Calcitonin

New developments and opportunities in oral mucosal drug delivery for local and systemic disease

The oral mucosa's accessibility, excellent blood supply, by-pass of hepatic first-pass metabolism, rapid repair and permeability profile make it an attractive site for local and systemic drug delivery. Technological advances in mucoadhesives, sustained drug release, permeability enhancers and drug delivery vectors are increasing the efficient delivery of drugs to treat oral and systemic diseases. When treating oral diseases, these advances result in enhanced therapeutic efficacy, reduced drug wastage and the prospect of using biological agents such as genes, peptides and antibodies. These technologies are also increasing the repertoire of drugs that can be delivered across the oral mucosa to treat systemic diseases. Trans-mucosal delivery is now a favoured route for non-parenteral administration of emergency drugs and agents where a rapid onset of action is required. Furthermore, advances in drug delivery technology are bringing forward the likelihood of transmucosal systemic delivery of biological agents.

Amyloidogenesis of natively unfolded proteins

Aggregation and subsequent development of protein deposition diseases originate from conformational changes in corresponding amyloidogenic proteins. The accumulated data support the model where protein fibrillogenesis proceeds via the formation of a relatively unfolded amyloidogenic conformation, which shares many structural properties with the pre-molten globule state, a partially folded intermediate first found during the equilibrium and kinetic (un)folding studies of several globular proteins and later described as one of the structural forms of natively unfolded proteins. The flexibility of this structural form is essential for the conformational rearrangements driving the formation of the core cross-beta structure of the amyloid fibril. Obviously, molecular mechanisms describing amyloidogenesis of ordered and natively unfolded proteins are different. For ordered protein to fibrillate, its unique and rigid structure has to be destabilized and partially unfolded. On the other hand, fibrillogenesis of a natively unfolded protein involves the formation of partially folded conformation; i.e., partial folding rather than unfolding. In this review recent findings are surveyed to illustrate some unique features of the natively unfolded proteins amyloidogenesis.

Acetyl-[Asn30,Tyr32]-calcitonin fragment 8-32 forms channels in phospholipid planar lipid membranes

The N-terminally truncated derivative of salmon calcitonin (sCt) (acetyl-[Asn(30),Tyr(32)]-calcitonin fragment 8-32) (AC 187) lacks hormonal activity and is a potent and selective antagonist of the hormone and amylin receptor. It was investigated for its capability to interact and form channels in palmitoleoylphosphatidylcholine:dioleoylphosphatidylglycerol planar lipid membranes. Interestingly, AC 187 exhibits channel activity, whose parameters, i.e., central conductance (Lambda (c)), occurrence (number of channels/min), voltage-dependence and lifetime, are similar to those found for sCt although, in the same experimental conditions, it takes longer to incorporate into the membrane than sCt. This channel activity can be modulated by changing either the holding potential or the pH of the medium, or by adding picomolar concentrations of SDS. One evident difference between the two peptides is that sCt is unselective (1.03) while AC 187 displays a cationic selectivity (P (K) (+)/P (Cl) (-) = 2.7) at pH 7, increasing to 3.87 when the pH drops to 3.8. The present findings indicate that the 1-7 disulfide bridge is sufficient but not necessary for membrane interaction, in accordance with the observation reported on the interaction with membrane receptors. Furthermore, the remarkable pH dependence of the cationic channel could be taken into consideration for full biotechnological study.

Rational design of aggregation-resistant bioactive peptides: reengineering human calcitonin

A high propensity to aggregate into intractable deposits is a common problem limiting the production and use of many peptides and proteins in a wide range of biotechnological and pharmaceutical applications. Many therapeutic polypeptides are frequently abandoned at an early stage in their development because of problems with stability and aggregation. It has been shown recently that parameters describing the physicochemical properties of polypeptides can be used as predictors of protein aggregation. Here we demonstrate that these and similar tools can be applied to the rational redesign of bioactive molecules with a significantly reduced aggregation propensity without loss of physiological activity. This strategy has been exemplified by designing variants of the hormone calcitonin that show a significantly reduced aggregation propensity, yet maintain, or even increase, their potency when compared to the current therapeutic forms. The results suggest that this approach could be used successfully to enhance the solubility and efficacy of a wide range of other peptide and protein therapeutics.

Interactions of the human calcitonin fragment 9-32 with phospholipids: a monolayer study

Human calcitonin and its C-terminal fragment 9-32 (hCT(9-32)) administered in a spray translocate into respiratory nasal epithelium with an effect similar to intravenous injection. hCT(9-32) is an efficient carrier to transfer the green fluorescent protein into excised bovine nasal mucosa. To understand the translocation of hCT(9-32) across plasma membranes, we investigated its interactions with phospholipids and its interfacial structure using model lipid monolayers. A combination of physicochemical methods was applied including surface tension measurements on adsorbed and spread monolayers at the air-water interface, Fourier transform infrared, circular dichroism, and atomic force microscopy on Langmuir-Blodgett monolayers. The results disclose that hCT(9-32) preferentially interacts with negatively charged phospholipids and does not insert spontaneously into lipid monolayers. This supports a nonreceptor-mediated endocytic internalization pathway as previously suggested. Structural studies revealed a random coil conformation of hCT(9-32) in solution, transforming to alpha-helices when the peptide is localized at lipid-free or lipid-containing air-water interfaces. Atomic force microscopy studies of monolayers of the peptide alone or mixed with dioleoylphosphatidylcholine revealed that hCT(9-32) forms filaments rolled into spirals. In contrast, when interacting with dioleoylphosphatidylglycerol, hCT(9-32) does not adopt filamentous structures. A molecular model and packing is proposed for the spiral-forming hCT(9-32).

Adjunctive agents in the management of chronic pain

Chronic pain syndromes include cancer-related pain, postherpetic neuralgia, painful diabetic neuropathy, and central poststroke pain and are common in the elderly. Adjunctive (or adjuvant) analgesics, defined as drugs that do not contain acetaminophen and those not classified as nonsteroidal antiinflammatory or opioid agents, play a role in the management of chronic pain. The term "adjunctive" (or "adjuvant") is a misnomer as several of these agents may constitute first-line therapy for many chronic pain syndromes. Tricyclic antidepressants have formed the backbone of therapy for chronic neuropathic pain for years. However, the difficulty with using agents of this class, due to their clinically significant adverse-event potential, has led to the evaluation of other agents, most notably, the antiepileptic drugs. The most useful are gabapentin, carbamazepine, and lamotrigine. In selected patients, baclofen, mexiletine, and clonidine may be useful as well. Cancer-related pain may respond substantially to corticosteroids, and pain associated with bone metastases to parenteral bisphosphonates and strontium. Practitioners should consider these alternative agents when treating chronic pain.

Osteoporosis therapies for rheumatoid arthritis patients: minimizing gastrointestinal side effects

OBJECTIVE

This manuscript identifies characteristics that put people with rheumatoid arthritis (RA) at high risk for osteoporosis or gastrointestinal (GI) disturbances. The manuscript then reviews therapies available for osteoporosis in the United States and makes recommendations about choosing therapies that minimize GI adverse effects in RA patients at high risk for such events.

DATA SOURCES

References identified through MEDLINE, abstracts, and prescribing information for individual drugs.

DATA EXTRACTION

Characteristics that predispose patients to osteoporosis and GI problems were identified. Data on individual osteoporosis therapies were assessed by risk-benefit analysis and appropriateness for use in patients at risk for GI disturbances.

DATA SYNTHESIS

High risk of osteoporosis in people with RA is caused by disease activity, medication effects, physical inactivity, and standard risk factors such as postmenopausal status and increased age. Patients with RA are frequently at high GI risk if they are receiving nonsteroidal anti-inflammatory drugs or corticosteroids. Because of the high potential for erosive esophagitis and other upper GI disorders with alendronate, caution is warranted in prescribing alendronate to RA patients with high GI risk. In such patients, estrogen replacement therapy, selective estrogen receptor modulators, or calcitonin should be considered for treatment, and either estrogen replacement therapy or selective estrogen receptor modulators should be considered for osteoporosis prevention.

CONCLUSIONS

Assessment of GI risk is important in patients with RA and osteoporosis. Risk factors should be considered when choosing osteoporosis therapies.

Osteoporosis. Pathogenesis, diagnosis, and treatment in older adults

Osteoporosis is a major cause of disability and excess mortality in older men and women. Hip fracture incidence accelerates approximately 10 years after menopause in women and after age 70 in men. Approximately 1 million Americans suffer fragility fractures each year at a cost of over 14 billion dollars. The disability, mortality, and cost of hip and vertebral fractures are substantial in the rapidly growing, aging population so that prevention of osteoporosis is a major public health concern. BMD is used to make the diagnosis of osteoporosis before incident fracture and predict fracture risk. Recommendations for treatment and prevention of osteoporosis based on BMD score have been published by the World Health Organization and the National Osteoporosis Foundation. In a process that continues throughout life, bone repairs itself by the coupled action of bone resorption followed by bone formation, sometimes referred to as bone turnover. Osteoblasts and osteoclasts are the primary cells involved in bone formation and resorption, respectively. The process of bone turnover is regulated by hormones, such as PIH and local factors such as IL-1 and prostaglandins. Following attainment of peak bone mass at age 25, bone loss begins, accelerates in women at menopause and slows again but continues into advanced years at a rate of 1% to 2% per year, similar to premenopausal bone loss rate. The leading theories of the mechanism of bone loss in older individuals is calcium deficiency leading to secondary hyperparathyroidism and sex hormone deficiency. Risk factors such as age, gender, ethnic background, smoking, exercise, and nutrition, and medical conditions associated with osteoporosis should be evaluated and modified when possible to prevent further bone loss. Osteoporosis treatment and prevention include weight-bearing exercise, calcium and vitamin D supplementation, estrogen replacement, bisphosphonates, selective estrogen receptor antagonists, and calcitonin. Although there is no currently approved treatment for osteoporosis in men, many of the treatments approved for osteoporosis in women hold promise to be beneficial in men.

Prevention and treatment of osteoporosis in the elderly

Due to age-associated bone losses, all elderly are prone to osteoporosis, which often leads to fractures. Fractures frequently result in dependency and institutionalization, as well as physical deformities that may lead to respiratory and cardiovascular problems. Currently, no drugs exist to promote new bone formation. Thus care of the elderly focuses primarily on lifestyle modification and increased dietary intake of calcium and vitamin D; decreased intake of caffeine, phosphates, and alcohol; smoking cessation; increased exercise; and drugs. Drugs for preventing osteoporosis include supplemental calcium and vitamin D, hormone replacement therapy, and alendronate. Drugs that enhance bone loss or increase the likelihood of falls should be eliminated, if possible, or the dosages adjusted. Making residences safer will also help to minimize the potential for falls. Drugs for treating osteoporosis include hormone replacement therapy, alendronate, and nasal calcitonin. The prevention and treatment plan is individualized for each patient, taking into account personal preferences, risk factors for osteoporosis and fracture, concomitant diseases and drug therapies, efficacy and tolerance of osteoporosis therapy, quality of life, life expectancy, finances, and health insurance coverage.