The role of Toll-like receptors in host defense against microbial infection.

The Toll family of proteins is central to Drosophila host defense against microbial infection. Maintained throughout evolution, mammalian Toll-like receptors (TLRs) are proteins that participate in innate immunity to bacteria in at least four ways. First, TLRs participate in the recognition of molecular patterns present on microorganisms. Second, TLRs are expressed at the interface with the environment, the site of microbial invasion. Third, activation of TLRs induces expression of co-stimulatory molecules and the release of cytokines that instruct the adaptive immune response. Fourth, activation of TLRs leads to direct antimicrobial effector pathways that can result in elimination of the foreign invader. The recent investigation of TLRs in these areas has provided new insights into mechanisms of innate immunity.

Host defense mechanisms triggered by microbial lipoproteins through toll-like receptors.

The generation of cell-mediated immunity against many infectious pathogens involves the production of interleukin-12 (IL-12), a key signal of the innate immune system. Yet, for many pathogens, the molecules that induce IL-12 production by macrophages and the mechanisms by which they do so remain undefined. Here it is shown that microbial lipoproteins are potent stimulators of IL-12 production by human macrophages, and that induction is mediated by Toll-like receptors (TLRs). Several lipoproteins stimulated TLR-dependent transcription of inducible nitric oxide synthase and the production of nitric oxide, a powerful microbicidal pathway. Activation of TLRs by microbial lipoproteins may initiate innate defense mechanisms against infectious pathogens.

Induction of a human carbonyl reductase gene located on chromosome 21.

Carbonyl reductase (EC 1.1.1.184) belongs to the group of enzymes called aldo-keto reductases. It is a NADPH-dependent cytosolic protein with specificity for many carbonyl compounds including the antitumor anthracycline antibiotics, daunorubicin and doxorubicin. Human carbonyl reductase was cloned from a breast cancer cell line (MCF-7). The cDNA clone contained 1219 base paires with an open reading frame corresponding to 277 amino acids encoding a protein of Mr 30,375. Southern analysis of genomic DNA digested with several restriction enzymes and analyzed by hybridization with a labeled cDNA probe indicated that carbonyl reductase is probably coded by a single gene and does not belong to a family of structurally similar enzymes. Southern analysis of 17 mouse/human somatic cell hybrids showed that carbonyl reductase is located on chromosome 21. Carbonyl reductase mRNA could be induced 3-4-fold in 24 h with 10 microM 2,(3)-t-butyl-4-hydroxyanisole (BHA), beta-naphthoflavone or Sudan 1.

Ionized calcium and the in vivo response of normal and hyperplastic parathyroid glands to beta-adrenergic agents.

We compared ionized serum calcium and parathyroid hormone (PTH) responses to the beta-adrenergic agents, isoproterenol and propranolol, in 14 patients with hyperparathyroidism following renal transplantation and 8 normal volunteers. Following isoproterenol, PTH rose in normal subjects concurrent with a significant (p less than 0.01) fall in ionized but not total, calcium. In the hyperparathyroid patients the PTH concentration decreased (p less than 0.001) coincident with a significant (p less than 0.01) increase in ionized, but not total, calcium. Changes in both PTH (p less than 0.05) and ionized calcium (p less than 0.05) were significantly different in hyperparathyroid patients compared to normal subjects. Propranolol did not affect PTH, ionized or total calcium in either group. We conclude that beta-adrenergic stimulation of PTH secretion may be mediated, in part, by antecedent changes in ionized calcium and not solely a direct effect of the agonist. Concurrent assessment of changes in ionized calcium is necessary for proper interpretation of investigations involving the sympathetic nervous system's regulation of PTH secretion.

Parathyroid hormone: a determinant of posttransplant blood pressure regulation.

Persistent hyperparathyroidism and its attendant hypercalcemia have been implicates as possible etiologic factors in posttransplant hypertension. To better define the role of parathyroid hormone (PTH) and calcium in posttransplant blood pressure homeostasis, we measured the acute response of blood pressure, ionized calcium (Ca++), plasma renin activity (PRA), and parathyroid hormone (PTH) to a 4-hr infusion of calcium (15 mg/kg) and an isoproterenol injection (0.15 mg SC) in seven normal subjects and 13 renal transplant (Tx) recipients with stable graft function and persistent hyperparathyroidism. Transient hypercalcemia produced a significant (p less than 0.01) increase in the systolic blood pressure (delta SBP) and suppression of PTH (p less than 0.001) in the posttransplant subjects. There was a significant (p less than 0.02) inverse correlation between changes (delta) in PTH and delta SBP in these subjects. There was no correlation between the delta SBP and either the change in Ca++ (delta Ca++) or the change in PRA (delta PRA) observed in the Tx recipients administered calcium. Following isoproterenol administration, SBP increased (p less than 0.01), PTH fell (p less than 0.05) and Ca++ was only minimally increased in the Tx recipients. A virtually identical, significant (p less than 0.05) inverse correlation existed between the delta PTH and delta SBP observed in the transplant subjects. Greater suppression of PTH was associated with a larger increase in systolic blood pressure. Transient hypercalcemia of comparable degree in normal subjects caused an insignificant increase in their blood pressure. The fact that PTH suppression in the normals was substantially (0.01) less (delta PTH -13 microliter/Eq/ml versus -65 microliter/Eq/ml in the transplant group) with a similar increase in serum calcium suggests that the blood pressure response to transient hypercalcemia is more dependent on PTH suppression than the level of ionized calcium. Plasma renin activity was unchanged during the blood pressure fluctuations induced by either the calcium or the isoproterenol administration to the normal subjects. Under the conditions of this study, endogenous parathyroid hormone has the characteristics of a vasodepressor hormone and may have a role in blood pressure regulation in transplant recipients with hyperparathyroidism. Since the vasodepressor effect can be dissociated from delta Ca+ and delta PRA, such a conclusion seems warranted. The implications of these findings for all subjects with renal disease requires further investigation.

Disturbances of calcium metabolism in the spontaneously hypertensive rat.

Ionized calcium is critical to the maintenance of normal cardiovascular function. Recently, vasoactive properties have also been attributed to parathyroid hormone (PTH). The present study characterizes the calcium-PTH axis in the spontaneously hypertensive rat (SHR) in order to determine the effects of chronic alterations in calcium intake on the development and maintenance of hypertension in this species. Thirty-six SHR and 36 Wistar-Kyoto (WKY) normotensive control rats were studied. The rats were fed one of three levels (percent of total diet) of calcium (normal 0.5%, low-normal 0.25%, high 4.0%) beginning at 10 weeks of age. Serum total and ionized calcium, serum PTHs, urinary electrolytes, and systolic blood pressures were assessed by repeated measurements between 10 and 48 weeks of age. Irrespective of calcium intake, the SHRs had lower serum ionized calcium concentrations (p less than 0.001) and higher PTH levels (p less than 0.001) than the WKYs. Serum total calcium were similar for the two strains. Urinary calcium excretion was greater in the SHR (p less than 0.001) relative to the WKY. The high (4.0%) calcium diet normalized the serum ionized calcium and attenuated the development of the SHRs' hypertension (p less than 0.001). The present study describes several previously unrecognized abnormalities of calcium metabolism in the SHR. These disturbances may be of pathogenetic importance in the development and maintenance of hypertension in the SHR.

Lithium's effect of parathyroid hormone.

Lithium has been reported to raise serum calcium and lower serum phosphate concentrations and to increase urinary calcium excretion. Because these changes may be effects of parathyroid hormone (PTH), PTH was measured in 19 patients receiving lithium. PTH was significantly higher in these patients than in 150 normal subjects. For all patients serum calcium concentrations correlated significantly with serum lithium concentrations. These results indicate that lithium may cause biochemical hyperparathyroidism. Secondary hyperparathyroidism in certain patients with lithium nephrotoxicity is also possible.

Urinary calcium excretion at extremes of sodium intake in normal man.

To elucidate the relationship between the renal regulation of sodium and calcium excretion at extremes of sodium intake, we studied 6 normal men ingesting a fixed, 400 mg/day calcium intake and four levels of sodium intake from 10 to 1,500 mEq/day. Serum ionized calcium was not influenced by sodium intake. Blood pressure and cardiac index increased modestly. Urinary calcium excretion increased to 262 +/- 53 mg/day (mean +/- SE). Plasma norepinephrine concentration, serum PTH levels, hematocrit, total serum protein concentrations and CO2 content decreased with increasing sodium intake. Urinary cAMP increased as sodium intake was raised from 10 to 300 mEq/day, but subsequently decreased to basal values. Urinary calcium and sodium excretion were related (p less than 0.001) in a nonlinear fashion as were the fractional excretions of these cations (p less than 0.001). The filtered calcium load and the fractional calcium excretion were directly and linearly related (p less than 0.001). We conclude that the effect of sodium intake on urinary calcium excretion principally reflects changes in the filtered calcium load rather than changes in renal sodium handling. Calcium homeostasis at extremes of sodium intake does not appear to be critically dependent upon PTH-mediated mechanisms. The data suggest that the proximal tubule has a remarkable capacity to dissociate calcium resorption from that of sodium.

Enhanced parathyroid function in essential hypertension: a homeostatic response to a urinary calcium leak.

Disorders of calcium metabolism are not generally considered important either clinically or pathophysiologically in essential hypertension. Recent reports, though, suggest that increased parathyroid gland function may be one of the more common endocrine disturbances associated with hypertension. We measured serum parathyroid hormone (PTH) concentrations as well as routine blood and urine chemistries in 34 hypertensives. Their mean PTH, 79.1 +/- 3.1 muliter Eq/muliter, was significantly higher (p less than 0.025) than the mean PTH, 66.9 +/- 3.3, of an age- and sex-matched normotensive control population. The mean serum calcium, 9.5 +/- 0.1 mg%, was identical in the two populations. Compared to a second age- and sex-matched normotensive population, the hypertensives demonstrated a significant (p less than 0.005) relative hypercalciuria. For any level of urinary sodium, hypertensives excreted more calcium. These preliminary data suggest that parathyroid gland function may be enhanced in essential hypertension. This increased gland activity appears, in part, to be an appropriate, physiologic response to a previously unrecognized relative hypercalciuria, or renal calcium leak, associated with essential hypertension. We conclude that the increased prevalence of hypertension in subjects with hyperparathyroidism probably represents the final event in a continuum that begins with obligatory urinary calcium losses in hypertensives, but whose pathological presentation is hyperparathyroidism. The results of this pilot study indicate a need for derivative experiments directed at defining the importance of our preliminary findings in the pathogenesis of human and experimental hypertension.

Parathormone and perinatal calcium homeostasis.

Plasma parathormone (PTH) and calcium concentrations were measured in 309 specimens collected from 190 newborns during the first 7 days of life. The patient material consisted of 51 preterm, 130 term, and 9 postterm infants, including 22 infants of diabetic mothers (IDM), 38 infants with hypocalcemia, and 25 asphyxiated infants. PTH was detectable, although in low concentrations, in cord blood samples despite the presence of elevated calcium concentrations. Postpartum, PTH concentrations in term, appropriate for gestational age (AGA) infants remained low during the first 2 days of life; a significant (P less than 0.05) and sustained increase in plasma hormone levels was noted starting on day 3. PTH concentrations in IDM and preterm infants remained low for 3 days and a significant hormone increase did not occur until day 4. Hypocalcemia was common in IDM and asphyxiated infants; these infants accounted for two-thirds of all hypocalcemic infants. The profile of plasma calcium in IDM during the first week of life was different than that of any other group of infants. Plasma calcium concentrations remained depressed over this period of time and exhibited a temporary drop on day 4 accompanied by an increase in plasma PTH levels. Asphyxiated infants exhibited low plasma calcium concentrations, despite PTH levels that were significantly (P less than 0.007) higher than those of age-matched term AGA newborns.