An in vitro study, using a colorimetric assay, demonstrated a Brazilian date fruit could inhibit angiotensin-converting enzyme activity, a potentially important target mediating blood pressure both in the pulmonary circulation and endothelial cells. Results from in vitro oxidant defense assays have been further supported by ex vivo and in vivo animal studies. These studies demonstrated positive effects of different date cultivars against a variety of toxicants that produce free radicals, including carbon tetrachloride, isoproterenol , cadmium, and from the oxidant-generating streptozotocin-induced diabetic rat model. The protective effects of dates against oxidative stress were attributed to improved activities of oxidant defense enzymes such as catalase , superoxide dismutase , glutathione peroxidase, glutathione reductase, and glutathione S-transferase, along with a significant reduction in malondialdehyde. Moreover, dates were demonstrated to diminish oxidative damage, inflammation and apoptosis in cardiac tissue of ISO-treated rats. Oral administration of lyophilized Ajwa date extract down regulated the expression of pro-inflammatory cytokines and apoptotic markers in injured Wistar rat heart tissue, further supporting the anti-inflammatory and anti-apoptotic potential of dates against ISO-induced myocardial damage. A more recent study investigated the possible cardioprotective effects of a nanopreparation mix of Ajwa date fruits and seeds on doxorubicin -associated cardiotoxicity in Wistar rats by studying hemodynamic, electrocardiological, and biochemical change. The results obtained suggest that rats pre-fed 1.4 g/kg of the preparation one hour before DOX infusion were protected from a significant elevation in left ventricular pressure observed in the control group.
In addition, pretreatment with the preparation prevented DOX-associated ischemia and increased the antioxidant capacity of reduced glutathione in cardiac tissue,blueberry package compared with the untreated group. Quantification of Ajwa pits and a mixture of Ajwa fruit/pits reported that the pits contained 47.4 g/kg of total flavonoids, while the mix of pits with fruits contained 23.8 g/kg of total flavonoids, including epicatechin-phloroglucinol and epicatechin.Extracts of high concentrations of phenolic and flavonoid compounds in four different varieties of dates exerted favorable effects in protecting and repairing tissue injury following myocardial infarction induced either by ISO or temporary ligation of the left anterior descending coronary artery in a rodent model via oxidant defense activities and mobilization of circulating progenitor cells from bone marrow and peripheral circulation. In this regard, oral pretreatment with date extracts for a period of 28 days prior to ISO injection significantly improved the state of MI compared to the control group. Elevated levels of glutathione, SOD, and CAT, and reduced levels of thiobarbituric acid reactive substances in heart tissue of rats were noted. A dose-dependent effect was evident in which 400 mg/kg had significantly greater effects compared to 200 mg/kg in most cases. Interestingly, following MI induction, compared to controls, date extracts significantly increased circulating levels of CD34 and CD133 positive progenitor cells that are involved in tissue repair. The quantity of total phenolics in the dry plant material varied from 21.53 ± 0.90 to 26.82 ± 0.92 mg GAEs/g and from 2.90 ± 0.13 to 4.92 ± 0.21 mg quercetin/g.A limited number of studies in animals has suggested beneficial effects of dates on plasma lipids. Golden Syrian hamsters fed a high cholesterol diet supplemented with 50% Khalas date pulp for 13 weeks showed significant decreases in plasma cholesterol, triglycerides and LDL-C compared to those consuming the high cholesterol diet alone.
Interestingly, the addition of dates to the high cholesterol diet significantly increased liver triglyceride levels compared to the high cholesterol diet alone. Although the mechanisms underlying this liver lipid-loading effect are not clear, fructose, which is present in dates, has been shown to stimulate hepatic triglyceride synthesis when consumed with a hypercaloric diet. Unfortunately, insufficient information was provided regarding the composition of the chow and high cholesterol diets , or how liver cholesterol and triglyceride concentrations were measured, limiting the interpretation of the reported effects. In another study, hyperlipidemia-induced albino male rats fed either 300 or 600 mg/kg body weight of Aseel date fruit suspension for eight weeks showed significant reductions in triglycerides and very low-density lipoprotein compared to the control group. Curiously, serum levels of cholesterol, LDL-C, HDL- cholesterol and the LDL-HDL ratio were also significantly decreased at the intake of 300 mg/kg but not at 600 mg/kg. Results from the animals receiving date intake at 300 mg/kg approached the same response as the positive control group receiving atorvastatin . While intriguing, these data must be interpreted with caution, since rodents have a different absorption, distribution, metabolism and excretion profile for lipids compared to humans. A search of English- and Arabic-language databases revealed two human studies on date intake. One is a pilot trial with ten healthy non-smokers consuming 100 g/day of either Medjool or Hallawi dates for four weeks in a crossover design with a four-week washout between groups. A significant 15% reduction in serum triglycerides with Hallawi dates was noted compared to baseline values. However, the baseline triglyceride levels for those who consumed Hallawi dates were considerably higher than that of the Medjool group, although the actual values are difficult to assess since they are only presented by a bar graph.
The study also noted that the intake of Hallawi, but not Medjool dates, significantly reduced markers of oxidative stress, as measured by the TBARS assay, the 2,20 -Azobis hydrochloride-induced serum lipid peroxidation method, and increased serum paraoxonase 1 aryl esterase activity, an enzyme necessary to protect serum lipoproteins from oxidation. The beneficial reductions in oxidative stress after consuming Hallawi, but not Medjool dates, could be related to the total phenolic concentration, which was significantly greater in the Hallawi dates by 20% to 31%. Although the major proportion of the soluble phenolics in both date varieties consisted of phenolic acids, only Hallawi dates contained a significant portion of catechins, which have been reported to exert potent oxidant defense actions. Differences in absorption, metabolism, and bio-activity of the different phenolic compounds in the two date varieties may also help explain the disparate outcomes. Unfortunately, the inclusion and exclusion criteria for participants was poorly defined, and no data were provided regarding whether a return to original baseline values were noted after the washout and crossover period. Due to the high fiber content of dates, which can alter gut micro-biome profiles, the influence of a carry-over effect from the intake of one date variety to the next must be considered. Future study designs would ideally include a separate, no-intervention control group as well as a parallel arm design, or ensure that the primary lipid outcome measures along with the gut micro-biome milieu at the start of the second intervention period returned to original baseline values. A second human study assessed the effects of the daily intake of three Khudary dates for 16 weeks among 100 Bahraini adults with diabetes and control group consuming no dates [n = 50]. This randomized, controlled, parallel-arm study trial reported a significant improvement in the date group in plasma cholesterol levels of approximately five percent from baseline, along with a trend for reduced LDL-C. However, the results did not reach statistical significance when thetreatment group was compared to the control group, suggesting that some of the reduction in cholesterol may have been due simply to participation in the project, independent of date intake. Other limitations include lack of details regarding the actual weight of dates provided,blueberry packaging and the overall macronutrient distribution and quantity of the diets. Taken together, the reports above suggest that dates can improve markers of cardiovascular health, particularly plasma lipid levels, indices of oxidative stress and inflammation, and circulating progenitor cells. These results are primarily from in vitro and animal models, which may be useful as pre-clinical models. Unfortunately, differences in study design, the amount and composition of dates or extracts tested, and lack of details about the control groups fail to provide specificity and limit the ability to draw conclusions about mechanisms and applications to humans. The selection of a control item is important when investigating cardiovascular effects of date products or extracts, because controls can have significant amounts of bio-active compounds that can potentially affect cardiovascular function. Polyphenols are among the most studied categories of dietary phytochemicals in relation to vascular health, and the subgroups of flavanols, anthocyanins and proanthocyanins have been of particular interest. Intake of flavanol- and PAC-rich foods and food extracts from strawberries, blueberries, and cocoa have demonstrated improvements in vascular markers that are associated with markers indicative of improved cardiovascular health. Several molecular mechanisms contribute to the physiological effects of flavanols, including enhancement of vasodilation through the induction of NO , free radical quenching , inhibitory effects on select prooxidants , and reduction in ET-1 activity.
Effects of dietary flavanols on markers of cardiovascular health have been discussed in detail elsewhere. Date cultivar and degree of ripeness are major determinants regarding their polyphenolic composition, as discussed above. Phenolic-acid and flavonol fractions isolated from Amari and Hallawi dates at the tamer stage were examined in vitro for antioxidant and antiatherogenic properties. The two fractions exhibited variable capacities to reduce ferric ions , scavenge radicals and inhibit LDL-C oxidation via TBARS and lipid peroxide assays, with the flavonol fractions showing the strongest effects. Only the flavonol fractions stimulated cholesterol removal from macrophages. The yields of isolated fractions in terms of µmol GAE per g fruit were considerably larger for Amari dates by approximately 10- and 3.5-fold for phenolic acids and flavonols , respectively. The two isolated fractions contained ferulic acid as a major component and comparably small amounts of coumaric acid, but differed considerably in the composition of their complementary set of phenolic acids. Amari dates contained primarily caffeic acid derivatives, whereas the Hallawi variety contained mostly a salicylic acid derivative. Seven prominent peaks of flavonols were evident. Based on an authentic standard library, all seven flavonols were tentatively classified as kaempferol derivatives. The two isolated fractions of date flavonols differed considerably in composition. In addition to one prominent flavonol peak shared by the two fractions, Amari consisted of significant amounts of five other flavonols, whereas Hallawi contained a single unique flavonol as the major component. The results demonstrated strong structure-activity relationships for date polyphenols and identified date flavonols as potential antiatherogenic bio-actives. Polyphenols derived from date syrup at concentrations of 60 and 600 µg/mL, predominantly from cinnamic acid and catechin derivatives, were found to significantly attenuate IL-6, IL-8 and vascular endothelial growth factor in human vascular endothelial cells. These observations corresponded to asignificant reduction of both cyclooxygenase-2 and VEGF induced by TNF-α at both the protein and gene expression levels in the assessment of inflammatory-associated angiogenesis in HECVs. Many polyphenols found in dates have been studied as isolated compounds in in vitro and ex vivo systems with respect to their effects on markers of vascular function. Protocatechuic acid, a metabolite of the anthocyanin cyanidin-3-glucoside , and its phase II metabolites were effective in modulating the production of the key inflammatory mediators IL-6 and vascular cell adhesion molecule-1 at dietary-relevant concentrations as low as 100 nmol L−1 , with maximum reduction observed for the sulfate conjugates in human umbilical vein endothelial cells stimulated with either oxidized LDL or a cluster of differentiation CD40L . In the same study, C3G and its metabolites reduced IL-6 production in CD40L-stimulated cells, whereas both C3G and its metabolite, ferulic acid, reduced VCAM-1 production. Anthocyanins and ferulic acid have also been found to significantly reduce monocyte adhesion to HUVECs under physiologically relevant conditions, an important step in reducing atherosclerosis development. In human intestinal cells in vitro, the addition of a freeze-dried date extract from California-grown dates with a total proanthocyanidin content of 13% was demonstrated to act as a potent co-agonist ligand for the farnesoid x receptor , a nuclear structure important for maintaining triglyceride and cholesterol homeostasis. This study provides a potential mechanism by which dates may exert a hypotriglyceridemic effect, as observed in the human study noted above. The tea catechin, epigallocatechin- 3-gallate , has also been shown to modulate FXR in a tissue- and gene-specific manner. Further studies are warranted with dates and their extracts using both wild-type and FXR knockout mouse models. While the above in vitro work is promising, data from dietary interventions that specifically examine the association between circulating date polyphenols or phenolic metabolites with physiological effects have yet to be reported.