Last update and review: September 14, 2021.
A Short Summary.
Beltzig et al., 2021 (1), add another study to the mountain of already existing literature that proclaims curcumin safe. There is a useful takeaway, however. Indeed, the results obtained by Beltzig et al., 2021 (1), indicate that curcumin alone is not senolytic even at high, cyto- and genotoxic doses. This finding by Beltzig et al., 2021 (1), contradicts the results of Yousefzadeh et al., 2018, who observed some senolytic activity of curcumin. However, the concentration of curcumin was about 5microMole(per liter?), and, therefore, too close to the cyto- and genotoxic concentration of 10microMole(per liter?) reported by Beltzig et al., 2021 (1). This high concentration is also not realistic with oral intake of curcumin.
Our article also contains a couple of words of caution on the safety of curcumin.
Some senolytic activity of curcumin alone was reported in the study of Yousefzadeh et al., 2018. Concentrations of all flavonoids are very high (unrealistic?).
At a dose of 5μM, fisetin was most effective in reducing the fraction of senescent cells (SA-ß-gal positive MEFs.
Figure 1 (A) from Yousefzadeh et al., 2018.
Yousefzadeh et al., 2018:
“(A) Passage 5Ercc1 −/− MEFs were treated with a panel of flavonoid compounds at a dose of 5μM and the viability of senescent cells (SA-β-gal + cells detected by C12FDG staining; red bars) and total cells (black bars) measured using an IN Cell Analyzer 6000. The number of viable cells is calculated relative to cellstreated with vehicle only (DMSO).n= 3 independent experiments, one-way ANOVA.”
The study by Beltzig et al., 2021 (1): “Cytotoxic, Genotoxic and Senolytic Potential of Native and Micellar Curcumin.”
Beltzig et al., 2021 (1) tested curcumin solubilised in ethanol and a formulation of curcumin embedded in micelles on PEG80 basis.
Beltzig et al., 2021 (1):
“When preparing dishes containing curcumin (e.g., “curry”), turmeric is usually suspended in oil under heat. From this suspension, in which micellar structures form, curcumin can better be absorbed in the gastrointestinal tract. To overcome uptake limitations, a formulation of curcumin embedded in micelles on PEG80 basis was developed and shown to have superb uptake properties.”
“We show that curcumin induces cyto- and genotoxicity in a narrow, high dose range between 10 and 60 µM.”
Beltzig et al., 2021 (1):
“First, we show that Cur-E and Cur-M reduce the viability of human cells irrespective of its origin, including human diploid fibroblasts, human primary pericytes, endothelian cells, smooth muscle cells, established endothel cells and human glioblastoma cells. In these cell models, the concentration range in which a decline in viability was observed was 10–60 µM, and Cur-E and Cur-M caused a similar response. The cytotoxic effect was confirmed showing that Cur-E and Cur-M induce cell death by apoptosis in human fibroblasts and cancer (glioblastoma) cells. Apoptosis increased dose-dependently, and the lowest concentration inducing a significant effect was 20 µM (48 h treatment). Again, Cur-E and Cur-M were similarly effective.”
Cytotoxicity is therefore an immediate, acute effect of curcumin.
Beltzig et al., 2021 (1):
“Curcumin-induced apoptosis was reported in various cell systems, including NIH3T3 and L929 mouse fibroblasts, human colon carcinoma cells (HT-29), human breast carcinoma cells (MCF-7) and rat glioma cells (C-6)] [28,47,48,49,50]. Induction of apoptosis was preceded by a ROS burst, which followed the activation of the mitochondrial apoptosis pathway through a release of AIF and cytochrome C from the mitochondria, activation of caspases and PARP-1 cleavage (as an indicator of apoptosis). The p53-p21-CDC2 signaling pathway was also shown to be activated, leading to cell cycle arrest via Rb dephosphorylation and downregulation of cyclin D1 and cyclin D3 [50]. It is interesting that, in all studies, the induction of apoptosis occurred in a narrow dose range of 10–80 µM curcumin (dissolved in DMSO). Apoptotic effects occurred in MCF-7 cells as early as 24 h after treatment with curcumin and reached a maximum 48 h after administration [50]. Cytotoxicity is therefore an immediate, acute effect of curcumin. Our data are in line with this. Irrespective of the cell type, cell death by apoptosis occurred with an exposure concentration of >10 µM. This was the case in a variety of human primary cells and cancer cell lines. According to our data, 10 µM can be considered as a cytotoxic threshold dose for human cells, which applies for both Cur-E and Cur-M.”
No difference in cyto- and genotoxicity of curcumin on cancer and normal cells.
Beltzig et al., 2021 (1):
“There was no difference between curcumin solubilised in ethanol (Cur-E) and the micellar formulation of curcumin (Cur-M) and between cancer and normal cells. Genotoxic effects vanished upon post-incubation in the absence of curcumin, indicating they are transient and subject to repair. Micelles not containing curcumin were negative in all assays, i.e., they do not bear a cytotoxic or genotoxic potential.”
“Curcumin was not senolytic.”
“Figure 3” from Beltzig et al., 2021 (1): Effect of curcumin on the viability of proliferating and senescent cells.
Beltzig et al., 2021 (1):
“Proliferating (Pro) and senescent (Sen) LN229 (A,C) and A172 (B,D) cells were treated with the indicated dosages of Cur-E or Cur-M. (A,B) Dose response of proliferating and senescent LN229 (A) and A172 (B) cells upon curcumin treatment. (C,D) Comparison of Cur-E and Cur-M in reduction in viability in LN229 (C) and A172 (D) cells. Viability (MTT OD570) of non-treated control was set to 1. The senolytic drug ABT-737 served as a positive control.”
Curcumin in a subtoxic concentration (10 µM) has no senolytic activity and does not impact the senescence level, irrespective of whether it is administered as curcumin solubilised in ethanol (Cur-E) or the micellar formulation of curcumin (Cur-M).
Beltzig et al., 2021 (1):
“To substantiate the data further, we measured the relative amount of senescent and apoptotic cells in the population eight days after temozolomide treatment and, following addition of Cur-E or Cur-M to the medium, two days later. The data revealed that curcumin (10 µM) had no impact on the yield of temozolomide-induced senescent cells and the total cell death (early and late apoptosis/necrosis) level in the population (Figure 4A,B). Overall, the data show that curcumin in a subtoxic concentration has no senolytic activity and does not impact the senescence level, irrespective of whether it is administered as Cur-E or Cur-M.”
“Figure 4” from Beltzig et al., 2021 (1): Curcumin does neither reduce the senescence level nor induces apoptosis in a senescent population.
Beltzig et al., 2021 (1):
“Temozolomide-induced senescent LN229 (A) and A172 (B) cells were treated with Cur-E and Cur-M in a concentration that was not apoptosis-inducing on proliferating cells. Senescence and cell death were measured by C12FDG and AV/PI staining, respectively, in a flow cytometer. Mean ± SEM, statistical analysis through Two-way ANOVA test. Differences between control, Cur-E and Cur-M were not significant.”
Curcumin, irrespective of the formulation, is not a senolytic agent, but the study has limitations.
Beltzig et al., 2021 (1):
“Our data suggest that curcumin, irrespective of the formulation, is not a senolytic agent. We are aware of the limitations of this study as we assessed the effect in only two cancer cell lines and under limited treatment conditions. More detailed studies are clearly required in order to come to a more generalized conclusion.”
Curcumin preparations cuased DNA damage in human fibroblast in a dose-dependent manner.
Beltzig et al., 2021 (1):
“The finding that curcumin is able to induce ROS (our data and [40]) prompted us to investigate in detail the question of DNA damage induction. Treatment with Cur-E and Cur-M dose-dependently induced DNA breaks in human fibroblasts.”
DNA breaks can be observed already after 1 h of exposure to curcumin, but short-term treatment did not result in permanent DNA damage.
Beltzig et al., 2021 (1):
“The observed effects are not a byproduct of cytotoxicity, as positive effects in the FPG comet assay can be observed already after 1 h of exposure. This indicates that oxidative DNA damage is induced immediately after curcumin treatment, which is in line with a previous report [40]. It is important to note that removal of Cur-E or Cur-M from the medium returned the DNA tail moment to the basal level, indicating efficient repair of DNA lesions. Thus, short-term treatment did not result in permanent DNA damage, indicating the effects are transitory and not stable. The finding indicates that, in assessing the genotoxic potential, it is important to take into consideration not only the exposure concentration, but also the period of exposure. This applies also to the endpoint apoptosis, which was measured 2 days after addition of Cur-E or Cur-M to the medium. The continuous presence of curcumin in the medium was necessary for eliciting a significant toxic and genotoxic effect on cells.”
Curcumin is not mutagenic.
Beltzig et al., 2021 (1):
“Curcumin is negative in bacterial test systems [25] and not mutagenic. It is considered an anti-oxidant in the low dose range, causing protection against some genotoxins, e.g., radiation-induced DNA damage [27]. However, in the high dose range (>5 µM), curcumin acts as a radical generator and pro-oxidant, causing a ROS burst and the associated oxidative DNA damage.”
Beltzig et al., 2021 (1), conclude that micelles, which have a nanosized structure based on “polyethylene glycol 80” (“PEG80”), can be considered as safe transport vehicles.
Beltzig et al., 2021 (1):
“Curcumin administered in a micellar formulation had a cytotoxic and genotoxic profile similar to curcumin dissolved in ethanol (similar data were obtained with curcumin dissolved in DMSO). Thus, the data demonstrate that micellar curcumin does not bear toxic and genotoxic properties that are different from native curcumin. From the available data, we define a cytotoxic and genotoxic threshold for curcumin at a concentration of 10 µM, which seems to be independent of the formulation and cell system (our data and data in the literature). Micelles without curcumin were completely devoid of cytotoxic and genotoxic activity. Therefore, micelles, which have a nanosized structure, can be considered as safe transport vehicles.”
Is “PEG80”safe? Another formulation of polyethylene glycol, PEG or macrogol-3350, has teratogenic effects, i.e. reproductive toxicity.
From an article on this website:
“One of the therapeutic agents for constipation mentioned by Spiller, 2016 (1), is Movicol (polyethylene glycol (PEG or macrogol-3350)).
The patient leaflet Movicol does not mention any significant toxicity and sais Movicol can be taken during pregnancy. We need to dig into the “information for health professionals” to learn that, in animal trials, serious negative effects were observed:
“Reduction in fetal and placental weights, reduced fetal viability, increased limb and paw hyperflexion and abortions, were noted in the rabbit at a maternally toxic dose that was 3.3 x the maximum recommended dose in humans for treatment of chronic constipation and 1.3 x for faecal impaction. Rabbits are a sensitive animal test species to the effects of GI-acting substances and the studies were conducted under exaggerated conditions with high dose volumes administered, which are not clinically relevant.”
Beltzig et al., 2021 (1), conclude that curcumin is safe because the normal human intake would result in blood concentrations that are about 100-fold lower than the cyto- and genotoxic concentration of 10-60 microMole(per litre?).
The acceptable daily intake (ADI) is from up to 3 mg/kg of body weight and the resulting concentration of curcumin in the blood serum of humans would be lower than 100 nM.
Beltzig et al., 2021 (1):
“Following uptake of Cur-M in the acceptable daily intake (ADI) range (max 3 mg/kg BW), the concentration of curcumin in the blood serum of humans was estimated to be lower than 100 nM (ref. [56] and J. Frank, personal communication). This is far below the cytotoxic and genotoxic level observed in vitro. It would be interesting to see whether beneficial effects of curcumin, e.g., anti-inflammatory responses, are evoked at curcumin concentrations that are below the toxic threshold.”
Beltzig et al., 2021 (1): “the natural form of curcumin and the micellar formulation do not bear harmful side effects.”
Beltzig et al., 2021 (1):
“Overall, curcumin reduces cell viability and induces apoptosis as well as genotoxicity in a narrow, overlapping concentration range between 10 and 60 µM. For inducing cytotoxicity through apoptosis, long-term treatment is required; short-term exposure (60 min) was insufficient to elicit toxic effects. Genotoxic effects, measured in the alkaline and comet assay, vanished after post-exposure of cells in curcumin-free medium, indicating that lesions were transiently induced and repaired. Cur-E and Cur-M did not show senolytic activity on cancer cells, in which senescence was induced by the chemotherapeutic temozolomide. Cur-M was not more effective than Cur-E in inducing DNA damage, as measured in comet assays, and micelles were completely devoid of these effects, indicating that micelles do not bear a cytotoxic and genotoxic potential. The concentration dependence of cytotoxicity and genotoxicity reported here, together with animal experiments [46], and the record of the long-term and extensive dietary exposure of humans to native curcumin and the absence of any reports of associated toxicity, support the notion that the natural form of curcumin and the micellar formulation do not bear harmful side effects. The normal intake quantities of curcumin and the recommended inclusion levels of supplements are about 100-fold lower than the concentration considered to be toxic in the in vitro assays, indicating a wide margin of safety.”
Is curcumin safe? Curcumin has estrogen-mimicking and androgen-antagonizing properties, affects male and female reproduction and sex organs in animal studies.
Murphy et al., 2012:
“Many of the noted (in the study by Murphy et al., 2012 (1), reproductive effects of curcumin-PEG could be attributed to estrogen-mimicking or androgen-antagonizing properties of curcumin.”
Uterine hypertrophy is the prototype estrogen bioassay and it was observed in the study by Murphy et al., 2012.
Murphy et al., 2012:
“Uterine hypertrophy is the prototype estrogen bioassay [9]. Likewise, vaginal opening in puberal rodents is a classical estrogenic response [10]. Indeed, curcumin displaced estradiol binding to its receptors [19; unpublished observations].”
The overall estrogenic action can therefore be reduced if some phytoestrogens competitively displace estradiol.
The fact that a phytoestrogen displaces estradiol from binging to estradiol receptors should not necessarily result in increased estrogenic action. Indeed, phytoestrogens are often allegedly weaker estrogens than estradiol. The overall estrogenic action can therefore be reduced if some phytoestrogens competitively displace estradiol. However, the impact of curcumin on sexual organs and function goes far beyond competitive binding to estrogen receptors. Curcumin reduces androgen receptor expression.
Effects of curcumin on androgenic tissues (“Figure 3” from Mohajeri et al., 2020).
Mohajeri et al., 2020:
“Prostate tissue is a target of androgenic and estrogenic effectors via estrogen receptor beta (ERß), and androgen receptor (AR). The induction of the prostatic tissue causes hypertrophy, enlargement and urethra obstruction. Chronic prostate (androgenic) stimulation may induce prostate cancer (PC). Curcumin effects on PC cell models include reduction of cell proliferation, cell migration and androgen receptor expression. The molecular mechanism involved the inhibition of AP-2γ and c-Jun. Curcumin also inhibits the activity of ß-catenin and NF-kB via Tcf-4, CBP and p300 proteins causing diminished cell growth and migration. Interestingly, curcumin may also induce pro-apoptotic processes by promoting Cyt-c release and increasing Bax activity. It was observed that curcumin diminishes PSA levels in cell models and clinical studies.”
Curcuma comosa extract reduced seminal vesicle weights in mice.
Murphy et al., 2012:
“In breast cancer cells, curcumin elicited gene expression profiles typical of estrogen/phytoestrogen actions [20, 21]. Estradiol (akin to a hexane extract of Curcuma comosa) reduced seminal vesicle weights in mice [22].”
Conclusions.
Beltzig et al., 2021 (1), add another study to the mountain of already existing literature that proclaims curcumin safe. There is a useful takeaway, however. Indeed, the results obtained by Beltzig et al., 2021 (1), indicate that curcumin alone is not senolytic even at high, cyto- and genotoxic doses.
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