Author
Summary: Prof. Gratiana Steinkamp, as published in Alpha1 Journal 1/2023.
Alpha-1 antitrypsin (AAT) is a very important protein in the body and belongs to the acute-phase glycoproteins. AAT regulates inflammation and therefore increases four- to fivefold when the body is fighting infections or inflammation. As a protease inhibitor, AAT suppresses many proteases that can damage lungs and other tissues. Furthermore, AAT boosts the body's defenses independently of protease inhibition due to its wide-ranging immunomodulatory effects.
The gene responsible for AAT production is SERPINA1. It is located on human chromosome 14. In the event of inflammation, this gene ensures that AAT is produced very rapidly, eventually leading to concentrations of more than 1-2 grams of AAT per liter circulating in the blood. An AAT deficiency occurs when individual amino acids in the AAT protein are altered. For example, if glutamic acid at position 264 is replaced by valine, the so-called S variant is formed; if lysine at position 342 is replaced, the Z-deficient variant is formed. The majority of AAT, approximately 70 %, is produced in the liver. In addition, many other tissues and cells contain the SERPINA1 gene. For example, the lungs, kidneys, and skin can also produce AAT.
Early research on AAT
The first protease inhibitors were discovered at the end of the 19th century. In 1894, the Italian researchers Fermi and Pernossi first described "anti-trypsin activity" in the blood. Half a century later, Arne Tiselius in Uppsala, Sweden, developed electrophoresis, a method for separating and differentiating proteins in the blood. In 1955, Herman Schultze from Marburg, Germany, first described an inhibitor of α1-antitrypsin in the α1-globulin protein fraction. The protein AAT itself was isolated three years later.
Researcher CB Laurell from Malmö, Sweden, succeeded in separating the proteins in the blood even more precisely. Using electrophoresis, he examined blood samples from many different patients and discovered that some people with lung diseases lacked the corresponding band in the α1 region. It quickly became clear that this primarily affected members of certain families. This suggested a familial, genetic predisposition. In fact, those affected often had pulmonary emphysema. Laurell and Eriksson first published the connection between AAT deficiency and the development of emphysema 60 years ago, in 1963.
Not only the lungs, but also the liver, are affected by AAT deficiency. Although AAT is produced in liver cells, it does not enter the bloodstream. Instead, it accumulates in the liver cells and is stored as inclusion bodies. Affected patients can develop cirrhosis and liver cancer.
The Pi system (protease inhibitor system), still in use today, was developed in 1970. It distinguishes the variants of AAT according to their ability to move more or less quickly in an electric field. This results in the formation of different bands during isoelectric focusing (a technique for separating different molecules based on differences in their isoelectric point). The classifications are M for medium, S for slow, Z for very slow, and F for fast. Furthermore, the AAT molecules exhibit differences in specific sugar structures, allowing different so-called glycoforms to be associated with health and disease.
„"Current studies offer hope that those suffering from the skin disease panniculitis could also benefit from AAT infusions."“
Therapy with AAT
After it became clear that some people with emphysema have an AAT deficiency, attempts were made to supply the body with the missing AAT. The first publication on this topic dates back to 1981 by the American research team led by Ronald Crystal (see Prof. Vogelmeier's presentation). The infusion treatment did indeed increase the AAT level in the blood. This replacement therapy has been used for decades in patients with AAT deficiency-related emphysema, provided the patient meets certain criteria.
Recent small studies offer hope that individuals with the skin disease panniculitis could also benefit from AAT infusions. Small reports are being published on people with AAT deficiency who are being treated with AAT therapy for bronchiectasis, asthma, and other conditions. Since AAT increasingly arises in the context of infections and injuries, other applications for AAT therapy are conceivable. However, animal models must first demonstrate the success of AAT application before human trials can begin.
In addition to classic infusion therapy with AAT, treatment via inhalation is also being tested. Another application method, a cream containing 5-10 % AAT applied to the skin, has only been tested in a small study. This option also requires further investigation.
AAT substitution and lung transplantation
When the lungs are severely damaged, people with AAT deficiency can undergo a lung transplant. After the procedure, AAT replacement therapy is discontinued. At the Hanover Transplant Center, patients who had either received regular AAT treatment before surgery or had not previously received AAT treatment were compared. Post-transplant survival differed significantly between these groups, as those without prior replacement therapy lived longer than those who had received AAT infusions for years: After 10 years, 69 of the patients who had not received replacement therapy before the transplant were still alive, compared to only 26 of the transplant recipients who had received prior replacement therapy. The reasons for this surprising result could not be identified in the study. It is possible that the two patient groups differed in certain characteristics and therefore had different prognoses. For those patients who received this therapy before lung transplantation, it may be important to continue replacement therapy after the transplant.
In animal models, mice treated with AAT after lung transplantation showed fewer rejection reactions. This was demonstrated by researchers in Hanover. Some experts are now considering whether patients should continue to receive AAT replacement therapy after lung transplantation. However, there are no good studies on this topic.
News from experimental research
Normal AAT has a specific spatial structure. In people with type Z AAT, the arrangement of the molecules is altered: several molecules clump together to form large "clumps," known as polymers. Such clumps of type Z AAT are found in many, but not all, liver cells. Polymers are also detected in the blood of all patients with type Z AAT. The question is whether or not this presents a clinical problem.
New studies focused on children with AATD. Some of them develop severe liver disease with cirrhosis as infants and even require a liver transplant. In others, newborns experience a blockage of the liver's bile ducts, a condition known as cholestasis, which later resolves. A third group remains free of liver problems throughout their lives. When researchers examined children in a small study, they found, based on liver biopsies, that polymers were present in the livers of all three groups. Therefore, the presence of polymers in the liver alone is not decisive; other environmental and genetic factors must also be present, such as alterations in lipid metabolism.
Several risk factors are known to contribute to the development of liver cirrhosis in adults with AATD over their lifetime. Alcohol consumption and viral liver infections such as hepatitis and diabetes are particularly significant. Modern methods already make it possible to prevent the formation of Z-AAT polymers. For patients with the Z mutation, one of the researchers' ideas was to inhibit AAT synthesis, thus reducing the production of Z-AAT. In a small phase 2 trial, they administered the substance fazirsiran to 16 people with liver disease. The results showed that the accumulation of Z-AAT in the liver and blood decreased significantly under this treatment. This was also confirmed by histological examination of liver biopsies. However, almost all patients experienced adverse effects such as back or chest pain, diarrhea, dizziness, or shortness of breath. The manufacturer has since launched a larger study to better assess the benefits and risks of fazirsiran.
Z-AAT polymers were studied in the blood of people with AATD and a lung disease. Patients with low polymer concentrations had neither better nor worse lung function scores than those with high polymer levels; therefore, there was no correlation with the extent of lung damage. Researchers are continuing to work on polymers to better understand their functions. Finally, considering that the Vikings spread AATD around the world more than 2,000 years ago, one has to wonder why the disease still occurs today. It is possible that AATD not only causes problems but may also have been beneficial to our ancestors under certain circumstances, such as protecting them from contamination by unprocessed foods.
Outlook on clinical trials
In conclusion, the speaker presented a timeline providing an overview of the human clinical trials, as presented at the 8th Patient Congress in Dublin in 2023. Various pharmaceutical companies are currently working on very different topics. New therapies are being tested, such as antiproteases in tablet form, subcutaneous administration of AAT via injection under the skin, and gene therapy. A wide variety of approaches are being used to try to manage AAT deficiency.
