Vitamin C is a key antioxidant in human blood plasma and hence could influence the outcome of conditions such as acute pancreatitis in which oxidative stress apparently plays a pivotal role. The concentrations of vitamin C and its immediately bioavailable form, ascorbic acid, in fasting plasma samples from 30 healthy volunteers were compared with those in admission samples from 29 consecutive patients with acute pancreatitis and 27 patients with other acute abdominal crises. Median (range) levels of vitamin C and ascorbic acid, respectively, were 15 (6.3-19) and 12 (4.5-18) micrograms/ml in the control group, 2.8 (0.3-10) and < 0.5 (< 0.5-6.0) micrograms/ml in patients with acute pancreatitis, and 3.7 (0.6-15) and 2.3 (< 0.5-15) micrograms/ml in those with other acute abdominal problems. Admission plasma samples showed equally low vitamin C levels in both groups of patients (P < 0.001 versus controls), but those from patients with acute pancreatitis were further characterized by a disproportionate reduction in ascorbic acid, such that the concentration of ascorbic acid and its ratio to vitamin C were both significantly lower than in samples from patients with an acute abdomen (P < 0.005 and P < 0.001 respectively). It is concluded that the stress of an acute intra-abdominal crisis is accompanied by a non-specific decrease in the plasma level of vitamin C. In acute pancreatitis early and profound oxidative stress compounds this problem by denaturing the available vitamin. There may be a case for the judicious parenteral administration of ascorbic acid to patients with acute pancreatitis to boost plasma antioxidant defence.
Oxidative stress, i.e. potential tissue injury f r a an excess of free radicals over the available antioxidants, seems to be the pivotal effector of experimental acute pancreatitis (AP) [l] and there is rounting evidence that this MY also hold true in the human disease 121. Admission blood samples from patients with AP show greatly increased levels of oxidatively altered linoleic acid [3] and vitamin C [I1 compared to controls or patients with other acute abdominal problers.The same samples show substantially reduced levels of the micronutrient antioxidants ascorbic acid, selenium, 8-carotene and a-towpherol [3,41.Glutathione (GSH) and ATP homeostasis are also known to be vulnerable to oxidative stress [5,61 and, indeed one or both of these vital substances have been shown to be depleted in experimental models of AP [7-91.Icethodology for both glutathione and ATP has been the subject of debate. We have recently developed and validated the assays [10,111. we have confirmed that the concentration of glutathione in whole blood, which essentially reflects the mass of red blood cells, is best determined by the glutathione reductase/ NADPH recycling method of Tietze 1121, and that there is little or no measurable oxidised glutathione (GSSG) in whole blood.With regard to plasma, total glutathione (GSH + GSSG) is measured by an analogous assay, and GSSG on a separate aliquot, after immediately trapping the GSH present, using N-ethylmaleimide [lo].Plasma GSH is then calculated by subtraction.
Blood samples for ATP are collected into heparin and extracted with perchloric acid [ll].ATP is determined using a luciferin/luciferase bioluminescent assay 1131. Pyruvate kinase cnnverts ADP to ATP and in combination with iyokinase also allows determination of total adenylates (ATP + ADP + AW). Prom these three assays, erythrocyte levels of ADP and AW can be calculated by subtraction, and the cellular energy charge estimated. whole blood and plasm GSH, and for plasma GSSG were derived from studies in 18 healthy volunteers, aged 20 to 48 years. The same blood samples were used to determine erythrocyte levels of ATP, ADP and AW and to calculate energy charge. Blood samples were obtained using a simple tourniquet by puncture of the brachial vein. Sample preparation was carried out immediately to minimise artefactual changes in levels of both GSH and ATP through oxidation after sample collection [10,111. Admission blood samples from 18 consecutive patients with acute pancreatitis were obtained similarly and were prepared at the bedside.Adenylates were determined in only 9 patients as the method was perfected later than that for glutathione. Data are summarised in Table 1. Four of the patients were regarded as severe AP by conventional criteria; there were no significant differences between the glutathione profiles of this subgroup and patients with mild disease.There was no correlation between plasma and whole blood GSH levels in either patients or controls.Likewise, there was no correlation between whole blood GSH and ATP concentratio...
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