Sharmilee P. Sawant

Renal and Hepatic Transporter Expression in Type 2 Diabetic Rats

Membrane transporters are critical for the uptake as well as elimination of chemicals and by-products of metabolism from the liver and kidneys. Since these proteins are important determinants of chemical disposition, changes in their expression in different disease states can modulate drug pharmacokinetics. The present study investigated alterations in the renal and hepatic expression of organic anion and cation transporters (Oats/Octs), multidrug resistance-associated proteins (Mrps), breast cancer resistance protein (Bcrp), P-glycoprotein (Pgp), and hepatic Na(+)-taurocholate cotransporting polypeptide (Ntcp) in type 2 diabetic rats. For this purpose, type 2 diabetes was induced by feeding male Sprague-Dawley rats a high fat diet followed by a single dose of streptozotocin (45 mg/kg, i.p., in 0.01 M citrate buffer pH 4.3) on day 14. Controls received normal diet and vehicle. Kidney and liver samples were collected on day 24 for generation of crude plasma membrane fractions and Western blot analysis of Oat, Oct, Mrp, Bcrp, Pgp, and Ntcp proteins. With regards to renal uptake transporters, type 2 diabetes increased levels of Oat2 (2.3-fold) and decreased levels of Oct2 to 50% of control kidneys. Conversely, efflux transporters Mrp2, Mrp4, and Bcrp were increased 5.4-fold, 2-fold, and 1.6-fold, respectively in type 2 diabetic kidneys with no change in levels of Mrp1, Mrp5, or Pgp. Studies of hepatic transporters in type 2 diabetic rats reveal that the protein level of Mrp5 was reduced to 4% of control livers with no change in levels of Bcrp, Mrp1, Mrp2, Mrp4, Ntcp, or Pgp. The changes reported in this study may have implications in type 2 diabetic patients.

Upregulation of calpastatin in regenerating and developing rat liver: Role in resistance against hepatotoxicity

Acute liver failure induced by hepatotoxic drugs results from rapid progression of injury. Substantial research has shown that timely liver regeneration can prevent progression of injury leading to a favorable prognosis. However, the mechanism by which compensatory regeneration prevents progression of injury is not known. We have recently reported that calpain released from necrotic hepatocytes mediates progression of liver injury even after the hepatotoxic drug is cleared from the body. By examining expression of calpastatin (CAST), an endogenous inhibitor of calpain in three liver cell division models known to be resistant to hepatotoxicity, we tested the hypothesis that increased CAST in the dividing hepatocytes affords resistance against progression of injury. Liver regeneration that follows CCl4‐induced liver injury, 70% partial hepatectomy, and postnatal liver development were used. In all three models, CAST was upregulated in the dividing/newly divided hepatocytes and declined to normal levels with the cessation of cell proliferation. To test whether CAST overexpression confers resistance against hepatotoxicity, CAST was overexpressed in the livers of normal SW mice using adenovirus before challenging them with acetaminophen (APAP) overdose. These mice exhibited markedly attenuated progression of liver injury and 57% survival. Whereas APAP‐bioactivating enzymes and covalent binding of the APAP‐derived reactive metabolites remained unaffected, degradation of calpain specific target substrates such as fodrin was significantly reduced in these mice. In conclusion, CAST overexpression could be used as a therapeutic strategy to prevent progression of liver injury where liver regeneration is severely hampered. (HEPATOLOGY 2006;44:379–388.)