Pure, fresh, amber colored Ziziphus honey was selected for this study, which was obtained from the northern areas of Pakistan.
Isolation of honey proteins
Equal volume of honey and tris–HCL were mixed using magnetic stirrer for 5 min, then spun to remove pollens at 2500xg for 25 min at 4˚C. Supernatant was collected and its total volume was measured, while pellet was discarded. The quantity of ammonium sulfate to be used for 80% saturation of total protein was estimated, and added to the mixture slowly to precipitate honey at 0ºC. After complete dissolution, and after overnight incubation at 4ºC, the whole mixture was spinned at 8300xg at 4˚C for 20 min. The pellet was washed with Tris–HCl buffer solution by spinning at 3000xg for 25 min at 4˚C. Finally, the supernatant was carefully collected which contain the proteins, isolated from honey in a crude form. Protein was estimated using Bradford Assay [29, 30].
In vitro assays
The studies on cells from human blood were carried out after approval from an independent ethics committee, ICCBS, UoK,No: ICCBS/IEC-008-BC-2015/Protocol/1.0. in accordance with the declaration of Helsinki (1964) with the amendments of Tokyo (1975) and Edinburgh (2000). The cell lines used in the study were obtained from Bio bank facility PCMD, ICCBS, UoK.
Chemillumenescence Immunoassay for Quantifying Intracellular Reactive Oxygen Species (ROS)
The effect of honey and its crude isolated proteins on luminol-enhanced ROS production was quantified using human whole blood which was collected from healthy volunteers of 25–30 years of age [31]. 25 μL of whole blood (1:20 dilution in sterile Hanks Balanced Salt Solution, containing calcium chloride and magnesium chloride (Gibco, USA) was mixed with 25 μL of test samples and incubated for 10 min in luminoskan chamber (Luminoscan RS, Labsystem, Helsinki, Finland). Honey and its proteins were tested at various concentrations (honey at 3.12 μg/mL-100 mg/mL and protein at 0.4 -400 ng/mL). Blood cells were stimulated with addition of 25 μL of serum opsonized zymosan (Wako, China) and intracellular ROS production was detected by adding 25 μL of luminol (Alfa Aesar, Germany). Both activator and detector were added in positive controls while the negative control contained cells and detector only. The plate was placed in the luminoskan chamber and measurements for luminescence as RLU were taken for 50 min with repeated scan mode.
Nitric oxide assay
The effect of honey and its proteins on NO production was analyzed using mouse macrophage cell line, J774.2 (ECACC, UK). DMEM media (Sigma, USA) supplemented with 10% FBS (Sigma, Canada) and, 1% penicillin/streptomycin (Gibco, USA) was used to culture cells. Upon reaching 70–80% confluency, the cells were harvested using cell culture grade scrappers and centrifuged at 400xg for 6 min at 25 ͦC. The pellet was resuspended in 1 mL of media. Cells were counted in hemocytometer (Marienfeld, Germany) by trypan blue assay. 150 μL of 1 × 106 cells/mL was added along with different dilutions of honey and protein (honey 0.1–100 μg/mL and protein 0.4–400 ng/mL) and 30 μg/mL of LPS (Difco, USA) which was used as an activator. Plate was incubated for 48 h at 37ͦ C in 5% CO2. Griess Method was used to determine nitrite accumulates in the supernatant. The absorbance was read at 550 nm using spectrophotometer (Spectra Max plus 340) [32].
MTT cytotoxicity assay
MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay was performed as described by [33] to test in vitro cytotoxicity of honey proteins. NIH-3T3 and BJ (ATCC, Manassas, USA) were used for toxicity assay upon 75% confluence cells were harvested by trypsinization, pelleted at 400xg for 5 min at RT, and resuspended in 1 mL of DMEM. The cell count was adjusted to 6000 cells/well were seeded in 96 well flat bottom culture plates and incubated in 5% CO2 at 37ºC. After 24 h, media was removed. 50 μL/well of different dilutions (400 ng, 40 ng, 4 ng, 0.4 ng) of proteins were added in triplicates along with 150µL of DMEM (Sigma, USA). The control wells received 200 µL of media. The plate was incubated for 48 h in the CO2 incubator (NU 8700, Nauire Autoflow, Plymouth, USA) at 37ͦ C. The media was removed from wells and 50 μL of 0.5 mg/mL MTT dye (Amresco, USA) was added in each well with 150 μL of media. After 4 h incubation, MTT dye was removed and 100 \(\mu\)L of DMSO (Fisher Scientific, USA) was added in each well to dissolve formazan crystals. Absorbance was read at 540 nm using spectrophotometer. % Inhibition values at different concentrations of compounds were obtained by the formula, which were used to achieve concentration that showed 50% growth inhibition (IC50) by MS Excel based formula.
$$\%\;Inhibition=100\;-\;({OD}_{\;sample}\;-\;{OD}_{\;blank})/\;({OD}_{\;control}\;-\;{OD}_{\;blank})\;\times\;100$$
In vivo assays
Induction of diabetes in rats
Animal procedures were performed on male Wistar healthy rats. Total 42 rats were used in the study weighing 220–250 gms, with the approval of ethical committee of Dr. Panjwani Center for Molecular Medicine and Drug Research, International Center for Chemical and Biological Sciences (ICCBS) (Protocol number 2016–0040), in accordance with the ICCBS Animal care and Laboratory use, issued by (The National Academics, Washington, DC) and ARRIVE guide lines. Prior to induction of diabetes, the animals were fasted overnight and 55 mg/kg of STZ (dissolved in 0.1 M citrate buffer), was administered intraperitoneal (IP). After 1 week, fasting glucose was measured using glucometer by pricking tail vein. The animals, with blood glucose level of 200 mg/dL or higher were considered as diabetic and included in study.
Treatment protocol
Animals were randomly allocated into 7 groups with n = 6 in each group including; normal control receiving distilled water (NC), diabetic control receiving distilled water (DC), diabetic rats receiving honey (2 g/Kg) orally (HO), diabetic rats receiving honey (2 g/Kg) intraperitoneally (HI), diabetic rats receiving honey proteins (1 mg/Kg) orally (PO), diabetic rats receiving honey proteins (1 mg/Kg)intraperitoneally (PI) and diabetic rats receiving standard anti-inflammatory drug indomethacin intraperitoneally (IND) (2 mg/Kg) once daily for 4 weeks.
Sample collection
After one-month treatment, animals were anesthetized by intraperitoneal administration of (50 mg/kg) sodium pentobarbital for the collection of blood. The 8–10 mL of blood was collected from renal vein and animals were euthanized by cervical dislocation [58].
RNA isolation and cDNA synthesis for qRT-PCR
RNA from blood collected from animals was isolated with RNA isolation kit (Thermofisher Scientific, Waltham, US). RNA quantification was done using Thermo Scientific nanodrop 2000 spectrophotometer. 1000 ng/1 μg of RNA was used to synthesize complementary DNA (cDNA) by using Revert Aid First Strand cDNA Synthesis Kit (Thermo Fisher scientific, US).
Quantitative real time polymerase chain reaction
To evaluate the immunomodulatory activity of honey and its isolated crude proteins, the expression analysis of various inflammatory genes carried out by using Maxima SYBR Green (Thermofisher scientific, United states) using Mx3000P QPCR System (Agilent Technologies, USA). Primers including Nuclear factor kappa B (NF- κB) forward primer 5'-CCCGAAATCAAAGACAAGGAGG-3', reverse primer 5'-CTGTGTTGGATTTAGTGGCTCC-3', Tumor necrosis factor alpha (TNF-α) forward primer 5'-CCACGTCGTAGCAAACCACCAAG-3', reverse primer 5'- CAGGTACATGGGCTCATACC-3', Caspase 1 forward primer 5'- GAGCTTCAGTCAGGTCCATCA-3', reverse primer 5'-TCTGAGGTCAACATCAGCTCC-3', Interferon-gamma (INF-γ) forward primer 5'-GCCCTCTCTGGCTGTTACTG-3', reverse primer 5'-CCAAGAGGAGGCTCTTTCCT-3', Interleukin 1 beta (IL-1β) forward primer 5'- AGGCTTCCTTGTGCAAGTGT-3', reverse primer 5'-ATCTTTTGGGGTCTGTCAGC-3', S100A8 forward primer 5'-TGCCCTCTACAGGGATGACT-3', reverse primer 5'- TCGAAGTTAATTGCGTTGTCA-3', and inducible nitric oxide synthase (iNOS) forward primer 5'- CAATAACCTGAAGCCCGAAG-3', reverse primer 5'- TCTGTGCTGAGAGTCATGGAG-3' and Hypoxanthine phosphoribosyl transferase 1 (HPRT) forward primer 5'-CTTTGCTGACCTGCTGGATT-3', reverse primer 5'-CCCGTTGACTGGTCATTACA-3' was used as a house keeping gene, were designed by obtaining the sequence from the website https://www.ensembl.org/index.html and submitted to BLAST at https://www.ncbi.nlm.nih.gov/ to check their specificity. All the primers were received from (Integrated DNA Technologies, Coralville, Iowa) in lyophilized form. They were reconstituted in nuclease free water. The thermal cycling conditions used were: 10 min at 95 °C for initial activation, for PCR amplification; denaturation at 95 °C for 30 s, annealing at 60 °C for 30 s and extension at 72 °C for 30 s, for 40 cycles. The relative fold change in gene expression in treatment group, compared with untreated control was calculated as 2−ΔΔCt method.
Statistical analysis
Statistical Analysis was performed using one-way ANOVA and Bonferroni post hoc test using IBM, SPSS, Statistics software, version 21. P-value less than 0.05, was considered as statistically significant.