Jaume Farrés

Differential Th1/Th2 cytokine patterns in chronic arthritis: interferon gamma is highly expressed in synovium of rheumatoid arthritis compared with seronegative spondyloarthropathies.

OBJECTIVE To investigate possible differences in Th1 and Th2 cytokine mRNA expression in the synovial tissue (ST) of patients with rheumatoid arthritis (RA) and seronegative spondyloarthropathies (SpA) with diagnostic and/or pathogenic interest. METHODS Eleven RA patients and 14 SpA patients (10 with undifferentiated spondyloarthropathy (USpA), two with ankylosing spondylitis (AS) and two with psoriatic arthritis (PsA)) were included. Th1 (interferon γ, interleukin 2) and Th2 (interleukin 4, interleukin 5 and interleukin 10) cytokine mRNA levels from arthritic knee ST were quantified by using an optimised polymerase chain reaction method with a computerised analysis system. Protein levels of proinflammatory cytokines (interleukin 1, tumour necrosis factor α and interleukin 6) in synovial fluid were quantified with a specific ELISA test. RESULTS Th1 cytokines were detected in all of RA ST samples in contrast with 58% (interferon γ) and 71% (interleukin 2) of SpA samples. Th2 cytokines were expressed in 90% of RA ST samples, but the findings in SpA were interleukin 10 in 90%, interleukin 4 in 60% and interleukin 5 in 40% of ST samples. However, when the mRNA levels of each cytokine were quantified and corrected for T cell mRNA levels, only interferon γ levels were significantly higher in RA than in SpA (p<0.003). Thus, the Th1/Th2 cytokine ratio in RA was fivefold that of SpA. Synovial fluid interleukin 1β concentrations were higher in RA than in SpA (p<0.05); there were also higher synovial fluid levels of tumour necrosis factor α in RA than in SpA, but without statistical significance. CONCLUSION This study has detected both Th1 and Th2 cytokine gene expression in ST from RA and SpA patients. Synovium interferon γ mRNA levels and SF interleukin 1β protein levels were significantly higher in RA than in SpA, so reflecting the known proinflammatory activity of interferon γ through macrophage activation. Thus, the Th1 (interferon γ)/Th2 (interleukin 4) ratio is significantly higher in RA than in SpA ST. These data confirm previous studies on ST Th1/Th2 balance in RA and extend previous work in comparing ST RA with subgroups of SpA distinct of ReA.

Stimulation of retinoic acid production and growth by ubiquitously expressed alcohol dehydrogenase Adh3

Influence of vitamin A (retinol) on growth depends on its sequential oxidation to retinal and then to retinoic acid (RA), producing a ligand for RA receptors essential in development of specific tissues. Genetic studies have revealed that aldehyde dehydrogenases function as tissue-specific catalysts for oxidation of retinal to RA. However, enzymes catalyzing the first step of RA synthesis, oxidation of retinol to retinal, remain unclear because none of the present candidate enzymes have expression patterns that fully overlap with those of aldehyde dehydrogenases during development. Here, we provide genetic evidence that alcohol dehydrogenase (ADH) performs this function by demonstrating a role for Adh3, a ubiquitously expressed form. Adh3 null mutant mice exhibit reduced RA generation in vivo, growth deficiency that can be rescued by retinol supplementation, and completely penetrant postnatal lethality during vitamin A deficiency. ADH3 was also shown to have in vitro retinol oxidation activity. Unlike the second step, the first step of RA synthesis is not tissue-restricted because it is catalyzed by ADH3, a ubiquitous enzyme having an ancient origin.

Human aldose reductase and human small intestine aldose reductase are efficient retinal reductases: consequences for retinoid metabolism

Aldo-keto reductases (AKRs) are NAD(P)H-dependent oxidoreductases that catalyse the reduction of a variety of carbonyl compounds, such as carbohydrates, aliphatic and aromatic aldehydes and steroids. We have studied the retinal reductase activity of human aldose reductase (AR), human small-intestine (HSI) AR and pig aldehyde reductase. Human AR and HSI AR were very efficient in the reduction of all- trans -, 9- cis - and 13- cis -retinal ( k (cat)/ K (m)=1100-10300 mM(-1).min(-1)), constituting the first cytosolic NADP(H)-dependent retinal reductases described in humans. Aldehyde reductase showed no activity with these retinal isomers. Glucose was a poor inhibitor ( K (i)=80 mM) of retinal reductase activity of human AR, whereas tolrestat, a classical AKR inhibitor used pharmacologically to treat diabetes, inhibited retinal reduction by human AR and HSI AR. All- trans -retinoic acid failed to inhibit both enzymes. In this paper we present the AKRs as an emergent superfamily of retinal-active enzymes, putatively involved in the regulation of retinoid biological activity through the assimilation of retinoids from beta-carotene and the control of retinal bioavailability.

Structural basis for the high all-trans-retinaldehyde reductase activity of the tumor marker AKR1B10

AKR1B10 is a human aldo-keto reductase (AKR) found to be elevated in several cancer types and in precancerous lesions. In vitro, AKR1B10 exhibits a much higher retinaldehyde reductase activity than any other human AKR, including AKR1B1 (aldose reductase). We here demonstrate that AKR1B10 also acts as a retinaldehyde reductase in vivo. This activity may be relevant in controlling the first step of retinoic acid synthesis. Up-regulation of AKR1B10, resulting in retinoic acid depletion, may lead to cellular proliferation. Both in vitro and in vivo activities of AKR1B10 were inhibited by tolrestat, an AKR1B1 inhibitor developed for diabetes treatment. The crystal structure of the ternary complex AKR1B10–NADP+–tolrestat was determined at 1.25-Å resolution. Molecular dynamics models of AKR1B10 and AKR1B1 with retinaldehyde isomers and site-directed mutagenesis show that subtle differences at the entrance of the retinoid-binding site, especially at position 125, are determinant for the all-trans-retinaldehyde specificity of AKR1B10. Substitutions in the retinaldehyde cyclohexene ring also influence the specificity. These structural features should facilitate the design of specific inhibitors, with potential use in cancer and diabetes treatments.

Comparative functional analysis of human medium-chain dehydrogenases, short-chain dehydrogenases/reductases and aldo-keto reductases with retinoids

Retinoic acid biosynthesis in vertebrates occurs in two consecutive steps: the oxidation of retinol to retinaldehyde followed by the oxidation of retinaldehyde to retinoic acid. Enzymes of the MDR (medium-chain dehydrogenase/reductase), SDR (short-chain dehydrogenase/reductase) and AKR (aldo-keto reductase) superfamilies have been reported to catalyse the conversion between retinol and retinaldehyde. Estimation of the relative contribution of enzymes of each type was difficult since kinetics were performed with different methodologies, but SDRs would supposedly play a major role because of their low K(m) values, and because they were found to be active with retinol bound to CRBPI (cellular retinol binding protein type I). In the present study we employed detergent-free assays and HPLC-based methodology to characterize side-by-side the retinoid-converting activities of human MDR [ADH (alcohol dehydrogenase) 1B2 and ADH4), SDR (RoDH (retinol dehydrogenase)-4 and RDH11] and AKR (AKR1B1 and AKR1B10) enzymes. Our results demonstrate that none of the enzymes, including the SDR members, are active with CRBPI-bound retinoids, which questions the previously suggested role of CRBPI as a retinol supplier in the retinoic acid synthesis pathway. The members of all three superfamilies exhibit similar and low K(m) values for retinoids (0.12-1.1 microM), whilst they strongly differ in their kcat values, which range from 0.35 min(-1) for AKR1B1 to 302 min(-1) for ADH4. ADHs appear to be more effective retinol dehydrogenases than SDRs because of their higher kcat values, whereas RDH11 and AKR1B10 are efficient retinaldehyde reductases. Cell culture studies support a role for RoDH-4 as a retinol dehydrogenase and for AKR1B1 as a retinaldehyde reductase in vivo.

Retinoids, ω‐hydroxyfatty acids and cytotoxic aldehydes as physiological substrates, and H2‐receptor antagonists as pharmacological inhibitors, of human class IV alcohol dehydrogenase

Kinetic constants of human class IV alcohol dehydrogenase (σσ‐ADH) support a role of the enzyme in retinoid metabolism, fatty acid ω‐oxidation, and elimination of cytotoxic aldehydes produced by lipid peroxidation. Class IV is the human ADH form most efficient in the reduction of 4‐hydroxynonenal (k cat/K m: 39 500 mM−1 min−1). Class IV shows high activity with all‐trans‐retinol and 9‐cis‐retinol, while 13‐cis‐retinol is not a substrate but an inhibitor. Both all‐trans‐retinoic and 13‐cis‐retinoic acids are potent competitive inhibitors of retinol oxidation (K i: 3–10 μM) which can be a basis for the regulation of the retinoic acid generation and of the pharmacological actions of the 13‐cis‐isomer. The inhibition of class IV retinol oxidation by ethanol (K i: 6–10 mM) may be the origin of toxic and teratogenic effects of ethanol. H2‐receptor antagonists are poor inhibitors of human and rat classes I and IV (K i>0.3 mM) suggesting a small interference in ethanol metabolism at the pharmacological doses of these common drugs.

Alcohol Dehydrogenase of Class IV (σσ-ADH) from Human Stomach

Human stomach mucosa contains a characteristic alcohol dehydrogenase (ADH) enzyme, sigma sigma-ADH. Its cDNA has been cloned from a human stomach library and sequenced. The deduced amino acid sequence shows 59-70% identities with the other human ADH classes, demonstrating that the stomach enzyme represents a distinct structure, constituting class IV, coded by a separate gene, ADH7. The amino acid identity with the rat stomach class IV ADH is 88%, which is intermediate between constant and variable dehydrogenases. This value reflects higher conservation than for the classical liver enzymes of class I, compatible with a separate functional significance of the class IV enzyme. Its enzymic features can be correlated with its structural characteristics. The residues lining the substrate-binding cleft are bulky and hydrophobic, similar to those of the class I enzyme; this explains the similar specificity of both classes, compatible with the origin of class IV from class I. Position 47 has Arg, in contrast to Gly in the rat class IV enzyme, but this Arg is still associated with an extremely high activity (kcat = 1510 min-1) and weak coenzyme binding (KiaNAD+ = 1.6 mM). Thus, the strong interaction with coenzyme imposed by Arg47 in class I is probably compensated for in class IV by changes that may negatively affect coenzyme binding: Glu230, His271, Asn260, Asn261, Asn363. The still higher activity and weaker coenzyme binding of rat class IV (kcat = 2600 min-1, KiaNAD = 4 mM) can be correlated to the exchanges to Gly47, Gln230 and Tyr363. An important change at position 294, with Val in human and Ala in rat class IV, is probably responsible for the dramatic difference in Km values for ethanol between human (37 mM) and rat (2.4 M) class IV enzymes.

Ocular alcohol dehydrogenase in the rat: Regional distribution and kinetics of the ADH-1 isoenzyme with retinol and retinal

Starch-gel electrophoresis of rat ocular tissues shows two anodic isoenzymes of alcohol dehydrogenase (ADH), designated as ADH-1 and ADH-2, ADH-1 is characteristic of the ocular tissues, and corresponds to more than 95% of all ADH activity in the eye. The well known cathodic forms of rat liver ADH, that we named ADH-3, are not observed in the ocular tissues. ADH-1 is detected in retina, pigment epithelium-choroid, ocular fluid, and cornea but not in the lens. The cornea exhibits the highest ADH activity [200 +/- 59 milliunits (munits) mg-1] followed by the pigment epithelium-choroid (11 +/- 7 munits mg-1). Activity in the retina is very small (0.6 +/- 0.2 munit mg-1) and represents only 0.6% of the total activity in the eye. Most of the rat ocular ADH is localized in the cornea (68%) where it could play a significant role in the detoxication of the alcohols of a broad range of structures. Purified ADH-1 shows a low Km for retinol oxidation (20 microM) and for retinal reduction (30 microM) indicating that this isoenzyme may have a function in the metabolism of retinoids. Ethanol competitively inhibits retinol oxidation, but with a very high apparent inhibition constant (0.6 M) demonstrating that the inhibitory effect is not significantly at the usual concentrations found in the blood during ethanol intoxication.

Aldo-keto reductases from the AKR1B subfamily: retinoid specificity and control of cellular retinoic acid levels.

NADP(H)-dependent cytosolic aldo-keto reductases (AKRs) have been added to the group of enzymes which contribute to oxidoreductive conversions of retinoids. Recently, we found that two members from the AKR1B subfamily (AKR1B1 and AKRB10) were active in the reduction of all-trans- and 9-cis-retinaldehyde, with K(m) values in the micromolar range, but with very different k(cat) values. With all-trans-retinaldehyde, AKR1B10 shows a much higher k(cat) value than AKR1B1 (18 min(-1)vs. 0.37 min(-1)) and a catalytic efficiency comparable to that of the best retinaldehyde reductases. Structural, molecular dynamics and site-directed mutagenesis studies on AKR1B1 and AKR1B10 point that subtle differences at the entrance of their retinoid-binding site, especially at position 125, are determinant for the all-trans-retinaldehyde specificity of AKR1B10. Substitutions in the retinoid cyclohexene ring, analyzed here further, also influence such specificity. Overall it is suggested that the rate-limiting step in the reaction mechanism with retinaldehyde differs between AKR1B1 and AKR1B10. In addition, we demonstrate here that enzymatic activity of AKR1B1 and AKR1B10 lowers all-trans- and 9-cis-retinoic acid-dependent trans-activation in living cells, indicating that both enzymes may contribute to pre-receptor regulation of retinoic acid and retinoid X nuclear receptors. This result supports that overexpression of AKR1B10 in cancer (an updated review on this topic is included) may contribute to dedifferentiation and tumor development.

Influence of liver disease on hepatic alcohol and aldehyde dehydrogenases

The hepatic activities and the isoenzyme patterns of both alcohol dehydrogenase and aldehyde dehydrogenase have been studied in 60 alcoholics with varying degrees of liver damage (from normal tissue or minimal changes to cirrhosis with alcoholic hepatitis) and in 24 nonalcoholics with chronic hepatitis or cirrhosis in order to ascertain their association with liver damage. In alcoholics both alcohol dehydrogenase and low-Km aldehyde dehydrogenase activities decreased proportionally with the severity of liver disease. In contrast, in nonalcoholics, there was a reduction of low-Km aldehyde dehydrogenase activity related to the severity of liver injury, but alcohol dehydrogenase was similar in patients with chronic hepatitis and nonalcoholic cirrhosis. There were no significant changes in total and high-Km aldehyde dehydrogenase activities among the different histologic groups studied, although the lowest activities were observed in patients with more severe liver injury. The prevalence of atypical alcohol dehydrogenase was similar in alcoholic (6.6%) and in nonalcoholic (8.3%) liver disease. All patients exhibited isoenzyme aldehyde dehydrogenase II, whereas isoenzyme I was not detected in 39.5% of the alcoholic patients and in 9.5% of those with nonalcoholic liver disease. The lack of aldehyde dehydrogenase I was observed in cases with the lowest enzymatic activities. These results suggest that the decrease of alcohol and aldehyde dehydrogenase activities in alcoholics is not a primary defect and, therefore, their decrease is secondary to liver damage. It is speculated that the diminution of alcohol dehydrogenase, found particularly in alcoholics, could be due to centrilobular cell necrosis.