Neuroprotective potential of Aloe arborescens against copper induced neurobehavioral features of Parkinson's disease in rat

Copper (Cu) is an important trace element for the organism survival, which ensures the normal functioning of different biosystems. However, excessive levels of this heavy metal are responsible for profound physiological alterations including the central nervous system. Numerous findings sustain the involvement of heavy metals, as an environmental risk factor such as copper (Cu), in the neuropathology of Parkinson's disease (PD) which is a chronic neurodegenerative disorder that principally affects the motor system. The classic and evident symptoms of PD namely rigidity, tardiness of movement, and difficulty with walking, result from progressive dopaminergic neurons death within substantia nigra. Whereas, few pharmacological trials have shown a beneficial role against Cu neurotoxicity, Aloe arborescens is one of the powerful medicinal plants with an array of therapeutic effects. Thus, we aimed through the present study, to evaluate the impact of acute Cu intoxication (10μg/g B.W. i.p) for 3days on the dopaminergic system and locomotor performance, together with the possible restorative effect of oral administration of aqueous extract of Aloe arborescens gel (AEAAG) (200mg/kg B.W.). By means of immunohistochemistry, we noted, in the Cu intoxicated rats, a significant loss of TH (tyrosine hydroxylase) expression within substantia nigra compacta (SNc), ventral tegmental area (VTA) and the subsequent striatal outputs, those alterations were correlated to behavioral abnormalities such as a severe drop of locomotor performance. While AEAAG administration to Cu intoxicated rats showed a noticeable beneficial effect; this potential was featured by a complete recovery of the TH expression and locomotor behavior deficiencies in the intoxicated rats. The present investigation have brought, on the one hand, an experimental evidence of an altered dopaminergic innervations following Cu intoxication and on the other hand, a new pharmacological property of Aloe arborescens that may be used as a neuroprotective plant for neurodegenerative disorders, such as PD, touching the dopaminergic system trigged by heavy metals.

A Systemic Review on Aloe arborescens Pharmacological Profile: Biological Activities and Pilot Clinical Trials

Since ancient times, plants and herbal preparations have been used as medicine. Research carried out in the last few decades has verified several such claims. Aloe arborescens Miller, belonging to the Aloe genus (Family Asphodelaceae), is one of the main varieties of Aloe used worldwide. The popularity of the plant in traditional medicine for several ailments (antitumor, immunomodulatory, antiinflammatory, antiulcer, antimicrobial and antifungal activity) focused the investigator's interest on this plant. Most importantly, the reported studies have shown the plant effectiveness on various cancer types such as liver, colon, duodenal, skin, pancreatic, intestinal, lung and kidney types. These multiple biological actions make Aloe an important resource for developing new natural therapies. However, the biological activities of isolated compounds such as glycoprotein, polysaccharides, enzyme and phenolics were insufficient. Considering all these, this contribution provides a systematic review outlining the evidence on the biological efficacy of the plant including the pharmacology and the related mechanisms of action, with specific attention to the various safety precautions, and preclinical and clinical studies, indicating the future research prospects of this plant.

Unraveling the medicinal potential of South African Aloe species

ETHNOPHARMACOLOGICAL RELEVANCE

Aloe species (family: Xanthorrhoeaceae) are widely used in ethnomedicine for treating various ailments. Approximately 125 Aloe taxa are documented as indigenous to South Africa. This review was aimed at critically evaluating the available data on the ethnomedicinal uses, pharmacological activities, safety and conservation status of the documented South African Aloe species.

MATERIALS AND METHODS

A detailed search using major electronic search engines (such as Google Scholar, Scopus and Scirus) and ethnobotanical literature was undertaken. Search terms used included 'medicinal properties of Aloe species', 'biological activity of South African Aloe species' and 'safety and toxicological evaluation of aloes'.

RESULTS

Although Aloe species are widely used as laxatives and for treating wound and skin-related ailments, only about 20% of South African Aloe species have been clearly documented for their medicinal uses. The pharmacological potential including the antimicrobial, antiinflammatory, antiplasmodial and anthelmintic activities of some of the species has been established, providing a rationale for their use in traditional medicine. Successful micropropagation protocols have been developed as a conservation strategy, but only for a few species.

CONCLUSIONS

The highlighted medicinal activities of some Aloe species indicate their therapeutic potential. Nonetheless, further research especially on the understudied species is required to properly document their ethnomedicinal uses and fully explore their pharmacological value.

Aloe vera as a functional ingredient in foods

The main scientific discoveries on Aloe vera published mainly in the last three decades are presented in this work. After describing Aloe from a botanical point of view, the papers related with the chemical composition of different parts of the leaf of Aloe, particularly those in which the gel is described and are presented in a synthetic manner. The chemical analyses reveal that Aloe gel contains mannose polymers with some glucose and other sugars, among which the most important is Acemannan. Besides these, other components such as glycoproteins, enzymes, amino acids, vitamins, and minerals are described. Different factors also affecting the chemical composition of the gel, such as species and variety, climatic and soil conditions, cultivation methods, processing and preservation, are enumerated and discussed. On the other hand, the main therapeutic applications have been revised and the possible damaging effects of Aloe are also commented upon. A special emphasis is placed on the biologically active compounds or groups of compounds responsible for the therapeutic applications and which are their action mechanisms. The paper concludes that more research is needed to confirm the therapeutic and beneficial effects and to definitively clarify the myth surrounding Aloe vera. A general view on the problem of the commercialization and establishment of the quality and safety of Aloe products in the food industry has been offered here. The main points and European regulations that need to be considered regarding the quality control of prepared Aloe products are presented in this paper.

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.

Tumour preventive effect ofAloe veraleaf pulp lectin (Aloctin I) onEhrlich ascitestumours in mice

In this study, the prophylactic effect of the main lectin present in Aloe vera leaf pulp extract (Aloctin I) was assayed against Ehrlich ascites tumours in mice. The lectin administered prophylactically before tumour implantation regressed tumour size, however, this activity was less potent than that of the A. vera leaf pulp extract previously shown in our laboratory. Accordingly, serum sialic acid and tumour necrosis factor alpha (TNFalpha) levels, chosen as tumour markers, were decreased significantly by the prophylactic administration of the lectin. The increase in spleen and thymus weights in the group given only Aloctin I, could be explained by the immunomodulatory and mitogenic effects of lectins. These findings, along with lymphoid hyperplasia observed in spleen and thymus, suggest that the tumour preventive effect of Aloctin I could be due to its immunomodulatory activity.

Effect of Aloe vera leaf pulp extract on Ehrlich ascites tumours in mice

Among the various known therapeutic effects of Aloe vera (L.) Burm. fil., a few recent studies have shown that preparations of the plant leaves can prevent or regress the growth of certain tumours. In this study, undertaken with A. vera leaf pulp extract against Ehrlich ascites tumours in mice, the animals were separated into five groups: I - healthy control, II - tumour control, III - experiment 1 (extract given before tumour inoculation), IV - experiment 2 (extract given with tumour inoculation) and V - experiment 3 (extract given after tumour inoculation). Ehrlich ascites tumours (0.33 ml) were injected subcutaneously into groups II-V. Aloe extract was injected at 55 mg protein/kg, twice a week for 21 days. Tumour size, thymus and spleen weights were measured, as well as leucocyte count, tumour necrosis factor-alpha and sialic acid as tumour markers. The best inhibitory effect on tumour growth was obtained with the extract given prophylactically before tumour implantation (experiment 1), although Aloe extract also regressed tumour sizes when given simultaneously with (experiment 2), or therapeutically after (experiment 3), tumour implantation. Accordingly, serum sialic acid and tumour necrosis factor-alpha levels, chosen as tumour markers, which were raised in the tumour control group, were significantly decreased by the prophylactic administration of the extract. The increase in leucocyte count seen in experiment 1 and 2 groups, along with lymphoid hyperplasia observed in spleen and thymus necroscopy, lead us to think that the tumour preventive effect of Aloe could be due to its immunomodulatory activity. According to our results, A. vera could be proposed as a prophylactic for cancer prevention.

Beneficial and adverse effects of chemopreventive agents

The beneficial and adverse effects of some chemopreventive agents, such as Vitamins A, C, E, beta-carotene, indole-3-carbinol, capsaicin, garlic, and aloe are reviewed. Two large randomized trials with a lung cancer endpoint, the Alpha-Tocopherol, Beta-Carotene (ATBC) Prevention Study and the Beta-Carotene and Retinol Efficacy Trial (CARET), suggested that antioxidants might be harmful in smokers. However, the results of the Linxian study and of the ATBC or the CARET studies were significantly different in this respect, and therefore, the relationship between antioxidant and carcinogenesis remains open to debate. Indole-3-carbinol has cancer promoting activities in the colon, thyroid, pancreas, and liver, whereas capsaicin alters the metabolism of chemical carcinogens and may promote carcinogenesis at high doses. Organosulfur compounds and selenium from garlic have no or a little enhancing effect on cancer promotion stage. Information upon chemopreventive mechanisms that inhibit carcinogenesis is imperfect, although the causes and natures of certain human cancers are known. Therefore, definitive preventive guidelines should be carefully offered for various types of tumors, which properly consider ethnic variations, and the efficacies and the safety of chemopreventive agents.

Chemopreventive effects of Aloe arborescens on N-nitrosobis(2-oxopropyl)amine-induced pancreatic carcinogenesis in hamsters

The modification effects of freeze-dried aloe (Aloe arborescens) whole leaf powder during the initiation phase of carcinogenesis were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Female Syrian hamsters were given four weekly subcutaneous injections of BOP at a dose of 10mg/kg and then given 0, 1 or 5% aloe in their diet for 5 weeks. At week 54 of the experiment, all surviving animals were sacrificed and development of neoplastic and preneoplastic lesions was assessed histopathologically. The incidences of pancreatic adenocarcinomas, atypical hyperplasias or total atypical hyperplasias plus adenocarcinomas were significantly (P<0.05) decreased with BOP+5% aloe, and that of adenocarcinomas were also significantly (P<0.05) reduced in the BOP+1% aloe as compared to the BOP alone group. Multiplicities of pancreatic adenocarcinomas, atypical hyperplasias or total lesions were also significantly (P<0.01 or P<0.05) lower in the BOP+5% aloe group than with the BOP alone. Quantitative data for neoplastic lesions in the lung, liver, gall bladder, kidney and urinary bladder of hamsters were not significantly different among the three groups. In a satellite experiment, pretreatment with aloe significantly (P<0.01) reduced the formation of O6-methyldeoxyguanosine in epithelial cells of pancreatic ducts as compared to the BOP alone value. Our results thus indicate that aloe prevents BOP-induced pancreatic neoplasia in hamsters in relation to decreased DNA adduct formation in the target tissue.

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.

Search for compounds that inhibit the genotoxic and carcinogenic effects of heterocyclic aromatic amines

Over the last 30 years approximately 160 reports have been published on dietary compounds that protect from the mutagenic and carcinogenic effects of heterocyclic aromatic amines (HAAs). In the first section of this review, the current state of knowledge is briefly summarized. Based on the evaluation of the available data, various protective mechanisms are described, and the use of different methodologies for the detection of protective effects is critically discussed. In most antimutagenicity studies (>70%) bacterial indicators (predominantly Salmonella strain TA98) were used, and about 600 individual compounds and complex mixtures have been identified that attenuate the effects of HAAs. The most frequently used in vivo method to detect protective effects are adduct measurements; anticarcinogenic dietary factors were identified by aberrant crypt foci assays and liver foci tests with rats. The mechanisms of protection include inactivation of HAAs and their metabolites by direct binding, inhibition of enzymes involved in the metabolic activation of the amines, induction of detoxifying enzymes, and interaction with DNA repair processes. The detection spectrum of conventional in vitro mutagenicity assays with metabolically incompetent indicator cells is limited. These procedures reflect only simple mechanisms such as direct binding of the HAAs to pyrroles and fibers. It has been shown that these compounds are also effective in rodents. More complex mechanisms, namely, interactions with metabolic activation reactions are not adequately represented in in vitro assays with exogenous enzyme homogenates, and false-negative as well as false-positive results may be obtained. More appropriate approaches for the detection of protective effects are recently developed test systems with metabolically competent cells such as the human Hep G2 line or primary hepatocytes. SCGE tests and DNA adduct measurements with laboratory rodents enable the detection of antigenotoxic effects in different organs, including those that are targets for tumor induction by the amines. Medium term assays based on aberrant crypt foci in colon and liver foci tests have been used to prove that certain compounds that prevented DNA damage by HAAs also reduced their carcinogenic effects. These experiments are costly and time consuming and, due to the weak induction capacity of the amines, only pronounced anticarcinogenic effects can be detected. Over the years, a large bulk of data on HAA protective compounds has accumulated, but only for a few (e.g., fibers, pyrroles, constituents of teas, and lactic acid bacteria) is there sufficient evidence to support the assumption that they are protective in humans as well.

Aloe vera leaf gel: a review update

Research since the 1986 review has largely upheld the therapeutic claims made in the earlier papers and indeed extended them into other areas. Treatment of inflammation is still the key effect for most types of healing but it is now realized that this is a complex process and that many of its constituent processes may be addressed in different ways by different gel components. A common theme running though much recent research is the immunomodulatory properties of the gel polysaccharides, especially the acetylated mannans from Aloe vera, which are now a proprietary substance covered by many patents. There have also been, however, persistent reports of active glycoprotein fractions from both Aloe vera and Aloe arborescens. There are also cautionary investigations warning of possible allergic effects on some patients. Reports also describe antidiabetic, anticancer and antibiotic activities, so we may expect to see a widening use of aloe gel. Several reputable suppliers produce a stabilized aloe gel for use as itself or in formulations and there may be moves towards isolating and eventually providing verified active ingredients in dosable quantities

Decreased levels of 2-amino-3-methylimidazo[4,5-f]quinoline-DNA adducts in rats treated with beta-carotene, alpha-tocopherol and freeze-dried aloe

To assess mechanisms of chemoprevention of hepatocarcinogenesis by trans-beta-carotene (beta-C), DL-alpha-tocopherol (alpha-T), and freeze-dried whole leaves of Kidachi aloe (Aloe), formation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-DNA adducts was measured by 32P-post-labeling analysis, and CYP1A1 and CYP1A2 protein levels were analyzed by ELISA. Group 1 rats were fed diet containing 0.02% beta-C, 1.5% alpha-T or 30% Aloe over an 8-day period, while group 2 was given basal diet alone. On day 7, all animals were subjected to two-thirds partial hepatectomy (PH). Twelve hours after PH, they received a single dose of the carcinogenic food pyrolysate IQ (100 mg/kg) intragastrically, to initiate hepatocarcinogenesis. Rats were killed 6, 12, 24 and 48 h after IQ administration. The levels of adducts, expressed as relative adduct labeling values in rats treated with beta-C, alpha-T and Aloe, were decreased as compared with the control group at hour 24 (36 h after PH), with a significant difference in the case of the beta-C group (46.4% of the control value). Similarly, all showed a tendency for decrease at hour 48. Furthermore, the levels of CYP1A2, known to be responsible for activation of IQ, showed a significant reduction at hour 24. It is concluded that beta-C, and possibly also alpha-T and Aloe, have the potential to reduce IQ-DNA adduct formation, presumably as a result of decreased formation of active metabolites. The results may explain, at least in part, the previously observed inhibitory effects of these compounds on induction of preneoplastic hepatocellular lesions.