Weight gain and antipsychotic medication: differences between antipsychotic-free and treatment periods.

BACKGROUND: We performed a retrospective analysis of data involving 121 inpatients to examine the rate of weight gain during antipsychotic-free periods and during treatment with various antipsychotic drugs. METHOD: Data were analyzed to determine differences in weekly weight change during antipsychotic-free (N = 65), typical antipsychotic (N = 51), or atypical antipsychotic (N = 130) treatment periods. Atypical antipsychotic treatment periods were further subdivided into olanzapine (N = 45), clozapine (N = 47), or risperidone (N = 36) treatment periods. A paired comparison was conducted on 65 patients who had an antipsychotic-free treatment period preceding or following a neuroleptic drug treatment period. In addition, patients were classified as either non-obese (with a body mass index [BMI] < or = 29.9 kg/ml) or obese (BMI > or = 30.0 kg/m2) to test whether the rate of weight gain during treatment periods was related to initial BMI. RESULTS: Across all treatment periods, weekly weight gain was as follows: 0.89 lb/wk (0.40 kg/wk) on atypical antipsychotic medication, 0.61 lb/wk (0.27 kg/wk) on typical antipsychotic medication, and 0.21 lb/wk (0.09 kg/wk) on no antipsychotic medications. The atypical antipsychotic versus antipsychotic-free comparison was significant (F = 3.51; df = 2,231; p = .031), while the typical antipsychotic versus antipsychotic-free comparison was not. Among the individual atypical antipsychotic medications, significantly more weight gain occurred during olanzapine treatment (1.70 lb/wk) (0.76 kg/wk) than with either clozapine (0.50 lb/wk) (0.22 kg/wk) or risperidone (0.34 lb/wk) (0.15 kg/wk) treatments (F = 7.77; df = 2,117; p = .001). In the paired analysis with patients serving as their own controls, the difference between weekly weight gain during atypical antipsychotic treatment and antipsychotic-free treatment was significant (t = -3.91; df = 44; p = .001), while the difference between weight gain during typical antipsychotic treatment and antipsychotic-free treatment was not significant. With the individual drugs. treatment with both olanzapine and clozapine caused significantly higher weekly weight gain than antipsychotic-free treatment (p = .001 and p = .036, respectively). while treatment with risperidone did not. Non-obese patients (BMI < 29.9 kg/m2) and obese patients (BMI > 30.0 kg/m2) did not differ significantly in their weight gain during typical or atypical antipsychotic treatment. CONCLUSION: Treatment with atypical antipsychotics was associated with more weight gain than treatment with typical antipsychotics. Among the atypical drugs, olanzapine was associated with more weight gain than either clozapine or risperidone. The patient's admission BMI was not associated with the amount of weight gained during subsequent antipsychotic treatment.

The first transmembrane segment of the dopamine D2 receptor: accessibility in the binding-site crevice and position in the transmembrane bundle.

The binding site of the dopamine D2 receptor, like that of homologous G-protein-coupled receptors (GPCRs), is contained within a water-accessible crevice formed among its seven transmembrane segments (TMs). Using the substituted-cysteine-accessibility method (SCAM), we are mapping the residues that contribute to the surface of this binding-site crevice. We have now mutated to cysteine, one at a time, 21 consecutive residues in TM1. Six of these mutants reacted with charged sulfhydryl reagents, whereas bound antagonist only protected N52(1.50)C from reaction. Except for A38(1.36)C, none of the substituted cysteine mutants in the extracellular half of TM1 appeared to be accessible. Pro(1.48) is highly conserved in opsins, but absent in catecholamine receptors, and the high-resolution rhodopsin structure showed that Pro(1.48) bends the extracellular portion of TM1 inward toward TM2 and TM7. Analysis of the conversation of residues in the extracellular portion of TM1 of opsins showed a pattern consistent with alpha-helical structure with a conserved face. In contrast, this region in catecholamine receptors is poorly conserved, suggesting a lack of critical contacts. Thus, in catecholamine receptors in the absence of Pro(1.48), TM1 may be straighter and therefore further from the helix bundle, consistent with the apparent lack of conserved contact residues. When examined in the context of a model of the D2 receptor, the accessible residues in the cytoplasmic half of TM1 are at the interface with TM7 and with helix 8 (H8). We propose the existence of critical contacts of TM1, TM7, and H8 that may stabilize the inactive state of the receptor.

The substituted-cysteine accessibility method (SCAM) to elucidate membrane protein structure.

The substituted-cysteine accessibility method (SCAM) provides an approach to identifying the residues in the membrane-spanning segments that line a channel, transporter, or binding-site crevice. SCAM can also be used to determine differences in the structures of the membrane-spanning segments in different functional states of the proteins, to map electrostatic potential in the membrane-spanning domains, and to size a channel or binding-site crevice. The protocol in this unit describes the use of SCAM to map the binding-site crevice of a G-protein coupled receptor (GPCR) which binds ligand within the transmembrane portion of the receptor.

The fourth transmembrane segment of the dopamine D2 receptor: accessibility in the binding-site crevice and position in the transmembrane bundle.

The binding site of the dopamine D2 receptor, like that of homologous G-protein-coupled receptors (GPCRs), is contained within a water-accessible crevice formed among its seven transmembrane segments (TMSs). Using the substituted-cysteine-accessibility method (SCAM), we are mapping the residues that contribute to the surface of this binding-site crevice. We have mutated to cysteine, one at a time, 21 consecutive residues in the fourth TMS (TM4). Eleven of these mutants reacted with charged sulfhydryl-specific reagents, and bound antagonist protected nine of these from reaction. For the mutants in which cysteine was substituted for residues in the cytoplasmic half of TM4, treatment with the reagents had no effect on binding, consistent with these residues being inaccessible and with the low-resolution structure of the homologous rhodopsin, in which TM3 and TM5 occlude the cytoplasmic half of TM4. Although hydrophobicity analysis positions the C-terminus of TM4 at 4.64, Pro-Pro and Pro-X-Pro motifs, which are known to disrupt alpha-helices, occur at position 4.59 in a number of homologous GPCRs. The SCAM data were consistent with a C-terminus at 4.58, but it is also possible that the alpha-helix extends one additional turn to 4.62 in the D2 receptor, which has a single Pro at 4.59. In homologous GPCRs, the high degree of sequence variation between 4.59 and 4.68 is more characteristic of a loop domain than a helical segment. This region is shown here to be very conserved within functionally related receptors, suggesting an important functional role for this putative nonhelical domain. This inference is supported by observed ligand-specific effects of mutations in this region and by the predicted spatial proximity of this segment to known ligand binding sites in other TMs.

Dopamine D4/D2 receptor selectivity is determined by A divergent aromatic microdomain contained within the second, third, and seventh membrane-spanning segments.

Conserved features of the sequences of dopamine receptors and of homologous G-protein-coupled receptors point to regions, and amino acid residues within these regions, that contribute to their ligand binding sites. Differences in binding specificities among the catecholamine receptors, however, must stem from their nonconserved residues. Using the substituted-cysteine accessibility method, we have identified the residues that form the surface of the water-accessible binding-site crevice in the dopamine D2 receptor. Of approximately 80 membrane-spanning residues that differ between the D2 and D4 receptors, only 20 were found to be accessible, and 6 of these 20 are conservative aliphatic substitutions. In a D2 receptor background, we mutated the 14 accessible, nonconserved residues, individually or in combinations, to the aligned residues in the D4 receptor. We also made the reciprocal mutations in a D4 receptor background. The combined substitution of four to six of these residues was sufficient to switch the affinity of the receptors for several chemically distinct D4-selective antagonists by three orders of magnitude in both directions (D2- to D4-like and D4- to D2-like). The mutated residues are in the second, third, and seventh membrane-spanning segments (M2, M3, M7) and form a cluster in the binding-site crevice. Mutation of a single residue in this cluster in M2 was sufficient to increase the affinity for clozapine to D4-like levels. We can rationalize the data in terms of a set of chemical moieties in the ligands interacting with a divergent aromatic microdomain in M2-M3-M7 of the D2 and D4 receptors.

Electrostatic and aromatic microdomains within the binding-site crevice of the D2 receptor: contributions of the second membrane-spanning segment.

The binding-site of the dopamine D2 receptor, like that of other homologous G protein-coupled receptors, is contained within a water-accessible crevice formed among its seven membrane-spanning segments. Using the substituted cysteine accessibility method (SCAM), we previously mapped the residues in the third, fifth, sixth, and seventh membrane-spanning segments that contribute to the surface of this binding-site crevice. We have now mutated to cysteine, one at a time, 22 consecutive residues in the second membrane-spanning segment (M2) and expressed the mutant receptors in HEK 293 cells. Eleven of these mutants reacted with charged, hydrophilic, lipophobic, sulfhydryl-specific reagents, added extracellularly, and 9 of these 11 were protected from reaction by a reversible dopamine antagonist, sulpiride. We infer that the side chains of the residues at the 11 reactive loci (D80, L81, V83, V87, P89, W90, V91, V92, L94, E95, V96) are on the water-accessible surface of the binding-site crevice and that 9 of these are occluded by bound antagonist. The pattern of accessibility suggests an alpha-helical conformation. A broadening of the angle of accessibility near the binding site is consistent with the presence of a kink at Pro89. On the basis of the enhanced rates of reaction of positively charged sulfhydryl reagents, we infer the presence of an electrostatic microdomain composed of three acidic residues in M2 and the adjacent M3 that could attract and orient cationic ligands. Furthermore, based on the enhanced reactivity of the hydrophobic cation-containing reagent, we infer the presence of an aromatic microdomain formed between M2, M3, and M7.