Hydrogen bond network in the distal site of peroxidases: spectroscopic properties of Asn70 --> Asp horseradish peroxidase mutant

The distal His in peroxidases forms a hydrogen bond with the adjacent Asn, which is highly conserved among many plant and fungal peroxidases. Our previous work [Nagano, S., Tanaka, M., Ishimori, K., Watanabe, Y., & Morishima, I. (1996) Biochemistry 35, 14251-14258] has revealed that the replacement of Asn70 in horseradish peroxidase C (HRP) by Val (N70V) and Asp (N70D) discourages the oxidation activity for guaiacol, and the elementary reaction rate constants for the mutants was decreased by 10-15-fold. In order to delineate the structure-function relationship of the His-Asn couple in peroxidase activity, heme environmental structures of the HRP mutant, N70D, were investigated by CD, 1H NMR, and IR spectroscopies as well as Fe2+/Fe3+ redox potential measurements. While N70D mutant exhibited quite similar CD spectra and redox potential to those of native enzyme, the paramagnetic NMR spectrum clearly showed that the hydrogen bond between the distal His and Asp70 is not formed in the mutant. The disappearance of the splitting in the 1H NMR signal of heme peripheral 8-methyl group observed in 50% H2O/50% D2O solution of N70D-CN suggests that the hydrogen bond between the distal His and heme-bound cyanide is also disrupted by the mutation, which was supported by the low C-N vibration frequency and large dissociation constant of the heme-bound cyanide in the mutant. Together with the results from various spectroscopies and redox potentials, we can conclude that the improper positioning of the distal His induced the cleavages of the hydrogen bonds around the distal His, resulting in the substantial decrease of the catalytic activity without large structural alterations of the enzyme. The His-Asn hydrogen bond in the distal site of peroxidases, therefore, is essential for the catalytic activity by controlling the precise location of the distal His.

A novel approach to assessing family history in the prevention of coronary heart disease

Family history serves as the most important risk factor in prevention of coronary heart disease from youth. Prevalent methods of assessing family history, however, have serious drawbacks: a sudden rise of risk when a family member develops the disease; insufficient control for age among family members. We propose a simple quantitative method overcoming such drawbacks. Data on family history were obtained by questionnaires sent to 2,393 male high school students and their cholesterol levels were measured. Family risk from each family member was calculated by (30/Risk age)4, where the risk age was age at onset expressed by decade; if absent, it was replaced by present age or age at death. A mean score in a family served as the family risk. A total of 1,584 students and 17,127 family members were analyzed. The proposed method yielded a statistically significant association (Odds ratio = 1.60; 95% confidence interval: 1.15-2.25) between the family risk (above or below the median) and the student's atherogenic index (above or below the 90th percentile) calculated from cholesterols. This association was stronger than those by conventional methods. The proposed method may be useful in prevention activities and its efficiency needs to be confirmed in other studies.

Albuminuria is directly associated with increased plasma PAI-1 and factor VII levels in NIDDM patients

Increased plasma plasminogen activator inhibitor type 1 (PAI-1), coagulation factor VII (FVII) and fibrinogen levels have been recognized as risk factors for cardiovascular disease. Because a substantially high incidence of cardiovascular disease has been reported in diabetic patients with nephropathy compared with those without nephropathy, we measured plasma levels of PAI-1, FVII activity and fibrinogen in non-insulin-dependent diabetic patients (NIDDM) with normoalbuminuria (without nephropathy), microalbuminuria (incipient nephropathy) and macroalbuminuria (overt nephropathy). PAI-1 and FVII levels were significantly increased in NIDDM with overt nephropathy compared with NIDDM without nephropathy. Fibrinogen levels were comparable between the patients with normo-, micro- and macro-albuminuria. Univariate regression analysis indicated that PAI-1 and FVII levels were significantly correlated with the albumin excretion rate (AER) in urine. PAI-1, FVII and fibrinogen levels were significantly correlated with the degree of insulin resistance estimated by the steady state plasma glucose concentration (SSPG) during the continuous infusion of glucose, insulin and octreotide. PAI-1 levels were correlated with plasma triglyceride (TG) levels. Multiple regression analysis revealed that AER was significantly associated with PAI-1 and FVII levels, whereas TG lost significant correlation with PAI-1 when AER, SSPG and plasma TG were entered as independent variables. SSPG retained an independent correlation with fibrinogen, PAI-1 and FVII levels. These results suggest that elevated plasma levels of PAI-1 and FVII in NIDDM patients with nephropathy are directly associated with renal damage, whereas insulin resistance widely regulates hemostatic components in NIDDM patients, irrespective of the presence of nephropathy.

Chronic inflammatory demyelinating polyneuropathy accompanied by hepatocellular carcinoma

We report a patient with chronic inflammatory demyelinating polyneuropathy (CIDP) accompanied by hepatocellular carcinoma (HCC). Due to the remarkable weakness in the lower limbs and loss of the position sense, he could not walk. On neurophysiological examination, he had impaired nerve conduction velocities. Biopsied nerve and muscle specimens demonstrated demyelination of nerve fibers and neurogenic degeneration of muscles. After steroid therapy he showed marked improvement in muscle strength and sensory function.

[Experience of 28 deliveries in 21 kidney transplant recipients]

BACKGROUND

Risk factors to induce graft dysfunction during pregnancy in kidney transplant recipients were studied.

METHODS

A total of 28 deliveries from 21 female kidney transplant recipients were analyzed.

RESULTS

All recipients were maintained on either azathioprine-based (n = 17) or cyclosporine-based (n = 11) immunosuppressive regimens. Graft dysfunction (creatinine clearance < 40 ml/min) occurred in 8 cases (8 patients) during pregnancy. No acute rejection, however, could be observed. In a case-controlled study comparing a group with graft dysfunction vs. a group with good graft function, there were significantly differences in the incidence of the cases with pre-existing hypertension (62.5% vs. 10.0%), the age of the grafted kidney (58.1 vs 47.6 year), the maternal anemia (Hb: 10.3 vs. 11.8 g/dl) and the creatinine level (1.4 vs. 1.0 mg/dl) at the first trimester. These findings suggested that poorer graft function had been underlying before pregnancy and that additional loading of the pregnancy reduced further graft function, while the deterioration would be recovered after delivery in all cases except one case.

CONCLUSION

Risk factors to induce graft dysfunction during pregnancy are as follows. 1) high age of the grafted kidney (> 50 year), 2) pre-existing hypertension, 3) maternal anemia (Hb: < 11 g/dl) and 4) high creatinine level (> 1.3 mg/dl) at the first trimester.

Catalytic roles of the distal site asparagine-histidine couple in peroxidases

There are highly conserved hydrogen bonds between the distal His and the adjacent Asn in many peroxidases. Although the crystal structure of horseradish peroxidase C (HRP) is not available, comparison of the amino acid sequence with cytochrome c peroxidase indicates that Asn70 is making the hydrogen bond with the distal His in the active site of HRP. To investigate the catalytic roles of the hydrogen bond, Asn70 in HRP was replaced with Val (N70V) or Asp (N70D). Though UV-vis, CD, and 1H-NMR spectra of native (plant enzyme), wild-type (recombinant enzyme), and mutant HRPs suggest that the active site and secondary structure are very similar even after mutation, the mutants exhibit low Vmax values for the hydroquinone oxidation (native, 281; wild-type, 283; and N70V, 18; and N70D, 33 microM.min-1). The rates of compound I formation were decreased to less than 10% of that of the native enzyme. The reduction rates of compounds I and II by guaiacol also were reduced to less than 10% of that of the native enzyme. Substituent effects of various phenol derivatives on the reduction of native, wild-type, and mutant compound I were examined. Large negative Hammett rho values (rho N70V:fast = -4.0, rho N70V:slow = -3.6, rho N70D = -3.8, rho native = -6.9, and rho wild-type = -6.8) are an indication of electron transfer being the rate-determining step in the phenol oxidation. However, these results also indicate the participation of the deprotonation step in the compound I reduction process. The proton abstraction from phenol must be harder for the mutants due to the decrease of basicity of the distal His upon mutation. Contrary to phenol oxidation, ABTS [2,2'-azinobis(3-ethybenzothiazoline-6-sulfonic acid)] oxidation activity was substantially increased by the mutations (native, 73; wild-type, 71; N70V, 217; and N70D, 234 microM.s-1). The redox potentials of N70V and N70D compounds II are 957 and 970 mV (vs NHE), which are 95 and 108 mV higher than that of native compound II (862 mV), respectively. Therefore, the high ABTS oxidation activities of mutants are attributed to these high redox potentials of compound II.

Preparation and reactions of myoglobin mutants bearing both proximal cysteine ligand and hydrophobic distal cavity: protein models for the active site of P-450

We have reported that H93C human myoglobin (Mb), in which proximal histidine (His93, F8) was replaced by cysteine, gave nearly identical spectroscopic features of P-450 [Adachi, S., Nagano, S., Ishimori, K., Watanabe, Y., Morishima, I., Egawa, T., Kitagawa, T., & Makino R. (1993) Biochemistry 32, 241-252]. More importantly, the thiolate ligand enhanced its oxygenation activities when supported by H2O2 due to the exclusive encouragement of heterolytic O-O bond cleavage of peroxides. While we have attributed the enhanced heterolysis to the electron donation from the thiolate ligand, possible participation of the distal histidine (H64, E7) in H93C Mb cannot be eliminated. In addition, the racemic product formation catalyzed by H93C Mb implied that its distal cavity could prevent substrates from accessing to the heme and the reactions may proceed other than by the P-450 type mechanism (ferryl oxygen transfer). In order to clarify whether the distal histidine is involved in the O-O bond cleavage step and to improve accessibility of substrates, the distal histidine of H93C Mb is replaced by smaller and nonpolar residues, glycine (H64G/H93C Mb) and valine (H64V/H93C Mb), by site-directed mutagenesis. Various spectroscopic studies on these double-mutated Mbs revealed the ligation of cysteine to the ferric heme as a thiolate form. In the reaction with cumene hydroperoxide, the anionic nature of the proximal cysteine in H64G/H93C and H64V/H93C Mbs was found to encourage the heterolytic O-O bond cleavage as observed for H93C Mb. The results clearly demonstrate that the distal histidine of H93C Mb is hardly involved in the O-O bond cleavage step and are in good agreement with the role of thiolate ligation for the formation of the reactive intermediate, equivalent to compound I, in the catalytic cycle of P-450 reactions. In the oxygenation of methyl p-tolyl sulfide, the ratios of ferryl oxygen transfer increased in H64G/H93C Mb (58%) and H64V/H93C Mb (78%) as compared to H93C Mb (53%). The increased ratios of ferryl oxygen transfer imply the active site of H64G/H93C and H64V/H93C Mbs being more accessible for substrates; however, the sulfoxidation by the ferric mutant Mbs/H2O2 system was much slower than that by H93C Mb. The poor activities of these mutant Mbs are attributed to the significantly discouraged binding of H2O2.

High prevalence of small LDL particles in non-insulin-dependent diabetic patients with nephropathy

To determine whether small-sized low density lipoprotein (LDL) is associated with a high incidence of coronary heart disease in diabetic nephropathy, we measured the LDL particle size in non-insulin-dependent diabetes mellitus (NIDDM) patients with various degrees of albuminuria (n = 95) and age-, weight-matched non-diabetic control subjects (n = 31). The diabetic subjects were divided into three groups, normoalbuminuric, microalbuminuric and macroalbuminuric NIDDM, based on the amount of albuminuria. The average diameter of LDL particles was determined by non-denaturing polyacrylamide gradient (2-16%) gel electrophoresis. The plasma lipid and lipoprotein concentrations were comparable between the non-diabetic controls and normoalbuminuric NIDDM, whereas the plasma triglyceride, very-low-density lipoprotein (VLDL) or LDL concentration was significantly increased in diabetic nephropathy. The mean LDL particle size was significantly smaller in microalbuminuric NIDDM compared with the controls or normoalbuminuric NIDDM, and the LDL size was further decreased in macroalbuminuric NIDDM. The incidence of small LDL (diameter < 255 A) was remarkably increased in microalbuminuric (58%) and macroalbuminuric NIDDM (67%) compared to the control (13%) and normoalbuminuric NIDDM (27%). Corresponding to the decreased LDL size, the cholesterol content of the LDL was significantly depleted in NIDDM with nephropathy. The high prevalence of small LDL in diabetic nephropathy was also observed even when hypertriglyceridemic or hypertensive subjects were excluded from each group. The increment in triglyceride-rich lipoprotein (d < 1.006) after oral fat-loading was increased, and postheparin lipoprotein lipase activity was decreased significantly in diabetic nephropathy. These abnormalities were significantly associated with LDL particle size. Multivariate regression analysis revealed that the amount of albuminuria was closely associated with the average LDL particle size, and this association was independent of the plasma triglyceride level. Neither insulin resistance nor glycemic control was directly associated with LDL particle diameter. The present study indicates that LDL particles become smaller in diabetic nephropathy, and this may be associated primarily with abnormal triglyceride metabolism. However, in addition to hypertriglyceridemia, other metabolic abnormalities caused by diabetic nephropathy may also be involved in the pathogenesis of small LDL particles.

Three-times-daily monotherapy with tacrolimus (FK 506) in kidney transplantation

BACKGROUND

Tacrolimus (FK 506) was introduced into organ transplantation as a powerful immunosuppressive but with several adverse effects. In fact, an appropriate protocol for using this agent has not yet been established. On the basis of pharmacokinetic studies and the reports of its administration as a continuous intravenous infusion, we designed the regimen of every eight hours in order to reduce the daily dosage.

METHODS

Tacrolimus was given to nine patients in the Japanese FK506 study. Although it was discontinued in two patients within two months because of adverse effects and acute rejection, seven other patients tolerated the agent for a long period and received the drug three times a day. Concomitant prednisolone was gradually tapered and finally withdrawn in these patients.

RESULTS

The smaller dosage of tacrolimus led to a higher trough concentration of 14.1 +/- 1.6 ng/mL in the three-times-a-day regimen compared with 12.7 +/- 1.9 ng/ml in twice-a-day therapy (P < 0.01). The daily dosage of tacrolimus proved to be reducible even further. Our target trough concentration was decreased finally to < 5 ng/mL. Concomitant prednisolone was withdrawn in all of the seven patients. The course of these patients has been uneventful for a year after withdrawal of prednisolone.

CONCLUSION

Our regimen of three-times-a-day oral administration of tacrolimus is a likely protocol for reduction of its daily dosage, which lowers its adverse effects while maintaining its immunosuppressive action at a lower trough concentration without concomitant prednisolone.

Decrease of serum ascorbic acid concentrations in patients with diabetic macroangiopathy

The relationship between serum ascorbic acid (AA) and diabetic macroangiopathy was studied. Fifty-six patients with noninsulin-dependent diabetes mellitus were examined, together with 20 healthy controls matched for age against the diabetes patients. Aortic pulse wave velocity (PWV) was taken as an index of the severity of atherosclerosis. The level of serum AA in diabetic patients was significantly lower than that of the controls. Among the diabetic groups, those with elevated PWV levels by age demonstrated a significant drop in AA. No significant differences were seen in the level of serum dehydroascorbic acid (DHAA) between patients and controls, nor were there any significant differences among patient groups. The concentration of serum AA was inversely related to the risk factors of atherosclerosis, such as body mass index, Apo B/ Apo A-I ratio, thiobarbituric acid-reactive substances (TBARS), and microalbumin in urine. It was inferred from these findings that the depletion of serum AA was apparent in diabetics with advanced atherosclerosis.

Radiographic study of bone loss of mandibular lingual cortical plate accompanied by third molar development

OBJECTIVE

The purpose was to determine the features of mandibular lingual cortical bone loss around the root of the mandibular third molar.

STUDY DESIGN

We examined occlusal radiographs in 2210 persons aged 11 to 78 years.

RESULTS

Prominent increase of incidence of bone loss was evident in subjects in their third decade compared with those in their second decade. The incidence was not decreased into the sixties. The incidence of bone loss in men was significantly higher than that in women. The incidence was not influenced by inflammation around the tooth crown of the third molar, by tooth caries, or by metal fillings present in the third molar.

CONCLUSIONS

The present observations suggest that bone loss is induced by physiologic processes that accompany root formation of the third molar after mandibular growth.

Intra- and interindividual variation in the pharmacokinetics of tacrolimus (FK506) in kidney transplant recipients--importance of trough level as a practical indicator

BACKGROUND

Tacrolimus (FK506) is currently used as the primary immunosuppressant in clinical kidney transplantation in some centers. The purpose of this study was to evaluate the pharmacokinetics of this drug and to see if trough level, which has been used widely in therapeutic drug monitoring, can be used as an appropriate substitute for other pharmacokinetic measurement tests.

METHODS

The blood concentration-time curve was studied in 10 kidney transplant recipients on 26 occasions after oral dosage of 2 to 18 mg every 12 hours. Whole blood concentration was measured by two-step immunoabsorption assay. Methylprednisolone was used as a concomitant immunosuppressive drug.

RESULTS

The blood concentration-time curves showed remarkable interindividual variation. Intraindividual variation was also found, but the degree of variation was slight compared with interindividual variation. On 17 occasions of measurement in one patient, the dose was significantly correlated with trough (r = 0.684), Cmax (r = 0.838) and AUC0-12 (r = 0.817). In nine patients on nine occasions, however, the dose was not significantly correlated with trough (r = 0.351), Cmax (r = 0.270) or AUC0-12 (r = 0.355). tmax ranged from one to four hours (mean + SD; 2.8 + 1.3) and fluctuated in both intra- and interindividual measurements. In spite of a wide variation in the blood concentration-time-curve patterns, a highly significant linear relationship between trough and Cmax or AUC0-12 was observed in both intraindividual (Cmax, r = 0.876; AUC0-12, r = 0.926) and interindividual (Cmax, r = 0.943; AUC0-12, r = 0.984) measurements.

CONCLUSIONS

We conclude that trough level is a practical acceptable indicator of the blood levels of tacrolimus, and can be used to monitor blood concentration.

Interferon alpha therapy for chronic active hepatitis type C after renal transplantation and allograft rejection

An acute type rejection episode occurred in one of two patients treated with Interferon alpha (IFN alpha) for type C hepatitis (CHC). Histopathological examination of the graft kidney revealed focal cellular infiltration and chronic transplant glomerulopathy which showed acute or chronic type rejection. In spite of bolus administration of methyl-prednisolone, the elevation of serum creatinine level continued. After administration of anti-human lymphocyte globulin (AHLG), renal function improved, but urinary protein was still positive. Another patient had no episode of rejection during or after IFN alpha therapy.

Putative hydrogen bond network in the heme distal site of horseradish peroxidase

The N delta 1 atom of the distal His of several peroxidases is known to make a hydrogen bond with the side chain oxygen of Asn. Thus, a mutant horseradish peroxidase, in which Asn70 is replaced by Val, has been expressed in Esherichia coli to disrupt the putative hydrogen bond. Substitution of Asn70 to Val reduces the rate constant for the compound I formation from 1.6 x 10(7) (native) to 6 x 10(5) M-1s-1. The rate constant for reduction of compound I of N70V by guaiacol has been also reduced from 7.8 x 10(6) (native) to 1.2 x 10(5) M-1s-1. While compound I of N70V is stable and reduced to the resting state of the mutant without apparent formation of compound II at neutral pH, compound II of N70V is obtained as a stable intermediate at alkaline pH. Similar alteration of the reactivity has been observed in the reaction with guaiacol.

Intracellular apoprotein B degradation is suppressed by decreased albumin concentration in Hep G2 cells

It is generally accepted that hepatic secretion of apoprotein (apo) B-containing lipoproteins is substantially increased in nephrosis. To elucidate the mechanisms for the oversecretion of apo B, we investigated the effect of a various concentration of albumin on apo B kinetics in the absence or presence of oleate in Hep G2 cells. Hep G2 cells were labeled with [3H]-leucine in leucine-free medium containing 0, 1.5, 3.0 or 4.5% BSA for 180 minutes, and the secreted radiolabeled apo B, apo A1 and albumin were isolated by immunoprecipitation and counted. The secretions of apo B and albumin were suppressed by BSA (bovine serum albumin) in a dose-dependent manner, but the secretion of apo A1 was not suppressed significantly. Oleate (0.4 mM) increased the rate of apo B secretion by 2.5-fold when oleate was bound to 1.5% BSA, but at higher concentrations of BSA (3.0 or 4.5%), apo B secretion was less responsive to oleate. A pulse-chase study indicated that early apo B degradation was significantly suppressed in cells incubated with lower concentrations of BSA (0 or 1.5% BSA), thereby rapidly stimulating apo B secretion. Oleate (0.4 mM) potently inhibited apo B degradation when oleate was bound to 1.5% BSA, whereas the inhibition was not observed when oleate was bound to 4.5% BSA. Intracellular albumin synthesis was stimulated in BSA-free medium, but intracellular decay of albumin was essentially unaffected by concentration of BSA. Similar to BSA, a higher concentration of dextran (3.0 or 4.5%) reduced apo B secretion, and this was the result of increased early apo B degradation in the cells. These results indicate that reduced albumin suppresses intracellular apo B degradation, and the inhibition of apo B degradation by oleate is manifested only at a low concentration of albumin. Therefore, the present study suggests that free fatty acids bound to low concentration of albumin in the circulating plasma play an important role on hepatic oversecretion of apo B-containing lipoprotein in hypoalbuminemic state, such as nephrotic syndrome.

Similar to oleic acid, eicosapentaenoic acid stimulates apolipoprotein B secretion by inhibiting its intracellular degradation in Hep G2 cells

We previously reported that oleic acid (OA) rapidly increased apolipoprotein (apo) B secretion by suppressing early intracellular degradation of nascent apo B in Hep G2 cells and suggested that the suppression of apo B degradation is associated with triglyceride (TG) biosynthesis from OA. To determine whether the inhibition of apo B degradation is associated with increased TG synthesis or is a direct effect of OA, we examined the effect of another fatty acid, eicosapentoenoic acid (EPA), on apo B kinetics in Hep G2 cells, since it is well known to have hypolipidemic action in clinical studies. The incorporation of [3H]glycerol into cellular TG was stimulated five-fold when Hep G2 cells were incubated for 2 h with EPA or OA (0.4 or 0.8 mM-1.5% bovine serum albumin (BSA) complex). The incorporation of [14C]acetic acid into cellular cholesteryl ester (CE) was significantly decreased by EPA treatment, whereas OA did not affect CE synthesis. Similar effects of these fatty acids on cellular lipid synthesis were observed in long-term incubation (24 h). Apo B was linearly secreted into the medium during 3 h, and EPA and OA doubled the rate of secretion. In long-term (24 h) incubations, both fatty acids significantly increased the incorporation of [3H]leucine into secreted apo B radioactivity or the accumulation of apo B mass in the medium. Pulse-chase studies revealed that both EPA and OA reduced intracellular apo B degradation to a similar degree. The inhibition of apo B degradation was also observed when the cells were preincubated with either EPA or OA for 24 h. These results suggest that increased TG synthesis leads to suppression of intracellular apo B degradation, which is independent of the source of exogenous fatty acid.

[Extracorporeal shock wave lithotripsy monotherapy for upper urinary tract stones using the Dornier lithotriptor MFL5000]

A total of 345 cases of upper urinary tract stones (188 renal and 157 ureteral stones) were treated by extracorporeal shock wave lithotripsy (ESWL) monotherapy using the Dornier lithotriptor MFL5000. Of these cases 294 (85.2%) had stones less than 20 mm in length. A double-J ureteral stent was placed in 40 cases of renal stones and 8 ureteral stones due to large stone burden or failure of in situ ESWL for impacted stones. Epidural or spinal anesthesia was necessary in 32 cases to maximize the generator voltage or to prevent intractable pain. The number of ESWL sessions and shock waves increased in accordance with the stone size, with an average of 1.6 and 4442, respectively. Multiple sessions were required in 68 cases of renal stones (36.2%) and 59 of ureteral stones (37.6%). With a 3-month follow-up, the stone-free rate was 60.5% for renal stones and 89.4% for ureteral stones, with the overall stone-free rate of 74.7%. Including the cases with residual fragments less than 4 mm, ESWL monotherapy was successful for 86.4% of renal stones and 93.6% of ureteral stones, achieving the overall success rate of 89.9%. No serious complications related to ESWL were observed. Four cases of impacted ureteral stones underwent ureteroscopic extraction or open ureterolithotomy for fragment removal. ESWL monotherapy using the Dornier MFL5000 is an effective and noninvasive method of treating upper urinary tract stones. Satisfactory fragmentation and clearance can be achieved with multiple sessions even for large or impacted stones, but alternative procedures may be necessary to salvage fragments of impacted stones.