Antitumor and antimetastatic actions of various natural products

A comprehensive analysis of royal jelly protection against cypermethrin-induced toxicity in the model organism Allium cepa L., employing spectral shift and molecular docking approaches

In this study, the toxicity of the pesticide cypermethrin and the protective properties of royal jelly against this toxicity were investigated using Allium cepa L., a model organism. Toxicity was evaluated using 6 mg/L cypermethrin, while royal jelly (250 mg/L and 500 mg/L) was used in combination with cypermethrin to test the protective effect. To comprehend toxicity and protective impact, growth, genotoxicity, biochemical, comet assay and anatomical parameters were employed. Royal jelly had no harmful effects when applied alone. On the other hand, following exposure to cypermethrin, there was a reduction in weight increase, root elongation, rooting percentage, mitotic index (MI), and chlorophyll a and b. Cypermethrin elevated the frequencies of micronucleus (MN) and chromosomal aberrations (CAs), levels of proline and malondialdehyde (MDA), and the activity rates of the enzymes catalase (CAT) and superoxide dismutase (SOD). A spectral change in the DNA spectrum indicated that the interaction of cypermethrin with DNA was one of the reasons for its genotoxicity, and molecular docking investigations suggested that tubulins, histones, and topoisomerases might also interact with this pesticide. Cypermethrin also triggered some critical meristematic cell damage in the root tissue. At the same time, DNA tail results obtained from the comet assay revealed that cypermethrin caused DNA fragmentation. When royal jelly was applied together with cypermethrin, all negatively affected parameters due to the toxicity of cypermethrin were substantially restored. However, even at the maximum studied dose of 500 mg/L of royal jelly, this restoration did not reach the levels of the control group. Thus, the toxicity of cypermethrin and the protective function of royal jelly against this toxicity in A. cepa, the model organism studied, were determined by using many different approaches. Royal jelly is a reliable, well-known and easily accessible protective functional food candidate against the harmful effects of hazardous substances such as pesticides.

Royal Jelly: Biological Action and Health Benefits

Royal jelly (RJ) is a highly nutritious natural product with great potential for use in medicine, cosmetics, and as a health-promoting food. This bee product is a mixture of important compounds, such as proteins, vitamins, lipids, minerals, hormones, neurotransmitters, flavonoids, and polyphenols, that underlie the remarkable biological and therapeutic activities of RJ. Various bioactive molecules like 10-hydroxy-2-decenoic acid (10-HDA), antibacterial protein, apisin, the major royal jelly proteins, and specific peptides such as apisimin, royalisin, royalactin, apidaecin, defensin-1, and jelleins are characteristic ingredients of RJ. RJ shows numerous physiological and pharmacological properties, including vasodilatory, hypotensive, antihypercholesterolaemic, antidiabetic, immunomodulatory, anti-inflammatory, antioxidant, anti-aging, neuroprotective, antimicrobial, estrogenic, anti-allergic, anti-osteoporotic, and anti-tumor effects. Moreover, RJ may reduce menopause symptoms and improve the health of the reproductive system, liver, and kidneys, and promote wound healing. This article provides an overview of the molecular mechanisms underlying the beneficial effects of RJ in various diseases, aging, and aging-related complications, with special emphasis on the bioactive components of RJ and their health-promoting properties. The data presented should be an incentive for future clinical studies that hopefully will advance our knowledge about the therapeutic potential of RJ and facilitate the development of novel RJ-based therapeutic opportunities for improving human health and well-being.

Revolutionizing the Use of Honeybee Products in Healthcare: A Focused Review on Using Bee Pollen as a Potential Adjunct Material for Biomaterial Functionalization

The field of biomedical engineering highly demands technological improvements to allow the successful engraftment of biomaterials requested for healing damaged host tissues, tissue regeneration, and drug delivery. Polymeric materials, particularly natural polymers, are one of the primary suitable materials employed and functionalized to enhance their biocompatibility and thus confer advantageous features after graft implantation. Incorporating bioactive substances from nature is a good technique for expanding or increasing the functionality of biomaterial scaffolds, which may additionally encourage tissue healing. Our ecosystem provides natural resources, like honeybee products, comprising a rich blend of phytochemicals with interesting bioactive properties, which, when functionally coupled with biomedical biomaterials, result in the biomaterial exhibiting anti-inflammatory, antimicrobial, and antioxidant effects. Bee pollen is a sustainable product recently discovered as a new functionalizing agent for biomaterials. This review aims to articulate the general idea of using honeybee products for biomaterial engineering, mainly focusing on describing recent literature on experimental studies on biomaterials functionalized with bee pollen. We have also described the underlying mechanism of the bioactive attributes of bee pollen and shared our perspective on how future biomedical research will benefit from the fabrication of such functionalized biomaterials.

Royal Jelly: Beneficial Properties and Synergistic Effects with Chemotherapeutic Drugs with Particular Emphasis in Anticancer Strategies

Cancer is one of the major causes of death globally. Currently, various methods are used to treat cancer, including radiotherapy, surgery, and chemotherapy, all of which have serious adverse effects. A healthy lifestyle, especially a nutritional diet, plays a critical role in the treatment and prevention of many disorders, including cancer. The above notion, plus the trend in going back to nature, encourages consumers and the food industry to invest more in food products and to find potential candidates that can maintain human health. One of these agents, and a very notable food agent, is royal jelly (RJ), known to be produced by the hypopharyngeal and mandibular salivary glands of young nurse honeybees. RJ contains bioactive substances, such as carbohydrates, protein, lipids, peptides, mineral salts and polyphenols which contribute to the appreciated biological and pharmacological activities. Antioxidant, anticancer, anti-inflammatory, antidiabetic, and antibacterial impacts are among the well-recognized benefits. The combination of RJ or its constituents with anticancer drugs has synergistic effects on cancer disorders, enhancing the drug’s effectiveness or reducing its side effects. The purpose of the present review is to emphasize the possible interactions between chemotherapy and RJ, or its components, in treating cancer illnesses.

In Vitro and In Vivo Antioxidant and Anticancer Potentials of Royal Jelly for Dimethylhydrazine-Induced Colorectal Cancer in Wistar Rats

Methods

This study was conducted among 60 rats, and groups consist of control, three separate groups for RJ, dimethylhydrazine (DMH), and vitamin E, and two separate treated groups with DMH + RJ and DMH + vitamin E. Additionally, the cytotoxicity of royal jelly was examined on HT-29 cell line. Findings. Based on the in vitro assessment using MTT assay, the LC50 of royal jelly was 1.781 mg/ml, and the highest cytotoxicity was observed at 25 mg/ml concentration after 48 hours. Meanwhile, in the in vivo study, after the 13th week, compared to the DMH group, the rats exposed to DMH + royal jelly experienced a significant less oxidative stress (P < 0.05) and a significantly greater total antioxidant capacity (TAC) level (P < 0.05). The expression of proliferating cell nuclear antigen (PCNA), platelet-derived growth factor (PDGF), and carcinoembryonic antigen (CEA) proteins significantly decreased among the animals receiving DMH + royal jelly compared to the DMH group. The pathological examinations revealed less congestion, necrosis, inflammation, and cell proliferation in the colon tissue of the RJ-treated group than that of the DMH group. Overall, the biochemical indices were better in the treatment groups in comparison with the DMH group.

Conclusion

The results represented the clinical usability of royal jelly, as a substance with anticancer properties, to prevent and treat colorectal cancer. This issue is related to its effective antioxidant potential, which even exhibits more effectiveness than the vitamin E, which is known as a strong antioxidant.

Royal jelly from different floral sources possesses distinct wound-healing mechanisms and ingredient profiles

In recent years, population aging together with the increased prevalence of diabetes and obesity has fuelled a surge in the instances of cutaneous non-healing wounds. Royal jelly (RJ) is a traditional remedy for wound repair; however, the subjacent mechanisms and ingredient profiles are still largely unknown. Our previous study found that Castanea mollissima Bl. RJ (CmRJ-Zj) possessed superior wound healing-promoting effects on both the in vivo and in vitro models than Brassica napus L. RJ (BnRJ-Zj). This study conducted an in-depth investigation on the wound-repairing mechanisms of CmRJ-Zj and BnRJ-Zj to explain the previously observed phenomenon and also comprehensively characterized their constituents. It was found that chestnut RJ could enhance cutaneous wound healing by boosting the growth and mobility of keratinocytes, modulating the expression of aquaporin 3 (AQP3), regulating MAPK and calcium pathways, and mediating inflammatory responses. By employing LC-MS/MS-based proteomic and metabolomic techniques, the comprehensive molecules present in CmRJ-Zj and BnRJ-Zj were elucidated, resulting in a clear discrimination from each other. A total of 15 and 631 differential proteins and compounds were identified, and 217 proteins were newly found in RJ proteome. With bioinformatic functional analysis, we speculated that some differential components were responsible for the wound-healing properties of CmRJ-Zj. Therefore, this study provides an insight into the wound-healing mechanisms of RJ and is the first to explore the compositions of RJ from different nectar plants. It will facilitate the development of therapeutic agents from RJ to treat difficult-to-heal wounds and the distinction of different RJ categories.

Enhanced anticancer efficacy of docetaxel through galbanic acid encapsulated into PLA-PEG nanoparticles in treatment of colon cancer, in vitro and in vivo study

Cancer is one of the most leading causes of human mortality and despite outstanding breakthrough in introducing new therapeutic approaches, the clinical outcomes are disappointing. Therefore, extensive research in design and preparation of more efficient drug delivery systems can open a window to shine light into the therapeutic modality. In this study, we evaluated the effect of galbanic acid (GBA) encapsulated into PLA-PEG nanoparticles (NPs) to enhanced anticancer efficacy of docetaxel (DOC) for the treatment of colon cancer. Prepared NPs were characterized by different methods in terms of size, zeta potential, and drug loading capacity. MTT assay was used to investigate the anti-proliferation of GBA-loaded PEG-PLA NPs along with DOC. The therapeutic efficacy of PEG-PLA@GBA NPs & DOC was further investigated in C26 tumor-bearing BALB/c mice model. The resulting NPs were narrowly distributed (PDI = 0.06) with the mean diameter of 148 ± 9 nm with somewhat negative charge. GBA were efficiently loaded into mPEG-PLA NPs with encapsulation efficiency of about 40% ± 3. Cytotoxicity studies showed that NPs loaded with GBA and fixed concentration of docetaxel (20 nM) have higher toxicity (IC50 = 6 ± 1.8 µM) than either PEG-PLA@GBA (IC50 = 8 ± 1.2 µM) or free GBA (IC50 = 15 ± 3.5 µM) in C26 cells. In vivo studies revealed a synergistic effect of PEG-PLA@GBA NPs and DOC on tumor growth inhibition and survival rate in comparison with monotherapy approach.

The Localization of Phytohormones within the Gall-inducing Insect Eurosta solidaginis (Diptera: Tephritidae)

The phytohormone production hypothesis suggests that organisms, including insects, induce galls by producing and secreting plant growth hormones. Auxins and cytokinins are classes of phytohormones that induce cell growth and cell division, which could contribute to the plant tissue proliferation which constitutes the covering gall. Bacteria, symbiotic with insects, may also play a part in gall induction by insects through the synthesis of phytohormones or other effectors. Past studies have shown that concentrations of cytokinins and auxins in gall-inducing insects are higher than in their host plants. However, these analyses have involved whole-body extractions. Using immunolocalization of cytokinin and auxin, in the gall inducing stage of Eurosta solidaginis, we found both phytohormones to localize almost exclusively to the salivary glands. Co-localization of phytohormone label with a nucleic acid stain in the salivary glands revealed the absence of Wolbachia sp., the bacterial symbiont of E. solidaginis, which suggests that phytohormone production is symbiont independent. Our findings are consistent with the hypothesis that phytohormones are synthesized in and secreted from the salivary glands of E. solidaginis into host-plant tissues for the purpose of manipulating the host plant.

Health Promoting Properties of Bee Royal Jelly: Food of the Queens

Royal jelly (RJ) demand is growing every year and so is the market for functional foods in general. RJ is formed by different substances, mainly carbohydrates, proteins, and lipids, but also vitamins, minerals, and phenolic or volatile compounds in lower proportion. Major royal jelly proteins (MRJP) are, together with 10-hydroxy-2-decenoic acid (10-HDA), key substances of RJ due to their different biological properties. In particular, 10-HDA is a unique substance in this product. RJ has been historically employed as health enhancer and is still very relevant in China due to the traditional medicine and the apitherapy. Nowadays, it is mainly consumed as a functional food or is found in supplements and other formulations for its health-beneficial properties. Within these properites, anti-lipidemic, antioxidant, antiproliferative, antimicrobial, neuroprotective, anti-inflammatory, immunomodulatory, antiaging, and estrogenic activities have been reported for RJ or its specific components. This manuscript is aimed at reviewing the current knowledge on RJ components, their assessment in terms of authenticity, their biological activities, and related health applications.

The in vitro and in vivo wound-healing effects of royal jelly derived from Apis mellifera L. during blossom seasons of Castanea mollissima Bl. and Brassica napus L. in South China exhibited distinct patterns

BACKGROUND

Non-healing wounds have been a severe issue in the global healthcare system. Regrettably, royal jelly, a traditional remedy for various skin injuries, has not been widely applied in cutaneous wounds in clinical practice nowadays, which may be due to the confusion and the lack of knowledge about the efficacies of different types of royal jelly, the bioactive constituents, and the precise mechanisms underlying the wound repairing activity. Since the compositions and bioactivities of royal jelly are predominantly influenced by nectar plants, this study aims to explore the differences in the wound-healing properties of royal jelly produced by Apis mellifera L. during the blossom seasons of different floral sources, to provide guidelines for the future rational application of royal jelly in cutaneous wounds, and to promote the further discovery of wound repair-promoting substances.

METHODS

Royal jelly samples were harvested during flowering seasons of Castanea mollissima Bl. (chestnut) and Brassica napus L. (rapeseed) in South China, from which hydrophilic and lipophilic fractions were extracted. The in vivo wound-healing potential was preliminarily assessed in Wistar rats' excisional full-thickness wounds, followed by investigating the mechanisms of action through in vitro assays with human epidermal keratinocytes and LPS-stimulated inflammation in macrophages.

RESULTS

The results indicated that different royal jelly samples exhibited distinct wound-healing potential, in which Castanea mollissima Bl. royal jelly was more potent. It sped up wound closure between day 2 and day 4 to 0.25 cm²/day (p < 0.05), and could accelerate wound repair by enhancing the proliferative and migratory capabilities of keratinocytes by 50.9% (p < 0.001) and 14.9% (p < 0.001), modulating inflammation through inhibiting nitric oxide production by 46.2% (p < 0.001), and promoting cell growth through increasing the secretion of transforming growth factor-β by 44.7% (p < 0.001). In contrast, Brassica napus L. royal jelly could regulate inflammation by reducing the amount of tumour necrosis factor-α by 21.3% (p < 0.001).

CONCLUSIONS

The present study improves the application of royal jelly for curing difficult-to-heal wounds, in which the hydrosoluble extract of Castanea mollissima Bl. royal jelly promises the greatest potential. It also provides clues which may lead towards the identification of substances derived from royal jelly to treat wounds.

New Insights into the Biological and Pharmaceutical Properties of Royal Jelly

Royal jelly (RJ) is a yellowish-white and acidic secretion of hypopharyngeal and mandibular glands of nurse bees used to feed young worker larvae during the first three days and the entire life of queen bees. RJ is one of the most appreciated and valued natural product which has been mainly used in traditional medicines, health foods, and cosmetics for a long time in different parts of the world. It is also the most studied bee product, aimed at unravelling its bioactivities, such as antimicrobial, antioxidant, anti-aging, immunomodulatory, and general tonic action against laboratory animals, microbial organisms, farm animals, and clinical trials. It is commonly used to supplement various diseases, including cancer, diabetes, cardiovascular, and Alzheimer's disease. Here, we highlight the recent research advances on the main bioactive compounds of RJ, such as proteins, peptides, fatty acids, and phenolics, for a comprehensive understanding of the biochemistry, biological, and pharmaceutical responses to human health promotion and life benefits. This is potentially important to gain novel insight into the biological and pharmaceutical properties of RJ.

Freeze-Dried Royal Jelly Proteins Enhanced the Testicular Development and Spermatogenesis in Pubescent Male Mice

Simple Summary

Spermatogenesis and hormones secretions are serious life-threating and complicated process, which can be improve through science-based approaches. Royal jelly is a thick white milky fluid secreted by the hypopharyngeal and mandibular glands of young nurse worker bees (Apis mellifera) and used to feed their queen to expand their life. The results of the study revealed that, the growth performance of testis in exposed mice to freeze-dried Royal Jelly for 35 consecutive days were significantly enhanced in moderate dose among other treated doses. However, at Post Natal Days (PNDs 14 and PNDs 21), obviously changes were observed in histological examination of the testis while at PNDs-07 no major changes were observed. The Tunnel assay showed that, less apoptotic cells were detected in the testis of mice in high dose of freeze-dried RJ and oral administration of freeze-dried royal jelly can aggravate adverse effects via tempestuous on sexual hormone secretion at both PNDs 21 and PNDs 35 respectively.

Abstract

Spermatogenesis and hormones secretions are crucial endocrine and physiological process for maintaining the life. Royal Jelly (RJ) bioactive components are Major Royal Jelly Proteins (MRJPs), owing exceptional biological properties. However, the effects of RJ on pup’s testicular development during neonatal and pubertal period exposure hasn’t been adequately studied. The aim of the study was to detect neonatal sexual hormones concentration and histopathological changes on testicular development of the male progeny after oral exposure to freeze-dried RJ for 35 consecutive days. After mice give birth, male pups were collected together, separated by sex, and randomly standardized to seven (7) male pups per dam. Male pups were assigned to control diet (CON group), low dose RJ (L-RJ group) diet (control diet + 125 mg/kg/day RJ), moderate dose RJ (M-RJ group) diet (control diet + 250 mg/kg/day RJ) and high dose of RJ (H-RJ group) diet (control diet + 500 mg/kg/day RJ). After weaning, male pups were continuously fed with freeze-dried RJ until the age of PNDs 35. The results revealed that, oral M-RJ (250 mg/kg/day) administration significantly (p < 0.05) increased the testis weight, the diameter of seminiferous tubule and the height of seminiferous epithelium of offspring mice at PNDs 14. However, high-dose RJ (500 mg/kg/day) decreased the diameter of seminiferous tubule but increased the height of seminiferous epithelium of male offspring (p < 0.05) at the same time point. Furthermore, oral M-RJ treatment significantly (p < 0.05) increased the testis weight and spermatogenesis at PNDs 21. Whereas, oral H-RJ treatment significantly (p < 0.05) reduced the diameter of seminiferous tubule and the height of seminiferous epithelium at PNDs 21. At PNDs 35, oral M-RJ treatment increased the testis weight, the diameter of seminiferous tubule and the level of FSH. While, high-dose of RJ reduced testis weight and size (diameter of seminiferous tubule and height of seminiferous epithelium), ratio of apoptotic germ cells and incomplete spermatogenesis collectively. In addition, sexual hormone secretions (FSH, LH, E2) were decreased after RJs treatment (L-RJ, M-RJ, H-RJ) at PNDs 21 respectively. In conclusion, the results concluded that oral administration of low and moderate doses of RJ could enhance the development of testis at neonate period until pubescent, whereas unfavorable adverse effects induced by high dose of RJ might remain.

Royal jelly-derived proteins enhance proliferation and migration of human epidermal keratinocytes in an in vitro scratch wound model

Background

Skin injury is inevitable in daily life. In recent years, with the increasing morbidity of diseases such as diabetes and metabolic disorders, chronic wounds have become a considerable challenge in clinical practice. Royal jelly, reported to have multifarious biological and physiological properties, has been used as a remedy for a variety of wounds since ancient times. However, the active components and mechanisms underlying the wound-healing properties of royal jelly are still largely unknown.

Methods

Water-soluble proteins of royal jelly were fractionated and investigated for the proliferative and migratory effects on human epidermal keratinocytes (HaCaT) in an in vitro wound healing model. The proteins present in bioactive fractions were characterised and quantified using Label-free protein quantification method. The potential functions of these proteins in biological systems were further analysed using bioinformatic tools.

Results

A protein fraction, mainly containing major royal jelly proteins 2 (MRJP2), MRJP3 and MRJP7, stimulated proliferative and migratory activities in HaCaT cells without visible cytotoxicity. It exerted the greatest effects on the growth of HaCaT cells in the first 48 h. Furthermore, when treated with this protein fraction, the closure rates of the in vitro scratch wound were significantly increased. Functional analysis indicated that MRJP2, MRJP3 and MRJP7 were associated with carbohydrate transport and metabolism.

Conclusions

We fractionated the water-soluble proteins of royal jelly and identified one fraction (Fraction 2) that induced both proliferative and migratory effects on a human epidermal keratinocyte cell line. Major royal jelly proteins (MRJP2, MRJP3 and/or MRJP7) were speculated to possess potential wound-healing bioactivity. This is the first report that royal jelly may improve wound closure via MRJP-induced cellular proliferation and migration. These proteins may be valuable lead compounds for the development of novel wound healing medications. Our findings would facilitate better understanding of the wound repair mechanisms of royal jelly.

Antioxidant and anti-apoptotic effects of royal jelly against nicotine-induced testicular injury in mice

This study describes the effects of royal jelly (RJ) on testicular injury induced by nicotine (NIC) in mice. Thirty-six male BALB/c mice were randomly divided into six groups (n = 6). Group 1 received normal saline, group 2 received 100 mg/kgBW/day RJ, groups 3 and 4 received NIC at doses of 0.50 and 1.00 mg/kgBW/day, respectively, and groups 5 and 6 received NIC at doses of 0.50 and 1.00 mg/kg BW/day, respectively, plus RJ. Following 35 days, the serum level of testosterone, histopathological changes, germ cell apoptosis, proliferating cell nuclear antigen (PCNA), malondialdehyde (MDA) content, and antioxidant indexes including total antioxidant capacity (TAC) and catalase (CAT) activity were determined. In addition, the mitochondria-dependent apoptosis was investigated by assessing the Bcl-2, p53, and Caspase-3 mRNA levels expression by reverse transcription-PCR (RT-PCR). Compared to NIC receiving groups, the concomitant administration of RJ could protect the testosterone reduction and histological damages. After RJ treatment, the level of tissue MDA content decreased, while tissue TAC and CAT levels were remarkably increased compared to NIC-exposed groups. Remarkable higher TUNEL-positive germ cells and low PCNA index were observed in NIC receiving groups. Besides, the expression level of Bcl-2 was significantly higher and the p53 and Caspase-3 levels were significantly lower in the RJ co-administration groups than NIC-only receiving groups. Our results confirmed that RJ effectively protects the testis against NIC evoked damages by antioxidant and anti-apoptotic effects involving the up regulation of the antioxidant status, mitochondria-dependent apoptosis pathway prevention, and the proliferating activity improvement.

Review of the anticancer activities of bee products

Bee products have long been used in traditional medicine. The raw materials, crude extracts and purified active compounds from them have been found to exhibit interesting bioactivities, such as antimicrobial, anti-inflammatory and antioxidant activities. In addition, they have been widely used in the treatment of many immune-related diseases, as well as in recent times in the treatment of tumors. Bee product peptides induce apoptotic cell death in vitro in several transformed (cancer) human cell lines, including those derived from renal, lung, liver, prostate, bladder and lymphoid cancers. These bioactive natural products may, therefore, prove to be useful as part of a novel targeted therapy for some types of cancer, such as prostate and breast cancer. This review summarizes the current knowledge regarding the in vivo and in vitro potential of selective bee products against tumor cells.

Evaluation of the genotoxicity of zerumbone in cultured human peripheral blood lymphocytes

The chromosomal aberrations (CA) assay and micronucleus (MN) test were employed to investigate the effect in vitro of zerumbone (ZER) on human chromosomes. ZER is a sesquiterpene compound isolated from the rhizomes of wild ginger, Zingiber zerumbet Smith. The rhizomes of the plant are employed as a traditional medicine for some ailments and as condiments. ZER has been shown to have anti-cancer and apoptosis-inducing properties against various human tumour cells. It has also been shown to be active in vivo against a number of induced malignancies. Studies on ZER genotoxicity in cultured human peripheral blood lymphocytes (PBL) have not been reported so far. Therefore, the present study was undertaken to investigate the ability of ZER to induce chromosomal aberrations and micronuclei formation in human lymphocytes in vitro. Human blood samples were obtained from four healthy, non-smoking males aged 25-35years. Cultures were exposed to the drug for 48h at four final concentrations: 10, 20, 40 and 80 microM. Mitomycin C (MMC) was used as a positive control. The results of chromosomal aberrations assay showed that ZER was not clastogenic, when compared to untreated control, meanwhile MN test results showed a dose-dependent increase in MN formation. The overall clastogenic effect of ZER on human PBL was statistically not significant. In conclusion, ZER is a cytotoxic but not a clastogenic substance in human PBL.