Vitamin E and Trolox™ reduce toxicity of Aloe barbadensis Miller juice in Artemia franciscana nauplii but individually are toxic at high concentrations
J Sirdaarta, I Cock
aloe vera, antioxidant, miller, oxidative stress, trolox™, vitamin e
J Sirdaarta, I Cock. Vitamin E and Trolox™ reduce toxicity of Aloe barbadensis Miller juice in Artemia franciscana nauplii but individually are toxic at high concentrations. The Internet Journal of Toxicology. 2007 Volume 5 Number 1.
This study reports on the acute toxic effects of Aloe barbadensis Miller (Aloe vera) juice as well as high doses of the antioxidants vitamin C, vitamin E and Trolox™ (a water soluble vitamin E analogue) to the salt water crustacean Artemia franciscana. Aloe vera juice exposure resulted in acute toxicity, being capable of inducing mortality at dilutions as low as 4 % juice and having an LC50 at 24 h of 4.6 % ± 0.3. 6% Aloe vera juice dilutions were capable of causing 100% mortality within 4 h of exposure to A. franciscana. All of the antioxidants tested were also toxic to A. franciscana when tested in high doses. Toxicity of the antioxidants at 24 h was in the following order of toxicity: vitamin C (LC50 203.1 µg/ml ± 11.3) > Trolox™ (LC50 = 283.3 µg/ml ± 25.8) > vitamin E (only low toxicity was observed at 24 h with the tested concentrations). However, in lower doses vitamin E and Trolox™ were non-toxic and could block the toxicity induced by Aloe vera juice. Vitamin E was more effective than Trolox™ at blocking Aloe vera juice induced toxicity. Treatment of A. franciscana with antioxidants prior to exposure to juice was significantly more effective than the simultaneous treatment of antioxidant and the toxin. These data suggest that the lethality induced by Aloe vera juice is due to oxidative stress which can be blocked by antioxidant addition.
Financial support of this work was provided by the School of Biomolecular and Physical Sciences, Griffith University.
Many active constituents have been isolated from
The use of antioxidants such as vitamin E and vitamin C to reduce the effects of oxidative stress has received much recent attention. However, these studies have proved confusing, with some studies showing therapeutic effects [ 16,17 ], whilst other studies indicate that these antioxidants may be toxic [ 18 ]. It has been shown in a variety of human and animal models that the effects of vitamin E and vitamin C are dose dependent, with low doses functioning as antioxidants and blocking toxicity, while high doses induce toxicity through oxidative stress [ 19 ].
Materials and Methods
Aloe vera juice was obtained from Aloe Wellness Pty Ltd, Australia and was stored at 4 °C until use. Aloe vera juice was serially diluted in deionised water for use in the
Reference toxins for biological screening
Potassium dichromate (AR grade, Chem-Supply) was prepared as a 1.6 mg/ml solution in distilled water and was serially diluted in artificial seawater for use in the
Toxicity was tested using a modified form of the
To determine the ability of antioxidants to block the toxic effect of Aloe vera juice, vitamin C was freshly prepared in deionised water as a 400 µg/ml solution. Vitamin E and Trolox™ were each dissolved in 60 % methanol and diluted in deionised water to a concentration of 400 µg/ml. Aloe vera juice was diluted in deionised water to give a 24 % solution. The 24 % juice was added to an equal volume of the relevant antioxidant (400 µg/ml) and mixed well. 400 µl of the juice/antioxidant mixtures was added to wells of a 48 well plate containing 400 µl of seawater containing
Aloe vera juice was prepared as a 24 % solution and the antioxidants were prepared as 400 µgml -1 solutions as described for the co-treatment experiments. 200 µl of the test antioxidants were added to wells of a 48 well plate containing 400 µl of seawater containing
Aloe vera juice toxicity
A 50 % dilution of Aloe vera juice was found to induce 100 % mortality within 4 h in the
Figure 2 shows the effect of Aloe vera juice dose on mortality in the
Toxicity of Antioxidants
To determine whether vitamin C and E and the water soluble vitamin E analogue Trolox™ were toxic in the
The effect of antioxidant concentration on mortality was measured at various times. Table 1 shows that the LC50 of the vitamin C (203.1 µg/ml ± 11.3) was substantially lower than the LC50 of the reference toxin Mevinphos (1336 µg/ml ± 70) at 24 h, demonstrating its relative toxicity. However, potassium dichromate had an LC50 of 73 µg/ml ± 4.0 at 24 h, nearly three fold more toxic than the vitamin C. Interestingly, whilst the toxicity of vitamin C was observed very rapidly, it reached its maximum lethality within 24 h.
Trolox™ was capable of inducing toxicity rapidly with a 4 h LC50 of 453.2 µg/ml ± 25.2. Trolox™ reached its maximum toxicity within 24 h and only small decreases in LC50 were seen over the next 2 days. Vitamin E treatment resulted in low
Effects of antioxidant co-treatment on Aloe vera juice toxicity
If the toxic effects of Aloe vera juice to
Effects of antioxidant pre-treatment on Aloe vera juice toxicity
The current study demonstrated the ability of Aloe vera juice to induce mortality in
Many studies have reported on the antioxidant and pro-oxidant potential of
These seemingly conflicting reports on the protective/toxic effects of Aloe vera components may be due to the different concentrations used in these various studies. Tian and Hua [ 14 ] have reported on the concentration dependence effects of two common Aloe vera components. Aloin has a pro-oxidant effect at low concentrations and had an antioxidant effect at higher concentrations. In contrast, aloe emodin was shown to function as a pro-oxidant only at high concentrations. Thus, the acute toxicity induced by Aloe vera juice in the current study may be due to a relatively high level of aloe emodin and/or aloin present in the juice. Interactions between the various components within the crude juice may also play a role in converting otherwise antioxidant molecules into pro-oxidants in the juice.
Similarly, other well studied antioxidants have also been shown to have opposing effects at different concentrations. Previous studies have shown the therapeutic effect of many vitamin antioxidants [ 16,24 ], whilst other work indicated that these antioxidants may be toxic [ 18 ]. As for the Aloe vera active phenolics, the antioxidant/pro-oxidant effects of these vitamins also seem to be dependent on their concentrations. Tafazoli et al. [ 16 ] have shown that a variety of vitamin E analogues, including α-tocopherol and Trolox™, behave as antioxidants at low concentrations and convert to pro-oxidants as the concentration increases. Trolox™ has also been shown to have direct therapeutic effects in
The current study demonstrates the toxicity of high doses vitamin C and vitamin E (and its analogue Trolox™) in
Whilst vitamin E exposure did not induce the level of mortality seen for vitamin C, vitamin E was itself toxic to
Trolox™ was also toxic to
Although both vitamin E and Trolox™ were toxic to
Vitamin E and Trolox™ proved more effective at blocking oxidative stress induced mortality when the
In conclusion, the current study demonstrated the toxicity of Aloe vera juice towards
The authors wish to thank John Gorringe of Aloe Wellness Australia Pty Ltd for the gift of
Dr Ian Cock, Biomolecular and Physical Sciences, Nathan Campus, Griffith University, 170 Kessels Rd, Nathan Queensland 4111, Australia Tel.: .: +61 7 37357637; fax: +61 7 37355282. E-mail address: I.Cock@griffith.edu.au