The role of the kidney in the catabolism of Bence Jones proteins and immunoglobulin fragments.

The role of the kidney in the catabolism of Bence Jones proteins, intact IgG molecules, and isolated L chains, Fab and Fc fragments of IgG, was studied. The proteins were purified, radioiodinated, and their survival times measured in nephrectomized, ureter-severed, and control mice. Active endogenous catabolism was the major factor in overall Bence Jones metabolism since excretion as proteinuria accounted for less than 25% of the total metabolism. The survival times of lambda- and kappa-type human Bence Jones proteins and the Bence Jones protein produced by mice with MPC-2 plasma cell tumor were exceedingly short in both unoperated and ureter-severed mice, with 50% of the injected protein catabolized in from 0.8-1.6 hr. In contrast, the survival of Bence Jones protein was markedly prolonged in nephrectomized animals, with 50% of the injected dose catabolized in from 9 to 17 hr. This ten-fold decrease in catabolic rate indicates that the kidneys are the major site of breakdown of Bence Jones proteins. Similar studies with other proteins indicated that the kidneys are also the major site for catabolism of isolated L chains but not of intact IgG molecules. The Fc immunoglobulin fragment was not catabolized and the Fab fragment only partially catabolized by the kidney. When ureter-severed animals were allowed to develop advanced uremia before being studied, the survival of Bence Jones protein was greatly prolonged, indicating that the catabolic process is impaired in the presence of uremia. The nature of this renal catabolism remains unknown. These observations suggest that the Bence Jones proteins and L chains observed in the urine of patients may reflect only a small fraction of such molecules synthesized by these patients. Furthermore, they provide an explanation for the prolongation of Bence Jones protein survival and the development of Bence Jones proteinemia observed in subjects with multiple myeloma and impaired renal function.

Hypercatabolism of normal IgG; an unexplained immunoglobulin abnormality in the connective tissue diseases.

The metabolism of radioiodinated IgG was studied in a series of 42 patients with connective tissue diseases (16 systemic lupus erythematosus, nine rheumatoid arthritis, five polymyositis, five vasculitis, and seven miscellaneous diagnoses). Fractional catabolic rates were increased and survival half-lives were shortened in all diagnostic categories indicating hypercatabolism of IgG. This hypercatabolism was masked by increased IgG synthesis, resulting in elevated serum concentrations of IgG in patients with systemic lupus erythematosus and rheumatoid arthritis and in generally normal concentrations in the others. The metabolism of iodinated IgM was also studied in eight patients with systemic lupus erythematosus, in seven with rheumatoid arthritis, and in 12 controls. The fractional catabolic rates were normal in both groups of patients. Serum concentrations of both IgM and IgA were moderately elevated in all diagnostic categories. Serum albumin metabolism was entirely normal in the nine subjects studied who were not receiving corticosteroids; in three who were receiving them, moderate hypercatabolism was observed. The hypercatabolism of IgG could not be accounted for by factors previously known to alter IgG metabolism. It was not observed in 15 patients with other chronic, inflammatory diseases and was not explained by concomitant administration of adrenal corticosteroids to some patients. Identical results were obtained whether the IgG was obtained from a patient himself or from a normal donor, demonstrating that the hypercatabolism is a host defect and not an abnormality of the protein. Thus, patients with connective tissue disease of several different diagnostic categories have been shown to have an unexplained immunoglobulin abnormality: they catabolize normal IgG at an accelerated rate.

Measurement of gastrointestinal protein loss using ceruloplasmin labeled with copper.

Ceruloplasmin labeled with (67)copper and administered intravenously to dogs, control human subjects, and patients with excessive gastrointestinal loss was shown to fulfill the requirements for a label for quantification of gastrointestinal protein loss. The radiocopper moiety was poorly absorbed from the gastrointestinal tract, not actively secreted into the intestinal tract, and did not alter significantly the metabolism of ceruloplasmin. Approximately 70% of the body pool of ceruloplasmin in both dog and man was within the intravascular space. In control human subjects the mean ceruloplasmin concentration was 30 mg per 100 ml with total circulating and total body ceruloplasmin pools of 15.5 and 22 mg per kg, respectively. In patients with excessive gastrointestinal protein loss secondary to intestinal lymphangiectasia, the serum ceruloplasmin concentration was reduced to 16 mg per 100 ml with a comparable reduction in the total circulating and total body ceruloplasmin pools to 8.8 and 12 mg per kg. The survival half-time of ceruloplasmin was 6.1 days in normal human subjects and 4.5 days in normal dogs. From 1.0 to 1.9% of the intravascular pool of ceruloplasmin was lost into the gastrointestinal tract of the dog per day, representing less than 11% of the over-all metabolism of this protein. In control human subjects from 1.9 to 3.9% of the intravascular pool was lost into the gastrointestinal tract each day, representing a maximum of from 11 to 22% of the over-all metabolism of this molecule. In contrast, patients with intestinal lymphangiectasia had a markedly shortened ceruloplasmin survival of 3.1 days, with from 15 to 40% of the intravascular pool of ceruloplasmin cleared into the gastrointestinal tract daily. This represented 76% of the over-all metabolism of this protein. Thus, although bulk loss of serum proteins into the gastrointestinal tract does not normally appear to be a significant factor in protein metabolism in normal dogs and men, such loss is a major factor in the pathogenesis of the hypoceruloplasminemia noted in patients with intestinal lymphangiectasia.

Intestinal lymphangiectasia: a protein-losing enteropathy with hypogammaglobulinemia, lymphocytopenia and impaired homograft rejection.

Intestinal lymphangiectasia is a disease characterized by dilated intestinal lymphatics, protein-losing enteropathy, hypoalbuminemia, and edema. The immunologic status of 18 patients with intestinal lymphangiectasia was studied. Concentrations of IgG, IgA, and IgM were measured by immune precipitation and metabolism of these three immunoglobulins was studied using purified radioiodinated proteins. The serum concentration and total body pool of each immunoglobin were greatly reduced. The fraction of the intravascular protein pool catabolized per day was increased to 34% for IgG, 59% for IgA, and 66% for IgM; these are in contrast with control values of 7%, 28%, and 17%, respectively. Synthetic rates of the immunoglobulins were normal or slightly increased. Primary circulating antibody response was tested in five patients with Vi and tularemia antigens. Titers elicited in patients with the Vi antigen were significantly lower than those seen in a control group, whereas no difference was seen between patient and control responses to the tularemia antigen. Lymphocytopenia was noted in patients with intestinal lymphangiectasia. The mean circulating lymphocyte count was 710 +/- 340/mm(3) in contrast to 2500 +/- 600/mm(3) in controls. Cellular hypersensitivity was studied with skin tests and skin grafts. 91% of normal individuals reacted to at least one of the four skin test antigens: purified protein derivative, mumps, Trichophyton, and Candida albicans; in contrast, only 17% of patients with intestinal lymphangiectasia had a positive reaction. Each of three patients tested with dinitrochlorobenzene had a negative reaction. Finally, all four patients who received skin homografts have retained these grafts for at least 12 months. The immunological disorders in patients with intestinal lymphangiectasia appear to result from loss of immunoglobulins and lymphocytes into the gastrointestinal tract secondary to disorders of lymphatic channels. Lymphocyte depletion then leads to skin anergy and impaired homograft rejection.

Immunoglobulin metabolism in ataxia telangiectasia.

Immunoglobulin metabolism has been studied in five patients with ataxia telangiectasia and in control subjects. Serum IgG levels were normal, increased, or decreased, reflecting normal, increased, or decreased synthetic rates, respectively. Serum IgM concentration was normal in three cases and slightly elevated in two cases. IgM turnover studies in the three cases with normal serum IgM levels showed normal IgM synthetic and catabolic rates. None of the five patients with ataxia telangiectasia had detectable serum IgA, and the maximum IgA synthetic rates possible for these patients were 0.3-10% of the normal mean synthetic rate (24 +/- 15 mg/kg per day) of 12 control individuals. Three of the patients had normal IgA fractional catabolic rates: 22% of the intravascular pool per day vs. 25 +/- 4% in controls. In two patients, fractional catabolic rates 4 and 20 times normal were found. In these cases, metabolic turnover, in vitro precipitation, radioimmunoelectrophoresis, and (or) the C'la fixation and transfer test provided evidence for the presence of a circulating antibody directed against IgA causing immune elimination of the molecule. These studies suggest that therapy with exogenous IgA may not be possible in some patients with ataxia telangiectasia or in other subjects with dysgammaglobulinemia.

Direct measurement of the rates of synthesis of plasma proteins in control subjects and patients with gastrointestinal protein loss.

The guanido carbon of hepatic arginine is the common precursor of urea and of the arginine of plasma proteins synthesized in the liver. It is possible to measure the momentary synthetic rates of plasma proteins by "pulse labeling" this arginine pool with bicarbonate-(14)C. In the current study, this method has been adapted in order to use urinary urea data and was applied to control subjects and patients with gastrointestinal protein loss. The assumptions required for this determination are discussed. There was close agreement between albumin synthetic rates measured by this method and albumin catabolic rates derived from simultaneous albumin-(131)I studies, supporting the validity of the method and suggesting that there is relatively little fluctuation in the rate of albumin synthesis from time to time. The albumin synthetic rates in six control subjects averaged 5.8 mg/kg per hr, while those of five patients with gastrointestinal protein loss averaged 7.2 mg/kg per hr. Thus in these patients, there was relatively little acceleration of albumin synthesis in response to continued loss of plasma proteins into the gastrointestinal tract. Fibrinogen synthetic rates averaged 1.9 mg/kg per hr in five control subjects and 3.2 mg/kg per hr in five patients with gastrointestinal protein loss. Transferrin synthetic rates exhibited considerable individual variation in both groups and averaged 0.24 mg/kg per hr in four control subjects and 0.31 mg/kg per hr in five patients with gastrointestinal protein loss. The method employed in this study offers several advantages in studying plasma protein metabolism. It provides a direct measurement of protein synthesis, applicable to several proteins simultaneously, does not require a long-term steady state in the metabolism of the proteins, and is capable of measuring short-term fluctuations in synthetic rates. Therefore, this approach is applicable to the investigation of the physiological factors controlling the rates of synthesis for plasma proteins.

Protein abnormalities in neuromuscular diseases--Part 2.

Different protein abnormalities have been found in several neuromuscular diseases and in some instances seem to be disease-specific. They do not necessarily represent "primary" defects and to date have only seldom led to beneficial therapy. But at the very least, these protein abnormalities provide handles which one may grasp in attempting to devise ways of arresting, curing, and preventing neuromuscular diseases.

Effect of fibrin degradation products and thrombin on fibrinogen synthesis.

The effect of intravenous administration of homologous fibrin degradation products and thrombin on fibrinogen synthesis was assessed in rabbits. The relative fibrinogen synthesis rate was calculated as a ratio of the amount of radiolabelled lysine incorporated into fibrinogen to the amount incorporated into albumin during the same measurement period. An increase in this ratio above control would indicate a relatively specific stimulation of fibrinogen synthesis as compared with albumin, which is not an acute-phase reactant. Injection of 45 mg of 'early' or 'late' fibrin degradation products failed to produce a significant increase in the relative fibrinogen synthesis rate, suggesting that fibrin degradation products play no feedback role in controlling fibrinogen synthesis. Infusion of small amounts of homologous thrombin (15--25 NIH u) was followed by a small but statistically significant elevation of the relative fibrinogen synthesis rate. This was not accompanied by any increase in the levels of fibrinogen degradation products in plasma, or by any decrease in plasma fibrinogen concentration, possibly suggesting that thrombin can stimulate fibrinogen synthesis by a mechanism independent of significant fibrinogenolysis or intravascular coagulation.

The roles of renal catabolism and uremia in modifying the clearance of fibrinogen and its degradative fragments D and E.

Elevated levels of fibrinogen/fibrin degradation products (FDP) occur in uremia, and have been thought to be in part related to intravascular coagulation in the kidney. More recent data indicated that delayed catabolism of fibrinogen fragment D occurred in anephric animals. To further evaluate FDP catabolism in the kidney, turnover studies of purified dog 131I-Fg-D and 125I-Fg-E were performed on dogs before and after acute subtotal nephrectomies, and later during chronic uremia. 131I-fibrinogen clearances were also perfomed. Slowed catabolism of Fg-D and Fg-E was observed in both the acute and chronic uremic stages. Altered urinary excretion was not a factor as only minimal amounts of Fg-D and Fg-E were excreted in the urine of the control animals. In the 131I-fibrinogen studies, there were significant changes in plasma volume, fibrinogen t 1/2, and intravascular/extravascular distribution, but not in fractional catabolic rate. To differentiate fully, the effects of uremia from those of loss of catabolic renal tissue, the Fg-D and Fg-E turnover studies were repeated on other animals with intact kidneys whose ureters were diverted into the peritoneum and compared to subsequent studies after total nephrectomy. The control and ureter-severed studies had the same clearance pattern, whereas decreased catabolism occurred in the nephrectomized dogs. The results demonstrate uremia per se does not have a major effect upon the catabolism of fibrinogen, Fg-D, and Fg-E. Loss of renal tissue does impair the clearance of Fg-D and Fg-E, indicating these proteins are normally catabolized in part by the kidneys. Thus elevated plasma FRA in uremic patients may reflect decreased Fg-D and Fg-E catabolism rather than increased FDP production from primary or secondary fibrinolysis.