Determination of aloenin, barbaloin and isobarbaloin in aloe species by micellar electrokinetic chromatography

New opportunities and perspectives on biosynthesis and bioactivities of secondary metabolites from Aloe vera

Historically, the genus Aloe has been an indispensable part of both traditional and modern medicine. Decades of intensive research have unveiled the major bioactive secondary metabolites of this plant. Recent pandemic outbreaks have revitalized curiosity in aloe metabolites, as they have proven pharmacokinetic profiles and repurposable chemical space. However, the structural complexity of these metabolites has hindered scientific advances in the chemical synthesis of these compounds. Multi-omics research interventions have transformed aloe research by providing insights into the biosynthesis of many of these compounds, for example, aloesone, aloenin, noreugenin, aloin, saponins, and carotenoids. Here, we summarize the biological activities of major aloe secondary metabolites with a focus on their mechanism of action. We also highlight the recent advances in decoding the aloe metabolite biosynthetic pathways and enzymatic machinery linked with these pathways. Proof-of-concept studies on in vitro, whole-cell, and microbial synthesis of aloe compounds have also been briefed. Research initiatives on the structural modification of various aloe metabolites to expand their chemical space and activity are detailed. Further, the technological limitations, patent status, and prospects of aloe secondary metabolites in biomedicine have been discussed.

Rapid quantification of aloin A and B in aloe plants and aloe-containing beverages, and pharmaceutical preparations by microchip capillary electrophoresis with laser induced fluorescence detection

A microchip capillary electrophoresis coupled with laser induced fluorescence detection method for the fast determination of aloin was developed and comprehensively applied for the quantification of aloin A and B present in seven aloe plant species, 42 aloin-containing crude drugs, ten aloe pharmaceutical preparations, and four aloe gel-containing functional foods. The excitation and emission wavelengths for detection of both aloins were set at 473 and 520 nm, respectively. Sample analysis on a 35 mm length of glass microchip channel was completed within 40 s. An interference study indicated that the other main anthraquinones present in the samples did not interrupt with the target aloins detection, demonstrating the good selectivity of this method. It is demonstrated that this method is fast, facile, and specific for determination of aloin A and B from matrix samples which can be applied to the quality control of a wide varieties of aloe species and aloe-derived products.

Nanosuspension-Based Aloe vera Gel of Silver Sulfadiazine with Improved Wound Healing Activity

The present study focuses on the development and characterization of nanosuspension of a poorly soluble drug, silver sulfadiazine (SSD) incorporated in Aloe vera gel (AV-gel) for improving its therapeutic efficacy. The SSD solution in ammonia was subjected to nanoprecipitation in surfactant solution and particle size was optimized by varying concentration of surfactant. Optimized formulation constituted of 5.5% (w/v) Span 20 and 5.5% (w/v) Tween 80 as a dispersing agent and 0.5% (w/v) Poloxamer 188 as a co-surfactant. The prepared nanosuspension was evaluated for particle size, polydispersity index, surface morphology, and x-ray diffraction study. The optimized nanosuspension was incorporated into nanogel formulation with the addition of 1% AV-gel and 0.5% Carbopol 940 for topical delivery of nanosized SSD. Evaluation of in vitro drug release exhibited a significant enhancement in release rate of the drug from developed nanogel formulation (77.16 ± 3.241%) in comparison to marketed formulation (42.81 ± 1.452%) after 48 h. In vivo histopathological studies in rats for 14 days of application of prepared nanogel showed improvement in the wound healing potential as compared to marketed formulation.

Chromatographic separation and detection methods of Aloe arborescens Miller constituents: A systematic review

Aloe arborescens Miller (Family Asphodelaceae) is a member of genus Aloe, which is used in traditional medicine to cure various diseases. The extracts of the plant have been reported to possess anticancer, immunomodulator, antidiabetic, anti-inflammatory and antioxidant activities. The phytochemical investigations have revealed diverse chemical constituents, including phenolics [anthraquinones, anthrones, pyrones, chromones and coumarins], polysaccharides [arborans [(1-4) linked glucomannans, polysaccharide (A, B and C): (A: a linear (1-6)-O-α-glucan, B: a branching (1-2)-O-l-arabinose with (1-2)-O-d-galactose linkages and C: (1-4)-O-β-mannan with 18% acetyl group)]], glycoproteins and carboxypeptidase enzyme. There are many reports, describing the different methodologies developed to perform chemical analysis as well as, separation, detection and identification of these constituents. Different chromatographic techniques were applied such as gas chromatography (GC), high-performance liquid chromatography (HPLC), liquid chromatography-electrospray ionization coupled with mass spectroscopy (LC-ESI/MS/MS) and gel filtration chromatography. Also the isolated compounds were identified based on the spectroscopic analysis; ultraviolet-visible spectroscopy (UV-vis), infra-red spectroscopy (IR), mass spectroscopy (MS) and nuclear-magnetic resonance (NMR). This study aims to pinpoint the active components besides finding out new structural leads for future drugs. Therefore, the review is targeted to provide evidence reported in the relevant literature on qualitative and quantitative research to assist scientists in isolation and characterization of bioactive compounds in A. arborescens.

Identification and discrimination of three common Aloe species by high performance liquid chromatography-tandem mass spectrometry coupled with multivariate analysis

Aloe arborescens, Aloe barbadensis and Aloe ferox are the most widely cultivated and used among 500 aloe species due to their potent bioactivity. However, the difference of aloe species is neglected and labeled only one name Aloe in the market without specifying aloe species discrimination in general. Furthermore, differences in bioactivity and side effects from different aloe species have not been well investigated. This study develops an effective method for simultaneous qualitative and quantitative determination of three common aloe species using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and high performance liquid chromatography-diode array detection (HPLC-DAD). The extraction conditions were optimized by response surface methodology (RSM) based on methanol concentration, extraction time and solvent-to-material ratio. A partial least squares-discriminant analysis (PLS-DA) was used to identify the three aloe species. The developed HPLC-MS/MS method coupled with multivariate analysis can be applied to discriminate three aloe species successfully.

Potential prevention: Aloe vera mouthwash may reduce radiation-induced oral mucositis in head and neck cancer patients

In recent years, more head and neck cancer patients have been treated with radiotherapy. Radiation-induced mucositis is a common and dose limiting toxicity of radiotherapy among patients with head and neck cancers. Patients undergoing radiation therapy for head and neck cancer are also at increased risk of developing oral candidiasis. A number of new agents applied locally or systemically to prevent or treat radiation-induced mucositis have been investigated, but there is no widely accepted prophylactic or effective treatment for mucositis. Topical Aloe vera is widely used for mild sunburn, frostbites, and scalding burns. Studies have reported the beneficial effects of Aloe gel for wound healing, mucous membrane protection, and treatment of oral ulcers, in addition to antiinflammatory, immunomudulation, antifungal, scavenging free radicals, increasing collagen formation and inhibiting collagenase. Herein the author postulates that oral Aloe vera mouthwash may not only prevent radiation-induced mucositis by its wound healing and antiinflammatory mechanism, but also may reduce oral candidiasis of patients undergoing head and neck radiotherapy due to its antifungal and immunomodulatory properties. Hence, Aloe vera mouthwash may provide an alternative agent for treating radiation-induced oral mucositis and candidiasis in patients with head and neck cancers.

Aloe vera for treating acute and chronic wounds

BACKGROUND

Aloe vera is a cactus-like perennial succulent belonging to the Liliaceae Family that is commonly grown in tropical climates. Animal studies have suggested that Aloe vera may help accelerate the wound healing process.

OBJECTIVES

To determine the effects of Aloe vera-derived products (for example dressings and topical gels) on the healing of acute wounds (for example lacerations, surgical incisions and burns) and chronic wounds (for example infected wounds, arterial and venous ulcers).

SEARCH METHODS

We searched the Cochrane Wounds Group Specialised Register (9 September 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 3), Ovid MEDLINE (2005 to August Week 5 2011), Ovid MEDLINE (In-Process & Other Non-Indexed Citations 8 September 2011), Ovid EMBASE (2007 to 2010 Week 35), Ovid AMED (1985 to September 2011) and EBSCO CINAHL (1982 to 9 September 2011). We did not apply date or language restrictions.

SELECTION CRITERIA

We included all randomised controlled trials that evaluated the effectiveness of Aloe vera, aloe-derived products and a combination of Aloe vera and other dressings as a treatment for acute or chronic wounds. There was no restriction in terms of source, date of publication or language. An objective measure of wound healing (either proportion of completely healed wounds or time to complete healing) was the primary endpoint.

DATA COLLECTION AND ANALYSIS

Two review authors independently carried out trial selection, data extraction and risk of bias assessment, checked by a third review author.

MAIN RESULTS

Seven trials were eligible for inclusion, comprising a total of 347 participants. Five trials in people with acute wounds evaluated the effects of Aloe vera on burns, haemorrhoidectomy patients and skin biopsies. Aloe vera mucilage did not increase burn healing compared with silver sulfadiazine (risk ratio (RR) 1.41, 95% confidence interval (CI) 0.70 to 2.85). A reduction in healing time with Aloe vera was noted after haemorrhoidectomy (RR 16.33 days, 95% CI 3.46 to 77.15) and there was no difference in the proportion of patients completely healed at follow up after skin biopsies. In people with chronic wounds, one trial found no statistically significant difference in pressure ulcer healing with Aloe vera (RR 0.10, 95% CI -1.59 to 1.79) and in a trial of surgical wounds healing by secondary intention Aloe vera significantly delayed healing (mean difference 30 days, 95% CI 7.59 to 52.41). Clinical heterogeneity precluded meta-analysis. The poor quality of the included trials indicates that the trial results must be viewed with extreme caution as they have a high risk of bias.

AUTHORS' CONCLUSIONS

There is currently an absence of high quality clinical trial evidence to support the use of Aloe vera topical agents or Aloe vera dressings as treatments for acute and chronic wounds.

Effects of the application of Aloe vera (L.) and microcurrent on the healing of wounds surgically induced in Wistar rats

PURPOSE

To investigate the effects of topical application of an Aloe vera gel combined or not with microcurrent application on the healing of skin wounds surgically induced in Wistar rats.

METHODS

The animals were randomly divided into the following groups: control group, animals topically treated with Aloe vera, animals treated with a microcurrent, and animals receiving topical application of Aloe vera combined with microcurrent application.

RESULTS

The results indicated differences in wound healing between the various treatments when compared to the control group. Tissue hyperplasia was lower in the control group compared to the other treated groups. Accelerated wound healing was observed in the group treated with Aloe vera compared to control. Animals submitted to microcurrent application only and the group treated with microcurrent plus Aloe vera presented an earlier onset of the proliferative phase compared to the control group and animals treated with Aloe vera gel alone. Morphometric data confirmed the structural findings.

CONCLUSION

Simultaneous application of Aloe vera gel and microcurrent is an excellent choice for the treatment of open wounds thus indicating a synergistic action of these two applications.

Equivocal colonic carcinogenicity of Aloe arborescens Miller var. natalensis berger at high-dose level in a Wistar Hannover rat 2-y study

A 2-y carcinogenicity study of Aloe, Aloe arborescens Miller var. natalensis Berger, a food additive, was conducted for assessment of toxicity and carcinogenic potential in the diet at doses of 4% or 0.8% in groups of male and female Wistar Hannover rats. Both sexes receiving 4% showed diarrhea, with loss of body weight gain. The survival rate in the 4% female group was significantly increased compared with control females after 2 y. Hematological and biochemical examination showed increase of RBC, Hb, and Alb in the 4% males. The cause of these increases could conceivably have been dehydration through diarrhea. AST and Na were significantly decreased in the males receiving 4%, and Cl was significantly decreased in both 4% and 0.8% males. A/G was significantly increased in the 4% females, and Cl was significantly decreased (0.8%) in the female group. Histopathologically, both sexes receiving 4% showed severe sinus dilatation of ileocecal lymph nodes, and yellowish pigmentation of ileocecal lymph nodes and renal tubules. Adenomas or adenocarcinomas in the cecum, colon, and rectum were observed in 4% males but not in the 0.8% and control male groups. Similarly, in females, adenomas in the colon were also observed in the 4% but not 0.8% and control groups. In conclusion, Aloe, used as a food additive, exerted equivocal carcinogenic potential at 4% high-dose level on colon in the 2-y carcinogenicity study in rats. Aloe is not carcinogenic at nontoxic-dose levels and that carcinogenic potential in at 4% high-dose level on colon is probably due to irritation of the intestinal tract by diarrhea.

Final report on the safety assessment of AloeAndongensis Extract, Aloe Andongensis Leaf Juice,aloe Arborescens Leaf Extract, Aloe Arborescens Leaf Juice, Aloe Arborescens Leaf Protoplasts, Aloe Barbadensis Flower Extract, Aloe Barbadensis Leaf, Aloe Barbadensis Leaf Extract, Aloe Barbadensis Leaf Juice,aloe Barbadensis Leaf Polysaccharides, Aloe Barbadensis Leaf Water, Aloe Ferox Leaf Extract, Aloe Ferox Leaf Juice, and Aloe Ferox Leaf Juice Extract

Plant materials derived from the Aloe plant are used as cosmetic ingredients, including Aloe Andongensis Extract, Aloe Andongensis Leaf Juice, Aloe Arborescens Leaf Extract, Aloe Arborescens Leaf Juice, Aloe Arborescens Leaf Protoplasts, Aloe Barbadensis Flower Extract, Aloe Barbadensis Leaf, Aloe Barbadensis Leaf Extract, Aloe Barbadensis Leaf Juice, Aloe Barbadensis Leaf Polysaccharides, Aloe Barbadensis Leaf Water, Aloe Ferox Leaf Extract, Aloe Ferox Leaf Juice, and Aloe Ferox Leaf Juice Extract. These ingredients function primarily as skin-conditioning agents and are included in cosmetics only at low concentrations. The Aloe leaf consists of the pericyclic cells, found just below the plant's skin, and the inner central area of the leaf, i.e., the gel, which is used for cosmetic products. The pericyclic cells produce a bitter, yellow latex containing a number of anthraquinones, phototoxic compounds that are also gastrointestinal irritants responsible for cathartic effects. The gel contains polysaccharides, which can be acetylated, partially acetylated, or not acetylated. An industry established limit for anthraquinones in aloe-derived material for nonmedicinal use is 50 ppm or lower. Aloe-derived ingredients are used in a wide variety of cosmetic product types at concentrations of raw material that are 0.1% or less, although can be as high as 20%. The concentration of Aloe in the raw material also may vary from 100% to a low of 0.0005%. Oral administration of various anthraquinone components results in a rise in their blood concentrations, wide systemic distribution, accumulation in the liver and kidneys, and excretion in urine and feces; polysaccharide components are distributed systemically and metabolized into smaller molecules. aloe-derived material has fungicidal, antimicrobial, and antiviral activities, and has been effective in wound healing and infection treatment in animals. Aloe barbadensis (also known as Aloe vera)-derived ingredients were not toxic in acute oral studies using mice and rats. In parenteral studies, the LD(50) using mice was > 200 mg/kg, rats was > 50 mg/kg, and using dogs was > 50 mg/kg. In intravenous studies the LD(50) using mice was > 80 mg/kg, rats was > 15 mg/kg, and dogs was > 10 mg/kg. The 14-day no observed effect level (NOEL) for the Aloe polysaccharide, acemannan, in the diet of Sprague-Dawley rats, was 50,000 ppm or 4.1 to 4.6 g/kg day(-1). In a 3-month study using mice, Aloe vera (extracted in ethanol) given orally in drinking water at 100 mg/kg produced reproductive toxicity, inflammation, and mortality above that seen in control animals. Aloe vera extracted in methanol and given to mice at 100 mg/kg in drinking water for 3 months caused significant sperm damage compared to controls. Aloe barbadensis extracted with water and given to pregnant Charles Foster albino rats on gestational days (GDs) 0 through 9 was an abortifacient and produced skeletal abnormalities. Both negative and positive results were found in bacterial and mammalian cell genotoxicity assays using Aloe barbadensis-derived material, Aloe Ferox-derived material, and various anthraquinones derived from Aloe. Aloin (an anthraquinone) did not produce tumors when included in the feed of mice for 20 weeks, nor did aloin increase the incidence of colorectal tumors induced with 1,2-dimethylhydrazine. Aloe-emodin (an anthraquinone) given to mice in which tumor cells had been injected inhibited growth of malignant tumors. Other animal data also suggest that components of Aloe inhibit tumor growth and improve survival. Various in vitro assays also demonstrated anticarcinogenic activity of aloe-emodin. Diarrhea was the only adverse effect of note with the use of Aloe-derived ingredients to treat asthma, ischemic heart disease, diabetes, ulcers, skin disease, and cancer. Case reports include acute eczema, contact urticaria, and dermatitis in individuals who applied Aloe-derived ingredients topically. The Cosmetic Ingredient Review Expert Panel concluded that anthraquinone levels in the several Aloe Barbadensis extracts are well understood and can conform to the industry-established level of 50 ppm. Although the phototoxicity anthraquinone components of Aloe plants have been demonstrated, several clinical studies of preparations derived from Aloe barbadensis plants demonstrated no phototoxicity, confirming that the concentrations of anthraquinones in such preparations are too low to induce phototoxicity. The characterization of aloe-derived ingredients from other species is not clear. In the absence of well-characterized derivatives, biological studies of these materials are considered necessary. The studies needed are 28-day dermal toxicity studies on Aloe Andongensis Extract, Aloe Andongensis Leaf Juice, Aloe Arborescens Leaf Extract, Aloe Arborescens Leaf Juice, Aloe Ferox Leaf Extract, Aloe Ferox Leaf Juice, and Aloe Ferox Leaf Juice (ingredients should be tested at current use concentrations). In Aloe-derived ingredients used in cosmetics, regardless of species, anthraquinone levels should not exceed 50 ppm. The Cosmetic Ingredient Review Expert Panel advised the industry that the total polychlorobiphenyl (PCB)/pesticide contamination of any plant-derived cosmetic ingredient should be limited to not more than 40 ppm, with not more than 10 ppm for any specific residue and that limits were appropriate for the following impurities: arsenic (3 mg/kg maximum), heavy metals (20 mg/kg maximum), and lead (5 mg/kg maximum).

One-year chronic toxicity study of Aloe arborescens Miller var. natalensis Berger in Wistar Hannover rats. A pilot study

This study was conducted to evaluate the chronic toxicity of Aloe arborescens Miller var. natalensis Berger (ALOE) in the diet at doses of 4.0%, 0.8% or 0.16% to groups of male and female Wistar Hannover rats. No deaths occurred at any dose level throughout the treatment period. Both sexes receiving 4.0% showed diarrhea, with a reduced body weight gain. Increase of WBCs in the male 4.0% group, decrease of Hb in the female 4.0% and 0.8% groups, decrease of IP in the male 4.0% and 0.8% groups and female 4.0% group, and decrease of Ca and ALT in the female 4.0% group were observed. Relative kidney weight showed increase in the female 4.0% group and relative heart and brain weights were decreased in the female 4.0% and 0.8% groups. Histopathologically, both sexes receiving 4.0% showed severe sinus dilatation of ileocecal lymph nodes, and yellowish pigmentation of ileocecal lymph nodes and renal tubules. In conclusion, the no observed adverse effect level (NOAEL) for ALOE was the 0.16% in diet, which is equivalent to 87.7 and 109.7 mg/kg/day in males and females, respectively.

Radical-scavenging effects of Aloe arborescens Miller on prevention of pancreatic islet B-cell destruction in rats

We evaluated the possible scavenging effects of Aloe arborescens Miller var. natalensis Berger (Kidachi aloe in Japanese) on free radicals generated by streptozotocin (Sz) or alloxan (Ax). The components of Kidachi aloe were added to a reaction system in which .OH radicals derived from Sz or Ax as pancreatic islet B-cell toxins and hypoxanthine-xanthine oxidase (HX-XO)-derived O(2) radicals destroy isolated islet B-cells, and we observed its preventive effects. The Kidachi aloe components inhibited the destruction of rat pancreatic islet B-cells by Sz, Ax or HX-XO. These components were prepared in the form of a freeze-dried powder of the boiled leaf skin of Kidachi aloe, and measurement of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity showed higher radical-scavenging activity in this boiled leaf skin powder than the non-boiled leaf skin powder.Furthermore, HPLC chromatograms of the "Boiled leaf skin powder" were similar to those of commercially available aloin (barbaloin content: approximately 20%). Therefore, the main component may be a phenol compound. In addition, the phenolic fraction of the Boiled leaf skin contained large amounts of 2'-O-p-coumaroylaloesin and 2'-O-feruloylaloesin, which have higher DPPH radical-scavenging activity than barbaloin. These results suggest that the action mechanism of Kidachi aloe Boiled leaf skin components, which prevent destruction of the pancreatic islets by specific pancreatic islet toxins such as Sz, Ax, and HX-XO, involves inhibition of free radical-scavenging effects, and may be associated with a thermostable low molecular component. The co-existence of Kidachi aloe-derived 2'-O-p-coumaroylaloesin, 2'-O-feruloylaloesin, and aloin may result in the potentiation of radical-scavenging activity.

The phytochemical profile and identification of main phenolic compounds from the leaf exudate of Aloe secundiflora by high-performance liquid chromatography-mass spectroscopy

The phytochemical profile of Aloe secundiflora (Aloeaceae) and the identity of eight major compounds, including the two main constituents, have been determined from the leaf exudate of this ethnoveterinary used species from Kenya and Tanzania. Analytical HPLC-MS studies of the exudate have revealed that it comprises a mixture of phenolic compounds, mainly anthrones (aloenin, aloenin B, isobarbaloin, barbaloin and other aloin derivatives), chromones and phenylpyrones with a low content of polysaccharides and aliphatic compounds. The high percentage of anthrones in the exudate could provide a first line of evidence for the use of the plant in ethnoveterinary practices.

Aloe arborescens extract inhibits TPA-induced ear oedema, putrescine increase and tumour promotion in mouse skin

The ethyl acetate extract of the acetone-soluble Aloe arborescens fraction was found to inhibit 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ear oedema, putrescine increase and tumour promotion in mouse skin. Chromatographic analyses of this extract revealed that phenolic compounds such as aloenin, barbaloin and isobarbaloin could be useful as cancer chemopreventive agents against tumour promotion.

Inhibition of azoxymethane-induced aberrant crypt foci formation in rat colorectum by whole leaf Aloe arborescens Miller var. natalensis Berger

We examined the modifying effect of whole-leaf Aloe arborescens Miller var. natalensis Berger (designated as 'ALOE') on azoxymethane (AOM)-induced aberrant crypt foci (ACF), putative preneoplastic lesions, in the rat colorectum. Male F344 rats (4 weeks old) were fed the basal diet, or experimental diets containing 1% or 5% ALOE for 5 weeks. One week later, all rats except those in the vehicle-treated groups were injected s.c. with AOM (15 mg/kg, once weekly for 3 weeks). At 9 weeks of age, all the rats were killed, and the colorectum and liver were evaluated for ACF and cytosolic quinone reductase (QR; a phase 2 enzyme), respectively. In rats given AOM and ALOE (1% or 5% in diet) the numbers of ACF/colorectum, aberrant crypts/colorectum, aberrant crypts/focus and large ACF/colorectum were significantly decreased compared with those of rats given AOM alone (all p < 0.01). No ACF were found in rats treated without AOM. In addition, ALOE significantly increased cytosolic QR activity in the liver (p < 0.01). These results indicated that ALOE inhibited the development of AOM-induced ACF in the rat colorectum, with increased QR activity in the liver, and therefore suggested that ALOE might have a chemopreventive effect against colon carcinogenesis at least in the initiation stage.