Arborescens Miller As An Immunomodulator

By Ken’ichi Imanishi
Department of Microbiology & Immunology, Tokyo Women’s Medical College Phytotherapy Research (1993) Vol 7, No. Special issue, pp. S20-S22. 15 ref.

 

Aloe has been used as a folk medicine for centuries all over the world. Among the components of Aloe, the low-molecular weight components have been well studied and used as purgatives. In the last few decades, the clinical application of Aloe extract, probably the components of high molecular weight, in skin injury and burns, as well as an anti-inflammatory, has been reported. Aloctin A is a highly purified glycoprotein with molecular weight of 1.8 x 104from the leaves of Aloe arborescens and exhibits various biological activities, such as mitogenic activity for T lymphocytes, binding reactivity for human a2-macroglobulin and activation of component 3 of complement system via the alternative pathway. (1)

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In this article, I would like to describe the antitumor activity of Alo A using methylcholanthrene-induced nurine fibrosarcoma (Meth A)²and lymphocytic leukemia (P388) (unpublished data) in syngeneic mouse systems.

One million of Meth A cells were implanted into the peritoneal cavity of BALB/c mice. Aloctin A were administered i.p. at an appropriate concentration in saline, once daily for 5 days, starting 24 hours after tumor implantation. Antitumor activity was evaluated by total cell packed cell volume ratio (Aloctin A-treated mice/control mice) calculated from collected whole ascites obtained from mice anesthetized with ether. A representative experiment is shown in table 1. Aloctin A obviously inhibited the growth of the tumor cells and administration at a dose of 10 mg/kg/day, for 5 days, remarkably inhibited it (p<0.001). It was important to determine whether this activity was due to cytotoxicity of Alo A for tumor cells or host-mediated effects of Aloctin A, since Aloctin A was administered i.p. Therefore, the effect of Aloctin A on the growth in vitro of Meth A and the other cell lines was examined by ³H-thymidine uptake. Aloctin A had almost no inhibitory effect on thegrowth of tumor cell lines tested including Meth A up to a concentration of 200 ug/ml, the highest concentration tested (table 2). This result suggests that Aloctin A is not directly cytotoxic to tumor cells.

 

One million of P388 cells were implanted intraperitoneally in CDF1 mice. Aloctin A was administered i.p. at an appropriate concentration in saline, once daily on the 1st and 5th days after tumor implantation. Antitumor activity was evaluated by survival time. The antitumor activity of Aloctin A is also obvious in this system (table 3).

 

The mechanisms of antitumor activity of Aloctin A seemed to be host-mediated. We have reported a couple of immunomodulatory activities, such as elevation of natural killer cell activity, augmentation of cytotoxicity of peritoneal exudate cells and generation of lymphokine-activated killer cells. We consider that Aloctin A is a promising candidate as an immunomodulator.

 

Table 1

The anti-tumor activity of Aloctin A against sarcoma Meth A (ascites form) in BALB/c

mice

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Antitumor test, 5-week-old BALB/c mice were used for this test. The tumor used was methylcholanthrene-induced fibrosarcoma (Meth A) maintained in the ascites form, 1 x 106 washed cells of Meth A were implanted i.p. into the mouse. Aloctin A as injected i.p. once daily for 5 days, starting 24 h after tumor implantation. Antitumor activity was evaluated by the total packed cell volume ratio (T/C %) on the 7th day.

 

ᵃTotal packed cell volume, *p<0.001, Significantly different from control.

 

Table 2

Cytotoxicity of Aloctin A in vitro

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Cytotoxicity test: Various concentrations of Aloctin A in 00ul of cell suspension, each containing 5 x 103cells. The mixture was incubated at 37 oC for 28 h in a humidified atmosphere of 5% CO2 and 95% air. After 24h, 1 uCi/well of 3H-thymidine was added. After a further 4 h of incubation, radioactivity incorporated into DNA was determined.

 

ᵃMean cpm of 3 wells.

 

Table 3

The anti-tumor activity of Aloctin A against P388 in CDF1 mice

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  1. S. T., Median Survival Time, T/C % = M. S. T. of treated group / M. S. T. of Control x 100. Evaluation of anti-tumor activity; T/C % in life-span *, **, Significantly different from Control * P<0.01, ** P<0.001.

 

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References

  1. Suzuki et al. (1979) J. Biochem. 85: 163.
  2. Imanishi et al. (1981) Experientia 37: 1186.