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Differential Transcriptomic Profiles Effected by Oil Palm Phenolics Indicate Novel Health Outcomes

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Differential Transcriptomic Profiles Effected by Oil Palm Phenolics Indicate Novel Health Outcomes

Soon-Sen Leow et al. BMC Genomics.

Abstract

Background: Plant phenolics are important nutritional antioxidants which could aid in overcoming chronic diseases such as cardiovascular disease and cancer, two leading causes of death in the world. The oil palm (Elaeis guineensis) is a rich source of water-soluble phenolics which have high antioxidant activities. This study aimed to identify the in vivo effects and molecular mechanisms involved in the biological activities of oil palm phenolics (OPP) during healthy states via microarray gene expression profiling, using mice supplemented with a normal diet as biological models.

Results: Having confirmed via histology, haematology and clinical biochemistry analyses that OPP is not toxic to mice, we further explored the gene expression changes caused by OPP through statistical and functional analyses using Illumina microarrays. OPP showed numerous biological activities in three major organs of mice, the liver, spleen and heart. In livers of mice given OPP, four lipid catabolism genes were up-regulated while five cholesterol biosynthesis genes were down-regulated, suggesting that OPP may play a role in reducing cardiovascular disease. OPP also up-regulated eighteen blood coagulation genes in spleens of mice. OPP elicited gene expression changes similar to the effects of caloric restriction in the hearts of mice supplemented with OPP. Microarray gene expression fold changes for six target genes in the three major organs tested were validated with real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and the correlation of fold changes obtained with these two techniques was high (R2 = 0.9653).

Conclusions: OPP showed non-toxicity and various pleiotropic effects in mice. This study implies the potential application of OPP as a valuable source of wellness nutraceuticals, and further suggests the molecular mechanisms as to how dietary phenolics work in vivo.

Figures

Figure 1
Figure 1
Physiology parameters of mice. (A) Body weights; n = 10. (B) Organ weights; n = 10. (C) Timeline of fluid intake; n = 2 cages (of 5 mice per cage). (D) Average daily fluid intake; n = 42 days. (E) Timeline of food intake, n = 2 cages (of 5 mice per cage). (F) Average daily food intake between week two to week three; n = 7 days. (G) Timeline of faecal output, n = 2 cages (of 5 mice per cage). (H) Average daily faecal output between week two to week three; n = 7 days. # P < 0.05 vs. Normal Diet + Distilled Water. Error bars indicate s.e.m.
Figure 2
Figure 2
OPP did not affect organ histology. Representative haematoxylin and eosin stained tissue slices from the three major organs in each group were viewed under a light microscope with a magnification of X200. (A) Liver. (B) Spleen. (C) Heart.
Figure 3
Figure 3
GenMAPPs showing functions and genes significantly changed by OPP in the liver. (A) Genes up-regulated in the liver fatty acid beta oxidation pathway. This GenMAPP represents an overview of three individual fatty acid beta oxidation GenMAPPs, and shows the up-regulation of fatty acid beta oxidation genes such as acetyl-CoA dehydrogenase (Acadl), acyl-CoA dehydrogenase (Acads) and hydroxyacyl-CoA dehydrogenases (Hadhb, Hadhsc). (B) Genes down-regulated in the liver cholesterol biosynthesis pathway. Note that the fold changes for most of the genes in this GenMAPP were negative, indicating down-regulation, even for genes which were not selected as significantly different based on the selection criteria used. Also note that Hmgcr which encodes for 3-hydroxy-3-methylglutaryl-CoA reductase, an enzyme inhibited by cholesterol-lowering statins, showed a negative fold change as well, although the value was not statistically significant.
Figure 4
Figure 4
Genes involved in the spleen blood coagulation network which were up-regulated by OPP. The up-regulation of various genes involved in blood coagulation such as those encoding Von Willebrand factor homologue (Vwf), P-selectin (Selp), various glycoproteins (Gp1ba, Gp1bb, Gp5, Gp6, Gp9) and thrombin receptors (F2rl2 and F2rl3), suggests a possible effect of OPP in clearing blood clots from the circulation via the spleen.
Figure 5
Figure 5
GenMAPPs showing functions and genes significantly changed by OPP in the heart. (A) Genes up-regulated and down-regulated in the heart tricarboxylic acid (TCA) cycle. Pdk4, which is involved in fuel selection in the heart by inhibiting pyruvate dehydrogenase and preventing the metabolic shift in ageing hearts from fatty acid beta oxidation towards glycolysis, was up-regulated, while other genes such as Mdh1, Shdb, Suclg1, Sucla2 and Dld were down-regulated. (B) Ucp3, a gene encoding an uncoupling protein which protects against mitochondrial oxidative damage by reducing the production of reactive oxygen species (ROS), was up-regulated, while other genes which encode adenine nucleotide translocators and proteins in Complex I, Complex II and Complex V in the electron transport chain were down-regulated.
Figure 6
Figure 6
Real-time qRT-PCR validation of microarray data analysis on the three major organs. (A) Gene expression fold changes of six target genes as determined by microarray and real-time qRT-PCR experiments. The direction and magnitude of fold changes obtained from the real-time qRT-PCR technique were comparable to those obtained from the microarray technique. # P < 0.05 for gene expression fold changes quantified by real-time PCR experiments as determined by two-tailed unpaired Student's t-test. (B) Correlation of gene expression fold changes between microarray and real-time qRT-PCR data. Validation of the microarray data via real-time qRT-PCR shows that correlation of fold changes obtained by these two gene expression profiling techniques was high with an R2 = 0.9653.

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