Obesity, a growing global concern, is often accompanied by chronic inflammation and an imbalance between pro-inflammatory and anti-inflammatory mediators. Adipose tissue (AT) inflammation plays a significant role in this process, with adipocytes releasing inflammatory cytokines like interleukin-6 (IL-6). Macrophage infiltration in obese AT is associated with the expression of proinflammatory adipocytokines, further contributing to the inflammatory pathology. Indole-3-carbinol (I3C), a compound found in cruciferous vegetables, has shown promise in mitigating inflammation and potentially aiding weight loss. This article explores the potential role of I3C in weight management, focusing on its effects on inflammation, adipogenesis, and angiogenesis.
I3C: A Bioactive Compound from Cruciferous Vegetables
I3C is a bioactive indolic compound derived from glucosinolates, which are found in cruciferous vegetables such as broccoli, cabbage, Brussels sprouts, kale, and cauliflower. Epidemiological studies have indicated that higher consumption of these vegetables may reduce the risk of cancer and cardiovascular diseases. I3C has demonstrated efficacy in preventing breast, endometrial, and cervical cancers. Research suggests that I3C can suppress lipopolysaccharide-induced iNOS, nitric oxide, and proinflammatory cytokines in macrophages.
I3C and Macrophage Infiltration in Adipose Tissue
Obesity is characterized by increased infiltration of macrophages into adipose tissue. Studies using anti-F4/80 antibodies have revealed appreciable positive staining in epididymal AT of mice fed a high-fat (HF) diet. However, there was no significant difference in the AT between the control group and the HF+I3C (HFI) group. The macrophage-specific marker, F4/80, is expressed significantly higher in the HF group as compared with the control diet group and significantly lower in the HFI group as compared with the HF group. The similar levels of F4/80 in the control group and HFI group indicate that I3C prevents HF-induced infiltration by macrophages.
Effects of I3C on Inflammatory Mediators
A study investigated the effects of I3C on adipogenesis- and angiogenesis-associated factors in mature adipocytes. The cross-talk between mature adipocytes and endothelial cells (ECs) was also explored by cultivating ECs in a conditioned medium (CM) by using I3C-treated adipocytes. The results revealed that I3C significantly inhibited triglyceride accumulation in mature adipocytes in association with significantly increased expression of AhR and CYP1B1 proteins as well as slightly decreased nuclear factor erythroid-derived factor 2-related factor 2, hormone-sensitive lipase, and glycerol-3-phosphate dehydrogenase expression by mature adipocytes. Furthermore, I3C inhibited CM-stimulated endothelial tube formation, which was accompanied by the modulated secretion of angiogenic factors in adipocytes, including vascular endothelial growth factor, interleukin-6, matrix metalloproteinases, and nitric oxide.
In Vitro Studies: I3C and Inflammatory Mediators in Co-cultured Adipocytes and Macrophages
Differentiated adipocytes were co-cultured with RAW 264.7 cells for 24 h and then treated with I3C (zero to 100 μM) for 24 h. The nitrite decreased as the concentration of I3C increased. The I3C treatment suppressed nitrite by 62.3% at 100 μM I3C, 15.9% at 10 μM, 6.0% at 1 μM compared with no I3C added. In primary adipocytes or RAW macrophages cultured alone, the concentration-response inhibitive effect of I3C on nitrite release was not evident. Interestingly, the nitrite production was dramatically increased during the co-culture of adipocytes and macrophage compared with the two cells cultured alone.
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The effect of I3C on expression of iNOS mRNA in co-culture of adipocytes and macrophages by reverse transcriptase polymerase chain reaction was also investigated. The level of iNOS mRNA expression changed downward as the concentration of I3C increased. The level of iNOS mRNA expression at concentration=10 μM was lower than at concentration=0 μM, and the level of iNOS mRNA expression at concentration=100 μM was lower than at other concentrations. The results indicate that the treatment of I3C reduced expression of iNOS.
High expression of IL-6 was detected when adipocytes were co-cultured with RAW 264.7 macrophages. Expression of IL-6 was reduced by adding I3C, suggesting that I3C may play a role in modulating the inflammatory response in obesity.
I3C and Adipogenesis
I3C has shown to exhibit antiobesity activity by reducing body weight and fat in animals fed a high-fat diet and by inhibiting the differentiation of 3T3-L1 preadipocytes. I3C may act through activating lipolysis and/or inhibiting lipogenesis to reduce TG accumulation in mature adipocytes from the evidence that I3C increased the glycerol released into the medium and suppressed the expression of GPDH, a key enzyme in lipogenesis, at high concentrations.
I3C and the Aryl Hydrocarbon Receptor (AhR)
Being an activator of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor crucial in adipogenesis and angiogenesis, it is considered that I3C executes its activities through the AhR. I3C is a naturally occurring AhR agonist that exhibits antiobesity activities, such as the reduction of body and WAT weights in high-fat-diet-induced obese mice and the inhibition of adipocyte differentiation by activating the silent mating type information regulation 2 homolog 1 and subsequently downregulating the expression of PPARγ2, C/EBPα, and aP2, factors crucial for differentiation.
I3C and Angiogenesis
Substantial tissue remodeling that occurs within adipose tissues during fat mass expansion is accompanied by angiogenesis. I3C (5-50 μM) inhibited endothelial tube formation stimulated by the CM from mature adipocytes, and this suppression was associated with the decreased secretion of angiogenic factors, including VEGF, IL-6, NO, and MMPs, by mature adipocytes.
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I3C's Potential Mechanisms in Anti-Angiogenesis
I3C (5-50 μM) suppresses adipocyte-induced angiogenesis both by reducing TG accumulation in mature adipocytes leading to reduce the secretion of angiogenic mediators, and by directly inhibiting IL-6 expression in mature adipocytes. Alternatively, I3C lowers leptin levels and increases serum adiponectin levels in obese animals; these effects may contribute to the antiangiogenic effect of I3C observed in this study.
I3C and Estrogen Metabolism
Indole-3-carbinol has been shown to act as a catalyst to decrease the body’s load of unhealthy estrogens and reduce symptoms of estrogen dominance. Indole-3-carbinol acts as a phytoestrogen (binds to bad estrogen to eliminate it from the body) blocking the ability of cancer cells to replicate. Studies show that indole-3-carbinol not only suppressed the cell division of certain breast cancer cells by inducing programmed cell death (apoptosis) while producing no such effect on normal breast cells. This effect may be one of the reasons that a high lifetime intake of cruciferous vegetables is associated with a significant reduction in breast cancer.
Practical Considerations and Safety
The estimated daily intake is at the equivalent of 6.4 mg of I3C in the UK, where the cruciferous vegetable tends to be a dietary staple. Ideally, this dose would generate ca. 9 μM of plasma I3C concentration in a 70 kg subject on the basis that blood volume comprises 7% of the body weight without considering digestion and absorption. Although the plasma I3C concentration from ordinary vegetable consumption is lower than the concentrations used in this study, higher plasma concentrations may be possibly achieved by taking I3C dietary supplements.
Studies in rats, chickens, guinea pigs, mice, and dogs suggest that I3C is safe at recommended doses. Human trials have found no significant side effects with I3C. However, one study in rats found increased abnormalities in male offspring, specifically related to their fertility. For this reason, I3C supplements should not be used by pregnant women.
Potential Interactions and Cautions
Persons who are taking any medication that contains estrogen (including birth control pills) should be aware that I3C might interfere with the action of this type of medication. Other studies found interactions with the antipsychotic Clozaril (clozapine) and the selective serotonin reuptake inhibitor Cymbalta (duloxetine). Persons who have already had cancer should not use I3C (or any other supplement) except under physician supervision. High doses of IC3 have been shown to cause gastrointestinal issues and tremors, and healthcare providers urge patients to consume IC3 from food sources rather than supplements until more studies confirm their effectiveness and safety.
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I3C as a Dietary Supplement
I3C is promoted as a dietary supplement for specific health benefits, with several common names, including Indolylmethanol, 3-Indolylcarbinol, 3-(Hydroxymethyl)indole, Indole-3-methanol, and I3C. It has been proposed as a chemopreventive agent, with other proposed uses including liver protection and respiratory papillomatosis.
Scientific Evidence and Therapeutic Dosages
A four-week, double-blind, placebo-controlled trial of fifty-seven women found that a minimum dose of 300 mg of I3C daily may be necessary to reduce the risk of estrogen-promoted cancers. Another study found benefits with 400 mg of I3C per day. However, until the overall effects of I3C are better understood, it is recommended that one obtain this substance through the consumption of broccoli family vegetables rather than by taking it as a supplement.