Biochemical medicine and metabolic biology最新文献

We investigated glucose phosphorylation at various concentrations of glucose (1, 5, 10, 25, 50, 100 mmol/liter) in rabbit optic nerve. In the 3000g supernatant of whole rabbit optic nerve homogenates from female albino rabbits (n = 10, 1.8-2.0 kg body weight, mean ± SEM morning glycemia: 8.25 ± 0.29 mmol/liter), the glucose phosphorylating activity (NADP reduction measured as change in optical density at 366 nm at pH 7.5) increased progressively with the increase in glucose concentration (r = 0.89; P < 0.05) and approached the maximum at a very high glucose level (100 mmol/liter), with values (mean ± SEM) of 8.75 ± 0.97 nanomol/min/mg protein and 11.57 ± 1.15 at 1 and 100 mmol/liter glucose, respectively (+32.23%; P < 0.01). At a more alkaline pH (8.2;, n = 5, mean ± SEM morning glycemia: 8.83 ± 0.07 mmol/liter) glucose phosphorylation was higher than at pH 7.5 and retained the glucose concentration dependence (r = 0.95, P < 0.01). These kinetic characteristics are reminiscent of those of the low-affinity enzyme glucokinase, which is typically present in the liver. By subtracting the activity at 1 mmol/liter glucose from that at higher glucose concentrations, we calculated the "glucokinase component," which, together with the "hexokinase component," forms the "total" glucose phosphorylating activity. In five rabbits (of similar age and weight) with spontaneous hyperglycemia (mean ± SEM: 11.71 ± 0.60 mmol/liter), the optic nerve glucose phosphorylating activity was lower (value at 1 mmol/liter glucose: 5.42 ± 1.31, −38.06%, P < 0.05). This could contribute to the hyperglycemia by reducing glucose utilization. As in the normal controls, the glucose phosphorylating activity increased progressively (r = 0.98, P < 0.001) with the rise of glucose until 100 mmol/liter, with the value at 100 mmol/liter glucose (8.91 ± 1.41) being increased by +64.39% (P < 0.01) compared to the value at 1 mmol/liter glucose. Thus, in the rabbit optic nerve glucose is phosphorylated through a glucokinase-like enzyme, which entails increased glucose phosphorylation (even if of moderate degree) upon nerve exposure to high-glucose concentrations. In spontaneously hyperglycemic rabbits the actual glucose phosphorylation would depend upon both enzyme level (which is decreased) and glucose concentration (which is increased). Due to the in vivo inhibition of the hexokinase component by glucose-6-phosphate, the glucokinase component may be prevalent, and, therefore, the chronic diabetic hyperglycemia might induce a tendency to increased glucose phosphorylation, which may be relevant to development of optic neuropathy in diabetes.

Hexokinase catalyzes the first step in cerebral glucose utilization and is a rate-limiting enzyme in glycolysis. Glucose utilization is tightly coupled to cerebral blood flow so that during ischemia the brain has a decreased supply of glucose, as well as oxygen. We studied hexokinase enzymatic activity in a newborn piglet model of ischemia-reperfusion to determine if any changes in the activity or mitochondrial binding of the enzyme occurred. We observed that mitochondrial binding of cortical HK increased from 55 to 71% with ischemia and returned toward control levels, but did not completely recover, after 2 h of reperfusion.

We show here that long-term streptozotocin diabetes affects differently the intracellular distribution of phosphofructokinase (PFK), the rate-limiting enzyme of glycolysis, in tibialis anterior and gastrocnemius muscles. Diabetes, which causes ultrastructural damage in both muscle fibers, induced a decrease in PFK binding to cytoskeleton in gastrocnemius muscle but not in the tibialis anterior muscle. However, the allosteric activity of cytoskeleton-bound and soluble PFK was reduced in both kinds of muscles, most probably due to the decrease in the level of glucose 1,6-bisphosphate, the potent allosteric activator of the enzyme. Levels of fructose 2,6-bisphosphate remained unchanged. A change in the allosteric properties of the cytoskeleton-bound PFK was found only in the diabetic tibialis anterior muscle; in contrast to normal muscle, where only the soluble but not the bound enzyme responded to allosteric effecters, in the diabetic tibialis anterior muscle, the bound enzyme exhibited allosteric properties similar to the soluble enzyme, The reduction in both cytosolic and cytoskeletal PFK, and, thereby, glycolysis in these two kinds of muscles, which results most probably from the reported high pathological intracellular Ca²⁺ concentration, may contribute to muscle damage in diabetes.

An impairment of protein charge selectivity has been invoked to explain the initial anionic proteinuria in diabetic nephropathy. The aims of this work were to investigate charge and size protein permselectivity abnormalities in experimental diabetes and to monitor these changes over time after diabetes induction. Diabetes was induced in 56 Sprague-Dawley male rats by streptozotocin; the control group was represented by 38 normal rats. Blood glucose, body weight, urine volumes, and proteinuria in 24-h urine collections were evaluated at 3, 6, 9, and 12 months of diabetes. The Bradford method and mono- and bidimensional gel electrophoresis were used to determine and characterize proteinuria. Body weight increase was lower (P < 0.05, P < 0.0001, P < 0.05 at 3, 6, and 12 months, respectively), urine volumes were greater (P < 0.001, P < 0.05, P < 0.05 at 6, 9, and 12 months, respectively) and the proteinuria was significantly increased (P < 0.05 at 3 months, P < 0.001 at 6 months, P < 0.01 at 9 months, and P < 0.05 at 12 months) in diabetic rats compared with the control group. When the charge and the size of urine proteins were considered, small (30 kDa) and anionic proteins were found to be mainly excreted in diabetic rats, at 3 months of the disease; at 6 months, higher amounts of albumin and cationic proteins with higher molecular weight (50 kDa) were also found in the urine; at 9 and 12 months the changes previously described were associated with an excretion of proteins weighing about 75 kDa. The 30- and 50-kDa proteins were found to be immunoglobulin fragments. In the control group the pattern of proteinuria remained unchanged throughout. Thus, a charge permselectivity abnormality does exist in animal diabetes and its evaluation, together with that of size-selective proteinuria, contributes to the understanding and the monitoring of the diabetic kidney disease.

Incomplete cerebral ischemia (30 min) was induced in the rat by bilaterally clamping the common carotid arteries. Peripheral venous blood samples were withdrawn from the femoral vein four times (once every 5 min) before ischemia (0 time) and 5, 15, and 30 min after ischemia. Plasma extracts were analyzed by a highly sensitive high-performance liquid chromatographic method for the direct determination of malondialdehyde, oxypurines, and nucleosides. During ischemia, a time-dependent increase of plasma oxypurines and nucleosides was observed. Plasma malondialdehyde, which was present in minimal amount at zero time (0.058 μmol/liter plasma; SD 0.015), increased after 5 min of ischemia, resulting in a fivefold increase after 30 min of carotid occlusion (0.298 μmol/liter plasma; SD 0.078). Increased plasma malondialdehyde was also recorded in two other groups of animals subjected to the same experimental model, one receiving 20 mg/kg b.w. of the cyclooxygenase inhibitor acetylsalicylate intravenously immediately before ischemia, the other receiving 650 μg/kg b.w. of the hypotensive drug nitroprusside at a flow rate of 103 μl/min intravenously during ischemia, although in this latter group malondialdehyde was significantly higher. The present data indicate that the determination of malondialdehyde, oxypurines, and nucleosides in peripheral blood, may be used to monitor the metabolic alterations of tissues occurring during ischemic phenomena. In addition, these results suggest that the experimental model adopted in the present study induces an incomplete brain ischemia in the rat responsible for the plasma variations of malondialdehyde, oxypurines, and nucleosides, which mainly reflect the consequence of an oxygen radical-mediated tissue injury and an alteration of energy metabolism.

Prevailing controversies regarding the identity and nature of S-(2,4-dinitrophenyl) glutathione (Dnp-SG) and GSSG transport system(s) led us to examine xenobiotic-SG transport from human erythrocytes and into inside-out vesicles (IOV) using N-ethylmaleimide-glutathione conjugate (NEM-SG) as substrate. Efflux of NEM-SG from intact erythrocytes was linear over a period of 4 h, occurred against a concentration gradient, and required energy. No transport of NEM-SG was observed when endogenous ATP was exhausted by preincubation of the erythrocytes for 8 h at 37°C in the absence of glucose. When cellular GSH was partially conjugated with NEM to form 1.5 and 1.0 mM NEM-SG, and the remaining GSH was oxidized with t-butylhydroperoxide to generate 0.2 and 0.4 mM GSSG, respectively, the extrusion of NEM-SG from erythrocytes was not inhibited. The kinetics of NEM-SG transport in intact erythrocytes were monophasic; the K_{m NEM-SG} was 0.62 mM ± 0.24. However, in IOV two components of NEM-SG transport with respect to NEM-SG and ATP were discernible. The low K_m for NEM-SG was 5.6 ± 1.51 μM with a V_max of 7.30 ± 0.69 nmol/mg protein/h and the high K_m for NEM-SG was 1.35 ± 0.14 mM with a V_max of 65.1 ± 3.5 nmol/mg protein h. With respect to ATP, the NEM-SG transport had a low K_m of 0.12 ± 0.004 mM and a high K_m of 0.52 ± 0.052 mM. Both components of NEM-SG transport were inhibited by fluoride, o-vanadate, p-hydroxymercuribenzoate and 5,5′-dithiobis(2-nitrobenzoic acid). However, NEM (1 mM) inhibited only the high K_m transport. GSH stimulated the low K_m transport 1.7-fold. Both low and high K_m components of NEM-SG transport significantly declined when ATP was substituted with CTP, UTP, or GTP. GSSG and Dnp-SG competitively inhibited the low K_m NEM-SG transport (K_i = 18.5 ± 2.9 and 1.32 ± 0.16 μM, respectively) whereas the high K_m transport was inhibited by Dnp-SG but not by GSSG, These findings suggest that glutathione S-conjugates may be transported out of erythrocytes by both the high and the low K_m mechanisms, the latter being shared by GSSG.

The 4-bp deletion in codons 41/42 (-TTCT) in the β-globin gene is a common mutation that causes β-thalassemia in Chinese. A simple method, which involved PCR amplification of the relevant region, was used for the antenatal diagnosis of a fetus at risk for this mutation. The fetal PCR product showed a single fragment of normal size on MetaPhor gel. The homozygous normal status was further confirmed by the generation of heteroduplexes only after addition of homozygous mutant DNA.

Interleukin-6 (IL-6), which is a multifunctional cytokine, has important roles in acute and chronic inflammation and may also be implicated in bone resorption. We examined the IL-6 production in periodontal ligament (PDL) cells which were treated with lipopolysaccharide (LPS) from several oral inflammatory pathogens. The LPS from Porphyromonas endodontalis, which was isolated from infected root canals and radicular cyst fluids, was more potent than the LPS from any other periodontal organisms examined. P. endodontalis LPS stimulated IL-6 release from PDL cells in a time- and dose dependent manner. Northern blot hybridization analysis revealed that the IL-6 mRNA level in PDL cells was increased by P. endodontalis LPS. These results suggest that stimulation of the IL-6 release of PDL cells by P. endodontalis LPS may have a role in the progression of inflammation and alveolar bone resorption in periodontal and periapical diseases.