A major problem associated with cellular cryopreservation is the recovery of cellular viability upon thawing. Current cryopreservation techniques use additives such as DMSO, sucrose and fetal bovine serum. However, each have their own respective cytotoxic issues. A significant factor in cryotoxicity is the formation of large ice crystals which can damage cellular components and cause dehydration. This has significant impacts for applications such as food preservation, scientific research, and tissue preservation. To this end, our laboratory is interested in synthesizing biologically-relevant compounds that can act as cryoprotectants by preventing the formation of large ice crystals in sub-zero temperatures. Our lab has previously synthesized structural analogues of native antifreeze glycoproteins (AFGPs, found in the blood of Antarctic cod), that possess the unique ability to inhibit ice-recrystallization. However, the mechanism by which they inhibit ice recrystallization is unclear. This thesis focuses on efforts made to understand this mechanism, and synthesize molecules that are more potent in ice recrystallization inhibition (IRI) activity compared to previously synthesized analogues. By assessing the IRI activity of various mono- and disaccharides, we have shown that the density of water molecules that surround a carbohydrate (Hydration Index) is directly proportional to the ability of sugars to inhibit ice crystal growth. In an effort to design functional AFGP analogues, various C-linked analogues were synthesized that contained different spacer lengths between the carbohydrate and the peptide backbone. Analyses of the solution conformations of these analogues showed that IRI-active AFGP analogues contain a distinct conformation in which the carbohydrate is oriented to form a hydrophobic pocket with the side chain. We hypothesize that this change in glycoconjugate hydration is responsible for disturbing its surrounding waters, thereby preventing water from adding to the ice lattice required for ice growth. Finally, SAR studies showed that threonine-containing AFGP and antifreeze proteins are more potent in antifreeze activity than serine-containing analogues. As the most potent AFGP analogue previously synthesized by our lab contains a C-linked-α-galactosyl -serine residue, we hypothesized that the analogous glycopeptide containing a C-α-galactosyl-threonine residue will be more potent in antifreeze activity. The final section describes efforts to synthesize a C-linked α-galactosyl-threonine glycoconjugate.

The unusually long Cytoplasmic tail (CT) of Human Immunodeficiency Virus Type-1 (HIV-1) glycoprotein-41 (gp41) is highly conserved and engineered large truncations often render the virus non-infectious in a cell-type dependent manner. While large CT truncations occur infrequently in natural isolates, little is known about the mechanisms involved in infectious virions harbouring a large CT truncation. This thesis characterises RFgp34, a replication competent laboratory HIV-1 isolate with an acquired 100 amino acid CT truncation, and how it diverged from wildtype RF. The CT truncation and two possible compensatory mutations in Matrix (E40K and F44I) were introduced into the HIV-1 isolate NL4-3. These mutants were tested for infectivity, syncytia formation and glycoprotein incorporation into virions, alternative co-receptor usage and sensitivity to the fusion inhibitor T-20. Compared with RFwt, RFgp34-infected cultures displayed delayed viral replication kinetics in all cell types. Similar sized (MT-4 cells, PBMC) or larger and more numerous syncytia (Hut78 cells) were detected in RFgp34-infected cultures. Similar (Hut78 cells) or decreased (MT-4 cells, PBMC) amounts of glycoprotein was incorporated into RFgp34 virions, compared with RFwt virions. The increased syncytia in RFgp34-infected Hut78 cultures and the reduced glycoprotein incorporation into RFgp34 virions from MT-4 cells and PBMCs may explain the delayed RFgp34 replication kinetics. The Matrix E40K and F44I mutations were not able to directly compensate for the CT truncation to restore infectivity in Hut78 and MT-4 cells, as secondary mutations or the reversion of the CT truncation to a full-length CT were observed. In PBMCs the Matrix mutations alone were able to partially restore infectivity, suggesting specific mutations may compensate for the CT truncation in different cell types. None of the viruses utilised alternative HIV-1 co-receptors, nor were more resistant to T-20 than wildtype HIV-1 suggesting that the CT does not directly play a role in these viral functions. This thesis suggests that the sequence of mutations acquired by RFgp34 to compensate for the CT truncation and restore infectivity in multiple cell types may have occurred in a specific order and the evolution of RFgp34 to out-compete RFwt occurred over many passages.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 126-155) Also available in print.

Abstract Apoptosis is a biochemically regulated mechanism leading to the destruction of an individual cell. An inadequate apoptosis is partly responsible for uncontrolled survival of malignantly transformed cells and formation of cancer. The growth of a tumor depends on the proliferative capacity and destruction of tumor cells either through apoptosis or necrosis. In this work, the extent of apoptosis and the expression of apoptosis-regulating proteins were studied by 3'-end labeling of fragmented DNA (TUNEL) and immunohistochemistry in a set of 166 tissue samples consisting of 33 HCCs, 39 gallbladder carcinomas, 7 gallbladder dysplasias and 87 pancreatic carcinomas. In addition, p53 protein and P-glycoprotein expression was studied immunohistochemically. The extent of apoptosis was estimated by using apoptotic index, defined as a percentage of apoptotic cells in the entire tumor cell population. The present results show an average apoptotic index of 0.73% in HCC, 0.68% in gallbladder and 0.69% in pancreatic carcinoma. Bcl-2 positivity was found in only 3% of the HCCs, 10% of gallbladder and 13% of pancreatic carcinomas. Bax positivity was seen in all of the gallbladder and pancreatic carcinoma cases. Mcl-1 positivity was found in 87% of gallbladder and 86% of pancreatic tumors. The apoptotic index in bcl-2 positive cases was lower (0.35%) than in cases showing no immunoreactivity (0.64%) in pancreatic tumors (P = 0.013). Apoptotic index was higher in pancreatic tumors with strong bax immunoreactivity (0.70%) than in other cases (0.34%) (P = 0.002). Caspase 3, 6 and 8 expression was found in 92%, 92% and 73% of HCC, 95%, 77% and 77% of gallbladder carcinoma and 80%, 80% and 74% of pancreatic carcinoma cases, respectively. p53 positivity was found in 23% of hepatocellular, 57% of gallbladder and 41% of pancreatic carcinomas. P-glycoprotein was observed in 65% of the HCCs. Patients with Pgp positive tumors had a significantly shorter disease-free interval than those with Pgp negative tumors (P < 0.05). To evaluate the growth potential of HCC and pancreatic carcinoma, a growth index from the scores obtained for apoptosis, necrosis and cell proliferation was designed. Patients with a high degree of proliferation relative to the degree of necrosis and apoptosis (i.e. had a positive growth index) in HCC lesions had a significantly shorter survival (P = 0.004) and disease-free interval after operation (P = 0.019) than those with a tumor predominated by apoptosis and necrosis. Results were in line with HCC in pancreatic carcinoma, but the association did not reach statistical significance (P = 0.09). According to the results the extent of apoptosis was similar in HCCs, gallbladder and pancreatic carcinomas. These tumors also showed here a similar expression pattern of the bcl-2 family of proteins and caspases. None of the individual parameters associated significantly with apoptosis except for bcl-2 and bax in pancreatic carcinoma, neither was there any association between p53 and P-glycoprotein expression and apoptosis. Calculation of a growth index might be helpful in assessing the prognosis of patients with tumors with a scant stroma, such as HCC.

A major problem associated with cellular cryopreservation is the recovery of cellular viability upon thawing. Current cryopreservation techniques use additives such as DMSO, sucrose and fetal bovine serum. However, each have their own respective cytotoxic issues. A significant factor in cryotoxicity is the formation of large ice crystals which can damage cellular components and cause dehydration. This has significant impacts for applications such as food preservation, scientific research, and tissue preservation. To this end, our laboratory is interested in synthesizing biologically-relevant compounds that can act as cryoprotectants by preventing the formation of large ice crystals in sub-zero temperatures. Our lab has previously synthesized structural analogues of native antifreeze glycoproteins (AFGPs, found in the blood of Antarctic cod), that possess the unique ability to inhibit ice-recrystallization. However, the mechanism by which they inhibit ice recrystallization is unclear. This thesis focuses on efforts made to understand this mechanism, and synthesize molecules that are more potent in ice recrystallization inhibition (IRI) activity compared to previously synthesized analogues. By assessing the IRI activity of various mono- and disaccharides, we have shown that the density of water molecules that surround a carbohydrate (Hydration Index) is directly proportional to the ability of sugars to inhibit ice crystal growth. In an effort to design functional AFGP analogues, various C-linked analogues were synthesized that contained different spacer lengths between the carbohydrate and the peptide backbone. Analyses of the solution conformations of these analogues showed that IRI-active AFGP analogues contain a distinct conformation in which the carbohydrate is oriented to form a hydrophobic pocket with the side chain. We hypothesize that this change in glycoconjugate hydration is responsible for disturbing its surrounding waters, thereby preventing water from adding to the ice lattice required for ice growth. Finally, SAR studies showed that threonine-containing AFGP and antifreeze proteins are more potent in antifreeze activity than serine-containing analogues. As the most potent AFGP analogue previously synthesized by our lab contains a C-linked-α-galactosyl -serine residue, we hypothesized that the analogous glycopeptide containing a C-α-galactosyl-threonine residue will be more potent in antifreeze activity. The final section describes efforts to synthesize a C-linked α-galactosyl-threonine glycoconjugate.

The domestic dog is the principal reservoir of rabies in Nigeria and the source of infection for over 99% of human cases that have been documented. The first recorded cases of human and dog rabies were in 1912 and 1928 respectively. The disease has been continually diagnosed in the domestic dog until to date. One of the control measures practiced in this West African country includes the vaccination of domestic dogs with readily available rabies vaccines. However, trend analyses show that dog rabies is increasing probably indicating that the vaccination programmes are inadequate. Rabies is a member of the Lyssavirus genus and currently comprises of seven genotypes (GT 1-7) namely the classical rabies virus (RABV) GT1, Lagos bat virus (LBV) GT2, Mokola virus (MOKV) GT3, Duvenhage (DUVV) GT4, European bat lyssavirus type-1 (EBLV-1) GT5, European bat lyssavirus type-2 (EBLV-2) GT6 and Australian bat lyssavirus (ABL) GT7. Three of these have been identified in Nigeria (classical rabies (RABV) (GT 1), Lagos bat virus (LBV) (GT 2) and Mokola virus (MOKV) (GT 3). The domestic dog is the major maintenance and vector species of rabies in this country and the West Africa sub-region. This study was therefore undertaken to further elucidate the epidemiology of dog rabies in Nigeria. Secondly, it was the aim of this study to determine the phylogenetic relationships of dog rabies viruses and the distribution of the respective rabies variants. Finally, to assess the phylogenetic relationships of the viruses in the study sample with those of the neighbouring countries (Chad, Cameroon, Benin and Niger). A panel of 100 viruses recovered primarily from the domestic dog was included in the study. Partial regions of the nucleoprotein gene (n=100) and the cytoplasmic domain of the glycoprotein and the G-L intergenic region (n=80) were successfully amplified, sequenced and phylogenetically analysed. Nucleotide sequences of representative rabies viruses of the partial N gene of the neighbouring countries and elsewhere in Africa available in the GenBank were also included in the phylogenetic analysis. The phylogenetic analysis demonstrated that the rabies viruses from the study sample were closely related with a 99% sequence homology for both the N and G regions but despite the close homogeneity the viruses segregated into two major clusters. Within the major cluster 1, three sub-clades were identified comprising of rabies isolates from the northern part of Nigeria whereas cluster 2 was made of viruses from the southern part of the country together with an isolate from a stray dog. Further analysis of representative viruses from the study sample with viruses from the GenBank revealed an evolutionary link with the viruses from Chad, Benin, Cameroon and Niger with a ≥96% sequence homology. The demonstration of the evolutionary link of rabies viruses in the study sample and those from neighbouring countries indicates the transboundary nature of rabies and the existence of an active rabies cycle in the region. The study data revealed that a single major virus variant is circulating in domestic dogs in Nigeria belonging to the Africa 2 dog lineage. These data suggest that control strategies including mass vaccination with effective coverage of ≥70% and the control of stray dogs will contribute to the breaking of the rabies cycle. This will dramatically reduce the demand for post-exposure prophylaxis which is costly and not readily available in most states of the country. There is also a need to enforce strict movement of animals across international borders so as to diminish the spread of the infection from one area to another, as rabies still inflicts a considerable public health burden in the region and many parts of Africa. / Dissertation (MSc)--University of Pretoria, 2009. / Veterinary Tropical Diseases / unrestricted

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