L-quebrachitol extracted from industrial rubber serum: a study on its antioxidant activities and bone mineral density enhancing functions

Abstract

In Southeast Asia, the natural rubber (Hevea brasiliensis) industry has expanded dramatically, and throughout the production process, a sizeable portion of industrial rubber serum is treated as effluent. L-quebrachitol has been proved as a natural product abundantly present in natural rubber serum. In order to improve the utilization rate of natural rubber, a method was provided to extract L-quebrachitol from industrial rubber serum, and the yield was 0.1∼0.2%. By using mass spectrometer, Fourier transform infrared, and nuclear magnetic resonance spectroscopy, the isolated molecule was identified as L-quebrachitol. Meanwhile, there is a lack of complete research on the antioxidant capacity of L-quebrachitol, and the effect of L-quebrachitol on bone mineral density remains at the cellular level. In this work, L-quebrachitol was confirmed to have a great ability to scavenge free radicals, especially at a concentration of 0.5 mg/mL. The protective capacity of antioxidant enzymes (catalase, total glutathione peroxidase, and superoxide dismutase) and the ability to inhibit lipid peroxidation of L-quebrachitol at concentrations of 50 and 100 μg/mL was remarkable. Furthermore, animal experiment showed that L-quebrachitol at 125 mg/kg·bw can significantly reduce weight gain, increase bone mineral density and bone calcium content of ovariectomized rats. Consequently, L-quebrachitol could be used as a novel antioxidant to prevent oxidative stress-related diseases or as an agent to increase bone density to prevent osteoporosis.

Introduction

Over the past few decades, the natural rubber (Hevea brasiliensis) industry has expanded widely in Southeast Asia, and rubber expansion has also occurred in China (Min et al., 2021). Xishuangbanna Dai Autonomous Prefecture, located upstream of the Mekong River in southwest China, is a typical example of how the rubber industry has developed. Since the 1980 s, smallholder rubber cultivation in Xishuangbanna has increased rapidly owing to the domestic rubber price protection and the use of innovative technologies, contributing to the rising prosperity of the rubber industry (Min et al., 2019).

In general, the rubber industry uses concentrated latex to produce solid products, while a considerable percentage of liquid rubber serum is treated as effluent (Danwanichakul et al., 2019). The liquid serum before filtration by microfiltration membrane was detected, and the components of rubber serum were shown in Table S1. There were many substances in rubber serum, and the main substances were ergotriene, glutathione, free amino acids, and quebrachitol. Previous research has reported the existence of L-quebrachitol in the waste water of the rubber industry (Danwanichakul et al., 2019, Liang et al., 2020). The traditional method involves extracting quebrachitol using hot alcohols, however this approach has significant security issues. (Xue et al., 2015) used hydrophilic interaction chromatography to quantitatively analyze L-quebrachitol, but this method may not be applicable to industrial rubber serum. In our previous work, a safer and more practical method was employed to extract L-quebrachitol from different source of rubber wastewater (Jiang et al., 2018). This method conducted by using membrane filtration to extract L-quebrachitol has already been applied for Chinese patent (CN201310007459. X) and has been verified. Furthermore, L-quebrachitol can be directly extracted without requirement for any prior pre-treatment or chemical addition. In light of the production process' complexity and operational challenges, we optimized and conducted the method for extracting L-quebrachitol form industrial rubber serum in this work. The measure of using industrial rubber serum to extract L-quebrachitol not only enhances the value of natural rubber serum as a whole, but also makes a contribution to environmental protection.

L-quebrachitol is a white crystalline compound, and an inositol methyl derivative with many of the same physiological characteristics, including antioxidation, anti-inflammatory, and anti-cancer properties. (Owczarczyk-Saczonek et al., 2018). While L-quebrachitol has a structure that is similar to that of glucose (Fig. 1), it does not raise blood glucose levels after consumption (McCance and Lawrence, 1933). Previous studies also reported that L-quebrachitol can against acute gastric lesions (de Olinda et al., 2008), as an initial material for the synthesis of β-glucosidase inhibitor (Falshaw et al., 2000), and scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals and peroxynitrite (ONOO−) (Kim et al., 2004, Lemos et al., 2006). At present, there is a lack of complete research on the antioxidant capacity of L-quebrachitol. It is reasonable to assume that the L-quebrachitol may have a large hydrogen supply capacity and can be used as an antioxidant due to its polyhydroxy structure.

Oxidative stress is a type of physiological state which characterized by an increase in reactive oxygen species (ROS) (Xie et al., 2022). On the one hand, ROS can play a vital role in inflammatory processes as a signal molecule, but on the other hand, high levels of ROS can lead to the oxidation of lipids, proteins, DNA, and other constituent molecules (Ferreira et al., 2022). Chronic disorders like cancer, cardiovascular disease, and neurological diseases are all directly linked to oxidative stress (Fernández-Tomé et al., 2014). In addition, ROS are known to activate the crucial factor (NF-κB) that involved in osteoclast formation, which leads to osteoporosis (Jagger et al., 2005). Osteoporosis is a highly prevalent bone disease and the prevalence of the elderly was relatively higher (Liu et al., 2020), especially in postmenopausal women (Liu et al., 2014). The mechanism of osteoporosis in postmenopausal women is that estrogen deficiency upregulates the level of proinflammatory factors, promoting osteoclast differentiation, and ultimately leading to osteoporosis (Fischer and Haffner-Luntzer, 2022). Previous studies have shown that oxidative stress could induce inflammatory changes that mediate bone loss through changes in bone remodeling (Chen et al., 2019, Tsay et al., 2010). Thus, it is a feasible way to prevent oxidative stress by increasing antioxidant defense (Wauquier et al., 2009).

Consequently, this study focused on the antioxidant capacity of L-quebrachitol, which was extracted from industrial rubber serum, to investigate the effect of reducing oxidative stress on bone loss in ovariectomized rats. Free radical scavenging and the impact on cell antioxidant of illustrated the antioxidant capacity of L-quebrachitol. A further investigation into the effectiveness of L-quebrachitol in organism was carried out on animals in order to open up its potential therapeutic applications. These new findings might increase the utilization of industrial rubber serum, and enhance the application range of L-quebrachitol.