Production of protein HC by human fetal liver explants

Kidney Protection with the Radical Scavenger α1-Microglobulin (A1M) during Peptide Receptor Radionuclide and Radioligand Therapy

α₁-Microglobulin (A1M) is an antioxidant found in all vertebrates, including humans. It has enzymatic reductase activity and can scavenge radicals and bind free heme groups. Infused recombinant A1M accumulates in the kidneys and has therefore been successful in protecting kidney injuries in different animal models. In this review, we focus on A1M as a radioprotector of the kidneys during peptide receptor radionuclide/radioligand therapy (PRRT/RLT). Patients with, e.g., neuroendocrine tumors or castration resistant prostate cancer can be treated by administration of radiolabeled small molecules which target and therefore enable the irradiation and killing of cancer cells through specific receptor interaction. The treatment is not curative, and kidney toxicity has been reported as a side effect since the small, radiolabeled substances are retained and excreted through the kidneys. In recent studies, A1M was shown to have radioprotective effects on cell cultures as well as having a similar biodistribution as the somatostatin analogue peptide ¹⁷⁷Lu-DOTATATE after intravenous infusion in mice. Therefore, several animal studies were conducted to investigate the in vivo radioprotective potential of A1M towards kidneys. The results of these studies demonstrated that A1M co-infusion yielded protection against kidney toxicity and improved overall survival in mouse models. Moreover, two different mouse studies reported that A1M did not interfere with tumor treatment itself. Here, we give an overview of radionuclide therapy, the A1M physiology and the results from the radioprotector studies of the protein.

Ferryl Hemoglobin and Heme Induce A1-Microglobulin in Hemorrhaged Atherosclerotic Lesions with Inhibitory Function against Hemoglobin and Lipid Oxidation

Infiltration of red blood cells into atheromatous plaques and oxidation of hemoglobin (Hb) and lipoproteins are implicated in the pathogenesis of atherosclerosis. α₁-microglobulin (A1M) is a radical-scavenging and heme-binding protein. In this work, we examined the origin and role of A1M in human atherosclerotic lesions. Using immunohistochemistry, we observed a significant A1M immunoreactivity in atheromas and hemorrhaged plaques of carotid arteries in smooth muscle cells (SMCs) and macrophages. The most prominent expression was detected in macrophages of organized hemorrhage. To reveal a possible inducer of A1M expression in ruptured lesions, we exposed aortic endothelial cells (ECs), SMCs and macrophages to heme, Oxy- and FerrylHb. Both heme and FerrylHb, but not OxyHb, upregulated A1M mRNA expression in all cell types. Importantly, only FerrylHb induced A1M protein secretion in aortic ECs, SMCs and macrophages. To assess the possible function of A1M in ruptured lesions, we analyzed Hb oxidation and heme-catalyzed lipid peroxidation in the presence of A1M. We showed that recombinant A1M markedly inhibited Hb oxidation and heme-driven oxidative modification of low-density lipoproteins as well plaque lipids derived from atheromas. These results demonstrate the presence of A1M in atherosclerotic plaques and suggest its induction by heme and FerrylHb in the resident cells.

Structure, Functions, and Physiological Roles of the Lipocalin α1-Microglobulin (A1M)

α₁-microglobulin (A1M) is found in all vertebrates including humans. A1M was, together with retinol-binding protein and β-lactoglobulin, one of the three original lipocalins when the family first was proposed in 1985. A1M is described as an antioxidant and tissue cleaning protein with reductase, heme- and radical-binding activities. These biochemical properties are driven by a strongly electronegative surface-exposed thiol group, C34, on loop 1 of the open end of the lipocalin barrel. A1M has been shown to have protective effects in vitro and in vivo in cell-, organ-, and animal models of oxidative stress-related medical conditions. The gene coding for A1M is unique among lipocalins since it is flanked downstream by four exons coding for another non-lipocalin protein, bikunin, and is consequently named α₁-microglobulin-bikunin precursor gene (AMBP). The precursor is cleaved in the Golgi, and A1M and bikunin are secreted from the cell separately. Recent publications have suggested novel physiological roles of A1M in regulation of endoplasmic reticulum activities and erythrocyte homeostasis. This review summarizes the present knowledge of the structure and functions of the lipocalin A1M and presents a current model of its biological role(s).

177Lu-PSMA-617 Therapy in Mice, with or without the Antioxidant α1-Microglobulin (A1M), Including Kidney Damage Assessment Using 99mTc-MAG3 Imaging

Anti-prostate specific membrane antigen (PSMA) radioligand therapy is promising but not curative in castration resistant prostate cancer. One way to broaden the therapeutic index could be to administer higher doses in combination with radioprotectors, since administered radioactivity is kept low today in order to avoid side-effects from a high absorbed dose to healthy tissue. Here, we investigated the human radical scavenger α₁-microglobulin (A1M) together with 177-Lutetium (¹⁷⁷Lu) labeled PSMA-617 in preclinical models with respect to therapeutic efficacy and kidney toxicity. Nude mice with subcutaneous LNCaP xenografts were injected with 50 or 100 MBq of [¹⁷⁷Lu]Lu-PSMA-617, with or without injections of recombinant A1M (rA1M) (at T = 0 and T = 24 h). Kidney absorbed dose was calculated to 7.36 Gy at 4 days post a 100 MBq injection. Activity distribution was imaged with Single-Photon Emission Computed Tomography (SPECT) at 24 h. Tumor volumes were measured continuously, and kidneys and blood were collected at termination (3–4 days and 3–4 weeks after injections). In a parallel set of experiments, mice were given [¹⁷⁷Lu]Lu-PSMA-617 and rA1M as above and dynamic technetium-99m mercaptoacetyltriglycine ([^99mTc]Tc-MAG3) SPECT imaging was performed prior to injection, and 3- and 6-months post injection. Blood and urine were continuously sampled. At termination (6 months) the kidneys were resected. Biomarkers of kidney function, expression of stress genes and kidney histopathology were analyzed. [¹⁷⁷Lu]Lu-PSMA-617 uptake, in tumors and kidneys, as well as treatment efficacy did not differ between rA1M and vehicle groups. In mice given rA1M, [^99mTc]Tc-MAG3 imaging revealed a significantly higher slope of initial uptake at three months compared to mice co-injected with [¹⁷⁷Lu]Lu-PSMA-617 and vehicle. Little or no change compared to control was seen in urine albumin, serum/plasma urea levels, RT-qPCR analysis of stress response genes and in the kidney histopathological evaluation. In conclusion, [^99mTc]Tc-MAG3 imaging presented itself as a sensitive tool to detect changes in kidney function revealing that administration of rA1M has a potentially positive effect on kidney perfusion and tubular function when combined with [¹⁷⁷Lu]Lu-PSMA-617 therapy. Furthermore, we could show that rA1M did not affect anti-PSMA radioligand therapy efficacy.

Pregnant alpha-1-microglobulin (A1M) knockout mice exhibit features of kidney and placental damage, hemodynamic changes and intrauterine growth restriction

Alpha-1-microglobulin (A1M) is an antioxidant previously shown to be elevated in maternal blood during pregnancies complicated by preeclampsia and suggested to be important in the endogenous defense against oxidative stress. A knockout mouse model of A1M (A1Mko) was used in the present study to assess the importance of A1M during pregnancy in relation to the kidney, heart and placenta function. Systolic blood pressure (SBP) and heart rate (HR) were determined before and throughout gestation. The morphology of the organs was assessed by both light and electron microscopy. Gene expression profiles relating to vascular tone and oxidative stress were analyzed using RT-qPCR with validation of selected gene expression relating to vascular tone and oxidative stress response. Pregnant age-matched wild type mice were used as controls. In the A1Mko mice there was a significantly higher SBP before pregnancy that during pregnancy was significantly reduced compared to the control. In addition, the HR was higher both before and during pregnancy compared to the controls. Renal morphological abnormalities were more frequent in the A1Mko mice, and the gene expression profiles in the kidney and the heart showed downregulation of transcripts associated with vasodilation. Simultaneously, an upregulation of vasoconstrictors, blood pressure regulators, and genes for osmotic stress response, ion transport and reactive oxygen species (ROS) metabolism occurred. Fetal weight was lower in the A1Mko mice at E17.5. The vessels in the labyrinth zone of the placentas and the endoplasmic reticulum in the spongiotrophoblasts were collapsed. The gene profiles in the placenta showed downregulation of antioxidants, ROS metabolism and oxidative stress response genes. In conclusion, intact A1M expression is necessary for the maintenance of normal kidney, heart as well as placental structure and function for a normal pregnancy adaptation.

Expression, Purification and Initial Characterization of Functional α1-Microglobulin (A1M) in Nicotiana benthamiana

α₁-Microglobulin (A1M) is a small glycoprotein that belongs to the lipocalin protein family. A major biological role of A1M is to protect cells and tissues against oxidative damage by clearing free heme and reactive oxygen species. Because of this, the protein has attracted great interest as a potential pharmaceutical candidate for treatment of acute kidney injury and preeclampsia. The aim of this study was to explore the possibility of expressing human A1M in plants through transient gene expression, as an alternative or complement to other expression systems. E. coli, insect and mammalian cell culture have previously been used for recombinant A1M (rA1M) or A1M production, but these systems have various drawbacks, including additional complication and expense in refolding for E. coli, while insect produced rA1M is heavily modified with chromophores and mammalian cell culture has been used only in analytical scale. For that purpose, we have used a viral vector (pJL-TRBO) delivered by Agrobacterium for expression of three modified A1M gene variants in the leaves of N. benthamiana. The results showed that these modified rA1M protein variants, A1M-NB1, A1M-NB2 and A1M-NB3, targeted to the cytosol, ER and extracellular space, respectively, were successfully expressed in the leaves, which was confirmed by SDS-PAGE and Western blot analysis. The cytosol accumulated A1M-NB1 was selected for further analysis, as it appeared to have a higher yield than the other variants, and was purified with a yield of ca. 50 mg/kg leaf. The purified protein had the expected structural and functional properties, displaying heme-binding capacity and capacity of protecting red blood cells against stress-induced cell death. The protein also carried bound chromophores, a characteristic feature of A1M and an indicator of a capacity to bind small molecules. The study showed that expression of the functional protein in N. benthamiana may be an attractive alternative for production of rA1M for pharmaceutical purposes and a basis for future research on A1M structure and function.

Inventory of Novel Animal Models Addressing Etiology of Preeclampsia in the Development of New Therapeutic/Intervention Opportunities

Preeclampsia is a pregnancy-related disease afflicting 3-7% of pregnancies worldwide and leads to maternal and infant morbidity and mortality. The disease is of placental origin and is commonly described as a disease of two stages. A variety of preeclampsia animal models have been proposed, but all of them have limitations in fully recapitulating the human disease. Based on the research question at hand, different or multiple models might be suitable. Multiple animal models in combination with in vitro or ex vivo studies on human placenta together offer a synergistic platform to further our understanding of the etiology of preeclampsia and potential therapeutic interventions. The described animal models of preeclampsia divide into four categories (i) spontaneous, (ii) surgically induced, (iii) pharmacologically/substance induced, and (iv) transgenic. This review aims at providing an inventory of novel models addressing etiology of the disease and or therapeutic/intervention opportunities.

Human Anti-Oxidation Protein A1M--A Potential Kidney Protection Agent in Peptide Receptor Radionuclide Therapy

Peptide receptor radionuclide therapy (PRRT) has been in clinical use for 15 years to treat metastatic neuroendocrine tumors. PRRT is limited by reabsorption and retention of the administered radiolabeled somatostatin analogues in the proximal tubule. Consequently, it is essential to develop and employ methods to protect the kidneys during PRRT. Today, infusion of positively charged amino acids is the standard method of kidney protection. Other methods, such as administration of amifostine, are still under evaluation and show promising results. α₁-microglobulin (A1M) is a reductase and radical scavenging protein ubiquitously present in plasma and extravascular tissue. Human A1M has antioxidation properties and has been shown to prevent radiation-induced in vitro cell damage and protect non-irradiated surrounding cells. It has recently been shown in mice that exogenously infused A1M and the somatostatin analogue octreotide are co-localized in proximal tubules of the kidney after intravenous infusion. In this review we describe the current situation of kidney protection during PRRT, discuss the necessity and implications of more precise dosimetry and present A1M as a new, potential candidate for renal protection during PRRT and related targeted radionuclide therapies.

A1M Ameliorates Preeclampsia-Like Symptoms in Placenta and Kidney Induced by Cell-Free Fetal Hemoglobin in Rabbit

Preeclampsia is one of the most serious pregnancy-related diseases and clinically manifests as hypertension and proteinuria after 20 gestational weeks. The worldwide prevalence is 3-8% of pregnancies, making it the most common cause of maternal and fetal morbidity and mortality. Preeclampsia lacks an effective therapy, and the only “cure” is delivery. We have previously shown that increased synthesis and accumulation of cell-free fetal hemoglobin (HbF) in the placenta is important in the pathophysiology of preeclampsia. Extracellular hemoglobin (Hb) and its metabolites induce oxidative stress, which may lead to acute renal failure and vascular dysfunction seen in preeclampsia. The human endogenous protein, α₁-microglobulin (A1M), removes cell-free heme-groups and induces natural tissue repair mechanisms. Exogenously administered A1M has been shown to alleviate the effects of Hb-induced oxidative stress in rat kidneys. Here we attempted to establish an animal model mimicking the human symptoms at stage two of preeclampsia by administering species-specific cell-free HbF starting mid-gestation until term, and evaluated the therapeutic effect of A1M on the induced symptoms. Female pregnant rabbits received HbF infusions i.v. with or without A1M every second day from gestational day 20. The HbF-infused animals developed proteinuria and a significantly increased glomerular sieving coefficient in kidney that was ameliorated by co-administration of A1M. Transmission electron microscopy analysis of kidney and placenta showed both intracellular and extracellular tissue damages after HbF-treatment, while A1M co-administration resulted in a significant reduction of the structural and cellular changes. Neither of the HbF-treated animals displayed any changes in blood pressure during pregnancy. In conclusion, infusion of cell-free HbF in the pregnant rabbits induced tissue damage and organ failure similar to those seen in preeclampsia, and was restored by co-administration of A1M. This study provides preclinical evidence supporting further examination of A1M as a potential new therapy for preeclampsia.

A1M, an extravascular tissue cleaning and housekeeping protein

Alpha-1-microglobulin (A1M) is a small protein found intra- and extracellularly in all tissues of vertebrates. The protein was discovered 40 years ago and its physiological role remained unknown for a long time. A series of recent publications have demonstrated that A1M is a vital part of tissue housekeeping. A strongly electronegative free thiol group forms the structural basis of heme-binding, reductase, and radical-trapping properties. A rapid flow of liver-produced A1M through blood and extravascular compartments ensures clearing of biological fluids from heme and free radicals and repair of oxidative lesions. After binding, both the radicals and the A1M are electroneutral and therefore do not present any further oxidative stress to tissues. The biological cleaning cycle is completed by glomerular filtration, renal degradation, and urinary excretion of A1M heavily modified by covalently linked radicals and heme groups. Based on its role as a tissue housekeeping cleaning factor, A1M constitutes a potential therapeutic drug candidate in treatment or prophylaxis of diseases or conditions that are associated with pathological oxidative stress elements.

The radical-binding lipocalin A1M binds to a Complex I subunit and protects mitochondrial structure and function

AIMS

During cell death, energy-consuming cell degradation and recycling programs are performed. Maintenance of energy delivery during cell death is therefore crucial, but the mechanisms to keep the mitochondrial functions intact during these processes are poorly understood. We have investigated the hypothesis that the heme- and radical-binding ubiquitous protein α1-microglobulin (A1M) is involved in protection of the mitochondria against oxidative insult during cell death.

RESULTS

Using blood cells, keratinocytes, and liver cells, we show that A1M binds with high affinity to apoptosis-induced cells and is localized to mitochondria. The mitochondrial Complex I subunit NDUFAB1 was identified as a major molecular target of the A1M binding. Furthermore, A1M was shown to inhibit the swelling of mitochondria, and to reverse the severely abrogated ATP-production of mitochondria when exposed to heme and reactive oxygen species (ROS).

INNOVATION

Import of the radical- and heme-binding protein A1M from the extracellular compartment confers protection of the mitochondrial structure and function during cellular insult.

CONCLUSION

A1M binds to a subunit of Complex I and has a role in assisting the mitochondria to maintain its energy delivery during cell death. A1M may also, at the same time, counteract and eliminate the ROS generated by the mitochondrial respiration to prevent oxidative damage to surrounding healthy tissue.

Pathological conditions involving extracellular hemoglobin: molecular mechanisms, clinical significance, and novel therapeutic opportunities for α(1)-microglobulin

Hemoglobin (Hb) is the major oxygen (O(2))-carrying system of the blood but has many potentially dangerous side effects due to oxidation and reduction reactions of the heme-bound iron and O(2). Extracellular Hb, resulting from hemolysis or exogenous infusion, is shown to be an important pathogenic factor in a growing number of diseases. This review briefly outlines the oxidative/reductive toxic reactions of Hb and its metabolites. It also describes physiological protection mechanisms that have evolved against extracellular Hb, with a focus on the most recently discovered: the heme- and radical-binding protein α(1)-microglobulin (A1M). This protein is found in all vertebrates, including man, and operates by rapidly clearing cytosols and extravascular fluids of heme groups and free radicals released from Hb. Five groups of pathological conditions with high concentrations of extracellular Hb are described: hemolytic anemias and transfusion reactions, the pregnancy complication pre-eclampsia, cerebral intraventricular hemorrhage of premature infants, chronic inflammatory leg ulcers, and infusion of Hb-based O(2) carriers as blood substitutes. Finally, possible treatments of these conditions are discussed, giving a special attention to the described protective effects of A1M.

Vitreous levels of oxidative stress biomarkers and the radical-scavenger α1-microglobulin/A1M in human rhegmatogenous retinal detachment

PURPOSE

To explore oxidative stress and the radical scavenger α(1)-microglobulin (A1M) in the vitreous body of human eyes with primary rhegmatogenous retinal detachment (RRD).

METHODS

Levels of carbonyl groups, a marker of oxidative stress, and A1M were measured by ELISA and RIA in 14 vitreous samples derived from patients suffering from RRD, and compared with 14 samples from macula hole (MH) patients. Carbonyl group and A1M levels in RRD samples were statistically related to detachment characteristics. Analysis of total protein level, SDS-PAGE, and Western blotting of A1M was also performed. In a separate experiment, mRNA expression of A1M was measured by RT-PCR in rat retina explants.

RESULTS

Levels of carbonyl groups and A1M varied widely in RRD vitreous samples, but were significantly higher in samples derived from eyes with large detachment area and macula-off status, while the presence of vitreous hemorrhage did not show any significant correlation. Compared with MH samples, RRD samples displayed significantly higher levels of A1M, whereas changes in total protein levels and carbonyl groups were not significant. Novel forms of A1M, not previously seen in plasma, were found in the vitreous body by Western blotting. Furthermore, A1M expression was seen in rat retina explants and was upregulated after 24 h of culturing.

CONCLUSION

Oxidative stress is a prominent feature of human eyes with primary RRD, and is directly related to detachment severity. Affected eyes can launch a protective response in the form of the radical scavenger A1M possibly derived from the retina. The results thus indicate potential therapeutic cell loss prevention in RRD by employing the endogeneous radical scavenger A1M.

Up-regulation of A1M/α1-microglobulin in skin by heme and reactive oxygen species gives protection from oxidative damage

During bleeding the skin is subjected to oxidative insults from free heme and radicals, generated from extracellular hemoglobin. The lipocalin α₁-microglobulin (A1M) was recently shown to have reductase properties, reducing heme-proteins and other substrates, and to scavenge heme and radicals. We investigated the expression and localization of A1M in skin and the possible role of A1M in the protection of skin tissue from damage induced by heme and reactive oxygen species. Skin explants, keratinocyte cultures and purified collagen I were exposed to heme, reactive oxygen species, and/or A1M and investigated by biochemical methods and electron microscopy. The results demonstrate that A1M is localized ubiquitously in the dermal and epidermal layers, and that the A1M-gene is expressed in keratinocytes and up-regulated after exposure to heme and reactive oxygen species. A1M inhibited the heme- and reactive oxygen species-induced ultrastructural damage, up-regulation of antioxidation and cell cycle regulatory genes, and protein carbonyl formation in skin and keratinocytes. Finally, A1M bound to purified collagen I (K_d = 0.96×10⁻⁶ M) and could inhibit and repair the destruction of collagen fibrils by heme and reactive oxygen species. The results suggest that A1M may have a physiological role in protection of skin cells and matrix against oxidative damage following bleeding.

The lipocalin α1-microglobulin binds heme in different species

The lipocalin alpha(1)-microglobulin (alpha(1)m), found in plasma and tissues of various vertebrates, is brown, forms complexes with other proteins and has immunomodulatory effects in vitro, but the physiological function is not yet established. Human alpha(1)m was recently shown to bind heme and, after cleavage of a C-terminal tetrapeptide, initiate heme degradation, thus suggesting a heme-scavenger function. In this work the heme-binding of alpha(1)m was characterized using heme immobilized on agarose beads, spectrophotometry, and electrophoresis. alpha(1)m, both in plasma and in purified form, displayed a concentration-dependent binding to heme-agarose. The apparent dissociation-constant was estimated to be around 2 x 10(-6)M for both free alpha(1)m and the IgA-alpha(1)m complex. Incubation with free heme resulted in two forms of alpha(1)m with different electrophoretic mobility. alpha(1)m, identified on Western blotting, was found in eluates from heme-agarose after incubation with human biological fluids as well as sera from non-human species, indicating evolutionary conservation of the heme-binding property. Heme-binding could be instrumental for isolating new alpha(1)m-homologues.

Distribution of iodine 125-labeled alpha1-microglobulin in rats after intravenous injection

The 28-kd plasma protein alpha(1)-microglobulin is found in the blood of mammals and fish in a free, monomeric form and as high-molecular-weight complexes with molecular masses above 200 kd. In this study, iodine 125-labeled free and high-molecular weight rat alpha(1)-microglobulin (a mixture of alpha(1)-microglobulin/alpha(1)-inhibitor-3 and alpha(1)-microglobulin/fibronectin complexes) were injected intravenously into rats. The distribution of the proteins was measured by using scintillation camera imaging. Both forms of (125)I-labeled alpha(1)-microglobulin were rapidly cleared from the blood, with a half-life of 2 and 16 minutes for the initial and late phase, respectively, for free alpha(1)-microglobulin; and a half-life of 3 and 130 minutes for the initial and late phase, respectively, for the complexes. After 45 minutes, 6%, 16%, 27%, 13%, and 34% of the free (125)I-labeled alpha(1)-microglobulin and 18%, 21%, 6%, 10%, and 42% of the (125)I-labeled alpha(1)-microglobulin complexes were found in the blood, gastrointestinal tract, kidneys, liver, and the remainder of the body, respectively. The local distribution of injected (125)I-labeled alpha(1)-microglobulin in intestines and kidneys was investigated by microscopy and autoradiography. In the intestine, both forms were distributed in the basal layers, villi, and luminal contents. The results also suggested intracellular labeling of epithelial cells. Well-defined local regions containing higher concentrations of injected protein could be seen in the intestine. In the kidneys, both forms were found mostly in the cortex. Free (125)I-labeled alpha(1)-microglobulin was found predominantly in epithelial cells of a subset of the tubules, whereas the (125)I-labeled complexes were more evenly distributed. Intracellular labeling was indicated for both alpha(1)-microglobulin forms. The results thus indicate a rapid transport of (125)I-labeled alpha(1)-microglobulin from the blood to most tissues.

alpha(1)-Microglobulin: a yellow-brown lipocalin

alpha(1)-Microglobulin, also called protein HC, is a lipocalin with immunosuppressive properties. The protein has been found in a number of vertebrate species including frogs and fish. This review summarizes the present knowledge of its structure, biosynthesis, tissue distribution and immunoregulatory properties. alpha(1)-Microglobulin has a yellow-brown color and is size and charge heterogeneous. This is caused by an array of small chromophore prosthetic groups, attached to amino acid residues at the entrance of the lipocalin pocket. A gene in the lipocalin cluster encodes alpha(1)-microglobulin together with a Kunitz-type proteinase inhibitor, bikunin. The gene is translated into the alpha(1)-microglobulin-bikunin precursor, which is subsequently cleaved and the two proteins secreted to the blood separately. alpha(1)-Microglobulin is found in blood and in connective tissue in most organs. It is most abundant at interfaces between the cells of the body and the environment, such as in lungs, intestine, kidneys and placenta. alpha(1)-Microglobulin inhibits immunological functions of white blood cells in vitro, and its distribution is consistent with an anti-inflammatory and protective role in vivo.

Alpha1-microglobulin is found both in blood and in most tissues

In this study we demonstrate that, in addition to blood, alpha1-microglobulin (alpha1m) is present in most tissues, including liver, heart, eye, kidney, lung, pancreas, and skeletal muscle. Western blotting of perfused and homogenized rat tissue supernatants revealed alpha1m in its free, monomeric form and in high molecular weight forms, corresponding to the complexes fibronectin-alpha1m and alpha1-inhibitor-3-alpha1m, which have previously been identified in plasma. The liver also contained a series of alpha1m isoforms with apparent molecular masses between 40 and 50 kD. These bands did not react with anti-inter-alpha-inhibitor antibodies, indicating that they do not represent the alpha1m-bikunin precursor protein. Similarly, the heart contained a 45-kD alpha1m band and the kidney a 50-kD alpha1m band. None of these alpha1m isoforms was present in plasma. Immunohistochemical analysis of human tissue demonstrated granular intracellular labeling of alpha1m in hepatocytes and in the proximal epithelial cells of the kidney. In addition, alpha1m immunoreactivity was detected in the interstitial connective tissue of heart and lung and in the adventitia of blood vessels as well as on cell surfaces of cardiocytes. alpha1m mRNA was found in the liver and pancreas by polymerase chain reaction, suggesting that the protein found in other tissues is transported via the bloodstream from the production sites in liver and pancreas. The results of this study indicate that in addition to its role in plasma, alpha1m may have important functions in the interstitium of several tissues. (J Histochem Cytochem 46:887-893, 1998)

Mitogenic effect of alpha 1-microglobulin on mouse lymphocytes. Evidence of T- and B-cell cooperation, B-cell proliferation, and a low-affinity receptor on mononuclear cells

Human alpha 1-m microglobulin (alpha 1-m), a low molecular weight plasma protein, was found to exert mitogenic effects on mouse lymphocytes from lymph nodes and spleen. The stimulatory effects appeared to be strain-restricted: alpha 1-m induced a varying degree of proliferation of lymphocytes from three strains, whereas one strain responded poorly. Experiments with lymphocyte subpopulations showed only weak stimulatory effects of alpha 1-m on purified T and B lymphocytes cultivated alone. The addition of mitomycin-treated cells of the other subpopulation could not restore the proliferative responses in either T or B lymphocytes. Strong stimulations were recorded only when both T and B lymphocytes were present, indicating that the T and B lymphocytes cooperate to achieve the proliferation. However, FACS studies on cultured splenocytes indicated that the proliferating cells are predominantly B lymphocytes. These data extend our earlier findings of a mitogenic effect of alpha 1-m on guinea pig lymphocytes. Furthermore, results were obtained indicating the presence of a receptor on mononuclear cells. Iodine-labelled alpha 1-m was bound to mononuclear cells prepared from spleens, and the binding could be blocked by an excess of non-labelled alpha 1-m. Scatchard plotting of the data gave an equilibrium constant of 0.7 x 10(5)/M for the binding between alpha 1-m and the receptor. Together with the documented inhibitory activity of alpha 1-m on antigen-driven proliferation of lymphocytes, these results suggest an immunoregulatory role for alpha 1-m.

Alpha 1-microglobulin is mitogenic to human peripheral blood lymphocytes. Regulation by both enhancing and suppressive serum factors

Human alpha 1-microglobulin (alpha 1-m), a 26 kilodalton serum glycoprotein, was found to exert mitogenic effects on human peripheral blood lymphocytes (PBL) in serum-free medium. Purified T cells, but not B cells, responded with proliferation to alpha 1-m, but only in the presence of monocytes. The mitogenic activity could be partially neutralized by a mouse monoclonal antibody against alpha 1-m. The mitogenicity was species-specific, since alpha 1-m homologues from rats, guinea pigs and rabbits had no effect on human PBL. In a previous study, no effect of alpha 1-m was seen on PBL in the presence of 20% serum, and, therefore, we studied the influence of different concentrations of serum on the alpha 1-m-induced mitogenicity. Thus, human serum enhanced the mitogenic effects of alpha 1-m on human PBL at 1% concentration (v/v) and suppressed the effects at 10%. The suppressing effect of serum at 10%, but not the enhancing effect at 1%, seemed to be conserved among several species. To test the effect of serum proteins of different molecular sizes, human autologous serum was separated by gel chromatography on Sephadex G-200 into four fractions. Fractions 1 and 2 (roughly containing proteins larger than 100 kilodaltons) suppressed the mitogenic effects of alpha 1-m, while fractions 3 and 4 enhanced the stimulation by alpha 1-m, at 0.5% and concentrations above. It is concluded that the mitogenic effect of alpha 1-m on lymphocytes is regulated by several serum factors, both enhancing and suppressive, that does not have any proliferative effect of their own. It can be speculated that the balance between enhancing and suppressing co-factors in the blood determines the degree of the stimulation of lymphocytes by alpha 1-m. This is compatible with an immunomodulatory role for alpha 1-m, in spite of its relatively constant plasma levels in health and disease.

Characterization of the gene encoding ovine beta-lactoglobulin. Similarity to the genes for retinol binding protein and other secretory proteins

Beta-lactoglobulin is the major whey protein in the milk of ruminants and is expressed in the mammary gland during pregnancy and lactation. Here we describe the isolation and characterization of genomic clones encoding ovine beta-lactoglobulin. Two very similar but non-identical, types of beta-lactoglobulin clone were obtained. DNA sequence analysis of one of these showed that the gene is 4900 bases long and contains seven exons. It codes for a protein of 180 amino acid residues, containing an 18-residue signal peptide, within exons I to VI; exon VII is non-coding. We show that the genes encoding serum retinol binding protein, major urinary protein, alpha-1-acid glycoprotein and apolipoprotein D have a similar organization of exons and introns to beta-lactoglobulin. In particular, a comparison between beta-lactoglobulin and retinol binding protein shows that both genes encode equivalent elements of three-dimensional protein structure within analogous exons. These proteins are all members of a large, diverse family of secretory proteins, many of which function in binding small hydrophobic molecules.

Purification of alpha 1-microglobulin produced by human hepatoma cell lines. Biochemical characterization and comparison with alpha 1-microglobulin synthesized by human hepatocytes

alpha 1-Microglobulin (alpha 1m) was determined by radio-immunoassay in the supernatants of five human hepatoma cell lines. High amounts of alpha 1m were produced by PLC/PRF/5, intermediate ones by Hep G2 and Hep 3B and very low ones by Malhavu and SK Hepl. alpha 1m isolated from hepatoma cell lines PLC/PRF/5 or Hep G2 supernatants displayed the same physicochemical properties as that purified from human urines: the apparent molecular mass was 26 kDa and the pI from 5.6 to 6.4 as measured after two-dimensional polyacrylamide gel electrophoresis in denaturating conditions; for the native molecule the pI was estimated to be 4.0-4.9. Both urinary and hepatoma alpha 1m migrate as a diffuse band in the alpha zone in agarose gel at pH 8.6 in non-denaturing conditions and present a brown chromophore covalently associated with the molecule. After biosynthetic labelling with [35S]methionine, proteins extracted from hepatoma cell line PLC/PRF/5 and from isolated hepatocytes of human liver were separated by two-dimensional PAGE and transferred to a nitrocellulose membrane. alpha 1m was identified and found to be identical in both cases. However, when compared with the alpha 1m isolated from cell supernatants, less charge heterogeneity but also minor additional spots of higher molecular mass were observed.

Cross-reacting monoclonal anti-alpha 1-microglobulin antibodies produced by multi-species immunization and using protein G for the screening assay

In order to generate monoclonal antibodies (MAb) directed against the low molecular weight glycoprotein alpha 1-microglobulin, a BALB/c mouse was immunized with a mixture of human, guinea pig, rat and rabbit alpha 1-microglobulin homologues (multi-species immunization) and boosted several times. On day 194, the mouse splenocytes were fused to SP2/0 myeloma cells. The resulting hybridomas were screened for anti-alpha 1-microglobulin activity against the alpha 1-microglobulin mixture or against the individual homologues. For this screening, protein G (the newly described IgG-binding streptococcal protein) was used in a solid-phase radioimmunoassay. The binding of protein G to immobilized antigen-antibody complexes was enhanced by pre-incubation with rabbit anti-mouse immunoglobulin G. The result was a panel of nine established hybridoma lines, all producing unique monoclonal antibodies, of IgG1 or IgG2a class, to alpha 1-microglobulin. The antibodies were not only reactive in solid-phase radioimmunoassay, but they could also immunoprecipitate 125I-labeled soluble alpha 1-microglobulin. Moreover, they reacted specifically with the alpha 1-microglobulin band in Western blots of urinary proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Such monoclonal antibodies are potentially valuable reagents for the further characterization of alpha 1-microglobulin.

Human protein HC and its IgA complex are inhibitors of neutrophil chemotaxis

Protein HC, a heterogeneously charged low molecular weight glycoprotein, and its IgA complex were isolated from human plasma and urine. Plasma from individuals with monoclonal IgA populations was used as starting material for the isolation of the protein HC-IgA complex to obtain homogeneous complex populations. Neither low molecular weight protein HC nor its IgA complex in the concentrations 30 and 600 mg/liter influenced the random migration of normal human neutrophils. The chemotactic response of neutrophils to endotoxin-activated serum was, however, attenuated in a dose-dependent way by both low molecular weight protein HC and protein HC-IgA complex. Concentrations of protein HC and its IgA complex producing significant inhibition of the chemotactic response were found to occur in plasma from healthy and diseased individuals as well as in synovial fluid from patients with rheumatoid arthritis. These results suggest that protein HC and its IgA complex play physiological roles in the regulation of the inflammatory response.

Rat alpha 1-microglobulin. Purification from urine and synthesis by hepatocyte monolayers

Rat alpha 1-microglobulin was isolated from the urine of rats treated with sodium chromate, and was purified by the use of gel chromatography, affinity chromatography on concanavalin-A-Sepharose and ion-exchange chromatography. The protein was heterogeneous in charge, had a tendency to form dimers, and was associated with a brown-coloured chromophore. The size of the protein (25 kDa) was similar to guinea pig alpha 1-microglobulin but smaller than the human protein, when measured with sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Immunological cross-reaction with human and guinea pig alpha 1-microglobulin was demonstrated. The concentration of alpha 1-microglobulin in rat serum was 16.4 mg/l (SD = 8.5 mg/l, n = 13) and rat serum alpha 1-microglobulin was eluted from a gel chromatography column at two different positions corresponding to monomeric alpha 1-microglobulin and IgA. The latter alpha 1-microglobulin activity could be absorbed by anti-IgA serum. Rat alpha 1-microglobulin and albumin were continuously released into the medium of rat hepatocyte monolayers, and alpha 1-microglobulin was isolated from the medium by the use of immunoprecipitation with anti-(alpha 1-microglobulin). Tritiated leucine, added to the medium, was incorporated into the protein, suggesting a de novo synthesis of alpha 1-microglobulin by the hepatocytes. The size of hepatic alpha 1-microglobulin was similar to that of purified urinary rat alpha 1-microglobulin, when determined with sodium dodecyl sulfate/polyacrylamide gel electrophoresis.

Alpha 1-microglobulin: a new antigenic component of the epidermo-dermal junction in normal human skin

Monoclonal antibodies to human alpha 1-microglobulin (alpha 1-m), a glycoprotein present in most biological fluids, reacted with the basement membrane of the epidermo-dermal junction and that of eccrine sweat glands in normal human skin. This immunofluorescence was specific in that control antibodies of known well-defined reactivity did not stain these structures. Therefore, alpha 1-m seems to be a new antigenic component of the junction and it may be an interesting antigen to study in diseases of this area.

Localization of alpha 1-microglobulin (HC protein) in normal human tissues: an immunohistochemical study using monoclonal antibodies

Alpha-1-microglobulin is a low molecular weight (approximately 30 000 d) glycoprotein present in biological fluids. It is heterogeneous in charge. A monoclonal antibody was used to investigate the tissue distribution of the protein in normal human tissues and cell lines by indirect immunofluorescence and immunoperoxidase techniques. The protein was demonstrable in cells of the monocyte-macrophage lineage, in thymus and T cell dependent areas of spleen, lymph node and tonsils. It was detected in several lymphoid or nonlymphoid cell lines but not in peripheral blood lymphocytes. The microglobulin was also detectable in the cytoplasm of hepatocytes. Finally, it was observed in glandular secretions (sudoral glands and mucosal glands of the digestive tract) where it may be associated with IgA. Possible explanations for the highly divergent results previously reported with polyclonal antisera to alpha 1 microglobulin are discussed.

Neutral microprotein, a novel human plasma and urinary protein associated with a yellow-brown chromophore. Isolation from protein HC preparations and partial characterization

An apparently novel human plasma and urinary protein of low molecular weight was isolated from several highly purified preparations of protein HC by gel chromatography and high voltage electrophoresis with a yield of about 8 mg/g. The protein has a molecular weight of about 20,000, neutral electrophoretic mobility at pH 6.5 and a high content of half-cystine. It is associated with a yellow-brown chromophore like protein HC and could be demonstrated in all investigated preparations of isolated human, rabbit and guinea-pig protein HC and alpha 1-microglobulin.

Synthesis of alpha 1-microglobulin by guinea-pig liver

Explants from perfused guinea-pig livers were found to release alpha 1-microglobulin into the culture medium. Tritiated leucine in the medium was incorporated into the protein, suggesting a de novo synthesis of alpha 1-microglobulin by the liver tissue. The size of the protein could not be distinguished from that of purified urinary alpha 1-microglobulin when tested with sodium dodecyl sulfate/polyacrylamide gel electrophoresis. After intravenous injections of tritiated leucine into guinea-pigs, the 105 000 X g pellet of homogenized liver rapidly increased its content of radioactive alpha 1-microglobulin, with a maximum after 20 min. 3H-Labelled alpha 1-microglobulin appeared in serum after a lag phase of 20 min, and by comparing the rate of accumulation with albumin, the synthesis of guinea-pig alpha 1-microglobulin could be estimated to 20 micrograms g liver-1 h-1.

Human alpha 1-microglobulin levels in various body fluids

alpha 1-Microglobulin levels in serum and urine were estimated by using single radial immunodiffusion, resulting in the following mean values: umbilical cord blood serum, 40.6 mg/l; normal adult serum, 44.2 mg/l; and normal urine, 5.7 mg/24 h urine volume. Slightly higher levels of serum alpha 1-microglobulin were found in infants and the aged. Serum and urine alpha 1-microglobulin levels in patients with renal failure, however, were greatly increased, mean levels being 231.5 mg/l and 100.7 mg/24 h urine volume, respectively. Serum alpha 1-microglobulin levels in these patients correlated well with both serum creatinine and beta 2-microglobulin levels. Serum alpha 1-microglobulin level did not correlate positively with serum levels of other plasma proteins, such as alpha 1-antitrypsin, haptoglobin, complement, etc. Ouchterlony immunodiffusion also revealed the presence of alpha 1-microglobulin in synovial fluid, ascites, pleural effusion, amniotic fluid, cyst fluid, and cerebrospinal fluid. The levels of alpha 1-microglobulin in these fluids were measured by single radial immunodiffusion, except that its level in cerebrospinal fluid was measured by radioimmunoassay. Mean alpha 1-microglobulin concentration was 20.8 mg/l in synovial fluid, 28.7 mg/l in ascites, 21.5 mg/l in pleural effusion, 2.7 mg/l in amniotic fluid, 8.2 mg/l in cyst fluid, and 42.3 ng/ml in cerebrospinal fluid.

Organ cultures of human fetal hepatocytes in the study of extra-and intracellular alpha1-antitrypsin

The rate of synthesis of alpha 1-antitrypsin has been studied in organ cultures of fetal human liver. By de novo synthesis, alpha 1-antitrypsin of the same electrophoretic mobility and molecular size as plasma alpha 1-antitrypsin was produced. Synthetic rate was comparable to in vivo conditions and was suppressed by cycloheximide, colchicine and neuraminidase. By increasing alpha 1-antitrypsin levels in cultre medium, suppression of alpha 1-antitrypsin release from the intra-to the extracellular site was achieved, i.e., synthesis does not proceed autonomously. This suppression was preceded by a temporary enhancement of synthesis. Both effects were found to be independent of degree of sialylation of add-d alpha 1-antitrypsin. In contrast to alpha 1-antitrypsin released in tissue culture, the intracellular protein, as analyzed by crossed immunoelectrophoresis of Triton X-100 extracts from fetal liver, was found to occur partly as slowly moving peaks. Whether these peaks represent proforms or incompletely glycosylated precursors of export alpha 1-antitrypsin or complexes with proteases remains unsettled. A variety of other plasma proteins are released in organ cultures making the system suitable for study of factors regulating plasma protein synthesis.