Alpha‐1‐Antitrypsin Deficiency

In the classical form of alpha1-antitrypsin (AT) deficiency, a point mutation in AT alters the folding of a liver-derived secretory glycoprotein and renders it aggregation-prone. In addition to decreased serum concentrations of AT, the disorder is characterized by accumulation of the mutant alpha1-antitrypsin Z (ATZ) variant inside cells, causing hepatic fibrosis and/or carcinogenesis by a gain-of-toxic function mechanism. The proteasomal and autophagic pathways are known to mediate degradation of ATZ. Here we show that the autophagy-enhancing drug carbamazepine (CBZ) decreased the hepatic load of ATZ and hepatic fibrosis in a mouse model of AT deficiency-associated liver disease. These results provide a basis for testing CBZ, which has an extensive clinical safety profile, in patients with AT deficiency and also provide a proof of principle for therapeutic use of autophagy enhancers.

We prosepctively studied 200,000 newborns to determine the frequency and clinical characteristics of alpha1-antitrypsin deficiency. One hundred and twenty Pi Z, 48 Pi SZ, two PI Z-and one Pi S-infants were identified and followed to the age of six months. Fourteen of 120 Pi Z infants had prolonged obstructive jaundice, nine with severe clinical and laboratory evidence of liver disease. Five had only laboratory evidence of liver disease. Eight other Pi Z infants had minimal abnormalities in serum bilirubin and hepatic enzyme activity and variable hepatosplenomegaly. All 22 Pi Z infants with hepatic abnormalities, two thirds of whom were made, appeared healthy at six months of age. Ninety-eight Pi Z infants did not have clinical liver disease, but liver-function tests gave abnormal results in 44 of 84 at three months, and in 36 of 60 at six months of age. The number of small-for-gestational-age infants was greater (P less than 0.001) among those with clinical liver disease. None of the 48 Pi SZ infants had clinical liver disease, but 10 of 42 at three months and one of 22 at six months of age had abnormal liver function. The Pi Z and Pi SZ phenotypes are associated with covert or readily apparent hepatic dysfunction in the first three months of life.

Alpha-1-antitrypsin (a1AT) deficiency is caused by homozygosity for the a1AT mutant Z gene and occurs in one in 2000 Americans. The Z mutation confers an abnormal conformation on the a1AT mutant Z protein, resulting in accumulation within the endoplasmic reticulum of hepatocytes and chronic liver injury. Autophagy is one of several proteolytic mechanisms activated to cope with this hepatocellular protein burden, and is likely important in disposal of the unique polymerized conformation of the a1AT mutant Z protein, which is thought to be especially injurious to the cell. Recent data indicate that rapamycin may more efficiently upregulate autophagy when given in weekly dose pulses, as compared with a daily regimen. Therefore, we evaluated the effect of rapamycin on PiZ mice, a well-characterized model which recapitulates human a1AT liver disease. Daily dosing had no effect on autophagy, on accumulation of a1AT mutant Z protein or on liver injury. Weekly dosing of rapamycin did increase autophagic activity, as shown by increased numbers of autophagic vacuoles. This was associated with reduction in the intrahepatic accumulation of a1AT mutant Z protein in the polymerized conformation. Markers of hepatocellular injury, including cleavage of caspase 12 and hepatic fibrosis, were also decreased. In conclusion, this is the first report of a successful in vivo method for reduction of intrahepatic a1AT mutant Z polymerized protein. Application of this finding may be therapeutic in patients with a1AT deficiency by reducing the intracellular burden of the polymerized, mutant Z protein and by reducing the progression of liver injury.