How Do Microplastics Damage The Kidneys?

A study in February this year showed that microplastics (MP) are widely present in the human body, not only in the lungs, intestines, liver, blood, urine, and kidneys, but also in the placenta. In addition, studies have shown that MP has gradually become a global problem, widely distributed in water, air, food, and soil, and the content of MP is associated with negative biological effects. Humans can be "invaded" by MP through diet, inhalation, or skin contact, which may lead to metabolic changes. Some previous evidence shows that MP promotes inflammation, oxidative stress organ dysfunction, and metabolic disorders, and there is a dose-dependent phenomenon.

Click to Cistanche for kidney disease

However, how MP affects the human kidneys and its relationship with kidney disease is not particularly clear at present. Therefore, Kidney International published a review from scholars from many countries2, reviewing the definition and source of MP, existing detection methods, main biological toxicity, and more importantly, describing some classic preclinical and clinical studies of MP in kidney disease. Scholars hope that this information can attract everyone's attention and help clinicians conduct relevant research.

Definition and Origin of MP

MP comes from plastic, which was invented by Belgian chemist Leo Hendrik Baekeland in 1909 and has a history of 100 years. Plastic has been widely used in our work and life. In the medical field, plastic is widely used. Test tubes, surgical drapes, catheters, probes, and venous/arterial access all contain plastic or are mainly made of plastic. It is precisely because plastic is widely present in our lives that plastic-related waste and pollution are also widely present around the world. For example, more than 250,000 tons of plastic waste has accumulated in the ocean.

Due to degradation or mechanical force, plastic can be decomposed into small particles, which are MP or nanoplastics. MP is an organic polymer particle with a size of less than 5 mm and various shapes, while nanoplastics (still controversial) are polymers with a size of less than 1 micron. Due to the long time for the complete degradation of plastic and the large daily production, our lives are full of plastic and MP.

Biotoxicity of MP

Many years ago, in vitro and in vivo studies have shown that MP is associated with inflammatory molecule disorders (such as interleukins, tumor necrosis factors, chemokines, transcription and growth factors, etc.) and oxidative stress. In addition, MP and nanoplastics can carry/encapsulate heavy metals and other organic compounds into the human body (like a Trojan horse), increasing the risk of cancer. Phthalates and other additives used in the manufacturing process of plastics can cause additional toxicity. In short, different MP and nanoplastics have different toxicities to humans and organisms depending on the process. However, regardless of the process used to produce plastics, their MP and nanoplastics are toxic to organisms.

Studies have confirmed that MP can accumulate in multiple organs. In 2022, scientists detected MP in human blood for the first time and found that MP can accumulate in human blood vessels, thereby endangering the cardiovascular system. Other studies have found that MP can affect the endocrine system of mammals, including but not limited to the thyroid, testicles, ovaries, pituitary glands, and adrenal glands. Therefore, MP has the potential to promote the progression of chronic diseases such as obesity, diabetes, and cancer. In addition, studies in mouse models suggest that MP can reduce the self-renewal ability of hematopoietic stem cells.

MP detection methods

Currently, measuring MP in vivo is a challenging task. Because there is currently no measurement method that can fully qualitatively or quantitatively examine various types of MP. Different types of microscopes can physically distinguish MP from non-MP tissues, but are more difficult to use for quantification and identification of different types of MP. Analytical techniques such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy can distinguish different MPs based on the type of plastic and/or additive. Mass spectrometry and gas chromatography can detect MP, but their sample preparation may be cumbersome.

In addition, different biological samples may require different measurement methods, such as pyrolysis-gas chromatography-mass spectrometry for blood samples, Raman spectroscopy for urine, infrared spectroscopy for feces, and microscopy (including staining and fluorescent light) for MP accumulation in solid tissues (such as liver and kidney). Therefore, attention should be paid to the examination methods in animal and clinical studies related to MP.

Effects of MP on the kidney

1 Research evidence

Currently, the evidence for the effect of MP on the kidney is mainly based on animal models, and there is less clinical evidence. However, some conclusions from animal models can provide a reference for clinical research. However, MP is present in the kidneys and urine of both humans and animal models.

A study in a male mouse model showed that MP may be excreted through urine. Mice were exposed to fluorescent polystyrene microparticles (100 nm and 3 μm) by tail vein injection, oral gavage, or pulmonary perfusion. The results showed that MP appeared in the glomerular tufts and could not pass the intact glomerular barrier. After MP left the glomerulus through the efferent artery and entered the capillaries of the renal tubules, it was taken up by the epithelial cells of the proximal tubules, excreted into the lumen of the renal tubules through the renal tubular secretory system, and excreted with urine.

However, another study confirmed that MP exposure was taken up through the cell membrane, and these particles also existed in the cytoplasm, which could lead to increased mitochondrial activity, overexpression of pro-apoptotic cytokines, and ultimately increased inflammation.

Another line of evidence showed that if MP was not injected once but multiple doses (0.2 or 0.4 mg/d), polystyrene microparticles could accumulate in the kidneys of mice and were the main cause of kidney and multi-organ damage in mice. If 1 μm polystyrene was given at a dose of 2 mg/kg for 28 days, the kidneys of mice showed significant oxidative stress, inflammation, and endoplasmic reticulum stress. If MP is taken orally, it is also nephrotoxic to young mice, which is manifested as weight loss, decreased kidney and heart function, and may also be accompanied by hematuria and a significant increase in serum creatinine.

The above evidence has been summarized in Figure 1. Figure 2 summarizes the effects of MP on biological tissues, especially the sites, tissues, or body fluids where MP accumulates.

Unfortunately, however, there are no studies on MP in humans.

2 Future research directions for MP and CKD

At present, although we have found that human kidneys and urine contain a large amount of MP, clinical studies on regular human consumption/exposure to MP have not been conducted. Therefore, it is not clear what the long-term effects of MP exposure on human kidneys are and what the minimum threshold of MP exposure is.

We can study the following three questions:

① Can human glomeruli filter MP? How much can be filtered?

② Is MP accumulation likely to aggravate CKD?

③ The accumulation of uremic toxins can damage the intestinal barrier, so does this damage help the body absorb MP?

However, based on animal models, we can see that MP can induce changes in kidney function and morphology, as well as cause multi-organ damage. Secondly, the accumulation of MP is related to the particle size of MP. Finally, no study has yet explored whether MP is related to the progression of CKD. Scholars believe that this should be explored in depth in the future.

In addition, we must conduct more analysis on patients undergoing hemodialysis and peritoneal dialysis. Peritoneal dialysis and hemodialysis patients are exposed to a large amount of plastic every day, such as catheters, dialyzers, and dialysate packaging, which are all related to plastic. Blood passes through plastic-containing catheters and dialyzers, and the peritoneum is in direct contact with the dialysate (which may have been in a plastic container the previous second), and the peritoneal catheter is also made of plastic. Therefore, we should focus on studying this group of people.

Currently, only one clinical study on PM and kidney disease is underway (NCT05155267), which aims to detect whether PM in the body fluids (including blood, lymph, etc.) of hemodialysis patients will cause genetic toxicity, immune damage, and renal damage.

In addition, we should conduct more clinical studies to remove and/or degrade PM in the human body, because existing evidence does show that PM is toxic to organisms. According to animal model studies, PM is excreted through the kidneys, so drugs or treatments targeting the kidneys should also be of concern to our colleagues.

How Does Cistanche Treat Kidney Disease?

Cistanche is a traditional Chinese herbal medicine used for centuries to treat various health conditions, including kidney disease. It is derived from the dried stems of Cistanche deserticola, a plant native to the deserts of China and Mongolia. The main active components of cistanche are phenylethanoid glycosides, echinacoside, and acteoside, which have been found to have beneficial effects on kidney health.

Kidney disease, also known as renal disease, refers to a condition in which the kidneys are not functioning properly. This can result in a buildup of waste products and toxins in the body, leading to various symptoms and complications. Cistanche may help treat kidney disease ase through several mechanisms.

Firstly, cistanche has been found to have diuretic properties, meaning it can increase urine production and help eliminate waste products from the body. This can help relieve the burden on the kidneys and prevent the buildup of toxins. By promoting diuresis, cistanche may also help Reduce high blood pressure, a common complication of kidney disease.

Moreover, cistanche has been shown to have antioxidant effects. Oxidative stress, caused by an imbalance between the production of free radicals and the body's antioxidant defenses, plays a key role in the progression of kidney disease. ies help neutralize free radicals and reduce Oxidative stress, thereby protecting the kidneys from damage. The phenylethanoid glycosides found in cistanche have been particularly effective in scavenging free radicals and inhibiting lipid peroxidation.

Additionally, cistanche has been found to have anti-inflammatory effects. Inflammation is another key factor in the development and progression of kidney disease. Cistanche's anti-inflammatory properties help reduce the production of pro-inflammatory cytokines and inhibit the activation of inflammation mandatory pathways, thus alleviating inflammation in the kidneys.

Furthermore, cistanche has been shown to have immunomodulatory effects. In kidney disease, the immune system can be dysregulated, leading to excessive inflammation and tissue damage. Cistanche helps regulate the immune response by modulating the production and activity of immune cells, such as T cells and macrophages. This immune regulation helps reduce inflammation and prevent further damage to the kidneys.

Moreover, cistanche has been found to improve renal function by promoting the regeneration of renal tubes with cells. Renal tubular epithelial cells play a crucial role in the filtration and reabsorption of waste products and electrolytes. In kidney disease, these cells can be damaged, leading to damaged renal function. Cistanche's ability to promote the regeneration of these cells helps restore proper renal function and improve overall kidney health.

In addition to these direct effects on the kidneys, cistanche has been found to have beneficial effects on other organs and systems in the body. This holistic approach to health is particularly important in kidney disease, as the condition often affects multiple organs and systems. che has been shown to have protective effects on the liver, heart, and blood vessels, which are commonly affected by kidney disease. By promoting the health of these organs, cistanche helps improve overall kidney function and prevent further complications.

In conclusion, cistanche is a traditional Chinese herbal medicine used for centuries to treat kidney disease. Its active components have diuretic, antioxidant, anti-inflammatory, immunomodulatory, and regenerative effects, which help improve renal function and protect the kidneys from further damage. , cistanche has beneficial effects on other organs and systems, making it a holistic approach to treating kidney disease.