Human dehydrogenase/reductase (SDR family) member 8 (DHRS8): a description and evaluation of its biochemical properties.

Dehydrogenase/reductase (SDR family) member 8 (DHRS8, SDR16C2) belongs to the short-chain dehydrogenase/reductase (SDR) superfamily, one of the largest enzyme groups. In addition to the well-known members which participate in the metabolism of important eobiotics and xenobiotics, this superfamily contains many poorly characterized proteins. DHRS8 is a member of the Multisubstrate NADP(H)-dependent SDR16C family, which generally contains insufficiently described enzymes. Despite the limited knowledge about DHRS8, preliminary indicators have emerged regarding its significant function in the modulation of steroidal activity, at least in the case of 3α-adiol, lipid metabolism and detoxification. The aim of this study was to describe additional biochemical properties of DHRS8 and to unify knowledge about this enzyme. The DHRS8 was prepared in recombinant form and its membrane topology in the endoplasmic reticulum as an integral protein with cytosolic orientation was demonstrated. The enzyme participates in the NAD(+)-dependent oxidation of steroid hormones as ß-estradiol and testosterone in vitro; apparent K m and V max values were 39.86 µM and 0.80 nmol × mg(-1) × min(-1) for ß-estradiol and 1207.29 µM and 3.45 nmol × mg(-1) × min(-1) for testosterone. Moreover, synthetic steroids (methyltestosterone and nandrolone) used as anabolics as well as all-trans-retinol were for the first time identified as substrates of DHRS8. This knowledge of its in vitro activity together with a newly described expression pattern at the protein level in tissues involved in steroidogenesis (adrenal gland and testis) and detoxification (liver, lung, kidney and small intestine) could suggest a potential role of DHRS8 in vivo.

Human DHRS7, promising enzyme in metabolism of steroids and retinoids?

The metabolism of steroids and retinoids has been studied in detail for a long time, as these compounds are involved in a broad spectrum of physiological processes. Many enzymes participating in the conversion of such compounds are members of the short-chain dehydrogenase/reductase (SDR) superfamily. Despite great effort, there still remain a number of poorly characterized SDR proteins. According to various bioinformatics predictions, many of these proteins may play a role in the metabolism of steroids and retinoids. Dehydrogenase/reductase (SDR family) member 7 (DHRS7) is one such protein. In a previous study, we determined DHRS7 to be an integral membrane protein of the endoplasmic reticulum facing the lumen which has shown at least in vitro NADPH-dependent reducing activity toward several eobiotics and xenobiotics bearing a carbonyl moiety. In the present paper pure DHRS7 was used for a more detailed study of both substrate screening and an analysis of kinetics parameters of the physiologically important substrates androstene-3,17-dione, cortisone and all-trans-retinal. Expression patterns of DHRS7 at the mRNA as well as protein level were determined in a panel of various human tissue samples, a procedure that has enabled the first estimation of the possible biological function of this enzyme. DHRS7 is expressed in tissues such as prostate, adrenal glands, liver or intestine, where its activity could be well exploited. Preliminary indications show that DHRS7 exhibits dual substrate specificity recognizing not only steroids but also retinoids as potential substrates and could be important in the metabolism of these signalling molecules.

Flavones Inhibit the Activity of AKR1B10, a Promising Therapeutic Target for Cancer Treatment.

AKR1B10 is an NADPH-dependent reductase that plays an important function in several physiological reactions such as the conversion of retinal to retinol, reduction of isoprenyl aldehydes, and biotransformation of procarcinogens and drugs. A growing body of evidence points to the important role of the enzyme in the development of several types of cancer (e.g., breast, hepatocellular), in which it is highly overexpressed. AKR1B10 is regarded as a therapeutic target for the treatment of these diseases, and potent and specific inhibitors may be promising therapeutic agents. Several inhibitors of AKR1B10 have been described, but the area of natural plant products has been investigated sparingly. In the present study almost 40 diverse phenolic compounds and alkaloids were examined for their ability to inhibit the recombinant AKR1B10 enzyme. The most potent inhibitors-apigenin, luteolin, and 7-hydroxyflavone-were further characterized in terms of IC50, selectivity, and mode of action. Molecular docking studies were also conducted, which identified putative binding residues important for the interaction. In addition, cellular studies demonstrated a significant inhibition of the AKR1B10-mediated reduction of daunorubicin in intact cells by these inhibitors without a considerable cytotoxic effect. Although these compounds are moderately potent and selective inhibitors of AKR1B10, they constitute a new structural type of AKR1B10 inhibitor and may serve as a template for the development of better inhibitors.

Molecular and biochemical characterisation of human short-chain dehydrogenase/reductase member 3 (DHRS3).

Dehydrogenase/reductase (SDR family) member 3 (DHRS3), also known as retinal short-chain dehydrogenase/reductase (retSDR1) is a member of SDR16C family. This family is thought to be NADP(H) dependent and to have multiple substrates; however, to date, only all-trans-retinal has been identified as a DHRS3 substrate. The reductive reaction catalysed by DHRS3 seems to be physiological, and recent studies proved the importance of DHRS3 for maintaining suitable retinoic acid levels during embryonic development in vivo. Although it seems that DHRS3 is an important protein, knowledge of the protein and its properties is quite limited, with the majority of information being more than 15 years old. This study aimed to generate a more comprehensive characterisation of the DHRS3 protein. Recombinant enzyme was prepared and demonstrated to be a microsomal, integral-membrane protein with the C-terminus oriented towards the cytosol, consistent with its preference of NADPH as a cofactor. It was determined that DHRS3 also participates in the metabolism of other endogenous compounds, such as androstenedione, estrone, and DL-glyceraldehyde, and in the biotransformation of xenobiotics (e.g., NNK and acetohexamide) in addition to all-trans-retinal. Purified and reconstituted enzyme was prepared for the first time and will be used for further studies. Expression of DHRS3 was shown at the level of both mRNA and protein in the human liver, testis and small intestine. This new information could open other areas of DHRS3 protein research.