Exploring the therapeutic potential of Aloin: unraveling neuroprotective and anticancer mechanisms, and strategies for enhanced stability and delivery

Abstract

We investigate the therapeutic potential of Aloin A and Aloin B, two natural compounds derived from Aloe vera leaves, focusing on their neuroprotective and anticancer properties. The structural differences between these two epimers suggest that they may exhibit distinct pharmacological properties. Our investigations revealed that both epimers are not stable in aqueous solution and tend to degrade rapidly, with their concentration decreasing by over 50% within approximately 12 h. These results underscore the importance of addressing issues such as the need for encapsulation into effective drug delivery systems to enhance stability. ThT fluorescence experiments showed that neither compound was able to inhibit Aβ amyloid aggregation, indicating that other mechanisms may be responsible for their neuroprotective effects. Next, an equimolar mixture of Aloin A and Aloin B demonstrated an ability to inhibit proteasome in tube tests, which is suggestive of potential anticancer properties, in accordance with antiproliferative effects observed in neuroblastoma SH-SY5Y and HeLa cell lines. Higher water stability and increased antiproliferative activity were observed by encapsulation in carbon dot nanoparticles, suggesting a promising potential for further in vivo studies.

Keywords: Amyloid; Anticancer; Carbon dots; Neurodegeneration; Proteasome.

Figure 1

Chemical structures of Aloin A and its epimer, Aloin B, highlighting the isomeric difference in the glycosidic linkage position (10S for Aloin A and 10R for Aloin B) and their shared anthrone C-glycoside structure.

Figure 2

Stability of Aloin A (Δ) and Aloin B (◊) at 37 °C in PBS at pH 7.4: % Aloin remaining in the 0–48 h range.

Figure 3

(A) Kinetics of fiber formation measured by ThT fluorescent emission for 10 μM Aβ1-40 (black line) and in presence of Aloin A at 1:1 ratio (red line) or Aloin B 1:1 ratio (blue line). (B) Kinetics of fiber formation measured by ThT fluorescent emission for Aβ1-40 10 μM (black line) and in presence of Aloin A at 1:2 ratio (red line) or Aloin B 1:2 ratio (blue line). All the experiments were conducted in phosphate buffer 10 mM, 100 mM NaCl, pH 7.4 at 37 °C. Traces are the average of three independent experiments.

Figure 4

(A) Normalized activity of human 20S proteasome compared to the control, in an equimolar mixture (AloAB): concentration range 1 × 10^–6–5 × 10^–4 M. (B) Normalized activity of human 20S proteasome compared to the control of individually isomer AloA and AloB. (C) Nonlinear fit of the concentration–response plot for the inhibition of ChT-L residual activities of human 20S proteasome in the presence of increasing concentrations of AloAB.

Figure 5

CDs-PNM/AloAB spectroscopical measurements: (A) optical absorption spectra of CDs–PNM 10 µg/µL (blue-line), Aloin-loaded CDs–PNM (black line) in water and AloAB in water (red line) and (B) CDs spectra of CDs-PNM/AloAB and CDs-PNM.

Figure 6

Optical absorption changes of (A) Alo B and (B) CDs-PNM/AloAB in water, after storage in the dark at room temperature.

Figure 7

Antiproliferative response in neuroblastoma SH-SY5Y cells to increasing concentrations (50–400 μM) of AloA (A) and AloB (B) as quantified by the Incucyte SX1 Live-Cell Analysis System. The readout of cellular growth was assessed every 6 h over 48 h. Values for each timepoint represent means ± SEM of 3 replicates and are normalized to control wells. (C) MTT analysis of the neuroblastoma cell lines treated with Alo A and Alo B. Cell viability was assessed after 48 h of treatment. Bars represent means ± SEM of three independent experiments with n = 3 each. ****P < 0.0001, versus Ctrl by one-way ANOVA + Dunnett’s test. (D) Representative optical images of human neuroblastoma cells after 48 h of exposure with AloA or AloB (50–400 μM).

Figure 8

MTT analysis of the neuroblastoma cell lines treated with CDPs-PNM (0.2 mg/mL) alone or loaded with increasing concentrations of AloAB (5–100 μM). Cell viability was assessed after 48 h of treatment. Bars represent means ± SEM of three independent experiments with n = 3 each. ****P < 0.0001, *P < 0.05 versus Ctrl by one-way ANOVA + Tukey test.