Liver disease in the alcoholic is due not only to malnutrition but also to ethanol's hepatotoxicity linked to its metabolism by means of the alcohol dehydrogenase and cytochrome P450 2E1 (CYP2E1) ...pathways and the resulting production of toxic acetaldehyde. In addition, alcohol dehydrogenase–mediated ethanol metabolism generates the reduced form of nicotinamide adenine dinucleotide (NADH), which promotes steatosis by stimulating the synthesis of fatty acids and opposing their oxidation. Steatosis is also promoted by excess dietary lipids and can be attenuated by their replacement with medium-chain triglycerides. Through reduction of pyruvate, elevated NADH also increases lactate, which stimulates collagen synthesis in myofibroblasts. Furthermore, CYP2E1 activity is inducible by its substrates, not only ethanol but also fatty acids. Their excess and metabolism by means of this pathway generate release of free radicals, which cause oxidative stress, with peroxidation of lipids and membrane damage, including altered enzyme activities. Products of lipid peroxidation such as 4-hydroxynonenal stimulate collagen generation and fibrosis, which are further increased through diminished feedback inhibition of collagen synthesis because acetaldehyde forms adducts with the carboxyl-terminal propeptide of procollagen in hepatic stellate cells. Acetaldehyde is also toxic to the mitochondria, and it aggravates their oxidative stress by binding to reduced glutathione and promoting its leakage. Oxidative stress and associated cellular injury promote inflammation, which is aggravated by increased production of the proinflammatory cytokine tumor necrosis factor-alpha in the Kupffer cells. These are activated by induction of their CYP2E1 as well as by endotoxin. The endotoxin-stimulated tumor necrosis factor-alpha release is decreased by dilinoleoylphosphatidylcholine, the active phosphatidylcholine (PC) species of polyenylphosphatidylcholine (PPC). Moreover, defense mechanisms provided by peroxisome proliferator-activated receptor alpha and omega fatty acid oxidation are readily overwhelmed, particularly in female rats and also in women who have low hepatic induction of fatty acid–binding protein (L-FABPc). Accordingly, the intracellular concentration of free fatty acids may become high enough to injure membranes, thereby contributing to necrosis, inflammation, and progression to fibrosis and cirrhosis. Eventually, hepatic
S-adenosylmethionine and PCs become depleted in the alcoholic, with impairment of their multiple cellular functions, which can be restored by PC replenishment. Thus, prevention and therapy opposing the development of steatosis and its progression to more severe injury can be achieved by a multifactorial approach: control of alcohol consumption, avoidance of obesity and of excess dietary long-chain fatty acids, or their replacement with medium-chain fatty acids, and replenishment of
S-adenosylmethionine and PCs by using PPC. Progress in the understanding of the pathogenesis of alcoholic fatty liver and its progression to inflammation and fibrosis has resulted in prospects for their better prevention and treatment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
C. S. Lieber
Alcohol Research and Treatment Center, Bronx Department of Veterans Affairs Medical Center, New York, USA.
The role of the microsomal ethanol-oxidizing system (MEOS) in hepatic
ethanol ...metabolism is reviewed, with focus on its constitutive,
ethanol-inducible cytochrome P-4502E1 (2E1). The MEOS was purified and
reconstituted using 2E1, phospholipids, and cytochrome P-450 reductase and
shown to oxidize ethanol to acetaldehyde, mainly as a monooxygenase and
secondarily via hydroxyl radicals, with transcriptional and
posttranscriptional regulation. Polymorphism of 2E1 was recognized, and
enzymology (including cofactors, role of lipids, inducers, and inhibitors)
as well as cellular and tissue distribution were chartered. Physiological
functions involve lipid metabolism and ketone utilization in starvation,
obesity, and diabetes. The most significant role of 2E1 is its adaptive
response to high blood ethanol levels with a corresponding acceleration of
ethanol metabolism. The associated free radical production, however,
contributes to liver injury in the alcoholic. Most importantly, 2E1 has a
unique capacity to activate many xenobiotics (85 of which are listed) to
hepatotoxic or carcinogenic products. Induction of 2E1 also results in
enhanced production of acetaldehyde, a highly reactive and toxic
metabolite. The proliferation of the endoplasmic reticulum associated with
2E1 induction is also accompanied by enhanced activity of other cytochrome
P-450s, resulting in accelerated metabolism of, and tolerance to, other
drugs, as well as increased degradation of retinol and its hepatic
depletion. Some substrates and metabolites, however, are innocuous and may
eventually be used as markers of heavy drinking. Recently discovered
effective 2E1 inhibitors also have great therapeutic potential.
In the past, alcoholic liver disease was attributed exclusively to dietary deficiencies, but experimental and judicious clinical studies have now established alcohol's hepatotoxicity. Despite an ...adequate diet, it can contribute to the entire spectrum of liver diseases, mainly by generating oxidative stress through its microsomal metabolism via cytochrome P4502E1 (CYP2E1). It also interferes with nutrient activation, resulting in changes in nutritional requirements. This is exemplified by methionine, one of the essential amino acids for humans, which needs to be activated to S-adenosylmethionine (SAMe), a process impaired by liver disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. In baboons, SAMe attenuated mitochondrial lesions and replenished glutathione; it also significantly reduced mortality in patients with Child A or B cirrhosis. Similarly, decreased phosphatidylethanolamine methyltransferase activity is associated with alcoholic liver disease, resulting in phosphatidylcholine depletion and serious consequences for the integrity of membranes. This can be offset by polyenylphosphatidylcholine (PPC), a mixture of polyunsaturated phosphatidylcholines comprising dilinoleoylphosphatidylcholine (DLPC), which has high bioavailability. PPC (and DLPC) opposes major toxic effects of alcohol, with down-regulation of CYP2E1 and reduction of oxidative stress, deactivation of hepatic stellate cells, and increased collagenase activity, which in baboons, results in prevention of ethanol-induced septal fibrosis and cirrhosis. Corresponding clinical trials are ongoing.
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DOBA, FSPLJ, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
Oxidation of ethanol via alcohol dehydrogenase (ADH) explains various metabolic effects of ethanol but does not account for the tolerance and a number of associated disorders that develop in the ...alcoholic. These were elucidated by the discovery of the microsomal metabolism of ethanol. The physiologic role of this system comprises gluconeogenesis from ketones, fatty acid metabolism, and detoxification of xenobiotics, including ethanol. After chronic ethanol consumption, the activity of the microsomal ethanol-oxidizing system (MEOS) increases, with an associated rise in cytochromes P-450, especially CYP2E1. This induction is associated with proliferation of the endoplasmic reticulum, both in experimental animals and in humans. The role of MEOS in vivo and its increase after chronic ethanol consumption was shown most conclusively in alcohol dehydrogenase-negative deer mice. Enhanced ethanol oxidation is associated with cross-induction of the metabolism of other drugs, resulting in drug tolerance. Furthermore, there is increased conversion of known hepatotoxic agents (such as CCl4) to toxic metabolites, which may explain the enhanced susceptibility of alcoholics to the adverse effects of industrial solvents. CYP2E1 also has a high capacity to activate some commonly used drugs, such as acetaminophen, to their toxic metabolites, and to promote carcinogenesis (e.g., from dimethylnitrosamine). Moreover, catabolism of retinol is accelerated and there also is induction of microsomal enzymes involved in lipoprotein production, resulting in hyperlipemia. Contrasting with the chronic effects of ethanol consumption, acute ethanol intake inhibits the metabolism of other drugs through competition for the at least partially shared microsomal pathway. In addition, metabolism by CYP2E1 results in a significant free radical release and acetaldehyde production which, in turn, diminish reduced glutathione (GSH) and other defense systems against oxidative stress. Acetaldehyde also forms adducts with proteins, thereby altering the functions of mitochondria and of repair enzymes. Increases of CYP2E1 and its mRNA prevail in the perivenular zone, the area of maximal liver damage. CYP1A2 and CYP3A4, two other perivenular P-450s, can also sustain the metabolism of ethanol, thereby contributing to MEOS activity and possibly liver injury. By contrast, CYP2E1 inhibitors oppose alcohol-induced liver damage, but heretofore available compounds were too toxic for clinical use. Recently, however, polyenylphosphatidylcholine (PPC), an innocuous mixture of polyunsaturated lecithins extracted from soybeans, was discovered to decrease CYP2E1 activity. PPC (and its active component dilinoleoylphosphatidylcholine) also oppose hepatic oxidative stress and fibrosis. PPC is now being tested clinically for the prevention and treatment of liver disease in the alcoholic.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Oxidation of ethanol via alcohol dehydrogenase (ADH) explains various metabolic effects of ethanol but does not account for the tolerance. This fact, as well as the discovery of the proliferation of ...the smooth endoplasmic reticulum (SER) after chronic alcohol consumption, suggested the existence of an additional pathway which was then described by Lieber and DeCarli, namely the microsomal ethanol oxidizing system (MEOS), involving cytochrome P450. The existence of this system was initially challenged but the effect of ethanol on liver microsomes was confirmed by Remmer and his group. After chronic ethanol consumption, the activity of the MEOS increases, with an associated rise in cytochrome P450, especially CYP2E1, most conclusively shown in alcohol dehydrogenase negative deer mice. There is also cross-induction of the metabolism of other drugs, resulting in drug tolerance. Furthermore, the conversion of hepatotoxic agents to toxic metabolites increases, which explains the enhanced susceptibility of alcoholics to the adverse effects of various xenobiotics, including industrial solvents. CYP2E1 also activates some commonly used drugs (such as acetaminophen) to their toxic metabolites, and promotes carcinogenesis. In addition, catabolism of retinol is accelerated resulting in its depletion. Contrasting with the stimulating effects of chronic consumption, acute ethanol intake inhibits the metabolism of other drugs. Moreover, metabolism by CYP2E1 results in a significant release of free radicals which, in turn, diminishes reduced glutathione (GSH) and other defense systems against oxidative stress which plays a major pathogenic role in alcoholic liver disease. CYP1A2 and CYP3A4, two other perivenular P450s, also sustain the metabolism of ethanol, thereby contributing to MEOS activity and possibly liver injury. CYP2E1 has also a physiologic role which comprises gluconeogenesis from ketones, oxidation of fatty acids, and detoxification of xenobiotics other than ethanol. Excess of these physiological substrates (such as seen in obesity and diabetes) also leads to CYP2E1 induction and nonalcoholic fatty liver disease (NAFLD), which includes nonalcoholic fatty liver and nonalcoholic steatohepatitis (NASH), with pathological lesions similar to those observed in alcoholic steatohepatitis. Increases of CYP2E1 and its mRNA prevail in the perivenular zone, the area of maximal liver damage. CYP2E1 up-regulation was also demonstrated in obese patients as well as in rat models of obesity and NASH. Furthermore, NASH is increasingly recognized as a precursor to more severe liver disease, sometimes evolving into "cryptogenic" cirrhosis. The prevalence of NAFLD averages 20% and that of NASH 2% to 3% in the general population, making these conditions the most common liver diseases in the United States. Considering the pathogenic role that up-regulation of CYP2E1 also plays in alcoholic liver disease (vide supra), it is apparent that a major therapeutic challenge is now to find a way to control this toxic process. CYP2E1 inhibitors oppose alcohol-induced liver damage, but heretofore available compounds are too toxic for clinical use. Recently, however, polyenylphosphatidylcholine (PPC), an innocuous mixture of polyunsaturated phosphatidylcholines extracted from soybeans (and its active component dilinoleoylphosphatidylcholine), were discovered to decrease CYP2E1 activity. PPC also opposes hepatic oxidative stress and fibrosis. It is now being tested clinically.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The causes of spontaneous chromosomal translocations in somatic cells of biological organisms are largely unknown, although double-strand DNA breaks are required in all proposed mechanisms. The most ...common chromosomal abnormality in human cancer is the reciprocal translocation between chromosomes 14 and 18 (t(14;18)), which occurs in follicular lymphomas. The break at the immunoglobulin heavy-chain locus on chromosome 14 is an interruption of the normal V(D)J recombination process. But the breakage on chromosome 18, at the Bcl-2 gene, occurs within a confined 150-base-pair region (the major breakpoint region or Mbr) for reasons that have remained enigmatic. We have reproduced key features of the translocation process on an episome that propagates in human cells. The RAG complex-which is the normal enzyme for DNA cleavage at V, D or J segments-nicks the Bcl-2 Mbr in vitro and in vivo in a manner that reflects the pattern of the chromosomal translocations; however, the Mbr is not a V(D)J recombination signal. Rather the Bcl-2 Mbr assumes a non-B-form DNA structure within the chromosomes of human cells at 20-30% of alleles. Purified DNA assuming this structure contains stable regions of single-strandedness, which correspond well to the translocation regions in patients. Hence, a stable non-B-DNA structure in the human genome appears to be the basis for the fragility of the Bcl-2 Mbr, and the RAG complex is able to cleave this structure.
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Much progress has been made in the understanding of the pathogenesis of alcoholic liver disease, resulting in improvement of prevention and therapy, with promising prospects for even more effective ...treatments. The most successful approaches that one can expect to evolve are those that deal with the fundamental cellular disturbances resulting from excessive alcohol consumption. Two pathologic concepts are emerging as particularly useful therapeutically. Whereas it continues to be important to replenish nutritional deficiencies, when present, it is crucial to recognize that because of the alcohol-induced disease process, some of the nutritional requirements change. This is exemplified by methionine, which normally is one of the essential amino acids for humans, but needs to be activated to S-adenosylmethionine (SAMe), a process impaired by the disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. Indeed, SAMe was found to attenuate mitochondrial lesions in baboons, replenish glutathione, and significantly reduce mortality in patients with Child A or B cirrhosis. Similarly, polyenylphosphatidylcholine (PPC) corrects the ethanol-induced hepatic phospholipid depletion as well as the decreased phosphatidylethanolamine methyltransferase activity and opposes oxidative stress. It also deactivates hepatic stellate cells, whereas its dilinoleoyl species (DLPC) increases collagenase activity, resulting in prevention of ethanol-induced septal fibrosis and cirrhosis in the baboon. Clinical trials with PPC are ongoing in patients with alcoholic liver disease. Furthermore, enzymes useful for detoxification, such as CYP2E1, when excessively induced, become harmful and should be down-regulated. PPC is one of the substances with anti-CYP2E1 properties that is now emerging. Another important aspect is the association of alcoholic liver disease with hepatitis C: a quarter of all patients with alcoholic liver disease also have markers of HCV infection, with an even higher incidence in some urban areas but, at present, no specific therapy is available since interferon is contraindicated in that population. However, in addition to antiviral medications, agents that oppose oxidative stress and fibrosis should also be tested for hepatitis C treatment since these two processes contribute much to the pathology and mortality associated with the virus. In addition to antioxidants (such as PPC, silymarin, α-tocopherol and selenium), anti-inflammatory medications (corticosteroids, colchicine, anticytokines) are also being tested as antifibrotics. Transplantation is now accepted treatment in alcoholics who have brought their alcoholism under control and who benefit from adequate social support but organ availability is still the major limiting factor and should be expanded more aggressively. Finally, abstinence from excessive drinking is always indicated; it is difficult to achieve but agents that oppose alcohol craving are becoming available and they should be used more extensively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We hypothesized that markedly increasing the number of cores obtained during prostate needle biopsy may improve the cancer detection rate in men with persistent indications for repeat biopsy.
We ...performed saturation ultrasound guided transrectal prostate needle biopsy in 224 men under anesthesia in an outpatient surgical setting in whom previous negative biopsies had been performed in the office. The mean number of previous sextant biopsy sessions plus or minus standard deviation before saturation biopsy was 1.8 (range 1 to 7). A mean of 23 saturation biopsy cores (range 14 to 45) were distributed throughout the whole prostate, including the peripheral, medial and anterior regions. Indications for repeat biopsy were persistent elevated serum prostate specific antigen (PSA) in 108 cases, persistent elevated PSA and abnormal rectal examination in 27, persistent abnormal rectal examination in 4, high grade prostatic intraepithelial neoplasia in the previous biopsy in 64 and atypia in the previous biopsy in 21.
Cancer was detected in 77 of 224 patients (34%). The number of previous negative sextant biopsies was not predictive of subsequent cancer detection by saturation biopsy. Median PSA was 8.7 ng./ml. and median PSA velocity was 0.63 ng./ml. yearly. Of the 77 patients in whom cancer was detected radical prostatectomy was performed in 52. Pathological stage was pT2 in 48 patients and pT3 in 4, while Gleason score was 4 to 5, 6 to 7 and 8 in 5, 46 and 1, respectively. At prostatectomy median cancer volume was 1.04 cc and 85.7% of removed tumors were clinically significant, assuming a 3-year doubling time. The overall complication rate for saturation needle biopsy was 12% and hematuria requiring hospital admission was the most common event.
Saturation needle biopsy of the prostate is a useful diagnostic technique in men at risk for prostate cancer with previous negative office biopsies. This technique allows adequate sampling of the whole prostate gland and has a detection rate of 34% in this cohort of patients.
Isozymes of alcohol and other dehydrogenases convert ethanol and retinol to their corresponding aldehydes in vitro. In addition, new pathways of retinol metabolism have been described in hepatic ...microsomes that involve, in part, cytochrome P450s, which can also metabolize various drugs. In view of these overlapping metabolic pathways, it is not surprising that multiple interactions between retinol, ethanol, and other drugs occur. Accordingly, prolonged use of alcohol, drugs, or both, results not only in decreased dietary intake of retinoids and carotenoids, but also accelerates the breakdown of retinol through cross-induction of degradative enzymes. There is also competition between ethanol and retinoic acid precursors. Depletion ensues, with associated hepatic and extrahepatic pathology, including carcinogenesis and contribution to fetal defects. Correction of deficiency through vitamin A supplementation has been advocated. It is, however, complicated by the intrinsic hepatotoxicity of retinol, which is potentiated by concomitant alcohol consumption. By contrast, beta-carotene, a precursor of vitamin A, was considered innocuous until recently, when it was found to also interact with ethanol, which interferes with its conversion to retinol. Furthermore, the combination of beta-carotene with ethanol results in hepatotoxicity. Moreover, in smokers who also consume alcohol, beta-carotene supplementation promotes pulmonary cancer and, possibly, cardiovascular complications. Experimentally, beta-carotene toxicity was exacerbated when administered as part of beadlets. Thus ethanol, while promoting a deficiency of vitamin A also enhances its toxicity as well as that of beta-carotene. This narrowing of the therapeutic window for retinol and beta-carotene must be taken into account when formulating treatments aimed at correcting vitamin A deficiency, especially in drinking populations.
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CMK, GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Gender Differences in Pharmacokinetics of Alcohol Baraona, Enrique; Abittan, Chaim S.; Dohmen, Kazufumi ...
Alcoholism, clinical and experimental research,
April 2001, Volume:
25, Issue:
4
Journal Article
Peer reviewed
Background: The enhanced vulnerability of women to develop alcohol‐related diseases may be due to their higher blood alcohol levels after drinking, but the mechanism for this effect is debated.
...Methods: Sixty‐five healthy volunteers of both genders drank 0.3 g of ethanol/kg of body weight (as 5%, 10%, or 40% solutions) postprandially. Blood alcohol concentrations were monitored by breath analysis and compared with those after intravenous infusion of the same dose. First‐pass metabolism was quantified (using Michaelis‐Menten kinetics) as the route‐dependent difference in the amount of ethanol reaching the systemic blood. Gastric emptying was assessed by nuclear scanning after intake of 300 μCurie of technetium‐labeled diethylene triamine pentacetic acid in 10% ethanol. The activities of alcohol dehydrogenase isozymes were assessed in 58 gastric biopsies, using preferred substrates for γ‐ADH (acetaldehyde) and for ς‐ADH (m‐nitrobenzaldehyde) and a specific reaction of χ‐ADH (glutathione‐dependent formaldehyde dehydrogenase).
Results: Women had less first‐pass metabolism than men when given 10% or 40%, but not 5%, alcohol. This was associated with lower gastric χ‐ADH activity; its low affinity for ethanol could explain the greater gender difference in first‐pass metabolism with high rather than with low concentrations of imbibed alcohol. Alcohol gastric emptying was 42% slower and hepatic oxidation was 10% higher in women. A 7.3% smaller volume of alcohol distribution contributed to the higher ethanol levels in women, but it did not account for the route‐dependent effects.
Conclusions: The gender difference in alcohol levels is due mainly to a smaller gastric metabolism in females (because of a significantly lesser activity of χ‐ADH), rather than to differences in gastric emptying or in hepatic oxidation of ethanol. The concentration‐dependency of these effects may explain earlier discrepancies. The combined pharmacokinetic differences may increase the vulnerability of women to the effects of ethanol.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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