Publications

BACKGROUND

HIV infection is associated with an increased risk of coronary artery disease, but the contribution of inflammation versus antiretroviral drugs is not well understood. Fibrinogen is an inflammatory factor associated with atherosclerosis.

METHODS

A total of 1131 HIV-infected patients and 281 controls [from the Coronary Artery Risk Development in Young Adults (CARDIA) study, a population-based study of cardiovascular risk assessment] in the Study of Fat Redistribution and Metabolic Change in HIV infection (FRAM) had plasma fibrinogen levels measured. Multivariable linear regression identified factors associated with fibrinogen.

RESULTS

HIV-infected patients had higher levels of fibrinogen compared with controls (males: 25 mg/dl higher, P = 0.006; females: 21 mg/dl higher, P = 0.39). Among HIV-infected persons, median levels of fibrinogen were 11% higher in patients currently using any protease inhibitor (PI) compared with those not using a PI (P < 0.0001). The strongest univariate associations were with the individual PIs, ritonavir and indinavir. Patients taking indinavir boosted with ritonavir had median fibrinogen levels 8% higher than those on indinavir alone (P = 0.049). Lower levels of fibrinogen were seen in those HIV-infected patients currently using any nonnucleoside reverse transcriptase inhibitor (NNRTI) compared to those not using an NNRTI (nevirapine -14.4%, P < 0.0001; efavirenz -7%, P = 0.0002). The associations of ritonavir, indinavir, efavirenz and nevirapine with fibrinogen levels persisted after multivariable analysis and were independent of other antiretroviral use.

CONCLUSION

Protease inhibitor use is associated with elevated fibrinogen levels which may contribute to increased risk of atherosclerosis in HIV-infected patients. Conversely, NNRTI use is associated with lower fibrinogen levels which may decrease risk of atherosclerosis.

To explore guinea pigs as models of chymase biology, we cloned and expressed the guinea pig ortholog of human chymase. In contrast to rats and mice, guinea pigs appear to express just one chymase, which belongs to the alpha clade, like primate chymases and mouse mast cell protease-5. The guinea pig enzyme autolyzes at Leu residues in the loop where human chymase autolyzes at Phe. In addition, guinea pig alpha-chymase selects P1 Leu in a combinatorial peptide library and cleaves Ala-Ala-Pro-Leu-4-nitroanilide but has negligible activity toward substrates with P1 Phe and does not cleave angiotensin I. This contrasts with human chymase, which cleaves after Phe or Tyr, prefers P1 Phe in peptidyl 4-nitroanilides, and avidly hydrolyzes angiotensin I at Phe8 to generate bioactive angiotensin II. The guinea pig enzyme also is inactivated more effectively by alpha1-antichymotrypsin, which features P1 Leu in the reactive loop. Unlike mouse, rat, and hamster alpha-chymases, guinea pig chymase lacks elastase-like preference for P1 Val or Ala. Partially humanized A216G guinea pig chymase acquires human-like P1 Phe- and angiotensin-cleaving capacity. Molecular models suggest that the wild type active site is crowded by the Ala216 side chain, which potentially blocks access by bulky P1 aromatic residues. On the other hand, the guinea pig pocket is deeper than in Val-selective chymases, explaining the preference for the longer aliphatic side chain of Leu. These findings are evidence that chymase-like peptidase specificity is sensitive to small changes in structure and provide the first example of a vertebrate Leu-selective peptidase.