Researchers from Clemson University’s Environmental Toxicology Program have published research connecting an enzyme associated with detoxification to obesity and fatty liver disease, especially in males.
William Baldwin, professor and graduate program coordinator in the College of Science’s department of biological sciences, and members of his laboratory used a novel mouse model developed in their laboratory to study the role of the Cyp2b gene in obesity.
Cyp2b is a key enzyme involved in metabolism, particularly in the detoxification of chemicals in the body.
Among other results, the research indicates a role for Cyp2b in unsaturated fatty acid metabolism, regardless of diet. Certain chemicals could inhibit Cyp2b, a phenomenon modeled by Cyp2b-null mice.
The study titled “Cyp2b-null male mice are susceptible to diet-induced obesity and perturbations in lipid homeostasis” was published in the Journal of Nutritional Biochemistry.
It is part of a three-year, $362,000 grant Baldwin received from the National Institutes of Health to continue studies on how exposure to chemicals is likely to inhibit our bodies’ internal mechanisms.
Contributing to the paper were Melissa Heintz, Ramiya Kumar, Meredith Rutledge and Baldwin.
“The male Cyp2b-null mice are obese – and much more obese – than the wild-type mice that are also fed a high fat diet,” Baldwin said.
There are several possible implications to human health.
“If you are exposed to chemicals that are metabolized by Cyp2b or inhibitors of Cyp2b, this might mean that you are not metabolizing something else in the body that is important,” Baldwin said.
“In turn, maybe your likelihood of retaining white adipose tissue increases and therefore your likelihood of being obese increases.”
In addition, male Cyp2b-null mice had increased fatty liver disease without being fed a high-fat diet.
“Cyp2b must be signaling something and telling the fat to go someplace, indicating that Cyp2b has dual roles: metabolizing toxicants and chemicals in the environment and pharmaceuticals, but it is also involved in metabolism of lipids and probably involved in signaling to tell us how to distribute fat,” Baldwin said.
With 40 percent of adults and 18.5 percent of youth in the United States now considered obese, the discovery that enzymes associated with detoxification may play a role in obesity – beyond the compounding effects of diet, exercise and general genetics – is critical.
Female Cyp2b-null mice did not show any greater propensity toward obesity, though there were indications that they have a higher rate of liver damage than wild-type female mice.
Gene expression was also affected. Cyp2b-null mice fed a normal diet have gene expression profiles similar to wild-type mice fed a high-fat diet.
“When the Cyp2b-null mice are fed a regular diet, their livers are acting like they are being fed a high fat diet,” Baldwin said.
Heintz, a third-year Ph.D. candidate in environmental toxicology, said there are still many pathways to explore in this area of research.
“You might be healthy but you might be exposing yourself to a chemical in the workplace,” she said.
“Even though your diet is pretty good, if you are losing this activity of an enzyme in your liver, what you may not have thought would be important may be important in metabolizing fat.”
This discovery also opens the door to exploring other enzymes that are currently thought to have one role but may also metabolize fat.
“Very little work has been done on this one particular enzyme, Cyp2b, and looking at its role in fatty acid metabolism,” Heintz said.
“It’s just one gene and there could be more that do similar things.”
“For all the obesity that occurred, the relative levels of fatty liver disease were not as high as we expected,” Baldwin added. “We did the study for only 10 weeks, and if we want to study liver disease, we need to go further.
We need to study the fatty liver disease phenomenon because that is the problem: 25 percent of the world’s population has nonalcoholic fatty liver disease. That’s increasing quite a bit.”
Kumar earned a Ph.D. at Clemson and is now a senior clinical process associate with a clinical research company in Bangalore, India.
Kumar said future research will show whether chemical inhibitors of these genes, such as plasticizers and pesticides, could also elicit a similar change in metabolism and lead to obesity.
“It will help us to plan better treatment regimens for obesity, along with changes in lifestyle and diet,” Kumar said.
This research has the potential to inform how scientists look at a host of metabolic disorders and chronic conditions, all with the goal of increasing human health.
“I think it tells us that obesity – and potentially fatty liver disease – is a multi-component disease,” Baldwin said.
“It is about, first and foremost, eating the wrong foods or eating too much.
But we can make it worse by external factors – whether that’s chemicals, a lack of exercise or the components of our diets.
There are a lot of little pieces to that, and this is one study that indicates that a healthy lifestyle involves a healthy diet, having the right calories and potentially avoiding some chemicals as well.”
In this study, we investigated the enzymes catalyzing the phaseⅠmetabolism of thiacalixarene (TCAS) based on in vitro system including cDNA-expressed P450 enzymes, human liver microsomes plus inhibitors and monoclonal antibodies. In addition, the inhibitory potential of TCAS on major CYP450 drug metabolizing enzymes (CYP1A2, CYP2C9, CYP2B6, CYP2D6 and CYP3A4) was assessed.
The results showed that CYP1A2 and CYP2C9 mediated TCAS hydroxylation.
IC50 values for TCAS in rat and human liver microsomes were greater than 50 µM, and it demonstrated a weak inhibition of rat and human CYP450 enzymes.
Finally, sandwiched hepatocytes were used to evaluate the induction of CYP1A and CYP3A to define the function of TCAS in vivo.
The results showed that incubation of TCAS at different concentrations for 72 h failed to induce CYP1A and CYP3A. However, incubation of the cells with 50 and 100 µM TCAS caused a profound decrease in the activities of CYP1A and CYP3A, which was probably due to cytotoxic effects, suggesting that exposure to TCAS might be a health concern.
Thiacalixarene (TCAS) is a cyclic oligomer containing multiple phenol units bound by sulfur atoms bridging the ortho phenolic hydroxyl groups.
It is considered the representative of the third-generation supramolecular receptor compounds .
Generally, thiacalixarene is categorized by the number of phenol units, for example, a thiacalixarene containing four phenol units is designated as thiacalixarene.
Its derivatives are generated by introducing different functional groups on the upper (phenyl ring groups) and the lower (phenolic hydroxyl groups) edges of its molecule.
Synergistic non-covalent interactions lead to formation of ionic and molecular complexes of thiacalixarene and its derivatives .
Further, the lipid-soluble thiacalixarene and its derivatives may be rendered water-soluble by introducing specific acid radical groups, for e.g., hydrosoluble sulfonated thiacalixarene is derived by introducing four sodium sulfonate groups into the phenyl ring of TCAS.
With the rapid industrialization and urbanization occurring in China, heavy metal pollution of the soil has reached a serious level, and is threatening the sustainable use of soil resources and the ecological safety of agricultural products.
Currently, soil replacement, which is not effective, is the most used approach to remediate heavy metal-contaminated sites in China.
Other methods are also used, but have limitations as well.
For example, contaminants processed by chemical fixation still remain in the soil, which is an environmental hazard that needs monitoring and evaluation for long-term safety .
Bioremediation is extensively used because of its cost-effective features and environmental safety, although it is associated with low efficiency and long running cycles.
In recent years, soil flushing technology has become an important chemical remediation method due to its advantages of stability and total effect, short cycle, user-friendly system, reduced waste, and extensive application .
In the early development of soil flushing technology, optimal decontamination rates were the focus.
In recent years, to address the needs of environmental protection and sustainable development, the technology has gradually evolved in a green and environmentally-friendly direction.
However, the current flushing agents are barely capable of simultaneously decontaminating heavy metal and organic pollutants in the soil.
A few flushing agents for heavy metals are not selective, which may cause large collateral losses of plant nutrients.
Therefore, exploration of flushing agents that specifically decontaminate metal ions is always the goal.
TCAS, the third-generation supramolecular receptor compound, has partial affinity for transition metals .
TCAS has very strong detection and binding affinity for metal ions of soft acids, such as Cd2+, Hg+, Pb2+, Sn2+, etc.
However, its binding affinity is extremely weak for metal ions of bases, such as K+, Na+, Ca2+ and Mg2+.
Previous studies indicated that TCAS not only has a flushing effect similar to EDTA for heavy metals such as Cd and Cu, but also avoids the massive loss of K+, Na+, Ca2+ and Mg2+, justifying its use in soil remediation.
Although no TCAS biosafety report is available, reports are available for calixarenes containing similar molecular structure and derivatives.
In 2000, Perret first reported that phosphated calixarenes had no toxic side effects on the growth of human fibrinogen cells .
Da Silva et al. reported that the solubility of red blood cells was not affected with sulfonated calixarene and its three derivatives with single substitution by phenolic hydroxyl groups at a concentration of 200 mmol·L−1 .
Sulfonated calixarene did not trigger an immune response and was nontoxic below 50 mmol·L−1. Anthony et al. studied the acute toxicity of sulfonated calixarene in mice using a 35S isotope tracer method.
The results suggested that sulfonated calixarene neither passed the blood-brain barrier nor entered the muscle cells in mice, but was rapidly excreted via urine. No sulfonated calixarene accumulated in the liver or spleen.
Sulfonated calixarene at levels below 100 mg·kg−1was non-toxic for mice .
In the absence of any biosafety assessment of TCAS or evaluation of the potential ecological risks of TCAS residues in soil after leaching, the safety risks of TCAS residues in environment were explored in this study. We elucidated its metabolic mechanisms using liver microsomes and recombinant enzymes and evaluated its effects on CYP450 enzyme in primary liver cells.
. . . . . .
In conclusion, TCAS was metabolized through CYP1A2 and CYP2C9, which was confirmed by a series of in vitro studies.
In addition, TCAS inhibited activities of CYP1A, CYP2C and CYP2D, but not CYP2B and CYP3A in rat liver microsomes.
It also exhibited weak inhibition against the activities of CYP1A2, CYP2C9, CYP2B6, CYP2D6 and CYP3A4 in human liver microsomes in vitro.
Taken together, the results suggested that TCAS manifested weak interactions with drugs that are metabolized by different CYP450 enzymes, as discussed above.
Our results revealed that TCAS had no effect on activities of CYP1A and CYP3A. Conversely, it exerted inhibitory effect on activities of CYP1A and CYP3A when the concentration of TCAS was greater than 50 µM, suggesting that human exposure to TCAS is not entirely safe.
More information: Melissa M Heintz et al, Cyp2b-null male mice are susceptible to diet-induced obesity and perturbations in lipid homeostasis, The Journal of Nutritional Biochemistry (2019). DOI: 10.1016/j.jnutbio.2019.05.004
Journal information: Journal of Nutritional Biochemistry
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