The kinetic parameters, steroid substrate specificity and identities of reaction products were determined for four homogeneous recombinant human 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) isoforms of the aldo-keto reductase (AKR) superfamily. The enzymes correspond to type 1 3alpha-HSD (AKR1C4), type 2 3alpha(17beta)-HSD (AKR1C3), type 3 3alpha-HSD (AKR1C2) and 20alpha(3alpha)-HSD (AKR1C1), and share at least 84% amino acid sequence identity. All enzymes acted as NAD(P)(H)-dependent 3-, 17- and 20-ketosteroid reductases and as 3alpha-, 17beta- and 20alpha-hydroxysteroid oxidases. The functional plasticity of these isoforms highlights their ability to modulate the levels of active androgens, oestrogens and progestins. Salient features were that AKR1C4 was the most catalytically efficient, with k(cat)/K(m) values for substrates that exceeded those obtained with other isoforms by 10-30-fold. In the reduction direction, all isoforms inactivated 5alpha-dihydrotestosterone (17beta-hydroxy-5alpha-androstan-3-one; 5alpha-DHT) to yield 5alpha-androstane-3alpha,17beta-diol (3alpha-androstanediol). However, only AKR1C3 reduced Delta(4)-androstene-3,17-dione to produce significant amounts of testosterone. All isoforms reduced oestrone to 17beta-oestradiol, and progesterone to 20alpha-hydroxy-pregn-4-ene-3,20-dione (20alpha-hydroxyprogesterone). In the oxidation direction, only AKR1C2 converted 3alpha-androstanediol to the active hormone 5alpha-DHT. AKR1C3 and AKR1C4 oxidized testosterone to Delta(4)-androstene-3,17-dione. All isoforms oxidized 17beta-oestradiol to oestrone, and 20alpha-hydroxyprogesterone to progesterone. Discrete tissue distribution of these AKR1C enzymes was observed using isoform-specific reverse transcriptase-PCR. AKR1C4 was virtually liver-specific and its high k(cat)/K(m) allows this enzyme to form 5alpha/5beta-tetrahydrosteroids robustly. AKR1C3 was most prominent in the prostate and mammary glands. The ability of AKR1C3 to interconvert testosterone with Delta(4)-androstene-3,17-dione, but to inactivate 5alpha-DHT, is consistent with this enzyme eliminating active androgens from the prostate. In the mammary gland, AKR1C3 will convert Delta(4)-androstene-3,17-dione to testosterone (a substrate aromatizable to 17beta-oestradiol), oestrone to 17beta-oestradiol, and progesterone to 20alpha-hydroxyprogesterone, and this concerted reductive activity may yield a pro-oesterogenic state. AKR1C3 is also the dominant form in the uterus and is responsible for the synthesis of 3alpha-androstanediol which has been implicated as a parturition hormone. The major isoforms in the brain, capable of synthesizing anxiolytic steroids, are AKR1C1 and AKR1C2. These studies are in stark contrast with those in rat where only a single AKR with positional- and stereo-specificity for 3alpha-hydroxysteroids exists.

The kinetic parameters, steroid substrate specificity and identities of reaction products were determined for four homogeneous recombinant human 3α-hydroxysteroid dehydrogenase (3α-HSD) isoforms of the aldo-keto reductase (AKR) superfamily. The enzymes correspond to type 1 3α-HSD (AKR1C4), type 2 3α(17β)-HSD (AKR1C3), type 3 3α-HSD (AKR1C2) and 20α(3α)-HSD (AKR1C1), and share at least 84 % amino acid sequence identity. All enzymes acted as NAD(P)(H)-dependent 3-, 17-and 20-ketosteroid reductases and as 3α-, 17β-and 20α-hydroxysteroid oxidases. The functional plasticity of these isoforms highlights their ability to modulate the levels of active androgens, oestrogens and progestins. Salient features were that AKR1C4 was the most catalytically efficient, with k cat \K m values for substrates that exceeded those obtained with other isoforms by 10-30-fold. In the reduction direction, all isoforms inactivated 5α-dihydrotestosterone (17β-hydroxy-5α-androstan-3-one ; 5α-DHT) to yield 5α-androstane-3α,17β-diol (3α-androstanediol). However, only AKR1C3 reduced ∆%-androstene-3,17-dione to produce significant amounts of testosterone. All isoforms reduced oestrone to 17β-oestradiol, and progesterone to 20α-hydroxypregn-4-ene-3,20-dione (20α-hydroxyprogesterone). In the oxidation direction, only AKR1C2 converted 3α-androstanediol to the active hormone 5α-DHT. AKR1C3 and AKR1C4 oxidized testosterone to ∆%-androstene-3,17-dione. All isoforms oxid-

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BackgroundUntil now, no risk score could predict hepatocellular carcinoma (HCC) in nucleos(t)ide analog (NA)-treated Asian patients.MethodsWe enrolled 1325 NA-naïve chronic hepatitis B patients with entecavir monotherapy for >12 months, with 883 and 442 patients randomly assigned to the development and validation groups, respectively, in the risk model.ResultsThe cumulative probabilities of HCC were 2.4%, 4.1%, and 9.9% after 2, 3, and 5 years of treatment, respectively. In the development group, age, platelet counts, and alpha-fetoprotein levels after 12 months of treatment were the independent predictors of HCC. We converted the Cox proportional hazards regression coefficients for these predictors into risk scores and developed the APA-B model, with the total risk scores ranging from 0 to 15. The risk scores accurately categorized patients with low (0–5), medium (6–9), and high (10–15) risks in the validation group (P <0.001). The areas under the receiver operating characteristic curve for predicting HCC risk after 2, 3, and 5 years were 0.877, 0.842, and 0.827, respectively, in the development group and 0.939, 0.892, and 0.862, respectively, in the validation group.ConclusionThe proposed HCC risk prediction model exhibited excellent predictive accuracy in NA-naïve Asian patients receiving entecavir therapy.