Search PubMed⌕ Search

Biomedical subjects

J R Bloomer

Publications and source records attributed to J R Bloomer.

At least 37 records · Page 2Linked to original sources
PubMed1991

Immunochemical studies of ferrochelatase protein: characterization of the normal and mutant protein in bovine and human protoporphyria.

Protoporphyria is a hereditary disorder characterized by a marked decrease in the activity of ferrochelatase, the terminal enzyme in the heme biosynthetic pathway. We have prepared specific polyvalent antibodies against bovine ferrochelatase in rabbits. The specificity of the antibody preparation against ferrochelatase was demonstrated by western blot analysis and immunoprecipitation of ferrochelatase activity. The antibody also cross-reacted weakly with ferrochelatase from human mitochondria. To quantify immunoreactive ferrochelatase in tissue samples, a kinetic-based enzyme-linked immunosorbent assay (k-ELISA) was developed. Ferrochelatase activity and the level of immunoreactive protein were measured in hepatic mitochondria isolated from six normal and nine protoporphyric (homozygous) cattle. Ferrochelatase activity was less than 10% of normal in mitochondria from protoporphyric animals; the amount of immunoreactive material was equivalent to that from normal animals. Similar studies were performed with samples from three normal and two protoporphyric (heterozygous) humans. Ferrochelatase activity was decreased in protoporphyric samples (about 17% of normal, but there was no concomitant decrease in immunoreactive material. These data demonstrate that a normal amount of ferrochelatase protein is present and suggest that bovine and human protoporphyria result from point mutations in the gene encoding ferrochelatase.

Animals↗
PubMed1990

Porphyria and porphyrin metabolism.

Porphyrins, their reduced congeners (porphyrinogens), and their precursors are accumulated and excreted in excessive amounts in the porphyrias because of defects in the enzymes of heme biosynthesis. The nature of these defects is being defined using biochemical and molecular biological techniques. The principal clinical manifestations in the porphyrias, photocutaneous lesions and neurological dysfunction, are linked to the biochemical abnormalities, and appropriate therapeutic interventions have accordingly been developed. The exogenous administration of metalloporphyrins and porphyrin derivatives, unlike the harmful effects of porphyrins in the porphyrias, may be of use in some clinical conditions, such as the treatment of hyperbilirubinemic states and the detection and therapy of certain cancers.

Animals↗
PubMed1990

Comparison of bile porphyrin concentrations in cattle and human beings with protoporphyria.

Blood and bile porphyrin concentrations were measured in cattle with protoporphyria and compared with those in human beings with the disease. Whereas the mean RBC porphyrin concentration in cattle was 18-fold greater than in human beings, the mean bile porphyrin concentration was only 78% greater. Sequential measurements over a 30-hour period in 1 animal with a bile fistula indicated that the ratio of total porphyrin to total bile acid in bile varied minimally. When the animal was given an IV infusion of taurocholate, the biliary excretion rate of porphyrin increased in parallel with that of bile acid, because of enhancement of bile flow. Thus, in cattle with protophorphyria, the concentration of porphyrin in bile is low compared with that of porphyrin in RBC, in contrast with findings in human beings, and adequate amounts of bile acids are secreted to maintain efficient protoporphyrin excretion. This explains, in part, why hepatobiliary disease has not been observed in cattle with protoporphyria, but has been seen in human beings with the disease.

Animals↗
PubMed1989

Modulation of hepatic ferrochelatase activity by dietary manipulation of mitochondrial phospholipid fatty acyl groups.

Ferrochelatase is an enzyme bound to the inner mitochondrial membrane, which is important in heme biosynthesis. Activity of purified ferrochelatase is affected by the presence of certain fatty acids. In the present study, we examined whether the activity of ferrochelatase is altered by dietary manipulation of the composition of mitochondrial membrane phospholipid fatty acyl groups. Rats were fed diets containing triolein, safflower or menhaden oil as 5% (w/w) of the diet. After 3 weeks, the animals were killed and liver mitochondria were isolated. Phospholipid fatty acid composition and ferrochelatase activity were assayed in the isolated mitochondria. Marked differences were seen. The proportion of oleic acid was highest in the triolein oil-fed group, that of linoleic and arachidonic acid was highest in the safflower oil-fed group and the proportion of eicosapentaenoic acid was highest in the menhaden oil-fed group. Ferrochelatase activity was greatest in the triolein oil-fed group and lowest in the menhaden oil-fed group regardless of whether the mitochondria were intact, sonicated or sonicated and treated with Tween 20. Mixing of mitochondria from menhaden oil-fed rats with triolein oil resulted in a significant increase in ferrochelatase activity. Membrane fluidity and activities of the mitochondrial membrane enzymes succinic dehydrogenase and cytochrome oxidase did not differ among the groups. We conclude that dietary manipulation of mitochondrial membrane phospholipid fatty acyl group composition can directly modulate hepatic ferrochelatase activity. This has potential application in the treatment of protoporphyria, the genetic disorder in which ferrochelatase activity is deficient.

Animals↗
PubMed1989

The porphyrias.

The porphyrias are metabolic disorders in which there are excessive accumulation and excretion of porphyrins and porphyrin precursors. Each of the porphyrias has a specific enzyme defect in the pathway of heme biosynthesis that explains the pattern of biochemical abnormalities that occur. However, some patients have the enzyme defect but do not have clinical or biochemical manifestations, indicating that other factors (e.g., demand for increased heme biosynthesis) are also important in causing disease expression. The major clinical manifestations are neurologic dysfunction and photosensitivity. The precise cause of the neurologic dysfunction has not been defined, but the likely possibilities are overproduction of delta-aminolevulinic acid, which may act as a neurotoxin, or a deficiency of heme (or both). The cutaneous lesions in the porphyrias are due to the photo-sensitizing and other effects of porphyrins that are deposited in the skin or are circulating in dermal blood vessels. Therapy is directed to modify the biochemical abnormalities. Most importantly, intravenous administration of hematin is used in the treatment of acute attacks of neurologic dysfunction. Prevention remains a cornerstone in management of patients with porphyria, and those with gene defects should be counseled regarding factors that precipitate acute attacks.

Heme↗
PubMed1989

Liver transplantation in a patient with protoporphyria.

A 38-yr-old woman with liver disease due to protoporphyria underwent orthotopic liver transplantation. The resected liver was cirrhotic and contained a massive amount of protoporphyrin, with numerous birefringent pigment deposits. Transplantation was accomplished without difficulty following blood volume exchange to reduce the blood protoporphyrin level. Sequential biopsy specimens obtained through the 13th month after transplantation showed no accumulation of protoporphyrin pigment deposits in the new liver. Portal inflammation observed in the liver biopsy specimen at 6 mo after transplantation resolved spontaneously. Erythrocyte and serum protoporphyrin levels returned to values similar to those in the pretransplantation period when the patient had normal hepatic function; the fecal level was lower. Thus orthotopic liver transplantation can be successfully done in patients with protoporphyria who have severe liver disease. Prolonged follow-up is needed to determine the ultimate outcome, however, as the new liver remains susceptible to protoporphyrin-induced damage.

Adult↗
PubMed1988

Hepatic and bile porphyrins in patients with protoporphyria and liver failure.

The livers of patients who have protoporphyria and hepatic failure contain large amounts of pigment crystals. Two such patients underwent liver transplantation, providing the opportunity to identify the pigment crystals. Portions of liver were digested enzymically, sedimented through a sucrose gradient, treated with 1% sodium dodecylsulfate, and centrifuged to purify the crystals. Spectrophotometric and high-performance liquid chromatography analysis demonstrated them to be composed of protoporphyrin. Bile samples were obtained from the 2 patients, 4 other patients who did not have liver disease, and 10 control subjects. The porphyrin concentrations in bile from the 6 patients were significantly increased above controls (range 254-7884 micrograms/dl compared with 11-109 micrograms/dl). The ratio of protoporphyrin to bile acid in bile distinguished the 2 patients with advanced liver disease (3105 and 2756 micrograms/mmol) from the 4 patients without liver disease (range 61-926 micrograms/mmol). Thus, analysis of bile from patients with protoporphyria may help in evaluating their hepatobiliary status.

Adult↗
PubMed1987

The enzyme defect in bovine protoporphyria. Studies with purified ferrochelatase.

Ferrochelatase was purified from the livers of normal and protoporphyria cattle by chromatography on Blue Sepharose CL-6B in order to investigate the enzyme defect in this disorder. The increase in specific activity (up to 2900-fold) indicated that the normal and protoporphyria enzymes were purified to a similar degree. The mutant enzyme had catalytic activity which was 10 to 15% of normal ferrochelatase, although the Michaelis constants for protoporphyrin and iron were similar. The molecular mass of the normal and protoporphyria enzyme protein was 40 kDa as evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In the presence of 15 mM sodium cholate, gel filtration demonstrated a similar size. However, at a lower concentration of sodium cholate (4 mM) the molecular mass was about 240 kDa, suggesting that the purified enzymes aggregate under this condition. Polyvalent antibodies were raised in rabbits using as antigens purified normal native enzyme and normal 40-kDa protein which had been further purified by preparative SDS-PAGE. In Western blots these antibodies complexed with both the normal and mutant 40-kDa proteins. The amount of 40-kDa protein in normal and protoporphyria mitochondrial fractions was also similar as evaluated by Western blots. These studies indicate that the ferrochelatase defect in bovine protoporphyria probably results from a point gene mutation that causes a minor change in enzyme structure.

Animals↗
PubMed1987

Red blood cell porphobilinogen deaminase in the evaluation of acute intermittent porphyria.

We measured the activity of the enzyme porphobilinogen deaminase in red blood cells of 222 persons. Ninety-seven of 107 patients with acute intermittent porphyria had enzyme activity below the normal range, whereas 55 of 56 patients with other types of porphyria had normal activity. This underscores the utility of this test in confirming the diagnosis of acute intermittent porphyria. Measurement of enzyme activity in 41 families with acute intermittent porphyria demonstrated that deficient activity is inherited as an autosomal dominant trait. Many latent carriers of the genetic defect were identified by family studies, permitting appropriate precautions to avoid potentially lethal porphyric attacks.

Acute Disease↗
PubMed1987

Progressive bile duct injury after thiabendazole administration.

A 27-yr-old man developed jaundice 2 wk after exposure to thiabendazole. Cholestasis persisted for 3 yr, at which time a liver transplant was performed. Two liver biopsy specimens and the hepatectomy specimen were remarkable for almost complete disappearance of interlobular bile ducts. Prominent fibrosis and hepatocellular regeneration were also present; however, the lobular architecture was preserved. This case represents an example of "idiosyncratic" drug-induced liver damage in which the primary target of injury is the bile duct. An autoimmune pathogenesis of the bile duct destruction is suggested.

Adult↗
PubMed1987

Contribution of extrahepatic tissues to biochemical abnormalities in hereditary tyrosinemia type I: study of three patients after liver transplantation.

Three patients with hereditary tyrosinemia type I were examined before and after liver transplantation to assess the role of extrahepatic tissues in the biochemical disorders of this disease. Before transplantation the three patients excreted excessive amounts of succinylacetoacetate (SAA), succinylacetone (SA), tyrosyl acidic compounds, and 5-aminolevulinate (ALA). The activity of 5-aminolevulinate dehydratase (ALA-D) in red blood cells was markedly inhibited (1% to 5% of control) in the three patients. Successful liver transplantation resulted in decreased excretion of urinary SAA plus SA, tyrosyl acidic compounds, and ALA. Two of the patients continued to excrete significant amounts of SAA plus SA, whereas those compounds were undetectable in the urine of the third patient. Tyrosine loading resulted in increased excretion of SAA plus SA in two patients, but those compounds remained undetectable in the third. All three patients continued to excrete higher than normal amounts of ALA, but the activity of ALA-D in red blood cells returned to normal after transplantation, indicating marked clearance of SA from the blood. Liver transplantation may not totally correct the biochemical abnormalities of hereditary tyrosinemia. It is likely that the kidney is the source of persistent biochemical aberrations in the urine without significant effects on the blood. Our results suggest the existence of heterogeneity for renal involvement in hereditary tyrosinemia.

Acetoacetates↗
PubMed1987

Liver allograft rejection. An analysis of the use of biopsy in determining outcome of rejection.

Two-hundred-seventy biopsy specimens from 47 patients undergoing liver transplants at the University of Minnesota were analyzed to determine if histological features could predict the eventual outcome of rejection episodes. Thirty-six patients (76.6%) rejected the transplant. Of these, five either suffered acute liver failure due to rejection (two cases) or developed chronic rejection (three cases). Features of significance in predicting such a bad outcome were arteritis, bile duct paucity, or simultaneous hepatocellular ballooning and hepatocellular dropout and necrosis. Other features, such as type and intensity of infiltrate, degree of bile duct damage, or simple presence of hepatocellular necrosis, were not predictive of outcome. Our conclusion is that biopsy is useful in predicting outcome. Since many of the histologic findings of predictive value were not present in initial pretreatment biopsy specimens, follow-up biopsies of patients being treated for rejection are recommended to assess efficacy of therapy.

Adolescent↗
PubMed1987

Cytomegalovirus infection of the liver in transplant recipients.

Thirty-two transplant recipients with cytomegalovirus (CMV) infection documented by positive culture of blood and/or organs other than the liver were evaluated for hepatic involvement. Thirteen of the 32 (41%) had evidence of hepatic involvement with CMV. Inclusions alone were present in three patients; liver cultures alone were positive for CMV in three; and both were present in seven. Although the presence of CMV inclusions was the only histological feature that clearly separated the groups with and without hepatic involvement, two items helpful in finding inclusions were lobular aggregates of polymorphonuclear cells and portal karyorrhexic debris. The presence of liver involvement had a significant correlation with multiple organ infection, indicating it is a good marker of widely disseminated disease. This study indicates that liver histology and culture are useful and complementary methods for documentation of hepatic involvement (hence, tissue invasion) in immunocompromised patients with CMV infection.

Cytomegalovirus Infections↗