Corn Silk Tea for Hypertension: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

An Umbrella Insight into the Phytochemistry Features and Biological Activities of Corn Silk: A Narrative Review

Corn silk (Zea mays L.) is the stigma of an annual gramineous plant named corn, which is distributed in many regions worldwide and has a long history of medicinal use. In recent years, with the sustainable development of traditional Chinese medicine, studies of corn silk based on modern technologies, such as GC-MS, LC-MS, and other analytical means, have offered more comprehensive analyses. Phytochemistry studies have shown that the main bioactive components in corn silk include flavonoids, polyphenols, phenolic acids, fatty acids, and terpenoids. Pharmacological studies have shown that corn silk extract has various pharmacological effects, such as reducing blood lipids, lowering blood pressure, regulating blood sugar levels, anti-inflammatory effects, and anti-oxidation effects. In this paper, the related research on corn silk from the past few years is summarized to provide a theoretical reference for the further development and utilization of corn silk.

A novel heat-stable angiotensin-converting enzyme zinc-binding motif inhibitory peptide identified from corn silk

ETHNOPHARMACOLOGICAL RELEVANCE

Hypertension is the most common and chronic severe health problem globally. Corn silk (CS), the silky fibers of corn (Zea mays L.), has a long history of traditional usage as a remedy for edema and hypertension.

AIM OF THE STUDY

The aim of the study was to explore the underlying mechanism by which CS exerts its anti-hypertensive effects and investigate the presence of bioactive molecules in CS aqueous extract.

MATERIALS AND METHODS

We analyzed the effects of boiling water extract of CS on angiotensin-converting enzyme (ACE) activities, the critical enzyme involved in the regulation of blood pressure. ACE inhibitory peptides from CS extract were identified using proteomics and bioinformatics tools. The binding interfaces between these peptides and ACE were defined by hydrogen-deuterium exchange mass spectrometry (HDX-MS). Subsequently, the anti-hypertensive effects of peptides were further investigated in spontaneously hypertensive rats (SHR).

RESULTS

Our data showed that CS extract exhibited dose-dependent inhibition of ACE activity. Liquid chromatography-tandem mass spectrometry identified a heat-stable peptide bank with 1313 distinct peptide fragments within the CS boiling water extract. Among these, CS-1 (LVPGWTKPICIGR) was selected through PeptideRanker and BIOPEP-UWM analyses. In vitro ACE inhibitory assays confirmed that CS-1 exhibited dose-dependent ACE inhibition, with IC50 values of 10.32 ± 0.41 μmol/L (using HHL as the substrate) and 13.74 ± 1.87 μmol/L (using ZFHL as the substrate). Oral administration of CS-1 led to a significant dose-dependent reduction in blood pressure, with the maximal decrease (42.33 ± 13.08 mmHg) occurring 0.5 h after ingestion. HDX-MS analysis revealed that CS-1 interacted with the zinc-binding motif of ACE, and hydrogen bond interactions were predicted between CS-1 and specific residues, including His361 in the N-domain, as well as His382, Gly386, and His387 in the C-domain of ACE. These findings suggested that the interaction of CS-1 with the residues in the zinc-binding motif of ACE led to ACE activity inhibition and a subsequent decrease in blood pressure in rats.

CONCLUSIONS

A novel heat-stable ACE inhibitory peptide, which interacted with the zinc-binding motif of ACE and reduced blood pressure in SHR, was identified in the CS extract. The presence of ACE inhibitory peptides in the CS extract supports its traditional use in ethnopharmacology for hypertension.

Extraction Optimization, Preliminary Identification, and Bioactivities in Corn Silk

For thousands of years, corn silk has been widely used as an antidiabetic, antioxidant, and antihyperlipidemic and for other effects, but there is a lack of studies that correlate the extracts of flavonoid composition with their biological activities. Thus, the objectives of this study were to optimize the conditions for extracting flavonoids, identify flavonoids, and correlate the flavonoid composition with the biological activities in corn silk. The response surface experiments showed that the highest flavonoid content was predicted at 45.321 min, 57.349°C, 26.089 mL/g, and 71.269%, respectively. The verification experiment results under these optimized conditions showed an ultrasonic time of 45 min, an ultrasonic temperature of 57°C, a liquid-to-material ratio of 26, and an ethanol volume fraction of 70%. No significant differences (the relative error is 4.378%) were observed between the theoretical and experimental TFC values, indicating that the developed models were accurate. Under these optimum extraction conditions, 20 major compounds were identified and quantified by UPLC-LTQ/Orbitrap MS. Furthermore, these optimum ethanol extracts of corn silk are effective against Bacillus subtilis and hypoglycemic activity compared with the traditional heating reflux extraction method. Six corn silk components seem to be the main contributors to the inhibitory effect against Bacillus subtilis and hyperglycemia activities. These results are useful for the application of corn silk in the food or pharmaceutical industry.

Comparative transcriptome profiling and weighted gene co-expression network analysis to identify core genes in maize (Zea mays L.) silks infected by multiple fungi

Maize (Zea mays L.) is the third most popular Poaceae crop after wheat and rice and used in feed and pharmaceutical sectors. The maize silk contains bioactive components explored by traditional Chinese herbal medicine for various pharmacological activities. However, Fusarium graminearum, Fusarium verticillioides, Trichoderma atroviride, and Ustilago maydis can infect the maize, produce mycotoxins, hamper the quantity and quality of silk production, and further harm the primary consumer's health. However, the defense mechanism is not fully understood in multiple fungal infections in the silk of Z. mays. In this study, we applied bioinformatics approaches to use the publicly available transcriptome data of Z. mays silk affected by multiple fungal flora to identify core genes involved in combatting disease response. Differentially expressed genes (DEGs) were identified among intra- and inter-transcriptome data sets of control versus infected Z. mays silks. Upon further comparison between up- and downregulated genes within the control of datasets, 4,519 upregulated and 5,125 downregulated genes were found. The DEGs have been compared with genes in the modules of weighted gene co-expression network analysis to relevant specific traits towards identifying core genes. The expression pattern of transcription factors, carbohydrate-active enzymes (CAZyme), and resistance genes was analyzed. The present investigation is supportive of our findings that the gene ontology, immunity stimulus, and resistance genes are upregulated, but physical and metabolic processes such as cell wall organizations and pectin synthesis were downregulated respectively. Our results are indicative that terpene synthase TPS6 and TPS11 are involved in the defense mechanism against fungal infections in maize silk.

Protection against Neurological Symptoms by Consuming Corn Silk Water Extract in Artery-Occluded Gerbils with Reducing Oxidative Stress, Inflammation, and Post-Stroke Hyperglycemia through the Gut-Brain Axis

Corn silk (Stigma maydis), rich in flavonoids, is traditionally used to treat edema, depression, and hyperglycemia and may alleviate ischemic stroke symptoms in Chinese medicine. This study examined whether corn silk water extract (CSW) could alleviate ischemic stroke symptoms and post-stroke hyperglycemia in Mongolian gerbils with transient cerebral ischemia and reperfusion (I/R). After being given 0.05% (I/R-LCSW) and 0.2% (I/R-HCSW), 0.02% aspirin (I/R-aspirin), and cellulose (I/R-control) in their 40 energy% fat diets for three weeks, the gerbils underwent an artery occlusion for eight minutes and reperfusion. They took the assigned diet for an additional three weeks. Sham-operated gerbils without artery occlusion had the same diet as Sham-control. CSW intake reduced neuronal cell death in gerbils with I/R and dose-dependently improved the neurological symptoms, including drooped eyes, crouched posture, flexor reflex, and walking patterns. CSW intake also alleviated the short-term memory and spontaneous alteration and grip strength compared to the I/R-control group. The protection against ischemic stroke symptoms was associated with the reduced tumor necrosis factor-α, interleukin-1β, superoxide, and lipid peroxide levels, promoting superoxide dismutase activity in the hippocampus in the CSW groups, compared to the I/R-control. The blood flow measured by Doppler was improved with CSW compared to the I/R-control. Furthermore, CSW intake prevented the post-stroke hyperglycemia related to decreasing pancreatic β-cell mass as much as the Sham-control, and it was related to protection against β-cell apoptosis, restoring the β-cell mass similar to the Sham-control. CSW intake elevated the relative abundance of Lactobacillus, Bifidobacterium, Allobaculum, and Akkermansia compared to the I/R-control. Picrust2 analysis showed that CSW increased the propionate and butyrate metabolism and the starch and glucose metabolism but reduced lipopolysaccharide biosynthesis compared to the I/R-control. In conclusion, CSW intake protects against neuronal cell death and post-hyperglycemia by reducing oxidative stress and inflammation and increasing blood flow and the β-cell mass. The alleviation was associated with promoting the gut-brain axis by changing the gut microbiome community.

Corn silk decoction for blood lipid in patients with angina pectoris: A systematic review and meta-analysis

The aims of this study were to evaluate the efficacy of corn silk decoction on lipid profile in patients with angina pectoris. PubMed, Cochrane, Embase, Google Scholar, Chongqing VIP Chinese Science and Technology Periodical Database, China National Knowledge Infrastructure, and Wanfang database were searched up to January 2019 for randomized controlled trials that assessed the impact of corn silk decoction on total cholesterol, triglycerides, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol in patients with angina pectoris. Study evaluation and synthesis methods were in accordance with the Cochrane Handbook, and data were analyzed using Review Manager (version 5.3) software. Random effects model was applied in this systematic review and meta-analysis to compensate for potential heterogeneity among the included studies. A total of four randomized controlled trials were eligible for meta-analysis. Pooled results of these studies indicated that corn silk decoction might improve high-density lipoprotein cholesterol and reduce total cholesterol, triglycerides, and low-density lipoprotein cholesterol in patients with angina pectoris. Subgroup analyses showed that corn silk decoction or modified corn silk decoction plus conventional pharmaceutical treatment could have favorable effects on blood lipids. However, the lack of blinding in most studies may have led to overestimation of these effects. Further studies with better design are needed to confirm these findings.

Antihypertensive Effects of Corn Silk Extract and Its Novel Bioactive Constituent in Spontaneously Hypertensive Rats: The Involvement of Angiotensin-Converting Enzyme Inhibition

Corn silk tea has been used in folk medicine for anti-hypertensive healthcare. Angiotensin-converting enzyme (ACE) plays a crucial role on the homeostasis of blood pressure. However, effects of corn silk tea on ACE activity and the presence of ACE inhibitory constituents in corn silk are still unknown. Here we applied proteomics and bioinformatics approaches to identify corn silk bioactive peptides (CSBps) that target ACE from the boiling water extract of corn silk (CSE). CSE significantly reduced systolic blood pressure (SBP) levels in spontaneously hypertensive rats and inhibited the ACE activity. By proteomics coupled with bioinformatics analyses, we identified a novel ACE inhibitory peptide CSBp5 in CSE. CSBp5 significantly inhibited the ACE activity and decreased SBP levels in a dose-dependent manner. Docking analysis showed that CSBp5 occupied the substrate-binding channel of ACE and interacted with ACE via hydrogen bonds. In conclusion, we identified that CSE exhibited anti-hypertensive effects in SHRs via the inhibition of ACE, the target of most anti-hypertensive drugs. In addition, an ACE inhibitory phytopeptide CSBp5 that decreased SBP levels in rats was newly identified. Our findings supported the ethnomedical use of corn silk tea on hypertension. Moreover, the identification of ACE inhibitory phytopeptide in corn silk further strengthened our findings.