Glucagon-like peptide 1 (GLP-1).

BACKGROUND: The glucagon-like peptide-1 (GLP-1) is a multifaceted hormone with broad pharmacological potential. Among the numerous metabolic effects of GLP-1 are the glucose-dependent stimulation of insulin secretion, decrease of gastric emptying, inhibition of food intake, increase of natriuresis and diuresis, and modulation of rodent ß-cell proliferation. GLP-1 also has cardio- and neuroprotective effects, decreases inflammation and apoptosis, and has implications for learning and memory, reward behavior, and palatability. Biochemically modified for enhanced potency and sustained action, GLP-1 receptor agonists are successfully in clinical use for the treatment of type-2 diabetes, and several GLP-1-based pharmacotherapies are in clinical evaluation for the treatment of obesity. SCOPE OF REVIEW: In this review, we provide a detailed overview on the multifaceted nature of GLP-1 and its pharmacology and discuss its therapeutic implications on various diseases. MAJOR CONCLUSIONS: Since its discovery, GLP-1 has emerged as a pleiotropic hormone with a myriad of metabolic functions that go well beyond its classical identification as an incretin hormone. The numerous beneficial effects of GLP-1 render this hormone an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, and neurodegenerative disorders.

Peptide-based multi-agonists: a new paradigm in metabolic pharmacology.

Obesity and its comorbidities, such as type 2 diabetes, are pressing worldwide health concerns. Available anti-obesity treatments include weight loss pharmacotherapies and bariatric surgery. Whilst surgical interventions typically result in significant and sustained weight loss, available pharmacotherapies are far less effective, typically decreasing body weight by no more than 5-10%. An emerging class of multi-agonist drugs may eventually bridge this gap. This new class of specially tailored drugs hybridizes the amino acid sequences of key metabolic hormones into one single entity with enhanced potency and sustained action. Successful examples of this strategy include multi-agonist drugs targeting the receptors for glucagon-like peptide-1 (GLP-1), glucagon and the glucose-dependent insulinotropic polypeptide (GIP). Due to the simultaneous activity at several metabolically relevant receptors, these multi-agonists offer improved body weight loss and glucose tolerance relative to their constituent monotherapies. Further advancing this concept, chimeras were generated that covalently link nuclear acting hormones such as oestrogen, thyroid hormone (T3 ) or dexamethasone to peptide hormones such as GLP-1 or glucagon. The benefit of this strategy is to restrict the nuclear hormone action exclusively to cells expressing the peptide hormone receptor, thereby maximizing combinatorial metabolic efficacy of both drug constituents in the target cells whilst preventing the nuclear hormone cargo from entering and acting on cells devoid of the peptide hormone receptor, in which the nuclear hormone might have unwanted effects. Many of these multi-agonists are in preclinical and clinical development and may represent new and effective tools in the fight against obesity and its comorbidities.

Anti-Obesity Therapy: from Rainbow Pills to Polyagonists.

With their ever-growing prevalence, obesity and diabetes represent major health threats of our society. Based on estimations by the World Health Organization, approximately 300 million people will be obese in 2035. In 2015 alone there were more than 1.6 million fatalities attributable to hyperglycemia and diabetes. In addition, treatment of these diseases places an enormous burden on our health care system. As a result, the development of pharmacotherapies to tackle this life-threatening pandemic is of utmost importance. Since the beginning of the 19th century, a variety of drugs have been evaluated for their ability to decrease body weight and/or to improve deranged glycemic control. The list of evaluated drugs includes, among many others, sheep-derived thyroid extracts, mitochondrial uncouplers, amphetamines, serotonergics, lipase inhibitors, and a variety of hormones produced and secreted by the gastrointestinal tract or adipose tissue. Unfortunately, when used as a single hormone therapy, most of these drugs are underwhelming in their efficacy or safety, and placebo-subtracted weight loss attributed to such therapy is typically not more than 10%. In 2009, the generation of a single molecule with agonism at the receptors for glucagon and the glucagon-like peptide 1 broke new ground in obesity pharmacology. This molecule combined the beneficial anorectic and glycemic effects of glucagon-like peptide 1 with the thermogenic effect of glucagon into a single molecule with enhanced potency and sustained action. Several other unimolecular dual agonists have subsequently been developed, and, based on their preclinical success, these molecules illuminate the path to a new and more fruitful era in obesity pharmacology. In this review, we focus on the historical pharmacological approaches to treat obesity and glucose intolerance and describe how the knowledge obtained by these studies led to the discovery of unimolecular polypharmacology.

The New Biology and Pharmacology of Glucagon.

In the last two decades we have witnessed sizable progress in defining the role of gastrointestinal signals in the control of glucose and energy homeostasis. Specifically, the molecular basis of the huge metabolic benefits in bariatric surgery is emerging while novel incretin-based medicines based on endogenous hormones such as glucagon-like peptide 1 and pancreas-derived amylin are improving diabetes management. These and related developments have fostered the discovery of novel insights into endocrine control of systemic metabolism, and in particular a deeper understanding of the importance of communication across vital organs, and specifically the gut-brain-pancreas-liver network. Paradoxically, the pancreatic peptide glucagon has reemerged in this period among a plethora of newly identified metabolic macromolecules, and new data complement and challenge its historical position as a gut hormone involved in metabolic control. The synthesis of glucagon analogs that are biophysically stable and soluble in aqueous solutions has promoted biological study that has enriched our understanding of glucagon biology and ironically recruited glucagon agonism as a central element to lower body weight in the treatment of metabolic disease. This review summarizes the extensive historical record and the more recent provocative direction that integrates the prominent role of glucagon in glucose elevation with its under-acknowledged effects on lipids, body weight, and vascular health that have implications for the pathophysiology of metabolic diseases, and the emergence of precision medicines to treat metabolic diseases.

Fibroblast growth factor 21 night watch: advances and uncertainties in the field.

Fibroblast growth factor (FGF) 21 belongs to a hormone-like subgroup within the FGF superfamily. The members of this subfamily, FGF19, FGF21 and FGF23, are characterized by their reduced binding affinity for heparin that enables them to be transported in the circulation and function in an endocrine manner. It is likely that FGF21 also acts in an autocrine and paracrine fashion, as multiple organs can produce this protein and its plasma concentration seems to be below the level necessary to induce a pharmacological effect. FGF21 signals via FGF receptors, but for efficient receptor engagement it requires a cofactor, membrane-spanning ßKlotho (KLB). The regulation of glucose uptake in adipocytes was the initial biological activity ascribed to FGF21, but this hormone is now recognized to stimulate many other pathways in vitro and display multiple pharmacological effects in metabolically compromised animals and humans. Understanding of the precise physiology of FGF21 and its potential medicinal role has evolved exponentially over the last decade, yet numerous aspects remain to be defined and others are a source of debate. Here we provide a historical overview of the advances in FGF21 biology focusing on the uncertainties in the mechanism of action as well as the differing viewpoints relating to this intriguing protein.

Basal activity profiles of NPH and [Nepsilon-palmitoyl Lys (B29)] human insulins in subjects with IDDM.

[Nepsilon-palmitoyl Lys (B29)] human insulin is a fatty acid-acylated derivative of insulin with extended action compared to unmodified insulin when infused intravenously (i.v.) secondary to its binding to circulating albumin. The duration and activity profile of the acylated (A) and NPH (B) insulins were assessed following subcutaneous (s.c.) doses of (A) 6 nmol/kg and (B) 1.2 nmol/kg (equivalent to 0.2 U/kg) in 9 subjects with IDDM. After overnight i.v. infusion of regular human insulin, morning glucose was (A) 6.9 +/- 0.1 and (B) 6.8 +/- 0.1 mmol/l. After the s.c. injection, i.v. human insulin or glucose was infused to maintain near-basal glycaemia and tracer glucose to assess hepatic glucose production (HGP). An activity profile was deduced for each study by expressing the glucose infusion rate at each time point, as a fraction (%) of the basal (measured) HGP, and the i.v. insulin infusion rate as a fraction (%) of the basal requirement. The two fractions are combined by adding the fractional glucose infusion rate and subtracting the fractional insulin infusion rate. Infusion rates of i.v. insulin in the morning were (A) 0.96 +/- 0.096 and (B) 1.22 +/- 0.09 pmol x kg(-1) x min(-1). After insulin injection, i.v. insulin requirements decreased and were below 10% of basal between 100 and 150 min. A constant activity profile of 0% represents a perfect substitution of the basal i.v. insulin infusion by the s.c. dose. The actual profile is defined by deviations from this (above) and was -17 +/- 11, 7 +/- 10, -9 +/- 6 and -18 +/- 18% for [Nepsilon-palmitoyl Lys (B29)] human insulin and 17 +/- 12, 5 +/- 6, -9 +/- 15, 22 +/- 18% for NPH insulin at 3, 6, 9 and 12 h after s.c. injection. HGP was similar for the two insulins, demonstrating similar metabolic actions and profiles both peripherally and at the liver.

Prevention of vascular and neural dysfunction in diabetic rats by C-peptide.

C-peptide, a cleavage product from the processing of proinsulin to insulin, has been considered to possess little if any biological activity other than its participation in insulin synthesis. Injection of human C-peptide prevented or attenuated vascular and neural (electrophysiological) dysfunction and impaired Na+- and K+-dependent adenosine triphosphate activity in tissues of diabetic rats. Nonpolar amino acids in the midportion of the peptide were required for these biological effects. Synthetic reverse sequence (retro) and all-D-amino acid (enantio) C-peptides were equipotent to native C-peptide, which indicates that the effects of C-peptide on diabetic vascular and neural dysfunction were mediated by nonchiral interactions instead of stereospecific receptors or binding sites.

Modifications in the B10 and B26-30 regions of the B chain of human insulin alter affinity for the human IGF-I receptor more than for the insulin receptor.

Inversion of the natural sequence of the B chain of human insulin (HI) from ProB28LysB29 to LysB28ProB29 generates an insulin analogue with reduced tendency to self-associate. Since this substitution increases the homology of insulin to insulin-like growth factor-I (IGF-I), we have examined the affinity of a series of insulin analogues with the general modified structure XaaB28ProB29 HI for binding to both human placental insulin and IGF-I receptors. The XaaB28ProB29 HI series is approximately equipotent to HI in binding to the insulin receptor with the exception of when Xaa = Phe, Trp, Leu, Ile, and Gly (40-60% relative to HI). Substitution with basic residues in the B28 position increased the relative affinity to the IGF-I receptor approximately 1.5-2-fold (ArgB28ProB29 > OrnB28ProB29 = LysB28ProB29). Substitution with acidic residues reduced relative affinity for the IGF-I receptor approximately 2-fold (CyaB28ProB29 = GluB28ProB29 > AspB28ProB29). Combination of AspB10 substitution in conjunction with a modification in the B28-29 position (e.g. AspB10LysB28ProB29 HI) showed an additional 2-fold selective increase in affinity for the IGF-I receptor, suggesting that these two effects are additive. Addition of Arg residues at B31-32, on the backbone of either HI or AspB10 HI, increased affinity for the IGF-I receptor 10 and 28 fold, respectively, compared to HI, confirming the significance of enhanced positive charge at the C-terminal end of the insulin B-chain in increasing selectivity for the IGF-I receptor. This relative increase in IGF-I receptor affinity correlated largely, but not completely, with enhanced growth promoting activity in human mammary epithelial cells. In the case of LysB28ProB29 HI, growth activity correlated with dissociation kinetics from the insulin receptor which were shown to be identical with those of human insulin.

Mealtime treatment with insulin analog improves postprandial hyperglycemia and hypoglycemia in patients with non-insulin-dependent diabetes mellitus. Multicenter Insulin Lispro Study Group.

BACKGROUND: Insulin lispro is an insulin analog that was recently developed particularly for a mealtime therapy. It has a fast absorption rate and short duration of action. The efficacy of insulin lispro in the clinical therapy of patients with non-insulin-dependent diabetes mellitus (NIDDM) has not been tested. OBJECTIVES: To compare insulin lispro and human regular insulin in the mealtime treatment of patients with NIDDM. METHODS: A 6-month, randomized, multinational (16 countries), multicenter (80 sites) clinical trial with an open-label, crossover design was performed in 722 patients with NIDDM. Insulin lispro was injected immediately before and human regular insulin 30 to 45 minutes before the meal. RESULTS: Throughout the study, the postprandial rise in serum glucose levels was significantly lower during insulin lispro than human regular insulin treatment. At end point the rise (mean +/- SEM) in serum glucose levels was 30% lower at 1 hour (2.6 +/- 0.1 mmol/L [46.8 +/- 1.8 mg/ dL] for lispro vs 3.7 +/- 0.1 mmol/L [66.6 +/- 1.8 mg/dL] for human regular insulin) and 53% lower 2 hours after the test meal (1.4 +/- 0.1 mmol/L [25.2 +/- 1.8 mg/dL] for lispro vs 3.0 +/- 0.1 mmol/L [54.0 +/- 1.8 mg/dL] for human regular insulin) with insulin lispro compared with human regular insulin therapy (P < .001 for both intervals). During insulin lispro therapy the rate of hypoglycemia overall (P = .01) and overnight (P < .001) was lower and the number of asymptomatic hypoglycemic episodes was smaller (P = .03) than during human regular insulin therapy. Associated with a similar 13% increase (P < .001) in the total daily insulin dose, the glycosylated hemoglobin level decreased (P < .001) equally in both treatment groups. Serum lipid and lipoprotein levels remained unchanged. There were no differences in the adverse events between the 2 treatment groups. CONCLUSIONS: Compared with human regular insulin therapy, mealtime therapy with insulin lispro reduced postprandial hyperglycemia and may decrease the rate of mild hypoglycemic episodes in patients with NIDDM.

Crystal structure of the obese protein leptin-E100.

Mutations in the obese gene (OB) or in the gene encoding the OB receptor(OB-R) result in obesity, infertility and diabetes in a variety of mouse phenotypes. The demonstration that OB protein (also known as leptin) can normalize body weight in ob/ob mice has generated enormous interest. Most human obesity does not appear to result from a mutant form of leptin: rather, serum leptin concentrations are increased and there is an apparent inability to transport it to the central nervous system (CNS). Injection of leptin into the CNS of overfed rodents resistant to peripheral administration was found to induce biological activity. Consequently, for the leptin to act as a weight-lowering hormone in human obesity, it appears that appropriate concentrations must be present in the CNS. This places a premium on understanding the structure of the hormone in order to design more potent and selective agonists. Here we report the crystal structure at 2.4A resolution of a human mutant OB protein (leptin-E100) that has comparable biological activity to wild type but which crystallizes more readily. The structure reveals a four-helix bundle similar to that of the long-chain helical cytokine family.

Bioavailability and bioeffectiveness of subcutaneous human insulin and two of its analogs--LysB28ProB29-human insulin and AspB10LysB28ProB29-human insulin--assessed in a conscious pig model.

In this study, human insulin was compared with two of its analogs--LysB28ProB29-human insulin and AspB10LysB28ProB29-human insulin-with respect to bioavailability and metabolic effectiveness. Absorption from the subcutaneous site was determined using kinetic parameters from the washout curve, following intravenous infusion of insulin or analog. Absorption was found to be more rapid for the two analogs, with 90% absorption by 100 min for the analogs and by 180 min for insulin. Total absorption was 97 +/- 10% for insulin, 99 +/- 7% for LysB28ProB29-human insulin, and 93 +/- 12% for AspB10LysB28ProB29-human insulin. Bioactivity was assessed from the glucose infusion and using tracer-determined metabolic clearance rates (MCRs) and glucose production rates. The fractional glucose requirements (relative to the total amount infused) increased more rapidly for the two analogs than for insulin, with 50% of the glucose infused by 105 min for both analogs vs. 145 min for insulin. The total amount of glucose required was, however, significantly less (19.7 +/- 1.5 mmol/kg) for AspB10LysB28ProB29-human insulin than for either LysB28ProB29-human insulin (25.9 +/- 3.0 mmol/kg) or human insulin (27.8 +/- 2.6 mmol/kg). The glucose requirements were reflected in a lower MCR for AspB10LysB28ProB29-human insulin but equivalent decreases in the rates of glucose production. Thus both analogs demonstrated more rapid rates of absorption, onset, and termination of action, but were not completely bioequivalent, with AspB10LysB28ProB29-human insulin demonstrating a 25% decrease in bioactivity.

Reduction of postprandial hyperglycemia and frequency of hypoglycemia in IDDM patients on insulin-analog treatment. Multicenter Insulin Lispro Study Group.

Insulin lispro, an insulin analog recently developed particularly for mealtime therapy, has a fast absorption rate and a short duration of action. We compared insulin lispro and regular human insulin in the mealtime treatment of 1,008 patients with IDDM. The study was a 6-month randomized multinational (17 countries) and multicenter (102 investigators) clinical trial performed with an open-label crossover design. Insulin lispro was injected immediately before the meal, and regular human insulin was injected 30-45 min before the meal. Throughout the study, the postprandial rise in serum glucose was significantly lower during insulin lispro therapy. At the endpoint, the postprandial rise in serum glucose was reduced at 1 h by 1.3 mmol/l and at 2 h by 2.0 mmol/l in patients treated with insulin lispro (P < 0.001). The rate of hypoglycemia was 12% less with insulin lispro (6.4 +/- 0.2 vs. 7.2 +/- 0.3 episodes/30 days, P < 0.001), independent of basal insulin regimen or HbA1c level. The reduction was observed equally in episodes with and without symptoms. When the total number of episodes for each patient was analyzed according to the time of occurrence, the number of hypoglycemic episodes was less with insulin lispro than with regular human insulin therapy during three of four quarters of the day (P < 0.001). The largest relative improvement was observed at night. In conclusion, insulin lispro improves postprandial control, reduces hypoglycemic episodes, and improves patient convenience, compared with regular human insulin, in IDDM patients.

Improved mealtime treatment of diabetes mellitus using an insulin analogue. Multicenter Insulin Lispro Study Group.

The absorption of regular human insulin from subcutaneous injection sites is delayed due to the self-association of insulin to multimeric forms. The insulin analogue insulin lispro has a weak self-association and a fast absorption rate. We examined the safety and efficacy of insulin lispro in the premeal treatment of patients with diabetes mellitus. A 12-month study was performed in 336 patients with insulin-dependent diabetes mellitus (IDDM) and 295 patients with non-insulin-dependent diabetes mellitus (NIDDM). The patients were randomized to inject either regular human insulin 30 to 45 minutes before eating, or insulin lispro immediately before each meal, in addition to basal insulin. The postprandial rise in serum glucose was lower in patients receiving insulin lispro than in those receiving regular human insulin therapy. At end point the increment was significantly lower at 1 hour (35%) and at 2 hours (64%) after the meal in IDDM patients; in NIDDM patients, the increment was nonsignificantly lower at 1 hour (19%) and significantly lower at 2 hours (48%). IDDM patients receiving insulin lispro achieved significantly lower glycated hemoglobin (HbA1c) levels in patients receiving regular human insulin (8.1% vs 8.3%). In NIDDM patients, HbA1c levels decreased equally in both treatment groups. Due to its fast absorption rate, insulin lispro improves postprandial control in diabetes. Insulin lispro can be considered one step toward optimal insulin therapy and improved patient convenience.

New advances in insulin treatment of diabetes: overcoming barriers.

OBJECTIVE: To discuss the optimal role of insulin in the treatment of patients with diabetes mellitus. METHODS: We review the complications of diabetes, highlight the attempts to improve control of plasma glucose, and summarize current recommendations for use of insulin in clinical practice. RESULTS: With the strict new guidelines for the diagnosis of diabetes issued by the American Diabetes Association in July 1997--a plasma glucose level of 126 mg/dL (7 mmol/L) rather than 140 mg/dL (7.8 mmol/L)--an additional 8 million persons will be diagnosed this year, and diabetes and its complications will be at the forefront of public health concerns. Strong evidence indicates that with reduction of plasma glucose levels and tight control of glycohemoglobin, the rate of complications can be considerably decreased. Although insulin replacement therapy is well known to be both the best and the most cost-effective way to control glucose levels in patients with type 1 diabetes, studies have no shown that those with type 2 diabetes can likewise benefit from appropriate insulin therapy. Other investigations have indicated that coronary events are as likely to occur in patients with recently discovered impaired glucose tolerance as in patients with known diabetes (at a 2-hour postprandial glucose threshold of 96 mg/dL [5.3 mmol/L]). Such finding suggest that there may be no such thing as "borderline diabetes" and give impetus to the search for improved types of insulin to treat all patients with diabetes. A recent candidate is the new insulin analogue lispro, which was developed by recombinant DNA techniques, with its design influenced by the structural analogy to another endogenous hormone, insulin-like growth factor I. Lispro is a fast-acting, rapidly dissipating insulin formulation. This profile allows lispro to be given less than 15 minutes before a meal, yet with little risk of postprandial hypoglycemia because its high mealtime peak is followed by rapid disappearance from the bloodstream. CONCLUSION: Lispro has been shown to improve postprandial control of plasma glucose and to decrease the occurrence of hypoglycemia episodes in comparison with regular insulin. Because of its stability and pharmacokinetic properties, lispro can also be used in insulin pump therapy.

Stimulation of glucose uptake by insulin-like growth factor II in human muscle is not mediated by the insulin-like growth factor II/mannose 6-phosphate receptor.

Although the growth-promoting effects of insulin-like growth factor II (IGF-II) have been intensively studied, the acute actions of this hormone on glucose metabolism have been less well evaluated, especially in skeletal muscle of humans. We and other groups have shown that IGFs reduce glycaemic levels in humans and stimulate glucose uptake in rat muscle. The purpose of the present study was to evaluate the effect of IGF-II on glucose transport in muscle of normal and obese patients with and without non-insulin-dependent diabetes mellitus (NIDDM), as well as to identify the receptor responsible for this action. 2-Deoxyglucose transport was determined in vitro using a muscle-fibre strip preparation. IGF-II were investigated in biopsy material of rectus abdominus muscle taken from lean and obese patients and obese patients with NIDDM at the time of surgery. In the lean group, IGF-II (100 nM) stimulated glucose transport 2.1-fold, which was slightly less than stimulation by insulin (2.8-fold) at the same concentration. Binding of IGF-II was approx. 25% of that of insulin at 1 nM concentrations of both hormones. Obesity with or without NIDDM significantly reduced IGF-II-stimulated glucose uptake compared with the lean group. In order to explore which receptor mediated the IGF-II effect, we compared glucose uptake induced by IGF-II and two IGF-II analogues: [Leu27]IGF-II, with high affinity for the IGF-II/Man 6-P receptor but markedly reduced affinity for the IGF-I and insulin receptors, and [Arg54,Arg55]IGF-II was similar to that of IGF-II, whereas [Leu27]IGF-II had a very diminished effect. Results show that IGF-II is capable of stimulating muscle glucose uptake in lean but not in obese subjects and this effect seems not to be mediated via an IGF-II/Man 6-P receptor.

Preparation of an insulin with improved pharmacokinetics relative to human insulin through consideration of structural homology with insulin-like growth factor I.

The Diabetes Control and Complications Trial has emphasized the need for improved control of blood glucose as a means to diminish long-term complications of diabetes. LysPro-insulin is an analog of human insulin whose design was modeled on structural homology with insulin-like growth factor I. An analysis of the structural conformation of insulin suggested that an inversion of amino acids B28 and B29 in the C-terminus of the B chain could yield an insulin analog with a faster onset of biological action. This insulin analog has proved to be virtually identical to human insulin in action, with one important exception. LysPro-insulin has demonstrated an improved time course of action in control of a mealtime glucose elevation. This offers the opportunity for improved convenience and safety for patients with insulin-dependent diabetes mellitus.

Altering the association properties of insulin by amino acid replacement.

The importance of ProB28 and LysB29 on the self-association of insulin was established by systematically truncating the C terminus of the B chain. The relationship between structure and association was further explored by making numerous amino acid replacements at B28 and B29. Association was studied by circular dichroism, size-exclusion chromatography and ultracentrifugation. Our results show that the location of a prolyl residue at B28 is critical for high-affinity self-association. Removal of ProB28 in a series of C-terminal truncated insulins, or amino acid replacement of ProB28, greatly reduced association. The largest disruption to association was achieved by replacing LysB29 with Pro and varying the amino acid at B28. Several of the analogs were predominantly monomers in solutions up to 3 mg/ml. These amino acid substitutions decreased association by primarily disrupting the formation of dimers. Such amino acid substitutions also substantially reduced the Zn-induced insulin hexamer formation. The formation of monomeric insulins through amino acid replacements was accompanied by conformational changes that may be the cause for decreased association. It is demonstrated that self-association of insulin can be drastically altered by substitution of one or two key amino acids.

Cross-reactive and serotype-specific antibodies against foot-and-mouth disease virus generated by different regions of the same synthetic peptide.

Synthetic peptides based on the VP1 proteins of two serotypes of foot-and-mouth disease virus (FMDV) and having the general formula C-C-(200-213)-P-P-S-(141-158)-P-C-G induce heterologous as well as homologous protection against challenge. Substitution of the sequence consisting of residues 200 to 213 (200-213 sequence) with a second copy of the homologous 141-158 sequence (i.e., homodimers) resulted in failure of either serotype peptide to protect heterologously. The antiviral and antipeptide titers of sera from guinea pigs immunized with the homodimeric 141-158 peptides showed serotype specificity and, with the data from the heterodimeric peptide vaccines, suggested that the C-terminal 141-158 sequence was more effectively recognized by the immune system than the N-terminal sequence. Whereas heterologous antiviral titers as measured by enzyme-linked immunosorbent assay and virus neutralization tests have not been observed with sera from cross-protected animals, epitope-mapping studies established that there was heterologous recognition of an octapeptide within the 200-213 sequence. That the 200-213 sequence was required for the induction of heterologous protection was also confirmed with a number of peptides, including hybrids based on the 200-213 sequence of one virus and the 141-158 sequence of a second virus. Thus, peptides of the general formula given above induce serotype-specific and serotype-cross-reactive protective antibodies and are unique in their induction of significant levels of heterologous protection, a property which has never been reported for whole FMDV vaccines.

Maturation of functional antibody affinity in animals immunised with synthetic foot-and-mouth disease virus.

A good correlation exists between specific neutralising antibody titre and protection against challenge with foot-and-mouth disease virus (FMDV) in infected or virus-vaccinated cattle, but not in the case of animals immunised with synthetic FMDV peptides. Therefore, mechanisms other than simple neutralisation are likely to be important in vivo. Antibody affinity may influence the protective capacity of sera from immunised animals and experiments were carried out to measure the functional affinity for synthetic FMDV peptide of sera from guinea pigs and cattle given various synthetic vaccines. In guinea pigs given a single dose of synthetic vaccine, antibody affinity increased with time after immunisation. In cattle, however, administration of a second dose of peptide 21 days after the first markedly retarded the process of affinity maturation. For guinea pig sera of equivalent neutralising activity, those of higher functional affinity had higher protective indices than those of lower functional affinity. Knowledge of the importance of antibody affinity in protection against FMD is important for an improved understanding of the mechanisms of protection and for the design of novel vaccines.

Modulation of T-cell reactivity to synthetic peptide analogues of foot-and-mouth disease virus in sheep by amino acid substitutions.

The ability of synthetic peptide analogues of foot-and-mouth disease virus VP1 capsid protein to induce T-cell proliferation in vitro following immunization of sheep with the uncoupled peptides was assessed. Elevated T-cell responses were obtained to a 21-residue peptide containing VP1 residues 141-158, and a 40-residue peptide containing residues 200-213 and 141-158 linked via a diproline-serine spacer. In contrast, no significant T-cell response was obtained with a 19-residue peptide containing residues 200-213 alone. In an attempt to engineer T-cell reactivity to this peptide, a sequence motif found in many peptides recognized by human or mouse T-cells was introduced by amino acid substitution. Substitution of a glycine or an aspartic acid for an alanine at position 207 in the 19-residue peptide resulted in the introduction of two such motifs running consecutively. Immunization of sheep with these peptides resulted in significant T-cell proliferative responses and elevated antibody responses. Analysis of further sequence variants showed that T-cell responsiveness was maintained with peptides containing single amino acid changes within these motifs, provided position 207 was glycine. The results thus suggest that increased T-cell reactivity, might be engineered via sequence manipulation of the 200-213 component of the 40-residue synthetic peptide. Such an additional T-cell epitope in the 40-residue peptide could potentially result in superior neutralizing antibody responses directed against the major epitope in residues 141-160 of VP1.