZnO and MgO have interacted with curcumin at its active sites [Figure 2] and that the synthesis of Cur-ZnO NPs and Cur-MgO NPs was successful.

Figure 2.

Structure of metal curcumin complex

UV-Vis spectrophotometer analysis

The UV-visible spectrum showed a maximum wavelength at 387 nm, representing the transition of zinc-aromatic oxygen. The maximum wavelength at 244 nm indicated the magnesium-aromatic oxygen transition in the Cur-MgO NP [Figure 3]. Because the substrate for both nanoparticles was the same (curcumin), similar spectra, as expected, were observed for both NPs.

Figure 3.

UV-visible spectra of Cur-ZnO NPs and Cur-MgO NPs

Morphological results from the FESEM and EDX analyses

The surface shape of both nanoparticles was examined using SEM. FESEM micrographs of the Cur-ZnO and Cur-MgO nanoparticles are shown in Figure 4a and b. ZnO and MgO particles were dispersed on the curcumin. The average size of the Cur-ZnO and Cur-MgO nanoparticles was 57 and 84 nm, respectively. Agglomeration was observed for both materials due to the strong interactions between individual nanoparticles.

Figure 4.

FESEM/EDX images of the surface morphology of the prepared nanoparticles and the average percentage of elements (a) Cur-ZnO NPs and (b) Cur-MgO NPs

The presence of Zn, Mg, O, and C elements was confirmed by EDX. The elemental mapping results indicated the maximum distribution of the main element of curcumin as oxides of zinc and magnesium. The average Zn, O, and C percentages in Cur-ZnO NPs were 14.6, 17.2, and 68.2, respectively [Figure 4a]. The average Mg, O, and C percentages in Cur-MgO NPs were 1.5, 16.2, and 82.3, respectively [Figure 4b]. Figure 5a and b show the dispersity of elemental content on the surface of the Cur-ZnO and Cur-MgO nanoparticles.

Figure 5.

MAP analysis of the elemental dispersion of (a) Cur-ZnO NPs and (b) Cur-MgO NPs

In vivo study

Open field test

Animals treated with ketamine (25 mg/kg) had a lower rate of central square entries; moreover, the mice spent less time in the central region and had lower rearing frequency and ambulation distance traveled compared to controls [Tables 1 and 2]. Curcumin (40 mg/kg) and lithium (45 mg/kg) inhibited the effect of ketamine-induced bipolar behavior as reflected in the increased frequency of central square entries, the time that was spent in the central area, rearing frequency, and ambulation distances (P < 0.05) [Tables 1and 2].

Table 1.

The effects of Cur-ZnO NPs on bipolar-like behavior in open field test in mice treated with 25 mg/kg of ketamine ip daily for 14 days

Group	Ambulation distance (cm)	Central square entries (number)	Time spent in central square (s)	Number of rearing
Control	34.00±0.56	19±2	18±1.1	34±1
Ketamine (25 mg/kg)	14.00±0.3a	6±1a	5.6±0.22a	21±0.16a
Ketamine + Curcumin (40 mg/kg)	18.00±0.25b	9±0.6b	10.1±0.96b	24±0.31b
Ketamine + Cur-ZnO NPs (10 mg/kg)	19.01±0.25b	11±5b	12±2b	29±0.91b
Ketamine + Cur-ZnO NPs (20 mg/kg)	22.01±0.19b&c	16±0.6b&c	14±1.9b&c	32±0.99b&c
Ketamine + Cur-ZnO NPs (40 mg/kg)	31.00±0.12b&c	17±1.1b&c	15±1.9b&c	33±1.1b&c
Ketamine + Zn (5 mg/kg)	14.00±2.00	6±2	7.1±2	20±4
Ketamine + lithium (45 mg/kg)	30.00±0.42b&c	18±1b&c	20±1b&c	33±2b&c

^aSignificant at P<0.05 vs. control group. ^bSignificant at P<0.05 vs. 25 mg/kg of ketamine. ^cSignificant at P<0.05 vs. 40 mg/kg of curcumin. Data are expressed as Mean±SEM (n=6)

Table 2.

The effects of Cur-MgO NPs on bipolar-like behavior in open field test in mice treated with 25 mg/kg of ketamine ip daily for 14 days

Group	Ambulation distance (cm)	Central square entries (number)	Time spent in central square (s)	Number of rearing
Control	36±0.69	17±1	16±1.46	32±0.81
Ketamine (25 mg/kg)	14±0.42a	4±0.58a	5.4±0.82a	20±0.23a
Ketamine + Curcumin (40 mg/kg)	17±0.31b	8±0.73b	9.25±0.82b	24±0.31b
Ketamine + Cur-MgO NPs (10 mg/kg)	17±0.19b	13±2b	11±1b	30±1.9b
Ketamine + Cur-MgO NPs (20 mg/kg)	20±0.14b&c	14±0.73b&c	12±2b&c	31±0.51 b&c
Ketamine + Cur-MgO NPs (40 mg/kg)	28±0.89b&c	15±2.1b&c	14±1.2b&c	32±1.9b&c
Ketamine + Mg (5 mg/kg)	11±1	5±3	5.1±1	18±3
Ketamine + lithium (45 mg/kg)	32±0.14b&c	19±1.53b&c	18±2b&c	32±1b&c

^aSignificant at P<0.05 vs. control group. ^bSignificant at P<0.05 vs. 25 mg/kg of ketamine. ^cSignificant at P<0.05 vs. 40 mg/kg of curcumin. Data are expressed as Mean±SEM (n=6)

Cur-ZnO NPs (10, 20, and 40 mg/kg) inhibited ketamine-induced behavioral changes, including increasing the frequency of central square entries, time spent in the central region, rearing frequency, and ambulation distances. These differences were statistically significant compared to the curcumin (40 mg/kg)-treated group at 20 and 40 mg/kg Cur-ZnO NPs (P < 0.05) [Table 1]. ZnO inhibited ketamine-induced behavioral changes, but the effect was not statistically significant compared to the control group [Table 1].

Cur-MgO NPs (10, 20, and 40 mg/kg) inhibited ketamine-induced behavioral changes in the open field test, where the frequency of central square entries, time spent in the central region, rearing frequency, and ambulation distances increased. These differences were statistically significant compared to the ketamine (25 mg/kg)-treated group (P < 0.05). These changes also were statistically significant compared to the curcumin (40 mg/kg)-treated group at 20 and 40 mg/kg (P < 0.05) [Table 2]. MgO inhibited ketamine-induced behavioral changes, but this effect was not statistically significant compared to the control group [Table 2].

Results of Cur-MgO NPs and Cur-ZnO NPs on brain-derived neurotrophic factor levels

Ketamine treatment decreased the hippocampal BDNF levels (P < 0.001) [Figure 6a and b]. The combination of ketamine and curcumin or ketamine and lithium induced a statistically significant increase in the levels of BDNF compared to the ketamine-only treated animals (P < 0.001) [Figure 6a and b]. Cur-MgO NPs and Cur-ZnO NPs suppressed the effect of ketamine, as shown by the increases in BDNF levels when compared to ketamine-only treated animals (P < 0.001) [Figure 6a and b]. MgO and ZnO inhibited ketamine-induced BDNF level reduction, although this effect was not statistically significant compared to the control group [Figure 6a and b].

Figure 6.

Effects of Cur-ZnO NPs and Cur-MgO NPs nanoparticle on ketamine-induced changes in the level of BDNF in the mouse hippocampus. Parts a and b indicate the effects of Cur-ZnO NPs and Cur-MgO NPs on BDNF levels, respectively. All data are expressed as Mean ± SEM (n = 6). *** P < 0.001 vs. control. ### P < 0.001 vs. Ketamine (25 mg/kg)

DISCUSSION

Treating BD is an enormous challenge.[46,47] Lithium, a mood-stabilizing drug, is a preferred treatment for acute manic episodes in bipolar patients[3,47]; however, due to its narrow therapeutic window and associated toxicity, lithium therapy has to be closely monitored.[3,48] Anticonvulsants (lamotrigine and valproate) are often used “off-label” to treat BD.[3,46] Psychiatrists have traditionally prescribed an antidepressant and a mood stabilizer when treatment with the mood stabilizer is ineffective. Antidepressants are also often ineffective in treating bipolar depression.[46] In addition to insufficient efficacy, the numerous side effects of these drugs limit current options even further.

Considering the serious mental dysfunction of BD, the time is ripe for novel treatment options that provide better efficacy and reduced side effects. Long-term ketamine administration disturbs motor activity and mood-related behavior in animal models[21,49] and humans.[50] Applying a nanomedicine strategy to herbal compounds with neuroprotective potential is an approach that has been suggested.[51,52] Curcumin[44,45,53] is an excellent candidate[21,54,55,56] because curcumin is known to inhibit ketamine-induced manic-depressive-like behavior.[3,47,48] In addition, previous work from our laboratory has reported the anxiolytic effects of curcumin in rodents.[24]

Targeted delivery has been recommended to reduce side effects while decreasing treatment expenses[23,57] Curcumin does not readily cross the blood-brain barrier.[25,57] Curcuminoid formulations, such as complexes with nanoparticles, should improve the pharmacokinetic barrier to the clinical use of curcumin[21,24,25,26,55] by increasing bioavailability and pharmacokinetic properties and reducing toxicity.[25,57,58] Mice treated with ketamine had a lower rate of central square entries, less time in the central region, lower rearing frequency, and decreased ambulation distance compared to the control group. Both Cur-MgO NPs and Cur-ZnO NPs inhibited the ketamine-induced manic-depression in our mouse model.

Acute administration of ketamine can act as an antidepressant, and following chronic administration can cause behavioral disturbances and induce psycho-affective like behavior in both humans and animals.[59,60,61] Results from our laboratory showed that prolonged administration of ketamine induced manic-depressive-like behavior in the open field test.[21,62]

In both BD and schizophrenia, the neurochemistry of the brain is disturbed.[63] Ketamine can induce oxidative damage by increasing lipid peroxidation, oxidative protein damage, and decreasing enzymatic defenses.[21,64,65] Since oxidative stress has been linked to manic depression, these findings may describe, at least in part, the mechanisms involved in ketamine-induced neurobehavioral changes.[21,64,65] However, the mechanism for ketamine-induced oxidative stress remains poorly understood.[21,64,65]

There are no published data on the pharmacological and clinical role of Cur-MgO NPs or Cur-ZnO NPs, and, for the first time, our data showed that both nanoparticles inhibited ketamine-induced behavioral changes.[66] They increased the frequency of central square entries, time spent in the central region, rearing frequency, and ambulation distances in ketamine-treated mice. This difference was statistically significant compared to the ketamine-treated group.

BDNF inhibits neural cell degeneration in neurobehavioral disorders.[67,68] BDNF levels are reduced in schizophrenia and bipolar diseases in humans and animals and may be a promising biomarker for such disorders.[67,69,70] The neurotrophic effect of curcumin on BDNF has been reported.[71,72,73,74] In our study, ketamine treatment markedly decreased hippocampal BDNF levels. In contrast, in mice treated with ketamine combined with curcumin or lithium, the BDNF levels were increased compared to ketamine-treated animals.

Although the role of Cur-MgO NPs and Cur-ZnO NPs on BDNF levels has not been reported, others have noted the neurotrophic role of curcumin in neuropsychiatric and neurodegenerative diseases.[16,71,75,76] Our rodent model showed that both Cur-MgO NPs and Cur-ZnO NPs suppressed ketamine-induced decreases in BDNF levels. In our research, MgO and ZnO decreased ketamine-induced BDNF levels, but the effect was not statistically significant, whereas ZnO or MgO complexed with curcumin as a nanoparticle significantly inhibited ketamine-induced BDNF levels in the mouse model, suggesting the potential of these two nanoparticles as possible candidates for managing ketamine-induced bipolar-like neurobehavioral changes.

One possible reason for the increase of BDNF by curcumin and its nanoparticles is the effect on kinase-related signaling pathways such as PKA (Protein Kinase A), CaMK (Ca2+/calmodulin-dependent protein kinase), MAPK (mitogen-activated protein kinase), AKT (Protein Kinase B), and CREB (cAMP-response element binding protein) transcription factors, the primary mechanism affected.[71,72,73,74] Our results suggested that curcumin nanoparticles can have beneficial effects by increasing the level of BDNF compared to curcumin alone because of their smaller size, resulting in increased delivery of nanoparticles to the brain.[77,78] The protective role of curcumin and its nanoparticles in anxiety disorders and bipolar behavior, as reflected in the Open Field Test, may also be due to the increase in BDNF.[79,80,81]

Although the role of Cur-MgO NPs and Cur-ZnO NPs has not been demonstrated in human BDs, based on our work in mice, Cur-MgO NPs and Cur-ZnO NPs may be potential treatments for bipolar and similar diseases in humans.[25,26] However, additional clinical studies are needed to confirm the translational value of this proposition.

CONCLUSION

Cur-ZnO and Cur-MgO nanoparticles were synthesized and evaluated for their effect against a mouse model of ketamine-induced BD. Cur-ZnO NPs and Cur-MgO NPs inhibited ketamine-induced behavioral disorders such as anxiety, depression, and motor activity disturbances observed in the open field test. Both nanoparticles also restored the hippocampal BDNF levels. Cur-ZnO NPs and Cur-MgO NPs were more potent than curcumin.[82,83,84,85,86] However, additional pharmacokinetics and safety information must be collected before these nanomaterials move into clinical trials.

Limitation

Although we did not use the zeta potential or PDI to determine the size of the nanoparticles, both nanoparticles were characterized using FTIR, UV-visible, FESEM, and EDX. Another limitation is the need for additional molecular and behavioral parameters to support and confirm the nanoparticles’ cellular and molecular mechanisms. We plan to conduct more chemical tests (zeta potential and PDI) on our nanoparticles and to undertake additional molecular and behavioral tests.

Ethics approval and consent to participate

All experimental procedures were approved by the animal use and care committee of the Masih Daneshvari Hospital, which is affiliated to the Shahid Beheshti University of Medical Sciences [Protocol and Ethical Code Number: I.R.SBMU.NRITLD.REC.1402.93].

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.