Slowing Alzheimer's disease progression through probiotic supplementation

The lack of affordable and effective therapeutics against cognitive impairment has promoted research toward alternative approaches to the treatment of neurodegeneration. In recent years, a bidirectional pathway that allows the gut to communicate with the central nervous system has been recognized as the gut-brain axis. Alterations in the gut microbiota, a dynamic population of trillions of microorganisms residing in the gastrointestinal tract, have been implicated in a variety of pathological states, including neurodegenerative disorders such as Alzheimer's disease (AD). However, probiotic treatment as an affordable and accessible adjuvant therapy for the correction of dysbiosis in AD has not been thoroughly explored. Here, we sought to correct the dysbiosis in an AD mouse model with probiotic supplementation, with the intent of exploring its effects on disease progression. Transgenic 3xTg-AD mice were fed a control or a probiotic diet (Lactobacillus plantarum KY1032 and Lactobacillus curvatus HY7601) for 12  weeks, with the latter leading to a significant increase in the relative abundance of Bacteroidetes. Cognitive functions were evaluated via Barnes Maze trials and improvements in memory performance were detected in probiotic-fed AD mice. Neural tissue analysis of the entorhinal cortex and hippocampus of 10-month-old 3xTg-AD mice demonstrated that astrocytic and microglial densities were reduced in AD mice supplemented with a probiotic diet, with changes more pronounced in probiotic-fed female mice. In addition, elevated numbers of neurons in the hippocampus of probiotic-fed 3xTg-AD mice suggested neuroprotection induced by probiotic supplementation. Our results suggest that probiotic supplementation could be effective in delaying or mitigating early stages of neurodegeneration in the 3xTg-AD animal model. It is vital to explore new possibilities for palliative care for neurodegeneration, and probiotic supplementation could provide an inexpensive and easily implemented adjuvant clinical treatment for AD.

Prevalence and antibiotic resistance of Staphylococcus aureus associated with a college-aged cohort: life-style factors that contribute to nasal carriage

Staphylococcus aureus is an opportunistic human pathogen that can frequently be found at various body locations, such as the upper respiratory tract, nostrils, skin, and perineum. S. aureus is responsible for causing a variety of conditions, which range from minor skin infections and food poisoning to life-threatening sepsis and endocarditis. Furthermore, S. aureus has developed resistance to numerous antimicrobial agents, which has made treatment of S. aureus infections difficult. In the present study, we examined lifestyle factors that could increase the likelihood of S. aureus carriage, the overall prevalence of S. aureus, as well as assessed the antibiotic resistance profiles of the S. aureus isolates among a population of college students. Five hundred nasal samples were collected and analyzed via selective growth media, coagulase and protein A testing, as well as polymerase chain reaction and DNA sequencing. One hundred four out of the 500 samples collected (21%) were identified as containing S. aureus. The S. aureus isolates were resistant to penicillin (74%), azithromycin (34%), cefoxitin (5%), ciprofloxacin (5%), tetracycline (4%), and trimethoprim (1%), but sensitive to gentamicin and rifampin. Lastly, we identified several lifestyle factors (i.e., pet exposure, time spent at the university recreational facility, musical instrument usage, and tobacco usage) positively correlated with S. aureus nasal colonization.

Chimera RNA interference knockdown of γ-synuclein in human cortical astrocytes results in mitotic catastrophe

Elevated levels of γ-synuclein (γ-syn) expression have been noted in the progression of glioblastomas, and also in the cerebrospinal fluid of patients diagnosed with neurodegenerative diseases. γ-Syn can be either internalized from the extracellular milieu or expressed endogenously by human cortical astrocytes. Internalized γ-syn results in increased cellular proliferation, brain derived neurotrophic factor release and astroprotection. However, the function of endogenous γ-syn in primary astrocytes, and the relationship to these two opposing disease states are unknown. γ-Syn is expressed by astrocytes in the human cortex, and to gain a better understanding of the role of endogenous γ-syn, primary human cortical astrocytes were treated with chimera RNA interference (RNAi) targeting γ-syn after release from cell synchronization. Quantitative polymerase chain reaction analysis demonstrated an increase in endogenous γ-syn expression 48 hours after release from cell synchronization, while RNAi reduced γ-syn expression to control levels. Immunocytochemistry of Ki67 and 5-bromodeoxyuridine showed chimera RNAi γ-syn knockdown reduced cellular proliferation at 24 and 48 hours after release from cell synchronization. To further investigate the consequence of γ-syn knockdown on the astrocytic cell cycle, phosphorylated histone H3 pSer10 (pHH3) and phosphorylated cyclin dependent kinase-2 pTyr15 (pCDK2) levels were observed via western blot analysis. The results revealed an elevated expression of pHH3, but not pCDK2, indicating γ-syn knockdown leads to disruption of the cell cycle and chromosomal compaction after 48 hours. Subsequently, flow cytometry with propidium iodide determined that increases in apoptosis coincided with γ-syn knockdown. Therefore, γ-syn exerts its effect to allow normal astrocytic progression through the cell cycle, as evidenced by decreased proliferation marker expression, increased pHH3, and mitotic catastrophe after knockdown. In this study, we demonstrated that the knockdown of γ-syn within primary human cortical astrocytes using chimera RNAi leads to cell cycle disruption and apoptosis, indicating an essential role for γ-syn in regulating normal cell division in astrocytes. Therefore, disruption to γ-syn function would influence astrocytic proliferation, and could be an important contributor to neurological diseases.

Time is on the Immune System's Side, Yes it is

From bacteria to mammals, nearly all organisms have adapted their physiology and behavior to a daily rhythm. These circadian (daily) rhythms influence virtually all aspects of physiological architecture (i.e., from gene expression to organismal behavior). Therefore, it is not surprising that several features of the immune response are regulated in a time-of-day dependent manner. The field of chrono-immunology has expanded tremendously over the past decade. In this abridged review, we present studies from the past five years that have revealed new parameters of the immune system that demonstrate daily variations in the control of pathogens and response to microbial components. These studies analyzed how the disruption of circadian rhythms impairs immune function, how microbial components alter the circadian clock, and how immune responses demonstrate daily variations in human subjects. Further elucidating the intricate connections between the circadian clock and the immune system will hopefully provide opportunities for chrono-immunotherapy in disease treatment and prevention.

The Use of Mouse Splenocytes to Assess Pathogen-associated Molecular Pattern Influence on Clock Gene Expression

From behavior to gene expression, circadian rhythms regulate nearly all aspects of physiology. Here, we present a methodology to challenge mouse splenocytes with the pathogen-associated molecular patterns (PAMPs) lipopolysaccharide (LPS), ODN1826, and heat-killed Listeria monocytogenes and examine their effect on the molecular circadian clock. Previously, studies have focused on examining the influence of LPS on the molecular clock using a variety of in vivo and ex vivo approaches from an assortment of models (e.g., mouse, rat, and human). This protocol describes the isolation and challenge of splenocytes, as well as the methodology to assess clock gene expression post-challenge via quantitative PCR. This approach can be used to assess not only the influence of microbial components on the molecular clock but other molecules as well that may alter expression of the clock. This approach could be utilized to tease apart the molecular mechanism of how PAMP-Toll-like receptor interaction influences clock expression.

Daily oscillations in expression and responsiveness of Toll-like receptors in splenic immune cells

Circadian rhythms refer to biologic processes that oscillate with an approximate 24-h period. These rhythms direct nearly all aspects of animal behavior and physiology. The aim of our study was to determine if Toll-like receptor (TLR) expression and responsiveness exhibit time-of-day dependent differences. Therefore, we isolated an adherent splenocyte population, which consisted primarily of B cells, dendritic cells, and macrophages, over the course of a 24-h light-dark period and measured daily changes in Tlr1-8 mRNA levels and cytokine expression after cells were challenged at Zeitgeber time (ZT) 1 or ZT13 with a TLR ligand. In addition, we assessed TLR3 protein levels in adherent splenocytes over the 24-h light-dark period and challenged mice at ZT1 or ZT13 with poly(I:C), the TLR3 ligand. Our study revealed that in this adherent cell population, all Tlrs exhibited rhythmic expression except Tlr2 and Tlr5, and all TLRs, except TLR8, demonstrated daily variations in responsiveness after challenge with their respective ligand. We also revealed that TLR3 protein levels fluctuate over the daily light-dark cycle in adherent splenocytes and mice exhibit a time-of-day dependent immune response when challenged with poly(I:C). Finally, we demonstrated that mRNA levels of Tlr2 and Tlr6 display rhythmic expression in splenic macrophages. Taken together, these findings could have important implications for TLR-directed therapeutics.

Pathogen-associated molecular patterns alter molecular clock gene expression in mouse splenocytes

Circadian rhythms are endogenous 24-h oscillations that influence a multitude of physiological processes. The pathogen-associated molecular pattern (PAMP), lipopolysaccharide, has been shown to modify the circadian molecular clock. The aim of this study was to determine if other PAMPs alter clock gene expression. Therefore, mRNA levels of clock genes (Per2, Bmal1, Rev-erbα, and Dbp) were measured after an ex vivo challenge with several PAMPs and to further test the relevance of PAMP alteration of the molecular clock, an in vivo poly(I:C) challenge was performed. This study revealed that several other PAMPs are also capable of altering clock gene expression.

MyD88 deficiency markedly worsens tissue inflammation and bacterial clearance in mice infected with Treponema pallidum, the agent of syphilis

Research on syphilis, a sexually transmitted infection caused by the non-cultivatable spirochete Treponema pallidum, has been hampered by the lack of an inbred animal model. We hypothesized that Toll-like receptor (TLR)-dependent responses are essential for clearance of T. pallidum and, consequently, compared infection in wild-type (WT) mice and animals lacking MyD88, the adaptor molecule required for signaling by most TLRs. MyD88-deficient mice had significantly higher pathogen burdens and more extensive inflammation than control animals. Whereas tissue infiltrates in WT mice consisted of mixed mononuclear and plasma cells, infiltrates in MyD88-deficient animals were predominantly neutrophilic. Although both WT and MyD88-deficient mice produced antibodies that promoted uptake of treponemes by WT macrophages, MyD88-deficient macrophages were deficient in opsonophagocytosis of treponemes. Our results demonstrate that TLR-mediated responses are major contributors to the resistance of mice to syphilitic disease and that MyD88 signaling and FcR-mediated opsonophagocytosis are linked to the macrophage-mediated clearance of treponemes.

Immunity's fourth dimension: approaching the circadian-immune connection

The circadian system ensures the generation and maintenance of self-sustained ~24-h rhythms in physiology that are linked to internal and environmental changes. In mammals, daily variations in light intensity and other cues are integrated by a hypothalamic master clock that conveys circadian information to peripheral molecular clocks that orchestrate physiology. Multiple immune parameters also vary throughout the day and disruption of circadian homeostasis is associated with immune-related disease. Here, we discuss the molecular links between the circadian and immune systems and examine their outputs and disease implications. Understanding the mechanisms that underlie circadian-immune crosstalk may prove valuable for devising novel prophylactic and therapeutic interventions.

The circadian clock controls toll-like receptor 9-mediated innate and adaptive immunity

Circadian rhythms refer to biologic processes that oscillate with a period of ~24 hr. These rhythms are sustained by a molecular clock and provide a temporal matrix that ensures the coordination of homeostatic processes with the periodicity of environmental challenges. We demonstrate the circadian molecular clock controls the expression and function of Toll-like receptor 9 (TLR9). In a vaccination model using TLR9 ligand as adjuvant, mice immunized at the time of enhanced TLR9 responsiveness presented weeks later with an improved adaptive immune response. In a TLR9-dependent mouse model of sepsis, we found that disease severity was dependent on the timing of sepsis induction, coinciding with the daily changes in TLR9 expression and function. These findings unveil a direct molecular link between the circadian and innate immune systems with important implications for immunoprophylaxis and immunotherapy.

Circadian expression of clock genes in mouse macrophages, dendritic cells, and B cells

In mammals, circadian and daily rhythms influence nearly all aspects of physiology, ranging from behavior to gene expression. Functional molecular clocks have been described in the murine spleen and splenic NK cells. The aim of our study was to investigate the existence of molecular clock mechanisms in other immune cells. Therefore, we measured the circadian changes in gene expression of clock genes (Per1, Per2, Bmal1, and Clock) and clock-controlled transcription factors (Rev-erbα and Dbp) in splenic enriched macrophages, dendritic cells, and B cells in both mice entrained to a light-dark cycle and under constant environmental conditions. Our study reveals the existence of functional molecular clock mechanisms in splenic macrophages, dendritic cells, and B cells.

Prevalence of genes encoding the type three secretion system and the effectors AexT and AexU in the Aeromonas veronii group

The prevalence of important virulence factors, the type III secretion system (T3SS) and two T3SS-dependent toxins, AexT and AexU, was evaluated in the Aeromonas veronii group (AVG). Members of the AVG have a broad host range, including vertebrates and invertebrates, and form a variety of associations, spanning from pathogenic to mutualistic. Our AVG strain collection consists of human, duck, eel, and leech isolates. These isolates were examined for the presence of the T3SS, AexT, and AexU through PCR analysis. Two loci of the T3SS, ascV and ascF-ascG, and aexT and aexU were PCR amplified and sequenced from these isolates. All 20 environmental and clinical isolates possessed the T3SS and both effectors, which indicates a much greater prevalence than reported by previous studies. Sequence analysis of the C-terminal domains of aexT and aexU revealed a much higher nucleotide substitution rate for aexU (19.7%) when compared to aexT (4%). The lack of sequence variability among aexT homologs suggests that it has a conserved function among the AVG. The increased variation of the aexU sequence suggests the presence of different alleles, which indicates that it may serve different functions.

Identification of Aeromonas veronii genes required for colonization of the medicinal leech, Hirudo verbana

Most digestive tracts contain a complex consortium of beneficial microorganisms, making it challenging to tease apart the molecular interactions between symbiont and host. The digestive tract of Hirudo verbana, the medicinal leech, is an ideal model system because it harbors a simple microbial community in the crop, comprising the genetically amenable Aeromonas veronii and a Rikenella-like bacterium. Signature-tagged mutagenesis (STM) was used to identify genes required for digestive tract colonization. Of 3,850 transposon (Tn) mutants screened, 46 were identified as colonization mutants. Previously we determined that the complement system of the ingested blood remained active inside the crop and prevented serum-sensitive mutants from colonizing. The identification of 26 serum-sensitive mutants indicated a successful screen. The remaining 20 serum-resistant mutants are described in this study and revealed new insights into symbiont-host interactions. An in vivo competition assay compared the colonization levels of the mutants to that of a wild-type competitor. Attenuated colonization mutants were grouped into five classes: surface modification, regulatory, nutritional, host interaction, and unknown function. One STM mutant, JG736, with a Tn insertion in lpp, encoding Braun's lipoprotein, was characterized in detail. This mutant had a >25,000-fold colonization defect relative to colonization by the wild-type strain at 72 h and, in vitro, an increased sensitivity to sodium dodecyl sulfate, suggesting the presence of an additional antimicrobial property in the crop. The classes of genes identified in this study are consistent with findings from previous STM studies involving pathogenic bacteria, suggesting parallel molecular requirements for beneficial and pathogenic host colonization.

Interaction between innate immune cells and a bacterial type III secretion system in mutualistic and pathogenic associations

Animals house a community of bacterial symbionts in their digestive tracts that contribute to their well being. The medicinal leech, Hirudo verbana, has a remarkably simple gut population carrying two extracellular microbes in the crop where the ingested blood is stored. This simplicity renders it attractive for studying colonization factors. Aeromonas veronii, one of the leech symbionts, can be genetically manipulated and is a pathogen of mammals. Screening transposon mutants of A. veronii for colonization defects in the leech, we found one mutant, JG752, with a transposon insertion in an ascU homolog, encoding an essential component of type III secretion systems (T3SS). Competing JG752 against the wild type revealed that JG752 was increasingly attenuated over time (10-fold at 18 h and >10,000-fold at 96 h). This colonization defect was linked to ascU by complementing JG752 with the operon containing ascU. Fluorescence in situ hybridization analysis revealed that at 42 h 38% of JG752 cells were phagocytosed by leech macrophage-like cells compared with <0.1% of the parental strain. Using mammalian macrophages, a lactate dehydrogenase release assay revealed that cytotoxicity was significantly reduced in macrophages exposed to JG752. In a mouse septicemia model, JG752 killed only 30% of mice, whereas the parent strain killed 100%, showing the importance of T3SS for both pathogenesis and mutualism. Phagocytic immune cells are important not only in defending against pathogens but also in maintaining the mutualistic symbiont community inside the leech, demonstrating that animals use similar, conserved mechanisms to control bacterial populations, even when the outcomes differ dramatically.

Renal blood flow changes induced with endothelin-1 and fenoldopam mesylate at quantitative Doppler US: initial results in a canine study

PURPOSE

To evaluate quantitative Doppler ultrasonography (US) for assessing renal blood flow changes induced with endothelin-1 (ET-1) and fenoldopam mesylate in conscious dogs.

MATERIALS AND METHODS

A blood flow probe was surgically implanted around the renal artery in eight adult dogs. Color and power Doppler US images were acquired in conscious restrained dogs during intravenous infusion of ET-1 and fenoldopam mesylate. Simultaneous with imaging, blood flow through the renal artery was measured with the implanted probe. The color level of the images within the region representing the kidney was analyzed to derive flow indices. These indices were compared with direct-flow measurements.

RESULTS

The flow indices, color-weighted flow area (CWFA), and percentage of area of color, derived from color and power Doppler US images, correlated linearly with direct flow. The mean color level of color and power Doppler US images correlated weakly with direct flow. Pre- versus postinfusion CWFA decreased with all ET-1 infusions (P < or =.032). Infusion of fenoldopam mesylate increased CWFA in all cases (P < or =.032).

CONCLUSION

Quantitative Doppler US enabled successful measurement of the flow changes induced with ET-1 and fenoldopam mesylate. Quantitative Doppler US is potentially useful as a noninvasive surrogate endpoint in evaluating the action of various therapeutic agents.

Investigation and validation of the affinity chromatography method for measuring glycated albumin in serum and urine

Affinity chromatography on m-aminophenyl boronate columns together with albumin measurement by radioimmunoassay has been validated as a method for determining glycated albumin in serum and urine. Optimisation of sample volume and of elution buffer composition and volume ensured reproducibility of results. Fructosamine assay confirmed the absence of glycated albumin species from the non-glycated fraction. It was possible to elute the glycated fraction from the affinity columns with Tris or glycine which do not contain 1,2 diols but have similar functional groups. Column affinity was, therefore, not specific for glycated protein moieties. Inhibition of binding by glucose, and other small molecules in urine, necessitated ultrafiltration or dialysis of samples before analysis. Reference ranges for glycated albumin in non-diabetic subjects were 0.6-1.8% in serum and 0.9-2.6% in urine. In patients with diabetes mellitus, glycated albumin ranged from 1.4-10.9% in serum and from 1.5-12.5% in urine.

Binding and degradation of NH2-terminal parathyroid hormone by opossum kidney cells

The binding and cellular processing of NH2-terminal parathyroid (PTH) hormone by confluent monolayers of opossum kidney (OK) cells was characterized using radiolabeled PTH peptide analogues. Time- and temperature-dependent specific binding of 125I-labeled (Nle-8,18, Tyr-34)-NH2-bovine(b)PTH-(1-34) was accompanied by the appearance of degraded radiolabel in the cell medium. Degrading activity was observed to be a specific consequence of binding by PTH receptors. Degrading activity was inhibited by monensin, chloroquine, and NH4+ but not by chymotrypsin inhibitors. Acid washing demonstrated that greater than 80% of total cell-associated specific binding at equilibrium was located in a rapidly internalized (acid-resistant) pool. Monensin pretreatment led to increased acid-resistant binding, presumably through inhibition of turnover of internalized receptor ligand and indicated that the degradation of radiolabel was probably associated with processing of the receptor-ligand complex. Release of intact radiolabel from the acid-resistant pool indicated that some of the internalized peptide was recycled out of the cell in an undegraded form (retroendocytosis). Acid-resistant binding and degradation of 125I-(Nle-8,18, Tyr-34)-NH2-bPTH-(3-34) was minimal, indicating that this ligand was not internalized. It is concluded that the binding and internalization of PTH-(1-34) fragment by confluent OK cells is a specific receptor-mediated process. Cellular processing of PTH-(1-34) conforms to established models of internalization by receptor-mediated endocytosis.

Intrinsic susceptibility of the kidney to acetaminophen toxicity in middle-aged rats

Acetaminophen (APAP)-induced nephrotoxicity is age-dependent in male Sprague-Dawley (SD) rats: middle-aged (9-12 months old) rats exhibit nephrotoxicity at lower dosages of APAP than do young adults (2-3 months old). The present study was designed to test the hypothesis that the intrinsic susceptibility of renal tissue to APAP toxicity is increased in middle-aged rats. APAP toxicity was evaluated in renal slices from naive 3- and 12-month-old male SD rats incubated with 0-50 mM APAP for 2-8 h. Renal slice glutathione (GSH) and APAP concentrations were determined; renal function was assessed by organic anion (para-aminohippurate, PAH) and cation (tetraethylammonium, TEA) accumulation; and cell viability was assessed by lactate dehydrogenase (LDH) leakage. At each concentration of APAP tested, accumulation of APAP by renal slices was similar in 3- and 12-month-olds. APAP toxicity in renal slices from both 3- and 12-month-old rats was characterized by concentration-dependent increases in LDH leakage. In contrast to APAP nephrotoxicity in vivo, APAP toxicity in renal slices was accompanied by decreased accumulation of PAH and TEA. Additionally, APAP produced marked reductions in renal slice GSH content in a concentration-dependent manner: however, in contrast to APAP nephrotoxicity in vivo, APAP-induced GSH depletion in vitro did not precede cytotoxicity. No consistent age-dependent differences in the time- and concentration-response curves for APAP nephrotoxicity were observed. These data suggest that APAP cytotoxicity in vitro is not increased in 12-month-old rats. However, since the pattern (and mechanisms) of APAP cytotoxicity in vitro appears to be different from that observed in vivo, extrapolation of in vitro cytotoxicity to in vivo nephrotoxicity is limited. Therefore, age differences in intrinsic susceptibility of the intact kidney cannot be excluded as a mechanism contributing to enhanced APAP nephrotoxicity in middle-aged rats.

Hypotension induced by vasopressin antagonists in rats: role of mast cell degranulation

SK&F 101926, a synthetic peptide, is a potent antagonist of vasopressin at both the V2 and the V1 receptors. Following intravenous administration of SK&F 101926 (5 mg/kg), mean arterial pressure (MAP) immediately fell 75 mm Hg. Heart rate increased approximately 50 beats/min. Cutaneous flushing and cyanosis appeared approximately 2 to 5 min after the SK&F 101926 administration. Three of the five rats died within 40 min with no improvement in either color or MAP. The two surviving animals slowly recovered from these symptoms. The hypotension and flushing recorded in these studies resembled the effects during hypotensive shock. SK&F 101926 degranulated rat peritoneal mast cells in vitro as measured by the liberation of histamine. Analogs of SK&F 101926 were identified having reduced activity to release histamine from mast cells in vitro. The activity of these analogs to release histamine in vivo was also tested, as reflected by rat paw edema. A positive correlation was found between the potency to produce edema in vivo and the potency to release mast cell histamine in vitro (r = 0.94, p less than 0.05). In addition, compounds that released mast cell histamine and induced rat paw edema also produced hypotension and death when administered intravenously, while analogs which produced minimal histamine release in vitro produced minimal or no cardiovascular changes or lethality in vivo at the same dosages (5 mg/kg). Finally, cyproheptadine (10 mg/kg), an antagonist at both the serotonin and the histamine receptors, blunted the effects of SK&F 101926 on MAP and blocked the lethality. Pretreatment with a combination of histamine (H1 and H2) antagonists provided little protection against the SK&F 101926-induced toxicity. These data indicate that the cardiovascular toxicity of SK&F 101926 (and related peptides) is mediated via the release of autocoids from mast cells. Serotonin appears to play a major role in mediating the cardiovascular toxicity of SK&F 101926.

Elevated serum intact parathyroid hormone levels in elderly patients with hip fracture

It has been postulated that secondary hyperparathyroidism contributes to bone loss and the high incidence of hip fractures in the elderly population, but there are no data on serum intact parathyroid hormone concentrations in these patients. In this study, serum intact parathyroid hormone (PTH) levels have been measured in 39 elderly patients with hip fracture; in addition, serum 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 concentrations have been measured. Twenty patients (51.3%) had elevated serum intact PTH concentrations whilst five (12.8%) had abnormally low serum 25-hydroxyvitamin D3 levels and serum 1,25-dihydroxyvitamin D3 was reduced in only two. These results provide the first direct evidence for secondary hyperparathyroidism in elderly patients with hip fracture. Vitamin D deficiency is unlikely to be the sole cause of secondary hyperparathyroidism in these subjects and calcium deficiency by itself may also contribute.

Measurement of circulating parathyroid hormone

The measurement of parathyroid hormone (PTH) is important in the investigation of disorders of mineral metabolism. Though the first immunoassay for PTH was described more than 25 years ago, it is only recently that methods have been developed which provide the required sensitivity and specificity to detect small changes in hormone secretion in normal subjects. These new methods take advantage of modern labelled antibody technology and have already been shown capable of yielding improvements in the diagnosis and monitoring of disorders which involve changes in PTH secretion. In addition, they are now providing fresh insight into the basic physiology of PTH secretion.