Effect of theophylline on calcium metabolism and circulating vitamin D metabolites

Therapeutic potential of phosphodiesterase inhibitors in the treatment of osteoporosis: Scopes for therapeutic repurposing and discovery of new oral osteoanabolic drugs

Cyclic nucleotide phosphodiesterases (PDEs) are ubiquitously expressed enzymes that hydrolyze phosphodiester bond in the second messenger molecules including cAMP and cGMP. A wide range of drugs blocks one or more PDEs thereby preventing the inactivation of cAMP/cGMP. PDEs are differentially expressed in bone cells including osteoblasts, osteoclasts and chondrocytes. Intracellular increases in cAMP/cGMP levels in osteoblasts result in osteogenic response. Acting via the type 1 PTH receptor, teriparatide and abaloparatide increase intracellular cAMP and induce osteoanabolic effect, and many PDE inhibitors mimic this effect in preclinical studies. Since all osteoanabolic drugs are injectable and that oral drugs are considered to improve the treatment adherence and persistence, osteogenic PDE inhibitors could be a promising alternative to the currently available osteogenic therapies and directly assessed clinically in drug repurposing mode. Similar to teriparatide/abaloparatide, PDE inhibitors while stimulating osteoblast function also promote osteoclast function through stimulation of receptor activator of nuclear factor kappa-B ligand production from osteoblasts. In this review, we critically discussed the effects of PDE inhibitors in bone cells from cellular signalling to a variety of preclinical models that evaluated the bone formation mechanisms. We identified pentoxifylline (a non-selective PDE inhibitor) and rolipram (a PDE4 selective inhibitor) being the most studied inhibitors with osteogenic effect in preclinical models of bone loss at ≤ human equivalent doses, which suggest their potential for post-menopausal osteoporosis treatment through therapeutic repurposing. Subsequently, we treated pentoxifylline and rolipram as prototypical osteogenic PDEs to predict new chemotypes via the computer-aided design strategies for new drugs, based on the structural biology of PDEs.

Assessing the Associations of Blood Metabolites With Osteoporosis: A Mendelian Randomization Study

Context

Osteoporosis is a metabolic bone disease. The effect of blood metabolites on the development of osteoporosis remains elusive.

Objective

To explore the relationship between blood metabolites and osteoporosis.

Design and Methods

We used 2286 unrelated white subjects for the discovery samples and 3143 unrelated white subjects from the Framingham Heart Study (FHS) for the replication samples. The bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Genome-wide single nucleotide polymorphism (SNP) genotyping was performed using Affymetrix Human SNP Array 6.0 (for discovery samples) and Affymetrix SNP 500K and 50K array (for FHS replication samples). The SNP sets significantly associated with blood metabolites were obtained from a reported whole-genome sequencing study. For each subject, the genetic risk score of the metabolite was calculated from the genotype data of the metabolite-associated SNP sets. Pearson correlation analysis was conducted to evaluate the potential effect of blood metabolites on the variations in bone phenotypes; 10,000 permutations were conducted to calculate the empirical P value and false discovery rate.

Results

We analyzed 481 blood metabolites. We identified multiple blood metabolites associated with hip BMD, such as 1,5-anhydroglucitol (Pdiscovery < 0.0001; Preplication = 0.0361), inosine (Pdiscovery = 0.0018; Preplication = 0.0256), theophylline (Pdiscovery = 0.0048; Preplication = 0.0433, gamma-glutamyl methionine (Pdiscovery = 0.0047; Preplication = 0.0471), 1-linoleoyl-2-arachidonoyl-GPC (18:2/20:4n6; Pdiscovery = 0.0018; Preplication = 0.0390), and X-12127 (Pdiscovery = 0.0002; Preplication = 0.0249).

Conclusions

Our results suggest a modest effect of blood metabolites on the variations of BMD and identified several candidate blood metabolites for osteoporosis.

Theophylline, a methylxanthine drug induces osteopenia and alters calciotropic hormones, and prophylactic vitamin D treatment protects against these changes in rats

The drug, theophylline is frequently used as an additive to medications for people suffering from chronic obstructive pulmonary diseases (COPD). We studied the effect of theophylline in bone cells, skeleton and parameters related to systemic calcium homeostasis. Theophylline induced osteoblast apoptosis by increasing reactive oxygen species production that was caused by increased cAMP production. Bone marrow levels of theophylline were higher than its serum levels, indicating skeletal accumulation of this drug. When adult Sprague-Dawley rats were treated with theophylline, bone regeneration at fracture site was diminished compared with control. Theophylline treatment resulted in a time-dependent (at 4- and 8 weeks) bone loss. At 8 weeks, a significant loss of bone mass and deterioration of microarchitecture occurred and the severity was comparable to methylprednisone. Theophylline caused formation of hypomineralized osteoid and increased osteoclast number and surface. Serum bone resorption and formation marker were respectively higher and lower in the theophylline group compared with control. Bone strength was reduced by theophylline treatment. After 8 weeks, serum 25-D3 and liver 25-hydroxylases were decreased in theophylline group than control. Further, theophylline treatment reduced serum 1, 25-(OH)2 vitamin D3 (1,25-D3), and increased parathyroid hormone and fibroblast growth factor-23. Theophylline treated rats had normal serum calcium and phosphate but displayed calciuria and phosphaturia. Co-administration of 25-D3 with theophylline completely abrogated theophylline-induced osteopenia and alterations in calcium homeostasis. In addition, 1,25-D3 protected osteoblasts from theophylline-induced apoptosis and the attendant oxidative stress. We conclude that theophylline has detrimental effects in bone and prophylactic vitamin D supplementation to subjects taking theophylline could be osteoprotective.

Long-term therapy in COPD: any evidence of adverse effect on bone?

Patients with COPD have high risk for osteoporosis and fractures. Hip and vertebral fractures might impair mobility, and vertebral fractures further reduce lung function. This review discusses the evidence of bone loss due to medical treatment opposed to disease severity and risk factors for COPD, and therapeutic options for the prevention and treatment of osteoporosis in these patients. A review of the English-language literature was conducted using the MEDLINE database until June 2009. Currently used bronchodilators probably lack adverse effect on bone. Oral corticosteroids (OCS) increase bone resorption and decrease bone formation in a dose response relationship, but the fracture risk is increased more than reflected by bone densitometry. Inhaled corticosteroids (ICS) have been associated with both increased bone loss and fracture risk. This might be a result of confounding by disease severity, but high doses of ICS have similar effects as equipotent doses of OCS. The life-style factors should be modified, use of regular OCS avoided and use of ICS restricted to those with evidenced effect and probably kept at moderate doses. The health care should actively reveal risk factors, include bone densitometry in fracture risk evaluation, and give adequate prevention and treatment for osteoporosis.

A review of drug-induced hypocalcemia

Hypocalcemia (defined as total serum calcium lower than 8.5 mg/dl or as ionized serum calcium lower than 4.7 mg/dl) is a relatively common metabolic abnormality observed in hospitalized patients. Although it is associated with certain pharmacological agents such as bisphosphonates and cisplatin, hypocalcemia may occasionally develop in the course of treatment with drugs used in everyday clinical practice, including antiepileptics, aminoglycosides, and proton pump inhibitors. Hypocalcemia associated with drug treatment can be easily missed as a consequence of coexistence of multiple factors contributing to low serum calcium levels. Drug-related hypocalcemia is usually mild and asymptomatic but may be severe as well. Effective clinical management can be handled through awareness of this adverse effect induced by certain pharmaceutical compounds on serum calcium concentrations. Herein, we review pertinent clinical information on the incidence of hypocalcemia associated with specific drug treatment and discuss the underlying pathophysiological mechanisms.

Evaluation of the effect of low-dose oral theophylline therapy on some bone turnover markers and serum prolidase I activity in mild asthmatics

Hypercalcemia and hypercalciuria observed both in humans and in animals who were on long-term theophylline therapy, prompted us to investigate whether oral theophylline treatment at optimal doses causes any adverse side effects on bone metabolism in mild asthmatics. Therefore, serum osteocalcin (BGP) and total alkaline phosphatase (TALP, EC 3.1.3.1) as bone formation markers, serum prolidase I (EC 3.4.13.9) activity as a marker for collagen metabolism, urinary deoxypyridinoline (Dpd), hydroxyproline (Hyp) and fasting urinary calcium as bone resorption markers, were measured in 18 mild asthmatics who had been treated with theophylline over 1-10 years. Among measured bone turnover markers, BGP, TALP, and Hyp levels were found to be increased in mild asthmatics; and BGP showed the greatest percent mean increase (98%) over the healthy subjects. However, these increments did not exceed the upper reference limits. Serum prolidase I activity was also increased in mild asthmatics receiving theophylline. Our results indicate that theophylline therapy at optimal doses may not exert adverse side effects on bone homeostasis, but patients receiving supratherapeutic doses of theophylline should be under close examination in order to predict future bone mass status.

Asthma and chronic obstructive airway diseases are associated with osteoporosis and fractures: a literature review

The objective was to assess the association between asthma and/or chronic obstructive airway diseases (COAD), and osteoporosis, and appraise treatments of osteoporosis in these patients. MEDLINE and Excerpta Medica were searched for original research with control groups which tested the above association. One cohort and nine cross-section studies of bone density in patients with asthma and/or COAD were retrieved. These demonstrated clinically important bone density reductions of up to 29% in subjects, dependent upon daily oral corticosteroids, by a variety of measurement techniques, at various bone sites. Bone density reduction has also been less consistently reported in the absence of oral corticosteroids, suggesting that other factors including high-dose inhaled corticosteroids may have a role. Fracture studies. Three studies in oral corticosteroid-dependent asthmatics demonstrated a vertebral fracture prevalence up to 56%, and annual vertebral fracture incidence of up to 42%. The strength of the available evidence is limited, but suggests that patients with asthma and/or COAD are at increased risk of osteoporosis. The evidence of the association between osteoporosis and inhaled corticosteroids is much more limited than for oral corticosteroids. Bisphosphonates are promising agents to maintain and/or promote bone mass in this patient group.

Interactions between dietary caffeine and calcium on calcium and bone metabolism in older women

OBJECTIVE

Our purpose was to determine the effect of 2 weeks of caffeine abstinence on calcium (Ca) and bone metabolism in women habitually consuming caffeine and either low or moderate amounts of Ca.

METHODS

Participants were 25 women, aged 39-76 years (mean 65 years, median 57 years) habitually consuming at least 200 mg caffeine daily. Three days of dietary records and 24-hour urine collections were made immediately prior to collection of fasting blood and 1-hour urine in a metabolic unit. Women were classified as low Ca consumers (414-584 mg daily) or moderate Ca consumers (662-1357 mg daily) based on 6 days of diet records.

RESULTS

Women in the low Ca group had higher levels of serum ultrafiltrable Ca (UFCa) after caffeine abstinence (1.40 mmol/L CAF+ vs 1.52 mmol/L CAF-, p < 0.01), while there were no differences between experimental periods for UFCa in the moderate Ca group (1.35 mmol/L CAF+ vs 1.38 mmol/L CAF-, ns). Women in the low Ca group also had lower serum bone isoenzyme alkaline phosphatase levels after caffeine abstinence (9.3 U/L CAF+ vs 8.8 U/L CAF-, p < 0.05), while no significant changes were seen in bone alkaline phosphatase in the moderate Ca consumers (8.7 U/L CAF+ vs 8.9 U/L CAF-, ns). Fasting total serum Ca, urinary hydroxyproline/creatinine, and Ca/creatinine ratios were unchanged in both dietary groups. Three-day mean 24-hour urinary Ca excretion decreased after caffeine abstinence in the moderate Ca group only. There were no differences in dietary intakes of Ca from dairy products between CAF+ and CAF- in either the low or moderate Ca groups.

CONCLUSION

Abstinence from moderate caffeine intake (mean 5.8 mg/kg lean body mass, 383 mg/day caffeine) raises ultrafiltrable Ca and decreases bone alkaline phosphatase in older women consuming < 600 mg Ca daily.

Risk of osteoporosis in men with chronic bronchitis

Theoretically, patients with chronic bronchitis are at risk for osteoporosis. Bone metabolism was assessed in 44 male chronic bronchitics treated with oral prednisolone (C+; n = 19) or with bronchodilatory drugs alone (C-; n = 25). In both groups, serum osteocalcin was lower (p less than 0.001) than in age- and sex-matched controls (mean (ng/ml) C+ 1.0, C- 1.9, controls 4.2), while testosterone was at the lower limit of the reference range. Low trabecular bone mineral density (BMD) was noted in the C- group (median Z score -1.0), but both cortical and trabecular BMD were depressed in the C+ group (-1.0 and -1.4, respectively). In conclusion, chronic bronchitics treated with corticosteroids, even at low doses, are at risk for osteoporosis. In both groups, additional factors such as hypogonadism might be responsible for low BMD and low osteocalcin levels. A decrease in bone formation is a possible mechanism of action.